• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.713-720
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• 2015

The sizes of the final blades of a low-pressure (LP) steam turbine have been getting larger for the development of high-capacity power plants. They are also larger than the other blades in the same system. As a result, fatigue damage is caused by a large centrifugal force and a low natural frequency of the blade. Recently, many failure cases have been reported due to repeated turbine startups and their prolonged use. In this study, the causes and mechanism of failure of a LP turbine blade were analyzed by using a finite element method to calculate the centrifugal force, the natural frequency of a stress-stiffening effect, and the harmonic response. It was observed that the expected fatigue damage position matched the real crack position at the airfoil's leading edge, and an equivalence fatigue limit approached a notch fatigue limit.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.3
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• pp.191-199
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• 2000

In this paper, a numerical analysis using the finite element method (FEM) is presented which models the eddy current testing (ECT) of tubes with 3-dimensional defects. For the description of 3-dimensional eddy current problems, the governing equation is derived from the Maxwell's equations. The 3-dimensional FEM formulation with hexahedral elements is carried out using the Galerkin weighted residual method. The INCONEL 600 steam generator tube with inner and outer diameter defects is adopted for the numerical analysis, and the ECT signal, which is the trajectory of the probe impedance, is calculated. For the verification of the numerical analysis method, results of numerical calculations and experiments are compared and they show good agreements. Based on this verification, several defect signals are predicted and their characteristics are investigated with the variation in the defect depth and the circumferential angle of the defect.

• Korean Journal of Medicinal Crop Science
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• v.10 no.3
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• pp.200-205
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• 2002

Platycodin D was isolated from n-butanol extract of Platycodi radix(Platycodon grandiflorum and identified by the spectroscopic analysis using $^1H$ and $^{13}C$ NMR techniques. A new method of analysis of platycodin D by high performance liquid chromatography(HPLC) was established using a reversed phase system with YMC-Pack ODS-AM( 250 X 4.6 mm) column and 30% acetonitrile as a mobile phase. Evaporative light scattering detector was used as detector. The kinds of extraction solvents and methods were examined to determine the efficient extraction condition and HPLC analysis was carried out to establish the optimum drying condition for the root of Platycodon grandiflorum. The contents of Platycodin D was highest as 0.083% when platycodon roots were dried at $60^{\circ}C$ using dry oven.

• Nuclear industry
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• v.27 no.4 s.290
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• pp.46-50
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• 2007

고리 1호기는 한국에서 최초로 규제 기관에 계속운전을 신청한 원전이다. 2007년 6월에 설계 수명 기간 만료가 되는 고리 1호기는 규제 기관으로부터 계속운전(Continued Operation)에 대한 안전성 심사를 받고 있다. 한수원은 고리 1호기 계속운전 승인을 금년 12월에 받기 위해 최선을 다하고 있으며 지역 주민의 사회적 수용성 확보를 위해 노력중이다. 고리 1호기의 계속운전 기간 동안 안전성을 평가하고 정리한 안전성평가보고서를 한수원은 2006년 6월에 정부에 제출하였다. 고리 1호기는 웨스팅하우스의 2루프 가압경수로이다. 이와 동일한 원전인 일본의 미하마 1,2호기와 겐까이1호기가 계속운전중이며, 미국의 기네이와 포인트 비치 1,2호기가 계속운전 승인을 받았다. 제출한 안전성평가보고서에 대해 한국원자력안전기술원이 심사중이며, 해외 원전과 같이 계속운전을 할 수 있을 것으로 예상하고 있다. 또한 계속운전을 위한 사회적 수용성(Public Acceptance) 확보는 설비의 철저한 안전성 확보 및 지역 주민의 공감대 형성을 통해서 이루어질 것이다. 설계 수명 이후 원자력발전소를 계속 운전하는 것은 이미 선진국에서 시행되고 있다. 2007년 3월 기준으로 미국에서 48기가 운영 허가 갱신 승인을 받았고, 영국은 8기, 일본은 12기가 계속운전중이다. 고리 1호기 성능 지표를 개선시키기 위해서 한수원은 증기발생기, 저압 터빈, 원자로 냉각재 펌프 내장품, 주변압기, 주발전기 등을 교체하였으며, 수명관리 연구, 주기적안전성 평가, 환경 영향 평가를 수행하였다. 2005년 9월에는 미국의 운영 허가 갱신 제도를 참조하여 원자력법이 개정되었다. 이에 한수원은 개정된 원자력법에 맞추어 주기적 안전성평가, 주요 기기에 대한 수명 평가 및 방사능 환경 영향평가를 하였다. 이 세가지 보고서들로 구성된 안전성평가보고서를 2006년 6월에 규제 기관에 제출하였다. 계속운전은 한국을 비롯하여 부존 자원이 부족한 국가들에게는 에너지 자원의 효율적 활용 및 온실 가스 배출을 고려할 때 반드시 필요한 것이다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6A
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• pp.524-532
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• 2002

