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   

Toward physical aspects affecting a possible leakage of geologically stored CO2 into the shallow subsurface     

Ashok Singh  Jens Olaf Delfs  Uwe Jens Görke  Olaf. Kolditz 《Acta Geotechnica》2014,9(1):81-86

In geological formations, migration of CO₂ plume is very complex and irregular. To make CO₂ capture and storage technology feasible, it is important to quantify CO₂ amount associated with possible leakage through natural occurring faults and fractures in geologic medium. Present work examines the fracture aperture effect on CO₂ migration due to free convection. Numerical results reveal that fracture with larger-aperture intensify CO₂ leakage. Mathematical formulation and equations of state for the mixture are implemented within the object-oriented finite element code OpenGeoSys developed by the authors. The volume translated Peng–Robinson equation of state is used for material properties of CO₂ and water.  相似文献   

Concept and workflow for 3D visualization of atmospheric data in a virtual reality environment for analytical approaches   总被引：2，自引：0，他引：2  

Carolin Helbig  Hans-Stefan Bauer  Karsten Rink  Volker Wulfmeyer  Michael Frank  Olaf Kolditz 《Environmental Earth Sciences》2014,72(10):3767-3780

In the future, climate change will strongly influence our environment and living conditions. Weather and Climate simulations that predict possible changes produce big data sets. The combination of various variables of climate models with spatial data from different sources helps to identify correlations and to study key processes. In this paper, the results of the Weather Research and Forecasting model are visualized for two regions. For this purpose, a continuous workflow that leads from the integration of heterogeneous raw data to 3D visualizations that can be displayed on a desktop computer or in an interactive virtual reality environment is developed. These easy-to-understand visualizations of complex data are the basis for scientific communication and for the evaluation and verification of models as well as for interdisciplinary discussions of the research results.  相似文献   

基于优化随机森林回归模型的土壤盐渍化反演   总被引：1，自引：0，他引：1  

杨练兵  陈春波  郑宏伟  罗格平  尚白军  Olaf Hellwich 《地球信息科学学报》2021,23(9):1662-1674

当前应用于土壤盐分含量（Soil Salinity Content, SSC）反演的随机森林回归（Random Forests Regression, RFR）较少关注对模型精度影响较大的反演参数子集和模型参数的同步优化。本研究选择渭-库绿洲和奇台绿洲为实验区,基于Landsat-5 TM、SRTM、MOD11A2.006遥感数据构建反演参数。首先,利用弹性网络（Elastic Net, EN）筛选出反演参数子集,然后利用遗传算法（Genetic Algorithm, GA）和贝叶斯优化算法（Bayesian Optimization Algorithm, BOA）分别优化随机森林回归（Random Forests Regression, RFR）参数,建立反演参数子集和模型参数分步优化的RFR模型（EN-GA-RFR、EN-BOA-RFR）。建立利用GA和BOA分别同步优化反演参数子集和模型参数的RFR模型（GA-RFR、BOA-RFR）。在每个实验区,对比EN-GA-RFR、EN-BOA-RFR、GA-RFR、BOA-RFR的预测精度。最后分析每个实验区各类盐渍土的空间分布,并对2个实验区的反演参数进行对比分析。结果表明：每个实验区模型预测精度由高到低的排序均为BOA-RFR>GA-RFR>EN-BOA-RFR=EN-GA-RFR,整体上BOA的优化性能均好于GA;渭-库绿洲和奇台绿洲面积占比最大的盐渍土类型分别为盐渍土和中度盐渍土;反演参数对SSC的表征能力存在空间分异性。  相似文献   

A nested-cell approach for in situ remediation     

Luo J  Wu W  Fienen MN  Jardine PM  Mehlhorn TL  Watson DB  Cirpka OA  Criddle CS  Kitanidis PK 《Ground water》2006,44(2):266-274

