bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Damage Detection Using a Minimum Rank Update Theory
Authors: Zimmerman D. C. , Kaouk M.
Published: June 2008

A computationally attractive algorithm is developed to provide an insight to the location and extent of structural damage. The algorithm makes use of an original finite element model and a subset of measured eigenvalues and eigenvectors. The developed theory approaches the damage location and extent problem in a decoupled fashion. First, a theory is developed to determine the location of structural damage. With location determined, an extent algorithm is then developed. The extent algorithm is a minimum rank update, which is consistent with the effects of many classes of structural damage on a finite element model. If the actual damage results in a rank p change to the finite element model, then the extent algorithm produces exact results if p eigenvalues and eigenvectors are measured exactly. In addition, the extent algorithm preserves any rigid body modes of the structure. The algorithms are demonstrated using both numerical and actual experimental data. The effects of eigenvector measurement and expansion errors are demonstrated and techniques to overcome the effects of noise are discussed.
Source Identification Using Multi-Input/Single-Output Modeling and Causality Checking of Correlated Inputs
Authors: Park Jung-Seok , Kim Kwang-Joon
Published: June 2008

This paper presents experimental results of a case study of source identification using multiple-input/single-output modeling in a case where the inputs are coherent to some extent and, hence, the priority among the correlated inputs must be decided before applying the partial coherence function approach. The basic idea is that either one of any two correlated signals causes the other and that this causality can be checked by observing the impulse response functions estimated in the negative time region, interpretations of which are provided for a system transfer function given in the fractional form of polynomials and for a case of wave propagation. The experimental results from a three inputs/single output acoustical system shows that the method works well and is promising in the source identification problems with coherent inputs.
Stability of Sliding Frictional Surfaces with Varying Normal Force
Authors: Dupont P. E. , Bapna D.
Published: June 2008

This paper presents the stability analysis of a single degree-of-freedom elastic system following a rate-and state-dependent friction law. Normal force is assumed to depend on the displacement, velocity and acceleration of the sliding interface. The history dependence of friction on normal force is included in the analysis. It is shown that to achieve steady sliding, system stiffness must exceed a critical value which depends on the expression for normal force. A system in which normal force depends on spring displacement is analyzed in detail. These results indicate that the functional dependence of normal force on system state can have a significant effect on the stability of low-velocity motion.
Predicting Random High-Cycle Fatigue Life With Finite Elements
Authors: Preumont Andre´ , Pie´fort Vincent
Published: June 2008

This paper extends the classical theory of random fatigue to multiaxial stress fields, using a quadratic criterion. An equivalent uniaxial random process is constructed by combining the power spectral densities of the normal and tangential stresses according to the von Mises criterion. This process, that we call the von Mises stress, is used to evaluate the damage with a uniaxial model of random fatigue. A finite element implementation is proposed.
Dynamic Coefficients of Axial Spline Couplings in High-Speed Rotating Machinery
Authors: Ku C. P. Roger , Walton J. F. , Lund J. W.
Published: June 2008

This paper provided the first opportunity to quantify the angular stiffness and equivalent viscous damping coefficients of an axial spline coupling used in highspeed turbomachinery. The bending moments and angular deflections transmitted across an axial spline coupling were measured while a nonrotating shaft was excited by an external shaker. A rotordynamics computer program was used to simulate the test conditions and to correlate the angular stiffness and damping coefficients. The effects of external force and frequency were also investigated. The angular stiffness and damping coefficients were used to perform a linear steady-state rotordynamics stability analysis, and the unstable natural frequency was calculated and compared to the experimental measurements.
Effects of Static Load on Dynamic Structural Properties in a Flexible Supported Foil Journal Bearing
Authors: Ku C. P. Roger , Heshmat H.
Published: June 2008

This paper describes an experimental investigation into the structural dynamic characteristics of corrugated foil (bump foil) strips used in one type of compliant surface foil journal bearings and dampers. The nonrotating journal was supported by a compliant foil journal bearing and driven by two shakers which were used to simulate dynamic forces acting on the bump foil strips. The dynamic structural stiffness and equivalent viscous damping coefficients were calculated based on the experimental measurements for a wide range of operating conditions. The results were compared to the analytical predictions obtained by a theoretical model developed earlier, and the agreement is considered reasonably well. Both experimental and theoretical results show that the direct structural stiffness and damping coefficients increase with increasing bearing static load.
Development of Phased Twin Flip-Flop Jets
Authors: Raman G. , Rice E. J.
Published: June 2008

