Research On Direct Finite Element Calculation For Structure Strength Of Semi-submersible Ships

Semi-submersible ships which count for a great deal in the areas of ocean energy exploration,large scaled machine transportation,heavy lift and salvage at sea have rapidly become the high-value-added ships during recent years.As the structural types of semi-submersible ships are relatively special,with the value of B/D being much larger than other ship types,to check its strength by a commonly used rule is inappropriate.In addition,semi-submersible ships commonly sail and operate in severe sea state,whose hull strength may be highly influenced by the sea wave.So far there are insufficient researches about the wave load and the structural strength of semi-submersible ships,and there is not any standardized system for structural strength assessment.So it is of great significance to conduct a research for assessing the whole hull structural strength of semi-submersible ships under different types of wave load.Based on the author's comprehension and experience of hull structural analysis,and with reference to relevant provisions of other ship types,this paper examines a method of whole hull structural analysis for semi-submersible ships.This paper introduces the general principle and process of hull structure finite element analysis,details a method of wave load direct calculation,and proposes an analysis method and process which is aimed at semi-submersible ships.Taking a 38000t semi-submersible ship as the example,this study checks its structure by using the calculating methods mentioned in this research.According to design paper,FEM model is built in Patran,and load is applied by three load cases.The wave pressure among all load conditions is calculated by Seasam.After load apply process,static and dynamic is adjusted to be balanced to make the load curve closed.Finally,the stress level of whole hull structure is evaluated by related stress criterion.Considering that hull transverse strength of target ship is required by rule,and existing wave load data,it comes up to check transverse strength of target ship by cargo FEM analysis.Following this method,transverse strength of target ship ischecked.Joint of flange in poop is a unique assembly unit of semi-submersible ship,and concerned by the companies and ship owners.Because whole hull calculation cannot show a stress level of this area,local model is built to assess the joint of flange in poop of target ship.This research provides analysis examples of semi-submersible ships.And the conclusion would be reference for the design and development of semi-submersible ships in similar types.