## 3 Results
### Pelvis and Lower Limbs  
Figure 10 showed the submarining results of three typical simulations during the impact in Simulation 1; the reclined passenger was restrained by a normal three-point seatbelt, and the lap belt was completely moved to the abdomen during the impact, as shown in Figure 10. Simulations 2-4 optimized the occupant restraint; however, submarining still occurred. In Simulations 5-20, the lap belt restrained well, and no submarining occurred.  
Figure 8: The maximum strain from T10 to L3 during impact: (**a–t**) represent the simulation results from 1 to 20.  
Figure 9: Spine morphology during the impact (**a**) with fixed seat (Simulation 7); and (**b**) with rotational seat (Simulation 18).  
A large pelvic constraint force causes pelvic injury, as assessed by the effective plastic strain of the cortical bone, as shown in Table 4. In the simulations with a swiveling seat, the maximum strain of the pelvis was less than the injury criterion of 2.57%, except for Simulation 13, in which the seat-pan spring might not have been able to absorb sufficient impact energy. When the occupant was on a fixed seat, the maximum strain of the pelvis ranged from 2.2 to 5.6, causing high injury risk. The risk of lower limb injury was also assessed. The maximum strain in the femur was less than the injury criterion of 2.14% in all simulations, indicating that the knee restraint did not cause additional damage to the lower limbs.  
Figure 11 shows the motion trajectories of the knees in the sagittal (x-z) plane for the 20 simulations. In Figure 11a, the knee excursions of occupants with a fixed seat were above the initial position of the knee during the impact. This makes the occupant's posture appear V-shaped, increasing the curvature of the spine and exacerbating the associated damage. Figure 11b depicts the knee trajectories of occupants with swiveling seats and three-point normal thoracic belts. In these simulations, the knee moved below its initial position in the z direction. When the retractors were integrated on the seatback (Simulations 12, 13 and 14), the maximum displacements of the knee in both the X and Z directions were approximately 100 mm larger than those with fixed retractors on the floor. Figure 11c shows the results of Simulations 15-20, in which the reclined occupants were placed on the swiveling seat and restrained with a four-point thorax belt. The maximum displacements in Simulations 17 and 20 were 300 mm.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Simulation No.** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** \\ \hline Pelvis Maximum Stain (\%) & 4.6 & 2.6 & 3.8 & 3.8 & 5.6 & 3.4 & 3 & 2.2 & 1.9 & 1.9 \\ Femur Maximum Stain (\%) & 0.38 & 0.35 & 0.54 & 0.59 & 1.3 & 1.2 & 1.1 & 0.5 & 0.4 & 0.4 \\ Knee Excursion (mm) & 273 & 252 & 260 & 251 & 154 & 116 & 95 & 113.2 & 162 & 185 \\ \hline
**Simulation No.** & **11** & **12** & **13** & **14** & **15** & **16** & **17** & **18** & **19** & **20** \\ \hline Pelvis Maximum Stain (\%) & 2 & 2.4 & 3 & 2.4 & 2.1 & 1.9 & 2.7 & 1.9 & 2 & 2.7 \\ Femur Maximum Stain (\%) & 0.4 & 0.8 & 0.7 & 0.7 & 0.5 & 0.5 & 0.8 & 0.5 & 0.6 \\ Knee Excursion (mm) & 185 & 265 & 278 & 272 & 182 & 180 & 300 & 245 & 270 & 313.1 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Pelvic injury summary.  
Figure 10: The position of pelvis and lap belt in (**a**) Simulation 1 at 120 ms; (**b**) Simulation 5 at 80 ms; and (**c**) Simulation 18 at 105 ms.