基于两步弥散算子的共反射面元射线束成像方法研究          下载免费PDF全文

陈宝书  杨锴  汪小将 《地球物理学报》2020,63(1):270-286

基于克希霍夫统一成像理论,对共反射面元射线束成像方法进行了深入分析.通过这种分析可以得到一种新的共反射面元射线束类成像实现方式:基于两步弥散算子的共反射面元射线束类成像方法.当仅实施第一步弥散时,即可获得信噪比大幅提高同时更为规则的叠前道集.二维、三维的理论和实际数据算例证实了上述观点.  相似文献   

论不同模式大气中的静力适应过程          下载免费PDF全文

郭海龙  刘宇迪  董毅 《地球物理学报》2018,61(1):52-64

为了研究大气静力平衡适应过程的本质，利用波动理论和能量转换角度，分别对完全可压缩的等温大气模型、滞弹近似下的等温大气模型和层结中性大气模型进行研究比较.结果表明：大气静力平衡适应过程的本质是声波和混合声重力波对扰动能量的频散过程，滞弹近似模型和层结中性模型均不能完全描述此适应过程；在波动假设下，此三类大气模型中扰动物理量之间的偏振关系同波动的性质有关，气团的运动方程均为椭圆方程，声波和混合声重力波对气团运动的作用差异较显著.
大气静力平衡适应过程中扰动能量以有效势能、有效弹性势能、动能或波动能量的形式存在并相互转换；扰动有效势能与其他形式能量之间的转换与混合声重力波或者重力内波有关，扰动有效弹性势能与其他形式能量之间的转换与声波有关.在完全可压缩的等温大气模型中，扰动有效势能增加1个单位，其中69.9%来自扰动垂直动能，其余30.1%来自扰动有效弹性势能.  相似文献   

铁路路基粗粒土填料临界动应力试验研究     

王康宇  庄妍  耿雪玉 《岩土力学》2020,41(6):1865-1873

粗粒土填料被广泛应用于铁路基床填料中，直接承受轨道结构传递的列车动循环荷载的长期作用，研究其在列车动荷载作用下的动力行为特征及塑性变形特性可为路基状态评估、沉降控制提供思路。采用GDS动三轴试验系统对铁路基床表层的粗粒土填料动力响应开展研究，通过引入塑性应变率和安定理论，将不同频率、围压、循环动应力比等条件下路基填料的轴向塑性应变的发展规律划分为塑性安定、塑性蠕变和增量塑性破坏3种类型，并确定了塑性安定和塑性蠕变状态的临界动应力水平。研究表明：粗粒土填料的临界循环应力比随着围压的增大而增大，随着荷载频率的增加而减小。通过对试验结果的拟合分析，提出了以围压为变量的临界动应力经验公式，为合理评估列车荷载作用下路基任意深度的动力稳定提供了理论依据。  相似文献   

爆破荷载作用下露天矿边坡稳定性的突变研究     

周子涵  陈忠辉  王建明  张凌凡  年庚乾 《岩土力学》2020,41(3):849-857

基于二维斜坡平面滑动失稳力学模型，引入爆破荷载因素，建立了露天爆破荷载作用下岩质边坡失稳的尖点突变理论模型。根据建立的突变模型，探讨了爆破荷载幅值和爆破荷载频率对边坡稳定性的影响规律，导出了边坡的动态自稳临界高度，并提出了失稳的判据条件，结果表明：爆破荷载幅值越大，爆破荷载频率越小，后缘裂缝深度越大，边坡失稳的可能性越高；在爆破荷载作用下，边坡的稳定程度是动态变化的，且随着应力波入射角的增大，边坡失稳破坏的可能性不断提高。以大孤山露天矿内的两处边坡为例，计算了边坡的动安全系数及动态自稳临界高度，利用边坡当前实际的稳定情况验证了提出的边坡失稳判据的合理性，为预防露天矿爆破在开挖过程中边坡岩体的动力失稳提供了一定的理论支持。  相似文献   

基于下一代性能设计理论的全概率抗震性能评估          下载免费PDF全文

董艳秋  王宪杰  王希  杨思昭  周潇凡  龙诗琪  吕龙 《世界地震工程》2020,(2):012-20

对建筑物灾变发生时经济损失和人员伤亡情况做出准确预估是未来建筑结构设计初期需要努力的方向。基于下一代性能化设计理论,通过精细化建模和动力时程分析对结构进行易损性分析,并以此得到抗震性能评估所需的各类地震响应参数,建立RC框架结构全概率抗震性能评估方法。以云南大学力行楼为例,通过地震损失预测得到了该栋建筑的经济损失、修复时间和人员伤亡情况。该方法直观清晰地展示了结果,便于业主及非本专业从业者理解。  相似文献   

