A three-dimensional model study on processes of stratification and de-stratification in the Limfjord     

Richard Hofmeister  Hans Burchard  Karsten Bolding 《Continental Shelf Research》2009,29(11-12):1515-1524

Investigations on stratifying and de-stratifying processes in the Limfjord in Denmark, stretching from the North Sea at the western end to the Kattegat at the eastern end, were carried out. The forcing of the Limfjord is dominated by mean sea surface elevation and salinity gradients, diffuse freshwater supply, as well as episodic saline inflow events from the North Sea boundary. The physical regime of the Limfjord switches periodically from stratified to mixed conditions. In order to investigate the complexity of the system, a realistic three-dimensional high-resolution numerical model study was conducted for the year 2003. The results are based on, and compared to, available field data. A central subject of this study is the anomaly of potential energy as a measure for stratification. The stratifying and de-stratifying processes are identified as contributing terms in a dynamic equation for the potential energy anomaly. The comparison of model results and observations shows that the model has the capability of reproducing the observed physical regimes. Changes in the simulated stratification turn out to be a complex interaction of differential advection, heating and turbulent mixing in the central Limfjord.  相似文献   

Documentation of Istanbul Historic Peninsula by Kinematic Terrestrial Laser Scanning     

Thomas P.  Kersten  Gürcan  Büyüksal&#;h  &#;brah&#;m  Baz  Karsten  Jacobsen 《The Photogrammetric Record》2009,24(126):122-138

Although the Historic Peninsula of old Istanbul was added to the UNESCO World Heritage List in 1985, complete documentation of this important area has not yet been carried out. In 2006 the Istanbul Metropolitan Municipality's Historical Environment Protection Directorate initiated the "Historic Peninsula Project", which covers an area of 1500 ha and includes approximately 48 000 buildings in crowded and frequently narrow streets. BİMTAŞ, a company owned by the Municipality, immediately started the documentation of all buildings in the project area using terrestrial laser scanning. This created the challenge of building up an efficient production environment with new high-end technology to fulfil the requirements of this project in a very short timeframe of 2 years. This paper describes the entire production environment for documentation of all buildings, detailing the frequent adaptations of the process resulting from learning on the job. Although the data acquisition and mapping environment was established in the course of production, it was always essential to optimise the technical solutions in order to meet the requirements for data quality and delivery deadlines. Only 80 ha of the required 1500 ha was completed using static scanning during the first 6 months, thus requiring a change from static to mobile terrestrial laser scanning in order to accelerate the work and to conclude the scanning phase for the remaining major area within 3 months.  相似文献   

Multi-Constrained Catchment Scale Optimization of Groundwater Abstraction Using Linear Programming     

Mehrdis Danapour  Michael N. Fienen  Anker Lajer Højberg  Karsten Høgh Jensen  Simon Stisen 《Ground water》2021,59(4):503-516

Due to increasing water demands globally, freshwater ecosystems are under constant pressure. Groundwater resources, as the main source of accessible freshwater, are crucially important for irrigation worldwide. Over-abstraction of groundwater leads to declines in groundwater levels; consequently, the groundwater inflow to streams decreases. The reduction in baseflow and alteration of the streamflow regime can potentially have an adverse effect on groundwater-dependent ecosystems. A spatially distributed, coupled groundwater–surface water model can simulate the impacts of groundwater abstraction on aquatic ecosystems. A constrained optimization algorithm and a simulation model in combination can provide an objective tool for the water practitioner to evaluate the interplay between economic benefits of groundwater abstractions and requirements to environmental flow. In this study, a holistic catchment-scale groundwater abstraction optimization framework has been developed that allows for a spatially explicit optimization of groundwater abstraction, while fulfilling a predefined maximum allowed reduction of streamflow (baseflow [Q95] or median flow [Q50]) as constraint criteria for 1484 stream locations across the catchment. A balanced K-Means clustering method was implemented to reduce the computational burden of the optimization. The model parameters and observation uncertainties calculated based on Bayesian linear theory allow for a risk assessment on the optimized groundwater abstraction values. The results from different optimization scenarios indicated that using the linear programming optimization algorithm in conjunction with integrated models provides valuable information for guiding the water practitioners in designing an effective groundwater abstraction plan with the consideration of environmental flow criteria important for the ecological status of the entire system.  相似文献   

