The aerodynamic characteristics of projectiles with triangular and circular cross sections are investigated respectively by use of free-flight experiment.Processed the experiment data,curves of flight velocity variati...The aerodynamic characteristics of projectiles with triangular and circular cross sections are investigated respectively by use of free-flight experiment.Processed the experiment data,curves of flight velocity variation and nutation of both projectiles are obtained,based on the curves,their aerodynamic force and moment coefficients are found out by data fitting,and their aerodynamic performances are compared and analyzed.Results show that the projectile with triangular cross section has smaller resistance,higher lift-drag ratio,better static stability,higher stability capability and more excellent maneuverability than those of the projectile with circular cross section,therefore it can be used in the guided projectiles;under lower rotation speed,the triangular section projectile has greater Magnus moment leading to bigger projectile distribution.展开更多
Level set methods are widely used for predicting evolutions of complex free surface topologies,such as the crystal and crack growth,bubbles and droplets deformation,spilling and breaking waves,and two-phase flow pheno...Level set methods are widely used for predicting evolutions of complex free surface topologies,such as the crystal and crack growth,bubbles and droplets deformation,spilling and breaking waves,and two-phase flow phenomena.This paper presents a characteristic level set equation which is derived from the two-dimensional level set equation by using the characteristic-based scheme.An explicit finite volume element method is developed to discretize the equation on triangular grids.Several examples are presented to demonstrate the performance of the proposed method for calculating interface evolutions in time.The proposed level set method is also coupled with the Navier-Stokes equations for two-phase immiscible incompressible flow analysis with surface tension.The Rayleigh-Taylor instability problem is used to test and evaluate the effectiveness of the proposed scheme.展开更多
The characteristics of sedimentary petrology are significant in determining geological provenance. By using field outcrop observation and indoor identification of thin sections, the characteristics of Jurassic system ...The characteristics of sedimentary petrology are significant in determining geological provenance. By using field outcrop observation and indoor identification of thin sections, the characteristics of Jurassic system Tuchengzi Formation clastic rocks exposed in the Beijing Yanqing “flowerpot” basin, which include rock types, clastic composition and cement type, etc. have been analyzed systematically to identify the provenance direction and tectonic setting and nature of the provenance. Research shows that the sedimentary rocks in this area belong to analluvial fan and braided river sedimentary rock system and include mainly conglomerates, lithic sandstone, and feldspathic lithic sandstone. The main compositions of the conglomerate are dolomite and limestone. Nearly 50% to 70% of the sandstones are mainly polycrystalline quartz;10% to 15% are feldspar;and 40% to 55% are composed of debris from mainly magmatic and metamorphic rocks. A Dickinson triangular diagram indicates that the provenance type in this area is recycled orogny evolving from clastic recycled orogeny such as a collisional orogenic belt to a transitional recycled orogeny. On the basis of the geographic position and tectonic setting, three types of provenance can be identified in the Jurassic system Tuchengzi Formation. The far source provenances are Archean erathem basement metamorphic rocks in the northern basin and granite or adamellite that intruded rocks of the Late Jurassic epoch of the Yanshanian period in the northeast. The nearby provenance is the Mesoproterozoic erathem Changchengian system and Jixianianian system dolomite in both the east and west.展开更多
In order to explore the advantages of the triangular weir fishway and the influence of the angle of the triangular weir fishway on fish migration,this paper simulates the internal flow field and free surface of the fi...In order to explore the advantages of the triangular weir fishway and the influence of the angle of the triangular weir fishway on fish migration,this paper simulates the internal flow field and free surface of the fishway by using large eddy simulation(LES)and volume of fluid(VOF)method,respectively,and analyzes the hydraulic characteristics of the triangular weir at the three angles,where for the analysis of turbulent structure,omega(Ω)eddy identification is also used.And based on the analysis results,the length of the pool chamber and the height of obstacles were changed to obtain a more stable flow regime.The results show that the main flow is obvious,the turbulent kinetic energy distribution is regular and small in value,and the angle has an effect on the return flow.The vortex structure mainly existed in the mainstream area with high flow velocity,the air-liquid interface and the porosity,and was distributed transversely.90°triangular weir had the largest vortex structure,and 105°triangular weir had the smallest.75°triangular weir fishway could effectively attenuate the energy of the main stream,and the area of high velocity flow was small,which made the migratory conditions more favorable.Adding obstructions to the mainstem area can reduce flow velocity and turbulent kinetic energy.The triangular weir structure can improve the flow structure of the fishway,and the different angles and water depths provide a variety of flow conditions for a variety of fish migrations,providing new ideas for the fishway.展开更多
基金Sponsored by Foundation of National Defense Key Laboratory
文摘The aerodynamic characteristics of projectiles with triangular and circular cross sections are investigated respectively by use of free-flight experiment.Processed the experiment data,curves of flight velocity variation and nutation of both projectiles are obtained,based on the curves,their aerodynamic force and moment coefficients are found out by data fitting,and their aerodynamic performances are compared and analyzed.Results show that the projectile with triangular cross section has smaller resistance,higher lift-drag ratio,better static stability,higher stability capability and more excellent maneuverability than those of the projectile with circular cross section,therefore it can be used in the guided projectiles;under lower rotation speed,the triangular section projectile has greater Magnus moment leading to bigger projectile distribution.
