Showing papers on "Discontinuous Deformation Analysis published in 2003"

Discontinuous modelling of masonry bridges

Abstract: Computational modelling frameworks for masonry bridges range from highly simplified methods to complex nonlinear finite element or discrete elements. In majority of cases the macro level nonlinear finite element models1 and homogenisation techniques are adopted. Attention has also been given to assessment methodologies (discrete element method, rigid block spring method, lattice modelling, discontinuous deformation analysis, combined discrete/finite elements), which deal more directly with the discontinuous nature of structural masonry in a simplified micro modeling manner. These methods model an inherently discontinuous medium, but are also applied to problems where the transition from a continuum to discontinuum is important. Principal computational issue is the treatment of large number of distinct interacting domains, where the contact conditions are continuously updated and enforced as the solution progresses. Modelling of masonry arches requires a consideration of deformable multi-bodies and their contact nonlinearity, which is here realised in the context of the discontinuous deformation analysis, based on an assumed deformation field within distinct domains of arbitrary shapes with a rigorous imposition of contact constraints.

Numerical modelling of rock fall using extended dda

Abstract: The reasonable design of protective structures to mitigate the hazards from rock fall depends on the knowledge of motion behaviors of falling stones,such as the falling paths,velocities,jump heights and distances.Numerical simulation is an effective way to gain such kind of knowledge,In this paper,the discontinuous deformation analysis (DDA) is applied to rock fall analysis.In order to obtain more reliable results,the following improvements and extensions are made on the original DDA.(1)Solve the problem of block expansions due to rigid body rotation error.(2) Add the function of modeling the drag resistance from air and plants so that the velocities of falling stones obtained by simulations are good enough in agreement with those by experiments in situ.(3)Add the capability to consider energy loss due to block collisions so that the jumping heights and distances obtained by simulations are good enough in agreement with thos by experiments even for the slope with very soft layer on its surface.One of application examples is presented to show that the extended DDA is very effective and useful in rock fall analysis.Therefore,the presented method is expected to be put into wide use in slop stability analysis.

Modified shear spring formulation for discontinuous deformation analysis of particulate media

Abstract: Ke and Bray (1995) presented the formulation of the discontinuous deformation analysis method (DDA) for a particulate medium consisting of two-dimensional disks This original DDA formulation calculated the shear force at each contact by considering the incremental displacement of the shear contact spring Other approaches that model particulate materials discretely generally use the cumulative spring displacement at each contact to calculate the shear contact force The modifications required to implement a cumulative spring formulation in DDA are presented A simple, single disk validation example demonstrates the improved performance of the modified algorithm An analysis of a biaxial compression test highlights the sensitivity of the response of disk assemblies to the shear spring formulation

Evaluation of Seismic Performance for Tunnel Retrofit Project

Abstract: A seismic retrofit program at Yerba Buena Island Tunnel is presented as a case history. The studies include evaluations of portal stability under earthquake excitation and performance of the tunnel liner as a result of seismic induced deformation. Due to different potential failure modes at the two portal areas, two separate evaluation techniques were utilized. Key block theory in conjunction with a Newmark type analysis was used to assess movements of a potential failure wedge at the west portal slope, while discontinuous deformation analysis was utilized at the east portal slope to evaluate a rotational mode of failure. To assess the performance of the liner subjected to design earthquakes, a two-step analysis procedure was adopted. The first step was to compute seismic induced deformations of the tunnel subjected to seismic wave propagation through the island rock without the presence of the liner. The second step, not reported in this paper, involved imposing the deformations of the tunnel onto the structural liner through spring elements that accounted for interaction between the liner and the surrounding rock. From the studies, performance of the existing tunnel supports was found to be acceptable.

A review on the discrete element method

Abstract: This paper summarizes the recent progress in theoretical bases, numerical algorithms and applications of the discrete element method (DEM). A more general definition for the DEM is made, by considering the key point of the model and its distinctions from the other numerical algorithms. The relationship between the DEM and the other algorithms, such as RBSM (Rigid Body Spring Model), DDA(Discontinuous Deformation Analysis), MD(Molecular Dynamics), DM2 (Discrete Meso-element Dynamic Method), MM(Meshless Method), is explained. The future research topics and development tendency of the DEM are discussed.

Stability and convergence of mixed discontinuous finite element methods for second-order differential problems

Abstract: In this paper we develop an abstract theory for stability and convergence of mixed discontinuous finite element methods for second-order partial differential problems. This theory is then applied to various examples, with an emphasis on different combinations of mixed finite element spaces. Elliptic, parabolic, and convection-dominated diffusion problems are considered. The examples include classical mixed finite element methods in the discontinuous setting, local discontinuous Galerkin methods, and their penalized (stablized) versions. For the convection-dominated diffusion problems, a characteristics-based approach is combined with the mixed discontinuous methods.

