Home About us Contact
|
Home About us Contact | ||
|
|
||
Flow Patterns (flow + pattern)
Kinds of Flow Patterns Selected AbstractsImpact of Effective Valvotomy in Mitral Stenosis on Pulmonary Venous Flow PatternECHOCARDIOGRAPHY, Issue 7 2006Solange Bernardes Tatani M.D. Aims: Transesophageal Doppler echocardiography (TEE) is a useful tool to investigate pulmonary venous flow (PVF) velocity, which is altered in patients with mitral stenosis (MS). This study used TEE to analyze the variations in the PVF pattern after successful valvar dilatation in MS patients. Methods/Results: A total of 15 MS patients, mean age 27.2 years, underwent effective percutaneous balloon valvotomy (PBV). All were submitted to TEE before and after PBV. TEE assessed systolic (SPFV) and diastolic (DPFV) peak flow velocities and their ratio (SPFV/DPFV), time-velocity integrals (STVI and DTVI) and their ratio, and diastolic flow deceleration (DFD). Valvotomy yielded statistically significant increases (P , 0.05) in the SPFV: increase on average by 67% and STVI by 120%, as well as in the diastolic component: increased on average by 35%, DTVI by 33%, and DFD by 75%. Conclusion: TEE demonstrated that PBV induced a global increase in velocities of PVF, probably related to improvement of left atrial emptying. [source] Rare Flow Pattern in a Patient with Cor TriatriatumECHOCARDIOGRAPHY, Issue 8 2005Michael Ghalchi M.D. Doppler echocardiography demonstrated a rare flow pattern due to cor triatriatum that is also present in subvalvular or supravalvular mitral stenosis: a forward gradient, in both systole and diastole. [source] Superior Flow Pattern of Internal Thoracic Artery over Saphenous Vein Grafts during OPCAB ProceduresJOURNAL OF CARDIAC SURGERY, Issue 1 2009Alberto Weber Methods: Serial intraoperative flow measurements were carried out in 306 consecutive patients (mean age 64 years, mean Euroscore 5.1) undergoing off-pump coronary artery bypass grafting (OPCAB). The LAD was grafted in 302 patients [293 ITA (97%), 9 SV], the Cx in 252 patients [117 ITA (46%), 135 SV], and the RCA in 260 patients [36 ITA (14%), 224 SV]. Results: Averages of 3.7 ± 1.0 distal anastomoses/patient were constructed. Mean pulsatile index (PI) was significantly better for the single ITA/Cx-grafts (2.8 ± 1.9, n = 92) than for the single SV/Cx-grafts (3.3 ± 1.7, n = 43, p < 0.05), whereas the mean flow did not differ (28 ± 22 and 31 ± 25 mL/min respectively, p = ns). Accordingly, the mean PI was significantly better for the single ITA/RCA-grafts (2.2 ± 1.2, n = 36) than for the single SV/RCA-grafts (3.4 ± 2.6, n = 178, p < 0.01), whereas the mean flow did not differ (30 ± 16 and 32 ± 22 mL/min respectively, p = ns). The incidence of perioperative myocardial infarction tended to be lower in patients receiving an ITA to either the Cx or the RCA than in those receiving a SV, but the difference did not reach statistical significance [2/92 of ITA/Cx (2.2%) vs. 2/43 of SV/Cx (4.6%), 1/36 of ITA/RCA (2.8%) vs. 8/178 of SV/RCA (4.5%)]. Conclusion: The internal thoracic artery provides superior flow properties than the SV to the Cx and RCA regions with reduced perioperative ischemia. Whether this advantage persists after adjusting for the grade of the proximal coronary stenosis needs further studies. [source] Four-Month-Olds' Discrimination of Optic Flow Patterns Depicting Different Directions of Observer MotionINFANCY, Issue 2 2003Rick O. Gilmore One of the most powerful sources of information about spatial relationships available to mobile organisms is the pattern of visual motion called optic flow. Despite its importance for spatial perception and for guiding locomotion, very little is known about how the ability to perceive one's direction of motion, or heading, from optic flow develops early in life. In this article, we report the results of 3 experiments that tested the abilities of 4-month-old infants to discriminate optic flow patterns simulating different directions of self-motion. The combined results from 2 different experimental paradigms suggest that 4-month-olds discriminate optic flow patterns that simulate only large (> 32°) changes in the direction of the observer's motion through space. This suggests that prior to the onset of locomotion, there are limitations on infants' abilities to process patterns of optic flow related to self-motion. [source] Analysis of Flow Patterns in a Ventricular Assist Device: A Comparative Study of Particle Image Velocimetry and Computational Fluid DynamicsARTIFICIAL ORGANS, Issue 4 2009Katsutoshi Sato Abstract:, In order to develop a diaphragm-type ventricular assist device (VAD), we studied the flow field change following structural modifications. We devised a center flow-type pump by putting a small projection on the center of the housing and/or diaphragm to provide a center in the flow field, and examined the following four types of VADs: N type without a projection, D type with a projection on the diaphragm, H type with a projection on the housing, and DH type with projections on both the diaphragm and housing. Computational fluid dynamics (CFD) was used for flow simulation. Particle image velocimetry (PIV) was also used to verify the reliability of the CFD method and to determine how the flow field changes in the presence of a projection. The results of the PIV and CFD analyses were comparable. The placement of a projection on the housing was most effective in rectifying the flow field. [source] Progress in the Modelling of Air Flow Patterns in Softwood Timber KilnsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2004T.A.G. Langrish Progress in modelling air flow patterns in timber kilns using computational fluid dynamics (CFD) is reviewed in this work. These simulations are intended to predict the distribution of the flow in the fillet spaces between boards in a hydraulic model of a timber kiln. Here, the flow regime between the boards is transitional between laminar and turbulent flow, with Reynolds numbers of the order of 5000. Running the simulation as a transient calculation has shown few problems with convergence issues, reaching a mass residual of 0.2% of the total inflow after 40 to 100 iterations per time step for time steps of 0.01 s. Grid sensitivity studies have shown that non-uniform grids are necessary because of the sudden changes in flow cross section, and the flow simulations are insensitive to grid refinement for non-uniform grids with more than 300,000 cells. The best agreement between the experimentally-measured flow distributions between fillet spaces and those predicted by the simulation have been achieved for (effective) bulk viscosities between the laminar viscosity for water and ten times that value. This change in viscosity is not very large (less than an order of magnitude), given that effective turbulent viscosities are typically several orders of magnitude greater than laminar ones. This result is consistent with the transitional flows here. The effect of weights above the stack can reduce the degree of non-uniformity in air velocities through the stack, especially when thick weights are used, because the stack may then be separated from the eddy at the top of the plenum chamber. [source] Bi-level Programming Formulation and Heuristic Solution Approach for Dynamic Traffic Signal OptimizationCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2006Dazhi Sun Conventional methods of signal timing optimization assume given traffic flow pattern, whereas traffic assignment is performed with the assumption of fixed signal timing. This study develops a bi-level programming formulation and heuristic solution approach (HSA) for dynamic traffic signal optimization in networks with time-dependent demand and stochastic route choice. In the bi-level programming model, the upper level problem represents the decision-making behavior (signal control) of the system manager, while the user travel behavior is represented at the lower level. The HSA consists of a Genetic Algorithm (GA) and a Cell Transmission Simulation (CTS) based Incremental Logit Assignment (ILA) procedure. GA is used to seek the upper level signal control variables. ILA is developed to find user optimal flow pattern at the lower level, and CTS is implemented to propagate traffic and collect real-time traffic information. The performance of the HSA is investigated in numerical applications in a sample network. These applications compare the efficiency and quality of the global optima achieved by Elitist GA and Micro GA. Furthermore, the impact of different frequencies of updating information and different population sizes of GA on system performance is analyzed. [source] Plasma Edge Physics with B2-EireneCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-2 2006R. Schneider Abstract The B2-Eirene code package was developed to give better insight into the physics in the scrape-off layer (SOL), which is defined as the region of open field-lines intersecting walls. The SOL is characterised by the competition of parallel and perpendicular transport defining by this a 2D system. The description of the plasma-wall interaction due to the existence of walls and atomic processes are necessary ingredients for an understanding of the scrape-off layer. This paper concentrates on understanding the basic physics by combining the results of the code with experiments and analytical models or estimates. This work will mainly focus on divertor tokamaks, but most of the arguments and principles can be easily adapted also to other concepts like island divertors in stellarators or limiter devices. The paper presents the basic equations for the plasma transport and the basic models for the neutral transport. This defines the basic ingredients for the SOLPS (Scrape-Off Layer Plasma Simulator) code package. A first level of understanding is approached for pure hydrogenic plasmas based both on simple models and simulations with B2-Eirene neglecting drifts and currents. The influence of neutral transport on the different operation regimes is here the main topic. This will finish with time-dependent phenomena for the pure plasma, so-called Edge Localised Modes (ELMs). Then, the influence of impurities on the SOL plasma is discussed. For the understanding of impurity physics in the SOL one needs a rather complex combination of different aspects. The impurity production process has to be understood, then the effects of impurities in terms of radiation losses have to be included and finally impurity transport is necessary. This will be introduced with rising complexity starting with simple estimates, analysing then the detailed parallel force balance and the flow pattern of impurities. Using this, impurity compression and radiation instabilities will be studied. This part ends, combining all the elements introduced before, with specific, detailed results from different machines. Then, the effect of drifts and currents is introduced and their consequences presented. Finally, some work on deriving scaling laws for the anomalous turbulent transport based on automatic edge transport code fitting procedures will be described. