Wall slip behavior of cemented paste backfill slurry during pipeline based on noncontact experimental detection

Wall slip is a microscopic phenomenon of cemented paste backfill(CPB)slurry near the pipe wall,which has an important influence on the form of slurry pipe transport flow and velocity distribution.Directly probing the wall slip characteristics using conventional experimental methods is difficult.Therefore,this paper established a noncontact experimental platform for monitoring the microscopic slip layer of CPB pipeline transport independently based on particle image velocimetry(PIV)and analyzed the effects of slurry temperature,pipe diameter,solid concentration,and slurry flow on the wall slip velocity of the CPB slurry,which refined the theory of the effect of wall slip characteristics on pipeline transport.The results showed that the CPB slurry had an extensive slip layer at the pipe wall with significant wall slip.High slurry temperature improved the degree of particle Brownian motion within the slurry and enhanced the wall slip effect.Increasing the pipe diameter was not conducive to the formation of the slurry slip layer and led to a transition in the CPB slurry flow pattern.The increase in the solid concentration raised the interlayer shear effect of CPB slurry flow and the slip velocity.The slip velocity value increased from 0.025 to 0.056 m·s^(-1)when the solid content improved from 55wt%to 65wt%.When slurry flow increased,the CPB slurry flocculation structure changed,which affected the slip velocity,and the best effect of slip layer resistance reduction was achieved when the transported flow rate was 1.01 m^(3)·h^(-1).The results had important theoretical significance for improving the stability and economy of the CPB slurry in the pipeline.

Flow behavior in microchannel made of different materials with wall slip velocity and electro-viscous effects

In a microfluidic system, flow slip velocity on a solid wall can be the same order of magnitude as the average velocity in a microchannel. The flow-electricity interaction in a complex microfluidic system subjected to joint action of wall slip and electro-viscous effect is an important topic. This paper presents an analytic solution of pressuredriven liquid flow velocity and flow-induced electric field in a two-dimensional microchannel made of different materials with wall slip and electro-viscous effects. The Poisson- Boltzmann equation and the Navier-Stokes equation are solved for the analytic solutions. The analytic solutions agree well with the numerical solutions. It was found that the wall slip amplifies the fow-induced electric field and enhances the electro-viscous effect on flow. Thus the electro-viscous effect can be significant in a relatively wide microchannel with relatively large kh, the ratio of channel width to thickness of electric double layer, in comparison with the channel without wall slip.

Numerical Simulation of Twin-Screw Extrusion with Wall Slip

Wall slip boundary condition is first introduced into twin-screw extrusion with the Navier slip law. Three-dimensional isothermal flow in the twin-screw extruder is simulated by using the finite element package POLYFLOW. Profiles of velocity contours in the screw channel and shear rate distributions in the intermeshing region are presented for different slip coefficients. Curves of axial pressure difference, average shear rate and dispersive mixing index vs. the slip coefficient are plotted and discussed. Comparisons are also made between the wall slip conditions and the non-slip condition. The simulation results indicate that, as the level of wall slip decreases, the axial pressure difference rises, the shear effect is intensified and the axial mixing is also enhanced. All these flow characteristics seem to level off with the increase of the slip coefficient. However, because of the inherent limitation of the Navier slip law, use of an overestimated slip coefficient would predict an over-sticky state between the screw surface and the polymer melt.

Influence of wall slip on the hydrodynamic behavior of a two-dimensional slider bearing

In the present paper, a multi-linearity method is used to address the nonlinear slip control equation for the hydrodynamic analysis of a two-dimensional （2-D） slip gap flow. Numerical analysis of a finite length slider bearing with wall slip shows that the surface limiting shear stress exerts complicated influences on the hydrodynamic behavior of the gap flow. If the slip occurs at either the stationary surface or the moving surface （especially at the stationary surface）, there is a transition point in the initial limiting shear stress for the proportional coefficient to affect the hydrodynamic load support in two opposite ways： it increases the hydrodynamic load support at higher initial limiting shear stresses, but decreases the hydrodynamic load support at lower initial limiting shear stresses. If the slip occurs at the moving surface only, no fluid pressure is generated in the case of null initial limiting shear stress. If the slip occurs at both the surfaces with the same slip property, the hydrodynamic load support goes off after a critical sliding speed is reached. A small initial limiting shear stress and a small proportionality coefficient always give rise to a low friction drag.

