有同心圆弧裂缝的圆柱体和圆管的弯曲

1.弯曲问题的数学提法 本文讨论有同心圆弧裂缝的圆柱和圆管的线弹性弯曲。直角坐标系z轴平行于柱轴;x,y轴是截面的惯性主轴;原点在柱体的端面;力W在另一端面z=l沿x方向作用,则受弯曲柱体的应力分布为:     

泊松方程中域积分化为边界积分的方法

本文讨论了二维和三维泊松方程中域积分化为边界积分的方法。对于形如x~ig_x(y,z)、y~ig_x(x,z)和z~ig_z(x,y)的荷载给出了域积分转化为边界积分的正确公式。而对于复杂荷载,利用泰勒展开将域积分近似地转化为边界积分并给出了误差估计。计算结果表明利用本文方法可大大节省计算时间。因此,本文方法是一种十分有效的方法。     

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对在光滑水平面上可自由移动的圆弧形凹槽内作纯滚动的圆柱体的运动进行了分析,给出了 圆柱体的质心及其边缘上任意一点在静止参考系中的运动轨迹方程和圆柱体严格等时摆动的 条件,并绘出了它们相应的轨迹. 求出了圆柱体在槽内作纯滚动的运动周期,并与圆柱体被 简化为质点时的周期作了比较.     

空投鱼雷入水载荷

为了研究空投鱼雷的入水过程,首先分析入水过程中的受力情况进行数值计算;然后使用数值模拟软件Msc.Dytran建立鱼雷入水的有限元模型,计算入水过程中雷体所遭受的冲击压力及其在冲击面上的分布情况,并对不同入水速度和角度下冲击压力峰值、不同头部形状冲击压力峰值特点及鱼雷入水弹道做了分析与讨论,结果表明:鱼雷入水速度和入水角度会对鱼雷壳体所受载荷产生重要影响,研究结果可为预测鱼雷入水冲击载荷提供参考。     

有任意径向单裂缝圆柱体的扭转

1.问题提法,保角映射和混合边值问题 本文讨论如图:半径为r,有一径向内裂缝的圆柱的线弹性扭转。直角坐标系z轴平行于圆柱轴。裂缝和正x轴上(a,b)段重合,b端较a端离圆周为近。坐标原点任取在圆内a端之左。若圆心c不在裂缝上,就取圆心为原点,问题大为简化。柱体各点翘曲w=(?)(x,y),其中(?)是扭率,(x,y)是翘曲     

Lorenz吸引子的微观结构

轨迹保稳降维是一种分析高维非线性系统稳定性的方法。其要点是先在高维空问中求取轨迹；再将F轨迹映射为n-1个R^2映像，并在变换中严格保持感兴趣的稳定特性：分析各映像轨迹的稳定性：最后聚合为原轨迹特性的描述。本文按此分析Lorenz吸引子的结构稳定性。例如，将其中的z变量处理为时变参量后，(x,y）子系统成为时变的线性2维系统，可得分岔集{zcr}及奇点特性沿z轴的变化规律。故对于特定的轨迹(x,y,z），可将其在各坐标平面上的投影轨迹分成短线段的有序队列，各相邻线段对应于特性不同的奇点，从而揭示Lorenz吸引子全局分岔的精细结构及其通往高维混沌的道路。     

仅在四边中点被支撑的方形板在均布载荷作用下的弯曲

1.挠度表达式和δ-函数的运用弹性薄板弯曲问题的微分方程为((?)~4W)/((?)x~4) 2((?)~4W)/((?)x~2(?)y~2) ((?)~4/W)/((?)y~4)=q/D (1)其中W 是板的挠度,常数q 和D 分别表示载荷强度和板的抗弯刚度.设坐标原点在方形板的中心,x、y 轴分别平行于板边,z 轴向下,每边长为α.根据对称条件,边界条件只需写出半条边(例如x=α/2,0≤y≤α/2)的条件,其形式为     

功能梯度平板的二维热弹性分析

本文研究正交各向异性功能梯度平板的二维热弹性问题.该平板在y方向无限长,x方向对边简支且温度恒定.从热弹性力学的基本方程出发,假设材料参数沿板厚方向(z方向)按同一函数规律变化,基于状态空间法,在板的上下表面作用机械荷载和热荷 载的情况下,获得了功能梯度平板二维热弹性问题的Peano-Baker级数解.通过算例,验证了Peano-Baker级数解的正确性;同时也分析了材料参数沿板厚方向不同的幂函数分布对平板响应的影响.     

