The “Xerox Particle Simulation Environment” (XPSE) computer codes have been extended to enable three-dimensional fluid-flow simulations based on the Smoothed-Particle Hydrodynamic (SPH) technique. Individual ink drops (e.g., from an inkjet print head) or molten toner particles are discretized into several thousand small fluid elements. Each element samples localized material properties, such as volume mass density and temperature, averaged over a small region of space. Forces are computed on each element, which are then moved in accordance with the laws of Newtonian mechanics. The result is a time-dependent three-dimensional simulation of fluid flow including free-surface effects, self-consistent temperature and viscosity, and diffusion into porous media (e.g., paper). Multiple material types, such as different colored inks or toners, can be handled within the same simulation. Examples are drawn from early numerical experiments relating to the microscopic flow of gel-like materials.