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  • 1.
    Ràfols, Francesc Pérez
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Generating randomly rough surfaces with given height probability distribution and power spectrum2019Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 131, s. 591-604Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work we present a simple method to generate surface topography. The main advantage of the presented method as compared with those available in the literature is that the power spectrum and the height probability distribution can be specified independently. In this article we present the method and show its versatility by generating surface topographies with three different height probability distributions: the Weibull distribution, a bimodal distribution and a distribution containing a delta function that represents worn surfaces. The MATLAB-code we used to generate the numerical examples are also provided to the reader.

  • 2.
    Ernens, Dennis
    et al.
    Shell Global Solutions International. University of Twente.
    Ràfols, Francesc Pérez
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Van Hoecke, Dennis
    Ocas N. V..
    Roijmans, Roel F. H.
    Shell Global Solutions International.
    van Rie, Egbert J.
    Shell Global Solutions International.
    Vande Voorde, John B. E.
    Ocas N.V..
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Bas de Rooij, Matthias
    University of Twente.
    Roggeband, Serge Mathieu
    Shell Global Solutions International.
    van Haaften, Willem Maarten
    Shell Global Solutions International.
    Vanderschueren, Marc
    Ocas N.V..
    Thibaux, Phillipe
    Ocas N.V..
    Pasaribu, Henry Rihard
    Shell Global Solutions International.
    On the Sealability of Metal-to-Metal Seals With Application to Premium Casing and Tubing Connections2019Ingår i: SPE Drilling & Completion, ISSN 1064-6671, E-ISSN 1930-0204Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metal-to-metal seals are used in connections of casing and tubing in oil and gas wells. This paper describes the mechanisms of sealing metal-to-metal seals as investigated using an experimental setup and a stochastic numerical sealing model. Experiments were conducted for a variety of thread compounds and applied pin/box surface coatings. The results were used to validate a stochastic numerical sealing model for sealability. The model couples a contact-mechanics model with a flow model and takes into account the influence of all the surface-topography features by introducing the concept of seal permeability. Once validated, the model was used together with the experimental results to better understand the sealing mechanisms of metal-to-metal seals.

    The sealing configuration is a face seal with an 80-mm roundoff radius on one face pressing against a flat on the other face. The face-seal specimens were manufactured from P110 tubing to ensure material properties that are representative for casing or tubing. The test setup used is designed for investigating only the metal-to-metal seal of the connection. The setup can perform rotary sliding under constant load to simulate surface changes during makeup and subsequently perform a leakage test. The sealing limit is determined by applying 700-bar fluid pressure and then gradually reducing the normal force until leakage is observed. The data are subsequently used to validate the previously published stochastic numerical sealing model.

    The results indicate a strong dependence on the type of thread compound used for the onset of leakage. The thread compound affects the amount of wear and thus changes the surface topography of the interacting surfaces. It is shown that the stochastic numerical sealing model is capable of predicting the onset of leakage within the experimental accuracy. The model shows further that certain surface topographical features improve the sealing performance. In particular, a surface manufactured by turning on a lathe that is in contact with, for instance, a smooth shot-blasted surface topography leads to highly localized contact areas, which in turn yield the best sealing performance.

  • 3.
    Ernens, Dennis
    et al.
    Shell Global Solutions International BV. University of Twente.
    Ràfols, Francesc Pérez
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Van Hoecke, Dennis
    OCAS NV.
    Roijmans, Roel F. H.
    Shell Global Solutions International BV.
    van Riet, Egbert J.
    Shell Global Solutions International BV.
    Voorde, John Vande
    OCAS NV.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Bas de Rooij, Matthijn
    University of Twente.
    Roggeband, Serge Mathieu
    Shell Global Solutions International BV.
    Van Haaften, Willem Maarten
    Shell Global Solutions International BV.
    Vanderschueren, Marc
    OCAS NV.
    Thibaux, Phillipe
    OCAS NV.
    Pasaribu, Henry Rihard
    Shell Global Solutions International BV.
    On the Sealability of Metal-to-Metal Seals with Application to Premium Casing Connections2019Konferensbidrag (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    Metal-to-metal seals are used in connections of casing in oil and gas wells. This paper describes the mechanisms of sealing of metal-to-metal seals as investigated using an experimental set-up and a sealability model. Experiments were conducted for a variety of thread compounds and applied pin/box surface coatings. The results were used to validate a numerical model for sealability. The stochastic model couples a contact mechanics model with a flow model and takes the influence of all the surface topography features into account. Once validated, the model was used together with the experimental results to explain the sealing mechanisms of metal-to-metal seals. The sealing configuration is a face seal with an R=80 mm round-off radius pressing against a flat. The face seal specimens were manufactured from P110 tubing. The used test set-up is designed for investigating only the metal-to-metal seal of the connection. The set-up can carry out rotary sliding under constant load to simulate surface evolution during make-up and subsequently perform a leakage test. The sealing limit is determined by applying 700 bar fluid pressure and then gradually reducing the normal force until leakage is observed. The data is subsequently used to validate a previously published model. The results indicate a strong dependence of the type of thread compound used on the onset of leakage. The thread compound affects the amount of wear and thus changes the surface topography of the interacting surfaces. It is shown that the sealability model is capable to predict the onset of leakage within the experimental accuracy. The model shows further that certain surface topographical features improve the sealing performance. Namely, a turned against a flat surface topography leads to highly localized contact areas, which in turn yields the best sealing performance. The combination of experimental data with the validated model leads to much deeper insights for the sealing mechanisms than what could be obtained using either on their own.

