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## [ht] switch on/off the outflow boundary condition as a time function

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RSS feed   |   Turn on email notifications   |   6 Replies   Last post: June 19, 2017 6:17am UTC

Jalu Naradi

June 13, 2017 4:24pm UTC

[ht] switch on/off the outflow boundary condition as a time function

Hi,

I am simulating a heat transfer in porous media [ht module].
I want to switch on/off the outflow boundary condition as a function of time.

For example:

Outflow 1 ON if t< 4 [d]
Outflow 1 OFF if t>= 4[d]

Outflow 2 ON if t>= 4[d]
Outflow 2 OFF if t< 4[d]

Thank you,

Best Regards

Lasse Murtomäki

June 15, 2017 6:05am UTC in response to Jalu Naradi

Re: [ht] switch on/off the outflow boundary condition as a time function

Use the Heviside function. Like this:

(1-flc2hs(t[1/d]-4,0.01))*(your function)

BR
Lasse

Hi,

I am simulating a heat transfer in porous media [ht module].
I want to switch on/off the outflow boundary condition as a function of time.

For example:

Outflow 1 ON if t< 4 [d]
Outflow 1 OFF if t>= 4[d]

Outflow 2 ON if t>= 4[d]
Outflow 2 OFF if t< 4[d]

Thank you,

Best Regards

Henrik Sönnerlind
COMSOL Employee
Sweden
Moderator

June 15, 2017 7:39am UTC in response to Lasse Murtomäki

Re: [ht] switch on/off the outflow boundary condition as a time function

Hi,

The Outflow condition is, with respect to temperature, identical to a Thermal Insulation (the default boundary condition).

Thermal Insulation (and Outflow) are actually boundary conditions 'doing nothing'. They have no input, and add neither constraints nor weak contributions.

So the question is what you really want to achieve here. What should happen during the time when it there is not an outflow?

Regards,
Henrik

Jalu Naradi

June 15, 2017 2:03pm UTC in response to Henrik Sönnerlind

Re: [ht] switch on/off the outflow boundary condition as a time function

Hi,

The Outflow condition is, with respect to temperature, identical to a Thermal Insulation (the default boundary condition).

Thermal Insulation (and Outflow) are actually boundary conditions 'doing nothing'. They have no input, and add neither constraints nor weak contributions.

So the question is what you really want to achieve here. What should happen during the time when it there is not an outflow?

Regards,
Henrik

Thank you for your response.
I'm simulating a reoriented potential mixing of geothermal reservoir. The reservoir is modelled as a 2D circular with 8 wells on its circumference with 45 degree distance between the wells.
The well in the model will act as injection well and production well.
For example: Well 1 is injection well at time 0-4 days and will be production well at time 16-20 days.
This way, geometrically I only have 8 wells but they will act as 8 injection wells and 8 production wells.

The problem is I cannot set all production wells as an Outflow. (If I do this, all injection wells will overridden by production wells)
What should happen is:

at time : 0-4 days --> injection well 1 and production well 1 active, another wells are deactivated.
at time : 4-8 days --> injection well 2 and production well 2 active, another wells are deactivated
And this scheme will continue until 32 days.

I tried to attach my mph file, but the site always say that the file extension is error.

Thank you very much for your help

Jalu Naradi

June 15, 2017 2:05pm UTC in response to Lasse Murtomäki

Re: [ht] switch on/off the outflow boundary condition as a time function

Use the Heviside function. Like this:

(1-flc2hs(t[1/d]-4,0.01))*(your function)

BR
Lasse

Hi Lasse,

Thank for your advice.
But I think I cannot implement your answer because I cannot put anything on the outflow boundary condition.

Jalu Naradi

June 17, 2017 11:09am UTC in response to Jalu Naradi

Re: [ht] switch on/off the outflow boundary condition as a time function

Hi Henrik,

My above question can be simplified as below:

If I want to set a boundary as an outlet, what is the node that I can choose as an alternative of outflow node?

Thank you in advance,

Regards,
JN

Henrik Sönnerlind
COMSOL Employee
Sweden
Moderator

June 19, 2017 6:17am UTC in response to Jalu Naradi

Re: [ht] switch on/off the outflow boundary condition as a time function

Hi,

There is not built-in setting for switching between different types of boundary conditions withing a single study step. You can however use the methods described in this blog post:

www.comsol.se/blogs/how-to-mak...onditional-in-your-simulation/

Regards,
Henrik

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