用于气动声学计算的完全耦合层吸收边界条件

根据伪时均流假设,推导了波动量的非守恒非线性欧拉方程;采用频率变化的方法,给出了一个时间与空间坐标变换关系,并将波动量的非守恒非线性欧拉方程变换至新坐标系;通过复数变换方法引入阻尼,构建了斜流非守恒非线性x层、y层及角层完全耦合层(PML)吸收边界条件;最后用算例测试了该吸收边界条件的精度和收敛性。研究结果表明：当吸收层数等于10时,最大反射量不超过0.5%,并且随着PML层数的增加而迅速减小;当吸收层数为40层时,最大反射量小于0.1%,达到收敛;在背景斜流下,该PML吸收边界条件能较好地吸收熵波与声波,可用于气动声学计算。     

全欧拉方程的理想匹配层边界条件

首先从声学的角度推导出了线性欧拉方程理想匹配层（PML）边界条件的变换系数;然后推导了笛卡儿坐标系和柱坐标系下全欧拉方程的PML方程,并说明了线性欧拉方程的PML方程只是全欧拉方程的PML方程的一个特例;最后利用柱坐标系下全欧拉方程的PML方程作为出流边界条件,计算了喷气发动机进气道处的流场,用实例证明了全欧拉方程的PML方程的正确性。     

薄油膜厚度分布超声测量机制研究

为了测量机械设备中的薄油膜厚度分布,对超声测量薄油膜厚度分布的方法进行了理论研究。基于声波在三层介质中传播的相关理论,对中间层油膜厚度远小于油膜中入射声波波长的情况,结合具体边界条件,建立斜入射时超声波在三层介质中传播的反射系数弹簧模型,获得反射系数和油膜刚度的函数关系,进而由刚度获得油膜厚度;分析超声波入射频率、入射角度和油膜厚度对反射系数的影响规律,通过测量油膜中各点的反射系数即可获得相应点的油膜厚度,实现油膜厚度分布的测量。     

基于“可控涡”的小流量斜流压气机气动设计研究

斜流压气机兼具轴流和离心压气机的特点,目前已经成为了研究的热点。针对斜流压气机S弯流道的特点,提出采用两段Bezier曲线进行子午流道的一体化设计方法;推导了适用于斜流压气机的准正交坐标系下的控制方程;采用了考虑叶轮出口倾斜角度的Qiu滑移模型;应用"可控涡"设计方法进行了斜流压气机设计,并进行了全三维粘性数值模拟。结果表明:该叶轮具有较好的气动性能,设计点下压比为3.4529,效率为0.8544。     

旋转管式膜分离器流型的研究

采用三相异步电动机的输入电磁转速与三相异步电动机的实际转速之差的变化来表征两旋转圆筒间流场特性的参数。主要研究了清水介质时无轴向流和有轴向流条件下流型的划分,并将无轴向流时的流型分成了6种：Couette层流,层流泰勒涡,层流波涡,层流调制波涡、湍流泰勒涡和湍流;有轴向流时的流型分成了4种：Couene层流、层流泰勒涡、湍流泰勒涡和完全湍流。并且验证了流型转变的滞后特性。     

基于点云与图像匹配的自动化喷涂系统坐标变换

针对当前个性化定制产品的喷涂工作需求,研发了一套自动化喷涂系统。为了实现系统中的坐标变换功能,提出一种基于点云与图像匹配的坐标变换方法。利用摄像机和三维扫描仪分别获取喷涂对象的二维图像和三维点云,并将点云进行投影获得点云投影图像;通过改进canny算子提取二维图像和点云投影图像的闭合边缘;计算得到边缘各点的曲率并将其展开为曲率链码的形式进行匹配,建立了点云坐标系与机器人坐标系的变换关系。通过实验验证了该方法的可行性。     

双层结构碳黑/ABS复合材料的吸波性能

制备了单、双层结构碳黑／ABS复合吸波材料,并对其在8～12GHz频段内的吸波性能进行了研究,比较了两种结构以及不同组合双层结构的吸波效能。结果表明：双层碳黑／ABS的吸波性比单层结构有明显改善。双层结构设计参数对吸波性能也有不同程度的影响,当吸收层参数一定时,用5％碳黑／ABS作为变换层吸波效果略好;当变换层参数一定时,吸收层中碳黑含量30％,或者吸收层厚度增至6mm,双层结构的吸波性能都得到了明显改善。较佳的双层结构组合为：3mm厚含5％碳黑的变换层加6mm厚含30％碳黑的吸收层。     

