bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of Rotating Pretwisted, Tapered Beams With Randomly Varying Speeds
Authors: Young T. H. , Lin T. M.
Published: February 2008

This paper presents a study of stability of coupled bending-bending vibration of pretwisted, tapered beams rotating at randomly varying speeds. The rotating speed is characterized as a wide-band, stationary random process with a zero mean and small intensity superimposed on a constant speed. This randomly varying speed may result in the existence of parametric random instability of the beam. The stochastic averaging method is used to derive Ito’s equation for an approximation solution, and expressions for stability boundaries of the system are obtained by the second-moment and sample stability criteria, respectively. It is observed that those system parameters which will raise the first natural frequency but not enhance the centrifugal force of the beam tend to stabilize the system.
Response Variance Reduction of a Nonlinear Mechanical System via Sliding Mode Control
Authors: Sun J. Q. , Xu Qing
Published: February 2008

An analysis of a target tracking mechanical system subject to random base excitations is presented in this paper. Sliding mode controls are proposed to minimize the random error of target tracking. Two special cases are studied. In the first case, it is assumed that all the system parameters are known and the state variables are measurable. A sliding mode control is then determined. This highly idealized example reveals the effect of sliding mode control parameters on the reduction of response variance and provides a benchmark for designing a robust controller that deals with systems with unknown parameters. The second case deals with a robust sliding mode control where some parameters of the system are assumed to fall in a known range of values. The proposed controls are proven stable in the mean square sense. The statistical aspects of the controlled system are studied by considering the first and second order moments of the state variables. The equations for these moments are derived and solved by using the method of Gaussian closure in order to investigate the variance reduction performance of the controls.
Generalized Random Decrement Method for Analysis of Vibration Data
Authors: Spanos P. D. , Zeldin B. A.
Published: February 2008

The Random Decrement method used in system identification for analysis of random vibration data is considered from a rigorous mathematical perspective. It is shown that the Random Decrement signature deviates from the system free vibration curve of an associated linear system, unless the corresponding input excitation is white. The error induced by approximating the system excitation by a white noise process is examined. Further, a generalized Random Decrement signature is introduced; it is used to estimate efficiently the auto-correlation function of an ergodic Gaussian random process. Several examples are discussed to elucidate the theoretical developments.
A Parametric Study of the Modified Model Reference Adaptive Control Scheme
Authors: Sardar H. M. , Ahmadian M.
Published: February 2008

The validity of the claim by many studies that the damping and stiffness forces can be ignored when designing a model reference adaptive controller, is examined. For a simple plant, the sensitivity of the closed loop system to the inertial, damping, and stiffness nonlinearities are investigated, through a simulation analysis. It is shown that the closed loop system is sensitive to the changes in the inertial nonlinearities, and relatively insensitive to variations in the damping and stiffness forces. This supports the assumption made in many previous studies.
Optimum Design of Vibration Absorbers for Structurally Damped Timoshenko Beams
Authors: Esmailzadeh E. , Jalili N.
Published: February 2008

A procedure in designing optimal Dynamic Vibration Absorbers (DVA) for a structurally damped beam system subjected to an arbitrary distributed harmonic force excitation, is presented. The Timoshenko beam theory is used to assess the effects of rotatory inertia and shear deformation. The method provides flexibility of choosing the number of absorbers depending upon the number of significant modes which are to be suppressed. Uniform cross-sectional area is considered for the beam and each absorber is modeled as a spring-mass-damper system. For each absorber with a selected mass, the optimum stiffness and damping coefficients are determined in order to minimize the beam dynamic response at the resonant frequencies for which they are operated. For this purpose, absorbers each tuned to a different resonance, are used to suppress any arbitrarily number of resonances of the beam. The interaction between absorbers is also accounted for in the analysis. The optimum tuning and damping ratios of the absorbers, each tuned to the mode of concern, are determined numerically by sloving a min-max problem. The Direct Updated Method is used in optimization procedure and the results show that the optimum values of the absorber parameters depend upon various factors, namely: the position of the applied force, the location where the absorbers are attached, the position at which the beam response should be minimized, and also the beam characteristics such as boundary conditions, rotatory inertia, shear deformation, structural damping, and cross sectional geometry. Through the given examples, the feasibility of using proposed study is demonstrated to minimize the beam dynamic response over a broad frequency range. The resulting curves giving the non-dimensional absorber parameters can he used for practical applications, and some interesting conclusions can be drown from the study of them.
Dynamic Behavior of the Band/Wheel Mechanical System of Industrial Band Saws
Authors: Chung Y. Y. , Sung C. K.
Published: February 2008

