New Method to Measure the Fill Level of the Ball Mill I——Theoretical Analysis and DEM Simulation

The accurate measurement of the fill level in the ball mill has not been resolved because of the interplay of many variable factors, which led the mill to be operated under the uneconomical condition and lost a lot of energy. At present, some methods, such as vibration method and acoustic method, have been applied for measuring the fill level by the researchers. Aiming at the problem of the traditional methods for measuring the fill level, that is, the feature variables of the fill level suffer the influences of the ball load and the water content of the coal, a novel method to measure the fill level is proposed and a possible relation between the fill level and the angular position of the maximum vibration point on the mill shell is investigated. The angular positions of the maximum vibration point on the mill shell for different fill level cases are calculated theoretically under two assumptions, respectively. Meanwhile the charge motions of the mill for different fill level cases are simulated with the discrete element method （DEM）. And the simulation results are verified by comparing the motion trajectories of steel balls and power draft of the mill. The simulated movement trajectories of the outmost layer steel balls in the mill are monitored and analyzed to obtain the angular positions of the maximum vibration point on the mill shell. Both the results of the theoretical calculation and the 3D DEM simulation show that the position of the maximum vibration point on the mill shell moves to a lower angular positions as the fill level decreasing, which provides a new idea for measuring the filllevel accurately.

Numerical simulation of single bubble rising in shear-thinning fluids by level set method

The behavior of single bubble rising in quiescent shear-thinning fluids was investigated numerically by level set method. A number of bubbles in a large range of Reynolds number and Eotvos number were investigated including spherical, oblate and spherical. The bubble shape and drag coefficient were compared with experimental results. It is observed that the simulated results show good conformity to experimental results over a wide range of Reynolds number. In addition, the detailed flow field based on the reference coordinate system moving with the bubble is obtained, and the relationship among flow field, bubble shape and velocity is discussed.

Using modified Soil Conservation Service curve number method to simulate the role of forest in flood control in the upper reach of the Tingjiang River in China

To improve flood control efficiency and increase urban resilience to flooding,the impacts of forest type change on flood control in the upper reach of the Tingjiang River(URTR) were evaluated by a modified model based on the Soil Conservation Service curve number(SCS-CN) method. Parameters of the model were selected and determined according to the comprehensive analysis of model evaluation indexes. The first simulation of forest reconstruction scenario,namely a coniferous forest covering 59.35km^2 is replaced by a broad-leaved forest showed no significant impact on the flood reduction in the URTR. The second simulation was added with 61.75km^2 bamboo forest replaced by broad-leaved forest,the reduction of flood peak discharge and flood volume could be improved significantly. Specifically,flood peak discharge of 10-year return period event was reduced to 7-year event,and the reduction rate of small flood was 21%-28%. Moreover,the flood volume was reduced by 9%-14% and 18%-35% for moderate floods and small floods,respectively. The resultssuggest that the bamboo forest reconstruction is an effective control solution for small to moderate flood in the URTR,the effect of forest conversion on flood volume is increasingly reduced as the rainfall amount increases to more extreme magnitude. Using a hydrological model with scenarios analysis is an effective simulation approach in investigating the relationship between forest type change and flood control. This method would provide reliable support for flood control and disaster mitigation in mountainous cities.

Numerical simulation of displacement characteristics of CO_2 injected in pore-scale porous media

Pore structure of porous media, including pore size and topology, is rather complex. In immiscible twophase displacement process, the capillary force affected by pore size dominates the two-phase flow in the porous media, affecting displacement results. Direct observation of the flow patterns in the porous media is difficult, and therefore knowledge about the two-phase displacement flow is insufficient. In this paper, a two-dimensional(2D) pore structure was extracted from a sandstone sample, and the flow process that CO_2 displaces resident brine in the extracted pore structure was simulated using the Navier eStokes equation combined with the conservative level set method. The simulation results reveal that the pore throat is a crucial factor for determining CO_2 displacement process in the porous media. The two-phase meniscuses in each pore throat were in a self-adjusting process. In the displacement process,CO_2 preferentially broke through the maximum pore throat. Before breaking through the maximum pore throat, the pressure of CO_2 continually increased, and the curvature and position of two-phase interfaces in the other pore throats adjusted accordingly. Once the maximum pore throat was broken through by the CO_2, the capillary force in the other pore throats released accordingly; subsequently, the interfaces withdrew under the effect of capillary fore, preparing for breaking through the next pore throat.Therefore, the two-phase displacement in CO_2 injection is accompanied by the breaking through and adjusting of the two-phase interfaces.

