Regional gravity field modeling based on rectangular harmonic analysis

Regional gravity field modeling with high-precision and high-resolution is one of the most important scientific objectives in geodesy,and can provide fundamental information for geophysics,geodynamics,seismology,and mineral exploration.Rectangular harmonic analysis(RHA)is proposed for regional gravity field modeling in this paper.By solving the Laplace’s equation of gravitational potential in local Cartesian coordinate system,the rectangular harmonic expansions of disturbing potential,gravity anomaly,gravity disturbance,geoid undulation and deflection of the vertical are derived,and so are the formula for signal degree variance and error degree variance of the rectangular harmonic coefficients(RHC).We also present the mathematical model and detailed algorithm for the solution of RHC using RHA from gravity observations.In order to reduce the edge effects caused by periodic continuation in RHA,we propose the strategy of extending the size of computation domain.The RHA-based modeling method is validated by conducting numerical experiments based on simulated ground and airborne gravity data that are generated from geopotential model EGM2008 and contaminated by Gauss white noise with standard deviation of 2 mGal.The accuracy of the 2.5′×2.5′geoid undulations computed from ground and airborne gravity data is 1 and 1.4cm,respectively.The standard error of the gravity disturbances that downward continued from the flight height of 4 km to the geoid is only 3.1 mGal.Numerical results confirm that RHA is able to provide a reliable and accurate regional gravity field model,which may be a new option for the representation of the fine structure of regional gravity field.     

低周反复荷载作用下矩形钢管混凝土柱与钢梁连接节点的受力性能

本文进行了2种矩形钢管混凝土柱与钢梁连接节点——翼缘全螺栓(BFP)连接节点与外加强环(WFP-BW)连接节点在柱端低周反复荷载作用下的抗震性能试验,分析比较了这2类节点与焊接翼缘板(WFP)连接节点在不同轴压比下的滞回性能、强度与刚度退化、延性比与耗能比、破坏机理与破坏特征,得出了一些有参考价值的结论。     

反复荷载下矩形钢管混凝土柱的抗震性能Ⅱ:分析研究

文中首先提出了钢管与内填混凝土界面的粘结-滑移滞回模型，建立了考虑包兴格效应的钢材单轴滞回模型和考虑矩形钢管约束效应后内填混凝土的单轴应力-应变滞回模型。在截面纤维模型的基础上，建立了考虑界面粘结-滑移的矩形钢管混凝土柱分析模型，用Fortran语言编制了相应的全过程分析程序。对作者等完成的试件进行了滞回全过程数值模拟计算，分析与试验结果在荷载-位移和荷载-应变两种层次上进行了对比。之后，利用该分析程序对矩形钢管混凝土柱中有代表性的混凝土和钢单元应力-应变发展全过程进行了跟踪分析。最后，以典型试件为对象，分析了钢-混凝土界面切向粘结强度对柱滞回性能的影响。本文工作可为从事组合结构研究时提供参考。     

投影网格中的坐标确定及在台风数值试验中的应用

在数值计算中,对于已知经纬度的某点,需确定其在不同投影法得到的矩形网格中的具体位置坐标.导出在极射赤面投影、麦卡托圆柱投影和兰勃脱正形圆锥投影等算法中确定位置坐标的精确公式.通过台风路径预报对比试验表明:该方法能有效地减少计算误差的引入,具有较好的应用价值.     

Delineation of long-wavelength magnetic anomalies over central India by rectangular harmonic analysis

The method of rectangular harmonic analysis is applied to the geomagnetic field data from central India to isolate long wavelength magnetic anomalies associated with largescale crustal structures. The long-wavelength anomalies have accounted for approximately 20 % of the spatial variability of the residual magnetic field over the International Geomagnetic Reference Field. On the magnetic anomaly map, reflecting the surface expression of longwavelength anomalies, the Tapi-Narmada-Son zone is characterized by a feeble positive anomaly bounded by a strong negative anomaly. The anomaly pattern is believed to be caused by the large-scale undulation in Moho and related variations in the thickness of the lower (basaltic) crust. The other two prominent anomalies, the magnetic low striking northwest and the magnetic high trending east-northeast, appear to be related to the deep structural feature of the Godavari graben and the eastern Rajasthan lineament respectively.     

