Studies On Ship Structural Optimization Based On Robustness

Conventional optimal design does not take the variations of variables into account,which makes conventional optimal solution in the edge of the feasible region. When thedesign variables fluctuate, the conventional optimal solution will deviate from the feasibleregion into unfeasible solution. While robust design takes the variations of variables intoaccount early in the design, and it makes objective function and constraints are robust,therefore robust design optimization solution has better robustness than the conventionalsolution.Modern robust design method is based on the Taguchi method and evolved. Thispaper mainly describes robust method based on the tolerance model, the minimumsensitivity method and sensitivity analysis. Tolerance model method taking into account thevariation of design variables which will cause the objective function and constraints havevariation, to find a new robust solution in the new feasible region.This method applies to thelinear model is not high and the variation is relatively small; minimum sensitivity methodand sensitivity analysis are the methods which don’t considere design variable tolerance.This paper combined theory and practice, and the major work done is as follows:(1) Use of tolerance model method for8700DWT bulk carrier’s midshipcross-sectional structure in robust optimal design. Plate thickness as design variables, theminimum cross-sectional area as objective function, and constraint functions using theworst-case tolerance for processing. The result is more robust than specification design.(2)It doesn’t consider the redundancy of the performance parameters, so the methodof minimum variation is proposed in this paper. The minimum variation being proposed inthis paper cooperates the method of minimum sensitivity and the redundancy of theperformance parameters, which will quantify the variations of the performance parameters.By the robust optimization of the midship section structure of40,000DWT bulk carrier,finding that the method proposed in this paper has better result than the minimum sensitivity.And the method proposed in this paper can also be extended to other robust optimizationdesigns.(3) In MSC.Patran environment27.6m catamaran finite element model was build, throughthe imposition of boundary conditions and load, got the result by the calculation ofMSC.Nastran. After analyzing the results, some catamaran’s structure needs to be improved.In this paper by using finite element techniques and structural analysis softwareMSC.Patran/Nastran, got the sensitivity to sheet thickness of mass, the Von.Mises of shell element, the Von.Mises of beam element, lateral stiffness and torsional stiffness. Throughcomprehensive analysis and comparison, got the optimization program, and achieved goodoptimization results, indicating the sensitivity analysis used in ship structural optimizationcan get better result. This paper can also be used as a reference for other ships’ sensitivityanalysis and optimization.