Explicit /implicit methods for some advection...
Transcript of Explicit /implicit methods for some advection...
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Explicit / implicit methods for some advection dominated
problems of transport and flow in porous media
Peter Frolkovič
K. Mikula, J. Urbán, T. KmeťoSlovak University of Technology, Bratislava
NM2PorousMedia, 2.10.2014, Dubrovnik
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Content
� Motivation� Fully implicit schemes� Fully explicit schemes� Semi-implicit schemes
P. Frolkovič: Application of level set method for groundwater flow with movingboundary. Adv. Wat. Res., 2012P. Frolkovič, K. Mikula, J. Urbán: Semi-implicit finite volume level set method for advective motion of interfaces in normal direction. Appl. Num. Meth., 2014T. Kmeťo: Semi-implicit numerical methods for the solution of advection equation. Dipl. Thesis, 2014
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MotivationAdvection dominated equations
� contaminant transport
P. Frolkovič, M. Lampe, G. Wittum: Numerical simulation of contaminant transport in groundwater using software tools of r3t. Comp. Vis. Sc., 2012, to appearP. Frolkovič, J. Kačur: Semi-analytical solutions of contaminant transport equation with nonlinear sorption in 1D, Computational Geosciences, 2006
Time dependant inflow concentration Stationary groundwater flow
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MotivationLevel set method
� moving boundaries and/or interfaces
P. Frolkovič: Application of level set method for groundwater flow with movingboundary. Advances in Water Resources, 2012
zero level set
Partially saturated zone (not solved here)
Fully saturated zone (Darcy’s law)
Groundwater table (moving boundary)
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MotivationLevel set method
� moving boundaries and/or interfaces
Partially saturated zone (not solved here)
Fully saturated zone (Darcy’s law)
Groundwater table (moving boundary)
P. Frolkovič: Application of level set method for groundwater flow with movingboundary. Advances in Water Resources, 2012
all level sets
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Moving groundwater table
� extension of flow velocity to whole domain� boundary conditions on implicitly given interface
� immersed interface methods
Motivation
P. Frolkovič: Application of level set method for groundwater flow with movingboundary. Advances in Water Resources, 2012
zero level set pressure velocity
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MotivationInterfaces moving in normal direction
P. Frolkovič, K. Mikula, J. Urbán: Semi-implicit finite volume level set method for advective motion of interfaces in normal direction. Appl. Num. Meth. 2014
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1D advection
� equivalent ``balance law’’ formulation
� space discretization
General scheme
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Properties
� obtained also by finite volume discretization in 2D/3D� in this form it is conservative
� particular scheme obtained by choice of
� explicit or implicit or explicit/implicit:� are known, are unknowns
� high-resolution form in the space discretization� involves 2nd and 1st order form, “limiters’’
General scheme
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1st order implicit upwind
� central difference?
Implicit schemes
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1st order implicit upwind
� central difference?
� upwind difference
� a system of linear algebraic eq’s, here it is simple� positive coefficients scheme for arbitrary time step
Implicit schemes
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Implicit schemes Comparison of 3 implicit schemes
P. Frolkovič, H. De Schepper: Numerical modelling of convection dominated transport coupled with density driven flow in porous media, Adv. Wat. Res.,2001
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Implicit schemes Advantage
� fully coupled with other implicit terms
Disadvantage
� poor resolution for pure advection
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1st order upwind
� upwind difference for
Explicit schemes
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1st order upwind
� upwind difference for
� explicit definition of unknowns
� positive coefficients scheme for restricted time step
Explicit schemes
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1st order upwind
� upwind difference for
� explicit definition of unknowns
� positive coefficients scheme for restricted time step � a remedy - flux-based method of characteristics
Explicit schemes
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Explicit schemes 1st order explicit upwind
P. Frolkovič: Flux-based method of characteristics for contaminant transport in flowing groundwater, Comp. Vis. Sc., 2002
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2nd order accurate upwind
� general idea like “finite Taylor series” for
Explicit schemes
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Explicit schemes Level set method
� capturing interfaces in applications
P. Frolkovič, K.Mikula: High-resolution flux-based level set method. SIAM J. Sci. Comp. 2007
zero level set many level sets velocity and streamlines
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Explicit schemes
2nd order accurate explicit upwind, done by Ch. Wehner
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Explicit schemes
1st order accurate explicit upwind on the same grid
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Explicit schemes Advantage
� good resolution for pure advection
Disadvantage
� decoupled from other terms
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Explicit schemes Time splitting errors
concentrations at t=0 …
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Explicit schemes Time splitting errors
… and after 2 large time stepsconcentrations at t=0 …
flux-based method of characteristics
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Explicit schemes Time splitting errors
… and after 2 large time stepsconcentrations at t=0 …
apparent time splitting error
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Inflow Implicit / Outflow Explicit Note that
� origin idea
Semi-implicit schemes
K.Mikula, M.Ohlberger: Inflow-Implicit/Outflow-Explicit Scheme for Solving Advection Equations, FVCA, 2011
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Inflow Implicit / Outflow Explicit Note that
� origin idea
� upwind method with finite Taylor series
Semi-implicit schemes
P. Frolkovič, K. Mikula, J. Urbán: Semi-implicit finite volume level set method for advective motion of interfaces in normal direction. Appl. Num. Math., 2014
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Inflow Implicit / Outflow Explicit
� non-conservative in general� they can be rewritten to a conservative form
� second order accurate� oscillatory in general
� standard limiter techniques can be used� linear system with matrices of special structures
� special solvers can be used � fast sweeping and fast marching methods
Semi-implicit schemes
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Illustrative 2D example
� expansion in normal direction with variable speed
Semi-implicit schemes
1 large time step256 small ime steps
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Conservative form Note that
Semi-implicit schemes
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Conservative form Note that
Limiter in implicit part
� choose such that
Semi-implicit schemes
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Illustrative 1D transport equation, V=const� 1st order accurate fully implicit upwind
Inflow Implicit/Outflow Explicit
dx=0.1CFL=1
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Illustrative 1D transport equation, V=const� 1st order accurate fully implicit upwind
Inflow Implicit/Outflow Explicit
dx=0.1CFL=1
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Illustrative 1D transport equation, V=const� 2nd order accurate semi-implicit upwind
Inflow Implicit/Outflow Explicit
dx=0.1CFL=1
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Illustrative 1D transport equation, V=const� 2nd order accurate semi-implicit upwind
Inflow Implicit/Outflow Explicit
dx=0.1CFL=2
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Illustrative 1D transport equation, V=const� 2nd order accurate method with limiter
Inflow Implicit/Outflow Explicit
dx=0.1CFL=2
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Illustrative 1D transport equation, V=const� 2nd order accurate method with limiter
Inflow Implicit/Outflow Explicit
dx=0.05CFL=2
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Conclusion
� (semi-) implicit methods for advection dominated problems may be revisited