• International Journal of Automotive Technology
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• v.7 no.1
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• pp.43-49
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• 2006

In this paper, an index for the evaluation of a vehicle intake booming noise and intake sound quality were developed through a correlation analysis and a multiple factor regression analysis of objective measurement and subjective evaluation data. At first, an intake orifice noise was measured at the wide-open throttle test condition. And then, an acoustic transfer function between intake orifice noise and interior noise at the steady state condition was estimated. Simultaneously, subjective evaluation was carried out with a 10-scale score by 8 intake noise and vibration expert evaluators. Next, the correlation analysis between the psychoacoustic parameters derived from the measured data and the subjective evaluation was performed. The most critical factor was determined and the corresponding index for intake booming noise and sound quality are obtained from the multiple factor regression method. And, the optimal design of intake system was studied using the booming noise and the sound quality evaluation index for expectation performance of intake system. Conclusively, the optimal designing parameters of intake system from noise level and sound quality whose point of view were extracted by adapting comparative weighting between the booming noise and sound quality evaluation index, which optimized the process. These work could be represented guideline to system engineers, designers and test engineers about optimization procedure of system performance by considering both of noise level and sound quality.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.4
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• pp.350-357
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• 2015

Many countries have been developing and operating an underwater surveillance system in order to protect their oceanic environment from infiltrating hostile marine forces which intend to lay mines, conduct reconnaissance and destroy friendly ships anchored at the harbor. One of the most efficient methods to detect unidentified submarine approaching harbor is sensing variation of magnetism of target by magnetic sensors. This measurement system has an advantage of high possibility of detection and low probability of false alarm, compared to acoustic sensors, although it has relatively decreased detection range. The contents of this paper mainly cover the analysis of possible effectiveness of magnetic sensors. First of all, environmental characteristics of surveillance area and magnetic information of simulated targets has been analyzed. Subsequently, a signal processing method of separating target from geomagnetic field and methods of estimating target location has been proposed.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.4
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• pp.505-513
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• 2017

Cavitation is a phenomenon caused by vapour cavities that is produced in rapid pressure changes. When the cavitation happened, the sound pressure level of a underwater radiated noise is increased rapidly. As a result, it can increase the probability of the identification or classification of a our warship's acoustic signature by an enemy ship. However, there is a problem that it is hard to precisely detect the occurrence of a cavitation noise. Therefore, this paper presents recent improvements in terms of the cavitation noise measurement by using continuous wavelet transform and DEMON(Detection of Envelope Modulation on Noise) signal processing. Then, we present that the suggested scheme is more suitable for detecting the cavitation than existing algorithms.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.329-330
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• 2007

Decay processes of accumulated charge in e-beam irradiated polymers during elevating temperature are observed using pulsed electro-acoustic measurement system. Since the polymeric materials have many superior properties such as light-weight, good mechanical strength, high flexibility and low cost, they are inevitable materials for spacecrafts. In space environment, however, the polymers sometimes have serious damage by irradiation of high energy charged particles. When the polymers of the spacecraft are irradiated by high energy charged particles, some of injected charges accumulate and remain for long time in the bulk of the polymers. Since the bulk charges sometimes cause the degradation or breakdown of the materials, the investigation of the charging and the decay processes in polymeric materials under change of temperature is important to decide an adequate material for the spacecrafts. By measuring the charge behavior in e-beam irradiated polymer, such as polyimide or polystyrene, it is found that the various accumulation and decay patterns are observed in each material. The results seem to be useful and be helpful to progress in the reliability of the polymers for the spacecraft.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1992-1993
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• 2007

Decay processes of accumulated charge in e-beam irradiated polymers during elevating temperature are observed using pulsed electro-acoustic measurement system. Since the polymeric materials have many superior properties such as light-weight, good mechanical strength, high flexibility and low cost, they are inevitable materials for spacecrafts. In space environment, however, the polymers sometimes have serious damage by irradiation of high energy charged particles. When the polymers of the spacecraft are irradiated by high energy charged particles, some of injected charges accumulate and remain for long time in the bulk of the polymers. Since the bulk charges sometimes cause the degradation or breakdown of the materials, the investigation of the charging and the decay processes in polymeric materials under change of temperature is important to decide an adequate material for the spacecrafts. By measuring the charge behavior in e-beam irradiated polymer, such as polyimide or polystyrene, it is found that the various accumulation and decay patterns are observed in each material. The results seem to be useful and be helpful to progress in the reliability of the polymers for the spacecraft.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.505-506
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• 2006

