bluuebunny/crossref_metadata_2025 huggingface dataset:
Mesh Stiffness Variation Instabilities in Two-Stage Gear Systems
Authors: Lin Jian , Parker Robert G.
Published: November 2020

Mesh stiffness variation, the change in stiffness of meshing teeth as the number of teeth in contact changes, causes parametric instabilities and severe vibration in gear systems. The operating conditions leading to parametric instability are investigated for two-stage gear chains, including idler gear and countershaft configurations. Interactions between the stiffness variations at the two meshes are examined. Primary, secondary, and combination instabilities are studied. The effects of mesh stiffness parameters, including stiffness variation amplitudes, mesh frequencies, contact ratios, and mesh phasing, on these instabilities are analytically identified. For mesh stiffness variation with rectangular waveforms, simple design formulae are derived to control the instability regions by adjusting the contact ratios and mesh phasing. The analytical results are compared to numerical solutions.
Explanation of Appearance and Characteristics of Intermittency Chaos of the Impact Oscillator
Authors: Peterka František , Kotera Tadashi , Čipera Stanislav
Published: November 2020

Chaotic motion of an intermittency type of the impact oscillator appears near segments of saddle-node stability boundaries of subharmonic motions with two different impacts in motion period, which is n multiple (n ≥ 3) of excitation period. Chaotic motion arises due to an additional impact, which interrupts the process of instability. It is proved and shown by numerical simulations of the system motion. More detail characteristics of the intermittency chaos are evaluated. Described phenomena present unusual example, when transition cross special segments of saddle-node stability boundaries of subharmonic impact motions is reversible.
Topological Solitons in Non-Degenerate One-Component Chains: Part I — Analytical Study
Authors: Manevitch Leonid I. , Savin Alexander V. , Sigalov Grigori M.
Published: November 2020

For the first time, the possibility of existence of topological solitons in one-component chain with a non-degenerate potential of gradient type is proven. The existence and stability of the solitons is ensured by competing piecewise-parabolic nearest-neighbor and parabolic second-nearest-neighbor interactions. The solitons are shown to move at a unique velocity. Soliton propagation may constitute an elementary event of structural transformations in the chain.
Study of an Elastoplastic Model With an Infinite Number of Degrees of Freedom
Authors: Bastien Jérôme , Lamarque Claude-Henri , Schatzman Michelle
Published: November 2020

We deal with the dynamical behavior of continuous elasto-plastic model of Masing, consisting of infinite number of springs and dry-friction elements. Using theory of differential inclusions we provide existence and uniqueness result. Moreover, we prove that continuous model is the limit of the discrete Masing model when the number of degrees of freedom tends to infinity. Starting from known results of numerical analysis, we build an implicit Euler-like numerical scheme of order one.
Piezoceramic Springs for Structural Semi-Active Multi-Modal Vibration Control
Authors: Corr Lawrence R. , Clark William W.
Published: November 2020

The ideal of controlling the vibrations of a structure by using variable stiffness members has been around for over fifteen years. Two types of mechanical springs, Type I and II, have been devised with control laws to reduce the dynamic response of structures due to disturbances. By comparing the mechanical springs and their control laws to the novel real-time piezoceramic shunt switching techniques, it is clear that piezoceramic actuators can act similar to Type I and II mechanical springs. In this paper, piezoceramic actuators are used with three different shunt circuits (capacitance ladder, switching ground circuit, and switching resistor/inductor circuit) and are compared to their mechanical spring counterparts. A new type of spring, Type III, is introduced along with a new semi-active multi-modal control scheme for piezoceramic actuators. The new multi-modal control technique is used on a simple six degree of freedom numerical example.
Comparison of Robust Residual Vibration Suppression Capabilities of Conventional Digital Filters
Authors: Economou D. , Mavroidis C. , Antoniadis I.
Published: November 2020

Digital filters consist a quite effective robust residual vibration tool, when they are used for preconditioning any excitation function, prior to its application in a flexible system. Since a quite large number of conventional digital filters already exist, each one obtained by a different design procedure and resulting to different characteristics, a systematic comparison of their capabilities is performed. Critical design parameters are addressed, influencing the filter behavior in vibration suppression, such as the total delay introduced by the filter, the permitted residual vibration error, the robustness degree achieved and the necessary computational requirements in their implementation. It is shown, that although mere does not exist a single type of filter, simultaneously conforming to an optimal degree to all the design requirements, a large variety of conventional filters can be effectively used for the several individual residual vibration suppression requirements.
Radial Direction Position Control of a Disk Type Integrated Motor-Bearing System
Authors: Han Woo-Sup , Lee Chong-Won , Park Sung-Ho , Okada Yohji
Published: November 2020

An integrated disk type motor-bearing system having axial magnetic flux is newly invented and its design, analysis, and control methods are presented. Sinusoidal motoring currents to four symmetrically placed winding groups produce a torque, whereas control currents of the same magnitude but opposite signs added to the opposite winding groups create radial forces. The control currents are intended to break force symmetry, resulting in unbalanced radial forces. It is shown that the prototype integrated motor-bearing system built in the laboratory succeeds in stable radial direction control and operation of the rotor.
Active Wave Cancellation of the Axially Moving String
Authors: Tan Chin An , Ying Shenger
Published: November 2020

