Wind Angle Research Articles

Influences of Attack Angles on Aerodynamic Derivatives and Flutter Characteristics of Flat Box Girders

The flutter response of Nanjing Fourth Bridge flat box girder under different wind attack angles was tested in detail through sectional model test. The evolution of unsteady and steady critical amplitude with wind speed was discussed. Based on the amplitude envelope of the flutter response and the Hilbert transform, the amplitude- dependent modal damping of the system is identified, and the mechanism of the flutter mode change in the wind angle of attack is initially explained. Secondly, the modal parameters of the system under different wind attack angles were extracted. Based on the bimodal coupled flutter analysis method, the nonlinear flutter derivatives of the section under different wind attack angles were identified, and the change law of the amplitude dependence of the key flutter derivatives on the wind attack angle and the potential influence on the flutter morphology and characteristics of the section were studied. Finally, the effect of wind attack angle on uncoupled and coupled aerodynamic damping is analyzed by deconstructing the modal damping one by one, and the dynamic mechanism of the differential flutter performance caused by fractional damping is illustrated.

Factors influencing ember accumulation near a building

Background Embers, also known as firebrands, are the leading cause of building ignition during wildland–urban fires. This is attributed both to direct ignition of material on, in, or attached to the building, and indirect ignition where they ignite vegetation or other combustible material near the building, which results in a radiant heat and/or direct flame contact exposure that ignites the building. Indirect ignition of a building can occur when embers accumulate on and ignite nearby combustible fuel, resulting in radiant heat or flame constant exposure. Aims/implications Factors that influence ember accumulation near a building include building geometry, such as flat wall and re-entrant corners, building wind angle, wind speed and the surface roughness characteristics of the horizontal landscape close to the building. Methods Experiments conducted at the Insurance Institute for Business & Home Safety (IBHS) Research Center using full-scale buildings with the above-mentioned factors provided a means to quantify ember accumulation on a mass per unit area basis. Key results Ember accumulation was greatest at locations immediately adjacent to the building and higher wind speeds allowed more embers to reach the building. Conclusions The work presented in this paper provides data and insight on wind-blown ember accumulation near a full-scale building.

Research on vibration suppression effect and energy dissipation mechanism of wind turbine piezoelectric blade

The smart wind turbine piezoelectric blade is a conceptual blade proposed for adaptive vibration suppression. However, it is still far from engineering application due to insufficient theoretical and experimental research. Some innovative research has been carried out in this paper in order to provide some basic reference for piezoelectric vibration suppression design for the ultra-long wind turbine blade. First, using a second-developed dynamic model of the wind turbine piezoelectric blade, the evolution patterns of electromechanical–aeroelastic coupling modal and the energy distribution characteristics of wind-induced vibration response were investigated. Then, an aeroelastic model design method of the wind turbine blade that is suitable for the three-dimensional (3D) variable cross-sections was proposed. Afterward, an aeroelastic wind tunnel test of the 15 megawatts (MW) wind turbine piezoelectric blade was conducted. Finally, the wind-induced vibration suppression effect of piezoelectric material was revealed by comparing the time–frequency characteristics and modal energy distribution between the piezoelectric blade and the ordinary blade. The research results demonstrated that the proposed aeroelastic wind tunnel test could accurately reflect the wind-induced vibration characteristics of the piezoelectric blade. The piezoelectric material can narrow the range of sensitive wind angles of the wind turbine blade, increase the critical wind speed for frequency-locked vibration, and prolong the energy accumulation time of aeroelastic instability. Piezoelectric material causes the associated vibration energy to be transferred in the modal space, weakens energy accumulation of the negative damping mode, and strengthens the energy dissipation of the positive damping mode.

