投影栅相移法中的相位波动误差及修正算法研究

分析了因测量系统非线性响应及局部饱和投影栅图像所导致的相位误差及其波动特性。经过实验验证,四步相移算法在抑制系统非线性响应所引起的相位误差方面优于三步相移算法。通过模拟分析得出,在采用传统相移算法对局部饱和条纹图像分析时,相位误差较大,且相位分布具有周期波动特性。为减小因图像局部饱和而产生的相位误差,文中采用了新的算法提取相位。实验分析结果验证了算法的正确性。     

Lattice Spring Models

Solid mechanics can be addressed by a Lattice Spring Model whose major ingredients are briefly described. It is applied to solve the dynamic equations of motions and the static equations derived by homogenization. Results relative to the macroscopic properties of solids are successfully compared to the ones obtained by analytical methods and by other techniques of numerical calculations. Wave velocities derived by direct simulations are in good agreement with the ones derived by homogenization.     

Alkali-activation reactivity of chemosynthetic Al_2O_3-2SiO_2 powders and their ~(27)Al and ~(29)Si magic-angle spinning nuclear magnetic resonance spectra

Pure Al_2O_3-2SiO_2 powders were prepared by sol-gel and coprecipitation methods,and their alkaliactivation reactivities were compared.The alkali-activation reactivity of the powder prepared by the sol-gel method was higher than that of the powder prepared by the coprecipitation method.The powders were investigated by ~(27)AI and ~(29)Si magic-angle spinning nuclear magnetic resonance spectroscopy(MAS NMR) to understand the relationship between their structure and alkali-activation reactivity.The ~(27)Al MAS NMR data showed that the five-coordinate AI content of the powder prepared by the sol-gel method was higher than that of the powder prepared by coprecipitation.The higher content of five-coordinate Al corresponded to higher alkali-activation reactivity.The ~(29)Si MAS NMR data showed that for the powder prepared by the sol-gel method,silicon was replaced by aluminum at secondary coordination sites of the central Si atoms during calcination.However,for the powder prepared by single-batch coprecipitation,the main change was from a low degree of polycondensation to a high degree of polycondensation.     

Minimizing end-effects in the coaxial cylinders viscometer: Viscoplastic flow inside the ConTec BML Viscometer 3

The ConTec BML Viscometer 3 is designed to measure the rheological properties of fresh concrete. The measuring unit of this device is composed of two parts, where the rheological properties are only registered by the part least affected by end-effects. Thus it is assumed that the measured data is not influenced by end-effects, allowing for the use of an algebraically derived equation to convert the data to fundamental physical quantities. In this work, this important assumption is supported by numerical analysis. This has been done by comparing values calculated by numerical means, where end-effects are included in the analysis, with values calculated by analytical means, where end-effects are excluded.     

Combined radiation and natural convection effects on graetz problem in horizontal isothermal circular tubes

A numerical analysis is performed on the combined thermal radiation and mixed convection for a gray fluid flow in a horizontal isothermally-heated circular tube. The governing equations of vorticity-velocity form are employed and solved by DuFort-Frankel method. The contribution of radiation is formulated by integral expression and solved by finite element nodal approximation. The effects of radiation and convection on local Nusselt number and the developing of bulk temperature are presented. The result shows that the heat transfer can be significantly enhanced by the effects of radiation and secondary flow induced by buoyancy. Besides, the fluctuation in local Nusselt number curve which is caused by the existence of secondary flow is reduced by the effect of thermal radiation.     

Book reviews

Book reviewed in this article:
By J.S. Rao and D.V. Dukkipati, John Wiley and Sons
Reviewed by H. Rajiyah, The Center for the Advancement of Computational Mechanics, The Georgia Institute of Technology, Atlanta, GA 30332-0356.
By P.L.B. Oxley, Ellis Horwood Limited, West Sussex, England
Reviewed by H. Rajiyah, The Center for the Advancement of Computational Mechanics
By Herbert Reismann, published by John Wiley and Sons
Reviewed by J.S. Epstein, The Center for the Advancement of Computational Mechanics
Edited by T.A. Cruse, ASTM STP 969, published by the American Society for Testing and Materials
Reviewed by J.S. Epstein, The Center for the Advancement of Computational Mechanics, The Georgia Institute of Technology, Atlanta, GA 30332-0355.
By S.P. Shah and S.E. Swartz, Springer Verlag
Reviewed by J.S. Epstein, The Center for the Advancement of Computational Mechanics, The Georgia Institute of Technology, Atlanta, GA 30332-0355.
Published by The American Society for Testing and Materials, Philadelphia
Reviewed by M.A. Abdallah, Hercules Aerospace     

