bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat and Mass Transfer in Packed Bed Liquid Desiccant Regenerators—An Experimental Investigation
Authors: Martin V. , Goswami D. Y.
Published: February 2008

Liquid desiccant cooling can provide control of temperature and humidity, while at the same time lowering the electrical energy requirement for air conditioning. Since the largest energy requirement associated with desiccant cooling is low temperature heat for desiccant regeneration, the regeneration process greatly influences the overall system performance. Therefore, the effects of variables such as air and desiccant flow rates, air temperature and humidity, desiccant temperature and concentration, and the area available for heat and mass transfer on the regeneration process are of great interest. Due to the complexity of the regeneration process, which involves simultaneous heat and mass transfer, theoretical modeling must be verified by experimental studies. However, a limited number of experimental studies are reported in the literature. This paper presents results from a detailed experimental investigation of the heat and mass transfer between a liquid desiccant (triethylene glycol) and air in a packed bed regenerator using high liquid flow rates. To regenerate the desiccant, it is heated to temperatures readily obtainable from flat-plate solar collectors. A high performance packing that combines good heat and mass transfer characteristics with low pressure drop is used. The rate of water evaporation, as well as the effectiveness of the regeneration process is assessed based on the variables listed above. Good agreement is shown to exist between the experimental findings and predictions from finite difference modeling. In addition, the findings in the present study are compared to findings previously reported In the literature. Also, the results presented here characterize the important variables that impact the system design.
Frequency Distributions of Daily Ambient Temperatures Through Generalized Parameters
Authors: Satyamurty V. V. , Sarath Babu K.
Published: February 2008

Studies on frequency distributions of ambient temperature available in the literature are limited and are developed assuming that the distributions are symmetric about its average value. The present article examines the suitability of a new parameter, T¯aˆ, and a variable, Taˆ to depict generalized distributions. T¯aˆ is a normalized monthly average daily ambient temperature, while Taˆ is a normalized daily ambient temperature. They comprise maximum and minimum ambient temperatures (Ta,max and Ta,min), in addition to monthly average daily ambient temperature, T¯a, and daily ambient temperature, Ta. Correlations have been developed to predict Ta,max and Ta,min needed, in the absence of data. The distributions, developed in terms of Taˆ and T¯aˆ have been suitably represented and tested over 269 locations, latitudes ranging from 8°N to 64°N. The daily ambient temperature values have been predicted within a %rms difference and standard deviations of 0.43% (when Ta’s are in K) and 1.19 K with the expressions developed in the present study.
Mechanisms of Localized Vibration Control in Complex Structures
Authors: Hannsen Su J. , Ruckman C. E.
Published: February 2008

This paper describes a numerical study of mechanisms for controlling all six degrees of freedom in localized areas of a complex structure. In localized vibration control, the controller attempts to stabilize one or more localized areas on the structure rather than attempting to stabilize the entire structure. The relative performance levels of different control strategies are evaluated by examining a frequency-dependent disturbance rejection property. A flat plate supported by two box girders is used as an example realistic structure. Plant dynamics from a finite-element model are used to draw general conclusions regarding the mechanisms by which localized vibration control is exerted.
Mechanical-Wave Filtering in a Periodically Corrugated Elastic Plate
Authors: Hawwa M. A. , Asfar O. R.
Published: February 2008

The method of multiple scales is employed to analyze the interaction of SH modes in an elastic plate having periodically corrugated outerfaces. Two types of resonant conditions leading to two-mode as well as four-mode interactions are considered. The results of the analysis are utilized to develop ultrasonic mechanical wave filters operating on frequency bands centered at the resonant frequency. The stop-band filter frequency response is presented in terms of the power reflection coefficient. The characteristics of reflection of these filters are enhanced by imposing amplitude taper on the periodic corrugations.
An Experimental Modal Analysis Technique for Miniature Structures
Authors: Wilson C. J. , Bogy D. B.
Published: February 2008

This paper describes an experimental modal analysis system which can effectively be used to obtain the modal parameters of small structures. The system uses an electromagnetic exciter to produce the excitation force, a piezoelectric transducer to measure this force, and a Laser Doppler Vibrometer to measure the response. Several designs of the magnetic actuator are discussed and evaluated. The system is verified by obtaining the modal parameters of a miniature cantilever plate, using two preferred exciter designs, and comparing the measured parameters with those acquired from a finite element model. Favorable agreement is obtained between the experimental and computational results. Finally, the two preferred exciters are compared and an optimal configuration is discussed.
Experimental Verification of the Importance of The Nonlinear Curvature in the Response of a Cantilever Beam
Authors: Anderson T. J. , Nayfeh A. H. , Balachandran B.
Published: February 2008

