ASME Conference Presenter Attendance Policy and Archival Proceedings

2015;():V008T00A001. doi:10.1115/DETC2015-NS8.

This online compilation of papers from the ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE2015) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Control and Adaptive Structures

2015;():V008T13A001. doi:10.1115/DETC2015-46091.

In the area of active control of structures, time delay consideration is an important parameter which must be taken into consideration for realistic numerical models. In this research, the performance of a new active control algorithm for several time delays under two different earthquake excitations was investigated numerically. The proposed performance index does not require a priori knowledge of seismic input and the solution of the nonlinear matrix Riccati equation to apply the control forces [1,2]. The proposed control introduces the seismic energy term into the performance index so that the mechanical energy of the structure, the control and the seismic energies are considered simultaneously in the minimization procedure, which yields cross terms in the performance index. A two story shear frame was modelled in Matlab-Simulink considering time-delay. A fully active tendon controller system is implemented to the system. 0–50 ms time delay was considered in the dynamic analysis. The change in the time delay steps was 5 ms. The effect of time-delay was investigated under synthetic and Erzincan NS (1995;95 Erzincan station) earthquakes. Kanai-Tajimi power spectral density function was used to generate synthetic earthquake motion. The behavior of the proposed control with time delay considerations is compared with the uncontrolled conventional structure.

Commentary by Dr. Valentin Fuster
2015;():V008T13A002. doi:10.1115/DETC2015-46140.

This study presents a new method to find the optimal control forces for active tuned mass damper. The method uses three algorithms: discrete wavelet transform (DWT), particle swarm optimization (PSO), and linear quadratic regulator (LQR). DWT is used to obtain the local energy distribution of the motivation over the frequency bands. PSO is used to determine the gain matrices through the online update of the weighting matrices used in the LQR controller while eliminating the trial and error. The method is tested on a 10-story structure subject to several historical pulse-like near-fault ground motions. The results indicate that the proposed method is more effective at reducing the displacement response of the structure in real time than conventional LQR controllers.

Commentary by Dr. Valentin Fuster
2015;():V008T13A003. doi:10.1115/DETC2015-46250.

An optimization strategy to reduce residual vibration of rest-to-rest maneuvers of overhead cranes is proposed. The proposed technique is based on generating shaped acceleration commands for a simple harmonic oscillator with damping included. Furthermore, the proposed technique solves the problem of discrete signal commands that result from using slow digital to analog convertors on real cranes. A discretized acceleration profile is derived analytically using finite step segments. These segments are integrated into a matrix, which is then coupled with a system response matrix through the system’s equations of motion. The resulting input acceleration matrix is then optimized to satisfy rest-to-rest maneuver conditions. The profile designer can control many parameters such as maneuver duration, discrete time step, hoisting speed, damping ratio, maximum velocity and acceleration. Unlike traditional command shapers, the proposed shaped profiles are independent of the natural period of the system, i.e., the acceleration profile duration is designer selectable. Through several examples, the performance of the proposed controller is validated numerically. Results show that the proposed shaping technique can effectively eliminate residual vibrations in rest-to-rest maneuvers of damped single-degree-of-freedom systems.

Commentary by Dr. Valentin Fuster
2015;():V008T13A004. doi:10.1115/DETC2015-46757.

In this work, a command shaping technique is used to reduce residual vibrations of rest-to-rest maneuvers of double pendulums. The proposed command shaper can produce a command shaper without the exact mathematical model; it is only dependent on the system natural frequencies. Furthermore, the proposed shaper has independent maneuvering time. Unlike most command shaper for multimode systems, the proposed technique has known formulas for its parameters. Both simulations and experiments are used to validate the shaper concept. Experiment and simulation results, through different examples, showed great shaper performances.

Topics: Waves , Pendulums
Commentary by Dr. Valentin Fuster
2015;():V008T13A005. doi:10.1115/DETC2015-46853.

An extension to the Generalized-Divide-and-Conquer Algorithm (GDCA) is presented in this paper in conjunction with the Computed-Torque-Control-Law (CTCL) to model and control fully actuated multibody systems. CTCL uses the inverse dynamics to provide control inputs to the system while, the dynamics of the system must be formed and solved in each iteration. Herein, the GDCA is extended to form and solve the inverse dynamics to find control torques. Further, this method is also extended to efficiently solve the equations of motion of the controlled system. This significantly reduces the complexity of modeling, simulating, and controlling the fully actuated multibody systems to O(n) or O(logn) operations in each iteration in the serial and parallel implementations, respectively.

Commentary by Dr. Valentin Fuster
2015;():V008T13A006. doi:10.1115/DETC2015-47019.

The light-activated shape memory polymer (LaSMP) is sensitive to ultraviolet light with specific wavelength. It is featured with dynamic stiffness. In this study, LaSMP is used to control the vibration of thin ring shells induced by external loading. Firstly the variation of LaSMP’s Young’s modulus is modeled. The mathematical model reflects the influence of light intensity, the decay coefficient and thickness of LaSMP. Besides, the model is suitable for LaSMPs with different reaction orders. Then, with Lamé parameters and the radii of rings the governing equations of the flexible ring laminated with LaSMP actuators are established. Love operators of LaSMP actuators are derived. Based on the mode expansion method, the modal forces of external loading and LaSMP actuators are given. The modal participation factors are analyzed with the modal forces. As the variation of Young’s modulus to the light intensity is nonlinear, the control effect of LaSMP actuators to common harmonic excitation is not perfect. Because the neural network control is effective to identify complex models, it is introduced to adjust the profile of light intensity. In the case study, the model of LaSMP’s Young’s modulus is validated with the experimental data. Then the forced harmonic responses of the ring are studied. For the mode n=2, the modal participation factor is reduced by 47.7% with the control of LaSMP actuator. To further enhance the control effect, the phase shift method is applied. With π/6 phase shift, the modal participation factor is reduced by 80.8%. With the neural network control method, the modal participation factor is cut down by 98.1%. The study shows that LaSMP actuator provides a new choice to control the forced vibration of flexible rings. It is also possible to apply LaSMP actuator to vibration control of other thin shell structures.

Commentary by Dr. Valentin Fuster
2015;():V008T13A007. doi:10.1115/DETC2015-47177.

Friction induced vibration (FIV) attracts extensive attention of researchers due to its ubiquitousness and intriguing complexity. Disc brake squeal is deemed one of the typical FIV problems with eigenvalues of the brake system locating on the right-hand side half of the complex plane. In this research, an active state feedback control strategy is proposed for shifting the unstable eigenvalues of the brake system to the stable region. The presented control method is constructed based on the receptance method in which the knowledge of mass, damping and stiffness matrices is not required. Moreover, the robustness of the control method is explored against uncertainty in friction coefficient. The numerical simulation results demonstrate that the proposed method successfully places the required poles of the system and thus stabilises an unstable system in the presence of an uncertain parameter.

Commentary by Dr. Valentin Fuster
2015;():V008T13A008. doi:10.1115/DETC2015-47304.

This paper presents a development of two model-based emergency tracking controllers which can be turned on when one of actuators of a system fails during motion. The system is represented by a manipulator possessing 3 degrees of freedom, which may work in horizontal or vertical planes. The control goal is to enable an end effector of a broken manipulator completing tracking a predefined task as good as possible and then get back to its rest position. Simulation results confirm good performance of the designed emergency tracking controllers.

Commentary by Dr. Valentin Fuster
2015;():V008T13A009. doi:10.1115/DETC2015-47812.

The current emphasis on increasing aeronautical efficiency is leading the way to a new class of lighter more flexible airplane materials and structures, which unfortunately can result in aeroelastic instabilities.

To effectively control the wings deformation and shape, appropriate modeling is necessary. Wings are often modeled as cantilever beams using finite element analysis. The drawback of this approach is that large aeroelastic models cannot be used for embedded controllers. Therefore, to effectively control wings shape, a simple, stable and fast equivalent predictive model that can capture the physical problem and could be used for in-flight control is required.

The current paper proposes a Discrete Time Finite Element Transfer Matrix (DT-FETMM) model beam deformation and use it to design a regulator. The advantage of the proposed approach over existing methods is that the proposed controller could be designed to suppress a larger number of vibration modes within the fidelity of the selected time step. We will extend the discrete time transfer matrix method to finite element models and present the decentralized models and controllers for structural control.

Commentary by Dr. Valentin Fuster
2015;():V008T13A010. doi:10.1115/DETC2015-47994.

The converse flexoelectric effect that the gradient of polarization (or electric field) induces internal stress (or strain) can be utilized to control the vibration of flexible structures. This study focuses on the microscopic actuation behavior and effectiveness of a flexoelectric actuator patch on an elastic ring. An atomic force microscope (AFM) probe is placed on the upper surface of the patch to implement the inhomogeneous electric field inducing stresses inside the actuation patch. The flexoelectric membrane force and bending moment, in turn, actuate the ring vibration and its actuation effect is studied. Actuator’s influence in the transverse and circumferential directions is respectively evaluated. For the transverse direction, the gradient of the electric field decays quickly along the ring thickness, resulting in a nonuniform transverse distribution of the induced stress and such distribution is not influenced by the patch thickness. The flexoelectric induced circumferential membrane force and bending moment resembles the Dirac delta function at the AFM contact point. The influence of the actuator can be regarded as a drastic bending on the ring. To evaluate the actuation effect, dynamic response of controllable displacements of the elastic ring under flexoelectric actuation is analyzed by adjusting the geometric parameters, such as the thickness of flexoelectric patch, AFM probe radius, ring thickness and ring radius. This study represents a thorough understanding of the flexoelectric actuation behavior and serves as a foundation of the flexoelectricity based vibration control.

Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Design and Optimization of Dynamical Systems

2015;():V008T13A011. doi:10.1115/DETC2015-46084.

An optimization method is proposed for the simultaneous design of structural and control systems using the equivalent static loads. The two structural and control systems are not completely independent and need to be considered in a unified fashion. Furthermore, an integrated system design is unavoidable to exhibit a good performance in the time domain. The analysis for the integrated system is conducted for the transient-state in a dynamic manner. The constraints for the structural and control systems are defined in the time domain as well. Therefore, a physically small scale problem in structural analysis easily becomes quite a large scale in an optimization problem. A new equivalent static loads (ESLs) method, which deals with the structural design variables as well as the control design variables, is proposed to solve physically large scale problems. A finite element dynamic equation is defined with control forces and a dynamic response optimization problem is formulated. Linear static response optimization is carried out with the ESLs. The control forces for the linear static response optimization are considered as design variables. Shape variables are utilized to handle the design variables for the control forces. Several examples are solved to validate the proposed method.

Commentary by Dr. Valentin Fuster
2015;():V008T13A012. doi:10.1115/DETC2015-46197.

Optimal designs of beams with multi-layers of corrugations are introduced in this paper. The dynamic characteristic of corrugated structures is investigated firstly using the impedance modeling technique. The dynamic response of a beam with layers of corrugations is formulated by dividing a corrugated beam into two kinds of structural segments: one, the corrugation modeled as a curved beam using finite element method and the other, the liner treated as a straight beam formulated analytically. Then the frequency equation is derived by assembling the impedance of each structure segment based on conditions of force equilibrium and velocity compatibility. The accuracy of the impedance modeling technique are compared to different existing methods, e.g. FEM, Guyan reduction, improved reduction system (IRS), improved reduction system (DIRS), and iterative improved reduction system (IIRS). Finally, examples of optimal design of corrugated beams are presented. Results further show that with an optimal number of corrugated layers and optimal thickness of liner and medium of each layer, the corrugated beam has a desirable dynamic characteristic, e.g. the first bending natural frequency may increase 40% as compared to that of the original design.

Topics: Design , Optimization
Commentary by Dr. Valentin Fuster
2015;():V008T13A013. doi:10.1115/DETC2015-46259.

The harmonic balance (HB) method has been widely used in the past few years, as a numerical tool for the study of nonlinear models. However, in its classical formulation the HB method is limited to the approximation of periodic solutions. The present paper proposes to extend the method to the detection and tracking of bifurcations in the codimension-2 system parameters space. To validate the methodology, the forced response of a real spacecraft is examined. The paper first provides some numerical evidence of the presence of quasiperiodic oscillations and isolated solutions. It then demonstrates how the tracking of Neimark-Sacker and fold bifurcations can help get a deeper understanding of these attractors.

Commentary by Dr. Valentin Fuster
2015;():V008T13A014. doi:10.1115/DETC2015-46863.

The optimal sensor placement (OSP) problem is integral to modern large scale structures for their health monitoring. Evolutionary algorithms for the OSP problem are attractive as they can result in global optima without gradient information. In this paper, a modification of the Monkey Algorithm with a chaotic search strategy and adaptive parameters is proposed. It includes chaotic initialization, variable search step length, and adaptive watching time.

The performance of the proposed chaotic Monkey Algorithm (cMA) is compared with the original Monkey Algorithm. Convergence property of cMA is established. The proposed method is applied to an optimal sensor placement problem for structural health monitoring. The OSP problem is solved for a mass-spring-damper system and then for a model of the I-40 bridge developed by the Los Alamos National Laboratory. Numerical results demonstrate that the proposed Chaotic Monkey Algorithm has capability of solving mixed-variable optimization problems and that it performs better than the originally proposed Monkey algorithm. Finally, nonparametric uncertainty modeling is used to evaluate variability in a model and its effect on the optimal sensor placement.

Commentary by Dr. Valentin Fuster
2015;():V008T13A015. doi:10.1115/DETC2015-46908.

