Two overlapping models · M02 · Learn to Program Ansys APDL Simulations

Two overlapping models

Selection is state: what is active affects every subsequent command.

Mental model: two overlapping models

MAPDL maintains two entity families in the same database. The solid model describes geometry; the finite element model describes its discretization.

Entity hierarchy: volume, areas, lines, and keypoints in the solid model; elements and nodes in the finite element model — A component contains a single entity class. `fixed_nodes` contains nodes; `mid_elems`Elements.

Physical question	Useful entity	Example APDL
Where does the solid end up?	Face area or nodes	`NSEL,...,LOC,X,...`
Which part will be embedded?	Nodal component	`CM,fixed_nodes,NODE`
What elements are in the center?	Elements by centroid	`ESEL,...,CENT,X,...`
Which entities are active now?	Selection Status	`*GET,...,COUNT`

Selecting does not mean deleting

Both NSEL and ESEL internal flags change. Entities do not selected remain in the database. The danger is not to lose them, but to forget that they are temporarily invisible to subsequent commands.

Quick check

What does ALLSEL,ALL restore?

All selectable entities to the complete set. Only the nodes in the active component. The default material.