Thanks, now it's clear.
It seems only computeValueAt function is needed for forces (see StructuralElement :: computeBoundarySurfaceLoadVector).
I solved for set up of loading in the input file. This can be used:
LinearSurfaceLoad 1 loadType 3 loadTimeFunction 2 Components 6 0e0 0e0 1e0 0e0 0e0 0e0 normValues 4 0 0 1 1
The normValues specifies the normalized factors for loading, referred to nodes. If number of values are less than nodes, 1 is assumed.
Each component will be multiplied by the coefficient given by spatial plane formed by these factors (if factors are not lying in the same plane, the nearest plane is used, since I'll implement this with least squares). This load distribution is applied to all components. Hence, interpolation order is 1 (bilinear in 2D).
Comments on that? Is in the code any tool already present to find out the plane?
Can the element node order and number can be reconstructed in this class?
thanks