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A global mantle conductivity model derived from 8 years of Swarm satellite magnetic data 被引量:2
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作者 HongBo Yao ZhengYong Ren +2 位作者 kejia pan JingTian Tang KeKe Zhang 《Earth and Planetary Physics》 EI CSCD 2023年第1期49-56,共8页
Mantle conductivity imaging is one of the scientific goals of the forthcoming Macao Science Satellite-1(MSS-1).To achieve this goal,we develop a data analysis and inversion scheme for satellite magnetic data to probe ... Mantle conductivity imaging is one of the scientific goals of the forthcoming Macao Science Satellite-1(MSS-1).To achieve this goal,we develop a data analysis and inversion scheme for satellite magnetic data to probe global one-dimensional(1D)mantle conductivity structures.Using this scheme,we present a new global mantle conductivity model by analyzing over 8 years of Swarm satellite magnetic data.First,after sophisticated data selection procedures and the removal of core and crustal fields,the inducing and induced spherical harmonic coefficients of magnetic potential due to the magnetospheric ring current are derived.Second,satellite Cresponses are estimated from the time series of these coefficients.Finally,the observed responses are inverted for both smooth and threejump conductivity models using a quasi-Newton algorithm.The obtained conductivity models are in general agreement with previous global mantle conductivity models.A comparison of our conductivity model with the laboratory conductivity model suggests the mean state of the upper mantle and transition zone is relatively dry.This scheme can be used to process the forthcoming Macao Science Satellite-1 magnetic data. 展开更多
关键词 Macao Science Satellite-1 satellite magnetic data mantle conductivity global electromagnetic induction
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The rapid densification behavior of powder metallurgy Ti alloys by induction heating sintering
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作者 kejia pan Xiaotao Liu +3 位作者 Bao Wang Shuai Gao Shixing Wu Ning Li 《Journal of Materials Science & Technology》 SCIE EI CAS CSCD 2024年第14期152-164,共13页
Micropores are decisive to mechanical properties and thermal deformation capabilities of powder met-allurgy(P/M)Ti alloys sintered compacts.As a result,achieving express densification is of prime im-portance and has a... Micropores are decisive to mechanical properties and thermal deformation capabilities of powder met-allurgy(P/M)Ti alloys sintered compacts.As a result,achieving express densification is of prime im-portance and has attracted increasing attention recently.Induction heating owns the merits of high effi-ciency,short process,and low cost,and thus has huge potential to be used as a sintering approach for the fabrication of P/M Ti alloys.Nevertheless,the facilitated densification behavior associated with induction heating sintering remains unclear so far.To address it,powder metallurgy Ti6Al4V is manufactured via induction heating sintering with which the underlying sintering mechanism is investigated in-depth.It is found that induction heating could generate a fully densified compact in a remarkably shortened time,demonstrating its superior sintering efficiency as compared with conventional resistance furnace heat-ing.COMSOL finite element analysis reveals that the maximum current density during induction heating can reach 10^(6)A m^(–2)though the magnetic field strength is solely 0.02 T,leading to a slight tempera-ture difference of approximately 30℃between the interior and exterior of the billet.Furthermore,the rapid heating essentially starts at sharp corners of particles due to the potent current concentration ef-fect,which facilitates the cracking of the particle surface oxide film and thus enhances the direct contact between them.Moreover,the electromigration effect caused by induction current promotes the diffusion capability of elements,giving rise to expedited densification,alloying,and chemical homogenization.This work provides not only critical insight into the sintering mechanism of induction heating sintering but also significant guidance for low-cost powder metallurgy materials preparation. 展开更多
关键词 Titanium alloy Powder metallurgy Induction heating sintering Radiation heating sintering Current field SIMULATION
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New Sixth-Order Compact Schemes for Poisson/Helmholtz Equations
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作者 kejia pan Kang Fu +2 位作者 Jin Li Hongling Hu Zhilin Li 《Numerical Mathematics(Theory,Methods and Applications)》 SCIE CSCD 2023年第2期393-409,共17页
Some new sixth-order compact finite difference schemes for Poisson/Helmholtz equations on rectangular domains in both two-and three-dimensions are developed and analyzed.Different from a few sixth-order compact finite... Some new sixth-order compact finite difference schemes for Poisson/Helmholtz equations on rectangular domains in both two-and three-dimensions are developed and analyzed.Different from a few sixth-order compact finite difference schemes in the literature,the finite difference and weight coefficients of the new methods have analytic simple expressions.One of the new ideas is to use a weighted combination of the source term at staggered grid points which is important for grid points near the boundary and avoids partial derivatives of the source term.Furthermore,the new compact schemes are exact for 2D and 3D Poisson equations if the solution is a polynomial less than or equal to 6.The coefficient matrices of the new schemes are M-matrices for Helmholtz equations with wave number K≤0,which guarantee the discrete maximum principle and lead to the convergence of the new sixth-order compact schemes.Numerical examples in both 2D and 3D are presented to verify the effectiveness of the proposed schemes. 展开更多
关键词 Poisson equation Helmholtz equation sixth-order compact scheme maximum principle staggered grid.
