• Wind and Structures
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• 제13권1호
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• pp.1-20
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• 2010

The recommended factored design wind load effects for overhead lattice transmission line towers by codes and standards are evaluated based on the applicable wind load factor, gust response factor and design wind speed. The current factors and design wind speed were developed considering linear elastic responses and selected notional target safety levels. However, information on the nonlinear inelastic responses of such towers under extreme dynamic wind loading, and on the structural capacity curves of the towers in relation to the design capacities, is lacking. The knowledge and assessment of the capacity curve, and its relation to the design strength, is important to evaluate the integrity and reliability of these towers. Such an assessment was performed in the present study, using a nonlinear static pushover (NSP) analysis and incremental dynamic analysis (IDA), both of which are commonly used in earthquake engineering. For the IDA, temporal and spatially varying wind speeds are simulated based on power spectral density and coherence functions. Numerical results show that the structural capacity curves of the tower determined from the NSP analysis depend on the load pattern, and that the curves determined from the nonlinear static pushover analysis are similar to those obtained from IDA.

• Wind and Structures
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• 제2권1호
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• pp.1-23
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• 1999

Wind effects are critical considerations in the design of topside structures, overall structural systems, or both, depending on the water depth and type of offshore platform. The reliable design of these facilities for oil fields in regions of hostile environment can only be assured through better understanding of the environmental load effects and enhanced response prediction capabilities. This paper summarizes the analysis and performance of offshore platforms under extreme wind loads, including the quantification of wind load effects with focus on wind field characteristics, steady and unsteady loads, gust loading factors, application of wind tunnel tests, and the provisions of the American Petroleum Institute Recommended Practice 2A - Working Stress Design (API RP 2A-WSD) for the construction of offshore structures under the action of wind. A survey of the performance of platforms and satellite structures is provided, and failure mechanisms concerning different damage scenarios during Hurricane Andrew are examined. Guidelines and provisions for improving analysis and design of structures are addressed.

• 한국항공우주학회지
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• 제46권10호
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• pp.833-844
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• 2018

본 연구에서는 무인 회전익기의 종류인 쿼드콥터의 로터 블레이드에 대해 바람 및 비행 조건의 따른 공력특성을 예측하고자 한다. 돌풍 및 비행 조건들을 고려하기 위해 바람의 좌표계 변환 개념을 제시하였다. 강체 블레이드 플래핑 운동방정식을 고려한 깃 요소 및 운동량 이론을 이용해 개별 로터의 제자리, 전진, 상승 비행을 해석하였다. XFOIL을 사용하여 공력결과를 도출하였고, 개발된 BEMT를 이용하여 제자리 비행, 전진, 상승 조건의 검증을 수행했다. 또한 제자리 비행 실험 환경 구축 및 실험 결과와 개발된 BEMT의 비교 및 검증을 수행하였다.

• 해양환경안전학회지
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• 제26권7호
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• pp.767-776
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• 2020

최근 지구온난화에 따른 기후변화에 따라 과거와는 다른 양상의 기상 변화가 발생하고 있으며, 해수 온도 상승으로 태풍의 대형화와 강도증가가 발생하고 있다. 이에 따라 선박이 접안 중 갑작스러운 돌풍 발생시 선박의 계류안전성 확보를 위해 사용할 수 있는 돌풍 대비용 직주의 필요성이 증대되고 있다. 본 연구에서는 항만 및 어항 설계기준상 곡주 및 직주 배치 기준을 분석하고 계류안전성 평가프로그램을 사용하여 12개 시나리오에 따른 직주 사용시 계류안전성 민감도 분석을 수행하였다. 평가 결과, 돌풍 대비용 직주에 선수 및 선미 브레스트라인을 추가하였을 경우, 일반적인 형태의 계류라인 배치에 비해 계류요소값이 감소하는 것으로 분석되었다. 본 연구 결과는 접안선박 및 항만의 특성을 고려한 돌풍 대비용 직주 배치를 제안하기 위한 기초 자료로 활용될 수 있으며, 부두에서 직주의 배치는 돌풍 발생시 선박운항자 측면에서 선박의 계류안전성을 확보하기 위한 효율적인 방안이 될 것으로 사료된다.

• Wind and Structures
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• 제24권2호
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• pp.185-204
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• 2017

High-resolution wind measurements at 2.25 m in height were used to investigate the mean and turbulence properties of an extreme thunderstorm wind event in West Texas. These data were combined with single Doppler scans from the Texas Tech University Ka-band mobile Doppler radars systems (TTUKa) to provide meteorological context over the surface measurement stations for portions of the outflow. Several features characteristic of a severe wind event were noted in the radar data, including a bowing portion of the thunderstorm complex and a small circulation on the leading edge. These features were reflected in the surface wind time histories and provided natural separation between various regions of the outflow. These features also contributed to the peak 1-s gust at all measurement stations. The turbulence characteristics of each outflow region were also investigated and compared. Reduced values of running turbulence intensity and elevated values of longitudinal integral scales were noted during the period of peak wind speed. Larger scales of turbulence within the outflow were also suggested via spectral analysis.

