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How to set periodic condition from year to year

Posted Jan 28, 2015, 10:09 a.m. EST Heat Transfer & Phase Change, Heat Transfer, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.4, Version 5.0 7 Replies

Tompson Last
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Hello!

I modelling thermo processes with phase change and have very long time of modelling (40-50 year). I want to set heat flux and temperature of surface time depented from year to year.
I have data:
MOUNTH HEAT FLUX TEMPERATURE
1 mounth - 0.3[W/(m*K)]; -26.4[degC];
2mounth - 0.27[W/(m*K)]; -26.4[degC];
3 mounth - 0.22[W/(m*K)]; -19.2[degC];
4 mounth - 0.23[W/(m*K)]; -10.3[degC];
5 mounth - 0.59[W/(m*K)]; -2.6[degC];
6 mounth - 12.99[W/(m*K)]; 8.4[degC];
7 mounth - 11.88[W/(m*K)]; 15.4[degC];
8 mounth - 11.66[W/(m*K)]; 11.3[degC];
9 mounth - 12.11[W/(m*K)]; 5.2[degC];
10 mounth - 1.98[W/(m*K)]; -6.3[degC];
11 mounth - 0.61[W/(m*K)]; -18.2[degC];
12 mounth - 0.38[W/(m*K)]; -24.0[degC];

Please, help! How to set this?

Best regards,
Tompson
7 Replies Last Post Feb 17, 2015, 10:33 a.m. EST
Rogelio Hernandez Aguirre
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Posted: 10 years ago Jan 28, 2015, 10:28 a.m. EST
I have the same kind of problem!, I dont know how to set up a temperature boundary condition changing over time. I am trying to use a Time dependent study but I don't know how.
I used a parametric sweep to change the temperature, but this option doesn't let me change the temperature according to the time.

I hope you can help me. I am sure is a really easy issue.
I have the same kind of problem!, I dont know how to set up a temperature boundary condition changing over time. I am trying to use a Time dependent study but I don't know how. I used a parametric sweep to change the temperature, but this option doesn't let me change the temperature according to the time. I hope you can help me. I am sure is a really easy issue.
Tompson Last
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Posted: 10 years ago Jan 28, 2015, 10:38 a.m. EST
Now I set the change temperature of time with help of interpolation function, but it is not convenient - get a huge table in Excel. For example, see attach file. First collumn - time [day], second - temp [degC].
But sometimes the temperature can not be read with the function and then, instead of a specific value is set the temperature of absolute zero.
Now I set the change temperature of time with help of interpolation function, but it is not convenient - get a huge table in Excel. For example, see attach file. First collumn - time [day], second - temp [degC]. But sometimes the temperature can not be read with the function and then, instead of a specific value is set the temperature of absolute zero.

Attachments:

Henrik Sönnerlind COMSOL Employee

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Posted: 10 years ago Jan 28, 2015, 10:58 a.m. EST
Hi,

You can use the modulo function to call your input periodically. In that way you only need to specify one cycle.

So if you have for example an 85 seconds long cycle described by myFunc, you can enter myFunc(mod(t,85)) in the boundary condition.

Note that when your data is given in days, you have to be a bit careful with the scaling of the time unit.

Regards,
Henrik
Hi, You can use the modulo function to call your input periodically. In that way you only need to specify one cycle. So if you have for example an 85 seconds long cycle described by myFunc, you can enter myFunc(mod(t,85)) in the boundary condition. Note that when your data is given in days, you have to be a bit careful with the scaling of the time unit. Regards, Henrik
Tompson Last
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Posted: 10 years ago Feb 16, 2015, 10:55 a.m. EST
How will be look this function? I'm not understand... Please, explain.
How will be look this function? I'm not understand... Please, explain.
Sergei Yushanov Certified Consultant
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Posted: 10 years ago Feb 16, 2015, 11:26 a.m. EST
Tompson,

Attached is implementation of periodic function.

Regards,
Sergei
Tompson, Attached is implementation of periodic function. Regards, Sergei

Attachments:

Tompson Last
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Posted: 10 years ago Feb 16, 2015, 2:09 p.m. EST
Sergei, thank you alot for your answer!

All right, model to solve good, but... but i have non stable solutions for first years... I attach picture. With unstable and stable solution respectively...

Best regards,
Tompson
Sergei, thank you alot for your answer! All right, model to solve good, but... but i have non stable solutions for first years... I attach picture. With unstable and stable solution respectively... Best regards, Tompson
Walter Frei COMSOL Employee

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Posted: 10 years ago Feb 17, 2015, 10:33 a.m. EST
Dear Tompson,

You may also find this information helpful for the type of modeling you are describing here:
www.comsol.com/blogs/modeling-a-periodic-heat-load/

Dear Tompson, You may also find this information helpful for the type of modeling you are describing here: http://www.comsol.com/blogs/modeling-a-periodic-heat-load/

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