双层非织造多孔材料吸声模型仿真

关于优化吸声降噪工程材料问题,传统硬质穿孔板吸声效果差.为了提高吸声性能,根据材料的重要结构参数变化和单层多孔材料吸声机理,研究了A、B两种材料的厚度、孔隙率和孔隙半径变化对吸声系数的影响.以建立的数学模型为基础,通过仿真研究了最大吸声系数与A、B两种材料结构参数的关系,为最优化双层非织造多孔吸声材料结构提供了实验基础.经仿真表明,双层非织造多孔纤维吸声材料模型具有良好的吸声效果,从而为产品研发提供了理论依据.     

背衬对隔声去耦瓦吸声性能的影响

基于传递矩阵法,建立了不同背衬情况下的水下隔声去耦吸声覆盖层模型,讨论了软背衬、硬背衬、单层壳体背衬和双层壳体背衬条件下隔声去耦瓦的吸声性能。结果表明:双层壳体背衬条件下吸声系数曲线存在明显的调制现象,且壳间水层增厚,吸声峰值向低频移动,峰增多、变密,峰值有所减小,而外层壳板厚度变化对吸声系数影响不大;单层壳背衬条件下,钢板的厚度越大,第一吸声峰值向低频移动,且峰值变小;当钢板的厚度达到一定的厚度时,其吸声系数曲线逐渐与刚性背衬下隔声去耦瓦的吸声曲线接近。     

双层薄膜型超材料夹层板的多带隙设计

本文将薄膜型声学超材料结构与格栅夹层板结构相结合,发展了一种双层薄膜型超材料夹层板结构.采用有限元方法,建立薄膜型超材料夹层板结构模型,并分析其带隙产生机理.在单层薄膜型超材料夹层板结构的基础上,提出了相同质量与不同质量的双层薄膜型超材料夹层板结构,将其产生的局域共振带隙与单层薄膜型超材料夹层板结构进行对比分析.结果表明,相较于只含单层薄膜结构的夹层板,具有相同振子质量的双层薄膜型超材料夹层板结构,可以有效拓宽带隙范围.不同质量双层薄膜型超材料夹层板结构,可以增加带隙数量.如果改变谐振器质量块的粘附位置,结构的不对称性会使双层薄膜型超材料夹层板产生多个局域共振带隙,且位置相近的带隙可能合并为较宽的带隙.     

等面密度钢/铝组合靶的抗侵彻性能研究

金属靶板的抗侵彻性能一直以来都是被重点关注的研究领域。为明确结构参数对钢/铝组合结构抗步枪弹垂直侵彻性能的影响,建立了步枪弹侵彻钢板和铝板的数值计算模型,并通过弹道冲击实验进行了验证;进而基于数值计算模型分析了相同厚度下钢-铝、铝-钢的组合形式、靶板间距对组合靶板抗侵彻性能的影响。仿真结果表明：相同厚度下,钢板在前的组合形式优于铝板在前的靶板,但不同组合形式的层板间距对其抗侵彻性能影响较小;另外,比较了不同初速度下钢-铝厚度比的变化对组合靶板的抗侵彻性能影响,均呈现出随厚度比增加,抗侵彻性能先降低后增加的趋势,最终趋于一个稳定值。变化过程中存在一个抗侵彻性能最差的低点,在结构设计中应尽可能避开。最后,依据 R-I 公式拟合了仿真数据,得到了步枪弹侵彻钢-铝组合结构的弹道极限公式。研究结果可为组合靶板的抗侵彻性能设计和人员、物资防护提供参考。     

薄膜在线厚度检测方法及应用

为了提高聚乙烯塑料薄膜质量,生产过程中实时对薄膜厚度进行检测非常重要,介绍一种基于电容式传感器测量原理、实现薄膜厚度在线测量的方法,满足生产过程中对制品进行连续测量监控的要求。同时由于薄膜生产线的工艺特点,生产过程一般采用双层折叠方式,在线检测通常只能测量双层总厚度,提出一种采用计算机软件运算方式将双层测量结果转换为单层厚度的方法,解决实现单层厚度在线测量的难题。     

双层矩形微板谐振器件中热弹性阻尼机理研究

基于Bishop和Kinra的理论框架,利用积分变换法,建立了周边固定条件下,双层矩形微板谐振器中热弹性阻尼解析模型。通过与先前解析模型以及有限元数值模型进行比较,验证了本文模型的有效性。结果分析表明:当基层材料与镀层材料的Zener模量相差较大时,热弹性阻尼频谱曲线会出现两个波峰;双层板的厚度对热弹性阻尼有很大的影响;当微板的厚度不变时,所得热弹性阻尼频谱曲线不随其他结构几何参数变化。     

