• 대한공간정보학회지
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• 제20권2호
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• pp.15-22
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• 2012

지면위의 풍속의 변화를 높이별 풍속변화(wind shear)아고 한다. 풍력자원 평가 분야에서 전통적으로 이런 높이별 풍속 변화특성을 수학적으로 두 가지 방법으로 분석한다. 이를 대수법칙(Lograthmic law)과 멱법칙(Power law)이라 한다. 대수법칙은 표면 거칠기를 파라미터로 멱법칙의 경우 멱지수를 파라미터로 사용한다. 높이별 풍속변화는 여러 가지 인자에 의하여 영항을 받는다. 대부분은 대기의 안정도와 주변의 지형에 의한 거칠기에 현저한 영향을 받는다. 대기안정도는 계절적, 하루의 시간 변화나 기상학적 변화에 의한 영항을 받는다. 표면의 거칠기와 멱지수 역시 시간의 변화에 따라 변화하는 경향을 보인다. 본 연구에서는 제주 평대와 한동 지역의 풍황 관측데이터를 이용하여 메트랩과 windograper를 이용하여 조도 길이와 멱지수를 계산 하였다. 이 결과는 참조데이터들과 유사한 결과를 보이긴 했지만 범위는 차이를 보이고 있었다. 선행 연구와 비교한 결과 해양의 경우 비슷한 결과를 보였지만 농작지의 경우 보다 높은 범위를 농촌마을이 경우 보다 낮은 범위를 보이고 있었다.

• Wind and Structures
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• 제23권3호
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• pp.231-251
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• 2016

This paper presents the experimental results of the wind tunnel tests for three symmetric, rectangular, tall building models on a typical open terrain considering the torsional motion-induced vibrations. The time histories of the wind pressure on these models under different reduced wind speeds and torsional amplitudes are obtained through the multiple point synchronous scanning pressure technique. Thereafter, the characteristics of both the Root Mean Square (RMS) coefficients and the spectra of the base shear/torque in the along-wind, across-wind, and torsional directions, respectively, are discussed. The results show that the RMS coefficients of the base shear/torque vary in the three directions with both the reduced wind speeds and the torsional vibration amplitudes. The variation of the RMS coefficients in the along-wind direction results mainly from the change of the aerodynamic forces, but sometimes from aeroelastic effects induced by torsional vibration. However, the variations of the RMS coefficients in the across-wind and torsional directions are caused by more equal weights of both the aerodynamic forces and the aeroelastic effects. As such, for the typical tall buildings, the modification of the aerodynamic forces in the along-wind, across-wind, and torsional directions, respectively, and the aeroelastic effects in the across-wind and torsional directions should be considered. It is identified that the torsional vibration amplitudes and the reduced wind speeds are two significant parameters for the aerodynamic forces on the structures in the three directions.

• 한국환경과학회지
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• 제7권3호
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• pp.335-348
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• 1998

The intensive meteorological observations including pibal balloon at Ungcheon, airsonde and 10m meteorological tower observations at Gulup-Do, where are located In the western coastal region, are taken to Investigate the characteristics of the upper and lower atmospheric structure and the local circulation pattern during the period of 17 to 22 September 1996. The diurnal variations of weather elements(i.e. air temperature, humidity, pressure, and Und speeds at Gulup-Do are analyzed and discussed with those at four inland meteorological stations. The vertical profiles of wind vector, ortho- gonality(Ω), and shear obtained from the pibal obsenrations are also presented to examine the change of wand structure according to the synoptic-scale pressure system's movement. The diurnal temperature changes at Gulup-Do are more sensitive than that of Inland meteorological stations In case of the mow of southwesterlies but are not dominant due to the ocean effect under the Influence of relatively cold northerlies. A well defined mixed layer Is developed from the 500m to the maximum 1700m with a significant capping Inversion layer on the top of it. It can be found from the vertical profiles of wind vector that the wind become generally strong at the interface heights between cloud lay- ers and non-cloud layers. The maximum Und shear Is appeared at the bel각t where the varlauon of wand direction Induced by the passage of synoptic-scale pressure system Is accompanied with the In- crease of Und speed. Based on the wind orthogonality, the change of wind direction with height is more complicated In cloudy day than In clear day. In case of a fair weather, the change of wand direction is showed to be at around 2km.