有限尺寸压电圆柱的三维耦合振动谐振频率分析

有限尺寸压电圆柱体的振动因为存在不同振动方向之间的耦合而变得复杂,分析时不能简单将其视为一维细长棒或二维薄圆片进行处理,而必须考虑不同振动方向之间的耦合.论文从表观弹性常数的定义出发,给出压电圆柱频率常数和其尺寸的方程.通过样品数据,验证压电圆柱体的频率常数与尺寸的非线性关系,说明一维细长棒或二维薄圆片是在样品尺寸满足一定条件下的简化处理;当样品厚度和直径尺寸接近时,不能简化处理,而必须考虑不同方向的振动耦合.     

六线涡量探针的测量原理与应用

介绍六线涡量探针和六通道热线风速仪的研制成果，应用该探针可同时测量两个涡量分量ωx和ωy（或ωx和ωz），以及3个速度分量u,υ，ω等相应的瞬时脉动值和统计平均值，从而可进一步测量湍流场内的湍能和雷诺应力，以及螺度和涡拟能等参量，还报道了应用该六线涡量探针，测量二维混合层内各湍流参量以及涡量分量ωx、ωy和ωz统计平均值的分布结果，并与前人的结果作了比较。     

Further analytical considerations of weak planar shock wave reflections over a concave wedge

A simplified analytical model of the Mach reflection of a planar shock wave over a concave cylindrical wedge has been used to predict the triple point trajectory and the triple point trajectory angle at glancing incidence.Comparison with experimental results suggests that the simplified approach for predicting the triple point trajectory is good for an incident shock wave Mach number, M_i, less than 1.1. However, the prediction of the triple point trajectory angle at glancing incidence is good for any value of M_i as long as the assumption of a perfect gas is valid.     

Mobile bed thickness in skewed asymmetric oscillatory sheet flows

A new instantaneous mobile bed thickness model is presented for sediment transport in skewed asymmetric oscillatory sheet flows. The proposed model includes a basic bed load part and a suspended load part related to the Shields parameter, and takes into account the effects of mass conservation, phase-lag, and asymmetric boundary layer development, which are important in skewed asymmetric flows but usually absent in classical models. The proposed model is validated by erosion depth and sheet flow layer thickness data in both steady and unsteady flows, and applied to a new instantaneous sediment transport rate formula. With higher accuracy than classical empirical models in steady flows, the new formula can also be used for instantaneous sediment transport rate prediction in skewed asymmetric oscillatory sheet flows.     

油松和落叶松根与土界面摩擦特性

通过直接拉拔试验研究了加载速率、根系埋深和不同树种对根系与土体的摩擦特性的影响.结果表明：被拉断的根系最大拉拔力和位移关系曲线分为陡峭上升和陡峭下降两个阶段,被拔出的根系最大拉拔力和位移关系曲线分为陡峭上升、陡峭下降和平缓下降3个阶段;加载速率或埋深增大时,根土静摩擦力及其对应位移亦增大;落叶松的根土静摩擦力及其对应位移比油松的根土静摩擦力及其对应位移大.     

On the evolution of lattice deformation in austenitic stainless steels—The role of work hardening at finite strains

In this work, a three dimensional crystal plasticity-based finite element model is presented to examine the micromechanical behaviour of austenitic stainless steels. The model accounts for realistic polycrystal micromorphology, the kinematics of crystallographic slip, lattice rotation, slip interaction (latent hardening) and geometric distortion at finite deformation. We utilise the model to predict the microscopic lattice strain evolution of austenitic stainless steels during uniaxial tension at ambient temperature with validation through in situ neutron diffraction measurements. Overall, the predicted lattice strains are in very good agreement with those measured in both longitudinal and transverse directions (parallel and perpendicular to the tensile loading axis, respectively). The information provided by the model suggests that the observed nonlinear response in the transverse {200} grain family is associated with a competitive bimodal evolution of strain during inelastic deformation. The results associated with latent hardening effects at the microscale also indicate that in situ neutron diffraction measurements in conjunction with macroscopic uniaxial tensile data may be used to calibrate crystal plasticity models for the prediction of the inelastic material deformation response.     

