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Loki: A Unified Multiphysics Simulation Framework for Production
Steve Lesser, Alexey Stomakhin, Gilles Daviet, Joel Wretborn, John Edholm, Noh-Hoon Lee, Eston Schweickart, Xiao Zhai, Sean Flynn, Andrew Moffat
Weta's unified solver where muscles, flesh, cloth, hair, and fluids all couple in one framework instead of chained single-physics passes.
Abstract
We introduce Loki, a new framework for robust simulation of fluid, rigid, and deformable objects with non-compromising fidelity on any single element, and capabilities for coupling and representation transitions across multiple elements. Loki adapts multiple best-in-class solvers into a unified framework driven by a declarative state machine where users declare 'what' is simulated but not 'when,' so an automatic scheduling system takes care of mixing any combination of objects. This leads to intuitive setups for coupled simulations such as hair in the wind or objects transitioning from one representation to another, for example bulk water FLIP particles to SPH spray particles to volumetric mist. We also provide a consistent treatment for components used in several domains, such as unified collision and attachment constraints across 1D, 2D, 3D deforming and rigid objects. Distribution over MPI, custom linear equation solvers, and aggressive application of sparse techniques keep performance within production requirements. We demonstrate a variety of solvers within the framework and their interactions, including FLIPstyle liquids, spatially adaptive volumetric fluids, SPH, MPM, and mesh-based solids, including but not limited to discrete elastic rods, elastons, and FEM with state-of-the-art constitutive models.
How to read this
- Category
- Production system: a unified multiphysics simulation framework
- Contributions
- Loki, a unified framework coupling fluid, rigid, and deformable objects with high single-element fidelity
- A declarative state machine where users declare what is simulated, with automatic scheduling of when
- Consistent collision/attachment constraints across 1D/2D/3D deforming and rigid objects, plus representation transitions (e.g. FLIP to SPH to volumetric mist)
- Context
- Adapts multiple best-in-class solvers (FLIP, adaptive volumetric fluids, SPH, MPM, finite-element solids/muscle) into one framework, with roots in musculoskeletal simulation (related to Teran et al.'s Creating and Simulating Skeletal Muscle, 2005).Builds on: Creating and Simulating Skeletal Muscle from the Visible Human Data Set
- Correctness
- Engineering at production scale (MPI distribution, custom linear solvers, sparse techniques) rather than a single new algorithm; results are production-proven, and a reader should view the fidelity and coupling claims as system-integration achievements meeting production requirements rather than head-to-head benchmarks.
- Clarity
- Broad and systems-oriented; a first pass conveys the unified architecture and declarative model, deeper passes for individual solver coupling are optional and selective.
- How to read it
- Read for the architecture: the declarative state machine, automatic scheduling, and unified constraints; dive deeper only into the specific solver couplings relevant to your work.
Related work
Keywords
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