bluuebunny/crossref_metadata_2025 huggingface dataset:
High Durability of Functionally Graded Piezoelectric Bending Actuators
Authors: Qiu Jinhao , Tani Junji , Morita Teppei , Takahashi Hirofumi
Published: November 2020

A new type of functionally graded (FG) piezoelectric bending actuator was proposed by the authors in the former study and the advantage of the new actuator over the traditional bimorph and unimorph actuators in internal stress distribution was illustrated by simulation results. In this study, functionally graded piezoelectric bending actuator was designed and fabricated. The material compositions with different dielectric and piezoelectric constants were selected from the Pb(Ni1/3Nb2/3)O3-PbZrO3-PbTiO3 (PNN-PZ-PT) family and used as the four layers in the new FG piezoelectric actuator. The piezoelectric constant and dielectric constant were graded oppositely in the thickness direction. Stress distribution of the FG piezoelectric actuator under external voltage was analyzed using finite element method (FEM) and the simulation results showed the stress discontinuity of the new actuator is smaller than that of traditional bimorph actuator. Durability of the fabricated FG piezoelectric actuators was measured in a vibration test and compared with that of the traditional bimorph actuator to evaluate the improvement of performance. The results showed that the durability of the FG piezoelectric actuators is much higher than that of the bimorph actuator.
Friction Induced Brake Vibrations
Authors: Rudolph Martin , Popp Karl
Published: November 2020

This paper deals with friction induced brake vibrations showing frequencies above 1 kHz and a narrow bandwidth. This phenomenon is usually called ‘brake squeal’.

After analyzing squeal excitation mechanisms, a rigid body brake model displaying the main features of a floating caliper disc brake is presented.

A brake noise test rig has been installed and is used to verify simulations which are based on the 14 DOF multibody model.

A stability analysis as well as a sensitivity analysis have been conducted in order to find recommendations for a brake design avoiding squeal. From the outcomes of these calculations design modifications have been derived which were tested by TRW Automotive Company. The dependence of squeal occurrence on brake pressure has been predicted by the developed theoretical model.
Spatial Contact Mechanics of CVT Chain Drives
Authors: Sedlmayr Martin , Pfeiffer Friedrich
Published: November 2020

A method for the simulation of spatial dynamics of CVT chain drives is proposed in this paper. Dealing with an elastic multibody system, special care has been taken to describe the contact mechanics of interconnected rigid and/or elastic bodies. Simulation results show the influence of the geometry and the kinematics on the vibrational behavior of the transmission. Furthermore effects on the efficiency and working forces are discussed.
Development and Experimental Validation of a Point Contact Model for Dynamical Problems With Friction
Authors: Sextro Walter
Published: November 2020

The contact forces are dependent on many parameters, such as contact stiffnesses, surface profiles, material parameters, temperature distribution, relative motion and normal pressure distribution. These parameters can change within the contact area and from here, it is impossible to derive a general force law. The only possibility to overcome this problem is to discretize the contact areas, since in general the relative motion and the contact parameters are not constantly distributed within the contact surface. This leads to a point contact model, which has to include all main physical effects as described above, which are important, when simulating dynamical contact problems with friction.

The friction model includes the main parameters such as the roughness of the contact surfaces, the nonlinear friction law, the contact stiffnesses in normal and tangential direction. The decreasing characteristic of the friction coefficient with respect to the relative velocity has to be modeled in a sufficient way. With respect to the dissipation of energy, the hysteretic behavior is studied with respect to the normal and tangential direction. Separation of the contact is included.

This point contact model is be applied to real dynamical contact problems. In the first example, a simple impact oscillator with an elastic contact is used to check the overall modeling with respect to the elastic normal contact. Then, a self excited friction oscillator is investigated with respect to the tangential contact. Here, the modeling of surface waviness leads to high periodic solutions, which is also observed within the experiments. In both examples, the comparison of measurements and calculated phase plots is good.

Furthermore, the influence of wear on to the surface profile, contact area and normal pressure distribution is investigated. From here, it follows, that friction leads to time dependent systems.
On Equivalence of the Moving Mass and Moving Oscillator Problems
Authors: Pesterev Alexander V. , Bergman Lawrence A. , Tan Chin An , Tsao T.-C. , Yang Bingen
Published: November 2020

Asymptotic behavior of the solution of the moving oscillator problem is examined for large values of the spring stiffness for the general case of nonzero beam initial conditions. In the limit of infinite spring stiffness, the moving oscillator problem for a simply supported beam is shown to be not equivalent in a strict sense to the moving mass problem; i.e., beam displacements obtained by solving the two problems are the same, but the higher-order derivatives of the two solutions are different. In the general case, the force acting on the beam from the oscillator is shown to contain a high-frequency component, which does not vanish, or even grows, when the spring coefficient tends to infinity. The magnitude of this force and its dependence on the oscillator parameters can be estimated by considering the asymptotics of the solution for the initial stage of the oscillator motion. For the case of a simply supported beam, the magnitude of the high-frequency force linearly depends on the oscillator eigenfrequency and velocity. The deficiency of the moving mass model is noted in that it fails to predict stresses in the bridge structure. Results of numerical experiments are presented.
Effects of Boundary Flexibility in the Moving Oscillator Problem
Authors: Tan Chin An , Chen Yonghong , Bergman Lawrence A.
Published: November 2020