Numerical Simulations for Rupture Processes of a Series of Strong Earthquakes (Ms > 7) in North China Since 1966

Abstract: The different rupture processes of strong earthquakes (M S=7), such as Xingtai earthquake in 1966, Bohai earthquake in 1969, Haicheng earthquake in 1975, and Tangshan earthquake in 1976, which occurred on the boundary faults of blocks in North China and in the systematic environment of tectonic blocks under mutually restricting, are simulated numerically by discontinuous deformation Analysis (DDA+FEM). In the paper, the results of numerically simulating include the principal stress field released in every large earthquakes, the contour picture of maximum shear stress change, the vector picture of displacement caused by the earthquakes, the sliding displacement on faults with time, the maximum strike sliding distance and stress drop. These results agree basically with focus mechanism, focus parameters from seismic wave, macroscopic isoseisms and horizontal displacement vector map from observation on surface of earth. Furthermore,the imageof contour picture of maximum shear stress change on orthographically rupture mode of Bohai earthquake in 1966is closer with the macroscopic isoseismal picture. The results about the complex focus of Tangshan earthquake in 1976 are more accordant with aftershock distribution picture at early period of the earthquake. It is indicated that DDA+FEM is a very suitable tool to simulate rupture process of earthquakes.

Numerical simulations of deformation and movement of blocks within North China in response to 1976 Tangshan earthquake

Abstract: Using methods of discontinuous deformation analysis and finite element (DDA+FEM), this paper simulates dynamic processes of the Tangshan earthquake of 1976, which occurred in the northern North China where its internal blocks apparently interacted. Studies focus upon both the movement and deformation of the blocks, in particular, the Ordos block, and variations of stress states on the boundary faults. The Tangshan earthquake was composed of three events: slipping motions of NNE-striking major fault, NE-striking fault near the northeastern end of the NNE-striking fault, and NW-striking fault on the southeastern side of the NNE-striking fault. Compared with previous studies, our model yields a result that is more agreeable with the configuration of aftershock distributions. A number of data are presented, such as the principle stress field during the earthquake, contours of the maximum shear stress, the strike-slip deformation between blocks near the earthquake focus, time-dependent variations of slips of earthquake-triggered faulting, the maximum slip distance, and stress drops. These results are in accord with the earthquake source mechanism, basic parameters from earthquake wave study, macro-isoseismic line, observed horizontal displacement vectors, etc. The Tangshan earthquake exerted different influences on the adjacent blocks and boundary faults between them, thus resulting in differential movement and deformation. The Ordos block seems to have experienced the small-scale counterclockwise rotation and deformation, but its northeast part, bounded on the east by the Taihangshan and on the north by the Yanshan and Yinshan belts, underwent relatively stronger deformation. The Tangshan earthquake also changed the stress state of boundary faults of the North China, leading to an increase in shear stress and a decrease in normal stress in the NW-trending Zhangjiakou-Penglai fault through Tangshan City and the northern border faults of the Ordos block, and therefore raises the potential risk of earthquake occurrence. This result is supported by the facts that a series of Ms ≥ 6 earthquakes took place at the northern margin of the Ordos block after the Tangshan earthquake.

Two-level preconditioning of a discontinuous Galerkin method for radiation diffusion

Abstract: Weproposea two-level preconditioning strategy for the iterative solution of large sparse linear systems arising from a discontinuous Galerkin discretization of the radiation diffusion equations The idea is to usea continuous finite element discretization of theoriginal, elliptic diffusion equation for preconditioning the discontinuous equations We show how our preconditioner is developed and applied to radiation diffusion problems on unstructured, tetrahedral meshes We present numerical results to illustrate its effectiveness

Space-time discontinuous Galerkin finite element method for inviscid gas dynamics

Abstract: In this paper an overview is given of the space-time discontinuous Galerkin finite element method for the solution of the Euler equations of gas dynamics. This technique is well suited for problems which require moving meshes to deal with changes in the domain boundary. The method is demonstrated with the simulation of the elastic deformation of a wing in subsonic and transonic flow.

Simulation of Rock Slope Failure with Three-Dimensional Discontinuous Deformation Analysis (3D DDA)

Abstract: In this paper, both the theory of Three-Dimensional Discontinuous Deformation Analysis (3D DDA), and its application to simulate rock slope failure problems are discussed. DDA belongs to one of the discontinuous numerical analysis methods, and the contact judgment and contact force computation should be concerned to produce contact forces when blocks contact to each other. It is shown that a normal contact spring is employed to calculate the normal contact forces to prevent blocks from penetrating to each other during contacts. However, the normal contact spring is deleted when blocks are leaving. In addition, the failure along discontinuous surfaces can be simulated easily by applying the Mohr-Coulomb failure criterion. The appropriate contact spring arrangement in 3D DDA follows the criterion of \"No-penetration and No-Tension\" to obtain correct contact forces during contacts. The new approach has been successfully applied to simulate a rock slope toppling at Amatoribashi-nishi site in Japan. The simulation results are quite in agreement with the video pictures obtained from the field. We believe that the simulation is very helpful on investigation of the failure mechanism and process, which can provide useful knowledge for study such events in future