用拉格朗日函数分析不同模量静不定桁架内力

在外载荷作用下的不同模量静不定桁架平衡问题,是任意有限多个自变量的多元函数在任意有限多个约束条件下的极值问题,对采用拉格朗日乘数法求解此类极值问题进行了数学证明．通过求解不同模量静不定桁架极限载荷的几个算例,阐述拉格朗日乘数法在计算不同模量静不定桁架极限载荷中的应用．研究结果表明：采用拉格朗日乘数法求解不同模量静不定桁架极限载荷的通用性较强,用拉格朗日乘数法求解不同模量静不定桁架极限载荷的方法不但克服了常规方法需利用几何关系建立协调方程的缺陷,且具有力学概念清晰直观、计算过程简便、便于工程设计人员在实际中掌握和应用．     

薄壁柱壳的圆度及三维变形测量技术

本文采用一种新的形状位置（Ｐｒｏｆｉｌｉｍｅｔｒｙ）自动测量计算机处理方法,对钢质圆柱壳的椭圆度进行了测试。具体使用投影光栅,于壳体表现形成栅线影象,自动形成栅线光频率线性编码,用ＣＣＤ摄象机采集到频率编码壳体光栅影象,构成形西半球工波图。将载波的图象经过计算机图象系统获得数值图象。计算机经过快速富立叶变换法解码,输出频率位相值,经数据处理可得到精确的壳面尺度。     

Twisting stresses in tape

An analysis is presented of the stresses induced in a thin tape by bending over pulleys, by axial tension and by twisting of the tape when running between two out-of-plane pulleys. Analytical results are compared with some photoelastic tests on tape models made of epoxy resin. The weak retardation produced by the thin tape is multiplied by repeated light passage through the tape and is measured by a bent-beam compensator. The tests are of especial interest because the rate of rotation of the principal stresses is higher than had been encountered before. Surprisingly, the experimental results uncorrected for rotation are in good agreement with the calculated stresses.     

混沌的抑制研究进展综述

综述了抑制混沌的４种主要方法:加随机噪声、加周期摄动、加动力吸振器和加输出变量反馈．概括了各种方法的一般形式,列举了各种方法应用的例子,还指出一些尚待研究的问题．      

应用同伦分析法研究Mathieu-Duffing振子的周期解

应用同伦分析法研究了Mathieu-Duffing振子的周期解,展示了Mathieu-Duffing振子的周期1和周期2解的求解过程,通过求解构造的非线性代数方程组而获得周期解,应用Floquet理论判别了周期解的稳定性。比较了同伦分析方法得到的周期解和数值方法得到的周期解,结果表明两者具有一致性。     

非均匀径向冲击下圆柱壳塑性动屈曲

本文采用王仁等提出的塑性动力屈曲的能量准则讨论了圆柱壳在不均匀的外部径向冲击下的塑性动屈曲问题，获得了屈曲的占优波数公式及临界冲击速度公式，初步的实验证明本文的结论是合理的。同时进一步证明该能量准则的有效性。     

External motion resistance caused by rut sinkage of a tracked vehicle

This paper deals with the external motion resistance of a tracked vehicle caused by rut formation (sinkage) or compression of soil under the tracks. It is shown that the relationship between the applied load and the sinkage for a loading test using a plate is represented by a hyperbola. Based on the above relationship, the external motion resistance caused by the rut formation of a tracked vehicle is estimated by considering the work done by overcoming the ground pressure and the resistance. Further, measurements of the external motion resistance were carried out by using a tracked vehicle and the experimental results are compared with the theoretical ones, and the reliability of the above method is confirmed experimentally.     

