Modelling of gas permeation through ceramic coatings produced by thermal spraying - ScienceDirect
JavaScript is disabled on your browser. Please enable JavaScript to use all the features on this page., February 2008, Pages 874-883Department of Materials Science and Metallurgy, Cambridge University, Pembroke Street, Cambridge CB2 3QZ, UKShow moreAbstractAn analytical model has been developed for simulation of gas permeation through thermal spray coatings, and for prediction of the permeability. The model is based on a geometrical representation of the coating microstructure. This involves thin splats, with limited inter-splat bridging, and microcracks within the splats. Important variables include the thickness (smallest dimension) of the inter-splat pores and intra-splat microcracks. Uniform values of these parameters are used in the model. Predicted permeabilities are compared with experimental data obtained using plasma-sprayed zirconia coatings, both in the as-sprayed state and after heat treatments sufficient to generate significant microstructural changes via sintering effects. In general, good agreement is obtained and it is concluded that the model constitutes a useful tool for exploration of gas permeation characteristics in coatings or layers produced by thermal spraying.KeywordsGas permeabilityAnalytical modellingPlasma spray coatingsPorous materialCheck if you have access through your login credentials or your institution.ororRecommended articlesCiting articles (0)Upwind schemes for the wave equation in second-order form - ScienceDirect
JavaScript is disabled on your browser. Please enable JavaScript to use all the features on this page., 1 July 2012, Pages Center for Applied Scientific Computing, L-422, Lawrence Livermore National Laboratory, Livermore, CA 94551, USAShow moreAbstractWe develop new high-order accurate upwind schemes for the wave equation in second-order form. These schemes are developed directly for the equations in second-order form, as opposed to transforming the equations to a first-order hyperbolic system. The schemes are based on the solution to a local Riemann-type problem that uses d’Alembert’s exact solution. We construct conservative finite difference approximations, although finite volume approximations are also possible. High-order accuracy is obtained using a space-time procedure which requires only two discrete time levels. The advantages of our approach include efficiency in both memory and speed together with accuracy and robustness. The stability and accuracy of the approximations in one and two space dimensions are studied through normal-mode analysis. The form of the dissipation and dispersion introduced by the schemes is elucidated from the modified equations. Upwind schemes are implemented and verified in one dimension for approximations up to sixth-order accuracy, and in two dimensions for approximations up to fourth-order accuracy. Numerical computations demonstrate the attractive properties of the approach for solutions with varying degrees of smoothness.KeywordsSecond-order wave equationsUpwind discretizationGodunov methodsHigh-order accurateFinite-differenceFinite-volumeCheck if you have access through your login credentials or your institution.ororRecommended articlesCiting articles (0)Covering Regular Graphs - ScienceDirect
JavaScript is disabled on your browser. Please enable JavaScript to use all the features on this page., September 1997, Pages 1-16Covering Regular GraphsaCharles University, Prague, Czech RepublicbUniversity of Oregon, Eugene, OregoncUniversity of Bergen, Bergen, NorwayShow moreopen archiveAbstractA covering projection from a graphGonto a graphHis a “local isomorphism”: a mapping from the vertex set ofGonto the vertex set ofHsuch that, for everyv∈V(G), the neighborhood ofvis mapped bijectively onto the neighborhood (inH) of the image ofv. We investigate two concepts that concern graph covers of regular graphs. The first one is called “multicovers”: we show that for any regular graphHthere exists a graphGthat allows many different covering projections ontoH. Secondly, we considerpartial covers, which require only thatGbe a subgraph of a cover ofH. As an application of our results we show that there are infinitely many rigid regular graphsHfor which theH-cover problem—deciding if a given graphGcoversH—is NP-complete. This resolves an open problem related to the characterization of graphsHfor whichH-COVER is tractable.Recommended articlesCiting articles (0)}