Interactive procedural simulation of paper tearing with sound

International audienceWe present a phenomenological model for the real-time simulation of paper tearing and sound. The model uses as input rotations of the hand along with the index and thumb of left and right hands to drive the position and orientation of two regions of a sheet of paper. The motion of the hands produces a cone shaped deformation of the paper and guides the formation and growth of the tear. We create a model for the direction of the tear based on empirical observation, and add detail to the tear with a directed noise model. Furthermore, we present a procedural sound synthesis method to produce tearing sounds during interaction. We show a variety of paper tearing examples and discuss applications and limitations

ACM Transactions on Graphics

We present a boundary element based method for fast simulation of brittle fracture. By introducing simplifying assumptions that allow us to quickly estimate stress intensities and opening displacements during crack propagation, we build a fracture algorithm where the cost of each time step scales linearly with the length of the crackfront. The transition from a full boundary element method to our faster variant is possible at the beginning of any time step. This allows us to build a hybrid method, which uses the expensive but more accurate BEM while the number of degrees of freedom is low, and uses the fast method once that number exceeds a given threshold as the crack geometry becomes more complicated. Furthermore, we integrate this fracture simulation with a standard rigid-body solver. Our rigid-body coupling solves a Neumann boundary value problem by carefully separating translational, rotational and deformational components of the collision forces and then applying a Tikhonov regularizer to the resulting linear system. We show that our method produces physically reasonable results in standard test cases and is capable of dealing with complex scenes faster than previous finite- or boundary element approaches

Real-time sound synthesis for paper material based on geometric analysis

International audienceIn this article, we present the first method to generate plausible sounds while animating crumpling virtual paper in real time. Our method handles shape-dependent friction and crumpling sounds which typically occur when manipulating or creasing paper by hand. Based on a run-time geometric analysis of the deforming surface, we identify resonating regions characterizing the sound being produced. Coupled to a fast analysis of the surrounding elements, the sound can be efficiently spatialized to take into account nearby wall or table reflectors. Finally, the sound is synthesized in real time using a pre-recorded database of frequency- and time-domain sound sources. Our synthesized sounds are evaluated by comparing them to recordings for a specific set of paper deformations

Real-time sound synthesis for paper material based on geometric analysis

International audienceIn this article, we present the first method to generate plausible sounds while animating crumpling virtual paper in real time. Our method handles shape-dependent friction and crumpling sounds which typically occur when manipulating or creasing paper by hand. Based on a run-time geometric analysis of the deforming surface, we identify resonating regions characterizing the sound being produced. Coupled to a fast analysis of the surrounding elements, the sound can be efficiently spatialized to take into account nearby wall or table reflectors. Finally, the sound is synthesized in real time using a pre-recorded database of frequency- and time-domain sound sources. Our synthesized sounds are evaluated by comparing them to recordings for a specific set of paper deformations

High-resolution brittle fracture simulation with boundary elements

We present a method for simulating brittle fracture under the assumptions of quasi-static linear elastic fracture mechanics (LEFM). Using the boundary element method (BEM) and Lagrangian crack-fronts, we produce highly detailed fracture surfaces. The computational cost of the BEM is alleviated by using a low-resolution mesh and interpolating the resulting stress intensity factors when propagating the high-resolution crack-front. Our system produces physics-based fracture surfaces with high spatial and temporal resolution, taking spatial variation of material toughness and/or strength into account. It also allows for crack initiation to be handled separately from crack propagation, which is not only more reasonable from a physics perspective, but can also be used to control the simulation. Separating the resolution of the crack-front from the resolution of the computational mesh increases the efficiency and therefore the amount of visual detail on the resulting fracture surfaces. The BEM also allows us to re-use previously computed blocks of the system matrix

