Question about Cauchy boundary condition.

Hello everyone,
For now, I am using FEFLOW version 7.4 to simulate groundwater flow to the drain, but I have a problem, so I try to build a box model and figure out this problem; please see the attached picture and help me.
I built a model with boundary conditions like the picture below.
And I want to assign the Cauchy boundary as a Drain boundary, so I assigned the In-transfer Rate = 0(1/s) and Out-transfer Rate = 99999 (1/s) to only let water flow from the aquifer to the boundary.
Although the In-transfer Rate assigned = 0, it still has the water flow from the boundary to the aquifer.
Please help me with this problem, I have tried many ways, but I figure out that the "Transfer Rate" does not care about "In-transfer Rate" or "Out-transfer Rate." How can I assign the Drain boundary condition for the model?
For more information on Drain boundaries, please visit this website.
https://www.xmswiki.com/wiki/GMS:DRN_Package
[img width=200 height=150]https://i.imgur.com/n6Qb33I.jpg[/img]
[img width=200 height=150]https://i.imgur.com/9VyuDG8.jpg[/img]
[img width=200 height=150]https://i.imgur.com/68396TD.jpg[/img]
[img width=200 height=150]https://i.imgur.com/8wkLrGL.jpg[/img]

Thank you!

1) I see no point in using Cauchy boundary in this case. Since you are using infinitely high transfer rate, you can simply use fixed head boundary instead.
2) The easiest option to make boundary conditions one way is to impose flow rate constraint.

Flow rate constraint for fluid transfer BCs (option for fixed head BC is equivalent):
[url=http://www.feflow.info/html/help/default.htm?turl=HTMLDocuments%2Freference%2Fparameters%2Fboundaryconditions%2Fflow%2Fbcc_flowrate_head_transfer.htm]http://www.feflow.info/html/help/default.htm?turl=HTMLDocuments%2Freference%2Fparameters%2Fboundaryconditions%2Fflow%2Fbcc_flowrate_head_transfer.htm[/url]

[quote author=Durchlassigkeitsbeiwert link=topic=22197.msg29534#msg29534 date=1622652392]
1) I see no point in using Cauchy boundary in this case. Since you are using infinitely high transfer rate, you can simply use fixed head boundary instead.
2) The easiest option to make boundary conditions one way is to impose flow rate constraint.

Flow rate constraint for fluid transfer BCs (option for fixed head BC is equivalent):
[url=http://www.feflow.info/html/help/default.htm?turl=HTMLDocuments%2Freference%2Fparameters%2Fboundaryconditions%2Fflow%2Fbcc_flowrate_head_transfer.htm]http://www.feflow.info/html/help/default.htm?turl=HTMLDocuments%2Freference%2Fparameters%2Fboundaryconditions%2Fflow%2Fbcc_flowrate_head_transfer.htm[/url]
[/quote]

Thank you so much; you are professional.
I have been stuck for two weeks about this problem.

I think you also deserve an explanation for why the pure use of an in-transfer rate of 0 does not work. AFAIK the flow direction as the basis for the decision on the transfer rate is determined before a steady-state solution (from initials) or before a time step. Flow conditions, however, can change over the step and there is no internal iteration to correct for the use of the in or out transfer rate in this case. The second reason for this not working can be a change in flow direction in between two nodes of the drain. The transfer rates are an elemental property, and thus the in/out decision is made on an elemental level. Nevertheless the BC is on nodes, so if on average for an element the nodes show an outflow, for this element the out-transfer rate will be used when assembling the equation system. Thus a node that has inflow into the model may be assigned an out-transfer rate.

[quote author=Peter Schätzl link=topic=22197.msg29536#msg29536 date=1622699517]
I think you also deserve an explanation for why the pure use of an in-transfer rate of 0 does not work. AFAIK the flow direction as the basis for the decision on the transfer rate is determined before a steady-state solution (from initials) or before a time step. Flow conditions, however, can change over the step and there is no internal iteration to correct for the use of the in or out transfer rate in this case. The second reason for this not working can be a change in flow direction in between two nodes of the drain. The transfer rates are an elemental property, and thus the in/out decision is made on an elemental level. Nevertheless the BC is on nodes, so if on average for an element the nodes show an outflow, for this element the out-transfer rate will be used when assembling the equation system. Thus a node that has inflow into the model may be assigned an out-transfer rate.
[/quote]

Thank you so much  :D you are professional.