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This paper presents a vortex‐induced vibration (VIV)‐based piezoelectric energy harvester that performs well for all wind directions, a so‐called omnidirectional wind energy harvester. The kinetic energy of this harvester stems from wind‐induced vibrations of a circular cylinder mounted on an orthogonal bibeam system, rather than a traditional single beam. Wind tunnel testing results show that compared to the traditional single‐beam energy harvester, the proposed harvester substantially enhances the effectiveness, in most cases that the beam is skew to the incoming flow. The reasons for the enhancement are explained in detail by examining the wind‐induced displacement response components of the cylinder identified by the image processing technique. For all wind directions, both the maximal output energy and the range of effectively working wind speed of the proposed bibeam wind energy harvester are significantly improved with respect to the single‐beam system, indicating excellent performance of the proposed omnidirectional harvester in a natural wind environment.

Sopite syndrome, centered around the drowsiness, lethargy, and irritability associated with motion sickness, can be induced by exposure to low-frequency motion. It is known that the vestibular apparatus plays an important role in the pathogenesis of motion sickness, which features several autonomic responses, and we have previously documented increased vestibular modulation of skin sympathetic nerve activity (SSNA) and an increase in skin blood flow associated with nausea. Here, we assessed whether imperceptibly slow sinusoidal motion, sufficient to induce sopite syndrome but not nausea, also modulates SSNA and skin blood flow. Participants were seated upright and exposed to a randomized set of sinusoidal linear accelerations, ranging from 0.03 Hz at 0.5 mG to 0.2 Hz at 5 mG, via a motorized platform. At all frequencies vestibular modulation was greater than the cardiac modulation of SSNA, but cardiac modulation and skin blood flow were both significantly lower during the motion than at baseline. We conclude that sopite syndrome is associated with a marked modulation of sympathetic outflow to the skin and cutaneous vasoconstriction.NEW & NOTEWORTHY Little is known about the autonomic consequences of sopite syndrome-the drowsiness that can be induced by low-amplitude cyclic motion. We recorded skin sympathetic nerve activity (SSNA) in seated participants exposed to slow sinusoidal linear acceleration (0.03-0.2 Hz), which preferentially activates hair cells in the utricular part of the otolithic organs, at amplitudes that generated no sensations of motion. At all frequencies, there was a clear vestibular modulation of SSNA and cutaneous vasoconstriction.

This paper proposes a computational fluid dynamics (CFD) model, along with dimensionless quantitative assessment standard—air pollution residual time (APRT) for the evaluation of local haze-fog (HF) dispersion in a built environment. A low APRT value ensures good ventilation. A building group model that comprises high-rise business building, mid-rise office buildings, low-mid-rise residential buildings (at the center of the building group), a mid-rise recreational center, and a local road (open terrain), was scaled down (1:100) to simulate the HF dispersion process. The orientation of the building group was numerically modified to generate a wind incidence normal to the high-rise building, mid-rise buildings, recreational center, and road. The results showed that the orientation of the building group largely determines the APRT. The most favorable orientation can reduce APRT by more than 50%. Our results strongly suggested that in order to reduce the consequential negative effect of air pollution, future urban designs should undergo a comprehensive ventilation assessment to ensure a low APRT value.

Gas cyclones are widely used to purify waste gases but are not effective in collecting fine particles. The cloud-air-purifying (CAP) technology was recently developed to overcome this deficiency by unitizing the supersaturated vapor in the cyclone. This paper presents a CFD study on the CAP cyclone. The condensational growth of particles is implemented in the CFD model. Its positive effect on the collection efficiency is confirmed and more clearly understood from microscopic investigations. Particles with the same initial size can grow into a narrow size distribution, yet the average growth ratio is increased with the increase of the supersaturation ratio and the decrease of the initial size, resulting in a significant improvement of the collection efficiency for fine particles, particularly in controlling those escaping through the middle-reverse flow. A predictive model is developed to consider the effect of the vapor. These results can help understand and optimize the CAP cyclone.

Cladding damage of tall buildings often occurs during hurricane events, and the damage is not only costly but also impacts the economy, and more importantly, threatens lives. One solution to reduce the cladding pressure is the application of modified double-skin facade (DSF) which is already of great interest to architects due to improving building energy efficiency. This paper investigates the effects on the cladding pressures of a building fitted with a DSF with vertical openings in the external skin mounted in front of the windward face of the building. The effects of the vertical openings on the building's surface pressure were investigated by conducting pressure measurements in the wind tunnel. The associated flow mechanisms were revealed by using particle image velocimetry technique. The DSF without opening increases both the mean suctions and fluctuating pressures on both side and leeward faces, and hence this common facade configuration leads to an undesirable effect on building claddings under strong winds. In contrast, the DSF with the opening(s) can effectively reduce wind pressures on the side and leeward faces. Therefore, creating vertical openings on the external skin of DSF is a practical approach to enhance the wind-resistance performance of building claddings.

Understanding the aerodynamics associated with the interaction of fire and cross-wind flow is of great importance because the consequence may have major implications in building design against bushfire (or wildland fire) attacks. However, a fundamental understanding of how the interaction of fire and wind can alter free stream flow aerodynamic properties has remained elusive. The scope of this study is to examine the pool fire and wind interaction under fixed wind velocity condition. This study dissects the fundamental mechanisms of how the interaction of horizontal momentum flow with a vertical buoyant plume leads to enhancement of wind velocity in the horizontal direction at a certain elevation. Changes in flow aerodynamics caused by the interaction of fire and wind were analysed using the computational fluid dynamics approach. The mechanisms causing the changes were explained. A module was developed and added to the FireFOAM solver to evaluate flow acceleration due to the pressure gradient, gravity, and viscous effects. The chosen computational model was validated against two sets of experimental data, namely, a buoyant diffusion fire plume in still air and the other in cross-wind condition. The numerical simulation revealed that due to the interaction of fire and wind, there is a negative longitudinal pressure gradient across the plume axis, causing the flow to accelerate and the velocity profile to alter. It was also shown that the distortion in velocity profile depends on the location downstream of the fire plume. The height of the distortion increases whilst the magnitude of the distortion diminishes as the longitudinal distance from the fire source increases. Investigation of the effects of heat release rate on wind enhancement further showed that fire with a higher heat release rate causes a greater pressure gradient and a lower density, culminating in higher flow acceleration and consequently increase of wind enhancement.

