Optimization Design Of NURBS-based Variable Stiffness Composite Cylinder Shell

Fiber-reinforced composite materials have the advantages of high specific strength,high specific stiffness,low density,and good corrosion resistance,which are of great benefit to the lightweight design of structures and the improvement of structural performance.Therefore,they are widely used in aerospace,marine structure,civil engineering,etc.Compared with the traditional straight fiber layup composite materials,the curved fiber layup variable stiffness(VS)composite materials have a larger design space,so the study on its optimal design has important academic significance and practical application value.In this thesis,the finite element model of the variable angle fiber laminated composite cylinder is established using the finite element analysis software ANSYS.The optimization of VS structure is considered:(1)The NURBS curve and surface,which are used to fit the fiber angle changes on the VS composite cylindrical shell,then constructing the optimization model of the curved fiber path considering both annular and axial directions,and optimizing the design of VS laminate structure to maximize the buckling load;(2)The influence of multiple VS lamina on the buckling response of the structure is studied,and the optimal buckling response of the structure under strength constraint is considered.In addition,in order to improve the efficiency of VS structural optimization calculation,Kriging meta-model is used to fit the structural response,and a mixed updating method is adopted to improve the accuracy of the Kriging model and global optimization capability.Analysis and calculation results show that,for the case of pure bending moment,the optimization results of NURBS surface fitting the shell surface VS and NURBS curve fitting the circular VS are similar,but superior to constant stiffness(CS),23.9%improvement is accomplished.Under the condition that the structure bears concentrated force in the middle of the axial direction,compared with simple annular VS design,theperformance of the annular and axial directions VS design is improved by 4.71%.In addition,for symmetrical balanced structure,increasing the number of VS lamina can effectively improve the buckling bearing capacity of the structure,and the position of VS lamina in the laminate structure will also affect the bearing capacity of the structure.Through VS layup design,the composite materials make the distribution of stiffness and internal force of the structure more reasonable,with the peak value of internal force falling and the bearing capacity rising.