[aspect-devel] boundary velocity function expressions

Tue Oct 11 07:18:52 PDT 2016

Thanks Anne and John
This is exactly what I needed to do with the vertical boundary. I had missed this in the new manual.

Cheers

payman

From: Aspect-devel [mailto:aspect-devel-bounces at geodynamics.org] On Behalf Of Glerum, A.C. (Anne)
Sent: October 11, 2016 4:14 AM
To: aspect-devel at geodynamics.org
Subject: Re: [aspect-devel] boundary velocity function expressions

Hi Mohamed,

I don't think anything has changed. The plugin file is called two_merged_boxes.cc, but to use the plugin, in the input file select "box with lithosphere boundary indicators".

Payman, there are two tests using this geometry model ("lithosphere_boundary_indicator.prm" for the 2d case), in case you'd like an example.

Cheers,
Anne

On 11 Oct 2016, at 08:32, Mohamed Gouiza <M.Gouiza at leeds.ac.uk<mailto:M.Gouiza at leeds.ac.uk>> wrote:

Hi Anne,

Is the two_merged_boxes geometry the new name for the box_with_lithosphere geometry?
If it is the case, then the manual needs to be updated

Mohamed

From: Aspect-devel [mailto:aspect-devel-bounces at geodynamics.org] On Behalf Of John Naliboff
Sent: 11 October 2016 07:14
To: aspect-devel at geodynamics.org<mailto:aspect-devel at geodynamics.org>
Subject: Re: [aspect-devel] boundary velocity function expressions

Hi Anne,

Thanks for pointing that out!

Payman - from the file two_merged_boxes.cc documentation section:
                "An example application of this geometry is to prescribe a velocity on "
                "the lithospheric plates, but use open boundary conditions underneath. "

Seems like this is exactly what you are looking for.

Cheers,
John

*************************************************
John Naliboff
Assistant Project Scientist, CIG
Earth & Planetary Sciences Dept., UC Davis

On Oct 10, 2016, at 10:37 PM, Glerum, A.C. (Anne) <A.C.Glerum at uu.nl<mailto:A.C.Glerum at uu.nl>> wrote:

Hi Payman and John,

It's possible to prescribe two different velocity boundary conditions on the vertical boundaries of a box domain when you use the geometry model "two merged boxes". For example, a prescribed inflow of the lithosphere and free slip in the mantle.

Cheers,
Anne

On 11 Oct 2016, at 06:55, John Naliboff <jbnaliboff at ucdavis.edu<mailto:jbnaliboff at ucdavis.edu>> wrote:
Hi Payman,

Glad the input file helped.

However, how can I prescribe velocity to a segment of a boundary and let the rest of that boundary be tangential?

In effect, you would like part of a vertical wall (right boundary) to be free-slip, while the other part has the vertical velocity prescribed?  Hmm, I’m not sure ASPECT is setup to do a ‘mixed’ velocity boundary.  In fact, I’m having a hard time thinking of a study that does this.

In the case you describe below, do you need to prescribed both the vertical velocity and not just the horizontal velocity?

Cheers,
John

*************************************************
John Naliboff
Assistant Project Scientist, CIG
Earth & Planetary Sciences Dept., UC Davis

On Oct 10, 2016, at 7:22 PM, Payman Janbakhsh <payman.janbakhsh at mail.utoronto.ca<mailto:payman.janbakhsh at mail.utoronto.ca>> wrote:

Thank you John,
Actually the continental extension prm file that you sent to Mohamed helped me to figure out the velocity prescription to different boundaries using functions.

However, how can I prescribe velocity to a segment of a boundary and let the rest of that boundary be tangential?
For instance, considering a right boundary, a mantle lithospheric slab having its own westward prescribed velocity, but the rest of that boundary (mantle) be tangential.

Thanks again

Payman

From: Aspect-devel [mailto:aspect-devel-bounces at geodynamics.org] On Behalf Of John Naliboff
Sent: October 10, 2016 12:25 PM
To: aspect-devel at geodynamics.org<mailto:aspect-devel at geodynamics.org>
Subject: Re: [aspect-devel] boundary velocity function expressions

Hi Payman,

Specifying the velocity on the boundaries works a bit differently than what you have outlined below.

In 2D you need to specify velocity components for x and y, which you do via the function.  You can control how the velocity on different boundaries (ex: left & right) by including conditional statements in your functions based on the position (defined by 'x' and 'y' in 2D).

You can also specify that only certain components of the function apply to a certain boundary (i.e. only x velocity from functions is applied to left/right boundary).

If there is a specific setup you are thinking of, can you sent over a basic parameter file that we can look over?

Cheers,
John

*************************************************

John Naliboff

Assistant Project Scientist, CIG

Earth & Planetary Sciences Dept., UC Davis
On 10/09/2016 03:08 PM, Payman Janbakhsh wrote:
Hi,
I’m trying to implement the following for a 2D problem:

Set Prescribed velocity boundary indicators = left : function  ,  right : function

But get error when trying to give  Function expressions in:     set Function expression =
I have tried separating 2 velocity components with semicolon and separate function expressions with comma .
Example:
                                                            Left boundary function                  right boundary function
Set Function expression =             if(z>=1000 , 1, 0) ; 0           ,           if(z>=1000, -1,0) ; 0

I’ve tried many ways including below but all give errors or nonsensical velocity Glyphs:
Set Function expression =          left:   if(z>=1000 , 1, 0) ; 0           ,     right:      if(z>=1000, -1,0) ; 0
Set Function expression =           left =   if(z>=1000 , 1, 0) ; 0           ,    right=       if(z>=1000, -1,0) ; 0
Set Function expression =           (  if(z>=1000 , 1, 0) ; 0     )      ,       (    if(z>=1000, -1,0) ; 0 )
…

How can I separate multiple function expressions each for its corresponding boundary indicator ?

Thanks

Payman

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