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D. Lummerzheim - One of the best experts on this subject based on the ideXlab platform.
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Magnetospheric reconnection driven by solar Wind Pressure fronts
Annales Geophysicae, 2004Co-Authors: A. Boudouridis, E. Zesta, L. R. Lyons, P. C. Anderson, D. LummerzheimAbstract:Recent work has shown that solar Wind dynamic Pressure changes can have a dramatic effect on the particle precipitation in the high-latitude ionosphere. It has also been noted that the preexisting interplanetary magnetic field (IMF) orientation can significantly affect the resulting changes in the size, location, and intensity of the auroral oval. Here we focus on the effect of Pressure pulses on the size of the auroral oval. We use particle precipitation data from up to four Defense Meteorological Satellite Program (DMSP) spacecraft and simultaneous POLAR Ultra-Violet Imager (UVI) images to examine three events of solar Wind Pressure fronts impacting the magnetosphere under two IMF orientations, IMF strongly southward and IMF Bz nearly zero before the Pressure jump. We show that the amount of change in the oval and polar cap sizes and the local time extent of the change depends strongly on IMF conditions prior to the Pressure enhancement. Under steady southward IMF, a remarkable poleward widening of the oval at all magnetic local times and shrinking of the polar cap are observed after the increase in solar Wind Pressure. When the IMF Bz is nearly zero before the Pressure pulse, a poleward widening of the oval is observed mostly on the nightside while the dayside remains unchanged. We interpret these differences in terms of enhanced magnetospheric reconnection and convection induced by the Pressure change. When the IMF is southward for a long time before the Pressure jump, open magnetic flux is accumulated in the tail and strong convection exists in the magnetosphere. The compression results in a great enhancement of reconnection across the tail which, coupled with an increase of magnetospheric convection, leads to a dramatic poleward expansion of the oval at all MLTs (dayside and nightside). For near-zero IMF Bz before the pulse the open flux in the tail, available for closing through reconnection, is smaller. This, in combination with the weaker magnetospheric convection, leads to a more limited poleward expansion of the oval, mostly on the nightside. Key words. Magnetospheric physics (solar Windmagnetosphere interactions; magnetospheric configuration and dynamics; auroral phenomena)
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effect of solar Wind Pressure pulses on the size and strength of the auroral oval
Journal of Geophysical Research, 2003Co-Authors: A. Boudouridis, E. Zesta, P. C. Anderson, R Lyons, D. LummerzheimAbstract:[1] It has recently been found that solar Wind dynamic Pressure changes can dramatically affect the precipitation of magnetospheric particles on the high-latitude ionosphere. We have examined the effect of large solar Wind dynamic Pressure increases on the location, size, and intensity of the auroral oval using particle precipitation data from Defense Meteorological Satellite Program (DMSP) spacecraft. Three events have been selected for study during the time period after 1997 when four DMSP spacecraft (F11–F14) were simultaneously operational. Interplanetary magnetic field (IMF) orientation is different from event to event. For each event, we determine equatorward and poleward boundaries of the auroral oval before and after an increase in solar Wind Pressure. Also, using measured integral fluxes, we construct precipitating particle energy input maps for the auroral oval. All cases studied show a significant change of the auroral oval location, size, and intensity in response to the solar Wind Pressure pulse. Most prominent are an increase of the auroral zone width and a decrease of the polar cap size when the solar Wind dynamic Pressure increases under steady southward IMF conditions. An increase in total precipitating particle energy flux is also observed. A smaller response is seen when the IMF Bz has a simultaneous northward turning and when it is nearly zero before the Pressure enhancement. Our results also point to significant differences between the auroral precipitation response to solar Wind Pressure changes and its response to isolated substorms, the former inducing a global auroral reaction while the latter is related to more localized premidnight disturbances. Auroral UV observations from the Polar spacecraft during our events are found to give results consistent with the results we get from the precipitating particle observations.
Ashok K. Ahuja - One of the best experts on this subject based on the ideXlab platform.
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Wind Pressure DISTRIBUTION ON CIRCULAR CANOPY ROOFS
Proceedings of International Structural Engineering and Construction, 2017Co-Authors: Neelam Rani, Ashok K. AhujaAbstract:The present study gives information related to Wind Pressure distribution on single span and multi span circular canopy roofs. The experiments are carried out in an open circuit boundary layer Wind tunnel. Wind Pressure is measured on both upper and lower roof surfaces of circular canopy roof model made of Perspex sheet. Models are tested under varying Wind incidence angles between 0° and 90° at an interval of 15° on isolated model and 0° to 180° at an interval of 30° on models with multi-span canopy roof. Values of mean Wind Pressure coefficients are evaluated from the measured values of Wind Pressures. Results of the study are presented in the form of contours, cross sectional variation and face average values of Pressure coefficients. The results of the study are of great use for the structural designers for designing circular canopy roofs.
