## 2 Topology Optimization Method Based on Abaqus and TOSCA  
Several commercial solvers, including TOSCA, OptiStruct, and PERMAS, are available on the market. Table 1 compares the characteristics and performance of these three solvers.  
TOSCA, developed by Dassault Systemes in France, represents an optimization tool widely utilized across diverse fields, including automotive, aerospace, and machinery manufacturing. Specifically, the TOSCA Structure module, grounded in finite element analysis theory, excels at performing efficient topology optimization of structures [16] (pp. 27-31). Owing to its exceptional performance, TOSCA has been integrated as a topology optimization module within Abaqus/CAE, enabling direct access via the Abaqus graphical user interface. This integration facilitates a closed-loop design process, seamlessly integrating structural finite element simulation and topology optimization.  
The topology optimization module in Abaqus/CAE provides two types of optimal solution algorithms for selection: condition-based algorithms and sensitivity-based algorithms. The former is typically suited for geometric and contact non-linear problems that are difficult to analyze using sensitivity-based approaches. However, its application is limited by the design response setting. On the other hand, the sensitivity-based algorithm enables the specification of design responses such as structural stiffness, displacement, stress, eigenfrequency, and quality (or volume). This algorithm is adept at addressing a wide range of optimization problems [17]. Considering the design requirements for optimizing the static and dynamic performance of the structure, this study employs a sensitivity-based algorithm for structural topology optimization.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Feature/Capability** & **TOSCA** & **OptiStruct** & **PERMAS** \\ \hline \multirow{2}{*}{Integration and usability} & Integrates with multiple FEA & Integration with & Integration with VisPER and \\  & solvers/Medium & HyperWorks/Easy & ANSA/Hard \\ \hline \multirow{3}{*}{Optimization capabilities} & Exels in topology & Highly regarded for & High efficiency and capability \\  & optimization and shape & multi-disciplinary & in handling large-scale \\  & optimization & optimization capabilities & problems \\ \hline \multirow{3}{*}{Computational efficiency} & Depends on the underlying & High computational efficiency & High performance \\  & FEA solver & & and efficiency \\ \hline \multirow{3}{*}{Industry applications} & Widely used in automotive & Used across automotive, & Predominantly used in \\  & and aerospace for optimizing & aerospace, heavy machinery, & aerospace and \\ \cline{1-1}  & structural components & and consumer goods & automotive sectors \\ \hline \hline \end{tabular} Note: In conclusion, while OptiStruct and PERMAS offer broad optimization capabilities and high computational efficiency, TOSCA distinguishes itself through its flexibility, specialized in topology and shape optimization, and seamless integration with various FEA solvers.  
\end{table}
Table 1: Comparison of TOSCA, OptiStruct, and PERMAS solvers.  
In this paper, we perform topology optimization design of the U-frame for spaceborne optoelectronic tracking and pointing turntables by integrating ABAQUS finite element analysis and TOSCA structural optimization modules. The process initiates with the import of the initial model into Abaqus/CAE and the execution of preprocessing tasks. This entails dividing the optimal design area and non-design area, setting material parameters, establishing static and modal analysis steps, defining load cases and boundary conditions, and executing mesh division. Subsequently, we create a topology optimization task that includes settings for design responses, objective functions, constraints, and geometric constraints. Finally, the job is submitted to acquire the optimization results, thus concluding the entire structural optimization process. The primary process is illustrated in Figure 4.