[overture] Rigidbody Torque / angular acceleration
- From: "#DOMINIC DENVER JOHN CHANDAR#" <DOMI0002@xxxxxxxxxx>
- To: <overture@xxxxxxxxxxxxx>
- Date: Fri, 20 Jun 2008 14:20:55 +0800
Hi Bill,
In OverBlown v21, the code RigidBodyMotion.C had the following lines
to compute the angular acceleration from the torque as :
for( axis=0; axis<3; axis++ )
{
omegaDot(axis)=(
(1.-alpha)*(
g(0,ip1)*e(0,axis,ip1)
+g(1,ip1)*e(1,axis,ip1)
+g(2,ip1)*e(2,axis,ip1))
+alpha *(
g(0,i)*e(0,axis,i)
+g(1,i)*e(1,axis,i)
+g(2,i)*e(2,axis,i))
)/mI(axis);
}
So this is equivalent to the statement G dot e_i = mI_i \omegaDot_i
(From Newtons Laws).
whereas in cg.v22, the same code is as follows :
for( axis=0; axis<3; axis++ )
{
const int axisp1=(axis+1) % 3;
const int axisp2=(axis+2) % 3;
omegaDot(axis)=(
(1.-alpha)*(
(mI(axisp1)-mI(axisp2))*w(axisp1,ip1)*w(axisp2,ip1)+
g(0,ip1)*e(0,axis,ip1)+
g(1,ip1)*e(1,axis,ip1)+
g(2,ip1)*e(2,axis,ip1))
+alpha *(
(mI(axisp1)-mI(axisp2))*w(axisp1,i)*w(axisp2,i)+
g(0,i)*e(0,axis,i)+
g(1,i)*e(1,axis,i)+
g(2,i)*e(2,axis,i))
)/mI(axis);
}
Now, both versions look alike except for the additional term in cg.v22 -
" (mI(axisp1)-mI(axisp2))*w(axisp1,ip1)*w(axisp2,ip1) " ~
(I2-I3)*w2*w3 ..
I'd like to know the basis for adding this term...
Regards,
Dominic
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