This paper presents a study of multi-objective optimal design of a slide mode control for an under-actuated nonlinear system with the parallel simple cell mapping method. The multi-objective optimal design of the slide mode control involves 6 design parameters and 5 objective functions. The parallel simple cell mapping method finds the Pareto set and Pareto front efficiently. The parallel computing is done on a graphic processing unit (GPU). Numerical simulations and experiments are done on a rotary flexible arm system. The results show that the proposed multi-objective designs are quite effective.

Commentary by Dr. Valentin Fuster
2015;():V008T13A016. doi:10.1115/DETC2015-47291.

The main scope of this paper is optimization of high speed rotor systems by using Evolutionary Algorithm. The target of the optimization is finding geometrical parameters of the shaft, in such a way that the critical speeds are not occurring in the operation speed range. Rotating machines have a wide range of applications in industrial machinery and applying numerical optimization techniques helps engineers to improve the performance of rotor bearing systems. A schematic of a turbine rotor system is studied. The rotor is modeled using finite element method and Timoshenko beam elements having four degrees of freedom (DOF) per node — two translational and two rotational. Critical speeds are identified using Campbell diagram. The outcome of the simulation is looking to find the widest safe margin for operation speed range without any critical speed in Campbell diagram within the operation range. Design parameters for optimization are overhang shafts lengths and diameters. Several simulation runs with different variables shows a significant effect of these parameters in dynamic behavior of the system. Comparison of the results with the basic design of turbine rotor reveals that all constraints are satisfied.

Topics: Optimization , Rotors
Commentary by Dr. Valentin Fuster
2015;():V008T13A017. doi:10.1115/DETC2015-47690.

This paper presents a methodology for the optimal design of intentional mistuning for a mistuned bladed disk with interval uncertainty. For a bladed disk where blades are weakly coupled, presence of random mistuning can easily induce vibration localization. This phenomenon will lead to great amplification in response amplitude of certain blades. To achieve desired reliability of a bladed disk, amplified response must be reduced to certain level, which requires probabilistic or reliability analysis. In this study, it is considered that blades have random distribution and coupling between blades has interval uncertainty. To treat the interval uncertainty appropriately, the worst-case combination of interval couplings is searched first, then probability of failure is evaluated under the worst-case condition. To increase reliability of a bladed disk, intentional mistuning is used in this study. While applying the intentional mistuning, it is also wanted to minimize the degree of intentional mistuning to minimize the cost of implementation. To find optimal combination of intentional mistuning parameters to achieve dual goals, gradient-based design optimization approach is utilized, which is expected to guarantee efficient convergence. To carry out gradient-based design optimization, sensitivities of objective function and probabilistic constraints with respect to intentional mistuning parameters are derived. During the sensitivity analysis, distribution of forced response amplitude is identified through Gaussian fit and eigenvalue perturbation theory is referred to. Monte Carlo simulation is utilized to accurately calculate probability of failure and its sensitivity. The proposed method is demonstrated with numerical examples of two distinct bladed disks.

Topics: Design , Disks , Uncertainty
Commentary by Dr. Valentin Fuster
2015;():V008T13A018. doi:10.1115/DETC2015-47745.

Bipeds’ trajectories and control during walking are closely coupled with the contact force distribution in time and space as an indeterminate problem. Therefore, generating the motion of redundant bipeds in presence of unilateral contact is usually formulated as a nonlinear constrained optimization problem. The optimal walking motion must be solved in terms of trajectories, control, contact status (i.e., when, where, and whether a foot is in contact), and contact response (i.e., ground reaction forces). The solution for this problem requires predictive methods within the general optimal motion planning framework. However, there is a lack of fully predictive methods that can concurrently solve for all the above mentioned unknowns. This represents an important challenge in the simulation, design, analysis, and control of general robotic systems. A novel approach for the optimal motion planning of multibody systems with contacts is developed, based on a Sequential Quadratic Programming (SQP) algorithm for Nonlinear Programming (NLP). The complete formulation is presented and demonstrated with numerical experiments on a simple planar biped with the assigned task of one complete step motion in forward progression.

Commentary by Dr. Valentin Fuster
2015;():V008T13A019. doi:10.1115/DETC2015-47891.

The multi-functional components layout design problem, which may have various options associated with it, including passive, active, and reactive components in given multibody dynamics systems, is defined in this study. The defined layout design problem is able to address the objective functions that are related to the dynamic responses of multibody dynamics systems, rather than static responses. The target of the multi-functional components layout design problem in given multibody dynamics systems is to seek the optimal interactive system layout between given multiple multibody dynamics system in order to maximize or minimize the dynamic objective function. The governing equations for the interactive system and the given multibody dynamics systems are derived first. The optimization objective is the first order natural frequency of the multibody dynamics system with multi-functional components in this study. The sensitivity analysis was then implemented based on the system eigen equation. Two numerical examples are presented in this study, it shows that the topology optimization method can be applied to the multibody dynamics system natural frequency optimization successfully.

Commentary by Dr. Valentin Fuster
2015;():V008T13A020. doi:10.1115/DETC2015-48080.

Base vibration of a linear motor motion stage has been reduced with passive RFC mechanism based on movable magnet track and springs. This paper presents design procedure of an eddy-current damper (ECD) type RFC mechanism for a linear motor motion stage. The RFC mechanism with a movable magnet track and an ECD can overcome disadvantages of the spring based RFC mechanism such as resonance and difficulty of assembly due to spring. A lumped parameter model for the ECD type RFC mechanism is derived considering sinusoidal magnetic flux density and effective width of the ECD according to magnet track motion. Then, a design procedure for ECD type RFC mechanism is proposed to meet system requirements such as transmission ratio of reaction force and maximum magnet track motion. Design example illustrates the effectiveness of the proposed design procedure for ECD type RFC mechanism.

Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Dynamics of Jointed Structures

2015;():V008T13A021. doi:10.1115/DETC2015-46029.

The uncertainty of a system is usually quantified with the use of sampling methods such as Monte-Carlo or Latin hypercube sampling. These sampling methods require many computations of the model and may include re-meshing. The re-solving and re-meshing of the model is a very large computational burden. One way to greatly reduce this computational burden is to use a parameterized reduced order model. This is a model that contains the sensitivities of the desired results with respect to changing parameters such as Young’s modulus. The typical method of computing these sensitivities is the use of finite difference technique that gives an approximation that is subject to truncation error and subtractive cancellation due to the precision of the computer. One way of eliminating this error is to use hyperdual numbers, which are able to generate exact sensitivities that are not subject to the precision of the computer. This paper uses the concept of hyper-dual numbers to parameterize a system that is composed of two substructures in the form of Craig-Bampton substructure representations, and combine them using component mode synthesis. The synthesis transformations using other techniques require the use of a nominal transformation while this approach allows for exact transformations when a perturbation is applied. This paper presents this technique for a planar motion frame and compares the use and accuracy of the approach against the true full system. This work lays the groundwork for performing component mode synthesis using hyper-dual numbers.

Commentary by Dr. Valentin Fuster
2015;():V008T13A022. doi:10.1115/DETC2015-46464.

Almost all mechanical structures consist of an assembly of components that are linked together with joints. If such a structure experiences vibration during operation, micro-sliding can occur in the joint, resulting in fretting wear. Fretting wear affects the mechanical properties of the joints over their lifetime and as a result impacts the non-linear dynamic response of the system. For accurate prediction of the non-linear dynamic response over the lifetime of the structure, fretting wear should be considered in the analysis.

Fretting wear studies require an accurate assessment of the stresses and strains in the contacting surfaces of the joints. To provide this information, a contact solver based on the semi-analytical method has been implemented in this study. By solving the normal and tangential contact problems between two elastic semi-infinite bodies, the contact solver allows an accurate calculation of the pressure and shear distributions as well as the relative slips in the contact area. The computed results for a smooth spherical contact between similar elastic materials are presented and validated against analytical solutions. The results are also compared with those obtained from finite element simulations to demonstrate the accuracy and computational benefits of the semi-analytical method. Its capabilities are further illustrated in a new test case of a cylinder with rounded edges on a flat surface, which is a more realistic contact representation of an industrial joint.

Commentary by Dr. Valentin Fuster
2015;():V008T13A023. doi:10.1115/DETC2015-46843.

An experimental investigation has been made of two identical beams of length 750mm bolted together (a composite beam) which have contact over the whole of the neutral plane. The objective is to determine how friction between the two beams influences the damping. In one set of experiments the beams were held apart using washers while in the second set the beams could contact each other over their whole length. The number of bolts used to hold the beams together was varied between three and 17. The damping of the first two or more modes of the beams was measured. The material damping of the beams when not bolted together was also measured. It was found that the material damping and the damping of the fully bolted composite beam were very similar (damping ratio 0.0005). However, when the beams were in contact and had few bolts (just 3) and the amplitude of vibration was large the damping ratio changed to a much larger value of 0.01.

The experiments suggest that the damping due to the bolts is similar to that of material damping. It is only when other friction sites, not involving bolts, are slipping that damping becomes large.

The consequences for the designer of a built-up structure who wishes to increase damping is thus to use the smallest number of bolts and to arrange for other surfaces to be in sliding contact.

Commentary by Dr. Valentin Fuster
2015;():V008T13A024. doi:10.1115/DETC2015-46856.

If a structure containing bolted joints is set into vibration and the subsequent motion measured it may be possible to determine some properties of the structure and the joints. However, it is not generally straightforward to interpret the decaying vibration signals and considerable signal processing may be necessary. Typically the vibration is nonlinear and this must be taken into account. Three methods for data analysis are investigated here: filtering time histories, working with short Fourier transforms and the use of empirical mode decompositions. Some progress is made with the first two but the third is disappointing but full of promise. The general scope of the objectives is to obtain properties such as frequency and damping that are changing in time. One of the key difficulties is that several nonlinear resonances are superimposed in a general decaying time history. Extracting the one required from the others is the main signal processing task.

Commentary by Dr. Valentin Fuster
2015;():V008T13A025. doi:10.1115/DETC2015-47946.

Several of the authors, and others, have explored the use of modal-like models for structures having nonlinearities associated with compressive joints (such as bolted connections.) In these models, the deformations are treated as consisting of modal expansions, but with the modal coordinates that evolving nonlinearly over time. There have been several theoretical treatments of this strategy and the authors report here on an early effort to confirm the approach through experiment.

For this purpose simple structures consisting of pairs of plates were assembled using four bolted connections. The structures were excited by modal hammer at various locations and the modes identified by scanning laser vibrometer. In each case, multiple modes were excited and the evolution of modal coordinates was achieved by band-pass filtering at the relevant frequencies.

Making some simple kinematic assumptions about relative deformations of the component plates and exploiting symmetries permits the mapping from ring-down of each mode to constitutive behavior of each joint. If the strategy of using joint-like modal models for bolted structures is valid, the joint constitutive models deduced from any mode should be adequate to predict the apparent, but nonlinear modal behavior at other resonances. Multiple test specimens were manufactured to assess this predictive capability in the context of part-to-part variability intrinsic to the dynamics of such structures.

Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Emerging Frontiers in Dynamical Systems

2015;():V008T13A026. doi:10.1115/DETC2015-47305.

The effects of mis-positioning a newly-designed noninvasive, cuffless blood pressure sensor are thoroughly investigated via simulation and analysis on a 3D fluid-solid-electric finite element model. A subsequent optimal design of this blood pressure is conducted based on the aforementioned mis-positioning effects. A highly-accurate, non-invasive, cuffless blood pressure (BP) sensor was successfully developed recently for an effective personal monitoring device on blood pressures. This new small-sized, portable blood pressure sensor is able to offer continuous BP measurements. The availability of continuous blood pressures are important for monitoring and evaluating personal cardiovascular systems. The sensor contains a strain-sensitive electrode encapsulated by flexible polymer. As the sensor placed on the position right on the top of the center of the wrist pulsation area, the deflection of the sensor induces the resistance changes of the electrode. By measuring the changes in electrode resistance, the level of pulsation is successfully quantified. Subsequent calculation based in this measurement can lead to fair estimates on blood pressures.

However, as the sensor is placed on the wrist area where pulsation occurs, the mis-positioning of the sensor to the desired location, the center of the pulsation area, is inevitable. This study is dedicated to investigate the effects of the mis-positioning via a 3D finite element model. A new 3D fluid-solid-electro coupling interaction finite element model of the wrist is built for predicting the vibration of radial artery and then diastolic and systolic blood pressures. The FEM includes sensor of gel capsule and strain-sensing electrodes, radial artery, blood, radius bones, tendon, muscles and the front-end readout circuit. The FEM is the multi physics FEM with fluid, solid and electric. The section of wrist is constructed from magnetic resonance imaging (MRI) and the length of the FEM is 40mm. The complete 3D FEM model successfully simulated the vibration of skin surface and the sensor module. The diastolic and systolic blood pressures can be accurately predicted by the simulated output resistance.

The pulsation levels due to varied mis-positionings are simulated by the built model, and simulation results are successfully validated by experiments. It is found that due to the unsymmetrical geometry of the wrist, the pulsation levels are also varied in an un-symmetric fashion with the mis-positionings in different directions. The maximum output of the BP sensor occurs when the sensor is placed ±3 mm away from the center of the pulsation area, while the sensor output remain valid for subsequent signal processing as the sensor is placed within ±5 mm from the pulsation center. Considering the inevitable mis-positionings by all possible users in different genders and ages, the sizes of the sensors are successfully optimized for satisfactory average signal quality over all possible users.

Commentary by Dr. Valentin Fuster
2015;():V008T13A027. doi:10.1115/DETC2015-47410.

