Movie physics

Numerical modelling is an important tool for most natural hazard researchers. Excellent codes now allow scientists and engineering practitioners the opportunity to simulate natural processes in both static and dynamic states. These codes typically grow from state-funded natural hazard research initiatives, and are principally aimed at understanding the ‘bigger picture’ in order to evaluate natural processes at the scale that poses a hazard to people and property.
Every now and then, however, it’s worthwhile remembering the hazard researcher’s not-so-distant, though often wealthier cousins in animation research. Although often dealing with smaller scale problems, the requirement for animators to come up with realistic-looking dynamic models for movies and computer games is currently driving a large amount of commercial research in scalable physics models. Physics-Based Animation is a useful blog detailing recent advances in simulating physics for visual consumption. This week Gizmodo featured work from the new movie Frozen, including an impressive Material Point Method snow simulation, applying real physical properties (compressibility, tensile strength, strain hardening, density, Young’s modulus, and Poisson’s ratio) to model snow as a dynamic, compressible granular material.

The models presented in the above video contain between 4×10^6 (snowplow) and 7×10^6 (rolling snowball) particles, sufficient for the evaluation of small to medium-scale rock or soil slope stability hazards, or possibly the design of protection structures which may interact with debris flows or snow avalanches. These simulations commonly use approximate solutions to replicate complex physical behaviors, however, as demonstrated in the above example, ‘expert knowledge’ (everyone’s seen a snow plow in action) can provide good verification for such visual models. As well as simulating situations with extremely large strains, models developed for animation purposes are also able to reproduce complex fracture behaviours, and examples such as that below may make their way into geohazard studies investigating, for example, particle fragmentation during rock avalanche, or rock slope failure as a result of earthquake shaking.

Blender – the free, open source alternative

Although the commercial nature of these codes often means the software itself is wrapped up in propriety licences, the maths and physics behind the above simulations are published in scientific journals (here and here). Blender is a free and open source 3D ‘creation pipeline’ (physics-based animation software) designed with fluid, rigid body physics, and particle tracking simulations in mind.

User-developed plugins and tutorials provide the opportunity for enthusiasts (or practitioners from generally unrelated fields) the opportunity to access these advanced simulation techniques, and drawing inspiration from commercial software, are often not far behind the state-of-the-art. Although limitations in terms of particle numbers and physical calibration mean that animation software is currently no match for specifically designed and calibrated geohazard simulation software such as RAMMS, these are not insurmountable obstacles. As demonstrated by the simulation below, projects such as Blender may soon provide some exciting opportunities for research and mitigation of dynamic gravitational hazards, and at least so far, provides useful insight which may improve snowman survival in the upcoming winter.