Optimum Design Of Curvilinearly Integral Stiffened Panels With Multiple Cutouts Based On NURBS

Because of high specific strength and stiffness,stiffened structures are currently widely used in the aerospace industry.For a variety of reasons,cutouts are usually inevitable,which may cause structural discontinuities.During the flight,the discontinuities decrease the loadcarrying capacity and stability.Therefore,the cutout reinforcement of the thin-walled structures is crucial.Compared with straight stiffeners,curvilinear stiffeners have greater potential and better effect on cutout reinforcement.The contents of this paper are: to establish a deterministic optimization design framework and reliability-based design optimization framework for multicutout curvilinearly stiffened panels.And the advantage of curvilinear stiffeners' reinforcement effect to the straight stiffeners' will be proved.The work is explained as follows:(1)The deterministic optimization design framework of curvilinearly stiffened panels is established.Using a typical aerospace stiffened panel example,under the same working conditions,the optimum design of straight stiffened panel and curvilinearly stiffened panel is carried out.It is found that straight stiffeners will reduce the design space.And stiffeners in curvilinearly stiffened panel have a larger weight ratio and a better cutout reinforcement effect.At the same time,the tension field formed by curvilinear stiffeners is more favorable for diffusion of load along stiffeners.Curvilinear stiffeners also can adaptively improve force transmission path according to the relative position and shape of cutouts.(2)Furthermore,a double-layer optimization design of curvilinearly stiffened panel with multiple variables and a optimization design of stiffened shell with multiple cutouts are carried out..The first design considers the reinforcement ring near the cutout,the unequal thickness of skin and stiffeners.The second design is a quarter cylindrical shell and only analyzes the unilateral effects of stiffeners layout.At the same time,imperfection sensitivity analysis is performed on the optimum stiffened panels.It is found that curvilinearly stiffened panel is more sensitive to imperfection due to its unique stiffener layout,but it still has great advantage.(3)The reliability-based design optimization framework of curvilinearly stiffened panels is established.The optimization consists of three steps.Firstly,deterministic optimization design is carried out based on the global optimization of all design variables.Then,the stiffeners layout is fixed and the reliability-based design optimization based on surrogate model of other design variables is carried out.Finally,the local deterministic optimization design of stiffeners layout is carried out.The optimum design of curvilinearly stiffened panel is given based on optimization framework.In this paper,a deterministic optimization design framework and a reliability-based design optimization framework for multi-cutout curvilinearly stiffened panels are established.At the same time,imperfection sensitivity analysis is performed.And the internal mechanism of curvilinear stiffeners' advantage is explored.It has certain reference value for the optimization design of curvilinearly stiffened panels.