hi! i'm beginner in the subject of vibrations. i'm trying to understand the waterfall plots. i have attached a waterfall plot. can someone please help me to understand it? waterfall plots are used when the operating speeds are varying (run up or coast down). in this plot, as the speed varies with increase in time, does the amplitude of the machine changes at a particular natural frequency? from elementary vibrations all i know is at a given natural frequency, a machine/component will start vibrating at natural frequency with large amplitude of a fixed value. for a case of a multi-cylinder IC engine, as the speed of the crankshaft is varied how is the rainflow plot going to look like when the speed of the engine crosses critical speed of shaft?