ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V008T00A001. doi:10.1115/DETC2018-NS8.

This online compilation of papers from the ASME 2018 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

30th Conference on Mechanical Vibration and Noise: Dynamics and Waves in Solids and Metamaterials

2018;():V008T10A001. doi:10.1115/DETC2018-85929.

Recent focus has been given to nonlinear periodic structures for their ability to filter, guide, and block elastic and acoustic waves as a function of their amplitude. In particular, two-dimensional (2-D) nonlinear structures possess amplitude-dependent directional bandgaps. However, little attention has been given to the stability of plane waves along different directions in these structures. This study analyzes a 2-D monoatomic shear lattice composed of discrete masses, linear springs, quadratic and cubic nonlinear springs, and linear viscous dampers. A local stability analysis informed by perturbation results retained through the second order suggests that different directions become unstable at different amplitudes in an otherwise symmetrical lattice. Simulations of the lattice’s equation of motion subjected to both line and point forcing are consistent with the local stability results: waves with large amplitudes have spectral growth that differs appreciably at different angles. The results of this analysis could have implications for encryption strategies and damage detection.

Topics: Stability
Commentary by Dr. Valentin Fuster
2018;():V008T10A002. doi:10.1115/DETC2018-85991.

We implement periodic stiffness time-modulation in a beam with piezoelectric patches and switchable shunted negative capacitance. The shunted negative capacitance circuits, connected in series with each piezoelectric patch through a switch, soften the structure. By alternatively opening and closing the switch, the beam’s stiffness effectively oscillates periodically between two values. We present a simplified theoretical model of time-periodic beams and describe the occurrence of flat bands in the dispersion diagrams. We show that a narrowband reflection from a time-modulated domain can be obtained for a broadband incident wave, hence qualifying the modulated domain as a single-port system with tunable response. We validate our theoretical findings by comparing time-domain simulations with experimental measurements of transient wavefields through scanning Doppler laser vibrometry.

Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: Dynamics of MEMS and NEMS (VIB/MNS-2)

2018;():V008T10A003. doi:10.1115/DETC2018-86138.

While the study of coupled resonant systems is a topic of significant research interest, comparatively little work has been done to study the dynamics of coupled electromechanical systems with many degrees of freedom containing features such as element-level mistuning. In this work we consider the dynamics of a system consisting of a large (N = 16) array of globally coupled, mistuned electromechanical resonators. An analytical and experimental framework is developed to enable the study of emergent behaviors in this system. A number of behaviors are identified, such as the appearance of additional resonance frequencies that are common to all of the resonators in the array. These behaviors are seen in both the analytical model and physical system and are dependent on the global properties of the system, such as the distribution of the parameters of the resonators and the strength of the coupling between the array’s constituent elements.

Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: Emerging Systems and Applications

2018;():V008T10A004. doi:10.1115/DETC2018-85512.

The advantages of a plastic gear are that it is light and can be used without any lubricant, and its disadvantages are that its strength is low and it has large environmental impact. Therefore, the development of a new gear that maintains the advantages while negating the disadvantages has been proposed. The development of sustainable and reproducible natural materials is particularly desired to address environmental problems. Therefore, in this study, a method was devised to extract high quality and highly precise bamboo fibers using a machining center. Then, the hot press method was used to produce a spur gear, which is a machine element with a complicated shape. The present paper describes the characteristics of the bamboo fiber gears investigated through experiments. The results of tooth root strain measurement showed the relationship between rotation speed and tooth root strain. In addition, we calculated the theoretical value of tooth root strain and compared it with the experimental value. The experimental value was lower than the calculated value. The results of acceleration measurement showed that that tooth root strain is associated with acceleration.

Commentary by Dr. Valentin Fuster
2018;():V008T10A005. doi:10.1115/DETC2018-86280.

The effects of mechanical impact forces on neurological health is a critical concern, likely due to issues of traumatic brain injury (TBI) in sports and brain damage stemming from the potential of “sonic terrorism.” The quantitative analysis and evaluation of such forces on brain tissue function is very difficult. To address this issue, this research proposes a novel approach of using a cellular model subjected to mechanical vibration for analysis. Here, neuron-like differentiated neuroblastoma cells were subjected to vibration at frequencies of 20, 200, 2000, and 20000 Hz for a period of 24 hours at constant amplitude. Cell proliferation and inflammatory cytokine production, including IL-6, IL-1β, and TGF-β1, was measured as response of the cells and indicators of cellular health after vibrational treatment. Cell proliferation was found to increase after 20, 200, and 20000 Hz treatments; p<0.05) and decrease after 2000 Hz treatment (p<0.05). IL-6 production was found to decrease after 200 and 20000 Hz treatments (p<0.01) and increase after 20 and 2000 Hz treatments (p<0.01). IL-1β protein production was found to decrease after 20 Hz and increase after 200 Hz treatments (p<0.001), while TGF-β1 was found to decrease after 200 Hz treatment (p<0.001). The results suggest that cell proliferation and cytokine production serve as a sensitive measure to external impact forces applied to the cells. In addition, it is suggested that inflammatory mechanisms exhibit inhibitory “cross-talk” between IL-6 and IL-1β signaling pathways at 20 and 200 Hz. Inflammatory cytokine data suggest frequency-specific responses, which can be used not only to better understand the mechanism of vibration induced cellular damage, but also to unveil the cellular signaling processes.

Topics: Vibration
Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: Industrial Applications of Dynamics, Vibration, and Acoustics

2018;():V008T10A006. doi:10.1115/DETC2018-85197.

Vibrotactile feedback may be able to compensate for the loss of sensory input in lower-limb prosthesis users. Designing an effective vibrotactile feedback system would require that users could perceive and correctly respond to vibrotactile stimuli applied by the tactors. Our study explored three key tactor configuration variables (i.e. vibratory intensity, prosthetic pressure, spacing between adjacent tactors) through two experiments. The vibration propagation experiment investigated the effects of tactor configurations on vibratory amplitude at the prosthesis-limb interface. Results revealed a positive relationship between vibratory amplitude and intensity, and a negative relationship between vibratory amplitude and prosthetic pressure. The vibrotactile perception experiment investigated the effects of tactor configurations on user response accuracy, and found that greater spacing between tactors, and higher prosthetic pressure resulted in more accurate responses from the subjects. These findings inform the design of a vibrotactile feedback system for use in lower-limb prostheses: 1) the tactors may be best placed in areas of slightly elevated pressure at the prosthesis-limb interface; 2) a higher vibratory intensity level should improve performance for vibrotactile feedback systems; and 3) more spacing between adjacent tactors improves user response accuracy.

Topics: Design , Prostheses , Feedback
Commentary by Dr. Valentin Fuster
2018;():V008T10A007. doi:10.1115/DETC2018-85385.

Optimization of bulkhead stiffener configuration has been an active area of research over the past decade, but no real practical solutions have been generated. This research investigates bulkhead stiffener configuration on a rudimentary level, by analyzing the modal parameters of three different stiffener configurations. Experimental data was used to validate the computational models of two modified bulkhead stiffener configurations. Operational boundary conditions were then applied to the computational models to assess the modal density of the modified bulkheads within the aircraft engine rotational frequency range. Removal of one horizontal stiffener reduced the overall stiffener mass by 12.2% without generating any modes within 4% of the engine rotational frequency. The inconsistencies of natural frequency changes due to stiffener configuration highlights the difficulty with applying generalized optimization approaches without a thorough understanding of the modes of interest. The results of this work suggest that the fundamental analysis performed herein is necessary to generate a complete understanding of the modal parameters of the bulkhead prior to performing in-depth optimization work.

Topics: Breakwaters
Commentary by Dr. Valentin Fuster
2018;():V008T10A008. doi:10.1115/DETC2018-85387.

