the rs-imex scheme for the low-froude shallow water equationsmhvignal/exposes/... · 2017. 11....

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The RS-IMEX scheme for the low-Froude shallow water equations Hamed Zakerzadeh joint work with: Sebastian Noelle Institut de Math´ ematiques de Toulouse, Universit´ e Toulouse III - Paul Sabatier Toulouse, France Nov. 22 nd 2017 This research was supported by the scholarship of RWTH Aachen university through Graduiertenf¨orderung nach Richtlinien zur F¨orderung des wissenschaftlichen Nachwuchses (RFwN).

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  • The RS-IMEX scheme forthe low-Froude shallow water equations¶

    Hamed Zakerzadeh

    joint work with: Sebastian Noelle

    Institut de Mathématiques de Toulouse, Université Toulouse III - Paul Sabatier

    Toulouse, FranceNov. 22nd 2017

    ¶This research was supported by the scholarship of RWTH Aachen university through Graduiertenförderung nach Richtlinien zurFörderung des wissenschaftlichen Nachwuchses (RFwN).

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Outline

    Introduction

    RS-IMEX scheme

    1d SWE

    2d SWENumerical experiments

    2d RSWENumerical experiments

    Recent progress

    1/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Outline

    Introduction

    RS-IMEX scheme

    1d SWE

    2d SWENumerical experiments

    2d RSWENumerical experiments

    Recent progress

    1/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    2/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    I g : gravity acceleration

    I f : Coriolis parameter

    I p : pressure

    I x := (x1, x2, x3)T

    I u := (u1, u2, u3)T

    Compressible Euler Equations∂t%+ divx (%u) = 0

    ∂t(%u) + divx (%u ⊗ u + pI3) =

    Gravitation︷ ︸︸ ︷−%g k̂

    Coriolis︷ ︸︸ ︷−%f k̂ × u

    3/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    I homogeneity =⇒ % constant

    I incompressibility =⇒ divxu = 0I shallowness =⇒ ∂x3p = −%g =⇒ u3 ∼ O(δ)

    Lh ∼ 102–103 kmLv ∼ 1–5 kmδ :=

    LhLv∼ 10−3 − 10−2

    I boundary conditions:I no normal flow at bottomI free surface at top

    Rotating Shallow Water Equations in horizontal plane (x1, x2){∂th + divx (hu) = 0

    ∂t(hu) + divx(hu ⊗ u + gh

    2

    2I2)

    = −gh∇xηb − fhu⊥

    ηb is the bottom function, u⊥ := (−u2, u1).

    4/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    I homogeneity =⇒ % constantI incompressibility =⇒ divxu = 0

    I shallowness =⇒ ∂x3p = −%g =⇒ u3 ∼ O(δ)

    Lh ∼ 102–103 kmLv ∼ 1–5 kmδ :=

    LhLv∼ 10−3 − 10−2

    I boundary conditions:I no normal flow at bottomI free surface at top

    Rotating Shallow Water Equations in horizontal plane (x1, x2){∂th + divx (hu) = 0

    ∂t(hu) + divx(hu ⊗ u + gh

    2

    2I2)

    = −gh∇xηb − fhu⊥

    ηb is the bottom function, u⊥ := (−u2, u1).

    4/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    I homogeneity =⇒ % constantI incompressibility =⇒ divxu = 0I shallowness =⇒ ∂x3p = −%g =⇒ u3 ∼ O(δ)

    Lh ∼ 102–103 kmLv ∼ 1–5 kmδ :=

    LhLv∼ 10−3 − 10−2

    I boundary conditions:I no normal flow at bottomI free surface at top

    Rotating Shallow Water Equations in horizontal plane (x1, x2){∂th + divx (hu) = 0

    ∂t(hu) + divx(hu ⊗ u + gh

    2

    2I2)

    = −gh∇xηb − fhu⊥

    ηb is the bottom function, u⊥ := (−u2, u1).

    4/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    I homogeneity =⇒ % constantI incompressibility =⇒ divxu = 0I shallowness =⇒ ∂x3p = −%g =⇒ u3 ∼ O(δ)

    Lh ∼ 102–103 kmLv ∼ 1–5 kmδ :=

    LhLv∼ 10−3 − 10−2

    I boundary conditions:I no normal flow at bottomI free surface at top

    Rotating Shallow Water Equations in horizontal plane (x1, x2){∂th + divx (hu) = 0

    ∂t(hu) + divx(hu ⊗ u + gh

    2

    2I2)

    = −gh∇xηb − fhu⊥

    ηb is the bottom function, u⊥ := (−u2, u1).

    4/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    I homogeneity =⇒ % constantI incompressibility =⇒ divxu = 0I shallowness =⇒ ∂x3p = −%g =⇒ u3 ∼ O(δ)

    Lh ∼ 102–103 kmLv ∼ 1–5 kmδ :=

    LhLv∼ 10−3 − 10−2

    I boundary conditions:I no normal flow at bottomI free surface at top

    Rotating Shallow Water Equations in horizontal plane (x1, x2){∂th + divx (hu) = 0

    ∂t(hu) + divx(hu ⊗ u + gh

    2

    2I2)

    = −gh∇xηb − fhu⊥

    ηb is the bottom function, u⊥ := (−u2, u1).

