Roll dynamic stability of an autonomous underwater vehicle with a fish-like hull shape

An autonomous underwater vehicle designed and manufactured with fish-like hull shape in order to subsea pipeline and cable inspection. The behavior of the vehicle is analysed hydrodynamically. Not only does having high hydrodynamic stability decrease energy consumption because of high course keeping ability, but also it facilitates dynamic behavior control of robot regarding the disturbances like marine currents in water. Roll dynamic instability would be an adverse phenomenon for underwater vehicles results in deviation from the main path. After mentioning governing motion equations of vehicle, hydrodynamic moment acting on the body has been computed numerically using computational fluid dynamics. The robot is assumed to be a solid body and the flow passing over it is considered steady and incompressible. Having extracted relationship between moment and flow angular velocity, the linear hydrodynamic coefficient needed for stability analysis is estimated. Using this damping coefficient, roll dynamic stability of the robot has been evaluated. To ensure accuracy of numerical results, computations are compared with axisymmetric body designed and manufactured in Ship Hydrodynamic Department of David Taylor Research Center; Comparisons show firmly good agreement with experiments. Results reveal that roll dynamic stability of proposed hull shape with triangular cross section is 10 times as great as that of conventional axisymmetric body with circular cross section.