It might not seem immediately important to a newcomer to analysis software, but the way you mesh your solid model ready for simulation can make a big difference.
A solid can be meshed either in a ‘free’ mesh – like tetrahedrons – with fewer restrictions of element shapes, and no specified pattern applied to it.
However, a ‘brick’ mesh – using hexahedrons – gives a regular pattern, in obvious rows of elements, filling a given volume more efficiently than other shapes (it takes roughly five or six tetrahedrons to fill one lovely brick), leading to to faster analysis solution times.
Problem is, if you want this type of mesh, you must build the solid model as a series of fairly regular volumes and/or areas that can accept a mapped mesh.
This tutorial by CAE Associates runs you through the basics to do this properly using a couple of standard approaches.