Long and frequent train delays, striking many periodically make headlines. The question is raised: what might be done about it? The on-going deregulation of the Swedish railway, with more actors entering the market, contributes to the question's topicality. In this thesis, problems and symptoms concerning punctuality are described and analysed. Herein, punctuality is defined as the extent to which an event takes place when agreed, for example the agreement between passengers and the company selling the ticket, considering the event that the train arrives at a certain time. The terminology in use on punctuality-related entities is floating. Causes for unpunctuality are related to the infrastructure, locomotives, wagons and personnel. Herein, primarily failures related to infrastructure are discussed. Maintenance, i.e. correcting and preventing failures, together with the track, rolling stock, weather, driver, other personnel and the timetable determine how good the punctuality will be. To the ore and steel transports studied it is more important to limit the lengths of the transport times, rather than having high punctuality, i.e. adherence to timetable. Generally, for freight transports it is difficult to give an estimation of the cost for unpunctuality. To find the root cause of a delay is vital, as is identification of symptoms and triggering events, in order to be able to carry out appropriate actions. Often the information needed to do so is lacking in the Ofelia database for infrastructure failures. Comparisons between regions or over time are complexified by the varying policies on how failure coding is to be performed. To improve punctuality by learning from others is made more difficult by e.g. different countries employing different ways of denoting punctuality. In the transport chain of post in Norway, terms related to punctuality varied even more among stakeholders. They considered being informed on estimated time of arrival as important, but getting this information was, despite this, not among the quantified goals. Few requirements were quantified, despite this often being simple to do. The consequences of failure are important to consider, not only e.g. the number of failures. Studying the variation in transport time on different line sections might help in identifying problems, because coding of delays shorter than five minutes is not carried out in the Swedish railway. Such causes of delay include low contact wire voltage, minor problems with locomotives and slippery rails due to leaves on the track. Disadvantageously, this variation is masked in the case of heavy trains or steep and curvy lines. In a studied maintenance organisation, the indicators of maintenance measured the result of the entire maintenance process. In order to manage each sub process better, it is more advantageous to measure the performance of them individually. Considering the specific sub process that decides which maintenance actions are to be carried out, it only uses expenses for the action itself when deciding, not resulting future costs and punctuality. The indicators focus on measuring past performance, not on facilitating planning for the future. A design of information systems facilitating information usage from different functions of the organisation would facilitate informed decisions. Information concerning technology, traffic and economy need to be integrated. / Godkänd; 2005; 20061218 (haneit)

No description available.

