1,721,589 research outputs found
Comparison of Braking Performance for Different Technologies of Heavy Hauled Freight Trains
Full text linkThe paper shows a comparison of different braking technologies for freight trains
and their effects on in-train forces. At this aim, the UIC certified software TrainDy
is employed. Freight train sets, having one and two remote locomotives, are
investigated both as coupled trains and as fixed train compositions. There is also an
evaluation of the in-train forces of freight train sets equipped by electro-pneumatic
brakes and disk brakes. The case of two remote locomotives is further explored
showing the minor benefits of an ad hoc activation of drivers brake valve, compared
to the benefits of an optimized mass distribution, for train sets both coupled and
fixed
Sull'analisi a crash di strutture automobilistiche: stato dell'arte della ricerca di settore (Parte I)
No full textAnalisi e ricerca di zone operative per treni a trazione distribuita
No full textIl necessario incremento di efficienza del trasporto ferroviario merci si orienta nella direzione di un aumento della lunghezza del treno, che può essere convenientemente ottenuto mediante l’utilizzo della trazione/frenatura distribuita. Il lavoro analizza le zone di funzionamento sicuro (in termini delle sole forze longitudinali scambiate tra veicoli adiacenti durante la frenatura) al variare della massa trasportata e della lunghezza del treno. Si dimostra che, all’aumentare di queste ultime, è necessario ottimizzare la disposizione delle masse lungo il treno per incrementare in sicurezza l’efficienza del trasporto ferroviario; si dimostra inoltre che l’ottimale disposizione della locomotiva secondaria verso i 2/3 della lunghezza complessiva del treno garantisce una notevole riduzione delle forze in compressione ed un bilanciamento con quelle in trazione. Il lavoro mostra, infine, come la variabilità dei parametri tecnici di funzionamento effettivo del treno contribuisca in modo rilevante al valore delle forze scambiate tra i veicoli durante una frenatura.The desired increment of freight railway transport is oriented towards an increment of train length, which can be conveniently achieved by means of distributed traction/braking. This paper analyses the zones of safe working (in terms of the only in-train forces) by considering the variation of transported mass and length of the train. By increasing these latter quantities, it is worthwhile to optimize the load distribution along the train in order to safely increase the efficiency of railway transportation; furthermore, the optimal position of the slave locomotive around 2/3 of total train length guarantees a considerable reduction of compressive in-train forces and a balance with the tension in-train forces. Finally, the paper shows that the variability of technical parameters, characterizing the actual behaviour of the train, significantly contributes to the value of in-train forces arising during a braking
Infezione da Pneumocystis carinii: aspetti immunologici e diagnostici
No full textAfter having discussed some important and controversial aspects of Pneumocystis carinii infection, the Authors report personal data concerning the immunodiagnosis and the antigenic characteristics
of the microrganism
Performance di frenatura di un treno merci con trazione distribuita
Full text linkIl presente lavoro focalizza l’attenzione sulle performance di frenatura e sulla dinamica longitudinale di un convoglio ferroviario formato dall’unione di due sotto-treni identici, a configurazione di un treno con trazione e frenatura distribuite, avente lunghezza di 1500 m e massa di circa 3500 t e dotato di comunicazione radio tra le due locomotive. Attualmente non esistono treni del genere in Europa, ma essi contribuiranno, con la loro prossima entrata in circolazione, ad aumentare l’efficienza del trasporto ferroviario merci, specialmente per lunghe distanze. Il lavoro stimolato dal grande interesse europeo, propone una modalità operativa attraverso la quale il treno possa circolare, anche in condizioni degradate, cioè senza la comunicazione radio tra le locomotive. Infine, si dimostra come, attraverso un’opportuna distribuzione, delle masse sia possibile ottimizzare fortemente la dinamica longitudinale del treno.This paper is focused on the braking performance and on the longitudinal dynamics of a train-set built by coupling two equal sub-trains in way of assembling a train with distributed traction and braking, having overall length and mass of 1500 m and 3500 t, respectively, and provided by a radio connection between the locomotives. Nowadays such trains do not exist in Europe, but they will contribute with their circulation to the increase of railway freight efficiency, especially on long distance routes. This paper, claimed by an high European interest on the subject, proposes an operative rule by means of which the train can run also in degraded mode, i.e. without the radio communication among the locomotives. Lastly, it is shown that by means of an appropriate mass distribution it is possible to strongly optimize the longitudinal dynamics of the train
Elastic stress analysis of non-linear variable thickness rotating disks subjected to thermal load and having variable density along the radius
No full textAbstractAn analytical procedure for evaluation of elastic stresses and strains in non-linear variable thickness rotating disks, either solid or annular, subjected to thermal load, and having a fictitious density variation along the radius is presented. Thickness variation of disks is described by means of a power of linear function, which can be used to describe a fourfold infinity of actual disk profiles. The procedure is based on two independent integrals of the hypergeometric differential equation describing the displacement field; this theoretical procedure is just general and does not present limitations and drawbacks of the approaches as the one found in technical literature. General unpublished relations of stress state and displacement field in non-linear variable thickness disks subjected, under elastic conditions, to thermal gradient, and featuring a density variation along the radius are defined. Particular consideration is given to some industrial example of turbine rotors carrying hub and rim with buckets on periphery or radial blades on lateral surfaces. The analytical results obtained by using the new general relations perfectly match those obtained by FEA and overlap those concerning the special cases of tapered conical disks found in literature
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