    4/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Non-dimensionalisation

    x̂ :=xL◦, t̂ :=

    t

    t◦, û :=

    uu◦, ĥ :=

    h

    H◦, η̂b :=

    ηb

    H◦, t◦ =

    L◦

    u◦

    Non-dimensionalised RSWESt∂t̂ ĥ + divx̂ (ĥû) = 0

    St∂t̂(ĥû) + divx̂

    (ĥû ⊗ û +

    ĥ2

    2Fr2I2

    )= −

    Fr2∇x̂ η̂b −

    Roû⊥

    St :=L◦/u◦

    t◦= 1, Fr :=

    u◦√gH◦

    , Ro :=u◦

    L◦f=

    f −1

    t◦

    We consider two singular limits:

    I Non-rotating: f = 0 and Fr = ε� 1

    I Rotating: Fr ∼ Ro = ε� 1

    5/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Non-dimensionalisation

    x̂ :=xL◦, t̂ :=

    t

    t◦, û :=

    uu◦, ĥ :=

    h

    H◦, η̂b :=

    ηb

    H◦, t◦ =

    L◦

    u◦

    Non-dimensionalised RSWESt∂t̂ ĥ + divx̂ (ĥû) = 0

    St∂t̂(ĥû) + divx̂

    (ĥû ⊗ û +

    ĥ2

    2Fr2I2

    )= −

    Fr2∇x̂ η̂b −

    Roû⊥

    St :=L◦/u◦

    t◦= 1, Fr :=

    u◦√gH◦

    , Ro :=u◦

    L◦f=

    f −1

    t◦

    We consider two singular limits:

    I Non-rotating: f = 0 and Fr = ε� 1

    I Rotating: Fr ∼ Ro = ε� 1

    5/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Analytical/Numerical issues

    What happens if ε→ 0?

    I Continuous level: Does the limε→0

    system exist?

    I comp. Euler → incomp. Euler [Klainerman and Majda, 1981]

    I RSWEquasi-geostrophic−−−−−−−−−→distinguished limit

    quasi-geostrophic equations [Majda, 2003]

    I Discrete/numerical level: How does the scheme behave?

    I Stiffness: wave speeds ∼ O( 1ε )- Explicit: CFL condition ∆t . ε∆x

    - Implicit: diffuses slow material waves

    I Inconsistency with the limit system

    6/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Analytical/Numerical issues

    What happens if ε→ 0?

    I Continuous level: Does the limε→0

    system exist?

    I comp. Euler → incomp. Euler [Klainerman and Majda, 1981]

    I RSWEquasi-geostrophic−−−−−−−−−→distinguished limit

    quasi-geostrophic equations [Majda, 2003]

    I Discrete/numerical level: How does the scheme behave?

    I Stiffness: wave speeds ∼ O( 1ε )- Explicit: CFL condition ∆t . ε∆x

    - Implicit: diffuses slow material waves

    I Inconsistency with the limit system

    6/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Asymptotic Preserving (AP) schemes

    Introduced by [Jin, 1999]

    - [Il’in, 1969]

    - [Larsen et al., 1987]

    I Asymptotic Efficiency (AEf): uniform CFL, efficient implicit step

    I Asymptotic Consistency (AC): consistent with the asymptotic system as ε→ 0

    I Asymptotic Stability (AS): uniformly stable in ε

    7/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Outline

    Introduction

    RS-IMEX scheme

    1d SWE

    2d SWENumerical experiments

    2d RSWENumerical experiments

    Recent progress

    7/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Reference Solution IMEX scheme (I)

    Hyperbolic system of balance laws for U ∈ Rq in Ω ⊂ Rd

    ∂tU(t, x ; ε) + divxF (U, t, x ; ε) = S(U, t, x ; ε),

    I IMEX: stiff + non-stiffimplicit + explicit

    I How to decompose?I non-linear stiff part → non-linear iteration [Degond and Tang, 2011]I linearly-implicit methods!

    ∂tU = N (U) =⇒ ∂tU = L(U) + (N −L)(U)

    I for ODEs [Rosenbrock, 1963]:

    x ′(t) = f (x) =⇒ x ′(t) = f ′(x) x(t) +[f (x(t))− f ′(x(t)) x(t)

    ]I for Euler with gravity [Restelli, 2007]I penalization method [Filbet and Jin, 2010]: ∂t f + v · ∇x f = 1εQ(f )

    Q(f ) = P(f ) + Q(f )− P(f ), P(f ) := Q′(M)(f −M)

    8/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Reference Solution IMEX scheme (I)

    Hyperbolic system of balance laws for U ∈ Rq in Ω ⊂ Rd

    ∂tU(t, x ; ε) + divxF (U, t, x ; ε) = S(U, t, x ; ε),

    I IMEX: stiff + non-stiffimplicit + explicit

    I How to decompose?I non-linear stiff part → non-linear iteration [Degond and Tang, 2011]I linearly-implicit methods!

