Open Terrain Conditions Research Articles

Effects of Traffic on Particulate Matter (PM2.5) in Different Built Environments

Globally, vehicular pollution is one of the greatest concerns in urban areas. Several studies on air pollution have been conducted using deterministic, statistical, and soft computing methods. However, there has been little research on how soft-computing methods like Artificial Neural Networks (ANN) can help us comprehend vehicular pollution’s non-linear and highly complex dispersion. This study uses an ANN-based vehicular pollution model to investigate the effect of vehicular traffic on PM2.5 concentrations in built-up and open terrain-surrounding environments. Five distinct pollution models were developed for two locations in Delhi, considering PM2.5 pollutants, meteorological variables, traffic flow, and traffic composition into account. The results concluded that under open terrain conditions, the significance of the traffic variable in its association with PM2.5 is almost half the significance observed under built-up conditions. Also, in terms of PM2.5 reductions, the maximum reduction observed at Location-1 (built-up environment), and Location-2 (open terrain environment) is 1.85 and 2.44 times the percent reduction in traffic during peak hours, respectively. The study’s findings have significant ramifications for the current practices of ignoring the contribution of traffic and the built environment to pollution and adopting measures like an odd-even rule and high fuel and parking prices to combat pollution.

Interaction of open-top, short, cylindrical tank with wind-driven rain

Driving rain or wind-driven rain (WDR) is defined as rain, falling in an inclined manner due to the driving force of the wind, inflicting damage to the envelope of building, due to rain droplet impingement, hygrothermal effect, and, rain water ingress. When rain is driven by wind, especially high wind (during storm, cyclone, etc.), the rain droplet impact can increase. There is no availability of literatures on the interaction of shell structures with driving rain, which incurs damage to the thin wall of the tank through droplet impact. This scope is the main motivation behind the present study, which is focused on fluid–structure interaction analysis of an open-top, ground-supported, cylindrical tank with a slenderness ratio of 1.0, affected by wind driven rain. The thickness of the tank wall is varied, and, open terrain condition is considered. The study exhibits that the force coefficient (Cf) of WDR is higher between 0° to 53° peripheral position and decreasing upto 140° circumferential location. Maximum 28% increase of force coefficient of WDR noticed for 45° position in comparison to the wind force coefficient. Also, the top of the tank wall exhibits greater deformation and vulnerable under the effect of wind-driven rain load. Also, it is evident that 0° to 18°, and, 0° to 27° circumferential area exhibit higher deformation for radius: thickness (R/t) ratios 500, and 250, respectively. In case of R/t ratios 125, and 166.67, the higher deformation zone is distributed 0° to 15° and 77° to 82° peripherally. This deformation behaviour of the tank wall, shows that the open-top tanks need to be stiffened at the top to withstand the wind-driven rain force. The magnitude of deformation exhibits increments with the decrease in the thickness of wall of the tank. Maximum deformation is observed for lowest thickness of the tank wall.

Experimental investigation of the aerodynamics of a large industrial building with parapet

The aerodynamic performance of a roof depends significantly on its shape and size, among other factors. For instance, large roofs of industrial low-rise buildings may behave differently compared to those of residential homes. The main objective of this study is to experimentally investigate how perimeter solid parapets can alter the flow pattern around a low-rise building with a large aspect ratio of width/height of about 7.6, the case of industrial buildings/shopping centers. Solid parapets of varied sizes are added to the roof and tested in an open-jet simulator in a comparative study to understand their impact on roof pressure coefficients. Roof pressures were measured in the laboratory for cases with and without parapets under different wind direction angles (representative of straight-line winds under open terrain conditions). The results show that using a parapet can alter wind pressures on large roofs. Parapets can modify the flow pattern around buildings and change the mean and peak pressures. The mean pressure pattern shows a reduction in the length of the separation bubble due to the parapet. The parapet of 14% of the building’s roof height is the most efficient at reducing mean and peak pressures compared to other parapet heights.