Wall slip behavior of polymer melts on capillary rheometer

Wall slip behavior of three commercial polymer melts polypropylene(iPP),low-density polyethylene(LDPE)(branched chains) and high-density polyethylene(HDPE)(linear chains) were studied by using a capillary rheometer with twin bores at different temperatures.The results show that a sudden first-stick-then-slip transition was observed for HDPE and a first-slip-then-stick transition was observed for LDPE and iPP as the shear rate sweep was done in an increased order,which shows that the chain structure has an obvious effect on the wall slip behavior of polymers.The critical shear stress for the onset of stick-slip transition increases linearly with temperature for HDPE,which accords with the disentanglement mechanism proposed by Brochard and de Gennes.While the extrapolation length used to quantify the magnitude of the transition remains about 0.05-0.09 mm for HDPE at 150-230 ℃.Also the relationship between the critical shear stress for the onset of wall slip and the molecular mass for polymer samples agrees with the disentanglement model of Brochard and de Gennes.The onset of slip-stick transition for LDPE and iPP at a critical shear stress may be interpreted as the shear thinning of the polymer chains at high shear rates,preventing further development of wall slip behavior.

The squeeze flow of a bi-viscosity fluid between two rigid spheres with wall slip

In this paper,the squeeze flow between two rigid spheres with a bi-viscosity fluid is examined.Based on lubrication theory,the squeeze force is calculated by deriving the pressure and velocity expressions.The results of the normal squeeze force are discussed,and fitting functions of the squeeze and correction coefficients are given.The squeeze force between the rigid spheres increases linearly or logarithmically with the velocity when most or part of the boundary fluid reaches the yield state,respectively.Furthermore,the slip correction coefficient decreases with the increase in the velocity.The investigation may contribute to the further study of bi-viscosity fluids between rigid spheres with wall slip.

The lubrication performance of water lubricated bearing with consideration of wall slip and inertial force

The lubrication mechanism and the performance parameters with consideration of wall slip and inertial force are studied in this paper. Based on the modified Reynolds equation, the finite difference method is used to study the lubrication mechanism and the performance. Effects of the wall slip and the inertial force on the performance parameters are obtained, and found in good agreement with the results of FLUENT. It is shown that the wall slip and the inertial force do not significantly change the distribution of the pressure, the load capacity and the friction force. The inertial force slightly increases the pressure and the load capacity by 1.2% and 4.8%, while the wall slip reduces them by 8.0% and 17.85%. The wall slip and the inertial force increase the friction by about 15.98%, 2.33%, respectively. Compared with the wall slip, the inertial force is smaller, but cannot be neglected.

PERIODICAL PRESSURE-DRIVEN FLOWS IN MICROCHANNEL WITH WALL SLIP VELOCITY AND ELECTRO-VISCOUS EFFECTS

In a microfluidic system, the flow slip velocity on a solid wall can be the same order of magnitude as the average velocity in the microchannel. The flow-electricity interaction in a complex microfluidic system subjected to a joint action of wall slip and electro-viscosity is an important topic. An analytical solution for the periodical pressure-driven flow in a two-dimensional uniform microchannel, with consideration of wall slip and electro-viscous effect is obtained based on the Poisson-Boltzmann equation for the Electric Double Layer （EDL） and the Navier-Stokes equations for the liquid flow. The analytic solutions agree well with the numerical solutions. The analytical results indicate that the periodical flow velocity and the Flow-Induced Electric Field （FIEF） strongly depend on the frequency Reynolds number （Re = （wh2/v ）, that is a function of the frequency, the channel size and the kinetic viscosity of fluids. For Re 〈 1, the flow velocity and the FIEF behave similarly to those in a steady flow, whereas they decrease rapidly with Re as Re 〉 1. In addition, the electro-viscous effect greatly influences the periodical flow velocity and the FIEF, particularly, when the electrokinetic radius kH is small. Furthermore, the wall slip velocity amplifies the FIEF and enhances the electro-viscous effect on the flow.

软土地基海堤滑移事故原因分析

该文通过对两起由于堤后堆载导致海堤发生滑移事故的案例进行总结,指出影响海堤发生滑移的原因有多种,事故的原因分析要查明事故发生时的水文、气象、地质条件、海堤结构、地形条件等因素,尽量准确还原事故发生前的状态,同时抗滑稳定计算要结合地质条件,当堤基下卧较薄的软弱土层时,沿折线形滑动更符合实际状态。另外对于软土地基,即使堤后堆载距离较远仍可能引起海堤滑移,应引起重视。

