1. A computer-implemented method for simulating a granular material, the method comprising: removing, from a layer of granular material in a virtual domain defined by a data structure stored in a computer readable storage medium, a portion of the granular material in a closed region where the portion and a part of an object impacting the granular material are defined as occupying a same space; determining a value for a size aspect of the portion based on applying a numerical solver to a differential equation that relates a first field which is the size aspect per unit area to a second field which is a second derivative of a potential field for the first field; placing additional granular material along a boundary of the closed region to create a shape resulting from the impact of the object; and generating an image using the data structure, the image reflecting the impact of the object on the granular material in the virtual domain.