Coupling effect of Brownian motion and laminar shear flow on colloid coagulation:a Brownian dynamics simulation study

Simultaneous orthokinetic and perikinetic coagulations（SOPCs） are studied for small and large Peclet numbers（P e） using Brownian dynamics simulation.The results demonstrate that the contributions of the Brownian motion and the shear flow to the overall coagulation rate are basically not additive.At the early stages of coagulation with small Peclet numbers,the ratio of overall coagulation rate to the rate of pure perikinetic coagulation is proportional to P 1/2 e,while with high Peclet numbers,the ratio of overall coagulation rate to the rate of pure orthokinetic coagulation is proportional to P 1/2 e.Moreover,our results show that the aggregation rate generally changes with time for the SOPC,which is different from that for pure perikinetic and pure orthokinetic coagulations.By comparing the SOPC with pure perikinetic and pure orthokinetic coagulations,we show that the redistribution of particles due to Brownian motion can play a very important role in the SOPC.In addition,the effects of redistribution in the directions perpendicular and parallel to the shear flow direction are different.This perspective explains the behavior of coagulation due to the joint effects of the Brownian motion（perikinetic） and the fluid motion（orthokinetic）.

Hydrodynamics of passing-over motion during binary droplet collision in shear flow

A combined experimental and numerical study is undertaken to investigate the hydrodynamic characteristics of singlephase droplet collision in a shear flow. The passing-over motion of interactive droplets is observed, and the underlying hydrodynamic mechanisms are elucidated by the analysis of the motion trajectory, transient droplet deformation and detailed hydrodynamic information（e.g., pressure and flow fields）. The results indicate that the hydrodynamic interaction process under shear could be divided into three stages: approaching, colliding, and separating. With the increasing confinement, the interaction time for the passing-over process is shorter and the droplet processes one higher curvature tip and more stretched profile. Furthermore, the lateral separation ?;/R;exhibits larger decrease in the approaching stage and the thickness of the lubrication film is decreased during the interaction. As the initial lateral separation increases, the maximum trajectory shift by the collision interaction is getting smaller. During the collision between two droplets with different sizes, the amplitude of the deformation oscillation of the larger droplet is decreased by reducing the size ratio of the smaller droplet to the bigger one.

Effect of seismic super-shear rupture on the directivity of ground motion acceleration

The effect of seismic super-shear rupture on the directivity of ground motions using simulated accelerations of a vertical strike-slip fault model is the topic of this study. The discrete wave number/finite element method was adopted to calculate the ground motion in the horizontal layered half space. An analysis of peak ground acceleration （PGA） indicates that similar to the sub-shear situation, directivity also exists in the super-shear situation. However, there are some differences as tbllows： （1） The PGA of the fault-normal component decreases with super-shear velocity, and the areas that were significantly affected by directivity in the PGA field changed from a cone-shaped region in the forward direction in a sub-shear situation to a limited near-fault region in a super-shear situation. （2） The PGA of the fault-parallel and vertical component is not as sensitive as the fault-normal component to the increasing super-shear velocity. （3） The PGA of the fault-normal component is not always greater than the fault-parallel component when the rupture velocity exceeds the shear wave velocity.

Shear velocity criterion for incipient motion of sediment

The prediction of incipient motion has had great importance to the theory of sediment transport. The most commonly used methods are based on the concept of critical shear stress and employ an approach similar, or identical, to the Shields diagram. An alternative method that uses the movability number, defined as the ratio of the shear velocity to the particle＇s settling velocity, was employed in this study. A large amount of experimental data were used to develop an empirical incipient motion criterion based on the movability number. It is shown that this approach can provide a simple and accurate method of computing the threshold condition for sediment motion.

Dynamic shear modulus of undisturbed soil under different consolidation ratios and its effects on surface ground motion

The dynamic shear modulus for three types of undisturbed soil under different consolidation ratios is presented by using the resonant column test method. Its effects on surface ground motion is illustrated by calculation. The test results indicate that the power function is a suitable form for describing the relationship between the ratio of the maximum dynamic shear modulus due to anisotropic and isotropic consolidations and the increment of the consolidation ratio. When compared to sand, the increment of the maximum dynamic shear modulus for undisturbed soil due to anisotropic consolidation is much larger. Using a one-dimensional equivalent linearization method, the earthquake influence factor and the characteristic period of the surface acceleration are calculated for two soil layers subjected to several typical earthquake waves. The calculated results show that the difference in nonlinear properties due to different consolidation ratios is generally not very notable, but the degree of its influence on the surface acceleration spectrum is remarkable for the occurrence of strong earthquakes. When compared to isotropic consolidation, the consideration of actual anisotropic consolidation causes the characteristic period to decrease and the earthquake influence factor to increase.

