Design Optimization Of Thin-walled Stiffened Structure For Dynamic Performance

Due to the advantages of high structural efficiency and superior dynamic and staticperformance,stiffened plate and shells are widely used in various types of mechanical equipment structures.In order to meet the increasingly dynamic requirements of equipment,a stiffened plate and shell structure with lower weight and higher performance can be designed by adjusting the distribution of stiffeners.However,the direct dynamic design has the problems of large computational cost and low efficiency.It needs a simplified approach to solve the transient dynamic optimization problem.The equivalent static load method can transform the direct transient optimization problem into a multi-case static load optimization problem.Such a transformation can greatly improve the design efficiency.The present thesis mainly carried out the dynamic design optimization of the stiffened plate and shell structures,and considered the improvement strategy of the stiffener layout and the efficiency problem of dynamic design optimization.At the same time,multiple levels of stiffeners distributed in different forms are considered as a view to expand the design space.Finally,in order to further reduce the vibration response of the stiffened plate and shell structure,a damping layer such as rubber is arranged on the basis of the stiffened plate to realize the collaborative optimization of the damping layer and the stiffened layer.The main work of the present thesis includes the following points:1.The ground structure method is used to establish the design model of the stiffened plate and shell structure,and the stiffener density in the ground structure is used as the design variable to realize the single-level and double-level design of the stiffeners.The single-level stiffener design optimization contains only one type of stiffener.In order to expand the design space,two types of stiffener configurations are introduced into the multi-level stiffener optimization model.2.For the stiffened plate and shell structures,the dynamic governing equation is solved by the Newmark method to conduct the transient dynamic analysis and sensitivity analysis.Furthermore,the direct transient dynamic design of the stiffened plate and shell structure is conducted.At the same time,due to the low efficiency of the general transient optimization,the equivalent static loads method is selected to transform the direct transient optimization problem into a multi-case static load optimization problem to achieve equivalent staticstructural optimization for the cases of transient loads.The present thesis also discusses the effect of choosing different key time points in the equivalent static loads optimization,i.e.selecting all time points and a small number of time points.3.The stiffener and damping optimization model is established based on the ground structure method.The Solid Isotropic Material with Penalization(SIMP)method is used to establish the damping material penalization model.Two independent design variables,namely stiffened rib density and damping element density,are introduced in the topology optimization.Taking the dynamic compliance of the structure as the objective and the allowable amount of stiffeners and damping materials as constraints,a collaborative optimization model of the layout of stiffened stiffeners and the topology of damping layers was established.Finally,numerical examples give the topological optimization results of the stiffeners and damping layer of the stiffened plate with different damping and different frequencies.The interaction between the stiffener optimization and the damping optimization is discussed.