共查询到20条相似文献,搜索用时 78 毫秒
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采用四球摩擦磨损试验机对表面修饰的纳米AlOOH粒子及纳米Fe3O4粒子在液体石蜡中的摩擦学性能进行了对比研究.结果表明:这2种纳米粒子均能提高液体石蜡的减摩耐磨性能和PB值,纳米AlOOH粒子因具有层状结构,表现出更好的减摩耐磨性能,随着纳米粒子粒径的增大,其减摩耐磨的最佳浓度出现升高的趋势.对磨斑表面的SEM、AFM和XPS分析结果表明,纳米粒子能沉积在摩擦副表面,减少摩擦副表面微凸体的直接接触,从而减少微凸体之间的犁削和黏着. 相似文献
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密度不同的颗粒在流体中的沉降特性 总被引:1,自引:0,他引:1
采用格子Boltzmann方法(LBM)对雷诺数范围为5≤Re≤12的双颗粒沉降进行了直接数值模拟研究,主要关注颗粒之间的密度差异k对其周期性振动的影响。根据雷诺数颗粒沉降特性可以分成三个阶段,即当Re较小时,颗粒的振动幅度随k的增大而减小,当Re较大时则正好相反,介于两者之间存在一个临界雷诺数,在此雷诺数附近,颗粒的沉降同时具有以上两种特征。同时还研究了两个颗粒的稳定沉降结构以及重颗粒摆脱轻颗粒的条件。 相似文献
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人体在吸入纳米颗粒时肺部的第一道生物屏障是肺表面活性剂(lung surfactant, LS),吸入的纳米颗粒可以到达肺部深处,从而干扰肺部的生物物理性能。目前关于金纳米粒子与LS单层的相互作用的机制研究及金纳米粒子对肺部功能的影响尚不清楚。本文使用粗粒化的分子动力学方法,研究了金纳米粒子与LS单层膜在纳米尺度上的相互作用,观察到金纳米粒子的存在使得单层膜的结构变形,改变了膜的生物物理性能,并且不同形状的纳米粒子对单层膜的影响也不相同。这些发现有助于识别空气中的纳米粒子对肺部的潜在影响。 相似文献
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受体介导的内吞是细胞与外界物质交换的常见方式. 采用配体修饰表面的纳米脂质体颗粒,将药物有针对性地投放到肿瘤细胞 以提高药物传输的效率,是药物传 输系统设计中的核心问题之一. 本文假设内吞是准静态过程,采用三维数学模型来模拟球状纳米颗粒的内吞,建立了包含绑定键的系统变形能方程,通过求 解能量方程的最小值,得到药物在每个内吞包裹阶段的变形以及药物的被动内吞所需最小能量,分析不同药物半径对内吞所 需最小能量的影响. 研究表明,细胞膜变形能与绑定键变形能占总能量的绝大部分,各组分随着包裹区域增加均有变化;在给定细胞膜和药物颗 粒的硬度、绑定键强度等物理特性下存在最优药物尺寸,使得内吞过程中总能耗最小;在药物内吞进行的后期,包裹区域边 缘的绑定键因伸长过大发生断裂,影响内吞的顺利完成. 本研究为受体介导的高效药物设计提供了理论支撑. 相似文献
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通过二次开发技术,将Merkle、Kunz、Kubota、Singhal四种不同的质量传输模型和液氮物质属性随温度变化函数等引入了计算软件CFX。在考虑热力学效应的条件下,对绕翼型的液氮空化流动进行了数值计算,并与实验结果进行对比分析。结果表明:由于传输方程的物理机制不同,造成各模型的计算结果尤其是对热力学效应影响的描述存在明显的差别。Merkle模型计算得到的压力和温度分布与实验最为接近,质量传输过程能较好地反映温度场变化的影响,从而能较好地反映热力学效应对空化发展的影响;Singhal模型计算得到的结果与实验数据差距最大,其模拟得到的质量传输过程不能很好地反应温度流场的变化的影响。 相似文献
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Nanoparticle transport and deposition in bends with circular cross-section are solved for different Reynolds numbers and Schmidt numbers. The perturbation method is used in solving the equations. The results show that the particle transport patterns are similar and independent of the particle size and other parameters when suspended nanoparticles flow in a straight tube. At the outside edge, particle deposition is the most intensive, while deposition at the inside edge is the weakest. In the upper and lower parts of the tube, depositions are approximately the same for different Schmidt numbers. Curvatures of tube, Reynolds number, and Schmidt number have second-order, forth-order, and first-order effects on the relative deposition efficiency, respectively. 相似文献
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Using k-εmodel of turbulence and measured wall functions.turbulent flows ofNewtonian(pure water)and a sort of non-Newtonian fluid(dilute,drag-reduction solutionof polymer in a180-degree curved bend were simulated numerically.The calculated resultsagreed well with the measured velocity profiles.On the basis of calculation andmeasurement,appropriateness of turbulence model to complicated flow in which the large-scale vortex exists was analyzed and discussed. 相似文献
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Turbulent flow through a duct of square cross-section gives rise to off-axis secondary flows, which are known to transfer momentum between fluid layers thereby flattening the velocity profile. The aim of this study is to investigate the role of the secondary flows in the transport and dispersion of particles suspended in a turbulent square duct flow. We have numerically simulated a flow through a square duct having a Reynolds number of Reτ = 300 through discretization of the Navier–Stokes equations, and followed the trajectories of a large number of passive tracers and finite-inertia particles under a one-way coupling assumption. Snapshots of particle locations and statistics of single-particle and particle pair dispersion were analyzed. It was found that lateral mixing is enhanced for passive tracers and low-inertia particles due to the lateral advective transport that is absent in straight pipe and channels flows. Higher inertia particles accumulate close to the wall, and thus tend to mix more efficiently in the streamwise direction since a large number of the particles spend more time in a region where the mean fluid velocity is small compared to the bulk. Passive tracers tend to remain within the secondary swirling flows, circulating between the core and boundary of the duct. 相似文献