基金King Mongkut’s University of Technology North Bangkok (KMUTNB)the Office of the Higher Education Commission (OHEC)the National Metal and Materials Technology Center (MTEC) for supporting this research work
文摘Level set methods are widely used for predicting evolutions of complex free surface topologies,such as the crystal and crack growth,bubbles and droplets deformation,spilling and breaking waves,and two-phase flow phenomena.This paper presents a characteristic level set equation which is derived from the two-dimensional level set equation by using the characteristic-based scheme.An explicit finite volume element method is developed to discretize the equation on triangular grids.Several examples are presented to demonstrate the performance of the proposed method for calculating interface evolutions in time.The proposed level set method is also coupled with the Navier-Stokes equations for two-phase immiscible incompressible flow analysis with surface tension.The Rayleigh-Taylor instability problem is used to test and evaluate the effectiveness of the proposed scheme.
文摘The characteristics of sedimentary petrology are significant in determining geological provenance. By using field outcrop observation and indoor identification of thin sections, the characteristics of Jurassic system Tuchengzi Formation clastic rocks exposed in the Beijing Yanqing “flowerpot” basin, which include rock types, clastic composition and cement type, etc. have been analyzed systematically to identify the provenance direction and tectonic setting and nature of the provenance. Research shows that the sedimentary rocks in this area belong to analluvial fan and braided river sedimentary rock system and include mainly conglomerates, lithic sandstone, and feldspathic lithic sandstone. The main compositions of the conglomerate are dolomite and limestone. Nearly 50% to 70% of the sandstones are mainly polycrystalline quartz;10% to 15% are feldspar;and 40% to 55% are composed of debris from mainly magmatic and metamorphic rocks. A Dickinson triangular diagram indicates that the provenance type in this area is recycled orogny evolving from clastic recycled orogeny such as a collisional orogenic belt to a transitional recycled orogeny. On the basis of the geographic position and tectonic setting, three types of provenance can be identified in the Jurassic system Tuchengzi Formation. The far source provenances are Archean erathem basement metamorphic rocks in the northern basin and granite or adamellite that intruded rocks of the Late Jurassic epoch of the Yanshanian period in the northeast. The nearby provenance is the Mesoproterozoic erathem Changchengian system and Jixianianian system dolomite in both the east and west.
基金supported by the National Natural Science Foundation of China(Grant No.52069009).
文摘In order to explore the advantages of the triangular weir fishway and the influence of the angle of the triangular weir fishway on fish migration,this paper simulates the internal flow field and free surface of the fishway by using large eddy simulation(LES)and volume of fluid(VOF)method,respectively,and analyzes the hydraulic characteristics of the triangular weir at the three angles,where for the analysis of turbulent structure,omega(Ω)eddy identification is also used.And based on the analysis results,the length of the pool chamber and the height of obstacles were changed to obtain a more stable flow regime.The results show that the main flow is obvious,the turbulent kinetic energy distribution is regular and small in value,and the angle has an effect on the return flow.The vortex structure mainly existed in the mainstream area with high flow velocity,the air-liquid interface and the porosity,and was distributed transversely.90°triangular weir had the largest vortex structure,and 105°triangular weir had the smallest.75°triangular weir fishway could effectively attenuate the energy of the main stream,and the area of high velocity flow was small,which made the migratory conditions more favorable.Adding obstructions to the mainstem area can reduce flow velocity and turbulent kinetic energy.The triangular weir structure can improve the flow structure of the fishway,and the different angles and water depths provide a variety of flow conditions for a variety of fish migrations,providing new ideas for the fishway.
