Simulation error

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SebastianM
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Simulation error

Post by SebastianM » Sun Jul 30, 2017 7:03 pm -1100

Hello,

I´ve encountered a problem with a simulation. I´ve simulated a concrete block, which has 3 adiabatic borders and on the remaining surface, a measured climate is attached. The simulation shows, that the concrete block loses water (in the first few years). The more water is lost, the more clearly can yearly moisture cycles be seen. On one point, a turning starts to occur. The concrete block starts adding up water again while the amplitudes of the cycles are increasing. Under Control Parameters I´ve increased the Maxit [to 1.5e6] and Convergence Crit. [to 5e-8] by about the power of 3. This seems the delay the turning point when the concrete is starting to add water. Physically once the water content has dropped to a certain limit, the yearly moisture cycles should fluctuate around it in more or less a steady state behaviour.

Is there any solution for this problem? Thank you for your tips.
I´ve attached a picture that describes the problem better.

Best regards,

Sebastian
Attachments
simulation erros.jpg
simulation erros.jpg (37.36 KiB) Viewed 9002 times

Christian Bludau
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Re: Simulation error

Post by Christian Bludau » Sun Jul 30, 2017 11:26 pm -1100

Dear Sebastian,
can you post a picture of your construction? Is there air included?
Christian

SebastianM
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Re: Simulation error

Post by SebastianM » Mon Jul 31, 2017 9:50 pm -1100

Hello Christian,

thank you for your response.

The construction is a layered concrete wall with thin "monitoring" layers in between. The material characteristics are the same, except the moisture storage function. There are no air layers in the model.

Sebastian
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model construction.jpg
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Christian Bludau
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Re: Simulation error

Post by Christian Bludau » Tue Aug 01, 2017 12:58 am -1100

What grid did you use? And what boundary conditions?
Is the picture of the water content posted the total water content or did you evaluate a special layer?

Christian

SebastianM
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Re: Simulation error

Post by SebastianM » Tue Aug 01, 2017 7:17 pm -1100

I´ve used a measured climate which is very similar to alpine region weather data from the TRY (2011) data. The water content in the picture is the water content of the whole construction. The grid size I´ve used = min = max = (x=75,y=75). Could using a too small grid size such erros?

Sebastian

Christian Bludau
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Re: Simulation error

Post by Christian Bludau » Thu Aug 03, 2017 12:49 am -1100

Hello Sebastian,

I´m not really sure if this is an error. It may be, but I have seen similar results due to effects of coupled redistribution and drying.
If it si an error, it can be caused by to less grid elements or, what is more possible an unfavorable course of the moisture storage function. Maybe try to approximate them based on the measured values.

Christian

Manfred Kehrer
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Re: Simulation error

Post by Manfred Kehrer » Mon Aug 07, 2017 2:21 am -1100

I agree with you that this should not look like that. I guess you have areas in your model having max. saturated elements. We know there is an unsolved numerical problem for this case, Fraunhofer IBP specialists may help you better to solve this.
Manfred
Wiss, Janney, Elstner Associates, Inc.
Official WUFI® Collaboration Partner for USA/Canada
Enjoy WUFI® :) .... It is easy and complex.

SebastianM
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Re: Simulation error

Post by SebastianM » Mon Aug 07, 2017 6:28 pm -1100

Thank you for your response and help!

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