Large-Eddy Simulations of Surface Heterogeneity Effects on the Convective Boundary Layer During the LITFASS-2003 Experiment   总被引：3，自引：3，他引：0  

Bj?rn Maronga  Siegfried Raasch 《Boundary-Layer Meteorology》2013,146(1):17-44

We investigate the impact of observed surface heterogeneities during the LITFASS-2003 experiment on the convective boundary layer (CBL). Large-eddy simulations (LES), driven by observed near-surface sensible and latent heat fluxes, were performed for the diurnal cycle and compare well with observations. As in former studies of idealized one- and two-dimensional heterogeneities, secondary circulations developed that are superimposed on the turbulent field and that partly take over the vertical transport of heat and moisture. The secondary circulation patterns vary between local and roll-like structures, depending on the background wind conditions. For higher background wind speeds, the flow feels an effective surface heat-flux pattern that derives from the original pattern by streamwise averaging. This effective pattern generates a roll-like secondary circulation with roll axes along the mean boundary-layer wind direction. Mainly the upstream surface conditions control the secondary circulation pattern, where the fetch increases with increasing background wind speed. Unlike the entrainment flux that appears to be slightly decreased compared to the homogeneously-heated CBL, the vertical flux of sensible heat appears not to be modified in the mixed layer, while the vertical flux of latent heat shows different responses to secondary circulations. The study illustrates that sufficient time averaging and ensemble averaging is required to separate the heterogeneity-induced signals from the raw LES turbulence data. This might be an important reason why experiments over heterogeneous terrain in the past did not give any clear evidence of heterogeneity-induced effects.  相似文献   

Book Review: Martin L.J. Turner: Expedition Mars,Springer/Praxis,London, 2004, 321 pages. ISBN: 1-85233-735-4     

Grieger  Björn 《Earth, Moon, and Planets》2003,93(3):234-234

Earth, Moon, and Planets -  相似文献   

Correlation of late precambrian and early Palaeozoic sequences by eustatic sea-level changes and the selection of the Precambrian-Cambrian boundary     

Knut Bjørlykke 《Precambrian Research》1982,17(2):99-104

The author argues for a pragmatic approach to the problem of defining the Precambrian-Cambrian boundary. A boundary at first occurrence of shelly fauna as recommended by the Precambrian-Cambrian working group will create severe difficulties in worldwide correlation. By placing the boundary stratigraphically somewhat higher (i.e. the Fallotaspis zone) with a more abundant fauna, there is a much better basis for biostratigraphic correlation.Eustatic sea-level changes may be another important tool for late Precambrian-early Palaeozoic correlation, and more detailed facies interpretation of such sequences should be carried out in order to recognise these eustatic sea-level changes.  相似文献   

Competitive firms in thin regions in Norway: The importance of workplace learning     

Bjørn-Tore Flåten  Arne Isaksen  James Karlsen 《Norsk geografisk tidsskrift. Norwegian journal of geography》2015,69(2):102-111

The article departs from empirical studies of two competitive firms in an organisationally thin region in Norway. The main question in the article is how these firms have achieved global competitiveness. The article focuses its inquiry on how the firms organise their innovation activity, giving special attention to the firms' organisational learning and absorptive capacity. It is found that find that workplace learning enables the firms to utilise knowledge in uncommon ways. The learning rests on specific organisational traits in the firms, such as broad participation, long-term on-the-job training, the use of practice-based knowledge in innovation projects, and links to national and global knowledge sources. The characteristics of thin regions indicate that these traits make up a generally applicable strategy in such regions.  相似文献   

Mobility and Transport of Nd Isotopes in the Vadose Zone During Weathering of Granitic Till in a Boreal Forest     

Björn Öhlander  Magnus Land  Johan Ingri  Anders Widerlund 《Aquatic Geochemistry》2014,20(1):1-17

