Sommaire
Littérature scientifique sur le sujet « 3-D S-wave velocity »
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les listes thématiques d’articles de revues, de livres, de thèses, de rapports de conférences et d’autres sources académiques sur le sujet « 3-D S-wave velocity ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Articles de revues sur le sujet "3-D S-wave velocity"
1
Agudo, Òscar Calderón, Nuno Vieira da Silva, George Stronge et Michael Warner. « Mitigating elastic effects in marine 3-D full-waveform inversion ». Geophysical Journal International 220, no 3 (18 décembre 2019) : 2089–104. http://dx.doi.org/10.1093/gji/ggz569.
Texte intégralRésumé :
SUMMARY The potential of full-waveform inversion (FWI) to recover high-resolution velocity models of the subsurface has been demonstrated in the last decades with its application to field data. But in certain geological scenarios, conventional FWI using the acoustic wave equation fails in recovering accurate models due to the presence of strong elastic effects, as the acoustic wave equation only accounts for compressional waves. This becomes more critical when dealing with land data sets, in which elastic effects are generated at the source and recorded directly by the receivers. In marine settings, in which sources and receivers are typically within the water layer, elastic effects are weaker but can be observed most easily as double mode conversions and through their effect on P-wave amplitudes. Ignoring these elastic effects can have a detrimental impact on the accuracy of the recovered velocity models, even in marine data sets. Ideally, the elastic wave equation should be used to model wave propagation, and FWI should aim to recover anisotropic models of velocity for P waves (vp) and S waves (vs). However, routine three-dimensional elastic FWI is still commercially impractical due to the elevated computational cost of modelling elastic wave propagation in regions with low S-wave velocity near the seabed. Moreover, elastic FWI using local optimization methods suffers from cross-talk between different inverted parameters. This generally leads to incorrect estimation of subsurface models, requiring an estimate of vp/vs that is rarely known beforehand. Here we illustrate how neglecting elasticity during FWI for a marine field data set that contains especially strong elastic heterogeneities can lead to an incorrect estimation of the P-wave velocity model. We then demonstrate a practical approach to mitigate elastic effects in 3-D yielding improved estimates, consisting of using a global inversion algorithm to estimate a model of vp/vs, employing matching filters to remove elastic effects from the field data, and performing acoustic FWI of the resulting data set. The quality of the recovered models is assessed by exploring the continuity of the events in the migrated sections and the fit of the latter with the recovered velocity model.
2
Zhang, Yan, Ping Wang et Chongbin Guo. « Low-velocity impact failure mechanism analysis of 3-D braided composites with Hilbert–Huang transform ». Journal of Industrial Textiles 46, no 5 (28 juillet 2016) : 1241–56. http://dx.doi.org/10.1177/1528083715619955.
Texte intégralRésumé :
This paper aimed to reveal the low-velocity impact responses characteristics and failure mechanism of 3-D braided composites with experimental and frequency domain analysis method, respectively. The low-velocity impact tests were carried out by Instron® 9250 drop-weight instrument with five different impact velocities from 1 m/s to 6 m/s. The results showed that the peak load and absorbed energy increased with the increase of impact velocity. The load–time curves which were in time domain were transformed into frequency domain with Hilbert–Huang Transform (HHT) method. Combined the failure morphologies of 3-D braided composites with frequency domain analysis results, it could be precisely found out the failure mechanism of 3-D braided composites. At the impact velocity of 1 m/s, the 3-D braided composites only had elastic deformations. With the increase of impact velocity, resin crack was the main failure mode of 3-D braided composites. The frequency of impact stress waves which caused the elastic deformation and resin crack mainly located at 0–10 kHz and 60 kHz. When the impact velocity increased to 6 m/s, fiber tows breakage was the main failure mode, and the frequency of impact stress wave located at 15–20 kHz.
3
Mathisen, Mark E., Paul Cunningham, Jesse Shaw, Anthony A. Vasiliou, J. H. Justice et N. J. Guinzy. « Crosswell seismic radial survey tomograms and the 3-D interpretation of a heavy oil steamflood ». GEOPHYSICS 60, no 3 (mai 1995) : 651–59. http://dx.doi.org/10.1190/1.1443804.
