GlobalStiffnessTimeStepper viscEl background

Asked by drasszkusz on 2020-01-08

Hi all!

I would like to ask about the GlobalStiffnessTimeStepper.
How does it calculate the timestep in case of elasctic and viscoelastic (viscEl=True) cases? I can see the sourcecode, but is there any paper which describes the mathematical background of the minimum eigen-period for the viscous contribution and which can be referenced? I have not found much in the Yade manual.

Thanks,
D

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drasszkusz
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2020-01-13
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2020-01-13
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2020-01-13
Robert Caulk (rcaulk) said : #1

Hello,

>> case of elasctic and viscoelastic (viscEl=True)

Can you please link to the materials/constitutive laws/parameters you are referring to? We have a class reference for this very purpose [1].

>> I can see the sourcecode

Please link to the the the location you are referring to.

>> I have not found much in the Yade manual

See "Stability Considerations" of the Yade manual [2] which also points to Abul Hosn et al. 2017 [3].

Cheers,

Robert

[1]https://yade-dem.org/doc/yade.wrapper.html
[2] http://yade-dem.org/doc/formulation.html#stability-considerations
[3] http://yade-dem.org/publi/AboulHosn_GRMA_2017.pdf

drasszkusz (drasszkusz) said : #2

Dear Robet,

Thank you for your reply.

>> Can you please link to the materials/constitutive laws/parameters you are referring to? We have a class reference for this very purpose [1].

I understand the minimum eigen-period for elastic contribution (spring only), but with viscEl=True in globalstiffnesstimestepper [1], the viscous contribution is also considered (dashpot part) when calculating minimum (critical) timestep for Law2_ScGeom_ViscElPhys_Basic [2].

>>Please link to the the the location you are referring to.

The source code can be found here [3].

>> See "Stability Considerations" of the Yade manual [2] which also points to Abul Hosn et al. 2017 [3].

As I can see, there are no dashpots used in that study [4], so there is nothing about viscous stability cosiderations there. Also I could not find anything in Yade manual about critical timestep considering mass-spring-viscous dampers (only mass-spring).

Cheers,
D

[1] http://yade-dem.org/doc/yade.wrapper.html?highlight=globalstiffness#yade.wrapper.GlobalStiffnessTimeStepper.viscEl
[2] https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.Law2_ScGeom_ViscElPhys_Basic
[3] https://gitlab.com/yade-dev/trunk/blob/master/pkg/dem/GlobalStiffnessTimeStepper.cpp
[4] http://yade-dem.org/publi/AboulHosn_GRMA_2017.pdf

Jérôme Duriez (jduriez) said : #3

Maybe you can try starting from Raphael's PhD Thesis, § 2.1.3 of [Maurin2015PhD, *]...

[*] https://yade-dem.org/publi/PhD_MAURIN_VF.pdf

Robert Caulk (rcaulk) said : #4

>>I understand the minimum eigen-period for elastic contribution

The timestep associated with viscoelastic dampers-case is estimated using identical logic to the stiffness-only case. GlobalStiffnessTimestepper computes both and uses the smallest one. This is apparent by working backwards from [1], and is confirmed by Jérôme's link on page 18.

[1] https://gitlab.com/yade-dev/trunk/blob/master/pkg/dem/GlobalStiffnessTimeStepper.cpp#L104

drasszkusz (drasszkusz) said : #5

Dear Jérôme and Robert,

thank you for your responses.

>> Maybe you can try starting from Raphael's PhD Thesis, § 2.1.3 of [Maurin2015PhD, *]...

Yes, it confirms the same as it is in the GlobalStiffnessTimestepper manual. The references in that study were also a dead end.

>> The timestep associated with viscoelastic dampers-case is estimated using identical logic to the stiffness-only case. GlobalStiffnessTimestepper computes both and uses the smallest one. This is apparent by working backwards from [1], and is confirmed by Jérôme's link on page 18.

In that case I have to reengineer the formula of the viscous part from the source code or search the internet for other studies. Because the references you provided only describe the elastic parts and just mention the viscous critical time step. Only the elastic formula can be found written down.

Cheers,
D