Visualization of periodic flows over a sunroof opening by using a phase-marked PIV measurement

Flows over cavity openings are known to be highly structured and periodic due to the strong sound pressures emitted by the cavities. This article is concerned with the measurement of flow fields over the sunroof opening of an SUV. Since the PIV system used in the present work is not capable of taking phase-locked velocity fields during the measurement stage, phase-marked PIV measurements are performed and the phase-locked velocity fields are retrieved during a post-processing stage. The new PIV measurement method is shown to yield fairly accurate results with a proper choice of a phase-bandwidth. By using the phase-marked PIV measurement method, the evolution of large-scale structures in shear flow over the sunroof opening as phase changes is revealed. The detached shear layer is shown to fluctuate and then form a discrete large vortex convecting and impinging on the rear roof edge of the SUV. The average convection velocity of the vortex is calculated to be 0.45 of the nominal free stream flow velocity. Flow fields are compared for four different cases of deflector protrusion and a case without a deflector. Installation of a deflector can significantly change the flow field. For a deflector that reduces the buffeting noise by more than 10 dB, it is shown that turbulent fluctuations are initiated by the deflector but do not grow in amplitude as they convect downstream. As the deflector protrusion is increased, the amount of flow under the deflector increases in general. The flow exiting from the channel formed by the deflector and an A-frame is shown to increase the thickness of the shear layer near the leading edge of the sunroof opening.     

带纱网导流的天窗风振噪声仿真研究

利用纱网单体测试的速度与压降,拟合出纱网的阻力曲线后,就带纱网导流的天窗进行了风振噪声的仿真研究.对基础状态的车型进行了不同车速的风振噪声仿真,针对风振问题最大的车速进行了不同纱网高度和不同天窗开度的仿真.将仿真结果与道路试验结果进行对比,验证了仿真方法的可行性.     

沥青搅拌设备蜗壳除尘器流场仿真与试验

为研究导流板位置对蜗壳除尘器内流场和粉尘粒径的影响,以指导回收粉在沥青搅拌设备中的实际使用,在导流板3种不同位置工况下,对蜗壳除尘器内部气相和气固两相流动状态进行了数值模拟和试验验证。数值模拟基于FLUENT软件,其中气相流场模拟选用雷诺应力模型,气固两相流场模拟选择相间耦合的随机轨道模型模拟粉尘的运动轨迹,分别追踪了16 400个粒径在50~1 000 μm的粉尘,计算了除尘效率。在沥青搅拌设备工地分别采集了导流板3种位置工况下的回收粉,结合筛分和电镜扫描试验,分析粉尘粒径分布,并对数值模拟结果的吻合性进行验证。结果表明：导流板处于O位时,除尘器内部气流的径向速度、轴向速度和静压分布轴对称性较W位和M位好,可有效抑制非对称性扰流及夹带涡流,并削弱涡核摆动现象;导流板处于不同位置时,通过与粉尘颗粒的碰撞反弹来改变粉尘的运动轨迹,进而影响除尘器对不同粒径粉尘的除尘效率,且当导流板处于O位时更有利于对粒径大于100 μm的粉尘的回收。导流板处于O位时,试验测量的粉尘平均粒径为117.6 μm,筛底平均粒径为49.9 μm,均大于W位和M位的粒径,且与数值模拟的结论相吻合。沥青搅拌设备在实际生产过程中,应优先选择导流板O位布置,并根据回收粉粒径的需要进行实时调整。     

汽车天窗噪声的数值分析和控制

应用计算流体动力学软件fluent中的大涡数值模拟,对某汽车简化模型进行天窗噪声分析,并采用在天窗前沿增加腔体的措施来抑制天窗噪声。分析结果表明：改进后的天窗在压力场分布和监测点处的声压级上均优于改进前。     

中倾侧向坡中一种岩体破坏过程的模拟研究

基于G318国道雅安市飞仙关隧道出口东侧约1 km处公路内侧失稳边坡岩体野外详细调查，运用三维离散元程序，对已失稳边坡还原地质体并进行数值计算分析，阐明岩质边坡在失稳破坏过程中速度和位移的变化规律。分析结果表明:边坡岩体失稳首先是关键块体受挤压发生剪切破坏，然后导致后缘岩体失去平衡而发生滑移；在失稳破坏过程中，整体位移演化大致分为5个阶段，速度演化大致分为4个阶段，关键块体的位移和速度较失稳岩体要小，随着计算时步增加，他们之间的差值增大。     

