Lateral Pressure Gradient Research Articles

Propagation and arrest of dikes under topography: Models applied to the 2014 Bardarbunga (Iceland) rifting event

AbstractDikes along rift zones propagate laterally downslope for tens of kilometers, often becoming arrested before topographic reliefs. We use analogue and numerical models to test the conditions controlling the lateral propagation and arrest of dikes, exploring the presence of a slope in connection with buoyancy and rigidity layering. A gentle downslope assists lateral propagation when combined with an effective barrier to magma ascent, e.g., gelatin stiffness contrasts, while antibuoyancy alone may be insufficient to prevent upward propagation. We also observe that experimental dikes become arrested when reaching a plain before opposite reliefs. Our numerical models show that below the plain the stress field induced by topography hinders further dike propagation. We suggest that lateral dike propagation requires an efficient barrier (rigidity) to upward propagation, assisting antibuoyancy, and a lateral pressure gradient perpendicular to the least compressive stress axis, while dike arrest may be induced by external reliefs.

Crustal deformation induced by mantle dynamics: insights from models of gravitational lithosphere removal

Mantle-based stresses have been proposed to explain the occurrence of deformation in the interior regions of continental plates, far from the effects of plate boundary processes. We examine how the gravitational removal of a dense mantle lithosphere root may induce deformation of the overlying crust. Simplified numerical models and a theoretical analysis are used to investigate the physical mechanisms for deformation and assess the surface expression of removal. Three behaviours are identified: (1) where the entire crust is strong, stresses from the downwelling mantle are efficiently transferred through the crust. There is little crustal deformation and removal is accompanied by surface subsidence and a negative free-air gravity anomaly. Surface uplift and increased free-air gravity occur after the dense root detaches. (2) If the mid-crust is weak, the dense root creates a lateral pressure gradient in the crust that drives Poiseuille flow in the weak layer. This induces crustal thickening, surface uplift and a minor free-air gravity anomaly above the root. (3) If the lower crust is weak, deformation occurs through pressure-driven Poiseuille flow and Couette flow due to basal shear. This can overthicken the crust, producing a topographic high and a negative free-air gravity anomaly above the root. In the latter two cases, surface uplift occurs prior to the removal of the mantle stress. The modeling results predict that syn-removal uplift will occur if the crustal viscosity is less than ∼10^(21) Pa s, corresponding to temperatures greater than ∼400–500 °C for a dry and felsic or wet and mafic composition, and ∼900 °C for a dry and mafic composition. If crustal temperatures are lower than this, lithosphere removal is marked by the formation of a basin. These results can explain the variety of surface expressions observed above areas of downwelling mantle. In addition, observations of the surface deflection may provide a way to constrain the vertical rheological structure of the crust.

An Euler–Lagrange approach for studying blood flow in an aneurysmal geometry

To numerically study blood flow in an aneurysm, the development of an approach that tracks the moving tissue and accounts for its interaction with the fluid is required. This study presents a mathematical approach that expands fluid mechanics principles, taking into consideration the domain’s motion. The initial fluid equations, derived in Euler form, are expanded to a mixed Euler–Lagrange formulation to study blood flow in the aneurysm during the cardiac cycle. Transport equations are transformed into a moving body-fitted reference frame using generalized curvilinear coordinates. The equations of motion consist of a coupled and nonlinear system of partial differential equations (PDEs). The PDEs are discretized using the finite volume method. Owing to strong coupling and nonlinear terms, a simultaneous solution approach is applied. The results show that velocity is substantially influenced by the pulsating wall. Intensification of polymorphic flow patterns is observed. Increments of Reynolds and Womersley numbers are evident as pulsatility increases. The pressure field reveals areas of a lateral pressure gradient at the aneurysm. As pulsatility increases, the diastolic flow vortex shifts towards the aortic wall, distal to the aneurysmal neck. Wall shear stress is amplified at the shoulders of the moving wall compared with that of the rigid one.

Anisotropic permeability in deterministic lateral displacement arrays.

