Finite Element Analysis Of Large Semi-submersible Vessel Hull Strength

Large semi-submersible vessel has a performance advantage can not be compared with other ships in carrying the huge heavy cargo because of its unique characteristics and method of loading. With the development of offshore and gas exploitation, transportation of special ships and equipment, maritime rescue and salvage needs, semi-submersible vessel has a booming market. As ability of large semi-submersible vessel carrying rising at the same time it also has higher requirements on the security of its structure. The semi-submersible vessel is playing a more important role as a new kind of auxiliary vessels in the ocean ographic engineering. Its structural style is so special that the standards for some normal vessels are not fit for the semi-submersible vessels. At present, there was the CCS having issued a few descriptions and the most of requirements are from oil tanker to guide the construction of the semi-submersible vessel in the 《 Rules for classification of sea-going steel ship 》. Meanwhile, it is greatly complicated and uncertain when the semi-submersible vessel is loading some cargo mostly with heavy weight and high price, during this condition, we need to precisely analyze its load and the response of the structure. This paper is based on the indepth study of the theory and calculation for hull structural strength. It will research and analysis on the calculation method of hull strength of a large semi-submersible vessel. This paper will apply finite element software ANSYS to calculate the transverse strength, the longitudinal strength and slip cargo loading process of a large semi-submersible vessel. It will form a direct calculation method suitable for large semi-submersible vessel hull structural strength and it can be used as reference engineering practice.In this paper, the main contents are as follows:(1) this paper will build mid-ship cabin model and the entire ship model to meet the requirements of calculation in finite element software ANSYS.(2)In the process of transverse strength calculation, this paper will analyze the load change and the response of ship hull structure in a variety of conditions. The factors to consider include: the ship draft change in the loading process; the symmetrical outboard water pressure in the process with the waves comparison of asymmetrical outboard water pressure when transverse waves hitting the hull; the comparison of hull sagging and hogging in the waves; changes on the deck of the cargo vessel pressure in loading and unloading process. For the semi-submersible vessels sailing in the transportation process, cargo deck stress is too large. This paper will analyses the local strength of the deck cargo area, research the impact of cargo load of different loading modes on the strength of deck cargo.(3) In the process of total transverse strength calculation, the key content is the use of inertia relief method for static analysis of the whole unconstrained ship structure. This method eliminates the influence of constraint reaction force in the finite element analysis in order to have a more reasonable and accurate analysis and evaluation of the whole hull structure.(4)This paper will study the dangerous working conditions of semi-submersible vessel when in slip loading process. It forces on the analysis of the influence of cargo movement on the whole ship structure strength and can be used as security for large semi-submersible vessel loading reference.