电控单体泵燃油系统等速供油凸轮设计

阐述了电控单体泵等速供油凸轮设计流程及方法,以平均供油速率为出发点,首先设计凸轮的基圆,然后进行升程段和回程段的设计;在设计过程中,使用加速度为直线方程的过渡段,使凸轮各段的加速度连续,避免了凸轮在工作中由于加速度不连续造成冲击。在实际应用中,利用所述凸轮设计流程和方法,设计并匹配了电控单体泵的等速凸轮,取得了良好的效果。     

大跨桥梁抖振时域分析的程序化方法

介绍了一套以通用有限元软件为平台进行抖振时域分析的程序化方法,重点分析了作用在有限元模型加载节点上的随机抖振荷载的模拟方法。依照改进的Deodatis谱表示法给出了脉动风速场模拟程序的流程图。基于准定常假定,推导了便于有限元软件加载的脉动风速和抖振力时程之间的简化转换公式。按照该程序化方法,使用ANSYS软件对龙潭河特大桥进行了风致抖振时域分析,验证了该方法的实用性和有效性。     

多排开孔钢板剪力键群受剪性能研究

采用有限元软件Abaqus,对多排开孔钢板剪力键群的抗剪性能进行模拟研究。考察不同参数(混凝土强度、贯穿钢筋直径、开孔孔径、开孔排数、开孔距离、钢板厚度)对PBL剪力键承载力的影响及其影响规律,同时研究了多排PBL剪力键内力分布规律。结果表明:混凝土强度越大,PBL剪力键承载力越大,同时较迟进入强化阶段;增大钢筋直径在提高PBL剪力键承载力的同时也提高了其屈服后的刚度,且钢筋直径与PBL剪力键承载力呈二次函数关系;孔距不变时增大孔径,PBL剪力键承载力将先增大后减小,这是由于孔距未满足最小孔距要求;开孔排数增多会明显提高PBL剪力键承载力和初始刚度,且开孔排数与承载力呈线性关系;钢板厚度基本不影响承载力;当PBL剪力键的排数达到一定界限以上时,前4排承担了90%的外力,当排数较少时,不同排的剪力键承担的剪力分布为哑铃型。     

A study on the formation of vertical vortex in the cylinder of an I.C. engine using CFD: Effect of intake valve closing timing

Air flows in the intake ports and cylinders of a four-valve gasoline engine were numerically analyzed by means of an original CFD code named “GTT”. In this code, the k-ε turbulence model was used and the Chakravarthy-Osher 3rd order TVD scheme was applied to the convection terms in all the governing differential equations. The validity of the code was confirmed by comparing the calculated results of the mean velocity and turbulence intensity with the measured ones by means of LDV. Using the present code, the effect of the intake valve closing timing on the formation of vertical vortex in the cylinder of a four-valve engine was investigated. It was found that the turbulence energy in the combustion chamber near compression TDC can be increased by the retardation of intake valve closing timing in the case of intense vertical vortex, because the vertical vortex is intensified by the back flow from the cylinder to the intake ports.     

设置中央稳定板对大跨度悬索桥抗风性能的影响

在润扬长江公路大桥南汊悬索桥的节段模型风洞试验中,研究了稳定板高度对动力抗风稳定性的影响,采用了增设0.65 m高中央稳定板的有效措施,并获得了原断面和增设中央稳定板断面的气动导数和三分力系数;采用非线性静风和颤抖振时域方法,研究了设置中央稳定板对静动力抗风性能影响。结果表明,恰当地设置中央稳定板,不仅能够提高桥梁的颤振临界风速,还能够降低结构的抖振响应,而结构的静风失稳风速在正攻角下有所降低。     

纵向力对带榫管片环缝剪切破坏机制影响研究

为明确带榫管片环缝剪切受力机制及剪切受力过程中纵向力对管片结构环间接缝抗剪性能的影响,采用苏通GIL （Gas Isolated Line）综合管廊工程所用带有分布式凹凸榫的原型管片衬砌,通过局部原型试验,对带榫管片结构在考虑不同纵向力作用下的受荷过程中环间螺栓应力、环间分布式凹凸榫表面应力、环缝张开量进行了研究。结果表明：①不同纵向力作用下带榫管片结构环缝剪切受力机制不同,纵向力较小时环缝凸榫受力破坏方式为多次的凸榫混凝土冲削损伤破坏,而纵向力较大时环缝凸榫破坏方式为单次的混凝土剪切破坏,凹凸榫之间形成剪切破坏面。②不同纵向力作用下带榫管片结构环缝凹凸榫破坏最严重位置均靠近纵向接头处,为中间凸榫;两侧凸榫损伤程度较弱,纵向力较小时两侧凸榫损伤程度高于纵向力较高时。③环间纵向力的增加有助于提高带榫管片结构环缝的抗剪能力,可使凸榫均匀受力,同时降低凸榫的损伤程度,避免局部区域环缝接头与凸榫表面的应力集中;实际工程中可通过螺栓复紧等方式保持环间纵向力。④对于环缝张开量的控制是保持纵向力的主要目的,在实际工程中,可通过环缝张开量的状态与发展,通过分阶段分析凸榫受力模式,评估环缝凹凸榫抗剪能力的发挥程度,以达到充分利用榫槽抗剪性能的目的。     

