Deformation of casting during the solidification process has puzzled many engineers and scientists for years. In order to attain the goal of near-net forming by casting, numerical simulation is a powerful tool. Tradit...Deformation of casting during the solidification process has puzzled many engineers and scientists for years. In order to attain the goal of near-net forming by casting, numerical simulation is a powerful tool. Traditional methods compute the thermal stress of both the casting and the mold. This method suffers the problem of massive calculation and failure of convergence. This paper proposes an improved Mold Surface Element Method, the main idea of which is to use the surface elements instead of body elements to express the interactions between the casting and the mold. The proposed method shows a high computation efficiency and provides satisfactory precision for engineering. Two practical casting products were used to verify the proposed method. The simulated results agree well with those observed in practical products. The proposed method is believed to benefit production practice and to provide theoretical guidance.展开更多
A program for calculating the aerodynamic properties of hypersonic vehicles based on the surface element method was developed using the general-purpose programming language C++. The calculated values of lift coefficie...A program for calculating the aerodynamic properties of hypersonic vehicles based on the surface element method was developed using the general-purpose programming language C++. The calculated values of lift coefficients, drag coefficients, and surface pressure coefficients are discussed with the results of wind tunnel experiments using the HL-20 lift body and the NASA hypersonic aircraft STS Columbia OV-102 as research subjects. Finally, the results of the experimental and wind tunnel studies of the aerodynamic characteristics of the HL-20 lift body at an altitude of 65 km and Mach numbers of 6 and 10 Ma are discussed. The maximum error in the aerodynamic characteristics at 6 Ma does not exceed 3%, consistent with the results. The maximum error at 10 Ma occurs in the 11° - 14° angle of attack and does not exceed 10%, which is still within the error tolerance. The STS results for NASA’s hypersonic aircraft were also tested using this procedure. Experimental aerodynamic data for the Colombian OV-102 aircraft. The results show that the program takes only 10 minutes to calculate the results, with no more than 2% error from the wind tunnel experimental results.展开更多
A surface edge element method is proposed and implemented in the study ofelectromagnetic scattering fields of general targets. The basis functions for surfaces of arbitraryshape are derived according to the geometrica...A surface edge element method is proposed and implemented in the study ofelectromagnetic scattering fields of general targets. The basis functions for surfaces of arbitraryshape are derived according to the geometrical properties of each triangular patch. The proposedbasis functions are 3-D linear functions and the tangential components of the vectors are continuousas the traditional edge element method. Combined field integral equations (CFIE) that include bothelectrical field and magnetic field integral equations are used to model the electromagneticscattering of general dielectric targets. Special treatment for singularity is presented to enhancethe quality of numerical solutions. The proposed method is used to compute the scattering fieldsfrom various targets. Numerical results obtained by the proposed method are validated by resultsfrom other numerical methods.展开更多
A new method,the stream surface strip element method,for simulating the three-dimensional deformation of plate and strip rolling process was proposed.The rolling deformation zone was divided into a number of stream su...A new method,the stream surface strip element method,for simulating the three-dimensional deformation of plate and strip rolling process was proposed.The rolling deformation zone was divided into a number of stream surface(curved surface)strip elements along metal flow traces,and the stream surface strip elements were mapped into the corresponding plane strip elements for analysis and computation.The longitudinal distributions of the lateral displacement and the altitudinal displacement of metal were respectively constructed to be a quartic curve and a quadratic curve,of which the lateral distributions were expressed as the third-power spline function,and the altitudinal distributions were fitted in the quadratic curve.From the flow theory of plastic mechanics,the mathematical models of the three-dimensional deformations and stresses of the deformation zone were constructed.Compared with the streamline strip element method proposed by the first author of this paper,the stream surface strip element method takes into account the uneven distributions of stresses and deformations along altitudinal direction,and realizes the precise three-dimensional analysis and computation.The simulation example of continuous hot rolled strip indicates that the method and the model accord with facts and provide a new reliable engineering-computation method for the three-dimensional mechanics simulation of plate and strip rolling process.展开更多
The computation model of shape and crown on 4-high CVC mill was established by combining the stream surface strip element method for analyzing three-dimensional plastic deformation of strip and the influence coefficie...The computation model of shape and crown on 4-high CVC mill was established by combining the stream surface strip element method for analyzing three-dimensional plastic deformation of strip and the influence coefficient method for elastic deformation of rolls, and the simulation of the shape and crown control on 4-high CVC hot strip mill was conducted. The simulated results indicate that the influence of the shifting of CVC work roll on shape and crown is very large, and the shifting of work roll can be used to preset shape and crown. The influence of the bending force of work roll on shape and crown is smaller, and it is suitable to use the bending force of work roll for shape and crown adjustment on line. With the increase of strip width, the exit crown of strip increases firstly and decreases then, and the roll gap becomes smoother increasingly. Meanwhile, the transverse difference of front tension stress decreases firstly and increases then.展开更多
