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Wang W.,Kyushu University | Wang W.,Wuhan University | Chen G.-Q.,Kyushu University | Zhang H.,Tongji University | And 4 more authors.
Engineering Analysis with Boundary Elements | Year: 2016

Large impulsive waves generated by slope failures and a subsequent landslide in a reservoir area may lead to serious damage to the dam, shoreline properties and lives. Therefore, analysis of landslide-generated impulsive waves is of significant importance for hazard prevention and reduction. There are three key points for analyzing this problem: (i) the landslide run-out, (ii) the free surface flow and (iii) the landslide-water interaction process. The Discontinuous Deformation Analysis (DDA) method was previously developed to investigate discontinuous block movements, while the Smoothed Particle Hydrodynamics (SPH) method was used mostly to model free surface flow. However, the solid-fluid interaction is seldom considered in the respective fields, which greatly restricts their applications. For this reason, the coupled DDA-SPH method was proposed in this study to solve the solid-fluid interaction problem. To validate this approach, this study considered a wedge sliding along an inclined plane and interacting with the water body. The corresponding Heinrich's experimental results were adopted to evaluate the accuracy of the coupled method in modeling the landslide movement and wave profile, proving that the landslide motion and wave profiles could be captured accurately by the coupled method. Finally, the effect of the governing parameters on the wave amplitude was discussed. © 2015 Elsevier Ltd. All rights reserved.


Zhang H.,Tongji University | Liu S.-G.,Tongji University | Han Z.,Central South University | Zheng L.,Hong Kong Polytechnic University | And 4 more authors.
Computers and Geotechnics | Year: 2016

In the contact theory for three-dimensional discontinuous deformation analysis (3-D DDA), the first step is to identify the types of contacts between the blocks. This paper presents a new algorithm to identify contact types between arbitrarily shaped polyhedral blocks for 3-D DDA. First, pairs of neighbouring blocks that are close enough to possibly be in contact are recognized using their axis-aligned bounding boxes. Four types of dominant contacts (i.e., vertex-to-vertex, vertex-to-edge, vertex-to-face and crossing edge-to-edge contacts) that control the movements of blocks, especially rotations, are then identified using an extended hierarchy territory algorithm. Finally, using a new loop search procedure, face-to-face contacts in which the interface strength depends on the friction angle, cohesion and tensile strength rather than only the friction angle, are formed from several interdependent dominant contacts. The results of three numerical examples demonstrate the ability of the new algorithm to address the complex problem of contacts between arbitrarily shaped polyhedral blocks. © 2016 Elsevier Ltd


Wu Y.,Institute of Geology | Wu Y.,Institute of Earthquake Science | Jiang Z.,Institute of Earthquake Science | Yang G.,First Crust Deformation Monitoring and Application Center | And 3 more authors.
Geophysical Journal International | Year: 2011

Using modelled and simulated data for comparison of several methods to compute GPS strain rate fields in terms of their precision and robustness reveals that least-squares collocation is superior. Large scale (75°E-135°E and 20°N-50°N) analyses of 1° grid sampling data and decimated 50 per cent data by resampling (then erasing data in two 5°× 10° region) reveal that the Delaunay method has poor performance and that the other three methods show high accuracy. The correlation coefficients between theoretical results and calculated results obtained with different errors in input data show that the order in terms of robustness, from good to bad, is least-squares collocation, spherical harmonics, multisurface function and the Delaunay method. The influence of data sparseness on different methods shows that least-squares collocation is better than spherical harmonics and multisurface function when sample data are distributed from a 2° grid to a 1° grid. Analysis to medium scale (90°E-120°E, 25°N-40°N) in 1°-0.5° grid sampling data reveals that least-squares collocation is superior to other methods in terms of robustness and sensitivity to data sparseness, but their difference is slight. Strain rate results obtained for the Chinese mainland using GPS data from 1999 to 2004 show that the spherical harmonics method has edge effects and that its value and range increase concomitantly with increased sparseness. The multisurface function method shows non-steady-state characteristics; the errors of results increase concomitantly with increased sparseness. The least-squares collocation method shows steady characteristics. The errors of results show no significant increase even though 50 per cent of input data are decimated by resampling. The spherical harmonics and multisurface function methods are affected by the geometric distribution of input data, but the least-squares collocation method is not. © 2011 The Authors Geophysical Journal International © 2011 RAS.


