Rayleigh waves in an isotropic elastic half-space coated by a thin isotropic elastic layer with smooth contact

In the present paper, we are interested in the propagation of Rayleigh waves in an isotropic elastic half-space coated with a thin isotropic elastic layer. The contact between the layer and the half space is assumed to be smooth. The main purpose of the paper is to establish an approximate secular equation of the wave. By using the effective boundary condition method, an approximate, yet highly accurate secular equation of fourth-order in terms of the dimensionless thickness of the layer is derived. From the secular equation obtained, an approximate formula of third-order for the velocity of Rayleigh waves is established. The approximate secular equation and the formula for the velocity obtained in this paper are potentially useful in many practical applications.     

GAS WAVE IN FUNCTIONALLY GRADED MAGNETO-ELECTRO-ELASTIC COUPLED STRUCTURE

研究了由均匀磁电弹半空间和功能梯度磁电弹层组成的耦合结构中间隙波的传播特性.假定功能梯度层的材料性能沿厚度方向呈指数变化,且其表面机械自由,但承受两种电磁边界条件.首先推导了频散方程,然后结合数值算例分析了功能梯度层材料性能的梯度变化、厚度及电磁边界条件对相速度的影响,结果对功能梯度磁电弹材料在声波器件中的应用具有参考价值.     

GAS-KINETIC UNIFIED ALGORITHM FOR BOLTZMANN MODEL EQUATION IN ROTATIONAL NONEQUILIBRIUM AND ITS APPLICATION TO THE WHOLE RANGE FLOW REGIMES

基于过去开展稀薄自由分子流到连续流气体运动论统一算法框架,采用转动惯量描述气体分子自旋运动,确立含转动非平衡效应各流域统一玻尔兹曼模型方程.基于转动能量对分布函数守恒积分,得到计及转动非平衡效应气体分子速度分布函数方程组,使用离散速度坐标法对分布函数方程所依赖速度空间离散降维;应用拓展计算流体力学有限差分方法,构造直接求解分子速度分布函数的气体动理论数值格式;基于物面质量流量通量守恒与能量平衡关系,发展计及转动非平衡气体动理论边界条件数学模型及数值处理方法,提出模拟各流域转动非平衡效应玻尔兹曼模型方程统一算法.通过高、低不同马赫数1：5～25氮气激波结构与自由分子流到连续流全飞行流域不同克努森数（9×10^-4～10）Ramp制动器、圆球、尖双锥飞行器、飞船返回舱外形体再入跨流域绕流模拟研究,将计算结果与有关实验数据、稀薄流DSMC模拟值等结果对比分析,验证统一算法模拟自由分子流到连续流再入过程高超声速绕流问题的可靠性与精度.     

ACOUSTOELASTIC THEORY FOR FLUID-SATURATED POROUS MEDIA

Based on the finite deformation theory of the continuum and poroelastic theory, the aeoustoelastic theory for fluid-saturated porous media （FSPM） in natural and initial coordi- nates is developed to investigate the influence of effective stresses and fluid pore pressure on wave velocities. Firstly, the assumption of a small dynamic motion superimposed on a largely static pre- deformation of the FSPM yields natural, initial, and final configurations, whose displacements, strains, and stresses of the solid-skeleton and the fluid in an FSPM particle could be described in natural and initial coordinates, respectively. Secondly, the subtraction of initial-state equations of equilibrium from the final-state equations of motion and the introduction of non-linear constitu- rive relations of the FSPM lead to equations of motion for the small dynamic motion. Thirdly, the consideration of homogeneous pre-deformation and the plane harmonic form of the small dynamic motion gives an acoustoelastic equation, which provides analytical formulations for the relation of the fast longitudinal wave, the fast shear wave, the slow shear wave, and the slow longitudinal wave with solid-skeleton stresses and fluid pore-pressure. Lastly, an isotropic FSPM under the close-pore jacketed condition, open-pore jacketed condition, traditional unjacketed condition, and triaxial condition is taken as an example to discuss the velocities of the fast and slow shear waves propagating along the direction of one of the initial principal solid-skeleton strains. The detailed discussion shows that the wave velocities of the FSPM are usually influenced by the effective stresses and the fluid pore pressure. The fluid pore-pressure has little effect on the wave velocities of the FSPM only when the components of the applied initial principal solid-skeleton stresses or strains are equal, which is consistent with the previous experimental results.     

Motion of a spherical particle in a fluid forced vortex by DO M and DTM

In this study, coupled equations of the motion of a particle in a fluid forced vortex were investigated using the differential transformation method （DTM） with the Pad6 approximation and the differential quadrature method （DO_M）. The significant contribution of the work is the introduction of two new, fast and efficient solutions for a spherical particle in a forced vortex that are improvements over the previous numerical results in the literature. These methods represent approximations with a high degree of accuracy and minimal computational effort for studying the particle motion in a fluid forced vortex. In addition, the velocity profiles （angular and radial） and the position trajectory of a particle in a fluid forced vortex are described in the current study.     

