• Composites Research
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• v.32 no.6
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• pp.307-313
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• 2019

Triboelectric nanogenerators (TENGs), which are combined effects of triboelectricity and electric induction, is a large-area and low-cost technology that can be applied easily in our life. In this work, we applied life supplies to TENGs and analyzed a type of chemical bonding with the ratio of C-C/C-H/C-O/C=O bonding. As the ratio of C-C bonding increases, the materials can be positively charge. On the other hands, as the ratio of C-H bonding increases, the materials can be negatively charged materials. Based on these behaviors, we got a voltage of 210V, a current of 14.6 ㎂ and a maximum power of 9.8mW. Finally, we could turn on 97 light emitting diodes (LEDs) by using a wrap as a negative material and a magnetic note as a positive material.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.2
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• pp.123-132
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• 2015

In this study, an arrangement design process for multiple wind turbines, placed on the 10MW class floating wave-offshore wind hybrid power generation system, was presented, and the aerodynamic performance was evaluated by using a computational fluid dynamics. An arrangement design, which produces a maximum power in the site wind field, was found by using a commercial program, WindPRO, based on a blade element momentum theory, then the effect of wake interference on the system between multiple wind turbines was studied and evaluated by using ANSYS CFX.

• Electrical & Electronic Materials
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• v.10 no.4
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• pp.327-333
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• 1997

Experiments on mechanical fatigue were conducted using the specimens which were cut from hydrogen cooled generator(rated 22kV and 50OMW) stator windings. We have investigated the aged mechanism of mica/epoxy insulation systems under air or hydrogen by both the tensile and compressive loadings. The fracture of generator stator windings is generally affected by mechanical stress. Thus, the tensile strength test were conducted. In this case, the maximum strength and strain are quite different between sound and aged specimens. It is observed that low bonded interface parts of tapes generally have lower strength than those of normal tapes which causes stress. In order to estimate the effects of cyclic load by the electromagnetic forces while the generator starts/stops, the mechanical fatigue test was also conducted. It is confirmed that the equation of expected life depends on stress amplitude and number of cycles. Though the stress amplitude and number of cycles are very tiny, the tensile fatigue of aged specimens under hydrogen atmosphere is bigger than those under air. In the case of hydrogen atmosphere, the tensile stress gives bigger effect than the compressive one.

• Environmental and Resource Economics Review
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• v.25 no.1
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• pp.113-140
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• 2016

Achieving the two goals of providing stable remuneration and promoting market based incentive for generation capacity with only one kind of capacity price is a difficult proposition. This paper suggests a market design in which two different kinds of capacity prices are used to achieve these goals. It maintains the current capacity price that is determined administratively based on the fixed cost of the gas-turbine generator. A second capacity price is added that covers generators with higher fixed costs and lower fuel costs such as combined-cycle gas turbine, coal-powered, and nuclear generators. This second capacity price is conditional on a lower energy price ceiling and determined by the interaction of the market supply and a demand schedule derived from the optimal fuel mixed principle.

• Journal of Korean Society of Forest Science
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• v.108 no.3
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• pp.429-439
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• 2019

The objectives of this study were to gauge the extent of the forestry business through establishing the definition of forestry industry from the perspective of economic convergence and to analyze key components that affect each growth phase of a forestry business entity by classifying them. A total of 1,397 "sixth-sector industry" management entities were certified by the Ministry of Agriculture, Food, and Rural Affairs in South Korea from 2012-2017. Of these, 259 (18.5%) were in the forestry sector. In this study, the 259 forestry management entities were further classified into three phases based on sales distribution: entrance, development, and maturity. The entrance phase (<100 million KRW), development phase (>100 million and <1 billion KRW), and maturity phase (>1 billion KRW) constituted 33.2%, 55.4%, and 12.4% of the total 259 entities, respectively. The results showed that most of the management entities were either in the entrance or development phases, and only a small portion was in the maturity phase. To identify the key variables that affect each of the phases, chi-square analysis was used. We designed the "sixth-sector industry" type as an independent variable, whereas selected region, business organization, manager age group, forest product, processing type, and service type were designated as dependent variables. The results of the analysis showed that the processing and service types influenced all three developmental phases. Moreover, as the phase advanced, processing type showed a higher proportion of health-functional ingredients, such as powder or extract from forest products, which enable to develop and produce a variety of products. Service type also changed from simple experience to integrated experience tourism and finally to tourism education. Distribution and sales channel also turned out to be a significant factor during the development phase. This study provides the basic information needed to guide government support in the implementation of a formal forestry business through convergence as well as to increase the efficiency of business management.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.4
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• pp.382-390
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• 2011

