二维梯形沉积盆地放大效应的数值模拟研究          下载免费PDF全文

包得志  荣棉水  喻烟 《地震工程学报》2021,43(6):1472-1479,1500

盆地效应作为场地效应的一种特殊类型,其对地震动的影响仍在持续研究当中。建立二维梯形沉积盆地模型,模型边界采用透射人工边界,利用显式有限元法作为求解方法。根据Buckingham提出的π定理定义了多个影响盆地效应的无量纲参数,包括盆地深宽比、介质波速比、盆地深度与入射波长之比、盆地开口宽度与入射波长之比。以Ricker子波作为输入波,研究SH波垂直入射盆地模型时,以上无量纲参数对盆地放大效应的影响。研究发现盆地深宽比越大盆地诱发的聚焦效应越明显,盆地深宽比越小盆地边缘效应越明显。在盆地的深宽比和入射波确定时,随着盆地开口宽度与入射波长之比不断增大盆地的最值放大系数逐渐从盆地中心移向盆地边缘,表现出越来越明显的边缘放大效应。其中波速比差异对放大系数的影响最大,波速比差异越大介质的波阻抗比越大,放大效应越显著。通过将影响盆地放大效应的参数无量纲化,使梯形盆地对地震动放大效应的研究的结论更具有普遍意义。  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   

基于贝叶斯定理的地震危险性概率预测研究     

邓世广  周龙泉  马亚伟  臧阳  王月  韩颜颜 《中国地震》2019,35(1):1-13

由于地震孕育过程的复杂性和观测技术的局限性,不同地震观测资料表现出异常变化与后续较大地震的对应关系存在不确定性,因此对预测意见进行概率表达是一种科学恰当的做法。本文基于泊松分布的危险区背景地震概率预测和单项预测方法(包括测震、流体、形变、电磁等学科)的历史预测效能,采用贝叶斯定理计算得到单项预测方法的短期或年度地震危险概率预测结果,进而采用综合概率方法,给出基于多种单项预测方法的短期或年度地震危险概率预测结果。短期概率预测初步结果表明,2018年2～9月,中国大陆72%的5级以上地震都位于相对高概率预测区域。  相似文献   

An improved return‐map stress update algorithm for finite deformation analysis of general isotropic elastoplastic geomaterials     

Junjie Huang  Qi Peng  Ming‐Xiang Chen 《国际地质力学数值与分析法杂志》2014,38(6):636-660

This paper develops a novel return mapping algorithm for the numerical integration of general isotropic finite strain elastoplastic constitutive models for geomaterials. The constitutive formulation is founded on multiplicative decomposition of the deformation gradient. The logarithmic strain measure as well as the exponential approximation of the plastic flow rule is utilized to restore the standard infinitesimal format return mapping algorithm. Central to the algorithm is the exploitation of a set of three mutually orthogonal unit base tensors for the representation of constitutive relations and the corresponding integration of the rate form of the constitutive equations. The base tensors constitute a local cylindrical coordinate system in the principal space, which allows to formulate the return mapping algorithm in the three‐dimensional space and reduce the dimension of the problem to be analyzed from six down to three. With the proposed approach, direct determination of the principal axes and the transformation procedure between the general space and the principal space, as required in traditional spectral decomposition, are avoided. Furthermore, the matrices that are involved in the inversion evaluation take simple forms, leading to extremely easy inverse computation. As a result, the consistent tangent operator can be streamlined into a form simpler and more compact than those by conventional integration methods. Following the formulation of the integration procedure, a numerical experiment is performed to assess the accuracy and efficiency of the proposed algorithm. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Modeling and Analysis of Airlift System Operating in Three-Phase Flow     

