Abstract
This article addresses the degree of success that may be achieved by using simple equipment–vehicle models that produce time history responses whose equipment fixed base modal maximum response values are equivalent to those found in the U.S. Navy's dynamic design analysis method. The criteria of success is measured by a comparison of the results with typical interim shock design values. The equipment models reported are limited to two- degree and three degrees of freedom systems; the model of the vehicle to which the equipment is attached consists solely of a rigid mass and an elastic spring; and the shock excitation is produced by an ideal impulse that is applied to the vehicle mass.
Highlights
The dynamic design analysis method (DDAM) (Belsheim and O'Hara, 1960), has been used for more than 30 years as part of the Navy's efforts to shock-harden heavy shipboard equipment
The practice of using some "typical" base motion for a class of structural systems as a design input is flawed, sometimes grievously so. This is because during a shock, the base motion includes the interactive effects between the equipment and its supporting structure
This is especially true when one compares shock design values derived from original base motions with those derived from average motions
Summary
The dynamic design analysis method (DDAM) (Belsheim and O'Hara, 1960), has been used for more than 30 years as part of the Navy's efforts to shock-harden heavy shipboard equipment. Likewise, trying to average base motions obtained at different points of a multifoundation system can and does lead to a wide range of results that are in error This is especially true when one compares shock design values derived from original base motions with those derived from average motions. Another method (Private communications, 1990), used a simple base mass to represent the vehicle to which the equipment is attached, and an impulsive force applied to the base mass to CCC 1070-9622/94/030241-11. A recent article by O'Hara and Cunniff (1991) examined the degree of success that may be achieved by the simple model to produce time history base motions for the equipment responses whose modal maximum response values are the prescribed shock design values. It will be shown that this new vehicle overcomes the shortcomings reported by O'Hara and Cunniff (1991) for two degrees of freedom equipment, and successfully accommodates the three degrees of freedom equipment
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