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PRESSURE FLUCTUATION MEASUREMENT TECHNIQUES IN A CIRCULAR DUCT WITH INCOMPRESSIBLE TURBULENT FLOW (FREQUENCY-WAVENUMBER SPECTRA)
Title
PRESSURE FLUCTUATION MEASUREMENT TECHNIQUES IN A CIRCULAR DUCT WITH INCOMPRESSIBLE TURBULENT FLOW (FREQUENCY-WAVENUMBER SPECTRA).
Creator
DAVIS, HARRY LEE., Florida Atlantic University, Cuschieri, Joseph M.
Abstract/Description
Turbulent pressure fluctuations and acoustical shock waves formed at pipe discontinuities are the primary source of flow noise. fhe pipe response is excited by the fluctuating forces associated with the turbulent pressure fluctuations. The forcing functions can be determined from the frequency-wavenumber spectrum of the pressure fluctuations. A procedure is developed here to obtain the frequency-wavenumber spectrum due to fully developed turbulent flow. The data analysis procedures developed...
Show moreTurbulent pressure fluctuations and acoustical shock waves formed at pipe discontinuities are the primary source of flow noise. fhe pipe response is excited by the fluctuating forces associated with the turbulent pressure fluctuations. The forcing functions can be determined from the frequency-wavenumber spectrum of the pressure fluctuations. A procedure is developed here to obtain the frequency-wavenumber spectrum due to fully developed turbulent flow. The data analysis procedures developed in this study to analyze the pressure fluctuations provide a good means to determine the frequency-wavenumber spectrum and represent this data in a clear form. Frequency-wavenumber spectra have been obtained for simulated pressure data. In the experimental system designed to collect turbulent pressure data, it was determined that a recessed transducer configuration cannot be used in water pipe flow turbulent pressure fluctuation studies because of the enhanced turbulence created by the upstream holes. Therefore, flush mounted transducers are required.
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Date Issued
1986
PURL
http://purl.flvc.org/fcla/dt/14330
Subject Headings
Turbulence--Measurement, Fluid dynamics
Format
Document (PDF)
Ocean turbulence measurement using an autonomous underwater vehicle
Title
Ocean turbulence measurement using an autonomous underwater vehicle.
Creator
Holappa, Kenneth Walter., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
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...
Show moreThe 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).
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Date Issued
1997
PURL
http://purl.flvc.org/fcla/dt/12532
Subject Headings
Oceanographic submersibles, Turbulence--Measurement
Format
Document (PDF)
Subsurface structure of an atmospherically forced water column in littoral waters
Title
Subsurface structure of an atmospherically forced water column in littoral waters.
Creator
Chernys, Michael., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The developing subsurface structure of a shallow sub-tropical water column during the passage of cold low-pressure atmospheric front is characterized through synoptic and in-situ observations during the passage of three separate fronts over South Florida. Subsurface distribution of current, salinity, temperature, density and dissipation rates were examined using an autonomous underwater vehicle (AUV), ship-based instruments, moored instruments and an Ocean Surface Current Radar (OSCR) as the...
Show moreThe developing subsurface structure of a shallow sub-tropical water column during the passage of cold low-pressure atmospheric front is characterized through synoptic and in-situ observations during the passage of three separate fronts over South Florida. Subsurface distribution of current, salinity, temperature, density and dissipation rates were examined using an autonomous underwater vehicle (AUV), ship-based instruments, moored instruments and an Ocean Surface Current Radar (OSCR) as the fronts passed through the region. Airfoil shear probes mounted in a package on the nose of the AUV were used to measure the level and distribution of small-scale turbulence in the water column and to estimate the in-situ dissipation rate of turbulent kinetic energy. Prevailing meteorological conditions were determined from two NOAA C-MAN stations and, for two of the experiments, from a local Air Sea Interaction Spar buoy (ASIS). The first atmospheric front examined was in December 1998. A significant 10°C drop in air temperature was recorded. The AUV carried out several pre-programmed surveys over a 6-day period. A turbulent kinetic energy dissipation rates of O(10-6W/kg) were observed in the water column during the passage of the front. Fetch-limited, offshore, wind-induced surface and subsurface currents were identified during the passage of the front on April 9, 2000. As the winds increased in magnitude and shifted direction, a change in surface current was apparent in the OSCR observations. A bottom-mounted ADCP and an AUV-mounted ADCP both recorded distinct corresponding contributions to the subsurface current due to the winds. Clockwise rotation of the current profile in the water column, consistent with wind-generated currents, was observed. A third low-pressure cold front passed through the region on April 18 an 19, 2000. AUV surveys were carried out as the front passed over the region for 19 hours within a 24-hour period. Dissipation rates reached O(10 -6W/kg) during the period of the survey and decreased to O(10 -8W/kg) subsequently. The distribution of dissipation rate appeared to agree with the characteristic log law for wind-induced turbulence at the start of the passage of the front, but was significantly higher subsequently and more dependent on the combination of convective fluxes and wind stress.