Wind Interference Effect of Neighbouring Square Buildings in Rhombic Arrangement on an Octagonal Building

Four square plan shaped tall buildings of the same height and lateral dimension are positioned at the vertices of a rhombus. The octagonal plan shaped tall building of same height is placed at the centroid of the rhombus. The wind-induced responses of the octagonal plan shaped tall building for specified interference cases are compared with that of the isolated cases. The octagonal plan shaped principal building is exposed to atmospheric boundary layer wind flow. The wind angle varies from 0° to 90° at an interval of 15° for both isolated and interfering conditions. Computational fluid dynamics is implemented to simulate the effect of wind-structure interaction on the principal and neighbouring buildings in the boundary layer wind flow. The wind-induced static responses like drag and lift coefficients, pressure coefficients for isolated and interference cases are evaluated and compared graphically. The responses of isolated and interference cases vary significantly with the varying wind incidence angle. The dynamic behaviour of wind is also thoroughly investigated to identify the adverse local effect on the different faces of the octagonal building. As the characterisation of wind-induced dynamic responses, peak pressure coefficients and power spectral densities are evaluated and plotted accordingly. The peak pressure coefficients are plotted against mean pressure coefficients. The power spectral densities for different interfering cases are compared with the isolated case. Significant variation in power spectral densities is observed in some cases, which portrays the different characteristics for formation and shedding of the vortices in the wake of the octagonal building. The comparison of various dynamic responses between isolated and interfering cases highlights the interference by the square plan shaped buildings.

Axial Compressive Behavior of Glass Fiber-Reinforced Hollow Concrete Columns

To investigate the axial compression behavior of glass fiber-reinforced polymer tubes filled with reinforced hollow concrete members, the finite element model was established in ABAQUS. The correctness of the finite element model was verified by comparing the simulation results with the existing test results. On this basis, the influence of the main parameters such as GFRP tube wall thickness, filament winding angle, concrete strength grade, and hollow ratio on the axial compression behavior was analyzed. The calculation formula of the bearing capacity under axial compression of the GFRP tube filled with reinforced hollow concrete members was established. The results show that the load and strain curves and failure modes of the model and the established bearing capacity formula are in good agreement with the test results. The axial compression capacity of the hollow members increases with the increase in the thickness of GFRP tube wall thickness, filament winding angle, and concrete strength grade and decreases with the increase in the hollow ratio. The GFRP tube filament winding angle and hollow ratio have significant influence on the bearing capacity of axial compression, followed by the GFRP tube wall thickness and concrete strength grade. The radius ratio of hollow part should be 0.250.5. The axial compression bearing capacity of the hollow members can be compensated by properly increasing the GFRP tube wall thickness, filament winding angle, or concrete strength grade. The research conclusion can provide some reference for the design of the structure.

Study on Probabilistic Properties of Fluctuating Wind Pressure Distribution of Low-Rise Buildings Affected by Slope Gradient in Mountain Forms

This study presents the results of experimental observation of wind pressure on low-rise buildings in three typical mountain forms through wind tunnel experiments. This research focuses on the distribution change in fluctuating wind pressure coefficients with slope gradient. The variation of power spectra and wind pressure’s probability distribution at representative measuring points with the slope gradient were also included. No obvious variation trend for the fluctuating wind pressure coefficient was identified on the windward side. When the slope gradient was 90°, there was just a slight change in distribution or value of the fluctuating wind pressure coefficient on the left. However, the coefficient on the leeward decreased and then increased, while on the roof, it gradually decreased. Furthermore, the experiments showed that the fluctuating wind pressure’s distribution in the middle of windward eaves and at the leeward eaves was significantly affected by the slope gradient. At 0° wind angle, the wind pressure probability density distribution gradually changes from symmetric to asymmetric at the measuring points of windward eaves and side centers when the slope gradient increases, which shows that the wind pressure probability density distribution changes from non-Gaussian to Gaussian.

Aerodynamic investigation of extremely efficient vehicles under side wind conditions

A vehicle is more stable when the geometric center, center of gravity, and stagnation point are in line. However, the inflow direction and velocity magnitude of the operational environment of road vehicles are varying. This study aims to investigate the aerodynamic behavior of a water-drop-shaped vehicle under side wind conditions. Some essential aerodynamic performances of the vehicle are numerically and graphically analyzed at 0 deg, 10 deg, and 20 deg of side wind directions. The value of the coefficient of drag, drag force, coefficient of lift, and lift force exponentially increases as the yaw angle elevates. The lower part on the area of the front-wheel compartment becomes the critical location indicated by the results on pressure coefficient, friction coefficient, and total wall shear stress distribution along the vehicle surface. Increasing the side wind angle triggers more significant vortex regions generated around the wheel compartment and on the leeward side of the vehicle.

