柱塞泵多目标优化设计及CFD仿真分析

液压泵噪声是液压系统的主要噪声源,针对轴向柱塞泵的流致振动噪声,提出一种改善泵配流特性的设计方案。首先,根据柱塞泵的工作原理对柱塞腔压力特性和泵出口流量特性准确建模并求解。通过分析压力冲击和流量脉动对错配角(φ0)的响应,得φ0=4°为佳。利用一种多目标遗传算法(NSGA-II),以减小压力超调量和流量脉动率为目标,对三角槽结构进行了优化;并获得该多目标优化问题的Pareto最优解集,通过对最优解集的分析知,深度角θ1=16°且宽度角θ2=85°时较为理想。最后,为了验证模型的正确性,建立流体域计算流体动力学(CFD)模型,对比两种模型计算结果发现吻合较好,能够相互验证。利用CFD分析结果可视化的特点,从柱塞泵流场的角度,进一步分析了泵压力冲击以及流量脉动产生的原因。     

基于转捩/尺度适应模型与FW-H声学方程的气动噪声数值模拟研究

采用计算流体力学(CFD)同"声类比"相结合的方法进行噪声模拟,利用CFD数值模拟 MD30P30N多段翼型失速攻角附近流场以及其气动特性来校核近场精度,进一步通过结合可穿透数据面的FW-H声学方程进行气动噪声分析。为了准确捕捉近场流场信息,为噪声预测提供可靠的声源精度,本文基于k-ω剪应力输运(SST)湍流模型,建立了尺度适应分离流(SAS)模型,并采用γ-Re_θt转捩模型耦合k-ω SST湍流模型建立了边界层转捩数值模拟技术;充分利用尺度适应模型在边界层表现为雷诺平均(RANS)方法这一特点,将γ-Re_θt转捩模型与SAS模型结合,建立针对包含转捩、分离现象复杂流场的数值模拟技术。文中以RANS为控制方程,分别采用全湍流k-ω SST模型、γ-Re_θtSAS转捩/分离流模型对多段翼进行近场数值模拟计算,结合可穿透数据面的FW-H声学方程进行气动噪声预测,在分析其对流场及气动噪声影响的基础上,得出了几点结论。     

On near-wall hot-wire measurements

A specially constructed hot-wire probe was used to obtain very near-wall velocity measurements in both a fully developed turbulent channel flow and flat plate boundary layer flow. The near-wall hot-wire probe, having been calibrated in a specially constructed laminar flow calibration rig, was used to measure the mean streamwise velocity profile, distributions of streamwise and spanwise intensities of turbulence and turbulence kinetic energy k in the viscous sublayer and beyond; these distributions compare very favorably with available DNS results obtained for channel flow. While low Reynolds number effects were clearly evident for the channel flow, these effects are much less distinct for the boundary layer flow. By assuming the dissipating range of eddy sizes to be statistically isotropic and the validity of Taylor's hypothesis, the dissipation rate ɛ _iso in the very near-wall viscous sublayer region and beyond was determined for both the channel and boundary layer flows. It was found that if the convective velocity U _c in Taylor's hypothesis was assumed to be equal to the mean velocity Uˉ at the point of measurement, the value of (ɛ⁺ _iso)₁ thus obtained agrees well with that of (ɛ ⁺)_DNS for y ⁺ ≥ 80 for channel flow; this suggests the validity of assuming U _c=Uˉ and local isotropy for large values of y ⁺. However, if U _c was assumed to be 10.6u _τ , the value of (ɛ⁺ _iso)₂ thus obtained was found to compare reasonably well with the distribution of (ɛ⁺ _iso)_DNS for y ⁺≤ 15. Received: 31 May 1999/Accepted: 20 December 1999     

Experiments on the effect of acceleration on the drag of tapwater bubbles

Three-dimensional (3D) trajectories of spherical air bubbles passing through a converging part of a rectangular channel have been measured. Bubble diameters, d _b, were less than 1 mm and the Reynolds numbers, Re _b, for stagnant tapwater and for mean liquid velocity vˉ _L=0.25 m/s were in about same range. Received: 15 January 2001 / Accepted: 12 June 2001     

