High‐resolution shallow‐seismic experiments in sand, Part II: Velocities in shallow unconsolidated sand

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1234-1240 ◽  
Author(s):  
Ran Bachrach ◽  
Jack Dvorkin ◽  
Amos Nur
Keyword(s):  
High Resolution ◽  
Velocity Profile ◽  
Contact Theory ◽  
Velocity Versus ◽  
Measured Velocity ◽  
Reflection And Refraction ◽  
Shallow Seismic ◽  
Unconsolidated Sand ◽  
Gassmann’S Equation ◽  
Vertical Velocity Profile

We conducted a shallow high‐resolution seismic reflection and refraction experiment on a sandy beach. The depth of investigation was about 2 m. We interpret the data using the Hertz‐Mindlin contact theory combined with Gassmann’s equation. These were used to obtain the vertical velocity profile. Then the profile was computed from seismic data using the turning‐rays approximation. The normal moveout (NMO) velocity at the depth of 2 m matches the velocity profile. As a result, we developed a method to invert measured velocity from first arrivals, i.e., velocity versus distance into velocity versus depth using only one adjustable parameter. This parameter contains all the information about the internal structure and elasticity of the sand. The lowest velocity observed was about 40 m/s. It is noteworthy that the theoretical lower bound for velocity in dry sand with air is as low as 13 m/s. We find that modeling sand as a quartz sphere pack does not quantitatively agree with the measured data. However, the theoretical functional form proves to be useful for the inversion.

Оdrеđivаnjе brzinе struјаnjа vаzduhа u prаvоugаоnоm zаtvоrеnоm cevovodu korišćenjem metoda polja brzina

2021 ◽  
Vol 23 (2) ◽  
pp. 57-63
Author(s):  
Marija Lazarevikj ◽  
◽  
Valentino Stojkovski ◽  
Viktor Iliev
Keyword(s):  
Velocity Profile ◽  
Flow Rate ◽  
Air Flow ◽  
Displacement Transducer ◽  
Linear Displacement ◽  
Local Velocity ◽  
Air Flow Rate ◽  
Mean Velocity ◽  
Measured Velocity ◽  
Integration Techniques

In the technical practice, it is often necessary to measure or control the fluid flow rate in pipelines and channels. The velocity-area method requires a number of meters located at specified points in a suitable cross-section of closed conduits. Simultaneous measurements of local mean velocity with the meters are integrated over the gauging section to provide the discharge. In this paper, three approaches of this method are applied on a rectangular closed conduit to determine the air flow rate with integration techniques used to compute the discharge assume velocity distributions that closely approximate known laws, especially in the neighborhood of solid boundaries. For this purpose, meters for velocity were 7 Pitot tubes placed vertically in predefined measurement points covering the conduit height, and moved horizontally along the conduit width. The position of the Pitot tubes along the conduit width was monitored and controlled by a linear displacement transducer. Pressure is measured using digital sensors. The first technique for determination of air flow rate is on basis of fixed (stopping) measuring points across the conduit width as averaged values of local velocity, the second one is semi continual measurement of velocity profile by applying interpolation between the average local velocity on fixed (stopping) points and measured velocity in the movement between two positions, and the third is by continuously moving the Pitot tubes without stopping. The results of the three techniques are calculated and presented using different types of software. Considering the last technique, comparison of results is made applying different movement speeds of the Pitot tubes in order to examine their influence on the velocity profile.

scholarly journals High-resolution, shallow, seismic reflection surveys of the Northwest Reelfoot Rift boundary near Marston, Missouri

1995 ◽  
Author(s):  
J.K. Odum ◽  
E.A. Luzietti ◽  
W.J. Stephenson ◽  
K.M. Shedlock ◽  
J.A. Michael
Keyword(s):  
High Resolution ◽  
Seismic Reflection ◽  
Shallow Seismic

scholarly journals PRELIMINARY STUDY OF HORIZONTAL AND VERTICAL WIND PROFILE OF QUASI-LINEAR CONVECTIVE UTILIZING WEATHER RADAR OVER WESTERN JAVA REGION, INDONESIA

2019 ◽  
Vol 15 (2) ◽  
pp. 177
Author(s):  
Abdullah Ali ◽  
Riris Adrianto ◽  
Miming Saepudin
Keyword(s):  
Velocity Profile ◽  
Vertical Velocity ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Convective Cloud ◽  
Vertical Wind ◽  
Squall Line ◽  
Vertical Velocity Profile ◽  
Preliminary Study ◽  
Wind Profiles

