Learning Forum

[Swen Groen]

Hello Everyone,

 

Currently I am working on the modelling of a cable-driven soft continuum robot. I am running into some issues though regarding my boundary conditions and the results.

 

I am running a static structural with large deformation turned on.

The model consists of 4 parts. 1 silicon base with 4 cylindrical holes in which 3 wires run (stainless steel), modelled as beams. The silicon is modelled with a mooney-rivlin non-linear model. During actuation of the robot the cables are being pulled, resulting in the deformation of the silicon and therefore the movement of my actuator.

 

I have the ends of the wires as a fixed joint at the end of the silicon part with a frictionless contact region between the wire and the cylindrical holes it is running through.

For the meshing I use 2 sizing steps. 1 for the base and 1 for all the wires.

 

However, When I run the model and show the results the silicon deforms as anticipated however, the wires are straight and are not deforming and get a message the contact region might have been broken.

 

I have tried the following alternatives:

Model the wires as a solid but there is no convergence in this method, regardless of mesh-size.

Model the beams as

Link

                Cable

                Beam

Reinforcement

Model the contact regions as:

                Frictional

                Frictionless

                No separation

Rough

 

Use cylindrical joints for the majority of the wires and cylindrical fits with flexible and deformable behaviour but I get these results which is not like expected or physically possible:

 

 

 

I know the model is possible seeing published results using the beam method and solid method (Abaqus):

https://cjme.springeropen.com/articles/10.1186/s10033-022-00701-8

 

Kind regards,

Swen

[peteroznewman]

Use Frictional Contact between Beams and holes as the model that will be the easiest to converge.

After you have meshed and defined the contact, insert a Contact Tool under the Connections folder and Generate Initial Contact Status.  You need to see that the contact is Near Open or Closed. If it is Far Open, you will need to increase the Pinball Radius until it changes.

Under Analysis Settings, you turn on Auto Time Stepping.  Set the Inital and Minimum Substeps to 100 and the Maximum Substeps to 1000.

[Aniket]

Also, in addition to the things Peter has mentioned, you will have to use the radius of the beam as the offset while setting your frictional contact. Also, make sure the pinball is slightly larger than the offset.

-Aniket

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[Swen Groen]

Thank you for the replies. I have been working on the pinball radius and some models, but the issue keeps persisting. I have the contact as Near Open but it still breaks the contact condition. I will add the offset to see whether that helps.