ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V006T00A001. doi:10.1115/DETC2018-NS6.

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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Computational Methods in Multibody Systems and Nonlinear Dynamics

2018;():V006T09A001. doi:10.1115/DETC2018-85174.

In this paper, the sling load dynamics of an aerial vehicle carrying a payload are investigated by employing three formulations of the governing equations. They are the hybrid formulation where the system exists in either a taut cable or slack cable configuration, with appropriate treatment of the transition between the two; the linear complementarity problem (LCP) formulation where the cable constraints are imposed as linear complementarity conditions and finally, the lumped parameter formulation where the cable is modelled with a series of spring-mass elements. The hybrid and LCP formulations neglect the elasticity of the cable while the lumped parameter model explicitly accounts for the elastic properties of the cable, albeit in a discrete way. The importance of the incorporation of elastic properties of the cable on the system is investigated for the variation in solution space of the payload. The three formulations are compared numerically, for information on the computational cost, motion of the payload, and tension profile, for several aerial maneuvers, including an aggressive obstacle avoidance with a window clearance flight.

Commentary by Dr. Valentin Fuster
2018;():V006T09A002. doi:10.1115/DETC2018-85429.

We present a principled method for dynamic simulation of rigid bodies in intermittent contact with each other where the contact is assumed to be a non-convex contact patch that can be modeled as a union of convex patches. The prevalent assumption in simulating rigid bodies undergoing intermittent contact with each other is that the contact is a point contact. In recent work, we introduced an approach to simulate contacting rigid bodies with convex contact patches (line and surface contact). In this paper, for non-convex contact patches modeled as a union of convex patches, we formulate a discrete-time mixed complementarity problem where we solve the contact detection and integration of the equations of motion simultaneously. Thus, our method is a geometrically-implicit method and we prove that in our formulation, there is no artificial penetration between the contacting rigid bodies. We solve for the equivalent contact point (ECP) and contact impulse of each contact patch simultaneously along with the state, i.e., configuration and velocity of the objects. We provide empirical evidence to show that if the number of contact patches between two objects is less than or equal to three, the state evolution of the bodies is unique, although the contact impulses and ECP may not be unique. We also present simulation results showing that our method can seamlessly capture transition between different contact modes like non-convex patch to point (or line contact) and vice-versa during simulation.

Topics: Simulation
Commentary by Dr. Valentin Fuster
2018;():V006T09A003. doi:10.1115/DETC2018-85823.

Multibody systems and associated equations of motion may be distinguished in many ways: holonomic and nonholonomic, linear and nonlinear, tree-structured and closed-loop kinematics, symbolic and numeric equations of motion. The present paper deals with a symbolic derivation of nonlinear equations of motion for nonholonomic multibody systems with closed-loop kinematics, where any generalized coordinates and velocities may be used for describing their kinematics. Loop constraints are taken into account by algebraic equations and Lagrange multipliers. The paper then focuses on the derivation of the corresponding linear equations of motion by eliminating the Lagrange multipliers and applying a computationally efficient symbolic linearization procedure. As demonstration example, a vehicle model with differential steering is used where validity of the approach is shown by comparing the behavior of the linearized equations with their nonlinear counterpart via simulations.

Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Contact and Interface Dynamics

2018;():V006T09A004. doi:10.1115/DETC2018-85034.

In this paper, a general contact stiffness model is proposed to study the mixed lubricated contact between a rough surface and a rigid flat plate, which is the equivalent model for the contact between two rough surfaces and is the general case for engineering contact interfaces. The total interfacial contact stiffness is composed of the dry rough surface contact stiffness and the liquid lubricant contact stiffness. The GW model is used for surface topography description and the contact stiffness of a single asperity is derived from the Hertz contact theory. The whole dry rough contact stiffness is obtained by multiple the single asperity contact stiffness with the number of contact asperities, which is derived based on the statistical model. The liquid film stiffness is derived based on a spring model. The stiffness contributions from the asperity contact part and lubricant layer part are separated and analyzed.

Commentary by Dr. Valentin Fuster
2018;():V006T09A005. doi:10.1115/DETC2018-85208.

In this paper, an analytical contact model is proposed to study the contact behavior between two rough surfaces. Elliptical function is employed to describe contact stiffness of a single asperity, and the contact area is characterized by polynomial function in elastoplastic deformation regime. Results show that the proposed model ensures the continuity and smoothness of contact variables across different deformation regimes for a single asperity. The accuracy of the contact model has been demonstrated by the good agreement between the proposed model and the existing statistical model. Influences of material properties on normal contact force and interfacial stiffness have been further studied using the established model.

Commentary by Dr. Valentin Fuster
2018;():V006T09A006. doi:10.1115/DETC2018-85491.

Bifurcations of periodic orbits of a one-dimensional granular array are numerically investigated in this study. A conservative two-bead system is considered without any damping or external forces. By using the Hertzian contact model, and confining the system’s total energy to a certain level, changes in in-phase periodic orbit are studied for various pre-compression levels. At a certain pre-compression level, symmetry breaking and period doubling occur, and an asymmetric period-two orbit emerges from the in-phase periodic orbit. Floquet analysis is conducted to study the stability of the in-phase periodic solution, and to detect the bifurcation location. Although the trajectory of period-two orbit is close to the in-phase orbit at the bifurcation point, the asymmetry of the period-two orbit becomes more pronounced as one moves away from the bifurcation point. This work is meant to serve as an initial step towards understanding how pre-compression may introduce qualitative changes in system dynamics of granular media.

Topics: Bifurcation
Commentary by Dr. Valentin Fuster
2018;():V006T09A007. doi:10.1115/DETC2018-86028.

Sandwich panels consisting of aluminum face-sheets and honeycomb core are widely used in transportation systems. The composite structure has a high stiffness and strength, but it is susceptible to impacts in service. An experimental investigation of surface deformation and core damage in a honeycomb sandwich panel subjected to three different low-velocity impact energies was undertaken. Surface damage evaluation using 3D laser scanning technology was conducted to assess the surface damage and a comparison was made with two typical indentation profiles which were proposed mathematically in the past. The experimental dent profile shows a good agreement with one of the two analytical dent profiles. The impacted sandwich panel was then cut transversely to study the damage inside the honeycomb core. The number of buckled or collapsed folds under the damaged top face-sheet and the depth of the core damage were utilized as two parameters to quantify the damage of the honeycomb core. It is concluded that the core damage depth and the number of folds is independent of impact energy and is constant within each dent.

Commentary by Dr. Valentin Fuster
2018;():V006T09A008. doi:10.1115/DETC2018-86126.

This work presents a new approach for resolving the unique invariant slip direction at Stick-Slip Transition during impact. The solution method presented in this work is applicable to both single-point and multi-point impact problems. The proposed method utilizes rigid body constraints to resolve the impact forces at all collision points in terms of a single independent impact forces parameter. This work also uses an energetic coefficient of restitution to terminate impact events, thereby yielding energetically consistent post-impact behavior.

Topics: Stick-slip
Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Dynamics and Control of Robotic and Mechatronic Systems

2018;():V006T09A009. doi:10.1115/DETC2018-85076.

With the aid of the Liyapunov first approximate stability criterion, the dynamic stability condition for the 3-RPR parallel mechanism to realize a deterministic motion at singular configurations is deduced. Based on this condition, the distributions of the kinematic parameters including input velocities and accelerations of the system corresponding to the stable motion at its singular configuration are investigated then. It is found that for a given singular configuration, increasing input velocities and accelerations, the sub-distributions of eigenvalues with positive real parts have a tendency to shrink and, consequently, the motion stability at the singular configuration can be enhanced; adjusting input velocities and accelerations only can not necessarily get all negative real parts of the eigenvalues sharing a common intersection of the distributing subintervals and, normally, the additional adjustment of initial velocities of the particle system should be added. Besides, while the movable platform goes through the singular configuration, if the control law of the input parameters makes the instantaneous velocity center of the movable platform far away from the singular point, the platform is able to go through the singular configuration with high stability and strong capability to resist external disturbances. This research indicates the effectiveness to improve the motion stability of the dynamics system at singular configurations via adjusting the input kinematic parameters. From this, a singularity-free approach via adjusting the input kinematic parameters can be utilized to exclude singularities of parallel mechanisms dynamically in the joint trajectory planning stage without introducing either redundancy or active mass.

