Optimal locations for heavy lifts for offshore platforms

Abstract

Lift installation of a major marine or offshore structure necessitates detailed evaluation of inter-dependent engineering and construction constraints that influence the feasibility, safety and cost-effectiveness of the lifting operations. Due to the advancements in heavy lift technology, large modularized ship blocks may be fully outfitted, and then lifted and joined to form the entire ship. Similarly, an offshore structure may be fabricated. in a yard, transported to the selected offshore location, and then installed by lifting. The objectives of this paper are to find the locations of optimum positions of offshore platform heavy lift points using the method of evolution strategies either minimizing the moment or maximizing the natural frequency. The results obtained are compared with the published results. The optimal positions of simple supports are located to maximize the fundamental frequency of beam or plate structure taking into account both elastic and rigid supports. The minimum stiffness of a simple support (or point) that raises a natural frequency of a beam to its limit is investigated for different boundary conditions. The solution also provides insight into dynamics of a beam with an intermediate support for more general boundary conditions. Finite element approach is used for solving the problems. The computer packages such as PREWIN/FEAST, SAP90 are used for performing finite element analysis.