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Hi

there are 2 ways, one is to leave both cylinders, if you are in Geometry Union mode, the Finish flag will decompose your objects into Domain Entities such that you get the two, differentiated.

The second way, if you need to continue to do other operations on your geometry is to:
1) take the Difference large cylinder - small one, BUT select keep input objects !
2) add a Delete entity node and select the full large cylinder (use the selection list, often easier) such to remain only with the difference and the small cylinder.

Now you can continue your work on the reamining geometry

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Good luck
Ivar

Thank you so much Ivar for the reply. I was able to follow both the steps you have suggested me. But i need some more help with the actual model i'm dealing with.

I had attached an image of the model its called Lumbar Spine Model. In the image as you see, there are two pictures again. The spine has to be covered by a muscle tissue and the muscle tissue should be just like an outer layer covering the parts of spine.

But in COMSOL as we draw a solid and extrude it, it might end up going through other solids, just similar to what would happen with my model. So, i followed the first step in your reply, using geometry union. After "buil all" in geometry union step, im left with seperate domain entities and i see the tissue is just as like an outer layer of the spine parts. Do you think is this a right way of doing for a model like mine or should i have to look into a different menthod?

I hope you understood the problem that i'm trying to solve for... i want the muscle tissue to be just like wrapped cover and NOT like a solid going through the parts of spine.

Hi

the CAD systems are based on different concepts, COMSOL's internal one is based on boolean operations mostly, but you have also the possibility to draw a 2D shape on a work-plane and extrude from there. If you are using only COMSOL's internal CAD I expect that you will have to do many create object, subtract (keep objects ) and delete extra objects.

Another point you should be aware about, if you have a complex geometry and you surround it fully by some other shape (air, liquid, or a muscle) your surrounding object might become quite complex with several loops etc., this might give you meshing issues, often its worth to cut the model into slices, and if you have several identical parts you can also build on repetition, but try then also to cut your surrounding entity.
It's a pity to spend hours to build a complex model and then find out you cannot mesh it without redoing the geometry

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Good luck
Ivar

Thanks Ivar

So, How can i go with it now?

if i have to go with the second step that you have suggested i.e,

1.Doing the difference between --->Muscle tissue-Parts (keep input objects)
2. Then, adding "Delete Entities"

is this going to solve the problem? And yeah it is very hard to make such a model work and later you realize you cannot go easy on meshing issues with such a complex geometry. But i'm trying to get the best model i can. Can you please provide me with a thumb rule where i can make muscle tissue as described above?

Hi

have you tried make a larger cylinder around your model and subtract all the current parts ?

You might want to combine several of your parts by a "union" then you have less parts to handle in the solver list

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Good luck
Ivar

Hi

yes i drew a large cylinder around the spine and then tried to delete the parts from the cylinder thing. But once i UNION the parts, now they are all one entity, which i don't want them to be, because different parts are given different properties later on.

Hi

do not confuse Geometry objects and the later FEM Entities.
If you do an "Union" with keep interior boundaries, then if you jump to the material node and check the selection list of domains, you will find all our domains as separate entities.
So long the boundaries are there the unique objects become an distinct entity and later you can but the same or different material properties to each domain entity

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Good luck
Ivar