The active wave control of the linear, axially moving string with general boundary conditions is presented in this paper. Considerations of general boundary conditions are important from both practical and experimental viewpoints. The active control law is established by employing the idea of wave cancellation. An exact, closed-form expression for the transverse response of the controlled system, consisting of the flexible structure, the wave controller, and the sensing and actuation devices, is derived in the frequency domain. Two actuation forces, one upstream and one downstream of an excitation force, are applied. The proposed control law shows that all modes of the string are controlled and the vibration in the regions upstream and downstream of the control forces can be cancelled. However, these results are based on ideal conditions and the assumption of zero initial conditions at the non-fixed boundaries. Effects of non-zero boundary motions at the instant of application of the control forces are examined and the control is shown to be effective under these conditions. The stability and robustness of the control forces are improved by the introduction of a stabilization coefficient in the control law. The effectiveness, robustness and stability of the control forces are demonstrated by simulations and verified by experiments on axially moving belt drive and chain drive systems.
A Computer Algebra Approach for the Modeling and Design of Smart Piezoelectric Structures
Authors: Kugi Andreas , Schlacher Kurt
Published: November 2020

The field of applications for smart structures based on piezoelectric devices is manifold. An advantage of this technology is that one can construct spatially distributed devices. This fact requires special control techniques to use the additional freedom for the design of the overall system. The structures under consideration are composite beams and plates consisting of a large number of thin layers of laminae with and without piezoelectric properties that can be well described by Lagrangian systems. Furthermore, there exists a wide range of controller design methods. To apply this machinery, one has to derive the potentials and energy functions related to the piezoelectric structures, which is a laborious task for more complex structures. But this task can be perfectly performed by a computer algebra system. Therefore, this contribution deals with the application of the Lagrangian formalism to the modeling and design of smart piezoelectric structures, and the implementation of the proposed approach in a computer algebra system.
Nonlinear Dynamics of a Cantilever Beam Actuated by Piezoelectric Layers
Authors: Wolf K. , Gottlieb O.
Published: November 2020

The nonlinear equations of motion for a silicon cantilever beam, covered symmetrically by piezoelectric ZnO layers are derived for voltage excitation. Starting with the nonlinear description of the strain distribution in the beam for finite displacement, the Lagrangeian of the system is obtained from the electric enthalpy density. By application of Hamilton’s principle, the nonlinear equations of motion are consistently derived and truncated to third order for perturbation analysis. The evolution equations are obtained by the multiple scales method and periodic solutions to the equations of motion are determined and discussed with respect to the influence of geometric nonlinearities and nonlinear properties of the piezoelectric layer.
Self-Moving Cell Linear Motor Using Piezo Actuators
Authors: Kim Jaehwan , Lee Jinho
Published: November 2020

The concept of a new linear motor that uses piezo-stack actuator is demonstrated. The working principle is far different from the conventional inchworm motor. This motor is based on the self-moving cell concept. The linear motor has three cells and each cell is constructed with one piezo-stack actuator and a shell structure. A cell train is constructed by connecting these cells and the train is fitted into a giudeway with interference. By activating each cell in succession, the train can move along the guideway. The moving motion of the motor is tested. Since this linear motor uses piezo-stack actuator with unified clamping cell, there is possibility to produce fast speed, high resolution and large push force.
Simulation-Based Design of Hybrid Vibration Mounts
Authors: Su J. Hannsen
Published: November 2020

The simulation-based design (SBD) in this paper is a methodology that integrates and streamlines the design and analysis processes for engineering products. Its methodology is presented by starting from the method development to some specific designs of different hybrid vibration mounts. In particular, two hybrid mount designs such as the “Passive-Active Extensional” mounts, incorporating an extensional active component between a conventional mount and the jointed structure, and the “Passive-Active” mounts, adding inertial actuators to the attachment plate of a conventional mount, are considered in a realistic example to illustrate the application of SBD. It is demonstrated that the functionality and feasibility of many design alternatives and concepts can be realized by this methodology. Each design and evaluation time takes only a few minutes when this methodology is implemented in engineering software. Therefore, more optimal designs can be achieved in less time and at lower cost.
Optimization in the Simulation Based Design Environment
Authors: Kusmik W. Aldo
Published: November 2020

Simulation based design methodologies have the potential to streamline the development and continuous improvement of complex products by addressing three fundamental aspects of team-based product development initiatives: coordination, collaboration, and optimization. On-going research funded by the Office of Naval Research is seeking to augment its baseline simulation based design environment with enhanced system integration, visualization, and optimization capabilities that address these three aspects of the product development process. The inherent strengths of the existing software environment are being leveraged to support the development of these enhanced capabilities including Multi-Disciplinary Optimization methodologies that will enable the rapid convergence on high payoff system alternatives.
CVT Gear Noise in the Hybrid Car Drive Train
Authors: Maier Stefan K. , Pfeiffer Friedrich
Published: November 2020