  • 4.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Ràfols, Francesc Pérez
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Scientific Computing with Applications in Tribology: A course compendium2019Övrigt (Övrigt vetenskapligt)
    Abstract [en]

    This compendium comprises models and numerical solution procedure for tribological interfaces. It describes the tribological contact and the classical lubrication regimes. A thorough derivation of the Reynolds equation, governing the fluid pressure, from the Navier-Stokes momentum equations and the continuity equation for conservation of mass, is presented along with its analytical solution for the infinitely wide linear slider bearing.

    The compilation of the compendium was conducted by the first author during his tenure as Professor at the Division of Machine Elements, Department of Engineering Sciences and Mathematics, Luleå University of Technology and by the second author during his tenure as a postdoctoral researcher at the same division.

    Although the compilation of this text is the work solely of the authors, the models and solution procedure presented herein is joint development of many good colleagues and co-authors. Our sincere gratitude is extended towards them all.

  • 5.
    Ràfols, Francesc Pérez
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    An Enhanced Stochastic Two-Scale Model for Metal-to-Metal Seals2018Ingår i: Lubricants, ISSN 2075-4442, Vol. 6, nr 4, artikel-id 87Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Leakage in static metal-to-metal seals is predominantly determined by the topography of the contacting surfaces. The topography consists of features that span the entire range from its carefully engineered geometry down to micro-sized surface asperities. The mesh density necessary to fully resolve all the features, in this large span of length scales, generates too many degrees of freedom for a direct numerical approach to be applicable. Some kind of sophistication, either incorporated in the mathematical model or in the numerical solution procedure or even a combination of both is therefore required. For instance, in a two-scale model, the geometrical features can be addressed in the global-scale model, while the features belonging to length scales smaller than a given cut-off value are addressed in the local-scale model. However, the classical two-scale approaches do not explicitly address the stochastic nature of the surfaces, and this has turned out to be a requirement in order to obtain quantitative predictions of leakage in metal-to-metal seals. In this work, we present a continued development of an already existing two-scale model, which incorporates a stochastic element. The novelty lies in the way we characterise the permeability at the local scale and how this is used to build a more efficient and useful approach

  • 6.
    Vakis, A.I.
    et al.
    Advanced Production Engineering, Engineering and Technology Institute Groningen, Faculty of Science and Engineering, University of Groningen.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Ciavarella, M.
    Politecnico di Bari, V. le Gentile 182, 70125 Bari, Italy.
    Modeling and simulation in tribology across scales: An overview2018Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 125, s. 169-199Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and micro-scales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions.

  • 7.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    MULTISCALE MODELLING OF ELASTOHYDRODYNAMIC TILTED-PAD BEARINGS: A METAMODEL APPROACH2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    6th European Conference on Computational Mechanics (ECCM 6)7th European Conference on Computational Fluid Dynamics (ECFD 7)11 – 15 June 2018, Glasgow, UK 

    MULTISCALE MODELLING OF ELASTOHYDRODYNAMIC TILTED-PAD BEARINGS: A METAMODEL APPROACH 

    G. N. de Boer1, A. Almqvist2, L. Gao3, R. W. Hewson4 and H. M. Thompson

    1 School of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT, UK, g.n.deboer@leeds.ac.uk, https://engineering.leeds.ac.uk/staff/1036/Dr_Greg_de_Boer 

    2 Division of Machine Elements, Luleå University of Technology, E837a Luleå, Sweden, a.almqvist@ltu.se, https://www.ltu.se/staff/a/almqvist 

    3 Department of Aeronautics, Imperial College London, London, SW7 2AZ, UK, leiming.gao@imperial.ac.uk, http://www.imperial.ac.uk/people/leiming.gao 

    4 Department of Aeronautics, Imperial College London, London, SW7 2AZ, UK, r.hewson@imperial.ac.uk, https://www.imperial.ac.uk/people/r.hewson 

    5 School of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT, UK, h.m.thompson@leeds.ac.uk, https://engineering.leeds.ac.uk/staff/140/Professor_Harvey_Thompson 

    Key Words: Elastohydrodynamic Lubrication; Surface Topography; Metamodelling; Moving Least Squares; Evolving Design of Experiments. 

    Elastohydrodynamic Lubrication (EHL) refers to the contact of two surfaces in relative motion under fully flooded conditions, pressure generated in the lubricant generates deformation of the bodies and this is coupled to determine a total load carrying capacity. In such contacts the size of surface topography and film thickness are of a similar order of magnitude and this therefore has a role in describing the phenomena. However the length scales associated with surface topography and the contact region are disparate and in order to model such effects authors have developed homogenisation based methods. 

    Recently the Heterogeneous Multiscale Methods (HMM) have been employed to study the problem. This has allowed the effects of micro-EHL to be explored and coupled into the macro-scale EHL problem. Fundamental to this is the separation of scales and periodicity applied at to simulations describing surface topography. de Boer [1] outlines a method for coupling the scales of the problem using Moving Least Squares metamodels to calculate flow factors. This was further used to optimise surface topographical features to produce the minimum possible coefficient of friction in an EHL contact [2]. This research focuses on the metamodelling approach of [1, 2] to explore more complex 3D titled-pad bearing geometries than have previously been investigated. The means by which the scales of the problem are coupled is complicated by an increase in the number of design variables. Additionally the choice of Design of Experiments and how this evolves with the solution procedure is vital to the accuracy of the approach. 

