Design and dynamic modeling of ROVs: estimating the damping and added mass parameters

Accurate estimations of the added mass and damping parameters are required to obtain the dynamic model of Remotely Operated Vehicles (ROVs) underwater. However, theoretical derivations of these parameters are only available for standard shapes (e.g., sphere, cube) and empirical formulations for complex shapes are not accurate. Moreover, experimental measurements are expensive and cannot be measured in the preliminary stages of the design. In this paper, we propose an efficient and simple numerical method to calculate the added mass and damping parameters needed in the initial design of a ROV. The added mass parameters of a ROV built in-house are calculated using COMSOL Multiphysics by simulating the free harmonic damped oscillations in the six degrees of freedom. The measured translational added mass terms are compared to the ones calculated using the potential theory and agree with a relative difference below 8.1% in the sway and heave directions, and 17.3% in the surge direction. A higher difference is obtained in the surge direction because the values obtained using the potential energy neglect the viscous effects that dominate the added mass terms in that direction. The damping parameters are obtained by a fitting function that relates the damping force (or moment) and its corresponding linear (or angular) velocity calculated using ANSYS FLUENT. It is shown that the coupled terms in the damping matrix are negligible at low velocities. The workflow is applicable to any complex shape ROV to efficiently calculate the initial design parameters.

Automated summary

This paper proposes an efficient and simple numerical method to calculate the added mass and damping parameters needed in the initial design of a ROV, using simulations of free harmonic damped oscillations and software tools like COMSOL Multiphysics and ANSYS FLUENT. The experimental measurements compared well with the potential theory calculations for added mass terms, with relatively small differences, while damping parameters were obtained through fitting functions related to damping force and linear/angular velocity calculations.