• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• Wind and Structures
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• v.27 no.4
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• pp.223-234
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• 2018

In this study, a simplified three-dimensional calculation model is developed for the dynamic analysis of soil-pile group-supertall building systems excited by wind loads using the substructure method. Wind loads acting on a 300-m building in different wind directions and terrain conditions are obtained from synchronous pressure measurements conducted in a wind tunnel. The effects of soil-structure interaction (SSI) on the first natural frequency, wind-induced static displacement, root mean square (RMS) of displacement, and RMS of acceleration at the top of supertall buildings are analyzed. The findings demonstrate that with decreasing soil shear wave velocity, the first natural frequency decreases and the static displacement, RMS of displacement and RMS of acceleration increase. In addition, as soil material damping decreases, the RMS of displacement and the RMS of acceleration increase.

• Wind and Structures
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• v.21 no.1
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• pp.63-84
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• 2015

The shape of a tall building has significant impact on wind force generation and wind-induced dynamic response. To study the effect of recessed cavities, wind excitations on a wind-tunnel model of an H-section tall building were compared with those on a square-section building model. Characteristics of the fluctuating wind pressures on the side faces of the two tall buildings and their role in the generation of crosswind forces on the buildings were investigated with the space-time statistical tool of proper orthogonal decomposition (POD). This paper also compares the use of different pressure data sets for POD analysis in situations where pressures on two different surfaces are responsible for the generation of a wind force. The first POD mode is found to dominate the generation of crosswind excitation on the buildings.

• Structural Engineering and Mechanics
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• v.46 no.5
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• pp.735-753
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• 2013

The wind load is always the dominant load of cooling tower due to its large size, complex geometry and thin-wall structure. At present, when computing the wind-induced response of the large-scale cooling tower, the wind pressure distribution is obtained based on code regulations, wind tunnel test or computational fluid dynamic (CFD) analysis, and then is imposed on the tower structure. However, such method fails to consider the change of the wind load with the deformation of cooling tower, which may result in error of the wind load. In this paper, the analysis of the large cooling tower based on the iterative method for wind pressure is studied, in which the advantages of CFD and finite element method (FEM) are combined in order to improve the accuracy. The comparative study of the results obtained from the code regulations and iterative method is conducted. The results show that with the increase of the mean wind speed, the difference between the methods becomes bigger. On the other hand, based on the design of experiment (DOE), an approximate model is built for the optimal design of the large-scale cooling tower by a two-level optimization strategy, which makes use of code-based design method and the proposed iterative method. The results of the numerical example demonstrate the feasibility and efficiency of the proposed method.

• Wind and Structures
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• v.6 no.2
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• pp.107-126
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• 2003

This paper describes a simple and practical approach through the application of Linear Stochastic Estimation (LSE) to reconstruct wind-induced pressure time series from the covariance matrix for structural load analyses on a low building roof. The main application of this work would be the reduction of the data storage requirements for the NIST aerodynamic database. The approach is based on the assumption that a random pressure field can be estimated as a linear combination of some other known pressure time series by truncating nonlinear terms of a Taylor series expansion. Covariances between pressure time series to be simulated and reference time series are used to calculate the estimation coefficients. The performance using different LSE schemes with selected reference time series is demonstrated by the reconstruction of structural load time series in a corner bay for three typical wind directions. It is shown that LSE can simulate structural load time series accurately, given a handful of reference pressure taps (or even a single tap). The performance of LSE depends on the choice of the reference time series, which should be determined by considering the balance between the accuracy, data-storage requirements and the complexity of the approach. The approach should only be used for the determination of structural loads, since individual reconstructed pressure time series (for local load analyses) will have larger errors associated with them.

