Spectral analysis of minimum structure platforms

This paper discusses the physical characteristics and frequency content of ship collision loads that are imparted to three minimum structures and a jacket platform, namely the shape and duration of the pulse load, and how they can be described by a half-sine pulse load. This was achieved by carrying out spectral analyses on the time histories of ship collision pulse loads and comparing those from a half-sine and a rectangular pulse load. The spectral analyses produced the frequency bandwidths within which most of the excitation energy was located and showed whether they coincided with the natural frequencies of the platform. Spectral analyses were also carried out on the dynamic response at the topside and the impact nodes, to identify those mode shapes that contributed prominently to the dynamic response of the platform. There is a discussion on how this information can be used in collaboration with the acceleration spectrum technique used in a previous paper by the authors, in order to assist the engineer in designing topside equipment to survive excessive vibrations resulting from a ship collision.