利用蒙特卡洛方法计算陶瓷刀具磨损可靠性

在连续切削条件下,陶瓷刀具的失效形式是以磨粒磨损为主的摩损失效,其磨损寿命由材料的断裂韧性、硬度和切削过程的参数决定,利用蒙特卡洛方法分别随机生成断裂韧性与硬度的样本值,利用连续车削试验确定切削过程参数,将得到的样本值与切削参数相结合可计算刀具在相应切削条件下的磨损寿命及其可靠性,计算结果表明：陶瓷刀具的断裂韧对磨损寿命的可靠性影响较为明显,因而可以利用断裂韧性来估算磨损可靠性。     

Acoustic forcing on swirling flow: experiments and simulation

We investigated the effect of sound irradiated from loudspeakers on the flow of preheated air in the combustion chamber of a swirl burner. The temporally periodic pattern of the flow generated by the sound was detected by fast particle image velocimetry (PIV), with a repetition rate that was adapted to the observation of 12 phase angles of the irradiated monochromatic sound. The strong observed movement of the air is related to the movement by the sound itself, as determined by the pressure measurements with microphones. The PIV measurements reveal also a nonlinear interaction between the irradiated sound and the precession of the vortex core. The accuracy of the sound measurements was tested by determining in quiescent air the acoustic velocity by microphones and as well by PIV; good agreement was obtained thereby. Numerical calculations, using large eddy simulation and accounting for the sound forcing by variation in the mass flow at the inlet of the computational domain, approximately reproduce some of the experimental results.     

Numerical solution of a viscous incompressible flow problem through an orifice

A steady flow problem of a viscous, incompressible fluid through an orifice is widely applicable to many physical phenomena and has been studied previously by many researchers. A problem of such type has been solved by applying LAD method given by Roache [1]. The resulting system of linear equations is solved by Hockney's method [2].     

Generation of stable solitary waves by a piston-type wave maker

The focus of present study is on how to generate solitary waves as pure as possible by using a piston type wave maker. A meshless numerical model, which can simulate the trajectories of fluid particles in a wave motion exerted by the wave paddle, is established for the purpose of present study. The present numerical model is verified by the comparison with experimental data before it is employed to the focused problem. Various wave paddle motions are considered. The results show that solitary waves generated by applying Fenton’s solitary solution to the paddle motion proposed by Goring are purer than those generated by other paddle motions.     

Objective tensorial representation of the pressure–strain correlations of turbulence

An explicit algebraic model for the fluctuating pressure–strain rate correlations of turbulence is developed by the use of representation theorems for tensor-valued isotropic tensors, and by invoking the principle of objectivity. The resulting model differs from others by the absence of the vorticity tensor from its formulation. The new model is calibrated by reference to data from homogeneous shear flows, and its potential as a practical tool for the analysis of turbulent flows is demonstrated by numerical simulations of a benchmark two-dimensional shear layer.     

DYNAMIC BUCKLING OF ELASTIC-PLASTIC COLUMN IMPACTED BY RIGID BODY

The dynamic buckling of an elastic-plastic column subjected to an axial impact by a rigid body was discussed by using the energy law. The traveling process of elastic-plastic waves under impact action was analyzed by characteristics method. The equation of lateral disturbance used to analyze the problem was developed by taking into account the effect of elastic-plastic stress wave. The power series solution of this problem has been the power series approach. The buckling criterion of this problem was proposed by analyzing the characteristics of the solution. The relationship among critical velocity and impact mass, critical buckling length, hardening modulus was given by using theoretical analysis and numerical computation.     

Three-dimensional Green’s functions for infinite anisotropic piezoelectric media

A direct, effective and concise method is adopted in this paper to find out the Green’s functions for infinite anisotropic piezoelectric media. The partial differential equations satisfied by the Green’s functions turn into a set of inhomogeneous algebraic equations after by using Fourier transform. Then inverse transform the solutions of the algebraic equations, the Green’s functions can be expressed by contour integral. Finally, the explicit expression can be obtained for the Green’s functions by using residual theory. The method demonstrated in this paper is easier to follow by people without knowledge of Radon transform, which has been used to obtain the Green’s functions by others.