The work presented in this thesis concerns computer simulations of the lubrication process. The main subject of interest is elastohydrodynamic lubrication (EHL) and, to some extent, hydrodynamic lubrication (HD). The thesis comprises an introductory section and three papers; referred to as A, B and C. Simulation of EHL is an inter-disciplinary task, incorporating the fields of fluid mechanics, solid mechanics, thermodynamics and rheology. In almost all numerical simulations of lubrication performed today, the hydrodynamics are modelled using the Reynolds equation. This equation is derived from the equations of momentum and continuity and using the thin film approximation. However, the assumptions made when deriving this equation limits the size of the computational/spatial domain and the equation cannot predict pressure variations across the lubricating oil film. The subject of papers A and B are numerical simulations using the full equations of momentum and continuity, (Paper B), and the equation of energy (Paper A). The main aim of the work was to investigate the possibilities of carrying out numerical simulations based on the above equations. The rheology was assumed to be Newtonian; the equations are then commonly referred to as the Navier-Stokes equations (N-S). The second aim of the work was to investigate the possibilities of using a commercial software, CFX 4.3 [1], to carry out the numerical simulations. The results in Paper A show that it is possible to simulate thermal EHL line contacts up to pressures of approximately 1 GPa. The limitations of the approach are due to a singularity that can occur in the equation of momentum when a critical shear stress is reached. With a more complete rheological model (non-Newtonian rheology) it should be possible to perform simulations at even higher contact pressures. Paper B presents the results of isothermal simulations comparing the N-S and Reynolds equation approaches. The result show that there may be some discrepancies between the two approaches; although only small discrepancies have been observed in the smooth line contact simulations made. The characteristics of the EHL-contact with a wide range of scales and large gradients in pressure, viscosity and temperature make developing accurate numerical simulations to a difficult task. The computational cost is high due to the small under-relaxations factors that must be used in order to obtain converged numerical solutions. The work to date has shown that is possible to use the extended approach in conjunction with a commercial software, CFX 4.3 [1]. This approach makes it possible to extend the computational domain in future in EHL-simulations, where the Reynolds approach is not valid. Paper C presents the results of simulations of a lubricated pivoted thrust bearing. The objective of this study was to verify a thermo-hydrodynamic (THD) model for this type of bearing. The model developed handles three-dimensional temperature distribution in the oil film and pad, as well as two-dimensional temperature variation in the runner. The viscosity and density are treated as functions of both temperature and pressure. Experiments have been performed in a test rig consisting of two identical equalising pivoted pad thrust bearings. Experimentally measured power loss, runner temperature and pressure profiles as a function of load and rotational speed were compared with the theoretical investigations. The results showed fairly good agreement when the oil inlet temperature and heat transfer coefficients were modified in order to obtain the same runner temperature in both theory and experiment. / Godkänd; 2001; 20070314 (ysko)

No description available.

Since the usage of pressurized systems, there has been a challenge to prevent and control leakage of different fluids. When a metal-to-metal face seal is designed, different aspects are to be considered. Its ring shaped sealing surface is designed to prevent leakage and also to maintain pressure. In this thesis, the main objective is to study how out-of-flatness affects the leakage. This property of sealing interface can be described by different wave parameters and in this case, by means of modelling and numerical simulations. The best approach is the usage of Heterogeneous Multiscale Method (HMM). The data obtained by means of the two-scale stochastic model showed that the pressure amplitude is the most important parameter of the out-of-flatness. In same level of importance, comes the mean pressure even though it is not considered an out-of-flatness parameter. From the data obtained, a simple mathematical expression for leak rate was constructed that shows the effect of out-of-flatness.

The purpose of this thesis is to summarize the research carried out that led to the development of measurement techniques which measure the water content of lubricating grease. A simple and effective grease mixing method for preparing grease samples was developed and tested for repeatability. Calcium sulphonate complex (CaS-X) grease was used in all experiments. The water content of these samples were also tested with time and temperature as added variables to study if and how much water will evaporate from the samples. Additionally, two measurement techniques were investigated: optical attenuation in the visible and near-infrared (NIR) region and with a dielectric measurement method. The optical attenuation investigation found that the attenuation ratio of two wavelengths of light appear to approximate the water content of grease samples with an acceptable coefficient of determination. Additionally, aged and oxidized grease were measured as well and were not found to affect the measurement results. The dielectric method uses the temperature dependence on the dielectric properties of water-contaminated grease to approximate the water content of the grease samples. An additional parameter of incomplete fill/coverage of the sensor has been investigated as a prestudy. Both methods were found to provide measurements of water content in the prepared grease samples (ranging from 0.22% to 5.5% added water). The dielectric measurement is likely going to be better for applications requiring the possibility of measuring a larger bulk of the grease within the bearing. It shows promise for providing an accurate and robust system for monitoring grease condition as well as the amount of grease contained. The optical measurement will likely provide additional information; however, it will only measure small point samples within the bearing instead of the larger bulk. This could be of use though, because the sensors could be small (in the several millimeter scale) and could measure where water damage is determined to be most important to detect at.

