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September 9, 2010 9:33pm UTC

BC for heat flux

Hello,

I´m trying to simulate le heat flux through a wall but I have the heat flux like a boundary condition and it change with the time. The problem is from a text book because i'm learning how to use the boundary condition variying with time.

I have the diferents values of Q for the 24 hours the day. It change every 3 hours but my simulations have a period of time in seconds like (0, 10, 900). The runs are every 15 minutes. I actually use the stored solutions options to take the last value like inicial value for the next run.

I found 2 ways to input the heat flux variying in time:

1) Put the values in a table in the options - fuctions - new - interpolate - table, but put the values of Q from 0 to 900 seconds

Can I enter a range of time for avoiding enter the same data every 3 hours?

2) the other way is enter a function that discribes the change of Q through the day.

If I put the data for all day from 0 seg to 86400 seg.. does COMSOL will only take the first 900 seconds for my range of times: range(0,100,900) ?


Thank you, in advance...

Ivette

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September 10, 2010 6:54am UTC in response to Ivette Prado

Re: BC for heat flux

Hi Ivette,

so if you defined your BC as tables or functions you have done everthing all right. I think the problem is, that you have choosen "time steps taken from solver" as "Free". So if COMSOL takes time steps, which a too big, COMSOL "jumps over" the changing BCs - since COMSOL does not really "know" where the steps of you BCs are. Do you have a 1D-problem? If yes, COMSOL should run really fast, so cou can set up low maximum time steps (e.g. delta t_max=20s or something like this).

In COMSOL you can choose "Periodic boundary conditions" - maybe this is something you can try -i never used it, and i don't really know what it exactly does - but it sounds quite interesting for you.


best regards

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