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Youjun Ning - One of the best experts on this subject based on the ideXlab platform.
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numerical studies on rockbolts mechanism using 2d discontinuous Deformation Analysis
Tunnelling and Underground Space Technology, 2014Co-Authors: Zhiye Zhao, Youjun NingAbstract:Abstract To understand the response of rockbolts under various loads is an important part in the design of rock reinforcement. In this paper, the rockbolt models are developed within the frame work of the two-dimensional discontinuous Deformation Analysis (DDA). The rockbolt material is modeled by the elastic, linear strain-hardening behavior. To simulate the anchored system employed in various rockbolts, different bond stiffness are used for the interface between the rock and the rockbolt. The rockbolt models for the expansion shell anchored bolt, the split set, the fully grouted rebar and the D-bolt are considered in the simulations of the pullout tests. Extreme pull-out loadings were also applied to examine the bearing capability and Deformation capability of the rockbolt system. In addition, two kinds of popular permanent rockbolts, the fully grouted rebar and D-bolt were further studied in the simulation of drop tests. The effects of impact amplitude and duration on the rockbolt behaviors were studied by single drops to demonstrate the advantage of D-bolt in energy dissipation. The results showed that the proposed rockbolt models can realistically predict the bonding forces and axial loading along the length of rockbolt.
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development of rock bolt elements in two dimensional discontinuous Deformation Analysis
Rock Mechanics and Rock Engineering, 2014Co-Authors: Zhiye Zhao, Youjun NingAbstract:Computer modeling can be used to explore and gain new insights into the impacts of rock bolt intersecting joints in rock masses, and to estimate the effectiveness of the rock reinforcement system. In order to achieve this goal, we couple a rock bolt element into the two-dimensional discontinuous Deformation Analysis (DDA2D) program. The coupling algorithm is based on the analytically-derived interface behavior between a rock bolt and the rock material for grouted rock bolts. The shear force generated by slippage along the interface is assumed to have a linear relationship with respect to the relative slipping distance between the rock bolt and the rock. The linear elastic criterion is applied to determine the material behavior of rock bolts before the axial stress reaches the yield value. The pullout tests are simulated to verify the coupling algorithm and the effects of the proposed rock bolt elements. Parametrical studies are also carried out to analyze the effectiveness of the rock bolts under various end conditions, joint locations and bond stiffness. In addition, the performance of the rock bolt during the interface debonding is analyzed using two types of constitutive laws, i.e., the friction law and the reduction law. The simulation results show that the proposed rock bolt models can predict the shear forces and axial loading along the rock bolts.
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modelling rock blasting considering explosion gas penetration using discontinuous Deformation Analysis
Rock Mechanics and Rock Engineering, 2011Co-Authors: Youjun Ning, Jun Yang, Pengwan ChenAbstract:Explosion gas plays an important role in rock mass fragmentation and cast in rock blasting. In this technical note, the discontinuous Deformation Analysis method is extended for bench rock blasting by coupling the rock mass failure process and the penetration effect of the explosion gas based on a generalized artificial joint concept to model rock mass fracturing. By tracking the blast chamber evolution dynamically, instant explosion gas pressure is derived from the blast chamber volume using a simple polytropic gas pressure equation of state and loaded on the blast chamber wall. A bench blasting example is carried out. The blast chamber volume and pressure time histories are obtained. The rock failure and movement process in bench rock blasting is reproduced and analysed.
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modelling rock blasting considering explosion gas penetration using discontinuous Deformation Analysis
Rock Mechanics and Rock Engineering, 2011Co-Authors: Youjun Ning, Jun Yang, Pengwan ChenAbstract:Explosion gas plays an important role in rock mass fragmentation and cast in rock blasting. In this technical note, the discontinuous Deformation Analysis method is extended for bench rock blasting by coupling the rock mass failure process and the penetration effect of the explosion gas based on a generalized artificial joint concept to model rock mass fracturing. By tracking the blast chamber evolution dynamically, instant explosion gas pressure is derived from the blast chamber volume using a simple polytropic gas pressure equation of state and loaded on the blast chamber wall. A bench blasting example is carried out. The blast chamber volume and pressure time histories are obtained. The rock failure and movement process in bench rock blasting is reproduced and analysed.
