• Wind and Structures
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• 제36권1호
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• pp.1-14
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• 2023

To evaluate the wind shielding effect of bridge towers with multiple limbs on high-speed trains, a wind tunnel test was conducted to investigate the aerodynamic characteristics of vehicles traversing multi-limb towers, which represented a combination of the steady aerodynamic coefficient of the vehicle-bridge system and wind environment around the tower. Subsequently, the analysis model of wind-vehicle-bridge (WVB) system considering the additional moments caused by lift and drag forces under nonuniform wind was proposed, and the reliability and accuracy of the proposed model of WVB system were verified using another model. Finally, the factors influencing the wind shielding effect of multi-limb towers were analyzed. The results indicate that the wind speed distributions along the span exhibit two sudden changes, and the wind speed generally decreases with increasing wind direction angle. The pitching and yawing accelerations of vehicles under nonuniform wind loads significantly increase due to the additional pitching and yawing moments. The sudden change values of the lateral and yawing accelerations caused by the wind shielding effect of multi-limb tower are 0.43 m/s² and 0.11 rad/s² within 0.4 s, respectively. The results indicate that the wind shielding effect of a multi-limb tower is the controlling factor in WVB systems.

• Wind and Structures
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• 제31권5호
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• pp.459-472
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• 2020

This study focused on the non-synoptic, tornado-like wind-induced effects on flexible horizontal structures that are extremely sensitive to winds. More specifically, the nonuniform, intensive vertical wind-velocity and transient natures of tornado events and their effects on the global behavior of a long-span bridge were investigated. In addition to the static part in the modeling of tornado-like wind-induced loads, the motion-induced effects were modeled using the semi-empirical model with a two-dimensional (2-D) indicial response function. Both nonlinear wind-induced static analysis and linear aeroelastic analysis in the time domain were conducted based on a 3-D finite-element model to investigate the bridge performance under the most unfavorable tornado pattern considering wind-structure interactions. The results from the present study highlighted the important effects due to abovementioned tornado natures (i.e., nonuniform, intensive vertical wind-velocity and transient features) on the long-span bridge, and hence may facilitate more appropriate wind design of flexible horizontal structures in the tornado-prone areas.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 춘계학술대회 논문집
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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.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.42.2-42.2
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• 2011

Noise generated from wind turbines has been predicted by numerical methods. Sound pressure level(SPL) on the turbines is predicted after aerodynamic analysis is carried out by Wind Turbine Flow, Aeroacoustics and Structure analysis (WINFAS) code. The level of each panel of acoustic sphere is determined by the sum of tonal, turbulence ingestion and airfoil self noise. With the noise source database, the acoustic sphere, SPL on the ground is calculated using the model based on acoustic ray theory. The model has been designed to consider the effects on the condition of terrain and atmosphere. The variations of SPL on the ground occur not only because of the different source level but also because of the nonuniform distributions of the sound speed along the height. Hence, the profile of an effective sound speed which is the sum of the contribution of sound speed to a temperature gradient and a wind speed variation is used by the theory based on atmospheric stability. With the integrated numerical method, the prediction of sound propagation on the wind farm is carried out with the states of the atmospheric stability.

• 농업과학연구
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• 제47권2호
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• pp.381-394
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• 2020

Accelerated soil wind erosion still remains to date to cause severe economic and environmental impacts. Revised and updated models to quantitatively evaluate wind induced soil erosion have been made for specific factors in the wind erosion equation (WEQ) framework. Because of increasing quantities of accumulated data, the WEQ, the revised wind erosion equation (RWEQ), the wind erosion prediction system (WEPS), and other soil wind erosion models have been established. These soil wind erosion models provide essential knowledge about where and when wind erosion occurs although naturally, they are less accurate than the field-scale. The WEQ was a good empirical model for comparing the effects of various management practices on potential erosion before the RWEQ and the WEPS showed more realistic estimates of erosion using easily measured local soil and climatic variables as inputs. The significant relationship between the observed and predicted transport capacity and soil loss makes the RWEQ a suitable tool for a large scale prediction of the wind erosion potential. WEPS developed to replace the empirical WEQ can calculate soil loss on a daily basis, provide capability to handle nonuniform areas, and obtain predictions for specific areas of interest. However, the challenge of precisely estimating wind erosion at a specific regional scale still remains to date.