The flip-flop nozzle is a device that can produce an oscillating jet flow without any moving parts. There is now a renewed interest in such nozzles due to their potential for use as excitation devices in practical applications. An experiment aimed at developing twin flip-flop jets that operate at prescribed frequencies and phase differences was performed. The phasing was achieved using two different nozzle interconnection schemes. In one configuration the two jets flapped in-phase and in another they flapped out-of-phase with respect to each other. In either configuration the frequencies of oscillation of both jets were equal. When one of the jets was run at a constant high velocity and the velocity of the second jet was increased gradually, the higher velocity jet determined the frequency of oscillation of both jets. The two flip-flop jet configurations described in this paper could be used to excite a primary jet flow in either an anti-symmetric (sinuous) or a symmetric (varicose) mode.
Flexural Instabilities in Axially Moving Bands
Authors: Asokanthan S. F. , Ariaratnam S. T.
Published: June 2008

Flexural instabilities in moving bands under harmonic tension fluctuation are investigated. The discretized equations of flexural motion represent a periodically perturbed linear gyroscopic system. Explicit conditions for the onset of instability are established employing the method of averaging. The effects due to damping, mean band speed, and the band compliance on the band stability are discussed. The present analysis is adequate in the design of moving bands where it is necessary to avoid critical speed ranges.
Mode Localization in Coupled Circular Plates
Authors: Orgun C. O. , Tongue B. H.
Published: June 2008

When analyzing structures that are comprised of many similar pieces (periodic structures), it is common practice to assume perfect periodicity. Such an assumption will lead to the existence of eigenmodes that are global in character, i.e., the structural deflections will occur throughout the system. However, research in structural mechanics has shown that, when only weak coupling is present between the individual pieces of the system, small amounts of disorder can produce a qualitative change in the character of the eigenmodes. A typical eigenmode of such a system will support motion only over a limited extend of the structure. Often only one or two of the smaller pieces that make up the structure show any motion, the rest remain quiescent. This phenomenon is known as “mode localization”, since the modes become localized at particular locations on the overall structure. This paper will examine the behavior of several circular plates that are coupled together through springs, a system that models a multiple disk computer disk drive. These drives typically consist of several disks mounted on a single spindle, coupled by read/write heads, which act as weak springs, thus leading one to suspect the possibility of localization. Since such an effect would impact accurate read/write operations at small fly heights, the problem deserves attention. Although computer disk drives contain space fixed read/write heads, this paper will consider springs that are fixed to the plates in order to understand the effect of localization on a set of infinite dimensional structures (the circular plates). Later work will extend the model to the case of space fixed springs and the wave behavior and destabilizing effects that such a configuration will induce.
A Piezothermoelastic Thin Shell Theory Applied to Active Structures
Authors: Tzou H. S. , Howard R. V.
Published: June 2008

“Smart” structures with integrated sensors, actuators, and control electronics are of importance to the next-generation high-performance structural systems. Piezoelectric materials possess unique electromechanical properties, the direct and converse effects, which, respectively, can be used in sensor and actuator applications. In this study, piezothermoelastic characteristics of piezoelectric shell continua are studied and applications of the theory to active structures in sensing and control are discussed. A generic piezothermoelastic shell theory for thin piezoelectric shells is derived, using the linear piezoelectric theory and Kirchhoff-Love assumptions. It shows that the piezothermoelastic equations, in three principal directions, include thermal induced loads, as well as conventional electric and mechanical loads. The electric membrane forces and moments induced by the converse effect can be used to control the thermal and mechanical loads. A simplification procedure, based on the Lame´ parameters and radii of curvatures, is proposed and applications of the theory to (1) a piezoelectric cylindrical shell, (2) a piezoelectric ring, and (3) a piezoelectric beam are demonstrated.
Experiments on Active Control of Plate Vibration Using Piezoelectric Actuators and Polyvinylidene Fluoride (PVDF) Modal Sensors
Authors: Gu Y. , Clark R. L. , Fuller C. R. , Zander A. C.
Published: June 2008

An experiment was performed to investigate the implementation of shaped PVDF modal sensors on a simply supported rectangular plate to control specific modes of the vibration. The plate was excited by a steady-state harmonic point force while the control was achieved by two independent piezoelectric actuators bonded to the surface of the plate. A two-channel adaptive controller based on the multi-input multi-output filtered X LMS algorithm was used to provide feed-forward control. Two PVDF modal sensors were shaped such that the (3,1) mode was the dominant structural mode observed by the sensors. With this configuration, the amplitude of the (3,1) mode can be minimized regardless of excitation frequency. A comparative test was performed by using two accelerometers as error sensors. Results indicate that for both on and off-resonance excitations, the shaped PVDF modal sensors are superior to point-error sensors, such as accelerometers for controlling specific structural modes.
Vibration Measurements on Rotating Machinery Using Laser Doppler Velocimetry
Authors: Rothberg S. J. , Halliwell N. A.
Published: June 2008

This paper explores the use of laser vibrometry for vibration measurement directly from a rotating component. The presence of a surface velocity component due to the rotation itself is shown to create a strong measurement dependency on vibration perpendicular to the intended measurement direction. Particular ambiguity results at synchronous frequencies. A mathematical means to resolve the genuine vibration components from two simultaneous laser vibrometer measurements is presented and shown to be effective in the study of nonsynchronous rotor vibrations.
Hybrid Damping Through Intelligent Constrained Layer Treatments
Authors: Shen I. Y.
Published: June 2008