The driveline of many crafts during mooring maneuvers operates in the “trolling” mode, which is characterized by large slippages of the clutch. Sometimes the properties of clutch material and oil lead to the onset of self-excited torsion vibrations and wide fluctuations in torque. To analyze this phenomenon a numerical model of a typical marine driveline is developed, friction characteristics of the clutch are simulated by means of a LuGre model. A parametric stability analysis is carried out to highlight the effect of the parameters of the LuGre friction model on the stability of torsion vibrations. A series of experimental tests is performed on a specific test bench to identify the parameters of the driveline and to validate the numerical model. Results shows that the updated numerical model is able to replicate experimental results.

Commentary by Dr. Valentin Fuster
2018;():V008T10A009. doi:10.1115/DETC2018-85477.

Landing gears (LG) are primarily designed to support the entire loads of an aircraft during landing, taxiing, and taking off. From aerodynamic design prospective, many of the LG components are exposed to the air flow giving rise to what so-called aerodynamic noise. Numerical study of complex systems such as LG as a three-dimensional (3D) model is not only CPU and memory consuming, but also it is way beyond the demand of industries for quick estimate during the design stage [1–3]. To understand the underlying physics of the flow induced noise, a two-dimensional (2D) flow past a circular cylinder is simulated using ANSYS Fluent. Two different Reynolds numbers, Re = 150 and 90000 are examined. For low Re, two distinct numerical conditions relevant to steady and unsteady flow are simulated and compared to examine the effect of the time dependency on the acoustic field. At high Re, the acoustic field is computed using the built-in Ffowcs William and Hawkings (FW-H) acoustic analogy solver in Fluent. The results show the importance of including the unsteady state term to extract the flow data. The far-field noise prediction is found to be highly dependent on the location of the near-field data.

Commentary by Dr. Valentin Fuster
2018;():V008T10A010. doi:10.1115/DETC2018-85628.

The focus of this investigation was to examine the acoustic trends present during operation of an automotive door closure at two impact speeds through experimental methods. Transient sound pressure of five different door closure mechanisms were collected in a semi-anechoic chamber using a three-element condenser microphone array. Post-processing methodologies such as Sound Pressure Level versus 1/3 Octave band and Continuous Wavelet Transform computations were conducted. These procedures provided an in-depth analysis on the overall generated sound in addition to identifying which frequencies dominate the response at specific impact events during latch operation. Computational model analyses of the closure system using Rigid Body Dynamic and Explicit Dynamic methods using ANSYS to obtain a clearer understanding of the latch component interactions. Recorded average sound pressure level, frequency decomposition, and impact reaction forces are presented in addition to the notable trends between both impacting speeds.

Commentary by Dr. Valentin Fuster
2018;():V008T10A011. doi:10.1115/DETC2018-85651.

Experimental and computational modal analysis has been completed as part of a larger project with the ultimate goal of understanding MRI vibration and implementing passive vibration isolation in the MRI machine support structure. The specific purpose of the modal analysis is to extract natural frequencies (eigenvalues) and mode shapes (eigenvectors) of the MRI support structure in order to validate the computational model of the base against the experimental results so that the former may be used as an analysis and design tool. From the model, the resonance points of the MRI support structure are determined within the expected frequency ranges of excitation.

Commentary by Dr. Valentin Fuster
2018;():V008T10A012. doi:10.1115/DETC2018-85906.

Portable electric air compressors produce noise which can be a nuisance or even hazardous to persons in the vicinity; therefore, noise reduction of these compressors is a desired design evolution. An experimental setup was developed to measure the sound and vibration of existing air compressors and to test new prototypes. The design of a quiet air compressor was performed in four stages: 1) compressor teardown and benchmarking, 2) noise source identification and isolation, 3) development of a morphological chart for quiet noise sources, and 4) integrated solution selection and testing. The systematic approach and results for each of these stages will be discussed. Two redesigned solutions were developed and measured to be approximately 65% quieter than the previous unmodified compressor. The benefits of using a specific design procedure to reverse engineer, test, and develop new concepts are discussed.

Commentary by Dr. Valentin Fuster
2018;():V008T10A013. doi:10.1115/DETC2018-85919.

An experimental apparatus has been designed and fabricated to assess the nonlinear dynamics of internal combustion engine (ICE) restart and shutdown. The final objective for the apparatus is to validate the application of two-scale command shaping (TSCS) for reduction of unwanted vibrations during ICE restart. The apparatus allows user-specified torque profiles to be applied to a three-cylinder ICE from an electric machine (EM). In turn, the apparatus can measure oscillations in the driveline and chassis, which will ultimately determine the efficacy of TSCS as applied to engine restart. Preliminary results from the apparatus document its ability to measure the unwanted oscillations in the response of the powertrain during ICE restart and shutdown. The apparatus is also expected to provide data, combined with parameter estimation techniques, to determine otherwise uncertain parameters associated with the ICE and EM.

Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: Jointed Structures, Contact, Friction, and Damping

2018;():V008T10A014. doi:10.1115/DETC2018-85349.

High cycle fatigue damage caused by resonance and forced vibration can significantly affect the life and reliability of turbine rotor blades in aero-engines. The friction damper has been widely used to reduce the resonant stress of blades, on which the turbine blade shroud dampers are highly used.

In order to solve the problems of vibration damping analysis and design of shrouded blades dampers, an analytical method without complex and time-consuming nonlinear vibration response has been proposed based on a given eigen-mode in this paper. For the serrated shrouded damper, two typical friction models, namely macro-slip model, and micro-slip model, have been introduced. Additionally, a complete set of damping analysis method has been introduced by the energy method, based on the vibration dynamics principle and eigen-mode analyzed by finite element method. Combined with the analysis of the natural vibration characteristics of the shrouded turbine blade, the law of the damping ratio with the relevant design parameters, such as the vibration stress, the pre-twist angle, the friction coefficient and the nodal diameter, was obtained through a calculation example. The method can also provide an important reference for the parameterized design of dampers.

Commentary by Dr. Valentin Fuster
2018;():V008T10A015. doi:10.1115/DETC2018-86099.

A discretization strategy for elastic contact on a half plane has been devised to explore the significance of different friction models on joint-like interface mechanics. It is necessary to verify that discretization and accompanying contact algorithm on known solutions. An extensive comparison of numerical predictions of this model with corresponding 2-D elastic, frictional contact solutions from the literature is presented.

Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: Nonlinear Systems and Phenomena

2018;():V008T10A016. doi:10.1115/DETC2018-85036.

In this paper, an efficient and accurate computational method for determining responses of high-dimensional bilinear systems is developed. Predicting the dynamics of bilinear systems is computationally challenging since the piecewise-linear nonlinearity induced by contact eliminates the use of efficient linear analysis techniques. The new method, which is referred to as the hybrid symbolic-numeric computational (HSNC) method, is based on the idea that the entire nonlinear response of a bilinear system can be constructed by combining linear responses in each time interval where the system behaves linearly. The linear response in each time interval can be symbolically expressed in terms of the initial conditions. The transition time where the system switches from one linear state to the other and the displacement and velocity at the instant of transition are solved using a numerical scheme. The entire nonlinear response can then be obtained by joining each piece of the linear response together at the transition time points. The HSNC method is based on using linear features to obtain large computational savings. Both the transient and steady-state response of bilinear systems can be computed using the HSNC method. Thus, nonlinear characteristics, such as subharmonic motion, bifurcation, chaos, and multistability, can be efficiently analyzed using the HSNC method. The HSNC method is demonstrated on a single degree of freedom system and a cracked cantilever beam model, and the nonlinear characteristics of these systems are examined.

Commentary by Dr. Valentin Fuster
2018;():V008T10A017. doi:10.1115/DETC2018-85202.