The impulsive behavior of piston plays a key role in the Noise, Vibration and Harshness (NVH) of internal combustion engines. There have been several studies on the identification and quantification of piston impacting action under various operation conditions. In the current study, the dynamics of piston secondary motion are briefly explored, since this is fundamental to understanding the aggressive oscillations, energy loss and noise generation. Concepts of controlling piston secondary motion (and thus, impacts) are investigated and a new passive control approach is presented based on the nonlinear energy absorption of the highly transient oscillations. The effectiveness of this new method on the improvement of piston impact behavior is discussed, using a preliminary optimization exercise (with respect to engine excitation/speed, damping and stiffness of the nonlinear oscillator) that leads to the conceptual design of a nonlinear energy absorber.

Commentary by Dr. Valentin Fuster
2015;():V008T13A028. doi:10.1115/DETC2015-47500.

In this work, an integrated reverse engineering strategy is presented that takes into account the complete process, from the developing of CAD model and the experimental modal analysis procedures to computational effective model updating techniques. Modal identification and structural model updating methods are applied, leading to develop high fidelity finite element model of geometrically complex and lightweight bicycle frame, using acceleration measurements. First, exploiting a 3D Laser Scanner, the digital shape of the real bike frame was developed and the final parametric CAD model was created. Next the finite element model of the frame was created by using quadrilateral shell and hexahedral solid elements. Due to complex geometry of the structure, the developed model consists of about one million degrees of freedom. The identification of modal characteristics of the frame is based on acceleration time histories, which are obtained through an experimental investigation of its dynamic response in a support-free state by imposing impulsive loading. A high modal density modal model is obtained. The modal characteristics are then used to update the finite element model. Single and multiobjective structural identification methods with appropriate substructuring methods, are used for estimating the parameters (material properties and shell thickness properties) of the finite element model, based on minimizing the deviations between the experimental and analytical modal characteristics (modal frequencies and mode shapes). Direct comparison of the numerical and experimental data verified the reliability and accuracy of the methodology applied.

Commentary by Dr. Valentin Fuster
2015;():V008T13A029. doi:10.1115/DETC2015-47587.

This paper develops a nonlinear mathematical model to describe the heart rate response of an individual during cycling. The model is able to account for the fluctuations of an individual’s heart rate while they participate in exercise that varies in intensity. A method for estimating the model parameters using a genetic algorithm is presented and implemented, and the results show good agreement between the actual parameter values and the estimated values when tested using synthetic data.

Commentary by Dr. Valentin Fuster
2015;():V008T13A030. doi:10.1115/DETC2015-47773.

Macro-fiber composite (MFC) piezoelectric structures with interdigitated electrodes can be used for effective hydrodynamic thrust generation by underwater actuation as well as low-power electricity production from underwater vibrations for powering wireless electronic components. In order to develop high-fidelity models to predict the electrohydroelastic dynamics of MFC structures, mixing rules based electroelastic mechanics modeling is coupled with the global electroelastic dynamics based on the Euler-Bernoulli kinematics and the nonlinear fluid loading based on Morison’s semi-empirical model. The focus is placed on the dynamic actuation problem for the first two bending vibration modes under geometrically, materially, and piezoelectrically linear, hydrodynamically nonlinear behavior. The electroelastic and dielectric properties of a representative volume element (piezoelectric fiber and epoxy matrix) between two subsequent interdigitated electrodes are correlated to physical parameters of MFC bimorphs and validated for different MFC types that have the same overhang length but different widths. Following the process of in-air electroelastic model development and validation, underwater experiments are conducted for different length-to-width aspect ratios (L/b), and empirical drag and inertia coefficients are extracted for Morison’s equation. The repeatability of these empirical coefficients is demonstrated for experiments conducted using aluminum cantilevers of different aspect ratios. Convergence of the nonlinear electrohydroelastic Euler-Bernoulli-Morison model to its hydrodynamically linear counterpart with increased L/b values is also reported. The proposed model, its harmonic balance analysis, and experimental results can be used for parameter identification as well as aspect ratio optimization for underwater piezoelectric actuation, sensing, and energy harvesting problems.

Commentary by Dr. Valentin Fuster
2015;():V008T13A031. doi:10.1115/DETC2015-47905.

Soldiers, fire fighters, athletes in contact sports and construction workers are often exposed to severe impact conditions like blast waves and blunt force trauma. They often end up suffering injuries that have life-long consequences resulting in huge health care costs. Even the state of the art in impact reduction technology is inadequate when it comes to absorbing impact. University of Texas Arlington’s research institute (UTARI) has developed a concept for reducing impact using arrays of interconnected bubbles filled with a fluid. The array is fabricated out of a soft elastic polymer that can be used as a helmet liner. When the helmet experiences an impact, the load is effectively distributed by the movement of the fluid among the array of interconnected bubble cells. A preliminary numerical modeling to demonstrate the ability of this design concept to reduce impact loads as the proof-of-concept has been carried out. Effect of various design parameters such as secondary bubble thickness, type of fluid, connecting channel size and impact velocity has been studied in this finite element simulation using ANSYS. This paper presents the results from this preliminary study.

Topics: Fluids , Simulation , Bubbles
Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Energy Transfer, Energy Harvesting, and Damping

2015;():V008T13A032. doi:10.1115/DETC2015-46217.

Recently, the power supply for portable electronic devices using the electricity extracted from human motion and ambient vibrations has received considerable attention from multidiscipline field. Among many energy converting mechanisms, the ease miniaturization of piezoelectric cantilever structure propels many research groups to investigate the potential of efficient energy harvesting from ambient vibration using resonant phenomena. However, the incapability of traditional linear energy harvesting from low frequency or varying frequency vibrations has become an open issue. This paper investigates the feasibility of nonlinear energy harvesters with different bistable potential well functions in harvesting energy from walking and running vibration. The portable nonlinear energy harvesting device and its measurement system has been established to obtain the model parameter and excitation signal from human motion. The electromechanical model for bistable energy harvesters with different nonlinear restoring force is derived from theoretical method and experimental data. Numerical investigation under human walking and running vibrations shows that large amplitude interwell motion are easily achieved to improve energy output while the proper potential well function of bistable oscillators is designed. The comparative experiments for nonlinear energy devices with different potential well function are performed. The history and frequency spectrum of output voltage demonstrate the effectiveness of numerical simulation and the clear potential of bistable energy harvesting from human motion by means of appropriate potential function design.

Commentary by Dr. Valentin Fuster
2015;():V008T13A033. doi:10.1115/DETC2015-46435.

A technique to suppress vibration using piezoelectric elements connected to a shunt circuit is called piezoelectric shunt damping. Many studies on this subject have been reported. Among them a technique called switched shunt damping exists. In switched shunt damping developed so far, a switch is placed in the shunt circuit in series to the piezoelectric element, and is used to switch the shunt circuit from an open circuit to a closed circuit. Depending on the elements used in the shunt circuit, various types of switched shunt damping exist. This paper presents a new approach for switched shunt damping on inductance. The presented shunt circuit is composed of a resistance, an inductance and a switch connected in parallel with the inductance. Thus, when the switch is open the shunt circuit becomes an LR circuit, and when the switch is closed it becomes a resistive circuit. Furthermore, switching is operated based on the charge on the piezoelectric element, so that no sensors to conduct the switching are needed. To check the performance of vibration suppression by the proposed method, numerical simulations and experiments are conducted. The results show that the presented switched shunt damping have high performance of vibration suppression.

Topics: Damping
Commentary by Dr. Valentin Fuster
2015;():V008T13A034. doi:10.1115/DETC2015-46468.

Magnetorheological (MR) dampers are controllable semi-active dampers capable of providing a range of continuous damping settings. MR dampers are often incorporated in suspension systems of vehicles where conflicting damping characteristics are required for favorable ride comfort and handling behavior. For control applications the damper controller determines the required damper current in order to track the desired damping force, often by using a suitable MR damper model. In order to utilise the fast switching time capability of MR dampers, a model that can be used to directly calculate damper current is desired. Unfortunately few such models exist and other methods, which often negatively affect the computational efficiency of the model, need to be used when implementing these models. In this paper a selection of MR damper models are developed and evaluated for both accuracy and computational efficiency while tracking a desired damping force. The Kwok model is identified as a suitable candidate for the intended suspension control application.

Topics: Dampers
Commentary by Dr. Valentin Fuster
2015;():V008T13A035. doi:10.1115/DETC2015-46654.

Linear cantilevered piezoelectric energy harvesters typically rely on excitation around a resonance frequency for peak operation. Compounding the problem, typical ambient environments either vary dynamically in time or possess energy distributed across a wide spectrum of frequencies. Nonlinear broadband techniques have been implemented with success, but rely on chance that steady-state high energy orbits result as opposed to the low energy or chaotic trajectories that coexist in the basin of attraction. This work aims to implement two high dimensional chaotic controllers for large period orbits located within the chaotic attractor. The first control law is defined using traditional OGY, while the second uses the principles of invariant manifolds and is therefore independent of the system Jacobian. Comparison of the two control methods aims to show that invariant principles are less computationally intensive and result in equivalent stabilized orbits. Furthermore, the only necessary measurement for control design is a single time series representing a state of the system. This article compares two methods of chaos control and their ability to stabilize a large period orbit within the chaotic attractor for improved broadband piezoelectric energy harvesting.

Commentary by Dr. Valentin Fuster
2015;():V008T13A036. doi:10.1115/DETC2015-46867.

A non-contact modal analysis method is implemented to estimate the structural damping ratios for four stacks of sheet-steel, each bound using a different method. The setup comprised the four subject stacks and, for comparison, two single homogeneous steel plates of the same length and width with thicknesses that approximated the layered stack heights. To carry out the modal analyses, each test item was hung to simulate a free-free boundary condition. A force and frequency adjustable impact hammer imparted transient vibration to each hanging test piece after which the local relative velocity for each one of an array of discrete target points across the entire length-to-width surface was measured using an optical transducer. Damping ratios were extracted from the frequency response curves using the half power bandwidth method. Comparing the results obtained for the layered sheet-steel stacks with those from the homogeneous steel plates showed that damping ratios and loss factors can be estimated using the proposed experimental technique. The consistent impacts and the elimination of test structure mass loading improves the accuracy of damping estimates. In comparison to the solid plates, the layered sheet-steel stacks were characterized by increased damping. The effect was most significant for the stack bound together by polymer rivets.

Topics: Steel sheet , Damping
Commentary by Dr. Valentin Fuster
2015;():V008T13A037. doi:10.1115/DETC2015-47289.

Recent studies have demonstrated that the energetic vibrations of strategically designed negative stiffness inclusions may lead to large and adaptable damping in structural/material systems. Many researchers examine these features using models of bistable elements. From the viewpoint of system integration, bistable, negative stiffness elements often interface with positive stiffness elastic members. Under such conditions, the structural/material system may exhibit coexisting metastable states. In other words, the macroscopic displacement/strain remains fixed while the reaction force statically and/or dynamically varies due to internal change similar to a phase transition. This coexistence of metastable states is not manifested in an individual (stand-alone) bistable element. Although the static and low frequency dynamics of structural/material systems possessing coexisting metastable states have been explored, much remains to be understood regarding the dynamics and energy dissipation characteristics of such systems when excited near resonance, where nonlinear dynamics may be more easily activated and damping design is of great importance. Thus, to effectively elucidate the enhanced versatility of damping properties afforded by exploiting negative stiffness inclusions in structural/material systems, this research investigates a mechanical module which leverages a coexistence of metastable states: an archetypal building block for system assembly. The studies employ analytical, numerical, and experimental findings to probe how near-resonant excitation can trigger multiple dynamic states, each resulting in distinct energy dissipation features. It is shown that, for lightly damped metastable mechanical modules, the effective energy dissipation may be varied across orders of magnitude via tailoring design and excitation parameters. Potential applications and prototype systems are discussed to bridge the discoveries to future practice.

Commentary by Dr. Valentin Fuster
2015;():V008T13A038. doi:10.1115/DETC2015-47301.

Symmetric piecewise nonlinearities are employed here to design highly efficient nonlinear energy sink (NES). These symmetric piecewise nonlinearities are usually called in the literature as dead-zone nonlinearities. The proposed dead-zone NES includes symmetric clearance about its equilibrium position in which zero stiffness and linear viscous damping are incorporated. At the boundaries of the symmetric clearance, the NES is coupled to the linear structure by either linear or nonlinear stiffness components in addition to similar viscous damping to that in the clearance zone. By this flexible design of the dead-zone NES, we obtain a considerable enhancement in the NES efficiency at moderate and severe energy inputs. Moreover, the dead-zone NES is also found here through numerical simulations to be more robust for damping and stiffness variations than the linear absorber and some other types of NESs.

Commentary by Dr. Valentin Fuster
2015;():V008T13A039. doi:10.1115/DETC2015-47309.

Enhanced nonlinear energy sink (NES) is addressed here by employing a non-traditional kind of a nonlinear restoring force. The usual nonlinear coupling element between the NES and the linear oscillator (LO) in the literature generates essentially nonlinear restoring force between the NES and the LO. Unlike Type I NES, here the nonlinear coupling force has varying components during the oscillation which appear in closed loops under the effect of damping terms. This NES attachment with the LO rapidly absorbs and immediately dissipates significant portion of the initial energy induced into the LO through a strong resonance capture between the NES and LO responses. The proposed design could also be promising for energy harvesting purposes. The obtained results by numerical simulation show that employing this type of nonlinear restoring force for passive targeted energy transfer (TET) is more promising than some other types of NESs in which purely cubic stiffness restoring forces have been incorporated.

