Hydrodynamic efficiency of suspended horizontal rows of half pipes used as a new type breakwater

The hydrodynamic efficiency (effect of structure on incident wave attenuation) of a new type breakwater was studied using physical models under regular waves. The breakwater was consisted of one or more horizontal rows of half pipes suspended on supporting piles. The hydrodynamic efficiency of the breakwater was validated through calculation of the wave transmission, reflection and energy dissipation coefficients for different wave and structural parameters. Results indicated that the transmission coefficient decreases with increasing the relative wavelengths (h/L and B/L), wave steepness (H-i/L) and relative breakwater width (B/d), and it increases with decreasing the relative draft (D/h). The reflection and dissipation coefficients take the opposite trend. The proposed breakwater system is more efficient than the smooth plate type by about 5 to 25\%. The use of a second row improves the breakwater efficiency by about 20 to 50\% and the use of the third row improves the efficiency by about 5 to 15\% more than the two rows system. Empirical equations were developed for estimating the transmission and reflection coefficients. The results of these equations were compared with other experimental and theoretical results giving a reasonable agreement. The proposed breakwater type was efficient when compared with other breakwater systems. (C) 2013 Elsevier Ltd. All rights reserved.