# [overture] Re: Rigidbody Torque / angular acceleration

• From: Bill Henshaw <henshaw@xxxxxxxx>
• To: overture@xxxxxxxxxxxxx
• Date: Fri, 20 Jun 2008 08:23:56 -0700
```Hi Dominic,
These are Euler's equations, see
http://en.wikipedia.org/wiki/Euler%27s_equations

...Bill

#DOMINIC DENVER JOHN CHANDAR# wrote:
```
```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++ )
```                 {
(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;
```
```                            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
```
```
```