An experimental and theoretical investigation into the first- and second-mode responses of a parametrically excited slender cantilever beam is presented. Inclusion of quadratic damping in the analytical model significantly improves the agreement between the experimental and theoretical results. In addition, the experimental results verify that the often ignored nonlinear curvature terms play a dominant role in the response of the first mode and that the nonlinear inertia terms play a dominant role in the response of the second mode.
Time Varying Passive Vibration Absorption for Flexible Structures
Authors: Quan R. , Stech D.
Published: February 2008

A time varying extension of the passive vibration absorber is described, which increases the effectiveness of a small number of passive vibration absorbers on large or changing flexible structures. Initially, the extended absorber is targeted on a subset of the modes of the flexible structure. A stable switching scheme is described, which allows the absorber to target different subsets of modes, or to adapt to changes in the flexible structure. Computer simulation and experimental work are given which demonstrate the effectiveness of the extended absorber.
Parametric Control of Structural Vibrations via Adaptable Stiffness Dynamic Absorbers
Authors: Lai J. S. , Wang K. W.
Published: February 2008

An energy-based algorithm is developed for dynamic absorbers with adaptable stiffness to suppress structural vibrations via real-time parametric control actions. A controller with multi-objective fuzzy logic is created to reduce the main structure energy while constraining the total system energy. To ensure stability, an adaptive-passive supervisor is designed to provide guidelines for implementing the control law. It is proved that the system using this supervisor is globally stable in the sense that all signals involved are bounded. The performance of the controller is demonstrated on a beam example. It is shown that the structure energy level and vibration amplitude can be suppressed effectively.
Use of dFRFs for Diagnosis of Asymmetric/Anisotropic Properties in Rotor-Bearing System
Authors: Joh Chee-Young , Lee Chong-Won
Published: February 2008

The diagnostic method, which utilizes the dFRFs defined in the stationary and rotating coordinate systems, is tested with a laboratory flexible rotor-bearing system, in order to verify its effectiveness in detection of the asymmetry in shaft and the anisotropy in stator. The experimental results indicate that the dFRFs can be effectively used for the diagnosis of anisotropy and/or asymmetry in rotor systems by the investigation of two kinds of dFRF estimates using the complex input and output signals defined in the stationary and rotating coordinate systems.
Estimation of Mass, Stiffness and Damping Matrices from Frequency Response Functions
Authors: Chen S. Y. , Ju M. S. , Tsuei Y. G.
Published: February 2008

A frequency-domain method for estimating the mass, stiffness and damping matrices of the model of a structure is presented. The developed method is based on our previous work on the extraction of normal modes from the complex modes of a structure. A transformation matrix is obtained from the relationship between the complex and the normal frequency response functions of a structure. The transformation matrix is employed to calculate the damping matrix of the system. The mass and the stiffness matrices are identified from the normal frequency response functions by using the least squares method. Two simulated systems are employed to illustrate the applicability of the proposed method. The results indicate that the damping matrix can be identified accurately by the proposed method. The reason for the good results is that the damping matrix is identified independently from the mass and the stiffness matrices. In addition, the robustness of the new approach to uniformly distributed measurement noise is also addressed.
Modeling and Analysis of the Intermediate Shaft Between Two Universal Joints
Authors: Sheu Pey-Pey , Chieng Wei-Hua , Lee An-Chen
Published: February 2008

Unlike a single universal joint, in which the output shaft rotates with a fluctuating speed depending on the misalignment angle, a double universal joint is used to connect two offset shafts. If a double universal joint is correctly arranged, with equal joint angles in perfect alignment, the output shaft rotates in a synchronous motion with uniform speed. However, in practice, the intermediate shaft of a double universal joint system suffers from bending moments induced by joint friction and velocity fluctuation induced by the joint angles. These factors distort the linear relationship between the input and output shafts. In this paper, the effects of joint angles and joint friction on the steady-state responses of a double universal joint system are examined. The mass matrix, damping matrix, stiffness matrix, and nonconservative force of a universal joint are derived analytically for finite element modeling. The formulation introduced generates an elementary matrix suitable for the analysis of complex rotor-bearing systems that include double universal joints.
Transient Response Technique Applied to Active Magnetic Bearing Machinery During Rotor Drop
Authors: Ishii T. , Kirk R. Gordon
Published: February 2008

The active magnetic bearing (AMB) is a relatively new technology which has many advantages compared with conventional bearing design. In an AMB system, the rolling-element back-up bearings are indispensable to protect the magnetic bearing rotor and stator, and other stationary seals along the rotor shaft. In this paper, a theoretical formulation is proposed and solved numerically to examine the transient response of the flexible rotor, from the time just previous to when the AMB shuts down and including the rotor drop onto the back-up bearing. The backward whirl of the rotor, which may lead to the destructive damage of the machinery, has been analytically predicted at very light support damping and very high support damping. Also, the vibration due to the nonlinearity of the contact point geometry has been included in the analysis. The influence of the support damping on the displacement of the disk and also the contact force between the journal and the inner-race of the back-up bearing have been computed for various rotor system parameters. By comparing these results with the optimum support damping for the simple flexible rotor model, it is shown that this support damping optimization can be applicable for specifying the required optimum range of support damping for the back-up bearings of AMB systems.
Identification of Stochastic System and Controller via Projection Filters
Authors: Lee Hyun Chang , Hsiao Min-Hung , Huang Jen-Kuang , Chen Chung-Wen
Published: February 2008

