基于有限元分析的金刚石钻头强度验算公式

在对81／2B125金刚石钻头进行有限元计算分析后，找出最大应力点在金刚石钻头冠部切削告处。通过改变各相关尺寸和结构型式，用有限元法模拟试验过程，在给定结构参数和工艺参数情况下获得多组数据。根据专业知识，参考有限元计算获取的各组数据变化特征，选出拟合较好的公式类型，再采用回归分析方法确定待定系数，最后得出工程上实用的金刚石钻头强度验算公式。用这个公式对81／2B461W和121／4B331金刚石钻头进行了强度验算，经改进设计后钻头在现场使用取得了良好的效果。     

A review of error estimation and adaptivity in the boundary element method

When using the boundary element method, the accuracy of the numerical solution depends critically on the discretization of the boundary into elements (panels). The distribution of the panels is one of the most important decisions taken when analyzing a problem, but still the vast majority of users employ empirical guidelines to distribute the panels. This paper reviews the various adaptive schemes that have been proposed for boundary elements. Numerical results are obtained for infinite fluid flow problems and free surface problems and are used to assess the reliability and effectiveness of each method.     

Finite element micromechanical modelling of unidirectional fibre-reinforced metal-matrix composites

Typical finite element formulations and models for unidirectional composite materials are reviewed. The application of micromechanical finite element analysis to the modelling of unidirectional fibre-reinforced metal-matrix composites is demonstrated by presenting some studies from recent publications. It is shown that while analytical models offer a simple tool for obtaining the overall response of composites, finite element analysis provides more accurate and detailed characterisation of composite properties for complicated geometries and constituent property variations. Various effects that influence the stress/strain response and fibre/matrix deformation of composites are studied through modelling. These effects include the fibre coating and reaction layer, fibre shape and distribution, metallurgical and environmental factors, stress distributions and damage. It is demonstrated that the properties and constituent phase interaction of metal-matrix composites are best modelled by finite element analysis. It is emphasized that in order to obtain good predictions, the models must be coupled with first-hand characterisations of the constituent phases and their interactions, including the thermal history of the specimens.     

Simulation of water and nitrogen dynamics in soils during wastewater applications by using a finite-element model

A mathematical model was developed to simulate water movement, mass transport, and nitrogen transformations in soils during wastewater applications. The model is one-dimensional and based on the Galerkin finite-element method. The submodel of mass transport of nitrogen incorporates the convection-dispersion processes of ammonium and nitrate nitrogen, nitrification, denitrification, ammonium exchange and uptake of ammonium and nitrate ions. The accuracy and validity of the proposed model was examined by comparison with an explicit-implicit finite-difference model results. The model was used for simulation of water and nitrogen dynamics during wastewater application in homogeneous and multi-layered soils under different N concentration, rate, duration and scheduling of application.     

Numerical simulation model of vibration responses of rectangular plates embedded with piezoelectric actuators

A numerical simulation model for random large amplitude vibration control of composite plate using piezoelectric material is presented. The H_∞ control design is employed to suppress the large amplitude vibrations of composites plates under random loading. The numerical simulation model is developed and based on the finite element method. The finite element governing equation includes fully coupled structural and electrical nodal degrees of freedom, and consider the von Karman large amplitude vibration. The modal reduction method using the structural modes is adopted to reduce the finite element equations into a set of modal equations with fewer degrees of freedom. The modal equations are then employed for controller design and time domain simulation. In the simulations without control, the value of the linear mode to the nonlinear deflection is quantified; and the minimum number of linear modes needed for accurate model is obtained. In the simulations with control, it is shown that the truncated modes, which are neglected in the control design, deteriorate the controller performance. Generally, the vibration reduction level is not monotonically increasing with the size of the piezoelectric actuator. The optimal piezoelectric actuator size depends on the excitation level. For higher excitation level, optimal actuator size is larger. The H_∞ controller based on the linear finite element formulation gives better vibration reduction for small amplitude vibration, but it still gives reasonable performance for large amplitude vibration provided that the piezoelectric actuator is big and powerful enough.     

FINITE ELEMENT ANALYSIS OF THE FLOW INDUCED BY ROTATING BLADES IN AN INCOMPRESSIBLE VISCOUS FLUID

Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction of local geometric angle of attack according to a free-wake modeling in addition to an empirical modification for the tip flow effect. The validity and efficiency of the present method were verified by the comparisons between numerical results and experimental data.     

Mesh‐independent p‐orthotropic enrichment using the generalized finite element method

This paper is aimed at presenting a simple yet effective procedure to implement a mesh‐independent p‐orthotropic enrichment in the generalized finite element method. The procedure is based on the observation that shape functions used in the GFEM can be constructed from polynomials defined in any co‐ordinate system regardless of the underlying mesh or type of element used. Numerical examples where the solution possesses boundary or internal layers are solved on coarse tetrahedral meshes with isotropic and the proposed p‐orthotropic enrichment. Copyright © 2002 John Wiley & Sons, Ltd.     

BIMORPH PIEZOELECTRIC ACTUATOR FOR SMALL PIPE ROBOT

An experimental bimorph piezoelectric element (PZT) actuator for small pipe robot is developed. The robot can move in φ20 mm pipe, and can carry a CCD camera for detecting cracks or fine holes on inner surface of pipe. The velocity of the robot can reach 17～22 mm/s for vertical pipe up/down, respectively. Moving principle and its performance characteristics are presented.     

补偿元件对载体催化元件输出特性的影响

阐述了矿井瓦斯传感器－载体催化元件在应用中，补偿元件发挥的作用和工作原理，着重分析了补偿元件对载体催化元件输出特性的影响，探讨了提高线性补偿效果的方法。