bluuebunny/crossref_metadata_2025 huggingface dataset:
Retrofitting Active Control into Passive Vibration Isolation Systems
Authors: Margolis D.
Published: February 2008

Active vibration control uses sensing and power actuators to attenuate vibrational energy due to external disturbances. Many of these systems are retrofitted into already existing passive ones. As a result allowable relative motions are prescribed, and this influences the performance of the active system. This paper exposes these limitations and shows realistic expectations for two excellent control strategies.
Fault Diagnosis of Joint Backlash
Authors: Pan M.-C. , Van Brussel H. , Sas P. , Verbeure B.
Published: February 2008

The aim of this paper is to develop appropriate techniques to detect and classify the joint backlash of a robot by monitoring its vibration response during normal operating conditions. In this investigation, Wigner-Ville distributions combined with two-dimensional correlation techniques have been employed to diagnose the joint faults of multi-link robots. In the study reported here, signal detection based on the Wigner-Ville distribution is proposed as a tool for pattern differentiation. To evaluate the performance of different detection procedures, the detection of a simulated impact transient embedded in three simulated observed signals is presented. To assess the validity of the proposed approaches, they have been successfully employed in the fault diagnosis of link-joints on both a two-link mechanism and an industrial robot.
Vibration Suppression of Rotating Shafts Passing Through Resonances by Switching Shaft Stiffness
Authors: Wauer J. , Suherman S.
Published: February 2008

A method suggested in the past to suppress the vibrations of flexible rotor systems passing through critical speeds is reconsidered. An appropriate switching of the system stiffness (by using shape memory alloys, for instance) is utilized. To model the nonstationary system behavior more realistically, the rotor is driven by a limited power supply. A special feature is the inclusion of unequal bending stiffnesses of the shaft. The stationary and transient behavior of the motor and system characteristic and the deformation amplitudes and phase angles, are examined. Attention is focussed on the strategy for switching the stiffness to yield small resonance deflections.
A Note on Computational Rotor Dynamics
Authors: Chen W. J.
Published: February 2008

Concise equations for improvements in computational efficiency on dynamics of rotor systems are presented. Two coordinate ordering methods are introduced in the element equations of motion. One is in the real domain and the other is in the complex domain. The two coordinate ordering algorithms lead to compact element matrices. A station numbering technique is also proposed for the system equations during the assembly process. The proposed numbering technique can minimize the matrix bandwidth, the memory storage and can increase the computational efficiency. Numerical examples are presented to demonstrate the benefit of the proposed algorithms.
Analytical and Experimental Evaluation of Instability in Rotordynamic System With Electromagnetic Eddy-Current Damper
Authors: Kligerman Y. , Grushkevich A. , Darlow M. S.
Published: February 2008

There have been a number of papers published that concern the design and operation of electromagnetic, eddy-current dampers for controlling lateral vibration of rotating machinery. Many of these papers have included analysis approaches and all have been generally effective for low-speed operations. There have been a few reports concerning high-speed (supercritical) operations and many of these have indicated instability problems, but none of these have provided a valid analysis to account for instability. That is, all of the analytical approaches have ignored the disk rotation, relative to the magnetic field, and no obvious sources of instability have been found. In this paper, we will present our work in which we have rederived the analyses of this system in which we have not made the common assumption of no rotation between the disk and the magnetic field. In this case, the potential of instability for supercritical speed operation is clear and, in fact, the equivalent negative damping contribution of the eddy-current damper, under these conditions, has a negative effect on the system even if not fully unstable. We have carefully performed a series of experimental tests which corroborate this analytical approach. Finally, we briefly discuss alternative eddy-current damper design approaches that could be considered to provide effective damping at all speeds and avoid these instability problems.
On Free Vibrations of Fiber Reinforced Doubly Curved Panels, Part 2: Applications
Authors: Singh A. V. , Kumar V.
Published: February 2008

The applications of a Ritz-type numerical scheme, in which the displacement fields are prescribed by Bezier surface patches, are presented for the analysis of doubly curved laminated open panels. The fundamental strain-displacement relations and energy expressions are developed in orthogonal curvilinear coordinates. The higher-order shear deformation theory and the effects of rotary inertia are considered in the formulation. Good comparisons of the results are obtained for a class of open panels. For example, values of the natural frequencies of open cylindrical and spherical panels made of isotropic material are compared with the results from the finite element analysis. Cases of cantilevered and simply supported angle-ply laminated cylindrical panel and a fully clamped isotropic conical panel are also examined for comparison with the available sources in the literature. In addition, the natural frequencies are presented for angle-ply laminated circular cylindrical, conical and spherical panels and the influence of the fiber orientation on the fundamental frequency is also examined for the angle ply having one, two [φ/−φ] and four [φ/−φ/φ/−φ] laminae arrangements.
Vibration and Stability of a Spinning Disk in Contact With Evenly-Spaced Stationary Load Systems
Authors: Chen Jen-San , Wong Cheng-Chou
Published: February 2008