This paper presents an analytical and experimental investigation on the dynamic behavior of the band/wheel mechanical system of an industrial metal-cutting band saws. In practice, this machine is equipped with two pairs of roller bearings to twist the saw blade perpendicularly to the surface of the workpiece. This results in the existence of the wheel tilt angle. The saw band is modeled as a finite moving beam span that composes three consecutive segments: the middle straight segment, that is, the cutting span, and the neighboring two segments that are considered as twisted beams. The deformation of the band must satisfy the continuity condition at the connections between segments. The equations of motion governing the dynamic behavior of the saw band in axial, torsional and transverse directions are derived using mixed variational principle. The axial motion of the span couples linearly with its torsional motion. The dynamic responses and the natural frequencies of the beam are computed when parameters vary, such as the transport velocity of the saw band, initial tension, wheel tilt angle, and the length of the cutting span. Finally, an experimental study is performed on an industrial band saw for the verification of the mathematical model and the predictive capability proposed in this investigation. Favorable comparisons between the analytical and experimental results are obtained.
Coupled Lateral-Torsional Vibration of a Gear-Pair System Supported by a Squeeze Film Damper
Authors: Chen Chin-Shong , Natsiavas S. , Nelson H. D.
Published: February 2008

This paper presents a model and analysis of the coupled lateral-torsional vibration of a gear-pair system supported by a squeeze film damper (SFD). Steady state dynamic characteristics of the system are considered. First, insight is gained into the dynamics of the system and the model is partially verified by investigating the linear characteristics of a specific configuration. Then, the response of the nonlinear system is examined for rotating unbalance excitation. The trigonometric collocation method (TCM) is employed to obtain steady-state responses, while direct integration is used to verify these results. The sensitivity of the system to lateral-torsional coupling is examined by comparing steady response with and without this effect. The response sensitivity to various system parameters, e.g., gear mesh stiffness and damping, SFD clearance to diameter ratio, and gear mass unbalance, is also studied. As expected, the numerical results reveal that the lateral motion dominant modes may be significantly attenuated by using an SFD, while the torsional motion dominant modes are sensitive to gear mesh damping. The strong nonlinearity of the SFD is responsible for complex dynamic response in some frequency ranges.
Theory Versus Experiment for the Effects of Pressure Ratio on the Performance of an Orifice-Compensated Hybrid Bearing
Authors: Mosher P. , Childs D. W.
Published: February 2008

This research investigates the effect of varying the concentric recess pressure ratio of hybrid (combination hydrostatic and hydrodynamic) bearings to be used in high-speed, high-pressure applications. Bearing flowrate, load capacity, torque, rotordynamic coefficients, and whirl frequency ratio are examined to determine the concentric, recess-pressure ratio which yields optimum bearing load capacity and dynamic stiffness. An analytical model, using two-dimensional bulk-flow Navier-Stokes equations and anchored by experimental test results, is used to examine bearing performance over a wide range of concentric recess pressure ratios. Typically, a concentric recess pressure ratio of 0.50 is used to obtain maximum bearing load capacity. This analysis reveals that theoretical optimum bearing performance occurs for a pressure ratio near 0.40, while experimental results indicate the optimum value to he somewhat higher than 0.45. This research demonstrates the ability to analytically investigate hybrid bearings and shows the need for more hybrid-bearing experimental data.
Active Noise Cancellation for a Three-Dimensional Enclosure by Using Multiple-Channel Adaptive Control and H∞ Control
Authors: Bai M. R. , Lin Z.
Published: February 2008

Active noise control (ANC) techniques for a three-dimensional enclosure are compared in terms of two control structures and two control algorithms. The multiple-channel filtered-x least-mean-square (FXLMS) algorithm and the H∞ robust control algorithm are employed for controller synthesis. Both feedforward and feedback control structures are compared. The Youla’s parameterization is employed in the formulation of the multiple-channel feedback FXLMS algorithm. The algorithms are implemented using a floating-point digital signal processor (DSP). Experiments are carried out to validate the ANC approaches for attenuation of the internal field in a rectangular wooden box. Position and number of actuators and sensors are also investigated. A broadband random noise and an engine noise are chosen as the primary noises in the experiments. The experimental results indicate that the feedforward structure yields a broader band of attenuation than the feedback structure. The FXLMS control and H∞, control achieve comparable performance.
Exact Solution for One-Dimensional Acoustic Fields in Ducts With Polynomial Mean Temperature Profiles
Authors: Kumar B. Manoj , Sujith R. I.
Published: February 2008

The purpose of this paper is to present closed form expressions for sound propagation in ducts with polynomial mean temperature profiles. It is shown that using appropriate transformations, the one-dimensional wave equation for ducts with an axial mean temperature gradient can be reduced to a standard differential equation whose form depends upon the specific mean temperature profile in the duct. The solutions are obtained in terms of Bessel and Neumann functions. The analysis neglects the effects of mean flow and therefore the solutions obtained are valid only for mean mach numbers that are less than 0.1. The developed solution is used to investigate the sound propagation in a quarter wave tube with an axial mean temperature gradient. The expressions for the four pole parameters are also presented.
Boundary Element Prediction of Sound Propagation in Ducts Containing Bulk Absorbing Materials
Authors: Seybert A. F. , Seman R. A. , Lattuca M. D.
Published: February 2008

