The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Zilong Zhou - One of the best experts on this subject based on the ideXlab platform.
-
Microscopic Failure Mechanism Analysis of Rock Under Dynamic Brazilian Test Based on Acoustic Emission and Moment Tensor Simulation
Frontiers in Physics, 2021Co-Authors: Zilong Zhou, Jing Zhou, Yuan Zhao, Lian-jun ChenAbstract:Dynamic tensile failure of Rock is a main failure mode in deep underground engineering projects. The microscopic failure mechanism analysis of this failure mode plays a key role in dynamic disaster warning. Moment tensor inversion is a very well-known method to analyze failure mechanism. However, the acoustic emission (AE) event cannot be accurately distinguished in Rock Dynamics experiments at laboratory scale. Because there will be hundreds of AE events generated within 250 μs in one dynamic test. Therefore, moment tensor analyze is rarely applied in Rock dynamic test with laboratory scale. In this paper, AE and moment tensor simulated with discrete element method (DEM) are introduced to analyze microscopic failure mechanism of Rock under dynamic Brazilian test. Comparing the simulation results of AE and moment tensor with the simulation results of micro-crack with DEM, the moment tensor discriminant method can obtain mechanical mechanism and energy level of micro-crack. Furthermore, R, which is the ratio of isotropic and deviatoric components of the moment tensor, is used to analyze AE source mechanism. The implosion, shear and tension of AE source mechanism can better explain the evolution process of main axial crack and the shear failure zones of the Brazilian disc specimen under dynamic tensile simulation. These findings can contribute to a better understanding of These results show that the moment tensor simulation is more intuitive and accurate to analyze the microscopic failure mechanism of Rock under dynamic tensile test than the statistical types of micro-cracks based on break bond with DEM.
-
obtaining constitutive relationship for rate dependent Rock in shpb tests
Rock Mechanics and Rock Engineering, 2010Co-Authors: Zilong Zhou, Kewei LiuAbstract:A large number of tests have recently been conducted with the Split Hopkinson pressure bar (SHPB) method to determine the characteristics of Rock Dynamics. However, it is still impossible to get test results at a perfect constant strain rate from this set-up owing to the rate dependency of Rock materials. For instance in most cases, dynamic behavior of Rock can only be described with an average strain rate. The results from these methods, including rich strain rate information, frequently tend to be inexplicable or self-contradictory. The obtained stress–strain curves can then never be directly treated as constitutive curves as in static tests. In this paper, the reasons behind the controversial stress–strain results with current methods are analyzed. In addition, the requirement for the Rock specimen to deform at a constant strain rate is demonstrated after theoretical analysis of correlations among specimen, deforming stress, incident stress, reflected stress and transmitted stress. With test results from SHPB by pulse shaper and special shape striker methods, the requirement is verified. Finally, the method of 3D scattergram considering stress–strain–strain rate simultaneously is brought up to get constitutive relationships of rate-dependent Rock. The new method gives reasonable predictions for constitutive relationships of Rock at different strain rates. At the same time, the new method has fewer requirements and has a wider application scope for SHPB tests.
G. Grasselli - One of the best experts on this subject based on the ideXlab platform.
-
An Example of Realistic Modelling of Rock Dynamics Problems: FEM/DEM Simulation of Dynamic Brazilian Test on Barre Granite
Rock Mechanics and Rock Engineering, 2010Co-Authors: O. K. Mahabadi, B. E. Cottrell, G. GrasselliAbstract:The scope of this study is to numerically simulate the behaviour of Brazilian disc specimens as observed in laboratory during dynamic, high-strain rate, indirect tensile tests using an innovative combined finite-discrete element method (FEM/DEM) research code. Laboratory experiments using a split Hopkinson pressure bar (SHPB) apparatus were conducted by the authors and the measured indirect tensile strength values were used to verify the FEM/DEM models. In the models the applied boundary conditions, related to the loading rate of the specimen, were matched with the experimental observations. The results of the numerical simulations, including tensile strength and failure time, are in agreement with the laboratory findings. The main failure mechanisms, i.e. tensile splitting along loading axis and shear failure close to loading platens are captured by the numerical model. A linear relationship between tensile strength and loading rate is found for the range of dynamic strain rates tested and simulated. The simulation results are in good agreement with laboratory observations and demonstrate the potential for using FEM/DEM to realistically model dynamic response of Rocks.
