# Step-by-Step Tutorial Session 3 - Yaw Angle Study (Part 2)

#45

Can you share your project as well as a picture of your pressure distribution @plakiasge?

Thanks!

Jousef

#46

Thank you very much @jousefm !
I couldnt see the solid_0_Barre in the list, that is why I could not find it before. I re-started the simulation and hope it finishes as soon as possible. Thank you again!

Best,

Vanessa

#47

Absolutely no problem Vanessa (@vbarreda)!

Hope you enjoy the sessions so far! Let me know if you need help with anything.

Happy SimScaling!

Jousef

#48

It seems to be fine. It was probably like the problem from @rishav997. Thank you for your respond @jousefm

#49

can i get some more time to submit my homework for this session?, actually i confronted some issues in meshing, and now i am late in submitting my homework

#50

@jousefm could you take a look at my convergence plot and let me know if there seems to be a mistake. We have not discussed the convergence plots specifically in this tutorial 3 but as I remember they are supposed to flat line towards the end which doesnāt seem to be the case in my project, although the individual forces have flat lined.

https://www.simscale.com/workbench/?pid=4962895595087045938#tab_0-0

#51

Should be no problem @hur_rehman! I will make sure you get in no trouble.

#52

Hi @nishank_a !

Question for you to make this more interesting and not just a question-answer-game. Would you say that the convergence is good enough with 10^{-4} or 10^{-5} ? Let me know what you think and discuss a bit

All the best!

Jousef

#53

@jousefm
10^-5 is considered to be a well converged result though in complicated problems 10^-5 is a pretty hard value to get.

#54

Hi @nishank_a!

I have found a very nice answer from @gholami on convergence in general:

The role of residuals in determining if simulation results are to be trusted should not be misunderstood. Reaching steady residuals means that the solution has converged to a value. Whether this value is correct or not can ultimately be concluded by monitoring the solution field.

There are a number of factors that could cause large pressure residuals. You could perform a convergence study to determine if results are reliable. In case of this simulation, consider the following:

Mesh quality could impose a lower limit on residual values. Even though your mesh looks good, convergence of the solution by refining the mesh should be studied. Specifically consider boundary vicinity and regions of high gradient.
Linear solvers have an impact on convergence behavior. You could try a different solver for pressure to see if residuals change.
Absolute and relative residuals must be considered carefully. We have had a discussion on this here. As demonstrated, residuals must be chosen in accordance with all variables. In your case, relative pressure residual could be reconsidered.
This list is in fact longer. You could reconsider the choice of the turbulence model, turbulence wall treatment, numerical schemes, etc. However, be aware that the residual value in itself is not the issue, e.g. one could under-relax to get smaller residuals, but this does not improve the solution. Whatever you do, convergence of the solution field is the deciding factor.

P.S.: Do you wish to get a SimWiki article for this subject to get a deeper understanding of the theory?

All the best!

Jousef

#55

@jousefm
Thanks for the detailed reply. Iāll take a look at the points mentioned and move forward from there.
The wiki would really be helpful.

#56

yes please review this issue, i am also getting this similar problem as multiple other usersā¦, could not figure out a fix though.

#57

Hi @hur_rehman!

Are you talking about the oscillations in the convergence plots? If so please share your project. Trying to find the culprit

All the best!

Jousef

#58

Kindly resolve this issue. I am stuck here

#59

Hi @hur_rehman!

As mentioned in previous posts you might first counter-check everything you have done with the tutorial. If that does not help sometimes the log file says something about the problem. Feel free to share the project with me.

Best,

Jousef

#60

Hi,
Iām having a problem with the simulation. After 20 to 30 minutes running it, shows a message saying āErrorā and nothing else. Iāve checked with the step by step tutorial and everything seems to be fine. Can anyone help me please?

#61

Hi @ricardo_3282, sorry for the small delay in my response.

Could you share the project you are referring to? Either @Get_Barried, @vgon_alves or me will check that out

Best,

Jousef

#62

Hi @jousefm,
here 's the link to my project:
https://www.simscale.com/projects/ricardo_3282/fsae_2017-workshop-s3-_yaw_angle-analysis-simulation_1/
Thank you so much.

#63

that seems to be the same issue like in this thread: FSAE CFD meshing and simulation convergence issue

Have to figure out whatās going on here.

Best,

Jousef

#64

Iām jumping in your project just now, but having a 1st look at your project, you need to put the same value to fwheel and MRF Front as you did for rwheel and MRF Rear: