A study on mechanism of self-excitation in Meco-Pogo

Simplified analytical equations are derived from numerical checking of the order of each terms in the theoretical equations in the authors' previous paper. These equations yield a simple mechanical explanation for the mechanism of self-excitation in Pogo. Furthermore a simple expression for discrimination of stability is derived for the case including the influences of the longitudinal vibration of liquid in the long feed pipe, of the cavitation in the pump, and of the function of an accumulator as a suppression device. The expression makes it easy to understand the effect of each factor on the self-excitation. A model experiment corresponding to the present simplified analytical model was carried out in laboratory. The test model was installed on an electro-magnetic shaker and the force corresponding to the thrust variation proportional to the flow velocity variation in the discharge pipe was given by the shaker. The occurrence of a self-excited oscillation under the mechanism clarified in the present analytical study was confirmed by this experiment. Furthermore the effect of oscillation of liquid surface was measured.