Experimental Study of a Method to Attenuate Surface Waves Using Artificially Generated Surface Currents

摘要

Previous studies showed the effectiveness of laterally-sheared wakes of towed rigid grids in achieving substantial attenuation of following regular wave trains by refraction. Significant attenuation could be obtained in wakes with widths comparable to the incident wave length, with depths of the order of 10% of the incident wave length and with grid tow speeds about 10% of the incident wave celerity. In the present study, model-scale experiments were conducted to extend the earlier results to the cases of random waves and of oblique waves, to determine attenuation for two possible operational scenarios for the prototype application of this method, and to test the effectiveness of a towed net to replace the towed rigid grid for full-scale use. Test results for random following seas were consistent with earlier tests with regular following waves. For oblique seas, the region of attenuation in the wake of the grid was shifted laterally towards the downwave side of the wake. In addition, peak attenuation was less than that expected from a simple extrapolation of the semi-empirical prediction formula developed for following seas to the case of oblique waves. Model tests with a towed flexible net held open with attached paravanes revealed that similar levels of attenuation could be obtained with this apparatus as that achieved with the towed rigid grids. Field tests of this wave attenuation method was conducted at intermediate scale in New York Harbor and at full-scale in the ocean off Miami.