声表面波与声板波激发特性对比研究

通过沉积在压电基片表面的叉指换能器可在基片上激发出声波。以部分波理论为基础,引入表面有效介电常数方法来对比研究压电基片上激发的声表面波和声板波,并通过实验证明了理论分析方法的有效性。特定切向和传播方向的压电晶体只能激发出一种声表面波模式,而其声板波则具有多种模式,且各高阶模式只有当基片厚度与声波波长之比大于某一特定值时才会出现。随着基片厚度增大,声板波各高阶模式的传播速度和机电耦合系数减小,两种低阶模式的传播速度则趋近于声表面波相应值。受基片背面的电学边界条件影响,其中一种低阶模式的机电耦合系数随着基片厚度增大而趋近于声表面波相应值,另一种低阶模式的机电耦合系数则接近于零。根据上述研究结果可以确定叉指电极激发声表面波或声板波的条件及两种声波之间的关系。
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表面等离子体激元透镜设计及其数值计算

提出了一种新的表面等离子体激元透镜的设计方案,该方案通过在两个亚波长小孔的外表面放置电介质光栅实现对入射光束的有效会聚。利用遗传算法研究了波导中表面等离子体激元的色散关系,结果表明,通过调节亚波长小孔的宽度和介电常数可以有效地调控有效折射率,从而实现对亚波长金属平板波导结构中表面等离子体激元传播特性的调控。利用时域有限差分方法(FDTD)结合完美匹配层(PML)边界条件数值模拟了此结构中的光场分布,讨论了光栅周期数对成像特性的影响,从而深入理解了纳米聚焦效应的物理机制。结果显示,随着表面光栅数的增多,焦距和焦斑大小都在增加。光栅数从5增加至11时,焦距由1.715μm增大至2.325μm,焦斑大小由0.615μm增大至1.715μm,这一结构有可能被用作未来集成光路中的纳米聚焦器件。     

基于激光超声技术的探损检测技术研究

超导声波结构损伤比较敏感,传输距离长、传输衰减小,在无损领域的应用越来越广泛。激光超声检测分辨率高、不需要接触等,在无损检测领域已成为新的研究热点问题。深入讨论和研究了基于激光超声技术的结构损伤检测方法,完成激光超声检测系统的搭建,并对该系统的硬件和控制方法进行了分析和研究,对Lamb波的传播状态和损伤之间的关系进行分析。从复波小波变换和色散能量补偿聚焦2个不同的角度进行信号分析和特征提取。完成小波变换法对铝板的损伤成像。为以后的实际工程应用,提供借鉴和参考。     

Time accurate finite difference method for performance prediction of a silencer with mean flow and nonlinear incident wave

Transmission losses of various reactive silencers are predicted, using a time accurate finite difference method. The numerical scheme is the 3rd order upwind scheme for axisymmetric Euler equations. Main advantage of the present method is that it can simulate linear and nonlinear wave propagation phenomena in a flow field directly with minimum numerical oscillation errors. The special treatments of incident wave condition, i.e. multiple harmonics of the transparent acoustic condition are applied to the transmission loss prediction for calculation efficiency. For the validation of the present approach, circular expansion chamber silencers without mean flow and an exponential pipe with mean flow are simulated in case of linear incident wave. The computed transmission losses have quite good agreements with those of the others. The nonlinear incident wave case is also investigated to check the usefulness of this method. The periodicN wave is clearly captured without numerical oscillation errors, and the insertion losses of two different incident frequencies are compared.     

Morphological transformation of shock waves behind a flat plate

The interaction of a travelling shock with the shear layer of a flat plate is studied computationally. The Euler and Navier-Stokes equations are solved numerically on quadrilateral unstructured adaptive grids. The flat plate is installed horizontally on the central axis of a shock tube. The shear layer is first created by two shock waves at different speeds splitted by a flat plate. A series of small vortices is developed as a consequence in the shear layer. The shock wave reflected at the end wall impinges the shear layer. The complicated shock dynamics in the evolution to the pseudo-steady state is represented with the morphological transformation of a planar shock into an oblique shock.     

A numerical study on the effect of the flow control using bleeding systems in a bump-type inlet

In many supersonic inlets, several oblique shock waves are followed by a terminal normal shock wave. The normal shock-wave/turbulent boundary-layer interaction is critical with respect to its influence on the development of boundary layer throughout the subsonic diffuser and the total pressure recovery at the engine face. In the current study, the bump-type inlet was designed for two oblique shock waves and a normal shock wave. In addition, a porous surface was installed underneath the root of the normal shock wave. The effect of flow control on the interaction between the normal shock wave and turbulent boundary layer in supersonic inlets by using the bleeding system was investigated numerically and was evaluated with respect to the inlet performance parameters.