The hybrid passenger car of the Technical University of Munich contains a complex i2-CVT-gearbox with one PIV-chain CVT-stage, six spur gears and internal clutches. This paper presents a method to access its noise emission and to identify important sources based on design parameters. A multibody system model of the gearbox and the entire drive train as set up on the testbed is built. Excitation mechanisms like impact and frictional forces between rocker pins of the chain and the discs of the CVT as well as toothing forces are modelled in detail by complex nonlinear stiffness functions. A method to calculate the A-rated equivalent continuous force level of the bearing forces, which is proportional to the sound is presented here. As it is based on a Fourier transform of the bearing force trajectories, the influence of excitation mechanisms on structural borne sound can be shown and confirmed by measurement.
Dynamics of Mechanisms With Slider Joints and Clearance
Authors: Marghitu Dan B. , Stoenescu Eleonor D.
Published: November 2020

In this study a planar mechanism with a rotating sliding joint is investigated. Periodic behavior is observed for zero clearance of the sliding joint. The sliding joint with clearance is modeled using a kinematic coefficient of restitution and a coefficient of friction. Nonlinear dynamics tools are applied to analyze the simulated data captured from the connecting rod of the mechanism. The stability of the motion is studied using the Lyapunov exponents. The largest Lyapunov exponents will be considered as a stability index for the chaotic behavior of the system with slider clearance. The chaotic behavior is studied for different clearances of the sliding joint and different angular velocities of the crank.
Squeal of a Wheel Brake With Double Shoes
Authors: Nakai Mikio , Matsushita Takuya , Yokoi Masayuki
Published: November 2020

The purpose of this paper is to investigate the squealing mechanism of a wheel brake with double shoes to develop effective treatments for the reduction. Detailed observations reveal that the squeal frequencies are closely related to the natural frequencies of the system. These squeal frequencies coincide with the frequencies of instability obtained by a linear analysis of the system. It is demonstrated that squeals are induced by the coupling of the modes of the disk and both beams, two modes of a single beam and the modes of the disk and a single beam.
An Experimental Method to Identify the Effects of Joints on Structures Using Laser Vibrometry
Authors: Ma Xianghong , Vakakis Alexander F. , Bergman Lawrence A.
Published: November 2020

A technique based on laser vibrometry is outlined for identifying the effects of bolted joints on the structural dynamics. The method is based on the comparison of the dynamics of the bolted structure to that of a “baseline” structure; e.g., a structure with similar geometry and material characteristics but no jointed interface. Hence, under identical forcing conditions, the difference in the dynamics between the actual and baseline structures can be attributed solely to the joint interface effects. Non-contacting laser vibrometry is utilized to experimentally measure these differences in the structural responses at specific frequencies. A numerical algorithm is then developed to post-process the experimental data and identify the joint effects on the dynamics. The method provides estimates for the equivalent, frequency and amplitude dependent complex modulus of the joint interface. The laser scans of the mode shapes of the systems under consideration reveal interesting dynamic phenomena such as nonlinear effects due to micro-impacts at the bolted joint as well as effects due to non-proportional damping distribution.
Vibration Control of Rope-Sway of Elevator for High-Rise Building
Authors: Otsuki Masatsugu , Nakada Ryohsuke , Yoshida Kazuo , Nagata Kosoku , Fujimoto Shigeru , Munakata Tadashi
Published: November 2020

This study presents a synthesis method of a nonstationary optimal controller with a time-varying criterion function for reducing vibration of a time-varying object such as rope of elevator and crane. For time-varying object a stationary optimal control is little effective in reducing vibration. Hence, a nonstationary optimal control method with time-varying weightings on a control input and state values is applied to the time-varying object. As an illustration, the performance of reducing vibration with respect to the rope-sway problem on a high-rise building is examined through numerical calculation. Moreover, from the viewpoint of wave propagation, we propose a method of reducing vibration with wave-absorbing controller to remove the reflected waves. Finally, the performance of these nonstationary optimal and wave-absorbing controllers are compared with that of the stationary optimal controller for case that the structure is subjected to Kobe earthquake.
Load Identification Through Wavelet Parameterization
Authors: Nordberg T. Patrik
Published: November 2020

A novel approach based on a simulation error method using a wavelet parameterization is assessed. The present study focuses on the case where the load location is known a priori as it is for the interaction between the road profile and the tyre patch for an automotive vehicle. The proposed method is a time domain technique and the resulting inverse problem is discussed from the viewpoint of two different parameterization approaches. One approach concerns Fourier coefficients and the other advocates the use of wavelet coefficients. The discretized road profile is parameterized into coefficients which greatly reduces the number of unknown parameters in the resulting non-linear optimization problem. Sensor locations are chosen in accordance with the concept of identifiability. Finally, a numerical five degree-of-freedom system illustrates the applicability and performance of the method.
Parametric Studies on Moving Axle Load Identification
Authors: Yu Ling , Chan Tommy H. T.
Published: November 2020

