1,721,040 research outputs found
Tecniche di transfer learning su dati multi-fedeltà per problemi di trasporto in acque sotterranee.
No full textDominant spatiotemporal structures in total water storage anomalies
Full text linkThis study employs Dynamic Mode Decomposition (DMD) to derive a global-scale linear model for the temporal evolution of Total Water Storage Anomaly (TWSA) measured by GRACE satellite missions, with the goal of extracting and analyzing the dominant spatiotemporal structures governing TWSA variability. Our analysis differentiates modes associated with a periodic dynamic – linked to precipitation-driven seasonal cycles and multi-year variations – from those incorporating trend effects indicating, on average, a progressive TWSA decline. Focusing on the latter, we examine patterns associated with extreme TWSA values and their intensification over time. In regions experiencing significant TWSA changes over the past decade, DMD effectively distinguishes natural variability from trends, aligning with previous findings that identify climate change and human impact effects in the same regions. This study underscores DMD’s potential in capturing essential hydrological dynamics in data, thus supporting the interpretation of these dynamics at the scale of the analysis
Distribution-Based Global Sensitivity Analysis in Hydrology
No full textGlobal sensitivity analysis (GSA) is routinely used in academic setting to quantify the influence of input variability and uncertainty on predictions of a quantity of interest. Practical applications of GSA are hampered by its high computational cost, which arises from the need to run large (e.g., groundwater) models multiple times, and by its reliance on the analysis of variance, which formally requires input parameters to be uncorrelated. The former difficulty can be alleviated by replacing expensive models with inexpensive (e.g., polynomial) surrogates, while adoption of distribution‐based (rather than variance‐based) metrics can, in principle, overcome the latter but at significantly increased computational cost. To make use of distribution‐based GSA feasible for regional‐scale models with a large number of degrees of freedom, we supplement it with a surrogate model built with polynomial chaos expansions with analytically updated coefficients. We demonstrate the computational efficiency of our algorithm on a case study dealing with evaluation of the effects of temperature variability on annual evapotranspiration at the regional scale
Dynamic mode decomposition of GRACE satellite data
No full textAdvancements in satellite technology yield environmental data with ever improving spatial coverage and temporal resolution. This necessitates the development of techniques to discern actionable information from large amounts of such data. We explore the potential of dynamic mode decomposition (DMD) to discover the dynamics of spatially correlated structures present in global-scale data, specifically in observations of total
water storage anomalies provided by GRACE satellite missions. Our results demonstrate that DMD enables data compression and extrapolation from a reduced set of dominant spatiotemporal structures. The accuracy of its predictions of global system dynamics is preserved in its reconstruction of local time series. These findings suggest potential uses of DMD in analysis of remote-sensing data for hydrologic applications
Polynomial chaos enhanced by dynamic mode decomposition for order-reduction of dynamic models
Full text linkThanks to their low computational cost, reduced-order models (ROMs) are indispensable in ensemble-based simulations used, e.g., for uncertainty quantification, inverse modeling, and optimization. Since data used to train a ROM are typically obtained by running a high-fidelity model (HFM) multiple times, a ROM’s efficiency rests on the computational cost associated with the data generation and training phase. One such ROM, a polynomial chaos expansion (PCE), often provides a robust description of an HFM’s response surface in the space of model parameters. To reduce the data-generation cost, we propose to train a PCE on multi-fidelity data, part of which come from the dynamic HFM and the remainder from dynamic mode decomposition (DMD); the latter is used to interpolate the HFM data in time. Our numerical experiments demonstrate the accuracy of the proposed method and provide guidelines for the optimal use of DMD for interpolation purposes
Hyporheic Flows in Stratified Sediments: Implications on Residence Time Distributions
Full text linkThe fate of nutrients and contaminants in fluvial ecosystems is strongly affected by the mixing dynamics between surface water and groundwater within the hyporheic zone, depending on the combination of the sediment's hydraulic heterogeneity and dune morphology. This study examines the effects of hydraulic conductivity stratification on steady-state, two-dimensional, hyporheic flows and solute residence time distribution. First, we derive an integral transform-based semi-analytical solution for the flow field, capable of accounting for the effects of any functional shape of the vertically varying hydraulic conductivity. The solution considers the uneven distribution of pressure at the water-sediment interface (i.e., the pumping process) dictated by the presence of dune morphology. We then simulate solute transport using particle tracking. Our modeling framework is validated against numerical and tracer data from flume experiments and used to explore the implication of hydraulic conductivity stratification on the statistics and pdf of the residence time. Finally, reduced-order models are used to enlighten the dependence of key residence time statistics on the parameters characterizing the hydraulic conductivity stratification.A new integral transform-based semi-analytical solution for hyporheic flows in stratified sediments is provided and tested against dataThe impact of hydraulic conductivity stratification on residence time distribution and its statistics is quantitatively analyzedROMs are used to approximate key residence time statistics in the space of variability of parameters characterizing the conductivity profil
Experimental verification of theoretical approaches for radial gravity currents draining from an edge
Full text linkWe present an experimental study of inertial gravity currents (GCs) propagating in a cylindrical wedge under different drainage directions (inward/outward), lock-release (full/partial gate width) and geometry (annulus/full cylinder). We investigate the following combinations representative of operational conditions for dam-break flows: (i) inward drainage, annular reservoir, full gate; (ii) outward drainage, full reservoir, full gate; and (iii) outward drainage, full reservoir, partial gate. A single-layer shallow-water (SW) model is used for modelling the first two cases, while a box model interprets the third case; the results of these approximations are referred to as “theoretical”. We performed a first series of experiments with water as ambient fluid and brine as intruding fluid, measuring the time evolution of the volume in the reservoir and the velocity profiles in several sections; in a second series, air was the ambient and water was the intruding fluid. Careful measurements, accompanied by comparisons with the theoretical predictions, were performed for the behaviour of the interface, radial velocity and, most important, the volume decay V(t) / V(0). In general, there is good agreement: the theoretical volume decay is more rapid than the measured one, but the discrepancies are a few percent and the agreement improves as the Reynolds number increases. Velocity measurements show a trend correctly reproduced by the SW model, although often a delay is observed and an over- or under-estimation of the peak values. Some experiments were conducted to verify the role of inconsistencies between experimental set-up and model assumptions, considering, for example, the presence or absence of a top lid, wedge angle much less than 2 π, suppression of the viscous corner at the centre, reduction of disturbances in the dynamics of the ambient fluid: all these effects resulted in negligible impacts on the overall error. These experiments provide corroboration to the simple models used for capturing radial drainage flows, and also elucidate some effects (like oscillations of the radial flux) that are beyond the resolution of the models. This holds also for partial width lock-release, where axial symmetry is lost
THE USE OF HAEMOSTATIC AGENTS (QUIXIL) IN TOTAL HIP ARTHROPLASTY.Abstracts from the 10th Congress of the European Hip Society, Hip Int 2012; 22 (04 ):
No full text- …
