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Multiphysics and Multiscale Models of Tribology

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A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (30 June 2018) | Viewed by 31397

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Special Issue Editor

Prof. Dr. Andreas Almqvist

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Guest Editor

Division of Machine Elements, Luleå University of Technology, SE-971 87 Luleå, Sweden
Interests: multiscale and multiphysics modelling and simulation of flows in narrow interfaces; application of topology optimisation methodology in hydrodynamic lubrication; application of artificial neural networks; homogenization; lower dimensional models; friction on snow and ice

Special Issue Information

Dear Colleagues,

This Special Issue, “Multiphysics and Multiscale Models of Tribology”, in the open access journal Lubricants, is open for submissions presenting modelling and simulations involving the multiphysics and/or multiscale nature of tribological interfaces found in bearings, gears, seals, etc. While it encourages a broad spectrum of contribution in tribology, its core interest lies in issues concerning the development, verification and validation of the models and their numerical solution procedures. Papers of transdisciplinary nature presenting and connecting fundamental research with more applied are particularly welcome.

Papers devoted to the purely mathematical aspects without a discussion of the physical implications of the results or the consideration of specific examples are discouraged. Papers should not be limited merely to the description and recording of observations and should include an elaborate verification of the numerical solution procedure, validation against experimental findings or against already well-established approaches. They should, preferably, also contain theoretical or quantitative discussion of the results.

We are enthusiastically looking forward to receiving your submission.

Prof. Dr. Andreas Almqvist
Guest Editor

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Elastohydrodynamic lubrication
Contact mechanics
Leakage/percolation
CFD
Fluid-structure interaction
Mechanical deformation
Thermal expansion
Roughness
Cavitation

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Published Papers (7 papers)

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Research

16 pages, 2676 KiB

Open AccessArticle

Effect of Shaft Surface Roughness on the Performance of Radial Lip Seals

by Emilia Kozuch, Petros Nomikos, Ramin Rahmani, Nick Morris and Homer Rahnejat

Lubricants 2018, 6(4), 99; https://doi.org/10.3390/lubricants6040099 - 13 Nov 2018

Cited by 15 | Viewed by 6057

Abstract

Reduction of leakage from the shaft–radial lip seal conjunction is critical in ensuring enduring performance of entire lubrication system. This paper investigates leakage from three types of shaft surfaces, finished using different manufacturing processes. The measurement of surface topography is conducted in order to determine the pertinent roughness parameters which correspond to the observed sealing performance in real practical applications. It is found that the skewness of the surface topography correlates well with the anecdotal leakage failure rate. To quantify this association, a hydrodynamic model, accounting for shaft roughness in a deterministic manner is developed. The results from the numerical analyses confirm that the lubricant mass flow rate is reduced in the case of negatively skewed surface height distributions, when compared with the positively skewed profiles. Full article

(This article belongs to the Special Issue Multiphysics and Multiscale Models of Tribology)

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15 pages, 1094 KiB

Open AccessArticle

Thermal Turbulent Flow in Leading Edge Grooved and Conventional Tilting Pad Journal Bearing Segments—A Comparative Study

by Philip Croné, Andreas Almqvist and Roland Larsson

Lubricants 2018, 6(4), 97; https://doi.org/10.3390/lubricants6040097 - 2 Nov 2018

Cited by 9 | Viewed by 4232

Abstract

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. Full article

(This article belongs to the Special Issue Multiphysics and Multiscale Models of Tribology)

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Graphical abstract

18 pages, 10206 KiB

Open AccessArticle

On an Elastoplastic Sliding Model for a Coated Single Asperity

by Can Wang and Dik J. Schipper

Lubricants 2018, 6(4), 96; https://doi.org/10.3390/lubricants6040096 - 1 Nov 2018

Cited by 7 | Viewed by 3547

Abstract

In this study, a sliding friction model for coated single asperity contacts is proposed. A displacement-driven layered contact algorithm is firstly introduced and verified by the finite element method. Then, this algorithm is applied to simulate the contact between two semispherical asperities. The full sliding contact process is discretized into a series of transient steps, and each of these steps are calculated by the displacement-driven contact algorithm. The effects of the interference depth and the properties of, respectively, the tribofilm (thickness, elastic modulus, and yield strength) and the nanocrystalline layer on the sliding coefficient of friction are investigated. The results suggest that when surface adhesion and asperity damage are ignored, the plastic deformation of the tribofilm is the main source of the sliding friction. Greater interference depth, tribofilm with greater thickness, higher elastic modulus or lower yield strength, and the presence of a nanocrystalline layer will lead to a higher coefficient of friction in single asperity sliding. Full article

