Free Vibration in Trucks

Everywhere!
Can you name a part that doesn't vibrate?
Maybe the seat squabs don't vibrate, and the seatbelts, but just about evrything else vibrates to some degree.

If you really insist on an answer, then I'd start with the exhaust system, and the suspension, which obviously has components inserted specifically to dampout vibration.
Del

thanks..for the description,i knew that.but

i am looking for the components that will exhibit free vibration?correct me if i am using the wrong term.A professor has asked me about it,i am also confused about the term free vibration..i know this type of vibration doesn't exist in real life but still free vibration with some damping in trucks is the question..

Not my area, but could your Prof be referring to sprung and un-sprung masses. The masses involved with the axles etc are unsprung, where the chassis and body etc are sprung. Engine is supported on "spring" system (mounting blocks), the passenger is "sprung " etc??????

Free vibration occurs in the rotating parts and is communicated throughout the vehicle.

I was going to give a good simple explanation of but thought the professors assignment had designated the student to do the research.

Free vibration occurs when a motion is induced and an oscillation develops about an equilibrium.

well i have searched on it already and found free vibration specifically in the cab of trucks..mostly due to the imbalance wheels not because of road condition..thats wot i have found...thanks ed weldon for the description its very helpful to me..

vote of thanks to all the friends also..

At 100 km/hour a truck with an unbalanced 1m dia wheel will produce a roughly sinusoidal vibration impulse at around 9 hz. This is well within the range of human perception although what you actually hear coming out of the truck cab are higher frequency components. You can also feel the vibrations and in some cases see them. Large sheet metal structures can easily have vibration modes in the 9 to 10 hz range, especially if there is any looseness in the connections (or maybe crude engineering that didn't identify and correct all the rattle makers at the design stage). Nevertheless what you are observing are primarily forced vibrations.

Free vibrations are really something we have defined to ease the teaching of the subject. So we say that it is a free vibration if we have a system with elasticity and mass and introduce potential energy into it without any significant motion of the system and then allow this energy to be released to set the system in motion. The system alternatively converts the energy from potential to kinetic and back again at some fundamental or "natural frequency". In the classroom we often start with a weight hanging from a soft spring attached to something solid at the top. We gently pull it straight down and carefully release it. It vibrates up and down at its fundamental frequency calculated as the square root of spring constant divided by mass.

We quickly go off to argue about the effect of the mass of the spring, dampening that eventually makes the whole thing stop moving, etc. What we miss at the beginning is the consideration that this vibration caused by a release of stored energy is a relatively rare phenomenon. Also rare is the simple system with only one mode of vibration, a point mass and a mass spring that has no mass but nevertheless moves part of the time and therefore has some kinetic energy during that time.

Most mechanical vibrations in our physical world have a component of energy that is from a forcing source and a component that is a free vibration. The question of whether a given vibration case is forced or free is really up to how one chooses to define the boundary between the two in numerical or mathematical terms as it may apply to the given case.

I suppose you could call it a free vibration if it is still "buzzing" after the truck stops. Of course if you have a sophisticated structural analyzer and accelerometer that can store a time domain vibration spectrum or an FFT vibration mode signature from an impact test and later calculate the difference between it and a vibration signature taken when the truck is operating you could set some boundary definition that would allow you to decide whether the observed vibration was free or forced.

Ed Weldon

Free vibration may be observed in the hollow drive shaft of trucks. In the instance a gear is engaged and the clutch brake not engaged the shaft may ring.

The closest thing I can recall is a store on US 1 that has buy 1 get 1 free on vibrators.

Are you a student?

Stud?