A new approach to modifying the stiffness and mass matrices of finite element models is presented to improve the calculation precision.By measuring the mode frequencies and shapes of both of the original and the new s...A new approach to modifying the stiffness and mass matrices of finite element models is presented to improve the calculation precision.By measuring the mode frequencies and shapes of both of the original and the new structures with changed stiffness and mass,the stiffness and mass matrices of the finite element model can be updated through matrices calculation and solving algebra equations.Taking a multi-freedom model as an example,the relation between the number of the modes and the correction precision of stiffness and mass matrix elements is researched.The facility and precision of the method are totally confirmed especially when the modeling error is known limited to a definite local range.The feasibility of the approach is proven by an effective engineering application to the model updating of a wing piece used in flutter test.展开更多
The milling-head machine tool is a sophisticated and high-quality machine tool of which the spindle system is made up of special multi-element structure. Two special mechanical configurations make the cutting performa...The milling-head machine tool is a sophisticated and high-quality machine tool of which the spindle system is made up of special multi-element structure. Two special mechanical configurations make the cutting performance of the machine tool decline. One is the milling head spindle supported on two sets of complex bearings. The mechanical dynamic rigidity of milling head structure is researched on designed digital prototype with finite element analysis（FEA） and modal synthesis analysis （ MSA ） for identifying the weak structures. The other is the ram structure hanging on milling head. The structure is researched to get dynamic performance on cutting at different ram extending positions. The analysis results on spindle and ram are used to improve the mechanical configurations and structure in design. The machine tool is built up with modified structure and gets better dynamic rigidity than it was before.展开更多
In order to improve the dynamic stability of precision instruments during the design process, a compositive design method based on modal analysis of structure is proposed. With uniform boundary conditions and material...In order to improve the dynamic stability of precision instruments during the design process, a compositive design method based on modal analysis of structure is proposed. With uniform boundary conditions and material characters, the results of Finite Element Analysis (FEA) vary with models. It should be checked whether the model is correctly simplified. Modal experiments can be used for such purpose. The method combines the high efficiency and agility of FEA with the reliability and accuracy of experiments, and avoids the drawbacks of FEA or experiments, such as uncertainty of FEA and high cost of experiments. Taking rotor frame structure as an example, this method is applied as follows: First the modal characters of structure are analyzed with FEA, and then the natural frequencies of the structure are tested by experiments to check the reliability of FEA method, and finally the design scheme is optimized by modifying structure parameters with confirmed FEA.展开更多
To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the gird...To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the girder with double ribs. Based on the simplified model four stiffness formulae were deduced according to Hamilton principle. These formulae reflect well the contribution of the flexural, shearing, free torsion and restricted torsion deformation, respectively. An identification method about modal parameters was put forward by combining method of peak value and power spectral density according to modal test under ambient excitation. The dynamic finite element method analysis and modal test were carried out in a long-span concrete cable-stayed bridge. The results show that the errors of frequencies between theoretical analysis and test results are less than 10% mostly, and the most important modal parameters for cable-stayed bridge are determined to be the longitudinal floating mode, the first vertical flexural mode and the first torsional mode, which demonstrate that the method of stiffness distribution for three beams model is accurate and method to identify modal parameters is effective under ambient excitation modal test.展开更多
Region partition(RP) is the key technique to the finite element parallel computing(FEPC),and its performance has a decisive influence on the entire process of analysis and computation.The performance evaluation index ...Region partition(RP) is the key technique to the finite element parallel computing(FEPC),and its performance has a decisive influence on the entire process of analysis and computation.The performance evaluation index of RP method for the three-dimensional finite element model(FEM) has been given.By taking the electric field of aluminum reduction cell(ARC) as the research object,the performance of two classical RP methods,which are Al-NASRA and NGUYEN partition(ANP) algorithm and the multi-level partition(MLP) method,has been analyzed and compared.The comparison results indicate a sound performance of ANP algorithm,but to large-scale models,the computing time of ANP algorithm increases notably.This is because the ANP algorithm determines only one node based on the minimum weight and just adds the elements connected to the node into the sub-region during each iteration.To obtain the satisfied speed and the precision,an improved dynamic self-adaptive ANP(DSA-ANP) algorithm has been proposed.With consideration of model scale,complexity and sub-RP stage,the improved algorithm adaptively determines the number of nodes and selects those nodes with small enough weight,and then dynamically adds these connected elements.The proposed algorithm has been applied to the finite element analysis(FEA) of the electric field simulation of ARC.Compared with the traditional ANP algorithm,the computational efficiency of the proposed algorithm has been shortened approximately from 260 s to 13 s.This proves the superiority of the improved algorithm on computing time performance.展开更多
