Bond rolling resistance and its effect on yielding of bonded granulates by DEM analyses

A discrete element modelling of bonded granulates and investigation on the bond effect on their behaviour are very important to geomechanics. This paper presents a two‐dimensional (2‐D) discrete element theory for bonded granulates with bond rolling resistance and provides a numerical investigation into the effect of bond rolling resistance on the yielding of bonded granulates. The model consists of mechanical contact models and equations governing the motion of bonded particles. The key point of the theory is that the assumption in the original bond contact model previously proposed by the authors (55th CSCE‐ASCE Conference, Hamilton, Ont., Canada, 2002; 313–320; J. Eng. Mech. (ASCE) 2005; 131 (11):1209–1213) that bonded particles are in contact at discrete points, is here replaced by a more reliable assumption that bonded particles are in contact over a width. By making the idealization that the bond contact width is continuously distributed with the normal/tangential basic elements (BE) (each BE is composed of spring, dashpot, bond, slider or divider), we establish a bond rolling contact model together with bond normal/tangential contact models, and also relate the governing equations to local equilibrium. Only one physical parameter β needs to be introduced in the theory in comparison to the original bond discrete element model. The model has been implemented into a 2‐D distinct element method code, NS2D. Using the NS2D, a total of 86 1‐D, constant stress ratio, and biaxial compressions tests have been carried out on the bonded granular samples of different densities, bonding strengths and rolling resistances. The numerical results show that: (i) the new theory predicts a larger internal friction angle, a larger yielding stress, more brittle behaviour and larger final broken contact ratio than the original bond model; (ii) the yielding stress increases nonlinearly with the increasing value of β, and (iii) the first‐yield curve (initiation of bond breakage), which define a zone of none bond breakage and which shape and size are affected by the material density, is amplified by the bond rolling resistance in analogous to that predicted by the original bond model. Copyright © 2006 John Wiley & Sons, Ltd.     

The Equatorial Atlantic Mid-Ocean Channel: An Ultra High-Resolution Image of Its Burial History Based on TOPAS Profiles

Multibeam bathymetric and ultra high-resolution seismic data reveal that the distal course of the Equatorial Atlantic Mid-Ocean Channel (EAMOC) extends further east and south than was previously known, and is controlled by the presence of morphologic highs related to the Fernando de Noronha Fracture Zone. Distal course of the EAMOC is buried by sediments, and does not have bathymetric expression on the seafloor. The channel fill consists of three seismic sequences, suggesting that the recent geological evolution of the channel is composed of successive phases of decreasing sedimentary activity that finally resulted in its complete burial. Tectonic and volcanic activity related to the Fernando de Noronha Fracture Zone and Ridge, together with the effect of strong pulses of the Antarctic bottom water current during the upper Pliocene are suggested to have contributed to the progressive burial and the final abandonment of the EAMOC.     

Analysis of seabed instability using element free Galerkin method

Wave-induced seabed instability, either momentary liquefaction or shear failure, is an important topic in ocean and coastal engineering. Many factors, such as seabed properties and wave parameters, affect the seabed instability. A non-dimensional parameter is proposed in this paper to evaluate the occurrence of momentary liquefaction. This parameter includes the properties of the soil and the wave. The determination of the wave-induced liquefaction depth is also suggested based on this non-dimensional parameter. As an example, a two-dimensional seabed with finite thickness is numerically treated with the EFGM meshless method developed early for wave-induced seabed responses. Parametric study is carried out to investigate the effect of wavelength, compressibility of pore fluid, permeability and stiffness of porous media, and variable stiffness with depth on the seabed response with three criteria for liquefaction. It is found that this non-dimensional parameter is a good index for identifying the momentary liquefaction qualitatively, and the criterion of liquefaction with seepage force can be used to predict the deepest liquefaction depth.     

On the parametric resonance of container ships

This work deals with parametric resonance which poses a great danger especially for container ships sailing in following or head seas. Important parameters that are effective in roll resonance are pointed out. For this purpose, a containership is taken as an example to analyze its stability in longitudinal waves based on the method worked out by American Bureau of Shipping (ABS). Unfavorable sailing conditions such as heading and speed, which directly depend on the environmental conditions, have been determined for this particular ship. These conditions may be reported to the master to guide him to keep his ship out of parametric resonance zones. Numerical details of the procedure have been worked out and provided as well.     

费尔干纳盆地油气资源潜力与勘探新领域

费尔干纳盆地是中亚地区的一个老油区,虽然经过了多年的勘探和开发,但仍有较大的资源潜力。主要勘探新领域有：寻找非构造油气藏（隐蔽油气藏）、老油田内部滚动勘探、钻探古中生界深层。费尔干纳盆地此前的钻探目标均是围绕大构造背景上的背斜圈闭进行,非背斜构造的研究和钻探很少。笔者研究认为费尔干纳盆地寻找非背斜圈闭油藏前景广阔;在对老油田内部钻采、试油资料的详细分析后,认为老油田内部主力逆断层的下盘和背斜构造的侧翼具有较大的资源潜力;盆地的古中生界不仅可以新生古储,而且其本身也可以生油,在盆地局部隆起及边部都存在古中生界成藏的条件。     

冲击压实技术在路基工程中的应用研究

通过介绍冲击压实机基本原理,分析冲击压实技术特点,结合工程实例,表明冲击压实技术具有减少路基工后沉降、提高路基整体强度及加固软弱地基作用效果显著,同时填石路堤施工工艺的改进和压实标准进行了研究.     

