A method and apparatus for accessing a data representation of a model associated with a fluid system, the data representation including at least one interior cell and at least one ghost cell, calculating a physical volume value and physical surface area value for at least one interior cell and at least one ghost cell, generating at least one control volume based on one or more physical volume values, generating at least one control surface based on one or more physical surface area values; substituting one or more of the at least one control volume parameter and the at least one surface area for corresponding elements of mathematical conservation equations representative of the fluid system, and solving the mathematical conservation equations representative of the fluid system.