An Experimental and Numerical Investigation on the Low-Velocity Impact Response of Nanoreinforced Polypropylene Core Sandwich Structures

Mechanics of Composite Materials - The impact behavior of sandwich structures was studied using experimental and numerical methods. Polypropylene with 0.5 wt% of graphene (PP/0.5% G) or pure...     

翼型绕流干涉噪声的实验与数值研究

来流湍流干扰噪声在风力机叶片气动总噪声级中占有重要地位．选取圆柱/翼型干涉模型从实验和数值两方面研究此类干涉发声现象．实验中通过对翼型表面非定常载荷的测量,重点研究了圆柱位置和翼型攻角的影响,选取的翼型包括两个NACA系列翼型（NACA0012和NACA0018）和两个风力机翼型（s809和s825）,同时利用PIV（particle image velocimetry）技术对低攻角状态下翼型的前缘流场进行了研究．实验结果表明翼型表面非定常压力与圆柱涡脱落存在一定相关性．与此同时采用非定常Reynolds平均(URANS)方法对圆柱/NACA0012翼型的干涉流场进行了非定常数值模拟,并将得到的翼型表面压力频谱与实验结果进行了对比．     

带有球凹/球凸的旋转通道内流动结构和强化换热的数值研究

对带有凹坑和凸包的内流通道在不同旋转数下的对流换热特性进行了数值分析,探讨了Coriolis力对通道中流场和换热特征的影响．研究发现,随着旋转数增加,通道前缘呈现出较弱的流动冲击,但存在较大的尾迹和延迟的流动再附着,后缘凹坑内部有一较小旋涡和较强射流使得后缘传热得到强化,最高可达60%．总体Nusselt数随着旋转数的增加先减小而后增大.     

冲击波作用下Air/SF6斜界面不稳定性实验和数值模拟研究

开展了Mach数为1.23和1.41的冲击波作用下的Air/SF6斜界面不稳定性激波管实验,并利用王涛等人发展的可压缩多介质粘性流体和湍流大涡模拟程序MVFT(multi-viscous-fluid and turbulence),对该激波管实验进行了数值模拟,二者相比较一致性较好,包括界面图像、湍流混合区TMZ(turbulent mixing zone)宽度、气泡和尖钉位移,确认了该计算代码对界面不稳定性问题模拟的可靠性和有效性.数值模拟再现了冲击波作用下,Air/SF6斜界面的演化过程及流动中复杂波系结构的发展如冲击波的传播、折射和反射.结果还显示冲击波Mach数较大时,冲击波和界面相互作用时混合区获得的能量也较大,扰动界面发展的也更快.     

An Experimental Investigation of a Nonlinear Mathieu Equation

A study of the equation , using an electronic model, provides a qualitative insight into thenature of its simplest periodic solutions and leads to simpleanalytical results in quantitative agreement with the experimentalobservations. A circuit diagram is given, with practical detailsand an analysis of its operation.     

Experimental and Numerical Investigation of Nonlinear Piezoelectric Effects Including Minor Hystereses

Piezoelectric ceramics are often used in active structures for shape and vibration control. Since the operation range is not limited to small signals the nonlinear behaviour of the actuator under high electric loads has to be known. There are several approaches in literature to model the hysteretic effects, each having its assets and drawbacks. When a model is able to reproduce the minor loops of the strain - electric field hysteresis, it often lacks the consideration of stress dependence which is fundamental for actuators attached to elastic structures. On the other hand constitutive models which take into account all ferroelectric and ferroelastic effects are not capable of representing the minor hystereses in acceptable calculation times. In this work a phenomenological constitutive model is verified using the experimental data of an active plate structure. Therefore, the ceramic is characterised under mechanically unconstrained conditions and afterwards attached onto a steel plate. The bonding to the substructure leads to a mechanical stress depending on the actuation state of the ceramic. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

An Experimental and Numerical Study of Deformable Bodies Contact

This study deals with the impact of a rotating disc elastically striking a strip. We establish an experimental setup including a disc with a throwing machine controlled by a dSPACE-Autobox to generate the translational and rotational motions of the disc, a properly fixed strip and a high-speed digital camera system with an image processing package to capture kinematical data of the disc. The effects of strip flexibility and disc initial normal velocity before impact are investigated in detail. For interpreting the experimental results a hybrid impact model is developed which can provide not only generally good predictions compared with measurements but also some insight into the influences of strip flexibility and disc initial motions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experimental Investigation of the Free Liquid Interface Oscillation upon Step Reduction in Gravity

Experiments have been carried out to investigate the reorientation behavior of a free liquid surface in a partly filled right circular cylinder upon step reduction in gravity. In the initial situation the system is dominated by hydrostatic forces. In this case the equilibrium of the free liquid surface is generally characterized by a flat shape with a curvature at the cylinder wall given by the static contact angle. After transition to reduced gravity, capillary forces govern the flow and a capillary driven reorientation of the liquid to the new equilibrium position is established in a damped oscillation. The particular interest of this study is to determine the main characteristics of the surface oscillation as well as the behavior of the dynamic contact angle.     

An Experimental Investigation of Resource Allocation in Multiactivity Projects

This paper describes a computer-based experiment in the scheduling of multiactivity projects with limited resources. The main interest lay in a comparison of the traditional sorting criteria used to allot priority to activities competing for resources inadequate to satisfy all the demands and criteria newly defined for this work. One aim was to isolate, if possible, a criterion equally as good as the Critical Path parameters usually employed and yet easier to compute in practice. A similar experiment was carried out by Pascoe but none of the criteria used satisfied the second condition. It was also possible to monitor the effects on the scheduling of network parameters such as shape and connectivity.     

