Search results for " numerical models."

Electromechanical Numerical Analysis of an Air-Core Pulsed Alternator via Equivalent Network Formulation

2017

In this paper, the numerical analysis on an air-core pulsed alternator is presented. Since compulsators are characterized by very fast electromechanical transients, their accurate analysis requires strong coupling between the equations governing the electrical and the mechanical behaviors. The device is investigated by using a dedicated numerical code capable to take into account eddy currents, compensating windings, as well as the excitation/control circuits. Furthermore, the code is capable of modeling centrifugal forces and vibrations acting on the shaft due to electric and mechanical unbalances or to misalignments of the shaft from its centered position. This makes the code a very power…

Numerical-Analytical Model for Nanotube-Reinforced Nanocomposites

2013

A novel numerical model able to predict the elastic properties of carbon nanotube/polymer composites containing a random distribution of CNTs has been developed. The new technique, which takes into account of the curvature that the nanotubes show when immersed in the polymer, is based on a numerical-analytical approach that has significant advances over micromechanical modeling and can be applied to several kinds of nanostructured composites. The nature of carbon nanotube/polymer bonding has arisen as key factor in the efficacy of the carbon nanotubes to actually provide any enhanced stiffness or strength to the composite. Here the effects of carbon nanotube interface interaction with the m…

ECOHYDROLOGICAL MODELLING IN MEDITERRANEAN AREAS AND WETLANDS

2010

La seguente dissertazione verte sul campo di ricerca noto come Ecoidrologia. Sebbene tale scienza, che studia le mutue interazioni fra ciclo idrologico e gli ecosistemi naturali, sia stata recentemente oggetto di svariati studi, alcuni dei suoi numerosi aspetti rimangono tuttavia ancora alquanto inesplorati. L’obiettivo principale della presente tesi è quello di rivisitare la letteratura scientifica esistente sull’argomento, cercando di adattare concetti e modelli sviluppati per certi ecosistemi anche alle peculiarità di altri ambienti meno studiati, come quelli aridi e semiaridi tipici della zona Mediterranea o le cosiddette “wetlands”, zone umide e paludose. In particolare, viene approfon…

Diffusive Modeling of Aggradation and Degradation in Artificial Channels

2008

The unsteady flow and solid transport simulation problem in artificial channels is solved using a three-equation model, coupled with a local erosion law. The three equations are the water mass and momentum balance equations, as well as the total solid load balance equation. It is shown that even during severe hydrological events inertial terms can be neglected in the momentum equation without any substantial change in the solution sought. Empirical equilibrium formulas were used to estimate the solid load as a function of the flow variables. Local erosion, due to the scour generated at the jump between two channels connected at different bottom elevations, was estimated adapting a literatur…

Kinetics of Ordered Phases in Finite Spin Systems

1989

We study the growth of the ordered phase in a spin system of finite size suddenly brought below the transition temperature. Such a growth is driven by the instability of the mode corresponding to the largest eigenvalue of the interaction matrix. The relaxation occurs through different regimes according to whether the unstable mode has a negligible or macroscopic amplitude. One regime is characterised by dynamical scaling properties whereas in the other we can distinguish the growth to a macroscopic amplitude followed by rare transitions from one equilibrium amplitude to another. The analysis is carried out in the framework of a dynamical generalisation of the spherical model assuming non-ra…

Calculation of the Electromechanical Properties of CNTs Under Deformation by Means of a Novel Numerical Model

The effects of mechanical deformation on the electron transport behavior of carbon nanotubes (CNTs) are of primary interest due to the enormous potential of nanotubes in making electronic devices and nanoelectromechanical systems (NEMS). Moreover it could help to evaluate the presence of defects or to assess the type of CNTs that were produced. Conventional atomistic simulations have a high computational expense that limits the size of the CNTs that can be studied with this technique. Here we present a novel numerical approach able to simulate the electromechanical behavior of SWNTs and MWNTs of the dimensions used in nano-electronic devices. The numerical model was designed to realize orde…

MAST solution of irrotational flow problems in 2D domains with strongly unstructured triangular meshes

2010

A new methodology for the solution of irrotational 2D flow problems in domains with strongly unstructured meshes is presented. A fractional time step procedure is applied to the original governing equations, solving consecutively a convective prediction system and a diffusive corrective system. The non linear components of the problem are concentrated in the prediction step, while the correction step leads to the solution of a linear system, of the order of the number of computational cells. A MArching in Space and Time (MAST) approach is applied for the solution of the convective prediction step. The major advantages of the model, as well as its ability to maintain the solution monotonicit…