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Combined effects of crucible geometry and Marangoni convection on silicon Czochralski crystal growthCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2009F. Mokhtari Abstract In order to understand the influence of crucible geometry combined with natural convection and Marangoni convection on melt flow pattern, temperature and pressure fields in silicon Czochralski crystal growth process, a set of numerical simulations was conducted. We carry out calculation enable us to determine temperature, pressure and velocity fields in function of Grashof and Marangoni numbers. The essential results show that the hemispherical geometry of crucible seems to be adapted for the growth of a good quality crystal and the pressure field is strongly affected by natural and Marangoni convection and it is more sensitive than temperature. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Numerical investigation of heat transport and fluid flow during the seeding process of oxide Czochralski crystal growth Part 1: non-rotating seedCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2007M. H. Tavakoli Abstract For the seeding process of oxide Czochralski crystal growth, the flow and temperature field of the system as well as the seed-melt interface shape have been studied numerically using the finite element method. The configuration usually used initially in a real Czochralski crystal growth process consists of a crucible, active afterheater, induction coil with two parts, insulation, melt, gas and non-rotating seed crystal. At first the volumetric distribution of heat inside the metal crucible and afterheater inducted by the RF coil was calculated. Using this heat source the fluid flow and temperature field were determined in the whole system. We have considered two cases with respect to the seed position: (1) before and (2) after seed touch with the melt. It was observed that in the case of no seed rotation (,seed = 0), the flow pattern in the bulk melt consists of a single circulation of a slow moving fluid. In the gas domain, there are different types of flow motion related to different positions of the seed crystal. In the case of touched seed, the seed-melt interface has a deep conic shape towards the melt. It was shown that an active afterheater and its location with respect to the crucible, influences markedly the temperature and flow field of the gas phase in the system and partly in the melt. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Meltwater discharge through the subglacial bed and its land-forming consequences from numerical experiments in the Polish lowland during the last glaciationEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2009Jan A. Piotrowski Abstract Numerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in NW Poland: primarily its flow pattern, velocities and fluxes. We have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady-state and transient conditions. The results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin. All model runs show water discharge at the ice forefield driven by ice-sheet-thickness-modulated, down-ice-decreasing hydraulic heads. In relation to non-glacial times, the transient 3D model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca. 90 m below the ice,bed interface and up to 40 km in front of the glacier. Comparison with empirical data suggests that, depending on the model run, only between 5 and 24% of the meltwater formed at the ice sole drained through the bed as groundwater. This is consistent with field observations documenting abundant occurrence of tunnel valleys, indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system. Groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely. In these areas the relief shows distinct palaeo-ice lobes, indicating fast ice flow, possibly triggered by the undrained water at the ice,bed interface. Owing to the abundance of low-permeability strata in the bed, the simulated groundwater flow depth is less than ca. 200 m. Copyright © 2009 John Wiley & Sons, Ltd. [source] Right Heart Function and Scleroderma: Insights from Tricuspid Annular Plane Systolic ExcursionECHOCARDIOGRAPHY, Issue 2 2007Chiu-Yen Lee M.D. Objective: The purpose of this study was to evaluate the use of echocardiographic parameters as predictors of rehospitalization in scleroderma patients. Methods: Echocardiographic studies were conducted in 38 patients with systolic scleroderma (SSc) to assess cardiopulmonary function. Forty-five age-matched volunteers without any sign of heart failure served as the control group. Transmitral flow pattern, tricuspid annular plane systolic excursion (TAPSE), left ventricular ejection fraction (LVEF), and right ventricular ejection fraction (RVEF) were evaluated. All patients were subsequently followed for one year. Results: Peak transmitral early-diastolic velocity (mitral E) and TAPSE measurements were significantly different between SSc and control patients (mitral E: 74.1 ± 16.3 vs. 83.5 ± 17.0 cm/s with P = 0.012; TAPSE: 2.4 ± 0.43 vs. 1.9 ± 0.39 cm with P < 0.0001). LVEF was similar, but RVEF was lower in the SSc group (LVEF: 61.7 ± 9.7 vs. 61.7 ± 5.8% with P = 0.962; RVEF: 49.6 ± 6.8 vs. 39.2 ± 6.7% with P < 0.0001). A strong correlation was found between TAPSE and RVEF. A TAPSE less than 1.96 cm indicted a RVEF less than 40% with a sensitivity of 81% and specificity of 78%. Contrary to expectation, pulmonary artery systolic pressure (PASP) did not correlate well