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• Problem in modeling BHE with time dependant &quot;Power&quot;

Hello all,

I have to model a BHE field (only 5) für my MSc Thesis.
When i run my model to validate it with MATLAB, i used a constant Power for my first BHE, which was -40 MJ/d.
So there everything was fine and it matches with the MATLAB calculation.

But now i built a timeseries for 10 years, and always after exactly one year the model explodes! Temperatures rise above several hundreds °C and my cooling flag break away. I even tried to discretisize my model more, but then i get this error after one month "Incomplete satisfaction of flow constraints within 30 iterative cycles at time=3.100000e+001 [d]. Termination of cycling".
I also set lower time steps (one day) but no success.
Right now i run the model without more refinements (original model from the beginning) but set the time steps to half a day, but now the cooling flag breaks after one month! When this happens my time steps go down to xx*10^-5. The only error FEFLOW gives me here is: "Math: Argument domain error in function sqrt!"

I hope anyone can help me, im realy desperate. I only have 2-3 weeks to get the model done, and i dont have any idea what is my fault.

Here you can see my burst model:

Kind regards, Michael
• BHE parametrization

Hello guys,

i wondered about the parametrization of my BHE in FEFLOW. I have to set:
- inlet temperature (~20°C)
- heat input rate (~7*10^8 )
- temp difference (3°C)
- power (?)

but i dont know which value i have to put in. I was looking for referee values in literature (values in braces), but i am not sure whether they´re reasonable or not. Besides i dont know the meaning of the parameters 100%. Do i set the temperature i gather from the soil, or the temperature after passing through the heat pump for inlet temperature? What i have to set für the temp difference? And what für power? I even specify my abstraction capacity in heat input rate, doesn´t i?

I hope you can help me.

Kind regards, Michael

Edit: my calculated heat input rate is one decimal power smaller than in literature. Is it good anyway? My BHE is only 38m big, maybe thats the reason for that?
• Re: Beginner questions

Hi Peter,

Ok, and setting elevation of the GW table means FEFLOW know that over this border i got an unsaturated zone, doesnt it? I´ve already seen the exercise on youtube, but owing the missing statements i dont understand every click they made. In the video for hydraulic head BC they mark the whole border (every slice), and set their hydraulic head value. But which value i have to insert? I tip the groundwater table hight, not the value over sea surface?
So i kill two birds with one stone. I got set my unsaturated/saturated zone AND i set the GW flow direction, am i right?

Ok so for soil temperature i´ll take the inflow boundary AND initial?

The Mesh inspector worked. In the tutorials i wondered what it is for. Thanks for that!

Regards, Michael
• Beginner questions

Hi all,

at the moment im modelling a problem in near-surface geothermics. Unfortunately my advisors dont know the feflow-stuff very good and during my study we dont get enough information and exercise. So please excuse my beginner questions. And sry for my bad english, i try my best.

I try to set my geometry bevor planting my BHE´s. But i meet some problems. I got a saturated and an unsaturated zone. My model is 60m deep but the upper slice is about 62m over sea surface. The groundwater lvl is 22,17m to ground lvl. A friend of mine said i easily had to set two hydraulic head boundary conditions to get a groundwater flow direction, which should be W-E. So i would set the first BC on the W-side with a hight of 22,1m and the second on the E-side with 22,2m to get a W-E-flow. Is this assumption right? Or do i have to take 40,x m above sea surface in order that FEFLOW understand what i want? Does FEFLOW understand that my unsaturated zone lies above this 22m? I hope i can get my problem across to you guys.

My second problem is the soil temperature. How can i insert this the best way? My first thought was to set a temperature BC at the W-border. So my groundwater flowing trough the border and take this temperature. My annual average temp is 11,3°C for the soil. Or is it better to set an initial condition over the whole model? How do i set initials? Simply insert it in "process variables --> heat transport --> temperature"?

Which brings me to another point. When i set initials or boundarys, where can i see my inserted values? When i set material properties they are shown in the slice view (on top of the view), but initials and boundarys are not shown. So i dont know later which values i inserted for these.

I hope i managed to explain my problems to u understandable and that you have any solutions für me.

Kind regards, Michael from Germany
• Re: Rate Budget Pending?

Ok i got it :D
The Problem was, that i run the tutorials 1-9 yesterday and today i planned to continue with tut10 in my save data. But to get my flow simulation i have to go back to tut9 and start the simulation. In the save data the simulation automatically stopped. Thats all!

Greetings
• Rate Budget Pending?

Hi all,

im completely new at FEFLOW an this forum. I need to create a heat flow model for my master thesis with FEFLOW and to get into the theme i tried the tutorials on youtube. In tut10 the rate budget  is neccesary for the flow simulation i think. But when i click on it the program says "pending..." instead of showing the boundary conditions. As a consequence of this, is think my "travel time, backward-streamline" legs weren´t shown in rainbow colours, like in the video. Is this assumption correct? What was my fault?

I hope you guys recognize what i mean. My english isn´t the best...

Greetings, Michael