Study of Star/Galaxy Classification Based on the XGBoost Algorithm     

《Chinese Astronomy and Astrophysics》2019,43(4):539-548

Machine learning has achieved great success in many areas today. The lifting algorithm has a strong ability to adapt to various scenarios with a high accuracy, and has played a great role in many fields. But in astronomy, the application of lifting algorithms is still rare. In response to the low classification accuracy of the dark star/galaxy source set in the Sloan Digital Sky Survey (SDSS), a new research result of machine learning, eXtreme Gradient Boosting (XGBoost), has been introduced. The complete photometric data set is obtained from the SDSS-DR7, and divided into a bright source set and a dark source set according to the star magnitude. Firstly, the ten-fold cross-validation method is used for the bright source set and the dark source set respectively, and the XGBoost algorithm is used to establish the star/galaxy classification model. Then, the grid search and other methods are used to adjust the XGBoost parameters. Finally, based on the galaxy classification accuracy and other indicators, the classification results are analyzed, by comparing with the models of function tree (FT), Adaptive boosting (Adaboost), Random Forest (RF), Gradient Boosting Decision Tree (GBDT), Stacked Denoising AutoEncoders (SDAE), and Deep Belief Nets (DBN). The experimental results show that, the XGBoost improves the classification accuracy of galaxies in the dark source classification by nearly 10% as compared to the function tree algorithm, and improves the classification accuracy of sources with the darkest magnitudes in the dark source set by nearly 5% as compared to the function tree algorithm. Compared with other traditional machine learning algorithms and deep neural networks, the XGBoost also has different degrees of improvement.  相似文献   

Elastic behavior of weakly cemented contact          下载免费PDF全文

V. Langlois 《国际地质力学数值与分析法杂志》2015,39(8):854-860

We investigate the elastic behavior of weakly cemented contact. We show that the radial distribution of stresses and the stiffnesses of a cemented contact are governed by the ratio a/RΛ, where R, a, and Λ are, respectively, the grain radius, the contact size, and the ratio of the elastic moduli of cement and grains. Moreover, we show that a cemented contact is always less stiff than a Hertzian contact having a similar size. Finally, we propose accurate approximate expressions of the contact stiffnesses. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Nonlinear steady states to Langmuir circulation in shallow layers: an asymptotic study     

D. T. Hayes 《地球物理与天体物理流体动力学》2017,111(1):65-90

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A network theory approach for a better understanding of overland flow connectivity          下载免费PDF全文

Rens J. H. Masselink  Tobias Heckmann  Arnaud J. A. M. Temme  Niels S. Anders  Harm P. A. Gooren  Saskia D. Keesstra 《水文研究》2017,31(1):207-220

Hydrological connectivity describes the physical coupling (linkages) of different elements within a landscape regarding (sub‐) surface flows. A firm understanding of hydrological connectivity is important for catchment management applications, for example, habitat and species protection, and for flood resistance and resilience improvement. Thinking about (geomorphological) systems as networks can lead to new insights, which has also been recognized within the scientific community, seeing the recent increase in the use of network (graph) theory within the geosciences. Network theory supports the analysis and understanding of complex systems by providing data structures for modelling objects and their linkages, and a versatile toolbox to quantitatively appraise network structure and properties. The objective of this study was to characterize and quantify overland flow connectivity dynamics on hillslopes in a humid sub‐Mediterranean environment by using a combination of high‐resolution digital‐terrain models, overland flow sensors and a network approach. Results showed that there are significant differences between overland flow connectivity on agricultural areas and semi‐natural shrubs areas. Significant positive correlations between connectivity and precipitation characteristics were found. Significant negative correlations between connectivity and soil moisture were found, most likely because of soil water repellency and/or soil surface crusting. The combination of structural networks and dynamic networks for determining potential connectivity and actual connectivity proved a powerful tool for analysing overland flow connectivity. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

On the robustness of the toroidal velocity theorem     

R. Kaiser  F. Busse 《地球物理与天体物理流体动力学》2017,111(5):355-368

In dynamo theory the toroidal velocity theorem in its classical version (Elsasser, Phys. Rev. 1946, vol. 69, pp. 106–116, Bullard and Gellman, Phil. Trans. R. Soc. Lond. 1954, vol. A247, pp. 213–278) rules out dynamo action in a spherical conducting volume provided that the fluid is incompressible, the conductivity is uniform, and the velocity field is purely toroidal. We prove in this note that this result is robust in the sense that slight compressibility of the fluid, small non-radial variations and even large radial variations in conductivity, and the presence of a small non-toroidal velocity component do not invalidate the theorem. Moreover, by proper choice of the conductivity distribution modelling the conducting volume, small deviations from spherical symmetry of the conductor can also be taken into account.  相似文献