• 한국공간구조학회논문집
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• 제13권3호
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• pp.83-90
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• 2013

A series of wind tunnel tests were conducted on 7 super-tall buildings with various polygon cross-sections, including triangle, square, pentagon, hexagon, octagon, dodecagon, and circular. The primary purpose of the present study is to investigate the effect of increasing number of sides on aerodynamic characteristics for super-tall buildings. Wind tunnel tests were conducted under the turbulent boundary layers whose power-law exponent is 0.27. Fluctuating wind pressures from more than 200 pressure taps were recorded simultaneously, and time series of overturning moments were calculated considering tributary area of each pressure tap. The results show that the overturning moment coefficients and the spectral values decrease with increasing number of sides, and the largest mean and fluctuating overturning moments were found for the triangular super-tall building, and the largest spectral values were found for the square super-tall building. The analysis should be conducted more in detail, but currently it can be roughly said that there seems to be a little differences in the aerodynamic characteristics for the super-tall buildings whose number of sides is larger than 5 or 6.

• Journal of Electrochemical Science and Technology
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• 제15권2호
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• pp.253-260
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• 2024

Proton exchange membrane water electrolysis (PEMWE) is an efficient method for utilizing renewable energy sources such as wind and solar powers to produce green hydrogen. For PEMWE powered by renewable energy sources, its durability is a crucial factor in its performance since irregular and fluctuating characteristics of renewable energy sources, especially for wind power, can deteriorate the stability of PEMWE. Triangular voltage cycle is well able to simulate fluctuating wind power, but its effect on the durability has not been investigated extensively. In this study, the performance degradation of the PEMWE cell operated with the triangular voltage cycling was investigated at different ramping rates. The measured current responses during the cycling gradually decreased for both ramping rates, and I-V curve measurements before and after the cycling confirmed the degradation of the performances of PEMWE. For both measurements, the degradation rate was larger for 300 mV s^-1 than 30 mV s^-1, and they were determined as 0.36 and 1.26 mV h^-1 (at the current density of 2 A cm^-2) at the ramping rates of 30 and 300 mV s^-1, respectively. The comparison with other studies on triangular voltage cycling also indicate that an increase in the ramping rate accelerates the deterioration of the PEMWE performance. X-ray photoelectron spectroscopy and transmission electron microscopy results showed that the Ir catalyst was oxidized and did not dissolve during the voltage cycling. This study suggests that the ramping rate of the triangular voltage cycling is an important factor for the evaluation of the durability of PEMWE cells.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2012년도 춘계학술대회
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• pp.833-836
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• 2012

최대수요전력 관리 장치는 현재 사용전력을 모니터링하여 예측 전력을 계산해 수용가에서 설정한 목표전력을 초과하지 않게 부하를 제어하는 장치이다. 부하의 제어는 예측된 최대수요전력이 목표전력을 초과할 경우 경보를 발생하고 부하를 차단하는 방식을 사용하기 때문에 최대수요전력에 대한 정확한 예측이 중요하다. 전력 변동이 심한 수용가에서는 기존의 예측 방법을 사용할 경우 최대수요전력 관리가 안정적이지 못하다는 단점이 있다. 본 논문에서는 기존의 최대수요전력 예측 방법 및 지수평활방법을 살펴보고 칼만 필터를 사용한 예측 방법을 제안한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.484_485
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• 2009

Power output of a wind farm fluctuates throughout a day. This affect a distance relay for wind farm intertie protection because a voltage of a relaying point varies due to fluctuating output of a wind farm. This paper describes the analysis of the response of a distance relay for intertie protection when the power output of a wind farm increases. A series of single phase to ground faults were also simulated and analyzed with PSCAD/EMTDC generated data.

• 전기학회논문지
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• 제67권1호
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• pp.22-28
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• 2018

In case of developing a combined system by a number of distributed resources with storage device, a number of application suggests a huge capacity can derive operational flexibility both power supply issues or when unexpected situation imposed. However, it is important to determine a resonable energy capacity because the device have many controversial cost issues in current power system industry. An ESS application which focusing essentially required points can induce appropriate storage capacity that required in economic operation. In this paper, a curtailment supporting algorithm based on storage device is introduced, and applied in the capacity calculation method. The main algorithm pursues handling minor exceeding quantities which can cause mechanical load at blade; This paper tries to include it for configuring hybrid algorithm with pitch control. Several fluctuating conditions are utilized in simulation to reflect critical situation. The analyzing process focuses on the control feasibility with applied capacity and control method.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.176.3-176
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• 2001

Hydraulic servo system has the characteristic of high power in itself, as combining its characteristics with excellent electro equipment that comes from the development of electronics, electro-hydraulic servo system is widely used in industry that are requested high precision and power Electro-hydraulic servo system is characteristic of very strong non-linearity in itself and it is mainly applied the field of the inner or outer fluctuating load or disturbance in industry. Evolutionary computation based on the natural evolutionary process may solve many engineering problems. Algorithms can represent the natural selection in crossovers, mutations, production of the offspring, selection, etc. Nature has already shown is the superiority through ...

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.373-376
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• 2002

The drift force acting on a floating OWC chamber in waves is studied taking account of fluctuating air pressure in the air chamber. A velocity potential in the water due to the free surface oscillating pressure patch is added to the conventional radiation-diffraction potential problem. The potential problem inside the chamber is formulated by making use of the Green integral equation associated with the Rankine Green function while the outer problem with the Kelvin Green function. The drift forces as well as the chamber motions are calculated taking account of the air pressure in the chamber.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1515-1521
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• 2007

In this paper, a unified regenerative inverter system for railway with DC line voltage simulator is proposed. In order to determine the operation characteristics of the regenerative inverter, the DC line voltage simulator is proposed. The DC line voltage simulator, which is based on the AC-DC PWM converter, varies the DC voltage according to the fluctuating voltage which is measured in the actual DC line. The suitable operating point of the regenerative inverter can be estimated from the simulation result. The regenerative inverter operates two modes. When the DC line voltage exceed the operating point, already set up, it works as regenerative inverter to return the excessive power of DC line to the grid. When the DC line voltage is under the operating point, it works as active power filter to compensate harmonic currents. In this paper, the control algorithm of the DC line voltage simulator and that of the regenerative inverter is proposed.

• Wind and Structures
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• 제27권2호
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• pp.111-121
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• 2018

Experiments were conducted in a large-scale Ward-type tornado simulator to study tornado-like vortices. Both flow velocities and the pressures at the surface beneath the vortices were measured. An interpretation of these measurements enabled an assessment of the mean flow field as well as the mean and fluctuating characteristics of the surface pressure deficit, which is a manifestation of the flow fluctuation aloft. An emphasis was placed on the effect of the aspect ratio of the tornado simulator on the characteristics of the simulated flow and the corresponding surface pressure deficit, especially the evolution of these characteristics due to the transition of the flow from a single-celled vortex to a two-celled vortex with increasing swirl ratio.

• Journal of Advanced Marine Engineering and Technology
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• 제28권2호
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• pp.309-314
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• 2004

The exhaust gas emission from marine diesel engines is one of the major environmental issues. The authors focus the use of photovoltaic energy for the electric power system on marine ships. This paper proposes an operation method of a photovoltaic/diesel hybrid generating system for a small ship in consideration of the fluctuating photovoltaic power due to solar radiation. The aim of the proposed operation method is to minimize the fuel consumption and storage capacity of the battery. The validity of the proposed control method is shown by the numerical simulation based on the experimental data of the photovoltaic system.