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modelling rock fracturing and blast induced rock mass failure via advanced discretisation within the discontinuous Deformation Analysis framework
Computers and Geotechnics, 2011Co-Authors: Jun Yang, Youjun Ning, Xinmei AnAbstract:Abstract Rock mass failure is a particularly complex process that involves the opening and sliding of existing discontinuities and the fracturing of the intact rock. This paper adopts an advanced discretisation approach to simulate rock failure problems within the discontinuous Deformation Analysis (DDA) framework. The accuracy of this approach in continuum Analysis is verified first. Then, the advanced discretisation approach for fracturing modelling is presented, and the discretisation strategy is discussed. Sample rock static failures are simulated and the results are compared with experimental results. Thereafter, with a generalised definition of the artificial joints, this approach is further extended and applied in the simulation of blast-induced rock mass failures in which the instant explosion gas pressure obtained by the detonation pressure equation of state is loaded on the main blast chamber walls and the induced surrounding connected fracture surfaces. In the simulation instance of rock mass cast blasting, the whole process, including the blast chamber expansion, explosion gas penetration, rock mass failure and cast, and the formation of the final blasting pile, is wholly reproduced.
Pengwan Chen - One of the best experts on this subject based on the ideXlab platform.
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modelling rock blasting considering explosion gas penetration using discontinuous Deformation Analysis
Rock Mechanics and Rock Engineering, 2011Co-Authors: Youjun Ning, Jun Yang, Pengwan ChenAbstract:Explosion gas plays an important role in rock mass fragmentation and cast in rock blasting. In this technical note, the discontinuous Deformation Analysis method is extended for bench rock blasting by coupling the rock mass failure process and the penetration effect of the explosion gas based on a generalized artificial joint concept to model rock mass fracturing. By tracking the blast chamber evolution dynamically, instant explosion gas pressure is derived from the blast chamber volume using a simple polytropic gas pressure equation of state and loaded on the blast chamber wall. A bench blasting example is carried out. The blast chamber volume and pressure time histories are obtained. The rock failure and movement process in bench rock blasting is reproduced and analysed.
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modelling rock blasting considering explosion gas penetration using discontinuous Deformation Analysis
Rock Mechanics and Rock Engineering, 2011Co-Authors: Youjun Ning, Jun Yang, Pengwan ChenAbstract:Explosion gas plays an important role in rock mass fragmentation and cast in rock blasting. In this technical note, the discontinuous Deformation Analysis method is extended for bench rock blasting by coupling the rock mass failure process and the penetration effect of the explosion gas based on a generalized artificial joint concept to model rock mass fracturing. By tracking the blast chamber evolution dynamically, instant explosion gas pressure is derived from the blast chamber volume using a simple polytropic gas pressure equation of state and loaded on the blast chamber wall. A bench blasting example is carried out. The blast chamber volume and pressure time histories are obtained. The rock failure and movement process in bench rock blasting is reproduced and analysed.
Hong Zheng - One of the best experts on this subject based on the ideXlab platform.
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a robust potential based contact force solution approach for discontinuous Deformation Analysis of irregular convex polygonal block particle systems
Acta Geotechnica, 2021Co-Authors: Hong Zheng, Xiaoying Zhuang, Yuyong Jiao, Fei Zheng, Timon RabczukAbstract:Contact interaction of two bodies can be modeled using the penalty function approach while its accuracy and robustness are directly associated with the geometry of contact bodies. Particularly, in the research fields of rock mechanics, we need to treat polygonal shapes such as mineral grains/particles at a mesoscale and rock blocks at a macroscale. The irregular shapes (e.g., polygons with small angles or small edges) pose challenges to traditional contact solution approach in terms of algorithmic robustness and complexity. This paper proposed a robust potential-based penalty function approach to solve contact of polygonal particles/block. An improved potential function is proposed considering irregular polygonal shapes. A contact detection procedure based on the entrance block concept is presented, followed by a numerical integral algorithm to compute the contact force. The proposed contact detection approach is implemented into discontinuous Deformation Analysis with an explicit formulation. The accuracy and robustness of the proposed contact detection approach are verified by benchmarking examples. The potential of the proposed approach in Analysis of kinetic behavior of complex polygonal block systems is shown by two application examples. It can be applied in any discontinuous computation models using stepwise contact force-based solution procedures.
