• 동력기계공학회지
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• 제19권4호
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• pp.17-23
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• 2015

Because of the energy resources shortage and global pollution, the wind power systems have been developed consistently. Among the components of the wind power system, the rotor blades are the most important component. Generally it is made of GFRP material. Recently, GFRP material has been replaced by CFRP composite material in the blade which has an aerodynamic profile and twisted tip. However the failures has occurred in the trailing edge of the blade by the severe wind loading. Thus, tougher material than CFRP material is needed as like the aramid fiber. In this study, we investigated the mechanical behaviors of the blade using aramid fiber composites about wind speed variation. One-way FSI (fluid-structure interaction)analysis for the wind rotor blade was conducted. The structural analyses using the surface pressure loading resulted from wind flow field analysis were carried out. The results and analysis procedure in this paper can be utilized for the best strength design of the blade with aramid fiber composites.

• Smart Structures and Systems
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• 제13권2호
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• pp.281-303
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• 2014

In order to suppress the wind-induced vibrations of the Canton Tower, a pair of active mass driver (AMD) systems has been installed on the top of the main structure. The structural principal directions in which the bending modes of the structure are uncoupled are proposed and verified based on the orthogonal projection approach. For the vibration control design in the principal X direction, the simplified model of the structure is developed based on the finite element model and modified according to the field measurements under wind excitations. The AMD system driven by permanent magnet synchronous linear motors are adopted. The dynamical models of the AMD subsystems are determined according to the open-loop test results by using nonlinear least square fitting method. The continuous variable gain feedback (VGF) control strategy is adopted to make the AMD system adaptive to the variation in the intensity of wind excitations. Finally, the field tests of free vibration control are carried out. The field test results of AMD control show that the damping ratio of the first vibration mode increases up to 11 times of the original value without control.

• Wind and Structures
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• 제25권6호
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• pp.507-535
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• 2017

In the strong wind shutdown state, the blade position significantly affects the streaming behavior and stability performance of wind turbine towers. By selecting the 3M horizontal axis wind turbine independently developed by Nanjing University of Aeronautics and Astronautics as the research object, the CFD method was adopted to simulate the flow field of the tower-blade system at eight shutdown positions within a single rotation period of blades. The effectiveness of the simulation method was validated by comparing the simulation results with standard curves. In addition, the dynamic property, aerostatic response, buckling stability and ultimate bearing capacity of the wind turbine system at different shutdown positions were calculated by using the finite element method. On this basis, the influence regularity of blade shutdown position on the wind-induced response and stability performance of wind turbine systems was derived, with the most unfavorable working conditions of wind-induced buckling failure of this type of wind turbines concluded. The research results implied that within a rotation period of the wind turbine blade, when the blade completely overlaps the tower (Working condition 1), the aerodynamic performance of the system is the poorest while the aerostatic response is relatively small. Since the influence of the structure's geometrical nonlinearity on the system wind-induced response is small, the maximum displacement only has a discrepancy of 0.04. With the blade rotating clockwise, its wind-induced stability performance presents a variation tendency of first-increase-then-decrease. Under Working condition 3, the critical instability wind speed reaches its maximum value, while the critical instability wind speed under Working condition 6 is the smallest. At the same time, the coupling effect between tower and blade leads to a reverse effect which can significantly improve the ultimate bearing capacity of the system. With the reduction of the area of tower shielded by blades, this reverse effect becomes more obvious.

• 한국환경과학회지
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• 제16권1호
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• pp.103-119
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• 2007

We have analysed the observed surface and vertical meteorological data to get atmospheric information over the Busan metropolitan area. For this, we have selected 10 days in all season such as spring, summer I(Jangma season), summer II(hot season), autumn and winter. The result which have performed cluster analysis using atmospheric data represented that these days are included to most frequently appeared synoptic cluster. We have simulated wind field around Busan metropolitan area which is assigned as $1km^2$ using RAMS. The calculated air temperature and the wind speed was similar to the observed the that, and the trends of daily variation showed good agreement. RMSE and IOA also showed reliable value. These results indicated the RAMS is able to simulate and predict detailed atmospheric phenomenon.

• 한국환경복원기술학회지
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• 제2권3호
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• pp.1-9
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• 1999

This paper described the results of the characteristics of the near-bottom flow and field analysis of the tidal flats sediment. It was the aim of this paper to grasp current flow of tidal flat's environment and influence factor for environmental change forecast of tidal flats. Field measurement of water velocity, water elevation, bed materials test, and temperature distribution of tidal flat were conducted. Thereafter, current flow, turbidity and temperature distribution of tidal flat sediment have been discussed. The field research results showed that the fluctuating velocity near the seabed before and after its appearance at low tide was strongly affected by the wind wave. The resuspension of the sea-bottom sediment took place with great intensity before and after the appearance of the seabed at low tide. Both the sea water level and the weather condition were a significant influential factors. Such as, temperature and turbidity just on the surface and the shallow layer of seabed sediments were varied largely with time and weather conditions, but that its deeper layers was almost constant. Temperature on the seabed sediments was strongly influenced by irradiance and water depth. The temperature variation of the tidal flat and the variation characteristics of the current flow and turbidity depend greatly on the inhabiting environment of the tidal flat benthic organism.

• Wind and Structures
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• 제38권4호
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• pp.325-339
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• 2024

The longitudinal force resulting from tornado loads on transmission line is considered a crucial factor contributing to the failure of transmission line structures during tornado events. Accurate estimation of this longitudinal force poses a challenge for structural designers. Therefore, the objective of this paper is to provide a set of charts that can be easily used to estimate the peak longitudinal forces transferred from the conductors to a tower. The critical wind field and corresponding configuration considered in this paper are previously studied and determined. The charts should account for all the conductor parameters that can affect the value of the longitudinal force. In order to achieve that, a parametric study is first conducted to assess the variation of the longitudinal forces with different conductor parameters, based on the critical tornado configuration. Results of this parametric study are used to develop the charts that can be used to calculate longitudinal forces by adopting a multi-variable line regression. The forces calculated from charts are validated by finite element analysis. An example for the usage of the charts is provided at the end of this paper.

