The invention provides an apparatus and methods for performing process simulation and structural analysis using a hybrid model. For example, a method of the invention automatically defines a hybrid solution domain by dividing a representation of a plastic component or mold cavity into two portions—a portion in which a simplified analysis may be conducted, and a portion in which a more complex analysis is required. The method may use as input any form of CAD data that describes the surface of a component or mold. Furthermore, the invention provides methods for simulating fluid flow within a mold cavity by automatically creating a hybrid solution domain, automatically discretizing the domain, and solving for the distribution of process variables within the solution domain.