Experimental study on the density wave oscillation in parallel rectangular channels with narrow gap

An experimental investigation was performed on the density wave oscillation (DWO) with two parallel rectangular channels, which have a cross section of 25 mm × 2 mm and a heated length of 1000 mm. Test parameters are 1 MPa to 10 MPa for pressure, 200–800 kg/m² s for mass velocity, and 10–50 °C for inlet subcooling. The results show that in general the flow becomes more stable while mass velocity, pressure, and inlet subcooling are increased. The period of oscillation becomes shorter if mass velocity is increased or inlet subcooling is decreased. Pressure has little effect on period of the DWO in this research. The dimensionless subcooling number N_sub and phase change number N_pch were adopted to compare results from rectangular channels with those from round tubes. The comparison indicates that the data from rectangular channels agree with those from the round tubes. The RELAP5 software was used to simulate the DWO in rectangular channels. The prediction show good consistency with experimental phenomenon. However, different two-phase flow model behaves differently when pressure changes in prediction.     

辐射诱导人肝细胞子代基因差异表达及生物信息学分析

利用基因芯片技术和实时荧光定量RT-PCR技术,采用不同剂量60Coγ射线照射人正常肝细胞系HL-7702细胞,观察比较受照细胞克隆子代基因表达图谱的变化,筛选出差异表达基因,利用生物信息学方法分析构建基因相互作用网络图,对部分差异表达基因进行验证。结果表明,与对照组相比,共同的差异表达基因有71个,其中上调的35个,...     

大倾角煤层回采巷道顶板结构体稳定性分析

通过对大倾角煤层回采巷道顶板＂三角形结构体＂的形成条件、破断特征以及影响因素和失稳形态的分析,得出顶板＂三角形结构体＂在重力的倾向分力和垂直于顶板分力作用下呈上拉剪、下压剪破断运动,并表现为切落或坠落失稳。构建了顶板＂三角形结构体＂稳定性力学模型,得出顶板＂三角形结构体＂不同失稳形态下顶板稳定性判别准则。     

风雪耦合作用下单层柱面网壳的动力稳定

强风带动积雪漂移可能使结构处于稳定最不利状态,而目前在这方面的研究很少。该文研究一单层柱面网壳在风雪耦合作用下的动力稳定性。首先阐述风雪耦合作用下动力稳定性的研究方法,然后介绍风雪耦合作用的数值模拟,并通过风洞试验获得网壳表面的非定常气动力,最后分析了风雪耦合作用下单层柱面网壳的动力稳定。研究表明,斜风作用和不均匀分布...     

A convected particle domain interpolation technique to extend applicability of the material point method for problems involving massive deformations

A new algorithm is developed to improve the accuracy and efficiency of the material point method for problems involving extremely large tensile deformations and rotations. In the proposed procedure, particle domains are convected with the material motion more accurately than in the generalized interpolation material point method. This feature is crucial to eliminate instability in extension, which is a common shortcoming of most particle methods. Also, a novel alternative set of grid basis functions is proposed for efficiently calculating nodal force and consistent mass integrals on the grid. Specifically, by taking advantage of initially parallelogram‐shaped particle domains, and treating the deformation gradient as constant over the particle domain, the convected particle domain is a reshaped parallelogram in the deformed configuration. Accordingly, an alternative grid basis function over the particle domain is constructed by a standard 4‐node finite element interpolation on the parallelogram. Effectiveness of the proposed modifications is demonstrated using several large deformation solid mechanics problems. Copyright © 2011 John Wiley & Sons, Ltd.     

On the mechanical behavior of a functionally graded micro-beam subjected to a thermal moment and nonlinear electrostatic pressure

In the present work, mechanical behavior of a functionally graded cantilever micro-beam subjected to a nonlinear electrostatic pressure and temperature changes has been studied. It has been assumed that the top surface is made of pure metal and the bottom surface from a metal–ceramic mixture. The ceramic constituent percent of the bottom surface varies from 0% to 100%. In addition to the Volume Fractional Rule of material, exponential function has been used for representation of continuous gradation of the material properties through micro-beam thickness. Attention being paid to the ceramic constituent percent of the bottom surface, five different types of FGM micro-beams have been investigated. Nonlinear integro-differential thermo-electro mechanical equation based on Euler–Bernoulli beam theory has been derived and solved using Step-by-Step Linearization Method and Finite Difference Method. The effects of temperature changes and the electrostatic pressure on the deflection and stability of FGM micro-beams having various amounts of the ceramic constituent have been studied and normal stress distributions in the cross section along the beam thickness have been given and compared with a classic metal beam.     

Parametric instability of functionally graded beams with an open edge crack under axial pulsating excitation

This paper studies the parametric instability of functionally graded beams with an open edge crack subjected to an axial pulsating excitation which is a combination of a static compressive force and a harmonic excitation force. It is assumed that the materials properties follow an exponential variation through the thickness direction. Theoretical formulations are based on Timoshenko beam theory and linear rotational spring model. The governing equations of motion are derived by using Hamilton’s principle and transformed into a set of Mathieu equations through Galerkin’s procedure. The natural frequencies with different end supports are obtained. The boundary points on the unstable regions are determined by using Bolotin’s method. Numerical results are presented to highlight the influences of crack location, crack depth, material property gradient, beam slenderness ratio, compressive load, and boundary conditions on both the free vibration and parametric instability behaviors of the cracked functionally graded beams.     

Influence of transverse shear on stochastic instability of symmetric cross-ply laminated plates

The dynamic instability problem of symmetrically laminated cross-ply plates, compressed by time-dependent stochastic membrane forces, is investigated. The effect of shear deformation is included in the formulation. By using the direct Liapunov method, bounds of the almost sure instability of cross-ply plates are obtained. Furthermore, it is shown how the viscous damping coefficient, variances of the stochastic forces, ratio of the principal lamina stiffnesses, number of layers, plate aspect ratio, and cross-ply ratio influence the instability regions. A special attention is given to the proper choice of two shear correction factors of the laminated plate. Numerical calculations are performed for the Gaussian process with a zero mean and variance σ² as well as for the harmonic process with an amplitude A.     

六角星型穹顶结构易损性分析

基于结构本身构型的易损性理论与结构失效机理相结合,分析了六角星型穹顶结构的易损性及杆件在荷载作用下的应力。结果表明,结构应力较大的杆件与易损性分析的失效杆件有对应关系,通过直接计算应力较大杆件的易损性参数,找到各种失效模式,可判断结构易损性。通过分析在反应谱拟合人工波和El Centro波作用下结构的失效模式,求得导致结构破坏的地震峰值加速度,研究了易损性特征参数与结构失效模式的关系。结果表明,结构连接能力小,易损性指数小时,结构呈现强度破坏,随着易损性指数的增大,结构失效模式由强度破坏转变为动力失稳。     

电网暂态相继失稳风险评估及协调阻断方法研究

以跨区互联电网为背景,以阻断电网发生暂态相继失稳、降低发生大停电事故风险、减少系统失稳控制代价为目的,提出了一种基于多代理技术的电网暂态相继失稳协调阻断方法。该方法首先基于确定性和风险分析方法,搜索多种工况下电网发生严重故障导致系统功角失稳情况后在相继事件作用下可能发生的暂态相继失稳模式及其事故链。然后,基于EEAC分群理论对控制策略进行搜索,解决不同失稳模式下的控制策略冲突问题,利用EEAC量化分析工具对不同控制措施进行排序。最后,以系统总风险最小为目标对预防控制和紧急控制进行协调优化。仿真验证了该方法的可行性。