Moment computation on floatings 2

AlanCattelliotAlanCattelliot
in DualSPHysics v5.0

Dear all,

Following the question i've made in the post :


I re-work, once again , my question. I simulate a stability experience, trying to determine the transversal righting moment value as a function of the heel angle of the hull.


To do so, the boat is free to move along Z, letting the code adjust the displacement. The boat can pitch around the Center of Gravity, which is taken in the YZ plane, in order balance the pitch of the hull. When I compute the Moment of Forces on the hull around the X axis, I do not observe no changes in the sign of the computed moment. Why ?

https://forums.dual.sphysics.org/uploads/444/HMPFYW7ZA8UY.png There was an error displaying this embed.


Here is the example of 2 simulations made. I represent here the converged state of 2 calculations for two heel angles.

Hull in Green :

+114 520 N.m-1

Hull in pink :

+51 286 N.m-1

The gravity forces induces no moment, since it passes by the origin. Only the buyoant forces shall produce a resulting moment. And because the buyoant center swaps from side to side, I expect the sign of the moment to change.

Can somenone help me, please ? What I am missing ?


Thanks for your attention and your kind help

Comments

  • AlanCattelliotAlanCattelliot

    I have made a few tests, trying to understand how are computed the moment using computeforce.Exe.

    Given these 2 simulations cases, which differ only by their initial rotation along X. Movements of the floatings are, in the two cases, limited to a Z translation ( see below), I want to compute the moment of the Archimedian force along ... watever....

           <floating mkbound="20">

          <massbody value="1829" />          

          <center x="-0.492" y="0.0" z="1.385" />

          <translationDOF x="0" y="0" z="1" />

          <rotationDOF x="0" y="1" z="0" />

           </floating>

    Capture.PNG

    Small maths .... I writhe the Buyoancy moment as M (a,O) in reference with "O", the origin of the referential, "ᴧ" is the cross product. Bold letters represent fthe forces a : buyoancy w : weight

    ∑ M = M (a,O) + M (g,O)

    Here, CoG is vertical to the origin so M (g,O) = O

    ∑ M = M (a,O)

    = (OG + GA)ᴧa

    = OGᴧa + GAᴧa

    ∑ M = M (a,G) + GAᴧa


    It seems that computeforce.Exe computes only OGᴧa. In that case, this routine is not able to compute the total moment applied on floatings. It lacks one term, GAᴧa.

    Is there any output of the coordinates of the Center of Buoyancy ?


    Thanks for your attention and your kind help.

  • AlexAlex

    Yes, it seems there is an issue there.

    Can you email us using dualsphysics@gmail.com so we will check it carefully before next release


    Regards

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