Draft of Manuscript Submitted to Society of Naval Architects and Marine Engineers Annual Meeting, November 1992
1992
Cunniff, P. F. | O'Hara, G. J.
Commonly perceived problems associated with the Dynamic Design Analysis Method include the following: a transient dynamic analysis is both a unique and better solution; if a structure has repeated fixed base frequencies DDAM fails to account for them; if a structure has two fixed base modal frequencies very close to each other, the beating response is so long in time that the combinatorial rules for response are not realistic; and a very small appendage attached to a larger component can cause erroneous values in shock inputs. Basic concepts and terminology associated with normal mode analysis are presented to demonstrate their role in DDAM, along with a procedure for developing transient equipment-vehicle models for some simple systems that produce time history responses that are different, and yet, equivalent to the damaging potential of a DDAM input. Having developed this background, the perceived problems with DDAM are examined by means of examples which should help to clarify these notions.
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