Particulate pollution is a serious health problem throughout the world, exacerbating a wide range of respiratory and vascular illnesses in urban areas. Urban plants play an important role in reducing particulate pollu...Particulate pollution is a serious health problem throughout the world, exacerbating a wide range of respiratory and vascular illnesses in urban areas. Urban plants play an important role in reducing particulate pollution. Physicochemical characteristics of ambient particles settling upon leaf surfaces of eleven roadside plants at four sites of Beijing were studies. Results showed that density of particles on the leaf surfaces greatly varied with plant species and traffic condition. Fraxinus chiuensis, Sophora japonica Ailanthus altissima, Syringa oblata and Prunus persica, had larger densities of particles among the tall species. Due to resuspension of road dust, the densities of particles of Euonymus japonicns and Parthenocissus quinquefolia with low sampling height were 2-35 times to other taller tree species. For test plant species, micro-roughness of leaf surfaces and density of particles showed a close correlation. In general, the larger micro-roughness of leaf surfaces is, the larger density of particles is. Particles settling upon leaf surfaces were dominantly PM30 （particulate matter less than 10 μm in aerodynamic diameter; 98.4%） and PM2.5 （particulate matter less than 2.5 μm in aerodynamic diameter; 64.2%） which were closely relative to human health. Constant elements of particles were C, O, K, Ca, Si, Al, Mg, Na, Fe, S, Cl and minerals with higher content were SiO2, CaCO3, CaMg（CO3）2, NaCI and 2CASO4. H2O, SiO2. CaCO3 and CaMg（CO3）2 mainly came from resuspension of road dust. 2CaSO4. H2O was produced by the reaction between CaCO3 derived from earth dust or industrial emission and SO2, H2SO4 or sulfate. NaCl was derived from sea salt.展开更多
In this paper, the relative orbital configurations of satellites in formation flying with non-perturbation and J<SUB>2</SUB> perturbation are studied, and an orbital elements method is proposed to obtain t...In this paper, the relative orbital configurations of satellites in formation flying with non-perturbation and J<SUB>2</SUB> perturbation are studied, and an orbital elements method is proposed to obtain the relative orbital configurations of satellites in formation. Firstly, under the condition of non-perturbation, we obtain many shapes of relative orbital configurations when the semi-major axes of satellites are equal. These shapes can be lines, ellipses or distorted closed curves. Secondly, on the basis of the analysis of J<SUB>2</SUB> effect on relative orbital configurations, we find out that J<SUB>2</SUB> effect can induce two kinds of changes of relative orbital configurations. They are distortion and drifting, respectively. In addition, when J<SUB>2</SUB> perturbation is concerned, we also find that the semi-major axes of the leading and following satellites should not be the same exactly in order to decrease the J<SUB>2</SUB> effect. The relationship of relative orbital elements and J<SUB>2</SUB> effect is obtained through simulations. Finally, the minimum relation perturbation conditions are established in order to reduce the influence of the J<SUB>2</SUB> effect. The results show that the minimum relation perturbation conditions can reduce the J<SUB>2</SUB> effect significantly when the orbital element differences are small enough, and they can become rules for the design of satellite formation flying.展开更多
We employed the discrete element method to study the effects of the impeller configuration(i.e.,blade diameter,inclination angle,and blade number),rotational speed,and fill level on the flow and mixing of particles in...We employed the discrete element method to study the effects of the impeller configuration(i.e.,blade diameter,inclination angle,and blade number),rotational speed,and fill level on the flow and mixing of particles in a cylindrical mixer equipped with flat and inclined blades.The coefficient of rolling friction,coefficient of static friction,and coefficient of restitution were experimentally determined before the simulation,and simulation results of the torque and surface particle distribution were validated in experiments,particularly when using a true Young's modulus in the discrete element method.The performance of the mixer was assessed using the Lacey mixing