UHF Fractal Antennas: Solutions for Radio Links Using Matlab Simulations

Abstract The paper proposes the use of MATLAB simulations as a first step in identifying proper antennas to be used in specific ultra-high frequency (UHF) communication links. Giving that fractal antennas provide interesting features, we aimed at comparing a few of their significant parameters with those of a monopole antenna so as to ensure signal coverage between two real sites situated at 5.82 km distance in a mixture of urban and flat – open terrain conditions. We started from the requirements imposed to the return loss of the antenna and to the link margin, we established their desired thresholds and then computed solutions regarding which antenna type in the set provide the highest received power and on which frequency sub-bands can be successfully used. The studied fractal antenna set were from the series Koch, Koch loop and Sierpinski. The chosen radio link refers to a real situation on the map. Generally, different narrow bands were provided by each antenna regardless of its type, but still, comparing them with the monopole, better solutions could be identified.

Experimental and computational investigation of outdoor wind flow around a setback building

In recent days, the behaviour of wind flow around the buildings receives more interest among urban planners, architects, researchers and wind engineers. Hence, these wind flow patterns are assessed extensively using CFD (Computational Fluid Dynamics) simulations, as it re-creates the atmospheric and wind tunnel environment following the turbulence parameters. This paper presents a logical assessment using IDDES (Improved Delayed Detached Eddy Simulation) turbulence model in CFD for predicting wind pressure coefficients and flow features on and around a 300:1 scaled setback tall building model at 0° and 90° AOI (Angle of Incidence) under open terrain condition. The computation is based on gird sensitivity study and validation with Boundary Layer Wind Tunnel (BLWT) experiment measurements. The evaluation shows that the downdraught and downwind effects are suppressed by the increasing wind pressure distribution along the height. The results demonstrate that IDDES can reproduce wind pressure coefficients and aerodynamic coefficients of the setback building accurately. The maximum deviation of the wind pressure coefficients (Cp rms) is found to be 12% in CFD when compared with wind tunnel measurements. Besides, the CFD simulation demonstrates the wind flow distribution patterns, size of re-circulation, wake separation zones and velocity profiles in a three-dimensional plane which are quantified concerning the width of the building.

ПРИВЕДЕННЯ ДАНИХ ВИМІРЮВАНЬ ШВИДКОСТІ ВІТРУ ДО УМОВ ВІДКРИТОЇ МІСЦЕВОСТІ

Wind speed spatial distribution over the territory of Ukraine built based on weather stations measurements has been analyzed. Interpolated field of wind speed averaged over 1981-2010 indicated fairly heterogeneous structure with a number of artificial spots of larger/smaller values compared to surrounding areas. The main reason of such heterogeneity might be associated with representativeness of observation site regarding the landscape zone. It is well known that surrounding obstacles have a great impact on wind flow in horizontal direction. In order to solve this problem we have corrected sub-daily wind speed data measured at 207 meteorological stations of Ukraine for the period of 1981-2010 according to the open terrain conditions and the standard height (10 m). Generally, aerodynamic characteristics (e.g. surface roughness length) of measurement sites are needed in order to perform such adjustment. However, the only usable parameter available at a climatological reference book is horizon closure degree. The research revealed significant relationship between this characteristic and wind speed records (Pearson correlation coefficient equals -0.58). Given that horizon closure degree could not be used in correction procedure directly, surface roughness length has been calculated for 10 stations and statistical relationship has been determined between these two parameters. Based on the obtained relation and additional information we have found roughness length for all 207 stations at eight directions. Supplementary materials for analysis included observation sites description and Google Earth snapshots as well. In the final step, there has been applied a correction formula derived from the neutral logarithmic profile of wind speed in the atmospheric surface layer. The output of the research is new database of corrected wind speed measurements for the multiyear period. These results have been compared with observations. Mean 30-yr corrected speeds are featured by more homogeneous distribution over Ukraine and mostly higher values (with positive mean spatial bias ~0.35 m/s). The applied method allowed us to remove uncertainties related to differences in vertical level of measurements and considerably eliminate influence of the micro-scale terrain inhomogeneity. Obtained datasets may facilitate to perform spatial interpolation and further development of Ukrainian Wind Atlas.

