巧解铅球最佳出手角

利用运动叠加原理通过对铅球运动的恰当分解, 提出了一种计算最佳出 手角的新方法, 并与传统方法就两种不同情形进行了对比, 说明了新方法的物理思想.     

差压式流量计示值修正公式问题出在哪里

讨论``国家标准GB/T18215.1-2000附录B'规范的差压式流量计示值修正公式适用性, 其中 仅有检测出干气体工作状态体积流量示值修正到设计状态这一条常用的公式基本可用, 其余: 干气体质量流量、干气体标准状态体积流量、湿气体干部分体积流量以及气体组份改变时体积流量与质量流量, 示值修正方向都是相反的, 越修正则示值误差越大.然后分析了问题产生的原因,提出了解决办法.     

Nanson公式证明的诠注及一个新证明

针对现行文献对Nanson公式证明的3种不同方法, 文章分别从数学演绎与力学概念明晰化的角度对3种证明的演绎过程及其特色进行了分析, 指出了相应的优劣之处以及各自需要改进的地方. 在此基础上, 文章给出了一个改进的易于理解的证明. 文章还提出了力学问题的演绎与证明应该充分反映力学规律的论点.     

《科学游戏的智慧与启示》序言

目前,从国家、学校到每一个家庭,都非常重视对下一代的教育. 的确,教育好下一代,是关乎我们国家未来和民族兴旺的大事. 教育,不能只是把已有的知识,整理好,按照一定的顺序灌输给孩子们. 如果按照这种模式,学生们有时会把学习知识当作沉重的负担,久而久之还会产生逆反心理,导致厌学、逃学的副作用. 可见,教育最重要的事情是要引起学生们对所学内容的兴趣,让他们主动地去获取知识. 孔子说：``知之者不如好之者,好之者不如乐之者. '爱因斯坦说：``在学校里和生活中,工作最重要的动机是工作中的乐趣,工作所得到的成果的乐趣,以及对该成果的社会价值的认识. 在年轻人的这些心理力量的觉醒和强化之中,我看到了学校被赋予的最重要的任务. 只有这样的心理基础才能导致一种快乐的愿望,去追求人类最高财富,即知识和艺术家般的技艺. '     

刚架桁架模型有效性的试验与数值研究

为了比较桁架模型和刚架模型的差异, 结合了一种简单试验结构,实测了试验刚架和桁架的特定截面的内力和中节点位移; 同时应用ANSYS软件对两种模型进行了有限单元模拟. 验证了刚架和桁架两种力学模型的有效性, 通过试验和数值计算的结果, 得到了两种结构的受力特点, 分析了实际桁架和理想桁架的差别, 对结构设计和教学具有一定的参考意义.     

永远的榜样与难忘的记忆——————纪念陆士嘉先生

一．创建中国的空气动力学专业 我在1954年考入北京航空学院飞机系的飞机设计专业,入学教育既简单又庄重,给我留下深刻的印象。教务长屠守锷先生介绍了全系的教学配置,教师情况和高班同学的情况以及上届同学的学习难点等等,屠先生提到当时飞机系只有一位女教授,她曾留学德国并取得优异成绩,她由清华大学航空系并入北航飞机系,是北航建校的元老之一。这是我第一次听到有关陆士嘉先生的介绍,因为我是女学生,所以对系里唯一的女教授格外关注,那天陆先生并不在场,我第一次看见陆先生是她在系楼的走廊里神态和蔼地与其他老师讲话。后来我听到更多有关她的介绍,知道她是在国难之中留学德国,先攻物理学,后来立志转学航空专业,要为建设中国的航空事业献力。她想从师著名的流体力学大师普朗特教授,但普朗特教授之前既未招收过亚裔学生,也从未招收过女性学生,并已宣布不再招收新学生。陆先生请求普朗特教授出题考她,陆先生通过了普朗特教授严格的考试,被普朗特教授收为关门弟子,仅这一点就让我十分敬佩陆先生的学识和勇气。陆先生跟我们说过师出名门只是她人生的一个阶段,她从不细讲期间克服了多少困难,重要的是为了中国的航空工业,她立志学习流体力学专业。陆先生的毕业论文《圆柱射流遇垂直气流时的上卷》中发表的理论结果与别人完成的实验结果吻合很好,得到了普朗特教授的赞赏,她于1942年获得一等哲学博士学位。陆先生提到在德国时作为中国学生她没有机会进实验室工作,她最深刻的体会是我们必须走自己的道路 – 理论和实验相结合,没有实验会让理论缺乏说服力,并且难以付之应用。在航院建院之初就设立了空气动力学教研室,之后空气动力学研究室的建立为开展科研与建设风洞提供了行政保证。     