胡东  康勇  唐川林  王晓川 《海洋工程》2015,29(1):121-132

Based on the momentum theorem, the fluid governing equation in a lifting pipe is proposed by use of the method combining theoretical analysis with empirical correlations related to the previous research, and the performance of an airlift pump can be clearly characterized by the triangular relationship among the volumetric flux of air, water and solid particles, which are obtained respectively by using numerical calculation. The meso-scale river sand is used as tested particles to examine the theoretical model. Results of the model are compared with the data in three-phase flow obtained prior to the development of the present model, by an independent experimental team that used the physical conditions of the present approach. The analytical error can be controlled within 12% for predicting the volumetric flux of water and is smaller than that (±16%) of transporting solid particles in three-phase flow. The experimental results and computations are in good agreement for air?water two-phase flow within a margin of ±8%. Reasonable agreement justifies the use of the present model for engineering design purposes.  相似文献   

Dynamic modeling and motion simulation for a winged hybrid-driven underwater glider   总被引：2，自引：0，他引：2  

王树新  孙秀军  王延辉  武建国  王晓鸣 《中国海洋工程》2011,25(1):97-112

PETREL,a winged hybrid-driven underwater glider is a novel and practical marine survey platform which combines the features of legacy underwater glider and conventional AUV (autonomous underwater vehicle).It can be treated as a multi-rigid-body system with a floating base and a particular hydrodynamic profile.In this paper,theorems on linear and angular momentum are used to establish the dynamic equations of motion of each rigid body and the effect of translational and rotational motion of internal masses on the attitude control are taken into consideration.In addition,due to the unique external shape with fixed wings and deflectable rudders and the dual-drive operation in thrust and glide modes,the approaches of building dynamic model of conventional AUV and hydrodynamic model of submarine are introduced,and the tailored dynamic equations of the hybrid glider are formulated.Moreover,the behaviors of motion in glide and thrust operation are analyzed based on the simulation and the feasibility of the dynamic model is validated by data from lake field trials.  相似文献   

奇异非线性二阶诺伊曼边值问题恰有5个正解的条件     

胡令雄  李德宜  任帅 《南京气象学院学报》2013,5(6):573-576

主要研究奇异非线性二阶诺伊曼边值问题的正解个数.应用比较原理、最大值原理和上界方法得出了在一定条件下,该问题恰好有5个正解的结果.  相似文献   

数字拓扑学和层析成像   总被引：1，自引：0，他引：1  

羡汝珙  崔力科 《CT理论与应用研究》1996,5(2):32-36

本文论述拓扑学在数字图像中的应用，首先定义数字图像子集的性概念，并论述当前正孕育着一门分支－数字拓扑学及其在层析成像的可能具有的联系。  相似文献   

Magnetic field generation by the motion of a highly conducting fluid     

M. M. Vishik 《地球物理与天体物理流体动力学》2013,107(1-3):151-167

Abstract

Using an asymptotic expansion of Green's function for the problem of magnetic field generation by 3D steady flow of highly conducting fluid a general antidynamo theorem is proved in the case of no exponential stretching of liquid particles. Explicit formulae connecting the spectrum of the magnetic modes with the geometry of the Lagrangian trajectories are obtained. The existence of the fast dynamo action for special flows with exponential stretching is proved under the condition of smoothness of the fields of stretching and non-stretching directions.  相似文献   

Magnetic topologies in the solar corona due to four discrete photospheric flux regions     

C. Beveridge  E.R. Priest  D.S. Brown 《地球物理与天体物理流体动力学》2013,107(5):429-445

Many dynamic phenomena in the solar corona are driven by the complex and ever-changing magnetic field. It is helpful, in trying to model these phenomena, to understand the structure of the magnetic field, i.e. the magnetic topology. We study here the topological structure of the coronal magnetic field arising from four discrete photospheric flux patches, for which we find that seven distinct, topologically stable states are possible; the changes between these are caused by six types of bifurcation. Two bifurcation diagrams are produced, showing how the changes occur as the relative positions and strengths of the flux patches are varied. A method for extending the analysis to higher numbers of sources is discussed.  相似文献