排序方式: 共有47条查询结果,搜索用时 15 毫秒
31.
Pore-to-field simulation of single-phase transport using continuous time random walks 总被引:2,自引:0,他引:2
Matthew E. Rhodes Branko Bijeljic Martin J. Blunt 《Advances in water resources》2008,31(12):1527-1539
32.
This study investigates the size, age and growth of Corallium rubrum which is a key species of the only large reef-like structure in the Mediterranean Sea, the coralligéne. Two populations were studied in the Ligurian Sea at a depth between 36 and 42 m. Basal diameter, colony height and numbers of branches of 230 colonies were measured, and age and growth rates were assessed from 25 colonies. Mean growth rate was 0.2 mm yr−1 of basal diameter growth, corresponding to a mean annual total branch length increase of 5 mm. These results point to a coral growth much slower than assumed in many earlier studies. Additionally, age and size at first reproduction were analysed. Male colonies were shown to become sexually mature at a minimum age of six years (1.2 mm of basal diameter), while female colonies reached maturity when at least 10 years old (2 mm of basal diameter). We further discuss the implications of slow growth and early sexual maturity for red coral management and conservation. 相似文献
33.
Along-Coast Features of Bora-Related Turbulence 总被引:1,自引:1,他引:0
?eljko Ve?enaj Danijel Belu?i? Vanda Grubi?i? Branko Grisogono 《Boundary-Layer Meteorology》2012,143(3):527-545
The along-coast, offshore turbulence structure of the Bora flow that occurred on 7 November 1999 during the Mesoscale Alpine Programme (MAP) Intensive Observation Period 15 is examined. In this analysis we employ the aircraft and dropsonde data obtained over the Adriatic Sea, where the turbulence structure is determined by estimating turbulent kinetic energy (TKE) and its dissipation rate along the flight legs. The turbulence characteristics of Bora in the lee of the Dinaric Alps is greatly influenced by the mesoscale Bora flow structure over the Adriatic Sea, which in the cross-wind direction features an interchange of jets and wakes related to mountain gaps and peaks. In order to establish the origin of turbulence, the Weather Research and Forecasting—Advanced Research WRF (WRF-ARW) numerical model is used and its results are compared to the measurements. All five TKE-prediction parametrization schemes available in the model show reasonable agreement with the measured values. Since these parametrization schemes do not have horizontal advection included, they suggest that the along-flight structure of the Bora turbulence is principally generated by the local vertical wind shear. Further evidence is needed to support this hypothesis. 相似文献
34.
Computations of Absolute Permeability on Micro-CT Images 总被引:2,自引:1,他引:1
We apply an accurate numerical scheme to solve for Stokes flow directly on binarized three-dimensional rock images, such as those obtained by micro-CT imaging. The method imposes no-flow conditions exactly at the solid boundaries and employs an algebraic multigrid method to solve for the resultant set of linear equations. We compute the permeability of a range of consolidated and unconsolidated porous rocks; the results are comparable with those obtained using the lattice Boltzmann method and agree with experimental measurements on larger core samples. We show that the Kozeny–Carman equation can over-estimate permeability by a factor of 10 or more, particularly for the more heterogeneous systems studied. We study the existence and size of the representative elementary volume (REV) at lamina scale. We demonstrate that the REV for permeability is larger than for static properties—porosity and specific surface area—since it needs to account for the tortuosity and connectedness of the flow paths. For the carbonate samples, the REV appeared to be larger than the image size. We also study the anisotropy of permeability at the pore scale. We show that the permeability of sandpacks varies by less than 10 % in different directions. For sandstones, permeability changes by 25 % on average. However, the anisotropy of permeability in carbonates can be up to 50 %, indicating the existence of connected pores in one direction which are not connected in another. 相似文献
35.
Branko KaučIč Borut Žalik 《International journal of geographical information science》2013,27(7):709-718
Site visibility analysis is an important research topic with many applications in Geographical Information Systems. This paper introduces a new paradigm in terrain guarding, called k-guarding. K-guarding is a generalization of the classic guarding problem where, instead of only one guard, each surface patch is guarded by at least k guards. Afterwards, two optimization problems based on k-guarding are defined: an optimum k-guarding, and a constrained k-guarding. There are three heuristic approaches—k-greedy add, k-stingy drop, and k-reverse greedy—that are proposed as a solution to the above-mentioned optimization problems. The first two are known approaches adapted to k-guarding, while k-reverse greedy is a new, original heuristic. The heuristics are compared using actual topographic surfaces. It is shown that our approach (k-reverse greedy) gives on average the best near optimum solutions. The most surprising finding of the experiments is that the combination of heuristics introduced here yields even better results. 相似文献
36.
