• Wind and Structures
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• v.31 no.6
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• pp.549-560
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• 2020

Methods for stochastic simulation of non-Gaussian wind pressure have increasingly addressed the efficiency and accuracy contents to offer an accurate description of the extreme value estimation of the long-span and high-rise structures. This paper presents a linear prediction and z-transform (LPZ) based Cumulative distribution function (CDF) mapping algorithm for the simulation of multivariate non-Gaussian fluctuating wind pressure. The new algorithm generates realizations of non-Gaussian with prescribed marginal probability distribution function (PDF) and prescribed spectral density function (PSD). The inverse linear prediction and z-transform function (ILPZ) is deduced. LPZ is improved and applied to non-Gaussian wind pressure simulation for the first time. The new algorithm is demonstrated to be efficient, flexible, and more accurate in comparison with the FFT-based method and Hermite polynomial model method in two examples for transverse softening and longitudinal hardening non-Gaussian wind pressures.

• Wind and Structures
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• v.20 no.4
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• pp.579-607
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• 2015

A Combination Random Flow Generation (CRFG) technique for obtaining the fluctuating inflow boundary conditions for Large Eddy Simulation (LES) is proposed. The CRFG technique was developed by combining the typical RFG technique with a novel calculation of k and ${\varepsilon}$ to estimate the length- and time-scales (l, ${\tau}$) of the target fluctuating turbulence field used as the inflow boundary conditions. Through comparatively analyzing the CRFG technique and other existing numerical/experimental results, the CRFG technique was verified for the generation of turbulent wind velocity fields with prescribed turbulent statistics. Using the turbulent velocity fluctuations generated by the CRFG technique, a series of LESs were conducted to investigate the wind flow around S-, R-, L- and U-shaped building models. As the pressures of the models were also measured in wind tunnel tests, the validity of the LES, and the effectiveness of the inflow boundary generated by the CRFG techniques were evaluated through comparing the simulation results to the wind tunnel measurements. The comparison showed that the LES accurately and reliably simulates the wind-induced pressure distributions on the building surfaces, which indirectly validates the CRFG technique in generating realistic fluctuating wind velocities for use in the LES. In addition to the pressure distribution, the LES results were investigated in terms of wind velocity profiles around the building models to reveal the wind flow dynamics around bluff bodies. The LES results quantitatively showed the decay of the bluff body influence when the flow moves away from the building model.

• Wind and Structures
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• v.11 no.5
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• pp.361-376
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• 2008

This paper considers internal pressure fluctuations for a range of building volumes and dominant wall opening areas. The study recognizes that the air flow in and out of the dominant opening in the envelope generates Helmholtz resonance, which can amplify the internal pressure fluctuations compared to the external pressure, at the opening. Numerical methods were used to estimate fluctuating standard deviation and peak (i.e. design) internal pressures from full-scale measured external pressures. The ratios of standard deviation and peak internal pressures to the external pressures at a dominant windward wall opening of area, AW are presented in terms of the non-dimensional opening size to volume parameter, $S^*=(a_s/\bar{U}_h)^2(A_W^{3/2}/V_{Ie})$ where $a_s$ is the speed of sound, $\bar{U}_h$ is the mean wind speed at the top of the building and $V_{Ie}$ is the effective internal volume. The standard deviation of internal pressure exceeds the external pressures at the opening, for $S^*$ greater than about 0.75, showing increasing amplification with increasing $S^*$. The peak internal pressure can be expected to exceed the peak external pressure at the opening by 10% to 50%, for $S^*$ greater than about 5. A dominant leeward wall opening also produces similar fluctuating internal pressure characteristics.

