Abstract
The use of a multi-functional autonomous underwater vehicle (AUV) as a platform for making turbulence measurements in the ocean is developed. The layout optimization of the turbulence package and platform motion performance are limitation problems in turbulent AUV design. In this study, the computational fluid dynamics (CFD) method has been used to determine the optimized layout position and distance of the shear probe integrated into an AUV. When placed 0.8 D ahead of the AUV nose along the axis, the shear probe is not influenced by flow distortion and can contact the water body first. To analyze the motion of the turbulence AUV, the dynamic model of turbulence AUV for planar flight is obtained. Then, the mathematical equations of speed and angle of attack under steady-state motion have also been obtained. By calculating the hydrodynamic coefficients of the turbulence AUV and given system parameters, the simulation analysis has been conducted. The simulation results demonstrated that the speed of turbulent AUV is 0.5–1 m/s, and the maximum angle of attack is less than 6.5°, which meets the observation requirements of the shear probe. In addition, turbulence AUV conducted a series of sea-trials in the northern South China Sea to illustrate the validity of the design and measurement. Two continuous profiles (1000 m) with a horizontal distance of 10 km were completed, and numerous high-quality spatiotemporal turbulence data were obtained. These profiles demonstrate the superior flight performance of turbulence AUV. Analysis shows that the measured data are of high quality, with the shear spectra being in very good agreement with the Nasmyth spectrum. Dissipation rates are consistent with background shear. When shear velocity is weak, the measurement of dissipation rate is 10−10 W Kg−1. All indications are that the turbulence AUV is suitable for long-term, contiguous ocean microstructure measurements, which will provide data needed to understand the temporal and spatial variability of the turbulent processes in the oceans.
Highlights
Because the shear probe is very sensitive to the autonomous underwater vehicle (AUV) speed and AOA, the dynamic model of the turbulence AUV was developed by using an analytical method based on Newton–Euler and its motion performance was simulated
As a mobile autonomous ocean observation platform, AUV has the advantage of long endurance and large range, being unaffected by sea conditions
The presented work and field tests demonstrate the successful integration of the cross-platform instrument for microstructure turbulence measurements (CPMTM) into the AUV
Summary
More and more observations show that ocean turbulence is intermittent in time and space, and noncontiguous in regimes of strong stratification [7] To resolve this structure, researchers began to measure turbulence with horizontally profiling instruments, including towed bodies, submersibles, and moored platforms. The second limitation of AUV-based turbulence measurements is motion performance, including the angle of attack (AOA or α) and the speed (U), which are very sensitive to microstructure shear estimation. Because the shear probe is very sensitive to the AUV speed and AOA, the dynamic model of the turbulence AUV was developed by using an analytical method based on Newton–Euler and its motion performance was simulated.
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