Academic literature on the topic 'Low velocity zone'
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Journal articles on the topic "Low velocity zone"
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Thybo, Hans. "The heterogeneous upper mantle low velocity zone." Tectonophysics 416, no. 1-4 (April 2006): 53–79. http://dx.doi.org/10.1016/j.tecto.2005.11.021.
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Hirschmann, Marc M. "Partial melt in the oceanic low velocity zone." Physics of the Earth and Planetary Interiors 179, no. 1-2 (March 2010): 60–71. http://dx.doi.org/10.1016/j.pepi.2009.12.003.
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Thorne, Michael S., Edward J. Garnero, Gunnar Jahnke, Heiner Igel, and Allen K. McNamara. "Mega ultra low velocity zone and mantle flow." Earth and Planetary Science Letters 364 (February 2013): 59–67. http://dx.doi.org/10.1016/j.epsl.2012.12.034.
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Lin-Gun, Liu. "Water, low-velocity zone and the descending lithosphere." Tectonophysics 164, no. 1 (July 1989): 41–48. http://dx.doi.org/10.1016/0040-1951(89)90232-1.
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Liu, Yike, Xu Chang, Futian Liu, and Ye Zheng. "Three-dimensional velocity images beneath the KangDian Tethyan tectonic zone of China." Canadian Journal of Earth Sciences 39, no. 10 (October 1, 2002): 1517–25. http://dx.doi.org/10.1139/e02-053.
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Three-dimensional velocity images of the crust and upper mantle beneath the KangDian Tethyan tectonic zone in China are constructed using P-wave travel-time residuals of earthquakes. The KangDian Tethyan tectonic zone is a transitional zone in tectonic structures and an important topographic border line. It is also a zone of concentration of shallow-focus earthquakes. The imaging results indicate that there is a significant lateral heterogeneity in the crust and upper mantle beneath the KangDian Tethyan tectonic zone in China. The velocity images of the upper crust show features closely related to the tectonic features on the surface. A low-velocity layer exists in a very wide range of the mid-crust. Almost all of the major earthquakes took place in the transition strips between high- and low-velocity zones in the crust above 20 km depth. From the velocity images at 20+0 and 50+0 km depth, respectively, we find that the epicenters of strong earthquakes with magnitude larger than 6.0 are almost entirely distributed in the low-velocity zones or on their boundaries.
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Hazarika, Devajit, Koushik Sen, and Naresh Kumar. "Characterizing the intracrustal low velocity zone beneath northwest India–Asia collision zone." Geophysical Journal International 199, no. 3 (September 30, 2014): 1338–53. http://dx.doi.org/10.1093/gji/ggu328.
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Park, Jin-Oh, Gou Fujie, Lalith Wijerathne, Takane Hori, Shuichi Kodaira, Yoshio Fukao, Gregory F. Moore, Nathan L. Bangs, Shin'ichi Kuramoto, and Asahiko Taira. "A low-velocity zone with weak reflectivity along the Nankai subduction zone." Geology 38, no. 3 (March 2010): 283–86. http://dx.doi.org/10.1130/g30205.1.
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Jan van Heijst, Hendrik, Roel Snieder, and Robert Nowack. "Resolving a low-velocity zone with surface-wave data." Geophysical Journal International 118, no. 2 (August 1994): 333–43. http://dx.doi.org/10.1111/j.1365-246x.1994.tb03965.x.
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Hough, S. E., Y. Ben-Zion, and P. Leary. "Fault-zone waves observed at the southern Joshua Tree earthquake rupture zone." Bulletin of the Seismological Society of America 84, no. 3 (June 1, 1994): 761–67. http://dx.doi.org/10.1785/bssa0840030761.
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Abstract Waveform and spectral characteristics of several aftershocks of the M 6.1 22 April 1992 Joshua Tree earthquake recorded at stations just north of the Indio Hills in the Coachella Valley can be interpreted in terms of waves propagating within narrow, low-velocity, high-attenuation, vertical zones. Evidence for our interpretation consists of: (1) emergent P arrivals prior to and opposite in polarity to the impulsive direct phase; these arrivals can be modeled as headwaves indicative of a transfault velocity contrast; (2) spectral peaks in the S wave train that can be interpreted as internally reflected, low-velocity fault-zone wave energy; and (3) spatial selectivity of event-station pairs at which these data are observed, suggesting a long, narrow geologic structure. The observed waveforms are modeled using the analytical solution of Ben-Zion and Aki (1990) for a plane-parallel layered fault-zone structure. Synthetic waveform fits to the observed data indicate the presence of NS-trending vertical fault-zone layers characterized by a thickness of 50 to 100 m, a velocity decrease of 10 to 15% relative to the surrounding rock, and a P-wave quality factor in the range 25 to 50.
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Hunt, Martin, Shawn Clark, and Rob Tkach. "Velocity distributions near the inlet of corrugated steel pipe culverts." Canadian Journal of Civil Engineering 39, no. 12 (December 2012): 1243–51. http://dx.doi.org/10.1139/l2012-112.
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This paper presents the findings of a study examining the velocity field within the inlet region of a corrugated steel pipe (CSP) culvert model with vertical headwall, 45° wingwall, and projecting end inlet treatments. Also examined are the effects of embedding the culvert below the stream bed and backfilling the culvert with granular material. Three-dimensional velocity distributions were measured in an effort to better understand how these inlet treatments may affect fish passage. The study examined velocity structure within a CSP culvert with a diameter of 0.8 m at a flow rate of 0.175 m3/s. Measurements were recorded using acoustic Doppler velocimeters at four locations; 0.25, 0.5, 1, and 2 diameters downstream of the inlet. The velocity field of each inlet configuration was dominated by a central jet of high velocity flow surrounded by a low velocity recirculation zone. Analysis of the percent area less than Uavg for each inlet treatment found that the projecting end configuration contained the largest low velocity zone. The usefulness of the low velocity recirculation zone as a fish passage corridor may however be limited by the presence of significant vertical and spanwise velocities as well as high shear zones.
