Flow Memory Effect on Open-Frame Remotely Operated Vehicle Motion

The flow memory effect is a kind of viscous force caused by acceleration between continuous phases and underwater vehicles and the development of the boundary layer near the interfacial surface. This paper establishes a 6-degrees-of-freedom unsteady equation of motion describing the flow memory effect on viscous hydrodynamic loads. Motion simulations based on the unsteady and steady equations of motion for a work-class open-frame remotely operated vehicle are studied. Comparative studies show that the flow memory effect decreases the roll amplitude by over 50% at the natural frequency and has a greater impact on the motions in directions without control forces. The flow memory increases the lateral distance of rotation motions by over 10%. Under the flow memory effect, velocity fluctuations that persist over 2–5 times the length of the remotely operated vehicle are induced after the thrust control stops. The application of the unsteady equation of motion as part of a controller is verified through simulation experiments. A sudden motion in the process of rotation is designed to study the improvement of the control ability of the unsteady model. The experimental results suggest a performance improvement of ~30% over the steady-model-based controller when the roll angle error reaches the extreme value. The lower sensitivity of the unsteady-model-based controller is proved by motion control under multiple gains.