Texte intégralRésumé :
S‐wave, P‐wave, and Poisson’s ratio tomograms have been used to interpret the 3-D distribution of rock and fluid properties during an early phase of a California heavy oil sand steamflood. Four lines of good quality crosswell seismic data, with source to receiver offsets ranging from 287 to 551 ft (87 to 168 m), were acquired in a radial pattern around a high temperature cemented receiver cable in four days. Processing, first‐arrival picking, and good quality tomographic reconstructions were completed despite offset‐related variations in data quality between the long and short lines. Interpretation was based on correlations with reservoir models, log, core, temperature, and steam injection data. S‐wave tomograms define the 3-D distribution of the “high flow” turbidite channel facies, the “moderate‐low flow” levee facies, porosity, and structural dip. The S‐wave tomograms also define an area with anomalously low S‐wave velocity, which correlates with low shear log velocities and suggests that pressure‐related dilation and compaction may be imageable. P‐wave tomograms define the same reservoir lithology and structure as the S‐wave tomograms and the 3-D distribution of low compressional velocity zones formed by previous steam‐heat injection and the formation of gas. The low P‐wave velocity zones, which are laterally continuous in the “high flow” channel facies near the top of most zones, indicate that the steam‐heat‐gas distribution is controlled by stratification. The stratigraphic control of gas‐bearing zones inferred from P‐wave tomograms is confirmed by Poisson’s ratio tomograms which display low Poisson’s ratios indicative of gas (<0.35) in the same zones as the low P‐wave velocities. The interpretation results indicate that radial survey tomograms can be tied at a central well and used to develop an integrated 3-D geoscience‐engineering reservoir model despite offset‐related variations in data quality. The laterally continuous, stratification‐controlled, low P‐wave velocity zones, which extend up‐dip, suggest that significant amounts of steam‐heat are not heating the surrounding reservoir volume but are flowing updip along “high flow” channels.
4
Movaghari, R., et G. Javan Doloei. « 3-D crustal structure of the Iran plateau using phase velocity ambient noise tomography ». Geophysical Journal International 220, no 3 (17 décembre 2019) : 1555–68. http://dx.doi.org/10.1093/gji/ggz537.
Texte intégralRésumé :
SUMMARY More accurate crustal structure models will help us to better understand the tectonic convergence between Arabian and Eurasian plates in the Iran plateau. In this study, the crustal and uppermost mantle velocity structure of the Iran plateau is investigated using ambient noise tomography. Three years of continuous data are correlated to retrieve Rayleigh wave empirical Green's functions, and phase velocity dispersion curves are extracted using the spectral method. High-resolution Rayleigh wave phase velocity maps are presented at periods of 8–60 s. The tomographic maps show a clear consistency with geological structures such as sedimentary basins and seismotectonic zones, especially at short periods. A quasi-3-D shear wave velocity model is determined from the surface down to 100 km beneath the Iran plateau. A transect of the shear wave velocity model has been considered along with a profile extending across the southern Zagros, the Sanandaj-Sirjan Zone (SSZ), the Urumieh-Dokhtar Magmatic Arc (UDMA) and Central Iran and Kopeh-Dagh (KD). Obvious crustal thinning and thickening are observable along the transect of the shear wave velocity model beneath Central Iran and the SSZ, respectively. The observed shear wave velocities beneath the Iran plateau, specifically Central Iran, support the slab break-off idea in which low density asthenospheric materials drive towards the upper layers, replacing materials in the subcrustal lithosphere.
5
Rowbotham, Peter S., et Neil R. Goulty. « Wavefield separation by 3-D filtering in crosshole seismic reflection processing ». GEOPHYSICS 59, no 7 (juillet 1994) : 1065–71. http://dx.doi.org/10.1190/1.1443662.
Texte intégralRésumé :
In processing crosshole seismic reflection data, it is necessary to separate the upgoing and downgoing primary reflections from each other, from the direct waves, and from other wave types in the data. We have implemented a 3-D f-k-k filter for wavefield separation that is applied in a single pass. The complete data set is treated as a data volume, with each sample defined by the three coordinates of source depth, receiver depth, and time. The filter works well because upgoing primaries, downgoing primaries, and direct waves lie in different quadrants in f-k-k space. The strongest multiples, including mode‐converted multiples, lie in the same quadrants in f-k-k space as the direct waves, so they are readily rejected together. Tube waves and mode‐converted primaries are also suppressed as most of the energy in these wave types lies outside the pass volume for P‐wave primaries. Some head wave and S‐wave primary energy will be passed by the filter; however, these waves tend to have low amplitudes and late arrival times, respectively, and will be smeared out on imaging with the P‐wave velocity field. We have processed a real crosshole data set using two different methods of wavefield separation: applying 2-D f-k filtering to common source gathers and applying a 3-D f-k-k filter to the whole data set. The migrated image produced after 3-D f-k-k filtering contains less coherent noise and consequently shows improved continuity of reflectors.
