Analytic scaling laws in planetary dynamo models

ABSTRACT

Numerical models of planetary MHD dynamos have led to many advances in the last twenty years. However, the accessible parameter space of these models is somewhat limited due to computational constraints. A number of numerically based scaling laws have been proposed, but it has been difficult to reliably confirm them from the simulation data alone. Since these scaling laws have to be used to extend the numerical models into the planetary parameter regime, getting correct scalings is an important issue. Here some possible balances between the relevant terms in the dynamo equations are considered, and a number of different known and new scaling laws are proposed and justified from analytical point of view. Some of these laws are compatible with the widely known Christensen and Aubert (Geophys. J. Int. 2006, 166) scaling for the magnetic field strength. Plausible estimates of the typical values of the important quantities in the Earth's core and other Terrestrial planets are made, and the extent to which the various scaling laws are consistent with these estimates is discussed.     

基于年际增量方法的云南省普洱雨季开始期气候预测

基于普洱雨季开始期年际增量变化规律和影响雨季开始期的环流形势及物理过程,采用年际增量方法和多元线性回归分析方法,选取5个具有物理意义的预测因子(包括前期1月南半球绕极环流、前期2月南太平洋高压、前期4月孟加拉湾至南海海平面气压、前期冬季加拿大北部海冰和前期冬季伊朗高原积雪深度),建立了普洱雨季开始期的预测模型,并对预测模型进行1967—2017年的交叉检验和1998—2017年的逐年独立样本检验。交叉检验中,雨季开始期预测值和观测值年际增量的相关系数为0.84,相对均方根误差为24%;独立样本检验中,雨季开始期年际增量的相对均方根误差为15%,模型对雨季开始期异常年份的预测误差小于7 d,表明该预测模型能很好再现1967—2017年雨季开始期的变化趋势。     

浅谈提高天气预报准确率

随着气象科技的进步以及社会经济发展对气象服务需求的不断增加,提高天气预报准确率显得日益重要,而正确应用数值预报产品是达到这一目的的有效途径。作者从正确认识"天气预报准确率"这一概念的相对性出发,探讨了合理应用数值预报产品的重要性以及预报员在其中扮演的关键角色。     

基于贝叶斯网络的地震液化概率预测分析

基于解释结构模型和因果图法,选取12个具有代表性的定性和定量因素,在大量数据不完备的情况下提出了建立贝叶斯网络液化模型的方法。以2011年日本东北地区太平洋近海地震液化不完备数据为例,采用总体精度、ROC曲线下面积、准确率、召回率和F1值5项指标对模型进行综合评估,并与径向基神经网络模型进行对比。结果表明：贝叶斯网络液化模型的回判和预测效果都优于径向基神经网络模型,且对于数据缺失的样本的预测效果也较理想。此外,该模型对于不同土质的液化评估均有较好的适用性。分类不均衡和抽样偏差会对模型的学习和预测效果产生很大影响,建议应同时采用上述5项评估指标进行综合评估模型的优劣。     

基于张量投票和目标追踪的墙体裂缝检测算法研究

针对墙体裂缝对比度低、受噪声干扰严重等特点,提出了一种基于张量投票和目标追踪的墙体裂缝检测算法。在对原始影像进行二值化的基础上,利用张量投票的聚类思想,突出线性区域目标的强度,然后在突出的线性目标上选取特征点,对特征点进行追踪得到裂缝的大致位置,再反投到原始影像上。实验结果表明,该算法能够正确检测出墙体裂缝信息,且检测率较高,具有一定的通用性。     

A macro‐model with nonlinear springs for seismic analysis of URM buildings

Seismic assessment of existing unreinforced masonry buildings represents a current challenge in structural engineering. Many historical masonry buildings in earthquake regions were not designed to withstand seismic loading; thus, these structures often do not meet the basic safety requirements recommended by current seismic codes and need to be strengthened considering the results from realistic structural analysis. This paper presents an efficient modelling strategy for representing the nonlinear response of unreinforced masonry components under in‐plane cyclic loading, which can be used for practical and accurate seismic assessment of masonry buildings. According to the proposed strategy, generic masonry perforated walls are modelled using an equivalent frame approach, where each masonry component is described utilising multi‐spring nonlinear elements connected by rigid links. When modelling piers and spandrels, nonlinear springs are placed at the two ends of the masonry element for describing the flexural behaviour and in the middle for representing the response in shear. Specific hysteretic rules allowing for degradation of stiffness and strength are then used for modelling the member response under cyclic loading. The accuracy and the significant potential of the proposed modelling approach are shown in several numerical examples, including comparisons against experimental results and the nonlinear dynamic analysis of a building structure. Copyright © 2016 John Wiley & Sons, Ltd.     

