The Absolute Value Modal Strain Energy Method

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Report Number: WL-TR-91-3078 Volume II, pages FDB-1 to FDB-16
Author(s): Morgenthaler, Daniel R.
Corporate Author(s): Martin Marietta Astronautics Group
Laboratory: Wright Laboratory
Date of Publication: 1991-08
Pages: 16
DoD Project: 2401
DoD Task: 240104
Identifier: This paper is part of a conference proceedings. See ADA241312

Abstract:
The Modal Strain Energy (MSE) method has become a significant design tool in the last decade. The MSE method allows the approximate solution to a complex eigenvalue problem using the solution to a real eigenvalue problem and knowledge of element loss factors and the percentage of MSE contained in each element. While the MSE method has been shown to be relatively accurate in many instances, particularly for design purposes, it can produce high errors even in simple cases with relatively low damping levels. This paper discusses a new MSE method which allows the approximate solution to complex eigenvalue problems while providing more accurate approximations. The Absolute Value MSE (AVMSE) method incorporates the absolute value of the individual element impedances to form a real "stiffness" matrix. From the solution of the eigenvalue problem associated with the system mass matrix and this real "stiffness" matrix; approximate mode shapes, natural frequencies, and damping ratios may be obtained. The new method provides greater accuracy than the standard MSE method in most instances, and more importantly provides conservative damping estimates while the standard method tend to overpredict damping ratios. The AVMSE provides more accurate results while remaining inexpensive to implement.

Provenance: University of Colorado Colorado Springs, Kraemer Family Library

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