机载光电平台内框架刚度及模态有限元分析

机载光电平台采用四框架二轴结构,它克服了二框架结构不能垂直对地跟踪的缺点,并提高了跟踪精度,随着精度的提高对框架的要求越来越高.应用有限元模态分析理论,对平台内框架的动态特性进行研究.在UG平台建立内框架三维实体模型,并对框架结构进行合理的简化.通过Patran有限元分析软件前后处理功能对框架采用合理单元进行网格划分,并建立有限元模型.计算出其前10阶固有频率和振型,根据计算的结果找出其结构的薄弱环节,提出改进方案并重新分析.另外,采用新型铝基复合材料以达到提高框架刚度和谐振频率从而达到提高整个平台精度的目的.最后对比三种分析的结果选出最优方案.     

Development of a methodology for a simplified finite element model and optimum design

As computer power is increased, refined finite element models are employed for structural analysis and design. However, it is still difficult and expensive to make and use refined finite element models in the design stage. The refined models usually cause problems in the preliminary design where the design is frequently changed. Therefore, the development of a simplified finite element model is desirable for use in the preliminary design stage. This paper describes the methodology for the simplified model and its optimum design. A Goal programming algorithm is used for system identification to make the simplified model. The developed methodology consists of three phases such as simplification, design, and inverse process. The simplified finite element model is used for the design change and the changed design is recovered onto the original design. The presented methodology is verified through a few examples.     

基于Karnopp摩擦的柔性滑移铰的建模与仿真

对含Karnopp摩擦的柔性滑移铰系统进行动力学建模和仿真.将滑移铰中的滑块视为柔性体,滑道视为刚性接触面,考虑滑道与滑块之间的间隙.由于柔性滑块与滑道的接触状态和摩擦情况比较复杂,采用有限元方法建立了柔性滑块的力学模型,基于罚函数方法建立含Karnopp摩擦柔性滑移铰接触力模型,通过试算迭代法判断柔性滑块各节点的接触状态,基于KED方法和Newmark方法给出了含该滑移铰机械系统动力学方程的数值算法.最后,以含Karnopp摩擦的柔性滑移铰和驱动摆杆构成的机械系统为例进行动力学仿真,分析了其动力学特性,验证了本文给出的方法的有效性.     

Numerical analysis and simulations of contact problem with wear

This paper presents a quasistatic problem of an elastic body in frictional contact with a moving foundation. The model takes into account wear of the contact surface of the body caused by the friction. We recall existence and uniqueness results obtained in Sofonea et al. (2017). The main aim of this paper is to present a fully discrete scheme for numerical approximation together with an error estimation of a solution to this problem. Finally, computational simulations are performed to illustrate the mathematical model.     

Development of hip joint prostheses with modular stems

Minimally invasive surgery for THR (Total Hip joint Replacement) is attractive for both surgeons and patients. Since such surgery needs an incision of only 3–4 inches around the hip joint for THR instead of the traditional, large incision of 10–12 inches, it causes less pain and enables early recovery for patients, besides facilitating THR for the operating surgeons. In this research, for minimally invasive THR, a unique type of a cementless stem, named a modular stem, is devised. It consists of two different parts in a stem that can be joined to and separated from each other. For actualizing the modular stem, Bio-CAD modeling technique is applied. The bony structure around the hip joint is three dimensionally reconstructed and its geometric solid model is fabricated. The geometric solid models of modular stems are designed and their prototypical models are fabricated using an acryl-based polymer. The geometric suitability of the prototypical modular stems is manually examined. The strength of the stem to sustain the applied load is evaluated using the finite element method. Finally, various sizes of actual modular stems with circular or rectangular cross-sections are fabricated using a biocompatible Ti alloy (Ti–6Al–4V). The developed modular stems will be used in the near future for minimally invasive THR surgery.     

Constitutive ply damage modeling, FEM implementation, and analyses of laminated structures

The present work is concerned with the modeling of progressive damage in fiber reinforced polymer laminates and its implementation into a finite element code as constitutive material law. The objective is to predict damage evolution and material degradation due to matrix dominated failure modes (“matrix cracking”). In a previous work, a ply-level continuum damage model based on ply failure mechanisms postulated by Puck has been presented. This model predicts the evolution of the complete tensor of elasticity for the damaged material and is able to capture the effects of stiffness recovery and slanted cracking under transverse compression. In the current work, this damage model is adapted for arbitrary loading paths and implemented within the finite element method in order to analyze complex structures and study their damage behavior including load redistribution due to damage. To demonstrate some key features and the application of the damage model in structural analysis, it is applied in a single element analysis as well as in the simulation of Open Hole Compression tests for which results are compared to experimental data from the literature.     

Numerical analysis of history-dependent hemivariational inequalities and applications to viscoelastic contact problems with normal penetration

In this paper numerical approximation of history-dependent hemivariational inequalities with constraint is considered, and corresponding Céa’s type inequality is derived for error estimate. For a viscoelastic contact problem with normal penetration, an optimal order error estimate is obtained for the linear element method. A numerical experiment for the contact problem is reported which provides numerical evidence of the convergence order predicted by the theoretical analysis.     

Numerical study on radiative MHD flow of viscoelastic fluids with distributed-order and variable-order space fractional operators

The magnetohydrodynamic (MHD) flow has been concerned widely for its widespread adoption in the field of astrophysics, electronics and many other industries over the years. The purpose of this article is to introduce the variable and distributed order space fractional models to characterize the MHD flow and heat transfer of heterogeneous viscoelastic fluids in a parallel plates. Based on the central difference approximation of Riesz space fractional derivative, the Crank–Nicolson difference scheme for the governing equations is established, and the effectiveness of the algorithm is verified by two numerical examples. We examine the effects of fractional-order model parameters on the velocity and temperature, our investigation indicates that for the constant fractional model, the larger the fractional order parameter, the smaller the velocity and temperature. The variable space fractional method can be used to describe dynamic behavior with time and space dependence, while the distributed space fractional model can describe various phenomena in which the number of differential orders varies over a certain range, characterizing their complex processes over space, and it is also more suitable for simulating the fluid flow and thermal behavior of complex viscoelastic magnetic fluid.