[CIG-SHORT] Direction of traction-normal for Neumann BC
Francisco Delgado
fjd49 at cornell.edu
Thu Jun 19 12:25:12 PDT 2014
Version 14.0.4, I've run the code line by line several times but I only get
to Surface 33, Surfaces 35 and 36 just do not appear.
On Thu, Jun 19, 2014 at 3:15 PM, Brad Aagaard <baagaard at usgs.gov> wrote:
> On 06/19/2014 12:13 PM, Francisco Delgado wrote:
>
>> Brad, I updated to Trelis but I still get the same error
>>
>
> What version of Trelis are you using?
>
> Brad
>
>
> On Thu, Jun 19, 2014 at 3:10 PM, Brad Aagaard <baagaard at usgs.gov> wrote:
>>
>> Francisco,
>>>
>>> CUBIT 12.0 is several years old. There have been some significant
>>> improvements, so it would be good to move to the current version. We try
>>> to
>>> keep our CUBIT/Trelis examples up to date for the current versions. As in
>>> this case, some small tweaks are sometimes necessary.
>>>
>>> CUBIT is no longer available to non-US gov't institutions, so you would
>>> have to get Trelis from csimsoft.com. There is a 30-day free trial
>>> available.
>>>
>>> Brad
>>>
>>>
>>>
>>> On 06/19/2014 12:03 PM, Francisco Delgado wrote:
>>>
>>> Brad, I'm using Cubit 12.0. Should I get a newer one??
>>>>
>>>>
>>>> On Thu, Jun 19, 2014 at 2:54 PM, Brad Aagaard <baagaard at usgs.gov>
>>>> wrote:
>>>>
>>>> Francisco,
>>>>
>>>>>
>>>>> Which version of CUBIT or Trelis are you using? I am using CUBIT 14.1.
>>>>> I
>>>>> did have to update the surface ids from when I originally used the
>>>>> script 3
>>>>> years ago (I don't recall which version of CUBIT I was using at the
>>>>> time).
>>>>>
>>>>> Brad
>>>>>
>>>>>
>>>>>
>>>>> On 06/19/2014 11:49 AM, Francisco Delgado wrote:
>>>>>
>>>>> Hello, I've been following the magma chamber example and I get some
>>>>>
>>>>>> errors
>>>>>> in Cubit when creating the geometry. In the geometry.jou file when I
>>>>>> get
>>>>>> to
>>>>>> lines 44 and 45, Cubit tells that those surfaces do not exist. What
>>>>>> faces
>>>>>> are 35 and 36?? The two pieces of the upper surface??
>>>>>>
>>>>>> Thanks
>>>>>>
>>>>>>
>>>>>> On Thu, Jun 19, 2014 at 10:56 AM, Brad Aagaard <baagaard at usgs.gov>
>>>>>> wrote:
>>>>>>
>>>>>> Satoshi,
>>>>>>
>>>>>>
>>>>>>> The Neumann BC is intended to be applied to an external boundary.
>>>>>>> For a
>>>>>>> spherical pressure source, the domain should not include the material
>>>>>>> inside the sphere (it needs to be a cavity). This will result in a
>>>>>>> consistent normal direction for the boundary.
>>>>>>>
>>>>>>> If the spherical boundary is all one surface, then you can still run
>>>>>>> into
>>>>>>> problems when PyLith initializes the boundary. It may find horizontal
>>>>>>> normal directions. This means the default way it uniquely defines the
>>>>>>> two
>>>>>>> tangential directions breaks down. The workaround is to subdivide the
>>>>>>> surface into quadrants so that you can use a user-defined
>>>>>>> up-direction
>>>>>>> to
>>>>>>> get consistent directions tangential and normal directions for the
>>>>>>> Neumann
>>>>>>> BC. Attached is a small magma chamber example that illustrates this.
>>>>>>>
>>>>>>> We are working on a more detailed magma chamber and dike example for
>>>>>>> a
>>>>>>> workshop next week and we will create an examples section under
>>>>>>> PyLith
>>>>>>> User
>>>>>>> Resources (http://wiki.geodynamics.org/software:pylith:start) in the
>>>>>>> next
>>>>>>> week and post it there.
>>>>>>>
>>>>>>> Regards,
>>>>>>> Brad
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 06/19/2014 02:09 AM, Satoshi Okuyama wrote:
>>>>>>>
>>>>>>> Hello,
>>>>>>>
>>>>>>>
>>>>>>>> Recently I started using pylith and I already love it. However, I
>>>>>>>> have
>>>>>>>> an question about Neumann boundary condition;
>>>>>>>>
>>>>>>>> What determines the direction of positive traction-normal?
