A laboratory-numerical approach for modelling scale effects in dry granular slides     

Matthew Kesseler  Valentin Heller  Barbara Turnbull 《Landslides》2018,15(11):2145-2159

Granular slides are omnipresent in both natural and industrial contexts. Scale effects are changes in physical behaviour of a phenomenon at different geometric scales, such as between a laboratory experiment and a corresponding larger event observed in nature. These scale effects can be significant and can render models of small size inaccurate by underpredicting key characteristics such as flow velocity or runout distance. Although scale effects are highly relevant to granular slides due to the multiplicity of length and time scales in the flow, they are currently not well understood. A laboratory setup under Froude similarity has been developed, allowing dry granular slides to be investigated at a variety of scales, with a channel width configurable between 0.25 and 1.00 m. Maximum estimated grain Reynolds numbers, which quantify whether the drag force between a particle and the surrounding air act in a turbulent or viscous manner, are found in the range 10²???10³. A discrete element method (DEM) simulation has also been developed, validated against an axisymmetric column collapse and a granular slide experiment of Hutter et al. (Acta Mech 109:127–165, 1995), before being used to model the present laboratory experiments and to examine a granular slide of significantly larger scale. This article discusses the details of this laboratory-numerical approach, with the main aim of examining scale effects related to the grain Reynolds number. Increasing dust formation with increasing scale may also exert influence on laboratory experiments. Overall, significant scale effects have been identified for characteristics such as flow velocity and runout distance in the physical experiments. While the numerical modelling shows good general agreement at the medium scale, it does not capture differences in behaviour seen at the smaller scale, highlighting the importance of physical models in capturing these scale effects.  相似文献   

Erosion feature reclamation in urban areas: typical unsuccessful examples from Brazil   总被引：1，自引：0，他引：1  

Cláudia Marisse dos Santos Rotta  Lázaro Valentin Zuquette 《Environmental Earth Sciences》2014,72(2):535-555

Erosion is responsible for environmental degradation in continental and coastal areas with varying degrees of intensity and spatial range. In continental areas, rills and gullies affect urban and non-urban areas and may occur isolated or in groups. In urban areas, many forms of degradation occur, ranging from relief modifications (with runoff and other hydrological changes) to channel and reservoir silting. Other forms of degradation include the destruction of infrastructure items, such as streets, power lines and pipelines. Many mechanical, structural, agricultural, ecological and bioengineering measures can be adopted to control and restore these areas, with various results. In many cases, the applied techniques are unsuccessful and worsen the environmental problems. To illustrate such cases in Brazil, this study examines the adoption of different techniques to restore gullies in the cities of São Pedro, Franca, São Carlos, Casa Branca and Cajuru, in the state of São Paulo. These areas are characterized by sandy geology in a variety of landscapes, and the erosion processes result from natural and anthropogenic conditions. Additionally, Brazil’s coastal area has been affected by erosion, as in Fortaleza (in the state of Ceará). This study demonstrates that the primary factor associated with erosion in coastal and continental urban areas is the lack of territorial planning that considers the geological, hydrological and geotechnical limitations. In some of the studied areas, positive results have been achieved. However, unsatisfactory results predominate primarily because appropriate geological, environmental and geotechnical studies were not performed before the interventions were selected and implemented.  相似文献   

Effects of climate change on bioclimatic indices in vineyards along Lake Neuchatel,Switzerland     

Comte  Valentin  Schneider  Léonard  Calanca  Pierluigi  Rebetez  Martine 《Theoretical and Applied Climatology》2022,147(1-2):423-436

Theoretical and Applied Climatology - In this study, we investigated the consequences of climate change on bioclimatic indices in vineyards along the edge of Lake Neuchatel in Switzerland. Like in...  相似文献   

Unstructured-mesh modeling of the Congo river-to-sea continuum     

Yoann Le Bars  Valentin Vallaeys  Éric Deleersnijder  Emmanuel Hanert  Loren Carrere  Claire Channelière 《Ocean Dynamics》2016,66(4):589-603

