• 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.

• 대한조선학회논문집
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• 제58권5호
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• pp.303-313
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• 2021

Recently, quality control of the Liquefied Natural Gas Carrier (LNGC) cargo hold and block-erection interference areas using 3D scanners have been performed, focusing on large shipyards and the international association of classification societies. In this study, as a part of the research on LNGC cargo hold quality management advancement, a study on deep-learning-based scaffolding system 3D point cloud object detection and post-processing were conducted using a LNGC cargo hold 3D point cloud. The scaffolding system point cloud object detection is based on the PointNet deep learning architecture that detects objects using point clouds, achieving 70% prediction accuracy. In addition, the possibility of improving the accuracy of object detection through parameter adjustment is confirmed, and the standard of Intersection over Union (IoU), an index for determining whether the object is the same, is achieved. To avoid the manual post-processing work, the object detection architecture allows automatic task performance and can achieve stable prediction accuracy through supplementation and improvement of learning data. In the future, an improved study will be conducted on not only the flat surface of the LNGC cargo hold but also complex systems such as curved surfaces, and the results are expected to be applicable in process progress automation rate monitoring and ship quality control.

• 대한조선학회논문집
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• 제58권3호
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• pp.137-143
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• 2021

In this study, the fracture strength of Flexible Secondary Barrier (FSB) composites was standardized by conducting a distribution analysis of the fracture probability, considering that the fracture strength of FSB composites such as glass fiber reinforced composites is relatively large. As the mechanical performance of FSB composites varies with the fiber direction, 20 replicate uniaxial tensile tests were performed for different temperatures ranging from the ambient to cryogenic conditions, considering the actual operating environment of liquefied natural gas. For the probability statistical analysis, the Weibull distribution analysis derived from the weakest link theory was used, considering the large variance in the fracture strength and brittle fracture behavior. The results of the Weibull distribution analysis were used to calculate the standard fracture strength of the FSB composites for different fiber directions. The findings can help ensure the reliability of the FSB mechanical properties in different fiber directions in the design of the secondary barrier and structural analyses.

• 대한조선학회논문집
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• 제58권1호
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• pp.17-23
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• 2021

The membrane-type Liquefied Natural Gas (LNG) cargo tank is equipped with a double barrier to seal the LNG, of which the secondary barrier serves to prevent LNG leakage and mainly uses fiber-reinforced composite materials. However, the composite materials have thermal expansion anisotropy, which deteriorates shape distortion and mechanical performance due to repeated thermal loads caused by temperature changes between cryogenic and ambient during the unloading of LNG. Therefore, in this study, the longitudinal thermal expansion characteristics of the composite materials were obtained using a vertical thermo-mechanical analyzer, and the elastic modulus was obtained through the tensile test for each temperature to perform thermal load analysis for each direction. This is considered that it is useful to secure reliability from the viewpoint of the design of materials for a LNG cargo hold.

• Composites Research
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• 제32권5호
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• pp.290-295
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• 2019

본 연구에서는 액화 천연 가스 운반선 단열 시스템에 적용되는 폴리우레탄 폼(Polyurethane foam, PUF)의 열적 성능 및 내충격성을 향상시키기 위한 목적으로, PUF에 복합 단열 매트를 보강하였다. 복합 단열 매트는 극저온 환경에서 운용이 가능한 케블라, 에어로겔, 그리고 크라이오겔 매트를 선정하였다. 열적 성능은 $20^{\circ}C$의 상온에서 열전도율을 측정하였으며, 내충격성은 $20^{\circ}C$의 상온 및 $-163^{\circ}C$의 극저온에서 30 J의 충격에너지로 낙하 충격 시험을 수행하여 측정하였다. 측정된 열전도율은 유효 열전도율 이론 값을 통해 보강되지 않은 PUF와 비교하였으며, 내충격성은 접촉력, 접촉 시간, 그리고 흡수에너지를 평가하였다. 실험 결과 크라이오겔 복합 매트 보강 시 가장 우수한 열적 성능을 나타났으며, 내충격성은 에어로겔 복합 매트 보강 시 가장 우수하게 나타났다.

• 한국해양공학회지
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• 제36권4호
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• pp.217-231
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• 2022

Reinforced polyurethane foam (R-PUF), a material for liquefied natural gas cargo containment systems, is expected to have different mechanical properties depending on its stacking position of foaming as the glass fiber reinforcement of R-PUF sinks inside R-PUF under the influence of gravity. In addition, since R-PUF is not a homogeneous material, it is also expected that the coordinate direction within this material has a great correlation with the mechanical properties. So, this study was conducted to confirm this correlation with the one between the mechanical properties and the stacking position. In particular, in this study, R-PUF of 3 different densities (130, 170, and 210 kg/m³) was used, and tensile, compression, and shear tests of this material were performed under 5 temperatures. As a result of the tests, it was confirmed that the strength and modulus of elasticity of the material increased as the temperature decreased. Specifically, the strength and modulus of elasticity in the Z direction, which was the lamination direction, tended to be lower than those in the other directions. Finally, the strength and elastic modulus of different specimens of the material found at the bottom of their lamination compared to the specimens with these properties found at positions other than their lamination bottom were evaluated. Further analysis confirmed that as the temperature decreased, hardening of R-PUF occurred, indicating that the strength and modulus of elasticity increased. On the other hand, as the density of R-PUF increased, a sharp increase in strength and elastic modulus of R-PUF was observed.