On the influence of near-wall forces in particle-laden channel flows

Computation of a turbulent dilute gas–solid channel flow has been undertaken to study the influence of using wall-corrected drag coefficients and of the lift force on the dispersed phase characteristics. The incompressible Navier–Stokes equations governing the carrier flow were solved by using a direct numerical simulation approach and coupled with a Lagrangian particle tracking. Calculations were performed at Reynolds number based on the wall-shear velocity and channel half-width, Re_τ ≈ 184, and for three different sets of solid particles. For each particle set, two cases were examined, in the first one the particle motion was governed by both drag and lift wall-corrected forces, whereas in the other one, the standard drag force (not corrected) was solely acting. The lift force model used represents the most accurate available expression since it accounts for weak and strong shear as well as for wall effects. For this study, we considered elastic collisions for particles contacting the walls and that no external forces were acting. Present results indicate that the use of the lift force and of the drag corrections does not lead to significant changes in the statistical properties of the solid phase, at the exception of some statistics for the high inertia particles.     

Analysis of blank thickening in deep drawing processes using the theory of a Cosserat generalized membrane

This paper analyzes a transient, nonlinear deep drawing process where a circular blank of a rigid-plastic material is forced by a rigid circular punch to deform into a cylindrical cup. Attention is focused on the plastic flow beneath the blank-holder. Using the Cosserat theory of a generalized membrane it is possible to obtain analytical solutions which examine the following two major effects: (a) the importance of added “rim pressure” acting on the outer edge of the blank; and (b) the importance of a controlled moveable blank-holder to allow blank thickening during the drawing process. Guided by these analytical results, a new deep drawing machine was built to exploit these effects and increase the limit drawing ratio (LDR) of the drawing process. Specifically, the LDR (in one stroke) reached the value of 3.16 compared with the value of about 2.0 in the conventional process. Moreover, the analytical prediction of the punch force versus the punch stroke is in good agreement with the experimental data and with simulations using the computer code DYTRAN.     

碎石桩复合地基若干问题的理论分析

由桩-土侧向变形及竖向变形协调条件，基于弹性理论导出了桩及桩周土的应力-应变关系、桩体材料屈服时桩-土应力比的计算式．推出了桩周土处于极限平衡状态下，碎石桩极限承载力计算式．指出了用碎石桩加固软土地基效果比较明显．但用碎石桩来加固土的变形模量大于8MPa的地基，加固效果十分有限．最后，通过工程实例，将计算结果与实验结果作了对比．     

Fluid-Damping Controlled Instability in Tube Bundles Subjected to Air Cross-Flow

There are different excitation mechanisms that cause fatal damages due to undesirable vibrations in heat exchanger tube bundles subjected to cross-flow. One of them is the fluid-damping-controlled instability (galloping) that is characterised by a sudden appearance of large amplitudes of the tubes exclusively in cross-flow direction. This paper reports on investigations using an experimental set-up in a wind tunnel where the galloping mechanism in a tube bundle can be observed as an isolated phenomenon. The apparatus allows to realise several tube bundle configurations and geometry's of real heat exchangers. The position of a flexible test tube with a linear iso-viscoelastic mounting inside the tube array is variable. The test tube is equipped with dynamical pressure sensors which are placed directly under pressure holes inside the tube. For the investigation of the acting fluid forces the non-stationary pressure distribution is measured simultaneously at 30 points on the circumference in mid plane and at 15 points in line along the tube together with the tube motion. The acting fluid forces are determined by integration of the whole pressure field process. The study gives insights into the effect of the fluid-damping-controlled instability that is still not fully understood. Moreover, a flow visualization gives an impression of the mechanism at relevant Reynolds-numbers. The results show that in case of instability due to galloping the correlation length of the forces acting along the tube axis increases suddenly to large values. The fluid forces are correlated well for the whole tube when galloping is dominant. The exciting fluid forces show harmonic character and lead to a classical resonance behaviour. Instead of a simple free vibration test in vacuum or still air, which is done mostly for fluid excited structures, the damping coefficient of the oscillating system is determined under operating conditions on the basis of the measured fluid forces. A comparison of the results with those of a free vibration test in still air is shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

钢丝帘线泊松比的实验研究

本文对钢丝帘线／橡胶复合材料中的钢丝帘线泊松比的定义提出了新的见解，建议用钢丝帘线横截面变化率代替其横向应变，并提出了利用扫描电子显微镜测定截面变化率的实验方法     

不同边界条件正交各向异性中厚板的振动与稳定分析

本文采用高阶剪切变形理论对正交各向异性中厚矩形板进行振动与稳定分析,数值计算采用样条有限点法,得出了六种不同边界条件矩形板的自振频率和屈曲载荷,并与相应的经典板理论的结果进行比较.结果说明横向剪切变形对复合材料层合板的影响与板的各向异性程度、板的宽厚比(b/h)、层合板的层数和板的支承条件有关,它随着层合板各向异性程度的增加而增加,随着层合板宽厚比的增加而逐渐消失.     

土-结构相互作用体系合成模态阻尼比的振动台模型试验研究

本文籍振动台模型试验。研究了SSI体系的合成模态阻尼比问题。文中首先阐明了在SSI体系直接动力分析中应采用合成模态阻尼比的观点。研究了合成模态阻尼纟的实测确定方法。并在不同工况下，通过对模型不同部位测点的传递函数，基本频率，基本合成模态阻尼比等实测数据考虑，验证了SSI体系合成模态的存在性，合成模态阻尼比与相同应变下不考虑相互作用的单纯地基土体或刚性地基结构阻尼比的差异性及其在递增动力作用下的变化规律。     

拉压性能不同材料厚壁圆筒和厚壁球壳的极限压力分析

本文用广义双剪应力强度理论对拉压性能不同的材料制成的厚壁圆筒和厚壁球壳进行了弹塑性应力分析，得出与拉压比有关的弹性极限内压力、塑性极限内压力、弹塑性区的应力以及弹塑性内压力与弹塑性半径之间的关系式．     

侧柱对串列双柱脉动压力的干扰

研究了串列双圆柱旁加上一个等直径的圆柱，组成一个等边三角形排列的三圆柱的脉动压力分布．着重研究侧柱对串列双圆柱脉动压力分布的影响．研究的结果表明，绕流等边三角形排列的三圆柱，受影响最严重的是后柱．脉动压力分布出现了严重的不对称，外侧的压力脉动极其强烈，内侧的压力脉动较弱，与时均压力分布，很好的对应关系．另外，侧柱对于串列双圆柱是否达到超过临界间距的绕流流态，有很大的影响     

马来酸酐接枝稀土异戊橡胶接枝率的测试方法

以马来酸酐(MAH)和稀土异戊橡胶(IR)聚合液为主要原料,采用溶液接枝改性反应制备了马来酸酐接枝稀土异戊橡胶(IR-g-MAH)。以IR-g-MAH接枝率的测试方法为研究对象,对比直接滴定法和返滴法,并进一步优化直接滴定法的测试条件。实验结果表明,直接滴定法测试的结果准确度高、重复性好,且测试过程简单。其较优的测试条件为:水解试剂为乙醇,样品用量为0.2~0.5g,KOH-乙醇标准溶液浓度为0.02~0.06mol/L。