Synthesis of a non-integer periodic function generator of a four-bar mechanism using a Haar wavelet

In this study, a synthesis method for a non-integer periodic function generator of a four-bar mechanism using a Haar wavelet is presented. Using wavelet theory, the mathematical model for the output of a four-bar mechanism is established. Next, the characteristics of the four-bar mechanism output variable are described by the wavelet feature parameters; the relationship of the wavelet feature parameters between the output and its translation or dilation is also investigated. Based on this finding, three numerical atlas databases comprising of 203,500 groups of basic dimensional types of planar four-bar mechanisms, 148,995 groups of basic dimensional types of spherical four-bar mechanism and 11,175 groups of basic dimensional types of planar slider–crank mechanism are compiled. According to the internal relationship between the wavelet feature parameters, the sizes of the objective mechanism can be obtained using fuzzy recognition. Based on a genetic algorithm, optimization of the link parameters can be realized. Three examples are presented to demonstrate the efficacy and practicality of the proposed theory.     

计算机辅助Watt型平面六连杆机构分支自动识别

针对Watt型平面六连杆机构解域分析问题,提出了基于欧拉公式和判别法的平面四环链和平面六环链的奇异点识别方法,并结合平面四环链和平面六环链的运动特征,对Watt型平面六连杆机构进行了分支自动识别研究。首先,基于提出的识别方法并结合MFC（microsoft foundation classes,微软基础类库）设计了计算机辅助识别软件,实现对Watt型平面六连杆机构的分支、构型位置以及奇异点坐标的自动识别。然后,基于识别结果分析Watt型平面六连杆机构的可行域,再根据Watt型平面六连杆机构的可行域生成机构的运动仿真视频,并通过仿真视频分析其运动学特性。最后,结合实例演示Watt型平面六连杆机构分支的自动识别过程。结果显示该计算机辅助识别软件能够对该机构分支进行自动判别。研究结果表明利用所提出的Watt型平面六连杆机构分支自动识别方法可简便快捷地实现对机构的可行域分析和运动学分析,具有较强的工程实用性。     

A PROCEDURE FOR THE OPTIMAL SYNTHESIS OF PLANAR MECHANISMS BASED ON NON-LINEAR POSITION PROBLEMS

The present paper describes a procedure for the optimal dimensional synthesis of mechanisms which is based on the solution of non-linear position problems. Planar mechanisms are modelled very easily by means of finite elements of bi-hinged rod type. The judicious choice of constraint conditions makes possible the solution of classical position problems: initial, finite-displacement, deformed and static-equilibrium problems, as well as the main types of dimensional synthesis: path generation, functions, rigid body guidance, mixed, and multiple. A single synthesis error function applies to all these types, and moreover is general since it is valid for mechanisms of any configuration. This function is based on the idea that the best mechanism for the given synthesis conditions is the one that least needs to be deformed when it is obliged to satisfy them exactly, to which end the elastic deformation of the elements is permitted. © 1997 by John Wiley & Sons, Ltd.     

某外能源转管机枪击发机构参数优化设计

运用多刚体动力学理论,利用动力学分析软件ADAMS对某转管机枪的击发机构进行参数化建模并进行优化,对多个重要的参数进行了敏感度分析,得到各参数最优设计值组合,为武器的改进设计起到指导作用。该方法对武器的其他机构的优化分析也具有一定参考价值。     

一种基于小波变换的心音激励源位置的检测

心音信号是心脏系统疾病诊断的一个重要的生理信号，本文在分析心音产生物理机制的基础之上，建立了准周期心音激励模型，并将时间局部定位性好，计算快速的小波变换方法引入到对心音信号的处理，能够很好地检测出瓣膜关闭这一突变信号发生的时刻，并将其作为心音信号的划分标准，这一方法还具有很好的抗噪性。     

包装送纸机构运动学及动力学仿真分析

目的 为了提高包装送纸装置的生产效率,使用一种六杆机构应用于包装送纸装置中,并对它进行运动学及动力学仿真分析,验证它在运动过程中是否满足实际工作要求。方法 使用矢量解析法和分离体法建立该六杆机构的运动学模型和动力学模型,并采用ADAMS仿真软件对该六杆机构进行运动学仿真和动力学仿真。结果 通过对六杆机构进行运动学仿真分析,得到了输出滑块4的位移、速度和加速度曲线,该机构在水平方向的行程为680.26 mm,满足实际工况要求。通过对六杆机构进行动力学仿真分析,得到了六杆机构各铰接点的受力大小和施加在曲柄1上的平衡力矩大小,该机构在送纸行程时,各铰接点受力和平衡力矩变化较小,该机构在送纸完成后的回返行程时,各铰接点受力和平衡力矩变化较大。结论 分析仿真结果后发现该六杆机构在运动过程中满足实际工作要求,能够较好地运用于包装送纸装置中。     

Stress analysis of a semi-infinite plate with a thin rigid body

Stress analysis of a semi-infinite plate with an oblique thin rigid body is carried out as a mixed boundary value problem. The complex variable method and a rational mapping function of a sum of fractional expressions are used. A closed solution is obtained for the shape, which is represented by a rational mapping function. Stress distribution, stress singularity at the tip of the thin rigid body, the resultant moment over the thin rigid body, and the rotation angle are investigated.     

