Effective and efficient SAR image segmentation has a significant role in coastal zone interpretation. In this paper, a coastal zone segmentation model is proposed based on Potts model. By introducing edge self-adaptio...Effective and efficient SAR image segmentation has a significant role in coastal zone interpretation. In this paper, a coastal zone segmentation model is proposed based on Potts model. By introducing edge self-adaption parameter and modifying noisy data term, the proposed variational model provides a good solution for the coastal zone SAR image with common characteristics of inherent speckle noise and complicated geometrical details. However, the proposed model is difficult to solve due to to its nonlinear, non-convex and non-smooth characteristics. Followed by curve evolution theory and operator splitting method, the minimization problem is reformulated as a constrained minimization problem. A fast alternating minimization iterative scheme is designed to implement coastal zone segmentation. Finally, various two-stage and multiphase experimental results illustrate the advantage of the proposed segmentation model, and indicate the high computation efficiency of designed numerical approximation algorithm.展开更多
Hydraulic fracturing is a powerful technology used to stimulate fluid production from reservoirs. The fully 3-D numerical simulation of the hydraulic fracturing process is of great importance to the efficient applicat...Hydraulic fracturing is a powerful technology used to stimulate fluid production from reservoirs. The fully 3-D numerical simulation of the hydraulic fracturing process is of great importance to the efficient application of this technology, but is also a great challenge because of the strong nonlinear coupling between the viscous flow of fluid and fracture propagation. By taking advantage of a cohesive zone method to simulate the fracture process, a finite element model based on the existing pore pressure cohesive finite elements has been established to investigate the propagation of a penny-shaped hydraulic fracture in an infinite elastic medium. The effect of cohesive material parameters and fluid viscosity on the hydraulic fracture behaviour has been investigated. Excellent agreement between the finite element results and analytical solutions for the limiting case where the fracture process is dominated by rock fracture toughness demonstrates the ability of the cohesive zone finite element model in simulating the hydraulic fracture growth for this case.展开更多
A three-dimensional finite element thermal model in direct metal laser sintering(DMLS) including the effect of powder-to-solid transition were established to predict sintering zone, which benefited the determination o...A three-dimensional finite element thermal model in direct metal laser sintering(DMLS) including the effect of powder-to-solid transition were established to predict sintering zone, which benefited the determination of suitable process parameters in DMLS. The nonlinear transient model of the metals thermal conductivity for powder-to-solid transition was developed. The model uses solid thermal properties of material in liquid-phase zone, transitional ones in sintering or sintered zone and powder ones in unsintered zones of powder bed to predict, respectively. Sintering zone boundary was estimated by maximum temperature history profile. Experiments were carried out using multi-component Cu-based metal powder. Compared experimental and predicted results, the mean error of sintering depth and width are 7.8% and 14.4%, respectively, which confirms the accuracy of the FEM prediction.展开更多
以2195铝锂合金搅拌摩擦焊接头为研究对象,开展基于相场法的脆性断裂数值模拟研究.相场法以Francfort-Marigo变分原理为理论基础,在系统总势能中考虑断裂能,并考虑应变能的拉伸和压缩分解.引入弥散裂纹模型近似非光滑的裂纹拓扑关系,以...以2195铝锂合金搅拌摩擦焊接头为研究对象,开展基于相场法的脆性断裂数值模拟研究.相场法以Francfort-Marigo变分原理为理论基础,在系统总势能中考虑断裂能,并考虑应变能的拉伸和压缩分解.引入弥散裂纹模型近似非光滑的裂纹拓扑关系,以序参量表征材料损伤.基于Abaqus软件联合用户自定义元素子程序(user element subroutine,UEL),采用交替解法实现位移场和相场的耦合,进而求解脆性断裂问题.通过与试验结果对比,基于相场法的紧凑拉伸试件焊接区脆性断裂的裂纹扩展路径模拟吻合较好,且最大载荷值误差仅为0.46%.文中进一步研究增量步步长△u、相场特征宽度L_(c)与网格尺寸h对相场法模拟结果的影响,并将相场法与扩展有限元法(extended finite element method,XFEM)和内聚力模型(cohesive zone model,CZM)进行对比.研究表明,当分析增量步为1×10^(-4)时,分析结果收敛. L_(c)与裂纹h存在2倍的关系时,模拟结果较为准确.相场法可以准确模拟2195铝锂合金搅拌摩擦焊接头脆性断裂演化过程.展开更多
