Semi-submersible Vessel Hull Structural Strength Analysis During Transportation Offshore Platform

As a kind of high value-added ships, semi-submersible vessel plays more and more important role in offshore engineering field. Due to the traditional mode of transportation such as barge drag, drag after loading methods, so transport capacity and transport speed is very limited. And along with marine structures are made more and more large and the transportation distance is more and more far, the requirements for this special semi-submersible vessel which can combine both speed and load capacity are more and more strict.So the research for the structural strength and connection structure design of semi-submersible vessel under the large capacity is very necessary.Because of semi-submersible vessel is a new type of ship and as the rapid development in recent years, the general specification requirements of the ship is not applicable for its special structure, and previous semi-submersible vessel structure analysis mainly focuses on semi-submerged ship hull strength, such as three compartment semi-submersible hull strength analysis, and etc. With the development of the direct calculation method, the check and analysis of structural strength for all kinds of vessels are more reasonable and effective. So the addition support structure of the semi-submersible vessel during transportation, where is between the platform and hull which need to add to a series of design and checking, is the focus of research in recent years. This paper is based on the Semi-submersible vessel BlueMarlin which is belong to Dockwise (the largest Semi-submersible vessel transportation company of the world) as the prototype,to simulate a weighs is forty thousand tons of offshore platform module. And the operation range is from East Asia to eastern Canada. To perform an strength analysis of hull structure, slide arm, new supporting structure, load spread structure and other related structures during a complete voyage,and choose the operation sea state as the load conditions.The analysis method of this paper is as follows: according to the voyage and platform information to determine the load condition. And according to the upper module SACS calculation model convert to ANSYS finite element model, and adjust the weight center information and base reaction force to consistent with the SACS model. Then build the finite element model of hull and new added structure in accordance with the hull drawings, and Moses software is used to perform the hydrodynamic calculation, the result is load mapping into the ANSYS model so the hydrodynamic load applied to the hull, and then combines with ANSYS technology spring unit to realize the buoyancy balance. Using the link element to connect each relevant structure, and use ANSYS inertia release function to eliminate the effects of unbalanced load. After analysis, compare the strength and deflection of the related structure with classification society requirements, and discuss two kinds of seafastening structure design which is connecting the upper module, in order to obtain best optimized scheme.