One of the weather phenomena that potentially cause extreme weather conditions is the linear-shaped mesoscale convective systems, including squall lines. The phenomenon that can be categorized as a squall line is a convective cloud pair with the linear pattern of more than 100 km length and 6 hours lifetime. The new theory explained that the cloud system with the same morphology as squall line without longevity threshold. Such a cloud system is so-called Quasi-Linear Convective System (QLCS), which strongly influenced by the ambient dynamic processes, include horizontal and vertical wind profiles. This research is intended as a preliminary study for horizontal and vertical wind profiles of QLCS developed over the Western Java region utilizing Doppler weather radar. The following parameters were analyzed in this research, include direction pattern and spatial-temporal significance of wind speed, divergence profile, vertical wind shear (VWS) direction, and intensity profiles, and vertical velocity profile. The subjective and objective analysis was applied to explain the characteristics and effects of those parameters to the orientation of propagation, relative direction, and speed of the cloud system’s movement, and the lifetime of the system. Analysis results showed that the movement of the system was affected by wind direction and velocity patterns. The divergence profile combined with the vertical velocity profile represents the inflow which can supply water vapor for QLCS convective cloud cluster. Vertical wind shear that effect QLCS system is only its direction relative to the QLCS propagation, while the intensity didn’t have a significant effect.

scholarly journals Implications of the form of the Flow Law for Vertical Velocity and Age–Depth Profiles in Polar Ice

1986 ◽  
Vol 32 (112) ◽  
pp. 366-370 ◽  
Author(s):  
E.W. Wolff ◽  
C.S.M. Doake
Keyword(s):  
Velocity Profile ◽  
Depth Profile ◽  
Vertical Velocity ◽  
Experimental Error ◽  
Ice Sheet ◽  
Polar Ice ◽  
Depth Profiles ◽  
Devon Island ◽  
Vertical Velocity Profile ◽  
Flow Law

AbstractTwo situations are studied in relation to the flow law of polar ice. In each case, models are used with a flow-law exponent of one, and with the more traditional exponent of three. The horizontal velocity profile at Devon Island, Arctic Canada, is better fitted byn= 1; for the vertical velocity profile,n= 3 gives a better fit, but both model profiles fall well within experimental error. For the Camp Century age–depth profile, onlyn= 1 gives an acceptable fit when temperature is allowed for. The large discrepancy between isothermal and non-isothermal models forn= 3 shows the importance of allowing for temperature in studies of ice-sheet properties.

P-wave velocity profile at very shallow depths in sand dunes

Geophysics ◽  
2020 ◽  
Vol 85 (5) ◽  
pp. U129-U137
Author(s):  
Sherif M. Hanafy ◽  
Ammar El-Husseiny ◽  
Mohammed Benaafi ◽  
Abdullatif Al-Shuhail ◽  
Jack Dvorkin
Keyword(s):  
Velocity Profile ◽  
Wave Velocity ◽  
Sand Dunes ◽  
Seismic Signal ◽  
Compressional Wave ◽  
Dominant Frequency ◽  
P Wave ◽  
Beach Sand ◽  
Low Velocity ◽  
Measured Velocity

We have addressed the problem of measuring the compressional wave velocity at a very shallow depth in unconsolidated dune sand. Because the overburden stress is very small at shallow depths, the respective velocity is small and the seismic signal is weak. This is why such data are scarce, in the lab and in the field. Our approach is to stage a high-resolution seismic experiment with a dense geophone line with spacing varying between 10 and 25 cm, allowing us to produce a velocity-depth relation in the upper 1 m interval. These results are combined with another survey in which the geophone spacing is 2 m and the dominant frequency is an order of magnitude lower than in the first survey. The latter results give us the velocity profile in the deeper interval between 1 and 7 m, down to the base of the dune. The velocity rapidly increases from about 48 m/s in the first few centimeters to 231 m/s at 1 m depth and then gradually increases to 425 m/s at 7 m depth. This is the first time when such a low velocity has been recorded at extremely shallow depths in sand in situ. The velocity profile thus generated is statistically fitted with a simple analytical equation. Our velocity values are higher than those published previously for beach sand. We find that using replacement or tomogram velocities instead of an accurately measured velocity profile may result in 23%–44% error in the static correction.

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