Higher-order modes of the neutron diffusion/transport equation can be used to study the temporal behavior of nuclear reactors and can be applied in modal analysis, transient analysis, and online monitoring of the reac...Higher-order modes of the neutron diffusion/transport equation can be used to study the temporal behavior of nuclear reactors and can be applied in modal analysis, transient analysis, and online monitoring of the reactor core. Both the deterministic method and the Monte Carlo(MC) method can be used to solve the higher-order modes. However, MC method, compared to the deterministic method, faces challenges in terms of computational efficiency and α mode calculation stability, whereas the deterministic method encounters issues arising from homogenization-related geometric and energy spectra adaptation.Based on the higher-order mode diffusion calculation code HARMONY, we developed a new higher-order mode calculation code, HARMONY2.0, which retains the functionality of computing λ and α higher-order modes from HARMONY1.0, but enhances the ability to treat complex geometries and arbitrary energy spectra using the MC-deterministic hybrid two-step strategy. In HARMONY2.0, the mesh homogenized multigroup constants were obtained using OpenMC in the first step,and higher-order modes were then calculated with the mesh homogenized core diffusion model using the implicitly restarted Arnoldi method(IRAM), which was also adopted in the HARMONY1.0 code. In addition, to improve the calculation efficiency, particularly in large higher-order modes, event-driven parallelization/domain decomposition methods are embedded in the HARMONY2.0 code to accelerate the inner iteration of λ∕α mode using OpenMP. Furthermore, the higher-order modes of complex geometric models, such as Hoogenboom and ATR reactors for λ mode and the MUSE-4 experiment facility for the prompt α mode, were computed using diffusion theory.展开更多
The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitivel...The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitively estimate the dynamic ModeⅡfracture toughness KⅡCof rocks under a triaxial stress state.However,the method for determining the dynamic KⅡCof rocks under a triaxial stress has not been developed yet.With an optimal sample preparation,the short core in compression(SCC)method was designed and verified in this study to measure the dynamic KⅡCof Fangshan marble(FM)subjected to different hydrostatic pressures through a triaxial dynamic testing system.The formula for calculating the dynamic KⅡCof the rock SCC specimen under hydrostatic pressures was obtained by using the finite element method in combination with secondary cracks.The experimental results indicate that the failure mode of the rock SCC specimen under a hydrostatic pressure is the shear fracture and the KⅡCof FM increases as the loading rate.In addition,at a given loading rate the dynamic rock KⅡCis barely affected by hydrostatic pressures.Another important observation is that the dynamic fracture energy of FM enhances with loading rates and hydrostatic pressures.展开更多
A B-spline active contour model based on finite element method is presented, into which the advantages of a B-spline active contour attributing to its fewer parameters and its smoothness is built accompanied with redu...A B-spline active contour model based on finite element method is presented, into which the advantages of a B-spline active contour attributing to its fewer parameters and its smoothness is built accompanied with reduced computational complexity and better numerical stability resulted from the finite element method. In this model, a cubic B-spline segment is taken as an element, and the finite element method is adopted to solve the energy minimization problem of the B-spline active contour, thus to implement image segmentation. Experiment results verify that this method is efficient for B-spline active contour, which attains stable, accurate and faster convergence.展开更多