• 대한기계학회논문집B
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• 제24권2호
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• pp.251-259
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• 2000

The ionic wind formed in a nonuniform electric field has been recognized to have a significant effect on particle collection in an electrostatic precipitator(ESP). Under normal operating conditions the effect of ionic wind is not pronounced. However, as the flow velocity becomes smaller, the ionic wind becomes pronounced and induces secondary flow, which has a significant influence on the flow field and the particle collecting efficiency. In this paper, experiments for investigating the effect of secondary flow on collection efficiencies were carried out by changing the flow velocities in 0.2-0.7m/s and the applied voltages in 9-11kV/cm. The particle size distributions and concentrations are measured by DMA and CNC. To analyze the experimental results, numerical analysis of electric filed in ESP was carried out. It shows that particle collection is influenced by two independent dimensionless numbers, $Re_{ehd}\;and\;Re_{flow}$ not by $N_{ehd}$ alone. When $Re_{flow}$, decreases for constant $Re_{ehd}$, the secondary flow prohibits the particle collection. But when $Re_{ehd}$ increases for constant $Re_{flow}$, it enhances the particle collection by driving the particles into the collection region.

• 한국자동차공학회논문집
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• 제9권4호
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• pp.10-17
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• 2001

The performance of a radiator is generally determined using a wind tunnel, in which the air velocity is uniform. However, when it is installed in a car, the distribution of the air velocity becomes nonuniform due to front-end openings, cross members, and horns etc., resulting in lower performance. In this study, several underhood flow simulations have been first performed to get flow rates and velocity distributions over the radiator. Secondly heat release rates are calculated by both a performance curve and a radiator model. Finally, using an engine cooling system simulator, radiator-top-tank temperature is predicted and the variations of heat release rate and radiator-top-tank temperature with nonuniformity of air velocity distributions are analyzed. The results show that the current engine cooling model successfully accounts for the nonuniformity effects that should be considered for higher accuracy in predicting engine cooling performance.

• 한국지구과학회지
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• 제36권3호
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• pp.210-221
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• 2015

지형적인 형태와 지표면의 물리적인 특성은 기상장 뿐 만 아니라 대기질 수치 모델링에서도 가장 중요한 입력변수가 된다. 대부분 복잡지형에서 일어나는 국지적인 기상의 일변동들이 지형적인 불균일성에 의해 지배되기도 한다. 이러한 지형적인 특징들은 열적으로 유도된 대기흐름에 영향을 일으키며 직접적으로는 풍계의 변화를 가져오거나 지표면 가열 온도 자체에서의 중요한 변화를 가져와 간접적으로 영향을 주기도 한다. 복잡지형에서 이러한 변화양상들은 지형적인 특징 즉, 지형적 경사와 성질에 의한 태양복사 에너지의 불균등한 분배에 기인한다. 그러므로 기상장 묘사가 어려운 복잡지형에서는 관측값에 더 가까운 정확한 바람장을 예측하기 위해 상세한 지형 정보와 지표면 자료가 중요하게 된다. 본 연구에서는 상세한 지표면과 지형자료를 지표 경계자료로 활용한 MM5-A2C 모델을 이용하여 복잡한 지형적 조건을 가진 산지지역에서의 바람장 수치모의를 하고자 한다. MM5-A2C에 의해 유도된 기상장은 국지규모의 산지주변에서의 지형강제력에 의한 기상장 해석을 정밀하게 예측하여 모델 내의 지형적 조건이 미치는 영향에 대해 직접적인 영향을 주고 있음을 알 수 있었다.