14 results on '"Almqvist, Andreas"'
Search Results
2. Generating randomly rough surfaces with given height probability distribution and power spectrum.
- Author
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Pérez-Ràfols, Francesc and Almqvist, Andreas
- Subjects
- *
ROUGH surfaces , *SURFACE topography , *COMPUTER algorithms , *ITERATIVE methods (Mathematics) , *WEIBULL distribution - Abstract
Abstract 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. Highlights • An algorithm for generation of non-Gaussian surfaces is presented. • Height probability distribution and power spectrum can be specified simultaneously. • Only few iterations are needed for a good solution to be obtained. • Delta functions on the height probability distributions can be handled. • Cut-off frequencies on the power spectrum can be handled, but with care. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
3. Component test for simulation of piston ring – Cylinder liner friction at realistic speeds.
- Author
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Söderfjäll, Markus, Almqvist, Andreas, and Larsson, Roland
- Subjects
- *
PISTON rings , *FRICTION , *CONTACT mechanics , *INTERNAL combustion engines , *OCEAN liners - Abstract
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. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
4. A model for twin land oil control rings.
- Author
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Söderfjäll, Markus, Almqvist, Andreas, and Larsson, Roland
- Subjects
- *
TRIBOLOGY , *DIESEL fuels , *SIMULATION methods & models , *ELASTICITY , *PREDICTION models - Abstract
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. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
5. A cavitation algorithm for arbitrary lubricant compressibility
- Author
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Sahlin, Fredrik, Almqvist, Andreas, Larsson, Roland, and Glavatskih, Sergei
- Subjects
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SURFACE roughness , *ALGORITHMS , *HYDRODYNAMICS , *PROPERTIES of matter - Abstract
Abstract: A general cavitation algorithm that accommodates for an arbitrary density–pressure relation is presented. It is now possible to model the compressibility of the lubricant in such a way that the density–pressure relation is realistic throughout the contact. The algorithm preserves mass continuity for cavitation caused by bearing geometry and surface topography. It is a commonly accepted physical assumption that the contribution of the pressure driven flow is negligible in the cavitated region. This phenomenon is adopted in the present algorithm, which is similar to that of Elrod, and is modeled by a switch function that terminates the pressure gradient at the cavitation regions. Results with this algorithm for different density–pressure relations are presented and discussed. The effects of inlet conditions, such as surface roughness and starvation, on the load carrying capacity of the contact are analyzed. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
6. Rough surface flow factors in full film lubrication based on a homogenization technique
- Author
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Sahlin, Fredrik, Almqvist, Andreas, Larsson, Roland, and Glavatskih, Sergei
- Subjects
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SURFACE roughness , *SURFACES (Technology) , *LUBRICATION & lubricants , *TRIBOLOGY - Abstract
Abstract: This paper describes a method to compute the flow factors that compensate for an arbitrary surface roughness in a compressible hydrodynamic lubrication based on a homogenization technique. The Reynolds equation is used as the governing equation and the two-scale expansion involved in the homogenization process enables the local roughness scale to be treated separately from the global geometry scale. With this method, it is possible to compute the flow factors for any deterministic roughness. Measured two-dimensional surface profiles are used as examples. Profiles having the same Abbot curve are also shown to have the same flow factors, providing an efficient classification of surfaces in hydrodynamic two-dimensional contacts. Flow factors are computed for the rough surface profiles, and solutions for global bearing geometry are obtained and compared with the corresponding solutions from a smooth geometry. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
7. Variational bounds applied to unstationary hydrodynamic lubrication
- Author
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Almqvist, Andreas, Essel, Emmanuel Kwame, Fabricius, John, and Wall, Peter
- Subjects
- *
SURFACES (Technology) , *SURFACE roughness , *DIFFERENTIAL equations , *ASYMPTOTIC homogenization - Abstract
Abstract: This paper is devoted to the effects of surface roughness in hydrodynamic lubrication. The numerical analysis of such problems requires a very fine mesh to resolve the surface roughness, hence it is often necessary to do some type of averaging. Previously, homogenization (a rigorous form of averaging) has been successfully applied to Reynolds type differential equations. More recently, the idea of finding upper and lower bounds on the effective behavior, obtained by homogenization, was applied for the first time in tribology. In these pioneering works, it has been assumed that only one surface is rough. In this paper we develop these results to include the unstationary case where both surfaces may be rough. More precisely, we first use multiple-scale expansion to obtain a homogenization result for a class of variational problems including the variational formulation associated with the unstationary Reynolds equation. Thereafter, we derive lower and upper bounds corresponding to the homogenized (averaged) variational problem. The bounds reduce the numerical analysis, in that one only needs to solve two smooth problems, i.e. no local scale has to be considered. Finally, we present several examples, where it is shown that the bounds can be used to estimate the effects of surface roughness with very high accuracy. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
8. New concepts of homogenization applied in rough surface hydrodynamic lubrication
- Author
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Almqvist, Andreas, Lukkassen, Dag, Meidell, Annette, and Wall, Peter
- Subjects
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ASYMPTOTIC homogenization , *PARTIAL differential equations , *HYDRODYNAMICS , *LUBRICATION & lubricants - Abstract
Abstract: This work introduces a new concept of homogenization that enables efficient analysis of the effects of surface roughness representations obtained by measurements in applications modeled by the Reynolds equation. Examples of such applications are trust- and journal-bearings. The numerical analysis of these types of applications requires an extremely dense computational mesh in order to resolve the surface roughness, suggesting some type of averaging. One such method is homogenization, which has been applied to Reynolds type equations with success recently. This approach is similar to the technique proposed by Patir and Cheng, who introduced flow factors determining the hydrodynamic action due to surface roughness. The difference is, however, that the present technique has a rigorous mathematical support. Moreover, the recipe to compute the averaged coefficients is simple without any ambiguities. Using either the technique proposed by Patir and Cheng or homogenization, the coefficients determining the averaged Reynolds equation are obtained by solving differential equations on a local scale. Unfortunately, this is detrimental when investigating the effects induced by real, measured, surface roughness, even though these local problems may be solved in parallel. The present work presents a solution by applying the technique based on bounds. This technique transforms the stationary Reynolds equation into two computationally feasible forms, one for the upper bound and one for the lower bound, where the flow factors are obtained by straightforward integration. Together with the preciseness of these bounds, the bounds approach becomes an eminent tool suitable for investigating the effect of real, measured, surface roughness on hydrodynamic performance. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
