通过分析统一电能质量调节器(Unified Power Quality Conditioner,简称UPQC)的工作原理,以最常用的左串-右并主电路结构为例,建立其基波稳态等效电路,对其能量流动关系进行分析。在此基础上,结合最小能量法论证推导串、并联侧功率需求公...通过分析统一电能质量调节器(Unified Power Quality Conditioner,简称UPQC)的工作原理,以最常用的左串-右并主电路结构为例,建立其基波稳态等效电路,对其能量流动关系进行分析。在此基础上,结合最小能量法论证推导串、并联侧功率需求公式,确定主电路的容量选取原则。最后通过实验验证主电路容量选取原则的合理性。展开更多
We construct and analyze a family of quadratic finite volume method(FVM)schemes over tetrahedral meshes.In order to prove the stability and the error estimate,we propose the minimum V-angle condition on tetrahedral me...We construct and analyze a family of quadratic finite volume method(FVM)schemes over tetrahedral meshes.In order to prove the stability and the error estimate,we propose the minimum V-angle condition on tetrahedral meshes,and the surface and volume orthogonal conditions on dual meshes.Through the technique of element analysis,the local stability is equivalent to a positive definiteness of a 9 × 9 element matrix,which is difficult to analyze directly or even numerically.With the help of the surface orthogonal condition and the congruent transformation,this element matrix is reduced into a block diagonal matrix,and then we carry out the stability result under the minimum V-angle condition.It is worth mentioning that the minimum V-angle condition of the tetrahedral case is very different from a simple extension of the minimum angle condition for triangular meshes,while it is also convenient to use in practice.Based on the stability,we prove the optimal H^(1) and L^(2) error estimates,respectively,where the orthogonal conditions play an important role in ensuring the optimal L^(2) convergence rate.Numerical experiments are presented to illustrate our theoretical results.展开更多
In this work,we study the coercivity of a family of quadratic finite volume element(FVE)schemes over triangular meshes for solving elliptic boundary value problems.The analysis is based on the standard mapping from th...In this work,we study the coercivity of a family of quadratic finite volume element(FVE)schemes over triangular meshes for solving elliptic boundary value problems.The analysis is based on the standard mapping from the trial function space to the test function space so that the coercivity result can be naturally incorporated with most existing theoretical results such as H^(1) and L^(2) error estimates.The novelty of this paper is that,each element stiffness matrix of the quadratic FVE schemes can be decomposed into three parts:the first part is the element stiffness matrix of the standard quadratic finite element method(FEM),the second part is the difference between the FVE and FEM on the element boundary,while the third part can be expressed as the tensor product of two vectors.As a result,we reach a sufficient condition to guarantee the existence,uniqueness and coercivity result of the FVE solution on general triangular meshes.Moreover,based on this sufficient condition,some minimum angle conditions with simple,analytic and computable expressions are obtained.By comparison,the existing minimum angle conditions were obtained numerically from a computer program.Theoretical findings are conformed with the numerical results.展开更多
为解决高速铁路牵引供电系统负序不平衡问题,在传统基于铁路功率调节器(Railway Power Conditioner,RPC)补偿的基础上,针对所需补偿容量较大的问题,提出了多变电站RPC协同补偿的理论.并对该方法进行了详细证明,推导了在各种情况下的安...为解决高速铁路牵引供电系统负序不平衡问题,在传统基于铁路功率调节器(Railway Power Conditioner,RPC)补偿的基础上,针对所需补偿容量较大的问题,提出了多变电站RPC协同补偿的理论.并对该方法进行了详细证明,推导了在各种情况下的安装容量和补偿方法,该方法较单个牵引变电站所需RPC容量可降低1/3的补偿容量,从而减小了成本.最后,进行了仿真验证,结果表明,该多站协同补偿方法具有可行性和有效性.展开更多
An inherent problem with both oil and natural gas production is the deposition of sand particles in pipeline,which could lead to problems such as excessive pressure drops,equipment failure,pipeline erosion,and product...An inherent problem with both oil and natural gas production is the deposition of sand particles in pipeline,which could lead to problems such as excessive pressure drops,equipment failure,pipeline erosion,and production decline.The characterization of sand particles transport and sedimentation in different flow systems such as sandemultiphase mixtures is vital to predict the sand transport velocity and entrainment processes in oil and gas transportation pipelines.However,it seems that no model exists able to accurately characterize the sand transport and deposition in multiphase pipeline.In fact,in the last decade several researchers tried to extend the modeling of liquid-solid flow to gas-liquid-solid flow,but no significant results have been obtained,especially in slug flow condition due to the complexity of the phenomenon.In order to develop and validate a mathematical model properly formulated for the calculation of the sand critical deposition velocity in gas-liquid flow,more and more experimental data are necessary.This paper presents a preliminary experimental study of three phase flows(air-water-sand)inside a horizontal pipe and the application of the sand-liquid models present in literature.Significant observations were made during the experimental study from which several conclusions were drawn.Different sand flow regimes were established by physical observation and data analysis:fully dispersed solid flow,moving dunes and stationary bed.The critical deposition velocities were determined at different sand concentrations.It was concluded that sand transport characteristics and the critical deposition velocity are strongly dependent on the gas-liquid flow regime and on sand concentration.展开更多
