Wind Load Characteristics Research Articles

Nonstationary time-varying extreme value of downburst-induced wind loads based on transformed stationary method

Downbursts exhibit pronounced transient effects and nonstationary characteristics. Herein, a pressure measurement test of a rigid segment model under a downburst-like wind is conducted on a 5:1 rectangular cylinder using a multi-fan active control wind tunnel. Based on the experimental results, downburst-like wind field and wind load characteristics are studied. The results show that the downburst-like wind, wind loads and evolution power spectrum density(EPSD) have prominent time evolution features, transient effects, and nonstationary time-varying characteristics. Subsequently, based on the generalized extreme value (GEV) distribution theory, the time-varying extreme values of the nonstationary random processes under the uniform modulation approximation are estimated, and the corresponding peak factors are given. The fitting accuracy of the generalized extreme value distribution is found to be good. The calculated peak factors of the wind pressure and overall aerodynamic lift are higher than those of the wind speed. Owing to flow separation, the peak factor of the pressure coefficients on the windward surface is smaller than those on the top and leeward surfaces. The peak factors in the flow separation and wake regions of the top surface are larger than those in the reattachment region.

Calculation model and experimental verification of equivalent ice thickness on overhead lines with tangent tower considering ice and wind loads

Overhead line icing will seriously affect the safety of power grid. Accurately predicting the ice thickness on power lines is a persistent research problem. Accurate prediction is essential for the anti-icing/de-icing measures of power grid and prevention of serious ice accidents. Based on fluid mechanics theory, a simulation model for the aerodynamic characteristics of the typical icing section of conductor is established. The influence of wind attack angle, wind speed, ice thickness and section shape on the aerodynamic parameters (lift and drag coefficients) is analysed. Combined mechanics principle and conductors icing characteristics, a calculation model of equivalent ice thickness on transmission lines with a tangent tower is developed. The tension and inclination angle of insulator suspension point to tangent tower, as well as the ice and wind load characteristics are considered. Based on the field data from the State Field Scientific Observation and Research Station of Xuefeng Mountain Energy Equipment Security of Chongqing University, it is verified that the results of proposed model strongly agree with the actual measurements. The model can meet the requirements of the engineering applications, with the deviation of all the results less than 10%. The theoretical reference for the design, construction, operation and maintenance of anti-icing and mitigation with power infrastructure can be provided.

Dynamic response analysis of a whole steel frame solar greenhouse under wind loads

In recent years, whole steel frame steel greenhouses have become increasingly prevalent. With the characteristics of large flexibility and small mass, whole steel frame steel greenhouses are sensitive to wind loads. However, studies on the safety of whole steel frame steel greenhouses under wind loads are still limited. In this study, a 10 m span whole steel frame solar greenhouse was taken as the research objective. Taking the Davenport spectrum as the target spectrum, the time history of the wind speed was simulated by the harmonic superposition method. The finite element model of the greenhouse structure was established using ANSYS software. The simulated wind pressure was applied on the greenhouse structure for dynamic response analysis. The dynamic response results were compared with the static analysis results under average wind load. The results showed that the greenhouse structure mainly bears bending stress under wind load. The bending stress, axial stress and displacement of the greenhouse skeleton under average wind loads are lower than those under instantaneous wind loads. It is necessary to consider the dynamic characteristics of wind loads in the design of solar greenhouses. A wind-induced vibration coefficient is obtained, which can be used to convert the dynamic load into the equivalent static load and improve its design efficiency.

Effects of Curved Wind Barrier on the Aerodynamic Characteristics of a Train–Bridge System and Its Static Wind Load

Wind barriers are important measures that guarantee the running safety of high-speed trains under crosswind conditions, however, they can change the aerodynamic coefficients of a train–bridge system and the distribution of the flow field around a train and bridge, and studies have often ignored the static wind load characteristics of wind barriers. In this paper, the effects of height and porosity on the curved and vertical fence-type wind barriers on the aerodynamic characteristics of a train–bridge system are investigated by using numerical simulation and wind tunnel test methods. The static wind loads of the two types of wind barriers are analyzed by comparing the drag coefficients and the surface wind pressure distributions. The results show that, compared with the vertical wind barrier, the curved wind barrier can reduce the drag force and moment of a train while reducing the impact of the aerodynamic forces on a bridge. The static wind load of the curved wind barrier is less than that of the vertical wind barrier, when a train is on the windward side of a bridge, the drag coefficient of the curved wind barrier is only about 35% of that of the vertical wind barrier.

