Abstract: A corrugated structure is designed by dividing a given length of a corrugated structure into a number of sections, or corrugations. The length is then divided by the number of sections to obtain a constant value which serves as a reference point for determining the varied pitches of the structure of the present invention. The varying pitch of each section is determined by adding or subtracting a variation value from the constant value to obtain a varying pitch. The variation values, and thus the varying pitches, of the sections of corrugated structure are empirically chosen. Whistles, or pure tones of noise, produced by the flow of a fluid relative to the corrugations are eliminated when the corrugated structure is designed according to three requirements: 1) the total of the pitches of a given section is approximately equal to the length of a given section; 2) no two adjacent sections can have the same pitch; 3) no two variations within a given set of sections can have the same value.

Abstract: A fluid distribution system, such as a valve, comprises a housing having a chamber which has a plurality of acoustic modes. The acoustic modes are excited when fluid flows through the chamber. An inlet passage and an outlet passage are disposed in fluid communication with the chamber. A plate is disposed in the inlet passage. A plurality of orifices are formed in the plate. The orifices conduct fluid from the inlet passage to the chamber and reduce the coupling between the flow of fluid through the inlet passage and the acoustic modes of the chamber. With this arrangement, the acoustic modes of the chamber and the resonance frequency of each of the orifices are substantially unexcited by the flow of fluid through the orifices.

Abstract: A silencer having multiple integrated channels arranged in a labyrinth configuration is provided. The channels have one open end and one closed end with the open end in communication with a common zone which is connected to a flow duct. The channels are tuned to provide a selected resonance frequency.

Abstract: A volumetric sound absorber for audible sound frequencies is made from a thin sheet material that is permeable to air with thickness mass, and flow resistance within specified ranges.

Abstract: Disclosed is a composite branch take-off and silencer for an air distribution system wherein an air stream from an input duct may be coupled to an output duct and one or more branch ducts. The take-off and silencer includes two series-coupled sections: a static pressure regain section and a channel section adapted for coupling the input duct to the output duct and the branch ducts. The static pressure regain section outer wall and the outer path-defining wall of the associated channel section have a composite cross section characterized by a continuous curve which results in smooth changes in air flow velocity without discontinuity in either magnitude or direction thereby providing efficient conversion of velocity pressure to static pressure. These continuous curves have a direction component along their length which is increasingly directed radially from the central axis of the input duct.

Abstract: An exhaust silencer especially for turbo-charged diesel locomotives with a single exhaust outlet combines a straight through exhaust duct preferably diverging to recover velocity pressure and minimize back pressure with dual silencing means including a large expansion tank around the duct tuned to attenuate a fundamental low frequency exhaust noise peak and smaller reactive chambered means in the duct sized to attenuate a selected mid range of higher frequency exhaust noise. Various features are included.

Abstract: A lined duct is divided into two parallel branches by means of a rigid partition. The phase speed of the fundamental mode in each branch depends on the liner configuration and can differ markedly from the free-space phase speed. When the liners in the two branches are not the same, the corresponding phase speeds will be different and a relative phase lag between the waves in the two branches results. This, in turn, leads to interference between these wave components (and their reflections) both at the exit and entrance of the parallel branch pair. This interference can be exploited for the purpose of obtaining a low-frequency attenuation which is substantially larger than the attenuation of the unpartitioned duct.

Abstract: An air distribution system for a building including a mixing plenum for receiving and mixing outside and return air. An input flow concentrator and integral silencer is disposed within and coupled to the mixing plenum. The flow concentrator and integral silencer is adapted to establish a substantially axially symmetrical flow path for air from the plenum to an output port. A fan is coupled to the output port to drive the air from the output port to the main duct for distribution throughout the building.

Abstract: A static pressure regain coupler for coupling an input duct and the upstream end of a branch take-off device having a main duct and one or more channel. The static pressure regain (SPR) coupler includes an upstream end which has substantially the same cross-section as the input duct. The SPR coupler also includes a downstream end which has a first port having the same cross-section as the main duct of the take-off device, and a second port having substantially the same cross-section as the channels of the take-off device. The SPR coupler is adapted to couple most of the input airflow to the take-off main duct, and a minor portion of that air flow to the take-off channels.

Abstract: An air distribution system for a building including a mixing plenum for receiving and mixing outside and return air. An input flow concentrator and integral silencer is disposed within and coupled to the mixing plenum. The flow concentrator and integral silencer is adapted to establish a substantially axially symmetrical flow path for air from the plenum to an output port. A fan is coupled to the output port to drive the air from the output port to the main duct for distribution throughout the building.

Abstract: A branch take-off and silencer apparatus for an air distribution system. The apparatus couples an input duct to one or more branch ducts and to a coaxial output duct having a similar but smaller cross-section than the input duct. Coaxial extensions of the input and output ducts define a shell region. The shell region is closed at its downstream end and open at its upstream end to oncoming air in the input duct. The shell region is divided at that upstream end by porous acoustical material into a plurality of adjacent channels which lead to a plenum near the downstream end of the shell region. The plenum is coupled to the branch ducts.