Identification of Drag Force of the Underwater Vehicles

Abstract

An inverse analysis is conducted for the estimation of drag coefficient and wake's width in incompressible turbulent flows over the moving underwater bodies. The inverse analysis uses the laws of momentum and mass conservation for a control volume to estimate the drag coefficient and the wake's width from the measured velocity in the wake. The drag coefficient and wake's width are determined as unknown parameters by the Levenberg-Marquardt algorithm. The proposed inverse method is applicable for an environment without boundaries (e.g., the sea). Several experiments are conducted to evaluate the developed inverse algorithm. The wake velocity behind a cylinder located in the flow field is measured by a calibrated pitot tube and is used as an input to the algorithm. The cylinder is selected as the test body, because its hydrodynamic information is available in the literature. The effects of the tunnel's wall and the turbulence intensity are considered in the results of the algorithm. The estimated drag coefficient is validated by the values presented in the literature. The estimated wake-velocity profiles are fitted favorably with the measured velocities at the corresponding locations. It is shown that the proposed inverse method can be used to estimate the drag coefficient and wake's width of the underwater vehicles with very good accuracy.

A Simple Approach to Estimate the Drag Coefficients of a Submerged Floater

“…The method relies on residual thrust measurements, i.e., the difference between the propulsive and resistive forces, performed in a water flume that allows the flow velocity to be adjusted along with an evaluation of the relation between the swimmer’s propulsion and drag. In [ 32 ], the Levenberg–Marquardt algorithm is used to estimate the drag coefficient of an AUV in a calibrated pitot tube. While accurate measurements are obtained, to the best of our knowledge, there is no robust method for estimating the drag of any object in-situ in realistic sea conditions.…”