• 한국음향학회:학술대회논문집
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• 한국음향학회 2000년도 학술발표대회 논문집 제19권 2호
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• pp.231-234
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• 2000

In relation to a non-destructive evaluation of irradiation damage of micro-structure of interstitial, void and dislocation, the changes in the hysteresis loop and Barkhausen noise amplitude and the harmonics frequency due to neutron irradiation were measured and evaluated. The Mn-Mo-Ni low alloy steel of reactor pressure vessel was irradiated to a neutron fluence of $2.3\times10^{19}n/cm^2$ $(E\ge1MeV)$ at $288^{\circ}C.$The saturation magnetization of neutron irradiated metal did not change. Neutron irradiation caused the coercivity to increase, whereas susceptibility to decrease. The amplitude of Barkhausen noise parameters associated with the domain wall motion were decreased by neutron irradiation. The spectrum of Barkhausen noise was analyzed with an applied frequency of 4Hz and 8Hz, and a sampling time of 50 $\mu$ sec and 20 $\mu$ sec. The harmonic frequency of Joule effect shows 4Hz, 8Hz, 12Hz and 16Hz reflected from an unirradiated specimen. On the contrary, the harmonic frequency disappeared for the irradiated specimen. Harmonic frequency of induced voltage of sinusoidal magnetic field And Spectrum of Barkhausen noise on material is determined.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.391-396
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• 2013

Psycho-acoustic experiments were carried out to know the inhabitant's response on floor impact noises due to floor structure types. The response values for tapping machine, bang machine and impact ball were 4.4~6.06. And children walking and adult walking were 1.67~2.97. Using 11 scale response tests, children and adult walking was not irritate to dwellers and children running was disturbing.

• 한국산학기술학회논문지
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• 제14권9호
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• pp.4313-4319
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• 2013

본 연구는 흑혈류영상 획득에서 고속스핀에코기법의 신호소실 현상을 이용하여 검사시간을 최소화시켜 환자의 불편을 줄이고 진단적 가치를 유지하고자 하였다. 연구방법은 흑혈류영상을 획득한 환자 32명을 대상으로, 기존의 이중역전회복기법과 새로운 기법인 고속스핀에코기법을 각각 적용한 후, 기법에 따른 혈류의 신호소거 차이를 알아보기 위해 T1, T2 강조영상에서 내경동맥 내강의 SNR과 CNR을 비교 평가하였다. 연구결과, SNR은 고속스핀에코기법이 이중역전회복기법 보다 T1, T2 강조영상에서 11.49%(4.73), 13.66%(6.03) 낮았으며, CNR은 고속스핀에코기법이 T1 강조영상에서 8.69%(15.04) 높았고, T2 강조영상에서 7.55% (13.17) 낮았으나, 통계적 수준에서 두 기법간의 SNR과 CNR의 차이는 유의하지 않았다. 그러므로 흑혈류영상 획득 시 고속스핀에코기법을 이용한다면 진단적 가치는 유지하면서 검사시간을 최소화하여 환자의 불편을 줄일 수 있다고 판단된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.681-687
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• 2001

Two-phase cross-flow exists in many shell-tube heat exchangers such as steam generators, condensers and reboilers. An understanding of flow-induced vibration excitation mechanism is necessary to avoid problems due to excessive tube vibration. This paper presents the results of a series of experiments done on tube bundles of different geometries subjected to two-phase cross-flow simulated by air-water mixtures. Normal(30$^{\circ}$) and rotated (60$^{\circ}$)triangular, and normal(90$^{\circ}$) and rotated (45$^{\circ}$) square tube bundle configurations of pitch-to-diameter ratio of 1.2 to 1.5 were tested over a range of mass fluxes from 0 to 1,000kg/$m^2$ㆍ s and void fraction from 0 to 100%. The effects of tube bundle geometry on vibration excitation mechanism such as fluidelastic instability and random turbulence, and on dynamic parameters such as damping and hydrodynamic mass are discussed. A lower pitch-to-diameter results in a higher hydrodynamic mass. The effect of tube bundle configurations on damping and random turbulence excitation is minor. The effect of pitch-to-diameter on the fluidelastic instability, however, is significant.

• 한국도로학회논문집
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• 제8권1호
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• pp.107-117
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• 2006

Recently, there has been a remarkable trend of using aggregates at sizes smaller than 13 mm for drainage asphalt pavement (DAP) in order to reduce the noise generated between vehicle tires and road surface. These DAPs have their performance and durability seriously worsen after several years in-service due to the clogging of void space and the abrasion. This paper proposes the use of large size aggregates in porous asphalt mixtures to overcome these defects. Results of laboratory and field experiments on asphalt mixtures with several aggregate gradations are investigated and compared. The study focuses on advantages of DAP using large size aggregate and on particle size combinations containing no fine aggregates of size 2.36 mm or less, which have not been considered in current engineering practice.

• Smart Structures and Systems
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• 제17권1호
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• pp.31-43
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• 2016

Applications of ultrasonic tomography to concrete structures have been reported for many years. However, practical and effective application of this tool for nondestructive assessment of internal concrete condition is hampered by time consuming transducer coupling that limits the amount of ultrasonic data that can be collected. This research aims to deploy recent developments in air-coupled ultrasonic measurements of solids, described in Part 1 of this paper set, to concrete in order to image internal inclusions. Ultrasonic signals are collected from concrete samples using a fully air-coupled (contactless) test configuration. These air coupled data are compared to those collected using partial semi-contact and full-contact test configurations. Two samples are considered: a 150 mm diameter cylinder with an internal circular void and a prism with $300mm{\times}300mm$ square cross-section that contains internal damaged regions and embedded reinforcement. The heterogeneous nature of concrete material structure complicates the application and interpretation of ultrasonic measurements and imaging. Volumetric inclusions within the concrete specimens are identified in the constructed velocity tomograms, but wave scattering at internal interfaces of the concrete disrupts the images. This disruption reduces defect detection accuracy as compared with tomograms built up of data collected from homogeneous solid samples (PVC) that are described in Part 1 of this paper set. Semi-contact measurements provide some improvement in accuracy through higher signal-to-noise ratio while still allowing for reasonably rapid data collection.

• 한국음향학회지
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• 제41권2호
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• pp.174-183
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• 2022

본 논문에서는 내부 유체를 갖는 수중에 몰수된 탄성 쉘이 기포층으로 둘러싸여 있을 때의 음향 방사를 모드 이론을 이용해 연구했다. 전 방향성의 점음원이 내부 유체의 중심에 위치해 있고 음향 소음원으로서 사용되었다. 모드 해의 미지수는 매질 사이의 경계조건으로부터 계산된다. 넓은 주파수 대역에서 모드 해의 안정성을 유지하기 위해, 모드 해의 규격 기법이 사용되었다. 기포 층은 Commander와 Prosperetti의 유효 매질 이론에 기반하여, 단일 모드 분포, 균일 분포, 정규 분포, 멱함수 분포를 이용해 각각 모의되었다. 각각의 기포 분포에 대해 삽입손실이 주파수에 대해 계산되었다. 추가적으로 공극비, 탄성 쉘의 매질 특성, 탄성 쉘과 기포층의 간극의 영향에 대한 수치해석을 수행했다.