• Wind and Structures
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• v.38 no.5
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• pp.367-379
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• 2024

Compared with traditional transmission towers, T-shaped angle towers have long cross-arms and are specially used for ultrahigh-voltage direct-current (UHVDC) transmission. Nevertheless, the wind loads of T-shaped towers have not received much attention in previous studies. Consequently, a series of wind tunnel tests on the T-shaped towers featuring cross-arms of varying lengths were conducted using the high-frequency force balance (HFFB) technique. The test results reveal that the T-shaped tower's drag coefficients nearly remain constant at different testing velocities, demonstrating that Reynolds number effects are negligible in the test range of 1.26 × 10⁴-2.30 × 10⁴. The maximum values of the longitudinal base shear and torsion of the T-shaped tower are reached at 15° and 25° of wind incidence, respectively. In the yaw angle, the crosswind coefficients of the tower body are quite small, whereas those of the cross-arms are significant, and as a result, the assumption in some load codes (such as ASCE 74-2020, IEC 60826-2017 and EN 50341-1:2012) that the resultant force direction is the same as the wind direction may be inappropriate for the cross-arm situation. The fitting formulas for the wind load-distribution factors of the tower body and cross-arms are developed, respectively, which would greatly facilitate the determination of the wind loads on T-shaped angle towers.

• Smart Structures and Systems
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• v.3 no.3
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• pp.341-356
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• 2007

A good understanding of normal modal variability of civil structures due to varying environmental conditions such as temperature and wind is important for reliable performance of vibration-based damage detection methods. This paper addresses the quantification of wind-induced modal variability of a cable-stayed bridge making use of one-year monitoring data. In order to discriminate the wind-induced modal variability from the temperature-induced modal variability, the one-year monitoring data are divided into two sets: the first set includes the data obtained under weak wind conditions (hourly-average wind speed less than 2 m/s) during all four seasons, and the second set includes the data obtained under both weak and strong (typhoon) wind conditions during the summer only. The measured modal frequencies and temperatures of the bridge obtained from the first set of data are used to formulate temperature-frequency correlation models by means of artificial neural network technique. Before the second set of data is utilized to quantify the wind-induced modal variability, the effect of temperature on the measured modal frequencies is first eliminated by normalizing these modal frequencies to a reference temperature with the use of the temperature-frequency correlation models. Then the wind-induced modal variability is quantitatively evaluated by correlating the normalized modal frequencies for each mode with the wind speed measurement data. It is revealed that in contrast to the dependence of modal frequencies on temperature, there is no explicit correlation between the modal frequencies and wind intensity. For most of the measured modes, the modal frequencies exhibit a slightly increasing trend with the increase of wind speed in statistical sense. The relative variation of the modal frequencies arising from wind effect (with the maximum hourly-average wind speed up to 17.6 m/s) is estimated to range from 1.61% to 7.87% for the measured 8 modes of the bridge, being notably less than the modal variability caused by temperature effect.

• Wind and Structures
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• v.6 no.1
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• pp.71-90
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• 2003

In recent years, high-strength, light-weight materials have been widely used in the construction of high-rise buildings. Such structures generally have flexible, low-damping characteristics. Consequently, wind-induced oscillation greatly affects the structural safety and the comfort of the building's occupants. In this research, wind tunnel experiments were carried out to study the wind-induced vibration of a building with a tuned liquid column damper (TLCD). Then, a model for predicting the aerodynamic response in the across-wind direction was generated. Finally, a computing procedure was developed for the analytical modeling of the structural oscillation in a building with a TLCD under the wind load. The model agrees substantially with the experimental results. Therefore, it may be used to accurately calculate the structural response. Results from this investigation show that the TLCD is more advantageous for reducing the across-wind vibration than the along-wind oscillation. When the across-wind aerodynamic effects are considered, the TLCD more effectively controls the aerodynamic response. Moreover, it is also more useful in suppressing the acceleration than the displacement in biaxial directions. As s result, TLCDs are effective devices for reducing the wind-induced vibration in buildings. Parametric studies have also been conducted to evaluate the effectiveness of the TLCD in suppressing the structural oscillation. This study may help engineers to more correctly predict the aerodynamic response of high-rise buildings as well as select the most appropriate TLCDs for reducing the structural vibration under the wind load. It may also improve the understanding of wind-structure interactions and wind resistant designs for high-rise buildings.

• Journal of Ocean Engineering and Technology
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• v.35 no.5
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• pp.382-392
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• 2021

In recent years, floating offshore wind turbines have attracted more attention as a new renewable energy resource while bottom-fixed offshore wind turbines reach their limit of water depth. Various projects have been proposed with the rapid increase in installed floating wind power capacity, but the economic aspect remains as a biggest issue. To figure out sensible approaches for saving costs, a comparison analysis of the levelized cost of electricity (LCOE) between floating and bottom-fixed offshore wind turbines was carried out. The LCOE was reviewed from a social perspective and a cost breakdown and a literature review analysis were used to itemize the costs into its various components in each level of power plant and system integration. The results show that the highest proportion in capital expenditure of a floating offshore wind turbine results in the substructure part, which is the main difference from a bottom-fixed wind turbine. A floating offshore wind turbine was found to have several advantages over a bottom-fixed wind turbine. Although a similarity in operation and maintenance cost structure is revealed, a floating wind turbine still has the benefit of being able to be maintained at a seaport. After emphasizing the cost-reduction advantages of a floating wind turbine, its LCOE outlook is provided to give a brief overview in the following years. Finally, some estimated cost drivers, such as economics of scale, wind turbine rating, a floater with mooring system, and grid connection cost, are outlined as proposals for floating wind LCOE reduction.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.12
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• pp.1164-1171
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• 2012

Recently, researches related to the green energy generation systems have increased significantly. Among them wind turbines are the most spread practical green energy generation systems. In order to enhance the power generation capacity of the wind turbine blade, the length of wind turbine blade has increased. It might cause undesirable excessive dynamic loads. Therefore dynamic characteristics of a wind turbine blade system should be identified for a safe design of the system. In this study, the equations of motion of a wind turbine blade system undergoing gravitational force are derived considering wind force and pitch angle. Effects of wind speed, variation of pitch angle of the wind turbine blade, rotating speed, and the blade length on its stability characteristics are investigated.

