# Moving a bead in a viscoelastic medium 3D

**URL:** <https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847>\
**Category:** General Discussion\
**Created:** [March 10, 2021, 8:01am UTC](https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847 "2021-03-10T08:01:31Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Srj](https://avatars.discourse-cdn.com/v4/letter/s/e9c0ed/32.png) [@Srj](https://community.freefem.org/u/Srj)\
**Post date:** [March 10, 2021, 8:01am UTC](https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847/1 "2021-03-10T08:01:31Z")

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I would like to model a (spherical) bead in a (spherical) 3D visco-elastic medium.  
The bead is first moved around actively by external forces.  
Once these forces stop, I want to find out the movement of the bead due to the visco-elastic relaxation.

Would that be possible to model in FreeFem ? Any pointer one where I should look to get started ?

Thanks !

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [March 10, 2021, 3:28pm UTC](https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847/2 "2021-03-10T15:28:30Z")

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Yes I think is possible, but first you need the mechanical model . If you do this in the framework of the bead, the domain are fixe or you have just small deformation. It will be not to hard to do.

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**Author:** ![Srj](https://avatars.discourse-cdn.com/v4/letter/s/e9c0ed/32.png) [@Srj](https://community.freefem.org/u/Srj)\
**Post date:** [March 11, 2021, 12:36pm UTC](https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847/3 "2021-03-11T12:36:30Z")

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Thanks for the reply !

So to be clear, the bead is moving inside a sphere of visco-elastic medium. The bead and its displacements are rather large compared to the sphere size so I don think I can work in the framework of the bead.

I guess I need a model for the bead, and I think a stiff linear elastic will do. I do not care about the bead deformation, and in the analytical formulation, the bead is mostly a moving boundary condition - albeit moved around by the visco-elastic medium.

Orders of magnitudes : bead radius is 1/4 of sphere radius ; bead displacement is also 1/4th of sphere radius.

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [March 15, 2021, 3:31pm UTC](https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847/4 "2021-03-15T15:31:04Z")

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Sorry, for me it very hard to understand what is you problem without graphic.  
Please a small hand plot will really help me.

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**Author:** ![Srj](https://avatars.discourse-cdn.com/v4/letter/s/e9c0ed/32.png) [@Srj](https://community.freefem.org/u/Srj)\
**Post date:** [March 16, 2021, 1:02pm UTC](https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847/5 "2021-03-16T13:02:39Z")

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Sorry if I was not clear ! Here is a schematic :

 ![illus](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/1X/a948d88fd0148842fd731849c2c2addab7bbf96e.png)

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**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [March 17, 2021, 4:26pm UTC](https://community.freefem.org/t/moving-a-bead-in-a-viscoelastic-medium-3d/847/6 "2021-03-17T16:26:26Z")

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So this is just a large non linear elastic problem, so problem for except the  
modele of the viscoelastic medium.