Experimental and numerical aerodynamic analysis of an elevated beachfront house

Elevating coastal houses enables residential communities to reduce the risk of flooding due to tropical cyclones. However, wind-induced damage during such events requires an understanding of the inherent wind forces to improve damage mitigation techniques and assessment of climate-related risk in insurance models. In this study, wind-tunnel experiments and computational fluid dynamics (CFD) simulations are conducted for a typical elevated 1:25 scale beachfront house, possessing a 5:12 pitched gable roof with overhanging eave. An atmospheric boundary layer (ABL) wind field is generated in a low-speed wind-tunnel to replicate conditions experienced during tropical cyclones. Testing is performed for a range of incident wind angles to understand the full aerodynamic consequences of strong winds. Measured pressure coefficient (Cp) distributions are compared with CFD simulations using steady-state and transient Delayed Detached-Eddy Simulation (DDES) within ANSYS Fluent 2021 R1. Net Cp values surrounding the overhanging eave are considered to evaluate the role of this typical geometrical feature. It was found that larger uplift suction occurred at incident wind angles of 45°and above, after which the suction remained stable. The roof panels are subjected to the greatest upward suction, where critical regions occur at the roof ridge. The size of the low-pressure regions is determined by the incident wind angle and ensuing flow separation wherein DDES is found to reproduce additional aerodynamic features arising from unsteady turbulent flow. DDES offers improved predictive capability when mean pressure forces are considered but falls short as an accurate means to efficiently evaluate peak Cp distributions.

Numerical simulation of the dust particles deposition on solar photovoltaic panels and its effect on power generation efficiency

The deposition of dust particles on the surface of solar photovoltaic panels leads to a decrease in power generation efficiency, so it is necessary to study the interaction mechanism between dust particles and solar photovoltaic panels. Aiming at the problem that the simplified two-dimensional model cannot reflect the actual photovoltaic power station in the traditional research, a geometric model of the distribution form of the 3 × 3 solar photovoltaic panel array is constructed. The shear stress transport k−ω turbulence model is used to predict the flow field changes around solar photovoltaic (PV). A discrete particle model is used to predict the particle deposition rate of photovoltaic panels. The effects of different wind speeds, particle sizes, and wind angles on particle deposition were analyzed. With the increase of wind speed, the deposition amount of the photovoltaic panels in the last two rows gradually decreased, while the photovoltaic panels in the first row showed a trend of first decreasing and then increasing. As the particle size increases, the particle deposition amount increases gradually. When the particle size is less than 60 μm, the deposition amount on the photovoltaic panel is less than 0.03g. When the particle size is greater than 60 μm, the deposition amount of particles increases exponentially. The maximum deposition amount is 3.98g, and the maximum deposition rate is 0.796% for 160 μm particles. Wind angle has different effects on the deposition on different rows of photovoltaic panels. When the wind Angle is 0°, the deposition amount of the first row of photovoltaic panels is the largest, the deposition amount is 4.66g, and the deposition rate is 0.932%. When the wind angle is 45°, the deposition amount on the second and third rows of photovoltaic panels is the largest, the deposition amount is 3.21g, and the deposition rate is 0.642%. Finally, the changes in the maximum output power of photovoltaic panels after 60 days of exposure were predicted using an improved dust particle occlusion model.

Flame spread over cables in a utility tunnel: Effect of longitudinal wind and inclination angle

Tables in utility tunnels pose a major fire hazard. This work aims to provide a comprehensive understanding of the effects of cable inclination angle and longitudinal wind (U∞) on the flame spread behaviors of cables in a utility tunnel. Flame inclination angle (β) increases with the increase of cable inclination angle and longitudinal wind speed, while the amplification decreases as the longitudinal wind speed increases. Both flame length (xf) and pyrolysis length (xp) increase linearly with sinθ when U∞ is smaller than 0.65 m/s and they also increase with the increase of longitudinal wind speed. The increasing inclination angle and longitudinal wind speed contribute to the increasing flame spread rates. The flame spread rate accelerates significantly when the longitudinal wind speed and inclination angle are 0.65 m/s and 12° respectively. In addition, a model based on heat transfer analysis was established to predict the flame propagation rate under different cable inclination angles, and the experimental results were in good agreement with the predicted results. The results of the study contribute to cable fire risk assessment, which is beneficial for cable fire prevention and control in utility tunnels.

