bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Analysis of a Friction Damped System Using Two Component Mode Methods
Authors: Pesheck E. , Pierre C. 
Published: February 2021

Abstract
Herein, two component mode methods are employed to investigate the forced dynamics of a cantilevered beam with an attached flexible friction damper. The first, traditional modal analysis, uses the free vibration modes of the unconstrained beam, while the second, a component mode synthesis approach, uses an alternative set of modes which confines the friction non-linearity to a single component mode. The convergence and efficiency of the two methods are compared for a particular case, and the component mode synthesis approach is found to converge at least as fast as, and usually faster than, the traditional modal analysis approach. Further analysis of the beam system is conducted and discussed using the component mode synthesis formulation.
Two-Dimensional Gas Pulsation Modeling of Compressor Manifolds
Authors: Lai Peter C.-C. , Soedel Werner 
Published: February 2021

Abstract
A general procedure for the analysis of curved or flat, thin two dimensional gas cavities such as thin compressor or engine manifolds or so-called thin shell type muffler elements, which can efficiently utilize the limited space of hermetically sealed compressors or small engine compartments, was developed. The basic assumption is that the thickness of the cavities is sufficiently small compared to the shortest wavelength of interest. The two dimensional inhomogeneous wave equation, which takes nonuniform thickness into account, is expressed in two dimensional curvilinear coordinates by the application of Hamilton’s principle. Four pole parameters are formulated from the pressure response solutions using the modal series expansion method and orthogonality property. Three gas cavities with simple geometries including a cylindrical thin cavity, a thin disk cavity and a thin spherical gas cavity are analyzed as examples. The convergence of the modal superposition is investigated. The transfer function of the thin disk cavity case is measured experimentally and compared to the theoretical results for verification. Because the back pressure at the valve location of a compressor or engine discharge port is an important issue for practical design applications, the input port impedance of the thin disk cavity from both theoretical and experimental approaches is compared. In addition, this particular thin disk model is successfully applied to a specific compressor head cavity. Both theoretical and experimental results are presented in this paper. Finally, active pulsation cancellation in the thin gas cavity can be achieved with the assistance of the above modeling procedure.
Friction Induced Vibrations: Experiments, Modelling and Analysis
Authors: Hinrichs N. , Oestreich M. , Popp K. 
Published: February 2021

Abstract
In the present paper, the dynamics of a nonsmooth friction oscillator under self and external excitation is investigated. The rich bifurcational behaviour predicted by numerical simulations is compared to experimental results. In order to predict the period and amplitude of the friction induced vibrations, the friction force can be modeled by means of friction characteristics. A more detailed look at the nonsmooth transition points of the trajectories shows that an extension of the friction model is necessary. For that aim, a bristle model, a friction contact with tangential stiffness and damping and a stochastic friction model are investigated.
Stability Analysis of Rotordynamic Systems Using Floquet Methods
Authors: Marghitu Dan B. , Flowers George T. , Szász György 
Published: February 2021

Abstract
A method of quantifying the relative stability of rotordynamic oscillations is developed. The approach is based upon application of Floquet theory, in conjunction with Poincaré mapping, to measured (and periodic) vibration data. Detailed knowledge of a dynamic model or of the internal dynamics of the system is not required. Example cases are evaluated for a rotor interacting with a clearance bearing in order to demonstrate the method. Results are presented and discussed for simulation data (obtained from a simplified model for the example system) and for measured data from an experimental test rig.
Relationships Between Acoustic Radiation Modes, Complex Acoustic Power, and Radiation Efficiency
Authors: Chen Pei-Tai 
Published: February 2021

Abstract
The paper explores the physical meaning underlying the surface complex acoustic power of a vibrating body, and its relationship to radiation efficiency under mono-frequency oscillations. The vibrating can be the entire wetted surface, or only a part of the surface with the remaining surface being held rigid. The surface complex acoustic power can be computed by the surface integral of pressure multiplying the complex conjugate of normal velocity. Based on the Gaussian Divergence theorem, it is shown that the real part of the complex power is the power radiated into a far field, while that the imaginary part pertains to the volume integral of the difference between the acoustic kinetic energy density with the potential energy density over the volume between the vibrating surface and the far field. The dynamical behavior of the acoustic field can be viewed as an infinite degree of freedom mass/spring/dashpot system, where the mass and spring are the inertia effects and acoustic compression effects of the acoustic particles and the dashpot is due to the plane wave relationship of the pressure waves at the far field that the acoustic energy propagates away from the acoustic field. By the model of the mass /spring/dashpot system, the phase angle of the complex acoustic power is identified as an indication of the ability of the vibrating surface to radiate acoustic power. The phase angle of the complex power depends on the distribution of the surface normal velocity. In order to study the normal velocity profile in relation to the ability to radiate acoustic energy, the previously established radiation mode (Chen and Ginsberg, 1995) is introduced and extended to situations in which a part of the surface is held rigid. An orthogonal condition for the velocity radiation modes is also established such that arbitrary velocity profiles can be decomposed into radiation modes. The acoustic modal radiation efficiency, defined as the radiated modal acoustic power divided by the surface integral of mean square normal velocity, is investigated in terms of the acoustic eigenvalue of that mode. Several different geometries of vibrating bodies are used to demonstrate the correlation of radiation efficiencies to eigenvalues of radiation modes, which include a rectangular baffled vibrating membrane, a box with only one of the six surfaces vibrating, a slender spheroidal body, and a spherical body. This correlation of acoustic radiation characteristics for different geometries is also demonstrated for a spheroidal body vibrating at some areas with other areas being held rigid.
Analytic Study of Discreteness Effects in a String Resting on a Periodic Array of Vibro-Impact Supports
Authors: Salenger Gary D. , Vakakis Alexander F. 
Published: February 2021