Zhang H.,Kyushu University | Zhang H.,Tongji University | Chen G.,Kyushu University | Zheng L.,Hong Kong Polytechnic University | And 5 more authors.
International Journal of Rock Mechanics and Mining Sciences | Year: 2015

A new algorithm to detect contacts between three-dimensional (3-D) arbitrarily shaped polyhedral blocks for the discontinuous deformation analysis (DDA) method is presented in this paper. The new algorithm includes three main steps, i.e. neighbor search, contact type examination, and entrance candidate identification, all of which are performed using the general features and relations of geometric elements of polyhedra. First, contact detection begins with searching neighbor blocks and vertices potential to be in contact in order to improve the computation efficiency. Then, pairs of neighbor blocks are examined in more detail for four basic contact types. Finally, corresponding contact points and planes for each contact type are identified by general entrance formulas, which is prepared for the subsequent contact force calculations in the program. The new algorithm has been implemented in the original 3-D DDA program and the extended 3-D DDA program can display the results using OpenGL. Three typical contact examples including concave blocks, i.e. vertex-to-concave-edge, convex-edge-to-concave-edge and vertex-to-concave-vertex contacts are provided to verify the new algorithm. Additionally, a practical example in rock engineering, sliding of a tetrahedral wedge, is also presented, and the 3-DDA results are compared with the analytical solutions. © 2015 Elsevier Ltd.


Wang C.-H.,China Earthquake Administration | Song C.-K.,First Crust Deformation Monitoring and Application Center | Guo Q.-L.,China Earthquake Administration | Zhang Y.-S.,China Earthquake Administration | Ding J.-M.,China Earthquake Administration
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

The MS7.0 Lushan Earthquake in the southern segment of Longmenshan Fault has brought great loss to the local natives and societies. To analyze the earthquake from the viewpoint of stress buildup in the upper crust is helpful and meaningful to understand more about the seismogenic mechanism. In the past 21 years, the research group accumulated and collected lots of in-situ stress data from 22 boreholes. These in-situ stress data show that the stress regime is of reverse faulting, and that the orientation of the maximum horizontal principal stress is N44°-64°W. At the same time, the stress measurements indicate that the stress state in the research area is relatively stable. In this paper, the authors suggest adopting the ratio of half maximum differential stress to the mean effective stress, μm, to reflect the capability and stress level of the upper crust. According to the theoretical analysis, μm has similar physical meaning with μ, so we can replace μ with μm to do rock friction analysis. The μm based on all the stress measurements ranges from 0.39 to 0.56, approximately approaching the lower limit defined by the Byerlee law, μ=0.6, which also agrees well with the static friction coefficients of gouge specimen from the Longmenshan fault after Wenchuan Earthquake tested in the laboratory. Therefore, the occurrence of the Lushan Earthquake proves that the upper crust of the research area is in the critical frictional equilibrium state or sub-equilibrium state. The focal mechanism solution of Lushan Earthquake is reverse faulting, with the main P axis of 122°, which is consistent with the stress state defined by the in-situ stress measurements. Compared with the research findings made by other geoscientists, the Lushan Earthquake can be regarded as one induced earthquake due to the stress increase caused by the Wenchuan Earthquake on the southern segment of Longmenshan fault.


Wang X.-W.,China Earthquake Administration | Wang X.-W.,National Continental Rift Valley Dynamics Observatory of Taiyuan | Song M.-Q.,China Earthquake Administration | Song M.-Q.,National Continental Rift Valley Dynamics Observatory of Taiyuan | And 4 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2010

Based on the focal mechanism solution database established by collecting 37 years initial motion of small earthquakes (1970 -2006), the space-time evolution characteristics of small-earthquake integrated mechanisms in Shanxi fault zone are studied in this paper. The results indicate that small-earthquake integrated mechanisms in Shanxi fault zone are mainly dominated by strike slip normal faults, at the two ends dominated by extension tectonics and in the central region by shearing. The difference between the stress field of Huabei and the regional stress fields of Xinding and Taiyuan Basins is very large. The relationship between horizontal motions and earthquake activities in Shanxi fault zone is analyzed according to the 12 stages of remeasuring data of GPS monitoring network along the Shanxi fault zone (1996 -2007). The results indicate that the Shanxi fault zone now is mainly controlled by compressional stress along NWW-SEE direction and tensile stress along NNE-SSW. One obvious stress disturbance occurred during the period of 1998 -1999, which was stronger in the south than in the north. This was followed by Datong-Yanggao M5. 6 earthquake on 1st Nov. 1999.


