Articoli di riviste: "Conduit geometry"

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Kozono, Tomofumi, Hidemi Ishibashi, Satoshi Okumura e Takahiro Miwa. "Conduit Flow Dynamics During the 1986 Sub-Plinian Eruption at Izu-Oshima Volcano". Journal of Disaster Research 17, n. 5 (1 agosto 2022): 754–67. http://dx.doi.org/10.20965/jdr.2022.p0754.

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We investigated conduit flow dynamics during the 1986 sub-Plinian eruption of Izu-Oshima volcano, Japan, using a 1-D steady conduit flow model. Following observations that the magma plumbing system beneath Izu-Oshima, characterized by the feeding of a dyke, generated a fissure-type sub-Plinian eruption, we considered a dyke-like conduit geometry by applying a pseudo-dyke conduit with an ellipsoidal horizontal cross-section. Under appropriate parameter settings constrained by geological, petrological, and geophysical observations, we identified a conduit geometry that enables steady solutions of a conduit flow that generates the sub-Plinian eruption. A dyke-like conduit geometry allows us to widen the range of geometric parameters of the solution. We found that the distribution of magma overpressure in the conduit strongly depends on conduit geometry. When the conduit geometry is composed of deeper and shallower dykes with large and small aspect ratios, respectively, localized overpressurization occurs in the region before magma fragmentation. This overpressurization in the dyke-like conduit may induce a characteristic crustal deformation similar to that caused by a vertical tensile fault. It is crucial to consider the effects of conduit flow with a dyke-like geometry on deformation for precise monitoring of eruption sequences based on geodetic signals in future eruptions at Izu-Oshima volcano.

2

Shimizu, Yukimaru, Yoshiki Futaki e C. Samuel Martin. "Secondary Flow and Hydraulic Losses Within Sinuous Conduits of Rectangular Cross Section". Journal of Fluids Engineering 114, n. 4 (1 dicembre 1992): 593–600. http://dx.doi.org/10.1115/1.2910072.

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This paper describes the relationship between hydraulic losses and secondary flow within sinuous conduits with complicated bends. It has been found that the nature of secondary flow present in the bends is quite sensitive to the geometric configuration of the bend and the actual aspect ratio of the conduit section. Indeed, many different secondary flow patterns have been found to exist as the bend geometry is altered. A wide range of experiments has been conducted for various aspect ratios of a rectangular conduit with different curvatures.

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Ostad, Hadi, Zargham Mohammadi e Francesco Fiorillo. "Assessing the Effect of Conduit Pattern and Type of Recharge on the Karst Spring Hydrograph: A Synthetic Modeling Approach". Water 15, n. 8 (19 aprile 2023): 1594. http://dx.doi.org/10.3390/w15081594.

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It is widely accepted that spring hydrographs are an effective tool for evaluating the internal structure of karst aquifers because they depict the response of the whole aquifer to recharge events. The spring hydrograph is affected by various factors such as flow regime, geometry, type of recharge, and hydraulic properties of conduit. However, the effect of conduit network geometry received less attention and required more comprehensive research studies. The present study attempted to highlight the impact of the two most frequent patterns of karst conduits (i.e., branchwork and network maze) on the characteristic of the spring hydrograph. Therefore, two conduit patterns, branchwork and network maze, were randomly generated with MATLAB codes. Then, MODFLOW-CFP was used to quantify the effect of conduit pattern, conduit density, and diffuse or concentrated recharge on the spring hydrograph. Results reveal that peak discharge, fast-flow recession coefficient, and the return time to baseflow are mainly affected by conduit network pattern, conduit network density, and recharge, respectively. In contrast, the time to reach peak flow only reacts to recharge conditions. Large variations in conduit density produce tangible changes in the baseflow recession coefficient.

4

Fountain, Andrew G., Robert B. Schlichting, Peter Jansson e Robert W. Jacobel. "Observations of englacial water passages:a fracture-dominated system". Annals of Glaciology 40 (2005): 25–30. http://dx.doi.org/10.3189/172756405781813762.

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AbstractTo test models of the hydraulics and geometry of englacial conduits, 48 holes (3900m of ice) were drilled into Storglaciaren, Sweden, in search of conduits. About 79% of the holes intersected a hydraulically connected englacial feature. A video camera was used to examine the features and measure local water-flow rates. Because of the extremely clear ice that surrounded most features, their geometry could not be discerned. Of the remaining features, 80% (36) were fracture-like, 16%(6) were of complex geometry, and 4%(2) exhibited a conduit-like geometry. The fracture-like features exhibited steep plunges (∼70˚), narrow openings (∼40mm) and slow water-flow speeds (∼10mms–1). We argue that these fracture-like features are indeed englacial fractures of unknown origin. The depth to fractures intersection varied from near the glacier surface to 96% of local ice depth, with a maximum depth of 131 m. Few hydraulically connected fractures exhibited water motion, indicating some preferential flow pathways exist. We found one ‘traditional’ englacial conduit after an intentional search in a field of moulins. These results suggest that englacial water flow is conveyed through a ubiquitous network of fractures and that conduits are relatively rare.

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Gunn, John, e Chris Bradley. "Characterising Rhythmic and Episodic Pulsing Behaviour in the Castleton Karst, Derbyshire (UK), Using High Resolution in-Cave Monitoring". Water 15, n. 12 (20 giugno 2023): 2301. http://dx.doi.org/10.3390/w15122301.

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The discharge from most karst springs exhibits a consistent and reasonably predictable response to recharge but a few exhibit short-term (‘rhythmic’) changes in flow that are commonly attributed to the geometry of feeder conduits and the action of siphons. This paper investigates water flow in a karst system that exhibits rhythmic and episodic changes in discharge due to variations in flow from two phreatic conduits (Main Rising (MR) and Whirlpool Rising (WR)) that pass through Speedwell Cavern en route to the springs. Water tracing experiments indicate that the conduits receive both allogenic and autogenic recharge. Flow dynamics and conduit behaviour were investigated using high-resolution (2-min) water depth data collected from MR and WR between 2012 and 2015 (when MR was dominant) and between 2021 and 2023 (when WR was dominant). Water depths were also logged in a cave at the upstream end of a conduit draining to both MR and WR and at springs. The short-term temporal variability in water depths at both MR and WR is greater than any documented in previous studies. This is attributed to conduit bedrock geometry and changes in conduit permeability due to sediment accumulation in phreatic loops, which together influence the response to recharge.

6

Imqam, Abdulmohsin, Ze Wang e Baojun Bai. "Preformed-Particle-Gel Transport Through Heterogeneous Void-Space Conduits". SPE Journal 22, n. 05 (22 marzo 2017): 1437–47. http://dx.doi.org/10.2118/179705-pa.

