Accurate modeling of bending behavior is one of the most important tasks in the field of cloth simulation. Bending stiffness is probably the most significant material parameter describing a given textile. Much work has been done in recent years to allow a fast and authentic reproduction of the effect of bending in cloth simulation systems. However, these approaches usually treat the textiles as consisting of a single, homogeneous material. The effects of seams, interlining and multilayer materials have not been considered so far. Recent work showed that the bending stiffness of a textile is greatly influenced by the presence of seams and that a good cloth simulation system needs to consider these effects.
In this work we show how accurate modeling of bending and seams can be achieved in a state-of-the-art cloth simulation system. Our system can make use of measured bending stiffness data, but also allows intuitive user control, if desired. We verify our approach using virtual draping tests and garments in the simulation and comparing the results to their real-world counterparts. Furthermore, we provide heuristics derived from measurements that can be used to approximate the influence of several common types of seams.
Category: Shells
Animating developable surfaces using nonconforming elements
We present a new discretization for the physics-based animation of developable surfaces. Constrained to not deform at all in-plane but free to bend out-of-plane, these are an excellent approximation for many materials, including most cloth, paper, and stiffer materials. Unfortunately the conforming (geometrically continuous) discretizations used in graphics break down in this limit. Our nonconforming approach solves this problem, allowing us to simulate surfaces with zero in-plane deformation as a hard constraint. However, it produces discontinuous meshes, so we further couple this with a “ghost” conforming mesh for collision processing and rendering. We also propose a new second order accurate constrained mechanics time integration method that greatly reduces the numerical damping present in the usual first order methods used in graphics, for virtually no extra cost and sometimes significant speed-up.
Real-Time Simulation of Thin Shells
This paper proposes a real-time simulation technique for thin shells undergoing large deformation. Shells are thin objects such as leaves and papers that can be abstracted as 2D structures. Development of a satisfactory physical model that runs in real-time but produces visually convincing animation of thin shells has been remaining a challenge in computer graphics. Rather than resorting to shell theory which involves the most complex formulations in continuum mechanics, we adopt the energy functions from the discrete shells proposed by Grinspun et al. [GHDS03]. For real-time integration of the governing equation, we develop a modal warping technique for shells. This new simulation framework results from making extensions to the original modal warping technique [CK05] which was developed for the simulation of 3D solids. We report experimental results, which show that the proposed method runs in real-time even for large meshes, and that it can simulate large bending and/or twisting deformations with acceptable realism.
Cubic Shells
Hinge-based bending models are widely used in the physically-based animation of cloth, thin plates and shells. We propose a hinge-based model that is simpler to implement, more efficient to compute, and offers a greater number of effective material parameters than existing models. Our formulation builds on two mathematical observations: (a) the bending energy of curved flexible surfaces can be expressed as a cubic polynomial if the surface does not stretch; (b) a general class of anisotropic materials—those that are orthotropic—is captured by appropriate choice of a single stiffness per hinge. Our contribution impacts a general range of surface animation applications, from isotropic cloth and thin plates to orthotropic fracturing thin shells.
TRACKS: Toward Directable Thin Shells
“We combine the often opposing forces of artistic freedom and mathematical determinism to enrich a given animation or simulation of a surface with physically based detail. We present a process called tracking, which takes as input a rough animation or simulation and enhances it with physically simulated detail. Building on the foundation of constrained Lagrangian mechanics, we propose weak-form constraints for tracking the input motion. This method allows the artist to choose where to add details such as characteristic wrinkles and folds of various thin shell materials and dynamical effects of physical forces. We demonstrate multiple applications ranging from enhancing an artist’s animated character to guiding a simulated inanimate object.”