• Journal of Advanced Marine Engineering and Technology
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• 제38권6호
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• pp.698-703
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• 2014

최근 기존 화석연료의 고갈로 인하여 대체에너지로써 천연액화가스의 수요 증가와 함께 LNG 운반선의 수요가 증가하고 있으며, 그로인해 극한의 환경에서 사용할 수 있는 LNG 선박용 벨로우즈의 수요 또한 증가할 것으로 예상된다. 현재 LNG 선박용 벨로우즈에 사용되는 재료는 저온취성과 해수부식에 강한 INCOLOY 825와 STS316L합금이다. 본 연구에서는 극저온에 사용되는 LNG용 벨로우즈 재질인 INCOLOY 825과 STS316L 합금에 대하여 최적의 용접조건을 설정하고, 에릭센 시험을 통하여 용접부의 성형성을 분석하였다. 최적 조건에서의 용접시 용접부의 인장강도는 모재에 비하여 90% 이상의 강도값을 나타내었다. 또한 에릭센 시험을 통한 성형성 분석의 결과, 용접부가 아닌 모재에서 파단이 발생하는 매우 양호한 용접부를 얻을 수 있었다.

• Journal of Biosystems Engineering
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• 제42권1호
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• pp.56-61
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• 2017

Purpose: High energy requirement and long cooking time are limiting consumption of pigeon pea (Cajanus cajan), a nutritious food. This study was performed to estimate energy and time demand by different methods of cooking pigeon pea. Methods: Pigeon pea (150 g) was soaked in 2.0 L of water at ambient temperature ($29{\pm} 2^{\circ}C$) to determine hydration behavior. Cooking experiments were conducted using aluminum and pressure-cooking pots. Efficiency of cooking was evaluated using four types of cooking appliances (kerosene, liquefied petroleum gas (LPG), electric, and charcoal stoves). Normal (continuous heating until the food was satisfactorily cooked) and control (controlling the energy input to closely match the actual energy required) cooking were conducted. Energy requirement and duration of cooking were determined using standard procedures. Results: Soaking increased moisture content from 11.99 to 30.01% in 90 min, while water absorption rate decreased with soaking duration. In cooking 150 g of pigeon pea using kerosene stove, presoaked normal pressure-pot cooking method consumed the least energy (10 800 kJ) and time (205 min), while unsoaked normal cooking consumed the highest energy (18 450 kJ) and time (336 min). Using LPG stove, unsoaked normal cooking method required the highest energy (52 470 kJ), while presoaked control pressure-pot required the least energy (14 405 kJ). For electric stove, the lowest energy (15 560 kJ) and shortest duration (105 min) were recorded during control cooking of presoaked sample in the pressure-pot. Conclusions: Control cooking was not practicable using charcoal stove. Generally, kerosene stove consumed the least energy, while electric stove was found to have the shortest duration of cooking.

• 한국수소및신에너지학회논문집
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• 제12권3호
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• pp.169-176
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• 2001

The purpose of study is to obtain low-emission and high-efficiency in LPG engine with hydrogen enrichment. The test engine was named heavy-duty variable compression ratio single cylinder engine (VCSCE). The fuel supply system provides LPG/hydrogen mixtures based on same heating value. Various sensors such as crank shaft position sensor (CPS) and hall sensor supply spark timing data to ignition controller. Displacement of VCSCE is $1858.2cm^3$. VCSCE was runned 1400rpm with compression ratio 8. Spark timing was set MBT without knocking. Relative air-fuel ratio(${\lambda}$) of this work was varied between 0.76 and 1.5. As a result, i) Maximum thermal efficiency occurred at ${\lambda}$ value 1.0. It was shown that thermal efficiency was increased approximately 5% with hydrogen enrichment at same ${\lambda}$ value. ii) Engine-out carbon monoxide (CO) emissions were decreased at a great rate under LPG/hydrogen mixture fuelling. iii) Total hydrocarbon (THC) emission was much exhausted in rich zone, same as CO. But THC was exhausted a little bit more in lean zone. iv) Finally, engine-out oxides of nitrogen (NOx) was increased with ${\lambda}$ value 1.0 zone at a greater rate with hydrogen enrichment due to high adiabatic flame temperature.

