Abstract: Fluidic constructs, including grouped stacks of fluidic elements, that provide countersound to control sound in a noisy environment, prevent radiation of sound from vibrating surfaces, reduce sound-induced vibration of surfaces, and absorb sound that might otherwise impact on surfaces, are provided. These constructs may have a wide range of geometries for specific applications, but generally include a face plate on one side, and a back plate on the other side. Supply ports on the back plate provide a supply of fluid that flows through the construct, while undergoing acoustic modulation through fluidic amplifiers. The face plate includes input ports that sense sound waves to be controlled, and transmits this sound to influence the acoustic modulation of the supplied fluid.

Abstract: The application of active noise control to influence the fan-noise components in engine ducts. The fan is used as a source of counter noise by introducing flow distortions upstream or downstream of the fan. Microphone arrays sense the noise and produce a control output signal for controlling a distortion producer. The control output signal for the distortion producer comes from a control algorithm utilizing the output of the microphone signals sampled at a defined rate based on the fan blade passing frequency.

Abstract: A method and apparatus for reducing multiple-source repetitive vibrations in a region or structure (12) by applying control vibrations to the region or structure via actuators (18), frequently recalculating the control vibrations based on source elements to accommodate for varying phase differences between the sources of the repetitive vibrations (14) and (16), and cyclically updating the source elements of the control vibrations is disclosed. The repetitive vibrations are sensed (20) synchronously with the repetitive vibration source chosen as the reference source and decomposed into a number of frequency components corresponding to the reference source. The control vibrations are formed of the same frequency components and applied synchronously with the reference source. Each frequency component of the control vibrations is defined by source elements, one for cancelling vibrations produced by each of the repetitive vibration sources.

Abstract: A method and apparatus for reducing repetitive vibrations in a region or structure by applying a plurality of control vibrations via a plurality of actuators (13) located in the region or structure (11) and cyclically updating the control vibrations to improve the reduction of the repetitive vibrations are disclosed. The repetitive vibrations are sensed (14) at a plurality of locations in the region or structure and decomposed into a number of frequency components. Next, a first estimate of each control vibration, formed of the same frequency components, that together will reduce the sensed vibrations is made. Each first control vibration estimate is applied to the region or structure via an actuator (13). Thereafter, each control vibration is cyclically updated to improve the reduction of the sensed vibrations whether or not changes occur in the repetitive vibrations, the region or structure (11), or the apparatus used to carry out the method of the invention.

Abstract: Apparatus for continuously actively balancing rotors by controlling the mass-distribution of a rotor (24) relative to an axis-of-rotation (27) about which the rotor rotates in a stator (26) is disclosed. The mass-distribution of the rotor is adjustable via a hydraulic subsystem (23) that can move the rotor relative to the axis-of-rotation. An electronic subsystem (22) controls the hydraulic subsystem (23) with control signals. More specifically, the sensors (100) of a sensor subsystem (21) sense the repetitive vibrations caused by an unbalanced rotot. The electronic subsystem (22) cyclically updates the control signals applied to the hydraulic subsystem (23) so as to reduce the sensed vibrations, i.e., to balance the rotor (24). The hydraulic subsystem (23) adjusts the position of the rotor (24) by varying the flow of a viscous fluid between the perimeter of a portion of the rotor (24) and an annular sleeve (34) encompassing that portion of the rotor. The annular sleeve (34) rotates with the rotor (24).

Abstract: Noise and vibration in a structure are reduced through application to the structure of an oscillatory torque. An electromechanical energy converter provides the oscillatory torque when the input signal to the electromechanical energy converter has a frequency and harmonics thereof required to counteract the noise and vibration desired to be attenuated.

Abstract: Noise and vibration in a structure is reduced through application to the structure of an oscillatory torque. An electromechanical energy converter provides the oscillatory torque when the input signal to the electromechanical energy converter has a frequency and harmonics thereof required to counteract the noise and vibration desired to be attenuated.

Abstract: A portable acoustic impedance measuring device 10 is provided for measuring the impedance properties of a panel 12. The device 10 includes a horn section 14 having a flexible plate 18. The plate 18 can assume the curvature of the duct panel 12. The horn section 14 is supported adjacent the panel's surface by a spindle shaft 28 which spans or bridges the inside diameter of the duct 12. The curvature of the plate 18 may be locked to hold the curvature of any of a variety of different panels having various sizes and shapes.

Abstract: The apparatus consists of a circular, flexible disc held at a constant distance from a curved absorbing surface by pins or flexible ribs. Sound from a loudspeaker is fed to the center of the disc and allowed to propagate radially in the space between disc and absorber. Radial arrays of microphones on the disc surface sense sound pressure amplitude and phase, from which impedance is calculated.

Abstract: A system for determining the spatial structure or composition of complex sound fields within a duct or other structural enclosure that is excited by acoustic energy is disclosed wherein at least two holograms are recorded and analyzed to provide both the amplitude and phase of the various modal components that comprise the sound field. In situations in which the sound field of interest is periodic, the desired amplitude and phase information is determined from a pair of holograms in which each hologram is formed by photographically recording the diffraction pattern resulting when an array of elastomeric regions, positioned on the wall of the acoustically excited structure, is illuminated by two pulses of coherent monochromatic light that are spaced apart in time by nT/2, where T is the period of the dominant acoustic excitation signal and n is an odd integer.

Abstract: A system for resolving a complex acoustic field, resulting when acoustic energy propagates through a duct, into component unit spatial pressure patterns or modes is disclosed. In each disclosed system arrangement, an acoustic filter, which includes one or more annular cavities, circumferentially surrounds the duct through which the acoustic energy propagates and sound is coupled from the duct into one end of each annular filter cavity via a series of openings which exhibit a relatively high acoustic impedance and a relatively high resistance to fluid flow. Each filter cavity is dimensioned such that it is excited into resonance when the circumferential distance between adjacent nodes of a modal component of the pressure pattern within the duct is mathematically related to the velocity of sound within a filter cavity by a predetermined factor.

Abstract: A burner can, including a noise suppressing cavity, for use in the combustor assembly of a gas turbine engine to minimize the combustion noise emitted by the engine, is disclosed. The cavity is mounted at an end of the burner can that includes a fuel nozzle for injection of fuel into the interior of the burner can and is in acoustic communication with the interior of the burner can via a perforated metal sheet that forms a partition between the burner can and the cavity. The cavity is dimensioned and arranged in view of the acoustic transmission system formed by the burner can and the duct system that interconnects the burner can with the engine turbine stage to exhibit an acoustic impedance which minimizes the propagation of combustion noise from the burner can through the engine turbine stages to thereby reduce the engine noise level.