• 한국가스학회지
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• 제12권1호
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• pp.13-18
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• 2008

지진 및 외부 진동에 의하여 구조물에 발생하게 되는 진동량은 진동 속도와 피해규모가 비례하는 관계에 있음을 고려하여 일반적으로 진동속도로 나타내어진다. 본 연구에서는 진동 속도 기반의 구조물 진동기준을 검토하고, 이를 고려하여 도로 하부 매설 가스 강관의 안정성 평가를 수행하였다. 가스공사 주사용 배관인 762 mm API 5L Gr. X65 강관을 해석 대상 배관으로 선정하였으며 도로설계기준에 의하여 지반 매설 조건 및 DB-24 하중을 다양한 속도에 대한 시간 함수로 고려하여 재하하였다. 진동속도는 차량 진행 속도 80 km/h까지 증가하다가 이후 감소하는 경향을 보였으며, 차량 진행 속도 80 km/h에서 0.034 cm/s의 진동 속도를 보임으로서 진동 기준 대비 매우 작은 값임을 확인하였다. 또한 감쇄법칙을 적용하여 진행파의 속도를 분석한 결과, 차량 진행 속도 80 km/h에서 가장 작은 속도를 나타내었다.

• 비파괴검사학회지
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• 제21권1호
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• pp.32-38
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• 2001

재료의 손상을 평가하기 위하여 초음파법에 대한 많은 연구가 진행되었고 널리 사용되고 있으나 대부분 균열의 성장 또는 두께의 감소와 같은 문제에 집중되고 있다. 본 연구에서는 2.25Cr-1Mo 강을 이용하여 반복하중에 의해 재료내부에 발생하는 미시균열을 조기에 감지하고, 피로에 의한 파괴를 미연에 방지할 수 있도록 초음파 표면파의 감쇠와 속도변화를 이용하여 균열길이 측정의 정량적인 평가방법을 제시하였다. 중심주파수 5MHz의 탐촉자를 이용하여 파단수명비 약 60%, 균열길이 약 2mm 정도에서 표면파의 속도 및 감쇠 변화를 탐지할 수 있었다. 고주파 탐촉자를 이용함으로써 미시균열의 발생을 조기에 탐지할 수 있으며, 파단수명을 예측하는 기초자료로 활용할 수 있다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 춘계 학술발표회 논문집
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• pp.12-19
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• 2002

A high frequency level of Fourier amplitude relates with stress drop and seismic moment. When we can not use this relation owing to absence of digital earthquake data, stress drop and seismic moment can be determined from Peak Ground Velocity(PGV) and felt area. We have qualitatively evaluated the seismic characteristics using PGV, and Magnitude from the well determined felt area in seismological records of Korea(1978~2001) by Korea Meteorological Administration(KMA). Observed relations between felt area and magnitude in the Korean Peninsula are explained by attenuation(Q), and stress drops comparing with the previous researches on stress parameter. This results are preliminary work for the study of stress parameter using the relationship of high frequency lavel, PGV, and felt area.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.31-37
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• 2000

Metal matrix composites(MMCs) are rapidly becoming one of the strongest candidates for structural materials for many high temperature application. Among the high temperature environment, thermal shock is known to cause significant degradation in most MMC system. Therefore, the nondestructive evaluation on thermal shock damage behavior of SiC/A16061 composite has been carried out using ultrasonic surface and SH-waves. For this study, Sic fiber reinforced metal matrix composite specimens fabricated by a squeeze casting technique were thermally cycled in the temperature range 25~$400^{\circ}C$ up to 1000 cycles. Three point bend test was conducted to investigate the effect of thermal shock damage on mechanical properties. The relationship between thermal shock damage behavior and the change of ultrasonic velocity and attenuation were discussed by considering SEM observation of fracture surface.

