bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of Damping at the Micromechanical Level in Polymer Composite Materials Under Transverse Normal Loading by the Use of Special Fiber Coatings
Authors: Finegan I. C. , Gibson R. F.
Published: February 2008

This paper describes preliminary results from a systematic analytical study of the improvement of damping in polymer composites at the micromechanical level under transverse normal loading by the use of special fiber coatings. Since shear deformations are important in damping of viscoelastic polymers, and large shear strains are generated in the region of the fiber/matrix interface, one idea for improving damping is to put a fiber coating made from a highly dissipative material in this region. A finite element model based on a “representative volume element” or repeating element of a continuously reinforced coated fiber composite is used to study damping under transverse normal loading. The micromechanical composite model investigated is a unidirectional graphite/epoxy with an acrylic polymer as the fiber coating material. Both two and three dimensional finite element models are analyzed in order to compare the influence of plane stress and plane strain conditions on the damping and stiffness properties of the composite micromechanical model. Parametric studies are conducted by using a two dimensional plane strain finite element model in order to illustrate how the coating applied to the fiber influences dynamic properties of the composite structure. The parametric studies are done with particular emphasis on the effects of frequency, temperature, and fiber coating thickness on the damping of the composite structure.
Finite Width Effects on the Critical Speed of Axially Moving Materials
Authors: Lin C. C.
Published: February 2008

An exact solution is provided to determine the effects of the free end boundary conditions and the slenderness ratios on the critical speed of two dimensional, axially moving materials. The axially moving beam theory and the mathematical, two-dimensional model with all edges simply supported are also considered for comparison.
Steady State Response Prediction of General Linear Structures Coupled by Local Nonlinear Elements
Authors: Xu K. Q. , Rice H. J.
Published: February 2008

This short paper is concerned with a direct application of the techniques developed by the authors in two previous publications. It is considered as a “booster” to the existing alternating frequency/time domain method which already has many important advantages over most other methods.
Exact Modeling of the Spatial Rigid Body Inertia Using the Finite Element Method
Authors: Christensen A. P. , Shabana A. A.
Published: February 2008

In the classical finite element literature beams and plates are not considered as isoparametric elements since infinitesimal rotations are used as nodal coordinates. As a consequence, exact modeling of an arbitrary rigid body displacement cannot be obtained, and rigid body motion does not lead to zero strain. In order to circumvent this problem in flexible multibody simulations, an intermediate element coordinate system, which has an origin rigidly attached to the origin of the deformable body coordinate system and has axes which are parallel to the axes of the element coordinate system in the undeformed configuration was introduced. Using this intermediate element coordinate system and the fact that conventional beam and plate shape functions can describe an arbitrary rigid body translation, an exact modeling of the rigid body inertia can be obtained. The large rigid body translation and rotational displacements can be described using a set of reference coordinates that define the location of the origin and the orientation of the deformable body coordinate system. On the other hand, as demonstrated in this investigation, the incremental finite element formulations do not lead to exact modeling of the spatial rigid body mass moments and products of inertia when the structures move as rigid bodies, and such formulations do not lead to the correct rigid body equations of motion. The correct equations of motion, however, can be obtained if the coordinates are defined in terms of global slopes. Using this new definition of the element coordinates, an absolute nodal coordinate formulation that leads to a constant mass matrix for the element can be developed. Using this formulation, in which no infinitesimal or finite rotations are used as nodal coordinates, beam and plate elements can be treated as isoparametric elements.
Transducer Placement for Broadband Active Vibration Control Using a Novel Multidimensional QR Factorization
Authors: Heck L. P. , Olkin J. A. , Naghshineh K.
Published: February 2008

This paper advances the state of the art in the selection of minimal configurations of sensors and actuators for active vibration control with smart structures. The method extends previous transducer selection work by (1) presenting a unified treatment of the selection and placement of large numbers of both sensors and actuators in a smart structure, (2) developing computationally efficient techniques to select the best sensor-actuator pairs for multiple unknown force disturbances exciting the structure, (3) selecting the best sensors and actuators over multiple frequencies, and (4) providing bounds on the performance of the transducer selection algorithms. The approach is based on a novel, multidimensional extension of the Householder QR factorization algorithm applied to the frequency response matrices that define the vibration control problem. The key features of the algorithm are its very low computational complexity, and a computable bound that can be used to predict whether the transducer selection algorithm will yield an optimal configuration before completing the search. Optimal configurations will result from the selection method when the bound is tight, which is the case for many practical vibration control problems. This paper presents the development of the method, as well as its application in active vibration control of a plate.
The Prediction of Substructure and System Modes by the Extended Complex Mode Indication Function
Authors: Lin A. C. Y. , Tsuei Y. G.
Published: February 2008