Study on unsteady gas jet and wall impingement jet — Comparison experimental results with numerical analysis by discrete vortex method

Generally speaking, it is very difficult to observe the growing process of large scaled vortices in a transient gas jet. The vortices have great effect on the mechanism of mixture formation between the jet itself and the surroundings. The objective of the study presented here is the clarification of this mechanism in both cases of a free jet and a jet impinging on a flat wall by means of the flow visualization of 21) image taken by thin sheet of laser light in the experiments and the numerical analysis by the discrete vortex method. The mechanism of the vortex growth and the coherent structure of vortices entraining the surroundings are observed in the case of the free jet. In the wall impinging jet, the structure inside the jet is divided into four regions, that is, free jet region, impingement region, wall jet region and wall jet vortex region. The results of the numerical analysis agree qualitatively well with the experimental data.     

土石混合料K-G模型参数试验研究

为获取土石混合料的物理力学特征,以指导土石混填路基的设计和施工,对土石混合料的本构特征以及如何有效地获取其本构参数进行了研究。采用修正的内勒K-G模型作为土石混合料的非线性弹性本构模型,推导出了切线体变模量Kt和切线剪切模量Gt的线性表达式。采用大型土石混合料三轴试验机,利用图解法确定Kt、Gt线性表达式中各个参数。结果表明:(1)采用修正的内勒K-G模型作为土石混合料的非线性弹性本构模型,力学概念清楚,参数易于测定;(2)采用大型三轴试验方法测定土石混合料的K-G模型参数切实可行;(3)K-G模型中考虑了剪应力对体积变形模量影响的修正,因而K-G模型适用于具有剪缩或剪胀性的土。     

Analysis of automotive disc brake squeal considering damping and design modifications for pads and a disc

The squeal noise occurring from the disc brakes of passenger cars has been analyzed by using the complex eigenvalue method numerically. The contact between a disc and two pads was analytically modeled as many linear springs and dampers in an effort to develop the improved equation of motion derived on the basis of Lagrange’s equation and the assumed mode method. The finite element modal analysis results for disc brake components constitute an eigenvalue matrix in the analytical equation of motion. The complex eigenvalue analyses based on the equations of motion are able to examine the dynamic instability of a brake system, which is an onset of squeal, by considering the disc rotational effect. Numerical analyses showed that the modes unstable in an undamped analysis became stable in a damped case, which illustrates the important effect of damping on the squeal instability in a brake squeal simulation. Then several modified brake models were suggested and investigated how effectively they suppressed the occurrence of squeal noise. The brake parts such as a pad chamfer and a disc vane were modified and the influence of pad chamfer and vane shapes on squeal occurrence was proved to be significant. The numerical results showed that proper structural modification of a disc brake system can suppress the brake squeal to some extent.     

预制节段干接缝体外预应力混凝土简支梁抗剪性能试验

预制节段干接缝体外预应力混凝土梁是一种适应于快速化施工的新型桥梁结构形式,然而预制节段干接缝体外预应力混凝土梁的斜截面抗剪破坏机理尚不明确。针对此类状况以文献[18]中推荐的箱型截面为原型,进行4根预制节段干接缝体外预应力混凝土梁和3根整体式体外预应力混凝土梁的1：8缩尺模型试验,揭示不同剪跨比（1.5,2.0和2.5）、接缝类型（整体式接缝和干接缝）以及接缝数量（2和4）对预制节段干接缝体外预应力混凝土梁斜截面抗剪性能的影响。在试验过程中观测裂缝的发展,记录体外束应力增量、挠度发展规律、接缝张开情况和破坏形态。试验结果表明：体外预应力预制节段干接缝混凝土梁在键齿处容易产生裂缝;剪跨比是影响节段梁和整体梁抗剪承载力的主要因素,随着剪跨比增大,节段梁和整体梁的抗剪承载力明显降低;在剪跨比小于或等于2.0时,预制节段干接缝体外预应力混凝土梁的抗剪承载力小于相应的整体式混凝土梁的抗剪承载力;根据节段式混凝土梁的接缝是否张开,节段式混凝土梁的受力过程可划分为接缝张开前、后2个阶段;在接缝张开前,节段式混凝土梁的力学行为与整体式混凝土梁的无异;接缝张开前、后,节段式混凝土梁的力学行为发生改变;接缝是控制梁抗剪承载力的主要因素,但接缝数量对节段式混凝土梁抗剪承载力的影响不显著。     