    REFERENCES 

    [1] de Boer G, Gao L, Hewson R, Thompson H. Heterogeneous Multiscale Methods for modelling surface topography in EHL line contacts. Tribol Int 2017, 113:262-278. 

    [2] de Boer G, Gao L, Hewson R, Thompson H, Raske N, Toropov V. A multiscale method for optimising surface topography in elastohydrodynamic lubrication (EHL) using metamodels. Struct Mulidisc Optim 2016, 54(3):483-497. 

  • 8.
    Pérez Ràfols, Francesc
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    On compressible and piezo-viscous flow in thin porous media2018Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 474, nr 2209, artikel-id 20170601Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    n this paper, we study flow through thin porous media as in, e.g. seals or fractures. It is often useful to know the permeability of such systems. In the context of incompressible and iso-viscous fluids, the permeability is the constant of proportionality relating the total flow through the media to the pressure drop. In this work, we show that it is also relevant to define a constant permeability when compressible and/or piezo-viscous fluids are considered. More precisely, we show that the corresponding nonlinear equation describing the flow of any compressible and piezo-viscous fluid can be transformed into a single linear equation. Indeed, this linear equation is the same as the one describing the flow of an incompressible and iso-viscous fluid. By this transformation, the total flow can be expressed as the product of the permeability and a nonlinear function of pressure, which represents a generalized pressure drop.

  • 9.
    Pérez-Ràfols, Francesc
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    van Riet, Egbert J.
    Shell Global Solutions International BV, Innovation, Research and Development.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    On the flow through plastically deformed surfaces under unloading: A spectral approach2018Ingår i: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 232, nr 5, s. 908-918Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study considers flow through the gap left between two surfaces during unloading, in other words, when an applied load is gradually reduced after loading to a state where plastic deformation occurs. In particular, the permeability of the gap is studied. It was found that a substantial reduction of the applied load is required before the permeability starts to increase significantly. The explanation for this phenomenon is given by the combination of components with different wavelengths present in the surface. Components with long wavelengths deform elastically and those with shorter wavelengths may also deform plastically. We found that plastic deformation acts to keep the permeability nearly constant at the beginning of the unloading and elastic spring-back is responsible for the rapid increase at lower loads. This principle constitutes a basis for the strategy that was developed in order to predict the load at which the rapid increase of permeability starts.

  • 10.
    Ràfols, Francesc Pérez
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Van Riet, Egbert J.
    Shell Global Solutions International BV, Innovation, Research and Development, Rijswijk, The Netherlands.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    On the loading and unloading of metal-to-metal seals: A two-scale stochastic approach2018Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, nr 12, s. 1525-1537Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During operation, the mating surfaces of a metal-to-metal seal typically undergo significant plastic deformation, which in turn can have beneficial effect on its performance. In previous studies, it has, for instance, been shown that plastic deformation can provide for better sealing during unloading. Those studies did, however, only consider flow through unrealistically small domains. Therefore, it is possible that this might be a size effect, which would not be apparent in a real situation with a much larger domain. In this paper, we develop a model which can handle real-sized seal domains at the same time as fine details of the surface topography. More precisely, we construct a two-scale model, in which the global scale represents the seal domain and where the influence of the fine details at the local scale are represented by a stochastic element. By means of this stochastic two-scale model, we show that the beneficial effect associated with the plastic deformation persists also when real-sized seal domains are considered.

  • 11.
    de Boer, Gregory
    et al.
    School of Mechanical Engineering, University of Leeds, Leeds, UK.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    On the Two-Scale Modelling of Elastohydrodynamic Lubrication in Tilted-Pad Bearings2018Ingår i: Lubricants, ISSN 2075-4442, Vol. 6, nr 3, artikel-id 78Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A two-scale method for modelling the Elastohydrodynamic Lubrication (EHL) of tilted-pad bearings is derived and a range of solutions are presented. The method is developed from previous publications and is based on the Heterogeneous Multiscale Methods (HMM). It facilitates, by means of homogenization, incorporating the effects of surface topography in the analysis of tilted-pad bearings. New to this article is the investigation of three-dimensional bearings, including the effects of both ideal and real surface topographies, micro-cavitation, and the metamodeling procedure used in coupling the problem scales. Solutions for smooth bearing surfaces, and under pure hydrodynamic operating conditions, obtained with the present two-scale EHL model, demonstrate equivalence to those obtained from well-established homogenization methods. Solutions obtained for elastohydrodynamic operating conditions, show a dependency of the solution to the pad thickness and load capacity of the bearing. More precisely, the response for the real surface topography was found to be stiffer in comparison to the ideal. Micro-scale results demonstrate periodicity of the flow and surface topography and this is consistent with the requirements of the HMM. The means of selecting micro-scale simulations based on intermediate macro-scale solutions, in the metamodeling approach, was developed for larger dimensionality and subsequent calibration. An analysis of the present metamodeling approach indicates improved performance in comparison to previous studies.