We uncover anisotropic permeability in microfluidic deterministic lateral displacement (DLD) arrays. A DLD array can achieve high-resolution bimodal size-based separation of microparticles, including bioparticles, such as cells. For an application with a given separation size, correct device operation requires that the flow remains at a fixed angle to the obstacle array. We demonstrate via experiments and lattice-Boltzmann simulations that subtle array design features cause anisotropic permeability. Anisotropic permeability indicates the microfluidic array's intrinsic tendency to induce an undesired lateral pressure gradient. This can cause an inclined flow and therefore local changes in the critical separation size. Thus, particle trajectories can become unpredictable and the device useless for the desired separation task. Anisotropy becomes severe for arrays with unequal axial and lateral gaps between obstacle posts and highly asymmetric post shapes. Furthermore, of the two equivalent array layouts employed with the DLD, the rotated-square layout does not display intrinsic anisotropy. We therefore recommend this layout over the easier-to-implement parallelogram layout. We provide additional guidelines for avoiding adverse effects of anisotropy on the DLD.

Flow regime analysis for geologic CO2 sequestration and other subsurface fluid injections

Carbon dioxide (CO2) injection into a confined saline aquifer may be modeled as an axisymmetric two-phase flow problem. Assuming the CO2 and brine segregate quickly in the vertical direction due to strong buoyancy, and neglecting capillary pressure and miscibility, the lubrication approximation leads to a one-dimensional nonlinear advection-diffusion equation that describes the evolution of the sharp CO2-brine interface. The interface evolution is driven by two forces: the force from fluid injection (the lateral pressure gradient due to injection), and buoyancy. Analytical solutions can be derived when one of the two forces is dominant. The solutions depend on the viscosity ratio (M) between the displaced and injected fluids, and a buoyancy parameter (Γ) that measures the relative importance of buoyancy compared to the driving force from injection. Different combinations of these two parameters give different forms of the solutions. But for all the solutions, the radius of the lateral spreading of the injected fluid follows,r∝t1/2 with the proportionality coefficient differing for the different solutions. In this paper, we identify the kinds of solutions appropriate for practical CO2 injection projects as well as other subsurface fluid injection applications. We use data from eight CO2 injection projects, twenty-four acid gas injection projects, two liquid waste disposal projects, and one CO2-WAG enhanced oil recovery project. The solutions provide guidance for the expected behavior of fluid spreading under the different injection operations while providing general insights into overall fluid flow behavior.

Isostatic compensation of Quaternary vertical crustal motions: coupling between uplift of Britain and subsidence beneath the North Sea

ABSTRACTNew data from offshore and onshore regions confirm the view that the Quaternary uplift of Britain and subsidence beneath the North Sea are coupled, mediated by lower‐crustal flow induced by the lateral pressure gradient caused by climate‐driven surface processes. Most measured onshore uplift rates, in both upland and lowland localities, are only applicable since the Mid‐Pleistocene Revolution; beforehand, generally lower rates prevailed. Earlier (?Oligocene–Pliocene) phases of uplift and subsidence had typically even lower rates; furthermore, the western margin of the North Sea depocentre was ∼200 km farther from the modern coastline of north‐east England. In the earliest Cenozoic, complex isostatic adjustments occurred in response to the magmatism associated with the Iceland mantle plume; the contemporaneous land surface (relative to the present‐day rock column) in northern England was typically ∼1500 m OD. However, this activity died out during the Palaeogene; the main effect of these events on the modern isostatic configuration was via the emplacement of thick mafic underplating, which now constricts the mobile lower‐crustal layer, explaining the Late Cenozoic ultra‐stability of Ireland. The evidence enables interpretations of the present‐day topography of Britain as static, caused by the Iceland mantle plume, or actively developing in response to plate motions or plate boundary forces, to be excluded.

Modeling Unequilibrated Oil Saturations in a Chalk Reservoir, the South Arne Field Case

