• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.4
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• pp.739-749
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• 2015

A new conceptual dual-buoy Wave Energy Converter (WEC) for the enhancement of energy extraction efficiency is suggested. Based on actual wave data, the design process for the suggested WEC is conducted in such a way as to ensure that it is suitable in real sea. Actual wave data measured in Korea's East Sea (position: $36.404N^{\circ}$ and $129.274E^{\circ}$) from May 1, 2002 to March 29, 2005 were used as the input wave spectrum for the performance estimation of the dual-buoy WEC. The suggested WEC, a point absorber type, consists of two concentric floating circular cylinders (an inner and a hollow outer buoy). Multiple resonant frequencies in proposed WEC affect the Power Ttake-off (PTO) performance of the WEC. Based on the numerical results, several design strategies are proposed to further enhance the extraction efficiency, including intentional mismatching among the heave natural frequencies of dual buoys, the natural frequency of the internal fluid, and the peak frequency of the input wave spectrum.

• Journal of Power Electronics
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• v.15 no.2
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• pp.356-365
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• 2015

This paper presents a new single phase front-end ac-dc bridgeless power factor correction (PFC) rectifier topology. The proposed converter achieves a high efficiency over a wide range of input and output voltages, a high power factor, low line current harmonics and both step up and step down voltage conversions. This topology is based on a non-inverting buck-boost (Zeta) converter. In this approach, the input diode bridge is removed and a maximum of one diode conducts in a complete switching period. This reduces the conduction losses and the thermal stresses on the switches when compare to existing PFC topologies. Inherent power factor correction is achieved by operating the converter in the discontinuous conduction mode (DCM) which leads to a simplified control circuit. The characteristics of the proposed design, principles of operation, steady state operation analysis, and control structure are described in this paper. An experimental prototype has been built to demonstrate the feasibility of the new converter. Simulation and experimental results are provided to verify the improved power quality at the AC mains and the lower conduction losses of the converter.

• Journal of Powder Materials
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• v.28 no.5
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• pp.417-422
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• 2021

In the present work, Inconel 718 alloy is additively manufactured on the Ti-6Al-4V alloy, and a functionally graded material is built between Inconel 718 and Ti-6Al-4V alloys. The vanadium interlayer is applied to prevent the formation of detrimental intermetallic compounds between Ti-6Al-4V and Inconel 718 by direct joining. The additive manufacturing of Inconel 718 alloy is performed by changing the laser power and scan speed. The microstructures of the joint interface are characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and micro X-ray diffraction. Additive manufacturing is successfully performed by changing the energy input. The micro Vickers hardness of the additive manufactured Inconel 718 dramatically increased owing to the presence of the Cr-oxide phase, which is formed by the difference in energy input.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.4_2
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• pp.491-499
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• 2021

Batteries are widely used for energy storage, such as ESS(Energy Storage System), electric vehicles, electric aircraft, and electric powered ships. Among them, a submarine uses a high power battery for an energy storage. When the battery of a submarine is discharged, a diesel generator generates AC power, and then AC/DC power converter change AC power to DC power for charging the battery. Therefore, in order to lower the current capacity of the diesel generator, it is necessary to use an AC/DC converter with a high input power factor. And, a power converter with a large power capacity must have high stability because it can lead to a major accident when a failure occurs. However, the control algorithm using the traditional PI controller is difficult to satisfy stability and dynamic characteristics. In this paper, we design the high power AC/DC converter with high input power factor for battery charging systems. And, we propose a stable control algorithm. The validity of the proposed method is verified through simulation and experiments.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.14 no.4
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• pp.61-67
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• 2018

Solar energy depends on the altitude and azimuth of the sun, and the amount of energy collected on the slope depends on the latitude of the area being installed. However, since most solar heating systems are fixed to the ground, it is necessary to analyze the optimal installation angle from the early design stage. However, problems arise when energy consumption is not considered together because heating systems are not used in the summer In this study, the optimum installation angles of the solar collectors according to the latitude of the installation area are not simply determined by the amount of energy collected, but because the system is overheated due to climate change or energy usage patterns, And the amount of additional energy input.

