WATCH: goopy simulated meltful armadillos

A. Peer, M. Ihmsen, J. Cornelis and M. Teschner's SIGGRAPH paper "An Implicit Viscosity Formulation for SPH Fluids," explored techniques for simulating the physics of smoothed-particle hydrodynamics -- solids that melt and squoosh into liquids and slimes. As interesting as the paper is, the video is a showstopper -- never have simulated anthropomorphic armadillo action-figures been so meltfully delightful!

We present a novel implicit formulation for highly viscous fluids
simulated with Smoothed Particle Hydrodynamics SPH. Compared
to explicit methods, our formulation is significantly more efficient
and handles a larger range of viscosities. Differing from existing
implicit formulations, our approach reconstructs the velocity field
from a target velocity gradient. This gradient encodes a desired
shear-rate damping and preserves the velocity divergence that is introduced
by the SPH pressure solver to counteract density deviations.
The target gradient ensures that pressure and viscosity computation
do not interfere. Therefore, only one pressure projection
step is required, which is in contrast to state-of-the-art implicit Eulerian
formulations. While our model differs from true viscosity
in that vorticity diffusion is not encoded in the target gradient, it
nevertheless captures many of the qualitative behaviors of viscous
liquids. Our formulation can easily be incorporated into complex
scenarios with one- and two-way coupled solids and multiple fluid
phases with different densities and viscosities

An Implicit Viscosity Formulation for SPH Fluids [Freiburg]

(via JWZ)