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[Star-CCM] Successive rotations of a flying body

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Old   May 15, 2014, 09:31
Default [Star-CCM] Successive rotations of a flying body
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Cyril Gomez
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Hi everyone,

I'm a young student and i need some help for my graduation project.

Here's the plot : i want to make a plane move in Star-CCM+. I need the plane to follow exactly an Excel table file in which the position and the orientation of the plane's center of gravity is specified for each point.

I know how to make a region move in space using a table file with (x, y, z) / time. I use user defined vertex motion option.

What i don't know is how to orient the plane, to make the plane rotate around the axises. Indeed the angles of roll, yaw and pitch are completely given in the table and my goal is to enforce these rotations guidelines to the plane. These are successive rotations : yaw then pitch then roll. The order is crucial because it's not the same if you rotate with pitch then roll then yaw for example.

Would you know a way to do that please ? i have been looking for this around the web but i didn't find. I use Star-CCM+ v8

This is my first post on the forum. If i did something wrong or have some questions tell me please because i really need the answer lol . If the answer has already been posted in another thread please let me know. <3

Thanks and cya guys,
johncoffey
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Old   May 15, 2014, 20:53
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I don't think you should move the plane. Doing so is rather difficult.

You should change the direction of the freestream dynamically instead. This is much simpler and probably cheaper.
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Old   May 16, 2014, 08:35
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Actually, there are two bodies in the simulation : the plane and a little rocket which is carried by the plane and then dropped. So i can't just change the flow direction.

I have tried to work with relative reference frame for the plane. Just changing the flow instead of moving the plane and thereby the mesh is much cheaper ; but it still doesn't solve my problem.
I don't know how to orientate my body correctly according to a given file table. That means rotating the plane around his z-axis, then y-axis, then x-axis, and so for every point.

thanks for your answer though

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Old   May 16, 2014, 11:41
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I don't see how the plane having a rocket changes anything. Holding the plane stationary and moving the flow is the same as holding the flow stationary and moving the plane.
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Old   May 18, 2014, 22:16
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Philhellene Ithaca
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Quote:
Originally Posted by johncoffey View Post
Actually, there are two bodies in the simulation : the plane and a little rocket which is carried by the plane and then dropped. So i can't just change the flow direction.

I have tried to work with relative reference frame for the plane. Just changing the flow instead of moving the plane and thereby the mesh is much cheaper ; but it still doesn't solve my problem.
I don't know how to orientate my body correctly according to a given file table. That means rotating the plane around his z-axis, then y-axis, then x-axis, and so for every point.

thanks for your answer though

If you opt for defining a motion, then:
-Define a Z-axis rotation around lab. Define a coord. system (as copy of lab). Letīs call it Zrot.
-Within the Z-axis rotation motion, tell the program that the Zrot coordinate system is managed by the motion (look under motion properties). That is, Zrot will follow the Z rotation.
-Now, define a new motion with respect to the Y-axis of the Zrot coordinate system. Again, define a, child to Zrot, coordinate system (lets call it Yrot) and tell the program that Yrot will be managed by this motion.
-Finally define your goal motion, as a rotation along X axis of Yrot.

If you opt for reference frames, the strategy is similar. Just give a look to the section "Embedded Reference Frame" in the help.
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Old   May 19, 2014, 11:24
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Cyril Gomez
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Hi,

thanks a lot for your answer.

My problem is almost solved ; except i need my plane to rotate along Zrot, Yrot and Xrot, and not only Xrot.

You told me how to create a X axis that is child of rotations along Z and Y, (which i didn't know it could be possible ^^) so i'm half way through.

Now i need to find a way to do successive rotations, i mean the plane rotates around Z in lab system, then around Y in the new Zrot coord system, then around X in the new Yrot system (to use your notations)

I'm going to search for it
Cya
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Old   May 20, 2014, 04:25
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Cyril Gomez
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Heya,

I just have found my happiness in the user guide. I don't know why i hadn't found it for 2 weeks lol.

It is not possible to do it with Rotation And Translation motion, that's why i didn't see it on my software. I have to create the Translation motion (trajectory of the center of gravity) ; then right click the "superposing motions" child node to add a rotation node for my Z rotation, then do it again for my Y rotation, then again for my X rotation.

For those who want to know, the guide thread is User Guide -> Modeling Physics -> Modeling Space, Time and Motion -> Modeling Motion -> Simulating Constant Rigid Motion -> Superposing Additional Rigid Rotations.

Few problems still remain (like how to enter a rotation rate when i only have a table of angles) but i think i will solve them.

Thanks for your answers and cya !
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