超声流量计管道流场的模拟与分析

针对非理想流场对超声流量计测量的影响,研究单、双弯管流场的流速分布特征。通过对理想层流、湍流的模拟计算,得出单、双弯管流场的流速分布关系。通过流速分布曲线和流速等值线分布情况可以看出,单弯管流场的二次流分量是两个对称的涡,纵向截面的线平均速度是对称的。双弯管流场的二次流是单一的涡,在截面侧后方会出现回流,使速度等值线及截面线的平均速度分布很不规则。     

应用流体力学理论优化气流流型

洁净室的气流流型应以有效地排除污染粒子为优先。分析指出,气流流型应符合下述原则,即单向气流应接近流体力学中的渐变流和非单向气流尽量接近平面流动。     

A flexible blood flow phantom capable of independently producingconstant and pulsatile flow with a predictable spatial flow profile forultrasound flow measurement validations

The validation of the ultrasound time-domain correlation method of measuring blood flow has required the development of a flexible blood flow phantom capable of generating predictable flow profiles under a wide variety of conditions. The purpose of the phantom is to generate flow with well-known flow properties and not to mimic actual in vivo vessels. This paper describes a flow phantom which can independently generate both constant and pulsatile flow over a wide range of flow rates with a spatially fully developed laminar flow profile. It incorporates a computer-controlled pulsatile pump, which can produce different temporal pulsatile waveforms. The flow phantom also supports multiple vessels, different vessel sizes, as well as different attenuating media. The fluid most commonly used in the phantom is Sephadex mixed with water, and the probability density function of ultrasound reflected from Sephadex is experimentally determined and compared with that of blood. Examples of different constant and pulsatile flow experiments using the phantom are presented.     

基于SVM的油水两相流流型识别算法

油水两相流流型不仅影响两相流的流动特性、热传和传质性能,而且影响系统运行时的可靠性和效率.采用统计理论、小波包理论相结合的方法对垂直上升管内油水两相流的电导波动信号进行分析,得到8个能反应油水两相流流动特性的特征参数.设计支持向量机寻优函数,将这些参数作为流型的特征向量,利用支持向量机进行训练并识别流型.实验结果表明:...     

Occlusion-aware optical flow estimation

Optical flow can be reliably estimated between areas visible in two images, but not in occlusion areas. If optical flow is needed in the whole image domain, one approach is to use additional views of the same scene. If such views are unavailable, an often-used alternative is to extrapolate optical flow in occlusion areas. Since the location of such areas is usually unknown prior to optical flow estimation, this is usually performed in three steps. First, occlusion-ignorant optical flow is estimated, then occlusion areas are identified using the estimated (unreliable) optical flow, and, finally, the optical flow is corrected using the computed occlusion areas. This approach, however, does not permit interaction between optical flow and occlusion estimates. In this paper, we permit such interaction by proposing a variational formulation that jointly computes optical flow, implicitly detects occlusions and extrapolates optical flow in occlusion areas. The extrapolation mechanism is based on anisotropic diffusion and uses the underlying image gradient to preserve structure, such as optical flow discontinuities. Our results show significant improvements in the computed optical flow fields over other approaches, both qualitatively and quantitatively.     

基于多组博弈的新型网络流量控制模型

该文研究了具有强分布式特征和分层结构的通信网络流量控制问题,借鉴多组博弈模型来研究新型的网络流量控制模型,构造了基于网络流量速率和时延为参数的流量效用函数,使之能适度地满足不同业务的用户流量QoS需求,利用多组博弈优化模型建立了基于Min-Max的公平的网络流量控制博弈模型。理论上证明了提出的网络流量控制模型的非劣纳什策略存在性。数值仿真验证了模型的正确性,仿真结果验证了用户流量在非劣纳什均衡点的效用值是帕累托占优的。     

Flow time measurements for underfills in flip-chip packaging

Flow time is a key material property for underfill materials in flip-chip applications. In this paper, we will discuss how to use flow time testing for underfill flow evaluation and material screening. The flow time of several underfills was measured at elevated temperatures using test pieces made from glass microscope slides. The material properties impacting underfill flow, such as viscosity, contact angle, and surface tension, were also experimentally measured and used to calculate estimated flow times using the Washburn equation. Empirical and calculated flow times were compared. The effects of channel width and flow distance on flow time were also studied. Additionally, the effect of a tilted stage on flow time, epoxy tongue, and void formation was evaluated.     

