Extrapolating motions to different locations

Discussion in 'Hydrodynamics and Aerodynamics' started by delta33582, Jan 17, 2019.

  1. delta33582
    Joined: Jan 2019
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    delta33582 New Member

    I am running a seakeeping simulation on a vessel and am tracking rigid body motions of a (single) reference point over time, regular waves. Does anybody have any references that advise on how I can use this data (displacements, velocity, accelerations) from a single tracked point and extrapolate it to a number of different locations? This would be within seakeeping, however I find no guidance in the texts.
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Do you have an accelerometer and want to know the motion at other locations in the vessel?
  3. delta33582
    Joined: Jan 2019
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    delta33582 New Member

    So we have accelerometer data for different points (about 10) from tank testing. I am running/writing a program that permits me to track a single point at a time. Without having to iterate through multiple runs for the sake of gather data at additional points (from the program), I was hoping that there is some kinematic formulation I can refer to?

    For instance if I track AP accelerations, can I accurately extrapolate and combine heave, pitch, roll accelerations for FP? If not, how many points should I collect data for in order to do so.

  4. jehardiman
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    jehardiman Senior Member

    This is simple rigid body dynamics, pick up any good dynamics text or see Section 301a of MIL-STD 1399. Since you are running simulation, I assume that you are getting 6-axis frequency data (amp and phase) at the CG out, because time domain out data is useless for seakeeping studies as you will always have the computer/real water issues. If you have tank test time domain data, you will need to spectrally analyze it (most likely using FFT so I have you have 20+ minutes of run time data) then correct it back to CG to get your 6-axis frequency data out. IIRC, there is a discussion of this issue in the WAMIT theory chapter and in Dynamics of Marine Vehicles by Rameswar Bhattacharyya.
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