Heave Natural Frequency - AQWA

Discussion in 'Hydrodynamics and Aerodynamics' started by Matheus, Apr 11, 2020.

  1. Matheus
    Joined: Apr 2020
    Posts: 3
    Likes: 0, Points: 1
    Location: BRAZIL

    Matheus New Member

    Im new user in AQWA. To find out the natural frequency in heave do I use the RAO generated by the hydronamic response or hydrodynamic diffraction? If it is through hydrodinamic response, do I select irregular waves and do a frequency statistical analysis?
    Photo 1 is from the hydrodynamic diffraction. Why is the curve like this? The geometry is attached in photo 2 and at the end there is a joint of the hinged type allowing only rotation

    Attached Files:

    • 1.png
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    • 2.png
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  2. jehardiman
    Joined: Aug 2004
    Posts: 2,803
    Likes: 366, Points: 83, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    First, don't use Hz, use omega (rads/sec), it will make everything easier.
    For response use the RAO's for response, and then handle it like any other spectral input problem. See Dynamics of Marine Vehicles by Bhattacharyya for a full walk through of the process.
    Why is the hydrodynamic diffraction curve like that? Think about it for a minute....what does the curve mean? What would hydrodynamic diffraction look like for omega = 0.0000007 (0.000046 Hz) or omega = 1273 (8 kHz)?
  3. DogCavalry
    Joined: Sep 2019
    Posts: 749
    Likes: 335, Points: 63
    Location: Vancouver bc

    DogCavalry Senior Member

    Interesting. I wouldn't have thought that heaven would have a natural frequency.... oh wait. Now I see it. Hydrodynamics is so cool.
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