Convergence Analysis On The Position Of Boundary Condition For The Ship Structure Analysis

In order to prevent accidents of ships and protect the marine environment,IMO's Maritime Safety Committee adopted an amendment of International Convention for Safety of Life at Sea?SOLAS?for Goal Based Standered?GBS?at 87^th conference in2010.In accordance with the requirements of GBS,IACS?International Association of Classification Societies?formulated the“Common Structure Rules for Bulk Carriers and Oil Tankers”by HPTs set up by IACS in 2008.CRS BC&OT was promulgated and effective at 1^st July in 2015 and will have a GBS acceptance test in May 2016.This paper studies rationality of CSR BC&OT FE model's extent for direct strength analysis,and does convergence research on the position of boundary condition for the separate local mesh.Some numeral calculations demonstrate that uncertainty is the definition of model extend in the local structural analysis.For the reason of application,it is necessary to study the model extend.In addition,this paper will study the rationality of the three cargo hold region of direct strength analysis of the CSR BC&OT.Through an oil tanker's FE model,select 4 typical loading patterns and apply the dynamic wave pressure by direct calculation of wave loads.Make the moment curve and shear curve closed by balance adjusting of whole ship.Two kinds of boundary condition,inertia relief and supports,are applied in the whole ship calculation.Selecting 3 different scope cargo hold region from whole ship,make the model load be the same and apply hull girder vertical moment on the model ends.Compare the 3models'result to the whole ship with Von Mises stress.The calculation result shows that the model scope has effect on the stress.Comparing to the result of whole ship,three cargo hold model has an advantage over other models and the method of CSR BC&OT is reasonable.The CSR BC&OT rules that it is necessary of taking fine mesh analysis for local structure strength analysis and fatigue analysis of hot spot.Affected by the boundary condition,CSR BC&OT's specifications of mandatory structures may not eliminate the influence of the boundary condition.This paper selectes two bulk carriers and one oil tanker.Based on the coarse mesh model,this paper analysises 4 mandatory separate local mesh models and incorporated mesh models.Comparing the different separate local mesh models to the incorporated model,analysis the effects of model scope and different treatments of boundary condition.The result shows that separate local mesh model has effects on the fine mesh zones.CSR BC&OT's specification for separated model is relatively small and it is necessary to get a bigger local model as taking local structural strength analysis.In addition,the result also shows that rotation displacement has effects on the stress of fine mesh zones.The primary supporting members boundary has little effects on the stress of fine mesh zones.