Numerical simulations of unsteady flow problems with moving boundaries commonly require the use of geometric conservation law(GCL).However,in cases of unidirectional large mesh deformation,the cumulative error caused ...Numerical simulations of unsteady flow problems with moving boundaries commonly require the use of geometric conservation law(GCL).However,in cases of unidirectional large mesh deformation,the cumulative error caused by the discrete procedure in GCL can significantly increase,and a direct consequence is that the calculated cell volume may become negative.To control the cumulative error,a new discrete GCL(D-GCL)is proposed.Unlike the original D-GCL,the proposed method uses the control volume analytically evaluated according to the grid motion at the time level n,instead of using the calculated value from the D-GCL itself.Error analysis indicates that the truncation error of the numerical scheme is guaranteed to be the same order as that obtained from the original D-GCL,while the accumulated error is greatly reduced.For validation,two challenging large deformation cases including a rotating circular cylinder case and a descending GAW-(1)two-element airfoil case are selected to be investigated.Good agreements are found between the calculated results and some other literature data,demonstrating the feasibility of the proposed D-GCL for unidirectional motions with large displacements.展开更多
Motion compensation is a key step of inverse synthetic aperture radar (ISAR) imaging. In this paper, the average absolute error measure (AAEM) is proposed for BAR translational motion compensation. Based on the AAEM,...Motion compensation is a key step of inverse synthetic aperture radar (ISAR) imaging. In this paper, the average absolute error measure (AAEM) is proposed for BAR translational motion compensation. Based on the AAEM, a technique for improving stepped-frequency IS AR imagery is presented. Image improvement is achieved in the frequency domain where the echo phase can be adjusted to compensate for translational motion. With help o f a search algorithm, the garget' s motion parameters which reduce AAEM to a minimum are determined. The signer-Vile distribution is used to find the initial values for a search algorithm. Based on AAEM, one can efficiently focus the image of the target. In the simulation, the target is assumed to fly in straight path and is illuminated by an X-band ground-based stationary stepped-frequency ISAR. The resulted image from simulation radal data is obtained. comparing the resulted image with that of the typical compensation method, the effectiveness of the proposed AAEM is verified.展开更多
Through the analysis of roundness error separation technique of three-point method and based on the invariability and periodicity of the geometrical characteristic of measured round contour, a new matrix algorithm, wh...Through the analysis of roundness error separation technique of three-point method and based on the invariability and periodicity of the geometrical characteristic of measured round contour, a new matrix algorithm, which can be used to solve directly the roundness of the measured round contour without Fourier transform, is presented. On the basis of the research and analysis of the rotation error movement which is separated by using the three-point method, a mathematical equation is derived, which can be used to separate the eccentric motion of least square center of measured round contour and the pure rotation motion error of spindle in rotation motion. The correctness of this method is validated by means of simulation.展开更多
基金supported by the National Basic Research Program of China(″973″Project)(No.2014CB046200)
文摘Numerical simulations of unsteady flow problems with moving boundaries commonly require the use of geometric conservation law(GCL).However,in cases of unidirectional large mesh deformation,the cumulative error caused by the discrete procedure in GCL can significantly increase,and a direct consequence is that the calculated cell volume may become negative.To control the cumulative error,a new discrete GCL(D-GCL)is proposed.Unlike the original D-GCL,the proposed method uses the control volume analytically evaluated according to the grid motion at the time level n,instead of using the calculated value from the D-GCL itself.Error analysis indicates that the truncation error of the numerical scheme is guaranteed to be the same order as that obtained from the original D-GCL,while the accumulated error is greatly reduced.For validation,two challenging large deformation cases including a rotating circular cylinder case and a descending GAW-(1)two-element airfoil case are selected to be investigated.Good agreements are found between the calculated results and some other literature data,demonstrating the feasibility of the proposed D-GCL for unidirectional motions with large displacements.
文摘Motion compensation is a key step of inverse synthetic aperture radar (ISAR) imaging. In this paper, the average absolute error measure (AAEM) is proposed for BAR translational motion compensation. Based on the AAEM, a technique for improving stepped-frequency IS AR imagery is presented. Image improvement is achieved in the frequency domain where the echo phase can be adjusted to compensate for translational motion. With help o f a search algorithm, the garget' s motion parameters which reduce AAEM to a minimum are determined. The signer-Vile distribution is used to find the initial values for a search algorithm. Based on AAEM, one can efficiently focus the image of the target. In the simulation, the target is assumed to fly in straight path and is illuminated by an X-band ground-based stationary stepped-frequency ISAR. The resulted image from simulation radal data is obtained. comparing the resulted image with that of the typical compensation method, the effectiveness of the proposed AAEM is verified.
基金Henan Innovation Project for University Prominent Research Talents (2004KYCX006)Ph.D.Inital Foundation of Henan University of Science &Techonologythe Natural Science Foundation of Henan Education Agency (2008A460007)
文摘Through the analysis of roundness error separation technique of three-point method and based on the invariability and periodicity of the geometrical characteristic of measured round contour, a new matrix algorithm, which can be used to solve directly the roundness of the measured round contour without Fourier transform, is presented. On the basis of the research and analysis of the rotation error movement which is separated by using the three-point method, a mathematical equation is derived, which can be used to separate the eccentric motion of least square center of measured round contour and the pure rotation motion error of spindle in rotation motion. The correctness of this method is validated by means of simulation.