-
an example of realistic modelling of Rock Dynamics problems fem dem simulation of dynamic brazilian test on barre granite
Rock Mechanics and Rock Engineering, 2010Co-Authors: O. K. Mahabadi, B Cottrell, G. GrasselliAbstract:The scope of this study is to numerically simulate the behaviour of Brazilian disc specimens as observed in laboratory during dynamic, high-strain rate, indirect tensile tests using an innovative combined finite-discrete element method (FEM/DEM) research code. Laboratory experiments using a split Hopkinson pressure bar (SHPB) apparatus were conducted by the authors and the measured indirect tensile strength values were used to verify the FEM/DEM models. In the models the applied boundary conditions, related to the loading rate of the specimen, were matched with the experimental observations. The results of the numerical simulations, including tensile strength and failure time, are in agreement with the laboratory findings. The main failure mechanisms, i.e. tensile splitting along loading axis and shear failure close to loading platens are captured by the numerical model. A linear relationship between tensile strength and loading rate is found for the range of dynamic strain rates tested and simulated. The simulation results are in good agreement with laboratory observations and demonstrate the potential for using FEM/DEM to realistically model dynamic response of Rocks.
Kewei Liu - One of the best experts on this subject based on the ideXlab platform.
-
obtaining constitutive relationship for rate dependent Rock in shpb tests
Rock Mechanics and Rock Engineering, 2010Co-Authors: Zilong Zhou, Kewei LiuAbstract:A large number of tests have recently been conducted with the Split Hopkinson pressure bar (SHPB) method to determine the characteristics of Rock Dynamics. However, it is still impossible to get test results at a perfect constant strain rate from this set-up owing to the rate dependency of Rock materials. For instance in most cases, dynamic behavior of Rock can only be described with an average strain rate. The results from these methods, including rich strain rate information, frequently tend to be inexplicable or self-contradictory. The obtained stress–strain curves can then never be directly treated as constitutive curves as in static tests. In this paper, the reasons behind the controversial stress–strain results with current methods are analyzed. In addition, the requirement for the Rock specimen to deform at a constant strain rate is demonstrated after theoretical analysis of correlations among specimen, deforming stress, incident stress, reflected stress and transmitted stress. With test results from SHPB by pulse shaper and special shape striker methods, the requirement is verified. Finally, the method of 3D scattergram considering stress–strain–strain rate simultaneously is brought up to get constitutive relationships of rate-dependent Rock. The new method gives reasonable predictions for constitutive relationships of Rock at different strain rates. At the same time, the new method has fewer requirements and has a wider application scope for SHPB tests.
Jian Zhao - One of the best experts on this subject based on the ideXlab platform.
-
An overview of particle-based numerical manifold method and its application to dynamic Rock fracturing
Journal of Rock Mechanics and Geotechnical Engineering, 2019Co-Authors: Jian ZhaoAbstract:Abstract This review summarizes the development of particle-based numerical manifold method (PNMM) and its applications to Rock Dynamics. The fundamental principle of numerical manifold method (NMM) is first briefly introduced. Then, the history of the newly developed PNMM is given. Basic idea of PNMM and its simulation procedure are presented. Considering that PNMM could be regarded as an NMM-based model, a comparison of PNMM and NMM is discussed from several points of view in this paper. Besides, accomplished applications of PNMM to the dynamic Rock fracturing are also reviewed. Finally, some recommendations are provided for the future work of PNMM.
-
3D polycrystalline discrete element method (3PDEM) for simulation of crack initiation and propagation in granular Rock
Computers and Geotechnics, 2017Co-Authors: Jian ZhaoAbstract:Abstract A three-dimensional Voronoi tessellation model based on the distinct element method (DEM) is proposed to model the representative part of the microstructures of granular brittle Rocks. Regularization is employed to decrease the frequency of polyhedrons with large edge ratio and contributes to a higher efficiency for element meshing. Sensitivity analyses are performed for a series of micro contact parameters in accordance with the macro responses observed in laboratory experiments (e.g. the uniaxial compression test, the Brazilian disc test and the triaxial compression test). Verifications by simulating the spalling test and plate impact test indicate that the 3D polycrystalline discrete element method (3PDEM) can be employed for efficiently simulating nonlinear mechanical behaviors, large deformation, strain softening and Rock Dynamics.
