A comparative simulation study of coupled THM processes and their effect on fractured rock permeability around nuclear waste repositories     

Jonny Rutqvist  Deborah Barr  Jens T. Birkholzer  Kiyoshi Fujisaki  Olaf Kolditz  Quan-Sheng Liu  Tomoo Fujita  Wenqing Wang  Cheng-Yuan Zhang 《Environmental Geology》2009,57(6):1347-1360

This paper presents an international, multiple-code, simulation study of coupled thermal, hydrological, and mechanical (THM) processes and their effect on permeability and fluid flow in fractured rock around heated underground nuclear waste emplacement drifts. Simulations were conducted considering two types of repository settings (1) open emplacement drifts in relatively shallow unsaturated volcanic rock, and (2) backfilled emplacement drifts in deeper saturated crystalline rock. The results showed that for the two assumed repository settings, the dominant mechanism of changes in rock permeability was thermal–mechanically induced closure (reduced aperture) of vertical fractures, caused by thermal stress resulting from repository-wide heating of the rock mass. The magnitude of thermal–mechanically induced changes in permeability was more substantial in the case of an emplacement drift located in a relatively shallow, low-stress environment where the rock is more compliant, allowing more substantial fracture closure during thermal stressing. However, in both of the assumed repository settings in this study, the thermal–mechanically induced changes in permeability caused relatively small changes in the flow field, with most changes occurring in the vicinity of the emplacement drifts.  相似文献   

Hybrid analytical and finite element numerical modeling of mass and heat transport in fractured rocks with matrix diffusion   总被引：1，自引：0，他引：1  

Christopher I. McDermott  Robert Walsh  Ralph Mettier  Georg Kosakowski  Olaf Kolditz 《Computational Geosciences》2009,13(3):349-361

Quantification of mass and heat transport in fractured porous rocks is important to areas such as contaminant transport, storage and release in fractured rock aquifers, the migration and sorption of radioactive nuclides from waste depositories, and the characterization of engineered heat exchangers in the context of enhanced geothermal systems. The large difference between flow and transport characteristics in fractures and in the surrounding matrix rock means models of such systems are forced to make a number of simplifications. Analytical approaches assume a homogeneous system, numerical approaches address the scale at which a process is operating, but may lose individual important processes due to averaging considerations. Numerical stability criteria limit the contrasts possible in defining material properties. Here, a hybrid analytical–numerical method for transport modeling in fractured media is presented. This method combines a numerical model for flow and transport in a heterogeneous fracture and an analytical solution for matrix diffusion. By linking the two types of model, the advantages of both methods can be combined. The methodology as well as the mathematical background are developed, verified for simple geometries, and applied to fractures representing experimental field conditions in the Grimsel rock laboratory.  相似文献   

ESR Dating of the Evolution of the Shuanghu Basin in the Northern Tibetan Plateau   总被引：3，自引：0，他引：3  

WU Zhenhan  JIANG Wan  Peter Blisniuk  BI Siwen  ZHANG Shukun  Olaf Kuchel  MAO Yi Institute of Geomechanics  CAGS  Minzu Xueyuan Nanlu  Beijing Institut fur Geowissenschaften  Universitat Potsdam  Postfach  D- Potsdam  Germany Liu Xinzhu 《《地质学报》英文版》1999,73(3):289-293

The Shuanghu basin is a NE-trending rift basin bounded by NE-striking normal faults and NW-striking shear-extensional faults of the northern Tibetan Plateau. Four samples from calcite veins in marginal faults and one sample from mudstone (S-3) were collected for dating the evolution of the Shuanghu basin by using the ESR spectrograph of EXM-type. Ages were calculated according to the close-equilibrium model on the basis of the measured ESR signal spectra of samples, providing good chronological information. It is known from the ESR dating that the extensional faulting and rifting of the Shuanghu area began at 4.92 Ma B.P., followed by regional folding in 3.56-1.36 Ma, NW-striking faulting in 0.60 Ma and normal faulting in 0.024 Ma in the Shuanghu basin.  相似文献   

Insect communities of Phragmites habitats used for sewage purification: Effects of age and area of habitats on species richness and herbivore-parasitoid interactions     

Olaf Athen  Teja Tscharntke   《Limnologica》1999,29(1):71-74

In 1994, 28 sewage purification plants based on common reed Phragmites australis were analyzed, to study fragmentation effects on diversity and on food web structure of insect communities. Purification plants differed in age (2 to 11 years) and area (10 to 2,500 m²). Both age and area were significantly correlated with species richness of herbivores. Populations of the two most abundant herbivores, the gall makers Lipara pullitarsis (Diptera, Chloropidae) and Giraudiella inclusa (Diptera, Cecidomyiidae), increased significantly with age and size of the Phragmites habitats, i.e. the purification plants. Incidence curves showed that only habitats older than 6 years and larger than 100 m² have a 50% probability of finding these two most abundant gall makers, and can correspondingly be considered to contribute to insect species conservation. Natural enemies were even more susceptible to habitat fragmentation than their phytophagous hosts or prey, thereby hampering possible biocontrol. Percent parasitism of both the Lipara and Giraudiella gall makers significantly increased with habitat age.  相似文献   

Is the North Atlantic Oscillation reflected in Scandinavian glacier mass balance records?     