Commentary by Dr. Valentin Fuster
2018;():V006T09A010. doi:10.1115/DETC2018-85217.

This paper focusses on the dynamic modeling of the machine tool including its Computer Numeric Control (CNC), and its interaction with the machining process. To properly simulate modern machine tools in machining condition, which show close interaction between the dynamic behavior of the mechanical structure, drives, and the CNC, we use an integrated methodology that combines control and MBS capabilities in a nonlinear FEA solver called SAMCEF Mecano. To fully capture the dynamic behavior of the machine, force interactions between the cutting tool and the workpiece are also considered. A strong coupling between the mechatronic model of the machine tool and a machining simulation tool is implemented. A specialized cutting force element has been developed. It considers the dynamics of the tool tip combined with the tool workpiece engagement to generate cutting forces. The use of such digital twin model is demonstrated considering some industrial machining operations.

Commentary by Dr. Valentin Fuster
2018;():V006T09A011. doi:10.1115/DETC2018-85263.

This paper is an extension of the authors’ previous paper on the analysis of sliding mode observers using a novel Time-Averaged Lyapunov function [1]. The paper presents the design of a sliding mode observer for a Lipschitz nonlinear system. The paper demonstrates that the external sensor noise (Gaussian) only affects the convergence rate of the observer without having any influence over its stability at steady state. Further, a condition for the existence of the observer is provided in the form of an LMI. The LMI can be solved offline using various commercial LMI solvers. An illustrative example is presented to demonstrate the effectiveness of this approach.

Commentary by Dr. Valentin Fuster
2018;():V006T09A012. doi:10.1115/DETC2018-85357.

The design of an accurate model often appears as the most challenging tasks for control engineers especially focusing to the control of nonlinear systems with unknown parameters or effects to be identified in parallel. For this reason, development of model-free control methods is of increasing importance. The class of model-free control approaches is defined by the non-use of any knowledge about the underlying structure and/or related parameters of the dynamical system. Therefore the major criteria to evaluate model-free control performance are aspects regarding robustness against unknown inputs and disturbances to achieve a suitable tracking performance including ensuring stability. Consequently it is assumed that the system plant model to be controlled is unknown, only the inputs and outputs are used as measurements. In this contribution a modified model-free adaptive approach is given as the extended version of existing model-free adaptive control to improve the performance according to the tracking error at each sample time. Using modified model-free adaptive controller, the control goal can be achieved efficiently without an individual control design process for different kinds unknown nonlinear systems. The main contribution of this paper is to extend the modified model-free adaptive control method to unknown nonlinear multi-input multi-output (MIMO) systems. A numerical example is shown to demonstrate the successful application and performance of this method.

Commentary by Dr. Valentin Fuster
2018;():V006T09A013. doi:10.1115/DETC2018-85435.

This paper presents a novel variable step size Kalman Filter by augmenting the event handling procedure of Ordinary Differential Equation (ODE) solvers with the predictor-corrector scheme of well-known discrete Kalman Filter (KF). The main goal is to increase the estimation performance of Kalman Filter in the case of switching/stiff systems. Unlike fixed step size Kalman Filter the sample time (ST) is adapted in the proposed approach based on current estimation performance (KF innovation) of system states and can change during the estimation procedure. The proposed event handling algorithm consists of two main parts: relaxing ST and restricting ST. Relaxing procedure is used to avoid high computational time when no rapid change exists in system dynamics. Restricting procedure is considered to improve the estimation performance by decreasing the Kalman filter step size in the case of fast dynamical behavior (switching behavior). The accuracy and computational time are controlled by using design parameters. The effectiveness of the proposed approach is verified by simulation results using the bouncing ball example as a switching system.

Commentary by Dr. Valentin Fuster
2018;():V006T09A014. doi:10.1115/DETC2018-86210.

External mechanical loading is a major contributing factor in pressure ulcer formation and is a major health concern for wheelchair users. Seat cushion technologies are employed to reduce the magnitude and duration of this loading using soft seating surfaces and pressure offloading techniques. However, pressure offloading often results in the creation of new high pressure points which can still lead to pressure ulcer formation. In order to mitigate the issue, a novel closed-loop controlled seat cushion system is developed with sensorized air cell arrays which can continuously monitor pressure profile of a seated person and modulate this interface pressure. This paper presents the control implementation of this seat cushion system using a novel scheduling control algorithm based on bang-bang control as well as the corresponding electronics and pneumatic layout. The effectiveness of the system is demonstrated for real-time pressure mapping, offloading, and redistribution of seating interface pressure and its capabilities of instantaneous local pressure measurement as well as automated pressure modulation are verified.

Topics: Pressure
Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Efficient Methods and Real-Time Simulation

2018;():V006T09A015. doi:10.1115/DETC2018-85232.

Modeling multibody systems subject to unilateral contacts and friction efficiently is challenging, and dynamic formulations based on the mixed linear complementarity problem (MLCP) are commonly used for this purpose. The accuracy of the MLCP solution method can be evaluated by determining the error introduced by it. In this paper, we find that commonly used MLCP error measures suffer from unit inconsistency leading to the error lacking any physical meaning. We propose a unit-consistent error measure which computes energy error components for each constraint dependent on the inverse effective mass and compliance. It is shown by means of a simple example that the unit consistency issue does not occur using this proposed error measure. Simulation results confirm that the error decreases with convergence toward the solution. If a pivoting algorithm does not find a solution of the MLCP due to an iteration limit, e.g. in real-time simulations, choosing the result with the least error can reduce the risk of simulation instabilities.

Commentary by Dr. Valentin Fuster
2018;():V006T09A016. doi:10.1115/DETC2018-85289.

In the context of a modern approach to the design of rotocraft, handling qualities should be the result of careful planning, rather than the output of a multitude of other choices, made primarily focusing on more immediate constraints. For a wide range of flight conditions and mission task elements, the test pilot feedback is the essential measure upon which the design choices are made. Thus, it is becoming of fundamental importance to be able to simulate a representative model of the vehicle in a pilot-in-the-loop environment as early as possible in the design stage. This work is intended to document the development process of one such system currently being realized at the facilities belonging to the Aerospace Science and Technology Department of Politecnico di Milano. Particular attention is given to the software architecture, based on the free and open-source multibody solver MBDyn. The development of a module specifically designed to exploit the environment visualization capabilities of FlightGear, also a free and open-source software, is presented.

Commentary by Dr. Valentin Fuster
2018;():V006T09A017. doi:10.1115/DETC2018-85719.

This paper presents a novel method for motion analysis of rigid multibody systems. In general, dynamics of multibody systems is described by differential algebraic equations with Lagrange multipliers. For efficient and accurate analysis, it is desirable to eliminate the Lagrange multipliers and dependent variables. Methods called nullspace method and Maggi’s method eliminate the Lagrange multipliers by using the nullspace matrix for the constraint Jacobian. In a previous report, the author presented a method in which the nullspace matrix is obtained by solving a differential equation together with the equation of motion of the system. In that method QR decomposition is used. In this report, reduction in computational time with the LU decomposition is attempted. In addition, treatment of singular configurations for accurate analysis is presented. Validity of the presented method is confirmed via numerical examples.

Commentary by Dr. Valentin Fuster
2018;():V006T09A018. doi:10.1115/DETC2018-86422.

In this paper, co-simulation procedure for a multibody system that includes reeving mechanism will be introduced. The multibody system under investigation is assumed to have a set of rigid bodies connected by flexible wire ropes using a set of sheaves and reels. In the co-simulation procedure, a wire rope is described using a combination of absolute position coordinates, relative transverse deformation coordinates and longitudinal material coordinates. Accordingly, each wire rope span is modeled using a single two-noded element by employing an Arbitrary Lagrangian-Eulerian approach.

Topics: Simulation
Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Flexible Multibody Dynamics

2018;():V006T09A019. doi:10.1115/DETC2018-85721.

