Ansys Aqwa Help!!!! Seed?

Discussion in 'Software' started by kojes, Sep 28, 2012.

  1. kojes
    Joined: May 2012
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    kojes Junior Member

    i have a problem to running ansys aqwa....
    there is input data that i don't understand named "seed"...

    what is seed????can any body help me???

    [​IMG]
     
  2. CWTeebs
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    CWTeebs AnomalyGenerator

    Last edited: Sep 28, 2012
  3. khabiran
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    khabiran Junior Member

    Hi
    Seed Definition defines the random seed for a wave spectrum. The options available are Program Controlled or User Defined. If you select User Defined, you can set the seed value.
     
  4. kojes
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    kojes Junior Member

    Thank you for the answer!!!!
    I can understand......
    but how can I find the exact value of seed??????

    there are different result if I give different value of seed.....

    regards,
    kojes
     
  5. Leo Lazauskas
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    Leo Lazauskas Senior Member

    That's the point of a random seed. You might need to read up on random generators.

    Run the program multiple times with different values of the seed and assemble the results. What do they show?
     
  6. khabiran
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    khabiran Junior Member

    It's dependent to your wave, you must check your resource data, however as a designer could increase it and find Design Curve which includes all picks and displacements.
    Finally it's better to refer to some classification booklet such as DNV or ABS.
     
  7. CWTeebs
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    CWTeebs AnomalyGenerator

    This is a good point. In my experience on several industrial projects, whose reports were submitted directly to the American classification society (ABS) on behalf of the clients, when trying to model a non-linear problem in the time domain with a given input spectrum we were required to, at a minimum, do the simulation with at least three different seed values for the spectrum. I believe this is also stipulated in the API (American Petroleum Institute) and, as you mentioned, the DNV (Det Norse Veritas) rules.

    If the problem can be linearized you really ought to stick with the frequency domain response (AQWA-FER, which means frequency evaluation of response). We used time domain to model the transient phase of mooring lines becoming separated.

    EDIT:
    Not quite. The random number seed actually has nothing to do with the wave height spectrum. The seed is merely the number used when 'seeding' the random number generator (yes, this is actually a computer science term). These random numbers are then used in AQWA when calculating the phase shift of each wave frequency component, thus making it seem like a chaotic system. But, if you use the same seed, you'll get the same wave.
     
  8. kojes
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    kojes Junior Member

    I want to say thank you very much for your help....
    I know about seed now.....

    your comments in this thread are helpfull....

    and I have more problem about start period and finish period as shown in picture above....

    if I input with different value, it will give different result....
     

  9. CWTeebs
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    CWTeebs AnomalyGenerator

    Yes, if you input different 'start frequency' and 'end frequency' values you'll probably get different results, sometimes significantly so. These values define the first and last frequencies to be used when doing any spectral integration. If you do this outside of Workbench you can actually leave these blank and AGS will determine the appropriate frequency range. Otherwise, just make sure you choose a wide range so you don't accidentally omit any spectral energy.
     
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