Search results for " numerical model"

Nonlinear Structural Mechanics Based Modeling of Carbon Nanotube Deformation

2003

A nonlinear structural mechanics based approach for modeling the structure and the deformation of single-wall and multiwall carbon nanotubes (CNTs) is presented. Individual tubes are modeled using shell finite elements, where a specific pairing of elastic properties and mechanical thickness of the tube wall is identified to enable successful modeling with shell theory. The effects of van der Waals forces are simulated with special interaction elements. This new CNT modeling approach is verified by comparison with molecular dynamics simulations and high-resolution micrographs available in the literature. The mechanics of wrinkling of multiwall CNTs are studied, demonstrating the role of the …

The MAST-edge centred lumped scheme for the flow simulation in variably saturated heterogeneous porous media

2012

A novel methodology is proposed for the solution of the flow equation in a variably saturated heterogeneous porous medium. The computational domain is descretized using triangular meshes and the governing PDEs are discretized using a lumped in the edge centres numerical technique. The dependent unknown variable of the problem is the piezometric head. A fractional time step methodology is applied for the solution of the original system, solving consecutively a prediction and a correction problem. A scalar potential of the flow field exists and in the prediction step a MArching in Space and Time (MAST) formulation is applied for the sequential solution of the Ordinary Differential Equation of…

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…

The finite element implementation of 3D fractional viscoelastic constitutive models

2018

Abstract The aim of this paper is to present the implementation of 3D fractional viscoelastic constitutive theory presented in Alotta et al., 2016 [1]. Fractional viscoelastic models exactly reproduce the time dependent behaviour of real viscoelastic materials which exhibit a long “fading memory”. From an implementation point of view, this feature implies storing the stress/strain history throughout the simulations which may require a large amount of memory. We propose here a number of strategies to effectively limit the memory required. The form of the constitutive equations are summarized and the finite element implementation in a Newton-Raphson integration scheme is described in detail. …

Interaction between seismicity and deformation on different time scales in volcanic areas: Campi Flegrei and Stromboli

2019

We study oscillations recorded at Stromboli and Campi Flegrei by different sensors: seismometers, strainmeters and tiltmeters. We examine both the high-frequency (>0.5 Hz) portion of the spectrum and very long period signals up to tidal scales. In this context, seismicity and deformation are investigated on different time scales (from minutes to days/years) in order to identify the basic elements of their interaction, whose understanding should provide new insights on the predictive models. In this work, the strict relation of tides and volcanic processes is shown. At Stromboli, indeed the transition from the stationary phase to the non-stationary phase seems to have a tidal precu…

Mathematical modelling of pressure oscillations in sewer pressurization

2008

SEWER PRESSURIZATION MODELLING BY A RIGID-COLUMN METHOD

2008

Mathematical modelling of pressurization transient by a rigid-column method is studied based on previous laboratory testing. Of course, such a method is not able to simulate the experimental intense pressure oscillations; however, it is considerably simpler than other feasible methods and more easily implementable within drainage network models. Starting from this operative point of view, the paper aims at recognizing “what” and “how much” of the transient can be simulated by a rigid-column method. Actually, better results were obtained than it was expected. The model proves to be successful in simulation of the filling pipe stage as well as the stabilization stage of flow to the final stea…

Modelling steel jacketed RC columns: Remarks by experimental-numerical comparisons

2015

The recent large use of nonlinear seismic assessment techniques requires the definition of highly reliable computational models. The retrofitting or strengthening of RC columns by steel angles and battens is a commonly adopted technique, used to improve strength and deformation capacity of existing RC buildings. In the case of steel angles not directly loaded, the numerical definition of the cross-section model has to be handled carefully since it is affected by more uncertainties. The vertical load carried by the angles is a function of the lateral confinement pressure, the cohesion and the friction coefficient between the materials, parameters which are not always easy to predict. The pap…

A numerical study on the effect of the interface material model on the tensile behaviour of FRCM strips

2019

Fibre Reinforced Cementitious Matrix (FRCM) composites are becoming increasingly popular for strengthening masonry structures for which the compatibility of the inorganic matrix with the chemical and physical properties of the support makes it advantageous to adopt such systems. However, despite the large use of FRCMs for strengthening applications, the characterization and modelling of the mechanical response in tension of these systems is an open issue. In fact, the constitutive tensile law of the composite shows to be affected by different variables, such as the clamping system adopted during tensile test, the gauge length used for recording strains, the monitoring of the number of yarns…

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…