Synthetic seismic sections for acoustic, elastic, anisotropic, and vertically inhomogeneous layered media

Geophysics ◽  
1986 ◽  
Vol 51 (3) ◽  
pp. 710-735 ◽  
Author(s):  
F. Hron ◽  
B. T. May ◽  
J. D. Covey ◽  
P. F. Daley
Keyword(s):  
Three Dimensional ◽  
High Amplitude ◽  
Density Functions ◽  
Degree Of Anisotropy ◽  
First Arrival ◽  
Media Types ◽  
Time Distance ◽  
Converted Waves ◽  
Seismic Sections ◽  
Velocity Spectra

Synthetic seismic sections computed during forward modeling differ depending upon the type of media used to define the model. Four media types considered here are acoustic, elastic, elliptically anisotropic, and vertically inhomogeneous; significant differences are found among the seismic sections for these cases. Automatic ray generation, using kinematic and dynamic analog groups, permits retention and explicit identification of all significant arrivals, including primaries, multiples, converted waves, etc., for three‐dimensional, horizontally layered structures. Comparisons between arrivals common to the various models are shown by synthetic trace sections, amplitude‐distance plots, and velocity spectra. Results show significant energy in converted waves in the elastic models and marked differences between amplitude‐distance curves for elastic and acoustic cases. Anisotropic media produce noticeable differences in both amplitude‐ and time‐distance curves as a function of the degree of anisotropy. Modeling with vertically inhomogeneous media is practical and appealing because of how velocity and density functions are defined. Interestingly, a diving wave of high amplitude shown in our seismograms closely resembles the strong first arrival often present on field‐recorded seismograms.

Experimental investigation on the momentumless wake using trailing edge blowing

2008 ◽  
Vol 222 (8) ◽  
pp. 1477-1486 ◽  
Author(s):  
Y Wu ◽  
X Zhu ◽  
Z Du
Keyword(s):  
Three Dimensional ◽  
Velocity Profiles ◽  
Axial Fan ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Piv Measurement ◽  
Image Velocimetry ◽  
Velocity Spectra ◽  
Momentumless Wake ◽  
Wake Characteristics

A developed plate stator model with and without trailing edge blowing (TEB) is studied using experimental methods. Wake characteristics of flow over the stator in the three-dimensional wake regimes are studied using hot-wire anemometry (HWA) and particle image velocimetry (PIV) techniques. First, the mean velocity profiles have been measured in the wake of the stator using HWA. Four wake characteristics have been obtained through momentum thickness judgments: pure wake, weak wake, momentumless wake, and jet. These velocity profiles show some differences in momentum deficit for the four cases. Then, the velocity spectra of the pure wake and momentumless wake obtained through the HWA measurements showed that TEB can eliminate the shedding vortex of the stator. Characteristic length scales based on the wake turbulent intensity profiles showed that the momentumless wake can reduce the wake width and depth. PIV measurement is carried out to measure the flow field of the four wakes. Finally, the application of TEB approaching momentumless wake status is used on an industrial ventilation low-pressure axial fan to assess noise reduction. The results show that TEB can make the outlet of the stator uniform, reduce velocity fluctuation, destroy the vorticity structure downstream of the stator, and reduce interaction noise level of the stator and rotor.

The structure of weakly compressible grid-generated turbulence

2001 ◽  
Vol 432 ◽  
pp. 219-283 ◽  
Author(s):  
G. BRIASSULIS ◽  
J. H. AGUI ◽  
Y. ANDREOPOULOS
Keyword(s):  
Mach Number ◽  
Large Scale ◽  
Isotropic Turbulence ◽  
Three Dimensional ◽  
High Amplitude ◽  
Time Dependent ◽  
Wide Range ◽  
Dynamical Flow ◽  
Set Up ◽  
Decay Exponent

