Full-scale wind pressure measurements on a twin-span 12.2 × 12.2 m inflated roof greenhouse

In recent years plastic film has been extensively used for cladding low cost greenhouses. A limitation of the material is its susceptibility to wind storm damage and its wider use is dependent on good design through a knowledge of wind loads.Results of a limited programme of measurements of wind pressure on a film clad inflated roof greenhouse are presented. The measurements were made on the full-scale structure under natural wind conditions. The shape of the roof was modified by the wind and has been calculated for the measured wind load pattern assuming inviscid uniform flow. The application of these results to design is discussed.     

Efficient models for wind turbine extreme loads using inverse reliability

The reliability of wind turbines against extreme loads is the focus of this study. A procedure to establish nominal loads for use in a conventional load-and-resistance-factor-design format is presented. The procedure, based on an inverse reliability approach, permits inclusion of randomness in the gross wind environment as well as in the extreme response given wind conditions. A detailed example is presented where three alternative nominal load definitions are used to estimate extreme bending loads for a 600 kW three-bladed horizontal-axis wind turbine. Only operating loads—here, flapwise (out-of-plane) bending moments—at a blade root are considered but the procedure described may be applied to estimate other loads and response measures of interest in wind turbine design. Results suggest that a full random characterization of both wind conditions and short-term maximum response (given wind conditions) will yield extreme design loads that might be approximated reasonably well by simpler models that include only the randomness in the wind environment but that account for response variability by employing appropriately derived “higher-than-median” fractiles of the extreme bending load conditional on inflow parameter values.     

Cross-wind response of tall buildings

A design procedure was developed using random vibration theory and uses mode-generalized cross-wind force spectra and aerodynamic data to calculate the cross-wind displacement and acceleration responses of tall buildings. The force spectra of a number of building shapes and sizes in both suburban and city centre type wind flow are presented. The proposed design procedure gives reasonable estimates of the cross-wind response, compared with wind tunnel measurements, at reduced wind velocities and at structural damping values consistent with modern habitable tall building design. This allows assessment of the structural requirements of tall buildings to be made at an early design stage, and also allows the designers to assess the need for more detailed and expansive wind tunnel model tests.     

低层双齿大棚屋面风致积雪分布研究

为研究低层双齿大棚屋面的风致积雪分布规律,基于FLUENT软件中的Mixture多相流模型,建立了风雪两相流场模型。为验证风雪两相流场的准确性并选择合适的湍流模型,采用k-w,SST k-w和k-kl-w湍流模型分别对立方体周围积雪分布进行数值分析,并将数值分析结果与试验结果进行对比以验证数值方法的正确性,进而详细研究了风速、风向角、屋面坡度比和结构双齿长宽比对低层双齿大棚屋面风致积雪分布的影响。结果表明:风雪两相流模型和k-kl-w湍流模型建立的风雪两相流流场可以较好地反映低层双齿大棚屋面的积雪分布情况; 大棚屋面积雪厚度随着风速和屋面坡度比增大而减小,且屋面坡度比的影响程度较风速与风向角的影响小; 大棚屋面积雪受侵蚀和堆积区域位置随风向角变化而变化; 大棚结构长宽比对屋面积雪分布的影响较小; 低层三齿大棚屋面和低层四齿大棚屋面的屋面积雪分布系数可参考低层双齿大棚屋面; 提出的低层双齿大棚屋面积雪不均匀分布系数可为低层双齿大棚屋面的冬季防雪灾设计提供参考。     

Extreme wind speeds in mixed wind climates

In this paper, a technique is discussed which enables extreme wind speed probabilities in mixed wind climates to be determined. It is shown that in such wind climates the method is likely to yield more accurate probability estimates than the traditional Gumbel analysis of annual wind speed maxima, particularly for annual probabilities of less than 2% (i.e. return periods greater than 50 years). The technique requires a separate analysis of each significant wind-producing meteorological phenomenon and practical methods of achieving this are presented. Extreme wind speed parameters obtained from each analysis may then be combined to yield a “composite extreme wind speed diagram” and several examples illustrating this procedure are shown. By means of a numerical simulation of a typical mixed wind climate, a detailed study is made of the distribution of extreme wind gusts from different meteorological phenomena. This study indicates that a Gumbel analysis of 20 annual maxima may severely underestimate low annual probability (i.e. long return period) gust speeds.     

The development of a fatigue loading spectrum for small wind turbine blades

This paper details a formulation to create a fatigue loading procedure for the blade of a small wind turbine using a combination of detailed short-term aeroelastic and wind measurements and averaged long-term wind data from the Australian Bureau of Meteorology. Detailed aeroelastic measurements from the blade of an operating small wind turbine were acquired simultaneously with wind speed measurements and show that the blade does not respond instantaneously to all changes in wind speed. A methodology has been developed to create a fatigue loading procedure using the blade stress cycles determined from the detailed measurements in conjunction with long-term wind data. The proposed method overcomes the necessity to acquire long-term detailed operational data before developing a blade fatigue loading procedure without compromising on accuracy.     