    ∂tU = N (U) =⇒ ∂tU = L(U) + (N −L)(U)

    I for ODEs [Rosenbrock, 1963]:

    x ′(t) = f (x) =⇒ x ′(t) = f ′(x) x(t) +[f (x(t))− f ′(x(t)) x(t)

    ]I for Euler with gravity [Restelli, 2007]I penalization method [Filbet and Jin, 2010]: ∂t f + v · ∇x f = 1εQ(f )

    Q(f ) = P(f ) + Q(f )− P(f ), P(f ) := Q′(M)(f −M)

    8/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Reference Solution IMEX scheme (II)

    U = U︸︷︷︸Reference solution

    + D V︸︷︷︸scaled perturbation

    with D = diag(εd1 , . . . , εdq ) for U = U(0) + εU(1) + ε2U(2)

    F = F (U) +

    Linear︷ ︸︸ ︷F ′(U)DV +

    Nonlinear︷ ︸︸ ︷F̂ (U,V ) = D

    RS+IM+EX︷ ︸︸ ︷(G + G̃ + Ĝ

    )S = S(U) + S ′(U)DV + Ŝ(U,V ) = D

    (Z + Z̃ + Ẑ

    )

    ∂tV = −T +

    =:R̃︷ ︸︸ ︷(−divx G̃ + Z̃

    )+

    =:R̂︷ ︸︸ ︷(−divx Ĝ + Ẑ

    )with scaled residual of the reference solution

    T := D−1∂tU + divxG − Z

    9/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Reference Solution IMEX scheme (II)

    U = U︸︷︷︸Reference solution

    + D V︸︷︷︸scaled perturbation

    with D = diag(εd1 , . . . , εdq ) for U = U(0) + εU(1) + ε2U(2)

    F = F (U) +

    Linear︷ ︸︸ ︷F ′(U)DV +

    Nonlinear︷ ︸︸ ︷F̂ (U,V ) = D

    RS+IM+EX︷ ︸︸ ︷(G + G̃ + Ĝ

    )S = S(U) + S ′(U)DV + Ŝ(U,V ) = D

    (Z + Z̃ + Ẑ

    )

    ∂tV = −T +

    =:R̃︷ ︸︸ ︷(−divx G̃ + Z̃

    )+

    =:R̂︷ ︸︸ ︷(−divx Ĝ + Ẑ

    )with scaled residual of the reference solution

    T := D−1∂tU + divxG − Z9/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Reference Solution IMEX scheme (III)

    RS-IMEX scheme

    DtV n∆ = −Tn+1

    ∆ + R̃n+1∆ + R̂

    n∆

    I Time integration Dtφ(t, x) := φ(t+∆t,x)−φ(t,x)∆tI Rusanov-type flux fi+1/2 :=

    f (ui )+f (ui+1)2

    −αi+1/2

    2(ui+1 − ui )

    I Central discretization of the source term

    1: get Un∆ and V n∆

    2: find Un+1∆ → compute Tn+1

    3: Explicit step DtV n∆ = R̂n∆ → V

    n+1/2∆

    4: Implicit step DtVn+1/2

    ∆ = −Tn+1

    ∆ + R̃n+1∆ → V

    n+1∆

    5: Un+1∆ = Un+1

    ∆ + DVn+1

    10/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    a bit of literature review

    System Reference solution U[Bispen et al., 2014] SWE LaR[Schütz and Kaiser, 2016] Van der Pol ∞ damping[Zakerzadeh, 2016a] 1dSWE LaR and lake eq.[Kaiser et al., 2016] isent. Euler incompressible eq.[Zakerzadeh, 2016b] 2dSWE lake eq.[Bispen et al., 2017] Euler + gravity hydrostatic equilib.[Zakerzadeh, 2017b] 2dSWE + Coriolis barotropic vorticity eq.[Kaiser and Schütz, 2017] extends [Kaiser et al., 2016] to high order dG

    I Non-rotating:[Degond and Tang, 2011; Haack et al., 2012; Noelle et al., 2014; Bispen et al., 2014;Dimarco et al., 2016; Zakerzadeh, 2017a], . . .

    I Rotating:[Bouchut et al., 2004; Audusse et al., 2009, 2011, 2015, 2017; Lukáčová-Medvid’ováet al., 2007; Hundertmark-Zaušková et al., 2011]

    11/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Outline

    Introduction

    RS-IMEX scheme

    1d SWE

    2d SWENumerical experiments

    2d RSWENumerical experiments

    Recent progress

    11/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    1d Shallow water equations with topography

    ∂th + ∂x (hu) = 0∂t(hu) + ∂x (hu2 + h22ε2

    )= −

    h

    ε2∂xηb

    Define: [Bispen et al., 2014]

    I Hmean − ηb =: −b > 0I h = z − bI m := hu

    U =[zm

    ], F =

    mm2z − b

    +z2 − 2zb

    2ε2

    , S = [ 0− zε2∂xb

    ].

