Positive pressure head in hydrus

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ES_92
Posts: 19
Joined: Sun Dec 06, 2020 11:22 am
Location: Italy

Positive pressure head in hydrus

Post by ES_92 » Tue Apr 27, 2021 4:23 am

Hello,
I am trying to simulate a subsurface porous pipe in sandy soil with constant pressure head. The model runs from -10 cm to 0 cm pressure head. If I try to run the model with positive pressure head for the porous pipe the model is not converging. The working pressure which I need to assign on the pipe boundary is 60 kPa. I have assigned the initial soil pressure head as -3000 cm.Can you please guide me how can I solve this issue? I have also attached the model.

Thanks in advance. Regards,
Afrida.
Attachments
H3D3_Model_01_MAR_sand(40X60cm_head).zip
(218.81 KiB) Downloaded 30 times

Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Positive pressure head in hydrus

Post by Jirka » Tue Apr 27, 2021 4:46 pm

We cannot help you given the information you provided. See FAQ 17: https://www.pc-progress.com/en/Default. ... q-11-20#k7. J.

ES_92
Posts: 19
Joined: Sun Dec 06, 2020 11:22 am
Location: Italy

Re: Positive pressure head in hydrus

Post by ES_92 » Wed Apr 28, 2021 4:12 am

Dear Prof Jirka,

Here is the model file in zip folder with .h3d2 file and output folder. Waiting eagerly for your response.

Regards,
Afrida.
Attachments
Model_Afrida.zip
(222.46 KiB) Downloaded 40 times

Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Positive pressure head in hydrus

Post by Jirka » Wed Apr 28, 2021 4:32 am

Before I look at it, you will need to explain me why do you think it is reasonable to apply the pressure head of 6 meters on a dripper, which is 15-20 cm below the ground. Also, have you look at the retention curve (for sand) before you applied the initial pressure of -30 m? J.

ES_92
Posts: 19
Joined: Sun Dec 06, 2020 11:22 am
Location: Italy

Re: Positive pressure head in hydrus

Post by ES_92 » Thu Apr 29, 2021 2:12 pm

Dear Prof. Jirka,

I am doing the simulation for a subsurface porous pipe. The minimum working pressure provided by the company is 0.6 bar. With this pressure the pipe infiltrates water uniformly. That is why I have chosen 0.6 bar pressure. For the initial water content of the sand, I tried to calculate the pressure head from the water content value using the Van Genuchten equation. I might be wrong in this case.

Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Positive pressure head in hydrus

Post by Jirka » Thu Apr 29, 2021 6:45 pm

You realize that if you apply pressure of 6 m 15 cm below the soil surface in a sandy soil, you will likely create a geyser at the surface above the dripper, right? J.

ES_92
Posts: 19
Joined: Sun Dec 06, 2020 11:22 am
Location: Italy

Re: Positive pressure head in hydrus

Post by ES_92 » Fri Apr 30, 2021 10:17 am

Dear Prof. Jirka,

I tried a short experiment with the porous pipe under sandy soil with 0.6 bar pressure using a pump. The flow in the air of the porous pipe at 0.6 bar is 1.2L/h/m. I also had this concern whether it will erode the soil on the top surface or not. I tried doing the simulation using the flow rate of the pipe but in that case it is independent of the soil type. That is why, I wanted to simulate the model with 0.6 bar pressure. I am also planning for a soil tank experiment for validating the model. But right now, I am not being able to proceed without the simulation result.

Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Positive pressure head in hydrus

Post by Jirka » Fri Apr 30, 2021 8:10 pm

I used the pressure head at the source of 100 cm, and got positive pressure heads at the surface in 6 minutes and a fully saturated profile in about 10 minutes. Your setup does not make much sense to me. J.
Attachments
Model_01_MAR_sand(40X60cm_head).rar
(124.16 KiB) Downloaded 26 times

ES_92
Posts: 19
Joined: Sun Dec 06, 2020 11:22 am
Location: Italy

Re: Positive pressure head in hydrus

Post by ES_92 » Wed May 26, 2021 4:55 pm

Dear Prof. Jirka,

Thank you very much for having a look into it. Also, I am sorry that I am bothering you regarding this issue again. The pipe which I am using for my experiment is permeable subterranean irrigation system (colloquial soaker tube) for industrial agriculture. It infiltrates water approximately 1.3 l/h/m at 0.6 bar pressure. after performing the experiment with this pipe in sandy soil for 13 hours, the wetting front did not reach the top soil surface, the flow was more downward. So, in my case how should I proceed? With 0.6 bar pressure my model is not converging.
Last edited by ES_92 on Thu May 27, 2021 9:10 am, edited 1 time in total.

Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Positive pressure head in hydrus

Post by Jirka » Wed May 26, 2021 6:14 pm

This seems like a relatively simple problem to simulate. We have posted tutorials for very similar problems (of subsurface flow). You should be able to figure it out. J.

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