There is a broad correlation between the ε_Nd values for rivers (including both the water and the particulate material it carries) and the age of the source terrain. This paper presents Nd isotope distribution data for soil, soil water, groundwater, and stream water samples gathered in a small catchment in northern Sweden. The results show that the release of Nd and Sm from boreal forests into streams and, eventually, into the oceans is more complicated than previously realized. The weathering of till causes changes in both the Nd isotopic composition and Sm/Nd ratios. Both the Sm/Nd ratio and ε_Nd were higher in strongly weathered soils horizons than in less weathered till, since minerals with high Sm/Nd ratios were, on average, more resistant to weathering than those with low Sm/Nd ratios. In contrast to the situation for the main minerals and the major elements, the weathering of rare earth elements (REE) was not restricted to the E-horizon: the measured REE concentrations continued to increase with depth in the C-horizon. In addition, REE released by weathering in the upper parts of the soil profile were partly secondarily retained at deeper levels. Therefore, the dissolved Nd released by weathering in the upper soil horizons was trapped and did not enter the groundwater directly. Rather, the Nd in the groundwater largely originated from weathering within the groundwater zone. However, this was not the only source of Nd in the stream water. The Nd isotope composition and Sm/Nd ratio were determined by the mixing between of Nd and Sm in the groundwater and REE-carrying organic material washed out of the soil profile. The groundwater close to the stream reaches the upper soil horizons during high discharge events such as snowmelts, and organic matter carrying Nd and Sm is washed out of the soils and thus released into the stream. Therefore, the Nd exported from catchment is derived from both the weathering within the groundwater zone, and the organic matter washed out from the soil. If longer timescales with more advanced weathering stages in the groundwater zone are considered, it cannot be ruled out that there will be a shift towards more radiogenic values in the exported Nd. Recorded shifts in the Nd isotopic composition in the ocean may thus not only reflect changed source regions, but also the weathering history of the same source region.  相似文献   

TESSIN VISLab—laboratory for scientific visualization     

Lars Bilke  Thomas Fischer  Carolin Helbig  Charlotte Krawczyk  Thomas Nagel  Dmitri Naumov  Sebastian Paulick  Karsten Rink  Agnes Sachse  Sophie Schelenz  Marc Walther  Norihiro Watanabe  Björn Zehner  Jennifer Ziesch  Olaf Kolditz 《Environmental Earth Sciences》2014,72(10):3881-3899

Scientific visualization is an integral part of the modeling workflow, enabling researchers to understand complex or large data sets and simulation results. A high-resolution stereoscopic virtual reality (VR) environment further enhances the possibilities of visualization. Such an environment also allows collaboration in work groups including people of different backgrounds and to present results of research projects to stakeholders or the public. The requirements for the computing equipment driving the VR environment demand specialized software applications which can be run in a parallel fashion on a set of interconnected machines. Another challenge is to devise a useful data workflow from source data sets onto the display system. Therefore, we develop software applications like the OpenGeoSys Data Explorer, custom data conversion tools for established visualization packages such as ParaView and Visualization Toolkit as well as presentation and interaction techniques for 3D applications like Unity. We demonstrate our workflow by presenting visualization results for case studies from a broad range of applications. An outlook on how visualization techniques can be deeply integrated into the simulation process is given and future technical improvements such as a simplified hardware setup are outlined.  相似文献   

Degradation of digested sewage sludge residue under anaerobic conditions for mine tailings remediation     

Yu Jia  Peter Nason  Lena Alakangas  Christian Maurice  Björn Öhlander 《Environmental Earth Sciences》2014,72(9):3643-3654

Previous studies showed that 85 % of total organic matter (TOM) in digested sewage sludge (biosolids) used as a sealing layer material over sulfide tailings at the Kristineberg Mine, northern Sweden, had been degraded 8 years after application, resulting in a TOM reduction from 78 to 14 %. To achieve a better understanding of the field observations, laboratory studies were performed to evaluate biodegradation rates of the TOM under anaerobic conditions. Results reveal that the original biosolid consisted of ca. 60 % TOM (48.0 % lignin and 11.8 % carbohydrates) that had not been fully degraded. The incubation experiments proved that 27.8 % TOM in the biosolid was further degraded anaerobically at 20–22 °C during the 230 days’ incubation period, and that a plateau to the biodegradation rate was approached. Based on model results, the degradation constant was found to be 0.0125 (day^?1). The calculated theoretical gas formation potential was ca. 50 % higher than the modeled results based on the average degradation rate. Cumulated H₂S equated to 0.65 μmoL g^?1 of biosolid at 230 days. However, the large sulfurous compounds reservoir (1.76 g SO₄ ^2? kg^?1 biosolid) together with anaerobic conditions can generate high concentrations of this gas over a long-term perspective. Due to the rate of biodegradability identified via anaerobic processes, the function of the biosolid to serve as an effective barrier to inhibit oxygen migration to underlying tailings, may decrease over time. However, a lack of readily degradable organic fractions in the biosolid and a large fraction of organic matter that was recalcitrant to degradation suggest a longer degradation duration, which would prolong the biosolid material’s function and integrity.  相似文献   

