This paper discusses the modal features of weakly-viscoelastic material structures both for single-modulus and multi-modulus materials. It is the eigenvalues of these structures that are the roots of a series of ratio...This paper discusses the modal features of weakly-viscoelastic material structures both for single-modulus and multi-modulus materials. It is the eigenvalues of these structures that are the roots of a series of rational fraction polynomial equations. A theorem about the roots of these equations is proved in the paper. Based on it, some important conclusions about the modal features of the weakly viscoelastic material structures are given according to their dynamic behaviors.展开更多
In order to acquire the dynamic characteristics of joint surfaces of complex assembled structures, a novel parameter identification technique was adopted. Virtual materials were introduced to simulate the stiffness an...In order to acquire the dynamic characteristics of joint surfaces of complex assembled structures, a novel parameter identification technique was adopted. Virtual materials were introduced to simulate the stiffness and damping features of the joint surfaces between two different structures. Properties of the virtual materials, including elasticity modulus, density, and Poisson ratio, were gradually modified. At last, FEM modal results of the assembled structures are consistent with the experimental ones. This proves the feasibility of the simulating method and paves a solid foundation of the further research of the dynamic simulation.展开更多
Background Fast simulation techniques are strongly favored in computer graphics,especially for the nonlinear inhomogeneous elastic materials.The homogenization theory is a perfect match to simulate inhomogeneous defor...Background Fast simulation techniques are strongly favored in computer graphics,especially for the nonlinear inhomogeneous elastic materials.The homogenization theory is a perfect match to simulate inhomogeneous deformable objects with its coarse discretization,as it reveals how to extract information at a fine scale and to perform efficient computation with much less DOF.The existing homogenization method is not applicable for ubiquitous nonlinear materials with the limited input deformation displacements.Methods In this paper,we have proposed a homogenization method for the efficient simulation of nonlinear inhomogeneous elastic materials.Our approach allows for a faithful approximation of fine,heterogeneous nonlinear materials with very coarse discretization.Modal analysis provides the basis of a linear deformation space and modal derivatives extend the space to a nonlinear regime;based on this,we exploited modal derivatives as the input characteristic deformations for homogenization.We also present a simple elastic material model that is nonlinear and anisotropic to represent the homogenized materials.The nonlinearity of material deformations can be represented properly with this model.The material properties for the coarsened model were solved via a constrained optimization that minimizes the weighted sum of the strain energy deviations for all input deformation modes.An arbitrary number of bases can be used as inputs for homogenization,and greater weights are placed on the more important low-frequency modes.Results Based on the experimental results,this study illustrates that the homogenized material properties obtained from our method approximate the original nonlinear material behavior much better than the existing homogenization method with linear displacements,and saves orders of magnitude of computational time.Conclusions The proposed homogenization method for nonlinear inhomogeneous elastic materials is capable of capturing the nonlinear dynamics of the original dynamical system well.展开更多
The metafunction propounded by Halliday is one of the most important parts of functional grammar.This paper is to analyzehow the interpersonal function, such as mood and modality,is embodied in the listening materials...The metafunction propounded by Halliday is one of the most important parts of functional grammar.This paper is to analyzehow the interpersonal function, such as mood and modality,is embodied in the listening materials and illustrate it by corresponding examples,with the intention of using functional grammar to guide the teaching of English listening and improving the students'listening skills.展开更多
模态分析是水电机组故障诊断的重要方法,但其传统方法缺少对接触部分非线性接触的模拟手段,直接影响模态分析的准确性,也无法对链接部位的失效过程及趋势进行分析。该文基于用户自定义单元子程序接口(user-defined element subroutine i...模态分析是水电机组故障诊断的重要方法,但其传统方法缺少对接触部分非线性接触的模拟手段,直接影响模态分析的准确性,也无法对链接部位的失效过程及趋势进行分析。该文基于用户自定义单元子程序接口(user-defined element subroutine interface,UEL),建立了结合部三维非线性专用分析单元模型。推导所提模型有限元格式的基本方程,获得表征材料非线性特性的本构关系;给出螺栓连接的固定结合部的静态分析,以及立式水轮发电机导轴承支架的模态分析算例;给出导轴承支架的支臂末端螺栓连接变刚度计算的工程应用实例。实验与仿真对比结果表明了建立的UEL三维非线性接触分析专用单元模型的正确性;连接失效分析表明了随着导轴承支架接触刚度的下降,会在整机模态频率计算中引入新的频率段这一结果的重要性。展开更多
文摘This paper discusses the modal features of weakly-viscoelastic material structures both for single-modulus and multi-modulus materials. It is the eigenvalues of these structures that are the roots of a series of rational fraction polynomial equations. A theorem about the roots of these equations is proved in the paper. Based on it, some important conclusions about the modal features of the weakly viscoelastic material structures are given according to their dynamic behaviors.
