Validation of a finite element model for slack ROV tethers

A three-dimensional lumped mass model was previously (Buckham et al., 1999) developed for use in simulating the dynamics of underwater remotely operated vehicles (ROVs). This paper presents the experimental validation of that model. In this experiment, the top end of a 4.12 m length of ROV tether was manipulated in a controlled aquatic environment, and video footage of the motion of the submerged tether was recorded. Simultaneously, the motion of the top end of the tether was recorded using a Litek Vscope 110/pro position sensing device. That motion data was then used to drive the numerical lumped mass model of the tether. The resulting tether motion was fed to an animation package, and the animation was compared to the video footage. Comparison of the experimental and simulated results showed only very minor differences between the real and simulated tether motions. An overestimation of the tether's bending stiffness is likely the reason for these differences. Analysis of the simulation results demonstrated that the bending forces generated in the tether maneuver approached the magnitude of the tension in the tether, and thus the inclusion of the bending effects is warranted.