6
Chen, Kai-Xun, Po-Fei Chen, Li-Wei Chen, Huajian Yao, Hongjian Fang et Po-Li Su. « South Ilan Plain High-Resolution 3-D S-Wave Velocity from Ambient Noise Tomography ». Terrestrial, Atmospheric and Oceanic Sciences 27, no 3 (2016) : 375. http://dx.doi.org/10.3319/tao.2016.01.29.02(tem).
Texte intégral
7
Earp, S., A. Curtis, X. Zhang et F. Hansteen. « Probabilistic neural network tomography across Grane field (North Sea) from surface wave dispersion data ». Geophysical Journal International 223, no 3 (8 août 2020) : 1741–57. http://dx.doi.org/10.1093/gji/ggaa328.
Texte intégralRésumé :
SUMMARY Surface wave tomography uses measured dispersion properties of surface waves to infer the spatial distribution of subsurface properties such as shear wave velocities. These properties can be estimated vertically below any geographical location at which surface wave dispersion data are available. As the inversion is significantly non-linear, Monte Carlo methods are often used to invert dispersion curves for shear wave velocity profiles with depth to give a probabilistic solution. Such methods provide uncertainty information but are computationally expensive. Neural network (NN) based inversion provides a more efficient way to obtain probabilistic solutions when those solutions are required beneath many geographical locations. Unlike Monte Carlo methods, once a network has been trained it can be applied rapidly to perform any number of inversions. We train a class of NNs called mixture density networks (MDNs), to invert dispersion curves for shear wave velocity models and their non-linearized uncertainty. MDNs are able to produce fully probabilistic solutions in the form of weighted sums of multivariate analytic kernels such as Gaussians, and we show that including data uncertainties as additional inputs to the MDN gives substantially more reliable velocity estimates when data contains significant noise. The networks were applied to data from the Grane field in the Norwegian North sea to produce shear wave velocity maps at several depth levels. Post-training we obtained probabilistic velocity profiles with depth beneath 26 772 locations to produce a 3-D velocity model in 21 s on a standard desktop computer. This method is therefore ideally suited for rapid, repeated 3-D subsurface imaging and monitoring.
8
Frankel, Arthur. « Three-dimensional simulations of ground motions in the San Bernardino Valley, California, for hypothetical earthquakes on the San Andreas fault ». Bulletin of the Seismological Society of America 83, no 4 (1 août 1993) : 1020–41. http://dx.doi.org/10.1785/bssa0830041020.
Texte intégralRésumé :
Abstract Three-dimensional finite difference simulations of elastic waves in the San Bernardino Valley were performed for two hypothetical earthquakes on the San Andreas fault: a point source with moment magnitude M5 and an extended rupture with M6.5. A method is presented for incorporating a source with arbitrary focal mechanism in the grid. Synthetics from the 3-D simulations are compared with those derived from 2-D (vertical cross section) and 1-D (flat-layered) models. The synthetic seismograms from the 3-D and 2-D simulations exhibit large surface waves produced by conversion of incident S waves at the edge of the basin. Seismograms from the flat-layered model do not contain these converted surface waves and underestimate the duration of shaking. The seismograms from the 3-D simulations have larger amplitude coda than do the seismograms from the 2-D case because of the presence of off-azimuth surface wave arrivals in the 3-D simulations that are not included in the 2-D simulations. Snapshots of the wavefield of the 3-D simulation show that these off-azimuth arrivals represent surface waves reflected from the edges of the basin. The anelastic attenuation of the sediments is a key parameter controlling the overall duration of motion. Some of the coda energy at rock sites near the basin edges represents leakage of surface wave energy out of the basin. For the M6.5 earthquake simulation, the largest ground velocities occur where surface waves reflected from the edge of the basin interfere constructively with the trapped waves that follow the direct S-wave. Maps of maximum ground velocity are produced for two directions of rupture propagation. The largest velocities occur in localized portions of the basin. The location of the largest velocities changes with the rupture propagation direction. Contours of maximum shaking are also dependent on asperity positions and radiation pattern.
