bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Double Holography Method and its Application to Engine Noise Research
Authors: Nakano Milsuo , Nagamatsu Masao , Suzuki Kohei , Yoshimura Takuya
Published: February 2021

The acoustic holography (AH) method with single measuring plane has been well known as the conventional method and can be implemented by far field measurement with simple instruments. However, the noise source resolution of the AH is not sufficient. In order to improve the resolution in the noise source identification, several kinds of the acoustic holography methods have been so far proposed.

For example, the near field acoustic holography (NAH) can provide high and accurate resolution of the holography by the nearfield measurement. However, the nearfield measurement within one wave length is sometimes impossible in the actual circumstances. The Acoustic Double Holography (A D H) proposed in this paper is a simplified approach with higher resolution of the noise source locations than that of the conventional AH methods. The ADH method basically uses dual measuring planes and does not require nearfield measurement. The sound pressure data detected on the rear plane are transformed into the virtual pressure data on the front plane taking into account of the distance between the plane and the object. Comparing the virtual pressure data with the actual data measured on the front plane, resolution on holography can be improved significantly.

Computer simulation and an experiment with two loud speakers were executed in order to confirm the fundamental feature of the proposed method. Several advantages on the method with respect to resolution over the conventional AH method were discussed. Furthermore, the ADH measurement was carried out on running engine under the full load operation. Through these results, the highly noise radiating areas on the engine surface were detected and reduced with noise shielding material. The overall engine noise level was reduced by 1.5dBA as the first stage in this noise control work.
On an Improvement of Hybrid Vibration Isolation System
Authors: Mizutani Kazuki , Fujita Yoshitaka , Ikeura Ryojun
Published: February 2021

This paper proposes a hybrid-type vibration isolation system controlled by a phase compensated LQ control method with a frequency shaped weighting function. The hybrid system is composed of a passive spring-damper system reducing vibrations of high frequency range and an active one reducing those of low frequency range. This system is controlled by the phase compensated digital LQ optimization method with a frequency shaped weighting function. By the proposed method, the phase-lag of the control system is compensated so that the vibration isolation performance is improved. Simulations for the active system are carried out and the effectiveness of the phase compensation is shown. Then, experiments for the hybrid system are carried out for sinusoidal or random excitations. It is confirmed that the purposed hybrid system has the excellent isolation performance for excited vibrations over the wide frequency range.
Vibration Control of a Self-Standing Quadrupedal Robot With YT-Mechanisms for Stable Walking
Authors: Takita Yoshihiro
Published: February 2021

We present the vibration control of a self-standing quadrupedal walking robot with one-degree-of-freedom mechanisms, which are called YT-mechanisms. Our developed robot walks with trot gait, in which its weight is supported alternately by each pair of diagonally opposite legs. The experimental results show that the natural frequency of first-mode vibration changes with the rotational angle of the mechanisms. The movement of its feet’s position generates an imbalance force which creates the elastic displacement of legs and the vibration during walking. In order to reduce the vibration, we propose to use a dynamic absorber as a passive vibration control device and investigate the influence of its tuned frequency. Experimental results show the advantages of this method.
Self-Regulating Variable Oil Damper for Structural Response Control
Authors: Kurino Haruhiko , Kobori Takuji
Published: February 2021

This paper proposes a simple semi-active control algorithm adopted for a variable damper whose damping coefficient is non-linearly controllable according to the signal. The physical constraint inherently associated with the variable damper expressed in a Maxwell model is taken into consideration for the study. We study a single-degree-of-freedom system under a harmonic excitation by paying attention to the nonlinear force-displacement relation of the device. It is concluded that the variable damper with the proposed algorithm can achieve twice as much damping augmentation as is expected from an ordinary passive damper under non-stationary random disturbances as well as a harmonic excitation. We also study a multi-degree-of-freedom system with the same algorithm and certify its control performance. The effectiveness of the proposed device is clearly seen from the numerical analyses using a 5-story structure model. Because of the nature of the algorithm, it is possible to replace all the complicated signal processor by an auto regulating valve controller housed on the device.
Solving Vibration Control Problems Using Reduced Order Models for Flexible Structures: A Genetic Algorithm Approach
Authors: Kundu Sourav , Kamagata Kentaro , Sugino Shigeru , Minowa Takeshi , Seto Kazuto
Published: February 2021

A Genetic Algorithm (GA) based approach for solution of optimal control design of flexible structures is presented in this paper. The method for modeling flexible structures with distributed parameters as reduced-order models with lumped parameters, which has been developed previously, is employed. Due to some restrictions on controller design it is necessary to make a reduced-order model of the structure. Once the model is established the design of flexible structures is considered as a feedback search procedure where a new solution is assigned some fitness value for the GA and the algorithm iterates till some satisfactory design solution is achieved. We propose a pole assignment method to determine the evaluation (fitness) function to be used by the GA to find optimal damping ratios in passive elements. This paper demonstrates the first results of a genetic algorithm approach to solution of the vibration control problem for practical control applications to flexible tower-like structures.
Semi-Active Vibration Isolation Control Using Feedforward Information of Disturbance
Authors: Yoshida Shigeaki , Yoshida Kazuo
Published: February 2021

Since the suppression of actuator power for active structural vibration control is an important problem, semi-active control methods receive much attention. In this paper, a new semi-active control method for the vibration isolation is presented. By taking the dynamics of disturbance into consideration, the optimal control method is applied to the augmented system that includes both the control object and the disturbance. By utilizing the obtained control law with a feedfoward link of disturbance, it is used for the semi-active control law based on the semi-active constraint of variable damper.