Summary The South Arne field presents an example of a North Sea chalk field with an oil distribution strongly affected by fluid dynamics, even at initial conditions. The oil-saturation variation in the South Arne field is effectively modeled with free-water-level (FWL) surfaces, the height above which defines the capillary pressure of oil vs. water. This FWL is in the shape of an elongated dome with a relief on the order of 200 m, corresponding to a smooth, lower-amplitude version of the field structure itself. Dip of the FWL exceeds 100 m/km locally. 2D geological time-scale reservoir simulation is successfully deployed to replicate observed oil-saturation distribution and geometry of the FWL surface. This modeling greatly improves the understanding of and ability to predict the saturation distribution. The anomalous doming of the FWL is thus shown to be because of anomalous lateral-pressure gradients mainly in the water phase, whereas pressure measurements show the oil phase to be without lateral-pressure gradients. The main doming occurs where the oil extends vertically down to a seal at the base of the reservoir. The strong FWL dip is thus maintained on geological time scales (but less than 5 million years) because of low relative permeability to water, whereas oil flows just as readily as in other chalk fields. Because the dip is controlled mainly by low relative mobility of the water, the dip tends to vanish in parts of the field where a water leg is present in permeable rock beneath the oil to allow dissipation of anomalous water pressures. Partial- to full-preproduction imbibition has been identified and modeled in some flank areas. This explains why these parts produce water while other areas at similar saturation and porosity levels flow oil owing to drainage conditions. Identification of degree of imbibition is thus of paramount importance for optimal well placement and prediction of performance. An additional anomaly is found on the northeast flank of the field, where oil in drainage conditions is found deeper than anywhere else in the field. This deep occurrence of oil owes its presence to an anomalously permeable sandy layer close to the northeast flank, stratigraphically above the reservoir. This layer partially drains overpressure, thereby allowing oil to move down the flank from the main field, again because of water-phase-pressure variation, possibly allowing oil to spill into the sandy layer.

Processes controlling the seasonal cycle of wave-dominated inlets

This paper reviews the physical processes controlling wave-dominated inlets, based on several studies conducted at two inlets located on the West Coast of Portugal. Once the observed hydrodynamics and morphological changes are reasonably simulated, numerical experiments are performed to explain the development of the inlet during fair weather conditions and its shoaling and closure during winter storms. The former behaviour is explained by a tidal distortion that promotes ebb-dominance while the latter is explained by the combination of several wave-related processes: (1) the -bulldozer effect- due to the shore-normal component of wave forces; (2) the presence of lateral barotropic pressure gradients, accelerating longshore flows towards the inlet; (3) wave blocking during the ebb and (4) a rise in mean sea level, peaking in late autumn. Recent results also suggest that infragravity waves may play a major role.

Lateral Circulation Generates Flood Tide Stratification and Estuarine Exchange Flow in a Curved Tidal Inlet

AbstractCross-channel transect measurements of microstructure and velocity in a well-mixed and curved tidal inlet in the German Wadden Sea show the occurrence of significant late flood stratification. This stratification is found to be a result of lateral straining. This study observes a strong single-cell lateral circulation, which is strongly pronounced at late flood and absent during most of ebb. This tidal asymmetry is caused by a systematic interplay between centrifugal forcing and the lateral baroclinic pressure gradient. During flood a positive feedback between the terms generates strong lateral circulation, whereas during ebb a negative feedback leads to a suppression of the cross-channel exchange. A theoretical framework based on vorticity is developed, which allows lateral and longitudinal circulation to be studied in a consistent way. With this framework it is possible to show that the tidal asymmetry of the lateral flow is a major driver of residual longitudinal estuarine circulation, here identified with the tidally averaged across-channel vorticity component.

Boundary Layers in Pressure-driven Flow in Smectic A Liquid Crystals

This article examines the steady flow of a smectic A liquid crystal sample that is initially aligned in a classical bookshelf geometry confined between parallel plates and is then subjected to a lateral pressure gradient which is perpendicular to the initial local smectic layer arrangement. The nonlinear dynamic equations are derived. These equations can be linearized and solved exactly to reveal two characteristic length scales that can be identified in terms of the material parameters and reflect the boundary layer behavior of the velocity and the director and smectic layer normal orientations. The asymptotic properties of the nonlinear equations are then investigated to find that these length scales apparently manifest themselves in various aspects of the solutions to the nonlinear steady state equations, especially in the separation between the orientations of the director and smectic layer normal. Non-Newtonian plug-like flow occurs and the solutions for the director profile and smectic layer normal share features identified elsewhere in static liquid crystal configurations. Comparisons with numerical solutions of the nonlinear equations are also made.