Dissertations / Theses on the topic "Low velocity zone"
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Schaeffer, Andrew John. "Nature of a low-velocity zone atop the transition zone in northwestern Canada." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/11762.
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Seismic studies over the past decade have identified a S-wave low-velocity zone (LVZ) above the transition zone at various locations around the globe. This layer is hypothesized to be a lens of dense, fluid-rich silicate melt ponding atop the 410 km discontinuity, beneath the silicate melt-density crossover predicted to exist within the upper mantle. We have assembled a P- and S-receiver function (PRF and SRF, respectively) dataset from the CNSN Yellowknife Array (YKA), the CANOE array, and the POLARIS-Slave array, to quantify the physical properties and geographical extent of the layer in Northwestern Canada. In order to compute the Poisson's ratio, an important discriminant of possible composition and/or fluid content, we generated a suite of 1-D velocity models based on IASP91, but with varying thicknesses and velocity ratios for a hypothetical layer above the 410 km discontinuity. From these models we computed moveout curves for the range of slowness represented in the YKA data. A grid search was performed over the model space of interval thickness and Poisson's ratio to obtain an estimate of the model that best accounts for the data. In addition, we performed a linearized inversion of transmission coefficient amplitudes to estimate the shear velocity contrast at the bounding interfaces of the LVZ. Results indicate a LVZ of thickness 36 km with a shear velocity contrast of -7.8%, and Poisson's ratio of 0.42. In combination, these two results require an associated increase in compressional velocity into the LVZ. The Poisson's ratio lies well above the IASP91 average of 0.29-0.3 for this depth range and favours the presence of high melt or fluid fractions. Geographic profiles of PRFs and SRFs 1-D migrated to depth from CANOE and POLARIS-Slave arrays reveal 410 km and 660 km discontinuities at nominal depths with little variation in transition zone thickness. PRF results from the Slave craton indicate a potential LVZ beneath many stations at an average nominal depth of 340 km, highlighted by events from the northwest. The CANOE array SRF profile images an emergent LVZ beginning at 280 km depth dipping eastwards to 310 km approaching YKA.
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Sayed, Ali Yawar. "In Situ Compressional Wave Velocity Across An Exposed Brittle Fault Zone." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/34336.
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The effects of lithology, fracturing, and gouge zone mineralization on the geophysical properties of fault zones are not very well understood. In situ seismic data collected over the exhumed San Gregorio Fault at Moss Beach, CA were used to relate in situ compressional wave velocity to internal fault zone properties. This active strike-slip fault is exposed in cross section on an uplifting and actively eroding wave-cut platform. It cuts shallow marine sediments that have been buried to depths of a few kilometers. The unweathered exposure containing seawater makes it a unique analog of subsurface faults. Previous structural analysis over this exposure observed damage caused by faulting over a ~100 m wide zone in cross-section. The fault zone is centered at a 10-17 m wide clay-rich fault core flanked by a ~30 m wide brecciated gouge zone. These gouge zones are bordered on either side by 30-40 m wide fractured zones. Resolving to a scale of a few meters, the seismic survey produced a continuous P-wave velocity profile analogous to a horizontal well log across the fault. Lateral variations in the velocity profile correlate exactly to previously mapped fault zone structure. The clay core and adjacent brecciated gouge create a ~50 m wide very low velocity zone, 25-50% slower than the surrounding host rock. Fractured bedrock on either side of the core causes a wider zone of 5-10% slow velocity, for a total fault signature ~100 m wide. Fault parallel fracture anisotropy was observed in the fractured zones, but surprizingly anisotropy was not observed in the strongly foliated gouge zones. The field measurements differ significantly from laboratory measurements at zero pressure and in some cases from expected values for saturated rock of this porosity, perhaps due to biased rock sampling, the long wavelength effects of macrofractures, frequency dispersion, and partial saturation. The velocity profile is similar in width and consistent in velocity contrast to low S-wave velocity zones derived from fault zone guided waves in other strike-slip faults. The traveltime delay across the fault zone is not large enough to cause the 2-3 km wide crustal low velocity zones modeled by refraction studies. Synthetic reflection seismograms in the typical frequency range show that the fault zone acts as a thick bed or as a constructively interfering thin bed. The models suggest that very large reflection coefficients observed across accretionary prism faults can be explained by fracturing, brecciation and clay content without elevated pore pressures. Comparison with a refraction study across the Punchbowl Fault shows a similar structural zonation of these two well-studied examples of brittle fault zones. This suggests that high-resolution seismic velocity models can be used to directly interpret internal deformation structure of brittle faults.Master of Science
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Hansen, Ralf Theodor Johannes. "Nature of the low velocity zone in Cascadia from receiver function waveform inversion." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37984.
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Dipping low-velocity zones (LVZs) are a ubiquitous structural element of subduction zones worldwide. In this study we map seismic attributes characterizing the LVZ beneath the Cascadia subduction zone from northern Vancouver Island to northern California using receiver function waveform inversion. Throughout this region, the LVZ is characterized by high Vp/Vs ratios (mean=2.77), strong S-velocity contrasts (~50%) and thicknesses averaging 3.38 km. The LVZ is immediately underlain by a second, weaker layer exhibiting moderate Vp/Vs ratios (mean=1.85) with mean thickness of 4.62 km. We interpret the combined structure in terms of subducting oceanic crust, based on classical structural/petrological descriptions and constraints from previous studies of ophiolites and ocean drill cores. The LVZ is identified with pervasively hydrated, high porosity pillow basalts and sheeted dikes of Layer 2 with possible contributions from sediments (Layer 1). Fluids released from metamorphic dehydration reactions are maintained near lithosphere fluid pressures through an impermeable plate boundary above, and a low porosity, gabbroic/mafic-cumulate dominated Layer 3 below.