     

Using the PML ABC for Air/Soil Wave Interaction Modeling in the Time and Frequency Domains

The Perfectly Matched Layer (PML) and absorbing boundary condition (ABC) is applied to two-dimensional Finite Difference Time Domain (FDTD) and Finite Difference Frequency Domain (FDFD) simulations of wave interactions with a two-layer air and soil geometry. Since the soil medium is lossy and dispersive, modeling of wave propagation and scattering is significantly more difficult than for free space and pure dielectrics. In addition, specifying an ABC which efficiently prevents reflections from both the free space termination and the adjacent soil is challenging. The theoretical basis for terminating dispersive media for both the time and frequency domains is presented, and simulation results for plane wave and point source excitations are demonstrated. For the former case, scattering is computed from a buried mine-like target. Although the absorbing characteristics of the PML for the air/soil interface are not as good as for free space, it is shown that maximum local reflections of as low as –15dB for FDTD and –50dB for FDFD are possible.     

高粘度流体在三维内肋管中层流强化传热性能研究

以润滑油为工质,采用正交原理试验设计方法,对高粘度流体在叉排列三维内肋管中的流动和传热性能进行了研究。结果表明:离散的三维内肋结构能够促进高粘度流体在较低的雷诺数下完成从层流向湍流的转变。说明在高粘度流体的换热问题中,采用三维内肋管可以有效促进流态转变,并因此获得明显的传热强化效果;对试验数据采用最小二乘法进行多元线性回归,获得了三维内肋管中高粘度流体在层流区的流阻和换热准则方程式;根据Webb定义的热力性能系数,作为强化传热性能的判断指标,得到了性能最优的三维肋结构组合,为结构优化指出了方向。     

Reconstruction of time-domain impedance boundary condition considering the incident intensity effect on perforated-plate acoustic liner

Based on impedance prediction methods for a perforated plate acoustic liner, time-domain impedance boundary conditions are enhanced with consideration of incident intensity. The impedance coefficient of the time-domain boundary condition is re-derived using parameters of the liner structure, and is classified by physical characteristics. To show the capability of the reconstructed impedance boundary condition, two numerical calculations are performed with comparison to analytical results. The first considers the one-dimensional wave propagation problem to account for the reflection wave due to an incident intensity variation on the acoustic liner. The second considers the excess attenuation of impedance surface. The numerical simulation is performed using the linearized Euler equations (LEEs). Dispersion-relation-preserving finite difference scheme and optimized Adams-Bashforth time-integration method are used spatial discretization / time integration, respectively. The numerical results show excellent agreement with analytical results. Moreover, a reconstruction method of impedance boundary condition can easily obtain the impedance coefficients under environments of variant magnitudes of incident waves.     

Oblique shock waves in dusty gas suspensions

The equations governing the flow field which is developed when a supersonic dusty-gas suspension passes through a straight oblique shock wave were formulated. A computer code for solving the governing equations was developed and used to obtain the solution for a variety of different intial conditions. In addition, the dependence of the post-shock suspension properties on the various physical properties of the dust particles, (namely the diameter of the dust particles, their specific heat capacity, their material density and the loading ratio of the dust in the suspension) was investigated.     

半空间内圆孔对稳态入射平面SH波的散射

利用复变函数方法、多极坐标移动技术和Graf加法公式讨论半空间内圆孔对稳态入射平面SH( shearing horizontal)波的散射问题.首先写出介质内的自由波场和散射波场,它们能够预先满足半空间边界自由应力条件;其次,利用Graf(格喇夫)加法公式,将虚源波函数进行数学变换,使之与圆孔产生的波函数共同表示为同一个无穷正交函数级数的形式;最后利用圆孔边界处的应力自由条件,得出确定散射波函数中未知系数的无穷线性代数方程组,该方法避免了散射波函数傅里叶级数展开中积分的数值计算,因而显著地提高收敛速度和计算精度.算例结果表明方法的可行性.     

对偶边界元法中对数奇异积分的计算

采用三次多项式坐标变换计算边界元积分的方法，对对偶边界法中含对数奇异积分的计算进行研究。几个解析积分算例和运用对偶边界元法以二给平面裂纹问题裂尖应力强度因子的计算结果表明，多项式坐标变换法对于计算对数奇异积分是一种简单有效的方法。