Resonance frequency semi trailer
Resonance frequency semi trailer
(OP)
Im trying to calculate the resonance freq. for a semi trailer
The different spring rates of the airspring itself and the tyre should be multiplied by the number on the trailer right?
So, basically 8x spring rate tyre and 4X spring rate airspring?
From my scriblings im somewhere around 1.2Hz for the trailer (loaded) - as attached
Somewhat close?
Peace
The different spring rates of the airspring itself and the tyre should be multiplied by the number on the trailer right?
So, basically 8x spring rate tyre and 4X spring rate airspring?
From my scriblings im somewhere around 1.2Hz for the trailer (loaded) - as attached
Somewhat close?
Peace





RE: Resonance frequency semi trailer
RE: Resonance frequency semi trailer
Thanks for your input, highly appreciated
p.s. what will actually happen when the trailer is experiencing a long duration of this frequency eventhough the vehicle is dampened?
Since it is dampened it will be limited to a degree but how far will this actually go?
RE: Resonance frequency semi trailer
At least with cars it doesn't cause any particular problems.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Resonance frequency semi trailer
Air-ride suspension on any trailer I've seen is not a closed system. There is a height control valve that will bleed or add air as required, so if it is tripped, the spring rate of the air-spring changes. I think there is a pressure relief valve as well to prevent overpressure.
RE: Resonance frequency semi trailer
RE: Resonance frequency semi trailer
I have calculated C critical and divided this by 10.
Ok, can I now use Formula Fdamper = c x vdamper to determine the actual required shock forces (of course dividing them by the number of actual shocks)?
I'm not sure what to use for the velocity since the bounce is a sinus motion with non-uniform velocity.
I have attached some more scribblings
Damper specs are force - speed, but since the are also tested with a sinus, what speed is this actually, max speed when passing true zero? But the body motion speed is not uniform, how to do this?
Gracias
RE: Resonance frequency semi trailer
yes
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Resonance frequency semi trailer
Can anybody perhaps explain why the stiffness value k will eventually become
keq=kspring*ktyre for the unsprung system and keq=kspring*ktyre/kspring+ktyre for the sprung system.
I thought k+k was two spring parallel and k*k was two springs in series, but how does this relate to the actual system
RE: Resonance frequency semi trailer
Would k then be the "equivalent k value", so kspring+ktyre(+ not *, mistake above) for the unsprung part of the system and kspring*ktyre/kspring+ktyre for the sprung part of the system?
It's been a long time...
RE: Resonance frequency semi trailer
For springs in parallel, apply a unit displacement and work out the forces, which will add.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Resonance frequency semi trailer
In the formula i'm not sure how to handle the speed term, since the damper speed is probably more or less a sinewave(cosinus function). How accurate is this formula, or nothing more than a rough ball park value?
Also i'm not sure if the damper ratio "i" is to the power or simply a ratio (like i assumed)
Is a given damper ratio also contant regardless of the actual amplitude of the suspension travel (assuming a contant frequency)?
I guess not since the damper force-speed function is not progressive enough in most cases?
Again, thanks a million
RE: Resonance frequency semi trailer
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Resonance frequency semi trailer
RE: Resonance frequency semi trailer
I basically made numerical calculations based on a spring mass damper system.
That way i could take in account the non-linear and asymmetrical behavior of the dashpot.
for instance m*a+d*v+k+x=0
peace