近源堆沉积土石体细观结构与抗剪强度指标关联分析

细观结构是认知土石体力学行为本质的关键科学问题。本文通过引入物理学和数学等方法,借助颗粒物质力学理论,从几何排列与接触力的空间分布来定量刻画水平固结与山前坡地堆积两种典型环境下土石体的细观结构特征,并建立其与抗剪强度指标的关联。研究表明,（1）两种环境的土石体在细观结构上存在较大差异。在几何排列上,水平固结环境下的土石体具有长程无序和短程有序的特点,坡地堆沉积环境下的土石体表现出了无序的无定形结构;在接触力与单位接触向量的空间分布上,两者较为相似,绝大多数接触力以小于均值接触力的形式存在,其概率密度曲线P（f）呈幂函数衰减;90%以上接触方位角集中在40°~160°和220°~340°范围内。（2）基于径向分布函数、接触力概率密度和单位接触向量分别定义细观结构的特征量K_a,K_s和K_o,发现三个特征量的增大对内摩擦角呈线性促进作用,对黏聚力呈非线性削弱作用。     

On the free energy and variational theorem of elastic problem in thermal shock

In some investigations on variational principle for coupled thermoelastic problems, the free energy Φ(e_ij,θ) ,where the state variables are elastic strain e_ij and temperature increment θ, is expressed as Φ(e_ij,θ)=λ/2e_kke_ij=ue_k1e_k1-γe_kkθ-c/2 p θ²/T₀(0.1) This expression is employed only under the condition of |θ|≤T₀(absolute temperature of reference) But the value of temperature increment is great, even greater than T₀ in thermal shock. And the material properties (λ ,μ ,ν ,c , etc.) will not remain constant, they vary with θ. The expression of free energy for this condition.is derived in this paper. Equation (0.1) is its special case.Euler’s equations will be nonlinear while this expression of free energy has been introduced into variational theorem. In order to linearise, the time interval of thermal shock is divided into a number of time elements Δt_k, (Δt_k=t_k-t_k-1,k=1,2…,n), which are so small that the temperature increment θ_k within it is very small, too. Thus, the material properties may be defined by temperature field T_k-1=T(x₁,x₂,x₃,t_k-1) at instant t_k-1 , and the free energy Φ_k expressed by eg. (0.1) may be employed in element Δt_k.Hence the variational theorem will be expressed partly and approximately.     

Rheological aspects of dense lignite-water suspensions; time dependence, preshear and solids loading effects

An investigation of the rheological properties of dense lignite-water suspensions is reported here in order to evaluate the parameters that affect the rheology of these suspensions. Different types of particle size distributions were achieved via wet grinding with particle sizes down to 1 μm. Polyelectrolytes and surfactants were used to improve the stability and rheology of suspensions. The achieved solid volume fraction, φ, with acceptable rheological behavior was 0.45, while the ratio of φ/φ _m was close to 0.85; φ _m is the maximum solid volume fraction. Various types of flow tests were performed on lignite-water suspensions with various preshear times and stress levels. Typical shear rates varied in the range between 10^–2 to 10² s^–1. The low shear behavior was found to be quite different from the high shear behavior for the most concentrated suspensions, with a plateau value at low shear rates indicating the appearance of a yield stress. These plateau values, however, depend on shear history, which is responsible for the development of different structures in the sample. The viscosity curves corresponding to the ascending and descending parts of the flow curve were found to be different; these flow curve parts can be described either by well established models or by modified ones. The non-Newtonian time dependent behavior of the lignite-water suspensions is attributed to the high value of the ratio φ/φ _m , the polydispersity of the particle size distribution, and the non-spherical shape of the lignite particles.     

Studying the stability of equilibrium solutions in a planar circular restricted four-body problem

The Newtonian circular restricted four-body problem is considered. We obtain nonlinear algebraic equations determining equilibrium solutions in the rotating frame and find six possible equilibrium configurations of the system. Studying the stability of equilibrium solutions, we prove that the radial equilibrium solutions are unstable, while the bisector equilibrium solutions are stable in Lyapunov’s sense if the mass parameter satisfies the conditions μ ∈ (0, μ₀, where μ₀ is a sufficiently small number, and μ ≠ μ_j, j = 1, 2, 3. We also prove that, for μ = μ₁ and μ = μ₃, the resonance conditions of the third order and the fourth order, respectively, are satisfied and, for these values of μ, the bisector equilibrium solutions are unstable and stable in Lyapunov’s sense, respectively. All symbolic and numerical calculations are done with the Mathematica computer algebra system. Published in Neliniini Kolyvannya, Vol. 10, No. 1, pp. 66–82, January–March, 2007.     