index.The input work per unit volume was used to represent the mixing efficiency.The circumferential velocity and axial diffusion coefficient of the particles were quantitatively analyzed to reveal the effect of particle flow on the mixing.It was found that the mixing performance and efficiency of a three-blade mixer are better than those of two-and four-blade mixers.For pitched blades,a three-fiat-blade mixer has better mixing performance than a three-45°-blade own-pumping or a three-45°-blade up-pumping mixer,but the mixing efficiency of the three-45°-blade up-pumping mixer is the best among these three mixers.As the rotational speed increases,the mixing performance improves but the mixing efficiency hardly changes.When the fill level is 0.4 times the cylinder diameter,the 160D two-flat-blade mixer has good mixing performance with high mixing efficiency.The circumferential velocity has the greatest effect on mixing performance for side-by-side initial loading.展开更多
The joined-wing configuration reduces induced drag and structural weight by connecting the rear wing to the front wing.In addition,the rear wing can replace the role of the horizontal tail of a conventional aircraft,t...The joined-wing configuration reduces induced drag and structural weight by connecting the rear wing to the front wing.In addition,the rear wing can replace the role of the horizontal tail of a conventional aircraft,thus eliminating the aerodynamic drag and weight associated with the horizontal tail.This particular shape creates a highly coupled relationship between aerodynamics and structure,which must be fully considered during the overall design process to enhance aircraft performance.In this research,an aero-structural design model of the joined-wing aircraft is constructed based on high-fidelity computational fluid dynamics and structural finite element methods.The model is able to obtain accurate aerodynamic loads for the non-planar wing and to simulate the statically indeterminate structure of the closed wing configuration.The influence of the joined-wing shape parameters on the aerodynamic and structural disciplines,as well as the influence of geometric nonlinear characteristics,deformation constraints and buckling constraints on the structural weight are all taken into consideration.The model is applied to complete the aero-structural design optimization of a high-altitude long-endurance joined-wing aircraft,and wind tunnel tests are conducted.The test results verify the credibility of the design model proposed and the validity of the design environment.展开更多
基金The National Natural Science Foundation of China (No. 30570338) the Natural Science Foundation of Beijing (No. 6053026) andthe Ministry of Education, China(No. 20040027020).
文摘Particulate pollution is a serious health problem throughout the world, exacerbating a wide range of respiratory and vascular illnesses in urban areas. Urban plants play an important role in reducing particulate pollution. Physicochemical characteristics of ambient particles settling upon leaf surfaces of eleven roadside plants at four sites of Beijing were studies. Results showed that density of particles on the leaf surfaces greatly varied with plant species and traffic condition. Fraxinus chiuensis, Sophora japonica Ailanthus altissima, Syringa oblata and Prunus persica, had larger densities of particles among the tall species. Due to resuspension of road dust, the densities of particles of Euonymus japonicns and Parthenocissus quinquefolia with low sampling height were 2-35 times to other taller tree species. For test plant species, micro-roughness of leaf surfaces and density of particles showed a close correlation. In general, the larger micro-roughness of leaf surfaces is, the larger density of particles is. Particles settling upon leaf surfaces were dominantly PM30 （particulate matter less than 10 μm in aerodynamic diameter; 98.4%） and PM2.5 （particulate matter less than 2.5 μm in aerodynamic diameter; 64.2%） which were closely relative to human health. Constant elements of particles were C, O, K, Ca, Si, Al, Mg, Na, Fe, S, Cl and minerals with higher content were SiO2, CaCO3, CaMg（CO3）2, NaCI and 2CASO4. H2O, SiO2. CaCO3 and CaMg（CO3）2 mainly came from resuspension of road dust. 2CaSO4. H2O was produced by the reaction between CaCO3 derived from earth dust or industrial emission and SO2, H2SO4 or sulfate. NaCl was derived from sea salt.