Isolating plasma from blood using a dielectrophoresis-active hydrophoretic device

Plasma is a complex substance that contains proteins and circulating nucleic acids and viruses that can be utilised for clinical diagnostics, albeit a precise analysis depends on the plasma being totally free of cells. We proposed the use of a dielectrophoresis (DEP)-active hydrophoretic method to isolate plasma from blood in a high-throughput manner. This microfluidic device consists of anisotropic microstructures embedded on the top of the channel which generate lateral pressure gradients while interdigitised electrodes lay on the bottom of the channel which can push particles or cells into a higher level using a negative DEP force. Large and small particles or cells (3 μm and 10 μm particles, and red blood cells, white blood cells, and platelets) can be focused at the same time in our DEP-active hydrophoretic device at an appropriate flow rate and applied voltage. Based on this principle, all the blood cells were filtrated from whole blood and then the plasma was extracted with a purity of 94.2% and a yield of 16.5% at a flow rate of 10 μL min(-1). This solved the challenging problem caused by the relatively low throughput of the DEP based device. Our DEP-active hydrophoretic device is a flexible and tunable system that can control the lateral positions of particles by modulating the external voltages without redesigning and fabricating a new channel, and because it is easy to operate, it is easily compatible with other microfluidic platforms that are used for further detection.

On-chip high-throughput manipulation of particles in a dielectrophoresis-active hydrophoretic focuser.

This paper proposes a novel concept of dielectrophoresis (DEP)-active hydrophoretic focusing of micro-particles and murine erythroleukemia (MEL) cells. The DEP-active hydrophoretic platform consists of crescent shaped grooves and interdigitated electrodes that generate lateral pressure gradients. These embedded electrodes exert a negative DEP force onto the particles by pushing them into a narrow space in the channel where the particle to groove interaction is intensive and hydrophoretic ordering occurs. Particles passing through the microfluidic device are directed towards the sidewalls of the channel. The critical limitation of DEP operating at a low flow rate and the specific hydrophoretic device for focusing particles of given sizes were overcome with the proposed microfluidic device. The focusing pattern can be modulated by varying the voltage. High throughput was achieved (maximum flow rate ~150 μL min−1) with good focusing performance. The non-spherical MEL cells were utilised to verify the effectiveness of the DEP-active hydrophoretic device.

Modeling of geothermal energy production from stratigraphic reservoirs in the Great Basin

Large, potentially commercial geothermal resources exist in sedimentary rocks beneath high heat-flow basins of the United States. Geothermal reservoir modeling was performed to explore the available power density (MWe/km2) attributable to two general classes of reservoir: a multi-layered “sandwich” and single high permeability layer. Variations in reservoir temperature (i.e. conductive heat flow), permeability, and layer thickness were evaluated. The high permeability layers were assumed to be horizontal and laterally extensive. Production wells were assumed to be pumped at a constant rate, and all produced water was injected at 75°C after being cooled in a power plant. Modeling was undertaken using the STARS Advanced Process and Thermal Reservoir Simulator, Version 2010, by Computer Modeling Group. Five reservoir models were simulated: (1) Sandwich (base) reservoir model to test heat sweep for a reservoir-seal configuration with an average reservoir temperature of 200°C at 3km depth; the reservoir comprised four 25m thick layers with a permeability of 100mD. (2) Single layer reservoir with the same initial temperature and transmissivity of the sandwich reservoir. (3) Low temperature (150°C) sandwich reservoir model. (4) Low permeability sandwich reservoir model, involving lower permeability layers than the sandwich base model. (5) Short-circuit sandwich reservoir model where a high permeability layer results in a higher transmissivity than the base sandwich model. All models assumed isotropic permeability, uniform porosity (10%), and an initial thermally conductive vertical temperature gradient and hydrostatic pressure gradient. All models utilized a five spot pattern with a 500m well spacing, with the flow rate in producer and injector wells being 1000 gallons per minute. The base sandwich model, which may be representative of stratigraphic bedrock reservoirs beneath some basins of the Great Basin, has a power density 3–10MWe/km2 over a 30 year period. During 30 years of production and injection, production wells in the low permeability model each generated 140MWe-years of power compared to 65–90MWe-years per production well in the single layer and short circuit models. A consistent result from all the models was that vertically distributed reservoir layers allow a much greater fraction of heat to be swept from lower permeability seal units. In all models, the lateral pressure gradient induced between injectors ranged between 30 and 60bars, which is not unusual for geothermal developments.

