## 3 Simulation and Crashworthiness Testing  
### Simulation  
Firstly, a computer-aided design software (i.e., SolidWorks) was used to establish the overall three-dimensional model of the seat. Secondly, the models of the seat and the Hybrid III 50 th percentile male dummy were imported into HyperMesh, which is a finite element pre-processing software used to complete the finite element modelling and settings of simulation parameters. Thirdly the output file was imported into the LS-DYNA for solving. Fourthly, calculation results such as structural deformation, stress nephgram and other data can be viewed using LS-Prepost.  
It is necessary to simplify the seat structure appropriately and establish a reasonable and effective structural finite element model. This provides simulation results which are close to the real test results while saving on computation time. The simplifications are as follows.  
1. The main force-bearing structures must be retained and the headrest, the seat cushion, the rotating device, etc., will be simplified.
2. Welded, riveted and bolted connections between components of the seat are simulated by using the rod elements connection method, the common element method and the common node method, respectively [35]. In the rod elements connection method, two parts are connected at the corresponding nodes by a mass-free rigid rod. In the common element method, two parts are connected by creating a common element. In the common node method, the element nodes of two parts are directly connected at the junction.
3. Chamfers and small holes will be ignored when their radiuses are smaller than the estimated size of the minimum element.  
In the process of finite element modelling of the seat, the solid element is used to simulate the frame structures, the cushions, the rails and so on. The shell element is used to simulate the thin-walled structures such as tubes and boards. The solid element corresponds to the single point integral method and the shell element corresponds to the Gaussian integral method.  
The key energy-absorbing structure and other major structures are made of 7075 aluminum alloy. The material of the seat cushion is low density polyurethane foam. The guide rails are considered to be rigid bodies with a high density to eliminate the effects of inertia of the ATD and the seat on the simulation results. Their parameters are shown in Table 1.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **7075 Aluminium Alloy** & **Low Density Polyurethane Foam** & **Rigid Body** \\ \hline Density/(kg/m\({}^{3}\)) & 2810 & 51.5 & 281,000 \\ Young’s modulus (GPa) & 71.7 & / & 210 \\ Poisson’s ratio & 0.33 & / & 0.28 \\ Yield stress (GPa) & 0.45 & / & / \\ Tangent modulus (GPa) & 0.65 & / & / \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters of the material.  
The following initial conditions were applied to the human-seat coupling system. The guide rail rotates around local axes to simulate the deformation of the floor. The front section of left floor is raised by 10\({}^{\circ}\). The right floor finishes the clockwise rotation and the angle is also 10\({}^{\circ}\). The acceleration-time curve is shown in Figure 5. The area enclosed by the horizontal and vertical axes is an isosceles triangle. G = 30 g. \(t_{1}=0.031\) s. The collision process lasts one second (1 s).