• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.746-751
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• 2001

We used a cylindrical model which simulates turbine blade leading edge to investigate the effects of free-stream turbulence intensity and blowing ratio on film cooling of turbine blade leading edge. Tests are carried out in a low-speed wind tunnel on a cylindrical model with three rows of injection holes. Mainstream Reynolds number based on the cylinder diameter was $7.1\times10^4$. Two types of turbulence grid are used to increase a free-stream turbulence intensity. The effect of coolant blowing ratio was studied for various blowing ratios. For each blowing ratios, wall temperatures around the surface of the test model are measured by thermocouples installed inside the model. Results show that blowing ratios have small effect on spanwise-averaged film effectiveness at high free-stream turbulence intensity. However, an increase in free-stream turbulence intensity enhances significantly spanwise-averaged film effectiveness at low blowing ratio.

• 전기학회논문지
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• 제64권12호
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• pp.1666-1672
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• 2015

Small islands are quite adequate places where microgrid system with renewable sources can replace diesel engines as operation costs of diesel engine in most small islands are very high. To get the large amount of renewable energy, the microgrid system has very large capacity of renewable sources. The system with large capacity of renewable sources can meet the case when supplied energy is greater than the load and the fluctuation of source output is very large. The battery energy storage system can be a solution to stabilize the system with large capacity of renewable sources. In this case, BESS can be utilized as a master source for the synchronous operation of all sources including diesel engine, wind turbine and PV. The diesel generators can be used as a backup in case the BESS SOC goes below a certain level. In this paper, we suggest a novel unit commitment of diesel generators and operation schedule of pump for water supply service with the information of wind forecast, PV forecast, and load forecast. The proposed methods has been implemented and tested at the test bed in Gasa-Island.

• 전기학회논문지
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• 제67권1호
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• pp.8-15
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• 2018

New methodology for probabilistic reliability based grid expansion planning of HVDC in power system including Wind Turbine Generators(WTG) is developed in this paper. This problem is focused on scenario based optimal selection technique to decide best connection bus of new transmission lines of HVDC in view point of adequacy reliability in power system including WTG. This requires two kinds of modeling and simulation for reliability evaluation. One is how is reliability evaluation model and simulation of WTG. Another is to develop a failure model of HVDC. First, reliability evaluation of power system including WTG needs multi-state simulation methodology because of intermittent characteristics of wind speed and nonlinear generation curve of WTG. Reliability methodology of power system including WTG has already been developed with considering multi-state simulation over the years in the world. The multi-state model already developed by authors is used for WTG reliability simulation in this study. Second, the power system including HVDC includes AC/DC converter and DC/AC inverter substation. The substation is composed of a lot of thyristor devices, in which devices have possibility of failure occurrence in potential. Failure model of AC/DC converter and DC/AC inverter substation in order to simulate HVDC reliability is newly proposed in this paper. Furthermore, this problem should be formulated in hierarchical level II(HLII) reliability evaluation because of best bus choice problem for connecting new HVDC and transmission lines consideration. HLII reliability simulation technique is not simple but difficult and complex. CmRel program, which is adequacy reliability evaluation program developed by authors, is extended and developed for this study. Using proposed method, new HVDC connected bus point is able to be decided at best reliability level successfully. Methodology proposed in this paper is applied to small sized model power system.

• 조명전기설비학회논문지
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• 제26권3호
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• pp.16-23
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• 2012

This paper relates to a study on the economic of electrical storage device for supplying power in sunless days, in the stand alone PV/Wind hybrid system, which it is applied to separate houses. In a photovoltaic/wind hybrid power system used in a separate house, when only the battery is used in sunless days, the capacity of the battery is become larger. For example, as in recent days, if cloudy days are frequent due to anomaly climate, it is difficult to supply power stably by only the battery based upon pre-estimated sunless days. Accordingly, in order to supply stably power of new renewable energy such as solar to any separate houses, it is preferable to reduce the capacity of battery by decreasing the number of sunless days when estimating the capacity of battery and to drive the small generator for compensation of the power shortage.

• KEPCO Journal on Electric Power and Energy
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• 제8권1호
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• pp.31-36
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• 2022

This paper presents the measuring process of dynamic properties of offshore wind power foundation and provides consideration of each step. This Guideline enables to maintain consistent measuring procedure and therefore increase the reliability of test results. Small scaled suction bucket foundation was fabricated to represent the commercial support structure installation mechanism and two cases(free-free, free-fixed) of dynamic tests were performed at workshop. From the tests, the importance of dynamic properties of connection part between suction bucket and tower was figured out. More over, types and configuration of measuring devices are recommended which can help find the natural frequency of wind turbine foundation correctly. In field test, it was found that the natural frequency of suction bucket foundation was increased linearly with the penetration depth due to the confining effect of ambient soil. Meanwhile, it was not easy to get an enough excitation force with normal impact hammer because the N.F of suction bucket model was in the lower range of 0 Hz ~ 5 Hz. Therefore, new excitation method which has enough force and can excite lower frequency range was devised. This study will help develop safety check procedure of suction bucket foundation in field at each installation stage using the N.F measurement.

