• 한국해양환경ㆍ에너지학회지
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• 제18권3호
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• pp.216-222
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• 2015

기존의 자동음파전달속도 측정시스템을 이용하여 해양퇴적물의 음향특성을 측정하는 경우 최초도달신호시간의 결정에 발생하는 오류와 측정 절차의 번거로움 등의 몇 가지 문제점들이 존재한다. 이러한 문제점을 개선하기 위하여 PXI모듈을 이용한 LabVIEW기반의 측정 시스템을 개발하였다. 새로운 측정시스템을 검증하기 위해 동일한 시료와 실험환경에서 기존 시스템과 병행하여 측정하였다. 그 결과 1~2%의 음파전달속도 측정오차를 보였으며 음파감쇠 역시 기존 시스템과 유사한 결과 값을 도출하였다. 새로이 개발된 PXI(PCI eXtentions for Instrumentation)를 이용한 LabVIEW 기반 음향특성 측정시스템은 퇴적물의 음향특성을 보다 신속하고 효율적으로 측정할 수 있고 측정 자료뿐만 아니라 분석된 신호의 원시자료에 대해서도 지속적인 데이터베이스를 구축할 수 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.182-186
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• 2000

The porous woven hose is recently considered as an effective element of automotive intake systems. In order to predict the acoustic performance of an intake system with a porous woven hose, the information on the acoustic wall impedance is required. In this article, a measurement technique that is valid over the low frequency range and without mean flow condition is presented. The measurement is performed in a cylindrical chamber with a concentric layout of the sample and the resistance is estimated from measured reactance and transmission loss data. It is observed that the measured transmission loss for a porous woven hose with an arbitrary length agrees well with the predicted one that uses the estimated impedance for a small sample length.

• 비파괴검사학회지
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• 제30권3호
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• pp.207-211
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• 2010

In this paper, the fluid AID(acoustic inspection device) was developed to measure SOS(speed of sound) since fluids used in most of industrial fields have different properties and its equipment is highly expensive. From AID developed, it is intended to get potentially the capability to distinguish the kind of fluid using the measurement by the SOS at various fields. In order to measure the sound speed of specific fluids, the measurement system and ultrasonic sensors are composed. The fluid used in the experimental work are soybean oil, glycerin, diesel oil and the error of time difference due to the container wall is extracted for preliminary experiment. As results, the variations of sound speed according to the temperature change of target fluid were analyzed and the polynomial equations were proposed.

• Geomechanics and Engineering
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• 제37권2호
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• pp.149-166
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• 2024

The acoustic emission (AE) technique is utilized to estimate the rock failure status in underground spaces. Understanding the AE characteristics under loading conditions is essential to ensure the reliability of AE monitoring. The AE characteristics depend on the material properties (p-wave velocity, density, UCS, and Young's modulus) and damage stages (stress ratio) of the target rock mass. In this study, two groups of granite specimens (based on the p-wave velocity regime) were prepared to explore the effect of material properties on AE characteristics. Uniaxial compressive loading tests with an AE measurement system were performed to investigate the effect of the rock properties using AE indices (count index, energy index, and amplitude index). The test results were analyzed according to three damage stages classified by the stress ratio of the specimens. Count index was determined to be the most suitable AE index for evaluating rock mass stability.

• 한국수산과학회지
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• 제37권4호
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• pp.312-322
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• 2004

Physical and geoacoustic properties of inner shelf sediment in the South and Southeastern Seas of Korea have been studied based on six piston core samples. The sediments are largely composed of homogeneous mud except the core from the southeasternmost part of the area. Both physical and geoacoustic properties and mean grain size are relatively uniform with sediment depth, suggesting little effect of sediment compaction and/or consolidation. Mean grain size appears to be the most Important variable to determine the physical and acoustic properties. In contrast, the attenuation shows more or less fluctuations. Correlations between physical properties and sediment texture show slight deviations from those of the compared data, caused by the difference of sedimentary processes, mineral composition, and the difference of measurement system. In particular, the velocity is lower (approximately 20-30 m/s) than that of the previous data measured in the same area. This is probably due to the difference in velocity measurement system (particularly, error by a length of sample). We propose new relationships for physical and geoacoustic characteristics of shelf sediment in the study area.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 춘계학술대회 논문집 센서 박막재료연구회 및 광주 전남지부
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• pp.69-72
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• 2008