The titled problem is studied numerically by finite element calculation. Attention is focused on the behavior of modal interactions when two modes are almost degenerate. In the case when the difference between the numbers of nodal diameters of these two modes is equal to a multiple of the number of the stationary load systems, the frequency loci may merge together (when one of these two modes is a reflected wave) or veer away (when both modes are non-reflected). Otherwise, the natural frequency loci simply cross each other and no instability is induced. When a backward wave meets its complex conjugate at the critical speed, it is found that divergence instability is induced when two times the number of nodal diameters is equal to a multiple of the number of stationary springs.
The Free Vibration of a Cylindrical Shell on an Elastic Foundation
Authors: Paliwal D. N. , Pandey Rajesh K.
Published: February 2008

The frequency equation for a thin circular cylindrical shell resting on an elastic foundation is developed by using the first order shell theory of Sanders and eigenfrequencies are calculated. These eigenfrequencies are plotted against the axial wave parameter. Effects of the axial wave parameter, circumferential wave number, non-dimensional thickness and foundation parameters on eigenfrequencies are investigated. It is found that the foundation modulus chiefly affects the radial mode eigenfrequency and has no effect on torsional and longitudinal modes. On the otherhand, shear modulus does have influence on radial as well as tangential modes of vibrations. Though the effect on radial mode frequency is more pronounced.
Vibration Analysis of a Rotor With Multiple Flexible Disks Using Assumed Modes Method
Authors: Lee Chong-Won , Chun Sang-Bok
Published: February 2008

An assumed modes method is developed to investigate the effect of multiple flexible disks on the vibrational modes of a flexible rotor system. The analysis rotor model consists of multiple disks on a flexible shaft, as used for steam turbines or computer storage devices. In modeling the system, centrifugal stiffening and disk flexibility effects are taken into account. To demonstrate the effectiveness of the method, a hard disk drive spindle system commonly used in personal computers and a simple flexible rotor system with two disks are selected as examples. In particular, the dynamic coupling between the vibrational modes of the shaft and the duplicate disks is investigated with the shaft rotational speed varied.
Identification of ’Effective’ Linear Joints Using Coupling and Joint Identification Techniques
Authors: Ren Y. , Beards C. F.
Published: February 2008

Almost all real-life structures are assembled from components connected by various types of joints. Unlike many other parts, the dynamic properties of a joint are difficult to model analytically. An alternative approach for establishing a theoretical model of a joint is to extract the model parameters from experimental data using joint identification techniques. The accuracy of the identification is significantly affected by the properties of the joints themselves. If a joint is stiff, its properties are often difficult to identify accurately. This is because the responses at both ends of the joint are linearly-dependent. To make things worse, the existence of a stiff joint can also affect the accuracy of identification of other effective joints (the term “effective joints” in this paper refers to those joints which otherwise can be identified accurately). This problem is tackled by coupling these stiff joints using a generalized coupling technique, and then the properties of the remaining joints are identified using a joint identification technique. The accuracy of the joint identification can usually be improved by using this approach. Both numerically simulated and experimental results are presented.
Designing for Optimal Energy Absorption, 1: Lumped Parameter Systems
Authors: Cox S. J.
Published: February 2008

Given a conservative dynamical system we determine where, and in what quantity, dissipative mechanisms should be placed in order to best absorb an initial disturbance. We work in the context of linear vibrating systems described by constant mass, M, stiffness, K, and damping, D, matrices. We suppose that M and K are fixed and proceed to minimize, with respect to D, two measures of energy absorption: (i) the least exponent for which the energy exhibits exponential decay and (ii) the maximum over initial disturbances of unit energy of the infinite time integral of the energy. We construct a general setting and provide explicit solutions in the special case of normal mode systems.
Cumulant Based Modal Parameter Extraction of Structures
Authors: Runarsson T. P. , Jonsson M. T. , Jonsson G. R.
Published: February 2008

This paper describes a nonlinear deterministic estimator based on cumulants for the extraction of modal parameters. The signal analysed is composed of multiple exponentially damped real sinusoids in unknown additive noise. Cumulants reduce significantly the effects of noise and are also an efficient way of compressing the sampled data. In modal analysis a sensor may be unable to detect some modes of vibration due to its location. Cumulants estimated from real data sampled at different locations and instances are added directly together. This average cumulant function will contain the eigenvalues for all excited modes of vibration. Finding the frequencies and corresponding damping factors is therefore reduced to solving a single average cumulant function. The performance of the proposed estimator is examined and compared with the Eigensystem Realization Algorithm via simulations.
In-Plane Vibration Modes of Arbitrarily Thick Disks
Authors: Tzou K. I. , Wickert J. A. , Akay A.
Published: February 2008