Commentary by Dr. Valentin Fuster
2015;():V008T13A040. doi:10.1115/DETC2015-47334.

Energy harvesting from vibrations has become, in recent years, a recurring target of a quantity of research to achieve self-powered operation of low-power electronic devices. However, most of energy harvesters developed to date, regardless of different transduction mechanisms and various structures, are designed to capture vibration energy from single predetermined direction. To overcome the problem of the unidirectional sensitivity, we proposed a novel multi-directional nonlinear energy harvester using piezoelectric materials. The harvester consists of a flexural center (one PZT plate sandwiched by two bow-shaped aluminum plates) and a pair of elastic rods. Base vibration is amplified and transferred to the flexural center by the elastic rods and then converted to electrical energy via the piezoelectric effect. A prototype was fabricated and experimentally compared with traditional cantilevered piezoelectric energy harvester. Following that, a nonlinear conditioning circuit (self-powered SSHI) was analyzed and adopted to improve the performance. Experimental results shows that the proposed energy harvester has the capability of generating power constantly when the excitation direction is changed in 360. It also exhibits a wide frequency bandwidth and a high power output which is further improved by the nonlinear circuit.

Commentary by Dr. Valentin Fuster
2015;():V008T13A041. doi:10.1115/DETC2015-47442.

The application of piezoelectric bender actuators as active resonators for energy harvesting may prove to be advantageous over uniaxial actuators as they can extract both rotary and translational energy from a flexible base. In addition, this minimizes the likelihood that the attachment location is the node of a mode (rotary or translational). In this paper, the equations of motion/boundary conditions are presented for a continuous two-beam system composed of a cantilevered, primary base beam with a secondary bender mounted to its surface. The secondary bender is composed of piezoelectric material. To generalize the analyses performed in this work, the equations were nondimensionalized. Using the nondimensionalized equations of motion, a tuning procedure is described to match the first natural frequency of the actuator beam to an arbitrary natural frequency of the base beam. The actuator beam was tuned to the first natural frequency of the base beam and a sensitivity study was performed to show the effect of the actuator beam attachment location on the system natural frequencies and mode shapes. Using the mode shape waterfall plots, a brief study was also performed to determine the percent strain energy in the actuator beam relative to the total system strain energy for the first four system modes.

Commentary by Dr. Valentin Fuster
2015;():V008T13A042. doi:10.1115/DETC2015-47539.

Piezoelectric energy harvesters typically perform poorly in the low frequency, low amplitude, and intermittent excitation environment of human movement. In this paper, a piezoelectric compliant mechanism (PCM) energy harvester is designed, modeled, and analyzed that consists of a PZT unimorph clamped at the base and attached to a compliant mechanism at the tip. The compliant mechanism has two flexures that amplify the tip displacement to produce large motion of a proof mass and a low frequency first mode with an efficient (nearly quadratic) shape. The compliant mechanism is fabricated as a separate, relatively rigid frame with flexure hinges, simplifying the fabrication process and surrounding and protecting the PZT unimorph. The bridge structure of the PCM also introduces an axial tensioning nonlinearity that self-limits the response to large amplitude impacts, improving the robustness of the device. Comparing the time domain performance based on realistic wrist acceleration data, the PCM produces 6 times more average power than a proof mass cantilever with the same unimorph area and natural frequency.

Commentary by Dr. Valentin Fuster
2015;():V008T13A043. doi:10.1115/DETC2015-47574.

Torsional vibration is present in various applications, such as in oil drilling pipes, engine crankshafts, and wind turbine gearboxes. In the case of oil drilling, ever deeper wells are being drilled and sensors used to gather data from the bottom of the well. Providing an energy source for these sensors is a big challenge. Harvesting energy from torsional vibrations presents a promising solution for powering the sensors on rotational systems. We investigated the concept of torsional vibration energy harvesting using a piezoelectric transducer attached to a shaft at an arbitrary angle with respect to the axis of the shaft. A comprehensive theoretical model considering all the working modes, including d15, d31, and d33 mode, has been developed to express the voltage outputs as functions of the mounting angle. The frequency responses of the voltage outputs over the input torque have also been studied and compared. A finite element model was also implemented to verify the theoretical results and illustrate the voltage distribution within the piezoelectric material under an external torque input.

Commentary by Dr. Valentin Fuster
2015;():V008T13A044. doi:10.1115/DETC2015-47647.

Vibration-based energy harvesting is a process by which ambient vibrations are converted to electrical energy, and is of interest for supplementing or replacing the batteries of individual nodes comprising wireless sensor networks among other applications. Generally, it is desired to match the resonant frequencies of the device with the primary ambient vibration frequencies for optimal energy harvesting performance. While previous work has demonstrated the use of magnetic forces to tune the resonant frequencies of vibrating energy harvesting structures, such efforts have been limited to one-dimensional analyzes. Here frequency tuning is realized by applying magnetic forces to the device in two-dimensional space, such that the resulting magnetic force has both horizontal and vertical components. In the case of a cantilever beam, the transverse force contributes to the transverse stiffness of the system while the axial force contributes to a change in the geometric stiffness of the beam. The effective resonant frequency of the device is then a function of the contributions of the original stiffness of the beam and the two additional stiffness components introduced by the presence of the magnet in 2D space. The simulation results from a COMSOL magnetostatics 3D model agree well with an analytical model describing the magnetic forces between the magnets as a function of location. Such 2D magnetic stiffness tuning approaches may be useful in applications where space constraints impact the available design space of the energy harvester.

Commentary by Dr. Valentin Fuster
2015;():V008T13A045. doi:10.1115/DETC2015-47698.

A three dimensional piezoelectric vibration energy harvester is designed to generate electricity from heartbeat vibrations. The device consists of several bimorph piezoelectric beams stacked on top of each other. These horizontal bimorph beams are connected to each other by rigid vertical beams making a fan-folded geometry. One end of the design is clamped and the other end is free.

One major problem in micro-scale piezoelectric energy harvesters is their high natural frequency. The same challenge is faced in development of a compact vibration energy harvester for the low frequency heartbeat vibrations. One way to decrease the natural frequency is to increase the length of the bimorph beam. This approach is not usually practical due to size limitations. By utilizing the fan-folded geometry, the natural frequency is decreased while the size constraints are observed. The required size limit of the energy harvester is 1 cm by 1 cm by 1 cm.

In this paper, the natural frequencies and mode shapes of fan-folded energy harvesters are analytically derived. The electro-mechanical coupling has been included in the model for the piezoelectric beam. The design criteria for the device are discussed.

Commentary by Dr. Valentin Fuster
2015;():V008T13A046. doi:10.1115/DETC2015-47700.

Particle damper is formed by granular particles enclosed in a container which is attached to or embedded in a vibrating structure. The energy dissipation mechanism of a particle damper is highly nonlinear, and derived from a combination of collision/impact and friction among particles and between particles and the enclosure. Meanwhile, the coupling between particle dampers and the host structure and among multiple dampers further increases the difficulty to analyze the particle damping performance. In this paper, a new coupling method is developed to integrate the continuous host system with multiple particle dampers to analyze the energy transfer between the host structure and the dampers. The discrete element method (DEM) is employed to describe and analyze the particle motion inside each damper, which accurately accounts for various energy dissipation mechanisms of the particle damping system. In order to enhance the computational efficiency, a Verlet table combined with LC method is also used to improve the contact detection since the long time simulation is needed to perform damping analysis under a wide range of frequencies. The damping effect under different arrangements of particle dampers on a clamped-free beam is analyzed, and the results indicate that the optimal positions of dampers not only rely on the mode shape of the system, but also are dependent upon the excitation level.

Commentary by Dr. Valentin Fuster
2015;():V008T13A047. doi:10.1115/DETC2015-47758.

This paper considers the use of a chain of springs and masses to reduce the transmission of shock and vibration through the system. The masses are equipped with internally rotating masses that absorb some of the axial vibration into internal kinetic energy of the masses. The internal masses have viscous damping, but no elastic or gravitational restraint. Previous research has shown that a single cart system attached to a vibrating structure can help mitigate shock through targeted energy transfer. This paper examines the potential for shock isolation provided by a chain of such systems. Through numerical simulations, tradeoffs are examined between displacement and transmitted force.

Commentary by Dr. Valentin Fuster
2015;():V008T13A048. doi:10.1115/DETC2015-47764.

Fluidic Flexible Matrix Composite (F2MC) tubes are a new class of high-authority and low-weight fluidic devices that can passively provide vibration damping, absorption, and isolation. In this paper, transverse cantilever beam vibration causes strain-induced fluid pumping in F2MC tubes bonded to the beam surface, generating flow through a fluidic circuit. The F2MC tubes and fluidic circuit are designed to significantly reduce moment and shear transmission at the root of the cantilever beam. An analytical model of a cantilever beam with F2MC tubes is used to perform a parametric study via Monte Carlo methods. An isolator is designed that simultaneously attenuates root shear and moment transmission by over 99% at the first bending mode. By modifying the fluidic circuit dimensions and F2MC tube attachment locations, over 99% root shear and moment transmission attenuation is achieved for the second beam bending mode. The tunability and pumping efficiency of the F2MC tube makes it a promising candidate for passive vibration control applications, including aerospace structures such as wings and rotorcraft landing gear.

Commentary by Dr. Valentin Fuster
2015;():V008T13A049. doi:10.1115/DETC2015-47766.

The design of isolation mounts is of critical importance in the protection of structures and sensitive equipment from damage or failure. Simultaneous protection from both shock and vibration is particularly challenging because of the broadband nature of the input signal and because of the deleterious effect of damping on high-frequency isolation. Prior work by the authors has shown that chains of translating mass/spring elements can act as a “mechanical filter” for input disturbances. However, in finite-length chains, wave reflections can result in secondary pulses that hit the structure and can diminish the effectiveness of the isolator. In this paper, a new type of isolator is developed that converts translational input forces into a combination of translational and rotational motion. If designed correctly, the rotational motion can be managed so that it does not result in additional forces transmitted to the structure. In effect, the isolator is able to trap some of the input energy into rotational vibration, preventing it from reaching the structure. Parametric simulation studies are conducted as various system parameters are varied.

Commentary by Dr. Valentin Fuster
2015;():V008T13A050. doi:10.1115/DETC2015-47775.

It has been shown by several research groups over the past few years that vibration energy harvesters with intentionally designed nonlinear stiffness components can be used for frequency bandwidth enhancement under harmonic excitation for sufficiently strong vibration amplitudes. In order to overcome the need for high excitation intensities that are required to exploit nonlinear dynamic phenomena, we have developed an M-shaped piezoelectric energy harvester configuration that can exhibit a nonlinear frequency response under low vibration levels. This configuration is made from a continuous bent spring steel with piezoelectric laminates and a proof mass, and no magnetic components. Careful design of this nonlinear architecture that minimizes piezoelectric softening further enables the possibility of achieving the jump phenomenon in hardening at base acceleration levels on the order of a few milli-g. In the present work, such a design is explored for both primary and secondary resonance excitations at different vibration levels and for different electrical loads. Following the primary resonance excitation case that offers more than 600 % increase in the half-power bandwidth as compared to the linear system at a root-mean-square excitation level as low as 0.04g, secondary resonance behavior is investigated with a focus on 1:2 and 1:3 superharmonic resonance neighborhoods. A multi-term harmonic balance formulation is employed for a computationally effective yet high-fidelity analysis of this high-quality-factor system with quadratic and cubic nonlinearities. In addition to primary resonance and secondary (superharmonic) resonance cases, multi-harmonic excitation is modeled and experimentally validated.

Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Experiments in Dynamical Systems

2015;():V008T13A051. doi:10.1115/DETC2015-46210.

The complex modes of an end-damped cantilevered beam are studied as an experimental example of a non-modally damped continuous system. An eddy-current damper was applied considering its noncontact and linear properties. The state-variable modal decomposition (SVMD) is applied to extract the modes from the impact responses in the cantilevered beam experiments. Characteristics of the mode shapes and modal damping are examined for various values of the damping coefficient. The modal frequencies and mode shapes obtained from the experiments have a good consistency with the results of the finite-element model. The variation of damping ratio and modal nonsynchronicity with varying damping coefficient also follow the prediction of the model. Over the range of damping coefficients studied in the experiments, we observe a maximum damping ratio in the lowest underdamped mode, which correlates with the maximum modal nonsynchronicity. Complex orthogonal decomposition (COD) is applied in comparison to the modal idenfication results obtained from SVMD.

Commentary by Dr. Valentin Fuster
2015;():V008T13A052. doi:10.1115/DETC2015-46347.

The conventional modal testing, hereafter referred as Displacement Modal Testing (DMT) is based on measurement of displacement, velocity or acceleration as well as excitation force. An enormous literature regards the DMT, on the contrary, a few papers address modal testing based on strain gauges or strain sensor, hereafter referred as Strain Modal Testing (SMT). The main reason of this scenario is due to practical problems in the use of strain gauges as calibration procedure, ground loop, sensitivity not adequate at high frequency, bonding quality. In this work, a novel piezoelectric strain sensor is used for SMT. It is demonstrated in the present work that this sensor overcomes the practical drawbacks related to the use of strain gauges. Thus, SMT based on piezoelectric strain sensors can be a valid alternative to DMT, usually based on accelerometers. Comparisons between the modal testing results concerning brackets with different constraint conditions using both accelerometers and strain sensors are given in terms of modal parameters, highlighting their pros and cons.

Topics: Testing , Displacement
Commentary by Dr. Valentin Fuster
2015;():V008T13A053. doi:10.1115/DETC2015-46555.