In this paper, the problem of an oscillator moving across an elastically supported Euler-Bernoulli beam is examined. The oscillator is modeled by a one-degree-of-freedom sprung mass and the end supports are modeled by linear springs in the transverse direction. Solution for the response of the beam is represented by an eigenfunction expansion series. Numerical results are obtained for the eigenvalues and the response of the elastically supported beam, and the interaction force (force in the oscillator spring). To guide the discussion, a critical value of the support stiffness is determined from the plot of the first natural frequency versus the support stiffness. Effects of the boundary flexibility on the maximum beam response and the maximum interaction force are discussed as a function of the speed and the oscillator frequency. The boundary flexibility is shown to have a significant implication in the design analysis of the moving oscillator problem, especially for shorter span beam structures.
Aquatic Mobile Robot Using Waving Motion of a Flexible Fin
Authors: Muramatsu Koichi , Watanabe Masahiro , Kobayashi Nobuyuki
Published: November 2020

This paper deals with an experimental study of propulsive performance of aquatic mobile robot using waving motion of a flexible plate modeled on the flexible caudal fin of fish. The flexible plate is attached at the trailing edge of the oscillating robot body in the shape of wing pitching and heaving around the leading edge of the body, and the waving motion of the flexible plate is excited by motion of the oscillating body. In the experiment, first, the propulsion force and the side force generated by the waving motion of the flexible plate are measured for various length, exciting frequency and flexibility of the flexible plate in stationary water in a channel. Secondly, the swimming speed and propulsive efficiency are examined. As a result, it is found that the propulsive performance of the robot using flexible plate is higher than that of the rigid plate. And the high propulsive performance of propulsive efficiency of 62% and mean swimming speed of 0.3m/s are obtained by using the waving motion of the flexible plate.
Sensorless Modal Stabilization for Three-Link Robotic Arm With Elastic Wrist Drive Belt
Authors: Hosek Martin
Published: November 2020

A control system for a three-link direct-drive robotic manipulator with inherent structural flexibilities is presented. The structural flexibilities introduce undesirable vibration modes which may affect operation of the robot motion controller, resulting in destabilization of the closed-loop system. This represents a major limiting factor for implementation of a conventional controller designed solely for the rigid body dynamics of the robotic manipulator. The fundamental idea in the presented approach is to use a composite controller which consists of a trajectory-tracking section designed for the rigid-body dynamics and a vibration-damping compensator added for attenuation of the dominant flexible dynamics. The vibration damping compensator operates on estimated states of the dominant flexible dynamics obtained from a reduced-order state observer. A mechanism is implemented which allows the robotic manipulator to move through or hold in positions where the dominant flexible dynamics is unobservable and uncontrollable. Results of laboratory tests document that the presented approach leads to improved stability and control performance.
Dynamic Modeling of a Non-Redundant Spatial Mobile Manipulator
Authors: Stiles James M. , Chung Jae H. , Velinsky Steven A.
Published: November 2020

Mobile manipulators are comprised of robot manipulators mounted upon mobile platforms which allow for both high mobility and dexterous manipulation ability. Although much research has been performed in the area of motion control of mobile manipulators, previous developed models are typically simplified and assume only planar motion and/or holonomic constraints. In this work, the equations of motion of a three dimensional non-redundant wheeled-vehicle based mobile manipulator system are developed using a Newton-Euler formulation. This model incorporates a complex tire model which accounts for tire slip and is thus applicable to high speed and high load applications. The model is systematically exercised to examine the dynamic interaction effects between the mobile platform and the robot manipulator, to illustrate the effects of wheel slip on system performance, and to establish bounds on the efficacy of the simplified existing kinematic models.
Nonlinear Behavior of an Inclined Cable: Experimental and Analytical Investigations
Authors: Berlioz A. , Lamarque C. H. , Malasoma J.-M.
Published: November 2020

Vibrations of an inclined cable subjected to external sinusoidal excitation are experimentally investigated and via a simplified model with one degree-of-freedom: external excitation looks like the loading that should be exerted on the cable by the superstructure of a bridge. The nonlinear one dof model is studied via the multiple scales method. Numerical and experimental results are compared.
An Analytical Approach to Model Disc Brake System for Squeal Prediction
Authors: Chowdhary Harsh V. , Bajaj Anil K. , Krousgrill Charles M.
Published: November 2020

