1. A method executed in a computer system for producing a model combining a plurality of physical systems having physical quantities represented as partial differential equations, said method comprising: representing each of said plurality of physical systems as an application mode modeling physical quantities of said physical system, one or more of said plurality of physical systems being a structural system, a fluids system, an electromagnetic system, a chemical system, or an acoustic system; for each application mode, determining via a processor a representation of a partial differential equation including one or more dependent variables associated with said physical quantities of said physical system, said one or more dependent variables including one or more non-local couplings of said plurality of physical systems, said one or more non-local couplings determining one or more expressions in at least a first portion of a first domain depending on an expression in at least a second portion of a second domain; determining, using said processor or another processor, a solution to said model of said combined plurality of physical systems, said solution based on said partial differential equations associated with each physical system, said model representing a mathematical expression of said physical quantities of said combined plurality of physical systems; and storing in a computer readable memory or in a computer readable data storage system said solution to said model.