[CIG-SHORT] traction_perturbation

[Brad Aagaard]

Huihui,

step13.cfg is a quasi-static problem with velocity boundary conditions 
and slip at multiple time steps. In your description of shear stress 
changes, what time steps are you referring to? As I change the normal 
traction from -10*MPa (negative is compressive) to -20*MPa the 
time-dependent behavior changes. For -10*MPa there are multiple slip 
events while for -20*MPa there is only one small slip event. The 
difference in behavior arises due to the greater shear loading (and 
deformation) required to generate slip with a compressive stress of 
-20*MPa and the free surface boundary conditions on the +y and -y faces. 
With the frictional interface, this is a nonlinear problem so the values 
don't simply scale.

Regards,
Brad

On 08/09/2012 08:45 PM, 翁辉辉 wrote:
>
>
>
> dear developers：
>
>    I'm confused about the traction_perturbation module.As a example in examples/3d/hex8/step13.cfg ,I add the code in it as follow  :
> [pylithapp.timedependent.interfaces.fault]
> traction_perturbation = pylith.faults.TractPerturbation
> [pylithapp.timedependent.interfaces.fault.traction_perturbation]
> db_initial.label = Initial fault tractions
> db_initial = spatialdata.spatialdb.UniformDB
> db_initial.values = [traction-shear-leftlateral,traction-shear-updip,traction-normal]
> db_initial.data = [0.0*MPa,0.0*MPa,0*MPa]
>
> The earthquake shear stress change on the center of the fault is about 2*MPa,5.83MPa to 4MPa.If I change the x_pos initial displacement which produce the fault normal stress(1*m equivalent to 10*M) from -1*m to 0*m and the traction-normal in above code from 0*MPa to 10*MPa, then the earthquake shear stress change is still the same. If I make the traction-normal be 20*MPa and the x_pos initial displacement be 0*m,the expected stress drop shall be 4*M(12*MPa to 8*MPa) using the static-coefficient(0.6) and dynamic-coefficient(0.4),but the actual shear stress change is 9*M (17.3*MPa to 8*MPa). how can this happen?
>
> thanks
> huihui
>
>
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