Zhang H.,Tongji University | Liu S.-G.,Tongji University | Zheng L.,Hong Kong Polytechnic University | Zhong G.-H.,Tongji University | And 3 more authors.
Computers and Geotechnics | Year: 2016

This paper extends the edge-to-edge (E-E) contact model for three-dimensional discontinuous deformation analysis (3-D DDA) by addressing the difficulties in determining the contact point pairs, contact candidates and mechanical properties of the interface required for friction analysis. Contact candidates and mechanical properties of the interface are determined using new judgment criteria. Contact point pairs are evaluated using path-dependent analysis. Complete formulations for the new E-E contact model are derived from the auxiliary-simplex method. These extensions have been implemented in the 3-D DDA program. Numerical tests demonstrate that the extended 3-D DDA can accurately model the frictional behavior of a block system. © 2015 Elsevier Ltd.


Wu Y.,Institute of Earthquake Science | Jiang Z.,Institute of Earthquake Science | Yang G.,First Crust Deformation Monitoring and Application Center | Zhao J.,Institute of Earthquake Science
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2012

Based on the analysis of fitting residual errors of GPS velocity, the errors of deformation parameters, and the applicability of block model, we use GPS velocity fields, strain rate fields, slipping rate of faults and GPS profile results from 1999-2007 and from 2007-2009 to identify the deformation difference of principle faults on the north section of North-South Seismic Zone. The results show that the laevorotation deformation of Zhuanglanghe Fault has increased, which the dextrorotation deformation rate calculated from Eulerian model is about 1.5±0.3 mm·a -1 in the period 1999-2007, and the laevorotation deformation rate is about 5.3±0.4 mm·a -1 in the period 2007-2009. On the other hand, the laevorotation slipping rate of north boundary of Qilian block has increased from 2.5±0.2 mm·a -1 to 7.0±0.2 mm·a -1 in these two periods. Otherwise, the extrusion deformation of Liupanshan and Haiyuan Faults has strengthened too, but the deformation magnitude is not big. These above deformation characteristics illustrate that the region of east side of Zhuanglanghe Fault has accumulated high strain energy.


Wu Y.,First Crust Deformation Monitoring and Application Center | Wu Y.,Prediction Institute | Jiang Z.,Prediction Institute | Liang H.,First Crust Deformation Monitoring and Application Center | And 5 more authors.
Tectonophysics | Year: 2016

The principal strain rate, derived from GPS velocities from the Tibetan Plateau and the India Plate, shows that the Himalayan tectonic belt exhibits compression deformation in a NE-NS-NE direction from the west to the east. The GPS velocity profiles reflect that the distribution of strain accumulation is uneven: there is a 17.1 mm/yr. compressive deformation distributed over 400 km along 85° E longitude, a 20.9-22.2 mm/yr. compressive deformation dispersed across 400-500 km along 79° E longitude, and a 15.3-16.9 mm/yr. compressive deformation spread across 500-600 km along 91° E longitude. The MW 7.8 Gorkha earthquake occurred at the edge of an intense compression deformation zone of about 6.0 × 10-8/yr. in a north-south direction, and an about 90% compressive strain is absorbed in the 300 km region near the Main Frontal Thrust (MFT). Coseismic displacements, larger than three standard deviations (3SD), are mainly concentrated within 360 km from the epicenter. The nodal plane of the main shock divides the areas where tensile strain release in an exponential attenuation pattern is dominant to the north, and where compressive strain with upward movement is dominant to the south. The results inversed by the SDM program reveal that the maximal slip of the Gorkha earthquake is 5.33 m, and its moment magnitude is MW 7.85, and the largest stress drop is 4.21 Mpa. Slips larger than 0.5 m are mainly distributed in a region approximately 135 km × 105 km, which show that the rupture of the Gorkha earthquake does not reach the surface. Finally, we estimate that the recurrence period of this earthquake is about 166 ± 20 years according to the strain accumulation before the earthquake and the coseismic release feature. © 2016 Elsevier B.V.


Luo S.,First Crust Deformation Monitoring and Application Center | Bo W.,First Crust Deformation Monitoring and Application Center | Huang Q.,First Geodetic Surveying Brigade | Wang X.,First Geodetic Surveying Brigade
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2012

Starting directly with coefficient matrix of condition equation or error equation, the least square solution by triangulation decomposition on coefficient matrix is carried on with improved Gram-Schmidt orthogonalization procedure. Then, the math formula and the calculation steps of solving generalized inverse matrix on improved Gram-Schmidt algorithm are deduced. The unknown solution vectors and the mathematical expression of the variance-covariance matrix are given through the generalized inverse expression. Two examples are used to verify its effect, and the results show that the modified Gram-Schmidt orthogonal method can process any matrix including rank defect array.

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