文摘通过分析统一电能质量调节器(Unified Power Quality Conditioner,简称UPQC)的工作原理,以最常用的左串-右并主电路结构为例,建立其基波稳态等效电路,对其能量流动关系进行分析。在此基础上,结合最小能量法论证推导串、并联侧功率需求公式,确定主电路的容量选取原则。最后通过实验验证主电路容量选取原则的合理性。
基金supported by National Natural Science Foundation of China(Grant Nos.12071177 and 11701211)the Science Challenge Project(Grant No.TZ2016002)the China Postdoctoral Science Foundation(Grant No.2021M690437)。
文摘We construct and analyze a family of quadratic finite volume method(FVM)schemes over tetrahedral meshes.In order to prove the stability and the error estimate,we propose the minimum V-angle condition on tetrahedral meshes,and the surface and volume orthogonal conditions on dual meshes.Through the technique of element analysis,the local stability is equivalent to a positive definiteness of a 9 × 9 element matrix,which is difficult to analyze directly or even numerically.With the help of the surface orthogonal condition and the congruent transformation,this element matrix is reduced into a block diagonal matrix,and then we carry out the stability result under the minimum V-angle condition.It is worth mentioning that the minimum V-angle condition of the tetrahedral case is very different from a simple extension of the minimum angle condition for triangular meshes,while it is also convenient to use in practice.Based on the stability,we prove the optimal H^(1) and L^(2) error estimates,respectively,where the orthogonal conditions play an important role in ensuring the optimal L^(2) convergence rate.Numerical experiments are presented to illustrate our theoretical results.
基金supported by the Guangdong Basic and Applied Basic Research Foundation,China(No.2022A1515012106)the project of Guangdong Polytechnic Normal University,China(No.2022SDKYA023)the project of promoting research capabilities for key constructed disciplines in Guangdong Province,China(No.2021ZDJS028).
文摘In this work,we study the coercivity of a family of quadratic finite volume element(FVE)schemes over triangular meshes for solving elliptic boundary value problems.The analysis is based on the standard mapping from the trial function space to the test function space so that the coercivity result can be naturally incorporated with most existing theoretical results such as H^(1) and L^(2) error estimates.The novelty of this paper is that,each element stiffness matrix of the quadratic FVE schemes can be decomposed into three parts:the first part is the element stiffness matrix of the standard quadratic finite element method(FEM),the second part is the difference between the FVE and FEM on the element boundary,while the third part can be expressed as the tensor product of two vectors.As a result,we reach a sufficient condition to guarantee the existence,uniqueness and coercivity result of the FVE solution on general triangular meshes.Moreover,based on this sufficient condition,some minimum angle conditions with simple,analytic and computable expressions are obtained.By comparison,the existing minimum angle conditions were obtained numerically from a computer program.Theoretical findings are conformed with the numerical results.
文摘为解决高速铁路牵引供电系统负序不平衡问题,在传统基于铁路功率调节器(Railway Power Conditioner,RPC)补偿的基础上,针对所需补偿容量较大的问题,提出了多变电站RPC协同补偿的理论.并对该方法进行了详细证明,推导了在各种情况下的安装容量和补偿方法,该方法较单个牵引变电站所需RPC容量可降低1/3的补偿容量,从而减小了成本.最后,进行了仿真验证,结果表明,该多站协同补偿方法具有可行性和有效性.
文摘An inherent problem with both oil and natural gas production is the deposition of sand particles in pipeline,which could lead to problems such as excessive pressure drops,equipment failure,pipeline erosion,and production decline.The characterization of sand particles transport and sedimentation in different flow systems such as sandemultiphase mixtures is vital to predict the sand transport velocity and entrainment processes in oil and gas transportation pipelines.However,it seems that no model exists able to accurately characterize the sand transport and deposition in multiphase pipeline.In fact,in the last decade several researchers tried to extend the modeling of liquid-solid flow to gas-liquid-solid flow,but no significant results have been obtained,especially in slug flow condition due to the complexity of the phenomenon.In order to develop and validate a mathematical model properly formulated for the calculation of the sand critical deposition velocity in gas-liquid flow,more and more experimental data are necessary.This paper presents a preliminary experimental study of three phase flows(air-water-sand)inside a horizontal pipe and the application of the sand-liquid models present in literature.Significant observations were made during the experimental study from which several conclusions were drawn.Different sand flow regimes were established by physical observation and data analysis:fully dispersed solid flow,moving dunes and stationary bed.The critical deposition velocities were determined at different sand concentrations.It was concluded that sand transport characteristics and the critical deposition velocity are strongly dependent on the gas-liquid flow regime and on sand concentration.