Magnetization loss of CORC cables under axial tensile loading

As a highly flexible and fully isotropic cable structure, CORC (Conductor on Round Core) cable wound with high-temperature superconducting (HTS) tapes has promise for giant magnets, including fusion magnets, high-energy accelerator magnets, and nuclear magnetic resonance. CORC cables are subjected to mechanical, thermal, and electromagnetic loadings during preparation and operation. Axial tension is one of the basic deformation modes of CORC cables. To investigate the impact of axial tension loads on the electromagnetic performance of CORC cables, a mechanical-electromagnetic model is created in this study. A comparison of numerical simulations and experiments was first performed for single straight tape and single-layer CORC cables to verify the model's reliability, with particular attention to the critical current reduction and the variation of magnetization loss during axial tension. The model developed in this paper may evaluate electromagnetic performance under applied AC magnetic fields with small amplitudes and mechanical response to axial tension loads. On this basis, the strain distribution of CORC cables under axial tension and their magnetization loss characteristics under various strain states are presented. The effects of different cable design parameters on the critical current and magnetization loss are discussed. The results show that the strain affects the magnetization loss of CORC cable significantly, especially for ones with larger winding angles. The magnetization loss can be reduced by choosing a narrower tape, a smaller winding angle, or a cable core material with a higher Poisson ratio. This study can provide a theoretical basis for the structure optimization design and practical application of CORC cables.

Direct Torque Control With Phase Commutation Optimization for Single-Winding Bearingless Switched Reluctance Motor

Compared with the traditional control method, the direct torque control and direct force control method significantly reduces the torque ripple and the root-mean-square current of the phase winding in the single-winding bearingless switched reluctance motor. However, due to the unreasonable selection of voltage vectors and full cycle control, this method has some problems, such as too many control objects, excessive switching times, and low torque–ampere ratio. This article proposes an improved method for the abovementioned problems. First, the turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> angle and conduction region of each phase winding are chosen as the control targets, and the operation principle is introduced accordingly. Second, according to the difference of the torque generated by the neighboring phases, the output torque can be distributed more properly to obtain the higher torque–ampere ratio in the commutation region. Finally, the sectors divided in the electrical space are reorganized and the corresponding voltage vectors are optimized. Experimental results show that the proposed method can secure lower torque ripples, fewer switching times, and copper loss. In addition, the torque–ampere ratio is improved as well.

Effect of resilient architecture in an ancient windmill in the Sistan region on natural ventilation enhancement

Over centuries different elements have been developed in architectures for ensuring adequate natural ventilation in residential units. This study assesses the different components of an ancient windmill in Sistan, Iran, on the structure's indoor air quality (IAQ) enhancement. Several climatic scenarios have been defined by the wind analysis of Sistan meteorological data and analyzed by CFD. The site measurements confirm the accuracy of the simulation results. In the windmill, two deflectors facing the prevailing wind are the significant elements which, in addition to directing wind toward the entrance, could form vortices near the east and west openings leading to suction ventilation. Alteration of the wind speed and angle from 10 to 15 m/s and 30° to 17° would increase the air change per hour (ACH) by 150% and 110%, respectively. Meanwhile, the ACHs were higher than the ASHRAE desired level (ACH > 0.35).