with RV function (r = 0.261, r2= 0.068, P = 0.016). Finally, the frequency of rehospitalization was inversely correlated with RVEF and TAPSE in SSc patients. Conclusions: We can predict the rehospitalization rate of SSc patients by TAPSE and RVEF, suggesting the involvement of heart, skin, lung, and other organs in scleroderma patients. [source] Unusual Pulmonary Venous Flow Profile in a Patient with Mitral Valve Perforation Secondary to Bacterial EndocarditisECHOCARDIOGRAPHY, Issue 2 2006Shalini Modi M.D. Pulmonary venous flow patterns have been well described in the literature to assess severity of mitral regurgitation (MR) and the degree of diastolic dysfunction. We report a case of posterior mitral leaflet perforation due to bacterial endocarditis causing an alteration of pulmonary venous flow, not previously described in the literature. This pulmonary venous flow pattern is unique in that it reflects dynamic changes in left atrial pressure in the background of severe MR. [source] Rare Flow Pattern in a Patient with Cor TriatriatumECHOCARDIOGRAPHY, Issue 8 2005Michael Ghalchi M.D. Doppler echocardiography demonstrated a rare flow pattern due to cor triatriatum that is also present in subvalvular or supravalvular mitral stenosis: a forward gradient, in both systole and diastole. [source] Accumulation and filtering of nanoparticles in microchannels using electrohydrodynamically induced vortical flowsELECTROPHORESIS, Issue 14 2008Maika Felten Abstract We present an approach for the accumulation and filtering of nano- and microparticles in microfluidic devices that is based on the generation of electric traveling waves in the radio-frequency range. Upon application of the electric field via a microelectrode array, complex particle trajectories and particle accumulation are observed in well-defined regions in a microchannel. Through the quantitative mapping of the 3-D flow pattern using two-focus fluorescence cross-correlation spectroscopy, two vortices could be identified as one of the sources of the force field that induces the formation of particle clouds. Dielectrophoretic forces that directly act on the particles are the second source of the force field. A thorough 2-D finite element analysis identifies the electric traveling wave mechanism as the cause for the unexpected flow behavior observed. Based on these findings, strategies are discussed, first, for avoiding the vortices to optimize electrohydrodynamic micropumps and, secondly, for utilizing the vortices in the development of microdevices for efficient particle accumulation, separation, and filtering. Such devices may find numerous biomedical applications when highly diluted nano- and microsuspensions have to be processed. [source] Development of equine upper airway fluid mechanics model for Thoroughbred racehorsesEQUINE VETERINARY JOURNAL, Issue 3 2008V. RAKESH Summary Reason for performing study: Computational fluid dynamics (CFD) models provide the means to evaluate airflow in the upper airways without requiring in vivo experiments. Hypothesis: The physiological conditions of a Thoroughbred racehorse's upper airway during exercise could be simulated. Methods: Computed tomography scanned images of a 3-year-old intact male Thoroughbred racehorse cadaver were used to simulate in vivo geometry. Airway pressure traces from a live Thoroughbred horse, during exercise was used to set the boundary condition. Fluid-flow equations were solved for turbulent flow in the airway during inspiratory and expiratory phases. The wall pressure turbulent kinetic energy and velocity distributions were studied at different cross-sections along the airway. This provided insight into the general flow pattern and helped identify regions susceptible to dynamic collapse. Results: The airflow velocity and static tracheal pressure were comparable to data of horses exercising on a high-speed treadmill reported in recent literature. The cross-sectional area of the fully dilated rima glottidis was 7% greater than the trachea. During inspiration, the area of highest turbulence (i.e. kinetic energy) was in the larynx, the rostral aspect of the nasopharynx was subjected to the most negative wall pressure and the highest airflow velocity is more caudal on the ventral aspect of the nasopharynx (i.e. the soft palate). During exhalation, the area of highest turbulence was in the rostral and mid-nasopharynx, the maximum positive pressure was observed at the caudal aspect of the soft palate and the highest airflow velocity at the front of the nasopharynx. Conclusions and clinical relevance: In the equine upper airway collapsible area, the floor of the rostral aspect of the nasopharynx is subjected to the most significant collapsing pressure with high average turbulent kinetic during inhalation, which may lead to palatal instability and explain the high prevalence of dorsal displacement of the soft palate (DDSP) in racehorses. Maximal abduction of the arytenoid cartilage may not be needed for optimal performance, since the trachea cross-sectional area is 7% smaller than the rima glottidis. [source] Trends in water quality and discharge confound long-term warming effects on river macroinvertebratesFRESHWATER BIOLOGY, Issue 2 2009ISABELLE DURANCE Summary 1.,Climate-change effects on rivers and streams might interact with other pressures, such as pollution, but long-term investigations are scarce. We assessed trends among macroinvertebrates in 50 southern English streams in relation to temperature, discharge and water quality over 18 years (1989,2007). 