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The threshold condition for leakage inception is of great interest to many engineering applications, and it is essential for seal design. In the current study, the leakage threshold is studied by means of a numerical method for a mechanical contact problem between an elastic bi-sinusoidal surface and a rigid flat surface. The coalesce process of the contact patches is first investigated, and a generalized form of solution for the relation between the contact area ratio and the average applied pressure is acquired. The current study shows that the critical value of the average applied pressure and the corresponding contact area required to close the percolation path can be represented as a power law of a shape parameter, if the effect of the hydrostatic load from the pressurized fluid is ignored. With contact patches merged under a constant applied load, the contact breakup process is investigated with elevated sealed fluid pressure condition, and it is shown that the leakage threshold is a function of the excess pressure, which is defined as a ratio between the average applied pressure and the critical pressure under dry contact conditions. Validerad;2023;Nivå 2;2023-03-20 (joosat);Funder: Vetenskapsrådet (2020-03635, 2019-04293)Licens fulltext: CC BY License

In cross-country skiing the time difference between a race winner and the person coming second is typically very small. Since much of the energy is spent on overcoming resistive forces, a relatively small reduction of these can have a significant impact on the results. The resistive forces come partly from the friction in the tribological interface, between the ski and the snow, and as with many tribological applications the characterisation of its origin, plays an important role in determining the frictional properties. Also in cross-country ski friction, there are several scales impacting the frictional performance, with the major contributors being the ski-camber profile and ski-base structure. Macro-scale measurements of the ski's camber profile under load, are often used to determine how adequate the ski is for a specific condition. The characteristic properties usually obtained are, the force required to collapse the ski to a certain camber height, the topography of the kick-wax zone, and by simple means a determined lengths of the frictional interface, i.e., the apparent contact length. To this date, there are some mathematical models, but there is no robust way of determining the macro-scale contact properties between a cross-country ski and a counter surface using simulations. In the present paper an Artificial neural networks (ANN) is trained to predict the ski-camber profile for various loads placed at different positions, and a well established deterministic approach is used to simulate the contact between the ANN-predicted ski-camber profile and a linearly elastic body with a flat surface, representing the snow. The results suggest that this method is feasible for the determination of the apparent contact characteristics of different skis. Moreover, we show that the apparent contact area does not linearly depend on the load, and that the elastic properties of the counter surface also has a large impact on the apparent contact area and the average apparent contact pressure.

Of the medals awarded at the 2022 Winter Olympics in Beijing, 24% were for events involving cross-country skiing, the biathlon and Nordic combined. Although much research has focused on physiological and biomechanical characteristics that determine success in these sports, considerably less is yet known about the resistive forces. Here, we specifically describe what is presently known about ski-snow friction, one of the major resistive forces. Today, elite ski races take place on natural and/or machine-made snow. Prior to each race, several pairs of skis with different grinding and waxing of the base are tested against one another with respect to key parameters, such as how rapidly and for how long the ski glides, which is dependent on ski-snow friction. This friction arises from a combination of factors, including compaction, plowing, adhesion, viscous drag, and water bridging, as well as contaminants and dirt on the surface of and within the snow. In this context the stiffness of the ski, shape of its camber, and material composition and topography of the base exert a major influence. An understanding of the interactions between these factors, in combination with information concerning the temperature and humidity of both the air and snow, as well as the nature of the snow, provides a basis for designing specific strategies to minimize ski-snow friction. In conclusion, although performance on “narrow skis” has improved considerably in recent decades, future insights into how best to reduce ski-snow friction offer great promise for even further advances.

In this work, I address challenges of situated alienation from people and place. Using interaction design for placemaking, light is shed on a design space of social places with opportunities for planned and spontaneous activities to be done alone, with known people or with strangers. In research through design, four conceptual design instances were created, drawing from first-person and participatory perspectives, to unpack potentials for engagement and considerations for encompassing respect (meaning vigilant of neoliberal capitalist and masculine power relations). I contribute with sensitizing questions making interaction design aspects more accessible for designers entering this public design space. Detta arbete fokuserar på utmaningar om platsbaserad främlingskap från människor och platsen ifråga. Interaktionsdesign används här för placemaking, där en designrymd för sociala platser med möjligheter för spontana och planerade aktiviteter att utföra ensam, med vänner eller med främlingar utforskas. Genom en research through design-metodik med förstapersons- och participatory-perspektiv skapades fyra designkoncept som användes för att tydliggöra potentialer för engagemang och omtanke för allomslutande respekt (vilket berör neoliberala kapitalist och maskulina maktrelationer). Jag bidrar med känsliggörande frågor som gör interaktionsdesignsaspekter mer tillgängliga för designers som ger sig i kast med denna publika designrymd.