Abstract
We analyze the forced oscillations of an infinite string supported by an array of vibro-impact supports. The envelope of the excitation possesses ‘slow’ and ‘fast’ scales and is periodic with respect to the ‘fast’ scale. The ‘fast’ spatial scale is defined by the distance between adjacent nonlinear supports. To eliminate the singularities from the governing equations of motion that arise due to the discrete nature of the supports, we employ the nonsmooth transformations of the spatial variable first introduced in (Pilipchuk, 1985) and (Pilipchuk, 1988). Thus, we convert the problem to a set of two nonhomogeneous nonlinear boundary value problems which we solve by means of perturbation theory. The boundary conditions of these problems arise from ‘smoothness conditions’ that are imposed to guarantee sufficient differentiability of the results. The transformed system of equations is simplified using regular perturbation and harmonic balancing. Standing solitary wave solutions reflecting the discreteness effects inherent in the discrete foundation are calculated numerically for the unforced system.
Numerical and Experimental Analysis of the Nonlinear Dynamics due to Impacts of a Continuous Overhung Rotor
Authors: Azeez Mohammed F. Abdul , Vakakis Alexander F. 
Published: February 2021

Abstract
This work is aimed at obtaining the transient response of an overhung rotor when there are impacts occurring in the system. An overhung rotor clamped on one end, with a flywheel on the other and impacts occurring in between, due to a bearing with clearance, is considered. The system is modeled as a continuous rotor system and the governing partial differential equations are set up and solved. The method of assumed modes is used to discretize the system in order to solve the partial differential equations. Using this method numerical experiments are run and a few of the results are presented. The different numerical issues involved are also discussed. An experimental setup was built to run experiments and validate the results. Preliminary experimental observations are presented to show qualitative comparison of theory and experiments.
Control Effectiveness of Segmented Actuators Laminated on Ring-Shells
Authors: Ye R. , Bahrami H. , Tzou H. S. 
Published: February 2021

Abstract
Distributed control effectiveness of ring-shells laminated with segmented actuators is investigated in this paper. A new laminated quadratic piezoelastic triangular shell FE is developed using the layerwise constant shear angle theory. Element and system equations are also derived. The developed piezoelastic triangular shell element is used to model a semi-circular ring shell with various segments of distributed piezoelectric actuators. Finite element (triangular shell FE) solutions are compared with the theoretical, experimental, and finite element first. Natural frequencies and distributed control effects of the ring shell with different length of piezoelectric actuators are also studied. Control effectiveness is evaluated and optimal length of the actuator is recommended.
Nonlinear Modes in Systems With Strong Nonlinearities
Authors: King Melvin E. 
Published: February 2021

Abstract
In this paper, a symbolic/numeric method is developed to compute nonlinear normal modes (NNMs) in conservative, two-degree-of-freedom (2-DoF) systems. Based upon the notion of NNMs, periodic motions are sought during which the two coordinates ‘vibrate-in-unison’. By parameterizing the response of one coordinate with respect to the response of the other (reference) coordinate and by imposing conservation of energy, we obtain a nonlinear, singular ordinary differential equation. Approximate solutions for these modal functions are obtained, for a given energy level, via truncated power-series expansions. The coefficients of the expansion, along with the maximum and minimum reference displacements, are then computed by (i) symbolically evaluating the singular differential equation at various (distinct) reference displacements, and then (ii) numerically solving the resulting set of nonlinear algebraic equations. Since the approximate solution inherently depends upon the order of the expansion, convergence studies must be performed in order to ensure sufficient accuracy. Note that even though the formulation presented herein is based on 2-DoF systems, the methodology is quite general and can readily be extended to higher-order discrete systems. Moreover, since it does not rely upon any ‘small-quantity’ assumptions, it can be used to investigate the dynamics of coupled, strongly nonlinear systems.
On Residual Vibration Control of Time-Varying Redundant Open-Chain Linkage With Joint and Link Flexibility
Authors: Shigang Yue 
Published: February 2021

