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1.
A new electromagnetic suspension model using a combination of high temperature superconductors (HTS) and copper conductors is proposed in this paper. A feasibility study showed that the magnets of our model can generate the 250 kg vertical suspension force. Three dimensional FEM and Design Sensitivity Analysis using the levitation gap length and cross sectional dimensions of the HTS magnets as design parameters were conducted to obtain the optimal shape of the cross section and the configuration of the HTS magnet. It was found that the gap length when optimized HTS magnet was used was much larger than that when copper conductor magnet was used, while the HTS coil volume was minimum, and the perpendicular field along the outer surface of the HTS coil was less than 0.12 T. 相似文献
2.
A k-ε-kp multi-fluid model was used to simulate confined swirling gas-solid two phase jet comprised of particle-laden flow from a center tube and a swirling air stream entering the test section from the coaxial annular. After considering the drag force between the two phases and gravity, a series of numerical simulations of the two-phase flow of 30μm, 45μm, 60μm diameter particles were performed on a x×r＝50×50 mesh grid respectively. The results showed that the k-ε-kp multi-fluid model can be applied to predict moderate swirling multi-phase flow. When the particle diameter is large, the collision of the particles with the wall will influence the prediction accuracy. The bigger the diameter of the particles, the stronger the collision with the wall, and the more obvious the difference between measured and calculated results. 相似文献
3.
A continuous-time nonlinear model predictive controller （NMPC） was designed for a boiler-turbine unit. The controller was designed by optimizing a receding-horizon performance index, with the nonlinear system approximated by its Taylor series expansion with a certain order, the magnitude saturation constraints on the inputs satisfied by increasing the predictive time, and the rate saturation conditions on the actuators satisfied by tuning the time constant of the reference trajectories in a reference governor. Simulation results showed that the controller can drive the drum pressure and output power of the nonlinear boiler-turbine unit to follow their respective reference trajectories throughout a varying operation range and keep the water level deviation within tolerances. Comparison of the NMPC scheme with the generic model control （GMC） scheme indicated that the responses are slower and there are more oscillations in the responses of the water level, fuel flow input and feed water flow input in the GMC scheme when the boiler-turbine unit is operating over a wide range. 相似文献
4.
Lattice Boltzmann method was used to numerically investigate the motion and orientation distribution of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio. The transient impulse model of 3D collisions between particles and between particle and wall is proposed. The numerical results are qualitatively in agreement with and quantitatively comparable to the experiment data. The results show that the increases of both the cylindrical particle to pipe size ratio and the particle aspect ratio decrease the rotation about all axes. All rotations of cubic particles decrease with increasing the particle concentration. The cubic particles, rotating more drastically in the flow with large Reynolds number, rotate faster than the cylindrical particles with the same size. The cylindrical particles align with the flow direction more obviously with decreasing Reynolds numbers. However, the orientations of cubic particles are spread all over the range with no significant difference in magnitude, and the Reynolds numbers have no obvious effect on the orientations of cubic particles. 相似文献
5.
A mathematic model of two-phase flow and a physical model of two-dimensional (2D) vertical section for the plate-type structured packing Mellapak 250.Y were set up and verified. The models were used to study the influence of packing’s surface microstructure on the continuity of liquid film and the amount of liquid holdup. Simulation results show that the round corner shape and micro wavy structure are favorable in remaining the continuity of liquid film and increasing the amount of liquid holdup. The appropriate liquid flow rate was determined by investigating different liquid loadings to obtain an unbroken liquid film on the packing surface. The pressure difference between inlet and outlet for gas phase allowed gas and liquid to flow countercurrently in a 2D computational domain. The direction change of gas flow occurred near the phase interface area. 相似文献
6.
Gas-liquid two-phase flow and heat transfer can be encountered in numerous fields, such as chemical engineering, refrigeration, nuclear power reactor, metallurgical industry, spaceflight. Its critical heat flux （CHF） is one of the most important factors for the system security of engineering applications. Since annular flow is the most common flow pattern in gas-liquid two-phase flow, predicting CHF of annular two-phase flow is more significant. Many studies have shown that the liquid film dryout model is successful for that prediction, and determining the following parameters will exert predominant effects on the accuracy of this model： onset of annular flow, inception criterion for droplets entrainment, entrainment fraction, droplets deposition and entrainment rates. The main theoretical results achieved on the above five parameters are reviewed; also, limitations in the existing studies and problems for further research are discussed. 相似文献
7.
