Abstract:The supporting bracket for the inertial platform is the key component in launch vehicles. The bracket is supporting the inertial platform during the flight condition of launch vehicles. Thus the axial load is more important than the radial load, which still needs to be considered. Lightweight design is of great significance for such a supporting bracket. In this study, the weight of the initial design of the supporting bracket is 13.8kg, however, the allowed weight is only limited to 8.0kg. Since the material is restricted to be the aluminum alloy, the problem is to seek the optimized topology design with a weight constraint of 8.0kg. Obtaining the loading path and removing the inefficient material in the supporting bracket can be solved by the topology optimization. The weighted multi-load cases topology optimization is utilized due to the different load conditions. The rectangle space and the circle space which are two different kinds of initial design space are given and the topology optimized reults are similar in the software of OptiStruct, where the topology optimization algorithm is the SIMP (Solid Isotropic Material with Penalization) method. Considering these two topology optimum results, the new model of the supporting bracket is designed. The simulation analysis comparisons of the two models (before and after optimization) including the static, modal analysis (including constrained and free), frequency response analysis and random analysis are carried out. The weight of the final optimum model is reduced to about 8.0kg for the new design. Even through the maximum Von Mises stress in the optimum model in one load case is larger than that of the initial model, but the value of the maximum is much smaller than the yield strength of the material aluminum alloy. But for the other load cases, the maximum Von Mises stress is much lower than that of the initial model, and the stress distribution of the supporting bracket is more uniformly due to the improved material utilization by the structural optimization.

Introduction

The  inertial  platform  provides  the  positions  and  attitudes  of  launch  vehicles  in  the  flight  which  is  the  key component  of  the  inertial  navigation.  The  supporting  bracket  supporting  inertial  platform  in  the  launch  vehicles provides the great environment for the inertial platform which means the enough stiffness, enough strengthen and enough stability.

In the aerospace field, the weight is much valuable. Less weight means more benefit. On the contrary, more weight as well as the more material brings the higher mechanical performance for the product. It seems a contradiction for obtaining the less material and the higher mechanical performance.

In  this  paper,  the  allowed  weight  of  the  supporting  bracket  is  limited  to  8.0kg,  while  the  initial  weight  of  the supporting bracket is 13.8kg. The material is restricted to be the aluminum alloy. We have to reduce the weight on the condition with the stratification of the mechanical performance of the supporting bracket. The basic idea is to increase the utility of the material, remove the useless material. Thus the problem is to seek the optimized topology design with a weight constraint of 8.0kg. Obtaining the loading path and removing the inefficient material in the supporting bracket can be solved by the topology optimization.

In applications regarding component design of aerospace and aeronautical structures, topology optimization has been employed for improving the structural and multi-disciplinary behaviors, such as overall stiffness, aerodynamic performance and fundamental frequencies under specified structural weight constraint. Krog and Tuck applied the topology optimization techniques to the optimal design of aircraft wing-box ribs. Chen et al. obtained the minimized  weight  on  the  constraint  of  the  modal  frequencies  in  structural  design  of  the  spacecraft  based  on NASTRAN. Maute and Allen presented a material density-based approach for the optimal placement of stiffeners in a flexible wing subject to aerodynamic forces. The material distribution formulation has also been used by Maute and Reich in the optimal design of actuator locations and the inner structures of adaptive wings. Afonso et al.  combined the topology optimization and the shape optimization for the design of stiffened shell structures, which have been widely used in the aerospace industry. Yin et al. [6] reduced the heat shield weight by 8.0% with the sequential quadratic programming (SQP) algorithm on the consideration of the first order frequency as the constraint. Kang et al. achieved the topology optimization results of the space vehicle structures considering attitude control effort. Chen et al. applied topology optimization techniques in the layout design of stiffeners in a storage tank of a space craft for minimum weight under stiffness and strength constraints.

In this paper, the weighted multi-load cases topology optimization is applied due to the different load conditions. The weight of the final optimum model is reduced to about 8.0kg. The simulation analysis comparisons of the two models (before and after optimization) including the static analysis, modal analysis (including constrained and free conditions),  frequency  response  analysis  and  random  analysis  are  carried  out.  Even  through  the  maximum  Von Mises stress in the optimum model in one load case is larger than that of the initial model, but the value of the maximum is much smaller than the yield strength of the material aluminum alloy. But for the other load cases, the maximum Von Mises stress is much lower than that of the initial model, and the stress distribution of the supporting bracket is more uniformly due to the improved material utilization by the structural optimization.

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