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Summary Preformed particle gels (PPGs) have been successfully applied as a plugging agent to solve the conformance problem in fractured reservoirs. They are injected to plug fractures and then divert displacing fluid into poorly swept zones/areas. However, PPG-propagation and -plugging mechanisms through open void-space conduits (VSCs) have not been studied thoroughly. This paper investigated various situations involving heterogeneous conduits and their geometrical effect on PPG injectivity. Five-foot tubes were used to mimic VSCs. Three models were designed to gain understanding on how conduit geometry and PPG properties affect gel transportation, including a single conduit with a uniform internal diameter (ID); a single conduit with a nonuniform ID along its length; and two parallel conduits with different ID ratios with respect to each other. Results obtained from single-conduit models with uniform and nonuniform diameters showed PPG-injection pressure increased significantly as the conduit became more heterogeneous. Particle gels accumulated at the choke point within each conduit and caused injection pressure to increase accordingly. When two parallel conduits are available for flow, the relative distance of PPG penetration into the conduits depends strongly on the ratio of the conduit diameters and the gel strength. In addition, the ratio of gel-particle-size diameter to conduit diameter contributes significantly to the gel-transport selection. This paper demonstrates important impact elements of gel propagation for different heterogeneous-conduit situations.

7

Tsamis, Alkiviadis, Alexander Rachev e Nikos Stergiopulos. "A constituent-based model of age-related changes in conduit arteries". American Journal of Physiology-Heart and Circulatory Physiology 301, n. 4 (ottobre 2011): H1286—H1301. http://dx.doi.org/10.1152/ajpheart.00570.2010.

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In the present report, a constituent-based theoretical model of age-related changes in geometry and mechanical properties of conduit arteries is proposed. The model was based on the premise that given the time course of the load on an artery and the accumulation of advanced glycation end-products in the arterial tissue, the initial geometric dimensions and properties of the arterial tissue can be predicted by a solution of a boundary value problem for the governing equations that follow from finite elasticity, structure-based constitutive modeling within the constrained mixture theory, continuum damage theory, and global growth approach for stress-induced structure-based remodeling. An illustrative example of the age-related changes in geometry, structure, composition, and mechanical properties of a human thoracic aorta is considered. Model predictions were in good qualitative agreement with available experimental data in the literature. Limitations and perspectives for refining the model are discussed.

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Rabah, Amal, Manuel Marcoux e David Labat. "Effects of Geometry on Artificial Tracer Dispersion in Synthetic Karst Conduit Networks". Water 15, n. 22 (7 novembre 2023): 3885. http://dx.doi.org/10.3390/w15223885.

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This paper presents the modeling results of tracer test simulations performed using COMSOL Multiphysics (version 6.1), a powerful software for multiphysics simulation. The simulations consist of the propagation of artificial tracers injected into different model configurations. This study is based on computational fluid dynamics (CFDs), which allows us to take into consideration the turbulent regime of the water flow in conduits. The objective of this contribution is to identify the relationship between the tracer dynamics and the geometric parameters of synthetic karstic systems via a systematic investigation of the occurrence of dual-peaked breakthrough curves (BTCs) in tracer tests. Various conduit structures were proposed by modifying five key factors: conduit diameter, presence of pools, connection angle between conduits, distance of the outlet from the inlet, and number of branches. The next step will be to confront these computational experiments with real-world tracer test experiments.

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KAMINTZIS, J. E., J. P. P. JONES, T. D. L. IRVINE-FYNN, T. O. HOLT, P. BUNTING, S. J. A. JENNINGS, P. R. PORTER e B. HUBBARD. "Assessing the applicability of terrestrial laser scanning for mapping englacial conduits". Journal of Glaciology 64, n. 243 (20 dicembre 2017): 37–48. http://dx.doi.org/10.1017/jog.2017.81.

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ABSTRACTThe morphology of englacial drainage networks and their temporal evolution are poorly characterised, particularly within cold ice masses. At present, direct observations of englacial channels are restricted in both spatial and temporal resolution. Through novel use of a terrestrial laser scanning (TLS) system, the interior geometry of an englacial channel in Austre Brøggerbreen, Svalbard, was reconstructed and mapped. Twenty-eight laser scan surveys were conducted in March 2016, capturing the glacier surface around a moulin entrance and the uppermost 122 m reach of the adjoining conduit. The resulting point clouds provide detailed 3-D visualisation of the channel with point accuracy of 6.54 mm, despite low (<60%) overall laser returns as a result of the physical and optical properties of the clean ice, snow, hoar frost and sediment surfaces forming the conduit interior. These point clouds are used to map the conduit morphology, enabling extraction of millimetre-to-centimetre scale geometric measurements. The conduit meanders at a depth of 48 m, with a sinuosity of 2.7, exhibiting teardrop shaped cross-section morphology. This improvement upon traditional surveying techniques demonstrates the potential of TLS as an investigative tool to elucidate the nature of glacier hydrological networks, through reconstruction of channel geometry and wall composition.

10

Schuler, Thomas, e Urs H. Fischer. "Elucidating changes in the degree of tracer dispersion in a subglacial channel". Annals of Glaciology 37 (2003): 275–80. http://dx.doi.org/10.3189/172756403781815915.

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AbstractTracer injections into a subglacial channel at Unteraargletscher, Switzerland, were repeated at intervals of about 2 hours over two diurnal discharge cycles in August and September 2000. Records of dye concentration reveal a pronounced hysteresis in the velocity–dispersion relationship, thereby indicating alterations in the drainage system. Theoretical considerations for Röthlisberger channels suggest an evolution of the conduit cross-section in response to a diurnally varying discharge. We studied the relation between conduit cross-section and tracer dispersion with numerical tracer experiments. The velocity field for steady flow through a given conduit geometry is calculated using a commercial flow solver. Tracer transport is represented by a scalar volume which is advected by the velocity field. Experiments were conducted for several scenarios by varying flow velocity, conduit geometry and conduit roughness. Results show only a weak dependence of dispersion on conduit size. In contrast, changes in roughness of the conduit walls reveal a strong effect on tracer dispersion. Therefore, to explain the observed hysteresis in the velocity–dispersion relationship, we suggest that the evolution of a subglacial flow path might involve changes in roughness.

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Aravena, A., R. Cioni, M. de’ Michieli Vitturi, M. Pistolesi, M. Ripepe e A. Neri. "Evolution of Conduit Geometry and Eruptive Parameters During Effusive Events". Geophysical Research Letters 45, n. 15 (4 agosto 2018): 7471–80. http://dx.doi.org/10.1029/2018gl077806.

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Jenson, Ryan M., Andrew P. Wollman, Mark M. Weislogel, Lauren Sharp, Robert Green, Peter J. Canfield, Jörg Klatte e Michael E. Dreyer. "Passive phase separation of microgravity bubbly flows using conduit geometry". International Journal of Multiphase Flow 65 (ottobre 2014): 68–81. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2014.05.011.

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Corte, M. D., R. C. Oliveski, M. G. Marques e M. Dai Pra. "CFD NUMERICAL ANALYSIS OF A PROPOSED CHANGE IN THE CHANNEL GEOMETRY DOWNSTREAM OF A REVERSED TAINTER GATE". Revista de Engenharia Térmica 14, n. 1 (30 giugno 2015): 71. http://dx.doi.org/10.5380/reterm.v14i1.62116.

