A numerical investigation of tsunami-induced scour around onshore coastal structures

Tsunami-induced scour around onshore coastal structures is a critical mechanism contributing to foundation instability and structural failure during extreme coastal hazard events. Although laboratory investigations have provided valuable insight into tsunami-induced scour processes, high-resolution numerical modelling is required to resolve the cou-pled flow, sediment-transport, and bed-deformation mechanisms governing local scour development. This study presents a three-dimensional numerical investigation of scour around an onshore cylindrical structure using the OpenFOAM-based SedInter-Foam solver.
The numerical model is developed from con-trolled laboratory flume experiments reported by McGovern et al. (2019) and Amiri et al. (2025). The computational domain reproduces the experimental wave flume geometry, structure configuration, sed-iment bed, and hydraulic conditions to enable direct comparison with measured data. The governing equations are based on the Reynolds-averaged Na-vier-Stokes formulation, with the air-water inter-face captured using the Volume of Fluid method. Sediment-water interaction is represented through granular rheology and interphase momentum-exchange terms, allowing sediment transport and bed deformation to be simulated directly. A struc-tured hexahedral mesh generated is applied throughout the computational domain, with local refinement layers introduced around the cylindrical structure to improve resolution of near-wall hydro-dynamics and sediment transport processes. Relaxa-tion zones are implemented at the inlet and outlet boundaries to generate the incoming wave and min-imise artificial reflection.
A comparable Eulerian multiphase modelling approach has previously been applied by Tiwari et al. (2026) to estimate current-induced scour around cofferdam structures, demonstrating its suitability for resolving sediment-water interaction and local bed deformation under hydraulic forcing. The pre-sent study extends this approach to tsunami-induced scour by applying it to a transient 20 s wave condi-tion around an onshore coastal structure. The nu-merical simulations are used to investigate free-surface evolution, near-structure flow behaviour, sediment transport patterns, and scour-depth devel-opment under wave-induced forcing. Comparisons between numerical and experimental results are used to evaluate the capability of the SedInterFoam framework for modelling tsunami-induced scour processes and its applicability to future coastal haz-ard assessment and engineering design.