• Wind and Structures
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• 제30권1호
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• pp.15-27
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• 2020

This paper reports the study on development and verification of numerical models and analyzes of flow at high speed around structural elements in the shape of a curved pipe (e.g., a fragment of a water slide). Possibility of engineering estimation of wind forces acting on an object in the shape of a helix is presented, using relationships concerning toroidal and cylindrical elements. Determination of useful engineering parameters (such as aerodynamic forces, pressure distribution, and air velocity field) is presented, impossible to obtain from the existing standard EN 1991-1-4 (the so-called wind standard). For this purpose, flow at high speed around a torus and helix, arranged both near planar surface and high above it, was analyzed. Analyzes begin with the flow around a cylinder. This is the simplest object with a circular cross-section and at the same time the most studied in the literature. Based on this model, more complex models are analyzed: first in the shape of half of a torus, next in the shape of a helix.

• Wind and Structures
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• 제24권3호
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• pp.249-265
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• 2017

An efficient and accurate algorithm is proposed to estimate flutter safety factor of suspension bridges satisfying prescribed reliability levels. Uncertainties which arise from the basic wind speed at the bridge deck location, critical flutter velocity, the wind conversion factor from a scaled model to the prototype structure and the gust speed factor are incorporated. The proposed algorithm integrates the concepts of the inverse reliability method and the calculation method of the critical flutter velocity of suspension bridges. The unique feature of the proposed method is that it offers a tool for flutter safety assessment of suspension bridges, when the reliability level is specified as a target to be satisfied by the designer. Accuracy and efficiency of this method with reference to three example suspension bridges is studied and numerical results validate its superiority over conventional deterministic method. Finally, the effects of various parameters on the flutter safety factor of suspension bridges are also investigated.

• 조명전기설비학회논문지
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• 제18권5호
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• pp.189-197
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• 2004

고가공도체의 최대허용전류인 열용량은 일반적으로 IEEE P738 기준에서 주어진 것과 같은 열평형 방정식을 기초로 계산된다. 이 정격은 기온, 풍속, 풍향 및 태양열과 같은 기상조건의 함수로 주어진다. 이러한 기상 파라미터들 중에 풍속은 그 값이 아주 작게 나타날 때 송전용량 결정에 강한 영향을 준다. 따라서 송전용량 모니터시스템에서 사용되는 풍속계 대부분은 낮은 감도와 실속 특성을 가지므로 부정확한 결과가 나타난다. 본 논문에서는 풍속계를 사용하지 않고 가공송전선의 동적송전용량을 결정하기 위한 새로운 방법을 도입한다. 풍속을 2개의 간접도체의 온도로 추정하고 실험을 통하여 추정풍속으로 구한 동적송전용량이 기상모델로 구한 결과와 매우 근접함을 밝혔다.

• 한국음향학회지
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• 제38권4호
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• pp.378-386
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• 2019

항해하는 선박으로부터 방사되는 선박소음과 달리 바람소음은 바람과 해수면의 상호작용으로 생성된 쇄파에 의해 발생한다. 본 논문에서는 바람의 소음원을 쇄파로 인해 발생되는 기포운으로 설정하여 바람소음준위를 모델링하였다. 모델링에서 바람소음의 음원준위는 동해 연안에서 운영되는 기상부이로부터 측정된 풍속 자료를 이용하여 계산하였다. 풍속을 측정함과 동시에 기상부이의 주변에 계류된 자가기록식 수중청음기를 이용하여 소음준위를 연속적으로 측정하였다. 측정된 수중소음에서 선박소음을 제거한 소음준위와 풍속에 따라 모델링된 바람소음준위를 저주파대역에서 비교하였다. 모델링된 바람소음준위와 측정된 소음준위의 전반적인 경향이 서로 유사하였다. 이에 따라 바람에 의해 발생된 소음원인 기포운의 음원준위 및 분포 수심을 고려하여 천해역에서 바람소음준위를 모델링하는 것이 가능함을 확인하였다.

• 한국측량학회지
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• 제30권3호
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• pp.295-303
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• 2012

풍력발전 단지의 수익성 평가를 위해 연간 에너지 생산량(AEP ; Annual Energy Production)의 계산이 중요하다. AEP를 계산하기 위해서는 바람의 확률밀도함수(PDF ; Probability Density Function)와 풍력발전기의 발전곡선(PC; Power Curve)이 필요하며, AEP 예측의 정확성을 향상시키기 위해서는 허브 높이에서의 PDF예측과 그 높이의 공기밀도에 따른 풍력발전기 PC의 결정이 중요하다. 본 연구에서는 제주도 한동, 평대의 실관측 풍황탑(met mast) 자료를 이용하였으며 풍속의 PDF를 Weibull 분포 함수로 가정 하였고 Weibull 함수의 파라미터의 값이 높이에 따라 변화하는 양상을 확인하였다. Weibul 함수의 계산은 모멘트법과 LN-least법을 사용하였으며, 모멘트법과 LN-least법에 의한 형상계수의 경우 높이의 증가에 따라 변화를 보이지 않았고 평균값에서 ${\pm}0.1$의 변화 패턴을 보였다. 척도계수의 경우 높이가 증가함에 따라 선형적으로 증가하였으며 지형별 분류에 따른 높이별 척도계수의 기울기는 확연한 차이를 보이고 있었다. 60m 높이에서 관측된 바람의 상대도수와 관측 값의 높이 보정에 의한 공기밀도와 일반식에 의한 공기밀도를 각각 계산하여 그 결과에 대응하는PC를 선택하여 AEP차이를 계산하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제15권2호
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• pp.153-160
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• 2011