Introduction of Simulating the Motion of Rigid Ellipsoidal Objects in Ductile Shear Zone Based on the Jeffery's Theory

Rigid ellipsoidal objects(gravels and porphyroclasts)in ductile zone is an important factor to indicate the kinematics and dynamics.Jeffery’s theory(Jeffery G,1922),a quantitative research method,for the rotation ofthe rigid objects(no deformation)in the Newtonian fluid of the simple deformation field has been widely applied by geologists to the study of fabrics in rocks.The theory

Incipient Motion of Sediment Under Currents

Summarized in the paper are the author's studies on incipient motion of sediment in recent 40 years. In addition to the forces of gravity, drag and lift, the cohesive force and the additional static pressure are important for fine particles. The relations between three stages of incipient motion are defined by use of instantaneous velocity. Formulas for initial velocity and critical shear stress are given and overall verified by the author's and others' experimental data.

Simotion D在攀钢冷轧厂2#横切机组飞剪的应用

较系统地论述了飞剪电气伺服控制系统Simotion D的特点。阐述了控制系统的结构组成、选型,飞剪控制系统的HMI人机监控界面,采用以太网和Profibus-DP总线实现现场传动设备与PC机及监控画面的通讯连接,实现了对飞剪的远程操作控制,重点介绍了该系统使用组态软件设计及在攀钢冷轧厂2#横切机组的实际应用。

Experimental Study on Silt Incipient Motion Under Wave Action

Experiments on silt incipient motion under wave action were carried out. Under wave action, for different wave periods, water depths and bulk densities of silt, the shear stress or height of waves for incipient motion was determined, and a relation between the shear stress and bulk density of silt was established. Results indicate that the critical shear stress depends on the structure of the silt itself, related to the tightness between the grains （or bulk density）. Exterior condition is only an external cause of silt incipient motion, and the critical shear stress for the incipient motion is the token of exterior condition.

A numerical method for spherical particle motion in turbulent flow with large Reynolds number

A new mathematical model, fluctuation spectrum random trajectory model (FSRTM) for the particle motion in environmental fluid was developed using Lagrangian method, in which the time mean velocity of the fluid was calculated by a time mean velocity formula for two dimensional homogeneous shear turbulent flows in open channel, the velocity fluctuation of the fluid was determined by Fourier expansion and fluctuation spectrum, and the particle motion equation was solved using Ronge Kutta method. For comparison, the spherical cation exchange resins with a density of 1 44 g/cm\+3 and diameters ranging from 0 50—0 60 mm, 0 60—0 70 mm and 0 80—0 90 mm were selected as the experimental solid particles, and their moving velocities and trajectories in shear turbulent flows with the flow Reynolds number of 4710, 10240, 11900 and 20760 were investigated. The comparing analyses of the modeled results with the measured results have shown that the model developed in this paper can describe the motions of the particles in shear turbulent flow.

综合物探在矿山深部资源勘查中的应用

矿产资源是社会和经济发展必不可少的物质基础,目前国内多数老矿山面临已探明储量枯竭的严峻形势,现有的勘查知识和技术难以解决矿山找矿勘查所遇到的特殊难题。针对矿山找矿的特殊性,本文结合安徽省霍邱某矿区的地质及物探资料,在采矿区选取典型剖面进行重磁、微动及可控源音频大地电磁法(Controllable Source Audio Magnetotelluric Method,CSAMT)。以微动和音频大地电磁数据分析推测浅部矿体采空及塌陷区;在深部将微动勘探与重力数据结合,取长补短,通过剪切模量将微动视横波速度与地下介质密度直接联系起来,经已知矿体位置剪切模量的分布规律并结合重磁反演在300 m以深推测了两条近平行层状分布的矿体,矿体长200~250 m,最厚处约50 m;在标高100~200 m的类似S形褶皱拐点处可能为成矿有利位置;同时推测已知主矿体在底板以深还有延伸。通过本次工作,证实了在当前老矿区内,将新技术微动勘探与传统物探方法相结合,各取其长,能提高矿山深边部及外围隐伏矿床(体)定位预测的有效性,挖掘新的找矿潜力。