2.,Long-term records, coupled with estimates from inter-site calibrations of 3,4 years, showed that mean stream temperatures in the study area had increased by 2.1,2.9 °C in winter and 1.1,1.5 °C in summer over the 26 year period from 1980 to 2006, with trends in winter strongest. 3.,While invertebrate assemblages in surface-fed streams were constant, those in chalk-streams changed significantly during 1989,2007. Invertebrate trends correlated significantly with temperature, but effects were spurious because (i) assemblages gained taxa typical of faster flow or well-oxygenated conditions, contrary to expectations from warming; (ii) more invertebrate families increased in abundance than declined and (iii) concomitant changes in water quality (e.g. declining orthophosphate, ammonia and biochemical oxygen demand), or at some sites changes in discharge, explained more variation in invertebrate abundance and composition than did temperature. 4.,These patterns were reconfirmed in both group- and site-specific analyses. 5.,We conclude that recent winter-biased warming in southern English chalk-streams has been insufficient to affect invertebrates negatively over a period of improving water quality. This implies that positive management can minimize some climate-change impacts on stream ecosystems. Chalk-stream invertebrates are sensitive, nevertheless, to variations in discharge, and detectable changes could occur if climate change alters flow pattern. 6.,Because climatic trends now characterize many inter-annual time-series, we caution other investigators to examine whether putative effects on ecological systems are real or linked spuriously to other causes of change. [source] Equations of state for basin geofluids: algorithm review and intercomparison for brinesGEOFLUIDS (ELECTRONIC), Issue 4 2002J. J. Adams ABSTRACT Physical properties of formation waters in sedimentary basins can vary by more than 25% for density and by one order of magnitude for viscosity. Density differences may enhance or retard flow driven by other mechanisms and can initiate buoyancy-driven flow. For a given driving force, the flow rate and injectivity depend on viscosity and permeability. Thus, variations in the density and viscosity of formation waters may have or had a significant effect on the flow pattern in a sedimentary basin, with consequences for various basin processes. Therefore, it is critical to correctly estimate water properties at formation conditions for proper representation and interpretation of present flow systems, and for numerical simulations of basin evolution, hydrocarbon migration, ore genesis, and fate of injected fluids in sedimentary basins. Algorithms published over the years to calculate water density and viscosity as a function of temperature, pressure and salinity are based on empirical fitting of laboratory-measured properties of predominantly NaCl solutions, but also field brines. A review and comparison of various algorithms are presented here, both in terms of applicability range and estimates of density and viscosity. The paucity of measured formation-water properties at in situ conditions hinders a definitive conclusion regarding the validity of any of these algorithms. However, the comparison indicates the versatility of the various algorithms in various ranges of conditions found in sedimentary basins. The applicability of these algorithms to the density of formation waters in the Alberta Basin is also examined using a high-quality database of 4854 water analyses. Consideration is also given to the percentage of cations that are heavier than Na in the waters. [source] A Combined Cluster and Interaction Model: The Hierarchical Assignment ProblemGEOGRAPHICAL ANALYSIS, Issue 3 2005Mark W. Horner This article presents a new spatial modeling approach that deals with interactions between individual geographic entities. The developed model represents a generalization of the transportation problem and the classical assignment problem and is termed the hierarchical assignment problem (HAP). The HAP optimizes the spatial flow pattern between individual origin and destination locations, given that some grouping, or aggregation of individual origins and destinations is permitted to occur. The level of aggregation is user specified, and the aggregation step is endogenous to the model itself. This allows for the direct accounting of aggregation costs in pursuit of optimal problem solutions. The HAP is formulated and solved with several sample data sets using commercial optimization software. Trials illustrate how HAP solutions respond to changes in levels of aggregation, as well as reveal the diverse network designs and allocation schemes obtainable with the HAP. Connections between the HAP and the literature on the p-median problem, cluster analysis, and hub-and-spoke networks are discussed and suggestions for future research are made. [source] Magma flow in the East Greenland dyke swarm inferred from study of anisotropy of magnetic susceptibility: magmatic growth of a volcanic marginGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2004Jean-Paul Callot SUMMARY Volcanic passive margins (VPMs) are characterized by large volumes of melt emplaced within the lithosphere during break-up processes. Several data and a recently proposed conceptual model of volcanic margin development suggest that VPMs are fed from localized crustal zones of magma storage, underlying large polygenetic volcanoes localized above diapir-like instabilities of the asthenosphere. We investigated the