Effect Of Wind Direction Research Articles

Change in drivers of mangrove crown displacement along a salinity stress gradient

Abstract Crown displacement in trees is an adaptive response driven by neighbours that optimizes space use and reduces competition. But it can also be the result of wind force. Although morphological responses to neighbours have been well studied, the interplay between neighbours and wind in driving crown shape, and the implications for plant interactions remain poorly understood. However, it is crucial to predict such changes in vegetation structure and function under the scope of global change. We test the hypothesis that aboveground interactions are reduced with increasing soil stress and that wind becomes the main driver of crown shape in mangrove forests. We investigated the effect of neighbours and wind intensity and direction on crown displacement of mangrove canopy and below canopy trees along a salinity gradient, and assessed crown asymmetry for three mangrove tree species, as well as the contribution of crown displacement on reducing crown‐projected area overlap and thus neighbourhood competition. Results show that crown displacement of canopy trees is strongly influenced by winds at all salinities. At low salinities, competition for space accounted for 48% of crown displacement away from neighbours, compared to 49% found for the synthetized effects of wind and neighbours. While trees below the canopy displace their crowns away from their neighbours, no response to wind could be detected. This can be due to the wind protection conferred by a dense canopy stand related to bigger crowns that effectively reduce wind drag. At higher salinities, there was a reduction in canopy overlap due to crown displacement, which suggests reduced aboveground plant interactions with increasing soil stress. While neighbourhood avoidance is a fundamental strategy for optimal light foraging, this study shows that wind strength and directionality are main drivers of crown shape with increasing stress and highlights their potential influence in plant interactions and forest structure, pointing to an increased susceptibility of trees to disturbances that should be further studied. A plain language summary is available for this article.

Efficient wind fragility analysis of RC high rise building through metamodelling

This paper deals with wind fragility and risk analysis of high rise buildings subjected to stochastic wind load. Conventionally, such problems are dealt in full Monte Carlo Simulation framework, which requires extensive computational time. Thus, to make the procedure computationally efficient, application of metamodelling technique in fragility analysis is explored in the present study. Since, accuracy by the conventional Least Squares Method (LSM) based metamodelling is often challenged, an efficient Moving Least Squares Method based adaptive metamodelling technique is proposed for wind fragility analysis. In doing so, artificial time history of wind load is generated by three wind field models: i.e., a simple one based on alongwind component of wind speed; a more detailed one considering coherence and wind directionality effect, and a third one considering nonstationary effect of mean wind. The results show that the proposed approach is more accurate than the conventional LSM based metamodelling approach when compared to full simulation approach as reference. At the same time, the proposed approach drastically reduces computational time in comparison to the full simulation approach. The results by the three wind field models are compared. The importance of non-linear structural analysis in fragility evaluation has been also demonstrated.

Prevention of malaria transmission around reservoirs: an observational and modelling study on the effect of wind direction and village location

Many large dams are constructed annually in Africa, with associated reservoirs that might exacerbate the risk of malaria in new villages built nearby. We aimed to investigate the heterogeneous risk of malaria around reservoirs related to the impact of wind direction on malaria transmission. Between June 15, 2012, and April 22, 2015, we obtained field data on climate and hydrological conditions, and monitored Anopheles mosquito populations around the Koka reservoir in Ethiopia using in-situ weather stations, mosquito light traps, and larval dipping. The field data were used to calibrate a field-tested, spatially explicit mechanistic malaria transmission model, the Hydrology, Entomology, and Malaria Transmission Simulator (HYDREMATS), to investigate the effect of relative wind direction on malaria transmission and associated mechanisms. We combined our simulation results and observational data to assess the association between village location around a reservoir and risk of malaria. HYDREMATS simulations showed that wind blowing from a village towards a reservoir increases the size of malaria vector populations, whereas wind blowing from a reservoir towards a village decreases the size of malaria vector populations, which was consistent with our field data. Larval mortality is low in locations with village-to-reservoir wind due to weak surface waves, and this wind direction creates conditions that enable mosquitoes to identify village locations more easily than in conditions caused by reservoir-to-village wind, which increases the size of malaria vector populations, and thus malaria transmission. Among the wind conditions investigated (0·5-5 m/s), the effect of CO2 attraction on the size of the Anopheles population was largest at wind speeds of 0·5 m/s and 1 m/s, decreasing with higher wind speed. At a wind speed of 5 m/s, the effect of CO2 attraction was negligible, whereas the effect of waves was strongest. The effect of advection on Anopheles population size was negligible at all wind speeds and wind directions. The effect of wind on malaria transmission around reservoirs can be substantial. The transmission of malaria can be minimised if the location of villages situated near a reservoir is carefully considered. For areas in which the environmental conditions surrounding a resevoir are equal, villages should be located downwind of reservoirs to reduce the incidence of malaria, although further research will be required in locations where wind direction changes in different seasons. US National Science Foundation, and Cooperative Agreement between the Masdar Institute of Science and Technology, Abu Dhabi, UAE, and the Massachusetts Institute of Technology, Cambridge, MA, USA.

