• 한국신재생에너지학회:학술대회논문집
• /
• 2008.05a
• /
• pp.278-281
• /
• 2008

This study demonstrates the advantages of a shear-free structure designed to modify vertical profiles of wind speed in the atmospheric surface layer. Computational fluid dynamics(CFD) software, FLUENT is used to interpret the velocity field modification around the structure and wind turbine. The shapes of shear-free structure, installed at upstream toward prevailing wind direction, would be fences, buildings and trees, etc. According to the simulation results, it is obvious that wind shear between heights of wind turbine's blades is decreased together with a speed-up advantage. This would lead decrease of periodic wind loading caused by wind shear and power-out increase by flow uniformity and wind speed-up.

• Advances in concrete construction
• /
• v.5 no.5
• /
• pp.469-479
• /
• 2017

Balanced cantilever construction is extensively used in the construction of prestressed concrete (PSC) box-girder bridges. Shear-lag effect is usually considered in finished bridges, while the cumulative shear-lag effect in bridges during balanced cantilever construction is considered only rarely. In this paper, based on the balanced cantilever construction sequences of large-span PSC box-girder bridges, the difference method is employed to analyze the cumulative shear-lag effect of box girders with varying depth under the concrete segments' own weight. During cantilever construction, no negative shear-lag effect is generated, and the cumulative shear-lag effect under the balanced construction procedure is greater than the instantaneous shear-lag effect in which the full dead weight is applied to the entire cantilever. Three cross-sections of Jianjiang Bridge were chosen for the experimental observation of shear-lag effect, and the experimental results are in keeping with the theoretical results of cumulative shear-lag effect. The research indicates that only calculating the instantaneous shear-lag effect is not sufficiently safe for practical engineering purposes.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.44 no.5
• /
• pp.399-406
• /
• 2016

The large scale wind turbine blades usually experience periodic change of inflow speed due to blade rotation inside the ground shear flow region. Because of the vertical wind shear, the inflow velocity in the boundary layer region is maximum at uppermost position and minimum at lowermost position. These spatial distribution of wind speeds can lead to the periodic oscillation of the 6-component loads at hub and low speed shaft of the wind turbine rotor. In this study we compare the aerodynamic loads between two inflow conditions, i.e, uniform flow (no vertical wind shear effect) and normal wind profile. From the computed results all of the relative errors for oscillating amplitudes increased due to the ground shear flow effect. Especially bending moment and thrust at hub, and bending moments at LSS increased enormously. It turns out that the aerodynamic analysis including the ground shear flow effect must be considered for fatigue analysis.

• The KSFM Journal of Fluid Machinery
• /
• v.19 no.6
• /
• pp.14-18
• /
• 2016

Multi-MW wind turbines have very large blades over 40~50 m in length. Some factors like wind shear and tower shadow make an effect on asymmetric loads on the blades. Larger asymmetric loads are produced as the length of blade is getting longer. In this paper, a 2 MW on-shore wind turbine is considered and variations of thrust on 3 blades and rotor hub under wind shear are calculated by using a commercial Bladed S/W and dynamic properties of the thrust variations are investigated. It is shown that the amplitude of the asymmetric thrust on each blade under wind shear is getting larger as the wind speed increases, the frequency of the thrust variation on each blade is same as the one of rotor speed, and the frequency of the thrust variation at rotor hub is 3 times as high as the one of rotor speed.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.11a
• /
• pp.182.2-182.2
• /
• 2010

A various algorism has been studied to extract possibly every energy from a wind turbine in conjunction with the increase of concern about wind power system. In order to verify these control algorism, it is essential to make the most similar conditions to the real wind turbine's environment. Therefore, using separately excited DC motor a wind turbine the most similar to the real turbine is simulated. Tower shadow effect and Wind shear effect are considered as well as inertia emulation. For the control of Back-to-Back Converter Vector current control methods and space vector pulse width modulation are used and for reducing THD of grid current LCL filter is considered. This simulation results verified the energy produced by wind all flows into the utility under the consideration of the characteristics of a wind turbine. The result of this paper is expected to be used as a basic material for analyzing the characteristics of the wind turbine generator.

