Mechanical Engineering - Research Publications
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ItemIdentifying regions of importance in wall-bounded turbulence through explainable deep learning(NATURE PORTFOLIO, 2024-05-13)Despite its great scientific and technological importance, wall-bounded turbulence is an unresolved problem in classical physics that requires new perspectives to be tackled. One of the key strategies has been to study interactions among the energy-containing coherent structures in the flow. Such interactions are explored in this study using an explainable deep-learning method. The instantaneous velocity field obtained from a turbulent channel flow simulation is used to predict the velocity field in time through a U-net architecture. Based on the predicted flow, we assess the importance of each structure for this prediction using the game-theoretic algorithm of SHapley Additive exPlanations (SHAP). This work provides results in agreement with previous observations in the literature and extends them by revealing that the most important structures in the flow are not necessarily the ones with the highest contribution to the Reynolds shear stress. We also apply the method to an experimental database, where we can identify structures based on their importance score. This framework has the potential to shed light on numerous fundamental phenomena of wall-bounded turbulence, including novel strategies for flow control.
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ItemNo Preview AvailableThe effect of cleaning and repainting on the ship drag penalty(TAYLOR & FRANCIS LTD, 2021-07-01)Although the hull of a recently dry-docked large ship is expected to be relatively smooth, surface scanning and experimentation reveal that it can exhibit an "orange-peel" roughness pattern with an equivalent sand-grain roughness height ks = 0. 101 mm. Using the known ks value and integral boundary layer evolution, a recently cleaned and coated full-scale ship was predicted to experience a significant increase in the average coefficient of friction %ΔC¯f and total hydrodynamic resistance %ΔR¯T during operation. Here the report also discusses two recently reported empirical estimations that can estimate ks directly from measured surface topographical parameters, by-passing the need for experiments on replicated surfaces. The empirical estimations are found to have an accuracy of 4.5 - 5 percentage points in %ΔC¯f.
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ItemNo Preview AvailableNon-k-type behaviour of roughness when in-plane wavelength approaches the boundary layer thickness(CAMBRIDGE UNIV PRESS, 2021-01-22)Abstract
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ItemNo Preview AvailableThe Effects of Anisotropic Surface Roughness on Turbulent Boundary-Layer Flow(The University of Queensland, 2020-01-01)