In this article we define a surface finite element method （SFEM） for the numerical solution of parabolic partial differential equations on hypersurfaces F in R^n＋1. The key idea is based on the approximation of F b...In this article we define a surface finite element method （SFEM） for the numerical solution of parabolic partial differential equations on hypersurfaces F in R^n＋1. The key idea is based on the approximation of F by a polyhedral surface Гh consisting of a union of simplices （triangles for n = 2, intervals for n = 1） with vertices on Г. A finite element space of functions is then defined by taking the continuous functions on Гh which are linear affine on each simplex of the polygonal surface. We use surface gradients to define weak forms of elliptic operators and naturally generate weak formulations of elliptic and parabolic equations on Г. Our finite element method is applied to weak forms of the equations. The computation of the mass and element stiffness matrices are simple and straightforward. We give an example of error bounds in the case of semi-discretization in space for a fourth order linear problem. Numerical experiments are described for several linear and nonlinear partial differential equations. In particular the power of the method is demorrstrated by employing it to solve highly nonlinear second and fourth order problems such as surface Allen-Cahn and Cahn-Hilliard equations and surface level set equations for geodesic mean curvature flow.展开更多
The three-dimensional plastic deformations of strip are analyzed using the stream surface strip element method, the elastic deformations of rolls are analyzed using the influence coefficient method, the analyzing and ...The three-dimensional plastic deformations of strip are analyzed using the stream surface strip element method, the elastic deformations of rolls are analyzed using the influence coefficient method, the analyzing and computing model of shape and crown of 4-high mill was established by combining them, and the rolling process of 1660 mm hot strip continuous mills was simulated. The simulated results tally well with the experimental results. The modei and the method for simulation of shape analysis and control of hot strip mills were provided.展开更多
In this article a math model for sound propagation in industrial enclosures is discussed. The model can be applied to an industrial enelosure with any shape, any boundary condition and any obstacles in it. The origina...In this article a math model for sound propagation in industrial enclosures is discussed. The model can be applied to an industrial enelosure with any shape, any boundary condition and any obstacles in it. The original purpose of developing this model is only to predict the noise field in power plants, but the results of measurement of sound propagation in power plant workshops indicate that this model has high predication accuracy and can he adanted to various kinds of complicated industrial enclosures.展开更多
基金financially supported by the Program for New Century Excellent Talents in University(No.NCET-13-0229)the National Science&Technology Key Projects of Numerical Control(No.2012ZX04010-031,2012ZX0412-011)Natural Science Foundation of Hubei Province,China(2011CDB279)
文摘Deformation of casting during the solidification process has puzzled many engineers and scientists for years. In order to attain the goal of near-net forming by casting, numerical simulation is a powerful tool. Traditional methods compute the thermal stress of both the casting and the mold. This method suffers the problem of massive calculation and failure of convergence. This paper proposes an improved Mold Surface Element Method, the main idea of which is to use the surface elements instead of body elements to express the interactions between the casting and the mold. The proposed method shows a high computation efficiency and provides satisfactory precision for engineering. Two practical casting products were used to verify the proposed method. The simulated results agree well with those observed in practical products. The proposed method is believed to benefit production practice and to provide theoretical guidance.
文摘A program for calculating the aerodynamic properties of hypersonic vehicles based on the surface element method was developed using the general-purpose programming language C++. The calculated values of lift coefficients, drag coefficients, and surface pressure coefficients are discussed with the results of wind tunnel experiments using the HL-20 lift body and the NASA hypersonic aircraft STS Columbia OV-102 as research subjects. Finally, the results of the experimental and wind tunnel studies of the aerodynamic characteristics of the HL-20 lift body at an altitude of 65 km and Mach numbers of 6 and 10 Ma are discussed. The maximum error in the aerodynamic characteristics at 6 Ma does not exceed 3%, consistent with the results. The maximum error at 10 Ma occurs in the 11° - 14° angle of attack and does not exceed 10%, which is still within the error tolerance. The STS results for NASA’s hypersonic aircraft were also tested using this procedure. Experimental aerodynamic data for the Colombian OV-102 aircraft. The results show that the program takes only 10 minutes to calculate the results, with no more than 2% error from the wind tunnel experimental results.