[Abstract] The wind flow around twin-box decks is particularly complex due to the very important role played by the slot distance between girders and the presence of the downwind box that is immersed in the wake of the upwind box. Detailed experimental studies on the three-dimensional flow features of this deck typology are certainly challenging, and CFD simulations have not tackled this problem so far. The goal of this 3D LES piece of research is to shed some light on the complex flow features around twin-box decks, particularly when the deck geometry is fully three-dimensional due to the presence of the transversal beams linking together the deck girders. Integral parameters, mean and instantaneous flow structures and spanwise correlations are studied for a segment of the Stonecutters Bridge. It has been found that the presence of the transversal beam plays a key role in the flow correlation loss, identifying, for instance, the out-of-phase shedding of vortices at different sides of the transversal beam. The numerical results agree well with experimental data in the literature, and offer a richer and more comprehensive explanation for the identified aerodynamic responses. This research has been funded by the Spanish Ministry of Economy and Competitiveness in the frame of the research project with reference BIA2016-76656-R and the Galician regional government with reference ED431C 2017/72. The first of the authors has been funded by the Spanish Ministry of Economy and Competitiveness in the frame of the National Program for Promotion of Talent and Employability through the BES-2014-068418 predoctoral contract grant, associated with the BIA2013-41965-P research project Xunta de Galicia; ED431C2017/72

This study investigated mean flow characteristics and structure of flow inside through-building openings with five different layout configurations for the purpose of wind energy harvesting. Two-dimensional Particle Image Velocimetry (PIV) was employed and validated against a series of Cobra probe measurements. The mean flow characteristics including streamwise and vertical mean velocity were investigated at the wind direction parallel to the corridors of the through-building openings. The coherent structure of flow was studied, using two-point cross-correlation and a simple flow visualisation. The results showed that creating recessed regions at inlet and outlet of the openings and using curved walls at corners increase the mean velocity at the middle of the corridor by approximately 25%. When using converging-diverging passages for openings, the mean velocity increases by approximately 33%. The two configurations exhibit better performance in attuning the flow to be more inform and steady in a larger portion of the corridor, and hence these configurations have the capacity to enhance the performance of a potential wind turbine inside the corridor. The confined area of corridors contributes to the progressive reduction of undesirable characteristics of the cavity flow including vertical mean velocity, and streamwise and vertical velocity fluctuations along the corridor.

The performance of a circular cylinder-based piezoelectric wind energy harvester with two small-size rod-shaped attachments on the main circular cylinder was experimentally investigated. The rod had three different cross-sectional shapes: circular, triangular, and square. The two rods were attached on two sides of the main circular cylinder at a series of circumferential locations. They were parallel to the cylinder axis and symmetrical to the stagnation line. It was found that attaching these three rod types at the circumferential locations of 45° and 60°, harvested power continuously beyond the critical wind speed. It was, therefore, dramatically superior over both the plain circular cylinder and the cases with other attachment locations. Additionally, the output voltage for a circumferential location of 60° was greater than that 45° one over the whole working wind speed range. Furthermore, attaching the triangular rods on the main circular cylinder showed a better performance than the other two rod types. The force measurement results indicated that the circular cylinder with triangular rods at the circumferential location of 60° had larger transverse force coefficients than the other two rod type cases, verifying the findings in the energy harvesting tests. Therefore, it is recommended to attach two triangular rods at the circumferential location of 60° on the main circular cylinder in order to enhance the performance of a circular cylinder-based wind energy harvester.

The increasing global concern about climate change and energy crisis has necessitated the development of techniques to reach and exploit renewable energy in unexplored regions. As such, decentralized small-scale wind energy harvesting in urban environments has gained momentum in recent years. In this study, a methodology has been developed to assess the performance of a special Double Skin Facade (DSF) system for wind energy generation using CFD simulations and local wind data. As a case study, a story-high corridor-type DSF system equipped with an array of wind turbines was integrated into a high-rise building, and its Annual Energy Production (AEP) within the context of four Australian cities was evaluated. The results showed that the free-stream wind speed can be amplified up to a maximum of 1.8 times inside the corridors of the DSF system. It was concluded that the benefit of the DSF system can be exploited the most in cities with strong bi-directional wind characteristics. Finally, it was shown that wind turbines inside the DSF system can annually generate up to 50% more energy at open terrain and 22%–45% more energy at dense urban and suburban terrains as compared with the same turbines in the free-stream condition.

To maximise the potential of decentralized micro-grid wind energy generation in urban environments, it is vital to develop techniques to enhance the flow characteristics in urban environments. This paper reports on an investigation of a new method of exploiting wind energy by utilizing a modified innovative Double Skin Facade (DSF) system. Computational Fluid Dynamics (CFD) simulation has been employed to investigate the effect of aerodynamic modifications, including recessed regions and curved walls, on the flow characteristics inside an empty corridor-type DSF for different wind directions. CFD results were validated against a series of wind tunnel tests. The results indicate that, compared with the original DSF, the modifications are capable of significantly enhancing the flow velocity inside the DSF at all wind directions, especially when the direction of the upstream wind aligns with the flow direction inside the DSF. The results also show the contribution of the confined area in diminishing the variations in velocity and reducing turbulence by a maximum of about 30%. It is concluded that the average available wind power density of an empty corridor-type DSF can be increased by a factor of 2 and 4.2, respectively, by creating recessed regions and curved walls.

