Page 85 - The Combined Finite-Discrete Element Method

68 PROCESSING OF CONTACT INTERACTION

Figure 2.37 Motion sequence of a tetrahedron with initial velocity confined between two fixed
tetrahedra–obtained using penalty term p = 1.0e + 4 Pa, initial impact.

Figure 2.38 Motion sequence of a tetrahedron with initial velocity confined between two fixed
tetrahedra–obtained using penalty term p = 5.5e + 6 Pa, moving up and hitting top tetrahedron.

For larger penalty terms (Figures 2.38 and 2.39), the middle discrete element is con-
tained by the end discrete elements. Thus, the middle discrete element oscillates between
the end discrete elements. The penetration depends upon the size of the penalty term.
However, irrespective of the size of the penalty term, the energy is preserved regardless
of penalty or penetration, as shown in Figure 2.40.
As theoretically predicted, these numerical examples clearly demonstrate the most
important property of the potential contact force algorithm in 3D, namely the preservation
of the energy irrespective of the shape and size of discrete elements, and irrespective of
the geometry, i.e. kinematics of contact. This is clearly demonstrated by energy balances
shown in Figure 2.40.
It should be emphasised that the potential contact force contact algorithm has some
other features apart from preservation of energy and momentum balance. For instance,
due to the discretised nature of the evaluation of contacts, the algorithm is suitable for
parallel or distributed computing, as discussed in Chapter 9. There is also an additional
advantage from the fact that the geometry is treated in a discretised manner, which greatly