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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1234-1239
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• 2000

KOMPSAT-1(Korea Multi-Purpose Satellite), which opened the space era in Korean peninsula, was developed from 1994 and launched successfully in December of 1999 at VAFB, USA. This paper presents a launch environment test of KOMPSAT and a short description of environment test facilities at Korea Aerospace Research Institute as well. The launch environment tests of KOMPSAT-1 satellite, such as vibration, acoustic, pyro-shock and mass properties measurement test, were performed during its system integration and test period. The participating engineers concluded that KOMPSAT-1 satellite would withstand environment during its launch period.

• 한국음향학회지
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• 제20권5호
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• pp.76-82
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• 2001

음향특성이 균일하지 않는 생체조직은 특정의 형태 유지가 어렵기 때문에 종래의 극소형 수중청음기의 스캐닝 방법에 의한 초음파 음장 전파특성 측정이 곤란하다. 본 연구에서는 PVDF (Polyvinylidene fluoride) 압전막을 사용하여 2차원 배열 수중청음기를 제작하고, 그것에 의한 음장 측정 시스템을 구축한 후, 생체조직에 적용하였다. 중심주파수 2.25 ㎒이고 직경이 13㎜인 원형평면 트랜스듀서에 의한 실험 결과, 구축한 시스템에 의해 비교적 정밀한 음장 측정이 가능한 것을 알았으며, 그 주파수에 대해 소와 돼지의 간에서는 각각 0.7∼l.3dB/cm (평균; 1.0 dB/cm), 1.0∼l.8 dB/cm (평균; 1.6 dB/cm), 근육에서는 각각 0.9∼2.9 dB/cm (평균; 2.1dB/cm), 1.7∼3.3 dB/cm (평균: 2.5 dB/cm)의 값을 갖는 감쇠계수의 공간적 분포를 측정할 수 있었다.

• 동력기계공학회지
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• 제17권2호
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• pp.56-62
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• 2013

A technique is presented that uses a circular waveguide for the measurement of the bulk shear (S-wave) velocities of unconsolidated, saturated media, with particular application to near surface soils. The technique requires the measurement of the attenuation characteristics of the fundamental torsional mode that propagate along an embedded pipe, from which the acoustic properties of the surrounding medium are inferred. From the dispersion curve analysis, the feasibility of using fundamental torsional mode which is non-dispersive and have constant attenuation over all frequency range is discussed. The principles behind the technique are discussed and the results of an experimental laboratory validation are presented. The experimental data are best fitted for the different depths of wetted sand and the shear velocities are evaluated as a function of depths. Also the characteristics of the reflected signal from the defects are examined and the reflection coefficients are calculated for identifying the relation between defect sizes and the magnitude of the reflected signal.

• Journal of the Korean Wood Science and Technology
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• 제36권6호
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• pp.1-12
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• 2008

주요 국산재의 여러 가지 응용물성을 지난 3년에 걸쳐 조사하였다. 전보(강 외 4인 2008, 변 외 5인 2008)에 이어 본보에서는 우리나라의 활엽수 주요 수종인 백합나무, 거제수나무, 오동나무를 재료로 사용하였다. 매년 동일한 장치와 실험조건으로 실험하였기 때문에 모든 수종에 대한 결과를 상호 비교 할 수 있었다. 수분흡착성 실험은 80메시 목분을 이용하였으며, 넓은 범위의 상대습도조건에 따른 평형 함수율과 흡착등온선을 구하였다. 열전도율과 열확산률은 열선열전도장치를, 전기의 부피저항률과 저 항은 고전기저항계를 이용하여 측정하였다. 정목재와 판목재의 열적 전기적 특성차이가 관찰되었는데 이는 해부학적 차이에 의한 것으로 보인다. 음향적 성질은 음향측정시스템을 사용하여 동적탄성률, 내부마찰을 측정하였다. 본 논문의 결과들은 목재구조물 설계, 휴대용 목재수분계 보정, 음향적 성질 등에 필요한 기본 자료를 제공한다.