大小每相从,排云结阵行──从雁群结阵飞行谈起

简述飞行中的升力、诱导阻力及其旋涡，分析雁群结阵的队形与飞行力之关系     

从窑洞的冬暖夏凉谈起--一种居室温度调节的节能前景

本文通过一个地表热传导模型的建立及求解,得出了地下温度变化与地表存在相位差并且振幅衰减,某个深度以下温度恒定为全年平均温度的结论.由此讨论了一种温度调节的设想,论证了可行性并与现有方案进行了比较.     

"野渡无人舟自横"的实验研究

对"野渡无人舟自横"进行了实验研究.     

滚动圆环的力学问题

讨论了带质量偏心的圆环在滚动过程中能否解除约束跳起腾空的问题. 从简单的动力学知识出发,导出圆环离地的充分必要条件.     

关于牛顿力学的力和拉格朗日力学的力------理论力学札记之九

讨论了牛顿力学和拉格朗日力学中的力. 在牛顿力学中着重讨论了主动力, 约束和理想约束力. 在拉格朗日力学中着重讨论了广义力的两种分解方法.     

超细长弹性杆的分析力学问题

超细长弹性杆作为DNA等生物大分子链的力学模型，其平衡和稳定性问题已成为力学与分子生物学交叉的研究热点．虽然在Kirchhoff动力学比拟的基础上，用分析力学方法讨论弹性杆的文章已见诸文献，但尚未形成弹性杆分析力学的严格理论．本文研究了超细长弹性杆分析力学的若干基础性问题．对杆截面的自由度、虚位移、约束方程及约束力等基本概念给出严格的定义和表达式．建立弹性杆平衡的D’Alembert-Lagrange原理、Jourdain原理和Gauss原理；从D’Alembert-Lagrange原理导出Hamilton原理．从变分原理出发导出Lagrange方程、Nielsen方程、Appell方程和Hamilton正则方程；对于受约束的弹性杆，导出了带乘子的Lagrange方程．讨论了Lagrange方程的首次积分．对于杆中心线存在尖点的情形，导出了微段杆平衡的近似方程。     

On universal relations in continuum mechanics

This paper is devoted to a systematic study of local universal relations in continuum mechanics. We show that it is possible to determine the complete set of independent universal relations whose characterization is obtained by linear universal rules. A historical review of the literature on the topic and various significant examples are given. Received: August 16, 1996     

On lack-of-knowledge theory in structural mechanics

Today, the validation of complex structural models – i.e. the assessment of their quality compared to an experimental reference – remains a major issue. Strictly speaking, the validation problem consists in comparing the response of the numerical model (whether deterministic or stochastic) with complete reality. A first answer to this problem, using Lack-Of-Knowledge (LOK) theory, was introduced at LMT-Cachan. This theory is an attempt to “model the unknown” by taking all the sources of uncertainties, including modeling errors, into account through the concept of basic LOKs. In this article, we introduce basic LOKs associated with both the amplitudes and directions of excitations. These basic LOKs are propagated rigorously throughout the mechanical model in order to determine intervals (with stochastic bounds) within which lies a given quantity of interest (stress or displacement). Then, we introduce a strategy for the reduction of lack of knowledge, which we illustrate through an academic example.     

如何用好土力学——对青年土木工程师谈土力学的理论与应用

针对青年学生和年轻的土木工程师在工程实践中如何使用好土力学的理论这一问题进行了讨论.指出了土力学理论与其它土木工程结构理论的根本区别,以及工程经验和判断力的重要性,并就工程经验和判断力以及如何进行培养展开了讨论.本文还对如何阅读土力学文献和如何选择土力学数学模型进行了论述.最后还列出了Casagrand[2]对实际应用土力学理论的要求.     

On discrete models in fracture mechanics

In two papers published in 1969, where the foundations of the theory of brittle fracture were laid, Valentin Valentinovich Novozhilov introduced a necessary and sufficient criterion for estimating the strength of an elastic body weakened by a cut and formulated the concept of brittle fracture. The criterion is based on taking account of the body discrete structure, and the fracture process is treated as loss of stability of elastic equilibrium. These two facts, fracture discreteness and loss of stability in the deformation of the breaking bond, underlie numerous phenomena, which could not be discovered in the framework of continuum mechanics. In the present paper, the following effects of taking these facts into account are briefly discussed: an unstable leg of the stress-strain diagram and the capture of part of the fracture energy by the lattice, the role of the lattice dimension, radiation in quasi-static and dynamic crack propagation including the radiation structure, the role of the dynamic factor, irregularities in the crack growth, crack propagation under the action of high-frequency waves including steady-state modes with periodically varying speed, and cracks in continuum discrete models.     

On identification in mechanics of nanocomposites

Composites whose some components are smaller in linear size by an order of magnitude than other components are considered. Such components are usually referred to as nanocomponents. Finding all material functions experimentally for components with nanostructure is extremely complicated and sometimes not possible at all. In this paper, an approach to the calculation of material functions from known effective characteristics of the whole composite and of the components with nanostructure is suggested. By way of example, a multilayered composite with isotropic elastic properties is considered.