Nonpremixed flame control with microjets

The hydrodynamic control of buoyant nonpremixed flames is investigated by injecting high-momentum fluid through a central microjet. The resulting flame characteristics are mapped for jets of different strengths. The flame height decreases linearly with an increase in the microjet Froude number as the flow changes from a buoyancy-dominated to a momentum-controlled regime. The flame luminosity is reduced by injecting stronger microjets. The jets alter the flame structure by establishing strong entrainment of the ambient air from the quiescent surroundings. The introduction of an inert species as the microjet fluid has a similar qualitative effect as air. Microjet assistance is as effective as partial premixing for reducing the flame height and luminosity.     

A study of the scattered-light technique in two-dimensional problems

The scattered-light method is applied to plane-stress problems. The study gives significance to the fringe spacing perpendicular as well as parallel to the direction of light propagation. The results show that one full-field photograph is sufficient to determine the state of stress in the model as well as to calibrate the model material. Results for the case of a ring in diametrical compression are presented.     

Influence of diffusion and kinetic characteristics on the combustion of a carbon particle

The spherically symmetric steady-state problem of heterogeneous combustion for a carbon particle is discussed. The exact solution of this problem is obtained. The dimensionless mass flux through the particle surface is graphically represented as a function of oxygen concentration in the external domain. The rate ratio for the diffusion process and the kinetic process is introduced as a dimensionless characteristic of the combustion process. The dimensionless mass fluxes through the particle surface are graphically represented as functions of external constitutive parameters. The resulting solution is approximated. The diffusion and kinetic modes of combustion are considered as limiting cases.     

Numerical computations of internal flows for axisymmetric and two-dimensional nozzles

MacCormack's explicit time-marching scheme is used to solve the full Navier–Stokes unsteady, compressible equations for internal flows. The requirement of a very fine grid to capture shock as well as separated flows is circumvented by employing grid clustering. The numerical scheme is applied for axisymmetric as well as two-dimensional flows. Numerical predictions are compared with experimental data and the qualitative as well as the quantitative agreement is found to be quite satisfactory. © 1997 John Wiley & Sons, Ltd.     

Large deflection analysis of plates on elastic foundation by the boundary element method

A boundary element method is developed for the large deflection analysis of thin elastic plates resting on elastic foundation. The subgrade reaction may depend linearly (Winkler-type) or nonlinearly on the deflection as well as on the point coordinates (nonhomogeneous subgrade). Moderately large deflections are examined as described by the von Karman equations. The plate may have arbitrary shape and its boundary may be subjected to any type of boundary condition. The proposed method uses the fundamental solution of the linear plate theory and treats the nonlinearities as well as the subgrade reaction as unknown domain forces. Numerical results are presented to illustrate the method and demonstrate its effectiveness and accuracy.     

On mechanics of saturated granular materials

A continuum theory of saturated granular materials is formulated. The basic balance laws for the solid phase as well as for the fluid phase are presented. The constitutive equations are derived and the basic equations of motion of the solid and fluid continua are obtained. Several cases of interest, such as incompressible granules saturated with liquids are discussed. It is shown that the theory contains, as its special cases, the Mohr-Coulomb criterion for a granular material as well as Darcy's law of flow through porous media.     

碳纳米管在润滑脂中的导电性和摩擦学性能研究

碳纳米管(CNTs)作为添加剂,制备了以油溶性聚醚为基础油,聚四氟乙烯(PTFE)作稠化剂的导电润滑脂.用体积表面电阻测定仪测定其体积电阻率,用扫描电子显微镜(SEM)观察钢盘磨斑表面形貌,EDS能谱仪分析磨损表面元素组成.结果表明:含碳纳米管的润滑脂与含导电炭黑的润滑脂相比较,不但具有优异的润滑性能,还具有低的体积电阻率.     