NONLINEAR FLUID FORCES IN CYLINDRICAL SQUEEZE FILMS. PART II: FINITE LENGTH

Two nonlinear models of finite-length cylindrical squeeze films are developed. The first finite-length model is formed using length-correction factors on a short cylindrical model, while the second finite-length model is constructed using side-leakage factors with an infinitely long model. Each model has seven force terms which are nonlinear functions of instantaneous cylinder position. The two models are evaluated through experimental measurements using two geometrical configurations where 50·6 mm and 25 mm diameter cylinders undergo 160 cases of radial and offset-linear motions. Comparing the theoretical predictions of squeeze force waveforms with measurements, and also with previous models by Lu & Rogers, shows that the present finite-length models are quite reasonable. By investigating each force term, the present models are modified slightly and better predictions are obtained for most test cases. Without empirical corrections, the models tend to underestimate the unsteady inertia terms and are unable to predict the frequency dependence of the viscous terms.     

峨口铁矿高陡边坡稳定性三维模型试验研究

据计算, 峨口铁矿边坡如增加1°坡角可减少剥离量5684万吨, 节约经费1.7亿元。在地质调查基础上, 应用三维物理模型对峨口铁矿边坡进行了设计最终边坡角开挖试验, 加陡边坡角以及陡帮强采试验研究, 以进一步验证矿山原设计最终边坡角的合理与否。     

低含水率砂土和饱和砂土场地爆炸成坑特性实验

爆坑是土中爆炸荷载作用下的主要响应形式,基于大型爆炸实验场地,开展了一系列低含水率砂土和饱和砂土中的爆炸成坑现场实验,研究了药量、埋深及含水率等因素对土中爆坑效应的影响。研究结果显示:根据药包的比例埋深,低含水率砂土场地的最终爆坑形态可以分为隐爆、塌陷型漏斗坑和抛掷型爆坑3类,发生封闭爆炸的临界比例埋深为2.3 m/kg1/3;形成抛掷型爆坑的条件为比例埋深小于1.5 m/kg1/3;当比例埋深为1.5~2.3 m/kg1/3时,形成塌陷型漏斗坑。土中孔隙水压力的增大导致坑壁周围土体发生了液化流动、坍塌,最终造成爆坑横向尺寸的扩大。相同爆源条件下,饱和砂土场地形成的坑面直径比低含水率砂土场地提高了25%~35%,饱和砂土场地发生封闭爆炸的极限比例埋深可达2.5 m/kg1/3。     

瓦斯爆炸载荷作用下矿用柱壳救生舱抗爆性分析及结构优化

矿用救生舱是矿井安全生产中必备的救生装备,其稳定性和抗爆性能决定着逃生人员的生存概率。本文中设计了一种圆柱壳结构救生舱,优化了该救生舱在瓦斯爆炸载荷作用下的抗爆性能:首先,采用ANSYS/LS DYNA软件模拟并验证了爆炸流场载荷;其次,采用ALE流固耦合算法揭示了真实环境下爆炸流场与救生舱的耦合作用;然后,对其进行抗爆性模拟分析及结构设计优化;最后,对比分析了原模型和优化模型的动力响应、强度及能量变化特征,结果表明优化后的救生舱抗爆性满足国家规范要求。     

A physical,mechanistic and fully coupled hillslope hydrology model

We present the mathematical development and numerical solution of a new model of flow processes on an infiltrating hillslope. We also present validation and sample applications. The model is a distributed, mechanistic, physically based hillslope hydrologic model. The model describes the small‐scale processes associated with overland flow, erosion, and sediment transport on an infiltrating surface and is capable of capturing small‐scale variations in flow depth, flow velocities, interactive infiltration, erosion rates, and sediment transport. The model couples the fully two‐dimensional hydrodynamic equations for overland flow, the one‐dimensional Richards equation for infiltration, and a sediment detachment and transport model. Two simulations are presented highlighting the model's ability to capture and describe the interaction between precipitation, overland flow, erosion and infiltration at very small scales. Results of the two‐dimensional simulations indicate the system of equations produces hillslopes possessing characteristics of self‐organization as observed in real world systems. Copyright © 2005 John Wiley & Sons, Ltd.     

基于三维细观力学模型的开孔泡沫弹性性能预测

泡沫材料的宏观力学性能主要取决于基体材料的力学特性及其微细观结构特征,基于细观力学模型的分析方法是泡沫材料力学性能研究的重要途径。文中基于Matlab语言和Abaqus软件构建了描述中等孔隙率开孔弹性泡沫材料微结构特征的三维随机分布球形泡孔模型,并采用有限元方法对弹性泡沫压缩变形进行了模拟,并计算给出了不同孔隙率弹性泡沫材料弹性模量、剪切模量、体积模量以及泊松比的分布,建立了相应的唯象表达式。与理论模型及测试结果的比较表明,本文基于三维随机泡孔模型模拟结果构建的唯象表达式能够对弹性泡沫材料的弹性力学性能给出很好的预测。