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Reversed Tainter gates are often used to control flow in the filling and emptying locks navigation systems of high fall. High speeds and pressure fluctuations may occur in the flow downstream of these gates, the flow cavitation may occur, damaging the structure. One way proposed to mitigate this problem is through geometric changes in the channel downstream of the gate. In this study was analyzed using CFD the effect of an expansion in the roof and the base of the conduit, followed by a straight section and a subsequent contraction until returning to the original geometry. It was observed that the pressure at the base of the conduit increases with the modification, however peaks of positive and negative pressures occur due to the shape change of the geometry of the corners not be smooth. The size of recirculation downstream of the gate increases with the geometrical alteration, increasing the distance required for pressure recovery.

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Adachi, Iki, Toshikatsu Yagihara, Koji Kagisaki, Ikuo Hagino, Toru Ishizaka, Masahiro Koh, Hideki Uemura e Soichiro Kitamura. "Fontan operation with a viable and growing conduit using pedicled autologous pericardial roll: Serial changes in conduit geometry". Journal of Thoracic and Cardiovascular Surgery 130, n. 6 (dicembre 2005): 1517–22. http://dx.doi.org/10.1016/j.jtcvs.2005.07.050.

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Costa, A., O. Melnik e R. S. J. Sparks. "Controls of conduit geometry and wallrock elasticity on lava dome eruptions". Earth and Planetary Science Letters 260, n. 1-2 (agosto 2007): 137–51. http://dx.doi.org/10.1016/j.epsl.2007.05.024.

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Pastore, Claudio, Eric Weber, Frédéric Doumenc, Pierre-Yves Jeannin e Marc Lütscher. "Dispersion of artificial tracers in ventilated caves". International Journal of Speleology 53, n. 1 (aprile 2024): 51–62. http://dx.doi.org/10.5038/1827-806x.53.1.2497.

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Artificial CO2 was used as a tracer along ventilated karst conduits to infer airflow and investigate tracer dispersion. In the karst vadose zone, cave ventilation is an efficient mode of transport for heat, gases and aerosols and thus drives the spatial distribution of airborne particles. Modelling this airborne transport requires geometrical and physical parameters of the conduit system, including the cross-sectional areas, the airflow and average air speed, as well as the longitudinal dispersion coefficient which describes the spreading of a solute. Four gauging tests were carried out in one mine (artificial conduit) and two ventilated caves (natural conduits). In this paper, we demonstrate that it is possible to gain reliable airflow rates and geometric information of ventilated karst conduits using CO2 as a tracer. Airflow was gauged along two caves and one mine and compared with punctual measurements made with a hot-wire anemometer. Cross-sectional areas estimated with CO2 tests were compared with those measured in situ. Moreover, breakthrough curve (BTC) analysis displayed an accentuated tailing along the investigated natural conduits due to the presence of dispersive singularities which possibly enable aerosol deposition. The long tailing observed in Milandre and Longeaigue Caves is probably due to cross-section variations. A 1-D advection-dispersion model tested for these sites was unable to fit BTC tailing in natural conduits. In Baulmes artificial conduit, where long tailing is not observed, the dispersion coefficient has been estimated using Chatwin’s method, and compared with the prediction of Taylor’s theory. Despite the regular geometry of Baulmes Mine, Taylor’s correlation significantly underestimates the dispersion coefficient deduced from field data, showing the need for more theoretical work on turbulent dispersion in mines. This paper gives a first insight into air motion and matter dispersion along ventilated karst conduits, preparing for proper aerosol dispersion modelling.

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Wu, Li-Li, Hong-Mei Sun e Ting Chen. "Effects of the conduit geometry on the air flow field in the spunbonding process". Thermal Science 19, n. 4 (2015): 1457–58. http://dx.doi.org/10.2298/tsci1504457w.

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In the spunbonding process, the air flow field of the drawing conduit affects the polymer drawing and therefore the filament diameter greatly. Effects of the conduit parameters on the air flow field are studied using the previously established air flow field model. The results show that longer narrow section, longer contracting section and larger height of narrow entry are of benefit to increasing the air velocity, thus helpful for decreasing the filament diameter.

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Church, Gregory, Melchior Grab, Cédric Schmelzbach, Andreas Bauder e Hansruedi Maurer. "Monitoring the seasonal changes of an englacial conduit network using repeated ground-penetrating radar measurements". Cryosphere 14, n. 10 (2 ottobre 2020): 3269–86. http://dx.doi.org/10.5194/tc-14-3269-2020.

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Abstract. Englacial conduits act as water pathways to feed surface meltwater into the subglacial drainage system. A change of meltwater into the subglacial drainage system can alter the glacier's dynamics. Between 2012 and 2019, repeated 25 MHz ground-penetrating radar (GPR) surveys were carried out over an active englacial conduit network within the ablation area of the temperate Rhonegletscher, Switzerland. In 2012, 2016, and 2017 GPR measurements were carried out only once a year, and an englacial conduit was detected in 2017. In 2018 and 2019 the repetition survey rate was increased to monitor seasonal variations in the detected englacial conduit. The resulting GPR data were processed using an impedance inversion workflow to compute GPR reflection coefficients and layer impedances, which are indicative of the conduit's infill material. The spatial and temporal evolution of the reflection coefficients also provided insights into the morphology of the Rhonegletscher's englacial conduit network. During the summer melt seasons, we observed an active, water-filled, sediment-transporting englacial conduit network that yielded large negative GPR reflection coefficients (<-0.2). The GPR surveys conducted during the summer provided evidence that the englacial conduit was 15–20 m±6 m wide, ∼0.4m±0.35m thick, ∼250m±6m long with a shallow inclination (2∘), and having a sinusoidal shape from the GPR data. We speculate that extensional hydraulic fracturing is responsible for the formation of the conduit as a result of the conduit network geometry observed and from borehole observations. Synthetic GPR waveform modelling using a thin water-filled conduit showed that a conduit thickness larger than 0.4 m (0.3× minimum wavelength) thick can be correctly identified using 25 MHz GPR data. During the winter periods, the englacial conduit no longer transports water and either physically closed or became very thin (<0.1 m), thereby producing small negative reflection coefficients that are caused by either sediments lying within the closed conduit or water within the very thin conduit. Furthermore, the englacial conduit reactivated during the following melt season at an identical position as in the previous year.

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Legros, François, Karim Kelfoun e Joan Martı́. "The influence of conduit geometry on the dynamics of caldera-forming eruptions". Earth and Planetary Science Letters 179, n. 1 (giugno 2000): 53–61. http://dx.doi.org/10.1016/s0012-821x(00)00109-6.

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Jung, Stephanie, Alexandra Höltzel, Steffen Ehlert, Jose-Angel Mora, Karsten Kraiczek, Monika Dittmann, Gerard P. Rozing e Ulrich Tallarek. "Impact of Conduit Geometry on the Performance of Typical Particulate Microchip Packings". Analytical Chemistry 81, n. 24 (15 dicembre 2009): 10193–200. http://dx.doi.org/10.1021/ac902069x.