Smart sensors embedable in composite wind turbine blades have been required to be researched for monitoring the health status of large wind turbine blades during real-time operation. In this research, the feasibility of packaged FBG sensor probes was studied through the experiments of composite blade trailing edge specimens in order to detect cracking and debonding damages. The instants of cracking and debonding generated in the shear web were confirmed by rapid changes of the wavelength shifts from the bare FBG sensor probes. Packaged FBG sensor probes were proposed to remove the fragile property of bare FBG sensor probes attached on composite wind blade specimens. Strain and temperature sensitivity of fabricated probes installed on the skin of blade specimen were almost equal to those of a bare FBG sensor. Strain sensitivity was measured to be ${\mu}{\varepsilon}$/pm in a strain range from to 0 to 600 ${\mu}{\varepsilon}$, and the calculated temperature sensitivity was to be 48 pm/$^{\circ}C$ in the heating test up to 80 degree.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.66-75
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• 2018

In this paper, a lightweight design of the spar cap of 2MW wind turbine blade was carried out using the ply reduction ratio (PRR) and CFRP with a trade-off study. The spar cap is one of the most critical factor in determining the mechanical performance of the blade. Tsai-Wu and Puck fracture theory were used to determine the fracture. As a result, the CFRP composite material could be lighter in terms of weight by about 30% than GFRP composite material under the same conditions. Based on the analytical results, we derive the optimal value of the laminate thickness of the composite material and present the structural performance improvement and the lightweight design result.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.6
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• pp.2739-2746
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• 2011

This paper proposes the method for more effectively calculating X/R which is the ratio of equivalent reactance(X) and resistance(R) of the bulk power system and analyses the characteristic of X/R values by applying the proposed method to the real bulk power systems. X/R is used to determine the rating of the relay in the bulk power systems and its value has been accepted to be big enough to ignore the equivalent resistance of the bulk power systems. However, X/R is calculated as a big number when only the upper transformer and transmission line are considered. The correct approach to calculating X/R needs to consider all the parameters including generators, transformers, lines and loads. This paper calculates X/R of the bulk power systems using dynamic models which have been used to analyse the power system stability. The effectiveness of the proposed method is verified by applying it to the test system and X/R values of the real bulk power systems are analyzed. In addition, the dependence of X/R on the closeness of its calculating locations to the generator is verified by using the marginal loss factor which has been used in the electricity market.

• Composites Research
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• v.29 no.6
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• pp.369-374
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• 2016

In this study, a structural optimal design of 10 MW composite blade was performed using bend-twist coupled(BTC) design concept. Bend-twist coupling of blade means the coupling behavior between the bending and torsional deflections due to the composite lamina with fiber angle biased from the blade longitudinal axis. This can potentially improve the overall performance of composite blade and reduce the dynamic loading. Parametric studies on layup angle, thickness and area of off-axis carbon UD were conducted to find the optimum coupling effect with weight reduction. Comparing the results of fatigue load analysis between conventional model and BTC applied model, the damage equivalent load(DEL) of blade root area were decreased about 3% in BTC model. To verify the BTC effect experimentally, a 1:29 scaled model was fabricated and the torsion at the tip under deflection behavior of blade stiffener model was measured by static load test.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.2
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• pp.147-155
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• 2012

Wind power, which is one of the promising renewable energies, has shown the high growth rate of 35 % of the annual average in the recent 5 years and also windmill related equipment market has been fast-growing. Yaw & Pitch bearing are the key parts of windmill and are machined by huge vertical lathe which is monopolized by the advanced countries. The purpose of this study is to develop the multi-tasking vertical lathe for 5 MW grade windmill bearings, which might be mass produced 3 or 5 years later. In this study, the structure of the crossrail and rotary table, which are the key units of the huge multi-tasking vertical lathe, were optimized through the finite element analysis. Also the basic performance of the rotary table has been evaluated.