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Berlin Brandenburg

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  • 1
    Language: English
    In: Transport in Porous Media, 2013, Vol.96(2), pp.271-294
    Description: The 3D description of the soil structure at the pore scale level can help to elucidate the biological functioning of soil. The water–air distribution in the 3D-pore space is of particular interest because it determines the diffusion pathways of nutrients and the localisation of active soil microorganisms. We used the Shan–Chen interparticle-potential approach to simulate spontaneous phase separation in complex academic and real 3D-porous media using the advanced TRT lattice Boltzmann scheme. The equation of state and phase diagram were calculated and the model was verified using hydrostatic laws. The 3D pattern of water/air interface in two complex academic pore geometries was accurately computed. Finally, 3D maps of static liquid–gas distribution were simulated in a real 3D X-ray computed tomography image obtained from an undisturbed soil column sampled in a silty clay loam soil. The simulated soil sample of 1.7 cm 3 was described at a voxel-resolution of 60 μm. The range of the simulated saturations (from 0.5 to 0.9) was in a good agreement with the expected saturations calculated from the phase diagram.
    Keywords: Lattice Boltzmann method ; Water meniscus ; TRT ; Shan–Chen ; Porous media
    ISSN: 0169-3913
    E-ISSN: 1573-1634
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  • 2
    Language: English
    In: Transport in Porous Media, 2014, Vol.105(2), pp.391-410
    Description: Numerical models that solve transport of pollutants at the macroscopic scale in unsaturated porous media need the effective diffusion dependence on saturation as an input. We conducted numerical computations at the pore scale in order to obtain the effective diffusion curve as a function of saturation for an academic sphere packing porous medium and for a real porous medium where pore structure knowledge was obtained through X-ray tomography. The computations were performed using a combination of lattice Boltzmann models based on two relaxation time (TRT) scheme. The first stage of the calculations consisted in recovering the water spatial distribution into the pore structure for several fixed saturations using a phase separation TRT lattice Boltzmann model. Then, we performed diffusion computation of a non-reactive solute in the connected water structure using a diffusion TRT lattice Boltzmann model. Finally, the effective diffusion for each selected saturation value was estimated through inversion of a macroscopic classical analytical solution.
    Keywords: Lattice Boltzmann method ; Effective diffusion ; TRT ; Unsaturated ; Porous media
    ISSN: 0169-3913
    E-ISSN: 1573-1634
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  • 3
    Language: English
    In: Transport in Porous Media, 2017, Vol.116(3), pp.975-1003
    Description: Hydrogen gas migration modeling through water-saturated engineering barriers and the host rock of a deep geological repository for radioactive waste is of concern for safety assessment of such facilities. A two-phase two-relaxation-time lattice Boltzmann model using the Rothman and Keller approach was parallelized on graphic processing units to simulate hydrogen gas migration in a 3D image obtained by X-ray microtomography of Opalinus clay microfractures. A dimensional analysis combined with a grid refinement analysis was carried out to set the model parameters to reproduce the realistic viscous, capillary and inertial forces of the natural system. Relative permeabilities curves were first calculated in a simple regular fracture with different initial two-phase configurations. We observed that segmented gas flow configurations led to a drop in the relative gas permeability by two orders of magnitude as compared to parallel flow configuration. The model was then applied to 4 $$\times $$ × refined 3D images. For lower water saturation values ( $$0.5 \le S_\mathrm{w} 〈 0.7$$ 0.5 ≤ S w 〈 0.7 ), hydrogen gas migrated through continuous gas paths oriented in the flow direction. At high water saturation values ( $$S_\mathrm{w}\ge 0.7$$ S w ≥ 0.7 ), the relative gas permeability dropped to zero because the hydrogen phase segmented into gas pockets that were stuck in local narrow throats of the clay fracture. The study pointed out that the high capillary forces prevented the gas bubbles from distorting themselves to pass through these narrow paths.