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de' Michieli Vitturi, M., A. B. Clarke, A. Neri e B. Voight. "Effects of conduit geometry on magma ascent dynamics in dome-forming eruptions". Earth and Planetary Science Letters 272, n. 3-4 (agosto 2008): 567–78. http://dx.doi.org/10.1016/j.epsl.2008.05.025.

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Massol, Hélène. "A combined 2-D/1-D magma ascent model of explosive volcanic eruptions". Geophysical Journal International 219, n. 3 (2 settembre 2019): 1818–35. http://dx.doi.org/10.1093/gji/ggz398.

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SUMMARY Explosive eruptions involve the fragmentation of magma that changes the flow regime from laminar to turbulent within the volcanic conduit during ascent. If the gas volume fraction is high, magma fragments and the eruption style is explosive, but if not, the magma flows effusively out of the vent. Gas escape processes depend on how the magma can rupture, and recent experimental studies measured rupture stress thresholds of the order of a few megapascals. It is thus critical to model the gas content and state of stress evolution in the flowing magma within the conduit. We present a new self-consistent model of an explosive eruption from the magma chamber to the surface, based on a critical gas volume fraction. Our model allows to explore irregular geometries below the fragmentation level (2-D). We first compare our model with classical 1-D models of explosive eruptions and find that in the case of straight conduits and fragmented flows, 1-D models are accurate enough to model the gas pressure and vertical velocity distribution in the conduit. However, in the case of an irregular conduit shape at depth, 2-D models are necessary. Despite a certain conduit radius visible at the surface, very different stress fields within the flow could be present depending upon the position and shape of any conduit irregularities. Stresses of the order of more than 1 MPa can be attained in some locations. High tensile stresses are located at the centre of the conduit, while high shear stresses are located at the conduit walls leading to several potential rupture locations. Due to the interplay between the velocity field and decompression rate, similar conduit radius visible at the surface might also lead to very different fragmentation depths with a difference of more than 1500 m between an enlarged conduit shape at some depth and a straight conduit. At depth, different conduit sizes might lead to the same order of magnitude for the mass flux, depending on the conduit geometry.

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Rempel, Alan W. "Effective stress profiles and seepage flows beneath glaciers and ice sheets". Journal of Glaciology 55, n. 191 (2009): 431–43. http://dx.doi.org/10.3189/002214309788816713.

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AbstractThe resistance to sliding and the extent of till deformation beneath soft-bedded glaciers depend on the spatially averaged level of effective stress , which is controlled by the distribution of water pressure at the bed. Major subglacial conduits that facilitate large-scale water transport are expected to be predominantly aligned with the direction of maximum hydraulic gradient, which is normally parallel to the slope of the glacier surface. When the basal heat flow promotes net melting or freezing, seepage transport can enable water exchange between these conduits and the rest of the basal surface area. For a simple glacier geometry with subglacial conduits that are aligned parallel to a uniform slope, the seepage transport is driven primarily by gradients in effective stress. Balance equations determine how varies with conduit spacing and the heat-flow regime. Considerations of thermodynamic equilibrium require that ice penetrates the pore space at high effective stress. Even when the glacier base experiences net melting, for a given heat-flow regime there are limits on the conduit spacing that can be attained before a finite till layer becomes partially frozen throughout. During net freezing, the resistance to flow through partially frozen sediments limits the steady-state conduit spacing. The partially frozen zone can actually be restricted to smaller thicknesses when the freezing rate is greater.

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Khirevich, Siarhei, Alexandra Höltzel e Ulrich Tallarek. "Transient and asymptotic dispersion in confined sphere packings with cylindrical and non-cylindrical conduit geometries". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369, n. 1945 (28 giugno 2011): 2485–93. http://dx.doi.org/10.1098/rsta.2011.0027.

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We study the time and length scales of hydrodynamic dispersion in confined monodisperse sphere packings as a function of the conduit geometry. By a modified Jodrey–Tory algorithm, we generated packings at a bed porosity (interstitial void fraction) of ε =0.40 in conduits with circular, rectangular, or semicircular cross section of area 100 πd 2 p (where d p is the sphere diameter) and dimensions of about 20 d p (cylinder diameter) by 6553.6 d p (length), 25 d p by 12.5 d p (rectangle sides) by 8192 d p or 14.1 d p (radius of semicircle) by 8192 d p , respectively. The fluid-flow velocity field in the generated packings was calculated by the lattice Boltzmann method for Péclet numbers of up to 500, and convective–diffusive mass transport of 4×10 6 inert tracers was modelled with a random-walk particle-tracking technique. We present lateral porosity and velocity distributions for all packings and monitor the time evolution of longitudinal dispersion up to the asymptotic (long-time) limit. The characteristic length scales for asymptotic behaviour are explained from the symmetry of each conduit’s velocity field. Finally, we quantify the influence of the confinement and of a specific conduit geometry on the velocity dependence of the asymptotic dispersion coefficients.

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Li, Yubo, Linjie Chen e Yonghong Shi. "Influence of 3D Fracture Geometry on Water Flow and Solute Transport in Dual-Conduit Fracture". Water 15, n. 9 (2 maggio 2023): 1754. http://dx.doi.org/10.3390/w15091754.

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The geometry of the fracture exerts an important impact on the flow of the fractures and the transport of the solutes. Herein, Forchheimer’s law and the weighted-sum ADE (WSADE) model were alternatively employed, and the obtained pressure gradient versus discharge curves for the fitting reveal that Forchheimer’s law adequately described the non-Darcy flow behavior and the robust capability of WSADE in capturing the non-Fickian transport in dual-conduit fractures (DCFs). Different boundary layer effects brought about obvious differences in water flow and solute transport trends between 2D and 3D fractures. Moreover, with the change in the distance between the main conduit and the diversion conduit, the hydraulic parameters were correlated with the fitting parameters in Forchheimer’s law and WSADE. The solute mixing process is dramatically altered by the results, which directly demonstrate major flow patterns at the intersection. The prediction of solute transport in naturally fractured rocks depends primarily on the depicted flow and its effects on mixing. The findings help to increase the understanding of transport processes in such systems, especially for characterizing the dual-peaked BTCs obtained in aquifers.

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Covington, M. D., A. F. Banwell, J. Gulley, M. O. Saar, I. Willis e C. M. Wicks. "Quantifying the effects of glacier conduit geometry and recharge on proglacial hydrograph form". Journal of Hydrology 414-415 (gennaio 2012): 59–71. http://dx.doi.org/10.1016/j.jhydrol.2011.10.027.

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Fountain, Andrew G. "Geometry and flow conditions of subglacial water at South Cascade Glacier, Washington State, U.S.A.; an analysis of tracer injections". Journal of Glaciology 39, n. 131 (1993): 143–56. http://dx.doi.org/10.1017/s0022143000015793.