Example-Based Fractured Appearance

International audienceA common weathering effect is the appearance of cracks due to material fractures. Previous exemplar-based aging and weathering methods have either reused images or sought to replicate observed patterns exactly. We introduce a new approach to exemplar-based modeling that creates weathered patterns on synthetic objects by matching the statistics of fracture patterns in a photograph. We present a user study to determine which statistics are correlated to visual similarity and how they are perceived by the user. We then describe a revised physically-based fracture model capable of producing a wide range of crack patterns at interactive rates. We demonstrate how a Bayesian optimization method can determine the parameters of this model so it can produce a pattern with the same key statistics as an exemplar. Finally, we present results using our approach and various exemplars to produce a variety of fracture effects in synthetic renderings of complex environments. The speed of the fracture simulation allows interactive previews of the fractured results and its application on large scale environments

Synthèse de son de papier adaptée au mouvement et à la géométrie de la surface

National audienceNous présentons une méthode pour générer en temps réel un son plausible pour une animation d'un papier virtuel que l'on froisse. Pour cela, nous analysons l'animation géométrique de la surface du papier pour détecter les événements à l'origine de sons puis calculons géométriquement les zones du papier qui vibrent de part la propagation des ondes au travers de la surface. Le son résultant est ensuite synthétisé à partir à la fois d'extraits pré-enregistrés, et d'une synthèse procédurale, tenant compte de la forme géométrique de la surface et de sa dynamique. Nous validons nos résultats en comparant le son généré par notre modèle virtuel par rapport à des enregistrements réels pour un ensemble de cas d'animations caractéristiques. Abstract In this article, we present a method to generate plausible sounds for an animation of crumpling paper in real-time. We analyse the geometrical animation of the deformed surface to detect sound-producing events and compute the regions which resonate due to the propagation of the vibrations though the paper. The resulting sound is synthesized from both pre-recorded sounds and procedural generation taking into account the geometry of the surface and its dynamic. Our results are validated by comparing the generated sound of the virtual model with respect to real recording for a set of specific deformations

Multi-Scale Simulation of Nonlinear Thin-Shell Sound with Wave Turbulence

International audienceThin shells — solids that are thin in one dimension compared to the other two — often emit rich nonlinear sounds when struck. Strong excitations can even cause chaotic thin-shell vibrations, producing sounds whose energy spectrum diffuses from low to high frequencies over time — a phenomenon known as wave turbulence. It is all these nonlinearities that grant shells such as cymbals and gongs their characteristic " glinting " sound. Yet, simulation models that efficiently capture these sound effects remain elusive. We propose a physically based, multi-scale reduced simulation method to synthesize nonlinear thin-shell sounds. We first split nonlinear vibrations into two scales, with a small low-frequency part simulated in a fully nonlinear way, and a high-frequency part containing many more modes approximated through time-varying linearization. This allows us to capture interesting nonlinearities in the shells' deformation, tens of times faster than previous approaches. Furthermore, we propose a method that enriches simulated sounds with wave turbulent sound details through a phenomenological diffusion model in the frequency domain, and thereby sidestep the expensive simulation of chaotic high-frequency dynamics. We show several examples of our simulations, illustrating the efficiency and realism of our model

A Materials Science Driven Pattern Generation Solution to Fracturing Computer Generated Glass for Films and Games

Believably and realistically fracturing computer generated glass for visual effects has been previously solved through various methods such as algorithmic approaches, utilizing texture maps, or finite element analysis. These solutions can achieve some believable results but often at the cost of one or more of the following: simulation time, preparation time, art directability, consistency with materials science research, or the requirement of creating or utilizing fixed assets or maps. In this thesis I present a novel method that draws from the appropriate literature and focuses on quickly generating accurate fracture patterns. The method takes inputs such as the artist’s animation of an impact and desired object properties, and outputs fracture patterns used for breaking objects apart based on input values, materials science literature, and fracture mechanics. After determining all of the fracture pattern variables such as the number of radial and concentric cracks, the artist is able to override the computed parameters to retain control and art directability. Implementation of this method was performed using MAXScript, the built-in scripting language for Autodesk 3ds Max. The result is a computationally fast and mechanically accurate tool while retaining art directability to fulfill film storyboards or game design