This node causes the fluid-structure interaction matrix to be generated and assembled to the LHS. Also, it transforms the structure normal velocity to discharge vector and apply it on the fluid nodes and transforms the fluid pressure to force vector and apply it on the structure nodes in the normal direction. In 2D elements the normal direction is determined by the cross product 
, where 
is the vector originated from the first local node to the second one as in the same order listed in the constraint control card. In 3D elements the normal will have the same direction as determined by the right hand rule of the direction of rotation used to number the element local nodes in the same order listed in the constraint control card.