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Ocean turbulence measurement using an autonomous underwater vehicle

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Date Issued:
1997
Summary:
The complex dynamics of the oceans are only beginning to be understood. There is a wide range of dynamic scales in the ocean from the Gulf Stream, with scales as large as the ocean itself, to the microstructure scales of turbulent dissipation. The program of work presented in this dissertation involves the implementation of a turbulence measurement package on board a recently developed small autonomous underwater vehicle (AUV), as well as the design of an optimized AUV platform and the development of new oceanographic sensors for measurement of micro-structure velocity. Attention is focused on ensuring that the platform is sufficiently quiet since small-scale, low level measurements are easily contaminated by the measurement process, structural vibrations, rigid-body motions and electrical interference; particularly so with the requisite machinery of a self-propelled AUV. Successful measurement entails making suitable modification to the AUV and its mode of operation. In addition to optimization of the measurement platform, consideration is given here to the optimization of the sensors for flow measurement using an AUV. Included in the research are laboratory tests of the new probes and a successful mission in making high quality measurements of ocean turbulence. Modern adaptation of the well-known Pitot tube shows promise in being less sensitive to vehicle self motion as well as yielding a greater spectral range, thereby facilitating more accurate measurement. Comparisons with shear probes and hot film probes, conducted in an axisymmetric water jet and in a wind tunnel, suggest that the pressure probe, developed as part of the work presented here, resolves the dissipation scales more fully than the shear probe. Additionally, the pressure probe does not suffer from the spectral distortion of the signal observed in measurements using a shear probe. In addition to measurement of velocity microstructure, consideration is given to the implementation of modern signal processing hardware in designing a method for the direct measurement of density microstructure. This basic property of the ocean has never before been measured directly. Results, obtained off the Florida coast in 18 meter deep water with the Ocean Explorer AUV; Cook, reveal a complex mixing event. Simultaneous measurement of two components of the velocity microstructure and measurements with a CTD package are analyzed and the instantaneous rates of viscous dissipation of turbulent energy are calculated. The dissipation rate was not stationary and showed a gradient vertically with depth as well as horizontally. The AUV platform, modified for low vibration noise, allowed measurement of dissipation rates of O(10^-8 W/kg).
Title: Ocean turbulence measurement using an autonomous underwater vehicle.
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Name(s): Holappa, Kenneth Walter.
Florida Atlantic University, Degree grantor
Dhanak, Manhar R., Thesis advisor
College of Engineering and Computer Science
Department of Ocean and Mechanical Engineering
Type of Resource: text
Genre: Electronic Thesis Or Dissertation
Issuance: monographic
Date Issued: 1997
Publisher: Florida Atlantic University
Place of Publication: Boca Raton, Fla.
Physical Form: application/pdf
Extent: 188 p.
Language(s): English
Summary: The complex dynamics of the oceans are only beginning to be understood. There is a wide range of dynamic scales in the ocean from the Gulf Stream, with scales as large as the ocean itself, to the microstructure scales of turbulent dissipation. The program of work presented in this dissertation involves the implementation of a turbulence measurement package on board a recently developed small autonomous underwater vehicle (AUV), as well as the design of an optimized AUV platform and the development of new oceanographic sensors for measurement of micro-structure velocity. Attention is focused on ensuring that the platform is sufficiently quiet since small-scale, low level measurements are easily contaminated by the measurement process, structural vibrations, rigid-body motions and electrical interference; particularly so with the requisite machinery of a self-propelled AUV. Successful measurement entails making suitable modification to the AUV and its mode of operation. In addition to optimization of the measurement platform, consideration is given here to the optimization of the sensors for flow measurement using an AUV. Included in the research are laboratory tests of the new probes and a successful mission in making high quality measurements of ocean turbulence. Modern adaptation of the well-known Pitot tube shows promise in being less sensitive to vehicle self motion as well as yielding a greater spectral range, thereby facilitating more accurate measurement. Comparisons with shear probes and hot film probes, conducted in an axisymmetric water jet and in a wind tunnel, suggest that the pressure probe, developed as part of the work presented here, resolves the dissipation scales more fully than the shear probe. Additionally, the pressure probe does not suffer from the spectral distortion of the signal observed in measurements using a shear probe. In addition to measurement of velocity microstructure, consideration is given to the implementation of modern signal processing hardware in designing a method for the direct measurement of density microstructure. This basic property of the ocean has never before been measured directly. Results, obtained off the Florida coast in 18 meter deep water with the Ocean Explorer AUV; Cook, reveal a complex mixing event. Simultaneous measurement of two components of the velocity microstructure and measurements with a CTD package are analyzed and the instantaneous rates of viscous dissipation of turbulent energy are calculated. The dissipation rate was not stationary and showed a gradient vertically with depth as well as horizontally. The AUV platform, modified for low vibration noise, allowed measurement of dissipation rates of O(10^-8 W/kg).
Identifier: 9780591616811 (isbn), 12532 (digitool), FADT12532 (IID), fau:9423 (fedora)
Collection: FAU Electronic Theses and Dissertations Collection
Note(s): College of Engineering and Computer Science
Thesis (Ph.D.)--Florida Atlantic University, 1997.
Subject(s): Oceanographic submersibles
Turbulence--Measurement
Held by: Florida Atlantic University Libraries
Persistent Link to This Record: http://purl.flvc.org/fcla/dt/12532
Sublocation: Digital Library
Use and Reproduction: Copyright © is held by the author, with permission granted to Florida Atlantic University to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Use and Reproduction: http://rightsstatements.org/vocab/InC/1.0/
Host Institution: FAU
Is Part of Series: Florida Atlantic University Digital Library Collections.