大射电天文望远镜悬索馈源系统驱动力的研究

针对大射电天文望远镜馈源系统中悬索呈现出的柔性特征，在已知馈源舱的位置，姿态，速度和加速度的情况下，将悬索离散为柔性索杆单元，建立了系统的逆运动学及逆动力学模型。分析计算了悬索上各离散点的位置、速度、加速度和惯性力，推导了在重力和惯性力共同作用下悬索的空间挠曲线方程，研究了悬索的刚体位移和弹性变形。在此基础上，通过刚体-柔性的迭代计算，求出悬索馈源系统的驱动力，为高精度的大射电天文望远镜提供了必要的设计参数。     

载重子午线轮胎帘线受力的有限元分析

以10.00R20轮胎为原型,针对特定的断面轮廓形状和帘线结构形式建立了轮胎结构计算的有限元模型,着重研究了额定充气压力状态以及受静负荷作用时各部分帘线受力的基本特征。结果表明:(1)充气状态下胎冠部和胎圈部的帘线结构参数之间的相互影响很小,因而在分析设计中可以相对独立地考虑;(2)静负荷作用下帘线受力在接地面附近的分布情况较复杂,尤其是负荷较大时可能出现胎冠中部帘线张力不足甚至受压以及0°带束层边缘受拉力过大的情况,这些对轮胎使用性能不利的受力状况可以通过帘线结构的合理设计来克服。     

筒形件液压拉深过程最优压边力的研究

结合筒形件液压拉深新装置的基本工作原理，提出了筒形件拉深法兰部分切向应变更为精确的简化计算公式，进一步获得了该法兰区域板料径向及切向应力的新的数学表达式。应用能量法重新建立了筒形件拉深时法兰区板料不起皱的最小压边力的数学表达式。明确指出液压拉深时拉深中的危险断面在板料凹模圆角区和筒壁区相交处，建立了相应的拉深力的计算公式，并获得了拉深破裂临界状态时极限拉深力及径向应力表达式。推导出了拉深破裂最大压边力的公式．指出实际拉深时最佳压边力应在防皱最小压边力和拉破最大压边力之间选取，同时根据该结果也能计算液体压力与最小拉深系数的关系。计算结果表明，该液压拉深方法可大幅度提高拉深变形程度，值得在工业实际中推广应用。     

考虑面力密度的力法找形和预应力精确确定

随着膜结构应用领域的拓宽,实践对膜结构形状的构造提出了各种不同的要求。考虑膜单元的面力密度的力法找形方法,通过调整面力密度能够获得不同形状的曲面。对索膜结构找力分析的优化复位平衡法,能够对给定的拓扑曲面求解获得精确的自平衡预应力分布。把面力密度的力法找形和优化的复位平衡法的找力分析结合起来,能够完成形状构造的全过程,丰富了索膜结构的形状构造理论。     

空间刚架结构的广义逆力法

在结构计算中，根据算法中所采用的基本未知量的不同．结构分析方法可以分为力法、位移法和混合法。其中位移法由于适宜计算机处理而在结构计算领域得到了广泛的应用．经典力法相比之下应用就远不如位移法普遍，虽然力法本身在力学上有其独特的优势。广义逆矩阵做为一种较新的数学工具，自二十世纪五十年代诞生以来正日益表现出越来越旺盛的生命力。广义逆力法就是一种基于力法和广义逆矩阵理论的新的迭代算法。这种算法是一种完全适合计算机处理的力法方法。该算法的思路以及对于求解线弹性空间刚架结构问题的具体公式均在文中给出并给出了算例。从算例计算结果可以看到广义逆力法有着较好的计算效率和计算精度。该算法的提出为力法在计算机计算领域的应用开拓了新的发展空间。该算法在材料非线性问题和结构并行计算方面也有着较好的应用前景。     

Using Vorticity as an Indicator for the Generation of Optimal Coarse Grid Distribution

An improved vorticity-based gridding technique is presented and applied to create optimal non-uniform Cartesian coarse grid for numerical simulation of two-phase flow. The optimal coarse grid distribution (OCGD) is obtained in a manner to capture variations in both permeability and fluid velocity of the fine grid using a single physical quantity called “vorticity”. Only single-phase flow simulation on the fine grid is required to extract the vorticity. Based on the fine-scale vorticity information, several coarse grid models are generated for a given fine grid model. Then the vorticity map preservation error is used to predict how well each coarse grid model reproduces the fine-scale simulation results. The coarse grid model which best preserves the fine-scale vorticity, i.e. has the minimum vorticity map preservation error is recognized as an OCGD. The performance of vorticity-based optimal coarse grid is evaluated for two highly heterogeneous 2D formations. It is also shown that two-phase flow parameters such as mobility ratio have only minor impact on the performance of the predicted OCGD.     

