Floating object in a fluid

benjaminm · November 13, 2009, 05:25

Hello,

I am currently performing a series of ventilation studies using cfx that require a meshed person (human body) within the space to be analyzed. Unfortunately when i try to integrate the body within the space in my cad program (rhino), the once perfect nurbs body now has a series of holes and cannot be properly meshed in ansys. Without trimming him however the are no meshing errors.

So now instead of basically welding his feet to the floor (to make a single interior volume), I would like to have him float in space (just above) but still act as an object within the fluid.

Can I have him act as a floating boundary/wall? How do I go about specifying his geometry in this way. I can't seem to figure this out although it is probably fairly basic. Atm he is just considred another fluid region.

Thanks for any help you can give,
Ben.

kingjewel1 · November 13, 2009, 05:37

What format is he?

benjaminm · November 13, 2009, 05:47

He was created in rhino by me using tsplines (A plugin).

So he can be any nurbs filetype really. The problem is within rhino. It creates errors when cutting him up. His geometry is perfect(spent hours to make sure it was) until trimmed.

That is why I have resolve to have him float in space since I don't have to cut him up. By floating I mean just no contact on the surface of the main wall boundary.

ghorrocks · November 13, 2009, 05:51

It makes no difference to CFX whether the person is attached to the floor or an isolated body levitating in space. It all gets treated the same - a wall boundary condition.

Sounds like you have a solid modelling problem. You would have to talk to Rhino people to resolve that I guess.

benjaminm · November 13, 2009, 05:55

Well when I have him floating in space it considers him an isolated fluid region and not just a wall for some reason. I get a isolated fluid region error. If I by pass it in advanced settings, the fluid just flows right through him.

Thanks for the reply! I appreciate it... (Problem is driving me crazy)

ghorrocks · November 13, 2009, 06:12

Sounds like you are splitting the block into two blocks rather than chopping a bit out of the big block. Still sounds like a solid modelling problem - although in CFX-Pre you can set the domain to only use one section of the mesh (in the mesh tree) and ignore the other section so if you know what you are doing you won't need to remesh.

kingjewel1 · November 13, 2009, 06:40

I've only had a small amount of contact with rhino so let me get this straight. When you do a Boolean subtraction, ie cutting the man out of the block, it leaves you with holes?

I think you can import both meshes separately into CFX and merge them by interfaces without any extra work. I may be wrong about solid-fluid though.

ghorrocks · November 14, 2009, 06:46

I have no experience with Rhino so cannot help you with using it. But make sure you know the difference between surface bodies and solid bodies - if you cut a surface body from a solid body it make well chop the solid body into two sections.

In CFX-Pre you can import these meshes and use them together or separately or merge them.

November 13, 2009, 05:25	Floating object in a fluid	#1
benjaminm New Member Ben Join Date: Nov 2009 Posts: 3 Rep Power: 17	Hello, I am currently performing a series of ventilation studies using cfx that require a meshed person (human body) within the space to be analyzed. Unfortunately when i try to integrate the body within the space in my cad program (rhino), the once perfect nurbs body now has a series of holes and cannot be properly meshed in ansys. Without trimming him however the are no meshing errors. So now instead of basically welding his feet to the floor (to make a single interior volume), I would like to have him float in space (just above) but still act as an object within the fluid. Can I have him act as a floating boundary/wall? How do I go about specifying his geometry in this way. I can't seem to figure this out although it is probably fairly basic. Atm he is just considred another fluid region. Thanks for any help you can give, Ben.

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November 13, 2009, 05:37		#2
kingjewel1 Senior Member Join Date: Jul 2009 Posts: 260 Rep Power: 18	What format is he?

November 13, 2009, 05:47		#3
benjaminm New Member Ben Join Date: Nov 2009 Posts: 3 Rep Power: 17	He was created in rhino by me using tsplines (A plugin). So he can be any nurbs filetype really. The problem is within rhino. It creates errors when cutting him up. His geometry is perfect(spent hours to make sure it was) until trimmed. That is why I have resolve to have him float in space since I don't have to cut him up. By floating I mean just no contact on the surface of the main wall boundary.

November 13, 2009, 05:51		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,862 Rep Power: 144	It makes no difference to CFX whether the person is attached to the floor or an isolated body levitating in space. It all gets treated the same - a wall boundary condition. Sounds like you have a solid modelling problem. You would have to talk to Rhino people to resolve that I guess.

November 13, 2009, 05:55		#5
benjaminm New Member Ben Join Date: Nov 2009 Posts: 3 Rep Power: 17	Well when I have him floating in space it considers him an isolated fluid region and not just a wall for some reason. I get a isolated fluid region error. If I by pass it in advanced settings, the fluid just flows right through him. Thanks for the reply! I appreciate it... (Problem is driving me crazy)

November 13, 2009, 06:12		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,862 Rep Power: 144	Sounds like you are splitting the block into two blocks rather than chopping a bit out of the big block. Still sounds like a solid modelling problem - although in CFX-Pre you can set the domain to only use one section of the mesh (in the mesh tree) and ignore the other section so if you know what you are doing you won't need to remesh.

November 13, 2009, 06:40		#7
kingjewel1 Senior Member Join Date: Jul 2009 Posts: 260 Rep Power: 18	I've only had a small amount of contact with rhino so let me get this straight. When you do a Boolean subtraction, ie cutting the man out of the block, it leaves you with holes? I think you can import both meshes separately into CFX and merge them by interfaces without any extra work. I may be wrong about solid-fluid though.

November 14, 2009, 06:46		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,862 Rep Power: 144	I have no experience with Rhino so cannot help you with using it. But make sure you know the difference between surface bodies and solid bodies - if you cut a surface body from a solid body it make well chop the solid body into two sections. In CFX-Pre you can import these meshes and use them together or separately or merge them.