Conformal contacts like those found in journal or inclined slider bearings are widely encountered in various types of machines from small engines to large turbines. These contacts involve convergent gaps that are used to separate the surfaces in relative motion and generate pressure in the lubricant film. The contacts have to carry a load while keeping friction as low as possible. Environmental and economic concerns require the machines to operate with minimal power loss. A number of design modifications have been proposed over the years in order to decrease bearing power consumption. There are indications that surface topography can have a significant and positive influence on hydrodynamic performance. Texturing of a load carrying surface is a process that would be beneficial in lubricated conformal contacts as it would be possible to obtain thicker films and reduced frictional losses. Textured lubricated contacts are analysed with Computational Fluid Dynamics (CFD) code through different geometries. The effects of the texture on hydrodynamic performance of the contact are investigated. For the simulations performed, the full Navier-Stokes equations are solved under steady-state conditions. The flow is taken to be laminar and two- dimensional. A journal bearing with several dimples created on the stationary part is firstly investigated. A realistic multiphase flow cavitation model is introduced and successfully validated. It is shown that the coefficient of friction can be reduced if dimples of suitable depth are introduced. This can be achieved either in the region of maximum hydrodynamic pressure for a bearing with high eccentricity ratio or just downstream of the maximum film for a bearing with low eccentricity ratio. A new effect of pressure build-up, generated by the surface texture, has been identified at low eccentricity ratios. This pressure build-up effect is more extensively investigated through the study of an inclined slider bearing with a texture located at the inlet part of the contact, i.e. just downstream of the maximum film. The governing mechanism at the origin of an optimum in load carrying capacity for a smooth slider bearing is analysed and the effects of the texture on the pressure build-up and load carrying capacity are explained. The energy received by the fluid from the moving wall is converted into pressure in the first part of the converging contact and into losses in the second part. Convergence ratio can be increased until the limit where flow recirculation begins to occur is reached in order to get the greatest pressure gradient. The texture appears to reach its maximum efficiency when its depth is such that the velocity profile is stretched at its maximum without incoming recirculating flow. Thus, the wall profile shape controlling the velocity profile can be optimized for many hydrodynamic contacts. For such contacts, heat is usually produced due to shearing of the flow and the lubricant is subjected to temperature variations. Since the dynamic viscosity of the lubricant is temperature dependent, variation of the viscosity as well as frictional losses and load carrying capacity is expected. Thermal effects are analysed for different shear rates in this inlet textured slider bearing. Shear losses and subsequent heating reduce load carrying capacity compared with isothermal conditions. Texture has a positive effect in a parallel surface contact when thermal effects are considered. It has been found that for the different convergence ratios considered, the texture enables the sustaining of a load only until a certain critical shear rate is reached. This critical shear stress depends on a number of factors such as the convergence ratio and lubricant parameters including the viscosity-temperature coefficient and the reference dynamic viscosity. / <p>Godkänd; 2007; 20070320 (ysko)</p>

Rail grinding has been employed since the 1980s in maintaining optimal rail profile as well as in the elimination of surface defects such as corrugations and head-checks. Likewise, the wheel sets also require re- turning to remove surface defects and restore the desired profile. The influence of surface roughness in the wheel/rail contact has been a concern for railway owners since the introduction of rail grinding as a maintenance strategy. Presently, there are no scientifically derived guidelines regarding the surface topographies of ground rails and re-turned wheels. There is thus a need to establish well defined guidelines regarding the surface topographies for new surfaces on the rails and wheels in order to minimize grinding cost/time and improve wheel/rail performance. This thesis concerns the influence of surface roughness of wheel/rail surfaces on running-in behaviour, wear, friction and resultant surface damage. The results presented in this thesis are based on both field measurements and experimental simulations in the laboratory. A two-disc rolling/sliding test machine has been used in the experimental work to simulate the wheel/rail contact. The test specimens were manufactured from actual wheel/rail parts. The maching/finishing parameters were chosen in such a way as to obtain different surface roughness on the test specimens. A Design of Experiment approach (DOE) has been used to conduct experiments and to analyse the results. Results obtained from the field measurements show that the surface roughness of a newly ground rail changes rapidly during the initial stages following grinding. It was also concluded that there is a considerable variation of the surface roughness of re-turned wheels depending on which workshop performed the turning operation. Experimental results show that the surface roughness of the test specimens in certain material pairs do influence wear, friction and resultant surface damage. There is also a significant difference in the tribological behaviour of tests run in dry conditions and those run with water lubrication. / <p>Godkänd; 2007; 20070820 (pafi)</p>

