## Useful simulations

Does the simulation software that you created help you to make a better car? If so how and how quickly?

I wanted to share this perspective about simulation software created and/or used by students for a while. The last design judging and conversations I had with students at FSAE Michigan convinced me I had to do it sooner than later.

I see some OK lap time prediction, vehicle dynamics, CFD, FEA etc.… software that decently simulate the car aerodynamics, handling, stiffness etc… but when I ask how a particular piece of software helps the students to design a better car I have little or no answer.

Two examples
1. A software that makes weight transfer calculations. I ask the student to change the springs stiffness in his simulation. To do so he had to scroll down several pages on his laptop screen to change spring stiffness number in his codes. Not nice. I would have like to see some sort of input graphical interface. I then asked him to overlay the weight transfer results, ideally Vs lateral acceleration (in case of nonlinear stiffness) with the new and old springs stiffness. He couldn’t. No output graphical representation.
What we need is at least some batch rum where the front and rear springs can be change from value X N/mm to value Y N/mm with steps of Z N/mm or a given number of steps.
When I asked the students how this software help him to decide what springs he wanted to put on the car he had no answers. When I asked him, what were the criteria he used to decide his spring stiffness, he did not have any either. He was just happy to show me a software that works. It painfully worked but it had absolutely no relevance
2. A software that shows how much the camber or the bump steer will change if a suspension point coordinates is changed. Good. But when I asked which bump steer is needed and which roll center movement he wants and why he could not give me any answer. What was the point of creating such software?

Students need to create software that are useful, relevant and easily usable. Practically that means: input and output graphical interface, automated batch run, trends, slope and tendencies. Ideally use tools such as heat map, parallel axis chart, scatter plot metrics..
Examples
1. if I raise the front roll center x mm how much do I want to raise my rear one to keep the same TLLTD. Is this relationship linear? How much do I need to soften my front and rear ARB if, after raising my front and rear roll centers, I want to keep the same roll gradient and the same TLTTD.
2. If I change the caster angle by changing the x coordinates of my front (or rear) top wishbone inboard pickup points does my bump steer change and if so how much do I need move vertically my outboard toe link rod end to keep the initial bumpsteer value? Show the result in a XY (X front roll center or froth ARB, Y rear roll center or rear ARB) graph of isolines bump steer values.
3. Show the aerobalance and the dynamic front and rear ride height Vs speed for front springs Kf1 and Kf2 and rear spring Kr1 and Kr2 rear or static front ride height of 20 and 25 mm and static rear ride height of 40 and 45 mm

Also make software that are relevant.
- A few years ago I judged a team of which one student crated an amazing virtual 7 post rig. When I asked him how he used it to define his dampers he told me he did not have the time. If the competition would have been about a 7 post rig simulation he would have scored close to a maximum of points but here I was judging the car design not the car simulation software design.
- Recently a student showed me a CFD study of his car - Formula One style, really amazing- but when I asked him what the tire coefficient of friction was he had no ideas. He told me his job was to create downforce not grip. Well, he is really ready for the hyper specialization of Formula One.
- This year at FSAE Michigan a student showed me his own vehicle dynamics / lap time simulation software and I thought we were going to have a interesting conversation but he could not define understeer and oversteer, neither control or stability. Let's be serious.

I think the problems occur because students spend too much time designing and manufacturing their car and not testing it. But I have been singing that song for a while....