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Old   November 11, 2011, 17:34
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Thomas Daniels
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Hello everybody,

I'm quiet new in CFX-Analysis and worked my way through the tutorials until now.

For the next step I want to analyse a simple rotation tyre in CFX.

I will present my ideas, maybe you can give me some advise if I'm wrong and help me with the next steps. I would really aopreciate your help!


I modeled a simple zylindrical tyre in CAD. I then made an offset of the surface to get a boundary layer where I can make a fine mesh. As a last step I created a "wind tunnel" over all and substracted the over stuff from this channel.

I then meshed everything. And try to setup the rolling tyre.

The "moving road" was no problem using CFX Pre. But when I tried to set the boundary for the tyre I first could choose the new cood. system on the tyre (around which I wanted to rotate the tyre model) and later I got error messages because I used wrong dimensions. But I guessed rad/s is the right angular velocity.

Am I doing this all wrong? Do I have to use Transient behaviour instead of Steady-State in this case?

I tried to search for this but got not what I'm looking for. I know that I probably can get better results with ICEM but as a first step I just used the CFX-Meshing tool.

Do I have to use a special mesh for my boundary layer around the tyre, or is this layer just useless?


Thank you very much for your help. Once again, I really appreciate it!

Greetings from Copenhagen!

Tom
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Old   November 13, 2011, 18:06
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Glenn Horrocks
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Wall boundaries with velocity need to have a velocity specified (length/time). You specified a rotational velocity, so need to convert that to a velocity.

Your model can be done in steady state from what you have described. No need for transient.
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Old   November 14, 2011, 19:08
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Thomas Daniels
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Thank you for your reply.

Can you help me figuring out, how to set the rotational axis right on the center of the tyre? And how do I insert the right velocity?

Is it correct to set "Wall velocity - Cylindrical Components - Angular component (in rad/s)"?

I don't know how to set the "Axis Definition" on my new Axis on the Tyre itself.

If i use "Rotating Wall" I have the same problem.

I tried to set the angular velocity in that way that the tyre should roll perfectly on the ground but it doesn't work because it says "Not dimensionless".

Do I have to set all the faces of the tire to the wall or only the "angular" ones? (The tread and the rounded top.. (I'm sorry my English fails here..))

Would it help if I would upload my files somewhere? (I would understand if it would be too risky for you to download some files from a random stranger...)


Once again, thanks for the help!

Tom
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Old   November 24, 2011, 17:09
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Thomas Daniels
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Hey guys,

I just have another small problem.

I created a new set with two tires, so now one tire isn't at the global coordinate axis and I need to specify a new coordinate axis to let the tire rotate.

I created a new coordinate axis on the center of my second tire in the meshing tool but I can't choose this new system when I wan't to set up the new rotating wall. I still can only choose "Global X, Global Y, Global Z".


Do I have to specify the coordinate axis in another tool or what am I missing?


Thank you for your help!

Tom
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Old   December 4, 2011, 19:53
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Thomas Daniels
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Does nobody have an idea on how to set the new coordinate axis in a way that I can choose them for the rotating wall?
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Old   December 5, 2011, 06:06
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Glenn Horrocks
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I have never used local coordinate axes to do what you propose so all I can recommend is give it a go and work it out. Of course you can always just do the maths in the global coordinate frame, the maths is more complex but still just an algebraic equation and then you do not need a local coordinate axis.
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