Yee and Tsuei (1989) developed the Modal Force Technique (MFT) as a tool for component synthesis. The approach utilizes the frequency response functions at connecting joints to predict the dynamical behavior of a synthesized system. The main difference between the MFT and the traditional impedance modeling approach is that no inversion of the frequency response functions is required for the MFT, which makes the Model Force Technique more efficient. The other major feature is that the Modal Force matrix of the synthesized system equation contains the information of both the substructure and the system modes. To determine the natural frequency and the damping of a complex mode based on the frequency response functions, the Extended Complex Mode Indication Function (Extended CMIF) technique was developed. It performs the singular value decomposition (SVD) of the Modal Force matrix at each spectral line. The peaks of the singular value plot indicate the location of the substructure modes, while the anti-peaks show the location of the system modes. This approach is simple, straightforward and can be efficiently implemented to identify complex modes.
A Comparison of Conventional and Impedance Methods for Modeling Piezoelectric Materials Actuation in Smart Structures
Authors: Wang Y. , Slater J. C.
Published: February 2008

In this paper two distinct methods, an impedance method and a “conventional” method, for modeling the dynamic interaction between the piezoelectric actuators/sensors and the substructures are summarized. It is demonstrated that both methods yield equivalent models for the beam with piezoceramic actuation. The pros and cons of each technique are discussed.
The Innovations Approach to Experimental Modeling of Flexible Structures
Authors: Kashani R.
Published: February 2008

A technique based on the innovations approach to linear least square identification is proposed for experimental state space modeling of flexible structures. Upon the selection of the model structure and order, the unknown parameters are identified by minimizing the sum of squares of the innovations process. Contrary to having a black-box approach to experimental modeling, this technique uses physical parameterization of the structural dynamics, as well as measurement noise properties. The innovations approach to experimental modeling of the flexible structures automates the identification of unknown parameters in the model and reduces the number of these unknowns to its minimum resulting in small variances in their estimated values. The effectiveness of this experimental modeling technique is demonstrated by accurately identifying the modal information of a rectangular flexible plate, free at two sides and fixed at the other two. The plate is patched with PZT actuators and nearly-collocated sensors at two locations.
Noise Propagation Through Helicopter Gearbox Support Struts—An Experimental Study
Authors: Brennan M. J. , Elliott S. J. , Heron K. H.
Published: February 2008

A dominant source of noise in a helicopter cabin is the meshing of the gears in the main rotor gearbox. The main structural noise transmission path from this gearbox to the cabin is through the gearbox support struts, and this is the transmission path which is the subject of this paper. An experimental study is described which quantifies the way in which vibration propagates through one of these struts and the experimental results are interpreted with the aid of some simple analytical models. The contribution of the various modes of vibration to the transmission of the structure-borne noise is quantified by calculating the kinetic energy of the receiving structure from measured data. The results show that although the dominant mode of vibration is longitudinal, flexural resonances occur at some frequencies, and the contribution of the flexural vibration to the kinetic energy of the receiving structure at these frequencies can be comparable with that due to the longitudinal motion. It is demonstrated that the lateral behavior of the strut is dependent upon the static loading but the longitudinal behavior is relatively insensitive to this loading.
Identification of the Dynamic Characteristics of Long Annular Seals Using a Time Domain Technique
Authors: Ismail M. , Brown R. D.
Published: February 2008

This paper describes experimental results from a research program aimed at a study of the static and dynamic characteristics of liquid long annular seals. A seal test rig permits the identification in the time domain of mass, stiffness, and damping coefficients using a least-squares technique based on the singular value decomposition method. The experimental method relies on the forced excitation of a flexibly supported stator by two hydraulic shakers. The forcing signal is composed from a small number of frequencies which are not related to the rotational frequency of the rigid shaft rotating inside the stator. The test data consisting of two inertia, four stiffness, and four damping coefficients is compared with theoretical predictions based on two theoretical models: (i) the model of Black et al. (1971 and 1981) and (ii) the model of Childs and Kim (1985).
An Active Control Design for a Class of Parametrically Excited Systems Based on the Gradient Algorithm
Authors: Chen Min-Shin , Fu Ren-Jay
Published: February 2008

This paper introduces a new control design for a dynamic system subject to stationary or nonstationary parametric excitations. In this new design, the system dynamics is transformed into one with a null system matrix using the variation of parameters method. A stabilizing state feedback control can then be immediately obtained by following the gradient algorithm that is originally developed for the parameter identification purpose. Such a design has the advantage that the control requires only past and present information of the time-varying parametric excitations while previous control designs usually require prediction of future information of the excitations. The closed-loop system stability is guaranteed if the open-loop state response does not diverge too fast. The control design approach can also be applied to the observer design in case where there is only partial observation of the system state.
Finite Element Analysis of the Lateral Vibration of Thin Annular and Circular Plates With Variable Thickness
Authors: Chen Dian-Yun , Ren Bao-Sheng
Published: February 2008