This paper is to propose a viable hybrid damping design that integrates active and passive dampings through intelligent constrained layer (ICL) treatments. This design consists of a viscoelastic shear layer sandwiched between a piezoelectric constraining cover sheet and the structure to be damped. According to measured vibration response of the structure, a feedback controller regulates axial deformation of the piezoelectric layer to perform active vibration control. In the meantime, the viscoelastic shear layer provides additional passive damping. The active damping component of this design will produce adjustable and significant damping. The passive damping component of this design will increase gain and phase margins, eliminate spillover, reduce power consumption, improve robustness and reliability of the system, and reduce vibration response at high frequency ranges where active damping is difficult to implement. To model the dynamics of ICL, an eighth-order matrix differential equation governing bending and axial vibrations of an elastic beam with the ICL treatment is derived. The observability, controllability, and stability of ICL are discussed qualitatively for several beam structures. ICL may render the system uncontrollable or unobservable or both depending on the boundary conditions of the system. Finally, two examples are illustrated in this paper. The first example illustrates how an ICL damping treatment, which consists of an idealized, distributed sensor and a proportional-plus-derivative feedback controller, can reduce bending vibration of a semi-infinite elastic beam subjected to harmonic excitations. The second example is to apply an ICL damping treatment to a cantilever beam subjected to combined axial and bending vibrations. Numerical results show that ICL will produce significant damping.
Dynamic Characteristics of Layered Beam with Flexible Core
Authors: Chen Y.-H. , Sheu J.-T.
Published: June 2008

This paper presents an analytical theory to define the dynamic characteristics of a layered beam which is composed of two parallel beams of uniform properties with a flexible core in-between. This flexible core may be made of a kind of viscoelastic material in order to achieve a high shock-absorbing performance. The dynamic interactions between these two parallel beams are especially studied. The dynamic shape functions and the dynamic stiffness matrix of a layered-beam element are established based on the analytical model of two parallel damped Timoshenko beams, connected to each other by the vertical springs and dashpots uniformly distributed along the beam length. Some simple layered beams are employed as the application examples for demonstrations and discussions.
Subharmonic and Quasi-Periodic Motions of an Eccentric Squeeze Film Damper-Mounted Rigid Rotor
Authors: Zhao J. Y. , Linnett I. W. , McLean L. J.
Published: June 2008

When a squeeze-film damper is operated eccentrically, the nonlinear damper forces are no longer radially symmetric and subharmonic and quasi-periodic vibrations may be excited by the rotor unbalance. In this study, the unbalance response of a rigid rotor, supported on an eccentric squeeze film damper, is first approximated by a harmonic series whose coefficients are determined by the collocation method, together with a nonlinear least-square regression. The stability of the resulting periodic solution is then examined using the Floquet transition matrix method. For sufficiently large values of the unbalance and the damper static radial misalignment, it is shown that the approximate harmonic motion loses its stability and bifurcates into a stable subharmonic motion and a quasi-periodic motion at speeds above twice the system critical speed. This analytical finding is verified by a numerical integration in forms of the Poincare´ map, the rotor trajectory, the bifurcation diagram, and the power spectrum. It is suggested that stability analysis and numerical integration should always be incorporated into an approximate analytical method to achieve an adequate approximation. The results of this study show that the introduction of squeeze-film dampers may give rise to the undesirable nonsynchronous vibrations, which limits the maximum speed at which dampers should be used.
Frequency Spectra of Laminated Piezoelectric Cylinders
Authors: Siao J. C.-T. , Dong S. B. , Song J.
Published: June 2008

A finite-element method is presented for determining the vibrational characteristics of a circular cylinder composed of bonded piezoelectric layers. Finite-element modeling occurs in the radial direction only using quadratic polynomials and the variationally derived partial differential equations are functions of the hoop and axial coordinates (θ, z) and time t. Using solution form Q exp {i(ξz + nθ + ωt)}, with Q as the nodal amplitudes, leads to an algebraic eigensystem where any one of the three parameters (n, ξ, ω), the circumferential or axial wave number or natural frequency, can act as the eigenvalue. Integer values always are assigned to n, leaving two possible eigenvalue problems. With ω as the eigenvalue and real values assigned to ξ, the solutions represent propagating waves or harmonic standing vibrations in an infinite cylinder. When ξ is the eigenvalue and real values assigned to ω, this eigensystem admits both real and complex eigendata. Real ξ’s represent propagating waves or harmonic standing vibrations as noted before. Complex conjugate pairs of ξ’s describe end vibrations, which arise when an incident wave impinges upon a free end of a cylindrical bar. They are standing waves whose amplitudes decay sinusoidally or exponentially from the free end into the interior. Two examples are given to illustrate the method of analysis, viz., a solid piezoelectric cylinder of PZT-4 ceramic material and a two-layer cylinder of PZT-4 covering an isotropic material.
Parametric Control of Flexible Systems
Authors: Rahn C. D. , Mote C. D.
Published: June 2008