A decaying compressible nearly homogeneous and nearly isotropic grid-generated turbulent flow has been set up in a large scale shock tube research facility. Experiments have been performed using instrumentation with spatial resolution of the order of 7 to 26 Kolmogorov viscous length scales. A variety of turbulence-generating grids provided a wide range of turbulence scales with bulk flow Mach numbers ranging from 0.3 to 0.6 and turbulent Reynolds numbers up to 700. The decay of Mach number fluctuations was found to follow a power law similar to that describing the decay of incompressible isotropic turbulence. It was also found that the decay coefficient and the decay exponent decrease with increasing Mach number while the virtual origin increases with increasing Mach number. A possible mechanism responsible for these effects appears to be the inherently low growth rate of compressible shear layers emanating from the cylindrical rods of the grid. Measurements of the time-dependent, three dimensional vorticity vectors were attempted for the first time with a 12-wire miniature probe. This also allowed estimates of dilatation, compressible dissipation and dilatational stretching to be obtained. It was found that the fluctuations of these quantities increase with increasing mean Mach number of the flow. The time-dependent signals of enstrophy, vortex stretching/tilting vector and dilatational stretching vector were found to exhibit a rather strong intermittent behaviour which is characterized by high-amplitude bursts with values up to 8 times their r.m.s. within periods of less violent and longer lived events. Several of these bursts are evident in all the signals, suggesting the existence of a dynamical flow phenomenon as a common cause.

Complex seismic trace analysis of thin beds

Geophysics ◽  
1984 ◽  
Vol 49 (4) ◽  
pp. 344-352 ◽  
Author(s):  
James D. Robertson ◽  
Henry H. Nogami
Keyword(s):  
Instantaneous Frequency ◽  
Trace Analysis ◽  
Frequency Tuning ◽  
Seismic Energy ◽  
High Amplitude ◽  
Opposite Polarity ◽  
Peak Period ◽  
Seismic Wavelet ◽  
Porous Sandstone ◽  
Seismic Sections

Displays of complex trace attributes can help to define thin beds in seismic sections. If the wavelet in a section is zero phase, low impedance strata whose thicknesses are of the order of half the peak‐to‐peak period of the dominant seismic energy show up as anomalously high‐amplitude zones on instantaneous amplitude sections. These anomalies result from the well‐known amplitude tuning effect which occurs when reflection coefficients of opposite polarity a half period apart are convolved with a seismic wavelet. As the layers thin to a quarter period of the dominant seismic energy, thinning is revealed by an anomalous increase in instantaneous frequency. This behavior results from the less well‐known but equally important phenomenon of frequency tuning by beds which thin laterally. Instantaneous frequency reaches an anomalously high value when bed thickness is about a quarter period and remains high as the bed continues to thin. In this paper, complex trace analysis is applied to a synthetic model of a wedge and to a set of broadband field data acquired to delineate thin lenses of porous sandstone. The two case studies illustrate that sets of attribute displays can be used to verify the presence and dimensions of thin beds when definition of the beds is not obvious on conventional seismic sections.

scholarly journals Filaments and striations: anisotropies in observed, supersonic, highly magnetized turbulent clouds

2019 ◽  
Vol 492 (1) ◽  
pp. 668-685 ◽  
Author(s):  
James R Beattie ◽  
Christoph Federrath
Keyword(s):  
Magnetic Field ◽  
Column Density ◽  
Three Dimensional ◽  
High Density ◽  
Systematic Analysis ◽  
Guide Field ◽  
Degree Of Anisotropy ◽  
Mach Numbers ◽  
Magnetohydrodynamic Simulations ◽  
The Magnetic Field

ABSTRACT Stars form in highly magnetized, supersonic turbulent molecular clouds. Many of the tools and models that we use to carry out star formation studies rely upon the assumption of cloud isotropy. However, structures like high-density filaments in the presence of magnetic fields and magnetosonic striations introduce anisotropies into the cloud. In this study, we use the two-dimensional power spectrum to perform a systematic analysis of the anisotropies in the column density for a range of Alfvén Mach numbers ($\operatorname{\mathcal {M}_{\text{A}}}=0.1{\!-\!10}$) and turbulent Mach numbers ($\operatorname{\mathcal {M}}=2{\!-\!20}$), with 20 high-resolution, three-dimensional turbulent magnetohydrodynamic simulations. We find that for cases with a strong magnetic guide field, corresponding to $\operatorname{\mathcal {M}_{\text{A}}}\lt 1$, and $\operatorname{\mathcal {M}}\lesssim 4$, the anisotropy in the column density is dominated by thin striations aligned with the magnetic field, while for $\operatorname{\mathcal {M}}\gtrsim 4$ the anisotropy is significantly changed by high-density filaments that form perpendicular to the magnetic guide field. Indeed, the strength of the magnetic field controls the degree of anisotropy and whether or not any anisotropy is present, but it is the turbulent motions controlled by $\operatorname{\mathcal {M}}$ that determine which kind of anisotropy dominates the morphology of a cloud.