• Earthquakes and Structures
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• 제10권5호
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• pp.1143-1179
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• 2016

Offshore wind turbines are considered as a fundamental part to develop substantial, alternative energy sources. In this highly flexible structures, monopiles are usually used as support foundations. Since the monopiles are large diameter (3.5 to 7 m) deep foundations, they result in extremely stiff short monopiles where the slenderness (length to diameter) may range between 5 and 10. Consequently, their elastic deformation patterns under lateral loading differ from those of small diameter monopiles usually employed for supporting structures in offshore oil and gas industry. For this reason, design recommendations (API and DNV) are not appropriate for designing foundations for offshore wind turbine structures as they have been established on the basis of full-scale load tests on long, slender and flexible piles. Furthermore, as these facilities are very sensitive to rotations and dynamic changes in the soil-pile system, the accurate prediction of monopile head displacement and rotation constitutes a design criterion of paramount importance. In this paper, the Fourier Series Aided Finite Element Method (FSAFEM) is employed for the determination of static impedance functions of monopiles for OWT subjected to horizontal force and/or to an overturning moment, where a non-homogeneous soil profile has been considered. On the basis of an extensive parametric study, and in order to address the problem of head stiffness of short monopiles, approximate analytical formulae are obtained for lateral stiffness $K_L$, rotational stiffness $K_R$ and cross coupling stiffness $K_{LR}$ for both rough and smooth interfaces. Theses expressions which depend only on the values of the monopile slenderness $L/D_p$ rather than the relative soil/monopile rigidity $E_p/E_s$ usually found in the offshore platforms designing codes (DNV code for example) have been incorporated in the expressions of the OWT natural frequency of four wind farm sites. Excellent agreement has been found between the computed and the measured natural frequencies.

• 한국추진공학회지
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• 제9권4호
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• pp.66-72
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• 2005

본 연구에서는 초음속 충동형 터빈의 유동특성을 알아보기 위해 소형 초음속 풍동을 설계하였으며 Single pass Schlieren system을 이용하여 유동을 가시화하였다. 실험은 2차원 초음속 노즐과 익렬을 조합하여 블레이드 앞전 형상과 노즐-익렬 간극에 따라 실시하였다. 실험을 통해 충격파를 포함한 복잡한 유동 형태와 노즐-익렬, 충격파-경계층 상호작용 등을 관찰할 수 있었다.

• 대한기계학회논문집
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• 제13권3호
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• pp.547-553
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• 1989

본 연구에서는 작동유체로서 수증기와 거동이 유사한 습공기를 대기 흡입식 풍동을 사용하여 원호 노즐로서 팽창시키는 경우에 대하여 응축충격파가 발생하는 흐름이 측정부내에 쐐기를 설치하여 발생시킨 경사충격파에 미치는 영향에 대해 실험적으로 조사하였다.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제3B권1호
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• pp.10-15
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• 2003

This paper presents the digital computer performance evaluations of the three-phase self-excited induction generator (SEIG) driven by the variable speed prime mover such as the wind turbine using the nodal admittance approach steady-state frequency domain analysis with the experimental results. The three-phase SEIG setup is implemented for small-scale rural renewable energy utilizations. The experimental performance results give a good agreement with those ones obtained from the digital computer simulation. Furthermore, a feedback closed-loop voltage regulation of the three-phase SEIG as a power conditioner which is driven by a variable speed prime mover employing the static VAR compensator (SVC) circuit composed of the thyristor phase controlled reactor (TCR) and the thyristor switched capacitor(TSC) is designed and considered herein for the wind-turbine driven the power conditioner. To validate the effectiveness of the SVC-based voltage regulator of the terminal voltage of the three-phase SEIG, an inductive load parameter disturbances in stand-alone are applied and characterized in this paper. In the stand-alone power utilization system, the terminal voltage response and thyristor triggering angle response of the TCR are plotted graphically. The simulation and the experimental results prove the effectiveness and validity of the proposed SVC which is controlled by the Pl controller in terms of fast response and high performances of the three-phase SEIG driven directly by the rural renewable energy utilization like a variable-speed prime mover.

• 대한기계학회논문집A
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• 제39권11호
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• pp.1183-1189
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• 2015

본 연구는 풍력발전기용 동력 전달부품의 테이퍼 연결장치 설계에 관한 것이다. 요구되는 전달토크의 크기, 동력을 전달하는 축의 직경, 테이퍼 링의 접촉면적 그리고 압축 면압을 부과하기 위한 볼트의 체결력 등이 테이퍼 연결장치 설계의 주요 변수이다. 테이퍼 연결의 계산은 축대칭 평면 변형률 조건의 복합링 구조로 가정하여 응력과 변형량을 계산 하였다. 축에 작용하는 면압은 요구 전달동력을 이용하여 계산하였고, 보강링에 작용하는 면압은 축과 허브의 변형량 일치 조건을 이용하여 계산하는 방법을 제안하였다. 복합링의 수식으로 구한 반경방향의 변형량으로 테이퍼 각도를 고려한 축방향 습동거리를 계산하였다. 수식으로 구한 응력과 상대습동거리의 타당성을 검증하기 위하여 유한요소해석을 수행하였으며 축방향의 하중이 발생하는 테이퍼면에서 원주방향의 응력이 최대 10% 수준의 오차를 보이고 있으나 그 외 응력분포와 상대습동거리는 수식적인 방법과 해석적인 방법이 일치함을 확인하였다.