The squeal noise arising due to friction-induced vibrations in brakes continues to be a major challenge for automotive manufacturers. To predict one of the mechanisms behind disc brake squeal, an analytical model is developed for the disc brake system. The brake rotor is represented by a thin plate of equivalent modal characteristics and the backing plates are modeled as thin annular sector plates using Rayleigh-Ritz approach. The two structural models are then coupled using linear elastic springs and Coulomb friction at the interface, and Lagrangian approach is used to derive the equations of motion of the coupled system. The resulting linear equations are solved by using complex eigenvalue analysis. The study shows that squeal is a flutter-type instability caused by coupling between the modes of structural components with very close natural frequencies. The sensitivity to friction material stiffness and the influence of hydraulic cylinder stiffness at backing plates are also discussed.
Out-of-Plane Vibrations of a Stepped Euler-Bernoulli Beam Clamped to a Rotating Hub
Authors: Naguleswaran S.
Published: November 2020

This paper is concerned with the vibrations of an Euler-Bernoulli stepped cantilever, clamped to a hub rotating at a constant speed. The system parameters are: the speed of rotation of the hub, the position of the step, the ratio of the mass per unit length of the two portions of the beam and the ratio of the flexural rigidity. Analytical solution of the mode shape differential equations for out-of-plane vibrations (normal to the plane of rotation) is developed. The frequency equation is expressed as a 4th order determinant equated to zero. A scheme is presented to derive the natural frequencies. The first three frequencies are tabulated for various combinations of the system parameters. Published results (which were obtained via finite element procedure) are compared with the analytical results.
Analysis of Degenerate Bifurcation in Machining Using a Nonlinear Model
Authors: Fofana M. S. , Bukkapatnam Satish
Published: November 2020

We present a two degrees of freedom model of machining dynamics that compactly captures the nonlinear effects of regeneration, tool wear and plowing under orthogonal machining. Extensive simulation experiments show that the solutions to the governing equations of the model bear distinct similarities to signals from our earlier experiments, as reflected by both visual state portraits as well as the values of the quantifiers of a steady state dynamic system. Governing equations of the model lead to nonlinear delay differential equations, which we reduce to ordinary differential equations using Hopf bifurcation theorem and centre manifold theorem. Despite the ongoing efforts by the authors of this paper to quantify the simulations results analytically and experimentally, we strongly believe that our proposed model will be found to be amenable for studying and analyzing bifurcations that can lead to chatter in machining.
Twinkling Phenomena in Snap-Through Oscillators
Authors: Feeny Brian F. , Diaz Alejandro R.
Published: November 2020

Oscillatory behavior in a chain of masses connected by continuous, non-monotonic stiffness (snap-through) elements can be induced under quasi-static loading. Insight into the birth of this behavior is obtained from a single mass system. A bifurcation study shows the potential for equilibrium jumps between multiple equilibria. As such, the transients occurring under quasi-static loading do not converge to the static loading case.
Unified Approach for Noisy Nonlinear Mathieu-Type Systems
Authors: Namachchivaya N. Sri , Sowers Richard B. , Van Roessel H. J.
Published: November 2020

The purpose of this work is to develop a unified approach to study the dynamics of a single degree of freedom system excited by both periodic and random perturbations. We consider the noisy Duffing-van der Pol-Mathieu equation as a prototypical single degree of freedom system and achieve a reduction by developing rigorous methods to replace, in some limiting regime, the original complicated system by a simpler, constructive, and rational approximation — a low-dimensional model of the dynamical system. To this end, we study the equations as a random perturbation of a two-dimensional weakly dissipative time-periodic Hamiltonian system. We achieve the model-reduction through stochastic averaging and the reduced Markov process takes its values on a graph with certain glueing conditions at the vertex of the graph. Examination of the reduced Markov process on the graph yields many important results, namely, mean exit times, probability density functions, and stochastic bifurcations.
Nonplanar Motion of a String due to Two-Frequency Excitation
Authors: Yasuda Kimihiko , Kamiya Keisuke
Published: November 2020

It is known that, under certain conditions, a stretched string subjected to a planar harmonic excitation executes nonplanar motions due to the instability of the palanar motion. In recent years, studies on bifurcations of such nonplanar motions to amplitude modulated quasiperiodic motions and chaotic motions have been reported. However no literatures on the problem of nonplanar motions due to a multi-frequency excitation are found.

In this paper, the possibility of nonplanar motions in a string due to a two-frequency excitation is studied. For this purpose two cases are considered, i.e. one in which both components of the excitation are in a plane, and one in which they are perpendicular to each other. In both cases the sum of the frequencies of the components is supposed to near to twice one of the natural frequencies of the string. Theoretical analysis using the perturbation method of multiple scales and numerical simulation are carried out to show that nonplanar motions occur.
Control of Rotary Cranes Using Fuzzy Logic
Authors: Al-mousa Amjed A. , Nayfeh Ali H. , Kachroo Pushkin
Published: November 2020

Rotary cranes (tower cranes) are common industrial structures that are used in building construction, factories, and harbors. These cranes are usually operated manually. With the size of these cranes becoming larger and the motion expected to be faster, the process of controlling them became difficult without using automatic control methods. In general, the movement of cranes has no prescribed path. Cranes have to be run under different operating conditions, which makes closed-loop control preferable.