抗滑挡墙加固小型滑坡墙背推力研究

以西南山区某小型村寨滑坡为对象,采用数值模拟方法,研究抗滑挡墙墙背滑坡推力的分布形式,并引入正交试验,采用极差分析法探讨多物理参数对滑坡推力的影响。结果表明:抗滑挡墙墙背滑坡推力的分布曲线为“鼓肚形”,在靠近坡面一定范围内滑坡推力趋于零;滑带黏聚力、内摩擦角的折减系数及抗滑挡墙埋深对滑坡推力的影响较大;抗滑挡墙埋深对作用点高度的影响较大;滑坡推力作用点介于挡墙底部向上垂直高度20%~29%的位置,与刚体极限平衡法中的假设存在偏差。

开洞刚性墙后土体破坏模式运动单元上限分析

超载作用下开洞地下刚性连续墙后土体稳定性问题具有广泛的工程应用背景。考虑墙体矩形开洞宽度足够大,且刚性墙与土体完全光滑接触等条件,参考构造刚性多块体上限法思路,预设墙后土体极简破坏机构并转化为初始三角网格,提出交替循环式新增节点、单元缩减、对角互换及成层加密等网格更新措施,同步开展基于刚体平动运动单元上限方法的刚性墙后土体破坏分析,通过多层级非线性规划运算获得高精度临界超载系数σ_(s)/c上限解,界定墙后土体滑移线网破坏模式及其定量范围与扩展边界。进一步依前述流程计算获得多参数影响下的临界超载系数σ_(s)/c上限解图表,结果表明:1)刚性墙后土体典型破坏特征表现为土体上方和开洞处的整体下沉刚性区域,开洞前方核心区域以密集滑移线网区隔的刚性滑块群,以及外围主要滑动面;2)临界超载系数σ_(s)/c随土体内摩擦角ϕ增大而增大,且后续增幅显著增加;3)σ_(s)/c随开洞深度比C/D的增大呈现出近似线性增大的趋势;4)相较于ϕ和C/D,土体重度参数γD/c的变化对于σ_(s)/c的影响不甚明显,σ_(s)/c随γD/c增大呈现近似线性减小的趋势;5)σ_(s)/c受剪胀角参数ψ/ϕ的影响与ϕ的增大程度密切相关。本研究结果可为开洞地下刚性连续墙后土体失稳破坏模式定量分析、破坏机理研究及工程措施制定等工作提供有力的数据支持。

分级尾砂充填料浆L管实验及阻力特性研究

管道输送阻力是充填料浆管道输送的一个重要参数,目前普遍采用基于宾汉流变模型推导的白金汉公式进行计算,而管壁滑移效应的影响在该公式中被忽略,导致管道输送阻力的计算产生一定的偏差。因此本文基于L管输送实验,提出了考虑管壁滑移效应影响的充填料浆输送阻力计算方法,采用全面实验设计方案,研究了料浆质量分数、灰砂比和管壁滑移效应对于充填料浆管输阻力的影响。结果表明:管输阻力与质量分数、灰砂比呈正相关,与管壁滑移效应呈负相关。管壁滑移效应通过滑移贡献率来量化,该系数受质量分数的影响较明显,随着质量分数增大逐渐减弱,在质量分数较小时,受灰砂比的影响不明显。通过回归分析,构建了基于管径、流速、质量分数、灰砂比四变量,考虑管壁滑移效应的充填料浆管输阻力数学模型,并进行了工程实践验证。

苏州某大型复杂商业连体结构设计

苏州某大型商业综合体项目位于7度抗震设防烈度区,为体型重叠建筑。通过5道防震缝将建筑整体划分为购物中心A区、购物中心B区、停车楼、商业街A区、商业街B区五个独立结构单元。购物中心A区为复杂连体高层建筑,1~5层采用框架-剪力墙结构,两个单体在3~5层中区由钢桁架相连,顶部(6层)钢桁架结构与两个单体通过成品球铰支座连接,形成强连体结构。充分考虑了周期比、位移比双指标平衡后对购物中心A区剪力墙布置进行了优化;屋顶钢桁架结构支座采用变刚度设计,局部设置滑动支座解决恒载下杆件应力比较高的问题。通过性能化设计,该复杂结构连体部位可以满足中震弹性、大震不屈服的性能目标要求。性能化设计及专项分析表明,影院钢结构具有良好的抗震性能、楼盖舒适度及防倒塌性能。