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Abstract Tracers were injected into South Cascade Glacier to determine the flow condition and geometry of the subglacial water system. Results indicate that two distinct drainage basins on the glacier feed the two main streams flowing from the glacier. In the largest basin, two parallel drainage networks exist, one englacial and the other subglacial. The englacial system is an arboresecent network of conduits, whereas the subglacial system is a distributed flow system. Both systems connect to a single subglacial conduit which appears as a stream at the glacier’s terminus. The comparison between the travel time of the tracers and stream discharge indicated that the single conduit was pressurized in July and partly filled in August and September. To estimate the flow geometry (e.g. path length, flow depth and velocity), the advection-diffusion equation was formulated to express the water velocity as a function of water depth. Longitudinal dispersion of the tracer was calculated from the shear in longitudinal water velocity. Results indicate that the flow is very wide compared to its depth and that the path is sinuous. The estimated flow speed in the conduits is an order of magnitude larger than the measured speed through the glacier, indicating that other flow processes, probably englacial, route the water much more slowly. The other, smaller, basin drains the water from the surface to the subglacial distributed flow system. Based on the travel time of the individual concentration peaks, the water could be flowing through a linked-cavity system or interconnected bands of highly permeable debris separated by zones of less permeability.

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Fountain, Andrew G. "Geometry and flow conditions of subglacial water at South Cascade Glacier, Washington State, U.S.A.; an analysis of tracer injections". Journal of Glaciology 39, n. 131 (1993): 143–56. http://dx.doi.org/10.3189/s0022143000015793.

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Abstract (sommario):

AbstractTracers were injected into South Cascade Glacier to determine the flow condition and geometry of the subglacial water system. Results indicate that two distinct drainage basins on the glacier feed the two main streams flowing from the glacier. In the largest basin, two parallel drainage networks exist, one englacial and the other subglacial. The englacial system is an arboresecent network of conduits, whereas the subglacial system is a distributed flow system. Both systems connect to a single subglacial conduit which appears as a stream at the glacier’s terminus. The comparison between the travel time of the tracers and stream discharge indicated that the single conduit was pressurized in July and partly filled in August and September.To estimate the flow geometry (e.g. path length, flow depth and velocity), the advection-diffusion equation was formulated to express the water velocity as a function of water depth. Longitudinal dispersion of the tracer was calculated from the shear in longitudinal water velocity. Results indicate that the flow is very wide compared to its depth and that the path is sinuous. The estimated flow speed in the conduits is an order of magnitude larger than the measured speed through the glacier, indicating that other flow processes, probably englacial, route the water much more slowly.The other, smaller, basin drains the water from the surface to the subglacial distributed flow system. Based on the travel time of the individual concentration peaks, the water could be flowing through a linked-cavity system or interconnected bands of highly permeable debris separated by zones of less permeability.

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Perne, M., M. Covington e F. Gabrovšek. "Evolution of karst conduit networks in transition from pressurized flow to free-surface flow". Hydrology and Earth System Sciences 18, n. 11 (24 novembre 2014): 4617–33. http://dx.doi.org/10.5194/hess-18-4617-2014.

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Abstract. Most of the existing models of speleogenesis are limited to situations where flow in all conduits is pressurized. The feedback between the distribution of hydraulic head and growth of new solution conduits determines the geometry of the resulting conduit network. We present a novel modeling approach that allows a transition from pressurized (pipe) flow to a free-surface (open-channel) flow in evolving discrete conduit networks. It calculates flow, solute transport and dissolution enlargement within each time step and steps through time until a stable flow pattern is established. The flow in each time step is calculated by calling the US Environmental Protection Agency Storm Water Management Model (US Environmental Protection Agency, 2014), which efficiently solves the 1-D Saint-Venant equations in a network of conduits. Two basic scenarios are modeled, a low-dip scenario and a high-dip scenario. In the low-dip scenario a slightly inclined plane is populated with a rectangular grid of solution conduits. The recharge is distributed to randomly selected junctions. The results for the pressurized flow regime resemble those of the existing models. When the network becomes vadose, a stable flow pathway develops along a system of conduits that occupy the lowest positions at their inlet junctions. This depends on the initial diameter and inlet position of a conduit, its total incision in a pressurized regime and its alignment relative to the dip of the plane, which plays important role during the vadose entrenchment. In the high-dip scenario a sub-vertical network with recharge on the top and outflow on the side is modeled. It is used to demonstrate the vertical development of karst due to drawdown of the water table, development of invasion vadose caves during vadose flow diversion and to demonstrate the potential importance of deeply penetrating conductive structures.

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Perne, M., M. D. Covington e F. Gabrovšek. "Evolution of karst conduit networks in transition from pressurised flow to free surface flow". Hydrology and Earth System Sciences Discussions 11, n. 6 (19 giugno 2014): 6519–59. http://dx.doi.org/10.5194/hessd-11-6519-2014.

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Abstract. We present a novel modelling approach to study the evolution of conduit networks in soluble rocks. Unlike the models presented so far, the model allows a transition from pressurised (pipe) flow to a free surface (open channel) flow in evolving discrete conduit networks. It calculates flow, solute transport and dissolutional enlargement within each time step and steps through time until a stable flow pattern establishes. The flow in each time step is calculated by calling the EPA Storm Water Management Model (EPA SWMM), which efficiently solves the 1-D Saint Venant equations in a network of conduits. We present several cases with low dip and sub-vertical networks to demonstrate mechanisms of flow pathway selection. In low dip models the inputs were randomly distributed to several junctions. The evolution of pathways progresses upstream: initially pathways linking outlets to the closest inputs evolve fastest because the gradient along these pathways is largest. When a pathway efficiently drains the available recharge, the head drop along the pathway attracts flow from the neighbouring upstream junctions and new connecting pathways evolve. The mechanism progresses from the output boundary inwards until all inputs are connected to the stable flow system. In the pressurised phase, each junction is drained by at least one conduit, but only one conduit remains active in the vadose phase. The selection depends on the initial geometry of a junction, initial distribution of diameters, the evolution in a pressurised regime, and on the dip of the conduits, which plays an important role in vadose entrenchment. In high dip networks, the vadose zone propagates downwards and inwards from the rim of the massif. When a network with randomly distributed initial diameters is supplied with concentrated recharge from the adjacent area, the sink point regresses up upstream along junctions connected to the prominent pathways. Large conductive structures provide deep penetration of high hydraulic head and give rise to high gradients and possible fast evolution of conduit systems deep within the massif.

31

Wang, Yanru, Cheen Sean Oon, Manh-Vu Tran e Joshua Yap Kee An. "Investigation on Heat Transfer and Pressure Drop Performance Utilizing GNP-based Colloidal Suspension Flow in Finned Conduit". IOP Conference Series: Earth and Environmental Science 945, n. 1 (1 dicembre 2021): 012056. http://dx.doi.org/10.1088/1755-1315/945/1/012056.