双层厚膜结构改善气敏元件灵敏度和选择性研究

研究了厚膜印刷技术制备的双层膜结构气敏元件的灵敏度和选择性.测量结果表明:在二氧化锡(SnO2)单层膜下再添加一层纳米三氧化钨(WO3)材料厚膜,可以提高气敏元件对酒精、丙酮、甲醛、甲苯还原气体的灵敏度和选择性.当浓度为900×10-6时,将SnO2覆盖在WO3之上形成双层膜时,较两种材料对应的单层膜灵敏度均有所提升.因此,双层厚膜结构为改善元件的灵敏度和选择性提供了一种可行的方法.初步认为,双层膜的作用与膜的上、下排列顺序有很大的关系,也与双层界面间由于扩散效应所形成的过渡层有关.     

弹头形状与界面强度对侵彻过程的数值仿真

研究B4C陶瓷复合防弹靶是轻质防护工程优化问题,传统应用陶瓷对变形和强度缺乏定性分析.为准确选复合板陶瓷种类,采用数值仿真对抗弹性能分析方法,对弹头形状、层间接触方式和层间界面强度对B4C陶瓷复合靶抗弹机制的影响进行数值分析.在LS-DYNA软件中用Lagrange算法进行仿真,结果表明,陶瓷复合靶板抗平头弹的穿透能力要优于圆头弹.层间采用不同的界面接触方式对结果有影响,提高靶板间界面强度可提高陶瓷复合靶抗弹性能,可以为实验设计提供参考.     

基于ANSYS/LS-DYNA高速弹头冲击仿真

高速弹头的侵彻问题是军工防护等领域研究的一个重要课题；采用有限元仿真软件ANSYS/LS-DYNA为平台对高速弹头侵彻靶板的过程进行了数值模拟；选取Johnson-Cook本构模型来描述侵彻过程,得到了速度为1 300 m/s的子弹侵彻6 mm靶板的速度、加速度、能量变化曲线和VonMises应力云图,从而直观地显示靶板的变形情况和动态响应,有助于分析高速弹头的撞击过程；验证了ANSYS/LS-DYNA有限元仿真在分析侵彻问题中的可行性和优越性,对改进弹头和防护材料设计具有重要意义；并为防护材料设计进行高速冲击实验的研究提供了新的途径和思路。     

阵列化锰铜高压传感器的研制

通过传感器的结构设计、敏感材料和封装材料的研制以及采用新的传感器制备工艺,制作了一种新型的薄膜式锰铜传感器。采用熔融石英材料作为绝缘基板。在绝缘基板上沉积锰铜敏感薄膜。并在敏感薄膜的上面沉积SiO2封装层薄膜。根据"后置"式传感器由阻抗匹配原则,计算出铝靶板中的最高压力为51.68GPa,SiO2封装材料中的压力为35.396GPa。     

On the use of shape functions in the cell centered finite volume formulation for plate bending analysis based on Mindlin–Reissner plate theory

This paper deals with a new formulation of the cell centered finite volume application for plate bending analysis based on Mindlin–Reissner plate theory. In this formulation shape functions are used to represent the variation of the unknown variables across the control volumes’ faces, which facilitates the calculation of stress resultants on the faces. The performance of the formulation for the computation of displacements and stress resultants for thin and thick plates is evaluated in a number of test problems. This testing reveals that the proposed approach enhances the predictive capability of the finite volume method in the analysis of thin to thick plates.     

Buckling of initially stressed mindlin plates using a finite strip method

The buckling of initially stressed Mindlin plates is considered using a thick finite strip method. The method is compared with a wide variety of published results and for both thin and moderately thick plates excellent accuracy is obtained. Some further results are obtained for initially stressed rectangular plates with two opposite edges simply supported and various support conditions on the remaining sides. In general, it is found that for moderately thick plates, Mindlin's plate theory gives lower buckling loads than those obtained using classical thin plate theory.     

Flexure of composite laminates using the thick finite strip method

A thick finite strip method is applied to the problem of flexure of composite laminates. The formulation which is based on Mindlin's plate theory takes account of transverse shear deformation. Examples are presented giving comparisons with exact three dimensional, thick plate and classical thin plate solutions.     