In recent years, inflatable structures have been a subject of interest for space applications such as communication antenna, solar thermal propulsion and entry/landing systems. The inflatable structures characterized ...In recent years, inflatable structures have been a subject of interest for space applications such as communication antenna, solar thermal propulsion and entry/landing systems. The inflatable structures characterized by high strength-to-mass ratios, minimal stowage volume, which makes them suitable for cost-effective large space structures. A typical example for the inflatable structure is the inflated torus which often used in order to provide structure support. In this study, our main focus is to understand the dynamic characteristics of an inflated torus in order to formulate an accurate mathematical model suitable for active vibration control applications. A commercial finite element package, ANSYS, is used to model the inflated torus. To verify the model the obtained frequencies and mode shapes are compared with the published results, which are derived using analytical approach, the verification shows a good agreement between the FEM and the analytical results. Based on the verified model, parametric study was investigated; the material thickness increase causes the natural frequencies decrease, while the increase of the inflation pressure simply results in stiffening the ring, which means that the natural frequency increased. The FEM analysis gives an easy and fast way for the vibration analysis of the structures compared with the complicated analytical solutions.展开更多
基于模态重分析技术,提出一种适合全局有限元模型(global finite element model, GFEM)的突风动响应高效计算方法。针对模型局部结构质量或刚度的细微变化,进行增量建模,充分利用现有构型结果,避免了传统分析中重复计算的步骤。对于质...基于模态重分析技术,提出一种适合全局有限元模型(global finite element model, GFEM)的突风动响应高效计算方法。针对模型局部结构质量或刚度的细微变化,进行增量建模,充分利用现有构型结果,避免了传统分析中重复计算的步骤。对于质量阵的变化,以已有构型模态向量为初始向量,通过迭代分析进行特征值求解,针对刚度阵的微小变化,特别引入Sherman-Morrison-Woodbury公式,实现刚度逆矩阵的增量分析,从而克服了大规模GFEM模型的特征值求解效率低的问题,最终建立了一套适合于工程应用的GFEM突风高效动响应分析方法。采用GTA模型进行了突风分析算法的验证,在此基础上,基于某模型机翼,对模态重分析算法在突风动响应分析中的应用进行了研究。结果表明,通过LU分解可避免保存稠密形式的刚度逆矩阵,通过合理的松弛因子和收敛阈值,可有效提升计算效率。展开更多
基金Supported by the National High Technology Research and Development Program of China(″863″Program)(2008AA12A205)the Aeronautical Science Foundation of China(2012ZA52001)
文摘A new approach to modifying the stiffness and mass matrices of finite element models is presented to improve the calculation precision.By measuring the mode frequencies and shapes of both of the original and the new structures with changed stiffness and mass,the stiffness and mass matrices of the finite element model can be updated through matrices calculation and solving algebra equations.Taking a multi-freedom model as an example,the relation between the number of the modes and the correction precision of stiffness and mass matrix elements is researched.The facility and precision of the method are totally confirmed especially when the modeling error is known limited to a definite local range.The feasibility of the approach is proven by an effective engineering application to the model updating of a wing piece used in flutter test.
基金supported by Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality,China.
文摘The milling-head machine tool is a sophisticated and high-quality machine tool of which the spindle system is made up of special multi-element structure. Two special mechanical configurations make the cutting performance of the machine tool decline. One is the milling head spindle supported on two sets of complex bearings. The mechanical dynamic rigidity of milling head structure is researched on designed digital prototype with finite element analysis（FEA） and modal synthesis analysis （ MSA ） for identifying the weak structures. The other is the ram structure hanging on milling head. The structure is researched to get dynamic performance on cutting at different ram extending positions. The analysis results on spindle and ram are used to improve the mechanical configurations and structure in design. The machine tool is built up with modified structure and gets better dynamic rigidity than it was before.
文摘In order to improve the dynamic stability of precision instruments during the design process, a compositive design method based on modal analysis of structure is proposed. With uniform boundary conditions and material characters, the results of Finite Element Analysis (FEA) vary with models. It should be checked whether the model is correctly simplified. Modal experiments can be used for such purpose. The method combines the high efficiency and agility of FEA with the reliability and accuracy of experiments, and avoids the drawbacks of FEA or experiments, such as uncertainty of FEA and high cost of experiments. Taking rotor frame structure as an example, this method is applied as follows: First the modal characters of structure are analyzed with FEA, and then the natural frequencies of the structure are tested by experiments to check the reliability of FEA method, and finally the design scheme is optimized by modifying structure parameters with confirmed FEA.