Polyaluminium chloride （PAC） synthetic water was selected as a coagulant and kaolin suspension particles as objects to be removed. Online instruments such as the turbidimeter and particle counter were employed to monitor the flocculation process online and collect test data. The aim of the experiments was to study the dynamic distribution characteristics of suspension particles in the flocculation process. The 3D flow field in the reacting vessel was also simulated at different slow stirring speeds. The experiments showed that particle collision and aggregation in the flocculation process is in compliance with the Sutherland cluster aggregation model. This study further indicated that under appropriate hydrodynamic conditions, the distribution of turbulent flow in the reactor could be improved to increase the odds of effective particle collision and restrain the breakup of formed flocs by vortex shearing force. A good flocculation effect could therefore be produced. 相似文献
8.
A coal slurry mixing tank is a key piece of equipment in the preparation of coal slurry for direct coal liquefaction.It is a gas-liquid-solid three-phase mixing device.Based on the performance of the existing coal slurry mixing equipment,a type of test equipment for horizontal continuous coal slurry preparation was developed,but to this point has limited research results.The test equipment consists of a mixing cylinder,mixer,stirring impeller and other components.Slurry mixing experiments were undertaken using the prototype,testing the performance of the device.A mathematical model was proposed specifically for the operation of a coal slurry mixing tank that is horizontally operated with high slurry concentration and rotary flow.The flow field in the horizontal coal mixing tank was simulated with the computational fluid dynamic （CFD） method.The experimental results match well with the CFD simulation results.Results show that the test device of a coal slurry mixing tank can be used to model the mixing of pulverized coal and the solvent oil.A strong correlation was obtained. 相似文献
9.
《重庆大学学报(英文版)》2002,1(1):27-31
To solve the problem of investment portfolio with single goal of maximal NPV,10-1 programming model was proposed and proved effective;and to solve that concerning more elements of a project such as risk level and social benefit,a goal programming model is then introduced.The latter is a linear programming model adopting slack variable called deviation variable to turn inequation constraint into equation constraint,introducing a priority factor to denote different improtance of the goals.A case study has demonstrated that this goal programming model can give different results according to different priorty requirement of each objective. 相似文献
10.
易树平 《重庆大学学报(英文版)》2002,1(1):27-31
To solve the problem of investment portfolio with single goal of maximal NPV, a 0- 1 programming model was proposed and proved effective; and to solve that concerning more elements of a project such as risk level and social benefit, a goal programming model is then introduced. The latter is a linear programming model adopting slack variable called deviation variable to turn inequation constraint into equation constraint, introducing a priority factor to denote different importance of the goals. A case study has demonstrated that this goal programming model can give different results according to different priority requirement of each objective. 相似文献
11.
吴洁 《天津师范大学学报(社会科学版)》2006,(2):14-18
建立社会主义和谐社会,“促进社会公平与正义”,是我们党从全面建设小康社会、开创中国特色社会主义事业新局面的全局出发提出的一项重大任务,指明了我国社会建设的方向。和谐社会的核心是人与人的和谐、人与社会的和谐,前提是维护和实现社会公平与正义、促使经济社会协调发展, 相似文献
12.
以全国各省份20042011年财政性社会保障支出水平为例,利用省级静态面板数据模型,引入GDP增长率、城市化水平、财政性社会保障支出水平三个指标的对数为自变量,以城乡居民收入差距的对数为因变量,进行多元面板回归分析,并重点研究社保支出水平的收入再分配效应.研究发现,自2004年以来,GDP增长率、城市化水平、财政性社会保障支出水平并未在缩小城乡居民收入差距方面起到较好的作用;GDP的增长率对扩大收入差距存在正效应,影响系数为0.85,城市化水平对扩大收入差距的正效应系数为0.19,社会保障支出对扩大收入差距的正效应系数为0.07.基于此结果,应继续努力扩大财政性社会保障支出的覆盖面,特别注重城乡之间的公平性;完善社会保障制度的筹资机制,加强对低收入人口的支持,提高农村社会保障支出占整个会保障支出的比重. 相似文献
13.
