快速路分、合流影响区交通特性及通行能力研究

分、合流区通行能力是影响快速路通行能力的重要因素之一,而分、合流影响区的通行能力是制约分、合流区通行能力的关键原因。文章从分析分、合流影响区内的车辆运行特性入手,根据北京、上海、广州等城市大量的实测数据,分别通过统计车头时距、速度-流量关系和饱和流时高频率出现的流率等方法推荐了快速路分、合流影响区的通行能力,为快速路分、合流区的交通规划和设计,交通组织和管理的改善提供了理论基础。

Microstructural evolution and mechanical properties of AZ31 Mg alloy fabricated by a novel bifurcation-equal channel angular pressing

In this work,a novel type of short-process deformation technology of Mg alloys,bifurcation-equal channel angular pressing(B-ECAP),was proposed to refine grain and improve the basal texture.The cylindrical billets were first compressed into the die cavity,then sequentially flowed downward through a 90°corner and two 120°shear steps.The total strain of B-ECAP process could reach 3.924 in a single pass.The results of microstructure observation showed that DRX occurred at upsetting process in the die cavity and completed at position D.The grains were refined to 6.3μm at being extruded at 300℃ and grew obviously with the extrusion temperature increase.The shear tress induced by 900 corner and two 120°shear steps resulted in the basal poles of most grains tilted to extrusion direction(ED)by±25°.Compared with the original billets,the extruded sheets exhibited higher yield strengths(YS),which was mainly attributed to the grain refinement.The higher Schmid factor caused by ED-tilt texture resulted in a fracture elongation(FE)more than that of the original bar in ED,while was equivalent to that in transverse direction(TD).As the extrusion temperature increased,the variation of UTS and YS in ED and TD decreased gradually without ductility obviously decrease.

Zonal Coupling Analysis Method of Seismic Response of Offshore Monopile Wind Turbine

The seismic safety of offshore wind turbines is an important issue that needs to be solved urgently.Based on a unified computing framework,this paper develops a set of seawater-seabed-wind turbine zoning coupling analysis methods.A 5 MW wind turbine and a site analysis model are established,and a seismic wave is selected to analyze the changes in the seismic response of offshore monopile wind turbines under the change of seawater depth,seabed wave velocity and seismic wave incidence angle.The analysis results show that when the seawater increases to a certain depth,the seismic response of the wind turbine increases.The shear wave velocity of the seabed affects the bending moment and displacement at the bottom of the tower.When the angle of incidence increases,the vertical displacement and the acceleration of the top of the tower increase in varying degrees.

辅助车道与集散车道在互通立交中的应用

在互通式立体交叉设计中，设置双车道的分、合流处，应保持基本车道数的连续性，并维持车道数的平衡，必要时应增设辅助车道。当不能保证主线出入口间的应有距离或遏转弯车流的紧迫交织干扰主线车流时，应采用与主线相分隔的集散道将出入口串联起来。本文以互通立交设计实例对集散道和辅助车道进行详细介绍。

Oxide distribution and microstructure in welding zones from porthole die extrusion

The oxide distribution and microstructure in longitudinal and transverse welding zones during the billet-to-billet extrusion process through porthole die were adequately investigated by means of finite element method,scanning electron microscopy and optical microscopy.The results indicate that the oxides exist at the interface between the matrix and transverse welding zone rather than longitudinal welding seam.The longitudinal welding zone reveals a darker band including the largest grain with irregular shape due to the abnormal grain growth under the heavy shear deformation and high temperature.The transverse welding zone consists of equiaxed recrystallized grains which are a little finer than those in the longitudinal welding seam.