A yarn has a flexible structure whose axial length is very long compared its diameter. When loose yarn twists at its end, the yarn intertwines with itself as shown in Fig. 1 to produce a shape called a snarl shape with motion referred to as snarl motion. The snarl shape sometimes cuts the yarn or reduces the yarn quality, and may reduce the productivity of textile machinery. As a preliminary step of handling snarl motion in the processes of textile machinery, this paper extends functions of a yarn model proposed in our previous study by appending a contact force and implementing a multithread computing method for fast simulation. The paper validates the yarn model by comparing the results of numerical simulation and experiment. Six-threads computing can make calculation at 5 times the rate possible with single-thread computing.

Commentary by Dr. Valentin Fuster
2018;():V006T09A020. doi:10.1115/DETC2018-85894.

We study the dynamic behavior of a belt-drive system to explore the effect of operating conditions and system moment of inertia on the generation of waves of detachment (i.e., Schallamach waves) at the belt-pulley interface. A self-excitation phenomenon is reported in which frictional fluctuations serve as harmonic forcing of the pulley, leading to angular velocity oscillations which grow in time. This behavior depends strongly on operating conditions (torque transmitted and pulley speed) and system inertia, and differs between the driver and driven pulleys. A larger net torque applied to the pulley generally yields more remarkable stick-slip oscillations with higher amplitude and lower frequency. Higher driving speeds accelerate the occurrence of stick-slip motion, but have little influence on the oscillation amplitude. Contrary to our expectations, the introduction of flywheels to increase system inertia amplified the frictional disturbances, and hence the pulley oscillations. This does, however, suggest a way of facilitating their study, which may be useful in follow-on research.

Topics: Waves , Belts , Excitation
Commentary by Dr. Valentin Fuster
2018;():V006T09A021. doi:10.1115/DETC2018-86073.

In this study, a higher-order finite element based on the absolute nodal coordinate formulation (ANCF) is applied in the dynamic analysis of high-speed rotating shafts. Static and modal tests are carried out to analyze the performance and accuracy of the introduced ANCF element. Also, via a transient dynamic benchmark test involving a rotating flexible shaft, the accuracy of the examined beam element in high-speed applications is analyzed. According to the results, the introduced beam element can adequately capture cross-section deformationin high-speed rotating shaft analysis.

Commentary by Dr. Valentin Fuster
2018;():V006T09A022. doi:10.1115/DETC2018-86142.

Various modal analysis methods are available for single-rotor wind turbines, but there is no report and guidance on the modal property analysis of multi-rotor wind turbines. This paper presents a dynamic modeling method for the modal response analysis of a wind turbine with two three-bladed isotropic rotors. The equations of motion are derived using Lagrange’s equations and are further linearized at a steady-state equilibrium. To avoid using Floquet Theory to remove the periodic coefficients, multi-blade coordinates are utilized. Comparison between the numerical simulations and a high-fidelity model in HAWC2 shows agreements in terms of modal frequencies. The results shows that the whirling modes splits into symmetric and asymmetric rotor modes.

Commentary by Dr. Valentin Fuster
2018;():V006T09A023. doi:10.1115/DETC2018-86143.

Multibody systems are often modeled as interconnected multibody and modal components: multibody components, such as rigid bodies, beams, plates, and kinematic joints, are treated via multibody techniques whereas the modal components are handled via a modal reduction approach based on the small strain assumption. In this work, the problem is formulated within the framework of the motion formalism. The kinematic description involves simple, straightforward frame transformations and leads naturally to consistent deformation measures. Derivatives are expressed in local frames, which results in the remarkable property that the tangent matrices are independent of the position and orientation of the modal component with respect to an inertia frame. This implies a reduced level of geometric non-linearity as compared to standard description. In particular, geometrically non-linear problems can be solved with the tangent matrices of the reference configuration, without re-evaluation and re-factorization.

Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Fluid-Structure Interaction and Multi-Physics

2018;():V006T09A024. doi:10.1115/DETC2018-85152.

Multibody dynamics models of a helicopter and two cycloidal rotor aircraft concepts capable of vertical take-off and landing (VTOL) are constructed. The first concept aircraft is a helicopter equipped with two lateral cycloidal rotors acting as a replacement for its tail rotor and is named the Heligyro. The other concept is named the Quadricyclogyro and is propelled exclusively by four cycloidal rotors whose axes are aligned. The autopilot algorithm is implemented as a proportional, integral, and derivative (PID) controller and is tuned using a genetic optimization algorithm directly on the multibody models. Aircraft vibration and energy requirements are monitored and fed as penalty functions to the genetic algorithm. The time-domain responses of the aircraft attempting to follow mission paths of variable complexity obtained from the literature are studied. Overall, the tuned VTOL aircraft are able to reproduce the requested routes with good accuracy if a certain speed threshold is respected.

Commentary by Dr. Valentin Fuster
2018;():V006T09A025. doi:10.1115/DETC2018-86176.

In this paper the dynamics of a tubular cantilever, simultaneously subjected to internal and external axial flows, is examined theoretically. The tube is discharging fluid downwards which then flows upwards through an annular region surrounding the tube. Thus, the internal and external flows are interdependent and in opposite directions. Also, the external flow is confined over a certain range of the cantilever length and unconfined over the rest. The Heaviside step function has been used in the literature, for such a system, to model the discontinuity in the external flow velocity occurring when the flow enters the annular region. A more accurate way to model this discontinuity is introduced in this study, in which the logistic function is used instead of the Heaviside step function. The stability of the system is investigated by analysis of the system eigenfrequencies, and the effects of varying the length of the confined region are theoretically studied. The obtained results are compared to theoretical predictions and experimental data from the literature having the same system parameters. The proposed theory captures the same dynamical behaviour as observed experimentally, and has a better estimation for the onset of instability and the frequency of oscillations compared to the theory in the literature.

Commentary by Dr. Valentin Fuster
2018;():V006T09A026. doi:10.1115/DETC2018-86179.

Pipes aspirating fluid have applications in the filling and recovery processes for underground caverns — large subterranean cavities used to store hydrocarbons, such as natural gas and oil. This paper deals with the dynamics of a vertical cantilevered flexible pipe, immersed in fluid. Fluid is aspirated from its bottom free end up to the fixed upper end. In this study, the working fluid is assumed to be water.

An existing analytical model is used to predict the dynamical behaviour of the aspirating pipe. This model is then discretized with Galerkin’s method, using Euler-Bernoulli eigen-functions for cantilevered beam as comparison functions. Once solved, the model results show a unique kind of flutter comprising three regions, denoted regions 01–03. These regions are delineated by two critical flow velocities, Ucf1 and Ucf2. In addition, two frequencies of oscillation, f1 and f2, are found to characterize the aforementioned flutter. The dominant frequency of oscillation changes from f1 to f2 as the flow velocity is increased from approximately 3 to 6 m/s — a frequency exchange phenomenon observed and reported here for the first time for this system. The analytical/numerical study was followed by a corresponding experimental study. Experiments were performed on a flexible (Silastic) pipe that was completely submerged in water. The behaviour observed experimentally was similar to the numerical study, as the aspirating fluid velocity was increased from zero to 7 m/s.

Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Modeling, Simulation, and Validation of Vehicle Dynamics

2018;():V006T09A027. doi:10.1115/DETC2018-85559.

Shimmy is a common instability of landing gear systems which has been known for a long time. Yet, it is often studied using simplified dynamic models in which the chief system nonlinearities are neglected. Particularly, the influence of worn components and loose joints manifesting itself as a freeplay nonlinearity has been only touched upon in few works. The present paper utilizes a fully nonlinear landing gear dynamic model to obtain nonlinear stability boundaries and to study the onset, severity, frequency jumps, and mode shifts of the system as a result of the torque link freeplay. Using stability maps in the parameter space and time histories of the oscillations the degrading effect of excessive clearance and wear in the torque links is demonstrated, which in turn offers insights for designing shimmy-free landing gears.

Topics: Gears
Commentary by Dr. Valentin Fuster
2018;():V006T09A028. doi:10.1115/DETC2018-86110.

