• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1442-1448
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• 2017

Recently, electric power systems have been operating with tight margins and have reached their operational limits. Many researchers consider a microgrid as one of the best solutions to relieve that problem. The microgrid is generally powered by renewable energies that are connected through power converters. In contrast to the rotational machines in the conventional power plants, the converters do not have physical rotors, and therefore they do not have rotational inertia. Consequently, a stand-alone microgrid has no inertia when it is powered by the only converter-based-generators (CBGs). As a result, the relationship between power and frequency is not valid, and the grid frequency cannot represent the power balance between the generator and load. In this paper, a superconducting flywheel energy storage system (SFESS) is applied to an inertia-free stand-alone (IFSA) microgrid. The SFESS accelerates or decelerates its rotational speed by storing or releasing power, respectively, based on its rotational inertia. Then, power in the IFSA microgrid can be balanced by measuring the rotor speed in the SFESS. This method does not have an error accumulation problem, which must be considered for the state of charge (SOC) estimation in the battery energy storage system (BESS). The performance of the proposed method is verified by an electromagnetic transient (EMT) simulation.

• The Korea Journal of Herbology
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• v.33 no.6
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• pp.1-8
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• 2018

Objectives : Herbal medicinal mixture (JMB) are consisted of Caryophylli Flos, Aucklandiae Radix and Angelicae Dahuricae Radix. Each of herbal medicines has studied on anti-oxidant effect. So this study was conducted to investigate efficacy and potency of JMB on anti-oxidation. Methods : The JMB was extracted at room temperature by 80% ethanol. And total polyphenol contents, total flavonoid contents in JMB ethanol extract were determined by colorimetric method. Also, DPPH, ABTS free radical scavenging capacity and reducing power of JMB ethanol extract were measured at 100, 500, 1000, $5000{\mu}g/m{\ell}$ concentrations by spectrometric assay. Positive control was used BHA (butylated hydroxyanisole). Results : The total polyphenol contents and total flavonoid contents of the extract were 55.38 mg/TAEg, 513.72 mg/RUEg, respectively. Also, DPPH free radical scavenging capacity and reducing power of JMB ethanol extract in treated concentrations (100, 500, 1000, $5000{\mu}g/m{\ell}$) increased dose dependently. In particular, DPPH free radical scavenging capacity of JMB ethanol extract at 500, 1000, $5000{\mu}g/m{\ell}$ was similar to positive control (BHA) at high concentration (50, $100{\mu}g/m{\ell}$). ABTS free radical scavenging capacity of JMB ethanol extract at 500, 1000, 5000 ug/ml was similar to BHA at high concentration (50, $100{\mu}g/m{\ell}$). Also, reducing power was showed that JMB ethanol extract at $5000{\mu}g/m{\ell}$ was similar to BHA at high concentration (50, $100{\mu}g/m{\ell}$). Conclusions : These results suggest that JMB ethanol extract has effects to scavenge free radicals. Therefore, JMB has potential and applicable benefits for development of materials and products to have anti-oxidation functions.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.2
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• pp.162-172
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• 2012

This paper presents a research about free piston linear engine (FPLE) fueled with hydrogen, in which, the numerical models are built to simulate the operation during the full stroke of the engine. Dynamic model, linear alternator model and thermodynamic model are used as the numerical models to predict piston velocity, in-cylinder pressure and electric power of FPLE. The spark timing and air gap length are changed to provide information for the prediction. Beside, the heat transfer problem is also investigated in the paper. The results of research are divided by two parts, including motoring mode and firing mode. The result of motoring mode showed that there is validation between simulation and experiment for volume and pressure in cylinder. For firing mode, by increasing spark timing, the velocity of piston, peak pressure and electric power also increase respectively. Beside, when increasing air gap length, the electric power increases accordingly while the motion of piston is not symmetric. The effect of heat transfer also observed clearly by reducing of the peak pressure, velocity of piston and electric power.