9. New insights on lubrication theory for compressible fluids.
- Author
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Almqvist, Andreas, Burtseva, Evgeniya, Pérez-Ráfols, Francesc, and Wall, Peter
- Subjects
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IDEAL gases , *REYNOLDS equations , *NAVIER-Stokes equations , *THIN films , *FLUIDS , *LUBRICATION & lubricants , *PSEUDOPLASTIC fluids , *COMPRESSIBLE flow - Abstract
The fact that the film is thin is in lubrication theory utilised to simplify the full Navier–Stokes system of equations. For incompressible and iso-viscous fluids, it turns out that the inertial terms are small enough to be neglected. However, for a compressible fluid, we show that the influence of inertia depends on the (constitutive) density-pressure relationship and may not always be neglected. We consider a class of iso-viscous fluids obeying a power-law type of compressibility, which in particular includes both incompressible fluids and ideal gases. We show by scaling and asymptotic analysis, that the degree of compressibility determines whether the terms governing inertia may or may not be neglected. For instance, for an ideal gas, the inertial terms remain regardless of the film height-to-length ratio. However, by means of a specific modified Reynolds number that we define we show that the magnitudes of the inertial terms rarely are large enough to be influential. In addition, we consider fluids obeying the well-known Dowson and Higginson density-pressure relationship and show that the inertial terms can be neglected, which allows for obtaining a Reynolds type of equation. Finally, some numerical examples are presented in order to illustrate our theoretical results. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
10. Influence on friction from piston ring design, cylinder liner roughness and lubricant properties.
- Author
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Söderfjäll, Markus, Larsson, Roland, Almqvist, Andreas, and Herbst, Hubert M.
- Subjects
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PISTONS , *SURFACE roughness , *LUBRICATION & lubricants , *LUBRICATION & lubricant testing ,DESIGN & construction - Abstract
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. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
11. Modelling of leakage on metal-to-metal seals.
- Author
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Pérez-Ràfols, Francesc, Larsson, Roland, and Almqvist, Andreas
- Subjects
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METAL-to-metal contacts , *SEALING (Technology) , *SURFACE roughness , *CONTACT mechanics , *METALLIC surfaces - Abstract
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. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
12. Low degree of freedom approach for predicting friction in elastohydrodynamically lubricated contacts.
- Author
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Shirzadegan, Mohammad, Björling, Marcus, Almqvist, Andreas, and Larsson, Roland
- Subjects
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DEGREES of freedom , *FRICTION , *ELASTOHYDRODYNAMIC lubrication , *CONTACT mechanics , *FRICTION measurements - Abstract
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. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
13. A traction coefficient formula for EHL point contacts operating in the linear isothermal region.
- Author
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Higashitani, Yuko, Kawabata, Sanemasa, Björling, Marcus, and Almqvist, Andreas
- Subjects
- *
COMPUTER simulation - Abstract
Many mechanical systems including rolling/sliding parts, require traction data across a spectrum of operating conditions to predict their motion effectively. Numerous studies have examined the thermal effects and shear-thinning concerning the traction curve, but only a few have focused on the traction coefficient in the linear isothermal regime for low SRR. In this work, we investigate traction coefficient characteristics of EHL point contacts in the linear isothermal regime, over a wide range of operational conditions. To this end, we conduct numerical simulations utilizing a fully-coupled finite element-based model, resulting in a prediction formula for the traction coefficient slope. With this formula, the traction coefficient slope could be predicted for the operating conditions considered. [Display omitted] [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
14. A traction coefficient formula for EHL line contacts operating in the linear isothermal region.
- Author
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Higashitani, Yuko, Kawabata, Sanemasa, Björling, Marcus, and Almqvist, Andreas
- Subjects
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COMPUTER simulation , *ELASTOHYDRODYNAMIC lubrication , *PSEUDOPLASTIC fluids - Abstract
Many mechanical products including rolling/sliding parts are used with various lubricants and operating conditions. Increasing the efficiency and reliability of products requires an essential understanding of the traction characteristics of the rolling/sliding parts. Many researchers have investigated the traction characteristics of rolling/sliding EHL contacts considering shear-thinning, thermal effects, and roller compliance. There are, however, only a few papers concerning the modeling of traction characteristics in the linear isothermal region at low slide-to-roll ratios. We propose a prediction formula for the dimensionless traction coefficient for EHL line contacts in the linear isothermal region. The formula was obtained by numerical simulations using a fully-coupled finite-element EHL line contact solver, and it is applicable for the piezoviscous rigid/elastic, and the isoviscous rigid/elastic regimes. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
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