Coupled depth-integrated and Navier–Stokes modeling of wave–current–structure interactions

This study presents a domain-decomposition framework that couples a fully nonlinear, depth-integrated wave–current model with a Navier–Stokes/VOF computational fluid dynamics (CFD) solver to achieve accurate and efficient simulations of complex wave–current–structure interactions. Unlike potential-flow or Boussinesq-based couplings, the depth-integrated component resolves wave transformation from deep to shallow water and vertically sheared currents, providing phase-resolving free surface elevations and velocity fields to a localized CFD domain. Coupling is achieved through compact relaxation zones with spatially weighted source terms that ensure effective wave–current generation and absorption, while the CFD solver is confined to the near-field region to resolve detailed fluid–structure interactions. Additional efficiency is achieved by initializing the CFD solver with flow fields precomputed by the depth-integrated model, avoiding the long propagation and spin-up phases typical of standalone CFD. Validation against analytical solutions and laboratory experiments includes (1) nonlinear deep-water wave propagation, (2) shoaling over a bar, (3) multidirectional random seas over a submerged shoal, (4) focused wave–cylinder interactions, and (5) wave–sheared-current–cylinder interactions. The model reproduces both wave kinematics and structural loading with high accuracy, achieving more than an order-of-magnitude gain in efficiency relative to full-domain CFD. The framework therefore offers a practical pathway to extend high-fidelity CFD capabilities toward realistic, large-scale coastal and ocean engineering applications. • Developed a domain-decomposition framework coupling a depth-integrated model with CFD. • Enabled efficient wave and current generation and absorption through compact relaxation zones. • Validated across deep-water, shoaling, irregular, and focused wave cases with strong agreement. • Accurately reproduced interactions of focused waves, vertically sheared currents, and cylinders. • Achieved more than an order-of-magnitude efficiency gain compared with full-domain CFD.