Effects of Wind, Temperature, and Barometric Pressure on Asian Citrus Psyllid (Hemiptera: Liviidae) flight behavior.

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is the vector of the bacterium responsible for huanglongbing, a deadly plant disease affecting citrus worldwide. We investigated the effects of wind direction and speed on flight duration and direction of D. citri, as well as the effects of temperature and barometric pressure on sustained flight duration of D. citri. Experiments were performed with laboratory flight mills and wind tunnels. Flight activity of D. citri increased with increasing temperature. Of the few insects that flew at 18°C, most performed short duration flights (<60 s). When exposed to temperatures between 21 and 28°C, D. citri performed long duration flights (>60 s). In addition, the distance covered increased with temperature. Interestingly, males were more sensitive to cold temperature and flew significantly shorter distances than females at 21 and 25°C. Barometric pressure recorded before and during the flight mill experiment suggested that decreasing pressure reduced distance flown by D. citri. Flight direction was strongly influenced by wind. In wind tunnel experiments where psyllids were challenged to reach citrus leaf flush positioned either downwind or upwind, most D. citri moved downwind when exposed to continuous airflow. In a subsequent experiment, we challenged psyllids to pulsed wind blowing at higher speeds. In this case, most psyllids progressed upwind, suggesting upwind movement by psyllids during pauses within pulsed airflow. Collectively, the results indicate that D. citri are able to modify their flight behavior in response to abiotic factors.

Effects of Wind Direction on Variations in Friction Velocity With Wind Speed Under Conditions of Strong Onshore Wind

AbstractThe effects of wind direction on variations in friction velocity with wind speed are studied under moderate (≥9 m/s) to strong (≥22 m/s) onshore wind conditions using 20‐Hz ultrasonic wind data from a coastal tower at three different heights. The effects of different averaging time intervals of 20, 10, 2, and 1 min on the variations are also investigated. Three typhoons passed by the tower during the 150 hr of observations. Regardless of wind direction, friction velocity increases with increasing wind speed, and linear regression shows that the rate of increase is ~50% less than previously reported. However, a leveling‐off or decrease in friction velocity with increasing wind speed is found under strong wind conditions using a bin‐averaged method. Wind direction affects the variations in friction velocity with wind speed. Friction velocity increases with increasing wind speed at a similar growth rate to that of previously published results, with a leveling‐off or decrease at wind speeds higher than 22 m/s when the wind blows roughly normal to the shoreline. Form drag induced by sea waves with longer wavelengths is suggested to be responsible for the effects of wind direction on the variations in friction velocity with wind speed. An averaging time interval of 1 min yields representative variations in friction velocity with wind speed using the observations described in this study.