  • 12.
    Söderfjäll, Markus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Texture-induced effects causing reduction of friction in mixed lubrication for twin land oil control rings2018Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 232, nr 2, s. 166-178Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Piston rings are responsible for a major part of the frictional losses in a heavy-duty diesel engine. Such losses can be reduced by applying texture, such as dimples, on the cylinder liner surface. This paper investigates the effect of such texture on the friction between a land of the oil control ring and a textured cylinder liner via numerical simulation. A simulation model considering inertia and mixed lubrication together with a mass-conserving cavitation model is developed. The model is used to determine the dimple parameters that yield the lowest amount of friction for a specific oil control ring of a heavy-duty diesel engine

  • 13.
    Philip, Croné
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Thermal Turbulent Flow in Leading Edge Grooved and Conventional Tilting Pad Journal Bearing Segments: A Comparative Study2018Ingår i: Lubricants, ISSN 2075-4442, Vol. 6, nr 4, artikel-id 97Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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. 

  • 14.
    Shirzadegan, Mohammad
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A low degree of freedom approach for prediction of friction in finite EHL line contacts2017Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 115, s. 628-639Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A low degree of freedom (LDOF) approach for expedient prediction of friction in finite EHL line contact is presented. Friction prediction are in good agreement with existing results for all of the reference cases tested. With the present LDOF approach, friction predictions can be obtained thousands of times faster than if using a fully coupled FE-based model. It can, therefore be used to simulated the tribological contacts in multi-body dynamic (MBD) systems with millions of degrees of freedoms. The model was utilised to study edge stress concentrations due to roller tilt. The results confirmed that increasing the tilting angle increases the maximum pressure and shifts its location towards the edge of roller. An increase in total friction was also observed.

  • 15.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Fabricius, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Flow in thin domains with a microstructure: Lubrication and thin porous media2017Ingår i: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 1798, artikel-id 020172Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper is devoted to homogenization of different models of flow in thin domains with a microstructure. The focus is on applications connected to the effect of surface roughness in full film lubrication, but a parallel to flow in thin porous media is also discussed. Mathematical models of such flows naturally include two small parameters. One is connected to the fluid film thickness and the other to the microstructure. The corresponding asymptotic analysis is a delicate problem, since the result depends on how fast the two small parameters tend to zero relative to each other. We give a review of the current status in this area and point out some future challenges.

  • 16.
    Söderfjäll, Markus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Herbst, Hubert M.
    Scania CV AB, Södertälje.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Influence on friction from piston ring design, cylinder liner roughness and lubricant properties2017Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 116, s. 272-284Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The piston rings are responsible for a large portion of the fuel consumption in heavy duty diesel engines. In this work a high speed component test rig for evaluation of piston ring friction is used. A number of different piston rings and cylinder liners are evaluated based on their friction performance. Shear thinning of typical multi grade oil is investigated by comparing it to single grade oil. Experimental simulation of higher speeds by decreasing the viscosity is evaluated. A method for indication of effects on oil consumption, without combustion, for different oil control rings is presented. Finally, a numerical simulation model for the oil control ring is validated by comparing the friction predicted with the model to the experimental results

  • 17.
    Xi, Yinhu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement. Theory of Lubrication and Bearing Institute, Key Laboratory of Education Ministry for Modern Design and Rotor–Bearing System, Xi'an Jiaotong University.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Shi, Yijun
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Mao, Junhong
    Theory of Lubrication and Bearing Institute, Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System, Xi’an Jiaotong University, Xi’an.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Linear Complementarity Framework for 3D Steady-State Rolling Contact Problems Including Creepages with Isotropic and Anisotropic Friction for Circular Hertzian Contact2017Ingår i: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 60, nr 5, s. 832-844Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, the problem of 3D steady-state rolling contacts with dry friction for circular Hertzian contacts is formulated mathematically as a linear complementarity problem (LCP). The complementarity variables are the traction and the relative slip of contact regions, in which a polyhedral friction law is employed. The present work uses the general expressions describing the surface deformations due to uniform traction over a rectangular area on an elastic half-space to derive the influence coefficient matrix for rolling contact problems. Three possible creepage types—that is, longitudinal, lateral, and spin creepage—are considered in this work. Firstly, the numerical results are verified against the existing numerical solutions and good agreement has been found. Secondly, the anisotropic friction is studied by the verified approach. Some numerical examples are provided to illustrate the current LCP method for both isotropic and anisotropic friction in which the combined effects of the three kinds of creepage on the traction distribution are shown.

  • 18.
    Xi, Yinhu
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Shi, Yijun
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Mao, Junhong
    Theory of Lubrication and Bearing Institute, Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System, Xi’an Jiaotong University, Xi’an.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A Complementarity Problem–Based Solution Procedure for 2D Steady-State Rolling Contacts with Dry Friction2016Ingår i: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 59, nr 6, s. 1031-1038Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of steady-state rolling contact between two cylinders with dry friction was formulated into standard linear complementarity problems (LCPs) by using the explicit physical definition. For normal contact, the complementarity variables are the normal pressure and the gap. For the tangential contact, the traction distribution and relative slip are the variables obtained by solving the LCP. The frictional behavior is assumed to be governed by the Coulomb friction law, and LCP formulations of both similar elastic (Carter problem) and dissimilar elastic rolling contacts are presented in this work. Good agreement was found between the current LCP approach and publicly available software for both the rolling contact of similar elastic and dissimilar elastic cylinders. Moreover, the surface roughness was taken into account in this paper by the verified approach. The results show the initial slope of the traction - relative creepage curve decreases as the surface roughness increases.

