• Nuclear Engineering and Technology
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• 제52권7호
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• pp.1443-1451
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• 2020

The objective of this study is to design a robust power control system for a small pressurized water reactor (PWR) to achieve stable power operations under conditions of external disturbances and internal model uncertainties. For this purpose, the multiple-input multiple-output transfer function models of the reactor core at five power levels are derived from point reactor kinetics equations and the Mann's thermodynamic model. Using the transfer function models, five local reactor power controllers are designed using an H infinity (H_∞) mixed sensitivity method to minimize the core power disturbance under various uncertainties at the five power levels, respectively. Then a multimodel approach with triangular membership functions is employed to integrate the five local controllers into a multimodel robust control system that is applicable for the entire power range. The performance of the robust power system is assessed against 10% of full power (FP) step load increase transients with coolant inlet temperature disturbances at different power levels and large-scope, rapid ramp load change transient. The simulation results show that the robust control system could maintain satisfactory control performance and good robustness of the reactor under external disturbances and internal model uncertainties, demonstrating the effective of the robust power control design.

• 한국콘텐츠학회논문지
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• 제7권12호
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• pp.123-130
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• 2007

기업의 국제화가 심화되면서 회계 및 재무정보 또한 국가경쟁력을 평가하는 주요지표로서 활용되기에 이르렀다. 그러나 아직도 국제사회에서 한국의 재무제표에 대한 신뢰성이 낮고, 결산관련 공시에도 반기보고와 정기 결산보고 등 연간 2회 발표만 있을 뿐이다. 따라서 투자가들은 기업에 관한 실질적인 정보가 없기 때문에 기업의 부도 가능성을 알 수 없고 경영자 자신들도 기업의 재무 상태에 관한 실시간 정보를 파악하기 어려워 금융위기와 같은 돌발 상황이나 급변하는 주요 경제변수들의 움직임에 대처할 능력이 없었다. 따라서 기업들의 부실 가능성을 신속히 예측하기 위하여 주식시장이나 채권시장에 나타난 재무정보를 이용하는 측정모형들이 연구되어 왔으며 이를 시스템으로 개발하고 필요한 콘텐츠를 이용하는 사례가 증가하고 있다. 본 논문의 목적은 기업의 부실을 회계자료에만 의존해서 연구하던 방법에서 해당기업의 재무정보를 이용한 부실예측모형을 이용해 기업의 부실확률을 산출하고, 주요 경제변수 변화에 따른 부실성의 민감도를 분석하는 데 있다. 연구방법으로는 부실확률 산출을 위해 블랙-숄즈 모형을 적용하는 한편, trans-log 함수를 이용하여 주요 경제변수 변화에 따른 기업 부실확률의 민감도분석을 행하였다. 본 논문의 연구결과에 의하면, 부실확률 변화에 미치는 영향에 있어서 오직 기업대출금 변수만이 연구기간(1997-1998)중 일관된 방향성을 유지했으며, 기업부실에 중대한 영향력을 미칠 것으로 예상되었던 경제 변수들의 경우에는 대기업과 중소기업 기업집단에서 상이한 결과를 도출하였다.

• Structural Engineering and Mechanics
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• 제27권4호
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• pp.425-438
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• 2007

Large changes in stiffness associated with cracking and yielding of reinforced concrete sections may be expected to occur during the dynamic response of reinforced concrete frames to earthquake ground shaking. These changes in stiffness in stories that experience cracking might be expected to cause relatively large peak interstory drift ratios. If so, accounting for such changes would add complexity to seismic design procedures. This study evaluates changes in an index parameter to establish whether this effect is significant. The index, known as the coefficient of distortion (COD), is defined as the ratio of peak interstory drift ratio and peak roof drift ratio. The sensitivity of the COD is evaluated statistically for five- and nine-story reinforced concrete frames having either uniform story heights or a tall first story. A suite of ten ground motion records was used; this suite was scaled to five intensity levels to cause varied degrees of damage to the concrete frame elements. Ground motion intensity was found to cause relatively small changes in mean CODs; the changes were most pronounced for changes in suite scale factor from 0.5 to 1 and from 1 to 4. While these changes were statistically significant in several cases, the magnitude of the change was sufficiently small that values of COD may be suggested for use in preliminary design that are independent of shaking intensity. Consequently, design limits on interstory drift ratio may be implemented by limiting the peak roof drift in preliminary design.

• 방사성폐기물학회지
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• 제18권4호
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• pp.537-548
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• 2020

Currently, radioactive waste for disposal has been restricted to low and intermediate level radioactive waste generated during operation of nuclear power plants, and these radioactive wastes were managed and disposed of the 200 L and 320 L of steel drums. However, it is expected that it will be difficult to manage a large amount of decommissioning waste of the Kori unit 1 with the existing drums and transportation containers. Accordingly, the KORAD is currently developing various and large-sized containers for packaging, transportation, and disposal of decommissioning waste. In this study, the radiation exposure doses of workers and the public were evaluated using RADTRAN computational analysis code in case of the domestic on-road transportation of new package and transportation containers under development. The results were compared with the domestic annual dose limit. In addition, the sensitivity of the expected exposure dose according to the change in the leakage rate of radionuclides in the waste packaging was evaluated. As a result of the evaluation, it was confirmed that the exposure dose under normal and accident condition was less than the domestic annual exposure dose limit. However, in the case of a number of loading and unloading operations, working systems should be prepared to reduce the exposure of workers.