Wind–structure interaction in conductor bundles in transmission lines

The use of transmission line conductors arranged in bundles is presently being considered as an attractive technology in order to reduce losses in long distance energy transportation. Although the technology leads to significant increases in power capacity per line, the dynamic behaviour of arbitrary bundle configurations under wind action has not yet been fully clarified. In this paper, a procedure to determine the dynamic response of the bundle under operating conditions is presented. The model considers the fluctuations of the incident turbulent wind flow and the motion of the conductors, as some cables may be immersed in the variable wake of others. A solution is obtained by numerical integration in the time domain of the equations of motion of a discrete non-linear model of the bundle, which includes criteria to assess the forces on spacers and cables by means of aerodynamic coefficients obtained experimentally in wind tunnel studies. The predicted response of a three-conductor bundle is compared with experimental results available in the technical literature. Results of simulation studies of various bundle configurations subjected to turbulent wind action are also given.     

Along-wind gust effect on elevated structures

The interest in the evaluation of the dynamic response of elevated structures to wind force has increased considerably in recent years. This paper introduces a random process approach and its application to these special structures. As an example, a skylight structure is analysed by random approach in regard to the gust effect. For comparison, the same effects are also evaluated by using some of the current available building codes.Results show that the effect due to the gust is greater than that due to the steady wind. Wind pressure obtained through the random approach are quite comparable with those obtained by using the building codes. However, the random approach presented in this paper provides more detailed procedure than the building code approach for evaluating gust effect on elevuated structures.     

Performance based design extreme wind loads on a tall building

This paper presents a procedure for the calculation of wind loads on a proposed 385 ft tall building located in strong wind and mixed strong wind and hurricane wind regions. The procedure for the computation of design wind loads uses mixed distribution and Monte Carlo simulation. The results of a probabilistic analysis of hurricane wind speeds are combined with the probability distribution of recorded extreme wind speeds (excluding hurricane data) at the site. A 50‐year sample of extreme wind speeds is created and the maximum 50‐year wind (from the hurricane and the recorded data) is noted. The simulation is repeated for a large number of samples (>10000) and the probability distribution of the 50‐year wind speed is computed for use in establishing the design wind speed Copyright © 2001 John Wiley & Sons, Ltd.     

Study of wind towers with different funnels attached to increase natural ventilation in an underground building

Finding ways to cool buildings by natural, passive techniques is crucial in the context of global warming. For centuries, wind towers (traditional windcatchers) have been used in the Middle East for cooling purposes. In this study, the use of funnels at the openings of wind towers for wind ingress and egress is proposed primarily to increase the mass flow captured by the wind tower. The use of funnels in the wind ingress openings increases the inlet area, improving the capture of wind. In parallel, the use of funnels in the egress openings modifies the wake of the tower, which aims to ease the exit of the flow from inside the building. Several design configurations are presented, where the length and width of the funnels are changed and tested separately by computational fluid dynamics (CFD). Results of over 120 CFD simulations are presented and compared. The volumetric flow entering the wind towers increases by 10.7% in several cases. These results indicate that adding funnels to wind towers could positively influence their performance. Changing the dimensions of the funnels affects their efficacy and can increase or decrease the airflow entering the tower.     

±800kV特高压T型长横担输电塔风振特性研究

±800kV特高压直流塔是T型长横担输电塔型,属于风敏感结构,风与结构的相互作用十分复杂,风荷载常常是设计的主要控制荷载。本文以某一±800kV直流塔为工程背景,建立了详细的有限元计算模型,获得了结构的自振动力特性。在考虑节点风荷载空间相关性的基础上,利用Kaimal谱对结构的风荷载进行了准确的数值模拟。结合动力时程积分法,计算得到了结构的风致振动响应时程。研究了结构位移平均值、位移均方根值和加速度均方根值的分布特点,同时分析了结构各层的风振系数分布特点,并与我国规范进行了对比。通过研究,揭示了直流塔的风致振动特性,结果可作为直流塔结构抗风设计的参考。     

银川设施园艺产业园特色温室结构设计

温室结构属于农业设施,屋面一般采用玻璃或PC板,结构较轻,荷载取值与民用建筑结构有所不同。介绍银川产业园特色温室的结构设计,参考国内外相关规范考虑荷载取值,并对其在两种极限状态下进行计算分析。建议采用合理的影响系数并制订我国相应的温室设计标准。     

The effects of simulated fire pressure and outside wind on the internal pressure distribution in a five-storey model building

This paper presents some of the wind tunnel pressure measurements made on a five-storey model building (32 cells), with a vertical shaft and fixed leakage characteristics. Internal and external pressures measurements are presented for various wind angles and a simulated fire pressure in a room on floor 2 and floor 4. Comparison is made to assess the effect of fire on internal pressure distribution. Although the results are presented for all the wind angles investigated, a detailed discussion is confined only to a single wind angle. Implications of the combined effect of wind and fire on the shaft pressurization system design calculations must take these two factors into account.