    Keywords: LBM ; Two-phase flow ; Relative permeability ; RK ; TRT ; GPU
    ISSN: 0169-3913
    E-ISSN: 1573-1634
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  • 4
    Language: English
    In: Environmental Science and Pollution Research, 2016, Vol.23(7), pp.6907-6918
    Description: Compost amendment on agricultural soil is a current practice to compensate the loss of organic matter. As a consequence, dissolved organic carbon concentration in soil leachates can be increased and potentially modify the transport of other solutes. This study aims to characterize the processes controlling the mobility of dissolved organic matter (DOM) in deep soil layers and their potential impacts on the leaching of organic contaminants (pesticides and pharmaceutical compounds) potentially present in cultivated soils receiving organic waste composts. We sampled undisturbed soil cores in the illuviated horizon (60–90 cm depth) of an Albeluvisol. Percolation experiments were made in presence and absence of DOM with two different pesticides, isoproturon and epoxiconazole, and two pharmaceutical compounds, ibuprofen and sulfamethoxazole. Two types of DOM were extracted from two different soil surface horizons: one sampled in a plot receiving a co-compost of green wastes and sewage sludge applied once every 2 years since 1998 and one sampled in an unamended plot. Results show that DOM behaved as a highly reactive solute, which was continuously generated within the soil columns during flow and increased after flow interruption. DOM significantly increased the mobility of bromide and all pollutants, but the effects differed according the hydrophobic and the ionic character of the molecules. However, no clear effects of the origin of DOM on the mobility of the different contaminants were observed.
    Keywords: Dissolved organic matter ; Pesticides ; Pharmaceutical compounds ; Undisturbed soil columns ; Non-equilibrium transport
    ISSN: 0944-1344
    E-ISSN: 1614-7499
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  • 5
    Language: English
    In: Journal of Geodesy, 2009, Vol.83(2), pp.147-159
    Description: Decades of cruise-based exploration have provided excellent snapshots of the structure of mid-ocean ridges and have revealed that accretion is a mixture of steady-state and quantum events. Observatory-type studies are now needed to quantify the temporal evolution of these systems. A multi-disciplinary seafloor observatory site is currently being set up at the Lucky Strike volcano, in the axial valley of the slow spreading Mid-Atlantic ridge as a part of the MoMAR (monitoring of the Mid-Atlantic Ridge) initiative. The aim of this observatory is to better understand the dynamics of the volcano and the hydrothermal vents hosted at its summit as well as their plumbing systems. In August 2006, the GRAVILUCK cruise initiated an experiment to monitor the deformation of Lucky Strike volcano. A geodetic network was installed, and seafloor pressure, gravity and magnetic data were collected. In this paper, we present the method used to monitor volcanic deformation, which involves measuring relative depth difference between points within a seafloor geodesy network. We show that, taking into account oceanographic variability and measurement noise, the network should be able to detect vertical deformations of the order of 1 cm.
    Keywords: Seafloor ; Geodesy ; Deformation ; MoMAR ; Volcano ; Pressure
    ISSN: 0949-7714
    E-ISSN: 1432-1394
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  • 6
    Language: English
    In: Journal of Geodesy, 2010, Vol.84(1), pp.65-77
    Description: Knowledge of the position and motion of points on the seafloor can be critically important in both fundamental research (for example, global geodesy and plate tectonics) and for more practical applications such as seismic risk evaluation, off-shore construction and pipeline monitoring. In the Vanuatu subduction zone, for example, measuring deformation underwater could provide valuable information for modeling deformation and understanding the seismic cycle. We report a shallow water experiment in Vanuatu to measure the relative and absolute depth of seafloor points. The experiment differs from previous efforts mainly in that it uses the height of the sea surface determined by kinematic GPS, allowing us to locate the points in a global reference frame. The ITRF2005 ellipsoidal height of a seafloor benchmark was determined with a 1-sigma uncertainty of 0.7–2.1 cm. The estimated ellipsoidal height differs only by a few tenths of a centimeter between measurements made in 2004 and another set made in 2006. These results are encouraging and open new perspectives for vertical underwater deformation monitoring in shallow water areas. Sea-surface GPS measurements can also help to reduce the uncertainty in depth difference determination for relative measurements.
    Keywords: GPS experiment ; Seafloor geodesy ; Seismic cycle ; Subduction zone processes ; Submarine tectonics and volcanism ; Pacific Ocean
    ISSN: 0949-7714
    E-ISSN: 1432-1394
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