Using Multiple Grids in Markov Mesh Facies Modeling     

Odd Kolbjørnsen  Marita Stien  Heidi Kjønsberg  Bjørn Fjellvoll  Petter Abrahamsen 《Mathematical Geosciences》2014,46(2):205-225

A multigrid Markov mesh model for geological facies is formulated by defining a hierarchy of nested grids and defining a Markov mesh model for each of these grids. The facies probabilities in the Markov mesh models are formulated as generalized linear models that combine functions of the grid values in a sequential neighborhood. The parameters in the generalized linear model for each grid are estimated from the training image. During simulation, the coarse patterns are first laid out, and by simulating increasingly finer grids we are able to recreate patterns at different scales. The method is applied to several tests cases and results are compared to the training image and the results of a commercially available snesim algorithm. In each test case, simulation results are compared qualitatively by visual inspection, and quantitatively by using volume fractions, and an upscaled permeability tensor. When compared to the training image, the method produces results that only have a few percent deviation from the values of the training image. When compared with the snesim algorithm the results in general have the same quality. The largest computational cost in the multigrid Markov mesh is the estimation of model parameters from the training image. This is of comparable CPU time to that of creating one snesim realization. The simulation of one realization is typically ten times faster than the estimation.  相似文献   

Rock Mass Grouting in the Løren Tunnel: Case Study with the Main Focus on the Groutability and Feasibility of Drill Parameter Interpretation     

Are Håvard Høien  Bjørn Nilsen 《Rock Mechanics and Rock Engineering》2014,47(3):967-983

The Løren road tunnel is a part of a major project at Ring road 3 in Oslo, Norway. The rock part of the tunnel is 915 m long and has two tubes with three lanes and breakdown lanes. Strict water ingress restriction was specified and continuous rock mass grouting was, therefore, carried out for the entire tunnel, which was excavated in folded Cambro-Silurian shales intruded by numerous dykes. This paper describes the rock mass grouting that was carried out for the Løren tunnel. Particular emphasis is placed on discussing grout consumption and the challenges that were encountered when passing under a distinct rock depression. Measurement while drilling (MWD) technology was used for this project, and, in this paper, the relationships between the drill parameter interpretation (DPI) factors water and fracturing are examined in relation to grout volumes. A lowering of the groundwater table was experienced during excavation under the rock depression, but the groundwater was nearly re-established after completion of the main construction work. A planned 80-m watertight concrete lining was not required to be built due to the excellent results from grouting in the rock depression area. A relationship was found between leakages mapped in the tunnel and the DPI water factor, indicating that water is actually present where the DPI water factor shows water in the rock. It is concluded that, for the Løren tunnel, careful planning and high-quality execution of the rock mass grouting made the measured water ingress meet the restrictions. For future projects, the DPI water factor may be used to give a better understanding of the material in which the rock mass grouting is performed and may also be used to reduce the time spent and volumes used when grouting.  相似文献   

Possible Concepts for Waterproofing of Norwegian TBM Railway Tunnels   总被引：1，自引：0，他引：1  

Øyvind Dammyr  Bjørn Nilsen  Kurosch Thuro  Jørn Grøndal 《Rock Mechanics and Rock Engineering》2014,47(3):985-1002

The aim of this paper is to evaluate and compare the durability, life expectancy and maintenance needs of traditional Norwegian waterproofing concepts to the generally more rigid waterproofing concepts seen in other European countries. The focus will be on solutions for future Norwegian tunnel boring machine railway tunnels. Experiences from operation of newer and older tunnels with different waterproofing concepts have been gathered and analyzed. In the light of functional requirements for Norwegian rail tunnels, some preliminary conclusions about suitable concepts are drawn. Norwegian concepts such as polyethylene panels and lightweight concrete segments with membrane are ruled out. European concepts involving double shell draining systems (inner shell of cast concrete with membrane) and single shell undrained systems (waterproof concrete segments) are generally evaluated as favorable. Sprayable membranes and waterproof/insulating shotcrete are welcomed innovations, but more research is needed to verify their reliability and cost effectiveness compared to the typical European concepts. Increasing traffic and reliance on public transport systems in Norway result in high demand for durable and cost effective solutions.  相似文献