Fields Input

The initial stress fields are set with the [fdfault.fields] header. This section has four entries:

Uniform initial stress tensor
Filename for spatially heterogeneous initial stress tensor
Filename for spatially heterogeneous elastic properties
    Boolean indicating if full plastic strain tensor is calculated

The uniform initial stress tensor is a list of 6 numbers, and the order is \({\sigma_{xx}}\), \({\sigma_{xy}}\), \({\sigma_{xz}}\), \({\sigma_{yy}}\), \({\sigma_{yz}}\), \({\sigma_{zz}}\)). Components not involved in a 2D problem are in some cases used in the problem, particularly for anti-plane (mode 3) problems, where the in-plane normal stress components determine the compressive normal stresses acting on the fault. Line breaks are ignored.

If a heterogeneous stress tensor will be used, it is specified with a filename here. If no heterogeneous file is to be read, this entry should be none. The file should contain a sequence of double precision binary floating point numbers (endianness should match the processor where the code will be run). Components are entered one at a time, with the number of entries matching the grid size using row major order (C order). For 2D mode 3 problems, the order is \({\sigma_{xz}}\), \({\sigma_{yz}}\). For 2D mode 2 problems, the order is \({\sigma_{xx}}\), \({\sigma_{xy}}\), \({\sigma_{yy}}\) (and for plasticity problems, \({\sigma_{zz}}\)). For 3D problems, the order is the same as for the uniform stress tensor. Entering heterogeneous stresses is greatly simplified if you use the Python module. Also note that entering the full heterogeneous stress tensor required additional memory.

Similarly, if a heterogeneous elastic properties will be used, it is specified with a filename here. If no heterogeneous file is to be read, this entry should be none. The format is the same as the stress tensor, but with three entries: density, first Lamé parameter, and shear modulus. Creation of these files is simplified with the Python module.

Note: for large 3D problems, the arrays for a heterogeneous stress field or elastic property may be too large to be handles by the Python module (Numpy seems to be limited to arrays that are 2 or 4 GB, depending on the version of Python that you use). In that case, you may need to generate these files manually.

The final a boolean (0 or 1) indicates whether or not the full plastic strain tensor is computed for plastic problems. This is an option because saving the full tensor requires significant additional memory. To turn it on, 0 should be entered here. This entry is ignored for elastic problems.