Geochronology and geochemistry of leucogranites from the southeast margin of the North China Block: Origin and migration

Systematic geochronological, geochemical and geological data for the Late Jurassic granitic intrusions from the Bengbu area in the southeastern margin of North China Block (NCB) are presented in this paper. The very low FeO+MgO+TiO2 contents and ferromagnesian mineral abundance as well as low Al-saturation indexes (ASI=0.92–1.09) of the rocks document that these granitic intrusions are metaluminous leucogranites. The Bengbu leucogranites contain abundant both inherited Neoproterozoic igneous and Triassic metamorphic zircons, showing a high agreement in ages with the ultrahigh-pressure (UHP) metamorphic rocks from the adjacent Dabie–Sulu orogen, but significant different from the country rocks. The magmatic overgrown zircon rims give the ages of 167–148Ma, consistent with the time of Jurassic migmatization in the Sulu orogenic belt. Mineral inclusions such as quartz, feldspar, apatite, titanite, biotite, muscovite and phengite (Si=3.58) without coesite occurring within the Triassic metamorphic zircons suggest that the source rocks of the leucogranites might have experienced only high-pressure (HP) rather than UHP metamorphism. Furthermore, steep HREE patterns of the inherited metamorphic zircons, plus very low bulk REE contents and Sr–Nd–Pb isotopic characteristics, suggest that the leucogranites were most likely derived from partial melting of subducted felsic gneiss rather than basaltic eclogite in Dabie–Sulu orogen, with residual allanite in the source. Their low Rb, high Sr contents and low Rb/Sr ratios suggest that the metaluminous leucogranites are derived from mica-poor orthogneiss. Melting temperature for the leucogranites is about 700–710°C as estimated using combined Ti-in-zircon and zirconium saturation thermometries. Inherited metamorphic zircons yielded metamorphic Ti-in-zircon temperature of 681±60°C, representing that for protolith-forming, which shows no significant difference from the melting temperature. H2O-present melting is thus required to generate the low-temperature melt. Sedimentary facies analysis of the Jurassic strata in the Hefei basin suggests that the Sulu orogen had been northward moved to the east of the Bengbu uplift by the Tan–Lu Fault in the Late Jurassic, resulting into a contrasting topography in this area and lateral pressure gradient in the local middle-lower crust. This lateral pressure gradient may drive the partially molten crust (migmatite) in Sulu orogen westward flow into the middle-lower crust of the Bengbu uplift in NCB. Gravity then drove melt to ascent into the middle-upper crust of the Bengbu uplift to form the leucogranitic intrusions. The NWW–SEE distribution of the later Jurassic leucogranites in Bengbu uplift may indicate the direction of ancient channel flow.

Comparative study of flow in right-sided and left-sided aortas: numerical simulations in patient-based models

A right-sided aorta is a rare malformation which may be associated with other various types of congenital heart disease. We utilised haemodynamic, echocardiographic measurements, computerised tomography and image reconstruction software packages that were integrated in a computational fluid dynamics model to determine blood flow patterns in patient-based aortas. In the left-sided aorta, a systolic clockwise rotational component was present, while helical flow was depicted in the aortic arch that was converted in the descending aorta as counter-rotating vortices with accompanying retrograde flow. The right-sided configuration has not altered the orientation of the three-dimensional vortex, but intensification of polymorphic flow patterns, alterations in wall shear stress distribution and development of a lateral pressure gradient at the area of an aneurysmal anomaly was observed. Moreover, increments of Reynolds, Womersley and Dean numbers were evident. These phenomena along with the formation of the aneurysm might influence cardiovascular risk in patients with right-sided aortas.

Numerical and experimental investigation of a new film cooling geometry with high P/D ratio

In order to improve the coolant surface coverage, in the past years new geometries have been proposed with higher lateral fan-shaped angle and/or greater inter-hole pitch distance (P/D). Unfortunately it is not possible to increase the fan angle or the pitch distance even further without inducing a coolant separation and a drop in the overall effectiveness.This study proposes an innovative design which improves the lateral coverage and reduces the jet lift off. The results have been validated by a combination of numerical and experimental analyses: the experimental work has been assessed on a flat plate using thermo chromic liquid crystals and the results have been confirmed numerically by the CFD with the same conditions. The CFD simulations have been carried out considering a stochastic distribution for the free stream Mach number and the coolant blowing ratio.The experimental and computational results show that the inducing lateral pressure gradients there is a minimum increase in lateral averaged adiabatic effectiveness of +30% than the baseline case until a distance downstream of 20 times the coolant diameter.