This paper reports and investigates paradoxical simulation results of the bouncing ball system. Chaos-like motion of the bouncing ball system with intermittent chattering (Zeno behaviour) is observed in simulations if the relative acceleration of the table exceeds a critical value. However, one can show that this is theoretically impossible. A detailed analysis is given by looking at the backward and forward dynamics of grazing solutions. It is shown in detail that a self-similar structure appears if the relative acceleration of the table exceeds the critical value.

Topics: Chaos
Commentary by Dr. Valentin Fuster
2018;():V008T10A018. doi:10.1115/DETC2018-85421.

In the presence of more than one stable state, assessment of stability is crucial for a proper device characterization. This is of particular importance in atomic force microscopy due to rich dynamics exhibited by the oscillating microcantilever probe that interacts with a sample. Indeed, the multistability can evolve in dramatic regime changes. This work aims at investigating the stochastic switching in which perturbations are responsible for shifts between alternative states with consequences in imaging and spectroscopy. The deceptively straightforward identification of the stability highlights noise-activated escapes. The barrier crossing from metastable wells in the atomic force microscopy leading to problematic configurations are observed in a variety of different configurations with the stochastic resonance as ultimate condition. Our analysis sheds light on the effect of combined additive noise and external excitation. The noise-induced erosion of the attractive domain shows a progressive reduction of the dynamical integrity of amplitude modulation atomic force microscopes.

Commentary by Dr. Valentin Fuster
2018;():V008T10A019. doi:10.1115/DETC2018-85531.

Control of flexible systems is effected by design requirements and also manufacturing aspects. The dynamics and control of such systems are challenging, especially in the case of an inverted flexible pendulum system. The experimental study of the dynamical behavior of this kind of system showing jumping phenomenon between three equilibria is not considered in detail in literatures so far. The paper focuses on studying the effects of some parameters to the dynamics of the flexible pendulum. By varying the excitation parameters, control parameters, as well as other distinguished mechanical parameters, different phenomena are observed in experiments discussed in this contribution. In this study, a custom built inverted flexible pendulum on cart system under PID-controlled harmonic excitation is considered. Data are collected from both cart excitation signal and displacement of the pendulum, also to observe their correlation towards jumping behavior. Effects of the variation of the parameters leading to changes in chaotic jumping patterns. Multiple equilibria are observed and analyzed. It can be concluded that depending on the excitation amplitudes, frequencies, and controller parameters, the minimum of two equilibria with an unstable third equilibrium can be detected while jumping phenomena between the equilibria are observed. Questions about the stimulation of the jumping by impulses resulting from imperfect sinusoidal excitation due to control limitations are discussed.

Topics: Pendulums , Excitation
Commentary by Dr. Valentin Fuster
2018;():V008T10A020. doi:10.1115/DETC2018-85859.

A state observer that only uses the collision time information has recently been developed for linear time-invariant multibody systems with unilateral constraints. The observer is based on synchronization and makes use of switched geometric unilateral constraints, which generate a unidirectional coupling in a master-slave setup. In presence of uncertainties, such as model inaccuracies or disturbances, an exact reconstruction of the observed state is not possible. As a first step in assessing the robustness of the proposed observer, we present an experimental verification of the observer’s performance. Furthermore, we account for dry friction in the observer design.

Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: Rotating Systems and Rotor Dynamics (VIB/MSNDC-6)

2018;():V008T10A021. doi:10.1115/DETC2018-85150.

Flapping insect wings deform under aerodynamic and inertial-elastic loads. Existing aeroelastic wing models are computationally expensive, and consequently, the physics governing flexible wing deformation are not well understood. This paper develops a low-order, one-way coupled aeroelastic model of an arbitrary geometry wing undergoing three-dimensional rotation. The model is developed using the Lagrangian formulation and generalized aerodynamic loads are determined through a blade-element-momentum approach. The in-air and in-vacuum responses of a simulated Hawkmoth wing are compared for various conditions. During normal flight, simulation results show aerodynamic loading causes a 25% increase in maximum wingtip deflection versus a wing flapping in vacuum. This suggests aerodynamics plays a moderate role in structural deformation. Further parametric studies indicate (1) deviations in flap frequency excite torsional resonance and (2) the relative phase between pitch and roll rotations dramatically affects in-air wing response. Both the aeroelastic model and simulation results can guide optimal wing design for small-scale flapping wing micro air vehicles.

Topics: Modeling , Wings
Commentary by Dr. Valentin Fuster
2018;():V008T10A022. doi:10.1115/DETC2018-85428.

This contribution is dedicated to the analysis of uncertainties affecting the vibration responses of a Francis hydropower unit. The system is composed by a vertical rotor and three hydrodynamic bearings: i) a combined tilting-pad guide/thrust bearing, located close to the generator; ii) an intermediate radial tilting-pad bearing; iii) and a cylindrical bearing located close to the Francis turbine. The bearings are represented by using linearized stiffness and damping coefficients. A fuzzy uncertainty analysis was applied aiming at determining the extreme vibration responses of the system. In this case, the bearings stiffness coefficients, generator mass, and Young’s modulus of the shaft were considered as uncertain information. The fuzzy analysis was carried out through the so-called α-level optimization approach due to its mathematical simplicity. Finally, a sensitivity analysis was performed based on the obtained results to determine the uncertain parameters that most affect the rotor responses. The obtained results demonstrate the representativeness of the conveyed methodology.

Commentary by Dr. Valentin Fuster
2018;():V008T10A023. doi:10.1115/DETC2018-85505.

Planetary gear trains (PGTs) are widely applied in various machines owing to their advantages, such as compactness, low weight, and high torque capacity. However, they experience the problems of vibration due to the structural and motional complexities caused by planet gears. In a previous study, it was shown that high speed monitoring is effective for evaluating the motion of planet gears under steady conditions and transient conditions including the influence of backrush. However graphical investigation was conducted manually, and improvement in accuracy is required. In this report, an improved method is proposed, which includes lighting conditions and measurement conditions. Throughout these improvement processes, instant center of rotation is calculated automatically with detected coordinates using software. This makes it possible to estimate the transient response of PGTs with planet gear motion.

Commentary by Dr. Valentin Fuster
2018;():V008T10A024. doi:10.1115/DETC2018-85656.

Much research has been carried out to investigate the dynamical response of a gear system because of its importance on vibration feature analysis. It is well known that the gearbox casing is one of the most important components of the gear system and plays an important role in signal propagation. However, its effects have widely been neglected within the dynamic simulations and few dynamic models have considered the gearbox casing when modeling a gear transmission. This paper proposes a gear transmission dynamical model with the consideration of the effects of gearbox casing. The proposed dynamical model incorporates TVMS, a time-varying load sharing ratio, as well as dynamic tooth contact friction forces, friction moments and dynamic mesh damping coefficients. The proposed gear dynamical model is validated by comparison with responses obtained from experimental test rigs under different speed conditions. Comparisons indicate that the responses of the proposed dynamical model are consistent with experimental results, in both time and frequency domains under different rotation speeds.

Commentary by Dr. Valentin Fuster
2018;():V008T10A025. doi:10.1115/DETC2018-85748.

Flexible, rotating structures can experience complex dynamics, when torsional and lateral motions are involved. Oilwell drill strings form one example of such structures. In the present study, the authors investigate the influence of sinusoidal drive speed modulation on whirling motions of flexible rotors with contact interactions. For two types of drilling-like operations, one with drill mud and another without drill mud, the stability of motions is studied. A laboratory-scale drill rig is used to study the dynamics of a flexible rotor, which is driven at one end and housed within a stator at the other end. Experimental results are presented and discussed for different drive speeds. The findings suggest that the addition of drill mud in the annular space between the rotor and stator along with high-frequency modulation in the drive input helps attenuate lateral motions. The torsional motions appear to be influenced more by the high-frequency drive speed modulation. A three-degree-of-freedom model has been constructed to study lateraltorsional dynamics of a rotor-stator system. The model predictions are compared with the experimental data. The findings of this work have relevance for constructing practical solutions to control whirl dynamics of flexible rotors such as drill strings.

