颗粒在大涡结构中的弥散

气相采用大涡模拟方法,颗粒相采用轨道模型研究了三维后台阶气粒两相湍流流动的大尺度涡结构的瞬时演变过程以及颗粒的瞬时弥散规律.比较了不同入流速度的颗粒在大涡结构中的瞬时弥散特性,尤其研究了高速释放大颗粒的弥散特性.三维流动中大尺度涡结构具有明显的脱离、发展、合并和破碎过程.小颗粒的分布受大涡结构的控制,其空间的弥散过程与流体 大涡结构的空间发展相一致,但是由于三维流动中大涡边缘和中心区的压力差,颗粒在大尺度 涡的边缘出现密集.而大颗粒在流场中的分布受其惯性控制,对气相的涡结构不敏感.高速释放到流场中的大颗粒受惯性影响最大,保持在其原有动量方向上运动.     

A cohesive zone model with a large displacement formulation accounting for interfacial fibrilation

Interfacial fibrilation is a typical mechanism that frequently occurs during delamination of a polymer coating from a steel substrate. It involves large displacements at the interface as well as large deformations in the bulk material. Classical small displacement cohesive zone formulations fail to describe such large deformations correctly. Therefore, a generic cohesive zone model is introduced that is suitable to describe both uniform and non-uniform fracture at an interface with large deformations in the delaminating bulk and large displacements at the crack tip.     

新型让压锚杆作用机理研究

软岩大变形工程存在因开挖卸荷导致较大的应力释放,在工程施工过程中将会产生较大变形的特点,如沿用传统的锚杆进行支护,岩体的大变形所产生的过大拉力将会造成锚杆的拉断破坏.针对软岩大变形工程存在的该类问题,介绍了一种新型的端部具有让压装置的新型压力分散型让压锚杆,并对该让压锚杆的作用机理和力学行为进行分析,得出锚固体的作用机理与传统压力分散型锚杆相比分为3个阶段,并通过试验的方式确定了该让压锚杆的让压力.这种新型让压锚杆在将锚固体压力分散的同时,实现大变形的让压,适宜在大变形工程中进行应用.     

Long-time Solvability of the Navier–Stokes Equations in a Rotating Frame with Spatially Almost Periodic Large Data

We consider existence of solutions, for large times, to the Navier–Stokes equations in a rotating frame with spatially almost periodic large data provided by a sufficiently large Coriolis force. The Coriolis force appears in almost all of the models of meteorology and geophysics dealing with large-scale phenomena. To show existence of solutions for large times, we use the ℓ ¹-norm of amplitudes. Existence for large times is proven by means of techniques of fast singular oscillating limits and bootstrapping from a global-in-time unique solution to the limit equation.     

The separation of large vortexes and the closed equations of turbulence model

This paper presents a new kind of average for the locally-generated large vortexes so that the physical quantities of the locally-generated large vortexes and the external large vortexes can be rigorously separated from the equations for the large vortexes proposed in a previous paper. To the equations for the two kinds of large vortexes, some auxiliary relations are introduced, and the value of the length-scale l_N of energy dissipation of the external large vortexes may be determined according to the actual circumstances of the disturbance of external sources. Thus, the resulting equations of the second moments of turbulent velocity fluctuations for the two kinds of large vortexes can be made closed, Meanwhile, the corresponding coefficients of diffusion in the previous paper are improved. Finally, a closed set of numerically-solvable equations of turbulence model are obtained.The Project Supported by National Natural Science Foundation of China. This paper was published in the Fourth National Fluid Mechanics Conference. Beijing, China. March (1989).     

FLOW BEHAVIOR AND MASS TRANSFER IN THREE-PHASE EXTERNAL-LOOP AIRLIFT REACTORS WITH LARGE PARTICLES

The flow behavior and mass transfer in a three-phase external-loop airlift reactor can be improved by adding large particles. The mass transfer and liquid dispersion behavior for a three-phase external-loop reactor with large particles are studied in terms of the effect of the diameter and loading of the large particles on the liquid dispersion coefficient and mass transfer coefficient, The results showed that increasing the diameter or loading of the large particles tend to decrease dispersion and intensify mass transfer, and that an increase in the diameter of the large particles remarkably decreases the particle loop rate, while the effect of fine particles is much less notable.     