최근들어 사장교나 현수교와 같은 케이블 형식의 장대교량이 많이 건설되거나 계획중에 있다. 하지만 도로교 설계기준에 제시된 풍하중 산정시 중요한 요인인 기본풍속 산정함에 있어서 1995년까지 측정된 풍속자료를 근거로 한 일반교량에 적합한 풍속을 명시하고 있어 장대교량에 적합한 풍속에 대한 재검토가 필요한 상황이다. 본 연구에서는 태풍의 빈도가 높고 대부분의 장대교량이 건설되고 있는 서남해안지역으로 구체화하였다. 풍하중기준과 같이 극치I형분포(Gumbel분포)에 의해 일반교량에 적용할 100년, 장대교량에 적용할 200년 재현기대풍속을 적률법과 최소자승법의 두 가지 방법으로 추정하고, 극한 상황인 해상에서 불어오는 풍속으로 보정하여 지상풍속보다 약 17%정도 큰 값을 추정하였다. RMS error 방법에 의해 재현기대풍속의 적합성을 평가한 결과 최소자승법이 서남해안지역의 경우 적합성이 우수하였다.

• 한국태양에너지학회 논문집
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• 제35권3호
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• pp.17-25
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• 2015

The main objective of this study is to predict the wind power generation at the wind farm using various wake models. Modeling of wind farm is a prerequisite for prediction of annual energy production at the wind farm. In this study, we modeled 20 MW class Seongsan wind farm which has 10 wind turbines located at the eastern part of Jeju Island. WindSim based on the computational fluid dynamics was adopted for the estimation of power generation. The power curve and thrust coefficient with meteorology file were prepared for wind farm modelling. The meteorology file was produced based on the measured data of the Korea Wind Atlas provided by Korea Institute of Energy Research. Three types of wake models such as Jensen, Larsen, and Ishihara et al. wake models were applied to investigate the wake effects. From the result, Jensen and Ishihara wake models show nearly the same value of power generation whereas the Larsen wake model shows the largest value. New positions of wind turbines are proposed to reduce the wake loss, and to increase the annual energy production of the wind farm.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.447-452
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• 2000

In this study, the design of Free-Fall Simulator was carried out using concept of vertical wind tunnel. Free-Fall Simulator is not an experimental equipment but a training equipment. Therefore Free-Fall Simulator needs a large training section compared with test section of wind tunnel and has critical limit of height. These limits bring about the difficulty of design for a return passage. Due to small area ratio, the downstream flow of training section with high speed is not decelerated adequately to the fan section. High-speed flow leads to great losses in the small area ratio diffuser and corner. So design of diffusers and corners located between training section and fan section has a great effect on the Free-Fall Simulator performance. This study used an estimation method of subsonic wind tunnel performance. It considered each section of Free-Fall Simulator as an independent section. Therefore loss of one section didn't affect loss of other sections. Because losses of corner with vane and $1^{st}$ diffuser are most parts of overall Free-Fall Simulator, this study focused on the design of these sections.

• 한국대기환경학회지
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• 제12권2호
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• pp.141-149
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• 1996

Lateral dispersion parameter(.sigma.$_{y}$) which is an important factor in atmospheric dispersion can be estimated byusing wind direction fluctuation(.sigma.$_{\theta}$). In this paper, we studied the characteristics of the .sigma.$_{\theta}$ in the Chunchon basin and calculated the .sig- ma.$_{y}$ by using the .sigma.$_{\theta}$. We could find some characteristics of the .sigma.$_{\theta}$ which showed small value, when the atmospheric condition was in weak unstable (C class) and neutral (D class). Moreover, when the atmospheric stability was neutral, there was no difference of .sigma.$_{\theta}$ with wind speed. On the other hand, .sigma.$_{\theta}$ showed large values at the strong unstable (A class) and strong stable (F class) condition with low wind speed. In this case, the .sigma.$_{\theta}$ increased as long as averaging time due to the long-period wind direction fluctuation by the terrain effect. In the result of calculation of .sigma.$_{y}$, it was smaller than that of pasquill-Gifford curve. Especially, when the atmospheric condition was in a neutral and stable, .sigma.$_{y}$ showed small increment as the downwind distance increased.creased.

• Ocean and Polar Research
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• 제43권1호
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• pp.1-14
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• 2021

In this study, extreme wind speeds in the Western North Pacific (WNP) were estimated using reanalysis wind fields synthesized with an empirical typhoon vortex model. Reanalysis wind data used is the Fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) data, which was deemed to be the most suitable for extreme value analysis in this study. The empirical typhoon vortex model used has the advantage of being able to realistically reproduce the asymmetric winds of a typhoon by using the gale/storm-forced wind radii information in the 4 quadrants of a typhoon. Using a total of 39 years of the synthesized reanalysis wind fields in the WNP, extreme value analysis is applied to the General Pareto Distribution (GPD) model based on the Peak-Over-Threshold (POT) method, which can be used effectively in case of insufficient data. The results showed that the extreme analysis using the synthesized wind data significantly improved the tendency to underestimate the extreme wind speeds compared to using only reanalysis wind data. Considering the difficulty of obtaining long-term observational wind data at sea, the result of the synthesized wind field and extreme value analysis developed in this study can be used as basic data for the design of offshore structures.