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Wind Pressure Distribution on Domical Roofs
International Journal of Engineering and Applied Sciences, 2015Co-Authors: Astha Verma, Ashok K. AhujaAbstract:Present paper describes the details of the experimental study carried out on the models of low-rise buildings with domical roofs. Wind Pressure measurements are made on rigid models by placing them in an open circuit boundary layer Wind tunnel. The study includes square and rectangular plan buildings with one and two domes respectively. The experimental results of Pressure measurements are reported in the form of contours of mean Wind Pressure coefficients on the surfaces of domes. Results presented in the paper are of great use for the structural designers while designing buildings with domical roofs. The experts responsible for revising Wind-loading codes from time to time can also use these values.
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Wind Pressure Distribution on Trough Canopy Roofs
International Journal of Engineering and Applied Sciences, 2015Co-Authors: Pradeep Singh, Ashok K. AhujaAbstract:Wind tunnel experiments are carried out to obtain the Wind Pressure distribution on trough canopy roof. The model made of Perspex sheet at a scale of 1:100 is tested in open circuit Wind tunnel under boundary layer flow. Effects of Wind incidence angle are studied y changing Wind angle. Values of Wind Pressure coefficients are calculated from the values of Wind Pressures measured at numerous Pressure points on upper and lower surfaces of the trough roof and are reported in the form of cross sectional variation of Pressure coefficient and Pressure contours. It is observed that the Wind Pressure distribution on the trough canopy roof is highly influenced by incident Wind direction.
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Effect of Wind incidence angle on Wind Pressure distribution on tall buildings
International Journal of Managment IT and Engineering, 2013Co-Authors: Ritu Raj, Ashok K. AhujaAbstract:This paper presents the results of an experimental study carried out on the model of I-shape tall building to examine the Wind Pressure distribution on its different surfaces. The model of the building is tested in an open circuit boundary layer Wind tunnel under varying Wind incidence angles. Wind Pressure values measured at numerous Pressure points are used to calculate Wind Pressure coefficients and the experimental observations are presented in the form of Pressure contours. It is observed that the magnitudes of Pressure coefficients vary considerably with the location and Wind direction.
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Effects of Wind incidence angle on Wind Pressure distribution on square plan tall buildings
2013Co-Authors: S. K. Verma, Ashok K. Ahuja, A. D. PandeyAbstract:Experimental study was carried out on rigid model of a square plan tall building made of Perspex sheet in a closed circuit Wind tunnel under boundary layer flow. Wind Pressure coefficients are calculated from Wind Pressure values measured at many Pressure points on all 4-wall surfaces of the model. Purpose of the study is to generate large amount of data for the designers to be able to design structural frame as well as wall claddings safely under Wind loads. The results of the experimental study are presented in the form of Pressure contours.
A. Boudouridis - One of the best experts on this subject based on the ideXlab platform.
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Magnetospheric reconnection driven by solar Wind Pressure fronts
Annales Geophysicae, 2004Co-Authors: A. Boudouridis, E. Zesta, L. R. Lyons, P. C. Anderson, D. LummerzheimAbstract:Recent work has shown that solar Wind dynamic Pressure changes can have a dramatic effect on the particle precipitation in the high-latitude ionosphere. It has also been noted that the preexisting interplanetary magnetic field (IMF) orientation can significantly affect the resulting changes in the size, location, and intensity of the auroral oval. Here we focus on the effect of Pressure pulses on the size of the auroral oval. We use particle precipitation data from up to four Defense Meteorological Satellite Program (DMSP) spacecraft and simultaneous POLAR Ultra-Violet Imager (UVI) images to examine three events of solar Wind Pressure fronts impacting the magnetosphere under two IMF orientations, IMF strongly southward and IMF Bz nearly zero before the Pressure jump. We show that the amount of change in the oval and polar cap sizes and the local time extent of the change depends strongly on IMF conditions prior to the Pressure enhancement. Under steady southward IMF, a remarkable poleward widening of the oval at all magnetic local times and shrinking of the polar cap are observed after the increase in solar Wind Pressure. When the IMF Bz is nearly zero before the Pressure pulse, a poleward widening of the oval is observed mostly on the nightside while the dayside remains unchanged. We interpret these differences in terms of enhanced magnetospheric reconnection and convection induced by the Pressure change. When the IMF is southward for a long time before the Pressure jump, open magnetic flux is accumulated in the tail and strong convection exists in the magnetosphere. The compression results in a great enhancement of reconnection across the tail which, coupled with an increase of magnetospheric convection, leads to a dramatic poleward expansion of the oval at all MLTs (dayside and nightside). For near-zero IMF Bz before the pulse the open flux in the tail, available for closing through reconnection, is smaller. This, in combination with the weaker magnetospheric convection, leads to a more limited poleward expansion of the oval, mostly on the nightside. Key words. Magnetospheric physics (solar Windmagnetosphere interactions; magnetospheric configuration and dynamics; auroral phenomena)