-
Parallelization of the distinct lattice spring model
International Journal for Numerical and Analytical Methods in Geomechanics, 2011Co-Authors: Gaofeng Zhao, Liang Sun, Jiannong Fang, Jian ZhaoAbstract:The distinct lattice spring model (DLSM) is a newly developed numerical tool for modeling Rock Dynamics problems, i.e. dynamic failure and wave propagation. In this paper, parallelization of DLSM is presented. With the development of parallel computing technologies in both hardware and software, parallelization of a code is becoming easier than before. There are many available choices now. In this paper, Open Multi-Processing (OpenMP) with multicore personal computer (PC) and message passing interface (MPI) with cluster are selected as the environments to parallelize DLSM. Performances of these parallel DLSM codes are tested on different computers. It is found that the parallel DLSM code with OpenMP can reach a maximum speed-up of 4.68x on a quad-core PC. The parallel DLSM code with MPI can achieve a speed-up of 40.886x when 256 CPUs are used on a cluster. At the end of this paper, a high-resolution model with four million particles, which is too big to handle by the serial code, is simulated by using the parallel DLSM code on a cluster. It is concluded that the parallelization of DLSM is successful.
-
Advances in Rock Dynamics and Applications - Advances in Rock Dynamics and Applications
2011Co-Authors: Yingxin Zhou, Jian ZhaoAbstract:* Introduction Yingxin Zhou & Jian Zhao * An overview of some recent progress in Rock Dynamics research Jian Zhao * Split Hopkinson pressure bar tests of Rocks: Advances in experimental techniques and applications to Rock strenght and facture Kaiwen Xia, Feng Dai and Rong Chen * Modified Hopkinson bar technologies applied to the high strain rate Rock tests Ezio Cadoni and Carlo Albertini * Wave shaping by special shaped triker in SHPB tests Xibing Li, Zilong Zhou, Deshun Liu, Yang Zou and Tubing Yin * Laboratory compressive and tensile testing of Rock dynamic properties Haibo Li, Junru Li and Jian Zhao * Penetration and perforation of Rock targets by hard projectiles Chong Chiang Seah, Tore Borvik, Sven Remseth and Tso-Chien Pan * Incubation time based fracture mechanics and optimization of energy input in the fracture process of Rocks Yuri Petrov, Vladimir Bratov, Grigory Volkov and Evgeny Dolmatov * Discontinuous approaches of wave propagation across Rock joints Xiaobao Zhao, Jianbo Zhu, Jungang Cai and Jian Zhao * Equivalent medium model with virtual wave source method for wave propagation analysis in jointed Rock masses Jianchun Li, Guowei Ma and Jian Zhao * Polycrystalline model for heterogeneous Rock based on smoothed particle hydroDynamics method Guowei Ma, Xuejun Wang and Lei He * Finite Element Method modeling of Rock dynamic failure Chun'an Tang and Yuefeng Yang * Discontinuum-based numerical modeling of Rock dynamic fracturing and failure Tohid Kazerani and Jian Zhao * Manifold and advanced numerical techniques for discontinuous dynamic computations Gaofeng Zhao, Gen-Hua Shi and Jian Zhao * Earthquakes as a Rock dynamic problem and their effects on Rock engineering structures Omer Aydan, Yoshimi Ohta, Mitsuo Daido, Halil Kumsar, Melih Genis, Naohiko Takashiki, Takashi Ito and Mehdi Amini * Constraining paleoseismic PGA using numerical analysis of structural failures in historic masonry structures: Review of recent results Yossef H. Hatzor and Gony Yagoda-Biran * Explosion loading and tunnel response, Yingxin Zhou * Rock support for underground excavations subjected to dynamic loads and failure Charlie Chunlin Li
-
advances in Rock Dynamics and applications
2011Co-Authors: Yingxin Zhou, Jian ZhaoAbstract:* Introduction Yingxin Zhou & Jian Zhao * An overview of some recent progress in Rock Dynamics research Jian Zhao * Split Hopkinson pressure bar tests of Rocks: Advances in experimental techniques and applications to Rock strenght and facture Kaiwen Xia, Feng Dai and Rong Chen * Modified Hopkinson bar technologies applied to the high strain rate Rock tests Ezio Cadoni and Carlo Albertini * Wave shaping by special shaped triker in SHPB tests Xibing Li, Zilong Zhou, Deshun Liu, Yang Zou and Tubing Yin * Laboratory compressive and tensile testing of Rock dynamic properties Haibo Li, Junru Li and Jian Zhao * Penetration and perforation of Rock targets by hard projectiles Chong Chiang Seah, Tore Borvik, Sven Remseth and Tso-Chien Pan * Incubation time based fracture mechanics and optimization of energy input in the fracture process of Rocks Yuri Petrov, Vladimir Bratov, Grigory Volkov and Evgeny Dolmatov * Discontinuous approaches of wave propagation across Rock joints Xiaobao Zhao, Jianbo Zhu, Jungang Cai and Jian Zhao * Equivalent medium model with virtual wave source method for wave propagation analysis in jointed Rock masses Jianchun Li, Guowei Ma and Jian Zhao * Polycrystalline model for heterogeneous Rock based on smoothed particle hydroDynamics method Guowei Ma, Xuejun Wang and Lei He * Finite Element Method modeling of Rock dynamic failure Chun'an Tang and Yuefeng Yang * Discontinuum-based numerical modeling of Rock dynamic fracturing and failure Tohid Kazerani and Jian Zhao * Manifold and advanced numerical techniques for discontinuous dynamic computations Gaofeng Zhao, Gen-Hua Shi and Jian Zhao * Earthquakes as a Rock dynamic problem and their effects on Rock engineering structures Omer Aydan, Yoshimi Ohta, Mitsuo Daido, Halil Kumsar, Melih Genis, Naohiko Takashiki, Takashi Ito and Mehdi Amini * Constraining paleoseismic PGA using numerical analysis of structural failures in historic masonry structures: Review of recent results Yossef H. Hatzor and Gony Yagoda-Biran * Explosion loading and tunnel response, Yingxin Zhou * Rock support for underground excavations subjected to dynamic loads and failure Charlie Chunlin Li
Florian Holzapfel - One of the best experts on this subject based on the ideXlab platform.
-
Constraint Enforcement Methods for Command Governor based Adaptive Control of Uncertain Dynamical Systems
AIAA Guidance Navigation and Control (GNC) Conference, 2013Co-Authors: Simon P. Schatz, Eric N. Johnson, Tansel Yucelen, Florian HolzapfelAbstract:Recently, research has been conducted in order to improve the transient behavior of adaptively-controlled uncertain nonlinear dynamical systems. In this paper, an adaptive control architecture is extended in order to achieve predictable transient performance in the presence of state constraints. The methodology at hand is based on a robust command governor framework, which is a dynamical system adjusting the trajectory of a given command in order to track a certain desired closed-loop reference model both in transient time and steady-state. Specifically, the command, which is applied on the reference model and the actual system, is changed by the command governor framework for improved transient performance with respect to classical adaptive control schemes and by a constraint enforcement command in order to keep the states within pre-defined bounds. The constraint enforcement method here is able to handle state constraints in the range space of the control input matrix. The application of command governor and constraint enforcement on nonlinear dynamic inversion controllers is discussed and an example is implemented using a helicopter model for illustration purposes. An example using the wing Rock Dynamics shows the performance and additional methods for enforcing state constraints outside of the range space of the input matrix are also introduced.
-
a concurrent learning adaptive optimal control architecture for nonlinear systems
Conference on Decision and Control, 2013Co-Authors: Girish Chowdhary, Maximillian Muhlegg, Jonathan P How, Florian HolzapfelAbstract:A concurrent learning adaptive-optimal control architecture is presented that combines learning-focused direct adaptive controllers with model predictive control for guaranteeing safety during adaptation for nonlinear systems. Exponential parameter convergence properties of concurrent learning adaptive controllers are leveraged to learn a feedback linearization signal that reduces a nonlinear system to an approximation of a linear system for which an optimal solution is known or can be easily computed online. Stability of the overall architecture is analyzed, and numerical simulations on a wing-Rock Dynamics model are presented in presence of significant system uncertainty, parameter variation, and measurement noise.
-
CDC - A concurrent learning adaptive-optimal control architecture for nonlinear systems
52nd IEEE Conference on Decision and Control, 2013Co-Authors: Girish Chowdhary, Maximillian Muhlegg, Jonathan P How, Florian HolzapfelAbstract:A concurrent learning adaptive-optimal control architecture is presented that combines learning-focused direct adaptive controllers with model predictive control for guaranteeing safety during adaptation for nonlinear systems. Exponential parameter convergence properties of concurrent learning adaptive controllers are leveraged to learn a feedback linearization signal that reduces a nonlinear system to an approximation of a linear system for which an optimal solution is known or can be easily computed online. Stability of the overall architecture is analyzed, and numerical simulations on a wing-Rock Dynamics model are presented in presence of significant system uncertainty, parameter variation, and measurement noise.
