Cad-based adaptive shape parameterisation for aerodynamic shape optimisation

Non-Uniform Rational B-Splines (NURBS) have become the industrial standard to represent and exchange a CAD geometry between CAD/CAE systems. CAD-based shape parameterisation uses parameters of a CAD model to modify the shape which allows to integrate a CAD model into the design loop. However, feature-trees of typical commercial CAD systems are not open and obtaining exact derivatives for gradient-based optimisation methods is not possible. Using the CAD-based NSPCC approach a designer can deform multiple NURBS patches in the design loop without violating geometric and/or thickness constraints. The NSPCC approach takes CAD descriptions as input and perturbs the control points of the NURBS boundary representation to modify the shape. In this work, an adaptive NSPCC method is proposed where the optimisation begins with a coarser design space and adapts to finer parametrisation during the design process where more shape control is needed. The refinement sensor is based on a comparison of smoothed node-based sensitivity compared to its projection onto the shape modes of the current parametrisation. Both static and adaptive parametrisation methods are coupled in the adjoint-based shape optimisation process to reduce the total pressure loss of a turbine blade internal cooling channel. The discrete adjoint flow solver STAMPS is used to compute the flow fields and their derivatives w.r.t. surface node displacements. The shape derivatives for gradient-based optimisation are obtained by application of reverse mode AD to the NSPCC CAD kernel. Since a CAD model is kept inside the design loop, the resulting optimal shape is directly available in CAD for further analysis or manufacturing. Based on the analysis regarding quality of the optima and rate of convergence of the design process adaptive NSPCC method outperforms static NSPCC approach

Probing long-range correlations in the Berezinskii-Kosterlitz-Thouless fluctuation regime of ultra-thin NbN superconducting films using transport noise measurements

We probe the presence of long-range correlations in phase fluctuations by analyzing the higher-order spectrum of resistance fluctuations in ultra-thin NbN superconducting films. The non-Gaussian component of resistance fluctuations is found to be sensitive to film thickness close to the transition, which allows us to distinguish between mean field and Berezinskii-Kosterlitz-Thouless (BKT) type superconducting transitions. The extent of non-Gaussianity was found to be bounded by the BKT and mean field transition temperatures and depend strongly on the roughness and structural inhomogeneity of the superconducting films. Our experiment outlines a novel fluctuation-based kinetic probe in detecting the nature of superconductivity in disordered low-dimensional materials.Comment: submitted to PR

Non-linear IVIV characteristics in two-dimensional superconductors: Berezinskii-Kosterlitz-Thouless physics vs inhomogeneity

One of the hallmarks of the Berezinskii-Kosterlitz-Thouless (BKT) transition in two-dimensional (2D) superconductors is the universal jump of the superfluid density, that can be indirectly probed via the non-linear exponent of the current-voltage $IV$ characteristics. Here, we compare the experimental measurements of $IV$ characteristics in two cases, namely NbN thin films and SrTiO$_3$-based interfaces. While the former display a paradigmatic example of BKT-like non-linear effects, the latter do not seem to justify a BKT analysis. Rather, the observed $IV$ characteristics can be well reproduced theoretically by modelling the effect of mesoscopic inhomogeneity of the superconducting state. Our results offer an alternative perspective on the spontaneous fragmentation of the superconducting background in confined 2D systems.Comment: Final version, as publishe

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

BIOLOGY OF EPILACHNA SEPTIMA DIEKE (COCCINELLIDAE : COLEOPTERA) INFESTING MOMORDICA CHARANTIA WITH A NOTE ON ITS FEEDING DAMAGE

A study on the biology of Epilachna septima Dieke, was conducted from April to August, 1995, in the Department of Zoology, Madras Christian College (MCC), Madras. The descriptions, measurements and the period occupied by the different life stages of E. septima including the pre-oviposition, oviposition and post-oviposition period have been presented. An account on the feeding damage by the developing stages of the insect has been included