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modeling wave propagation in rock masses using the contact potential based three dimensional discontinuous Deformation Analysis method
Rock Mechanics and Rock Engineering, 2021Co-Authors: Yongtao Yang, Hong Zheng, Da HuangAbstract:The most recently proposed three-dimensional (3D) contact potential-based discontinuous Deformation Analysis (3D-CPDDA) method is further applied for wave propagation problems in rock masses. A viscous non-reflecting boundary is incorporated into the 3D-CPDDA method to minimize the wave reflections. Furthermore, a force input method is incorporated to eliminate the contamination of scattered waves in the numerical solution and to accurately input the incident wave. Several benchmark problems about P-wave/S-wave propagation in homogeneous rock masses and jointed rock masses are solved to validate the modified 3D-CPDDA method. The numerical results assessed by the modified 3D-CPDDA method agree well with those obtained from analytical methods, which means that the modified 3D-CPDDA method can reliably and correctly simulate wave propagation in rock masses. The modified 3D-CPDDA method warrants further investigation.
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kinetic Analysis of polyhedral block system using an improved potential based penalty function approach for explicit discontinuous Deformation Analysis
Applied Mathematical Modelling, 2020Co-Authors: Fei Zheng, Hong Zheng, Xiaoying Zhuang, Yuyong Jiao, Timon RabczukAbstract:Abstract The complexity of polyhedral block systems (e.g., small blocks, flat blocks with small angles, edges, or faces) poses challenges in the kinetic Analysis of rock block systems. This paper proposed an improved potential-based penalty function approach within an explicit three-dimensional (3D) discontinuous Deformation Analysis (DDA) framework for efficient and robust kinetic Analysis of rock block systems. An explicit formulation of 3D DDA based on velocity verlet algorithm is first derived. A novel definition of potential function is then proposed with details of the key algorithms for overlap judgment of convex polyhedron, construction of intersection polyhedron and numerical integral for computation of contact force. The improved potential-based penalty function method is robust and efficient for complex convex polyhedral shapes. Several benchmark and application examples verify the feasibility, accuracy and robustness of the proposed methods in solving contact of polyhedral block systems.
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a new contact potential based three dimensional discontinuous Deformation Analysis method
International Journal of Rock Mechanics and Mining Sciences, 2020Co-Authors: Yongtao Yang, Feng Liu, Hong ZhengAbstract:Abstract The three-dimensional discontinuous Deformation Analysis (3D-DDA) method was developed for the Deformation simulation of rock block system cut by the natural discontinuities in rock mass engineering. In the conventional DDA, open-close iteration is used to deal with the contact constraints, which needs to apply or remove the normal or tangential springs repeatedly to meet the equilibrium equations at each time step. DDA provides a time step adjustment strategy to meet the fast convergence of open-close iterations, but when solving large-scale problems, the adjusted time step often reaches a very small order of magnitude, which makes the calculation time-consuming increase sharply. In the framework of the original 3D-DDA, a new contact potential based three-dimensional discontinuous Deformation Analysis method (3D-CPDDA) is developed. The proposed method not only retains the advantage of the original DDA method in defining local displacement functions on a single patch, but also integrates the simplicity and rapidity of potential based contact processing. The improved method is easier to be implemented in the parallel way, which can further improve the computational efficiency. Numerical examples have confirmed the correctness and feasibility of the proposed procedure.
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a generalized contact potential and its application in discontinuous Deformation Analysis
Computers and Geotechnics, 2018Co-Authors: Huo Fan, Hong Zheng, Jianfeng WangAbstract:Abstract The distributed contact force that is determined from the contact potential can be used to deal with the contact between discrete bodies. The current study defines the generalized contact potential (GCP). The GCP is independent of the shape and size of body and possesses the thorough geometric locality. If and only if the contact regions are exactly the same, the contact potentials are identical. By combining discontinuous Deformation Analysis (DDA) and GCP a new DDA, named GCP-DDA, is produced, in which the generalized-α method is adopted to discretize the time domain. The GCP-DDA can make the global controlling equation and the open-close iteration (OCI), which may cause the reduction of time step size and the rebuilding and solving of global controlling equation, become unnecessary. The intractable issues related to convex-convex contact in the original DDA can be accordingly bypassed.