Study on laterally loaded piles with rectangular and circular cross sections

The conventional approach in the design of laterally loaded piles with rectangular cross section involves the simplification of converting the rectangular cross section of the pile to an equivalent circular cross section. An analysis to determine the response of laterally loaded rectangular or circular piles in elastic soil is presented in which this simplification is not required. The analysis is based on the solution of differential equations governing the displacements of the pile–soil system derived using energy principles. The pile geometry and the elastic constants of the soil and pile are the input parameters to the analysis. Using this analysis, comparisons are made between the response of rectangular and circular piles in elastic soil. Based on the proposed solution scheme, a user-friendly spreadsheet program (LATPAXL) was developed that can be used to perform the analysis. In addition, simple equations obtained by regression analysis of the pile head deflection and bending moment profiles are proposed. Examples illustrate the use of the analysis.     

Stresses from linearly distributed pressures over rectangular areas

This paper presents a general algebraical formula to determine the vertical stresses resulting from a linearly distributed surface pressure resting on an elastic medium. This problem and its various derivations has received considerable attention because of its applications in foundation engineering [1–5]. The equation presented in this paper has been determined by the integration of the Boussinesq [6] equation with respect to the general surface function of a linearly distributed loading regime. The equation can be applied to the case of an optimally designed rectangular footing subjected to biaxial bending. Unlike the current design formulae [1–7], it provides the flexibility of having various contact pressures at each of the four corners of the rectangular area. This may enable more accurate design procedures for pad foundations in the future. This paper explains the validity of the new formula by comparing its results with those produced by classical methods. It shows how it can be applied to determine the vertical stress distributions resulting from all types of linearly distributed surface pressures which occupy a rectangular area on an elastic mass. Copyright © 2000 John Wiley & Sons, Ltd.     

TRANSFER FUNCTIONS FOR RIGID RECTANGULAR FOUNDATIONS

Closed-form expressions and comprehensive numerical solutions are presented for the transfer functions of surface-supported, rigid, rectangular foundations excited by horizontally polarized, incoherent shear waves for which the motions are parallel to one of the foundation sides. The free-field ground motion is specified stochastically in terms of a local power spectral density function and an orthotropic incoherence function which decays exponentially with the square of the excitation frequency and the separation distance. The response quantities examined include the lateral and torsional components of the foundation motion. Displayed graphically, the results elucidate the effects and relative importance of the numerous parameters involved. For vertically incident incoherent wave fields, the lateral transfer function of a rectangular foundation is related to that of a judiciously selected square foundation, and the interrelationship of the results is examined. © 1997 by John Wiley & Sons, Ltd.     

瞬变电磁法中心回线装置资料解释方法的改进

中心回线装置是瞬变电磁勘探中最常用的装置之一.中心回线装置的视电阻率一般从回线中心点场的公式出发导出.在现场实际施工中,为提高工作效率,把发射回线中部三分之一的区域作为观测范围.通过对场分布特征的分析研究表明,与中心点相比,观测区边缘处的感应电动势数值偏离达15%~25%,这与广泛存在于华北型煤系中赋存深度为400~1000 m的陷落柱、导水小断层等引起的异常相比,已经不可忽略.大定源回线公式可以准确地表示任意场点的感应电动势,由此导出视电阻率无边缘效应影响;观测按照中心回线方式并保持在近区进行,可使感应电动势和视电阻率之间的转换简单而直接.理论和实际应用结果表明,这些措施进一步提高了瞬变电磁探测中心回线方法的探测精度.在有上覆低阻屏蔽层的情况下,对埋深500~700 m的陷落柱给出了明显的异常反映,并被井下掘进所验证.     

地震荷载沉箱码头大变形分析的离散元法初探

探讨了应用离散元分析方法求解地震荷载下沉箱和背后填土大变形问题的可能性,开发了能描述沉箱的平面形状及沉箱与土体摩擦特性的矩形单元。并通过简单实例分析了地震时沉箱码头的变形,再现了沉箱码头地震灾害的发生过程,为沉箱在地震情况下的大变形分析提供了一种新途径。比较了两种沉箱模型对分析结果的影响,提出了相应的方法。