Variable flux BC as evaporating BC

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mGohar
Posts: 33
Joined: Wed Jul 15, 2015 11:16 pm
Location: USA

Variable flux BC as evaporating BC

Post by mGohar » Fri Sep 11, 2015 2:52 am

Hi,

I am simulating a drip irrigation in a 3D container. to account for drippers I've created a circle (2.3 cm in radius) around each dripper with the variable flux boundary condition. I'd like these areas participate in the evaporation process too, so when there is no irrigation, I set the flux to be equal the evaporation rate. Simulating with constant head initial condition, what I get is that in the circles soil dries faster than the surfaces with atmospheric boundary condition with the same value for evaporation rate (this happens even before any irrigation is applied). Could you please help me in this regard?

Thanks,
Mohammad

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

Re: Variable flux BC as evaporating BC

Post by Jirka » Sat Sep 12, 2015 6:32 pm

You should select the “Boundary Option” “Treat the Time-Variable Flux boundary condition as the Atmospheric BC”, so that the boundary pressure head cannot drop below the critical pressure head hCritA (used at atmospheric BCs). J.

mGohar
Posts: 33
Joined: Wed Jul 15, 2015 11:16 pm
Location: USA

Re: Variable flux BC as evaporating BC

Post by mGohar » Sun Sep 13, 2015 6:21 am

Thanks Dr. Jirka for your response!

Actually I've enabled that option but still there are some sensible differences as the time increases (again just evaporation fluxes). Here please find the project file if you like to take a look at it:
https://drive.google.com/file/d/0B467Yc ... sp=sharing

Best,
Mohammad

Jirka
Posts: 4695
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Variable flux BC as evaporating BC

Post by Jirka » Sun Sep 13, 2015 7:55 am

This is likely because you have such a dramatic difference between the spatial discretization at the boundaries with “Time-Variable Flux” and “Atmospheric”. I have quickly created a project that would have the same discretization on both boundaries, and got the same fluxes from both. J.

mGohar
Posts: 33
Joined: Wed Jul 15, 2015 11:16 pm
Location: USA

Re: Variable flux BC as evaporating BC

Post by mGohar » Sun Sep 13, 2015 8:22 pm

Thanks a lot for your help and time !

Umair
Posts: 3
Joined: Thu Dec 07, 2017 9:55 am
Location: China

Re: Variable flux BC as evaporating BC

Post by Umair » Sat Aug 04, 2018 4:33 pm

Evaporation simulation in subsurface drip by using Hydrus 3D
Dear Sir, Do you have any example paper on evaporation simulation in subsurface drip irrigation by using hydrus-3D . I am trying to simulate soil Evaporation in subsurface drip by using Hydrus 3D during maize germination. I done experiment in glass box size 50*50*100cm and having measured soil water dynamics & daily evaporation data during maize germination period. Hydrus 3d simulate well in soil water dynamic but for evaporation simulation, I am confused about surface area associated to evaporation in subsurface drip. Do you guide me about atmospheric & system dependent boundary condition for soil surface? I am confused about boundary condition.
Thanks

Jirka
Posts: 4695
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Variable flux BC as evaporating BC

Post by Jirka » Sun Aug 05, 2018 8:33 pm

Evaporation is usually modeled using the Atmospheric Boundary Condition. “Surface area associated with transpiration” is usually the entire soil surface. I recommend that you read the Help topic for “Time-Variable Boundary Conditions” J.

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