旋转不变纹理特征用于两级图像检索

针对图像中常见的旋转问题提出一种旋转不变纹理特征进行两级图像检索的方法。粗检中,通过坐标变换把图像的旋转转换为行移,并提取近似行移不变的小波特征,结合粗比较算法对整个图像库进行粗检。然后对通过粗检的图像进行 Gabor 变换,提取旋转不变精检索特征,并使用Canberra 距离进行相似性度量。通过对旋转图像库的测试表明,该方法不仅加快了运算速度,且当参数选择适当时,在相同特征条件下,检索率比直接使用精检索方法检索时还提高了 1.625%。     

基于ADAMS的柴油机曲轴扭振仿真

以某V型8缸柴油机为研究对象,通过多体动力学方法对该曲轴进行扭振研究。首先在ADAMS中建立曲柄连杆机构的刚体模型;然后把曲轴作为柔性体,建立曲轴的有限元模型并对其进行模态计算;最后用曲轴的柔性体模型代替曲柄连杆机构的曲轴刚体模型,得到曲柄连杆机构的刚-柔混合体动力学仿真模型。对曲轴在正常工况下和单缸熄火时的扭振进行研究,得到曲轴在正常工况下和单缸熄火时的扭振特性。     

基于随机卷积特征和集成超限学习机的快速SAR目标识别

深度卷积神经网络在目标检测与识别等方面表现出了优异性能,但将其用于SAR目标识别时,较少的训练样本和深度模型的优化设计是必须解决的两个问题。本文设计了一种结合二维随机卷积特征和集成超限学习机的SAR目标识别算法。首先,随机生成具有不同宽度的二维卷积核,对输入图像进行卷积与池化操作,提取随机卷积特征向量。其次,为提高分类器的泛化能力,并降低训练时间,基于集成学习思想对提取的卷积特征进行随机采样,然后采用超限学习机训练基分类器。最后,通过投票表决法对基分类器的分类结果进行集成。采用MSTAR数据集进行了SAR目标识别实验,实验结果表明,由于采用的超限学习机具有快速训练能力,训练时间降低了数十倍,在无需进行数据增强的情况下,分类精度与采用数据增强和多层卷积神经网络的深度学习算法相当。提出的算法具有实现简单、需要调整参数少等优点,采用集成学习思想提高了分类器的泛化能力。

     

Rotating compressible flow between non torsionally oscillating disks

A viscous compressible gas between two disks is initially in a state of rigid rotation. The initial density distribution depends on the distance from the axis of rotation. A three dimensional flow is created relative to a rotating frame by imposing small amplitude non torsional oscillations on the disks. The solution is obtained using the Laplace transform. The structure of the boundary layers formed on the disks due to interaction of viscous force, Coriolis force and compressibility is analysed for various ranges of values of the forcing frequency. The theory reveals interesting features in comparison with the non oscillatory case or the case of an incompressible fluid.     

基础振动对离心机平均向心加速度的影响分析

根据基础振动的特征,从刚体运动学的角度,分别建立了基础随机振动和正弦振动对精密离心机平均向心加速度影响的数学模型,进行了理论分析和数值仿真,提出了减小基础振动影响的方法,即通过时间平均可减小随机振动和正弦振动的影响。平均时间延长有利于减小基础振动引入的误差。当平均时间为离心机旋转周期的整数倍时,可部分消除由离心机旋转引起的与转速同频的正弦振动的影响;由于相位差的影响,与离心机转速同频的正弦振动会引入一个系统误差项,该项误差不能通过平均的方式减小,相应的补偿方法还应进一步研究。     

基于响应面法的无芯模成形精度研究

目的 提高无芯模旋压零件的尺寸精度.方法 利用双旋轮旋压机床,采用响应面实验优化设计方法,对铝合金零件分别从旋轮进给速度、芯模转速、锥形件的成形角度、坯料与成形件最大开口直径比等方面进行研究,建立其与尺寸精度的预测模型,采用Design-Expert软件对尺寸精度进行回归系数及方差分析,并对此工艺参数进行优化,得到最优...     

