• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1127-1132
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• 2013

The failure of reactor internals may have a significant effect on the safe operation and shutdown of a reactor. Various agings related to neutron irradiation occur or can potentially occur in the reactor internals owing to high neutron irradiation levels. Austenitic stainless steel, one of the principal materials constituting the reactor internals, shows different mechanical material behaviors such as tensile/creep properties and fracture toughness with neutron irradiation levels. This variation should be considered when the structural integrity of the reactor internals against agings during the design lifetime or continued operation period is evaluated. In this study, user subroutine programs considering the variation of mechanical material behaviors with neutron irradiation levels were developed. The programs were validated by testing them for various conditions.

• Journal of the Korean Geotechnical Society
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• v.21 no.4
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• pp.5-12
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• 2005

Recently, geophysical prospecting methods have played very important roles in civil and environmental engineering problems. Technical advances in geophysical instruments and computer system made it possible to get underground images with very high resolution far purposes to resolve those problems. It was possible partly due to ever increasing demand for development of technologies needed to precisely detect polluted areas and prevent ground-related accidents. Based on the same demand, integrity tests of cast-in place piles draw more attention and development of accurate test procedures is required. Ultrasonic methods is one of most advanced non-destructive procedures. In the paper, a geotomography method is employed for the cast-in place pile integrity test using ultrasonic waves. The image of pile interior is scanned and scrutinized far better and more accurate decision in the cast-in place pile integrity. In this study, we firstly examined the accuracy fur tomography program with idealized synthetic models built in water tank: their position and size were changed in the tank and each case was studied. In the next stage, real concrete pile models were fabricated and images of anomaly areas inside the pile were scanned to successfully locate those areas.

• Korean Security Journal
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• no.25
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• pp.1-25
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• 2010

This research aims to provide a solution for the improvement of private security according to the change in criminal environment. The main cause of crime can be found in the anti-functional dimensions including value set disorder, social phenomenon variation, information-based, globalization and urbanization. In this environment, the private security sector has dramatically increased in a quantitative viewpoint, but it is insufficient in a qualitative viewpoint. This paper recognized this problem and demonstrates a solution for improvement through classifying elements of private security into relevant legislation, education institutions, security companies and security associations. The analysis result is a follows: First, motivation and satisfaction rate of escort and security related major has shown to be high. However, respondents evaluated the guard educational institution negatively. Second, the motivation of entering into the private security sector for internal staffs has shown to be positive and sound. However, the job satisfaction rate has shown to be low due to excessive competition, negative perception of occupation and low earning. Third, respondents gave an average mark to the Security Association's management and operation. In addition, the mutual-aid project received the same mark. Negative feedbacks were given to the protection of member's interest and to association operation and policy, while positive feedbacks were given to the degree of member's cooperation towards association policies.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.5
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• pp.362-368
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• 2014

Fiber optic sensors (FOS) have advantages such as electromagnetic interference (EMI) immunity, corrosion resistance and multiplexing capability. For these reasons, they are widely used in various condition monitoring systems (CMS). This study investigated a muscular condition monitoring system using fiber optic sensors (FOS). Generally, sensors for monitoring the condition of the human body are based on electro-magnetic devices. However, such an electrical system has several weaknesses, including the potential for electro-magnetic interference and distortion. Fiber Bragg grating (FBG) sensors overcome these weaknesses, along with simplifying the devices and increasing user convenience. To measure the level of muscle contraction and relaxation, which indicates the musle condition, a belt-shaped FBG sensor module that makes it possible to monitor the movement of muscles in the radial and circumferential directions was fabricated in this study. In addition, a uniaxial tensile test was carried out in order to evaluate the applicability of this FBG sensor module. Based on the experimental results, a relationship was observed between the tensile stress and Bragg wavelength of the FBG sensors, which revealed the possibility of fabricating a muscular condition monitoring system based on FBG sensors.