In conventional modeling of air pollution dispersion, pollutants are treated as passive scalars or inert species even though most of them are chemically reactive [1]. Chemical reactions contribute to pollutant dispersion via the generation and depletion of pollutants, in addition to other two mechanisms: advection and turbulent diffusion. This study investigated how chemical reactions affect near-field pollution dispersion by integrating the simple NOx-O3 chemistry into RANS-based computational fluid dynamics (CFD) simulation. CFD simulation was used to model a mixed emission of NO and NO2 from a short stack attached to a building into ambient O3, prompting chemical reactions between the NO, NO2, and O3. Various degrees of chemical reactivity were modeled by varying the Damkholer number (Da) between 0.073 and 4.363. The results showed significant chemical reactivity for cases where Da [NO] > 1, while cases with Da [NO]

This paper presents an approach to predict crosswind force spectra and associated response of tall buildings with rectangular cross-section based on machine learning (ML) technique and random vibration-based response analysis. An efficient ML algorithm, light gradient boosting machine (LGBM), was trained to predict crosswind force spectra of the tall buildings by using the database from the Wind Engineering Research Center at the Tamkang University embedded in the aerodynamic database of NatHaz Modelling Laboratory. Furthermore, an unsupervised ML algorithm, K-means clustering, was employed to advance the understanding of the crosswind force spectrum characteristics of the tall buildings. The effects of three factors, i.e., ground roughness, aspect ratio and side ratio, on the force spectra were discussed based on clustering. To predict the crosswind response of tall buildings, case studies were carried out to validate the predictive accuracy of the LGBM model combined with random vibration-based response analysis. The results demonstrate that the proposed method combined with the multiple database-enabled design module for high-rise buildings developed by the NatHaz Modelling Laboratory at the University of Notre Dame is effective and computationally efficient to provide fast and accurate predictions of the crosswind force spectrum and associated crosswind responses of rectangular tall buildings.

The influences of building layouts on pollutant dispersion within urban street canyons have been widely studied, although they have been rarely considered with envelope features. Different envelope features, such as wing walls, balconies and overhangs, have not yet been quantitatively assessed for their effects on the wind flow patterns around street canyons to a certain degree. Adopting the evaluation indicators of personal intake fraction and daily pollutant exposure, this study aims to investigate the potential influences of building layouts and envelope features that affect pollutant exposure risks for pedestrians and near-road residents via computational fluid dynamics (CFD). The turbulence modelling approach and numerical methods are validated by reported experiments in the literature. Asymmetric street canyons with an aspect ratio of 2 and two typical building layouts, namely, step-up and step-down notch configurations, are further investigated to test their effects. The results indicate that the step-down configuration provides worse situations for wind environments and pollutant dispersion than symmetric and step-up configurations. More specifically, the presence of overhangs has the greatest impact on the personal intake fraction (P_IF) change ratio, followed by balconies. The largest P_IF change ratio occurs on the fifth floor of an upstream building when overhangs are applied to the step-down street canyon. The aforementioned findings are helpful to understand the influences of building layouts together with envelope features on the wind environment as well as pollutant exposure risks experienced by pedestrians and near-road residents.

This paper presents a CFD study on the air ventilation assessment (AVA) in urban topology with twisted wind profiles (TWP). At present, most AVAs were conducted through wind tunnel experiments, and conventional wind profile (CWP) with no deviation of wind direction along the heights was employed. However, in practice, the hilly terrain around cities such as Hong Kong results in twisted wind flow that wind directions vary along the heights. This paper presents an LES-based CFD model based on the best practice guidelines (BPGs). Two twisted wind profiles (TWP) were introduced, and six simulation cases were performed. The CFD predicted wind speeds were validated against wind tunnel measurements in the literature, and good agreement was achieved. With the aid of the CFD model, wind conditions over heights were investigated, and the effects of twisted wind were evaluated. The results indicated a significant influence of TWPs on the AVA’s outcomes and the wind speeds’ vertical distribution. In addition, with the CFD results, it is possible to investigate the wind-structure interactions in specific urban areas and provide a better understanding of the effects of buildings on the local wind conditions, which could be useful to the urban plan for sustainable cities.

To date the engineering community has seen double-skin facade systems as non-structural elements on buildings for the aesthetic desire, improving the indoor environment, reducing the energy use, and even improving acoustics in buildings. In this study, the effects of a double-skin facade system on the wind-induced responses of a tall building were investigated via a program of wind tunnel tests. Two types of wind tunnel tests, i.e. aeroelastic test and pressure test, were performed. It was found that a double-skin facade with/without vertical openings installed in front of the windward face of the building model results in very different effects on the wind-induced responses in alongwind and crosswind directions. In the alongwind direction, the facade with/without openings induces negligible effects on the wind-induced response. However, in the crosswind direction, the facade with opening(s) reduces the wind-induced response significantly, whereas the facade without any opening increases the response, compared to the bare tall building model. Therefore, in addition to achieve the purposes of the aesthetic desire, improving indoor environment and reducing energy use, the double-skin facade system with vertical opening(s) can also be used to effectively reduce crosswind responses without inducing larger alongwind responses.

Owing to the void space at lower heights, lift-up buildings have high building permeability at ground level and subsequently improve the air circulation in congested urban areas. Despite this advantage, the lift-up design has been sparsely adopted for buildings in urban areas partly because of the lack of understanding of the combined effects of building dimensions and lift-up design on the surrounding pedestrian level wind (PLW) field. Therefore, this study aims to investigate the influence of lift-up buildings with different aspect ratios (height/width) on the surrounding PLW field and pedestrian wind comfort level. Five lift-up buildings with aspect ratios 4:1 to 0.5:1 were tested in a boundary layer wind tunnel and results were compared with those of five buildings with similar dimensions but without lift-up design. The results reveal a strong dependence of the maximum wind speed in lift-up areas with building height, which results subsequently a small area of acceptable wind conditions near tall and slender lift-up buildings. Lift-up designs adopted for short and wide buildings produce larger areas of pedestrian wind comfort. The central cores modified with corner modifications are effective in increasing the pedestrian wind comfort in the lift-up area of tall and slender buildings., Highlights • Tall and slender buildings generate high-speed wind flows in lift-up areas. • Modified corners of lift-up cores improve the pedestrian wind comfort. • Lift-up cores with modified corners are recommended for tall and slender buildings.