A method based on projection filters is presented for identifying an open-loop stochastic system with an existing feedback controller. The projection filters are derived from the relationship between the state-space model and the AutoRegressive with eXogeneous input (ARX) model including the system, Kalman filter and controller. Two ARX models are identified from the control input, closed-loop system response and feedback signal using least-squares method. Markov parameters of the open-loop system, Kalman filter and controller are then calculated from the coefficients of the identified ARX models. Finally, the state-space model of the open-loop stochastic system and the gain matrices for the Kalman filter and controller are realized. The method is validated by simulations and test data from an unstable large-angle magnetic suspension test facility.
Band Brake Squeal
Authors: Nakai M. , Yokoi M.
Published: February 2008

The purpose of this paper is to investigate the squealing mechanism of band brakes in order to develop effective treatments for the reduction or elimination of squeal noise. With increasing rotational drum speed, squeal frequency increases up to a constant frequency. This constant squeal frequency coincides precisely with the frequency of instability obtained by a linear analysis of the motion of a band on an elastic foundation when the frictional force between the lining of the band and the drum is taken into account. Through experiments and analyses, it will be demonstrated that squeals are induced by the coupling between two modes of the band.
Parametric Identification of Systems With Dry Friction and Nonlinear Stiffness Using a Time Series Model
Authors: Chen Q. , Tomlinson G. R.
Published: February 2008

A new type of time series model, the AVD model which accommodates the Acceleration, Velocity and Displacement simultaneously, has been used to estimate the characteristics of nonlinear single and multi-degree of freedom systems with dry Coulomb friction, viscous damping and nonlinear stiffness. Numerical results via simulation are compared with those from a Fourier transform method, which suggests that the AVD model is a powerful technique for nonlinear system parameter identification.
Selection of Component Modes for Craig-Bampton Substructure Representations
Authors: Kammer D. C. , Triller M. J.
Published: February 2008

Three measures of modal dynamic importance are studied for the purpose of ranking Craig-Bampton substructure fixed interface mode shapes based upon their contribution to forces at the substructure interface, modal velocity, or modal displacement. These measures can be employed to identify mode shapes which are dynamically important and thus should be retained in a reduced analytical representation, or identified during a modal survey of the substructure. The first method considered. Effective Interface Mass, has been studied previously. However, new results are presented showing the relation between Effective Interface Mass and a commonly used control dynamics measure of modal importance called approximate balanced singular values. In contrast to the general case of approximate balanced singular values, Effective Interface Mass always gives an absolute measure of the dynamic importance of mode shapes. The EIM method is extended to consider modal velocity and modal displacement outputs. All three measures are applied to a simple substructure called the General Purpose Spacecraft. It is shown that each of these measures provides an efficient method for ranking the dynamic importance of Craig-Bampton fixed interface modes such that a reduced representation will accurately reproduce the substructure’s response in the frequency range of interest.
A Modal Correlation Coefficient for Detection of Kinks in Mode Shapes
Authors: Samman M. M.
Published: February 2008

A measure of correlation between mode shapes is introduced. This measure is a modification of the standard Modal Assurance Criterion (MAC). The new form, called the Modal Correlation Coefficient (MCC), is more sensitive to the existence of kinks in mode shapes. Its advantages are realized in diagnostic and structural health monitoring applications.
Integrated Estimation/Identification Using Second-Order Dynamic Models
Authors: Crassidis J. L. , Mook D. J.
Published: February 2008

An algorithm is presented which accurately identifies multi-input-multi-output systems characterized by vibrating structures. More specifically, an identification technique is integrated with an optimal estimator in order to develop an algorithm which is robust with respect to measurement and process noise. The unique functional form of the integrated approach utilizes systems described by second-order models. Therefore, theoretical mass, damping, and stiffness matrices, associated with lumped parameter models, are tailored with experimental time-domain data for system estimation and identification. This leads to an algorithm that is computationally efficient, producing realizations of complex multiple degree-of-freedom systems. The combined estimation/identification algorithm is used to identify the properties of an actual flexible truss from experimental data. Comparison of experimental frequency-domain data to the predicted model characteristics indicates that the integrated algorithm produces near-minimal realizations coupled with accurate modal properties.
Nonstationary Oscillation of a Rotating Shaft With Nonlinear Spring Characteristics During Acceleration Through a Major Critical Speed (A Discussion by the Asymptotic Method and the Complex-FFT Method)
Authors: Ishida Y. , Yasuda K. , Murakami S.
Published: February 2008

