Typical representation of dimension and geometric accuracy is limited to the self-representation of dimension and geometric deviation based on geometry variation thinking, yet the interactivity affection of geometric ...Typical representation of dimension and geometric accuracy is limited to the self-representation of dimension and geometric deviation based on geometry variation thinking, yet the interactivity affection of geometric variation and gesture variation of multi-rigid body is not included. In this paper, a kinematic matrix model based on Lagrangian coordinate is introduced, with the purpose of unified model for geometric variation and gesture variation and their interactive and integrated analysis. Kinematic model with joint, local base and movable base is built. The ideal feature of functional geometry is treated as the base body; the fitting feature of functional geometry is treated as the adjacent movable body; the local base of the kinematic model is fixed onto the ideal geometry, and the movable base of the kinematic model is fixed onto the fitting geometry. Furthermore, the geometric deviation is treated as relative location or rotation variation between the movable base and the local base, and it＇s expressed by the Lagrangian coordinate. Moreover, kinematic matrix based on Lagrangian coordinate for different types of geometry tolerance zones is constructed, and total freedom for each kinematic model is discussed. Finally, the Lagrangian coordinate library, kinematic matrix library for geometric deviation modeling is illustrated, and an example of block and piston fits is introduced. Dimension and geometric tolerances of the shaft and hole fitting feature are constructed by kinematic matrix and Lagrangian coordinate, and the results indicate that the proposed kinematic matrix is capable and robust in dimension and geometric tolerances modeling.展开更多
Element stiffness equation is very important in structural analysis, and directly influences the accuracy of the results. At present, derivation method of element stiffness equation is relatively mature under ambient ...Element stiffness equation is very important in structural analysis, and directly influences the accuracy of the results. At present, derivation method of element stiffness equation is relatively mature under ambient temperature, and the elastic phrase of material stress-strain curve is generally adopted as physical equation in derivation. However, the material stress-strain relationship is very complicated at elevated temperature, and its form is not unique, which brings great difficulty to the derivation of element stiffness equation. Referring to the derivation method of element stiffness equation at ambient temperature, by using the continuous function of stress-strain-temperature at elevated temperature, and based on the principle of virtual work, the stiffness equation of space beam element and the formulas of stiffness matrix are derived in this paper, which provide basis for finite element analysis on structures at elevated temperature.展开更多
The concept of virtual manufacturing and measuring cell (VMMC) is proposed, the systematic architecture of the VMMC is established and two key problems: the error fusion in machining and the reconstructable modeling o...The concept of virtual manufacturing and measuring cell (VMMC) is proposed, the systematic architecture of the VMMC is established and two key problems: the error fusion in machining and the reconstructable modeling of workpiece during virtual manufacturing and measuring, are discussed. An actual VMMC is presented as an example and its modularized frame is introduced.展开更多
The standard formula for geometric stiffness matrix calculation, which is convenient for most engineering applications, is seen to be unsatisfactory for large strains because of poor accuracy, low convergence rate, an...The standard formula for geometric stiffness matrix calculation, which is convenient for most engineering applications, is seen to be unsatisfactory for large strains because of poor accuracy, low convergence rate, and stability. For very large compressions, the tangent stiffness in the direction of the compression can even become negative, which can be regarded as physical nonsense. So in many cases rubber materials exposed to great compression cannot be analyzed, or the analysis could lead to very poor convergence. Problems with the standard geometric stiffness matrix can even occur with a small strain in the case of plastic yielding, which eventuates even greater practical problems. The authors demonstrate that amore precisional approach would not lead to such strange and theoretically unjustified results. An improved formula that would eliminate the disadvantages mentioned above and leads to higher convergence rate and more robust computations is suggested in this paper. The new formula can be derived from the principle of virtual work using a modified Green-Lagrange strain tensor, or from equilibrium conditions where in the choice of a specific strain measure is not needed for the geometric stiffness derivation (which can also be used for derivation of geometric stiffness of a rigid truss member). The new formula has been verified in practice with many calculations and implemented in the RFEM and SCIA Engineer programs. The advantages of the new formula in comparison with the standard formula are shown using several examples.展开更多