    12/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    I U := (z, 0)T lake at rest =⇒ T = 0I D := diag(ε2, 1) ⇐= η(0) = const.

    Ĝ =

    0v22z + ε2v1 − b

    +ε2

    2v21

    G̃ = [ v2/ε2(z − b)v1

    ]

    Ẑ = 0 Z̃ =[

    0−∂xb v1

    ]λ̂ = 0, 2 upert λ̃ = ±

    √z − bε

    V n+1/2i = Vni −

    ∆t

    ∆x

    (Ĝni+1/2 − Ĝ

    ni−1/2

    )(Explicit step)

    V n+1i = Vn+1/2i −

    ∆t

    ∆x

    (G̃n+1

    i+1/2− G̃n+1

    i−1/2

    )+ ∆t Z̃n+1i (Implicit step)

    13/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Asymptotic analysis

    Asymptotic analysis in 1d

    Theorem [Zakerzadeh, 2016a]

    For 1d SWE with topography in Ω = T and under an ε-uniform CFL condition, withwell-prepared initial data and LaR reference solution, the RS-IMEX scheme is

    (i) solvable: a unique solution for all ε > 0

    (ii) ε-stable: limε→0‖V n+1∆ ‖ = O(1)

    (iii) Rigorously AC: for the fully-discrete settings

    (iv) AS: there exists a constant CN,Tf such that

    ‖V n∆ ‖`2 ≤ CN,Tf ‖V0

    ∆ ‖`2

    (v) well-balanced: preserves the lake at rest equilibrium state

    (vi) possible O(ε2) checker-board oscillations for z

    14/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Asymptotic analysis

    Sketch of the proof: asymptotic consistency

    I recast the linear implicit step as JεV n+1∆ = Vn+1/2∆︸ ︷︷ ︸O(1)

    Jε :=

    [IN

    β

    ε2Q

    βRb IN

    ], β :=

    ∆t

    2∆x, α̃ = 0

    Q := Circ (0, 1, 0, . . . , 0,−1)

    (Rb)i = (bi+1 − bi−1, hi+1, 0, . . . , 0,−hi−1)

    I show that limε→0‖J−1ε ‖

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Asymptotic analysis

    Sketch of the proof: asymptotic stability

    V n∆ = Eimp EexpVn−1

    I Implicit: ‖Eimp‖`2 ≤ 1 + Cimp∆tI Explicit: ‖EexpV n−1∆ ‖`2 ≤ ‖V

    n−1∆ ‖`2 + Cexp∆t‖V

    n−1∆ ‖

    2`2

    ‖V n∆ ‖`2 ≤ (1 + Cimp∆t)(

    1 + Cexp∆t ‖V n−1∆ ‖`2)‖V n−1∆ ‖`2

    discrete Gronwall’s inequality [Willett and Wong, 1965]=⇒ requires smallness of the initial datum

    16/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Outline

    Introduction

    RS-IMEX scheme

    1d SWE

    2d SWENumerical experiments

    2d RSWENumerical experiments

    Recent progress

    16/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    2d Shallow water equations with topography

    F =

    m1 m2

    m21z − b

    +z2 − 2zb

    2ε2m1m2

    z − bm1m2

    z − bm22

    z − b+

    z2 − 2zb2ε2

    , S = 0−z∂xb/ε2−z∂yb/ε2

    .

    G := G(U), G̃ := G ′(U)V , Ĝ := G − G − G̃

    Z := Z(U), Z̃ := Z ′(U)V , Ẑ := Z − Z − Z̃

    I U : zero-Froude limit (lake equations){divxm = 0∂tm − divx ( m⊗mb )− b∇xπ = 0

    I Chorin’s projection method to update UI D = diag(ε2, 1, 1)

    17/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    V n+1/2ij = Vnij −

    ∆t

    ∆x

    (Ĝn1,i+1/2j − Ĝ

    n1,i−1/2j

    )−

    ∆t

    ∆y

    (Ĝn2,i j+1/2 − Ĝ

    n2,i j−1/2

    )V n+1ij = V

    n+1/2ij −

    ∆t

    ∆x

    (G̃n+1

    1,i+1/2j− G̃n+1

    1,i−1/2j

    )−

    ∆t

    ∆y

    (G̃n+1

    2,i j+1/2− G̃n+1

    2,i j−1/2

    )+ ∆t Z̃n+1ij −∆t T

    n+1ij

    T n+11,ij =(∇h,xm1n+1ij +∇h,xm2

    n+1ij

    )/ε2

    T n+12,ij = Dtm1nij +∇h,x

    (m1

    n+1,2ij

    z − bij

    )+∇h,y

    (m1

    n+1ij m2

    n+1ij

    z − bij

    )

