In order to get some useful parameters for grid generation of catamaran, the CFD software FLUENT is used to investigate the main effects of grid generation on flow field calculation. The influences of some elements ar...In order to get some useful parameters for grid generation of catamaran, the CFD software FLUENT is used to investigate the main effects of grid generation on flow field calculation. The influences of some elements are investigated with a series of calculations in the present paper, and some alteratives are proposed. The proposed alteratives based on the analysis of the effects are used for a catamaran resistance calculation, comparisons of the calculated results with experimental data show good agreement. It shows that the research result of this paver is useful for the numerical calculation of catamaran.展开更多
When discussing the roots of Arab theatre, we find ourselves confronting two main streams of thought. The first one, represented by prominent Arab writers like Najib Mahfuz, Abbas A1-Aqqad, M. Badawi, and other critic...When discussing the roots of Arab theatre, we find ourselves confronting two main streams of thought. The first one, represented by prominent Arab writers like Najib Mahfuz, Abbas A1-Aqqad, M. Badawi, and other critics, rejects the theory that an Arab theatre existed before the mid-19th century. The second stream, represented by prominent scholars like Ali A1-Rai, Ibrahim Hamada and S. Moreh, see modern Arab theatre as part of a continuum, emphasizing of some elements of dramatic manifestations in Arab literary heritage. This paper intends to examine these two streams, their evidences and arguments. Such examination will shed some light on the origin of Arab theatre as a literary genre, and how it was influenced, if any, by Western theatrical heritage. Thus, answering the main question of this paper, whether Arab theatre is original or simply a Western imitation.展开更多
Dambreak-induced bed scouring may undermine the foundation of bridge piers and other structures,and that destruction can pose a serious threat.Consequently,this paper aims at exploring the mechanisms of scouring and a...Dambreak-induced bed scouring may undermine the foundation of bridge piers and other structures,and that destruction can pose a serious threat.Consequently,this paper aims at exploring the mechanisms of scouring and armoring.Firstly,the incipient velocity for nonuniform sediment particles was studied,and a formula was derived based on the angle of repose of nonuniform sediment.The results showed that the mechanism of incipient motion for sand and fine gravel differed from that for coarse gravel and cobbles.Also,comparison between experimental and field data shows that the results from the proposed formula agree well with those observed for all conditions.Secondly,a birth-death,immigration-emigration Markov process was developed to describe the bed load transport rate associated with scouring and armoring.The comparison between experimental data and computed results shows that our model can predict the bed load transport rate,although there may be some limitations,the chief of which is that there are many variables in the model to be determined through experiment.This makes its application in river engineering inconvenient.展开更多
Based on the EOF analyses of Absolute Dynamic Topography satellite data, it is found that, in summer, the northern South China Sea (SCS) is dominated by an anticyclonic gyre whilst by a cyclonic one in winter. A con...Based on the EOF analyses of Absolute Dynamic Topography satellite data, it is found that, in summer, the northern South China Sea (SCS) is dominated by an anticyclonic gyre whilst by a cyclonic one in winter. A connected single-layer and two-layer model is employed here to investigate the dynamic mechanism of the circulation in the northern SCS. Numerical experi- ments show that the nonlinear term, the pressure torque and the planetary vorticity adveetion play important roles in the circulation of the northern SCS, whilst the contribution by seasonal wind stress curl is local and limited. Only a small part of the Kuroshio water intrudes into the SCS, it then induces a positive vorticity band extending southwestward from the west of the Luzon Strait (LS) and a negative vorticity band along the 200 m isobath of the northern basin. The positive vorticity field induced by the local summer wind stress curl is weaker than that induced in winter in the northern SCS. Besides the Kuroshio intrusion and monsoon, the water trans- ports via the Sunda Shelf and the Sibutu Passage are also important to the circulation in the northern SCS, and the induced vorticity field in summer is almost contrary to that in winter. The strength variations of these three key factors (Kuroshio, monsoon and the water transports via the Sunda Shelf and the Sibutu Passage) determine the seasonal variations of the vorticity and eddy fields in the northern SCS. As for the water exchange via the LS, the Kuroshio intrusion brings about a net inflow into the SCS, and the monsoon has a less effect, whilst the water transports via the Sunda Shelf and the Sibutu Passage are the most important influencing factors, thus, the water exchange of the SCS with the Pacific via the LS changes dramatically from an outflow of the SCS in summer to an inflow into the SCS in winter.展开更多