In this paper, a hierarchical FE-DE multiscale soil model is implemented and validated for use in multibody dynamics simulation. In order to describe complex soil failure phenomena including strain localization, the finite-element (FE) model is utilized to predict macroscale soil deformation, while the microscale constitutive behavior is modeled by representative volume elements (RVEs) using the discrete-element (DE) method. Brick elements integrated in the general multibody dynamics algorithm are used for developing the macroscale model. An open-source DE code LIGGGHTS is integrated in this simulation framework to add multiscale simulation capabilities for modeling complex soil behavior. Several numerical examples are presented to demonstrate the use of multiscale simulation capabilities for high-fidelity multibody off-road mobility simulations.

Commentary by Dr. Valentin Fuster
2018;():V006T09A029. doi:10.1115/DETC2018-86171.

This paper presents two different ways of modeling a road vehicle for general vehicle dynamics investigation and especially to optimize the suspension geometry. Therefore a numerically highly efficient model is sought such that it can be used later in gradient-based optimization of the suspension geometry. Based on a formula style vehicle with double wishbone suspension setup, a vehicle model based on ODE-formulation using a set of minimal coordinates is built up. The kinematic loops occurring in the double wishbone suspension setup are resolved analytically to a set of independent coordinates. A second vehicle model based on a redundant coordinate formulation is used to compare the efficiency and accuracy. The performance is evaluated and the accuracy is validated with measurement data from a real formula car.

Commentary by Dr. Valentin Fuster
2018;():V006T09A030. doi:10.1115/DETC2018-86396.

A passive vibration control strategy to mitigate the accelerations of roller batteries in cableways caused by the vehicle transit is investigated. The vibration control strategy makes use of a group of Tuned Mass Dampers (TMDs) placed in different positions along the roller battery. When the frequencies of the TMDs are properly tuned to the modes to control, the energy provided by the dynamic forcing to the roller battery is transferred as kinetic energy to the TMDs. This work investigates the effectiveness of an array of linear TMDs in comparison with the performance of hysteretic TMDs that exploit the restoring forces provided by an assembly of wire ropes. First a dynamical characterization of the roller battery (modal analysis) is carried out. Then an optimization of the assembly of linear TMDs against skew-symmetric harmonic excitations is achieved by means of the Differential Evolution algorithm (DE). Subsequently, the performance of the linear TMDs assembly against the vehicle transit across the tower is assessed. Finally the performance of a network of hysteretic TMDs is studied together with practical feasibility considerations.

Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Nonlinear Dynamics of Structures

2018;():V006T09A031. doi:10.1115/DETC2018-85058.

This paper is focused on the chaotic dynamics of a composite laminated circular cylindrical shell with radially pre-stretched membranes at both ends and clamped along a generatrix. Based on the two-degree-of-freedom non-autonomous nonlinear equations of this system, the method of multiple scales is employed to obtain the four-dimensional nonlinear averaged equation. The resonant case considered here is the primary parametric resonance-1/2 subharmonic resonance and 1:1 internal resonance. Corresponding to several selected parameters, the periodic and chaotic motions of the composite laminated circular cylindrical shell clamped along a generatrix are demonstrated by the bifurcation diagrams, the maximum Lyapunov exponents, the phase portraits, the waveforms, the power spectrums and the Poincaré map. The temperature parameter excitation shows that the Pomeau-Manneville type intermittent chaos occur under the certain initial conditions. It is also found that there exist the twin phenomena between the Pomeau-Manneville type intermittent chaos and the period-doubling bifurcation.

Commentary by Dr. Valentin Fuster
2018;():V006T09A032. doi:10.1115/DETC2018-85447.

The dynamic stability of a cantilevered beam actuated by a nonconservative follower force has previously been studied for its interesting dynamical properties and its applications to engineering designs such as thrusters. However, most of the literature considers a linear model. A modest number of papers considers a nonlinear model. Here, a system of nonlinear equations is derived from a new energy approach for an inextensible cantilevered beam with a follower force acting upon it. The equations are solved in time, and agreement is shown with published results for the critical force including the effects of damping (as determined by a linear model). This model readily allows the determination of both in-plane and out-of-plane deflections as well as the constraint force. With this novel transparency into the system dynamics, the nonlinear post-critical limit cycle oscillations are studied including a concentration on the force which enforces the inextensibility constraint.

Commentary by Dr. Valentin Fuster
2018;():V006T09A033. doi:10.1115/DETC2018-85449.

Flagella and cilia are examples of actively oscillating, whiplike biological filaments that are crucial to processes as diverse as locomotion, mucus clearance, embryogenesis and cell motility. Elastic driven rod-like filaments subjected to compressive follower forces provide a way to mimic oscillatory beating in synthetic settings. In the continuum limit, this spatiotemporal response is an emergent phenomenon resulting from the interplay between the structural elastic instability of the slender rods subjected to the non-conservative follower forces, geometric constraints that control the onset of this instability, and viscous dissipation due to fluid drag by ambient media. In this paper, we use an elastic rod model to characterize beating frequencies, the critical follower forces and the non-linear rod shapes, for pre-stressed, clamped rods subject to two types of fluid drag forces, namely, linear Stokes drag and non-linear Morrison drag. We find that the critical follower force depends strongly on the initial slack and weakly on the nature of the drag force. The emergent frequencies however, depend strongly on both the extent of pre-stress as well as the nature of the fluid drag.

Topics: Rods
Commentary by Dr. Valentin Fuster
2018;():V006T09A034. doi:10.1115/DETC2018-85478.

In this paper, the homotopy analysis method (HAM) is proposed to study the nonlinear oscillators of planetary gear trains, in which the periodically time-varying mesh stiffness and gear backlash are included through a nonlinear displacement function. In contrast to the traditional perturbation methods, the HAM does not require a small parameter in the equation under study, and then can be applied to both of the weakly and strongly nonlinear problems. In this article, firstly the closed-form approximations for the dynamic response of planetary gear trains are obtained by HAM. The analytical solutions give insight into the nonlinear dynamics and the impact of system parameters on dynamic response. The accuracy of HAM solutions is evaluated by numerical integration simulations. Results indicate that with large tooth separation times, the amplitude-frequency curves obtained by HAM agree better with the results obtained by NI than those obtained by the MMS.

Commentary by Dr. Valentin Fuster
2018;():V006T09A035. doi:10.1115/DETC2018-85539.

In this paper, we investigate experimentally and theoretically the two-to-one (2:1) internal resonance between the first two symmetric vibrational modes of microelectromechanical (MEMS) arch resonator electrothermally tuned and electrostatically driven. Applying electrothermal voltage across the beam anchors controls its stiffness and then its resonance frequencies. Hence the ratio between the two frequencies can be tuned to a ratio of two. Then, we study the dynamic response of the arch beam during internal resonance. In the studied case, the presence of high AC bias excitation leads to the direct simultaneous excitation of the 1st and 3rd frequencies in addition to the activation of the internal resonance. A reduced order model and perturbation techniques are presented to analyze the nonlinear response of the structure. In the perturbation technique, the direct excitation of the 3rd resonance frequency is taken into consideration. Results show the presence of Hopf bifurcations, which can lead to chaotic motion at higher excitation. A good agreement among the theoretical and experimental results is shown.

Commentary by Dr. Valentin Fuster
2018;():V006T09A036. doi:10.1115/DETC2018-85622.

The present contribution reports some preliminary results obtained applying a simple finite element formulation, developed for discretizing the partial differential equations of motion of a novel beam model. The theoretical model we are dealing with is geometrically exact, with some peculiarities in comparison with other existing models. In order to study its behavior, some numerical investigations have already been performed through finite difference schemes and other methods and are reported in previous contributions. Those computations have enlightened that the model under analysis turns out to be quite hard to handle numerically, especially in dynamics. Hence, we developed ad hoc the total-lagrangian finite-element formulation we report here. The main differences between the theoretical model and its numerical formulation rely on the fact that in the latter the absolute value of the shear angle is assumed to remain much smaller than unity, and strains are piecewise constant along the beam. The first assumption, which actually simplifies equations, has been taken on the basis of results from previous integrations, mainly through finite difference schemes, which clearly showed that, while other strains can achieve large values in their range of admissibility, shear angle actually remains small. The second assumption led us to define a two-nodes constant-strain finite element, with a fast convergence, in terms of number of elements versus solution accuracy. Although, at the present stage of this ongoing research, we have only early results from finite elements, they appear encouraging and start to shed new light on the behavior of the beam model under analysis.