• 해양환경안전학회지
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• 제14권2호
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• pp.119-125
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• 2008

본 연구는 낙동강 하구 주변해역의 파랑 특성을 분석하기 위해 2007년 춘계(4월, 5월)에 낙동강 하구 중앙 해상 지점에서 관측된 파랑자료와 기상청에서 운영하고 있는 거제도 해양기상 부이에서 동일시점에 관측된 결과와 비교 검증하고 관측기간동안의 두 지점에서의 기상인자(기압, 기온, 풍속 및 풍향)와의 상관성을 비교하였다. 이상에서 얻어진 결과는 다음과 같다. (1) 2007년 춘계(4월과 5월)의 거제도 해양기상 부이 파랑 관측자료가 최대파고 약 3-4m, 유의파고 약 2m, 주기 약 5-8sec의 범위에 해당하는 반면에 낙동강 하구에서의 파랑 관측자료는 파고가 대체적으로 1m미만의 상태로 정온한 상태를 보이며 주기는 4-7sec의 범위를 가진다. (2) 춘계 파랑 관측자료에서 바람에 의한 파랑 감쇄가 없을 경우 거제도 해양기상 부이에서부터 천수 또는 굴절에 의한 파랑변형의 효과로 인해 낙동강 하구 중앙부까지 파랑이 전달되면서 최대파고값은 약 2.2m, 유의파고값은 약 1.3m정도 감소된다. (3) 낙동강 하구역으로 내습하는 해양파랑은 대상해역의 기상조건, 특히 바람의 영향(풍속 및 풍향)에 따라서 증감하는 것을 알 수 있는데, 특히 풍향이 역풍이 부는 경우 유의파고는 감소하는 경향을 나타내며 풍속이 클수록 그 감소 기울기도 더욱 커짐을 알 수 있다.

• Journal of Astronomy and Space Sciences
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• 제25권2호
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• pp.129-138
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• 2008

This study attempts to show how the geomagnetic indices, AU, AL and Dst, respond to the interplanetary parameters, more specifically, the solar wind electric field VBz during southward interplanetary magnetic field (IMF) period. The AU index does not seem to respond linearly to the variation of southward IMF. Only a noticeable correlation between the AU and VBz is shown during summer, when the ionospheric conductivity associated with the solar EUV radiation is high. It is highly likely that the effect of electric field on the eastward electrojet intensification is only noticeable whenever the ionospheric conductivity is significantly enhanced during summer. Thus, one should be very cautious in employing the AU as a convection index during other seasons. The AL index shows a significantly high correlation with VBz regardless of season. Considering that the auroral electrojet is the combined result of electric field and ionospheric conductivity, the intensification of these two quantities seems to occur concurrently during southward IMF period. This suggests that the AL index behaves more like a convection index rather than a substorm index as far as hourly mean AL index is concerned. Contrary to the AU index, the AL index does not register the maximum value during summer for a given level of VBz. It has something to do with the findings that discrete auroras are suppressed in sunlight hemisphere (Newell et al. 1996), thus reducing the ionospheric conductivity during summer. As expected, the Dst index tends to become more negative as VBz gets intensified. However, the Dst index (nT) is less than or equal to 15VBz(mV/m) + 50(Bz < 0). It indicates that VBz determines the lower limit of the storm size, while another factor(s), possibly substorm, seems to get further involved in intensifying storms. Although it has not been examined in this study, the duration of southward IMF would also be a factor to be considered in determining the size of a storm.

• 한국해양공학회지
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• 제27권4호
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• pp.98-106
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• 2013

Seismic fragility curves for an offshore wind-turbine structure were obtained. The dynamic response of an offshore wind turbine was analyzed by considering the nonlinear behavior of layered soil and the added mass effect due to seawater. A pile-soil interaction effect was considered by using nonlinear p-y, t-z curves. In the analysis, the amplification effect of ground acceleration through layered soil was considered by applying ground motion to each of the soil layers. The vertical variation in ground motion was found by one-dimensional free-field analysis of ground soils. Fragility curves were determined by damage levels in terms of tower stress and nacelle displacements that were found from static pushover analysis of the wind-turbine structure.

• 국제초고층학회논문집
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• 제11권4호
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• pp.241-263
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• 2022

The conventional wind and twisted-wind effect on aerodynamic properties of neighboring buildings arranged in side-by-side and tandem systems at 2B and 5B spacings are systematically investigated by large eddy simulation. Different physical interactions between different wind profiles and neighboring buildings will be deeply understood. The neighboring-building system under two different types of wind profiles, i.e., conventional wind profile (CWP), twisted wind profiles (TWP) with the maximum twisted angle of 30°, is used to evaluate the variation of physical mechanism between wind and buildings. Aerodynamic characteristics including mean and RMS pressure coefficient, and velocity field were systematically analyzed and compared between different scenario. It was found that the distribution of mean pressure, root-mean-square x velocity and the streamline of wind flow for TWP greatly deviated from CWP, and the effect of TWP on the downstream building, was drastically different from that of CWP, such as the size of vortexes after the lower stream building being bigger when exposed to TWP, and the mean pressure distribution on the building surfaces are also different. Moreover, evidence of buildings arranged in side-by-side and tandem configurations having interchangeable properties under TWP was also discovered, that two buildings being arranged side-by-side exposed to TWP could be identified as being arranged in tandem with a different wind twist angle, or vice versa.