Discussion Forum

Posted: 1 decade ago 25 févr. 2013, 06:59 UTC−5

Hallo Suhail, you should gives us more information, if you really need help. The error message from the solver indicates that you do not have enough Dirichlet constraints. (Shot in the dark) The message [QUOTE] and a warning-->New constraint force nodes detected: These are not stored. [/QUOTE] tells me that you are doing something complicated. I suggest to start simple if you learn the software. Regards Jens

Posted: 1 decade ago 26 févr. 2013, 14:11 UTC−5

Hi jens, Thanks alot for your reply. Actually I donno more to tell as this is my first simulation in comsol. so iam attaching the mph file with this reply. You can have a look at it and help me. Thank you very much again.

Attachments:

• sample_test.mph

Posted: 1 decade ago 27 févr. 2013, 03:35 UTC−5

Hi, Unfortunately I do not have thre required modules. So I cannot help, But waves are complicated to model. Did you start learning the software with something simpler? Did you work through the tutorals? Regards Jens

Posted: 1 decade ago 27 févr. 2013, 10:47 UTC−5

Hi jens, Ok, Thank you for atleast coming forward to help me. Iam trying to design a Split Ring Resonator(a spiral ) for my project. Iam struggling with it, as iam very new to comsol. can you give me an idea how i can start with this and proceed. I attaching a image of the spiral. I read some where that i can create a spiral usind the parametric funcion. Thank you.

Attachments:

• srr.png

Posted: 1 decade ago 9 juil. 2014, 06:07 UTC−4

I am trying to built a simple structure and I also have same error. I design a simple heater and use the joule heating physics in comsol 4.4. I have tried all at my level best, read many documents but not result found, Pleas it u have any solution suggest me And please not give any suggestions accept my problem

Posted: 1 decade ago 11 juil. 2014, 03:43 UTC−4

Dear Kaushlesh, This is typically caused by a mistake in the setup of the physics. Probably your model is over constrained. As your are talking about Joule Heating, this could be caused by a mismatch of the in- and the outflux of current or thermal energy. Best is to check your results (COMSOL stores the results after an error), and see where the error comes from. If you see strange values in either the potential or the temperatures, that might be the cause of the error. Posting your model to this forum can also help so that other people can see what the cause is. Best regards, Frank

Posted: 7 years ago 27 juin 2017, 23:04 UTC−4

Updated: 7 years ago 28 juin 2017, 21:24 UTC−4

[QUOTE] Iam a newbie to comsol. And Iam learning comsol for my research. I simulated my first simulation and I got the below mentioned errors. Failed to find a solution. The relative error (4.6e+004) is greater than the relative tolerance. Returned solution is not converged. Later I did some modifications and the error was 'Failed to find a solution. The relative residual (0.0036) is greater than the relative tolerance. Returned solution is not converged. and a warning-->New constraint force nodes detected: These are not stored. Can anyone help me to eliminate this errors. [/QUOTE] Hello Suhail Khan, Increase the relative tolerance, you will get the most accurate solution if your problem can converge. you can change the relative tolerance by going to the "stationary solver1" under "study1", and then go to the 'setting' window, you can change the 'relative tolerance' value. Change that value from 0.001 (default value) to any other value (less than 1). It will allow you to complete the solution process but you will get less accurate solution. Regards, Ali

Posted: 7 years ago 28 juin 2017, 05:55 UTC−4

Updated: 7 years ago 28 juin 2017, 05:55 UTC−4

Parts of the suggestions in the forum linked above are dubious. The explanation of what the tolerance measures is not fully correct either. Using tolerances of the order of 0.1 is, in most cases, dangerous. It can be used temporarily for investigating a problematic model, but that implies that you accept 10% error. If you are interested in gradients of the dependent variable (as stresses in solid mechanics), this is not good enough. The errors in the gradients can be significantly larger. Also, in a nonlinear analysis with several steps (time steps or an auxiliary sweep), a sloppy tolerance may lead to convergence problems later on, since you are too far from the true solution. Regards, Henrik

Posted: 7 years ago 28 juin 2017, 06:11 UTC−4

Dear Henrik Sönnerlind, Thank you very much for your response. I have used 0.01 relative tolerance instead of default value which is 0.001 (as it is giving the tolerance error) in one of my simulation for shock analysis of a MEMS microphone.. By increasing the ''g'' acceleration force (for e,g 65000 g), it is giving the tolerance error. So if 0.01 value for relative tolerance is not correct then what can be the possible solution to solve this problem? Hope to hear from you. Regards.

Posted: 7 years ago 29 juin 2017, 09:23 UTC−4

Hi Muhammad, Using 0.01 is not that bad. Still, for any well-behaved problem, it should be possible to converge to almost any tolerance level just by allowing a large enough number of iterations. You can try to increase the number of allowed iterations. Also, you should check the scaling of the dependent variables. Using manual scaling rather than automatic may help. Regards, Henrik