  • 19.
    Söderfjäll, Markus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A model for twin land oil control rings2016Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 95, s. 475-482Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simulation model for predicting performance of a twin land oil control ring (TLOCR) in a heavy duty diesel engine (HDDE) has been developed. The simulation model takes into account the tribological interfaces of the TLOCR both against the cylinder liner and the piston ring groove. It also accounts for the elastic deformation of the ring cross section as well as the dynamics of the TLOCR. This work describes the model and discusses the challenges and compromises that had to be made. Included are also examples of the models capability to quantify design changes of the TLOCR.

  • 20.
    Söderfjäll, Markus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A new test rig for simulation of piston ring friction2016Konferensbidrag (Refereegranskat)
  • 21.
    Rafols, Francesc Perez
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Lundström, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A stochastic two-scale model for pressure-driven flow between rough surfaces2016Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences, ISSN 1364-5021, E-ISSN 1471-2946, Vol. 472, nr 2190, artikel-id 20160069Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Seal surface topography typically consists of global-scale geometric features as well as local-scale roughness details and homogenization-based approaches are, therefore, readily applied. These provide for resolving the global scale (large domain) with a relatively coarse mesh, while resolving the local scale (small domain) in high detail. As the total flow decreases, however, the flow pattern becomes tortuous and this requires a larger local-scale domain to obtain a converged solution. Therefore, a classical homogenization-based approach might not be feasible for simulation of very small flows. In order to study small flows, a model allowing feasibly-sized local domains, for really small flow rates, is developed. Realization was made possible by coupling the two scales with a stochastic element. Results from numerical experiments, show that the present model is in better agreement with the direct deterministic one than the conventional homogenization type of model, both quantitatively in terms of flow rate and qualitatively in reflecting the flow pattern.

  • 22.
    Furustig, Joel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Pelcastre, Leonardo
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Bates, Charles Anthony
    Danfoss Power Solutions ApS, Nordborg.
    Ennemark, Poul
    Danfoss Power Solutions ApS, Nordborg.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A strategy for wear analysis using numerical and experimental tools, applied to orbital type hydraulic motors2016Ingår i: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 230, nr 12, s. 2086-2097Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An accurate and reliable wear analysis requires detailed knowledge of the tribological conditions of the studied system. In this work, a numerical model which can quantify wear and is applicable to hydraulic motors is developed. Detailed tribological knowledge can be acquired through strategic experimental testing and numerical simulations. The model is constructed to include the effect on wear from varying lubricant film thickness. The development of the wear model includes consideration of wear observed in the Scanning Electron Microscopy (SEM) analysis of tested motors. The model is of the Archard type, in which the k-value is estimated from experiments, after considering the effect of lubrication. The contact pressure is the solution to a lubrication model that governs both the hydrodynamics of the lubricant film and the direct contact between the rough surfaces. To validate the model, a hydraulic motor is run at different operating conditions and the apparent wear depth is analysed after the tests. Numerical simulations mimicking the same configuration are performed and the predicted wear depths are compared to the experimental results. Similarities and differences are discussed and it is evident that a clear correlation exists between the wear predicted with the model and the measurement data of the apparent wear in the hydraulic motor. There are also discrepancies because of the model simplicity and the uncertainty in the specifications of the tested system. The results imply that wear analysis using numerical simulations aid the understanding of wear in machinery. The combined knowledge of physical conditions on different important scales enables in-depth analysis with numerical tools which cannot be achieved through experimental investigations alone. Furthermore, the numerical model can be refined leading to better wear predictions.

  • 23.
    Söderfjäll, Markus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Component test for simulation of piston ring: Cylinder liner friction at realistic speeds2016Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 104, s. 57-63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The piston ring cylinder liner contact is a large contributor to mechanical friction losses in internal combustion engines. It is therefore important to have methods and tools available for investigations of these frictional losses. This paper describes the design of a novel component test rig which is developed to be run at high speeds with unmodified production piston rings and cylinder liners from heavy duty diesel engines. A simplified floating liner method is used and the test equipment is developed to fill the gap in between a full floating liner engine and typical component bench test equipment. The functionality and repeatability of the test are investigated and an unexpected behaviour of the twin land oil control ring is found

  • 24.
    Shirzadegan, Mohammad
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Fully coupled EHL model for simulation of finite length line cam-roller follower contacts2016Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 103, s. 584-598Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a fully coupled multiphysics model developed for numerical simulation of the elastohydrodynamically lubricated contact between a cam and roller, typically found in cam mechanisms controlling fuel injection in an internal combustion engine. Special attention was focused on enabling systematic analyses of effects associated with, roller crowning and edge geometries, lubricant rheology as well as typical cam mechanism operating conditions. The interaction between the cam and roller follower result in high generated pressure and narrow film thickness that increase the risk of wear and fatigue. Furthermore, this article highlights the variation of pressure and film thickness under tilting conditions. The model was also validated against some particular model problems, found in the literature.