• Journal of the Korean Association of Geographic Information Studies
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• v.8 no.2
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• pp.175-185
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• 2005

Governmental authorities have been trying to develop our city in respect to the growth of economy and it is true that their developmental policies have negative effects on ecosystem without doubt. To estimate these negative effects, this study is mainly focused on analysing the usage of the land according to the urban growth, and the temporal and spatial patterns between the elements which consist of the landscape of Daegu Metropolitan Sphere, by using the GIS method and the landscape indices. The results of the this study are as follow; the urban areas widened for $193.4km^2$ due to the shift of the urban function, and the forest areas were encroached for $455.6km^2$ into other landcover patterns. It was the shift of the agriculture areas that are given the most influence in those procedures since those developmental conditions are relatively satisfactory. Moreover the forest areas are structurally fragmented into the complicated form, and also the patterns of adjacent patches are become complex. These transitions are regarded as causes of increased external interventions to the forest areas, and these could possibly deteriorate the soundness of forest areas by reducing the core areas which are habitats of species. In conclusion, the results of this study evaluate the influence of much broader urban development on environment structure around urban and mutual relationship between them. In addition, it can provide methods and basic informations for the establishment of metropolitan urban plan after due considerations of the landscape ecological principle.

• Tunnel and Underground Space
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• v.18 no.6
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• pp.491-502
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• 2008

A certain range of the original ground around the tunnel should be preserved to ensure structural safety of the tunnel when other structures are made around the tunnel, and thus this range is defined as safety zone of the tunnel. The main points to ensure the stability of an existing tunnel when constructing a new tunnel in an inter-crossing area are distance between two tunnels, size of the new tunnel, excavation method for the new tunnel, ground condition around the tunnel, and lining type of the existing tunnel etc. When the new tunnel is excavated above the existing tunnel, the existing tunnel is likely to suffer deformation at a crown zone, damage of arching effect, and live load of the new tunnel etc. On the other hand, when the new tunnel is excavated below the existing tunnel, the existing tunnel is likely to be damaged due to settlement. This study has been made on the behavior of the existing tunnel by means of model test and numerical analysis when the new tunnel is excavated below the existing tunnel. Safety zone of the tunnel was estimated by the results of strength/stress ratio obtained from numerical analysis, and the movement of ground was estimated by the model test. The results of earth pressure, ground displacements, and convergence of the tunnel obtained from model test were compared with those of numerical analysis, and show a similar trend.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.6
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• pp.479-493
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• 2023

The need for safety management has arisen due to the increasing number of years of operated underground structures, such as tunnels and utility tunnels, and accidents caused by those aging infrastructures. However, in the case of privately managed underground utility ducts, there is a lack of detailed guidelines for facility safety and maintenance, resulting in inadequate safety management. Furthermore, the absence of basic design information and the limited space for safety assessments make applying currently used non-destructive testing methods challenging. Therefore, this study suggests non-destructive inspection methods using ultrasonic and impact-echo techniques to assess the quality of underground structures. Thickness, presence of rebars, depth of rebars, and the presence and depth of internal defects are assessed to provide fundamental data for the safety assessment of box-type general underground structures. To validate the proposed methodology, different conditions of concrete specimens are designed and cured to simulate actual field conditions. Applying ultrasonic and impact signals and collecting data through multi-channel accelerometers determine the thickness of the simulated specimens, the depth of embedded rebar, and the extent of defects. The predicted results are well agreed upon compared with actual measurements. The proposed methodology is expected to contribute to developing safety diagnostic methods applicable to general underground structures in practical field conditions.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.2179-2183
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• 2008