Open-jet boundary-layer processes for aerodynamic testing of low-rise buildings

Investigations on simulated near-surface atmospheric boundary layer (ABL) in an open-jet facility are carried out by conducting experimental tests on small-scale models of low-rise buildings. The objectives of the current study are: (1) to determine the optimal location of test buildings from the exit of the open-jet facility, and (2) to investigate the scale effect on the aerodynamic pressure characteristics. Based on the results, the newly built open-jet facility is well capable of producing mean wind speed and turbulence profiles representing open-terrain conditions. The results show that the proximity of the test model to the open-jet governs the length of the separation bubble as well as the peak roof pressures. However, test models placed at a horizontal distance of 2.5H (H is height of the wind field) from the exit of the open-jet, with a width that is half the width of the wind field and a length of 1H, have consistent mean and peak pressure coefficients when compared with available results from wind tunnel testing. In addition, testing models with as large as 16% blockage ratio is feasible within the open-jet facility. This reveals the importance of open-jet facilities as a robust tool to alleviate the scale restrictions involved in physical investigations of flow pattern around civil engineering structures. The results and findings of this study are useful for putting forward recommendations and guidelines for testing protocols at open-jet facilities, eventually helping the progress of enhanced standard provisions on the design of low-rise buildings for wind.

Interaction of severe convective gusts with a street canyon

Severe convective gusts lead to wind conditions that differ from those of atmospheric boundary layer (ABL) flows. Main differences are high velocities at ground level and transient flow conditions. Their interaction with inner-city areas has only rarely been examined and is the aim of the present work. In the experimental study the convective gusts were simulated by a jet, imbedded in an ABL flow generated by a wind-tunnel. The gust impinged on a street canyon model. Both steady experiments (continuous jet) and non-steady experiments (pulsed jet) were conducted. Flow fields within the street canyon were measured by means of a 2D/2C TR-PIV system.Comparisons of the steady flow field within a street canyon model and for a gust propagation on open terrain revealed an average increase of the maximum horizontal velocity of 50% within the canyon, an increase of the outflow's height, and a conservation of high velocities over a distance more than 3 times larger compared to open terrain conditions. Further experiments with a transient gust included the generation of a ring vortex. This vortex propagates above the street canyon and results in an additional increase of peak velocities.

Effect of Boundary Layer Fence Location on HAWT Power Performance

Even though wind energy is a deep-rooted technology, but not yet mature and hence there are bounteous scopes for improvement to reduce the cost of wind energy. An experimental investigation has been carried out on 1:25 scaled S809 aerofoil blade featuring boundary layer fence at various span wise location. Quantifying electrical power obtained by rotation of wind turbine rotor coupled with dynamic testing system. A baseline model with no flow control and an upgraded model with detachable boundary layer fence have been studied in the wind tunnel. For upgraded model, fences were placed along the location of 40% to 90% of the blade span. The rotor blades are then tested dynamically in wind tunnel at open terrain condition for 7 m/s, 9 m/s and 11 m/s velocities. In order to study the effect of boundary layer fence test has been carried out in the low speed wind tunnel having test section of size 0.9 m × 1.2 m × 2 m. Scope corder DL 750 is used to measure time varying voltage and proximity sensor with its compatible display unit is used to measure the rotor RPM. The flow behaviour was found to be considerably favourable from conventional rotor blades. Installation of fence has been found promising for increased energy extraction from air column by controlling the three dimensional span wise flow. Results demonstrate the potential of the proposed model which can obtain a maximum of about 11.8% increase in the power. In addition, the significance of the location of wing fence and blade pitch angle has been analysed.

Comparison of Wind Pressure Coefficients with Wind Load Provisions

This study has compared the equivalent external pressure coefficients, (GCpf)eq, with 6 wind load provisions and wind tunnel test data. The wind load provisions are the ASCE 7-10, NBCC 2010, AS/NZS 2011, EN 2005, AIJ 2004 and KBC 2009. Experiment data on low-rise building have been obtained at the University of Western Ontario (UWO) to contribute to the NIST aerodynamic database [. For the experiment, a model with 1:12 of roof slope and 4.9 and 12.2m of eave height was used under open terrain conditions (See also Ref. [). (GCpf)eq was re-normalized based on the external pressure coefficients, GCpf, of ASCE 7-10. When compared to (GCpf)eq of the experiment data with 4.9m of eave height, consequently, ASCE 7-10 (81%), NBCC 2010 (84%), AS/NZS 2011 (70%), AIJ 2004 (68%) and KBC 2009 (53%) were all underestimated. Among them, KBC 2009 reveals the lowest value. On the contrary, EN2005 was overestimated with 122%. When the eave height was 12.2m, in addition, the same pattern was observed in most codes. EN2005 was slightly overestimated with 115%.

