Experimental research on horizontal rotation of ROV induced by external forces near sea surface

A remotely operated vehicle (ROV) is lowered by means of an underwater cable from a vessel. The ROV near the sea surface is forced to rotate due to external forces. So, we focused on the waves and the wake flow of thrusters as possible causes of the external forces. And we conducted experiments using a model of the ROV in a tank. Two kinds of experiments were conducted. One is to investigate the influence of the waves. The experiments were conducted by changing a wave height, a wave length and a submerged depth of the model. And configuration of the model such as the type of fins and outer covers were also changed. The other is to investigate the influence of the wake flow of the thrusters. The experiments were conducted by changing a horizontal offset of a propeller and the submerged depth of the model. And the type of the fins was also changed. As a result, the horizontal rotation was observed in some cases. It is found that the wave and the wake flow were possible causes inducing the horizontal rotation of the ROV. According to the results, the wave characteristics influence on the generation of the horizontal rotation. The offsets and the submerged depth influence on the generation of the horizontal rotation in the wake flow as well. It is also found that a horizontal fin and extended vertical fins will be one of the countermeasures to improve the characteristics of the horizontal rotation.