An accurate prediction of flows using CFD depends on a large number of factors. In addition to discretizing the flow region, the correct definition of boundary or initial conditions and the choice of suitable numerica...An accurate prediction of flows using CFD depends on a large number of factors. In addition to discretizing the flow region, the correct definition of boundary or initial conditions and the choice of suitable numerical methods, the applied turbulence model influences the results of the flow simulation to a great extent. Therefore, a validation of the results with the experimental data is of great importance for a correct selection of a turbulence model. It is the scope of this paper to assess different turbulence models for the simulation of pipe flows. The calculation results of pipe flows through a combination of 90~ elbows and a 1/3 segmental orifice are compared with experimental measurement results. This has the advantage that the suitability of the turbulence models for simulating both shear and swirl flows can be investigated. Thus, the k-ω, k-ε model and the Launder Reece Rodi Reynolds stress model are compared with each other and experimental results. Furthermore, this investigation is extended through including a much more c detached-eddy simulation. This model provides better prediction of the flow by resolving the large eddies and modeling the small ones. The experimental results originate from LDV measurements over the entire pipe cross-section. This measuring method provides velocity vectors over the measured surface.展开更多
A new method is developed to assess and analyze the dynamic performance of hydrostatic bearing oil film by using an amulets-layer dynamic mesh technique. It is implemented using C Language to compile the UDF program o...A new method is developed to assess and analyze the dynamic performance of hydrostatic bearing oil film by using an amulets-layer dynamic mesh technique. It is implemented using C Language to compile the UDF program of a single oil film of the hydrostatic bearing. The effects of key lubrication parameters of the hydrostatic bearing are evaluated and analyzed under various working conditions,i.e. under no-load,a load of 40 t,a full load of 160 t,and the rotation speed of 1r/min,2r/min,4r/min,8r/min,16r/min,32r/min. The transient data of oil film bearing capacity under different load and rotation speed are acquired for a total of 18 working conditions during the oil film thickness changing. It allows the effective prediction of dynamic performance of large size hydrostatic bearing. Experiments on hydrostatic bearing oil film have been performed and the results were used to define the boundary conditions for the numerical simulations and validate the developed numerical model. The results showed that the oil film thickness became thinner with the increase of the operating time of the hydrostatic bearing,both the oil film rigidity and the oil cavity pressure increased significantly,and the increase of the bearing capacity was inversely proportional to the cube of the change of the film thickness. Meanwhile,the effect of the load condition on carrying capacity of large size static bearing was more important than the speed condition. The error between the simulation value and the experimental value was 4.25%.展开更多
The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable an...The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable and differs greatly between laboratory flumes and field streams. This paper presents an improved surface-based hiding fimction. The force balance for particle inception was formulated and the allocation of the overall bed shear stress into each group of sediments was mimicked. The new hiding function was examined against and agrees well with the documented field and flume data. It was shown that the hiding fimction is closely related to the relative flow depth and the reference elevation in the velocity profile in addition to the bed material gradation. The power law of velocity profile that applies to both flume flows and natural streams can link the flume and field data together. The hiding function with b = 1/6 and b = 1/2 is applicable to natural streams and laboratory flumes, respectively. The value orb = 0.263 also works well for gravel bed rivers. The range of the reference elevation, namely z0 = 0.4Dm-1.4Dm, is recommended for either the flume or field data. The new hiding function contributes to addressing clearer physical meanings and a useful perspective for further improvement.展开更多
The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed i...The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are pro- posed, especiaUy data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.展开更多
Seepage is a vital reason that may bring many adverse consequences such as subsidence,inclination and fracture to the channel,and is harmful to the safety and stability of the channel.Thus,a 3D visualization model is ...Seepage is a vital reason that may bring many adverse consequences such as subsidence,inclination and fracture to the channel,and is harmful to the safety and stability of the channel.Thus,a 3D visualization model is established for the engineering geological information of the research channel section by using NURBS-TIN-BRep hybrid data structure.Coupled with the VOF(volume of fluid)method,the N-S(Navier-Stokes)equations are applied to seepage simulation of the research channel section.Then the stability of the channel is studied coupled with the seepage simulation results,to comprehensively analyze the stress and displacement conditions of the channel under the impact of different factors such as seepage and underground goafs.The results of this study illustrate that the channel seepage has great influence on its stability,especially on the displacement field:it will lead to a significant sedimentation to the foundation.Therefore,during the practical construction,it is suggested that the certain part of the channel should be reinforced and effective seepage control measures should be taken.展开更多
基金Supported by the Foundation of Multihull Ship Technology,Key Laboratory of Fundamental Science for National Defence under Grant No.002010260737
文摘In order to get some useful parameters for grid generation of catamaran, the CFD software FLUENT is used to investigate the main effects of grid generation on flow field calculation. The influences of some elements are investigated with a series of calculations in the present paper, and some alteratives are proposed. The proposed alteratives based on the analysis of the effects are used for a catamaran resistance calculation, comparisons of the calculated results with experimental data show good agreement. It shows that the research result of this paver is useful for the numerical calculation of catamaran.
