• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.18-21
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• 2004

A GFRP based composite blade was developed for a 750kW wind energy conversion system of type class I. The blade sectional geometry was designed to have a general shell-spar structure. The load cases specified in the IEC61400-1 international specification were considered. For withstanding all relevant extreme loads, the structural analysis for the complete blade was performed using a commercial FEM code. The static load carrying capacity, buckling stability, blade tip deflection and natural frequencies at various rotational speeds were evaluated to satisfy the strength requirements in accordance with the IEC61400-1 and GL Regulations. For designing a lightweight blade, the thickness and the lay-up pattern of the skin-foam sandwich structures were optimized iteratively using the DOT program T-bolts were used for joining the blade root and the hub, which were modeled using a 3D FE volume model. In order to confirm the safety of the root connection, the static stresses of the thick root laminate and the steel. bolts were predicted by taking account of the bolt pretension and the root bending moments. The calculated stresses were compared with the material strengths.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.301-304
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• 2001

Wind power generation system is one of the most useful energy resource using natural environment. One of the biggest problem we encountered is toot the wind speed is fluctuating sharply according to the weather conditions rather than it is stable. In this paper we do the equivalent modeling the mechanical energy of wind power turbine according to wind speed into the synchronous generator. We analyse the equivalent modeling output part of rectifier into DC/DC converter input part theoretically. We analyse a battery charging characteristics for power storage enabling the supply of stable power to the load. We design a system and do the modeling of it analytically so that it supplies a stable power to the load by constructing a DC-AC inverter point. Also we make a small size model usable in actual wind power generation system of 30kw and make an experiment and confirm its validity.

• 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.

• 한국소음진동공학회논문집
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• 제13권6호
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• pp.467-473
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• 2003

This paper describes the fluttering characteristics of the upper pad in a tilting pad journal bearing(6-pad, LOP type) using a steam turbine. In order to investigate the phenomena of the upper pad fluttering experimentally, the absolute vibration of the upper pads, the relative vibration between bearing and shaft and the circumferential distribution of the film thickness are measured under the different values of supply oil flow rate, shaft speed and bearing load. It can be known that the fluttering mechanism of the upper pads has a tendency of the self-excited vibration from the study of fluttering frequencies and amplitudes with the change of shaft speed. Furthermore, it is observed that the incipient upper pad fluttering velocity is increased by the increase of oil supply flow rate and the fluttering amplitude of the upper pads is increased by the decrease of the ell flow rate and by the increase of the bearing load.

• 플랜트 저널
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• 제17권3호
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• pp.34-36
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• 2021

기존의 중앙집중식 발전의 탈피와 에너지 전환 및 환경문제 인식에 의해 신재생에너지 기반의 분산발전시스템에 대한 관심이 증가하고 있다. 본 연구에서는 에너지저장장치로 납축전지를 사용하는 PV 및 WT 기반의 분산발전시스템을 모사하여 최적용량을 선정하였다. 기존 발전원으로 CHP를 채택하였으며 시스템의 최적용량은 기존발전원의 운전상황(전부하/부분부하)에 따라 MOGA를 통해 도출하였다. 또한 동일한 배터리 용량에서 배터리 충전방식이 달라지면 배터리의 수명이 달라지는 것을 확인하였다. 따라서 경제적이고 안정적인 전력수급을 위해서는 배터리 충전방식을 고려한 분산발전시스템의 용량선정이 수행되어야 한다.

• Geomechanics and Engineering
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• 제19권1호
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• pp.79-91
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• 2019

Renewed interest in the long-term pile foundations has been driven by the increase in offshore wind turbine installation to generate renewable energy. A monopile subjected to repetitive loads experiences an evolution of displacements, pile rotation, and stress redistribution along the embedded portion of the pile. However, it is not fully understood how the embedded pile interacts with the surrounding soil elements based on different pile geometries. This study investigates the long-term soil response around offshore monopiles using finite element method. The semi-empirical numerical approach is adopted to account for the fundamental features of volumetric strain (terminal void ratio) and shear strain (shakedown and ratcheting), the strain accumulation rate, and stress obliquity. The model is tested with different strain boundary conditions and stress obliquity by relaxing four model parameters. The parametric study includes pile diameter, embedded length, and moment arm distance from the surface. Numerical results indicate that different pile geometries produce a distinct evolution of lateral displacement and stress. In particular, the repetitive lateral load increases the global lateral load resistance. Further analysis provides insight into the propagation of the shear localization from the pile tip to the ground surface.

• 신재생에너지
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• 제20권2호
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• pp.17-25
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• 2024

In this study, the effect of the time step specified in a computational fluid dynamics (CFD) simulation on load response is analyzed and the drag coefficients of the floating body of floating offshore wind turbines (FOWTs) are estimated. By evaluating the error in the FOWT load response and the change in the drag-coefficient values based on the density of the time intervals, this study aims to establish a time-interval setting that minimizes the time and cost of CFD simulations for selecting drag-coefficient values. Practical CFD utilization strategies necessary for the calibration of medium-to high-fidelity analysis tools are presented. Based on a comparative analysis of CFD simulations conducted at various time intervals, the results confirmed that under a certain time interval that sufficiently considers various factors, the accuracy of the FOWT response with respect to density shows minimal differences, thereby providing an efficient utilization method for CFD simulations in FOWT design and analysis.

• Wind and Structures
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• 제18권2호
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• pp.117-134
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• 2014

It is believed that offshore wind farms may satisfy an increasing portion of the energy demand in the next years. This paper presents a comparative study of the fatigue performances of tripod and jacket steel support structures for offshore wind turbines in waters of intermediate depth (20-50 m). A reference site at a water depth of 45 m in the North Atlantic Ocean is considered. The tripod and jacket support structures are conceived according to typical current design. The fatigue behavior is assessed in the time domain under combined stochastic wind and wave loading and the results are compared in terms of a lifetime damage equivalent load.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.689-696
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• 2001

Exergetic and thermoeconomic analysis were performed for a 200kW Phosphoric Acid Fuel Cell(PAFC) plant which offers many advantage for cogeneration in the aspect of high electrical efficiency and low emission. This analytical study was based on the data obtained by in-field measurement of PC25 fuel cell plant to find whether this system is viable economically. For 100% load condition, the electrical efficiency and the unit cost of electricity are about 45% and 0.032 $/kWh respectively, which turn out to be much better than those for the 1000kW gas turbine cogeneration plant. Further, at lower loads, the unit costs of electricity and hot water increase slightly and consequently more economic operation is possible at any loads.

• Journal of Mechanical Science and Technology
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• 제17권4호
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• pp.469-476
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• 2003

Despite of considerable research results or uniaxial tension creep available for superalloys, few studies have been made on high temperature creep using the Initial Stram Method (ISM) In this paper, the real-time prediction of high temperature creep strength and creep lift for the nickel-based superalloy Udimet 720 (high-temperature and high-pressure gas turbine engine materials) was performed on round-bar type specimens under pure static load at the temperatures of 538$^{\circ}C$. 649$^{\circ}C$, and 704$^{\circ}C$. The predictive equation derived from the ISM in creep tests showed better reliability than those from LMP (Larson-Miller Parameter) and LMP-lSM (Larson Miller Parameter-Initial Strain Method) specially for long time creep prediction (10$^3$∼10$\^$5/h).