• Smart Structures and Systems
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• 제13권1호
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• pp.155-171
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• 2014

Various monitoring techniques are now available for structural health monitoring and Acoustic Emission (AE) is one of them. One of the major advantages of the AE technique is its capability to locate active cracks in structural members. AE crack locating approaches are affected by the signal attenuation and dispersion of elastic waves due to inhomogeneity and geometry of reinforced concrete (RC) members. In this paper, a novel technique is described based on signal processing and sensor arrangement to process multisensory AE data generated by the onset and propagation of cracks and is validated with experimental results from an in-situ load test. Considering the sources of uncertainty in the AE crack location process, a methodology is proposed to capture and locate events generated by cracks. In particular, the relationship between AE events and load is analyzed, and the feasibility of using the AE technique to evaluate the cracking behavior of two RC slab strips during loading to failure is studied.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 추계 학술발표회 논문집
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• pp.155-162
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• 2002

A technique for the seismic reliability evaluation of electric power transmission systems(EPTS) adapted to ground motion characteristics of Korea has been developed to evaluate reliability indices corresponding to the whole system and to each node within. A network model with nodes and links for EPTS has been established, and a seismic substation-fragility curve obtained from seismic fragilities of power system facilities has been derived. A point source model, the doubly truncated Gutenberg-Richter relationship, and earthquake intensity attenuation formula have been applied to simulate seismic events. Using Monte-Carlo simulation method, the seismic reliability of EPTS is evaluated and, it appeared that seismic effect on EPTS in low and moderate seismicity regions has to be considered.

• 비파괴검사학회지
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• 제25권3호
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• pp.215-221
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• 2005

It is required to evaluate nondestructively depth of surface-breaking cracks in structures. In this paper, the self-compensated technique by laser-based ultrasound is used to measure the depth of surface-breaking defect. Optical generation of ultrasound produces a well defined pulse with reliable frequency content. It is broad banded and suitable for measurement of attenuation and scattering over a wide frequency range. The self-calibrated signal transmission data of surface wave shows good sensitivity as a practical tool far assessment of surface-breaking defect depth. It is suggested that the relationship between the signal transmission and crack depth can be used to predict the surface-breaking crack depths in structures.

• 대한방사선기술학회지:방사선기술과학
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• 제20권1호
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• pp.35-38
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• 1997

Scintigraphic measurement of gastric emptying time has been reported to be influenced by the variation in depth of radionuclide within the stomach. This study was designed to clarify whether a part of the variability in gastric emptying could be ascribed to a relationship between anterior image, the total anteroposterior Image and the tissue attenuation correction(geometric mean). A dual-head scintillation camera(ADAC, USA) was used to investigate effect of such changes. We were performed 16 normal subject gastric emptying studies with $^{99m}TC$ labelled scramble egg, milk and solid meal(610 Kcal, 300 g) The results are as follows; On anterior Image, $T_{1/2}$ emptying time was delayed by 5 min, 6.5%(range $3{\sim}18\;min,\;5{\sim}31.4%$) compared with the geometric mean. But there was no different gastric emptying time between the total anteroposterior image and geometric mean. Therefore, if will be useful to use the method of geometric mean or the total anteroposterior image to evaluate the gastric emptying time accurately.

• 비파괴검사학회지
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• 제10권1호
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• pp.56-64
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• 1990

It is well-known that the defects (existing in structures) and the material degradation(caused by the fatigue load) generally initiate the failure of structures. The NDE such as ultrasonic technique which can be used to detect the size and the orientation of defects has been utilized to estimate the life and stability of structures. However, only few experimental reports made by using the ultrasonic technique have been published for the case of fatigue estimation of materials and structures. The purpose of this study is, thus, to derive the relationship between ultrasonic attenuation and fatigue behavior of Polycarbonate and PMMA through ultrasonic characterization. It is also attempted to offer NDE experimental procedure which may be useful to predict fatigue life.

• International Journal of Computer Science & Network Security
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• 제21권12호
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• pp.93-100
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• 2021

Satellite communication for high altitude platform stations (HAPS) and geostationary orbit (GEO) systems suffers from sand and dust (SANDU) storms in desert and arid regions. The focus of this paper is to propose common relations between HAPS and GEO for the atmospheric impairments affecting the satellite communication networks operating above Ku-band crossing the propagation path. A double phase three-dimensional relationship for HAPS and GEO systems is then presented. The comparison model present the analysis of atmospheric attenuation with specific focus on sand and dust based on particular size, visibility, adding gas effects for different frequency, and propagation angle to provide systems' operations with a predicted vision of satellite parameters' values. Thus, the proposed system provides wide range of selecting applicable parameters, under different weather conditions, in order to achieve better SNR for satellite communication.