[aspect-devel] AGU meeting feedback

[Juliane Dannberg]

Hi Timo,
>>> - C.T. showed in his talk (hereby attached) that the Rayleigh-Taylor
>>> experiment as
>>> presented in van Keken et al. (JGR 1997) run with ASPECT yields
>>> abnormal results. It is of course understood that this experiment
>>> does not constitute a true benchmark since no analytical solution is
>>> known, but having a look at ASPECT's results vs. the results obtained
>>> with many other codes over the past 15 years leads to the inescapable
>>> conclusion that ASPECT (as provided to the user in version r1889)
>>> is the most 'off' in terms of second Vrms peak location and height.
>>> Even more worrying is the lack of convergence to stable results
>>> when resolution is increased.
>>> Despite varying many parameters this puzzling effect could not be
>>> eliminated.
>>> Since many users are currently busy studying plume dynamics, it is our
>>> belief that this problem should be addressed within the briefest delay.
> I would be interested in rerunning this exact setup. Cedric, can you
> please send me the .prm?
>
> A couple of things that come to my mind:
> 1. Are these tests using the intel compilers? We have been struggling
> with intel compiler bugs with the latest deal.II release and I am not
> trusting the compiler settings we used before 8.1 (which we in the
> process of releasing right now)
> 2. Could the second peak be initiated by an instability that depends
> on the mesh? All the runs are on a mesh with an even number of
> elements. It would be easy to test this by changing the geometry model
> to call subdivided_hyper_rectangle() with an odd number of repitions
> instead of hyper_rectangle().
> 3. What is that strange smearing at the top right half (starting at
> t=1000 on slide 15) on the bottom of the plume? This looks
> non-physical to me.
Just a short answer concerning your questions about the van Keken 
Benchmark:
(1) Cedric sent his input file to some of the aspect users and we tested 
it on different machines (among others I ran the benchmark on Wolfgang's 
machine with his deal.ii when I was in Texas, although back then I did 
not know it was the van Keken benchmark), and there was no difference in 
the results. I can attach the .prm file that Cedric sent to us.
(2) I also tried an adaptive mesh and the second peak was still too 
early (however, I did not check yet if it converged to any solution).
Finally, I thought about which methods were different in aspect compared 
to other codes and changed the timestepping scheme (I just used the old 
solution everywhere where aspect normally uses BDF2 to extrapolate), but 
this did not change the solution either.
I agree this is a problem we should resolve as soon as possible and when 
I get back to work in one week I would like to run some more tests, e.g. 
I would like to try Wolfgang's idea with setting cR to infinity.

Cheers,
Juliane

PS: Timo, I heard you might be there at CIDER next year? I considered 
going there as well, as I heard they might want to use aspect.


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############### Global parameters
# We use a 3d setup. Since we are only interested
# in a steady state solution, we set the end time
# equal to the start time to force a single time
# step before the program terminates.

set Dimension                              = 2
set Start time                             = 0
set End time                               = 2000
set Use years in output instead of seconds = false
set CFL number                             = 1.0
set Output directory                       = output_cedric

subsection Geometry model
  set Model name = box
  subsection Box
    set X extent  = 0.9142
    set Y extent  = 1.0000
  end
end

subsection Model settings
  set Include adiabatic heating               = false
  set Include shear heating                   = false # default: true
  set Tangential velocity boundary indicators = 0,1
  set Zero velocity boundary indicators       = 2,3
end

subsection Material model
  set Model name = simple
  subsection Simple model
    set Reference density             = 1010
    set Viscosity                     = 1e2
    set Thermal expansion coefficient = 0
  end
end

subsection Gravity model
  set Model name = vertical
  subsection Vertical
    set Magnitude = 10
  end
end


############### Parameters describing the temperature field
# As above, there is no need to set anything for the
# temperature boundary conditions.

subsection Boundary temperature model
  set Model name = box
end

subsection Initial conditions
  set Model name = function
  subsection Function
    set Variable names      = x,z
    set Function constants  = pi=3.14159
    set Function expression = if( (z>0.2+0.02*cos(pi*x/0.9142)) , 0 , 1 )
  end
end


############### Parameters describing the compositional field

subsection Compositional fields
  set Number of fields = 1
end

subsection Compositional initial conditions
  set Model name = function
  subsection Function
    set Variable names      = x,z
    set Function constants  = pi=3.14159
    set Function expression = if( (z>0.2+0.02*cos(pi*x/0.9142)) , 0 , 1 )
  end
end

subsection Material model
  subsection Simple model
    set Density differential for compositional field 1 = -10
  end
end

############### Parameters describing the discretization

subsection Mesh refinement
  set Initial adaptive refinement        = 0
  set Strategy                           = composition
  set Initial global refinement          = 7
  set Time steps between mesh refinement = 1000000
  set Coarsening fraction                = 0.05
  set Refinement fraction                = 0.3
end


##subsection Discretization
##  set Composition polynomial degree = 2
##  subsection Stabilization parameters
##    set beta  = 0.5
##    set cR  = 1e15
##  end
#3end



############### Parameters describing the what to do with the solution

subsection Postprocess
  set List of postprocessors = visualization, velocity statistics, composition statistics
  subsection Visualization
    set List of output variables = all
    set Output format                 = vtu
    set Time between graphical output = 100
  end
end