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Old   March 22, 2021, 14:43
Default Warnings in IC engine simulation
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Saket
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Hello Community,
I am getting many warnings in my IC engine simulation (GDI RANS, SAGE). Can anyone help me to get rid of these warnings? which parameter I should look in CONVERGE?

1. (Rank 1) WARNING: Stuck film parcel: ncyc=8111, RANK=1, location (3.902065e-02,-6.000000e-03,-3.442074e-02)

This warning starts 20 CAD after spray and lasts 20 CAD after ignition. I checked the locations and they are at the intersection of piston and liner. I tried compressing small area in piston but it didn't help.

2. recovering .... because transport equations did not converge or energy extrapolations

I tried changing relaxation parameter but again didn't get rid of these warning.

3. WARNING: max iterations exceeded on pstar, continuing for compressible simulation

increased max no of iterations for pressure to 700 from 500 default value, but it still doesn't converge.


Although I am still able to get results but still I would like to know the solutions for these.

Thanks
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Old   March 24, 2021, 12:17
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John Etcheverry
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Hello!

Let me address these one by one.

1 - This literally means a film parcel is stuck. It likely has something to do with the geometry near the location it provides. Check for sliver triangles, overlapping triangles, etc. - things that CONVERGE can run with but can sometimes cause problems. However, if you're not getting a large number of these warnings it should be safe to run with this warning.

2 - Recoveries indicate that the code wants to run at a lower timestep for stability. Plot num_recovers in time.out vs cycle number. How many times do you see a recovery? Are they clustered around an event occuring in the simulation? Valves/ports opening, spark firing, combustion, etc.

3 - This can be caused by taking large timesteps or poor initial conditions. Again, you can run through it, though it would be ideal to fix the root cause of it. How often are you seeing this warning and how long does it show up for?

- John

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Originally Posted by Sahus View Post
Hello Community,
I am getting many warnings in my IC engine simulation (GDI RANS, SAGE). Can anyone help me to get rid of these warnings? which parameter I should look in CONVERGE?

1. (Rank 1) WARNING: Stuck film parcel: ncyc=8111, RANK=1, location (3.902065e-02,-6.000000e-03,-3.442074e-02)

This warning starts 20 CAD after spray and lasts 20 CAD after ignition. I checked the locations and they are at the intersection of piston and liner. I tried compressing small area in piston but it didn't help.

2. recovering .... because transport equations did not converge or energy extrapolations

I tried changing relaxation parameter but again didn't get rid of these warning.

3. WARNING: max iterations exceeded on pstar, continuing for compressible simulation

increased max no of iterations for pressure to 700 from 500 default value, but it still doesn't converge.


Although I am still able to get results but still I would like to know the solutions for these.

Thanks
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Old   March 26, 2021, 01:27
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Quote:
Originally Posted by jetcheve View Post
Hello!

Let me address these one by one.

1 - This literally means a film parcel is stuck. It likely has something to do with the geometry near the location it provides. Check for sliver triangles, overlapping triangles, etc. - things that CONVERGE can run with but can sometimes cause problems. However, if you're not getting a large number of these warnings it should be safe to run with this warning.

2 - Recoveries indicate that the code wants to run at a lower timestep for stability. Plot num_recovers in time.out vs cycle number. How many times do you see a recovery? Are they clustered around an event occuring in the simulation? Valves/ports opening, spark firing, combustion, etc.

3 - This can be caused by taking large timesteps or poor initial conditions. Again, you can run through it, though it would be ideal to fix the root cause of it. How often are you seeing this warning and how long does it show up for?

- John
Hi John,
thanks for the reply.

1. I have checked through diagnosis tab, there are no overlapping or any other geometrical issues. I don't know what does silver triangle means and how to check it. There are however small area triangles in the piston but the location of stuck parcel is at the intersection between piston and liner. The warnings are actually quite large in numbers, I guess once the parcel is stuck, it moves with piston till it gets evaporated/burned and it shows warning till then for every location it travels.

2. I use minimum timestep of 1e-8 s. It occurs during combustion event for around 30 CA duration. There are 50+ or so recoveries which I think is not good.

3. Again minimum timestep is 1e-8 s and I use default simulation time as well as solver parameters. This warning is also quite large in number there is no specific event it occurs. As far as initial condition is concerned, would it matter if go for multi-cycle simulation?

Thanks
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