Hollow cylinder and other similar geometries

[Lucas]

Hi there,

I have a question: I need to create a cylindrical container (i.e. a hollow cylinder) but I've noticed that this type of geometry is not present in chrono. I thought of performing a sort of boolean subtraction between an inner and outer cylinder by setting false to the EnableCollision command, however this causes me problems since I would have to use the cylinder as a container and the EnableCollision of the outer cylinder remains set to true.

Is there a simple method without resorting to CAD imports to create geometries of this type or similar?

Thanks.

[Radu Serban]

Please clarify what module in Chrono you are interested in using.  Defining collision geometry is different for different modules.

--Radu

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[Lucas]

I'm undecided and I'm considering between multicore and granular, but for now I'm using multicore. Since I was considering just the development of the geometry I didn't consider there was a difference for the modules regarding the collision.

[Lucas]

I'm undecided and I'm considering between multicore and granular, but for now I'm using multicore. Since I was considering just the development of the geometry I didn't consider there was a difference for the modules regarding the collision.

On Friday, June 28, 2024 at 4:28:36 PM UTC+2 Radu Serban wrote:

[nevio lo stirato]

Hello, Is there any news? I'm finally going with multicore.

Thank you in advance. 

Lucas

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[Radu Serban]

Luca,

 

Sorry for the late reply.  Concave geometries cannot be treated with primitive shapes.  To model a hollow cylinder container, you will need to use some approximation.

 

1. You can use a mesh (that you create in some external authoring tool and export as a Wavefront OBJ file).  Note that, unless you are also interested in contact interactions with the outside of this cylindrical container, it is most efficient to only model it as a single surface mesh (of course, making sure the face normal point towards the inside).  No matter what, when you create the Chrono collision shape (ChCollisionShapeTriangleMesh), make sure to set a non-zero value for the last constructor argument. That represents the radius of a sweeping sphere which provides a “thickness” to the mesh for collision detection purposes and is important for robustness of the numerical collision detection algorithm (use a value that is meaningful for your particular problem; some experimentation may be needed).
   
   
2. Alternatively, you can use a collection of boxes arranged in a circle to model the cylindrical container.  In fact, a utility function to create such a container is already provided in Chrono: see chrono::utils:: CreateCylindricalContainerFromBoxes.  This is no worse an approximation that using a triangular mesh (after all, they both provide a “faceted” approximation of the cylindrical surface) and you can control the resolution by increasing the number of boxes.

 

--Radu

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