新型大双叶片搅拌器的实验研究与结构优化

针对过程工业体系复杂多变的特点，开发了新型大双叶片宽适应性搅拌器，且通过实验建立了不同结构参数下的单位体积功率与混合时间数的关系曲线，确定了新型大双叶片搅拌器的优化结构，并与目前工业上应用较广的双螺带搅拌器和FZ搅拌器进行了对比。实验结果表明，新型大双叶片搅拌器的混合时间数随单位体积功率的增加而下降，但下降幅度在高黏体系中会变小；在消耗相同单位体积功率的前提下，当新型大双叶片搅拌器的结构为上下叶片全开栅格、互成45°夹角、轴向间距比0．09、离底距离比O．19～0．24时，其混合时间数较小，混合速率较快；在达到相同混合效果的前提下，新型大双叶片搅拌器较同规格的双螺带搅拌器和FZ搅拌器的功率消耗更少，节能效果明显。此外，新型大双叶片搅拌器开设栅格必须兼顾强度的要求。

Improvement of Prandtl mixing length theory and application in modeling of turbulent flow in circular tubes

In order to correctly predict tube cross section time-smoothed velocity distribution, friction factor and mass transfer behavior, two models for turbulent flow in circular tubes based on classical Prandtl mixing length theory and a modified mixing length were established. The results show that the modified mixing length includes the introduction of a damping function for the viscous sublayer and the second-order derivative to approximate eddy velocity. The calculated dimensionless time-smoothed velocity from the model based on Prandtl mixing length is much better than the result from the concept of eddy viscosity. The calculated eddy viscosity from the model based on modified mixing length is much better than the result from the model based on the classical Prandtl mixing length theory. And the friction factor calculated from the model based on the modified mixing length agrees well with the reported empirical relationships.

A Contraction-expansion Helical Mixer in the Laminar Regime

A contraction-expansion helical mixer which combines several features, viz. helical pipes for induction of secondary flows and sudden expansion and contraction array tor expansion vortices, has been designed to en- hance flow mixing. A fast competitive-consecutive diazo coupling reaction is used to test the mixing efficiency of contraction-expansion helical mixer. Furthermore, an image processing technique is applied for data visualization and monitoring the extent of mixing. The mixing performance is found to be superior in comparison to the regular helical mixer in the range of Reynolds number from 170 to 1540. Moreover, the mixing time of contraction-expansion helical mixer was found to be reduced by more than 25% compared to the regular helical pipe. Finally, a simple correlation is proposed for predicting the mixing time.

A SDN-Based Energy Saving Strategy in Wireless Access Networks

This paper investigates on the base stations(BSs) sleeping control and energy saving in wireless network. The objective is to find the sleeping control and energy saving configuration between total power consumption and average video's quality. On the Software Defined Network(SDN) access network architecture, a type of sleeping control and active BSs' optimal transmitting time strategy is considered, the BS sleeps when there is no active users, and wakes up after a period of vacation time. In this paper, we study the active users grouping strategy, In order to spare more BSs into sleeping mode. Then this paper proposes an active BS transmitting time optimal strategy according to the users' Qo S. In the proposed strategy, the active BSs' transmitting time is minimized in order to save energy. This paper employs the mixed integer-programming model to present this optimization problem. Then we utilized a novel algorithm to save the energy in access networks and also meet the Qo S requirements. Both the analytical and simulation results show that the algorithm can effectively save energy in the access network BSs.

浮选过程中搅拌调浆特性研究

调浆是浮选过程中影响后续分选段作业效率的关键环节之一,对二折叶桨式叶轮、四折叶开启式涡轮、四直叶开启式涡轮以及推进式叶轮等搅拌叶轮及其与导流筒、挡板的组合进行功率准数(NP)及混合时间数(Nθ)等特性参数的研究.结果表明:径流式叶轮相对轴流式叶轮,NP较大,能耗较高,而Nθ较小,更容易快速混合;导流筒可以节省能耗,加快混合;挡板则增加能耗,减小混合速率,对径流式叶轮作用流场影响更大,四直叶开启式涡轮的NP增加5倍以上,Nθ增加38%;同功耗下单叶轮以四折叶开启式涡轮的混合时间最短,混合效率最高.通过典型流场的数值模拟,解析了相应的搅拌特性.