基于多水准的高强钢框架-D形偏心支撑结构层剪力分布研究

高强钢框架GD形偏心支撑结构中耗能梁段采用Q355钢,非耗能构件(即框架梁和柱)采用高强度钢材,形成一种新型结构体系.耗能梁段在结构遭遇罕遇地震时充分发挥塑性变形耗能,保护高强钢框架处于弹性受力状态,高强钢框架GD形偏心支撑结构由于在塑性状态下结构刚度发生改变,其层剪力分布模式不再符合基于强度的设计理论,因此,本文研究了高强钢框架GD形偏心支撑结构在多水准地震动状态下的层剪力分布模式.本文设计了四种不同层数(4层,8层,12层和16层)和三种不同耗能梁段长度(900mm,1000mm和1100mm)的高强钢框架GD形偏心支撑结构,输入40条近场脉冲地震和40条远场地震记录,得到结构在多遇地震、设防地震、罕遇地震以及极罕遇地震下的层剪力分布模式,并对罕遇地震下的层剪力分布模式进行参数标定,获取塑性状态下结构的弹塑性侧向力分布状态.

非基岩场地基础隔震核岛厂房抗震性能分析

为了研究非基岩场地条件下基础隔震核电工程结构的抗震性能,本文依据外源波动理论提出了考虑土-结构相互作用效应的基础隔震核电工程结构抗震分析方法,该方法实现了地震动的高精度输入以及整体系统的直接求解,通过与传统封闭体系振动法计算结果的对比验证了其有效性。建立了基础隔震核岛厂房-地基整体有限元模型,开展了核岛厂房地震响应分析,讨论了不同剪切波速场地条件下核岛厂房的基础隔震性能。研究结果表明:非基岩场地条件下基础隔震核岛厂房表现出良好的隔震效果;随着场地剪切波速的降低,基础隔震的隔震能力逐渐下降,与剪切波速为1067 m/s的场地相比,当场地的剪切波速为305 m/s时,核岛厂房结构顶部的楼层反应谱、加速度放大系数和层间位移角的隔震率分别减小了14.30%、13.50%和23.41%。为了保证核电工程结构的安全性,在基础隔震设计中应充分考虑非基岩场地条件下的SSI效应。

青藏高原及其周缘的各向异性研究

本文利用中国国家台网在青藏地区布设的台站记录到的近5年震级在5.8以上、震中距在东经88°~120°之间的39个远震地震事件进行SKS横波分裂测量,来研究青藏高原及其周缘地区的各向异性及变形特征。在青藏内部地区,SKS横波分裂测量的快轴自西向东逐渐从NE—SW向转为E—W向,再转为NNE向,与GPS速度场方向基本一致,呈顺时针方向变化。造成此地区SKS分裂测量结果的原因可能为缅甸板块向东俯冲时发生向西的后撤运动,使得此区域的岩石圈产生环状变形。川滇地区南部的GPS数据显示了近ES向的地表形变且走滑断层走向为NW—SE向,Pms地壳各向异性快轴方向主要为S—N向或NNE—SSW向,SKS分裂结果揭示了E—W向的上地幔各向异性特征,与Pms快轴方向以大角度相交或垂直,说明云南地区深部软流圈地幔流动场与地壳及地表变形特征不一致,地幔和地壳的变形机制和各向异性来源不同,发生解耦变形。

原子力显微镜加工轨迹测压电剪切叠堆二维高频运动位移

针对两轴压电剪切叠堆在高频电压驱动下的二维高频运动的位移测量问题,提出使用(AFM)探针在敲击模式下的加工痕迹测量压电剪切叠堆运动位移的方法,首先制备热塑性聚合物聚甲基丙烯酸甲酯(PMMA)薄膜,随后进行AFM探针敲击加工实验,扫描AMF探针加工轨迹并对其进行后处理,成功得到压电剪切叠堆的二维高频运动位移,实现了以半接触的方式对压电剪切叠堆二维高频复杂运动的准确检测,并依据实验数据对压电剪切叠堆二维运动位移随电压幅值及频率的变化情况进行分析。实验结果表明,在10 Hz~5 kHz的激励信号频率范围内,所提出的方法能准确测量压电剪切叠堆的运动位移。

高速列车转向架区域积雪问题的数值研究

当高速列车在高寒雨雪地区行驶时,转向架区域容易形成积雪,对高速列车的安全行驶造成威胁。在积雪轨道上行驶的高速列车,其转向架区域积雪中雪粒来源于地面积雪,因此基于壁面切应力,建立风致积雪雪粒运动模型,研究地面积雪中雪粒在列车风作用下的运动情况。采用欧拉-拉格朗日方法,基于雪粒沉积准则,建立转向架区域雪粒沉积边界模型,研究风致雪粒运动情况下转向架区域积雪分布。研究结果表明:高速气流在转向架正下方区域出现高速上扬的现象;转向架区域的车体板件、构架和轴箱等为主要的积雪部位;转向架区域雪粒沉积数量与转向架的位置、雪粒的密度和直径及壁面条件有关。

