正多边形和狭缝的等效菲涅耳数

以正边形的内切圆半径和狭缝的半宽度为特性尺度,给出了匀幅平面波入射时正多边形和狭缝的等效菲涅耳数。     

不平衡电桥法电池内阻测量装置的原理与设计

介绍不平衡电桥法测量电池内阻装置的原理及设计,不平衡电桥法测量电池内阻利用电池本身的电动势在电一对对解点间产生的直流电压,在给定条件下不随另一对对角点间放电电流大小变化的特点构成的,测量装置不需在电桥上施加信号源,电桥的平衡指示信号取自对角点电压及等效电阻的变化成分。     

Local Petrov-Galerkin method for a thin plate

The meshless local Petrov-Galerkin (MLPG) method for solving the bendingproblem of the thin plate were presented and discussed. The method used the moving least-squares approximation to interpolate the solution variables, and employed a local symmetricweak form. The present method was a truly meshless one as it did not need a finite elementor boundary element mesh, either for purpose of interpolation of the solution, or for theintegration of the energy. All integrals could be easily evaluated over regularly shapeddomains ( in general, spheres in three-dimensional problems ) and their boundaries. Theessential boundary conditions were enforced by the penalty method. Several numericalexamples were presented to illustrate the implementation and performance of the presentmethod. The numerical examples presented show that high accuracy can be achieved forarbitrary grid geometries for clamped and simply-supported edge conditions. No postprocessing procedure is required to computer the strain and stress, since the originalsolution from the present method, using the moving least squares approximation, is already smooth enough.     

薄板的局部Petrov-Galerkin方法

利用薄板控制微分方程的等效积分对称弱形式和对变量(挠度)采用移动最小二乘近似函数进行插值,研究了薄板弯曲问题的无网格局部Petrov-Galerkin方法．这是一种真正的无网格方法,它不需要任何有限元或边界元网格,不管这种网格是用于能量积分还是进行插值的目的．所有的积分都在规则形状的子域及其边界上进行,并用罚因子法施加本质边界条件．数值例子表明,无网格局部Petrov-Galerkin法不但能够求解二阶微分方程的边值问题,而且求解四阶微分方程的边值问题也很有效,也具有收敛快、稳定性好、对挠度和内力都具有精度高的特点．     

中心碳极性反转的酰基化试剂的理论研究Ⅱ: H~2C=C(OH)Na 的理论研究

用MP2/6-31+G^*解析梯度方法,研究乙酰基负离子等效物CH~2=C(OH)Na的结构,得到了四个平衡构型。偏位取代的三元环结构1最稳定,将是最易存在的结构。H~2C=C(OH)Na具有双重反应性,结构4是发生亲核反应的中间体,发生类卡宾反应时经过类似构型2的中间状态。同H~2C=C(OH)Li相比较,H~2C=C(OH)Na碳负离子反应将更突出,发生类卡宾反应则更加困难。     

基于光子计数能谱CT的含能材料等效原子序数测量方法

双能CT或能谱CT可以测量材料的等效原子序数,对含能材料的成分检测和生产工艺改进具有重要意义,但现有方法存在复杂度高、设备要求高等缺点.为提高等效原子序数的测量精度,并降低设备要求和算法复杂度,提出了一种基于新型CeT e光子计数探测器的等效原子序数测量方法.该方法利用材料的衰减特性,重新推导了两个能量区间线性衰减系数...     

基于等效静态载荷法的非线性动态拓扑优化

等效静态载荷法是目前解决动态拓扑优化问题的一种有效方法,但是由于未考虑塑性变形中应力应变关系的时效性,会导致等效载荷偏大和载荷方向偏差,因此无法有效处理材料的非线性问题.据此,提出一种基于模量比率因子的等效静态载荷计算方法.首先,根据结构应力、应变和杨氏模量之间的函数关系,计算各时刻的计算杨氏模量;然后,得到各时刻的模...     

蠕变历程中电厂承压材料SA508-Ⅲ钢的细观应力研究

长期服役温度下(300℃以上)的承压容器及管道极易发生热老化和高温蠕变,微观组织表征为晶内粗大第二相粒子、晶界粗化和蠕变空洞,因而材料的细观非均匀性也使得细观应力分析变得更加复杂.首先详细阐述了Eshelby等效夹杂理论,针对电厂服役承压材料SA508-Ⅲ钢的微观组织变化,当基体中夹杂一种掺入体时,即稀疏材料系统(夹杂...     

STEADY-STATE RESPONSE OF A TIMOSHENKO BEAM ON AN ELASTIC HALF-SPACE UNDER A MOVING LOAD

By introducing the equivalent stiffness of an elastic half-space interacting with a Timoshenko beam, the displacement solution of the beam resting on an elastic half-space subjected to a moving load is presented. Based on the relative relation of wave velocities of the half-space and the beam, four cases with the combination of different parameters of the half-space and the beam, the system of soft beam and hard half-space, the system of sub-soft beam and hard half-space, the system of sub-hard beam and soft half-space, and the system of hard beam and soft half-space are considered. The critical velocities of the moving load are studied using dispersion curves. It is found that critical velocities of the moving load on the Timoshenko beam depend on the relative relation of wave velocities of the half-space and the beam. The Rayleigh wave velocity in the half-space is always a critical velocity and the response of the system will be infinite when the load velocity reaches it. For the system of soft beam and hard half-space, wave velocities of the beam are also critical velocities. Besides the shear wave velocity of the beam, there is an additional minimum critical velocity for the system of sub-soft beam and hard half-space. While for systems of (sub-) hard beams and soft half-space, wave velocities of the beam are no longer critical ones. Comparison with the Euler-Bernoulli beam shows that the critical velocities and response of the two types of beams are much different for the system of (sub-) soft beam and hard half-space but are similar to each other for the system of (sub-) hard beam and soft half space. The largest displacement of the beam is almost at the location of the load and the displacement along the beam is almost symmetrical if the load velocity is smaller than the minimum critical velocity (the shear wave velocity of the beam for the system of soft beam and hard half-space). The largest displacement of the beam shifts behind the load and the asymmetry of the displacement along the beam increases with the increase of the load velocity due to the damping and wave radiation. The displacement of the beam at the front of the load is very small if the load velocity is larger than the largest wave velocity of the beam and the half space. The results of the present study provide attractive theoretical and practical references for the analysis of ground vibration induced by the high-speed train.     

AN EQUIVALENT CONTINUUM METHOD OF LATTICE STRUCTURES

An equivalent continuum method is developed to analyze the effective stiffness of three-dimensional stretching dominated lattice materials. The strength and three-dimensional plastic yield surfaces are calculated for the equivalent continuum. A yielding model is formulated and compared with the results of other models. The bedding-in effect is considered to include the compliance of the lattice joints. The predicted stiffness and strength are in good agreement with the experimental data, validating the present model in the prediction of the mechanical properties of stretching dominated lattice structures.