Optimization for sag-free simulations

Twigg, Christopher D.; Kačić-Alesić, Zoran

doi:10.1145/2019406.2019437

Cited by 22 publications

(12 citation statements)

References 31 publications

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“…Hadap [2006] and Derouet-Jourdan et al [2010] leverage exact inverse statics for fibers under gravity, but consider only isolated (i.e., non contacting) fibers. Twigg and Kačić-Alesić [2011] propose to reduce the sagging effect of masssprings systems (including hair) through nonlinear optimization. In their approach, the net force applied onto each particle (including internal elastic forces, gravity, and contacts modeled as penalty forces) is minimized over the physical parameters of the system.…”

Section: Related Workmentioning

confidence: 99%

Inverse dynamic hair modeling with frictional contact

et al. 2013

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Figure 1: Our inversion method makes the hair synthesis pipeline consistent: (a) Raw hair geometry (a set of polylines) resulting from the manual design or the automatic capture of a static hairstyle (here, a capture from [Herrera et al. 2012]); (b) Input geometry is automatically converted into a dynamic hair model (a set of super-helices) at equilibrium under gravity and frictional hair-body and hair-hair contact forces; Unlike classical hair simulators (c) which ignore surrounding forces when initializing the hairstyle and are thus prone to undesired sagging, our simulator (b) exactly matches the original hair geometry at initial state and (d) yields a realistic, character-specific hair animation. AbstractIn the latest years, considerable progress has been achieved for accurately acquiring the geometry of human hair, thus largely improving the realism of virtual characters. In parallel, rich physics-based simulators have been successfully designed to capture the intricate dynamics of hair due to contact and friction. However, at the moment there exists no consistent pipeline for converting a given hair geometry into a realistic physics-based hair model. Current approaches simply initialize the hair simulator with the input geometry in the absence of external forces. This results in an undesired sagging effect when the dynamic simulation is started, which basically ruins all the efforts put into the accurate design and/or capture of the input hairstyle. In this paper we propose the first method which consistently and robustly accounts for surrounding forcesgravity and frictional contacts, including hair self-contacts -when converting a geometric hairstyle into a physics-based hair model. Taking an arbitrary hair geometry as input together with a corresponding body mesh, we interpret the hair shape as a static equilibrium configuration of a hair simulator, in the presence of gravity as well as hair-body and hair-hair frictional contacts. Assuming that hair parameters are homogeneous and lie in a plausible range of physical values, we show that this large underdetermined inverse problem can be formulated as a well-posed constrained optimization problem, which can be solved robustly and efficiently by leveraging the frictional contact solver of the direct hair simulator. Our method was successfully applied to the animation of various hair geometries, ranging from synthetic hairstyles manually designed by an artist to the most recent human hair data automatically reconstructed from capture.

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Section: Related Workmentioning

confidence: 99%

Inverse dynamic hair modeling with frictional contact

et al. 2013

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“…so that the input configuration is the rest configuration under gravity [Derouet-Jourdan et al 2010;Twigg and Kačić-Alesić 2011].…”

Section: Resultsmentioning

confidence: 99%

Interactive authoring of simulation-ready plants

Zhao

Barbič

2013

ACM Trans. Graph.

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Figure 1: Simulation of a peach tree with anatomically realistic geometry (Prunus Persica), with fracture. Peaches fall from the tree swaying in the space-time Perlin wind. 299,707 triangles, 237 branches, 3,556 twigs, 18,536 leaves, 330 fruits, 2,950 reduced DOFs, 7 hierarchy levels, 5 msec of simulation per graphical frame. AbstractPhysically based simulation can produce quality motion of plants, but requires an authoring stage to convert plant "polygon soup" triangle meshes to a format suitable for physically based simulation. We give a system that can author complex simulation-ready plants in a manner of minutes. Our system decomposes the plant geometry, establishes a hierarchy, builds and connects simulation meshes, and detects instances. It scales to anatomically realistic geometry of adult plants, is robust to non-manifold input geometry, gaps between branches or leaves, free-flying leaves not connected to any branch, spurious geometry, and plant self-collisions in the input configuration. We demonstrate the results using a FEM model reduction simulator that can compute large-deformation dynamics of complex plants at interactive rates, subject to user forces, gravity or randomized wind. We also provide plant fracture (with prespecified patterns), inverse kinematics to easily pose plants, as well as interactive design of plant material properties. We authored and simulated over 100 plants from diverse climates and geographic regions, including broadleaf (deciduous) trees and conifers, bushes and flowers. Our largest simulations involve anatomically realistic adult trees with hundreds of branches and over 100,000 leaves.

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“…Derouet-Jourdan [2013] treated hair shape as a static equilibrium configuration of a hair simulator and solve an inverse problem for finding a physically valid rest shape for a given hairstyle. Twigg and Kačić-Alesić [2011] proposed a solution to the inversion problem with contact of mass-springs systems to reduce sagging in animations through nonlinear optimization. In our work, we go beyond finding static equilibrium and optimize for self-supporting structures that are as stable as possible even under external load cases.…”

Section: Simulation and Optimization Of Rodsmentioning

confidence: 99%

Computational design of stable planar-rod structures

2016

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Figure 1: Given a set of planar input contours (left), our system computes a stable, self-supporting wire sculpture. The physical prototype (right) can be easily fabricated using a 2D wire bending machine and assembled without the need of connectors between crossing wires. AbstractWe present a computational method for designing wire sculptures consisting of interlocking wires. Our method allows the computation of aesthetically pleasing structures that are structurally stable, efficiently fabricatable with a 2D wire bending machine, and assemblable without the need of additional connectors. Starting from a set of planar contours provided by the user, our method automatically tests for the feasibility of a design, determines a discrete ordering of wires at intersection points, and optimizes for the rest shape of the individual wires to maximize structural stability under frictional contact. In addition to their application to art, wire sculptures present an extremely efficient and fast alternative for low-fidelity rapid prototyping because manufacturing time and required material linearly scales with the physical size of objects. We demonstrate the effectiveness of our approach on a varied set of examples, all of which we fabricated.

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Optimization for sag-free simulations

Cited by 22 publications

References 31 publications

Inverse dynamic hair modeling with frictional contact

Inverse dynamic hair modeling with frictional contact

Interactive authoring of simulation-ready plants

Computational design of stable planar-rod structures

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