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Abstract Heat exchangers have been widely used in various engineering applications. It is important to develop a highly efficient heat transfer equipment to reduce carbon footprint. In the current research, the effect of 0.025wt% CGNP/water nanofluid on convective heat transfer and pressure drop performance is investigated numerically in finned conduits with circular and square geometry. ANSYS FLUENT is used to analyze the turbulent flow inside the conduits with Reynolds number ranging from 7360 to 28011 and constant heat flux 12254.90W/m2 and 9615.38W/m2 in circular and square geometry, respectively. Only 1/8 of the pipe was constructed in the simulation as the geometry is symmetrical. The numbers of mesh elements are 465488 and 469144 for circular and square conduits. SST k-omega viscous model, SIMPLEC scheme and second-order upwind solvers are used in this model, where SST k-omega viscous model is good at solving turbulence parameters in the near wall boundary regions. It is found that the use of CGNP/water nanofluid can increase convective heat transfer coefficient without increasing pressure drop compared with water. Besides, the circular pipe shows higher heat transfer enhancement compared with square pipe. Furthermore, the increase in Reynolds number enhances the Nusselt number and heat transfer coefficient in both circular and square geometries. It is recommended that circular finned pipe and CGNP/water colloidal suspension could be applied in low turbulence flow setting heat exchanger.

32

Deleu, Romain, Sandra Soarez Frazao, Amaël Poulain, Gaëtan Rochez e Vincent Hallet. "Tracer Dispersion through Karst Conduit: Assessment of Small-Scale Heterogeneity by Multi-Point Tracer Test and CFD Modeling". Hydrology 8, n. 4 (10 novembre 2021): 168. http://dx.doi.org/10.3390/hydrology8040168.

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Tracer tests are widely used for characterizing hydrodynamics, from stream-scale to basin-wide scale. In karstic environments, the positioning of field fluorometers (or sampling) is mostly determined by the on-site configuration and setup difficulties. Most users are probably aware of the importance of this positioning for the relevance of data, and single-point tests are considered reliable. However, this importance is subjective to the user and the impact of positioning is not well quantified. This study aimed to quantify the spatial heterogeneity of tracer concentration through time in a karstic environment, and its impact on tracer test results and derived information on local hydrodynamics. Two approaches were considered: on-site tracing experiments in a karstic river, and Computational Fluid Dynamics (CFD) modeling of tracer dispersion through a discretized karst river channel. A comparison between on-site tracer breakthrough curves and CFD results was allowed by a thorough assessment of the river geometry. The results of on-site tracer tests showed significant heterogeneities of the breakthrough curve shape from fluorometers placed along a cross-section. CFD modeling of the tracer test through the associated discretized site geometry showed similar heterogeneity and was consistent with the positioning of on-site fluorometers, thus showing that geometry is a major contributor of the spatial heterogeneity of tracer concentration through time in karstic rivers.

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Khirevich, Siarhei, Alexandra Höltzel, Dzmitry Hlushkou e Ulrich Tallarek. "Impact of Conduit Geometry and Bed Porosity on Flow and Dispersion in Noncylindrical Sphere Packings". Analytical Chemistry 79, n. 24 (dicembre 2007): 9340–49. http://dx.doi.org/10.1021/ac071428k.

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Paredes-Mariño, Joali, Bettina Scheu, Cristian Montanaro, Alejandra Arciniega-Ceballos, Donald B. Dingwell e Diego Perugini. "Volcanic ash generation: Effects of componentry, particle size and conduit geometry on size-reduction processes". Earth and Planetary Science Letters 514 (maggio 2019): 13–27. http://dx.doi.org/10.1016/j.epsl.2019.02.028.

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35

Ronayne, Michael J. "Influence of conduit network geometry on solute transport in karst aquifers with a permeable matrix". Advances in Water Resources 56 (giugno 2013): 27–34. http://dx.doi.org/10.1016/j.advwatres.2013.03.002.

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36

Borghi, Andrea, Philippe Renard e Fabien Cornaton. "Can one identify karst conduit networks geometry and properties from hydraulic and tracer test data?" Advances in Water Resources 90 (aprile 2016): 99–115. http://dx.doi.org/10.1016/j.advwatres.2016.02.009.

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37

Ahlstrøm, Andreas P., Johan J. Mohr, Niels Reeh, Erik Lintz Christensen e Roger LeB Hooke. "Controls on the basal water pressure in subglacial channels near the margin of the Greenland ice sheet". Journal of Glaciology 51, n. 174 (2005): 443–50. http://dx.doi.org/10.3189/172756505781829214.

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AbstractAssuming a channelized drainage system in steady state, we investigate the influence of enhanced surface melting on the water pressure in subglacial channels, compared to that of changes in conduit geometry, ice rheology and catchment variations. The analysis is carried out for a specific part of the western Greenland ice-sheet margin between 66° N and 66°30′N using new high-resolution digital elevation models of the subglacial topography and the ice-sheet surface, based on an airborne ice-penetrating radar survey in 2003 and satellite repeat-track interferometric synthetic aperture radar analysis of European Remote-sensing Satellite 1 and 2 (ERS-1/-2) imagery, respectively. The water pressure is calculated up-glacier along a likely subglacial channel at distances of 1, 5 and 9 km from the outlet at the ice margin, using a modified version of Röthlisberger’s equation. Our results show that for the margin of the western Greenland ice sheet, the water pressure in subglacial channels is not sensitive to realistic variations in catchment size and mean surface water input compared to small changes in conduit geometry and ice rheology.

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Sharpe, David R., Susan E. Pullan e Timothy A. Warman. "A Basin Analysis of the Wabigoon Area of Lake Agassiz, a Quaternary Clay Basin in Northwerstern Ontario". Géographie physique et Quaternaire 46, n. 3 (29 novembre 2007): 295–309. http://dx.doi.org/10.7202/032916ar.

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ABSTRACT Information from a wide range of sources is integrated in a basin analysis of the Wabigoon Basin, a Quaternary clay basin located on the Canadian Shield in northwestern Ontario. The basin sediments were deposited between 10.9 ka and 9.5 ka, along the margin of the Rainy Lobe of the Laurentide Ice Sheet, which formed the northern boundary of proglacial Lake Agassiz. The basin architecture is dominated by four major elements: end moraines, eskers, kames and a clay plain, all of which overlie irregular bedrock topography. End moraines, eskers and kames are composed mainly of a fining upward sequence of gravels and sands. The geometry of these sedimentary units, and their sedimentary structures indicates they were deposited mainly by high and low-density turbidity currents, on ice-marginal subaqueous outwash fans. Eskers contain a core of coarse gravel and sand deposited within subglacial meltwater conduits, overlain by subaqueous fan sediments deposited at the conduit mouth. Esker ridges were formed during conduit filling events and flanking deposits were formed when a conduit remained in use during ice-marginal retreat. Where conduits were shortlived, isolated subaqueous fans (kames) were formed. A depositional model is proposed which relates moraine formation to catastrophic releases of subglacial meltwater and sediment simultaneously along the entire margin of the Rainy Lobe. The clay plain forms a broad blanket of fine-grained, rhythmically-bedded sediment which obscures bedrock topography, and often buries esker and kame deposits. Seismic profiles and overburden drilling reveal deep (50-70 m) bedrock lows beneath the clay plain. These lows, oriented sub-parallel to the ice margin, acted as sediment traps, and were infilled by the deposits of underflows generated at the ice margin.