Motion Planning for a Mobile Robot with Two Steerable Wheels

A nonholonomic model of a wheeled robot with two steerable wheels is considered. The model accounts for dynamic effects. The motion-planning problem for this model is solved by reducing it to a linear two-point boundary-value problem__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 5, pp. 107–115, May 2005.     

斜拉桥桥索张力测量

本文主要介绍了斜拉桥桥索张力的测量原理，指出了目前人们常用的直接频差法的不足之处，提出了一种确定斜拉桥桥索基频的新方法．后一种方法无论从理论还是从测量上都优于前一种．实测结果证明了这一点．     

重型车辆撞击桥墩的碰撞力峰值参数分析

车辆撞击桥墩的碰撞力受很多因素影响,现行桥梁规范中仅以恒定的静力进行设计,不能正确反映碰撞过程的动力效应以及桥墩与车辆的耦合作用影响,难以满足现代交通和基础设施高速发展的需求．为了考察桥梁结构参数对碰撞力峰值的影响及不同参数间相对重要性,在有限元软件LS-DYNA平台上,建立了车桥碰撞精细化数值模型,对桥梁下部结构遭受重型车辆碰撞过程进行数值仿真,分析了桥墩高度、混凝土抗压强度等级、箍筋间距、纵筋和箍筋的屈服强度、纵筋和箍筋配率等结构参数对碰撞力峰值的影响规律．     

Generalized Mathematical Model of an Inverted Multilink Pendulum with Follower Force

A problem formulation and differential equations are given to describe the plane-parallel motion of an inverted multilink pendulum with an asymmetric follower force acting at the elastically restrained upper end. The physical nonlinearities of the springs are taken into account. The possible mechanisms of energy dissipation are described__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 5, pp. 124–130, May 2005.     

微加工中原子力显微镜金刚石针尖的磨损研究

考察了用原子力显微镜对单晶硅进行微加工时金刚石针尖的磨损行为 ,对针尖的磨损率、磨损机理以及针尖磨损对微加工过程的影响进行了实验研究和理论分析 .结合对单晶硅所进行的摩擦磨损试验 ,应用计算模型得出针尖的磨损率为 1.7× 10 - 1 0 m m3/(N·m) ;通过对针尖磨损特征的原子力显微镜观察 ,结合金刚石针尖上应力集中的有限元计算及单位切削力计算 ,推测其磨损机制主要为化学磨损     

Complex Dynamics of a Pyranose Ring Structure Molecule Attached to an Atomic Force Microscope

Dynamic numerical simulations were performed for a pyranose ring structure molecule attached to an Atomic Force Microscope (AFM) using a standard semiempirical potential energy surface model. The fundamental static force-extension behavior was first determined using a slow pulling base excitation at the AFM probe. The static force-extension curve displays a stiffness nonlinearity, both softening and hardening, that depends upon level of the pulling force. For the dynamic analysis, a single harmonic base excitation is applied to the AFM probe. A typical evolution process from periodic to aperiodic or chaotic motion obtained by varying the excitation frequency and amplitude is discussed. A strong chaotic response motion was generated for certain system parameters. The numerical analysis shows this chaotic response arises from a molecular structure conformational change.     