We characterize the hydraulics of an extraction-injection well pair in arbitrarily oriented regional flow by the recirculation ratio, area, and average residence time in the recirculation zone. Erratic regional flow conditions may compromise the performance of the reactor between a single well pair. We propose an alternative four-well system: two downgradient extraction and two upgradient injection wells creating an inner cell nested within an outer cell. The outer cell protects the inner cell from the influence of regional flow. Compared to a two-well system, the proposed four-well system has several advantages: (1) the recirculation ratio within the nested inner cell is less sensitive to the regional flow direction; (2) a transitional recirculation zone between the inner and outer cells can capture flow leakage from the inner cell, minimizing the release of untreated contaminants; and (3) the size of the recirculation zone and residence times can be better controlled within the inner cell by changing the pumping rates. The system is applied at the Field Research Center in Oak Ridge, Tennessee, where experiments on microbial in situ reduction of uranium (VI) are under way.  相似文献   

Analyzing bank filtration by deconvoluting time series of electric conductivity   总被引：4，自引：0，他引：4  

Cirpka OA  Fienen MN  Hofer M  Hoehn E  Tessarini A  Kipfer R  Kitanidis PK 《Ground water》2007,45(3):318-328

Knowing the travel-time distributions from infiltrating rivers to pumping wells is important in the management of alluvial aquifers. Commonly, travel-time distributions are determined by releasing a tracer pulse into the river and measuring the breakthrough curve in the wells. As an alternative, one may measure signals of a time-varying natural tracer in the river and in adjacent wells and infer the travel-time distributions by deconvolution. Traditionally this is done by fitting a parametric function such as the solution of the one-dimensional advection-dispersion equation to the data. By choosing a certain parameterization, it is impossible to determine features of the travel-time distribution that do not follow the general shape of the parameterization, i.e., multiple peaks. We present a method to determine travel-time distributions by nonparametric deconvolution of electric-conductivity time series. Smoothness of the inferred transfer function is achieved by a geostatistical approach, in which the transfer function is assumed as a second-order intrinsic random time variable. Nonnegativity is enforced by the method of Lagrange multipliers. We present an approach to directly compute the best nonnegative estimate and to generate sets of plausible solutions. We show how the smoothness of the transfer function can be estimated from the data. The approach is applied to electric-conductivity measurements taken at River Thur, Switzerland, and five wells in the adjacent aquifer, but the method can also be applied to other time-varying natural tracers such as temperature. At our field site, electric-conductivity fluctuations appear to be an excellent natural tracer.  相似文献   

Determination of first-order degradation rate constants from monitoring networks   总被引：1，自引：0，他引：1  

Beyer C  Chen C  Gronewold J  Kolditz O  Bauer S 《Ground water》2007,45(6):774-785

In this article, different strategies for estimating first-order degradation rate constants from measured field data are compared by application to multiple, synthetic, contaminant plumes. The plumes were generated by numerical simulation of contaminant transport and degradation in virtual heterogeneous aquifers. These sites were then individually and independently investigated on the computer by installation of extensive networks of observation wells. From the data measured at the wells, that is, contaminant concentrations, hydraulic conductivities, and heads, first-order degradation rates were estimated by three 1D centerline methods, which use only measurements located on the plume axis, and a two-dimensional method, which uses all concentration measurements available downgradient from the contaminant source. Results for both strategies show that the true rate constant used for the numerical simulation of the plumes in general tends to be overestimated. Overestimation is stronger for narrow plumes from small source zones, with an average overestimation factor of about 5 and single values ranging from 0.5 to 20, decreasing for wider plumes, with an average overestimation factor of about 2 and similar spread. Reasons for this overestimation are identified in the velocity calculation, the dispersivity parameterization, and off-centerline measurements. For narrow plumes, the one- and the two-dimensional strategies show approximately the same amount of overestimation. For wider plumes, however, incorporation of all measurements in the two-dimensional approach reduces the estimation error. No significant relation between the number of observation wells in the monitoring network and the quality of the estimated rate constant is found for the two-dimensional approach.  相似文献   

Cambrian sedimentary dykes in the Proterozoic basement of the Västervik area (southeast Sweden): episodic formation inferred from macro- and microfabrics     

Nadine Friese  Axel Vollbrecht  Bernd Leiss  Olaf Jacke 《International Journal of Earth Sciences》2011,100(4):741-752