The method of annular finite elements with variable thickness is applied for analyzing the lateral vibration of thin annular and circular plates. The material of the plates may be of isotropic or polar orthotropic and the plate thickness may vary arbitrarily with the radius. Natural frequencies and mode shapes of the axisymmetric and nonaxi-symmetric modes are obtained. The numerical convergence of the method has been tested and comparisons have been made with the results obtained in other studies. It has been proved that the convergence of this method is very rapid and obtained results are very accurate.
State Space Modeling of an Acoustic Duct With an End-Mounted Speaker
Authors: Venugopal R. , Bernstein D. S.
Published: February 2008

This paper develops a state space model of the dynamics of an acoustic duct with end-mounted speakers. The initial model formulation includes the forcing term as part of the boundary conditions. The shifted particle velocity is then defined to transform the nonhomogeneous boundary conditions into homogeneous boundary conditions and thus develop the state space model. It is shown that the speaker and acoustic dynamics interact by means of feedback in which the speaker creates an acoustic field, which, in turn, affects the motion of the speaker cone. This interaction is studied using positive real closed-loop feedback analysis, and shifts in the modal frequencies of the duct due to the presence of the end-mounted speaker are predicted.
Free Vibration and Stability Analysis of Internally Damped Rotating Shafts With General Boundary Conditions
Authors: Melanson J. , Zu J. W.
Published: February 2008

Vibration analysis of an internally damped rotating shaft, modeled using Timoshenko beam theory, with general boundary conditions is performed analytically. The equations of motion including the effects of internal viscous and hysteretic damping are derived. Exact solutions for the complex natural frequencies and complex normal modes are provided for each of the six classical boundary conditions. Numerical simulations show the effect of the internal damping on the stability of the rotor system.
Vibration of High-Speed Spur Gear Webs
Authors: Arakere N. K. , Nataraj C.
Published: February 2008

High cycle fatigue loading of gear webs due to in-plane stresses, caused by forced excitation resulting from centrifugal loading and dynamic tooth loads, has been known to cause radial fatigue cracks. This is especially prevalent in high-speed gears used in aerospace applications, with small web thickness, for weight reduction. Radial cracks have also been observed to originate at the outer edge of lightening holes machined in gear webs for weight reduction. This paper presents an analytical treatment of the in-plane vibration of high-speed gear webs resulting from rotational effects and periodic excitation from dynamic tooth loading. Dynamic tooth loads result from the combined effect of inertia forces of gear wheels which are significant at high speeds, the periodic variation of gear mesh stiffness, and involute tooth profile errors. The gear web is modeled as a thin rotating disc and the governing differential equations of motion and the associated boundary conditions are derived from first principles. The equations are then nondimensionalized which leads to some essential nondimensional parameters. A comprehensive tooth stiffness model for spur gears is used that accounts for periodic variation of mesh stiffness. The dynamic tooth loads are obtained by solving the pertinent equations of motion, using a collocation method, that yields a closed-form expression for the periodic excitation, that is used as an input for the in-plane vibration problem. The in-plane vibration equations are solved by an approximate method of weighted residuals. It is found that the displacement fields and the resulting stresses can be significant under certain speeds and loading conditions. The interaction between the forcing frequencies due to gear teeth dynamics and the in-plane vibration natural frequencies can result in resonances that induce high fatigue stresses in the gear web. The in-plane stresses leading to high cycle fatigue loading, and frequency components of the resulting response are discussed in detail.
A Higher Order Finite Element Model for the Vibration Analysis of Laminated Beams
Authors: Marur S. R. , Kant T.
Published: February 2008

A higher order displacement model based on a cubic axial strain, cubic transverse shear strain and quadratic transverse normal strain across the thickness of the beam, to model exactly the warping of the cross section is proposed which maintains zero stress at the top and bottom of the beam with out the aid of any shear correction factor. Numerical experiments carried out clearly bring out the efficacy of this model over the first order theory for laminated beams.
Dynamics of a Rotating System With a Nonlinear Eddy-Current Damper
Authors: Kligerman Y. , Gottlieb O.
Published: February 2008

