• Wind and Structures
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• v.30 no.1
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• pp.85-97
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• 2020

The accurate estimation of the buffeting response of a bridge pylon is related to the quality of the bridge construction. To evaluate the influence of wind field characteristics on the buffeting response of a pylon in a trumpet-shaped mountain pass, this paper deduced a multimodal coupled buffeting frequency domain calculation method for a variable-section bridge tower under the twisted wind profile condition based on quasi-steady theory. Through the long-term measurement of the wind field of the trumpet-shaped mountain pass, the wind characteristics were studied systematically. The effects of the wind characteristics, wind yaw angles, mean wind speeds, and wind profiles on the buffeting response were discussed. The results show that the mean wind characteristics are affected by the terrain and that the wind profile is severely twisted. The optimal fit distribution of the monthly and annual maximum wind speeds is the log-logistic distribution, and the generalized extreme value I distribution may underestimate the return wind speed. The design wind characteristics will overestimate the buffeting response of the pylon. The buffeting response of the pylon is obviously affected by the wind yaw angle and mean wind speed. To accurately estimate the buffeting response of the pylon in an actual construction, it is necessary to consider the twisted effect of the wind profile.

• International Journal of High-Rise Buildings
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• v.11 no.4
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• pp.241-263
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• 2022

The conventional wind and twisted-wind effect on aerodynamic properties of neighboring buildings arranged in side-by-side and tandem systems at 2B and 5B spacings are systematically investigated by large eddy simulation. Different physical interactions between different wind profiles and neighboring buildings will be deeply understood. The neighboring-building system under two different types of wind profiles, i.e., conventional wind profile (CWP), twisted wind profiles (TWP) with the maximum twisted angle of 30°, is used to evaluate the variation of physical mechanism between wind and buildings. Aerodynamic characteristics including mean and RMS pressure coefficient, and velocity field were systematically analyzed and compared between different scenario. It was found that the distribution of mean pressure, root-mean-square x velocity and the streamline of wind flow for TWP greatly deviated from CWP, and the effect of TWP on the downstream building, was drastically different from that of CWP, such as the size of vortexes after the lower stream building being bigger when exposed to TWP, and the mean pressure distribution on the building surfaces are also different. Moreover, evidence of buildings arranged in side-by-side and tandem configurations having interchangeable properties under TWP was also discovered, that two buildings being arranged side-by-side exposed to TWP could be identified as being arranged in tandem with a different wind twist angle, or vice versa.

• Journal of the Korean Society of Safety
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• v.33 no.1
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• pp.81-87
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• 2018

The seismic response, the natural frequencies and the mode shapes of an offshore wind turbine with twisted tripod substructure subject to various pile-ground interactions are discussed in this paper. The acceleration responses of the tower head by four historical earthquakes are presented as the seismic response, while the other loads are assumed as ambient loads. For the pile-ground interactions, the fixed, linear and nonlinear models are employed to simulate the interactions and the p-y, t-z and Q-z curves are utilized for the linear and nonlinear models. The curves are designed for stiff, medium and soft clays, and thus, the seven types of the pile-ground interactions are used to compare the seismic response, the acceleration of the tower head. The mode shapes are similar to each other for all types of pile-ground interactions. The natural frequencies, however, are almost same for the three clay types of the linear model, while the natural frequency of the fixed support model is quite different from that of the linear interaction model. The wind turbine with the fixed support model has the biggest magnitude of acceleration. In addition, the nonlinear model is more sensitive to the stiffness of clay than the linear pile-ground interaction model.

• Journal of the Korean Society of Visualization
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• v.13 no.1
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• pp.15-20
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• 2015

Sensitivity studies of blade angle and twisted angle are numerically investigated to optimize the Savonius blade. As blade angle increases, the contact area between blade and wind decreases, showing the suppression of the vortex generation near blade. Compared to the blade angle of 0 degree, the blade angle of 20 degree shows about 2.6% increment of power efficiency. Based on the blade angle of 20 degree, sensitivity studies of the twisted angle are performed. The result indicates that the adjustment of the twisted angle causes the torque of blade to increase. Optimized blade can suppress the formation of the vortex structure in rear region. Also, wind flows without disturbance of vortex when passing through the optimized blade. The 1kw vertical wind turbine system with optimized blade can generate 4442.2kWh per year and have 53% capacity factor.