Finite element models have been widely employed in an effort to quantify the stress and strain distribution around human bones as well as implanted prostheses and to explore the influence of these distributions on their long-term stability. In order to provide meaningful predictions, such models must contain an appropriate reflection of mechanical properties. Detailed geometrical and density information is now readily available from CT scanning. However, there are still many complications regarding patient-specific geometrical differences and bone dynamic behavior in-vivo. Experimental studies on animal bones, due to their convenience and accessibility, have always played a key role in simulating human bone behavior. In current study, a modal experiment has been done on an ox femoral and tibial bones and the results have been compared with those reported from human bones. Results have been obtained in terms of natural frequencies of medio-lateral bending mode shapes and damping ratios, and compared with those obtained by some previous studies. The results suggest similar pattern in modal behavior, but considerable difference between natural frequencies due to geometrical differences. To consider structural damping ratios, due to existence of moisture and marrow in bone in-vivo, samples have been obtained few hours post-mortem and the ratio has been extracted for each natural frequency.

Finally, conclusions have been made on the similarity of the models and how to improve the FE models of human tibial and femoral components.

Topics: Bone
Commentary by Dr. Valentin Fuster
2015;():V008T13A054. doi:10.1115/DETC2015-47398.

In computer vision, cameras more and more accurate, fast, 3D featured are used. These still evolutions generate more data, which is an issue for users to store it with standard compression for example for recording proof in case of products manufacture defective.

The aim of this work is to develop a specific solution adapted for vision systems which have a known scenario and can be described by dynamic models. In this framework, Kalman filters are used for data compression, observable variable prediction, and augmented reality. The developed concepts are tested with a scenario of a ruler on a table. The experiment aims to check the data compression level, the estimation of the friction forces coefficient of the ruler and the prediction of the stop position.

Commentary by Dr. Valentin Fuster
2015;():V008T13A055. doi:10.1115/DETC2015-47820.

In the dynamic calibration of force transducers using swept-sine excitation, the sensitivity (the output voltage divided by the applied force) of the transducer can start to decrease (or roll-off) at higher frequencies. It has been proposed that this roll-off originates from the finite stiffness and dissipation of the transducer. In other words, the roll-off is caused by a mechanical frequency response of the transducer, and the sensitivity is proportional to this frequency response function via a constant. The focus of this study is the origin of the observed roll-off in sensitivity. The findings of this study have application to the dynamic calibration and use of force transducers.

Commentary by Dr. Valentin Fuster
2015;():V008T13A056. doi:10.1115/DETC2015-48018.

The aim of this study was to make a method usable in an early detection of malfunction, e.g., abnormal vibration/fluctuation in recorded signals. We conducted experimentations of heart health and structural health monitoring. We collected natural world signals, e.g., heartbeat fluctuation and mechanical vibration. For the analysis, we used modified detrended fluctuation analysis (mDFA) method that we have made recently. mDFA calculated the scaling exponent (SI, the acronym SI is derived from the scaling indices) from the time series data, e.g., R-R interval time series obtained from electrocardiograms. In the present study, peaks were identified by our own method. In every single mDFA computation, we identified ∼2000 consecutive peaks from a data: “2000” was necessary number to conduct mDFA. mDFA was able to distinguish between normal and abnormal behaviors: Normal healthy hearts exhibited an SI around 1.0, which is a phenomena comparable to 1/f fluctuation. Job-related stressful hearts and extrasystolic hearts both exhibited a low SI such as 0.7. Normally running car’s vibration — recorded steering wheel vibration — exhibited an SI around 0.5, which is white noise like fluctuation. Normally spinning ball-bearings (BB) exhibited an SI around 0.1, which belongs to the anti-correlation phenomena. A malfunctioning BB showed an increased SI. At an SI value over 0.2, an inspector must check BB’s correct functioning. Here we propose that healthiness in various cyclic vibration behaviors can be quantitatively analyzed by mDFA.

Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Industrial Applications of Dynamics, Vibration, and Acoustics

2015;():V008T13A057. doi:10.1115/DETC2015-46509.

Automatic machines for the preparation of coffee from the bean to the cup have now a wide diffusion among coffee amateurs. Since these machines are usually installed at home and in offices, low noise emission is an important design requirement. These small appliances are complex dynamic systems from the point of view of noise and vibration control, because they include some electric motors, a transmission, a grinder, some mechanisms, a suspension system, cavities and radiating panels. In the last decades various methods for the experimental study of vibrations have been developed in the aerospace and automotive fields, like transfer path analysis and modal testing. The first section of this paper describes the potentialities and the limits of these methods, when a small appliance (maximum size 300 mm) has to be tested in an industrial environment. Then a specific method for the study of the flux of energy from the motor-grinder group to the acoustic field is presented. It is based on the physical variation in the stiffness of the resilient connections, which is carried out with the design of experiments approach. The noise spectra measured outside the machine and the vibration spectra measured in critical points inside the machine are analyzed with correlation techniques. Results show that the resilient mounts are effective, but one transmission path influences noise transmission more than the others, mainly owing to the asymmetrical construction of the motor-grinder group and of the appliance structure. Suggestions for improved noise control are given.

Commentary by Dr. Valentin Fuster
2015;():V008T13A058. doi:10.1115/DETC2015-47495.

This paper presents a high-resolution measurement system for fast-rotating tires. The developed system is compatible with and can be integrated with the tire testing machines used in industry research facilities. A field programmable gate array controller with a high clock rate triggers a short duration strobe flash capturing a clear instant image of a rotating tire based on an encoder reference signal. Since the rotation of a tire on a testing machine is periodic, the system can effectively capture the deformation of a rotating tire at a high equivalent sampling frequency. The Complementary Metal-Oxide-Semiconductor (CMOS)-based high-resolution low-cost system can be employed to measure tire deformation associated with sound generation. This was implemented by synchronously measuring sound with a microphone array. The validity of the developed system was investigated by experimental evaluation. Then, the system was implemented at the tire testing facility, and tested by rotating a tire at a drum speed up to 100 km/h and capturing images at every 0.025 degree rotation.

Commentary by Dr. Valentin Fuster
2015;():V008T13A059. doi:10.1115/DETC2015-47618.

When crane payloads are lifted off the ground, the payload may unexpectedly swing sideways. This occurs when the hoist cables are at an angle relative to vertical and the payload is not directly beneath the hoist. Because the hoist point is far above the payload, it is difficult for crane operators to know if the hoist cable is perfectly vertical before they start to lift the payload. Some amount of horizontal motion of the payload will always occur at lift off. If an off-centered lift results in significant horizontal motion, then it creates a hazard for the human operators, the payload, and the surrounding environment. This paper develops dynamic models of off-centered lifts and presents experimental verification of the theoretical predictions. To mitigate the detrimental effects of off-centered lifts, autonomous-centering solutions are proposed.

Topics: Cranes
Commentary by Dr. Valentin Fuster
2015;():V008T13A060. doi:10.1115/DETC2015-47916.

This paper describes an open source parallel simulation framework capable of simulating large-scale granular and multi-body dynamics problems. This framework, called Chrono::Parallel, builds upon the modeling capabilities of Chrono::Engine, another open source simulation package, and leverages parallel data structures to enable scalable simulation of large problems. Chrono::Parallel is somewhat unique in that it was designed from the ground up to leverage parallel data structures and algorithms so that it scales across a wide range of computer architectures and yet has a rich modeling capability for simulating many different types of problems. The modeling capabilities of Chrono::Parallel will be demonstrated in the context of additive manufacturing and 3D printing by modeling the Selective Layer Sintering layering process and simulating large complex interlocking structures which require compression and folding to fit into a 3D printer’s build volume.

Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Rotordynamics and Rotating Systems

2015;():V008T13A061. doi:10.1115/DETC2015-46016.

Modern wind turbines are enormous large-scale electromechanical systems. They operate in complex conditions, determined by a turbulent wind field, by possible disturbances in the electricity grid and by the behavior of sea waves for offshore turbines. Guaranteeing the structural integrity of these machines during a lifetime of 20 years is an enormous challenge. In this paper the dynamics of a wind turbine drive train high speed subsystem is studied both by modeling and experiments with focus on system torsional and flexural vibrations and transient events which can reduce fatigue life of functional components (gearbox, bearings, shafts, couplings, others). A scaled down drive train high speed shaft test rig has been developed. Main components of the test rig are six-pole motor with variable frequency drive controller (up to 1000 rpm), shafts’ disk coupling and flexible mounting structure representing gearbox housing with output high speed bearing. The test rig is equipped with measurement system comprising a set of accelerometers and displacement sensors, data acquisition hardware and software (SKF WindCon3.0). Mathematical and computational models of the test rig have been developed and went through validation tests. The system kinematic and dynamic responses are studied for different operational scenarios and structural parameters (ratio of shaft bending stiffness and stiffness of mounting structures, unevenly inertia load distribution, others). The ultimate goal of the test rig is to get insight into interaction between internal dynamics of drive train functional components to be used the results obtained in developing novel methods to detect, predict and prevent faults and failures in wind turbine drive trains arising due to misalignments and transient external loads.

Commentary by Dr. Valentin Fuster
2015;():V008T13A062. doi:10.1115/DETC2015-46262.

Turbomachines are continuously developing in order to reach higher levels of speed, power and efficiency and the classical Fixed Geometry Journal Bearings have been replaced by Tilting Pad Journal Bearings to avoid instability phenomena. In this paper, the authors propose an innovative quasi-3D TPJB modelling approach that allows the simultaneous and coupled analysis of the typical phenomena involved in TPJB operations. The authors focused on the accurate analysis of the interactions between the rotor and the lubricant supply plant and on the fluid dynamical effects due to the bearing that cause those couplings, aiming at reaching a good compromise between the accuracy and the numerical efficiency of the model (mandatory to analyze systems with many bearings).

The TPJB model has been developed and experimentally validated in collaboration with Nuovo Pignone General Electric S.p.a. which provided the technical data of the system and the results of experimental tests.

Commentary by Dr. Valentin Fuster
2015;():V008T13A063. doi:10.1115/DETC2015-46416.

In order to analyze turbine blades vibration caused by flutter, it is necessary to understand both aerodynamic damping and structural damping of high vibration stress. Flutter Vibration mode occurring in rated speed is non-synchronous mode. For measuring non-synchronous mode damping ratio of turbine blades, AC-type electromagnet which can generate high frequency excitation force was developed. Damping ratio characteristics of non-synchronous mode of nodal diameter 12,4 was measured in rotational test. For comparison, synchronous mode of nodal diameter 4 was measured, too. It was concluded as follows. (1) It is possible to excite non-synchronous mode by high frequency excitation electromagnet and calculate damping ratio from measurement resonance curve. (2) Damping ratio of non-synchronous mode ND12,4 was increased by increasing the excitation force. Synchronous mode ND4 is also a similar trend. (3) Nodal diameter 4 damping ratio of non-synchronous mode (Resonant speed=100%) was lower than synchronous mode (Resonant speed=75%).

Commentary by Dr. Valentin Fuster
2015;():V008T13A064. doi:10.1115/DETC2015-46422.

The common impulse feature model is oscillating and attenuated signal with a single maximum peak, while the formation principle of actual impulse feature is ignored. Considering the continuous dual impulse waveform feature of rolling bearing fault in the vibration signal and the matching effects of the single impulse waveform with Morlet wavelet, a “dual impulse Morlet wavelet” model is proposed. Through ant colony algorithm with the indicator of the maximum cross-correlation, 4 types of parameters are optimized adaptively which affect the similar degree between dual impulse Morlet wavelet and the dual impulse waveform intercepted from the bearing vibration signal. Then, the optimal model is obtained. The bearing fault experiment verification shows that the optimal dual impulse Morlet wavelet can effectively improve the analytical precision and energy concentration of impulse feature in both of time domain and frequency domain, which overcomes the disadvantages of Morlet wavelet effectively.

Commentary by Dr. Valentin Fuster
2015;():V008T13A065. doi:10.1115/DETC2015-46477.

Gyroscopic systems are multi-body systems which present coupled three dimensional motion. The configuration space and the state space are differentiable manifolds, and differential geometric concepts are frequently useful in the process of modeling. This paper deals with a Control Moment Gyroscope (CMG), which is not asymptotically stable, so it needs a stabilizing control law. We apply a new methodology of modeling kinematics and dynamics of rigid multi-body systems, based in the concept of Cartan’s connection and covariant derivative. The systems has two inputs (torques) and two outputs (angles) that will be controlled by a robust linear closed-loop control technique (LQG/LTR). Experimental results are presented in order to validate the proposal.

Commentary by Dr. Valentin Fuster
2015;():V008T13A066. doi:10.1115/DETC2015-46567.

Competition and high quality requirements in the industries have necessitated the need for reliable rotating machines. This can be partly achieved by continuous monitoring of operation conditions to detect any fault before it causes serious problem or breakdown of rotating machines. The detection of faults in rotating blades via direct blade vibration measurements and analysis is somewhat difficult because blades often operate in a very harsh environment (gas turbine blades are rotating in high temperature and pressure environment). This paper presents indirect detection of blade faults from lateral vibrations of a rotor-disk-blade system, which can easily be measured, using laboratory test-rig. A rotor, disk, 6 normal blades and 3 blades with different defects were designed. The modal parameters of the normal and defective blades were determined experimentally and by modal analysis using ANSYS. The lateral vibrations, in the x- and y-axis, of the rotor-disk system with normal 6 blades and with 5 normal blades and 1 defective blade at a time were measured and analyzed. The results revealed that defective blades showed some distinct characteristics in the frequency domain, which can be used to identify blade faults in a bladed rotor-disk system.