In this work a fuzzy logic controller is introduced with the idea of split-horizon; that is, fuzzy inference engines (FIE) are used for tracking the position and others are used for damping the load oscillations. The controller consists of two independent controllers: radial and rotational. Each of these controllers has two fuzzy inference engines (FTEs). Computer simulations are used to verify the performance of the controller. Three simulation cases are introduced: radial, compound, and damping. The results from the simulations show that the fuzzy controller is capable of keeping the load-oscillation angles small throughout the maneuvers while completing them in a relatively reasonable time.
Optimal Control of Homoclinic Bifurcation in a Periodically Driven Helmholtz Oscillator
Authors: Lenci Stefano , Rega Giuseppe
Published: November 2020

The problem of avoiding the homoclinic bifurcation of the hilltop saddle of the Helmholtz equation by a shrewd choice of the shape of the external excitation is considered. The distance between the perturbed manifolds is computed by means of the Melnikov’s method, and its dependence on the shape of the excitation is emphasized. Successively, it is shown how it is possible to determine a theoretical optimal excitation which maximizes the distance between stable and unstable manifolds for a fixed excitation amplitude or, equivalently, which maximizes the critical amplitude for homoclinic bifurcation.

The practical case of a finite number of subharmonics is considered in detail. The corresponding optimal problems are solved numerically and the related optimal excitations are given. It is shown that when the number of subharmonics increases, the critical threshold for homoclinic bifurcation tends to double with respect to the reference case of harmonic excitation. Some numerical simulations are finally performed to verify the theoretical predictions and the effectiveness of the control procedure.
Control of an Elasto-Plastic Pendulum
Authors: Gerstmayr Johannes , Irschik Hans
Published: November 2020

An elasto-plastic pendulum performing large rigid-body rotations and vibrating in the small-strain regime is studied. Spatial distribution of plastic zones within the beam-type pendulum is taken into account. The problem is described by a differential algebraic system of equations for the flexural coordinates and the rotation of the pendulum. This system of equations can be interpreted as a model for an elastic background pendulum under the action of additional sources, formed by the plastic parts of strain. Since the elastic pendulum is a Hamiltonian system, it is possible to control the motion of the elastic pendulum by means of a collocated PD-controller. Especially, we consider the problem of bringing the tip of the elastic pendulum into its upward (inverted) position by means of a control moment acting at the fixed end. We then apply the controller designed for the elastic pendulum to the elasto-plastic model, assuming that the yield level of the material was lowered considerably by some environmental influences. Since the effect of plasticity is dissipative, the controlled elasto-plastic pendulum turns out to reach an equilibrium position, which however does not exactly coincide with the upward target position. This deviation is due to the permanent deformations induced in the pendulum by plasticity, and it is demonstrated in a numerical study.
Application of a Sliding Mode Observer for Dynamic Positioning of Ships
Authors: Kim Myung-Hyun , Inman Daniel J.
Published: November 2020

A robust nonlinear observer, utilizing the sliding mode concept, is developed for the dynamic positioning of ships. The observer provides the estimates of linear velocities of the ship and bias from slowly varying environmental loads. It also niters out wave frequency motion to avoid wear of actuators and excessive fuel consumption. The main advantage of the proposed observer is in its robustness. In particular, the observer structure with a saturation function makes the proposed observer robust against neglected nonlinearities, disturbances and uncertainties. Since the mathematical model of DP ships is difficult to obtain and includes uncertainties and disturbances, it is very important for the observer to be robust. A nonlinear output feedback controller is derived based on the developed observer using the observer backstepping technique, and the global stability of the observer and control law is shown by Lyapunov stability theory. A set of simulations was carried out to investigate the performance of the proposed observer for dynamic positioning of a ship.
Dynamics of Oscillator With Soft Impacts
Authors: Peterka František
Published: November 2020

The impact oscillator is the simplest mechanical system with one degree of freedom, the periodically excited mass of which can impact on the stop. The aim of this paper is to explain the dynamics of the system, when the stiffness of the stop changes from zero to infinity. It corresponds to the transition from the linear system into strongly nonlinear system with rigid impacts. The Kelvin-Voigt and piecewise linear model of soft impact was chosen for the study. New phenomena in the dynamics of motion with soft impacts in comparison with known dynamics of motion with rigid impacts are introduced in this paper.
The Use of Experimental Tests in the Formulation of Analytical Models for the Finite Forced Dynamics of Planar Arches
Authors: Alaggio Rocco , Benedettini Francesco
Published: November 2020

The role of the experimental analysis in the formulation of reduced analytical models of planar arches under a vertical, sinusoidally varying, concentrated force on the tip is analyzed in this work. After recalling the theory describing the continuous problem for different initial geometries, using a standard Galerkin procedure, two ode’s are derived and used to enlighten all the interesting phenomena exhibited by different prototypes tested in a companion experimental analysis whose results are also used to validate the shape functions used in the discretization procedure. The principal region of instability of the unimodal symmetric solution in which the nonlinear modal coupling excites antisymmetric components is studied analyzing the bifurcation conditions and the post-critical behavior.
Comparison of the Dynamics of Low Immersion Milling and Cutting With Varying Spindle Speed
Authors: Insperger Tamás , Stépán Gábor , Namachchivaya Sri N.
Published: November 2020