Special-Shaped Carton Visual CAD Research Based on Components

2011 ◽  
Vol 127 ◽  
pp. 511-515
Author(s):  
Ruo Lei Li ◽  
Zhi Jian Duan ◽  
Chao Ma
Keyword(s):  
Design Process ◽  
3D Model ◽  
Market Competition ◽  
Three Dimensional ◽  
Planar Structure ◽  
Cad Cam ◽  
Time Distance ◽  
Design Ideas ◽  
Cam Systems ◽  
Great Development

With the great development of commodity economy, the packaging of goods has become an extremely important factor to get the advantages in the market competition. As to paper packaging, people are taking more and more attention on the design of Special-shaped Cartons.Limited by the three-dimensional way of paper, the carton CAD/CAM systems generally use the design process of "carton shape chose from the carton library →parameters set and modified →the 3D model established following the existing way", development for new carton shapes are still depended on the folding-test by the designer's hand. Design of the Carton Planar Structure usually has a time distance with Design of the Carton 3D Model, as a results, inconvenience to Special-shaped Carton designing was caused, and designers can not express their design ideas quickly and effectively.

Groundwater exploration using combined controlled-source and radiomagnetotelluric techniques

Geophysics ◽  
2005 ◽  
Vol 70 (1) ◽  
pp. G8-G15 ◽  
Author(s):  
Laust B. Pedersen ◽  
M. Bastani ◽  
L. Dynesius
Keyword(s):  
Transfer Functions ◽  
Three Dimensional ◽  
Groundwater Exploration ◽  
Impedance Tensor ◽  
Two Dimensional ◽  
Controlled Source ◽  
Reflection Seismic ◽  
Seismic Sections ◽  
Clay Layers ◽  
Clay Lenses

Radiomagnetotelluric (RMT) (14–250 kHz) combined with controlled-source magnetotelluric (CSMT) (1–12 kHz) measurements were applied to the exploration of groundwater located in sandy formations at depths as great as 20 m below thick clay lenses. A combination of approximately 30 radio frequencies and controlled-source frequencies is essential for penetrating the thick clay layers. The electromagnetic transfer functions of impedance tensor and tipper vectors point toward a structure that is largely two-dimensional, although clear three-dimensional effects can be observed where the sandy formation is close to the surface. The determinant of the impedance tensor was chosen for inversion using two-dimensional models. The final two-dimensional model fits the data to within twice the estimated standard errors, which is considered quite satisfactory, given that typical errors are on the level of 1% on the impedance elements. Comparison with bore-hole results and shallow-reflection seismic sections show that the information delivered by the electromagnetic data largely agrees with the former and provides useful information for interpreting the latter by identifying lithological boundaries between the clay and sand and between the sand and crystalline basement.

Effect of hydrophone arrays on offshore Texas seismic signals

Geophysics ◽  
1978 ◽  
Vol 43 (6) ◽  
pp. 1083-1098
Author(s):  
M. E. Arnold
Keyword(s):  
Dynamic Range ◽  
High Amplitude ◽  
Early Event ◽  
Seismic Signals ◽  
Multiple Reflections ◽  
Surface Reflection ◽  
Field Recording ◽  
First Arrival ◽  
Slope Line ◽  
Water Bottom

