Gust Effect Research Articles

Peak factors of wind load for main frame design of rooftop structures

ABSTRACT Technology is being developed to unitize structures installed on apartment rooftops during construction. The rooftop is located at the top of a high-rise building with a flexible structure. However, the rooftop structure itself is close to a rigid body and is not integrated with the building. Therefore, it is difficult to calculate the gust effect coefficient of the rooftop structure. The peak factor provided by the Korean Design Standard (KDS) uses an equation for general buildings and may be inaccurate to a certain extent when used to calculate the wind load on rooftop structures. Therefore, in this study, wind pressure tests were conducted on three research models to calculate the appropriate peak factors for rooftop structures. For each model, the peak factor trend was analyzed according to the wind pressure coefficient, and the peak factor was presented. When the evaluation time was 10 min, the positive pressure peak factor converged to three and the negative pressure peak factor converged to four. Additionally, a formula for calculating the peak factor of rooftop structures based on the wind load evaluation time is proposed. Hence, the peak factor of rooftop structures can be calculated based on various evaluation times.

Numerical modelling of aerodynamic response to gusts and gust effect mitigation

Unmanned aerial vehicle (UAV) flights in urban environments are challenging due to the complex flow structures and elevated turbulence around buildings. Consequently, research has shifted towards investigating the impact of gusts on the aerodynamic stability and control of UAVs. This study focuses on enhancing gust numerical modelling capabilities to understand the aerodynamic response, specifically exploring gust mitigation strategies for UAVs operating in turbulent urban environments. The split-velocity method, originally designed for two-dimensional compressible inviscid flows, where the velocity components were decomposed into a prescribed gust velocity and the remaining velocity components, is extended to three-dimensional incompressible viscous flows. To facilitate effective gust mitigation techniques, a radial basis function is applied to the modified split-velocity method to numerically model wings in pitching motions under gust encounters. A novel strategy is proposed to correct the discretized gust velocities and ensure gust flux conservation, showing effective improvement to the numerical predictions. The computed results agreed well with the experimental data available in the public domain, confirming that wing pitch motion can effectively mitigate the effects of gusts.

Large-scale sinusoidal gust effect on aerodynamic pressures and forces on a square cylinder

Aerodynamic pressures and forces on a two-dimensional square cylinder were experimentally investigated in large-scale sinusoidal gusts. The effects of streamwise and transverse gusts with a wide range of gust amplitudes were studied at a Reynolds number of Re = 2.1 × 104. To enhance our understanding of the large-scale sinusoidal gust effect, the pressure fields and global aerodynamic forces of the square cylinder in large-scale gusts were compared with those in smooth and grid-generated turbulent flows. This study shows that both large-scale streamwise and transverse gusts can promote early pressure recovery, resulting in larger mean pressures on the side and leeward surfaces. The root mean square (RMS) of the pressures on the side surface increased and decreased with an increase in the streamwise and transverse gust amplitudes, respectively. The mean drag on the square cylinder was reduced under the effects of large-scale streamwise and transverse gusts. The increase in the streamwise and transverse gust amplitudes significantly affected the RMS of the drag and lift on the square cylinder, respectively. A proper orthogonal decomposition (POD) analysis showed that the contribution of the first POD mode switched from fluctuating lift to drag when the streamwise gust amplitude was very high. The spectral analysis demonstrated that the alternating von Kármán vortex-shedding process still dominated the fluctuating lift under the effect of large-scale gusts. In addition, the spanwise correlations of drag were significantly strong under the effects of large-scale streamwise gusts. However, the spanwise correlations of lift were reduced under the effects of large-scale gusts with high gust amplitudes.

