IN-PLANE WAVE MOTION IN FINITE ELEMENT MODEL

The analysis method of lattice dynamics in classical physics is extended to study the properties of in-plane wave motion in the hybrid-mass finite element model in this paper. The dispersion equations of P and SV waves in the discrete model are first obtained by means of separating the characteristic equation of the motion equation, and then used to analyse the properties of P-and SV-homogeneous, inhomogeneous waves and other types of motion in the model. The dispersion characters, cut-off frequencies of P and SV waves, the polarization drift and appendent anisotropic property of wave motion caused by the discretization are finally discussed.

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅱ): with saturated poroelastic soil layers

As the continuation study on amplification of in-plane seismic ground motion by underground group cavities in layered half-space, this study extends to the case of poroelastic half-space with dry poroelastic and saturated poroelastic soil layers. The influence of poroelastic layers on the amplification of seismic ground motion is studied both in frequency domain and time domain using indirect boundary element method （IBEM）. It is shown that for the example of a saturated poroelastic site in Tianjin under the excitation of Taft wave and E1 Centro wave, the amplification of seismic ground motion in poroelastic case is slightly smaller than that in the elastic case, and the amplification of PGA （peak ground acceleration） and its PRS （peak response spectrum）.. can be increased up to 38.8% and 64.6%; the predominant period of response spectra in poroelastic case becomes shorter to some extent compared with that in the elastic case. It is suggested that the effect of underground group cavities in poroelastic half-space on design seismic ground motion should be considered.

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅰ)

Amplification of in-plane seismic ground motion by underground group cavities in layered half-space is studied both in frequency domain and time domain by using indirect boundary element method （IBEM）, and the effect of cavity interval and spectrum of incident waves on the amplification are studied by numerical examples. It is shown that there may be large interaction between cavities, and group cavities with certain intervals may have significant amplification to seismic ground motion. The amplification of PGA （peak ground acceleration） and its PRS （peak response spectrum） can be increased up to 45.2% and 84.4%, for an example site in Tianjin, under the excitation of Taft wave and E1 Centro wave; and group cavities may also affect the spectra of the seismic ground motion. It is suggested that the effect of underground group cavities on design seismic ground motion should be considered.

Surface motion of a semi-cylindrical hill for incident plane SV waves: Analytical solution

An analytical solution for surface motion of a semi-cylindrical hill for incident plane SV waves was derived by using the wave function expansion method and the auxiliary function technique, and convergence of the solution and accuracy of truncation were verified. The effect of incident frequency and angle as well as hill width on the surface motion of the hill was discussed by numerical examples. It was shown that, a hill greatly amplifies incident plane SV waves, and the maximal amplification may reach 4 times of that for free-field response; and for incident waves of low frequency, the maximal displacement amplitudes emerge mostly at the half-space, however, for incident waves of high frequency, the maximal displacement amplitudes appear mostly at the hill.

Surface motion of a semi-elliptical hill for incident plane SH waves

A closed-form analytical solution of surface motion of a semi-elliptical cylindrical hill for incident plane SH waves is presented. Although some previous analytical work had already dealt with hill topography of semi-circular and shallow circular, our work aims at calculating surface motion of very prolate hill for high incident frequency, and explaining the special vibrating is checked by boundary conditions, numerical results for and some conclusions are obtained. properties of very prolate hill. Accuracy of the solution surface motion of oblate and prolate hills are calculated,

The Motion of a Sphere with Weak Nutation on a Rough Horizontal Plane

For the motion of a sphere on a rough horizontal plane, in the previous paper[1]the author aimed at providing approximate analytical solutions while the nutation is neglected,In this paper ,the control equations for the sphere with nutation have beendeduced on the basis of paper [1]. Through the medium of solving these equations,the conclusion for the velocity of contact point in paper [1]is still proved true for the case with nutation.What is more ,some interesting results are gained ,for example the ve-locity of centre and contact point is relative to the angular velocity of spin and nuta-tion the direction of velocity of centre and contact point is constant.Under the condi-tion which is supposed to be weak nutation,the approximate analytical solutions are obtained,so that the results of paper [1]is proved to be true.

High-precision method of detecting motion straightness based on plane mirror interference

A high-precision method of detecting motion straightness was proposed based on the prin- ciple of plane mirror interference after analyzing the motion straightness error of a linear stage. De- tection experiments were carried out and the motion straightness errors were separated by the linear regression method. Finally, linear measurement uncertainty of the detection method was estimated. The results showed that this detection method was simple and accurate, and was especially suitable for precision detection of motion straightness error in the small travel movement of ultra-precision machining.