In this paper the sound propagation in a rectangular duct containing a bulk absorbing foam liner is investigated. The foam is characterized by the complex characteristic impedance and propagation constant which are measured using an improved two-cavity method. These quantities are used to predict the normal incidence impedance and absorption coefficient of the foam which is compared to measured data obtained using the ASTM E-1050 test method. The complex characteristic impedance and propagation constant are also used to predict the attenuation through a layer of foam in a plane-wave tube for which measured results are also available. Finally, the boundary element method is used to predict the attenuation of sound in a rectangular duct where one surface is replaced by a foam-filled cavity. Comparison with experiment is shown for several frequencies.
On the Analysis of Hopf Bifurcation Associated with a Two-Fold Zero Eigenvalue, Part 1: Autonomous System
Authors: Moh’d M. , Huseyin K.
Published: February 2008

The static and dynamic bifurcations of an autonomous system associated with a twofold zero eigenvalue (of index one) are studied. Attention is focused on Hopf bifurcation solutions in the neighborhood of such a singularity. The family of limit cycles are analyzed fully by applying the formula type results of the Intrinsic Harmonic Balancing method. Thus, parameter-amplitude and amplitude-frequency relationships as well as an ordered form of approximations for the periodic motions are obtained explicitly. A verification technique, with the aid of MAPLE, is used to show the consistency of ordered approximations.
Development and Implementation of a Semi-Adaptive H∞ Active Control Algorithm for Duct Noise
Authors: Bai M. R. , Lin H. , Lin Z.
Published: February 2008

A hybrid active noise control (ANC) scheme for suppressing duct noise based on the H∞ control synthesis is proposed. The controllers are designed in terms of performance, stability, and robustness using a general framework of the H∞ robust control theory. In addition to the fixed controller, the system is further enhanced by introducing an adaptive compensator based on the least-mean-square (LMS) algorithm. Youla parameterization is employed in designing the adaptive compensator so that the resulting system is stable. Experimental investigations demonstrate that the proposed methods are effective in suppressing broadband random noise in a finite-length duct.
Classical Electrodynamics and Acoustics, Part 2: Sound Radiation by Moving Quadrupoles
Authors: Gaunaurd G. C. , Eisler T. J.
Published: February 2008

Our earlier work in Part 1 of this paper [1] is here extended to quadrupole distributions and point quadrupoles (i.e., stresses) in arbitrary motion. Radiation patterns are obtained and displayed in many relevant cases.
Evaluation of Floating Ring Seals for Centrifugal Compressors Using the Finite Element Method
Authors: Kirk R. Gordon , Baheti S. K.
Published: February 2008

The use of liquid ring type oil seals in centrifugal compressors was essential for high pressure applications dating back to the early 1960’s. The analysis of high pressure oil seals was first documented in the literature in the mid-1970’s following a series of compressor instability problems that made it clear that a better understanding of how seals influence the overall rotor stability was necessary. To produce compressor designs at higher speeds requires that an adequate method of predicting the oil seal influence on rotor dynamic stability be available for the designer. With the enhanced capability of personal computers and improved finite element models of the oil film thermal and hydrodynamic solutions, it is now possible to more accurately predict the dynamic characteristics of the oil seals. This paper presents a series of predicted results from a currently available advanced state of the art computer analysis for high pressure oil seals. The evaluation of several high pressure compressor seal designs illustrates the current capability for analytical predictions for various seal bore geometries. Conclusions and recommendations for the design of liquid ring seals are presented, which can give the compressor designer guidance for application to future high performance compressor liquid seal designs.
Wave Characteristics and Vibration Control of Translating Beams by Optimal Boundary Damping
Authors: Lee Seung-Yop , Mote C. D.
Published: February 2008

The transverse motion of a translating tensioned Euler-Bernoulli beam is controlled by passive or active damping applied at a boundary. Even for an undamped beam with a symmetric boundary configuration, the interaction between the translating continuum and the stationary or moving boundary leads to energy variation in free motion. With the time-varying energy chosen as a Lyapunov functional, boundary control laws are designed based on Lyapunov’s second method. For various types of translating beams, energy dissipation by boundary damping is quantified using the method of traveling waves. The optimal value of damping, maximizing the energy dissipation, is also explicitly represented by system parameters. The analytical results are compared with numerical simulations using the finite difference scheme.
Dynamic Torsional Response of a Laminated Circular Disc
Authors: Zhang Xiangzhou , Hasebe Norio
Published: February 2008

Harmonic and transient torsional responses of a laminated circular disc (or a laminated circular cylinder), caused by torques applied on both ends of the disc, is investigated with use of a continuous analysis. By the analysis, the difficulty brought about by multitudinous reflections and transmissions, taking place at the interfaces of the laminated medium, can be bypassed. The continuous analysis is based on the recognition that stresses at periodic locations in a periodic structure must vary smoothly; therefore these discrete values as a whole approximately form a continuous function, which can be treated analytically. Via the analysis, it is concluded that the real, heterogeneous laminated disc can be modelled into a homogeneous, effective one. The corresponding effective solution provides accurate or exact values of displacements and stresses at the periodic locations of the laminated disc. The density of the effective disc is not a geometric-material constant; it depends on, among others, the frequency and other vibration parameters in the problem. Numerical results are given to validate the analysis.
Hydroelastic Vibration of Free-Edge Annular Plates
Authors: Kwak M. K. , Amabili M.
Published: February 2008