A comparative study between a conventional- and leading edge grooved (LEG) tilting pad journal bearing (TPJB) segment is performed. The developed model uses the Shear Stress Transport (SST) turbulence model, coupled with the energy equation and a partial differential equation for the fluid domain mesh displacement to predict the thermal flow characteristics. Instead of using an effective boundary condition to determine the inlet temperature of the LEG pad and excluding the additional LEG portion, as is common practice, the whole geometry of the LEG is modeled. Several sizes of the LEG portion is investigated and it is shown to have quite a small influence on pressure, temperature, film thickness and turbulence intensity. Moreover, the results also show that the conventional pad gives rise to higher levels of turbulence in the mid plane compared to its LEG counterpart, while the latter has a marginally higher value of turbulence when the volume average value is computed. The maximum value of turbulence is however present in the conventional model.

Godkänd; 2016; 20160620 (sodmar)

In this chapter we will present a derivation of a mathematical model describing how cavitation influences the pressure distribution in a thin lubricant film between two moving surfaces. The main idea in the derivation is to first describe the influence of cavitation on the mass flow and thereafter using a conservation law for the mass. This leads to a nonlinear system with two complementary variables: one is the pressure distribution and the other is related to the density, i.e. a nonlinear complementarity problem (NLCP). The proposed approach is used to derive a mass conserving cavitation model considering that density, viscosity and film thickness of the lubricant depend on the pressure. To demonstrate the applicability and evaluate the proposed model and the suggested numerical implementation, a few model problems are analysed and presented.

This composition investigates the challenges and problems that Domnarvets workers union had to relate to under its pioneering time 1890-1891. In my investigation I used the protocols from the union meetings where their interests where discussed. My purpose is to reveal these problems, and I have selected a couple of them in this composition. The issues are the harassments from the management and the difficulties in obtain place for their meetings. The relation to the state church, revivalist movement and the temperance movement and the difficulties of enthuse the workers in Domnarvet to the union. Finally I have been looking at the union´s relation to the major working class issues at the time, the eight hour day and the voting right. My method is to analyze the protocols of the meetings and point out the issues that I find interesting to my investigation. I have been looking for strategies from the union and for political ideologies in the protocols. I have also had an open eye for arguments and ideas that showed the unions stand in the issues I was interested in. The results are that these workers were not hesitating to do things that could anger the management and attempted to obtain places for their meetings. They did delete the religious agenda at the meeting after a while. The major working class issues of eight hour day and voting right disappeared after harassments from the management. But the management did finally get the union on its knee, at least for this time.

I rapporten har vi förklarat vilka problem som kan uppstå med dagens teknik och vilka eventuella lösningar som man kan förbättra med tiden. Med hjälp av Trafikverket har vi genomfört detta examensarbete. Vi hade fått tydliga direktiv från Trafikverket gällande examensarbetets syfte. Det gjorde det enkelt för oss att avgränsa arbetet efter de riktlinjer som var angivna och möjliga att genomföra. Studiens syfte var att förstå varför det inte går ge ut relevant trafikinformation. I dagsläget har man tekniken för ett väl fungerande system. Ett system där man enkelt kan få realtidsinformation i samband med trafiken, vägarbeten och eventuella hinder. I rapporten har vi även sammanfattat alla navigationssystem som man kan ha användning av som trafikant. Vi har gjort en omvärldsanalys på hur man i andra länder ger ut trafikinformation och hur de står sig jämtemot Sveriges trafikinformationssystem. För vårt examensarbete har vi använt oss av diverse olika rapporter och intervjuer. Detta tillsammans med personer som har kunskap inom området. Vi har även använt oss av åtskilliga hemsidor för att inhämta information. Rekommendationer för examensarbetet kommer att beskrivas genom fem teman. I rapporten har vi utfört en mängd olika intervjuer som vi sammanställt till teman. Teman var utformade efter det vi kände var mest relevant från intervjuerna. Våra teman speglar bilden av vad vi har lagt vikt med detta examensarbete. In this report, we have explained the problems that may occur with today's technology and what possible solutions to improve with time. With the help of the Swedish Transport Administration, we have implemented this thesis. We got the clear directions from the Swedish Transport Administration regarding purpose of this thesis. This made it easy for us to delineate our work after the guideline that was definer. The study's purpose was to try to understand why you can´t give out the relevant traffic information. Today we have the technology create a well smooth operation system. A system where you can easily get real-time information related to traffic, road works and obstructions. In this report we have summarized all the navigation system that you could use as a road user. We have done an analysis of how other countries give out their traffic information and how good they are against the Swedish traffic information system. For our thesis we have used various of different reports and interviews. The interviews have been with people who have knowledge in the field. We have also used numerous websites to gather information. Recommendations for the thesis will be described through five themes. In this report, we have conducted a variety of interviews that we have compiled for themes. Themes were designed for what we felt was most relevant from the interviews. Our themes are a mirror image of what we thought was the most relevant part in our thesis.