Efficient wind energy harvesting by utilizing small-scale wind turbines in the urban environment requires techniques to enhance the desirable flow characteristics, including velocity magnitude and uniformity, and diminish the unfavorable characteristics, including high turbulence and intermittence. This study proposed a Double-Skin Facade (DSF) system with strategic openings to harvest wind energy in the built environment. A series of wind tunnel tests and CFD simulations have been conducted to investigate the characteristics and related mechanisms of flow within the cavity of DSF integrated with a tall building model at different incident wind angles. The discrepancy between numerical and experimental results generally remains within an acceptable range of 15% which validates the capability and accuracy of the developed CFD simulations in predicting the flow characteristics. It was found that the flow becomes more uniform while the turbulence progressively decays as flow progresses through the cavity for all wind directions. Hence the regions in the middle of both the leading and trailing sides of the cavity are favorable locations for installing small-scale, building-mounted wind turbines. Overall, the DSF system with a strategic opening can effectively enhance the flow within the cavity for a wide range of incident wind angles and can be adapted for wind energy harvesting purposes.

The hilly terrain in Hong Kong detour winds and generate twisted wind profiles, which have varying wind directions along the profile's height. Twisted winds considerably influence the wind environments in built-up areas. Particularly the wind conditions around building arrays have paramount importance in Hong Kong as most of the building arrays are closely-spaced tall residential towers with some recreational areas located at buildings’ lower levels. This paper aims at the systematic investigation of the surrounding wind conditions of building arrays in twisted wind flows by a series of wind tunnel tests. There were 9 building models with different heights and passage widths tested in two twisted wind profiles at a number of wind incidence angles. Each model had three identical buildings and two similar passages among buildings. The observed wind environments in twisted wind flows were asymmetric near building arrays and wind speeds were dissimilar in the two passages. Compared to the building height, the passage width has more significant influences on wind conditions in passages in twisted wind flows. The effective wind direction, which is the vector summation of wind twist and wind incidence angle, is important in understanding the influence of approaching wind directions of twisted wind flows.

The objective of the study is to develop a new construction material as an alternative for expensive dampers. A Tuned Liquid Damper (TLD) system that is cast in a concrete masonry unit has been proposed. The block has been examined in its individual characteristics to consider the resonant effect of the building subjected to a wide range of water depth, dw, from 5 mm to 80 mm. The TLD block was designed to internal dimensions of 190 mm (length) × 60 mm (width) × 90 mm (height) in accordance to the Uniform Building Code (UBC) and Eurocode 8. Sine-sweep responses results were plotted in transmissibility ratio, ut/ug to frequency ratio, ω/ωn. The block at a depth of dw was simulated and empirically calculated. Tests for dw of 50 mm, 60 mm, and 70 mm have verified the fundamental frequency, fn, to be similar with the simulated and calculated eigenvalues. Further study of the combined structural model and TLD blocks test as a system has been compared with the numerical simulations. The results varied by approximately 2%. The system has recorded reduction of responses immediately at the test of dw, 5–80 mm. Optimum performance has been recorded at 60 mm. The test results employed half-power bandwidth to obtain the damping ratio. The damping has been contributed by both viscous damping component and inertia of the moving water body. The Rayleigh stiffness damping component has not been identified to participate in the forced excitation performance reduction. It was found that the new innovative block with tuned liquid can significantly increase the damping characteristics. Hence, the research is necessary to propose an alternative new construction material to withstand earthquake and wind disasters on buildings.

This paper identifies seven areas where an increase in our fundamental understanding of the human response to building motion will facilitate the design of next-generation serviceability criteria for wind-induced building motion. These advances in knowledge address: (1) understanding the effects of wind-induced building motion on occupants, (2) metrics for building performance assessment, (3) understanding of habituation to building motion, (4) potential and real benefits of education, (5) motion characteristics to predict adverse occupant effects, (6) differentiation between residential and office serviceability criteria, and (7) multidisciplinary research methods and measures used in occupant comfort research. Each is discussed with reference to engineering literature and incorporates a multidisciplinary perspective including psychological and physiological research. Finally, methodological issues in the occupant comfort literature are discussed and recommendations for future research are offered to facilitate the design of next-generation serviceability criteria for wind-induced building motion.

Modern megacities are teeming with closely-spaced tall buildings, which limit air circulation at the pedestrian level. The resultant lack of air circulation creates poorly ventilated areas with accumulated air pollutants and thermal discomfort in the summer. To improve air circulation at the pedestrian level, buildings may be designed to have a ‘lift-up’ shape, in which the main structure is supported by a central core, columns or shear walls. However, a lack of knowledge on the influence of the ‘lift-up’ design on the surrounding wind environment limits the use of ‘lift-up’ buildings. This study aims to investigate the influence of ‘lift-up’ buildings and their dimensions on the pedestrian-level wind environments using wind tunnel tests. A parametric study was undertaken by using 9 ‘lift-up’ building models with different core heights and widths. The results were compared with the surrounding wind environment of a control building with similar dimensions. The results reveal that the ‘lift-up’ core height is the most influential parameter and governs the area and magnitude of high and low wind speed zones around such buildings. Based on wind tunnel test results and a selected comfort criterion, appropriate core dimensions could be selected to have acceptable wind conditions near lift-up buildings., Highlights • The effects of ‘lift-up’ buildings and their dimensions on the surrounding wind environments are studied. • The ‘lift-up’ core height is the most important parameter of a ‘lift-up’ design. • Appropriate lift-up dimensions are selected by combining wind speed data with a predetermined wind comfort criterion.

The pedestrian level wind environment is seriously deteriorated by moderated local wind flow in a densely built-up subtropical city like Hong Kong. In order to improve the weak wind condition, the lift-up design has been used for some time. However, there is a lack of understanding and quantitative assessment of its modification on the pedestrian level wind comfort around different building configurations under different wind directions. This paper aims to study the effects of lift-up design in four common building configurations on the wind comfort via computational fluid dynamics (CFD) simulations. The turbulence model and numerical method are firstly validated by comparing the simulated wind flow data with the wind tunnel test results. The validated model is then utilized to simulate the four building configurations, including the “─”, “L”, “U” and “□” shaped buildings. The mean wind velocity ratio ( MVR ) and mean wind velocity change ratio ( Δ MVR ) are employed to identify the wind comfort and to quantitatively evaluate the improvements due to the lift-up design. Results show that the lift-up design can improve the wind comfort in building surroundings and its influence is highly dependent on the incident wind direction. Specifically, the wind comfort is better under the oblique wind direction than the other two wind directions. These findings can provide us a better understanding of the lift-up design and will be helpful in better precinct planning.