Commentary by Dr. Valentin Fuster
2018;():V008T10A026. doi:10.1115/DETC2018-86029.

This paper aims at the modelling and investigation of unstable journal bearing with an emphasis on instabilities such as oil-whirl or further induced oil-whip. For this reason, a test rig for the investigation of these phenomena was built. Geometry, parameters and operating cases of the rig are described in detail in the presented paper. Computational analysis of the test rig was performed using two methods — the finite element method and a multi-body approach. The calculations of pressure distribution in journal bearings were also performed applying two methods — the finite difference method and the finite element method. The results of the analysis are properly introduced and discussed at the end of this paper. The results suggest that a yet unknown sub-synchronous component may appear under specific conditions. The component typically appears at frequency 0.9–0.98 of shaft speed and is likely caused by a location of a bore for oil supply.

Commentary by Dr. Valentin Fuster
2018;():V008T10A027. doi:10.1115/DETC2018-86203.

This paper deals with a second-order perturbation analysis of the in-plane dynamic responses of both tuned and mistuned three-blade-hub horizontal-axis wind-turbine equations. The blades are under effect of gravitational and cyclic aerodynamics forces and centrifugal forces. Although the blades and hub equations are coupled, they can be decoupled by changing the independent variable from time to rotor angle and by using a small parameter approximation. A second-order method of multiple scales is applied in the rotor-angle domain to analyze in-plane blade-hub dynamics. A superharmonic resonance case at one third the natural frequency was revealed. This resonance case was not captured by a first-order perturbation expansion. The relationship between response amplitude and frequency is studied. The effect of blade mistuning on the coupled blade-hub dynamics are taken into account.

Commentary by Dr. Valentin Fuster
2018;():V008T10A028. doi:10.1115/DETC2018-86334.

This paper investigates the dynamic behaviour of a rotating ring that forms an essential element in ring-based vibratory gyroscopes that utilize oscillatory electromagnetic forces. Understanding the effects of nonlinear actuator dynamics is considered important for characterizing the dynamic behavior of such devices. A suitable theoretical model to generate nonlinear electromagnetic force that acts on the ring structure is formulated. In order to predict the dynamic behaviour of a ring system subjected to external excitation and body rotation, discretized equations obtained via Galerkin’s procedure is employed to investigate the time as well as frequency response behavior. Dynamic response in the driving and the sensing directions are examined via time responses, phase diagram, Poincare’ map and bifurcation plots when the input angular motion and the nonlinear electromagnetic force are considered simultaneously. The analysis is envisaged to aid ongoing experimental research as well as for providing design improvements in Ring-based Gyroscopes.

Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: Structures and Continuous Systems

2018;():V008T10A029. doi:10.1115/DETC2018-85659.

In this paper, the Reduced Order Method (ROM) and the Method of Multiple Scales (MMS) are used to investigate the influences of dimensionless damping and voltage parameters on the amplitude-frequency response of an electrostatically actuated double-walled carbon nanotube (DWCNT). The forces responsible for the nonlinearities in the vibrational behavior are intertube van der Waals and electrostatic forces. Soft AC excitation and small viscous damping forces are assumed. Herein, the coaxial case is investigated. In this mode of vibration, the outer and inner carbon nanotubes move synchronously (in-phase) with the same maximum tip deflection. The DWCNT structure is modelled as a cantilever beam with Euler-Bernoulli beam assumptions since the DWCNT is characterized with high length-diameter ratio. The results shown assume steady-state solutions in the first-order MMS solution. The analytical approximate solutions provided by MMS are validated numerically by two-term (2T) Time Reponses and AUTO-07P. The two methods in this paper are found to be in excellent agreement at lower amplitudes. Additionally, the two methods are assessed for their advantages and limitations. The importance of the results in this paper are the effect of damping and voltage on the stability of the DWCNT vibration.

Commentary by Dr. Valentin Fuster
2018;():V008T10A030. doi:10.1115/DETC2018-86078.

This paper presents an equivalent continuum model to study the bending-torsion-axial coupled vibrations of a cable-harnessed beam. The pre-tensioned cable is wrapped periodically around the beam in a diagonal manner. The host structure is assumed to behave as a Euler-Bernoulli beam. The system is modeled using energy methods. The diagonal wrapping pattern results in variable coefficient strain and kinetic energies. Homogenization technique is used to convert spatially varying coefficients into a constant coefficient one. Coupled partial differential equations representing the bending, torsion and the axial modes are derived using Hamilton’s principle. The free vibration characteristics such as the natural frequencies and the mode shapes of the coupled system are analyzed for a fixed-fixed boundary condition and compared to results from the uncoupled and finite element analysis models.

Topics: Cables , Torsion , Vibration
Commentary by Dr. Valentin Fuster
2018;():V008T10A031. doi:10.1115/DETC2018-86212.

In Pressurized Water Reactors (PWR), fuel assemblies are composed of fuel rods, long slender tubes filled with uranium pellets, bundled together using spacer grids. These structures are subjected to fluid-structure interactions, due to the flowing coolant surrounding the fuel assemblies inside the core, coupled with large-amplitude vibrations in case of external seismic excitation. Therefore, understanding the non-linear response of the structure and, particularly, its dissipation, is of paramount importance for the choice of safety margins. To model the nonlinear dynamic response of fuel rods, the identification of nonlinear stiffness and damping parameters is required. The case of a single fuel rod with clamped-clamped boundary conditions was investigated by applying harmonic excitation at various force levels. Different configurations were implemented testing the fuel rod in air and in still water; the effect of metal pellets simulating nuclear fuel pellets inside the rods was also recorded. Non-linear parameters were extracted from some of the experimental response curves by means of a numerical tool based on the harmonic balance method. The axisymmetric geometry of fuel rods resulted in the presence of a one-to-one internal resonance phenomenon, which has to be taken into account modifying accordingly the numerical identification tool. The internal motion of fuel pellets is a cause of friction and impacts, complicating further the linear and non-linear dynamic behavior of the system. An increase of the equivalent viscous-based modal damping with excitation amplitude is often shown during geometrically non-linear vibrations, thus confirming previous experimental findings in the literature.

Commentary by Dr. Valentin Fuster
2018;():V008T10A032. doi:10.1115/DETC2018-86223.

This paper deals with the voltage response of electrostatically actuated NEMS resonators at superharmonic resonance. In this work a comparison between Boundary Value Problem (BVP) model, and Reduced Order Model (ROM) is conducted for this type of resonance. BVP model is developed from the partial differential equation by replacing the time derivatives with finite differences. So, the partial differential equation is replaced by a sequence of boundary value problems, one for each step in time. Matlab’s function bvp4c is used to numerically integrate the BVPs. ROMs are based on Galerkin procedure and use the mode shapes of the resonator as a basis of functions. Therefore, the partial differential equation is replaced by a system of differential equations in time. The number of the equations in the system is equal to the number of mode shapes (or modes of vibration) used in the ROM. One mode of vibration ROM is solved using the method of multiple scales. Two modes of vibration ROM is numerically integrated using Matlab’s function ode15s in order to obtain time responses, and a continuation and bifurcation analysis is conducted using AUTO 07P. The effects of different nonlinearities in the system on the voltage response are reported. This work shows that BVP model is a valid method to predict the voltage response of a micro/nano cantilevers.

Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: System Identification, Damage Detection, and Diagnostics

2018;():V008T10A033. doi:10.1115/DETC2018-85060.