Commentary by Dr. Valentin Fuster
2018;():V006T09A037. doi:10.1115/DETC2018-85661.

The rotating blade is simplified as a rotating cylindrical panel with a presetting angle and a pretwist angle. Nonlinear dynamic behaviors of the rotating cylindrical panel under higher-frequency primary resonance and lower-frequency primary resonance in the presence of 1:2 internal resonance are discussed. We use the Green strain tensor to derive an strain-displacement relationship. Based on the first-order shear deformation theory, Hamilton principle and Galerkin method is utilized to acquire nonlinear ordinary differential equations of the system, which contains coupling between linear stiffness terms of the two transverse modes. The modulation equations are obtained by using the method of multiple scales. Matcont package is used to portray frequency-amplitude response curves and force-amplitude response curves of the system under higher-frequency primary resonance and lower-frequency primary resonance.

Topics: Resonance
Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Nonlinear Energy Transfers and Harvesting (MSNDC/VIB-3)

2018;():V006T09A038. doi:10.1115/DETC2018-85811.

Energy transfer is present in many natural and engineering systems which include different scales. It is important to study the energy cascade (which refers to the energy transfer among the different scales) of such systems. A well-known example is turbulent flow in which the kinetic energy of large vortices is transferred to smaller ones. Below a threshold vortex scale the energy is dissipated due to viscous friction. We introduce a mechanistic model of turbulence which consists of masses connected by springs arranged in a binary tree structure. To represent the various scales, the masses are gradually decreased in lower levels. The bottom level of the model contains dampers to provide dissipation. We define the energy spectrum of the model as the fraction of the total energy stored in each level. A simple method is provided to calculate this spectrum in the asymptotic limit, and the spectra of systems having different stiffness distributions are calculated. We find the stiffness distribution for which the energy spectrum has the same scaling exponent (−5/3) as the Kolmogorov spectrum of 3D homogeneous, isotropic turbulence.

Commentary by Dr. Valentin Fuster
2018;():V006T09A039. doi:10.1115/DETC2018-85820.

In this paper a variant nonlinear energy sink (NES) is developed for the purpose of simultaneous vibration suppression and energy harvesting in a broad frequency band. The NES consists of a cantilever beam attached by a mass at its free end and a pair of so-called double-stop blocks. The beam is formed by a piezoelectric energy harvester and a thin steel plate. It is placed between the double-stop blocks. The constraint of the double-stop blocks forces the beam to deflect nonlinearly. First, the developed apparatus is described. Subsequently, system modeling and parameter identification are addressed. The performance of the apparatus under transient responses is examined through both numerical simulation and experimental study. The results show that the proposed apparatus behaves similarly as the NES with the following features: 1:1 resonance, targeted energy transfer, initial energy dependence, etc.

Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Nonlinear Rotordynamics and Rotating Systems (MSNDC/VIB-8)

2018;():V006T09A040. doi:10.1115/DETC2018-85066.

Rotating beams are quite common in rotating machinery e.g. fans of compressors in an airplane. This paper presents the experimental, hybrid, structural vibration control of flexible structures to enhance the vibration behavior of rotating beams. Smart materials have been used as sensors as well as actuators. Passive constrained layer damping (PCLD) treatment is combined with stressed layer damping technique to enhance the damping characteristics of the flexible beam. To further enhance the damping parameters, a closed form robust feedback controller is applied to reduce the broadband structural vibrations of the rotating beam. The feed forward controller is designed by combing with the feedback controller using a pattern search based optimization technique. The hybrid controller enhances the performance of the closed loop system. Experiments have been conducted to validate the effectiveness of the presented technique.

Commentary by Dr. Valentin Fuster
2018;():V006T09A041. doi:10.1115/DETC2018-85716.

The effect of 2 lobes journal bearing parameters such as L/D ratio and pad preload on the bifurcation of the rigid rotor is investigated in comparison with the circular bearing. Nonlinear bearing force in the equation of motion is obtained by solving Reynolds equation using the finite difference method. Shooting method and Floquet multiplier analysis are employed to obtain limit cycles and their stability. The results show that, for some bearing parameters, multiple limit cycles coexist at a specific shaft rotational speed range. Comparing with the circular bearing of same L/D ratio, the 2 lobes bearing without pad preload decreases the onset speed of instability and also decreases speed range from the onset speed of instability (Hopf) point to the limit point of the bifurcation (saddle-node) in the subcritical bifurcation case. Increasing the pad preload only increases the onset speed of instability significantly in the small L/D ratio case. For both circular and 2 lobes bearing, increasing the L/D ratio decreases the onset speed of instability and tends to change the type of the bifurcation from supercritical to subcritical.

Commentary by Dr. Valentin Fuster
2018;():V006T09A042. doi:10.1115/DETC2018-85883.

In turbomachinery, seals are used to prevent fluid leakage. At seal part, rotordynamic fluid force (RD fluid force), which causes whirling motion of rotor, is generated. Under certain conditions, the RD fluid force may contribute to instability of the machine. There are several cases that the whirling is accompanied by eccentricity due to the influence of gravity, or the whirling orbit becomes elliptical due to the influence of the bearing support anisotropy. In these cases, mathematical modeling of the RD fluid forces becomes increasingly complex. As a result, the RD fluid force measurement is more preferable. To improve the measurement and evaluation technology of the RD fluid force, a method to arbitrarily control whirling of the orbit is required.

In this paper, RD fluid force measurement by controlling the shape of the orbit using an active magnetic bearing (AMB) is proposed. A contact type mechanical seal is used as a test specimen. When the rotating shaft is whirling, the RD fluid force due to hydrodynamics lubrication and the frictional force due to contact occur on the sliding surface. The resultant force of these forces is taken as the reaction force of mechanical seal and the measurement is performed. The measured reaction force of the mechanical seal is compared with simulation results and the validity of the proposed measurement method is confirmed.

Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Optimization, Sensitivity Analysis, and Uncertainty Quantification in Dynamic Systems

2018;():V006T09A043. doi:10.1115/DETC2018-85912.

Compared with regular mechanical operating mechanisms, the hydraulic operating mechanism has widespread industrial applications in large hydraulic systems such as ultra-high voltage circuit breakers due to its requirements of fast response, high flow rate and instantaneous super power. This paper intends to analyze the characteristics of hydraulic operating mechanism for ultra-high voltage circuit breakers from a systemic perspective. A comprehensive mathematical model of hydraulic operating mechanism system including pipelines and all valves has been developed. Meanwhile, experiments focusing on the dynamic and pressure characteristics of hydraulic operating mechanism are conducted to validate simulation models. The proposed research methods can provide significant theoretical guidance and practical value for further study of hydraulic operating mechanism of high standard hydraulic system like ultra-high voltage circuit breakers.

Commentary by Dr. Valentin Fuster
2018;():V006T09A044. doi:10.1115/DETC2018-86211.

The combination of analysis and optimization methods in mechanical engineering, also known as design optimization, has great potential in product development. Robust sensitivity analyses that provide reliable and efficient objective function gradients play a key role in design optimization. This paper presents a discrete adjoint method for the sensitivity analysis of flexible mechanical systems. The ultimate goal is to be able to relate the physical properties of beam cross-sections to the dynamic behavior of the system, which is key to design realistic flexible elements. The underlying flexible multibody formulation is one that supports large-amplitude motion, beams with sophisticated composite cross-sections, and kinematic joints. A summary of the kinematic and dynamic foundations of the forward equations is presented first. Then, a discrete adjoint method, along with meaningful examples and validation, is presented. The method has proven to provide extremely accurate and reliable sensitivities.

Commentary by Dr. Valentin Fuster
2018;():V006T09A045. doi:10.1115/DETC2018-86427.

Vibrational behavior of epicyclic gearing a critical aspect as this can lead to detrimental structural-mechanical effects including fatigue, comfort and acoustics. In order to better understand this behavior, lumped-parameter models are used in early development phases. Here the eigenfrequencies as well as frequency responses are ascertained with and without consideration of uncertainty. Uncertainty is critical in the early design phases and beyond. In such systems, there is variation in parameter values from a variety of sources. Here the uncertain stiffness will be considered.