The control method was applied to the 4-DOF structural vibration isolation. The numerical analysis showed that the method has high control performance in a wide frequency range, and it is effective for the vibration isolation of building structures.
Design of Shape Memory Alloy Damper for Base Isolated Structure
Authors: Wilde Krzysztof , Gardoni Paolo , Fujino Yozo , Besseghini Stefano
Published: February 2021

Base isolation provides a very effective passive method of protecting the structure from the hazards of earthquakes. The proposed isolation system combines the laminated rubber bearing with the device made of shape memory alloy (SMA). The smart base isolation uses hysteretic behavior of SMA to increase the structural damping of the structure and utilizes the different responses of the SMA at different levels of strain to control the displacements of the base isolation system at various excitation levels. The performance of the smart base isolation is compared with the performance of isolation by laminated rubber bearings to assess the benefits of additional SMA damper for isolation of three story building.
Centrifugal Delayed Resonator: Theory and Experiments
Authors: Hosek Martin , Elmali Hakan , Olgac Nejat
Published: February 2021

A novel active vibration absorption technology, the Centrifugal Delayed Resonator (CDR), is presented as an efficient method for eliminating undesired torsional oscillations in rotating mechanical structures. The core idea is to reconfigure the dynamics of a damped centrifugal pendulum arrangement so that it behaves like an ideal real-time tunable absorber. This objective is achieved by applying a control torque based on proportional position feedback with variable gain and time delay. Fundamentals of the control strategy and its basic properties are explained, effects of the CDR absorber on a single-degree-of-freedom rotating structure are studied, and representative results of laboratory tests are presented. The strengths of this vibration control technology consist in complete elimination of a fundamental frequency component of undesired torsional oscillations, full effectiveness of vibration suppression in problems where the fundamental frequency of oscillations varies with time, very wide range of operating frequencies, complete decoupling of the feedback control from the mechanical properties of the rotating structure, comparatively simple implementation of the control algorithm, and fault-tolerant performance in the case of control failure.
Analytical and Experimental Investigation of an Impact Oscillator
Authors: Oestreich M. , Hinrichs N. , Popp K. , Budd C. J.
Published: February 2021

In the present paper a single-degree-of-freedom, periodically forced impact oscillator is investigated by numerics and experiments. At first the different types of motion and bifurcation diagrams are determined from experiments and compared to numerical results on the basis of the identified impact model. Also the nonsmooth third order system shows a rich bifurcational behaviour. On the basis of the identified nonsmooth model further analytical and numerical analysis can be applied. The Lyapunov exponents and the winding number are evaluated for the non-smooth system.
Periodic Response of Front End Accessory Drives With Dry Friction
Authors: Leamy Michael J. , Perkins Noel C.
Published: February 2021

Belt drives have long been utilized in engine applications to power accessories such as alternators, pumps, compressors and fans. Drives employing a single, flat, ‘serpentine belt’ tensioned by an ‘automatic tensioner’ are now common in automotive engine applications. The automatic tensioner helps maintain constant belt tension and to dissipate unwanted belt drive vibration through dry friction.

The objective of this study is to predict the periodic rotational response of the entire drive to harmonic excitation from the crankshaft. To this end, a multi-degree of freedom incremental harmonic balance (IHB) method is utilized to compute periodic solutions to the nonlinear equations of motion over a wide range of engine speeds. Computed results illustrate primary and secondary resonances of accessories and tensioner stick-slip motions.
Rattle Reduction of Automotive Component: A FEM Approach
Authors: Hsieh Shang-Rou , Shaw Steven W. , Borowski Victor J. , Her Jen Yaun , Moss Keith D.
Published: February 2021

Due to the continual diminishment of engine, power train and tire noise levels, squeak and rattle as become a primary source of undesired noise in automobiles. This article presents a finite-element-based methodology for the improvement of rattle performance of vehicle components. This approach attacks complicated nonlinear impact problems involving rigid and flexible structures by a rather indirect method that allows for the generation of design sensitivity information related to impact frequency and severity from large-scale computer models. This is done by adjusting the system parameters of a related linear problem in such a manner that the nonlinear system response is improved. For implementation purposes, it has been applied to study the rattle of the latch and corner rubber snubbers of a glove compartment. Results from the glove compartment study are summarized herein. Extensions to other rattle problems are also highlighted.
Impact Dynamics of a Supercavitating Underwater Projectile
Authors: Rand Richard , Pratap Rudra , Ramani Deepak , Cipolla Jeffery , Kirschner Ivan
Published: February 2021