Thermal analysis for brake disks of SiC/6061 Al alloy co-continuous composite for CRH3 during emergency braking considering airflow cooling

The mass of high-speed trains can be reduced using the brake disk prepared with SiC network ceramic frame reinforced 6061 aluminum alloy composite （SiCn/Al）. The thermal and stress analyses of SiCn/Al brake disk during emergency braking at a speed of 300 km/h considering airflow cooling were investigated using finite element （FE） and computational fluid dynamics （CFD） methods. All three modes of heat transfer （conduction, convection and radiation） were analyzed along with the design features of the brake assembly and their interfaces. The results suggested that the higher convection coefficients achieved with airflow cooling will not only reduce the maximum temperature in the braking but also reduce the thermal gradients, since heat will be removed faster from hotter parts of the disk. Airflow cooling should be effective to reduce the risk of hot spot formation and disc thermal distortion. The highest temperature after emergency braking was 461 °C and 359 °C without and with considering airflow cooling, respectively. The equivalent stress could reach 269 MPa and 164 MPa without and with considering airflow cooling, respectively. However, the maximum surface stress may exceed the material yield strength during an emergency braking, which may cause a plastic damage accumulation in a brake disk without cooling. The simulation results are consistent with the experimental results well.

CFD-supported optimization of flow distribution in quench tank for heat treatment of A357 alloy large complicated components

The flow distribution in quench tank for heat treatment of A357 alloy large complicated components was simulated using FLUENT computational fluid dynamics（CFD） software.The flow velocity and the uniformity of flow field in two types of quench tanks（with or without agitation system） were calculated.The results show that the flow field in the quench tank without agitation system has not evident regularity.While as for the quench tank with agitation system,the flow fields in different parameters have certain regularity.The agitation tanks have a distinct advantage over the system without agitation.Proper process parameters were also obtained.Finally,the tank model established in this work was testified by an example from publication.This model with high accuracy is able to optimize the tank structures and can be helpful for industrial production and theoretical investigation in the fields of heat treatment of large complicated components.

Context-attributed graph grammar framework for specifying visual languages

Since the specifications of most of the existing context-sensitive graph grammars tend to be either too intricate or not intuitive, a novel context-sensitive graph grammar formalism, called context-attributed graph grammar（CAGG）, is proposed. In order to resolve the embedding problem, context information of a graph production in the CAGG is represented in the form of context attributes of the nodes involved. Moreover, several properties of a set of confluent CAGG productions are characterized, and then an algorithm based on them is developed to decide whether or not a set of productions is confluent, which provides the foundation for the design of efficient parsing algorithms. It can also be shown through the comparison of CAGG with several typical context-sensitive graph grammars that CAGG is more succinct and, at the same time, more intuitive than the others, making it more suitably and effortlessly applicable to the specification of visual languages.

城市道路加减速车道长度取值的研究与探讨

结合城市高架快速道路匝道出入口勘察设计实践,本文针对城市道路平行式加减速车道长度的设计进行研究与探讨,提出科学合理的设计方案与长度取值,选用合理的设计规范。

Bi-level programming model and algorithm for optimizing headway of public transit line

Due to the fact that headway is a key factor to be considered in bus scheduling, this paper proposes a bi-level programming model for optimizing bus headway in public transit lines. In this model, with the interests of bus companies and passengers in mind, the upper-level model＇s objective is to minimize the total cost, which is affected by frequency settings, both in time and economy in the transit system. The lower-level model is a transit assignment model used to describe the assignment of passengers＇ trips to the network based on the optimal bus headway. In order to solve the proposed model, a hybrid genetic algorithm, namely the genetic algorithm and the simulated annealing algorithm （GA-SA）, is designed. Finally, the model and the algorithm are tested against the transit data, by taking some of the bus lines of Changzhou city as an example. Results indicate that the proposed model allows supply and demand to be linked, which is reasonable, and the solving algorithm is effective.

EXPERIMENT ON FLOW CHARACTERISTICS OF SYNTHETIC JET DRIVEN BY PIEZOELECTRIC MEMBRANE

The characteristics of the flowfields of a synthetic jet actuator are experimentally investigated with the slot-nozzle driven by the piezoelectric membrane. The particle image velocimetry （PIV） and the hot-wire anemometer are utilized to measure the flowfields and the velocity profiles of the actuator with different actuating factors. Analytical results show that pairs of counter-rotating vortices are generated near the nozzle. With the development of the synthetic ject, the synthetic jet rapidly spreads in the slot-width direction; while in the slot-length direction, it contracts firstly and slowly spreads. The centerline velocity distribution has a up-down tendency varying with axial distances, and accelerates to its maximum at z/b= 10. The transverse velocity profile across the slot-width is centro-symmetric and self-similar. However, the velocity profiles across the slot-length are saddle-like near the nozzle. It shows that there are two resonance frequencies for the actuator. If the actuator works with the resonance frequency, the vorticity and the velocity of the synthetic jet are higher than those of other frequencies. Compared with the continuous jet, the synthetic jet shows special flow characteristics.