An Iterative Image Registration Algorithm by Optimizing Similarity Measurement

A new registration algorithm based on Newton-Raphson iteration is proposed to align images with rigid body transformation. A set of transformation parameters consisting of translation in x and y and rotation angle around z is calculated by optimizing a specified similarity metric using the Newton-Raphson method. This algorithm has been tested by registering and correlating pairs of topography measurements of nominally identical NIST Standard Reference Material (SRM 2461) standard cartridge cases, and very good registration accuracy has been obtained.     

基于小波包分析的拉索损伤声发射信号特征提取

结合显式有限元和小波包分析技术开展了拉索损伤声发射信号特征提取的仿真分析。采用ANSYS/LS-DYNA模拟得到拉索损伤声发射信号的仿真信号,基于小波包能量谱对拉索声发射的有限元仿真信号进行了特征提取,从小波包分解层次、特征频带数量的选择及特征参数的噪声鲁棒性三个方面开展了讨论分析。结果表明:(1)通过选择适当的小波包分解层次,小波包能量谱可以精细地反映信号的特征;(2)选取少数特征频带就能使得小波包能量谱反映声发射信号的特征信息;(3)基于小波包能量谱的特征参数具有良好的损伤敏感性及噪声鲁棒性,能在强噪声影响下实现对拉索不同损伤类型的判别。     

高转速FSW工艺特征及焊缝组织性能演变规律研究

目的研究不同转速的焊缝性能变化对组织的影响,以期为高转速搅拌摩擦焊工艺参数的优化和更大范围的应用提供指导。方法在3000~8000 r/min的高转速范围内对3A21-O态铝合金进行搅拌摩擦焊试验,焊后分析了焊缝成形特征和晶粒形态并测试了接头截面显微硬度。结果当转速由1000~4000 r/min区间升高至5000~8000 r/min区间时,焊核宽度急剧增大了近50%。这是由于焊具产热机制以滑移摩擦为主向以粘着摩擦为主转变,导致上述焊核宽度增大的行为。随着转速的增大,焊缝温度呈现出常规搅拌摩擦焊工艺中鲜见的先增大而后趋于稳定的变化趋势;温度随转速的这一演变特征导致焊缝焊核区的亚结构数量比例以及显微硬度都随转速呈现出与此相近的演变规律。结论在高转速搅拌摩擦焊中,转速提高能提高焊缝性能,且增强的焊缝性能能够在较宽的高转速区间内保持相对稳定的状态。     

基于鱼雷导引弹道的目标回声特性研究

将板块元方法应用到鱼雷导引弹道计算中,对运动目标的回声特性进行了研究。用刚性球Rayleigh简正级数解检验了板块元方法对运动目标回声特性的计算,在此基础上把板块元方法应用到鱼雷尾追法、固定提前角法、平行接近法三种导引弹道下复杂Benchmark模型目标回声特性的研究。此方法为研究水下运动目标回声特性提供了重要的理论依据。     

A new Leapfrog scheme for rotational motion in 3D

Discrete element codes use complex geometric solid particles, so it is necessary to integrate three‐dimensional rigid‐body rotation correctly with external torque. This article presents an interpretation of the Leapfrog scheme. We begin with some rotation formulae before presenting an efficient and high‐order recurrent Taylor series method for rotation. Integrating this method with Leapfrog interpretation provides a complete scheme for rotational motion with external torque. This new Leapfrog scheme has been integrated into the CeaMka3D Discrete Element code, and we present some verifications and simulations to illustrate the capabilities of this scheme. Copyright © 2016 John Wiley & Sons, Ltd.     

用1(1/2)维谱结合小波包能量提取地震动信号特征

针对车辆（轮式车、履带式车）引起的地震动信号中,具有非平稳、非高斯性特征相互重叠的实际情况,研究了地面活动目标产生的地震动信号特性;从理论上说明了1(1/2)维谱可消除车辆引起的地震动信号中的高斯白噪声或有色噪声,在将[112]维谱分析和小波包能量谱相结合的基础上,提出一种特征提取方法,以便区分不同的车辆目标。在时频域构建以[112]维谱和小波包能量谱作为地震动信号的联合特征向量,建立以训练误差为目标的BP神经网络模式分类器;然后对两类车辆信号进行识别。地震动信号的车辆实测数据表明,该方法能够准确和有效地识别车辆引起的地震动信号。     

Dynamics of spatial beams in quaternion description based on the Newmark integration scheme

The rotational quaternions represent a unique four dimensional parametrization of rotations in the three dimensional Euclidean space. In the present paper they are used as the basic rotational parameters in formulating the finite-element approach of geometrically exact beam-like structures. The classical concept of parameterizing the rotation matrix by the rotational vector is completely abandoned so that the only rotational parameters are the rotational quaternions representing both rotations and rotational strains in the beam. The space discretization based on the collocation method is used and the adjustment of the Newmark time-integration algorithm to the quaternion parameterizations of rotation is presented.