PARALLEL ADAPTIVE SIMULATION OF A PLUNGING LIQUID JET

This paper is concerned with three-dimensional numerical simulation of a plunging liquid jet. The transient processes of forming an air cavity around the jet, capturing an initially large air bubble, and the break-up of this large toroidal-shaped bubble into smaller bubbles were analyzed. A stabilized finite element method （FEM） was employed under parallel numerical simulations based on adaptive, unstructured grid and coupled with a level-set method to track the interface between air and liquid. These simulations show that the inertia of the liquid jet initially depresses the pool＇s surface, forming an annular air cavity which surrounds the liquid jet. A toroidal liquid eddy which is subse- quently formed in the liquid pool results in air cavity collapse, and in turn entrains air into the liquid pool from the unstable annular air gap region around the liquid jet.

A general multi-objective programming model for minimum ecological flow or water level of inland water bodies

Assessment of ecological flow or water level for water bodies is important for the protection of de- graded or degrading ecosystems caused by water shortage in arid regions, and it has become a key issue in water resources planning. In the past several decades, many methods have been proposed to assess ecological flow for rivers and ecological water level for lakes or wetlands. To balance water uses by human and ecosystems, we proposed a general multi-objective programming model to determine minimum ecological flow or water level for inland water bodies, where two objectives are water index for human and habitat index for ecosystems, respectively Using the weighted sum method for multi-objective optimization, minimum ecological flow or water level can be determined from the breakpoint in the water index-habitat index curve, which is similar to the slope method to de- termine minimum ecological flow from wetted perimeter-discharge curve. However, the general multi-objective programming model is superior to the slope method in its physical meaning and calculation method. This model provides a general analysis method for ecological water uses of different inland water bodies, and can be used to define minimum ecological flow or water level by choosing appropriate water and habitat indices. Several com- monly used flow or water level assessment methods were found to be special cases of the general model, including the wetted perimeter method and the multi-objective physical habitat simulation method for ecological river flow, the inundated forest width method for regeneration flow of floodplain forest and the lake surface area method for eco- logical lake level. These methods were applied to determine minimum ecological flow or water level for two repre- sentative rivers and a lake in northern Xinjiang of China, including minimum ecological flow for the Ertix River, minimum regeneration flow for floodplain forest along the midstream of Kaxgar River, and minimum ecological lake level for the Ebinur Lake. The results illustrated the versatility of the general model, and can provide references for water resources planning and ecosystem protection for these rivers and lake.

Modeling and simulation of material distribution in the sequential co-injection molding process

In co-injection molding,the properties and distribution of polymers will affect the application of products.The focus of this work is to investigate the effect of molding parameters on the skin/core material distribution based on three-dimensional(3-D)flow and heat transfer model for the sequential coinjection molding process,and the flow behaviors and material distributions of skin and core melts inside a slightly complex cavity(dog-bone shaped cavity)are predicted numerically.The governing equations of fluids in mold are solved by finite volume method and Semi-Implicit Method for Pressure Linked Equations(SIMPLE)algorithm on collocated meshes,and the domain extension technique is employed in numerical method for this cavity to assure that the numerical algorithm is implemented successfully.The level set transport equation which is used to trace the free surfaces in co-injection molding is discretized and solved by the 5 th-order Weighted Essentially Non-Oscillatory(WENO)scheme in space and 3 rd-order Total Variation Diminishing Runger-Kutta(TVD-R-K)scheme in time respectively.Numerical simulations are conducted under various volume fraction of core melt,skin and core melt temperatures,skin and core melt flow rates.The predicted results of material distribution in length,width and thickness directions are in close agreement with the experimental results,which indicate that volume fraction of core melt,core melt temperature and core melt flow rate are principal factors that have a significant influence on material distribution.Numerical results demonstrate the effectiveness of the 3-D model and the corresponding numerical methods in this work,which can be used to predict the melt flow behaviors and material distribution in the process of sequential co-injection molding.