针对传统平行线阵的二维波达方向(direction of arrival,DOA)估计算法阵列自由度受限且计算复杂度较高的问题,提出了一种双平行扩展互质阵列下的二维DOA估计算法。首先采用平行扩展互质线阵,利用阵元间距的差集构造虚拟平行均匀线阵,计...针对传统平行线阵的二维波达方向(direction of arrival,DOA)估计算法阵列自由度受限且计算复杂度较高的问题,提出了一种双平行扩展互质阵列下的二维DOA估计算法。首先采用平行扩展互质线阵,利用阵元间距的差集构造虚拟平行均匀线阵,计算该虚拟阵列的自协方差矩阵和互协方差矩阵,并构造Toeplitz矩阵;然后构造增广矩阵,并结合旋转不变技术的信号参数估计(estimation of signal parameters via rotational invariance technique,ESPRIT)算法,将二维DOA估计转化为两个一维DOA估计问题,获得唯一且自动配对的二维DOA估计参数。仿真实验结果表明,所提算法较传统算法具有更好的DOA估计性能和更低的计算复杂度。展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51305140,61203060)Fundamental Research Funds of the Central Universities of China(Grant No.D2132730)Guangdong Provincial Science and Technology Planning Project of China(Grant No.2013B010402011)
文摘Typical representation of dimension and geometric accuracy is limited to the self-representation of dimension and geometric deviation based on geometry variation thinking, yet the interactivity affection of geometric variation and gesture variation of multi-rigid body is not included. In this paper, a kinematic matrix model based on Lagrangian coordinate is introduced, with the purpose of unified model for geometric variation and gesture variation and their interactive and integrated analysis. Kinematic model with joint, local base and movable base is built. The ideal feature of functional geometry is treated as the base body; the fitting feature of functional geometry is treated as the adjacent movable body; the local base of the kinematic model is fixed onto the ideal geometry, and the movable base of the kinematic model is fixed onto the fitting geometry. Furthermore, the geometric deviation is treated as relative location or rotation variation between the movable base and the local base, and it＇s expressed by the Lagrangian coordinate. Moreover, kinematic matrix based on Lagrangian coordinate for different types of geometry tolerance zones is constructed, and total freedom for each kinematic model is discussed. Finally, the Lagrangian coordinate library, kinematic matrix library for geometric deviation modeling is illustrated, and an example of block and piston fits is introduced. Dimension and geometric tolerances of the shaft and hole fitting feature are constructed by kinematic matrix and Lagrangian coordinate, and the results indicate that the proposed kinematic matrix is capable and robust in dimension and geometric tolerances modeling.
基金the National Natural Science Foundation of China(No.50578093)
文摘Element stiffness equation is very important in structural analysis, and directly influences the accuracy of the results. At present, derivation method of element stiffness equation is relatively mature under ambient temperature, and the elastic phrase of material stress-strain curve is generally adopted as physical equation in derivation. However, the material stress-strain relationship is very complicated at elevated temperature, and its form is not unique, which brings great difficulty to the derivation of element stiffness equation. Referring to the derivation method of element stiffness equation at ambient temperature, by using the continuous function of stress-strain-temperature at elevated temperature, and based on the principle of virtual work, the stiffness equation of space beam element and the formulas of stiffness matrix are derived in this paper, which provide basis for finite element analysis on structures at elevated temperature.
文摘The concept of virtual manufacturing and measuring cell (VMMC) is proposed, the systematic architecture of the VMMC is established and two key problems: the error fusion in machining and the reconstructable modeling of workpiece during virtual manufacturing and measuring, are discussed. An actual VMMC is presented as an example and its modularized frame is introduced.
文摘The standard formula for geometric stiffness matrix calculation, which is convenient for most engineering applications, is seen to be unsatisfactory for large strains because of poor accuracy, low convergence rate, and stability. For very large compressions, the tangent stiffness in the direction of the compression can even become negative, which can be regarded as physical nonsense. So in many cases rubber materials exposed to great compression cannot be analyzed, or the analysis could lead to very poor convergence. Problems with the standard geometric stiffness matrix can even occur with a small strain in the case of plastic yielding, which eventuates even greater practical problems. The authors demonstrate that amore precisional approach would not lead to such strange and theoretically unjustified results. An improved formula that would eliminate the disadvantages mentioned above and leads to higher convergence rate and more robust computations is suggested in this paper. The new formula can be derived from the principle of virtual work using a modified Green-Lagrange strain tensor, or from equilibrium conditions where in the choice of a specific strain measure is not needed for the geometric stiffness derivation (which can also be used for derivation of geometric stiffness of a rigid truss member). The new formula has been verified in practice with many calculations and implemented in the RFEM and SCIA Engineer programs. The advantages of the new formula in comparison with the standard formula are shown using several examples.
文摘针对传统平行线阵的二维波达方向(direction of arrival,DOA)估计算法阵列自由度受限且计算复杂度较高的问题,提出了一种双平行扩展互质阵列下的二维DOA估计算法。首先采用平行扩展互质线阵,利用阵元间距的差集构造虚拟平行均匀线阵,计算该虚拟阵列的自协方差矩阵和互协方差矩阵,并构造Toeplitz矩阵;然后构造增广矩阵,并结合旋转不变技术的信号参数估计(estimation of signal parameters via rotational invariance technique,ESPRIT)算法,将二维DOA估计转化为两个一维DOA估计问题,获得唯一且自动配对的二维DOA估计参数。仿真实验结果表明,所提算法较传统算法具有更好的DOA估计性能和更低的计算复杂度。
