Why ban the mass damper?

[ReubenG]

Dave, could you expand a little on why the TMD operated at 7Hz, rather than 9~10Hz. My understanding of vibration absorbers was that they are only effective in a very narrow frequency band.

BTW, my explanation has a statement which can be misinterpreted: the frequency that the absorber is tuned to is not the natural frequency of the moving mass and spring on its own. By adding an additional mass and spring, the system has more than one degree of freedom - I didn't want to launch into a discussion of Eigen modes of vibrational systems in my original reply.

For those who are interested, there is an explanation without too much maths at:
http://paws.kettering.edu/~drussell/Demos/absorber/DynamicAbsorber.html

[marcush.]

would a hammer shaped piece of ballast (or integral part of the monocoque)acting as a mass damper be legal?,no moving parts ,just not stiff enough..

It would. Just a question of efficiency. The force generated by a TMD is proportional to mass & acceleration (Newton says). Hence more stroke = less mass for a given force. How to cantilever your "hammer" so that it can use the full depth of the nose box without fatiguing its "handle"?

Incidentally, The moving mass of a TMD was totally enclosed in a container hard bolted to the nose, just as the moving pistons in an engine are totally enclosed. Are engine pistons considered to be "moving ballast"?

so effectively my idea is to -hinge it by a flexure -like a leafspring made of carbonfibre widening towards the end to a heavy mass that is allowed to move up and down by outside exitation .The mass could be even tungsten filled resin /carbonfibre... so no additional parts just flex in it ...you could even buildt a web around it ...to make it look like it was fixed ....only allowing for up and down movement under shockloads..a certain amount and cushion the limits of movement

the blade type hinge could double up as nosecone tip....? this would even fit into Mercedes banana nosecone.. maybe we will see this later in the year?? but no they are busy developping their car at this time ...no chance to look into forums..

[DaveW]

Dave, could you expand a little on why the TMD operated at 7Hz, rather than 9~10Hz. My understanding of vibration absorbers was that they are only effective in a very narrow frequency band.

Ugh... I was hoping you wouldn't ask that question.

Road inputs to a race vehicle are broad-band, rather than single frequency. They also tend to be "phased" (hit the rear wheels after the fronts). So, a vehicle always responds to road inputs in both heave & pitch. However, the heave/pitch phasing changes with input frequency. Normally (for an F1 vehicle), inputs at the heave mode frequency are controlled by the rear dampers, whilst inputs at the pitch mode frequency are controlled (inefficiently, perhaps) by the front dampers. There is a "gap" at intermediate frequencies where inputs are not so well controlled. This is normally the frequency at which a vehicle will "porpoise" (caused when vehicle motion extracts energy from the airstream at a greater rate than can be dissipated by the dampers & tyres). That frequency usually lies between 6.5 & 7.5 Hz.

Interestingly (& surprisingly, perhaps), the effect of adding a TMD is very clear on a multi-post rig (where "aero" is applied, but is not coupled with vehicle response). The "optimum" TMD natural frequency is very clearly defined, and agrees precisely with track tests.

[DaveW]

...so effectively my idea is to -hinge it by a flexure -like a leafspring made of carbonfibre widening towards the end to a heavy mass that is allowed to move up and down by outside exitation .The mass could be even tungsten filled resin /carbonfibre... so no additional parts just flex in it ...you could even buildt a web around it ...to make it look like it was fixed ....only allowing for up and down movement under shockloads..a certain amount and cushion the limits of movement

A sprung nose-box joint would work, but would be vetoed by our "aerostatics" friends.

[marcush.]

...so effectively my idea is to -hinge it by a flexure -like a leafspring made of carbonfibre widening towards the end to a heavy mass that is allowed to move up and down by outside exitation .The mass could be even tungsten filled resin /carbonfibre... so no additional parts just flex in it ...you could even buildt a web around it ...to make it look like it was fixed ....only allowing for up and down movement under shockloads..a certain amount and cushion the limits of movement

A sprung nose-box joint would work, but would be vetoed by our "aerostatics" friends.

oh no its not aero..it is integrated non moveable ballast that is ..

[richard_leeds]

hmmm.....

Perhaps....

No....

Well possibly ....

Is this the function of the RB flexible wing?

[mep]

by Dave:
Normally (for an F1 vehicle), inputs at the heave mode frequency are controlled by the rear dampers, whilst inputs at the pitch mode frequency are controlled (inefficiently, perhaps) by the front dampers.

Oh, interesting comment can you explain that?

[DaveW]

Oh, interesting comment can you explain that?

A consequence of the suspension set-up. In one, fairly extreme, case energy dissipation for a heave input was 3.5% front & 83% rear at the heave mode & 32% front & 26% rear at the pitch mode. The "missing" percentages were dissipated mainly by the tyres. That isn't the whole story, because those numbers don't describe the "efficiency" of the dampers. In this case, for example, the front tyres dissipated more energy than the front dampers almost everywhere...

[mep]

So is it caused by soft and hard dampers?
With hard damper dissipating more energy.
How can a damper be good at heave but bad at pitch where is the difference?
Is it becaue of the phase shift producing different frequencies or pitch generally having lower frequencies?
When you say the front tire has better dissipation abilities can we conclude that the tire is "harder" damper than the damper itself?
I must admit that I am not very good informed when it comes to oscillations.

[DaveW]

So is it caused by soft and hard dampers?
With hard damper dissipating more energy.
How can a damper be good at heave but bad at pitch where is the difference?
Is it becaue of the phase shift producing different frequencies or pitch generally having lower frequencies?
When you say the front tire has better dissipation abilities can we conclude that the tire is "harder" damper than the damper itself?
I must admit that I am not very good informed when it comes to oscillations.

mep, it has more to do with springs. For example, locked front springs will mean that the front dampers will do no work, regardless of settings. Away from that extreme case, the "efficiency" of the dampers depends upon the ratio of spring/tyre stiffness.

Optimizing damper settings is quite complex, because energy input to the vehicle will be dissipated, but front/rear springs, tyres & dampers will dictate where, & how quickly that happens, & also the magnitudes of the resulting variations in contact patch load.