We investigate the nonlinear dynamics and stability of a rotating system with an electromagnetic noncontact eddy-current damper. The damper is modeled by a thin nonmagnetic disk that is translating and rotating with a shaft in an air gap of a direct current electromagnet. The damper dissipates energy of the rotating system lateral vibration through induced eddy-currents. The dynamical system also includes a cubic restoring force representing nonlinear behavior of rubber o-rings supporting the shaft. The equilibrium state of the balanced rotating system with an eddy-current damper becomes unstable via a Hopf bifurcation and exact solutions for the limit cycle radius and frequency of the self-excited oscillation are obtained analytically. Forced vibration induced by the rotating system mass imbalance is also investigated analytically and numerically. System response includes periodic and quasiperiodic solutions. Stability of the periodic solutions obtained from the balanced self-excited motion and the imbalance forced response is analyzed by use of Floquet theory. This analysis enables an explanation of the nonlinear dynamics and stability phenomena documented for rotating systems controlled by electromagnetic eddy-current dampers.
Combining Subset Selection and Parameter Constraints in Model Updating
Authors: Friswell M. I. , Mottershead J. E. , Ahmadian H.
Published: February 2008

Model updating often produces sets of equations whose solution are ill-conditioned and extra information must be used to produce a well-conditioned estimation problem. One possibility is to change all the parameters, but to introduce extra constraints, for example by taking the minimum norm solution. This paper takes a different approach, by considering only a subset of the parameters to be in error. The critical decision is then the choice of parameters to include in the subset. The methods of subset selection are outlined and extended to the selection of groups of parameters. The incorporation of side constraints is considered and demonstrated using an experimental example.
Input Force Reconstruction Using a Time Domain Technique
Authors: Kammer D. C.
Published: February 2008

A time domain method is presented for estimating the discrete input forces acting on a structure based upon its measured response. The structure is essentially transformed into its own loads transducer. A set of inverse system Markov parameters, in which the roles of input and output are reversed, is estimated from forward system Markov parameters using a linear predictive scheme. Inputs and acceleration outputs are assumed to be collocated to maintain minimum phase. Subsequently, any set of measured operational sensor data of any time duration can be convolved with the inverse Markov parameters to produce estimates of the input forces. This problem is ill-posed, so a regularization technique is employed to stabilize computations. A stability analysis is performed to illustrate the effects of the regularization. Predicted pseudo-forces qualitatively approximate the actual input forces and, when applied back to the structure, produce accelerations which accurately match the measured operational sensor data.
Evaluation of an Actuator Placement Method for Active Noise Control Applications
Authors: Naghshineh K. , Heck L. P. , Olkin J. A. , Kamman J. W.
Published: February 2008

In our previous work, we developed a new actuator placement algorithm that is capable of selecting the best actuator placement for active noise control problems over a broad band of frequencies. The actuator selection algorithm is based on a novel extension of the Householder QR subset selection algorithm. The QR algorithm uses the l2 matrix norm as a performance measure. In this paper, numerical results generated by that algorithm are compared with numerical results generated using five different performance measures. These measures, which are based on different matrix norms and functions of the actuator frequency responses, yield actuator placements that result in active noise control systems with improved performance and robustness.
The Dynamics of a Flexible Beam With a Lubricated Prismatic Kinematic Pair
Authors: Marghitu D. B. , Guran A.
Published: February 2008

In this article we consider the influence of the prismatic kinematic pair lubrication film on the planar vibrations of a constant cross-sectional straight link that is attached to the joint. The main objective is to develop an analytical model that incorporates the effect of the lubricant film on the vibration of elastic links in mechanisms. It has been assumed that the beam on which the prismatic kinematic pair translates is a linear elastic body. Equations for the translational and rotational motions of the link are developed by applying Hamilton’s principle. Kinetic energy that is required for the application of this principle has been derived by utilizing a generalized velocity field theory for elastic solids. This approach provides means to include the inertia terms directly in the equations of motion. The pressure field exerted through the viscous, incompressible, lubricant film is obtained from the solution of the Reynolds equation of lubrication. We introduce a scheme to solve the resulting two sets of equations for the vibrations of the link and the motion of the fluid. The pressure field is used to compute the external force exerted by the fluid on the link. The utility of the method is demonstrated by considering a planar mechanism that includes an elastic element with a prismatic joint.
Characteristics of Enhanced Active Constrained Layer Damping Treatments With Edge Elements, Part 1: Finite Element Model Development and Validation
Authors: Liao W. H. , Wang K. W.
Published: February 2008

This paper is concerned with the enhanced active constrained layer (EACL) damping treatment with edge elements. A finite element time-domain-based model (FEM) is developed for the beam structure with partially covered EACL. The edge elements are modeled as equivalent springs mounted at the boundaries of the piezoelectric layer. The Golla-Hughes-McTavish (GHM) method is used to model the viscoelastic layer. The GHM dissipation coordinates can describe the frequency-dependent viscoelastic material properties. This model becomes the current active constrained layer (ACL) system model as the stiffness of the edge elements approaches zero. Without the edge elements and viscoelastic materials, the purely active system model can also be obtained from the EACL model as a special case. Lab tests are conducted to validate the models. The frequency responses of the EACL, current ACL, and purely active systems predicted by the FEM match the test results closely. Utilizing these models, analysis results are illustrated and discussed in Part (2) of this paper.
Characteristics of Enhanced Active Constrained Layer Damping Treatments With Edge Elements, Part 2: System Analysis
Authors: Liao W. H. , Wang K. W.
Published: February 2008

