Estimating movement and falling distances of underwater free-falling cuboid models for marine habitat enhancement structures considering horizontal water flow

Abstract

Considering the movement of quarried rocks falling freely in water is important, because these are often used in marine habitat enhancement structures such as artificial reefs. Few studies have accounted for the horizontal movement of these rocks due to water flow, which is likely to be significant in oceans. Consideration of horizontal water flows is important because these cause free-falling objects to move horizontally, and ultimately determine where they settle on the seabed. Thus, we estimated the movement and falling distances of free-falling quarried rocks in the presence of a horizontal water flow. First, we constructed a reference cubic model, the movement and falling distances of which were measured experimentally using high-speed camera and particle image velocimetry, and numerically simulated using the finite volume method. Consequently, the movement and falling distances of the cubic model were estimated successfully for various flow velocities, with relative errors <9%. Second, we estimated the movement and falling distances of 25 cuboid models. From the simulation results, for fixed dimensionless length, we identified significant correlations of dimensionless volume with dimensionless movement and falling distances, respectively. Finally, we confirmed that regression equations provided reasonably accurate predictions via simulation of another free-falling cuboid model.