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The Cauchy problem for the homogeneous time-dependent Oseen system in 3 : spatial decay of the velocity

Paul Deuring (2013)

Mathematica Bohemica

We consider the homogeneous time-dependent Oseen system in the whole space 3 . The initial data is assumed to behave as O ( | x | - 1 - ϵ ) , and its gradient as O ( | x | - 3 / 2 - ϵ ) , when | x | tends to infinity, where ϵ is a fixed positive number. Then we show that the velocity u decays according to the equation | u ( x , t ) | = O ( | x | - 1 ) , and its spatial gradient x u decreases with the rate | x | - 3 / 2 , for | x | tending to infinity, uniformly with respect to the time variable t . Since these decay rates are optimal even in the stationary case, they should also be the best possible...

The combination technique for a two-dimensional convection-diffusion problem with exponential layers

Sebastian Franz, Fang Liu, Hans-Görg Roos, Martin Stynes, Aihui Zhou (2009)

Applications of Mathematics

Convection-diffusion problems posed on the unit square and with solutions displaying exponential layers are solved using a sparse grid Galerkin finite element method with Shishkin meshes. Writing N for the maximum number of mesh intervals in each coordinate direction, our “combination” method simply adds or subtracts solutions that have been computed by the Galerkin FEM on N × N , N × N and N × N meshes. It is shown that the combination FEM yields (up to a factor ln N ) the same order of accuracy in the associated...

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