Accuracy of semi-analytical sensitivities and its improvement by the “natural method”

The semi-analytical method is a very convenient tool for the computation of sensitivities in shape design. It was, however, shown in the past that this method may have serious accuracy problems, e.g. in the shape design of beams. In this paper the natural method is employed to locate the decisive defect in the incremental stiffness and to develop an alternative procedure that provides nondefective incremental stiffnesses. This approach is then extended to the more common Cartesian element description. Examples demonstrate that the error of the sensitivities in critical cases can be almost totally removed, if we employ the nondefective incremental stiffness formulation in the sensitivity computation.