Effects of petrophysical parameters on attenuation and dispersion of seismic waves in the simplified poroelastic theory: Comparison between the Biot's theory and viscosity‐extended theory

The simplified macro‐equations of porous elastic media are presented based on Hickey's theory upon ignoring effects of thermomechanical coupling and fluctuations of porosity and density induced by passing waves. The macro‐equations with definite physical parameters predict two types of compressional waves (P wave) and two types of shear waves (S wave). The first types of P and S waves, similar to the fast P wave and S wave in Biot's theory, propagate with fast velocity and have relatively weak dispersion and attenuation, while the second types of waves behave as diffusive modes due to their distinct dispersion and strong attenuation. The second S wave resulting from the bulk and shear viscous loss within pore fluid is slower than the second P wave but with strong attenuation at lower frequencies. Based on the simplified porous elastic equations, the effects of petrophysical parameters (permeability, porosity, coupling density and fluid viscosity) on the velocity dispersion and attenuation of P and S waves are studied in brine‐saturated sandstone compared with the results of Biot's theory. The results show that the dispersion and attenuation of P waves in simplified theory are stronger than those of Biot's theory and appear at slightly lower frequencies because of the existence of bulk and shear viscous loss within pore fluid. The properties of the first S wave are almost consistent with the S wave in Biot's theory, while the second S wave not included in Biot's theory even dies off around its source due to its extremely strong attenuation. The permeability and porosity have an obvious impact on the velocity dispersion and attenuation of both P and S waves. Higher permeabilities make the peaks of attenuation shift towards lower frequencies. Higher porosities correspond to higher dispersion and attenuation. Moreover, the inertial coupling between fluid and solid induces weak velocity dispersion and attenuation of both P and S waves at higher frequencies, whereas the fluid viscosity dominates the dispersion and attenuation in a macroscopic porous medium. Besides, the heavy oil sand is used to investigate the influence of high viscous fluid on the dispersion and attenuation of both P and S waves. The dispersion and attenuation in heavy oil sand are stronger than those in brine‐saturated sandstone due to the considerable shear viscosity of heavy oil. Seismic properties are strongly influenced by the fluid viscosity; thus, viscosity should be included in fluid properties to explain solid–fluid combination behaviour properly.     

在役公路梁式桥综合震害等级预测研究

为客观预测在役公路梁式桥综合震害状况,考虑在役桥梁在运营期存在的病害问题,从压力和承压两方面建立在役公路梁式桥综合震害预测评价指标体系。以桥梁作为承灾体,建立在役公路梁式桥综合震害物元可拓模型,运用熵权法进行赋权,确定桥梁的综合震害状况。以一座在役梁式桥为例,运用上述模型确定算例的综合震害状况。研究结果表明,该桥的综合震害等级为Ⅲ级,破坏等级中等,且根据结果分析影响桥梁震害程度的主要影响因素;该模型通过对多个指标关联系数的综合分析来评价在役梁式桥的综合震害等级,极大地提高了该模型评估的准确率及可靠性,为桥梁震害等级的预测提供一定的参考,对提升桥梁综合抗震能力具有积极意义。     

Configuration analysis of deepwater S-lay pipeline

The safety of offshore pipeline has drawn a great deal of attention during deepwater installation due to the combined actions of high external pressure, axial tension, and bending moment. Meanwhile, the pipeline configuration has a remarkable effect on the structural behaviour of the tube. The special studies focus on the deepwater S-lay technique in the present paper. The stiffened catenary theory is applied to establish the static equilibrium governing differential equation of a pipe element, and the solution equations of the total pipeline configuration from a lay-barge over a stinger to the seabed are derived. The numerical iteration method for solving pipeline configuration is described in detail, and the corresponding program is developed to conduct the analysis of effects of various parameters such as laying water depth, pipe diameter, thickness of concrete weighted coating layer, stinger length, control strain, and axial tension on pipeline configuration. The results show that the laying water depth, the submerged weight of the pipe, and the axial tension are the critical factors influencing pipeline configuration. In addition, geometrical parameters of the stinger such as length, radius, and shape have an important effect on the pipe-laying capacity of the vessel. The validity of the program is further verified by means of a comparison with results obtained from the commercial finite element software OFFPIPE.     

