Compressive response of glass fiber composite sandwich structures

Sandwich panels with crushable foam cores have attracted significant interest for impulsive load mitigation. We describe a method for making a lightweight, energy absorbing, glass fiber composite sandwich structure and explore it is through thickness (out-of-plane) compressive response. The sandwich structure utilized corrugated composite cores constructed from delamination resistant 3D woven E-glass fiber textiles folded over triangular cross section prismatic closed cell, PVC foam inserts. The corrugated structure was stitched to 3D woven S2-glass fiber face sheets and infiltrated with a rubber toughened, impact resistant epoxy. The quasi-static compressive stress-strain response of the panels was experimentally investigated as a function of the strut width to length ratio and compared to micromechanical predictions. Slender struts failed by elastic (Euler) buckling which transitioned to plastic microbuckling as the strut aspect ratio increased. Good agreement was observed between experimental results and micromechanical predictions over the wide range of core densities investigated in the study.

On high-frequency noise scattering by aerofoils in flow

Abstract A theoretical model is developed for the sound scattered when a sound wave is incident on a cambered aerofoil at non-zero angle of attack. The model is based on the linearization of the Euler equations about a steady subsonic flow, and is an adaptation of previous work which considered incident vortical disturbances. Only high-frequency sound waves are considered. The aerofoil thickness, camber and angle of attack are restricted such that the steady flow past the aerofoil is a small perturbation to a uniform flow. The singular perturbation analysis identifies asymptotic regions around the aerofoil; local 'inner' regions, which scale on the incident wavelength, at the leading and trailing edges of the aerofoil; Fresnel regions emanating from the leading and trailing edges of the aerofoil due to the coalescence of singularities and points of stationary phase; a wake transition region downstream of the aerofoil leading and trailing edge; and an outer region far from the aerofoil and wake. An acoustic boundary layer on the aerofoil surface and within the transition region accounts for the effects of curvature. The final result is a uniformly-valid solution for the far-field sound; the effects of angle of attack, camber and thickness are investigated. © 2013 Cambridge University Press.

Designing folding rings using polynomial continuation

© 2014 by ASME. Two types of foldable rings are designed using polynomial continuation. The first type of ring, when deployed, forms regular polygons with an even number of sides and is designed by specifying a sequence of orientations which each bar must attain at various stages throughout deployment. A design criterion is that these foldable rings must fold with all bars parallel in the stowed position. At first, all three Euler angles are used to specify bar orientations, but elimination is also used to reduce the number of specified Euler angles to two, allowing greater freedom in the design process. The second type of ring, when deployed, forms doubly plane-symmetric (irregular) polygons. The doubly symmetric rings are designed using polynomial continuation, but in this example a series of bar end locations (in the stowed position) is used as the design criterion with focus restricted to those rings possessing eight bars.

Temperature measurements of the bluff body surface of a Swirl Burner using phosphor thermometry

Flames are often stabilised on bluff-bodies, yet their surface temperatures are rarely measured. This paper presents temperature measurements for the bluff body surface of the Cambridge/Sandia Stratified Swirl Burner. The flame is stabilized by a bluff body, designed to provide a series of turbulent premixed and stratified methane/air flames with a variable degree of swirl and stratification. Recently, modellers have raised concerns about the role of surface temperature on the resulting gas temperatures and the overall heat loss of the burner. Laser-induced phosphorescence is used to measure surface temperatures, with Mg4GeO6F:Mn as the excitation phosphor, creating a spatially resolved temperature map. Results show that the temperature of the bluff body is in the range 550-900 K for different operating conditions. The temperature distribution is strongly correlated with the degree of swirl and local equivalence ratio, reflecting the temperature distribution obtained in the gas phase. The overall heat loss represents only a small fraction (<0.5%) of the total heat load, yet the local surface temperature may affect the local heat transfer and gas temperatures. © 2014 The Combustion Institute.

