wind overturning moment and heeling moment for jack up rig in autohydro

Discussion in 'Software' started by vipul29, Feb 4, 2016.

  1. vipul29
    Joined: Feb 2016
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    Location: delhi, india

    vipul29 New Member

    hello,
    I am doing stability analysis for jack up rig in autohydro. I wanted to know if the software is capable of calculating the wind overturning moment and heeling moment for different angle of heel and wind angle at a given draft for the vessel. if yes, can i get the set of commands to be used for the same?

    Also, can i get allowable/max vcg for different drafts at a series of wind angle from 15* to 345*

    thankyou
     
    pavel915 likes this.
  2. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    I think there are some unclear things in your question. In general the maximum heeling moment due to the wind is calculated and, using a function of the cosine of the angle, is calculated its variation with heel. That makes it perfectly Autohydro as explained in the user manual.
    The vcg should not vary with the heel or the draft. The vcg only changes if the weights or their on board position are changed.
    On the other hand, the moment due to wind for angles greater than 90 degrees, with the sail in the water, it makes little sense.
    You've probably misspoke or I misunderstood you, but just in case, review the concepts.
     
  3. vipul29
    Joined: Feb 2016
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    Location: delhi, india

    vipul29 New Member

    thanks tansl,
    i think i got what you tryna say. so do i have to calculate the maximum wind heeling moment manually and then use the cosine function to get the variation because of heel in autohydro. can i get the set of commands to be used for the same?

    for max vcg i meant to say that if there is a change in draft due to loading conditions (say draft 1,2,3,4 at four different loading condition) there will be some allowable vcg value which should not be exceeded for the positive stability of the vessel i.e calculated vcg value of the vessel should be less than the allowable vcg value. The allowable/max vcg is the value which is calculated separately.
     
  4. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I do not know if there is a script that allows to carry, automatically, these calculations. What you can always do is to draw, on the curve of GZ values por several heeling degrees (for a certain load condition), the curve of heeling arms due to wind. The intersection of the two curves marks the equilibrium point.
    Regarding vcg indeed you can do a calculation of the maximum permissible KG for various possible displacement of the boat. These values are obtained by checking for each displacement, the maximum value of KG that allows fulfill all stability criteria to be met by ship. You need to go up gradually the value of KG and verifying compliance with the criteria.
     
  5. vipul29
    Joined: Feb 2016
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    Location: delhi, india

    vipul29 New Member

    i read in autohydro help index that if the wind command is useful in conjuction with the hmmt command as it provides data which together with model geometry allows wind heeling moments to be derived automatically, any idea about it?
    can you tell me whether i have to consider the wind drag coefficient as default (automaticaly considers the height and shape factor dependent on effictiveness of componenets added in modelmaker) or it will vary for diiferent shapes and height and i have to give command for that. drag coefficient is 1.2 as default.
     

  6. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    I'm sorry but I do not know how to answer your questions. What I can tell you is that the various regulations, including ISO 12217-1 and 2 (for small boats), indicate formulas that everyone uses to get the wind heeling moment.
     
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