Commentary by Dr. Valentin Fuster
2015;():V008T13A067. doi:10.1115/DETC2015-46598.

Tilting–pad journal bearings (TPJBs) are widely used in rotating machinery to support the rotors efficiently at elevated speeds under light/heavy loadings. Because of the importance of this machine component, many authors have published several theoretical and experimental studies, to evaluate the influence of clearance, lubricant temperature, oil flow-rate and thermal effects on behavior of TPJB. However, the investigations of the influence of loading direction on properties of TPJB are very limited. In bearing models as well as in experimental tests, the load is often assumed along the vertical direction only and the geometry of the bearing is the same for each pad, which corresponds to an axial symmetry of the bearing. This paper presents first a theoretical analysis of the influence of the load direction on both the static and the dynamic behavior of a five-pad TPJB with a non-uniform clearance: that is, the different bearing configurations in the range between load-on-pad (LOP) and load-between-pads (LBP) are investigated. Then, the analytical results are compared with experimental measurements. The tests were performed with a nominal diameter of 100 mm and a length–to–diameter ratio of 0.7, using a suitable test-rig, in which it is possible to apply the static load in any direction. The procedure for the estimation of the bearing geometry from experimental measurement of the non-uniform clearance profile is also described. The results show that the load direction has considerable effects on both the static and the dynamic characteristics of the TPJB. Besides, the influence of load directions is stronger on the dynamic characteristics of tilting pad bearing than on the static ones.

Commentary by Dr. Valentin Fuster
2015;():V008T13A068. doi:10.1115/DETC2015-46601.

Journal bearings have been widely used in high-speed rotating machinery. The dynamic coefficients of oil-film force affect the machine unbalance response and machine stability. The oil-film force of hydrodynamic bearing is often characterized by a set of linear stiffness and damping coefficients. However the linear oil-film coefficients with respect to an equilibrium position of the journal are inaccurate when the bearing system vibrates with large amplitudes due to a dynamic load. The study on nonlinear oil-film forces is still rare and most papers are confined to theoretical analyses. The purpose of this paper is to derive some new non-linear force models (28-co., 24-co. and 36-co. models) to identify these dynamic coefficients based on experimental data. The fundamental test model is obtained from a Taylor series expansion of bearing reaction force. Tests were performed with a nominal diameter of 100mm and a length–to–diameter ratio of 0.7 using a suitable test rig in which it is possible to apply the static load in any direction. The results show that these three models are feasible to identify the oil-film forces in which the second-order oil-film coefficients received from the 24-co. model are more stable compared to those of other two nonlinear models.

Commentary by Dr. Valentin Fuster
2015;():V008T13A069. doi:10.1115/DETC2015-46609.

In the field of rolling element bearing, the degradation of bearing health could be detected by means of suitable damage indexes. Band-Kurtosis index, that is the kurtosis value of the band-filtered signal, is often assumed. The critical point of this approach is the selection of a suitable filter band. In the paper, the use of a chaos metrics, namely the Higuchi fractal dimension as damage indicator is described. The trend of this index is compared with the common approach of band-kurtosis indicator for an experimental case of a rolling element bearing in which the defect developed until a permanent failure.

Commentary by Dr. Valentin Fuster
2015;():V008T13A070. doi:10.1115/DETC2015-46621.

Modern aero-engines have reached a high level of sophistication and only significant changes will lead to the improvements necessary to achieve the economic and environmental targets of the future. Open rotors constitute a major leap in this direction, both in terms of efficiency and of technological innovation. This calls for a revision of the accepted design practices, and a new focus on phenomena that have been little investigated in the past, such as the Coriolis effect, or the gyroscopic coupling of the blades with the shaft. Experimental results from modern fans, with large blades and strong stagger angles, are showing dependence on Coriolis gyroscopic effects already, an effect that is expected to be strongly enhanced with the proposed open rotor designs.

For an accurate prediction of the Coriolis and gyroscopic effects in rotating assemblies a fully experimentally validated approach is needed. Today’s FE models can capture the basic physical phenomena, but experimental confirmation is still needed for the evolution of the mode shapes with angular speed, and the influence of damping and geometric nonlinearities when gyroscopic coupling is considered. To support this validation effort a new rotating test rig will be introduced, initial measurement data will be discussed, and a comparison with a finite element analysis presented.

Different forcing patterns, including forward and backward travelling-wave engine order excitation could be experimentally excited in the new rig, Coriolis-induced frequency splits were found in the dynamic response, showing a significant change in the dynamic behaviour of the investigated dummy disk, and only a minor impact of the mistuning was observed on the frequency splits due to Coriolis effects. The experimental results have been compared to a finite element analysis, and after some updating a good agreement between the predicted and measured Campbell diagrams could be obtained, demonstrating the reliability of the modelling approach.

Topics: Coriolis force , Disks
Commentary by Dr. Valentin Fuster
2015;():V008T13A071. doi:10.1115/DETC2015-46718.

The increased speed and power level of rotating machinery most often bring the problem of non-synchronous instability. Many of the current most interesting problems, have been caused by synchronous thermal instability. These problems are related to the machinery overhangs predominantly, many are due to heavy couplings and the associated fluid film bearing non-uniform heating of the rotor shaft coupling end journal area. For couplings with long spacer tubes, other causes of excessive synchronous vibration are worthy of discussion. Long coupling spacer tubes with balance correction made at low speed and operating in service too near the coupling spacer critical speed can result in excessive synchronous vibration. Once the spacer has large mid-span amplitude, additional nonlinear vibration can occur. This paper discusses a recent occurrence of this interesting problem and will show why it should not be overlooked in future coupled multi-body high speed machinery trains, or any driveshaft balanced only at the shaft end plains.

Topics: Machinery , Vibration
Commentary by Dr. Valentin Fuster
2015;():V008T13A072. doi:10.1115/DETC2015-46809.

This work describes the analysis of helicopter ground resonance when nonlinearity and non-isotropy of the problem are taken into account. Ground resonance is a dynamic instability caused by the interaction between the rotor and the airframe of a helicopter. Sources of nonlinearity can be geometrical (finite blade lead-lag motion) and constitutive (hydraulic lead-lag dampers and shock absorbers). Standard methods use special coordinate transformations that make it possible to cast the problem in linear, time invariant form when considering small oscillations of an isotropic rotor about a reference solution. However, potential non-isotropy of the rotor (e.g. resulting from degraded performance of lead-lag dampers) may turn the problem into linear, time periodic. In such cases, the Floquet-Lyapunov method is normally used to study the stability of the coupled system. In this work the problem is investigated using Lyapunov Characteristic Exponents (LCE). The analysis shows that in some cases, characterized by a marked contribution of the nonlinearity of the blade lead-lag dampers, the problem assumes a nearly chaotic behavior. The stability of the system is investigated, and the sensitivity of the LCEs with respect to system parameters is determined, in an attempt to provide a consistent analysis framework and useful design guidelines.

Topics: Resonance , Dampers
Commentary by Dr. Valentin Fuster
2015;():V008T13A073. doi:10.1115/DETC2015-46816.

In nonlinear rotordynamics, techniques can take advantage of the periodic steady state behavior to predict quickly and accurately the mass unbalance response to a series of parameters, especially with the presence of certain nonlinearities which leads to nonlinear dynamics and complicated responses. The method proposed here calculates the response curve by combining Harmonic Balance Method, Alternating Frequency-Time method and continuation. The singular points where a stability change often arises are detected with the sign change of the Jacobian determinant and then located through a penalty method that increases the solving equation system by a completing constraint. Tracking these points, which provides an efficient way to analyze parametrically the nonlinear behavior of a system, can be fulfilled, once again, by the continuation technique.

Commentary by Dr. Valentin Fuster
2015;():V008T13A074. doi:10.1115/DETC2015-47062.

The semi-floating ring bearings (SFRBs) are developed to attenuate rotor vibrations by providing damping, but the subsynchronous oscillations cannot be avoided. The subsynchronous oscillations of the rotor are the self-excited whirl motions for the instability of the oil films. Their frequencies are usually less than the half of the rotor speed, but difficult to be predicted because the effects of SFRB’s parameters on the subsynchronous oscillation frequency are not clear. In this paper, an analytical expression is proposed to estimate the subsynchronous whirl frequency of SFRB. To verify the accuracy of the predicting expression, the two-dimensional nonlinear responses of the SFRB are calculated by the Finite Element (FE) method. After confirming the accuracy, the predicting expression is generalized to the rotor-SFRBs (flexible rotor supported by SFRBs). The nonlinear responses of rotor-SFRBs are simulated. Two typical subsynchronous oscillations excited by the two SFRBs respectively are observed, and their frequencies coincide the prediction of the expression as expected.

Topics: Bearings , Rotors , Whirls
Commentary by Dr. Valentin Fuster
2015;():V008T13A075. doi:10.1115/DETC2015-47122.

Conventional Vibration-based Condition Monitoring (VCM) is well known and well accepted in industries to identify the fault(s), if any, in rotating machine since decades. However over the last 3 decades, significant advancement in both computational and instrumentation technologies has been noticed which resulted in number of research studies to find the alternate and efficient methods for fault(s) diagnosis. But most of the research studies may not be leading to an Integrated Modern VCM (IMVCM). It may be because of mainly 2 reasons; (a) the recent proposed methods in the literature are based on numerically simulated studies and a very limited experimental studies and (b) none of the recent studies applied on all kind of faults. In this paper, a summary of a couple of methods proposed and published earlier by author to meet the requirement of the IMVCM is presented.

Commentary by Dr. Valentin Fuster
2015;():V008T13A076. doi:10.1115/DETC2015-47586.

This paper is dedicated to the analysis of uncertainties affecting the load capability of a 4-pad tilting-pad journal bearing, in which the load is applied between two pads (load on pad configuration; LOP). A well-known stochastic method has been extensively used to model uncertain parameters, the so-called Monte Carlo simulation. However, in the present contribution, the inherent uncertainties of the bearings’ parameters (i.e. the pad radius, the oil viscosity, and the radial clearance) are modeled by using a fuzzy logic based analysis. This alternative methodology seems to be more appropriate when the stochastic process that characterizes the uncertainties is unknown. The analysis procedure is confined to the load capability of the bearing, being generated by the envelopes of the pressure fields developed on each pad. The hydrodynamic supporting forces are determined by considering a nonlinear model, which is obtained from the solution of the Reynolds’ equation. The most significant results are associated to the changes in the dynamic behavior of the bearing because of the reaction forces that are modified according the uncertainties introduced in the system. Finally, it is worth mentioning that the uncertainty analysis in this case provides relevant information both for design and maintenance of tilting-pad hydrodynamic bearings.

Commentary by Dr. Valentin Fuster
2015;():V008T13A077. doi:10.1115/DETC2015-47889.

We consider the nonlinear vibration response of rotating flexible shafts fitted with centrifugally driven pendulum vibration absorbers (CPVAs) that are used to address engine-order torsional vibrations. The model used to represent the behavior of the flexible shaft consists of two lumped inertial elements with an interconnecting stiffness element, which captures the rigid body and fundamental torsional vibration modes of the rotor. The absorbers are centrifugally driven pendulums fitted to a rotor element, such that their natural frequencies scale with the rotor speed, and can thus tuned to a given order of rotation. Previous analysis of a linearized version of this coupled rotor-absorber system revealed frequency veering behavior as the rotation speed varies, and showed that one can detune the absorber to eliminate key system resonances. In this paper the behavior of the system is analyzed for large absorber amplitudes using perturbation methods and numerical simulations. It is shown that the absorbers remain effective in reducing torsional vibration when moving through large amplitudes, and that the resonance avoidance is similarly robust. This has practical implications for the tuning of absorbers in certain applications.

Commentary by Dr. Valentin Fuster
2015;():V008T13A078. doi:10.1115/DETC2015-48106.

In this paper, the time series response of a rotor with bearing outer race faults is analyzed. The recurrence quantification analysis (RQA) parameters deduced from the recurrence plot (RP) of the system response are used to delve into characterization of the specific and overall behavior of the system. Attention is focused on the variation of the RQA parameters for healthy and defective states of the system. The results of this investigation are encouraging for further application of the method of RP in the diagnostics and analysis of bearing faults. In fact, it is shown that appropriate classification of the RQA can be effectively used to detect outer race faults and serve as a discriminant for fault severity.

Commentary by Dr. Valentin Fuster
2015;():V008T13A079. doi:10.1115/DETC2015-48107.

Most of the current approaches in gear fault diagnostic analysis do not provide a clear indication for discrimination between various common faults. This is almost certainly because failure in gear systems is always accompanied with a complex dynamic response. The inherent nonlinearities in geared systems and additional nonlinearity due to faults conspire to make the diagnostics problem extremely complex. The main goal of this paper is to exploit the nonlinear response in an attempt to solve this challenging problem. We aim to demonstrate effective discrimination between four kinds of common defects in gears by utilizing the method of recurrence analysis. We consider a healthy system, a system with a single crack, a system with multiple cracks and a system with a missing tooth. Careful measurements are collected from an experimental set up which is a mock-up of a real industrial gear box system. We develop and apply recurrence plot analysis to this data. Our results show that recurrence analysis parameters such as recurrence rate, trapping time, entropy and maximal diagonal length can be very effective in successful discrimination of gear faults.

Topics: Gears
Commentary by Dr. Valentin Fuster
2015;():V008T13A080. doi:10.1115/DETC2015-48108.