保护气体对接头形貌及熔滴过渡的影响与模拟

为了研究保护气体流量对复合焊接接头形貌及熔滴过渡的影响，采用5mm厚的高强钢板材进行了激光电弧复合焊接试验的理论分析和实验验证，获得了不同气流量下的焊缝形貌以及焊接过程中电弧和熔滴图像。结果表明，随着保护气体流量的增大，焊接熔深先增大后减小；当保护气体流量在25L/min，焊接熔深达到最大；且焊缝的铺展性较好，飞溅较少；保护气体流量通过影响熔滴过渡的形式，对熔滴过渡频率产生影响；随着气流量的增大，熔滴过渡频率减小，且在25L/min时，熔滴过渡频率较稳定；采用FLUENT软件对气流量进行数值模拟，气流量越大，保护气体流速越大，在工件表面的作用面积减小。该研究结果为实际工程应用中选择保护气体流量制备高质量的焊缝奠定了基础。     

数据流计算机研究

数据流计算机解决了传统计算机时钟偏移的问题，具有低功耗和高并行性等优点。本文介绍了数据流计算机的发展驱动、基本概率、设计方法、编程语言，以及现有的数据流计算机；最后展望了数据流计算机的研究方向和重点。数据流计算机虽然还没有得到实际应用，但具有很高的研究价值。     

扩散炉管气体流动分析和流量计算数学模型

环境温度气体通过进气管进入高温扩散炉管后迅速膨胀,气体流量和流速均数倍增加;气体射流在炉尾形成的紊流区延伸到工艺恒温区范围,导致靠近炉尾恒温区的气体流动不稳定。通过放置挡板或挡片的方式可以减轻炉尾紊流区对恒温区Si片工艺的影响。根据扩散炉管内气体的流动状态和气体动力学有关参数和计算方法,推导出计算气体流量的数学模型公式,只需利用扩散炉管的基本参数就可以计算出需要通入炉管的环境温度气体流量,减少凭经验判定气体流量参数的盲目性,减少不必要的气体材料消耗。     

流程设计的系统思想及QFD的应用

流程设计应该进行系统思考,从顾客需求的获取及流程特性需求,利用QFD(质量功能展开)转化为可操作的流程参数,并同时考虑流程风险控制.同时本文以案例形式介绍如何在流程设计阶段引入QFD.     

高超声速拦截弹绕流红外辐射特性数值模拟

研究拦截弹绕流红外辐射特性对红外导引头设计具有重要意义。基于求解化学非平衡Navier-Stokes方程的方法,对高超声速拦截弹化学反应绕流进行数值模拟。在此基础上,基于谱带辐射模型,对拦截弹侧面的光学窗口附近流场在0.8~20 m波段的光谱辐射特性进行数值计算,分析窗口附近流场红外光谱辐射随飞行参数的变化特征和规律。研究表明:拦截弹窗口流场光谱辐射主要来源于CO2和NO分子的振动-转动谱带;飞行马赫数一定,窗口流场光谱辐射沿飞行高度的变化规律主要由流场中气体分子的数密度分布主导;飞行高度一定,窗口流场光谱辐射随飞行马赫数的变化规律主要由流场温度控制,随着飞行马赫数增大,流场中NO分子的光谱辐射效应增强。     

The effects of rheological and wetting properties on underfill filler settling and flow voids in flip chip packages

As the bump diameter and bump pitch of flip chip packages get smaller, the underfill becomes more resistant to flow. Therefore, low viscosity underfills are used in the process to increase the throughput. Problems associated with low viscosity underfills include filler settling and flow induced voids due to fast edge flow. In this paper, we will discuss how the rheological properties can affect underfill filler settling and flow voids. The effects of yield stress of underfill on filler settling and the effects of shear thickening of underfill at large shear rates on flow voids of underfill were investigated. It was shown that the underfills with small fillers have shear-thickening viscosity and yield stress. The filler settling of underfills with yield stress was greatly reduced. A video underfill flow metrology with quartz die packages was developed for flow void observation. The correlation between underfill, substrate properties, and flow voids formation based on the video underfill flow measurement will be discussed.     

