Application of solid-shell finite elements in fabric drape/cloth simulations

Abstract

The solid-shell elements which possess only translational but no rotational degrees of freedom have gained flourishing success in large deformation analyses in the last few decades. However, they have rarely been applied to fabric drape/cloth simulations. Probably the only attempt in the literature was employing solid-shell elements in static fabric drape analyses. Their results demonstrate the potential of solid-shell elements in static fabric drape analyses as well as the non-physical interpenetration of top and bottom element surfaces noticed in convergent solutions for fabrics with large free-hanging length. In this thesis, possible remedies are developed to resolve the interpenetration deficiency and then the elements are applied to both static and dynamic fabric drape/cloth simulations.

The linear and geometric nonlinear formulations of two-dimensional solid-shell elements are presented. The assumed natural strain methods(ANS)are employed to alleviate the transverse shear and trapezoidal lockings whilst the plane-stress enforcement is used to overcome thickness locking. Several remedies are attempted on avoiding interpenetration occurred in the nonlinear curved cantilever problem and the enhanced bending energy is most successful. The three-dimensional linear and geometric nonlinear triangular and quadrilateral solid-shell elements are evolved from the two-dimensional one. Due to the superior accuracy of the quadrilateral element over its triangular counterpart, the former is used to attempt the static fabric drape problems.

In dynamic fabric drape/cloth simulations, techniques including the explicit time integration, cloth-to-object collision handling, local adaptive mesh generation, lower human body modeling and virtual sewing forces are employed and synergized with both quadrilateral and triangular solid-shell element models. In particular, the reversible local adaptive mesh generator based on the 1-4 splitting method is developed for circumventing the interpenetration deficiency by locally reducing the mesh size at low computational cost. The hybrid macro-transition elements formed by the quadrilateral and triangular element models are employed to ensure the mesh conformity. Meanwhile, the discrete Kirchhoff constraints derived by using a co-rotated framework are proposed to obtain the kinematic variables of the new-inserted nodes so that the oscillation appeared after each local subdivision is attenuated. The predicted steady-state shapes of draped fabrics look realistic and similar to the convergent static solutions. Those of the sewing garments also conform to our daily perception. Dynamic processes for cloth simulations including the sewed garments dressed on human body model with movement also appear realistic.

This thesis focuses on avoiding the non-physical interpenetration of solid-shell elements and exploring the application of two solid-shell elements in dynamic fabric drape/cloth simulation which can shorten the fashion design cycle and enhance the visual reality of clothes on manikins in e-commerce of clothes and animated movies. Compared with the grid-based or particle-based computational method, the finite element method is less stringent in grid-point arrangement and more convenient in handling boundary, sewing and integration treatments. Compared with other shell elements, the solid-shell elements are more efficient in finite displacement analysis due to the absence of rotational freedoms.