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Posted:
9 years ago
Jul 14, 2015, 8:58 a.m. EDT
Look "flc1hs" or "flc2hs".
Look "flc1hs" or "flc2hs".
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Posted:
9 years ago
Jul 14, 2015, 11:49 p.m. EDT
Thank you very much for the reply, I tried this equation,
0.25*(flc1hs(x^2,-0.5)+flc1hs(y^2,-0.5)) and I am getting this as the initial condition (initial_comsol.jpg).
I want to achieve something like this, (initial_malab.jpg)
Thank you very much for the reply, I tried this equation,
0.25*(flc1hs(x^2,-0.5)+flc1hs(y^2,-0.5)) and I am getting this as the initial condition (initial_comsol.jpg).
I want to achieve something like this, (initial_malab.jpg)
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Posted:
9 years ago
Jul 15, 2015, 2:46 a.m. EDT
What happens if you write
0.4*flc1hs(0.04 - x^2 - y^2, 0.01)?
What happens if you write
0.4*flc1hs(0.04 - x^2 - y^2, 0.01)?
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Posted:
9 years ago
Jul 16, 2015, 1:59 a.m. EDT
yep that worked. I am getting this white border around the initial cell. Do you know why?
yep that worked. I am getting this white border around the initial cell. Do you know why?
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Posted:
9 years ago
Jul 16, 2015, 2:13 a.m. EDT
I do not understand the image. How dense is the mesh around the circle? Please send a height plot.
I do not understand the image. How dense is the mesh around the circle? Please send a height plot.
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Posted:
9 years ago
Jul 16, 2015, 2:36 a.m. EDT
attached are the screenshots of initial stage and after 0.6seconds
attached are the screenshots of initial stage and after 0.6seconds
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Posted:
9 years ago
Jul 16, 2015, 3:16 a.m. EDT
White areas probably represent function values < 0 and also shows your mesh. If you have a time dependent problem the initial steps tend to give negative values as the step function is numerically rather tricky thing to realize. Have you tried flc2hs which has also continuous second derivative? But in principle it appears to work. Defining the second parameter as 0.001 makes the transition range very sharp; values below that I have not found to have any improvement.
White areas probably represent function values < 0 and also shows your mesh. If you have a time dependent problem the initial steps tend to give negative values as the step function is numerically rather tricky thing to realize. Have you tried flc2hs which has also continuous second derivative? But in principle it appears to work. Defining the second parameter as 0.001 makes the transition range very sharp; values below that I have not found to have any improvement.
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Posted:
9 years ago
Jul 16, 2015, 3:28 a.m. EDT
Thank you very much for the quick reply
I tried flc2hs, and I'm getting a similar result. I changed the second parameter to 0.001 and it is the same,
It is like this only for the initial step. at 0.1s onward white boundary is gone
Thank you very much for the quick reply
I tried flc2hs, and I'm getting a similar result. I changed the second parameter to 0.001 and it is the same,
It is like this only for the initial step. at 0.1s onward white boundary is gone
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Posted:
8 years ago
Aug 3, 2016, 9:12 a.m. EDT
You can also trying using logicals.
for instance (x^2 + y^2 > 0.4) will return 1 when true and 0 when false.
You can also trying using logicals.
for instance (x^2 + y^2 > 0.4) will return 1 when true and 0 when false.
Jeff Hiller
COMSOL Employee
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Posted:
8 years ago
Aug 3, 2016, 2:57 p.m. EDT
Hello Ashan,
I get the feeling that this may be a case of the situation that's been discussed in this Discussion Forum before (I cannot find the thread right now) where the user tries to impose a very rapid variation of a quantity at the nodes of a single quadratic element, not realizing that this can cause the quantity to overshoot or undershoot in between the nodes.
E.g. if you imagine a 1D quadratic element covering [-2;2] and you impose at the 3 nodes u(-2)=1, u(0)=0 and u(2)=0, then u will take negative values in [0;2]. This can be counter-intuitive but it's true. If your plot is set up so that only values of u between 0 and 1 are displayed, then you will naturally get a "hole" in your plot, like what your screenshots above show.
The solution is to use a finer mesh, one that uses more than one element to capture the gradient that you're imposing.
Jeff
Hello Ashan,
I get the feeling that this may be a case of the situation that's been discussed in this Discussion Forum before (I cannot find the thread right now) where the user tries to impose a very rapid variation of a quantity at the nodes of a single quadratic element, not realizing that this can cause the quantity to overshoot or undershoot in between the nodes.
E.g. if you imagine a 1D quadratic element covering [-2;2] and you impose at the 3 nodes u(-2)=1, u(0)=0 and u(2)=0, then u will take negative values in [0;2]. This can be counter-intuitive but it's true. If your plot is set up so that only values of u between 0 and 1 are displayed, then you will naturally get a "hole" in your plot, like what your screenshots above show.
The solution is to use a finer mesh, one that uses more than one element to capture the gradient that you're imposing.
Jeff
