Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a cry...Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.展开更多
Numerical simulations based on a new regularized phase-field model were presented, to simulate the solidification of hexagonal close-packed materials with strong interfacial energy anisotropies. Results show that the ...Numerical simulations based on a new regularized phase-field model were presented, to simulate the solidification of hexagonal close-packed materials with strong interfacial energy anisotropies. Results show that the crystal grows into facet dendrites,displaying six-fold symmetry. The size of initial crystals has an effect on the branching-off of the principal branch tip along the<100> direction, which is eliminated by setting the b/a(a and b are the semi-major and semi-minor sizes in the initial elliptical crystals, respectively) value to be less than or equal to 1. With an increase in the undercooling value, the equilibrium morphology of the crystal changes from a star-like shape to facet dendrites without side branches. The steady-state tip velocity increases exponentially when the dimensionless undercooling is below the critical value. With a further increase in the undercooling value, the equilibrium morphology of the crystal grows into a developed side-branch structure, and the steady-state tip velocity of the facet dendrites increases linearly. The facet dendrite growth has controlled diffusion and kinetics.展开更多
In this work,we extend the recently proposed adaptive phase field method to model fracture in orthotropic functionally graded materials(FGMs).A recovery type error indicator combined with quadtree decomposition is emp...In this work,we extend the recently proposed adaptive phase field method to model fracture in orthotropic functionally graded materials(FGMs).A recovery type error indicator combined with quadtree decomposition is employed for adaptive mesh refinement.The proposed approach is capable of capturing the fracture process with a localized mesh refinement that provides notable gains in computational efficiency.The implementation is validated against experimental data and other numerical experiments on orthotropic materials with different material orientations.The results reveal an increase in the stiffness and the maximum force with increasing material orientation angle.The study is then extended to the analysis of orthotropic FGMs.It is observed that,if the gradation in fracture properties is neglected,the material gradient plays a secondary role,with the fracture behaviour being dominated by the orthotropy of the material.However,when the toughness increases along the crack propagation path,a substantial gain in fracture resistance is observed.展开更多
The effect of a high magnetic field up to 30T on phase transformation temperature and microstructure of Fe-based alloys has been reviewed. A high magnetic field accelerates ferrite transformation, changes the morpho...The effect of a high magnetic field up to 30T on phase transformation temperature and microstructure of Fe-based alloys has been reviewed. A high magnetic field accelerates ferrite transformation, changes the morphology of the transformed microstructures and increases the A3 and A1 temperature. In a magnetic field of 30T, the A1 temperature increases by about 37.1℃ for Fe-0.8C, the A3 temperature for pure Fe increases by about 33.1℃. The measured transformation temperature data are not consistent with calculation results using Weiss molecular field theory. Ferrite grains are elongated and aligned along the direction of magnetic field in Fe-0.4C and Fe-0.6C alloys by ferrite transformation, but elongated and aligned structure was not found in pure Fe, Fe-0.05C alloy and Fe-1.5Mn-0.11C-0.1V alloy.展开更多
The total electric field(TEF) at ground level induced by high-voltage direct current(HVDC) overhead transmission lines is one of the important indexes for evaluating the lines' electromagnetic environment.Based on...The total electric field(TEF) at ground level induced by high-voltage direct current(HVDC) overhead transmission lines is one of the important indexes for evaluating the lines' electromagnetic environment.Based on analyzing the existing TEF sensors and the measurement principle of ion-current density,the influence from ions on TEF measurements is quantitively studied.The results show that the ions generated by the corona from a HVDC transmission line in operation cause errors in the measurement of TEF.This error is determined through analyzing the component of total measuring current on the filed mill's sensing electrode: if no appropriate approach taken,the maximum measurement error reaches up to 4.3%.Furthermore,a method that can eliminate such error,and hence improve the accuracy of TEF sensors is designed.展开更多
Most of the direction of arrival(DOA) estimation methods often need the exact array manifold, but in actual applications,the gain and phase of the channels are usually inconsistent, which will cause the estimation inv...Most of the direction of arrival(DOA) estimation methods often need the exact array manifold, but in actual applications,the gain and phase of the channels are usually inconsistent, which will cause the estimation invalid. A novel direction finding approach for mixed far-field and near-field signals with gain-phase error array is provided. Based on simplifying the space spectrum function by matrix transformation, DOA of far-field signals is obtained. Consequently, errors of the array are acquired according to the orthogonality of far-field signal subspace and noise subspace.Finally, DOA of near-field signals can be estimated. The method merely needs one-dimensional spectrum searching, so as to improve the computational efficiency on the premise of ensuring a certain accuracy, simulation results manifest the effectiveness of the method.展开更多
