Abstract: In the present invention an improved sound absorbing panel is provided. The panel comprises an array of wall defining means configured to provide two or more contiguous hollow cells having adjacent open ends and adjacent closed impermeable ends, the open ends defining a sound receiving end of the array, at least one impermeable three dimensional closed surface disposed in at least one of the cells, and a flow resistive permeable facing sheet covering the sound receiving end. Approximately 50 percent of the cells may be filled in a periodic arrangement. The three dimensional closed surface may be a sphere or a cylinder and may be bonded to the closed impermeable ends or to the wall defining means. A drainage notch is provided. The present invention is particularly suitable for sound attenuation in jet engines and other applications having adverse environmental conditions and requiring sound absorptive panels, baffles, duct liners, and duct splitters.

Abstract: A sound barrier (22) comprising a pair of spaced apart members (24,26), a medium (34) disposed between the members capable of propagating sound waves, and one or more acoustical resonators (30) coupled to the medium and tuned to one or more selected frequencies. The resonators may be disposed between the members or may be disposed around the outer periphery of the members to permit construction of a sound barrier window. The resonators may form an integral part of one of the members or may be suspended between the members by netting or sound insulating material.

Abstract: An acoustical silencer for a gas passage or exhaust duct for a gas turbine engine, which is composed of three parts. The first comprises an absorptive surface to absorb incident low frequency sound the second comprises an acoustically lined duct attenuating high frequency sound transmitted therethrough. The entrance to the first part and the entrance to the second part are essentially coplanar. The third part is a horn-shaped plenum or conical diffuser to contain the flow and distribute the sound over the entry surface of the first part and the entrance to the second part. The entrances to both the first and second parts, being coplanar, present acoustically parallel paths to sound impinging on their common plane. The input impedances of the absorptive surface of the first part and the entrance to the second part are adjusted such that a disproportionately larger share of the incident low frequency acoustical energy passes into the first part and is dissipated.

Abstract: Apparatus for attenuating waves on the surface of a fluid and for providing a protective calm area is provided comprising means (20) for causing the waves to break, means (30) for directing the broken waves to induce a downward flow of surface fluid, means (34) for discharging the downward flow of surface fluid a preselected distance below the surface of the fluid, and means (48,50,60,62,64) for orienting the wave breaking means to provide a preselected orientation of the wave breaking means relative to the resultant flux vector of the energy of the waves. In a particular embodiment, one or more submerged refractive structures (20) each in the form of a dome-shaped shell, are provided to cause the waves to break. Guide vanes (36) direct the broken surface waves into a centrally disposed vertical standpipe (34) where the fluid flows downward and is then discharged at the bottom of the shell.

Abstract: A noise control device which relies upon retroreflection for sound attenuation. The device comprises an array of corner reflectors recessed into a surface and forming a sound retroreflecting panel. This cavitated surface provides the desired retroreflection of impinging sound waves so as to preclude undesirable onward propagation. The invention is particularly suitable for noise control applications in the presence of severe environmental conditions, and may also be used in combination with sound absorbing materials.

Abstract: Apparatus for extracting material floating on the surface of a fluid having waves thereon is provided comprising means (20) for causing the waves to break, means (36) for directing the broken waves to induce a downward flow of surface fluid and the material thereon, means (34) for discharging the downward flow of fluid and said material a preselected distance below the surface of the fluid, and means (20, 22) for containing the discharged material. In a particular embodiment, a submerged refractive structure in the form of a dome-shaped shell (20) is provided to cause the waves to break. Guide vanes (36) direct the broken surface waves into a centrally disposed vertical standpipe (34) where the fluid and the entrained floating material flows downward and is then discharged at the bottom of the shell. The material accumulates at the upper interior portion (22) within the shell. An access opening (50) is provided through the wall of the shell to facilitate removal of the material accumulated within the shell.

Abstract: A sound absorbing structure for a flow duct composed of a bundle of parallel, terminated, acoustical waveguides. The bundle of waveguides is cut obliquely so that the individual waveguides vary substantially in length along the cut. The bundle is arranged within a structure which is revolvable about its longitudinal axis. The exterior surface of the structure is spaced from the interior wall of the duct. The longitudinal axis of each of the waveguides is located substantially perpendicular to the axis of revolution. The structure revolves during passage of gas through the duct.

Abstract: A noise barrier wall having a transition area in the region of at least one unbounded edge and which employs controlled diffraction of sound to enhance the sound reducing properties thereacross. The transition area of the noise barrier is provided with either a row of absorptive shaped splitter panels, or a row of pickets, or other means of controlled transparency which provide acoustical shadowing equal to or greater than that of a solid wall for the frequency regions of interest.

Abstract: A noise barrier wall having a transition area in the region of at least one unbounded edge and which employs controlled diffraction of sound to enhance the sound reducing properties thereacross. The transition area of the noise barrier is provided with either a row of absorptive shaped splitter panels, or a row of pickets, or other means of controlled transparency which provide acoustical shadowing equal to or greater than that of a solid wall for the frequency regions of interest.

Abstract: Apparatus for converting ocean surface wave energy into useful rotational kinetic energy. A refractive horn and ramp provides reflectionless impedance transformation of ocean surface wave energy at the input to the system. Wave energy, in the form of breakers, which are massive pulses of essentially pure kinetic energy, from the output of the horn/ramp are then smoothed and transformed directly to mechanical rotation. Smoothing is accomplished by the inertial properties of a "liquid flywheel". The rotational kinetic energy may be extracted by means of a turbine to provide useful work. Discharged water is returned to the ambient ocean through a low terminal velocity diffuser. The entire structure may be located offshore and the discharged fluids may be used for auxiliary purposes.

Abstract: A broadband sound attenuating, acoustically lined, duct of varying cross-sectional shape but in the usual case having a constant cross-sectional area, and wherein the duct liner is configured to maintain an essentially constant acoustic resistance and scaled acoustic reactance throughout provided by means of changes in the effective depth of the liner. Design tradeoffs permit some variation in the cross-sectional area of the duct with concomitant changes in liner properties. In all cases, the duct is designed so that every section along its major axis is optimally tuned to absorb most efficiently some part of the frequency spectrum of interest. The device is particularly suitable for sound suppression of jet aircraft engines.

Abstract: Apparatus and method for measuring the impedance of oscillatory systems, or elements of such systems, which exhibit nonlinear behavior at high excitation amplitudes. Excitation of the element being tested, which element may be either acoustical, electrical, or mechanical, is in the form of a combination of a high-intensity biasing signal having a broadband spectrum, and a low-intensity pure sinusoidal tracer signal. The tracer signal is retrieved at an appropriate measuring point in the test system by means of highly-selective filtering. Although the broadband signal comprises the real or basic test signal input to the test element, the retrieved tracer signal is substituted therefor for the purpose of deriving the element's impedance through the use of conventional impedance algorithms. Algorithm solutions thus provided correspond to the response of the element to the entire spectrum of the broadband excitation.

Abstract: A broadband sound attenuating, acoustically lined, duct of varying cross-sectional shape but in the usual case having a constant cross-sectional area, and wherein the duct liner is configured to maintain an essentially constant acoustic resistance and scaled acoustic reactance throughout provided by means of changes in the effective depth of the liner. Design tradeoffs permit some variation in the cross-sectional area of the duct with concomitant changes in liner properties. In all cases, the duct is designed so that every section along its major axis is optimally tuned to absorb most efficiently some part of the frequency spectrum of interest. The device is particularly suitable for sound suppression of jet aircraft engines.