Wind load characteristics of photovoltaic panel arrays mounted on flat roof

To quantify design wind load of photovoltaic panel array mounted on flat roof, wind tunnel tests were conducted in this study. Results show that the first and the last two rows on the roof are the most unfavorable ones regarding to the wind load. Influences of array spacing, panels’ tilt angle and parapet height on wind load of the panels are studied. Most unfavorable lift force of panels decreases with increase of array spacing for middle located panels. The aerodynamics are similar to flow over repeated hills. Middle located unit got greater turbulence, which leading to unfavorable C fp_min. While the changing amplitude of most unfavorable wind pressure is small increase with array spacing. C fp_max and C fp_min of panel units shows quite strong dependence on tilt angle. There is significant pressure equalization for small tilt angle cases. The local flow separation is responsible for C fp_min of larger tilt angle cases. Parapet height of 2 h (h is the panel height projected on the vertical plane) is the critical height for C fp_max and C fp_min. Increasing parapet height can significantly reduce the wind load of panel units. Design pressure coefficient of the basic working condition with different area sizes at different location are proposed.

FIELD MEASUREMENT AND NUMERICAL STUDY OF EXTERNAL WIND PRESSURE OF RIBBED COOLING TOWER

The hyperbolic thin-shell cooling tower is a typical wind-sensitive structure. The full-size measurement is the most direct and important way to study the distribution of wind pressure on the surface of the cooling tower. Due to the limitations of engineering conditions and meteorological conditions, the field measured data are relatively lacking, and the field test data of ribbed cooling towers are less. In order to analyze the wind pressure distribution on the surface of the cooling tower, we chose a ribbed cooling tower in Toksun County, Xinjiang, China, where there are strong winds all year round, and field measurements were carried out to understand the wind load characteristics of the tower under the perennial dominant wind direction and the maximum wind direction. It was found that the absolute value of the negative pressure on the leeward side was larger than that in the code and the fluctuating wind pressure coefficient fluctuates greatly when the field measured wind speed was greater than 10m/s (15 meters above the ground). For circular section cooling tower, the Reynolds number (Re) has great influence on wind pressure. With the increase of Re, the absolute value of the average negative pressure of the tail wind pressure coefficient increases, which should be paid attention to in design. The regression curves of the average wind pressure coefficients measured on site under several typical working conditions are given by using the least square method, and its form is consistent with the standard (but the coefficients are different). In addition, Fluent software was used to calculate the external wind pressure of the cooling tower, and the field measured results were compared with the Chinese code, German code and numerical calculation, and the results were consistent.

Characteristics of wind loads on Twin-Tower structure in comparison with single tower

To provide a general guidance for the wind-resistant design of super-tall twin towers, a study was conducted to investigate the aerodynamic and structural dynamic characteristics of twin towers in comparison with the isolated single tower. It was found that the mutual aerodynamic interference between two towers may have a beneficial effect of disrupting the regular shedding of vortices and causing the across-wind oscillation of the twin towers appreciably smaller than that of the single tower. This beneficial effect is a function of the relative spacing between two towers and the wind direction. When the twin towers are side-by-side to wind, the beneficial effect is apparent if the relative spacing is about 1.0 or less, but it becomes negligible when the relative spacing reaches 2.0. When the twin towers are in tandem configuration to wind, the beneficial effect will remain valid until the maximum tested relative spacing of 2.0. It is also found that wind forces applied to the twin towers may contain a large proportion of out-of-phase components, which act on the two towers in opposite directions, and the corresponding structural response can be well controlled by structural links between the two towers. Therefore, the role and effectiveness of structural links in controlling wind-induced structural responses can be evaluated by the percentage of the out-of-phase components over the total wind forces, which is again a function of the relative spacing, design wind speed, wind direction of concern, and reduced building frequencies. A case study of the 570 m super-tall twin towers verified the conclusions drawn from the general study, and the use of structural links was proved to be able to reduce the design wind loads and building accelerations by more than 20%.