magma flow pattern within the coast-parallel dyke swarm of the East Greenland VPM, which is the only outcropping VPM, over a distance of 125 km. The 44 sampled dykes are representative of the successive families of intrusions. Igneous petrofabrics are constrained by the measurements of the anisotropy of magnetic susceptibility. The magnetic fabrics are of medium to low anisotropy (P, < 1.08) and show moderately oblate ellipsoids (T > 0). Flow-related fabrics are recorded in 75 per cent of the sampled dykes. We infer the flow directions from the imbrication geometry of the magnetic foliation planes at the dyke margins, and check the results by measuring the preferred orientation of plagioclase in thin sections cut in the magnetic principal planes. Due to probable fabric superposition, the magnetic lineation represents the zone axis for the distribution of magnetic foliation plane. We obtained 23 reliable flow directions that are predominantly horizontal and directed away from identified crustal reservoirs. This flow pattern supports the proposed model of VPM growth, and emphasizes the localized nature of the magma sources in the mantle. The entire flood basalt sequence appears to have been fed by a restricted number of crustal reservoirs and associated dyke swarms. [source] Convection in the Earth's core driven by lateral variations in the core,mantle boundary heat fluxGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000Steven John Gibbons Summary Moving core fluid maintains an isothermal core,mantle boundary (CMB), so lateral variations in the CMB heat flow result from mantle convection. Such variations will drive thermal winds, even if the top of the core is stably stratified. These flows may contribute to the magnetic secular variation and are investigated here using a simple, non-magnetic numerical model of the core. The results depend on the equatorial symmetry of the boundary heat flux variation. Large-scale equatorially symmetric (ES) heat flux variations at the outer surface of a rapidly rotating spherical shell drive deeply penetrating flows that are strongly suppressed in stratified fluid. Smaller-scale ES heat flux variations drive flows less dominated by rotation and so less inhibited by stratification. Equatorially anti-symmetric flux variations drive flows an order of magnitude less energetic than those driven by ES patterns but, due to the nature of the Coriolis force, are less suppressed by stratification. The response of the rotating core fluid to a general CMB heat flow pattern will then depend strongly on the subadiabatic temperature profile. Imposing a lateral heat flux variation linearly related to a model of seismic tomography in the lowermost mantle drives flow in a density stratified fluid that reproduces some features found in flows inverted from geomagnetic data. [source] Moderate Bioclogging Leading to Preferential Flow Paths in BiobarriersGROUND WATER MONITORING & REMEDIATION, Issue 3 2006Katsutoshi Seki Permeable reactive barriers (PRBs) are an alternative technique for the biological in situ remediation of ground water contaminants. Nutrient supply via injection well galleries is supposed to support a high microbial activity in these barriers but can ultimately lead to changes in the hydraulic conductivity of the biobarrier due to the accumulation of biomass in the aquifer. This effect, called bioclogging, would limit the remediation efficiency of the biobarrier. To evaluate the effects bioclogging can have on the flow field of a PRB, flow cell experiments were carried out in the laboratory using glass beads as a porous medium. Two types of flow cells were used: a 20- × 1- × 1-cm cell simulating a single injection well in a one-dimensional flow field and a 20- × 10- × 1-cm cell simulating an injection well gallery in a two-dimensional flow field. A mineral medium was injected to promote microbial growth. Results of 9 d of continuous operation showed that conditions, which led to a moderate (50%) reduction of the hydraulic conductivity of the one-dimensional cell, led to a preferential flow pattern within the simulated barrier in the two-dimensional flow field (visualized by a tracer dye). The bioclogging leading to this preferential flow pattern did not change the hydraulic conductivity of the biobarrier as a whole but resulted in a reduced residence time of water within barrier. The biomass distribution measured after 9 d was consistent with the observed clogging effects showing step spatial gradients between clogged and unclogged regions. [source] Transient flow patterns in a microfluidic chip with a complicated microstructureHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2008Wei Zhang Abstract The transient flow patterns of the boiling flow in a microfluidic chip with a complicated microstructure were studied at low mass fluxes and high heat fluxes. The periodic flow pattern in the timescale of milliseconds and the stratified flow pattern were observed. For a specific separated zone, the liquid film thickness was increased along the flow direction and the dry-out always occurred earlier at the microchannel upstream rather than downstream. However, for different microchannel zones, the dry-out took place earlier in the downstream zone. It was determined that the low liquid Froude number was responsible for the formation of the stratified flow. The large boiling number resulted in a large shear stress at the vapor,liquid interface, leading to the accumulation of the liquid in the microchannel downstream, causing the increased liquid film thickness along the flow direction. