Numerical simulation of fluid flow caused by buoyancy forces during vacuum arc remelting process

The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting (VAR) process have important effect on the subsequent mechanical processes like forging, rolling and welding. In order to determine the fluid motion of molten pool, a 2D finite element model is established using ANSYS10.0 software, combined with the turbulent fluid flow and heat transfer. The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study. The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile. It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.     

320kA预焙铝电解槽电磁场分布计算与优化

利用ANSYS电磁场有限元法,建立了320 kA预焙铝电解槽三维电磁场有限元模型,计算了铝电解槽内的电场分布及磁场分布,计算结果与实测结果相吻合,验证了该模型的正确性.在此基础上提出了一种新型电解槽结构,并应用参数化设计语言（APDL）建立该结构的电磁场计算模型,以磁场为目标对该结构进行了整体优化.最终优化后电磁场分布表明：该结构铝电解槽能减小铝液层水平电流,磁场分布对称性好,有利于改善槽内铝液的流动状态,具备较大的节能潜力.     

送粉激光熔覆温度场数值分析

在ANSYS平台上,建立了瞬态三维送粉激光熔覆熔池温度场的物理模型,对在特种钢材34CrNiMo为基材上进行Ni基粉末激光熔覆的过程进行了数值模拟.使用生死单元法来模拟熔覆粉末在熔池形成前后与熔池的交互作用,计算出了激光熔覆熔池的自由表面形状、熔池温度场.计算所得熔池截面形状与试验熔池截面形状基本吻合,证明所建立的瞬态三维激光熔覆熔池温度场的物理模型是正确合理的.     

Microstructure evolution during remelting of high solid fraction ZL101 alloy

This work deals with the reheating process for semi-solid thixoforming of ZL101 (AlSi7Mg) alloy. The semi-solid state can decrease the viscosity and the resistance while sheared because of the evolutional behavior, which is characterized by a solid-like behavior at rest and a liquid flow during shearing. The microstructure evolution of ZL101 alloy at different temperatures from 540 to 580 °C has been studied. Results show that the eutectic temperature can affect the transformation speed of semi-solid structure. Semi-solid microstructures with high solid fraction can be obtained by controlling the reheating time in less than 20min, while at the temperature lower than the eutectic temperature it needs more than one hour. Another character of semi-solid ZL101 alloy is the segregation of microstructures in semi-solid state, in which the liquid phase between the solid phases can flow freely and lead to the shrinkage of the sample during the heating process. As the holding time goes on, more shrinkage holes appear and change the surface of the specimen. These shrinkage holes are replenished by the liquid phase during compression deformation, resulting in the segregation of the components.     

铁水运输调度双层多目标约束优化模型

为实现铁水运输作业排程与资源分配的协同优化，基于约束程序累积调度和字典序多目标优化理论，研究了铁水运输调度双层多目标约束优化方法.首先，基于铁水罐周转率最高和作业效率最高2个字典序优化目标，考虑作业时序、作业实施逻辑、铁水温降时限、铁水罐作业次数限制、资源容量限制和铁水罐资源池等约束条件，建立了上层的铁水运输作业排程约束优化模型；其次，以资源利用均衡度最高为目标，将作业实施唯一性和资源容量限制作为约束条件，建立了下层的铁水运输资源分配约束优化模型；最后，通过约束传播与多点构建性搜索的混合算法迭代求解整个模型.通过实例验证表明：设计的混合算法求得的铁水罐周转率目标和运输作业效率目标，比基本深度优先回溯算法分别提高了14.29%和60.53%；字典序多目标模型比加权和单目标模型求解效率和求解质量分别提高了20.3%和11.11%.     

Application of Computer in the Design of Process Thermal Cycle of Steel

IntroductionSteelingot.steelslabbecomest6elproductsafterheatingandrollingorforging.Steelproductsofforgingneedtobeheattfeatedinheattreatingfumace,fOrexampleannealingnormalization.Heattreatinentcandecreasestress,reducehydrogenconcentrationandimprovetheorganizationandperformanceofsteel.Everyprocessofproductionthatsteelingotschangeilltosteelproductsisaprocessofthermalcycleofsteel.Thisprocesswillconsumealargeamountofeneasmaterialandequipment.Inthepast,inmetallurgicalenterpriseofourcountrythetimeo…     

Steady state analysis of towed marine cables

Efficient numerical schemes were presented for the steady state solutions of towed marine cables. For most of towed systems, the steady state problem can be resolved into two-point boundary-value problem, or initial value problem in some special cases where the initial values are available directly. A new technique was proposed and attempted to solve the two-point boundary-value problem rather than the conventional shooting method due to its algorithm complexity and low efficiency. First, the boundary conditions are transformed into a set of nonlinear governing equations about the initial values, then bisection method is employed to solve these nonlinear equations with the aid of 4th order Runge-Kutta method. In common sense, non-uniform (sheared) current is assumed, which varies in magnitude and direction with depth. The schemes are validated through the DE Zoysa's example, then several numerical examples are also presented to illustrate the numerical schemes.     

