Amplitude Variability in Simulated Incoherent Seismic Ground Motions

This note compares in detail four commonly used schemes for the simulation of spatially variable ground motions. Emphasis is placed not only on the conformity of the simulations with the power and cross spectral density of the random field but, also, on the examination of the consistency of the simulations with the homogeneity condition, and the (Fourier) amplitude variability of the simulations. It is shown that, whereas three techniques that simulate ground motions in parallel satisfy the homogeneity requirement, produce simulations with random amplitudes, and amplitude and phase variability consistent with that of recorded data, one technique that simulates motions in sequence does not.     

Combined Continua and Lumped Parameter Modeling for Nonlinear Response of Structural Frames to Impulsive Ground Shock

The response of a beam-column frame to impulsive ground shock, such as those induced by an underground explosion, has characteristics of both impact and natural earthquake responses. The critical effects may be governed by the dynamic response of individual elements as continuous mass systems, while to a certain extent the global vibration (as of lumped-mass systems) may also be involved. To incorporate both dynamic features, the present study proposes a combined continua and lumped parameter (CCLP) model, which consists of the basic beam-column element with distributed stiffness and mass, along with concentrated mass-springs at element ends to form the reduced dynamic system. To take into account of the shear deformation and rotary inertia which become important in the impulsive response, the governing equations are formulated based on the Timoshenko beam theory. The nonlinearities are described through three mechanisms, namely the distributed nonlinear flexural and diagonal shear behavior, and the direct sliding shear at the member ends. A generic restoring force model is adopted to describe the hysteretic behavior. Comparison with a scaled model test demonstrates that the CCLP model is capable of representing the primary dynamic features in a frame structure under impulsive ground shock. Extended parametric studies indicate that, with increase of the ground shock frequency, the failure tends to become shear dominant. For ground shocks of frequency at 20–30?Hz and above, the failure in a reinforced concrete column will require a peak ground velocity (PGV) on the order of 3?m/s, whereas failure in a beam would occur at PGV of about 1.5?m/s.     

Numerical Study of Particle Motion in Jet Milling

Jet mills are common devices used in industry for fine milling of dry particulate materials. The size reduction is caused by repeated events of impacts between particles. Although many parameters affect the performance of a jet mill, only a few of them were investigated. Particles' motions in a jet mill have great influence on the comminution process and energy consumption. Therefore, as a first step for a full simulation of the jet-mill process, it was decided to investigate the particle motion inside the jet mill by neglecting particle-particle interaction and particle breakage. In this way, the numerical simulations provide a better understanding of the classification process. In the present study, three-dimensional numerical simulations of particle motion in an industrial full-scale jet mill were conducted. The predictions of the numerical simulations were compared with experimental data and used to analyze the flow field characteristics.     

尺蠖型压电直线驱动器的运动稳定性分析

为了深入研究尺蠖型压电驱动器的性能，分析了尺蠖型压电直线驱动器的工作原理，研究了直线动子对驱动器性能的影响．通过实验方法分析了钳位机构调整前后对钳住稳定性的影响．采用驱动器输出单步位移的步距失稳系数和驱动电压与输出位移拟合曲线斜率和截距偏差率的方法评价尺蠖型压电直线驱动器的运动稳定性．经实验测试发现驱动器的步距失稳系数与驱动电压关系密切，当驱动电压较高时，驱动器具有较好的步距稳定性．驱动器的驱动电压与输出位移拟合曲线斜率和截距偏差率分别为1．8％和9．07％，说明所开发的驱动器具有很好的运动稳定性．     

物体运动路线多样化模拟

在现代仿真技术和游戏动画中,越来越多的物体可以按照实时指定的关键位置在平面上进行移动,然而,早期的运动控制算法只是在需要转弯的关键点进行机械的转向.通过引入样条曲线,可以获得较好的运动路线.然而,在不同的物体依照同一路线进行运动时,运动路线是相似的,没有考虑到物体间的差异.设计的算法在原有通过样条曲线插值计算运动路线的基础上,将物体的重量、形状特征以及当前的运动速度加入到路线计算的影响因素中,可以根据物体相关运动属性实时生成运动路线.     

一种基于运动估计的MPEG-4对象分割算法

针对传统的视频分割算法因偏重于分割效果而导致计算量过大、实时性能差的缺点,文章提出一种在MPEG-4编码过程中通过双重筛选和利用运动估计结果提取运动对象的算法。此算法首先在运动估计过程中加入背景优先准则进行第一重筛选;然后根据运动估计后宏块的最小平均绝对差值分利用区域自适应门限进行第二重筛选,从而获得运动区域掩模;最后对掩模进行形态滤波和填充消除噪声点,最终得到运动区域。算法分别在硬件和软件平台上进行测试,结果表明,该算法不仅取得了理想的分割效果,还大幅度缩减了计算量,明显提高了实时性。     

基于运动控制器的开放式数控系统运动控制模块的构建

在给出了利用固高GT-400-SV运动控制器构建的“PC＋运动控制器”型开放式数控系统硬件平台和系统软件主要功能模块的基础上，重点阐述了系统软件中运动控制模块的构建方法和过程．     

两栖作战武器横摇动力学分析

横摇动力学是两栖作战武器的一个重要研究内容,横摇是两栖作战武器在通过内陆江河水系和抢滩登陆作战中存在的重要问题,它直接影响着乘员和装备的战斗力发挥.依据船舶的有关理论,对两栖作战武器的水上横摇运动动力学进行了分析研究.首先对两栖作战武器进行了受力分析并给出了横摇动力学方程,研究了两栖作战武器横摇无因次幅频特性和相频特性与横摇调谐系数和无因次阻尼衰减系数之间的关系,可供两栖作战武器设计参考借鉴.     

基于正弦调相的ISAR干扰方法

为了实现对ISAR干扰,本文从目标一维距离像及ISAR运动补偿的角度,提出了基于正弦调相的ISAR干扰方法。文中对干扰信号如何影响距离像、影响运动补偿进行了详细的理论分析,给出了干扰造成ISAR图像失真的理论依据。并进行了基于实测数据的仿真实验。结果表明,基于正弦调相的ISAR干扰方法可以较好地干扰ISAR的一维距离像和最终的二维像,并具有压制干扰和类似欺骗干扰的双重效果,是一种对付ISAR的有效干扰手段。     

Linear systems with fractional Brownian motion and Gaussian noise

Methods are presented for calculating the evolution in time of the second moment properties of the output of linear systems subjected to fractional Brownian motion and fractional Gaussian noise, defined as the formal derivative of fractional Brownian motion. The study also examines whether the output of linear systems to fractional Brownian motion and fractional Gaussian noise exhibits long range dependence. Numerical examples are presented to illustrate the calculation of output statistics for some linear systems with fractional Brownian motion and fractional Gaussian noise input, and show that output of linear systems to these input processes may not have long memory.