• Journal of electromagnetic engineering and science
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• v.14 no.4
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• pp.329-331
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• 2014

A simple realization of an alignment-free wireless power transmission (WPT) system is presented in this letter. The WPT system consists of a transmitter with three reconfigurable modes corresponding to various controllable magnetic field directions in the azimuthal plane and an algorithm for the optimum mode selection carried by sensing the reflected voltage of the system. Twelve light emitting diodes (LEDs) are used to confirm the on- and off-state of LEDs powered wirelessly by the transmitter at every $15^{\circ}$ of the azimuthal plane. A criterion voltage from the reflected power of the system is found by using the correlation between the reflected voltage and the on- and off-state of the LEDs. Simply by continuous; monitoring of the voltage from the system, the system maintains power to the LEDs. The system is realized by MATLAB/Simulink and a National Instrument data acquisition device (DAQ) board. Measurements using the system show on-state LEDs in the azimuthal plane except at the angles of $60^{\circ}$, $75^{\circ}$, $180^{\circ}$, and $300^{\circ}$.

• 한국초전도학회:학술대회논문집
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• v.16
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• pp.89-89
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• 2006

• 한국초전도학회:학술대회논문집
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• 2009.07a
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• pp.90-90
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• 2009

• Proceedings of the Korea Information Processing Society Conference
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• 2012.11a
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• pp.304-306
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• 2012

유비쿼터스 환경에서의 무선 센서 네트워크에는 수많은 소형 센서 노드들이 넓은 지역에 분포하는 관계로 센서노드들에 대한 지속적인 전력공급이 가장 큰 문제 중 하나로 인식되고 있다. 본 논문에서는 무선센싱에 있어 전력자체수급 방식에 의한 상시 초저전력 센싱과 무선통신을 커버할 수 있는 연구결과에 대하여 기술한다.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2699-2708
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• 2020

Helical-coil steam generator (HCSG) technology is a major design candidate for small modular reactors due to its compactness and capability to produce superheated steam with high generation efficiency. In this paper, we investigate the feasibility of the passively autonomous power maneuvering by coupling the 3-D transient multi-physics of a soluble-boron-free (SBF) core with a time-dependent HCSG model. The predictor corrector quasi-static method was used to reduce the cost of the transient 3-D neutronic solution. In the numerical system simulations, the feedwater flow rate to the secondary of the HCSGs is adjusted to extract the demanded power from the primary loop. This varies the coolant temperature at the inlet of the SBF core, which governs the passively autonomous power maneuvering due to the strongly negative coolant reactivity feedback. Here, we simulate a 100-50-100 load-follow operation with a 5%/minute power ramping speed to investigate the feasibility of the passively autonomous load-follow in a 450 MW_th SBF PWR. In addition, the passively autonomous frequency control operation is investigated. The various system models are coupled, and they are solved by an in-house Fortran-95 code. The results of this work demonstrate constant steam temperature in the secondary side and limited variation of the primary coolant temperature. Meanwhile, the variations of the core axial shape index and the core power peaking are sufficiently small.

• Geomechanics and Engineering
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• v.16 no.1
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• pp.1-9
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• 2018

In this paper an efficient and simple refined shear deformation theory is presented for the free vibration of Functionally Graded Plates Under Various Boundary Conditions. The theory accounts for a quadratic variation of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. The number of independent unknowns of present theory is four, as against five in other shear deformation theories. The plates are considered of the type having two opposite sides simply-supported, and the two other sides having combinations of simply-supported, clamped, and free boundary conditions. The mechanical properties of functionally graded material are assumed to vary according to power law distribution of the volume fraction of the constituents. Equations of motion are derived using Hamilton's principle. The results of this theory are compared with those of other shear deformation theories. Various numerical results including the effect of boundary conditions, power-law index, plate aspect ratio, and side-to-thickness ratio on the free vibration of FGM plates are presented.

• Journal of computational fluids engineering
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• v.7 no.3
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• pp.44-52
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• 2002

An analytic methodology was developed for free surface motions between liquid metal coolant and cover gas in order to calculate the phenomena of gas entrainment in hot pool surface through IHX EMP and reactor core. The methodology was setup by applying the first order VOF convection model to CFX4 general purpose fluid dynamics analysis code. The methodology was validated by applying it to an experimental apparatus designed for free surface motions of KALIMER reactor. The distributions of free surface calculated by the present methodology were almost coincident with the experimental data. The developed methodology was applied to the KALIMER reactor of full power operating condition. The shapes of the free surface were nearly uniform. From the results, it was found that the altitude of the free surface from the IHX inlet nozzle of KALIMER reactor is high enough not to affect to free surface motions of generating gas bubbles from the turbulent shear flows such as hydraulic jump and water falls.