This paper presents some important characteristics of enhanced active constrained layer damping (EACL) treatments for vibration controls. Specific interests are on understanding how the edge elements will influence the active action authority, the passive damping ability, and their combined effects in EACL. Analysis results indicate that the edge elements can significantly improve the active action transmissibility of the current active constrained layer damping (ACL) treatment. Although the edge elements will slightly reduce the viscoelastic material (VEM) passive damping, the EACL will still have significant damping from the VEM. Combining the overall active and passive actions, the new EACL with sufficiently stiff edge elements not only could achieve better performance with less control effort compared to the current ACL system, but also could outperform the purely active system. With careful analysis, we can map out the required critical edge element stiffness for successful designs. In addition, analysis also shows that the EACL treatment is a more robust design. That is, it could outperform both the purely active and passive systems throughout a much broader design space than the current ACL configuration. With these desirable characteristics, the EACL could be used to realize an overall optimal active-passive hybrid system.
Nonlinear Periodic Response of Engine Accessory Drives With Dry Friction Tensioners
Authors: Leamy M. J. , Perkins N. C.
Published: February 2008

Belt drives have long been utilized in engine applications to power accessories such as alternators, pumps, compressors and fans. Drives employing a single, flat, “serpentine belt” tensioned by an “automatic tensioner” are now common in automotive engine applications. The automatic tensioner helps maintain constant belt tension and to dissipate unwanted belt drive vibration through dry friction. The objective of this study is to predict the periodic rotational response of the entire drive to harmonic excitation from the crankshaft. To this end, a multi-degree of freedom incremental harmonic balance method (IHB) is utilized to compute periodic solutions to the nonlinear equations of motion over a wide range of engine speeds. Computed results illustrate primary and secondary resonances of the accessory drive and tensioner stick-slip motions.
Nonconservative Stability of a Friction Loaded Disk
Authors: Tseng J.-G. , Wickert J. A.
Published: February 2008

This paper investigates the vibration of an annular disk that is subjected to rotation and in-plane frictional traction distributed over a sector of the disk’s two faces. Technical applications include noise, vibration, and harshness in automotive and aircraft disk brakes, clutches, transmissions, and other rotating machine components. To the degree that the rotor-to-stator friction in such cases is directed along the disk’s deformable surface, it is treated here as a nonconservative follower-type load. The vibration model incorporates membrane stiffness which derives both from rotation, and from the stresses established as a result of friction. The plane stress state is determined in closed form as a Fourier series, and that solution is compared with the companion, but computationally intensive, results from finite element analysis. For the cases of sector-shaped and full annular loading, the vibration model predicts the critical mode, which is defined as the one that becomes dynamically unstable at the lowest friction level. Vibration modes and propagating waves that fall into opposite symmetry classes are shown to have opposite stability characteristics in the presence of frictional loading.
Distributed Photostrictive Actuation and Opto-Piezothermoelasticity Applied to Vibration Control of Plates
Authors: Liu B. , Tzou H. S.
Published: February 2008

Conventional hard-wired sensor/actuator systems are likely sensitive to strong electromagnetic fields, cross-talks, electric noises, etc. Noncontact distributed opto-electromechanical actuators driven by high-energy lights do not require direct hardwire connections. These opto-electromechanical actuators can operate in hostile and extreme environments with strong magnetic and/or electric disturbances. In this study, detailed photostriction, pyroelectricity, thermoelasticity and photodeformation of 2-D opto-electromechanical photostrictive actuators are analyzed. A servo control system is proposed and its governing system equation is derived. The opto-electromechanical actuators are used in vibration control of a rectangular plate. Experimentally calibrated simulation results show that the opto-electromechanical actuators are effective in vibration control and the highest frequency of controllable vibration can achieve several hundred Hertz.
Experimental Determination of Local Structural Stiffness by Disassembly of Measured Flexibility Matrices
Authors: Doebling S. W. , Peterson L. D. , Alvin K. F.
Published: February 2008

A new method is presented for identifying the local stiffness of a structure from vibration test data. The method is based on a projection of the experimentally measured flexibility matrix onto the strain energy distribution in local elements or regional superelements. Using both a presumed connectivity and a presumed strain energy distribution pattern, the method forms a well-determined linear least squares problem for elemental stiffness matrix eigenvalues. These eigenvalues are directly proportional to the stiffnesses of individual elements or superelements, including the cross-sectional bending stiffnesses of beams, plates, and shells, for example. An important part of the methodology is the formulation of nodal degrees of freedom as functions of the measured sensor degrees of freedom to account for the location offsets which are present in physical sensor measurements. Numerical and experimental results are presented which show the application of the approach to example problems.
Modelling of a Flexible Slewing Link
Authors: Oguamanam D. C. D. , Heppler G. R. , Hansen J. S.
Published: February 2008

