From road profile PSD to road profile history
From road profile PSD to road profile history
(OP)
Hi all,
I need to perform a simulation of a vehicle modelled as lumped masses. So I have in mind to excite the model with a road elavation and to use the ISO 8608, that it lists road profiles of different kind of roads. how could I get the road profile history?
thanks
Pietro
I need to perform a simulation of a vehicle modelled as lumped masses. So I have in mind to excite the model with a road elavation and to use the ISO 8608, that it lists road profiles of different kind of roads. how could I get the road profile history?
thanks
Pietro





RE: From road profile PSD to road profile history
2) synthesise a profile history that gives the same psd as the one you want. Obviously there are inifinitely many histories that would satisfy this, and some will cause different responses to others. Even if you have an amplitude probabilty distribution for the road then you still can have substantially different profile histories, and I'm guessing you don't have that.
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: From road profile PSD to road profile history
thanks for your reply. Of course that it's not possible to derive just one time history from a PSD. I tried to assume that the phase is null and to apply the inverse fourier transform, but I get a very odd time history, so I was wondering if there is another way to get the signal.
Thanks
Pietro
RE: From road profile PSD to road profile history
That's precisely what Greg was referring to.
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: From road profile PSD to road profile history
thanks for your reply, the problem is the signal generated is not correct, there is a huge spike, so somehow I should assume a phase for the signal, but I don't know how to do that. Do you have an idea?
RE: From road profile PSD to road profile history
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: From road profile PSD to road profile history
So, assign a random phase to each frequency bin and IFFT the resulting complex spectrum. This will give you a set of random numbers with a gaussian amplitude distribution function (that is a good thing) but you need to check that the crest factor (peak/RMS) suits your road type. I do not have a good source for values there, experience says 3-5 for uniform sections of road without potholes. If you end up with an unreasonable crest factor, try a different set of random phases.
Here's Tom Irvine's script for the same job
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: From road profile PSD to road profile history
thanks a lot for your reply. I take a look to Irvine's matlab script.
Cheers
Pietro