Analysis of stress and strain fields of laser cladding process on ring circular orbit

The cracking of coatings and the deformation of base frustrate the application of laser cladding technology especially on surface of the ring circular orbit. In order to solve the two problems above, the stress and strain fields of the laser cladding process on the ring circular orbit were analyzed through the finite-element method, based on the temperature field. The wedge module of the ring circular ring was the subject investigated. The calculating results show that during the cladding process the crank point tends to generate the transversal crack; the centre point on the coating/base interface tends to generate longitudinal crack; the intersecting edge of the coating and base tends to generate toe crack. Moreover, the cracking tendency of the outer marginal point is obviously greater than that of the inner marginal point. The rather high stress appears at the border position where the constraint exists, and the stress on the point in front of molten pool under the range of laser irradiation is large as well. And the displacement becomes larger as the cladding process proceeds.     

Current Density Distribution in Gas Tungsten Arc Welding Process

IntroductionWeldingisacriticaltechnologyinbuildingnuclearreactors,shins,piPelinesandinatomobilemanufaCtuing.BatuPtil1noWtheearemanyproblemsinPractice,understandingthedeVlopmentoftheweldpoolduringweldingisofconsiderablePracticalsignificance.BecauseofthecomPlexityoftheprocessandtl1ePresenceofthebrightarc,directexPerimentalinvestigationsareextremelyexPensiveandoftenimPossibleorimPracticable,thensomemathematicalmethodsareadoptedtosett1PthetfansiellttemPerattirefieldandthefluidflowfieldofthew…     

静压桩对邻近埋地管道性能影响的数值分析

为了分析静压沉桩过程对邻近埋地管道性能的影响,基于位移贯入法模拟静压沉桩的二维有限元数值方法,建立了桩-土、管-土接触面并在桩顶施加位移荷载实现动态压桩过程,并综合分析了压桩过程中沉桩深度、桩径大小、管道中心与桩体中心的水平距离以及管道的埋深等因素对管道变形与力学性能的影响.研究结果表明:同等条件下,增加管-桩水平距离,管道水平位移、径向变形和管周应力相应减小,近桩侧管周土体的最大水平应力约为不设置管道时的1.5倍;随着沉桩深度增大,初始使管道产生明显水平位移的临界沉桩深度约为管道上方1 m处,随后管道水平位移呈现先增大后略微减小,并最终趋于稳定的趋势,且当沉桩深度为2倍埋深时管道水平位移最大;管道埋深越大,管道受沉桩挤土效应的影响越明显;当埋深为5倍管径时,沉桩桩径减少25%时管道最大水平位移减少27.8%,表明减小桩径可显著降低沉桩对周边管道性能的影响.      

青藏高原机场跑道多年冻土地基温度场特征

对比了青藏高原多年冻土地区机场跑道地基温度场与公路路基温度场, 分析了其地基温度分布、温度沿深度的变化以及地基最大融化深度, 研究了宽幅沥青混凝土道面机场跑道地基温度场特征, 对比了不同道面宽度条件下其地基温度分布、不同时间地基温度沿深度的变化以及跑道中部及道肩的最大融化深度, 并基于道面宽度、时间建立了沥青混凝土道面机场跑道道中地基融化深度的表达式。研究结果表明: 多年冻土地区机场跑道地基温度场与公路路基温度场存在明显差异, 机场跑道地基融土核位置更低, 且全部位于天然地面以下, 而公路路基融土核位置相对较高, 可以通过抬高路堤使融土核全部位于路堤内, 便于通风管等温控措施的施工, 可见由于机场跑道无路堤、道面幅度宽等特点, 使得多年冻土地区公路与铁路建设的现有研究成果不能完全应用于机场跑道建设中; 对于沥青混凝土道面的机场跑道多年冻土地基, 随着道面宽度的增加, 跑道地基稳定性降低, 道面宽度每增加1%, 地基0℃等温线约下降0.17%, 地基融土核最高温约上升0.46%, 道中地基融化深度约加深0.19%, 但当道面宽度超过35 m时, 道中地基融化深度趋于平稳; 相对于道中地基温度场, 道肩受道面宽度的影响较小, 当道面宽度超过25 m时, 其地基融化深度趋于平稳; 道中地基融化深度表达式相关系数为0.988 6, 相对误差在1%以内。      

一种无环流数字控制STS模块的研制

分析了静态转换开关（STS）的无环流切换控制的工作原理。针对其中关键的电流状态检测问题,提出了一种根据晶闸管门极电压来检测晶闸管导通状态的方案。设计了1个TMS320LF2406控制的12A静态转换开关模块,描述了DSP中电压掉电时的控制时序,实际测试表明模块断电时间小于规定时间,提出的电流检测方法正确。     

基于LCAS虚级联实现EOS及性能分析

对链路容量调整机制（LCAS）实现EOS进行了分析,对低阶虚级联LCAS的复帧结构及实现LCAS过程进行了论述,对虚级联组（VCG）实现多通道虚级联初始化过程、LCAS虚级联稳定工作时状态迁移、链路容量带宽增减的动态调整过程及链路临时删除或恢复进行了研究,给出了LCAS虚级联初始化过程和稳态工作过程流程图.对多通道实现虚级联过程中的时延差进行了剖析.对LCAS的实现、估算多通道的时延差和设计接收缓冲储器容量提供了方法和依据.     

