SCA 17: Eurographics/SIGGRAPH Symposium on Computer Animation

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https://diglib.eg.org/handle/10.2312/2631998

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Browsing SCA 17: Eurographics/SIGGRAPH Symposium on Computer Animation by Subject "Computing methodologies Physical simulation"

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    Hierarchical Vorticity Skeletons
    (ACM, 2017) Eberhardt, Sebastian; Weissmann, Steffen; Pinkall, Ulrich; Thuerey, Nils; Bernhard Thomaszewski and KangKang Yin and Rahul Narain
    We propose a novel method to extract hierarchies of vortex filaments from given three-dimensional flow velocity fields. We call these collections of filaments Hierarchical Vorticity Skeletons (HVS). They extract multi-scale information from the input velocity field, which is not possible with any previous filament extraction approach. Once computed, these HVSs provide a powerful mechanism for data compression and a very natural way for modifying flows. The data compression rates for all presented examples are above 99%. Employing our skeletons for flow modification has several advantages over traditional approaches. Most importantly, they reduce the complexity of three-dimensional fields to one-dimensional lines and, make complex fluid data more accessible for changing de ning features of a flow. The strongly reduced HVS dataset still carries the main characteristics of the flow. Through the hierarchy we can capture the main features of di erent scales in the flow and by that provide a level of detail control. In contrast to previous work, we present a fully automated pipeline to robustly decompose dense velocities into filaments.
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    Long Range Constraints for Rigid Body Simulations
    (ACM, 2017) Müller, Matthias; Chentanez, Nuttapong; Macklin, Miles; Jeschke, Stefan; Bernhard Thomaszewski and KangKang Yin and Rahul Narain
    The two main constraints used in rigid body simulations are contacts and joints. Both constrain the motion of a small number of bodies in close proximity. However, it is often the case that a series of constraints restrict the motion of objects over longer distances such as the contacts in a large pile or the joints in a chain of rigid bodies. When only short range constraints are considered, a large number of solver iterations is typically needed for long range effects to emerge because information has to be propagated through individual joints and contacts. Our basic idea to signi cantly speed up this process is to analyze the contact or joint graphs and automatically derive long range constraints such as upper and lower distance bounds between bodies that can potentially be far apart both spatially and topologically. The long range constraints are either generated or updated at every time step in case of contacts or whenever their topology changes within a joint graph. The signi cant increase of the convergence rate due to the use of long range constraints allows us to simulate scenarios that cannot be handled by traditional solvers with a number of solver iterations that allow real time simulation.
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    A Micropolar Material Model for Turbulent SPH Fluids
    (ACM, 2017) Bender, Jan; Koschier, Dan; Kugelstadt, Tassilo; Weiler, Marcel; Bernhard Thomaszewski and KangKang Yin and Rahul Narain
    In this paper we introduce a novel micropolar material model for the simulation of turbulent inviscid fluids. The governing equations are solved by using the concept of Smoothed Particle Hydrodynamics (SPH). As already investigated in previous works, SPH fluid simulations su er from numerical di usion which leads to a lower vorticity, a loss in turbulent details and finally in less realistic results. To solve this problem we propose a micropolar fluid model. The micropolar fluid model is a generalization of the classical Navier- Stokes equations, which are typically used in computer graphics to simulate fluids. In contrast to the classical Navier-Stokes model, micropolar fluids have a microstructure and therefore consider the rotational motion of fluid particles. In addition to the linear velocity field these fluids also have a field of microrotation which represents existing vortices and provides a source for new ones. However, classical micropolar materials are viscous and the translational and the rotational motion are coupled in a dissipative way. Since our goal is to simulate turbulent fluids, we introduce a novel modi ed micropolar material for inviscid fluids with a non-dissipative coupling Our model can generate realistic turbulences, is linear and angular momentum conserving, can be easily integrated in existing SPH simulation methods and its computational overhead is negligible.
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    Physically-Based Droplet Interaction
    (ACM, 2017) Jones, Richard; Southern, Richard; Bernhard Thomaszewski and KangKang Yin and Rahul Narain
    In this paper we present a physically-based model for simulating realistic interactions between liquid droplets in an e cient manner. Our particle-based system recreates the coalescence, separation and fragmentation interactions that occur between colliding liquid droplets and allows systems of droplets to be meaningfully represented by an equivalent number of simulated particles. By considering the interactions speci c to liquid droplet phenomena directly, we display novel levels of detail that cannot be captured using other interaction models at a similar scale. Our work combines experimentally validated components, originating in engineering, with a collection of novel modi cations to create a particle-based interaction model for use in the development of mid-to-large scale dropletbased liquid spray e ects. We demonstrate this model, alongside a size-dependent drag force, as an extension to a commonly-used ballistic particle system and show how the introduction of these interactions improves the quality and variety of results possible in recreating liquid droplets and sprays, even using these otherwise simple systems.