Vibration performances of roller bearings are greatly affected by various localized defects. Thus, it is very important to analyze vibration characteristics of the roller bearings with the localized defects. In this paper, a nonlinear dynamic model is developed to formulate the effect of a localized defect on the vibration characteristics of a cylindrical roller bearing (CRB). A bump defect is formulated in this model. The defect profile is defined as a spherical one. The time-varying displacement excitation caused by the defect is modelled. Effects of the defect sizes on the vibration characteristics of the roller bearing are discussed. The simulation results show that the developed method can provide some guidance for understanding the vibration characteristics of the CRB with a bump defect.

Commentary by Dr. Valentin Fuster
2018;():V008T10A034. doi:10.1115/DETC2018-85126.

Impedance based structural health monitoring using piezoelectric material is a high frequency method for detection of tiny damage. For modeling of structure in high frequency using conventional finite element method very fine mesh is needed. For large structure, this leads to very large mass and stiffness matrices. So very high RAM is needed to save these matrices and simulation time would be very low. In this paper a method combined finite element method and boundary element method named scaled boundary finite element method is studied for health and cracked 2D structure. Impedance of healthy and cracked structure is compared and verified by finite element method. A good agreement is presented and very low degree of freedom is obtained compared with finite element method.

Commentary by Dr. Valentin Fuster
2018;():V008T10A035. doi:10.1115/DETC2018-85165.

The kurtogram is a spectral analysis tool used to detect non-stationarities in a signal. It can be effectively used to determine the optimal filter for bearing fault feature extraction from a blurred vibration signal, since the transients of the bearing fault-induced signal can be regarded as non-stationary. However, the effectiveness of the kurtogram is diminished when the signal is collected from a bearing operating under time-varying speed conditions. There is a need to improve the performance of the kurtogram under time-varying speed conditions. In this paper, a short-time kurtogram method is proposed for bearing fault feature extraction under time-varying speed conditions. The performance of the short-time kurtogram is examined with experimental data. The results demonstrate that the short-time kurtogram can effectively be used to extract bearing fault features under time-varying speed conditions.

Commentary by Dr. Valentin Fuster
2018;():V008T10A036. doi:10.1115/DETC2018-85196.

Compressive sensing (CS) theory allows measurement of sparse signals with a sampling rate far lower than the Nyquist sampling frequency. This could reduce the burden of local storage and remote transmitting. The periodic impacts generated in rolling element bearing local faults are obviously sparse in the time domain. According to this sparse feature, a rolling element bearing fault feature extraction method based on CS theory is proposed in the paper. Utilizing the shift invariant dictionary learning algorithm and the periodic presentation characteristic of local faults of roller bearings, a shift-invariant dictionary of which each atom contains only one impact pattern is constructed to represent the fault impact as sparsely as possible. The limited degree of sparsity is utilized to reconstruct the feature components based on compressive sampling matching pursuit (CoSaMP) method, realizing the diagnosis of the roller bearing impact fault. A simulation was used to analyze the effects of parameters such as sparsity, SNR and compressive rate on the proposed method and prove the effectiveness of the proposed method.

Commentary by Dr. Valentin Fuster
2018;():V008T10A037. doi:10.1115/DETC2018-85253.

On-line cutting tool wear monitoring plays a critical role in industry automation and has the potential to significantly increase productivity and improve product quality. In this study, we employed the long short-term memory neural network as the decision model of the tool condition monitoring system to predict the amount of cutting tool wear. Compared with the traditional recurrent neural networks, the long short-term memory (LSTM) network can capture the long-term dependencies within a time series. To further decrease the training error and enhance the prediction performance of the network, a genetic algorithm (GA) is applied to find the initial values of the networks that minimize the objective (training error). The proposed methodology is applied on a publicly available milling data set. Comparisons of the prediction performance between the Elman network and the LSTM with and without using GA optimization proves that the GA based LSTM shows an enhanced prediction performance on this data set.

Commentary by Dr. Valentin Fuster
2018;():V008T10A038. doi:10.1115/DETC2018-85336.

Machining of large components, such as multi-megawatt wind turbine parts, is currently done using large expensive CNC machines. Using small parallel kinematic machines can provide an economical attractive alternative. Optimization of the conditions for a stable and accurate machining process is necessary. Knowledge of position dependent dynamic response is key when performing such optimization. This contribution is a part of current research striving towards efficient parameter identification for dynamic models of 6-SPS parallel kinematic manipulators for machining purposes. Stiffness and damping are updated for a small set of manipulator poses using Operational Modal Analysis and a two step parameter identification routine. The model obtained contains information of the dynamic response for all poses in the workspace. In this study a six degree of freedom 6-SPS model is derived and operational modal analysis experiments are simulated. The obtained modal parameters are used for parameter identification. It is concluded that the operational modal analysis performs well in estimating frequencies and mode shapes of the symmetric structure, but damping estimates are poor. Parameter identification routine performance is satisfactory, but the poor damping estimates from modal analysis causes incorrect and uncertain parameter identification.

Commentary by Dr. Valentin Fuster
2018;():V008T10A039. doi:10.1115/DETC2018-85550.

Vibration monitoring is an effective method for mechanical fault diagnosis. Wind turbines usually operated under varying-speed condition. Time-frequency analysis (TFA) is a reliable technique to handle such kind of nonstationary signal. In this paper, a new scheme, called current-aided TFA, is proposed to diagnose the planetary gearbox. This new technique acquires necessary information required by TFA from a current signal. The current signal is firstly used to estimate the rotating speed of the shaft. These parameters are applied to the demodulation transform to obtain a rough time-frequency distribution (TFD). Finally, the synchrosqueezing method further enhances the concentration of the obtained TFD. The validation and application of the proposed method are presented by a simulated signal and a vibration signal captured from a test rig.

Commentary by Dr. Valentin Fuster
2018;():V008T10A040. doi:10.1115/DETC2018-85552.

The planetary gearbox is one of the key components in the rotating machinery. The planetary gearbox is prone to malfunction, which increases downtime and repair costs. Hence, the fault diagnosis of the planetary gearbox is an important research topic. The acquired signal from the planetary gearbox exhibit strongly time-variant and nonstationary features since the planetary gearbox usually works at time-varying speeds. In this study, a new time-frequency analysis method is proposed. This method takes the spectrum shape into account and partitions the time-frequency into several components. Then the fault feature of the planetary gearbox is detected by analyzing the decomposed components. The simulated signal and the experimental signals under nonstationary conditions are analyzed to verify the effectiveness the proposed method. Results show that the proposed method can efficiently extract the fault feature of the planet gear.

Commentary by Dr. Valentin Fuster
2018;():V008T10A041. doi:10.1115/DETC2018-85554.

Reliability assessment of Structural Health Monitoring systems applied to the diagnosis of faults in elastic structures is discussed in this contribution. In the field of Non Destructive Testing (NDT), Probability of Detection (POD) is used as a performance measure for quantifying the reliability of NDT approaches. However, reliability measures applied to Fault Detection and Isolation (FDI) is not discussed much in this research area. In this contribution the reliability of vibration-based monitoring approaches with respect to their principal ability to detect changes, realize diagnosis, and isolate causes (as FDI) is discussed. Using eigenfrequency and band power as attributes, a novel feature-based POD is proposed and implemented as a reliability measure for vibration-based FDI. The a90/95 criteria which represents 90% probability of detecting a fault with 95% level of confidence is successfully implemented to an experimentally realized monitoring system. Emphases is made on improving the detection quality through sensor/information fusion. Acceleration, strain, and deflection measurement paths are utilized for diagnosis purposes based on experimental results.

Commentary by Dr. Valentin Fuster
2018;():V008T10A042. doi:10.1115/DETC2018-85889.

