# What is the IGNORE flag good for?

## IGNORE=1

At any point during the simulation, if a node is suddenly found to be below the surface (say, it was moving very fast and wasn't detected before penetration), the old style (IGNORE=0) algorithm just moves the node to the master surface without applying any forces (we term this "shooting node logic"). If the shooting node logic is turned off (SNLOG=1), then you would likely get large forces suddenly appearing, and negative contact energy. If IGNORE is set to 1 then the shooting node logic flag SNLOG has no affect. Rather the amount of sudden penetration is noted and compensated for by adjusting the contact thickness locally. So at any time during the simulation, if a sudden penetration is detected, the program doesn't apply any large forces nor are any nodes moved. Contact forces, however, will resist FURTHER penetration.

## Shooting Node Logic

shooting node logic moves nodes throughout the calculation and in fact does not move nodes initially. We do try to move nodes to eliminate initial penetration, but this is not shooting node logic. The shooting node logic moves nodes back to the surface when they are first found to be in contact. If you turn shooting node logic off, then we still move nodes initially, but not throughout the calculation. If the ignore option is turned on, then nodes are not moved during initialization, and shooting node logic is turned off.

## SOFT=2

Segment based contact (SOFT=2) does not use the shooting node logic parameter. There is no need for shooting node logic because the segment based contact ignores initial penetrations. Penalty forces are proportional to penetration in excess of the initial penetration. In equation form, this is `f = k*(d-di)` where f is a force, k is penalty stiffness, d the current penetration depth, and di the initial penetration depth.

The ignore option (optional card C, or 4th card of `*CONTROL_CONTACT`) causes the default contact to ignore initial penetrations which also makes shooting node logic unnecessary.

jpd, lpb revised 3/14/2003