1. A method of simulating a fluid system, comprising: using a computational mesh of cells to represent a fluid system, each cell having faces, vertices and a volume, the system characterized by governing equations and having a set of boundaries, at least one of which is a moving boundary; representing the fluid system with a computer-based model, the fluid system having at least one boundary, the model simulating the fluid system with at least a plurality of cells; identifying interior cells as those cells having a cell center within an interior of the fluid system; identifying moving cell faces as those separating an interior cell and a ghost cell and which are in proximity to a moving boundary of the fluid system at the beginning of a time-step; wherein each cell vertex that is disposed, at the beginning of the time-step, at an initial location on a respective moving cell face is a moving boundary vertex, and wherein each interior cell vertex that is disposed, at the beginning of the time-step, at an initial location not touching a moving cell face is an interior vertex; accessing system pressure values; calculating the value of at least one representative thermodynamic property of the system; determining a Lagrangian location of each interior vertex at the end of the time-step, as each interior vertex moves with the fluid flow in a Lagrangian fashion; determining a Lagrangian location of each moving boundary vertex at the end of the time step, as each moving boundary vertex moves with the respective moving cell face; determining the change in volume of each interior cell over the time-step, based on the displacement of its respective cell vertices to their respective Lagrangian locations; calculating the value of at least one representative thermodynamic property of the system based on the changes in the interior cell volumes; and calculating at least one representative flux value across one or more interior cell volumes by returning the respective interior vertices from their Lagrangian locations to their respective initial locations.