基金Project(50608008) supported by the National Natural Science Foundation of Chinaproject(20050536002) supported by the Specialized Research Fund for the Doctoral Program of Higher Education
文摘To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the girder with double ribs. Based on the simplified model four stiffness formulae were deduced according to Hamilton principle. These formulae reflect well the contribution of the flexural, shearing, free torsion and restricted torsion deformation, respectively. An identification method about modal parameters was put forward by combining method of peak value and power spectral density according to modal test under ambient excitation. The dynamic finite element method analysis and modal test were carried out in a long-span concrete cable-stayed bridge. The results show that the errors of frequencies between theoretical analysis and test results are less than 10% mostly, and the most important modal parameters for cable-stayed bridge are determined to be the longitudinal floating mode, the first vertical flexural mode and the first torsional mode, which demonstrate that the method of stiffness distribution for three beams model is accurate and method to identify modal parameters is effective under ambient excitation modal test.
基金Project(61273187)supported by the National Natural Science Foundation of ChinaProject(61321003)supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China
文摘Region partition(RP) is the key technique to the finite element parallel computing(FEPC),and its performance has a decisive influence on the entire process of analysis and computation.The performance evaluation index of RP method for the three-dimensional finite element model(FEM) has been given.By taking the electric field of aluminum reduction cell(ARC) as the research object,the performance of two classical RP methods,which are Al-NASRA and NGUYEN partition(ANP) algorithm and the multi-level partition(MLP) method,has been analyzed and compared.The comparison results indicate a sound performance of ANP algorithm,but to large-scale models,the computing time of ANP algorithm increases notably.This is because the ANP algorithm determines only one node based on the minimum weight and just adds the elements connected to the node into the sub-region during each iteration.To obtain the satisfied speed and the precision,an improved dynamic self-adaptive ANP(DSA-ANP) algorithm has been proposed.With consideration of model scale,complexity and sub-RP stage,the improved algorithm adaptively determines the number of nodes and selects those nodes with small enough weight,and then dynamically adds these connected elements.The proposed algorithm has been applied to the finite element analysis(FEA) of the electric field simulation of ARC.Compared with the traditional ANP algorithm,the computational efficiency of the proposed algorithm has been shortened approximately from 260 s to 13 s.This proves the superiority of the improved algorithm on computing time performance.
文摘In recent years, inflatable structures have been a subject of interest for space applications such as communication antenna, solar thermal propulsion and entry/landing systems. The inflatable structures characterized by high strength-to-mass ratios, minimal stowage volume, which makes them suitable for cost-effective large space structures. A typical example for the inflatable structure is the inflated torus which often used in order to provide structure support. In this study, our main focus is to understand the dynamic characteristics of an inflated torus in order to formulate an accurate mathematical model suitable for active vibration control applications. A commercial finite element package, ANSYS, is used to model the inflated torus. To verify the model the obtained frequencies and mode shapes are compared with the published results, which are derived using analytical approach, the verification shows a good agreement between the FEM and the analytical results. Based on the verified model, parametric study was investigated; the material thickness increase causes the natural frequencies decrease, while the increase of the inflation pressure simply results in stiffening the ring, which means that the natural frequency increased. The FEM analysis gives an easy and fast way for the vibration analysis of the structures compared with the complicated analytical solutions.
文摘基于模态重分析技术,提出一种适合全局有限元模型(global finite element model, GFEM)的突风动响应高效计算方法。针对模型局部结构质量或刚度的细微变化,进行增量建模,充分利用现有构型结果,避免了传统分析中重复计算的步骤。对于质量阵的变化,以已有构型模态向量为初始向量,通过迭代分析进行特征值求解,针对刚度阵的微小变化,特别引入Sherman-Morrison-Woodbury公式,实现刚度逆矩阵的增量分析,从而克服了大规模GFEM模型的特征值求解效率低的问题,最终建立了一套适合于工程应用的GFEM突风高效动响应分析方法。采用GTA模型进行了突风分析算法的验证,在此基础上,基于某模型机翼,对模态重分析算法在突风动响应分析中的应用进行了研究。结果表明,通过LU分解可避免保存稠密形式的刚度逆矩阵,通过合理的松弛因子和收敛阈值,可有效提升计算效率。