9
Kato, Kenichi, Keiiti Aki et Ta-Liang Teng. « 3-D simulations of surface wave propagation in the Kanto sedimentary basin, Japan—part 1 : Application of the surface wave Gaussian beam method ». Bulletin of the Seismological Society of America 83, no 6 (1 décembre 1993) : 1676–99. http://dx.doi.org/10.1785/bssa0830061676.
Texte intégralRésumé :
Abstract The goal of this study is to simulate the displacement waveforms of 8 sec-period Love waves observed at Tokyo and Yokohama stations in the Kanto sedimentary basin during the Izu-hanto-toho-oki Earthquake of 29 June 1980 (M0 = 7 × 1025 dyne · cm). The surface wave Gaussian beam method is applied for this purpose. On the basis of the 3-D seismic velocity and density structure of the Kanto basin and assuming that the earth medium is laterally homogeneous outside the Kanto basin, waveforms of Love waves are synthesized. The synthesized seismograms underestimate the observed peak amplitudes at Yokohama station. This is primarily because the station is located in the direction of the nodal plane of the Love-wave radiation. As indicated by Yamanaka et al. (1992), a Quaternary basin exists in the Sagami Bay between the source location and the Kanto basin. We include the Sagami basin in our model by the approximation of a circular low-velocity region. Excellent agreement between observed and synthesized waveforms was achieved not only for amplitude but also for phase for the early parts of the wave trains at both stations. We conclude that the low velocity Quaternary basin in the Sagami Bay acts like a lens to focus surface wave energy resulting in high amplitudes. The later arriving waves, in particular the long duration observed at Tokyo station, however, cannot be adequately explained by this method. One possible reason for the failure of simulating the later phases is that this method disregards the secondary Love waves converted from S-waves and/or surface waves at a laterally discontinuous boundary. Although the surface wave Gaussian beam method cannot adequately predict the duration of observed seismograms, it provides us with a satisfactory prediction of amplitudes and phases for early arrivals in laterally slowly-varying media at drastically lower computation costs and less memory requirements than does other methods.
10
Pujol, Jose, et Richard Aster. « Joint hypocentral determination and the detection of low-velocity anomalies. An example from the Phlegraean Fields earthquakes ». Bulletin of the Seismological Society of America 80, no 1 (1 février 1990) : 129–39. http://dx.doi.org/10.1785/bssa0800010129.
Texte intégralRésumé :
Abstract Arrival time data from the Phlegraean Fields (Italy) earthquake swarm recorded by the University of Wisconsin array in 1983 to 1984 were reanalyzed using a joint hypocentral determination (JHD) technique. The P- and S-wave station corrections computed as part of the JHD analysis show a circular pattern of central positive values surrounded by negative values whose magnitudes increase with distance from the center of the pattern. This center roughly coincides with the point of the maximum uplift (almost 2 m) associated with the swarm. Corrections range from −0.85 to 0.10 sec for P-wave arrivals and from −1.09 to 0.70 sec for S-wave arrivals. We interpret these patterns of corrections as caused by a localized low-velocity anomaly in the epicentral area, which agrees with the results of a previous 3-D velocity inversion of the same data set. The relocated (JHD) epicenters show less scatter than the epicenters obtained in the velocity inversion, and move more of the seismic activity to the vicinity of the only presently active fumarolic feature. The capability of the JHD technique to detect low-velocity anomalies and at the same time to give reliable locations, particularly epicenters, was verified using synthetic data generated for a 3-D velocity model roughly resembling the model obtained by velocity inversion.
Thèses sur le sujet "3-D S-wave velocity"
1
Lin, Cai-Yi, et 林采儀. « 3-D S-Wave Velocity Structure in South China Sea ». Thesis, 2015. http://ndltd.ncl.edu.tw/handle/50865775938369652298.
