Dynamic Simulation of Shear-induced Particle Migration in a Two-dimensional Circular Couette Device

The shear-induced migration of neutrally-buoyant non-colloidal circular particles in a two-dimensional circular Couette flow is investigated numerically with a distributed Lagrange multiplier based fictitious domain method.The effects of inertia and volume fraction on the particle migration are examined.The results indicate that inertia has a negative effect on the particle migration.In consistence with the experimental observations,the rapid migration of particles near the inner cylinder at the early stage is observed in the simulation,which is believed to be related to the chain-like clustering of particles.The migration of circular particles in a plane Poiseuille flow is also examined in order to further confirm the effect of such clustering on the particle migration at early stage.There is tendency for the particles in the vicinity of outer cylinder in the Couette device to pack into concentric rings at late stage in case of high particle concentration.

SHEAR EFFECTS ON LARGE AMPLITUDE FORCED VIBRATIONOF SYMMETRICALLY LAMINATED RECTILINEARLYORTHOTROPIC CIRCULAR PLATES

In this paper, nonlinear forced vibration of symmetrically laminated rectilinearly orthotropic circular plates excited by a harmonic force q(0)cos omega t including effects of transverse shear deformation is discussed. The analytical solution for the relationship between forcing frequency and amplitude of vibration is obtained by Galerkin's method. Finally, the paper analyses the effect of the transverse shear on the vibration of the plate and gives the ratio of nonlinear period to linear period for nonlinear free vibration of the plate.

ON SEPARATED SHEAR LAYER OF BLUNT CIRCULAR CYLINDER

Separated shear layer of blunt circular cylinder has been experimentally investigated for the Reynolds numbers (based on the diameter) ranging from 2.8 x 10(3) to 1.0 x 10(5), with emphasis on evolution of separated shear layer, its structure and distribution of Reynolds shear stress and turbulence kinetic energy. The results demonstrate that laminar separated shear layer experiences 2 similar to 3 times vortex merging before it reattaches, and turbulence separated shear layer takes 5 similar to 6 times vortex merging. In addition, relationship between dimensionless initial frequencies of K-H instability and Reynolds numbers is identified, and reasons for the decay of turbulence kinetic energy and Reynolds shear stress in reattachment region are discussed.

An expert system for predicting shear stress distribution in circular open channels using gene expression programming

The shear stress distribution in circular channels was modeled in this study using gene expression programming(GEP). 173 sets of reliable data were collected under four flow conditions for use in the training and testing stages. The effect of input variables on GEP modeling was studied and 15 different GEP models with individual, binary, ternary, and quaternary input combinations were investigated. The sensitivity analysis results demonstrate that dimensionless parameter y/P, where y is the transverse coordinate, and P is the wetted perimeter, is the most influential parameter with regard to the shear stress distribution in circular channels. GEP model 10, with the parameter y/P and Reynolds number(Re) as inputs, outperformed the other GEP models, with a coefficient of determination of 0.7814 for the testing data set. An equation was derived from the best GEP model and its results were compared with an artificial neural network(ANN) model and an equation based on the Shannon entropy proposed by other researchers. The GEP model, with an average RMSE of 0.0301, exhibits superior performance over the Shannon entropy-based equation, with an average RMSE of 0.1049, and the ANN model, with an average RMSE of 0.2815 for all flow depths.

新型横向连接装配整体式榫卯剪力墙结构抗震性能模拟分析

为加强装配整体式剪力墙的竖向接缝性能和墙体的整体性,在传统榫卯接缝的基础上,研究提出一种采用新型横向连接的装配式榫卯剪力墙,设置横向凹槽处的封闭环形钢筋闭合连接,并与纵向孔洞处的竖向钢筋绑扎形成钢筋骨架,以提高剪力墙的整体稳定性。设置1组现浇剪力墙、1组传统装配式榫卯连接装配式剪力墙、1组采用新型横向连接的装配式榫卯剪力墙,使用ABAQUS有限元软件模拟在低周往复荷载作用下不同墙体的受力情况及破坏过程,并且对比分析不同竖向接缝对剪力墙工作性能和抗震能力的影响。研究结果表明,采用新型榫卯横向连接的装配式榫卯剪力墙的刚度和承载能力与现浇剪力墙基本一致,能够满足“等同现浇”的要求。

