# Triangular Position Multi-Bolt Layout Structure Optimization
###### Abstract
In order to simulate the bolted structure more accurately, more and more scholars apply artificial intelligence to the simulation. [PERSON] et al. [8] improved the genetic algorithm, applied the improved objective function to the connection structure, took the average acceleration at the corner of the component as the objective function of the algorithm, adopted the idea of parametric modeling, realized the interaction between MATLAB and NASTRAN, and reduced the stress value at the corner of the component. The layout of the bolt on the edge of the component is optimized and the safety of the component is improved. [PERSON] et al. [9] used the gray wolf algorithm to optimize the motion trajectory of each joint of the robotic arm, which takes time efficiency and smoothness as the objective function, and the results show that the gray wolf algorithm can effectively perform trajectory optimization. [PERSON] et al. [10] improved the thresholds and weights of an Elman neural network by particle swarm algorithm and applied the method to clock difference forecasting, which can improve the stability and forecasting accuracy of a satellite clock. [PERSON] et al. [11] carried out layout optimization experiments on bolt sets based on the firefly algorithm, and carried out simulation analysis on double-row bolts and three-row bolts, and the optimized bolt layout reduced the perimeter stress of the holes and improved the safety of the structure. However, the optimization of multi-bolt joint structures in the existing literature is limited to symmetric bolt structures [12; 13; 14; 15; 16], while there are few studies on asymmetric bolt structures, especially the optimization of a multi-bolt layout in a triangular position. In addition, researchers rarely apply the gray wolf optimization algorithm to the layout optimization of the connection structure of large complex equipment. Therefore, based on the gray wolf algorithm, this paper optimizes the bolt group of the triangular multi-bolt layout structure, seeks the optimal bolt margin and spacing, and reduces the surface stress of the connection structure and maximum stress on the surface of the bolt group; to prevent excessive stress around the bolt hole, resulting in fatigue damage of the bolt hole or plastic deformation of the connector, thus affecting the stability and reliability of the connection. Nickel steel has the advantages of strong compressive resistance, corrosion resistance, low temperature toughness and so on, and is widely used in aerospace and other large complex important equipment, and there is little research on nickel steel. Therefore, the connection structure of this paper chooses nickel steel. Based on the above background, this paper analyzes the hole surrounding stress, maximum shear stress of the bolt and bending stress of the nickel steel plate; and adopts the gray wolf algorithm to optimize the bolt spacing and bolt diameter, which can accurately find the optimal bolt spacing and bolt radius. The results of the fruit fly optimization algorithm [17], particle swarm optimization algorithm [18], gray wolf optimization algorithm [19], multiverse optimization algorithm [20] and wind driven optimization algorithm [21] for triangular multi-bolt layout structure optimization were compared, and the accuracy of the gray wolf optimization algorithm was verified. The optimized bolts still met the requirements of the design specification, and the efficiency of the joint design is improved. ABAQUS-2022 software was used to establish the finite element model of the optimal solution, and the stress conditions of the nickel steel plate and bolts before and after optimization were compared to verify the correctness of the algorithm, objective function and constraint conditions.