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.11a
• /
• pp.387-390
• /
• 2007

Recently the diameter of the 5MW wind turbine reaches 126m, and the tower height is nearly the same with the wind turbine diameter. The blade will experience periodic inflow oscillation due to blade rotation inside the ground shear flow region, that is, the inflow velocity is maximum at uppermost position and minimum at lowermost position. In this study we compare the aerodynamic data between two inflow conditions, i.e, uniform flow and normal wind profile. From the computed results all of the relative errors for oscillating amplitudes increased due to the ground shear flow effect. Especially My at hub and $F_x$, $M_y$, $M_z$ at LSS increased enormously. It turns out that the aerodynamic analysis including the ground shear flow effect must be considered for fatigue load analysis.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.4
• /
• pp.407-414
• /
• 2016

As wind turbines are getting larger in size with multi-MW capacity, the blades are getting longer, over 40 m, and hence the asymmetric loads produced during the rotation of the rotor blades are increasing. Some factors such as wind shear, tower shadow, and turbulence have an effect on the asymmetric loads on the blades. This paper focuses on a method of modeling the dynamic load acting on a blade because of thrust variation under wind shear. A method that uses thrust coefficient is presented. For this purpose, "wind shear coefficient of thrust variation" is defined and introduced. Further, we calculate the values of the "wind shear coefficient of thrust variation" for a 2 MW on-shore wind turbine, and analyze them for speeds below the rated wind speed. Then, we implement a dynamic model that represents the thrust variation under wind shear on a blade, using MATLAB/Simulink. It is shown that it is possible to express thrust variations on three blades under wind shear by using both thrust coefficient and "wind shear coefficient of thrust variation."

• Journal of Korean Association for Spatial Structures
• /
• v.11 no.1
• /
• pp.47-56
• /
• 2011

In general, shear walls are employed as lateral resistance system. Most of shear wall structures require openings in shear walls and thus shear walls are linked by floor slabs or coupling beams resulting in the coupled shear wall structures. In this study, an LRB (lead rubber bearing) was introduced in the middle of the coupling beam of the coupled shear wall structures and the wind-induced response reduction effect of this system was investigated. In order to evaluate the control performance of the proposed method, 20- and 30-story building structures were used as example structures and boundary nonlinear time history analyses have been performed using artificial wind excitation. Japanese vibration evaluation criteria was employed to evaluate whether the proposed system could improve the serviceability of the tall coupled shear wall structures under wind excitation. Based on analytical results, it has been shown that the proposed method that connects shear walls with LRBs can improve the wind-induced response control effect.

• Wind and Structures
• /
• v.36 no.3
• /
• pp.201-213
• /
• 2023

In this study, the effect of sea surface temperature (SST) on the distribution of vertical wind speed in the atmospheric boundary layer of coastal areas was analyzed. In general, coastal areas are known to be more susceptible to various meteorological factors than inland areas due to interannual changes in sea surface temperature. Therefore, the purpose of this study is to analyze the relationship between sea surface temperature (ERA5) and wind resource data based on the meteorological mast of Høvsøre, the test bed area of the onshore wind farm in the coastal area of Denmark. In addition, the possibility of coastal disasters caused by abnormal vertical wind shear due to changes in sea surface temperature was also analyzed. According to the analysis of the correlation between the wind resource data at met mast and the sea surface temperature by ERA5, the wind speed from the sea and the vertical wind shear are stronger than from the inland, and are vulnerable to seasonal sea surface temperature fluctuations. In particular, the abnormal vertical wind shear, in which only the lower wind speed was strengthened and appeared in the form of a nose, mainly appeared in winter when the atmosphere was near-neutral or stable, and all occurred when the wind blows from the sea. This phenomenon usually occurred when there was a sudden change in sea surface temperature within a short period of time.

• Wind and Structures
• /
• v.17 no.6
• /
• pp.589-608
• /
• 2013

A model is proposed to analyse the along-wind dynamic response of upwind turbines with horizontal axis under service wind conditions. The model takes into account the dynamic coupling effect between rotor blades and supporting tower. The wind speed field is decomposed into a mean component, accounting for the well-known wind shear effect, and a fluctuating component, treated through a spectral approach. Accordingly, the so-called rotationally sampled spectra are introduced for the blades to account for the effect of their rotating motion. Wind forces acting on the rotor blades are calculated according to the blade element momentum model. The tower shadow effect is also included in the present model. Two examples of a large and medium size wind turbines are modelled, and their dynamic response is analysed and compared with the results of a conventional static analysis.