It is also the goal of this work to dimension the epicyclic gear train to optimize performance. The early design phase is plagued by uncertainty and if this is neglected in the design optimization, this can lead to drastically suboptimal designs. In this work, a methodology is introduced to optimally design and dimension epicyclic gear trains under uncertainty. Though specifically aimed at epicyclic gearing, the methods developed here are general enough for further application fields.

Mass and inertia terms are chosen as design variables, though others are possible in this framework. The constraints are so formulated so that the eigenfrequencies avoid the harmonics of the mesh frequencies and its side bands. The uncertain parameters are treated as bounded and therefore intervals are used instead of statistical distributions. Statistical information needed for probabilistic methods of the uncertain parameters are assumed here to be unavailable in early development phases.

Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Time-Varying and Time-Delay Systems

2018;():V006T09A046. doi:10.1115/DETC2018-85146.

In this article we consider the Lyapunov stability of mechanical systems containing fractional springpot elements. We obtain the potential energy of a springpot by an infinite dimensional mechanical analogue model. Furthermore, we consider a simple dynamical system containing a springpot as a functional differential equation and use the potential energy of the springpot in a Lyapunov functional to prove uniform stability and discuss asymptotic stability of the equilibrium with the help of an invariance theorem.

Commentary by Dr. Valentin Fuster
2018;():V006T09A047. doi:10.1115/DETC2018-85524.

In the present contribution, alternating energy transfers across modes of vibration, induced by impulsive stiffness excitation applied at equidistant instants of time are investigated. Therefore, effective damping measures are used, and it is shown that they clearly indicate modal energy transfers and their effect on the decay rate of transient vibrations. It is demonstrated that outstanding values of the time span between adjacent impulses exist, where a strong energy transfer to higher modes, which possess enhanced damping properties, occurs. Hence, the modal redistribution of vibration energy allows the intrinsic structural damping to be more efficient, resulting in a much faster decrease of vibrations compared to the system without impulsive excitation. It is demonstrated that the effective damping measures provide a proper method to investigate mechanical systems with impulsive stiffness excitation.

Commentary by Dr. Valentin Fuster
2018;():V006T09A048. doi:10.1115/DETC2018-86140.

Floquet theory is combined with harmonic balance to study parametrically excited systems with two harmonics of excitation, where the second harmonic has twice the frequency of the first one. An approximated solution composed of an exponential part with unknown exponents and a periodic term consisting of a truncated Fourier series is considered. When applied to a two-harmonic Mathieu equation the analysis shows that the second harmonic alters stability characteristics, particularly in the primary and superharmonic instabilities. We also look at the initial conditions response and its frequency content. The second excitation harmonic in the system with parametric damping is seen to disrupt the coexistence phenomenon which is observed in the single-harmonic case.

Topics: Excitation
Commentary by Dr. Valentin Fuster
2018;():V006T09A049. doi:10.1115/DETC2018-86145.

A machining tool can be subject to different kinds of excitations. The forcing may have external sources (such as rotating imbalance or misalignment of the workpiece) or it can arise from the cutting process itself (e.g. chip formation). We investigate the classical tool vibration model which is a delay-differential equation with a quadratic and cubic nonlinearity and periodic forcing. The method of multiple scales was used to derive the slow-flow equations. The resonance curves of the system are similar to those for the Duffing-equation, having a hardening characteristic. Stability analysis for the fixed points of the slow-flow equations was performed. Local and global bifurcations were studied and illustrated with phase portraits and direct numerical integration of the original equation. Subcritical Hopf, saddle-node and heteroclinic bifurcations were found.

Commentary by Dr. Valentin Fuster

14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control: Transfer Matrix Method for Multibody Systems and its Applications

2018;():V006T09A050. doi:10.1115/DETC2018-85120.

In many cases, vibration is a serious problem, undesirable, wasting energy and creating unwanted sound. Transfer Matrix Method for Multibody Systems (MSTMM) is one of the sophisticated methods that can be used efficiently to (1) Model large systems with a large number of subsystems and rigid-flexible structures, and (2) Calculate the vibration characteristics and dynamic responses of the multibody systems. The size of matrices in MSTMM remains small regardless of the number of elements in the model. Having smaller matrix sizes helps to have less computational expense leading to a faster answer. Based on the MSTMM advantages, vibration characteristic of a rotating cantilever beam with an attached tip mass is modeled and simulated in the present paper while the beam undergoes flapwise vibration. This system can be thought of as an extremely simplified model of a helicopter rotor blade or a blade of an auto-cooling fan. The overall transfer equation in the MSTMM context only involves boundary state vectors, whereas the state vectors at all other connection points do not appear. The state vectors at the boundary include the displacements, rotation angles, bending moments and shear forces. These are partly known and partly unknown. The eigenvalue problem is solved by using Frobenius method of solution in power series. Recursive eigenvalue search algorithm is used to determine the system frequencies. Numerical examples are performed to validate with those published in the literature and produced by Workbench ANSYS.

Commentary by Dr. Valentin Fuster
2018;():V006T09A051. doi:10.1115/DETC2018-85179.

Natural vibration characteristics and dynamics response of multiple launch rocket system (MLRS) are of fundamental importance from the viewpoint of vibration levels, firing dispersion, and stability. In this study, a new launch vehicle-supports-rockets coupling dynamic model for a practical MLRS is established. Rui method, namely the transfer matrix method for multibody systems (MSTMM) is a new and efficient method for multibody system dynamics (MSD) and is used to obtain the vibration characteristics and dynamics response. The dynamics model, the topology figure of dynamics model, the transfer equations of elements, the overall transfer equation, the eigenfrequency equation, the body dynamics equations, the generalized coordinate equations, and the dynamics simulation system for the MLRS are established. Based on the advantages of MSTMM in studying MSD, the vibration characteristics and dynamics response of complex MLRS are computed rapidly. Finally, the new model is validated in three ways: (1) modal experiment of MLRS, (2) launch dynamics experiment of non-full loading rockets, and (3) launch dynamics experiment of full loading rockets. The results show that the proposed model can not only simulate the natural vibration characteristics of the MLRS but also effectively perform dynamic simulations of the MLRS during launching process.

Commentary by Dr. Valentin Fuster
2018;():V006T09A052. doi:10.1115/DETC2018-85354.

Transfer matrix method is a practical technology for vibration analysis of engineering mechanics. In this paper, Differential Quadrature Discrete Time–Transfer Matrix Method (DQ-DT-TMM) is presented for solving vibration mechanics. Firstly ordinary differential equations of the sub-structure or the element of the mechanical system are determined by classical mechanics rule and transformed as a set of algebraic equations at some discrete time points by the application of differential quadrature method. Then by extending the state vector of transfer matrix method, new transfer equations and transfer matrices of the sub-structures of the mechanical system are developed. The Riccati transform can be used to improve the computational convergence of the method. Several numerical examples show the proposed method can be regarded as an efficient tool for transient response analysis of vibration system.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2018;():V006T09A053. doi:10.1115/DETC2018-85533.

The obtaining of the overall transfer equation of a linear controlled multibody system is one of the key problems when the transfer matrix method for multibody systems (MSTMM) is applied to study controlled multibody dynamics. This paper applies the theory of matrix signal flow graphs (MSFG) to MSTMM. The transfer matrix signal flow graphs (TMSFG) of a mechanical element and a control subsystem can be drawn according to their transfer equations. By merging the nodes corresponding to the same state vector, the TMSFG of the entire system can be obtained. Eventually, the overall transfer equation of the linear controlled system can be systematically obtained according to the reduction rules of MSFG. An example is taken to sketch the idea and the simulation results are compared with other ordinary dynamics methods to validate the proposed method. This paper lays a foundation for automatic deduction of overall transfer equations of linear controlled multibody systems.

Commentary by Dr. Valentin Fuster
2018;():V006T09A054. doi:10.1115/DETC2018-85545.

Natural vibration characteristics play a very important role in the evaluation of the dynamics characteristics and the machined surface of a single-point diamond fly cutting machine tool (SDFCMT). In this paper, the natural vibration characteristics are studied from aspects of theory, computation, and experiment. By adopting the transfer matrix method for multibody systems (MSTMM), the dynamics model and its topology figure are established, and its natural vibration characteristics are computed. The computation results are verified by a modal test.