文摘When discussing the roots of Arab theatre, we find ourselves confronting two main streams of thought. The first one, represented by prominent Arab writers like Najib Mahfuz, Abbas A1-Aqqad, M. Badawi, and other critics, rejects the theory that an Arab theatre existed before the mid-19th century. The second stream, represented by prominent scholars like Ali A1-Rai, Ibrahim Hamada and S. Moreh, see modern Arab theatre as part of a continuum, emphasizing of some elements of dramatic manifestations in Arab literary heritage. This paper intends to examine these two streams, their evidences and arguments. Such examination will shed some light on the origin of Arab theatre as a literary genre, and how it was influenced, if any, by Western theatrical heritage. Thus, answering the main question of this paper, whether Arab theatre is original or simply a Western imitation.
基金supported by 973 Program (2008CB425803)the National Natural Science Foundation of China (Grant No. 50979064)
文摘Dambreak-induced bed scouring may undermine the foundation of bridge piers and other structures,and that destruction can pose a serious threat.Consequently,this paper aims at exploring the mechanisms of scouring and armoring.Firstly,the incipient velocity for nonuniform sediment particles was studied,and a formula was derived based on the angle of repose of nonuniform sediment.The results showed that the mechanism of incipient motion for sand and fine gravel differed from that for coarse gravel and cobbles.Also,comparison between experimental and field data shows that the results from the proposed formula agree well with those observed for all conditions.Secondly,a birth-death,immigration-emigration Markov process was developed to describe the bed load transport rate associated with scouring and armoring.The comparison between experimental data and computed results shows that our model can predict the bed load transport rate,although there may be some limitations,the chief of which is that there are many variables in the model to be determined through experiment.This makes its application in river engineering inconvenient.
基金supported by theNational Natural Foundation of China (NSFC) Grants Nos. 41025019,40976009 and 41206009
文摘Based on the EOF analyses of Absolute Dynamic Topography satellite data, it is found that, in summer, the northern South China Sea (SCS) is dominated by an anticyclonic gyre whilst by a cyclonic one in winter. A connected single-layer and two-layer model is employed here to investigate the dynamic mechanism of the circulation in the northern SCS. Numerical experi- ments show that the nonlinear term, the pressure torque and the planetary vorticity adveetion play important roles in the circulation of the northern SCS, whilst the contribution by seasonal wind stress curl is local and limited. Only a small part of the Kuroshio water intrudes into the SCS, it then induces a positive vorticity band extending southwestward from the west of the Luzon Strait (LS) and a negative vorticity band along the 200 m isobath of the northern basin. The positive vorticity field induced by the local summer wind stress curl is weaker than that induced in winter in the northern SCS. Besides the Kuroshio intrusion and monsoon, the water trans- ports via the Sunda Shelf and the Sibutu Passage are also important to the circulation in the northern SCS, and the induced vorticity field in summer is almost contrary to that in winter. The strength variations of these three key factors (Kuroshio, monsoon and the water transports via the Sunda Shelf and the Sibutu Passage) determine the seasonal variations of the vorticity and eddy fields in the northern SCS. As for the water exchange via the LS, the Kuroshio intrusion brings about a net inflow into the SCS, and the monsoon has a less effect, whilst the water transports via the Sunda Shelf and the Sibutu Passage are the most important influencing factors, thus, the water exchange of the SCS with the Pacific via the LS changes dramatically from an outflow of the SCS in summer to an inflow into the SCS in winter.