• 해양환경안전학회지
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• 제20권1호
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• pp.78-85
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• 2014

일반상선 중 액화천연가스(LNG) 재기화 선박은 기존의 LNG 운반선에 액화된 LNG를 다시 기화할 수 있는 추가설비를 갖춘 선박이다. 이 선박은 해상에서 천연가스를 해저 터미널을 통해 이송하는 수중 터렛 시스템을 보유한다. 하역작업을 완료한 선박이 운항 시에는 수중 터렛이 없음으로 인해 선수부 바닥이 열려 있는 개구부 즉, 오프닝 상태가 발생한다. 본 연구의 주 목적은 오프닝 상태로 운항 시 발생되는 속도손실을 CFD를 이용한 유동해석과 예인수조에서의 모형시험을 통하여 정확하게 파악하였다. 모형시험에서는 나선 상태와 오프닝 상태에서 저항 및 자항성능을 평가하였다. 실험에서는 터프트 법에 의한 유선조사시험을 이용하여 오프닝 내부유동의 변화를 정량적 또는 정성적으로 보다 더 상세한 조사를 하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권2호
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• pp.227-245
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• 2013

Reliable strength assessment of the Liquefied Natural Gas (LNG) cargo containment system under the sloshing impact load is very difficult task due to the complexity of the physics involved in, both in terms of the hydrodynamics and structural mechanics. Out of all those complexities, the proper selection of the design sloshing load which is applied to the structural model of the LNG cargo containment system, is one of the most challenging one due to its inherent randomness as well as the statistical analysis which is tightly linked to the design sloshing load selection. In this study, the response based strength assessment procedure of LNG cargo containment system has been developed and proposed as an alternative design methodology. Sloshing pressure time history, measured from the model test, is decomposed into wavelet basis function targeting the minimization of the number of the basis function together with the maximization of the numerical efficiency. Then the response of the structure is obtained using the finite element method under each wavelet basis function of different scale. Finally, the response of the structure under entire sloshing impact time history is rapidly calculated by synthesizing the structural response under wavelet basis function. Through this analysis, more realistic response of the system under sloshing impact pressure can be obtained without missing the details of pressure time history such as rising pattern, oscillation due to air entrapment and decay pattern and so on. The strength assessment of the cargo containment system is then performed based on the statistical analysis of the stress peaks selected out of the obtained stress time history.

• 한국재료학회지
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• 제24권8호
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• pp.434-442
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• 2014

Serious environmental problems have been caused by the greenhouse effect due to carbon dioxide($CO_2$) or nitrogen oxides($NO_x$) generated by the use of fossil fuels, including oil and liquefied natural gas. Many countries, including our own, the United States, those of the European Union and other developed countries around the world; have shown growing interest in clean energy, and have been concentrating on the development of new energy-saving materials and devices. Typical non-fossil-fuel sources include solar cells, wind power, tidal power, nuclear power, and fuel cells. In particular, organic solar cells(OSCs) have relatively low power-conversion efficiency(PCE) in comparison with inorganic(silicon) based solar cells, compound semiconductor solar cells and the CIGS [$Cu(In_{1-x}Ga_x)Se_2$] thin film solar cells. Recently, organic cell efficiencies greater than 10 % have been obtained by means of the development of new organic semiconducting materials, which feature improvements in crystalline properties, as well as in the quantum-dot nano-structure of the active layers. In this paper, a brief overview of solar cells in general is presented. In particular, the current development status of the next-generation OSCs including their operation principle, device-manufacturing processes, and improvements in the PCE are described.

• 한국수소및신에너지학회논문집
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• 제23권4호
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• pp.382-389
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• 2012

Power generation cycle using ammonia-water mixture as working fluid has attracted much attention because of its ability to efficiently convert low-temperature heat source into useful work. If an ammonia-water power cycle is combined with a power cycle using liquefied natural gas (LNG), the conversion efficiency could be further improved owing to the cold energy of LNG at $-162^{\circ}C$. In this work parametric study is carried out on the thermodynamic performance of a power cycle consisted of an ammonia-water Rankine cycle as an upper cycle and a LNG cycle as a bottom cycle. As a driving energy the combined cycle utilizes a low-temperature heat source in the form of sensible heat. The effects on the system performance of the system parameters such as ammonia concentration ($x_b$), turbine 1 inlet pressure ($P_{H_1}$) and temperature ($T_{H_1}$), and condenser outlet temperature ($T_{L_1}$) are extensively investigated. Calculation results show that thermal efficiency increases with the increase of $P_{H_1}$, $T_{H_1}$ and the decrease of $T_{L_1}$, while its dependence on $x_b$ has a downward convex shape. The changes of net work generation with respect to $P_{H_1}$, $T_{H_1}$, $T_{L_1}$, and $x_b$ are roughly linear.

