Plane Deformations in Incompressible Nonlinear Elasticity

The substantially general class of plane deformation fields, whose only restriction requires that the angular deformation not vary radially, is considered in the context of isotropic incompressible nonlinear elasticity. Analysis to determine the types of deformations possible, that is, solutions of the governing systems of nonlinear partial differential equations and constraint of incompressibility, is developed in general. The Mooney-Rivlin material model is then considered as an example and all possible solutions to the equations of equilibrium are determined. One of these is interpreted in the context of nonradially symmetric cavitation, i.e., deformation of an intact cylinder to one with a double-cylindrical cavity. Results for general incompressible hyperelastic materials are then discussed. The novel approach taken here requires the derivation and use of a material formulation of the governing equations; the traditional approach employing a spatial formulation in which the governing equations hold on an unknown region of space is not conducive to the study of deformation fields containing more than one independent variable. The derivation of the cylindrical polar coordinate form of the equilibrium equations for the nominal stress tensor (material formulation) for a general hyperelastic solid and a fully arbitrary cylindrical deformation field is also given. This revised version was published online in August 2006 with corrections to the Cover Date.     

The influence of semiconducting properties of passive films on the cavitation erosion resistance of a NbN nanoceramic coating

To alleviate the cavitation damage of metallic engineering components in hydrodynamic systems operating in marine environments, a NbN nanoceramic coating was synthesized on to a Ti-6Al-4V substrate via a double cathode glow discharge technique. The microstructure of the coating consisted of a ~13 μm thick deposition layer of a hexagonal δ′-NbN phase and a diffusion layer ~2 μm in thickness composed of face-centered cubic (fcc) B1-NaCl–structured (Ti,Nb)N. The NbN coating not only exhibited higher values of H/E and H²/E than those measured from NbN coatings deposited by other techniques, but also possessed good adhesion to the substrate. The cavitation erosion resistance of the NbN coating in a 3.5 wt% NaCl solution was investigated using an ultrasonic cavitation-induced apparatus combined with a range of electrochemical test methods. Potentiodynamic polarization measurements demonstrated that the NbN coated specimens demonstrated both a higher corrosion potential (E_corr) and lower corrosion current density (i_corr) than the uncoated substrate. Mott-Schottky analysis, combined with the point defect model (PDM), revealed that, for a given cavitation time, the donor density (N_D) of the passive film on the NbN coating was reduced by 1 ~ 2 orders of magnitude relative to the uncoated Ti-6Al-4V, and the diffusivity of the point defects (D₀) in the passive film grown on the NbN coating was nearly one order of magnitude lower than that on the uncoated substrate. In order to better understand the experimental observations obtained from Mott-Schottky analysis and double-charge layer capacitance measurements, first-principles density-functional theory was employed to calculate the energy of vacancy formation and the adsorption energy for chloride ions for the passive films present on both the NbN coating and bare Ti-6Al-4V.     

Luminescence intensity of vortex cavitation in a Venturi tube changing with cavitation number

Hydrodynamic cavitation in a Venturi tube produces luminescence, and the luminescence intensity reaches a maximum at a certain cavitation number, which is defined by upstream pressure, downstream pressure, and vapor pressure. The luminescence intensity of hydrodynamic cavitation can be enhanced by optimizing the downstream pressure at a constant upstream pressure condition. However, the reason why the luminescence intensity increases and then decreases with an increase in the downstream pressure remains unclear. In the present study, to clarify the mechanism of the change in the luminescence intensity with cavitation number, the luminescence produced by the hydrodynamic cavitation in a Venturi tube was measured, and the hydrodynamic cavitation was precisely observed using high-speed photography. The sound velocity in the cavitating flow field, which affects the aggressive intensity of the cavitation, was evaluated. The collapse of vortex cavitation was found to be closely related to the luminescence intensity of the hydrodynamic cavitation. A method to estimate the luminescence intensity of the hydrodynamic cavitation considering the sound velocity was developed, and it was demonstrated that the estimated luminescence intensity agrees well with the measured luminescence intensity.     

叶片背面不连续凸起对轴流泵空化的控制研究

为控制轴流泵空化的发生与发展,提出了一种在轴流泵叶片背面布置不连续凸起结构的方案。基于ANSYS CFX软件,对350ZQ-125-30型潜水轴流泵进行数值模拟,对比分析改进模型与原模型流道内压力、湍动能、空泡及流线分布的变化.结果表明,改进后叶片背面低压区域减小,工作面高压区域明显增大,临界空化余量降低;在空化的各个阶段空泡体积分数都有所减小,其中空化初生阶段最为明显,相比原模型减小了38.3%,有效地控制了空化的发生,空化性能明显提升;在空化发展阶段,凸起的存在能够有效阻挡回射流的冲击,控制了空泡的脱落,同时抑制了叶轮流道内梢涡空化的产生。     

Effects of gas saturation and sparging on sonochemical oxidation activity in open and closed systems,part II: NO2−/NO3− generation and a brief critical review