Al-Cu-Mg-Ag alloys have become a research hotspot because of its good heat resistance.Its excellent mechanical properties are inseparable from the regulation of the structure by researchers.The method of material stru...Al-Cu-Mg-Ag alloys have become a research hotspot because of its good heat resistance.Its excellent mechanical properties are inseparable from the regulation of the structure by researchers.The method of material structure simulation has become more and more perfect.This study employs numerical simulation to investigate the microstructure evolution of Al-Cu-Mg-Ag alloys during solidification with the aim of controlling its structure.The size distribution of Ti-containing particles in an Al-Ti-B master alloy was characterized via microstructure observation,serving as a basis for optimizing the nucleation density parameters for particles of varying radii in the phase field model.The addition of refiner inhibited the growth of dendrites and no longer produced coarse dendrites.With the increase of refiner,the grains gradually tended to form cellular morphology.The refined grains were about 100μm in size.Experimental validation of the simulated as-cast grain morphology was conducted.The samples were observed by metallographic microscope and scanning electron microscope.The addition of refiner had a significant effect on the refinement of the alloy,and the average grain size after refinement was also about 100μm.At the same time,the XRD phase identification of the alloy was carried out.The observation of the microstructure morphology under the scanning electron microscope showed that the precipitated phase was mainly concentrated on the grain boundary.The Al_(2)Cu accounted for about 5%,and the matrix phase FCC accounted for about 95%,which also corresponded well with the simulation results.展开更多
To describe the shielding ability of materials accurately and comprehensively,the frequency-domain and time-domain shielding effectiveness(SE) of material is investigated.The relevance between them was analyzed based ...To describe the shielding ability of materials accurately and comprehensively,the frequency-domain and time-domain shielding effectiveness(SE) of material is investigated.The relevance between them was analyzed based on the minimum phase method,and the time-domain SE can be derived from frequency-domain SE.The SE of an energy selective surface(ESS) made of a novel material is investigated,and the relationship between SE and radiation field intensity are analyzed.The results show that not only material,but also the intensity of radiation electric field shows influence on SE in its frequency; for some materials,the dependence of SE on radiation electric field intensity needs to be considered.Therefore,it is necessary to research on the SE of shielding material in high-intensity electromagnetic environment.展开更多
基金Project(11102164)supported by the National Natural Science Foundation of ChinaProject(G9KY101502)supported by NPU Foundation for Fundamental Research,China
文摘Numerical simulation based on a new regularized phase field model was presented to simulate the dendritic shape of a non-isothermal alloy with strong anisotropy in a forced flow. The simulation results show that a crystal nucleus grows into a symmetric dendrite in a free flow and into an asymmetry dendrite in a forced flow. As the forced flow velocity is increased, both of the promoting effect on the upstream arm and the inhibiting effects on the downstream and perpendicular arms are intensified, and the perpendicular arm tilts to the upstream direction. With increasing the anisotropy value to 0.14, all of the dendrite arms tip velocities are gradually stabilized and finally reach their relative saturation values. In addition, the effects of an undercooling parameter and a forced compound flow on the faceted dendrite growth were also investigated.
基金Project(10834015) supported by the National Natural Science Foundation of ChinaProject(12SKY01-1) supported by the Doctoral Fund of Shangluo University,ChinaProject(14JK1223) supported by the Scientific Research Program of Shaanxi Provincial Education Department,China
文摘Numerical simulations based on a new regularized phase-field model were presented, to simulate the solidification of hexagonal close-packed materials with strong interfacial energy anisotropies. Results show that the crystal grows into facet dendrites,displaying six-fold symmetry. The size of initial crystals has an effect on the branching-off of the principal branch tip along the<100> direction, which is eliminated by setting the b/a(a and b are the semi-major and semi-minor sizes in the initial elliptical crystals, respectively) value to be less than or equal to 1. With an increase in the undercooling value, the equilibrium morphology of the crystal changes from a star-like shape to facet dendrites without side branches. The steady-state tip velocity increases exponentially when the dimensionless undercooling is below the critical value. With a further increase in the undercooling value, the equilibrium morphology of the crystal grows into a developed side-branch structure, and the steady-state tip velocity of the facet dendrites increases linearly. The facet dendrite growth has controlled diffusion and kinetics.
基金E.Martínez-Paneda acknowledges financial support from the Royal Commission for the 1851 Exhibition through their Research Fellowship programme(RF496/2018).
文摘In this work,we extend the recently proposed adaptive phase field method to model fracture in orthotropic functionally graded materials(FGMs).A recovery type error indicator combined with quadtree decomposition is employed for adaptive mesh refinement.The proposed approach is capable of capturing the fracture process with a localized mesh refinement that provides notable gains in computational efficiency.The implementation is validated against experimental data and other numerical experiments on orthotropic materials with different material orientations.The results reveal an increase in the stiffness and the maximum force with increasing material orientation angle.The study is then extended to the analysis of orthotropic FGMs.It is observed that,if the gradation in fracture properties is neglected,the material gradient plays a secondary role,with the fracture behaviour being dominated by the orthotropy of the material.However,when the toughness increases along the crack propagation path,a substantial gain in fracture resistance is observed.
