CAD-based shape optimisation of the NASA CRM wing-body intersection using differentiated CAD-kernel

In industrial design existence of a master CAD geometry of a product enables simultaneous multi-disciplinary collaboration. Adjoint CFD methods have become increasingly accepted for aerodynamic shape optimisations due to their low computational cost. However, use of CAD-based parametrisations for aerodynamic gradient-based shape optimisation is not widely used, one reason being that current CAD systems to do not compute derivatives. In this work, we present the automatically differentiated (AD) version of Open Cascade Technology (OCCT) CAD kernel which can provide derivatives with respect to CAD parameters. OCCT is differentiated in block-vector AD mode which significantly reduces the cost for computing the derivatives. This work contains further OCCT extension for NURBS-based optimisation with intersecting patches and a description of the surface mesh movement linked to the change of the intersection line. These techniques are applied to the drag reduction of the NASA Common Research Model via the modification of the intersection between the root fairing and the wing