bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Influence of Coating Discontinuity on Sound Radiation of Submerged Structures
Authors: Pyshin Alexandr V. 
Published: March 2021

Abstract
Rubber based coatings are successfully used to reduce sound radiation of submerged structures. In some cases it is impossible to put coating continuously on the surface of a complex structure. The existing relations of architectural acoustics estimate the effect of a coating with broken continuity at high frequencies and do not work correctly at low frequencies. The solution of the task of sound radiation from a surface with given vibration and a coating layer with discontinuities is presented. New expressions for estimating an influence of coating discontinuities on the coating effect at low frequencies are obtained. It is shown that at low frequencies coating discontinuities can cause an additional gain of the noise reduction. The explanation of this phenomenon is given and the conditions of its existence are formulated. Sound radiation in dependence of the area of uncoated surface parts and the loss factor of coating material is studied.
Acoustic Finite Element Analysis of Coupled Cavities Having Bulk-Reacting Absorbing Materials
Authors: Qian A. , Ballinger R. S. 
Published: March 2021

Abstract
This research presents the finite element formulation of a bulk-reacting sound absorbing material for use in interior cavity solutions. The bulk properties of the absorbing material are represented by complex density and complex propagation speed. Coupling between the vibrating cavity structure and the acoustic medium is considered. The continuity of sound pressure and the particle velocity at the interface between the acoustic domains having different properties is satisfied. Two case studies, a one-dimensional duct and a three-dimensional cavity, are considered. Analytical solutions and experimental results are compared to the finite element results. Excellent agreement has been achieved.
Acoustic Scattering by Rigid or Elastic Structures: Case of a Shell With a “Line” Shape
Authors: Trad A. , Ravel P. 
Published: March 2021

Abstract
A modified Werner’s method is used to study, at any real arbitrary frequency, the scattering problem of full axisymetric elastic structures and for any axisymetric elastic shell. It leads to a coupled system of integral equations on the surface of the structure which governs the scattering pressure and the normal component of the displacement vector on the boundary’s structure. A finite element method is computed to calculate the scattering of elastic structures for low and medium frequency ranges. Then this method is tested on the case of a steel made sphere in a radial field and applied to a « LINE » shaped structure, which is a right cylinder ended by two half spheres on its extremities.
Friction Induced Instabilities and Sound Generation
Authors: Raous M. , Barbarin S. , Vola D. , Martins J. A. C. 
Published: March 2021

Abstract
This paper deals with the characterization of occurrence of instabilities during the sliding of a deformable body on a rigid obstacle. We focus here on the analysis of the mechanical phenomenon which leads to local microshocks that could induce noise by exciting some eigenmodes of the structure. A model with constant friction coefficient is presented to characterize the occurrence of instabilities related to friction during a quasi-static sliding by using various instability criteria : energetic (power rate) criterion, dynamic divergence instability, dynamic flutter instability. Models and numerical processes are given. A first example concerns the characterization of stress waves and friction force jumps for a photoelastic solid sliding on a plane. A second exemple is related to the noise generation during the sliding of a rubber licker on a car window. The model is applied to an experiment conducted so as to characterize the friction coefficient of the material and where instabilities have been observed in some cases.
Modeling of Rotor Shafting for Lower Mode Accuracy: Influence of Section L/D
Authors: Kirk R. G. , Baheti S. , Ramesh K. 
Published: March 2021

Abstract
The transfer matrix and finite element methods are currently widely used to model rotor shafting for calculation of critical speeds, forced response, and stability. For many rotors, long uniform shafting sections occur on the ends of the rotors which could be treated without consideration of section L/D. The use of finite element continuous mass models makes it possible to consider longer sections than previously considered using lumped inertia models. This paper will review a major mass reduction technique which has been used for transfer matrix lumped mass models and compares the results to those obtained by the continuous mass finite element method. The required section L/D for desired accuracy of the lowest eight modes of a uniform shaft (4 forward, 4 backward) will be studied for both simple property splitting and a modified major mass reduction technique. The necessary section L/D for desired accuracy for varying bearing to shaft stiffness ratios will be presented. A comparison of the finite element method required section L/D to that of the transfer matrix major mass method is presented for both a uniform shafting geometry and a typical centrifugal compressor model.
Conclusions and recommendations will be given concerning the required section L/D for improved rotor system analysis accuracy when using lumped inertia rotor models.
Prediction of Periodic Response of Rotor Dynamic Systems With Nonlinear Supports
Authors: Wang Yu 
Published: March 2021

