Shape optimisation with differentiated CAD-kernel for U-bend testcase

A gradient-based optimisation of a parametric CAD model requires the calculation of shape sensitivities, i.e., the derivatives of surface points with respect to the design parameters. Typically, this information is not available within a CAD system and can be obtained by applying Automatic Differentiation (AD) to the CAD sources. This paper demonstrates the differentiated open-source CAD kernel OpenCascade Technology (OCCT) using the AD software tool ADOL-C (Automatic Differentiation by OverLoading in C++) for the optimisation of pressure loss in a U-bend pipe. The U-bend geometry is parametrised in OCCT and its derivatives are used in CFD optimisation loops.