Research On Optimization And Design Methodology Of Composite Material Submersible Pressure Hull

Compared with the traditional metallic materials,fiber reinforced composites have high specific modulus and specific strength,which minimize the weight of the structure,meanwhile meet the structure performance requirements.This is very important for increasing the load carrying and energy resources saving of submersible.Except that,the excellent comprehensive performance such as corrosion resistance,fatigue resistance and good designability and the economy trend of the composites make a broad prospects of application of composite materials in submersibles.However,the anisotropy and the layers property of structures bring both the flexibility in design and at the same time,the difficulty in structure analysis.Until now,the application of composites in submersibles is still in its infancy,resulting in a lack of relevant structure analysis methods and the rules can refer to.Focusing on the pressure hull structures of submersibles,the structural calculations and optimization design method are studied in this paper.The main work is presented as follows:Taking the characteristics of submersible and the properties of constitute material of composites into consideration,the Carbon fiber/ epoxy composites are recommended for submersible structures and the superiority are elaborated briefly.The molding process can be applied in submersibles are summarized.The basis theory of composites mechanics,the failure criterion and the FEA method can be used in ANSYS for composites are introduced.Based on the continuum damage mechanics(CDM)theory,stiffness degradation method is proposed to predict the progressive failure properties of composite pressure hulls.Three failure modes:fiber breakage,matrix cracking and interface shear failure are considered according to Tsai-Wu failure criterion.The failure material stiffness will be degraded based on CDM model.The analysis is implemented in ANSYS by using APDL.To validate the feasible of this method,an experiment of unidirectional tensile test of laminates are carried out to compare with the FEA results.Load displacements curve and the number of failure elements with different pressure which can be used to predict the damage propagation of the pressure hulls are obtained by applying this method to composite material pressure hull.Tsai-Wu factors of the structure under design pressure can be regarded as strength indicator of composite pressure hulls by observing the results.The structure performance of composite material pressure hull is studied based on the approximation method.By studying typical examples,the efficiency and accuracy of Radial Basis Functions(RBF)model and Response Surface Model(RSM)are determined.Taking the results of FEA as samples,mechanical property approximation of composite material pressure hull are established.Based on the approximation,research on how component material engineering constant,the percentage of fiber and ply angles affect the structure mechanical performance of pressure hull are carried out,which can be regard as a reference for material selection and structure design.The optimization of composite material pressure hull is carried out based on lamination parameters.A two level Collaborative Optimization framework is employed to optimize the battery cabin of a 2000-meter operating depth submersible.The efficiency of the optimization is improved by using lamination parameters.The global searching method muti-island genetic algorithm combining with sequential quadratic programming are adopted in the iteration,which improved the optimization precision.Compared with titanium alloy pressure hull with the same mission requirement of “Cheng Sha” submersible,the weight of composite material hull decreased by more than 50%.The reliability analysis and design for 6 sigma of composite pressure hull are carried out in this paper.Take the dispersion of material characteristic and the tolerance in processing into consideration,reliability analysis based on Monte-Carlo sampling are employed to estimate the reliability of the optimization design of composite material pressure hull.It turns out that there is great probability of structure failure because of buckling.Based on this,the 6 sigma design optimization is employed to improve the reliability of the hull.By increasing the thickness of the shell by 1.5mm,the reliability reach to 8 sigma level,namely 100% reliable.