지금까지 분포형 모형 개발에 대한 많은 노력이 있음에도 불구하고 여러 제약사항들에 의해 잠재력을 보여주는 정도로 활용되어 왔으나, 최근 급속도로 발전하는 컴퓨터의 계산능력, DEM 등 디지털정보의 구축이 진행되어 오고 있고, GIS 및 인공위성 영상기법의 발달로 공간적인 비균질성을 고려하여 유출과정에서 운동역학적인 이론을 기반으로 물의 흐름을 수리학적으로 추적해 나가는 물리적기반의 분포형 유출모형의 활용도가 높아지고 있다. 본 모형개발에 있어 이론적 배경이 된 모형은 1998년부터 일본 교토대학 방재연구소 코지리 연구실에서 개발 중인 Hydro-BEAM으로 유역 물순환의 건전성을 평가하기 위하여 장기간의 유역 내 유량, 수질을 시계열 및 공간적으로 파악하여 유역의 영향평가를 위해 개발된 물리적 기반의 격자구조를 가진 분포형 장기유출 모형이다. 유출량 계산은 유역내 수평 유출량산정 모듈로서 평면 분포형의 격자형을, 연직 분포형으로는 $A{\sim}B$층의 수평유출량은 하천으로 유입하고, C층은 하천유량에 영향을 미치지 않는 지하수층으로 가정하는 다층모형을 이용해서 A층, 지표 및 하도흐름은 운동파 법(kinematic wave)으로, $B{\sim}C$층의 유출량은 선형저류법으로 계산하는 모형이다. 본 연구에서는 격자흐름방향을 4방향에서 8방향으로 개선하였고, 모형의 각종 수문매개변수들을 GIS와 연계하여 직접 입력할 수 있도록 하였으며, 물리적기반의 침투과정을 모의할 수 있도록 Green & Ampt모듈을 추가하고, 향후 레이더 강우 및 수치예보강우의 홍수유출예측을 염두에 두고 격자강우량을 활용할 수 있도록 하는 등 홍수유출해석을 위한 분포형 강우-유출모형으로 개선 하였고, 이를 남강댐유역에 적용해 봄으로써 모형의 적용성을 검토해 보고자 하였다. 홍수기동안의 지표흐름과 지표하 흐름의 시간적 변화와 공간적 분포를 모의할 수 있었으며, 전처리과정으로서 ArcGIS 혹은 ArcView등의 GIS 프로그램을 이용하여 모형에 필요한 ASCII형태의 입력 매개 변수 자료들을 가공하였다. 또한 후처리과정으로서 모형의 수행결과인 유역내의 유출량 분포 등을 GIS상에서 나타낼 수 있도록 ASCII형태로 출력하도록 구성하였다. 남강댐유역을 대상으로 유역을 500m의 정방형 격자로 분할하고 수계망을 통하여 유역 출구까지 운동파이론에 의해 추적 계산하였으며, 수문곡선 비교결과 재현성 높은 결과를 보여주었다. 모형의 정확성 및 실용성에 대한 보다 정확한 평가를 위해서는 향후 다양한 강우 사상 혹은 다양한 크기의 유역에 대한 유출량의 재현성 및 매개변수 등에 검증이 이루어져야 할 것이다.

• Composites Research
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• v.15 no.2
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• pp.11-17
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• 2002

The piezoelectric thin film sensor can be used to interpret variations in structural and material properties, e.g. for structural integrity monitoring and assessment. To illustrate one of this potential benefit, PVDF (polyvinylidene fluoride) film sensors are used for monitoring impact damage in Gr/Ep composite panels. Both PVDF film sensors and strain gages are attached to the surface of Gr/Ep specimens. A series of impact tests at various impact energy by changing impact mass the height are performed on the instrumented drop weight impact tester. The sensor responses are carefully examined to predict the onset of impact damage such as indentation, matrix cracking, and delamination, etc. Test results show that the particular waveforms of sensor signals implying the damage initiation and development are detected above the damage initiation impact energy. As expected, the PVDF film sensor is found to be more sensitive to impact damage initiation event than the strain gage.

• Transactions of the KSME C: Technology and Education
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• v.4 no.2
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• pp.93-99
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• 2016

High pressure nozzles and turbines of a gas turbine engine should be required to be operated under extreme operating conditions in order to maximize the performance. Engine manufactures have utilized nickel-base superalloys, enhanced cooling design, and thermal barrier coating techniques to overcome them and furthermore, material modeling, finite element analysis, optimization techniques, and etc. have been utilized widely for elaborate predictions. We aim to evaluate the effects on the low cycle fatigue life of the high pressure turbine blade caused by thermal barrier coatings and the cooling design of the endwall of the first stage turbine nozzle. To achieve it, the structural analysis, which utilized the results of conjugate heat transfer analysis as loading boundary conditions, was performed and then the results were the input for the assessment of low cycle fatigue life at several critical zones.