Description
The increased interest in floater designs for ultra-deep water has produced a number of dry tree semisubmersible designs that allow the use of top tensioned risers (TTRs). The primary advantage in using TTRs is that they facilitate direct vertical access to production wells and thereby offer access for well completions and interventions. The principle behind several of the dry tree semisubmersible designs is to reduce the motions of a traditional shaped semisubmersible to a level that can accommodate TTRs. This is accomplished by using heave plates that are positioned beneath the semisubmersible hull and are supported by a lower structure, such as a truss. To a certain extent, the motion responses above and below the response amplitude operator (RAO) cancellation period can be manipulated by designing the relative sizes of the pontoons and columns as well as the size and depth of the heave plates such that the sum of the forces interact to minimize the heave motion. This presentation looks beyond the traditional solutions. It presents and discusses the design and performance of two dry tree semisubmersible designs that use heave plates to reduce heave motion the ESEMI II (E SEMI) and the Truss Semisubmersible (Truss Semi). The analysis demonstrates the sensitivities in the geometry of the hull design and how they can be used to optimize the heave response.
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