One position sensor, a bilinear observer, and quadratic, observer-based feedback to a parametric actuator asymptotically stabilize n-modes of a flexible system. Using a perturbation approach, the transient and forced response of a controlled mode are approximated. The decay rate and resonance amplitude are related to the control gains, initial conditions, and forcing amplitude. A forced spillover instability is discovered that can destabilize uncontrolled modes with insufficient damping. A control bound is determined, based on the damping coefficients and frequencies of the modes, that prevents this instability. Experiments on a tension-controlled, pinned-pinned beam demonstrate that parametric control provides substantially faster transient decay and constrained response at resonance.
Modeling and Control of Acoustic Structure Interaction Problems Via Piezoceramic Actuators: 2-D Numerical Examples
Authors: Banks H. T. , Silcox R. J. , Smith R. C.
Published: June 2008

The modeling and active control of acoustic pressure in a 2-D cavity with a flexible boundary (a beam) is considered. Control is implemented in the model via piezoceramic patches on the beam, which are excited in a manner so as to produce pure bending moments. Approximation techniques are discussed and, by writing the resulting system as an abstract Cauchy equation, the problem of reducing interior pressure fluctuations can be posed in the context of an LQR time domain state space formulation. Examples illustrating the dynamic behavior of the coupled system, as well as demonstrating the viability of the control method on a variety of problems with periodic forcing functions, are presented.
On the Structural Nonlinearity of Rotating Shafts
Authors: Leinonen Tatu
Published: June 2008

This paper presents a nonlinear model to describe the bending behavior of a rotating shaft, based on the general theory of a bending bar. Justification for this theoretical model is provided by tests, the resulting curves fitting the observed results more closely than those of other models. In particular, the model explains why infinite points of deformation coming from linear theories can be avoided.
Wavelet Analysis of Vibration: Part 1—Theory
Authors: Newland D. E.
Published: June 2008

Wavelets provide a new tool for the analysis of vibration records. They allow the changing spectral composition of a nonstationary signal to be measured and presented in the form of a time-frequency map. The purpose of this paper, which is Part 1 of a pair, is to introduce and review the theory of orthogonal wavelets and their application to signal analysis. It includes the theory of dilation wavelets, which have been developed over a period of about ten years, and of harmonic wavelets which have been proposed recently by the author. Part II is about presenting the results on wavelet maps and gives a selection of examples. The papers will interest those who work in the field of vibration measurement and analysis and who are in positions where it is necessary to understand and interpret vibration data.
Wavelet Analysis of Vibration: Part 2—Wavelet Maps
Authors: Newland D. E.
Published: June 2008

Wavelet maps provide a graphical picture of the frequency composition of a vibration signal. This paper, which is Part 2 of a pair, describes their construction and properties. In the case of harmonic wavelets, there are close similarities between wavelet maps and sonograms. A range of practical examples illustrate how the wavelet method may be applied to vibration analysis and some of its advantages.
A Transfer-Function Formulation For Nonuniformly Distributed Parameter Systems
Authors: Yang B. , Fang H.
Published: June 2008

This paper studies a transfer-function formulation for general one-dimensional, nonuniformly distributed systems, subject to arbitrary boundary conditions and external disturbances. In the development, the governing equations of the nonuniform system are cast into a state-space form in the Laplace transform domain. The system response and distributed transfer functions are derived in term of the fundamental matrix of the state-space equation. Two approximate methods, the step-function approximation and truncated Taylor series, are proposed to evaluate the fundamental matrix. With the transfer-function formulation, various dynamics and control problems for the nonuniformly distributed system can be conveniently addressed. The transfer-function analysis also is applied to constrained/combined nonuniformly distibuted systems. The method developed is illustrated on two nonuniform beams.
Nonlinear Vibrations of a Beam-Spring-Mass System
Authors: Pakdemirli M. , Nayfeh A. H.
Published: June 2008

The nonlinear response of a simply supported beam with an attached spring-mass system to a primary resonance is investigated, taking into account the effects of beam midplane stretching and damping. The spring-mass system has also a cubic nonlinearity. The response is found by using two different perturbation approaches. In the first approach, the method of multiple scales is applied directly to the nonlinear partial differential equations and boundary conditions. In the second approach, the Lagrangian is averaged over the fast time scale, and then the equations governing the modulation of the amplitude and phase are obtained as the Euler-Lagrange equations of the averaged Lagrangian. It is shown that the frequency-response and force-response curves depend on the midplane stretching and the parameters of the spring-mass system. The relative importance of these effects depends on the parameters and location of the spring-mass system.
Surface Waves in Functionally Gradient Piezoelectric Plates
Authors: Liu G. R. , Tani J.
Published: June 2008