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Roth, Wolff-Michael. "Rules of bending, bending the rules: the geometry of electrical conduit bending in college and workplace". Educational Studies in Mathematics 86, n. 2 (8 gennaio 2012): 177–92. http://dx.doi.org/10.1007/s10649-011-9376-4.

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Meierbachtol, T., J. Harper e N. Humphrey. "Basal Drainage System Response to Increasing Surface Melt on the Greenland Ice Sheet". Science 341, n. 6147 (15 agosto 2013): 777–79. http://dx.doi.org/10.1126/science.1235905.

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Surface meltwater reaching the bed of the Greenland ice sheet imparts a fundamental control on basal motion. Sliding speed depends on ice/bed coupling, dictated by the configuration and pressure of the hydrologic drainage system. In situ observations in a four-site transect containing 23 boreholes drilled to Greenland’s bed reveal basal water pressures unfavorable to water-draining conduit development extending inland beneath deep ice. This finding is supported by numerical analysis based on realistic ice sheet geometry. Slow meltback of ice walls limits conduit growth, inhibiting their capacity to transport increased discharge. Key aspects of current conceptual models for Greenland basal hydrology, derived primarily from the study of mountain glaciers, appear to be limited to a portion of the ablation zone near the ice sheet margin.

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Wu, Chunxiao, Yu Lu, Shewen Liu, Zhiyuan Li, Zhuhao Gu, Wu Shao e Chuang Li. "Research on Optimization Design of Fully Parameterized Pump-Jet Propulsion". Journal of Marine Science and Engineering 10, n. 6 (1 giugno 2022): 766. http://dx.doi.org/10.3390/jmse10060766.

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A pump-jet propulsion system is composed of rotor, stator, and duct. The stator has the front stator type and the rear stator type; the conduit also has the acceleration conduit and the deceleration conduit two forms. It is difficult to design and evaluate the performance of a pump-jet propulsion system because of its complex structure and many changes in component parameters. Due to the limitation of time and cost in the design process of the pump-jet propulsion system, it is difficult to find the optimal scheme in the design space. However, under the guidance of an optimization algorithm, the automatic optimization method can fill the design space with a large number of design schemes. In this paper, the geometry reconstruction technique, hydraulic performance evaluation technique and optimization technique of the pump-jet propulsion system are combined to realize the automation of the whole design process. Firstly, the geometric modeling of the pump-jet propulsion system is completed by a full parametric modeling method, and then the hydrodynamic performance of the pump-jet propulsion system is calculated based on the numerical simulation technique. The radial parameters in the fully parametric configuration of the pump-jet propulsion system were selected as the optimization design variables, and the hydro-dynamic performance was optimized as the objective function. Finally, the pump-jet propulsion system optimization design system was constructed by using the global intelligent optimization algorithm. This study provides a theoretical basis and technical guidance for numerical calculation and configuration optimization design of pump-jet propulsion system.

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Bodin, Jacques, Gilles Porel, Benoît Nauleau e Denis Paquet. "Delineation of discrete conduit networks in karst aquifers via combined analysis of tracer tests and geophysical data". Hydrology and Earth System Sciences 26, n. 6 (1 aprile 2022): 1713–26. http://dx.doi.org/10.5194/hess-26-1713-2022.

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Abstract. Assessment of the karst network geometry based on field data is an important challenge in the accurate modeling of karst aquifers. In this study, we propose an integrated approach for the identification of effective three-dimensional (3D) discrete karst conduit networks conditioned on tracer tests and geophysical data. The procedure is threefold: (i) tracer breakthrough curves (BTCs) are processed via a regularized inversion procedure to determine the minimum number of distinct tracer flow paths between injection and monitoring points, (ii) available surface-based geophysical data and borehole-logging measurements are aggregated into a 3D proxy model of aquifer hydraulic properties, and (iii) single or multiple tracer flow paths are identified through the application of an alternative shortest path (SP) algorithm to the 3D proxy model. The capability of the proposed approach to adequately capture the geometrical structure of actual karst conduit systems mainly depends on the sensitivity of geophysical signals to karst features, whereas the relative completeness of the identified conduit network depends on the number and spatial configuration of tracer tests. The applicability of the proposed approach is illustrated through a case study at the Hydrogeological Experimental Site (HES) in Poitiers, France.

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Carbotte, Suzanne M., Adrien Arnulf, Marc Spiegelman, Michelle Lee, Alistair Harding, Graham Kent, Juan Pablo Canales e Mladen Nedimović. "Stacked sills forming a deep melt-mush feeder conduit beneath Axial Seamount". Geology 48, n. 7 (27 aprile 2020): 693–97. http://dx.doi.org/10.1130/g47223.1.

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Abstract Magmatic systems are composed of melt accumulations and crystal mush that evolve with melt transport, contributing to igneous processes, volcano dynamics, and eruption triggering. Geophysical studies of active volcanoes have revealed details of shallow-level melt reservoirs, but little is known about fine-scale melt distribution at deeper levels dominated by crystal mush. Here, we present new seismic reflection images from Axial Seamount, northeastern Pacific Ocean, revealing a 3–5-km-wide conduit of vertically stacked melt lenses, with near-regular spacing of 300–450 m extending into the inferred mush zone of the mid-to-lower crust. This column of lenses underlies the shallowest melt-rich portion of the upper-crustal magma reservoir, where three dike intrusion and eruption events initiated. The pipe-like zone is similar in geometry and depth extent to the volcano inflation source modeled from geodetic records, and we infer that melt ascent by porous flow focused within the melt lens conduit led to the inflation-triggered eruptions. The multiple near-horizontal lenses are interpreted as melt-rich layers formed via mush compaction, an interpretation supported by one-dimensional numerical models of porous flow in a viscoelastic matrix.

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Ferrill, David A., Kevin J. Smart e Alan P. Morris. "Resolved stress analysis, failure mode, and fault-controlled fluid conduits". Solid Earth 11, n. 3 (15 maggio 2020): 899–908. http://dx.doi.org/10.5194/se-11-899-2020.

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Abstract. Failure behaviors can strongly influence deformation-related changes in volume, which are critical in the formation of fault and fracture porosity and conduit development in low-permeability rocks. This paper explores the failure modes and deformation behavior of faults within the mechanically layered Eagle Ford Formation, an ultra-low permeability self-sourced oil and gas reservoir and aquitard exposed in natural outcrop in southwest Texas, USA. Particular emphasis is placed on analysis of the relationship between slip versus opening along fault segments and the associated variation in dilation tendency versus slip tendency. Results show that the failure mode and deformation behavior (dilation versus slip) relate in predictable ways to the mechanical stratigraphy, stress field, and specifically the dilation tendency and slip tendency. We conclude that dilation tendency versus slip tendency patterns on faults and other fractures can be analyzed using detailed orientation or structural geometry data and stress information and employed predictively to interpret deformation modes and infer volume change and fluid conduit versus barrier behavior of structures.