SHORT PERIOD CHANGE DETECTION OF SPERCHIOS LOWER DELTA AREA USING SPACE RADAR IMAGES

Being highly dynamic by nature, due to their changing hydrological regime and to the encroachment of urbanization, industrialization and changing patterns in agriculture, reliable and timely information of coastal areas is a prerequisite for their effective management. The aim of this paper is to assess the use of ERS-2 SAR satellite data to detect short period changes in the case of the R. Sperchios coastal area that is located at the eastern part of the Maliakos Gulf (near the middle of the east coast of the Greek mainland). A Landsat 7 (ΕΤΜ+) image served as a reference for the interpretation of the ERS images. In order to highlight and detect the changes occurred in the study area two methods were applied. The first method is based on the creation of a Temporal Differentiate Image, consisted of the three ERS-2 images (Figure 1). The second method concerns the implementation of Principal Component Transform (PCT) on the three multitemporal scenes. The final images derived from the two different methods were compared and evaluated. Both methods didn't show any significant change along the coastline. PCT method illustrates more clearly the seasonal changes of crops in the lower delta area. Eventually, radar technology gave the opportunity to discriminate shallow areas, which does not appear in satellite optical data. Concurrently, the effect of wind direction was investigated.

Impacts of wind fields on the distribution patterns of traffic emitted particles in urban residential areas

Traffic emissions are a major contributor to urban atmospheric pollution. The wind fields also play an important role in the dispersion of air pollutants from the traffic emissions. However, the effects of different regional wind fields on the diffusion patterns of traffic-emitted fine particulate matter (PM2.5) in urban areas are still unclear and lack quantified measurements. To provide guidance to urban planning and design, as well as urban governance and management, it is especially important to identify the extent to which wind fields affect the diffusion of traffic-emitted particles. To understand the effect, field measurements and numerical simulations were conducted in this study. The field measurements mainly focused on collecting three-dimensional (3D) distributions of concentrations of traffic-emitted particles in a student dormitory zone at a university using instrumented unmanned aerial vehicles (UAVs). The collected PM2.5 measurements were used to verify and calibrate numerical models. Then, computational fluid dynamics (CFD) simulations were used to track the progress of pollutant dispersion and evaluate its relationship to urban forms. The effects of different wind directions (northwest and southeast) on the distribution and deposition of the traffic-emitted particles in the residential area were studied under different wind velocity conditions (1 m s−1, 5 m s−1 and 20 m s−1). As efficient observation platforms, the UAVs employed in the study allowed the capture of the 3D variations in the distributions of atmospheric pollutants in urban areas. The result provides a better understanding of the dispersion of atmospheric pollutants in a specific urban built environment under different wind fields, which can support urban governance and planning and design practice leading to effective mitigation of traffic-induced air pollution in urban areas.

Enhanced wind-driven infiltration model by incorporating wind direction for design purpose

Research has been conducted to improve and enhance existing LBNL infiltration model in order to incorporate wind direction effect on flow rate. Existing wind driven infiltration of LBNL model only consider terrain and shielding parameter as correction factor. Supplemental analytical model considered in this research was Swami-Chandra model, which the calculation was based on average wind pressure coefficient (Cp). It was evident that for same wind direction, Cp value will not change regardless of wind velocity. Process of simulation shows that infiltration modelling has to be performed in three-dimensional environment with transient calculation in order to achieve convergent result. Wind direction strongly affects infiltration flow rate. However, as the infiltration hole has relatively small size compared to wind velocity, flow rate variation is marginal for energy-based design. Nevertheless, for pollutant and particulate matter analysis, wind direction will give significant change in term of concentration and flow direction.

