Jersey Tom wrote: ↑
Sat Dec 23, 2017 2:33 pm
There are two halves of this, one of which is more pure theory, the other perhaps more empirical.
Vibrations and system dynamics - this falls under classical engineering education. I don't have a particular textbook in mind that I'd recommend, I've been out of the classroom for 10 years and didn't feel like I was great with the topic back then!
Something to bear in mind though is that it's relatively easy to have a pure, closed-form solution to a trivially simple system - e.g. quarter car with a constant mass, constant linear spring rate, and constant linear damping rate. It's good for illustrating the general concepts, tinkering around and seeing how forces and displacements change as you alter parameters. In reality though, dampers don't have purely linear responses - nor purely dependent on velocity - so a closed-form solution is probably either impractical or impossible.
If you're an engineering student and have access to something like Simulink or Dymola, you can quickly and easily create a quarter car model as a block diagram - and take advantage of built-in blocks to where you could add a non-linear table damper or other things and see what they do.
Assuming you had mastered the pure science or modeling aspect (a significant venture in itself!) there's then the question of... what do you do with it. How do you know what the results mean? How do you know what's going to be faster on the racetrack?
I would say there is no closed-form obvious answer to this. You
need to come up with the answer - often by lots of experimenting and track testing, finding your own rules and recommendations. In my experience, success in pro motorsport engineering is highly contingent on building up a good notebook of your own experiences, particularly between theory and real world measurement
. "The answer" doesn't just jump out at you - it's an empirical endeavor that builds on itself over time.
Often there's some tradeoff or relative weighting to "mechanical grip" (control of tires) versus the sprung aerodynamic platform. I suppose if you had a target ride height and could get better platform control without a mechanical grip penalty - that's perhaps an obvious free lunch. Of course that assumes your aero data is truly accurate and it's the "right" ride height to be targeting for the right reasons (downforce and drag trade offs, etc). Or you might easily postulate that it's probably not a good thing for a vehicle to be wildly under-damped, that's another freebie you might come up with. Otherwise - it's a compromise. You'll have to find out, for your type of vehicle, what the weighting is for platform vs. mechanical. Or how much front versus rear. Main springs versus the tires as springs. How over-damped or under-damped. Etc. etc.
If it seems like a daunting task with a lot
of design space to cover - it is - especially early on when you're starting from scratch and scanning a broad range of things. Eventually though you may find patterns and things that correlate, or tangible measurements you can work with. Maybe you discover, "Okay... at the race track, it seems like X ratio of critical damping is best for speed and driver feel. Now if I want to try Y amount stiffer springs, I'll have to add Z overall damping to get back to X damping ratio since I believe that's a good quantity." Things like that.
Of course, there are those on this forum with a lot more industry experience with this specific topic - but it's my two cents.