Hi Onno,

"- has there been an update with a gmsh example in which solid walls and inflow/outflow/specified flow conditions have been imposed at the boundaries"

There has not as of yet. The current set-up conditions are only for firedrake Mesh's and for reflective boundary conditions off of solid walls.

"has the time step been made adaptable based on flood/signal speeds"

Again not as yet, this will definitely be done though. At the moment, we specify a value of dt/dx and this dictates the timestep. This is an argument labelled as Courant in Timestepper class. See help(Timestepper).

"I tried daybreak over uniform beach and lowered the time step (adaptable one preferred) but am not sure whether

the slope limiter causes some spurious oscillations. Does the Ern slope limiter approach add an extra time step restriction above and beyond

the normal CFL* min_dx/|lambda| with CFL<1 and lambda = |u|+ sort (g h)?"

So this was a bug that came about from not slope limiting the momentum as well as the depth. This is in the latest pull request of the package but hasn't yet been accepted to merge. If you want to try this out, you may just copy straight off of the branch in which this update is on. There isn't an extra condition as I know of.

"Also the speed seems a bit low although I aim to run it against a 2D c-code I once made."

The speed is slow for 2D but this is as fast as I can get it for the time being. I will continue to look further into why this could be.

Hope this helps and gives you an update.

Many Thanks,

Ali

Alastair Gregory
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From: firedrake-bounces@imperial.ac.uk <firedrake-bounces@imperial.ac.uk> on behalf of Onno Bokhove <O.Bokhove@leeds.ac.uk>
Sent: 09 August 2016 12:56:03
To: firedrake
Subject: [firedrake] flood drake query

Hi,

Using/adapting flood drake:

- has there been an update with a gmsh example in which solid walls and inflow/outflow/specified flow conditions have been imposed at the boundaries

- has the time step been made adaptable based on flood/signal speeds.

- I tried daybreak over uniform beach and lowered the time step (adaptable one preferred) but am not sure whether

the slope limiter causes some spurious oscillations. Does the Ern slope limiter approach add an extra time step restriction above and beyond

the normal CFL* min_dx/|lambda| with CFL<1 and lambda = |u|+ sort (g h)?

- Also the speed seems a bit low although I aim to run it against a 2D c-code I once made.

Thank you,

Onno

See code snippet below.

""" demo file for simple 2d shallow water equations flooding on a slope """

from __future__ import division

from firedrake import *

from flooddrake import *

# Meshsize

n = 5

mesh = UnitSquareMesh(10*n, n)

# mixed function space

v_h = FunctionSpace(mesh, "DG", 1)

v_mu = FunctionSpace(mesh, "DG", 1)

v_mv = FunctionSpace(mesh, "DG", 1)

V = v_h*v_mu*v_mv

# for slope limiter

v_hcg = FunctionSpace(mesh, "CG", 1)

v_mucg = FunctionSpace(mesh, "CG", 1)

v_mvcg = FunctionSpace(mesh, "CG", 1)

VCG = v_hcg*v_mucg*v_mvcg

# setup free surface depth

g = Function(V)

x = SpatialCoordinate(V.mesh())

g.sub(0).interpolate(conditional(x[0] < 0.2, 3.0/9.8, 0.0))

# setup bed

bed = Function(V)

# setup actual depth

w = g.assign(g - bed)

x = SpatialCoordinate(V.mesh())

bed.sub(0).interpolate(0.25*x[0])

# setup source (is only a depth function)

source = Function(v_h)

# timestep

solution = Timestepper(V, VCG, bed, source, 0.0065)

solution.stepper(0, 2, w, 0.025)