Seismic properties of the upper mantle beneath Lanzarote (Canary Islands): Model predictions based on texture measurements by EBSD   总被引：1，自引：0，他引：1  

Pierre Vonlanthen  Karsten Kunze  Luigi Burlini  Bernard Grobety 《Tectonophysics》2006,428(1-4):65-85

We present a petrophysical analysis of upper mantle xenoliths, collected in the Quaternary alkali basalt fields (Series III and IV) from the island of Lanzarote. The samples consist of eight harzburgite and four dunite nodules, 5 to 15 cm in size, and exhibit a typical protogranular to porphyroclastic texture. An anomalous foliation resulting from strong recovery processes is observed in half of the specimens. The lattice preferred orientations (LPO) of olivine, orthopyroxene and clinopyroxene were measured using electron backscatter diffraction (EBSD). In most samples, olivine exhibits LPOs intermediate between the typical single crystal texture and the [100] fiber texture. Occasionally, the [010] fiber texture was also observed. Simultaneous occurrence of both types of fiber textures suggests the existence of more than one deformation regime, probably dominated by a simple shear component under low strain rate and moderate to high temperature. Orthopyroxene and clinopyroxene display a weaker but significant texture. The LPO data were used to calculate the seismic properties of the xenoliths at PT conditions obtained from geothermobarometry, and were compared to field geophysical data reported from the literature. The velocity of P-waves (7.9 km/s) obtained for a direction corresponding to the existing seismic transect is in good agreement with the most recent geophysical interpretation. Our results are consistent with a roughly W–E oriented fastest P-wave propagation direction in the uppermost mantle beneath the Canary Islands, and with the lithosphere structure proposed by previous authors involving a crust–mantle boundary at around 18 km in depth, overlaid by intermediate material between 11 and 18 km.  相似文献   

Post-deformational annealing of calcite rocks   总被引：3，自引：3，他引：3  

Auke Barnhoorn  Misha Bystricky  Luigi Burlini  Karsten Kunze 《Tectonophysics》2005,403(1-4):167-191

The evolution of microstructure and crystallographic preferred orientation (CPO) during post-deformational annealing was studied on three calcite rock types differing in purity and grain size: Carrara marble (98% calcite, mean grain size of 115 μm), Solnhofen limestone (96%, 5 μm) and synthetic calcite aggregates (99%, 7 μm). Samples were first deformed in torsion at 727 °C at a shear strain rate of 3 × 10^{− 4} s^{− 1} to a shear strain of 5 and subsequently heat-treated at 727 °C for various durations between 0 and 24 h. Microstructures and CPOs were analysed by optical microscopy, image analysis and electron backscatter diffraction (EBSD).All rock types deformed in the dislocation creep field at the same applied conditions, but their microstructures and CPOs after deformation and after annealing differed depending on starting grain size and material composition. In Carrara marble and in the synthetic calcite aggregate, a strong CPO developed during deformation accompanied by dynamic recrystallisation with significant changes in grain size. During annealing, widespread grain growth and subtle changes of CPO occurred, and equilibrated foam microstructures were approached after long annealing times. The CPO is the only feature in annealed samples indicating an earlier deformation phase, although it is not always identical to the CPO formed during deformation. In the more impure Solnhofen limestone, secondary phases on grain boundaries suppressed grain boundary mobility and prevented both the formation of a recrystallisation CPO during deformation and grain size modification during deformation and annealing.  相似文献   