  • 25.
    Shirzadegan, Mohammad
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Björling, Marcus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Low degree of freedom approach for predicting friction in elastohydrodynamically lubricated contacts2016Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 94, s. 560-570Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A low degree of freedom, semi-analytical model for rapid estimation of the friction coefficient in elastohydrodynamically lubricated contacts was developed and tested. Its estimates are based on the shear rate dependent Carreau equation for the apparent viscosity, together with the hydrodynamic pressure and the temperature of the lubricant. To validate the approach, the model's predictions were compared to experimental coefficient of friction measurements acquired using a ball-on-disc test device at various applied loads, entrainment velocities, and slide to roll ratios. The model’s predictions were in good agreement with the experimental results, showing that it is suitable for use in multibody dynamics analyses where rapid computation of elastohydrodynamic friction is required to minimize computing time and resource consumption.

  • 26.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Modelling cavitation in (elasto)hydrodynamic lubrication2016Ingår i: Advances in tribology / [ed] Pranav H. Darji, Croatia: INTECH, 2016, s. 198-213Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    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.

  • 27.
    Rafols, Francesc Perez
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Modelling of leakage on metal-to-metal seals2016Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 94, s. 421-427Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Surfaces in a typical seal exhibit both waviness and roughness. The influence of the interaction between these two scales on the leakage behaviour is expected to be relevant. Therefore, a model, which can study it, is developed here. The model is composed of state-of-the-art models for the contact mechanics between rough metal surfaces and for the liquid flow through the rough aperture in-between them. Correlation between percentage real contact area and actual contact topology and leak rate was confirmed through numerical analysis. Small changes in relative position between the contacting surfaces showed large deviation in leak rate. The validity of the model was justified by comparing results from numerical simulations using the model and experimental results found in literature qualitatively.

  • 28.
    Shirzadegan, Mohammad
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Numerical analysis of EHL in cam mechanisms2016Ingår i: Nordic Symposium on Tribology - NORDTRIB 2016, 2016Konferensbidrag (Refereegranskat)
  • 29.
    Lintzén, Nina
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Grip, Niklas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Span curve temperature dependence of classic style cross country skis2016Ingår i: Sports Technology, ISSN 1934-6182, E-ISSN 1934-6190Artikel i tidskrift (Refereegranskat)
  • 30.
    Furustig, Joel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Dobryden, Illia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Nils
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The measurement of wear using AFM and wear interpretation using a contact mechanics coupled wear model2016Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 350-351, s. 74-81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Detailed understanding of wear processes is required to improve the wear resistance and lifetime of machine components. Atomic force microscopy (AFM) is used to measure surface height profiles with high precision, before and after a wear experiment. The distribution and depth of wear on steel surfaces is then calculated using a relocation method. A numerical investigation of wear based on Archard's equation is conducted on the same measured surfaces. A good correlation was found between the model and experiment for wear larger than a hundred nm. The wear mechanisms considered in the numerical simulation was thus found to be the cause of the majority of the wear. On the scale of tens of nm the correlation was limited, but the measured wear was still analysed in detail.

  • 31. Furustig, Joel
    et al.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Bates, C.A.
    Danfoss Power Solutions ApS, Nordborg.
    Ennermark, P.
    Danfoss Power Solutions ApS, Nordborg.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A two scale mixed lubrication wearing-in model, applied to hydraulic motors2015Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 90, s. 248-256Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wearing-in of a machine component can increase the conformity between contacting pairs and smoothen the surface topography. A two scale model, combining the wearing-in effects, resulting in changes in the surface topography, with the wear that occurs on the component, is presented. The geometry of the components are represented with measured coordinates. Wear leads to changes of the geometry, which has an effect on several tribological conditions, such as contact forces, relative velocities and conformity. Due to the wear on the topography scale, the load sharing is also affected. The model is applied to orbital hydraulic motors. The wear depth predicted with the model, is qualitatively in good agreement with the wear depth recorded in experiments.

  • 32.
    Furustig, Joel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Bates, C.A.
    Danfoss Power Solutions ApS, Nordborg.
    Ennermark, P.
    Danfoss Power Solutions ApS, Nordborg.
    A wear model for EHL contacts in gerotor type hydraulic motors2015Ingår i: Proceedings of the Institution of mechanical engineers. Part C, journal of mechanical engineering science, ISSN 0954-4062, E-ISSN 2041-2983, Vol. 229, nr 2, s. 254-264Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The heart of gerotor motors is a gear-set. The gear-set consists of an inner gear which is rotating and orbiting in contact with an outer gear. Wear in these contacts is investigated experimentally and with a numerical implementation of an Archard based wear model in combination with a load sharing concept. The model utilizes the symmetry of the motor and is based on a three-scale approach to estimate the wear on the gears. The global model calculates contact forces, relative surface velocities and contact radii in the contacts between inner and outer gear. The calculations performed on the local scale are used to collect information about the influence of the surface roughness on lubricant film thickness. The wear depth is calculated on a semi-local scale, involving only one tooth on the outer gear. In partial elastohydrodynamic lubrication, load is carried by the part of the conjunction where there is direct contact between the mating surfaces and by the lubricant pressure. In the wear model, wear only occurs as a direct consequence of contact between the mating surfaces. Experimental results are compared with the model predictions for equivalent running conditions. The wear predicted by the model agrees with the experimental results. For this reason, it is concluded that wear in the gerotor motor is dominated by the wear mechanisms which are considered in the tribological model.

