A NEW CRITERION FOR OCCURRENCE OF STICK-SLIP MOTION IN DRIVE MECHANISM

This paper, using Karnopp's model of friction force and phase plane method, studies the stick-slip motion of the flexible drive mechanism. It is explained that a sudden drop of friction force is the essential source of stick-slip motion when the sliding is impending. A new criterion for occurrence of stick-slip motion is established. The stick-slip region and the stable region in a parameter plane are separated by a critical parameter curve. Moreover, for the stick-slip motion of the flexible drive mechanism without viscous damping, a parameter expression is obtained. The results may be used in design of the flexible drive mechanism.

Three independent parameters to describe conventional triaxial compressive strength of intact rocks

The strengths of 12 rocks cited from literatures increase in a nonlinear way with increasing confining pressure against the Coulomb criterion. The criteria with power forms like the generalized Hoek-Brown criterion are not available for describing the strength properties in the whole test range for Indiana limestone, Yamaguchi marble and Vosges sandstone, of which the differential stresses are approximately constant at high confining pressures. The exponential criterion with three parameters fits the test data of those 12 rocks well with a low misfit. The three parameters are independent of the uniaxial compressive strength (UCS), the initial increasing rate of strength with confining pressure, and the limitation of differential stress.

A simplified approach to directly consider intact rock anisotropy in Hoek——Brown failure criterion

Many rock types have naturally occurring inherent anisotropic planes, such as bedding planes, foliation,or flow structures. Such characteristic induces directional features and anisotropy in rocks＇ strength anddeformational properties. The HoekeBrown （HeB） failure criterion is an empirical strength criterionwidely applied to rock mechanics and engineering. A direct modification to HeB failure criterion toaccount for rock anisotropy is considered as the base of the research. Such modification introduced a newdefinition of the anisotropy as direct parameter named the anisotropic parameter （Kb）. However, thecomputation of this parameter takes much experimental work and cannot be calculated in a simple way.The aim of this paper is to study the trend of the relation between the degree of anisotropy （Rc） and theminimum value of anisotropic parameter （Kmin）, and to predict the Kmin directly from the uniaxialcompression tests instead of triaxial tests, and also to decrease the amount of experimental work. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Effects of time-delayed vibration absorber on bandwidth of beam for low broadband vibration suppression

The effects of time-delayed vibration absorber(TDVA) on the dynamic characteristics of a flexible beam are investigated. First, the vibration suppression effect of a single TDVA on a continuous beam is studied. The first optimization criterion is given,and the results show that the introduction of time-delayed feedback control(TDFC) is beneficial to improving the vibration suppression at the anti-resonance band. When a single TDVA is used, the anti-resonance is located at a specific frequency by the optimum design of TDFC parameters. Then, in order to obtain low-frequency and broad bands for vibration suppression, multiple TDVAs are uniformly distributed on a continuous beam,and the relationship between the dynamic responses and the TDFC parameters is investigated. The obtained relationship shows that the TDVA has a significant regulatory effect on the vibration behavior of the continuous beam. The effects of the number of TDVAs and the nonlinearity on the bandgap variation are discussed. As the multiple TDVAs are applied, according to the different requirements on the location and bandwidth of the effective vibration suppression band, the optimization criteria for the TDFC parameters are given, which provides guidance for the applications of TDVAs in practical projects such as bridge and aerospace.

TC4钛合金电子束焊缝形状特征分类研究

论述了理论解析、数值模拟、回归分析、人工神经网络等多种焊缝形状的研究方法,采用多种预测方法结合将是较为理想的焊缝形状研究方案。在所获取的电子束焊缝截面上取一系列控制点,利用B样条曲线实现焊缝形状的参数化再现,分析了控制点参数与焊缝形状特征参数的关系,建立了焊接形状分类准则,获得了特征尺寸临界值,并将电子束焊缝分为漏斗型、钟罩型、楔型和钉型四类。

一类参数曲线的积累平均弧长参数化方法

通过用指定方法及约束准则进行局部插值,为高效求解采用从局部传递到整体的思想,给出积累平均弧长参数化法的一般框架,并在该框架下给出3种具体的积累平均弧长参数化法及相应的数值算法.积累平均弧长参数化法的目标是降低传统方法求得的曲线关于光顺性的目标函数值,并使方法具有可根据设计者需求生成满足条件曲线的灵活性.实例验算表明:在同一约束准则下,该方法求得的全局插值曲线的目标函数值小于弦长参数化和向心参数化所对应的目标函数值.

基于协调组合参数化的改进连续潮流计算方法

基于连续潮流法对静态电压稳定性问题进行研究,提出了一种协调组合参数化法。在PV曲线的不同区域采用不同的参数化法,以当前预测次数来表征参数化切换断点;以“接近校正不收敛”作为组合切换的判据;对切换判据的阈值进行动态设定,以使得组合切换更加合理有效。基于IEEE标准节点系统进行仿真验证,结果表明了所提协调组合参数化法的有效性与优越性。