MeshFilter rotation

[pshriwise]

Description

A translation property on MeshFilter is currently available that allows meshes to be applied in multiple locations in the OpenMC model with only one representation of the mesh in memory. This has been applied in pebble bed reactor models to effectively replicate an unstructured mesh at the location of each pebble, which would be otherwise untenable for ~300,000 pebbles.

An extension of this capability would be to provide a rotation attribute to the MeshFilter class that also allows meshes to be rotated in space. This would provide the ability for meshes to be rotated to align with off-axis features of models.

Similar machinery that is used to adjust particle positions for rotated fills should be able to be applied in this feature as well

openmc/src/geometry.cpp

Lines 199 to 201 in b4a796e

	if (!c.rotation_.empty()) {
	coord.rotate(c.rotation_);
	}

but applied in the same location where the MeshFilter's translation is applied

openmc/src/tallies/filter_mesh.cpp

Lines 45 to 46 in b4a796e

	if (translated_) {
	last_r -= translation();

Alternatives

• Provide a rotation capability on the Mesh objects themselves.

Compatibility

Any changes involved in this should be a pure addition to the code and won't affect backward compatibility.