In a fire situation it is possible that escapers may leave some of the shaft doors open or the fire room door may burn down. In such a case the pressurization system can become ineffective, causing escape routes to get smoke-logged. The effect of a combination of fire door openings was also investigated. The results for the following door opening combinations are presented and discussed:

1. (i) shaft door open alone;

2. (ii) fire room door open alone;

3. (iii) shaft and fire room doors open together.

It is shown quite clearly that these openings are significant for a range of wind angles.     

Towards better estimation of extreme winds

The use of dynamic pressure in place of wind speed as the variable when fitting extreme values to the Fisher—Tippett (Type 1) model is discussed. A procedure is proposed by which estimates of extreme winds may be obtained that are superior to those from the standard Gumbel method. The procedure is extended to allow the estimation of extreme winds according to direction, in sectors 30° wide. Adoption of the sectorial estimates leads to substantial reductions in design wind loads over a large range of wind directions in the U.K.     

A novel wind speed modeling approach using atmospheric pressure observations and hidden Markov models

Modeling the wind speed data has important implications in wind studies, providing valuable insight and parametric quantities for further engineering analysis. The classical modeling approach is to fit the probability distribution to a known model and estimate statistical parameters like mean and variance. Such models lack the time variation properties and ignore cross-dependencies between other meteorological data. In this paper a procedure is developed to model the wind speed data using a dependent process of atmospheric pressure in the form of hidden Markov models (HMMs). Consequently, the inherent dependencies between the wind speed and pressure are exploited. HMMs relate the two quantities in a framework which eliminates the necessity of direct sample-wise correlations, and avoid direct time-series analysis complications of the stochastic wind speed data at a marginal expense of easy pressure measurements. The experimental data were obtained from recordings of hourly atmospheric pressure and wind speed values for two cities in Turkey, namely Izmir and Kayseri. Model details and numerical results are presented.     

义乌游泳馆倒置铝合金格构式屋盖设计

义乌游泳馆屋盖采用大跨度倒置式铝合金格构式结构在我国工程应用中尚属首次。由于这种屋盖具有风敏感的柔性结构的特点,本文通过风洞试验和数值仿真分析对"盆式"外形的风荷载体型系数和风致响应进行了深入研究。阐述了铝合金格构式屋盖的设计方法,并对分析结果进行了讨论。     

Dynamics of wind-rail vehicle-bridge systems

An analytical model for dynamics of wind-vehicle-bridge (WVB) systems is presented in this paper in the time domain with wind, rail vehicles and bridge modeled as a coupled vibration system. The analytical model considers many special issues in a WVB system, which include fluid-solid interaction between wind and bridge, solid contact between vehicles and bridge, stochastic wind excitation on vehicles and bridge, time dependence of the system due to vehicle movement, and effect of bridge deck on vehicle wind load and vice versa. The models of wind, vehicles and bridge are presented with wind velocity fluctuations simulated using the simplified spectral representation method, with vehicles modeled as mass-spring-damper systems, and with bridge represented by a finite element model. The interactions between wind and bridge are similar to those considered in conventional buffeting analysis for long span bridges. In considering difficulties in measuring aerodynamic coefficients of moving vehicles on bridge deck, the cosine rule is adopted for the aerodynamic coefficients of moving vehicles to consider yaw angle effect, and expressions of wind forces on moving vehicles are then derived for engineering application. To include mutual effects of wind loads, aerodynamic parameters of vehicles and bridge deck are measured, respectively, using a composite section model test and a specially designed test device. The dynamic interaction between vehicle and bridge depends on both geometric and mechanical relationships between wheels of vehicles and rails on the bridge deck. The equations of motion of the coupled WVB system are derived and solved with a nonlinear iterative procedure. A cable-stayed bridge in China is finally selected as a numerical example to demonstrate dynamic interaction of the WVB system. The results show the validity of the present model as well as wind effects on the rail vehicles and the bridge.     

辰山植物园温室铝合金结构设计

上海辰山植物园温室建筑群具有流畅、通透的建筑效果,建筑群体型庞大,单体最大长度达到204 m。温室的结构形式为单层铝合金网壳结构,节点采用铆拴盘节点。从温室结构设计的关键点出发,对温室结构的整个设计过程予以全面的介绍,为同类建筑结构的设计提供借鉴。     

Reliability-Based Optimal Design of Electrical Transmission Towers Using Multi-Objective Genetic Algorithms

Abstract:   A hybrid methodology for performing reliability-based structural optimization of three-dimensional trusses is presented. This hybrid methodology links the search and optimization capabilities of multi-objective genetic algorithms (MOGA) with structural performance information provided by finite element reliability analysis. To highlight the strengths of the proposed methodology, a practical example is presented that concerns optimizing the topology, geometry, and member sizes of electrical transmission towers. The weight and reliability index of a tower are defined as the two objectives used by MOGA to perform Pareto ranking of tower designs. The truss deformation and the member stresses are compared to threshold values to assess the reliability of each tower under wind loading. Importance sampling is used for the reliability analysis. Both the wind pressure and the wind direction are considered as random variables in the analysis. The research results presented demonstrate the benefit of implementing MOGA optimization as an integral part of a reliability-based optimization procedure for three-dimensional trusses.