    T n+13,ij = Dtm2nij +∇h,x

    (m1

    n+1ij m2

    nij

    z − bij

    )+∇h,y

    (m1

    n+1,2ij

    z − bij

    )

    18/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Asymptotic analysis

    Asymptotic analysis in 2d

    Theorem [Zakerzadeh, 2016b]

    For 2d SWE with topography in Ω = T2 and under an ε-uniform CFL condition, withwell-prepared initial data and zero-Froude limit reference solution, the RS-IMEXscheme is

    (i) solvable: a unique solution for all ε > 0

    (ii) “ε-stable”: limε→0‖V n+1∆ ‖ = O(1) (if U = 0 and ∇xη

    b = 0)

    (iii) Rigorously AC: for the fully-discrete settings

    (iv) “AS”: there exists a constant CN,Tf such that

    ‖V n∆ ‖`2 ≤ CN,Tf ‖V0

    ∆ ‖`2

    provided the reference solver is stable in some suitable sense

    (v) “well-balanced”: preserves the LaR state (if U∆,V∆ ∈ ULaR∆ )(vi) possible O(ε2) checker-board oscillations for z

    19/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Numerical experiments

    Travelling vortex

    I Exact solution is available [Ricchiuto and Bollermann, 2009]

    I Initial condition as [Bispen et al., 2014] with periodic domain Ω = [0, 1)2:

    z(0, x , y) = 1[r≤ π

    ω]

    (Γε

    ω

    )2(g(ωr)− g(π)) ,

    u1(0, x , y) = u0 + 1[r≤ πω

    ]Γ (1 + cos(ωr)) (yc − y),u2(0, x , y) = 1[r≤ π

    ω]Γ (1 + cos(ωr)) (x − xc ),

    with b(x , y) = −110, u0 = 0.6 and

    r := dist(x , xc ), xc = (0.5, 0.5)T , Γ = 1.4, ω = 4π,

    g(r) := 2 cos r + 2r sin r +1

    8cos 2r +

    r

    4sin 2r +

    3

    4r2.

    20/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Numerical experiments

    Travelling vortex: initial condition

    Initial condition for the travelling vortex example with ε = 0.8, computed on the 100 × 100 grid.

    21/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Numerical experiments

    Uniform accuracy (I)

    ε = 0.8. ε = 0.01.

    Error of the RS-IMEX scheme, computed on the 80 × 80 grid with CFL = 0.45 and Tf = 1

    22/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Numerical experiments

    Uniform accuracy (II)

    Experimental order of convergence for the travelling vortex example with Tf = 1.

    ε = 0.8N ez,`∞ EOCz,`∞ eu1,`∞ EOCu1,`∞20 2.61e-2 - 1.04e-1 -

    40 2.00e-2 0.38 6.80e-2 0.61

    80 1.23e-2 0.70 3.63e-2 0.91

    160 6.20e-3 0.99 1.65e-3 1.14

    ε = 10−6

    N ez,`∞ EOCz,`∞ eu1,`∞ EOCu1,`∞20 4.08e-14 - 1.04e-1 -

    40 3.13e-14 0.38 6.80e-2 0.61

    80 1.92e-14 0.71 3.63e-2 0.91

    160 9.69e-15 0.99 1.65e-3 1.14

    23/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Numerical experiments

    Should we invest in U?

    I solving for U takes around 1% of the total timeI the quality matters!

    ε = 0.01, U = U(0) . ε = 0.01, U = 0 .

    24/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Outline

    Introduction

    RS-IMEX scheme

    1d SWE

    2d SWENumerical experiments

    2d RSWENumerical experiments

    Recent progress

    24/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    2d Rotating shallow water equations with topography

    ∂t̂(Θẑ) + divx̂ (ĥû) = 0,

    ∂t̂(ĥû) + divx̂

    (ĥû ⊗ û +

    ĥ2

    2Fr2I2

    )= −

    Θ

    Fr2ĥ∇x̂ η̂b −

    Rou⊥,

    I two height scales: H◦ for Hmean, and Z◦ for z and ηb

    I ĥ = 1 + Θ(ẑ − η̂b)I Θ := Z◦

    H◦

    I F 1/2 := fL◦/√gH◦ = O(1)

    Quasi-geostrophic distinguished limit [Majda, 2003]

    Ro = ε� 1, Fr = F 1/2ε, Θ = Fε

    Θ ∼ ε =⇒ the variation of ηb and z are mild:

    ‖z‖, ‖∇xηb‖ = O(ε)

    25/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    ∂tz +1Θdivxm = 0,

    ∂tm + divx(

    m ⊗mΘz − b

    +Θz2 − 2bz

    2εI2)

    = −1

    εz∇xb −

    1

    εm⊥,

    with m := (Θz − b)u and 1−Θηb = −b.