Texte intégralRésumé :
碩士國立臺灣海洋大學
應用地球科學研究所
103
The South China Sea (SCS), located at the junction of Eurasian plate, Indo-Australian plate and Pacific plate, is one of the marginal seas along the western Pacific. In the past, some studies investigated the plate features of the SCS by geophysical explorations using magnetic field, gravity, heat flow and seismic waves. For providing additional evidence in the tectonic evolution, the purpose of this study was to investigate the 3-D S-wave velocity structure in the SCS on the basis of Rayleigh-wave group and phase velocities. Earthquakes with magnitude from 5.5 to 7.0 and the focal depths of less than 100-km occurred from 1995 to 2012 at the region of 88-132E and 4S-32N were used to analyze Rayleigh-wave dispersion curves at periods of 12-150 seconds. At last, we adopted about 7000 Rayleigh-wave paths travelling across the SCS and its adjacent areas. Building a 3-D S-wave velocity structure by using surface waves requested a two-step inversion. First, the study area was divided into 375 sub-regions with each size of 22 in latitude and longitude. A block inversion with smoothing constraints, i.e., a tomographic method, was used to image 2-D maps of Rayleigh-wave group- and phase-velocity. Subsequently, the secondary inversion was to invert the S-wave velocity structure of each sub-region using its group- and phase-velocities. Finally, we combined the S-wave velocity structure of all sub-regions to construct the 3-D velocity model in the SCS. The model showed the lateral heterogeneity up to depths of 200 km, that is, the tectonic structure was complex in the crust and upper mantle under the SCS. The vertical velocity profiles along the EW-direction showed a high-velocity zone at a depth of about 50 km, which can be also found from north to south. This depth indicated the position where it is the lid of upper mantle. In additional, the crustal thickness decreased gradually toward the center of the SCS, where the crust is about 10-km-thick. The lithospheric thickness beneath the SCS is about 45-50 km. Low velocities in the Reed Bank and Dangerous Ground were related to the thick sediments; whereas the low velocity under the Tibet Plateau was in connection with its thicker crust. There are also low velocity in Sulu Sea and Central Philippine Islands, to be associated with high heat flow. The Nan-Uttaradit Suture and Sagaing Fault were also importantly geological boundaries, where the velocity differences can be obviously identified across these geological units. Along the NS-direction vertical profiles, the velocity variation in the Celebes Sea was relatively smooth than that in the Sulu Sea, in which the topography is complicated. This implied that the Sulu Sea has relatively higher action in plate tectonics than the Celebes Sea. The velocity discrepancy between the two sides of the Red-River Fault zone only was down to the crust, not to the lithosphere. For this reason, we inferred the Red-River Fault zone as a crustal fault.
2
Cheng, I.-Hsiu, et 鄭亦修. « 3-D Multi-scale Finite-frequency Ambient Noise Rayleigh Wave Tomography of Crustal S-Wave Velocity Structure beneath Central Tibet ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/70487862466898554989.
Texte intégralRésumé :
碩士國立臺灣大學
地質科學研究所
101
Surface wave travel-time tomography has been widely used as a powerful strategy to image shear wave velocity structure of the Earth’s crust and upper mantle. Traditionally with either ray theoretical great-circle approximations or 2-D phase kernels, phase velocity maps are first obtained at multiple frequencies. They are then combined to invert for shear wave velocity structure using 1-D depth-varying Frechet derivatives of phase velocity with respect to shear wave speed. Such approach runs short on considering the directional- and depth-dependence of scattering while surface wave propagating through laterally heterogeneous Earth. We here present a fully 3-D finite-frequency method based on the Born scattering theory in conjunction with surface-wave mode summation and apply it to regional fundamental Rayleigh wave tomography in central Tibet. Our data were collected from Hi-CLIMB array in the central Tibet during 2004-2005. Following a standard procedure to obtain empirical Green’s functions of Rayleigh waves from ambient noise cross correlation functions (CCFs) between station pairs, the phase differences between the CCFs and corresponding synthetics are measured by a multi-taper cross-spectral method. We apply the 3-D sensitivity kernels at individual frequencies convolved with the same eigentapers used in the phase measurement to conduct a 3D tomography of shear wave velocity perturbations with respect to a spherically-symmetric earth model suitable for central Tibet. A wavelet-based, multi-scale parameterization is invoked in the tomographic inversion to deal with the intrinsic problem of unevenly distributed data and resolve the structure with data-adaptive spectral and spatial resolutions. The result shows that the crust is generally slower to the north of the Bangong-Nujiang Suture (BNS) in marked contrast to the south with higher speeds. The absence of pervasive low velocity anomalies in the mid-to-lower crust indicates that the ductile channel flow of the lower crust may be inactive beneath southern Tibet. The model resolution in the lithospheric mantle can be improved by integrating longer-period surface data from distant earthquakes, which will yield better constrains on the geodynamic process of the Himalayan-Tibetan orogeny.