The three-dimensional vibration of an arbitrarily thick annular disk is investigated for two classes of boundary conditions: all surfaces traction-free, and all free except for the clamped inner radius. These two models represent limiting cases of such common engineering components as automotive and aircraft disk brakes, for which existing models focus on out-of-plane bending vibration. For a disk of significant thickness, vibration modes in which motion occurs within the disk’s equilibrium plane can play a substantial role in-setting its dynamic response. Laboratory experiments demonstrate that in-plane modes exist at frequencies comparable to those of out-of-plane bending even for thickness-to-diameter ratios as small as 10−1. The equations for three-dimensional motion are discretized through the Ritz technique, yielding natural frequencies and mode shapes for coupled axial, radial, and circumferential deformations. This treatment is applicable to “disks” of arbitrary dimension, and encompasses classical models for plates, bars, cylinders, rings, and shells. The solutions so obtained converge in the limiting cases to the values expected from the classical theories, and to ones that account for shear deformation and rotary inertia. The three-dimensional model demonstrates that for geometries within the technologically-important range, the natural frequencies of certain in- and out-of-plane modes can be close to one another, or even identically repeated.
Calculation of Component Mode Synthesis Matrices From Measured Frequency Response Functions, Part 2: Application
Authors: Morgan J. A. , Pierre C. , Hulbert G. M.
Published: February 2008

This paper demonstrates how to calculate Craig-Bampton component mode synthesis matrices from measured frequency response functions. The procedure is based on a modified residual flexibility method, from which the Craig-Bampton CMS matrices are recovered, as presented in the companion paper, Part I (Morgan et al., 1998). A system of two coupled beams is analyzed using the experimentally-based method. The individual beams’ CMS matrices are calculated from measured frequency response functions. Then, the two beams are analytically coupled together using the test-derived matrices. Good agreement is obtained between the coupled system and the measured results.
Active Control of Structure-Borne Road Noise Using Vibration Actuators
Authors: Dehandschutter W. , Sas P.
Published: February 2008

Structure-borne road noise is generated by road induced excitation forces. The control approach presented here relies on the use of vibration actuators to modify the vibration behavior of the car body such that its noise radiation efficiency is decreased (Active Structural Acoustic Control—ASAC). The controller is optimized using laboratory experiments and numerical tools to simulate the performance a complete vehicle control set-up. Road tests yield a 6.9 dB noise reduction in the frequency range 75–105 Hz at the error microphone and 6.1 dB noise reduction at the passenger’s ear.
An Approach to Vibration Control of Multiple-Pendulum System by Wave Absorption
Authors: Saigo M. , Tanaka N. , Tani K.
Published: February 2008

In this paper, a new wave-absorbing strategy has been studied to suppress the vibration of a multiple-pendulum system by controlling the lateral movement of the support. The wave-absorbing condition is derived from the difference between the equation of motion of the boundary pendulum and that of an inner pendulum. An online real-time simulation method using the numerical solution is proposed to control the movement that satisfies the wave-absorbing condition. According to this method, vibration of a multiple-pendulum system with arbitrary degrees of freedom can be controlled by measuring only the deflection angle of the uppermost pendulum adjacent to the support if the dimensions of the uppermost pendulum and the total mass of the system are known. Both the numerical simulations and the experiments have confirmed the effectiveness of this method. The basic idea of this control method can easily be applied to any discrete vibrating system whose equations of motion have no traveling-wave solution.
Adaptive Virtual Autobalancing for a Rigid Rotor With Unknown Mass Imbalance Supported by Magnetic Bearings
Authors: Lum Kai-Yew , Coppola Vincent T. , Bernstein Dennis S.
Published: February 2008

The objective of this paper is to describe an imbalance compensation scheme for a rigid rotor supported by magnetic bearings that performs on-line identification of rotor imbalance and allows imbalance cancellation under varying speed of rotation. The proposed approach supplements existing magnetic bearing controls which are assumed to achieve elastic suspension of the rotor. By adopting a physical model of imbalance and utilizing measurements of the spin rate, the proposed algorithm allows the computation of the necessary corrective forces regardless of variations in the spin rate. Convergence of the algorithm is analyzed for single-plane balancing, and is supported by simulation in single- and two-plane balancing, as well as by experimental results in single-plane implementation.
Venturi Tubes: Acoustic Attenuation With Flow Loss Considerations
Authors: Selamet A. , Dickey N. S. , Kim Y. , Novak J. M.
Published: February 2008

The acoustic wave attenuation performance of Venturi tubes with zero mean fluid flow is investigated by: (1) combining analytical solutions for one-dimensional wave propagation in conical reducers, diffusers, and straight ducts; (2) employing a computational time-domain technique; and (3) conducting experiments in an extended impedance tube setup with four fabricated Venturi tubes and matching contraction chambers. The results from both analytical and computational approaches compare well with each other and the experimental data. The numerical technique is also applied to address the effects of a compressible mean flow on the acoustic behavior. Finally, the flow performance of the fabricated Venturi tubes is measured and the trade-offs are discussed between flow efficiency and acoustic performance.
Free Vibration Response Characteristics of a Simple Elasto-Hereditary System
Authors: Muravyov A. , Hutton S. G.
Published: February 2008

