Theoretical study of stereodynamics for the O（3P） ＋ H2 → OH ＋ H reaction

This paper employs the quasi-classical trajectory calculations to study the influence of collision energy on the title reaction on the potential energy surface of the ground ³A' triplet state developed by Rogers et al. (J. Phys. Chem. A 2000 104 2308). It calculates the product angular distribution of P(θ_r), P(φ_r) and P(θ_r, φ_r) which reflects vector correlation. The distribution P(θ_r) shows that product rotational angular momentum vectors j' of the products are strongly aligned along the relative velocity direction k. The distribution of P(φ_r) implies a preference for left-handed product rotation in planes parallel to the scattering plane. Four different polarisation-dependent cross-sections are also presented in the centre-of-mass frame. Results indicate that OH is sensitively affected by collision energies of H₂.     

Track dynamic behavior at rail welds at high speed

As a vehicle passing through a track with different weld irregularities, the dynamic performance of track com- ponents is investigated in detail by using a coupled vehi- cle-track model. In the model, the vehicle is modeled as a multi-body system with 35 degrees of freedom, and a Timoshenko beam is used to model the rails which are dis- cretely supported by sleepers. In the track model, the sleepers are modeled as rigid bodies accounting for their vertical, lat- eral and rolling motions and assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the study of the coupled vehicle and track dynamics, the Hertizian contact theory and the theory proposed by Shen-Hedrick-Elkins are, respectively, used to calculate normal and creep forces between the wheel and the rails. In the calculation of the normal forces, the coefficient of the normal contact stiffness is determined by transient contact condition of the wheel and rail surface. In the calcu- lation of the creepages, the lateral, roll-over motions of the rail and the fact that the relative velocity between the wheel and rail in their common normal direction is equal to zero are simultaneously taken into account. The motion equations of the vehicle and track are solved by means of an explicit integration method, in which the rail weld irregularities are modeled as local track vertical deviations described by some ideal cosine functions. The effects of the train speed, the axle load, the wavelength and depth of the irregularities, and the weld center position in a sleeper span on the wheel-rail impact loading are analyzed. The numerical results obtained are greatly useful in the tolerance design of welded rail pro- file irregularity caused by hand-grinding after rail welding and track maintenances.     

一个不容忽视的教学问题——巧用柯尼希定理求解两体碰撞

从柯尼希定理出发,给出了两体碰撞前后的机械能关系,并以两个具体习题为例,说明了利用柯尼希定理求解两体碰撞问题的方法,要比用动量守恒结合能量守恒的方法更为简洁、可行.揭示了加强柯尼希定理的习题教学对培养学生一题多解的发散思维能力的重要性.     

恰当选择参考系解决运动学问题

在解决一些运动学的习题时，我们常常习惯以地面为参考系，然而这样选择参考系在处理多个相对运动物体的有关问题时，往往很繁琐，如果恰当地选择参考系来分析问题，常常能使复杂的问题简单化．     

关于弹性碰撞中的相对速度

1　问题的提出弹性碰撞是中等物理中重要内容之一 ,虽然教材中已经明确指出 :两个物体在弹性碰撞中动能与动量都守恒 ,但还是有很多学生在遇到这类问题时表现得束手无策 ,主要是学生还没有对弹性碰撞问题有更深一层的认识 ,有的同学也能列出动能守恒与动量守恒的方程组 ,但由于繁琐的求解不但耗费了大量时间 ,还容易出现求解的错误 .现在我们就对弹性碰撞的相对速度问题进行讨论 ,发现有关速度的规律 ,简化解题过程 .设两质量分别为ｍ1 、ｍ2 的物体分别以ｖ1 、ｖ2的速度向右运动 ,发生弹性正碰后速度分别变为ｖ′1 、ｖ′2 ,碰撞前后的两…     

点的复合运动中任意相切型问题速度分析的一种特殊解法

对于相切型问题,实际作定轴转动刚体外形可能为任意封闭曲线,传统利用圆心到接触点距离保持不变特性选择动点的方法无法求解。针对这类问题,在教学中采用瞬时运动学分析方法,即找一特殊动点。该瞬时相对速度为零,从而得到所需要求解的运动学量,方法简单且直观。本文首先证明该特殊动点的存在性和唯一性,然后给出特殊动点的确定方法,最后给出3个求解实例。该方法在本校理论力学教学中得以实践,学生反映容易掌握和理解。     

处理相对运动的一种简洁方法

相对运动是运动学中的重要内容,其中的绝对速度、相对速度和牵连速度都是十分重要的概念,这些概念既是解决有关问题的基础,也是教学中的重点和难点.笔者在教学中根据相对运动的特点,利用一种简洁的处理方法——下标标注法,成功地化解了这一难点.此方法通过多次教学检验,均收到了事半功倍的效果.     

杆条类杀伤元素终点毁伤威力

动能杆反导战斗部作为新型的反导战斗部，在国外得到了广泛关注，动能杆战斗部的反导威力评估研究中，大长径比杆条杀伤元素的终点毁伤能力分析是关键内容之一。相对于传统破片及长杆穿甲弹的穿甲过程，动能杆反导的终点毁伤杀伤元素质量大（一般为几十至几百克）、长径比大（高达10以上）、散布密度高（每平方米可高达几十枚杀伤元素）、着靶速度高（弹目相对速度高达3-4km/s）、着靶姿态复杂（存在较大的着角及攻角）及存在多层靶毁伤等特点，建立准确的动能杆类杀伤元素的终点毁伤威力评估模型，对于实现战斗部反导威力的高精度评估有着重要的意义。     

相向运动二粒子的相对速度

给出了相向运动二粒子的相对速度的7种解法．