基于可靠性的海洋立管疲劳安全系数研究

综合考虑了立管疲劳安全系数取值的相关因素——立管的安全等级、设计寿命、检验周期、载荷和损伤计算方法等的不确定性,提出了基于可靠度的疲劳安全系数确定方法,筛选了用于计算波致疲劳和VIV(涡激振动)疲劳的随机变量,给出了立管波致疲劳与VIV疲劳安全系数的计算流程,并以某SCR(钢悬链线立管)为例进行了安全系数计算。结果表明,该方法的计算结果优于传统的安全系数确定方法,尤其适合于特殊工程方案或新颖设计的立管疲劳校核。     

西部戈壁荒漠区大极距激电找矿试验分析

本文主要介绍在西部戈壁荒漠区东天山土屋铜矿上进行大极距激电方法的试验效果,讨论各参数变化对测量结果的不同影响,阐述在该类地区进行大极距激电工作时应采取的原则和措施。     

Numerical Prediction of Induced Pressure and Lift of the Planing Surfaces

This paper discusses the numerical prediction of the induced pressure and lift of the planing surfaces in a steady motion based on the potential flow solver as well as the spray drag by use of the practical method.The numerical method for computation of the induced pressure and lift is potential-based boundary element method.Special technique is identified to present upwash geometry and to determine the spray drag.Numerical results of a planing flat plate and planing craft model 4666 are presented.It is shown that the method is robust and efficient and the results agree well with the experimental measurements with various Froude humors.     

燕山水库的主要环境工程地质问题

本文在简要介绍燕山水库工程地质环境的基础上,分析论述了可能产生的环境工程地质问题。指出水库淹没及浸没、水库诱发地震、坝基渗透变形及膨胀土体稳定问题是该水库的主要环境工程地质问题,并提出了进一步研究的途径。     

Ekman drift and vortical structures

In this article, the authors study the influence of a constant wind on the displacement of a vortex. The well known Ekman current develops in the surface layer and is responsible for a transport perpendicular to the wind: the Ekman drift.An additional process is, however, evidenced, whose importance is as strong as the Ekman drift. There indeed exists a curl of the wind-driven acceleration along isopycnic surfaces when they are spatially variable (they enter and leave the depth where the wind stress acts), which generates potential vorticity anomalies. This diabatic effect is shown to generate potential vorticity anomalies which acts on the propagation of vortical waves and non linear vortices.It is shown that this effect drastically reduces the effect of the Ekman drift for linear waves and surface intensified vortices, while extending its effect to subsurface vortices. It also generates along wind propagation, whose sign depends on the vortex characteristics.     

北半球环状模和东北冷涡与我国东北夏季降水关系分析

利用国家气象信息中心提供的1951～2004年全国160个测站月平均降水资料和欧洲中心提供的ERA-40再分析资料,对近50多年东北地区夏季降水、东北冷涡与前期北半球环状模和海温的关系进行了统计分析,定义了一个夏季(6～8月)东北冷涡强度指数(NECVI)。结果表明:NECVI能够较好表征东北低涡的气候效应;夏季东北冷涡强度与降水存在显著的正相关,东北冷涡强年,降水偏多,前期2月北半球环状模(NAM)偏弱;东北冷涡偏弱年,降水偏少,前期2月NAM偏强。此外,夏季东北冷涡与前期的中国近海海温存在显著的负相关,前期NAM和中国近海海温的异常可以作为夏季东北冷涡异常的一个前兆信号,进而为东北地区夏季降水异常的预测提供参考依据。     

Structure and collapse of three-dimensional magnetic neutral points

Abstract

The structure and collapse of linear three-dimensional magnetic neutral points is studied by varying the four parameters (p, q,j_|,j_⊥ ) that define, in general, the linear field of a neutral point. The effect of these parameters on both the skeleton structure (i.e. the fan and spine) and the actual field line structure of the null is considered. It is found that one current component (j_⊥ ) causes the skeleton structure of the null to fold up from its potential state, whereas the other current component (j _|;) causes the field lines to bend. The two other parameters (p,q) determine the potential structure of the null and cause the null to transform from a three-dimensional null to a two-dimensional null and from a positive (type B) null to a negative (type A) null.

To investigate the collapse of three-dimensional nulls, solutions to the linear, low-β ideal magnetohydrodynamic equations are found. It is found that three-dimensional null points can collapse if the field line foot-points are free and energy can propagate into the system.     

Preconditioned IDR(s) iterative solver for non‐symmetric linear system associated with FEM analysis of shallow foundation

Non‐associated flow rule is essential when the popular Mohr–Coulomb model is used to model nonlinear behavior of soil. The global tangent stiffness matrix in nonlinear finite element analysis becomes non‐symmetric when this non‐associated flow rule is applied. Efficient solution of this large‐scale non‐symmetric linear system is of practical importance. The standard Krylov solver for a non‐symmetric solver is Bi‐CGSTAB. The Induced Dimension Reduction [IDR(s)] solver was proposed in the scientific computing literature relatively recently. Numerical studies of a drained strip footing problem on homogenous soil layer show that IDR(s = 6) is more efficient than Bi‐CGSTAB when the preconditioner is the incomplete factorization with zero fill‐in of global stiffness matrix K_ep (ILU(0)‐K_ep). Iteration time is reduced by 40% by using IDR(s = 6) with ILU(0)‐K_ep. To further reduce computational cost, the global stiffness matrix K_ep is divided into two parts. The first part is the linear elastic stiffness matrix K_e, which is formed only once at the beginning of solution step. The second part is a low‐rank matrix Δ, which is re‐formed at each Newton–Raphson iteration. Numerical studies show that IDR(s = 6) with this ILU(0)‐K_e preconditioner is more time effective than IDR(s = 6) with ILU(0)‐K_ep when the percentage of yielded Gauss points in the mesh is less than 15%. The total computation time is reduced by 60% when all the recommended optimizing methods are used. Copyright © 2013 John Wiley & Sons, Ltd.     

准各向异性粘弹介质地震波的数字仿真

本文论述准各向异性粘弹波动方程有限元数值解地震波响应的原理与计算方法,并给出地震衰减因子与方程中粘滞系数的计算关系式。列出了所研制的地面记录地震剖面与井中记录垂直地震剖面,以及波场时间切片图、散度与旋度图、应变能与动能的时间切片图。本方法适于任意分层形态且层间物性参数为强间断的实际地震剖面的仿真,旨在研究正问题以实现反问题。