Abstract
Residual vibration control of time-varying redundant open-chain linkage with link and joint flexibility is studied in this paper. The control equations of the flexible open-chain linkage is time-varying. Computer simulation of a planar flexible open-chain linkage with only one degree of redundancy shows that the residual vibration is decreased effectively, thus the endpoint is almost stabel at the fixed point though compensation is not considered.
Dynamics of Two Coupled Van der Pol Oscillators With Delay Coupling
Authors: Wirkus Stephen , Rand Richard 
Published: February 2021

Abstract
We investigate the dynamics of a system of two van der Pol oscillators with delayed velocity coupling. We use the method of averaging to reduce the problem to the study of a slow-flow in three dimensions. In particular we study the stability of the in-phase and out-of-phase modes, and the bifurcations associated with changes in their stability. Our interest in this system is due to its relevance to coupled laser oscillators.
A Comparison of Analytical Methods for Studying a Single-DOF Nonlinear System
Authors: Guttalu Ramesh S. , Flashner Henryk 
Published: February 2021

Abstract
Qualitative analysis of periodic nonlinear dynamical systems is often carried out using perturbation and averaging methods. Important topics of study for this class of systems are determination of periodic solutions, their stability analysis and their bifurcation characteristics. Since perturbation and averaging methods rely on expanding the solution in terms of a small parameter, important questions such as convergence and accuracy of the solution arise which are often difficult to answer. This paper presents a preliminary study of the comparison of the method of averaging, Liapunov-Floquet transformation, and point mapping. The methods are applied for the analysis of a damped pendulum subjected to periodic support motion. To evaluate the accuracy of various methods, the results of stability analysis are compared with direct numerical solution for different parameter values of the system.
Dynamic Response of a Spinning Timoshenko Shaft With Coupled Bending and Torsion
Authors: Zu Jean W. , Wong Edward 
Published: February 2021

Abstract
The dynamic behavior of a simply-supported spinning Timoshenko shaft with coupled bending and torsion is analyzed. This is accomplished by transforming the set of nonlinear partial differential equations of motion into a set of linear ordinary differential equations. This set of ordinary differential equations is a time-varying system and the solution is obtained analytically in terms of Chebyshev series. The analytical method is a viable alternative to numerical methods and can provide the full range of the required solutions. A beating phenomenon is observed from the numerical simulations. This phenomenon occurs when the system has two natural frequencies close to each other. It is also shown that the period of torsional vibrations is much shorter than the period of oscillations in transverse deflections and in bending angles.
Prevention of Low-Frequency Vibration of High-Capacity Steam Turbine Units
Authors: Kanki H. , Kaneko Y. , Kurosawa M. , Yamamoto T. , Yamamoto Y. , Ninomiya F. 
Published: February 2021

Abstract
The causes of low-frequency vibration (subsynchronous vibration) of a high pressure turbine were investigated analytically and also via vibration excitation tests on actual machines under operation. From the results, it was concluded that low-frequency vibrations may be caused by either the decrease of the rotor system damping or by external forces, such as flow disturbance in the control stage and the rubbing between the rotor and casing. After identifying the cause of the low-frequency vibration, appropriate countermeasures such as installation of a squeeze-film damper and modification of valve opening sequence were taken. Vibration measurements and vibration excitation tests for the high pressure turbine under actual operating conditions were carried out in order to verify the validity of the countermeasures. These field tests confirmed that the problems of low-frequency vibration can be solved completely by taking the appropriate countermeasure depending on the cause of the vibration.
This paper presents some field experiences of low-frequency vibration and the effective solution approach.
Wave Propagation Analysis of an Axially Strained, Rotating Timoshenko Shaft: Part I
Authors: Kang Bongsu , Tan Chin An 
Published: February 2021

Abstract
In this paper, transverse waves propagating in an infinitely long, rotating Timoshenko shaft subjected to axial forces are studied. The model includes the contributions of axial deformation to the transverse vibration of the rotating shaft. Four different types of wave motions, two cutoff frequencies and frequency spectra are defined and discussed. The wave reflection and transmission characteristics of the shaft at arbitrary point supports are also examined by deriving the reflection and transmission matrices for an incident waves upon a general intermediate support. Numerical results showing the effects of axial force, shaft rotation speed, shear deformation, and rotary inertia on the wave reflection and transmission coefficients for classical supports are presented for both the Timoshenko and Euler-Bernoulli beams. It is found that the wave motions are generally independent of the rotation speed and the axial load affects significantly the wave motions at small real wavenumbers.
Unidirectional Excitation Technique for Complex Modal Testing of Asymmetric Rotor Systems: Application to DTG
Authors: Lee Seok-Ku , Lee Chong-Won 
Published: February 2021