盐渍土工程与力学性质研究进展

介绍我国西部地区大开发高等级公路、铁路网建设中盐渍土病害的力学相关问题. 综述了对盐胀、溶陷和腐蚀3大工程危害的机理研究以及对盐渍土的工程及力学特性的研究进展, 回顾了盐渍土水、盐、热的数学运移模型的发展, 盐渍土水、盐、热、力4场耦合模型的数值与实验探索, 对盐渍土研究领域中亟待进一步研究的问题进行了展望.     

槽型宽翼受压构件剪力滞分析的传递矩阵法

利用能量变分法,建立了槽型宽翼受压构件考虑剪力滞效应时的平衡控制微分方程,给 出了该方程在轴向均布载荷作用下的初参数解,导出了求解槽型宽翼受压构件内力、应力和 位移的场矩阵和点矩阵,提出一种研究槽型宽翼受压构件剪滞效应的传递矩阵法. 数值算例 表明,该方法计算便捷、精度好、具有较高的工程应用价值.     

第四届全国空间轨道设计竞赛与第六届国际全局轨道优化竞赛结果与排名

2012 年6 月至10 月期间, 第四届全国空间轨道设计竞赛与第六届国际全局轨道优化竞赛相继举行, 在国内、国际掀起了空间轨道设计的研究热潮. 今年的竞赛题目比起往届更具挑战性, 并引出了更多新的设计方法以及可以进一步研究的问题. 其中, 第四届全国空间轨道设计竞赛题目已发表在《力学与实践》2012 年第3 期上[1]. 这里对两次竞赛的结果与排名情况作一个简要报道.     

近空间高超声速飞行器防热隔热与热力耦合研究进展

概述近空间的战略价值与世界主要国家在近空间高超声速飞行器研制方面的竞争, 高超声速飞行器热防护系统及其基础科学问题, 包括防热隔热技术原理与热力耦合问题的研究进展.     

High shear microfluidics and its application in rheological measurement

High shear rheology was explored experimentally in microchannels (150×150 m). Two aqueous polymer solutions, polyethylene oxide (viscoelastic fluid) and hydroxyethyl cellulose (viscous fluid) were tested. Bagley correction was applied to remove the end effect. Wall slip was investigated with Mooneys analysis. Shear rates as high as 10⁶ s^–1 were obtained in the pressure-driven microchannel flow, allowing a smooth extension of the low shear rheological data obtained from the conventional rheometers. At high shear rates, polymer degradation was observed for PEO solutions at a critical microchannel wall shear stress of 4.1×10³ Pa. Stresses at the ends of the microchannel also contributed to PEO degradation significantly.     

An instrumented fastener for shear force measurements in joints

A preliminary investigation has been conducted on instrumented fasteners for use as sensors to measure the shear loads transmitted by individual fasteners installed in double-splice joints. Calibration and load verification tests were conducted for instrumented fasteners installed at three fastener torque levels. Results from calibration tests show that the shear strains obtained from the instrumented fasteners vary linearly with the applied load and that the instrumented fasteners can be effectively used to measure shear loads transmitted by individual fasteners installed in double-splice joints. Tests were also conducted with three instrumented fasteners installed in a typical double-splice joint. The test results showed that the load distribution between individual fasteners is dependent on the location of the fastener in the joint and the fastener torque level. The fastener located near the end of the joint with the single plate carried more load than the fasteners located near the end of the joint with the two plates. Installing the fasteners with a torque greater than finger tight results in a significant amount of the load being carried by friction between the faying surfaces of the plates even if the faying surfaces are polished and lubricated. Increasing the fastener torque increases the load being carried by friction between the faying surfaces of the joint. Increasing friction between the faying surfaces of the joint. Increasing the fastener torque also results in a more uniform distribution of the loads between the individual fasteners for joints in aluminum plates with two fasteners, but does not have a significant effect for joints in steel plates with three fasteners. Paper was presented at the 1992 SEM Spring Conference on Experimental Mechanics held in Las Vegas, NV on June 8–11.     