Magnetic reconnection and tearing mode instability play a critical role in many physical processes.The application of Galerkin spectral method for tearing mode instability in two-dimensional geometry is investigated i...Magnetic reconnection and tearing mode instability play a critical role in many physical processes.The application of Galerkin spectral method for tearing mode instability in two-dimensional geometry is investigated in this paper.A resistive magnetohydrodynamic code is developed,by the Galerkin spectral method both in the periodic and aperiodic directions.Spectral schemes are provided for global modes and local modes.Mode structures,resistivity scaling,convergence and stability of tearing modes are discussed.The effectiveness of the code is demonstrated,and the computational results are compared with the results using Galerkin spectral method only in the periodic direction.The numerical results show that the code using Galerkin spectral method individually allows larger time step in global and local modes simulations,and has better convergence in global modes simulations.展开更多
We compare three different methods to extract coherent modes from Doppler backscattering （DBS）, which are center of gravity （COG） of the complex amplitude spectrum, spectrum of DBS phase derivative （phase derivat...We compare three different methods to extract coherent modes from Doppler backscattering （DBS）, which are center of gravity （COG） of the complex amplitude spectrum, spectrum of DBS phase derivative （phase derivative method）, and phase spectrum, respectively. These three methods are all feasible to extract coherent modes, for example, geodesic acoustic mode oscillation. However, there are stilI differences between dealing with high frequency modes （several hundred kHz） and low frequency modes, （several kHz） hiding in DBS signal. There is a significant amount of power at low frequencies in the phase spectrum, which can be removed by using the phase derivative method and COG. High frequency modes are clearer by using the COO and the phase derivative method than the phase spectrum. The spectrum of DBS amplitude does not show the coherent modes detected by using COG, phase derivative method and phase spectrum. When two Doppler shifted peaks exist, coherent modes and their harmonics appear in the spectrum of DBS amplitude, which are introduced by the DBS phase.展开更多
针对刚性挡墙绕基底转动与平动耦合(rotation around the base and translation coupling,简称RBT)模式下砂土非极限主动土压力的分布问题,选取转动中心位置参数n=0.5、1.0、5.0共3组转动中心对其进行离散元模拟研究。结果表明,RBT模式...针对刚性挡墙绕基底转动与平动耦合(rotation around the base and translation coupling,简称RBT)模式下砂土非极限主动土压力的分布问题,选取转动中心位置参数n=0.5、1.0、5.0共3组转动中心对其进行离散元模拟研究。结果表明,RBT模式下主动土压力兼具绕基底转动(rotation around base,简称RB)模式下凹型分布和平动(translational,简称T)模式直线分布的特点。在破坏过程中,墙土摩擦角往往先于内摩擦角达到极限值,墙后滑裂面为一曲面,且土体滑裂面处有明显的主应力偏转现象。基于数值模拟结果,根据中间对称圆弧拱得到了层间等效内摩擦角与n的函数关系式,利用水平层分析法,建立了曲边梯形微分单元的受力平衡方程,采用有限差分法求解得到了RBT模式非极限主动土压力数值解。参数分析表明,墙体位移、内摩擦角及转动中心位置参数n对主动土压力具有显著的影响。通过与数值模拟和模型试验的对比,验证了所提理论的合理性和可靠性,研究成果可为刚性挡土墙土压力计算提供参考。展开更多
基金supported by the National Natural Science Foundation of China(No.U2267207)Science and Technology on Reactor System Design Technology Laboratory(No.KFKT-05-FWHTWU-2023004).
文摘Higher-order modes of the neutron diffusion/transport equation can be used to study the temporal behavior of nuclear reactors and can be applied in modal analysis, transient analysis, and online monitoring of the reactor core. Both the deterministic method and the Monte Carlo(MC) method can be used to solve the higher-order modes. However, MC method, compared to the deterministic method, faces challenges in terms of computational efficiency and α mode calculation stability, whereas the deterministic method encounters issues arising from homogenization-related geometric and energy spectra adaptation.Based on the higher-order mode diffusion calculation code HARMONY, we developed a new higher-order mode calculation code, HARMONY2.0, which retains the functionality of computing λ and α higher-order modes from HARMONY1.0, but enhances the ability to treat complex geometries and arbitrary energy spectra using the MC-deterministic hybrid two-step strategy. In HARMONY2.0, the mesh homogenized multigroup constants were obtained using OpenMC in the first step,and higher-order modes were then calculated with the mesh homogenized core diffusion model using the implicitly restarted Arnoldi method(IRAM), which was also adopted in the HARMONY1.0 code. In addition, to improve the calculation efficiency, particularly in large higher-order modes, event-driven parallelization/domain decomposition methods are embedded in the HARMONY2.0 code to accelerate the inner iteration of λ∕α mode using OpenMP. Furthermore, the higher-order modes of complex geometric models, such as Hoogenboom and ATR reactors for λ mode and the MUSE-4 experiment facility for the prompt α mode, were computed using diffusion theory.