Actes de conférences sur le sujet "3-D S-wave velocity"
1
Sugimoto, Yoshihiro, Genyuu Kobayashi, Yutaka Mamada et Hideaki Tsutsumi. « Construction of 3-D S-wave velocity model by joint inversion method ». Dans Proceedings of the 11th SEGJ International Symposium, Yokohama, Japan, 18-21 November 2013. Society of Exploration Geophysicists, 2013. http://dx.doi.org/10.1190/segj112013-134.
Texte intégral
2
Zhang, Sheguang, Daniel Liut, Kenneth Weems et Woei-Min Lin. « A 3-D Finite Volume Method for Green Water Calculations ». Dans ASME 2005 24th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2005. http://dx.doi.org/10.1115/omae2005-67318.
Texte intégralRésumé :
A 3-D Finite Volume method (FV3D) is developed and applied to green water problems. The Navier-Stokes (N-S) equations are discretized with the 3-D finite volume method on collocated Cartesian grids. The free surface motion is captured with the Volume of Fluid (VOF) method. The velocity and pressure fields are solved by the SIMPLER scheme with an alternating direction implicit solver. FV3D is validated against existing experimental and numerical results for tank sloshing and ship green-water-on-deck cases. This method is applicable to calculation of the green water effect on advanced wave-piercing hull forms.
3
Culverhouse, D., P. St J. Russell et F. Farahi. « Forward-stimulated Brillouin scattering at 514.5 nm in dual-mode single-core fiber ». Dans Integrated Photonics Research. Washington, D.C. : Optica Publishing Group, 1990. http://dx.doi.org/10.1364/ipr.1990.mc6.
Texte intégralRésumé :
There has been a recent growth of interest in dual-moded (DM) optical fibers for a variety of nonlinear switching and modulation schemes.1-3 We report here what we believe to be the first observation of forward-stimulated Brillouin scatter (FSBS) between the LP01 and LP11 modes of a dual-mode (DM) fiber. Unlike normal SBS, forwhich the threshold power depends inversely on the laser linewidth, FSBS is easily observable with multimode light. This is because the pump (L) and Brillouin (B) waves propagate along exactly the same optical path and hence can maintain mutual coherence over kilometer lengths of fiber. Conservation of momentum in both cases is given by k L 01 = k B 11 + K(Ω) and k L 11 = k B 01 − K(Ω), where k L ij = ωn ij /c, k B ij = (ω−Ω)n ij /c, and K(Ω) = Ω/|v a | = 2π/Λ, where v a and Λ are the acoustic phase velocity and wavelength; the other parameters have their usual meanings. In FSBS the direction of the phonon wave depends on whether the frequency downconversion is LP01 → LP11 or vice versa (Fig. 1). In the DM fiber used, conventional SBS at 5145 nm yielded a shift of 32.4 GHz, which, because Λ = 0.176μm gives a phonon velocity v a = 5702 m/s, in close agreement with vext = 5760 for silica. An Ar+ laser running single-mode at 5145 nm was used to deliver light to 500 m of DM fiber (Fig. 2). To verify true single-frequency operation, part of the laser output was split off and monitored directly at a photodiode and confocal Fabry-Perot. A shutter system allowed for independent monitoring of the light emerging from the fiber. After careful adjustment of the launching conditions, the frequency spectrum in Fig. 3 was obtained at the photodiode. A clear frequency component is apparent at 16.6 MHz; no such signal was present in the laser output. In FSBS intermodal beating excites a flexural wave with A equal to the beat period L b , which couples the LP01 and LP11 modes by microbending. For our fiber parameters, L b = 0.17 mm at 5145 m/s. At Ω/2π = 16.6 MHz, a fiber diameter d = 125 μm and a shear velocity v t = 3764 m/s, Ωd/4πv t = 0.274, corresponding4 to a flexural wave velocity vaf ≈ 0.5vext = 2880 m/s. The product of L b and Ω/2π gives an independent estimate of vaf = 2822 m/s; the excellent agreement confirms that FSBS is taking place. For single-frequency excitation, the Brillouin gains are of the same order for SBS5 and FSBS; the ~105× smaller modal overlap in FSBS is compensated for by an ~105× smaller spontaneous acoustic absorption per acoustic wave length. The measured thresholds were ~45 mW/μm2 for SBS and ~5 mW/μm2 for FSBS.