The stability properties of cutting processes are strongly limited by the so-called regenerative effect. This effect is originated in the presence of a time-delay in the dynamical system of the machine tool. This delay is inversely proportional to the cutting speed. Consequently, conventional cutting with a single-edge tool is modeled by an autonomous delay-differential equation (DDE). In case of milling, the varying number of cutting edges results in a kind of parametric excitation, and the corresponding mathematical model is a non-autonomous DDE. In case of low-immersion milling, this affects the stability boundaries in a substantial way. Cutting with varying spindle speed results non-autonomous DDEs where the time delay itself depends on the time periodically. A new semi-discretization method is proposed to handle the stability of these non-autonomous systems. The stability properties and corresponding bifurcations are compared in the above different cases of machining.
A Unified Framework for the Study of Periodic Solutions of Nonlinear Delay Differential Equations
Authors: Fofana M. S.
Published: November 2020

Periodic solutions of delay differential equations (DDEs) splitting into stable and unstable branches are examined in an infinite-dimensional space for fixed and multiple time delays. The center manifold theorem and the classical Hopf bifurcation theorem for the study of periodic solutions of ordinary differential equations (ODEs) are employed to reduce the infinite-dimensional character of the DDEs to finite-dimensional ODEs. Using integral averaging method, the vector field of the ODEs is converted and averaged into amplitude a and phase φ relations. From these relations bifurcation equations of the form ℑ(a, φ) = 0 for the solution branches are derived.
A Study of Chaotic Motion on Non-Linear Vibration-Isolation System
Authors: Ouyang Qing , Zhu Shi-Jian , Shi Yin
Published: November 2020

This paper deals with the vibration isolation efficiency of non-linear vibration-isolation system in a desired chaotic state. Numerical calculation shows that the response of a non-linear vibration system might have broad frequency band characterization, even though the excitation is a harmonic one if some physical parameters of the system is in certain value regimes, hence the force transferred to the supporting foundation from the isolated body will be a broad frequency band one.

The practical experimental set was designed. In order to control the system in a desired chaotic state, the isolator must be a non-linear one with variable stiffness and damping. The chaotic motion of the system was identified through phase space reconstruction and spectral analysis based on the measured test data. The result shows that it is feasible to decrease the single line spectrum component significantly in the response by means of controlling chaotic vibration.
Vibration of an Asymmetrical Shaft With Gravity and Nonlinear Spring Characteristics
Authors: Ishida Yukio , Inoue Tsuyoshi , Liu Jun , Suzuki Akihiro
Published: November 2020

When an asymmetrical shaft is supported by single-row deep groove ball bearings, nonlinear spring characteristics appear due to clearance of bearings and the stiffness of support at the shaft end differs depending on the direction because the equilibrium position of the shaft center line shifts from the center of the clearance due to gravity and misalignment of assembly. Due to the coexistence of the rotating difference in shaft stiffness, the static difference in stiffness at bearing supports and the nonlinear spring characteristics, various kinds of nonlinear parametric resonances and nonlinear forced resonances occur. In this paper, we studied vibrations of harmonic type and super-combination type. As a result, we clarified the following phenomena, such as, division of unstable range, convergence of an unstable vibration to a limit cycle, resonance curve of a hard spring type, and coexistence of a forward and a backward frequency components.
Influence of Seal Geometry on the Rotordynamic Characteristics of a Round-Hole Pattern Damping Seal
Authors: Darden J. Mark , Earhart Eric M. , Flowers George T.
Published: November 2020

In the design of high-speed rotating machinery, engineers are seeking ways to enhance rotordynamic stability margins while minimizing vibration levels. An attractive option to improve stability margins is the use of annular seals. These seals are versatile because they are effective sealing elements, possess both stiffness and damping characteristics, and are easily incorporated into a pump. Design of an effective seal requires insight into the parameters that can influence its rotordynamic characteristics. Analysis indicates that changes in clearance and taper can significantly affect direct stiffness as well as other seal characteristics. With this in mind, test results are presented for seals with identical round-hole pattern stator surface treatments at two constant radial clearances and one tapered-seal configuration. Testing is performed with a realistic, high inlet fluid preswirl condition that enables an evaluation of a given seal’s stabilizing capacity. All test results presented are for a centered seal condition at multiple shaft speeds and pressure levels. Experimental trends are consistent with theory in that gains in direct stiffness are realized with both a decrease in a seal’s radial clearance and with a convergent-taper. Also, the stabilizing capacity of the seals was significantly influenced by the configurations tested.
Driving Characteristics of Traveling Wave Ultrasonic Motor: Effect of Rotor Vibration
Authors: Nakashima Takeshi , Yoshizawa Masatsugu , Kuno Hitoshi , Tsukui Michio , Takatsuka Koro , Akuto Tsuneo
Published: November 2020