Experimental and Numerical Investigations of Al/Mg Compounds

Al/Mg compounds produced by hydrostatic extrusion exhibit unique characteristics regarding high strength and low weight, which are required by safety part applications in lightweight constructions. Between the two materials an interface in form of a brittle intermetallic phase consisting of Al₂Mg₃ and Al₁₂Mg₁₇ arises during the production process. However, a certain plastic deformability of the semi-finished product is essential for further forming processes. Even under multi-axle load during a radial upsetting process, the interface maintains a full material joint although a fragmentation and a new secondary interface between the fragments can be observed. Due to the evaluations of light microscopy images and Eulerian Hencky strain values at the interface, which are obtained with the help of the Digital Image Correlation, a relation between the strain and the boundary layer's appearance seems reasonable. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Drag Reduction in Wall Bounded Flows: The Effect of Polymers on the Dynamics of Turbulence

Experiments in a refractive index matched pipe flow facility were conducted using state-of-the-art laser-Doppler anemometry to study turbulent drag reduction by dilute addition of high polymers. The results were analyzed employing the invariant theory of turbulence. It was thus possible to confirm the major conclusion of preceding theoretical work, namely that the mechanism of drag reduction by long-chain polymers is associated with an increase in anisotropy of turbulence at the wall. Furthermore, theoretical considerations based on the elastic behavior of a polymer and spatial intermittency of turbulence at small scales enabled quantitative estimates to be made for the relaxation time of a polymer and its concentration that ensures maximum drag reduction. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

An Experimental Investigation of Some Heuristic Strategies for Component Placement

The purpose of this study is to examine the relative efficacy of several promising heuristic approaches to a classic problem of component placement. Four "construction" and nine "improvement" algorithms were chosen for investigation and compared experimentally on a CDC 6400 computer. The improvement methods were selected to test some basic strategies of pairwise-interchanging of components and the construction procedures were chosen primarily to evaluate the effects of the quality of starting solution on the improvement methods. The algorithms were tested on 75 problems generated from the literature and compared with respect to the produced solution quality and CPU run-time requirements. A construction approach due to Graves and Whinston produced the best results, both when used to generate starting solutions for the improvement methods and when evaluated on its own merit against the improvement methods using other starts. Construction approaches have previously been regarded in the the past as relatively inferior techniques.     

关于一个新型转捩模式的研究与应用

采用了新型的转捩预测模式,将间歇因子耦合到湍流脉动输运方程中去,计及流体转捩的内在因素,因而能够反映转捩的具体发展过程.以二维不可压平板边界层和二维NACA0012翼型为例,研究了该转捩模式在预测不可压转捩流动时的作用,得到与实验值符合良好的计算结果.同时也研究了该转捩模式在不同网格分辨率下的计算能力和对近壁面网格分辨率的要求.     

关于定积分数值计算的探讨

本文概括地讨论了现有的等距内插求积公式,并从定积分定义出发建立了一个更一般的等距内插求积公式。     

Probability Distribution of Solution Time in GRASP: An Experimental Investigation

A GRASP (greedy randomized adaptive search procedure) is a multi-start metaheuristic for combinatorial optimization. We study the probability distributions of solution time to a sub-optimal target value in five GRASPs that have appeared in the literature and for which source code is available. The distributions are estimated by running 12,000 independent runs of the heuristic. Standard methodology for graphical analysis is used to compare the empirical and theoretical distributions and estimate the parameters of the distributions. We conclude that the solution time to a sub-optimal target value fits a two-parameter exponential distribution. Hence, it is possible to approximately achieve linear speed-up by implementing GRASP in parallel.     

基流风速包含垂直变化时的三维无旋Non-Boussinesq流的地形重力波拖曳解

用WKB近似方法建立了表达三维地形重力波拖曳的解析Non-Boussinesq扰动模型,其中在大Richardson数条件下给出了(静力和非静力模型的)重力波拖曳及其地表扰动气压的二阶表达式.通过针对经典的理想化三维圆钟型山体的一个算例证明,当基流风速切变为线性时,重力波拖曳随着切变的增强而减弱;并且前向垂直切变(forward-shear,风速随高度增加)所对应的重力波拖曳比反向切变(backward-shear,风速随高度减小)所对应的重力波拖曳减弱得更快.这种现象与模型是否采用静力近似无关.     

Numerical and Experimental Investigation of the Burst Resistance of Glass-Fiber Thermoplastic Composite Pipes under Internal Pressure

Mechanics of Composite Materials - Experimental tests and numerical studies were performed to investigate the burst performance of thermoplastic composite pipes (TCPs) under internal pressure. A...     

关于行列式计算的另类降阶法

由于二阶行列式的计算仅须求两对角线元素的乘积之差,所以计算非常简单．一般地,对高阶行列式求值,虽然可用Laplace展开公式或Gauss消去法,但是展开式会非常繁杂或计算量会很大．本文利用降阶原理,得到一种只需计算二阶行列式就可求出n（n≥3）阶方阵行列式值的另类方法．     

扁球旋转大气阻力对人造卫星运动的影响

描述了在地球扁率和大气阻力联合作用的人造卫星运动。导出了系统的哈密顿运动方程，其中包括括直到J4的重力热带调和函数的阻力加速度。大气模型采用带扁椭球旋转模型，随着离地距离的增加，大气旋转滞后于地球旋转，首先，借助两次正则变换，接连消去短期项和长期项求得无阻力问题的解，然后再定义一个算子，并利用无阻力问题中带“两撇形式的变量”，给出求解阻力速度的公式。