4
Chen, Hua, Strong Guo, Xiao-Cheng Zhu, Zhao-Hui Du et Stone Zhao. « Numerical Simulations of Onset of Volute Stall Inside a Centrifugal Compressor ». Dans ASME Turbo Expo 2008 : Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50036.
Texte intégralRésumé :
In a previous publication (Guo & Chen et al., 2007), the authors solved the unsteady, 3-D Navier-Stokes equations with the k-ε turbulence model using CFX software to show that there is a volute stall coincided with the stage stall of a turbocharger centrifugal compressor operated at 423m/s tip speed and the stage stall frequency is dictated by a volute standing wave. This paper presents the flow condition at the vaneless diffuser and volute from the same simulation at various mass flow rates from stage peak efficiency to deep stage stall. Time averaged flow conditions show that (1) the influence of exducer blade passing at the volute inlet rapidly diminishes at the compressor peak pressure ratio point and the influence vanishes when the stage is in stall; (2) only at the peak pressure ratio point, circumferentially averaged, spanwise distribution of radial velocity at the volute inlet has an inflection point and the distribution meets the requirement of the Fjo̸rtoft instability theorem; (3) in the volute discharge section, the flow stalls after the stage stalls and the vortex core at the cross sectional center of the section breaks down; (4) impeller total pressure rise curve has a flat region in the middle before the stage stalls and (5) diffuser stall triggers the stage stall and drives the volute into stall.
5
Yamamoto, Yoshihito, Soichiro Okazaki, Hikaru Nakamura, Masuhiro Beppu et Taiki Shibata. « Crack Propagation and Local Failure Simulation of Reinforced Concrete Subjected to Projectile Impact Using RBSM ». Dans ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/omae2016-54969.
Texte intégralRésumé :
In this paper, numerical simulations of reinforced mortar beams subjected to projectile impact are conducted by using the proposed 3-D Rigid-Body-Spring Model (RBSM) in order to investigate mechanisms of crack propagation and scabbing mode of concrete members under high-velocity impact. The RBSM is one of the discrete-type numerical methods, which represents a continuum material as an assemblage of rigid particle interconnected by springs. The RBSM have advantages in modeling localized and oriented phenomena, such as cracking, its propagation, frictional slip and so on, in concrete structures. The authors have already developed constitutive models for the 3D RBSM with random geometry generated Voronoi diagram in order to quantitatively evaluate the mechanical responses of concrete including softening and localization fractures, and have shown that the model can simulate cracking and various failure modes of reinforced concrete structures. In the target tests, projectile velocity is set 200m/s. The reinforced mortar beams with or without the shear reinforcing steel plates were used to investigate the effects of shear reinforcement on the crack propagation and the local failure modes. By comparing the numerical results with the test results, it is confirmed that the proposed model can reproduce well the crack propagation and the local failure behaviors. In addition, effects of the reinforcing plates on the stress wave and the crack propagation behaviors are discussed from the observation of the numerical simulation results. As a result, it was found that scabbing of reinforced mortar beams subjected to high velocity impact which is in the range of the tests is caused by mainly shear deformation of a beam.
6
Johansen, Per Michael, et Arne Skov Jensen. « Dynamics of Magnetophotorefractive Wave Mixing ». Dans Photorefractive Materials, Effects, and Devices II. Washington, D.C. : Optica Publishing Group, 1993. http://dx.doi.org/10.1364/pmed.1993.fre.1.