文摘In order to acquire the dynamic characteristics of joint surfaces of complex assembled structures, a novel parameter identification technique was adopted. Virtual materials were introduced to simulate the stiffness and damping features of the joint surfaces between two different structures. Properties of the virtual materials, including elasticity modulus, density, and Poisson ratio, were gradually modified. At last, FEM modal results of the assembled structures are consistent with the experimental ones. This proves the feasibility of the simulating method and paves a solid foundation of the further research of the dynamic simulation.
基金the National Natural Science Foundation of China(61902340)the Science and Technology Project of Hebei Education Department(QN2019157).
文摘Background Fast simulation techniques are strongly favored in computer graphics,especially for the nonlinear inhomogeneous elastic materials.The homogenization theory is a perfect match to simulate inhomogeneous deformable objects with its coarse discretization,as it reveals how to extract information at a fine scale and to perform efficient computation with much less DOF.The existing homogenization method is not applicable for ubiquitous nonlinear materials with the limited input deformation displacements.Methods In this paper,we have proposed a homogenization method for the efficient simulation of nonlinear inhomogeneous elastic materials.Our approach allows for a faithful approximation of fine,heterogeneous nonlinear materials with very coarse discretization.Modal analysis provides the basis of a linear deformation space and modal derivatives extend the space to a nonlinear regime;based on this,we exploited modal derivatives as the input characteristic deformations for homogenization.We also present a simple elastic material model that is nonlinear and anisotropic to represent the homogenized materials.The nonlinearity of material deformations can be represented properly with this model.The material properties for the coarsened model were solved via a constrained optimization that minimizes the weighted sum of the strain energy deviations for all input deformation modes.An arbitrary number of bases can be used as inputs for homogenization,and greater weights are placed on the more important low-frequency modes.Results Based on the experimental results,this study illustrates that the homogenized material properties obtained from our method approximate the original nonlinear material behavior much better than the existing homogenization method with linear displacements,and saves orders of magnitude of computational time.Conclusions The proposed homogenization method for nonlinear inhomogeneous elastic materials is capable of capturing the nonlinear dynamics of the original dynamical system well.
文摘The metafunction propounded by Halliday is one of the most important parts of functional grammar.This paper is to analyzehow the interpersonal function, such as mood and modality,is embodied in the listening materials and illustrate it by corresponding examples,with the intention of using functional grammar to guide the teaching of English listening and improving the students'listening skills.
文摘模态分析是水电机组故障诊断的重要方法,但其传统方法缺少对接触部分非线性接触的模拟手段,直接影响模态分析的准确性,也无法对链接部位的失效过程及趋势进行分析。该文基于用户自定义单元子程序接口(user-defined element subroutine interface,UEL),建立了结合部三维非线性专用分析单元模型。推导所提模型有限元格式的基本方程,获得表征材料非线性特性的本构关系;给出螺栓连接的固定结合部的静态分析,以及立式水轮发电机导轴承支架的模态分析算例;给出导轴承支架的支臂末端螺栓连接变刚度计算的工程应用实例。实验与仿真对比结果表明了建立的UEL三维非线性接触分析专用单元模型的正确性;连接失效分析表明了随着导轴承支架接触刚度的下降,会在整机模态频率计算中引入新的频率段这一结果的重要性。
