Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Pince-nez type
Patent
1992-10-21
1994-10-11
Isen, Forester W.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Pince-nez type
381190, G10K 1116
Patent
active
053554175
ABSTRACT:
An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz.
REFERENCES:
patent: 2043416 (1936-06-01), Leug
patent: 4044203 (1977-08-01), Swinbanks
patent: 4715559 (1987-12-01), Fuller
patent: 4947434 (1990-08-01), Ito
patent: 5091953 (1992-02-01), Tretter
Burdisso Ricardo
Dungan Mary E.
Fuller Chris R.
O'Brien Walter F.
Thomas Russell H.
Isen Forester W.
The Center for Innovative Technology
Virginia Polytechnic Institute & State University
Virginia Tech Intellectual Properties Inc.
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