Floral surveys on Gomphonemaceae and Cymbellaceae (Bacillariophyta) from the headwaters of the Yangtze River, Qinghai, China

Gomphonemaceae and Cymbellaceae from the headwaters of the Yangtze River, Qinghai Province, China, comprised 84 taxa belonging to four genera. The dominant species were Gomphonema kaznakowi Mer., G. hedini Hust., G. olivaceum (Lyngbye) Kutz., Cymbella cistula (Ehr.) Kirchn. var. cistula and C. minuta Hilse ex Rabh. var. minuta. Some arctic and alpine forms also occurred, and the following taxa were unique to this region: C. cistula var. asiatica Mer., C. cistula var. capitata Grun., C. yabe Skvortzow var. punctata Li and Shi, G. olivaceum (Lyngbye) Kutzing var. brevistriatum Li and Shi and G. staurophorum (Pant.) Cleve-Euler var. oblongum Li and Shi. Different morphological forms of G. kaznakowi Mer. may be related to the upheaval of the plateau. Species diversity of the diatoms appears to be related not only to macro-environment (e.g., geographic zonation) but also to microhabitat and microclimate.

Hybrid numerical methods for exponential models of growth

A series of novel numerical methods for the exponential models of growth are proposed. Based on these methods, hybrid predictor-corrector methods are constructed. The hybrid numerical methods can increase the accuracy and the computing speed obviously, as well as enlarge the stability domain greatly. (c) 2005 Published by Elsevier Inc.

斜爆轰波面上多维复杂结构的数值研究

本文利用Euler方程和单步化学反应模型,对斜爆轰波进行了数值模拟,重点研究了斜爆轰波面上多维复杂结构的形成机理。数值结果显示在斜爆轰波面上,存在两种小尺度的激波、火焰耦合结构:第一种结构由一道横波和三角形火焰组成,是斜爆轰波中特有的结构;另一种由两道横波和凸起的火焰面组成,类似于正爆轰波面上的胞格结构。数值结果表明这两种结构能够相互转化,其形成和发展过程受到来流马赫数、化学反应放热速度等参数的影响。

三维双楔面定常激波相互作用

本文通过理论分析,将三维对称双楔面上定常激波相互作用简化到二维截面进行分析,利用二维非定常激波楔面反射理论求解该三维激波相互作用结构。同时,通过采用二阶精度的NND格式求解三维Euler方程,对该理论分析结果做出数值模拟验证。理论分析和数值模拟结果显示,对于三维双楔面超声速定常流动在取定的二维截面上激波结构兼有二维非定常及定常激波反射的性质,即形成了类似于二维非定常激波楔面反射的规则反射、单马赫反射、过渡马赫反射及双马赫反射等结构,同时其规则—马赫反射转变却遵循适用于二维定常激波反射的von Neumann准则。理论分析得出的各种反射结构的存在范围与数值模拟结果吻合良好。同时,探讨了两楔面间夹角以及楔面前缘后掠角对该激波结构的影响。

三维非定常激波双楔面反射的数值研究

本文采用有限体积方法,在非结构自适应网格上求解三维Euler方程,数值研究了三维非定常激波在双楔面上的反射现象。结果显示,三维激波在双楔面上也会反射形成三维马赫反射和规则反射;此外,还会形成一种非典型的三维准马赫反射。由于三维影响,通过二维激波反射理论预测的三维马赫反射区域存在一定的误差,该误差在文中得到了修正。

硝基甲烷热解化学反应流的数值研究

本文对激波管硝基甲烷热解化学反应流进行了研究，给出了一个严格考虑到化学反应流中化学反应、体积和流动效应的一维Euler方程的全解析耦合算法。对硝基甲烷激波管热解进行了模拟，并把耦合算法得到的模拟结果和激波管实验数据进行了对比验证，两者符合较好。此外，本文还对耦合算法与等温、等压和等容三种简化模型的计算结果进行了对比分析，结果表明，当化学反应流热效应显著增强时，等温假设失效，等压和等容简化模型也偏离实际情形，而全解析耦合算法可以有效解决化学反应与流动相互耦合的问题。

用双流体模型模拟超声速气固两相流动

采用了双流体模型对JPL(Jet Propulsion Laboratory)喷管中气固两相流动以及超声速射流两相流动进行了数值模拟,并研究了可压缩两相流动中气相与颗粒的相互作用规律.自主开发的一般曲线坐标系下二维轴对称可压缩双流体程序Solve2D,对气相求解Navier-Stokes(N-S)方程组,采用k-ε湍流模型,颗粒相求解Euler方程组.对JPL喷管内的两相流场和湍流两相射流流场进行了数值模拟,研究了不同颗粒质量百分数以及不同颗粒直径时的气固两相流场的流动规律.