This study addresses the effects of various parameters on moving axle load identification when vehicles move across a bridge. Main emphases are placed on evaluation of two solutions, pseudo-inverse (PI) and Singular value decomposition (SVD) solutions, to an over-determined set of equations established under the time domain method (TDM) and frequency-time domain method (FTDM). The effects of vehicle-bridge system parameters and of measurement system parameters on the TDM and FTDM are also investigated. Assessment results based on experiments in laboratory show that the TDM is a better and non-sensitive method. The SVD technique can effectively improve identification accuracy when using TDM and FTDM particularly in the case of the FTDM.
Open-Loop Control of a Flexible Manipulator With Two Links: Experimental Results
Authors: Mimmi G. , Frosini L. , Pennacchi P. , Rottenbacher C.
Published: November 2020

This paper describes the experimental results of an open-loop control technique applied to a flexible manipulator, specially designed for space duties, in order to reduce the residual vibrations at the end of the positioning. The experimental set-up is a system with two flexible links with rectangular section connected by rotational joints. First, the experimental identification of the system parameters has been carried out. Then, four different motion inputs have been implemented. The performances of these motion inputs are compared in terms of residual vibration at the end of the positioning. The experimental results confirm the effectiveness of the motion input pre-shaping technique in the reduction of the residual vibrations.
Modal Voltages and Distributed Signal Analysis of Conical Shells of Revolution
Authors: Tzou H. S. , Chai W. K. , Wang D. W.
Published: November 2020

Conical shells and components are widely used as nozzles, injectors, rocket fairings, turbine blades, etc. Dynamic and vibration characteristics of conical shells have been investigated over the years. In this paper, electromechanics and distributed sensing phenomena of a generic double-curvature shell and a conical shell are discussed, and governing sensing signal-displacement equations are derived. Spatially distributed modal voltages and signal generations of conical shells laminated with distributed piezoelectric sensor layers or neurons are investigated based on the Donnel-Mushtari-Valsov theory. Distributed modal voltages and their various signal components of conical shell models reveal that the dominating signal component among the four contributing signal components is the circumferential membrane component. This dominance is even more significant for lower shell modes and/or deep shells. In general, high strain regions result in high signal magnitudes. Accordingly, the spatially distributed signal patterns — the modal voltages — clearly represent the modal dynamic and strain characteristics of conical shells.
Non-Linear Behavior of Flexible Rotor-Bearing System of Aero Gas Turbine
Authors: Barad Sanjay , Giridhar R. K. , Rangan P. S. Kasthuri
Published: November 2020

Turbomachineries are generally high-energy systems operating at supercritical speeds. Often, nonlinear effects and latent instabilities are encountered during its operation which significantly influence the synchronous and asynchronous response of the rotor. The cause may be fluid film bearing, seal rubs, shaft joints and couplings, varied acceleration rates. Accordingly one may have a varied response behavior viz. Sub and super-harmonic oscillations, jump phenomenon, limit cycles, etc. The development phase of an aero gas turbine engine faces such challenges and these problems have to be addressed to achieve a flight-worthy engine.

The present paper discusses two case studies encountered during the development phase of an aero-engine in detail. First, is a case study of self-excited vibration caused due to oil inadvertently trapped in the internal cavity of hollow rotor and second, is the case demonstrating jump phenomena in case of a shaft with diaphragm couplings. The results acquired are well corroborated with the feedback and benchmarks. Wherever necessary, theoretical modeling has been resorted to validate the findings and get a better insight into the problem.
Effects of Initial Geometric Imperfections on Parametric Instability of Rectangular Plates
Authors: St-Georges Lyne , Ostiguy G. L.
Published: November 2020

The authors present a rational analysis of the effect of initial geometric imperfections on the dynamic behaviour of rectangular plates activated by a parametric excitation. This subject has been extensively investigated theoretically in the past, but no experimental data seems to be complete enough to validate the theory. The main objective of this investigation is to fill this void by performing experimental tests on geometrically imperfect plates, and to highlight the geometric imperfection’s influence on resonance’s curves. The study is carried out for an isotropic, elastic, homogeneous, and thin rectangular plate. The plate under investigation is subjected to the action of an in-plane force uniformly distributed along two opposite edges, is initially stress free and simply supported. Theoretical calculation and experimental tests are performed. In the theoretical approach, a dynamic version of the Von Kármán non-linear theory is used to evaluate the lateral displacement of the plate. The test rig used in the experimentation simulates simply supported edges and can accept plates with different aspect ratio. The test plates are pre-formed with lateral deflection or geometrical imperfections, in a shape corresponding to various vibration modes. Comparison between experimental and theoretical results reveals good agreement and allows the determination of the theory’s limitations. The theory used correctly describes the behaviour of the plate when imperfection amplitude is inferior to the plate thickness.
On the Response of a Shaken Cable-Suspended Mass
Authors: Virgin L. N. , Nichols J. M. , Simmons W. N. , Plaut R. H.
Published: November 2020

A small mass is suspended by two cables which are attached at angles to a rigid frame. The frame is shaken harmonically in the horizontal direction, causing the mass to respond typically in an erratic manner as the cables alternately become taut and slack. Since the cables are assumed to be inextensional, they provide an effective impulsive force to the mass as they become taut, causing an elastic rebound (which is modeled using a coefficient of restitution) [Plaut and Farmer, 2000]. The mass is assumed to be a point mass, and motion takes place within a vertical plane. One of the practical motivations for this work is the potential for using moored buoyant devices in an attempt to mitigate wave energy.

