恒定水深拖拉铺管管线的三维大挠度静态应力分析

海洋管线具有复杂的工程结构,在恶劣的海洋环境中,承受着比陆地管线更为复杂的载荷。为了保证管线安全工作,需对其进行准确的应力分析。本文应用有限元法对恒定水深拖拉铺管的管线内力、应力及位移进行了计算,并将结果与已有的计算结果进行对比,进一步分析了各种海洋环境因素对管线弯曲效应的影响,取得了有一定实用性的成果,可供海洋拖拉铺管施工时参考。     

A new distributed approximation algorithm for constructing minimum connected dominating set in wireless ad hoc networks

In recent years, constructing a virtual backbone by nodes in a connected dominating set (CDS) has been proposed to improve the performance of ad hoc wireless networks. In general, a dominating set satisfies that every vertex in the graph is either in the set or adjacent to a vertex in the set. A CDS is a dominating set that also induces a connected sub‐graph. However, finding the minimum connected dominating set (MCDS) is a well‐known NP‐hard problem in graph theory. Approximation algorithms for MCDS have been proposed in the literature. Most of these algorithms suffer from a poor approximation ratio, and from high time complexity and message complexity. In this paper, we present a new distributed approximation algorithm that constructs a MCDS for wireless ad hoc networks based on a maximal independent set (MIS). Our algorithm, which is fully localized, has a constant approximation ratio, and O(n) time and O(n) message complexity. In this algorithm, each node only requires the knowledge of its one‐hop neighbours and there is only one shortest path connecting two dominators that are at most three hops away. We not only give theoretical performance analysis for our algorithm, but also conduct extensive simulation to compare our algorithm with other algorithms in the literature. Simulation results and theoretical analysis show that our algorithm has better efficiency and performance than others. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of vibration condition and inter-particle frictions on the packing of uniform spheres

We present a numerical study of the packing of uniform spheres under three-dimensional vibration using the discrete element method (DEM), focusing on the effects of vibration condition (amplitude and frequency) and inter-particle frictions (sliding and rolling frictions). The results are analysed in terms of packing density, coordination number (CN), radial distribution function (RDF) and pore structure. It is shown that increasing either the vibration amplitude or frequency causes packing density to increase initially to a maximum and then decrease. Both vibration frequency and amplitude should be considered to characterize the effect of vibration process on packing structure. The sliding and rolling frictions between particles can decrease packing density since they dissipate energy, although the effect of rolling friction is less significant. In line with the change of packing density, microstructural properties such as CN, RDF and pore distribution also change: a looser packing often corresponds to smaller CN, less peaked RDF and larger but more widely distributed pores.     

潜油电机碟形弹簧的动力学分析

为了降低潜油电泵机组的振动对止推轴承性能的影响,在潜油电机中节和下节的止推轴承静块底部安装了蝶形弹簧。用有限元方法进行模态分析,确定了蝶形弹簧的主振型和固有频率,然后进行瞬态动力学分析,求解蝶形弹簧在一定载荷下的应力和位移。依此设计的蝶形弹簧将进一步延长止推轴承的使用寿命。     

基于遗传算法的土钉支护结构优化设计研究

通过建立三维有限元模型,对土钉支护的变形和受力性能进行分析,得出土钉力的合理分布。在此基础上,考虑土钉支护的水平位移,采用遗传算法,对土钉支护的结构优化设计进行研究,建立了土钉支护结构的优化设计数学模型,并编制了相应的计算程序。通过算例分析,并与基于极限平衡分析的优化结果相比较,得出合理的土钉支护结构设计的参考结论。     

高压射流冲击破碎岩石的有限元计算

高压射流冲击破岩是一个复杂的非线性问题。通过MSC．Marc建立模型，分别使用动态接触作为非线性冲击载荷模拟高压水射流冲击岩石。通过动力计算分析，根据岩石内部应力的变化使用Hoffman失效准则研究了岩石的破碎过程。分析表明，增加射流冲击速度可以提高射流破碎岩石的效率，当射流速度迭到某一临界值时，射流水锤作用使得岩石发生大块破碎。     

微量元素对管道焊缝性能的改善

在焊条中添加微量元素Ce、Y、Ca、Ba和Zr，有利于改善石油天然气管道焊缝的金属性能，俄罗斯专家对此做了一系列实验和研究。结果表明添加微量元素有利于提高焊缝金属平面应变断裂韧性KIC，提高裂纹张开位移δc，减小裂纹扩展速率dα／dN改善焊缝金属的组织结构。通过大量的试验和研究，俄罗斯焊接学者确定了焊缝中微量元素的最佳含量，并建立了相关参数的数学模型。     

Full Complex Amplitude Digital Holograms： Design, Fabrication and Optical Characterization

Diffractive optical elements have a large number of industrial applications, such as beam shaping and optical filtering. Traditionally, these elements modulate the phase of the incoming light or its amplitude, but not both. To overcome this limitation, full complex-amplitude modulation diffractive optical elements were developed. Well-established integrated circuit fabrication steps were employed to fabricate the devices with high precision. Using this approach, the new element‘s optical performances are improved also for near field operations. With this device it is possible to obtain 100% efficient spatial filtering and low noise reconstructed images.     

Three dimensional boundary element analysis of internal cracks under sliding contact load with a spherical indenter

Using boundary element based three dimensional modelling for linear fracture mechanics, we present an analysis of cracking in a homogeneous medium subject to contact load. The proposed iterative solution procedure allows a simultaneous treatment of a reasonable number of partially closed cracks. It is shown that the most probable direction of propagation of a vertical internal crack is strongly dependent on its size compared to the contact radius and its location with respect to the axis of maximum normal load.     

A p‐version,first order shear deformation,finite element for geometrically non‐linear vibration of curved beams

A p‐version, hierarchical finite element for curved, moderately thick, elastic and isotropic beams is introduced. The convergence properties of the element are analysed and some results are compared with results published elsewhere or calculated using a commercial finite element package. It is verified that, with the proposed element, shear locking does not affect the computation of the natural frequencies and that low dimensional, accurate models are obtainable. Geometrically non‐linear vibrations due to finite deformations, which occur for harmonic excitations with frequencies close to the first three natural frequencies of vibration, are investigated using Newmark's method. The influence of the thickness, longitudinal inertia and curvature radius on the dynamic behaviour of curved beams are studied. Copyright © 2004 John Wiley & Sons, Ltd.