An analysis is conducted of the free vibration response characteristics of a single-degree-of-freedom (SDOF) elasto-hereditary (viscoelastic) system. The viscoelasticity is characterized by a relaxation kernel consisting of one exponential term. For this problem analytical results are presented that define the regions of oscillatory and nonoscillatory response. A possible application of the described technique to multi-degree-of-freedom diagonalizable viscoelastic systems is shown.
Transient Behavior of a Springless Flapper Valve: Closing Motion
Authors: Temple K. A. , Goldschmidt V. W. , Jones J. D.
Published: February 2008

The closing of a springless flapper valve was investigated in order to gain a better understanding of the transient behavior of the valve. An experimental investigation included simultaneous measurement of pressure and flapper velocity. An analytical investigation included the development of a model to predict the closing of the flapper valve. The flapper closing was experimentally determined to require from 18 to 24 percent of a cycle, and the model predictions were in good agreement with experimental data for the flapper closing time. The present study should be a useful contribution to future modeling of flapper valves and other springless valves.
ARMAV Techniques for Traffic Excited Bridges
Authors: Garibaldi L. , Giorcelli E. , Piombo B. A. D.
Published: February 2008

In this paper ARMAV (Auto Regressive Moving Average Vector) models are used for system identification and modal analysis purposes. This time domain technique allows to estimate a discrete time system response function without performing any domain change (i.e. it doesn’t use FFT and IFFT to evaluate the model parameters) and without applying any time window (also when sampled data are non periodic): this leads to well-estimated system parameters, also for short data records. These models are useful to perform system identification for multiple input-output cases also when the excitation is just statistically known. The present analysis is dedicated to a scaled bridge, designed according to the theory of models, whose static and dynamic characteristics are compatible to those of real bridges. The aim of the tests is to collect a series of supervised measurements in a controlled environment, with statistically defined traffic conditions; the comparison of the model results with those acquired on the real bridge is the compulsory step towards a correct modelling of bridges for their identification and monitoring. The paper reports encouraging results obtained with experimental simulations on the model.
Use of dFRFs for Identification of Travelling Wave Modes in Rotating Disks
Authors: Kim Myeong-Eop , Lee Chong-Won
Published: February 2008

Use of the wave directional frequency response function (dFRF), which is composed of conventional frequency response functions, is proposed for identification of the forward and backward travelling wave modes of isotropic rotating disks. The driving point dFRF, which is a weighted sum of complex wave dFRFs defined in the complex wave coordinates, is also derived for separation of the forward and backward travelling wave modes in the frequency domain. Numerical examples of rotating disks are treated to demonstrate the analytical developments. Experiments with a laboratory rotating disk are also performed to verify the theoretical findings.
Stability and Bifurcation of a Rotor-Fluid Film Bearing System With Squeeze Film Damper
Authors: Zhang Jiazhong , Xu Qingyu , Zheng Tiesheng
Published: February 2008

The dynamical behaviors of a flexible rotor supported by two plain cylindrical bearings surrounded by squeeze film damper are investigated. In this study, the Hopf bifurcation theory is used to investigate the stability of the equilibrium position of the system, then the unbalanced rotor response is determined by the shooting method and the stability of these solution is examined using the Floquet transition matrix method. It is shown that the quasi-periodic motion and period-doubling motion may be excited by the rotor unbalance.
Analysis of Ball Bearing Vibrations Caused by Outer Race Waviness
Authors: Ono K. , Okada Y.
Published: February 2008

An analytical investigation of the shaft vibration caused by a ball bearing is presented in this paper. Bearing vibration could be caused by a number of factors, such as defects occurring on the race track or the rolling elements. A common problem with defective bearings is the generation of waviness on the outer race track during the manufacturing process. The vibration of an automobile drive shaft caused by rolling elements rolling over the waviness surface is transmitted to the passenger cabin, and produces undesirable noise. In this paper an analytical study is undertaken to evaluate the effect of waviness number, radial gap and shaft imbalance on the bearing vibration. An experimental investigation was carried out to confirm the analytical study. The results show that the analytical study and experimental investigation agree very well.
The Optimum Stepped-Pipe String With Vibration Absorbers for Mining Manganese Nodules, to Reduce Its Maximum Axial Stress
Authors: Cui Gang , Aso Kazuo
Published: February 2008

In order to reduce the maximum axial stress produced in the pipe string for mining manganese nodules from deep-sea floors by a pump-lift system, the string is assumed to be a two-stepped pipe string with larger diameter in the upper part. Moreover, a buffer and two pump-modules attached to the string are assumed to be equipped with a vibration absorber. Then, the longitudinal vibration and axial stress caused in the string by the heave-motion of the mining ship are analyzed theoretically for practical cases. The result shows that the maximum axial stress in the optimum stepped pipe-string with the buffer having the optimum vibration absorber is found to be smaller by about 42 percent than the one produced in the uniform pipe string with the same mass and no vibration absorbers.
Free Vibration of Beams With Two Sections of Distributed Mass
Authors: Chan Kwok-Tung , Wang Xiao-Quan , Leung Tin-Pui
Published: February 2008

