Optimisation Methods for Shell-Structures

Based on the axiom of uniform stress, which is a basic design rule for biological load carriers, and by use of the Finite Element Method (FEM) the computer program CAO (Computer Aided Optimisation) has been developed at Forschungszentrum Karlsruhe to transfer this biological optimisation mechanism to mechanical engineering. CAO leads to an optimised shape with a high fatigue resistance due to homogeneous stresses on the surface of the component. The conventional CAO method has been modified for the optimisation of shell structures. One modification of the CAO method allows a variation of the wall thickness of shell or membrane elements. Another modification is for the optimised corrugation of sheets of uniform thickness. The methods can be combined and are very useful for the reduction of the maximum stress or the minimization of the weight of load bearing sheets.