Optimal Leading-Edge Geometry of a Three-Girder Deck Subjected to Hydrodynamic Loads Using CFD and Surrogate Models

The fairing, as an auxiliary structure attached to the deck body, plays an important role in mitigating the hydrodynamic loads on the deck. In this study, we first conducted a series of experiments to investigate the hydrodynamic performance of a three-girder deck under two different configurations, i.e., a bare deck and a deck with a circular fairing corresponding to a quarter-cylinder. Experimental observations showed that the effectiveness of this fairing is highly dependent on the flow conditions, generally leading to a reduction in drag coefficients while having a limited impact on lift coefficients. Subsequently, we focused on a representative hydraulic condition, which was simulated numerically using a CFD model implemented in OpenFOAM. The validated CFD model was then adopted to simulate the hydraulic characteristics of the system under identical hydraulic conditions (i.e., the same discharge and downstream water level) but with different fairing geometries, parameterized by a generalized hyperelliptic function. The drag coefficients obtained from simulations were used to build Kriging surrogate models, linking fairing geometry to force coefficients. This enabled efficient exploration of the design space and the identification of the optimal shape. Compared with the bare deck configuration, the optimized fairing reduced the drag coefficient by 15.5%, performing comparably to a circular fairing (14.0%). Flow field analysis confirmed that the presence of the fairing locally alters the flow characteristics. The optimized fairing was then tested under different hydraulic conditions to evaluate its robustness. The results showed that it is generally effective under critical conditions, confirming its performance stability.