Atle Nesje   yvind Lie  Svein Olaf Dahl 《第四纪科学杂志》2000,15(6):587-601

The North Atlantic Oscillation (NAO) is one of the modes of climate variability in the North Atlantic region. The atmospheric circulation during the winter season in this region commonly displays a strong meridional (north–south) pressure contrast, with low air pressure (cyclone) centred close to Iceland and high air pressure (anticyclone) near the Azores. This pressure gradient drives the mean surface winds and the mid‐latitude winter storms from west to east across the North Atlantic, bringing mild moist air to northwest Europe. The NAO index is based on the difference of normalised sea‐level pressures (SLP) between Ponta Delgada, Azores and Stykkisholmur, Iceland. The SLP anomalies at these stations are normalised by division of each monthly pressure by the long‐term (1865–1984) standard deviation. Interannual atmospheric climate variability in northwest Europe, especially over Great Britain and western Scandinavia has, during the last decades, been attributed mainly to the NAO, causing variations in the winter weather over the northeast North Atlantic and the adjacent land areas. A comparison between the NAO index and the winter (December–March) precipitation between ad 1864 and 1995 in western Norway shows that these are strongly linked (correlation coefficient 0.77). Variations in the NAO index are also reflected in the mass balance records of glaciers in western Scandinavia. The NAO index is best correlated with mass balance data from maritime glaciers in southern Norway (e.g. Ålfotbreen R² = 0.51). The record of Holocene (last ca. 11 500 cal. yr) glacier variations of maritime glaciers in western Scandinavia is thus a proxy of pre‐instrumental NAO variations. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Gamma rays from colliding winds of massive stars     

Anita Reimer  Olaf Reimer  Martin Pohl 《Astrophysics and Space Science》2007,309(1-4):351-357

Colliding winds of massive binaries have long been considered as potential sites of non-thermal high-energy photon production. This is motivated by the detection of non-thermal spectra in the radio band, as well as by correlation studies of yet unidentified EGRET γ-ray sources with source populations appearing in star formation regions. This work re-considers the basic radiative processes and its properties that lead to high energy photon production in long-period massive star systems. We show that Klein–Nishina effects as well as the anisotropic nature of the inverse Compton scattering, the dominating leptonic emission process, likely yield spectral and variability signatures in the γ-ray domain at or above the sensitivity of current or upcoming gamma ray instruments like GLAST-LAT. In addition to all relevant radiative losses, we include propagation (such as convection in the stellar wind) as well as photon absorption effects, which a priori can not be neglected. The calculations are applied to WR 140 and WR 147, and predictions for their detectability in the γ-ray regime are provided. Physically similar specimen of their kind like WR 146, WR 137, WR 138, WR 112 and WR 125 may be regarded as candidate sources at GeV energies for near-future γ-ray experiments. Finally, we discuss several aspects relevant for eventually identifying this source class as a γ-ray emitting population. Thereby we utilize our findings on the expected radiative behavior of typical colliding wind binaries in the γ-ray regime as well as its expected spatial distribution on the γ-ray sky.  相似文献   

Use of a parsimonious rainfall–run‐off model for predicting hydrological response in ungauged basins          下载免费PDF全文

Thomas Skaugen  Ivar Olaf Peerebom  Anna Nilsson 《水文研究》2015,29(8):1999-2013

A new parameter parsimonious rainfall–run‐off model, the Distance Distribution Dynamics (DDD) model, is used to simulate hydrological time series at ungauged sites in the Lygne basin in Norway. The model parameters were estimated as functions of catchment characteristics determined by geographical information system. The multiple regression equations relating catchment characteristics and model parameters were trained from 84 calibrated catchments located all over Norway, and all model parameters showed significant correlations with catchment characteristics. The significant correlation coefficients (with p‐value < 0.05) ranged from 0.22 to 0.55. The suitability of DDD for predictions in ungauged basins was tested for 17 catchments not used to estimate the multiple regression equations. For ten of the 17 catchments, deviations in Nash–Sutcliffe efficiency (NSE) criteria between the calibrated and regionalised model were less than 0.1, and for two calibrated catchments within the Lygne basin, the deviations were less than 0.08. The median NSE for the regionalized DDD for the 17 catchments for two time series was 0.66 and 0.72. Deviations in NSE between calibrated and regionalised models are well explained by the deviations between calibrated and regressed parameters describing spatial snow distribution and snowmelt respectively. The quality of the simulated run‐off series for the ungauged sites in the Lygne basin was assessed by comparing flow indices describing high, medium and low flow estimated from observed run‐off at the 17 catchments and for the simulated run‐off series. The indices estimated for the simulated series were generally well within the ranges defined by the 17 observed series. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Multipole borehole acoustic theory: Source imbalances and the effects of an elastic logging tool     