Due to its special modulation mechanism with multiple units (eg. shafts, gears, etc.) under various conditions, the related fault information of gear fault would distribute in a broad frequency band. In this manner, it is not easy about accurately detecting the early-stage gear fault by detecting the fault frequency in a limited frequency band. In this paper, a new spectral analysis, called multiscale sparse spectrum (MSS), is proposed to achieve fault frequency detection in a sound way. The overall frequency information about the raw signal is firstly sensed by a series of frequency-window function, which can be reached by short-frequency Fourier transform. Then, according to orthogonal matching pursuit, harmonic atoms are further employed to sparsely mine the modulation components from these multiscale pseudo mono-components. Finally, MSS is proposed to synthesize the existing harmonic-related components. Furthermore, a synthesized sparse spectrum (SSS) is obtained by searching the frequency-frequency ridge from MSS. Compared with EMD and fast-kurtogram analysis, the results show the effectiveness of the proposed method of gear fault detection.

Commentary by Dr. Valentin Fuster
2018;():V008T10A043. doi:10.1115/DETC2018-86160.

A worldwide round robin study is sponsored by the Society of Experimental Mechanics to detect damage in a composite plate with a scanning laser Doppler vibrometer (SLDV). The aim of this round robin study is to explore the potential of a SLDV for detection of damage in composite plates. In this work, a curvature-based damage detection method with use of a continuously SLDV (CSLDV) is proposed. A CSLDV can be regarded as a real-time moving sensor, since the laser spot from the CSLDV continuously moves on a structure surface and measures velocity response. An operating deflection shape (ODS) of the damaged composite plate can be obtained from velocity response by the demodulation method. The ODS of the associated undamaged composite plate is obtained by using polynomials to fit the ODS of the damaged plate. A curvature damage index (CDI) using differences between curvatures of ODSs (CODSs) associated with the ODSs from the demodulation method and the polynomial fit is proposed to detect damage. With the proposed curvature-based damage detection method, locations of two possible damage are detected in areas with consistently high CDI values at two excitation frequencies, which are in good agreement with prescribed damage locations.

Commentary by Dr. Valentin Fuster
2018;():V008T10A044. doi:10.1115/DETC2018-86234.

Time-frequency method is a good tool to analysis the vibration signal for condition monitoring of rotational machinery under non-stationary conditions. However, the fault feature of bearing cannot be directly revealed using the time-frequency method, because the fault causes complex modulation of resonance frequency. To resolve this problem, this paper proposes a joint application of Spectral Kurtosis (SK) and Velocity Synchrosqueezing Transform (VST). The vibration is firstly processed by spectral kurtosis method to extract the impulse features of the signal. After this, amplitude demodulation techniques are applied to obtain the impulse envelope. Finally the VST is applied to reveal the time-frequency feature of the envelope signal. The fault, if any, can be diagnosed by identifying the uncovered signal components. The effectiveness of the proposed method is validated using experimental signals collected under non-stationary condition.

Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: Vibration and Stability of Mechanical Systems

2018;():V008T10A045. doi:10.1115/DETC2018-85114.

Femur bone is the longest and largest bone in the human skeleton. This bone connects the pelvic bone to the knee and carries most of the body weight. The static behavior of femur bone has been a center of investigation for many years while little attention has been given to its dynamic and vibrational behavior, which is of great importance in sports activities, car crashes and elderly falls. Investigation of natural frequencies and mode shapes of bone structures are important to understand the dynamic and vibrating behaviors. Vibrational analysis of femoral bones is presented using finite element method. In the analysis, the bone was modeled with isotropic and orthotropic mechanical properties. The effect of surrounding bone muscles has also been accounted for as a viscoelastic medium embedding the femur bone. Natural frequencies extracted considering the effects of age aggravated by weakening the elastic modulus and density loss. The effects of real complex bone geometry on natural frequencies are studied and are compared with a simple circular cross-sectional model.

Topics: Bone
Commentary by Dr. Valentin Fuster
2018;():V008T10A046. doi:10.1115/DETC2018-85353.

One of the important issues in turbomachinery flutter analysis is the intra-row interaction effects. The present work is aimed at a systematic research of the adjacent rows effects on aerodynamic damping. Three models, the isolated rotor, the IGV-rotor and the rotor-stator model, are performed to identify the upstream and downstream stator effects on the rotor blade. It is found that the aerodynamic damping from the stage flutter simulations are quite different from that from isolated rotor. In addition, the mixing-plane method is also applied to calculate the stage flutter characteristics and its accuracy of flutter predictions is compared with the time-marching method. It is indicated that the main difference of aerowork density between MP and TM is in the tip area, and in some cases the result from MP method can be misleading. Furthermore, study with different axial gaps illustrates that there is a nonmonotonic relationship between the rotor blade aerodynamic damping and the gap in the rotor-stator model, while the rotor blade aerodynamic damping monotonically increases with the gap in the IGV-rotor model.

Commentary by Dr. Valentin Fuster
2018;():V008T10A047. doi:10.1115/DETC2018-85372.

In order to explore the effects of the initial temperature on the clutch hot judder, the thermodynamic analysis was conducted during the clutch engagement process. The finite element analysis was adopted to explore the contact pressure based on the consideration of the concentrated reactive force on the circlip. A 4-degree-of-freedom torsional vibration model was established to evaluate the hot judder behavior. The results demonstrated that the closer the surface was to the circlip, the greater the friction torque generated on friction surfaces was. Moreover, the higher the initial temperature was, the shriller the clutch hot judder was. The increased initial temperature not only resulted in the increase in the maximum surface temperature, but also could make the clutch engagement much shorter.

Topics: Temperature
Commentary by Dr. Valentin Fuster
2018;():V008T10A048. doi:10.1115/DETC2018-85386.

This paper deals with aligning knee geometrical anatomical data with kinematic data from experimental work in order to develop a two-dimensional inverse dynamics anatomical model of human knee. Motion capture cameras were used to collect the experimental data for a knee extension exercise. Reflective markers were placed on the subjects’ skin during the experiment. In this model, joints such as hip, knee, and ankle are represented by axes of rotation. These axes are determined by calculating the relative instantaneous center of rotation of one body segment with respect to an adjacent body segment. Body-fixed coordinate systems were defined using three reflective markers attached to the subject. The origin of each body fixed-coordinate system was located between the three markers on that body segment, the body-fixed x-axis was pointing towards the marker on the lateral side of the body segment, and the body-fixed y-axis fell on the same plane as the three reflective markers on the body segment. Moreover, the axis of rotation that represents the hip was determined by calculating the instantaneous center of rotation of reflective markers located on the pelvis with respect to a body fixed coordinate system on the thigh. The axis of rotation on the knee was determined by calculating the instantaneous center of rotation of reflective markers on the shin (tibia) with respect to the body-fixed coordinate system on the thigh (femur). The axis of rotation on the ankle was determined by calculating the instantaneous center of rotation of reflective markers on the shin with respect to a body-fixed coordinate system on the foot. Bone anatomical geometries of femur and tibia were represented mathematically as polynomials and superimposed over the experimental data. This was done by matching the center of rotation from experimental data with the geometric center of the femoral condyle. This is necessary for estimating the insertions/origins of knee ligaments. These ligaments are modeled as nonlinear elastic springs. Furthermore, ligaments were divided into separate fiber bundles. Both the posterior and anterior cruciate ligaments were divided into an anterior and posterior fiber bundle. The cruciate ligament forces for both exercises are discussed in this paper.

Commentary by Dr. Valentin Fuster
2018;():V008T10A049. doi:10.1115/DETC2018-85765.