This paper is concerned with the virtual mass effect due to the presence of water on the natural frequencies of free-edge annular plates resting on free surface or completely submerged, which has never been studied theoretically. Experiments were carried out for free-edge annular plates to find the so-called nondimensionalized added virtual mass incremental factors. In this paper, theoretical nondimensional added virtual mass incremental factors are obtained by employing the Hankel transformation technique in conjunction with the Fourier-Bessel series approach. It is found that the theoretical nondimensionalized added virtual mass incremental factors for free-edge annular plates resting on free-surface agree well with experimental ones. The proposed method can be applied to different boundary conditions of plates.
Adaptive Vibration Control of an Axially Moving String
Authors: de Queiroz M. S. , Dawson D. M. , Rahn C. D. , Zhang F.
Published: February 2008

In this paper, the displacement of an axially moving string is regulated using a control force and a control torque applied to the string via a mechanical guide. Given the hybrid model of the string system (i.e., distributed parameter field equation coupled to discrete actuator equations), Lyapunov-type arguments are utilized to design model-based and adaptive control laws that exponentially and asymptotically stabilize the string displacement, respectively. The proposed control laws are based on measurements of the string displacement, velocity, slope, and slope rate at the mechanical guide. While the model-based controller requires exact knowledge of the actuator/string parameters (e.g., actuator mass and string tension), the adaptive controller estimates the parameters online. Dynamic simulation results demonstrate the vibration damping provided by the control strategies.
Theoretical and Experimental Study on Airflow Damping of Vibrating Microcantilevers
Authors: Hosaka H. , Itao K.
Published: February 2008

The damping characteristics of microcantilevers are clarified analytically and experimentally to establish a dynamic design method of micromechanical systems. First, an approximate formula of airflow damping was derived using the Navier-Stokes equation. A precise measurement apparatus was then developed to verify the theory. The damping ratios of cantilevers ranging from 0.1 mm to 100 mm in length were measured, and the effects of beam size, vibrational mode number, and vibrational amplitude on the damping ratio were studied.
Two-Mode Interaction of a Beam with a Nonlinear Boundary Condition
Authors: Lee Won Kyoung , Yeo Myeong Hwan
Published: February 2008

In order to investigate modal interactions in a subharmonic resonance of a beam with a nonlinear boundary condition, we consider a beam constrained by a nonlinear spring to a harmonic excitation. The resonance conditions considered are ωn ≈ 3ωm and Ω ≈ 3ωn, where 3ωm and 3ωn are the natural frequencies and Ω is the excitation frequency. This nonlinear problem is governed by a linear partial differential equation, initial conditions and a nonlinear and inhomogeneous boundary condition. The method of multiple scales is used to transform the problem into a system of autonomous ordinary differential equations for amplitude and phase variables. The steady-state responses and their stability are determined by use of this system. In order to check the validity of the analytical solution we solve the initial and boundary value problem by means of a finite difference analysis.
A Compensated Acoustic Actuator for Systems with Strong Dynamic Pressure Coupling
Authors: Birdsong C. B. , Radcliffe C. J.
Published: February 2008

This study improves the performance of a previously developed acoustic actuator in the presence of an acoustic duct system with strong pressure coupling. The speaker dynamics and the acoustic duct dynamics are first modeled separately. The two systems are then coupled, and the resulting system is modeled. A velocity sensor is developed and used in feedback compensation. The resulting speaker system has minimal magnitude and phase variation over a 20–200 Hz bandwidth. These conclusions are verified through experimental results.
Vibration Control of Bridge Towers Using a Lumped Modeling Approach
Authors: Seto K. , Doi F. , Ren M.
Published: February 2008

A lumped modeling method and a simple robust control design based on this method are proposed in this paper for controlling the multiple vibration modes of a bridge tower structure under construction. The method is specified by a physical state-space suboptimal controller, designed upon a lumped model, combined with the so-called “structure filters” and the software filters for preventing spillover of neglected high modes. Effectiveness of the method is experimentally demonstrated by showing that the first five vibration modes of a model structure of a flexible bridge tower are well controlled without spillover of neglected higher modes.
Dynamic Gear Loads Due to Coupled Lateral, Torsional and Axial Vibrations in a Helical Geared System
Authors: Choi S. H. , Glienicke J. , Han D. C. , Urlichs K.
Published: February 2008

