A stabilized Smoothed Particle Hydrodynamics,Taylor–Galerkin algorithm for soil dynamics problems     

T. Blanc  M. Pastor 《国际地质力学数值与分析法杂志》2013,37(1):1-30

Modelling of failure under dynamic conditions in geomaterials with finite elements presents a series of complex problems, among which we can mention those of (i) volumetric locking, which results on higher failure loads, (ii) influence of mesh alignment, resulting to unrealistic failure surfaces, (iii) diffusion of the shear band over some element widths, (iv) nonoptimal propagation properties (numerical diffusion and dispersion), (v) fulfilling Babuska–Brezzi conditions when using the same order of interpolation for displacement and pressures in coupled problems and (vi) large deformation analysis. This paper is based on previous work done by the authors, who developed a mixed approximation based on (i) casting the dynamic problem in the form of a system of first order PDEs and (ii) using stresses and velocities as nodal variables. The equations were discretized following a Taylor–Galerkin algorithm, first in time using a Taylor expansion and then in space using Galerkin method. The model was limited to small deformations. The purpose of this paper is to show how Taylor–Galerkin method can be extended to meshless formulations, such as the SPH method. The algorithm consists of (i) discretizing in time using a Taylor series expansion complemented with integration of source terms using a Runge–Kutta scheme and then (ii) discretizing in space using the SPH method. It is shown how the proposed method keeps the advantages of the Taylor–Galerkin method in Finite Elements (good propagation properties and capturing of shear bands) and avoids the tensile instability. A set of test problems ranging from elastic propagation of a wave in a bar to failure of a slope on a cohesive softening material are used to assess the performance of the method. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Spectral analysis of nonlocal regularization in two‐dimensional finite element models     

Xilin Lu  Jean‐Pierre Bardet  Maosong Huang 《国际地质力学数值与分析法杂志》2012,36(2):219-235

Strain‐softening in geomaterials often leads to ill‐posed boundary‐valued problems (BVP), which cannot be solved with finite element methods without introducing some kind of regularization such as nonlocal plasticity. Hereafter we propose to apply spectral analysis for testing the performance of nonlocal plasticity in regularizing ill‐posed BVP and producing mesh‐independent solutions when local plasticity usually fails. The spectral analysis consists of examining the eigenvalues and eigenvectors of the global tangential stiffness matrix of the incremental equilibrium equations. Based on spectral analysis, we propose a criterion for passing or failing the test of constitutive regularization in the context of BVP. If the eigenvalues of the tangential operator are all positive then the regularization succeeds, otherwise it fails and may not prevent artificial mesh‐dependent solutions from appearing. The approach is illustrated in the particular case of a biaxial compression with strain‐softening plasticity. In this particular case, local softening plasticity is found to produce negative eigenvalues in the tangential stiffness matrix, which indicates ill‐posed BVP. In contrast, nonlocal softening plasticity always produces positive eigenvalues, which regularizes ill‐posed BVP. The dominant eigenvectors, which generate localized deformation patterns, have a bandwidth independent of mesh size, provided that the mesh is fine enough to capture localization. These mesh‐independent eigenmodes explain why nonlocal plasticity produces numerical solutions that are mesh‐independent. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

TOPOGRAPHIC DEPENDENT HORIZONTAL LOCALIZATION SCALE SCHEME IN GRAPES-MESO HYBRID EN-3DVAR ASSIMILATION SYSTEM     

夏宇  陈静  智协飞  庄照荣  陈良吕  王婧卓 《热带气象学报(英文版)》2019,25(2):245-256

Based on the GRAPES-MESO hybrid En-3DVAR (Ensemble three-dimension hybrid data assimilation for Global/Regional Assimilation and Prediction system) constructed by China Meteorological Administration, a 7-day simulation (from 10 July 2015 to 16 July 2015) is conducted for horizontal localization scales. 48h forecasts have been designed for each test, and seven different horizontal localization scales of 250, 500, 750, 1000, 1250, 1500 and 1750 km are set. The 7-day simulation results show that the optimal horizontal localization scales over the Tibetan Plateau and the plain area are 1500 km and 1000 km, respectively. As a result, based on the GRAPES-MESO hybrid En-3DVAR, a topography-dependent horizontal localization scale scheme (hereinafter referred to as GRAPES-MESO hybrid En-3DVAR-TD-HLS) has been constructed. The data assimilation and forecast experiments have been implemented by GRAPES-MESO hybrid En-3DVAR, 3DVAR and GRAPES-MESO hybrid En-3DVAR-TD-HLS, and then the analysis and forecast field of these three systems are compared. The results show that the analysis field and forecast field within 30h of GRAPES-MESO hybrid En-3DVAR-TD-HLS are better than those of the other two data assimilation systems. Particularly in the analysis field, the root mean square error (RMSE) of u_wind and v_wind in the entire vertical levels is significantly less than that of the other two systems. The time series of total RMSE indicate, in the 6-30h forecast range, that the forecast result of En-3DVAR-TD-HLS is better than that of the other two systems, but the En-3DVAR and 3DVAR are equivalent in terms of their forecast skills. The 36-48h forecasts of three data assimilation systems have similar forecast skill.  相似文献   

Thermo-acoustic sound generation in the interaction of pulsed proton and laser beams with a water target     