The equation of free transverse vibration of beams with two sections of partially distributed mass is derived and its exact solution has been obtained. Experimental data for a cantilever beam are given to verify the computational results. Using a cantilever beam as an example, some interesting features of changes of natural frequencies with mass length and position are described. The method is finally generalized for the case of beams with multiple spans of distributed mass.
3-D Exact Free Vibration Analysis of Transversely Isotropic Cylindrical Panels
Authors: Weiqiu Chen , Jinbiao Cai , Guiru Ye , Haojiang Ding
Published: February 2008

This paper presents an exact analysis of the free vibration of simply supported, transversely isotropic cylindrical panels. Based on the three dimensional elasticity for transversely isotropic media, three displacement functions are introduced so that the equations of motion are uncoupled and simplified. After expanding these functions with orthogonal series, the equations of free vibration problems are further reduced to three second order ordinary differential equations. A modified Bessel function solution with complex arguments is then directly used for the case of complex eigenvalues, which, to the authors’ knowledge, has never been reported before. To clarify the correctness and effectiveness of the developed method, numerical examples are presented and compared to the results of existent papers.
Dissipative Feedback Control of a Reverberant Enclosure Using a Constant Volume Velocity Source
Authors: Lane S. A. , Clark R. L.
Published: February 2008

Loudspeakers are commonly used as actuators in active noise control applications. In this work, a loudspeaker is compensated so that it approximates a constant volume velocity source over the piston mode frequency range (up to approximately 600 Hz). This moves the speaker dynamics out of the desired control bandwidth (20 Hz–500 Hz). A static gain feedback controller using the compensated speaker is applied to a rigid-wall enclosure to reduce the acoustic potential energy of the system while being subjected to low frequency broadband noise. The results are compared to the performance of a similar control law using an uncompensated speaker, and a model based H2 optimal controller. The results indicate that the controller using the compensated speaker offers definite advantages in terms of stability and performance, while requiring a minimal amount of control effort.
Reliability of the Piezoelectric Layer Application to Vibration and Noise Controls
Authors: Lee U. , Lesieutre G. A.
Published: February 2008

In this Tech Brief, the local curvature induced peeling tensile stress within the piezoactuator patch is qualitatively estimated, and the detailed stress analysis for an ACLD beam is conducted to show the high stresses concentration at the edges of a piezoactuator patch.
On the Use of Diagonal Modes in the Elastic Identification of Thin Plates
Authors: Ayorinde E. O. , Yu Lin
Published: February 2008

This paper relates a further development of an earlier work by the first author and others, in which they presented a method of deriving the elastic constants of composite materials from resonance data obtained from the modal analysis of freely-supported plates made out of orthotropic or isotropic materials. In the present work, the diagonal modes are included in the optimized Rayleigh three-term displacement representation for the square isotropic or almost isotropic composite plates. The use of sensitivity analysis of the frequencies including the diagonal modes to each elastic constant is also investigated in the procedure of the identification of elastic properties. Comparison of results obtained using diagonal-inclusive modes with those excluding the diagonal modes suggest that lower diagonal modes have relatively higher sensitivities to the elastic constants and can significantly improve accuracy when included in the elastic identification method applied here to square isotropic or almost isotropic plates.
Effect of Two-to-One Internal Resonances in a Nonlinearly Restrained Fluid Valve
Authors: Anlas¸ G.
Published: February 2008

The effect of two-to-one internal resonances on the nonlinear response of a pressure relief valve is studied. The fluid valve is modeled as a distributed parameter system at one end and nonlinearly restrained at the other. The method of multiple scales is used to solve the system of partial differential equation and boundary conditions. Frequency-response curves are presented for the primary resonance of either mode in the presence of a two-to-one internal resonance. Stability of the steady-state solutions is investigated. Parameters of the system leading to two-to-one internal resonances are tabulated.
Evaluation of AMB Turbomachinery Auxiliary Bearings
Authors: Kirk R. G.
Published: February 2008

The use of active magnetic bearings (AMB) for turbomachinery has experienced substantial growth during the past two decades. The advantages for many applications make AMB’s a very attractive solution for potentially low loss and efficient support for both radial and thrust loads. New machinery must be shop tested prior to shipment to the field for installation on-line. For AMB turbomachinery, one additional test is the operation of the auxiliary drop or overload bearings. A major concern is ability of the selected auxiliary bearing to withstand the contact forces following an at speed rotor drop. The proper design of AMB machinery requires the calculation of the anticipated loading for the auxiliary bearings. Analytical techniques to predict the rotor transient response are reviewed. Results of transient response evaluation of a full-size compressor rotor are presented to illustrate some of the important parameters in the design for rotor drop.
Optimal Vibration Feedback Control of an Euler-Bernoulli Beam: Toward Realization of the Active Sink Method
Authors: Tanaka N. , Kikushima Y.
Published: February 2008