In this paper, the large eddy simulation method is used combined with the marker and cell method to study the wave propagation or shoaling and breaking process. As wave propagates into shallow water, the shoaling lead...In this paper, the large eddy simulation method is used combined with the marker and cell method to study the wave propagation or shoaling and breaking process. As wave propagates into shallow water, the shoaling leads to the increase of wave height, and then at a certain position, the wave will be breaking. The breaking wave is a powerful agent for generating turbulence, which plays an important role in most of the fluid dynamic processes throughout the surf zone, Such as transformation of wave energy, generation of near-shore current and diffusion of materials. So a proper numerical model for describing the turbulence effect is needed. In this paper, a revised Smagorinsky subgrid-scale model is used to describe the turbulence effect. The present study reveals that the coefficient of the Smagorinsky model for wave propagation or breaking simulation may be taken as a varying function of the water depth and distance away from the wave breaking point. The large eddy simulation model presented in this paper has been used to study the propagation of the solitary wave in constant water depth and the shoaling of the non-breaking solitary wave on a beach. The model is based on large eddy simulation, and to track free-surface movements, the Tokyo University Modified Marker and Cell (TUMMAC) method is employed. In order to ensure the accuracy of each component of this wave mathematical model, several steps have been taken to verify calculated solutions; with either analytical solutions or experimental data. For non-breaking waves, very accurate results are obtained for a solitary wave propagating over a constant depth and on a beach. Application of the model to cnoidal wave breaking in the surf zone shows that the model results are in good agreement with analytical solution and experimental data. From the present model results, it can be seen that the turbulent eddy viscosity increases from the bottom to the water surface in surf zone. In the eddy viscosity curve, there is a turn-point obviously, dividing water depth into two parts, in the upper part, the eddy viscosity becomes very large near the wave breaking position.展开更多
Over the past twenty years, there has been a growing interest in the development of numerical modelsthat can realistically capture the progressive failure of rock masses. In particular, the investigation ofdamage deve...Over the past twenty years, there has been a growing interest in the development of numerical modelsthat can realistically capture the progressive failure of rock masses. In particular, the investigation ofdamage development around underground excavations represents a key issue in several rock engineeringapplications, including tunnelling, mining, drilling, hydroelectric power generation, and the deepgeological disposal of nuclear waste. The goal of this paper is to show the effectiveness of a hybrid finitediscreteelement method （FDEM） code to simulate the fracturing mechanisms associated with theexcavation of underground openings in brittle rock formations. A brief review of the current state-of-theartmodelling approaches is initially provided, including the description of selecting continuum- anddiscontinuum-based techniques. Then, the influence of a number of factors, including mechanical and insitu stress anisotropy, as well as excavation geometry, on the simulated damage is analysed for threedifferent geomechanical scenarios. Firstly, the fracture nucleation and growth process under isotropicrock mass conditions is simulated for a circular shaft. Secondly, the influence of mechanical anisotropy onthe development of an excavation damaged zone （EDZ） around a tunnel excavated in a layered rockformation is considered. Finally, the interaction mechanisms between two large caverns of an undergroundhydroelectric power station are investigated, with particular emphasis on the rock mass responsesensitivity to the pillar width and excavation sequence. Overall, the numerical results indicate that FDEMsimulations can provide unique geomechanical insights in cases where an explicit consideration offracture and fragmentation processes is of paramount importance. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.展开更多