The analytical solution for Helmholtz boundary problem in non-horizontally stratified domains

There are N domains D_j(j=0,1,...,N-1) of different physical parameters in the whole space and their interfaces S_j,i+1 are non-horizontally smooth curved surfaces. The following boundary problem is called Hclinholiz boundary problem:V²H⁽¹⁾+K_jH⁽¹⁾=0 (j=0,1,…,N-1)(H⁽⁰⁾-H⁽¹⁾)=δ(S) (δ(S):generalized function)(H¹-Hⁱ⁺¹)=0 (j=0,1,…,N-2)The analytical solution of the above problem is given in this paper.     

Havelock型格林函数振荡项数值积分的稳定性研究

Havelock型格林函数的传播项被积函数是高频振荡且奇异的复变函数,文献[4]引入变量代换获得了一种兼具积分效率和精度的积分方法, 本文研究了该方法的积分稳定性,发现该方法仍存在如下的积分困难: (1) θ=γ时复函数中分母为零引起的计算溢出;(2) θ=π/2是复函数在y及z方向偏导数的无穷间断点;(3) 场点与源点横坐标相同时伪奇异点变为真奇点。针对这些积分困难,采用极限公式计算θ=γ处复函数的值避免计算溢出;在保证积分精度的前提下采用截断方法略去θ=π/2邻近区域的积分消除无穷间断处的奇异;针对(3)采用分区法处理以避开原被积函数的高频振荡,并消除奇异性。伪奇异性存在的条件是场点必须在点源传播波的传播范围内,伪奇异点最多为2个。     

Preface

This special issue of PARTICUOLOGY is devoted to the first UK-China Particle Technology Forum taking place in Leeds, UK, on 1-3 April 2007. The forum was initiated by a number of UK and Chinese leading academics and organised by the University of Leeds in collaboration with Chinese Society of Particuology, Particle Technology Subject Group （PTSG） of the Institution of Chemical Engineers （IChemE）, Particle Characterisation Interest Group （PCIG） of the Royal Society of Chemistry （RSC） and International Fine Particle Research Institute （IFPRI）. The forum was supported financially by the Engineering and Physics Sciences Research Council （EPSRC） of United Kingdom,     

The 7th International Conference on Fluid Mechanics May 24-27,2015,Qingdao,China

正http://www.icfm7.org First Announcement and Call for PapersThe objective of International Conference on Fluid Mechanics(ICFM)is to provide a forum for researchers to exchange new ideas and recent advances in the fields of theoretical,experimental,computational Fluid Mechanics as well as interdisciplinary subjects.It was successfully convened by the Chinese Society of Theoretical and Applied Mechanics(CSTAM)in Beijing(1987,     

INFORMATION FOR CONTRIBUTORS

Contributions： The Journal, Acta Mechanica Solida Sinica, is pleased to receive papers from engineers and scientists working in various aspects of solid mechanics. All contributions are subject to critical review prior to acceptance and publication.     

Guide for authors

正Each of the sections below provides essential information for authors.We recommend that you take the time to read them before submitting a contribution to Acta Mechanica Sinica.We hope our guide to authors may help you navigate to the appropriate section.How to prepare a submission This document provides an outline of the editorial process involved in publishing a scientific paper in Acta Mechanica Sinica.     

基于鲁棒滤波的捷联导引头视线角速度估计方法

针对捷联导引头无法直接获取视线角速度等信息的问题,研究了鲁棒滤波在大气层外飞行器捷联导引头视线角速度估计中的应用。为了建立非线性滤波估计模型,考虑目标视线角速度的慢变特性,采用一阶马尔科夫模型建立了状态方程;推导了视线角速度的解耦模型,并建立了量测方程;考虑到实际应用中存在系统噪声统计特性失准的问题,基于Huber-Based鲁棒滤波方法,设计了视线角速度滤波器,并完成了基于Huber-Based滤波方法和扩展卡尔曼滤波方法的数学仿真。仿真结果表明Huber-Based滤波方法的视线角、视线角速度及视线角加速度估计精度分别达到0.1140'、0.1423'/s、0.0203'/s2,而扩展卡尔曼滤波方法的视线角、视线角速度及视线角加速度估计精度仅分别为0.6577'、0.6415'/s、0.0979'/s~2。仿真结果证明了该方法可以有效地估计出相对视线角速度等信息,并且在非高斯噪声的条件下,依然可获得较高的估计精度,具有一定的鲁棒性。     

Guide for authors

正Each of the sections below provides essential information for authors.We recommend that you take the time to read them before submitting a contribution to Acta Mechanica Sinica.We hope our guide to authors may help you navigate to the appropriate section.How to prepare a submission This document provides an outline of the editorial process involved in publishing a scientific paper in Acta Mechanica