Hydroelastic dynamic characteristics of a slender axis-symmetric body

The slender axis-symmetric submarine body moving in the vertical plane is the object of our investigation. A coupling model is developed where displacements of a solid body as a Euler beam (consisting of rigid motions and elastic deformations) and fluid pressures are employed as basic independent variables, including the interaction between hydrodynamic forces and structure dynamic forces. Firstly the hydrodynamic forces, depending on and conversely influencing body motions, are taken into account as the governing equations. The expressions of fluid pressure are derived based on the potential theory. The characteristics of fluid pressure, including its components, distribution and effect on structure dynamics, are analyzed. Then the coupling model is solved numerically by means of a finite element method (FEM). This avoids the complicacy, combining CFD (fluid) and FEM (structure), of direct numerical simulation, and allows the body with a non-strict ideal shape so as to be more suitable for practical engineering. An illustrative example is given in which the hydroelastic dynamic characteristics, natural frequencies and modes of a submarine body are analyzed and compared with experimental results. Satisfactory agreement is observed and the model presented in this paper is shown to be valid.

压电驱动器应变传递模型分析

随着压电材料结构在航空航天结构控制领域的广泛应用, 压电驱动器与主体结构间的应变传递问题的研究日益重要. 该文首先对压电驱动器应用中的应变传递模型----均匀应变模型与Bernoulli-Euler模型进行了优缺点的分析对比; 其次将Bernoulli-Euler模型用于考虑胶层影响情况, 考虑到压电驱动器在航空航天领域的应用, 着重类似于翼面结构的模型分析, 得到了实际应用中压电驱动器沿结构厚度方向的应变传递表达式; 最后通过数值计算的方法确定了所得应变表达式适用的胶粘剂弹性模量及厚度的范围. 结果表明此表达式的有效性, 使 Bernoulli-Euler模型的应用更接近于实际情况, 同时为智能结构实际应变分布的分析提供了一定的依据与基础

细长轴对称体的水弹性振动特性分析

以在水中做纵向平面内运动的细长轴对称体为研究对象.在建立描述流体-结构耦合振动系统的计算模型时,对固体采用位移(包括刚体运动位移和弹性Euler梁振动位移),对流体采用压力作为基本变量,首先建立了考虑流体作用力的结构动力学方程,推导了考虑结构运动的流体压力表达式,分析了水动力载荷的特征:包括水动压力的来源,组成,分布形式与影响范围等.在此基础上给出了描述水中运动物体的位移(结构)-压力(流体)格式的流固耦合系统模型.然后利用有限元数值方法(FEM)对方程进行了求解,克服了解析解对研究对象外形的限制,同时避免了流固耦合直接数值模拟中CFD+FEM的复杂性,对于典型的工程结构非常适用.最后,通过算例给出了水中运动物体的水弹性频率和模态,并将计算结果与试验结果进行了对比,证明了本文计算模型的有效性

不同积分变分原理的统一

依据定量因果原理的数学表示,统一地导出了Lagrange量中含坐标关于时间一阶、二阶导数的积分型的Hamilton原理、Voss原理、Hlder原理和Maupertuis-Lagrange原理等,给出了这些原理的本质联系和统一描述.得出f0=0并不是通常的保持Euler-Lagrange方程不变的结果,而是满足定量因果原理的结果.还得出Lagrange量的所有的积分型变分原理等价地对应于两类满足定量因果原理的不变形式.同时发现所有积分型变分原理的运动方程都是Euler-Lagrange方程,但不同条件的变分原理所对应的不同群G作用下的守恒量是不同的.从而可对过去众多零散的积分型变分原理有一个系统和深入的理解,并使这些变分原理自然地成为定量因果原理的推论.