The effect of airspeed and wind direction on human's thermal conditions and air distribution around the body

The purpose of this research was to investigate the effects of airspeed and wind direction on a human's thermal conditions and of air distribution around the body. In addition, this study presents the equivalent temperature, which is the most effective index to evaluate the effect of air movement. The effect of convection and radiation on each part of the human body was estimated through numerical calculation, and the results were verified through a combination of thermal manikin experiments and radiation analysis. The experiments were conducted in a climate chamber and wind tunnel under conditions of natural convection and forced convection, respectively. An airspeed of 0.05 m/s was selected for the natural convection condition and an airspeed range of 0.2–2.0 m/s for forced convection conditions. The natural convective heat transfer coefficient in the stagnant environment was 3.27 W m−2 K−1 in the sitting posture and 2.67 W m−2 K−1 in the standing posture because the natural upward airflow caused by human body heat is more likely to diffuse to the surrounding environment in a sitting posture than in a standing posture. The equivalent temperature change of the whole body was greater in the standing posture than in the sitting posture when the airspeed was 0–0.2 m/s. The equivalent temperature change of the whole body was similar in both sitting and standing postures when the airspeed was greater than 0.2 m/s.

Effect of wind direction and incidence angle on polarimetric SAR observations of slicked and unslicked sea surfaces

The objective of this paper is to investigate the dependency of oil spill observations in polarimetric SAR data on imaging geometry, i.e., on incidence angle and look direction relative to the wind. The study is based on quad-polarization data acquired by the Uninhabited Aerial Vehicle Synthetic Aperture Radar over experimental oil slicks under relatively high winds of 10–12 m/s over an 8-hour period. The data is collected over a wide range of incidence angles and alternates between looking upwind (UW) and downwind (DW). The unique time series enables a detailed study of the behavior of multipolarization parameters over clean sea and oil slicks under varying imaging geometry to be carried out for the first time. For clean sea backscatter, our findings are in agreement with previous studies, showing decreasing backscatter as the incidence angle increases and from UW to DW, with the highest sensitivity in the HH channel. We also find similar variations in oil covered areas. The results suggest that the oil slick backscatter is slightly more sensitive to the relative wind direction than the clean sea, and higher oil-sea damping ratios are found in DW than in UW cases, particularly in the HH channel. All multipolarization features investigated have some degree of dependency on imaging geometry. The lowest sensitivities are found in the magnitude of the copolarization correlation coefficient, the standard deviation of the copolarized phase difference, the polarization difference, the mean scattering angle and the entropy. Several features clearly change behavior when the signal approaches the sensor noise floor, and we find that the measurements and derived parameters may be affected at even higher signal-to-noise ratio (SNR) levels than previously proposed, i.e., closer to 7–9 dB above the sensor noise floor. Overall, the polarization difference is clearly identified as the most interesting parameter for oil spill observation, producing high oil-sea contrast in addition to low sensitivity to imaging geometry. The results show that both the relative wind direction and the incidence angle, in combination with the SNR, should be taken into account when developing operational methods based on multipolarization SAR data.

SHM-based probabilistic representation of wind properties: statistical analysis and bivariate modeling

The probabilistic characterization of wind field characteristics is a significant task for fatigue reliability assessment of long-span railway bridges in wind-prone regions. In consideration of the effect of wind direction, the stochastic properties of wind field should be represented by a bivariate statistical model of wind speed and direction. This paper presents the construction of the bivariate model of wind speed and direction at the site of a railway arch bridge by use of the long-term structural health monitoring (SHM) data. The wind characteristics are derived by analyzing the real-time wind monitoring data, such as the mean wind speed and direction, turbulence intensity, turbulence integral scale, and power spectral density. A sequential quadratic programming (SQP) algorithm-based finite mixture modeling method is proposed to formulate the joint distribution model of wind speed and direction. For the probability density function (PDF) of wind speed, a double-parameter Weibull distribution function is utilized, and a von Mises distribution function is applied to represent the PDF of wind direction. The SQP algorithm with multi-start points is used to estimate the parameters in the bivariate model, namely Weibull-von Mises mixture model. One-year wind monitoring data are selected to validate the effectiveness of the proposed modeling method. The optimal model is jointly evaluated by the Bayesian information criterion (BIC) and coefficient of determination, R2. The obtained results indicate that the proposed SQP algorithm-based finite mixture modeling method can effectively establish the bivariate model of wind speed and direction. The established bivariate model of wind speed and direction will facilitate the wind-induced fatigue reliability assessment of long-span bridges.