TORSIONAL VIBRATIONS OF A RIGID CIRCULAR PLATE ON SATURATED STRATUM OVERLAYING BEDROCK

The torsional vibration of a rigid plate resting on saturated stratum overlaying bedrock has been analysed for the first time. The dynamic governing differential equations for saturated poroelastic medium are solved by employing the technology of Hankel transform. By taking into account the boundary conditions, the dual integral equations of torsional vibration of a rigid circular plate are established, which are further converted into a Fredholm integral equation of the second kind. Subsequently, the dynamic compliance coefficients of the foundation on saturated stratum, the contact shear stress under the foundation and the angular amplitude of the foundation are evaluated. Numerical results indicate that, when the dimensionless height is bigger than 5, saturated stratum overlaying bedrock can be treated as saturated half space approximately. When the dimensionless frequency is low, the permeability of the soil must be taken into account. Furthermore, when the vibration frequency is a constant, the height of the saturated stratum has a slight effect on the dimensionless contact shear stress under the foundation.

基于多薄壁圆管套装假设的圆轴扭转切应力-变形量分析

针对材料力学、工程力学等教材中圆轴扭转章节的切应力-变形量公式,提出了一种基于多个薄壁圆管套装假设的新推理方法,导出了厚壁圆管及实心圆轴的切应力公式、单位长度扭转角公式等.提出用薄壁圆管扭转实验测量切应变和切应力参数,并验证两者之间的正比例关系即剪切胡克定律的正确性,从而测量材料切变模量G.提出用受扭薄壁圆管实例辅助证明切应力互等定理.研究结果有助于提高教学质量.

TORSIONAL VIBRATIONS OF RIGID CIRCULAR PLATE ON TRANSVERSELY ISOTROPIC SATURATED SOIL

An analytical method was presented for the torsional vibrations of a rigid disk resting on transversely isotropic saturated soil. By Hankel transform, the dynamic governing differential equations for transversely isotropic saturated poroelastic medium were solved. Considering the mixed boundary-value conditions, the dual integral equations of torsional vibrations of a rigid circular plate resting on transversely isotropic saturated soil were established. By appropriate transform, the dual integral equations were converted into a Fredholm integral equation of the second kind. Subsequently, the dynamic compliance coefficient, the torsional angular amplitude of the foundation and the contact shear stress were expressed explicitly. Selected examples were presented to analyse the influence of saturated soil＇s anisotropy on the foundation＇s vibrations.

复合材料环形试样力学性能检测研究

本文对纤维增强复合材料环形试样的制备方法、剪切和拉伸性能的检测方法进行了研究。本文阐述了环缠绕法和圆筒切环法两种试样制备方法;明确了玻璃纤维、碳纤维、芳纶纤维和玄武岩纤维的干燥处理条件、缠绕张力、缠绕速度、固化前存放时间等技术参数;验证了剪切试验中,试样外观尺寸、加载头直径、加载速率等对剪切性能的影响;验证了拉伸试验中,试样外观尺寸、加载速率等对拉伸性能的影响。结果表明,剪切试验中,试样厚度为3mm,宽度为6mm,玻璃纤维试样长度为21mm~30mm,碳纤维、芳纶纤维试样长度为18mm~21mm,夹具加载头直径为6mm,加载速率为1mm/min~2mm/min;拉伸试验中,试样厚度为1.5mm,玻璃纤维增强塑料加载速率为3mm/min~5 mm/min,碳纤维和芳纶纤维增强塑料加载速率为2mm/min~3mm/min时,试验数据稳定,具有较好的可重复性,且试样破坏形式正常。