In this paper we investigate the rotordynamics of a geared system with coupled lateral, torsional and axial vibrations, with a view toward understanding the severe vibration problems that occurred on a 28-MW turboset consisting of steam turbine, double helical gear and generator. The new dynamic model of the shaft line was based on the most accurate simulation of the static shaft lines, which are influenced by variable steam forces and load-dependent gear forces. The gear forces determine the static shaft position in the bearing shell. Each speed and load condition results in a new static bending line which defines the boundary condition for the dynamic vibration calculation of the coupled lateral, torsional and axial systems. Rigid disks and distributed springs were used for shaft line modeling. The tooth contact was modeled by distributed springs acting normally on the flank surfaces of both helices. A finite element method with distributed mass was used for lateral and torsional vibrations. It was coupled to a lumped mass model describing the axial vibrations. The forced vibrations due to unbalances and static transmission errors were calculated. The eigenvalue problem was solved by means of a stability analysis showing the special behavior of the coupled system examined. The calculation was successfully applied, and the source of the vibration problem could be located as being a gear-related transmission error. Several redesign proposals lead to a reliable and satisfactory vibrational behavior of the turboset.
Modal Analysis of Rotor on Piecewise Linear Journal Bearings Under Seismic Excitation
Authors: Gaganis B. J. , Zisimopoulos A. K. , Nikolakopoulos P. G. , Papadopoulos C. A.
Published: February 2008

A rotor bearing system is expected to exhibit large vibration amplitudes when subjected to a large seismic excitation. It is possible that these vibrations can lead to large values the eccentricity of the bearings. Then the bearing is operated in highly nonlinear region because the stiffness and the damping coefficients are nonlinear as functions of the eccentricity. To solve this problem numerical integration must be performed with high cost in computer time. The idea of this paper was to divide the nonlinear area into more areas where the stiffness and damping coefficients could be considered to be constants. In other words the bearing coefficients are considered to be piecewise constant. The excitation due to the earthquake is modelled as a movement of the base of the bearings using the El Centro data for the acceleration. Then a simplified modal analysis for each of these piecewise linear regions can be performed. The equation of motion of the rotor contains rotational speed depended terms, known as gyroscopic terms, and terms due to base excitation. The response and the variation of the dynamic properties of this complicated rotor bearing system are investigated and presented.
Dynamics Simulation of Flexible Frame Structures with Time-Varying Shape and Attitude
Authors: Utsumi M.
Published: February 2008

A new computation scheme is presented for the response analysis of flexible frame structures with time-varying shape and attitude. The governing equations for a continuum are derived in the form of integral equations for the member joint displacements alone. The integral equations can be solved easily by transforming them into ordinary differential equations and introducing additional mass corresponding to the inertial force due to the rigid-body axial translation and rotation of members. The scheme is applied to deploying, extending, and rotating space structures and a three-dimensionally moving link-connected structure.
Analysis of Torsional Vibration Systems by the Extended Transfer Matrix Method
Authors: Huang Yuan Mao , Horng C. D.
Published: February 2008

This study applies the extended transfer matrix method and Newton-Raphson technique with complex numbers for torsional vibration analysis of damped systems. The relationships of the vibratory amplitude, the vibratory torque, the derivatives of the vibratory angular displacement and the vibratory torque between components at the left end and the right end of the torsional vibration system are derived. The derivatives of the vibratory angular displacement and the vibratory torque are used directly in the Newton-Raphson technique to determine the eigensolutions of systems that are compared and show good agreement with the available data.
Structural-Acoustic Design at High Frequency Using the Energy Finite Element Method
Authors: Bernhard R. J. , Huff J. E.
Published: February 2008

Energy flow analysis methods, particularly as implemented using the finite element method, are useful as design techniques for high frequency structural-acoustic applications. In this paper, the derivation of energy flow analysis techniques are summarized. Particular attention is given to the specification of joint models for situations where there is a discontinuity in either geometric properties or material properties. The finite element formulation of this approach is also summarized. A case study is included to illustrate the utility of the method as a design technique.
Numerical Estimation of End Corrections in Extended-Duct and Perforated-Duct Mufflers
Authors: Torregrosa A. J. , Broatch A. , Payri R. , Gonza´lez F.
Published: February 2008

One-dimensional models for extended-duct and perforated-duct mufflers require the introduction of end corrections in order to account for multidimensional effects at the junctions. In this paper, a numerical two-dimensional finite element calculation has been used in order to obtain information on these end corrections. The results have been validated through comparison with experimental measurements performed with a modified version of the impulse method. Then, the influence of the different geometric characteristics of the mufflers on the end correction have been studied. A general correlation in terms of relevant nondimensional parameters is given for extended-duct mufflers, whereas for perforated mufflers a general correlation has not been obtained due to the eventual coupling with other attenuation mechanisms.
A Time-Frequency Distribution for Analysis of Signals with Transient Components and Its Application to Vibration Analysis
Authors: Zheng G. T. , McFadden P. D.
Published: February 2008