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Beale, Jacob N. "Local Earthquake Tomography at Mt. Pinatubo, Philippines." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/34635.
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A new high-resolution 3-dimensional P-wave velocity model for Mt. Pinatubo volcano was developed by tomographic inversion of P-wave arrivals from 3,007 earthquakes recorded during a four month period from May to August, 1991. The arrivals were recorded by a network of seismic stations, consisting of seven pre-eruption stations and seven post-eruption stations. Two stations survived the June eruptions. First-arrival travel times were calculated using a finite-difference solution to the eikonal equation. An iterative, linearized approximation of the nonlinear tomography problem was used to solve separately for both velocity structure and hypocenter locations. Several inversions performed with different initial parameters and convergence schemes, and synthetic checkerboard reconstructions indicate a horizontal spatial resolution of velocity perturbations near 4 km. However, the network sparseness allows for a substantial trade-off between focal depth, origin time, and the vertical velocity profile. Many hypocenter clusters collapse from diffuse clouds into tighter features after 3-D relocation. These bands of earthquakes appear to represent fault-related structures. Three low-velocity (relative to the horizontal average) anomalies exist within the well-resolved portion of the velocity model. These anomalies are spatially associated with pre- and post-eruption earthquakes oriented along mapped surface fault zones. Similar anomalies observed at different volcanoes have been previously interpreted as magma related. The low-velocity anomalies at Pinatubo are interpreted as highly fractured, hot volumes of mostly competent rock, which may contain partial melt.Master of Science
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Lucchi, Andrea. "Numerical simulation of low velocity impact on fiber metal laminates." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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The diffusion of composite laminates in aerospace industry has been slowed down by complexity in the prediction of fracture behaviours. In this respect the delamination phenomenon caused by Low-Velocity Impacts has been a critical issue. Several criteria that predict the delamination onset and growth have been analysed. The subsequent study has been focused on Cohesive Zone Models able to predict both initiation and propagation of delamination. Several models that represent the dynamic response of composite structures to impacts have been presented. An explicit FEM has been developed to perform 3D simulations of different layup configurations of Al2024T3 and Woven Carbon Prepreg Laminates subjected to a Low-Velocity Impact. ABAQUS, Dassault Systèmes Simulia Corp. has been employed to perform the numerical simulations. Specific attention is paid to the cohesive failure representing delamination.
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Wu, Jiedi. "New Constraints on Fault-Zone Structure from Seismic Guided Waves." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28873.
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The structure of fault zones (FZs) plays an important role in understanding fault mechanics, earthquake rupture and seismic hazards. Fault zone seismic guided waves (GW) carry important information about internal structure of the low-velocity fault damage zone. Numerical modeling of observed FZGWs has been used to construct models of FZ structure. However, the depth extent of the waveguide and the uniqueness of deep structure in the models have been debated. Elastic finite-difference synthetic seismograms were generated for FZ models that include an increase in seismic velocity with depth both inside and outside the FZ. Strong GWs were created from sources both in and out of the waveguide, in contrast with previous homogenous-FZ studies that required an in-fault source to create GW. This is because the frequency-dependent trapping efficiency of the waveguide changes with depth. The near-surface fault structure efficiently guides waves at lower frequencies than the deeper fault. Fault structure at seismogenic depth requires the analysis of data at higher frequencies than the GWs that dominate at the surface. Adapting a two-station technique from surface wave studies, dispersive differential group arrival times between two earthquakes can be used to solve for FZ structures between the earthquakes. This method was tested with synthetic data and shallow events recorded in the SAFOD borehole in the San Andreas Fault. A pair of deep earthquakes recorded in the SAFOD borehole indicate a ~150 m wide San Andreas Fault waveguide with >20% velocity contrast at 10-12 km depth. With additional earthquakes, the full FZ structure at seismogenic depth could be imaged. Subsurface FZ structure can also be derived from a surface source and receiver array analogous to a body-wave refraction survey. Synthetic seismograms for such source-receiver geometry were generated and verified that FZGWs are refracted by the increase in velocity with depth. Synthetic data from a surface array were successfully inverted to derive FZ structure in the subsurface. The new methods presented in this dissertation extend the potential of FZGWs to image deeper FZ structure than has been uniquely constrained in the past.Ph. D.
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Audibert, Clément. "Contribution à la caractérisation des mécanismes dissipatifs sous sollicitation d'impact de structures composites sandwichs intégrant des fibres naturelles. Proposition d'une zone d'absorption pour siège pilote." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0030/document.