This paper discusses the optimal vibration feedback control of an Euler-Bernoulli beam from a viewpoint of active wave control making all structural modes inactive (more than suppressed). Using a transfer matrix method, the paper derives two kinds of optimal control laws termed “active sink” which inactivates all structural modes; one obtained by eliminating reflected waves and the other by transmitted waves at a control point. Moreover, the characteristic equation of the active sink system is derived, the fundamental properties being investigated. Towards the goal of implementing the optimal control law that is likely to be non-causal, a “classical” velocity feedback control law (Balas, 1979) widely used in a vibration control engineering is applied, revealing a substantial shortcoming. Introduction of a “classical” displacement feedback to the velocity is found to realize the optimal control law in a restricted frequency range. Finally, two kinds of stability verification for closed feedback control systems are presented for distributed parameter structures.
Vibration Analysis of Discontinuous Mindlin Plates by Differential Quadrature Element Method
Authors: Liu F.-L. , Liew K. M.
Published: February 2008

A new numerical technique, the differential quadrature element method (DQEM), has been developed for solving the free vibration of the discontinuous Mindlin plate in this paper. By the DQEM, the complex plate domain is decomposed into small simple continuous subdomains (elements) and the differential quadrature method (DQM) is applied to each continuous subdomain to solve the problems. The detailed formulations for the DQEM and the connection conditions between each element are presented. Several numerical examples are analyzed to demonstrate the accuracy and applicability of this new method to the free vibration analysis of the Mindlin plate with various discontinuities which are not solvable directly using the differential quadrature method.
The Effect of Thread Dimensional Conformance on Vibration-Induced Loosening
Authors: Dong Yubo , Hess Daniel P.
Published: February 2008

This paper presents the results from dynamic tests that investigate the effect of thread dimensional conformance of fasteners on vibration-induced loosening. Test specimens include combinations of bolts and nuts within dimensional conformance as specified by ASME Standard B1. 1-1992, as well as bolts with undersized pitch and major diameters and nuts with oversized pitch and minor diameters. Tests were performed using an inertial loaded compound cantilever beam apparatus that subjects the test fasteners to a vibration environment. Data from the tests show a significantly degraded resistance to vibration for the fastener combinations with undersized pitch and major bolt diameters or oversized pitch and minor nut diameters, compared to fastener combinations within conformance. Specifically, the lower 90 percent confidence limit for the time to failure for conforming specimens was 782 seconds compared to 8 to 29 seconds for nonconforming specimens.
Linear Time-Varying Dynamic Systems Optimization via Higher-Order Method Using Shifted Chebyshev’s Polynomials
Authors: Xu Xiaochun , Agrawal Sunil K.
Published: February 2008

For optimization of classes of linear time-varying dynamic systems with n states and m control inputs, a new higher-order procedure was presented by the authors that does not use Lagrange multipliers. In this new procedure, the optimal solution was shown to satisfy m 2p-order differential equations with time-varying coefficients. These differential equations were solved using weighted residual methods. Even though solution of the optimization problem using this procedure was demonstrated to be computation efficient, shifted Chebyshev’s polynomials are used in the paper to solve the higher-order differential equations. This further reduces the computations and makes this algorithm more appropriate for real-time implementation.
Helicopter Gearbox Fault Detection: A Neural Network Based Approach
Authors: Dellomo M. R.
Published: February 2008

One of the most dangerous problems that can occur in both military and civilian helicopters is the failure of the main gearbox. Currently, the principal method of controlling gearbox failure is to regularly overhaul the complete system. This paper considers the feasibility of using a neural network to perform fault detection on vibration measurements given by accelerometer data. The details and results obtained from studying the neural network approach are presented. Some of the elementary underlying physics will be discussed along with the preprocessing necessary for analysis. Several networks were investigated for detection and classification of the gearbox faults. The performance of each network will be presented. Finally, the network weights will be related back to the underlying physics of the problem.
Transverse Vibration of a Rectangularly Orthotropic Spinning Disk, Part 1: Formulation and Free Vibration
Authors: Phylactopoulos A. , Adams G. G.
Published: February 2008

