• Journal of the Korea Convergence Society
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• v.2 no.2
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• pp.47-56
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• 2011

Korea Ministry of Knowledge Economy has estimated that wind power (WP) will be occupied 37% in 2020 and 42% in 2030 of the new energy sources, and also green energies such as photovoltaic (PV) and WP are expected to be interconnected with the distribution system because of Renewable Portfolio Standard (RPS) starting from 2012. However, when a large scale wind power plant (over 3[MW]) is connected to the traditional distribution system, protective devices (mainly OCR and OCGR of re-closer) will be occurred mal-function problems due to changed fault currents it be caused by Wye-grounded/Delta winding of interconnection transformer and %impedance of WP's turbine. Therefore, when Double-Fed Induction Generator (DFIG) of typical WP's Generator is connected into distribution system, this paper deals with analysis three-phase short, line to line short and a single line ground faults current by using the symmetrical components of fault analysis and PSCAD/EMTDC modeling.

• Journal of the Korean GEO-environmental Society
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• v.16 no.5
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• pp.55-66
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• 2015

Big tidal differences, which range from 3.0 m to 8.0 m, exist with regional locations at south and west shores of Korea. Under this ocean circumstance, since a large scour may occur due to multi-directional tidal current and transverse stress of the wind, the scour surrounding the wind turbine structure can make instability of the system due to unexpected system vibration. The hydraulic resistance capacity of soils consolidated under different pressures are evaluated by Erosion Function Apparatus (EFA) under unidirectional and bi-directional flows in this study. It was found that the flow direction change affects significantly on the sour rate and critical shear stress, regardless of soil types while the consolidation pressure affects mainly cohesive soil. Among geotechnical parameters, the undrained shear strength can be well-correlated with the hydraulic resistance capacity, regardless soil type while the shear wave velocity shows the proportional relationships with the hydraulic resistance capacities of fine grained soil and coarse grained soil, respectively.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.5
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• pp.375-387
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• 2023

The subsea power cables are increasingly important for harvesting renewable energies as we develop offshore wind farms located at a long distance from shore. Particularly, the continuous flexural motion of inter-array dynamic power cable of floating offshore wind turbine causes tremendous fatigue damages on the cable. As the subsea power cable consists of the helical structures with various components unlike a mooring line and a steel pipe riser, the fatigue analysis of the cables should be performed using special procedures that consider stick/slip phenomenon. This phenomenon occurs between inner helically wound components when they are tensioned or compressed by environmental loads and the floater motions. In particular, Vortex-induced vibration (VIV) can be generated by currents and have significant impacts on the fatigue life of the cable. In this study, the procedure for VIV fatigue analysis of the dynamic power cable has been established. Additionally, the respective roles of programs employed and required inputs and outputs are explained in detail. Demonstrations of case studies are provided under severely sheared currents to investigate the influences on amplitude variations of dynamic power cables caused by the excitation of high mode numbers. Finally, sensitivity studies have been performed to compare dynamic cable design parameters, specifically, structural damping ratio, higher order harmonics, and lift coefficients tables. In the future, one of the fundamental assumptions to assess the VIV response will be examined in detail, namely a narrow-banded Gaussian process derived from the VIV amplitudes. Although this approach is consistent with current industry standards, the level of consistency and the potential errors between the Gaussian process and the fatigue damage generated from deterministic time-domain results are to be confirmed to verify VIV fatigue analysis procedure for slender marine structures.

• Journal of Navigation and Port Research
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• v.38 no.1
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• pp.39-44
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• 2014

Due to the oil price is increasing continuously, active researches on sources of renewable energy has been invigorated. Above all, ocean energy has high-usability because of ocean current has high density and large quantity compared to the wind energy. In this paper, efficiency enhancement of the wave power generation was described through horizontal plate installation at the break water wave power generation system that converts the ocean energy into electricity. The power-conversion efficiency can be improved by horizontal plate installation at existing system, but there has been insufficient studies domestically. The purpose of this paper is to analyze about the effects of the horizontal plate installation on the breakwater wave power generation system by wave basin experiment and to propose a position of horizontal plate installation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.4
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• pp.277-282
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• 2018

In this study, the accuracy and efficiency of a composite rotor blade cross-section analysis program, Ksec2d-AE, which is available at an educational web-based platform called EDISON-CSD, are assessed for possible use in undergraduate structural analysis projects. To this purpose, the convergence of cross-sectional constants by varying the number of finite elements in the cross-section of a wind turbine blade is investigated. The stiffness constants along with the cross-sectional engineering offsets obtained using Ksec2d-AE are validated against a 3D finite element analysis program MSC NASTRAN.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.337-342
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• 2016

A spudcan is mounted on the lower leg of the jack-up rig, a device for preventing a rollover of a structure and to support the structure in a stable sea floor. At the time of inserting the surface of the spud can to penetrate when the sand layer is stable and smoothly pulled to the clay layer, and at that time of recovery when uploading the spud can is equipped with a water injection device. In this study, it is significant to optimize the shape of pipelines holes for water injection device and it was set in two kinds of shape, the oval and round. Interpretation of the subject into the site of Gulf of Mexico offshore Wind Turbine Installation Vessels (WTIV) was chosen as a target platform. Using the ANSYS Workbench commercial programs, optimal design was conducted. The results of this study can be applied to the hole-shaped design of various marine structures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.316-328
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• 1997

