A set of basic deformation modes for hybrid stress finite elements are directly derived from the element displacement field. Subsequently, by employing the so-called united orthogonal conditions, a new orthogonalizati...A set of basic deformation modes for hybrid stress finite elements are directly derived from the element displacement field. Subsequently, by employing the so-called united orthogonal conditions, a new orthogonalization method is proposed. The result- ing orthogonal basic deformation modes exhibit simple and clear physical meanings. In addition, they do not involve any material parameters, and thus can be efficiently used to examine the element performance and serve as a unified tool to assess different hybrid elements. Thereafter, a convenient approach for the identification of spurious zero-energy modes is presented using the positive definiteness property of a flexibility matrix. More- over, based on the orthogonality relationship between the given initial stress modes and the orthogonal basic deformation modes, an alternative method of assumed stress modes to formulate a hybrid element free of spurious modes is discussed. It is found that the orthogonality of the basic deformation modes is the sufficient and necessary condition for the suppression of spurious zero-energy modes. Numerical examples of 2D 4-node quadrilateral elements and 3D 8-node hexahedral elements are illustrated in detail to demonstrate the efficiency of the proposed orthogonal basic deformation mode method.展开更多
A method for beam diffraction sidelobe suppression based on the combination of volume Bragg gratings（VBGs）with different thicknesses or periods for angular filtering is proposed and performed. Simulated and experime...A method for beam diffraction sidelobe suppression based on the combination of volume Bragg gratings（VBGs）with different thicknesses or periods for angular filtering is proposed and performed. Simulated and experimental results show that the beam diffraction sidelobe is reduced from 12% to less than 1% with the non-sidelobe angular filter. The non-sidelobe angular filtering based on VBGs with thicknesses of 2.5 and 2.9 mm is simulated and demonstrated. The near-field distribution of filtered beams through the non-sidelobe angular filter is obviously smoother than that of the single VBG. The near-field modulation and contrast ratio（C） of filtered beams are found to be improved 1.17 and 1.66 times that of the single VBG. The far-field C of the filtered beam is improved to about 100∶1 and the power spectral density analysis shows that the cutoff frequency of the angular filter is greatly optimized with the VBG combination.展开更多
基金Project supported by the National Natural Science Foundation of China(No.10972188)the Fundamental Research Funds for the Central Universities of China(No.2010121073)the Scientific Program of Fujian Province of China(No.2007F3096)
文摘A set of basic deformation modes for hybrid stress finite elements are directly derived from the element displacement field. Subsequently, by employing the so-called united orthogonal conditions, a new orthogonalization method is proposed. The result- ing orthogonal basic deformation modes exhibit simple and clear physical meanings. In addition, they do not involve any material parameters, and thus can be efficiently used to examine the element performance and serve as a unified tool to assess different hybrid elements. Thereafter, a convenient approach for the identification of spurious zero-energy modes is presented using the positive definiteness property of a flexibility matrix. More- over, based on the orthogonality relationship between the given initial stress modes and the orthogonal basic deformation modes, an alternative method of assumed stress modes to formulate a hybrid element free of spurious modes is discussed. It is found that the orthogonality of the basic deformation modes is the sufficient and necessary condition for the suppression of spurious zero-energy modes. Numerical examples of 2D 4-node quadrilateral elements and 3D 8-node hexahedral elements are illustrated in detail to demonstrate the efficiency of the proposed orthogonal basic deformation mode method.
基金supported by the National Natural Science Foundation of China(Nos.61275140,61370182,and11504255)the Natural Science Foundation of JiangsuProvince(No.DK20141232)+1 种基金a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the National“863”Program of China
文摘A method for beam diffraction sidelobe suppression based on the combination of volume Bragg gratings（VBGs）with different thicknesses or periods for angular filtering is proposed and performed. Simulated and experimental results show that the beam diffraction sidelobe is reduced from 12% to less than 1% with the non-sidelobe angular filter. The non-sidelobe angular filtering based on VBGs with thicknesses of 2.5 and 2.9 mm is simulated and demonstrated. The near-field distribution of filtered beams through the non-sidelobe angular filter is obviously smoother than that of the single VBG. The near-field modulation and contrast ratio（C） of filtered beams are found to be improved 1.17 and 1.66 times that of the single VBG. The far-field C of the filtered beam is improved to about 100∶1 and the power spectral density analysis shows that the cutoff frequency of the angular filter is greatly optimized with the VBG combination.
