Assessment and formulation of data assimilation techniques for a 3D Richards equation-based hydrological model

The main objectives of de DAUFIN project are: to develop a unifying modeling framework applicable at the catchment scale and based on rigorous conservation equations for the study of hydrological processes in the stream channel, land surface, soil, and groundwater components of a river basin; to implement data assimilation methodologies within this modeling framework and for other control models to enable the optimal use of remote sensing, ground-based, and simulation data; to test and apply the models and the data assimilation methods at various catchment scales, including hillslopes and subcatchment of the Ourthe water shed in Belgium and the entire Meuse river basin, one of the major basins in Europe with a drainage area of 33000 km² that comprises the Ourthe

comparison of hydrodynamic loading models for vertical cylinders in nonlinear waves

Abstract This paper introduces a comparison study between various hydrodynamic loading models in highly nonlinear waves and discusses its first phase - comparing Morison equation and Rainey corrections on a fixed cylinder in regular steep waves. In this study both of these two models showed similar results when compared against experimental data. Morison equation is found to capture the amplitude of the loading sufficiently well. However, neither model was able to capture higher-order loading components which are apparent in very steep waves and are associated with ringing. The main conclusion of this work is the identification of the need of a more appropriate loading model

Comparison of nonlinear wave-loading models on rigid cylinders in regular waves

© 2019 by the authors. Monopiles able to support very large offshore wind turbines are slender structures susceptible to nonlinear resonant phenomena. With the aim to better understand and model the wave-loading on these structures in very steep waves where ringing occurs and the numerical wave-loading models tend to lose validity, this study investigates the distinct influences of nonlinearities in the wave kinematics and in the hydrodynamic loading models. Six wave kinematics from linear to fully nonlinear are modelled in combination with four hydrodynamic loading models from three theories, assessing the effects of both types of nonlinearities and the wave conditions where each type has stronger influence. The main findings include that the nonlinearities in the wave kinematics have stronger influence in the intermediate water depth, while the choice of the hydrodynamic loading model has larger influence in deep water. Moreover, finite-depth FNV theory captures the loading in the widest range of wave and cylinder conditions. The areas of worst prediction by the numerical models were found to be the largest steepness and wave numbers for second harmonic, as well as the vicinity of the wave-breaking limit, especially for the third harmonic. The main cause is the non-monotonic growth of the experimental loading with increasing steepness due to flow separation, which leads to increasing numerical overpredictions since the numerical wave-loading models increase monotonically

Lectures on Solid Mechanics

This volume presents the theoretical basics of solid mechanics collecting the lectures held by the Authors for the course of Mechanics of Solids to environmental engineering students at the University of Florence. Lectures on Solid Mechanics is organized in two parts. The first one introduces the theory of three-dimensional elasticity where, after a preparatory synthesis of the basic concepts of mathematics and geometry, the fundamental framework of strain and stress in elastic bodies are introduced. Then the classical law of linear elasticity is presented and finally the part concludes with the "Principle of Virtual Work and variational methods". Moreover, at the end of selected chapters the essential notions of the theory of shells are discussed. The second part concerns the traditional theory of beams focusing on the four fundamental cases: beam under axial forces, terminal couples, torsion, bending and shear. The Readers addressed by this volume are mainly the undergraduate students of Engineering Schools

On the Stability of Gated Graph Neural Networks

In this paper, we aim to find the conditions for input-state stability (ISS) and incremental input-state stability ($\delta$ISS) of Gated Graph Neural Networks (GGNNs). We show that this recurrent version of Graph Neural Networks (GNNs) can be expressed as a dynamical distributed system and, as a consequence, can be analysed using model-based techniques to assess its stability and robustness properties. Then, the stability criteria found can be exploited as constraints during the training process to enforce the internal stability of the neural network. Two distributed control examples, flocking and multi-robot motion control, show that using these conditions increases the performance and robustness of the gated GNNs

Implementazione del modello SWAT per uno studio metodologico sull'utilizzo dei dati di un modello meteorologico a scala regionale in un modello idrologico a scala di bacino

In questo lavoro si è cercato di accostare due campi di ricerca tradizionalmente separati: la meteorologia, che verrà introdotta nella prima parte, e l’idrologia, di cui si parlerà nella seconda. Entrambe hanno come scopo la previsione di eventi naturali, quali, per esempio, gli uragani e le alluvioni per la meteorologia e le onde di piena, per l’idrologia. In questo lavoro utilizzeremo una gerarchia di applicazioni: limited area model (LAM), per quanto riguarda la meteorologia, geographic information systems (GIS), per la gestione della topografia e l’utilizzo del suolo ed il modello Soil and Water Assesment Tool (SWAT), per l’idrologia, mediante le quali, a partire dalla scala globale, saremo in grado di simulare un vento di precipitazione intensa e a simulare i suoi effetti in termini di deflusso al suolo. Il caso di studio è relativo ad un evento di precipitazione particolarmente intenso verificatosi nel novembre del 1999 in Sardegna. Le numerose problematiche legate all’integrazione dei tre strumenti applicativi e dei risultati provenienti da ognuno di essi (si pensi al downscaling dei campi di precipitazione per passare dalla scala regionale a quella di bacino) non verranno affrontate perché non sono lo scopo di questo lavoro. Si sono effettuate una serie di simulazioni idrologiche usando l’interfaccia GIS di SWAT2000 partendo dai dati di precipitazione generati dal modello atmosferico sulla Sardegna e effettuando un confronto con i risultati ottenuti mediante dati di precipitazione misurati al suolo e dati costruiti teoricamente