A flexible rotating beam is modelled using Timoshenko beam theory and a non-inertial reference frame that leads to a pseudo-pinned-pinned formulation. The frequency equation and orthogonality conditions are derived and compared with those for the pseudo-pinned and pseudo-clamped formulations. A finite dimensional model is presented and is used to derive the transformations between the three formulations.
Stability of a Flexible Wheelset for High Speed Rail Vehicles With Constant and Varying Parameters
Authors: Lieh J. , Yin J.
Published: February 2008

The stability of an elastic wheelset coupled with torsional spring and damper is studied in this paper. With flexible elements between two wheels, the advantages of both rigid and independently rotating wheel systems may be obtained. Previous investigations indicated that axle flexibility will affect the vehicle dynamic behavior and an optimal design may improve the system performance. Those studies were limited to constant wheel/rail geometry as the wheelset rolls along the track. In this paper, it is intended to determine the critical speed regions for both constant and time-varying models. The variation in conicity is assumed to be periodic thus the Floquet stability concept may be employed. The computation of the state-transition matrix is based on a Runge-Kutta algorithm.
On the Analysis of Hopf Bifurcation Associated with a Two-Fold Zero Eigenvalue, Part 2: Nonautonomous System
Authors: Moh’d M. , Huseyin K.
Published: February 2008

This paper extends the bifurcation and stability analysis of the autonomous system considered in Part 1 to the case of a corresponding nonautonomous system. The effect of an external harmonic excitation on the Hopf bifurcation is studied via a modified Intrinsic Harmonic Balancing technique. It is observed that a shift in the critical value of the parameter occurs due to the external excitation. The analysis is carried out with the aid of MAPLE which is also instrumental in verifying the consistency of the approximations conveniently.
Dynamic Response of a Coupled Spinning Timoshenko Shaft System
Authors: Wong E. , Zu J. W.
Published: February 2008

The dynamic behavior of a simply-supported spinning Timoshenko shaft with coupled bending and torsion is analyzed. This is accomplished by transforming the set of nonlinear partial differential equations of motion into a set of linear ordinary differential equations. This set of ordinary differential equations is a time-varying system and the solution is obtained analytically in terms of Chebyshev series. A beating phenomoenon is observed from the numerical simulations, which is not observed for shaft systems where only bending vibration is considered.
Identifying Damping of a Gyroscopic System Through the Half-Power Method and Its Applications to Rotating Disk/Spindle Systems
Authors: Heo B. , Bittner H. , Shumway M. L. , Shen I. Y.
Published: February 2008

This paper applies the half-power method to identify damping of a gyroscopic system. At first, the underlying principle of the half-power method for damped, gyroscopic systems is explained. Then the method is demonstrated on a rotating disk/spindle system often used in computer hard disk drives. The disk/spindle system consists of multiple elastic disks mounted on a rigid spindle supported by ball bearings. The flexibility of the bearings allows the spindle to undergo rigid-body translation and rocking. Calibrated experiments were conducted in vacuum to obtain frequency response functions at different rotational speed. Application of the half-power method shows that the disk and bearing dampings are independent of rotational speed and can be modeled adequately as viscous damping. Moreover, the damping of the ball bearings is two orders of magnitude smaller than that of a fluid-film bearing of similar size.
Steady-State Dynamic Behavior of a Flexible Rotor With Auxiliary Support from a Clearance Bearing
Authors: Xie H. , Flowers G. T. , Feng L. , Lawrence C.
Published: February 2008

This paper investigates the steady-state responses of a rotor system supported by auxiliary bearings in which there is a clearance between the rotor and the inner race of the bearing. A simulation model based upon the rotor of a production jet engine is developed and its steady-state behavior is explored over a wide range of operating conditions for various parametric configurations. Specifically, the influence of rotor imbalance, clearance, support stiffness and damping is studied. Bifurcation diagrams are used as a tool to examine the dynamic behavior of this system as a function of the aforementioned parameters. The harmonic balance method is also employed for synchronous response cases. The observed dynamical responses is discussed and some insights into the behavior of such systems are presented.
Gas Path Sound Transmission in Spherically-Shaped Reciprocating Compressors: Theory and Experiment
Authors: Pan F. , Jones J. D.
Published: February 2008

