Corannulene Molecular Rotor with Flexible Perfluorobenzyl Blades: Synthesis,Structure and Properties

Two members of a new class of organic‐acceptor perfluorobenzyl corannulenes were prepared by gas‐phase and highly‐selective solution‐phase reactions at elevated temperatures. The peculiar single‐crystal X‐ray structure of C₅‐C₂₀H₅(CF₂C₆F₅)₅ revealed two high‐energy conformers with drastically different bowl depths and orientations of perfluorobenzyl blades; the conformers are alternating in columnar packing arrangements and every pair is sandwiched by toluene molecules.     

DYNAMIC BEHAVIOR OF THIN RECTANGULAR PLATE ATTACHED TO MOVING RIGID

A nonlinear dynamic model of a thin rectangular plate attached to a moving rigid was established by employing the general Hamilton's variational principle. Based on the new model, it is proved theoretically that both phenomena of dynamic stiffening and dynamic softening can occur in the plate when the rigid undergoes different large overall motions including overall translational and rotary motions. It was also proved that dynamic softening effect even can make the trivial equilibrium of the plate lose its stability through bifurcation. Assumed modes method was employed to validate the theoretical result and analyze the approximately critical bifurcation value and the post-buckling equilibria.     

运动柔性梁振动主动控制的有限段法分析

基于柔性梁的多刚性－弹簧系统模型，采用分段线性化的思想，由线性二次优化理论导出了有闭环反馈控制的以分段压电片为执行器的平面运动柔性杆梁结构非线性振动的主动控制的分析方法。两个算例验证了所提方法的有效性。     

碳纳米管纤维及其传感器力电性能实验研究

基于UTM T150微纳米力学测试系统搭建了纤维力电耦合测试平台,并对碳纳米管纤维进行了多组力电耦合作用下的拉伸性能实验研究。通过观察分析碳纳米管纤维的电阻-应变曲线,发现其电阻变化与应变大小密切相关,随着应变的不断变大,碳纳米管纤维的电阻也在逐渐增加。基于此,设计制作了碳纳米管纤维柔性应变传感器,并将其贴在标准试件上分别进行了弯曲变形测试、单次/循环加载性能测试以及标定实验。结果表明:当对试件进行加载时,碳纳米管纤维柔性应变传感器的电阻会随着载荷的增大而增大;当载荷逐渐消失时,其电阻会逐渐减小直至回归初始电阻值附近。这表明碳纳米管纤维具备优异的电学与力学特性,并且利用它所制作的柔性应变传感器也有着较好的灵敏度与稳定性。     

Experimental observations of a flexible slider crank mechanism at very high speeds

A slider crank mechanism has been constructed and operated for the purpose of investigating steady state rod bending vibration induced by a very high speed crank. Features include a combination flywheel and adjustable length crank, a thin aluminum connecting rod, and a piston sliding on steel rod slide axes. A strain gage on the rod and magnetic pickup on the crank sensed rod strain and crank speed, respectively.For this system configuration, experimental results are categorized as small, intermediate and large crank length response. Small and intermediate cranks response was amplified due to a large superharmonic component of twice the crank speed frequency and at crank speeds near 1/2 the first natural frequency of the rod. Beyond that speed, period doubling occurred over a range of speeds for intermediate length cranks. The occurrence of period doubling was experimentally sudden and audibly noticeable, and characterized by the onset of frequency components of 1/2, 3/2, 5/2, and 7/2 times the crank speed. For large crank sizes of 0.5, 1, and 2 inches an amplified response also appeared in each at a certain speed, but at speeds lower than in the small and intermediate crank cases. Larger cranks required more frequency components to describe the response than smaller cranks. Experimental responses were correlated with computer simulations of a one mode nonlinear ordinary differential equation model, and over a wide range of speeds and for a representative of a small, intermediate, and large crank length.     

柔性瓣架对生物心脏瓣膜应力的影响

采用非线性大变形超参数八结点板壳元，针对用猪主动脉瓣制成的人工心瓣所用的瓣架材料，形状，侧边高度等对其应力的影响进行数值模拟分析，其中瓣叶的几何形式保持不变。结果表明：弹性瓣架存在一个合适的弹性模量范围，能使瓣叶的最大应力降低较明显；对同一种瓣叶和具有相同弹性模量的瓣架而言、使瓣架立柱顶端产生位移最大的瓣架形状，往往亦是使瓣叶最大应力降低２的最明显的瓣架形状。     

柔性桥台合理加筋间距的力学模型试验

桥头跳车是公路工程中普遍且复杂的问题，加筋土结构的柔性桥台的应用，可能在根本上避免错台的出现和桥头跳车的产生。然而，其加筋间距的确定具有较大的盲目性。对土工织物加筋柔性桥台进行了4组大模型结构力学试验，对不同加筋间距下柔性桥台的工程特性进行了详尽的对比分析。试验结果表明，土工织物加筋柔性桥台的合理间距为30—50cm。     

An Internal Damping Model for the Absolute Nodal Coordinate Formulation

Introducing internal damping in multibody system simulations is important as real-life systems usually exhibit this type of energy dissipation mechanism. When using an inertial coordinate method such as the absolute nodal coordinate formulation, damping forces must be carefully formulated in order not to damp rigid body motion, as both this and deformation are described by the same set of absolute nodal coordinates. This paper presents an internal damping model based on linear viscoelasticity for the absolute nodal coordinate formulation. A practical procedure for estimating the parameters that govern the dissipation of energy is proposed. The absence of energy dissipation under rigid body motion is demonstrated both analytically and numerically. Geometric nonlinearity is accounted for as deformations and deformation rates are evaluated by using the Green–Lagrange strain–displacement relationship. In addition, the resulting damping forces are functions of some constant matrices that can be calculated in advance, thereby avoiding the integration over the element volume each time the damping force vector is evaluated.     

有限转动张量的保角参量及在多柔体系统中的应用

采用保角转动参数描述了多体系统中的大转动张量．该方法消除了传统的欧拉参数描述所必需的约束方程，并且适于大变形部件的建模需要．利用以上结果建立了含大变形梁状部件的多体系统的力学模型．     

刚弹耦合的机器人机构动力学方程及其解

本文给出了一般开链弹性机器人机构动力学方程。该方程是由关节广义坐标和杆件模态坐标联立的非线性微分方程组。对方程的刚性性质作了讨论,根据Rosenbrock的二级二阶半隐式Runge—Kutta公械,导出了一种求解弹性机器人机构动力学方程的算法。对一平面二杆操作手机构作了计算。对该例同时也用Gill方法作了计算,验证了上述算法的精度和效率。