The rotor of a traveling wave ultrasonic motor was treated just only as a rigid or flexible body until now. However we examine the effects of the rotor vibration on the driving characteristics of the motor, under the assumption that the bending vibration of the rotor is induced by the stator vibration. Consequently, it is clarified theoretically that the rotor vibration produces six contact patterns between the rotor and the stator. Furthermore the experiments confirm the main theoretical results.
Friction, Instability and Parametric Studies of a Nonlinear Model for an Aircraft Brake Whirl Analysis
Authors: Sinou Jean-Jacques , Thouverez Fabrice , Jezequel Louis , Mazet Guy-Bernard
Published: November 2020

This paper presents a research devoted to the study of instability phenomena in non-linear model with a constant brake friction coefficient. The condition of stability is based on the resolution of a generalized eigenvalue problem and the limit cycle amplitude are determined by the center manifold reduction. A model is presented for the analysis of whirl mode vibration in aircraft braking systems.

In this study, a non-linear material behaviour of the brake heat stack is considered. This non-linearity is expressed as a polynomial. The model does not require the use of brake negative damping and predicts that instability can occur with a constant brake friction coefficient.

The center manifold approach is used to obtain equations for the limit cycle amplitude. The brake friction coefficient is used as unfolding parameter of the fundamental Hopf bifurcation point. The analysis shows that stable and unstable limit cycles can exist for a given constant brake friction coefficient.
Transient Dynamic Analysis of Friction Induced Vibration in Aircraft Brakes
Authors: Glaznieks Dene , Trustee Carl
Published: November 2020

This paper discusses a transient dynamic finite element approach to the investigation of aircraft brake vibration. Specific to this paper, a single wheel and brake model has been used to demonstrate the effectiveness of this approach in the prediction and resolution of brake whirl. The methodology behind this technique is discussed including the modelling of contact interface friction and brake hydraulics.
Design of a Scaled Model for a High Rise, High Speed Elevator
Authors: Zhu W. D. , Teppo L. J.
Published: November 2020

A novel scaled model is developed to simulate the linear lateral dynamics of a hoist cable with variable length in a high rise, high speed elevator. The dimensionless groups used to formulate the scaling laws are derived through dimensional analysis. The model parameters are selected based on the scaling laws subject to space and hardware constraints. It is demonstrated that while it is almost impossible to obtain a fully scaled model unless the model is extremely tall, a reasonably sized model can be constructed with sufficient accuracy. The scaling laws that are not satisfied can be rendered to have a minimal effect on the scaling between the model and prototype. In conjunction with the model design, an analysis of model tension in a closed cable loop is developed. A new movement profile, which ensures a continuous jerk function during the entire period of motion, is derived. Practical considerations that occur in the design of the model are addressed. The methodology can be used to investigate the vibration of a very long cable in other applications.
Order Reduction of Bilinear Systems Containing a Clearance
Authors: Butcher Eric A.
Published: November 2020

A technique for order reduction of nonsmooth bilinear systems of arbitrary dimension containing a clearance is presented. First, a linear-based order reduction transformation is applied. When only one master coordinate is retained, the frequency of the reduced order model may be used to approximate the bilinear normal mode (BNM) frequency of the full model. By utilizing other approximation methods previously developed via the well-known bilinear frequency relation (BFR), this result is in turn used to construct improved reduced order models whose frequencies are even better approximations to the BNM frequencies for the full model. The technique is applied to two and four degree-of-freedom bilinear systems with nonvanishing clearance or interference. The resulting approximate frequencies are compared with those obtained from numerical simulations. The advantages of the present technique include a reduced order model which uses a subset of the original physical coordinates, contains the form of the nonsmooth nonlinearity of the full model, and whose time series closely tracks that of the corresponding BNM in the full model.
Limitations in the Modal Superposition for Two-Degree-of-Freedom Systems With Impact Non-Linearities
Authors: Lamarque C.-H. , Janin O.
Published: November 2020

The possibility of building a modal superposition formula for two-degree-of-freedom mechanical systems with impacts is investigated in this paper. This formula is obtained by following the usual procedure which consists in defining generalized frequencies, masses and modes. The example of two rigid bodies colliding underlines the efficiency, as well as the limitations, of the method.
A Theoretical Model of Oscillations of Paramagnetic or Diamagnetic Structures Subject to Passive Magnetic Elements
Authors: Piombo Bruno A. D. , Bonisoli Elvio , Ruzzene Massimo
Published: November 2020

The paper presents the model of the dynamic behavior of vibrating structures where paramagnetic or diamagnetic conducting materials (such as Aluminum, Copper, Brass) are interacting with passive magnetic elements.

The magnetic model is based on the analogy of the equivalent currents method in a quasi-static open-circuit-type configuration and it is used to determine the influence of eddy currents on the dynamic behavior of structures made of conducting materials.

The effect of the magnetic interactions consists in a viscous-type damping effect as well as in an interesting stiffening effect denoted as “phantom effect”, which is modeled by adding an imaginary term to the damping coefficient.

