Use of multi-able mass dampers

[DaveW]

A postscript to this thread, which might be of interest to some:

Those who have tested their vehicles on my multi-post rig will know that I assess each set-up using a "Performance Index" (PI), which is a cost function that weights & puts together response parameters that I believe affect the mechanical performance of a race vehicle. The idea is that a minimum value of PI represents the "best" mechanical set-up compromise.

Before TMD's were banned I was invited by one F1 team to help to optimize a TMD attached to the nose bulkhead using their multi-post rig & trial TMD hardware. The test was somewhat inconclusive, so I spent some time after the test modelling the vehicle, complete with TMD, playing with device parameters. I assessed the various parameter selections by carrying out a "rig test" with each model, processing the results in the same way as I would with a real vehicle. A summary of the results is shown here.

The plot requires some explanation. Each point corresponds to a run identified in the panel shown on the left. The run identifier refers to "PDA" (an acronym meaning Pitch Dynamic Absorber, I recall), & four parameters. The parameters were Mass (kg), Position (% wheelbase aft of the front axle), TMD natural frequency (Hz) and TMD damping ratio (% of critical). Quite clearly the "best" compromise, by my prejudices, was achieved with the natural frequency set to 7 Hz.

The result was a surprise both to me & the team, because we had assumed that the ideal natural frequency would be close to that of the pitch mode, which was around 9.5 Hz. Track tests demonstrated the model result to be correct.

The result was satisfying for me, of course, but it did demonstrate that the "obvious" solution for mechanical set-up is not always the correct one. It was the reason I suggested in an earlier post that Ferrari's claim that TMD's didn't work with Bridgestone tyres was probably because they had not tuned their version of the device to the correct frequency.

[PlatinumZealot]

Are these tests more of trial and error?

A guy once made a "vibration absorber" for his final year project, I was helping him with the CAD files. It was an adjustable stiffness type so that it could work at different frequencies. His application was for structures. The principle that it works on, if I recall, was that it doesn't dissipate energy like a regular damper, but it instead transfers the energy into its oscillating mass. The vibration of the housing of course disappears when you reach the working frequency. All you had to do was turn a knob to adjust the frequency you want to absorb. The vibrating mass was cantilevered as well.

Really not too sure if it is related to the Mass damper though. Maybe it is.

[DaveW]

Are these tests more of trial and error?

They were (& it was much easier to explore many options with a model). The complication in the vehicle application is that the vehicle responds to inputs in both heave & pitch, not pure pitch. Interestingly, perhaps, 7 Hz is very close to the frequency at which an F1 vehicle will porpoise (i.e. when it is extracting energy from the air). Hindsight is a wonderful thing.

An interesting article on the use of TMD's in various applications may be found here.

[munudeges]

"It is a bit like mass dampers, where its first use was fairly benign when it came to aerodynamics. But the more it got developed the more extreme the designs were. There were four, five, six mass dampers on the car, and they were clearly being used for aero reasons."

Load of rubbish. Mass dampers were never an aerodynamic device. They were, at best, a purely mechanical device that had an effect on aerodynamics somewhere down the line as all mechanical parts tend to do. It was never in contact with the air and as such was never an aerodynamic device in a month of Sundays.

It sound as if Brabham's ex-spanner man has had to justify a dodgy and questionable decision by dredging up yet another dodgy and questionable decision.

[Jeffsvilleusa]

An interesting article on the use of TMD's in various applications may be found here.

Taken from that link:

Tuned mass dampers are widely used in production cars, typically on the crankshaft pulley to control torsional vibration and bending modes of the crankshaft, on the driveline for gearwhine, and other noises. They are also used on the exhaust, on the body and on the suspension. Almost all cars will have one mass damper, some may have 10 or more.

Could this be what hardingfv32 was after? Anyone know why a production car would have 10 mass dampers? Could it be the case on an F1 too?

[DaveW]

Could this be what hardingfv32 was after? Anyone know why a production car would have 10 mass dampers? Could it be the case on an F1 too?

Good spot! I guess it depends what one calls a mass damper. So far as I'm aware, few vehicles actually incorporate explicit mass dampers (though BMW would be one), simply because they represent additional weight & require packaging space.

However, any two masses that are (or can be) connected together flexibly could be called a mass damper, tuned or otherwise. A luxury car might have front & rear sub frames, a power train, a ladder chassis supporting a body within which are seats to support the occupants, all flexibly tied together. Such a vehicle could be said to have many mass dampers, but I suspect the truth is they are not tuned as such - more cobbled together & adjusted until an acceptable ride has been obtained.

And that is the point. With the possible exception of the engine & powertrain, none of these is designed to enhance vehicle performance. All are attempts to improve "ride". In other words they are used to manipulate response mode shapes, rather than to absorb energy. TMD(s), as used by Renault F1 for example, will still modify response mode shapes (hopefully), but here the objective is to gain some "leverage" (amplitude multiplication) of the TMD mass to promote energy absorption. The objective is contact patch load control, not ride.

It might be added that the first step when converting a road car to a race vehicle is usually to remove the plethora of bushes & flexible mounts so that the original wobbling jelly can be controlled predictably.

