Research On The Methods Of Direct Strength Analysis For Large Semi-submersible Vessel

Because of great needs of ocean exploitation and the dispatchments of special ships andequipments,even marine salvages, semi-submersible vessel has broad market prospect and ischaracterized by high technologies and high added value. There is a strict structuralrequirment for the huge semi-submersible vessel and it needs an accurate analytic approachfor the structural strength. Taking a huge semi-submersible vessel as example, this paper aimsto develop a direct calculation method for this kind of ship, which is based on thestandardized methods of conventional ships and can be took as a reference.Motives for this paper are as follow:1. As is unconventional, there is no standardized guidance for direct strength analysis forsemi-submersible vessel.2. For the uncertainty and considerable value of the caogoes, it needs an accurateapproach to analyze the structural strength in different loadcases.3. The development of FEM method provides the possibility of more accuratecalculation.The main contents of this paper are as follow:1. Fix the structures that should be modelled in FEM and work on the automaticgenerating of hull lines base on the AutoCAD secondary development, then develop a methodto simulate the exact offsets of beam elements in PATRAN. In order to control the shear forceand bending moment at the target locations, nodal forces by local loads are calculated todetermine the ends moments. Finally, a huge semi-submersible vessel is taken as an example.2. The SESAM system is employed to achieve the calculations of wave-induced loadsfor different ships, then an analysis that focuses on the short-crested waves’ effect on ship’swave-induced loads is made, and the wave-induced loads for target vessel are confirmed.