MODEL STUDY OF RADIATION FROM AN EXPLOSION IN A CIRCULAR DISK

Geophysics ◽  
1969 ◽  
Vol 34 (2) ◽  
pp. 213-221 ◽  
Author(s):  
Dhari S. Bahjat ◽  
Carl Kisslinger
Keyword(s):  
Solid Medium ◽  
Circular Disk ◽  
Peak Frequency ◽  
Approximate Theory ◽  
Low Velocity ◽  
P Waves ◽  
Compressional Waves ◽  
Model Study ◽  
Disk Material ◽  
Solid Circular Cylinder

The effect of the medium immediately surrounding the shot on the properties of the primary compressional waves has been studied by means of two‐dimensional models. Circular disks of Plexiglas and Styrofoam of various diameters were inserted in large sheets of aluminum and of Plexiglas, respectively. Charges were fired in the center of the disk. An approximate theory for radiation from a simple harmonic line source of P waves on the axis of a solid circular cylinder embedded in an infinite homogeneous solid medium has been developed. The transfer function of the disk has been calculated from the observed spectra in order to compare it with the frequency response calculated from theory. The results show that for these cases of a low‐velocity disk a peak frequency exists which decreases with increasing diameter. The maximum peak frequency is that for a shot in an infinite sheet of the high‐velocity material, and the minimum peak frequency is that for a shot in a sheet of the low‐velocity disk material. This minimum peak frequency is approached rapidly as the disk diameter increases. The geometric effect of radiation from the circular inhomogeneity is important only over a narrow range of cavity diameters for which the resonance associated with the cavity happens to fall near the peak of the spectrum of the explosion‐generated wave.

Evaluation of direct hydrocarbon indicators through comparison of compressional‐ and shear‐wave seismic data: a case study of the Myrnam gas field, Alberta

Geophysics ◽  
1985 ◽  
Vol 50 (1) ◽  
pp. 37-48 ◽  
Author(s):  
Ross Alan Ensley
Keyword(s):  
Shear Wave ◽  
Seismic Data ◽  
Compressional Wave ◽  
Bright Spot ◽  
Low Velocity ◽  
Gas Reservoir ◽  
Gas Field ◽  
Compressional Waves ◽  
The Relationship

Shear waves differ from compressional waves in that their velocity is not significantly affected by changes in the fluid content of a rock. Because of this relationship, a gas‐related compressional‐wave “bright spot” or direct hydrocarbon indicator will have no comparable shear‐wave anomaly. In contrast, a lithology‐related compressional‐wave anomaly will have a corresponding shear‐wave anomaly. Thus, it is possible to use shear‐wave seismic data to evaluate compressional‐wave direct hydrocarbon indicators. This case study presents data from Myrnam, Alberta which exhibit the relationship between compressional‐ and shear‐wave seismic data over a gas reservoir and a low‐velocity coal.

Experimental Investigation of Low Velocity Impact and Residual Compressive Properties of Composite Laminates Based on AE

2013 ◽  
Vol 345 ◽  
pp. 214-217
Author(s):  
Shi Yan ◽  
Ying Guo ◽  
Xia Mei Lu
Keyword(s):  
Composite Laminates ◽  
Fracture Process ◽  
Peak Frequency ◽  
Low Velocity Impact ◽  
Displacement Curve ◽  
Compressive Failure ◽  
Compressive Properties ◽  
Low Velocity ◽  
Velocity Impact ◽  
Fracture Processes

The low-velocity impact and residual compressive failure processes of composite laminate were investigated by the acoustic emission (AE) technique in this paper. The AE energy, amplitude, and the peak frequency were analyzed. At the same time, combining with the load-displacement curve varying feature, the compressive fracture processes were divided into different stages to deeply understand the damaged mechanisms of the composites. Results reveal that the behavior of AE parameters described well the fracture process of the composites.

Long‐wave elastic anisotropy in transversely isotropic media

Geophysics ◽  
1979 ◽  
Vol 44 (5) ◽  
pp. 896-917 ◽  
Author(s):  
James G. Berryman
Keyword(s):  
Elastic Anisotropy ◽  
Transversely Isotropic ◽  
Layered Media ◽  
Seismic Signal ◽  
Perturbation Scheme ◽  
Low Velocity ◽  
Compressional Waves ◽  
Long Wave ◽  
Transversely Isotropic Media ◽  
Isotropic Media

