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| 2. |
- Almqvist, Andreas, et al.
(författare)
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On the dry elasto-plastic contact of nominally flat surfaces
- 2007
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 40:4, s. 574-579
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Tidskriftsartikel (refereegranskat)abstract
- A model to be used for numerical simulation of the contact of linear elastic perfectly plastic rough surfaces was developed. Energy dissipation due to plastic deformation is taken into account. Spectral theory and an FFT-techique are used to facilitate the numerical solution process. Results of simulations using four two-dimensional profiles with different topographies in contact with a rigid plane for a number loads are reported. From the results it is clear that the real area of contact (Ar) changes almost linearly with load and is only slightly affected by the difference in topography. A plasticity index is defined as the ratio of plastically deformed area (Ap) and Ar. Plastic deformation occurs even at low loads and there is a significant difference in plasticity index between the surface profiles considered. An investigation on how the spectral content of the surface profile influences the results presented is also performed. This is to ensure that the metrological limitations of the optical profilerused to measure the surfaces do not have a significant influence. It is concluded that the highest frequencies of the measured profile have a negligible influence on the real area of contact.
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| 3. |
- Nystedt, Björn, et al.
(författare)
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The Norway spruce genome sequence and conifer genome evolution
- 2013
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 497:7451, s. 579-584
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Tidskriftsartikel (refereegranskat)abstract
- Conifers have dominated forests for more than 200 million years and are of huge ecological and economic importance. Here we present the draft assembly of the 20-gigabase genome of Norway spruce (Picea abies), the first available for any gymnosperm. The number of well-supported genes (28,354) is similar to the >100 times smaller genome of Arabidopsis thaliana, and there is no evidence of a recent whole-genome duplication in the gymnosperm lineage. Instead, the large genome size seems to result from the slow and steady accumulation of a diverse set of long-terminal repeat transposable elements, possibly owing to the lack of an efficient elimination mechanism. Comparative sequencing of Pinus sylvestris, Abies sibirica, Juniperus communis, Taxus baccata and Gnetum gnemon reveals that the transposable element diversity is shared among extant conifers. Expression of 24-nucleotide small RNAs, previously implicated in transposable element silencing, is tissue-specific and much lower than in other plants. We further identify numerous long (>10,000 base pairs) introns, gene-like fragments, uncharacterized long non-coding RNAs and short RNAs. This opens up new genomic avenues for conifer forestry and breeding.
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| 4. |
- Sahlin, Fredrik, et al.
(författare)
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2D CFD-analysis of micro-patterned surfaces in hydrodynamic lubrication
- 2004
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Ingår i: Proceedings of the ASME/STLE international joint tribology conference 2004. - New York. ; , s. 1637-1645, s. 1637-1645
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Konferensbidrag (refereegranskat)abstract
- Results of a numerical study of the influence of micro-patterned surfaces in hydrodynamic lubrication of two parallel walls are reported. Two types of parameterized grooves with the same order of depth as the film thickness are used on one stationary wall. The other wall is smooth and is sliding with a specified tangential velocity. Isothermal incompressible two dimensional full film fluid flow mechanics is solved using a Computational Fluid Dynamics method. It is shown that, by introducing a micro-pattern on one of two parallel walls, a net pressure rise in the fluid domain is achieved. This produces a load carrying capacity on the walls which is mainly contributed by fluid inertia. The load carrying capacity increases with Reynolds number. The load carrying capacity is reported to increase with groove width and depth. However, at a certain depth a vortex appears in the groove and near this value the maximum load carrying capacity is achieved. It is shown that the friction force decreases with deeper and wider grooves. Among all geometries studied, optimum geometry shapes in terms of hydrodynamic performance are reported.
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| 5. |
- Sahlin, Fredrik, et al.
(författare)
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A cavitation algorithm for arbitrary lubricant compressibility
- 2007
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 40:8, s. 1294-1300
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Tidskriftsartikel (refereegranskat)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.
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| 6. |
- Sahlin, Fredrik, et al.
(författare)
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A cavitation algorithm for arbitrary lubricant compressibility
- 2005
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Ingår i: Proceedings of the World Tribology Congress III - 2005. - New York : American Society of Mechanical Engineers. ; , s. 541-542, s. 541-542
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Konferensbidrag (refereegranskat)abstract
- A general cavitation algorithm is presented that accommodates for an arbitrary density-pressure relation. Here it is possible to model the compressibility of the lubricant in such way the density-pressure relation is realistic from sub-cavity to high pressure regions respectively. The algorithm preserves mass continuity which is of importance when inter-asperity cavitation of rough surfaces is considered. Results with this algorithm for different density-pressure relations are presented and discussed.
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| 7. |
- Sahlin, Fredrik, et al.
(författare)
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Rough surface flow factors in full film lubrication based on a homogenization technique
- 2007
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 40:7, s. 1025-1034
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Tidskriftsartikel (refereegranskat)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.
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| 8. |
- Sahlin, Fredrik, et al.
(författare)
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Two-Dimensional CFD-Analysis of Micro-Patterned Surfaces in Hydrodynamic Lubrication
- 2005
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 127:1, s. 96-102
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Tidskriftsartikel (refereegranskat)abstract
- Results of a numerical study of the influence of micro-patterned surfaces in hydrodynamic lubrication of two parallel walls are reported. Two types of parameterized grooves with the same order of depth as the film thickness are used on one stationary wall. The other wall is smooth and is sliding with a specified tangential velocity Isothermal incompressible two dimensional full film fluid flow mechanics is solved using a Computational Fluid Dynamics method. It is shown that, by introducing a micro-pattern on one of two parallel walls, a net pressure rise in the fluid domain is achieved. This produces a load carrying capacity on the walls which is mainly contributed by fluid inertia. The load carrying capacity increases with Reynolds number The load carrying capacity is reported to increase with groove width and depth. However at a certain depth a vortex appears in the groove and near this value the maximum load carrying capacity is achieved. It is shown that the friction force decreases with deeper and wider grooves. Among all geometries studied, optimum geometry shapes in terms of hydrodynamic performance are reported.
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