This paper presents the dynamic modelling of a rigid-flexible tether management system (TMS) of ROV (Remotely-operated Underwater Vehicle) during the ROV launching and recovery processes. In the present study, modelling of TMS includes rigid-flexible multibody dynamics of a ROV, a tether and a rotating winch. The mathematical model of tether cable is developed based on the nonlinear finite element method called Absolute Nodal Co-ordinate Formulation (ANCF). Hook model was used to calculate the normal contact forces around the winch circumference, and the Coulomb model was used to calculate the friction forces. By applying the above, the simulation of launching and recovering process was carried out.

INTRODUCTION

The seabed contains mineral resources such as oil, natural gas, cobalt rich crust, submarine hydrothermal deposits, and rare earth mud. The technology development is carried out to utilize these resources effectively. ROV is used for research and development of these resources. ROV is an underwater vehicle that is connected to the mother ship by a tether cable consisting of signal lines and power lines. Because of its low bending stiffness and complex composition, its motion greatly affects the maneuverability of the ROV, and consequently, it complicates the job of a human pilot. Therefore, the pilots must have a competency and adequate training experience to operate the ROV in any scenario. For this purpose, an accurate ROV simulator is a promising and effective tool for training the operators.

In the literature, the motion analysis of ROV and tether cable has been carried out mostly using the lumped mass method (Buckhum et al. 2003 and Quiang et al. 2008). This method, has an advantage of ease of implementation exercises to the simple formation of mass matrix which is, in most cases, a diagonal matrix and stiffness matrices. On the other hand, the disadvantage is that the accuracy of describing the flexible bodies declarations decreases as the number of elements increase and deformation becomes larger and this does not lead to exact modeling of the mass matrix of the beam in case of an arbitrary rigid body motion. A numerical motion estimation method for ROVs including tether cable using ANCF were studied in (Suzuki, et al. 2017, 2018 and Htun, et al. 2019).

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