OOF2: The Manual

8.4. Adding New Material Properties
	Chapter 8. Writing OOF2 Extensions

8.4. Adding New Material Properties

	Warning
	This section has not yet been updated for OOF2 version 2.1. A partial discussion of the differences between the 2.0 and 2.1 extension APIs may be found at http://www.ctcms.nist.gov/oof/oof2/property_api_21.html.

Adding new Material Properties is the most complicated part of creating an OOF2 extension. Just to make it simpler, there are two ways of doing it. Properties can be written in C++ or they can be written in Python. Python Properties are a bit easier to write and install, but will run significantly more slowly. It may be convenient to develop new Properties in Python and translate them to C++ after the bugs have been worked out.

Whether a Property is written in C++ or Python, the same code elements must be present. Not all of them are necessary for every Property. It is safe simply to omit the unnecessary ones.

A Property definition contains a class definition, which is either a C++ subclass of Property or a Python subclass of oof2.SWIG.engine.pypropertywrapper, and a PropertyRegistration object, which contains metadata about the Property.

Property classes perform the following types of tasks (the links below each task lead to detailed documentation):

Identification. Properties have names by which they are identified in the user interface. They also have a propertyType. A propertyType is a string that identifies the Property's physical role. Each Material instance can have at most one Property of each propertyType. For example, all Properties that provide an elastic modulus have the type 'Elasticity', and all thermal expansion Properties have the type 'ThermalExpansion'. Authors of new types of Property should invent new propertyType strings. Authors of new versions of a preexisting Property should examine the existing PropertyRegistrations and reuse the same propertyType.
- PropertyRegistration
- Property constructor
There are also a few functions that Properties may define that influence the way they're used or the way a computation is done:
- Property::is_symmetric
- Property::integration_order
Cross Referencing. Sometimes a Property needs to use data from other Properties in the same Material. For example, any anisotropic Property will need to find out its Material's Orientation. Cross referencing allows a Property to use propertyType information to locate other Properties. This is done after a Material is constructed but before it is used for numerical computations.
- Property::cross_reference
Precomputation. When constructing the finite element stiffness matrix, the OOF2 program loops over all Elements and asks their Materials to ask their Properties to make their contributions to the matrix. For efficiency, Properties may want to precompute some quantities before this process begins. There are two possible precomputation points: Element- and Node-independent computations that are done before looping over Elements, and Element-dependent ones that are done before looping over Nodes.
Computation. Properties can make contributions to the finite element stiffness matrix and to the right-hand side vector of external “forces”.
- Property::fluxmatrix
- Property::fluxrhs
Postcomputation. This is just like precomputation, but later. It can be done either after the computation on each Element, or after a full solution has been obtained.
Outputs. Many output quantities, such as Field invariants, are defined without reference to Properties, but there are also many outputs, such as energy densities, that depend upon a Property in one way or another, and rely upon the Property's code. See Section 8.5 to learn how to add new outputs.
- Property::output


8.3. Conjugate Pairs		8.5. Adding New Outputs