Gust effect factors for regions of separated flow around rigid low-, mid-, and high-rise buildings

This paper examines the gust effect factor model for regions of separated flow on rigid buildings. Boundary layer wind tunnel data for a total of 58 buildings, with heights ranging from low-rise to high-rise were analyzed. The results show that the characteristics of separated flow determine the statistical distribution of surface pressures. It was found that the reattachment of separated flows onto building surfaces reduces the skewness and kurtosis of area-averaged surface pressures, causing them to follow the Gaussian distribution more closely. However, the pressures tend to have non-Gaussian distributions for surfaces without flow reattachment. Strong Karman-like vortex shedding increases aerodynamic admittance functions around the Strouhal number, along with the peak factors and gust effect factors of area-averaged side wall pressures. For surfaces with flow reattachment, Solari's (1993a) model predicts the gust effect factors with reasonable accuracy, particularly for uplift on low-rise buildings, mid-rise buildings with height-to-width ratios, H/W = 1 and high-rise buildings with height-to-width ratios, H/W > 4, and length-to-breadth ratios, L/B > 2. For separated flows without reattachment on the building, particularly for H/W > 4 and L/B < 2, periodic Karman-like vortex shedding tends to cause inaccuracies in the gust effect factor model, as might be expected.

Pressure Feedback Control of Aerodynamic Loads on a Delta Wing in Transverse Gusts

A feedback active flow control (AFC) scheme is studied for control of unsteady aerodynamic loads that act on a generic tailless delta wing during transverse gust encounters. The transverse gust and the roll angle of the wing create an unsteady roll moment. The trailing edge actuators generate unbalanced lift increments on the two sides of the model to control the roll moment. Spatially distributed pressure sensors measure surface pressure on the suction side of the wing, and the real-time aerodynamic loads are estimated through models that are identified by the Sparse Identification of Nonlinear Dynamics algorithm. The aerodynamic load estimation is then used as a surrogate to provide the AFC system with a feedback signal to alleviate the unsteady roll moment due to the gust effect. A physical interpretation of the model identification results is made to locate the source of the lift and roll moment fluctuations in gust encounters. Experimental results show that the AFC effect with a momentum coefficient input of 2% is equivalent to 26° elevon deflection in terms of the roll moment change, and the AFC doubles the control authority relative to elevons. The real-time control results show that the pressure feedback control system reduces the mean roll moment error and suppresses the fluctuations to less than 20% of the uncontrolled fluctuation level at a high angle of attack.

Effects of streamwise gust amplitude on the flow around and forces on two tandem circular cylinders

Three-dimensional large eddy simulations are carried out to investigate the effect of streamwise gust amplitude ratio AR on the flow structure around and dynamic forces on two tandem circular cylinders at a subcritical Reynolds number of Re = 1 × 103. The center-to-center space L between the two cylinders is fixed at 3.5D, where D is the cylinder diameter. The velocity U of sinusoidal streamwise gust is set as U = U0 (1+ARsin2πfut), where the velocity amplitude ratio AR is varied from 0 to 0.25, U0 is the mean velocity, fu is the frequency of the sinusoidal streamwise gust, and t is the time. In order to enhance the understanding of the streamwise gust effect on the physical properties of the flow around the two tandem cylinders, the shear-layer reattachment, flow separation, wake recirculation, Strouhal number (St), unsteady forces, and phase lag (φ) between the fluctuating lift forces of the two cylinders are explicated. The results show that the flow structure around the cylinders is sensitive to AR. A change in AR thus leads to modification of reattaching flow (AR ≤ 0.15) to co-shedding flow (AR ≥ 0.20). The St, fluctuating forces and φ thus jumps at the boundary between the reattaching and co-shedding regimes. A stronger gust effect appears on the fluctuating drag of the upstream cylinder than that of the downstream cylinder. Besides the dominant component of the fluctuating lift induced by the vortex shedding, two other components are observed with the frequencies equaling to the superposition and subtraction of the gust and vortex-shedding frequencies, respectively. In addition, two more cases with L/D = 1.5 and 6.0 are conducted for deeper understanding of AR effects.

Discussion of Design Wind Loads on a Vaulted Free Roof

This paper discusses the wind loads for designing vaulted free roofs based on a wind tunnel experiment, in which the wind force coefficients for the main wind force resisting system and the peak wind force coefficients for cladding are considered. The focus is on the dynamic load effects of fluctuating wind pressures on the wind force coefficients. Wind pressure distributions on the top and bottom surfaces were measured in a turbulent boundary layer. The results indicated that the distributions of wind force coefficients changed significantly with wind direction. Then, the wind direction providing the maximum load effect on the structural frame was detected from a dynamic response analysis using the time histories of wind pressure coefficients. In the analysis, the focus was on the bending moment at the windward column base and the axial force in the leeward column as the most important load effects. The LRC method proposed by Kasperski was employed for evaluating the equivalent static wind force coefficients providing the maximum load effects. Based on the results, a model of design wind force coefficient was proposed in the framework of the conventional gust effect factor approach. Finally, positive and negative peak wind force coefficients for designing the cladding were proposed based on the most critical maximum and minimum peak wind force coefficients among all wind directions.