Effects of extreme low temperatures on the impact behavior of boron nitride nanofillers added carbon fiber/epoxy composite tubes

This study aims to investigate the low-velocity impact response of boron nitride nanoparticles (BNNPs) added carbon fiber reinforced pipes (CFRPs) at various temperature values. Carbon fiber/epoxy composite specimens with (±55°)3 winding angles were manufactured with the filament winding method. Low-velocity impact tests were performed with a 15 J energy level at five different temperatures between −196°C and 23°C ranges to understand the cryogenic environment effect on BNNP added carbon fiber reinforced tubes and neat carbon fiber reinforced tubes. The force-displacement and contact force-time graphs were attained in consequence of low-velocity impact tests. The damage areas, their size and characteristics were scrutinized both visually and with the aid of a Microscope. The test results showed that when ambiance temperatures decreased, the damage areas considerably increased both filled with BNNP and without BNNP filament wound carbon fiber reinforced tubes.

Numerical Method to Generate and Evaluate Environmental Wind Over Hills: Comparison of Pedestrian Winds Over Hills and Plains

It is well known that the wind profile at altitudes below 10m from mean sea level (MSL) depends on the geometry of terrain, due to the boundary layer phenomenon. Hence, the profile of wind changes for hilly terrains and mountainous regions when compared with the plain regions. This phenomenon has become important to study due to the large-scale urbanisation taking place over hilly regions. The changing wind profile presents a challenge to evaluate the pedestrian winds, as depending on the aspect of the terrain an additional vertical velocity component is experienced due to the upwind climb of the winds. This creates a wind profile that is twisted in form. While wind tunnel studies have attempted to recreate this twisted wind profile (TWP), due to the inherent deficiency of wind tunnels to simultaneously map velocity and flow conditions, a lack of three-dimensional flow profile hinders pedestrian comfort evaluation. In the wind tunnel studies, it was also observed that small vertical eddies and wakes behind the interfering building were not identified which are an important factor to determine the pollution load dispersion. The authors have developed a numerical model to generate the twisted wind profile. The specialty of the numerical model lies in it’s unique boundary conditions that enable the visualization and quantification of the complete 3D wind profile, when the wind over a hilly terrain interacts with urban infrastructures. The developed model was validated with the wind tunnel experiments done previously by Tse and colleagues. The specialty of the model is that it ensures horizontal homogeneity while creating vertical heterogeneity. From the 3D flow profile hence generated the authors were able to deduce that the impact of twisted wind profile depends on the yaw angle of wind interacting with the structure and not on the wind attack angle. Also, the more the twist of the wind, more is the clockwise shifting of the far wakes behind the building. It was also seen that there are more low velocity zones in the pedestrian winds over a hill in comparison to that over the plains. The vertical eddies that aid in convective removal of pollutants were also missing in case of pedestrian winds over hilly terrains, which raises the risk of pollutant accumulation. The same was also observed in Hong-Kong during COVID 19, where due to the twisted nature of wind flow, the virus load increased and natural ventilation was inadequate in the removal of the viral load in the air near urban areas.

Filament winding pattern design for diameter-varying tube

The traditionally diameter-varying tube is a combination part of cylinder and cone with unsmooth transition region, which is usually a weak link. Using spline technique, we present a smooth diameter-varying tube consisting of cylinder and revolution surface with interpolation spline as meridian, and study the stability of three categories of typical curves used for filament winding, geodesics, semi-geodesics, and constant winding angle curve. A sufficient condition that makes fiber path non-bridging is introduced by analyzing normal curvature, and furthermore there is a sufficient and necessary condition of non-bridging geodesics. For constant angle winding, an efficient algorithm for determining whether constant winding angle curve is stable or not is presented by investigating its slippage coefficient , and a novel winding pattern design metthod is proposed for filament winding diameter-varying tube. These methods have been applied to our computer aided filament winding software. The experimental and simulation results show that our method can design winding pattern of uniformly covering the mandrel, and efficiently shortens the design time.

