Modify the contact model in source code

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Qihan Xuan

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Jun 14, 2022, 1:59:22 PMJun 14
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Hi all,

I have a question about changing the contact model in the Chrono. By the way, I am using (the core module of) Chrono.
The viscoelastic model shows the damping term is proportional to velocity. Can we change it?
4.png
We are studying fish motion on mud, which is shear-thinning interaction. For example, we hope the damping term is proportional to the square root of the velocity. Can it be tuned by ourselves? 


Thanks,
Qihan

Luning Fang

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Jun 14, 2022, 3:08:03 PMJun 14
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In the core module of Chrono, you can modify your contact force model in this file, src/chrono/physics/ChContactSMC.h 

The function you need to look at is CalculateForce()

 

    ChVector<> CalculateForce(

        double delta,                      ///< overlap in normal direction

        const ChVector<>& normal_dir,      ///< normal contact direction (expressed in global frame)

        const ChVector<>& vel1,            ///< velocity of contact point on objA (expressed in global frame)

        const ChVector<>& vel2,            ///< velocity of contact point on objB (expressed in global frame)

        const ChMaterialCompositeSMC& mat  ///< composite material for contact pair

    ) 

 

The following two lines match the equations you screenshotted. Note that kn, gn, kt, gt are computed differently depending on the contact force model you choose. forceN and forceT are normal and tangential force magnitude.

 

        // Calculate the magnitudes of the normal and tangential contact forces

        double forceN = kn * delta - gn * relvel_n_mag;

        double forceT = kt * delta_t + gt * relvel_t_mag;

 

You can implement the model however you want. 

 

Thank you,

Luning

Qihan Xuan

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Jun 14, 2022, 10:03:33 PMJun 14
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Thanks! It works.

By the way, I find I have to compile Chrono after modifying the source code.
If you want want to check whether your Chrono is updated, you can check this file: D:/Chrono_v7_build/lib/Release/ChronoEngine.lib

Thanks,
Qihan

Radu Serban

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Jun 18, 2022, 7:53:04 AMJun 18
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Qihan,

 

Indeed, if you change any of the Chrono sources, you will obviously have to rebuild.

 

I have somewhere code that allows changing the contact force calculation in user code only (which would not require rebuilding the Chrono libraries).  That uses a mechanism similar to what I implemented for overriding the default composite material combination laws (which Luning also mentioned in another reply).  I will consider pushing that to the Chrono repository one of these days.

 

--Radu

Hi all,

We are studying fish motion on mud, which is shear-thinning interaction. For example, we hope the damping term is proportional to the square root of the velocity. Can it be tuned by ourselves? 

 

 

Thanks,

Qihan

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Radu Serban

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Jun 26, 2022, 3:16:48 AMJun 26
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Qihan,

 

I pushed code to allow overriding the default SMC contact force calculation with a user-defined function.
See https://github.com/projectchrono/chrono/blob/develop/CHANGELOG.md#added-user-defined-smc-contact-force-calculation

 

--Radu

Qihan Xuan

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Jun 27, 2022, 11:53:09 AMJun 27
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Thanks!
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