The role of acoustics theory in Noise Control Research is reviewed. The classical sound theory of ∂2ρ/∂t2 − c2 ∂2ρ/∂xi2 = 0 which deals only with the wave propagation problem is compared with the unified acoustic theory derived by Lighthill, ∂2ρ/∂t2 − c2 ∂2ρ/∂xi2 = ∂Q/∂t − ∂Fi/∂xi + ∂2Tij/∂xi ∂xj, which deals with the sound propagation problems as well as the sound generation problems. With this unified theory, the problems of fan noise, axial compressor noise, jet noise, flow noise, and turbulent noise all become apparent. The unified theory clearly illustrates the limitation of the nearfield and farfield sound measurement that can be confidently performed. Examples of various types of noise sources and their radiation directivity will be discussed.
The device described herein is a microprocessor-controlled ultrasonic imaging system, the Ultra Image III, originally developed for the inspection of corrosion/erosion inside seawater pipelines. It has been used successfully for many other types of nondestructive testing (NDT) applications, including intergranular stress corrosion cracking detection in nuclear piping systems. It consists of four packages each with a weight of less than 13.6 kg (30 lb): the microprocessor, the dual-diskette drive, the ultrasonic pulser/receiver/gate package, and the display package that consists of an A-scan scope and a two-dimensional imaging scope. The scanner, equipped with pulse/echo or pitch/catch transducers, can function automatically or manually. Information for operational controls is input using a hand-held terminal that can be placed at remote distances from the test site. Output results are displayed in two-dimensional format in gray scale indicating the thickness of the pipe wall after corrosion/erosion effects. Test results are stored permanently on floppy diskettes for on-site overview and off-site detailed analysis.
The system is further equipped with a variety of software packages providing capabilities for a multicolor display of the size, configuration, and distributions of erosion patterns or flaw and crack orientations or both inside the tested material. The portability and versatility of the system is demonstrated with examples of different applications.
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