We investigate the in-flight dynamics of a simplified model of a supercavitating body. In particular we are interested in the nature and frequency of the impacts which occur as the tail of the body touches the cavity walls. Referring to laboratory experiments conducted at Cal Tech in the 1950’s, we show that the tip force by the fluid is approximately directed along the length of the body. This gives zero moment about the body’s center of mass which leads us to assume that the body moves as if it were a moment-free rigid body pinned at its tip. To simplify the analysis, we assume that the body is not spinning about its symmetry axis. Then the motion between impacts is a plane motion with constant angular velocity. Using elementary fluid mechanics, we model the impact occurring when the tail touches the cavity walls, and we show that it is reasonable to assume that the impact is instantaneous with coefficient of restitution unity. Using this simplified model, we offer a simulation for typical parameters.
Smart Material Control Without Wire Leads or Electrodes: New Methods and Devices
Authors: Main John A.
Published: February 2021

Presented in this paper is a method for application of control signals to piezoelectric material patches that eliminates the need for both distributed electrodes and wire leads. The aim of this method is to provide a design solution for smart structural applications that require a very high spatial resolution over a relatively large area. The need for separate electrodes and leads is eliminated by depositing the control charges directly on the surface of the piezoelectric material using an electron gun. Both positive and negative electric displacements can be applied with an electron gun. This is accomplished by controlling the energy of the incident electron beam so that the secondary electron yield is either greater than or less than one. The spatial resolution of this control method is as small as the spot size of the electron beam, which in a focused beam may be as small as a few microns. One great advantage of this method is that it eliminates the need for discrete electrodes. This allows the control system design of a smart structural system to reside in signal processing rather than hardware.
Cyclic Deformation and Fatigue of a TiNi Shape-Memory Alloy Wire Subjected to Rotating-Bending
Authors: Tobushi H. , Hachisuka T. , Hashimoto T. , Yamada S.
Published: February 2021

The cyclic deformation and fatigue of a TiNi shape-memory alloy wire was studied by carrying out rotating-bending fatigue tests at various strain amplitudes, temperatures and rotational speeds in air and in water. The results were summarized as follows: (1) for strain amplitudes in the rhombohedral-phase transformation region, the fatigue life was longer than 107 cycles and the deformation properties did not change under cyclic deformation; (2) for the strain amplitudes in the martensitic transformation region, the fatigue life was shorter than 105 cycles and the higher the temperature, the shorter was the fatigue life; (3) the rotational speed did not affect the fatigue life in water but a higher rotational speed led to a shorter fatigue life in air.
Vibration Mode Localization in Randomly Disordered Weakly Coupled Two-Dimensional Systems
Authors: Xie Wei-Chau
Published: February 2021

In this paper, a general method of regular perturbation for linear eigenvalue problems is presented, in which the orders of perturbation terms are extended to infinity. The method of regular perturbation is applied to study vibration mode localization in randomly disordered weakly coupled two-dimensional cantilever-spring arrays. Localization factors, which characterize the average exponential rates of decay or growth of the amplitudes of vibration, are defined in terms of the angles of orientation. First-order approximate results of the localization factors are obtained using a combined analytical-numerical approach. For the systems under consideration, the direction in which vibration is originated corresponds to the smallest localization factor; whereas the “diagonal” directions correspond to the largest rate of decay or growth of the amplitudes of vibration. When plotted in the logarithmic scale, the vibration modes are of a hill shape with the amplitudes of vibration decaying linearly away from the cantilever at which vibration is originated.
Invariant NNM Manifolds for Studying Localized and Chaotic Dynamics of an Array Composed of STIFF/SOFT Elements
Authors: Georgiou Ioannis T. , Vakakis Alexander F.
Published: February 2021

This study concerns propagation of waves in a coupled array of soft/stiff oscillators. We show that the array supports a family of purely slow waves, including a solitary one, and a family of purely fast waves. The slow and fast waves interact to give rise to chaotically modulated slow/fast and fast/slow waves. Slow and fast waves are realized as two-dimensional invariant manifolds (normal modes) in phase space of a singular perturbation problem.
Gear Crack Detection With the Wavelet Transform
Authors: Boulahbal D. , Golnaraghi M. F. , Ismail F.
Published: February 2021

The wavelet transform has the ability to extract global information as well as localized small features from a given signal. This property makes it very well suited to the study of time-varying vibration signals generated by the operation of faulty gears. For a healthy and properly designed gear set, the vibration signal consists mainly of the gear meshing frequency component and its harmonics. Developing fatigue cracks introduce short-time transients that modulate both the amplitude and phase of the otherwise steady vibration signal. These transients are often difficult to detect with the traditional time-only or frequency-only techniques. Being a joint time-frequency distribution, the Wavelet transform allows one to look at the evolution in time of a signal’s frequency content. It thus appears to be the ideal tool to detect the localized transients. In this study, we use both the amplitude and phase maps of the wavelet transform to assess the condition of an instrumented gear test rig. With the proposed technique, simulated cracks as small as 20% of the tooth width at the root are easily detectable.
An Experimental Study of Vibrations of Nonideal Systems
Authors: de Mattos M. C. , Balthazar J. , Wieczorek S. , Mook D.
Published: February 2021

