小波分析用于陀螺仪漂移测试信号分析的研究

为建立陀螺仪漂移特性模型，需对其进行测试。由测试得到的数据是含有噪声的，且一般是非平稳的，用小波分析测试数据是一种很有效的方法。在简述小波分析中的多分辨分析理论的基础上，用其对某型陀螺仪的实测数据进行了分析－预处理，其结果证实了所研究方法的有效性。     

The Role of Capillarity in Two-Phase Flow through Porous Media

When determining experimentally relative permeability and capillary pressure as a function of saturation, a self-consistent system of macroscopic equations, that includes Leverett's equation for capillary pressure, is required. In this technical note, such a system of equations, together with the conditions under which the equations apply, is formulated. With the aid of this system of equations, it is shown that, at the inlet boundary of a vertically oriented porous medium, static conditions pertain, and that potentials, because of the definition of potential, are equal in magnitude to pressures. Consequently, Leverett's equation is valid at the inlet boundary of the porous medium, provided cocurrent flow, or gravity-driven, countercurrent flow is taking place, and provided the porous medium is homogeneous. Moreover, it is demonstrated that Leverett's equation is valid for flow along the length of a vertically oriented porous medium, provided cocurrent flow, or gravity-driven, countercurrent flow is taking place, and provided the porous medium is homogeneous and there are no hydrodynamic effects. However, Leverett's equation is invalid for horizontal, steady-state, forced, countercurrent flow. When such flow is taking place, it is the sum of the pressures, and not the difference in pressures, which is related to capillary pressure.     

基于CFD-DEM的高炉风口回旋区形状和传热特性数值模拟研究

采用计算流体力学-离散单元法(CFD-DEM)耦合方法,对高炉风口回旋区进行了数值模拟研究。首先通过与实验结果对比,验证了CFD-DEM模型的正确性;然后考察了不同气速对风口回旋区形状和传热特性及颗粒接触的影响。数值模拟结果表明:风口回旋区的大小和形状均受气速影响较大,在较大进气速度下,颗粒受到的曳力大于颗粒间的摩擦阻力并破坏颗粒间的桥力,形成较大尺寸的回旋区;且颗粒之间接触力较小,形成较大的空隙结构,更有利于热气体向周围扩散以强化传热。目前考察的三种气速结果表明:当气速为11m/s时,热量向下方传递速度最快;当气速为13m/s时,热量向上方传递速度最快;而当气速为15m/s时,热量向右方传递速度最快;此外,气速越大流态化越明显,颗粒间接触越少,接触力也越小。     

A VIEWPOINT OF THE TENSORAL PROPERTY OF COORDINATE TRANSFORMATION COEFFICIENT AND ANALYSISON THE CONCEPT OF HYBRID TENSOR1)

本文致力于澄清一个十分基本的问题：坐标变换系数是否为张量?传统观念认为,坐标变换系数不是张量。为了揭示坐标变换系数的本质,本文采用“从一般到特殊”的研究策略,重塑了张量的内涵和外延,引入了杂交张量概念,进而颠覆了坐标变换系数不是张量的传统观念,确切地讲,它就是度量张量的杂交分量。这一结果扩张了张量概念的集合,提升了张量分析学内在的统一性、对称性和不变性,减少了连续介质力学的运算量。     

Steady sliding frictional contact problem for a 2d elastic half-space with a discontinuous friction coefficient and related stress singularities

The steady sliding frictional contact problem between a moving rigid indentor of arbitrary shape and an isotropic homogeneous elastic half-space in plane strain is extensively analysed. The case where the friction coefficient is a step function (with respect to the space variable), that is, where there are jumps in the friction coefficient, is considered. The problem is put under the form of a variational inequality which is proved to always have a solution which, in addition, is unique in some cases. The solutions exhibit different kinds of universal singularities that are explicitly given. In particular, it is shown that the nature of the universal stress singularity at a jump of the friction coefficient is different depending on the sign of the jump.     