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Ce travail s’inscrit dans la problématique de réduction de masse, de sécurité inhérent au domaine aéronautique, il concerne plus spécifiquement les sièges de pilotes d’avion de ligne. Un nouveau concept d’assise composite sandwich multifonctionnel est proposé. Il est composé d’une peau carbone, d’une âme nid d’abeille Nomex et d’une peau hybride Kevlar/lin. L’assemblage de plusieurs matériaux engendre des comportements parfois complexes et rend difficile la prédiction de la ruine de la structure. Une démarche expérimental/numérique est mise en place pour appréhender l’endommagement de l’assise et ainsi permettre un pré-dimensionnement via un outil numérique.Tout d’abord, des essais de caractérisation permettent d’élaborer les lois de comportement des différents matériaux constituant le sandwich. Le composite hybride présente un comportement élasto-plastique-endommageable-anisotrope. Le nida Nomex est représenté par un réseau de ressort et une loi couplant le comportement en compression et en cisaillement qui est implémentée dans ABAQUS. Des essais d’impacts permettent d’évaluer les modes de rupture et l’énergie dissipée par les concepts d’assises réalisés. Des simulations numériques intégrant les comportements matériaux identifiés sont mises en places pour corréler l’essai d’impact. L’analyse couplée des résultats expérimentaux et numériques permet d’identifier les couplages entre les différents mécanismes. Enfin, le modèle est utilisé pour dimensionner une assise composite qui s’avère sans optimisation fine, comparable à une assise existante en aluminium de l’A350This work is part of the problem of mass reduction, safety inherent in the aeronautical field, it concerns more specifically the seats of pilots of airliner. A new multi-functional sandwich composite seat pan is proposed, composed by a carbon skin, a Nomex honeycomb core and a Kevlar/flax hybrid skin. The assembly of several materials generates complex behaviors and makes the ruin of the structure difficult to predict. An experimental/numerical approach is used to understand the damage mechanism of the seat and to create a pre-dimensioning numerical tool.Firstly, characterization tests allow identifying the mechanical behaviors of each material and constituting a database for the creation of material laws. The hybrid composite shows an elastoplastic-damaging-anisotropic behavior. The honeycomb is represented by a spring network and a law coupling the compression and shear behavior is implemented. Impact tests are used to evaluate the failure modes and the energy dissipated by the different concepts. The impact tests are correlates by numerical simulation using the identified material behaviors. The analysis of the experimental and numerical results makes it possible to identify the coupling between the different mechanisms. Finally, the model is used to design a new composite seat pan. This one is comparable to the existing aluminum seat pan without optimization phase
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Franken, Thijs. "Analysing partial melting in the Réunion mantle plume." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7129.
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La fusion partielle dans la partie supérieure du manteau est fréquente dans les zones de remontée d’eau du manteau, comme les rifts, les dorsales médio-océaniques et les points chauds. Des zones de faible vitesse d’ondes de cisaillement dans le manteau peu profond (∼ 80 km) sont souvent associées à ces endroits, révélant des anomalies de vitesse de 4 à 5 % généralement attribuées à la présence de matériau fondu. Cependant, les études sur la quantité de matière fondue responsable de la réduction de la vitesse conduisent, suivant leur nature, à des conclusions différentes: les résultats expérimentaux de la pétrologie, des observations géochimiques et des modèles géodynamiques suggèrent une rétention de la matière fondue inférieure à 1 %, alors que les interprétations sismiques exigent une rétention supérieure à 1%. Dans cette thèse, j’essaie de résoudre le désaccord sur la rétention de la masse fondue dans l’asthénosphère en croisant des modèles de production de matériau en fusion et de propagation des ondes sismiques pour relier directement les conditions géodynamiques de la fusion partielle aux observations sismiques du panache mantellique de la Réunion. J’ai mis au point un modèle 1D de production de fusion qui évalue la rétention de la matière fondue selon le coefficient de perméabilité, la températures initiale du manteau et la vitesses de remontée d’eau selon un problème de Stokes modifié supposant un écoulement poreux. 210 scénarios de modèles de fusion sont convertis en vitesses d’ondes P et S sismiques anharmoniques à l’aide d’une base de données de paramètres minéraux, qui sont ensuite incorporés dans le modèle de référence de la terre ak135 pour générer des sismogrammes synthétiques des scénarios de fusion pour 21 tremblements de Terre. J’analyse l’effet du matériau fondu sur les composantes radiale, transversale et verticale de l’onde pour les arrivées de phase P, S, Pdiff et SKS. Grâce à une procédure automatisée de corrélation croisée, je calcule les différences relatives de temps de parcours entre les sismogrammes observés et les 210 traces synthétiques, pour chacun des 21 événements, 4 arrivées de phase, 3 composantes d’onde et 4 fréquences différentes de filtrage. J’analyse 70 896 points de données de temps de parcours relatifs pour trouver une solution optimale rendant compte des temps de parcours relatifs entre les traces du modèle et les observations sismiques, afin de découvrir quel scénario de fusion décrit le manteau supérieur sous la Réunion. La solution au scénario du modèle le mieux adapté n’est pas unique, puisque plusieurs combinaisons du coefficient de perméabilité, de température et de vitesse de remontée peuvent donner la même solution. En analysant séparément la distribution des paramètres du modèle sur la solution de temps de parcours relatif minimisé des 70 896 points de données pour les différentes arrivées de phase et composantes des ondes, on peut identifier deux régimes probables des conditions du manteau supérieur pouvant rendre compte des observations sismiques. Les conditions de manteau sous la Réunion se situent soit dans la plage de température de 1300 à 1350°C avec des fractions en fusion de ∼ 1 %, soit dans la plage de température de 1400 à 1450 °C avec des fractions en fusion inférieures à 0,3 %. Les contraintes des études sur la température du manteau supérieur, la perméabilité et les vitesses de transport du matériau fondu correspondent à ce dernier cas, ce qui souligne qu’une faible rétention de matériau fondu dans le manteau peu profond sous la Réunion satisfait simultanément les observations sismiques et les conditions géodynamiques prévuesPartial melting in the upper mantle is prevalent in areas of mantle upwelling such as rifts, mid-ocean ridges and hotspots. The presence of low shear-wave velocity zones in the shallow mantle (∼ 80km) are often associated with these locations, revealing velocity anomalies of −4 to −5% which are generally attributed to the presence of melt. However, studies on the quantity of melt responsible for the velocity