The vibrations excited by a rotating mass at the end of a cantilever beam are studied experimentally at the two universities given above. The mass is connected to the shaft of a DC motor with limited power. The response to changes in the applied voltage near resonance differs markedly from the response away from resonance: away from resonance, changes in the voltage applied to the motor are nearly linearly related to changes in the speed of the shaft and the amplitude of the motion remains small; near resonance changes in the voltage produce changes in the amplitude of the motion but have little or no effect on the speed of the shaft. Consequently, if the voltage is limited, it may not be possible to accelerate the motor-structure system through resonance. The Sommerfeld effect was observed, and it was found the jump associated with it could be extended by increasing the mass; however, the power needed to pass through resonance increased as the unbalanced mass increased. Regions of significantly modulated motions were found.
Friction Induced Vibrations in Aircraft Disk Brakes
Authors: Hagler Lisle B. , Reinhall Per G.
Published: February 2021

This paper presents a detailed analysis of the dynamic behavior of a single rotor/stator brake system. Two separate mathematical models of the brake are considered. First, a non-rotational model is constructed with the purpose of showing that friction induced vibration can occur in the stator without assuming stick-slip behavior and a velocity dependent friction coefficient. Self-induced vibrations are analyzed via the application of the method of multiple scales. The stability boundaries of the primary resonance, as well as the super-harmonics and sub-harmonics are determined.

Secondly, rotational effects are investigated by considering a mathematical brake model consisting of a spinning rotor engaging against a flexible stator. Again, a constant friction coefficient is assumed. The stability of steady whirl is determined as a function of the system parameters. We demonstrate that only forward whirl is stable for no-slip motion of the rotor.

The interactions between chatter, squeal, and rotor whirl are investigated through numeric simulation. It is shown that rotor whirl can be an important source of the torsional oscillations (squeal) of the stator and that the settling time to no-slip decreases as the ratio of the stator to rotor stiffness is increased.
Analysis of Ball Bearing Vibrations Caused by Outer Race Waviness
Authors: Ono Koichiro , Okada Yohji
Published: February 2021

Even with the use of highly efficient machine, the manufacturing of rolling elements bearings still results in defective bearings. The defects could be on the race track or the rolling elements. A common problem with defective bearing is the generating waviness on the outer race track during the manufacturing process. The vibrations caused by rolling elements rolling over the waviness surface is transmitted to the passenger cabin and produced unwanted noise. In this paper an analytical study was first undertaken to evaluate the effect of waviness number, radial gap and shaft unbalance on the vibration spectrum. Experimental investigation was carried out to confirm the analytical study. The experimental results agreed very well with the numerical analysis.
Analysis of Models for Torsional Vibration of Shaft System With Planetary Gearing
Authors: Sun Jinghui , Liu Lee , Patten William N.
Published: February 2021

The kinematics of planetary gearing are complex; thus, making it difficult to build an effective dynamic model. In this paper, a single-mass model of a planetary gear and shaft system is developed to study the torsional vibration of the mechanism. Two new models of the system are proposed: (a) a fictitious co-planar model and (b) an equivalent shaft model. The results from the calculations and analyses using these models indicate that: 1) the single-mass model and the general rotary model are both limited, either mathematically or geometrically; 2) the fictitious co-planar model includes all of the geometric and dynamic parameters of the general rotary model, and it can be connected with the shaft system easily; and 3) using a mathematical treatment, the equivalent shaft model is demonstrated to be the most useful and most effective model for the calculation of torsional vibration of a shaft and planetary gear train.
Clearance Effects on Spiral Vibrations due to Rubbing
Authors: Childs Dara W. , Jordan Leland T.
Published: February 2021

Kellenberger’s (1980) model for spiral vibrations due to rubbing is extended to include the effects of a radial clearance at the rub location. Black’s (1968) model is used to incorporate the influence of clearance. Clearances at the rub location introduce a nonlinearity and are shown to modestly improve stability. A review of Kellenberger’s model reveals that his equations defining the growth of the shaft due to rubbing are only correct if two (previously unspecified) conditions are met, and simulations show that both conditions are violated. However, an alternative, “kinematically-correct”, model yields results which are significantly less consistent with the observed behavior of spiral vibrations than Kellenberger’s original model.
Modal Analysis of a Rotating Shaft-Disk-Blades System With a Cracked Blade
Authors: Wu Ming-Chuan , Huang Shyh-Chin
Published: February 2021

