Abstract
This paper presents some waveform analyses of the recorded pressure fluctuation in a water hammer due to collapse of a cooling cavity and the estimated velocity of the liquid column in collision with the blind end of a pipe. Real damping and peak period shortening, whose effects are similar in appearance on a graph of the change with time, are separated from each other by drawing graphs of the change with cycle number. The discussion on the damping is generalized using logarithmic decrements. It is proved that the air in the cavity strengthens the damping, the strengthening is greater earlier in the water hammer cycle, and the peak period shortening takes place rapidly not later than between the 2nd and the 3rd peaks in the case where the initial air concentration is over 30%, and is almost completed within this interval. In addition, considering the minor fluctuation in pressure bottoms, physical mechanisms of the damping and the peak period shortening are discussed.