A hydrologic model for the uppermost oceanic crust constrained by temperature estimates from carbonate minerals

[1] Hydrologic models of the oceanic crust commonly assume that the uppermost igneous extrusive layer of the aquifer is thermally well mixed, although this assumption has not been rigorously tested. Here, the assumption of a thermally well-mixed aquifer is tested against the geological record using O isotope-derived crystallization temperatures of carbonates in the lavas as a record of the temperatures experienced by the aquifer. It is found that carbonate formation temperatures are higher than can be explained by a model of outcrop-to-outcrop flow in a well-mixed aquifer at four of the seven drilling locations analyzed. A poorly mixed aquifer is developed to further explore the crustal hydrology at these locations. Relative to a well-mixed aquifer, a poorly mixed aquifer can achieve higher average temperatures, develops larger lateral pressure gradients driving flow, and requires a lower permeability to achieve a given lateral fluid flux. O isotope data from most of the carbonate samples analyzed are consistent with temperatures achievable in a poorly mixed aquifer; those samples which are not consistent can be explained by plausible special circumstances (such as formation at a discharge zone, where ascending fluid may warm the uppermost aquifer).

Instability of a lithospheric step beneath western North Island, New Zealand

Research Article| April 01, 2013 Instability of a lithospheric step beneath western North Island, New Zealand Tim Stern; Tim Stern 1Institute of Geophysics, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand Search for other works by this author on: GSW Google Scholar Gregory Houseman; Gregory Houseman 2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK Search for other works by this author on: GSW Google Scholar Michelle Salmon; Michelle Salmon 3Research School of Earth Sciences, Australian National University, Acton, ACT 0200, Australia Search for other works by this author on: GSW Google Scholar Lynn Evans Lynn Evans 4School of Geosciences, Monash University, Clayton, VIC 3800, Australia Search for other works by this author on: GSW Google Scholar Geology (2013) 41 (4): 423–426. https://doi.org/10.1130/G34028.1 Article history received: 09 Sep 2012 rev-recd: 15 Oct 2012 accepted: 18 Oct 2012 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Tim Stern, Gregory Houseman, Michelle Salmon, Lynn Evans; Instability of a lithospheric step beneath western North Island, New Zealand. Geology 2013;; 41 (4): 423–426. doi: https://doi.org/10.1130/G34028.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Lithospheres of different thicknesses are often juxtaposed by movement on a continental-transform boundary. Such a boundary with a step change in densities may trigger a gravitational instability as lateral pressure gradients are created where normal mantle lithosphere terminates against less dense asthenospheric mantle. Here we show, for plausible values of the lithospheric viscosity, a mechanism by which the thicker mantle lithosphere will drip off into the lower density asthenosphere. As the mantle deforms it also progressively thickens and then thins the overlying crust, creating a topographic wave that migrates in concert with the removal of mantle lithosphere. Within western North Island, New Zealand, geophysical data define a sharp lithospheric step across the Taranaki-Ruapehu line, and geological observations provide a history of uplift and subsidence that has propagated southward in the past 12 m.y. The rate of observed north to south migration of the wave (∼30 mm/yr), its wavelength (∼250 km), and amplitude (∼±1 km) are compatible with it being caused by progressive removal of mantle lithosphere, if the viscosity of the uppermost lithospheric mantle is ∼5 × 1020 Pa·s, providing one of the clearest examples yet of this fundamental geological process. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

