## 2. Cube in Gravitational Field

A a solid cube is placed in the gravitational field g=(0, 0, -9.81) at time t=0 and released. The cube must move in 'free fall' along the negative z-axis with

z = 0.5 g z t 2

and the falling speed

v = g z t

with the acceleration a = g z being constant. The model consists of HE8.S, HE20.S.TL, or HE27.S.TL elements. Different mesh densities a tested. The figure below displays the displacement, velocity, and acceleration functions for an integration time of 2s (solid lines are theoretical values).

The dynamic solution is relatively sensitive with respect to the error tolerance. Values of case options (see input file he.mdl)

tol_residuum 2e-3
tol_solution 1e-4

have been found to lead all element types to convergence.