# TRM Simulation Convergence Issue with Low Permeability Soil

**URL:** <https://discourse.opengeosys.org/t/trm-simulation-convergence-issue-with-low-permeability-soil/1626>\
**Category:** Help & Support\
**Created:** [May 20, 2025, 6:34pm UTC](https://discourse.opengeosys.org/t/trm-simulation-convergence-issue-with-low-permeability-soil/1626 "2025-05-20T18:34:47Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![maripicod](https://discourse.opengeosys.org/user_avatar/discourse.opengeosys.org/maripicod/32/1209_2.png) [@maripicod](https://discourse.opengeosys.org/u/maripicod)\
**Post date:** [May 20, 2025, 6:34pm UTC](https://discourse.opengeosys.org/t/trm-simulation-convergence-issue-with-low-permeability-soil/1626/1 "2025-05-20T18:34:47Z")

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Dear all,

I am currently running a simulation of a pile embedded in soil using the ThermoRichardsMechanics (TRM) process. However, when I decrease the soil permeability, the simulation fails to converge.

I have already tried reducing the time step size, but the issue persists. I’m wondering if anyone has encountered a similar problem or has suggestions on additional parameters or strategies I could try to improve convergence.

Below is the solver configuration I am currently using:

```auto
  <nonlinear_solvers>
        <nonlinear_solver>
            <name>basic_newton</name>
            <type>Newton</type>
            <max_iter>50</max_iter>
            <linear_solver>general_linear_solver</linear_solver>
        </nonlinear_solver>
    </nonlinear_solvers>
    <linear_solvers>
            <linear_solver>
            <name>general_linear_solver</name>
            <eigen>
                <solver_type>PardisoLU</solver_type>
                <precon_type>DIAGONAL</precon_type>
                <max_iteration_step>10000</max_iteration_step>
                <error_tolerance>1e-8</error_tolerance>
            </eigen>
        </linear_solver>

```

 ![image](https://discourse.opengeosys.org/uploads/default/original/2X/a/a8075dff6d68c0f1e262934170b1b06d217f0894.png)

I would really appreciate any suggestion.  
Regards,  
María

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<div class="post-metadata">

**Author:** ![dmitri.naumov](https://discourse.opengeosys.org/user_avatar/discourse.opengeosys.org/dmitri.naumov/32/561_2.png) [@dmitri.naumov](https://discourse.opengeosys.org/u/dmitri.naumov)\
**Post date:** [May 20, 2025, 6:59pm UTC](https://discourse.opengeosys.org/t/trm-simulation-convergence-issue-with-low-permeability-soil/1626/2 "2025-05-20T18:59:14Z")

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Hi María,  
the pressure actually diverges, `Convergence criterion, component 1: |dx|=1...e+10....` So something goes wrong with the pressure. Do you have any oscillations? Then maybe [mass lumping](https://doxygen.opengeosys.org/dd/d17/ogs_file_param __prj__ processes __process__ thermo_richards_mechanics__mass_lumping) could help…

Try similar but simpler simulation (assembly time of 23s means you have large mesh), maybe go 2D first (if it is not already).

What are your non-linear solver convergence criteria?

As for the linear solver setting, the more correct one would be:

```xml
            <eigen>
                <solver_type>PardisoLU</solver_type>
                <scaling>true</scaling>
            </eigen>

```

where I added scaling, which might help (but not the problem in this particular case).

– d

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<div class="post-metadata">

**Author:** ![dmitri.naumov](https://discourse.opengeosys.org/user_avatar/discourse.opengeosys.org/dmitri.naumov/32/561_2.png) [@dmitri.naumov](https://discourse.opengeosys.org/u/dmitri.naumov)\
**Post date:** [May 20, 2025, 7:02pm UTC](https://discourse.opengeosys.org/t/trm-simulation-convergence-issue-with-low-permeability-soil/1626/3 "2025-05-20T19:02:44Z")

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and if you would post the complete log as text file, it might be helpful for analysis…

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<div class="post-metadata">

**Author:** ![maripicod](https://discourse.opengeosys.org/user_avatar/discourse.opengeosys.org/maripicod/32/1209_2.png) [@maripicod](https://discourse.opengeosys.org/u/maripicod)\
**Post date:** [May 20, 2025, 7:24pm UTC](https://discourse.opengeosys.org/t/trm-simulation-convergence-issue-with-low-permeability-soil/1626/4 "2025-05-20T19:24:52Z")

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Hi,

Thank you for your reply. Regarding the nonlinear solver, I currently have the following configuration:

```auto
> <nonlinear_solvers>
> <nonlinear_solver>
> <name>basic_newton</name>
> <type>Newton</type>
> <max_iter>50</max_iter>
> <linear_solver>general_linear_solver</linear_solver>
> </nonlinear_solver>
> </nonlinear_solvers>

```

I’m already using a 2D mesh, but I could try reducing its size.

I’ve attached the project file in case you’re able to take a look, I would really appreciate it.

Please let me know if you have any further suggestions.

Regards,  
María

[Mechanical\_NC\_layers\_GWT\_heating\_6hours\_correctper.zip](https://discourse.opengeosys.org/uploads/short-url/uOYgSZQpFHTWVGFMEmvr0y7Q1qo.zip) (6.1 KB)

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<div class="post-metadata">

**Author:** ![dmitri.naumov](https://discourse.opengeosys.org/user_avatar/discourse.opengeosys.org/dmitri.naumov/32/561_2.png) [@dmitri.naumov](https://discourse.opengeosys.org/u/dmitri.naumov)\
**Post date:** [May 20, 2025, 7:33pm UTC](https://discourse.opengeosys.org/t/trm-simulation-convergence-issue-with-low-permeability-soil/1626/5 "2025-05-20T19:33:15Z")

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The convergence criteria a a little loose (from your prj file):

```xml
                <convergence_criterion>
                    <type>PerComponentDeltaX</type>
                    <norm_type>NORM2</norm_type>
		    <abstols>1e0 1e-1 1e-1 1e-1</abstols>
                </convergence_criterion>

```

A guess would be, that you run into some state, which is not a valid solution (not close enough) of the system…

Try something like `1e-6 1e-4 1e-8 1e-8`…

If you could provide the meshes as well, I could take a look, how it would run on my computer. (and probably I’d need the mfront file as well → you can send the whole project to [dmitri.naumov@ufz.de](mailto:dmitri.naumov@ufz.de))

– d

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<div class="post-metadata">

**Author:** ![dmitri.naumov](https://discourse.opengeosys.org/user_avatar/discourse.opengeosys.org/dmitri.naumov/32/561_2.png) [@dmitri.naumov](https://discourse.opengeosys.org/u/dmitri.naumov)\
**Post date:** [May 20, 2025, 7:44pm UTC](https://discourse.opengeosys.org/t/trm-simulation-convergence-issue-with-low-permeability-soil/1626/6 "2025-05-20T19:44:45Z")

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As the problem seems to be in the pressure, you could try to “downgrade” the problem to the RichardsFlow first, just to see how things go for the pressure.