文摘An accurate prediction of flows using CFD depends on a large number of factors. In addition to discretizing the flow region, the correct definition of boundary or initial conditions and the choice of suitable numerical methods, the applied turbulence model influences the results of the flow simulation to a great extent. Therefore, a validation of the results with the experimental data is of great importance for a correct selection of a turbulence model. It is the scope of this paper to assess different turbulence models for the simulation of pipe flows. The calculation results of pipe flows through a combination of 90~ elbows and a 1/3 segmental orifice are compared with experimental measurement results. This has the advantage that the suitability of the turbulence models for simulating both shear and swirl flows can be investigated. Thus, the k-ω, k-ε model and the Launder Reece Rodi Reynolds stress model are compared with each other and experimental results. Furthermore, this investigation is extended through including a much more c detached-eddy simulation. This model provides better prediction of the flow by resolving the large eddies and modeling the small ones. The experimental results originate from LDV measurements over the entire pipe cross-section. This measuring method provides velocity vectors over the measured surface.
基金Supported by the National Natural Science Foundation of China(No.51005063,51375123)National Science and Technology Cooperation Projects of China(No.2012DFR70840)
文摘A new method is developed to assess and analyze the dynamic performance of hydrostatic bearing oil film by using an amulets-layer dynamic mesh technique. It is implemented using C Language to compile the UDF program of a single oil film of the hydrostatic bearing. The effects of key lubrication parameters of the hydrostatic bearing are evaluated and analyzed under various working conditions,i.e. under no-load,a load of 40 t,a full load of 160 t,and the rotation speed of 1r/min,2r/min,4r/min,8r/min,16r/min,32r/min. The transient data of oil film bearing capacity under different load and rotation speed are acquired for a total of 18 working conditions during the oil film thickness changing. It allows the effective prediction of dynamic performance of large size hydrostatic bearing. Experiments on hydrostatic bearing oil film have been performed and the results were used to define the boundary conditions for the numerical simulations and validate the developed numerical model. The results showed that the oil film thickness became thinner with the increase of the operating time of the hydrostatic bearing,both the oil film rigidity and the oil cavity pressure increased significantly,and the increase of the bearing capacity was inversely proportional to the cube of the change of the film thickness. Meanwhile,the effect of the load condition on carrying capacity of large size static bearing was more important than the speed condition. The error between the simulation value and the experimental value was 4.25%.
基金the Beijing Municipal Science&Technology Project(Grant No.Z141100003614052)the National Natural Science Foundation of China(Grants No.51525901&51379100)as well as by China Ministry of Science and Technology(Grant No.2011CB409901)
文摘The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable and differs greatly between laboratory flumes and field streams. This paper presents an improved surface-based hiding fimction. The force balance for particle inception was formulated and the allocation of the overall bed shear stress into each group of sediments was mimicked. The new hiding function was examined against and agrees well with the documented field and flume data. It was shown that the hiding fimction is closely related to the relative flow depth and the reference elevation in the velocity profile in addition to the bed material gradation. The power law of velocity profile that applies to both flume flows and natural streams can link the flume and field data together. The hiding function with b = 1/6 and b = 1/2 is applicable to natural streams and laboratory flumes, respectively. The value orb = 0.263 also works well for gravel bed rivers. The range of the reference elevation, namely z0 = 0.4Dm-1.4Dm, is recommended for either the flume or field data. The new hiding function contributes to addressing clearer physical meanings and a useful perspective for further improvement.
基金supported by the Science Foundation of National University of Defense Technology (No. JC11-01-02)the Hunan Provincial Natural Science Foundation of China (No.12jj4047)
文摘The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are pro- posed, especiaUy data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.
基金supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No.51021004)the National Basic Research Program of China ("973" Program) (Grant No. 2013CB035904)National Key Technology R&D Program in the 12th Five-Year Plan of China (Grant No. 2011BAB10B06)
文摘Seepage is a vital reason that may bring many adverse consequences such as subsidence,inclination and fracture to the channel,and is harmful to the safety and stability of the channel.Thus,a 3D visualization model is established for the engineering geological information of the research channel section by using NURBS-TIN-BRep hybrid data structure.Coupled with the VOF(volume of fluid)method,the N-S(Navier-Stokes)equations are applied to seepage simulation of the research channel section.Then the stability of the channel is studied coupled with the seepage simulation results,to comprehensively analyze the stress and displacement conditions of the channel under the impact of different factors such as seepage and underground goafs.The results of this study illustrate that the channel seepage has great influence on its stability,especially on the displacement field:it will lead to a significant sedimentation to the foundation.Therefore,during the practical construction,it is suggested that the certain part of the channel should be reinforced and effective seepage control measures should be taken.