Study On Ship Sheet Structure Deformation Of A RORO

The sheet have many advantages: they have light weight and they are easy to be processed and easy to be connected and shaped.These characteristics make sheet structures have less weight and consume less fuel.So more and more sheet structures are used in modern shipbuilding technology,they are often seen used in the Ro-Ro ships,warships and superstructure.In addition to advantages,sheet also had many advantages,such as: sheet structures have poor stability and they are easy to be out of shape.These shortcomings may cause many problems to ship construction,not only affect the appearance,reducing the accuracy of the construction,but also reduces local structural strength and stability,which may lead to security problems.There are two forms of sheet deformation: the welding deformation and the non-welding deformation.There are many factors affecting welding deformation,so it is difficult to control welding deformation.Non-welding deformation mainly produced in the phase of lifting and turning over sheet structures.Welding sequence is one of the key factors affecting sheet deformation,for the choice of the welding sequences,most shipyards are mainly based on experience,lack of necessary guidance.This paper chooses two thin plate structures of a RORO as objects of studying sheet deformation situation under the different welding sequence with Numerical simulation method.According to the actual welding sequence,four welding sequences are set for each model.The finite element models are established based on ANSYS software,APDL is used to write command stream to simulate Moving heat source.To simulate the formation of weld line need to use birth-death element method to simulate,the welding units are killed before analysis,and will be activated gradually with the moving of the heat source then.Thermodynamic analysis of the finite element models should be performed,calculating the temperature field of every load moment and the cooling stage.Structure analysis is conducted on the basis of thermal analysis,APDL commands are written to Read the temperature load of every load moment and the cooling stage and then the stress field and displacement field are concluded.According to the results of calculation,we can observe the deflection of the thin plate structure under different welding sequence visually,so as to identify the optimum welding sequence.The prevention and control measures of sheet welding deformation should be take at each construction stage,from design phase to blocks closure phase.The paper discusses the commonly used measures to control welding deformation of sheet structures in different stages.Measures to control deformation can be divided into three kinds generally: Before welding,the welding process measures and measures after welding.The control effect is good or bad directly affects the subsequent manufacturing stage,so appropriate measures to control deformation should be formulated at every stage of construction.The deformation degree should meet the accuracy requirement before coming into the next construction stage.The non-welding deformation mainly generate at periods of Lifting and turning over Thin plate structures.Specifications,quantity and installation location of lifting rings are three main factors affecting non-welding deformation.To optimize these three factors and to choose the proper ways of Lifting and turning over sheet structures can effectively control the deformation degree.In addition,local reinforcement is also commonly used.Through research and analysis,this paper determines the optimum welding sequence of two typical plate components,discusses the factors of the non-welding deformation,and introduces the technological measures to control the deformation of sheet structure.