考虑延迟效应的交通流宏观流体力学模型

【目的】研究延迟效应的高阶宏观流体力学模型及其对交通流密度波产生的影响。【方法】通过宏观转化法将微观量转换成宏观量,推导出关于延迟效应的高阶动力学模型。同时结合交通流的守恒连续性方程,对新的动力学模型进行线性分析和非线性分析。用迎风格式数值模拟研究在不同延迟时间和密度下的交通流的成簇效应和系统的稳定性。【结果】推导出的模型具有各向异性的特性。在线性稳定性分析和非线性分析中分别推导出在微扰的条件下交通流的稳定性条件和描述密度波的KdV-Burgers方程,并求得密度波解。数值模拟结果表明考虑了延迟效应的模型系统不稳定状态范围在缩小。【结论】考虑了延迟效应的宏观流体力学模型,交通流成簇效应减弱。这表明交通流的拥堵得到抑制,有利于系统稳定。     

基于OpenFOAM的正弦形沙丘表面流场特性研究

基于开源计算流体力学软件OpenFOAM,对沙丘表面流场进行数值模拟,将所得到的沙丘表面风速分布与野外观测结果进行对比,验证数值模拟的准确性.在此基础上,获得了距沙丘表面不同高度的速度分布曲线和沙丘表面上的速度矢量场,探讨了数值模拟结果对计算网格的敏感性,考察了沙丘宽高比对流场特性的影响.结果表明:OpenFOAM的标准k-ε模型能够预测低矮正弦形沙丘表面流场的速度转变特性;在贴近沙丘表面的内层,沙丘表面特定高度处的速度分布曲线相对于沙丘轮廓存在相位提前,随着高度的增加,相位提前量减少,速度变化趋于平缓;网格数目对外层速度分布影响较小,但对内层的速度分布则有重要影响;足够多的网格数目是获得精确的沙丘表面流场信息的必要条件,在沙丘流场数值模拟中应当引起重视;保持沙丘宽度不变,随着沙丘宽高比的减小,沙丘表面速度分布曲线的相位提前量变大,背风坡出现回流区,宽高比越小,回流区的长度与强度越大.     

磁化处理的全尾砂料浆沉降参数优化模型

为了提高全尾砂料浆的脱水浓缩效果,将磁化处理技术引入到全尾砂料浆脱水浓缩中,并建立GA-SVM模型优选全尾砂料浆的沉降参数。建立支持向量机(SVM)沉降参数优化模型,以磁感应强度、磁化处理时间、料浆流速、料浆浓度、絮凝剂单耗为输入因子,沉降速度为综合输出因子,通过正交试验建立样本数据对SVM模型进行训练与检验,采用遗传算法(GA)对SVM模型参数进行优化,进而得到磁化全尾砂料浆沉降参数的GA-SVM优化模型。将GA-SVM模型运用到某铁矿磁化全尾砂料浆沉降参数优化中,得到的最佳沉降参数为磁感应强度0.192T、磁化处理时间1.85min、料浆速度1.92m/s、PAC单耗28g/t,沉降速度可达约155cm/h。研究表明:适宜的磁化处理条件可提高全尾砂料浆的脱水浓缩效果,节约30.0%~42.5%PAC用量,GA-SVM模型对全尾砂料浆沉降参数预测结果相对误差在5%以内、预测精度高,为全尾砂料浆脱水浓缩及其参数优选提供了一种新思路。     

双基地FDA-MIMO雷达角度、距离及速度联合估计方法

在传统的相控阵雷达中,由于受到脉冲重复周期(PRF)的限制,距离估计精度和速度估计精度往往难以同时得到提高。该文将频控阵(FDA)和双基地多输入多输出(MIMO)雷达相结合,提出了一种基于双基地FDA-MIMO雷达的角度、距离及速度联合估计方法。由于采用了FDA技术,雷达的发射矢量中包含了目标的角度、距离甚至速度信息。考虑到发射矢量中距离-速度的耦合现象,该文提出了基于子阵的波形设计和相应的解耦合方法。然后利用ESPRIT算法和基于FDA的解模糊方法,对目标的发射角(DOD)、接收角(DOA)、距离和速度进行无模糊估计。另外,该文推导了该方法下参数估计的克拉美罗界(CRB)并分析了其性能。最后,仿真结果验证了所提出方法的能够对目标的角度、距离和速度进行无模糊的联合估计。     

路面行驶质量差异的当量出行时间费用

以国际平整度指数为中间指标,构建路面行驶质量指数与出行时间费用之间的定量关系,给出路面行驶质量变化带来的当量出行时间费用差异.通过已有四分之一车模型的动力方程,以高速公路为研究对象,对选定的50条道路在13个速度下的国际平整度指数进行仿真计算.以国际平整度指数为中间指标,利用已有不同速度下平整度指数与行驶质量指数的关系,给出每条道路在不同速度下的行驶质量指数.以80km·h-1的路面行驶质量指数为基准,给出了路面行驶质量指数差异与达到相同行驶质量时的行驶车速差异之间的关系.分析结果表明,两者具有良好的相关性.路面行驶质量变化对出行时间费用有显著影响,在出行选择行为分析、道路维修养护效益评估等相关研究中应予以考虑.