Simulations capture the unpredictable dynamic response of the mass, despite the relatively simplistic nature of the modeling. Special care is taken to accurately model the sudden transition when a cable instantaneously becomes taut. In the general case, the motion has chaotic characteristics and Poincaré sampling provides a useful diagnostic tool [Virgin, 2000].

The experimental results also show the complex nature of the behavior. The motion of the center of mass is obtained using a video camera and the IMAQ image processing package within LabVIEW. The results agree qualitatively with simulation.
Exploiting Results of Experimental Nonlinear Dynamics for Reduced-Order Modeling of a Suspended Cable
Authors: Alaggio Rocco , Rega Giuseppe
Published: November 2020

The role of experimental nonlinear dynamics in the proper reduced-order modeling of an elastic suspended cable undergoing finite-amplitude vibrations is analyzed. Two main aspects of the problem are addressed, namely (i) the number of discretizing functions to be used in a low-order finite-degree-of-freedom theoretical model in order to detect the main features of the observed nonlinear regimes, and (ii) the capability of different orthonormal function bases employed in a specific reduced-order model to reproduce complex regimes and bifurcation scenarios. Based on results of in-depth experimental investigations of a quasiperiodic scenario to chaos in a cable/mass system, a three-degree-of-freedom model of suspended cable is formulated, and different truncated bases of approximating functions are considered. They include standard linear normal modes, and proper orthogonal modal functions obtained from variable sets of experimental proper orthogonal modes identified in different intervals of the frequency range wherein the quasiperiodic scenario develops. The performances of the ensuing discretized models and their capability to qualitatively detect some main features of the actual regular and nonregular experimental responses are investigated through computer simulations.
The Influence of Nonlinear Boundary Conditions on the Nonplanar Autoparametric Responses of an Inextensible Beam
Authors: Arafat Haider N. , Nayfeh Ali H.
Published: November 2020

The nonplanar responses of a beam clamped at one end and restrained by nonlinear springs at the other end is investigated under a primary resonance base excitation. The beam’s geometry and the springs’ linear stiffnesses are such that the system possesses a one-to-one autoparametric resonance between the nth in-plane and out-of-plane modes. The beam is modeled using Euler-Bernoulli theory and includes cubic geometric and inertia nonlinearities. The objective is to assess the influence of the nonlinear boundary conditions on the beam’s oscillations. To this end, the method of multiple scales is directly applied to the integral-partial-differential equations of motion and associated boundary conditions. The result is a set of four nonlinear ordinary-differential equations that govern the slow dynamics of the system. Solutions of these modulation equations are then used to characterize the system’s nonlinear behavior.
Equations of Motion of an Aircraft Wing Modeled As a Composite Plate-Beam Model Including the Rigid-Body Motion
Authors: Emam Samir A. , Nayfeh Ali H. , Hendricks Scott L.
Published: November 2020

The equations of motion of an aircraft wing modeled as a composite beam are presented. The contribution of the rigid-body motion is taken into account; it affects the response of the wing, especially in maneuvers. The Hamilton principle is used to derive the equations of motion and the corresponding boundary conditions.
Nonlinear Dynamics of a Flexible Spinning Disc Subjected to Combined External and Parametric Excitation
Authors: Jana Anirban , Raman Arvind
Published: November 2020

This paper analyzes the nonlinear transverse vibrations of a clamped-free, uniform, flexible, annular disc, spinning about its axis with a constant angular velocity, and subjected to transverse loading from a pre-compressed spring. This is representative of a large class of loadings in rotating disc systems including air jet and electromagnetic excitation. Such loading can induce a simultaneous critical speed resonance and parametric instability. The disc is modelled by the Von Karman field equations, which are then discretized by a Galerkin projection onto a pair of 1-1 internally resonant modes. First order averaging is used to predict the dynamics of the forward and backward travelling waves (FTW and BTW). Equilibrium branches of the BTW amplitude and phase equations and their stability are studied for various combinations of parameters. The response is substantially different from that arising from a critical speed resonance or of a parametric instability alone. As many as five equilibrium solutions can coexist. Two distinct regimes of large amplitude response appear to exist depending on the relationship between the strength of the parametric excitation and the damping. The existence of these regimes underscores the subtle competition between critical speed resonance and parametric instability in such systems.
Studies on Codimension-3 Degenerate Bifurcations of the Flexible Beam
Authors: Zhang Wei , Wang Feng-Xia , Wen Hong-Bo
Published: November 2020