The influence of twisted wind flows on pedestrian-level wind environments was evaluated by using two twisted wind profiles (TWP) in a boundary layer wind tunnel. Simulated wind profiles had maximum yaw angles of 13° and 22° to represent ‘high’ and ‘extreme’ wind twist conditions, respectively. Five buildings with the aspect ratio (Height: Width) of 4:1 to 0.5:1 were tested for a number of wind incidence angles to assess the influences of building dimensions and approaching wind directions. All test cases were repeated in a conventional wind profile (CWP) with similar mean wind speeds and turbulence intensities for the purpose of comparison. The results reveal that pedestrian-level wind environments in TWPs are different than in CWPs owe to asymmetric wind fields, displaced flow features, and variations in areas of high and low wind speeds. The increased areas of low wind speeds and displaced downstream far-field low wind speed (DFLWS) zone are the two important flow modifications that would have negative impacts on outdoor thermal comfort and air pollutant dispersion in built-up areas where TWPs exist. Due to the embedded wind twist angles, wind incidence angles have different effects on flow modifications in twisted wind profiles than in conventional wind profiles.

Fire-wind enhancement is a phenomenon associated with the increase of free-stream wind velocity due to the interaction of fire and free stream flow. The potential adverse effects of enhanced wind on the pressure loads around buildings highlight the necessity of investigating the phenomenon. The interaction of wind and fire has long been a subject of interest however, investigation of the factors affecting the phenomenon has not received due attention. One of the factors that affect this phenomenon is terrain slope. This paper used a Computational Fluid Dynamic solver called FireFoam to evaluate the effect of terrain slope on fire-wind enhancement. The results revealed that the enhancement of wind velocity due to fire increases with an increase in terrain slope. This is because fire-wind interaction leads to the generation of a favourable longitudinal pressure gradient whose magnitude increases with the increase of terrain slope.

Wind enhancement triggered by fire-wind interaction can potentially pose significant damage to structures built in bushfire prone areas. The effect of terrain slope is one of the parameters contributing to the enhancement of wind by fire that needs to be taken into account. This study employs a validated model of Computational Fluid Dynamics to assess the effects of terrain slope on this phenomenon. A module was developed and appended to the FireFOAM solver to output individual component of flow acceleration. Multiple analyses were used to explain the effects of terrain upslope and downslope on the phenomenon. The results reveal that although the enhancement of wind velocity due to fire increases with an increase in terrain upslope, a terrain downslope reduces flow enhancement by fire. The results also established that while an upslope terrain reinforces the Coanda effects and intensifies attachment of the plume to the ground, the downslope condition mitigates Coanda effects and reduces the flow's tendency to attach to the ground downstream of the fire source. Furthermore, under a constant heat release rate and upstream wind velocity, the maximum magnitude of wind enhancement linearly increases with the increase of upslope angle. Keywords: Upslope, Downslope, Wind enhancement, Fire, CFD, Coanda effects

Highlights • CFD model validated for predicting pollutant dispersion around a HRR building. • Effects of distance and position angle of emission source studied. • Critical range of position angle of low risk found for pollutant source. • Pollutant concentration on building as a function of source location modelled. • Overall view of risk of pollutant emission from regions nearby building obtained., This article investigates the dispersion of airborne pollutants emitted from different locations near a high-rise building. A Computational Fluid Dynamics (CFD) model for simulating the wind flow field and the pollutant dispersion was developed and validated by wind tunnel data. Then the spreading of the pollutant emitted from different locations to a rectangular-shaped high-rise residential (HRR) building was numerically studied. The pollutant source location was set in a wide range of the position angle and distance between the source and the building. It was found that the pollutant concentration on the building decreases with an increase in the emission distance whereas the effect of the position angle is more complicated. Interestingly, there is a critical range of the position angle from which the emitted pollutants will not spread to the building in a significant way. The effect of the source location was linked to the wind flow field around the building, particularly with several major flows. The vertical distributions of the pollutant concentration on different faces were also investigated, and it was found that these are more affected by the vertical flow near each face. Finally, a mathematical model was developed to evaluate the pollutant concentration as a function of the emission distance and position angle. These findings are helpful to the understanding of the dispersion of airborne pollutants around high-rise buildings and the related hazard management in urban design.

This research investigates the effect of building cross-section shape on the air pollutant dispersion around an isolated building. A Computational Fluid Dynamic (CFD) model was developed and validated based on detailed wind tunnel experimental data. Both Large Eddy Simulation (LES) and Realizable k-e models were used for turbulence closure and LES was found to provide a better agreement with experimental results than the RANS model, particularly in replicating pollutant dispersion characteristics associated with wind-structure interaction. The LES model was then utilized to study the effect of building cross-section shape. Four building cross-section shapes, square, chamfered, curved and circular, along with different air pollutant emission locations were studied. It has been found that the area around an isolated building can be categorized into three emission regions, namely the windward critical emission region, the leeward critical emission region and the side non-critical emission region. The air pollutant emissions from the leeward critical emission region affect the building the most. Furthermore, the size of this region depends on the building cross-section shape, with the circular and curved buildings having a smaller leeward critical emission region than those for the chamfered and square buildings. Evidently, air pollutant dispersion around a building is dominated by wind-structure interaction which in turn is dependent on the building cross-sectional shape. These characteristics can be utilized to mitigate air pollutant dispersion in urban environments in conjunction with careful consideration of the air pollutant emission location relative to a building.

