Deformation Analysis And Optimization Design Of The Airship Cable-Membrane Structure

The system design technology of the airship structure has been relatively mature,but the research on detailed structure design is less.Increasing the cables on the airship membrane structure can effectively enhance the bearing capacity and change the shape of the inflatable airship.This paper studies the deformation analysis and the optimization design of the airship cable-membrane structure,which can provide technical support for the refined design of the refined airship structure.The airship cable-membrane structure is taken as research object in this paper and the structure shape changes and optimization design due to the reinforced cables are studied systematically.By studying the tapered inflatable beam model,the initial analysis of the overall structure can be quickly completed,which is convenient to provide an initial model for the subsequent refined design of the airship structure.The increase of the reinforced cables would bring about the "bulge" deformation of the airship structure.The deformation law and the influence on the stress distribution were studied by form-finding analysis.The layout of the reinforced cables also has an important impact on the improvement of structural performance.Through structural optimization based on NSGA-? genetic algorithm,the results and laws of the optimal distribution of reinforcement cables were studied and the pressure-bearing strength was verified through simulation and experiments.The main research works are listed as follows:1.For the deformation of inflatable structures with large curvature changes,a mechanical model of a tapered inflatable beam was proposed considering the variable curvature and the need for inflation of the airship membrane structure.The following forces resulting from internal pressure and taper ratio were converted into equivalent internal force in the equilibrium equations and the influence of the two factors on bending stiffness could be analyzed easily.Then,the effect of the taper ratio on the beam deformation was studied and the optimum taper ratio was obtained.Finally,the theoretical method based on the model was applied to deformation analysis of the airship membrane structure and the results were consistent with the ones of the FEM method.Because the beam model belongs to volume element,the number of elements is much smaller than the number of FEM shell elements,which greatly reduces the amount of calculation.2.New methods for two types of form-finding problems of the airship cable-membrane structure were presented based on the nonlinear finite element form-finding theory.The form-finding problem of the airship membrane structure belongs to inverse analysis problem because the initial shape is determined by the known target shape.The inverse form-finding method was proposed and the initial shape was obtained through inverse iteration by taking the geometric error as the control parameter.For the airship cable-membrane structure,“bulges” would appear because of stiffness difference between the cable and membrane material.Therefore,the form-finding work was to find the target optimization shape based on the initial shape.Taking fixed volume,fixed cable membrane maximum stress ratio and uniform stress distribution as optimization targets,the multiple target optimization solution was presented to find the optimization shape with “bulges” which can improve material utilization of the cables and membrane.3.The method based on NSGA-? genetic algorithm was proposed for the distribution of the reinforced cables and the optimal results are obtained by comparative study.In order to improve the bearing capacity of the airship and reduce the structure weight,the advanced NSGA-?genetic algorithm was applied to realize the optimization process by using ABAQUS software and Isight platform.With the help of ABAQUS subroutine functions,Python language program was used to establish the airship cable-membrane structure model and transfer data between ABAQUS and Isight.Compared with the results of DOE optimization method,the results of NSGA-? genetic algorithm were better by reducing more both the maximum stress and the average area density.4.For the pressure-bearing strength of the airship cable-membrane structure,one new simulation method was presented based on tensile experiments of membrane and welded structures.Firstly,according to uniaxial tensile test of membrane specimens and stress distribution of airship cable-membrane structure,a set of tensile tests of welded specimens were designed including the uniaxial tensile test,uniaxial cyclic test and biaxial tensile test.Besides,the influence of the welded structure on the tensile strength of membrane is studied and the strength reduction can be up to 20%.Then,the form-finding analysis was added before the nonlinear static analysis of the pressure-bearing strength because of the nonlinear deformation of the airship cable-membrane structure at the initial stage of inflation.