Raj K. Rai Larry K. Berg Branko Kosović Jeffrey D. Mirocha Mikhail S. Pekour William J. Shaw 《Boundary-Layer Meteorology》2017,163(1):69-89
The Weather Research and Forecasting (WRF) model can be used to simulate atmospheric processes ranging from quasi-global to tens of m in scale. Here we employ large-eddy simulation (LES) using the WRF model, with the LES-domain nested within a mesoscale WRF model domain with grid spacing decreasing from 12.15 km (mesoscale) to 0.03 km (LES). We simulate real-world conditions in the convective planetary boundary layer over an area of complex terrain. The WRF-LES model results are evaluated against observations collected during the US Department of Energy-supported Columbia Basin Wind Energy Study. Comparison of the first- and second-order moments, turbulence spectrum, and probability density function of wind speed shows good agreement between the simulations and observations. One key result is to demonstrate that a systematic methodology needs to be applied to select the grid spacing and refinement ratio used between domains, to avoid having a grid resolution that falls in the grey zone and to minimize artefacts in the WRF-LES model solutions. Furthermore, the WRF-LES model variables show large variability in space and time caused by the complex topography in the LES domain. Analyses of WRF-LES model results show that the flow structures, such as roll vortices and convective cells, vary depending on both the location and time of day as well as the distance from the inflow boundaries. 相似文献
37.
Organic Matter Derived from a Seagrass Meadow: Origin, Properties, and Quality of Particles 总被引:1,自引:0,他引:1
Abstract. An investigation of the properties of particles found in wrack beds and suspended in the water body of a Posidonia oceanica system led to the following conclusion: except for the period of the leaf fall and at times of strong water movement (e. g. winter storms), the majority of the particles in the water show no similarity with seagrass particles. This is based on the comparison of C: N ratios and SEM inspection. Information on the magnitude of DOC fluxes in this system led to the formulation of the phase shift hypothesis from DOM to POM. Because wrack particles were shown to have relatively fast settling rates, it is expected that processes like adsorption onto inorganic particles, micellation and aggregate formation have more importance in regulating particle density in the water body than the resuspension of directly fractionated Posidonia debris. The implication of these findings are discussed and the importance of the Mediterranean seagrass P. oceanica as an energy source supporting secondary production in adjacent ecosystems is questioned. 相似文献
38.
Branko Grisogono 《Boundary-Layer Meteorology》1990,52(3):221-225
A simple equation of diffusion is derived from the longwave radiative flux transfer equation for the atmospheric stable nocturnal boundary layer. This simplification is valid with clear-sky conditions, light wind speeds and near the top of the inversion layer which has already been established.The known physical behavior of such a layer in the given conditions (the weak and slow destabilization, and spreading of the top of the inversion layer) is explained by this simple equation of mathematical physics instead of a complicated expression written in terms of the net longwave radiative flux divergence. 相似文献
39.
Sergej Zilitinkevich Hannu Savijärvi Alexander Baklanov Branko Grisogono Kai Myrberg 《Boundary-Layer Meteorology》2006,119(3):591-593
In this short communication we highlight the NATO Advanced Research Workshop (ARW) “Atmospheric Boundary Layers: Modelling and Applications for Environmental Security”, to be held in Dubrovnik, Croatia, 18–22 April 2006 (http:// pbl-nato-arw.dmi.dk) and the “Summer School on Air-Sea Interaction” to be held in Helsinki, Finland, 28 August–1 September 2006 (http://www.scasi.fi). These two events are connected to the ongoing Ev Marie Curie Chair Project “Planetary boundary layers – Theory, modelling and role in earth systems” (PBL – TMRES, Contract MEXC-CT-2003-509742, www.atm.helsinki.fi/PBL/). 相似文献
40.
Smiljana Đukičin Vučković Jasmina Đorđević Jelena Milanković Jovanov Branko Protić Tijana Đorđević 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2018,118(1):101-113
In the last decades, the development of transport infrastructure has been necessary because of the population increase and expansion of urban centres. Infrastructure development leads to modification and changes in areas characterized by high human population density. The lack of adequate transport infrastructure inhibits local economic and social performance. In the period of economic stability (from 1970 to 1990), important roads that increased the connectedness of the Kolubara District (Western Serbia) with other parts of the country and the surrounding countries were built, but there is still a need for the construction of new roads. In order to examine the attitude of the local population in regard to transport infrastructure, a survey was conducted using a questionnaire consisting of closed questions. This topic is one that has not previously been examined. The data obtained were analyzed statistically and showed that local people have a positive attitude towards the existing infrastructure and towards the construction of new roads. There are statistically significant differences between the attitudes of the local population in different municipalities. The results from this research offer an opportunity to develop guidelines which can influence traffic development in these and similar areas. 相似文献