• Journal of the Korean Institute of Gas
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• v.20 no.4
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• pp.7-14
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• 2016

The economic crisis in North Korea has reduced its capacity to invest in the energy industries. The country is going through a vicious cycle of decreased investment in the energy industries and reduced energy production. This suggests that the energy industries would come to the top priority of investment once the economy improves. This paper calculated the economic ripple effect of the investment on North and South Korean economies based on the assumption that 390 billion won was invested in the construction of a natural gas combined-cycle power plant in Gaesong Industrial Complex. In order to analyze the economic ripple effect of the investment on North Korean economy, we constructed the inter-industry relation table of North Korea for year 2014 and used the input-output model. The ripple effect of the investment in the natural gas industry turned out to be 1.012 billion dollars. In order to analyze the effect of the investment on South Korean economy, we constructed the inter-industry relation table of South Korea for year 2013 and used the demand-driven model for inter-industry analysis. As a result, production, added-value and employment inducement coefficients of the investment in the natural gas industry were calculated as 2.02073, 0.62697 and 8.99409 respectively.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.4
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• pp.283-296
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• 2008

The numerical simulations for groundwater flow were carried out to support the input parameters for safety assessment in LILW repository site. As the input parameters for safety assessment, the groundwater flux into the underground facilities during construction, flow rate through the disposal silo after closure of disposal silo and flow pathway from the disposal silo to discharge area were analyzed using the 10 cases groundwater flow simulations. From the total 10 numerical simulation results, the statistics of estimated output were similar to among 10 cases. In some cases, the analyzed input parameters were strongly governed by locally existed high permeable fracture zone at radioactive waste disposed depth. Indeed, numerical simulation for well scenario as a human intrusion scenario was carried out using the hydraulically severe case model. Using the results of well scenario, the input parameters for safety assessment were also obtained through the numerical simulation.

• Journal of Energy Engineering
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• v.25 no.4
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• pp.214-225
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• 2016

Gasification is one of the important contribution to resource recycling by conversion of biomass to a variety of energy sources such as alcohol, SNG etc., and to global warming prevention by reduction of green house gases such as $CO_2$. The aim of this study is to draw the optimal operation condition of dual fluidized-bed gasifier with biomass fuel, to verify SNG production efficiency and to establish the basis for the domestic commercialization of dual fluidized bed gasification. As a result, dual fluidized-bed gasifier has the optimal conditions at $826^{\circ}C$ with steam input 1,334 g/hr, air input 5.56 L/min. The carbon conversion is 81% and SNG production efficiency was $CH_4$ 92%.

• Journal of Hydrogen and New Energy
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• v.24 no.6
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• pp.535-542
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• 2013

To enhance the performance of SEWGS system by holding the WGS catalyst in a SEWGS reactor using bed inserts, effect of bed insert geometry on CO conversion of WGS catalyst was measured and investigated. Small scale fluidized bed reactor was used as experimental apparatus and tablet shaped WGS catalyst and sand particle were used as bed materials. The cylinder type and the spring type bed inserts were used to hold the WGS catalysts. The CO conversion of WGS catalyst with the change of steam/CO ratio was determined based on the exit gas analysis. Moreover, gas flow direction was confirmed by bed pressure drop measurement for each case. The measured CO conversion using the bed inserts showed high value comparable to previous results even though at low catalyst content. Most of input gas flowed through the bed center side when we charged tablet type catalyst into the cylinder type bed insert and this can cause low $CO_2$ capture efficiency because the possibility of contact between input gas and $CO_2$ absorbent is low in this case. However, the spring type bed insert showed good reactivity and good distribution of gas, and therefore, the spring type bed insert was selected as the best bed insert for SEWGS process.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.4
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• pp.520-526
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• 2006

Wave Energy is a derivative of the solar energy input to the earth, which is accumulated on open water surfaces by the action of the winds Waves are disturbances in the water surface. This paper is interested primarily in progressive waves, which carry energy from one place to another Waves are irregular in size and frequency. Moreover the surface of the sea is one of the most hostile environments for engineering structures and materials. The idea of harnessing the tremendous power of the ocean's waves is not new. Hundreds of wave energy conversion techniques have been suggested over the last two centuries. Although many WECS (Wave Energy Conversion Systems) have been invented, only a few systems have been tested and evaluated. This paper describes the characteristic of WES (Wave Energy System) in terms of, devices, resource and potential, etc.. Finally, this paper provides a summary of general and specific conclusions and recommendations concerning WECS potential in Korea.