[CIG-SHORT] Direction of traction-normal for Neumann BC

[Brad Aagaard]

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
>>>>>>> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-short
>>>>>>>
>>>>>>>
>>>>>>>
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>>>>>>
>>>>>
>>>>>
>>>>>
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