基于伪距宽巷组合的GPS模糊度固定方法

中长基线模糊度快速解算是GPS网络差分技术的核心内容。根据网络差分模糊度固定只用于基线解算而不用于定位的特点,通过对常用GPS原始观测数据组合方式的分析,提出伪距宽相组合的数据处理方法,有效消除了电离层、对流层传播误差,形成抗差性强、大气误差自由的GPS组合观测值;在此基础上引入双差伪距宽相组合进行模糊度浮点解并建立法方程,应用高度角与大气误差的关系构造权阵,对常规LAMBDA算法进行了改进,形成一种适合GPS网络差分的中长基线模糊度解算方法。对三个参考站同步观测数据的实际测试结果表明：使用该方法网络模糊度解算时间小于300s,基线长超过60km,并满足闭合性原则。     

单步辛算法的相位误差分析及修正

若一个算法的幅值误差和相位误差都不累加，则该算法就是最理想的算法， 但这样的算法难以构造. 辛几何算法解决了幅值误差的累加问题，但相位误差累加问题仍然 存在. 给出了单步隐式辛算法相位误差的精确估计公式，提出了简单而实用的修正方法. 以 Euler中点隐式辛差分格式为例，针对几个线性动力学系统，对相位误差进行了数值分析和 修正.     

基于统一强度理论抗滑桩桩间距的计算

在已有抗滑桩桩间距研究的基础上,对桩间土拱进行受力分析。从侧阻力条件和土拱强度条件两个方面对抗滑桩桩间距进行了计算,将统一强度理论引入土拱强度的分析,藉此分别判断拱顶前缘、后缘及拱脚处土体是否处于临界状态,可得3个桩间距值,取相应的最小桩间距作为设计桩间距。此方法对于滑坡推力的矩形、三角形和梯形分布形式均适用,并可考虑土体自重应力的影响,同时可推及锚索抗滑桩桩间距的计算。对两个计算实例进行了分析,本方法的计算值与已有计算值或设计值的比较表明本方法效果良好。具体计算中统一强度参数b取0.2~0.7较为合适,滑坡推力为矩形分布时b值约为0.3,滑坡推力为三角形分布时b值约为0.6,滑坡推力为梯形分布时b值介于两者之间。     

Hydraulic analysis of free-surface flows with solidification

Summary The paper is concerned with a one-dimensional analysis of plane open-channel flow with continuous solidification. The process is of relevance for recent developments in the casting of steel and other metals. The bottom of the channel consists of a rotating casting roll and a horizontal cooling table, where the solidified material is withdrawn with given velocity. The study is restricted to the region downstream of the top of the casting roll. Surface tension is neglected. In the main part of the analysis inviscid fluid flow is considered since the Reynolds number is very large in the applications. It is found that the steady-state solutions are nonunique in a certain parameter range. In addition to a continuous solution, there are two solutions including hydraulic jumps, with one hydraulic jump being located on the casting roll, the other one on the cooling table. Regarding the stability of the non unique solutions, the evolution of disturbances is investigated numerically as an initial-value problem. It is concluded that the hydraulic jump on the cooling table is unstable, while the other discontinuous solution as well as the continuous solution are stable for sufficiently small disturbances. Which stable solution is attained in the steady state, depends on the history of the process. Friction at the liquid/solid interface is taken into account in the last part of the analysis. A constant friction coefficient is assumed. It is found that the history of the process determines the steady-state solution if, and only if, the friction coefficient is sufficiently small. For larger values of the friction coefficient, the steady-state solution is unique and independent of the history of the transient process. Furthermore, for sufficiently large friction coefficients, stable hydraulic jumps are found, in contrast to the inviscid case, also on the cooling table. Received 19 March 1999; accepted for publication 3 May 1999     

X80管道双腐蚀缺陷间相互作用规律研究

为了对腐蚀管道进行准确的安全评价,本文针对X80管道相邻双腐蚀缺陷间的相互作用规律进行了研究。借鉴现有X80管道爆破实验的数据,对数值计算中的单元划分、边界条件设置等进行验证。采用ANSYSWORKBENCH软件对X80管道在腐蚀缺陷下的应力应变状态进行了分析。数值分析结果显示:轴向间距一定时,腐蚀深度越大,轴向相邻双腐蚀间相互作用越明显;当两个相邻腐蚀缺陷轴向距离在3(Dt)1/2以内或环向处于0.07pD以内时,需要考虑两个腐蚀缺陷的相互影响;当两个相邻腐蚀缺陷轴向距离大于3(Dt)1/2或环向间距大于0.07pD时,不需要考虑腐蚀间的相互作用。     

Non-linear argumental oscillators: Stability criterion and approximate implicit analytic solution

The behaviour of a space-modulated, so-called “argumental” oscillator, is studied. The oscillator is submitted to an external harmonic force, which is amplitude-modulated by the oscillator's position in space. An analytic expression of a stability criterion is given. Using the averaging method, an integrating factor and a Van der Pol representation in the (amplitude, phase)-space, an exact implicit analytic solution is given when there is no damping, and an approximate implicit analytic solution is given when there is damping, allowing the plotting of the separatrix curve. An attractor is identified.     

