## 18.1. Output - Part Summary Variables

The Part summary variable includes three sets of optional data:

Contact energy

Hourglass energy

External forces

This data is accumulated per Part and is available for review
via the print file (using the energy summary option) or as time history
data (using the Part summary option).

Note that by default, these additional variables are not available
for history plotting. The variables must be activated using the Output,
History, Select Part Summary Variables option.

**Hourglass energy**

The 2D and 3D Lagrangian volume and shell elements in Autodyn use
hourglass control to remove zero energy modes of deformation. The
forces of the hourglass control algorithms dissipate energy in resisting
the zero energy modes of deformation.

In Autodyn, this energy is calculated and accumulated in the
element internal energy. In version 6.1, the hourglass energy is now
also accumulated independently to the internal energy to allow users
to interrogate and assess the relevance of hourglass energy in a simulation.

**Contact energy**

Contact energy is accumulated on a per part basis as:

For the purpose of energy accountancy, the contact energy is
added to the work done on the system.

**External forces**

The resultant external forces on a Part can now be easily extracted
from a simulation by selecting the appropriate components as Part
summary variables. The components available are:

**X/Y/Z contact forces**

External forces applied to a Part from Lag/Lag contact

**X/Y/Z coupling forces**

External forces applied to a Part from Euler/Lag coupling

**X/Y/Z boundary forces**

External forces applied to Part from all boundary conditions

**X/Y/Z total external forces**

The sum of all external forces acting on a Part

Note: External forces are not extracted for polygon based Euler
Lagrange coupling in 2D