Large-Scale Gust Effect on Aerodynamic Pressures and Forces on a Square Cylinder

Large-Scale Gust Effect on Aerodynamic Pressures and Forces on a Square Cylinder

Gust mitigation with an oscillating airfoil at low Reynolds number

The encounter between micro-aerial vehicles (MAVs) and gusts is often detrimental and mitigating the effects of the gust is important for operating MAVs under severe environmental conditions. This study investigates the impact of vertical gusts on stationary and oscillating NACA0012 (National Advisory Committee for Aeronautics) airfoils at low Reynolds numbers using high-order computational fluid dynamics methods, and identifies key dynamics that dominate gust mitigation. The interaction of the gusts with the stationary airfoil generates large unsteady forces, which exceed the peak static lift coefficient. A simple pitch-down maneuver and oscillating airfoil motion were tested as methods for mitigating the effects of the gusts. A rapid and significant pitch-down maneuver is observed to inadvertently cause a stall event by exceeding the negative stall angle. A stepwise change in the angle of attack (AoA), as the gust develops, is shown to be more effective at mitigating the gust effect. However, this gust mitigation strategy is still not effective if the gust continues to grow in magnitude. Low amplitude wing oscillations were then tested as a novel method for gust mitigation. Increasing the reduced frequency of the oscillating airfoil is shown to dominate the gust and results in a predictable oscillatory lift and drag/thrust behavior. Results also show that this effect is relatively insensitive to variations in the Strouhal number. These results suggest there may be gust mitigation strategies leveraging oscillating wing behaviors on MAVs.

Aeroelastic modeling to study the wind-induced response of a self-supported lattice tower

The results from a 1:50 scale aeroelastic model of a self-supported steel lattice tower subjected to simulated hurricane winds are presented. The lattice tower considered is a typical structure that is used as part of a tower-insulator-conductor system for electrical transmission infrastructure. The aeroelastic tests were conducted at the NSF Wall of Wind Experimental Facility (WOW EF) at the Florida International University (FIU). The tower was tested at various wind speeds ranging from 50 m/s to 92 m/s (equivalent full-scale speeds) for varying wind directions. Two system identification (SID) techniques were utilized to evaluate along-wind aerodynamic damping and compare with theoretical estimates. The SID techniques were also utilized to evaluate crosswind aerodynamic damping. A buffeting analysis was conducted to estimate the response of the tower and compare it to measured values at the WOW. Drag and moment coefficients were calculated from the measured responses, and the dynamic amplification factors (DAF) as well as gust effect factors were computed. The analysis required consideration of the variation of the turbulence intensity along the height of the tower in the buffeting analytical equations. The drag coefficients are shown to agree with values proposed in the current standards. However, there might be a need to introduce base moment coefficients in lattice tower design. The resonance contribution is shown to reach a maximum of 18% of the peak response of the tower.

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.

Gust effect factors for windward walls of rigid buildings with various aspect ratios

This paper examines the aerodynamic mechanisms associated with gust effect factors for windward walls of rigid buildings. The analysis utilizes two experimental databases with 58 rectangular-plan building models. Statistical characteristics of windward wall pressures, such as skewness, kurtosis, and peak factors, are examined along with parameters related to the wind spectra and the aerodynamic admittance. It was found that the statistical characteristics depend primarily on the aspect ratio defined as the ratio of height to breadth, H/B. The results also show that the area-averaged windward wall pressures present Gaussian distributions when the aspect ratio exceeds 6. Moreover, the measured aerodynamic admittance function for area-averaged windward wall pressures, referenced to the mid-height velocity spectra, matches reasonably well with Vickery’s model. The energy content of the wind-induced pressure on windward walls are influenced by horseshoe vortex of low-rise buildings with H/B ​< ​1. The pressure fluctuations at windward wall locations near the edge conjunct with side walls are also influenced by the vortex shedding over side walls for high-rise buildings. The gust effect factor model adopted in ASCE 7–16 is able to accurately assess the gust effect factors for rigid high-rise buildings, but is inaccurate for low-rise buildings, primarily because of the role of the horseshoe vortices.