Abstract
A numerical-analytical method for estimating steady-state periodic behavior of nonlinear rotordynamic systems is presented. Based on a finite element formulation in the time domain, this method transforms the nonlinear differential equations governing the motion of large rotor dynamic systems with nonlinear supports into a set of nonlinear algebraic equations with unknown temporal nodal displacements. A procedure is proposed to reduce the resulting problem to solving nonlinear algebraic equations in terms of the coordinates associated with the nonlinear supports only. The result is a simple and efficient approach for predicting all possible fundamental and sub-harmonic responses. Stability of the periodic response is readily determined by a direct use of Floquet’s theory. The feasibility and advantages of the proposed method are illustrated with two examples of rotor-bearing systems of deadband supports and squeeze film dampers, respectively.
Rotor Bearing System Design on Magnetic Bearings
Authors: De Choudhury Pranabesh 
Published: March 2021

Abstract
The rotordynamic analysis of a high speed multistage centrifugal compressor supported on radial magnetic bearings, which has been running successfully in the field for 9000 hours to date, is presented. Iterations required to achieve an acceptable rotor configuration using magnetic bearings are discussed. The results of the rotor-bearing system on standard fluid film five shoe tilting pad journal bearings are compared to the dynamics of the rotor on magnetic bearings.
Correlation of the observed peak responses with those predicted on magnetic bearings is presented. The actual orbit plots and frequency plots during the coastdown of the rotor-bearing system on auxiliary ball bearings are discussed.
Asymptotic Analysis of the Torsional Vibrations in Reciprocating Machinery
Authors: Ashrafiuon Hashem , Whitman Alan M. 
Published: March 2021

Abstract
A class of two degree of freedom reciprocating machines is analysed and simple asymptotic expressions for both the steady state and transient vibration levels are obtained. The results are compared with those of a standard numerical modeling package, and are found to be in good agreement for parameter values typical of real machines. This happens because real machines are designed so that the vibration levels are small, thereby satisfying the conditions for the validity of the approximation.
Entrance Effects in Annular Seal Flows
Authors: Arghir Mihai , Frene Jean 
Published: March 2021

Abstract
The paper presents the theoretical results for a test case proposed by Staubli (1993) that allows testing the procedures for predicting rotordynamic coefficients of plain annular seals. The calculations were made using the time averaged Navier-Stokes equations. The results underline the weaknesses of the traditional turbulence models. Comparisons with a thin fluid film based procedure show that the entrance zone in the seal, where the flow is not a parallel one, influences the radial force and so the direct dynamic stiffness coefficient.
Studies on Determination of Natural Frequencies of Industrial Turbine Blades
Authors: Bhat Mahesh M. , Ramamurti V. , Sujatha C. 
Published: March 2021

Abstract
Steam turbine blade is a very complex structure. It has geometric complexities like variation of twist, taper, width and thickness along its length. Most of the time these variations are not uniform. Apart from these geometric complexities, the blades are coupled by means of lacing wire, lacing rod or shroud. Blades are attached to a flexible disc which contributes to the dynamic behavior of the blade. Root fixity also plays an important role in this behavior. There is a considerable variation in the frequencies of blades of newly assembled turbine and frequencies after some hours of running. Again because of manufacturing tolerances there can be some variation in the blade to blade frequencies. Determination of natural frequencies of the blade is therefore a very critical job. Problems associated with typical industrial turbine bladed discs of a 235 MW steam turbine are highlighted in this paper.
Modal Analysis of a Laminated Stator Core
Authors: Dias M. , Weber H. I. 
Published: March 2021

Abstract
One of the main reasons for the acoustical noise and vibrations in electrical machines is the excitation of the stator due to the presence of magnetic harmonics in motors and generators. During the design of these machines one must care that the frequencies of the excitation forces do not coincide with the natural frequencies of the stator, which would increase considerably the acoustic noise levels and the vibrations.
This work concerns the study of dynamic behavior of segmented (laminated) structures that will define the natural frequency of stators. Our main interest consists in the longitudinal modes of cylindrical segmented shells where the effect of discontinuous layers is more concentrated. A comparison of proposals for modelling of stators is done with the results of experimental modal analysis of a stack of metal sheets, clamped with tie rods and with the clamping pressure controled through strain gages. A study of these structures considered orthotropic (and not isotropic as one normally assumes) is done.
Vibration Control in Turbomachinery Blading Using Lacing Wires
Authors: Wang Robert X. , Chapman Graham M. 
Published: March 2021

Abstract
In turbomachinery practice the use of inter-blade coupling is an accepted procedure. The use of lacing wires in highly stressed short blading introduces damping and also modifies the vibration characteristics of the blading. This paper reports on a study into the dynamic characteristics of single blades with a lacing wire. Vibration analysis is carried out using finite element modelling. The theoretical results are verified using Electronic Speckle Pattern Interferometry technique (ESPI).
Adaptive Virtual Autobalancing for a Magnetic Rotor With Unknown Mass Imbalance: Part I — Static Balancing
Authors: Lum Kai-Yew , Bhat Sanjay P. , Bernstein Dennis S. , Coppola Vincent T. 
Published: March 2021

