# The viscosity field changes intermittently

Hello everyone!

This is a problem in my calculation example, the viscosity field is changing intermittently, I don’t know whether it is the problem of the parameters I set, or the problem of interpolation or the problem of calculation, I read some articles also have such a problem, can someone give me some explanation?

Thank you！

Hi @Xiao,

Welcome and thank you for posting to the forum.

At this stage, we really don’t have enough information to provide input on the issue you reported.

Can you provide the following:

1. A summary of what the model goals (i.e., what processes are you trying to model)?
2. The prm file
3. Add a scale bar or axis tick marks to the figures, add additional images that show the mesh, and multiple figures that show how the viscosity field is changing with time).

read some articles also have such a problem, can someone give me some explanation?

Can you provide links to these articles and also provide a short summary of what they report the issue to be?

Cheers,
John

Hi @jbnaliboff ,

Thank you so much for your replies.

I want to implement a model that is coupled with ASPECT and FastScape. That compositional boundary conditions are that the top boundary is the defined function and the others are the initial matter field. The velocity boundary condition is a push velocity on the left ,a free slip boundary on the right , and I want to set an outflow boundary condition on the bottom . Is there anything wrong with this setup?

subsection Boundary composition model
set List of model names = function,initial composition
set Fixed composition boundary indicators = left , bottom
#set Allow fixed composition on outflow boundaries = true

subsection Function
set Coordinate system = cartesian
set Variable names = x,y,t
set Function constants = tsed=2e6 # duration of sedimentation switch time intervall
set Function expression =if(y>620e3 && t==0, 1,0);
0;
0;
0;
if(y>662e3 && t==0, 1,0);
0;
if(y>662e3 && sign( sin( t/tsed * pi) ) == 1,1,0);
if(y>662e3 && sign( sin( t/tsed * pi) ) == -1,1,0);
if(y>662e3, t/1e6, 0) ;
0;
0;
0
end
subsection Initial composition
end
end
subsection Boundary traction model
set Prescribed traction boundary indicators = bottom:initial lithostatic pressure
subsection Initial lithostatic pressure
set Number of integration points = 1800
set Representative point = 2800000, 670000
end
end
subsection Boundary velocity model
set Tangential velocity boundary indicators = right
set Prescribed velocity boundary indicators = left x:function

subsection Function
set Function constants = cm=100.0 #3600.024.0*365.25

``````set Function expression =  \
if(z<440000.0, -(360.0/490.0)/cm, \
if(z>540000.0, 2.0/cm, \
((((360.0/490.0)+2.0)/-100.0)*((z/1000.0)-540.0)-2.0)*(-1.0/cm))); \
0
set Variable names      = x,z
``````

end
end

Error reporting is not convergent.

Cheers,
Xiao

Hi Xiao,

Sorry for the delay, I missed your response when it was first sent.

Is there anything wrong with this setup?

In principal all of what you outlined is possible, but as to what the specific issue is in your setup.

Here is my suggestion - go through the parameter files on this github page, which are for an in-review rift inversion with Fastscape coupling study led by Frank Zwann.

Compare the PRM files in the aforementioned repository, and from there try to assess the differences in the setup. At first glance, my guess is one issue is the defined Boundary composition settings.

The zenodo repositories linked in another recent ASPECT rift + fastscape study (led by Anne Glerum) may also provide helpful points of comparison.

Can you do a comparison with those prm files, do additional testing, and report back?

Thanks!
John