Gas pulsations within the refrigerant gas cavity is one of the principal noise propagating paths in reciprocating compressors. This paper provide a physical insight to the relationship between the gas pulsations inside the cavity and noise radiation of reciprocating compressors. The refrigerant gas cavity of the test compressor is modeled as a space between concentric spherical shells and analyzed with modal expansion techniques. Gas pulsations within the cavity are mathematically represented as the forcing terms of the inhomogeneous wave equation in spherical coordinates. The pressure distribution inside the cavity is then estimated accordingly. Based on the orthogonality principles, the noise radiation patterns associated with the gas pulsations are predicted. Acoustic modal analysis, directivity test and running speed sensitivity test are conducted to identify the acoustic characteristics of cavity and to verify the analytical model. The experimental results are in good agreement with the prediction of the analytical model. Thus, the concentric, spherical shell model well describes the acoustic characteristics of cavity within the test compressor. This model can also be employed as a design tool to analyze the effects of system parameter variation on overall noise radiation.
Ridge and Phase Identification in the Frequency Analysis of Transient Signals by Harmonic Wavelets
Authors: Newland D. E.
Published: February 2008

It is difficult to generate high-definition time-frequency maps for rapidly changing transient signals. New details of the theory of harmonic wavelet analysis are described which provide the basis for computational algorithms designed to improve map definition. Features of these algorithms include the use of ridge identification and phase gradient as diagnostic features.
Dynamic Instability of a Turbine Generator due to Microslip
Authors: Wettergren H. L. , Csaba G.
Published: February 2008

The present paper is concerned with dynamic instability of a turbine generator due to friction between rotor slot wedges and the rotor. When the normal force on the wedge is constant the dissipated energy is of the same type as hysteretic material damping in the sense that for a circular motion excluding gravity it is independent of the rotational frequency, but changes sign when the rotational frequency exceeds the vibrational frequency. The magnitude of the dissipated energy will however depend on the rotational frequency as the normal force does. The transferred energy due to friction is a nonlinear phenomenon and approximately proportional to the amplitude cubed and may be much larger than material damping. It is also shown that when gravity is included or the motion is elliptical the energy transferred is larger than for a simple circular motion.
Wave Analysis of Mode Localization and Delocalization in Elastically Constrained Strings and Beams
Authors: Tan C. A. , Riedel C. H.
Published: February 2008

The free vibration response of both a string and a Euler-Bernoulli beam supported by intermediate elastic constraints is studied and analyzed. For both the string and beam systems, curve veering and mode localization are observed in the lower modes when the distance between the elastic constraints is varied. As the mode number increases, the modes of the system become extended indicating that the coupling springs have little effect on the systems at higher modes. A wave analysis is employed to show the effects of the constraints on the coupling of the subsystems and high frequency behavior. The beam may exhibit a delocalization phenomenon where a particular mode experiences no localization while other neighboring modes may be localized. The frequency (termed the delocalization frequency) at which this occurs corresponds to a transmission resonance. The delocalization frequency is predicted well by the vibration ratio (Langley, 1995). The existence and behavior of the delocalization are explained analytically by the wave approach.
Interaction Dynamics Between a Flexible Rotor and an Auxiliary Clearance Bearing
Authors: Lawen J. L. , Flowers G. T.
Published: February 2008

This study investigates the application of synchronous interaction dynamics methodology to the design of auxiliary bearing systems. The technique is applied to a flexible rotor system and comparisons are made between the behavior predicted by this analysis method and the observed simulation response characteristics. Of particular interest is the influence of coupled shaft/bearing vibration modes on rotordynamical behavior. Experimental studies are also performed to validate the simulation results and provide insight into the expected behavior of such a system.
Simulation of Vehicle Pass-by Noise Radiation
Authors: Wu S. F. , Zhou Z.
Published: February 2008

This paper presents an extended Kirchhoff integral formulation for predicting sound radiation from an arbitrarily shaped vibrating structure moving along an infinite baffle. In deriving this formulation, the effect of sound reflection from the baffle is taken into account by using the image source theory. Moreover, the effect of source convection motion and that of motion-induced fluid-structure interaction at the interface on the resulting acoustic pressure field are considered. The formulation thus derived is used to calculate sound radiation from a simplified vehicle model cruising along a solid ground at constant speeds. Since analytical and benchmark numerical solutions for an arbitrarily shaped vibrating object in motion are not available, validations of numerical results are made with respect to those of a point source. Next, sound radiation from a full-size vehicle is simulated. For simplicity, the vehicle is assumed to be made of a shell-type structure and excited by harmonic forces acting on its four tires. Vibration responses subject to these excitations are calculated using finite element method (FEM) with HyperMesh® version 2.0 as pre- and post-processors. Once the normal component of the surface velocity is specified, the radiated acoustic pressure fields are determined using boundary element method (BEM). Numerical results show that the effect of source convection motion enhances sound radiation in the forward direction, but reduces that in the rearward direction. Changes in the resulting sound pressure fields become obvious when the Mach number exceeds 0.1, or equivalently, when a vehicle cruises at 70 mph or higher.
Finite Elements with Nonreflecting Boundary Conditions Formulated by the Helmholtz Integral Equation
Authors: Wu Shu-Wei
Published: February 2008