Observations, analysis and understanding of out-of-the-ordinary rotordynamic phenomena (including several instabilities and nonlinear responses) observed in aircraft gas turbine engines and other high-speed rotating machinery over the course of the author’s career in the design and development of aircraft gas turbine engines are described. Some observed phenomena were already widely recognized in the rotordynamic community such as:

• Hysteretic whirl

• The tip clearance effect on stability of turbomachinery rotors

• Instability due to trapped liquids in the rotor

• Hysteresis in the resonant peak amplitude

• Effective suppression of rotor instability by anisotropy in the engine support structure

Other observations were fairly new to the field of rotordynamics at that time they were observed but were identified as being new manifestations of vibration phenomena already familiar to vibration technologists in fields other than high-speed rotordynamics such as:

• Sum-and-difference frequency response

• Relaxation oscillations

• Nonlinear effects of anisotropic clearance in roller and gas bearings

At that time these phenomena were observed, the pressure for remediation of the problems they represented in the context of ongoing aircraft engine development resulted in intense attention and analysis which, in turn, often resulted in new insights, useful diagnoses, and effective remedial actions.

Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Structures and Continuous Systems

2015;():V008T13A081. doi:10.1115/DETC2015-46163.

Nonlinear free vibration analysis of piezoelectric functionally graded (PFG) beams in thermal environment with any boundary conditions are investigated. The nonlinear governing Equation of motion is derived based on the Euler-Bernoulli beam theory and Von Karman’s strain-displacement relation. Simple analytical expression is presented for the nonlinear natural frequency using energy balanced method (EBM). Results are validated and compared with available results in the literature. Effects of different parameters such as vibration amplitude, boundary conditions, material inhomogenity, electrical and thermal loading on the nonlinear behavior of PFG beams are presented.

Topics: Free vibrations
Commentary by Dr. Valentin Fuster
2015;():V008T13A082. doi:10.1115/DETC2015-46364.

The free undamped vibrations of cables undergoing stretching, bending and twisting are investigated. To this end, a geometrically exact model of elastic cables accounting for bending and torsional stiffness is employed. The cable kinematics retain the full geometric nonlinearities. Starting from a prestressed catenary configuration, the nonlinear equations of motion are linearized about the initial equilibrium. In particular, two initial equilibrium states (shallow and taut) are considered while varying the cable elastic axial stiffness. The influence of the bending flexibility on the cable frequencies is assessed by direct comparisons with the frequencies predicted by classical cable theories of purely extensible cables.

Commentary by Dr. Valentin Fuster
2015;():V008T13A083. doi:10.1115/DETC2015-46584.

This paper investigates parametric resonance of electrostatically actuated MEMS circular plates for resonator sensing applications. The system consists of a clamped circular elastic plate over a ground plate. Soft AC voltage of frequency near natural frequency of the plate gives the electrostatic force that leads the elastic plate into vibration, more specifically into parametric resonance which can be used afterwards for biosensing purposes. Frequency response and corresponding bifurcations are reported. The effects of damping and voltage are predicted.

Commentary by Dr. Valentin Fuster
2015;():V008T13A084. doi:10.1115/DETC2015-46620.

The vibration model of a wind turbine blade can be approximated as a rotating pretwisted nonsymmetric beam, with damping and gravitational and aeroelastic loading. In this work, the out-of-plane (flapwise) and in-plane (edgewise) motion are examined with simple aeroelastic damping effects. The aeroelastic model used is based on a simple quasisteady blade-element airfoil theory. The linear velocity dependent terms are isolated and incorporated into the damping, which then turns out to be generally non modal (non Caughey). The complex modes are analyzed while neglecting the effects of rotation to single out the effect that aerodynamic damping may have on the modes. The analysis is done by first discretizing the system with assumed modes, and then solving an eigenvalue problem for the state-variable description of the discretized system. The eigen modes are recombined with the assumed mode functions to approximate the modes in the original system. The analysis is performed on the National Renewable Energy Laboratory (NREL) 23-meter blade, the NREL 63-meter blade, and the Sandia 100-meter blade. The effects of nonproportional damping are seen to become more significant as the blade size increases. The results provide some experience for the validity of making modal damping assumptions in blade analyses.

Commentary by Dr. Valentin Fuster
2015;():V008T13A085. doi:10.1115/DETC2015-46644.

This paper aims to develop an accurate nonlinear mathematical model which may describe the coupled in-plane motion of an axially accelerating beam. The Extended Hamilton’s Principle was utilized to derive the partial differential equations governing the motion of a simply supported beam. The set of the ordinary differential equations were obtained by means of the assumed mode method. The derived elastodynamic model took into account the geometric non-linearity, the time-dependent axial velocity and the coupling between the transverse and longitudinal vibrations. The developed equations were solved numerically using the Runge-Kutta method and the obtained results were presented in terms of the vibrational response graphs and the system natural frequencies. The system dynamic characteristics were explored with a major focus on the influence of the velocity, acceleration and the excitation force frequency. The obtained results showed that the natural frequency decreased significantly at high axial velocities. Also it was found that the system may exhibit unstable behavior at high accelerations.

Commentary by Dr. Valentin Fuster
2015;():V008T13A086. doi:10.1115/DETC2015-46787.

The motion equations of a rolling flexible spherical shell are derived using a Lagrangian formulation. The motion equations developed capture the nonholonomic nature of the flexible sphere rolling without slip on a flat surface. The free vibrations of the spherical shell are modeled using the Rayleigh-Ritz discretization method. Numerical simulations are performed to validate the dynamic model developed and to investigate the effect of the flexibility of the spherical shell on its trajectory.

Commentary by Dr. Valentin Fuster
2015;():V008T13A087. doi:10.1115/DETC2015-46791.

Twisting and bending dynamics of biological filaments such as DNA play a central role in their biological activity including gene expression. The elastic rod model is an efficient tool to simulate such deformations. However, the accuracy of elastic rod predictions depend strongly on the constitutive law, which follows from the atomistic structure of the DNA molecule and is known to be nonlinear and to vary along the length according to the base pair sequence of the DNA. Unfortunately, it is impractical to derive the constitutive law analytically from the atomistic structure. Identification of the nonlinear sequence-dependent constitutive law from experimental data and feasible molecular dynamics simulations remains a significant challenge. In this paper, we extend earlier work by employing techniques based on input reconstruction and state estimation filters to estimate the constitutive law using molecular dynamics data of deformations in bio-filaments.

Commentary by Dr. Valentin Fuster
2015;():V008T13A088. doi:10.1115/DETC2015-46855.

The aim of this study is to model and investigate the nonlinear transversal vibration of a carbon nanotube carrying an intermediate mass along the structure considering the nonlocal and non-classical theories. Due to the application of the proposed system in sensors, actuators, mass detection units among others, the analysis of forced vibration of such systems is of an important task being considered here. The governing equation of motion is developed by combining the Euler-Bernoulli beam theory and the Eringen non-local theory. The Galerkin approach is employed to obtain the governing differential equation of the system and the transient beam response for the clamped-hinged boundary condition. A strong perturbation method is utilized to solve the equation obtained and the system responses subjected to a harmonic excitation is examined. The steady-state motion is studied and the frequency response in an analytical form is obtained. Finally, results are evaluated for some numerical parameter values and their effect on the frequency responses are presented and fully discussed.

Commentary by Dr. Valentin Fuster
2015;():V008T13A089. doi:10.1115/DETC2015-46860.

Nonlinear forced vibration of the carbon nanotubes based on the Euler-Bernoulli beam theory is studied. The Euler-Bernoulli beam theory is implemented to find the governing equation of the vibrations of the carbon nanotube. The Pasternak and Nonlinear Winkler foundation is assumed for the objective system. It is supposed that the system is supported by hinged-hinged boundary conditions. The Galerkin procedure is employed in order to find the nonlinear ordinary differential equation of the vibration of the objective system considering two modes of vibrations. The primary and secondary resonant cases are developed for the objective system employing the multiple scales method. Influence of different factors such as length, thickness, position of applied force, Pasternak and Winkler foundation are fully shown on the primary and secondary resonance of the system.

Commentary by Dr. Valentin Fuster
2015;():V008T13A090. doi:10.1115/DETC2015-47147.

In order to accurately predict the fatigue life and wear life of a belt, the various stresses that the belt is subjected to and the belt slip over the pulleys must be accurately calculated. In this paper, the effect of material and geometric parameters on the steady-state stresses (including normal, tangential and axial stresses), average belt slip for a flat belt, and belt-drive energy efficiency is studied using a high-fidelity flexible multibody dynamics model of the belt-drive. The belt’s rubber matrix is modeled using three-dimensional brick elements and the belt’s reinforcements are modeled using one dimensional truss elements. Friction between the belt and the pulleys is modeled using an asperity-based Coulomb friction model. The pulleys are modeled as cylindrical rigid bodies. The equations of motion are integrated using a time-accurate explicit solution procedure. The material parameters studied are the belt-pulley friction coefficient and the belt axial stiffness and damping. The geometric parameters studied are the belt thickness and the pulleys’ centers distance.

Topics: Stress , Steady state , Belts
Commentary by Dr. Valentin Fuster
2015;():V008T13A091. doi:10.1115/DETC2015-47248.

Recent multidisciplinary advances enable actively controlled bar-tendon structures. A major control related challenge is the dynamic stability of these systems. Their low internal damping may result in less stable systems than desired, requiring special attention. This paper investigates the nonlinear dynamic stability of such assemblies, focusing on the situation when linearization fails to provide an answer. Conditions for simple and asymptotic nonlinear stability of prestressable configurations of these systems are derived using Lyapunov-LaSalle theory. Examples are included to illustrate theoretical results, emphasize connections between stability, mechanisms, and natural modes, and explain why only nonlinear asymptotic stability, instead of exponential stability, is achieved even when tendons are linearly damped.

Commentary by Dr. Valentin Fuster
2015;():V008T13A092. doi:10.1115/DETC2015-47681.

This paper presents vibration analysis and structural optimization of a self-assembled structure for swimming. The third mode shape of the structure in the longitudinal direction resembles the body waveform of a swimming eel fish. At the final destination, the box self-assembles using shape memory alloys. MFCs (Piezoelectric Micro Fiber Composites) are actuated at the fundamental natural frequency of the structure. This excites the primary mode of resonance. We optimize the thickness of the panels and the stiffness of the joints to most efficiently generate the swimming waveforms that resembles the body waveform of eel. Traveling wave is generated using two piezoelectric batches actuators bonded on the first and fourth segments of the beams in the longitudinal direction. Excitation of the piezoelectrics results in coupled system dynamics equations that can be translated into generation of waves. Theoretical analysis based on the distributed parameter model was conducted in this paper.

A scalar measure of the traveling to standing wave ratio was created using 2-dimensional Fourier Transform of the wave form. The results then were compared to common method in the literature for assessment of standing to traveling wave ratio.

Commentary by Dr. Valentin Fuster
2015;():V008T13A093. doi:10.1115/DETC2015-47947.

Switched reluctance (SR) motors are becoming more and more prominent in both industry and academia due to their simple design characteristics and flexibility [3]. However, the pulsating nature of the torque in this kind of motor tends to generate unwanted accoustical noise and large, undesirable vibrations [2]. Many researchers have conducted complex experimental and finite-element studies to determine the sources of these vibrations, but comparatively little work has been done to analytically model these phenomena using first principles [2] [8] [3]. The goal of this paper then is to derive an anlytical model for the vibrations of an SR motor, and to predict the frequency response of a particular motor configuration. These results will help guide future work to reduce vibrations in these motors, therby making them more industrially viable.

Topics: Motors , Modeling , Vibration
Commentary by Dr. Valentin Fuster
2015;():V008T13A094. doi:10.1115/DETC2015-48061.

It is necessary to calibrate the equipment during each test in modal testing. This paper presented a practical method for the calibration of the measured FRFs based on mass identification method. One advantage of this proposed method is that the calibration is performed directly on the test structure. Thus, it is more reliable and convenient. It is shown that if the mass identification method is applied to the uncalibrated system, a different level between the identified mass and the given exact mass reveals that the set up is not calibrated. And the measured FRFs can be calibrated using the ratio factor of the identified mass and exact mass. The simulation testing demonstrates good performance. In practical testing, however, the accuracy of mass identification results may be vulnerable to the noise and further work is necessary in order to solve this difficulty.

Topics: Calibration
Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: System Identification, Damage Detection, and Diagnostics

2015;():V008T13A095. doi:10.1115/DETC2015-46022.

The collected vibration signals from defective rolling element bearings are generally non-stationary and corrupted by strong background noise. The weak fault feature extraction is crucial to mechanical fault diagnosis and machine condition monitoring. A new method EWT-based (Empirical Wavelet Transform) for bearing fault diagnosis is proposed in this paper. It consists of four parts. Firstly, the frequency ranges of meaningful modes are self-adaptively obtained by combining scale-space representation and Otsu’s method. Secondly, the meaningful modes are acquired by utilizing EWT to decompose the raw vibration signal. Thirdly, the first two modes possessing maximum kurtosis are selected as fault components. Lastly, the fault-related features could be observed in the time domain and envelope spectra of the selected modes. Experimental results verify that the proposed method is very effective for bearing weak fault diagnosis and the performance of proposed method is obviously better than the method of empirical mode decomposition (EMD).

Commentary by Dr. Valentin Fuster
2015;():V008T13A096. doi:10.1115/DETC2015-46057.