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Date Issued
2002
PURL
http://purl.flvc.org/fau/fd/FADT12001
Subject Headings
Turbulence--Measurement, Oceanographic submersibles
Format
Document (PDF)
Design and testing of an untethered vertically ascending profiler for use in measuring near-surface turbulence
Title
Design and testing of an untethered vertically ascending profiler for use in measuring near-surface turbulence.
Creator
Bogin, Jeffrey Isaac., Florida Atlantic University, Dhanak, Manhar R.
Abstract/Description
The Vertically Ascending Micro-scale Profiler, or VAMP, has been designed, constructed, and tested to be used in conjunction with FAU's Turbulence Package in order to collect vertical turbulence profiles close to the free surface. Unique to VAMP is that it has been specifically designed as an untethered ascending profiler. Examination of turbulence data collected using VAMP shows that the measured shear spectrum and the turbulent kinetic energy dissipation closely matches the Nasmyth Spectrum...
Show moreThe Vertically Ascending Micro-scale Profiler, or VAMP, has been designed, constructed, and tested to be used in conjunction with FAU's Turbulence Package in order to collect vertical turbulence profiles close to the free surface. Unique to VAMP is that it has been specifically designed as an untethered ascending profiler. Examination of turbulence data collected using VAMP shows that the measured shear spectrum and the turbulent kinetic energy dissipation closely matches the Nasmyth Spectrum. Data processing techniques made it possible to filter out motion generated by surface wave action, which allowed VAMP to collect data at depths as shallow as the troughs of the surface waves. VAMP can be launched, deployed several times, and recovered all within a thirty minute time frame by a crew of four.
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Date Issued
2003
PURL
http://purl.flvc.org/fcla/dt/13020
Subject Headings
Turbulence--Measurement, Surface waves (Oceanography)
Format
Document (PDF)
TURBULENCE CURRENT METER DESIGN, CONSTRUCTION AND USE
Title
A TURBULENCE CURRENT METER DESIGN, CONSTRUCTION AND USE.
Creator
KIDERA, EDWARD HENRY, IV., Florida Atlantic University, Tennant, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The objectives of this investigation were - 1) design and build a turbulence current meter capable of measuring velocity fluctuations in a geophysical scale flow and 2) the measurement of such flow including subsequent analysis of near bottom turbulence. An unique device capable of sensing velocity fluctuations in the region 25cm above the bottom was constructed based on concepts original to the study of turbulence. A review of previous equipment and research is included for a comparison. The...
Show moreThe objectives of this investigation were - 1) design and build a turbulence current meter capable of measuring velocity fluctuations in a geophysical scale flow and 2) the measurement of such flow including subsequent analysis of near bottom turbulence. An unique device capable of sensing velocity fluctuations in the region 25cm above the bottom was constructed based on concepts original to the study of turbulence. A review of previous equipment and research is included for a comparison. The instrument's usefulness was illustrated in the open channel flow of a tidal estuary by its ability to detect the horizontal velocity field. The data obtained for the turbulence shows large variation in velocity of the lateral component on the order of 50-75% of the "mean" current speed. Digital filtering of the data reveals distinct structures of high energy, intermittent in their nature and analogous to "bursting". The energy spectrum of the longitudinal component follows the predicted slope of -1 for over two decades (.01 to 1.3 + Hz).
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Date Issued
1978
PURL
http://purl.flvc.org/fcla/dt/13943
Subject Headings
Turbulence--Measurement, Water current meters
Format
Document (PDF)
Analysis of Turbulence Observed in the Florida Current using an ADCP
Title
Analysis of Turbulence Observed in the Florida Current using an ADCP.
Creator
Denton, John E., Dhanak, Manhar, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The observation of turbulence in the Florida Current is presented with the use of velocity measurements collected with an Acoustic Doppler Current Profiler (ADCP). The research is conducted through application of the theories of Taylor and Kolmogorov and related derivations, and processing tools of MATLAB software to this Eulerian observation of flow [1]. The velocity profile of the Florida Current is deduced in terms of its turbulent character with shear, acceleration, gradient, Reynolds...
Show moreThe observation of turbulence in the Florida Current is presented with the use of velocity measurements collected with an Acoustic Doppler Current Profiler (ADCP). The research is conducted through application of the theories of Taylor and Kolmogorov and related derivations, and processing tools of MATLAB software to this Eulerian observation of flow [1]. The velocity profile of the Florida Current is deduced in terms of its turbulent character with shear, acceleration, gradient, Reynolds Number, Reynolds Stress, Welch power spectrum density of current velocity, wavenumbers of Taylor’s hypothesis and Kolmogorov, wavenumber spectrum, eddy diameters, diapycnal diffusivity, and the Richardson Number. Processing methods are validated with results of other research conducted in the Florida Current with the use of a Multi-Scale Profiler, and an Advanced Microstructure Profiler for determination of shear, dissipation, diffusivity, and estimates of turbulent eddy diameters based on Taylor’s Hypothesis [1][4]. A spectral analysis is developed and is compared with Kolmogorov’s -5/3-Law. The process and the results of the analysis are described.
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Date Issued
2018
PURL
http://purl.flvc.org/fau/fd/FA00013173
Subject Headings
Florida Current, Turbulence--Measurement, Underwater acoustics--Data processing, Doppler effect
Format
Document (PDF)