본 연구에서는 풍동실험을 통해 345kV급 송전철탑에 작용하는 공기력계수를 측정하고 IEC-60826 기준과 비교하였다. 이를 위하여 본체와 크로스암을 포함한 총 6개 세그먼트로 분리될 수 있는 축척 1:25인 강체 모형을 제작하였다. 그리고 다양한 바람 수평 입사각에 대하여 철탑 전체 및 각 세그먼트에 작용하는 공기력을 측정하였다. 풍동실험 결과를 보면, 전체 철탑에 작용하는 공기력계 수가 IEC 기준치와 비교하여 수평입사각의 변화에 따른 경향이 잘 일치한다. 그리고 IEC 기준치가 풍동시험치보다 전반적으로 약간 커서 안전측의 결과를 제공하고 있다. 송전철탑을 구성하는 세그먼트 중에서 철탑본체에 작용하는 공기력계수는 풍동실험치가 설계기 준치보다 작았다. 하지만 철탑 크로스암에서는 풍동실험치가 설계치를 약간 넘는 경우가 일부 나타났다. 이를 볼 때 기존 설계기준은 철탑본체에 대해서는 안전측의 결과를 제시하나, 일부 바람 입사각에서 크로스암에 작용하는 공기력은 과소평가할 가능성이 있는 것 으로 판단된다.

본 논문에서는 한국의 서남해상에 건설예정인 해상풍력발전타워의 지지구조물로 고려되고 있는 세발구조와 자켓구조의 선박충 돌 거동을 비선형동적해석을 통하여 비교‧분석하였다. 이 구조물은 3MW용량의 풍력타워를 지지하기 위하여 설계되었다. 두 지지구 조는 쉘요소를 이용하여 비선형 거동을 고려할 수 있도록 모델링하였고, 발전기를 포함하는 상부의 타워구조물은 탄성재료를 이용하 여 보요소와 집중질량으로 모델링하였다. 전체 질량은 세발구조가 자켓구조에 비하여 약 1.66배 정도였다. 바지선과 상선을 충돌선박 으로 선정하여 모델링하였다. 조수차의 조건을 고려하여 충돌선박의 충돌위치를 평균해수면의 상하로 3.5m변동하는 것으로 고려하 였다. 또한 각 선박의 최소충돌속도(=2.6m/s)에서의 충돌에너지를 각각 4배까지 증가시키면서 충돌거동을 산정하였다. 해석결과 지 지구조 충돌부위의 강성이 클수록 선박의 소성에너지 소산량이 상대적으로 증가하였다. 충돌조건에 따라 풍력타워의 변형은 진동에 서 붕괴까지 발생하였다. 세발구조가 자켓구조에 비하여 큰 충돌저항력을 보였다. 이는 중앙부에 강성이 집중된 구조적 특성과 상대 적으로 많은 강재의 사용량에 기인한 것으로 판단된다.

타워형 집광태양열발전의 핵심요소인 헬리오스타트는 경량화를 통한 설비비 저감이 매우 중요한다. 반사판 면적 16m2의 기 존 헬리오스타트 대비 샌드위치 패널을 사용하여 무게를 50% 경량화한 헬리오스타트의 풍하중 평가를 수행하였다. 반사판이 수직, 45 도 경사인 경우에 대해 전산유체역학 해석을 하여 반사판에 작용하는 풍압을 산정하고 구조해석을 수행하여 최대응력의 발생부위 및 반사판의 변위에 의한 반사각도의 이격을 계산하였다. 45도 경사진 반사판이 바람이 불어오는 반대편으로 향한 경우가 바람을 마주보 는 배치보다 최대 풍하중이 더 크게 나타났으며, 반사판 풍하측으로의 유동박리에 의한 후류의 발달도 반사판의 배치에 따라 매우 상 이한 형태를 보였다. 경량화 모델의 경우 반사판 구동을 위한 기어의 배치를 변경하여 핵심 지지체인 기둥의 강성을 확보할 필요가 있 음을 확인하였다.

본 연구에서는 해상 풍력용 기상탑의 파단 원인을 찾기 위하여 실측된 풍속 자료를 분석하고, 변동 풍하중과 파랑하중에 의한 동적 변위를 산정하였으며, 와류진동에 대한 피로 검토를 수행하였다. 그 결과를 보면, 베인 풍속계와 초음파 풍속계의 10분 최대 풍속을 비교하여 기상탑에서 4시간 지속된 진동이 발생했음을 확인하였다. 그리고 파랑하중보다 풍하중이 기상탑의 동적 응답에 미치는 영향이 훨씬 크지만, 두 하중이 동시에 작용해도 기상탑의 부재력이 설계력보다 훨씬 낮아서 직접적인 파단의 원인이 아닌 것으로 나타났다. 하지만 와류진동은 연결부 볼트에서 피로 파괴를 일으키는 것으로 나타나서, 기상탑의 파단 원인은 유체의 변동 성분이 아닌 와류진동인 것으로 판단된다.