Sergio Mondillo - One of the best experts on this subject based on the ideXlab platform.
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left atrial Deformation Analysis by speckle tracking echocardiography for prediction of cardiovascular outcomes
American Journal of Cardiology, 2012Co-Authors: Matteo Cameli, Matteo Lisi, Marta Focardi, Rosanna Reccia, Benedetta Maria Natali, S. Sparla, Sergio MondilloAbstract:The incremental value of left atrial (LA) Deformation Analysis by speckle tracking echocardiography compared with LA volume or LA ejection fraction as a cardiovascular risk marker has not been evaluated prospectively. We sought to compare LA function by speckle tracking echocardiography to other conventional LA parameters for prediction of adverse cardiovascular outcomes. This prospective study included 312 adults (mean age 71 ± 6 years, 56% men) in sinus rhythm who were followed for development of first atrial fibrillation, congestive heart failure, stroke, transient ischemic attack, myocardial infarction, coronary revascularization, and cardiovascular death. Global peak atrial longitudinal strain (PALS) by speckle tracking echocardiography was measured in all subjects by averaging all atrial segments. Left atrium was assessed with biplane LA volume, LA ejection fraction, 4-chamber LA area, and M-mode dimension. Of 312 subjects at baseline, 43 had 61 new events during a mean follow-up of 3.1 ± 1.4 years. All LA parameters, traditional parameters, and parameters derived by speckle tracking echocardiography were independently predictive of combined outcomes (p <0.0001 for all comparisons). Overall performance for prediction of cardiovascular events was greatest for global PALS (area under receiver operator characteristic curve: global PALS 0.83, indexed LA volume 0.71, LA ejection fraction 0.69, LA area 0.64, LA diameter 0.59). A graded association between degree of LA enlargement and risk of cardiovascular events was evident only for global PALS and indexed LA volume. In conclusion, global PALS is a strong and independent predictor of cardiovascular events and appears to be superior to conventional parameters of LA Analysis.
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Left Atrial Deformation Analysis by Speckle Tracking Echocardiography for Prediction of Cardiovascular Outcomes
The American journal of cardiology, 2012Co-Authors: Matteo Cameli, Matteo Lisi, Marta Focardi, Rosanna Reccia, Benedetta Maria Natali, S. Sparla, Sergio MondilloAbstract:The incremental value of left atrial (LA) Deformation Analysis by speckle tracking echocardiography compared with LA volume or LA ejection fraction as a cardiovascular risk marker has not been evaluated prospectively. We sought to compare LA function by speckle tracking echocardiography to other conventional LA parameters for prediction of adverse cardiovascular outcomes. This prospective study included 312 adults (mean age 71 ± 6 years, 56% men) in sinus rhythm who were followed for development of first atrial fibrillation, congestive heart failure, stroke, transient ischemic attack, myocardial infarction, coronary revascularization, and cardiovascular death. Global peak atrial longitudinal strain (PALS) by speckle tracking echocardiography was measured in all subjects by averaging all atrial segments. Left atrium was assessed with biplane LA volume, LA ejection fraction, 4-chamber LA area, and M-mode dimension. Of 312 subjects at baseline, 43 had 61 new events during a mean follow-up of 3.1 ± 1.4 years. All LA parameters, traditional parameters, and parameters derived by speckle tracking echocardiography were independently predictive of combined outcomes (p
Toshihiro Noda - One of the best experts on this subject based on the ideXlab platform.