全球区位论、非场所理论与襄樊都市区建设

依据全球区位论和非场所理论,运用定性定量相结合的方法,深入分析了襄樊都市区建设的背景、意义和现状条件,并在襄樊都市区中心城市建设,城市化进程和都市区的基本框架构筑,人流、物流和信息流快速通道建设,产业结构调整和企业竞争力培育,都市区内各县市协作以及经济社会环境持续发展等方面提出了相应的对策。     

湖南省地市经济差异综合评价及分区研究

文章运用主成分分析的数理统计方法,选择14项指标,对湖南省地市经济发展水平的区域差异进行了综合评价和区域聚类划分。评价结果表明:湖南各地市的经济发展水平存在明显差异,可划分为5个层次。在此基础上,文章还提出了实现地市经济协调发展的对策:重视经济发展效率;坚持"点-轴"开发模式,优化空间开发结构;加快长株潭发展极产业一体化发展步伐等。     

The statistical properties of Λ cold dark matter halo formation

We present a comparison of the statistical properties of dark matter halo merger trees extracted from the Millennium Simulation with Extended Press–Schechter (EPS) formalism and the related galform Monte Carlo method for generating ensembles of merger trees. The volume, mass resolution and output frequency make the Millennium Simulation a unique resource for the study of the hierarchical growth of structure. We construct the merger trees of present-day friends-of-friends groups and calculate a variety of statistics that quantify the masses of their progenitors as a function of redshift, accretion rates, and the redshift distribution of their most recent major merger. We also look in the forward direction and quantify the present-day mass distribution of haloes into which high-redshift progenitors of a specific mass become incorporated. We find that the EPS formalism and its Monte Carlo extension capture the qualitative behaviour of all these statistics, but as redshift increases they systematically underestimate the masses of the most massive progenitors. This shortcoming is worst for the Monte Carlo algorithm. We present a fitting function to a scaled version of the progenitor mass distribution and show how it can be used to make more accurate predictions of both progenitor and final halo mass distributions.     

Neutralino annihilations and the gas temperature in the dark ages

Assuming that the dark matter is entirely made up of neutralinos, we re-visit the role of their annihilation on the temperature of diffuse gas in the high-redshift universe  ( z > 10)  , before the formation of luminous structures. We consider neutralinos of particle mass 36 and 100 GeV. The former is able to produce  ∼7  e ⁻ e ⁺  particles per annihilation through the fremionic channel, and the latter ∼53 particles assuming a purely bosonic channel. High-energy   e ⁻ e ⁺  particles up-scatter the cosmic microwave background (CMB) photons into higher energies via the inverse-Compton scattering. The process produces a power-law   e ⁻ e ⁺  energy spectrum of index −1 in the energy range of interest, independent of the initial energy distribution. The corresponding energy spectrum of the up-scattered photons is a power law of index −1/2, if absorption by the gas is not included. The scattered photons photoheat the gas by releasing electrons which deposit a fraction (14 per cent) of their energy as heat into the ambient medium. For uniformly distributed neutralinos, the heating is insignificant. The effect is greatly enhanced by the clumping of neutralinos into dense haloes. We use a time-dependent clumping model which takes into account the damping of density fluctuations on mass-scales smaller than  ∼10⁻⁶ M_⊙  . With this clumping model, the heating mechanism boosts the gas temperature above that of the CMB after a redshift of   z ∼ 30  . By   z ≈ 10  , the gas temperature is nearly 100 times its temperature when no heating is invoked. Similar increase is obtained for the two neutralino masses considered.