• Structural Engineering and Mechanics
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• 제25권4호
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• pp.445-466
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• 2007

As the LNG (Liquefied Natural Gas) tank contains cryogenic liquid, realistic thermal analyses are of a primary importance for a successful design. The structural details of the LNG tank are so complicated that some strategies are necessary to reasonably predict its temperature distribution. The proposed heat transfer model can consider the beneficial effects of insulation layers and a suspended deck on temperature distribution of the outer concrete tank against cryogenic conditions simply by the boundary conditions of the outer tank model. To this aim, the equilibrium condition or heat balance in a steady state is utilized in a various way, and some aspects of heat transfer via conduction, convection and radiation are implemented as necessary. Overall thermal analysis procedures for the LNG tank are revisited to examine some unjustifiable assumptions of conventional analyses. Concrete and insulation properties under cryogenic condition and a reasonable conversion procedure of the temperature-induced nonlinear stress into the section forces are discussed. Numerical examples are presented to verify the proposed schemes in predicting the actual temperature and stress distributions of the tank as affected by the cryogenic LNG for the cases of normal operation and leakage from the inner steel tank. It is expected that the proposed schemes enable a designer to readily detect the effects of insulation layers and a suspended deck and, therefore, can be employed as a useful and consistent tool to evaluate the thermal effect in a design stage of an LNG tank as well as in a detailed analysis.

• 한국전산구조공학회논문집
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• 제27권4호
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• pp.265-271
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• 2014

304L 스테인리스강판은 멤브레인타입 LNG선 단열시스템의 1차 방벽으로 이용된다. 304L 스테인리스강은 변태유기소성(TRIP)강으로 복잡한 재료거동을 보이는데, 이는 소성변형이 발생하는 동안 상변태를 경험하기 때문이다. 본 연구에서는 304L 스테인리스 강의 비선형 기계적 거동분석을 위한 온도의존 일축인장시험을 수행하였으며 재료의 파단이나 비선형 거동을 예측하기 위한 점소성모델을 제안하였다. 수치해석의 결과와 시험 결과를 비교 분석하여 유효성을 검증하였으며 LNG 멤브레인에 대한 적용성을 검토하기 멤브레인 구조시편을 제작하여 구조해석 및 유한요소해석을 수행하였다. 재료모델은 개발 서브루틴을 이용하였으며 ABAQUS 사용자지정 재료 서브루틴을 탑재한 유한요소해석 결과와 극저온 구조인장시험을 수행한 결과를 비교하여 구조적용성을 검증하였다.

• 대한조선학회논문집
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• 제56권6호
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• pp.515-522
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• 2019

Since Liquefied Natural Gas (LNG) is normally carried at 1.1 bar pressure and at -163℃, special Cargo Containment System (CCS) are used. As LNG carrier is becoming larger, typical LNG insulation systems adopt a method to increase the thickness of insulation panel to reduce sloshing load and Boil-off Rate (BOR). However, this will decrease LNG cargo volume and increase insulation material costs. In this paper, silica aerogel, glass bubble were synthesized in polyurethane foam to increase volumetric efficiency by improving mechanical and thermal performance of insulation. In order to increase dispersibility of particles, ultrasonic dispersion was used. Dynamic impact test, quasi-static compression test at room temperature (20℃) and cryogenic temperature (-163℃) was evaluated. To evaluate the thermal performance, the thermal conductivity at room temperature (20℃) was measured. As a result, specimens without ultrasonic dispersion have a little effect on strength under the compressive load, although they show high mechanical performance under the impact load. In contrast, specimens with ultrasonic dispersion have significantly increased impact strength and compressive strength. Recently, as the density of Polyurethane foam (PUF) has been increasing, these results can be a method for improving the mechanical and thermal performance of insulation panel.