交叉口交通流仿真研究

针对交通网络中的交叉口车流具有连续时间特性,动态信号灯的切换具有离散事件特性的情况,以4相位单交叉口为对象,建立了1个4相位交叉口的混杂自动机模型,该模型中以车辆排队长度为连续状态变量描述连续车流动态,以信号灯状态为离散状态变量描述离散信号灯动态。在该模型的基础上分析了交叉口各个方向的输入、输出车流动态,采用CheckMate3．6工具箱进行仿真。仿真结果表明该模型不仅能够刻画交叉口车流的动态混杂特性,而且能够验证信号灯配时方案对车流疏导是否有效,从而为信号灯配时设计提供1种检验方法。     

Optimal Preview Control of a Two-dof Vehicle Model Using Stochastic Optimal Control Theory

An optimal preview control algorithm is applied to a two degree of freedom(dof) vehicle model travelling with constant velocity on a randomly profiled road. The road roughness is modelled as a homogeneous random process being the output of a linear first order filter to white noise. The input from the road irregularity is assumed to be measured at some distance in front of the vehicle and this measured infonnation is utilized by the active controller to prepare the system for the ensuing input. The preview control algorithm is obtained by minimizing a quadratic performance index and by describing the average behaviour of the system by the covariance matrix of the vehicle response state vector. Results are presented for full state feedback and significant improvements in sprung mass acceleration, suspension working space and road holding are observed.     

汽车排气催化转化装置气流特性分析

运用计算流体动力学对汽车排气污染物控制装置———催化转换器进行了研究。通过对 4种不同引流区结构的速度场、压力场的计算 ,证明引流区的结构对催化转化装置的气流分布影响很大 ,应尽量避免采用直壁无引流过渡的结构 ,采用平滑过渡的引流区 ,不仅可减少涡流损失 ,而且压力损失大大小于其它结构。对实际汽车用催化转化器在不同排气流量下的速度场和压力损失进行了计算和对比。采用Ansys/FlotranCFD计算流体动力学软件 ,其计算结果与试验结果吻合较好 ,证明采用的方法是可靠的。     

非液化场地中桩-结构体系地震响应与桩基失效模式分析

基于非液化场地-群桩基础-上部结构大型振动台试验,建立了非液化场地-桩-结构体系地震响应数值计算模型,在分析桩-结构体系动力响应基础上,深入探讨动力荷载下非液化场地中的桩基失效模式。通过对比数值计算模型所得典型地震响应结果与试验结果,验证了数值计算模型的有效性和合理性,进一步探讨了非液化地基中土-结构体系地震响应规律,重点关注在地震作用下桩基失效过程及桩基-结构体系地震破坏模式。结果表明：在地震作用下,土体加速度在松砂层中不再放大,在最上部出现一定放大,且桩基加速度反应也有相似规律;各深度处土体动剪应力-动剪应变滞回曲线表现出对角线斜率小幅减小的趋势,说明等效剪切模量也出现不同程度的降低,也即地基各处土体抗剪强度均有一定下降;桩身最大弯矩出现在桩身中下部,在桩头与土层交界面附近桩身剪力较大,说明可能发生桩头剪切破坏或桩身弯曲破坏。     

An Optimization Model for Guiding Pedestrian–Vehicle Mixed Flows During an Emergency Evacuation

In most metropolitan areas, an emergency evacuation may require a potentially large number of pedestrians to walk some distance to access their passenger cars or resort to transit systems. In this process, the massive number of pedestrians may place a tremendous burden on vehicles in the roadway network, especially at critical intersections. Thus, the effective road enforcement of the vehicle and pedestrian flows and the proper coordination between these two flows at critical intersections during a multimodal evacuation process is a critical issue in evacuation planning. This article presents an integrated linear model for the design of optimized flow plans for massive mixed pedestrian–vehicle flows within an evacuation zone. The optimized flow can also be used to generate signal timing plans at critical intersections. In addition, the linear nature of the model can circumvent the computational burden to apply in large-scale networks. An illustrating example of the evacuation around the M&T Bank Stadium in downtown Baltimore, MD, is presented and used to demonstrate the model's capability to address the complex interactions between vehicle and pedestrian flows within an evacuation zone. Results of simulation experiments verify the applicability of our model to a real-world scenario and further indicate that accounting for such conflicting movements will yield more reliable estimation of an evacuation's required clearance time.