Showing papers in "Journal of Vibration and Acoustics in 1990"
TL;DR: In this article, a technique is proposed which systematically adjusts a finite element model of a structure to produce an updated model in agreement with measured modal results, by considering the desired perturbations in stiffness and damping matrices as gain matrices.
Abstract: A technique is proposed which systematically adjusts a finite element model of a structure to produce an updated model in agreement with measured modal results. The approach suggested here is to consider the desired perturbations in stiffness and damping matrices as gain matrices in a fedback control algorithm designed to perform eigenstructure assignment
81 citations
78 citations
TL;DR: In this paper, the model uses a momentum balance method and a coefficient of restitution, and enables one to predict the rigid body motion as well as the elastic motion before and after impact.
Abstract: The model uses a momentum balance method and a coefficient of restitution, and enables one to predict the rigid body motion as well as the elastic motion before and after impact
77 citations
TL;DR: In this article, a procedure for determining the optimal design of friction dampers for high speed turbomachinery blading is presented, which integrates analytical and experimental results to determine optimal design parameters when the levels of excitation and damping in the system are unknown.
Abstract: A procedure is outlined for determining the optimal design of friction dampers for high speed turbomachinery blading. The procedure includes: an integration of bench test results with finite element analysis and a single mode blade model to ensure accuracy of the analytical model and improve reliability of the friction damper design; an extension of the single mode blade model to predict the engine behavior of friction dampers; and a new way of viewing analytical and experimental results to determine optimal design parameters when the levels of excitation and damping in the system are unknown. Analysis and experiments are performed on a test disk in order to demonstrate and verify the accuracy of the design procedure.
65 citations
TL;DR: In this paper, the effect of seismic waves on the stability of a Jeffcott rotor supported by oil film bearings is investigated by calculating loci of the centers of the journal and the disk using the Runge-Kutta-Gill method.
Abstract: The effect of seismic waves on the stability of a Jeffcott rotor supported by oil film bearings is investigated by calculating loci of the centers of the journal and the disk using the Runge-Kutta-Gill method. It will be shown that a linearly stable rotor can become unstable under a strong artificial shock and a real seismic wave, if it is running at speeds above twice the first critical speed, which is close to the natural frequency of the rotor
51 citations
TL;DR: In this paper, the free and forced linear response of a string which is translating across an elastic foundation was examined, and exact solutions for the free vibration of the string which translates between fixed eyelets and across elastic foundations represented by a single interior spring and a uniform step foundation.
Abstract: This paper examines the free and forced linear response of a string which is translating across an elastic foundation. Exact solutions are derived for the free vibration of the string which translates between fixed eyelets and across elastic foundations represented by a single interior spring and a uniform step foundation. Results illustrate the dependence of the string natural frequencies and mode shapes on the foundation stiffness, the foundation geometry, and the string translation speed
49 citations
43 citations
TL;DR: In this article, the experimental results are presented and they are compared with simulations using the momentum balance model described in Part. 1. Excellent agreement was found between the experiments and simulation and sensitivity studies were employed to show that the model is applicable for a fairly wide range of parameter values.
Abstract: The experimental results are presented and they are compared with simulations using the momentum balance model described in Part. 1. Excellent agreement was found between the experiments and simulation. Sensitivity studies were employed to show that the model is applicable for a fairly wide range of parameter values
36 citations
TL;DR: In this article, the time-varying energy transmitted between two point-coupled plates is related to the subsystem energies by an apparent time-changing coupling loss factor and it is shown that the apparent coupling loss factors approach the asymptotic (or steady-state) coupling losses as response energies and transferred energies are integrated over progressively larger times.
Abstract: The prediction, by the statistical energy analysis (SEA) method, of transient vibration envelopes for coupled systems is investigated. The relation between the time-varying energy transferred between two coupled subsystems and time-varying energies of the subsystems is studied numerically and experimentally. These studies indicate that time-varying energy transmitted between two subsystems is related to the subsystem energies by an apparent time-varying coupling loss factor. It is shown that the apparent coupling loss factor approaches the asymptotic (or steady-state) coupling loss factor as response energies and transferred energies are integrated over progressively larger times. Both the apparent time-varying coupling loss factor and the asymptotic coupling loss factor, determined experimentally, are used in energy balance equations to predict the time-varying vibration envelopes of a system of two point-coupled plates and the results are compared. Although overall response predictions are similar, considerable differences are noted in individual frequency bands. However, no general method for a priori determination of the apparent time-varying coupling loss factor is suggested.
36 citations
TL;DR: In this article, an overview of aero-acoustics is provided, beginning with a discussion of the properties of point sources of sound of various orders, and then treatment of the sound generated by a free aerodynamic flow (in the absence of rigid surfaces).