PD(partial discharge) occurred from variable PD sources in air may be the cause of breakdown in high voltage equipment which affect huge outage in power system. Identification and localization of PD sources is very important for engineer to cope with huge accident beforhand. PD phenomena can be detected by acoustic emission sensor or electromagnetic sensor like antenna. This paper has investigated the identification method using PCA(principal component analysis) for the PD signals from variable PD sources, for which the electric field distribution and PD inception voltages were simulated by using commercial FEM program. PD signals was detected by ultra wideband antenna. Their own features were extracted as the frequency coefficients transformed with FFT(fast fourier transform) and used to obtain independent pincipal components of each PD signals.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.384-388
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• 2000

One-port acoustic characteristics of an in-duct source can be measured by the multi-load method using an overdetermined set of open pipes with different lengths as applied loads. The input data. viz. load pressure and load impedance, are usually contaminated by measurement error in the actual measurements, which result in errors in the calculated source parameters. In this paper, the effects of the errors in the input data on the results have been studied numerically, varying the number of loads and their impedances in order to determine what combination of the loads will yield the best result. An error analysis is applied to each case of possible loads, which consist of open pipes. It is noted that, frequently, only a set of open pipes is used when applying the multi-load method to the intake or exhaust sides of internal combustion engines. A set of pipe lengths which cause the calculated results to be least sensitive to the input data error can be found when using open pipe loads. The present work is intended to produce guidelines for preparing an appropriate load set in order to obtain accurate source properties of fluid machines.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.462-462
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• 2016

하천의 유량은 다양한 방법으로 측정가능한데 그중에 ADCP(Acoustic Doppler Current Profiler)는 1980년대 말 도입된 이래 현재 국내외에서 광범위하게 사용되고 있고, 그 활용성은 점점 더 커지고 있다. 이러한 이유로 최근 미국, 호주, 뉴질랜드 등에서는 ADCP 측정유량에 대한 품질관리와 생산된 자료에 대한 평가를 통해 신뢰성을 확보하기 위한 방안을 마련하고 있다. 본 연구에서는 ADCP 이동보트법 측정유량에 대한 3개국(미국, 호주, 뉴질랜드)의 품질관리 및 신뢰도 확보 방안에 대한 문헌조사를 수행하였고, 각 방안들에 대하여 7개 항목으로 비교 및 분석하였다. 그리고 분석된 내용을 바탕으로 ADCP 이동보트법 측정유량의 품질평가 방안을 제시하고, 유량조사사업단에서 수행한 ADCP 이동보트법 측정유량 자료(2013년~2014년)를 대상으로 측정유량 품질평가 방안을 적용하여 결과를 품질등급으로 제시하였다. 이 지표는 사용자가 ADCP 이동보트법 측정유량의 품질을 확인하고 신뢰할 수 있게 함으로써 향후 활용성을 더욱 향상 시킬 수 있을 것으로 기대된다.

• The Journal of the Acoustical Society of Korea
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• v.38 no.3
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• pp.247-255
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• 2019

In this study, to predict the noise of a submarine propeller which is going to become bigger and faster, the non - cavitating propeller noise was predicted based on the numerical analysis which considering the interaction of the hull - appendages - propeller. In order to predict the radiated noise of the propeller, the flow field for the entire region of hull-appendages-propeller was computed by CFD (Computational Fluid Dynamics). And the noise for the thickness noise and the load noise was numerically predicted using FW-H (Ffwocs Williams-Hawkings) acoustic analogy. Numerical noise prediction results were verified by model tests and showed good agreement with the measurement results in predicting total noise level and low frequency noise.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.56.2-56.2
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• 2019

Measurement of the location of the baryon acoustic oscillation (BAO) feature in the clustering of galaxies has proven to be a robust and precise method to measure the expansion of the Universe. The best constraints so far have been provided from spectroscopic surveys because the errors on the redshift obtained from spectroscopy are minimal. This in turn means that the errors along the line-of-sight are reduced and so one can expect constraints on both angular diameter distance $D_A$ and expansion rate $H^{-1}$. But, future surveys will probe a larger part of the sky and go to deeper redshifts, which correspond to more number of galaxies. Analysing each galaxy using spectroscopy, which is a time consuming task, will not be practically possible. So, photometry will be the most convenient way to measure redshifts for future surveys such as LSST, Euclid, etc. The advantage of photometry is measuring the redshift of vast number of galaxies in a single exposure, but the disadvantage are the errors associated with the measured redshifts. Using a wedge approach, wherein the clustering is split into different wedges along the line-of-sight ${\pi}$ and across the line-of-sight ${\sigma}$, we show that the BAO information can be recovered even for photometric catalogues with errors along the line-of-sight. This means that we can get cosmological distance constraints even if we don't have spectroscopic information.