# ANSYS FSAE monocoque tutorial videos

Member Posts: 3

Hello,

I have been working on my schools FSAE team doing simulation for our monocoque in ANSYS. This is our first year designing the monocoque, and I am trying to calculate torsional stiffness from my ANSYS sim. I used this set of tutorial videos on youtube. https://www.youtube.com/watch?v=5mvHCx-qftk&t=214s

In this video linked, why is a force of 6870 N used for the car? Im a little confused about this and there is not much explanation.

I was able to set our cars chassis up exactly the way that it was done in the videos, and I am on part 6 and trying to calculate the torsional stiffness. Near the end of the video, some math is shown on how to calculate the stiffness based on the directional deformation, the 6870 N force, and the length from both of the sphericals. https://www.youtube.com/watch?v=Zp8qp0fYYHo

Im a little confused about this math, as when I plug in some of the numbers listed, it doesn't match the answers you have given. For example, for the moment force M, multiplying (2)(6780)(825) is equal to 11335500, and not 5667.7. Along with that, some of the math for finding the angle of twist seems wrong. Our team calculates our frame stiffness in Nm/deg, and using these equations with the given numbers for your chassis, I receive a chassis stiffness of 149.5 Nm/deg. This does not seem right to me, as our teams current chassis stiffness is roughly 1,500 Nm/deg.

Im looking to calculate our teams monocoque stiffness in Nm/deg, but whatever way i use these equations given I get a super low number.

I know this is a lot to post, but would anyone be able to help with this?

• Posts: 130Ansys Employee

The values shown in the video should not be copied directly. To determine the torsional stiffness in a linear analysis, though, the force value doesn't matter since linear analyses have a linear relationship of input to output. (If you double the force, you double the displacement, but the ratio remains the same.)

The equation for moment converts the moment arm from "mm" to "m", which represents a factor of 1000. Although a moment is a 'force couple' with 2*F, in this case, it's just taking "F", so that factor of 2 with the unit conversion of 1000 is why the number differs by 2000 from what you calculated.

The model is for demonstration purposes, to show the process of using Ansys Composite PrepPost. Your design and materials used would affect your calculations and results, so unless you were using a very similar design with very similar materials, I wouldn't compare your design with the one in the video, as they could be expected to be very different.

Regards,

Sheldon