A study on wear evaluation of railway wheels based on multibody dynamics and wear computation

The wear evolution of railway wheels is a very important issue in railway engineering. In the past, the reprofiling intervals of railway vehicle steel wheels have been scheduled according to designers' experience. Today, more reliable and accurate tools in predicting wheel wear evolution and wheelset lifetime can be used in order to achieve economical and safety benefits. In this work, a computational tool that is able to predict the evolution of the wheel profiles for a given railway system, as a function of the distance run, is presented. The strategy adopted consists of using a commercial multibody software to study the railway dynamic problem and a purpose-built code for managing its pre- and post-processing data in order to compute the wear. The tool is applied here to realistic operation scenarios in order to assess the effect of some service conditions on the wheel wear progression

Digital image watermarking: its formal model, fundamental properties and possible attacks

While formal definitions and security proofs are well established in some fields like cryptography and steganography, they are not as evident in digital watermarking research. A systematic development of watermarking schemes is desirable, but at present their development is usually informal, ad hoc, and omits the complete realization of application scenarios. This practice not only hinders the choice and use of a suitable scheme for a watermarking application, but also leads to debate about the state-of-the-art for different watermarking applications. With a view to the systematic development of watermarking schemes, we present a formal generic model for digital image watermarking. Considering possible inputs, outputs, and component functions, the initial construction of a basic watermarking model is developed further to incorporate the use of keys. On the basis of our proposed model, fundamental watermarking properties are defined and their importance exemplified for different image applications. We also define a set of possible attacks using our model showing different winning scenarios depending on the adversary capabilities. It is envisaged that with a proper consideration of watermarking properties and adversary actions in different image applications, use of the proposed model would allow a unified treatment of all practically meaningful variants of watermarking schemes

Cardiorespiratory hysteresis during incremental high altitude ascent-descent quantifies the magnitude of ventilatory acclimatization

Maintenance of arterial blood gases is achieved through sophisticated regulation of ventilation, mediated by central and peripheral chemoreflexes. Respiratory chemoreflexes are important during exposure to high altitude due to the competing influence of hypoxia and hypoxic hyperventilation‐mediated hypocapnia on steady‐state ventilatory drive. Inter‐individual variability exists in ventilatory acclimatization to high altitude, potentially affecting the development of acute mountain sickness (AMS). We aimed to quantify ventilatory acclimatization to high altitude by comparing differential ascent and descent values (i.e. hysteresis) in steady‐state cardiorespiratory variables. We hypothesized that (a) the hysteresis area formed by cardiorespiratory variables during ascent and descent would quantify the magnitude of ventilatory acclimatization, and (b) larger hysteresis areas would be associated with lower AMS symptom scores during ascent. In 25 healthy, Diamox‐free trekkers ascending to and descending from 5160 m, cardiorespiratory hysteresis was measured in the pressure of end‐tidal (PET)CO2, peripheral oxygen saturation (SpO2), minute ventilation (V̇E), chemoreceptor stimulus index (SI; PETCO2/SpO2) and the calculated steady‐state chemoreflex drive (SS‐CD; V̇E/SI) using portable devices (capnograph, peripheral pulse oximeter and respirometer, respectively). AMS symptoms were assessed daily using the Lake Louise Questionnaire. We found that (a) ascent‐descent hysteresis was present in all cardiorespiratory variables, (b) SS‐CD is a valid metric for tracking ventilatory acclimatization to high altitude and (c) highest AMS scores during ascent were significantly, moderately and inversely‐correlated to SS‐CD hysteresis magnitude (rs = ‐0.408, P = 0.043). We propose that ascent‐descent hysteresis is a novel and feasible way to quantify ventilatory acclimatization in trekkers during high altitude exposure

Railway-induced ground vibrations – a review of vehicle effects

This paper is a review of the effect of vehicle characteristics on ground- and track borne-vibrations from railways. It combines traditional theory with modern thinking and uses a range of numerical analysis and experimental results to provide a broad analysis of the subject area. First, the effect of different train types on vibration propagation is investigated. Then, despite not being the focus of this work, numerical approaches to vibration propagation modelling within the track and soil are briefly touched upon. Next an in-depth discussion is presented related to the evolution of numerical models, with analysis of the suitability of various modelling approaches for analysing vehicle effects. The differences between quasi-static and dynamic characteristics are also discussed with insights into defects such as wheel/rail irregularities. Additionally, as an appendix, a modest database of train types are presented along with detailed information related to their physical attributes. It is hoped that this information may provide assistance to future researchers attempting to simulate railway vehicle vibrations. It is concluded that train type and the contact conditions at the wheel/rail interface can be influential in the generation of vibration. Therefore, where possible, when using numerical approach, the vehicle should be modelled in detail. Additionally, it was found that there are a wide variety of modelling approaches capable of simulating train types effects. If non-linear behaviour needs to be included in the model, then time domain simulations are preferable, however if the system can be assumed linear then frequency domain simulations are suitable due to their reduced computational demand

The Relationship Between Knee Motion and Articular Surface Geometry

No abstract