Hydrodynamic behaviour of dual bio-mimetic tubular sponge systems under wave forcing

Coral reefs serve as critical habitats for diverse marine species and function as natural barriers against coastal flooding. However, these ecosystems are increasingly threatened by anthropogenic activities and climate change. To mitigate such impacts, bio-mimetic technologies, particularly single bio-mimetic sponges inspired by natural forms, have been proposed as protective interventions for coral reefs. This study investigates the influence of dual bio-mimetic tubular sponges arranged in various configurations (parallel, perpendicular, and at a 45° angle) and spacing on wave-induced hydrodynamics. A three-dimensional Reynolds-Averaged Navier–Stokes (RANS) model employing the standard k–ω SST turbulence closure was utilized to simulate the complex flow dynamics associated with these structures. To enhance visualization and qualitatively illustrate flow patterns and regions of vortical motions, Surface Line Integral Convolution (SurfaceLIC) and three-dimensional stream tracing techniques were applied. The results demonstrate that dual sponge configurations can increase turbulent kinetic energy (TKE) by approximately 50 % while reducing wave energy dissipation by up to 54 %. Image processing analyses further reveal that both the spatial arrangement and interspacing of the sponges significantly influence the morphology of the effluent cloud (EC), which transitions from symmetric, rounded forms to elongated or mirror-imaged patterns. Notably, longitudinal sponge arrangements generate double-paired recirculating vortices, which may exacerbate seabed scouring on sandy substrates. These findings offer novel insights into the hydrodynamic behavior induced by dual bio-mimetic tubular sponges, contributing to a broader understanding of fluid-structure interactions and informing future strategies for coastal ecosystem management. • The sponges locally attenuate wave energy, limited to about one wavelength. • TKE increases by over 50 % when diagonal sponge positioning is used. • Distinct arrangement of sponges induces elliptical circulation patterns in the wake. • Interaction of outflow and bleeding flow generates dual recirculation zones.