Parkes problems revisited - Application of response number

Response number R-n(n), proposed in [3, 4], is an important independent dimensionless number for the dynamic response of structures [2]. In this paper, the response number is applied to the dynamic plastic response of the well-known Parkes' problem, i.e., beams struck by concentrated mass.

Damage evaluation and damage localization of rock

Knowledge of damage accumulation and corresponding failure evolution are prerequisite for effective maintenance of civil engineering so as to avoid disaster. Based on statistical mesoscopic damage mechanics, it was revealed that there are three stages in the process of deformation, damage and failure of multiscale heterogeneous elastic-brittle medium. These are uniformly distributed damage, localized damage and catastrophic failure. In order to identify the transitions from scattering damage to macroscopically localized one, a condition for damage localization was given. The experiments of rock under uniaxial compression with the aid of observations of acoustic emission and speckle correlation do support the concept of localization. This provides a potential approach to properly evaluate damage accumulation in practice. In addition, it is found in the experiments that catastrophic failure displays critical sensitivity. This gives a helpful clue to the prediction of catastrophic failure. (C) 2004 Elsevier Ltd. All rights reserved.

第16届国际理论和应用力学大会

<正> 1.一般情况 国际理论和应用力学联合会(IUTAM)召开的第16届国际理论和应用力学大会(ICTAM),于1984年8月20—25日在丹麦的哥本哈根举行。会议参加者共700余人。会议除开幕大会报告(Alfven:空间研究和宇宙中流体介质力学的新方法)和闭幕大会报告(Keller:力学研究的进展和问题)外,还按分组报告、分组开场报告,一般报告和墙报等多种方式进行,大会重点主题是一个:“海洋与结构的波相互作用”, “多组分介质的微

在半无限双层含水层中排水管列的渗流计算

<正> (一) 前言 地表水经过下伏土层渗流到水平排水管列(成无限链状分布)的研究,是合理的进行给水,盐田冲洗,排水等工程的理论基础。维捷尔尼科夫用复变数函数保角映射的方法,得出一系列排水管渗流计算公式。不足的是他只考虑了均质上的情况,然而实际的地质条件表明:有时下伏土层不是均质的,而是由渗透系数为K_1(上层)和K_2(下层)的双层土

变形过程中纳米金属镍的微结构演变

利用透射电镜对冷轧变形所致纳米结构金属镍的微结构组织演变特征进行了研究。结果表明，经过轧制变形后，纳米晶的平均晶粒尺寸为50-70mm，有少量位错结构，但没有发现位错堆积缠结；在晶界处及附近有台阶界面结构，以及与台阶形状相对应的应力场衬度。在变形后期，可以靠晶界发射不全位错从而促使层错生成，并依赖层错尺寸长大（即层错界面位错）的运动进行。而当层错尺寸长大时，其前沿局部变形应力逐渐变大，直至该应力大到一定值时，位错停止运动，层错尺寸也不再长大，并留下了台阶结构。

大射电望远镜馈源支撑系统建模与仿真

根据500m口径球面射电望远镜(FAST)原始设计方案,基于多体系统动力学建模方法,建立了馈源支撑系统的机械模型,并对此模型进行了动力响应分析,为此项目最终方案的选择提供了参考。

天然气水合物分解对地层和管道稳定性影响的数值模拟

利用ABAQUS有限元程序,对海底管道及其附近地层的应力和位移场随着水合物分解范围逐渐扩大的变化情况进行了数值模拟计算。结果表明,水合物分解对管道、地层的变形和应力分布的影响显著,随着水合物分解范围的扩大,管道和地层的变形显著扩大,管道由小变形逐渐变化为整体倾倒变形,即失稳。在工程设计中,为保证地层中管道的安全,应严格控制管道附近水合物的分解范围。

摄动有限体积法重构近似高精度的意义

研讨有限体积(FV)方法重构近似高精度的作用问题．FV方法中积分近似采用中点规则为二阶精度时，重构近似高精度(精度高于二阶)的意义和作用是一个有争议的问题．利用数值摄动技术"。0构造了标量输运方程的积分近似为二阶精度、重构近似为任意阶精度的迎风型和中心型摄动有限体积(PFV)格式．迎风 PFV格式无条件满足对流有界准则(CBC)，中心型PFV格式为正型格式，两者均不会产生数值振荡解．利用 PFV格式求解模型方程的数值结果表明：与一阶迎风和二阶中心格式相比，PFV格式精度高、对解的问断分辨率高、稳定性好、雷诺数的适用范围大，数值地"证实"重构近似高精度和PFV格式的实际意义和好处．

低渗透多孔介质和微管液体流动尺度效应

常规多孔介质和圆管中液体的流动都遵循Hagen_Poisseuille定理 ,即液体流速和压力梯度成正比 .而对于低渗透多孔介质中液体渗流 ,存在拟启动压力梯度 ,即存在微尺度效应 .那么对于微圆管 ,由于流动的通道具有较小的空间尺度 ,因此在物理本质上 ,也应该存在微尺度效应 ,但由于目前实验手段的局限 ,还未能证明这一点 .本文通过对比和分析低渗透多孔介质和微管中液体流动规律 ,预测了微管中液体流动出现微尺度效应的尺度约为 1微米

Rarefied gas dynamics: fundamentals, simulations and micro flows

Hydroelectric Voltage Generation Based On Water-Filled Single-Walled Carbon Nanotubes

A DFT/MD mutual iterative method was employed to give insights into the mechanism of voltage generation based on water-fitted single-walled carbon nanotubes (SWCNTs). Our calculations showed that a constant voltage difference of several mV would generate between the two ends of a carbon nanotube, due to interactions between the water dipole chains and charge carriers in the tube. Our work validates this structure of a water-fitted SWCNT as a promising candidate for a synthetic nanoscale power cell, as well as a practical nanopower harvesting device at the atomic level. 

A Dynamic Model For Ice-Induced Vibration Of Structures

A dynamic model for the ice-induced vibration (IIV) of structures is developed in the present study. Ice properties have been taken into account, such as the discrete failure, the dependence of the crushing strength on the ice velocity, and the randomness of ice failure. The most important prediction of the model is to capture the resonant frequency lock-in, which is analog to that in the vortex-induced vibration. Based on the model, the mechanism of resonant IIV is discussed. It is found that the dependence of the ice crushing strength on the ice velocity plays an important role in the resonant frequency lock-in of IIV. In addition, an intermittent stochastic resonant vibration is simulated from the model. These predictions are supported by the laboratory and field observations reported. The present model is more productive than the previous models of IIV.

Surface-enhanced resonance Raman scattering spectroscopy of single R6G molecules

Surface-enhanced resonance Raman scattering (SERRS) of Rhodamine 6G (R6G) adsorbed on colloidal silver clusters has been studied. Based on the great enhancement of the Raman signal and the quench of the fluorescence, the SERRS spectra of R6G were recorded for the samples of dye colloidal solution with different concentrations. Spectral inhomogeneity behaviours from single molecules in the dried sample films were observed with complementary evidences, such as spectral polarization, spectral diffusion, intensity fluctuation of vibrational lines and even "breathing" of the molecules. Sequential spectra observed from a liquid sample with an average of 0.3 dye molecules in the probed volume exhibited the expected Poisson distribution for actually measuring 0, 1 or 2 molecules. Difference between the SERRS spectra of R6G excited by linearly and circularly polarized light were experimentally measured.