文摘The effect of a high magnetic field up to 30T on phase transformation temperature and microstructure of Fe-based alloys has been reviewed. A high magnetic field accelerates ferrite transformation, changes the morphology of the transformed microstructures and increases the A3 and A1 temperature. In a magnetic field of 30T, the A1 temperature increases by about 37.1℃ for Fe-0.8C, the A3 temperature for pure Fe increases by about 33.1℃. The measured transformation temperature data are not consistent with calculation results using Weiss molecular field theory. Ferrite grains are elongated and aligned along the direction of magnetic field in Fe-0.4C and Fe-0.6C alloys by ferrite transformation, but elongated and aligned structure was not found in pure Fe, Fe-0.05C alloy and Fe-1.5Mn-0.11C-0.1V alloy.
基金Project supported by National Natural Science Foundation of China （61273165 51207005）.
文摘The total electric field(TEF) at ground level induced by high-voltage direct current(HVDC) overhead transmission lines is one of the important indexes for evaluating the lines' electromagnetic environment.Based on analyzing the existing TEF sensors and the measurement principle of ion-current density,the influence from ions on TEF measurements is quantitively studied.The results show that the ions generated by the corona from a HVDC transmission line in operation cause errors in the measurement of TEF.This error is determined through analyzing the component of total measuring current on the filed mill's sensing electrode: if no appropriate approach taken,the maximum measurement error reaches up to 4.3%.Furthermore,a method that can eliminate such error,and hence improve the accuracy of TEF sensors is designed.
基金supported by the National Natural Science Foundation of China(6150117661505050)+5 种基金the University Nursing Program for Young Scholars with Creative Talents in Heilongjiang Province(UNPYSCT-2016017)the Natural Science Foundation of Heilongjiang Province(F2015015)the Outstanding Young Scientist Foundation of Heilongjiang University(JCL201504)the China Postdoctoral Science Foundation(2014M561381)the Postdoctoral Foundation of Heilongjiang Province(LBH-Z14178)the Special Research Funds for the Universities of Heilongjiang Province(HDRCCX-2016Z10)
文摘Most of the direction of arrival(DOA) estimation methods often need the exact array manifold, but in actual applications,the gain and phase of the channels are usually inconsistent, which will cause the estimation invalid. A novel direction finding approach for mixed far-field and near-field signals with gain-phase error array is provided. Based on simplifying the space spectrum function by matrix transformation, DOA of far-field signals is obtained. Consequently, errors of the array are acquired according to the orthogonality of far-field signal subspace and noise subspace.Finally, DOA of near-field signals can be estimated. The method merely needs one-dimensional spectrum searching, so as to improve the computational efficiency on the premise of ensuring a certain accuracy, simulation results manifest the effectiveness of the method.
文摘Al-Cu-Mg-Ag alloys have become a research hotspot because of its good heat resistance.Its excellent mechanical properties are inseparable from the regulation of the structure by researchers.The method of material structure simulation has become more and more perfect.This study employs numerical simulation to investigate the microstructure evolution of Al-Cu-Mg-Ag alloys during solidification with the aim of controlling its structure.The size distribution of Ti-containing particles in an Al-Ti-B master alloy was characterized via microstructure observation,serving as a basis for optimizing the nucleation density parameters for particles of varying radii in the phase field model.The addition of refiner inhibited the growth of dendrites and no longer produced coarse dendrites.With the increase of refiner,the grains gradually tended to form cellular morphology.The refined grains were about 100μm in size.Experimental validation of the simulated as-cast grain morphology was conducted.The samples were observed by metallographic microscope and scanning electron microscope.The addition of refiner had a significant effect on the refinement of the alloy,and the average grain size after refinement was also about 100μm.At the same time,the XRD phase identification of the alloy was carried out.The observation of the microstructure morphology under the scanning electron microscope showed that the precipitated phase was mainly concentrated on the grain boundary.The Al_(2)Cu accounted for about 5%,and the matrix phase FCC accounted for about 95%,which also corresponded well with the simulation results.
基金Project supported by National Basic Research Program of China（973 Program） （6131380301） National Natural Science Foundation of China （61001050）.
文摘To describe the shielding ability of materials accurately and comprehensively,the frequency-domain and time-domain shielding effectiveness(SE) of material is investigated.The relevance between them was analyzed based on the minimum phase method,and the time-domain SE can be derived from frequency-domain SE.The SE of an energy selective surface(ESS) made of a novel material is investigated,and the relationship between SE and radiation field intensity are analyzed.The results show that not only material,but also the intensity of radiation electric field shows influence on SE in its frequency; for some materials,the dependence of SE on radiation electric field intensity needs to be considered.Therefore,it is necessary to research on the SE of shielding material in high-intensity electromagnetic environment.
