Two kinds of simulation, Finite Elements from engineering and Qualitative Physics from computer science, have inspired our simulator of Lego brick structures.
Finite Element Modeling (FEM) is a structural mechanics technique for discretizing an object in order to analyze its behavior in the presence of stresses and holds [141]. The principle is to construct a network or ``mesh'' to model the piece as a discrete network and have the nodes communicate with their neighbors in order to cancel out all forces.
Qualitative Physics (QP) is a subfield of AI which deals with mechanical and physical knowledge representation. It starts with a logical representation of a mechanism, such as a heat pump [41] or a string [52], and produces simulations, or envisionments, of the future behavior of the mechanism.
QP simulations have not been used for evolutionary design, but they express an idea of great potential for reality-grounded evolution: not all aspects of the world need to be simulated to their fullest detail. Sometimes one can create an approximate model using ad hoc qualitative rules instead of the more complex equations of Newtonian physics.