The method of determination of transient hydrodynamic coefficients for a single DOF underwater manipulator

In this work a single degree-of-freedom (DOF) underwater manipulator operating in still water is considered. The paper presents the method of determination of transient hydrodynamic coefficients for the robotic arm, based on previously established time-dependent hydrodynamic load which can be obtained either from experiments or numerical simulations. The method involves normalization of the coefficients by the relative distance traveled by the center of mass of the arm. This enables us to form an approximation function for each coefficient dependent only on the shape of the manipulator. The so obtained approximation functions allow computing the hydrodynamic load and coefficients for the particular manipulator operating under any kinematic conditions or for the manipulator of different size, but geometrically similar to the investigated one, without the need of repeating expensive experimental research or complex simulations. In the present study the transient hydrodynamic load was obtained by the use of CFD simulations with dynamic mesh employed to generate the motion of the arm, performed for several kinematic conditions, differing in angular velocity and angular acceleration.