Hi,
Is it possible to solve dimensionless equations in COMSOL?
How to do that?
So, all post processing results will be in dimensionless form?
I need some expert comment.
Please someone answer.
Thanks,
Vivek
It is easy to model in COMSOL. At first non-dimensionalise your governing equations. Then find the coefficient in place of rho, mu, k, c_p etc and use it in the respective place. You will get non-dimensional solutions.
Defining a set of normalizing constants and ignoring any unit warnings that Comsol generates is sufficient to do non-dimensional analysis. But a piece of advice, the non-dimensional approach, especially if you have coupled physics, may lead you to unreasonable results. There are numerous threads on the Comsol forum discussing this, just google : non dimensional comsol, and go through them before proceeding.
Defining a set of normalizing constants and ignoring any unit warnings that Comsol generates is sufficient to do non-dimensional analysis. But a piece of advice, the non-dimensional approach, especially if you have coupled physics, may lead you to unreasonable results. There are numerous threads on the Comsol forum discussing this, just google : non dimensional comsol, and go through them before proceeding.
Thanks all.
This is to S C Saha. If N-S equation is non dimensionalized, we will put rho=1 and eta= 1/Re. right? Re= DVrho/eta (with actual value of properties)
This is to George. Why there will be a unreasonable result? Because we are solving alll physics in no dimensional form with the equations coupled through non dimensional variale.
Please reply.
Thanks,
Vivek
Hi,
this is related to the previous answers.
Does this require to scale the geometry (during drawing the geometry in COMSOL) according to the nondimensionalization?
I mean if the length of the geometry is 10 m and after non dimensionalization it becomes 1. So shall i draw the geometry of length 10 m or 1?
Please reply asap.
Thanks
Vivek
Hi Vivek. Yes you are right. Yes you should consider the charactteritic length = 1m to compare your results with non-dimensional results.
Cheers
Suvash
Hi George,
I could not understand your advice! The good think for COMSOL is, it is an equation solver unlike ANSYS. In Ansys we can not see the equations we are solving. But in COMSOL you can see all equations you are solving. If you have the correct non-dimensional equations with proper boundary conditions I don't see any problem.
Cheers
Suvash
can anybody please share a simple file of fluid flow in non dimension
I also would like to solve the N_S equation in dimensionless, have you solve this problem?
Hi Li,
Send me the dimensionless NS equations you want to solve (as different people use different dimensionless form). I will advise you how to choose parameters.
Regards
Suvash
Hi, Professor,
The attachment is the N-S equation. Thank you very much in advance.
Best regards
Li CK
Define all parameters with values first. If we divide two momentum equations by Re then you have to use rho = 1/(Re*Ca), eta = 1/Re, body force = -1/(Re*Ca). Rests just use 1.
Thats it.
Regards
Suvash
Dear Professor：
Thank you very much for your reply. Is the process of dimensionless in COMSOL as follows:
1)choose NONE in unit system;
2)define the parameter of Re can Ca
3) modificate the material property in the constitutive equations as you have told me.
Is the understanding right?
Thank you very much!
Best regards to you!
Li CK
Just as a follow-up, it is now possible to define dimensionless Geometry and Physics (including boundary and initial conditions) in newer versions of Comsol.
In the component, unit system, simply choose "None". I hope this helps other researcher...
Hi Li Changkun .
Is the way you mentioned here(in your last comment) is the correct way to tackle non-dimensionlise equations?
Thanks and Regards.
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