Correlations of aerodynamic pressures for prediction of across wind response of structures

Correlation length is one of the four important aerodynamic parameters, which is required for prediction of across-wind response of a structure subjected to vortex shedding. Pressure measurement studies on models of three structures with different plan shapes- a circular, an octagonal and an irregular shape, were conducted under simulated open terrain conditions using the boundary layer wind tunnel. This paper presents experimental details and test results on pressure distributions and measurement of correlation lengths. It is shown that for the circular and octagonal models studied, the modified value of rms lift coefficient, C L, V ′ is found to be close to 0.088. Further, for the irregular shaped tower block model also, for the wind angle where the mean across wind force is very small, the value of C L, V ′ is found to be around 0.088. Further research is necessary for validating the value of 0.088 for structures with other cross-sectional shapes.

Across-wind aerodynamic parameters of tall chimneys with circular cross section—a new empirical model

The prediction of across-wind response of circular cylinders remains a challenging task, despite extensive research efforts. An attempt has been made to correlate the rms lift coefficient due only to vortex shedding, C′ L,VS both in wind tunnel and full-scale conditions by separating the local rms lift coefficient, C′ L, into two components, one due to the lateral turbulence and the other due to the vortex shedding. Based on the literature, and also using test results measured by the authors, it is found that the final value of C′ L,V, as discussed in the paper, show a mean value of 0.089 with a coefficient of variation of 18%, independent of Reynolds number regime. The above value plus 1.66 times the standard deviation gives a value of 0.115 which is in excellent agreement with the value of C′ L,VS=0.12 recommended for design of chimneys under open terrain conditions, as per the Indian Standard Code of Practice: IS: 4998 Part-2, 1992. Further it is shown that the Griffin universal Strouhal number, G attains a mean value of 0.065 with a coefficient of variation (cov) of 8%, independent of sub-critical and trans-critical Reynolds number regime.

Analysis of hurricane directionality effects using event-based simulation

This paper presents an approach for evaluating directionality effects for both wind speeds and wind loads in hurricane-prone regions. The focus of this study is on directional wind loads on low-rise structures. Using event-based simulation, hurricane directionality effects are determined for an open-terrain condition at various locations in the southeastern United States. The wind speed (or wind load) directionality factor, defined as the ratio of the N-year mean recurrence interval (MRI) wind speed (or wind load) in each direction to the non-directional N-year MRI wind speed (or wind load), is less than one but increases toward unity with increasing MRI. Thus, the degree of conservatism that results from neglecting directionality effects decreases with increasing MRI. It may be desirable to account for exposure effects (siting effects such as shielding, orientation, etc.) in design. To account for these effects in a directionality adjustment, the factor described above for open terrain would need to be transformed to other terrains/exposures. A local directionality factor, therefore, must effectively combine these two adjustments (event directionality and siting or exposure directionality). By also considering the direction-specific aerodynamic coefficient, a direction-dependent wind load can be evaluated. While the data necessary to make predictions of directional wind loads may not routinely be available in the case of low-rise structures, the concept is discussed and illustrated in this paper.

Fast vortex methods for predicting wind-induced pressures on buildings

The random vortex method is a Lagrangian particle-based numerical simulation scheme especially appropriate for fluid flows characterized by high Reynolds numbers and complex geometries. When coupled with a fast solver for computing vortex interactions, it becomes ideally suited for wind engineering simulations. Fast vortex methods have several advantages over grid-based methods because they do not suffer from numerical diffusion, are simpler to implement particularly as the geometry becomes more complex, and are likely to exploit the architecture of distributed-memory computers more effectively. In this paper, initial results are presented for a fast vortex two-dimensional simulation of the atmospheric boundary layer wind flow around a bluff body under open terrain conditions. The results compare favorably with full-scale measurements for the well known instrumented Texas Tech Building.

Role of multiple reflections and reverberation in urban noise propagation

Various studies of sound transmission in urban areas that involve multipath propagation or multiple reflections are reviewed. Studies of propagation in a single street or corridors display important descrepancies between theoretical analyses and field experiments. Model studies suggest that scattering may play an important, but as yet unexplained role. Sources above the street show good correspondence between field and laboratory data and theory. Intrusion of aircraft noise into an urban area shows that sound may be slightly amplified above an open-terrain condition due to channeling effects. The general urban background noise appears to be accounted for by surface transportation sources distributed over the city, aside from a shielding factor of 10–15 dB of as yet undetermined origin.