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Distributed Optical Fiber Vibration Sensor Based on Phase-Sensitive Optical Time Domain ReflectometryRen, Meiqi January 2016 (has links)
In this thesis, the work focuses on developing distributed optical fiber vibration sensors based on phase-sensitive optical time domain reflectometry (Φ-OTDR). Three works have been accomplished to improve the performances of Φ-OTDR for distributed vibration sensing. Firstly, Φ-OTDR based on a polarization diversity scheme is demonstrated to mitigate the polarization mismatch effect occurring in traditional systems. A theoretical analysis is performed in different polarization cases corresponding to coherent and polarization diversity detection. Φ-OTDR based polarization diversity shows a great potential in the multi-events sensing application. Two vibration events are simultaneously detected and their signal to noise ratios are improved by 10.9 dB and 8.65 dB, respectively, compared to the results obtained by a conventional coherent scheme.
Intensity fluctuation in a phase-sensitive optical-time domain reflectometry (Φ-OTDR) system caused by stochastic characteristics of Rayleigh backscattering has limited relative vibration strength measurement, which is proportional to dynamic strain. A trace-to-trace correlation coefficient is thus proposed to quantify the Φ-OTDR system stability and a novel approach of measuring the dynamic strain induced by various driving voltages of lead zicronate titanate (PZT) is demonstrated. Piezoelectric vibration signals are evaluated through analyzing peak values of the fast Fourier transform spectra at fundamental frequency and high-order harmonics based on Bessel functions. Experimental results show high correlation coefficients and good stability of our Φ-OTDR system, as well as the small measurement uncertainty of measured peak values.
To reduce the intra-band noise caused by the finite extinction ratio of optical pulses, Φ-OTDR based on high extinction ratio generation is studied. Two methods are developed for achieving high extinction ratio of optical pulse generation. One of the approaches is to synchronize two cascaded electro-optic modulators to achieve high extinction ratio operation. The other one is to use the nonlinear optical fiber loop mirror as an optical switch to suppress the continuous wave portion of optical pulse. The sensing range of 1.8 km and 8.4 km with corresponding spatial resolution of 0.5 m and 2 m have been demonstrated based on cascaded two electro-optic modulators and nonlinear optical fiber loop mirror setup, respectively.
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Effect of clay type and clay content on moisture content and bulk soil electrical conductivity as measured using time domain reflectometryLiaghat, Abdolmajid January 1993 (has links)
No description available.
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Use of time domain reflectometry to monitor water content and electrical conductivity of saline soilEntus, Jonathan January 2000 (has links)
No description available.
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The use of time domain reflectometry (TDR) to determine and monitor non-aqueous phase liquids (NAPLS) in soilsQuafisheh, Nabil M. January 1997 (has links)
No description available.
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A comparative study of inclinometers and time domain reflectometry for slope movement analysisSargent, Lisa M. January 2004 (has links)
No description available.
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Monitoring Slope Stability Problems Utilizing Electrical and Optical TDRMomand, Farid A. January 2010 (has links)
No description available.
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Ultrasonic-time-domain-reflectometry as a real time non-destructive visualisation technique of concentration polarisation and fouling on reverse osmosis membranesKoen, Louis Johannes 12 1900 (has links)
Thesis (MIng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Fouling is readily acknowledged as one of the most critical problems limiting the
wider application of membranes in liquid separation processes. A better
understanding of fouling layer formation and its monitoring is needed in order to
improve on existing cleaning techniques. Plant operation can be optimised if fouling
can be monitored by noninvasion means either on the plant itself or on an attached
monitoring device.
The overall scope of this research was to develop a non-destructive, real-time, in situ
visualisation technique or device for concentration polarisation and fouling layer
monitoring. Ultrasonic-time-domain-reflectometry (UTDR) was employed as a
visualisation technique to provide real-time characterisation of the fouling layer.