Stability and capsizing analysis of nonlinear ship rolling in wind and stochastic beam seas

Considering the actual seaway condition, stability and capsizing of nonlinear ship rolling system in stochastic beam seas is of significant importance for voyage safety. Safe zone are defined in the phase space plan of the unperturbed Hamilton system to qualitatively distinguish ship motions as capsize and noncapsize. Capsize events are defined by solutions passing out of the safe zone. The probability of such an occurrence is studied by virtue of the random Melnikov function and the concept of phase space flux. In this paper, besides conventional wave excitation, the effect of wind load is also taken into account. The introduction of wind load will lead to asymmetry, in other words, it transforms the symmetric heteroclinic orbits into asymmetric homoclinic orbits. For asymmetric dynamical system, the orbital analytic solutions and its power spectrum are not readily available, and the technique of discrete time Fourier transformation (DTFT) is used. In the end, as verification of theoretical critical significant wave height, capsizing probability contour diagram is generated by means of numerical simulation. The contour diagram shows that these analytical methods provide reliable and predictive results about the likelihood of a vessel capsizing in a given seaway condition.     

卫星地面站雷电直击效应防护设计探讨

卫星地面站雷电防护工程通常采用接闪杆作为天线主体的雷电直击效应防护措施,接闪杆的高度不仅影响其保护范围,而且影响其截闪概率。通过计算年预计雷击次数对截闪概率进行量化分析,结果表明,截闪概率近似与接闪杆高度平方成正比,采用过高的接闪杆将增大地面站遭受雷击电磁脉冲损坏的风险。为优化接闪杆设计,定义了保护体积的概念,并利用折线法与滚球法分别计算了三维立体空间内的保护范围。结果表明:接闪杆的保护范围与高度呈现非线性相关,当接闪杆超过一定高度(折线法超过30m,滚球法超过0.8倍滚球半径)后,对保护范围的影响十分有限;当接闪杆高度低于0.4倍滚球半径时,滚球法保护范围较大,反之则折线法保护范围较大。对接闪杆接闪瞬间周边的磁场强度分析结果表明,无屏蔽环境下地面站电子系统与接闪杆的常规距离远小于两者的理论安全距离,实际工程中难以通过增大接闪杆与卫星地面站的间距消除雷击电磁脉冲危害。为降低这一风险,卫星地面站直击雷防护应优先采用天线自带接闪杆的方式,条件不具备时也应尽量避免采用单支高大接闪杆,可选取适当的计算方法,采用多支较低接闪杆共同防护的方案。     

不规则三角网数字水深模型缓冲面快速构建的滚动球加速优化算法

针对TIN_DDM缓冲面构建与应用中存在的数据类型特殊、算法效率与模型精度不匹配的问题,本文将滚动球模型应用扩展至TIN_DDM缓冲面的构建过程。在分析滚动球模型构建精度局限的基础上,建立了滚动球半径关联的滚动球模型整体精度控制方法;结合大数据量TIN_DDM缓冲面多次构建的应用效率需求,阐明了关键采样点与滚动球半径对TIN_DDM缓冲面构建效率的影响规律;设计了TIN_DDM缓冲面构建关键采样点的判定准则,建立了关键采样点与滚动球半径的数值关联关系;提出了一种基于滚动球加速优化模型的TIN_DDM缓冲面快速构建算法,算法时间复杂度为O(n)。试验结果表明:本文算法可实现任意缓冲半径条件下TIN_DDM缓冲面的多次快速构建,且算法精度控制在2σ内。     

耐压柱壳参数化设计与灵敏度分析

为提高耐压柱壳设计效率,设计了耐压柱壳参数化分析流程。研究了有限元分析所涉及的材料属性、载荷施加、边界条件设置等内容,确定了采用弧长法分析耐压柱壳稳定性。利用Python语言对于ABAQUS软件进行了二次开发,利用Isight软件实现了ABAQUS的集成,实现了耐压柱壳有限元分析模型的网格自动划分、自动分析计算等。选择样本点进行参数化分析,利用响应面模型对于样本点进行了拟合,得到了具有较高拟合精度、满足工程需要的近似模型,进行了设计变量的灵敏度分析。研究结果表明:参数化分析流程可实现耐压柱壳的自动分析、近似模型及灵敏度分析,可降低耐压柱壳分析难度,均可提高耐压柱壳设计效率。