We describe a method for extending the load range of a vibration isolator using a foldable cylinder consisting of a twist buckling pattern (Kresling’s Pattern), and evaluate the vibration isolating performance through excitation experiments. In a previous study, it was determined that the foldable cylinder is bistable and acts as a vibration isolator with nonlinear characteristics in a displacement region where the spring stiffness is zero. Its spring characteristics and vibration isolating performance were clarified by numerical analysis and excitation experiments, and indicated that vibration in a certain frequency range is reduced where the spring stiffness is zero. However, this vibration isolator has a disadvantage in that it can only support an initial load that transfers to the zero-spring-stiffness region. Therefore, in this research, we improve the design variables of the isolator and the position of the linear spring attached to the isolator. As a result, the initial load range is extended by two to three times that of the conventional vibration isolator. Furthermore, the isolating performance is maintained even when the initial load is changed within a given load range.

Commentary by Dr. Valentin Fuster
2018;():V008T10A050. doi:10.1115/DETC2018-86418.

The nonlinear dynamic response of short cables with a tip mass subject to base excitations and undergoing primary resonance is investigated via experimental tests and by employing an ad hoc nonlinear mechanical model. The considered cables are made of several strands of steel wires twisted into a helix forming composite ropes in a pattern known as ‘laid ropes’. Such short span ropes exhibit a hysteretic behavior due to the inter-wire frictional sliding. A nonlinear one-dimensional (1D) continuum model based on the geometrically exact Euler-Bernoulli beam theory is conveniently adapted to describe the cable dynamic response. The Bouc-Wen law of hysteresis is incorporated in the moment-curvature constitutive relationship to reproduce the hysteretic behavior of short steel wire ropes subject to flexural cycles. The frequency response curves show a pronounced softening nonlinearity induced by hysteresis and inertia nonlinearity as confirmed by the experimental data acquired on a wire rope with a tip mass excited at its base by a shaker. The experimental nonlinear resonance response will be exploited to identify the constitutive parameters of the wire rope that best fit the frequency response curves at various forcing amplitudes.

Commentary by Dr. Valentin Fuster

30th Conference on Mechanical Vibration and Noise: Vibration Control, Energy Harvesting, and Smart Structures (VIB/MSNDC-1)

2018;():V008T10A051. doi:10.1115/DETC2018-85131.

A hybrid control scheme that combines a self-tuning PID-feedback loop and TDC-based feedforward scheme is proposed in this study to cope with an active pneumatic vibration isolator. In order to establish an effective TDC feedforward control a reliable mathematical model of the pneumatic isolator is required and developed firstly. Numerical and experimental investigations on the validity of the mathematical model are performed. It is found that although slight discrepancy exists between predicted and observed behaviors of the system, the overall model performance is acceptable. The resultant model is then applied in the design of the TDC feedforward scheme. A neuro-based adaptive PID control is integrated with the TDC feedforward algorithm to form the hybrid control. Numerical and experimental isolation tests are carried out to examine the suppression performances of the proposed hybrid control scheme. The results show that the proposed hybrid control method outperforms solely TDC feedforward while the latter outperforms the passive isolation system. Moreover, the proposed hybrid control scheme can suppress the vibration near the system’s resonance.

Commentary by Dr. Valentin Fuster
2018;():V008T10A052. doi:10.1115/DETC2018-85308.

The possibility of improving the performance of a piezoelectric harvester by means of a cantilever dynamic vibration absorber (CDVA) is investigated. The CDVA cancels the original mode of vibration of the harvester and generates two new modes. Some prototypes are developed using a mathematical model for predicting the natural frequencies of the coupled system. Impulsive tests were performed on prototypes. Experimental results show that a small CDVA can lower the main resonance frequency of an harvester of the same extent as a larger tip mass. The measured voltage shows also an high frequency resonance peak, which can be exploited for collecting energy. A multi-physics numerical model is developed for performing modal analysis and stress analysis. Numerical results show that the stress inside the piezoelectric material of the harvester with CDVA results smaller than the stress inside the harvester with a tip mass tuned to the same frequency.

Topics: Cantilevers , Springs
Commentary by Dr. Valentin Fuster
2018;():V008T10A053. doi:10.1115/DETC2018-85398.

A general algorithm is developed for input shaping on the basis of the deadbeat state feedback control theory in discrete-time. This algorithm is easily extended to generate input sequence robust to parametric uncertainties in a flexible structure. Numerical results are presented for systems with one and two vibratory modes.

Topics: State feedback
Commentary by Dr. Valentin Fuster
2018;():V008T10A054. doi:10.1115/DETC2018-85400.

This paper presents experimental results from the testing of a semi-active damping system in an off-road bicycle (bike). Magnetorheological dampers are being increasingly used in automotive applications to enhance damping capability of a suspension system or to mitigate the trade-off between ride comfort and handling. A magnetorheological (MR) damper requires a relatively low amount of energy to control damping characteristics, and behaves as a passive damper in the absence of any power input. This study investigates the use of a semi-active magnetorheological damper for the rear suspension of a mountain bike. The performance of this damper has been compared to the current shock absorber on the bike. All testing has been performed on a shaker table and the performance of the damper has been evaluated by comparing the input acceleration at the hub of the rear wheel to the acceleration at the seat of the bike. The main aim of this study is to investigate the viability of using an MR damper in a mountain bike suspension system. Test results indicate that the performance of the semi-active MR damper is comparable to the current shock absorber. Furthermore, the MR damper lends itself to hands-off control that will be investigated in a future study. Therefore, it can be concluded from preliminary testing that an MR damper can be used in a mountain bike to effectively control damping.

Topics: Damping , Bicycles , Roads
Commentary by Dr. Valentin Fuster
2018;():V008T10A055. doi:10.1115/DETC2018-85476.

In this study, we present triboelectric nanogenerators (TENGs) for vibrational energy harvesting in oil pipelines. The generators are designed to replenish the batteries of leak detection sensor, thereby increasing their lifespan and reducing the need for maintenance. The TENGs were designed to harvest energy from a 12-inch diameter pipeline, vibrating with at 32 Hz. Three alternative materials were used for the upper plate of a 4 × 4 cm TENG, namely Polytetrafluoroethylene (PTFE), unstructured polydimethylsiloxane (PDMS) and structured PDMS. Tests revealed that the unstructured PDMS TENG outperformed the PTFE TENG and generated 47.6 μW of power. Structuring the PDMS by patterning open channels on half of the surface increased the output power to 200.0 μW. When the spring constant of the structured PDMS TENG was optimized, the output power was further increased to 297.7 μW. These results demonstrate that structured PDMS shows promise in triboelectric energy harvesting, specifically because it can be surface-modified using inexpensive techniques that do not require a clean room.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
2018;():V008T10A056. doi:10.1115/DETC2018-85479.

In recent decades, the technique of piezoelectric energy harvesting has drawn a great deal of attention since it is a promising method to convert vibrational energy to electrical energy to supply lower-electrical power consumption devices. The most commonly used configuration for energy harvesting is the piezoelectric cantilever beam. Due to the inability of linear energy harvesting to capture broadband vibrations, most researchers have been focusing on broadband performance enhancement by introducing nonlinear phenomena into the harvesting systems. Previous studies have often focused on the symmetric potential harvesters excited in a fixed direction and the influence of the gravity of the oscillators was neglected. However, it is difficult to attain a completely symmetric energy harvester in practice. Furthermore, the gravity of the oscillator due to the change of installation angle will also exert a dramatic influence on the power output. Therefore, this paper experimentally investigates the influence of gravity due to bias angle on the output performance of asymmetric potential energy harvesters under harmonic excitation. An experimental system is developed to measure the output voltages of the harvesters at different bias angles. Experimental results show that the bias angle has little influence on the performance of linear and monostable energy harvesters. However, for an asymmetric potential bistable harvester with sensitive nonlinear restoring forces, the bias angle influences the power output greatly due to the effect of gravity. There exists an optimum bias angle range for the asymmetric potential bistable harvester to generate large output power in a broader frequency range. The reason for this phenomenon is that the influence of gravity due to bias angle will balance the nonlinear asymmetric potential function in a certain range, which could be applied to improve the power output of asymmetric bistable harvesters.