Abstract
An adaptive control scheme is proposed for stabilizing a planar rotor mounted on a magnetic bearing. The control strategy involves the concept of virtual autobalancing, where the control algorithm emulates the dynamics of a mechanical autobalancer by applying forces that are equivalent to the action of the autobalancer on the rotor. Equations of motion for a planar, torque-free, elastically suspended rotor equipped with an autobalancer are derived. Based on these equations, an adaptive controller for the magnetic rotor is formulated. The results are demonstrated in simulation.
Analytical Study of Dispersion of Stress Waves in a Weakly Coupled Layered System
Authors: Vakakis A. F. , Cetinkaya C. 
Published: March 2021

Abstract
Dispersion of transient stress waves in the first layer of a weakly coupled semi-infinite bi-layered system is carried out. Fourier transform inversions are performed analytically by making use of the fact that the weakly coupled system possesses small propagation zones (PZs) in the frequency domain. Low- and high-frequency asymptotic approximations to the transient waves are computed, taking into account frequency components of the transfer function in the first and second PZs, respectively. The derived analytic expressions are superpositions of non-oscillating terms and convolution integrals with decaying oscillatory kernels. Depending on the frequency and the amplitude of the convolution kernels, the dispersed waves overshoot or undershoot the applied impulsive excitation. This result is of significant practical importance in the design of layered systems as stress attenuators.
Vibration Localization in Rotating Shafts: Part I — Theory
Authors: Ulsoy A. Galip , Pierre Christophe , Choi Suhyun 
Published: March 2021

Abstract
This paper presents a theoretical study of vibration localization in single-span, flexible, rotating shafts. A non-circular cross-section of the rotating shaft, leading to dissimilar lateral moments of inertia, can introduce disorder. Internal coupling between the principal directions of vibration is provided by the rotational speed through the gyroscopic moments. It is shown, using both exact and perturbation solutions, that directional vibration localization can occur for certain appropriate combinations of disorder and coupling.
Vibration Localization in Rotating Shafts: Part II — Experiment
Authors: Ulsoy A. Galip , Pierre Christophe , Choi Suhyun 
Published: March 2021

Abstract
This paper presents an experimental study of vibration localization in single-span, flexible, rotating shafts. It was shown in a companion paper (Part I) that a non-circular cross-section of the rotating shaft, leading to dissimilar lateral moments of inertia, can introduce disorder. Internal coupling between the principal directions of vibration is provided by the rotational speed through the gyroscopic moments. It is experimentally demonstrated here that directional vibration localization can occur for certain appropriate combinations of disorder and coupling. The steady state response, due to mass unbalance, of a simply supported rotating shaft is considered. It is shown that disorder and gyroscopic coupling lead to directional vibration localization; i.e., larger vibration amplitudes in one of the two orthogonal principal directions of the shaft cross section.
Active Vibration Control of a Triple Flexible Structures Combined With Actuators
Authors: Seto Kazuto , Toba Yoshihiro , Doi Fumio 
Published: March 2021

Abstract
In order to realize living comfort of tall buildings by reducing the vibration of higher floors by strong winds, this paper proposes a new method of vibration control for flexible structures with a large scale. The higher a tall building the lower its natural frequency. Since obtaining sufficient force to control the lower frequency vibrations of tall buildings is a difficult task, controlling the vibration of ultra-tall buildings using active dynamic absorbers is nearly impossible. This problem can be overcome by placing actuators between a pair of two or three ultra-tall buildings and using the vibrational force of each building to offset the vibrational movement of its paired mate. Therefore, it is able to obtain enough control force under the low frequency when the proposed method is used. In this paper, a reduced-order model expressed by 2DOF system under taking into consideration for preventing spillover instability is applied to control each flexible structure. The LQ control theory is applied to the design of such a control system. The effectiveness of this method is demonstrated theoretically as well as experimentally.
Sliding Mode Control for Flexible Structures With μ Control-Based Frequency-Shaping Hyperplane
Authors: Nonami Kenzo , Nishimura Hidekazu 
Published: March 2021

Abstract
This paper proposes a new sliding mode control method using μ synthesis theory. This concept is based on the frequency-shaped approach. A conventional hyperplane consisits of a desired reference model without dynamics. Therefore, the sliding mode control system becomes often unstable based on spillover phenomena in a higher frequency region. On the other hand, the proposed design method can completely suppress such spillover phenomena because of the frequency-shaped hyperplane. Also, it has good robustness and robust performance in cases of parameter variations on the hyperplane to minimize the maximum singular value and structured sigular value from some noise to the controlled variables. We have just applied this new method to the flexible structure of the miniature test rig with four stories like high rise building. We have verified from simulations and experiments that the new sliding mode control method proposed in this paper has good performances and it is very useful to suppress the spillover in a higher frequency region.
The Trajectory Tracking Control of 2-Link Flexible Arm Using Tendon Mechanism
Authors: Cao Hui , Yoshida Kazuo 
Published: March 2021

