The motion of a deep-sea remotely operated vehicle system Part 2: Analytical model

We developed a continuous linear-elastic one-dimensional analytic model that should accurately represent a vertically tethered system subject to surface excitation. Our model accurately predicts: (a) the transfer function between the motion of the ship and cage, (b) the transfer function between ship motion and tension in the tether and (c) the natural frequency and its harmonics of the ROPOS deep-sea ROV system for depths between 0 and 1765 m up to moderately rough sea conditions. By solving the ship-cage motion transfer function for the onset of zero tension in the tether, we were able to predict the amplitude of ship motion that triggers a snap load. The solution to our model requires only two non-dimensional parameters representing the mass ratio of the cage and tether and the force ratio of drag to tension. The predicted transfer function and natural frequency are not excessively sensitive to the value of these parameters for the ROPOS ROV system. (C) 1999 Elsevier Science Ltd. All rights reserved.