Issue with DRAWROTATE

AlanCattelliotAlanCattelliot
in DualSPHysics v5.0

Dear,

I just came not to understand the way drawrotate works. The first example states the problem.

When I prescribe a rotation around the Z axis (second example), the X and Y axis seem to swap.

As a result, when I add a rotation around the X axis, the model does rotate, but around the Y axis (third example).

If I add a rotation around the Y axis, the model does rotate, but around the X-axis (fourth example), in inverse trigonometric direction.

As a result, I am not so sure where to put the Center of Gravity of the floatings...

Do someone has the same issue ?


<geometry>

   <drawfilestl file="TF10_Assembly.stl">

      <drawscale x="0.001" y="0.001" z="0.001" />

                         <drawmove x="0" y="0.0" z="0.0" />

      <drawrotate angx="0" angy="0.0" angz="0.0" />         

<floatings>

            <floating mkbound="20">

      <massbody value="1633" />          

      <center x="4.604" y="0.00" z="1.426" />


image.png


<geometry>

   <drawfilestl file="TF10_Assembly.stl">

      <drawscale x="0.001" y="0.001" z="0.001" />

                         <drawmove x="0" y="0.0" z="0.0" />

      <drawrotate angx="0" angy="0.0" angz="90.0" />         

<floatings>

            <floating mkbound="20">

      <massbody value="1633" />          

      <center x="0.0" y="4.604" z="1.426" />

image.png


<geometry>

   <drawfilestl file="TF10_Assembly.stl">

      <drawscale x="0.001" y="0.001" z="0.001" />

                         <drawmove x="0" y="0.0" z="0.0" />

      <drawrotate angx="20.0" angy="0.0" angz="90.0" />         

<floatings>

            <floating mkbound="20">

      <massbody value="1633" />          

      <center x="0.0" y="3.8386" z="2.9146" />

image.png


<geometry>

   <drawfilestl file="TF10_Assembly.stl">

      <drawscale x="0.001" y="0.001" z="0.001" />

                         <drawmove x="0" y="0.0" z="0.0" />

      <drawrotate angx="0.0" angy="20.0" angz="90.0" />         

<floatings>

            <floating mkbound="20">

      <massbody value="1633" />          

      <center x="0.0" y="3.8386" z="2.9146" />


image.png


Comments

  • TPouzolTPouzol

    Hello,

    Angle rotation are applied in a certain order (X, Y then Z) !

    I see you are using Blender, the axis referential in Blender is not a"scientific" one (not direct), so angle can have different signs.

    Best Regards

  • AlanCattelliotAlanCattelliot

    Dear,

    In fact, Euler's transformation are no conformal, and I was so used to make my transformation Z, Y,X order. Thanks 🙏.

  • AlexAlex

    Please use the transformations applied in PARAVIEW first, since those are the same we used in our XML file

    Regards

  • AlanCattelliotAlanCattelliot

    Thank you Alex, with your help, I manage to initiate my xml entry card with a transformation of the importated model, as a combinaison of drawmove and drawrotate :

    <drawfilestl file="TF10_Assembly.stl">

             <drawscale x="0.001" y="0.001" z="0.001" />

                           <drawmove x="-5.0" y="1.6961358168190843e-16" z="2.77" />

             <drawrotate angx="180.0" angy="0" angz="0" />   

    That allow me to keep my center of gravity at the same place.

    <floatings>

               <floating mkbound="20">

          <massbody value="1829" />          

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

    Providing that angx and angy are related to drawmove_x,drawmove_y,drawmove_y by conventional transformations (I do not treat rotation along Z axis) :

    drawrotate.set('angx',str(heel))

    drawrotate.set('angy',str(trim))

    drawrotate.set('angz',str(0))

    drawmove.set('x',str(Gxp-xp))

    drawmove.set('y',str(Gyp-yp))

    drawmove.set('z',str(Gzp-zp))


    with :


    Gxp = "X position of the gravity center on the vtk importated model"

    Gyp = "Y position of the gravity center..."

    Gzp = "Z position of the gravity center..."

    x1 = Gxp

    y1 = Gyp*np.cos(math.radians(heel))-Gzp*np.sin(math.radians(heel))

    z1 = Gyp*np.sin(math.radians(heel))+Gzp*np.cos(math.radians(heel))

    xp = x1*np.cos(math.radians(trim))-z1*np.sin(math.radians(trim))

    yp = y1

    zp = x1*np.sin(math.radians(trim))+z1*np.cos(math.radians(trim))

    xp = "X position of the gravity center on the DSP model after transformations"

    yp = "Y position of the gravity center..."

    zp = "Z position of the gravity center..."

  • AlanCattelliotAlanCattelliot

    That works well. It allows me to study hydrostatics of floating bodies with your code. And now have a big question regarding this subject !!

    This is an embed external element. It can be deleted using the delete key or the backspace key. To view the full element, press the preview button below.

    Moment computation on floatings 2

    AlanCattelliot

    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

    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


    where I simulate a static stability experiment using DSP. Please follow the post if interested.

    regards,

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