Texte intégralRésumé :
In resonant photorefractive experiments the charge-density distribution in the conduction band is moving and an intrinsic magnetic field proportional to the velocity of the distribution is produced. In such cases the free electron plasma can interact with an externally applied magnetic field. On top of that materials exposed to a magnetic field exhibit Faraday rotation (Voigt birefringence) of the state of polarization of the optical bean.*. The purpose of the present summary is to describe the effect of both phenomena in a standard wave mixing setup. The photorefractive band transport model in the case v here magnetic fields are present is only modified via a term in the current density equation and reads (1) where e is the numeric elementary charge, µ the free electron mobility, n the number density' of free electrons, E the total electric field which may consist of an externally applied term and the norihnear generated spacecharge field, D the diffusion constant, and B the magnetic field term which may consist of an external part and an internal part (stemming from electronic motion). The remaining equations describing the photorefractive effect are the conventional ones. Now, by inferring the small modulation approximation, a perturbational relation for the physical quantities and, by Fourie- transforming in space-time, a steady-state response function for the space-charge electric field are found. ThL photorefractive frequency response function, expressed as a function of the conventional photorefractive parameters, is given by where the function P is given by (3) The actual definition of the parameters in Eqs. (2) and (3) can be found in Ref. [1]. Equation (2) is taken in the case where an externally magnetic field is applied perpendicular to the grating wave vector K. If it is assumed that the constituents of the incident intensity are monochromatic plane waves, that may be frequency shifted a small amount, the Fourier transformation of the perturbed intensity is a sum of δ-functions peaking at k = ±K and at ω = ±Ω. The space-charge field is now given by (4) A typical response function for GaAs:Cr is shown in Fig. 1. The characteristic parameters used in the calculation are taken from Refs. [2, 3, 4], The externally applied electric field is Eθ = 10 V/m, the applied magnetic field is Bθ = 2 T, the angle between the applied electric field and the grating wave vector is 20°, and the angle between the applied magnetic field and the z-axis is 45°. Recently, experiments on photorefr?ctive wave mixing with Faraday rotation in a diluted magnetic semiconductor of Cd] MnTe have been demonstrated. The gain showed an oscillatory behaviour as a function of the' magnetic field, and it was demonstrated that the magnetic field controls the direction and magnitude of the energy transfer. In what follows the coupled wave equations including uie effect of optical activity, the Faraday effect, and the effect of linear absorption will be given. Mcreover, the magnetic effects in the space-charge field given above will be taken into account. Numeric solutions to the coupled differential equations will be given. The equations are given in the following form (5) (6) (7) (8) where α is the absorption constant, Γθ the birefringence coupling constant, p the rotatory power, V the Verdet constant, <5 the angle between the z-axis and the magnetic field vector, and Γ (K,Ω) the photorefractive coupling parameter. A(. and are the polarization components perpendicular and^ parallel to the plane of incidence, respectively. In Fig. 2 a typical numerical solution to the above equations is given for photorefractive GaAs:Cr. The applied magnetic field is Bθ = 2 T, The electric field is Eθ - 106 V/m, the grating spacing is A - 34 µm, and the frequency shift is Ω = 94 rad/s. In such a material the optical activity is zero so the oscillations are due to the Faraday effect. Figure 1. The space-charge response function for GaAs:Cr. Figure 2. Intensity of the probe beam in GaAs:Cr as a function of distance in the crystal for a 10 mm crystal.
7
Zhao, Jiyun, Pradip Saha et Mujid S. Kazimi. « One Dimensional Thermal-Hydraulic Stability Analysis of Supercritical Fluid Cooled Reactors ». Dans 12th International Conference on Nuclear Engineering. ASMEDC, 2004. http://dx.doi.org/10.1115/icone12-49075.
Texte intégralRésumé :
A one-dimensional single-channel thermal-hydraulics model has been developed to investigate possible occurrence of density-wave instability in two U. S. Gen-IV reactors cooled by supercritical fluids, i. e., the Supercritical Water-cooled Reactor (SCWR) and Gas-cooled Fast Reactor (GFR). Water density in the SCWR core changes from 780 kg/m3, to 90 kg/m3, whereas the density of supercritical carbon-dioxide in the reference GFR changes from 155 kg/m3 to around 110 kg/m3. The standard frequency domain approach with a decay ratio of induced velocity amplitude of 0.5 has been used to determine the onset of flow instability. With suitable inlet orificing, the hot channel of SCWR has been found to be stable. Sensitivity studies show that the hot channel decay ratio reaches the critical value of 0.5 when either the reactor power is raised to 118% of full power or the core flow rate is reduced to 86% of nominal flow rate. System pressure has only a moderate effect. Detailed 3-D studies, preferably with neutronic feedback, should be carried out for the SCWR design because of its sensitivity to various important parameters. The GFR reference design has been found to be very stable since the density change in the GFR core is rather small compared to that in the SCWR design.