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

Thu Jun 19 12:13:49 PDT 2014

Brad, I updated to Trelis but I still get the same error

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
>>>>>> _______________________________________________
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>>>>>>
>>>>>>
>>>>>>
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>>>>>
>>>>
>>>>
>>>>
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-- 
--------------------------------------------------------
Francisco Delgado
PhD student in Geophysics
Cornell University
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