Constructing a metro station by enlarging shield tunnels combined with a mining/cut-and-cover method provides a new method to solve the contradictions of construction time limits of shield tunnels and stations. As a n...Constructing a metro station by enlarging shield tunnels combined with a mining/cut-and-cover method provides a new method to solve the contradictions of construction time limits of shield tunnels and stations. As a new-style construction method, there are several specific risks involved in the construction process. Based on the test section of Sanyuanqiao station on Beijing metro line 10, and combined with the existing methods of risk identification at present, including a review of world-wide operational experience of similar projects, the study of generic guidance on hazards associated with the type of work being undertaken, and discussions with qualified and experienced staff from the project team, etc., the specific risks during the construction process of the metro station constructed by enlarging shield tunnels combined with the cut-and-cover method are identified. The results show that the specific risks mainly come from three construction processes which include constructing upper enclosure structures, excavating the soil between shield tunnels and demolishing shield segments. Then relevant risk mitigation measures are put forward. The results can provide references for scheme improvement and a comprehensive risk assessment of the new-style construction method.展开更多
The vortex-induced vibrations （VIV） of barrel-shaped mast are calculated by three numerical metods, i.e. New- mark- β, HPD-L （High Precision Direct integration scheme-Linear form）, and HPD-S （High Precision Dire...The vortex-induced vibrations （VIV） of barrel-shaped mast are calculated by three numerical metods, i.e. New- mark- β, HPD-L （High Precision Direct integration scheme-Linear form）, and HPD-S （High Precision Direct integration scheme-Sinusoidal form）. According to the measured value, the accuracy curves are given to show the advantages of HPD-S method over others. Based on the comparison above, HPD-S method is used to calculate the influence of ice covering on the mast to VIV responses. It has been proved that the vortex-induced responses of barrel-shaped mast are changed along with ice thicknesses and types.展开更多
使用2021年GRAPES(Global/Regional Assimilation and Prediction System)模式数据和FY-4A卫星数据分析酒泉地区云量时空特征,采用时间自适应方法、动态变参数方法以及随机森林方法建立云量预测模型。结果表明:酒泉及周边地区总云量日...使用2021年GRAPES(Global/Regional Assimilation and Prediction System)模式数据和FY-4A卫星数据分析酒泉地区云量时空特征,采用时间自适应方法、动态变参数方法以及随机森林方法建立云量预测模型。结果表明:酒泉及周边地区总云量日变化幅度不大,季节变化特征明显,春、夏季多,秋、冬季较少,北部云量较少、南部云量多。不同格点的云量受到不同因素的影响,使用动态变参数方法,即根据预报因子和云量相关性在不同格点上动态选取预报因子构建随机森林模型,云量预测准确率为0.55~0.80。采用时间自适应方法使随机森林模型能够更新换代,云量预测准确性在0.55左右,数据量不足导致随机森林模型预测云量的准确率下降。展开更多
The design and management of the objects about the numerical manifold method are studied by abstracting the finite cover system of numerical manifold method as independent data classes and the theoretical basis for th...The design and management of the objects about the numerical manifold method are studied by abstracting the finite cover system of numerical manifold method as independent data classes and the theoretical basis for the researching and expanding of numerical manifold method is also put forward. The Hammer integration of triangular area coordinates is used in the integration of the element. The calculation result shows that the program is accuracy and effective.展开更多
Numerical quadrature is an important ingredient of Galerkin meshless methods. A new numerical quadrature technique, partition of unity quadrature （PUQ）,for Galerkin meshless methods was presented. The technique is b...Numerical quadrature is an important ingredient of Galerkin meshless methods. A new numerical quadrature technique, partition of unity quadrature （PUQ）,for Galerkin meshless methods was presented. The technique is based on finite covering and partition of unity. There is no need to decompose the physical domain into small cell. It possesses remarkable integration accuracy. Using Element-free Galerkin methods as example, Galerkin meshless methods based on PUQ were studied in detail. Meshing is always not required in the procedure of constitution of approximate function or numerical quadrature, so Galerkin meshless methods based on PUQ are “truly” meshless methods.展开更多
The numerical manifold method(NMM)can be viewed as an inherent continuous-discontinuous numerical method,which is based on two cover systems including mathematical and physical covers.Higher-order NMM that adopts high...The numerical manifold method(NMM)can be viewed as an inherent continuous-discontinuous numerical method,which is based on two cover systems including mathematical and physical covers.Higher-order NMM that adopts higher-order polynomials as its local approximations generally shows higher precision than zero-order NMM whose local approximations are constants.Therefore,higherorder NMM will be an excellent choice for crack propagation problem which requires higher stress accuracy.In addition,it is crucial to improve the stress accuracy around the crack tip for determining the direction of crack growth according to the maximum circumferential stress criterion in fracture mechanics.Thus,some other enriched local approximations are introduced to model the stress singularity at the crack tip.Generally,higher-order NMM,especially first-order NMM wherein local approximations are first-order polynomials,has the linear dependence problems as other partition of unit(PUM)based numerical