There were appreciable progresses on the study of shock wave / boundary layer interaction control in the transonic flow without nonequilibrium condensation. But in general, the actual flows associated with those of the airfoil of high speed flight body, the cascade of steam turbine and so on accompany the nonequilibrium condensation, and under a certain circumstance condensation shock wave occurs. Condensation shock wave / boundary layer interaction control is quite different from that of case without condensation, because the droplets generated by the result of nonequilibrium condensation may clog the holes of the porous wall for passive control and the flow interaction mechanism between the droplets and the porous system is concerned in the flow with nonequilibrium condensation. In these connections, it is necessary to study the condensation shock wave / boundary layer interaction control by passive cavity in the flow accompanying nonequilibrium condensation with condensation shock wave. In the present study, experiments were made on a roof mounted half circular arc in an indraft type supersonic wind tunnel to evaluate the effects of the porosity, the porous wall area and the depth of cavity on the pressure distribution around condensation shock wave. It was found that the porosity of 12% which was larger than the case of without nonequilibrium condensation produced the largest reduction of pressure fluctuations in the vicinity of condensation shock wave. The results also showed that wider porous area, deeper cavity for the same porosity of 12% are more favourable "passive" effect than the cases of its opposite. opposite.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.4
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• pp.527-536
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• 2014

In this paper, the 50kW aerogenerator which is applicable to the microgrid was designed and analyzed by using commercial simulation program Maxwell 2D. Particularly, the suggested PMSG to reduce the cogging torque introduced the offset and skew concept. The suggested optimal value of offset and skew was decided by 2mm and 60 degree of electric angle. The simulation results of the PMSG when load operation condition showed the average harmonic distortion 1.3%, voltage 322.41V, current 94.95A, and iron loss 9.73W, eddy current loss 73.68W, copper loss 3.52kW. The capacity of aerogenerator calculated 61.56kW, and the suggested design process can be applied to higher capacity generator.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.163-163
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• 2011

풍력타워 기둥구조물에는 유지관리 등의 이유로 출입구 역할을 하는 개구부가 존재하게 된다. 다각형 타워구조물에 개구부형상이 존재하게 되면 압축좌굴 강도에 영향이 있을 것으로 예상되지만, 이를 정량적으로 평가하거나 예측하기는 용이하지 않고 간접적으로 판단할 만한 관련 기준이나 지침도 부족한 상태이다. 이에 최병호 등(2011)에서 다룬 다각형 단면 기둥구조물의 하단에 개구부를 형상화한 수치해석 모델을 수립하고 축방향 압축하중을 재하하는 탄성좌굴 해석 및 비선형비탄성해석을 수행하였다. 본 논문에서는 기존 다각형 단면 기둥모델 중에서 6각형 단면모델에 관해 중점적으로 다루고 있다. 다각형 단면 기둥 해석모델은 단순한 다각형 단면 타워구조에 대해서 뿐 만 아니라, 각 subpanel에 종방향 보강재를 둔 모델에 대해서도 추가적으로 검토하였다. 개구부의 형상은 높이 2000mm, 폭 800mm이며 상하부에 만곡부를 둔 형태이다. 수치해석은 3차원 유한요소해석프로그램인 ABAQUS를 이용하여 수행하였으며, 보강방안으로는 일정범위까지의 모듈 subpanel의 판두께를 보강하는 방안과 edge stiffener를 적용하는 방안에 대해서 검토하였다. 각각의 보강방식에 따른 효과를 비교해 보기 위해 개구부가 없는 모델, 단순히 개구부만 설정한 모델, 판두께를 보강한 모델, edge stiffener로 보강한 모델에 대해 비교해석을 수행하였다. 보강재 없는 단순 다각형 타워구조 모델에 대한 해석결과로부터 개구부로 인한 강도저하는 미미한 수준인 것으로 나타났다. 반면, 종방향 보강재가 적용된 6각형 단면 타워구조 모델에서는 개구부로 인한 강도저감이 22.9%로 높게 나타났으며 상당한 영향이 있는 것으로 분석되었다. 또한 개구부 주변의 판두께 보강이나 edge stiffener보강 등으로 상당한 강도향상 효과가 확인되었으나, 개구부로 인해 손실된 강도 수준을 완전히 회복하는 수준에 미치지 못하는 것으로 나타났다. 따라서, 향후 다양한 보강방식에 대한 보다 포괄적인 변수연구를 통해 개구부의 영향 없이 온전한 다각형 단면 타워 구조의 극한강도에 도달되기 위한 보강 조건에 대해 검토될 필요가 있을 것으로 사료된다.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.5
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• pp.389-395
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• 2017

This paper showed the difference in the optimum conditions by using the ANSYS CFX simulation program with the changes of the main-blade angle and sub-blade angle. Main-blade Shape 4,which had angle $45^{\circ}$ while other Shapes with angle $0^{\circ}$, was increased to 157.2[%] to 263.2[%] in the power and was increased to 110[%] to 250[%] in the power coefficient. Moreover, when the Shape 5 Fin length of main-blade doubled, the power was 70.8[%] when compared with Shape 1 and 27.5[%] with shape 4.If the main-blade geometry equals shape 1 in the case structure, The power of Case1 was increased to 13.3[%] when compared with Case2. Also, the power coefficient was increased to 15.4[%]. When sub-blade angle was $45^{\circ}$, main-blade was better than the Fin type than the Bended type. The power of Case4 was increased to 47[%] when compared with Csae1 and increased to 13.6[%] with Case 3. Also, the power coefficient was 46.7[%] when compared with Case 1 and 15.8[%] with Case 3.