Tim W. Geerits  Xiaoming Tang  Olaf Hellwig  Thomas Bohlen 《Journal of Applied Geophysics》2010,70(2):113-143

In recent years the emphasis in acoustic logging has been shifting from the wireline to the Logging While Drilling (LWD) environment, the latter being far different from the former in that both tool rigidity and tool radius are considerably greater. In this paper we present a generic mathematical formulation for the multipole borehole acoustic measurement (alternate and equal polarity case), including a detailed analysis on the effects of multipole source amplitude imbalances. It is shown that source imbalance induced mode contaminants have excitation amplitudes that are scaled by the sum of the relative source imbalances between diametrically opposed sources. Furthermore it is shown that for mode contaminants with odd modal number there can be a significant offset in the associated directivity pattern, even at low levels of source imbalance. However, it is also shown that source imbalance induced mode contaminants can be completely eliminated if the multipole source is accompanied with a ‘vertically’ (but not azimuthally) offset multipole receiver. Mathematically, it is demonstrated (for a centered tool) that a polarity weighted stack of these multipole receivers completely eliminates the source imbalance induced mode contaminants. Excitation amplitudes and phase slowness of borehole guided modes are presented for the most common excitation regimes, i.e., monopole, dipole, quadrupole and the hexapole excitation, the latter one showing to have the advantage of a higher formation shear cut-off frequency than the quadrupole mode. Special emphasis will be on the analysis of the dipole excitation and the differences that occur due to variations in tool rigidity, tool diameter and (isotropic) formation properties with the resulting conclusion that a formation flexural mode is not observable as a result of a LWD dipole excitation (this opposed to its dipole wireline counterpart). The guided mode excitation amplitudes are calculated as residues using a Laurent series expansion. This (unconventional) way of calculating the residue has the advantage that it is independent of the pole order, does not require the numerical evaluation of derivatives with respect to the vertical wavenumber and allows for an accurate and efficient FFT implementation.  相似文献   

Magnetostratigraphy of deep drilling core SG-1 in the western Qaidam Basin (NE Tibetan Plateau) and its tectonic implications   总被引：1，自引：0，他引：1  

Weilin Zhang  Erwin Appel  Xiaomin Fang  Chunhui Song  Olaf Cirpka 《Quaternary Research》2012,78(1):139-148

The Qaidam Basin is the largest intermontane basin of the northeastern Tibetan Plateau and contains a continuous Cenozoic sequence of lacustrine sediments. A ~ 1000-m-deep drilling (SG-1) with an average core recovery of ~ 95% was carried out in the depocenter of the Chahansilatu playa (sub-depression) in the western Qaidam Basin, aimed to obtain a high-resolution record of the paleoenvironmental evolution and the erosion history. Stepwise alternating field and thermal demagnetization, together with rock magnetic results, revealed a stable remanent magnetization for most samples, carried by magnetite. The polarity sequence consisted of 16 normal and 15 reverse zones which can be correlated with chrons 1n to 2An of the global geomagnetic polarity time scale. Magnetostratigraphic results date the entire core SG-1 at ~ 2.77 Ma to ~ 0.1 Ma and yielded sediment accumulation rate (SAR) ranging from 26.1 cm/ka to 51.5 cm/ka. Maximum SARs occurred within the intervals of ~ 2.6–2.2 Ma and after ~ 0.8 Ma, indicating two episodes of erosion, which we relate to pulse tectonic uplift of the NE Tibetan Plateau with subsequent global cooling.  相似文献   

Evaluation of thermal equations of state for CO2 in numerical simulations     

Norbert B?ttcher  Joshua Taron  Olaf Kolditz  Chan-Hee Park  Rudolf Liedl 《Environmental Earth Sciences》2012,67(2):481-495

Three commonly used thermal equations of state for carbon dioxide, as well as the ideal gas law, have been compared against a large number of measurement data taken from the literature. Complex equations of state reach a higher accuracy than simple ones. The inaccuracy of the density function can cause large errors in fluid property correlations, such as heat capacity or viscosity. The influence of this inaccuracy on the results of numerical simulations have been evaluated by two examples: The first one assumes isothermal gas expansion from a volume, while the second one considers heat transport along a fracture. For both examples, different equations of state have been utilized. The simulations have been performed on the scientific software platform OpenGeoSys. The difference among the particular simulation results is significant. Apparently small errors in the density function can cause considerably different results of otherwise identical simulation setups.  相似文献