Month: August 2018

Physical Simulation of Environmentally Induced Thin Shell Deformation

Hsiao-yu Chen, Arnav Sastry, Wim M. van Rees, Etienne Vouga

We present a physically accurate low-order elastic shell model that incorporates active material response to dynamically changing stimuli such as heat, moisture, and growth. Our continuous formulation of the geometrically non-linear elastic energy derives from the principles of differential geometry, and as such naturally incorporates shell thickness, non-zero rest curvature, and physical material properties. By modeling the environmental stimulus as local, dynamic changes in the rest metric of the material, we are able to solve for the corresponding shape changes by integrating the equations of motions given this non-Euclidean rest state. We present models for differential growth and shrinking due to moisture and temperature gradients along and across the surface, and incorporate anisotropic growth by defining an intrinsic machine direction within the material. Comparisons with experiments and volumetric finite elements show that our simulations achieve excellent qualitative and quantitative agreement. By combining the reduced-order shell theory with appropriate physical models, our approach accurately captures all the physical phenomena while avoiding expensive volumetric discretization of the shell volume.

Physical Simulation of Environmentally Induced Thin Shell Deformation

Mechanical Characterization of Structured Sheet Materials

Christian Schumacher, Steve Marschner, Markus Gross, Bernhard Thomaszewski

We propose a comprehensive approach to characterizing the mechanical properties of structured sheet materials, i.e., planar rod networks whose mechanics and aesthetics are inextricably linked. We establish a connection between the complex mesoscopic deformation behavior of such structures and their macroscopic elastic properties through numerical homogenization. Our approach leverages 3D Kirchhoff rod simulation in order to capture nonlinear effects for both in-plane and bending deformations. We apply our method to different families of structures based on isohedral tilings— a simple yet extensive and aesthetically interesting group of space-filling patterns. We show that these tilings admit a wide range of material properties, and our homogenization approach allows us to create concise and intuitive descriptions of a material’s direction-dependent macromechanical behavior that are easy to communicate even to non-experts. We perform this characterization for an extensive set of structures and organize these data in a material browser to enable efficient forward exploration of the aesthetic-mechanical space of structured sheet materials. We also propose an inverse design method to automatically find structure parameters that best approximate a user-specified target behavior.

Mechanical Characterization of Structured Sheet Materials

Methodology for Assessing Mesh-Based Contact Point Methods

Kenny Erleben

Computation of contact points is a critical sub-component of physics-based animation. The success and correctness of simulation results are very sensitive to the quality of the contact points. Hence, quality plays a critical role when comparing methods, and this is highly relevant for simulating objects with sharp edges. The importance of contact point quality is largely overlooked and lacks rigor and as such may become a bottleneck in moving the research field forward. We establish a taxonomy of contact point generation methods and lay down an analysis of what normal contact quality implies. The analysis enables us to establish a novel methodology for assessing and studying quality for mesh-based shapes. The core idea is based on a test suite of three complex cases and a small portfolio of simple cases. We apply our methodology to eight local contact point generation methods and conclude that the selected local methods are unable to provide correct information in all cases. The immediate benefit of the proposed methodology is a foundation for others to evaluate and select the best local method for their specific application. In the longer perspective, the presented work suggests future research focusing on semi-local methods.

Methodology for Assesing Mesh-Based Contact Point Methods

The Human Touch: Measuring Contact with Real Human Soft Tissues

D. K. Pai, A. Rothwell, P. Wyder-Hodge, A. Wick, Y. Fan, E. Larionov, D. Harrison, D. R. Neog, and C. Shing

Simulating how the human body deforms in contact with clothing, wearables, and other objects is of central importance to many fields. However, the tissue material properties needed to accurately simulate real human bodies had been sorely lacking. We showed that these mechanical properties can be directly measured using a novel hand-held device. We have developed a complete pipeline for measurement, modelling, parameter estimation, and simulation using the finite element method. Our unique data may be used to create personalized models of an individual human or of a population. Consequently, our methods may have many potential applications in apparel design, e-commerce, computer animation, and medicine.

The Human Touch: Measuring Contact with Real Human Soft Tissues