2023年2月6日土耳其双震地震动显著持时特征

2023年2月6日土耳其东安纳托利亚断裂带连续发生2次M_(W)7.8、M_(W)7.5强震,震害调查表明地震序列下工程结构更易发生破坏。本研究选取2次强震中台站记录的311组地震动数据,通过随机效应回归方法给出了土耳其双震下水平及竖直方向5%~75%显著持时D_(S5-75)和5%~95%显著持时D_(S5-95)回归模型,与现有研究结果进行比较,验证了本研究回归模型的合理性。研究结果表明,土耳其2次地震竖直方向D_(S5-75)和D_(S5-95)均明显高于水平方向,断层距>10 km时显著持时回归结果随断层距增大速率大于其他模型。本研究得到的地震动水平和竖直方向显著持时特征可为此次土耳其双震部分震害特征提供合理解释,同时表明了地震动竖向显著持时研究的重要性,可为序列型地震显著持时研究提供参考。

远近场地震动对隔震建筑抗震韧性影响分析

不同类型的地震动对隔震结构的地震响应和抗震韧性影响不同,为进一步探究其影响的差异,本文以北京地区某7层RC框架-剪力墙隔震结构为例,分别选取近场脉冲地震动、近场无脉冲地震动和远场地震动各11条进行设防地震和罕遇地震下的弹塑性分析计算及抗震韧性评价。分析结果表明:在地震作用下,远场地震动与近场无脉冲地震动响应相近;近场脉冲地震动对层间位移角、楼层加速度的影响远大于其他两类地震动,隔震层位移均值接近规定限值;近场脉冲地震动因其极大的地震响应导致抗震韧性评价各项指标远不如其他两类地震动,设防地震下远近场地震动均满足抗震韧性一星水准,罕遇地震下近场无脉冲地震动和远场地震动均满足韧性三星,而近场脉冲地震动只能达到韧性二星水准。研究结果可为地震灾害防范和隔震结构韧性设计提供参考。

不同类型地震动下RC框剪结构协同工作对比分析

确保强震下双重抗侧力结构的协同工作是实现多道抗震防线的关键。基于地震动特性分析,对比了普通地震动、远场长周期地震动、近断层向前方向性地震动及近断层滑冲型地震动作用下RC框架-剪力墙结构的协同工作性能,并分析了刚度特征值及结构周期对其的影响;最后初步提出了特殊地震动作用下RC框架-剪力墙结构考虑内力重分配的框架剪力调整方法,并将其与规范中的调整方法进行了对比。结果表明:三类特殊地震动作用下的框架剪力分担率均大于普通地震动,尤其是远场长周期地震动,在地震动强度较小时也能使框架剪力出现较大增长;周期较大结构的中下部楼层框架剪力增大较快;结构框架剪力分担率随刚度特征值的增大而增大,但内力重分配程度逐渐减小;建议在结构抗震设计时,考虑不同类型地震动特性和刚度特征值对结构内力重分配的影响。

基于仿真动力学模型的缺陷轴承动态特性分析

滚动轴承是数控机床主轴传动系统中重要的支撑部件,轴承组件出现缺陷会影响整个数控机床传动系统的使用性能和工作效率。为了探究缺陷状态下轴承内部动态特性的差异,以7002C角接触球轴承为研究对象,进行了缺陷轴承动态特性研究。首先,利用有限元仿真软件,构建了轴承组件存在凹坑缺陷的仿真动力学模型;随后,对轴承不同转速下的滚珠公转速度仿真结果和理论计算结果进行了比较,验证了所建立动力学仿真模型的准确性;最后,综合分析了轴承外圈缺陷、滚珠缺陷及两者复合缺陷时的动态特性。研究结果表明:复合缺陷相对于单一缺陷有更高的剪切应力,且呈现波动剧烈的趋势;不同故障状态展现出振动信号的差异,滚珠缺陷表现出较小波动,外圈缺陷较稳定,而复合缺陷最不稳定,振动幅度最大;滚珠的公转速度表现出不规则和不一致的变化,滚珠缺陷、外圈缺陷和复合缺陷在速度曲线上表现出相似但略有不同的周期性和峰谷延迟。所构建的有限元模型可用于研究不同故障状态下滚动轴承的动态特性,为轴承优化设计提供参考。