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Song, Sunmin, Jun Oh Kim, Sang-Woo Kang, Won Chegal, Jae-Soo Shin e Sung-Kyu Lim. "Prediction of changes in the pumping speed characteristics of dry pumps with the geometry of the conduit". Journal of the Korean Physical Society 80, n. 4 (5 gennaio 2022): 337–46. http://dx.doi.org/10.1007/s40042-021-00388-5.

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Spina, L., A. Cannata, D. Morgavi e D. Perugini. "Degassing behaviour at basaltic volcanoes: New insights from experimental investigations of different conduit geometry and magma viscosity". Earth-Science Reviews 192 (maggio 2019): 317–36. http://dx.doi.org/10.1016/j.earscirev.2019.03.010.

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Ferrill, David A., Kevin J. Smart e Alan P. Morris. "Fault failure modes, deformation mechanisms, dilation tendency, slip tendency, and conduits v. seals". Geological Society, London, Special Publications 496, n. 1 (8 novembre 2019): 75–98. http://dx.doi.org/10.1144/sp496-2019-7.

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AbstractFaults have complicated shapes. Non-planarity of faults can be caused by variations in failure modes, which in turn are dictated by mechanical stratigraphy interacting with the ambient stress field, as well as by linkage of fault segments. Different portions of a fault or fault zone may experience volume gain, volume conservation and volume loss simultaneously depending on the position along a fault's surface, the stresses resolved on the fault and the associated deformation mechanisms. This variation in deformation style and associated volume change has a profound effect on the ability of a fault to transmit (or impede) fluid both along and across the fault. In this paper we explore interrelated concepts of failure mode and resolved stress analysis, and provide examples of fault geometry in normal faulting and reverse faulting stress regimes that illustrate the effects of fault geometry on failure behaviour and related importance to fluid transmission. In particular, we emphasize the utility of using relative dilation tendency v. slip tendency on fault patches as a predictor of deformation behaviour, and suggest this parameter space as a new tool for evaluating conduit v. seal behaviour of faults.

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Luhmann, A. J., M. D. Covington, J. M. Myre, M. Perne, S. W. Jones, E. C. Alexander Jr. e M. O. Saar. "Thermal damping and retardation in karst conduits". Hydrology and Earth System Sciences 19, n. 1 (9 gennaio 2015): 137–57. http://dx.doi.org/10.5194/hess-19-137-2015.

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Abstract. Water temperature is a non-conservative tracer in the environment. Variations in recharge temperature are damped and retarded as water moves through an aquifer due to heat exchange between water and rock. However, within karst aquifers, seasonal and short-term fluctuations in recharge temperature are often transmitted over long distances before they are fully damped. Using analytical solutions and numerical simulations, we develop relationships that describe the effect of flow path properties, flow-through time, recharge characteristics, and water and rock physical properties on the damping and retardation of thermal peaks/troughs in karst conduits. Using these relationships, one can estimate the thermal retardation and damping that would occur under given conditions with a given conduit geometry. Ultimately, these relationships can be used with thermal damping and retardation field data to estimate parameters such as conduit diameter. We also examine sets of numerical simulations where we relax some of the assumptions used to develop these relationships, testing the effects of variable diameter, variable velocity, open channels, and recharge shape on thermal damping and retardation to provide some constraints on uncertainty. Finally, we discuss a multitracer experiment that provides some field confirmation of our relationships. High temporal resolution water temperature data are required to obtain sufficient constraints on the magnitude and timing of thermal peaks and troughs in order to take full advantage of water temperature as a tracer.

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Luhmann, A. J., M. D. Covington, J. M. Myre, M. Perne, S. W. Jones, E. C. Alexander e M. O. Saar. "Thermal damping and retardation in karst conduits". Hydrology and Earth System Sciences Discussions 11, n. 8 (13 agosto 2014): 9589–642. http://dx.doi.org/10.5194/hessd-11-9589-2014.

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Abstract. Water temperature is a non-conservative tracer in the environment. Variations in recharge temperature are damped and retarded as water moves through an aquifer due to heat exchange between water and rock. However, within karst aquifers, seasonal and short-term fluctuations in recharge temperature are often transmitted over long distances before they are fully damped. Using analytical solutions and numerical simulations, we develop relationships that describe the effect of flow path properties, flow-through time, recharge characteristics, and water and rock physical properties on the damping and retardation of thermal peaks/troughs in karst conduits. Using these relationships, one can estimate the thermal retardation and damping that would occur under given conditions with a given conduit geometry. Ultimately, these relationships can be used with thermal damping and retardation field data to estimate parameters such as conduit diameter. We also examine sets of numerical experiments where we relax some of the assumptions used to develop these relationships, testing the effects of variable diameter, variable velocity, open channels, and recharge shape on thermal damping and retardation to provide some constraints on uncertainty. Finally, we discuss a tracer experiment that provides field confirmation of our relationships. High temporal resolution water temperature data are required to obtain sufficient constraints on the magnitude and timing of thermal peaks and troughs in order to take full advantage of water temperature as a tracer.

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Dur, Onur, Ergin Kocyildirim, Ozlem Soran, Peter D. Wearden, Victor O. Morell, Curt G. DeGroff e Kerem Pekkan. "Pulsatile venous waveform quality affects the conduit performance in functional and “failing” Fontan circulations". Cardiology in the Young 22, n. 3 (19 ottobre 2011): 251–62. http://dx.doi.org/10.1017/s1047951111001491.

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AbstractObjectiveTo investigate the effect of pulsatility of venous flow waveform in the inferior and superior caval vessels on the performance of functional and “failing” Fontan patients based on two primary performance measures – the conduit power loss and the distribution of inferior caval flow (hepatic factors) to the lungs.MethodsDoppler angiography flows were acquired from two typical extra-cardiac conduit “failing” Fontan patients, aged 13 and 25 years, with ventricle dysfunction. Using computational fluid dynamics, haemodynamic efficiencies of “failing”, functional, andin vitro-generated mechanically assisted venous flow waveforms were evaluated inside an idealised total cavopulmonary connection with a caval offset. To investigate the effect of venous pulsatility alone, cardiac output was normalised to 3 litres per minute in all cases. To quantify the pulsatile behaviour of venous flows, two new performance indices were suggested.ResultsVariations in the pulsatile content of venous waveforms altered the conduit efficiency notably. High-frequency and low-amplitude oscillations lowered the pulsatile component of the power losses in “failing” Fontan flow waveforms. Owing to the offset geometry, hepatic flow distribution depended strongly on the ratio of time-dependent caval flows and the pulsatility content rather than mixing at the junction. “Failing” Fontan flow waveforms exhibited less balanced hepatic flow distribution to lungs.ConclusionsThe haemodynamic efficiency of single-ventricle circulation depends strongly on the pulsatility of venous flow waveforms. The proposed performance indices can be calculated easily in the clinical setting in efforts to better quantify the energy efficiency of Fontan venous waveforms in pulsatile settings.

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