The UIC railway braking system is a complex pneumatic plant whose performance and reliability are safety relevant. The plant is controlled by the transmission of pneumatic signals; different train compositions involve large parametric variations of plant response. The problem is critical for long freight trains where the delayed plant response involves heavy longitudinal forces between vehicles. Even for simple compositions of 10-15 vehicles, the number of components involved in the plant response is quite high. The distributor valve, a complex pneumo-mechanic device, is devoted to control the brake response on every vehicle and it is perhaps the most difficult component to be simulated.Authors have developed simulation models of the pneumatic plant of the UIC railway brake including libraries of pneumatic submodels that can be parametrically calibrated in order to reproduce different train compositions.In this work, a case study concerning the simulation of a convoy composed by the SAADKMS freight wagon is presented. Simulation results are compared with experimental data kindly supplied by Trenitalia SPA. Model formulation and calibration procedures are shown in order to explain the followed workflow.identify the response of the plant from a reduced set of experimental results available from the Trenitalia SPA.The proposed procedure may be interesting in order to produce a robust tuning of simulation models against errors due to the uncertainty of parameters.
A better integration and interoperability between rail and road transportation is a key factor in order to reduce pollution and increase railway freight traffic.Development of special freight wagons like "SAADKMS" for the transportation of trucks by railway is a successful solution that is meeting an increasing consensus and popularity among many European countries. In order to accelerate truck loading on wagons and reduce the limitation of normal clearance (structure/vehicle/loading gauges) it is necessary to reduce the wheel diameter as much as possible. This is not a drawback-free solution since an excessive reduction of wheel diameter involves many troubles concerning the stability of the vehicle, maximum axle load, wear of bearings and rolling surfaces of rails and axles. Also designing the braking system is very complicated because the reduced number of encumbrances available makes the placement of internal disks on the axles difficult.In order to solve these problems a very original solution concerning wheelset, wheel profiles and more general bogie design have been applied in the development of "SAADKMS" freight wagons so the resulting vehicle is very different from the conventional one. As a matter of fact, many past experiences and know-how for conventional freight wagons are not applicable for this kind of application, so numerical simulations are very important to deeply understand the behaviour of the system and propose criteria for further optimization.The authors of this paper have developed models on commercial multibody software in order to simulate the behaviour of the "SAADKMS" freight wagon in different conditions (stability, steering performances). Also important results such as position of the contact point or wear-number are shown to be useful parameters for further optimization of the rolling surface profiles.
Nowadays, the search for increasing performances in turbomachinery applications has led to a growing utilization of active magnetic bearings (AMBs), which can bring a series of advantages thanks to their features: AMBs allow the machine components to reach higher peripheral speeds; in fact there are no wear and lubrication problems as the contact between bearing surfaces is absent. Furthermore, AMBs characteristic parameters can be controlled via software, optimizing machine dynamics performances. However, active magnetic bearings present some peculiarities, as they have lower load capacity than the most commonly used rolling and hydrodynamic bearings, and they need an energy source; for these reasons, in case of AMBs overload or breakdown, an auxiliary bearing system is required to support the rotor during such landing events. During the turbomachine design process, it is fundamental to appropriately choose the auxiliary bearing type and characteristics, because such components have to resist to the rotor impact; so, a supporting design tool based on accurate and efficient models of auxiliary bearings is very useful for the design integration of the Active Magnetic Bearing System into the machine. This paper presents an innovative model to accurately describe the mechanical behavior of a complete rotor-dynamic system composed of a rotor equipped with two auxiliary rolling bearings. The model, developed and experimentally validated in collaboration with Baker Hughes a GE company (providing the test case and the experimental data), is able to reproduce the key physical phenomena experimentally observed; in particular, the most critical phenomenon noted during repeated experimental combined landing tests is the rotor forward whirl, which occurs in case of high friction conditions and greatly influences the whole system behavior. In order to carefully study some special phenomena like rotor coast down on landing bearings (which requires long period of time to evolve and involves many bodies and degrees of freedom) or other particular events like impacts (which occur in a short period of time), a compromise between accuracy of the results and numerical efficiency has been pursued. Some of the elements of the proposed model have been previously introduced in literature; however the present work proposes some new features of interest. For example, the lateral and the axial models have been properly coupled in order to correctly reproduce the effects observed during the experimental tests and a very important system element, the landing bearing compliant suspension, has been properly modelled to more accurately describe its elastic and damping effects on the system. Furthermore, the model is also useful to characterize the frequencies related to the rotor forward whirl motion.
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