Kinematic models compute the temperature distribution by prescribing a constant convergent velocity for the subducting slab,resulting in an artificial velocity discontinuity,which may accelerate the heating of subduct...Kinematic models compute the temperature distribution by prescribing a constant convergent velocity for the subducting slab,resulting in an artificial velocity discontinuity,which may accelerate the heating of subducting slabs.For the purpose to moderate the influence of such artificial discontinuity, we construct a 2D thermal model for subduction zones with a velocity boundary layer,within which the velocities decrease linearly with the distance from the interfaces of slabs.Temperatures are calculated展开更多
基金supported by the China Postdoctoral Science Foundation under Grant No.2015M571993the Shandong Provincial Natural Science Foundation,China under Grant No.ZR2017MD004+1 种基金the National Natural Science Foundation of China under Grant No.61602269Qingdao Postdoctoral Application Research Funded Project
文摘Effective and efficient SAR image segmentation has a significant role in coastal zone interpretation. In this paper, a coastal zone segmentation model is proposed based on Potts model. By introducing edge self-adaption parameter and modifying noisy data term, the proposed variational model provides a good solution for the coastal zone SAR image with common characteristics of inherent speckle noise and complicated geometrical details. However, the proposed model is difficult to solve due to to its nonlinear, non-convex and non-smooth characteristics. Followed by curve evolution theory and operator splitting method, the minimization problem is reformulated as a constrained minimization problem. A fast alternating minimization iterative scheme is designed to implement coastal zone segmentation. Finally, various two-stage and multiphase experimental results illustrate the advantage of the proposed segmentation model, and indicate the high computation efficiency of designed numerical approximation algorithm.
文摘Hydraulic fracturing is a powerful technology used to stimulate fluid production from reservoirs. The fully 3-D numerical simulation of the hydraulic fracturing process is of great importance to the efficient application of this technology, but is also a great challenge because of the strong nonlinear coupling between the viscous flow of fluid and fracture propagation. By taking advantage of a cohesive zone method to simulate the fracture process, a finite element model based on the existing pore pressure cohesive finite elements has been established to investigate the propagation of a penny-shaped hydraulic fracture in an infinite elastic medium. The effect of cohesive material parameters and fluid viscosity on the hydraulic fracture behaviour has been investigated. Excellent agreement between the finite element results and analytical solutions for the limiting case where the fracture process is dominated by rock fracture toughness demonstrates the ability of the cohesive zone finite element model in simulating the hydraulic fracture growth for this case.
文摘A three-dimensional finite element thermal model in direct metal laser sintering(DMLS) including the effect of powder-to-solid transition were established to predict sintering zone, which benefited the determination of suitable process parameters in DMLS. The nonlinear transient model of the metals thermal conductivity for powder-to-solid transition was developed. The model uses solid thermal properties of material in liquid-phase zone, transitional ones in sintering or sintered zone and powder ones in unsintered zones of powder bed to predict, respectively. Sintering zone boundary was estimated by maximum temperature history profile. Experiments were carried out using multi-component Cu-based metal powder. Compared experimental and predicted results, the mean error of sintering depth and width are 7.8% and 14.4%, respectively, which confirms the accuracy of the FEM prediction.
文摘以2195铝锂合金搅拌摩擦焊接头为研究对象,开展基于相场法的脆性断裂数值模拟研究.相场法以Francfort-Marigo变分原理为理论基础,在系统总势能中考虑断裂能,并考虑应变能的拉伸和压缩分解.引入弥散裂纹模型近似非光滑的裂纹拓扑关系,以序参量表征材料损伤.基于Abaqus软件联合用户自定义元素子程序(user element subroutine,UEL),采用交替解法实现位移场和相场的耦合,进而求解脆性断裂问题.通过与试验结果对比,基于相场法的紧凑拉伸试件焊接区脆性断裂的裂纹扩展路径模拟吻合较好,且最大载荷值误差仅为0.46%.文中进一步研究增量步步长△u、相场特征宽度L_(c)与网格尺寸h对相场法模拟结果的影响,并将相场法与扩展有限元法(extended finite element method,XFEM)和内聚力模型(cohesive zone model,CZM)进行对比.研究表明,当分析增量步为1×10^(-4)时,分析结果收敛. L_(c)与裂纹h存在2倍的关系时,模拟结果较为准确.相场法可以准确模拟2195铝锂合金搅拌摩擦焊接头脆性断裂演化过程.