Nonstationary oscillations during acceleration through a major critical speed of a rotating shaft with nonlinear spring characteristics are discussed. First, the first approximate solutions of steady-state and nonstationary oscillations are obtained by the asymptotic method. Second, the amplitude variation curves of each oscillation component are obtained by the complex-FFT method. It is clarified that the first approximation of the asymptotic method has comparatively large quantitative error in the case of nonstationary solutions. In addition, the influences of each nonlinear component in polar coordinate expression on nonstationary oscillations are investigated.
Parameter Selection Strategies in Finite Element Model Updating
Authors: Ahmadian H. , Gladwell G. M. L. , Ismail F.
Published: February 2008

In FE model updating, as in any identification procedure, we select some parameters in the model, and try to fine-tune them to minimize the discrepancy between the model predictions and the measured data. The paper compares the performance of the generic element matrices, recently introduced by the authors, with other selection strategies for finite element model updating. The updated models obtained from these methods are compared with the measured data and rated according to their ability to produce the measured data within and beyond the frequency range used in the updating, and more importantly, according to their ability to predict the effect of design changes.
Identification of Linearized Dynamic Characteristics of Rolling Element Bearings
Authors: Chen Juhn-Horng , Lee An-Chen
Published: February 2008

This study presents a new method for estimating linearized coefficients of rolling element bearings. The rotor-bearing systems considered here are composed of a flexible shaft, which may be changed stepwise along the axial direction, and multiple rigid disks supported on anisotropic bearings. The main feature of this identification technique is that it eliminates the need to measure the external input force. The estimator is constructed by using the relations of unbalance responses and known system parameters to estimate the coefficients of rolling element bearings incorporated with the least-squares method without using an input force device. The theoretical development of the procedures is presented together with simulation and experimental results.
Free Vibrations of Thick Hollow Circular Cylinders From Three-Dimensional Analysis
Authors: So Jinyoung , Leissa A. W.
Published: February 2008

A three-dimensional (3-D) method of analysis is developed for the free vibration frequencies of hollow circular cylinders of elastic material. The method is based upon local coordinates whose origin is attached to the center of cylindrical wall. It assumes for the three displacement components a Fourier series in the circumferential (θ) direction and algebraic polynomials in the radial (q) and axial (z) directions. Convergence studies for completely free cylinders show that the analysis can yield frequencies which are exact to five or six significant figures. These accurate frequencies are compared with those from other 3-D analyses available for free hollow circular cylinders having various length-to-outside diameter (L/Do) and inside-to-outside diameter (Di/Do) ratios. Extensive, accurate data are presented for the first 10 frequencies of each circumferential wave number 0 through 5 for hollow circular cylinders having Di/Do of 0.1, 0.5, and 0.9, with L/Do = 0.2, 1 and 5 and a Poisson’s ratio (v) = 0.3.
Harmonic Balance Vibration Analysis of Turbine Blades With Friction Dampers
Authors: Sanliturk K. Y. , Imregun M. , Ewins D. J.
Published: February 2008

Although considerable effort has been devoted to the formulation of predictive models of friction damper behavior in turbomachinery applications, especially for turbine blades, the problem is far from being solved due to the complex nonlinear behavior of the contact surfaces. This paper primarily focuses on analytical and numerical aspects of the problem and addresses the problem in the frequency domain while exploring the viability of equivalent time-domain alternatives. The distinct features of this work are: (i) the modelling of nonlinear friction damper behavior as an equivalent amplitude-dependent complex stiffness via a first-order harmonic balance method (HBM), (ii) the use of sine sweep excitation in time-marching analysis, (iii) the application of the methodology to numerical test cases, including an idealised 3D turbine blade model with several friction dampers, (iv) the verification of the numerical findings using experimental data, and (v) a detailed assessment of the suitability of HBM for the analysis of structures with friction dampers.
Wave Mode Conversion in Stiffened Cylindrical Shells With Periodic Axial Curvature
Authors: Accorsi M. L. , Bennett M. S.
Published: February 2008

Free wave propagation in periodically stiffened cylindrical shells is investigated using a periodic finite element method developed by the authors. The modification of longitudinal wave modes was a primary objective because of their long wavelengths and poor attenuation characteristics. Cylinder configurations that utilize periodic axial curvature are examined and are shown to have significantly more coupling between longitudinal and fiexural wave modes than cylinders without axial curvature. This coupling significantly modifies the stop and pass band behavior. In this paper, the periodic finite element method is first reviewed. The method is then applied to a one-dimensional periodic structure consisting of circular beam sections. The longitudinal/flexural wave mode conversion in this simple structure is illustrated. Finally, results for cylindrical shells with and without axial curvature are presented.
Modeling and Vibration Analysis of Spinning-Disk and Moving-Head Assembly in Computer Storage Systems
Authors: Huang S. C. , Chiou W. J.
Published: February 2008

