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-   -   6DOF: can't compute angular acceleration (http://www.cfd-online.com/Forums/fluent/65516-6dof-cant-compute-angular-acceleration.html)

 laurentb June 17, 2009 08:27

6DOF: can't compute angular acceleration

I everybody,

When i use the following 6dof properties :
prop[SDOF_MASS]=0.0014;
prop[SDOF_IXX]=2.333333e-8;
prop[SDOF_IYY]=2.333333e-8;
prop[SDOF_IZZ]=2.333333e-8;

Fluent display the message :
Info: 6DOF: can't compute angular acceleration.
Check moments/products of inertia.

If i increase moments of inertia (1e-6 for example) the message disapear. Any idea ?

 Will Anderson January 5, 2011 10:03

Fluent Limitation

The SDOF variables can only process solid body moments of inertia>=1e-06.

Unfortunately.

 Centurion2011 December 12, 2013 05:34

Quote:
 Originally Posted by Will Anderson (Post 289359) The SDOF variables can only process solid body moments of inertia>=1e-06. Unfortunately.
If this is correct than I am dissapointed in fluent developers :)

Also, when looking into 6 dof theory one cannot but wonder how brief it is. One could hope for better explanations about conservation of angular momentum equations (or Euler equations), specially since 6 dof solver is "solving" these equations using already establieshed numerical method.

I wrote with my friend our own "6 DOF solver code" in under 80 lines of code and it can calculate Euler angles (pitch roll and yaw angles) for bodies with body moments of inertia>=1e-06. :)

 youiithe March 26, 2015 23:14

Quote:
 Originally Posted by Will Anderson (Post 289359) The SDOF variables can only process solid body moments of inertia>=1e-06. Unfortunately.
Unbelievable! How come!

 Far October 23, 2015 01:49

how to stop this message from appearing in Fluent TUI? As I don't want to calculate rotational motion (yaw, pitch or roll). And I am not using shear stress terms in Six DOF UDF.

 nettesheim2 October 26, 2015 10:56

Small Moment of Inertia

For small moments of inertia, try typing this in Fluent's command line:

(rpsetvar 'dynamesh/sdof/minimum-cutoff-moments 1e-50)

Include the parenthesis and the '

Hope this helps

 Far October 27, 2015 04:05

do we need to provide torque (using speical command in UDF) to body or Fluent has some internal mechanism to calculable torque from the given forces?

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