For efficient smooth particle hydrodynamics using more particle information, virtual particles are created. Each virtual particle represents an averaging of properties for the fluid particles in a cell. For density, force, or other calculations for a given fluid particle, the interaction between the particles within a cell are calculated. For calculating the influence of particles outside the cell on the particle in the cell, the virtual particles from the neighboring cells are used. The interaction with these aggregate particles reduces the number of calculations while still including the influence from particles of other cells.