关于科氏加速度与科氏力理论力学札记之十一

理论力学的运动学部分有加速度合成定理：点的绝对加速度等于相对加速度、牵连加速度与科氏加速度的矢量和。在相对运动动力学部 分有牵连惯性力和科氏惯性力。一般都说,科氏加速度和科氏力由科里奥利(Coriolis GG, 1792—1843)于1835年首先提出。本文简述科氏力的历史与发展。     

侵彻钢筋混凝土过程中弹丸过载特性的实验研究

实验测试了侵彻钢筋混凝土过程中弹丸的过载情况,得到侵彻过程中弹丸的加速度时程曲线。通过将实验测得的加速度时程曲线按其本身的特点划分成四个部分,每个部分代表弹丸与钢筋混凝土作用的不同阶段,分析了不同阶段弹丸与钢筋混凝土相互作用的特点。实验结果表明,含筋率为2%的钢筋混凝土靶板的抗侵彻能力明显高于含筋率为1%的钢筋混凝土靶板。研究结果为理论模型的建立打下了基础,也可为相关弹药和防护工程的优化设计提供参考。     

本科力学实验中的创新思维培养方法探索

本文介绍了改革本科力学实验教学方法,在常规的教学实验中启迪学生的创新意识,培养学生在实验实践过程中善于发现问题的创新思维,并举例阐述了具体做法和实际效果.     

运用课堂演示实验,促进学生创新能力培养1)

如何激发学生的创新意识、培养创新能力是当前教学的中心任务之一。本文笔者根据在流体力学课程教学中将简单易行、灵活多样的演示实验带进课堂,引发学生兴趣,启发创新思维方面的教学实践,总结了几点经验和体会。     

疲劳过程中生热机理的实验探讨

传统的疲劳试验方法确定材料的疲劳极限时试验周期长、需要试件多,故高试验成本成为疲劳试验中一个难以解决的问题.文中利用具有准确、快速、便捷、低成本等优点的热像法测定了多种载荷工况下Q235钢的疲劳极限,并对不同的黏或/和塑性效应主导的生热机制进行了探讨.材料疲劳过程中,疲劳极限之下的载荷引起的温度波动来源于热弹性效应,温升来源于材料的非弹、塑性效应(如黏性效应);而疲劳极限之上的载荷引起塑性功累计,导致疲劳损伤产生,使得温升机制出现转折.通过对试验数据的分析,求出了材料的黏性系数,给出了利用塑性能耗的起点确定材料疲劳极限的方法.     

岩石变形演化诱致灾变破坏过程的同步实验观测

将试样变形场演化特征与试样的宏观载荷位移曲线的演化特征结合起来研究是揭示非均匀脆性介质变形演化诱致灾变破坏的一个重要途径.本文发展了一套实验系统,通过对试样表面变形场的演化、宏观载荷和位移信号的同步观测,对单轴加载下岩石试样变形演化和灾变破坏的过程进行了实验研究.揭示了试样变形场由加载初期的随机涨落到灾变破坏前出现明显的变形局部化的演化特征现象,试样最终在变形局部化区内形成宏观破裂面.     

壁湍流猝发过程中速度分量的相位差对雷诺应力影响的实验研究

用IFA300恒温热线风速仪和×形二分量热线探针,以采样间隔小于最小湍流时间尺度的分辨率,精细测量了风洞中平板湍流边界层不同法向位置的瞬时流向、展向速度分量的时间序列信号.用子波分析辨识壁湍流相干结构猝发事件的能量最大准则,确定壁湍流相干结构猝发事件的时间尺度;用条件相位平均技术提取了相干结构猝发过程中流向、展向脉动速度分量条件相位平均波形,用互相关方法研究了相干结构猝发过程中流向、展向脉动速度分量条件相位平均波形的相位差关系及其对雷诺应力的影响,发现在缓冲层和对数律区,展向脉动速度与流向脉动速度的条件相位平均波形具有不同的相位;当两者相位基本一致时,雷诺应力达到正的最大值,此时湍流相干结构的产生非常活跃;当两者相位差分别集中在90°和270°附近时,雷诺应力的幅值减小并接近于零,此时湍流相干结构的产生和猝发都得到了抑制.     

FLASH hydrodynamic simulations of experiments to explore the generation of cosmological magnetic fields

We report the results of FLASH hydrodynamic simulations of the experiments conducted by the University of Oxford High Energy Density Laboratory Astrophysics group and its collaborators at the Laboratoire pour l'Utilisation de Lasers Intenses (LULI). In these experiments, a long-pulse laser illuminates a target in a chamber filled with Argon gas, producing shock waves that generate magnetic fields via the Biermann battery mechanism. The simulations show that the result of the laser illuminating the target is a series of complex hydrodynamic phenomena.     