    F =

    m1/Θ m2/Θ

    m21Θz − b

    +Θz2 − 2zb

    m1m2

    Θz − bm1m2

    Θz − bm22

    Θz − b+

    Θz2 − 2zb2ε

    SB =

    0−z∂xb/ε−z∂yb/ε

    SC = 0m2/ε−m1/ε

    26/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    I U : quasi-geostrophic equations [Majda, 2003]

    u = ∇⊥x z (geostrophic balance)∆xz = ζ, with ζ := ‖∇x × u‖

    (∂t + u · ∇x ) (ζ − Fz + Fηb) = 0 (potential vorticity eq.),

    I Arakawa method to update U [Arakawa, 1966]I D = I3

    G := G(U), G̃ := G ′(U)V , Ĝ := G − G − G̃

    Z := Z(U), Z̃ := Z ′(U)V , Ẑ := Z − Z − Z̃

    27/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Asymptotic analysis

    Asymptotic analysis in 2d rotating case

    Theorem [Zakerzadeh, 2017b]

    For 2d RSWE with topography in Ω = T2 and under an ε-uniform CFL condition, withwell-prepared initial data and the QGE reference solution, the RS-IMEX scheme is

    (i) solvable: a unique solution for all ε > 0

    (ii) “ε-stable”: limε→0‖V n+1∆ ‖ = O(1)

    (iii) Rigorously AC: for the fully-discrete settings

    (iv) “AS”: there exists a constant CN,Tf such that

    ‖V n∆ ‖`2 ≤ CN,Tf ‖V0

    ∆ ‖`2

    provided the reference solver is stable in some suitable sense

    (v) “well-balanced”: preserves the LaR state if U∆,V∆ ∈ ULaR∆(vi) possible O(ε) checker-board oscillations for the surface perturbation

    28/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Numerical experiments

    2d stationary vortex

    in periodic domain [0, 1)2, pressure gradient is balanced with the Coriolis force and theadvective terms [Audusse et al., 2009]:

    u0(r , θ) = ϑθ(r)θ̂, ϑθ(r) := 5r1[r< 15

    ] + (2− 5r)1[ 15≤r< 2

    5],

    z ′0(r) = ϑθ + εϑ2θr,

    where r is the distance to the vortex center (0.5, 0.5)T and Hmean = 2.

    29/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Numerical experiments

    Relative error for z.|z∆(t) − z∆(0)| for t = 10 and ε = 10

    −4.

    =⇒ the scheme is uniformly accurate and AS!

    30/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Numerical experiments

    Absolute divergence of the velocity field for ε = 10−4 at t = 1. Geostrophic balance for ε = 10−4 at t = 1.

    =⇒ the scheme is AC!

    31/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Numerical experiments

    Should we invest in U?

    ε = 0.1, U = U(0) . ε = 0.1, U = 0 .

    32/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    Outline

    Introduction

    RS-IMEX scheme

    1d SWE

    2d SWENumerical experiments

    2d RSWENumerical experiments

    Recent progress

    32/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    How to refine estimates?I following [Giesselmann, 2015]: (semi-discrete)

    I for Etot :=12‖h|u|

    2‖L1(Ω) +1

    2ε2‖z‖2L2(Ω) and all ε > 0

    E n+1tot ≤ Entot +O(∆t

    2)

    I for Ekin,(0) :=12‖|u(0)|

    2‖L1(Ω), when ε→ 0

    E n+1kin,(0) ≤ Enkin,(0) +O(∆t

    2)

    I following [Bispen et al., 2017]: (fully-discrete)I L1 estimate for non-linear explicit stepI L2 estimate for linear implicit stepI interpolation between the norms

    I follwoing [Gallouët et al., 2017; Feireisl et al., 2016; Berthon et al., 2016; Fischer,2015]?

    New applications?I Euler with congestion? (with Charlotte Perrin)

    33/34

  • Introduction RS-IMEX scheme 1d SWE 2d SWE 2d RSWE Recent progress

    ConclusionWe have analyzed the RS-IMEX scheme for shallow water equations:

    I 1d, 2d, 2d + Coriolis

    I “rigorous” asymptotic analysis =⇒ AP!I reasonable numerical results

    I H.Z., Asymptotic analysis of the RS-IMEX scheme for the shallow water equations in onespace dimension, HAL: hal-01491450.

    I H.Z., Asymptotic consistency of the RS-IMEX scheme for the low-Froude shallow waterequations: Analysis and numerics, XVI International Conference on Hyperbolic Problems.

    I H.Z., The RS-IMEX scheme for the rotating shallow water equations with the Coriolis force,In International Conference on Finite Volumes for Complex Applications, pp. 199–207.

    Springer, Cham (2017).

    Merci de votre attention !