Due to the complexity of crosswind vibrations of rectangular cylinders, current research on crosswind vibrations of rectangular cylinders mainly relies on expensive wind tunnel tests and time-consuming numerical simulation techniques. In this study, in order to evaluate crosswind vibrations of rectangular cylinders, machine learning method was used to build an efficient and effective prediction model for supplementing the above two research tools. 5 machine learning models based on decision tree regression, k-nearest neighbor regression, random forest, gradient boosting regression tree (GBRT) and histogram gradient boosting regression tree algorithms were trained based on the existing high-quality and reliable wind tunnel test datasets of crosswind responses of rectangular cylinders. The hyper-parameters were optimized by using particle swarm optimization method. 4 types of crosswind vibration phenomena, including over-coupled, coupled, semi-coupled and decoupled, were predicted. It was found that the GBRT model is capable of predicting crosswind responses of rectangular cylinders at side ratios from 0.75 to 3 and Scruton numbers from 0 to 150 under wind flow with turbulence intensities from 0 to 16%. Evidently, GBRT model can be an effective and economical method to study crosswind vibrations of rectangular cylinders and hence supplement traditional wind tunnel tests and numerical simulation techniques.

Topography-induced twisted wind flows are frequently observed in Hong Kong due to the abundance existence of mountains. Observed twisted wind profiles are with larger wind twist angles and are confined to the lower 500 m of the atmosphere, thus may impose significant effects on both structures and near-ground wind conditions. In order to investigate the influences of twisted wind flows on the pedestrian-level wind environment, two twisted wind profiles were simulated in a boundary layer wind tunnel by using 1.5 m tall wooden vanes. The maximum guide angles of vanes were 15° and 30° at the ground level to represent two nominal yaw angles of ‘high’ and ‘extreme’ twisted wind flows. Simulated twisted wind profiles followed the power-law profile and have acceptable longitudinal and lateral turbulence power spectra similar to conventional wind flows. The yaw angle profiles were exponentially decayed with the height but had smaller maximum yaw angles than of the guide vanes. The evaluation of wind conditions near an isolated building and a row of buildings in twisted wind flows has displayed substantially modified flow features such as asymmetric wind speed distributions about the building centre line and reduced wind speeds in the passages between buildings., Highlights • The characteristics of twisted wind profiles observed in Hong Kong are analysed. • A novel vane system is developed to simulate twisted wind profiles in a boundary layer wind tunnel. • The flow quality of simulated twisted wind profiles is evaluated. • The influence of twisted wind profiles on the pedestrian-level wind environment near a building and a building array is demonstrated.

The occupant response to wind-induced building motion is complex, governed by human physiology, and moderated by the psychological response to motion and discomfort within a sophisticated engineered environment. This paper aims to consolidate and critique the early research on the occupant response to building motion and to present recent multidisciplinary research that identifies a broader range of responses to, and consequences of, exposure to building motion. Recent field-based research shows that mild motion sickness, known as sopite syndrome, can cause significantly reduced work performance and occupant comfort. This is supported by laboratory-based physiological studies showing low-amplitude acceleration induces physiological changes in humans well below the threshold of motion perception (∼6·5 milli-g) which are consistent with the early onset of nausea. Current design criteria, based on perception thresholds, do not include the wider range of possible effects, particularly sopite syndrome and nausea. As a consequence, building occupants may suffer from a range of effects, including sopite syndrome and reduced work performance, that are not considered in current guidelines.

Tall buildings vibrate in response to strong winds at frequencies below 1 Hz, which can cause motion sickness and sopite syndrome in humans. Sopite syndrome is characterized by sleepiness, low motivation and low mood that can reduce productivity in office workers. This paper uses recent multidisciplinary research to estimate the cost of building motion on organizations in tall buildings, and provides a framework for future research. The potential costs of wind-induced building motion to organizations are highly variable, depending on the local weather climate, but are likely to be significant in the long-term. It is argued that wind-induced building motion is a negative externality, a cost of inadequate design passed to building users. A three-factor approach towards reducing adverse impacts of wind-induced building motion is discussed: (1) further research investigating the characteristics of motion that provoke sopite syndrome, (2) create a new generation of serviceability criteria, and (3) regu...

Previous studies on inter-unit dispersion are limited to isolated buildings. The influence of an upstream interfering building may significantly modify the indoor airflow characteristics of the wind-induced natural ventilated downstream interfered building. Motivated by the findings in previous studies, namely that infectious respiratory aerosols exhausted from a unit can re-enter into another unit in the same building through building envelope openings, this study investigates the inter-unit pollutant dispersion around a multi-story building in two wind directions by employing the computational fluid dynamics (CFD) method. The CFD model employed in this study has been validated against previous experimental data. The results show that the presence of an upstream building greatly changes the path lines around the downstream target building and the pollutant transportation routes around it. The presence of a low upstream building also greatly increases the average air exchange rate (ACH) values and the pollutant re-entry ratios (Rk) below the source unit on the windward side of the downstream target building for normal wind incidence. However, the presence of a high upstream building greatly increases the average ACH values on the windward side and increases the Rk on the leeward side of the downstream building for oblique wind incidence., Highlights • Interunit pollutant dispersion in a naturally ventilated building was investigated. • Effect of an upstream interfering building on the target building was examined. • A high and a low upstream buildings were considered. • An upstream building improves ventilation performance of the target building. • An upstream building enhances Interunit dispersion in the target building.

We perform Computational Fluid Dynamics (CFD) analyses of a low-rise building immersed in a turbulent boundary layer. The Silsoe 6 m cube is chosen as the main case study aiming at representing the key features of the typical wind conditions experienced by low-rise buildings. The turbulent inflow condition is generated by employing a precursor technique. A sensitivity study is conducted to investigate the effects of eight subgrid-scale (SGS) models on the flow around the cube. The incoming turbulence intensity and mesh sizing for each of the SGS models are also explored. The results in terms of time-averaged pressure fields for relatively well-resolved simulations are well compliant with available experimental data and insensitive to the selection of the SGS model. We demonstrate that, while the effect of the aforementioned factors has a limited impact on the first-order statistics of the pressure coefficients, their influence becomes much more pronounced when analysing higher-order statistics (i.e. variance, skewness and kurtosis) and extreme values. The extent of their relative importance depends on the location of the point under investigation and the quantity of interest. The current study provides guidelines on the choice of factors which can strongly affect the results obtained employing CFD simulations when the local peak pressures are of interest, for example, as in the case of cladding design.