• Wind and Structures
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• v.31 no.6
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• pp.523-532
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• 2020

As the height and flexibility of high-rise buildings increase, the wind loads become more dominant and the combination coefficient of Equivalent Static Wind Loads (ESWLs) should be considered when they are used in the structural design. In the first phase of the study, a brief introduction to the theory on the combination coefficient for high-rise buildings was given and then the time history of wind-induced responses of a 208-meter high-rise building with an elliptical cross-section was presented based on the wind tunnel test results for pressure measurement. The correlation between wind-induced responses was analyzed and the combination coefficients of ESWLs of the high-rise buildings using Turkstra's rule, and Asami's method, were calculated and compared with related design codes, e.g., AIJ-RLB, ASCE 7-10, and China Load Code for structural design. The results of the study showed that the combination coefficients from Asami's method are conservative compared with the other three methods. The results of this paper would be helpful to the wind-resistant design of high-rise buildings with elliptical cross-section.

• Wind and Structures
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• v.34 no.5
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• pp.437-450
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• 2022

Vortex-induced vibration (VIV) is a significant concern when designing slender structures with square cross sections. VIV strongly depends on structural dynamics and flow states, which depend on the conditions of the approaching flow and shape of a structure. Therefore, the effects of the angle of attack on the coupling effects of VIV for a square cylinder are expected to be significant in practice. In this study, the aerodynamic forces for a fixed and elastically mounted square cylinder were measured using wind pressure tests. Aerodynamic forces on the stationary cylinder are firstly discussed by comparisons of variation of statistical aerodynamic force and wind pressure coefficient with wind angle of attack. The coupling effect between the aerodynamic forces and the motion of the oscillating square cylinder by VIV is subsequently investigated in detail at typical wind angels of attack with occurrence of three typical flow regimes, i.e., leading-edge separation, separation bubble (reattachment), and attached flow. The coupling effect are illustrated by discussing the onset of VIV, characteristics of aerodynamic forces during VIV, and interaction between motion and aerodynamic forces. The results demonstrate that flow states can be classified based on final separation points or the occurrence of reattachment. These states significantly influence coupling effects of the oscillating cylinder. Vibration enhances vortex shedding, which creates strong fluctuations in aerodynamic forces. However, differences in the lock-in range, aerodynamic force, and interaction process for angles of attack smaller and larger than the critical angle of attack revealed noteworthy characteristics in the VIV of a square cylinder.

• Computational Structural Engineering
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• v.25 no.1
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• pp.13-16
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• 2012

• Wind and Structures
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• v.8 no.3
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• pp.197-212
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• 2005

Tall buildings under wind action usually oscillate simultaneously in the along-wind and across-wind directions as well as in torsional modes. While several procedures have been developed for predicting wind-induced loads and responses in along-wind direction, accurate analytical methods for estimating across-wind and torsional response have not been possible yet. Simplified empirical formulas for estimation of the across-wind dynamic responses of rectangular tall buildings are presented in this paper. Unlike established empirical formulas in codifications, the formulas proposed in this paper are developed based on simultaneous pressure measurements from a series of tall building models with various side and aspect ratios in a boundary layer wind tunnel. Comparisons of the across-wind responses determined by the proposed formulas and the results obtained from the wind tunnel tests as well as those estimated by two well-known wind loading codes are made to examine the applicability and accuracy of the proposed simplified formulas. It is shown through the comparisons that the proposed simplified formulas can be served as an alternative and useful tool for the design and analysis of wind effects on rectangular tall buildings.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.271-280
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• 2004

Assessment of image registration for Pressure Sensitive Paint (PSP) was performed. A 16 bit camera and LED lamp were used with Uni-FIB paint (ISSI). Because of model displacement and deformation at 'wind-on' condition, a large error of the intensity ratio was induced between 'wind-on' and' wind-off images. To correct the error, many kinds of image registrations were tested. At first, control points were marked on the model surface to find the coefficients of polynomial transform functions between the 'wind-off' 'wind-on' images. The 2nd-order polynomial function was sufficient for representing the model displacement and deformation. An automatic detection scheme was introduced to find the exact coordinates of the control points. The present automatic detection algorithm showed more accurate and user-friendly than the manual detection algorithm. Since the coordinates of transformed pixel were not integer, five interpolation methods were applied to get the exact pixel intensity after transforming the 'wind-on' image. Among these methods, the cubic convolution interpolation scheme gave the best result.