Padding grids

[JuergenMey]

Dear Andy,
I hope you're doing well.

I recently worked with gflex and I ran into the following issue.
I want to compute the deflection for an ice load that extents close to the grid boundaries. I have a variable Te. Now I padded the load and Te grids with one flexural wavelength. The padded values are 0 for the load grid and the mean of the Te for the Te grid. When I run gflex I get deflections in places where there is no load nearby. I have done several tests: When padding a constant Te it works fine, only when padding a variable Te with some constant value this behavior appears.

The ice load:

The padded Te grid:

The deflection pattern:

Deflection grid when using a constant Te of 40 km:

Any ideas why this happens? BCs are 0Displacement0Slope. Is there some in-built functionality of gflex that can do this padding?
Thanks for your time.
Regards,
Jürgen

[awickert]

Thanks @JuergenMey, especially for such a detailed description of what you have done.

I think that the problem that you are encountering is due to the sudden change in Te when reaching the "padding". This discontinuity causes all of the derivatives of D to become suddenly quite large, and can affect the implicit numerical solution in unrealistic ways, as you noted here.

Equation 10 from the gFlex paper

Would you be able to generate a smoother transition to your padded Te and then test the result? One idea could be to fill the outer area with a constant Te value and then interpolate.

[JuergenMey]

Thanks for your answer! I will try and report back.