Study On Influence Of Postures And Body Shape On Pedestrian Kinematics And Injuries In Accidents

In past decades,fatalities in pedestrian traffic accidents had become a global social and economic problem.Current researches concerning pedestrian safety protection have to some extent reduced fatalities and mitigated injury severity in pedestrian accidents.However,on one hand,population variability in body dimension cannot be neglected in evaluation of impact response;on the other hand,accident data shows that pedestrian exhibit various prior-to-impact postures.Such issues have restrict current vehicle from effectively protecting pedestrian in real-world accident.This study first developed a platform to generate finite element human body model(FE-HBM)with different anthropometry and postures.And based on the developed approach,mechanism of how postures and body shape influencing pedestrian response during impact was investigated.This study provides insights into response and injury mechanism of pedestrian lower extremity and guidance on countermeasure design in future.Conventional method to reposition a FE HBM was by pre-simulation,which is timeconsuming and presents lower bio-fidelity.This study has developed an algorithm to rapidly reposition lower extremity of a FE HBM,concerning anatomical features and kinematical constraints of human body.The repositioning algorithm includes prediction and realization of hip,knee and ankle joint motion in human body model.Hip and ankle joints were treated as spherical hinges.Flexion of knee joint was predicted based on characteristics of reconstructed local surface.Tibial internal rotation was realized approximately by referring to experimental data of medical researches.Nodal coordinates of transitional parts were calculated by mesh morphing method.Comparing to currently used pre-simulation method in posture adjustment of FE HBM,the algorithm is both time efficient and anatomically accurate.In the development of parametric model,geometry of external body shape,ribcage,pelvis,femur and tibia with target anthropometries were predicted by previously developed statistical model.Co-registration was conducted to integrated different body parts as a whole entity.Radial basis function based mesh morphing was used to morph the baseline GHBMC model into the target geometry.Comparing to traditional way to build a FE HBM from medical images,parametric modeling is time efficient and capable to predict body geometry in a wide range.The current study has developed parametric finite element(FE)pedestrian HBMs based on 50 th percentile GHBMC pedestrian model with mesh morphing method.And referring to studies from gait analysis,rapid algorithm to reposition lower extremities of pedestrian model has been developed.Combining the two methods,pedestrian models with arbitrary body dimensions and postures could be generated.By appling generated models with different body dimensions and postures,the current study investigated influence initial postures on pedestrian kinematics and injury response when impacted by vehicle front end.It was shown that irregular shape of femur condylar surfaces led to deviation of response for postures with different knee flexion angle.The study took obesity as an example to look into how body shape affects pedestrian impact response.It was revealed that increased injury risk for lower extremities of obese pedestrian was attributed to inertial effect induced by increased mass.The results pointed out that current experiment setup cannot cover all potential situations with high injury risks that may happen in real-world accident.And the study provided guidance to future countermeasure design by implying that inducing knee natural bending during impact could reduce injury risk for lower extremity during impact.