Compressional waves in horizontally layered media exhibit very weak long‐wave anisotropy for short offset seismic data within the physically relevant range of parameters. Shear waves have much stronger anisotropic behavior. Our results generalize the analogous results of Krey and Helbig (1956) in several respects: (1) The inequality [Formula: see text] derived by Postma (1955) for periodic isotropic, two‐layered media is shown to be valid for any homogeneous, transversely isotropic medium; (2) a general perturbation scheme for analyzing the angular dependence of the phase velocity is formulated and readily yields Krey and Helbig’s results in limiting cases; and (3) the effects of relaxing the assumption of constant Poisson’s ratio σ are considered. The phase and group velocities for all three modes of elastic wave propagation are illustrated for typical layered media with (1) one‐quarter limestone and three‐quarters sandstone, (2) half‐limestone and half‐sandstone, and (3) three‐quarters limestone and one‐quarter sandstone. It is concluded that anisotropic effects are greatest in areas where the layering is quite thin (10–50 ft), so that the wavelengths of the seismic signal are greater than the layer thickness and the layers are of alternately high‐ and low‐velocity materials.

scholarly journals A MICROSCOPIC CLUSTER MODEL STUDY OF 3He + p SCATTERINGS

2010 ◽  
Vol 25 (21n23) ◽  
pp. 1750-1753
Author(s):  
K. ARAI ◽  
S. AOYAMA ◽  
Y. SUZUKI
Keyword(s):  
Cluster Model ◽  
Nucleon Nucleon ◽  
Phase Shifts ◽  
Minor Role ◽  
S Wave ◽  
P Waves ◽  
Model Study ◽  
Three Body ◽  
A Minor

3 He + p scattering phase shifts for the S- and P-waves are studied in a microscopic cluster model in order to investigate the role of the d + 2p channel in the low-energy phase shifts. In the present cluster model, the description of the 3 He wave function is extended from a simple (0s)3 model to a three-body model and two different nucleon-nucleon interactions, the Minnesota and AV8' potentials, are employed. The present extended cluster model shows that the d + 2p channel is indispensable to reproduce the resonant phase shifts in the AV8' potential while it plays a minor role in the MN potential. On the contrary, the role of this channel in the S-wave non-resonant phase shifts is negligible in both potentials.

Rapid map and inversion of P-SV waves

Geophysics ◽  
1991 ◽  
Vol 56 (6) ◽  
pp. 859-862 ◽  
Author(s):  
Robert R. Stewart
Keyword(s):  
Spatial Resolution ◽  
Seismic Data ◽  
P Wave ◽  
Rock Properties ◽  
Low Velocity ◽  
P Waves ◽  
Near Surface ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
And Inversion

Multicomponent seismic recordings are currently being analyzed in an attempt to improve conventional P‐wave sections and to find and use rock properties associated with shear waves (e.g. Dohr, 1985; Danbom and Dominico, 1986). Mode‐converted (P-SV) waves hold a special interest for several reasons: They are generated by conventional P‐wave sources and have only a one‐way travel path as a shear wave through the typically low velocity and attenuative near surface. For a given frequency, they will have a shorter wavelength than the original P wave, and thus offer higher spatial resolution; this has been observed in several vertical seismic profiling (VSP) cases (e.g., Geis et al., 1990). However, for surface seismic data, converted waves are often found to be of lower frequency than P-P waves (e.g., Eaton et al., 1991).

The horizontal propagation of P waves through scattering media: Analog model studies relevant to long-range Pn propagation

1983 ◽  
Vol 73 (1) ◽  
pp. 125-142
Author(s):  
William Menke ◽  
Paul G. Richards
Keyword(s):  
Long Range ◽  
Crustal Material ◽  
Scattering Media ◽  
Uppermost Mantle ◽  
Low Velocity ◽  
P Waves ◽  
Model Studies ◽  
Homogeneous Models ◽  
Amplifying Effect ◽  
Lateral Heterogeneities

abstract We compare seismograms produced through the use of analog models of scattering and nonscattering Earth structure to access the effect of lateral heterogeneities on the horizontal propagation of P waves. Our results are applicable to propagation out to 16° and to periods as short as 5 sec. We find that layers of scatterers within the mantle near the turning points of P waves can cause these phases to have long coda similar in certain respects to the coda observed in long-range Pn. The overall appearance of this coda is similar to that produced in laterally homogeneous models that include low-velocity crustal material near their surfaces. Scatterers at shallower depths in the mantle or crust have a different effect. Those in very uppermost mantle seem to suppress the horizontal propagation of P waves while those in the crust have very little overall effect, at least at the perod range we studied. We also find that the scatterers have an amplifying effect on the horizontal propagation of the very longest periods (>20 sec), an effect that may be related to the scattering-controlled boundary waves discovered by Biot (1968).

