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- Rafols, Francesc Perez, et al.
(författare)
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A stochastic two-scale model for pressure-driven flow between rough surfaces
- 2016
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Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 472:2190
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Ràfols, Francesc Pérez
(författare)
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Modelling and numerical analysis of leakage through metal-to-metal seals
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metal-to-metal seals are critical components as their failure can lead to leakage of hazardous fluids to the environment or to fatal failure of the systems they operate on. Most systems are subjected to increasingly more demanding conditions and deeper knowledge about how different parameters affect the leakage is necessary to design seals with the desired performance. Fundamental knowledge can be obtained by means of numerical simulations, since it can provide in-situ information which would be extremely difficult, if not impossible, to obtain by means of physical experiments only. Moreover, in the virtual experiments it is possible isolate the effect of variations in a single parameter. However, no model that can serve as a predictive tool and thus has been tested against experimental results has been found in literature. The reason for this is the complexity in accounting for both the multi-scale nature of surface roughness and its intrinsic randomness. This lack have defined the main objective of this work, i.e., to develop a model for the leakage through metal-to-metal seals, which can output quantitative results that can be used for comparison against experimental work. This has been accomplished by including the stochastic nature of the surface topography explicitly in a two-scale method. The model constructed following this approach fulfills the requirement of giving a quantitative prediction of metal-to-metal seals. Moreover, it also provides new insight on the expected variability in leakage introduced by the stochastic nature of the roughness.A secondary objective has been to investigate the seal behaviour during unloading, i.e., when the applied load is gradually released after having caused significant plastic deformation. The reason for assessing this topic is that metal-to-metal seals subjected to a certain load cycle exhibit, at any given load, a significantly larger leakage during the first loading than it does during the subsequent unloading for the same load. The numerical simulations of the seal behavior during unloading also confirmed the smaller leakage during unloading. Moreover, it was observed that a substantial load release was required before a significant leakage increase could be detected and that the leakage remained nearly constant up to that point. This is an important finding that can be used when designing seals in order to account for stress relaxation during service live.
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- Rafols, Francesc Perez, et al.
(författare)
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Modelling of leakage on metal-to-metal seals
- 2016
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 94, s. 421-427
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Tidskriftsartikel (refereegranskat)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.
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