Tuned Mass Damper Part Deux

[gcdugas]

With certain parts of a car having a significant weight, chiefly the batteries, might a team get creative and mount it dynamically in the chassis as a sort of tuned mass damper. That way the ride height for ground effects might be more stable through the corners resulting in a more consistent range of DF which would not only increase outright performance but in increased driver confidence that the car won't suddenly step out on him. Even the movement of fuel in the tank, which is always going to be dynamic, could be controlled by carefully designing internal baffles in the tank so that the vertical movement of the fuel mass is designed to maximize ride height stability over bumps. Right now the tanks have some baffles mostly designed to insure proper scavenging but why not get creative and think about how to manage the mass of the fuel with other concerns in mind?

[Greg Locock]

That's not really how a TMD works, but yes, compliantly mounting any large mass can be used as a TMD. It's been done on production cars since at least 1949.

[gcdugas]

Mounting mass dynamically is EXACTLY how a tuned mass damper works.

[Zynerji]

I believe that if you can reasonably pinpoint the frequency that is harming traction that you could target a single frequency with this idea. The problem is that there are probably a dozen other frequencies as well and better ways to handle them.

But in F1, a .001% benefit seems to be worth the trouble, so maybe.

[Just_a_fan]

Mounting mass dynamically is EXACTLY how a tuned mass damper works.

Fuel wouldn't work as a TMD because it is free to move in any direction and is not attached to the chassis. Fuel slopping around is going to have a whole lot of different things going on - perhaps even being loose as a "blob" in mid air within the tank if subjected to a particular acceleration.

But mounting a heavy item in a designed manner so that it has freedom in a particular way could be useful. Not that there are many bits that could be so mounted.

And the teams would have to explain why a clever mounting system was being used - if it looks to the stewards like a TMD then it's illegal.

[Zynerji]

Mounting mass dynamically is EXACTLY how a tuned mass damper works.

Fuel wouldn't work as a TMD because it is free to move in any direction and is not attached to the chassis. Fuel slopping around is going to have a whole lot of different things going on - perhaps even being loose as a "blob" in mid air within the tank if subjected to a particular acceleration.

But mounting a heavy item in a designed manner so that it has freedom in a particular way could be useful. Not that there are many bits that could be so mounted.

And the teams would have to explain why a clever mounting system was being used - if it looks to the stewards like a TMD then it's illegal.

A "vibration isolation" mount could just happen to resonate at a desired frequency..

[Greg Locock]

Mounting mass dynamically is EXACTLY how a tuned mass damper works.

Yes, but your description of the effect of TMD in F1 is incorrect. The Renault at least was tuned to suppress wheelhop and hence improve grip after kerbing etc, nothing to do directly with ride heights.

[gcdugas]

A car that hops is a car that has exceeded its range of ride height. If you stabilize the hop you will stabilize the height. And by "stabilize" I mean that you will cut down on the amplitude of variance in ride height and vertical load variation. My guess is that you would need about 3 inches of controlled (tuned) vertical movement in order to have any measurable benefit. But with the battery under the fuel tank these 3 inches would come at the expense of CG height... which seems less important than aero these days considering that teams are mounting some weighty components high in the centerline just after the airbox. But will there be enough benefit to offset a 3 inch increase of a full tank?

[Greg Locock]

How to tell me you don't know what wheelhop is without telling me you don't know what wheelhop is. Unsprung mass bouncing mainly on the tire radial stiffness. Sprung mass hence floorpan is not much affected.

[gcdugas]

Does the TMD treat wheel hop by altering the tire flex? No, it does it by altering the chassis height that is adversely affected by the tire flex properties. It keeps the chassis height relatively stable in regard to the track surface. You could see it in the camera footage. The Renault wouldn't hop up as much when hitting the kerbs. This was the most visible benefit but along with this better behavior over the big bump of kerbs was better behavior over smaller bumps and a more consistent downward pressure at the contact patch of the tire. (less variance in the amplitude of contact pressure) Your understanding, whether you have thought it through or not, is that the TMD somehow affected the tire sidewall flex properties. Rather it altered the effect the tire flex properties had on the chassis stability which certainly stabilizes the ride height.

[Greg Locock]

The TMD sucks vibration energy out of the system at the wheelhop frequency and so calms it down. Write the equations for a 2 dof spring mass/damper in series model and play around with the effect of mass ratio, tune, and damping. Add an intermediary third mass the sprung mass of the vehicle). That reduces the effectiveness but the tune remains the same. I doubt the ride height is changed b the wheelhp vibration to any significant extent, the mass ratios are wrong. Say unsprung mass is 15 kg, sprung mass of a quarter car is say 150 kg, wheelhop amplitude 10mm - gives floorpan change perhaps 1mm.