>>>>>>>>
>>>>>>>> or
>>>>>>>>
>>>>>>>> What determines the order of the vertices when pylith construct
>>>>>>>> faces
>>>>>>>> from a group of vertices for boundary condition?
>>>>>>>>
>>>>>>>>
>>>>>>>> Here is my story,
>>>>>>>>
>>>>>>>> I am trying to simulate the deformation caused by a pressure
>>>>>>>> source. I
>>>>>>>> created a mesh with spherical source and put all the vertices on
>>>>>>>> source
>>>>>>>> surface into a group, then applied Neumann BC with just
>>>>>>>> traction-normal.
>>>>>>>>
>>>>>>>> However, the deformation of the source was far from isotropic. I
>>>>>>>> checked
>>>>>>>> the initial traction and found that deflation (traction toward
>>>>>>>> source
>>>>>>>> center) is applied to some faces, while inflation is applied to the
>>>>>>>> others.
>>>>>>>>
>>>>>>>> Following is an example of initial-traction output. I placed 5
>>>>>>>> vertices
>>>>>>>> on a plane of z=0 and formed 4 triangle face. Then I applied +1Pa of
>>>>>>>> traction-normal to this group.
>>>>>>>>
>>>>>>>> ############################################################
>>>>>>>> ###########
>>>>>>>> # vtk DataFile Version 2.0
>>>>>>>> Simplicial Mesh Example
>>>>>>>> ASCII
>>>>>>>> DATASET UNSTRUCTURED_GRID
>>>>>>>> POINTS 5 double
>>>>>>>> -1.000000e+00 -1.000000e+00 0.000000e+00
>>>>>>>> 1.000000e+00 -1.000000e+00 0.000000e+00
>>>>>>>> 1.000000e+00 1.000000e+00 0.000000e+00
>>>>>>>> -1.000000e+00 1.000000e+00 0.000000e+00
>>>>>>>> 0.000000e+00 0.000000e+00 0.000000e+00
>>>>>>>> CELLS 4 16
>>>>>>>> 3 2 1 4
>>>>>>>> 3 3 0 4
>>>>>>>> 3 3 2 4
>>>>>>>> 3 4 1 0
>>>>>>>> CELL_TYPES 4
>>>>>>>> 5
>>>>>>>> 5
>>>>>>>> 5
>>>>>>>> 5
>>>>>>>> CELL_DATA 4
>>>>>>>> VECTORS initial_traction double
>>>>>>>> 0.000000e+00 0.000000e+00 -1.000000e+00
>>>>>>>> 0.000000e+00 0.000000e+00 1.000000e+00
>>>>>>>> 0.000000e+00 0.000000e+00 -1.000000e+00
>>>>>>>> 0.000000e+00 0.000000e+00 -1.000000e+00
>>>>>>>> ############################################################
>>>>>>>> ###########
>>>>>>>>
>>>>>>>> As you see, 2nd cell (or face) receives traction of (0,0,1) while
>>>>>>>> other
>>>>>>>> cells receives (0,0,-1). I noticed that if I consider 2 vectors -
>>>>>>>> 1st
>>>>>>>> vertex to 2nd, and 1st to 3rd - the direction of the traction vector
>>>>>>>> is
>>>>>>>> equal to the cross product of them.
>>>>>>>>
>>>>>>>> cell #1:
>>>>>>>> v1: #2 -> #1 = ( 0,-2,0)
>>>>>>>> v2: #2 -> #4 = (-1,-1,0)
>>>>>>>> v1 x v2 = (0,0,-2)
>>>>>>>>
>>>>>>>> cell #2:
>>>>>>>> v1: #3 -> #0 = ( 0,-2,0)
>>>>>>>> v2: #3 -> #4 = ( 1,-1,0)
>>>>>>>> v1 x v2 = (0,0,2)
>>>>>>>>
>>>>>>>> One step closer to the answer, I believe. But I have no idea how
>>>>>>>> this
>>>>>>>> order is determined. The order of the vertices for 2nd cell is
>>>>>>>> 3-0-4,
>>>>>>>> not 3-4-0. But why?
>>>>>>>>
>>>>>>>>
>>>>>>>> Regards,
>>>>>>>> ----
>>>>>>>> Satoshi Okuyama
>>>>>>>> _______________________________________________
>>>>>>>> CIG-SHORT mailing list
>>>>>>>> CIG-SHORT at geodynamics.org
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>>>>>>>>
>>>>>>>>
>>>>>>>>
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
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--
--------------------------------------------------------
Francisco Delgado
PhD student in Geophysics
Cornell University
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