Repositioning Methodology For FE-HBM Pelvis Flesh To Account For Upper Extremity Posture Change

Many research groups are developing Human Body FE Models (FE-HBM) as a tool to be used in safety research. The FE-HBM's currently available are in certain fixed postures. Repositioning of model in alternate postures is needed for use in out of position (OOP) occupant simulations and different pedestrian posture simulations. Postural change in upper extremity can be split two processes, viz, repositioning of spinal vertebra and repositioning of the soft tissue associated with the spine. The objective of this study is to establish a methodology to regenerate pelvis flesh with change in spine/pelvis position. The outer profile of the pelvis flesh should ideally be parametrically described with respect to the associated hard tissues which is not the case in existing FE-HBM's. The affine invariant (Farin, 1990) property of cubic Bezier curves is used in this study. It is hence implied that applying affine mapping to either the control points or to the points on the curve itself yields the same result. Initially, for each pelvis flesh contour, four points are identified (end points and two other points of significant curvature) to define a cubic Bezier curve and identify the associated control points. The upper extremity posture changes are described with respect to hip, pelvis, and thorax angles. The end points defining the contour of the pelvis flesh are relocated by affine transformations. The new shape of the pelvis flesh contour is then obtained using the control points located earlier. Mesh morphing using Barycentric coordinates is proposed to be used for repositioning of the interior pelvis flesh. The paper presents a new method which employs inverse parameterization of Bezier curve to re-compute the shape of the pelvis flesh. These computer graphics techniques used are time efficient and do not involve active user intervention. Further, the element quality and time steps are not significantly affected, thus preserving computational efficiency of the FE model. The method has been demonstrated through repositioning of the pelvis flesh with change in posture of lower spine segment in this paper. It will be extended to repositioning the upper spine segment of FE-HBM with change in spinal/pelvic posture.