基金supported by the Natural Sciences and Engineering Research Council of Canada(NSERC)(No.72031326)the National Natural Science Foundation of China(No.52079091)+2 种基金supported by Academy of Finland under Grant No.322518supported by the opening project of State Key Laboratory of Explosion Science and Technology(Beijing Institute of Technology)The opening project number is KFJJ20-01M。
文摘The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitively estimate the dynamic ModeⅡfracture toughness KⅡCof rocks under a triaxial stress state.However,the method for determining the dynamic KⅡCof rocks under a triaxial stress has not been developed yet.With an optimal sample preparation,the short core in compression(SCC)method was designed and verified in this study to measure the dynamic KⅡCof Fangshan marble(FM)subjected to different hydrostatic pressures through a triaxial dynamic testing system.The formula for calculating the dynamic KⅡCof the rock SCC specimen under hydrostatic pressures was obtained by using the finite element method in combination with secondary cracks.The experimental results indicate that the failure mode of the rock SCC specimen under a hydrostatic pressure is the shear fracture and the KⅡCof FM increases as the loading rate.In addition,at a given loading rate the dynamic rock KⅡCis barely affected by hydrostatic pressures.Another important observation is that the dynamic fracture energy of FM enhances with loading rates and hydrostatic pressures.
基金the National Natural Science Foundation of China (No.59975057).
文摘A B-spline active contour model based on finite element method is presented, into which the advantages of a B-spline active contour attributing to its fewer parameters and its smoothness is built accompanied with reduced computational complexity and better numerical stability resulted from the finite element method. In this model, a cubic B-spline segment is taken as an element, and the finite element method is adopted to solve the energy minimization problem of the B-spline active contour, thus to implement image segmentation. Experiment results verify that this method is efficient for B-spline active contour, which attains stable, accurate and faster convergence.
基金Project supported by the Sichuan Science and Technology Program(Grant No.22YYJC1286)the China National Magnetic Confinement Fusion Science Program(Grant No.2013GB112005)the National Natural Science Foundation of China(Grant Nos.12075048 and 11925501)。
文摘Magnetic reconnection and tearing mode instability play a critical role in many physical processes.The application of Galerkin spectral method for tearing mode instability in two-dimensional geometry is investigated in this paper.A resistive magnetohydrodynamic code is developed,by the Galerkin spectral method both in the periodic and aperiodic directions.Spectral schemes are provided for global modes and local modes.Mode structures,resistivity scaling,convergence and stability of tearing modes are discussed.The effectiveness of the code is demonstrated,and the computational results are compared with the results using Galerkin spectral method only in the periodic direction.The numerical results show that the code using Galerkin spectral method individually allows larger time step in global and local modes simulations,and has better convergence in global modes simulations.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10990210 and 11475173the National Magnetic Confinement Fusion Energy Program of China under Grant Nos 2013GB106002 and 2014GB109002
文摘We compare three different methods to extract coherent modes from Doppler backscattering （DBS）, which are center of gravity （COG） of the complex amplitude spectrum, spectrum of DBS phase derivative （phase derivative method）, and phase spectrum, respectively. These three methods are all feasible to extract coherent modes, for example, geodesic acoustic mode oscillation. However, there are stilI differences between dealing with high frequency modes （several hundred kHz） and low frequency modes, （several kHz） hiding in DBS signal. There is a significant amount of power at low frequencies in the phase spectrum, which can be removed by using the phase derivative method and COG. High frequency modes are clearer by using the COO and the phase derivative method than the phase spectrum. The spectrum of DBS amplitude does not show the coherent modes detected by using COG, phase derivative method and phase spectrum. When two Doppler shifted peaks exist, coherent modes and their harmonics appear in the spectrum of DBS amplitude, which are introduced by the DBS phase.
文摘针对刚性挡墙绕基底转动与平动耦合(rotation around the base and translation coupling,简称RBT)模式下砂土非极限主动土压力的分布问题,选取转动中心位置参数n=0.5、1.0、5.0共3组转动中心对其进行离散元模拟研究。结果表明,RBT模式下主动土压力兼具绕基底转动(rotation around base,简称RB)模式下凹型分布和平动(translational,简称T)模式直线分布的特点。在破坏过程中,墙土摩擦角往往先于内摩擦角达到极限值,墙后滑裂面为一曲面,且土体滑裂面处有明显的主应力偏转现象。基于数值模拟结果,根据中间对称圆弧拱得到了层间等效内摩擦角与n的函数关系式,利用水平层分析法,建立了曲边梯形微分单元的受力平衡方程,采用有限差分法求解得到了RBT模式非极限主动土压力数值解。参数分析表明,墙体位移、内摩擦角及转动中心位置参数n对主动土压力具有显著的影响。通过与数值模拟和模型试验的对比,验证了所提理论的合理性和可靠性,研究成果可为刚性挡土墙土压力计算提供参考。