In this work, the tribological behaviour of different sealing elastomers has been studied. The influence of aging of a sealing elastomer in different lubricants on its tribological behaviour has been investigated. Tribological behaviour of sealing elastomers in dry condition and the mechanisms occurring in run-in period have been studied. Further studies pertaining to the influence of lubrication on the abrasive wear of a sealing elastomer have also been carried out. / <p>Godkänd; 2007; 20071128 (ysko)</p>

Interacting surfaces are found in mechanical systems and components. Since engineered surfaces are not perfectly smooth, only a fraction of the nominal surface area is actually in contact. This fraction is denoted as the real area of contact, Ar, and is formed by the sum of the contact spots between the two touching surfaces. If these contacting surfaces are sliding, then friction and wear occur in these actual contacts. Friction and wear may be controlled by lubrication: depending on the operating conditions different types of lubrication regime exist. When the surfaces are completely separated by the fluid film and load is carried by hydrodynamic action, contacts operate in hydrodynamic regime. When the load is carried by the lubricating fluid and asperity contact, the regime becomes mixed lubrication. In boundary lubrication, surfaces are in contact and the load is carried by surface asperities. In many cases this is the critical lubrication regime that governs the life of the components. Due to the complexity of thin film boundary lubrication, design of lubricated interfaces is still a trial-and-error process. The mechanism of formation and rupture of oxide layers and boundary layers is not completely known and a reliable model for rough surfaces in boundary lubrication is currently lacking. This study focuses on boundary lubrication regime: the effect of surface roughness on the real area of contact is investigated and a numerical model for the sliding interaction between two asperities in sliding contact is developed. Numerical simulations of normal, dry, friction free, linear elastic contact of rough surfaces are performed. A variational approach is followed and the FFT-technique is used to speed up the numerical solution process. Five different steel surfaces are measured using a Wyko optical profilometer and several 2-D profiles are taken. The real area of contact and the pressure distribution over the contact length are calculated for all the 2-D profiles. A new slope parameter is defined. An artificial neural network is applied to determine the relationship between the roughness parameters and the real area of contact. Boundary lubrication mechanism is usually controlled by the additives present in the oil that form low friction, protective layers on the wearing surfaces. Chemical reactions between the lubricant molecules and the asperity surface may take place. These reactions are activated by certain values of pressure and temperature. Fundamental research on the influence of surface roughness on contact conditions is hence required and is a key factor in understanding the wear mechanism in boundary lubrication condition since pressure distribution, shear stresses, frictional heating, mechanical wear highly depends on surface topography. Modelling boundary lubrication requires knowledge in many fields: contact mechanics, thermodynamics, surface chemistry etc, thus different sub-models interacting each other must be created. It is complicated and may be not feasible within a foreseeable time period to take into account all the different parameters and evaluate them. Artificial intelligence is a way to overcome the problem and determine the relationship between input parameters and desired outputs. An elasto-plastic analytical model is used to determine the variation of pressure distribution and shear stress during the collision process of two asperities in sliding contact. The outputs of the elasto-plastic model are inputs of the thermal model that calculates the temperature rise during the collision process. The desorption of the adsorbed layer is determined by using existing adsorption theories and finally the probability of wear is computed at each time step of the collision process. Different results obtained using different adsorption theories and different input parameters are compared. / <p>Godkänd; 2008; 20080512 (ysko)</p>