基金This research project was supported by the National Natural Science Foundation of China and The Hong Kong Research Grants under contracts No. 59809006 and No. 59890200, also by the Science Foundation of Tianjin Municipality under contract No. 9837020
文摘In this paper, the large eddy simulation method is used combined with the marker and cell method to study the wave propagation or shoaling and breaking process. As wave propagates into shallow water, the shoaling leads to the increase of wave height, and then at a certain position, the wave will be breaking. The breaking wave is a powerful agent for generating turbulence, which plays an important role in most of the fluid dynamic processes throughout the surf zone, Such as transformation of wave energy, generation of near-shore current and diffusion of materials. So a proper numerical model for describing the turbulence effect is needed. In this paper, a revised Smagorinsky subgrid-scale model is used to describe the turbulence effect. The present study reveals that the coefficient of the Smagorinsky model for wave propagation or breaking simulation may be taken as a varying function of the water depth and distance away from the wave breaking point. The large eddy simulation model presented in this paper has been used to study the propagation of the solitary wave in constant water depth and the shoaling of the non-breaking solitary wave on a beach. The model is based on large eddy simulation, and to track free-surface movements, the Tokyo University Modified Marker and Cell (TUMMAC) method is employed. In order to ensure the accuracy of each component of this wave mathematical model, several steps have been taken to verify calculated solutions; with either analytical solutions or experimental data. For non-breaking waves, very accurate results are obtained for a solitary wave propagating over a constant depth and on a beach. Application of the model to cnoidal wave breaking in the surf zone shows that the model results are in good agreement with analytical solution and experimental data. From the present model results, it can be seen that the turbulent eddy viscosity increases from the bottom to the water surface in surf zone. In the eddy viscosity curve, there is a turn-point obviously, dividing water depth into two parts, in the upper part, the eddy viscosity becomes very large near the wave breaking position.
基金supported by the Natural Science and Engineering Research Council (NSERC) of Canada in the form of discovery grant No. 341275the Swiss National Cooperative for the Disposal of Radioactive Waste (NAGRA)
文摘Over the past twenty years, there has been a growing interest in the development of numerical modelsthat can realistically capture the progressive failure of rock masses. In particular, the investigation ofdamage development around underground excavations represents a key issue in several rock engineeringapplications, including tunnelling, mining, drilling, hydroelectric power generation, and the deepgeological disposal of nuclear waste. The goal of this paper is to show the effectiveness of a hybrid finitediscreteelement method （FDEM） code to simulate the fracturing mechanisms associated with theexcavation of underground openings in brittle rock formations. A brief review of the current state-of-theartmodelling approaches is initially provided, including the description of selecting continuum- anddiscontinuum-based techniques. Then, the influence of a number of factors, including mechanical and insitu stress anisotropy, as well as excavation geometry, on the simulated damage is analysed for threedifferent geomechanical scenarios. Firstly, the fracture nucleation and growth process under isotropicrock mass conditions is simulated for a circular shaft. Secondly, the influence of mechanical anisotropy onthe development of an excavation damaged zone （EDZ） around a tunnel excavated in a layered rockformation is considered. Finally, the interaction mechanisms between two large caverns of an undergroundhydroelectric power station are investigated, with particular emphasis on the rock mass responsesensitivity to the pillar width and excavation sequence. Overall, the numerical results indicate that FDEMsimulations can provide unique geomechanical insights in cases where an explicit consideration offracture and fragmentation processes is of paramount importance. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.
文摘Kinematic models compute the temperature distribution by prescribing a constant convergent velocity for the subducting slab,resulting in an artificial velocity discontinuity,which may accelerate the heating of subducting slabs.For the purpose to moderate the influence of such artificial discontinuity, we construct a 2D thermal model for subduction zones with a velocity boundary layer,within which the velocities decrease linearly with the distance from the interfaces of slabs.Temperatures are calculated
