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Mas de les Valls E.,University of Barcelona | Batet L.,University of Barcelona | de Medina V.,University of Barcelona | de Medina V.,Sediment Transport Research Group GITS | Sedano L.A.,CIEMAT
Magnetohydrodynamics | Year: 2012

Lead lithium flowing inside breeding blanket's channels in a fusion reactor is subject to a Hartmann number of ~10 4 and a Grashof number ~10 9- 10 12. Since under such conditions buoyancy can be of the same order of magnitude as the electromagnetic force, a deep understanding of the coupled phenomena is required. In the present study, a horizontal channel with dimensions, mean velocity and thermal load taken from HCLL blanket design and considering a Hartmann number of 3000 is analysed using different thermal strategies. The unstable nature of the resulting flow is studied as well as its influence on relevant thermal parameters. Source

Mujal-Colilles A.,Sediment Transport Research Group GITS | Mier J.M.,University of Illinois at Urbana - Champaign | Christensen K.T.,University of Illinois at Urbana - Champaign | Christensen K.T.,Kyushu University | And 2 more authors.
Experiments in Fluids | Year: 2014

Exploratory measurements of oscillatory boundary layers were conducted over a smooth and two different rough beds spanning the laminar, transitional and turbulent flow regimes using a multi-camera 2D-PIV system in a small oscillatory-flow tunnel (Admiraal et al. in J Hydraul Res 44(4):437-450, 2006). Results show how the phase lag between bed shear stress and free-stream velocity is better defined when the integral of the momentum equation is used to estimate the bed shear stress. Observed differences in bed shear stress and phase lag between bed shear stress and free-stream velocity are highly sensitive to the definition of the bed position (y = b). The underestimation of turbulent stresses close to the wall is found to explain such differences when using the addition of Reynolds and viscous stresses to define both the bed shear stress and the phase lag. Regardless of the flow regime, in all experiments, boundary-layer thickness reached its maximum value at a phase near the flow reversal at the wall. Friction factors in smooth walls are better estimated using a theoretical equation first proposed by Batchelor (An introduction to fluid dynamics. Cambridge University Press, Cambridge, 1967) while the more recent empirical predictor of Pedocchi and Garcia (J Hydraul Res 47(4):438-444, 2009a) was found to be appropriate for estimating friction coefficients in the laminar-to-turbulent transition regime. © Springer-Verlag Berlin Heidelberg 2013. Source

Ciervo F.,University of Salerno | Papa M.N.,University of Salerno | Medina V.,Sediment Transport Research Group GITS | Bateman A.,Sediment Transport Research Group GITS
Journal of Flood Risk Management | Year: 2015

The hydrological and hydraulic processes of the flash flood that affected Atrani village (Amalfi Coast of Southern Italy) on 9 September 2010 are analysed using post-flood surveys and numerical modelling. Observations in this case are particularly challenging because of the small spatial and temporal scales of the event, relative to the sampling characteristics of conventional rain and discharge measurement networks. Given these aspects, some of the relevant characteristics of the event were deduced by analysing field data that were collected immediately after the event. A width function instantaneous unit hydrograph (WFIUH) rainfall-runoff model is applied to derive a flow hydrograph for the area immediately upstream of the village. This hydrograph is inputted as an upstream boundary condition for the simulation of the propagation processes. A two-dimensional innovative hydraulic model is used to reproduce the flood within the village. The use of an unstructured mesh enabled a detailed simulation of water flow within the narrow and winding alleyways of the village. The results of the simulations indicate agreement with the field observations. The implemented approach is suitable for simulating flash floods in similar contexts and, therefore, may be used to predict potential future events. © 2015 The Chartered Institution of Water and Environmental Management (CIWEM) and John Wiley & Sons Ltd. Source

Chevalier G.G.,Sediment Transport Research Group GITS | Chevalier G.G.,Polytechnic University of Catalonia | Medina V.,Sediment Transport Research Group GITS | Hurlimann M.,Polytechnic University of Catalonia | Bateman A.,Sediment Transport Research Group GITS
Environmental Earth Sciences | Year: 2015

Geomorphometry of headwater catchments has been poorly reported in the Central-Eastern Pyrenees. This study presents a series of parameters obtained for Central-Eastern Pyrenean headwater catchments. The database consists of 3,005 first- and 655 second-order catchments. These catchments have been digitalised, identified, and attributed a value for each parameter. The parameters investigated are divided into three groups: relative to catchments, relative to streams and morpho-hydrological ratios. Histograms reveal similarities between orders for some parameters such as mean slope or orientation, while stream orders seem to condition metrical parameters (area, perimeter, stream length). Streams have been fragmented to assess different values for slope. Values for slope over a small portion of the stream near the outlet seem to show clearer differences between orders. With regard to morpho-hydrological ratios, catchments show better distinctions between orders for the Melton and Lemniscate ratios than for the form factor or the basin elongation. The power–law relationship between catchment area and stream length recognised for large fluvial systems is shown here to follow a linear trend at small values. An attempt to identify the morpho-structural regionalisation differentiating the Axial Pyrenees from the pre-Pyrenees is made based on the parameters. However, applying the methodology to other environments could improve the context of the current results. Similar studies could also benefit from the development of such databases. © 2014, Springer-Verlag Berlin Heidelberg. Source

Chevalier G.G.,Polytechnic University of Catalonia | Chevalier G.G.,Sediment Transport Research Group GITS | Medina V.,Sediment Transport Research Group GITS | Hurlimann M.,Polytechnic University of Catalonia | Bateman A.,Sediment Transport Research Group GITS
Natural Hazards | Year: 2013

Based on debris-flow inventories and using a geographical information system, the susceptibility models presented here take into account fluvio-morphologic parameters, gathered for every first-order catchment. Data mining techniques on the morphometric parameters are used, to work out and test three different models. The first model is a logistic regression analysis based on weighting the parameters. The other two are classification trees, which are rather novel susceptibility models. These techniques enable gathering the necessary data to evaluate the performance of the models tested, with and without optimization. The analysis was performed in the Catalan Pyrenees and covered an area of more than 4,000 km2. Results related to the training dataset show that the optimized models performance lie within former reported range, in terms of AUC, although closer to the lowest end (near 70 %). When the models are applied to the test set, the quality of most results decreases. However, out of the three different models, logistic regression seems to offer the best prediction, as training and test sets results are very similar, in terms of performance. Trees are better at extracting laws from a training set, but validation through a test set gives results unacceptable for a prediction at regional scale. Although omitting parameters in geology or vegetation, fluvio-morphologic models based on data mining, can be used in the framework of a regional debris-flow susceptibility assessment in areas where only a digital elevation model is available. © 2013 Springer Science+Business Media Dordrecht. Source

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