An Examination of the Gust Effect Factor for Rigid High-Rise Buildings

In order to systematically investigate the gust effect factor for rigid buildings, the derivation of the gust effect factor in ASCE 7–16 is carefully reviewed and scale model pressure tests were carried out for rectangular-plan high-rise buildings with plan aspect ratios ranging from 0.11 to 9. The gust effect factor and the aerodynamic admittance function (AAF) for area-averaged pressure coefficients and base drag coefficients were obtained and discussed in detail. The results show that the AAF has direct influence on the value of the gust effect factor, depending on whether effects of non-contemporaneous gust actions or body-generated turbulence are playing a leading role. The ASCE 7–16 gust effect factor for rigid buildings underestimates the measured values for individual walls due to differences in the AAF, peak factors, and the employment of the 3 s moving average filter. However, the ASCE 7–16 gust factor for overall drag is estimated within 5% or better.

Comparison of the Canadian standard and other standards for wind loading on self-supporting telecommunication towers

Designing telecommunication towers to withstand wind loads requires specific considerations, which has led the international civil engineering community to develop specific standards for these structures. The recent internationalization of the construction business has made it imperative for engineers to acquire knowledge and interpretation of codes from different countries. In light of the 2018 update of Canadian Standard CSA-S37-18 (CSA), evaluating its differences against other international standards for telecommunication towers has become important. This paper presents a comparison of the wind loading specifications for self-supporting telecommunication towers according to CSA; Australian Standard; Eurocode EN-1993-1; and US Standard TIA-222-G. The different standards have also been evaluated with respect to the values of the axial forces and the elements ratio for two self-supporting telecommunication towers. The parameters related to the wind profiles and the gust effect factor presented the highest difference between the standards.

A coupled HDG-FV scheme for the simulation of transient inviscid compressible flows

A methodology that combines the advantages of the vertex-centred finite volume (FV) method and high-order hybridisable discontinuous Galerkin (HDG) method is presented for the simulation of the transient inviscid two dimensional flows. The resulting method is suitable for simulating the transient effects on coarse meshes that are suitable to perform steady simulations with traditional low-order methods. In the vicinity of the aerodynamic shapes, FVs are used whereas in regions where the size of the element is too large for finite volumes to provide an accurate answer, the high-order HDG approach is employed with a non-uniform degree of approximation. The proposed method circumvents the need to produce tailored meshes for transient simulations, as required in a low-order context, and also the need to produce high-order curvilinear meshes, as required by high-order methods. Numerical examples are used to test the optimal convergence properties of the combined HDG-FV scheme and to demonstrate its potential in the context of simulating the wind gust effect on aerodynamic shapes.

Anti-disturbance trajectory tracking of quadrotor vehicles via generalized extended state observer

During the trajectory tracking process and low altitude flight of quadrotor, wind gust and ground effect will significantly affect the accuracy and stability of the controller. Therefore, it is vital for a quadrotor to have a robust controller against multiple disturbances. To mitigate this challenge, an active anti-disturbance control strategy based on generalized extended state observer is proposed in this article. Firstly, quadrotor dynamics is modeled as cascaded translational and rotational loops, and the characteristics of wind gust and ground effect are analyzed. Secondly, two generalized extended state observers are constructed for those loops respectively to estimate and attenuate the impact of wind gust and ground effect, and the position and attitude controller are designed based on backstepping method. Finally, real time experiments are carried out on hovering and circle trajectory tracking conditions. The results illustrate that the proposed controller has more advantages in high precision trajectory tracking and low altitude flight of quadrotor in existence of multiple disturbances.

Robust Gain-Scheduled Flight Controller for an In-Flight Simulator

In-Flight Simulators (IFSs) require flight controllers, which mimic other aircraft's dynamics in a certain operation range, which is the problem addressed in this paper. The design problem of a linear parameter-varying type gain-scheduled flight controller, which simultaneously suppresses gust effect and reproduces low-and-middle frequency commands as IFS's motions in a certain speed range, for the lateral-directional motions of an airplane is addressed via linear matrix inequality formulation. Our controller performance is examined by flight tests.

Effects of plan dimensions on gust wind loads for high-rise buildings

Scale-model wind tunnel pressure measurements were carried out for rectangular-plan high-rise buildings with plan ratios ranging from 0.11 to 9. Mean, fluctuating, and peak wall pressure coefficient distributions and area-averages were investigated. In addition, comparisons with the ASCE 7–16 provisions for the Main Wind Force-Resisting System (MWFRS) were made. The results show that the plan ratio has significant effects on pressure coefficients on the leeward and side walls for plan ratios less than about 4. The largest mean base shear coefficient occurs for plan ratio of about 0.67, with large values in the range of 0.5–1, but decreasing for larger or smaller plan ratios. ASCE 7–16 mean load coefficients tend to underestimate the data, particularly because of the values on leeward walls. ASCE 7–16 also underestimates the peak load coefficients due to the value of the gust effect factor. For rigid buildings, ASCE 7–16 has a gust effect factor of 0.85, while measurements indicate that it is closer to 1 for plan ratios between 0.67 and 2. Thus, the overall mismatch between the ASCE 7–16 MWFRS loads and the measured data is due to both the mean pressure coefficients and the gust effect factor. For plan ratios below 0.67, the decrease in plan ratio tends to be favorable for the MWFRS load coefficients; while for plan ratios above 4, the effects of plan ratios on the MWFRS load coefficients are limited.

Analysis of Wind Effect on High-Rise Building for Different Terrain Category

This paper analyzed the effect of wind loadings on high-rise building for different terrain categories. The wind speed and design wind pressure for the different terrain categories adopted for this study were calculated as per logarithmic wind profile equation and BS6399-2:1997 respectively. Also, the nodal displacement of a 3D high-rise building model with reference to the calculated design wind loads were performed using finite element analysis software(STADDPROV8I). From the result obtained, it was shown that Terrain category IV when compared to other terrain categories recorded lower wind speed and pressure from the ground to a height of about 10m. The writers also observed that at greater terrain category(TC4), the wind speed and pressure tends to be much higher at the top floors(10m-48m) of the high-rise building whereas, terrain categories (TC3, TC2, TC1) recorded lower wind speed and pressure at that same height(10m-48m). this disparity however was discovered to be due to a phenomenon known as gust effect. Also, the nodal displacement for the different terrain category (TC4, TC3, TC2 and TC1) on each floor of the high-rise building increased uniformly in respective pattern as the height of the 3D model increases. In conclusion, the authors therefore remark “the greater the terrain category, the lowest is the wind speed in the roughness sub layer and the longer height it takes to reach gradient wind speed”.

Analysis of Wind Effect on High-Rise Building for Different Terrain Category

This paper analyzed the effect of wind loadings on high-rise building for different terrain categories. The wind speed and design wind pressure for the different terrain categories adopted for this study were calculated as per logarithmic wind profile equation and BS6399-2:1997 respectively. Also, the nodal displacement of a 3D high-rise building model with reference to the calculated design wind loads were performed using finite element analysis software(STADDPROV8I). From the result obtained, it was shown that Terrain category IV when compared to other terrain categories recorded lower wind speed and pressure from the ground to a height of about 10m. The writers also observed that at greater terrain category(TC4), the wind speed and pressure tends to be much higher at the top floors(10m-48m) of the high-rise building whereas, terrain categories (TC3, TC2, TC1) recorded lower wind speed and pressure at that same height(10m-48m). this disparity however was discovered to be due to a phenomenon known as gust effect. Also, the nodal displacement for the different terrain category (TC4, TC3, TC2 and TC1) on each floor of the high-rise building increased uniformly in respective pattern as the height of the 3D model increases. In conclusion, the authors therefore remark “the greater the terrain category, the lowest is the wind speed in the roughness sub layer and the longer height it takes to reach gradient wind speed”.