Abstract: An overview of aeroacoustics is provided, beginning with a discussion of the properties of point sources of sound of various orders. This is followed by treatment of the sound generated by a free aerodynamic flow (in the absence of rigid surfaces), and finally by a discussion of the effects of surfaces—very small (aeolian tones), very large (boundary layers), and the important effect of the edge of a large surface (trailing edge noise). In the first part, it is assumed that the aerodynamic flow is given, and that the sound produced by the flow does not act on the flow itself. In the second part, there is a reaction on the flow, and the effect is first order. Then a flow resonance occurs, even though no physical resonator is present; and of course, a physical resonator can be present, as in the familiar case of the organ pipe.
36 citations
TL;DR: The modal assurance criterion as mentioned in this paper measures the degree of proportion between two modal vectors, in the form of a correlation coefficient of a least squares ration estimate, which can be used to indicate regions of poor measurement-model correlation, to complete measured vectors, and to judge approximate eigenvalue solvers.
Abstract: The modal assurance criterion measures the degree of proportion between two (modal) vectors, in the form of a correlation coefficient of a least squares ration estimate. Applications might be hepful tools to indicate regions of poor measurement-model correlation, to complete measured vectors, to judge approximate eigenvalue solvers, or to improve model updating procedures
TL;DR: In this article, the generalized impulse momentum approach was used to model impact or collision in the constrained motion of deformable bodies, where the coefficients of restitution and the kinematic constraint Jacobian matrix were used to predict the jump discontinuity in the velocity vector as well as the joint reaction forces.
Abstract: In elastic systems, impulsive forces that act at a point on a deformable body produce stress waves that travel with finite speeds. This paper examines, both theoretically and numerically, the validity of using the generalized impulse momentum approach in modeling impact or collisions in the constrained motion of deformable bodies. The generalized impulse momentum equations that involve the coefficient of restitution and the kinematic constraint Jacobian matrix are used to predict the jump discontinuity in the velocity vector as well as the joint reaction forces
TL;DR: In this article, a geometrically nonlinear rod theory is used to describe the planar bending and extension of the rod centerline, and numerical solutions for free vibration are determined using a variational formulation of the associated eigenvalue problem.
Abstract: The model utilizes a geometrically nonlinear rod theory to describe the planar bending and extension of the rod centerline. The equations of motion are linearized about an elastica equilibrium and numerical solutions for free vibration are determined using a variational formulation of the associated eigenvalue problem. Results from an experimental modal test provide support for the model
TL;DR: In this article, an active control of the far-field radiation pressure generated by the vibration of a simply-supported rectangular elastic plate is considered, which is carried out by active means, i.e., by feedback control.
Abstract: This paper is concerned with the problem of suppressing the acoustic radiation pressure generated by a structure vibrating in air. The approach is to control the vibration of the modes of the structure most responsible for the radiation pressure. This control is carried out by active means, i. e., by feedback control. As a numerical example, the problem of active control of the far-field radiation pressure generated by the vibration of a simply-supported rectangular elastic plate is considered. The influence on the control effectiveness of various design parameters, such as the number of controlled modes, the choice of controlled modes, the number of actuators and the location of the actuators, is investigated. The conclusion is that, depending on the magnitude of the excitation frequency, satisfactory control can be achieved by using a sufficient number of actuators and by controlling a relatively large number of modes.
TL;DR: In this article, a criterion in the form of nonproportionality indices is developed, in order to measure the extent of the modal coupling and to predict the error introduced by neglecting this coupling either partially or completely.
Abstract: Modal analysis is used to transform the governing equations of motion to the respective modal coupled equations of motion. The Laplace transform is performed to transfer to the frequency domain. The modal coupling is then analyzed through coupling terms. A criterion in the form of nonproportionality indices is developed, in order to measure the extent of the modal coupling and to predict the error introduced by neglecting this coupling either partially or completely. An attempt to interpret the frequency spectrum of the modal coupling is also made
TL;DR: In this article, a condensation technique is proposed to reduce the nonlinear algebraic equations to those only related to the physical coordinates associated with nonlinear components, which can be used to locate limit cycles of an autonomous system.
Abstract: A set of nonlinear differential equations is transformed to a set of nonlinear algebraic equations. A condensation technique is proposed to reduce the nonlinear algebraic equations to those only related to the physical coordinates associated with nonlinear components. The method allows for the inclusion of searching for sub, super, ultra-sub and ultra-super harmonic components of the system response. It can be used to locate limit cycles of an autonomous system
TL;DR: In this article, a finite element formulation is proposed for solution of the time-dependent coupled wave equation over an infinite fluid domain, which is based on a finite computational fluid domain surrounding the structure and incorporates a sequence of boundary operators on the fluid truncation boundary.
