Search results for "modeling"
showing 10 items of 4489 documents
Capturing shock waves in inelastic granular gases
2005
Shock waves in granular gases generated by hitting an obstacle at rest are treated by means of a shock capturing scheme that approximates the Euler equations of granular gas dynamics with an equation of state (EOS), introduced by Goldshtein and Shapiro [J. Fluid Mech. 282 (1995) 75-114], that takes into account the inelastic collisions of granules. We include a sink term in the energy balance to account for dissipation of the granular motion by collisional inelasticity, proposed by Haff [J. Fluid Mech. 134 (1983) 401-430], and the gravity field added as source terms. We have computed the approximate solution to a one-dimensional granular gas falling on a plate under the acceleration of grav…
A flux-split algorithm applied to conservative models for multicomponent compressible flows
2003
In this paper we consider a conservative extension of the Euler equations for gas dynamics to describe a two-component compressible flow in Cartesian coordinates. It is well known that classical shock-capturing schemes applied to conservative models are oscillatory near the interface between the two gases. Several authors have addressed this problem proposing either a primitive consistent algorithm [J. Comput. Phys. 112 (1994) 31] or Lagrangian ingredients (Ghost Fluid Method by Fedkiw et al. [J. Comput. Phys. 152 (1999) 452] and [J. Comput. Phys. 169 (2001) 594]). We solve directly this conservative model by a flux-split algorithm, due to the first author (see [J. Comput. Phys. 125 (1996) …
Present-day use of an empirical wave prediction method
2016
Knowledge of the offshore wave climate is key to the design of coastal engineering structures and to the study of shoreline evolution. To date, the available wave data have been limited both in time and space; even though there are several options for obtaining wave data calculated using complex numerical models at basin scale, design issues can in some cases be solved by means of simpler models. This paper shows whether, under certain conditions and in an enclosed basin, an old empirical model can provide results that are good enough to determine the design condition necessary for engineering purposes. The empirical model chosen to answer this question is called Sverdrup–Munk–Bretschneide…
A Shoreline model for breaking waves
2011
In order to simulate the wave motion and, in turn, the flow, within the nearshore region, in the last decades the derivation and the application of depth-integrated type of models have been widely investigated and developed. However, in such models, the problems of facing wave breaking and the moving shoreline are not trivial and therefore several approaches have been proposed. About wave breaking, approaches both based on the adoption of an artificial eddy viscosity Zelt (1991) and on the concept of roller Veeramony (2000), Karambas (2003), Musumeci (2005) have been implemented. As regards the shoreline boundary condition, a couple of numerical techniques have been mainly adopted, namely t…
On the hidden significance of differing micro-sites on tree-ring based climate reconstructions
2015
Tree-ring chronologies are commonly extended back in time by combining samples from living trees with relict material preserved in man-made structures or natural archives (e.g. lakes). Although spatially close, these natural archives and living-tree-sites often comprise different micro-climates. Inhomogeneous growth conditions among these habitats, which may yield offsets in growth-rates, require caution in data processing. Here we assess species-specific growth dynamics in two micro-habitats and their potential effects on long chronologies by combining tree-ring data from different living-tree-sites with an âartificialâ subfossil dataset. Well replicated (nâ>â80) Norway spruce (…
Field run-up measurements: Calibration of a physically based lagrangian shoreline model
2012
In the present contribution a measurement technique based on video imaging has been selected for the assessment of the maximum run-up. Such measurements have been used for the calibration of a numerical model and of an empirical formulation. The on-site run-up measurements have been carried out at “Lido Signorino” beach, near Marsala, Italy. The positions of the swash have been localized on a transect, normal to the shore, constituted by stakes placed at 0.5 m intervals each other. The video camera was placed orthogonally to the line of the stakes. For the numerical simulations a 1DH Boussinesq-type of model for breaking waves has been applied which takes into account the wave run-up by a L…
A New Model for Sigma-Delta Modulator Oriented to Digitally Controlled DC/DC Converter
2007
Recent research activities have shown the feasibility and advantages of using digital controller ICs specifically developed for high-frequency switching converters, highlighting a challenging future trend in Switched-mode power supplies (SMPS) applications. Up to a few years ago, the application of digital control for SMPS was impractical due to the high cost and low performance of DSP and microcontroller systems, even if the advantages that digital controllers offer were well known, such as immunity to analog component variations and ability to implement sophisticated control schemes and system diagnostics. Digital controller ICs potentially offer other advantages from the integrated desig…
Dynamic Regret Analysis for Online Tracking of Time-varying Structural Equation Model Topologies
2020
Identifying dependencies among variables in a complex system is an important problem in network science. Structural equation models (SEM) have been used widely in many fields for topology inference, because they are tractable and incorporate exogenous influences in the model. Topology identification based on static SEM is useful in stationary environments; however, in many applications a time-varying underlying topology is sought. This paper presents an online algorithm to track sparse time-varying topologies in dynamic environments and most importantly, performs a detailed analysis on the performance guarantees. The tracking capability is characterized in terms of a bound on the dynamic re…
Active Learning Methods for Efficient Hybrid Biophysical Variable Retrieval
2016
Kernel-based machine learning regression algorithms (MLRAs) are potentially powerful methods for being implemented into operational biophysical variable retrieval schemes. However, they face difficulties in coping with large training data sets. With the increasing amount of optical remote sensing data made available for analysis and the possibility of using a large amount of simulated data from radiative transfer models (RTMs) to train kernel MLRAs, efficient data reduction techniques will need to be implemented. Active learning (AL) methods enable to select the most informative samples in a data set. This letter introduces six AL methods for achieving optimized biophysical variable estimat…
Toward a Collective Agenda on AI for Earth Science Data Analysis
2021
In the last years we have witnessed the fields of geosciences and remote sensing and artificial intelligence to become closer. Thanks to both the massive availability of observational data, improved simulations, and algorithmic advances, these disciplines have found common objectives and challenges to advance the modeling and understanding of the Earth system. Despite such great opportunities, we also observed a worrying tendency to remain in disciplinary comfort zones applying recent advances from artificial intelligence on well resolved remote sensing problems. Here we take a position on research directions where we think the interface between these fields will have the most impact and be…