A Theoretical and Experimental Implementation of a Control Method Based on Saturation

A novel approach for implementing an active nonlinear vibration absorber is presented. The absorber, which is built in electronic circuitry, takes advantage of the saturation phenomenon that occurs when two natural frequencies of a system with quadratic nonlinearities are in the ratio of two-to-one. When the system is excited at a frequency near the higher natural frequency, there is a small ceiling for the system response at the higher frequency and the rest of the input energy is channeled to the low-frequency mode.A working model of using saturation to suppress the vibrations of a rigid beam connected to a DC motor has been built. An electronic oscillator is built, and its frequency is set at one-half the frequency of the beam. The output from a sensor on the beam is multiplied by the output from the electronic oscillator and a suitable gain, and the result is used as the forcing term for the oscillator. At the same time, the output from the oscillator is squared and multiplied by a suitable gain, and that result is used as the input to the motor. The oscillator/actuator and the beam act as the two modes of a two-degree-of-freedom quadratically coupled system with a 2:1 autoparametric resonance. When the beam is excited by a harmonic force, its motion quickly becomes saturated, and most of the energy imparted to the beam by the harmonic force is transferred to the electronic circuit and from there to the actuator. Thus, the harmonic force is made to work against itself. As a result, the motion of the beam always remains small.     

圆柱形爆轰波的二维数值模拟

基于带化学反应的二维Euler方程,对圆柱形爆轰波的直接起爆和传播过程进行了二维数值模拟研究,拟分析起爆条件和初始压强对圆柱形爆轰波形成和传播的影响。研究发现,圆柱形爆轰波起爆成功向外传播的过程中,新的三波结构的生成标志着爆轰波进入稳定传播阶段。在起爆能量足够的情况下,起爆半径(曲率)的大小决定着三波结构初始形成时的数目和传播半径,起爆压强对其基本不产生影响;起爆半径大(曲率小)时,三波结构初始形成时的传播半径大、数目多,圆柱形爆轰波进入稳定传播阶段的传播距离长;数值模拟中,初始压强的提高,有助于圆柱形爆轰在较短的传播距离内进入稳定传播阶段。     

STATIC AEROELASTICITY METHOD BASED ON EXTERNAL AERODYNAMIC FORCE AND STRIP METHOD

本文通过对载荷设计中的静气动弹性分析方法进行研究,发展了一种基于外部刚性气动力数据和改良片条理论修正的弹性载荷修正方法。其中结构变形通过工程梁方法提取部件刚度阵进行计算,气动力通过网格化模型基于外部试验或CFD气动力数据库插值得到。结构和气动之间位移和力的数据传递分别利用曲面样条和形函数面积坐标加权法插值,弹性载荷修正通过改良后的片条理论计算,由此迭代循环直至结构变形收敛。同时通过对相关工程实例进行分析计算并与成熟方法对比,验证了该方法的可行性和高效性。     

Rayleigh-Taylor instability of an interface in a nonwettable porous medium

The diffusion of vapor through the roof of an underground structure located beneath an aquifer is considered. In the process of evaporation, an interface between the upper water-saturated layer and the lower layer containing an air-vapor mixture is formed. A mathematical model of the evaporation process is proposed and a solution of the steady-state problem is found. It is shown that in the presence of capillary forces in the case of a nonwettable medium the solution is not unique. Using the normal mode method, it is shown that Rayleigh-Taylor instability of the interface can develop in the nonwettable porous medium. It is found that there are two scenarios of loss of stability corresponding to the occurrence of the most unstable wavenumber at zero and at infinity, respectively. It is shown that for zero wavenumber the stability limit is reached at the same time as the solution of the steady-state problem disappears.     

