Boundary condition

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tarek
Posts: 39
Joined: Mon Aug 30, 2010 6:46 am
Location: Sweden

Boundary condition

Post by tarek » Thu Apr 21, 2016 9:47 am

Hi
I want to simulate a laboratory soil column experiment with water applied from the lower boundary (upward flow) of the soil column. In this experiment, initially the soil in the columns will be dry and the water will be injected with a given amount for a certain time from the bottom of the soil columns. After that, water will be applied (from the lower boundary)several times until soil reachs the saturation state which will be recoginzed by the apperance of water on the top surface of the soil
My question is what is the boundary conditions that i can use? I think the lower boundary will be variable flux and what will be the suitable upper boundary condition that allowed me to know that the soil reached to saturation state?
Regards
Tarek

Jirka
Posts: 5216
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Boundary condition

Post by Jirka » Thu Apr 21, 2016 1:25 pm

Bottom BC: Variable flux.
Upper BC: Constant flux=0.

J.

Rakesseh
Posts: 2
Joined: Mon Jun 15, 2020 6:47 am
Location: Australia

Re: Boundary condition

Post by Rakesseh » Tue Dec 01, 2020 1:06 am

Hi,
I want to simulate drying and wetting cycles in a laboratory column experiment. The column is saturated by applying water from the lower boundary.
The saturation is maintained for one week while allowing water to leave the column only by evaporation. After one week, flow at the lower boundary to maintain saturation is stopped. However, water is allowed to leave the column from the upper boundary only.
The drying only cycle is maintained for three weeks.
The wetting and drying cycles are repeated over several weeks.
What appropriate upper and lower boundary conditions can I use for such drying and wetting scenario.

Kind regards,
Akesseh

Jirka
Posts: 5216
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Boundary condition

Post by Jirka » Tue Dec 01, 2020 1:31 am

Surface: Atmospheric BC or Variable Flux BC
Bottom: Variable Flux BC

J.

Rakesseh
Posts: 2
Joined: Mon Jun 15, 2020 6:47 am
Location: Australia

Re: Boundary condition

Post by Rakesseh » Tue Dec 01, 2020 1:53 am

Hello Jirka,
Thank you very much for the response.
I have tried the atmospheric boundary and variable flux at the lower boundary. I realised that the pressure head at the upper boundary was always increasing. How do I maintain the pressure head at upper boundary at 0 during wetting (i.e. saturation).

Kind regards,
Raphael

Jirka
Posts: 5216
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Boundary condition

Post by Jirka » Tue Dec 01, 2020 3:05 pm

Atmospheric BC is meant for unsaturated soil surface, which can occasionally become saturated, but should be mostly saturated. You do not need a numerical model for conditions when the column is fully saturated. J.

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