• Wind and Structures
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• v.27 no.1
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• pp.41-57
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• 2018

Concentrated Solar Photovoltaic (CPV) is a promising alternative to conventional solar structures. These solar tracking structures need to be optimized to be competitive against other types of energy production. In particular, the selection of the structural parameters needs to be optimized with regards to the dynamic wind response. This study aims to evaluate the effect of the main structural parameters, as selected in the preliminary design phase, on the wind response and then on the weight of the steel support structure. A parametric study has been performed where parameters influencing dynamic wind response are varied. The study is performed using a semi-deterministic time-domain wind analysis method. Unsteady aerodynamic model is applied for the shape of the CPV structure collector at different configurations in conjunction with a consistent mass-spring-damper model with the corresponding degrees of freedom to describe the dynamic response of the system. It is shown that, unlike the static response analysis, the variation of the peak wind response with many structural parameters is highly nonlinear because of the dynamic wind action. A steel structural optimization process reveals that close attention to structural and site wind parameters could lead to optimal design of CPV steel support structure.

• Journal of the Korean Solar Energy Society
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• v.37 no.6
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• pp.13-24
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• 2017

Finding promising wind farm sites in islands of Korea is performed in this study. Total ten islands that have been measuring wind speed and direction using automatic weather stations for at least ten years were subjects of this study. Conditions for finding suitable wind farm sites including wind resource and various exclusion factors were applied and two islands that were found not to be suitable for wind farms were excluded. Micositing of a single wind turbine for the remaining eight islands was performed to estimate the annual energy production and the capacity factor.. Based on the simulation results, the wind farm sites selected within the eight islands were found to be suitable for wind power. The capacity factors were varied between 22.3% and 33.0% for a 100 kW wind turbine having a hub height of 30 m.

• Wind and Structures
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• v.18 no.6
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• pp.599-618
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• 2014

In this study, a square rectangular tall building is considered to investigate the effects of turbulence integral length scale and turbulence intensity on the along-wind responses, across-wind responses and torsional responses of the tall building by Large Eddy Simulation (LES). A recently proposed inflow turbulence generator called the discretizing and synthesizing random flow generation (DSRFG) approach is applied to simulate turbulent flow fields. It has been proved that the approach is able to generate a fluctuating turbulent flow field satisfying any given spectrum, desired turbulence intensity and wind speed profiles. Five profiles of turbulence integral length scale and turbulence intensity are respectively generated for the inflow fields by the DSRFG approach for investigating the effects of turbulence integral length scale and turbulence intensity on the wind-induced responses of the tall building. The computational results indicate that turbulence integral length scale does not have significant effect on the along-wind (displacement, velocity and acceleration) responses, across-wind displacement and velocity responses, while the across-wind acceleration and torsional responses vary without a clear rule with the parameter. On the other hand, the along-wind, across-wind and torsional responses increase with the growth of turbulence intensity.

• Wind and Structures
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• v.30 no.2
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• pp.141-153
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• 2020

Probabilistic information regarding directional extreme wind speeds is important for the precise estimation of the design wind loads on structures. A joint probability distribution model of directional extreme typhoon wind speeds is established using Monte Carlo simulation and empirical copula function to fully consider the correlations of extreme typhoon wind speeds among the different directions. With this model, a procedure for estimating directional extreme wind speeds for given return periods, which ensures that the overall risk is distributed uniformly by direction, is established. Taking 5 typhoon-prone cities in China as examples, the directional extreme typhoon wind speeds for given return periods estimated by the present method are compared with those estimated by the method proposed by Cook and Miller (1999). Two types of directional factors are obtained based on Cook and Miller (1999) and the UK standard's drafting committee (Standard B, 1997), and the directional risks for the given overall risks are discussed. The influences of the extreme wind speed correlations in the different directions and the simulated typhoon wind speed sample sizes on the estimated extreme wind speeds for a given return period are also discussed.

• Wind and Structures
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• v.31 no.5
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• pp.473-482
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• 2020

The first-order method for estimating the extreme wind pressure on building envelopes with consideration of the directionality of wind speed and wind pressure is improved to enhance its computational efficiency. In this improved method, the result is obtained directly from the empirical distribution of a random selection of annual maximum wind pressure samples generated by a Monte Carlo method, rather than from the previously utilized extreme wind pressure probability distribution. A discussion of the relationship between the first- and full-order methods indicates that when extreme wind pressures in a non-typhoon climate with a high return period are estimated with consideration of directionality, using the relatively simple first-order method instead of the computationally intensive full-order method is reasonable. The validation of this reasonableness is equivalent to validating two assumptions to improve its computational efficiency: 1) The result obtained by the full-order method is conservative when the extreme wind pressure events among different sectors are independent. 2) The result obtained by the first-order method for a high return period is not significantly affected when the extreme wind speeds among the different sectors are assumed to be independent. These two assumptions are validated by examples in different regions and theoretical derivation.