Interference effects of tall buildings have attracted numerous studies due to the boom of clusters of buildings in megacities. To fully understand the interference effects, it often requires a substantial amount of wind tunnel tests. Limited wind tunnel tests that only cover part of interference scenarios are unable to fully reveal the interference effects. This study used machine learning techniques to resolve the conflicting requirement between limited wind tunnel tests that produce unreliable results and a completed investigation of the interference effects that is costly. Four machine learning models including decision tree, random forest, XGBoost, generative adversarial networks (GANs), were trained based on 30% of a dataset to predict wind pressure coefficients on the principal building. The GANs model exhibited the best performance in predicting these pressure coefficients. A number of GANs models were then trained based on different portions of the dataset ranging from 10% to 90%. It was found that the GANs model based on 30% of the dataset is capable of predicting pressure coefficients under unseen interference conditions accurately. By using this GANs model, 70% of the wind tunnel test cases can be saved, largely alleviating the cost of this kind of wind tunnel testing study.

Numerous studies have been carried out to measure wind pressures around circular cylinders since the early 20th century due to its engineering significance. Consequently, a large amount of wind pressure data sets have accumulated, which presents an excellent opportunity for using machine learning (ML) techniques to train models to predict wind pressures around circular cylinders. Wind pressures around smooth circular cylinders are a function of mainly Reynolds number (Re), turbulence intensity (Ti) of the incident wind, and circumferential angle of the cylinder. Considering these three parameters as the inputs, this study trained two ML models to predict mean and fluctuating pressures respectively. Three machine learning algorithms including decision tree regressor, random forest, and gradient boosting regression trees (GBRT) were tested. The GBRT models exhibited the best performance for predicting both mean and fluctuating pressures, and they are capable of making accurate predictions for Re ranging from 104 to 106 and Ti ranging from 0% to 15%. It is believed that the GBRT models provide an efficient and economical alternative to traditional wind tunnel tests and computational fluid dynamic simulations for determining wind pressures around two-dimensional smooth circular cylinders within the studied Re and Ti range.

We tested the hypothesis that random variations in the magnitude of sinusoidal linear acceleration cause greater modulation of skin sympathetic nerve activity (SSNA), but not muscle sympathetic nerve activity (MSNA), than sinusoidal stimuli of the same frequency but constant amplitude. Subjects (n = 22) were seated in a sealed room mounted on a linear motor that could deliver peak sinusoidal accelerations of 30 mG in the antero-posterior direction. Subjects sat on a padded chair with their neck and head supported vertically, thereby minimizing somatosensory cues, facing the direction of motion in the anterior direction. Each block of sinusoidal motion was delivered at 0.2 Hz, either with a constant-amplitude (root mean square 14 mG) or randomly fluctuating amplitudes of the same mean amplitude. MSNA (n = 12) and SSNA (n = 10) were recorded via tungsten microelectrodes inserted into muscle or cutaneous fascicles of the common peroneal nerve. Cross-correlation analysis was used to measure the magnitude of vestibular modulation. The modulation index for SSNA was significantly higher during delivery of random vs constant-amplitude acceleration (31.4 ± 1.9 vs 24.5 ± 2.5%), but there was no significant difference in the modulation indices for MSNA (28.8 ± 2.9 vs 33.4 ± 4.1%). We conclude that the pattern of vestibular stimulation affects the magnitude of modulation of sympathetic outflow to skin but not to muscle. Presumably, this is related to the subperceptual development of nausea, which is known to be associated with greater vestibular modulation of SSNA but not MSNA.

A new linear wind generator (LWG), named PowerWindow, is introduced. The modular and scalable LWG is capable of generating power in low wind velocity condition, and hence can be an effective and safe power generator in built environments. The aerodynamic mechanism of the LWG power generation is elucidated using computational fluid dynamic (CFD) simulations, and the results are validated against the experimental data obtained from the prototype wind tunnel tests. The simulations provide important insights into the flow field in and around LWG particularly over the front and rear blades and how each one contributes to the power generation. This study shows that PowerWindow can generate power with an acceptable coefficient of performance (CP≈0.15) in very low linear velocity ratio (λ≈0.2), which is not achievable in most conventional wind turbines at comparable size.

In this study, we used a computational fluid dynamics (CFD)–discrete element method (DEM) model to analyze the triggering of sand movement below an offshore pipeline. The advantage of this CFD–DEM model is that it considers the motion and force applied to every individual particle, thereby facilitating detailed simulations of seepage flow and the breakdown of the water–sand mixture beneath the pipeline. The simulation results were similar to previous experimental studies, which showed that scouring occurs after the driving pressure beneath the pipe generates a floating gradient in the sand layer near the wake. Furthermore, the computed critical current velocity that leads to the onset of scour was in reasonable agreement with the observational data. Thus, we consider that CFD–DEM is a promising numerical tool for future investigations of the mechanism that underlies the onset of scour.

This study investigated aerodynamic characteristics of an inclined square prism experimentally. Pressure measurements were performed on a static square prism with a series of inclinations including forward inclinations (inclined to the upwind direction) and backward inclinations (inclined to the downwind direction). The prism with a vertical attitude was also tested for comparisons. Based on the pressure data, influences of the inclinations on aerodynamic characteristics (e.g., force coefficients, pressure distributions on the surfaces, and vortex shedding features) of the square prism were evaluated in detail. The results show that the inclinations have significant effects on these aerodynamic characteristics. Furthermore, the influences of the forward and backward inclinations are quite different.

Low airflow or poor outdoor ventilation around building blocks can negatively influence pollutant dispersion in the surroundings and indoor air quality, and increase the risks of airborne transmission of infectious diseases. However, there have been few studies addressing the wind environment, thermal comfort and other concerns at the pedestrian level. Buildings with a lift-up design may have a number of impacts on the pedestrian-level wind and thermal environments. Three building configurations that resulted in the lowest wind speed zones were identified from a previous study. A 3.5 m high open ground floor was added to each of the three configurations, and scale models of the three designs were studied in a wind tunnel to assess their influences on airflow and ventilation around the buildings. Undesirable areas of low wind speed leading to poor air ventilation and, on the other side of extreme, areas of discomfort due to strong wind conditions were both identified, and their practical implications are discussed.

