An experimental study of rip channel flow   总被引：2，自引：0，他引：2  

Nils Drnen  Harshinie Karunarathna  Jrgen Fredse  B. Mutlu Sumer  Rolf Deigaard 《Coastal Engineering》2002,45(3-4)

A laboratory study of the flow over a bar with a single rip channel has been performed. First, the well-known pattern of a bar circulation cell with a strong offshore-directed current out through the rip channel and a weaker onshore-directed return flow over the bar is documented. Then measurements of the three-dimensional structure of the flow in the area where the rip channel, the bar and the trough meet and well inside the rip channel are presented. These measurements reveal that 3D effects play an important role, and that a depth-integrated viewpoint may not always be sufficient for predicting the flow in the near bed region. Particle-tracking experiments illustrate the near bed flow pattern over the entire area. These demonstrate how the overall trajectory pattern changes as a function of the distance of wave breaking from the bar crest: For some conditions, the rip current is fed from the trough and for other conditions it is fed directly from the bar. Both the 3D measurements and the trajectory tests show the existence of a weaker onshore-directed near-bed drift in the area where the rip current ceases. Finally, in a series of sensitivity tests, measurements of the rip current intensity for different wave climate and water level conditions reveal a strong correlation between the rip current intensity and the wave height (both normalized).  相似文献   

Comparison of stomach contents of haddock (Melanogrammus aeglefinus) from the 1981 and 1991 North Sea International Stomach Sampling Projects     

Adlerstein  Sara A.; Temming  Axel; Mergardt  Nils 《ICES Journal of Marine Science》2002,59(3):497-515

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Home range and elevated egg densities within an inshore spawning ground of coastal cod     

Espeland  Sigurd Heiberg; Gundersen  Ailin Fernlof; Olsen  Esben Moland; Knutsen  Halvor; Gjosaeter  Jakob; Stenseth  Nils C. 《ICES Journal of Marine Science》2007,64(5):920-928

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Historical population assessment of Barents Sea harp seals (Pagophilus groenlandicus)     

Skaug  Hans J.; Frimannslund  Lennart; Oien  Nils I. 《ICES Journal of Marine Science》2007,64(7):1356-1365

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Tentative Detection of Circumstellar CO2 from the AGB Star R Crateris     

N. Ryde  K. Eriksson  B. Gustafsson  M. Lindqvist  H. Olofsson 《Astrophysics and Space Science》1997,255(1-2):301-302

We report on and discuss the detection of an emission feature at 14.98 μm from the oxygen-rich, semi-regularly pulsating Asymptotic Giant Branch star R Crateris, a feature which we suggest to be due to the ₀ ¹ Q-branch of circumstellar CO2. We also suggest a reasonable excitation mechanism, which could explain the height, the width and the asymmetry of the feature. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Fluid–Rock Interactions in Geothermal Reservoirs,Germany: Thermal Autoclave Experiments Using Sandstones and Natural Hydrothermal Brines     

Schäffer  Rafael  Götz  Emilia  Schlatter  Nils  Schubert  Gabriela  Weinert  Sebastian  Schmidt  Stefanie  Kolb  Ute  Sass  Ingo 《Aquatic Geochemistry》2022,28(2):63-110

As renewable energy, geothermal can contribute substantially to the energy transition. To generate electricity or to harvest heat, high-saline fluids are tapped by wells of a few kilometres and extracted from hydrothermal reservoirs. After the heat exchanger units have been passed by, these fluids are reinjected into the reservoir. Due to the pressure and temperature differences between the subsurface and the surface, as well as the cooling of the fluids in the power plant, unwanted chemical reactions can occur within the reservoir, in the borehole, and within the power plant itself. This can reduce the permeability of the reservoir as well as the output of the geothermal power plant. This study aims to simulate real subsurface reactions using batch and leaching experiments with sandstone or sandstone powder as solid phase, and deionised water or natural brine as liquid phase. It is demonstrated that fluid composition changes after only a few days. In particular, calcite, aragonite, clay minerals, and zinc phases precipitate from the natural brine. In contrast, in particular minerals containing potassium, arsenic, barium, and silica are dissolved. Due to the experimental set-up, these mineral reactions mainly took place on the surface of the samples, which is why no substantial changes in petrophysical properties could be observed. However, it is assumed that the observed reactions on the reservoir scale have a relevant influence on parameters such as permeability.