I rapporten har vi förklarat vilka problem som kan uppstå med dagens teknik och vilka eventuella lösningar som man kan förbättra med tiden. Med hjälp av Trafikverket har vi genomfört detta examensarbete. Vi hade fått tydliga direktiv från Trafikverket gällande examensarbetets syfte. Det gjorde det enkelt för oss att avgränsa arbetet efter de riktlinjer som var angivna och möjliga att genomföra. Studiens syfte var att förstå varför det inte går ge ut relevant trafikinformation. I dagsläget har man tekniken för ett väl fungerande system. Ett system där man enkelt kan få realtidsinformation i samband med trafiken, vägarbeten och eventuella hinder. I rapporten har vi även sammanfattat alla navigationssystem som man kan ha användning av som trafikant. Vi har gjort en omvärldsanalys på hur man i andra länder ger ut trafikinformation och hur de står sig jämtemot Sveriges trafikinformationssystem. För vårt examensarbete har vi använt oss av diverse olika rapporter och intervjuer. Detta tillsammans med personer som har kunskap inom området. Vi har även använt oss av åtskilliga hemsidor för att inhämta information. Rekommendationer för examensarbetet kommer att beskrivas genom fem teman. I rapporten har vi utfört en mängd olika intervjuer som vi sammanställt till teman. Teman var utformade efter det vi kände var mest relevant från intervjuerna. Våra teman speglar bilden av vad vi har lagt vikt med detta examensarbete. In this report, we have explained the problems that may occur with today's technology and what possible solutions to improve with time. With the help of the Swedish Transport Administration, we have implemented this thesis. We got the clear directions from the Swedish Transport Administration regarding purpose of this thesis. This made it easy for us to delineate our work after the guideline that was definer. The study's purpose was to try to understand why you can´t give out the relevant traffic information. Today we have the technology create a well smooth operation system. A system where you can easily get real-time information related to traffic, road works and obstructions. In this report we have summarized all the navigation system that you could use as a road user. We have done an analysis of how other countries give out their traffic information and how good they are against the Swedish traffic information system. For our thesis we have used various of different reports and interviews. The interviews have been with people who have knowledge in the field. We have also used numerous websites to gather information. Recommendations for the thesis will be described through five themes. In this report, we have conducted a variety of interviews that we have compiled for themes. Themes were designed for what we felt was most relevant from the interviews. Our themes are a mirror image of what we thought was the most relevant part in our thesis.

Typically engineering surfaces are characterized with traditional roughness parameters that perform some type of height averaging over the surface. Although these parameters describe the topography of the surface none of them necessarily describe the ability of the surface to carry out its function in a tribological contact. In this study an ICE cylinder liner has been investigated.The traditional Rk parameters (based on the Abbott curve) have been calculated as well as functional ‘flow factors’which modify the Reynolds equation to incorporate the effects of surface topography.To calculate flow factors the homogenization technique has been implemented and a full 3D contact mechanics model has been incorporated so that surface functionality in mixed lubrication can be studied. Furthermore, the cylinder liner surface has been measured with both white light interferometery and an AFM so that the effect of measuring technique on roughness and functional parameters can be investigated. Godkänd; 2011; 20111213 (spencer)

The collision of cylindrical asperities is simulated by means of a commercial multiphysics software in this paper. The model combines a computational structure mechanics approach with a contact algorithm. Numerical results are first compared to classical Hertzian theory. Effects of the bulk material under the mating surfaces have been included in the simulation. Materials of top and bottom surfaces have been assigned different properties. Development of plastic deformation and friction are presented along the process of collision. Strain hardening is included in the elastic-plastic deformation. The effect of interference change and friction coefficient variation on deformation and friction has been studied. Deformed shape and subsurface residual stress in asperity are output parameters from this study. Godkänd; 2010; Bibliografisk uppgift: CD-ROM; 20100629 (ysko)

Godkänd; 2011; 20110120 (almqvist)

Godkänd; 2010; Bibliografisk uppgift: Invited presentation; 20100914 (rola)