Abstract
This paper deals with the trajectory tracking control of a 2-link flexible arm using tendon control mechanism. The purpose of this research is to establish modeling and control method for flexible arm. First, the equations of kinematic relationship and equations of motion are derived by using static deflection curve. From these equations, the relationship between tip trajectory and joint input torque is established. Second, a trajectory tracking controller is designed for real-time control of the flexible arm by using the resolved acceleration control method. Then the controller is carried out to track the designed straight line and circular trajectory. The simulation results show the effectiveness of the proposed method. To summarize these results, it was demonstrated that the tendon mechanism can be used to solve the tracking problem of the flexible arms and it also has a higher tracking precision than traditional method.
New Control Algorithms for Semi-Active Dynamic Vibration Absorbers
Authors: Abé M. , Igusa T. 
Published: March 2021

Abstract
A semi-active dynamic vibration absorber is proposed for controlling the free-vibration impulse response of structures. It is assumed that (i) the initial displacement for the absorber spring can be set to non-zero values and (ii) the viscous damping coefficient for the absorber damping can be adjusted. The theory is first developed for a single-degree-of-freedom structure, and is then generalized to continuous structures. The extensive use of closed-form analytical results provides useful insight into the complex interaction between the structure and absorber. This makes it possible to solve the design problem without recourse to numerical optimization. The semi-active vibration absorber is found to be far more effective than conventional passive devices.
Parametric Studies of Photo Deformation and Optical Actuation
Authors: Tzou H. S. , Chou C.-S. 
Published: March 2021

Abstract
Optically driven actuators can introduce remote actuation and control effects without any hard-wire connections. In this study, photostrictive {opto-piezoelectric) characteristics and photodeformation of distributed photostrictive optical actuators are investigated and a parametric study of design parameters is conducted. Photodeformation induced by the photostrictive (opto-piezoelectric) effect (a combination of the photovoltaic effect and the converse piezoelectric effect) is discussed and its two-dimensional (2-D) constitutive relations are presented. 2-D equivalent control forces and moments induced by the photodeformation effect of distributed actuators are formulated, and system governing equations derived. Static and dynamic applications are discussed, and simulation studies of design parameters are conducted and evaluated.
Orthogonal Bases for Eigenvalue Sensitivities—Torsional Vibration
Authors: Nayfeh S. A. , Asada H. 
Published: March 2021

Abstract
The sensitivity of the natural frequencies of torsional vibration of an initially uniform shaft to nonuniform changes in its radius is studied. For the particular example of a fixed-fixed shaft, a set of design changes are found that modify a single natural frequency without modifying any of the others. The possibility of finding such a set of design changes for general boundary conditions is then investigated, and conditions for the existence of such a set are determined.
On the Analysis and Fundamental Frequency of Slightly Curved Sandwich Beams With a Delamination
Authors: Rossettos John N. 
Published: March 2021

Abstract
An analysis of the vibration of sandwich beams with small iinitial curvature and a delamination between the core and face sheet is presented. The combined effects of initial curvature, transverse shear deformation and extent of delamination are evaluated and discussed. It is shown that the sensitivity to delamination damage is greater for straight beams than for initially curved beams. It is also greater for high modulus cores (less shear deformation). Also the influence of shear deformation on the fundamental frequency becomes smaller as the curvature increases.
A Comparison Between the Use of Physical Parameters and Correction Factors in Dynamic Model Updating
Authors: D’Ambrogio Walter , Fregolent Annalisa 
Published: March 2021

Abstract
The selection of quantities and/or variables that have to be corrected during the updating process is addressed in this paper. Among quantities, the major alternative is the choice between correction factors and physical parameters. The former represent scale factors used to adjust mass and stiffness submatrices of the analytical model, while the latter include parameters such as the elasticity modulus, mass density, geometrical dimensions, etc. Advantages and limitations in the process of updating physical parameters instead of correction factors are highlighted: it can be shown that only a limited number of physical parameters can be simultaneously updated for each element. The two approaches are compared using a previously developed updating procedure to solve an experimental test case.
Non-Linear Spring and Damping Forces Estimation During Free Vibration
Authors: Feldman Michael , Braun Simon 
Published: March 2021

Abstract
A method for dynamic analysis of sophisticated nonlinear single-degree-of-freedom systems, based on the Hilbert transform in the time domain is described. Using the Hilbert transform together with the proposed method for system identification, we obtain both instantaneous modal parameters together with non-linear force characteristics during free vibration analysis under impulse excitation without long resonance testing. Using the Hilbert transform in the time domain is a new method of studying linear and non-linear vibrating systems exposed to impulse or shock inputs.