L'indice di modellato come parametro di qualità nella progettazione illuminotecnica di interni ed esterni.

La presente tesi si pone come obiettivo la valutazione della qualità dell’illuminazione dapprima in un ambiente interno caratterizzato da sola illuminazione artificiale e successivamente in un ambiente esterno in condizioni notturne. Sono state misurate ed analizzate le principali grandezze illuminotecniche coinvolte in entrambi i casi studio: illuminamento orizzontale, illuminamento verticale, illuminamento semicilindrico, illuminamento cilindrico, indice di modellato e luminanza. Sono stati presi in analisi due casi studio: un corridoio in un edificio destinato ad uffici per lo studio dell’illuminazione di interni ed un tratto di percorso pedonale per l’illuminazione di esterni. Sui casi studio esaminati sono state compiute una serie di indagini e misurazioni volte a valutare l’efficacia dell’illuminazione

Computational analysis of a vortex ingesting bioreactor for hydrogen production

In this work, the fluid dynamics behaviour of a bioreactor specifically designed for a fermentative hydrogen production process is investigated by Computational Fluid Dynamics (CFD) simulations. The geometrical features of the bioreactor, which is a dual impellers baffled stirred tank provided with a draft tube, and the gas-liquid characteristics of the vortex ingesting operating mode make the modelling and the numerical solution tasks particularly challenging. The computational strategy is based on the two-phase formulation of the Reynolds Averaged Navier-Stokes equations in an Eulerian framework for both the continuous and the dispersed phase. The results of the simulations are compared with available experimental data collected in a parallel investigation under the same operating conditions and a identical bioreactor geometry. The reliability of the predicted overall hydrodynamics behaviour and the accuracy of the turbulent two-phase mean velocity field are evaluated and critically discussed. The results confirm that the proposed CFD approach is a suitable tool for the design and optimization of stirred bioreactors.Fil: Montante, Giuseppina. Universita Di Bologna; ItaliaFil: Coroneo, Mirella. Universita Di Bologna; ItaliaFil: Francesconi, Javier Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo y Diseño (i); ArgentinaFil: Paglianti, Alessandro. Universita Di Bologna; ItaliaFil: Magelli, Franco. Universita Di Bologna; Itali

Development of numerical and experimental tools for the simulation of train braking operations

L'abstract è presente nell'allegato / the abstract is in the attachmen

Study of Adhesion Recovery phenomenon using a Multi-axle Roller-rig

When a railway vehicle is running on a contaminated track, the available friction is reduced, and large creep values arise at the wheel-rail interface. However, the work of the friction forces of the leading wheelsets produces a cleaning effect on both the track and the wheels, so that the contaminant layer is partially removed, and adhesion increases on the leading as well as on the trailing wheelsets. The investigation of these adhesion recovery phenomena is the key to develop new solutions aiming to improve the vehicle dynamic behaviour in degraded adhesion conditions. Since on-field tests are usually expensive and time-consuming, roller-rigs are the typical apparatus used to simulate the vehicle dynamic behaviour in laboratory conditions. The paper describes the mechanical design of an innovative roller rig specifically designed to study adhesion recovery phenomena, consisting of four wheelsets running over the same pair of rollers. Experimental tests are performed on the test bench to obtain adhesion characteristics under dry and contaminated conditions

Development of a 2D finite element model for the investigation of the tread braked railway wheels thermo-mechanical behaviour

The main drawback of tread braking is the rail wheel heating due to friction sliding. Thermal stresses and strains can lead to wheel surface damages while at the same time fast cooling from high temperature can cause microstructural changes, with possible local formation of brittle martensite. Nowadays, the investigation of the wheel and shoe thermomechanical interaction is typically performed using finite element (FE) codes. The paper shows the development, implementation and preliminary validation of a 2D plane FE model for the calculation of the thermal field produced in a tread braked wheel due to drag and stop braking operations. The model includes a structural contact module for the static calculation of the normal and tangential contact pressure at the wheel-shoe interface and a thermal transient module, which computes the wheel temperature considering the friction heat flux and the cooling due to air convection and rail chill

Dynamical Effects of the Increase of the Axle Load on European Freight Railway Vehicles

The development of an efficient freight railway system requires minimizing the travel time and maximizing the load capacity of trains. This objective can be achieved through three different strategies which can be adopted separately or in synergy. These strategies substantially consist of improvement of the load capacity of a single vehicle, increase in the train length, and increment of the vehicle velocity. The option to adopt simultaneously all three strategies is possible only when operating on dedicated infrastructures and specifically designing the vehicles and the track. This work shows the effect of the increment of the axle load, over the actual Italian limitation, on the most important indicators defined by the UIC regulation to homologate the vehicles. The calcula-tions have been performed on a high-quality real track using a numerical model of a vehicle based on the Y25 bogie. In order to take into account higher axle loads, the vehicle primary suspension has been redesigned. The results show that an increment of the axle load is feasible until an axle load of 32.5 ton if speed is limited to 80 km/h, or until 30 ton if speed is limited to 120 km/h