基金The project supported by the National Natural Science Foundation of China(10202008)Specialized Research Fund for the Doctoral Program of Higher Education(20020003024)
文摘In this paper, the relative orbital configurations of satellites in formation flying with non-perturbation and J<SUB>2</SUB> perturbation are studied, and an orbital elements method is proposed to obtain the relative orbital configurations of satellites in formation. Firstly, under the condition of non-perturbation, we obtain many shapes of relative orbital configurations when the semi-major axes of satellites are equal. These shapes can be lines, ellipses or distorted closed curves. Secondly, on the basis of the analysis of J<SUB>2</SUB> effect on relative orbital configurations, we find out that J<SUB>2</SUB> effect can induce two kinds of changes of relative orbital configurations. They are distortion and drifting, respectively. In addition, when J<SUB>2</SUB> perturbation is concerned, we also find that the semi-major axes of the leading and following satellites should not be the same exactly in order to decrease the J<SUB>2</SUB> effect. The relationship of relative orbital elements and J<SUB>2</SUB> effect is obtained through simulations. Finally, the minimum relation perturbation conditions are established in order to reduce the influence of the J<SUB>2</SUB> effect. The results show that the minimum relation perturbation conditions can reduce the J<SUB>2</SUB> effect significantly when the orbital element differences are small enough, and they can become rules for the design of satellite formation flying.
基金The authors gratefully acknowledge financial support from the Scientific Research and Technology Development Projects of the China National Petroleum Corporation(No.2016B-2605).
文摘We employed the discrete element method to study the effects of the impeller configuration(i.e.,blade diameter,inclination angle,and blade number),rotational speed,and fill level on the flow and mixing of particles in a cylindrical mixer equipped with flat and inclined blades.The coefficient of rolling friction,coefficient of static friction,and coefficient of restitution were experimentally determined before the simulation,and simulation results of the torque and surface particle distribution were validated in experiments,particularly when using a true Young's modulus in the discrete element method.The performance of the mixer was assessed using the Lacey mixing index.The input work per unit volume was used to represent the mixing efficiency.The circumferential velocity and axial diffusion coefficient of the particles were quantitatively analyzed to reveal the effect of particle flow on the mixing.It was found that the mixing performance and efficiency of a three-blade mixer are better than those of two-and four-blade mixers.For pitched blades,a three-fiat-blade mixer has better mixing performance than a three-45°-blade own-pumping or a three-45°-blade up-pumping mixer,but the mixing efficiency of the three-45°-blade up-pumping mixer is the best among these three mixers.As the rotational speed increases,the mixing performance improves but the mixing efficiency hardly changes.When the fill level is 0.4 times the cylinder diameter,the 160D two-flat-blade mixer has good mixing performance with high mixing efficiency.The circumferential velocity has the greatest effect on mixing performance for side-by-side initial loading.
基金supported by the Fundamental Research FundsfortheCentralUniversities,China(No. 56XCA2205402)。
文摘The joined-wing configuration reduces induced drag and structural weight by connecting the rear wing to the front wing.In addition,the rear wing can replace the role of the horizontal tail of a conventional aircraft,thus eliminating the aerodynamic drag and weight associated with the horizontal tail.This particular shape creates a highly coupled relationship between aerodynamics and structure,which must be fully considered during the overall design process to enhance aircraft performance.In this research,an aero-structural design model of the joined-wing aircraft is constructed based on high-fidelity computational fluid dynamics and structural finite element methods.The model is able to obtain accurate aerodynamic loads for the non-planar wing and to simulate the statically indeterminate structure of the closed wing configuration.The influence of the joined-wing shape parameters on the aerodynamic and structural disciplines,as well as the influence of geometric nonlinear characteristics,deformation constraints and buckling constraints on the structural weight are all taken into consideration.The model is applied to complete the aero-structural design optimization of a high-altitude long-endurance joined-wing aircraft,and wind tunnel tests are conducted.The test results verify the credibility of the design model proposed and the validity of the design environment.