Bilinear time-frequency distributions, which provide simultaneous high resolution in both time and frequency domains, offer advantages for the analysis of vibration signals where the harmonic components and sidebands may be closely spaced. However, the Choi-Williams exponential distribution is found to be unsuitable, and aliasing produced by distributions of the Cohen class also causes problems. An aliasfree exponential time-frequency distribution is introduced, which combines features of distributions of the Cohen class and the generalized Wigner distribution. The new distribution is shown to be well suited to the analysis of signals with transient components.
Analytical and Experimental Evaluation of an Air Damped Dynamic Vibration Absorber: Design Optimizations of the Three-Element Type Model
Authors: Asami Toshihiko , Nishihara Osamu
Published: February 2008

In this paper, we propose a dynamic vibration absorber (DVA) with an air damper consisting of a piston and a cylinder. First, it will be shown that the air damper can conveniently be represented by the Maxwell model where a spring element and a dashpot are connected in series. The air damper has no ability to return the piston to its original position. For this reason, it is necessary for the piston to be supported by a spring which is placed in parallel with the damper. The air damped DVA can then be modeled by the three-element model. Many studies have been done on the Voigt type of DVA, and the accurate expressions of optimum tuning and damping parameters have already been derived by Hahnkamm and Brock et al. However, only a few papers have been published on the three-element type of DVA, and reliable expressions for it have not been derived until now. Therefore, we began our work by trying to derive expressions for optimum parameters of the three-element type of DVA. It was clear that the optimized three-element type of DVA is superior to the conventional Voigt type of DVA. The optimum parameters which we obtained from our expressions were tested on a vibratory model. The experiments showed that the our expression is very useful for designing the air damped DVA.
A New Lateral Vibration Damper Using Leaf Springs
Authors: Jei Yang-Gyu , Kim Jong-Soo , Hong Seong-Wook , Jung Si-Young
Published: February 2008

The present paper introduces a new lateral vibration damper using leaf springs and oil. This damper, named as a leaf spring damper (LSD), has several beneficial rotordynamic advantages. The leaf spring vibration damper, unlike the well-known squeeze film damper, is simple and easy enough to design the required stiffness and damping coefficients. Furthermore, the damper can be designed as a unit product joined with a rolling element bearing. A theoretical modeling procedure for leaf spring damper is presented in detail. Prototypes of the leaf spring damper are manufactured to test the dynamic characteristics of the damper. Experiments are performed to measure the stiffness and the damping coefficients of the damper.
Free Vibration and Stability of a Spinning Disk-Spindle System
Authors: Parker R. G. , Sathe P. J.
Published: February 2008

This work examines the free vibration and stability of a spinning, elastic disk-spindle system. The extended operator formulation is exploited to discretize the system using Galerkin’s method (Parker, 1999). The coupled vibration modes of the system consist of disk modes, in which the disk dominates the system deformation, and spindle modes, in which the spindle dominates the system deformation. Both the natural frequencies and vibration modes are strongly affected by disk flexibility. If the membrane stresses associated with disk rotation are neglected then the system exhibits flutter instabilities, but these instabilities are not present when membrane stresses are modeled. Natural frequency veering between disk and spindle frequencies is prominent at low speeds and substantially affects the spectrum and stability. No veering is observed at high speeds where rotational stress stiffening diminishes disk-spindle coupling and causes the natural frequencies to converge to those of a rotating spindle carrying a rigid disk. Changes to the vibration modes are examined in terms of a strain energy ratio measuring the contribution of the disk strain energy to the total modal strain energy.
Analysis of Acousto-Ultrasonic Characteristics for Contact-Type Transducers Coupled to an Orthotropic Composite Plate
Authors: Liu T. , Kitipornchai S. , Liew K. M. , Wang G.
Published: February 2008

Acousto-ultrasonic input-output characteristics for contact-type transmitting and receiving transducers coupled to a thin orthotropic composite plate are analyzed in this paper. By introducing the point source/point receiver assumption, the governing equations of the problem, which relates to wave generation, wave propagation and wave reception, are first established. Using the multiple integral transform method, contour integration technique and some complex function theories, a spectral analysis method which is completely different from the present wave path tracing method for this problem is developed. From this approach, the spectral response of the normal contact force between the receiving transducer and the plate, due to an arbitrary input interrogation pulse excited by the transmitting transducer, is expressed in explicit form. Based on this, some physical properties involved with the output of the receiver are examined in the frequency domain. Finally, combining the fast Fourier transform (FFT) technique, some time domain numerical results are calculated to show the input-output characteristics of the AU system considered.
Dynamic Effects in Elastothermodynamic Damping of Metal-Matrix Composites with Spherical Reinforcement
Authors: Srivastava S. K. , Mishra B. K. , Jain S. C.
Published: February 2008

When a composite material is subjected to a time varying strain field, energy is dissipated because of the thermoelastic effect (elastothermodynamic damping or ETD). Evaluation of ETD in particle-reinforced MMCs has been reported in literature. These works follow a quasi-static approach. In the present work, a full dynamic solution for the energy dissipation is obtained, using the entropic approach. It is observed that the specific damping capacity predicted by the dynamic solution deviates from the quasi-static solution at high normalized frequencies, for low inclusion radius and low volume fraction.
Two-Stage Adaptive Line Enhancer and Sliced Wigner Trispectrum for the Characterization of Faults from Gear Box Vibration Data
Authors: Lee S. K. , White P. R.
Published: February 2008