In this study, the fragility for transmission tower subjected to wind disaster, which has the greatest influence on transmission tower, was developed for 154kV transmission tower located between Yangyang and Sokcho city. The resistance capacity and the limit state required for the evaluation of the fragility were divided into the major part and the auxiliary part in the steel tower. Moreover, the failure of tower was defined as the yielding stress of each member in the tower which could be used to determine their resistance performance. Domestic wind design guideline and criteria for transmission tower was used to determine the wind loads demand on the tower. By comparing the loading demand and resistance capacity, the failure of tower could be determined which in turn used to derive the wind fragility. The results obtained in this study could be used as a reference for damage prediction system of transmission tower and similar structures.

As the size of the wind turbine tower becomes larger and larger, research on assembled wind turbine tower that is advantageous for transportation and installation is continuing. Large wind turbine tower require door openings for maintenance. The opening of the tower has an irregular cross section, and an excessive stress is generated due to the door opening. The result is structural damage to the tower and many accidents. In this research, stress analysis was performed on a model with internal stiffener to prevent excessive stress. The stress was investigated around the openings where the tower was resonant and excessive stressed, and the shape of the openings was optimized. Through optimization, we confirmed that the maximum stress was reduced by about 6% with respect to the initial value.

Wind tower structure has relatively simple shape compared to other structures, but due to its characteristics, various and irregular environmental loads are applied. These loads cause vibrations at tower, and can cause failure of the structure if over vibration occurs. Vibration occurred at structures is gradually exhausted by damping of the structures, and if high damping is ensured, the failure of the structure due to over vibration can be prevented. In this study, the vibration reduction effects are to be analyzed through FEM analysis by examining the top displacement, bottom moment, and bottom fatigue damage of the structure depending on damping ratio of the wind tower structure.

Recently, for efficiency increase of the wind turbine tower, turbine has been enlarged and installation location has been transferring to offshore. The importance of the support structure is emphasized when a wind turbine tower is installed on offshore. The support structure is influenced not only by the system operating loads but also by various marine condition loads. Accurate and safe design is essential because the connection between the support structure and the wind tower can be relatively fragile. In particular, the type of foundation pile and sleeve grout connection were adapted from DNV, API, and ISO that are typically used for wind towers, and they have been continuously studied by many researchers. However, the experimental results by researchers are different from the design equations, and it needs to modify the formula according to connection properties and material. Therefore, this study investigates the design equation presented in existing design criteria and the results of research conducted by existing researchers, and analyzes ultimate strength and failure modes.

This study investigates dynamic characteristics of a 2MW wind turbine structure by long-term response monitoring with accelerometers, tiltmeter and strain gauges. The object wind turbine structure is located in Jeju Island, Korea. The natural frequency and damping ratio were evaluated by least-square frequency domain decomposition and random decrement technique using acceleration response data. As a result, it was found that natural frequencies with 1st, 2nd and 3rd modes, and blade passing frequencies with 1P, 2P and 3P were clearly showed from power spectral densities of acceleration reponses. Furthermore, 1st model frequencies were almost constant with increase in standard deviations of acceleration responses. Another notable observation was that when standard deviations of acceleration responses were small, damping ratios showed to diverge. However, when standard deviations of acceleration responses had large values, damping ratios were converged to about 0.5%.

Cylindrical steel shell sections have been applied in various engineering fields particularly in recent installations of wind turbine towers. Hence, many researchers are interested in studying cylindrical steel shell structures. However, studies on the effect of the presence or absence of openings are insufficient. Thus, the design criteria for the opening as well as the behavior of wind turbine tower are not clearly presented. Therefore, this study examines the ultimate strength and the behavior of wind tower in consideration of openings, presence of stiffeners, changes in opening width, and thickness variation of stiffeners. ABAQUS, a universal finite element analysis program, was used in to conduct this research. Finally, the results of this study can be a reference for the design and production of wind towers with openings.

As the size of the wind power becomes larger, the development of the assembly type wind power which is advantageous in transportation and installation is active. This advantage comes from the economic point of view, and the stiffener is applied to the inner side, so that the safety is high. Large wind power require door openings for maintenance. The door opening has an irregular cross-section, and an excessive stress active due to the door opening. In this paper, the stresses occurring around the door opening was analyzed. As a result, small stress values were appeared in the tower, as the number of stiffeners were increased. Also, stress values were decreased a little in the tower as the opening shape become to ellipse was closer.