Ermakov System and Plane Curve Motions in Affine Geometries

It is shown that the Pinney equation, Ermakov systems, and their higher-order generalizations describeself-similar solutions of plane curve motions in centro-affine and affine geometries.

Group—Invariant Solutions in Plane Curve Motions

Group-invariant solutions to certain plane curve motions in Euclidean and centro-affine geometries areobtained. The behavior of some solutions is also presented.

AN UNCERTAINTY PRINCIPLE ON THE GROUP OF RIGID MOTIONS OF THE PLANE

Let M(2)be the group of rigid motions of the plane.The Fourier transform and the Piancherel formula on M(2)can be explicitly given by the general group representation theory.Using this fact.we establish a kind of uncertainty principle on M(2).The result can easily be generalized to higher dimensional cases.An application of the result yields an uncertainty principle on the Euclidean spaces obtained by R.S.Strichartz.

On the Kinematics for the Closed Planar Homothetic Inverse Motions in Complex Plane

In this paper, the Steiner area formula and the polar moment of inertia were expressed during one-parameter closed planar homothetic inverse motions in complex plane. The Steiner point was defined when the rotation number was different zero and it was called the Steiner normal when the rotation number was equal to zero. The fixed pole point was given with its components and its relation between Steiner point or Steiner normal was explained. The sagittal motion of a telescopic crane was considered as an example. This motion was described by a double hinge consisting of the fixed control panel of the telescopic crane and the moving arm of the telescopic crane. The theoretical concepts and results were applied for this motion.

一种基于位平面和位运动估计的视频数据压缩算法

高分辨率和高刷新率使得带宽传输的压力加倍。通常,视频压缩被用来解决这个问题。但传统的视频压缩方法不根据位平面进行编码和解码,会增加存储区域的成本。因此本文首先介绍了一种位恰可察觉失真(BJND)模型,计算了结合视点因子的位平面恰可察觉失真模型的阈值,并将亮度因子和纹理因子的恰可察觉失真(JND)阈值映射到位平面上,综合得出了位恰可察觉失真模型。然后提出了一种基于位运动估计算法的视频压缩方案。该方案使改进后的搜索范围不仅包括时间维度,还包括灰度维度。根据人眼的视觉特点和概率统计分析,方案新增了补充匹配块来替代残差数据,从而保证了压缩比的恒定性。实验结果表明,所提方案对低5位平面压缩具有最佳的综合效果,压缩比为1.38,数据传输量恒定,且恢复后的图像与原始图像并无明显差异,更加符合人眼的直观感受。

电磁涡旋波斜平面旋转目标运动参数估计方法

相较于传统平面电磁波,电磁涡旋波具有螺旋分布的波前相位、特殊的环形天线方向图、独特的涡旋方位维信息等特点。近几年来,得益于其特殊的物理特性,电磁涡旋波在目标运动参数估计领域受到了广泛的关注,其目标多普勒效应具有线性多普勒与旋转多普勒两维多普勒信息。现有参数估计方法实现了运动平面与涡旋天线口面平行时的目标旋转参数测量。然而,目标斜平面旋转下,现有方法将不再适用。基于电磁涡旋波所提供的目标旋转多普勒信息,提出一种斜平面旋转目标运动参数估计方法。该方法推导了一般形式下旋转目标的多普勒信号模型,通过分析斜平面下的多普勒信息特征,建立了目标运动参数表征式,给出了斜平面目标旋转参数的计算方法。最后通过仿真分析,验证了模型及参数计算方法的正确性及有效性。

热效应作用下S波入射弹性地基自由场地地震响应研究

基于热弹性介质中波的传播理论,建立了平面S波入射下弹性地基自由场地模型,采用亥姆霍兹矢量分解原理,对热效应作用下弹性地基自由场地中的波场进行分析,获得了热效应作用下平面S波入射弹性地基自由场地地震地面运动的解析解答。通过数值计算,分析了热传导系数、介质温度、热膨胀系数等热物性参数对弹性地基自由场地地震地面运动所产生的影响规律。研究结果表明:考虑热效应和不考虑热效应的两种理论模型下所得到的水平和竖向位移放大系数有着明显差异;地表水平和竖向位移放大系数以及相应的加速度随着热膨胀系数和介质温度的增大而增大;热传导系数和热通量相位延迟对地表位移放大系数和加速度的影响较小;随着入射波频率的增大,地表位移放大系数和加速度均逐渐增大。