methods does.To overcome this problem,an extended NMM is developed based on a new local approximation derived from the triangular plate element in the finite element method(FEM),which has no linear dependence issue.Meanwhile,the stresses at the nodes of mathematical mesh(the nodal stresses in FEM)are continuous and the degrees of freedom defined on the physical patches are physically meaningful.Next,the extended NMM is employed to solve multiple crack propagation problems.It shows that the fracture mechanics requirement and mechanical equilibrium can be satisfied by the trial-and-error method and the adjustment of the load multiplier in the process of crack propagation.Four numerical examples are illustrated to verify the feasibility of the proposed extended NMM.The numerical examples indicate that the crack growths simulated by the extended NMM are in good accordance with the reference solutions.Thus the effectiveness and correctness of the developed NMM have been validated.展开更多
A new photonic bandgap (PBG) cover for a patch antenna with a photonic bandgap substrate is introduced. The plane wave expansion method and the FDTD method were used to calculate such an antenna system. Numerical re-s...A new photonic bandgap (PBG) cover for a patch antenna with a photonic bandgap substrate is introduced. The plane wave expansion method and the FDTD method were used to calculate such an antenna system. Numerical re-sults for the input return loss, radiation pattern, surface wave, and the directivity of the antennas are presented. A com-parison between the conventional patch antenna and the new PBG antenna is given. It is shown that the new PBG cover is very efficient for improving the radiation directivity. The physical reasons for the improvement are also given.展开更多
The typical quadrangular and triangular elements for thin plate bending based on Kirchhoff assumptions are the non- conforming elements with low computational accuracy and limitative application range in fmite element...The typical quadrangular and triangular elements for thin plate bending based on Kirchhoff assumptions are the non- conforming elements with low computational accuracy and limitative application range in fmite element method（FEM）. Some compatible elements can be developed by the means of supplementing correction functions, increasing nodes in element or on the boundaries, expanding nodal degrees of freedom（DOF）, etc, but these elements are inconvenient to apply in practice for the high calculation complexity. In this paper, in order to overcome the defects of thin plate bending finite element, numerical manifold method（NMM） was introduced to solve thin plate bending deformation problem. Rectangular mesh was adopted as mathematical mesh to form f＇mite element cover system, and then 16-cover manifold element was proposed. Numerical manifold formulas were constructed on the basis of minimum potential energy principle, displacement boundary conditions are implemented by penalty function method, and all the element matrixes were derived in details. The 16-cover element has a simple calculation process for employing only the transverse displacement cover DOFs as the basic unknown variables, and has been proved to meet the requirements of completeness and full compatibility. As an application, the presented 16-cover element has been used to analyze bending deformation of square thin plate under different loads and boundary conditions, and the results show that numerical manifold method with compatible element, compared with finite element method, can improve computational accuracy and convergence greatly.展开更多
基金Beijing Science and Technology Planning Project(No.D0604003040921)
文摘Constructing a metro station by enlarging shield tunnels combined with a mining/cut-and-cover method provides a new method to solve the contradictions of construction time limits of shield tunnels and stations. As a new-style construction method, there are several specific risks involved in the construction process. Based on the test section of Sanyuanqiao station on Beijing metro line 10, and combined with the existing methods of risk identification at present, including a review of world-wide operational experience of similar projects, the study of generic guidance on hazards associated with the type of work being undertaken, and discussions with qualified and experienced staff from the project team, etc., the specific risks during the construction process of the metro station constructed by enlarging shield tunnels combined with the cut-and-cover method are identified. The results show that the specific risks mainly come from three construction processes which include constructing upper enclosure structures, excavating the soil between shield tunnels and demolishing shield segments. Then relevant risk mitigation measures are put forward. The results can provide references for scheme improvement and a comprehensive risk assessment of the new-style construction method.
文摘The vortex-induced vibrations （VIV） of barrel-shaped mast are calculated by three numerical metods, i.e. New- mark- β, HPD-L （High Precision Direct integration scheme-Linear form）, and HPD-S （High Precision Direct integration scheme-Sinusoidal form）. According to the measured value, the accuracy curves are given to show the advantages of HPD-S method over others. Based on the comparison above, HPD-S method is used to calculate the influence of ice covering on the mast to VIV responses. It has been proved that the vortex-induced responses of barrel-shaped mast are changed along with ice thicknesses and types.
