[CIG-SHORT] Rate and state friction friction.linear_slip_rate nondimentional?

[Brad Aagaard]

Ekaterina,

In a quasi-static simulation with a linear elastic material model, there 
is no physical meaning to relaxation time. However, you can related it 
to your time step needed to resolve the slip rate dependent frictional 
behavior. We usually use a time step that is about 0.1 times the 
relaxation time, so you could set the relaxation time to 10 times your 
time step. This should give you a reasonable scale for 
nondimensionalizing time.

Regards,
Brad


On 03/01/2018 12:47 PM, Ekaterina Bolotskaya wrote:
> Dear Brad,
> 
> Thanks a lot!
> 
> My simulation is elastic.
> I there any physical meaning of relaxation_time (I'm currently just setting it for nondimentional slip rates to make sense with regard to each other)?
> 
> Thanks.
> 
> Best regards,
> Ekaterina Bolotskaya
> 
> PhD student in Geophysics,
> Earth, Atmospheric and Planetary Science Department,
> Massachusetts Institute of Technology
> E-mail. bolee at mit.edu
> Mob. +1 (857) 284-2805
>           +7 (963) 995-36-33
> 
> ________________________________________
> From: CIG-SHORT [cig-short-bounces at geodynamics.org] on behalf of Brad Aagaard [baagaard at usgs.gov]
> Sent: Wednesday, February 28, 2018 19:04
> To: cig-short at geodynamics.org
> Subject: Re: [CIG-SHORT] Rate and state friction friction.linear_slip_rate nondimentional?
> 
> Ekaterina,
> 
> The linear_slip_rate value is used to regularize the log term as slip
> rates approaches zero. It is most closely related to the solver
> tolerances (which are nondimensional), which is why I chose to use a
> nondimensional value. I would try using a value for the linear slip rate
> that is about one order of magnitude larger than your SNES absolute
> tolerance. I would expect these values to be a few orders of magnitude
> smaller than the nondimensionalized reference slip rate. Slip rate is
> nondimensionalized by dividing the slip rate in m/s by the velocity
> scale (length scale in meters divided by the time scale in seconds).
> 
> Regards,
> Brad
> 
> 
> On 02/28/2018 03:50 PM, Ekaterina Bolotskaya wrote:
>> Dear Pylith developers,
>>
>> I'm using rate and state friction model in my simulations.
>> I found in the manual that friction.linear_slip_rate is a nondimentional
>> quantity that should be about one order of magnitude larger than
>> absolute tolerance in solve.
>>
>> Could you tell me how Pylith uses this nondimentional value
>> (*friction.linear_slip_rate*) with my dimentional*slip rate* and
>> *reference slip rate*? Or how does it nondimentionalize dimentional
>> rates? And what should the relation between the three approximately be?
>> I just want to make sure the three of them are reasonable with regard to
>> each other.
>>
>> Thanks!
>>
>>
>> Best regards,
>> Ekaterina Bolotskaya
>>
>> PhD student in Geophysics,
>> Earth, Atmospheric and Planetary Science Department,
>> Massachusetts Institute of Technology
>> E-mail. bolee at mit.edu
>> Mob. +1 (857) 284-2805 <tel:%2B1%20%28857%29%20284-2805>
>> +7 (963) 995-36-33 <tel:%2B7%20%28963%29%20995-36-33>
> 
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