应用粒子图像测速技术建立铸造浇注过程水模拟充型液体自由表面速度场

采用粒子图像测速技术对平板类铸件浇注过程水模拟的充型自由表面速度场进行了测试分析。用气泡作为示踪粒子。对底注式、阶梯式和缝隙式浇注系统进行了水模拟研究，建立了底注武浇注系统液体充型过程的自由表面速度场。结果表明，所建立的自由表面速度场能定量地反映充型过程的液体自由表面状态。     

基于不规则网格模型的充型及凝固过程数值模似

采用直接差分法建立了液态金属充型过程模拟计算的数值模型。该模型对采用不规则单元剖分的网格模型进行充型及传热模拟计算具有广泛的适用性，能较好地处理具有复杂形状的铸件充型过程模拟。采用过流单元流量分配方法处理充型过程自由表面单元，并考虑了表面单元液态金属部分充填对传热计算的影响。对计算过程中速度和压力的修正、自由表面单元压力的计算及过流单元流量分配等进行了研究，应用上述模型开发了三维模拟计算程序，并成功地应用于薄壁铸件的充型过程模拟。     

充型过程中自由表面的数值模拟

采用守恒标量法确定充型过程中的自由表面,通过采用两个不同的时间步长计算充型过程的流场和自由表面,克服了流场计算时间步长过小的缺点,使得充型过程数值模拟的计算速度大大提高,而计算结果仍能满足工程实用的要求。     

基于Projection VOF方法的熔模铸造蜡模充型过程数值模拟

针对熔模铸造蜡模充型过程数值模拟软件自主开发，建立了流动场和温度场数学模型，采用Cross-WLF粘度模型描述蜡料的流变性能，基于Projection VOF方法进行蜡料流动过程速度场、压力场以及自由表面的求解。通过试验测量获取了K512型蜡料的热物理性能和流变性能的相关数据，拟合得到粘度模型参数。分别在蜡料常粘度和变粘度模型两种条件下对扳机铸件蜡模充型过程进行模拟，结果表明，所建立蜡模充型过程数学模型能较好地描述蜡料的动态流变特性和传热行为。     

充型过程的数值模拟技术

铸造充型过程的数值模拟技术是铸造领域的前沿技术。本文对充型过程数值模拟的发展过程、数学模型、计算方法以及自由表面的处理进行了介绍，并指出了当前研究中存在的问题。     

铝合金铸件充型过程及氧化膜卷入的数值模拟

对于直接有限差分法，提出了单元表面无量纲距离、表面充填比率和体积充填比率，以描述铸件充型过程中自由表面的形状，建立了相应的充型过程数学模型，考虑了自由表面形状对动量、质量和能量传输的影响；提出了充型过程自由表面碰撞中表面氧化膜破碎，及其后破碎氧化膜流动的计算模型。对实验铝合金铸件进行了模拟应用，通过实际铸件充型过程的特殊X射线实时观察和记录。及实际铸件的气孔、收缩缺陷分布的检测，对模拟结果进行了验证分析。结果表明：充型过程模拟结果与X射线实时观察结果吻合较好，尤其是自由表面的变化；氧化膜卷入模拟结果与实际铸件气孔、收缩缺陷的分布存在一定的对应关系。     

柴油机机体铸造充型过程有限元模拟

应用有限元法研究了12150V柴油机机体铸造的充型过程。使用有限法求解不可压缩牛顿流体流动控制方程,用体积函数法跟踪金属液自由表面的移动,预测了机体充型过程的流动速度场和温度场。以此为基础对机体铸造充型过程进行了评价,计算结果为发动机机体铸造工艺参数提供有益的参考。     

铝液充型过程计算机可视化技术研究

采用透明的耐高温石英玻璃观察窗,观察和记录铝液充型过程的图像信息,分析铝液的充型过程;以图像处理技术和计算机技术为基础,通过充型过程铝液自由表面的边缘检测及提取技术,获取液体充型的自由表面曲线,定量分析铝液充型过程的自由表面变化;定量分析的试验结果表明,铝液实际充型过程自由表面的变化对浇注系统设计的合理性具有一定的指导意义.     