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(4): 224,231, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20201 [source] Lattice Boltzmann simulation on flow fields connected with multiple side-channelsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 2 2007Shohji Tsushima Abstract For this study, using the lattice Boltzmann method (LBM), we conducted flow-field analyses in which two straight channels were mutually connected with multiple side-channels. Results showed that calculated flow fields can be categorized into three types of flow pattern depending on flow field geometry and flow conditions. The following typical flow patterns were identified: case 1, the incoming flow passes uniformly through the side channels; case 2, the flow passes preferentially through the side channel in the inlet and the outlet; and case 3, the flow passes mainly through the side channel of the outlet side. Results also indicate that these flow patterns depend on two dimensionless parameters: the ratio of permeability of the side channels to the channel width, and the Reynolds number. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(2): 96,104, 2007; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/htj.20143 [source] A simplified model of gas,liquid two-phase flow pattern transitionHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2004Koji Ito Abstract An experiment of upward gas,liquid two-phase flow was conducted in an air,water isothermal system under atmospheric pressure. The differential pressure was measured at the fully developed section by using a variable reluctance type transducer to classify the flow patterns and their transitions. The flow behavior was observed with a high-speed video camera. The probability density function (PDF) of the differential pressure signal was employed to identify the flow pattern. A simplified one-dimensional flow model was proposed to clarify dominant factors affecting the formation and transitions of flow patterns. The model dealt with the gas-component advection based on the spatiotemporal void fraction behaviors by considering the gas compressibility, the wake, and the liquid phase redistribution mechanism. The simulation results of the model indicated four kinds of the void wave patterns (ripple-like, rectangular, distorted rectangular, and uniform wave patterns) depending on gas and liquid volumetric fluxes. These void wave patterns corresponded well to the experimentally observed flow patterns. The transitions among void wave patterns agree well with the Mishima,Ishii flow pattern map. The friction loss estimated by the present model coincides fairly well with Chisholm's empirical formula. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(7): 445,461, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20029 [source] Modelling lake stage and water balance of Lake Tana, EthiopiaHYDROLOGICAL PROCESSES, Issue 25 2009Yirgalem A. Chebud Abstract The level of Lake Tana, Ethiopia, fluctuates annually and seasonally following the patterns of changes in precipitation. In this study, a mass balance approach is used to estimate the hydrological balance of the lake. Water influx from four major rivers, subsurface inflow from the floodplains, precipitation, outflow from the lake constituting river discharge and evapotranspiration from the lake are analysed on monthly and annual bases. Spatial interpolation of precipitation using rain gauge data was conducted using kriging. Outflow from the lake was identified as the evaporation from the lake's surface as well as discharge at the outlet where the Blue Nile commences. Groundwater inflow is estimated using MODular three-dimensional finite-difference ground-water FLOW model software that showed an aligned flow pattern to the river channels. The groundwater outflow is considered negligible based on the secondary sources that confirmed the absence of lake water geochemical mixing outside of the basin. Evaporation is estimated using Penman's, Meyer's and Thornwaite's methods to compare the mass balance and energy balance approaches. Meteorological data, satellite images and temperature perturbation simulations from Global Historical Climate Network of National Oceanographic and Atmospheric Administration are employed for estimation of evaporation input parameters. The difference of the inflow and outflow was taken as storage in depth and compared with the measured water level fluctuations. The study has shown that the monthly and annually calculated lake level replicates the observed values with root mean square error value of 0·17 and 0·15 m, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Soil water repellency in a Japanese cypress plantation restricts increases in soil water storage during rainfall eventsHYDROLOGICAL PROCESSES, Issue 17 2007Masahiro Kobayashi Abstract Forest soils in Japan are often water repellent. Substantial water repellency frequently occurs and impedes water infiltration into the soil matrix, but continuous overland flow is not necessarily observed because forest soils usually have macropores through which the water can enter the subsoil. Although this flow pattern may influence the manner of water storage in forest soils at the solum scale, field evidence has not yet indicated this process. We monitored soil water storage during natural rainfall events in a 60-cm deep solum using time domain reflectometry (TDR) moisture sensors, and observed stained flow patterns in the soil following simulated rainfall