Movement Function Assessment Based on Human Pose Estimation from Multi-View

Human pose estimation is a basic and critical task in the field of computer vision that involves determining the position(or spatial coordinates)of the joints of the human body in a given image or video.It is widely used in motion analysis,medical evaluation,and behavior monitoring.In this paper,the authors propose a method for multi-view human pose estimation.Two image sensors were placed orthogonally with respect to each other to capture the pose of the subject as they moved,and this yielded accurate and comprehensive results of three-dimensional(3D)motion reconstruction that helped capture their multi-directional poses.Following this,we propose a method based on 3D pose estimation to assess the similarity of the features of motion of patients with motor dysfunction by comparing differences between their range of motion and that of normal subjects.We converted these differences into Fugl–Meyer assessment(FMA)scores in order to quantify them.Finally,we implemented the proposed method in the Unity framework,and built a Virtual Reality platform that provides users with human–computer interaction to make the task more enjoyable for them and ensure their active participation in the assessment process.The goal is to provide a suitable means of assessing movement disorders without requiring the immediate supervision of a physician.

P波入射下饱和冻土自由场地地震地面运动分析

地震波的放大或衰减受场地条件的影响,因而选择符合实际情况的场地模型来分析地震地面运动极为重要。为了研究西部高寒地区冻土场地的地震地面运动特征,基于弹性波在单相弹性介质与冻结饱和多孔介质中的传播理论,建立了P波入射下基岩上覆饱和冻土自由场地模型,求得了平面P波入射情况下基岩上覆饱和冻土自由场地地震地面运动的解析解答。通过数值计算,分析了平面P波在不同入射角度下,入射频率、孔隙率、介质温度、胶结参数和接触参数等物理力学参数对饱和冻土自由场地地震地面运动的影响规律。分析结果表明:平面P波的入射频率对基岩上覆饱和冻土自由场地地表位移有显著影响。基岩上覆饱和冻土自由场地的水平位移随着平面P波入射频率增大而减小,竖向位移随入射频率增大而增大;孔隙率的增大也会导致饱和冻土自由场地水平位移增大,但其增幅随着平面P波入射角度的增加先增大后减小,竖向位移也增大,但增幅随入射角度增加逐渐减小;冻土场地中介质温度的降低会导致饱和冻土自由场地的水平位移和竖向位移减小。这表明冰相对于冻土场地中地震波传播具有重要影响;此外,泊松比也会对自由场地的位移产生一定影响,水平位移随泊松比增大而减小,增幅随平面P波入射角度增加先增大后减小。随着泊松比增大,饱和冻土自由场地的竖向位移显著增大,增幅随平面P波入射角度增加逐渐减小;接触参数的增加会导致自由场地的水平位移增大,增幅先增大后逐渐减小。同时,地表竖向位移也会增大,但增幅逐渐减小。

刚体平面运动中坐标轴正方向的选取

平面运动作为刚体的一种重要运动类型,成为物理学专业力学和理论力学课程中的重点教学内容.平面运动因为同时涉及平动和定轴转动且二者之间常常存在一定的约束关系,所以也是一个教学难点,主要问题在于初学者往往因为随意规定坐标轴正方向而遗漏约束关系中可能出现的负号.根据受力分析,在假定了刚体平面运动趋势后,适当选取坐标轴的正方向可以避开约束方程中的负号,从而使学生分析刚体运动问题更加快速准确.

专家控制-改进S面算法在近水面航行器运动控制中的应用研究

[目的]旨在提高舵板响应速度和效率,以满足近水面航行器在静水及波浪干扰下的深度保持和姿态控制要求。[方法]在S面算法的基础上,提出一种具有更快收敛速度的改进S面控制算法,并与专家智能控制相结合,建立闭环专家控制-改进S面算法的混合控制模型,构建混合算法控制器。对比分析PID算法、S面算法、改进S面算法以及专家控制-改进S面算法在近水面航行器航行深度、姿态控制间的差异,并进行波浪干扰下的运动预报。[结果]预报结果表明:改进S面算法在静水航行控制中可提高收敛速度,波浪干扰下可降低纵摇幅度;专家控制-改进S面算法能够提高舵的控制效率,在静水中快速实现航行状态稳定转换,在波浪中有效降低近水面航行器垂荡和纵摇幅值30%以上。[结论]所提专家控制-改进S面算法对近水面航行器运动稳定性的提高适用性良好。

A series solution for surface motion amplification due to underground twin tunnels:incident SV waves

A series solution of displacement response of the ground surface in the presence of underground twin tunnels subjected to excitation of incident plane SV waves is derived by using Fourier-Bessel series expansion method.The numerical parametric study shows that underground twin tunnels significantly amplify the nearby surface ground motion.It is suggested that the effect of subways on ground motion should be considered when the subways are planned and designed.

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.