Vibration of a spinning disk subject to a moving head, that is frequently encountered in computer storage system, is studied. The magnetic head moving on the spinning disk is modeled as a harmonically varying load traveling in the radial direction. The spinning disk responses are solved for analytically through an approach that employs the Galerkin’s method and some solution techniques. Examples of various loading conditions are then illustrated and discussed. The load’s moving speed was found to act as a driving frequency and it would cause resonances at certain speeds. The resonances caused by individual parameters were addressed and marked as critical Spinning speed and critical moving speed. A resonant equation that correlated the three parameters, disk spinning speed (Ω), load moving speed (v), and load frequency (ω), was derived and the corresponding resonant surfaces were shown in graphs. The resonant phenomena due to the interactions of parameters are then realized. The disk’s transient responses to moving loads are also illustrated. The results showed that a constant-amplitude moving load caused no oscillatory motion as it moved from fixed end to free end but it did cause oscillation as the load moved in reverse way. A harmonic moving load, however, always results in oscillations as expected.
Regenerative Systems for Vibration Control
Authors: Jolly M. R. , Margolis D. L.
Published: February 2008

The potential for energy regeneration in vibration control systems is investigated. Such control systems hold the possibility of self-sustainability by alternately extracting and releasing energy originating from the vibrating system in a controlled non-passive manner. To be self-sustaining, more energy must on average flow into the control system than flows out. Generally speaking, the performance of such a system will approach that of an active system while theoretically requiring no externally supplied power. As research progresses in this area, an increasing number of viable applications for regenerative vibration control systems are being uncovered. This paper examines two broad applications: base-excited suspensions and periodically excited compound mounts. Some experimental results of the former are presented to support our claims.
Mechanical and Electrical Run-Out Removal on a Precision Rotor-Vibration Research Spindle
Authors: Horattas G. A. , Adams M. L. , Dimofte F.
Published: February 2008

Experimental determination of both steady-state and dynamic performance of a journal bearing requires the use of a high precision spindle with a vanishingly small range of run-out. This was achieved by first eliminating the mechanical run-out of the spindle by grinding the journal specimen while rotating in place. Once the mechanical run-out was removed, the electrical run-out sensed by the displacement proximity-probe-transducers was also removed. Using this procedure the mechanical and electrical run-outs of a research spindle were reduced to less than 0.2 micron (10 μin.), which is better than the resolution of the data acquisition system, 1 micron (50 μin.).
Classical Electrodynamics and Acoustics: Sound Radiation by Moving Multipoles
Authors: Gaunaurd G. C. , Eisler T. J.
Published: February 2008

In classical electrodynamics (CED) P. Dirac used the average of retarded and advanced fields to represent the bound field and their difference to represent the free field in his derivation of the (Lorentz-Dirac) equation of motion for an electron. The latter skew-symmetric combination filtered out the radiation part of the field. It can also be used to derive many properties of the power radiated by acoustic sources, such as angular and frequency distributions. As in CED there is radiation due to source acceleration and radiation patterns exhibit the “headlight effect.” Power radiation patterns are obtained by this approach for point multipoles undergoing various motions. Applications to sound radiation problems from rotating machinery are shown. Numerous computed plots illustrate all cases.
An Experimental Investigation of the Behavior of Droplets in Axial Acoustic Fields
Authors: Sujith R. I. , Waldherr G. A. , Jagoda J. I. , Zinn B. T.
Published: February 2008

This paper describes an experimental investigation of the behavior of water droplets in axial acoustic fields. It was motivated by the increasing interest in the use of pulsations to improve the performance of energy intensive, industrial processes. The presence of an acoustic field is believed to enhance heat and mass transfer to and from the droplets, probably because of the relative motion between the droplets and the gas phase. This relative motion is characterized by the ratio of the amplitude of the oscillatory droplet velocity to that of the acoustic velocity (entrainment factor), and by the phase between the droplet and gas phase oscillations. An experimental set-up was developed to investigate the effect of acoustic oscillations on the motion of individual droplets. In these experiments a droplet produced by a piezo-ceramic droplet generator is allowed to fall through a transparent test section in which an acoustic field has been set up using a pair of acoustic drivers. Images of the droplets in the test section acquired at consecutive instants using a high speed, intensified imaging system were used to determine the time dependent droplet trajectory and velocity. The acoustic velocity was calculated from measured acoustic pressure distributions. The entrainment factor and the phase difference were then determined from these data. The results show how the entrainment factor decreases and the phase difference increases with increasing droplet diameter and frequency, indicating that larger diameters and higher frequencies reduce the “ability” of the droplets to follow the gas phase oscillations. The measured data are in excellent agreement with the prediction of the Hjelmfelt and Mockros model. Both theoretical predictions and measured data were correlated with the Stokes number, which accounts for the effects of droplet diameter and frequency. It was also shown that acoustic oscillations decrease the mean terminal velocity of the droplets.
Application of Hybrid Frequency Domain Substructuring for Modelling an Automotive Engine Suspension
Authors: Huizinga A. T. M. J. M. , van Campen D. H. , de Kraker A.
Published: February 2008