Damage detection and diagnostics is a key area of research in structural analysis. This paper presents results from the analysis of mixed-mode damage initiation in a composite beam under thermal and mechanical loads. A finite element model in conjunction with a cohesive zone model (CZM) is used in order to determine the location of joint separation as well as the contribution of each mode in damage (debonding) initiation. The composite beam is modeled by using two layers of aluminum that are bonded together through a layer of adhesive. Simulation results show that the model can successfully detect the location of damage under a thermo-mechanical load. The model can also be used to determine the severity of damage due to a thermal load, a mechanical load and a thermo-mechanical load. It is observed that integrating thermal analysis has a significant influence on the fracture energy.

Commentary by Dr. Valentin Fuster
2015;():V008T13A097. doi:10.1115/DETC2015-46715.

Localization of damages becomes rather challenging when the associated stiffness reduction is small in presence of structural uncertainties. This work presents a sensitivity analysis and an improvement of a novel pseudo-modal approach, recently proposed by the authors. Starting from free vibrations of the undamaged and damaged states, the method aims to maximize the damage signature embedded in the data exploiting the peculiar features of the Orthogonal Empirical Mode Decomposition technique. The role of the length of the signals and the boundary effects are here investigated; a cut-off rule useful for reducing the latter issue is also proposed.

Commentary by Dr. Valentin Fuster
2015;():V008T13A098. doi:10.1115/DETC2015-46763.

One of the most important issues in civil and in mechanical engineering is the detection of structural damages, which are defined as changes of material properties, of boundary conditions and of system connectivity, which adversely affect the system’s performances. The damage identification process generally requires establishing existence, localization, type and intensity of the damage.

During its service life, a structure, besides his natural aging, can be subjected to earthquakes. These events may have a deep impact on building safety and a continuous monitoring of the structure health conditions, through Structural Health Monitoring (SHM) techniques, is necessary in many cases.

Within this a background, the purpose of this work is to propose an integrated novel approach for the diagnosis of structures after a seismic event. The proposed monitoring system is based on recording the accelerations of the real structure during a seismic input, and the reintroduction of them into a numerical model, suitably tuned, in order to outline a possible post-earthquake scenario.

This approach provides an estimation of the health of the building and of its residual life, and to detect and quantify the damage, some of the crucial aspects of SHM. Actually, we also get both online and self-diagnosis of the structural health.

The technique is applied to a real structure, an industrial building liable of some seismic vulnerabilities. It it did not undergo an earthquake, so we have not recordered accelerations, and get them from a different numerical models subjected to the ground acceleration of a realistic earthquake.

Commentary by Dr. Valentin Fuster
2015;():V008T13A099. doi:10.1115/DETC2015-46914.

Fault detection methods are significant in health monitoring of critical system components, including aerospace applications. Failure in such systems is unacceptable, even though engineers try to achieve very low failure probability in these systems. The ability to accurately model and analyze the characteristics of such systems would reduce the rates of false positives and missed detections in structural health monitoring. Previously, a detection model was developed to investigate the effects of combined impact of geometrical variations of machining errors and crack presence in beams. The model utilized the Leap Frog finite difference method, which had a restrictive condition on stability of the numerical method. This restriction would show to be critical with materials with high modulus and low density values. The proposed work will overcome the drawback of the current detection model by utilizing other finite difference methods to remove or relax the stability condition of the method; namely, the Weighted Average method and Du Fort-Frankel method. The presented result clearly shows that the Theta method could be used to obtain an unconditionally stable finite difference model with high accuracy. It is also observed that the result from the Du Fort-Frankel method is still conditionally stable, but the stability condition is more relaxed compared to the Leap Frog method. The results obtained from the improved model show good agreement with the example in the literature. The improved model is also applied to investigate a cantilevered beam with the presence of cracks and geometrical variations.

Commentary by Dr. Valentin Fuster
2015;():V008T13A100. doi:10.1115/DETC2015-47413.

In the current work, the optical three-dimensional point-tracking (3DPT) measurement approach is used in conjunction with a recently developed modal expansion technique. These two approaches (empirical and analytical) complement each other and enable the prediction of the full-field dynamic response on the surface of the structure as well as within the interior points. The practical merit of the approach was verified using a non-spinning and spinning wind turbine rotor. The three-bladed wind turbine rotator was subjected to different loading scenarios and the displacement of optical targets located on the blades was measured using 3DPT. The measured displacement was expanded and applied to the finite element model of the turbine to extract full-field strain on the turbine. The sensitivity of the proposed approach to the number of optical targets was studied in this paper. It is shown the approach can accurately predict the strain even with very few set of measurement points.

Topics: Wind turbines
Commentary by Dr. Valentin Fuster
2015;():V008T13A101. doi:10.1115/DETC2015-47659.

This paper has studied the identification problem of linear mechanical systems where inputs are unknown and only displacement data are accessible for measurement. Eigensystem Realization Algorithm (ERA) has been used along with physical constraints considerations in time domain to simultaneously identify two separate models for the physical system and the unknown inputs. Inputs are assumed to be an arbitrary combination of harmonic signals with frequencies higher than natural frequencies of the physical system by which a linear mechanical system is meant in this paper. Adding physical constraints and utilizing canonical real Jordan form of the identified system leads to a unique analytical solution. To validate the theory part, a set of simulations has been run that demonstrates the physical parameters and input model can be estimated accurately.

Commentary by Dr. Valentin Fuster
2015;():V008T13A102. doi:10.1115/DETC2015-47724.

Uncertainty quantification is an important aspect in structural dynamic analysis. Since practical structures are complex and oftentimes need to be characterized by large-scale finite element models, component mode synthesis (CMS) method is widely adopted for order-reduced modeling. Even with the model order-reduction, the computational cost for uncertainty quantification can still be prohibitive. In this research, we utilize a two-level Gaussian process emulation to achieve rapid sampling and response prediction under uncertainty, in which the low- and high-fidelity data extracted from CMS and full-scale finite element model are incorporated in an integral manner. The possible bias of low-fidelity data is then corrected through high-fidelity data. For the purpose of reducing the emulation runs, we further employ Bayesian inference approach to calibrate the order-reduced model in a probabilistic manner conditioned on multiple predicted response distributions of concern. Case studies are carried out to validate the effectiveness of proposed methodology.

Commentary by Dr. Valentin Fuster
2015;():V008T13A103. doi:10.1115/DETC2015-47779.

Modal properties of a structure can be identified by experimental modal analysis (EMA). Discrete frequency response functions (FRFs) and impulse response functions (IRFs) between responses and excitation are bases for EMA. In calculation of a discrete FRF, discrete Fourier transform (DFT) is applied to both response and excitation data series, and a transformed data series in DFT is virtually extended to have an infinite length and be periodic with a period equal to the length of the series; the resulting periodicity can be physically incorrect in some cases, which depends on an excitation technique used. There are various excitation techniques in EMA, and periodic extension in DFT for EMA using periodic random and burst random excitation is physically correct. However, EMA using periodic random excitation needs a relatively long excitation time to have responses to be steady-state and periodic, and EMA using burst random excitation needs a long sampling period for responses to decay to zero, which can result in relatively long response and excitation data series and necessitate a large number of spectral lines for associated DFTs, especially for a high sampling frequency. An efficient and accurate methodology for calculating discrete FRFs and IRFs is proposed here, by which fewer spectral lines are needed and accuracies of resulting FRFs and IRFs can be maintained. The relationship between an IRF from the proposed methodology and that from the least-squares method is shown. A new coherence function that can evaluate qualities of FRFs and IRFs from the proposed methodology in the frequency domain is used, from which meaningful coherence function values can be obtained even with response and excitation series of one sampling period. Based on the new coherence function, a fitting index is used to evaluate overall qualities of the FRFs and IRFs. The proposed methodology was numerically and experimentally applied to a two-degree-of-freedom mass-spring-damper system and an aluminum plate to estimate their FRFs, respectively. In the numerical example, FRFs from the proposed methodology agree well with the theoretical one; in the experimental example, a FRF from the proposed methodology with a random impact series agreed well with the benchmark one from a single impact test.

Commentary by Dr. Valentin Fuster
2015;():V008T13A104. doi:10.1115/DETC2015-48000.

The chatter marks may be caused by the roll misalignment during the grinding process of roll grinder, which can affect the quality of the roll surface of the strip steel. Based on a doubly regenerative time delay grinding model, a 2-degree-of-freedom lumped parameter model of a roll grinder with the roll misalignment fault is presented to investigate the effect of a roll misalignment on its vibration responses. A Runge-Kutta numerical integration method is applied to calculate the vibration response from the presented model. The effects of the roll misalignment and the rolling speed are investigated. Moreover, an experiment setup is presented. Numerical results from the presented model are compared with experimental results to validate the presented model. It seems that the results may provide some guidance for the detection of the misalignment fault and monitoring of the operation state of the roll grinder.

Commentary by Dr. Valentin Fuster

27th Conference on Mechanical Vibration and Noise: Wave Propagation and Acoustics

2015;():V008T13A105. doi:10.1115/DETC2015-46033.

In this paper, flexural vibration in a locally-resonant (LR) beam with periodically attached separated force and moment beam-like resonators is investigated theoretically and experimentally. The relationship between the distance parameter and the band structure of an Euler-Bernoulli beam with proposed locally resonators is provided using the transfer matrix theory. The frequency response functions of finite periodic systems are calculated with the finite element method over a range of different parameters of the resonators. Finally, we use LR beam specimens with separated force and moment resonators mounted on a free-free host beam for experimental measurements of the vibration transmittance. The experimental results show a good agreement with those of the theoretical and numerical except some small discrepancies at high frequencies. Our study confirms that the bandwidth of band-gaps will become wider with the increasing of the distance parameter until it reaches its peak, which provides an effective way for LR periodic structures with resonators to obtain broad band-gaps in low-frequency range, and makes the structure had potential applications in the control of vibration and wave propagation in flexural beams.

Topics: Resonance , Waves , Energy gap
Commentary by Dr. Valentin Fuster
2015;():V008T13A106. doi:10.1115/DETC2015-46539.

This paper describes the application of a material parameter identification method based on elastic shear wave propagation to simulated and experimental data from magnetic resonance elastography (MRE). In MRE, the displacements of traveling transverse and longitudinal waves in elastic, biological tissue are captured as complex 3D images. Typically, the magnitude of these waves is small, and the equations of waves in linear elastic media can be used to estimate the material properties of tissue, such as internal organs, muscle, and the brain. Of particular interest are fibrous tissues which have anisotropic properties. In this paper, an anisotropic material model with three material parameters (shear modulus, shear anisotropy, and tensile anisotropy) is the basis for parameter identification. This model relates shear wave speed, propagation direction, and polarization to the material properties. A directional filtering approach is applied to isolate the speed and polarization of shear waves propagating in multiple directions. The material properties are then estimated from the material model and isolated shear waves using weighted least squares.

Commentary by Dr. Valentin Fuster
2015;():V008T13A107. doi:10.1115/DETC2015-46805.

By applying an excitation dependent, on-site restoring force to oscillators in a uniform one-dimensional chain with nearest neighbor coupling, this paper demonstrates the feasibility of reversible passive bandgap reconfiguration. Waveguide devices are most commonly tuned using active controls, component replacement, or by manually varying design parameters. Recent studies on wave propagation have pursued passive controls, where high amplitude environmental excitation triggers a potential well escape in an asymmetric, bi-stable system, automatically changing its linear spectra without user interaction. Current designs, however, do not return to their initial state upon later excitation amplitude reduction, instead requiring manual reset for continued operation. In order to allow fully autonomous function, a passively reconfigurable system must also be designed to return to its low amplitude state after environmental excitation amplitude decreases. This paper proposes a system in which reversible bifurcations are observed by introducing an excitation dependent on-site stiffness. Instead of a fixed, bi-stable potential energy curve, the oscillators have a single mono-stable curve at low energy levels and a different mono-stable curve with its own distinct linear spectrum at high energy levels. Numerical simulations are provided to demonstrate system transitions from propagation zone to attenuation zone behavior, and back, when subjected to increasing and decreasing excitation amplitudes.

Commentary by Dr. Valentin Fuster
2015;():V008T13A108. doi:10.1115/DETC2015-48013.

This study presents on a recent semi-analytical boundary collocation technique, the singular boundary method (SBM), for exterior wave propagation analysis. The SBM is mathematically simple, easy-to-program, meshless and applies the concept of source intensity factors to eliminating the singularity of the fundamental solutions and avoiding singular numerical integrals in the boundary element method. The Burton and Miller’s method is introduced to the present SBM to enhance the quality of the solution, particularly in the vicinity of irregular frequencies. Then the present SBM is applied to water wave-structure interaction with four-cylinder structure and SH wave scattering in 2D hill.

Commentary by Dr. Valentin Fuster
2015;():V008T13A109. doi:10.1115/DETC2015-48017.

Rotary Pressure exchanger (RPE) is an efficient device which recovers pressure energy from liquid streams in process industries. In this work, a multi-scale numerical investigation of pressure propagation in RPE and the pipeline is carried out. A system model including pipe system and RPE component is firstly presented, and is then solved by the integration of 1-D Method of characteristics (MOC) and CFD method. The simultaneous data exchange between the pipeline and RPE is enabled by making use of the existing programming interfaces. At last, the mutual effect of wave phenomenon in pipeline and RPE is evaluated by the synchronous interaction under transient operating conditions. The proposed multi-scale coupling approach in this work could either provide the internal flow details in RPE device or the dynamic behavior of the system, making the numerical simulation more reasonable with system-level accuracy and time-saving.

Topics: Pressure , Simulation , Pipes
Commentary by Dr. Valentin Fuster

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