Impulsive sound and vibration signals in gears are often associated with faults which result from impacting and as such these impulsive signals can be used as indicators of faults. However it is often difficult to make objective measurements of impulsive signals because of background noise signals. In order to ease the measurement of impulsive sounds embedded in background noise, it is proposed that the impulsive signals are enhanced, via a two stage ALE (Adaptive Line Enhancer), and that these enhanced signals are then analyzed in the time and frequency domains using a Wigner higher order time-frequency representation. The effectiveness of this technique is demonstrated by application to gear fault data.
Vibration Control of Smart Composite Beams with Embedded Optical Fiber Sensor and ER Fluid
Authors: Leng Jinsong , Asundi A. , Liu Yanju
Published: February 2008

This paper proposes the use of a fiber optic sensor (FOS) and electrorheological (ER) fluid actuator for vibration monitoring of smart composite structures. A new intensity modulated fiber optic vibration sensor is developed following the face coupling theory. It has high sensitivity similar to the traditional piezoelectric sensor. Also it is lower in cost. The experiment of vibration control of smart composite beam with embedded intensity modulated optical fiber vibration sensor and ER fluids are described in this paper. It is noted that the most significant change in the structural properties of smart composite beam is the change of structural damping and natural frequency, which varies with the electric field intensity imposed upon ER fluid. So the structural vibration can be monitored and controlled effectively utilizing FOS and ER fluids.
On Stability of Time-Varying Multidimensional Linear Systems
Authors: Wu Jinn-Wen , Fung Rong-Fong
Published: February 2008

In this Technical Brief, a sufficient condition to guarantee the exponential stability for a time-varying system X¨ + DX˙ + K(t)X = 0 is obtained. We mainly made up the condition by estimating the minimum amount of the damping to cope with a time-varying stiffness matrix K(t).
Changes in the membrane components of nondividing cambial cells
Authors: Rao K. S. , Catesson A. -M.
Published: February 2008

Horse-chestnut cambial cells are characterized by the formation of numerous plasmalemma invaginations and the accumulation of membrane whorls in the vacuoles during the transition from activity to rest. This suggests an active membrane trafficking which was investigated with conventional electron microscopy methods combined with selective cytochemical staining. After the cessation of meristematic activity, cell wall thickening is accompanied by increased dictyosome activity. The incorporation of dictyosome vesicles into the plasma membrane produces an increase in plasmalemma surface area in these nongrowing cells. This increase is compensated for by endocytosis accomplished by the formation of saclike plasmalemma invaginations into the peripheral cytoplasm. These invaginations often contain vesicles and tubules. When these invaginations come in contact with a vacuole, they appear to push the tonoplast into the vacuole and form double-membrane protrusions which may eventually separate from the plasmalemma. ER cisternae situated in the intermembrane zone also appear to be transported into the vacuole. Other cisternae may be directly sequestered into the vacuole or take part in the formation of the myelinlike structures which were observed in the cytoplasm. Thus, the vacuoles appear to fill progressively with complex membranous structures of various origins (plasmalemma, tonoplast, ER). It is suggested that their subsequent disappearance during the winter is a consequence of the hydrolytic action of vacuolar contents.
Crown architecture of Larix laricina saplings: an analysis of higher order branching
Authors: Remphrey W. R. , Powell G. R.
Published: February 2008

Quantitative analysis and simulation modelling of Larix laricina (Du Roi) K. Koch branches revealed a complex system of architectural patterns and correlations. Numbers of lateral buds and long shoots were positively correlated with parent-shoot length, but the relationships varied among shoot orders and for sylleptic shoots. For order 2 and sylleptic shoots, numbers of lateral long shoots were also correlated with associated terminal-shoot lengths. Sylleptic shoots produced more lateral long shoots than equivalent proleptic shoots. Lateral long-shoot lengths decreased basipetally and were correlated with terminal-shoot lengths. Lengths of order 2 lateral long shoots also varied independently with crown position. Generally, the degree of apical control decreased and the proportion of short shoots increased with positions of less vigour in the crown. Terminal long-shoot lengths varied with parent-shoot length, location, and to some extent parent-axis leader length. Terminal short-shoot production was associated with shorter parent shoots. Shorter order 2 shoots (<60 mm) and most order 3 shoots produced no lateral long shoots. The net result was that branch structural development ceased in less vigorous crown positions. The spatial disposition of shoots, as defined by elevation and divergence angles, varied with position of origin around and along parent shoots. Although variable, elevation angles decreased and divergence angles increased basipetally.
Modifications structurales des faisceaux vasculaires primaires de la tige de Cordyline indivisa (Agavaceae). 2. Répartition des différents stades structuraux dans le cylindre primaire, en fonction de la distance sous l'apex
Authors: Laliberté Sylvie , Vieth Joachim
Published: February 2008