A practical application of hybrid FRF-coupling (Frequency Response Function) in the development of a passenger car is presented. First, a short review is given about FRF-coupling in general. Next, some problems are discussed which may be encountered when both analytical and experimental FRF-data is used in FRF-coupling. This is also known as hybrid modelling. The main part of this paper presents a successful application of hybrid FRF-coupling to analyze and solve an interior noise problem of a passenger car. Both analytical and experimental FRFs were used to create a hybrid dynamic model of a complete passenger car. The engine and its suspension system were modelled using finite elements, while the remainder of the car was modelled by experimentaly derived FRFs. This hybrid model was then used to compute the response of the vehicle due to the engine excitation. Measured noise transfer function were used next to compute the interior sound pressure level using forced response results of the hybrid car model. Subsequently, the hybrid model was used to analyze the problem, and to predict the effects of an alternative design of the engine suspension on interior noise. Numerical results indicated that the alternative design would have a significant positive effect on noise. This was confirmed by verification measurements on a car.
Three-Dimensional Vibrations of Cross-ply Laminated Hollow Cylinders With Clamped Edge Boundaries
Authors: Ye J. Q. , Soldatos K. P.
Published: February 2008

Using fully three-dimensional elasticity considerations, this paper presents a free vibration analysis of cross-ply laminated hollow cylinders having clamped edge boundaries. The analysis is based on a recursive solution that has been published elsewhere and is suitable for three-dimensional vibration analysis of corresponding simply supported cylinders. Clamped boundary conditions are initially imposed by means of a number of fixed circles located at the edge(s) of the cylinder considered. Using certain dynamic considerations together with the Lagrange multipliers method, this is achieved by suitably coupling a certain number of different normal modes of vibration of the corresponding simply supported cylinder. Hence, an approximate solution, which however is practically very close to the exact three-dimensional solution, is finally obtained by appropriately increasing either the number of the coupled vibration modes or the number of fixed circles on a clamped edge.
Extension of the Wittrick-Williams Algorithm to Mixed Variable Systems
Authors: Wanxie Zhong , Williams F. W. , Bennett P. N.
Published: February 2008

A precise integration algorithm has recently been proposed by Zhong (1994) for dynamic stiffness matrix computations, but he did not give a corresponding eigenvalue count method. The Wittrick-Williams algorithm gives an eigenvalue count method for pure displacement formulations, but the precise integration method uses a mixed variable formulation. Therefore the Wittrick-Williams method is extended in this paper to give the eigenvalue count needed by the precise integration method and by other methods involving mixed variable formulations. A simple Timoshenko beam example is included.
Identification of Principal Rigid Body Modes Under Free-Free Boundary Condition
Authors: Okuma Masaaki , Shi Qinzhong
Published: February 2008

This paper focuses on the problem of identifying all individual principal rigid body modes and the associated mass or principal inertia of moment, which can be called modal mass, of flexible structures under the free-free boundary condition with fewer multi-location excitations than the number of those modes. The rigid body mass matrix of the structure can be identified by using both the parameters of inertia, which are determined previously by a modal parameter estimation, and the coordinates of measurement points. As all rigid body properties can be obtained from the mass matrix, it becomes possible to simulate the FRFs between any two measurement points with inclusion of the contribution of rigid body motions even by only experimental modal analysis technique. First, the theory is explained. Then, a numerical simulation and two actual identifications for a plate structure and an automotive body component are carried out to demonstrate the validity and the usefulness of the theory.
Relationship Between Improved Inverse Eigensensitivity and FRF Sensitivity Methods for Analytical Model Updating
Authors: Lin R. M. , Lim M. K.
Published: February 2008

Improved inverse eigensensitivity method and improved frequency response function (FRF) sensitivity method developed for analytical model updating have become increasingly popular among other methods and have been successfully applied to the practice of analytical model improvement. This paper examines the mathematical relationship between these two powerful methods for updating analytical models of undamped systems with objectives of demonstrating the advantages and disadvantages of each method as well as their specific practical application conditions. The problem of solution uniqueness associated with these methods is addressed. Computational considerations regarding the practical application of the methods are discussed. Numerical simulations are given to demonstrate the practical applications of these methods.
Nonlinear Piezothermoelasticity and Multi-Field Actuations, Part 2: Control of Nonlinear Deflection, Buckling and Dynamics
Authors: Tzou H. S. , Zhou Y. H.
Published: February 2008

