A numerical program for Railway vehicle-track-structure dynamic interaction using a modal substructuring approach

This work presents a program for simulations of vehicle-track and vehicle-trackstructure dynamic interaction . The method used is computationally efficient in the sense that a reduced number of coordinates is sufficient and doesn’t require high efficiency computers. The method proposes a modal substructuring approach of the system by modelling rails , sleepers and underlying structure with modal coordinates, the vehicle with physical lumped elements coordinates and by introducing interconnection elements between these structures (wheel-rail contact, railpads and ballast) by means of their interaction forces. The Frequency response function (FRF) is also calculated for both cases of track over a structure (a bridge, a viaduct ...) and for the simple vehicle-track program; for each case the vehicle effect on the FRF is then analyzed through the comparison of the FRFs obtained introducing or not a simplified vehicle on the system.

Applying partial virtualization on ELF binaries through dynamic loaders

The technology of partial virtualization is a revolutionary approach to the world of virtualization. It lies directly in-between full system virtual machines (like QEMU or XEN) and application-related virtual machines (like the JVM or the CLR). The ViewOS project is the flagship of such technique, developed by the Virtual Square laboratory, created to provide an abstract view of the underlying system resources on a per-process basis and work against the principle of the Global View Assumption. Virtual Square provides several different methods to achieve partial virtualization within the ViewOS system, both at user and kernel levels. Each of these approaches have their own advantages and shortcomings. This paper provides an analysis of the different virtualization methods and problems related to both the generic and partial virtualization worlds. This paper is the result of an in-depth study and research for a new technology to be employed to provide partial virtualization based on ELF dynamic binaries. It starts with a mild analysis of currently available virtualization alternatives and then goes on describing the ViewOS system, highlighting its current shortcomings. The vloader project is then proposed as a possible solution to some of these inconveniences with a working proof of concept and examples to outline the potential of such new virtualization technique. By injecting specific code and libraries in the middle of the binary loading mechanism provided by the ELF standard, the vloader project can promote a streamlined and simplified approach to trace system calls. With the advantages outlined in the following paper, this method presents better performance and portability compared to the currently available ViewOS implementations. Furthermore, some of itsdisadvantages are also discussed, along with their possible solutions.

Dynamic characterisation of four nine-story large-panel R.C. buildings in Bishkek (Kyrgyzstan): A comparison between experimental ambient vibration analysis and numerical finite element modeling

With the outlook of improving seismic vulnerability assessment for the city of Bishkek (Kyrgyzstan), the global dynamic behaviour of four nine-storey r.c. large-panel buildings in elastic regime is studied. The four buildings were built during the Soviet era within a serial production system. Since they all belong to the same series, they have very similar geometries both in plan and in height. Firstly, ambient vibration measurements are performed in the four buildings. The data analysis composed of discrete Fourier transform, modal analysis (frequency domain decomposition) and deconvolution interferometry, yields the modal characteristics and an estimate of the linear impulse response function for the structures of the four buildings. Then, finite element models are set up for all four buildings and the results of the numerical modal analysis are compared with the experimental ones. The numerical models are finally calibrated considering the first three global modes and their results match the experimental ones with an error of less then 20%.

Leap Aided Modelling (LAM) in Blender

L'evoluzione tecnologica e l'utilizzo crescente della computer grafica in diversi settori stanno suscitando l'interesse di sempre più persone verso il mondo della modellazione 3D. I software di modellazione, tuttavia, si presentano spesso inadeguati all'utilizzo da parte di utenti senza esperienza, soprattutto a causa dei comandi di navigazione e modellazione poco intuitivi. Dal punto di vista dell'interazione uomo-computer, questi software devono infatti affrontare un grande ostacolo: il rapporto tra dispositivi di input 2D (come il mouse) e la manipolazione di una scena 3D. Il progetto presentato in questa tesi è un addon per Blender che consente di utilizzare il dispositivo Leap Motion come ausilio alla modellazione di superfici in computer grafica. L'obiettivo di questa tesi è stato quello di progettare e realizzare un'interfaccia user-friendly tra Leap e Blender, in modo da potere utilizzare i sensori del primo per facilitare ed estendere i comandi di navigazione e modellazione del secondo. L'addon realizzato per Blender implementa il concetto di LAM (Leap Aided Modelling: modellazione assistita da Leap), consentendo quindi di estendere le feature di Blender riguardanti la selezione, lo spostamento e la modifica degli oggetti in scena, la manipolazione della vista utente e la modellazione di curve e superfici Non Uniform Rational B-Splines (NURBS). Queste estensioni sono state create per rendere più veloci e semplici le operazioni altrimenti guidate esclusivamente da mouse e tastiera.