We present the analysis of codimension-3 degenerate bifurcations of a simply supported flexible beam subjected to harmonic axial excitation. The equation of motion with quintic nonlinear terms and the parametrical excitation for the simply supported flexible beam is derived. The main attention is focused on the dynamical properties of the global bifurcations including homoclinic bifurcations. With the aid of normal form theory, the explicit expressions of normal form associated with a double zero eigenvalues and Z2-symmetry for the averaged equations are obtained. Based on the normal form, it has been shown that a simply supported flexible beam subjected to the harmonic axial excitation can exhibit homoclinic bifurcations, multiple limit cycles, and jumping phenomena in amplitude modulated oscillations. Numerical simulations are also given to verify the good analytical predictions.
Perturbation Solution for Secondary Bifurcation in the Quadratically-Damped Mathieu Equation
Authors: Ramani Deepak V. , Rand Richard H. , Keith William L.
Published: November 2020

This paper concerns the quadratically-damped Mathieu equation:x..+(δ+ϵcos⁡t)x+x.|x.|=0. Numerical integration shows the existence of a secondary-bifurcation in which a pair of limit cycles come together and disappear (a saddle-node bifurcation of limit cycles). In δ–ϵ parameter space, this secondary bifurcation appears as a curve which emanates from one of the transition curves of the linear Mathieu equation for ϵ ≈ 1.5. The bifurcation point along with an approximation for the bifurcation curve is obtained by a perturbation method which uses Mathieu functions rather than the usual sines and cosines.
The Role of Nonlinear Strain-Displacement Relation on the Geometric Stiffening of Rotating Flexible Beams
Authors: Trindade Marcelo A. , Sampaio Rubens
Published: November 2020

Geometric stiffening of rotating flexible beams has been largely discussed in the last two decades. Several methodologies have been proposed in the literature to account for the stiffening effect in the dynamics equations. This work aims first to present a brief review of the open literature on this subject. Then, a general nonlinear model is formulated using a nonlinear strain-displacement relation. This model is then used to deeply analyze simplified models arising in the literature. In particular, the assumption of steady-state values for the centrifugal load is analyzed and its consequences are discussed.
Efficient Dynamic Simulation of Flexible Link Manipulators With PID Control
Authors: Arts Ronald G. K. M. , Jonker J. B.
Published: November 2020

For accurate simulations of the dynamic behavior of flexible manipulators the combination of a perturbation method and modal analysis is proposed. First, the vibrational motion is modeled as a first-order perturbation of a nominal rigid link motion. The vibrational motion is then described by a set of linear time-varying equations. Next, the number of degrees of freedom is reduced by applying a modal reduction technique. The proportional part of the control system is explicitly included in the modal analysis. The applicability of the method is demonstrated by simulating the controlled trajectory motion of a spatial flexible three-degree of freedom manipulator with PID control.
Power-Electronics Converters: A Field Rich in Discontinuities
Authors: Nayfeh Ali H. , Mazumder Sudip K.
Published: November 2020

We demonstrate the need for treating switching converters as discontinuous systems in order to properly analyze their dynamics and stability. We also outline some concepts related to the stability analysis of these variable-structure systems. Using these concepts, we investigate the stability and dynamics of a stand alone and an integrated DC-DC buck converter, which represents a nonlinear dynamical system under closed-loop operation. We compare the results with some of the existing ones, which are based on small-signal analyses, and demonstrate the shortcomings of the latter.
A Simple Method of Chaos Detection in Mechanical Systems With Discontinuities
Authors: Stefanski Andrzej , Kapitaniak Tomasz , Brindley John
Published: November 2020

A novel method of estimation of the largest Lyapunov exponent for discrete maps is introduced and evaluated for chosen examples of non-smooth dynamical systems. The method exploits the phenomenon of synchronization of two identical discrete maps when one of them is disturbed. Applications of the method for mechanical systems with discontinuities are presented and discussed.
Finding All Solutions of Non-Linear Oscillators via Interval Analysis
Authors: Karashima Kosuke , Nakai Mikio
Published: November 2020

When on finding all solutions of non-linear equations, there are some problems on the initial value. The problems remain in our developed R-B method which is one of the search procedures for finding all solutions of non-linear oscillators. The Krawczyk algorithm of the interval analysis for finding all solutions of nonlinear equations is useful for solving the initial value problem. In this paper, the Krawczyk algorithm is applied to the R-B method to find all solutions. The validity of this method is verified by an application to find all steady state periodic solutions in the Duffing equation.
Experimental and Simulational Investigation of Chaotic Behavior in Bilinear System With Clearance
Authors: Hossain Md. Zahid , Mizutani Kazuki , Sawai Hideki
Published: November 2020

Chaos and multiple periods have been demonstrated in this paper for harmonically excited bilinear spring and damping system with clearance. Experiment along with the simulation is considered for the investigation on the bilinear characteristics with clearance problem. The investigation is based on frequency response curves, and has been taken advantages of all data displaying techniques to understand the dynamics of the system. The position of the balance point of the system, spring stiffness ratio of the two spring of the bilinear model, and the extent of the clearance have been found very important factors to be shown chaotic motion. The effects on motion by the changing of the each factors are elaborately discussed in this study through the frequency response and the bifurcation in the both of the experiment and the simulation for a wide frequency region.
The Swing Vibration and Transverse Oscillation of a Cracked Rotor and the Intermittence Chaos
Authors: Meng G. , Qin W. Y. , Zhang T.
Published: November 2020