The hybrid numerical method, which has been proposed by the present authors for wave propagation analysis in anisotropic laminated plates, is extended for functionally gradient piezoelectric material (FGPM) plates. The properties of the plate changes continuously in the thickness direction. Characteristics of waves in the plates, and responses of the plates in the time and frequency domain are considered. A technique for calculating responses in the frequency domain is presented. Energy velocities, mode shapes of the waves in an FGPM plate, and the responses of the plate excited by mechanical loads and electrodes are computed. It is found that waves of lower modes in the FGPM plates for large wave numbers appear as surface waves and that a strong surface wave is excited on the softer surface of the FGPM plate. These surface waves can be expected to be used in surface acoustic wave devices.
Unsteady Aerodynamics and Vortex-Induced Aeroelastic Response of a Structural Angle Section
Authors: Modi V. J. , Slater J. E.
Published: June 2008

Wake-body interactions for a two-dimensional structural angle member during stationary and vortex induced oscillatory conditions are studied using a conventional low turbulence wind tunnel. The response of an angle section with combined plunging and torsion indicates that the oscillations occur essentially in one of the two degrees-of-freedom. The measurements of frequency and phase substantiated this observation. The plunging resonance exhibits the familiar vortex capture phenomenon where the shedding frequency is controlled by the cylinder motion over a finite wind speed range. On the other hand, the torsional vibration shows a vortex control phenomenon where the vortex shedding governs the frequency of oscillation. The vortex-induced torsional resonance was found to be severe even at moderate damping levels. The results should prove useful in structural designs such as high-voltage transmission towers, antenna masts, bridges, etc., where angle sections are often used as secondary members.
Membrane and Flexural Waves on Thin Shells
Authors: Norris A. N. , Rebinsky D. A.
Published: June 2008

Membrane and flexural waves are limiting short wavelength solutions of the equations of motion for arbitrarily curved, smooth shells. Each distinct wave type is found using a geometrical or ray method based upon asymptotics in the small parameters h/R, where h is thickness and R a minimum radius of curvature. Useful, asymptotic formulae are found for the normal displacement associated with membrane waves, group velocities, and other physically significant quantities. Ray paths on a conical shell are illustrated for each wave type, and it is found that flexural rays form a caustic near the vertex.
On the Vibration of Bolted Plate and Flange Assemblies
Authors: Tseng J.-G. , Wickert J. A.
Published: June 2008

The vibration of an annular plate that is free along its outer edge, and that is connected to a flange along its inner edge by bolts that are equally spaced in the circumferential direction, is studied. A disk with this geometry, or a stacked array of such disks, is common in applications involving data storage, rotating machinery, or brake systems. The periodic structural imperfections that are associated with the bolt pattern can have interesting implications for the plate’s dynamic response. Changes that occur in the natural frequencies and mode shapes as a result of such deviations from an ideally clamped inner edge are studied through laboratory measurements, and through an approximate model that captures the rotationally periodic character of the bolted plate and flange system. In the axisymmetric case, the natural frequencies of the plate’s “sine” and “cosine” vibration modes are repeated for a specified number of nodal diameters. Under the influence of a regular bolt pattern, and the resulting local variations of the stiffness and compression at the plate/flange interface, some natural frequencies are repeated and others split. This process depends on the number of bolts used to mount the plate, and on the number of nodal diameters present in a specific vibration mode. A straightforward criterion to predict the split and repeated modes is discussed.
Chaotic Normal Vibrations and Friction at Mechanical Joints with Nonlinear Elastic Properties
Authors: Hess D. P. , Wagh N. J.
Published: June 2008

This paper describes an investigation of the dynamics of contact systems that exhibit nonlinear stiffness characteristics. A dynamic contact model that accommodates normal motions with either analytical or empirical descriptions of nonlinear interface compliance has been formulated. Other joint nonlinearities, such as play and discontinuous changes in friction, which have been considered previously, are avoided in this study. The interface friction is related to the normal motion through the adhesion theory of friction. Numerical analyses of the model using common joint component materials and interface finishes under dynamic loads reveal that chaotic joint motion and, by implication, chaotic friction can occur over a significant range of contact parameters and operating conditions. Even though the chaotic motions are found to be on the order of microns, the instantaneous friction force is found to fluctuate considerably in the presence of such micro-scale normal motions.
Nonlinear Resonances in a Flexible Cantilever Beam
Authors: Anderson T. J. , Balachandran B. , Nayfeh A. H.
Published: June 2008