The effect of hydrophone arrays in the recording of seismic signals during offshore Texas seismic marine experiments is judged by comparing traces of spatially tapered hydrophone array signals with traces that are combinations of simultaneously recorded wavetest hydrophone signals. Each spatially tapered hydrophone group array consists of 26 hydrophones nonuniformly spaced over 212 ft. The wavetest streamer section consists of 36 groups of two hydrophones, each pair connected in parallel and with hydrophones back‐to‐back for acceleration cancellation, with 5-ft spacing between groups. Reflection from deep subsurface interfaces are negligibly affected by hydrophone arrays except for very long arrays and/or long‐range distances. Consequently, the report is primarily concerned with the effects of simulated and real hydrophone arrays on first‐arrival signal and early subbottom reflections. Comparison of theoretical and actual seismic traces from an Aquapulse source for near range distances (835 ft) used in normal operations indicates that (1) near‐simultaneous arrival of the direct wave and surface reflection result in their virtual cancellation, (2) the early event with largest amplitude is associated with constructive interference between source and receiver ghost reflections, and (3) the “pseudo‐bubble” period effectively fixed the predominant frequency of all seismic events at values near 28 Hz. At medium range distances (4755 ft), such comparisons indicate that (1) first arrivals are refracted waves traveling in subbottom layers; (2) the water‐bottom reflection is beyond critical angle and is, therefore, complex; (3) the early events with largest amplitude are multiple reflections; and (4) at least two orders of water‐bottom multiples are identified. The attenuation of the high‐amplitude, first‐arrival signal that includes the water‐bottom reflection permits greater dynamic range in field recording and higher levels of “true” amplitude for later reflections without overload distortion of early events on playback. However, if improved resolution of reflection from moderate depths (∼4000 ft) is important, then arrays of length studied in this report (∼200 ft) should not be used to record signals at range distances greater than about 2000 ft because frequencies above 50 Hz are attenuated severely. Spectral analysis of wavetest records in the absence of signals shows that the wavenumber distribution of the noise is located along a slope line equivalent to 5000 ft/sec between wavenumbers that imply a spectral distribution of 30 to 100 Hz. Theoretical array response studies show that both the 36‐element Chebyshev array and the 26‐element spatially tapered array are superior to a 36‐element uniformly weighted array in rejection of seismic noise in the spectral range of 30 to 100 Hz.

Three-dimensional kinematic depth migration of converted waves: application to the 2002 Molise aftershock sequence (southern Italy)

2008 ◽  
Vol 56 (4) ◽  
pp. 587-600 ◽  
Author(s):  
Diana Latorre ◽  
Pasquale De Gori ◽  
Claudio Chiarabba ◽  
Alessandro Amato ◽  
Jean Virieux ◽  
...  
Keyword(s):  
Southern Italy ◽  
Three Dimensional ◽  
Aftershock Sequence ◽  
Depth Migration ◽  
Converted Waves

Effects of Mechanical Vibration on Double Curvature Creep Aging Forming of 2124 Aluminum Alloy

2018 ◽  
Vol 913 ◽  
pp. 83-89
Author(s):  
Yu Wang ◽  
Yun Lai Deng ◽  
Jin Zhang ◽  
Yong Zhang ◽  
Xin Ming Zhang
Keyword(s):  
Aluminum Alloy ◽  
Creep Deformation ◽  
Volume Fraction ◽  
Mechanical Vibration ◽  
Three Dimensional ◽  
Forming Process ◽  
Double Curvature ◽  
Vibration Field ◽  
Precipitation Behaviour ◽  
Degree Of Anisotropy

This Paper studied the precipitation behaviour and creep deformation of 2124 aluminum alloy based on the concept of complex field. A mechanical vibration field was introduced into the creep aging forming process of 2124 aluminum alloy, and its effects on creep deformation, precipitations behaviour and mechanical properties under the condition of double curvature loading and aging temperature were investigated by three-dimensional scanning technique, TEM and tensile test, respectively. The results showed that the spring back value along the rolling and transverse direction presented after creep aging forming were reduced by 25% and 15% respectively. The volume fraction of precipitates increased and distributed more densely and uniformly. Meanwhile, the yield stress improved by 15MPa and the degree of anisotropy decreased by 17% with mechanical vibration field applied to the manufacturing process.

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