Structure Optimization Of Oil Tanker Bulkhead And Analysis Of Welding Residual Stress

With the increasing demand for oil,the structural design of oil tankers has also put forward higher requirements.In the process of designing oil tankers,the weight of empty vessels needs to be strictly controlled so as to reduce construction costs and improve economic efficiency.Therefore,based on the Guide to Direct Calculation of Tanker Structures,this paper investigates and optimises the flat bulkhead structure of a 30,000 DWT tanker,and explores the slotted bulkhead that can reduce the mass of the empty vessel and improve the mechanical properties of the hull structure by means of shape optimisation.The distribution of stress after welding.Firstly,the finite element model of the mother ship is established,the working conditions are selected and the loads are calculated according to the specifications;the bulkhead structure optimisation model is established,the transverse bulkhead is the optimisation design area and the weighted flexibility value of each working condition of the bulkhead section is minimised under the displacement constraint as the objective function for its shape optimisation,according to the shape optimisation results combined with the technical requirements the optimal form of the slotted bulkhead structure is given,and the comparison reveals that the optimised slotted bulkhead has a lower mass compared to the flat The optimized slotted bulkhead is found to have a lower mass and better mechanical properties than the flat bulkhead.Secondly,according to the quasi-static tensile test,high temperature quasi-static tensile test,dynamic tensile test results at room temperature using optimisation algorithms for Q235 steel thermomechanical model parameters to optimise calibration,to obtain a closer fit to the test results of the thermomechanical model for welding simulation.The simulation model at room temperature and strain rate is established,the model is monitored to obtain the simulated mechanical properties curve,Poisson’s ratio and Johnson-Cook strength model parameters as design variables,to minimize the simulation and test yield stress difference,fracture stress difference and curve difference of the linear weighting value as the objective function,using a variety of optimization algorithms to optimize the calibration of the room temperature and strain rate model,five kinds of parameters The global response surface algorithm was determined to be the most suitable algorithm for this optimisation problem by comparing the optimisation results.A sensitivity analysis was carried out to investigate the effect of the model parameters on the objective function.The global response surface algorithm is then used to optimise the calibration of the high temperature and high strain rate models respectively,so that the material strain regimes over a wide range of temperatures and strain rates are more consistent with the actual test results.Finally,based on the optimised Johnson-Cook model,the residual stress distribution of the flat specimen at different post-weld heat treatment temperatures was simulated by the welding finite element method to select a suitable post-weld heat treatment temperature for bulkhead structural welding simulation.Under the same post-weld heat treatment conditions,the results of welding residual stress distribution in flat bulkhead structures and slotted bulkhead structures are analysed and evaluated.This paper uses the method of shape optimization to determine the tanker slotted bulkhead structure type,through the finite element iteration to find the optimal shape parameters,can quickly and effectively achieve the optimal design of the tanker bulkhead structure;through the optimization method to calibrate the thermodynamic model parameters of Q235 steel under high temperature and high strain rate,so that the model in a wide range of temperature and strain rate strain mechanism more consistent with the actual test results,to improve the welding simulation Through the welding finite element method,the welding residual stress distribution between the flat bulkhead and the slotted bulkhead was simulated,and it was found that the optimized slotted bulkhead was better than the flat bulkhead in terms of stiffness and welding residual stress,and the manufacturing cost was lower,which had reference significance for the optimal design of the bulkhead structure of tankers.