The

ACM SIGGRAPH Publications program contains ones of the the most comprehensive publications in Computer Graphics and Physics Simulation.

Let's do a recap of some other interesting papers, revealed on the eve of

**SIGGRAPH 2013** conference.

**A Two-Continua Approach to Eulerian Simulation of Water Spray**Michael B. Nielsen (Aarhus University), O. Osterby (Aarhus University)

**Abstract:**Physics based simulation of the dynamics of water spray - water droplets dispersed in air - is a means to increase the visual plausibility of computer graphics modeled phenomena such as waterfalls, water jets and stormy seas.

Spray phenomena are frequently encountered by the visual effects industry and often challenge state of the art methods. Current spray simulation pipelines typically employ a combination of Lagrangian (particle) and Eulerian (volumetric) methods - the Eulerian methods being used for parts of the spray where individual droplets are not apparent. However, existing Eulerian methods in computer graphics are based on gas solvers that will for example exhibit hydrostatic equilibrium in certain scenarios where the air is expected to rise and the water droplets fall.

To overcome this problem, we propose to simulate spray in the Eulerian domain as a two-way coupled two-continua of air and waterphases co-existing at each point in space. The fundamental equations originate in applied physics and we present a number of contributions that make Eulerian two-continua spray simulation feasible for computer graphics applications.

The contributions include a Poisson equation that fits into the operator splitting methodology as well as (semi-)implicit discretizations of droplet diffusion and the drag force with improved stability properties. As shown by several examples, our approach allows us to more faithfully capture the dynamics of spray than previous Eulerian methods.

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Video**Near-exhaustive Precomputation of Secondary Cloth Effects**Doyub Kim (Carnegie Mellon University), Woojong Koh (University of California, Berkeley), Rahul Narain (University of California, Berkeley), Kayvon Fatahalian (Carnegie Mellon University), Adrien Treuille (Carnegie Mellon University), James F. O?Brien (University of California, Berkeley)

**Abstract:**The central argument against data-driven methods in computer graphics rests on the curse of dimensionality: it is intractable to precompute ?everything? about a complex space. In this paper, we challenge that assumption by using several thousand CPU-hours to perform a massive exploration of the space of secondary clothing effects on a character animated through a large motion graph.

Our system continually explores the phase space of cloth dynamics, incrementally constructing a secondary cloth motion graph that captures the dynamics of the system. We find that it is possible to sample the dynamical space to a low visual error tolerance and that secondary motion graphs containing tens of gigabytes of raw mesh data can be compressed down to only tens of megabytes. These results allow us to capture the effect of high-resolution, off-line cloth simulation for a rich space of character motion and deliver it efficiently as part of an interactive application.

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Video**Super Space Clothoids**Romain Casa, Florence Bertails-Descoubes

**Abstract:**Thin elastic filaments in real world such as vine tendrils, hair ringlets or curled ribbons often depict a very smooth, curved shape that low-order rod models ? e.g., segment-based rods ? fail to reproduce accurately and compactly.

In this paper, we push forward the investigation of high-order models for thin, inextensible elastic rods by building the dynamics of a G2-continuous piecewise 3D clothoid: a smooth space curve with piecewise affine curvature. With the aim of precisely integrating the rod kinematic problem, for which no closed-form solution exists, we introduce a dedicated integration scheme based on power series expansions. It turns out that our algorithm reaches machine precision orders of magnitude faster compared to classical numerical integrators. This property, nicely preserved under simple algebraic and differential operations, allows us to compute all spatial terms of the rod kinematics and dynamics in both an efficient and accurate way.

Combined with a semi-implicit time-stepping scheme, our method leads to the efficient and robust simulation of arbitrary curly filaments that exhibit rich, visually pleasing configurations and motion. Our approach was successfully applied to generate various scenarios such as the unwinding of a curled ribbon as well as the aesthetic animation of spiral-like hair or the fascinating growth of twining plants.

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VideoReference:

Physics Based Animation