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Simulation-based engineering science: The physics of Frozen

Originally published April 2, 2014

Frozen has surpassed $1B in ticket sales. Countless fans and critics point to most every element of the Oscar-winning film as the source for its far-reaching appeal. One area in particular, its portrayal of snow, has earned the admiration of many animators and technicians in the industry. The variation of the types of snow and how they interact with the characters and environments within the film have never been depicted in animation with the same attention to detail and adherence to the laws of physics as Frozen. At the heart of this incredible artistic achievement was not a team of talented visual artists inspired by their own creative techniques but rather a complex methodology called simulation-based engineering science (SBES).

SBES typically allows scientific researchers to engage in relatively inexpensive and controllable experiments needed to predict chaotic events such as the effects of explosions, earthquakes and natural disasters upon buildings, not snowy settings for cartoon characters.

Using a $400,000, five-year CAREER grant from the National Science Foundation, SBES researchers at the University of Missouri developed the Material Point Method (MPM) a computer-generated tool that not only creates scenarios that evaluate blast and impact resistant materials and designs, but also is crossing over into Hollywood animation projects such as Frozen.

SFL spoke with Zhen Chen, C.W. LaPierre Professor of Civil and Environmental Engineering at the College of Engineering at Missouri University to discuss his work within the field of MPM and how it was used by Disney’s animators.

SFL: How did the MPM find its way into Frozen?

Zhen Chen, C.W. LaPierre Professor of Civil and Environmental Engineering at the College of Engineering at Missouri University

Zhen Chen: We developed the MPM because we were motivated by the need for better simulations that demonstrate impact and penetration phenomena. Since then, the MPM has been further developed and applied by many global research teams to real-world problems including fire, explosions and impacts in buildings and structures.

Our first study on the MPM has been cited more than 400 times, and Disney’s technical artists stumbled across our work as they were searching for physics-based simulation methods that could assist them with their efforts.

SFL: Can you break down the Material Point Method for a layperson?

Chen: Briefly speaking the Material Point Method is an extension from computational fluid dynamics to computational solid dynamics. We developed this method to simulate multiphase connections, that is to say, connections between solid and fluid and gas.

As I mentioned, the MPM can create computer-based model scenarios that help determine which materials and designs respond most favorably to impact and blast loadings. Using the information and analysis provided by these simulations, designers can then validate the results with laboratory tests before applying them to full-scale construction projects or when their including stronger building components such as columns, walls and windows. The tool not only saves construction costs but it also saves lives as well.

SFL: Animators at Disney used the MPM to develop snow simulations that mimicked snowball drops and smashes, characters walking through snowy fields, trees covered with falling and accumulating snow. Did you ever think your work would be applied in such a manner within an animated film?

Chen: Yes and no. Having the SBES tool used in animation and popular media makes sense on many levels. Although children are more touch-oriented through tablets and smartphones and SBES simulations are natural fit within such environments, a thoughtful animator can see that the tool can be applied across a large screen to a great effect as well.

We’re proud of the computational methods we’ve developed through the years. By having SBES and the MPM at Disney, we hope children get excited about STEM (science, technology, engineering and mathematics) fields and see how work in these areas may be applied in so many different directions. We would be thrilled if our methods help shape and inspire not only the next generation of scientists and engineering researchers but the next generation of animators and film makers as well.

SFL: How did you find out that the MPM tool was used in Frozen?

Chen: I got the news from one of my regular students. He found an item on Google News saying Walt Disney is using the MPM for its animations. It was a great surprise and it was great to see how it energized my adult students. It really encouraged them to learn more about the Material Point Method.

SFL: Have you seen the film?

Chen: Yes. I brought my kids to watch it at our local theater. They were very excited. I was too because, like I said, it is great to see that we can use computer modeling and simulations to encourage younger generations to study mass physics.

SFL: What did you think of the physics of the effects?

Chen: Well, the thing is, in the olden days when they made animated movies, they were mainly based on artistic effects, but now they can incorporate sophisticated physics. The whole art form is now a physics-based type of animation. The artists at Disney animate first, then generate simulations using the MPM, then they use the snap shots from those simulations to represent the slow impacts of things like falling snow. Then they can make the final animated scene. It is a very different process and final product than what was created in the past and I think Disney did a great job in Frozen. Everything looked very believable and realistic.

2020 Update: Chen is still Professor of Civil and Environmental Engineering at the College of Engineering at Missouri University. He has published many academic papers in the past 7 years and regularly presents research at conferences all over the world. In 2017, he co-authored a textbook entitled, “The Material Point Method: A Continuum-Based Particle Method for Extreme Loading Cases”‚ (Tsinghua University Press Computational Mechanics Series, 1st).