reduction are divided, where experimental results from petrology, geochemical observations and geodynamical models suggest melt retention of < 1%, whereas seismic interpretations call for 1 > %. In this thesis I attempt to resolve the disagreement on melt retention in the asthenosphere by combining forward modelling of melt production and seismic wave propagation to relate geodynamic condition of partial melting directly to seismic observations of the Réunion mantle plume. I developed a 1D model of melt production that approximates melt retention for a range of permeability coefficients, initial mantle temperatures and upwelling velocities through a set of modified Stokes equations assuming porous flow. 210 melting model scenarios are converted to anharmonic seismic P- and S-wave velocities using a mineral parameter database, which are embedded into the ak135 earth reference model to generate synthetic seismograms of the melting scenarios for 21 source events using the Direct Solution Method for a laterally homogeneous and spherically symmetrical Earth. I explore the effect of melt presence on the radial, transverse and vertical wave component for the P, S, Pdiff and SKS phase arrivals, band-pass filtered to upper corner frequencies of 0.05, 0.1, 0.15 and 0.2 Hz. Through an automated cross-correlation procedure I compute relative traveltime differences between the observed seismograms and the 210 synthetic model traces for each iteration of the 21 source events, 4 phase arrivals, 3 wave components, and 4 band-pass filter frequencies. I analyse 70,896 relative traveltime datapoints to reach a solution for the minimised relative traveltimes between the model traces and the seismic observations, in order to discover which melting model scenario describes the upper mantle beneath Réunion. The solution to the best-fit model scenario is non-unique, since several combinations of the permeability coefficient, temperature and upwelling velocity give the same solution. By seperately analysing the parameter distribution of the free model parameters over the minimised relative traveltime solution of the 70,896 datapoints for the different phase arrivals and wave components, two likely regimes of upper mantle conditions can be constrained that can resolve the seismic observations. These regimes indicate that mantle conditions beneath Réunion are either in the 1300−1350 °C temperature range with melt fractions of ∼ 1%, or in the 1400−1450 °C temperature range with melt fractions of < 0.3%. Constraints from studies on upper mantle temperature, permeability and melt transportation velocities correspond to the latter case, showing that low retention of melt in the shallow mantle beneath Réunion simultaneously satisfy seismic observations and the expected geodynamic conditions
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Wells, Anne, and Anne Wells. "Analysis of Off-axis, Low-velocity Zones on the Flanks of the Endeavour Segment of the Juan de Fuca Ridge." Thesis, University of Oregon, 2012. http://hdl.handle.net/1794/12319.
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Seismic data from the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge reveal several crustal-level, low-velocity, high-attenuation regions on the eastern and western ridge flanks 7 to 16 km from the neovolcanic zone. I examine Pg amplitude anomalies for a wide variety of source-receiver azimuths in the Endeavour active source seismic tomography data. I use finite difference waveform forward modeling to estimate the dimensions, depth, and seismic properties of the best-observed inferred anomalous regions. The attenuating regions extend 10-15 km beneath axis-parallel bathymetric highs and from 2 to 4 km below the seafloor. The velocity reduction is small (~8%) and the attenuation large (QP ≈ 8-40) suggesting the presence of partial melt. I infer that melt focusing toward the neovolcanic zone is incomplete and that tectonic interactions with the Heckle seamount chain and/or the large segment-bounding overlapping spreading centers may promote off-axis melt delivery at the Endeavour segment.
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Hilairet, Nadège. "Rôle des serpentines dans la dynamique des zones de subduction : approche expérimentale à Haute Pression et Haute Température." Lyon, École normale supérieure (sciences), 2007. http://www.theses.fr/2007ENSL0429.
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Les serpentines, résultant de l'hydratation des minéraux mantelliques, pourraient être acteur majeur dans le transport de l'eau dans le manteau terrestre. Ayant une faible viscosité elle pourraient jouer un rôle déterminant dans la déformation et la répartition des contraintes dans les zones de subduction. Les équations d'état P-V des trois principales variétés de serpentines, lizardite, chrysotile et antigorite ont été obtenues expérimentalement. Une loi de déformation a été extraite d'expériences de déformation sur l'antigorite à HP-HT (200°C-500°C et 1à 4 GPa) et faible vitesse de déformation , réalisées sur synchroton avec une presse D-DiA. Les résultats expérimentaux permettent de discuter i) de la dynamique du coin de manteau dans la zone de subduction, ii) du rôle des serpentines dans la sismicité, et la relaxation inter-sismique et post-sismique.
Book chapters on the topic "Low velocity zone"
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Song, Teh-Ru Alex, and Don V. Helmberger. "Low Velocity Zone Atop the Transition Zone in the Western US from S Waveform Triplication." In Earth's Deep Water Cycle, 195–213. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/168gm15.
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Kocharyan, Gevorg G., Alexey A. Ostapchuk, and Dmitry V. Pavlov. "Fault Sliding Modes—Governing, Evolution and Transformation." In Springer Tracts in Mechanical Engineering, 323–58. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-60124-9_15.
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AbstractA brief summary of fundamental results obtained in the IDG RAS on the mechanics of sliding along faults and fractures is presented. Conditions of emergence of different sliding regimes, and regularities of their evolution were investigated in the laboratory, as well as in numerical and field experiments. All possible sliding regimes were realized in the laboratory, from creep to dynamic failure. Experiments on triggering the contact zone have demonstrated that even a weak external disturbance can cause failure of a “prepared” contact. It was experimentally proven that even small variations of the percentage of materials exhibiting velocity strengthening and velocity weakening in the fault principal slip zone may result in a significant variation of the share of seismic energy radiated during a fault slip event. The obtained results lead to the conclusion that the radiation efficiency of an earthquake and the fault slip mode are governed by the ratio of two parameters—the rate of decrease of resistance to shear along the fault and the shear stiffness of the enclosing massif. The ideas developed were used to determine the principal possibility to artificially transform the slidding regime of a section of a fault into a slow deformation mode with a low share of seismic wave radiation.