This paper presents an integrated computational design optimization method for the performance-based design of tall buildings subjected to various levels of wind excitation. A performance-based wind engineering design framework is proposed by defining various performance objectives associated with multiple levels of wind hazards. A nonlinear static pushover analysis is employed to predict the inelastic drift performance of tall buildings subject to very rare extreme wind events. The optimal performance-based design problem considering inelastic deformation is formulated and solved by the augmented optimality criteria method. The effectiveness and practicality of the optimal wind-resistant performance-based design technique are illustrated by a practical 40-story residential building.

The current study uses a longitudinal within-subjects design to investigate the effects of wind-induced tall building motion on occupant wellbeing and work performance. 47 office workers on high floors of wind-sensitive buildings and 53 control participants completed 1909 surveys across 8 months and over a range of wind conditions. The results show that the effects of building motion are emergent, as motion sickness develops after a duration of exposure to motion, which mostly manifest as symptoms of sopite syndrome, or low-dose motion sickness (tiredness, low motivation, distraction from work activities, and low mood), which occur at 2–3 times baseline rates. As motion sickness increases, work performance significantly decreases by 0.76–0.90 standard deviations below baseline. Affected individuals attempt to manage their own discomfort, and indicate a preference to work a different location during motion, take 30–40% longer breaks, and attempt to self-medicate using analgesics. Humans are adaptable, allowing most occupants to continue their work activities, but at reduced levels of performance and comfort. Design criteria for tall buildings should attempt to minimise the environmental stress of building motion on work performance and wellbeing rather than motion tolerance or formal complaint to building owners.

Variation in flow characteristics triggered through the fire-wind interface can potentially damage the buildings during bushfires. Fire-wind enhancement which is referred to as the increase of wind velocity, caused by the fire-wind interaction, is one of the destructive phenomena in this regard. In spite of the significance, the underlying mechanism contributing to this phenomenon is still not well understood. This study employs computational fluid dynamic (CFD) simulation to fundamentally investigate the effects of free-stream wind velocity on fire-wind enhancement through analyzing the momentum and buoyancy of fluid. Fire-wind interaction is shown to cause the generation of fire-induced longitudinal negative pressure gradient which results in fire-induced pressure and viscous forces in longitudinal direction. These forces are further found as the prime reason for the distortion of the wind velocity profile. A module is implemented to the FireFOAM solver to calculate and extract these forces quantitatively. The results reveal that under a constant fire intensity, the level of distortion and/or enhancement in the wind velocity profile comparatively reduces with the increase of free-stream wind velocity. A new non-dimensional group (modified Euler number) is introduced to take into account dominant fire-induced forces causing fire-wind enhancement. Richardson number and the modified Euler number are employed to determine the influence of free-stream wind velocity and longitudinal distance from the fire source on wind velocity enhancement. Large-eddy simulation (LES) results indicate that while the level of enhancement generally depends on both Richardson and the modified Euler number, the location of the maximum level of enhancement along the plume centreline coincides with the maximum value of modified Euler number under a constant free-stream wind velocity scenario.

This study evaluated the performance of wind energy harvesters with multiple shape-optimized circular cylinders in tandem via computational fluid dynamics simulations. The circular cylinders were optimized by attaching triangular protrusions on their surface. The circumferential location of the protrusion plays a crucial role in the efficiency of this kind of wind energy harvester. The protrusions at the circumferential angles of α = 60°and 90°significantly extend the wind velocity range with remarkable energy generation. When the reduced wind velocity is lower than 10, the harvester with three plain cylinders in tandem generates the most power. However, when the speed is higher than 10, the most power is generated by the harvester having three cylinders in tandem with protrusions at α = 60°. Therefore, in a low wind velocity environment, the harvester with three plain circular cylinders in tandem is superior to other tested configurations, whereas in a high wind velocity environment, the harvester with three circular cylinders with protrusions at α = 60°in tandem outstands from other tested configurations. The associated flow mechanisms are detailed as well.

This study evaluated the performance of twin adjacent galloping-based piezoelectric wind energy harvesters based on mutual interference. The relative position between the twin harvesters is crucial to their energy generation efficiency. A series of wind tunnel tests were conducted to test energy generation of the two harvesters in tandem or staggered arrangements. The optimal relative position, a streamwise center to center spacing of 1.2B (B is the width of the harvester's square prism) and a transverse center to center spacing of 1.0B, was identified. The total output power of the two harvesters placed in the optimal relative position is up to 2.2 times that of two isolated harvesters. The output power is also much larger than that of the harvesters in tandem arrangements that have been widely tested in previous studies. Therefore, it is recommended to position two adjacent harvesters in optimal relative position(s) to deliver an optimal power output.

1014 central business district workers in Wellington, New Zealand, were surveyed about their experiences of wind-induced building motion, susceptibility to motion sickness, reported compensatory behaviours, and complaints about building motion. Overall, 41.7% of the respondents reported that they had felt wind-induced building motion, and 41.6% of those respondents reported perceptible motion at least once a month. Difficulty in concentrating was the most frequently reported effect of building motion, reported by 41.9% of the respondents who had felt building motion. This suggests that early onset motion sickness develops in many building occupants. Despite a strong preference to avoid working in tall buildings, highly susceptible individuals were equally likely to work on high floors as low floors, increasing their potential exposure to building motion. These highly susceptible individuals were more likely to report symptoms of motion sickness due to building motion. Despite the reported adverse effects of motion sickness, building occupants in general almost never make formal complaints about building motion, contradicting the widely held assumption that complaint is an effective index of building performance. Some building occupants then actively compensate for the effects of building motion by taking more breaks and in some cases taking motion sickness tablets. Implications for occupant comfort, motion sickness, the rate of occupant complaint and compensatory behaviours are discussed.