Abstract: An overhead conductor monitoring device includes a simulation conductor designed to have thermal characteristics similar to those of the overhead conductor. The simulation conductor is placed in the same ambient atmosphere as the overhead conductor and is selectively heated by a coil embedded within the simulation conductor. The power supply to the coil is computed by a microcomputer to be the same as the power of the overhead conductor. Temperature sensors are placed in or on the simulation conductor to monitor the temperature thereof. As the temperature of the simulation conductor increases, the power of the overhead conductor is recomputed to reflect changes in the characteristics of the overhead conductor. An alarm signal is generated if the temperature of the simulation conductor exceeds a predetermined temperature and theoretical values of overhead conductor power can be supplied microprocessor to determine the effects on the temperature of the overhead conductor.

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.