Numerical Schemes for Advection Reaction Equation Ramaz Botchorishvili Faculty of Exact and Natural Sciences Tbilisi State University GGSWBS,Tbilisi, July 07-11,
Outline 2 Equations Operator splitting Baricentric interpolation and derivative Simple high order schemes Divided differences Stable high order scheme Multischeme Discretization for ODEs
Equation 3 v(t,x) - velocity f (u,t) – reaction smooth functions
Operator splitting 4
5 LA -> ODE ->LA -> ODE-> … - first order accurate
Operator splitting 6 LA -> ODE ->LA -> ODE-> … - first order accurate LA -> ODE ->ODE->LA -> LA->ODE-> … - second order accurate
Interpolation 7
Lagrange interpolation 8
9 Pros & cons
Barycentric interpolation 10
Barycentric interpolation 11
Barycentric interpolation 12 Advantages Efficient in terms of arithmetic operations Low cost for introducing or excluding new nodal points = variable accuracy
Baricentric derivative 13
Baricentric derivative 14 Advantages: Easy for implementing Arithmetic operations High order accuracy
High order scheme for LA 15 Approximation for N=1, 2 nd order N=2, 4th order N=4, 8 th order …
High order scheme for LA 16 First order accurate in time, 2n order accurate in space
High order scheme for LA 17 First order accurate in time, 2n order accurate in space Possible Problems conservation & stability
Firs order upwind 18
Firs order upwind 19 Numerical flux functions
Firs order upwind 20 Numerical flux functions Properties 1.Consistency 2.Conditional stability (CFL) 3.First order in space and in time 4.conservative
Firs order upwind 21 Numerical flux functions Properties 1.Consistency 2.Conditional stability (CFL) 3.First order in space and in time 4.conservative
High order conservative discretisation 22
High order conservative discretisation 23 Harten, Enquist, Osher, Chakravarthy: given function in values in nodal points, how to interpolate at cell interfaces in order to get higher then 2 accuracy
Special interpolation/reconstruction procedure 24
Special interpolation/reconstruction procedure 25
Special interpolation/reconstruction procedure 26
Special interpolation/reconstruction procedure 27
Special interpolation/reconstruction procedure 28
Special interpolation/reconstruction procedure 29
Special interpolation/reconstruction procedure 30
Special interpolation/reconstruction procedure 31
Special interpolation/reconstruction procedure 32
Special interpolation/reconstruction procedure 33
Special interpolation/reconstruction procedure 34
Special interpolation/reconstruction procedure 35
Special interpolation/reconstruction procedure 36
Special interpolation/reconstruction procedure 37 High order accurate approximation
Special interpolation/reconstruction procedure 38 High order accurate approximation
Components of high order scheme 39 Discretization of the divergence operator baricentric interpolation baricentric derivative ENO type reconstruction procedure (Harten, Enquist, Osher, Chakravarthy): Given fluxes in nodal points Interpolate fluxes at cell interfaces in such a way that central finite difference formula provides high order (higher then 2) approximation Use adaptive stencils to avoid oscillations
Adaptation of interpolation 40 Use adaptive stencils to avoid oscillations interpolate with high order polynomial in all cell interfaces inside of the stencil of the polynomial If local maximum principle is satisfied then value at this cell interface is found If local maximum principle is not satisfied then change stencil and repeat interpolation procedure for such cell interfaces If after above procedure local maximum principle is not respected then reduce order of polynomial and repeat procedure for those interfaces only
Convergence in one space dimension 41 Algorithm ensures Uniform bound of approximate solutions Uniform bound of total variation Conclusions Approximate solution converge a.e. to solution of the original problem
Extension to higher spatial dimension 42 Cartesian meshes: strightforward Hexagonal meshes: Directional derivates => div needs three directional derivatives in 2D Implementation with baricentric derivatives without adaptation procedure See poster ( Tako & Natalia) Implementation with adaptation – not yet
Better ODE solvers 43 Different then polinomial basis fanctions, e.g approach B.Paternoster, R.D’Ambrosio
44 Thank you