Unable to understand equation mentioned on Altair documentation site

Sudip_Chavan

Hello Everyone,

As per the picture attached below it shows the expression for left wheel steer angle change, but what exactly are those numbers.

rtod*(C(6,3)+C(6,9))/(C(3,3)+C(3,9))*1000

I read somewhere that those are the numbers for reference markers in the model.

Can anyone share any document for those details?

If someone can  breakdown above expression then it will be really helpful.

 

Thanks and Regards

Sudip Chavan

GTT Adam

Hi Sudip,

The C terms are for the SDF definition compliance matrix and is used to compute various SDF parameters.

These SDF calculations can happen only during Static/Quasi-static analyses. The compliance matrices work only in those solver modes. They can no be used for a runtime calculation.

Here is a snippet from the documentation:

"For non-steerable suspensions, the compliance matrix is the partial derivatives of the left and right wheel center displacements with respect to forces and moment forces at the wheel centers. To compute the first column of the compliance matrix, for example, MotionSolve applies a unit force in the global X direction to the left wheel center, performs a static analysis, and the resulting change in position and orientation of the left and right wheel centers becomes the first column of the 12 x 12 matrix. The process is repeated for the remaining 11 columns.

In the documentation for SDF parameters, terms in the compliance matrix are referenced using C(i,j):

• i = 1-6 X Y Z RX RY RZ displacements of the left wheel center
• i = 7-12 X Y Z RX RY RZ displacements of the right wheel center
• j = 1-6 X Y Z RX RY RZ forces on the left wheel center
• j = 7-12 X Y Z RX RY RZ forces on the right wheel center

When reading entries in the compliance matrix, i is the degree of freedom which is being displaced by a force in the j degree of freedom. For example, C(3,9) is the vertical displacement of the left wheel center due to a unit vertical force at the right wheel center."

 

Relevant documentation can be found here:

https://help.altair.com/hwdesktop/hwx/topics/motionview/suspension_design_factors_r.htm?zoom_highlight=compliance+matrix

 

Hope this helps!

Adam Reid