The sonochemical generation of NO₂⁻ and NO₃⁻ is considered to be one of the reasons for the low sonochemical oxidation activity in the presence of N₂ in the liquid phase. In this study, the generation characteristics of NO₂⁻ and NO₃⁻ were investigated using the same 28 kHz sonoreactor and the 12 gas conditions used in Part I of this study. Three gas modes, saturation/closed, saturation/open, and sparging/closed, were applied. N₂:Ar (25:75), N₂:Ar (50:50), and O₂:N₂ (25:75) in the saturation/closed mode generated the three highest values of NO₂⁻ and NO₃⁻. Ar and O₂ were vital for generating relatively large concentrations of NO₂⁻ and NO₃⁻. The absorption of N₂ from the air resulted in high generation of NO₂⁻ and NO₃⁻ for Ar 100 % and Ar/O₂ mixtures under the saturation/open mode. In addition, gas sparging enhanced the generation of NO₂⁻ and NO₃⁻ for N₂:Ar (25:75), O₂:N₂ (25:75), and N₂ significantly because of the change in the sonochemically active zone and the increase in the mixing intensity in the liquid phase, as discussed in Part I. The ratio of NO₃⁻ to NO₂⁻ was calculated using their final concentrations, and a ratio higher than 1 was obtained for the condition of Ar 100 %, Ar/O₂ mixtures, and O₂ 100 %, wherein a relatively high oxidation activity was detected. From a summary of the results and findings of previous studies, it was revealed that the observations of NO₂⁻ + NO₃⁻ could be more appropriate for investigating the NO₂⁻ and NO₃⁻ generation characteristics. In addition, H₂O₂/NO₂⁻/NO₃⁻ related activity rather than H₂O₂ activity was suggested to quantify the OH radical activity more appropriately in the presence of N₂.     

双泡模型共振频率的超声空化动力学研究

该研究旨在研究双泡模型的自然共振频率对超声空化的影响,通过理论计算研究了自然共振频率的影响因素,以及单频超声和双频超声与自然共振频率的关系。研究结果表明：气泡初始半径是影响自然共振频率的主要因素;低频驱动下的非线性波动程度会比高频的更加剧烈,当驱动频率等于气泡自然共振频率时,超声空化的效果更好;双频超声取气泡自然共振频率时超声空化效果远远优于单频超声驱动。该研究在超声医学和理解超声空化特性方面有着重要的意义。     

旋转圆盘空蚀试验中的硅材料破坏过程研究

利用自制旋转圆盘空蚀试验装置,以流动自来水为介质,对磨片、化抛片、抛光片和刻蚀片等4种硅片进行连续8 h试验以及对磨片进行连续14 h跟踪观察试验,研究硅材料的微观破坏过程,并利用扫描电子显微镜、触针式表面形貌仪和原子力显微镜对其表面微观形貌进行分析.结果表明:经连续8 h空蚀试验后,磨片原始表面的片状层基本消失,表面破坏程度最严重,化抛片次之,其表面尖锐的边缘发生了钝化,抛光片和刻蚀片的表面变化不大;化抛片的表面粗糙度Ra值由227.79 nm降至173.31 nm,抛光片的Ra值由0.483 nm增加至3.455 nm,磨片在14 h试验后其Ra值由0.3304 μm降至0.1965 μm;一定尺度的表面微观形貌对硅材料产生显著影响.     

水下航行体通气超空泡非对称性研究

超空化水下高速航行体为了满足运动平衡性和稳定性要求,需要采用非对称超空泡流动模式。为了探索满足要求的非对称超空泡流型,在水洞中开展了水下航行体通气超空泡非对称性实验研究。采用通气的方法在较低水速(V=7～12m/s)下生成人工超空泡,通过分析和测量不同弗劳德数、模型攻角、空化器攻角与舵角等实验条件下的超空泡图像,获得了航行体超空泡非对称性与影响因素之间的定量和定性关系。研究表明,当组合参数F_r~2(1 σ)>50时,重力引起的超空泡变形量小于5‰;由模型攻角、空化器攻角和舵角产生的非对称超空泡流型可以满足超空化水下航行体的平衡性要求。     

High-speed observation of ultrahigh-speed submerged water jets

Some peculiar phenomena occur around ultrahigh-speed submerged water jets accompanied by very severe cavitation erosion. Using the flow visualization technique with a xenon flash, the water jets were carefully observed, and the spatial distributions of highly erosive impulsive pressures around the jets were measured by means of a pressure-sensitive film technique. The effects of the injection pressure and the nozzle configuration are systematically clarified. Thus, the characteristics and structures of ultrahigh-speed submerged water jets are clearly shown.     

超声增强藻酸钙凝胶支架材料孔隙率的研究

藻酸钙凝胶具有三维立体多孔结构, 能为细胞生长提供充分的附着空间, 且具有良好的生物相容性和一定的机械强度, 是一种理想的细胞支架材料. 本文研究了藻酸钙三维支架材料的力学特性与氯化钙/藻酸钠的配比的关系, 并提出采用低强度脉冲超声处理藻酸钙凝胶、基于超声空化效应增强藻酸钙凝胶孔隙率的新方法. 实验采用交联合成方法制备藻酸钙凝胶支架材料, 测量力学特性、孔洞的联通性与孔隙率, 并利用绿色荧光蛋白的表达评价细胞的增殖能力. 结果表明, 当氯化钙/藻酸钠的配比为3:5时, 凝胶的机械强度和弹性较好, 力学性能稳定, 为最佳配比参数. 采用声压0.055 MPa的脉冲超声作用20 min, 可以有效提高凝胶支架的孔隙率; 且细胞在该支架中生长状态良好, 呈现团簇状生长趋势.