How Can I get MATLAB to divide a periodic time history of acceleration data into several chunks?

Hi Everyone,

I am working with sets of acceleration data recorded under passing trains.

Due to the transient nature of the loading (moving wheels), the recorded acceleration signatures look like periodic functions with successive periods of oscillation and rest (no oscillation) about the horizontal time axis - the configuration of train axles (the distance between adjacent axles) makes this happen.

What I want to do is to double integrate the acceleration signatures to obtain the corresponding displacement time histories.

I have no problem with the integration process itself, but I note that if I perform the integration on just a small part of data (and not the whole acceleration trace), the results will be more accurate, probably due to minimised effect of inherent noise in the recorded data.

So, I have decided to divide the whole acceleration signature into several parts, double integrate each part individually, and then re-assemble the calculated displacement to get the whole displacement time history.

Based on the configuration of train axles, every four wheels can be grouped and considered for double integration at a time.

Also, the periodic representation of the acceleration signatures allows me to set clear boundaries (start and end points) for each chunk of the data (each time interval - between two successive periods of rest - over which the double integration is performed). However, I really do not know how to get MATLAB to automatically pick those "start" and "end" time spots on the acceleration signatures?

I hope that my question is clear.

Any assistance with this matter is much appreciated.

Thanks