• Steel and Composite Structures
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• v.18 no.1
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• pp.121-134
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• 2015

This paper is to investigate the potentials of the elastic seismic design of twisted high-rise steel diagrid frame buildings in the strong wind and moderate/low seismicity regions. First, the prototypes of high-rise steel diagrid frames with architectural plans that have a twist angle of 0 (regular-shaped), 1, and 2 degrees were designed to resist wind. Then, the effects of the twist angle on the estimated quantities and structural redundancies of the diagrid frames were examined. Second, the seismic performance of the wind-designed prototype buildings under a low seismicity was evaluated. The response spectrum analysis was conducted for the service level earthquake (SLE) having 43-year return period and the maximum considered earthquake (MCE) having 2475-year return period. The evaluation resulted that the twisted high-rise steel diagrid frames resisted the service level earthquake elastically and most of their diagrid members remained elastic even under the maximum considered earthquake.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.144-149
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• 2012

The transfer matrix method is used to determine the dynamic characteristics(natural frequencies and mode shapes) by rotational speed of wind turbine blade. The problems treated on this study is coupled flapwise bending and chordwise bending of pre-twisted nonuniform wind turbine blade. The orthogonality relations that exist between the vibrational modes is derived and the algorithm for determination of the natural vibrational characteristics is suggested.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.125-132
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• 2019

This paper presents a seismic reliability analysis method for an offshore wind turbine with a twisted tripod support structure under earthquake loading. A three dimensional dynamic finite element model is proposed to consider the nonlinearity of the ground-pile interactions and the geometrical characteristics of the twisted tripod support structure where out-of-plane displacement occurs even under in-plane lateral loadings. For the evaluation of seismic reliability, the failure probability was calculated for the maximum horizontal displacement of the pile head, which is calculated from time history analysis using artificial earthquakes for the design return periods. The application of the subset simulation method using the Markov Chain Monte Carlo(MCMC) sampling is proposed for efficient reliability analysis considering the limit state equation evaluation by the nonlinear time history analysis. The proposed method can be applied to the reliability evaluation and design criteria development of the offshore wind turbine with twisted tripod support structure in which two dimensional models and static analysis can not produce accurate results.

• Solar Energy
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• v.6 no.2
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• pp.86-92
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• 1986

This paper presents the aerodynamic performances of horizontal axis wind turbines with non-twisted but taperd blades. Five configurations of blades, namely, one straight blade and four tapered blades with taper ratio of ranging from 0.1 to 0.7 have been simulated. The aerodynamic performances of the wind turbines have been determined over blade incidence angle of ranging from $2^{\circ}$ to $6^{\circ}$ and keeping same solidity and radius of them. The results are presented comparing straight blade from four tapered blades for maximum power coefficient and tip looses against variation of taper ratio. It also shows that the wind turbine with taper ratio of 0.5 has the highest maximum power coefficient than others. And wind turbines with taper ratio below 0.2 have lower values of maximum power coefficients than straight one. The tip loss of straight blade is the largest and reduces Slightly with the decrementation of taper ratio.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.333-334
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• 2008

Overhead transmission lines are classified by the number of sub conductors per phase. Korean transmission lines use two, four, or six-conductor bundle. Bundle of conductors must have spacers or spacer dampers which keep the proper distance between sub conductors. They can prevent conductors from being vibrated or twisted due to the wind. As for the two-conductor bundle, alternating current flow generates absorption force between sub conductors which may cause a collision of sub conductors. To prevent sub conductors from being vibrated, twisted, and collided, spacer or spacer damper installation method is designed considering vibration characteristics of sub conductors. We have spacer installation method for four or six-conductor bundle lines. However, we don't have it for two-conductor bundle ones. So we have installed spacers at regular intervals in two-conductor bundle lines, and it caused rigid body oscillation of conductors due to the wind which made a flashover between conductors. This paper introduces a vibration characteristic analysis of two-conductor bundle and proposes a spacer installation method for two-conductor bundle lines.

• New & Renewable Energy
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• v.4 no.3
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• pp.36-44
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• 2008

This paper discusses about the mathematical modelling of a new conceptual shape of horizontal axis wind turbine. The geometrical characteristic of wind turbine is studied for the variation of azimuthal angles and elevation angles. The projecting trajectories of Cuban-8 blade due to rotation are analyzed on the each plane in the Cartesian coordinate system. Trajectories show several interesting graphical patterns since the geometrical shape is complicated with the rotational motion of two twisted circumferential blades with elevation angles.