An experimental investigation into the response of a nonlinear continuous systems with many natural frequencies in the range of interest is presented. The system is a flexible cantilever beam whose first four natural frequencies are 0.65 Hz, 5.65 Hz, 16.19 Hz, and 31.91 Hz, respectively. The four natural frequencies correspond to the first four flexural modes. The fourth natural frequency is about fifty times the first natural frequency. Three cases were considered with this beam. For the first case, the beam was excited with a periodic base motion along its axis. The excitation frequency fe was near twice the third natural frequency f3, which for a uniform isotropic beam corresponds to approximately the fourth natural frequency f4. Thus the third mode was excited by a principal parametric resonance (i.e., fe ≈ 2f3) and the fourth mode was excited by an external resonance (i.e., fe ≈ f4) due to a slight curvature in the beam. Modal interactions were observed involving the first, third, and fourth modes. For the second case, the beam was excited with a band-limited random base motion transverse to the axis of the beam. The first and second modes were excited through nonlinear interactions. For the third case, the beam was excited with a base excitation along the axis of the beam at 138 Hz. The corresponding response was dominated by the second mode. The tools used to analyze the motions include Fourier spectra, Poincare´ sections, and dimension calculations.
A New Approach to the Early Prediction of Turning Chatter
Authors: Bao Shan-Fei , Zhang Wen-Guo , Yu Jun-Yi , Qiao Si-Mao , Yang Fu-Lun
Published: June 2008

A new approach to the early prediction of turning chatter is described in this paper; the interval frequency difference H in the amplitude domain of the dynamic cutting force is taken as a prediction parameter. The theoretical analysis and experiments results indicate that the approach presented can lead to a quick prediction of turning chatter with higher accuracy and adaptability.
Piezothermoelasticity and Precision Control of Piezoelectric Systems: Theory and Finite Element Analysis
Authors: Tzou H. S. , Ye R.
Published: June 2008

Piezothermoelastic effects of distributed piezoelectric sensor/actuator and structural systems are studied. Distributed controls (static and dynamic) of piezoelectric laminates subjected to a steady-state temperature field are investigated. Piezothermoelastic constitutive equations are defined, followed by three energy functionals for the displacement, electric, and temperature fields, respectively. A new 3-D piezothermoelastic thin hexahedron finite element with three internal degrees of freedom is formulated using a variational formulation which includes thermal, electric, and mechanical energies. A system equation for the piezoelectric continuum exposed to combined displacement, electric, and temperature fields is formulated. Distributed sensing and control equations of piezoelectric laminates in a temperature field are derived. Thermal influences on the sensing and control of piezoelectric PZT/steel laminates are investigated in case studies.
Power Transmission from a Vibrating Source through an Intermediate Flexible Panel to a Flexible Cylinder
Authors: Pan Jiaqiang , Hansen C. H.
Published: June 2008

When active control is used to reduce the vibration transmission through machine isolators into supporting structures, the vibratory power transmission through the isolators is often used as the cost function to be minimized. To apply active control effectively to machine isolation systems, it is necessary to investigate the nature of the vibratory power transmission from a vibrating machine to its supporting structure through the isolators. In this study the reduction of vibratory power transmission from a vibrating rigid body into a flexible simply supported cylinder through a flexible, completely free intermediate panel and multiple connected isolators is investigated theoretically and numerically. The system studied in this paper can be taken as a simplified dynamical model of equipment mounting configurations in submarines.
An Integrated Approach Toward the Dynamic Analysis of High-Speed Spindles: Part I—System Model
Authors: Chen C. H. , Wang K. W. , Shin Y. C.
Published: June 2008

Experimental evidence (Shin, 1992) has shown that the natural frequencies of high-speed spindles with angular contact ball bearings decrease with increasing rotational speed. A recent study (Wang et al., 1991) illustrated that this phenomenon is caused by stiffness change of the bearings. A simplified approximation was used in the past analysis to examine the bearing radial stiffness at high speeds. While the investigation explained the experimental observations in a qualitative sense, the analytical results so far are not sufficient to quantitatively describe the spindle behavior under high speed and load operations due to the assumptions and approximations made in the modeling process. This paper presents an integrated approach toward the modeling of flexible spindles with angular contact ball bearings from basic principles. The local dynamics of the bearings are coupled with the global shaft motion. The model derived includes both the longitudinal and transverse vibrations of the shaft interacting with the nonlinear bearings. The influences of shaft speed on the bearing stiffness matrix and the system frequencies are studied. It is shown that the spindle dynamic behavior can vary substantially as speed increases due to the bearing gyroscopic moment and centrifugal force. These effects have been ignored in most of the previous spindle models. This unique characteristic, which is critical to high-speed machinery, is rigorously studied for the first time. Lab tests are conducted to validate the model. The analytical predictions are quantitatively verified by the experimental results.
An Integrated Approach Toward the Dynamic Analysis of High-Speed Spindles: Part 2—Dynamics Under Moving End Load
Authors: Chen C. H. , Wang K. W.
Published: June 2008

This paper presents an integrated study of a rotor/bearing structure, with specific interests toward high-speed spindle systems under rotating end loads. Considering the coupling between the rotating shaft and the nonlinear bearings, an iterative method is developed to derive the system equilibrium configuration for given operating conditions. With moving end loads, structural instability caused by high rotational speed is analyzed. The critical speeds and unstable speed regions are discussed. Machining chatter instability lobes are also derived using the spindle model. It is shown that significant errors will occur in predicting spindle characteristics and stability if the speed and load effects on the shaft/bearing dynamics are neglected.
Frequency Domain State-Space System Identification
Authors: Chen Chung-Wen , Juang Jer-Nan , Lee G.
Published: June 2008

