用矩阵摄动法修改结构动力参数

作者应用模型简化技术中的矩阵摄动法来修改结构动力参数，从而避免了修改后结构动力参数的重计算，减少了系统仿真、分析和设计的计算量。算例表明，该方法有较好的计算效率。     

地球非球形引力位中田谐项摄动的有关问题

在人造卫星绕地球运动中,地球非球形引力摄动是最重要的讨论了容易被忽视的田谐项摄动,尽管它对低轨卫星的影响,只相当于J2项的二阶量,又是短周期效应,但它却包含了大10多倍的地球自转项,必须给以重视.还导出包含全部阶次田谐项的摄动解,并分离出地球自转项,对轨道半长径a还增加了(J2×Jlm)联合摄动的地球自转项,既为理论分析提供依据又可用于分析法定轨和预报.     

塔里木盆地西南部的三维密度扰动成像

塔里木盆地西南部位于昆仑造山带东北方,地壳构造特殊,是中国天然气勘探的重要区域。在地面重力调查的基础上,笔者等对2~15 km的盆地西南部的密度扰动结构进行成像计算,并结合电阻率三维结构对地壳构造进行分析。本文根据重力场小波变换的尺度—源深度转换律,进行地面重力异常场多尺度分解,取得了反映中国地壳不同埋藏深度的小波细节,揭示了研究区地壳的密度结构。结果表明,网度足够密的区域高精度重力场测量可以获得关于沉积盆地深部构造的丰富信息,应用小波多尺度分析和三维反演方法可以把与深层构造有关的地质信息提取出来,客观地为沉积盆地内部构造演化和油气勘探提供依据。塔里木盆地西南部上地壳三维密度扰动成像揭示了昆仑山脉向北仰冲推覆构造楔和山前坳陷带的立体结构,为盆山耦合动力学研究和深层油气勘探提供了新的认识。大地电磁数据三维反演取得的盆地三维电阻率模型,从电性结构角度得到了盆地的三维构造,和盆地西南部的密度结构有很好的相关性,支持了密度扰动成像的有关结论。     

汶川Mw7.9地震余震序列触发机制研究

余震触发机制的Dieterich解析模型被广泛应用于区域地震活动性的定量分析以及依赖时间的概率地震预测模型的建立等方面.基于滑移速率和状态相依赖的摩擦定律和弹簧-滑块模型,从Dieterich断层滑移速率方程出发,给出了静态应力扰动下触发地震的时钟提前或推后的近似解,从而明确地阐明了触发地震的产生机制与断层的演化过程密切相关,并与传统位错模型下库仑应力扰动时间提前或推后量作了比较.采用对数线性拟合方法求得了汶川Mw7.9主震后余震序列持续时间,符合Dieterich理论结果.以汶川余震序列为例,给出了两种不同的应力扰动模式在该余震序列中的应用.结果表明,经典Dieterich扰动解无法给出主震发生后即时余震数量的异常增加,而考虑主震前后剪应力速率变化的Dieterich分段解则可反映出余震发生率及个数随时间的演化特征.     

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Abstract

This paper develops a new analytical solution for the aquifer system, which comprises an unconfined aquifer on the top, a semi-confined aquifer at the bottom and an aquitard between them. This new solution is derived from the Boussinesq equation for the unconfined aquifer and one-dimensional leaky confined flow equation for the lower aquifer using the perturbation method, considering the water table over-height at the remote boundary. The head fluctuation predicted from this solution is generally greater than the one solved from the linearized Boussinesq equation when the ratio of the tidal amplitude to the thickness of unconfined aquifer is large. It is found that both submarine groundwater discharges from upper and lower aquifers increase with tidal amplitude–aquifer thickness ratio and may be underestimated if the discharge is calculated based on the average head fluctuation. The effects of the aquifer parameters and linearization of the Boussinesq equation on the normalized head fluctuation are also investigated.

Editor D. Koutsoyiannis; Associate editor J. Simunek

Citation Chuang, M.-H., Mahdi, A.-A. and Yeh, H.-D., 2012. A perturbation solution for head fluctuations in a coastal leaky aquifer system considering water table over-height. Hydrological Sciences Journal, 57 (1), 162–172.     

New class of solutions for water infiltration problems in unsaturated soils

This paper presents the results of approximate analytical solutions to Richards' equation, which governs the problem of unsaturated flow in porous media. The existing methods generally fall within the category of numerical and analytical methods, often having many restrictions for practical situations. In the present study, two approximate analytical methods known as the differential transform method (DTM) and homotopy perturbation method (HPM) were employed to find analytical solutions to Richards' equation. The methods were found to be robust in finding solutions practically identical to those from the existing analytical and numerical methods. Two representative examples were considered in order to evaluate the accuracy of the solutions obtained by DTM and HPM, revealing high level of accuracy in both cases.     

Weakly nonlinear analysis of the α effect

We address mathematical issues raised by the so-called α?effect of dynamo theory, which is a dynamo mechanism arising in conducting flows with small scale fluctuations. Analytical results on the α?effect concern the linear induction equation, and are usually claimed to hold for the whole magnetohydrodynamics (MHD) system, as long as the amplitude of the perturbations is small. We discuss the justification of that claim, in the case of periodic fluctuations of the fields. We show a nonlinear instability result on the MHD system, that predicts dynamo action for a large class of high frequency periodic flows, up to the fully nonlinear regime.     

侧向应力扰动对断层摩擦影响的实验研究

利用双向伺服控制装置,对含有与最大主压应力σ1呈45°夹角的预切面的花岗闪长岩标本进行了摩擦实验,结果表明,在σ1方向位移速率恒定、侧向应力σ2恒定的条件下,粘滑间隔随滑动面上正应力的增加而增加,粘滑应力降也随滑动面上正应力的增加而呈线性增加。但当σ2叠加了高频小振幅的正弦波扰动时,这种相关性发生了明显的变化,应力降大小和粘滑间隔的离散度均显著提高,特别是应力降可能会大幅度增加。与σ1扰动的实验结果相比,σ2扰动对断层粘滑的影响更为显著,这主要归因于正应力变化使滑动面的非均匀性加剧