This report is concerned with the conversion of liquid-flow energy to acoustie energy, as achieved through a self-excited, flow-interruption process. The interrupting element is a valve, or variable-area orifice, which exhibits the properties of power amplification (i.e., the work required to alter the discharge is less than the acoustic power that results from the con version operation). When amplification occurs, a fraction of the modulated flow power may be fed back to control and sustain the modulation process, while the remaining energy is available to be consumed by an acoustic load. Certain conditions exist for which flow variations through a variable-area orifice act quasistatically, or as a succession of slowly changing equilibrium states. In this case, the acoustic circuit representation of a pressure-actu-ated orifice assembly closely resembles the equivalent circuit of a vacuum tube, or electron valve. The similarities and differences between these analogous structures are investigated. Furthermore, various types of "inter terminal coupling" that exist in practical valving structures are analysed, and expressed in circuit form. A number of self-excited hydrodynamic os cillators are devised, some of whose circuit diagrams resemble well-known electronic systems. The properties of these oscillators are investigated from the standpoint of linear circuit instability, using methods due to H. Nyquist. In a concluding chapter the results obtained with a group of experimental oscillators are compared with the performance predicted by the linear theory. In one particular case, the large signal operation has been investigated, using a graphical analysis borrowed from the electronics field and applied to the static characteristic curves of orifice discharge.
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