基于VAR的高速公路与经济发展关系动态效应分析

利用1988～2005年高速公路与经济发展状况的年度数据,构建反应我国高速公路与经济发展动态关系的VAR(向量自回归)模型。在模型的基础上,运用脉冲响应函数和方差分解分析了高速公路与经济发展之间的动态效应。结果表明,两者之间存在协整关系以及Granger因果关系。进一步得出以下结论:高速公路的变动趋势比国民经济更加敏感,且高速公路受国民经济的影响大于对国民经济的影响,我国高速公路建设应当适度超前并与国民经济均衡发展。     

风成跃移模拟的一种数值方法

在Ungar模型的理论基础上,给出吹过无限大平坦沙床面的稳定风场中,风和跃移沙粒相互耦合作用下沙粒二维跃移轨迹的一种计算格式,并利用给出的计算格式对模型进行求解．通过预先设定沙粒起跳速度大小和方向,调整跃移轨迹顶端沙粒水平速度和最大跃移高度,使计算得出的沙粒起跳速度与设定值吻合,以此确定沙粒跃移轨迹,这种计算格式可以计算任意起跃角和任意起跳速度沙粒的跃移轨迹．计算结果与Ungar模型的计算结果非常吻合,这一计算格式拓展了风沙跃移数值模拟的计算方法．     

热压自然通风室内污染物浓度演变特性

为探究热压自然通风向稳态发展过程室内气态污染物的迁移规律,对不同高度处污染物浓度演化进行了分析.首先结合预测热分层瞬时变化的非均匀三层模型,针对室内不同的下层污染物混合特性,建立了均匀混合和纯置换两种热压自然通风室内污染物输送模型;其次,采用4阶龙格-库塔(Runge-Kutta)方法迭代求解,得到了通风过程室内污染物...     

基于HyperXtrude的薄壁铝型材挤压成形仿真模拟

基于HyperXtrude软件分析薄壁六边形结构挤压成形稳态过程,研究不同状态下金属材料的应力应变、挤压力变化、流速变化和温度等物理参数量的变化趋势,以这些物理参数变化趋势来量化预测该型材挤压成形性。通过仿真模拟清楚反应薄壁六边形结构铝型材在挤压过程的变化特性,预测薄壁结构挤压成形过程中的变形、翘曲、开裂和流速不均等缺陷,为及时对挤压成形工艺方案调整或模具结构改进设计提供指导。     

城市道路交通网络容量问题分析

城市道路网络容量是判断现状城市道路网是否处于一种平衡稳定状态的重要决策变量。在对路网容量影响因素进行分析的基础上,将路网容量计算方法按照微观和宏观2个层面划分。针对研究路网容量存在的问题,提出一种新的基于出行者随机路径选择的研究路网容量方法,为今后深入研究在复杂道路条件下的路网容量提供科学理论依据和技术路线。     

Fe-C 合金激光熔凝硬化研究

采用大功率ＣＯ２激光器对不同含Ｃ量的Ｆｅ－Ｃ合金进行了激光熔凝处理，用光学显微镜、电子探针及Ｘ射线衍射仪等研究了激光熔凝层的组织与性能以及激光加工工艺参数和含Ｃ量对熔池尺寸、硬度的影响，结果表明，Ｆｅ－Ｃ合金经激光熔凝处理后，表层组织细化，硬度显著提高，熔化层中存在碳烧损和氧化现象．     

大功率PEMFC空气系统电流跟随分段PID控制方法研究

为优化大功率燃料电池系统空压机控制效果,基于离心式空压机系统模型,提出了大功率质子交换膜燃料电池(proton exchange membrane fuel cell, PEMFC)空气供给系统的电流跟随分段PID控制方法.该方法以离心式空压机响应特性为基础,以实际工作电流为跟随目标,在动态响应与稳态控制阶段采用不同的PID参数进行闭环控制,并进行了模拟仿真研究.最后,在实验室已有的150 kW燃料电池系统基础上的实验验证,模拟仿真与实验验证结果表明,仿真模型计算误差控制在5%以内,准确的反映了离心式空压机与空气供给系统的特性,所提出的大功率PEMFC空气供给系统的电流跟随分段PID控制方法不仅能够满足PEMFC电堆稳态控制要求,同时将动态响应时间缩短至3 s以内,控制效果良好.