Fabrics of Cambrian sedimentary dykes formed in Proterozoic granites of the Västervik area (Southeast Sweden) evidence repeated opening/filling and mineralisation/cementation events under varying conditions. Diagnostic features include (1) wall-parallel boundaries between epiclastic fillings and (2) early formed dyke sediments that appear as lithoclasts in subsequently formed sedimentary fillings. The psammitic components mostly consist of well-rounded quartz grains related to a coastal environment and fragments from the granitic host rock. Platy calcitic fragments embedded in the epiclastic matrix originally formed as microveins within already-lithified dyke sediments and the adjacent host rock. Convex downward-pointing, internal sagging structures, together with the preferred orientation of compositional boundaries and long axes of grains/rock fragments parallel to the dyke walls, are interpreted as the result of suction-controlled flow of unconsolidated fillings during episodes of downward dyke growth. Pressure solution of quartz grains are evidence of extensional phases with dyke propagation that were interrupted by phases of horizontal compression normal to the dyke walls. The N–S and NE–SW striking sedimentary dykes formed by opening of a pre-existing joint set during NW–SE oriented rifting during the Cambrian.  相似文献   

Short-term fluctuations in vegetation and phytoplankton during the Middle Eocene greenhouse climate: a 640-kyr record from the Messel oil shale (Germany)     

Olaf K. Lenz  Volker Wilde  Walter Riegel 《International Journal of Earth Sciences》2011,100(8):1851-1874

The Palaeogene was the most recent greenhouse period on Earth. Especially for the Late Palaeocene and Early Eocene, several superimposed short-term hyperthermal events have been described, including extremes such as the Palaeocene?CEocene Thermal Maximum. Major faunal and floral turnovers in the marine and terrestrial realms were recorded in association with these events. High-resolution palynological analysis of the early Middle Eocene maar lake sediments at Messel, near Darmstadt, Germany, provides an insight into the dynamics of a climax vegetation during the Middle Eocene greenhouse climate in a time span without significant climatic excursions. Numerical techniques like detrended correspondence analysis and wavelet analysis have been applied to recognize cyclic fluctuations and long-term trends in the vegetation through a time interval of approximately 640?kyr. Based on the numerical zoning of the pollen diagram, three phases in the development of the vegetation may be distinguished. Throughout these phases, the climax vegetation did not change substantially in qualitative composition, but a trend towards noticeably less humid conditions probably in combination with a drop of the water level in the lake may be recognized. A shift in algal population from the freshwater dinoflagellate cyst Messelodinium thielepfeifferae to a dominance of Botryococcus in the uppermost part of the core is interpreted as a response to changes in acidity and nutrient availability within the lake. Time series analyses of pollen assemblages show that variations in the Milankovitch range of eccentricity, obliquity and precession can be distinguished. In addition, fluctuations in the sub-Milankovitch range are indicated. This demonstrates that floral changes during steady depositional conditions in the Middle Eocene of Messel were controlled by orbital forcing.  相似文献   

Development of a 3D groundwater model based on scarce data: the Wadi Kafrein catchment/Jordan   总被引：2，自引：2，他引：0  

Yajie Wu  Wenqing Wang  Mathias Toll  William Alkhoury  Martin Sauter  Olaf Kolditz 《Environmental Earth Sciences》2011,64(3):771-785

In this work, a 3D groundwater flow model integrating all important geological features of the hydrogeological system is developed to investigate hydrological processes in the Wadi Kafrein area of Jordan. A large amount of available geological and hydrological data is integrated to construct a 3D groundwater flow model for the Wadi Kafrein area. Using the newly developed mapping approach, the translation of the highly detailed geological formations to an unstructured finite element grids, can be accomplished with high precision. The existing data set for model calibration is scarce, which is a typical situation for many hydrogeological case studies. At first, the steady state calibration of the groundwater model is carried out based on the observation wells. Then, the time and space-dependent recharge from precipitation are applied at the top surface of the finite element model. The transient simulation is conducted during the period of 1996–2008 considering the abstraction rates of the production wells and discharge of the springs. The calculated water levels are close to the observed values. The difference is partly caused by return flows from irrigation and the groundwater inflow from the adjacent aquifers which are not taken into consideration so far. Since the Wadi Kafrein area is an important agricultural area in the semiarid region of the Lower Jordan Valley, the model developed in this study can be regarded as a useful tool for analyzing the hydrological processes and improving groundwater management practices elsewhere affected by similar geological and hydrogeological conditions.  相似文献