露天地下楔形转接过渡诱导冒落控制边坡岩移危害技术研究

露天地下楔形转接过渡模式的安全管控是利用崩落法开采挂帮矿形成的塌陷坑阻止边坡岩移威胁露天采场,但地采扰动下的高陡边坡破坏过程不易控制,因而制约了楔形转接过渡模式在大型深凹露天矿山中的应用。针对上述问题,结合极限平衡分析方法,揭示出崩落法开采扰动下的高陡边坡渐进破坏规律,提出了边坡滑移体体积计算方法,以及通过调控回采顺序控制边坡滑移进程以实现塌陷坑完全承接边坡滑移体的边坡岩移危害控制技术。研究表明:边坡岩体不会随挂帮矿向下开采而发生持续破坏,只有当挂帮矿开采至关键分段时,边坡岩体受力状态超过极限平衡状态才发生滑移破坏,可通过滞后回采关键分段上盘三角矿延缓边坡滑移,以及通过滞后回采关键分段下盘矿体和采用下向阶梯状回采工作面增大塌陷坑容积,最终实现塌陷坑有序承接边坡滑移体。研究成果完善了大型深凹露天矿楔形转接过渡的安全管控方法,提高了楔形转接过渡模式的适用性。

侧围外板尾灯处成形问题解决方法

针对侧围外板尾灯处拉深产生滑移、翻边整形产生起皱的问题,对拉深工艺补充、零件轮廓、工艺方案等进行可行性分析,改善成形过程,通过CAE软件进行成形验证,解决了零件成形起皱问题,达到了客户质量要求。

文物建筑墙体加固施工方法及工程应用

文物建筑作为历史的见证,可起到重要的文化传承作用,但由于自然老化和人为破坏,许多文物建筑墙体出现涂层破损、局部开裂,甚至滑移坍塌,存在较大的安全隐患,因此墙体加固施工方法及其工程应用备受关注。基于理论与实践研究,总结了文物建筑加固施工原则,对常用的墙体加固方法进行了说明,并比较其优劣势与适用条件,依托实际工程案例分析各种墙体加固方法的施工工艺流程、质量控制要点以及应用场景,可为同类型文物建筑加固项目提供参考。

建宁县某水厂边坡支护与排水设计

依托于建宁县某新建水厂边坡支护工程,采用动态设计法对场地的填方段边坡和挖方段边坡进行支护和排水设计,通过对安全性、施工难度、经济性、稳定性、效果等对比分析,最终选择挖方段边坡采用框架锚杆支护,而填方段边坡采用抗滑桩+锚索和挡土墙联合支护方案以及采用地表集水明排+坡体软式透水管或泄水管泄水的排水设计,采用极限平衡法验证了支护后的边坡稳定性。

基于楔形椎体模型工作面煤壁稳定性研究

针对大同矿区复杂地质条件工作面回采期间煤壁稳定性较差的问题,以大同矿区某煤矿1022工作面为工程背景,通过理论分析、数值模拟,对影响煤壁稳定性的因素进行了研究。结果表明:工作面采动期间,煤壁失稳片帮过程分为煤体损伤破坏阶段和煤壁剪切滑移失稳阶段。在煤体损伤破坏阶段,工作面前方煤体应力环境被恶化,加剧了应力畸变区煤岩体单元的损伤破坏,增大了煤壁片帮机率;在煤壁剪切滑移失稳阶段,根据楔形椎体力学模型,发现煤壁稳定性系数K随支架护帮力P0、结构面内聚力C和内摩擦角φ的增大而增大,随顶板压力的增大而减小,并据此提出了煤壁稳定性控制措施。

高速公路顺层路堑边坡超前支护技术研究

鄂西山区地质条件复杂,雨量充沛,顺层路堑边坡施工过程中极易发生滑塌。文中以恩施土家族苗族自治州某高速隧道出口左、右两侧顺层高边坡为依托,针对2处边坡开挖过程中发生不同程度的顺层滑塌现象,对顺层路堑边坡的超前支护技术展开研究。根据2处边坡的工程地质条件,对2处边坡的稳定性进行评价分析;并分别提出抗滑桩、钢轨桩+抗滑挡墙的超前支护处治方案.通过对2种超前支护处治方案对比分析可知,抗滑桩的超前支护处治方案效果更为显著,且更加经济环保。

高填方机场超高挡墙边坡深层抗滑敏感性分析

为满足山区高填方机场的建设需求,针对超高挡墙建设的难题,开展边坡深层抗滑敏感性分析。通过计算分析,对比基岩软弱层、层面和反倾结构面的不同组合工况,探究各敏感因素对深层抗滑稳定性的影响,明确最不利组合工况。结果表明:局部发育软弱层对深层抗滑稳定性的影响较小;层面和反倾结构面分布越深对深层抗滑稳定性的影响越小;层面过墙踵,拐点位于墙趾竖直面时为最不利工况。