Target reliability index for serviceability limit state of single piles

The objective is to develop an approach for the determination of the target reliability index for serviceability limit state(SLS) of single piles. This contributes to conducting the SLS reliability-based design(RBD) of piles. Based on a two-parameter,hyperbolic curve-fitting equation describing the load-settlement relation of piles, the SLS model factor is defined. Then, taking into account the uncertainties of load-settlement model, load and bearing capacity of piles, the formula for computing the SLS reliability index(βsls) is obtained using the mean value first order second moment(MVFOSM) method. Meanwhile, the limit state function for conducting the SLS reliability analysis by the Monte Carlo simulation(MCS) method is established. These two methods are finally applied to determine the SLS target reliability index. Herein, the limiting tolerable settlement(slt) is treated as a random variable. For illustration, four load test databases from South Africa are compiled again to conduct reliability analysis and present the recommended target reliability indices. The results indicate that the MVFOSM method overestimates βsls compared to that computed by the MCS method. Besides, both factor of safety(FS) and slt are key factors influencing βsls, so the combination of FS and βsls is welcome to be used for the SLS reliability analysis of piles when slt is determined. For smaller slt, pile types and soils conditions have significant influence on the SLS target reliability indices; for larger slt, slt is the major factor having influence on the SLS target reliability indices. This proves that slt is the most key parameter for the determination of the SLS target reliability index.

On the Transient Numerical Simulation of Solid Rocket Motor by Coupling Quasi One⁃Dimension Internal Flow with Three⁃Dimension Propellant Grain Burnback

The quasi one⁃dimension compressible flowfield coupled to the three⁃dimension propellant grain regression solved by the level⁃set method was used to simulate the transient internal ballistics of solid rocket motor.One⁃dimension flowfield instead of three⁃dimension can save computational cost on the premise of calculation accuracy because the radial and azimuthal variations parameters have little contribution to the internal flowfield.The grain regression in real⁃time could provide accurate geometrical information for simulation.A combination of flowfluid solver and grain regression can reappear in a relatively real internal ballistic flowfield,so it is good for further studying the instability of solid rocket motor.For level⁃set equations,the total variation⁃diminishing second⁃order Runge⁃Kutta method for temporal derivatives and a fifth⁃order weighted⁃essentially⁃non⁃oscillatory scheme for spatial derivatives were used.The total variation⁃diminishing MacCormack method was used to discrete the Euler equations in flowfield solver.Two modules of this code were tested in this study:one is the burning rate module and the other is the nozzle erosion module.Results show that the burning rate influenced the solid rocket motor efficiency,and the velocity profile in the chamber was affected by the nozzle shape,and the nozzle erosion could influence the head⁃end pressure spike.

Liquid-Gas Two-Phase Flow Simulation in Mold Filling Process with Level Set Method

Air entrapped in liquid metal during the mold filling process seriously affects the casting quality, thus it is important to track its behavior in the mold cavity. A liquid-gas two-phase flow model is developed to describe the mold filling process and predict the air entrapment defect. The model is based on the combination of SOLA and Level Set Method. The pressure and velocity fields are calculated by SOLA,and the interface movement is simulated by Level Set method as the most common interface tracking method in recent years.In order to validate the feasibility of the model,the liquid-gas two-phase simulation results were tested by the broken dam problem and the S-shaped experiment. Comparison between the experiments and simulation results show that Level Set method might be a very promising tool in two-phase flow simulation during the mold filling process.

Three-Dimensional Simulations with Fields and Particles in Software and Inflector Designs

Particles and fields represent two major modeling paradigms in pure and applied science at all. In this paper a methodology and some of the results for three-dimensional (3D) simulations that include both field and particle abstractions are presented. Electromagnetic field calculations used here are based on the discrete differential form representation of the finite elements method, while the Monte Carlo method makes foundation of the particle part of the simulations. The first example is the simulation of the feature profile evolution during SiO2 etching enhanced by Ar + /CF4 non-equilibrium plasma based on the sparse field method for solving level set equations. Second example is devoted to the design of a spiral inflector which is one of the key devices of the axial injection system of the VINCY Cyclotron.

基于三维VOF方法研究上室体型对调压室涌浪的影响

为了探究上室体型对调压室内最高涌浪的影响,基于三维VOF方法,对某水电站机组甩全负荷工况下调压室内的涌浪过程进行数值模拟,验证了数值模拟方法的可靠性.研究结果表明:在地形结构等条件允许的情况下,上室断面积越大,调压室内最高涌浪越低.相同断面积的上室,调压室内最高涌浪随长宽比增大而升高,但涨幅不大.当长宽比L/B=8.6时,最高涌浪降低0.07m.本文研究结果为调压室内涌浪过程优化提供依据.

