• 설비공학논문집
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• 제13권6호
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• pp.505-513
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• 2001

A revised VX cycle using ammonia/water as the working fluid is a cycle which is suitable to produce cooling utilizing low temperature hat sources. The cycle was analyzed numerically to investigate the effects of the design and operating conditions on the performance. It was shown that both COP and cooling capacity were significantly influenced by the performance of he rectifier. Insufficient UA of the rectifier reduced both ammonia mass fraction and mass flow rate of the vapor entering the condenser, which produced cooling effect in the evaporator. As the temperature and the mass flow rate of the heat source increased, both COP and exergetic efficiency decreased due to the irreversibilities produced in heat exchangers, but cooling capacity did not vary much. Cooling capacity increased significantly as the coolant temperature decreased, although COP and exergetic efficiency remained nearly constant.

• 동력기계공학회지
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• 제9권4호
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• pp.65-70
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• 2005

A liquid storage rectangular tank structures are used in many fields of civil, mechanical and marine engineering. Especially, Ship structures have many tanks in contact with inner or outer fluid, like ballast, fuel and cargo tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these thin walled tanks in contact with fluid near engine propeller are strongly affected by added mass of containing fluid. Therefore it is essentially important to estimate the added mass effect to predict vibration of the tank structures. Many authors have studied vibration of cylindrical and rectangular tanks structures containing fluid. Few research on dynamic interaction among tank walls through fluid are reported in the vibration of rectangular tanks recently. In case of rectangular tanks, structural coupling between adjacent panels and effect of vibration modes of multiple panels on added mass have to be considered. In the present paper, coupling effect between panels of tank structure on added mass of containing fluid, the effect of structural constraint between panels on each vibration mode for fluid region have investigated numerically and experimentally.

• 한국물환경학회지
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• 제21권3호
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• pp.219-229
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• 2005

The analytical methods for dioxins in water sample from wastewater to tap water were reviewed. For extraction method, liquid-liquid extraction (LLE) has been widely used, however, this process needs too much time and man power. New approach including solid phase extraction (SPE) is now applicable to large volume of water sample with high extraction efficiency. Column clean up in classical analytical methods were very complex and time consuming procedures during decade. Modifications were tried to decrease solvent and reagents volume. Moreover, use of column connection method has been demonstrated in the environmental matrices. Instrumental configurations also have been improved, in which GC/MS/MS with large volume injection approach can analyze picogram levels. Absolute sensitivities of HRMS increased compared to old versions of double focusing sector type mass spectrometers. Based on these analytical evolutions during last 10 years, we tried to optimize the analytical method for dioxins in water sample from sample extraction to instrumental analysis.

• 대한환경공학회지
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• 제36권6호
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• pp.387-395
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• 2014

본 연구에서는 SBSE 전처리 장치와 GC-MS/MS를 이용하여 합성 향물질 11종을 동시 분석할 수 있는 분석법을 개발하기 위해 흡착 bar의 교반시간, 교반속도, 시료수의 pH, 시료수 용량, 염석제 투입량 및 메탄올 주입량 변화 등 SBSE (stir bar sorptive extraction) 전처리 조건과 GC-MS/MS (gas chromatography/tandem mass spectrometry)의 기기조건을 다양하게 변화시켜 SBSE-GC-MS/MS를 이용한 분석법을 개발하였다. 11종의 합성 향물질들에 대한 검출한계(LOD)는 2.1~4.1 ng/L였으며, 정량한계(LOQ)는 6.6~12.9 ng/L였다. 수돗물, 낙동강 원수, 하수처리장 최종방류수 및 해수를 이용하여 시료수의 matrix 영향을 살펴본 결과, 11종의 합성 향물질들의 회수율 및 RSD의 경우 각각 88%~119% 및 0.8%~7.5%로 양호한 결과를 나타내어 시료수의 matrix 영향을 받지 않는 것으로 나타났다. 본 연구에서 개발된 SBSE-GC-MS/MS 분석법은 40 mL 정도의 적은 시료수량으로도 고감도 분석이 가능하며, 용매류를 사용하지 않기 때문에 분석자의 건강 및 환경친화적인 분석법이라는 장점뿐만 아니라 간편하고, 빠르며 자동화된 방법이라는 장점을 가진다.

• 분석과학
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• 제13권3호
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• pp.277-281
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• 2000

16종의 휘발성 유기화합물을 blank water에 첨가하고 고정상으로 $100{\mu}m$ polydimethyl siloxane을 입힌 solid phase microextraction(SPME) fiber를 사용하는 headspace SPME방법으로 추출하여 gas chromatography/mass spectrometry (GC/MS)로 분석하였다. 이 방법의 평균회수율은 97%, 평균상대표준편차는 4.7%, 그리고 검출한계는 $0.01-0.5{\mu}g/l$를 나타냈다. 즉 SPME 방법을 이용한 수용액 중의 휘발성 유기화합물의 결과는 현재 많이 사용되고 있는 기존의 다른 방법보다 우수하고 편리한 방법으로 나타났다.