A New Meshless Method — Finite-Cover Based Element Free Method

Abstract: Presented in the paper is a so-called finite-cover-based element-free method that is aimed to solve both continuous and discontinuous deformation problems in a mathematically consistent framework as manifold method, but no requiring mesh generation. The method is mathematically based on finite circular cover numerical technique and multiple weighted moving least square approximation. In this method, overall volume of materials is overlaid by a series of overlapped circular mathematical covers. While cut by joints, interfaces of different media and physical boundaries, a mathematical cover may be divided into two or more completely disconnected parts that are defined as physical covers. Discontinuity of materials is characterized by discontinuity of physical cover instead of disconnection of influence support. Hence, influence domain, i.e. mathematical cover can be kept regular even in a discontinuous problem. On a set of physical covers containing unknown point under consideration, the multiple weighted moving least square approximation in conjunction with cover weighting functions defined on each mathematical cover is used to determine shape functions of the unknown point for variational principle. Afterwards, discrete equations of the boundary-value problem with discontinuity can be established using variational principle. Through numerical analyses, it is shown that the proposed method that shares successfully advantages of both the manifold method and mesh-free methods is theoretically rational and practically applicable.

Dynamic failure test and numerical simulation of model concrete-faced rockfill dam

Abstract: In this paper, the dynamic failure phenomena of two kinds of model dams, i.e., homogeneous rock fill dams and faced rock fill dams, are investigated by large scale shaking table tests. Numerical simulations of model dams are performed by Discontinuous Deformation Analysis that takes the displacement discontinuity of filled materials and contact between facing slab and dam body into consideration. The results obtained from numerical simulations are consistent with those from the corresponding dynamic experiments. Based on the results from the experiments and numerical simulations, some beneficial conclusions are obtained.

Structure analysis by second-order Manifold Method

Abstract: The Manifold Method is a newly developed numerical procedure.By a unique arrangement of numerical meshes and treatment to contact,the method is able not only to accurately analyze the structure displacement and stress distribution as can be done by applying Finite Element Method,but also to simulate the deformation of structures with many discontinuities and block movement as can be done by using Discontinuous Deformation Analysis.Based on the original first\|order Manifold Method,the author developed a second\|order Manifold Method together with corresponding computational code.Application examples included analysis of contact stress of a cylinder compressed between rigid plates,large deformation problem of a cantilever beam and failure of a side slope with discontinuities.The results showed that the second\|order Manifold Method was capable of analyzing structure deformation,stress,contact problems and large\|scale deformation problems with relatively high accuracy.It would provide also the failure process and block movement with acceptable accuracy.

Seismic stability analysis of rolled compacted concrete dam based on approach of DDA coupled with FEM

Abstract: Comprehensive research on the dynamic responses and the failure process of a high RCCD are performed using the discontinuous deformation analysis (DDA) coupled with finite element method (FEM). Some additional functions have been incorporated into the current DDA code, including coupling algorithm of DDA and FEM and an improved four-node isoparametric element generator for deformable elements. The corresponding program is developed based on the MS-Windows~(TM) computing environment. The results show that RCCD is safe under the design loadings. Furthermore, the ability of over loading and the failure mode are calculated and discussed. The results demonstrate that the failure of the RCC dams usually occurs at the top of the dams and the opening and sliding between the RCC layers will cause the failure of the RCC dams, and the effects of different earthquakes input on the dynamic response behaviors and the collapse pattern of the systems are significant.

An analysis of propagationg discontinuities by the finite cover method

Abstract: We develop an analysis method for discontinuous deformation without re-meshing. The proposed method is based on the Finite Cover Method (FCM), which is actually an alias for the Manifold Method. By virtue of the mesh-free nature of the FCM, propagating discontinuous boundaries can be traced regardless of initial mesh discretization. Furthermore, the nonlocal material modeling is introduced to avoid the dependency on mesh size. Representative numerical examples demonstrate the performance of the proposed method and well simulate the propagation of discontinuities with independently generated FCM mesh.

Study of Ice-Structure Interaction by Discontinuous Deformation Analysis

Abstract: Process of dynamic interaction between a sea ice sheet and an erected structure was simulated by discontinuous deformation analysis, which has the advantages that the whole process of collision between the ice and the structure can be shown visually with a series of pictures. Meanwhile, the dynamic response of the structure at each time step after the ice bumping against the structure can be calculated. Numerical example shows that the discontinuous deformation analysis is more effective and reasonable compared with FEM or BEM in simulating dynamic ice-structure interactions. 

Discontinuous Deformation Analysis of Seismic Failure Behavior in a Narrow Area of Railroad Ballast

Abstract: The seismic failure behavior of railroad ballasts in response to earthquakes was analyzed using Discontinuous Deformation Analysis.Several sinusoidal waves with different frequencies and accelerations were inputted into the discontinuous numerical model of a railroad ballast ,which consists of an assemblage of polygonal crushed stones,rails,sleepers and a roadbed .The dependencies of railroad failure activities on frequency and acceleration were evaluated with such parameters as;increase in void volume,horizontal,vertical and angular displacements at different points with respect to the areas under the sleeper and the shoulder of ballast .The results indicated that initial dilation by the rotational behavior of the crushed stones triggers the succeeding failure process.