Determining the Horizontal and Vertical Water Velocity Components of a Turbulent Water Column Using the Motion Response of an Autonomous Underwater Vehicle

Abstract

This work introduces a new method to calculate the water velocity components of a turbulent water column in the x, y, and z directions using Autonomous Underwater Vehicle (AUV) motion response (referred to as the 'WVAM method'). The water column velocities were determined by calculating the difference between the motion responses of the vehicle in calm and turbulent water environments. The velocity components obtained using the WVAM method showed good agreement with measurements from an acoustic Doppler current profiler (ADCP) mounted to the AUV. The standard deviation between the two datasets were below 0.09 m s −1 for the velocity components in the x, y, and z directions, and were within the uncertainty margin of the ADCP measurements. With the WVAM method, it is possible to estimate the velocity components within close proximity to the AUV. This region encompasses the vehicle boundary layer and the ADCP blanking distance, which is not typically resolved. Estimating vertical and horizontal velocities around the boundary layer of the AUV is important for vehicle navigation and control system optimization, and to fill the blanking distance gap within a water column velocity profile, which is important for flow field characterization. The results show that it is possible to estimate the flow field in the vicinity of AUVs and other self-propelled vehicles.

Autonomous Underwater Vehicle Motion Response: A Nonacoustic Tool for Blue Water Navigation

“…Above this threshold angle, the hydrodynamic coefficients usually become nonlinear. The hydrodynamic coefficients estimated for the simulation model using the curve fitting method are only valid for small angles of incidence of the vehicle, that is, when the coefficients are in the linear range (Randeni et al, 2015b). Therefore, when the pitch and yaw angles are above the linear range, the accuracy of the simulation model decreases, and the uncertainty of the vertical and transverse water velocity components obtained from the WVAM method increases.…”

“…For the WVAM method (Randeni et al, 2015a(Randeni et al, , 2015b, the AUV needs to undergo a straight line, constant (a) Omarama Primary School (Lake Ohau, New Zealand) students inspecting the Gavia, the modular AUV that was utilized to test the WVAM method; (b) the tested configuration of the vehicle; and (c) the body-fixed coordinate system (origin at the center of buoyancy-marked by the circle) showing the ADCP beam geometry.…”

“…In this method, the water velocities are determined by comparing the motion response of the vehicle when operating within turbulent and calm water environments. A key advantage of the WVAM method is that it is able to estimate the flow velocities at the vehicle's center of buoyancy; however, the authors indicated that the accuracy of the WVAM method might vary with the intensity of the measuring velocity components (Randeni et al, 2015b). That is, the precision of the water velocity measurements from a highly turbulent environment with relatively large velocities may be different than those of low turbulence conditions with lower velocities.…”

“…The authors previously introduced a nonacoustic method to calculate the water velocity components of a turbulent water column using the AUV motion response without the aid of an ADCP referred to as the WVAM method (Randeni et al, 2015b). In this method, the water velocities are determined by comparing the motion response of the vehicle when operating within turbulent and calm water environments.…”

Autonomous Underwater Vehicle Model-Based High-Gain Observer for Ocean Current Estimation

“…The estimation error means of the HGO using the LMI are smaller than the pole placement method in both xi and yi axes, which results in an estimation improvement of 45 % and 1% respectively. [20]. During the field tests, the AUV underwent a straight-line, constant altitude mission at 10 m depth as illustrated in Fig.…”