scholarly journals Estimating the shear velocity profile of Quaternary silts using microtremor array (SPAC) measurements

2005 ◽  
Vol 58 (1) ◽  
pp. 34-40
Author(s):  
James Roberts ◽  
Michael Asten
Keyword(s):  
Velocity Profile ◽  
Shear Velocity

scholarly journals Generation of Gravity-Capillary Wind Waves by Instability of a Coupled Shear-Flow

2022 ◽  
Vol 10 (1) ◽  
pp. 46
Author(s):  
Malek Abid ◽  
Christian Kharif ◽  
Hung-Chu Hsu ◽  
Yang-Yih Chen
Keyword(s):  
Velocity Profile ◽  
Unstable Mode ◽  
Wind Waves ◽  
Surface Current ◽  
Viscous Flows ◽  
Shear Velocity ◽  
Threshold Value ◽  
Surface Velocity ◽  
Mixing Length ◽  
Flow Turbulence

The theory of surface wave generation, in viscous flows, is modified by replacing the linear-logarithmic shear velocity profile, in the air, with a model which links smoothly the linear and logarithmic layers through the buffer layer. This profile includes the effects of air flow turbulence using a damped mixing-length model. In the water, an exponential shear velocity profile is used. It is shown that this modified and coupled shear-velocity profile gives a better agreement with experimental data than the coupled linear-logarithmic, non smooth profile, (in the air)–exponential profile (in the water), widely used in the literature. We also give new insights on retrograde modes that are Doppler shifted by the surface velocity at the air-sea interface, namely on the threshold value of the surface current for the occurrence of a second unstable mode.

Seabed property estimation from ambient-noise recordings: Part I — Compliance and Scholte wave phase-velocity measurements

Geophysics ◽  
2007 ◽  
Vol 72 (2) ◽  
pp. U21-U26 ◽  
Author(s):  
Everhard Muyzert
Keyword(s):  
Velocity Profile ◽  
Ambient Noise ◽  
Shear Velocity ◽  
Love Waves ◽  
Surface Shear ◽  
Near Surface ◽  
Wave Phase ◽  
Seafloor Compliance ◽  
Scholte Waves ◽  
Scholte Wave

The ability to derive a near-surface shear-velocity profile from ambient-noise records is useful for seismic applications such as shear-wave statics estimation and geohazard prediction. Measurements of seafloor compliance and Scholte wave velocity and amplitude are all related to the near-surface shear-velocity profile. I analyzed a data set of [Formula: see text] of continuous noise records recorded by an ocean bottom cable deployed in [Formula: see text] deep water for seafloor compliance and Scholte waves. I failed to observe seafloor compliance because of limitations in the record length. I have detected Scholte waves on the inline and vertical component geophones and Love waves on the crossline component using [Formula: see text] spectra. Both the Scholte and Love wave phase-velocities can be explained by a simple 1D isotropic near-surface model. The Scholte waves may have been excited by acoustic energy from the recording vessel, while no satisfactory excitation mechanism has been found for the Love waves.

Mapping formation shear-velocity variation by inverting logging-while-drilling quadrupole-wave dispersion data

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. D491-D498 ◽  
Author(s):  
Yuan-Da Su ◽  
Xiao-Ming Tang ◽  
Chun-Xi Zhuang ◽  
Song Xu ◽  
Long Zhao
Keyword(s):  
Velocity Profile ◽  
High Frequency ◽  
Shear Velocity ◽  
Wave Dispersion ◽  
Physical Principle ◽  
Equivalent Model ◽  
Velocity Variation ◽  
Inversion Method ◽  
Dispersion Data ◽  
Logging While Drilling

The logging-while-drilling (LWD) quadrupole wave is a dispersive wave mode guided along the borehole with a drill collar. The wave is sensitive to the formation alteration caused by drilling. We inverted LWD quadrupole-wave dispersion data to estimate a radial shear-velocity profile away from the wellbore. We also explored the nonuniqueness of the inverse problem and solved it by using a constrained inversion method. This was done by constraining the high-frequency portion of the model dispersion curve with another curve calculated using the near-borehole velocity. The constraint condition is based on the physical principle that a high-frequency LWD quadrupole wave has a shallow penetration depth and is therefore sensitive to the near-borehole shear velocity. Particularly, we found that a monotonically continuous velocity profile can be well approximated using a one-zone equivalent model, allowing for a drastic simplification of the inversion process. We used theoretical modeling and real data examples to validate the method for the LWD wave data. The quadrupole dispersion data and the inversion results clearly demonstrated that formation alteration can occur even while the well is being drilled.

Investigation of the influence of the flow structure on the accuracy of flow measurement before a hydrometric structure in an open channel

2020 ◽  
pp. 41-44
Author(s):  
Anatoly Kusher
Keyword(s):  
Velocity Profile ◽  
Flow Velocity ◽  
Water Flow ◽  
Flow Measurement ◽  
Water Discharge ◽  
Critical Depth ◽  
Flow Measurements ◽  
Study Results ◽  
Flow Velocity Profile ◽  
Upstream Flow

The reliability of water flow measurement in irrigational canals depends on the measurement method and design features of the flow-measuring structure and the upstream flow velocity profile. The flow velocity profile is a function of the channel geometry and wall roughness. The article presents the study results of the influence of the upstream flow velocity profile on the discharge measurement accuracy. For this, the physical and numerical modeling of two structures was carried out: a critical depth flume and a hydrometric overfall in a rectangular channel. According to the data of numerical simulation of the critical depth flume with a uniform and parabolic (1/7) velocity profile in the upstream channel, the values of water discharge differ very little from the experimental values in the laboratory model with a similar geometry (δ < 2 %). In contrast to the critical depth flume, a change in the velocity profile only due to an increase in the height of the bottom roughness by 3 mm causes a decrease of the overfall discharge coefficient by 4…5 %. According to the results of the numerical and physical modeling, it was found that an increase of backwater by hydrometric structure reduces the influence of the upstream flow velocity profile and increases the reliability of water flow measurements.

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