With the second largest outflow in the world and one of the widest hydrological basins, the Congo River is of a major importance both locally and globally. However, relatively few studies have been conducted on its hydrology, as compared to other great rivers such as the Amazon, Nile, Yangtze, or Mississippi. The goal of this study is therefore to help fill this gap and provide the first high-resolution simulation of the Congo river-estuary-coastal sea continuum. To this end, we are using a discontinuous-Galerkin finite element marine model that solves the two-dimensional depth-averaged shallow water equations on an unstructured mesh. To ensure a smooth transition from river to coastal sea, we have considered a model that encompasses both hydrological and coastal ocean processes. An important difficulty in setting up this model was to find data to parameterize and validate it, as it is a rather remote and understudied area. Therefore, an important effort in this study has been to establish a methodology to take advantage of all the data sources available including nautical charts that had to be digitalized. The model surface elevation has then been validated with respect to an altimetric database. Model results suggest the existence of gyres in the vicinity of the river mouth that have never been documented before. The effect of those gyres on the Congo River dynamics has been further investigated by simulating the transport of Lagrangian particles and computing the water age.  相似文献   

The Effect of Scale on the Applicability of Taylor’s Frozen Turbulence Hypothesis in the Atmospheric Boundary Layer     

Chad W. Higgins  Martin Froidevaux  Valentin Simeonov  Nikki Vercauteren  Caitlin Barry  Marc B. Parlange 《Boundary-Layer Meteorology》2012,143(2):379-391

Taylor’s frozen turbulence hypothesis is the central assumption invoked in most experiments designed to investigate turbulence physics with time resolving sensors. It is also frequently used in theoretical discussions when linking Lagrangian to Eulerian flow formalisms. In this work we seek to quantify the effectiveness of Taylor’s hypothesis on the field scale using water vapour as a passive tracer. A horizontally orientated Raman lidar is used to capture the humidity field in space and time above an agricultural region in Switzerland. High resolution wind speed and direction measurements are conducted simultaneously allowing for a direct test of Taylor’s hypothesis at the field scale. Through a wavelet decomposition of the lidar humidity measurements we show that the scale of turbulent motions has a strong influence on the applicability of Taylor’s hypothesis. This dependency on scale is explained through the use of dimensional analysis. We identify a ‘persistency scale’ that can be used to quantify the effectiveness of Taylor’s hypothesis, and present the accuracy of the hypothesis as a function of this non-dimensional length scale. These results are further investigated and verified through the use of large-eddy simulations.  相似文献   

Low-temperature hydrothermal alteration of intra-caldera tuffs,Miocene Tejeda caldera,Gran Canaria,Canary Islands     

Eleanor Donoghue  Valentin R. Troll  Chris Harris  Aoife O'Halloran  Thomas R. Walter  Francisco J. Pérez Torrado 《Journal of Volcanology and Geothermal Research》2008

The Miocene Tejeda caldera on Gran Canaria erupted ~ 20 rhyolite–trachyte ignimbrites (Mogán Group 14–13.3 Ma), followed by ~ 20 phonolitic lava flows and ignimbrites (Fataga Group 13–8.5 Ma). Upper-Mogán tuffs have been severely altered immediately within the caldera margin, whereas extra-caldera Mogán ignimbrites, and overlying Fataga units, are apparently unaltered. The altered intra-caldera samples contain minerals characteristic of secondary fluid–rock interaction (clays, zeolites, adularia), and relics of the primary mineral assemblage identified in unaltered ignimbrites (K-feldspar, plagioclase, pyroxene, amphibole, and groundmass quartz). Major and trace-element data indicate that Si, Na, K, Pb, Sr, and Rb, were strongly mobilized during fluid–rock interaction, whereas Ti, Zr, and Nb behaved in a more refractory manner, experiencing only minor mobilization. The δ¹⁸O values of the altered intra-caldera tuffs are significantly higher than in unaltered extra-caldera ignimbrites, consistent with an overall low-temperature alteration environment. Unaltered extra-caldera ignimbrites have δD values between − 110‰ and − 173‰, which may reflect Rayleigh-type magma degassing and/or post-depositional vapour release. The δD values of the altered intra-caldera tuffs range from − 52‰ to − 131‰, with ambient meteoric water at the alteration site estimated at ca. − 15‰. Interaction and equilibration of the intra-caldera tuffs with ambient meteoric water at low temperature can only account for whole-rock δD values of around − 45‰, given that ?D_clay–water is ca. − 30‰ at 100 °C, and decreases in magnitude at higher temperatures. All altered tuff samples have δD values that are substantially lower than − 45‰, indicating interaction with a meteoric water source with a δD value more negative than − 15‰, which may have been produced in low-temperature steam fumaroles. Supported by numerical modeling, our Gran Canaria data reflect the near-surface, epithermal part of a larger, fault-controlled hydrothermal system associated with the emplacement of the high-level Fataga magma chamber system. In this near-surface environment, fluid temperatures probably did not exceed 200–250 °C.  相似文献   