So how many are used in race vehicles? I am aware of only one explicit TMD that has been used successfully in an F1 vehicle, though two have been tried recently, & I tried 4 unsuccessfully. Having opened the road vehicle can of worms, however, the possibility remains (after the ban) for incorporating implicit TMD's. The driver, who is "flexibly mounted" in structural terms, would be one, & I am sure he does have an effect on the response of an F1 vehicle. However, I don't know of a team that has invoked that, or similar, options deliberately.

Maybe Mr. Whiting did read the Wikipedia article...

[PlatinumZealot]

I am not aware of any BMW's with mass dampers (and I am a BMW fan) . Though an argument can be made for the exhaust pipe since it is free to vibrate.

A mass damper is easy to spot because it usually is a freely vibrating mass that is rigidly fixed to the object you want to dampen.

[marcush.]

as I understand the whole drivetrain of productioncars is used as a mass damper .
The soft mounts will invariably give when you hit a road bump that cannot be soaked up by the suspension..

[PlatinumZealot]

That is dampening vibration due to imbalances. You have objects that dissipate energy on the drive shaft, but those objects are not freely vibrating so as one whole object they share the same natural frequency. So that is not like a mass damper (or I think the proper term is "vibration absorber")

The thing is a mass damper is not really a damper (to how I understand it). It is a vibration absorber. It doesn't really dissipate energy using viscous effects or friction like a rubber mount, a shock or "dash pot." It's harmonic frequency is tuned to the frequency of the vibration you want to absorb.

And so with a drive-shaft those frequencies are not absorbed by the masses on it. you only balance the drive-shaft assembly to move the harmonic frequency higher than a range it will encounter in it's use.

I have a video of the vibration I helped my friend with. I have the CG version, the actual fabricated object worked too. I do not have a video of that though.

Watch the video very closely....

[PlatinumZealot]

It is not so hard to Imagine now, that you can have 10 or 20 small freely vibrating masses bonded to the bodywork of the car. Tuned to resonate at different frequencies, and thereby creating a destructive interference with the vibration of the car.

[747heavy]

I am not aware of any BMW's with mass dampers (and I am a BMW fan) . Though an argument can be made for the exhaust pipe since it is free to vibrate.

A mass damper is easy to spot because it usually is a freely vibrating mass that is rigidly fixed to the object you want to dampen.

BMW M3 (E46) transmission mount/brace part#7 is the mass ~1.6 kg, together with the "rubber" mounts (springs) it will form a TMD.

you will probably find more of them, if you keep looking

and

Z3 [E36 2.8] rear "bumper weigth" 6.4-7kg depending on side

[bill shoe]

These simple vibration absorbers are also found on suspension control arms, and on the outside of damper bodies (!), etc. They are an NVH issue rather than a vehicle dynamics or grip issue. They try to change the frequencies of the suspension compenents so that vibrations originating at the tire don't have a good transfer path into the car body.

I like n smikle's idea of using 10 or 20 of these little things to sneak a kind of TMD capability onto a current F1 car. However, I think this would be very difficult. The small size of these devices makes them naturally suited to higher frequencies (20, 50, 300 Hz) rather than the slower frequencies that concern the mechanical and aero setup of an F1 car (5-10 Hz?).

I do think there are some plausible F1 applications for these small vibration absorbers, although I have not actually seen or heard of any. These would include coolant pipes between the engine and heat exchanger, and the exhaust pipes themselves (especially in their longer "blown-diffuser" form).

Is there any way you could sneak in a low-frequency TMD by putting a reserve oil tank on the front of the monocoque and then somehow designing the tank so the oil sloshes up and down at the desired frequency? Easier said than done but stranger things have been accomplished.

[PlatinumZealot]

you will probably find more of them, if you keep looking

and

Z3 [E36 2.8] rear "bumper weigth" 6.4-7kg depending on side

M3's and Z4's are not really common you see. but still Interesting.

[bill shoe]

It makes sense that vibration absorbers and/or tuned mass dampers work well if they operate in a mode that has little or no effective conventional suspension (i.e. vertical mode for front suspension on typical modern F1 car).

What if you take a car with an effective conventional suspension and put a TMD system on the unsprung weight, perhaps attached to the upright. Tires have little damping in vertical bouncing mode, does this qualify as "little or no effective suspension" for the purposes of TMD? Would TMD be useful overall, or would it just influence frequencies that the conventional suspension could deal with anyway?

My idea is that the TMD would reduce tire-bouncing or wheel-hopping, which in turn would improve contact-patch load consistency and ride. It might also allow more conventional damping at lower frequencies.

I am having difficulty conceiving exactly how this would work, but a TMD typically has a small damper on it, and I would think anything that adds damping to the relatively undamped tire has potential to improve the situation.

EDIT: corrected "sprung" to "unsprung" per 747's comment.

[747heavy]

What if you take a car with an effective conventional suspension and put a TMD system on the sprung weight, perhaps attached to the upright.

if you would put it onto the upright, it would be on the "unsprung weight" of the car.

The Citroen 2CV used such a system.



see the black vertical cylinders near the brake drums

that´s, more or less, what you find inside