[CIG-SHORT] Mesh interpenetration

[Li, Teng]

Hi Brad,

Thank you. Actually, I asked the similar questions in the last month. I find normal traction become zero in the junction area. And also shear traction become zero in this area. After analyzing HDF5 file, I find there are both positive and negative normal slip occur in different time steps. Last time, we thought it was because the inappropriate parameters chosen for my problem. For my problem, the mesh size is 12.5m. And I first choose nordimensinalizer: normalizer.shear_wave_speed = 1*km/s,  normalizer.wave_period = 1*s. Now I change them to 0.1*km/s and 0.1s. Furthermore, I add formulation.norm_viscosity = 0.4. And I still see the both positive and negative normal slips. The magnitudes for both are about 0.005m. 

Is it because the rounding error brought by Matlab? Or is it because the mesh? I use Trellis to mesh all the domain.

Best,
Teng

Teng Li

Master Candidate in Structures

Department of Civil and Environmental Engineering

University of Illinois at Urbana-Champaign

205 North Mathews Ave, Urbana, IL. 61801

Phone:(217)8196210, Email: tengli2 at illinois.edu



________________________________________
From: CIG-SHORT [cig-short-bounces at geodynamics.org] on behalf of Brad Aagaard [baagaard at usgs.gov]
Sent: Wednesday, November 01, 2017 10:32 AM
To: cig-short at geodynamics.org
Subject: Re: [CIG-SHORT] Mesh interpenetration

Teng,

When you use the Warp filter in ParaView with a scale larger than 1.0,
the deformation is exaggerated. As a result, *sometimes* it looks like
there is interpenetration or opening, when in fact there is not. You
should look at the opening component of the fault slip field (and the
corresponding displacements) to see if there is really fault opening or
interpenetration.

As Joe Andrews pointed out many years ago, most fault intersections are
geometrically incompatible so one does expect some fault opening if
there is slip on all faults at an intersection. If the solution is
converging properly, then we would never expect interpenetration.

Regards,
Brad


On 10/31/2017 09:05 PM, Li, Teng wrote:
> Hi,
>
> Please see the attached picture which shows the junction of the
> secondary fault and the main fault. I used paraview to visualize the vtk
> file. In the paraview, I used wrap by vector filter to show the
> displacement of the junction. As we can see, it seems interpenetration
> occurs in this area. And two faces separate from each other.  I wonder
> whether this is a valid result? And if it is not right, what might be
> the reason? Thanks.
>
> Best,
> Teng
>
> Teng Li
>
> Master Candidate in Structures
>
> Department of Civil and Environmental Engineering
>
> University of Illinois at Urbana-Champaign
>
> 205 North Mathews Ave, Urbana, IL. 61801
>
> Phone:(217)8196210, Email: tengli2 at illinois.edu
>
>
>

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