Abstract: Considerable progress has been made in the development of numerical methods for the time-harmonic exterior structural acoustics problem involving solution of the coupled Helmholtz equation. In contrast, numerical solution procedures for the transient case have not been studied so extensively. In this paper a finite element formulation is proposed for solution of the time-dependent coupled wave equation over an infinite fluid domain. The formulation is based on a finite computational fluid domain surrounding the structure and incorporates a sequence of boundary operators on the fluid truncation boundary. These operators are designed to minimize reflection of outgoing waves and are based on an asymptotic expansion of the exact solution for the time-dependent problem. In the fluid domain, a mixed two-field finite element approximation, based on a specialization of the Hu-Washizu principle for elasticity, is proposed and employs pressure and displacement potential as independent fields. Since radiation dissipation renders the coupled system nonconservative, a variational formalism based on the Morse and Feshbach concept of a “mirror-image” adjoint system is used. The variational formalism also accommodates viscoelastic dissipation in the structure (or its coatings) and this is considered in the paper. Very accurate results for model problems involving a single layer of fluid elements have been obtained and are discussed in detail.
TL;DR: In this paper, an alternative procedure is obtained which indirectly calculates the desired acoustic variables, and a subspace iteration technique is outlined to solve the generalized unsymmetric eigenvalue problem.
Abstract: In this paper, an alternative procedure is obtained which indirectly calculates the desired acoustic variables. A subspace iteration technique is outlined to solve the generalized unsymmetric eigenvalue problem
TL;DR: In this paper, a theoretical model to study the flexural vibration of a bonded lap joint system is described, where the adhesive is assumed to be linearly viscoelastic and the widely used Kelvin-Voight model is used to represent the viscous behavior of the adhesive.
Abstract: A theoretical model to study the flexural vibration of a bonded lap joint system is described in this paper. First, equations of motion at the joint region are derived using a differential element approach. The transverse displacements of the upper and lower beam are considered to be different. The adhesive is assumed to be linearly viscoelastic and the widely used Kelvin-Voight model is used to represent the viscoelastic behavior of the adhesive. The shear force at the interface between the adhesive and the beam is obtained from the simple bending motion equations of the two beams. The resulting equations of motion are combined with the equations of transverse vibration of the beams in the unjointed regions. These are later solved as a boundary value problem to obtain the eigenvalues and eigenvectors of the system. The model can be used to predict the natural frequencies, modal damping ratios, and mode shapes of the system for free vibration. Good agreement between numerical and experimental results was obtained for a system of graphite epoxy beams lap-jointed by an epoxy adhesive.
TL;DR: In this paper, an analytical technique has been developed to compute the statistics of forced response of a mistuned bladed disk assembly with friction dampers, which is based on the statistical linearization approach and predicts the probability distribution function of a blade's amplitude.
Abstract: In this paper, an analytical technique has been developed to compute the statistics of forced response of a mistuned bladed disk assembly with friction dampers. The method is based on the statistical linearization approach and predicts the probability distribution function of a blade's amplitude. The validity of this technique has been corroborated by comparison with the results from numerical simulations. Using this technique, the optimal value of the slip load at the friction joint has been computed to minimize the probability that a blade's amplitude will exceed a critical value
TL;DR: In this paper, the time-integrated transient response of each oscillator was derived for N coupled multimodal subsystems, and the energy balance equations for each subsystem were derived using statistical concepts.
Abstract: Energy relations, analogous to steady-state SEA power flow relations, are derived for the time-integrated transient response of each oscillator. These energy flow relations can be combined using statistical concepts, to obtain a set of energy balance equations for N coupled multimodal subsystems. It is shown that the time-integrated response of each subsystem can be described in terms of transient input energies and conventional SEA parameters, i.e., modal densities, loss factors and coupling loss factors. By solving the energy balance equations, the time-integrated response of each subsystem can be obtained
TL;DR: In this article, the reduction of high order models generated by finite element analysis is considered and the effect of the reduction process on the modelled receptances is demonstrated, and the available order reduction algorithms and their properties are introduced.
Abstract: This paper considers the reduction of high order models generated by a finite element analysis. After reviewing the methods of structural parameter identification, the available order reduction algorithms and their properties are introduced. Modal truncation is determined to be the most suitable method and the standard algorithm is extended to accommodate unknown parameters. Finally the effect of the reduction process on the modelled receptances is demonstrated
TL;DR: In this paper, the idealization of an unbounded medium is applicable if the source is replaced by a periodic array of forces, the repetition distance being the cylinder circumference, and fundamental results that can be superimposed to predict vibration fields resulting from arbitrary excitations are given.
Abstract: The idealization of an unbounded medium is applicable if the source is replaced by a periodic array of forces, the repetition distance being the cylinder circumference. The analysis includes all three possible directions of the exciting force and gives fundamental results that can be superimposed to predict vibration fields resulting from arbitrary excitations