• Wind and Structures
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• 제29권3호
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• pp.209-223
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• 2019

The assessment of wind-induced vibration for tall reinforced concrete (RC) buildings requires the accurate estimation of their dynamic properties, e.g., the fundamental vibration periods and damping ratios. In this study, RC frame-shear wall systems designed under gravity and wind loadings have been evaluated by utilising 3D FE modelling incorporating eigen-analysis to obtain the elastic periods of vibration. The conducted parameters consist of the number of storeys, the plan aspect ratio (AR) of buildings, the core dimensions, the space efficiency (SE), and the leasing depth (LD) between the internal central core and outer frames. This analysis provides a reliable basis for further investigating the effects of these parameters and establishing new formulas for predicting the fundamental vibration periods by using regression analyses on the obtained results. The proposed constrained numerically based formula for vibration periods of tall RC frame-shear wall office buildings in terms of the height of buildings reasonably agrees with some cited formulas for vibration period from design codes and standards. However, the same proposed formula has a high discrepancy with other cited formulas from the rest of design codes and standards. Also, the proposed formula agrees well with some cited experimentally based formulas.

• Wind and Structures
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• 제3권2호
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• pp.73-81
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• 2000

Snowdrifts around buildings can cause serious problems when formed on undesirable places. The formation of snowdrifts is highly connected to the wind pattern around the building, and the wind pattern is again dependent on the building design. The shear stress on the surface and snowdrifting around different buildings are investigated through CFD analysis and compared to measurements. The computations of shear stress shows local minima in the same areas as snowdrifts are formed. The snowdrifting computations utilises a drift-flux model where a fluid with snow properties is allowed to drift through a fluid with air properties. An apparent dynamic viscosity of the snow/air mixture is defined and used as a threshold criterion for snowdrifting. The results from the snowdrifting computations show increased snow density where snowdrifts are expected, and are in agreement with previous large-scale snowdrift measurements. The results show that computational fluid dynamics can be a tool for planning building design in snowdrifting areas.

• 한국지반공학회논문집
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• 제30권1호
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• pp.17-25
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• 2014

해상풍력발전기의 기초는 바람, 조류, 그리고 파도 하중을 받기 때문에 해상풍력발전기 기초를 설계하는 데 있어 반복하중을 받는 기초지반의 전단거동 평가가 필요하다. 지반의 비배수 동적 전단거동은 반복하중 횟수, 수직 유효응력, 반복 전단변형률, 상대 밀도, 그리고 평균 및 반복전단응력의 조합에 영향을 받는다. 본 연구에서는 해양 실트질 모래의 비배수 동적 거동에 대한 평균 및 반복전단응력의 영향을 평가하기 위하여 반복단순전단시험(CDSS)을 수행하였으며 상대밀도 85%, 수직 유효응력 200kPa과 300kPa의 시험조건에서 15%의 이중진폭 동적전단변형률(${\gamma}_{cyc}$)과 영구전단변형률(${\gamma}_p$)를 파괴 기준으로 적용하였다. 시험결과는 설계 그래프와 등고선도로 나타내었다. 결과에 따르면 해양 실트질 모래의 비배수 동적 거동은 평균 및 반복전단응력과 두가지 전단응력의 조합에 의해 크게 변하는 경향을 보였다. 평균전단응력이 존재하는 경우에는 반복전단변형보다는 영구변형에 의해 파괴가 결정되는 것으로 나타났다.