• Wind and Structures
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• v.26 no.4
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• pp.191-204
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• 2018

This article presents a study of the largest-ever (height = 220 m) cooling tower using the large eddy simulation (LES) method. Information about fluid fields around the tower and 3D aerodynamic time history in full construction process were obtained, and the wind pressure distribution along the entire tower predicted by the developed model was compared with standard curves and measured curves to validate the effectiveness of the simulating method. Based on that, average wind pressure distribution and characteristics of fluid fields in the construction process of ultra-large cooling tower were investigated. The characteristics of fluid fields in full construction process and their working principles were investigated based on wind speeds and vorticities under different construction conditions. Then, time domain characteristics of ultra-large cooling towers in full construction process, including fluctuating wind loads, extreme wind loads, lift and drag coefficients, and relationship of measuring points, were studied and fitting formula of extreme wind load as a function of height was developed based on the nonlinear least square method. Additionally, the frequency domain characteristics of wind loads on the constructing tower, including wind pressure power spectrum at typical measuring points, lift and drag power spectrum, circumferential correlations between typical measuring points, and vertical correlations of lift coefficient and drag coefficient, were analyzed. The results revealed that the random characteristics of fluctuating wind loads, as well as corresponding extreme wind pressure and power spectra curves, varied significantly and in real time with the height of the constructing tower. This study provides references for design of wind loads during construction period of ultra-large cooling towers.

• Wind and Structures
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• v.4 no.5
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• pp.399-412
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• 2001

Simultaneous pressure and force measurements have been conducted on a stationary box deck section model for two configurations (namely without and with New Jersey traffic barriers) at various angles of incidence. The mean and fluctuating aerodynamic coefficients and pressure coefficients were derived, together with their spectra and with the coherence functions between the pressures and the total aerodynamic forces. The mean aerodynamic coefficients derived from force measurements are first compared with those derived from the integration of the pressures on the deck surface. Correlation between forces and local pressures are determined in order to gain insight on the wind excitation mechanism. The influence of the angle of incidence on the pressure distribution and on the fluctuating forces is also analysed. It is evidenced how particular deck section areas are more responsible for the aerodynamic excitation of the deck.

• Wind and Structures
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• v.24 no.5
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• pp.501-528
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• 2017

In this work, wind tunnel tests of pressure measurements are carried out to assess the global aerodynamic interference factors, the local wind pressure interference factors, and the local lift spectra of an square high-rise building interfered by an identical cross-sections but lower height building arranged in various relative positions. The results show that, when the interfering building is located in an area of oblique upstream, the RMS of the along-wind, across-wind, and torsional aerodynamic forces on the test building increase significantly, and when it is located to a side, the mean across-wind and torsional aerodynamic forces increase; In addition, when the interfering building is located upstream or staggered upstream, the mean wind pressures on the sheltered windward side turn form positive to negative and with a maximum absolute value of up to 1.75 times, and the fluctuating wind pressures on the sheltered windward side and leading edge of the side increase significantly with decreasing spacing ratio (up to a maximum of 3.5 times). When it is located to a side, the mean and fluctuating wind pressures on the leading edge of inner side are significantly increased. The three-dimensional flow around a slightly-shorter disturbing building has a great effect on the average and fluctuating wind pressures on the windward or cross-wind faces. When the disturbing building is near to the test building, the vortex shedding peak in the lift spectra decreases and there are no obvious signs of periodicity, however, the energies of the high frequency components undergo an obvious increase.

• Wind and Structures
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• v.24 no.2
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• pp.119-144
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• 2017

The traditional method for the simulation of high Reynolds number (Re) effects on wind loads on cooling tower models in wind tunnels focuses only on the mean wind pressure distribution. Based on observed effects of some key factors on static/dynamic flow characteristics around cooling towers, the study reported in this paper describes a comprehensive simulation method using both mean and fluctuating wind pressure distributions at high Re as simulation targets, which is indispensable for obtaining the complete full-scale wind effects in wind tunnels. After being presented in this paper using a case study, the proposed method is examined by comparing the full covariance matrices and the cross-spectral densities of the simulated cases with those of the full-scale case. Besides, the cooling tower's dynamic structural responses obtained using the simulated wind pressure fields are compared with those obtained by using the full-scale one. Through these works, the applicability and superiority of the proposed method is validated.

