Hello everyone,

I’m doing 3d simulations where I evaluate the dynamic topography. I got results I was not expecting and thought that the unremoved Nullspace net rotation was the problem. But after I removed the net rotation the resulting dynamic topography is the same. Why is it not effected?Because the flow pattern looks drastically different.

The original problem is that I got a result for dynamic topography for a model where there is no density contrast (or temperature) only viscosity. (I know this is very unrealistic but I wanted to see what this would result in.) As I understand it if there is no lateral density variation the dynamic topography should be zero. The following skript gives a non zero dynamic topography that has quite a complex pattern even though the model is very simple. When a do the same with a density anomaly instead of viscosity the result looks reasonable.

Thanks in advance, Maja

Here is my Skript:

# A simple setup for convection in a 3d shell. See the

# manual for more information.

set Dimension = 3

set Use years in output instead of seconds = true

set End time = 1000

set Output directory = output-mu_23_const_rm

subsection Material model

set Model name = multicomponent

subsection Multicomponent

set Densities = 4400

set Viscosities = 1e22, 1e23

set Viscosity averaging scheme = harmonic

end

end

subsection Compositional fields

set Number of fields = 1

end

subsection Initial composition model

set Model name = function

subsection Function

set Coordinate system = spherical

set Variable names =r,phi,theta

set Function expression = if(r>3480000 & r< 4480000 & phi > 0 & phi < pi/2 & theta>pi/4 & theta<3*pi/4 || r>3480000 & r< 4480000 & phi > pi & phi < 3*pi/2 & theta>pi/4 & theta<3*pi/4,1,0)

end

end

subsection Initial temperature model

set Model name = function

subsection Function

set Coordinate system = spherical

set Variable names =r,phi,theta

set Function expression = if(r>3480000 & r< 4480000 & phi > 0 & phi < pi/2 & theta>pi/4 & theta<3*pi/4 || r>3480000 & r< 4480000 & phi > pi & phi < 3*pi/2 & theta>pi/4 & theta<3*pi/4,1500,1500) #erst llsvp, dann mantel

end

end

subsection Geometry model

set Model name = spherical shell

subsection Spherical shell

set Inner radius = 3480000

set Outer radius = 6371000

set Custom mesh subdivision = list of radial values

set List of radial values = 3586033.3333333335, 3682066.6666666665, 3778100.0, 3874133.3333333335, 3970166.6666666665, 4066200.0, 4162233.333333333, 4258266.666666667, 4354300.0, 4450333.333333333, 4546366.666666666, 4642400.0, 4738433.333333333, 4834466.666666666, 4930500.0, 5026533.333333333, 5122566.666666666, 5218600.0, 5314633.333333333, 5410666.666666666, 5506700.0, 5602733.333333333, 5698766.666666666, 5794800.0, 5890833.333333333, 5986866.666666666, 6082900.0, 6178933.333333333, 6274966.666666666

set Initial lateral refinement = 2

end

end

subsection Boundary velocity model

set Tangential velocity boundary indicators = top, bottom

end

subsection Boundary temperature model

set Fixed temperature boundary indicators = top, bottom

set List of model names = spherical constant

subsection Spherical constant

set Inner temperature = 1500

set Outer temperature = 1500

end

end

subsection Nullspace removal

set Remove nullspace = net rotation

end

subsection Gravity model

set Model name = radial constant

end

subsection Mesh refinement

set Initial global refinement = 1

set Initial adaptive refinement = 1

set Strategy = temperature

set Time steps between mesh refinement = 15

end

subsection Postprocess

set List of postprocessors = visualization, dynamic topography, geoid

subsection Visualization

set Output format = vtu

set Time between graphical output = 1e6

set Number of grouped files = 1

set List of output variables = density,viscosity

end

subsection Depth average

set Time between graphical output = 1.5e6

set Output format = vtu

end

end

subsection Checkpointing

set Steps between checkpoint = 50

end