By using a deterministic FFT-accelerated contact mechanical tool to calculate pressure and elastic-plastic deformation, a wear model is utilized to simulate the time dependent wear from a sphere on at contact. The results of the simulated wear are compared to experimental results form a SRV ball on disk tribometer, from which worn surfaces are optically measured. The conditions of the simulation and the experiments are independently adjusted to match. Agreement and diversity shows upon the usefulness and limitation of wear modeling of this type. Godkänd; 2010; Bibliografisk uppgift: CD-ROM; 20100629 (ysko)

During the operation of hydrodynamically lubricated devices a fully formulated lubricant has the ability to form layers at the surfaces. A friction modifier's task is to adjust the interaction between lubricant and the surface so that friction is lowered. An antiwear additive creates a protective layer on the surface and this definitely influence the performance of the lubricated device. To gain fundamental understanding, models that address the modified liquid - solid interaction due to the formation of layers, but also models that may be used to study the effects of layers already formed on the contacting surfaces are required. In this paper, two non-Newtonian lubricant rheology models that may be used to simulate reacted layers resembling those created by lubricant additives are adopted for the simulation of the piston ring - cylinder liner lubrication problem. The possibility of layer to layer interaction, which is likely to occur in the convex conjunction between the ring and the liner, is considered and this extends the models found in the literature. The effects induced by this type of layering are studied by using a modified Reynolds' equation where the coefficients have been corrected with factors that accounts for the layer properties. This enables, effectively, studies of layers resembling those created by lubricant additives during the operation of the lubricated conjunction between a piston ring and a cylinder liner. Godkänd; 2009; 20091201 (almqvist)

Godkänd; 2007; 20070905 (ysko)

Tribology is a multidisciplinary field defined as the science and technology of interacting surfaces in relative motion, and embraces the study of friction, wear and lubrication. A typical tribological application is the rolling element bearing. Tribological contacts may also be found in other types of bearings, cam-mechanisms, gearboxes and hydraulic systems. Examples of bearings inside the human body are the operation of the human hip joint and the contact between teeth during chewing. To fully understand the operation of this type of application one has to understand the couplings between the lubricant fluid dynamics, the structural dynamics of the bearing material, the thermodynamical aspects and the resulting chemical reactions. This makes modeling tribological applications an extremely delicate task. Because of the multidisciplinary nature, such theoretical models lead to mathematical descriptions generally in the form of non-linear integro-differential systems of equations. Some of these systems of equations are sufficiently well posed to allow numerical solutions to be carried out, resulting in accurate predictions on performance. In this work, the influence on performance of a surface microscopical nature, the surface roughness, in contact interfaces between different types of machine element components is the subject of study. An example is the non-conformal lubricated contact between one of the rollers and the inner ring in a rolling element bearing. The tribological contact controlling the operation of the human hip joint is also very similar to this. Another example of a non-conformal contact occurs when driving on rainy roads, where the hydrodynamic action of the water separates the tire. To enable investigations of these types of problems, different theoretical models were studied; for the selected model, a numerical solution technique was developed within this project. This model is based on the Reynolds equation coupled with the film thickness equation. The numerical solution technique involves a multilevel technique to facilitate the solution process. Results presented in this thesis, utilizing this approach, study elementary surface features such as ridges and indentations passing each other inside the lubricated conjunction. The Reynolds equation is derived under the assumptions of thin fluid film and creeping flow, and considers in its most general form shear thinning of the lubricant. This type of equation describes the hydrodynamic action of the lubricant flow and may be used when the interfaces consist of either conformal or non-conformal conjunctions. Examples of applications having conformal interfaces are thrust- and journal- bearings or the contact between the eye and a (optical) contact lens. In such types of applications the load carried by the interface is distributed over a fairly large area that under certain circumstances helps to prevent mechanical deformation of the contacting surfaces. Such applications are said to operate in the hydrodynamic lubrication (HL) regime. Lubricant compressibility and cavitation are important aspects and have received some attention. However, the main objective when modeling HL has been to investigate and develop methods that enable the influence of surface roughness to be to be studied efficiently. Homogenization is a rigorous mathematical concept that when applied to a certain problem may be regarded as an averaging technique as well as it provides information about the induced effects of local surface roughness. Homogenization inflicts no restrictions on the surface roughness representation other than the representative part of the chosen surface roughness being assumed periodically distributed and of course the assumptions of thin film flow made through the Reynolds equation. The homogenization process leads to a two sets of equations one for the local scale describing surface roughness, scale and one for the global scale describing application geometry. The unequivocally determined coefficients of the global problem, which may be regarded as flow factors, are obtained through the solution of local problems. This makes homogenization an eminent approach to be used investigating the influence of surface roughness on hydrodynamic performance. In the present work, homogenization has been used to derive computationally feasible forms of problems originating from incompressible and compressible Reynolds type equations that describe stationary and unstationary flows in both cartezian and cylindrical co-ordinates. This technique enables simulations of surface roughness induced effects when considering surface roughness descriptions originating from measurements. Moreover, the application of homogenization facilitates the interpretation of results. Numerical investigations following the homogenization process have been carried out to verify the applicability of homogenization in hydrodynamic lubrication. Homogenization has also been shown here to enable efficient analysis of rough hydrodynamically lubricated problems. Also of note, in connection to the scientific contribution within tribology, collaboration with a group in applied mathematics has lead to the development of novel techniques in that area. These ideas have also been successfully applied, with some results presented in this thesis. At start-ups, the contact in a rolling element bearing could be both starved and drained from lubricant. In this case the hydrodynamic action becomes negligible in terms of load carrying capacity. The load is carried exclusively by surface asperities, the tribo film, or both. This is hereby modeled as the unlubricated frictionless contact between rough surfaces, i.e. a contact mechanical approach. A variational principle was used in which the real area of contact and the contact pressure distribution minimize the total complementary potential energy. The material model is linear elastic-perfectly plastic and the energy dissipation due to plastic deformation is accounted for. The numerics of this contact mechanical approach involve the fast Fourier transformation (FFT) technique in order to facilitate the solution process. Investigation results of the contact mechanics of realistic surfaces are presented in this thesis. In this investigation the variation in the real area of contact, the plasticity index and some surface roughness parameters due to applied load were studied. Godkänd; 2006; 20061116 (pafi)