Non-linear analysis and quench control of chatter in plunge grinding

This paper aims at mitigating regenerative chatter in plunge grinding. To begin with, a dynamic model is proposed to investigate grinding dynamics, where eigenvalue and bifurcation analyses are adopted, respectively, for prediction of grinding stability and chatter. Generally, it is found that most grinding chatter is incurred by subcritical Hopf bifurcation. Compared with supercritical instability, the subcritical generates coexistence of stable and unstable grinding in the stable region and increases chatter amplitude in the chatter region. To avoid these adverse effects of the subcritical instability, bifurcation control is employed, where the cubic non-linearity of the relative velocity between grinding wheel and workpiece is used as feedback. With the increase of feedback gain, the subcritical instability is transformed to be supercritical not only locally but also globally. Finally, the conditionally stable region is completely removed and the chatter amplitude is decreased. After that, to further reduce the chatter amplitude, quench control is used as well. More specifically, an external sinusoid excitation is applied on the wheel to quench the existing grinding chatter, replacing the large-amplitude chatter by a small-amplitude forced vibration. Through the method of multiple scales, the condition for quenching the chatter is obtained.     

浮筏的主动吸振控制实验研究

浮筏在低频减振方面存在较大不足,而这恰是主动减振的优势.将两者相结合,研究了浮筏的主动吸振控制问题.研制了一种主动吸振器,建立了以DSP F2812为核心的控制系统;提出了符号LMS算法,与广泛使用的滤波x-LMS等算法相比,该算法不需要精确的模型信息;在此基础上设计了自适应前馈主动吸振控制律,并在浮筏实验平台上进行主动吸振控制实验.实验结果表明,通过主动吸振控制,浮筏的低频减振能力得到了显著的改善.     

AN IMPEDANCE ANALYSIS FOR CRACK DETECTION IN THE TIMOSHENKO BEAM BASED ON THE ANTI-RESONANCE TECHNIQUE

An alternative technique for crack detection in a Timoshenko beam based on the first anti-resonant frequency is presented in this paper.Unlike the natural frequency,the anti-resonant frequency is a local parameter rather than a global parameter of structures,thus the proposed technique can be used to locate the structural defects.An impedance analysis of a cracked beam stimulated by a harmonic force based on the Timoshenko beam formulation is investigated.In order to characterize the local discontinuity due to cracks,a rotational spring model based on fracture mechanics is proposed to model the crack.Subsequently,the proposed method is verified by a numerical example of a simply-supported beam with a crack.The effect of the crack size on the anti-resonant frequency is investigated.The position of the crack of the simply-supported beam is also determined by the anti-resonance technique.The proposed technique is further applied to the"contaminated"anti-resonant frequency to detect crack damage,which is obtained by adding 1-3% noise to the calculated data.It is found that the proposed technique is effective and free from the environment noise.Finally,an experimental study is performed,which further verifies the validity of the proposed crack identification technique.     

夯击能应用于高填土地基的一些探讨

大量工程实践表明 ,对填土及软土地基进行夯击加固时 ,夯击能的选取不仅与填土层的厚度有关 ,而且与填土层下覆土质的工程地质条件等因素密切相关。本文结合南方某港口填土地基加固工程实例 ,对在高填土地层中夯击能的使用问题进行了探讨 ,分析了当填土层的下卧层分别为坚硬土层和软弱土层、以及当填土层的填料分别为粗颗粒料和含水量较高的粘性土等细粒填料时 ,填土层加固的机理 ,制定了在不同条件下选取夯击能的标准 ,并根据现场检测资料 ,评价了该场地的地基加固效果 ,进一步验证了所确定夯击能标准的可靠性。     

介质参数反演的广义射线近似方法

在对无粘性介质参数反演问题进行的研究中，引入一种全波场广义射线近似形式，提出一种新的反演参数的方法，文中，首先对由弹性波动方程演变成的声波方程进行分析，引入背景场量和扰动量，并结合Ｇｒｅｅｎ函数理论，得到了介质参数的积分方程；然后结合前人对非均匀介质中波函数局部理论的定性分析，引入一种全波场广度射线近似形式，把问题归结为一个第一类Ｆｒｅｄｈｏｌｍ积分方程；最后对半空间问题层状介质模型进行了反演，算