Design Patterns for Multiphysics Modeling in Fortran 2003 and C++

We present three new object-oriented software design patterns in Fortran 2003 and C++. These patterns integrate coupled differential equations, facilitating the flexible swapping of physical and numerical software abstractions at compile-time and runtime. The Semi-Discrete pattern supports the time advancement of a dynamical system encapsulated in a single abstract data type (ADT). The Puppeteer pattern combines ADTs into a multiphysics package, mediates interabstraction communications, and enables implicit marching even when nonlinear terms couple separate ADTs with private data. The Surrogate pattern emulates C++ forward references in Fortran 2003. After code demonstrations using the Lorenz equations, we provide architectural descriptions of our use of the new patterns in extending the Rouson et al. [2008a] Navier-Stokes solver to simulate multiphysics phenomena. We also describe the relationships between the new patterns and two previously developed architectural elements: the Strategy pattern of Gamma et al. [1995] and the template emulation technique of Akin [2003]. This report demonstrates how these patterns manage complexity by providing logical separation between individual physics models and the control logic that bridges between them. Additionally, it shows how language features such as operator overloading and automated memory management enable a clear mathematical notation for model bridging and system evolution.