This paper reports that the Lambert W function applies to a non-iterative design of minimum mean square-error scalar quantizers for a Laplacian source. Specifically, it considers a non-iterative design algorithm for optimum quantizers for a Laplacian source; it finds that the solution of the recursive nonlinear equation in the non-iterative design is elegantly expressed in term of the principal branch of the Lambert W function in a closed form; and it proves that the non-iterative algorithm applies only to exponential or Laplacian sources. The contribution of the paper is in the reduction of the time needed for the design and the increased accuracy in resulting quantization points and thresholds, because the algorithm is non-iterative and the Lambert W function can be evaluated as accurately as desired. Also, numerical results show how optimal quantization distortion converges monotonically to the Panter-Dite constant and help derive an approximation formula for the key parameters of optimum quantizers.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.8 s.173
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• pp.143-150
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• 2005

To verify applicability of multi-dimensional spectral analysis (MDSA) fur noise source identification two different approaches which are frequency response and coherent function have been investigated. The coherence function approach appears able to separate the correlated system when the noise sources were coherent. In this study, we identify contribution of structure-borne-noise of vehicle HVAC system using MDSA method. Firstly, to identify the applicability of MDSA method, 4-inputs of vehicle HVAC system were the signals measured by accelerometers attached on the selected noise sources which were composed of blower, evaporator, heater and duct. While 1-output which was driver's position sound was the SPL signals measured by a remote microphone, when the blower motor was operating. We identify efficiency of systems modeled with four Inputs/single output through ordinary coherence function (OCF) and partial coherence function (PCF). As a result of experiment, the blower accounted for $62-88\%$ of the overall level of sound energy density. Also, according to the analysis of acoustic signal and vibration signals measurement, an investigation of the noise source identification in the vehicle HVAC is presented. With the sound intensity method, the major sources of the vehicle HVAC radiation are verified. Also the method of improving the noise reduction is proposed by attaching damping patch access to blower motor and noise reduction is verified.

• Applied Chemistry for Engineering
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• v.27 no.3
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• pp.335-341
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• 2016

In this study, impurity effects on diffusive-convection flow fields by physical vapor transport under terrestrial and microgravity conditions were numerically analyzed for the mixture of $Hg_2Cl_2-I_2$ system. The numerical analysis provides the essence of diffusive-convection flow as well as heat and mass transfer in the vapor phase during the physical vapor transport through velocity vector flow fields, streamlines, temperature, and concentration profiles. The total molar fluxes at the crystal regions were found to be much more sensitive to both the gravitational acceleration and the partial pressure of component $I_2$ as an impurity. Our results showed that the solutal effect tended to stabilize the diffusive-convection flow with increasing the partial pressure of component $I_2$. Under microgravity conditions below $10^{-3}g_0$, the flow fields showed a one-dimensional parabolic flow structure indicating a diffusion-dominant mode. In other words, at the gravitational levels less than $10^{-3}g_0$, the effects of convection would be negligible.