The dynamic behavior of a rotating shaft-disk-blades system containing a cracked blade is investigated. With the crack released energy, the flexibility due to crack is evaluated. An energy principle in conjunction with the assumed-mode method is applied to yield the discrete equations of motion. Numerical examples are given for cases with between two and five symmetrically arrayed blades. The results show that there exist both torsion-bending coupled modes and blade-coupling modes, which occur at repeated frequencies. When there is a cracked blade, the frequencies of torsion-bending coupled modes decrease due to the crack, and blade-coupling modes have the phenomena of frequency bifurcation. Finally, the effects of shaft speed on the natural frequencies are illustrated.
In-Plane Bending Modal Analysis of Circular Rings and Ring Segments: Use of ‘Exact’ Dynamic Stiffness Matrix
Authors: Azimi Saeed Z.
Published: February 2021

The ‘exact’ dynamic stiffness matrix for the case of a circular ring segment, considering the in-plane bending vibration only, is presented and its use for different situations of classical boundary conditions is discussed. In this formulation one can also include the flexibilities of the end supports in the radial and rotational directions and/or consider the flexible or rigid intermediate supports for a multi-span structure. Dynamic analysis of structures composed of circular ring segments with different load applications can also be investigated using this formulation.
The Response of a Nonconservative Distributed System to a Moving Oscillator
Authors: Pesterev Alexander V. , Bergman Lawrence A.
Published: February 2021

The problem of calculating the response of a nonconservative distributed parameter system of a general type excited by a moving concentrated load is investigated. A method of solution based on the expansion of the response in a series in terms of complex eigenfunctions of the distributed system is proposed. A set of ordinary differential equations in the time-dependent coefficients of the expansion is established first, in terms of the unknown force acting on the continuum from a moving vehicle, which allows one to investigate different models of concentrated loads. Then, for the case of a conservative oscillator moving with an arbitrarily varying speed, the coefficients of the equations are obtained in explicit terms.
An Experimental Method to Determine Poisson’s Ratio in a Small Beam Subject to Seismic Excitation
Authors: Caracciolo Roberto , Gasparetto Alessandro , Giovagnoni Marco
Published: February 2021

An experimental method to determine Poisson’s ratio in a small beam subject to seismic excitation is presented. Poisson’s ratio is computed by measuring longitudinal and transverse strains by means of electric strain gauges. A first set of tests is carried out with different materials, and it is observed that the measured Poisson’s ratio decreases with frequency. However, to determine whether the observed decrease is true or it is due to an error caused by the plate effect of the beam, a second set of tests at different temperatures is carried out. Then, by applying the reduced variables method, a unique plot for Poisson’s ratio on a much broader frequency range is obtained, which allows to state that the decrease of Poisson’s ratio is true. An iterative procedure is described, which has been developed to gather the curves at different temperatures in a master curve.
On the Free Vibrations of a Whirling Rod
Authors: O’Reilly Oliver M. , Turcotte Major Jeffrey S.
Published: February 2021

In this work, the problem of a whirling rod is examined. The governing equations for the steady motion of the rod and small amplitude vibrations superposed on the steady motion are formulated and discussed. This formulation uses the theory of a directed or Cosserat rod which was developed by A. E. Green, P. M. Naghdi and several of their co-workers. The present work also involves extensions to recent work by O’Reilly on properly invariant approximate theories.
Free and Forced Vibration of an Axially Moving String With an Arbitrary Velocity Profile
Authors: Zhu W. D. , Guo B. Z.
Published: February 2021

The exact response of an axially moving string with an arbitrary velocity profile is determined under general initial conditions and external excitation. In terms of the curvilinear characteristic coordinates the time-dependent governing equation reduces to one with constant coefficients. The domain of interest in the characteristic coordinate plane is bounded by two monotonic curves with the same shape corresponding to the spatial boundaries of the string. Solution of the transformed equation is derived for the free and forced responses. The displacement of the free response is shown to be bounded under arbitrary variation of the transport speed in the subcritical regime. Parametric resonances do not exist. The method is demonstrated on two illustrative examples with piecewise constant and sinusoidal accelerations.
Frequencies of Axial Vibrations of the Beam
Authors: Cveticanin Livija
Published: February 2021

In this paper the free longitudinal vibrations of the beam on which the strong nonlinear force of Winkler type acts are analyzed. The vibrations are described with a second order strong nonlinear partial differential equation. Various approximate analytical methods for solving this equation are developed in the paper. The lowest frequency of vibration obtained by the suggested method are compared. It can be seen that some differences appear.
A Mechanical Filter Concept to Suppress Crane Load Oscillations
Authors: Balachandran B. , Li Y.-Y.
Published: February 2021

In this article, preliminary results obtained in the exploration of a mechanical filter concept for suppressing crane-load oscillations on a ship vessel are presented. The pivot point about which the load oscillates is constrained to follow a circular track in the considered filter. The governing dynamical systems for the cases with and without the filter are presented, and the nonlinear dynamics of these systems is studied with respect to quasi-static variation of different scalar control parameters. It is shown that the presence of the filter helps in eliminating some of the sub-critical bifurcations that may arise in the crane-load response during periodic ship-roll excitations.
Magnetorheological Fluid Dampers for Seismic Control
Authors: Carlson J. David , Spencer B. F.
Published: February 2021