• Wind and Structures
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• 제31권2호
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• pp.143-152
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• 2020

The wind design of buildings is typically based on strength provisions under ultimate loads. This is unlike the ductility-based approach used in seismic design, which allows inelastic actions to take place in the structure under extreme seismic events. This research investigates the application of a similar concept in wind engineering. In seismic design, the elastic forces resulting from an extreme event of high return period are reduced by a load reduction factor chosen by the designer and accordingly a certain ductility capacity needs to be achieved by the structure. Two reasons have triggered the investigation of this ductility-based concept under wind loads. Firstly, there is a trend in the design codes to increase the return period used in wind design approaching the large return period used in seismic design. Secondly, the structure always possesses a certain level of ductility that the wind design does not benefit from. Many technical issues arise when applying a ductility-based approach under wind loads. The use of reduced design loads will lead to the design of a more flexible structure with larger natural periods. While this might be beneficial for seismic response, it is not necessarily the case for the wind response, where increasing the flexibility is expected to increase the fluctuating response. This particular issue is examined by considering a case study of a sixty-five-story high-rise building previously tested at the Boundary Layer Wind Tunnel Laboratory at the University of Western Ontario using a pressure model. A three-dimensional finite element model is developed for the building. The wind pressures from the tested rigid model are applied to the finite element model and a time history dynamic analysis is conducted. The time history variation of the straining actions on various structure elements of the building are evaluated and decomposed into mean, background and fluctuating components. A reduction factor is applied to the fluctuating components and a modified time history response of the straining actions is calculated. The building components are redesigned under this set of reduced straining actions and its fundamental period is then evaluated. A new set of loads is calculated based on the modified period and is compared to the set of loads associated with the original structure. This is followed by non-linear static pushover analysis conducted individually on each shear wall module after redesigning these walls. The ductility demand of shear walls with reduced cross sections is assessed to justify the application of the load reduction factor "R".

• Journal of Advanced Marine Engineering and Technology
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• 제27권6호
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• pp.753-758
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• 2003

In this study. an experiment has been performed to investigate distributions of static pressure around a circular cylinder in a uniform shear flow which is made by a specially designed wind tunnel. From the computation program(BLAYER), various boundary layer value are obtained depending on the shear flow rate. It is basical design data that boundary layer flow phenomenon of nuclear power plant heat exchanger tube surroundings. airfoil. and others flow fields.

• Wind and Structures
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• 제17권6호
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• pp.589-608
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• 2013

A model is proposed to analyse the along-wind dynamic response of upwind turbines with horizontal axis under service wind conditions. The model takes into account the dynamic coupling effect between rotor blades and supporting tower. The wind speed field is decomposed into a mean component, accounting for the well-known wind shear effect, and a fluctuating component, treated through a spectral approach. Accordingly, the so-called rotationally sampled spectra are introduced for the blades to account for the effect of their rotating motion. Wind forces acting on the rotor blades are calculated according to the blade element momentum model. The tower shadow effect is also included in the present model. Two examples of a large and medium size wind turbines are modelled, and their dynamic response is analysed and compared with the results of a conventional static analysis.

• 대한공간정보학회지
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• 제21권4호
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• pp.65-71
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• 2013

고도에 따른 풍속변화를 의미하는 Wind shear는 풍력발전기의 에너지 생산량에 직접적으로 영향을 미치는 중요한 요소이다. 풍속을 보정하는 방법으로는 멱법칙(Power Law)이 사용되는데, 일반적으로 쓰이는 0.143(1/7)의 멱지수(Power Law exponent) 값을 이용한 보정식을 1/7th 멱법칙이라 한다. 하지만 멱지수는 해당 지역의 대기 안정도, 지표면의 상태 등에 의해 많은 영향을 받으므로, 실제 정확한 풍력에너지 예측을 위해서는 관심지역의 멱지수의 정확한 계산이 필요하다. 본 연구에서는 제주도 북동부 연안지역 3곳에 Met-mast를 설치하여 풍력자원을 측정하였고, 이를 바탕으로 제주도 북동부 지역에 적합한 멱지수를 계산하여 제안하였다. 제주도 북동부 연안지역의 멱지수를 계산한 결과, 한동 0.141, 평대 0.138, 우도 0.1254의 값을 얻었다. 0.143(1/7)의 멱지수 값, 제안한 멱지수 값을 적용하여 계산한 연간에너지생산량과 실제 측정된 풍황자료를 이용하여 계산한 연간에너지생산량을 비교한 결과, 세 지역 모두 제안한 멱지수 값을 적용하여 계산한 연간에너지생산량이 실제 측정된 풍황자료를 이용하여 계산한 연간에너지생산량과 유사한 결과를 보였고, 따라서 제안한 멱지수 값의 적용이 가능하다고 판단된다.