Commentary by Dr. Valentin Fuster
2018;():V008T10A057. doi:10.1115/DETC2018-85635.

Many common environmental vibration sources exhibit low and broad frequency spectra. In order to exploit such excitations, energy harvesting architectures utilizing nonlinearity, especially bistability, have been widely studied since the energetic interwell oscillations between their stable equilibria can provide enhanced power harvesting capability over a wider bandwidth compared to the linear counterpart. However, one of the limitations of these nonlinear architectures is that the interwell oscillation regime may not be activated for a low excitation level that is not strong enough to overcome the potential energy barrier, thus resulting in low amplitude intrawell response which provides poor energy harvesting performance. While the strategic integration of bistability and additional dynamic elements has shown potential to improve broadband energy harvesting performance by lowering the potential barrier, there is a clear opportunity to further improve the energy harvesting performance by extracting electrical power from the kinetic energy in the additional element that is induced when the potential barrier is lowered. To explore this opportunity and advance the state of the art, this research develops a novel hybrid bistable vibration energy harvesting system with a passive mechanism that not only adaptively lowers the potential energy barrier level to improve broadband performance but also exploits additional means to capture more usable electrical power. The proposed harvester is comprised of a cantilever beam with repulsive magnets, one attached at the free end and the other attached to a linear spring that is axially aligned with the cantilever (a spring-loaded magnet oscillator). This new approach capitalizes on the adaptive bistable potential that is passively realized by the spring-loaded magnet oscillator, which lowers the double-well potential energy barrier thereby facilitating the interwell oscillations of the cantilever across a broad range of excitation conditions, especially for low excitation amplitudes and frequencies. The interwell oscillation of the cantilever beam enhances not only the piezoelectric energy harvesting from the beam but also the electromagnetic energy harvesting from the spring-loaded magnet oscillator by inducing large amplitude vibrations of the magnet oscillator. Numerical investigations found that the proposed architecture yields significantly enhanced energy harvesting performance compared to the conventional bistable harvester with fixed magnet.

Commentary by Dr. Valentin Fuster
2018;():V008T10A058. doi:10.1115/DETC2018-85682.

In order to improve the performance of vibration energy harvesters over a broad frequency range, this paper proposes a use of piezoelectric nonlinear energy sink (NES) for energy harvesting from ambient vibrations. A standard rectifying direct current (DC) interface circuit is considered to generate DC power from the piezoelectric NES under harmonic excitation. Harmonic balance method is used to obtain the dynamic response and energy harvesting performance of the proposed piezoelectric NES, verified by the equivalent circuit simulation. Analytical and numerical results show that the design, by applying NES, improves the efficiency of energy harvesting without increasing the vibration of the primary structure in a broadband manner. The effects of the electromechanical coupling, excitation level and load resistance on the magnitude and bandwidth of the output DC power are investigated.

Commentary by Dr. Valentin Fuster
2018;():V008T10A059. doi:10.1115/DETC2018-85813.

Tuned Mass Damper (TMD) are largely used in many domains like aerospace or civil engineering. While very simple and robust, their damping capability is proportional to their mass, which represents an important shortcoming. Hybrid-TMDs propose to combine active systems to an optimal passive device. Nevertheless, stability problems can result from this association. In this study, the passivity concept is used to design a control law enforcing the hybrid-TMD to be hyperstable. Consequently, the resulting Hybrid TMD is fail-safe and unconditionally stable. An analysis of the active and reactive powers also illustrates the energy flux in the device and its passive nature. Simulations based on an experimental model show the performance of such system.

Commentary by Dr. Valentin Fuster
2018;():V008T10A060. doi:10.1115/DETC2018-85873.

In this paper, a two-body self-react wave energy converter with a novel mechanical Power Take-off (PTO) is introduced. The PTO rectifies the mechanical motion and regulates the flow with a mechanism called Mechanical Motion Rectifier (MMR), which converts the reciprocating motion of the ocean wave into unidirectional rotation of the generator. The overall system is analyzed in both time and frequency domain. In time domain, the piecewise non-linear dynamic model of the MMR PTO is derived, and parameters that could significantly influence the MMR property is extracted. By building the model into WEC-Sim, a time domain wave energy converter (WEC) simulation tool, to simulate and evaluate the performance of the PTO. In addition, the system is modelled as a two-body vibration system for frequency domain analysis in order to further investigate and optimize the proposed wave energy converter. The tunable parameters within the system, including the equivalent mass, the equivalent damping coefficient, and the PTO stiffness, are discussed based on the criteria of maximization of the total output power. To verify the theoretical analysis, a bench test prototype is developed and tested on a hydraulic test machine. The experimental results in line with the derived model and can be used for reasonable estimation on the output power of the proposed system in real ocean conditions.

Commentary by Dr. Valentin Fuster
2018;():V008T10A061. doi:10.1115/DETC2018-85915.

Vibration Energy Harvesters (VEHs) are devices used to collect mechanical energy from the surrounding environment to supply low power electronic systems such as Wireless Sensor Nodes. In this paper, we introduce an electromagnetic VEH model and a semi-analytical method called Moment Equation Copula Closure (MECC) that is compared to Monte Carlo simulations. Those methods are then used to derive the maximum power that can be extracted from random vibration before analyzing the effect of cubic stiffness nonlinearity on the VEH robustness against the variation of the excitation spectrum. Unlike bistable nonlinearity, it is shown that Duffing nonlinearity can be used to enhance the VEH power density and robustness with a limited effect on the harvested power.

Commentary by Dr. Valentin Fuster
2018;():V008T10A062. doi:10.1115/DETC2018-86068.

In this study the dynamic and electrical performance of a novel hybrid Electromagnetic-Triboelectric energy harvester is studied. The mechanism incorporates a linear tubular electromagnetic (EMG) transducer as well as a free-standing grating triboelectric (TENG) transducer. The heaving of the slider inside the stator triggers both EMG and TENG which results in electricity generation. The dynamic model of the system is firstly developed and the system response under external excitation is carried out. Then, the electrical output characteristics of each harvesting unit are developed based on the dynamic response. Then, the effects of various parameters such as frequency of excitation and external electrical load on the output performance of the harvester including voltage, current, and power density of the EMG and TENG units are investigated. This study provides a guideline toward the design and analysis of novel mechanical energy harvesters.

Commentary by Dr. Valentin Fuster
2018;():V008T10A063. doi:10.1115/DETC2018-86214.

Shock isolation systems are often modeled as having lumped stiffness and damping characteristics. However, the isolation performance may be improved if the isolation mount is allowed to have internal dynamics. Previous work has considered several different ways of disrupting the disturbance as it propagates along the length of a multi-degree-of-freedom mount. In this paper, the role of internal damping of the mount is re-examined. Furthermore, the damping model is extended to allow different levels of damping in different response regimes. Through simulation of the shock response, the findings show that the optimal level of internal damping depends on the magnitude of the input shock. For small shocks, performance is best for a relatively high level of damping, but for larger shocks, the best damping value drops to a much lower value. The effect on isolation performance of having different damping levels in different response regimes is shown to be fairly modest, and is shown to depend on the input excitation level.

Commentary by Dr. Valentin Fuster
2018;():V008T10A064. doi:10.1115/DETC2018-86426.

The nonlinear dynamic response of a scale steel structure equipped with a hysteretic tuned mass damper (TMD) is investigated. Identification of the parameters of a nonlinear model of the structure is carried out via experimental tests while the optimal parameters of the TMD are obtained by using a differential evolution algorithm. Such optimization algorithm can search the best solution in a large parameter space without making restrictive assumptions on the optimization problem. The seismic performance of the optimized hysteretic TMD mounted on a nonlinear structure is compared with that of a more conventional, linear tuned mass damper.

Topics: Steel
Commentary by Dr. Valentin Fuster

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