    34/34

  • References

    The basic idea: stability of the modified equation

    Linear system ∂tU + A∂xU = 0 [Schütz and Noelle, 2014]:

    ∂tU + A∂xU = Dν∂2xU, Dν :=∆t

    2

    (α∆x∆t

    Iq − Â2 + Ã2 + [Ã, Â])

    is stable if P(ξ) := −iAξ − ξ2Dν has only eva with negative real parts.[Ĝ ′, G̃ ′

    ]=[G ′(U),G ′(U)

    ]=⇒ smaller, for smaller ‖U −U‖

    modified version as in [Zakerzadeh and Noelle, 2016]

    P̃(ξ) := −iξΛ− ξ2∆t

    2

    [α∆x∆t

    Iq − Λ2 + 2QR→R̃ Λ̃Q−1R→R̃

    Λ].

    limε→0‖U −U‖ = 0 =⇒ R and R̃ get closer =⇒ Q

    R→R̃ → Iq

    1/6

  • References

    T n+11,ij = Dtznij +

    1

    Θ

    (∇h,xm1 ij +∇h,xm2 ij

    )n+1T n+12,ij = Dtm1

    nij +∇h,x

    (m1

    2ij

    Θz ij − bij

    )n+1+∇h,y

    (m1 ijm2 ij

    Θz ij − bij

    )n+1+

    1

    2 ε∇h,x

    (Θz2ij − 2bijz ij

    )n+1+

    1

    εzn+1ij ∇h,xbij −

    1

    εm2

    n+1ij

    → one can check that ‖T n+1∆ ‖ = O(1)

    2/6

  • References

    References I

    Akio Arakawa. Computational design for long-term numerical integration of the equations of fluid motion:Two-dimensional incompressible flow. Part I. Journal of Computational Physics, 1(1):119–143, 1966.

    Emmanuel Audusse, Rupert Klein, and Antony Z. Owinoh. Conservative discretization of Coriolis force in a finitevolume framework. Journal of Computational Physics, 228(8):2934–2950, 2009.

    Emmanuel Audusse, Rupert Klein, Duc D. Nguyen, and Stefan Vater. Preservation of the discrete geostrophicequilibrium in shallow water flows, pages 59–67. Springer Berlin Heidelberg, 2011. doi:10.1007/978-3-642-20671-9 7.

    Emmanuel Audusse, Stéphane Dellacherie, Pascal Omnes Do Minh Hieu, and Yohan Penel. Godunov type schemefor the linear wave equation with Coriolis source term. HAL: hal-01254888, 2015.

    Emmanuel Audusse, Minh Hieu Do, Pascal Omnes, and Yohan Penel. Analysis of modified Godunov type schemesfor the two-dimensional linear wave equation with Coriolis source term on cartesian meshes. HAL: hal-01618753,2017.

    Christophe Berthon, Marianne Bessemoulin-Chatard, and Hélène Mathis. Numerical convergence rate for a diffusivelimit of hyperbolic systems: p-system with damping. arXiv preprint arXiv:1609.01436, 2016.

    Georgij Bispen, Koottungal Revi Arun, Mária Lukáčová-Medvid’ová, and Sebastian Noelle. IMEX large time stepfinite volume methods for low Froude number shallow water flows. Communications in Computational Physics,16:307–347, 2014.

    Georgij Bispen, Mária Lukáčová-Medvid’ová, and Leonid Yelash. Asymptotic preserving IMEX finite volumeschemes for low mach number Euler equations with gravitation. Journal of Computational Physics, 335:222–248, 2017.

    François Bouchut, Julien Le Sommer, and Vladimir Zeitlin. Frontal geostrophic adjustment and nonlinear wavephenomena in one-dimensional rotating shallow water. Part 2. High-resolution numerical simulations. Journal ofFluid Mechanics, 514:35–63, 2004.

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  • References

    References II

    Pierre Degond and Min Tang. All speed scheme for the low Mach number limit of the isentropic Euler equation.Communications in Computational Physics, 10(1):1–31, 2011.

    Giacomo Dimarco, Raphaël Loubère, and Marie-Hélène Vignal. Study of a new asymptotic preserving scheme forthe Euler system in the low Mach number limit. HAL: hal-01297238, April 2016.

    Eduard Feireisl, Mária Lukáčová-Medvid’ová, Šárka Nečasová, Antońın Novotnỳ, and Bangwei She. Asymptoticpreserving error estimates for numerical solutions of compressible Navier–Stokes equations in the low Machnumber regime. Preprint 49-2016, Czech Academy of Sciences, 2016.

    Francis Filbet and Shi Jin. A class of asymptotic-preserving schemes for kinetic equations and related problemswith stiff sources. Journal of Computational Physics, 229(20):7625–7648, 2010.

    Julian Fischer. A posteriori modeling error estimates for the assumption of perfect incompressibility in theNavier–Stokes equation. SIAM Journal on Numerical Analysis, 53(5):2178–2205, 2015.

    Thierry Gallouët, Raphaèle Herbin, David Maltese, and Antońın Novotnỳ. Implicit MAC scheme for compressibleNavier–Stokes equations: Low Mach asymptotic error estimates. hal-01462822, 2017.