Magnetorheological (MR) fluid dampers have recently emerged as enabling technology for implementing semi-active control in a variety of applications. The successful use of a linear and rotary MR fluid damper in a variety of real-time control applications in the field has recently been demonstrated. Examples of several of these controllable MR fluid actuators, that are now either in commercial production or extended field test, are described herein. This technology is presently being extended to dampers for seismic control applications. Because of their mechanical simplicity, high dynamic range, low power requirements, large force capacity and robustness, magnetorheological (MR) fluid dampers mesh well with application demands and constraints to offer an attractive means of protecting civil infrastructure systems against severe earthquake and wind loading. Following an overview of the current status of MR fluid technology, this paper presents both laboratory and full-scale studies of the efficacy of MR dampers for seismic hazard mitigation.
Deconvolution by Wavelets for Extracting Impulse Response Functions
Authors: de Moraes Francisco José Vicente , Weber Hans Ingo
Published: February 2021

The extraction of Impulse Response Functions (Markov parameters) is a major feature on dynamic systems identification. The convolution integral is a most important input-output relationship for linear systems. Existing methods for calculating the IRFs from the convolution integral are carried out in time or frequency domains. The orthonormal wavelet transform consists on decomposing a given signal on mutually orthogonal local basis functions. It is possible to make use of the orthogonal properties of wavelets for calculating the convolution integral. The wavelet domain preserves the temporal nature of data and, simultaneously, different frequency bands are isolated by the multiresolution analysis, without loosing the orthogonality of the wavelet terms. Algorithm matrices are well conditioned and the method is not very sensitive to output noise. Simulated and experimental analysis are performed and results presented.
A Model Updating Method Based on the Concept of Frequency Shift Between Analytical and Experimental FRFs
Authors: Pascual Rodrigo , Golinval Jean-Claude , Razeto Mario
Published: February 2021

Up to now, model updating methods based on forced responses and local matrix sensitivities use both experimental and analytical quantities (FRFs and model impedance matrices) all evaluated at the same frequency(ies). However, this approach does not consider that between a reference system (the experimental model) and a perturbed one (the initial finite elements model), it exists a shift along the frequency axis that can be estimated using the Frequency Domain Assurance Criterion.

In this paper, a model updating method based on this observation is introduced. It can be interpreted as a generalisation of the existent techniques.
New Geometric Properties for Modelled Planar Vibration
Authors: Blanchet Pat , Lipkin Harvey
Published: February 2021

A novel analysis is used to identify new geometric properties for a seemingly well-known model — the linear vibration of an elastically suspended rigid body in planar motion. Vibration centers describe the modes shapes and are shown to be constrained to regions specified by the center-of-elasticity, center-ofmass, and stiffness principal directions. Responses are classified by the number of pure translational modes and conditions for existence are given. Vibration centers are also applied to forced vibration problems where there is a simple relation between an applied force and the resulting mode amplitudes. Numerical examples illustrate the results.
Reduction of Vibrations in Complex Structures With Viscoelastic Neutralizers: A Generalized Approach and a Physical Realization
Authors: de Espíndola J. J. , Bavastri C. A.
Published: February 2021

A general procedure for the optimization of the parameters of dynamic neutralizers is reviewed. It can be applied to the minimization of the vibration response and sound radiation of linear structures subjected to excitations in a specified frequency range.

Modal theory and generalized equivalent quantity concept for the neutralizers, introduced by Espíndola and Silva (1992), as applied to a non-linear optimization scheme, are also reviewed for clarity. That proposed procedure can be applied to relaxed and time invariant structures. It is not dependent on the structure complexity and the degree of discretization adopted.

In such conditions, a significant reduction in computing work is achieved, if compared with the more traditional methods.

Experimental results are compared with numerical ones.
Simulations of a Truck Driving on a Flexible Bridge
Authors: Friberg Olof , Möller Peter , Thorvald Boris
Published: February 2021

In this work, the main object was to perform simulations using a realistic model of a truck and trailer passing over a flexible bridge structure. Two driving cases were considered: straight forward driving with and without braking. In the latter case control logic was used to distribute the braking torques to the wheel axles.