Simulation of wheel and rail profile wear: a review of numerical models

The development of numerical models able to compute the wheel and rail profile wear is essential to improve the scheduling of maintenance operations required to restore the original profile shapes. This work surveys the main numerical models in the literature for the evaluation of the uniform wear of wheel and rail profiles. The standard structure of these tools includes a multibody simulation of the wheel-track coupled dynamics and a wear module implementing an experimental wear law. Therefore, the models are classified according to the strategy adopted for the worn profile update, ranging from models performing a single computation to models based on an online communication between the dynamic and wear modules. Nevertheless, the most common strategy nowadays relies on an iteration of dynamic simulations in which the profiles are left unchanged, with co-simulation techniques often adopted to increase the computational performances. Work is still needed to improve the accuracy of the current models. New experimental campaigns should be carried out to obtain refined wear coefficients and models, while strategies for the evaluation of both longitudinal and transversal wear, also considering the effects of tread braking, should be implemented to obtain accurate damage models

Adapting a scaled twin-disc device for tread braking investigations based on an ad-hoc thermal similitude model

The present paper shows the design of a scaled tread braking system to be included in a scaled twin-disc system, to carry out thermomechanical investigations on wheel and shoe materials. The test bench consists of two discs, pressed against each other, simulating the wheel-rail contact. A pneumatic cylinder pushes scaled brake shoes against the wheel tread surface, and a fan-nozzle device improves convection cooling. As a major novelty, both systems are designed to comply with a new thermal scaling method, that is specifically identified to obtain the same temperature field on the scaled twin-disc as for a full-scale system. The paper thoroughly describes the mathematical background of the new thermal scaling method, which is then preliminarily validated with finite element thermal models for both the brake block and wheel. The greatest advantage of the final twin-disc configuration is that it allows to carry out investigations of wheel-rail wear phenomena as well as studies on the thermomechanical interaction between wheels and brake shoes, while adhering to scaling rules that corroborate the validity of the experimental results

Study on the influence of the modelling strategy in the calculation of the worn profile of railway wheels

As changes in the wheel and rail profiles strongly affect vehicle dynamics, running stability and safety, maintenance operations such as wheel turning and rail grinding are necessary. The availability of numerical models for wear prediction can be a huge support to optimize the scheduling of such operations. Thanks to the computational power of modern computer architectures, allowing parallelization and co-simulation, the typical strategy is based on a dynamic module performing the vehicle dynamics simulation, usually developed in commercial multibody (MB) software packages, and on a wear module for the calculation of the worn material. The latter can be implemented in the same MB code or in a separate software, such as Matlab/Simulink, which exchanges data with the MB code. Wear modules rely on wear laws relating the amount of worn material to the normal load and sliding distance or to the energy dissipated at the contact interface. Both types of law can be applied locally, calculating the worn depth in each cell of the discretized contact patch from the contact pressures and sliding speeds, or globally, hence calculating the worn volume or mass starting from the global forces and creepages. In the latter case, the worn material is calculated on the whole contact patch rather than only on the slip zone, and a proper distribution is required to relate the worn depth to the worn volume. The present work aims to further investigate the differences between the two approaches in the computed worn profiles in a specific case study in terms of reference vehicle and track, carrying out the dynamic simulations through the Simpack MB code. The paper is intended to highlight the differences in both the numerical results and computational efforts, comparing the wear computed by a local model with the outputs of the Simpack wear module

Monitoring systems for railways freight vehicles

Monitoring systems are a key tool to improve the safety of railway vehicles and to support maintenance activities. Their on-board application on railway vehicles is currently well established on newly built passenger vehicles, while their use on freight vehicles is not yet sufficiently widespread. This is due to the complex management of the operating procedures of the freight wagons, to the substantial impact of the cost of these systems compared to the cost of the wagon and to the common lack of electrification on freight wagons. This work illustrates the characteristics of a monitoring system developed at Politecnico di Torino and previously installed on freight vehicles and operationally tested as regards the detection of accelerations and temperatures as diagnostic parameters. This system has been improved by adding diagnostics of the vehicle braking system, in order to detect anomalies during braking operations and to support maintenance procedures. The activity described in the present work aims to identify, beyond the specific diagnostic system that has been implemented, the basic characteristics that a modern monitoring system, intended to be installed on railway freight wagons, should feature. The new version of the monitoring system that has been developed at Politecnico di Torino has been preliminarily tested on a scaled roller-rig in order to monitor the braking system even in abnormal operating conditions, which would be difficult to reproduce safely on a real vehicle. The monitoring system is equipped with an axle generator capable of autonomously supporting its operation, and it is also provided with a diagnostic information processing system and communication protocols to send outside this information