A theoretical study of surface‐to‐borehole electromagnetic logging in cased holes

Geophysics ◽  
1989 ◽  
Vol 54 (1) ◽  
pp. 90-99 ◽  
Author(s):  
A. M. Augustin ◽  
W. D. Kennedy ◽  
H. F. Morrison ◽  
K. H. Lee
Keyword(s):  
Theoretical Study ◽  
Enhanced Recovery ◽  
Field Studies ◽  
Drill Hole ◽  
Repeated Measurements ◽  
Low Frequencies ◽  
First Finding ◽  
Horizontal Stratification ◽  
Whole Space ◽  
Logging Tool

A new electromagnetic logging method, in which the source is a horizontal loop coaxial with a cased drill hole and the secondary axial fields are measured at depth within the casing, has been analyzed. The analysis, which is for an idealized model of an infinite pipe in a conductive whole space, has shown that the casing and formation are uncoupled at the low frequencies that would be used in field studies. The field inside the casing may be found by first finding the field in the formation and then using this field as an incident field for the pipe alone. This result permits the formation response to be recovered from the measured field in the borehole by applying a correction for the known properties of the casing. If the casing response cannot be accurately predicted, a separate logging tool employing a higher frequency transmitter could be used to determine the required casing parameters in the vicinity of the receiver. This logging technique shows excellent sensitivity to changes in formation conductivity, but it is not yet known how well horizontal stratification can be resolved. One of its most promising applications will be in monitoring, through repeated measurements, changes in formation conductivity during production or enhanced recovery operations.

Using Ambient Noise to Inverse Geo-Acoustic Parameters

2012 ◽  
Vol 588-589 ◽  
pp. 851-855
Author(s):  
Chun Xia Meng ◽  
Gui Juan Li ◽  
Liang Zhang
Keyword(s):  
Shallow Water ◽  
Ambient Noise ◽  
Theoretical Study ◽  
Ocean Surface ◽  
Ray Theory ◽  
Acoustic Parameters ◽  
Low Frequencies ◽  
Research Results ◽  
Noise Data ◽  
Stratified Ocean

This paper presents a theoretical study of the vertical coherence of ocean ambient noise as the source is the windy ocean surface on the ray theory. At low frequencies less than 2 kHz, the sensitivity of stratified fluid seabed to the vertical coherence of ambient noise in shallow water is analyzed under the condition of distance-irrespective stratified ocean. Using ambient noise data from Chinese north shallow water seabed geo-acoustics parameters are obtained, and the research results show that the inverted method is effective.

The Tuned and Damped Gyrostatic Vibration Absorber

1947 ◽  
Vol 157 (1) ◽  
pp. 1-19 ◽  
Author(s):  
R. N. Arnold
Keyword(s):  
Theoretical Prediction ◽  
Torsional Vibration ◽  
Forced Vibration ◽  
Theoretical Study ◽  
Experimental Investigations ◽  
Vibration Absorber ◽  
Viscous Damping ◽  
Mean Velocity ◽  
Mass System ◽  
Low Frequencies

The vibration absorber described in this paper consists of a gyrostat suspended symmetrically about an axis perpendicular to that of the torsional vibration which it is desired to suppress. The gyrostat is fitted with springs and a viscous damping mechanism which allow limited vibration about its axis. This device is a modification of that employed by Schlick (1904)†, in his attempt to stabilize the rolling of ships at sea. The new arrangement, however, is more efficient, is not restricted to very low frequencies, and is, in general, capable of application to vibration superposed on a mean velocity. A theoretical study is made of the response of such an absorber to one- and two-mass vibratory systems under both forced and self-induced vibration, and design methods are derived by which the essential dimensions for any given application may be readily determined. Experimental investigations with a gyrostatic absorber applied to a one-mass system under forced vibration are recorded, and the results compared with theoretical prediction. The design of a full-scale absorber built to suppress vibration of the table of a heavy planing machine is also given, together with the results obtained with the apparatus on trial.

Properties of Acoustic Reflex Adaptation

1977 ◽  
Vol 86 (3) ◽  
pp. 348-356 ◽  
Author(s):  
Harold Kaplan ◽  
Samuel Gilman ◽  
Donald D. Dirks
Keyword(s):  
Dynamic Behavior ◽  
Stimulus Frequency ◽  
Repeated Measurements ◽  
Intersubject Variability ◽  
Acoustic Reflex ◽  
Descriptive Model ◽  
Major Purpose ◽  
Low Frequencies ◽  
Time Constants ◽  
Reflex Threshold

The dynamic behavior of the acoustic reflex to continuous sinusoidal stimuli was investigated. The major purpose was to determine the temporal characteristics of reflex adaptation as frequency (0.5, 1.0, 2.0, 3.0, 4.0 kHz) and suprathreshold level (6, +12, +18 dB re reflex threshold) were systematically varied. Repeated measurements were made with an impedance bridge on six normal listeners. Both relative and absolute impedance changes were analyzed. The results revealed large intersubject variability. Four general conclusions were reached regarding the effect of stimulus frequency and suprathreshold level on adaptation: 1) as the stimulus frequency increases, the rate of adaptation increases; 2) the adaptation curves appear to form distinct groups, at the low frequencies adaptation rates are significantly slower than those at 2.0 kHz and above; 3) the onset of adaptation occurs at an earlier time for the higher frequencies; and 4) the rate of adaptation was found to be independent of suprathreshold level. The changes in adaptation with frequency of the stimulus may be expressed by an equation involving inter-related time constants for the growth and adaptation portions of the reflex curve in accordance with a descriptive model suggested by Tietze.

