Re: How to solve the problem of negative concentration
Hello Tero, I think about this issue again. I use the method that you mentioned, all positive values of concentration could be obtained. However, maybe it just related to the range of the values that...
View ArticleRe: How to solve the problem of negative concentration
Hi, I not sure did I understand you correctly...? This is just modeling trick how to get over problems during solving. Like Ivar said other things (mesh etc) are still main solution to this problems...
View ArticleRe: How to solve the problem of negative concentration
Hello, good morning. For my model, the concentration should be between 0-1 mol/l. However, some values are over 1, the largest values are about 1.03 (3%of the expectable largest value), and some values...
View ArticleRe: How to solve the problem of negative concentration
Hi often in time series models you have steep gradients at t=0 i.e. concentration at a boundary, nothing inside the domain. Then I have noticed that using a "boundary mesh" on the c=1 (or T=cnst)...
View ArticleRe: How to solve the problem of negative concentration
Hello Ivar, Thank you so much. My model is stationary model with laminar flow and transport of diluted specie models. To my model I used the boundary layer mesh for the laminar flow, and got physical...
View ArticleRe: How to solve the problem of negative concentration
Hi indeed my remark was more for time dependent cases with high gradients due to initialcondition steps. The next on the list, in my view, is the numerical stabilisation parameters, but I'm not use to...
View ArticleRe: How to solve the problem of negative concentration
Hi, Try this: if(c<0,eps,if(c>1,1,c)). Best regards Tero Thank you so much, Tero. I appreciate your helps.
View ArticleRe: How to solve the problem of negative concentration
if(c<0,eps,if(c>1,1,c)) Dear Tero, First i would like to say thank you because ,i am doing my MS project "modeling of electrosorption" using comsol version 4.3 at Hindustan Unilever...
View ArticleRe: How to solve the problem of negative concentration
Hi, Eps is coming from Comsol and it is about 2.2e-16. I have used it instead of zero. If c is between 0 and 1 it is keeping original value of c. For example if: c is -1 => return value is 2.2e-16...
View ArticleRe: How to solve the problem of negative concentration
Hi, Here is one trick to solve negative concentrations. I made variable "C" which is defined by "if(c<0,eps,c)" under Definitions => Variables. Instead of concentration "c" I used variable "C"....
View ArticleRe: How to solve the problem of negative concentration
Hi, Diffucult to say without seeing your model... have you check your model mesh? I have never tested this method with unsteady case. Best regards Tero
View ArticleRe: How to solve the problem of negative concentration
Hi Suresh, Thanks for the analysis. Is there any way to solve with logarithmic concentration(or any alternative approach) for time dependent drift-diffusion equation. Physically why we can't use your...
View ArticleRe: How to solve the problem of negative concentration
Dear All, I met the exactly same problem as you described. I am working on 3 coupled PDEs, two from the Joule heating, one PDE form diffusion-drift equation. The domain is a rectangle. The boundary...
View ArticleRe: How to solve the problem of negative concentration
Up Up Up Please see the up message. Thank you for your help.
View ArticleRe: How to solve the problem of negative concentration
Hi, Here is one trick to solve negative concentrations. I made variable "C" which is defined by "if(c<0,eps,c)" under Definitions => Variables. Instead of concentration "c" I used variable "C"....
View ArticleRe: How to solve the problem of negative concentration
(1) C=if(c<0,eps,c). No problems caused by negative ion concentration. However, there is a time step within which the maximum iterations of (constant damping) newton's method has been reached....
View ArticleRe: How to solve the problem of negative concentration
Hi, I am working with COMSOL 5.2 a. Is there still a same function to set as what you said about "if(c<0,eps,c)" ? Cause when I try with Definitions--> variables, it goes red (means can not...
View ArticleRe: How to solve the problem of negative concentration
Hello, With regards to the issue of negative concentration in general, please see:www.comsol.com/support/knowledgebase/952/ Based upon some of the previous questions about stabilization in this thread,...
View ArticleRe: How to solve the problem of negative concentration
Hi, I know it is in response to your very old post. But I also have the same negative concentration. And I am not able to incorporate the trick you suggested in this post. How do you have 2 variables...
View ArticleRe: How to solve the problem of negative concentration
Hi, I haven't use Comsol for ages but I try to remember how this was done. Yes, I have two variables where "c" is Comsol own parameter and "C" is new variable for calcuation purposes. "C" is used in...
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