数值模拟在缸盖铸造充型过程研究中的应用

应用数值模拟的方法研究了发动机缸盖铸造的三维充型过程。使用有限单元法求解不可压缩牛顿体流动控制方程,用体积函数法跟踪金属液自由表面的移动。数值模拟预测了金属液充型过程的流动速度场和温度场,并对充型过程进行了评价。模拟结果为发动机缸盖铸造工艺参数提供有益的参考。     

铸件三维充型过程耦合数值模拟

采用改进后的ＳＯＬＡ－ＶＯＦ方法处理自由表面,有效地克服了传统的ＳＯＬＡ－ＶＯＦ法中的“施体－受体”法在处理三维自由表面时精度差和时间步和菠的缺点。在自由表面处理上采用了新的压力插值函数,使三维自由表面的处理变得简单明了。用有限差分法建立了铸件三维充型过程流动与传热的耦合计算数值模型,并对大型灌壁铅合金件进行了数值计算。后处理中采用插值技术,直观地显示了充填过程中自由表面的位置和形状。     

磁性流体行波泵驱动能力因素分析

由于磁性流体内磁性颗粒的存在,使得在磁场作用下磁性流体的磁性颗粒也对外加磁场产生作用。采用迭代解偶计算法分析磁场作用下磁性流体的偶合问题。磁场强度、磁性流体的饱和磁化强度对行波泵的驱动能力产生直接的影响,随着磁场强度、磁性流体饱和磁化强度的不断增大,行波泵的驱动能力也不断增强。磁性流体的粘度对行波泵的驱动能力产生间接影响。随着磁场强度的变化,磁性流体的粘度也发生变化。其变化规律为：粘度随着磁场强度的增大而逐渐增大并且变化率逐渐变小。粘度越大,行波泵的驱动能力就越差。磁极形状的变化对磁性流体行波泵的驱动能力产生影响,随着磁极形状的变化,泵腔内磁感应强度也不断变化。当磁极同圆心的夹角到达45°时,驱动能力达到最大。     

Simulation of dendritic growth of magnesium alloys with fluid flow

Fluid flow has a significant impact on the microstructure evolution of alloys during solidification. Based on the previous work relating simulation of the dendritic growth of magnesium alloys with hcp (hexagonal close-packed) structure, an extension was made to the formerly established CA (cellular automaton) model with the purpose of studying the effect of fluid flow on the dendritic growth of magnesium alloys. The modified projection method was used to solve the transport equations of flow field. By coupling the flow field with the solute field, simulation results of equiaxed and columnar dendritic growth of magnesium alloys with fluid flow were achieved. The simulated results were quantitatively compared with those without fluid flow. Moreover, a comparison was also made between the present work and previous works conducted by others. It can be concluded that a deep understanding of the dendritic growth of magnesium alloys with fluid flow can be obtained by applying the present numerical model.     

Simulation of dendritic growth of magnesium al oys with fluid flow

Fluid flow has a significant impact on the microstructure evolution of alloys during solidification. Based on the previous work relating simulation of the dendritic growth of magnesium alloys with hcp(hexagonal closepacked) structure, an extension was made to the formerly established CA(cellular automaton) model with the purpose of studying the effect of fluid flow on the dendritic growth of magnesium alloys. The modified projection method was used to solve the transport equations of flow field. By coupling the flow field with the solute field, simulation results of equiaxed and columnar dendritic growth of magnesium alloys with fluid flow were achieved. The simulated results were quantitatively compared with those without fluid flow. Moreover, a comparison was also made between the present work and previous works conducted by others. It can be concluded that a deep understanding of the dendritic growth of magnesium alloys with fluid flow can be obtained by applying the present numerical model.     