Texture development of polycrystalline anhydrite experimentally deformed in torsion     

Florian Heidelbach  Iona C. Stretton  Karsten Kunze 《International Journal of Earth Sciences》2001,90(1):118-126

A polycrystalline aggregate of anhydrite was deformed in torsion to a maximum shear strain of 8.1 at 700°C and a maximum shear strain rate of 5᎒^-3 s^-1. The crystallographic preferred orientation (CPO or texture) was investigated as a function of shear strain/shear strain rate in a radial profile from the centre to the edge of the sample. A deformation texture developed at shear strains of 1.5-2 (corresponding to shear strain rates of 1 to 1.3᎒^-3 s^-1) and reached a stable position relative to the kinematic frame at a shear strain of 3.7 (2.3᎒^-3 s^-1). Further shear strain only led to a small increase in texture strength but no change in the orientation relative to the kinematic frame. The CPO is very similar to naturally observed textures and can be explained by the activity of the {001}<010> and {012}<121> slip systems. Although independent mechanical data indicate that a change of mechanism from dislocation- to diffusion-controlled creep occurred at a shear strain of approximately 1.5, the texture does not weaken, but rather increases, in strength with higher shear strains.  相似文献   

CO₂-H₂O mixtures in the geological sequestration of CO₂. I. Assessment and calculation of mutual solubilities from 12 to 100°C and up to 600 bar     

Nicolas Spycher  Karsten Pruess 《Geochimica et cosmochimica acta》2003,67(16):3015-3031

Evaluating the feasibility of CO₂ geologic sequestration requires the use of pressure-temperature-composition (P-T-X) data for mixtures of CO₂ and H₂O at moderate pressures and temperatures (typically below 500 bar and below 100°C). For this purpose, published experimental P-T-X data in this temperature and pressure range are reviewed. These data cover the two-phase region where a CO₂-rich phase (generally gas) and an H₂O-rich liquid coexist and are reported as the mutual solubilities of H₂O and CO₂ in the two coexisting phases. For the most part, mutual solubilities reported from various sources are in good agreement. In this paper, a noniterative procedure is presented to calculate the composition of the compressed CO₂ and liquid H₂O phases at equilibrium, based on equating chemical potentials and using the Redlich-Kwong equation of state to express departure from ideal behavior. The procedure is an extension of that used by King et al. (1992), covering a broader range of temperatures and experimental data than those authors, and is readily expandable to a nonideal liquid phase. The calculation method and formulation are kept as simple as possible to avoid degrading the performance of numerical models of water-CO₂ flows for which they are intended. The method is implemented in a computer routine, and inverse modeling is used to determine, simultaneously, (1) new Redlich-Kwong parameters for the CO₂-H₂O mixture, and (2) aqueous solubility constants for gaseous and liquid CO₂ as a function of temperature. In doing so, mutual solubilities of H₂O from 15 to 100°C and CO₂ from 12 to 110°C and up to 600 bar are generally reproduced within a few percent of experimental values. Fugacity coefficients of pure CO₂ are reproduced mostly within one percent of published reference data.  相似文献   

Modelling of convective turbulence with a two-equation k-ɛ turbulence closure scheme     

Adolf Stips  Hans Burchard  Karsten Bolding  Walter Eifler 《Ocean Dynamics》2002,52(4):153-168