水泥搅拌桩施工挤土效应分析

水泥搅拌桩施工过程中叶片的切削作用和水泥浆的注入对桩周土体产生挤土效应,基于受剪圆孔扩张模型,采用摩尔-库仑屈服准则,对塑性区半径公式进行修正,得出施工影响因数和成桩扰动位移,更加准确地模拟水泥土搅拌桩的挤土问题,对水泥搅拌桩施工的挤土效应有定量化的描述。通过水泥搅拌桩施工引起桩周超孔隙水压力实测数据和有限元计算结果对比,验证结果的可靠性。

用高阶剪切理论研究层合圆管弯曲时力学特性

采用高阶剪切理论研究了层合圆管弯曲时的力学行为,建立了层合圆管弯曲微分方程,推导了外荷载作用下层合圆管的挠曲线方程及正应力、剪应力公式。有关算例证明,该方法计算精度很高。计算分析表明,剪切变形对层合圆管弯曲有较大影响,实际工程中层合圆管的设计不能忽略剪切变形的影响。

砂土直剪力学性状的非圆颗粒模拟与宏细观机理研究

基于PFC2D非圆颗粒单元的二次开发,对砂土直剪力学过程进行了非圆颗粒仿真模拟,分析了数值试样的应力–剪胀关系并与实际砂土进行对比,探讨了颗粒位移与颗粒旋转特征及其与剪切带演化的内在关联,研究了主应力与主应变增量的非共轴效应,揭示了细观组构各向异性的演化规律及其与宏观剪切强度之间的宏细观关联。研究结果表明,数值试验能够较好的模拟实际砂土的应力–剪胀关系和剪切过程主应力与主应变增量的非共轴效应;剪切带的演化与颗粒位移和颗粒旋转密切相关,颗粒形状影响剪切带的厚度;试样宏观的剪切强度主要受控于粒间法向接触力的分布及其各向异性演化;整个加荷过程中,剪切带内大主应力的偏转方向与法向接触力各向异性的主方向保持了良好的一致性。

线性剪切流作用下设置沉井施工期受力特性研究

为研究水流作用对设置沉井施工期受力特性的影响,采用线性剪切流模拟非均匀流,建立水流-圆形设置沉井相互作用模型,分析不同施工阶段圆形设置沉井与水流的相互作用情况,并与均匀流作用进行对比。结果表明:线性剪切流作用下圆形设置沉井水流力及水流力矩随流速的增加均呈平方关系。线性剪切流呈表面流速大、底层流速小的规律,对结构尾流区的涡漩有显著抑制作用,与均匀流作用相比,线性剪切流作用下结构受力偏小。随着沉井不断下沉,结构吃水深度增加,过水断面进一步压缩形成了绕流,引起局部压力及水流力成倍增加。

一种边坡多滑动面搜索的新方法

近年来关于边坡最危险滑动面的搜索的研究方法主要集中在算法的优化方面,事实上对边坡内次级潜在滑动面的搜索也有必要,而目前相关研究并不多。本文提出一种在FLAC-3D中通过控制强度折减法中的折减系数来实现多条滑动面搜索的新方法,并通过算例来说明。同时采用Bishop法与该方法作对比分析,结果表明两者的计算结果十分接近,局部边坡安全系数误差不到1%,整体边坡安全系数误差不到4%,由此论证了该方法的合理性和可行性。

圆形截面玻璃纤维筋混凝土桩体抗剪承载力研究

用GFRP筋来部分代替钢筋或预应力钢筋用于混凝土结构中,国内外已有大量研究和应用。目前对玻璃纤维(GFRP)筋混凝土结构受剪性能的研究,主要都是尺寸较小的矩形截面梁,关于圆形截面构件的斜截面受剪承载力的研究却极少。根据实际工程桩尺寸首次制作了比例为1∶1的试件,进行了二集中力三分点加载试验,试验中发现玻璃纤维筋混凝土梁具有剪切破坏的特征,通过对试验结果的分析并结合美国ACI规范与中国混凝土设计规范中抗剪承载力公式,推导出圆形截面GFRP筋混凝土梁的抗剪承载力公式,采用该公式计算的结果与实测值非常相近。进一步将上述理论应用在北京某地铁车站的基坑围护桩中,校核计算了盾构接收过程中围护桩的安全性,据此提出增大配筋率的建议。

砼深受弯构件及圆形截面构件受剪承载力

结合 GBJ10 - 89混凝土结构设计规范修订课题 ,提出了混凝土深受弯构件和圆形截面偏压构件抗剪承载力的计算方法 .这些方法与试验资料吻合良好 ,并与矩形截面一般受弯构件的计算方法在一定程度上得到了统一 .