A Simple Weighted Integration Method for Calculating Surface Tension Force to Suppress Parasitic Flow in the Level Set Approach

Parasitic flows may occur in the numerical simulation of incompressible multiphase flow due to errors in the calculation of surface tension terms, specifically for the curvature and unit normal vector. An improved method for calculating the surface tension based on the level set approach is proposed, in which the contribution of not only the center node but also the rest area of a control volume to the calculation of surface tension is considered in a balanced manner. The weighted integration method (WIM) is more consistent with the concept of a banded in- terface in the level set method. It is applied to the temporal evolution of a two-dimensional neutrally buoyant liquid drop and a buoyancy driven deformable bubble in an immiscible fluid for the validation of WIM. The results show that the parasitic flows are evidently suppressed by the weighted integration method. The weight factors for WIM in 3-D cases are also suggested.

Key Technologies of Urban TIA and Their Application

With the high speed development of Chinese economy, urban traffic problems have become increasingly serious. Based on an analysis of the significance and function of TIA (Traffic Impact Analysis), the characteristics, procedure and key techniques of TIA are elaborated according to the overseas experience. Then, in combination with the domestic practice, the standard of executing TIA, the prediction of traffic volume, the standard of appraisement, etc ., are discussed in detail. Finally, construction of the commercial pedestrian street of Chunxi road in Chengdu city is taken as an example for analysis.

Numerical simulation of Marangoni effects of single drops induced by interphase mass transfer in liquid-liquid extraction systems by the level set method

The mathematical model of mass transfer-induced Marangoni effect is formulated. The drop surface evolution is captured by the level set method, in which the interface is represented by the embedded set of zero level of a scalar distance function defined in the whole computational domain. Numerical simulation of the Marangoni effect induced by interphase mass transfer to/from deformable single drops in unsteady motion in liquid-liquid extraction systems is performed in a Eulerian axisymmetric reference frame. The occurrence and development of the Marangoni effect are simulated, and the re- sults are in good agreement with the classical theoretical analysis and previous simulation.

射频异构集成微系统多层级协同仿真建模与PDK技术综述

作为后摩尔技术的可选路径之一,基于异构集成工艺实现的集成微系统具有高集成度、低成本、高性能等优点,引起学术界和工业界的广泛关注。异构集成微系统设计是以系统为中心的多层级协同设计,对传统以晶体管为中心的设计方法和设计流程带来新的挑战,同时对设计环境的开发带来新的要求。本文对射频集成微系统设计中所需的基础器件/结构建模方法、多工艺混合工艺设计套件(Process Design Kit,PDK)技术、以及电路-模块-系统多层级协同仿真等技术最新进展进行综述。

Level Set方法及其在两相流数值模拟研究中的应用

本文介绍了一种崭新的捕捉两相流相界面的 Ｌｅｖｅｌ Ｓｅｔ方法，并应用该方法对两种互不相容流体间的平面界面波动现象进行了数值模拟，捕捉到了两相流界面波动过程中的一些复杂现象。计算结果与实验观测现象符合良好，表明这种方法是一种很有前途的两相流数值模拟方法，很值得进一步研究和推广。

桌面级协作机械臂设计与仿真分析

由于桌面级协作机器人具有低成本、小型化、模块化等特点,被广泛的应用在医疗、食品、科研、3C等行业。针对模块化关节,设计了满足强度刚度要求、额定负载为1kg的桌面级协作机器人,建立了基于CoppeliaSim与Matlab的实验仿真平台。首先利用旋量法建立了机器人正、逆运动学模型,提出了基于最小变化角为准则的位置控制算法,成功的实现了机器人的运动控制,验证了正、逆运动学求解模型的准确性。实验平台的仿真结果表明,该算法能够有效的控制机器人的运动,具有实用性。

基于Level set方法的微观水驱油模拟分析

通过引入Level set方法,构建两相界面运移数学表征方法,结合Navier-Stokes方程建立两相微观渗流数学模型,借助有限元方法进行求解,并利用微观玻璃刻蚀模型驱替实验验证数值模拟结果。结果表明,基于该渗流数学模型的数值模拟结果与实验结果的吻合度很高。利用Navier-Stokes方程并结合Level set方法实现了两相流体驱替的微观数值模拟,从而为研究微观两相渗流特征及驱油机理提供了一种新方法。在不等径并联喉道单元模型基础上,进行了不同驱替条件下的数值模拟计算,分析了发生孔隙尺度两相窜流的临界喉道直径比的变化特征,结果表明驱替压差及油水两相黏度比越大,越容易发生微观窜流,更易导致在较小喉道中形成微观残余油。本文研究结果为微观水驱油机理的进一步研究奠定了基础。