containing a colour dye, on a slope planted with Japanese cypress (Chamaecyparis obtusa). The surface soil at the research plot exhibited strong water repellency at water contents lower than the threshold critical water content of 0·29 m3 m,3. Under dry antecedent moisture conditions, increases in soil water storage were small compared to the cumulative rainfall, despite the low wetness of the soil matrix. In contrast, under moderate moisture conditions, increases in the water content corresponded to the cumulative rainfall. Under dry conditions, rainwater may have entered the subsoil at a few limited locations connected with continuous vertical macropores, such as decayed root channels or interstructural voids. Therefore, the water seemed to bypass a large part of the soil matrix away from the macropores. Such preferential water flow was confirmed by the stained flow patterns after the rainfall simulation. The flow patterns visualized by the dye were discontinuous and scattered under dry conditions and diffuse under moderate moisture conditions. Repellency induced preferential flow led to restricted increases in solum scale water storage during rainfall events, reflecting a physical nonequilibrium in soil water storage. Copyright © 2007 John Wiley & Sons, Ltd. [source] A three-dimensional integral equation model for calculating poro- and thermoelastic stresses induced by cold water injection into a geothermal reservoirINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2009X. X. Zhou Abstract Poro-mechanical and thermo-mechanical processes change the fracture aperture and thus affect the water flow pattern in the fracture during the cold water injection into enhanced geothermal systems (EGS). In addition, the stresses generated by these processes contribute to the phenomenon of reservoir seismicity. In this paper, we present a three-dimensional (3D) partially coupled poro-thermoelastic model to investigate the poroelastic and thermoelastic effects of cold water injection in EGS. In the model, the lubrication fluid flow and the convective heat transfer in the fracture are modeled by the finite element method, while the pore fluid diffusion and heat conductive transfer in the reservoir matrix are assumed to be 3D and modeled by the boundary integral equation method without the need to discretize the reservoir. The stresses at the fracture surface and in the reservoir matrix are obtained from the numerical model and can be used to assess the variation of in situ stress and induced seismicty with injection/extraction. Application of the model shows that rock cooling induces large tensile stresses and increases fracture conductivity, whereas the rock dilation caused by fluid leakoff decreases fracture aperture and increases compressive total stresses around the injection zone. However, increases in pore pressure reduce the effective stresses and can contribute to rock failure, fracture slip, and microseismic activity. Copyright © 2009 John Wiley & Sons, Ltd. [source] An investigation of pulsatile flow in a model cavo-pulmonary vascular systemINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2009K. Chitra Abstract The complexities in the flow pattern in a cavo-pulmonary vascular system,after application of the Fontan procedure in the vicinity of the superior vena cava, inferior vena cava, and the confluence at the T-junction,are analysed. A characteristic-based split (CBS) finite element scheme involving the artificial compressibility approach is employed to compute the resulting flow. Benchmarking of the CBS scheme is carried out using standard problems and with the flow features observed in an experimental model with the help of a dye visualization technique in model scale. The transient flow variations in a total cavo-pulmonary connection (TCPC) under pulsatile conditions are investigated and compared with flow visualization studies. In addition to such qualitative flow investigations, quantitative analysis of energy loss and haemodynamic stresses have also been performed. The comparisons show good agreement between the numerical and experimental flow patterns. The numerically predicted shear stress values indicate that the pulsatile flow condition is likely to be more severe than steady flow, with regard to the long-term health of the surgically corrected TCPC. Copyright © 2008 John Wiley & Sons, Ltd. [source] Laminar and turbulent flow calculations through a model human upper airway using unstructured meshesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2007P. Nithiarasu Abstract In this paper, numerical investigation of airflow through a human upper airway is presented using an unstructured-based characteristic-based split (CBS) scheme. The CBS scheme used in the present study employs a fully explicit matrix-free solution procedure along with artificial compressibility. A one equation Spalrat,Allmaras (SA) turbulence model is employed to study low and moderate Reynolds number flows. A detailed discussion of the qualitative and quantitative results is presented. The results show a strong influence of the Reynolds number on the flow pattern and quantities of interest, pressure drop and wall shear stress. It is also apparent that SA model can be employed on unstructured meshes to predict the steady flow with good accuracy. Thus, the novelties of the present paper are: use of the unstructured mesh-based solution algorithm and the successful application of the SA model to a typical human upper airway. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||