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Published Articles

The Volume 2, No 4, December 1997

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An Experimental Study on the Measurement of Objective Sound under Contamination of Wind Noise

Y. Takakuwa, M. Ohta, M. Nishimura and H. Minamihara


This paper proposes a new simple method of determining the steady sound pressure level of machinery contaminated with wind noise in the measurement of low-frequency environmental noise in windy conditions. First, the cross-correlation characteristics between the spectrum levels and the band pressure levels measured in a particular frequency range of the wind noise are discussed. Next, a simple and practical static estimation method for the objective sound is discussed by employing only the conditional mean of the spectrum. Finally, the effectiveness of the proposed method is shown through experiments made in breezy conditions in the open air. The estimation accuracy of the method is discussed and compared with that of another method employing the wind speed observed simultaneously in the vicinity of the measurement microphone.

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Active Control of Dynamic Bearing Loads in Rotating Machinery Using the Deflection Coefficient Method for Load Estimation

William W. Clark, Joo-Hyung Kim, Roy D. Marangoni


A new technique is presented for measuring and actively controlling dynamic bearing loads in rotating machinery subject to periodic excitations. Bearing loads are estimated using the Deflection-Coefficient Method, a technique which does not rely on a full system model, and which applies commonly-used shaft-deflection measurement equipment to obtain estimates of bearing loads. The estimated bearing load is used as an error signal in an adaptive feedforward disturbance rejection controller. The result is a control system which can selectively minimize dynamic bearing loads in real time in rotating machinery systems. The method is applied to a numerical model of a typical rotating machinery system to suppress dynamic reaction forces at bearing supports, and then it is experimentally verified on a beam test rig.

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Optimal Sizes and Locations of Piezoelectric Actuators for Curved Panel Sound Sources

Xun Li, Colin H. Hansen and Xiaojun Qiu


Nowadays lead zirconate titanate (PZT) actuators are widely used in active noise and vibration control (ANVC). One of the research areas concerning PZT actuators involves the optimisation of the piezoelectric actuator parameters, including size and location etc., to minimise sound radiated by a vibrating structure. Another practical application of PZT actuators in ANVC is their use to drive a panel which can be utilised as a control source. In this case, it is important to be able to maximise the radiated sound pressure level. This paper presents procedures for optimising sizes and locations of PZT actuators on a resonant curved panel/cavity system to maximise the radiated sound power at a number of discrete frequencies.

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Flow-induced Vibration of Reactor Internals Structures

Huinam Rhee and Heuy Gap Song


A flow-induced vibration assessment program has been performed for a pressurized water reactor in Korea in order to verify the structural integrity of the reactor internal structure for flow-induced vibration during normal and transient operating conditions. Through structural analysis, the theoretical evaluation for the structural integrity of the reactor internal structure and the basis for the necessary measurement and inspection are provided. Flow-induced hydraulic loads and reactor internal structure vibration response data were measured during pre-core hot functional testing. Then, the measured data were reduced to obtain auto- and cross-power spectral densities, coherence and phase information for appropriate sensor signals. After that the reduced data were analyzed and compared with the predicted data obtained from structural analysis. The measured structural frequencies agreed well with the results from the analysis. The measured stresses are less than the predicted values and also less than the allowable limits. It is concluded that the structural analysis procedure used for the reactor internal structure is appropriate and that the vibration response of the reactor internal system due to flow induced vibration under normal and transient operations is acceptable for long term operation.

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Studies of Elastic and Unelastic Properties of Ferroelectrics under High Uniaxial Stress

Valery M. Tsaplev


Ferroelectric ceramics are widely used in various acoustical applications as active materials for different transducers. These transducers often operate under the influence of high mechanical stresses, both hydrostatic and uniaxial. Uniaxial stresses significantly change the properties of ferroelectrics. The study of the uniaxial stress dependence of the elastic moduli and internal friction is, therefore, important for two reasons. First - from a practical point of view, for the purposes of designing transducers to operate under such conditions. Second - the elastic modulus and internal friction of the material depend on its internal physical structure (domain structure, point defects, dislocations, etc.). Consequently, acoustical methods of studying these properties, being highly precise, can provide much very useful information from a physical point of view. While the dependence of the dielectric properties on uniaxial stress have been studied by a great number of investigators, information on the dependence of the elastic modulus and internal friction on stress is very limited, though such studies began long ago. Mostly the lack of such investigations is accounted by the difficulties in making measurements. In this paper the resonance method of measuring the internal friction and elastic modulus under the influence of rather high uniaxial stresses is described. The method and apparatus were designed by the author long ago, but since then they have been improved significantly and new results have been obtained that have not been published before. This paper is concerned with only the results obtained by the resonance method and is not concerned with the results obtained by the pulse-interference method that was used in the MHz-frequency range.

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