(This article belongs to the Special Issue Multiphysics and Multiscale Models of Tribology)

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Graphical abstract

18 pages, 1382 KiB

Open AccessArticle

An Enhanced Stochastic Two-Scale Model for Metal-to-Metal Seals

by Francesc Pérez-Ràfols and Andreas Almqvist

Lubricants 2018, 6(4), 87; https://doi.org/10.3390/lubricants6040087 - 1 Oct 2018

Cited by 4 | Viewed by 3213

Abstract

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. Full article

(This article belongs to the Special Issue Multiphysics and Multiscale Models of Tribology)

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17 pages, 3577 KiB

Open AccessArticle

Contact-Patch-Size Distribution and Limits of Self-Affinity in Contacts between Randomly Rough Surfaces

by Martin H. Müser and Anle Wang

Lubricants 2018, 6(4), 85; https://doi.org/10.3390/lubricants6040085 - 20 Sep 2018

Cited by 20 | Viewed by 5061

Abstract

True contact between solids with randomly rough surfaces tends to occur at a large number of microscopic contact patches. Thus far, two scaling regimes have been identified for the number density

n (A)

of contact-patch sizes A in elastic, non-adhesive, self-affine [...] Read more.

True contact between solids with randomly rough surfaces tends to occur at a large number of microscopic contact patches. Thus far, two scaling regimes have been identified for the number density

n (A)

of contact-patch sizes A in elastic, non-adhesive, self-affine contacts. At small A,

n (A)

is approximately constant, while

n (A)

decreases as a power law at large A. Using Green’s function molecular dynamics, we identify a characteristic (maximum) contact area

A_{c}

above which a superexponential decay of

n (A)

becomes apparent if the contact pressure is below the pressure

p_{cp}

at which contact percolates. We also find that

A_{c}

increases with load relatively slowly far away from contact percolation. Results for

A_{c}

can be estimated from the stress autocorrelation function

G_{σ σ} (r)

with the following argument: the radius of characteristic contact patches,

r_{c}

, cannot be so large that

G_{σ σ} (r_{c})

is much less than

p_{cp}^{2}

. Our findings provide a possible mechanism for the breakdown of the proportionality between friction and wear with load at large contact pressures and/or for surfaces with a large roll-off wavelength. Full article

(This article belongs to the Special Issue Multiphysics and Multiscale Models of Tribology)

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12 pages, 3751 KiB

Open AccessArticle

Multiscale Modeling Applied to the Hydrodynamic Lubrication of Rough Surfaces for Computation Time Reduction

by Noël Brunetière and Arthur Francisco

Lubricants 2018, 6(3), 83; https://doi.org/10.3390/lubricants6030083 - 15 Sep 2018

Cited by 5 | Viewed by 3954

Abstract

This paper presents a multiscale finite element method applied to the simulation of a lubricating film flowing between rough surfaces. The objective of this approach is to study flows between large rough surfaces needing very fine meshes while maintaining a reasonable computation time. For this purpose, the domain is split into a number of subdomains (bottom-scale meshes) connected by a coarse mesh (top-scale). The pressure distribution at the top-scale is used as boundary conditions for the bottom-scale problems. This pressure is adjusted to ensure global mass flow balance between the contiguous subdomains. This multiscale method allows for a significant reduction of the number of operations as well as a satisfactory accuracy of the results if the top-scale mesh is properly fitted to the roughness lateral scale. Furthermore the present method is well-suited to parallel computation, leading to much more significant computation time reduction. Full article

(This article belongs to the Special Issue Multiphysics and Multiscale Models of Tribology)

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25 pages, 3031 KiB

Open AccessArticle

On the Two-Scale Modelling of Elastohydrodynamic Lubrication in Tilted-Pad Bearings

by Gregory De Boer and Andreas Almqvist

Lubricants 2018, 6(3), 78; https://doi.org/10.3390/lubricants6030078 - 3 Sep 2018

Cited by 12 | Viewed by 3997

Abstract

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. Full article

(This article belongs to the Special Issue Multiphysics and Multiscale Models of Tribology)

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