A general multibody dynamics computer program, DADS, and its tire subroutines were interfaced with our FEM routines in order to create a vehicle/structure interaction computer program. A part of this process was to integrate different time stepping algorithms from the multibody dynamics and FEM disciplines into a “common” time integration procedure. Another part was to write code to search for finite elements where tire/structure interaction takes place.
Computational Schemes for Nonlinear Elastic Multi-Body Systems
Authors: Bauchau O. A.
Published: February 2021

This paper is concerned with the analysis of nonlinear elastic multi-body systems, i.e. a collection of bodies in arbitrary motion with respect to each other while each body is undergoing large displacements and rotations with respect to a body attached frame of reference. The focus is on problems where the strains within each elastic body remain small.
A New Numerical Method for the Dynamic Analysis of Impact Loads in Flexible Beams
Authors: Escalona José L. , Mayo Juana M. , Domínguez Jaime
Published: February 2021

The aim of this investigation is to compare the classical St. Venant’s solution of the axial impact on flexible rods with the numerical result from a finite element computational procedure involving component mode synthesis. A new technique developed to simulate impacts is used to this end. The impacts treated are those mainly governed by the propagation of elastic waves along the complete flexible body. Local effects at the vicinity of the contact surfaces are neglected. The phenomenon of succession of impacts is analytically proved, a second period of contact is found in a particular case. A numerical method is developed to solve the collision based on the theoretical solution. This technique is able to identify the elastic waves which travel along the rod and a force balance is continuously made to yield the contact stress and the velocity of the surfaces in contact. Numerical solution shows an excellent agreement between the numerically obtained displacements histories with the theoretical results. The capability of the eigenvectors to describe the wave propagation is analysed as well as the effect of the elements boundaries.
An Approach for the Dynamics of Robotic Manipulators With Structural Flexibility of Links and Joints
Authors: Kövecses J. , Fenton R. G. , Cleghorn W. L.
Published: February 2021

In this paper, an approach is presented for the dynamic modeling and analysis of robotic manipulators having structural flexibility in the links and joints. The formulation allows the user to include different types of flexibilities, as required. This approach includes the dynamic effects of joint driving systems by considering the mass and moments of inertia of their elements, the rotor-link interactions, and the gear reduction ratios; all of which can have significant influences on the behavior of the manipulator. Both distributed-discrete and discretized-discrete parameter models of a robot can be analysed. In the discretized-discrete case, dynamic equations of motion are developed for four model types: rigid link - rigid joint, rigid link - flexible joint, flexible link - rigid joint, and flexible link - flexible joint. An example of a two-link manipulator is considered. Simulation results are presented for different models (flexible joint - rigid link, rigid joint - flexible link, flexible joint - flexible link) of the manipulator. The computations show the influence of joint and link flexibilities on the manipulator performance.
Parallel O(log2N) Algorithm for the Motion Simulation of General Multi-Rigid-Body Mechanical Systems
Authors: Anderson Kurt S.
Published: February 2021

This paper presents a new highly efficient procedure for the determination of the dynamical equations of motion for complex multibody systems and their subsequent temporal integration using parallel computing. The method is applicable to general systems of rigid bodies which may contain arbitrary joint types, multiple branches, and/or close loops. The method is based on the explicit determination of constraint forces at key joint locations and the subsequent highly efficient determination of system state time derivatives. The algorithm uses a novel hybrid direct and iterative solution scheme which allows a substantially higher degree of parallelization than is generally obtainable using the more conventional recursive O(N) procedures. It is shown that at the coarsest level the parallelization obtainable easily exceeds that indicated by the topology of the system. The procedure can produce a theoretical and time optimal O(log2N) performance on computational throughput with a processor optimal O(N) processors on a MDMD distributed architecture processing system.
Fatigue Life Analysis Using Linear Transient Dynamics for Automotive Sheet Metal Structures
Authors: Huang Liping , Agrawal Hari
Published: February 2021

Since the environment of vehicle operation is dynamic in nature, dynamic method should be used in vehicle durability analysis. Due to the constraints in current computer resources, simulation of vehicle durability test and vehicle structural Me analysis need special approaches and efficient CAE tools. A methodology and an integrated analysis process is presented in this paper. Three examples of structural life analysis using transient dynamics are given. The examples show that dynamics analysis for vehicle life prediction is feasible by employing efficient methods and proper process. Results from the analysis demonstrate that dynamic stress levels are much higher than static stress at some locations and that dynamic methods give a significantly different structural life compared with static analysis.
Identifiability Issues for Parameter-Varying and Multidimensional Linear Systems
Authors: Lee Lawton H. , Poolla Kameshwar
Published: February 2021

This paper considers the identifiability of state space models for a system that is expressed as a linear fractional transformation (LFT): a constant matrix (containing identified parameters) in feedback with a finite-dimensional, block-diagonal (“structured”) linear operator. This model structure can represent linear time-invariant, linear parameter-varying, uncertain, and multidimensional systems. Families of input-output equivalent realizations are characterized as manifolds in the parameter space whose tangent spaces — and orthogonal complements — can be obtained via singular value decomposition. As illustrated by a numerical example, restricting iterative parameter estimation algorithms (e.g., maximum-likelihood with nonlinear programming) to the orthogonal directions offers significant computational advantages.
Benefits of Model Updating: A Case Study Using the Micro-Precision Interferometer Testbed
Authors: Joshi Sanjay S. , Melody James W. , Neat Gregory W. , Kissil Andrew
Published: February 2021