The influence of both terms on the dynamic response of a single degree of freedom system immersed in a magnetic field is discussed for varying magnitudes of the gradient of magnetic induction.
Localization and Control of Wave Propagation in Active Periodic Fluid-Loaded Shells
Authors: Ruzzene M. , Baz A.
Published: November 2020

Periodically placed actuators are used to control the wave propagation and to localize the vibration and sound radiation of fluid-loaded shells. The filtering capabilities of the resulting periodic structure can be actively tuned by modifying the feedback control gain of the actuators thus allowing for controlling the spectral width and location of the stop and pass bands as well as introducing controlled aperiodicity in the structure.

A finite element model is developed to study the fundamental phenomena governing the coupling between the shell, actuators and the fluid domain surrounding the shell. The geometry of the shell and the fluid domain allows for the formulation of a harmonic-based model with uncoupled circumferential modes. The model is used to predict the pass and stop frequency bands for different proportional control gains and to evaluate the shell harmonic response and the sound radiation into the surrounding fluid. The obtained results indicate that the location and width of the stop bands as well as the attenuation characteristics of the shell can be modified by proper choice of the proportional control gain. Numerical simulations also demonstrate that the location of the stop bands can be identified from the frequency response function of the shell and from the sound intensity.

The tunable characteristics of the proposed active shells allow for the introduction of controlled aperiodicty through proper adjustments of the actuators’ feedback gains. Disorder in periodic structures typically extends the stopbands into adjacent propagation zones and, more importantly, localizes the vibration energy near the excitation source. Both structural response and sound radiation are evaluated for increasing levels of aperiodicity. The results presented demonstrate the effectiveness of the proposed concept as an effective means for controlling the attenuation characteristics of fluid-loaded shells and for confining both vibration and sound radiation near the excitation source. Also, the presented analysis provides an invaluable means for designing fluid-loaded shells, which are quiet over desired frequency bands and where the energy can be spatially confined in well-defined restricted areas.
Gear Vibration Analysis: An Analytical and Experimental Study
Authors: Berri Sidi M.
Published: November 2020

The present study is a combined experimental/analytical investigation of the effect of a cracked pinion tooth on the vibrational characteristics of a power transmission system. A system of nonlinear equations representing the analytical model of an experimental test rig is presented. The model includes the effect of crack size on the time-varying gear mesh stiffness. The relationship of the dynamic tooth loads to the crack size of a single cracked tooth of a spur gear pair is also shown. Comparison of the experimental and analytical vibration signals processed by using the wavelet transform show excellent agreement over a range of crack sizes and running speeds.
Simulation on the Vibration of the Hydraulic Hammer
Authors: Li Yongtang , Ting Kwun-Lon , Lei Bufang
Published: November 2020

The vibration dynamics of the lower tup slightly moved hydraulic hammer is researched for the first time by means of the method of mechanical dynamics combined with digital simulation. The blowing process and energy transformation of hydraulic hammer is analyzed. The mechanics model and the mathematical model of vibration of the hammers are established. As an example the digital simulation of vibration of 25KJ hydraulic hammer is performed. The variation curves of vibration of the lower tup and the base are obtained. It is shown from comparative research that the vibration of this new kind of hammer is much less than that of steam-driven anvil hammer. Some measures to eliminate vibration produced by the hammer furthermore are put forward.
Remedying Stereotype Threat Effects in Spectator Sports
Authors: Chang Yonghwan , Schull Vicki , Kihl Lisa A.
Published: November 2020

Attempts were made to explore the value of the multiple social identities approach in reducing the detrimental effects of stereotype threats in the context of spectator sports. A total of 150 females were recruited for a laboratory experiment. The following manipulations were implemented: (a) stereotype threat, (b) threat along with the implicit team identification activation, and (c) control. The results revealed that females in the threat condition showed a reduced level of psychological well-being; paradoxically, negative stereotypes positively influenced their self-esteem. The activation of implicit team identification alleviated the detrimental consequences of threat by inhibiting the spreading activation of harmful stereotypes regarding women in sports. The main theoretical frameworks of this study consisted of the process account of stereotype threat suggested in cognitive psychology. The authors attempted to offer a stronger understanding of the underlying mental processes of stereotype threat on women as well as an effective means to deal with its detrimental consequences.
Draft Genome Sequence of
Okeania
sp. Strain KiyG1, Assembled from Single-Amplified Genomes Collected from Cape Kiyan, Okinawa, Japan
Authors: Lewaru Muhammad Wahyudin , Nishikawa Yohei , Ide Keigo , Kogawa Masato , Hosokawa Masahito , Samuel Ashok Zachariah , Sumimoto Shinpei , Nuryadi Handung , Suda Shoichiro , Takeyama Haruko
Published: November 2020