The transverse vibration of a spinning circular disk with rectangular orthotropy is investigated. Two dimensionless parameters are established in order to characterize the degree of disk anisotropy and solutions are sought for a range of these parameters. The orthotropic bending stiffness is transferred into polar coordinates and is found to differ from a classical formulation for a stationary disk. A Fourier series expansion is used in the circumferential direction. Unlike the isotropic disk, the Fourier components determining the transverse vibration modes of the orthotropic disk do not separate. This condition results in an eigenvalue problem involving a coupled set of ordinary differential equations which are solved by a combination of numerical integration and iteration. Thus the natural frequencies and normal modes of vibration are determined. Because each eigenfunction contains contributions from more than one Fourier component, the normal modes do not possess distinct nodal diameters or nodal circles. Furthermore, disk orthotropy causes the natural frequencies corresponding to the sine and cosine modes to split; the degree of splitting decreases as the rotational speed increases.
Stabilization of 1/3-Order Subharmonic Resonance Using an Autoparametric Vibration Absorber
Authors: Yabuno Hiroshi , Endo Yasuhiro , Aoshima Nobuharu
Published: February 2008

The paper proposes a stabilization method for 1/3-Order subharmonic resonance with an autoparametric vibration absorber. A main system with nonlinear spring stiffness and harmonic excitation, i.e., subjected to a sinusoidally changed magnetic force, is introduced as a model which produces 1/3-Order subharmonic resonance. A damped pendulum system, whose natural frequency is in the neighborhood of one-half of the main system, is attached to the main system as an absorber, in order to induce 1:2 internal resonance. The 1/3-Order subharmonic resonance which occurs in the case of locked pendulum is avoided due to energy transfer between the main system and the absorber, and due to energy dissipation by the absorber. It is also theoretically shown that a stable nontrivial steady state with respect to the 1/3-Order subharmonic frequency component is changed into an unstable one due to the absorber. Experimental results show the validity of the autoparametric vibration absorber for the 1/3-Order subharmonic resonance.
Analytical Characterization of the Unique Properties of Planetary Gear Free Vibration
Authors: Lin Jian , Parker R. G.
Published: February 2008

This work develops an analytical model of planetary gears and uses it to investigate their natural frequencies and vibration modes. The model admits three planar degrees of freedom for each of the sun, ring, carrier and planets. It includes key factors affecting planetary gear vibration such as gyroscopic effects and time-varying stiffness. For the linear, time-invariant case, examination of the associated eigenvalue problem reveals the well-defined structure of the vibration modes, where the special structure results from the cyclic symmetry of planetary gears. Vibration modes are classified into rotational, translational and planet modes. The unique characteristics of each type of mode are analytically investigated in detail. For each class of mode, reduced-order eigenvalue problems are derived.
An Efficient Analysis of High-Order Dynamical System with Local Nonlinearity
Authors: Zheng Tiesheng , Hasebe Norio
Published: February 2008

This paper deals with dynamical systems including spatially localized nonlinear substructures. In these cases, the differential equations of motion consist of the coupled linear and nonlinear subsets. According to the feature of such systems, a modal transformation is used, by means which the number of degrees of freedom of the linear subset is reduced significantly and the localized feature of the nonlinear subset still remains. In accordance with this reduced model, a modified Newmark method that is unconditionally stable is proposed to integrate the responses of the reduced system. The advantage of this method is that the nonlinear iterations only need to be executed on localized nonlinear parts of the system equations. The numerical schemes of this study are applied to a large-order flexible rotor with two elliptical bearing supports. The periodic solutions and long term behaviors of the system are investigated numerically, which reveals many interesting phenomena.
On Equivalent Linearization Using Wavelet Transform
Authors: Basu B. , Gupta V. K.
Published: February 2008

This paper proposes a wavelet-based formulation for linearizing a base-excited single-degree-of-freedom nonlinear system to a time-variant linear (TVL) system. The given system is assumed to be nonlinear in stiffness, and the time-dependent natural frequency of the equivalent system is proposed to he estimated through instantaneous minimization of the mean-square error. A duffing oscillator has been considered to illustrate the performance of the proposed TVL system.
Adaptive Vibration Isolation for Flexible Structures
Authors: Ertur David , Li Yugang , Rahn Christopher D.
Published: February 2008

Vibration isolation control for flexible structures restricts the response resulting from external disturbances to areas not requiring high precision positioning and/or pointing. This paper introduces adaptive feedback isolation controllers, based on Lyapunov theory, that regulate and allow tracking of the undisturbed (controlled) coordinates in a flexible structure. Under assumptions of inertially decoupled controlled and uncontrolled coordinates, symmetric and positive definite mass matrix for the controlled subsystem, asymptotically stable eigenvalues for the uncontrolled subsystem, and bounded disturbances, an adaptive regulator asymptotically drives the controlled coordinates to zero. Under similar assumptions, an adaptive tracking algorithm drives the controlled coordinates to desired time trajectories. Experimental results on a three mass system compare the response of the adaptive isolation controllers with standard PID control. The adaptive regulator provides faster transient decay than PID control using the same control effort. The adaptive tracking controller has the same tracking error as PID using 30 percent less control effort.
Modelling a Structural-Acoustic Coupled System with an Equivalent Lumped Parameter Mechanical System
Authors: Kim S. M. , Brennan M. J.
Published: February 2008