Study on Full-scale Measurements of Wind Field Characteristics of Coastal Complex Mountainous Terrains

Based on full-scale wind field measurements of coastal complex mountainous terrains, data of fluctuating wind velocities at the height of 30m for four sites, including mountaintop and hillsides, are obtained. The wind load characteristics of mean wind velocities, wind directions, turbulence intensities and speed-up ratios of wind velocities are comprehensively examined. Results show that the maximum mean wind velocity at the mountaintop site is 12.4 m/s. The probability density distributions of mean wind velocities for the four measurement sites can be well represented by the Weibull probability model. The predominant wind directions are around the northeast and southwest. The longitudinal, lateral and vertical turbulence intensities decrease with the increase of mean wind velocities. The turbulence intensities for the mountaintop site are as many as 0.13,0.12 and 0.089 under maximum wind velocities, respectively for the previously mentioned three directions. The speed-up ratios of wind velocities between mountaintop and hillside sites are reduced, as the wind velocities increase. However, in cases of intensive wind with mean wind velocities larger than 8 m/s, the speed-up effects of wind velocities can also appear. The maximum speed-up ratio can reach 1.17.

Effect of the combined aerodynamic control on the amplitude characteristics of wind loads on a tall building

Experimental investigation of the amplitude characteristics of wind loads on a square cross-sectional tall building under the combined aerodynamic control, which consists of the shape modification and air suction, has been conducted, and the effects of the suction flux coefficients CQ and wind direction angles on the wind pressure coefficients and aerodynamic force coefficients of five test models (includes a square cylinder and its corner modifications such as recession and chamfer, tapered cylinder and Y-shaped cylinder, and they are denoted as the Models 1–5 respectively) with and without air suction control have been analyzed. The Model 1 without suction control is defined as the benchmark model. The results show that the shape modifications have significant control effects on the mean and RMS pressure drag coefficients (CD and CσD) as well as the RMS pressure lift coefficient CσL of the Models 2, 3 and 5 at 0° wind direction, with the maximum reduction rates (CDR, CσDR and CσLR) of 39.2%, 44.0% and 38.4% for the Models 2, 5 and 2 respectively. When compared with the benchmark model, the most significant control effects of the combined aerodynamic control on CDR, CσD and CσL of the Models 2–5 with the suction speed of 9 m/s are also at 0° wind direction, with the maximum reduction rates of 61.8%, 65.8% and 5.7% for the Models 2, 2 and 5 respectively, which indicates that the combined aerodynamic control is more effective on the drag reduction than the passive or active aerodynamic control individually, and the Model 2 with suction control has the best wind-resistant performance. This study contributes to an effective aerodynamic measure to control the amplitude characteristics of wind loads on tall buildings, which can be an important reference for further studies or potential engineering applications of the combined aerodynamic control in mitigating the wind loads and wind-induced responses of tall buildings.

Experimental investigation of wind pressure characteristics and aerodynamic optimization of a large-span cantilevered roof

Cantilevered roof is particularly vulnerable to wind because high suction loads often occur on the rooftop due to flow separation. However, wind load characteristics associated with cantilevered roof have not been fully understood. In this paper, a 1/100 scale model of a cantilevered roof, over a grandstand, has been tested in a turbulent boundary layer flow, with particular emphasis on characterizing the wind pressure distribution on the cantilevered roof, and assessing the performance of several aerodynamic optimization devices. The results indicate that large wind suction generally occurs near the windward edge on rooftop surface. The effect of approaching wind direction is evident, which can influence the distribution pattern and value of wind pressure. For the effect of roof inclination, the down-sloping roof is found to be more appropriate since it results in most significant reduction in mean wind pressure, as well as the net lifting and bending moment coefficients. Furthermore, it is shown that adding a vented leading edge slot can effectively reduce the rooftop wind suctions. The maximum reduction in mean and peak suction loads is respectively 30% and 45%.

Study of wind loading and flow characteristics on an array of parabolic trough collectors

Wind loads and structure of the flow field around an array of parabolic trough collectors (PTCs) were investigated using Delayed Detached Eddy Simulation (DDES) method. A scaled three-dimensional (3D) model was adopted and simulated using the ANSYS-Fluent software. Several pitch angles, including θ = 0°, 45°, 135°, and 180° and the stow mode with the pitch angle, θ = 90°, and flow Reynolds number of 2×105, are considered for numerical solutions. For validation of the numerical model, the mean wind load coefficient on a stand-alone PTC and an array model of PTCs were simulated and compared with the wind tunnel data. Detailed analysis of wind characteristics and wind loading on an array for five-pitch angles was provided. Results demonstrated that except for the stow mode, the first PTC in the array experienced the maximum mean pressure in the upwind side of the PTCs model and corresponded to the maximum mean drag coefficient. Besides, the minimum mean drag coefficient belongs to the second row in the array except for the stow mode. A comparison between flow patterns around the PTCs revealed the high vorticity concentration in front of the collectors for pitch angles θ = 0° and θ = 180°.