Linear dynamics and distributed control of piezoelectric laminated continua have been intensively investigated in recent years. In this study, dynamics, electromechanical couplings, and control of thermal buckling of a nonlinear piezoelectric laminated circular plate with an initial large deformation are investigated. It is assumed that the transverse nonlinear component is much more prominent than the other two in-plane components—the von Karman type geometrical nonlinearity. In addition, the piezoelectric layers are uniformly distributed on the top and bottom surfaces of the circular plate. Accordingly, the control effect is introduced via an equivalent control moment on the circumference. Dynamic equations and boundary conditions including the elastic and piezoelectric couplings are formulated, and solutions are derived. Active control of plate’s nonlinear deflections, thermal buckling, and natural frequencies using high control voltages are studied, and their nonlinear effects are evaluated.
Vibration Control of Rotor Systems With Noncollocated Sensor/Actuator by Experimental Design
Authors: Yang S. M. , Sheu G. J. , Yang C. D.
Published: February 2008

This paper presents a controller design methodology for vibration suppression of rotor systems in noncollocated sensor/actuator configuration. The methodology combines the experimental design method of quality engineering and the active damping control technique such that their advantages in implementation feasibility and performance-robustness can be integrated together. By using the locations of sensor/actuator and the feedback gains as design parameters, the controller design is shown to achieve a near optimal performance within the two-sigma confidence among all possible parameter combinations. Compared with LQ-based designs, the controller order is smaller and it is applicable to systems in an operation speed range. In addition, neither preselected sensor/actuator location(s) nor state measurement/ estimation is needed.
On the Combined Effect of Mean Flow and Acoustic Excitation on Structural Response and Radiation
Authors: Frendi A. , Maestrello L.
Published: February 2008

Numerical experiments in two dimensions are carried out in order to investigate the response of a typical aircraft structure to a mean flow and an acoustic excitation. Two physical problems are considered; one in which the acoustic excitation is applied on one side of the flexible structure and the mean flow is on the other side while in the second problem both the mean flow and acoustic excitation are on the same side. Subsonic and supersonic mean flows are considered together with a random and harmonic acoustic excitation. In the first physical problem and using a random acoustic excitation, the results show that at low excitation levels the response is unaffected by the mean flow Mach number. However, at high excitation levels the structural response is significantly reduced by increasing the Mach number. In particular, both the shift in the frequency response spectrum and the broadening of the peaks are reduced. In the second physical problem, the results show that the response spectrum is dominated by the lower modes (1 and 3) for the subsonic mean flow case and by the higher modes (5 and 7) in the supersonic case. When a harmonic excitation is used, it is found that in the subsonic case the power spectral density of the structural response shows a subharmonic (f/4) while in the supersonic case no subharmonic is obtained.
An Experimental Investigation of Multimode Responses in a Cantilever Beam
Authors: Tabaddor M. , Nayfeh A. H.
Published: February 2008

An experimental investigation into the planar, multimode response of a cantilever metallic beam to a transverse harmonic excitation is presented. The cantilever beam was tested in both the horizontal and vertical directions. In the vertical configuration, the beam was excited near its fourth natural frequency and energy was transferred from the directly excited fourth mode to a low-frequency mode through both resonant and nonresonant modal interactions. In the latter case, the response contained contributions from the first and fourth modes, whereas in the former case, the response contained contributions from the fourth, second, and fifth modes. The mechanism responsible for the resonant interaction involving the three modes is a subcombination internal resonance of the additive type; that is, Ω ≈ ω4 ≈ 1/2(ω2 + ω5), where the ωi are the natural frequencies of the beam. This type of resonance occurs in systems with a dominant cubic nonlinearity. In the horizontal configuration, the beam was excited near its fourth and sixth natural frequencies. Again, energy was transferred to a low-frequency mode, but in this case only through a resonant interaction due to a subcombination internal resonance of the additive type. Power spectra, time series, and frequency- and amplitude-response curves were obtained for characterization of the dynamic multimode responses.
Modal Sensitivity Analysis of Coupled Acoustic-Structural Systems
Authors: Luo Jianhui , Gea Hae Chang
Published: February 2008

Modal analysis of coupled acoustic-structural systems leads to unsymmetric eigenproblem of special form which introduce different left and right eigenvectors. In this paper, the relation between left and right eigenvectors is first established by symmetrization of the unsymmetric eigensystem, and then Nelson’s method is extended to coupled acoustic-structural systems for calculating the sensitivities of the eigenvalues and eigenvectors. The method only needs to calculate the sensitivities of the right eigenvectors and can treat the Helmholtz resonance mode naturally. Numerical examples of an acoustic box model solved by the proposed approach are compared with finite difference approach and good agreement is noted.
Noise Transmission Through a Vehicle Side Window Due to Turbulent Boundary Layer Excitation
Authors: Wu S. F. , Wu G. , Puskarz M. M. , Gleason M. E.
Published: February 2008

