How to calculate the moment of inertia for a half Ship

Discussion in 'Stability' started by Anum, Jan 27, 2017.

  1. Anum
    Joined: Feb 2013
    Posts: 11
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: China

    Anum Junior Member

    Dear All,

    I want to simulate the flow around a displacement ship hull with trim and sinkage. Only the half symmetric hull will be modeled. 2 DOF will only allow translational motion along the z-axis and rotational motion around the y- axis. The udf for dynamic mesh is given below.

    #include "udf.h"
    DEFINE_SDOF_PROPERTIES(ship, prop, dt, time, dtime)
    prop[SDOF_MASS] = ; I know the mass of half of my ship
    prop[SDOF_IYY] = ; This is moment of inertia for a half ship, i do not know how to calculate this value
    prop[SDOF_IXX] = 1;
    prop[SDOF_IZZ] = 1;
    prop[SDOF_ZERO_ROT_X] = TRUE;
    prop[SDOF_ZERO_ROT_Y] = FALSE;
    prop[SDOF_ZERO_ROT_Z] = TRUE;

    I want to know how can I calculate the moment of inertia for a half ship (IYY) from the offset data?
    (I know the formula for the second moment of water-plane area is ∫ B(x, z)x^2dx from –L/2 to L/2, where B(x, z) is the width of the water plane at the position (x, z), L is the length of ship and z is the draft)

    Thanks in Advance

    Attached Files:

  2. b1ck0
    Joined: Mar 2010
    Posts: 128
    Likes: 3, Points: 18, Legacy Rep: 40
    Location: Varna/Hamburg

    b1ck0 Senior Member

  3. Heimfried
    Joined: Apr 2015
    Posts: 380
    Likes: 59, Points: 28, Legacy Rep: 37
    Location: Berlin, Germany

    Heimfried Senior Member

    To calculate the mass moment of intertia regarding to the y-axis (Iyy) you need other data than the offsets.

    The Iyy of every (small) part of the ship has to be calculated with its own mass and its perpendicular distance of its centroid to the y-axis. The Iyy of the ship is the sum of all this Iyy parts.

  4. Mermaid Co
    Joined: Oct 2012
    Posts: 50
    Likes: 4, Points: 8, Legacy Rep: 10
    Location: Singapore

    Mermaid Co Junior Member

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.