Optimum design of thin-walled box beams with coupled bending and torsion using frequency constraints

A rectangular box cross-section applicable to a typical airfoil design is presently treated by an optimum structural design method for beams vibrating in coupled bending and torsion, employing as many as three natural frequency constraints. In addition to the structural mass, nonstructural masses were added. Optimum flange thickness distribution, natural frequencies, and design iteration histories are given for the cantilever and simply supported end conditions. The optimal flange- thickness distribution followed the pattern of the dominant vibration mode. (O.C.)