This work addresses the challenges of distributing large physics-based simulations often encountered in the visual effects industry. These simulations, based on partial differential equations, model complex phenomena such as free surface liquids, flames, and explosions, and are characterized by domains whose shapes and topologies evolve rapidly. In this context, we propose a novel partitioning algorithm employing optimal transport —which produces a power diagram—and designed to handle a vast variety of simulation domain shapes undergoing rapid changes over time. Our Power partitioner ensures an even distribution of computational tasks, reduces inter-node data exchange, and maintains temporal consistency, all while being intuitive and artist-friendly. To quantify partitioning quality we introduce two metrics, the surface index and the temporal consistency index, which we leverage in a range of comparisons on real-world film production data, showing that our method outperforms the state of the art in a majority of cases.

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. Our framework has proven powerful and intuitive enough for voluntary artist adoption and has delivered creature and FX simulations for multiple major movie productions in the preceding four years.