Shooting node

To prevent instabilities resulting from shooting nodes, LS-DYNA uses a so-called "shooting node logic" routine, which is activated via SNLOG=0 (default).

"Shooting node logic" puts a penetrating node back to the master surface without applying any contact force. This occurs on the first cycle that a penetration is sensed. In subsequent cycles, penetration produces contact forces.  After the penetrating node is pushed back so that it is no longer penetrating a master surface, "shooting node logic" can  again be invoked the next time penetration occurs.

"Shooting node logic" can be beneficial in the case where a slave node suddenly finds itself well behind it's master segment (whereas there was no penetration in the preceding cycle). In such a case, the logic prevents a huge contact force that might  otherwise cause an instability. The penetrating node is simply placed back on the master surface.   

If the "shooting node logic" doesn't prevent shooting nodes, then consider the following potential root causes:

• inappropriate use of fully integrated element formulations in areas of large deformation

• a stability issue that may be rectified simply by reducing the timestep scale factor

• out-of-control hourglassing that may be brought under control by an alternate hourglass control or refinement of the mesh

• poor choice of contact type possibly aggravated by detected and/or undetected initial penetrations.

NOTE:

Setting IGNORE=1 supersedes use of "shooting node logic".