Immersed boundary method in the TELEMAC three-dimensional model for a diversion-wall lateral intake

Submerged diversion structures are commonly employed in lateral water withdrawal projects to enhance flow patterns and stability. In numerical simulations, terrain elevation methods are traditionally adopted to represent submerged obstacles. However, such simplifications cannot accurately reproduce underwater structures with vertical sidewalls. To address this limitation, an improved immersed boundary method (IBM) is developed and integrated within the TELEMAC hydrodynamic modeling software (TELEMAC) via its three-dimensional hydrodynamic module (TELEMAC-3D). The method is assessed for a lateral water intake at the Rong River Estuary. First, the submerged diversion wall is simulated using IBM boundary conditions, and numerical results exhibit strong agreement with experimental data, with most relative errors with 4%. Subsequently, simulations comparing the classical mesh-deletion method, the terrain-elevation method, and IBM are conducted for conditions where the diversion wall height matches the water surface elevation. The deficiencies inherent in the terrain-elevation approach are highlighted through these comparisons. Furthermore, by systematically refining mesh quality, the comparative analysis underscores IBM's superior capability to accurately simulate vertical underwater structures. Notably, the IBM approach achieves equivalent simulation accuracy while reducing computational time by approximately 80%. These findings indicate that IBM significantly enhances numerical modeling efficiency and accuracy for submerged hydraulic structures.