不同尺寸的圆形隧洞剪切应变局部化过程模拟

利用FLAC模拟了两个不同直径圆形隧洞的剪切应变局部化过程。为了模拟隧洞开挖,利用编写的FISH函数删除隧洞内部的单元。岩石服从莫尔库仑剪破坏与拉破坏复合的破坏准则,破坏之后呈现应变软化-理想塑性行为。本文的模拟分为3步:首先,将静水压力施加在模型上,直至达到静力平衡状态;然后,利用编写的FISH函数,开挖隧洞;最后,计算重新开始,直至达到静力平衡状态(对于小孔隧洞)或者塑性流动状态(对于大孔隧洞)。模拟结果表明,多个"狗耳"形或V形坑在小孔隧洞周边附近产生,最终,围岩处于平衡状态。这一结果与陆家佑和王昌明(1994)的实验结果及许多现场观察结果一致。对于大孔隧洞,由于在围岩中出现了多条剪切带,因而隧洞的整个断面均遭到了破坏。这一现象与现场观察到的猛烈破坏现象类似。隧洞的剪切应变局部化受隧洞尺寸的影响。

考虑剪切变形的圆弧深拱参数共振稳定性分析

基于结构弹性稳定理论,根据能量法推导出以位移为基本未知量的圆弧深拱总势能,从Hamilton原理出发,建立了考虑剪切变形的圆弧深拱的动力稳定微分方程。利用Galerkin方法将该方程转化为二阶常微分Mathieu型参数共振方程,推导出圆弧深拱主参数共振的临界频率方程式,从而求得周期解所包围的动力不稳定区域。通过分析剪切变形、圆弧半径、圆心角等参数对圆弧深拱动力稳定性的影响,探讨了圆弧深拱发生参数共振的动力稳定性问题,为拱型结构动力分析与设计提供参考依据。

周期径向荷载作用下圆弧格构拱动力稳定性分析

基于结构弹性稳定理论,根据能量法推导出以位移为基本未知量的圆弧格构拱总势能,从Hamilton原理出发,建立了考虑剪切变形的圆弧格构拱的动力稳定微分方程。利用Galerkin方法将其转化为二阶常微分Mathieu型参数共振方程,求得周期解所包围的动力不稳定区域,探讨了圆弧格构拱发生参数共振的动力稳定性问题,分析了缀条面积、圆弧半径、圆心角等参数对圆弧格构拱动力稳定性的影响,为拱型结构动力分析与设计提供参考依据。

软索连接装配式混凝土圆孔墙抗震性能试验研究

为研究软索连接装配式圆孔剪力墙的抗震性能,分析翼墙对主墙的影响,设计一字形、L形、工字Ⅰ形和工字Ⅱ形4类共8个足尺装配式圆孔剪力墙试件,进行拟静力试验,通过对试验现象和数据进行分析,研究构件的破坏形态、特征荷载、变形性能、受剪承载力等特性。结果表明:采用软索连接的翼墙能有效提高主墙的抗裂性能,有效避免主墙沿圆孔的竖向裂缝,同时能改变主墙的应力分布和破坏形态;翼墙能够有效提高主墙的屈服荷载和极限荷载,但对屈服位移、延性的影响不明显;墙体弹性层间位移角能够满足我国规范中对剪力墙的要求,弹塑性层间位移角较小,宜提高软索锚固设计;墙体中的圆孔会大大降低墙体的受剪承载力;通过规范公式对该类型墙体进行受剪承载力计算,发现多数墙体的计算值远大于试验值,基于试验结果,建议将规范公式进行0.5倍折减后,再用于该类型墙体的受剪计算。