Commentary by Dr. Valentin Fuster
2018;():V006T09A055. doi:10.1115/DETC2018-85557.

An important way to improve the dynamical test accuracy of an inertial measurement unit (IMU) is to suppress its vibration. In this paper, the dynamics model of a laser gyro strapdown IMU is developed based on the new version of the transfer matrix method for multibody systems (MSTMM). According to the dynamics model, acceleration responses of the IMU system with and without control are numerically computed under random excitation. The results show that the work situation of the IMU can be significantly improved by adopting magnetorheological elastomer (MRE) isolators, which provides a new technical means of upgrading the output precision of IMU.

Commentary by Dr. Valentin Fuster
2018;():V006T09A056. doi:10.1115/DETC2018-85675.

Rui method, namely the transfer matrix method for multibody systems (MSTMM) is a new and efficient method for multibody system dynamics (MSD) for its features as follows: without global dynamics equations of the system, high programming, low order of system matrix and high computational speed. Riccati transfer matrix method for multibody systems was developed by introducing Riccati transformation in MSTMM, for improving numerical stability of MSTMM. In this paper, based on Riccati MSTMM, applying the thought of direct differentiation method, by differentiation of Riccati transfer equations of rigid bodies and joints, generalized acceleration and its differentiation can be obtained. Combined with Backward Euler algorithm, implicit algorithm for Riccati MSTMM is proposed in this paper. The formulation and computing procedure of the method are presented. The numerical examples show that results obtained by first order accurate implicit algorithm proposed in the paper and the fourth order accurate Runge-Kutta method have good agreement, which indicates that this implicit method is more numerical stability than explicit algorithm with the same order accurate. The implicit algorithm for Riccati MSTMM can be used for improving the computational accuracy of multibody system dynamics.

Commentary by Dr. Valentin Fuster
2018;():V006T09A057. doi:10.1115/DETC2018-85684.

Transfer Matrix Method for Multibody Systems (MSTMM) has the advantages of no need to establish the global system dynamics equations, low order of the system matrix, high programming, and fast calculation speed compared to the ordinary dynamics methods. In this paper, the topological graph of the dynamics model, transfer equations, transfer matrix of overall system and the simulation program of dynamics of the self-propelled artillery system are established by using the new version of the transfer matrix method for multibody systems and the automatic deduction theorem of overall transfer equation of systems. Realize the rapid calculation of the deviation of the pitch angle and the revolution angles of the turret versus time in the self-propelled artillery. It provides a theoretical basis and simulation means for the dynamics analysis of the self-propelled artillery.

Commentary by Dr. Valentin Fuster
2018;():V006T09A058. doi:10.1115/DETC2018-85700.

Natural vibration characteristics are important factors affecting the processing quality for an ultra-precision machine tool. The rapid and accurate calculation method for solving natural vibration characteristics has a significance in machine tool dynamics design. By applying the transfer matrix method for multibody systems (MSTMM), the dynamics model of a single-point diamond fly cutting machine tool is established and the rapid computation of natural vibration characteristics at different rotational speed is completed. The results calculated by MSTMM is compared with those by finite element software ABAQUS, the error between the first ten frequencies calculated by MSTMM and ABAQUS is less than 5.68%. However, as the rotational speed increases, the first eight frequencies and mode shapes have no obvious change, while the 9th and 10th modal change significantly. The mode shapes of 9th and 10th orders are vacillation of the spindle. The results show that the rotation of aerostatic spindle has significant effect on the spindle system and little effect on the other parts.

Commentary by Dr. Valentin Fuster
2018;():V006T09A059. doi:10.1115/DETC2018-85733.

Aiming at the problems of complex modeling and low calculation efficiency during dynamical optimization of tracked vehicles, a method for the closed-loop system called Riccati transfer matrix method for multibody system is proposed. In order to reduce the vibration acceleration of track shoes in the driving process, this paper uses the PSO algorithm and utilizes a strategy of decreasing the inertia weight to optimize the structural parameters of tracked vehicles. The research shows that the root mean square of vibration acceleration of track shoes above the support rollers is obviously reduced. This method provides a theoretical reference for the design of tracked vehicles and is beneficial to the dynamic design of complex systems.

Commentary by Dr. Valentin Fuster
2018;():V006T09A060. doi:10.1115/DETC2018-85763.

Vortex-induced vibration (VIV) is one of the main reasons for failure of risers. Therefore, it is very important to predict the VIV behavior of risers by establishing an efficient model suitable for the field of ocean engineering. Based on the transfer matrix method for multibody systems (MSTMM), the main idea about simulating the vibration characteristics and fluid-structure interaction of a marine riser system is presented in this paper for the first time, using the MSTMM coupled with a Van der Pol model. The influence of different parameters, such as riser length, top tension, stream speed and steel joints, on the dynamic response of the riser is investigated.

Commentary by Dr. Valentin Fuster
2018;():V006T09A061. doi:10.1115/DETC2018-85768.

The paper presents the dynamic response of an Euler-Bernoulli beam supported by an elastic foundation and subjected to a moving step load. The Riccati transfer matrix method for linear multibody systems (Riccati MSTMM) is employed to find eigenfrequencies and mode shapes of the supported beam. A comparison of results obtained with the finite element method (FEM) indicates that the Riccati MSTMM is more accurate when using the same number segments. Based on these results, the dynamic response of the beam with moving step load is investigated for different propagation velocities by mode superposition, and the effect of loads is discussed.

Commentary by Dr. Valentin Fuster
2018;():V006T09A062. doi:10.1115/DETC2018-85770.

Vibration control in launching process is an effective way to improve the dispersion characteristics of Multiple Launch Rocket System (MLRS). In this paper, a novel methodology for MLRS vibration controller design with the application of pulse thrusters and its parameters optimization is introduced. Based on the Transfer Matrix Method for Multibody Systems (MSTMM), the dynamic model of the controlled MLRS with pulse thrusters is established and the launch dynamic simulation system of controlled MLRS is developed. To suppress vibrations of the elevation part using the annularly arranged pulse thrusters, a management scheme based on impulse equivalence approach is presented to adapt the continuous force generated by the PID control law to impulse force. Controller optimization is achieved coupling Particle Swarm Optimization-Genetic Algorithm (PSO-GA) with the established simulation system of controlled MLRS. Finally, the simulation results verify the effectiveness of the proposed controller and demonstrate the engineering practicability value of this methodology.

Commentary by Dr. Valentin Fuster
2018;():V006T09A063. doi:10.1115/DETC2018-85778.

In this paper, the dynamic model and simulation system of armored vehicle with semi-active control of magnetorheological fluid damper (MRFD) are presented. The MRFD for the semi-active suspension of armored vehicle is developed and tested. The effects of skyhook semi-active control on vertical, pitch and rolling vibration of armored vehicle body are evaluated under different road conditions with different speeds. The research results provide the theoretical basis and technical solutions for controlling the vehicle body vibration of armored vehicles.

Commentary by Dr. Valentin Fuster
2018;():V006T09A064. doi:10.1115/DETC2018-85779.

A new approach for active vibration control design of multi-rigid-flexible-body systems based on transfer matrix method for multibody systems (MSTMM) is presented in this paper. The vibration characteristics are computed by solving homogeneous linear algebraic equations. Then, the augmented eigenvector and body dynamics equation are adopted to derive the state space representation by combining modal superposition method. Furthermore, Linear Quadratic Gaussian (LQG) control strategy is employed to design the control law. Compared with the conventional methods, the proposed method has the following features: without system global dynamics equation, high programming, low order of system matrix and high computational speed. Formulations as well as a numerical example are given to validate the proposed method.

Commentary by Dr. Valentin Fuster
2018;():V006T09A065. doi:10.1115/DETC2018-85782.

Compared to classical mechanics, the transfer matrix method for multibody systems is a rather novel approach for analyzing multibody system dynamics. For its features that it avoids the global dynamics equation of the system, keeps a high computational speed and allows highly formalized programming, this method has been widely used in science research as well as design of dynamics performance and experiments for various complicated mechanical systems. Up to now, there have been more than 50 research directions in science research and key engineering applications based on this method. In this paper, the following aspects are systematically reviewed: history, basic principles, formulas, algorithm, automatic deduction theorem of overall transfer equation, visualized simulation and design software, comparison with other dynamics methods, tendency, and future research directions.