In the field of tribology, there are numerous theoretical models that may be described mathematically in the form of integro-differential systems of equations. Some of these systems of equations are sufficiently well posed to allow for numerical solutions to be carried out resulting in accurate predictions. This work has focused on the contact between rough surfaces with or without a separating lubricant film. The objective was to investigate how surface topography influences contact conditions. For this purpose two different numerical methods were developed and used. For the lubricated contact between rough surfaces the Reynolds equation were used as a basis. This equation is derived under the assumptions of thin fluid film and creeping flow. In highly loaded, lubricated, non- conformal contacts of surfaces after running-in, the load concentration no longer results in plastic deformations, however large elastic deformations will be apparent. It is the interaction between the hydrodynamic action of the lubricant and the elastic deformations of the surfaces that, in certain applications, enable the lubricant film to fully separate the surfaces. This is commonly referred to as full film elastohydrodynamic (EHD) lubrication. Typical machine elements that operates in the full film EHD lubrication (FL) regime include rolling element bearings, cams and gears. Unfortunately, a cost effective way of machining engineering surfaces seldom results in a surface topography that influence contact conditions in the same way as a surface after running-in. Such topographies may prevent the lubricant from fully separating the surfaces because of deteriorated hydrodynamic action. In this case the applied load is carried in part by the lubricant and in part by surface asperities and/or surface active lubricant additives. This could also be the case in lubricant starved contacts, which is a common situation in not only grease lubricated contacts but also in many liquid lubricated contacts, such as high speed operating rolling element bearings. The load sharing between the highly compressed lubricant and the surface and/or surface active lubricant additives is the reason why this lubrication regime is most commonly referred to as mixed EHD lubrication (ML). Machine elements that while running operate in the FL regime may experience a transition into the ML regime at stops or due to altered operating conditions. It is not possible to simulate direct contact between the surfaces using a numerical method based on Reynolds equation. A parameter study, of elementary surface features passing each other inside the EHD lubricated conjunction, was performed. The results obtained, even though no direct contact could be simulated, does indicate that a transition from the FL to the ML regime would occur for certain combinations of the varied parameters. At start-ups, the contact in a rolling element bearing could be both starved and drained from lubricant. In this case the hydrodynamic action becomes negligible in terms of load carrying capacity. The load is carried exclusively by surface asperities and/or surface active lubricant additives. This regime is referred to as boundary lubrication (BL). Operation conditions could also make both FL and ML impossible to achieve, for example, in the case in a low rpm operating rolling element bearing. The BL regime is in this work modeled as the unlubricated frictionless contact between rough surfaces, i.e., a dry contact approach. A variational principle was used in which the real area of contact and contact pressure distribution are those which minimize the total complementary energy. A linear elastic-perfectly plastic deformation model in which energy dissipation due to plastic deformation is accounted for was used. The dry contact method was applied to the contact between four different profiles and a plane. The variation in the real area of contact, the plasticity index and some surface roughness parameters due to applied load were investigated. The surface roughness parameters of the profiles differed significantly. Godkänd; 2004; 20070128 (ysko)