Dissipated Energy
There are many possible mechanisms for energy dissipation in a structure:
•
Material damping (loss factor, Rayleigh damping, or viscous damping)
•
Viscoelasticity
•
Dissipation by plasticity or creep
•
Viscous damping in boundary conditions, springs and joints
•
Friction in mechanical contact
The general form of dissipation loss is
The treatment of dissipated energy is fundamentally different depending on whether the analysis is in frequency domain or not. For stationary or time-dependent cases, the dissipated energy must be accumulated over parameter ranges or time, which means extra degrees of freedom must be added. For this reason, you must explicitly select to compute the mechanical dissipation in these cases. This is done in the
Energy Dissipation
section of the material model.
In frequency domain, the dissipated energy per cycle is computed using a closed form expression. It is always available as postprocessing variables. The expression used is
In the case of Rayleigh damping, the stresses are not directly affected by the damping, since it is not part of the stress-strain relation. In a problem which is linear elastic except for the Rayleigh damping, the stresses and strains are in phase with each other, and does thus not give any damping contribution. This is handled by explicitly adding an extra contribution to dissipation.
