Calculation of Roll stiffness, Roll Gradient, Turning Radius and suspension frequency

Sudip_Chavan

Hello Everyone,

I have prepared working MBD model of front trailing arm suspension with pitman arm steering. I am able to run all kinematic analysis events on it.

I gone through all predefined sdf outputs available but not able to find above parameters anywhere. 

We want to calculate those parameters regarding our vehicle for corelation and validation of our design.

Can anyone help me out for calculation of those parameters?

1. Roll Stiffness (Laden & Unladen)

2. Vertical Stiffness (with and without stabar)

3. Turning Circle Diameter

4. Suspension Frequency and Pitch Frequency (Laden & Unladen)

5. Roll Gradient

 

Thanks and Regards,

Sudip Chavan

GTT Adam

Hi Sudip,

Some of these results will require the creation of new events and manual calculation.

1. Roll Stiffness - This is a SDF output, and can be seen after generating a standard report after the completion of a half-car Static Roll Analysis. Roll rates can then be seen on Page 12: Roll - Roll Rate, Tramp Rate. The slopes of the curves will determine the roll rate of choice.
2. Vertical Stiffness - This is also an SDF output, and can be seen after generating a standard report after the completion of a half-car Static Ride Analysis. Vertical Stiffness can then be seen as the slope of the curves on Page 7: Ride Test - Vertical Force vs. Wheel Travel.
3. Turning Circle Diameter - This will require the creation of an event, like the Road Course, where the steering angle is increased via a Motion entity until the steering limits are reached (specific to your vehicle). Make sure to complete the event at low speed. Measure the displacement of the vehicle using a marker, usually attached to the front outer wheel center (if no bodywork available) or the outer front corner (if bodywork available).
4. Suspension Frequency - If this is referring to suspension natural frequencies, then you will need to complete a modal analysis. Normally this is done as a half-car model, so there is no interference from the opposing suspension components. Run a Linear analysis on the half-car model and then review the Modes until you come upon the mode of interest. For example, in the GIF below, this would be the ride frequency for this half-car model:
   1. Note - the displacements are always exaggerated, so this is not a realistic visual of the ride mode. 
5. Roll Gradient - This is typically calculated during a constant radius lateral acceleration event, at different speeds. The body roll angle is then divided by the vehicle lateral acceleration to get the roll gradient. 

 

Hope this helps!

Adam Reid

GTT Adam

Hi Sudip,

Some of these results will require the creation of new events and manual calculation.

1. Roll Stiffness - This is a SDF output, and can be seen after generating a standard report after the completion of a half-car Static Roll Analysis. Roll rates can then be seen on Page 12: Roll - Roll Rate, Tramp Rate. The slopes of the curves will determine the roll rate of choice.
2. Vertical Stiffness - This is also an SDF output, and can be seen after generating a standard report after the completion of a half-car Static Ride Analysis. Vertical Stiffness can then be seen as the slope of the curves on Page 7: Ride Test - Vertical Force vs. Wheel Travel.
3. Turning Circle Diameter - This will require the creation of an event, like the Road Course, where the steering angle is increased via a Motion entity until the steering limits are reached (specific to your vehicle). Make sure to complete the event at low speed. Measure the displacement of the vehicle using a marker, usually attached to the front outer wheel center (if no bodywork available) or the outer front corner (if bodywork available).
4. Suspension Frequency - If this is referring to suspension natural frequencies, then you will need to complete a modal analysis. Normally this is done as a half-car model, so there is no interference from the opposing suspension components. Run a Linear analysis on the half-car model and then review the Modes until you come upon the mode of interest. For example, in the GIF below, this would be the ride frequency for this half-car model:
   1. Note - the displacements are always exaggerated, so this is not a realistic visual of the ride mode. 
5. Roll Gradient - This is typically calculated during a constant radius lateral acceleration event, at different speeds. The body roll angle is then divided by the vehicle lateral acceleration to get the roll gradient. 

 

Hope this helps!

Adam Reid