Commentary by Dr. Valentin Fuster
2018;():V006T09A066. doi:10.1115/DETC2018-85784.

This paper studies test dynamics method of non-full loading firing for multiple launch rocket system (MLRS) and provides a new test method for reducing rocket consumption in MLRS firing precision test. Based on the theories of launch dynamics and Rui method, namely the transfer matrix method for multibody systems (MSTMM), launch dynamics model, characteristic equations and dynamics response equations of MLRS are established. The launch and flight dynamic simulation system for MLRS is developed combining the Monte Carlo simulation technology. The simulated results of vibration characteristics, rocket initial disturbance, and firing precision are verified by modal test, pulse thrust test and firing test, which show the simulation system can more accurately reflect the dynamic characteristics of the actual system and its dynamics computation has sufficient accuracy. The relationship between the initial state of MLRS and the mean value and median error of the impact points are established. Based on the idea of equal initial disturbance, non-full loading firing test dynamics method is presented for reducing the rocket consumption in firing precision test, by optimizing the loading position, firing orders and firing intervals of the rockets. For a practical MLRS, a seven-shot test scheme is designed and tested. The experimental results show that the amount of the rockets in firing precision test is reduce by 61% compared with the conventional test method, which saves a lot of testing costs.

Commentary by Dr. Valentin Fuster
2018;():V006T09A067. doi:10.1115/DETC2018-85788.

In order to study dynamics response of a launch vehicle under ground wind loads, the dynamics model of a launch vehicle erected on the pad is developed based on transfer matrix method for multibody systems and the theory of structural wind engineering. The overall transfer equation, overall transfer matrix, and characteristics equation of the system are deduced based on the automatic deduction theorem of overall transfer equation of multibody system. The equation governing the motion of the launch vehicle is obtained by using the orthogonality of augmented eigenvector. The vibration characteristics, and frequency domain and time domain dynamics response under ground wind loads of the launch vehicle are simulated. The simulation results show that the eigenfrequencies obtained by the proposed method and ordinary dynamics method have good agreements. The paper provides an effective approach to compute the dynamics response of the launch vehicle under ground wind loads.

Commentary by Dr. Valentin Fuster
2018;():V006T09A068. doi:10.1115/DETC2018-85790.

The purpose of this paper is to present a comprehensive multibody system dynamics model of a multiple launch rocket system (MLRS), and implement its simulation and experimental studies. The new version of transfer matrix method of multibody system and the launch dynamics theory are used in deriving the equations of motion coupled with rockets and barrels. The obtained model accounts for the complete process of the rockets’ ignition, movement in the barrels, airborne flight and landing. Launch dynamics of an 18-tube 122mm MLRS is investigated in this paper. Considering the effects of random factors, such as the impact and clearance between the rockets and barrels, the mass eccentricity and dynamic unbalance of the rockets and the thrust misalignment in this model, and combining the Monte Carlo method, the simulation of the dynamics of MLRS is carried out. Finally, the experimental implementation is proposed and the experimental results emphasize the feasibility of the multibody system launch dynamics model as a viable alternative for modeling accurately the dynamics characteristics of a practical MLRS. Meanwhile, the correctness of the numerical results is validated.

Commentary by Dr. Valentin Fuster
2018;():V006T09A069. doi:10.1115/DETC2018-85835.

Considerable research attentions have recently been paid toward a mobile manipulator (a robot arm standing on a mobile platform) due to its extended workspace beyond the manipulator reach. Mobile manipulators have a wide range of potential applications where it is desirable to achieve higher degree of flexibility in transport and handling task. However, a vast number of research publications only focus on trajectory planning. This preliminary research work presents dynamic modeling and analysis of a mobile flexible robot arm with aims to provide insights for the design and control of such mobile robot manipulators. In this work, the dynamic model is developed using a computationally efficient method: Discrete Time Transfer Matrix Method (DT-TMM). The concepts and principle of DT-TMM are briefly overviewed, and then are applied to a mobile flexible robot arm for dynamic modeling with the detailed procedure. Numerical simulations and dynamic analyses are performed to illustrate the effectiveness of the proposed dynamic modeling method, and to provide the clues for our ongoing research work in the design and control of mobile robot manipulators.

Commentary by Dr. Valentin Fuster
2018;():V006T09A070. doi:10.1115/DETC2018-85856.

Transfer Matrix Method for Multibody Systems (MSTMM) is easy to formulate, systematic to apply, simple to code and the matrices are low order which contributes to higher computational efficiency than ordinary dynamics methods. The main idea about how to simulate the vibration characteristic and hydroelastic behavior of a submarine sail mounted hydroplanes system based on MSTMM and coupled with Theodorsen flow model is presented in this paper. The simulation results are compared with those theoretical and experimental reported in the existing literature and commercial software simulation, and good results are obtained. The main idea of this paper provides a reference for dynamics of system with fluid-structure interaction (FSI) simulation and analysis of similar problems in the field of engineering.

Commentary by Dr. Valentin Fuster
2018;():V006T09A071. doi:10.1115/DETC2018-85987.

The dynamics response optimization of an ultra-precision machine tool system is the key to improve machining accuracy. Based on the transfer matrix method for multibody systems (MSTMM), the dynamics model as multi-rigid-flexible-body system is established. The overall transfer equation, overall transfer matrix, eigenfrequency equation and dynamics equation with respect to generalized coordinates are derived in this paper. Considering the environmental micro-vibration, cutting force and spindle centrifugal force during the machining process as external excitations, the vibration characteristics and dynamics response are simulated by using MSTMM. The computational results are in good agreement with test results, which validates the proposed method and dynamics model used in this paper.

Commentary by Dr. Valentin Fuster
2018;():V006T09A072. doi:10.1115/DETC2018-86338.

Riccati transfer matrix method for multibody systems (RMSTMM) has lower matrix order and better numerical stability than transfer matrix method for multibody systems (MSTMM). In order to make technicians more convenient to apply RMSTMM in practical engineering to improve the computational efficiency of dynamics, in this paper, a linear RMSTMM solver is developed based on the linear RMSTMM theory. A solver input document with good compatibility and extensibility is designed based on extensible markup language (XML); The data structure of multibody system is designed based on object-oriented programming method. The technique of auto selecting the cut hinges of closed-loops of the multibody system is established by introducing the correlation matrix and the dynamic connectivity matrix which depict the connecting state of elements. The automatic generation of the derived tree system by cutting off the closed-loops in the multibody system is realized based on the technique. The automatic regularly numbering of dynamics elements of multibody systems is realized based on the depth first recursive traversal algorithm; Finally, the Riccati transfer matrix recursive technique is implemented based on the regular numbers of dynamics elements of the multibody system. An example is given to verify the effectiveness of the solver which provides a powerful tool for extending the application of RMSTMM in practical engineering.

Commentary by Dr. Valentin Fuster
2018;():V006T09A073. doi:10.1115/DETC2018-86411.

Ball bearings are essential parts of mechanical systems to support the rotors or constitute the revolute joints. The time-varying compliance (VC), bearing clearance and the Hertzian contact between the rolling elements and raceways are three fundamental nonlinear factors in a ball bearing, hence the ball bearing can be considered as a nonlinear system. The hysteresis and jumps induced by the nonlinearities of rolling bearings are typical phenomena of nonlinear vibrations in the rolling bearing-rotor systems. And the corresponding hysteretic impacts have direct effects on the cleavage derivative and fatigue life of the system components. Therefore, the behaviors of hysteresis and jumps are given full attentions and continued studies in the theoretical and engineering fields. Besides, many researchers have done a lot of calculations to depict the various characteristics of bifurcations and chaos in the rolling bearings and their rotor systems, but few researches have been addressed on the inherent mechanism of the typical intermittency vibrations in rolling bearings. With the aid of the HB-AFT (the harmonic balance method and the alternating frequency/time domain technique) method and Floquet theory, this paper will investigate deeply the resonant hysteresis and intermittency chaos in ball bearings.

Commentary by Dr. Valentin Fuster

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