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The results of an experimental study to investigate the local pressure drop characteristics in a square cross-sectioned smooth channel with a sharp 180° bend rotating about an axis normal to the free-stream direction are reported here. The sharp 180° turn was obtained by dividing a rectangular passage into two channels using a divider wall with a rounded tip at the location where the flow negotiates the turn. The study was carried out for three ratios of divider wall thickness to hydraulic diameter (W/D), namely, 0.24, 0.37 and 0.73 all with a rounded tip divider wall and only for a bend with a W/D ratio of 0.37, the influence of a sharp tip divider wall was studied. Experiments were conducted for a Reynolds number varying from 10 000 to 17 000 with the rotation number (ωD/V) varying from 0 to 0.38. The pressure drop distribution, normalized with the mainstream fluid dynamic pressure head, is presented for the leading, trailing and the outer surfaces. The results indicate that the local pressure drop characteristics in the bend region are significantly affected by a change in the rotation number but the influence of the Reynolds number is weak. The friction factor is less sensitive to rotation for the bend with a W/D ratio of 0.24 when compared to bends with W/D ratios of 0.37 and 0.73. Friction factor correlations are presented which fit the experimental data within 10% for the range of parameters studied. 相似文献
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Turbulent heat transfer in a ribbed square duct of three different blockage ratios are investigated using direct numerical simulation (DNS). The results of ribbed duct cases are compared with those of a heated smooth duct flow. It is observed that owing to the existence of the ribs and confinement of the duct, organized secondary flows appear as large streamwise-elongated vortices, which intensely interact with the rib elements and four sidewalls and have profound influences on the transport of momentum and thermal energy. This study also shows that the drag and heat transfer coefficients are highly sensitive to the rib height. It is observed that as the rib height increases, the impinging effect of the flow on the windward face of the rib strengthens, leading to enhanced rates of turbulent mixing and heat transfer. The influence of sidewalls and rib height on the turbulence structures associated with temperature fluctuations are analyzed based on multiple tools such as vortex swirling strengths, temporal auto-correlations, spatial two-point cross-correlations, joint probability density functions (JPDF) between the temperature and velocity fluctuations, statistical moments of different orders, and temperature spectra. 相似文献
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为研究方形蜂窝铝板在爆炸荷载作用下的动力学响应,基于LS-DYNA非线性有限元软件,建立了TNT炸药-前后面板-蜂窝夹芯-空气的三维有限元模型。采用ALE(任意的拉格朗日欧拉)多物质流固耦合算法分析了蜂窝铝板在冲击荷载作用下的变形机理、塑性变形、能量吸收以及结构的优化。数值模拟结果表明:随着面板厚度、核心高度的增加,蜂窝铝板在冲击荷载作用下的塑性变形明显减小,抵抗变形的能力增强;随着爆轰入射角度的增加,结构的破坏程度有所减小,入射角越大这种效果越发明显。对结构给定边长和受冲击面积以及面板厚度配合比、夹芯量纲为一的高度进行了局部的优化分析,为设计优质铝蜂窝板提供参考。 相似文献
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In this paper, a detailed investigation on the flow past a porous covering cylinder is presented through the lattice Boltzmann method. The Brinkman‐Forchheimer‐extended Darcy model is adopted for the entire flow field with the solid, fluid, and porous medium. The effects of several parameters, such as porous layer thickness, Darcy number, porosity, and Reynolds number on flow field are discussed. Compared with the case of a solid cylinder, the present work shows that the porous layer may play an important role on the flow, the lift and drag force exerted on the cylinder. The numerical results indicate that the maximal drag coefficient Cd and maximal amplitude of lift coefficient Cl exist at certain Darcy number which is in the range of 10?6–10?2. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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含污染物的弱弯曲明渠弯道湍流数值模拟 总被引:3,自引:0,他引:3
建立了可模拟弯道中含污染物湍流的三维部分抛物型代数应力模型。针对左右两岸分别泄放污染物的环流非充分发展弯道流进行了计算。分析了水流结构及污染物浓度分布的特点。 相似文献