This paper describes the way in which a structural acoustic coupled system can be modelled using an equivalent lumped parameter mechanical model. The impedance-mobility approach is first used to model the system, and by relating the physical parameters to equivalent mass and stiffness, lumped parameter models can be derived provided that damping in the acoustic system is neglected in all modes, but the first (zero order) mode. A limitation of this approach, however, is that these simple mechanical models formulated in terms of the uncoupled structural and acoustic modes are only possible for either a single structural mode coupled to many acoustic modes, or a single acoustic mode coupled to many structural modes. These models facilitate physical insight into the dynamic behavior of a lightly-damped structural-acoustic system at frequencies close to the resonance frequencies of the coupled system.
Biomarkers of cardiovascular disease risk in 40–65-year-old men performing recommended levels of physical activity, compared with sedentary men
Authors: Perkins G M , Owen A , Kearney E M , Swaine I L
Published: February 2008

Objective:

Both the UK Department of Health and the US Centers for Disease Control and Prevention have recommended at least 30 minutes of moderate-intensity physical activity on most days for health. Specific mention is made of beneficial effects upon blood lipids. The purpose of this study was to compare biomarkers of cardiovascular disease risk in men who perform physical activity in accordance with these recommendations with those who do not.

Methods:

128 healthy men, aged 40–65 years, were recruited. 61 were classified as active (performing at least the minimum recommended physical activity of ⩾4 metabolic equivalents (METs), for 6 months immediately before the study) and 67 as sedentary. Fasting blood was drawn for total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), triglycerides, and apolipoproteins (Apo) A-1 and B. Low-density lipoprotein cholesterol (LDL-C) was estimated using the Friedewald equation.

Results:

The median (interquartile range) physical activity level was 7.0 (5.0–10.7) versus 1.0 (0–1.8) hour/week at ⩾4 METs (active versus sedentary; p<0.001). Apo A-1 was higher in the active men (p = 0.032). No significant differences were found for TC, HDL-C, LDL-C, TC:HDL-C, triglycerides, Apo B, or the Apo B:A-1 ratio.

Conclusions:

These findings suggest that physical activity performed according to the recommendations used in this study favourably influenced Apo A-1. The finding that cholesterol and triglycerides were not different in men achieving the recommended physical activity levels compared with sedentary men contradicts some of the claims made within the published recommendations. However, intervention studies are needed to clarify these preliminary findings.
The use of medication and nutritional supplements during FIFA World Cups 2002 and 2006
Authors: Tscholl P , Junge A , Dvorak J
Published: February 2008

Objective:

To examine medication use in male top-level football players prior to and during international tournaments.

Design:

Prospective survey.

Material:

2944 team physicians’ reports on players’ medication intake.

Methods:

Each team physician was asked to document all medication and nutritional supplements taken in the 72 h prior to each match.

Results:

A total of 10 384 substances were reported (1.8 substances/player/match); 4450 (42.9%) of these were medicinal and 5934 (57.1%) nutritional supplements. The medications prescribed most frequently were non-steroidal anti-inflammatory agents (n = 2092; 20.1%); more than half of the players took these at least once during a tournament and more than 10% prior to every match (156 out of 1472). β-2-Agonists were reported for 1.4% (n = 20) and inhaled corticosteroids for 1.6% (n = 23) of participating players. Injected corticosteroids were reported for 73 players.

Conclusions:

The high intake of medication in international football – especially of non-steroidal anti-inflammatory drugs – is alarming and should be addressed. The results raise questions as to whether the medication was taken solely for therapeutic reasons. In view of the potential side effects, more restrictive recommendations for sport need to be developed.
Molecular testing for somatic cancer mutations: a survey of current and future testing in UK laboratories
Authors: Wordsworth S , Papanicolas I , Buchanan J , Frayling I , Taylor J , Tomlinson I
Published: February 2008

Background:

Genetics clinical practice has paid limited attention to non-inherited aspects of cancer, namely mutations occurring during carcinogenesis. These somatic mutations are likely to be the primary determinants of cancer behaviour and treatment response, with a recent example being Her2/Neu gene status and response to Herceptin in breast cancer.

Aim:

To assess the feasibility of widespread testing of tumours by surveying UK histopathology and genetics laboratories.

Methods:

The questionnaire asked: which of the common cancers or other malignancies are routinely assessed; which molecular and cytogenetic methods are used; who orders and funds testing; what is the future demand for somatic testing; and what are the barriers to widespread testing?

Results:

Of 50 laboratories surveyed, 33 responded, 22 of which are currently using molecular tests. The survey shows that the most common tests are immunohistochemistry, fluorescence in-situ hybridisation and DNA testing of somatic mutations. Most laboratories predict testing will increase over the next 10 years, particularly for DNA testing using microarrays. Respondents perceived the main barriers to expanding molecular testing were a lack of laboratory funding and scientific evidence and testing not considered an NHS priority.

Conclusion:

These results provide important information for healthcare commissioners faced with managing demand for molecular testing of cancers.