• 방사성폐기물학회지
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• 제18권4호
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• pp.549-562
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• 2020

Deionized water, methanol, and ethanol were investigated for their effectiveness at dissolving LiCl-KCl-UCl3 at 25, 35, and 50℃ using inductively coupled plasma mass spectrometry (ICP-MS) to study the concentration evolution of uranium and mass ratio evolutions of lithium and potassium in these solvents. A visualization experiment of the dissolution of the ternary salt in solvents was performed at 25℃ for 2 min to gain further understanding of the reactions. Aforementioned solvents were evaluated for their performance on removing the adhered ternary salt from uranium dendrites that were electrochemically separated in a molten LiCl-KCl-UCl3 electrolyte (500℃) using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). Findings indicate that deionized water is best suited for dissolving the ternary salt and removing adhered salt from electrodeposits. The maximum uranium concentrations detected in deionized water, methanol, and ethanol for the different temperature conditions were 8.33, 5.67, 2.79 μg·L-1 for 25℃, 10.62, 5.73, 2.50 μg·L-1 for 35℃, and 11.55, 6.75, and 4.73 μg·L-1 for 50℃. ICP-MS analysis indicates that ethanol did not take up any KCl during dissolutions investigated. SEM-EDS analysis of ethanol washed uranium dendrites confirmed that KCl was still adhered to the surface. Saturation criteria is also proposed and utilized to approximate the state of saturation of the solvents used in the dissolution trials.

• 한국전산구조공학회논문집
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• 제29권3호
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• pp.209-218
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• 2016

최근 신재생 에너지 중 하나인 풍력발전에 대한 관심이 증가하고 있다. 풍력발전은 토지구입비, 소음문제에 자유로운 해상풍력으로 추세가 옮겨가고 있으며 이를 위한 연구개발이 전 세계적으로 활발히 이루어지고 있다. 그러나 해상에 위치한 풍력발전을 위한 설계기준은 국내, 국외 모두 없는 실정이다. 이 점을 고려하여 국내, 국외의 구조설계기준인 도로교 설계기준, 항만 및 어항 설계기준, DNV OS를 참고하여 다중 파일기초 콘크리트 지지구조물(MCF)의 내진해석을 수행하여 결과를 비교하였다. 또한 시간에 의한 효과를 확인하기 위하여 시간이력 해석 또한 수행되었다. 부가질량법(Added-mass method)을 사용하여 물과 구조의 상호작용을 고려하였고 물의 유무에 따라 구조물의 반응을 비교하였다.

• 한국수소및신에너지학회논문집
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• 제29권2호
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• pp.148-154
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• 2018

This paper presents a comparative analysis of thermodynamic performance of ammonia-water Rankine cycles with and without regeneration and Kalina cycle for recovery of low-temperature heat source. Special attention is paid to the effect of system parameters such as ammonia mass fraction and turbine inlet pressure on the characteristics of the system. Results show that maximum net power can be obtained in the regenerative Rankine cycle for high turbine inlet pressures. However, Kalina cycle shows better net power and thermal efficiency for low turbine inlet pressures, and the optimum ammonia mass fractions of Kalina cycle are lower than Rankine cycles.

• Structural Engineering and Mechanics
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• 제86권5호
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• pp.621-633
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• 2023

Stability analysis and support system estimation of the Beheshtabad water transmission tunnel is investigated in this research. A combination approach based on the rock mass rating (RMR) and rock mass quality index (Q) is used for this purpose. In the first step, 40 datasets related to the petrological, structural, hydrological, physical, and mechanical properties of tunnel host rocks are measured in the field and laboratory. Then, RMR, Q, and height of influenced zone above the tunnel roof are computed and sorted into five general groups to analyze the tunnel stability and determine its support system. Accordingly, tunnel stand-up time, rock load, and required support system are estimated for five sorted rock groups. In addition, various empirical relations between RMR and Q i.e., linear, exponential, logarithmic, and power functions are developed using the analysis of variance (ANOVA). Based on the significance level (sig.), determination coefficient (R²) and Fisher-test (F) indices, power and logarithmic equations are proposed as the optimum relations between RMR and Q. To validate the proposed relations, their results are compared with the results of previous similar equations by using the variance account for (VAF), root mean square error (RMSE), mean absolute percentage error (MAPE) and mean absolute error (MAE) indices. Comparison results showed that the accuracy of proposed RMR-Q relations is better than the previous similar relations and their outputs are more consistent with actual data. Therefore, they can be practically utilized in designing the tunneling projects with an acceptable level of accuracy and reliability.

• 대한조선학회지
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• 제17권2호
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• pp.11-16
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• 1980

For vibration analysis of stiffened plates the orthotropic plate analogy is commonly accepted. As to stiffened plates in contact with water, however, there is still much uncertainty in estimation of the added mass because of the lack of direct methods. The authors, considering that for added mass of plates there are many reliable data derived theoretically or experimentally available, suggest a method to estimate the added mass of a stiffened plate by combining the mass increase factor, $\beta$, of an equivalent orthotropic plate and the correction factor, $\kappa$, for the effects of stiffeners. The latter is to be derived from systematic experimental investigations. Then, the natural frequency in water, f', can be calculated from that in air, f, by the equation $f'=f/\sqrt{1+\kappa\beta}$. To investigate practical applicability of this method, a systematic experiment was carried out with five uniaxially stiffened plates. Each of them had a plate of same size, $600mm{\times}600mm{\times}3.2mm$, but stiffeners of different size in the web-depth, 41.6mm, 51.2mm or 66.8mm and of different spacing 75mm, 100mm, or 150mm. Natural frequencies were measured under simply supported-edge conditions in both air and water, and corresponding $\kappa$ values derived. In spite of wide variations of web-depth and spcae of stiffeners, the experimental results show that the diversity of $\kappa$ values is not remarkable; mean values of $\kappa$ are 1.31 with standard deviation of 0.025 for the first modes and 1.27 with that 0.077 for the second modes. Hence, the authors concluded that the above $\kappa$ values can be used generally for the cases of uniaxially stiffened plates both sides of which contact with water, and that $\kappa$ values of general use for the cases of cross-stiffened plates may also be obtainable from similar experiments.