This paper studies the nonlinear dynamic response of a cracked rotor by taking the swing vibration of disc into consideration. The results show that if small crack appears, the frequency of transverse oscillation is synchronous with rotating speed ratio (Ω), and the frequency of swing vibration is NΩ (N = 1, 2 …). As the crack increases, the response becomes chaos in some range of Ω. The deeper the crack is, the wider the chaos range of Ω is. Routes to chaos include intermittence to chaos and quasi-period to chaos. When crack is fairly deep, there come some new resonance regions. In these regions, the response becomes infinity rapidly. The appearance of intermittence chaos is induced by the frequent frustration of stable oscillation, which is resulted from the continuous increase of swing amplitude. Unbalance parameter U is effective in suppressing chaos. Crack angle β can not affect the essence of response but can influence the amplitude of synchronous response.
Application of Finite Element Method in Time Domain to a Rotor System With Nonlinear Supports
Authors: Wang Liguo , Huang Wenhu , Hu Chao
Published: November 2020

A new method for analyzing periodic response of rotor dynamic system with nonlinear supports is presented in this paper. Based on a finite element formulation in the time domain, this method transforms nonlinear differential equations governing the dynamic behavior of rotor-bearing system into a set of nonlinear algebraic equations that can be reduced and calculated by the characteristic set of Wu elimination method. The analytic solution of the nodal displacement has been obtained finally. According to this result the behavior of periodic response is analyzed. The feasibility and advantage of the proposed method are illustrated with an example of flexible Jeffcott rotor-bearing system with nonlinear supports.
Coupling Vibration Analysis of Blood Vessels
Authors: Miao Jingliang , Liu Haixiang
Published: November 2020

This paper proposes and analyzes a simple dynamic model of blood vessel wall. By studying the coupled vibration of blood flow and vessel wall, one can get the natural frequency of a blood vessel. The method used here is generalized calculus of variations. The results show that the flexibility of blood vessels has a greater influence on the fundamental frequency of the coupled vibration and the viscosity of blood vessel has little effect on the frequency of the coupled vibration but has a greater effect on the amplitude of the vibration. Therefore it is important to control both the viscosity and flexibility of blood vessels.
Control of Magnetic Bearing Spindles During N-Waved Machining
Authors: Gosiewski Zdzislaw , Sawicki Jerzy T. , Bischof Kenneth R.
Published: November 2020

The parametric equations of the desired spindle shaft motion in tool plane are derived and the optimal motions of the shaft in the magnetic bearing planes are calculated. It is assumed that the non-circular orbit of the spindle shaft is a desired operating points set from a control system point of view, and this operation point is a known (i.e., programmed) function of time and angular position. The function is programmed in such a way, that its time constants are much bigger than time constants of the control system that should place the geometrical center of the shaft in the operation point, so dynamics of the programmed motion can be omitted. The parameters of linearized model of the open-loop system are strongly influenced by the position of the operating point. Therefore, the adaptive control system namely gain-scheduling method is designed.
Smart Structures: Gas Turbine Engine Applications
Authors: Fleeter Sanford , Lawless Patrick B.
Published: November 2020

This paper is directed at providing the smart structure technology community an introduction to aircraft gas turbine engines issues that might be addressed, i.e. smart/active propulsion systems. Specifically, in gas turbine engines, smart structures can (1) influence performance, stability, noise and high cycle fatigue by providing airfoil aerodynamic control, (2) alleviate or avoid high cycle fatigue due to flutter and forced response by introducing damping intra structures, and (3) provide health monitoring. However, the benefits-to-cost ratio of the added complexity of incorporating smart materials into gas turbine engines must be large as smart materials and actuator/control systems are not a simple solution to complex problems. The prime selling point of smart structure technology to current state-of-the-art gas turbine engines may be adaptability to age, mission, and the environment.
Using Triaxial Accelerometer Data for Vibration Monitoring of Helicopter Gearboxes
Authors: Tumer Irem Y. , Huff Edward M.
Published: November 2020

Typical vibration monitoring systems for helicopter gearboxes rely on single-axis accelerometer data. This paper investigates whether triaxial accelerometers can provide crucial flight regime information for helicopter gearbox monitoring systems. The frequency content of the three different directions is compared and analyzed using time-synchronously averaged vibration data. The triaxial data are decorrelated using a mathematical transformation, and compared to the original axes to determine their optimality. The benefits of using triaxial data for vibration monitoring and diagnostics are explored by analyzing the changes in the direction of the principal axis of vibration formed using all three axes of vibration. The statistical variation introduced due to the experimental variables is further analyzed using an Analysis of Variance approach to determine the effect of each variable on the overall signature. The results indicate that triaxial accelerometers can provide additional information about the frequency content of helicopter gearbox vibrations, providing researchers and industry with a novel method of capturing and monitoring changes in the baseline vibration signatures.
Modelling and Analysis of Frictional Phenomena in Dynamical Systems
Authors: Bogacz Roman , Ryczek Boguslaw
Published: November 2020

