Learning Forum

[Atish Gawale]

Is there an example which explain how to use *CESE and *CHEMISTRY keycards together?

I want to use chemkin, thermodynamics and transport files in my model. 

[Reno Genest]

Hello Atish,

What exactly are you trying to simulate? Have you seen the following papers?

https://www.dynalook.com/conferences/16th-international-ls-dyna-conference/cese-t2-2/t2-2-e-cese-039.pdf

https://www.dynalook.com/conferences/13th-european-ls-dyna-conference-2021/multiphysics/nasouri_university_of_texas.pdf/view

Reno.

[Atish Gawale]

Hello,

I am trying to simulate same problem mentioned in this paper (Eg: Response of concrete wall subjected to hydrogen explosion).

https://www.dynalook.com/conferences/13th-european-ls-dyna-conference 2021/multiphysics/nasouri_university_of_texas.pdf/view

When I use *CESE and *CHEMISTRY together I get following errors.

*** Error 150209 (CHEM+209)
     Chemistry EOS nonlinear temperature solver failed to converge.
     Error code = 50 Last iterate temperature = NaN

CHEM_COMBUSTION_T: Failed to converge.

In current database, I dont see any examples which explains use for *CESE and *CHEMISTRY keycards together. Hence I am looking for support in terms on LS Dyna examples with .k files or guidance from ANSYS support team.

[Reno Genest]

Hello Atish,

I don't know if we have an example model. Let me check with the developer.

 

Reno.

[Reno Genest]

Hello Atish,

Please try running your model with the latest R14.1 solver:

https://user:computer@ftp.lstc.com/user/mpp-dyna/R14.1.0/

https://user:computer@ftp.lstc.com/user/ls-dyna/R14.1.0/

Also, note that R15 should be released in the next few weeks and so you will be able to try with it soon.

Also, the plan is "to port the chemically-reacting flow capability to the *DUALCESE solver". 

At last, Ansys employees are not allowed to share files and models on the Ansys Forum. Hopefully you are able to debug your model and run with the latest solver. Also, maybe other users will be able to share their models with you.

If you have a commercial license, please create a support case on the Ansys Customer Support Space (ACSS) and we will be able to better help you:

customer.ansys.com

 

Let me know how it goes.

 

Reno.

[Atish Gawale]

Hello,

I am getting same error while using the latest R14.1 solver.

*** Error 150209 (CHEM+209)
     Chemistry EOS nonlinear temperature solver failed to converge.
     Error code = 50 Last iterate temperature = NaN

CHEM_COMBUST_T: Failed to converge.

Regards,
Atish

[Reno Genest]

Hello Atish,

Ansys employees are not allowed to upload and download models on the Ansys Forum. If you are a commercial customer, please create a support case on the Ansys Customer Support Space and we will be able to better assist you:

customer.ansys.com

Also, note that R15 should be released soon and it should include the latest developments for *CESE and *CHEMISTRY. You can check back in a few weeks and try R15.

You can still post your model here on the Forum and maybe another user will be able to have a look and help you.

 

Reno.

 

[Atish Gawale]

Hi,

I have simplified my model further similar to example 2.1 described in below paper.

https://www.dynalook.com/conferences/13th-european-ls-dyna-conference-2021/multiphysics/nasouri_university_of_texas.pdf/view

Geometry consists of 200X20X20mm 3D rectangular box with 100 and 10 elements across length and thickness direction respectively.

CESE CHEMISTRY_INITIAL to define chemistry for full 3D fluid domain and CESE CHEMISTRY SET to define hotspot pressure and temperature. CHEMISTRY_COMPOSITION /CHEMISTRY_CONTROL_FULL /CHEMISTRY_MODEL are chemistry keycards which define the species and finite rate chemistry model.

I suspect during finite rate chemistry calculations the temperatures might be falling below out of range temperatures and hence getting the error. I changed Tmin in CHEMISTRY_CONTROL_FULL and still unable to resolve the error.

[Atish Gawale]

Could the disparity in units systems between LS Dyna files and Chemkin files be the cause of this error?

My LS Dyna model is in CGS units system.

[Reno Genest]

Hello Atish,

Yes, the difference in units could cause the problem. Make sure to have your LS-DYNA CESE model in MKS and the Chemkin data in CGS. CGS is required for  chemkin data. Also, the *CESE chemically reacting flow solver assumes MKS units.

 

Let me know how it goes.

 

 

Reno.

[Atish Gawale]

Hi,

Just to clarify further, units will be cal/mol for the activation energy and mol-cm-s-K for the preexponential factor defined using modified Arrhenius equation?

Thanks. 

[Reno Genest]

Hello Atish,

Yes, the default units for activation energy is cal/mol and I would say mol-cm-s-K is correct fo preexponential factor. Here is more information from the developer:

"The chemkin data units are restricted as described next:

1. CGS is required
2. The rate constants are expressed in cm^3/mol.s for bimolecular reactions and in s^(-1) for unimolecular reactions.
3. The energy unit is erg for internal energies, enthalpies, entropies, free energies, and heat capacities.
4. For activation energies, the default unit is cal/mol;  however, the user can choose another unit for the activation energies by including a supplementary key word as JOULE/MOLE after the key work REACTION to switch to use J/mol as the unit for activation energies."

 

Reno.

[Atish Gawale]

Hi,

This is very useful information and I am able to resolve my error now. 

I have another question. How to define % vol of gas( or volume fraction) and air in a given volume using *CHEMISTRY COMPOSITION keyword or is there another way to define same. I need to define two different CHEMICAL COMPOSITION for inner volume and outer volume. How can I control the volume fraction of gas (say 10-30%) for inner volume. Refer example shown below.

[ynovozhilov]

So, CE/SE can use MKS units, and the Chemical part should use CGS. 

[ynovozhilov]

Hi Reno!

What could be a best practice to solver problem like next?

CHEM_COMBUST_T: Failed to converge
*** Error 150209 (CHEM+209)
     Chemistry EOS nonlinear temperature solver failed to converge.
     Error code = 50 Last iterate temperature = NaN

[Atish Gawale]

Try to reduce timestep size, or lower your CFL number.

Also, check if your model doesnt have any non-physical boundary conditions or initial conditions.

[ynovozhilov]

 

 

Could you please tell me in what units the pressure is set in *CHEMISTRY_CONTROL_0D cards? As I understand it, it’s not Pa. Could it be barye (Ba) or atm?

 

 

[Atish Gawale]

Units should be Pa if you are using MKS units system.

[ynovozhilov]

But this card is a part of Chemistry solver, and Chemistry solver works with CGS unit system, as it was mentioned already.

[Atish Gawale]

Chemkin files used in Chemistry_Model needs to be in CGS units, otherwise it should be MKS units.