Analysis of the Dynamic Response of ROV System Experiencing Vessel Motion During Deployment and Recovery Processes

Abstract Remotely operated vehicle (ROV) system is significantly affected by the excitations coming from the top-end vessel motion and the hydrodynamic disturbances. Especially, during initial deployment and final recovery stages, the cable length might be so short that the relative motion between the ROV and the vessel may cause a severe collision. At the same time, the cable tension can also be changed by the ROV motion, and consequently cable slack may occur, which seriously affects structural safety. This study focuses on the dynamic responses of ROV system induced by the vessel heave during initial deployment and final recovery processes. Through numerical simulation, the ROV response and cable tension time histories of the ROV system with moving boundary, also considering hydrodynamic force on ROV, are presented. It is found that the vessel heave induces the parametric excitation response to the ROV system. The influences of vessel motion amplitude, vessel motion frequency, and initial angular displacement of ROV on the responses of ROV system are discussed. Meanwhile, the governing equation of ROV motion with a vertical moving boundary is established, and a dimensionless control parameter called amplitude-frequency factor which characterizes the strength of vessel heave is proposed. Under the nonlinear damping generated by hydrodynamic force, the parametric resonance can be excited when the amplitude-frequency factor reaches the threshold. The hydrodynamic damping ratio is fitted based on the numerical simulation results. Finally, under consideration of the nonlinear damping effect, the unstable regions of vessel motion amplitude and frequency at different displacement amplitudes are obtained.