Hydrodynamic modelling of recreational water quality using Escherichia coli as an indicator of microbial contamination

Microbial contamination of recreational beaches is often at its worst after heavy rainfall events due to storm floods that carry fecal matter and other pollutants from the watershed. Similarly, overflows of untreated sewage from combined sewerage systems may discharge directly into coastal water or via rivers and streams. In order to understand the effect of rainfall events, wind-directions and tides on the recreational water quality, GEMSS, an integrated 3D hydrodynamic model was applied to assess the spreading of Escherichia coli (E. coli) at the Sandvika beaches, located in the Oslo fjord. The model was also used to theoretically investigate the effect of discharges from septic tanks from boats on the water quality at local beaches. The model make use of microbial decay rate as the main input representing the survival of microbial pathogens in the ocean, which vary widely depending on the type of pathogen and environmental stress. The predicted beach water quality was validated against observed data after a heavy rainfall event using Nash-Sutcliffe coefficient (E) and the overall result indicated that the model performed quite well and the simulation was in – good agreement with the observed E. coli concentrations for all beaches. The result of this study indicated that: 1) the bathing water quality was poor according to the EU bathing water directive up to two days after the heavy rainfall event depending on the location of the beach site. 2) The discharge from a boat at 300-meter distance to the beaches slightly increased the E. coli levels at the beaches. 3) The spreading of microbial pathogens from its source to the different beaches depended on the wind speed and the wind direction.

Subtidal variability of the Tagus river plume in winter 2013

The subtidal variability of surface plume response to local wind and river runoff is studied off central Portugal using a hindcast model for the Tagus Estuary (TE) plume. In addition to the model, the main patterns of variability of the TE plume were extracted in an automated mode using Self Organizing Maps (SOM). Three characteristic spatial patterns are extracted in a 3 × 2 SOM array: in synoptic time scales, northward and southward propagation of the plume and transitional periods. Results suggest that river runoff and wind induce strong variability in the coastal ocean, and that the TE plume has a rapid response to their changes. Under high river runoff there is a southern propagation of the plume, even during downwelling favorable winds, revealing bi-directional patterns due to the combined effect of estuarine outflow, wind direction and coastline in establishment the plume direction. The same is found during transitional periods, revealing that the TE plume has significant influence both north and south of the estuary mouth. SOM was applied for the first time to extract spatial and temporal features of the TE plume and prove to be a reliable tool to study large quantities of data in addition to the model results analysis.

Short-term power output forecasting of hourly operation in power plant based on climate factors and effects of wind direction and wind speed

Short-term power output forecasting is a fundamental and mandatory task in the power plants. Since the restructuring and privatization of power plants in Iran are in progress, this is particularly important in the operational planning and cost control in the power plants. Numerous factors affect power output forecasting especially climate factors. In this paper, besides several climate factors, two factors including wind speed and wind direction that have been rarely considered simultaneously for power output forecasting in previous studies, have been used. These two factors have many fluctuations and usually create a significant noise in forecasting models. To illustrate this claim, the mechanical simulations are used to demonstrate the necessity of these factors for short-term power output forecasting. For this purpose, a neural network-based approach is proposed using six variables. This approach uses the mixture models of Kohonen's self-organizing map (SOM) as clustering method and radial basis function (RBF) as classification method for accurate power output forecasting in a power plant. Furthermore, the real case study in Iranian power plant is used to show the ability of the proposed approach. Furthermore, the statistical tests are provided to indicate the advantages and capabilities of the proposed approach.

