样条有限条塑性铰法分析板梁的极限荷载

用样条有限条塑性铰法分析了板梁的极限荷载。首先对条单元以样条位移函数表达的总势能进行求导而推导了位移-荷载关系式。然后用塑性铰法推导了单元的塑性刚度矩阵。因此该方法兼具二者优点:样条有限条法的位移量少和塑性铰法形成塑性刚度矩阵的便利。它还可以考虑梁的初始缺陷,如残余应力和初弯曲。通过与相关的试验数据比较,证明该方法有效与可靠。     

八次对称二维准晶材料接触问题

本文通过引入位移函数和应用Fourier分析与对偶积分方程理论圆满解决了在一个刚性平头冲头作用下八次对称二维准晶材料的接触问题，得到了此材料接触问题应力与位移的解析表达式。结果表明，如果接触位移在接触区域内为一常数，则接触应力在接触边缘具有1／2阶奇异性，这为准晶材料的接触变形提供了重要的力学量。     

基于非线性有限元的索穹顶施工模拟分析

索穹顶结构的成形和施工模拟分析是该体系的基础问题。由于包含着刚体位移的分析使得跟踪难度相当大。本文采用了基于非线性有限元的施工过程分析 ,适应性强、分析精度高 ,避免了刚体位移假定。从而使得索穹顶体系的成形过程、受荷状态的全过程分析方法获得了统一。通过与试验模型对比分析表明本文方法操作简单且分析精度较高 ,分析的结果能够很好地指导施工     

三维含裂纹有限大体剪切型应力强度因子能量释放率方法的封闭解

本文利用能量释放率法,导出三维含裂纹有限大体剪切型应力强度因子的封闭解。这种方法非常节省机时,可获得大量K_Ⅱ和K_Ⅲ的有用结果,所得结果与现有少量结果基本吻合。     

电流比较仪电桥在静电陀螺转子位移测量中的应用

用耦合电感原理研究了电流比较仪电桥非平衡测量的原理及特性,导出了在不同激励信号(电压或电流)和不同输出信号(电压或电流)情况下电桥测量输出的表达式,并据此提出了现有静电陀螺转子位移测量电路的改进措施.研究表明,采用电流输出模式时,变压器的电感大小对检测结果没有影响,且能消除后续电路输入端寄生电容的影响;电流激励、电流输出模式具有最好的综合性能,但高精度交流恒流源的实现较为困难;电压激励、电流输出模式兼具两者的优点,是比较仪电桥较为理想的工作模式.     

Transient response of a cracked piezoelectric strip under arbitrary electro-mechanical impact

By using the well-developed integral transform methodology, the dynamic response of stress and electric displacement around a finite crack in an infinite piezoelectric strip are investigated under arbitrary dynamic anti-plane loads. The dynamic stress intensity factors and electric displacement are obtained analytically. It is shown that the dynamic crack-tip stress and electric field still have a square-root singularity. Numerical computations for the dynamic stress intensity factor show that the electric load has a significant influence on the dynamic response of stress field. The higher the ratio of the crack length to the width of the strip, the higher the peak value of the dynamic stress intensity factor is. On the other hand, the dynamic response of the electric field is determined solely by the applied electric load. The electric field will promote or retard the propagation of the crack depending on the time elapse since the application of the external electro-mechanical loads. The project supported by the National Natural Science Foundation of China and the Post-Doctor Science Foundation of China     

Onset of viscous fingering for miscible liquid-liquid displacements in porous media

The displacement of one fluid by another miscible fluid in porous media is an important phenomenon that occurs in petroleum engineering, in groundwater movement, and in the chemical industry. This paper presents a recently developed stability criterion which applies to the most general miscible displacement. Under special conditions, different expressions for the onset of fingering given in the literature can be obtained from the universally applicable criterion. In particular, it is shown that the commonly used equation to predict the stable velocity ignores the effects of dispersion on viscous fingering.Nomenclature C Solvent concentration - Unperturbed solvent concentration - D _L Longitudinal dispersion coefficient [m²/s] - D _T Transverse dispersion coefficient [m²/s] - g Gravitational acceleration [m/s²] - I _sr Instability number - k Permeability [m²] - K Ratio of transverse to longitudinal dispersion coefficient - L Length of the porous medium [m] - L _x Width of the porous medium [m] - L _y Height of the porous medium [m] - M Mobility ratio - V Superficial velocity [m/s] - V _c Critical velocity [m/s] - V _s Velocity at the onset of instability [m/s] - µ Viscosity [Pa/s] - Unperturbed viscosity [Pa/s] - µ ₀,µ _s Viscosities of oil and solvent, respectively [Pa/s] - Density [kg/m³] - ₀, _s Densities of oil and solvent, respectively [kg/m³] - Porosity - Dimensionless length     

平稳随机激励下随机智能桁架结构振动主动控制中的优化

研究了平稳随机激励下随机智能桁架结构振动主动控制中主动杆的配置位置和闭环控制系统增益的优化问题。考虑结构物理参数、几何尺寸、阻尼同时具有随机性以及作用荷载为平稳随机激励，基于系统最小储存能，构建了具有位移响应均方值、应力响应均方值可靠性约束的主动杆配置和控制增益的优化模型；并对结构平稳随机动力响应的数字特征进行了推导。通过算例，验证了该优化配置模型的合理性和有效性，获得了若干有意义的结论。     

Wave-Like Solutions for a Class of Parabolic Models

A reduction aproach is developed for determining exact solutions of anonlinear second order parabolic PDE. The method in point makes acomplementary use of the leading ideas of the theory of quasilinearhyperbolic systems of first order endowed by differential constraintsand of the techniques providing multiple wave-like solutions ofnonlinear PDEs. The searched solutions exhibit a inherent wave featuresand they are obtained by solving a consistent overdetermined system ofPDEs. Remarkably, in the process it is possible to define nonlinearmodel equations which allow special classes of initial or boundary valueproblems to be solved in a closed form. Within the present reductionapproach exact solutions and model material response functions areobtained for an equation of widespread application in many fields ofinterest.     

运用Hoek-Brown经验准则分析圆形硐室围岩弹塑性应力和位移

Hoek-Brown经验准则能够较容易地用来估计节理岩体的强度,在岩石工程界已得到广泛的应用和认可。只要用定量指标合理地描述岩体质量,就可确定岩体的强度,因此Hoek-Brown经验准则为通过岩体质量评分评价岩体稳定性架起了一座桥梁,并对需要采取的加固支护措施提出建议。地下硐室开挖后改变了岩体的初始应力状态,围岩应力产生应力重分布现象。当硐室周边围岩应力状态超过岩体弹性极限状态而进入塑性状态时,塑性区内岩体的应力满足极限平衡条件。本文简单回顾了当侧压力系数为1时,圆形硐室围岩的弹性应力和位移,在此基础上以Hoek-Brown经验准则为极限平衡条件,得到圆形硐室轴对称平面应变问题的围岩弹塑性应力和位移的分析解。