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effect of solar Wind Pressure pulses on the size and strength of the auroral oval
Journal of Geophysical Research, 2003Co-Authors: A. Boudouridis, E. Zesta, P. C. Anderson, R Lyons, D. LummerzheimAbstract:[1] It has recently been found that solar Wind dynamic Pressure changes can dramatically affect the precipitation of magnetospheric particles on the high-latitude ionosphere. We have examined the effect of large solar Wind dynamic Pressure increases on the location, size, and intensity of the auroral oval using particle precipitation data from Defense Meteorological Satellite Program (DMSP) spacecraft. Three events have been selected for study during the time period after 1997 when four DMSP spacecraft (F11–F14) were simultaneously operational. Interplanetary magnetic field (IMF) orientation is different from event to event. For each event, we determine equatorward and poleward boundaries of the auroral oval before and after an increase in solar Wind Pressure. Also, using measured integral fluxes, we construct precipitating particle energy input maps for the auroral oval. All cases studied show a significant change of the auroral oval location, size, and intensity in response to the solar Wind Pressure pulse. Most prominent are an increase of the auroral zone width and a decrease of the polar cap size when the solar Wind dynamic Pressure increases under steady southward IMF conditions. An increase in total precipitating particle energy flux is also observed. A smaller response is seen when the IMF Bz has a simultaneous northward turning and when it is nearly zero before the Pressure enhancement. Our results also point to significant differences between the auroral precipitation response to solar Wind Pressure changes and its response to isolated substorms, the former inducing a global auroral reaction while the latter is related to more localized premidnight disturbances. Auroral UV observations from the Polar spacecraft during our events are found to give results consistent with the results we get from the precipitating particle observations.
Dongxue Zhao - One of the best experts on this subject based on the ideXlab platform.
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sensitivity analysis of Wind Pressure coefficients on caarc standard tall buildings in cfd simulations
Journal of building engineering, 2018Co-Authors: Fan Qin Meng, Dongxue Zhao, Jin Zhu, Amos Darko, Zi Qi ZhaoAbstract:Abstract Constructing tall buildings has been a common trend for many cities due to rapid increase of population, therefore, it is essential to analyze Wind Pressure around and over these tall buildings. CFD simulation is an effective approach to realize this, in which CAARC (Commonwealth Advisory Aeronautical Research Council) standard tall building has been a well-acknowledged model to validate and calibrate tall building models. Nevertheless, less work has been conducted to study sensitivity of Wind Pressures over CAARC standard tall building to geometric and computational parameters in CFD simulation. This paper is therefore designed to fill this gap by analysing impacts of various parameters like turbulence model, approaching-flow speed and grid type on Wind Pressure coefficients over CAARC buildings. In this paper, Wind Pressure coefficients over CAARC models subjected to four Wind directions were numerically analyzed for validating the correctness and effectiveness of numerical model. Sensitivity of Wind Pressures to geometric and computational parameters was analyzed through comparisons of deviation and absolute deviation. Results indicated that various phenomena such as fluid separation, vortex, wake effect and reattachment were sensitive to Wind direction, resulting in great variations in Wind Pressure. Maximum positive Wind Pressure coefficients emerged around 0.8–0.85 H of Windward surface, while maximum negative one occurred at foreside of top surface. Furthermore, turbulence model had significant influences on the accuracy of numerical results, where Realizable k-e and SST were the most accurate turbulence models, and standard k-e and RNG k-e models were the second accurate ones, but BSL was not recommended for Wind resistance design. Approaching-flow speed and grid type exerted insignificant influences on Pressure coefficient distribution, while grid resolution had significant effects on negative Wind Pressure distribution. In general, conclusions obtained in this study can assist structural engineers to select practical geometric and computational parameters in predicting Wind Pressure distribution against tall buildings.
