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

Supun Randeni P,Remo Cossu,Alexander Forrest,Dev Ranmuthugala,Zhi Leong

doi:10.3390/jmse5030025

Supun Randeni P, Remo Cossu + Show 3 more

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https://doi.org/10.3390/jmse5030025

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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.

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Measuring water column velocities is an essential component of physical oceanographic surveys but is important for many applications, such as determining sediment transport [1] and assessing the turbulent flux in the surface mixed layer [2]
This study presents the WVAM method to estimate the flow velocity components of a turbulent water column, relative to the Earth, in x, y, and z axes of the Autonomous Underwater Vehicle (AUV) body-fixed coordinate system using the motion response of the vehicle
The water column velocities were determined by calculating the difference between the motion responses of the AUV observed in calm and turbulent water column conditions

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Introduction

Measuring water column velocities is an essential component of physical oceanographic surveys but is important for many applications, such as determining sediment transport [1] and assessing the turbulent flux in the surface mixed layer [2]. Subsea mobile platforms, such as autonomous underwater vehicles (AUVs), provide increased potential for such surveys that are logistically not possible using surface-borne techniques. AUVs are more reliable to undertake missions in areas logistically difficult or inaccessible for surface vessels and other types of underwater vehicles such as remotely-operated vehicles (ROVs) and manned submersibles. For this reason, combined with the relative stability of the vessel and being decoupled from surface noise and reflectance, AUV mounted ADCPs have been adopted to measure water column velocities [5,6]

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