《Astroparticle Physics》2015

The generation of hydrodynamic radiation in interactions of pulsed proton and laser beams with matter is explored. The beams were directed into a water target and the resulting acoustic signals were recorded with pressure sensitive sensors. Measurements were performed with varying pulse energies, sensor positions, beam diameters and temperatures. The obtained data are matched by simulation results based on the thermo-acoustic model with uncertainties at a level of 10%. The results imply that the primary mechanism for sound generation by the energy deposition of particles propagating in water is the local heating of the medium. The heating results in a fast expansion or contraction and a pressure pulse of bipolar shape is emitted into the surrounding medium. An interesting, widely discussed application of this effect could be the detection of ultra-high energetic cosmic neutrinos in future large-scale acoustic neutrino detectors. For this application a validation of the sound generation mechanism to high accuracy, as achieved with the experiments discussed in this article, is of high importance.  相似文献   

声学探测技术在天津隐伏断层探测中的应用   总被引：4，自引：0，他引：4  

陈宇坤  郑彦鹏  高武平  王志胜 《震灾防御技术》2007,2(2):116-127

利用单道地震等水上声学探测技术,对天津海河断裂的浅部构造和地层错断信息进行了探测。探测结果表明,在水深较深,相对宽阔的河道内该方法可以获得较好的结果。在天津塘沽地区,海河断裂的上断点深度位于河底面以下30m左右,对应的最新活动时代为Q_p~3—Q_h~1,这与前期的钻孔勘探结果基本吻合。在渤海近海海域,海河断裂呈一组NWW-NEE向分布的断裂带,其上断点距离海底的深度小于30m,断层断错和影响的地层年代为全新世早中期,断层活动特征与塘沽地区的基本一致。  相似文献   

基于四麦克风阵列的三维声源定位     

王文龙  张艳萍 《南京气象学院学报》2010,(5):410-413

设计了一个三维声源定位系统,提出了一个新的系统模型,并对传统的基于声波到达时间差TDOA的算法进行了优化。通过检测麦克风接收到信号的时间差,结合已知的阵列元的空间位置确定声源的位置。该系统声源采集部分由4个阵列成正四面体的麦克风组成。算法的硬件实现由TMS320C5416DSP芯片完成''整个系统实现了声源定位的功能。  相似文献   

岩石受压状态的损伤分析   总被引：2，自引：0，他引：2  

谢晔  张东明  亢会明 《地质灾害与环境保护》2001,12(4):56-58

以损伤力学的方法对岩石在受压状态下的破坏行为进行了分析，损伤力学（CDM）方法近年来在金属、混凝土及复合材料等工程材料的蠕变、断裂等问题的研究中得到大量应用。损伤演变是物质内部结构的不可逆变化过程，损伤变量是与塑性变形一样的内变量，文中据实验数据推导出某类岩石的损伤变量演化曲线，以及损伤与应力的变化关系，以期用损伤学方法研究岩石变形的局部化行为。  相似文献   

雁列式断层变形过程中物理场演化的实验研究（一）   总被引：21，自引：3，他引：21  

马胜利  邓志辉 《地震地质》1995,17(4):327-335

在双轴压缩条件下对挤压型和拉张型雁列式断层变形破坏过程中声发射、断层位移及应变场的时空演化进行了实验研究。研究表明，两类雁列式断层具有类似的变形破坏过程，即前期以雁列区的破裂贯通为主，后期以沿断层的滑动为主。但挤压型雁列区内可积累较高的应变能，有较强的应变释放和声发射活动，雁列区对滑动始终起着阻碍作用；而拉张型雁列区内难以产生快速的应变释放和较强的声发射活动，雁列区对后期的滑动也无明显的阻碍作用。两类雁列区贯通所引起的失稳均有明显的前兆，而在随后滑动过程中失稳前兆的出现，取决于断层不同部位或段落之间是否有应变传递  相似文献   

雁列式断层变形过程中物理场演化的实验研究（二）   总被引：6，自引：1，他引：6  

马胜利  刘力强 《地震地质》1995,17(4):336-343

在双轴压缩条件下对由挤压型和拉张型雁列式断层组合而成的复杂雁列断层系变形过程中声发射、断层位移及应变的时空演化进行了实验研究，结果表明，复杂雁列式断层系的变形过程及相应的物理场演化并非是两种雁列式断层的简单叠加，而是包含着它们之间的相互作用。能量较强的声发射事件成核部位主要集中在应力水平较低的张性雁列区附近的主于断层上，而不是应力水平较高的压性雁列区，但这种事件发生的时间则明显受控于压性雁列区的变形过程  相似文献   

Highly Localized Vernacular Regionalization in the Allentown-Bethlehem Area,PA-NJ*     

Douglas E. Heath 《The Professional geographer》1993,45(3):251-263

Yi-Fu Tuan's cognitive theory of the construction of place suggests the need for a higher level of resolution in research on American local vernacular regions. A survey-based case study of the Allentown-Bethlehem area demonstrates that municipal data can substantially refine an existing county-based delimitation by revealing previously undocumented regions and subregions, areas with mixed regional identity, and areas lacking regional identity. The resulting delimitations of subcounty vernacular regions are sufficiently precise to disclose a striking correspondence with area school districts.  相似文献