• 한국가구학회지
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• 제24권3호
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• pp.286-292
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• 2013

Space given at home, furniture is an important condition to determine its size. As a method for satisfying outer and functional human needs, ever changing, shaped form has also been developed. Modern people tend to decorate the beautiful living space to the needs of the beauty and space of living. In order to satisfy these requirements, the development of furniture to suit the taste of modern people is required. In this study, we add together the design and contemporary design of traditional Korean and use of raw wood can feel the natural and applied to furniture retro design. It is possible to have a motif characteristic of Hanok traditional to suggest a design where you can feel the sensitivity with retro in the direction of the current design change is large and diverse, and in harmony with the living space of modern it is an object that you study the production lighting and storage furniture with the complexity of the traditional and modern.

• 대한기계학회논문집A
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• 제33권8호
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• pp.760-766
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• 2009

In the manufacturing process of HDD, ball swaging method is commonly used to joint the Head Gimbal Assembly(HGA) with the arm of the actuator. The hub on the HGA is placed into the hole of the actuator arm, and the hub and arm is bonded by the pressure of steel ball. The pressure for plastic deformation on the baseplate causes the undesirable deformation on HGA, such as tilting, flying height change of head. After obtaining the key parameters that have large sensitivity on the swaging process, the optimal shape of baseplate is proposed to increase the static performance during swaging process. Contribution of the proposed design for the swaging performance is verified by contact simulation with elasto-plastic deformation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.403-405
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• 1999

Power transformers have a tendency of ultra-high voltage and huge capacity as power demand increases day after day. Therefore, the fault by insulation destruction gives rise to large area of power failure in huge capacity transformers. On-line predictive diagnostics is very important In power transformers because of economic loss and its spreading effect. Hence, this study presents experiments of partial discharge method using ultrasonic sensor in order to confirm the possibility of ultrasonic sensor in power transformers. It carries out the experiments of measuring delay time between ultrasonic sensor and transducer, sensitiities by temperature change of oil and by barriers inside transformers. It is also Included wave analysis by ultrasonic sensor for needle-plate electrode powered on through high-voltage equipments.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.423-426
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• 2001

Recently we have reported that the meander-patterned amorphous FeCoSiB films exhibit large change in their high frequency impedance by applying a strain, suggesting that the films are very attractive for making of a highly sensitive strain sensor elements. In this study, the effect of anisotropy on a change in the impedance of sputtered amorphous film patterns was investigated in the frequency range from 1MHz to 1GHz. As a function of applied strains, the high frequency impedance was extremely changed in the case of film patterns with transverse anisotropy due to excellent magnetomechanical coupling properties. As a summary, the maximum figure of merit f has measured about 2600 in the case of transverse anisotropy, and about 500 in the case of longitudinal anisotropy at 500 MHz. These values of F are approximately more than 1000 times higher than that of a conventional metal strain gauge (F 2) and more than 10 times higher than that of a semiconductor gauge (F 200).

• Structural Monitoring and Maintenance
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• 제3권3호
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• pp.297-314
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• 2016

As the study of internal corrosion of pipeline need a large number of experiments as well as long time, so there is a need for new computational technique to expand the spectrum of the results and to save time. The present work represents a new non-destructive evaluation (NDE) technique for detecting the internal corrosion inside pipeline by evaluating the dielectric properties of steel pipe at room temperature by using electrical capacitance sensor (ECS), then predict the effect of pipeline environment temperature (${\theta}$) on the corrosion rates by designing an efficient artificial neural network (ANN) architecture. ECS consists of number of electrodes mounted on the outer surface of pipeline, the sensor shape, electrode configuration, and the number of electrodes that comprise three key elements of two dimensional capacitance sensors are illustrated. The variation in the dielectric signatures was employed to design electrical capacitance sensor (ECS) with high sensitivity to detect such defects. The rules of 24-electrode sensor parameters such as capacitance, capacitance change, and change rate of capacitance are discussed by ANSYS and MATLAB, which are combined to simulate sensor characteristic. A feed-forward neural network (FFNN) structure are applied, trained and tested to predict the finite element (FE) results of corrosion rates under room temperature, and then used the trained FFNN to predict corrosion rates at different temperature using MATLAB neural network toolbox. The FE results are in excellent agreement with an FFNN results, thus validating the accuracy and reliability of the proposed technique and leads to better understanding of the corrosion mechanism under different pipeline environmental temperature.

• 한국환경과학회지
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• 제33권7호
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• pp.463-476
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• 2024

This study examined the effects of riverbed slope and roughness coefficient on flood level and flow velocity. A numerical experiment was conducted by installing HEC-RAS in the valley of a sub-basin in Geochang-gun, Gyeongsangnam-do. For each basin, three slopes of riverbeds (slopes-15.0%, 5.0%, and 1.0%) were chosen with different characteristics, and four coefficients of roughness were applied to each slope to parameterize the flow. Flow velocity and flood level were intensively investigated. It was found that in the cases of 15.0% and 5.0%, where the riverbed slopes are steep, the slope dominates the change in flow velocity and flood level, while in the case of 1%, where the riverbed slope is small, the change in flow velocity and flood level caused by changes in roughness coefficient is insignificant. Usually, the riverbed slope is large in the valley part of the watershed, so in this case, the slope will play a dominant role in the results of flow velocity and flood level when designing water-related structures.