Characteristics of tornado wind loads and examinations of tornado wind load provisions in ASCE 7–16

This paper aims to study the characteristics of tornado-induced wind loads over smooth and rough ground and subsequently examine the tornado wind load provisions in ASCE 7–16. The pressure measurement on a cubic building subjected to stationary tornado vortices was conducted in the tornado simulator at Tongji University, China. The overall uplift and base shear for MWFRS and wind loads for Components & Cladding are analyzed to assess the newly proposed tornado wind load provisions. The results indicate that the simulated tornado vortices with swirl ratio of 0.72 can represent the EF3 Spencer tornado vortices. In addition, the external building surfaces are significantly affected by the terrain when they are immersed below 3 to 5 times the roughness element height. Tornado would induce more intense aerodynamic loads on roof, leeward wall and side wall than those from conventional boundary-layer winds. The Extended method by amplifying the gust effect factor to 0.9 and the Simplified method by introducing a tornado factor in ASCE 7–16 are able to conservatively evaluate the overall uplift and base shear on the building without dominant openings. However, these two approaches would significantly underestimate the overall uplift on building with a dominant opening as much as 21% and 22%, respectively. The underestimation of peak negative force on the edge zone of wall can reach 39% ~ 48% using Extended method.

Field measurement research of wind pressure inside ribbed cooling tower

Due to the limitation of engineering conditions and meteorological conditions, the on-site measured data inside the cooling tower is relatively lacking. Field test data for ribbed cooling towers is even less. In order to provide a scientific wind load basis for engineering design, we choose a bibbed cooling tower for field measurement in Toksun County, Xinjiang, which is windy all the year round, so as to understand the inner wind load characteristics of the cooling tower under the prevailing wind direction and the maximum wind speed direction. It is found that the average wind pressure coefficient measured in the field is not completely consistent with the wind pressure coefficient in the Code.

Comparison of the seismic and wind analyses of two tower cranes

Tower cranes act as essential support equipment for the development of the city’s construction projects, not only for new projects but also in the rehabilitation of old structures. In the present study, we analyze and compare two different tower cranes, where the differences are essentially based on the geometry, weight, and consequently the reach and load capacity of each structure. In general, these types of structures correspond to slender steel structures designed to carry high loads. Despite the great importance given to these structures, many disasters have occurred causing damage to people or to urban equipment in the vicinity due to total or partial collapse. We developed a 3-D mathematical linear model of the structures in SAP2000 and compared the analytical frequencies with in situ measurements. The maximum error for the first two translationally identified modes in the x and y directions was 4.9 %. These structures are very flexible, with frequencies below 0.5 Hz. We then applied and evaluated the impact of two types of exceptional action, seismic (maximum reference acceleration of 1.5 m/s2 and 1.7 m/s2) and wind load characteristics of an urban area (surrounded by buildings), for the two structures not carrying any load. The effects resulted in no serious consequences, with wind being the most severe action in certain cross-sections and seismic action in others. One very important and innovative aspect of this study was the in situ characterization of the frequencies and the verification that the mathematical model reproduced the behavior of the real structure very well. We complemented this study by measuring four more structures and proposing a law to estimate the frequency as a function of the length of the tower plus jib. However, we also found from a literature review of recently published work that, contrary to the six structures that we analyzed, it is difficult to extrapolate this law for other types of tower cranes.

Study on simulation of wind load characteristics for photovoltaic generation systems

Photovoltaic generation systems can automatically track the angle of sunlight. The system consists of four photovoltaic (PV) panels which can adjust pitch angle and azimuth angle according to the sunlight. The variation of the wind coefficient and wind load characteristics of the PV panels with the pitch angle and azimuth angle is obtained through the wind tunnel simulation based on FLUENT to determine the flow characteristics around the PV panels.

Influence of non-Gaussian characteristics of wind load on fatigue damage of wind turbine

Based on translation models, both Gaussian and non-Gaussian wind fields are generated using spectral representation method for investigating the influence of non-Gaussian characteristics and directivity effect of wind load on fatigue damage of wind turbine. Using the blade aerodynamic model and multi-body dynamics, dynamic responses are calculated. Using linear damage accumulation theory and linear crack propagation theory, crack initiation life and crack propagation life are discussed with consideration of the joint probability density distribution of the wind direction and mean wind speed in detail. The result shows that non-Gaussian characteristics of wind load have less influence on fatigue life of wind turbine in the area with smaller annual mean wind speeds. Whereas, the influence becomes significant with the increase of the annual mean wind speed. When the annual mean wind speeds are 7 m/s and 9 m/s at hub height of 90 m, the crack initiation lives under softening non-Gaussian wind decrease by 10% compared with Gaussian wind fields or at higher hub height. The study indicates that the consideration of the influence of softening non-Gaussian characteristics of wind inflows can significantly decrease the fatigue life, and, if neglected, it can result in non-conservative fatigue life estimates for the areas with higher annual mean wind speeds.