The mechanism for the formation of slug flow in vertical gas–liquid two-phase flow

This paper studies the mechanism for the formation of a slug flow in vertical gas–liquid two-phase flow. By analyzing void fraction waves and their instability, it is proved that the formation of a slug flow regime is due to the increase of void fraction waves, which causes the conglomeration of gas bubbles and the coalescence of bubble clusters in unstable bubbly flow. Experiments and analysis show that intense turbulence can restrain the formation of Taylor bubbles. Therefore, in a large diameter vertical pipe, a Taylor bubble can form under a condition of low continuous volume flux due to the action of void fraction waves. However, the coalescence effect of void fraction waves as it affects bubbles is suppressed in high continuous volume flux, and therefore, a slug flow regime cannot be observed in the evolution of flow patterns. Under a condition of high continuous volume flux (V_L=0.15 m/s) described in the paper, the flow pattern evolution is from cap bubbly flow to cap churn flow, and then gradually to churn flow with the increase of void fraction.     

广电企业业务流程的分析和优化

介绍了广电网络业务流程的整体结构,对目前广电业务流程的评价指标体系进行了分析,提出了以流程时间、流程速率、工作队列等组成广电网络业务流程的实例--业务流程的评价指标,以及基于Little法则的广电网络业务流程评价指标体系曲简化方法.研究了采用时间Petri网建模对企业业务流程分析的方法和分析优化步骤,并针对广电网络业务流程的具体业务流程给出的实际案例进行了分析.     

基于小波的稳健光流计算方法

针对系统误差导致光流计算稳健性较差及精度较低的问题,该文提出一种基于小波多分辨理论的稳健光流计算方法。所提算法基于小波多尺度分辨率特性,将光照条件变化及传感器噪声引起的系统误差包含进光流计算中以改善光流计算的稳健性及估计精度,并通过总体最小二乘法求解超定小波光流方程组以获得光流矢量。仿真结果表明,与传统的Lucas-Kanade算法、Horn-Schunck算法及基于小波的全向图像光流估计方法相比,所提算法可显著改善光流估计精度及稳健性。     

Preserving quality of service guarantees in spite of flowaggregation

We investigate how quality of service may be guaranteed to a flow of packets in the presence of flow aggregation. For efficiency, multiple flows, known as the constituent flows, are merged together resulting in a single aggregate flow. After the network node where the aggregation occurs, packet schedulers are aware of the aggregate flow, but are unaware of its constituent flows. In spite of this, we show that quality of service may be guaranteed to the constituent flows, provided the aggregation is performed fairly. When the delay bound of a flow is de-coupled from the flow's reserved rate, flow aggregation preserves the delay bound. When the delay bound of a flow is coupled to the flow's reserved rate, flow aggregation preserves, and in some cases improves, the delay bound     

遗传算法优化支持向量机的交通流量预测

交通流量预测是智能交通系统中的关键技术,针对当前交通流量预测模型存在不足,提出一种遗传算法优化支持向量机的交通流量预测模型。首先收集交通流量历史数据,并基于混沌理想对其进行相空间重构,然后将训练样本输入到支持向量机中进行学习,并采用遗传算法优化支持向量机参数,建立交通流量预测模型,最后采用测试样本对模型的性能进行测试。结果表明,相对于经典交通流量预测模型,本文模型可以更加准确描述交通流量预测复杂的变化趋势,提高了交通流量的单步和多步预测精度。     

倒装芯片下填充流动二维化数值分析方法的应用

下填充流动是确保倒装芯片可靠性的重要封装工艺,其流场和流动过程具有明显的二维特征,通过降维得到的二维化数值分析新方法能高效地模拟下填充流动过程.针对一种焊球非均匀、非满布的典型倒装芯片,用该数值分析方法模拟了单边下填充流动的过程,并用实验对模拟结果进行了检验.实验采用了可视化的下填充流动装置,倒装芯片试样采用硅-玻璃键合(SOG)方法制作.将数值模拟结果与实验结果比较发现,无论是流动速度还是流动前沿的形态,两者均呈现出较高的吻合度.这表明:针对下填充流动的二维化数值分析方法兼具高效性和准确性,具有较高的应用价值.