 In this study we aim at comparing turbulence parameters from field observations and model simulations under convective conditions. The comparison is focused on the depth dependence and temporal dynamics of viscous and diffusive dissipation rates ɛ and χ. The near-surface observations were obtained by using a quasi-free-rising profiler which measured small-scale shear and temperature fluctuations to within the vicinity of the water surface. Convective conditions during the experiment are characterized by low wind speeds (between 0 and 4 m s⁻¹) and a typical heat loss of about 150 Wm⁻². We applied a state-of-the-art two-equation k-ɛ turbulence model with an algebraic second-moment closure scheme. The qualitative agreement of the turbulence quantities resulting from observations and simulations is rather good. The temporal dynamics of the temperature field is simulated correctly, whereas in the spatial dynamics some deficiencies of the model due to its local character can be seen. It is concluded that such models realistically reproduce convective turbulence and therefore represent a reasonable compromise between complexity and simplicity, so that they can be used with acceptable costs in large-scale models. Received: 31 October 2001 / Accepted: 20 September 2002 Acknowledgements The whole project was intitiated by Peter Schlittenhardt, who strongly supported the development of the observational technique in uprising mode and encouraged us to undertake the experiment in Lake Maggiore; for which we will thank him most. Performing the measurement campaign was only possible with the help of several colleagues from the Marine Environment Unit at the Joint Research Centre. Thanks to all of them, but especially to Dirk van d. Linde, Ulisse Devisioni, Bjarke Rasmussen and Hartmut Prandke. The Istituto Italiano di Idrobiologia, Verbania Pallanza, provided the boat Livia for the installation and removal of the measurement system; thanks to the master Stefano Maurizio for his engagement. Ute Tschesche provided the data evaluation and presentation software and Judith Challis helped to polish our English. Part of the study was␣supported by the PROVESS project (MAS3-CT97-0159); thanks to our sponsors at the European Commission. We are further grateful to two anonymous referees for their constructive comments. Responsible Editor: Charitha Pattiaratchi  相似文献   

Multiphase flow dynamics during CO2 disposal into saline aquifers   总被引：2，自引：0，他引：2  

Karsten Pruess  Julio García 《Environmental Geology》2002,42(2-3):282-295

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Climatic and limnological changes at Lake Karakul (Tajikistan) during the last ~29 cal ka     

Liv Heinecke  Steffen Mischke  Karsten Adler  Anja Barth  Boris K. Biskaborn  Birgit Plessen  Ingmar Nitze  Gerhard Kuhn  Ilhomjon Rajabov  Ulrike Herzschuh 《Journal of Paleolimnology》2017,58(3):317-334

We present results of analyses on a sediment core from Lake Karakul, located in the eastern Pamir Mountains, Tajikistan. The core spans the last ~29 cal ka. We investigated and assessed processes internal and external to the lake to infer changes in past moisture availability. Among the variables used to infer lake-external processes, high values of grain-size end-member (EM) 3 (wide grain-size distribution that reflects fluvial input) and high Sr/Rb and Zr/Rb ratios (coinciding with coarse grain sizes), are indicative of moister conditions. High values in EM1, EM2 (peaks of small grain sizes that reflect long-distance dust transport or fine, glacially derived clastic input) and TiO₂ (terrigenous input) are thought to reflect greater influence of dry air masses, most likely of Westerly origin. High input of dust from distant sources, beginning before the Last Glacial Maximum (LGM) and continuing to the late glacial, reflects the influence of dry Westerlies, whereas peaks in fluvial input suggest increased moisture availability. The early to early-middle Holocene is characterised by coarse mean grain sizes, indicating constant, high fluvial input and moister conditions in the region. A steady increase in terrigenous dust and a decrease in fluvial input from 6.6 cal ka BP onwards points to the Westerlies as the predominant atmospheric circulation through to present, and marks a return to drier and even arid conditions in the area. Proxies for productivity (TOC, TOC/TN, TOC _Br ), redox potential (Fe/Mn) and changes in the endogenic carbonate precipitation (TIC, δ¹⁸O _Carb ) indicate changes within the lake. Low productivity characterised the lake from the late Pleistocene until 6.6 cal ka BP, and increased rapidly afterwards. Lake level remained low until the LGM, but water depth increased to a maximum during the late glacial and remained high into the early Holocene. Subsequently, the water level decreased to its present stage. Today the lake system is mainly climatically controlled, but the depositional regime is also driven by internal limnogeological processes.  相似文献