[CIG-LONG] CIG-LONG Digest, Vol 51, Issue 2 Alleviating pressure singularity in corner-flow mantle-wedge subduction zone model

Tue Feb 15 08:57:43 PST 2011

Hi Walter,

Thank you for the advice and input file.  I am having trouble using  
the gradient region to alleviate the negative pressure singularity  
with velocities that diverge from the corner.

Specifically, if the left side has a velocity of vy = -1 and vx = 0  
and then the top is either fixed with vx=vy=0 or extending vx = 1 and  
vy = 0 a source like flow forms radiating out of the corner.  Since no  
material is allowed into the corner, due to the fixed velocities in  
the triangular corner shape, a huge negative pressure singularity  
develops.  It grows from ~300 with no triangular gradient region to ~  
800 with vx=vy=0 and 1400 with vx = 1 and vy =0.

I have attached my input file.  It is currently in the configuration:

Left:  vx =0 and vy = -1
Top vx = 1 and vy = 0

Thank you,
Karen

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Pressure and Velocity Field with no fixed corner region:

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Pressure and Velocity Field with a fixed corner region:

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On Feb 12, 2011, at 2:48 PM, cig-long-request at geodynamics.org wrote:

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> Today's Topics:
>
>   1. Alleviating pressure singularity in corner-flow	mantle-wedge
>      subduction zone model (Karen Paczkowski)
>   2. Re: Alleviating pressure singularity in corner-flow
>      mantle-wedge subduction zone model (Bradford H. Hager)
>   3. Re: Alleviating pressure singularity in corner-flow
>      mantle-wedge subduction zone model (Walter Landry)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 11 Feb 2011 15:06:36 -0500
> From: Karen Paczkowski <karen.paczkowski at yale.edu>
> Subject: [CIG-LONG] Alleviating pressure singularity in corner-flow
> 	mantle-wedge subduction zone model
> To: cig-long at geodynamics.org
> Message-ID: <8278D009-9828-40B1-B7C4-90C534D5965A at yale.edu>
> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
>
> Hi,
>
> I am trying to write a simple corner-flow mantle-wedge subduction zone
> model using Gale.  Since, in the corner of the wedge the velocity
> abruptly changes from v=vslab along the slab to v=0 along the
> overriding plate a pressure singularity develops in the corner of the
> wedge.
>
> I was wondering if anyone else has encountered this issue and what
> they did to alleviate the pressure singularity in the corner?
>
> I have tried adding a small shape along the slab-mantle interface
> right near the corner that has a velocity with a gradient going from
> v=0 to v=slab over a couple of resolution points.  This mainly seems
> to move my pressure singularity around, but not elimiate it.
>
> Any advice people have on alleviating the pressure singularity in a
> corner-flow subduction model would be greatly appreciated.
>
> Thank you,
> Karen
>
>
>
>
>
> ------------------------------
>
> Message: 2
> Date: Fri, 11 Feb 2011 18:02:54 -0500
> From: "Bradford H. Hager" <bhhager at MIT.EDU>
> Subject: Re: [CIG-LONG] Alleviating pressure singularity in
> 	corner-flow	mantle-wedge subduction zone model
> To: Karen Paczkowski <karen.paczkowski at yale.edu>
> Cc: CIG <cig-long at geodynamics.org>
> Message-ID: <5A320C85-2D13-44B7-9F5E-702C3679C2CE at mit.edu>
> Content-Type: text/plain; charset=us-ascii
>
> Instead of imposing a velocity gradient, try allowing a few nodes to  
> be free - that way they can determine the appropriate velocity  
> gradient.
>
> Brad Hager
>
> On Feb 11, 2011, at 3:06 PM, Karen Paczkowski wrote:
>
>> Hi,
>>
>> I am trying to write a simple corner-flow mantle-wedge subduction  
>> zone
>> model using Gale.  Since, in the corner of the wedge the velocity
>> abruptly changes from v=vslab along the slab to v=0 along the
>> overriding plate a pressure singularity develops in the corner of the
>> wedge.
>>
>> I was wondering if anyone else has encountered this issue and what
>> they did to alleviate the pressure singularity in the corner?
>>
>> I have tried adding a small shape along the slab-mantle interface
>> right near the corner that has a velocity with a gradient going from
>> v=0 to v=slab over a couple of resolution points.  This mainly seems
>> to move my pressure singularity around, but not elimiate it.
>>
>> Any advice people have on alleviating the pressure singularity in a
>> corner-flow subduction model would be greatly appreciated.
>>
>> Thank you,
>> Karen
>>
>>
>>
>> _______________________________________________
>> CIG-LONG mailing list
>> CIG-LONG at geodynamics.org
>> http://geodynamics.org/cgi-bin/mailman/listinfo/cig-long
>
>
>
> ------------------------------
>
> Message: 3
> Date: Sat, 12 Feb 2011 11:47:44 -0800 (PST)
> From: Walter Landry <walter at geodynamics.org>
> Subject: Re: [CIG-LONG] Alleviating pressure singularity in
> 	corner-flow mantle-wedge subduction zone model
> To: karen.paczkowski at yale.edu
> Cc: cig-long at geodynamics.org
> Message-ID:
> 	<20110212.114744.1837452039028910477.walter at geodynamics.org>
> Content-Type: text/plain; charset="us-ascii"
>
> Karen Paczkowski <karen.paczkowski at yale.edu> wrote:
>> Hi,
>>
>> I am trying to write a simple corner-flow mantle-wedge subduction  
>> zone
>> model using Gale.  Since, in the corner of the wedge the velocity
>> abruptly changes from v=vslab along the slab to v=0 along the
>> overriding plate a pressure singularity develops in the corner of the
>> wedge.
>>
>> I was wondering if anyone else has encountered this issue and what
>> they did to alleviate the pressure singularity in the corner?
>>
>> I have tried adding a small shape along the slab-mantle interface
>> right near the corner that has a velocity with a gradient going from
>> v=0 to v=slab over a couple of resolution points.  This mainly seems
>> to move my pressure singularity around, but not elimiate it.
>>
>> Any advice people have on alleviating the pressure singularity in a
>> corner-flow subduction model would be greatly appreciated.
>
> Have you tried fixing the velocity within the box near the corner?
> Specifically, you can try using a MeshShapeVC on a region near the  
> corner.
> This should remove the pressure singularity, because you are no longer
> solving near the singular point.
>
> To illustrate, I am attaching two input files.  There are still some
> issues at the edge of the MeshShapeVC because the matching is not
> exact, but the error is much smaller.  Without the fix, the pressure
> goes up to 213.  With the fix, the max pressure is about 7.
>
> Cheers,
> Walter Landry
> walter at geodynamics.org
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> ------------------------------
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> End of CIG-LONG Digest, Vol 51, Issue 2
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