Abstract
Unidirectional excitation technique is presented for the complex modal testing of asymmetric rotor systems. The theoretical development, which is made strictly in the stationary coordinate system, enables the unidirectional excitation to effectively estimate the directional frequency response functions. It far lessens the testing efforts a numerical example of the dynamically tuned gyroscope (DTG) is treated to demonstrate the practicality of the complex modal testing.
A Comprehensive Torsional Vibration Analysis Procedure: Part I
Authors: Corbo Mark A. , Malanoski Stanley B. 
Published: February 2021

Abstract
One of the foremost concerns facing turbomachinery users today is that of torsional vibration. In contrast to lateral vibration problems, torsional failures are especially heinous since the first symptom of a problem is often a broken shaft, gear tooth, or coupling. The difficulty of detecting incipient failures in the field makes the performance of a thorough torsional vibration analysis an essential component of the turbomachinery design process.
The aim of this paper1 is to provide users with a practical design procedure that can be used to ensure that their systems will not encounter major difficulties in the field. It has been the authors’ experience that most turbomachinery users encounter little difficulty in determining their machine’s natural frequencies due to the large number of resources available in that area. However, problems often arise when they must translate this information into an accurate prediction of whether or not their design will experience torsional vibration problems. Accordingly, this two-part paper concentrates on the steps that should be taken once the natural frequencies have been found.
Effect of Crack on the Natural Frequency of Rotating Twisted Blades
Authors: Neogy Sumanta , Ramamurti V. 
Published: February 2021

Abstract
Cracks appearing in turbo machine blades during manufacture or operation is not an impossibility. Such cracks may lead to failure of the blade. Previous work by the authors has considered the feasibility of natural frequency as a parameter for damage detection of blades by assuming them to be nonrotating. The present work more realistically models a blade by accounting for the effect of rotation. It not only brings out as to how rotation affects the fall of frequency in presence of crack but also hints at the unsuitability of natural frequency as a criterion for crack diagnosis.
Experimental Investigation of Dynamic Nonlinearities in Rotating Machinery
Authors: Horattas Georgios A. , Adams Maurice L. , Abdel Magied Mohammed F. , Loparo Kenneth A. 
Published: February 2021

Abstract
This paper presents laboratory experiments that confirm and further explore earlier computer simulations related to oil-whip and rub-impact. Both phenomena were explored using Spectrum Analysis, and Chaos tracking techniques (e.g. Poincare’ maps). The results show that oil-whip induces quasi-periodic rotor vibrations, while rub-impact generates complex dynamical behavior, such as chaotic vibrational motion. The nonlinear oil-whip hysteresis loop results presented confirm phenomena uncovered in previous computer simulations. A Sommerfeld number-consistent “instability threshold load” was experimentally observed, along with its corresponding hysteresis loop similar to the classic instability speed hysteresis loop, but probably the most important experimental discovery was a second Hopf bifurcation-Saddle node instability hysteresis loop (i.e., at higher speed than the classical hysteresis loop), separated by a region of stable-in-the-small operation. Another result of especially high practical importance, was the discovery that spectrum analysis of speed-up, or coast-down rotor-vibration data can be effectively used to locate the saddle node speed.
Large Amplitude Radial Oscillations of Viscoelastic Cylindrical Shells
Authors: Yu Jang-Horng 
Published: February 2021

Abstract
We study the large amplitude oscillation of a viscoelastic cylindrical shell where the energy is dissipated through the material relaxation property and the material memory function is of the farm of an exponentially decaying influence function. We construct a Lyapunov functional and show that the equilibrium is nonlineariy stable in free oscillations. Numerical simulations indicate that the equilibrium state is globally stable. For materials with fast relaxation, the motion is similar to that of Newtonian viscous solids. However, for sufficiently slow relaxation where the history effect becomes dominant, we exhibit that the solution trajectory traces a cyclone pattern in the phase plane. We finally examine a forced oscillation case with three equilibria.
Observations on the Performance of Vibration-Isolated Railway Track
Authors: Hunt Hugh E. M. 
Published: February 2021

Abstract
Vibration generated by underground railways is difficult to control because of the very limited space available in a tunnel. A popular approach is to use ‘floating slab track’ whereby the rails are fixed to a large concrete foundation separated from the tunnel wall by a resilient material. This paper investigates some of the vibration characteristics of floating slab track from measurements made in situ. These measurements are compared with the theoretical response of an infinite beam on an elastic foundation taking into account the torsional response of the beam. The transmission of vibration through the tunnel wall and into the surrounding medium is discussed with reference to the relative speed of travelling waves and the coincidence frequencies.