John F. Thurston

Fluidic vibration cancellation. Mount and method

A vibration cancellation mount for use in a vibration cancellation system is provided that includes a fluidic driver providing a modulated air stream to an elastomeric air spring. The pressure of the air stream is caused to fluctuate by an acoustical cancelling signal generated by an electroacoustic transducer electrically coupled to cancellation controller. As this pressure varies the air spring is filled and vented so that it responds at the same frequency and phase as the cancellation signal and thereby cancels the vibrations emanating from a vibrating structure mounted thereto. By employing a fluidic driver, the vibration cancellation mount is not frequency limited and can cancel vibrations having frequencies anywhere in the audio frequency spectrum.

Beampattern synthesis and computation for cylindrical arrays

The synthesis and calculation of beampatterns for cylindrical arrays can be greatly simplified by factoring the problem into a line array of identical hoops under very mild restrictions on array geometry. For example, elements may be directive and hoops may be nonuniformly spaced. This result has particular significance for large arrays of many elements. The design approach consists of using one of several techniques to design a good hoop beampattern combined with a standard technique for designing a good line array beampattern. The technique is illustrated by application to an array of more than 2000 directional elements where other design techniques are impractical and straightforward computation of beampatterns is several orders of magnitude more time consuming. [Work supported by ONR.]