文摘A surface edge element method is proposed and implemented in the study ofelectromagnetic scattering fields of general targets. The basis functions for surfaces of arbitraryshape are derived according to the geometrical properties of each triangular patch. The proposedbasis functions are 3-D linear functions and the tangential components of the vectors are continuousas the traditional edge element method. Combined field integral equations (CFIE) that include bothelectrical field and magnetic field integral equations are used to model the electromagneticscattering of general dielectric targets. Special treatment for singularity is presented to enhancethe quality of numerical solutions. The proposed method is used to compute the scattering fieldsfrom various targets. Numerical results obtained by the proposed method are validated by resultsfrom other numerical methods.
基金Sponsored by National Natural Science Foundation of China(50175095)Provincial Natural Science Foundation of Hebei of China(502173)
文摘A new method,the stream surface strip element method,for simulating the three-dimensional deformation of plate and strip rolling process was proposed.The rolling deformation zone was divided into a number of stream surface(curved surface)strip elements along metal flow traces,and the stream surface strip elements were mapped into the corresponding plane strip elements for analysis and computation.The longitudinal distributions of the lateral displacement and the altitudinal displacement of metal were respectively constructed to be a quartic curve and a quadratic curve,of which the lateral distributions were expressed as the third-power spline function,and the altitudinal distributions were fitted in the quadratic curve.From the flow theory of plastic mechanics,the mathematical models of the three-dimensional deformations and stresses of the deformation zone were constructed.Compared with the streamline strip element method proposed by the first author of this paper,the stream surface strip element method takes into account the uneven distributions of stresses and deformations along altitudinal direction,and realizes the precise three-dimensional analysis and computation.The simulation example of continuous hot rolled strip indicates that the method and the model accord with facts and provide a new reliable engineering-computation method for the three-dimensional mechanics simulation of plate and strip rolling process.
文摘The computation model of shape and crown on 4-high CVC mill was established by combining the stream surface strip element method for analyzing three-dimensional plastic deformation of strip and the influence coefficient method for elastic deformation of rolls, and the simulation of the shape and crown control on 4-high CVC hot strip mill was conducted. The simulated results indicate that the influence of the shifting of CVC work roll on shape and crown is very large, and the shifting of work roll can be used to preset shape and crown. The influence of the bending force of work roll on shape and crown is smaller, and it is suitable to use the bending force of work roll for shape and crown adjustment on line. With the increase of strip width, the exit crown of strip increases firstly and decreases then, and the roll gap becomes smoother increasingly. Meanwhile, the transverse difference of front tension stress decreases firstly and increases then.
文摘In this article we define a surface finite element method （SFEM） for the numerical solution of parabolic partial differential equations on hypersurfaces F in R^n＋1. The key idea is based on the approximation of F by a polyhedral surface Гh consisting of a union of simplices （triangles for n = 2, intervals for n = 1） with vertices on Г. A finite element space of functions is then defined by taking the continuous functions on Гh which are linear affine on each simplex of the polygonal surface. We use surface gradients to define weak forms of elliptic operators and naturally generate weak formulations of elliptic and parabolic equations on Г. Our finite element method is applied to weak forms of the equations. The computation of the mass and element stiffness matrices are simple and straightforward. We give an example of error bounds in the case of semi-discretization in space for a fourth order linear problem. Numerical experiments are described for several linear and nonlinear partial differential equations. In particular the power of the method is demorrstrated by employing it to solve highly nonlinear second and fourth order problems such as surface Allen-Cahn and Cahn-Hilliard equations and surface level set equations for geodesic mean curvature flow.
基金This work was supported by the National Natural Science Foundation of China,No.50175095(Theory system and mechanism model of shape control of high precision plate and strip mills) 50374058(Stream surface strip element method and its application in shape control of hot rolling plate and strip).
文摘The three-dimensional plastic deformations of strip are analyzed using the stream surface strip element method, the elastic deformations of rolls are analyzed using the influence coefficient method, the analyzing and computing model of shape and crown of 4-high mill was established by combining them, and the rolling process of 1660 mm hot strip continuous mills was simulated. The simulated results tally well with the experimental results. The modei and the method for simulation of shape analysis and control of hot strip mills were provided.
文摘In this article a math model for sound propagation in industrial enclosures is discussed. The model can be applied to an industrial enelosure with any shape, any boundary condition and any obstacles in it. The original purpose of developing this model is only to predict the noise field in power plants, but the results of measurement of sound propagation in power plant workshops indicate that this model has high predication accuracy and can he adanted to various kinds of complicated industrial enclosures.