为了改善原有碎片分配方案仅以节点响应效率为主而对节点分配次数、节点空间利用率、安全性能欠缺考虑的现状,提出分布式文件存储系统的碎片分配优化模型。优化模型由节点响应状况检测、大范围节点数据完整性审计和包含剩余存储空间大小、最近存储碎片时间戳以及响应时间长短的综合评估3方面构成。对其进行仿真实验,对比原有方案,优化方案没有出现节点倾斜现象,选取次数最大落差不超过95;节点效率得到了均衡,最大落差缩减至15%。优化方案提高了碎片分配的公平性、安全性和可靠性,实现了最优节点的自动化选择。 相似文献
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15.
王妍 《昭通师范高等专科学校学报》2007,29(6):9-12
农民工向城市的流动是经济社会发展的必然结果。然而,农民工在城市从业、社会保障、子女入学等方面并没有享受到应有的保障,因而造成了农民工阶层流动的障碍,使产业结构与社会结构不协调,很不利于和谐社会建设。为解决这一问题,需要清除一切阻碍农民工向城市流动的障碍;调节收入差距,健全社会保障制度,制定并完善保护城市农民工的法规;提倡农民"离土不离乡"。 相似文献
16.
中国城乡差距现状、风险和对策研究 总被引：5，自引：0，他引：5
刘志英 《华中科技大学学报(社会科学版)》2006,20(6):117-120
随着改革的渐进,城乡差距的矛盾越来越突出,过分悬殊的城乡差距不利于和谐社会的建立、经济的发展和社会的稳定。但是,通过一系列的制度建设与完善,可以缓解城乡差距所带来的各类风险。通过加快城镇化进程、完善社会保障体系和加大财政转移支付力度,可以提高农村居民的收入水平,缩小城乡差距,构建起一个真正的和谐社会。 相似文献
17.
“北欧模式”又称“斯堪的纳维亚模式”,是北欧瑞典、芬兰、丹麦、挪威、冰岛五个国家针对于社会保障所采取的“高福利、高消费、高税收”的社会保障模式。这种模式在近些年来不断地促进北欧五国经济的持续增长,使其成为世界上贫富差距最小的地区。当然作为社会保障的一个重要的组成部分,成人教育在北欧也施行得相当的成功,其特点和经验也值得我国借鉴。 相似文献
18.
随着社会经济的发展,城乡差距越来越大,农村各种问题日益显现,因此要实现社会平衡健康发展,缩小城乡差距,建立完善的农村社会保障制度是必然要求。文章分析二元体制下武汉农村社会保障存在的问题,如农村社会保障资金缺乏,资金管理不科学,相关政策宣传力度不足等,并有针对性的提出保障农村社会保障资金,完善资金监督,提高保障层次,加大宣传等对策与建议。通过完善农村社会保障,确保农村社会的稳定和谐,为城乡一体化的构建与发展打下坚实的基础。 相似文献
19.
Gas-liquid two-phase flow and heat transfer can be encountered in numerous fields, such as chemical engineering, refrigeration, nuclear power reactor, metallurgical industry, spaceflight. Its critical heat flux (CHF) is one of the most important factors for the system security of engineering applications. Since annular flow is the most common flow pattern in gas-liquid two-phase flow, predicting CHF of annular two-phase flow is more significant. Many studies have shown that the liquid film dryout model is successful for that prediction, and determining the following parameters will exert predominant effects on the accuracy of this model: onset of annular flow, inception criterion for droplets entrainment, entrainment fraction, droplets deposi-tion and entrainment rates. The main theoretical results achieved on the above five parameters are reviewed; also, limitations in the existing studies and problems for further research are discussed. 相似文献
20.
随着音频、视频和图像等数据流传输在代理服务器上的应用越来越广泛,有关如何保障数据传输的安全性和服务质量方面的研究也越来越深入。讨论了代理服务器数据分层传输的控制模型,在提出关于模型的链路振荡和公平性问题的基础上,着重就接收端数据分层安全性的检测进行研究,并提出了改进方法。结果表明,此控制模型对网络数据的稳定具有较好的性能。 相似文献