Effects of the method of identification of the diffusion coefficient on accuracy of modeling bound water transfer in wood

An alternative approach to determining the bound water diffusion coefficient is proposed. It comprises a method for solving the inverse diffusion problem, an improved algorithm for the bound-constrained optimization as well as an alternative submodel for the diffusion coefficient’s dependency on the bound water content. Identification of the diffusion coefficient for Scots pine wood (Pinus sylvestris L.) using the proposed inverse approach is presented. The accuracy of predicting the diffusion process with the use of the coefficient values determined by traditional sorption methods as well as by the inverse modeling approach is quantified. The similarity approach is used and the local and global relative errors are calculated. The results show that the inverse method provides valuable data on the bound water diffusion coefficient as well as on the boundary condition. The results of the identification can significantly improve the accuracy of mass transfer modeling as studied for drying processes in wood.     

组合超弹性材料中的空穴生成与增长

本文研究了一种组合不可压超弹性材料圆柱体中空穴的生成与增长问题，得到了这种材料受表面均布拉伸死荷载和轴向拉压共同作用下空穴生成问题的解析解，得到了不同组合情况下圆柱体中空穴生成时的临界载荷及分叉曲线，发现组合材料可以发生右分叉，也可以发生左分叉；给出了空穴生成后的应力分布，并讨论了所存在的应力间断和应力集中问题；通过能量比较分析了解的稳定性，讨论了发生右分叉或左分叉的条件，并分析了材料中预存微孔的增长情况。     

The rivulet flow pattern during oil–water horizontal flow through a 12 mm pipe

The present study reports the hydrodynamics of the rivulet pattern during oil–water flow through a 12 mm horizontal acrylic pipe. The interfacial distribution has been observed visually and characterized from signals obtained from an optical probe as well as by isokinetic sampling. The probability density function (PDF) and fast Fourier transform (FFT) of the signals have provided an understanding of the flow configuration. The experiments have revealed that although rivulet flow is a typical separated flow pattern, it has different characteristics as compared to the stratified and annular flow patterns. The holdup and pressure drop under such conditions have been compared with the drift flux model for horizontal flow as well as the two-fluid model as proposed by Brauner and Maron [9] for liquid–liquid flows.     

Application of BEM and optimization technique to wear problems

In this paper a new method for solving wear problems, using the Boundary Element Method (BEM) is proposed. The proposed method uses a shape optimization technique for rapid calculation of the maximum wear depth and the final geometry of the bodies in contact after a specified service period. The optimization method solves the wear problem directly, without using increments of the sliding distance as in the classical methods. The BEM is used for modelling both bodies in contact, treating the problem as a multi-region problem. The material loss is presented in terms of the applied load and the sliding distance, and is modelled using a linear wear model. The proposed method is shown to be robust as it requires only few iterations to achieve a converged solution. The reduction in computational effort, as compared to the classical incremental method, becomes more significant as the sliding distance increases.     

Multi-frequency analysis of the double circular plate system non-linear dynamics

This paper presents a multi-frequency analysis of non-linear dynamics in a double circular plate system. The original series of the amplitude–frequency and phase–frequency graphs as well as eigen forced time functions–frequency graphs are obtained and analyzed for stationary resonant states. The series of the frequency characteristic of the forced time non-linear harmonics are presented first. The analyses identify the presence of singularities and triggers of coupled singularities, as well as resonant jumps.     

粗粒土与结构接触面受载过程中的损伤

进行了粗粒上与结构接触面单调和循环加载试验,基于宏细观测量结果,扩展了损伤概念以描述该类接触面在受载过程中的物态演化,及由于物态演化导致的力学特性从初始状态到最终稳定状态的连续变化过程.揭示了接触面损伤的细观物理基础主要是接触面内土的颗牲破碎和剪切压密这两种物态演化;指出接触面的剪胀体应变可以划分为可逆性和不可逆性剪胀体应变两部分,其中不可逆性剪胀体应变可作为接触面损伤发展的宏观量度,因此其归一化形式可作为一种损伤因子的定义;提出了建立粗粒土与结构接触面一种损伤本构关系的基本思路.     