文摘使用2021年GRAPES(Global/Regional Assimilation and Prediction System)模式数据和FY-4A卫星数据分析酒泉地区云量时空特征,采用时间自适应方法、动态变参数方法以及随机森林方法建立云量预测模型。结果表明:酒泉及周边地区总云量日变化幅度不大,季节变化特征明显,春、夏季多,秋、冬季较少,北部云量较少、南部云量多。不同格点的云量受到不同因素的影响,使用动态变参数方法,即根据预报因子和云量相关性在不同格点上动态选取预报因子构建随机森林模型,云量预测准确率为0.55~0.80。采用时间自适应方法使随机森林模型能够更新换代,云量预测准确性在0.55左右,数据量不足导致随机森林模型预测云量的准确率下降。
基金This project is supported by National Natural Science Foundation of China.
文摘The design and management of the objects about the numerical manifold method are studied by abstracting the finite cover system of numerical manifold method as independent data classes and the theoretical basis for the researching and expanding of numerical manifold method is also put forward. The Hammer integration of triangular area coordinates is used in the integration of the element. The calculation result shows that the program is accuracy and effective.
文摘Numerical quadrature is an important ingredient of Galerkin meshless methods. A new numerical quadrature technique, partition of unity quadrature （PUQ）,for Galerkin meshless methods was presented. The technique is based on finite covering and partition of unity. There is no need to decompose the physical domain into small cell. It possesses remarkable integration accuracy. Using Element-free Galerkin methods as example, Galerkin meshless methods based on PUQ were studied in detail. Meshing is always not required in the procedure of constitution of approximate function or numerical quadrature, so Galerkin meshless methods based on PUQ are “truly” meshless methods.
基金supported by the National Key R&D Program of China (Grant No.2018YFC0407002)the National Natural Science Foundation of China(Grant Nos.11502033 and 51879014)
文摘The numerical manifold method(NMM)can be viewed as an inherent continuous-discontinuous numerical method,which is based on two cover systems including mathematical and physical covers.Higher-order NMM that adopts higher-order polynomials as its local approximations generally shows higher precision than zero-order NMM whose local approximations are constants.Therefore,higherorder NMM will be an excellent choice for crack propagation problem which requires higher stress accuracy.In addition,it is crucial to improve the stress accuracy around the crack tip for determining the direction of crack growth according to the maximum circumferential stress criterion in fracture mechanics.Thus,some other enriched local approximations are introduced to model the stress singularity at the crack tip.Generally,higher-order NMM,especially first-order NMM wherein local approximations are first-order polynomials,has the linear dependence problems as other partition of unit(PUM)based numerical methods does.To overcome this problem,an extended NMM is developed based on a new local approximation derived from the triangular plate element in the finite element method(FEM),which has no linear dependence issue.Meanwhile,the stresses at the nodes of mathematical mesh(the nodal stresses in FEM)are continuous and the degrees of freedom defined on the physical patches are physically meaningful.Next,the extended NMM is employed to solve multiple crack propagation problems.It shows that the fracture mechanics requirement and mechanical equilibrium can be satisfied by the trial-and-error method and the adjustment of the load multiplier in the process of crack propagation.Four numerical examples are illustrated to verify the feasibility of the proposed extended NMM.The numerical examples indicate that the crack growths simulated by the extended NMM are in good accordance with the reference solutions.Thus the effectiveness and correctness of the developed NMM have been validated.
文摘A new photonic bandgap (PBG) cover for a patch antenna with a photonic bandgap substrate is introduced. The plane wave expansion method and the FDTD method were used to calculate such an antenna system. Numerical re-sults for the input return loss, radiation pattern, surface wave, and the directivity of the antennas are presented. A com-parison between the conventional patch antenna and the new PBG antenna is given. It is shown that the new PBG cover is very efficient for improving the radiation directivity. The physical reasons for the improvement are also given.
基金supported by National Natural Science Foundation of China (Grant No. 50775044, Grant No. 50975050)Guangdong Provincial and Ministry of Education Industry-University-Research Integration Project of China (Grant No. 2009B090300044)
文摘The typical quadrangular and triangular elements for thin plate bending based on Kirchhoff assumptions are the non- conforming elements with low computational accuracy and limitative application range in fmite element method（FEM）. Some compatible elements can be developed by the means of supplementing correction functions, increasing nodes in element or on the boundaries, expanding nodal degrees of freedom（DOF）, etc, but these elements are inconvenient to apply in practice for the high calculation complexity. In this paper, in order to overcome the defects of thin plate bending finite element, numerical manifold method（NMM） was introduced to solve thin plate bending deformation problem. Rectangular mesh was adopted as mathematical mesh to form f＇mite element cover system, and then 16-cover manifold element was proposed. Numerical manifold formulas were constructed on the basis of minimum potential energy principle, displacement boundary conditions are implemented by penalty function method, and all the element matrixes were derived in details. The 16-cover element has a simple calculation process for employing only the transverse displacement cover DOFs as the basic unknown variables, and has been proved to meet the requirements of completeness and full compatibility. As an application, the presented 16-cover element has been used to analyze bending deformation of square thin plate under different loads and boundary conditions, and the results show that numerical manifold method with compatible element, compared with finite element method, can improve computational accuracy and convergence greatly.
