[CIG-LONG] Initial temperature conditions

[Walter Landry]

Robert Gray <graywacke at gmail.com> wrote:
>>> Robert Gray <graywacke at gmail.com> wrote:
>>> > Hello everyone,
>>> > I'm trying to set up an initial temperature profile in Gale that
>>> increases
>>> > steadily from 273 K to 1623 K in the top 120 km of the box, while
>>> > everything below that is 1623 K.  To do this I've used the following
>>> > condition:
>>> >
>>> >  "value": "(y>=0.48e6) ? -1.125e-2*y + 7023.0 : 1623.0"
>>> >
>>> > It works great for the first time step, but after that temperatures jump
>>> > several orders of magnitude to unrealistic values.  That said, the
>>> > incremental increase :
>>> >
>>> > "value": "(-1350.0/0.6e6)*y + 1623.0"
>>> >
>>> > works fine but does not produce the initial temperature profile I need.
>>>
>>> Can you send the input file to the mailing list?

The resulting viscosity structures are very different.  For the linear
temperature gradient, the mantle is still relatively high viscosity.
So with the boundary conditions you have, pushing at the top right,
you get strain dissipated throughout the mantle.

For the more realistic temperature profile, the mantle is very low
viscosity.  This allows the crust to slide along the top of the
mantle.  Since there is also a low viscosity block in the center, the
right side slides as a unit and you get strong vertical movement in
the middle at the top.

With the realistic temperature, you also have a very strong thermal
gradient.  It turns out that the step size that Gale automatically
computes is too large.  If you reduce the step size by a factor of 4
by running it with the options

  ./build/Gale wedgeThermal.json --dtFactor=0.25

then the temperature in the next step is not so bad.  However, I think
that there are "drunken seaman" problems after that.  To fix that, you
will have to reduce the step size much farther.  I tried
--dtFactor=0.01 and it seemed stable.  You should experiment to see
how large you can make it.

Cheers,
Walter Landry