Modeling (geometry and domain)
Simple geometries can be easily created by few geometric parameters (e.g. circular pipe)
Complex geometries must be created by the partial differential equations or importing the database of the geometry(e.g. airfoil) into commercial software
Domain: size and shape
CAD/CAE integration: use of industry standards such as Parasolid, ACIS, STEP, or IGES, etc.
The three coordinates: Cartesian system (x,y,z), cylindrical system (r, θ, z), and spherical system(r, θ, Φ) should be appropriately chosen for a better resolution of the geometry (e.g. cylindrical for circular pipe).