Benefits of Random Wave Testing in Shallow Basin Physical Models for Harbor Wave Tranquility Studies

Abstract

Laboratory experiments were conducted by generating regular and random short period gravity waves on a lagoon type of artificial harbor with a long approach channel. Harbour breakwaters were removed in order to understand the wave attenuation and transformation phenomenon during the waves travel along long approach channel with different side slopes. Regular and random short period gravity waves were generated and time series of surface elevations were recorded simultaneously at salient locations along the channel and shallower sea bed adjacent sides in the model. The phenomenon of wave attenuation was noticed during all the side slopes studied and with the increase in channel section a gradual increase in wave attenuation was observed. This wave energy dissipation was 87% for vertical, and increased gradually to 90%, 92% and 93% for side slopes 1/5, 1/10 and 1/20 respectively. The results of the experiments show that random wave provides more realistic results by attaining the fully developed sea state within a short reach from the wave generation where partially developed wave condition prevails. Testing with regular waves for different channel slopes indicated more variation in the heights measured at different locations in the channel as compared to random waves. This phenomenon may be attributed to single wave height and period generated in regular wave as compared to multi wave heights and periods in random wave generation. Based on these findings it is recommended to carryout laboratory tests for harbour wave tranquility with random waves for more realistic results.