Overview of Reaction Force

Parameter Name	Formula
REACTION_FORCE_ABS	$F = \| \sum K_{e} u_{i} \|$
REACTION_FORCE_X, REACTION_FORCE_Y, REACTION_FORCE_Z	$F = \sum K_{e} u_{i}$
REACTION_FORCE_X_ABS, REACTION_FORCE_Y_ABS, REACTION_FORCE_Z_ABS	$F = \| \sum K_{e} u_{i} \|$
REACTION_MOMENT_ABS	$F = \| \sum K_{e} u_{i} \|$
REACTION_MOMENT_X, REACTION_MOMENT_Y, REACTION_MOMENT_Z	$F = \sum K_{e} u_{i}$
REACTION_MOMENT_X_ABS, REACTION_MOMENT_Y_ABS, REACTION_MOMENT_Z_ABS	$F = \sum K_{e} u_{i}$

Where e are the elements connected to the nodes i on supported DOFs.

Analysis Types: Static Linear or Non-Linear Analysis

K u = F

where K may be linear or non-linear.

For reaction forces the following table shows the allowed combinations between strategy and the items OBJ_FUNC and CONSTRAINT with C for controller and S for sensitivity based optimization.

	TOPO	SHAPE	BEAD	SIZING
OBJ_FUNC	S	S	S	S
CONSTRAINT	S	S	S	S

Differences between reaction forces can be defined using group operations.
Examples for combinations of reaction forces can be found in Group Operations for Reaction Forces/Moments.

Important:

The reaction forces and the reaction moments can only be defined as a DRESP (design response) in the sensitivity based optimization approaches.
A reference coordinate system (CS_REF) cannot be used for the reaction force responses defined using REACTION_FORCE_ABS and REACTION_MOMENT_ABS.
The reaction force, reaction moment, internal force and/or internal moment in a given DOF of a node applied in the optimization formulation has to have stiffness in the DOF direction similar to the DOF direction of the reaction force or internal force used in the optimization formulation. Meaning that at least one of the elements surrounding the node has to have stiffness in the DOF direction similar to the reaction force or internal force direction applied in the optimization formulation. Hence, this criterion is also physical meaningful since a structure having no stiffness in a given direction will always have zero reaction force in this direction.