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钛合金感应熔炼用陶瓷坩埚研究现状与展望 被引量:5
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作者 赵超 王如愿 +2 位作者 潘科嘉 孙明翰 李宁 《科学通报》 EI CAS CSCD 北大核心 2022年第11期1155-1166,共12页
钛合金因具有高比强度、强耐蚀性、无磁等诸多优异特性,被认为是空天海等战略领域最理想的轻型结构材料.然而,采用铸锭冶金技术制造钛合金及其构件,仍存在高能耗、高成本等世界性难题.研究表明,坩埚式真空感应熔炼是解决上述难题的有效... 钛合金因具有高比强度、强耐蚀性、无磁等诸多优异特性,被认为是空天海等战略领域最理想的轻型结构材料.然而,采用铸锭冶金技术制造钛合金及其构件,仍存在高能耗、高成本等世界性难题.研究表明,坩埚式真空感应熔炼是解决上述难题的有效途径之一,但钛的高化学活性使其几乎能与目前已知的所有耐火材料发生反应.因此,新型熔钛坩埚材料及其制备技术是实现钛合金低成本、优质、高效熔炼的关键.对此,本文重点综述国内外钛合金感应熔炼用陶瓷坩埚材料(耐蚀机制、成分优选)及坩埚耐久性两大方面的研究现状,并结合华中科技大学的近期研究进展,对其未来发展方向提出新的思考. 展开更多
关键词 钛合金 真空感应熔炼 陶瓷坩埚 钛液腐蚀 抗热震性
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TIME-EXTRAPOLATION ALGORITHM (TEA) FOR LINEAR PARABOLIC PROBLEMS 被引量:2
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作者 Hongling Hu Chuanmiao Chen kejia pan 《Journal of Computational Mathematics》 SCIE CSCD 2014年第2期183-194,共12页
The fast solutions of Crank-Nicolson scheme on quasi-uniform mesh for parabolic prob- lems are discussed. First, to decrease regularity requirements of solutions, some new error estimates are proved. Second, we analyz... The fast solutions of Crank-Nicolson scheme on quasi-uniform mesh for parabolic prob- lems are discussed. First, to decrease regularity requirements of solutions, some new error estimates are proved. Second, we analyze the two characteristics of parabolic discrete scheme, and find that the efficiency of Multigrid Method (MG) is greatly reduced. Nu- merical experiments compare the efficiency of Direct Conjugate Gradient Method (DCG) and Extrapolation Cascadic Multigrid Method (EXCMG). Last, we propose a Time- Extrapolation Algorithm (TEA), which takes a linear combination of previous several level solutions as good initial values to accelerate the rate of convergence. Some typical extrapolation formulas are compared numerically. And we find that under certain accuracy requirement, the CG iteration count for the 3-order and 7-level extrapolation formula is about 1/3 of that of DCG's. Since the TEA algorithm is independent of the space dimension, it is still valid for quasi-uniform meshes. As only the finest grid is needed, the proposed method is regarded very effective for nonlinear parabolic problems. 展开更多
关键词 Parabolic problem Crank-Nicolson scheme Error estimates Time-extrapolationalgorithm CG-iteration.
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Extrapolation Cascadic Multigrid Method for Cell-Centered FV Discretization of Diffusion Equations with Strongly Discontinuous and Anisotropic Coefficients
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作者 kejia pan Xiaoxin Wu +2 位作者 Yunlong Yu Zhiqiang Sheng Guangwei Yuan 《Communications in Computational Physics》 SCIE 2022年第5期1561-1584,共24页
Extrapolation cascadic multigrid(EXCMG)method with conjugate gradient smoother is very efficient for solving the elliptic boundary value problems with linearfinite element discretization.However,it is not trivial to g... Extrapolation cascadic multigrid(EXCMG)method with conjugate gradient smoother is very efficient for solving the elliptic boundary value problems with linearfinite element discretization.However,it is not trivial to generalize the vertex-centred EXCMG method to cell-centeredfinite volume(FV)methods for diffusion equations with strongly discontinuous and anisotropic coefficients,since a non-nested hierarchy of grid nodes are used in the cell-centered discretization.For cell-centered FV schemes,the vertex values(auxiliary unknowns)need to be approximated by cell-centered ones(primary unknowns).One of the novelties is to propose a new gradient transfer(GT)method of interpolating vertex unknowns with cell-centered ones,which is easy to implement and applicable to general diffusion tensors.The main novelty of this paper is to design a multigrid prolongation operator based on the GT method and splitting extrapolation method,and then propose a cell-centered EXCMG method with BiCGStab smoother for solving the large linear system resulting from linear FV discretization of diffusion equations with strongly discontinuous and anisotropic coefficients.Numerical experiments are presented to demonstrate the high efficiency of the proposed method. 展开更多
关键词 Diffusion equation discontinuous coefficients anisotropic coefficients Richardson extrapolation finite volume scheme cell-centered multigrid method
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An Extrapolation Cascadic MultigridMethod for Elliptic Problems on Reentrant Domains
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作者 kejia pan Dongdong He Chuanmiao Chen 《Advances in Applied Mathematics and Mechanics》 SCIE 2017年第6期1347-1363,共17页
This paper proposes an extrapolation cascadic multigrid(EXCMG)method to solve elliptic problems in domains with reentrant corners.On a class ofλ-graded meshes,we derive some new extrapolation formulas to construct a ... This paper proposes an extrapolation cascadic multigrid(EXCMG)method to solve elliptic problems in domains with reentrant corners.On a class ofλ-graded meshes,we derive some new extrapolation formulas to construct a high-order approximation to the finite element solution on the next finer mesh using the numerical solutions on two-level of grids(current and previous grids).Then,this high-order approximation is used as the initial guess to reduce computational cost of the conjugate gradient method.Recursive application of this idea results in the EXCMG method proposed in this paper.Finally,numerical results for a crack problem and an L-shaped problem are presented to verify the efficiency and effectiveness of the proposed EXCMG method. 展开更多
关键词 Richardson extrapolation Cascadicmultigrid gradedmesh elliptic problems corner singularity
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