高参数金属波纹管集装式机械密封腔内流场动力学特性研究

以计算流体动力学(CFD)数值计算理论及方法为基础,对处于高速、高温、高压复杂工况的波纹管集装式机械密封装置腔内流场进行了数值模拟分析,得到了密封腔内介质的温度场、压力场、湍动能及流场区域涡量分布,分析了腔内流体的流动及传热动力学特性,为动、静环温度场的热流固耦合数值算法提供依据.     

在线布流调节影响铸嘴型腔熔体流场和温度场的研究

建立了在线布流调节时铸嘴型腔熔体非定常流动和传热数学模型，应用数值方法仿真分析了入口速度斜坡变化时铸嘴型腔流场、温度场、压力场的动态演化过程。结果表明，对型腔进行在线布流调节来改善铸嘴型腔流场、温度场是可行的。     

旋转型磁性流体行波泵仿真研究

以旋转型磁性流体行波泵为研究对象,理论分析了旋转磁场作用下磁性流体特性和压强的关系。通过磁场和力场解耦计算分析旋转磁场作用下磁性流体的运动特性、磁场特性以及与压强的关系。用实验验证分析计算的科学性和合理性。在旋转磁场的作用下,磁性流体行波泵内填充磁性流体后,外加磁场对磁性流体在泵腔内的分布产生影响,同时由于磁性流体内磁性颗粒的存在对外加磁场也会产生影响;磁性流体在泵腔内会产生流动的现象;随着磁场的不断增强,磁性流体的流量也不断增加。     

铝电磁铸轧中熔体的频率响应

介绍了在铝铸轧工艺中用频率交替变化的电磁场抑制晶粒长大的方法,阐述了粘性流体与电磁波频率响应的关系,分析了电磁场频率与熔体波动对晶粒细化效果产生的影响。结果表明在d650mm×1600mm铸轧机系统中,电磁场的最佳频域范围为11～15Hz。     

A 2-D FINITE ELEMENT MODEL SIMULATION OF THE MELTING PROCESS OF AI-Ti ALLOY IN VACUUM INDUCTION FURNACE WITH COLD CRUCIBLE （VIFCC）

The development of a numerical model for the melting process of AI-Ti alloy target material in vacuum induction furnace with cold crucible (VIFCC) was described. It is a two-dimensional computational methodology to calculate electromagnetic field, heat transfer field and fluid flow field . Based on the aid of the finite element method with the commercial software--ANSYS, a superimposition method of a layer of copper and a slit to simulate the VIFCC melting process was used. The method was effective to save large quantity of memory and computing time. Meanwhile, a temperature distribution profile during the melting process was obtained. Validity of the model was confirmed by comparison between the result from calculation and those from direct measurement by optical pyrometer and indirect investigation by ingot macrostructure. A relatively good agreement was found. Further, a nearly directional solidification structure was obtained under properly controlling the cooling rate and heating power. Therefore. such model developed in this article is feasible.     

A study on the fabrication of curved surfaces using magnetorheological fluid finishing

A fabrication method of curved surfaces on silicon-based micro-structures using magnetorheological finishing is studied. Thorough explanations are made on the procedures for the evaluation and analysis of surface characteristics of a workpiece and on the fabrication method of the curved surface profile associated with the experiments using magnetorheological finishing. The effect of magnetic field around tool assembly on finished surface profiles is investigated using a finite element method (FEM). The analysis on the magnetic field is performed separately from that of the fluid flow field with the assumption that the field is weakly coupled to the working fluid at steady state with a certain geometric configuration adopted in this work. Several experiments were performed under controlled conditions and the results are demonstrated along with the physical interpretations thereof. The edge effect is turned out to be very important as the target workpiece gets smaller, which can be actively used for the fabrication of curved surfaces on millimeter-scale structures. Response surface methodology (RSM) is applied to predict the profile and roughness of the curved surface of the workpiece to be proceeded with a set of known experimental conditions. In order to use the RSM method, two control input and two response variables are chosen deliberately. Among the multi-regression models generally used in the modeling area, a second-order regression model is employed. The predicted results are verified through additional experiments performed independently.