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Healy, J. H. "A Comment on the Evidence for a Worldwide Zone of Low Seismic Velocity at Shallow Depths in The Earth's Crust." In Geophysical Monograph Series, 35–40. Washington D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm014p0035.
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Filippov, Alexander E., and Valentin L. Popov. "Study of Dynamics of Block-Media in the Framework of Minimalistic Numerical Models." In Springer Tracts in Mechanical Engineering, 143–68. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-60124-9_7.
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AbstractOne of the principal methods of preventing large earthquakes is stimulation of a large series of small events. The result is a transfer of the rapid tectonic dynamics in a creep mode. In this chapter, we discuss possibilities for such a transfer in the framework of simplified models of a subduction zone. The proposed model describes well the basic characteristic features of geo-medium behavior, in particular, statistics of earthquakes (Gutenberg Richter and Omori laws). Its analysis shows that local relatively low-energy impacts can switch block dynamics from stick–slip to creep mode. Thus, it is possible to change the statistics of seismic energy release by means of a series of local, periodic, and relatively low energy impacts. This means a principal possibility of “suppressing” strong earthquakes. Additionally, a modified version of the Burridge-Knopoff model including a simple model for state dependent friction force is derived and studied. The friction model describes a velocity weakening of friction between moving blocks and an increase of static friction during stick periods. It provides a simplified but qualitatively correct stability diagram for the transition from smooth sliding to a stick–slip behavior as observed in various tribological systems. Attractor properties of the model dynamic equations were studied under a broad range of parameters for one- and two-dimensional systems.
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"low-velocity zone." In Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik, 826. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-41714-6_122615.
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"low-velocity zone." In Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik, 826. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-41714-6_122616.
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"Low-Velocity Zone." In Dictionary of Geotourism, 369. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-13-2538-0_1462.
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"Gutenberg low-velocity zone." In Dictionary Geotechnical Engineering/Wörterbuch GeoTechnik, 653. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-41714-6_73006.
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Sposito, Garrison. "The Statistical Physics of Subsurface Solute Transport." In Vadose Zone Hydrology. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780195109900.003.0007.
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The first detailed study of solute movement through the vadose zone at field scales of space and time was performed by Biggar and Nielsen (1976). Their experiment was conducted on a 150-ha agricultural site located at the West Side Field Station of the University of California, where the soil (Panoche series) exhibits a broad range of textures. Twenty well-separated, 6.5-m-square plots, previously instrumented to monitor matric potential and withdraw soil solution for chemical analysis, were ponded with water containing low concentrations of the tracer anions chloride and nitrate. After about 1 week, steady-state infiltration conditions were established, and 0.075 m of water containing the two anions at concentrations between 0.1 and 0.2 mol L-1 was leached through each plot at the local infiltration rate, which varied widely from 0.054 to 0.46 m day-1, depending on plot location. Once this solute pulse had infiltrated (< 1.5 days), leaching under ponded conditions was recommenced with the water low in chloride and nitrate. Solution samples were extracted before and after the solute pulse input at six depths up to 1.83 m below the land surface in each plot. Analyses of these samples for chloride and nitrate produced a broad range of concentration data which nonetheless showed an excellent linear correlation between the concentrations of the two anions (R2= 0.975), with a proportionality coefficient equal to that expected on the basis of the composition of the input pulse. Values of the measured solute concentrations at each sampling depth were tabulated as functions of the leaching time. Biggar and Nielsen (1976) decided to fit their very large concentration-depth-time database to a finite-pulsc-input solution of the one-dimensional advection-dispersion equation, leaving both the dispersion coefficient D and advection velocity u as adjustable parameters. The 359 field-wide values of u obtained in this way were highly variable (CV ≈ 200%), but also highly correlated (R2 = 0.84) and proportional to values of the advection velocity calculated directly as the ratio of water flux density to water content in each field plot (Biggar and Nielsen, 1976, figure 4).
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Presnall, Dean C., and Gudmundur H. Gudfinnsson. "Carbonate-rich melts in the oceanic low-velocity zone and deep mantle." In Plates, plumes and paradigms. Geological Society of America, 2005. http://dx.doi.org/10.1130/0-8137-2388-4.207.
Full textConference papers on the topic "Low velocity zone"
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Pilet, Sebastien, Jules Reymond, Massimo Chiaradia, and Rosa Anna Corsaro. "Etna Lavas are Melts Leaking from the Low Velocity Zone." In Goldschmidt2020. Geochemical Society, 2020. http://dx.doi.org/10.46427/gold2020.2087.
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Powell, Christine, and Berk C. Biryol. "WHAT IS THE ORIGIN OF THE UPPER MANTLE LOW VELOCITY ZONE BELOW THE MISSISSIPPI EMBAYMENT?" In GSA Annual Meeting in Indianapolis, Indiana, USA - 2018. Geological Society of America, 2018. http://dx.doi.org/10.1130/abs/2018am-323411.
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Deng, Yangbo, Jingming Dong, and Xu Zhen. "Study on Flow Field Characteristics of Low Swirl Injector." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37423.