In the proposed approach, an acoustic domain is split into two parts by an arbitrary artificial boundary. The surrounding medium around the vibrating surface is discretized with finite elements up to the artificial boundary. The constraint equation specified on the artificial boundary is formulated with the Helmholtz integral equation straightforwardly, in which the source surface coincides with the vibrating surface discretized with boundary elements. To ensure the uniqueness of the numerical solution, the composite Helmholtz integral equation proposed by Burton and Miller was adopted. Due to the avoidance of singularity problems inherent in the boundary element formulation, this method is very efficient and easy to implement in an isoparametric element environment. It should be noted that the present method also can be applied to thin-body problems by using quarter-point elements.
Analytical Dynamic Performance Modeling for Individual C-block Actuators
Authors: Moskalik A. J. , Brei D.
Published: February 2008

C-blocks are mid-range piezoelectric actuators that show promise for use in dynamic applications, such as noise and vibration control. This paper presents an analytical model of an individual C-block actuator, including the identification of the natural frequencies and the description of the amplitude response across the frequency spectrum. In addition, an experimental study with three case studies is presented investigating the accuracy of the model and the sensitivity of the overall dynamic performance to C-block design parameters. The experimental results showed a good match to the analytical model and outlined the trade-offs between displacement amplitude and bandwidth.
A Numerical Analysis for Perforated Muffler Components with Mean Flow
Authors: Wang Chao-Nan
Published: February 2008

A boundary element approach for analyzing the perforated muffler components with mean flow is developed. Most of the research on perforated mufflers is based on the assumption of plane wave propagation. In the present method, the effects of mean flow, including the convection effect in governing equation and the change of acoustic impedance of perforated tube, are considered and the influences of higher order modes are also included. The acoustic performance prediction is performed on the perforated intruding tube mufflers and also on the plug muffler with and without mean flow. Comparisons of the influences of various porosity, the mean flow velocities, the tube thickness and the hole diameters are investigated. However, the results need to be verified by further experimental measurement.
Simultaneous Optimization of Structure and Control for Vibration Suppression
Authors: Zhu Ye , Qiu Jinhao , Tani Junji , Urushiyama Yuta , Hontani Yasuharu
Published: February 2008

A method of simultaneous optimization of structure and control using mixed H2 and H∞ norms of the transfer function as the objective function is proposed and the modeling and formulation of simultaneous optimization problems associated with this approach are discussed in this paper. Simultaneous optimization is realized by iteratively executing structural optimization and controller optimization. Both serial and parallel approaches to combine structural optimization and controller optimization are investigated. They are applied to the simultaneous optimization of the cross-sectional parameters of a spring-supported beam and the parameters of the controller used to actively suppress the vibration of the beam. The performance of both displacement output and control input is improved significantly after simultaneous optimization. The simulation results show the great potential advantages of simultaneous optimization over traditional design methods and the effectiveness of the proposed approach.
Free Vibration Analysis of Shafts on Resilient Bearings Using Timoshenko Beam Theory
Authors: Karunendiran S. , Zu J. W.
Published: February 2008

This paper presents an analytical method adopted for the free vibration analysis of a shaft, both ends of which are supported by resilient bearings. The shaft is modeled by Timoshenko beam theory. Based on this model exact frequency equation to calculate complex eigenvalues is derived and presented in complex compact form for the first time. Explicit expressions to compute the corresponding mode shapes are also presented.
Transverse Vibration of a Rectangularly Orthotropic Spinning Disk, Part 2: Forced Vibration and Critical Speeds
Authors: Phylactopoulos A. , Adams G. G.
Published: February 2008

The transverse forced vibration of a rectangularly orthotropic spinning disk is investigated. The disk is subjected to a constant stationary point-load. Although the deflection of an isotropic disk under these loading conditions is time-invariant in a space-fixed coordinate system, the orthotropic disk undergoes time-dependent oscillatory motion. This phenomenon occurs as a result of the continually changing orientation of material properties with respect to the load. The disk deflection under-the-load is determined as a function of time. Also the deflection along a disk radius and circle containing the load are determined at a fixed instant of time. The occurrence of critical speeds is also investigated. Without damping, virtually any angular speed of the orthotropic disk is found to be critical. This behavior is due to the occurrence of more than one Fourier component in each of the eigenfunctions of the free vibration problem. With damping included, a large amplitude response is found at a speed much less than the lowest classical critical speed of an isotropic disk.