Wind Resistance Analysis for H-shaped Hanger of Long-span Steel Arch Bridge

This paper presents the development history of arch bridge and the structural system of long-span steel arch bridge as well as the damage and load types of wind-induced vibration. It also analyses the characteristics of wind load on an arch bridge especially the half-through or through-type steel arch bridges, the effect of wind-induced vibration on H-shaped hangers. Finally, it introduces the measures to reduce wind-induced effect on long-span steel arch bridges with H-shaped hangers.

Investigation on aerodynamic performance of luxury cruise ship

Due to the high superstructures and complex configurations of luxury cruise ships, the impacts of wind loads on the ships must be analyzed during design. In this study, the aerodynamic performance of a Vista-class cruise ship was investigated through wind tunnel measurements, empirical formulae and numerical calculations. Wind tunnel experiments were conducted in a simulated atmospheric boundary layer wind field, and the measured data exhibited reliable wind load characteristics of the cruise ship. Three empirical formulae were employed to estimate the wind loads on the cruise ship. The comparison between the estimated results and the experimental data indicated that the general characteristics of the wind loads on generic ship types summarized by empirical formulae were not consistent with those on the Vista-class cruise ship. Numerical simulations based on the Reynolds-averaged Navier-Stokes (RANS) equations were performed under the same conditions as those of the wind tunnel experiments. Mesh independence and Reynolds number independence analyses were carried out. The numerical results of the wind loads matched well with the experimental data. Valuable flow field details captured by the numerical calculations were also extracted to analyze the flow characteristics around the cruise ship. The results demonstrated that the Vista-class cruise ship is a typical blunt body. The wind loads on the cruise ship were sensitive to the Reynolds number. The reversed-flow zones around the ship were primarily distributed over the front/back sides of the ship, the top deck, and the ship's leeward side. These reversed-flow zones were mostly induced by the flow separation at the corners of the bow and aft decks and the sharp edges of the top deck. The analysis of the flow characteristics around the ship can provide guidance for future optimization of the aerodynamic performance of the Vista-class cruise ship.

Wind tunnel investigation on the wind load of large-span coal sheds with porous gables: Influence of gable ventilation

Recently a novel coal shed with porous gables emerged as the production and environmental protection requirements of the coal yards. In this study, the wind load characteristics on such coal shed are investigated through wind tunnel tests. The influences of gable ventilation on the overall aerodynamic loads, wind pressure distributions, and peak wind loads are discussed by comparing with the wind tunnel results on coal sheds with solid and open gables. It is found that the gable ventilation might significantly alleviate wind suctions on the roof and gables induced by separation flows whereas the positive pressure could be enhanced. The wind loads on such coal sheds can be different from those on conventional coal sheds with solid or open gables. However, the wind load seems insensitive to the gable porosity within the common range. Consequently, the zone values of mean and peak wind loads for the main structures and claddings are summarized respectively for engineering reference. Finally, it is evident that adopting porous gables would be beneficial for not only providing a fine wind environment but also reducing the unfavorable wind loads, which are of great promise in engineering application.

Probabilistic and spectral modelling of dynamic wind effects of quayside container cranes

Quayside container cranes are important delivery machineries located in the most frontiers of container terminals, where strong wind attacks happen occasionally. Since the previous researches on quayside container cranes mainly focused on the mean wind load and static response characteristics, the fluctuating wind load and dynamic response characteristics require further investigations. In the present study, the aerodynamic wind loads on quayside container cranes were obtained from wind tunnel tests. The probabilistic and spectral models of the fluctuating aerodynamic loads were established. Then the joint probabilistic distributions of dynamic wind-induced responses were derived theoretically based on a series of Gaussian and independent assumption of resonant components. Finally, the results were validated by time domain analysis using wind tunnel data. It is concluded that the assumptions are acceptable. And the presented approach can estimate peak dynamic sliding force, overturning moments and leg uplifts of quayside container cranes effectively and efficiently.