The Effect of Wind Direction and Distance Between Axes on Two Rotating Straight Wing Vertical Axis Wind Turbines

The Effect of Wind Direction and Distance Between Axes on Two Rotating Straight Wing Vertical Axis Wind Turbines

Turbidity in response to wind speed, wind direction and wind duration in Gonghu Bay, Lake Taihu

水体浊度是影响水下光场及营养盐循环的关键要素之一，其变化过程与水生生态环境演变关系密切.基于2015-2016年7个时段于太湖贡湖湾内外的金墅和上山村两站点的水体浊度及东山气象站的逐时风场数据，利用分位统计等方法，探讨了风速、风向及时间累积效应对水体浊度的影响.结果表明：在以风场驱动为主要动力来源的大型浅水湖泊中，春、秋两季水体浊度的变化频率高于夏、冬两季，且春季变率更为突出；冬季风场和水体浊度的变率均较夏季明显.风场（包括风速、风向及其累积时间）是影响水体浊度变化的关键因素.其中风速是主要决定性因子；风向对水体浊度有较明显的影响，其通过对风速效应的修正进而影响水体浊度，该修正作用可用三角函数表征；水体浊度变化同时还受前期风场累积的影响，其前期时间累积效应的有效时段为2~10 h.该研究给出了风速、风向及风场累积效应的耦合对水体浊度的影响模型，有助于弄清风场对水体浊度变化的影响机制.;Turbidity is one of the key factors that affect the underwater light climate and nutrient circulation, and its change is closely related to the evolution of aquatic ecosystem. Based on the turbidity data at the two sites near Jinshu and Shangshan Village in Gonghu Bay of Lake Taihu from 2015 to 2016 and the hourly wind field measurement in Dongshan weather station, the effects of wind speed, wind direction and wind duration on turbidity was analyzed with quantile regression technique. The results show as follows. In large shallow lakes where wind as the primary driving force, the turbidity change frequency in spring and autumn is higher than that in summer and winter, with spring as the most prominent. The change of water turbidity in winter is more obvious than that in summer. The variability of wind field (the speed, direction and duration), particularly the wind speed, is the key factor regulating turbidity. The wind direction can affect the turbidity by the correction of the wind speed. The correction can be characterized by a trigonometric function. The turbidity was mainly affected by the northern wind, and followed by the east-west wind. The influence of the south wind is the weakest. The change of turbidity is influenced by the wind field preceding measurement time, and the valid wind duration is about 2-10 hours. This study developed a model elucidating the influence of wind speed, wind direction and wind duration on the turbidity, which is helpful to clarify the mechanism on turbidity variation in Lake Taihu.

Numerical Analysis of the Effect of Active Wind Speed and Direction on Circulation of Sea of Azov Water with and without Allowance for the Water Exchange through the Kerch Strait

The effect of seawater movement through the Kerch Strait for extreme deviations in the level and speed of currents in the Sea of Azov caused by the action of climate wind fields has been studied using the Princeton ocean model (POM), a general three-dimensional nonlinear model of ocean circulation. Formation of the water flow through the strait is caused by the long-term action of the same type of atmospheric processes. The features of the water dynamics under conditions of changing intensity and active wind direction have been studied. Numerical experiments were carried out for two versions of model Sea of Azov basins: closed (without the Kerch Strait) and with a fluid boundary located in the Black Sea. The simulation results have shown that allowance for the strait leads to a significant change in the velocities of steady currents and level deviations at wind speeds greater than 5 m/s. The most significant effect on the parameters of steady-state movements is exerted by the speed of the wind that generates them; allowance for water exchange through the strait is less important. Analysis of the directions of atmospheric circulation has revealed that the response generated by the movement of water through the strait is most pronounced when a southeast wind is acting.

Satellite and ground atmospheric particulate matter detection over Tucumán city, Argentina, space-time distribution, climatic and seasonal variability