Travel-time curves for a low-velocity channel in the upper mantle

1964 ◽  
Vol 54 (6A) ◽  
pp. 1981-1996 ◽  
Author(s):  
John Dowling ◽  
Otto Nuttli
Keyword(s):  
Velocity Gradient ◽  
Upper Mantle ◽  
Body Wave ◽  
Shadow Zone ◽  
Low Velocity ◽  
P Waves ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Time Distance ◽  
Velocity Channel

abstract Velocities within the earth can be determined from body wave time-distance (T-D) data by the Herglotz-Wiechert method provided the velocity does not decrease too rapidly with depth. Until the present time, the properties of T-D curves for rapid decreases of velocity with depth have been considered only qualitatively. This paper presents a technique for calculating a T-D curve for any velocity distribution, including continuous and discontinuous increases and decreases of velocity with depth. Some properties of T-D curves are quantitatively studied by systematically varying the characteristics of a single model and noting the corresponding variations in the calculated T-D curves. From this it is concluded that a significant low-velocity channel may not be evidenced by a shadow zone but rather by an overlapping of two distinct branches of the T-D curve. It is further concluded that the presence of a shadow zone implies a very gentle velocity gradient below the low-velocity channel. By fitting a calculated T-D curve to observed data one can determine velocity as a function of depth even when the velocity decreases rapidly with depth, when a low-velocity channel exists. Observed T-D data for two underground nuclear explosions (gnome and bilby) measured in four different azimuths were fitted with T-D curves calculated for assumed velocity distributions. It is concluded that these data can be satisfied by a low-velocity channel for P waves in the upper mantle. The character of this channel (depth, thickness and velocity) was determined in each azimuth. The depth to its top was shallow (70 ± km) in the western U.S. and deep (125 ± km) in the eastern U.S. The velocity gradient below the channel is sharp enough to produce no prominent shadow zones. There are significant lateral changes in upper mantle velocities in the western U. S.

VARIATIONS IN SPECTRA OF P WAVES RECORDED AT CANADIAN ARCTIC SEISMOGRAPH STATIONS

1966 ◽  
Vol 3 (5) ◽  
pp. 597-621 ◽  
Author(s):  
Tokuji Utsu
Keyword(s):  
Surface Layer ◽  
Epicentral Distance ◽  
Canadian Arctic ◽  
The Arctic ◽  
Spectral Amplitude ◽  
Layered System ◽  
Low Velocity ◽  
P Waves ◽  
Low Frequencies ◽  
Spectral Curves

To investigate the effects of location of a seismograph station on the records obtained, P waves from seismograms of Alaskan earthquakes recorded at four Canadian Arctic stations, Coppermine, Mould Bay, Resolute, and Alert have been analyzed spectrally. Differences in spectral amplitude at very low frequencies among the stations and between earthquakes can reasonably be explained by a consideration of earthquake magnitude, epicentral distance, and mechanism. Differences in the shape of the spectral curves between stations result mainly from local crustal structures beneath the station. Increased absorption of waves is observed beneath Resolute. Use of the vertical to radial-horizontal spectral amplitude ratios gives an approximate estimate of the thickness of the crust and surface layer beneath these stations, although some phenomena noted cannot be explained by the theory of signal reverberation in a horizontally layered system with perfect elasticity. This analysis suggests that the crust thins toward the Arctic Ocean: the best estimates of crustal thickness are about 45 km at Coppermine, about 33 km at Resolute, about 23 at Alert, and about 18 km at Mould Bay. The latter depth is the most uncertain. There is a low velocity surface layer with a thickness of several hundred meters at Mould Bay, Resolute, and Alert.

Hydraulic Model Study on a Special CSO Chamber

2013 ◽  
Vol 353-356 ◽  
pp. 2614-2619
Author(s):  
Yong Min Chen
Keyword(s):  
Contour Line ◽  
Low Flow ◽  
Scale Model ◽  
Sediment Surface ◽  
Inlet Pipe ◽  
Low Velocity ◽  
Field Inspection ◽  
Model Study ◽  
Sonar System ◽  
Straight Line

In order to research the siltation problem of pressurized CSO chamber with the outlet pipe elevation higher than that of the inlet pipe, a 1:5 scale model was made of plexiglass for laboratory experiments. The velocity field of the CSO chamber was measured by PIV system. VOF and DPM models were adopted in the numerical simulation, and the results were applied to the comparison and analysis with the field inspection images obtained by SONAR system. Research results show that this special CSO chamber is liable to result in siltation in dry weather flow. The deposit location and shape of sediment depend on the flow field distribution. At low flow, there is low velocity eddy zone at the central region of CSO chamber, and then there is a bulge in the middle of sediment contour line in horizontal plane. With the increase of flow, the scouring force of middle region enhances, and then the sediment contour line tends to a straight line. Furthermore, there are relatively strong scour areas at both sides of inflow which result in the trend to be flat of sediment surface. These analyses are validated by field inspection of SONAR.

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