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Phase-scanning approach to correct time-shift inaccuracies in the surface-wave walk-away method   总被引：1，自引：0，他引：1  

Edwin A. Obando  Choon B. Park  Nils Ryden  Peter Ulriksen 《Soil Dynamics and Earthquake Engineering》2010

In order to maintain lateral resolution while maximizing investigation depth in a multichannel surface wave method, it is beneficial to implement the walk-away approach by using a relatively short receiver spread. Combined walk-away records, however, normally suffer from time-shift inaccuracies that adversely influence the subsequent dispersion imaging process. Time-shift inaccuracies produce phase discontinuities which can generate false apparent higher modes in the dispersion images misleading the correct interpretation of the dispersion curve. To minimize these adverse effects, we present a phase-scanning approach that searches for an optimum phase shift to correct the phase shift generated by the walk-away method. Results obtained from synthetic and real-world field data show that for the specific case of a single dominating mode the proposed approach reduces the distortions in the dispersion image caused by the walk-away approach. The proposed method is especially efficient in the presence of ambient random noise.  相似文献   

Black hole dynamics: A survey of black hole physics from the point of view of perturbation theory     

Nils Andersson 《Journal of Astrophysics and Astronomy》1999,20(3-4):269-280

This article is a brief survey of the contribution of perturbative studies to our understanding of black hole physics. For natural reasons, I will not be able to discuss all details required for an exhaustive understanding of a field that has been active for the last forty years. Neither will — I be able to cover all problem areas where perturbation theory has been applied. My aim is simply to provide the interested reader with a few pointers that can serve as useful starting points for an odyssey through the literature.  相似文献   

Seasonal,tidal, and geomorphic controls on sediment export to Amazon River tidal floodplains     

Daniel J. Nowacki  Andrea S. Ogston  Charles A. Nittrouer  Aaron T. Fricke  Nils E. Asp  Pedro Walfir M. Souza Filho 《地球表面变化过程与地形》2019,44(9):1846-1859

Mainstem–floodplain material exchange in the tidal freshwater reach of major rivers may lead to significant sequestration of riverine sediment, but this zone remains understudied compared to adjacent fluvial and marine environments. This knowledge gap prompts investigation of floodplain-incising tidal channels found along the banks of tidal rivers and their role in facilitating water and suspended-sediment fluxes between mainstem and floodplain. To evaluate this role, and how it evolves along the tidal river and with time, we measured water level, flow velocity, temperature, and suspended-sediment concentration (SSC) in four tidal channels along the tidal Amazon River, Brazil. Eleven deployments were made during low, rising, high, and falling seasonal Amazon discharge. Generally, channels export high-SSC water from the mainstem to the tidal floodplain on flood tides and transfer low-SSC water back to the mainstem on ebbs. Along the length of the tidal river, the interaction between tidal and seasonal water-level variations and channel–floodplain morphology is a primary control on tidal-channel sediment dynamics. Close to the river mouth, where tides are large, this interaction produces transient flow features and current-induced sediment resuspension, but the importance of these processes decreases with distance upstream. Although the magnitude of the exchange of water and sediment between mainstem and floodplain via tidal channels is a small percentage of the total mainstem discharge in this large tidal-river system, tidal channels are important conduits for material flux between these two environments. This flux is critical to resisting floodplain submergence during times of rising sea level. © 2019 John Wiley & Sons, Ltd.  相似文献   

A Triggered Depth‐Dependent Sampling System to Overcome the Carry‐Over Effects of the Membrane Interface Probe          下载免费PDF全文

Jan Bumberger  Kilian Peisker  Nils Reiche  Dirk Radny  Peter Dietrich 《Ground Water Monitoring & Remediation》2016,36(3):54-61

The membrane interface probe (MIP) is widely used for the in situ characterization of volatile organic compounds (VOCs) in the subsurface. A main problem using the MIP system is the carry‐over effect of VOCs during the transport from the point of measurement to the detector using a conventional transfer line. This effect results in compound specific retention times, which is shown in disproportionately high measuring signals after the actual penetration of contaminated zones. In consequence, the lower extent of contamination is not clearly identifiable and may be overestimated. The presented field study presents an evaluation of different methods to overcome the carry‐over effect, especially with regard to the required measurement times that are needed to wait for a complete disappearance of the detector signals before forwarding the probe. This was accomplished by comparing data collected with a MIP system with (1) unheated transfer line and (2) a system including a heated transfer line to data collected with a system using (3) a depth‐dependent triggered sampling behind the membrane including two transfer lines. A comparison with analytical results from soil samples gave a good correlation for all three methods. Furthermore, it could be shown that the use of a heated transfer line has a time improvement of 30% compared to an unheated transfer line while the depth dependent triggered sampling using two separate transfer lines yielded a time improvement of over 90%. These results confirm the benefit of the latter method, particularly for the use in highly contaminated sediments.  相似文献