• Proceedings of the KSME Conference
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• 2008.11a
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• pp.560-564
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• 2008

풍력발전에 사용하는 풍력터빈의 블레이드의 적어도 20년 이상의 설계수명이 요구된단. 블레이드는 바람에 의한 압력, 지지대 구조에 의해서 가해지는 힘과 모멘트에 의해 블레이드에 변형이 가해진다. 특히 바람에 의해 블레이드는 연속적인 하중을 받아서 재료를 손상시킨다. 본 연구에서는 블레이드와 허브로 구성된 모델을 이용하여, 전산유체해석을 일차적으로 수행하여 블레이드 주변의 압력분포를 구하였다. 계산된 압력을 이용하여 다음 단계로 유한요소해석을 수행하여 블레이드 재료에 발생하는 응력을 계산하여 피로해석을 수행하였다. 피로해석을 통해 재료에 미치는 손상률을 구하였다. 다양한 블레이드 피치 각도과 바람의 속도에 따라 해석결과를 비료 분석하였다.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1861-1868
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• 2016

In this paper, a three-phase AC-DC high step-up converter is developed for application to microscale wind-power generation systems. Such an AC-DC boost converter prossessess the property of the single-switch high step-up DC-DC structure. For power factor correction, the advanced half-stage converter is operated under the discontinuous conduction mode (DCM). Simulatanously, to achieve a high step-up voltage gain, the back half-stage functions in the continuous conduction mode (CCM). A high voltage gain can be obtained by use of an output-capacitor mass and a coupled inductor. Compared to the output voltage, the voltage stress is decreased on the switch. To lessen the conducting losses, a low rated voltage and small conductive resistance MOSFETs are adopted. In addition, the coupled inductor retrieves the leakage-inductor energy. The operation principle and steady-state behavior are analyzed, and a prototype hardware circuit is realized to verify the performance of the proposed converter.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5334-5337
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• 2013

In this paper, the structure of traffic lights removed the wire for the completion of urban aesthetics is analyzed. The finite element model consists of shell elements from three-dimensional CAD model of actual traffic signal. Traffic light pole, horizontal stand shape, thickness, stiffeners, etc. are considered in this study. Analysis of stress and deformation is performed by applying wind load. When the wind load is applied, the result on traffic signal is analyzed. This study is to perform the basic tasks for improving the design.

• 한국해양학회지
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• v.18 no.1
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• pp.10-20
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• 1983

A thee-dimensional hydrodynamic numerical model of Kyonggi Bay is described. Experiments have been performed with the model to determine the response of the bay to stationary wind stress fields suddenly imposed on the bay for wind directions of uniform NW, W and stresses of 10 dyne/$\textrm{cm}^2$ respectively. Features of the wond onduced three-dimensional current structure determined from the computation have been examined and discussed. M$\_$2/ tidal currents have also been which are dominant in the region. Some of preliminary results are preaented and discussed.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.5
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• pp.411-416
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• 2014

In this research we present design optimization methods for a vehicle-mounted satellite antenna positioner. Our initial antenna positioner was conservatively designed to satisfy a worst case scenario where wind blew across the positioner at the speed of 120 km/h. Investigating stresses and safety based on Finite Element Methods (FEM), we find reflector support frames can be optimized to significantly reduce the weight of the positioner system. Thus, we optimize the reflector support frame from the given initial design while considering weight, maximum stress, maximum allowable deflection, cross section, and thickness. As a result, Shape C and the thickness of 2 mm are determined for the cross section of the reflector support frame. Applying this result, the weight of the new antenna positioner is 57.343 kg, which is decreased by 10.74% compared to the initial conservative design.

• Wind and Structures
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• v.10 no.5
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• pp.437-462
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• 2007

A non-translating, long duration thunderstorm downburst has been simulated experimentally and numerically by modelling a spatially stationary steady flow impinging air jet. Velocity profiles were shown to compare well with an upper-bound of velocity measurements reported for full-scale microbursts. Velocity speed-up over a range of topographic features in simulated downburst flow was also tested with comparisons made to previous work in a similar flow, and also boundary layer wind tunnel experiments. It was found that the amplification measured above the crest of topographic features in simulated downburst flow was up to 35% less than that observed in boundary layer flow for all shapes tested. From the computational standpoint we conclude that the Shear Stress Transport (SST) model performs the best from amongst a range of eddy-viscosity and second moment closures tested for modelling the impinging jet flow.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.77-84
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• 2017

Recently, interest in safety has been increasing in every area, especially in the field of transportation. The accurate evaluation of the stability of road facilities is needed to improve the level of safety in the field of transportation and the application of new technologies is required to reduce the number of natural disasters. In this study, the wind data were compared and analyzed according to the type of measurement, and an evaluation of the stability of road signs using the wind data was conducted. In addition, a stability plan to secure road signs was elaborated and its effect on the wind load was analyzed. It was found that the wind data measured by a mobile atmospheric observing system (MAOS) was 2.43 times bigger than that measured by the Korea meteorological administration (KMA) and road weather information system (RWIS). In terms of their stability, the road signs were susceptible to failure caused by gusty winds and it was found necessary to ensure their stability. In the future, it will be possible to evaluate the stability of road facilities using road line weather data and the application of wind load reduction technologies is expected to improve road safety.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.4
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• pp.70-75
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• 2011

Nowadays, modern gearboxes are characterized by high torque load demands, low running noise and compact design. Also durability of gearbox is specially a major issue for the industry. For the gearbox which used in wind turbine, gear transmission error(T.E.) is the excitation that leads the tonal noise known as gear whine, and radiated gear whine is also the dominant source of noise in the whole gearbox. In this paper, tooth modification for the high speed stage is used to compensate for the deformation of the teeth due to load and to ensure a proper meshing to achieve an optimized tooth contact pattern. The gearbox is firstly modeled in Romax software, and then the various combination analysis of the tooth modification is presented by using Windows LDP software, and the prediction of transmission error under the loaded torque for the helical gear pair is investigated, the transmission error, contact stress, root stress and load distribution are also calculated and compared before and after tooth modification under one torque condition. The simulation result shows that the transmission error and stress under the loads can be minimized by the appropriate tooth modification.

• Journal of Korean Society of Steel Construction
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• v.12 no.6
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• pp.681-690
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• 2000

Recently, a long span is often required for the spacious building. Therefore the increase of stiffness is necessary to prevent floor vibration and control deformation of the building under earthquake and wind loads. For this purpose, steel beams with stiffened ends by reinforced concrete are effective. To realize such an effective reinforcement method, the smoothening of bending and shear stress transmission at the boundaries between middle-part of the steel beam and both end-parts of the steel beam with stiffened ends by reinforced concrete is required. Therefore, the fixed plate was installed at the boundary with the view of transferring the stress smoothly. This paper evaluates the method of effective transmission of bending and shear stress through the numerical analysis that is based on advanced experimental tests.

• Geomechanics and Engineering
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• v.19 no.1
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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.