Numerical analysis of active chordwise flexibility on the performance of non-symmetrical flapping airfoils

This paper investigates the effect of active chordwise flexing on the lift, thrust and propulsive efficiency of three types of airfoils. The factors studied are the flexing center location, standard two-sided flexing as well as a type of single-sided flexing. The airfoils are simulated to flap with four configurations, and the effects of flexing under these configurations are investigated. Results show that flexing is not necessarily beneficial for the performance of the airfoils. However, with the correct parameters, efficiency is as high as 0.76 by placing the flexing centre at the trailing edge. The average thrust coefficient is more than twice as high, from 1.63 to 3.57 with flapping and flexing under the right conditions. Moreover, the single-sided flexing also gives an average lift coefficient as high as 4.61 for the S1020 airfoil. The shape of the airfoil does alter the effect of flexing too. Deviating the flexing phase angle away from 90° does not give a significant improvement to the airfoil’s performance. These results greatly enhance the design of a better performing ornithopter wing.     

Extreme wave solutions: Parametric studies and wavelet analysis

Wave fields for near homoclinic, single mode rogue-wave solutions of the periodic nonlinear Schrödinger equation are presented. Parameters of candidate solutions are estimated and refined through an eigenvalue solution procedure. An overview of the estimation and refining procedure used by the authors is provided. Solutions are scaled to facilitate experimental implementation. The continuous wavelet transform is used to carry out time–frequency analyses and the results obtained are demonstrative of the dispersion relation as well as the time varying side band energy transfer associated with the Benjamin–Feir instability. The analysis framework and approach used are validated with the Peregrine solution. Other extreme wave solutions are analyzed as well. The framework presented here could serve as a basis for experimental investigations into single mode rogue waves as well as other localizations in wave fields.     

The occurrence of periodic distortions in the extrusion of polymeric melts

In the extrusion of polymeric melts at high flow rates, often flow instabilities observed as surface distortions of the extrudate occur. The flow instability ‘spurt’ in piston-driven flows is accompanied by persistent oscillations in the pressure. In this paper spurt is explained in terms of constitutive instabilities (mechanical failure of the polymeric fluid itself), while the no-slip boundary condition at the wall of the die is maintained. The influence of compression on the onset of spurt is investigated. The polymeric melt is modelled as a JSO-fluid, but two other constitutive models are also considered. Numerical computations disclose that persistent oscillations in the pressure as well as in the volumetric flow rate occur for a bounded range of prescribed plunger speeds. The occurrence of the persistent oscillations is also explained by a linearized stability analysis. The frequency of the persistent oscillations is determined both from the linearized stability theory as well as by means of a Fourier spectral analysis. In conclusion, the theory is validated by a qualitative comparison with experimental results. Received March 3, 1998     

The effect of residual contamination on Marangoni convection in a spherical liquid system

The thermocapillary convection which results from both a temperature field as well as residual contamination applied at the surface of a spherical liquid system in a microgravity environment has been studied both analytically and numerically. Such an investigation is relevant to containerless materials processing in a microgravity environment. The analysis is linear. Temperature and concentration fields are steady, but have a non-axisymmetric spatial variation. The compound fluid drop system as well as the simple drop system are studied. Results are compared to those of Marangoni flow, driven only by a thermal field.     

A geometrically nonlinear analysis of rotational shells using B-spline function

In this paper, based on the nonlinear thin shell theory, a geometrically nonlinear formulation using the total Lagrangian approach for rotational shells, as well as rotational shells on the Winkler-type elastic foundation, is presented. The displacements of the middle surface are approached by a B-spline function. All nonlinear terms of membrane strains are reserved. Two cases in which the arc length as well as ordinate is used as the coordinate parameter along meridional direction are discussed at the same time.The project supported by National natural Science Foundation of China.     

Numerical simulation of the flow field in the vicinity of an axial flow fan

The main purpose of the current investigation is the development and evaluation of a numerical model used to simulate the effect of an axial flow fan on the velocity field in the vicinity of the fan blades. The axial flow fan is modeled as an actuator disc, where the actuator disc forces are calculated using blade element theory. The calculated disc forces are expressed as sources/sinks of momentum in the Navier–Stokes equations solved by a commercially available computational fluid dynamic (CFD) code, Flo⁺⁺. The model is used to determine the fan performance characteristics of an axial flow fan as well as the velocity fields directly up‐ and downstream of the fan blades. The results are compared with experimental data. In general, good agreement is obtained between the numerical results and experimental data, although the fan power consumption, as well as radial velocity downstream of the fan blades, is underpredicted by the fan model. Copyright © 2001 John Wiley & Sons, Ltd.