Active learning-based hydrodynamic shape optimization and numerical simulation of auxiliary structures for circular bridge piers

Abstract

Cylinders as a common form of bridge piers are widely used in engineering practices, yet the hydrodynamic forces and local scouring of the cylinder due to the fluid flow cause significant concern about the functionality of circular bridge piers. In this paper, two novel auxiliary structural types are proposed for passive control of flow around bridge piers, and their optimal structural parameters are determined efficiently using a surrogate model-based hydrodynamic shape optimization framework. Specifically, a Kriging-based active learning algorithm is proposed for hydrodynamic shape optimization of auxiliary structures, which are placed at the rear and both the front and rear of a cylinder. The hydrodynamic performance of the circular bridge pier with the optimized auxiliary structures (F3 and F6) is investigated through 2D and 3D numerical simulations. The effectiveness of the optimized auxiliary structures in mitigating the adverse effect of local scouring around a cylinder is also revealed through a case study. Results indicate that the optimized auxiliary structures F3 and F6 can dramatically reduce the drag coefficient compared with the bare cylinder, i.e., with a reduction rate of 69.8% and 77.2%, respectively; and the reduction rate is more pronounced for the lift coefficient, i.e., with a reduction rate higher than 90% for both F3 and F6. The reduction of drag and lift coefficients is mainly attributed to the positive effects of the optimized auxiliary structures for adjusting the pressure distribution around the cylinder, elongating the free shear layer, improving the wake stability etc. Interestingly, the auxiliary structure F6 also exhibits a high potential to mitigate the scouring effect of fluid flow around a cylinder by decreasing the flow velocity and bed shear stress around the cylinder. However, it should be noted that placing the auxiliary structure at the rear of a cylinder (such as the auxiliary structure type F3) could introduce an adverse effect on reducing local scouring. This study provides valuable guidance for designing effective auxiliary structures for passive control of fluid flow around cylinders.