Optimization of Roasted Green Tea Winnowing via Fluid–Solid Interaction Experiments and Simulations

In the tea industry, achieving a high winnowing accuracy to produce high-quality tea is a complex challenge. The complex shape of the tea leaves and the uncertainty of the flow field lead to the difficulty in determining the wind selection parameters. The purpose of this paper was to determine the accurate wind selection parameters of tea through simulation and improve the precision of tea wind selection. This study used three-dimensional modeling to establish a high-precision simulation of dry tea sorting. The simulation environment of the tea material, flow field, and wind field wall were defined using a fluid–solid interaction method. The validity of the simulation was verified via experiments. The actual test found that the velocity and trajectory of tea particles in the actual and simulated environments were consistent. The numerical simulations identified wind speed, wind speed distribution, and wind direction as the main factors affecting the winnowing efficacy. The weight-to-area ratio was used to define the characteristics of different types of tea materials. The indices of discrete degree, drift limiting velocity, stratification height, and drag force were employed to evaluate the winnowing results. The separation of tea leaves and stems is best in the range of the wind angle of 5–25 degrees under the same wind speed. Orthogonal and single-factor experiments were conducted to analyze the influence of wind speed, wind speed distribution, and wind direction on wind sorting. The results of these experiments identified the optimal wind-sorting parameters: a wind speed of 12 m s−1, wind speed distribution of 45%, and wind direction angle of 10°. The larger the difference between the weight-to-area ratios of the tea leaves and stems, the more optimized the wind sorting. The proposed model provides a theoretical basis for the design of wind-based tea-sorting structures.

Inner blast response of fiber reinforced aluminum tubes

In this work, the dynamic failure of Fiber Reinforced Metal Tubes (FRMTs) under inner blast load was experimentally investigated. The FRMTs was prepared by winding the basalt fiber or H-glass fiber onto the aluminum lining through filament winding process. The influence of explosive mass, winding angle and number of layers on the failure modes of FRMTs were obtained and discussed. The results showed that the fiber reinforced metal tubes performed better anti-blast performance compared to metallic tubes, in terms of deformation amount and failure severity. The FRMTs with winding angle of ±55° provided the best anti-explosion performance under inner blast as a result of the balance between circumferential and axis stresses, and the blast resistance can further be enhanced by optimizing the circumferential strength of inner layers through changing the inner winding angle. With higher strength and flexibility, the H-glass fiber reinforced metal tube had less penetration cracks, small expansion ratio and axial deformation width compared with basalt fiber reinforced metal tubes. It is believed that the current study can be a good reference for the design of fiber reinforced metal tubes or vessels.

Flexural behaviour of hollow reinforced concrete-filled fibreglass tubular beams

An experimental and numerical study of hollow reinforced concrete-filled glass-fibre-reinforced polymer tubular beams was carried out. Based on bending tests, the working mechanism and failure modes were studied. A finite-element model was established and the validity was assessed by comparing the experimental and numerical results. The main parameters included the wall thickness of the fibreglass tube, reinforcement ratio, hollow ratio, concrete strength and fibre winding angle. The results indicated that the composite beams failed gradually with considerable ductility. The bending capacity increased by about 12% with every 1 mm increment of the fibreglass tube thickness, increased by about 40% as the reinforcement ratio increased from 2.28% to 4.56%, and increased by about 6% with every 5 MPa increment of the concrete strength. The bending capacity decreased and then increased as the fibre winding angles ranged from 10° to 90°, and a small fibre winding angle was preferable for the flexural member. A hollow ratio of 0.375 is proved to be applicable to obtain lighter member self-weight with minimal decrease in strength.

CFD Numerical Simulation of Wind Field and Vehicle Aerodynamic Characteristics on Truss Bridge Deck under Crosswind

Due to the complexity and changeability of the wind field in deep-cut gorges, the vehicles on the bridge deck are easily affected by a strong crosswind. Thus, to accurately evaluate the wind field characteristics of a suspension bridge deck, the wind profiles of wind speed and angle of attack (AoA) and the vehicle aerodynamic parameters were investigated by the CFD. The results show that the shape of wind speed profile is mainly controlled by the AoA but less affected by the Reynolds number. The main girder's shielding effect can accelerate the local wind field, and the closer to the windward lane, the less the interference; thus, a suitable location of measuring points to represent the incoming flow is found. Furthermore, the equivalent wind speed based on the equivalent side force is generally larger than the value based on the rolling moment, and the responding value is greatly affected by the AoA. In addition, the vortex is a time-dependent phenomenon, the averaged flow field produced less force in the wake, but the high local wind speed variations may affect the traffic unfavorably. The results provide an essential reference significance for studying the local wind field characteristics of the bridge deck.