mili111

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:
http://www.directupload.net/file/d/3810/eva369yz_png.htm

Kind regards, Michael

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?

Hi Peter,

thx for your quick answer.

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

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

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

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