Structural Optimization And Analysis Of The Lightweight Underwater Robot's Pressure Hull Based On Finite Element Method

The lightweight underwater robot is mainly powered by its own portable charging power supply, in order to extend cruising time and increase the maximum load capacity under certain conditions of energy supply, it require to reduce the quality of the underwater robot's pressure hull on the condition of meeting strength and stability requirements, it need structural optimization for the initail model of underwater robot's pressure hull in order to seeking the optimization parameters to reduce the weight of the pressure hull. The comprehensive strength analysis should be conduct for the pressure hull after structural optimization, including compressive strength analysis, stability analysis, modal analysis, lifting components strength analysis.This paper focuse on the research of the underwater robot's structual optimization and strength analysis based on finite element method and with the help of FEA software ANSYS, the main containts are as follows:(1)Lightweight autonomous underwater robot's pressure hull optimizationOptimization process is divided into preliminary and final optimization, preliminary optimization including material optimization of the underwater robots'pressure hull and preliminary structural optimization, material optimization is that considering the material processing performance, cost, and other factors to choose the most suitable manufacturing material; preliminary structural optimization changes the original form of the cylinder pressure hull structure to ring-stiffened cylindrical pressure hull. The aim of final optimization is to determine thickness and size of ribs of pressure hull to reduce the quaility of it. Each cabin of pressure hull divided into the barrel portion and the wedge-ring connecting portion, the design and checking criteria of these two portion are different, so the final optimization is divided into two parts of the optimization process:a. Wedge-ring connection optimizationBased on the response surface method(RSM), combined with three different experimental methods to design the experiments for the underwater robot's wedge-ring connection with four parameters,with the help of FEA software ANS YS to get the respond value of structure stress and mass of wedge-ring connection, Design-Expert was used to fitting the samples' date to quadratic response surface, the constraint condition of optimization is structure's stress requirements, the optimization objective is to minimum the mass of wedge-ring connection. Compare the optimization results with different optimization algorithm and get the final optimization results.b. Cabins of pressure hull structure optimizationBased on the response surface method to optimize underwater robot pressure hull with five optimization variables, using ANSYS to solve the structural stress response value, reduces the optimized variable range of response surface experimental using combined experiment method, the constraint condition of optimization is structure's stress and stability requirements, the optimization objective is to minimum the mass of underwater robot's pressure hull, using experimental design software Design-Expert to obtain response surface optimization solution, compared the result with the optimization results got from 1 stOpt optimization software based on different algorithms and get the final optimization results.(2) Lightweight underwater robot pressure hull strength analysisComprehensive strength analysis is needed for the pressure hull after the structure optimization, the containts of strength analysis are as follows:a. Compressive strength analysisUsing FEA software ANSYS to simulate real working conditions (200m deep)and get the cabin stress nephogram of underwater robot's pressure hull, then check the strength of pressure hull according to "Dive Systems and Submersibles Rules for The Classification and Construction".b.Stability analysisWith the help of FEA software ANSYS to do linear buckling analysis for the underwater robot's pressure hull, compare numerical simulation solutions with theoretical calculation results in order to get more accurate buckling analysis solution, then check the buckling strength of pressure hull according to"Dive Systems and Submersibles Rules for The Classification and Construction".c. Modal analysisThe main aim of modal analysis is to get the natural frequency of pressure hull, compare the pressure hull's natural frequency with the working waters' wave frequency in order to avoiding resonance, at the same time, we can avoid excessive deformation position to put lifting device.d. Lifting component strength analysisLifting beams and lifting hoops bear the full weight of the underwater robot in lifting working conditions, the strength analysis of lifting components including lifting beams, lifting hoop and connection bolts strength analysis, using theoretical analysis to check the strength of connection bolts and using ANS YS to get stress analysis results of other lifting component.This paper has given a comprehensive structural optimization process and structural strength analysis of the lightweight underwater robot's pressure hull. The results provide technical support in the lightweight underwater robot structural design and analysis.