FLOW BEHAVIOR AND MASS TRANSFER IN THREE-PHASE EXTERNAL-LOOP AIRLIFT REACTORS WITH LARGE PARTICLES

The flow behavior and mass transfer in a three-phase external-loop airlift reactor can be improved by adding large particles. The mass transfer and liquid dispersion behavior for a three-phase external-loop reactor with large particles are studied in terms of the effect of the diameter and loading of the large particles on the liquid dispersion coefficient and mass transfer coefficient. The results showed that increasing the diameter or loading of the large particles tend to decrease dispersion and intensify mass transfer, and that an increase in the diameter of the large particles remarkably decreases the particle loop rate, while the effect of fine particles is much less notable.     

Flows around two airfoils performing fling and subsequent translation and translation and subsequent clap

The aerodynamic forces and flow structures of two airfoils performing “fling and subsequent translation“ and “translation and subsequent clap“ are studied by numerically solving the Navier-Stokes equations in moving overset grids. These motions are relevant to the flight of very small insects. The Reynolds number, based on the airfoil chord length c and the translation velocity U, is 17. It is shown that: (1) For two airfoils performing fling and subsequent translation, a large lift is generated both in the fling phase and in the early part of the translation phase. During the fling phase,a pair of leading edge vortices of large strength is generated; the generation of the vortex pair in a short period results in a large time rate of change of fluid impulse, which explains the large lift in this period. During the early part of the translation, the two leading edge vortices move with the airfoils;the relative movement of the vortices also results in a large time rate of change of fluid impulse, which explains the large lift in this part of motion. (In the later part of the translation, the vorticity in the vortices is diffused and convected into the wake.) The time averaged lift coefficient is approximately 2.4 times as large as that of a single airfoil performing a similar motion. (2) For two airfoils performing translation and subsequent clap, a large lift is generated in the clap phase. During the clap, a pair of trailing edge vortices of large strength are generated; again, the generation of the vortex pair in a short period (which results in a large time rate of change of fluid impulse) is responsible for the large lift in this period. The time averaged lift coefficient is approximately 1.6 times as large as that of a single airfoil performing a similar motion. (3) When the initial distance between the airfoils (in the case of clap, the final distance between the airfoils) varies from 0.1 to 0.2c, the lift on an airfoil decreases only slightly but the torque decreases greatly. When the distance is about lc， the interference effects between the two airfoils become very small.     

双列圆锥滚子轴承滚子大端-引导边润滑接触分析

针对铁路客车中使用的双列圆锥滚子轴承,发展了一个系统的计算模型以模拟滚子大端与引导边间的润滑接触状态.首先通过理论分析确定滚子大端与内圈挡边的接触点位置和滚动体的自转与公转转速,分别得出二者在接触点的滑动速度;然后考虑滚子的离心力,通过求解内圈位移控制方程,计算轴承的载荷分布,并分别求出滚子与外滚道、内滚道以及引导边的作用力;最后建立润滑分析模型,对圆锥滚子大端与引导边的接触进行润滑分析计算,实现滚子大端与引导边接触的润滑模拟,并研究了滚子大端球面半径、工况条件等对润滑性能的影响.     

Bifurcations of double homoclinic flip orbits with resonant eigenvalues

Concerns double homoclinic loops with orbit flips and two resonant eigen- values in a four-dimensional system.We use the solution of a normal form system to construct a singular map in some neighborhood of the equilibrium,and the solution of a linear variational system to construct a regular map in some neighborhood of the double homoclinic loops,then compose them to get the important Poincarémap.A simple cal- culation gives explicitly an expression of the associated successor function.By a delicate analysis of the bifurcation equation,we obtain the condition that the original double homoclinic loops are kept,and prove the existence and the existence regions of the large 1-homoclinic orbit bifurcation surface,2-fold large 1-periodic orbit bifurcation surface, large 2-homoclinic orbit bifurcation surface and their approximate expressions.We also locate the large periodic orbits and large homoclinic orbits and their number.     

Stress Magnification due to Stretching and Bending of Thin Ligaments between Voids

Stress magnification in thin ligaments between small and large cylindrical voids is obtained by matching the inner field approximation by beam theory to the outer rigid-body field in the bulk of the material. A void between two larger voids is modeled as a large hole within a strip of straight edges (boundaries of the holes with infinite radii of curvature). Both stretching and bending types of loading are applied to the strip. Comparison of different orders of stress magnification for different geometries and loading conditions is made. It is shown that the order of stress magnification in thin ligaments is (R/δ) ⁿ , where n=1/2 in the ligament between one small and one large void, n=1 in the ligament between one small void and two large voids, or between two small and two large voids, and n=2 in the ligament between a large void and a small void coalescing with another large void. The relevance of these results for the study of material failure by void growth and coalescence is discussed.     

