A numerical flume for waves on variable sheared currents using smoothed particle hydrodynamics (SPH) with open boundaries

Combinations of waves and currents exist in a wide range of marine environments. The resulting, often complex, combined wave-current conditions largely determine the loading, response and survivability of vessels, offshore platforms and systems. Smoothed Particle Hydrodynamics (SPH) has becoming increasingly popular for freesurface flow problems which do not require special treatment to detect the free surface. The present work implements open boundaries for wave-current conditions within the SPH-based DualSPHysics solver. Open boundaries are applied for the generation of wave-alone, current-alone and combined wave-current conditions. A modified damping zone acting on the vertical velocity component is used for wave absorption and combined with open boundaries to allow particles to leave or enter the fluid domain when a current exists. Results of wave-alone (regular, irregular and focused) and current-alone (uniform, linearly sheared and arbitrary sheared) test cases demonstrate a general numerical flume is achieved. Tests of focused waves interacting with arbitrary sheared currents are validated with analytical linear solutions for surface elevation and velocities, demonstrating excellent agreement. The numerical flume may be extended to steep waves well suited to SPH and thus enable modelling complex and extreme wave-current conditions interacting with offshore platforms and systems.