Experimentally and coupled CFD/CSD assisted structural and aeroelastic modelling of the Javelin UAV outboard wing section

This study presents the procedure followed to make a prediction of the critical flutter speed for a composite UAV wing. At the beginning of the study, there was no information available on the materials used for the construction of the wing, and the wing internal structure was unknown. Ground vibration tests were performed in order to detect the structure’s natural frequencies and mode shapes. From tests, it was found that the wing possesses a high stiffness, presenting well separated first bending and torsional natural frequencies. Two finite element models were developed and matched to experimental results. It has been necessary to introduce some assumptions, due to the uncertainties regarding the structure. The matching process was based on natural frequencies’ sensitivity with respect to a change in the mechanical properties of the materials. Once experimental results were met, average material properties were also found. Aerodynamic coefficients for the wing were obtained by means of a CFD software. The same analysis was also conducted when the wing is deformed in its first four mode shapes. A first approximation for flutter critical speed was made with the classical V - g technique. Finally, wing’s aeroelastic behavior was simulated using a coupled CFD/CSD method, obtaining a more accurate flutter prediction. The CSD solver is based on the time integration of modal dynamic equations, requiring the extraction of mode shapes from the previously performed finite-element analysis. Results show that flutter onset is not a risk for the UAV, occurring at velocities well beyond its operative range.

Analysis, modelling and design of a groin as coastal protection structure at Lido di Dante, Ravenna

An analysis and a subsequent solution is here presented. This document is about a groin design able to contrast the erosion actions given by waves in Lido di Dante. Advantages will be visible also for Fiumi Uniti's inlet, in the north side of the shoreline. Beach future progression and growth will be subjected to monitoring actions in the years after groin construction. The resulting effects of the design will have a positive impact not only on the local fauna and environment, but also, a naturalistic appeal will increase making new type of tourists coming not only for recreational purposes. The design phase is focused on possible design alternatives and their features. Particular interest is given to scouring phenomena all around the groin after its construction. Groin effects will impact not only on its south side, instead they will cause an intense erosion process on the downdrift front. Here, many fishing hut would be in danger, thus a beach revetment structure is needed to avoid any future criticality. In addiction, a numerical model based on a generalized shoreline change numerical model, also known as GENESIS, has been applied to the study area in order to perform a simplistic analysis of the shoreline and its future morphology. Critical zones are visible in proximity of the Fiumi Uniti's river inlet, where currents from the sea and the river itself start the erosion process that is affecting Lido di Dante since mid '80s, or even before. The model is affected by several assumptions that make results not to be interpreted as a real future trend of the shore. Instead the model allows the user to have a more clear view about critical processes induced by monochromatic inputed waves. In conclusion, the thesis introduce a wide analysis on a complex erosion process that is affecting many shoreline nowadays. A groin design is seen as a hard solution it is considered to be the only means able to decrease the rate of erosion.

Analysis of the impact of stationary energy storage systems in trolleybus grids using Simulink-based modelling

The voltage profile of the catenary between traction substations (TSSs) is affected by the trolleybus current intake and by its position with respect to the TSSs: the higher the current requested by the bus and the further the bus from the TSSs, the deeper the voltage drop. When the voltage drops below 500V, the trolleybus is forced to decrease its consumption by reducing its input current. This thesis deals with the analysis of the improvements that the installation of an BESS produces in the operation of a particularly loaded FS of the DC trolleybus network of the city of Bologna. The stationary BESS is charged by the TSSs during off-peak times and delivers the stored energy when the catenary is overloaded alleviating the load on the TSSs and reducing the voltage drops. Only IMC buses are considered in the prospect of a future disposal of all internal combustion engine vehicles. These trolleybuses cause deeper voltage drops because they absorb enough current to power their traction motor and recharge the on board battery. The control of the BESS aims to keep the catenary voltage within the admissible voltage range and makes sure that all physical limitations are met. A model of FS Marconi Trento Trieste is implemented in Simulink environment to simulate its daily operation and compare the behavior of the trolleybus network with and without BESS. From the simulation without BESS, the best location of the energy storage system is deduced, and the battery control is tuned. Furthermore, from the knowledge of the load curve and the battery control trans-characteristic, it is formulated a prediction of the voltage distribution at BESS connection point. The prediction is then compared with the simulation results to validate the Simulink model. The BESS allows to decrease the voltage drops along the catenary, the Joule losses and the current delivered by the TSSs, indicating that the BESS can be a solution to improve the operation of the trolleybus network.