Divergent Bifurcations of a Double Pendulum under the Action of an Asymmetric Follower Force

The paper studies the influence of the orientation parameter of the follower force on the behavior of the pendulum with a simple zero eigenvalue in the linearization matrix     

桁架结构几何非线性问题的力密度法

桁架结构大都具有较强的几何非线;浊,受荷载后易出现较大的脯变形。提出一种基于力密度的针对桁架结构几何大变形问题的解法;引入杆件单元的力密度矩阵,推导出相应非线性方程的Jacobi矩阵;与有限单元法集成求解的思想相同,采用力密度矩阵建立结构变形后整体的精确非线性平衡方程。研究结果表明：应用Newton-Raphson迭代法求解,采用适当的迭代收敛精度可得到较精确的桁架结构位移解。     

适用于永磁悬浮轨道及永磁轴承的解析磁力模型研究

基于由磁荷法和虚位移法给出的永磁体磁力数值积分公式,结合两块平行矩形截面永磁体的结构特点,推导出适用于永磁悬浮导轨及永磁轴承的解析磁力模型,并对双筒嵌套永磁轴承及轴向放置双环永磁轴承的轴向磁力计算结果进行实验验证.结果表明:两块平行矩形截面永磁体的磁力分别与永磁体剩磁的平方和永磁体纵向平均长度成正比,磁力随永磁体的截面增加而增大,随永磁体的间距增加而减小;模型计算值与实测值吻合.该模型计算简单,通过代数运算可以得到具有较高精度的磁力计算结果.     

漂浮基双臂空间机器人姿态与末端抓手惯性空间轨迹协调运动的模糊滑模控制

本文讨论了载体姿态受控、位置不受控制的双臂空间机器人系统的控制问题.利用拉格朗日方法并结合系统动量守恒关系,建立了双臂空间机器人系统的非线性系统动力学模型.以此为基础,考虑到空间机器人系统结构的复杂性及其某些参数的变动性,根据具有较强鲁棒性的变结构控制理论,设计了双臂空间机器人载体姿态与两机械臂末端抓手惯性空间轨迹协调运动的滑模变结构控制方案.为了克服滑模变结构控制器抖振的缺点,附加设计了一个模糊控制器,以便根据系统的输出来动态调节滑模变结构控制器等速趋近率的系数,从而既确保了系统的快速响应而又消除了原有的抖振.系统数值仿真,证明了上述控制方案良好的控制效果.     

冲压板材拉伸筋阻力的一种有效数值计算方法

将弹塑性有限变形的拟流动角点本构理论和厚向各向异性屈服函数引入弹塑性动力显式有限元列式,对板材通过拉伸筋的变形过程及拉伸筋阻力进行了数值模拟,并与有关实验结果进行了比较很好的一致性,表明了该计算方法的有效性。进而,数值研究了拉伸筋形状、界面摩擦状况以及材料的厚向各向异性对拉伸筋阻力的影响,为实际覆盖件冲压成形中拉伸筋的设置提供了重要的定量依据。     

Three-Dimensional Stress State of an Orthotropic Rectangular Prism under a Transverse Force Applied at its End

The exact three-dimensional elastic solution is found for an orthotropic composite rectangular prism (plate) bent by a transverse force applied to its end. The three-dimensional distribution of stresses and displacements is obtained. The distribution of tangential stresses in the prism and plate is analyzed numerically. New qualitative features of the distribution are established. The strength of the plate is estimated, and the transverse force and torque are determined. The Kirchhoff-Love relations of plate bending are partially justified__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 4, pp. 30–37, April 2005.     

Optimal multi-block mesh generation for CFD

An assessment of various automatic block topology generation techniques for creating structured meshes has been performed in the first part of the paper. The objective is to find out optimal blocking methods for generating meshes suitable for flow simulations. The comparison has been carried out using an adjoint-based error analysis of the meshes generated by these block topologies. Different objective functions and numerical schemes have been used for this assessment. It is found that, in general, the medial axis-based approaches provide optimal blocking and yields better accuracy in computing the functional of interest. This is because the medial axis-based methods produce meshes which have better flow alignment specially in case of internal flows. In the second part of the paper, the adjoint-based error indicator has been used to adapt the block topology in the regions of large error.     

杆件去除与内力变更时空间网架结构的简捷计算法

本文采用矩阵位移法,引入初内力的概念,提出并建立了初内力准方程式,再运用性叠加原理来简化分析计算杆件去除与内力变更时的空间时的空间网架结构。这种简捷计算法的所讨论的工况下只要一次性的建立、分解和应用网架结构的总刚度矩阵,无须重复多次建立和分解总刚度矩阵,从而使会计工作量成倍地甚至几十倍地大幅度减少。特别是当网架结构多根杆、依次先后断杆、预应力及分期分批施加预应力时,采用本文方法可更方便地求得各工况