“加约束”与“拆约束”的艺术——浅谈结构力学的学习

浅析了结构力学与约束的关系,从几何构造分析,平面静定结构,平面超静定结构,虚功法和能量法以及结构矩阵法等方面尝试探讨了贯着结构力学的一条主线－加约束与拆约束。     

从坐标系到张量1）--学习和理解张量的一条捷径

学习和掌握张量基本知识是研究连续介质力学的基础,然而,当前对张量的讲述和介绍方式比较复杂,造成理解和运用的困难.本文利用笛卡尔坐标系引入张量概念及其基本运算,阐明张量本质上是坐标变换,熟悉求和约定和指标表示是其关键,从而使张量能体现出数学本身的简单、和谐和美的统一,也能使读者比较顺利地学习、理解并运用张量.     

从坐标系到张量——学习和理解张量的一条捷径

学习和掌握张量基本知识是研究连续介质力学的基础,然而,当前对张量的讲述和介绍方式比较复杂,造成理解和运用的困难.本文利用笛卡尔坐标系引入张量概念及其基本运算,阐明张量本质上是坐标变换,熟悉求和约定和指标表示是其关键,从而使张量能体现出数学本身的简单、和谐和美的统一,也能使读者比较顺利地学习、理解并运用张量.     

Mechanical experiments to identify homogeneous bodies

All bodies are inhomogeneous at some scale but experience has shown that some of these bodies can be idealized as a homogeneous body. Here we examine which bodies can be idealized as a homogeneous body when they are subjected to a non-dissipative mechanical process. This is done by studying circumstances in which an inhomogeneous body admits pure stretch homogeneous deformations. Then, we devise experiments wherein these circumstances are prevented. If homogeneous deformation is observed in these devised experiments, the body could be modeled as a homogeneous body. We limit our analysis to a class of isotropic elastic bodies deforming from a stress free reference configuration whose Cauchy stress is explicitly related to left Cauchy–Green deformation tensor. It is further assumed that the constitutive relation is differentiable function of the position vector of material particles in the stress free reference configuration. Then, we find that a cuboid made of compressible and isotropic material could be modeled as a homogeneous body if it deforms homogeneously due to the application of the normal stresses on all of its six faces and the magnitude of the normal stresses on three orthogonal faces are different. A cuboid made of incompressible and isotropic material could be modeled as a homogeneous body, if it deforms homogeneously in two different biaxial experiments, such that the plane in which the forces are applied in the two biaxial experiments is mutually orthogonal.     

Two laser-driven mix experiments to study reshock and shear

In an effort to better understand mix in Inertial Confinement Fusion (ICF) implosion cores, a series of laser-driven mix experiments has been designed for the University of Rochester's OMEGA laser. Our objective is to perform experiments to investigate the turbulent mixing at material interfaces when subject to multiple shocks and reshocks or high-speed shear. Ultimately, these experiments are providing detailed quantitative measurements to assist in validation efforts for the BHR-2 mix model, which is implemented in the RAGE hydrodynamics code. The Reshock experiment studies the physical process of shocking and reshocking mix layers. Radiographs are recorded to compile a temporal evolution of the mixing layer and its subsequent reshock, compression, and re-growth phases. The Shear experiment investigates shear-driven growth of a mix layer, and radiography captures the time evolution of the development of turbulent mixing due to shear. Simulations of both the Reshock and Shear experiments using RAGE and the BHR-2 mix model demonstrate good agreement with the mix evolution seen in the experimental data, giving confidence that BHR-2 is capable of simulating the behavior of both compressive and shear-driven turbulent flows.     

材料力学实验教学的改革与开放

 就材料力学实验教学的改革和实行开放实验的问题谈了一些认 识, 讲述了我们的做法、体会及初步效果.     

石英光纤探针在非金属材料冲击实验中的应用

使用石英光纤探针成功测量了Teflon样品中的冲击波速度和电炮加载的厚度为75 m的Mylar膜飞片的平均速度和到达时间一致性。实验证明,石英光纤探针技术为非金属材料的冲击实验提供了一种直接的、不受电磁干扰的、精确的测量手段。     

Image correlation applied to single crystal plasticity experiments and comparison to strain gage data

Experimental Techniques - The results from compression tests on Mo single crystals using the 6DOF apparatus show that at small strains the image correlation system is able to match the data...