In Cordyline indivisa Kunth, an anatomical modification occurs in the primary bundles, in relation to the pattern of their longitudinal course. Consequently, in a given transverse section of the stem, the bundles may be in different structural stages (collateral, intermediate types 1 and 2, amphivasal). All the procambial or primary vascular bundles in the upper 8.59 mm of the stem of an 18-month-old plant were recorded. At regular intervals below the apex, the numbers and percentages of bundles showing each of the structural stages were also recorded. Based on the pattern of bundle construction previously shown for this species, the constitution of the primary cylinder at various distances below the apex is explained in relation to the distribution of the different structural stages.
Gametophytic density and sex expression in Ceratopteris
Authors: Warne Thomas R. , Lloyd Robert M.
Published: February 2008

Gametophytic population density influences sex expression in the fern Ceratopteris Brongn. Extensive variation occurs among gametophyte families, both in the response of sex expression to density and in the covariate (density) adjusted frequency of hermaphroditic gametophytes. These differences are probably a function of genetic variability in the antheridiogen mediation of sex expression. In general, the frequency of hermaphroditic gametophytes decreases and becomes asymptotic and more stable with increased density. Higher gametophytic densities probably promote maleness through the more rapid attainment of effective concentrations of antheridiogen. Environmental factors that modify sex expression, e.g., gametophytic density and the response of any given gametophytic family to density, may ultimately influence the mating system.
Positional differences in size, morphology, and in vitro performance of pea axillary buds
Authors: Gould K. S. , Cutter E. G. , Young J. P. W. , Charlton W. A.
Published: February 2008

Numbers of buds within a leaf axil and of leaf primordia within a bud varied with node of insertion, both in intact pea (Pisum sativum) seedlings and in cultured axillary shoots. Normally one or more nodes bore no visible buds. At the higher nodes naked buds and aberrant forms were observed. Shoots dissected from the embryo bore five or six leaf primordia and buds were present at the cotyledonary node and at three nodes immediately above. Benzylaminopurine in the nutrient medium promoted vegetative growth of cultured shoots. The height and extent of proliferation of cultured shoots varied both with the parental node from which explants were derived and with benzylaminopurine concentration. Results are discussed in relation to correlative inhibition.
Development and survival of leaves in Magnolia obovata in a deciduous broad-leaved forest in Hokkaido, northern Japan
Authors: Kikuzawa Kihachiro
Published: February 2008

Seasonal changes were determined for leaf numbers on shoots and primordial and embryonic leaf numbers in terminal buds of Magnolia obovata growing in a deciduous broad-leaved forest in Hokkaido, northern Japan. Leaf-emergence pattern was "flush and succeeding type," i.e., many of the preformed leaves in a bud emerged at one time and after that several leaves appeared one by one successively. The lamina of the basal leaf was abortive in the bud and fell immediately after budbreak. The laminae of the shoot-tip leaves aborted after leaf emergence stopped, leaving stipules of the same leaves enclosing the bud. Such abortive laminae indicate that the shoot structure of M. obovata was evolved from homonomous to heteronomous structure. Magnolia obovata was consistently found in many types of forest but did not become dominant in number or in volume. This species was usually found in forest gaps and occasionally attained the canopy of the stand. Shoot structure of M. obovata was assumed to have changed in accordance with the leaf-emergence pattern, which is an adaptation of this species to its habitat.
Effects of ammonium sulphate on the community structure and biomass of ectomycorrhizal fungi in a Norway spruce stand in southwestern Sweden
Authors: Kårén Ola , Nylund Jan-Erik
Published: February 2008

Effects of nitrogen and sulphur deposition on the community structure and biomass of ectomycorrhizal fungi in a Norway spruce (Picea abies (L.) Karst.) forest were examined following fertilization with ammonium sulphate. The treated plots had been fertilized three times a year from 1988 with (NH4)2SO3 (100 kg N and 114 kg S ∙ ha−1 ∙ year−1). Sampling was carried out in the organic layer of the fertilized and control plots in late autumn in 1992 and 1993. The fungal biomass was estimated in 1992 using ergosterol analysis. The nitrogen treatment reduced the fine-root biomass (to 49% of the control) but did not decrease the mycorrhizal frequency (close to 100%) or concentration of ergosterol in fine roots. To identify mycorrhizas fungal ribosomal DNA was amplified using the polymerase chain reaction and digested with endonucleases. Of the 58 samples analysed, 21 different restriction profiles could be distinguished. Only four of the restriction profiles matched the restriction patterns of the dominant sporocarps on the site. It is suggested that nitrogen deposition will primarily change the community structure of ectomycorrhizal fungi, whereas the number of species may be less affected than has been previously inferred from sporocarp inventories. Key words: air pollution, biomass, diversity, ectomycorrhiza, identification, polymerase chain reaction.