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971.
972.
关于高强螺栓摩擦型连接和承压型连接区别的探讨 总被引:1,自引:0,他引:1
从高强螺栓摩擦型连接和承压型连接的极限状态着手,通过对两种连接的计算方法和使用及构造要求的具体分析,全面探讨了高强螺栓两种连接的区别,为工程中高强螺栓的设计和使用提供参考。 相似文献
973.
通过阐述黄柏峪铜钼矿床的地质特征及地球化学特征,来探讨其成矿地质条件,认为该区不仅存在矽卡岩型矿床,而且也有斑岩型及热液型矿床存在的可能。 相似文献
974.
Analysis of a Gyroscope's Rotor Nonlinear Supported Magnetic Field Based on the B-Spline Wavelet-FEM
LIU Jian-feng YUAN Gan-nan HUANG Xu YU Li 《国际设备工程与管理》2005,10(3):152-159
A supported framework of a gyroscope's rotor is designed and the B-Spline wavelet finite element model of nonlinear supported magnetic field is worked out. A new finite element space is studied in which the scaling function of the B-spline wavelet is considered as the shape function of a tetrahedton. The magnetic field is spited by an artificial absorbing body which used the condition of field radiating, so the solution is unique. The resolution is improved via the varying gradient of the B-spline function under the condition of unchanging gridding. So there are some advantages in dealing with the focus flux and a high varying gradient result from a nonlinear magnetic field. The result is more practical. Plots of flux and in the space is studied via simulating the supported system model. The results of the study are useful in the research of the supported magnetic system for the gyroscope rotor. 相似文献
975.
To identify material parameters from suitable experiments it is prevalent to use global informations like force–displacement or force–necking curves. The quality of accordance between measured and calculated forces at given displacements can be expressed by a least-squares functional. In this contribution a non-linear optimization method will be presented, which minimizes the least-squares functional by use of a gradient based method. The gradient of this functional is calculated in a semi-analytical sensitivity analysis. To determine the derivatives of the force with respect to the material parameters, the local sensitivities on an intersection will be added together. On this intersection, the total nodal force and the external force have to be equal and the normal displacements have to be independent on the material parameters. The parameter identification is embedded in the finite element code SPC-PMHP for solving non-linear boundary and initial value problems on parallel computers. The Gurson–Tvergaard–Needleman model is used to describe the plastic deformation and damage behaviour of the ductile structural steel StE 690. The developed algorithm is applied to tensile tests with notched cylindrical bars. 相似文献
976.
977.
S. Gerlach A. Matzenmiller 《International journal for numerical methods in engineering》2005,63(3):428-454
Viscoelastic line spectra are identified from creep or relaxation data of static experiments with different numerical methods, which may or may not depend on additional informations, to be provided by the user, about the unknown parameters. If the least square method is applied, a non‐linear optimization problem with non‐negative constraints on the parameters has to be solved. Its solution can be achieved directly by using a gradient‐based optimization algorithm like the projected Newton method of Bertsekas. However, appropriate starting values for the unknown parameters must be chosen. The problem can be alleviated by dividing the identification task into three successive steps, based on the Tschebyscheff approximation and the quadratic optimization method by Wolfe. Alternatively, the identification task can be reduced to a quadratic optimization problem, if the user provides additional informations about the distribution of the respondance times of the spectra. The windowing‐method of Emri and Tschoegl is based on this assumption. If the line spectrum is assumed to have equally distributed spectrum lines on the logarithmic axis, the identification problem can also be solved by standard regularization techniques, like the truncated singular value decomposition or the Tikhonov regularization. The choice of qualified respondance times as additional information requires some experience with the identification task at hand. Its results may be improved after several reruns of the algorithms. Various applications of the methods to test and experimental data are given and a comparison of their performance is discussed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
978.
Vince J. van Joolen Beny Neta Dan Givoli 《International journal for numerical methods in engineering》2005,63(7):1041-1068
Recently developed non‐reflecting boundary conditions are applied for exterior time‐dependent wave problems in unbounded domains. The linear time‐dependent wave equation, with or without a dispersive term, is considered in an infinite domain. The infinite domain is truncated via an artificial boundary ??, and a high‐order non‐reflecting boundary condition (NRBC) is imposed on ??. Then the problem is solved numerically in the finite domain bounded by ??. The new boundary scheme is based on a reformulation of the sequence of NRBCs proposed by Higdon. We consider here two reformulations: one that involves high‐order derivatives with a special discretization scheme, and another that does not involve any high derivatives beyond second order. The latter formulation is made possible by introducing special auxiliary variables on ??. In both formulations the new NRBCs can easily be used up to any desired order. They can be incorporated in a finite element or a finite difference scheme; in the present paper the latter is used. In contrast to previous papers using similar formulations, here the method is applied to a fully exterior two‐dimensional problem, with a rectangular boundary. Numerical examples in infinite domains are used to demonstrate the performance and advantages of the new method. In the auxiliary‐variable formulation long‐time corner instability is observed, that requires special treatment of the corners (not addressed in this paper). No such difficulties arise in the high‐derivative formulation. Published in 2005 by John Wiley & Sons, Ltd. 相似文献
979.
980.
山羊绒与相似毛绒类纤维鉴别方法的比较 总被引:6,自引:0,他引:6
从山羊绒纤维和相似毛绒类纤维的鳞片结构特性出发。分析了山羊绒与改性羊毛、80支细羊毛、拉细羊毛、兔毛纤维的结构特征。对目前使用的几种鉴别方法比较分析,认为计算机图像法是能全面将毛绒类纤维的鳞片结构特征参数反映出来的一种方法。 相似文献