• Journal of Ocean Engineering and Technology
• /
• v.33 no.4
• /
• pp.358-363
• /
• 2019

The acoustic power is used as a primary index characterizing underwater sound sources and could be defined by its source level. The source level has been assessed using various experimental techniques such as the reverberation time method and reverberant tank plot method. While the reverberation time method requires reverberation time data extracted in a preliminary experiment in a reverberant water tank, the reverberant tank plot method only needs acoustic pressure data directly obtained at the reverberation water tank. In this research, these experimental techniques were studied in comparative experiments to estimate the source levels of underwater sources in a reverberant water tank. This paper summarizes the basic theories and procedures of these experimental techniques and presents the experimental results for an underwater source in a long cuboid water tank using each technique, along with a discussion.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.5 no.2
• /
• pp.83-89
• /
• 1996

The objective of this study is to find experimentally the characteristics of the noise generated by the impinging jet on the normal plate, and also to compare the noise characteristics of the impinging jet with those of the free jet. The experiment is performed for the measurement of the noise specturm, the noise power, and the directivity for the free and impinging jets. From the experiment. it is found that the power of noises generated by the free jet as well as the impinging jet is proportional to the eighth power of the jet velocity through the circular converging nozzle, and that the noise power of the impinging jet is 15dB as high as one of the free jet when the plate distance is about within one to three times the nozzle diameter at the pressure ratio 1.39. The sound pressure level of the impinging jet depends upon the jet pressure and the plate distance. The plate distance with the maximum overall sound pressure level is increased with the jet pressure. The directivities with 1/3 octave band frequency for both the free jet and the impinging jet are greatly influenced by the convection effect.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1994.06a
• /
• pp.785-790
• /
• 1994

The active noise control which regards the acoustic power as a target function to be minimized, is analyzed to test its feasibility of which simplifies the measurement system compared with the global acoustic energy based active noise control system. In fact, it is found that the acoustic power based active noise control strategy is equally likely as good as the global acoustic energy based active noise control method if the acoustic field of interest is diffusive or very low model density one. In the intermediate model density field, we also demonstrate that the power based control gives the similar results as the energy based control in terms of global sound energy reduction for the lightly damped enclosure which might be most important system in practical application. From all the theoretical and power based control strategy is dependent on the characteristics of the acoustic field to be controlled; i.e., the model density distribution, the degree of reverberation, and on the strength of modal interaction of the control source with the primary source; i.e., the location of control source.

• Journal of the Korean Society for Railway
• /
• v.9 no.1 s.32
• /
• pp.1-6
• /
• 2006

The purpose of this study is to calculate transmission loss of the high speed railway's wall section accurately. Transmission loss measurement of ideal case i.e. the wall in the laboratory condition was carried out in first, which results were compared with those by statistical energy method. Transmission loss values of high speed railway calculated out by experimental method are compared with those from closed form solution. Commercial statistical energy analysis was also used to predict the outside pressure level using those measured transmission loss values. Simple SEA model could estimate reasonable exterior sound pressure level.

• The Journal of the Acoustical Society of Korea
• /
• v.39 no.2
• /
• pp.105-112
• /
• 2020

An analysis model of noise map is proposed to evaluate and reduce the acoustical noise of power plant and its surroundings. The sound powers of many noise sources are estimated by measuring the sound levels of major equipments in the power plant. The analysis of noise has been made by using ENPro that is a commercial program for environmental noise prediction. The proposed model is verified by comparing the results from noise analysis and measurement at several points of the power plant units 1 through 4, and residential areas. It is shown that noise map simulation using the proposed model has a reliability, since the overall noise level approximates within the error of ±2 dB. Furthermore, through noise analysis, the increasing effect of noise due to newly established units 5 and 6 on residential areas is also analyzed. Consequently, the noise barrier is designed to meet an environmental noise standard and satisfy low cost and safety conditions.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2004.04a
• /
• pp.281-286
• /
• 2004

The vacuum cleaner motor runs on very high speed for the suction power. Specially, the motive power is provided by the impeller being rotate on very high speed. And centrifugal fan consists of the impeller, the diffuser, and the circular casing. Due to the high rotating speed or the impeller and small gap distance between the impeller and diffuser, the centrifugal fan makes very high noise level at BPF and harmonic frequencies. In order to calculate the sound pressure of centrifugal fan, the unsteady flow data is needed. And Noise cause is dividing to fluid noise by exhaust flow of fan and vibration noise by rotational vibration of vacuum cleaner fan motor. Until now, measuring method has been used to measure vibration by the accelerometer; this method has been not measured for the vibration in some parts of brush and commutator because of motor construction and 3-D vibrating mode. This paper was purposed on the accurate analysis, using laser vibration analyzer,. By using this measured data of noise cause against the difficult part in old times, we would like to use for the design of silent fan motor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2013.10a
• /
• pp.605-610
• /
• 2013

This study proposes an analysis model to simulate a noise map and estimate noise distribution for a location and its surroundings of a power plant. The noise map analysis was executed by using ENPro that is a commercial program for environmental noise prediction. Experimental evaluation for the proposed analysis model was carried out by comparing the results from noise analysis and measurement at several major points of the power plant and residential areas.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.10
• /
• pp.1327-1336
• /
• 2001

The structural modes driven by the low wave-number components of smooth elastic wall pressure provide a relatively weak coupling between the flow and the wall motion. If the elastic thin plate has any resonant mode whose wave-number of resonance coincides with $\omega$/U$\sub$c/, the power will be transmitted to those modes of vibration by the flows. We examine the problem in which the elastic thin plate is subject to pressure fluctuations under turbulent boundary layer. Measurements are presented of the frequency spectra of the near- and far-field pressures and radiated sound contributed by the various wave modes of the thin elastic plate. Dispersion equation for wave motions of elastic plate is used to investigate the effect of bending waves of relatively low wave number on radiated sound. The low wave-number motion of elastic plate is observed to have much less influence on the low-frequency energy of wall pressure fluctuations than that of the rediated sound. High amplitude events of the wall pressure are observed to weakly couple with high-frequency energy of radiated sound for case of low tension applied to the plate. The sound source localization is applied to the measurement of radiated sound by using acoustic mirror system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.03a
• /
• pp.622-627
• /
• 2008

Experiment of active noise control on supersonic jet noise was conducted by use of microjet injection. The microjets were injected to the shear layer of the main jet through 22 small holes at the lip of a rectangular nozzle. Based on the measurement of farfield sound pressure, it was found that the jet noise was effectively reduced by several dB(in some cases up to 10 dB). The power levels of all measurement points were also reduced by use of microjet injection. The microjet affected not only the broadband noise but also the screech tone noise. The sound pressure level, the frequency of the screech tone, and the structure of the jet could be changed by the microjet. Flow visualization with schlieren technique was also made to observe the effect of microjet on the flow field.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11b
• /
• pp.853-856
• /
• 2002

Rocket propulsion systems generate very high-level noise (acoustic loads), which is due to supersonic jet emitted by rocket engine. In practice, the sound power level of rocket propulsion systems is over 180 dB. This high level noise excites rocket structures and payloads, so that it causes the structural failure and electronic malfunction of payloads. Prediction method of acoustic loads of rocket enables us to determine the safety of payloads. A popular prediction method is based on NASA SP-8072. This method was used to predict the acoustic loads of KSR-III rocket. Measurement of acoustic loads by KSR-III propulsion system was performed in the stage qualification test. The predicted results were compared with the measured ones.