New technique for preparing A356 alloy semisolid slurry and its rheo-diecast microstructure and properties

A new technique for preparing semisolid slurry,namely,distributary-confluence runner(DCR),was combined with die-casting(DC)to conduct rheological die-casting(R-DC)of A356 alloy.The mechanism of DCR for semisolid slurry preparation was determined via numerical simulations and experiments.The microstructure and mechanical properties of A356 alloys prepared via DC and R-DC were studied.High-quality slurry containing numerous primary α-Al(α1-Al)with an average size of 49μm and a shape factor of 0.81 could be prepared via DCR.Simulation results indicated that the unique flow state and physical field changes during slurry preparation were conducive to accelerating the uniformity of melt temperature and composition fields,nucleation exfoliation,and spherical growth.Compared with the alloy prepared via DC,the tensile strength,yield strength,and elongation of A356 alloy prepared via R-DC increased by 19%,15%,and 107%,respectively.

Veno occlusive disease: Update on clinical management

Hepatic veno-occlusive disease is a clinical syndrome characterized by hepatomegaly, ascites, weight gain and jaundice, due to sinusoidal congestion which can be caused by alkaloid ingestion, but the most frequent cause is haematopoietic stem cell transplantation （STC） and is also seen after solid organ transplantation. The incidence of veno occlusive disease （VOD） after STC ranges from 0 to 70%, but is decreasing. Survival is good when VOD is a mild form, but when it is severe and associated with an increase of hepatic venous pressure gradient 〉 20 mmHg, and mortality is about 90%. Prevention remains the best therapeutic strategy, by using non-myeloablative conditioning regimens before STC. Prophylactic administration of ursodeoxycholic add, being an antioxidant and antiapoptotic agent, can have some benefit in reducing overall mortality. Defibrotide, which has pro-fibrinolytic and antithrombotic properties, is the most effective therapy; decompression of the sinusoids by a b-ansjugular intrahepatic portosystemic shunt （TIPS） can be tried, especially to treat VOD after liver transplantation and when multiorgan failure （HOF） is not present. Liver transplantation can be the last option, but can not be considered a standard rescue therapy, because usually the concomitant presence of multiorgan failure contraindicates this procedure.

Effects of different poses and wind speeds on flow field of dish solar concentrator based on virtual wind tunnel experiment with constant wind

In order to improve structure performance of the dish solar concentrator,a three-dimensional model of dish solar concentrator was established based on the high-precision numerical algorithms.And a virtual wind tunnel experiment with constant wind is adopted to investigate the pressure distribution of the reflective surface,velocity distribution of the fluid domain for the dish solar concentrator in different poses and wind speeds distribution.Some results about wind pressure distribution before and after dish solar concentrator surface and wind load velocity distribution in the entire fluid domain had been obtained.In particular,it is necessary to point out that the stiffness at the center of the dish solar concentrator should be relatively raised.The results can provide a theoretical basis for the improvement of solar concentrator dish structure as well as the failure analysis of dish solar concentrator in engineering practice.

Fluid solid coupling model based on endochronic damage for roller compacted concrete dam

According to the characteristics of thin-layer rolling and pouting construction technology and the complicated mechanical behavior of the roller compacted concrete dam （RCCD） construction interface, a constitutive model of endochronic damage was established based on the endochronic theory and damage mechanics. The proposed model abandons the traditional concept of elastic-plastic yield surface and can better reflect the real behavior of rolled control concrete. Basic equations were proposed for the fluid-solid coupling analysis, and the relationships among the corresponding key physical parameters were also put forward. One three-dimensional finite element method （FEM） program was obtained by studying the FEM type of the seepage-stress coupling intersection of the RCCD. The method was applied to an actual project, and the results show that the fluid-solid interaction influences dam deformation and dam abutment stability, which is in accordance with practice. Therefore, this model provides a new method for revealing the mechanical behavior of RCCD under the coupling field.

