RAOs transformation

Discussion in 'Software' started by musiice, Sep 2, 2013.

  1. musiice
    Joined: Sep 2013
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    musiice Junior Member

    Hello all,

    I am using ANSYS AQWA to model a floating platform. I have gone throught LINE, LIBRIUM and finally NAUT to obtain the RAOs for a chosen range of frequencies.

    Let's say I extract the RAO BASED POSITION values in the different motions from the *.LIS files in the latter analysis, AQWA-NAUT. This RAO is given on the centre of mass of my structure.

    Does anyone knows how to 'translate' the values to another point? For example the SWL, or still water level?

    Thank you :)
     
  2. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    What information or output are you exactly trying to get?

    There are transformations that are meaningful, and transformations that are not. The absolute transformation follows 6-DOF rigid body motion transformation with phaseing, but that is not very useful for real word problems. Stoichastics is the perfered method.
     
  3. CWTeebs
    Joined: Apr 2011
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    CWTeebs AnomalyGenerator

    Hi,

    I wrote a program that does this for a very specific set of conditions.
    What's this for?
     
  4. musiice
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    musiice Junior Member

    I have a semi-submersible, and after defining all the point masses there is a global centre of mass. So far, after running AQWA-NAUT, I understand that in the *.LIS files when we get the list of position, forces at moments at centre of gravity for each time step, all these are referred to the 'global centre of gravity'.

    I want to compute RAOs in FAST for the same semisub and this program gives the motions respect the SWL. So my objective is to compare both, but for that I think that first I need the motions referred to the same point.
     
  5. jehardiman
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    jehardiman Senior Member

    Then all you want is a simple 6-DOF rigid body motion transformation with phaseing. First year dynamics stuff and good for you to work out on your own. Or you could look it up, try the first chapter of Advanced Dynamics of Marine Structures by Hooft.
     
  6. musiice
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    musiice Junior Member

    Hi jehardiman,


    Where can I extract the phaseing in AQWA?

    Thanks
     

  7. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

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