Calculating the weighted RMS acceleration (ISO 2631) 1

[claudiodeviaje]

Hello everyone!

I simulated the vertical acceleration of a tractors cab with a semi active damping system. The model works perfect, but need to be optimized. For this, I need to analyse the vertical acceleration using the frequency weighted RMS acceleration according to the ISO 2632. The explanation is extremely complicated since they explain the complete mathematic theory.

My model delivers a ASCII table with the vertikal acceleration, and through a Fourier Transformation I get the frequency spectrum but not the actual acceleration for each frequency.

Could someone point me to a website where its explained how to calculate the RMS acceleration?

Thanks!
Claudio

 

[Rob45]

Are you asking how to calculate the RMS value?

 

[CESSNA1]

claudiodeviaje: If you have the Fourier Transform in PSD format, the vertical axis is G^2(rms)/Hz. The horizontal axis is Hertz. To get the rms value at a frequency go to the frequency desired and read its value. Let's at 250 Hertz the amplitude (G^2(rms)/Hz) is .02. That is the square of the rms value. Take the square root and you find the rms value at that frequency is .141 G. Multiply this by 1.414 to get the peak acceleration of .199 G or 5.34 ft/sec^2

To get the overal G value integrate the PSD surve. Be careful the axis are in Log-Log format and integration is not strightforward.

Regards
Dave

 

[BobM3]

Dave -

You also have to multiply the g^2 value by the bandwidth of the filters (or frequency resolution if digital) to get the RMS. So, using your number, if the bandwidth was .2 hz then you would have .02 g^2/hz * .2 hz = .004 g^2.