This paper presents an algorithm for identifying state-space models of linear systems from frequency response data. A matrix-fraction description of the transfer function is employed to curve-fit the frequency response data, using the least-squares method. The parameters of the matrix-fraction representation are then used to construct the Markov parameters of the system. Finally, state-space models are obtained through the Eigensystem Realization Algorithm using the Markov parameters. The main advantage of this approach is that the curve-fitting and the Markov-parameter-construction are linear problems which avoid the difficulties of non-linear optimization of other approaches. Another advantage is that it avoids windowing distortions associated with other frequency domain methods.
Vibration of Rectangular Mindlin Plates with Intermediate Stiffeners
Authors: Liew K. M. , Xiang Y. , Kitipornchai S. , Lim M. K.
Published: June 2008

A first known investigation into the vibratory characteristics of rectangular Mindlin plates with intermediate stiffeners is presented. The Rayleigh-Ritz method is used, with displacement and rotational functions assumed in the form of mathematically complete algebraic polynomials. Sets of numerical frequency parameters for rectangular plates of various boundary conditions, thicknesses and plate dimensions are presented. In the study, the effects of shear deformation and rotary inertia on the vibrational response of the plate structures are investigated. The influence of torsional rigidity and geometric properties of stiffeners on the natural frequency parameters are included. To validate the proposed formulation, numerical results for some simplified problems have been determined where existing literature for these problems can be found. Finally sets of new vibration frequencies for plates with one or more stiffeners in various directions are presented.
Dynamic Effects in Mechanical Structures with Gaps and Impacting: Order and Chaos
Authors: Goldman P. , Muszynska A.
Published: June 2008

The paper discusses orderly and chaotic dynamic responses of simple mechanical structures with clearances and impacting. Experimental results from a simulator of a rotating machine with one loose pedestal are presented, and a summary of analytical results for this case is given. The orderly and chaotic responses obtained through numerical integration are presented in the form of bifurcation diagrams. The second part of the paper discusses an existence of the main and higher order resonances in structures with clearances and impacting, which are excited by external periodic forces. For a one-degree-of-freedom nonlinear system, the application of a discontinuous variable transformation, followed by an averaging method provides analytical formulae describing the system response amplitudes and phases in the proximity of the main and harmonic resonances. A numerical example illustrates the results. The discussed methodology can be generalized for the cases of more complex systems.
Mechanisms of Noise Transmission through Helicopter Gearbox Support Struts
Authors: Brennan M. J. , Pinnington R. J. , Elliott S. J.
Published: June 2008

Helicopter gearbox support struts are structural members designed to take large compressive and tensile mechanical loads. They also act as vibration transmission paths connecting the major noise and vibration generators of the main rotor and gearbox to the fuselage and cabin. In this paper the mechanisms of vibration transmission through these struts are examined. The differences between the low frequency behavior that is important in the transmission of the rotor vibrations, and the high frequency behavior that is important in the transmission of gear noise are discussed. A flexible element is introduced in series with the strut, and the limitations of this simple passive measure in attenuating longitudinal and flexural vibrations are highlighted. The analysis shows that there is a difference in the mechanisms of vibration transmission between low and high frequencies, and that there are difficulties in applying effective passive vibration isolation measures to this system.
On Localization in Coupled, Spinning, Circular Plates
Authors: Orgun C. O. , Tongue B. H.
Published: June 2008

The vibrational response of multiple rotating circular plates, stacked together on a central spindle and coupled through stationary springs, is investigated. An analytical model is derived and a Rayleigh-Ritz approach employed in order to obtain the system’s modal response. Mode localization is shown to occur at all speeds of rotation for weakly coupled subcomponents and the degree to which the system exhibits localized behavior is shown to increase with rotation speed.
Application of System Identification to the Absolute Calibration of Acoustic Emission Signals
Authors: Liu Pei-Ling , Song Tseng-Hwa , Wu Tsung-Tsong
Published: June 2008

This paper studies the absolute calibration of acoustic emission signals. The experiments were conducted on a thin plate. Fracture of a glass capillary was adopted to generate a vertical force with a unit-step source function, and an NBS conical transducer was used to record the surface response. It is found that the output of the conical transducer contains surplus wiggles and exhibits amplitude decay. The system identification method is introduced to determine the dynamic model of the system. Calibration using the system model successfully recovers the amplitude and greatly suppresses the surplus wiggles. The method is further improved by subtracting the characteristic curve of the wiggles from the experimental data before the system identification approach is carried out.
A Numerical Solution for the Transient Displacement of a Circumferentially Moving Cylindrical Shell
Authors: Mu¨ftu¨ S. , Benson R. C.
Published: June 2008