• Wind and Structures
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• v.19 no.4
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• pp.443-465
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• 2014

Hyperbolic thin-shell cooling towers have complicated vibration modes, and are very sensitive to the effects of group towers and wind-induced vibrations. Traditional aero-elastic models of cooling towers are usually designed based on the method of stiffness simulation by continuous medium thin shell materials. However, the method has some shortages in actual engineering applications, so the so-called "equivalent beam-net design method" of aero-elastic models of cooling towers is proposed in the paper and an aero-elastic model with a proportion of 1: 200 based on the method above with integrated pressure measurements and vibration measurements has been designed and carried out in TJ-3 wind tunnel of Tongji university. According to the wind tunnel test, this paper discusses the impacts of self-excited force effect on the surface wind pressure of a large-scale cooling tower and the results show that the impact of self-excited force on the distribution characteristics of average surface wind pressure is very small, but the impact on the form of distribution and numerical value of fluctuating wind pressure is relatively large. Combing with the Complete Quadratic Combination method (hereafter referred to as CQC method), the paper further studies the numerical sizes and distribution characteristics of background components, resonant components, cross-term components and total fluctuating wind-induced vibration responses of some typical nodes which indicate that the resonance response is dominant in the fluctuating wind-induced vibration response and cross-term components are not negligible for wind-induced vibration responses of super-large cooling towers.

• Wind and Structures
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• v.23 no.4
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• pp.367-383
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• 2016

The influence mechanism of mean value components, noted as $P_0$, on POD applications for complete random fields $P_C(t)$ and fluctuating random fields $P_F(t)$ are illustrated mathematically. The critical philosophy of the illustration is introduction of a new matrix, defined as the correlation function matrix of $P_0$, which connect the correlation function matrix of $P_C(t)$ and $P_F(t)$, and their POD results. Then, POD analyses for several different wind pressure fields were presented comparatively as validation. It's inevitable mathematically that the first eigenmode of $P_C(t)$ resembles the distribution of $P_0$ and the first eigenvalue of $P_C(t)$ is close to the energy of $P_0$, due to similarity of the correlation function matrixs of $P_C(t)$ and $P_0$. However, the viewpoint is not rigorous mathematically that the first mode represents the mean pressure and the following modes represent the fluctuating pressure when $P_C(t)$ are employed in POD application. When $P_C(t)$ are employed, POD results of all modes would be distorted by the mean value components, and it's impossible to identify $P_0$ and $P_F(t)$ separately. Consequently, characteristics of the fluctuating component, which is always the primary concern in wind pressure field analysis, can only be precisely identified with $P_0$ excluded in POD.

• Wind and Structures
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• v.34 no.5
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• pp.421-435
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• 2022

To investigate the non-Gaussian properties of fluctuating wind pressures and the error margin of extreme wind loads on a long-span curved roof with matching and mismatching ratios of turbulence integral scales to depth (L_u^x/D), a series of synchronized pressure tests on the rigid model of the complex curved roof were conducted. The regions of Gaussian distribution and non-Gaussian distribution were identified by two criteria, which were based on the cumulative probabilities of higher-order statistical moments (skewness and kurtosis coefficients, S_k and K_u) and spatial correlation of fluctuating wind pressures, respectively. Then the characteristics of fluctuating wind-loads in the non-Gaussian region were analyzed in detail in order to understand the effects of turbulence integral-scale. Results showed that the fluctuating pressures with obvious negative-skewness appear in the area near the leading edge, which is categorized as the non-Gaussian region by both two identification criteria. Comparing with those in the wind field with matching L_u^x/D, the range of non-Gaussian region almost unchanged with a smaller L_u^x/D, while the non-Gaussian features become more evident, leading to higher values of S_k, Ku and peak factor. On contrary, the values of fluctuating pressures become lower in the wind field with a smaller L_u^x/D, eventually resulting in underestimation of extreme wind loads. Hence, the matching relationship of turbulence integral scale to depth should be carefully considered as estimating the extreme wind loads of long-span roof by wind tunnel tests.