Showing papers on "Modal testing published in 1981"

Modal methods in the dynamics of systems with non-classical damping

Abstract: When damping in a system is both significantly high and its distribution is non-classical the solution of dynamical problems by conventional modal analysis is complicated by the presence of coupling between the normal co-ordinates. Further, the convergence of a solution may be erratic with successive modal additions, leading to the need to include a larger number of modes than would otherwise be expected. In this paper methods of modal analysis in structural dynamics are discussed and their derivations briefly given. These include the conventional mode displacement method and the force summation method, employing normal modes, and the analogous procedures with damped modes. In the latter, dynamic response equations are not coupled. Dynamic loading solutions by the four approaches, each taking account of the non-classical damping distribution, are demonstrated with a simple model representing a structure on a compliant foundation. The results strongly suggest that the use of damped modes with force summation could be the most effective procedure when damping is non-classical.

Nonlinear Dynamic Analysis by Modal Superposition

Abstract: A modified modal superposition method is developed and used to evaluate the nonlinear dynamic response of a cable network composed of a linkage of straight members with lumped masses. The method is compared with Newmark's B method for accuracy and the time interval requirements for stability. To show the usefulness of the method a number of parameter studies are presented using the cable network as an example.

Modelling of Mechanical Structures Based on Modal Parameters

Abstract: Modal Analysis has become a well known tool to derive the mode shapes of existing machine structures. In this paper, it will be shown that modal parameters derived from modal testing can be used to investigate the effect of potential design changes on a test structure.

Modal analysis using a Fourier analyzer, curve-fitting, and modal tuning

Abstract: The proposed modal test program differs from single-input methods in that preliminary data may be acquired using multiple inputs, and modal tuning procedures may be employed to define closely spaced frquency modes more accurately or to make use of frequency response functions (FRF's) which are based on several input locations. In some respects the proposed modal test proram resembles earlier sine-sweep and sine-dwell testing in that broadband FRF's are acquired using several input locations, and tuning is employed to refine the modal parameter estimates. The major tasks performed in the proposed modal test program are outlined. Data acquisition and FFT processing, curve fitting, and modal tuning phases are described and examples are given to illustrate and evaluate them.