The Black Sea Ecosystem Changes Related to the Introduction of New Mollusc Species   总被引：1，自引：0，他引：1  

Valentin  Zolotarev 《Marine Ecology》1996,17(1-3):227-236

Abstract. The unintentional introduction of the new mollusc species Rupunu rhomasiuna, Mya arenaria , and Scuphurcu inaequivulvis has become a significant reason for modern transformations of certain bottom biocoenoses in the Black Sea. These molluscs have been passed across natural barriers in fouling of ships or in ship seawater ballast and have successfully acclimatized in the new region, forming communities with a high density and biomass. The resulting changes in the structure of the bottom biocoenoses after these introductions are in many cases comparable with or exceed the consequences of other episodic environmental events and other kinds of anthropogenic activity. The intense spreading of the introduced species in the new area is the result of their high adaptive capability and the instability of the Black Sea ecosystem, the latter being due to its few species, low level of competitive interactions, and constant growth of diverse anthropogenic loads.  相似文献   

Population parameters of Pleopis polyphemoides (Crustacea, Cladocera) in a tropical bay     

Andrea Marazzo  Jean Louis Valentin   《Estuarine, Coastal and Shelf Science》2003,57(5-6):1015-1021

Populations of Pleopis polyphemoides were studied in Guanabara Bay, southeastern Brazil, to assess temporal variations in density and population parameters. The abundance of P. polyphemoides varied widely during summer, and collapsed in fall–winter. These variations probably resulted from the combined effects of water temperature and predation pressure. It is assumed that the planktonic population began by hatching from resting eggs, while the collapse of the planktonic population in April seemed to be related to lower temperatures and high densities of predatory chaetognaths.  相似文献   

Reply to: Bonev N,Spikings R and Marchev P (2016) Comment on Georgiev et al. “Structure and U–Pb zircon geochronology of an Alpine nappe stack telescoped by extensional detachment faulting (Kulidzhik area,Eastern Rhodopes,Bulgaria)”     

Neven Georgiev  Nikolaus Froitzheim  Zlatka Cherneva  Dirk Frei  Valentin Grozdev  Silke Jahn-Awe  Thorsten J. Nagel 《International Journal of Earth Sciences》2016,105(7):2171-2173

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Nannofossils: the smoking gun for the Canarian hotspot          下载免费PDF全文

Valentin R. Troll  Frances M. Deegan  Steffi Burchardt  Kirsten Zaczek  Juan‐Carlos Carracedo  Fiona C. Meade  Vicente Soler  Mario Cachao  Jorge Ferreira  Abigail K. Barker 《Geology Today》2015,31(4):137-145

The origin of volcanism in the Canary Islands has been a matter of controversy for several decades. Discussions have hinged on whether the Canaries owe their origin to seafloor fractures associated with the Atlas Mountain range or to an underlying plume or hotspot of superheated mantle material. However, the debate has recently come to a conclusion following the discovery of nannofossils preserved in the products of the 2011–2012 submarine eruption at El Hierro, which tell us about the age and growth history of the western‐most island of the archipelago. Light coloured, pumice‐like ‘floating rocks’ were found on the sea surface during the first days of the eruption and have been shown to contain fragments of pre‐island sedimentary strata. These sedimentary rock fragments were picked up by ascending magma and transported to the surface during the eruption, and remarkably retained specimens of pre‐island Upper Cretaceous to Pliocene calcareous nannofossils (e.g. coccolithophores). These marine microorganisms are well known biostratigraphical markers and now provide crucial evidence that the westernmost and youngest island in the Canaries is underlain by the youngest sediment relative to the other islands in the archipelago. This finding supports an age progression for the onset of volcanism at the individual islands of the archipeligo. Importantly, as fracture‐related volcanism is known to produce non‐systematic age‐distributions within volcanic alignments, the now‐confirmed age progression corroberates to the relative motion of the African plate over an underlying mantle plume or hotspot as the cause for the present‐day Canary volcanism.  相似文献