This paper presents results of an investigation on noise transmission through an aluminum panel clamped to a greenhouse vehicle model subject to random acoustics, random vibration, and turbulent boundary layer excitations. Experiments on random acoustics and random vibration excitations were carried out in a reverberation chamber, and those on turbulent boundary layer excitation were conducted in the wind tunnel at the Chrysler Technology Center. The transmitted noise spectra were also calculated using a single computer program VibroAcoustic Payload Environment Prediction System (VAPEPS) based on Statistic Energy Analysis (SEA). The acoustic absorption coefficient (AAC) and the damping loss factor (DLF) for the vehicle were determined based on experimental data. Results showed that the largest differences between the measured and calculated sound pressure levels in any frequency band above 500 Hz were less than 2.5 dB for random acoustics excitation, 5.0 dB for random vibration excitation, and 5 dB for turbulent boundary layer excitation. In spite of the presence of differences in individual frequency bands, the calculated total sound pressure levels compared well with the measured ones. The differences between the calculated and measured total sound pressure levels were 0.7 dB for random acoustics excitation, 0.4 dB for random vibration excitation, and 1.8 dB for turbulent boundary layer excitation.
On the Active-Passive Hybrid Control Actions of Structures With Active Constrained Layer Treatments
Authors: Liao W. H. , Wang K. W.
Published: February 2008

This paper is concerned with the analysis of active and passive hybrid actions in structures with active constrained damping layers (ACL). A system model is derived via Hamilton’s Principle, based on the constitutive equations of the elastic, viscoelastic, and piezoelectric materials. The model converges to a purely active piezotronic system as the thickness of the viscoelastic material (VEM) layer approaches zero. A mixed Galerkin-GHM (Golla-Hughes-McTavish) method is employed to discretize and analyze the model in time domain. With an LQR (linear quadratic regulator) optimal control, the effects of the active constrained layer configuration on the system vibration suppression performance and control effort requirements are investigated. Analysis illustrates that the active piezoelectric action with proper feedback control will always enhance the damping ability of the passive constrained layer. When compared to a purely active configuration, while the viscoelastic layer of the ACL treatment will enhance damping, it will also reduce the direct control authorities (active action transmissibility) from the active source to the host structure. Therefore, whether the ACL treatment is better than a purely active configuration depends on whether the effect of damping enhancement is greater than that of transmissibility reduction caused by the VEM layer. The significance of these effects depends very much on the viscoelastic layer thickness and material properties. With some parameter combinations, the ACL configuration could require more control effort while achieving less vibration reductions compared to a purely active system. Through analyzing the performance and control effort indices, the conditions where this active-passive hybrid approach can outperform both the passive and active configurations are quantified. Based on this study, design guidelines can be set up to effectively integrate the host structure with the piezoelectric and viscoelastic materials, such that a truly beneficial active-passive hybrid control system could be achieved.
A Subharmonic Vibration Absorber for Rotating Machinery
Authors: Lee Cheng-Tang , Shaw S. W. , Coppola V. T.
Published: February 2008

We demonstrate a dynamic vibration absorber system which can be used to reduce speed fluctuations in rotating machinery. The primary system is modeled as a simple rotating disk, and the idealized absorber system consists of a pair of equal point masses which are free to move along identical, prescribed paths relative to the disk. The unique features of the proposed arrangement are that the absorbers are tuned to one-half of the frequency of the applied torque and, more importantly, that they are effective in the fully nonlinear operating range. These absorbers can, in the undamped case, exactly cancel a pure harmonic applied torque of a given order without inducing any higher harmonics, thus rendering a perfectly constant speed of rotation. A perturbation method is used to extend the results to the small damping case and to investigate the dynamic stability of the desired motion. Simulations are used to verify the analysis and to demonstrate the effectiveness of the device.
Rotational Compliance Measurements of a Flexible Plane Structure Using an Attached Beam-like Tip, Part 1: Analysis and Numerical Simulation
Authors: Cheng L. , Qu Y. C.
Published: February 2008

The present paper describes a simple, indirect technique for measuring the rotational compliance of an attached thin-walled plane structure. The technique, called “Tip Excitation Technique (TET),” uses an L-shaped beam tip fixed at one point of the original structure where the rotational compliance is to be evaluated. The tip acts as a mechanical converter transforming an exciting force applied at the tip into an excitation moment applied to the original structure and reciprocally, to convert a rotational response into a translational one. The rotational compliance is evaluated using simple analytical relations that partially eliminate the effect of tip inertia on the structure. Finite element simulations show that the technique can he applied to the study of a typical plate over a frequency range involving relatively strong modal behavior. The low sensitivity of the technique to variations of different physical factors of the tip-plate configuration demonstrates its potential for experimental purposes.