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Old   March 7, 2004, 14:09
Default MFR model of rudder
  #1
Michael Rasmussen
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Hi Forum

I have seen in CFX 5.6 that it is possible to model eg. a propeller with a frozen geometry and then rotate the geometry around. The example I have seen is with a constant rotational velocity.

My question is if it is possible to model a rudder ( on a ship) which alternates from one position (port) to another (starbord) and back again. This should be done as a sinus motion. I would like to vary how much the rudder is moved (The amplitude) and how fast ( The frequency)

any ideas ?

Regards

Michael
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Old   March 7, 2004, 17:44
Default Re: MFR model of rudder
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Glenn Horrocks
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Hi Michael,

There are many different ways of modelling this, and the method you choose will depend on what you are trying to get out of the simulation.

If you want to model the full transient effect then you can model this with MFR using the "transient rotor stator" model. This model will include the full physics of the rudder movement, but will require a transient simulation which can be time consuming.

If the rudder motion can be considered slow against the ship motion then you can model it as a series of steady state models. These models would not include any transient effects, but would be much simpler and faster to model.

There are also other methods which try to include the transient effects, but in a quasi-static way such that some of the transient effects can still be captured but the simulation is still steady state.

Regards, Glenn
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Old   March 7, 2004, 18:57
Default Re: MFR model of rudder
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Michael Rasmussen
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Okay -thanks Glenn

I'm going for the transient solution - the rudder deflections is relative fast compared to the forward motion.

So - in your opinion - I should be able to "wriggle" the rudder back and forward ? - I surpose that it would need some CCL scripting to do that in practice ?

any opinion on that ?

Regards Michael
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Old   March 9, 2004, 19:13
Default Re: MFR model of rudder
  #4
Glenn Horrocks
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Hi Michael,

Yes, you can wiggle the rudder backwards and forwards. There are two main ways I can think you to do this type of simulation - The preferred method is to use a transient rotor/stator GGI in a multiple frames of reference simulation. I think you can define the frame rotation as a ccl function (I have not done it, but cannot see why it cannot be done).

The alternate method is to use the deforming grid option. This method uses one domain for the liquid and imposes the rudder motion as a deformation of the grid. This is only a beta feature in 5.6, so best wait until CFX5.7 for this option as it has a far more robust moving mesh algorithm.

Regards, Glenn
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Old   March 10, 2004, 12:12
Default Re: MFR model of rudder
  #5
Michael Rasmussen
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Thank you Glenn

I think I know what to do now.

BTW - do you have idea of when 5.7 is released ?. Last time (5.6) it took a couple of months from when CFX said the release date was until it actually was released.

The grid deforming option sounds very handy in a lot of situations. I my case it could be very effective. But I fear that we first will se 5.7 in 6 months.

Best regards

Michael
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Old   March 10, 2004, 18:03
Default Re: MFR model of rudder
  #6
Glenn Horrocks
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Hi Michael,

I am not sure when 5.7 will be released. Talk to your CFX representative.

Regards, Glenn
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Old   March 10, 2004, 21:55
Default Re: MFR model of rudder
  #7
Neale
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Final release of CFX-5.7 is shooting for the end of March beginning of April. It is in the final testing and debugging stages now. Normally minor delays at near the end of the release are due to quality concerns. You just can't release a poor quality product. If development is not satisfied with the quality level then it doesn't get sent out.

It will also take a bit of time from when development is finished to create/package and send out the final CDs.

That being said, if you ask your CFX Rep nicely they will be able to get you a pre-release version now.

Neale
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