Effect of thickness on the behaviour of plates on foundations

A technique is presented for the analysis of transversely loaded thin rectangular plates on Winkler foundations and is used in a parametric study of plate behaviour. The technique is based on Fourier series expansions and is similar to one already described for thick slabs. For thin plates only flexural deformation is accounted for, whereas for thick plates the energy due both to transverse shear and transverse direct strains is included. Both methods of analysis are then used on a variety of plates of different thicknesses and material properties and under various loading conditions. From the results, general conclusions can be drawn on the range of applicability of “thin” plate theory and conversely point to situations when the use of “thick” plate theory is essential.     

A finite element method for the free vibration of plates allowing for transverse shear deformation

An isoparametric quadrilateral plate bending element is introduced and its use for the free vibration analysis of both thick and thin plates is examined. Plates of rectangular planform and of orthotropic materials are analysed and excellent results are obtained. The element performance is assessed by comparison with well established analytical and numerical solutions based on Mindlin's thick plate theory, three dimensional elasticity solutions and solutions based on thin plate theory. The ease with which the element may be implemented is stressed. The use of an eigenvalue economiser which produces considerable economy in the computer solution is demonstrated. Various mass lumping schemes and numerical integration rules used in the construction of the element mass matrix are also examined.     

A modified ACM element for thick plate analysis

A modified version of the ACM thin plate bending element is presented for the analysis of thick plates. The shape functions used are homogeneous solutions of Mindlin's equations plus a particular solution associated with the applied load on the element. The approximation is consistent for both thick and thin plates, enabling the element to be developed in a straightforward manner without any special techniques. The examples demonstrate the good accuracy that is achieved by the element for both static and dynamic problems.     

A simple displacement-based 3-node triangular element for linear and geometrically nonlinear analysis of laminated composite plates

A simple displacement-based 3-node, 18-degree-of-freedom flat triangular plate/shell element LDT18 is proposed in this paper for linear and geometrically nonlinear finite element analysis of thin and thick laminated composite plates. The presented element is based on the first-order shear deformation theory (FSDT), and the total Lagrangian approach is employed to formulate the element for geometrically nonlinear analysis. The deflection and rotation functions of the element boundary are obtained from the Timoshenko’s laminated composite beam functions, hence convergence to the thin plate solution can be achieved theoretically and shear-locking problem is avoided naturally. The plane displacement interpolation functions of the Airman’s triangular membrane element with drilling degrees of freedom are taken as the in-plane displacements of the element. Numerical examples demonstrate that the present element is accurate and efficient for linear and geometrically nonlinear analysis of thin to moderately thick laminated composite plates.     

Free vibrations of laminated composite plates using second-order shear deformation theory

A complete set of linear equations of the second-order theory of laminated composite plates are obtained. A generalized Levy type solution in conjunction with the state space concept is used to analyze the free vibration behavior of cross-ply and antisymmetric angle-ply laminated plates. Exact fundamental frequencies of cross-ply plate strips are obtained for arbitrary boundary conditions. The exact analytical solutions are obtained for thick and moderately thick plates as well as for thin plates and plate strips. It is shown that the results of the second-order theory are very close to the results of the first-order and third-order theories reported in the literature, and different from those of the classical Kirchhoff’s theory for thick laminates.     

基于一阶剪切板理论的FGM板刚柔耦合动力学建模与仿真

对作大范围运动功能梯度材料(functionally graded materials,FGM)厚板的刚柔耦合动力学问题进行了研究,基于一阶剪切变形理论,从连续介质理论出发,计及了变形位移场中的二次耦合变形量,利用Lagrange方法推导了FGM厚板的刚柔耦合动力学方程,该方程适用于普通均质板和FGM板的动力学分析.采用20自由度矩形单元对变形场进行离散,对不同转速下的悬臂板进行动力学仿真,比较了本文建立的基于一阶剪切理论的模型和基于经典薄板理论的模型,验证了本文模型的正确性以及经典薄板理论的一些不足.研究了不同功能梯度指数下,FGM厚板的横向变形、速度响应频率和固有频率.结果表明,随着转速增大,剪切项对结构动力学行为影响变大;考虑横向剪切项的情况下,计算结果更偏柔性.     

A hybrid-stress quadratic serendipity displacement mindlin plate bending element

A hybrid-stress plate bending element is developed for thin and moderately thick plates based on a Serendipity-type quadratic displacement assumption. The through-thickness displacement behavior is consistent with Mindlin plate theory, and all components of stress are included. By proper choice of the transverse shear stress distributions, the element stiffness possesses correct rank, and results show no signs of locking in the thin plate limit; these and other considerations discussed herein suggest that the stress assumption used is optimum for the 8-node element. Results are compared with 8-node Serendipity and 9-node Lagrange assumed-displacement elements. The present element demonstrates high accuracy for all problems considered and has no apparent deficiencies.