克拉通岩石圈对流减薄的数值模拟

采用二维有限元数值模拟的方法研究了岩石圈的对流减薄过程,特别是克拉通岩石圈的对流减薄过程.模型的主要参数包括增厚岩石圈的宽度x、增厚倍数γ、以及与岩石圈组分变化导致的黏性和密度变化密切相关的黏性比(ηc)和浮力数(B)或等效密度变化(Δρtc).数值计算结果显示,地幔对流将逐渐减薄增厚的岩石圈部分,(1)当B=0和ηc=1时,即对一般地幔岩石圈,增厚岩石圈对流减薄的时间可表示为0.0073γ0.70 x0.26.将数值结果应用于地球,意味着增厚到300km的岩石圈,如宽度为300km,对流移除增厚部分回到初始平衡厚度120km大约需要225 Ma;如宽度为1500km,移除增厚部分大约需要342 Ma.(2)当B和ηc较小,克拉通岩石圈对流减薄过程与一般加厚岩石圈的对流减薄过程类似,但减薄时间受克拉通组分浮力和黏性比的影响而显著增长,克拉通岩石圈对流减薄的时间可表示为0.0057ηc0.52Δρ-0.21tcγ0.78ηc-0.36 x0.04.因而,对300km厚的克拉通岩石圈,如克拉通岩石圈的密度比周围地幔的密度低0.4%(即B=0.1),宽度1500km,若克拉通岩石圈黏性因组分影响比普通地幔岩石圈大10倍,其被对流减薄到120km大约需要1.18Ga.(3)当B和ηc增大到一定量时(如B≥0.2且ηc10),克拉通岩石圈被移除的过程将发生变化,由于组分浮力的影响,对流主要不是将克拉通岩石圈带到软流圈地幔中,而主要是将较厚的岩石圈物质向两边推送.在此情况下,克拉通岩石圈能长时间(3Ga)保持稳定.     

过套管电阻率测井的地层电阻率快速反演算法

过套管电阻率测井是通过测量套管壁电势实现测量地层的视电阻率,基于传输线方程理论,针对层状地层,给出了套管壁电势、电流对地层横向电阻导数的微分方程(称Jacobi矩阵微分方程)及边界条件;利用Jacobi矩阵微分方程边值问题导出了过套管电阻率测井反演地层参数的Jacobi矩阵系数的解析表示,利用Marquardt方法实现了过套管测井的地层电阻率反演;通过计算对Jacobi矩阵的特性进行了探讨,并获得了较快的计算速度(因为Jacobi矩阵是用解析解表示的),反演结果与地层模型取得了较好的逼近.本文实现了过套管电阻率测井地层参数的Jacobi系数矩阵的快速计算及地层电阻率反演,为进一步开展电阻率测井数据处理提供了理论依据和快速反演算法.     

Seismic reliability assessment of lifeline networks using clustering‐based multi‐scale approach

Seismic reliability assessment of lifeline networks gives rise to various technical challenges, which are mostly caused by a large number of network components, complex network topology, and statistical dependence between component failures. For effective risk assessment and probabilistic inference based on post‐hazard observations, various non‐simulation‐based algorithms have been developed, including the selective recursive decomposition algorithm (S‐RDA). To facilitate the application of such an algorithm to large networks, a new multi‐scale approach is developed in this paper. Using spectral clustering algorithms, a network is first divided into an adequate number of clusters such that the number of inter‐cluster links is minimized while the number of the nodes in each cluster remains reasonably large. The connectivity around the identified clusters is represented by super‐links. The reduced size of the simplified network enables the S‐RDA algorithm to perform the network risk assessment efficiently. When the simplified network is still large even after a clustering, additional levels of clustering can be introduced to have a hierarchical modeling structure. The efficiency and effectiveness of the proposed multi‐scale approach are demonstrated successfully by numerical examples of a hypothetical network, a gas transmission pipeline network, and a water transmission network. Copyright © 2014 John Wiley & Sons, Ltd.