Paper 29. Yaw Control in Waves

1972 ◽  
Vol 14 (7) ◽  
pp. 211-228
Author(s):  
H. Eda
Keyword(s):  
Control System ◽  
Automatic Control ◽  
Theoretical Study ◽  
Model Tests ◽  
Low Frequencies ◽  
Following Seas ◽  
Yaw Control ◽  
Hull Forms ◽  
The Stability ◽  
The Waves

Results are given of a recently broadened investigation into the stability of ships in following seas, based on a theoretical study and model tests on Series 60 hull forms. The analysis is derived from perturbations to the steady yaw, sway, surge and automatic control equations. At low frequencies of encounter, corresponding to high ship speeds, it is found that significant destabilizing effects arise from the large surge forces generated by the waves, leading to broaching: stability is greatly improved by appropriate characteristics of the control system. At higher encounter frequencies, typical of lower speed ships, oscillating yaw and sway motions are induced and the rudder has little influence. The study clarifies the influences of wave encounter frequency, encounter angle, control system constants and ship configuration.

Theoretical study on the phase sensitivity of condenser type acoustic transducers at low frequencies

2021 ◽  
pp. 146134842110623
Author(s):  
Aibing Liu ◽  
Di Liu ◽  
Fan Zhang ◽  
Huiheng Wang ◽  
Jixing Wu ◽  
...  
Keyword(s):  
Large Scale ◽  
Theoretical Study ◽  
Phase Variation ◽  
Sound Field ◽  
Time Domain Analysis ◽  
Phase Lag ◽  
Phase Sensitivity ◽  
Low Frequencies ◽  
Phase Lead ◽  
Acoustic Transducers

The phase sensitivity of the condenser type acoustic transducers at low frequencies is crucial for locating large-scale natural and manmade activities, but is now commonly calibrated based on comparison methods. Although the primary method, which traces its sensitivity back to the international standard unit is few studied. Recently, the explicit sensitivity models of the condenser type acoustic transducers based on the laser-pistonphone technique are built, and can be used to study the phase responses of acoustic transducers at infrasonic frequencies. So that, in this paper, the phase sensitivities of acoustic transducers when its rear vent connected to the calibrating sound field or outside atmosphere are studied in detail. Secondly, time domain analysis of generated sound pressures by displacement excitation are derived to reveal the mechanism of phase variation. Calculations show two distinct sensitivities with 90° phase lead and −10° phase lag limits for vent in field and vent out field calibrations, which are dominated by the pressure leakage and heat conduction effects at infrasonic frequencies.

scholarly journals Subspace Detours Meet Gromov–Wasserstein

Algorithms ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 366
Author(s):  
Clément Bonet ◽  
Titouan Vayer ◽  
Nicolas Courty ◽  
François Septier ◽  
Lucas Drumetz
Keyword(s):  
Shape Matching ◽  
Optimal Transport ◽  
Matching Problem ◽  
Optimal Plan ◽  
Specific Cost ◽  
First Finding ◽  
Whole Space ◽  
Transport Plan ◽  
Specific Geometry

In the context of optimal transport (OT) methods, the subspace detour approach was recently proposed by Muzellec and Cuturi. It consists of first finding an optimal plan between the measures projected on a wisely chosen subspace and then completing it in a nearly optimal transport plan on the whole space. The contribution of this paper is to extend this category of methods to the Gromov–Wasserstein problem, which is a particular type of OT distance involving the specific geometry of each distribution. After deriving the associated formalism and properties, we give an experimental illustration on a shape matching problem. We also discuss a specific cost for which we can show connections with the Knothe–Rosenblatt rearrangement.

The S-SH Confusion Test and the Effects of Frequency Lowering

2019 ◽  
Vol 62 (5) ◽  
pp. 1486-1505
Author(s):  
Joshua M. Alexander
Keyword(s):  
Cognitive Processing ◽  
Hearing Aids ◽  
Response Times ◽  
Nonlinear Frequency ◽  
Low Frequencies ◽  
Frequency Compression ◽  
Negative Side ◽  
Minimal Word ◽  
Low Pass ◽  
Negative Side Effects

PurposeFrequency lowering in hearing aids can cause listeners to perceive [s] as [ʃ]. The S-SH Confusion Test, which consists of 66 minimal word pairs spoken by 6 female talkers, was designed to help clinicians and researchers document these negative side effects. This study's purpose was to use this new test to evaluate the hypothesis that these confusions will increase to the extent that low frequencies are altered.MethodTwenty-one listeners with normal hearing were each tested on 7 conditions. Three were control conditions that were low-pass filtered at 3.3, 5.0, and 9.1 kHz. Four conditions were processed with nonlinear frequency compression (NFC): 2 had a 3.3-kHz maximum audible output frequency (MAOF), with a start frequency (SF) of 1.6 or 2.2 kHz; 2 had a 5.0-kHz MAOF, with an SF of 1.6 or 4.0 kHz. Listeners' responses were analyzed using concepts from signal detection theory. Response times were also collected as a measure of cognitive processing.ResultsOverall, [s] for [ʃ] confusions were minimal. As predicted, [ʃ] for [s] confusions increased for NFC conditions with a lower versus higher MAOF and with a lower versus higher SF. Response times for trials with correct [s] responses were shortest for the 9.1-kHz control and increased for the 5.0- and 3.3-kHz controls. NFC response times were also significantly longer as MAOF and SF decreased. The NFC condition with the highest MAOF and SF had statistically shorter response times than its control condition, indicating that, under some circumstances, NFC may ease cognitive processing.ConclusionsLarge differences in the S-SH Confusion Test across frequency-lowering conditions show that it can be used to document a major negative side effect associated with frequency lowering. Smaller but significant differences in response times for correct [s] trials indicate that NFC can help or hinder cognitive processing, depending on its settings.

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