The paper deals with investigation of a self-excited vibrating system with dry friction. The system is composed of a mass connected by viscoelastic element with the referring frame and interacting with a moving belt by means of dry friction. An experimentally identified, multi-parametric dry friction model for the pair composed of soft and hard elements like steel-polyester pair, describing both the case of stick-slip and quasi-harmonic vibration, has been applied. Additionally, the system is influenced by external, two-frequency kinematic excitation. The results of computer simulation for different excitation conditions is submitted in the present paper.
Investigating Coaching Behaviors During the COVID-19 Pandemic: A Case Study Within a Case Study
Authors: Glen Jonathan , Gordon Julie , Lavallee David
Published: November 2020

The purpose of this case study is to offer reflections for both applied researchers and practitioners on our experiences of investigating coaching behaviors during the COVID-19 pandemic. The case is based on the delivery of remote, online tennis coaching sessions to children over a period of 3 weeks. Questionnaire, observation, and focus group data were collected from tennis players, coaches, and parents/guardians. Analyses revealed similarities and differences with previous investigations measuring coaching behaviors, as well as the perceived effectiveness of sports coaching in an online environment. Novel insights and recommendations for applied researchers and practitioners in sport and exercise psychology are highlighted, including the importance of staying connected during the pandemic, keeping players and parents motivated, and creativity. The authors consider the context of conducting a case study into coaching behaviors during the COVID-19 pandemic itself, and conclude by providing reflections on our case studywithinthe case study of COVID-19. These include enhanced communication (as it was easier to connect with each other), the nature of the online delivery improving presession preparation, and the research process being relatively more straightforward to implement, all due to barriers being removed as a direct result of COVID-19 quarantine, stay-at-home restrictions.
Seroprevalence of anti–SARS-CoV-2 IgG antibodies in Kenyan blood donors
Authors: Uyoga Sophie , Adetifa Ifedayo M. O. , Karanja Henry K. , Nyagwange James , Tuju James , Wanjiku Perpetual , Aman Rashid , Mwangangi Mercy , Amoth Patrick , Kasera Kadondi , Ng’ang’a Wangari , Rombo Charles , Yegon Christine , Kithi Khamisi , Odhiambo Elizabeth , Rotich Thomas , Orgut Irene , Kihara Sammy , Otiende Mark , Bottomley Christian , Mupe Zonia N. , Kagucia Eunice W. , Gallagher Katherine E. , Etyang Anthony , Voller Shirine , Gitonga John N. , Mugo Daisy , Agoti Charles N. , Otieno Edward , Ndwiga Leonard , Lambe Teresa , Wright Daniel , Barasa Edwine , Tsofa Benjamin , Bejon Philip , Ochola-Oyier Lynette I. , Agweyu Ambrose , Scott J. Anthony G. , Warimwe George M.
Published: November 2020

Pandemic progress in Kenya

By the end of July 2020, Kenya had reported only 341 deaths and ∼20,000 cases of COVID-19. This is in marked contrast to the tens of thousands of deaths reported in many higher-income countries. The true extent of COVID-19 in the community was unknown and likely to be higher than reports indicated. Uyoga
et al.
found an overall seroprevalence among blood donors of 4.3%, peaking in 35- to 44-year-old individuals (see the Perspective by Maeda and Nkengasong). The low mortality can be partly explained by the steep demographics in Kenya, where less than 4% of the population is 65 or older. These circumstances combine to result in Kenyan hospitals not currently being overwhelmed by patients with respiratory distress. However, the imposition of a strict lockdown in this country has shifted the disease burden to maternal and child deaths as a result of disruption to essential medical services.

Science
, this issue p.
79
; see also p.
27
A Chimeric Plasmodium vivax Merozoite Surface Protein Antibody Recognizes and Blocks Erythrocytic P. cynomolgi Berok Merozoites
In Vitro
Authors: Shen Fei-hu , Ong Jessica Jie Ying , Sun Yi-fan , Lei Yao , Chu Rui-lin , Kassegne Kokouvi , Fu Hai-tian , Jin Cheng , Han Eun-Taek , Russell Bruce , Han Jin-Hee , Cheng Yang
Published: November 2020

Research on erythrocytic
Plasmodium vivax
merozoite antigens is critical for identifying potential vaccine candidates in reducing
P. vivax
disease. However, many
P. vivax
studies are constrained by its inability to undergo long-term culture
in vitro
.
Effective Inhibition of SARS-CoV-2 Entry by Heparin and Enoxaparin Derivatives
Authors: Tandon Ritesh , Sharp Joshua S. , Zhang Fuming , Pomin Vitor H. , Ashpole Nicole M. , Mitra Dipanwita , McCandless Martin G. , Jin Weihua , Liu Hao , Sharma Poonam , Linhardt Robert J.
Published: November 2020

The emergence of severe acute respiratory syndrome coronavirus (SARS-CoV-2) in Wuhan, China, in late 2019 and its subsequent spread to the rest of the world has created a pandemic situation unprecedented in modern history. While ACE2 has been identified as the viral receptor, cellular polysaccharides have also been implicated in virus entry.