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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Use long time series as boundary condition

Posted 2011年11月22日 GMT-5 11:26 Version 4.2 3 Replies

Alex Sun
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HI,

I have this 100-year daily precipitation time series (2 columns of data, one for time and the other for precipitation) that I want to use as time-dependent boundary flux. My question is whether I can import daily data into an interpolation function and use it in my model. Right now, int1(t [1/s]) seems to be the only way to go. However, doing so would require that I prepare my input in [m/s], which leads to large file size. Can I use something like int1(t [1/day])? If so, how do I tell COMSOL that my inputs are in days?
3 Replies Last Post 2011年11月23日 GMT-5 10:04
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2011年11月22日 GMT-5 15:20
Hi

check the doc, you have seconds hours and days at least as predefined units, so you can read in a series in days and get your units to convert the time t to the right value, as you wrote it (just check if it's "day" or "d"

it's at p473 in my 4.2a user manual ;)

--
Good luck
Ivar
Hi check the doc, you have seconds hours and days at least as predefined units, so you can read in a series in days and get your units to convert the time t to the right value, as you wrote it (just check if it's "day" or "d" it's at p473 in my 4.2a user manual ;) -- Good luck Ivar
Alex Sun
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Posted: 1 decade ago 2011年11月23日 GMT-5 09:36
Ivar,

Thanks. I wonder if I need to limit the maximum step size to less than 1 day because of the daily variable inward flux. Do you have experience? I did some simple experiments and found minor difference between with timestep upperlimit and without.

Alex



Hi

check the doc, you have seconds hours and days at least as predefined units, so you can read in a series in days and get your units to convert the time t to the right value, as you wrote it (just check if it's "day" or "d"

it's at p473 in my 4.2a user manual ;)

--
Good luck
Ivar


Ivar, Thanks. I wonder if I need to limit the maximum step size to less than 1 day because of the daily variable inward flux. Do you have experience? I did some simple experiments and found minor difference between with timestep upperlimit and without. Alex [QUOTE] Hi check the doc, you have seconds hours and days at least as predefined units, so you can read in a series in days and get your units to convert the time t to the right value, as you wrote it (just check if it's "day" or "d" it's at p473 in my 4.2a user manual ;) -- Good luck Ivar [/QUOTE]
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2011年11月23日 GMT-5 10:04
Hi

The principles remain, for time as for spatial, if you have fluctuations in any signal, and you need to resolve it you need a couple (if not several) points along the line over the variation (or gradient or flux ...)
So for me your comments sounds right: Nyquist does not only apply the frequency sampling ...

--
Good luck
Ivar
Hi The principles remain, for time as for spatial, if you have fluctuations in any signal, and you need to resolve it you need a couple (if not several) points along the line over the variation (or gradient or flux ...) So for me your comments sounds right: Nyquist does not only apply the frequency sampling ... -- Good luck Ivar

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