Vehicle Vibration Calculations

[K87]

Bit of a toughie here and hopefully there's some resident experts who can help.

For a uni project I'm looking at mathematically modelling the z axis vibrations a vehicle occupant would be exposed to whilst the vehicle is in motion.

I'm thinking a basic model of this would involve 3 degrees of freedom in the Z axis. 1 for the tyres 1 for the suspension, and 1 for the vehicle seat as this should have some form of damping in a road car.

The speed of the vehicle would be known, and the profile of the road would also be known.

First of does this sound right using 3 degrees of freedom or should there be more? And also how would this be applied through 4 tyre / suspension?

Does anyone know of any good books or online sources of similar work?

Thanks in advance.

[CrashTD]

There is an interesting lecture about engines at your university tomorrow. You should go to it.

I am not about to do your coursework for you but Look at the bigger picture. X and Y components will contribute to your overall displacement in z.

The DOF depends on the vehicle/chassis/suspension/seat/seat belt arrangement. Factors such as the seat padding and mass of the driver will have an effect on the vibrations.

[spikeyhead]

MIL-SPEC 810 is your friend.

[bitwrx]

K87 said:

Bit of a toughie here and hopefully there's some resident experts who can help.

For a uni project I'm looking at mathematically modelling the z axis vibrations a vehicle occupant would be exposed to whilst the vehicle is in motion.

I'm thinking a basic model of this would involve 3 degrees of freedom in the Z axis. 1 for the tyres 1 for the suspension, and 1 for the vehicle seat as this should have some form of damping in a road car.

The speed of the vehicle would be known, and the profile of the road would also be known.

First of does this sound right using 3 degrees of freedom or should there be more? And also how would this be applied through 4 tyre / suspension?

Does anyone know of any good books or online sources of similar work?

Thanks in advance.

Just remember: all models are approximations. They are all wrong, but some are useful.

You could find hundreds of DoF if you wanted. eg. 4 tyres. They can move up and down. That's one DoF each. If you're feeling fancy, you could make it a polar DoF because the suspension arm ascribes an arc. But it's probably easier to approximate it to linear. Don't forget the flex in the bushes mind. That'll be 3 DoF for each bush in each joint, on each wheel. Oh and tyres. They bend as well.

I'd also assume the driver was made out of stone, and the seat made out of granite. And the car is driving on its rims. And it's a unicycle. Now we're getting towards the problem I could think about solving.

Once you've done that, give him a suspension seat post.

Now make it a motorbike.

Now give him a bouncy seat.

Etc.

Start simple then refine it till you get a useful result.

Or that's how I'd do it (had I known then what I know now. Which isn't much).

[chevronb37]

A mate of mine has recently been awarded a PhD from Manchester Uni. His thesis was all about engine vibration calculations. I realise this isn't directly applicable to your situation, but if you feel he could help, let me know and I'll pass on his email. I struggle to understand most of what his brain is able to deal with...

[CrashTD]

chevronb37 said:

A mate of mine has recently been awarded a PhD from Manchester Uni. His thesis was all about engine vibration calculations. I realise this isn't directly applicable to your situation, but if you feel he could help, let me know and I'll pass on his email. I struggle to understand most of what his brain is able to deal with...

Since we are veering off topic - There is a dissertation out there about using electromagnets as engine mounts.

[K87]

CrashTD said:

There is an interesting lecture about engines at your university tomorrow. You should go to it.

First I've heard of it, anymore info?

[chevronb37]

CrashTD said:

chevronb37 said:

A mate of mine has recently been awarded a PhD from Manchester Uni. His thesis was all about engine vibration calculations. I realise this isn't directly applicable to your situation, but if you feel he could help, let me know and I'll pass on his email. I struggle to understand most of what his brain is able to deal with...

Since we are veering off topic - There is a dissertation out there about using electromagnets as engine mounts.

That has the potential to be completely awesome.

[K87]

so if it fails will or your battery goes flat would the engine just fall out!?? heehee

[CrashTD]

Ramphal Building 6.30.

James Turner
Chief Engineer, Powertrain Research,
Lotus Engineering.


As for the engine mounts - it was all theoretical. The amount of current needed to oppose 400Nm is never going to come from a car.

[K87]

CrashTD said:

Ramphal Building 6.30.

James Turner
Chief Engineer, Powertrain Research,
Lotus Engineering.


As for the engine mounts - it was all theoretical. The amount of current needed to oppose 400Nm is never going to come from a car.

Not my uni that isn't.