The analysis of atmospheric particles (aerosols) is of special interest due to their potential effects on human health and other applications. In this paper the climatic and seasonal effects on aerosols have been characterized in Tucuman city (26°50’ S, 65° 13’ W,450 masl),Argentina, for the 2006–2013 period. The atmospheric aerosols in Tucuman city result from both stationary and mobile sources such as: industrial activity of sugar cane and alcohol distilleries, paper industry, biomass burning (mainly sugarcane waste crop and grasslands), household waste burning and transport emissions. The peak of industrial activity is seasonal, coincident with the austral winter (July-August-September), when accumulation of particles in the lower atmosphere occurs. In this region, there are no studies like the present one that evaluate, using “in situ” equipment, the temporal variation of aerosols and its causes, by applying modern analytical techniques. A continuous volumetric and isokinetic sampler of Hirst type (Burkard), was used for atmospheric particle sampling, in weekly records between 2006 and 2013. The particle concentration (number of particles per cubic meter) showed an increasing trend in the studied period. The monthly variation of: the particle concentration; the aerosol optical thickness at a wavelength of 550 nm (AOD550) obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard Aqua (NASA) satellite, and the AOD from different aerosol tracers (black and organic carbon, sea salt, sulfates, dust) obtained from the Modern-Era Retrospective Analysis for Research and Applications (MERRA-2), were also analyzed. The temporal variation in particle concentration was explained mostly by wind direction, while the corresponding variation for AOD550(MODIS) was explained by temperature and seasonality (as by-product of climatic variation and anthropogenic particle emission sources). The variation in the AOD550(MERRA-2) data series were explained by temperature, humidity, precipitation, and seasonality, with less effect of wind speed and direction. Particle concentration, AOD550(MODIS), and AOD550(MERRA-2) were highly variable. The cross-correlation between AOD550(MODIS) and AOD550(MERRA-2) time series was significantly positive at lag zero. Other contribution was the determination of the space-time distribution of aerosols on a monthly basis considering AOD550 MODIS (3 km × 3 km) data. The present study suggests that these variables are affected by temperature and wind dynamics driven by seasonal and high-order autoregressive non-linear processes.

Vulnerability analysis of steel roofing cladding: Influence of wind directionality

Steel roofing is widely used for non-residential facilities. However, it is vulnerable to high winds. This paper addresses a damage estimation framework that incorporates wind loading correlation and wind directionality effects for steel roofing. In this framework, external pressures were measured from wind tunnel testing. At positions where pressure measurements are not available, a proper orthogonal decomposition (POD) method is introduced to interpolate external wind pressures. Internal pressures due to openings in the building envelope are taken into account by simulation. Then, the internal forces on fasteners distributed on the steel roof are evaluated by the influence-surface-based method, with corresponding peak values estimated by a Gumbel conversion approach. Furthermore, the failure probability of a single cladding element and the damage ratio for the whole roof are determined based on Monte Carlo simulation (MCS), where the correlation among internal forces of fasteners is incorporated by a Nataf transformation. Finally, wind directionality effects are integrated in order to provide a comprehensive damage assessment for the roofing. Although the proposed framework works for existing buildings, it may potentially benefit the performance-based design for new low-rise buildings.

Numerical and wind tunnel investigation of Hot Air Recirculation across Liquefied Natural Gas Air Cooled Heat Exchangers

Air Cooled Heat Exchangers (ACHE)s are used for heat rejection in Liquefied Natural Gas (LNG) plants. Their thermal performance decreases under elevated ambient temperatures and windy conditions as exhaust air recirculates back into the ACHE units causing Hot Air Recirculation (HAR). This paper investigates the effect of various incident wind speed and directions on HAR. Understanding HAR helps to avoid undesirable work conditions. Three dimensional Computational Fluid Dynamics (CFD) studies were utilized to simulate the airflow around a full scale LNG plant. The simulations clearly captured HAR between parallel ACHE banks (Cross-HAR) and within a single ACHE unit (Self-HAR). Wind tunnel smoke visualization was used to qualitatively assess the CFD model. The impact of removing downstream ACHE protection screens on the HAR was computationally investigated showing an exhaust air temperature reduction of 5 °C. Different HAR mitigation methods were proposed using different configurations of side winglets. Horizontal winglets were shown to be more effective than vertical winglets as they decreased intake and exhaust air temperatures by about 5 °C and 8 °C respectively and increased exhaust air velocity by 1.2 m/s. This work provides a thorough understanding of HAR around ACHEs and proposes mitigation methods to reduce its effects on plant production.