• The Journal of the Acoustical Society of Korea
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• v.16 no.6
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• pp.76-84
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• 1997

Loose parts monitoring system(LPMS), which is used to detect metallic loose parts in the nuclear power plant, plays an important role in safe and reliable operation of the plant. To prevent from the damage due to the loose parts, most domestic nuclear power plants are using, or planning to use LPMS. However, these LPMS's, which are all invented from overseas and thereby depend on the oversea technologies, are very expensive, and are known to be inefficient to diagnose loose parts due to the lack of fundamental know-how of LPMS. Therefore, the main purpose of this paper is to propose and to realize a new loose parts localization algorithm which is simple and efficient enough even for the inexperienced operators to diagnose loose parts accurately and promptly. Considering practical nuclear power plant circumstances, some simulations for estimating the loose parts location have been done. The results show that the proposed method, called a modified circle intersection method, performs high resolved loose parts localization with 3.4% of error.

• Journal of Navigation and Port Research
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• v.26 no.1
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• pp.120-126
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• 2002

ZnS thin films were prepared on glass substrate at various deposition conditions by a HW apparatus and were systematically investigated the growth characteristics, in terms of deposition edges by a double beam spectro- photometer, and structural analysis by a x-ray diffraction rates were increased with incresing the cell temperature and vapor pressure of sulfur, but were decreased with increasing substrate temperature. The optical characteristics of thin films depends on the deposition rates. The band gap energies of 3.46∼3.52eV measured at room temperature are smaller than the theoretical value of 3.54eV, indicating that impurities exist in the crystal. All ZnS thin films are oriented in the (III) principal direction of a zincblende structure. By introducing the S vapor, optical and crystalline properties have been improved.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.67-67
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• 2010

탄소나노튜브(CNT)는 우수한 기계적, 화학적, 전기적 특성으로 인해 다양한 분야에서 차세대 응용재료로서 각광을 받고 있다. 다양한 CNT의 합성방법 중 CNT 구조제어가 가장 용이한 방법으로는 열화학증기증착법(TCVD)와 플라즈마지원(PE) CVD법이 있으며, 대량합성을 위해서는 TCVD가 보다 일반적으로 이용되어지고 있다. 일반적으로 CNT를 합성하기 위해서는 전이금속의 촉매가 필요하며 촉매의 활성화 및 탄소를 포함하는 원료가스의 분해를 위하여 고온공정이 요구된다. 그러나 향후 산업적 응용을 고려한다면 저온합성법의 개발은 시급하게 해결해야 할 과제로 인식되고 있다. 또한 기판 위에 CNT를 합성하는 경우 촉매와 기판재료 사이의 합금화를 방지하기 위하여 산화막층을 삽입하게 되는데, 이는 CNT의 높은 전도성을 이용하고자 할 경우 저해요소로 작용하게 된다. 따라서 CNT를 완충층의 도움 없이 금속기판 위에 직접 성장시키는 기술 역시 향후 CNT응용에 있어서 중요한 과제라 할 수 있다. 상기와 같은 배경으로 본 연구에서는 금속기판 위 CNT의 저온성장을 목적으로 연구를 진행하였다. CNT 합성기판으로는 SUS316L 및 Inconel과 같은 촉매금속을 자체 함유한 금속기판을 선정하였고, 플라즈마 전처리를 통한 기판표면 제어를 통하여 CNT의 저온성장을 도모하였다. 직류전원의 아르곤 플라즈마를 이용하여 금속기판을 처리하였을 때 기판온도 및 플라즈마 파워가 증가함에 따라 기판의 표면조도가 증가하는 것을 AFM분석을 통해 확인할 수 있었다. 아세틸렌 가스를 원료가스로 이용한 TCVD합성에 있어서는 플라즈마 처리한 기판이 무처리 기판보다 동일 합성온도에서 더 두꺼운 CNT박막을 형성하였고, 합성온도는 $400^{\circ}C$ 부근까지 내릴 수 있었다. 이는 플라즈마 처리로 증가된 기판의 표면조도가 저온에서 CNT의 핵생성에 유리하게 작용했음을 추측하게 한다.