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effects of architectural shapes on surface Wind Pressure distribution case studies of oval shaped tall buildings
Journal of building engineering, 2017Co-Authors: Dongxue Zhao, Baojie HeAbstract:Abstract Natural ventilation has been an important strategy for the improvement of indoor air quality and human thermal comfort, and the reduction of energy consumption of buildings. Many investigations have been conducted to examine the natural ventilation of low, multi-rise buildings rather than tall buildings. Starting from enlarging the Wind Pressure difference to create Wind-driven natural ventilation, this paper aims to analyze characteristics of surface Pressure coefficients over tall buildings and to identify the influence of building shapes on coefficient distribution. Taking oval-shaped high-rise buildings as examples, this paper numerically investigated the effects of height-width ratio (HWR) and height-thickness ratio (HTR) on mean Wind Pressure coefficients ( C m ) of building surfaces. Results indicated that Windward side of oval-shaped buildings suffered from positive Wind Pressure, while side, top and back surfaces were basically in negative Pressure areas. The absolute values of C m on building surfaces increased as the decrease of HWR. On the contrary, C m near central axis of side surfaces showed opponent trend due to fluid separation. In HTR scenario, C m on Windward and top surfaces were greatly affected, increasing along the HTR values. However, with the decrease of HTR, properties of Wind field on leeward surface changed. Through this work, the architects and HVAC engineers can get a master plan of in which place they can set possible openings for the creation of possible ventilation paths.
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numerical simulation of the effects of building dimensional variation on Wind Pressure distribution
Engineering Applications of Computational Fluid Mechanics, 2017Co-Authors: Ben Mou, Dongxue Zhao, Kwokwing ChauAbstract:ABSTRACTKnowledge of Wind effects is of great significance in structural, environmental, and architectural fields, where excessive relevance among Wind Pressure, building load, and natural ventilation has been formerly confirmed. Within the scope of high-rise buildings, functions of their layout, separation and height in altering Wind Pressure have been inquired on purpose, while a few investigations in relation to impacts of plane dimensions have been explored. This study consequently intends to ascertain Wind Pressure distributions on and around various squared-shaped tall buildings by the application of Computational Fluid Dynamics techniques. To start with, models established by the Common Advisory Aeronautical Research Council (CAARC) were simulated, for the purpose of correctness comparison, and reliability verification. Hereafter, Wind Pressure distributing on buildings was predicted under two scenarios, namely height-width (HW) and height-thickness (HT). Results evidenced that both HW ratio and HT...
Raymond M Zehr - One of the best experts on this subject based on the ideXlab platform.
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reexamination of tropical cyclone Wind Pressure relationships
Weather and Forecasting, 2007Co-Authors: John A Knaff, Raymond M ZehrAbstract:Abstract Tropical cyclone Wind–Pressure relationships are reexamined using 15 yr of minimum sea level Pressure estimates, numerical analysis fields, and best-track intensities. Minimum sea level Pressure is estimated from aircraft reconnaissance or measured from dropWindsondes, and maximum Wind speeds are interpolated from best-track maximum 1-min Wind speed estimates. The aircraft data were collected primarily in the Atlantic but also include eastern and central North Pacific cases. Global numerical analyses were used to estimate tropical cyclone size and environmental Pressure associated with each observation. Using this dataset (3801 points), the influences of latitude, tropical cyclone size, environmental Pressure, and intensification trend on the tropical cyclone Wind–Pressure relationships were examined. Findings suggest that latitude, size, and environmental Pressure, which all can be quantified in an operational and postanalysis setting, are related to predictable changes in the Wind–Pressure rela...
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Reexamination of Tropical Cyclone Wind–Pressure Relationships
Weather and Forecasting, 2007Co-Authors: John A Knaff, Raymond M ZehrAbstract:Abstract Tropical cyclone Wind–Pressure relationships are reexamined using 15 yr of minimum sea level Pressure estimates, numerical analysis fields, and best-track intensities. Minimum sea level Pressure is estimated from aircraft reconnaissance or measured from dropWindsondes, and maximum Wind speeds are interpolated from best-track maximum 1-min Wind speed estimates. The aircraft data were collected primarily in the Atlantic but also include eastern and central North Pacific cases. Global numerical analyses were used to estimate tropical cyclone size and environmental Pressure associated with each observation. Using this dataset (3801 points), the influences of latitude, tropical cyclone size, environmental Pressure, and intensification trend on the tropical cyclone Wind–Pressure relationships were examined. Findings suggest that latitude, size, and environmental Pressure, which all can be quantified in an operational and postanalysis setting, are related to predictable changes in the Wind–Pressure rela...
