×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Road surface model

Road surface model

Road surface model

(OP)
Hi all,

I've built a simple quarter car suspension model which I am using for my own education.  Does anyone have, or have a link to, a road surface model, for use in a quarter car model?  I've seen power (or amplitude) vs. frequency distribution plots, but these are good for linear systems, and not good enough for nonlinear models.  A simple power distribution model doesn't have information regarding the probability distribution of peak accelerations of bumps and dips.  IOW you can synthesize 2 different road models with the same amplitude/frequency characteristic, but have a completely different distribution of the size of the bumps/dips.  Thus the reaction of a nonlinear model (e.g. in terms of RMS acceleration of the car's body), will be completely different.

My model has a PWL (non straight line, multiple breakpoints) model for the damper's F-V characteristic, so the size of the bumps matter...

TIA.
 

RE: Road surface model

(OP)
Bueller?  Anyone?  

Would a probability density function of instantaneous acceleration, with a spectral density function, adequately describe a given "type" of road surface?  

 

RE: Road surface model

(OP)
Thanks for the tip!  I will go and digest it.

RE: Road surface model

No problem.
 

peace
Fe

RE: Road surface model

(OP)
I digested it, <burp!>, and I learned something, but the author didn't touch on the subject of the distribution of the road displacement.

IIRC a random input variable can be described as having a given spectral density, and a distribution curve.

For example, noise with a flat spectral density, white noise, can have any distribution function.  White noise doesn't imply gaussian or uniform distribution.

I believe that a quarter car model with a non-linear damper model, e.g. has a blowoff, will react differently in terms of RMS passenger vertical acceleration, with different distribution curves, for a given spectral distribution, despite the RMS displacement of the road surface model being the same.

http://en.wikipedia.org/wiki/White_noise

"It is often incorrectly assumed that Gaussian noise (i.e., noise with a Gaussian amplitude distribution — see normal distribution) is necessarily white noise, yet neither property implies the other. Gaussianity refers to the probability distribution with respect to the value, in this context the probability of the signal reaching an amplitude, while the term 'white' refers to the way the signal power is distributed over time or among frequencies.'

RE: Road surface model

Quote:


I believe that a quarter car model with a non-linear damper model, e.g. has a blowoff, will react differently in terms of RMS passenger vertical acceleration, with different distribution curves

I agree with you on this. Assuming that the nonlinearity is a 'hardening' effect the larger amp. RMS input should impend harder on the passengers. Size of bumps do matter as you say smile

peace
Fe

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close