← ArchivePaper2023
Sag-Free Initialization for Strand-Based Hybrid Hair Simulation
Jerry Hsu, Tongtong Wang, Zherong Pan, Xifeng Gao, Cem Yuksel, Kui Wu
Four-stage framework computing stable quasistatic configurations for hybrid strand-based hair so simulations start without gravity-induced sag.
Abstract
Lagrangian/Eulerian hybrid strand-based hair simulation techniques have quickly become a popular approach in VFX and real-time graphics applications. With Lagrangian hair dynamics, the inter-hair contacts are resolved in the Eulerian grid using the continuum method, i.e., the MPM scheme with the granular Drucker-Prager rheology, to avoid expensive collision detection and handling. This fuzzy collision handling makes the authoring process significantly easier. However, although current hair grooming tools provide a wide range of strand-based modeling tools for this simulation approach, the crucial sag-free initialization functionality remains often ignored. Thus, when the simulation starts, gravity would cause any artistic hairstyle to sag and deform into unintended and undesirable shapes. This paper proposes a novel four-stage sag-free initialization framework to solve stable quasistatic configurations for hybrid strand-based hair dynamic systems. These four stages are split into two global-local pairs. The first one ensures static equilibrium at every Eulerian grid node with additional inequality constraints to prevent stress from exiting the yielding surface. We then derive several associated closed-form solutions in the local stage to compute segment rest lengths, orientations, and particle deformation gradients in parallel.
How to read this
- Category
- Method: sag-free initialization for hybrid hair simulation
- Contributions
- A four-stage framework that solves stable quasistatic configurations for hybrid (Lagrangian/Eulerian) strand-based hair
- Two global-local solver pairs, the first enforcing static equilibrium at Eulerian grid nodes with constraints to keep stress within the yield surface
- Lets simulations start from the authored hairstyle without gravity-induced sag
- Context
- Targets MPM-based hybrid hair with Drucker-Prager granular contact, grounded in strand dynamics descending from Discrete Elastic Rods (Bergou et al.).Builds on: Discrete Elastic Rods
- Correctness
- Assumes a quasistatic equilibrium exists and can be solved under the yield-surface constraints for the hybrid model; demonstrated for strand-based hair grooms, so applicability to other materials or solvers is not claimed.
- Clarity
- Technically dense; a first pass conveys the goal and four-stage structure, but the constraint formulation needs a careful second or third pass.
- How to read it
- First pass for the problem and the staged global-local structure; budget a slow second and third pass on the equilibrium constraints and yield-surface handling if implementing.
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Related work
- Anisotropic Elastoplasticity for Cloth, Knit and Hair Frictional Contact 2017 / TOG
- Estimating Cloth Elasticity Parameters From Homogenized Yarn-Level Models 2024 / MIG
- Interactive Hair Simulation on the GPU Using ADMM 2023 / SIGGRAPH
- Gravity Preloading for Maintaining Hair Shape Using the Simulator as a Closed-Box Function 2022 / SIGGRAPH
Keywords
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