1. A computer-implemented method, comprising: accessing a database having a data representation of a fluid system, the fluid system having a system boundary, at least one interior cell with a plurality of interior cell faces and at least one ghost cell with a plurality of ghost cell faces; determining a physical volume value and a physical surface area value for a plurality of interior cells and at least one ghost cell; generating a control volume for each of the interior cells based on one or more physical volume values; identifying a set of interior cells that contact a particular ghost cell; dividing the physical volume of the particular ghost cell among the interior cells of the set; generating a control surface area for each of the interior cells based on one or more physical surface area values; dividing the physical surface area of the particular ghost cell among the interior cells of the set; substituting one or more of the control volumes and the control surface areas for corresponding elements of mathematical conservation equations representative of the fluid system; and generating a model of the fluid system based on solutions to the mathematical conservation equations.