    Jan Giesselmann. Low Mach asymptotic-preserving scheme for the Euler–Korteweg model. IMA Journal ofNumerical Analysis, 35(2):802–833, 2015.

    Jeffrey Haack, Shi Jin, and Jian-Guo Liu. An all-speed asymptotic-preserving method for the isentropic Euler andNavier–Stokes equations. Communications in Computational Physics, 12(4):955–980, 2012.

    Anna Hundertmark-Zaušková, Mária Lukáčová-Medvid’ová, and Florian Prill. Large time step finite volumeevolution Galerkin methods. Journal of Scientific Computing, 48(1):227–240, 2011.

    Arlen M. Il’in. Differencing scheme for a differential equation with a small parameter affecting the highestderivative. Mathematical Notes of the Academy of Sciences of the USSR, 6(2):596–602, 1969.

    Shi Jin. Efficient asymptotic-preserving (AP) schemes for some multiscale kinetic equations. SIAM Journal onScientific Computing, 21(2):441–454, 1999.

    4/6

  • References

    References III

    Klaus Kaiser and Jochen Schütz. A high-order method for weakly compressible flows. Communications inComputational Physics, 22(4):1150–1174, 2017.

    Klaus Kaiser, Jochen Schütz, Ruth Schöbel, and Sebastian Noelle. A new stable splitting for the isentropic Eulerequations. Journal of Scientific Computing, pages 1–18, 2016.

    Sergiu Klainerman and Andrew Majda. Singular limits of quasilinear hyperbolic systems with large parameters andthe incompressible limit of compressible fluids. Communications on Pure and Applied Mathematics, 34(4):481–524, 1981.

    Edward W. Larsen, J. E. Morel, and Warren F. Miller. Asymptotic solutions of numerical transport problems inoptically thick, diffusive regimes. Journal of Computational Physics, 69(2):283–324, 1987.

    Mária Lukáčová-Medvid’ová, Sebastian Noelle, and Marcus Kraft. Well-balanced finite volume evolution Galerkinmethods for the shallow water equations. Journal of Computational Physics, 221(1):122–147, 2007.

    Andrew Majda. Introduction to PDEs and waves for the atmosphere and ocean, volume 9. American MathematicalSociety, 2003.

    Sebastian Noelle, Georgij Bispen, Koottungal Revi Arun, Mária Lukáčová-Medvid’ová, and Claus-Dieter Munz. Aweakly asymptotic preserving low Mach number scheme for the Euler equations of gas dynamics. SIAM Journalon Scientific Computing, 36(6):B989–B1024, 2014. doi: 10.1137/120895627.

    Marco Restelli. Semi-Lagrangian and semi-implicit discontinuous Galerkin methods for atmospheric modelingapplications. PhD thesis, 2007.

    Mario Ricchiuto and Andreas Bollermann. Stabilized residual distribution for shallow water simulations. Journal ofComputational Physics, 228(4):1071–1115, 2009.

    Howard H. Rosenbrock. Some general implicit processes for the numerical solution of differential equations. TheComputer Journal, 5(4):329–330, 1963. doi: 10.1093/comjnl/5.4.329.

    Jochen Schütz and Klaus Kaiser. A new stable splitting for singularly perturbed ODEs. Applied NumericalMathematics, 107:18–33, 2016.

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    References IV

    Jochen Schütz and Sebastian Noelle. Flux splitting for stiff equations: A notion on stability. Journal of ScientificComputing, pages 1–19, 2014. ISSN 0885-7474. doi: 10.1007/s10915-014-9942-x.

    D. Willett and J. S. W. Wong. On the discrete analogues of some generalizations of Gronwall’s inequality.Monatshefte für Mathematik, 69(4):362–367, 1965.

    Hamed Zakerzadeh. Asymptotic analysis of the RS-IMEX scheme for the shallow water equations in one spacedimension. HAL: hal-01491450, 2016a. IGPM report 455, RWTH Aachen University, Submitted for publication.

    Hamed Zakerzadeh. Asymptotic consistency of the RS-IMEX scheme for the low-Froude shallow water equations:Analysis and numerics. In Proceedings of XVI International Conference on Hyperbolic Problems, Aachen, 2016b.

    Hamed Zakerzadeh. On the mach-uniformity of the Lagrange-projection scheme. ESAIM: Mathematical Modellingand Numerical Analysis, 51(4):1343–1366, 2017a.

    Hamed Zakerzadeh. The RS-IMEX Scheme for the rotating shallow water equations with the Coriolis force, pages199–207. Springer International Publishing, Cham, 2017b. doi: 10.1007/978-3-319-57394-6 22.

    Hamed Zakerzadeh and Sebastian Noelle. A note on the stability of implicit-explicit flux-splittings for stiff systemsof hyperbolic conservation laws. IGPM report 449, RWTH Aachen University, Submitted for publication, 2016.

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    IntroductionRS-IMEX scheme1d SWE2d SWENumerical experiments

    2d RSWENumerical experiments

    Recent progress