This paper presents a case study on the benefits of model updating using the Micro-Precision Interferometer (MPI) testbed, a full-scale model of a future spaceborne optical interferometer located at JPL. The MPI testbed is composed of several active and passive optical elements distributed across a 7 m × 7 m × 6.5 m truss structure. Successful operation of this complex optomechanical system requires positional stabilities of these optical elements down to the ten-nanometer level. Design of such systems for space requires a disturbance modeling capability that integrates optical modeling, structural modeling and control system design. An integrated model of MPI was built in parallel with the testbed, enabling a unique model updating and validation opportunity. Physical parameters of the structural finite element model were updated based on two separate modal tests: a comprehensive modal test of the base structure alone and an in situ component modal test. This paper quantifies the effect of these physical parameter updates on MPI integrated model prediction capability. Specifically, the paper compares three sets of disturbance-input to optical-output transfer functions: (1) measured data from the testbed, (2) predictions from a high-fidelity model without any parameter updates, and (3) similar predictions for the model with updated physical parameters. Results from this study indicate that physical parameter updating has provided little benefit for disturbance modeling on the MPI testbed. These results will have significant impact on the modeling strategy adopted for the Spaceborne Interferometer Mission (SIM).
Project Step: A Randomized Controlled Trial Investigating the Effects of Frequent Feedback and Contingent Incentives on Physical Activity
Authors: Kerrigan Stephanie G. , Forman Evan M. , Williams Dave , Patel Mitesh , Loyka Caitlin , Zhang Fengqing , Crosby Ross D. , Butryn Meghan L.
Published: February 2021

Background: Financial incentives and feedback on behavior offer promise for promoting physical activity. However, evidence for the effect of each of these techniques is inadequate. The present study evaluated the effects of daily versus weekly feedback and incentives contingent on reaching a daily walking goal versus noncontingent incentives in a 2 × 2 trial. Methods: Participants (N = 57) had a body mass index >25 kg/m2 and were insufficiently active. Participants received a daily walking goal that adapted weekly. Results: Participants receiving daily feedback increased daily steps (P = .03) more than those receiving weekly feedback. Participants receiving contingent incentives did not significantly increase steps (P = .12) more than those receiving noncontingent incentives. A trend-level effect (P = .09) suggested that there may be an interaction such that the combination of daily feedback and contingent incentives is most effective. Conclusions: Results indicate that feedback is an important component of remotely delivered PA interventions and that evaluating each component of low-intensity interventions may help to improve efficacy. Moreover, results indicate that possible synergistic effects of feedback and rewards should be investigated further to help optimize interventions.
SARS-CoV-2 M
pro
inhibitors with antiviral activity in a transgenic mouse model
Authors: Qiao Jingxin , Li Yue-Shan , Zeng Rui , Liu Feng-Liang , Luo Rong-Hua , Huang Chong , Wang Yi-Fei , Zhang Jie , Quan Baoxue , Shen Chenjian , Mao Xin , Liu Xinlei , Sun Weining , Yang Wei , Ni Xincheng , Wang Kai , Xu Ling , Duan Zi-Lei , Zou Qing-Cui , Zhang Hai-Lin , Qu Wang , Long Yang-Hao-Peng , Li Ming-Hua , Yang Rui-Cheng , Liu Xiaolong , You Jing , Zhou Yangli , Yao Rui , Li Wen-Pei , Liu Jing-Ming , Chen Pei , Liu Yang , Lin Gui-Feng , Yang Xin , Zou Jun , Li Linli , Hu Yiguo , Lu Guang-Wen , Li Wei-Min , Wei Yu-Quan , Zheng Yong-Tang , Lei Jian , Yang Shengyong
Published: February 2021

Targeting the SARS-CoV-2 main protease

Vaccines are an important tool in the fight against COVID-19, but developing antiviral drugs is also a high priority, especially with the rise of variants that may partially evade vaccines. The viral protein main protease is required for cleaving precursor polyproteins into functional viral proteins. This essential function makes it a key drug target. Qiao
et al.
designed 32 inhibitors based on either boceprevir or telaprevir, both of which are protease inhibitors approved to treat hepatitis C virus. Six compounds protected cells from viral infection with high potency, and two of these were selected for in vivo studies based on pharmokinetic experiments. Both showed strong antiviral activity in a mouse model.

Science
, this issue p.
1374
Tracing orbital images on ultrafast time scales
Authors: Wallauer R. , Raths M. , Stallberg K. , Münster L. , Brandstetter D. , Yang X. , Güdde J. , Puschnig P. , Soubatch S. , Kumpf C. , Bocquet F. C. , Tautz F. S. , Höfer U.
Published: February 2021

Electron dynamics in time and space

Following molecular excitation and electron transfer processes in time and space within a single experiment is a long-standing goal of spectroscopy in the field of chemistry. Wallauer
et al.
combined tomographic photoemission imaging with a femtosecond pump-probe scheme to trace the excited state molecular orbitals of surface-adsorbed molecules with both spatial and temporal resolution. The present demonstration opens a new window for investigating the ultrafast electron transfer dynamics in such processes as chemical reactions on surfaces and intermolecular charge transfers.

Science
, this issue p.
1056