Wave transmission of tandem breakwater with various angles of wave attack

Abstract

This paper explains the study of wave transmission of a tandem breakwater physically modelled with various angles of wave attack. Tandem breakwater is an arrangement of a conventional rubble mound breakwater sheltered by a submerged breakwater located at some distance. The experimental works were carried out in a wave basin with dimensions of 25 m length, 18 m width and 1.2 m height. Setting still water depth of 0.45 m, 0.50 m and 0.60 m, waves with T=2.05 sec, 2.20 sec and 2.50 sec were generated from a piston type multi element wave maker. Multi directional waves were generated with angle of wave attack of 0, 15, 30 and 60 degree. Wave gauge was located at eight different positions to record water level and by using the measured data, the wave transmission, Kt was calculated. Besides the effect of various angle of wave attack, the effects of relative distance between submerged and rubble mound breakwater towards wave transmission was investigated. Experiments are done for two breakwater structures with different spacing (X/d = 8.33-15.56) and for various heights (h/d = 0.42-0.56). The results show that for angle of wave attack of 0 degree, the wave height attenuation (WHA = 1-Kt) achieved are 24.5% (0.45m), 20.7% (0.50m) and 10.4% (0.60 m), respectively. WHA are increasing along with the increasing of angle of wave attack but it is declining with increasing of water depth. The highest WHA is for the depth of 0.45m and at the angle of 60°, which is 55.02%. The values of Kt for X/d = 10.0-13.33(6 m) are more approaching to 0 compare to X/d = 6.67-8.89(4 m). Kt drops with an increase in H/gT2 and increase in relative depth, d/gT2 as submerged breakwater is efficient in breaking the steeper waves.