Trade credit in Europe: Financial constraint and substitution effect in crisis times

This paper aims to prove whether financial rationing condition leads European enterprises to increase trade debt during the period 2008–2016 and whether companies offering deferred payments to customers obtain trade debt from suppliers. The work contributes to the existing literature by finding new empirical evidence on the substitution and matching hypotheses in times of crises, measuring the specific rationing conditions for businesses and distinguishing large, medium, small and micro-sized companies. The results revealed that, in times of crisis, medium, small and micro firms, highly likely to be constrained, employ trade credit more extensively, as those granting deferred payment terms.publishedVersio

coupling effects on the dynamic response of moored floating platforms for offshore wind energy plants

Abstract The increasing importance of offshore deep-water wind energy together with the complexity of the wind-wave-structure interaction problem makes the dynamic analysis of floating platforms a case of considerable interest. In this work, the dynamics of moored floating platforms for deep-water wind energy purposes is analysed in regular waves in order to discuss the effects on the motion due to the coupling of different degrees of freedom, usually associated with the operation of the mooring system and the hydrodynamic action, and the role of the main parameters affecting the motion. The platform is modelled as a rigid body and the associated differential dynamic problem is solved by using a suitable Lie group time integrator. The loads associated with mooring lines and waves are respectively assessed through a quasi-static model and a linear hydrodynamic model. The coupling of different degrees of freedom is usually related to loads with higher-frequency components and non-zero mean value that could bring the system into a mean dynamic configuration rather different from the static equilibrium configuration. Moreover, very interesting to limit the oscillations of the body is the effect of the location of the center of mass, the lower the center the lower the amplitude of pitch and roll response

Calcolo del bilancio idrico della regione Sardegna con il modello idrologico SWAT

Una diminuzione del 20% delle precipitazioni nell’ultimo trentennio e perdite del 40% nella rete di distribuzione hanno causato un sensibile abbassamento dei livelli idrici medi nei laghi e negli invasi artificiali della Sardegna, con la conseguenza che negli ultimi anni le municipalità, il comparto agricolo e quello industriale hanno subito le impopolari misure di razionamento. Fino ad oggi, gli enti regionali preposti alla gestione delle acque si sono serviti di modelli a scatola chiusa di tipo black box. Tuttavia da un lato appare incerta l’applicabilità di tali modelli in aree prive di misure e dall’altro tale approccio si dimostra carente nel tenere in conto le trasformazione di uso del territorio e le variazioni climatiche. Questo studio presenta l’applicazione del modello idrologico distribuito e fisicamente basato SWAT per la stima del bilancio idrologico della regione Sardegna. La procedura di caratterizzazione del tipo e della copertura del suolo ha seguito un approccio regionale, utilizzando e valorizzando al massimo le frammentarie informazioni disponibili. Per compensare la mancanza di dati di pioggia a passo giornaliero, necessari al modello idrologico, è stato sviluppato un generatore di tempo basato sull’analisi statistica di dati climatici registrati. In base alla distribuzione spaziale delle grandezze statistiche, le stazioni pluviometriche sono state raggruppate in due gruppi. Lo studio ha prodotto una serie di archivi informatici a scala regionale, creati secondo i formati di input del modello SWAT. L’applicazione del modello ai bacini idrologici della Sardegna ha tenuto conto della qualità dell’informazione descrittiva del territorio come, ad esempio, la risoluzione spaziale delle carte di base, la densità delle reti climatiche e la qualità del dato di pioggia, al fine di garantire la massima verosimiglianza del modello concettuale con le singole realtà in studio. Il sistema informatico è stato progettato ed implementato per supportare studi ed analisi mirati alla pianificazione della gestione della risorsa idrica regionale, all’individuazione di aree soggette a stress idrico e allo studio di fenomeni legati al ciclo dell’acqua, quali il ciclo dei sedimenti e dei nutrienti.A 20% rainfall decrease in the last 30 years, prolonged periods of drought and 40% losses in the distribution pipes have substantially lowered available water reserves in Sardinia, with the result of unpopular rationing measures on municipal, industrial and agricultural uses. Up to now black-box models have been the most commonly used methodologies to estimate the regional water budget. Despite their wide use, these models have shown severe limitations in estimating watershed outlet outputs far from the monitoring stations and in covering climate changes properly. In this study, we present the application of the hydrological distributed SWAT model to evaluate the water budget at the regional scale. The model parameterizations with regards to the land cover and soil type are estimated at the regional scale on the basis of available geographic data. In order to generate weather daily inputs for the SWAT model a weather generator has been developed on the basis of a statistical analysis of the Sardinian climatic data. Through a clusterization procedure the climatic gages have been grouped into two homogeneous groups. The regional databases have been formatted in the SWAT fashion. The resulting model input data along with the watershed and HRU spatial discretization criteria have been carefully checked to ensure global consistency at the overall scale. The informatics system has been developed and designed to support decision related to the management of the water resources, to identify areas under water stress, or to evaluate complementary phenomena related to the water cycle as the sediment and the nutrient fate at the catchment’s scale.29-38Pubblicat