The following equation should hold at all times during an analysis.
Internal energy includes elastic strain energy and work done in permanent deformation. External work includes work done by applied forces and pressures as well as work done by velocity, displacement or acceleration boundary conditions.
Energy associated with hourglassing is excluded by default, but can be included by setting HGEN to 2 on
*CONTROL_ENERGY (Control Card 19, Column 5).
The computation of Rayleigh damping energy dissipation can be activated by setting RYLEN to 2 on
*CONTROL_ENERGY (Control Card 19, Column 20). When activated, this energy dissipation is added to the internal energy.
The terms in the equation can all be plotted using LS-POST and ASCII database glstat. If the equation does not hold the user should suspect an error. If the left hand side of the equation rises above the right hand side, energy is being introduced artificially - for example, by numerical instability, or the sudden detection of artificial penetration through a contact surface (see Section ??). The latter condition is often shown by sudden jumps in the total energy. If the left hand side falls below the right hand side, energy is being absorbed artificially, perhaps by excessive hourglassing or by stonewalls or over-compliant contact surfaces.
The energy in each material can also be plotted using LS-POST. If the total energy indicates an error, plotting by material can sometimes indicate where the problem is occurring.
The energy ratio is defined by
This energy ratio may be used as a criterium for termination of calculation by defining ENDENG on
*CONTROL_TERMINATION (Control Card 8, Columns 31-40).