  • 33.
    Shirzadegan, Mohammad
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Björling, Marcus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Low degree of freedom EHL friction: Through fast estimation2015Ingår i: 42nd Leeds-Lyon Symposium on Tribology, 2015Konferensbidrag (Refereegranskat)
  • 34.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Fabricius, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    A new approach for studying cavitation in lubrication2014Ingår i: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 136, nr 1, artikel-id 11706Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The underlying theory, in this paper, is based on clear physical arguments related to conservation of mass flow and considers both incompressible and compressible fluids. The result of the mathematical modeling is a system of equations with two unknowns, which are related to the hydrodynamic pressure and the degree of saturation of the fluid. Discretization of the system leads to a linear complementarity problem (LCP), which easily can be solved numerically with readily available standard methods and an implementation of a model problem in matlab code is made available for the reader of the paper. The model and the associated numerical solution method have significant advantages over today's most frequently used cavitation algorithms, which are based on Elrod-Adams pioneering work

  • 35.
    Hardell, Jens
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Neville, Anne
    School of Mechanical Engineering, University of Leeds.
    Liśkiewicz, Tomasz W.
    School of Mechanical Engineering, University of Leeds.
    Editorial2014Ingår i: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, nr 2, s. 55-56Artikel i tidskrift (Övrigt vetenskapligt)
  • 36.
    Furustig, Joel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Pelcastre, Leonardo
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    On a strategy of wear analysis using numerical and experimental tools2014Konferensbidrag (Refereegranskat)
  • 37.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Hardell, Jens
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Prakash, Braham
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Selected papers from those presented at the 3rd International Tribology Symposium of IFToMM2014Ingår i: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 26, nr 5, s. 273-275Artikel i tidskrift (Refereegranskat)
  • 38.
    Söderfjäll, Markus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Isaksson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Spencer, Andrew
    Scania CV AB, Södertälje.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The effect of three-dimensional deformations of a cylinder liner on the tribological performance of a piston ring–cylinder liner system2014Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 228, nr 10, s. 1080-1087Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes a numerical simulation model for prediction of the tribological effects of an oil control ring running against an out-of-round cylinder liner in a heavy duty diesel engine. The model considers the full three-dimensional geometry of the oil control ring and includes the effect of both surface roughness and global deformation. Results that test the model’s ability to do this under stationary conditions are presented. Furthermore, stationary results for prediction of the friction reduction possible by reduced ring tension in combination with reduced out-of-roundness are given. The model predicts the friction for the oil control ring at mid-stroke to be 78% larger in an out-of-round cylinder liner compared to a perfectly cylindrical one.

  • 39.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    A new concept in cavitation modelling2013Ingår i: Tribo Lyon 2013: book of abstracts : a joint event of WTC 2013, Lyon, 2013, s. 170-Konferensbidrag (Refereegranskat)
  • 40.
    Kang, Shaojie
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Furustig, Joel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A running-in model for the boundary lubricated contact2013Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    During the running-in period of a boundary lubricated contact, the surface roughness will be dramatically changed, involving large plastic deformation and wear on the asperity summits. This paper presents a running-in model. The model is based on the Boundary Element Method (BEM) and will focus on the investigation of large plastic deformations. The BEM model is based on the minimization of the complementary potential energy and deals with the contact at interfaces. The BEM model used in this paper previously adopted a linearly elastic- perfectly plastic material model and was frictionless, therefore a correction factor is needed for the model to improve its ability to account for high friction and large plastic deformation. The correction factor is made by improving the yield criterion and is derived with the assistance of the Finite Element Method (FEM). Both the friction and the strain hardening mechanism taken from the real material are implemented in the FEM model; the load and the contact area are required to match in both simulations. With the correction factor, results are promising for the current model to simulate the running-in process.

  • 41.
    Spencer, Andrew
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Avan, Emin Yusuf
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Dwyer-Joyce, Rob S
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    An experimental and numerical investigation of four cylinder liner variants for a heavy duty diesel engine2013Konferensbidrag (Övrigt vetenskapligt)
  • 42.
    Spencer, Andrew
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Avan, Emin Yusuf
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Dwyer-Joyce, Rob S
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    An experimental and numerical investigation of frictional losses and film thickness for four cylinder liner variants for a heavy duty diesel engine2013Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 12, s. 1319-1333Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The piston ring pack is the single greatest contributor to mechanical losses in a heavy duty diesel engine, accounting for 1.1–6.8% of the total losses. Therefore, the piston ring-cylinder liner contact is potentially the most rewarding area to study when attempting to reduce mechanical losses in a heavy duty diesel engine. In this work, four different heavy duty diesel engine cylinder liner variants have been tested to evaluate the lubricating conditions that occur when a section of top compression ring is reciprocated against them in a lubricated environment. Two of the cylinder liners were traditional grey cast iron and plateau honed with different honing angles, one had ANS Triboconditioning® applied and the last was plasma sprayed with a stainless steel and ceramic coating, then honed. An experimental test rig was used where friction and film thickness was recorded, by means of an ultrasonic technique. A numerical model was also developed to calculate the friction and film thickness. Comparisons are made between the simulation and experiment, and the four cylinder liner variants are also evaluated. It was found that both simulation and experiment could differentiate between all surfaces and the results from the model and experiment also correlated well with each other. A lower plateau average surface roughness, as exhibited by the ANS Triboconditioning® and plasma liners, led to a significant reduction in friction.

