Non-smooth developable geometry for interactively animating paper crumpling

International audienceWe present the first method to animate sheets of paper at interactive rates, while automatically generating a plausible set of sharp features when the sheet is crumpled. The key idea is to interleave standard physically-based simulation steps with procedural generation of a piecewise continuous developable surface. The resulting hybrid surface model captures new singular points dynamically appearing during the crumpling process, mimicking the effect of paper fiber fracture. Although the model evolves over time to take these irreversible damages into account, the mesh used for simulation is kept coarse throughout the animation, leading to efficient computations. Meanwhile, the geometric layer ensures that the surface stays almost isometric to its original 2D pattern. We validate our model through measurements and visual comparison with real paper manipulation, and show results on a variety of crumpled paper configurations

Developable Surfaces from Arbitrary Sketched Boundaries

International audienceDevelopable surfaces are surfaces that can be unfolded into the plane with no distortion. Although ubiquitous in our everyday surroundings, modeling them using existing tools requires significant geometric expertise and time. Our paper simplifies the modeling process by introducing an intuitive sketch-based approach for modeling developables. We develop an algorithm that given an arbitrary, user specified 3D polyline boundary, constructed using a sketching interface, generates a smooth discrete developable surface that interpolates this boundary. Our method utilizes the connection between developable surfaces and the convex hulls of their boundaries. The method explores the space of possible interpolating surfaces searching for a developable surface with desirable shape characteristics such as fairness and predictability. The algorithm is not restricted to any particular subset of developable surfaces. We demonstrate the effectiveness of our method through a series of examples, from architectural design to garments

Discrete Differential Geometry of Thin Materials for Computational Mechanics

Instead of applying numerical methods directly to governing equations, another approach to computation is to discretize the geometric structure specific to the problem first, and then compute with the discrete geometry. This structure-respecting discrete-differential-geometric (DDG) approach often leads to new algorithms that more accurately track the physically behavior of the system with less computational effort. Thin objects, such as pieces of cloth, paper, sheet metal, freeform masonry, and steel-glass structures are particularly rich in geometric structure and so are well-suited for DDG. I show how understanding the geometry of time integration and contact leads to new algorithms, with strong correctness guarantees, for simulating thin elastic objects in contact; how the performance of these algorithms can be dramatically improved without harming the geometric structure, and thus the guarantees, of the original formulation; how the geometry of static equilibrium can be used to efficiently solve design problems related to masonry or glass buildings; and how discrete developable surfaces can be used to model thin sheets undergoing isometric deformation

A yarn interaction model for circular braiding

Machine control data for the automation of the circular braiding process has been generated using previously published mathematical models that neglect yarn interaction. This resulted in a significant deviation from the required braid angle at mandrel cross-sectional changes, likely caused by an incorrect convergence zone length, in turn caused by this neglect. Therefore the objective is to use a new model that includes the yarn interaction, assuming an axisymmetrical biaxial process with a cylindrical mandrel and Coulomb friction. Experimental validation with carbon yarns and a 144 carrier machine confirms a convergence zone length decrease of 25% with respect to a model without yarn interaction for the case analyzed, matching the model prediction using a coefficient of friction of around 0.3

Multi-Panel Unfolding with Physical Mesh Data Structures

In this thesis, I demonstrate that existing mesh data structures in computer graphics can be used to categorize and construct physical polygonal models. In this work, I present several methods based on mesh data structures for transforming 3D polygonal meshes into developable multi-panels that can be used in physical construction. Using mesh data structures, I developed a system which provides a variety of construction methods. In order to demonstrate that mesh data structures can be used to categorize and construct physical polygonal models, this system visualizes the mathematical theory and generates developable multi-panels that can be printed and assembled to shapes similar to original virtual shapes. The mesh data structures include ones that are orientable: Quad-Edge, Half-Edge, Winged-Edge; and also one that is non-orientable: Extended GRS. The advantages of using mesh data structures as guides for physical construction include: There is no restriction on input design model as long as it is manifold, it can be of any genus with n-sided polygon faces; Different mesh data structures provide more options to better fit the input design while taking the physical constraints and material properties in consideration; Developable panels are easy to obtain from thin planar materials using a laser-cutter; When we use mesh data structures, it is also intuitive to assemble such planar panels using mesh information. Laser-cut developable panels based on mesh data structures provide, therefore, a cost-efficient alternative to 3D printing when dealing with large structures

Lagrangian-on-Lagrangian Garment Design

Since the discovery of elastomeric materials, such as spandex or lycra, skintight clothing has revolutionized many different areas of the clothing industry, such as body-shaping clothing, athletic wear, and medical garments, among others. Often, this kind of clothing is designed to fulfill a given purpose, such as providing comfort, mobility, or improving recovery in the case of an athlete, provide support or exert some desired pressure in the case of medical garments, or actively deform the body to acquire some desired shape. Additionally, some designs aim to improve the life of the garment by, for example, minimizing tractions across the seams. While many tight-skin garments are sold in the market for generic body shapes, many of the purposes here mentioned are only achievable through a personalized fitting. To this end, we introduce a novel model, where the cloth is modeled as a membrane, parameterized as a function of the body. The cloth, is then able to slide on the body and deform it while staying always in contact. We call this model Lagrangian-on-Lagrangian. Based on this model, we develop an optimization framework, based on sensitivity analysis, capable of developing sewable patterns such that, when worn by a person, satisfy a given design target. With the framework, we include several design targets such as, body shape, stretch, pressure, sliding under motion, and seam traction. We evaluate our method on a variety of applications, as well as body shapes