A 24 cm-long rectangular flat sheet aluminium cell was designed and used as
separation device for a desalination system. The experimental results obtained using
this module confirmed that there are an excellent correspondence between the flux
decline behaviour and the UTDR response from the membrane. The ultrasonic
technique could effectively detect fouling layer initiation and growth on the
membrane in real-time. In addition to the measurement of fouling, the ultrasonic
technique was also successfully employed for monitoring membrane cleaning. Since
no real-time permeation data is available during cleaning operations in industrial
applications, a UTDR monitoring device may prove to be a very valuable technique
in optimising cleaning strategies.
The technique was further tested on an 8-inch diameter spiral wrap industrial
module and good results were obtained. Stagnant zones, as well as flux flow
behaviour inside the module could be determined. However, more research IS
needed to fully understand the complex phenomena inside a spiral wrap module.
Overall, the UTDR technique and its use in monitoring devices have a major impact
in the membrane industry due to its extremely powerful capabilities. / AFRIKAANSE OPSOMMING: Membraan-bevuiling of -verstopping is die grootste struikelblok wat die algemene
aanwending van membrane vir verskillende watersuiweringsprosesse negatief
beinvloed. 'n Beter begrip van membraan-bevuiling, asook beter metingsmetodes
daarvan is nodig om op bestaande skoonmaaktegnieke te verbeter.
Die hoofdoel van hierdie studie was die ontwikkeling van 'n nie-destruktiewe-in-lyn
visuele tegniek vir die meting van konsentrasie polarisasie en membraan-bevuiling.
Deur gebruik te maak van ultrasoniese klank golwe, is 'n tegniek ontwikkel wat 'n
direkte visuele aanduiding kon gee van die toestand van membraan-bevuiling binnein
die module.
'n Reghoekige aluminium-module, 24 cm lank, is ontwerp en gebou waarbinne die
membraan geplaas is vir die skeidingsproses. Resultate dui daarop dat daar 'n
uitstekende verband bestaan tussen die afname in permeaatvloei en die ultrasoniese
eggo vanaf die membraan. Die ultrasoniese tegniek kon die vorming van en toename
in membraan-bevuiling doeltreffend karakteriseer. In teenstelling hiermee, is die
tegniek ook suksesvol aangewend om die skoonmaak-proses van membrane te
ondersoek. Met min of geen data beskikbaar vir die skoonmaak-proses van
membrane in die industriële sektor, het die tegniek enorme potensiaal in die
optimisering van bestaande skoonmaak-tegnieke.
Die tegniek is verder aangewend op 'n industriële 8-duim deursnee spiraal-module
en goeie resultate is verkry. Stagnante sones asook vloed-vloei-patrone binne-in die
module kon suksesvol bepaal word. Baie navorsing is egter nog nodig om die
ingewikkelde data wat gegenereer word tydens die ondersoek van 'n spiraal-module
ten volle te verstaan.
Die enorme potensiaal en moontlikhede van die ultrasoniese tegniek kan die begin
wees van 'n revolusie in die membraan-industrie.