  • 43.
    Kang, Shaojie
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Orellana, Roger Fadurdo
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Deformation in silicon compressed by a steel ball2013Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Most of the studies dealing with contact mechanics are focused on the pressure and the deformation at the surfaces of the contacting bodies. However, the stress and deformation in the material underneath the actual surface are also important to study. In this work, the elastic deformations arising in a silicon block that is compressed by a steel ball is studied. More precisely, an optical metrology technique is employed to obtain the deformation in the substrate at a fixed depth. A finite element based model, is also developed in order to numerically estimate the elastic deformation of the silicon block. Moreover, the deformation and corresponding stress fields are also analysed with closed form analytical solutions. Comparisons of the results obtained from the experiments, the numerical simulations and analytical solution show that a good prediction of the deformation can be obtained by the finite element model.

  • 44.
    Avan, Evan Y.
    et al.
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Spencer, Andrew
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Dwyer-Joyce, Rob S.
    Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Experimental and numerical investigations of oil film formation and friction in a piston ring–liner contact2013Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 2, s. 126-140Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The piston ring–cylinder liner contact is a major source of the total parasitic losses in an internal combustion engine. The lubrication process of this contact highly influences the amount of friction, oil consumption and wear that occurs. In this work, a reciprocating test rig combined with an ultrasonic film thickness measurement system was developed and then used for tribological investigation of the piston ring–cylinder liner contact under idealised cold conditions. A special piston ring and cylinder liner holder were designed and five sensors were glued on to the back side of the liner specimen. Ultrasonic reflections captured by the sensors, used to obtain the film thickness, and friction were continuously recorded as the piston ring section reciprocated over the liner. Several experiments were performed at different speed and load conditions. Furthermore, a numerical model has been developed to predict film thickness and friction in all lubrication regimes. The experimentally measured film thickness and friction were compared with the output from the numerical model and good correlation was found. The parameters affecting the accuracy of the ultrasound measurements and numerical simulations of film thickness and friction are then discussed.

  • 45.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Homogenization of the Reynolds equation2013Ingår i: Encyclopedia of Tribology, Berlin: Springer-Verlag New York Inc. , 2013, s. 1685-1690Kapitel i bok, del av antologi (Refereegranskat)
  • 46.
    Söderfjäll, Markus
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Isaksson, Patrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Spencer, Andrew
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The effect of 3D deformations of a cylinder liner on the tribological performance of a piston ring-cylinder liner system.2013Konferensbidrag (Refereegranskat)
  • 47.
    Spencer, Andrew
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Dobryden, Illia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Almqvist, Nils
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    The influence of AFM and VSI techniques on the accurate calculation of tribological surface roughness parameters2013Ingår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 57, s. 242-250Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vertical Scanning Interferometry (VSI) may induce optical artefacts in surface topography measurements. The influence of these optical artefacts on the calculation of Rk surface roughness parameters, contact stiffness and flow factors were studied. Two surface measurement techniques were used: Atomic Force Microscopy (AFM) and VSI. Calibration grids were used to make it easier to isolate the causes of these artefacts, while a real engineering surface was used to compare these two techniques in an industrially applied case. It was found that the optical artefacts have a large influence on all the roughness parameters, contact stiffness and flow factors calculated on the calibration grids. However, for the engineering surface the differences between AFM and VSI measurements were much smaller.

  • 48.
    Almqvist, Andreas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Fabricius, John
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Homogenization of a Reynolds equation describing compressible flow2012Ingår i: Journal of Mathematical Analysis and Applications, ISSN 0022-247X, E-ISSN 1096-0813, Vol. 390, nr 2, s. 456-471Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We homogenize a Reynolds equation with rapidly oscillating film thickness function hε, assuming a constant compressiblity factor in the pressure-density relation. The oscillations are due to roughness on the bounding surfaces of the fluid film. As shown by previous studies, homogenization is an effective approach for analyzing the effects of surface roughness in hydrodynamic lubrication. By two-scale convergence theory we obtain the limit problem (homogenized equation) and strong convergence in L2 for the unknown density ρε. By adding a small corrector term we also obtain strong convergence in the Sobolev norm.

  • 49.
    Andersson, Joel
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Grahn, Mattias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Minami, Ichiro
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Semi-deterministic chemo-mechanical model of boundary lubrication2012Ingår i: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 156, s. 343-360Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A model for tribofilm growth is developed. The model is used in combination with numerical contact mechanics tools to enable evaluation of the combined effects of chemistry and contact mechanics. The model is tuned with experimental data and is thereafter applied to rough surfaces. The growth of the tribofilm is evaluated for 3 different contact cases and short-term tribofilm growth behaviour is analyzed. The results show how tribofilms grow in patches. The model is expected to be used as a tool for analysis of the interaction between rough surfaces.

  • 50.
    Spencer, Andrew
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Almqvist, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Larsson, Roland
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    A numerical model to investigate the effect of honing angle on the hydrodynamic lubrication between a combustion engine piston ring and cylinder liner2011Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, nr 7, s. 683-689Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A numerical model has been developed to investigate the effect of cylinder liner honing angle on hydrodynamic lubrication between piston ring and cylinder liner. The Reynolds equation was solved in 2D with periodic boundary conditions. An artificial surface texture was generated, based on a real surface measured with white light interferometry. Cavitation was modelled with the Vijayaraghavan and Keith algorithm. Honing angles between 25° and 75° were investigated to find the effect of honing angle on film thickness.

12 1 - 50 av 99
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