Novel load cell for measuring axial force,shear force,and bending movement in large-scale structural experiments

This paper describes the design, construction and testing of a load cell to measure the axial force, shear force, and bending moment at the end of a structural beam. The capacities of the load cell are 780 kN in axial load, 350 kN in shear, and 200 kNm in bending. These magnitudes, together with the requirement that the load cell should be kept as slim as possible, necessitated a novel design comprising three steel double-spring elements machined with semicircular channels to provide localized strain amplification. The load cell was designed with the aid of detailed finite element analysis and was machined from grade 55 steel. After strain gaging, it was subjected to an extensive series of calibration tests. Results from these tests are reported, together with those from some early experiments in which two load cells were used to measure the behavior of structural steel knee elements.     

Beck's rod with shear,compressibility and pulsating force

In-plane motion of an elastic rod, subjected to a compressive follower force is analyzed. Equations of motions are derived for the case when deformations are not small. It is assumed that the compressive force has a periodic component, so that a parametric instability is possible. The stability bound is estimated analytically and determined numerically. In deriving the differential equations of motion a generalized constitutive equation taking into account compressibility of the rod axis and the influence of shear stresses is used.     

Velocity profiles in shear force driven wall films

A wind tunnel experiment was carried out to investigate the structure, thickness and velocity profiles of a shear force driven liquid film. The local, time resolved film thickness was measured by means of a fluorescence technique, and a dedicated LDA system enabled the measurement of velocity profiles inside the thin and wavy film. The application of both techniques is briefly described.     

改进的泰勒公式及其数值验证

将光滑粒子法（smoothed particle hydrodynamics method, SPH）应用于金属平板爆轰驱动过程的数值模拟,得到了炸药与金属相互作用的清晰的图像和平板抛射角的变化。根据抛射角方程对泰勒公式进行了修正,得到了改进的泰勒公式。利用数值模拟得到的结果比较了平板驱动几种不同的抛射角公式,改进的泰勒公式准确反映出了抛射角下降并趋于终态的规律,其对平板抛射角的描述更为准确。     

摩擦力判别函数的引入及应用

在涉及摩擦力的力学问题中,首次提出了摩擦力判别函数的概念.该函数的引入完善了库仑摩擦定律的表达式形式.为含有摩擦力、特别是对具有多处摩擦力的问题的清晰分析及解决提供了方便.应用该函数求解摩擦力问题时,无论研究对象处于何种状态、摩擦力的方向均可根据约束的性质作出任意假设,假设正确与否由摩擦力判别函数来确定.举例说明了该函数的适用性.     

Failure criterion for reinforced concrete beams and plates subjected to membrane force,bending and shear

In this paper, a failure criterion for reinforced concrete plates is derived through the kinematic method in the framework of the limit analysis theory. This criterion is expressed in terms of the stress resultant variables: membrane force, shear force and bending moment at once. The aim of the authors is to be able to predict the failure of reinforced concrete plate structures in statics or in slow dynamics using directly the internal forces (membrane and shear forces and moment) resulting from a finite-element computation.In a first step, a beam criterion is derived. The closed form expression of the criterion shows that it is made up of two parts, one independent of the moment (i.e. depending only on the normal force and the shear force) and one depending on the normal force, the shear force and the bending moment. This structure of the criterion allows to determine two failure modes: shear failure and bending failure.Then in a second step, the beam criterion is extended to the case of reinforced concrete plates. The obtained criterion is partly numerical and partly a close form expression. It gives an upper bound of the load, and when this limit load is reached, the criterion is able to supply, on one hand, the failure mode (as seen in the beam case) and, on the other hand, the angles of the failure plane in the reinforced concrete plate section.Thirdly, the criterion is implemented in the finite element software Europlexus and validated with respect to punching experimental tests. We show that the criterion must be used with an effectiveness factor applied on the concrete compressive strength.