Determining the weights of two types of artificial reefs required to resist wave action in different water depths and bottom slopes

WOS: 000270162500002The interaction between waves and artificial reefs (ARs; a hollow cube weighing 8.24 kN (0.84 t) and a water pipe weighing 1.27 kN (0.13 t)) in shallow waters was investigated with respect to variations in design weight, orientation (for cube: 45 degrees and 90 degrees angles, for pipe; 0 degrees, 90 degrees, and 180' angles to flow), depth (1-20 m), and bottom slope (10(-1), 30(-1), and 50(-1)). Physics equations and FLUENT software were used to estimate resisting and mobilising forces, and drag coefficients. Drag coefficients for the hollow cube were 0.76 and 0.85 at 45 degrees and 90 degrees angles to the current, respectively, and 0.97, 0.38, and 1.42 for the water pipe at 0 degrees, 90 degrees, and 180 degrees angles to the current, respectively. Deepwater offshore wave conditions at six stations were transformed into shallow nearshore waters representative of the artificial reef site. Waters deeper than 12 and 16m are safe to deploy blocks with angles of 45 degrees and 90 degrees, respectively. However, water pipes constructed at angles of 90 degrees and 180 degrees to the current were estimated as being unstable for 365 out of 720 cases at all stations (only one station was stable for all cases). Water pipes angled at 0 degrees were found to be stable in all 360 cases. Slope had a significant effect on weight and depth. Results from this study provide an important reference for engineers performing projects aiming to increase the performance and service life of ARs. (C) 2009 Elsevier Ltd. All rights reserved