4.7 Article

Machine-specified ground structures for topology optimization of binary trusses using graph embedding policy network

Journal

ADVANCES IN ENGINEERING SOFTWARE
Volume 159, Issue -, Pages -

Publisher

ELSEVIER SCI LTD
DOI: 10.1016/j.advengsoft.2021.103032

Keywords

Topology optimization; Reinforcement learning; Graph embedding; Binary trusses; Machine-specified ground structures

Funding

  1. China Scholarship Council (CSC) [201906260152]
  2. JSPS KAKENHI [JP20H04467]

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This paper introduces the concept of machine-specified ground structures for topology optimization, which can generate sparse stable structures without the need for re-training for different-sized node-sets, effectively assisting structural topology design. In topology optimization problems, machine-specified ground structures have an advantage in achieving global optimal solutions.
This paper proposes the concept of machine-specified ground structures for topology optimization of trusses. Unlike general ground structures with dense and regular connectivity, machine-specified ground structures are sparse stable ground structures with a specified number of members designed by machines. Firstly, the generation process of machine-specified ground structures from a given node-set is formulated as a reinforcement learning task. Graph embedding is used to integrate the structural information into a comprehensive feature matrix to describe the state. By establishing the policy network, the probability of each action, i.e., selecting each node in the node-set, is obtained based on the comprehensive feature matrix. The task is solved using a gradient based algorithm called REINFORCE. A randomized 4 x 4 node-set is used to train the agent. The policy converges with a high average reward, and generates different yet reasonable structures because a stochastic policy is employed. Besides, the agent can handle different-sized node-sets without re-training. Hence, the machine specified ground structures generated by the trained agent can be utilized to assist the structural topology design. Subsequently, a method for a typical problem with singular optimal solutions, i.e., topology optimization of binary trusses with stress and displacement constraints, is proposed based on machine-specified ground structures. Finally, through different-sized numerical examples, it is demonstrated that the machine-specified ground structures lead to a variety of optimal solutions, and it is more likely to obtain the global optimum than fully-connected ground structures. It is worth noting that machine-specified ground structures can also be applied to other problems without re-training.

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