10. Overset

Nalu supports simulations using an overset mesh methodology to model complex geometries. Currently the codebase utilizes a native STK based overset grid assembly algorithm for all overset assembly. STK searches are performed to remove elements which intersect bounding shapes. Three shapes are supported:

  1. Axis-aligned bounding boxes (AABB),

  2. Oriented bounding boxes (OBB), and

  3. Oriented cylinders (OC).

AABB directly uses efficient STK search routines to remove elements which have an AABB that intersects the overset mesh’s AABB. OBB instead removes elements which have nodes within an oriented bounding box that follows an overset block’s movement. OC behaves similarly where now a cylindrical volume is removed that follows the block’s motion. The oriented cutting shapes provide more consistent overlap for moving cases and are generally suggested over the AABB strategy for such cases.