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Calibration of water content reflectometer in Rocky Mountain arsenal soilTang, Yucao 2009 August 1900 (has links)
This paper describes how water content reflectometers (WCRs) were analyzed to develop a calibration equation. Time domain reflectometry (TDR) technique is the most prevalent method in in-situ moisture monitoring; and WCR is a type of low frequency TDR sensors, which is sensitive to soil type. Developing soil-specific calibration and investigating different environmental effects on WCR calibration is important. This study focused on investigation of the soil dry density and temperature effects on WCR calibration in RMA soil. Two series of tests to develop soil-specific calibration with dry density and temperature offset were conducted. Results from testing program showed that WCR response was positive related to volumetric water content, dry density, and temperature. Equations were developed to illustrate the response-density-temperature-moisture relation. Application to a field site was also presented to illustrate the difference in volumetric water contents obtained by using manufacturer method and the calibration procedure drawn in this paper. / text
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A High Frequency Transformer Winding Model for FRA ApplicationsTavakoli, Hanif January 2009 (has links)
<p>Frequency response analysis (FRA) is a method which is used to detect mechanical faults in transformers. The FRA response of a transformer is determined by its geometry and material properties, and it can be considered as the transformer’s fingerprint. If there are any mechanical changes in the transformer, for example if the windings are moved or distorted, its fingerprint will also be changed so, theoretically, mechanical changes in the transformer can be detected with FRA.</p><p>The purpose of this thesis is to partly create a simple model for the ferromagnetic material in the transformer core, and partly to investigate the high frequency part of the FRA response of the transformer winding. To be able to realize these goals, two different models are developed separately from each other. The first one is a time- and frequency domain complex permeability model for the ferromagnetic core material, and the second one is a time- and frequency domain winding model based on lumped circuits, in which the discretization is made finer and finer in three steps. Capacitances and inductances in the circuit are calculated with use of analytical expressions derived from approximated geometrical parameters.</p><p>The developed core material model and winding model are then implemented in MATLAB separately, using state space analysis for the winding model, to simulate the time- and frequency response.</p><p>The simulations are then compared to measurements to verify the correctness of the models. Measurements were performed on a magnetic material and on a winding, and were compared with obtained results from the models. It was found that the model developed for the core material predicts the behavior of the magnetic field for frequencies higher than 100 Hz, and that the model for the winding predicts the FRA response of the winding for frequencies up to 20 MHz.</p>
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High Resolution Geophysical Characterization of a Gasoline Release into a Sand ColumnVakili, Fatemeh January 2008 (has links)
A controlled column experiment was conducted to investigate the geophysical response of gasoline spills into the partially saturated sand column. The column was 0.61 diameter (ID) and 2 m high cylindrical polyvinyl chloride, which was packed with the Borden sand to a height of 1.95 m, flushed with CO2, saturated, and drained to a height of 0.73 m. The monitoring techniques used for this experiment was DC resistivity and time domain reflectometry (TDR) methods. The column was equipped with resistivity electrodes and TDR probes, which were placed on the column wall vertically with 3 cm intervals, on opposite sides, two monitoring wells, an injection well, a manometer, an outlet/inlet system, and a vent. A total amount of 5 liters of standard API 91-01 gasoline was added to the system in steps of 1, 2, and 2 liters to examine the geophysical response to different amounts of gasoline.
Measurements were taken before and after each injection and also during subsequent fluctuation of the water table. Both monitoring techniques were able to record even the minor changes in the trend of conductivity and permittivity profiles due to the addition of the small amount of gasoline during the first spill. The conductivity and permittivity profiles obtained before lowering the water level below the original level and those obtained after the water level reached to the original level do not match, which is an indication of entrapped gasoline inside the pores. Two core samples was taken from the sand symmetrically after each water table fluctuation and analyzed for total petroleum hydrocarbon (TPH) analysis and the results were compared to the conductivity and permittivity results.
The conductivity profile obtained using DC resistivity method was compared to that of obtained using TDR method. The profiles match in the saturated zone where all of the pores are connected with water and therefore electrolytic conduction is predominant. In the unsaturated zone, where there is low pore water connectivity, TDR measured conductivity values are higher than those measured using the resistivity method.
Water saturation values were calculated using conductivity and permittivity values before and after each injection. Different values of saturation exponent (n) were tested for Archie’s law until an appropriate value was found which gave the best water saturation from conductivity data for clean Borden sand. Then, the water saturation obtained from permittivity values using Topp’s equations for different materials were compared to that of obtained from conductivity values using Archie’s equation. Topp’s equation for 30 µm glass beads provided the best match. Furthermore, other equations developed by other researchers were examined to obtain water saturation profiles from the permittivity values; all of them overestimate the water saturation for Borden sand. The water saturation profiles after the gasoline spills obtained using both Archie’s law and Topp’s equation do not match, perhaps because both equations were developed for three-phase (water-solid-air) systems.
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