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study on the pore water pressure dissipation method as a liquefaction countermeasure using soil water coupled finite Deformation Analysis equipped with a macro element method
Soils and Foundations, 2015Co-Authors: Toshihiro Noda, Shotaro Yamada, Toshihiro Nonaka, Mutsumi TashiroAbstract:A numerical simulation of the pore water pressure dissipation method was performed using the GEOASIA soil–water coupled finite Deformation Analysis code, which is capable of accounting for inertial forces, together with the elasto-plastic constitutive SYS Cam-clay model based on the soil skeleton structure concept, with the goal of quantitatively assessing the effects of this method as a countermeasure to liquefaction. At the same time, an effort was made to improve/enhance the calculation efficiency of the GEOASIA Analysis code by incorporating a macro-element method, which up to this point has only been applied to consolidation problems. The main findings of this study are as follows: (1) the macro-element method is capable of yielding highly accurate approximations even for dynamic problems, (2) the method is capable of reproducing the suppression effect of the increase in pore water pressure associated with the pore water pressure dissipation method, even when a relatively coarse mesh is used, (3) the method is capable of reproducing the suppression effect of the decrease in effective stress due to the pore water pressure dissipation method, along with the resulting reduction in shear stiffness, lateral ground movement, and settlement and (4) it is possible to efficiently design the pore water pressure dissipation method with this method by first performing calculations using a 1-D mesh to determine the effective drain spacing prior to performing calculations using 2-D or 3-D meshes.
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realization of uniform Deformation of soil specimen under undrained plane strain condition based on soil water coupled finite Deformation Analysis considering inertia forces
Soils and Foundations, 2013Co-Authors: Toshihiro Noda, Binbin Xu, Asaoka AkiraAbstract:Based on a soil–water coupled finite Deformation Analysis, theoretical considerations and numerical calculations were carried out under the undrained plane strain condition in order to reproduce a uniform Deformation field. Rather than the “quasi-static” equation of motion, which does not include inertia forces, a dynamic equation of motion which includes inertia forces was used. At first, a theoretical consideration was carried out to realize uniform Deformation for a saturated soil that satisfied the element-wise undrained/constant-volume condition. This presents an “infinitely slow loading” case without ignoring the inertia term based on the u–p formulation. In other words, it can be seen that under general slow loading that is not infinitely slow, a gradient in the pore water pressure will always be produced, resulting in the migration of pore water and loss/collapse of uniformity. This first conclusion is useful for verifying numerical Analysis code made in the finite Deformation regime. Next, the uniform Deformation of a plane strain rectangular soil specimen was measured under constant cell pressure and undrained boundary conditions using a dynamic soil–water coupled Analysis in which the SYS Cam-clay model was employed as the elasto-plastic constitutive model for the soil skeleton. In addition, the effects of the loading rates as well as loading applications, with/without inertia forces, on the loss of uniformity in Deformation were shown to have a significant influence on the inertia term even though the loss itself was extremely small.
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soil water coupled finite Deformation Analysis based on a rate type equation of motion incorporating the sys cam clay model
Soils and Foundations, 2008Co-Authors: Toshihiro Noda, Akira Asaoka, Masaki NakanoAbstract:This paper presents a new method of soil-water coupled finite Deformation Analysis of saturated soils that considers inertial forces. This method allows changes in the geometric shape of the soil to be taken into account and is capable of dealing with all types of external forces irrespective of whether they are static or dynamic. To be more specific, the paper describes the following points, which differ from the conventional methods: 1) the governing equations for saturated soil including the rate-type equation of motion containing a jerk term of the soil skeleton conforming to u-p formulation and updated Lagrangian, 2) derivation of a weak form of the rate-type equation of motion and discretization of the finite elements, and 3) use of the implicit time integration method for application of the conventional linear acceleration method (which assumes linear variation of acceleration) to the jerk term. By mounting the elasto-plastic constitutive equation (SYS Cam-clay model), which can cover a wide range of soils and soil conditions, onto the above method of Analysis, examples of simulation of dynamic/static triaxial laboratory testing of saturated soil specimens are described. The soil specimens were assumed to be medium dense sand under conditions of small-amplitude cyclic loading, partial drainage, and constant cell pressure. The simulation yielded the following results: (1) In the case of low frequencies, compaction occurs during loading and compression progresses over the entire specimen. (2) In the case of high frequencies, during loading and in the period in which wave propagation continues within the specimen after the end of loading, compaction occurs at the drained end of the specimen, whereas liquefaction occurs in its interior. After this stage, massive compression takes place within the specimen, leading to consolidation (consolidation after liquefaction).