• 한국대기환경학회지
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• 제22권6호
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• pp.888-903
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• 2006

This study analyze the change of wind pattern and intensity according to the transform of surface conditions, such as land use and height of terrain, over the leeward region. In order to do this, we have employed 'Envi-met' microscale atmospheric numerical model. When the same wind condition is considered, the wind speed of base case having natural surface condition of Chunsudae shows the weakest strength among different cases such as the 'bare case' and the '20 m case' which the plants is removed and the height of terrain is flatted as 20 m above the sea level over the Chunsudae, respectively. The weakening of wind speed is a maximum of $4{\sim}8 m/s$ when the inflow wind speed is 55 m/s.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.287-292
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• 2005

This paper presents a rational polynomial approximation method to estimate modal parameters of wind excited structures using incomplete noisy measurements of structural responses and partial measurements of wind velocities only. A stochastic model of the excitation wind force acting on the structure is estimated from partial measurements of wind velocities. Then the transfer functions of the structure are approximated as rational polynomial functions. From the poles and zeros of the estimated rational polynomial functions, the modal parameters, such as natural frequencies, damping ratios, and mode shapes are extracted. Since the frequency characteristics of wind forces acting on structures can be assumed as a smooth Gaussian process especially around the natural frequencies of the structures according to the central limit theorem (Brillinger, 1969; Yaglom, 1987), the estimated modal parameters are robust and reliable with respect to the assumed stochastic input models. To verify the proposed method, the modal parameters of a TV transmission tower excited by gust wind are estimated. Comparison study with the results of other researchers shows the efficacy of the suggested method.

• Wind and Structures
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• 제9권4호
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• pp.255-270
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• 2006

Several analytical procedures available in literature, for the evaluation of wind induced fatigue damage of structures, either assume the wide band random stress variations as narrow band random process or use correction factors along with narrow band assumption. This paper compares the correction factors obtained using the Rainflow Cycle (RFC) counting of the measured stress time histories on a lamp mast and a lattice tower, with those evaluated using different frequency domain methods available in literature. A Bi-modal spectral method has been formulated by idealising the single spectral moment method into two modes of background and resonant components, as considered in the gust response factor, for the evaluation of fatigue of slender structures subjected to "along-wind vibrations". A closed form approximation for the effective frequency of the background component has been developed. The simplicity and the accuracy of the new method have been illustrated through a case study by simulating stress time histories at the base of an urban light pole for different mean wind speeds. The correction factors obtained by the Bi-modal spectral method have been compared with those obtained from the simulated stress time histories using RFC counting method. The developed Bi-modal method is observed to be a simple and easy to use alternative to detailed time and frequency domain fatigue analyses without considerable computational and experimental efforts.

• Wind and Structures
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• 제21권2호
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• pp.241-272
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• 2015

In the current study, dynamic and quasi-static analyses were performed to investigate the response of multiple-spanned and single-spanned transmission line conductors under both downburst and synoptic winds considering different wind velocities and different length spans. Two critical downburst configurations, recommended in the literature and expected to cause maximum conductor reactions, were considered in the analyses. The objective of the study was to assess the importance of including the dynamic effect when predicting the conductor's reactions on the towers. This was achieved by calculating the mean, the background and the resonant reaction components, and evaluating the contribution of the resonant component to the peak reaction. The results show that the maximum contribution of the resonant component is generally low (in the order of 6%) for the multiple-spanned system at different wind velocities for both downburst and synoptic winds. For the single-spanned system, the result show a relatively high maximum contribution (in the order of 16%) at low wind velocity and a low maximum contribution (in the order of 6%) at high wind velocity for both downburst and synoptic winds. Such contributions may justify the usage of the quasi-static approach for analyzing transmission line conductors subjected to the high wind velocities typically used for the line design.

• Wind and Structures
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• 제32권5호
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• pp.439-452
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• 2021

The concept of Performance objective assessment is extended to wind engineering. This approach applies using the Database-Assisted Design technique, relying on the aerodynamic database provided by the National Institute of Standards and Technology (NIST). A structural model of a low-rise building is analyzed to obtain influence coefficients for internal forces and displacements. Combining these coefficients with time histories of pressure coefficients on the envelope produces time histories of load effects on the structure, for example knee and ridge bending moments, and eave lateral drift. The peak values of such effects are represented by an extreme-value Type I Distribution, which allows the estimation of the gust wind speed leading to the mean hourly extreme loading that cause specific performance objective compromises. Firstly a fully correlated wind field over large tributary areas is assumed and then relaxed to utilize the denser pressure tap data available but with considerably more computational effort. The performance objectives are determined in accordance with the limit state load combinations given in the ASCE 7-16 provisions, particularly the Load and Resistance Factor Design (LRFD) method. The procedure is then repeated for several wind directions and different dominant opening scenarios to determine the cases that produce performance objective criteria. Comparisons with two approaches in ASCE 7 are made.