Stability Analysis of Continuous Systems with Structural Perturbations

The paper is a survey of the development of the direct Lyapunov method based on matrix-valued functions for systems with structural perturbations. Sufficient conditions for stability in the large, uniform asymptotic stability in the large, exponential stability in the large, and instability of nonlinear continuous systems under structural perturbations are presented.     

模型昆虫翼作非定常i运动时的气动力特性

基于Navier-Stokes方程的数值解,研究了一模型昆虫翼在小雷诺数(Re=100)下作非定常运动时的气动力特性.这些运动包括翼启动后的常速转动,快速加、减速转动,常速转动中快速上仰(模拟昆虫翼的上挥或下拍、翻转等运动).有如下结果在小雷诺数下,模型昆虫翼以大攻角(α=35°)作常速转动运动时,由于失速涡不脱落,可产生较大的升力系数.其机理是翼转动时,翼尖附近(该处线速度大)上翼面压强比翼根附近(该处线速度小)的小得多,因而存在展向压强梯度,同时存在着沿展向的离心力,此展向压强梯度和离心力导致的展向流动在失速涡的轴向方向,其可避免失速涡脱落.模型昆虫翼在快速加、减速转动和快速上仰运动中,虽然雷诺数小,但由于在短时间内产生了大涡量,也可产生十分大的气动力,例如在快速上仰运动中,升力系数可大于10.     

Numerical simulation of particle-laden flow in an industrial wastewater sedimentation tank

Meccanica - The wastewater of steel production factories consists of a large amount of very small metal particles. The metal particles in this wastewater enter a large sedimentation tank and are...     

Hammering in diesel-engine driveline systems

The gears of driveline systems in diesel engines must be designed with large backlashes within the gear meshes due to the large temperature operating range of such systems. This leads to hammering processes with extremely high overloads where hammering is an impulsive separation process of the tooth flanks caused by the large torques as generated by the injection pumps. This paper presents a theoretical model for such processes and gives a comparison with measurements.     

Lattice model applied to the fracture of large strain composite

An improved lattice model is developed to simulate the fracture behavior of large strain composite. Based on equivalent relation between the continuum and the lattice model for small deformation, the equivalent relation between large strain continuum and improved lattice model is established by introducing large strain elastic law into the lattice system. The theory can simulate large deformation. The program of large strain lattice model simulates several representative problem of large strain elasticity. The results agree with the theoretical results. Assumed failure criterion is used to describe the fracture process of large strain elasticity and large strain composite. The improved lattice model provides an effective method for fracture simulation of large strain composite.     

Wave propagation in heterogeneous anisotropic plates involving large deflection

Equations of motion for laminated plates of composite materials are derived for motions of large amplitudes as well as for incremental deformations superposed on large deflections. Free waves of large and small amplitudes propagating, respectively, in initially flat and deformed plates are investigated. By using a special substitution for the extensional displacement components the governing equations appear to be linear and consequently the analysis of free wave propagation greatly simplified. It is found that a train of free wave consists of a finite number of simple harmonic waves.     

Fracture process zone analysis of concrete using moiré interferometry

The fracture process zone (FPZ) ahead of a crack tip in concrete and mortar beams subjected to threepoint bending was studied using moiré interferometry. A large FPZ can occur in concrete before the external load reaches its maximum value. Comparing the experimental results between concrete and mortar suggests that the aggregate contributes to the formation of the large FPZ in concrete. The formation of this large FPZ makes concrete less brittle than mortar. The effect of the FPZ on the fracture property, such as stress intensity factor, is investigated by combining moiré interferometry measured displacements with the smoothing FEM method. The study shows that a large FPZ significantly affects the value of the stress intensity factor.     

边坡监测信息可视化查询分析系统及其应用

大型边坡监测系统数据庞大,项目及测点繁多。传统的数据库管理系统很难直观地查询分析监测数据。作者用在Window 系统下面向对象的程序设计语言VisualBasic和面向对象的数据库管理开发系统Access 开发了具有可视化查询分析特征的监测信息分析管理系统。本文以五强溪水电站左岸船闸边坡为例,介绍了系统的设计和程序功能。