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The flow characteristics of six kinds of LSIs, which are designed by different pore sizes in the center channel screen, are analyzed. The velocity vectors on the spanwise sections and the vertical sections in a channel at atmospheric condition are captured using a Particle Image Velocimetry (PIV) system. The swirl number of the airflow through the LSIs ranges from 0.5 to 0.58, and the inlet velocity is kept at 14m/s. The results show that the swirl number under a threshold can form low swirl flow. The velocity vector distribution of the low swirl flow is a diffuse shape without recirculation, and has the self-similar characteristic. The separation of low speed flow in the center zone and the high speed in the annulus zone generates the unique “W” shape distribution of the through the LSI. With the swirl number increasing, the area of the low vorticity zone decreases, and the vorticity value of the flow in the outer annular zone increases.
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Murawski, Christopher G., Rolf Sondergaard, Richard B. Rivir, Kambiz Vafai, Terrence W. Simon, and Ralph J. Volino. "Experimental Study of the Unsteady Aerodynamics in a Linear Cascade With Low Reynolds Number Low Pressure Turbine Blades." In ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-095.
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Low pressure turbines in aircraft experience large changes in flow Reynolds number as the gas turbine engine operates from takeoff to high altitude cruise. Low pressure turbine blades are also subject to regions of strong acceleration and diffusion. These changes in Reynolds number, strong acceleration, as well as elevated levels of turbulence can result in unsteady separation and transition zones on the surface of the blade. An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. The intent was to assess the effects of changes in Reynolds number, and freestream turbulence intensity. Flow Reynolds numbers, based on exit velocity and suction surface length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent. Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a slightly rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number resulted in a shrinkage of the separation region on the suction surface. Increasing both flow Reynolds numbers and freestream turbulence intensity compounded these effects such that at a Reynolds number of 300,000 and a freestream turbulence intensity of 8.1%, the separation zone was almost nonexistent. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. The width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. Numerical simulations were performed in support of experimental results. The numerical results compare well qualitatively with the low freestream turbulence experimental cases.
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Fareed, Shamsoon, and Ian May. "Response of Mild Steel Pipes Under High Mass Low Velocity Impacts." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-23366.
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Accidental loads, for example, due to heavy dropped objects, impact from the trawl gear and anchors of fishing vessels can cause damage to pipelines on the sea bed. The amount of damage will depend on the impact energy. The indentation will be localized at the contact area of the pipe and the impacting object, however, an understanding of the extent of the damage due to an impact is required so that if one should occur in practice an assessment can be made to determine if remedial action needs to be taken to ensure that the pipeline is still serviceable. There are a number of parameters, including the pipe cross section and impact energy, which influence the impact behaviour of a pipe. This paper describes the response, and assesses the damage, of mild steel pipes under high mass low velocity impacts. For this purpose full scale impacts tests were carried out on mild steel pipe having diameter of 457 mm, thickness of 25.4 mm and length of 2000 mm. The pipe was restrained along the base and a 2 tonnes mass with sharp impactor having a vertical downward velocity of 3870 mm/sec was used to impact the pipe transversely with an impact energy of 16 kJ. It was found from the impact tests that a smooth indentation was produced in the pipe. The impact tests were then used for validation of the non-linear dynamic implicit analyses using the finite element analysis software ABAQUS. Deformations at the impact zone, the rebound velocity, etc, recorded in the tests and the results of the finite element analysis were found to be in good agreement. The impact tests and finite element analyses described in this paper will help to improve the understanding of the response of steel pipes under impact loading and can be used as a benchmark for further finite element modelling of impacts on pipes.
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Rout, Mrutyunjay, Sasank Shekhar Hota, and Amit Karmakar. "Multiple Low Velocity Impact on Twisted Composite Stiffened Blade: A Finite Element Approach." In ASME 2017 Gas Turbine India Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gtindia2017-4772.
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This paper presents the numerical modeling of a twisted stiffened cylindrical shell employing finite element approach to investigate the transient response due to impact of multiple masses, wherein the shell and the stiffener are modeled as 8 noded isoparametric shell element with five degrees of freedom per node and 3 noded isoparametric curved beam element having four degrees of freedom per node, respectively. The stiffener element is considered as a discrete beam element and its nodal degrees of freedom are transferred to the corresponding degrees of freedom of the shell element considering curvature and eccentricity. The impact force is predicted by employing modified Hertzian contact law relating the contact force to local indentation. As indentation takes place the impactor induces damage and permanent deformation in the contact zone of stiffened panel, as a result the loading and unloading curves are different. Different mathematical equations are considered for both loading and unloading cases in the stiffened panel during low-velocity impact. The accuracy and effectiveness of the finite element approach is verified by comparing the results with the corresponding solutions of analytical as well as standard computational methods available in the open literature. The optimum design of a structure can only be obtained by understanding the impact behavior and the roles of various parameters affecting the response. Hence, parametric study has been carried out to predict the time histories of contact force, displacement of the impact point and in-plane stresses during low-velocity concurrent/delayed impact at multiple locations of the stationary and rotating stiffened shell.
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Hurlburt, Evan T., Larry B. Fore, and Richard C. Bauer. "A Two Zone Interfacial Shear Stress and Liquid Film Velocity Model for Vertical Annular Two-Phase Flow." In ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98512.
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The standard approach in estimating the interfacial shear between the vapor and the liquid film in annular two-phase flow is to include the effect of waves using a two-phase friction factor. This has been successful for low pressure annular flows in large hydraulic diameter ducts (wave heights ≪ H/2). It does not, however, work well for high pressure flows in smaller hydraulic diameter ducts (wave heights ∼ H/2). This suggests the need for a more detailed approach to incorporate wave effects in annular flow.
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Liu, Enhui, Xiao Liu, Hongtao Zheng, Jinghe Lu, Zhihao Zhang, and Binchuan You. "Investigation on Mixing Characteristics of Methane Fuel in Low Emission Combustor." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-14342.