In magnetic tape recording it is important to control the tape displacement as it is transported over guides and recording heads. In this paper a numerical solution is presented for the transient motion of a tape that is circumferentially transported. The tape may be modelled as a thin cylindrical shell, with “gyroscopic” effects arising from the tape transport. Spatial derivatives are discretized with finite difference approximations, and time derivatives are discretized by Newmark’s method. The result is a robust computer algorithm that is used in making 3D-transient simulations of flexural waves following a radial load. This ability is demonstrated to be important for realizing that reflection of the waves from the lateral sides of the tape has significant effect on the transient displacement. Results that have been previously published on “critical” speeds, wave shapes near a concentrated load point, and the dominant period of the load point displacement are further developed. A better approximation of the critical tape speed is presented, and the dominant period of the load point displacement is found to be dependent on the tape velocity.
Isolation of the Spectrograms and Rosettes of Insonified Sets of Submerged, Concentric, Thin Shells
Authors: Gaunaurd G. C. , Akay A.
Published: June 2008

The resonance features present, and observable, in the form-functions of submerged, fluid-filled, elastic, thin shells, usually appear combined with smooth, undesirable, background components that tend to obscure them. In order to isolate these features in the frequency domain, at fixed angles of observation, (i.e., the “spectograms”), or in the angular domain, at selected frequencies (i.e., the “rosette” patterns), one usually attempts to suppress the background components by subtracting “suitable” background coefficients. Since the rigid/soft background coefficients of solid elastic bodies/cavities in solids yield unsatisfactory results for thin shells, various other background coefficients have been tried with various levels of success. We present here a more general scattering formulation, valid for many concentric shells, that permits the isolation of these resonance features without having to subtract any type of background coefficients. This resonance feature extraction is achieved either conceptually, or physically, filling the various spaces in between the various concentric shells, with the same fluid present in the outer ambient medium. The extraction of these echo-features is crucial for purposes of active classification by sonar.
Operation of an Electromagnetic Eddy-Current Damper with a Supercritical Shaft
Authors: Frederick J. R. , Darlow M. S.
Published: June 2008

A basic problem inherent with the operation of supercritical shafting is the application of appropriate external damping, which is generally necessary to suppress nonsynchronous instabilities and limit the synchronous response of even a well-balanced shaft. Typically, coulomb or squeeze film-type dampers are used, in which case the damping properties tend to change with temperature, and the necessary contact results in additional torque loading and wear. An alternative damping method currently under investigation is the application of a noncontact electromagnetic damper that dissipates energy through induced eddy-currents generated in a small disk mounted to, and rotating with the shaft (Frederick, 1990). Research is underway on the design and development of a damper of this type that could eventually lend itself to active control applications. The objectives of this investigation are the initial design of a magnetic circuit, an appropriate d-c power supply, and the characterization of preliminary performance experiments on a composite shaft. Damper operation was evaluated during rotating shaft tests and compared to prior tests which involved the use of a permanent magnet eddy-current damper. This Note concerns some interesting results obtained from these preliminary tests. The damper worked well at low speeds, but some high-speed stability problems were encountered. Potential solutions to these problems as well as areas of future research are discussed.
Gains of chromosome region 3q26 in intraepithelial neoplasia and invasive squamous cell carcinoma of the vulva are frequent and independent of HPV status
Authors: Aulmann S , Schleibaum J , Penzel R , Schirmacher P , Gebauer G , Sinn H P
Published: June 2008

Aims:

Two different forms of vulvar intraepithelial neoplasia (VIN) are recognised: (1) usual-type (bowenoid) VIN, which is related to high-risk papillomavirus infection, and (2) differentiated (simplex) VIN, which is associated with chronic inflammation. The aim of this study was to investigate the presence of chromosome 3q26 gains in the spectrum of precancerous lesions and invasive squamous cell carcinomas (SCCs) of the vulva.

Methods:

3q26 gains were analysed using fluorescence in situ hybridisation in a series of usual-type VINs, VINs of the differentiated type and invasive squamous cell carcinomas. In addition, all cases were examined for human papillomavirus (HPV) DNA, p53 mutations, and p16 and p53 protein expression.

Results:

Gains of chromosome 3q26 were present in all VINs of the differentiated type and in 50% of the usual-type VIN lesions. 81% of SCCs were positive for 3q26 gains irrespective of the HPV status and of the associated precursor lesion. HPV-associated lesions exhibited the typical, strong cytoplasmic p16 accumulation while mutated p53 was only detected in HPV-negative VINs or SCCs, and was associated with an overexpression of p53 protein.

Conclusions:

Immunohistochemical evaluation of p16 and p53 expression aids in the differential diagnosis of squamous cell alterations of the vulva. However, detection of 3q26 imbalance is of additional diagnostic value in difficult cases of HPV-unrelated usual-type VINs and VINs of the differentiated type.