The genus
Okeania
is a globally distributed group of microorganisms that live in shallow seabed regions. These organisms play several environmentally important roles and are also known producers of several active secondary metabolites with potential human applications. Here, we present a draft genome of
Okeania
sp. strain KiyG1 (92.7% completeness) that was assembled from four single-amplified genomes.
Genome Sequence of Citrobacter freundii AMC0703, Isolated from the Intestinal Lumen of an 11-Year-Old Organ Donor
Authors: Marsh Alan J. , Chandrashekhar Kshipra , Ng Sandy , Roach Jeff , Magness Scott T. , Azcarate-Peril M. Andrea
Published: November 2020

Citrobacter freundii
AMC0703 was isolated from the intestinal mucosa of an 11-year-old organ donor. Genome analysis revealed the presence of multiple factors potentially aiding in pathogenicity, including fimbriae, flagella, and genes encoding resistance to fluoroquinolones, cephamycin, fosfomycin, and aminocoumarin.
Whole-Genome Sequence of Fluoroquinolone-Resistant Escherichia coli HUE1, Isolated in Hokkaido, Japan
Authors: Munby Montgomery , Fujiki Jumpei , Aoki Kotaro , Kawaguchi Chika , Nakamura Keisuke , Nakamura Tomohiro , Sasaki Michihito , Sato Toyotaka , Usui Masaru , Sawa Hirofumi , Yokota Shin-ichi , Tamura Yutaka , Iwano Hidetomo
Published: November 2020

We report the complete genome sequence of
Escherichia coli
strain HUE1, isolated from the urinary catheter of a female patient, showing fluoroquinolone resistance without quinolone resistance-determining region mutations. To facilitate the exploration of the molecular characteristics of HUE1, the whole genome was sequenced using long- and short-read platforms.
Longitudinal relationship of diabetes and depressive symptoms in older adults from Mexico: a secondary data analysis
Authors: Alvarez-Cisneros Teresa , Roa-Rojas Paloma , Garcia-Peña Carmen
Published: November 2020

Introduction

Several studies have argued a causal relationship between diabetes and depression, while others have highlighted that their association is a result of common risk factors. Because Mexico is a country with a high prevalence of diabetes, and diabetes and depression are a frequent comorbidity, we chose this country to investigate the longitudinal relationship of these two conditions, focusing on the influence of demographic, health, and socioeconomic factors which could act as common risk factors for both conditions.

Research design and methods

Using the harmonized Mexican Health and Aging Study, a nationally representative sample of adults older than 50 with a response rate of 93%, we analyzed the longitudinal relationship of diabetes and depressive symptoms using ‘between-within’ random-effects models, focusing on the effect of demographic, socioeconomic and health factors.

Results

While older adults with diabetes reported a higher prevalence of depressive symptoms in the four waves of the study, there was no causal longitudinal association between them once controlling for demographic, socioeconomic and health factors (between-effect OR=0.88, 95% CI 0.77 to 1.01; within-effect OR=0.87, 95% CI 0.69 to 1.11).

Conclusions

There is no causal longitudinal association between diabetes and depression; the higher prevalence of depression among older adults with diabetes seems a result of socioeconomic and health factors that are not exclusive to respondents with diabetes but are more frequent in this group. Our results highlight the importance of prevention and control of chronic conditions as well as the role of socioeconomic inequalities in mental health.
Gestational weight gain in low-income and middle-income countries: a modelling analysis using nationally representative data
Authors: Wang Dongqing , Wang Molin , Darling Anne Marie , Perumal Nandita , Liu Enju , Danaei Goodarz , Fawzi Wafaie W
Published: November 2020

Introduction

Gestational weight gain (GWG) has important implications for maternal and child health and is an ideal modifiable factor for preconceptional and antenatal care. However, the average levels of GWG across all low-income and middle-income countries of the world have not been characterised using nationally representative data.

Methods

GWG estimates across time were computed using data from the Demographic and Health Surveys Program. A hierarchical model was developed to estimate the mean total GWG in the year 2015 for all countries to facilitate cross-country comparison. Year and country-level covariates were used as predictors, and variable selection was guided by the model fit. The final model included year (restricted cubic splines), geographical super-region (as defined by the Global Burden of Disease Study), mean adult female body mass index, gross domestic product per capita and total fertility rate. Uncertainty ranges (URs) were generated using non-parametric bootstrapping and a multiple imputation approach. Estimates were also computed for each super-region and region.

Results

Latin America and Caribbean (11.80 kg (95% UR: 6.18, 17.41)) and Central Europe, Eastern Europe and Central Asia (11.19 kg (95% UR: 6.16, 16.21)) were the super-regions with the highest GWG estimates in 2015. Sub-Saharan Africa (6.64 kg (95% UR: 3.39, 9.88)) and North Africa and Middle East (6.80 kg (95% UR: 3.17, 10.43)) were the super-regions with the lowest estimates in 2015. With the exception of Latin America and Caribbean, all super-regions were below the minimum GWG recommendation for normal-weight women, with Sub-Saharan Africa and North Africa and Middle East estimated to meet less than 60% of the minimum recommendation.

Conclusion

The levels of GWG are inadequate in most low-income and middle-income countries and regions. Longitudinal monitoring systems and population-based interventions are crucial to combat inadequate GWG in low-income and middle-income countries.