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Abstract With the increasingly environmental problems and strict pollutant emission limits, pollutant emission has become a critical consideration for gas turbine. Mixing uniformity index of fuel-air has a significant effect on NOx emission. Previous works conducted basic research on mixing mechanism based on jet in crossflow, while few people studied a single real swirler channel in gas turbine combustor. The present work aims to bridge this gap and investigates the effects of fuel injection from the windward and leeward sides on the fuel concentration distribution and mixing uniformity index, based on a typical radical swirler channel. The qualitative analysis of velocity field and vortices structure and the quantitative analysis of velocity ratio and uniformity index are carried out. Due to the presence of sharp corner at the inlet of swirler, a recirculation zone is formed by the flow separation. The recirculation zone at the leeward side decreases the flow velocity and increases the area and time for fuel-air mixing. The velocity ratio plays a key role in the characteristics of flow and mixing. Under the same inlet conditions, the effective velocity ratio (R = 40) in the near field of the leeward side is about 10 times that of windward side (R = 4), and the maximum jet depth can be achieved in the near field. Therefore, the outlet uniformity index on the windward and leeward sides are 38.85% and 49.43%, respectively. From the perspective of mixing uniformity, fuel injection from the leeward side is beneficial to realize quick mixing in short distance. The present study is expected to provide insightful information for understanding mixing characteristics of methane fuel in low emission combustor.
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Song, Jinkwan, Johnathan Wilson, and Jong Guen Lee. "Experimental Investigation of a High Velocity Gaseous Jet Injection Into an Oscillating Crossflow." In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-60122.
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Abstract This paper presents the experimental results of a gaseous jet injected into an oscillating-air crossflow. The jet to crossflow momentum flux ratios are chosen as 19, 30 and 58, and the mean air crossflow velocities are chosen as 10m/s, 25 m/s, and 60 m/s. The crossflow is modulated at frequencies up to 280 Hz with a maximum crossflow velocity fluctuation of 30% of its mean velocity. Acetone planar laser-induced fluorescence is used to record the instantaneous jet concentration field. Three distinct regions are observed near the injection location (x/d < 18); the jet core, the fast bending zone, and the fully developed plume zone. The location of the end of potential core can be determined primarily by the momentum flux ratio. Based on observations of these three regions, a set of correlations for the trajectory of maximum jet concentration is proposed for the potential core region and for the fully developed plume zone. The potential core responds quasi-steadily to the crossflow oscillation and the fluctuation of penetration of the potential core zone linearly increases with respect to the crossflow velocity fluctuation level. The jet penetration under oscillating crossflow is slightly lower than that under steady crossflow, especially when the mean crossflow velocity is low (10–25 m/s). However, the differences of trajectories between the oscillating and the steady crossflow cases become almost negligible as the mean crossflow velocity increases further. The axial decay of jet concentration under oscillating crossflow occurs at faster rate than that under steady crossflow, indicating that the oscillating air crossflow enhances the mixing between the jet and the crossflow. The vertical jet concentration profile at different axial location confirms that the main effect of crossflow modulation is enhanced mixing of jet with crossflow. However, no noticeable effect of modulation frequency of crossflow on the jet penetration is found.
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Cheng, Xiao, Zhenhai Pan, and Huiying Wu. "Experimental Study of the Suspension Flow Past Confined Low-Aspect-Ratio Cylinder Arranged Microchannels." In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-86980.
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The recirculating wake behind the obstacle at moderate Reynolds numbers was devoid of particles, this was discovered by Haddadi et al. (J. Fluid Mech., 2014). However, only one obstacle and narrow Reynolds numbers were considered in their work. In this work, we constructed more confined environment, where the suspensions of solid fraction 0.25% with different particle diameters of 1, 5 and 10 μm flow past the critical confined low-aspect-ratio cylinder arrays (H/D = 0.3) with different arrangements were experimentally carried out. Reynolds numbers performed in the experiments ranged from 14∼550, and different flow patterns were observed. It was found that particles could flow into the region behind cylinder at low flow rate. Then, particle-depleted wake zone was formed behind the cylinder when increasing Re, which is similar with reported literature. It was interesting to find that when increasing Re further, the particles could flow into the recirculating wake zone behind cylinder. We generalized the particle behavior behind cylinder as from “entry” to “particle-free” and to “re-entry”. Additionally, the influence of different layout modes with inline and staggered cylinder arrays were also investigated. We found the particle-depleted wake zones behind the in-line cylinder array were larger than the one of the staggered cylinder array as the velocity were the same at “particle-free” stage. The in-line cylinder array possessed higher ability of allowing 1 μm particles to fill with the recirculating wake, whereas there were always existing particle-free zones in the core of recirculating wake of staggered cylinder array at “re-entry” stage. In order to understand particle-free mechanism better, microparticle image velocimetry (μPIV) technique was utilized to quantitatively measure the flow fields of in-line and staggered arranged cylinders. The obtained fluorescence pictures demonstrated that few particles flow into the zone behind cylinder at the “particle-free” stage, and fluorescence particles can flow into the wake at “re-entry” stage. That is, fluorescence particles also experienced the stages from “entry” to “particle-free” and to “re-entry”.
Reports on the topic "Low velocity zone"
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Larsen, S., and D. Harris. Seismic wave propagation through a low-velocity nuclear rubble zone. Office of Scientific and Technical Information (OSTI), October 1993. http://dx.doi.org/10.2172/10130414.
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Chanson, Hubert. Physical modelling of semi-circular channels and low velocity zones - application to pipe culverts and upstream fish passage at less-than-design flows. School of Civil Engineering, The University of Queensland, October 2019. http://dx.doi.org/10.14264/1ed47e8.
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