소조기 홍수시 한강하구 석모수로에서의 횡 방향 2차 흐름 및 운동량 분석

본 연구에서는 지속적인 담수유입이 존재하고 S자의 수로형태를 가진 경기만 석모수로에서 소조기 홍수시 13시간 동안 7개의 정선에서 단면유속 및 염분을 관측하였다. 각 단면의 최강 창조와 낙조시의 유속 크기와 방향을 파악하였고, 단면 내의 유속 분포 및 염분구조를 분석하였다. 또한 정선 별로 나타나는 횡 방향 흐름이 어떠한 운동량에 의해 지배되는지 파악하고자 횡 방향의 운동량 분석을 수행하였다. 운동량 분석에서는 석모수로의 S자 형태의 영향을 고려하기 위해서 원심력을 고려하였다. 분석 결과 소조기 홍수시 석모수로는 횡 방향 압력 경도력과 수직적 마찰력이 가장 우세하기 때문에 염분 분포와 성층에 의한 흐름이 주로 나타났다. 수로의 특성은 크게 북단과 남단으로 나누어 볼 수 있는데 상대적으로 조간대가 넓게 형성되고 담수의 영향이 큰 석모수로 북단의 4개 정선중에서 수심이 깊은 정선에서는 횡 방향 압력 경도력이 우세하지만 수직적으로 크기가 다르며, 수심이 낮은 정선에서는 수직 마찰항이 우세하였다. 이와는 달리 수심이 깊고 수로의 굴곡이 심한 석모수로 남단에서는 낙조시 지형학적 원인과 담수의 영향에 따라 이류 가속항과 원심력이 강해지게 된다. 이와 같은 결과를 종합할 때, 석모수로는 위치와 수심, 수로의 굴곡 등에 따라 운동량 분포가 각기 달리 나타나며 이러한 영향으로 인해 횡 방향 흐름 특성이 발생했음을 알 수 있다. This research observed the cross section current of 7 survey lines in Seokmo Channel of Gyeonggi bay with a lot of freshwater inflow and S-shaped for 13 hours during flood season and neap tide. We indicated the distribution of the current velocity by comprehending the speed and direction of the current velocity of each line during maximum flood, ebb tide and observed the distribution of salinity. Moreover, in order to understand what lateral momentum causes the lateral flow in each survey line, we practiced the momentum analysis through the observation data. As a result, the lateral baroclinic pressure gradient force and vertical friction of the Seokmo channel during neap tide were the strongest, and this is why the flow by the distribution of salinity and stratification most often occurs. In north of the Seokmo channel, where have wide intertidal and a lot of freshwater inflow, the secondary circulation is caused by balance of lateral baroclinic pressure gradient force and other forces, and the vertical friction was strong in the lines with small depth. On the other hand, in the southern part of the Seokmo channel where the water is deep and the waterway is curved, the advective acceleration and centrifugal force become stronger by the geographical causes during ebb and the influence of fresh water. Therefore, the lateral flow in the Seokmo channel was caused by the distribution of the momentum that differs by location, depth, curve, etc.

Numerical analysis of the effect of momentum ratio on the dynamics and sediment‐entrainment capacity of coherent flow structures at a stream confluence

The flow and turbulence structure at stream confluences are characterized by the formation of a mixing interface (MI) and, in some cases, of streamwise‐oriented vortical (SOV) cells flanking the MI. Depending on the junction angle and planform symmetry, as well as the velocity ratio across the MI, the MI can be in the Kelvin‐Helmholtz (KH) mode or in the wake mode. In the former case, the MI contains predominantly co‐rotating large‐scale quasi two‐dimensional (2‐D) eddies whose growth is driven by the KH instability and vortex pairing. In the latter case, the MI is populated by quasi 2‐D eddies with opposing senses of rotation. This study uses eddy resolving simulations to predict details of flow structure for KH‐ and wake‐mode conditions at a confluence for which field measurements are available. Results indicate that SOV cells at this confluence, which occur in both modes, redistribute momentum and mass, enhancing the potential for entrainment of bed material beneath the cells and for extraction of fluid and suspended sediment from the MI. The simulations predict that the cores of some of the primary SOV cells are subject to large‐scale bimodal oscillations toward and away from the MI that contribute to amplification of the turbulence close to the MI and enhance the capacity of the SOV cells to entrain sediment. At this confluence, which has a concordant bed and a large angle between the incoming streams ‐ conditions that generate strong adverse lateral pressure gradients adjacent to the MI ‐ the oscillating SOV cells interact with MI eddies to generate large bed friction velocities in the zone of scour immediately downstream of the confluence.