The result of the previous work leads to the idea that the inner area of the hyperbolic shell generator should be minimized for the cooling tower with higher first natural frequency. In this study the inner area of the hyperbolic shell generator was graphically established under varying height of the throat and angle of the base lintel. From the graph, several shell geometries were selected and analysed in the aspect of the natural frequency. Three representative towers reinforced differently due to different first natural frequencies were analysed non-linearly and evaluated using a damage indicator based on the change of natural frequencies. The results demonstrated that the damage behaviour of the tower reinforced higher due to a lower first natural frequency was not necessarily advantageous than the others

Determining of the shape in the process of design for natural draught cooling tower is very important, because the shape of hyperbolic shell is respond sensitively to dynamic behavior of the whole cooling tower against wind load. In engineering practice, the geometric parameters have been determining based on the natural frequency. This study analyses influence of the tower shell geometric parameters on the structural behavior. For three representative models were selected, they were analyzed based on evaluation of damage by means of nonlinear FE-method. As a result, a hyperbolic rotational shell with the small radius overall was the lowest damage index induced by sufficient capacity of the stress redistribution and thus a wind-insensitive structure.

The initial production scale of wind tower is very few. But recently, the production scale of wind tower structure has increased gradually because it maximizes the efficiency in green energy. Many researchers are studying the wind tower, but there is no study about the difference of allowable buckling stress of the wind tower with and without opening. Guideline of codes and standards are very limited when designing a wind tower with an opening. It is also rarely that a study considers the design of the wind tower to be a tubular shell with or without an opening. ABAQUS, a general purpose finite element program, which provides safety evaluation and economical standards for the design and behavior of the wind tower considering the effect of opening was used in the study. Finally, results from this study can serve as reference for structural engineers, manufacturers and further studies of wind turbine when designing a tubular shell wind tower with an opening.

Recently, wind power has received attention as one of remarkable renewable energy resources, and worldwide researches about wind power are actively being proceeded. Wind turbine tower has a major role for safety in the wind turbine systems. It is necessary for design tower structure to consider various environmental conditions. Earthquake, as one of the such environmental loads, is ground motion that applied to bottom of the tower structure and has a possibility of critical effect to the wind tower structure. There are various ways for seismic analysis, but design specifications that are in use do not suggest detailed method for seismic analysis. In this study, seismic responses are analyzed through different ways and the adequacy of seismic design methods is examined.

This study analyzes buckling in the lower segment of a tubular steel shell that exhibits the characteristics of a 3MW wind tower with opening and reinforcement. Analytical method using parametric equations based on Eurocode 3 - Design of Steel Structures and numerical method of finite element are used to analyze the critical meridional buckling stress. ABAQUS, a finite element program, is used for the numerical method analysis. Four different cases of tubular steel tower is modeled: without door opening and without reinforcement; with door opening and without reinforcement; without door opening and with reinforcement; and with door opening and with reinforcement. Using the ABAQUS, a linear buckling analysis is done for all cases to recognize five of its buckling mode shapes and its corresponding eigenvalues. Mode shapes from the previous analysis are considered in performing the non-linear analysis using Static Riks. Buckling capacity and its trends in the localized area near the opening is investigated, tabulated and shown in illustrative charts. Moreover, comparison is made between the parametric and finite element analyses.

풍력발전 타워는 높은 세장비를 갖는 형상으로 인해 바람에 의해 발생하는 횡하중에 취약한 구조를 가지고 있기 때문에 바람은 풍력발전 타워를 설계하는데 있어서 중요한 설계요소 중 하나라고 할 수 있다. 본 논문에서는 타워 운송 편의성 향상을 위해 설계된 8각 및 6각 단면형상을 가지는 조립식 강관 타워 및 일반 원형 강관 타워의 일정 높이 이상에서부터 4개의 작은 기둥으로 분리되는 형상을 가지는 멀티기둥 강관 타워에 대한 2차원 단면모형 풍동실험과 3차원 모형 풍동실험을 수행하여 각 형상별 풍력계수를 산정하여 그 특성을 비교하였다. 또한 풍동실험 축소모형에 대한 CFD 해석을 수행하여 산정된 풍력계수값의 신뢰성을 확인하였으며, 마지막으로 실제스케일 풍력타워에 대한 CFD 해석을 수행하여 각 형상별 특성을 분석하였다.