Flow computations of multi-stages by URANS and flux balanced mixing models

The quasi-steady methods based on mixing models have been widely applied to flow computations of turbomachinery multi- stages in aerospace engineering. Meanwhile, the unsteady numerical simulation has also been used due to its ability in obtaining time-dependent flow solutions. In the paper, two different mixing treatments and the corresponding flux balanced ones are presented to exchange the flow solutions on the interfaces between adjacent blade rows. The four mixing treatments are then used for flow computations of a subsonic 1.5-stage axial turbine and a quasi-l.5-stage transonic compressor rotor. The results are compared with those by unsteady numerical method, which is implemented by using the sliding mesh technique. The effects of the quasi-steady and unsteady computation methods on the conservation of flow solutions across the interfaces are presented and addressed. Furthermore, the influence of mixing treatments on shock wave and flow separation of the transonic compressor rotor is presented in detail. All the results demonstrate that the flux balanced mixing treatments can be used for multi-stage flow computations with improved performance on interface conservation, even in the complex flows.

Survival analysis of car travel time near a bus stop in developing countries

This paper presents an important investigation into car travel time affected by mixed traffic flow near a bus stop on the basis of survival analysis theory.Travel time data associated with mixed traffic characteristics near a bus stop were collected by video cameras.A hazard-based duration model was introduced to analyze the effects of mixed traffic flow on car travel time.The results indicate that mixed traffic flow impacts car travel time significantly.And the presence of bus berthing violation would delay car travel time.The proposed model can be used to forecast temporal shifts in car travel time due to changes in mixed traffic flow.The influential factors related to mixed traffic flow should be given full consideration in the planning and designing of bus stops in developing countries.

STRICT LYAPUNOV FUNCTIONS FOR IMPULSIVE HYBRID TIME-VARYING SYSTEMS WITH DISCONTINUOUS RIGHT-HAND SIDE

In this paper, explicit closed form expressions of nonsmooth strict Lyapunov tunctlons for impulsive hybrid time-varying systems with discontinuous right-hand side is provided. Lyapunov functions are expressed in terms of known nonstrict Lyapunov functions for the dynamics and finite sums of persistency of excitation parameters.

Efficiently Counting Affine Roots of Mixed Trigonometric Polynomial Systems

Estimating the number of isolated roots of a polynomial system is not only a fundamental study theme in algebraic geometry but also an important subproblem of homotopy methods for solving polynomial systems. For the mixed trigonometric polynomial systems, which are more general than polynomial systems and rather frequently occur in many applications, the classical B6zout number and the multihomogeneous Bezout number are the best known upper bounds on the number of isolated roots. However, for the deficient mixed trigonometric polynomial systems, these two upper bounds are far greater than the actual number of isolated roots. The BKK bound is known as the most accurate upper bound on the number of isolated roots of a polynomial system. However, the extension of the definition of the BKK bound allowing it to treat mixed trigonometric polynomial systems is very difficult due to the existence of sine and cosine functions. In this paper, two new upper bounds on the number of isolated roots of a mixed trigonometric polynomial system are defined and the corresponding efficient algorithms for calculating them are presented. Numerical tests are also given to show the accuracy of these two definitions, and numerically prove they can provide tighter upper bounds on the number of isolated roots of a mixed trigonometric polynomial system than the existing upper bounds, and also the authors compare the computational time for calculating these two upper bounds.

MIP FORMULATIONS AND HEURISTICS FOR SOLVING PARALLEL BATCHING PROBLEMS

This paper addresses the scheduling problem involving batch processing machines, which is Mso known as parallel batching in the literature. The presented mixed integer programming formulation first provides an elegant model for the problem under study. Fhrthermore, it enables solutions to the problem instances beyond the capability of exact methods developed so far. In order to alleviate computational burden, the authors propose MIP-based heuristic approaches which balance solution quality and computing time.