Analysis of barrel structure optimization for a mortar

Considering the maximum elastic limitation of the used material with newly advanced technology,the study focuses on optimization of a mortar barrel structure by thinning the wall to reduce the weight.Firstly,static analysis of barrel structure parameters is done based on finite element analysis（FEA）method and 3Dsolid model of the barrel is established based on Unigraphics NX（UG）.Secondly,the 3Dsolid model is simplified and transplanted to ANSYS for barrel wall pressure calculation.Thus,the change curves of the stress exerted on the barrel wall at different locations perpendicular to the axial direction with wall thinning are drawn.By analyzing all possible optimization schemes,the optimal design that enables the barrel to have higher bearing capacity is got.The optimized barrel structure is verified by means of fluid-solid coupling dynamic response analysis.The results show that the static analysis results are closer to real stress conditions than dynamic analysis results.Finally,the barrel weight is reduced by 13%after simulation optimization and the light weight design of the barrel is effective and reliable.

Horizontal gas mixing in rectangular fluidized bed:A novel method for gas dispersion coefficients in various conditions and distributor designs

In a rectangular fluidized bed combustor, the tracer gas is injected continuously into the bed from a point source at the center of the distributor plate. In this study, a general governing equation is formulated for tracer gas dispersion in the bed. An analytical solution is derived to estimate the dispersion coefficients, Dxand Dy, in a horizontal plane. The concentration profiles at different sampling heights with various gas velocities are plotted.Subsequently, to estimate the dispersion coefficients, surface fitting of the obtained analytical solution to the experimental data is performed. The dispersion coefficients obtained from this model are compared with those of a conventional model. Additionally, the effect of walls, bed height and gas injection rate on the dispersion coefficients in a horizontal plane is investigated, and the effect of distributor design on the dispersion coefficients in a horizontal plane is investigated with different tracer positions. It is found that Dxand Dyare nearly equivalent at a lower tracer gas ratio of the injected gas to the total gas flow rate. It is also demonstrated that the effect of bed height on Dxis minor. This model is also able to estimate the dispersion coefficients in the case of a multihorizontal nozzle distributor.

Is Terzaghi's effective stress a stress variable under seepage conditions?

From the continuum mechanics perspective, an attempt was made to clarify the role of Terzaghi's effective stress in the theoretical analysis of saturated soil subjected to seepage. The necessity of performing a coupled hydromechanical analysis to solve the seepage-deformation interaction problem was illustrated by examining the equations of static equilibrium among the effective stress, seepage force, pore-water pressure and total stress. The conceptual definition of stress variable that satisfies the principles of continuum mechanics is applied in the coupled hydromechanical analysis. It is shown that Terzaghi's effective stress is in fact not a stress variable under seepage conditions, and the seepage force acting on the soil skeleton cannot be viewed as a body force. This offers a clue to the underlying cause of a paradox between the real Pascal's hydrostatic state and the hydrostatic state predicted by a class of continuum hydromechanical theories.

Influence of dynamic recrystallization on microstructure and mechanical properties of welding zone in Al-Mg-Si aluminum profile during porthole die extrusion

The effect of dynamic recrystallization(DRX)on the microstructure and mechanical properties of 6063 aluminum alloy profile during porthole die extrusion was studied through experiment and simulation.The grain morphology was observed by means of electron backscatter diffraction(EBSD)technology.The results show that,at low ram speeds,increasing the ram speed caused an increase in DRX fraction due to the increase of temperature and strain rate.In contrast,at high ram speeds,further increasing ram speed had much less effect on the temperature,and the DRX faction decreased due to high stain rates.The microhardness and fraction of low angle boundaries in the welding zones were lower than those in the matrix zones.The grain size in the welding zone was smaller than that in the matrix zone due to lower DRX fraction.The decrease of grain size and increase of extrudate temperature were beneficial to the improvement of microhardness.

A Com binatorial Approach for Topological Classification of Graphlike M anifolds

The concept of graphlike manifolds was presented in [1] and the problem of counting the homeomorphic classes of graphlike manifolds has been studied in a series of articles, e.g., [1～8]. In this paper we suggest an approach based on the graph colouring, Abelian group and the combinatorial enumeration method.