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91.
92.
海底作为声波在水中传播的下边界,其声学特性对水中声场分布的影响巨大。在近60年的研究中,海底沉积物的声学特性建模研究已取得众多成果,然而这些成果还远远不能满足现代化水声技术发展的要求。文章从基本的海底结构组成出发,在海底地声建模的基础上揭示出声波与海底的作用关系。 相似文献
93.
可变坡水槽作为研究水流及泥沙运动特性和水力学实验的一种设备已被广泛应用，本文论述了作者所研制的小型可变坡水槽的结构及其特点。 相似文献
94.
基于四种超声悬浮液模型Urick, Urick-Ament, HT, Mcclements分析了Scholte波在两相流体与多孔介质固体界面处的传播特性. 结合各模型的复波数表达式建立含泥沙流体-多孔介质固体界面波特征方程, 分析了Scholte波速与两相流体积含量、粒径等介质属性的关系. 通过仿真实验获得界面波信号, 运用时延估计获得Scholte波速与泥沙含量、粒径的关系, 发现所得的波速与Urick-Ament和HT理论有相对好的一致性.关键词：Scholte波两相流体多孔介质泥沙含量 相似文献
95.
The shear rheology of dense colloidal and granular suspensions is strongly nonlinear, as these materials exhibit shear-thinning and shear-thickening, depending on multiple physical parameters. We numerically study the rheology of a simple model of soft repulsive particles at large densities, and show that nonlinear flow curves reminiscent of experiments on real suspensions can be obtained. By using dimensional analysis and basic elements of kinetic theory, we rationalize these multiple rheological regimes and disentangle the relative impact of thermal fluctuations, glass and jamming transitions, inertia and particle softness on the flow curves. We characterize more specifically the shear-thickening regime and show that both particle softness and the emergence of a yield stress at the jamming transition compete with the inertial effects responsible for the observed thickening behaviour. This allows us to construct a dynamic state diagram, which can be used to analyze experiments.https://doi.org/10.1209/0295-5075/107/28009 相似文献
96.
We report an experimental study of the crack pattern formed during the drying of a colloidal suspension. A horizontal fiber, which provides a one-dimensional, boundary-free substrate, is coated by a film of micronic thickness. The geometry imposes a remarkable annular crack pattern and allows precise measurements of the crack spacing over a short range of film thickness (between 2 and 10 μ m) which varies linearly with the film height. We compare our experimental data with a model proposed by Kitsunezaki which suggests that the variation of the crack spacing with the film thickness depends on the ratio between a critical stress at cracking and a critical stress for slipping on the substrate. By measuring the friction force of the colloidal gels on a hydrophobic surface through a cantilever technique, we can deduce the critical crack stress for these colloidal gels simply by measuring the crack spacing of the pattern.https://doi.org/10.1209/0295-5075/102/39002 相似文献
97.
Fayssal Benkhaldoun Mohammed Seaï d & Slah Sahmim 《advances in applied mathematics and mechanics.》2011,3(4):470-492
The accuracy and efficiency of a class of finite volume methods are investigated for numerical solution of morphodynamic problems in one space dimension. The governingequations consist of two components, namely a hydraulic part described by the shallowwater equations and a sediment part described by the Exner equation. Based on differentformulations of the morphodynamic equations, we propose a family of three finite volumemethods. The numerical fluxes are reconstructed using a modified Roe's scheme thatincorporates, in its reconstruction, the sign of the Jacobian matrix in the morphodynamicsystem. A well-balanced discretization is used for the treatment of the source terms.The method is well-balanced, non-oscillatory and suitable for both slow and rapidinteractions between hydraulic flow and sediment transport. The obtained results forseveral morphodynamic problems are considered to be representative, and might be helpfulfor a fair rating of finite volume solution schemes, particularly in long time computations. 相似文献
98.
We study the relationship between microscopic structure and viscosity in non-Brownian suspensions. We argue that the formation and opening of contacts between particles in flow effectively leads to a negative selection of the contacts carrying weak forces. We show that an analytically tractable model capturing this negative selection correctly reproduces scaling properties of flows near the jamming transition. In particular, we predict that i) the viscosity η diverges with the coordination number z as η ∼(z c −z )−(3+θ )/(1+θ ), ii) the operator which governs flow displays a low-frequency mode that controls the divergence of viscosity, at a frequency ω min∼(z c −z )(3+θ )/(2+2θ ), and iii) the distribution of forces displays a scale f * that vanishes near jamming as f */⟨f ⟩∼(z c −z )1/(1+θ ) where θ characterizes the distribution of contact forces P (f )∼f θ at jamming, and where z c is the Maxwell threshold for rigidity.https://doi.org/10.1209/0295-5075/99/58003 相似文献
99.
A Rhine river sediment sample was spiked with tributyltin (TBT), equilibrated for ten days and the tributyltin extraction efficiency was optimised using a simplex algorithm. Analysis was effected using hydride generation gas chromatography-atomic absorption spectroscopy (GC-AAS) apparatus. The results show that, in this sediment sample, different molarities of HCl in methanol extract different species with varying extraction efficiencies. The least polar extraction solution extracted TBT more efficiently, whilst DBT and MBT require molar solution of HCl in methanol for efficient extraction. 相似文献
100.
The evaluation of the use of alkaline peroxodisulfate digestion with low pressure microwave, autoclave or hot water bath heating for the determination of total phosphorus and nitrogen in turbid lake and river waters is described. The efficiency of these digestion procedures were compared to a Kjeldahl digestion procedure with sulphuric acid-potassium sulfate and copper sulfate. The final solution before digestion was 0.045 M in potassium peroxodisulfate and 0.04 M in sodium hydroxide. Procedures were evaluated by the analysis of suspensions of two reference materials, National Institute of Environmental Science, Japan, no. 3 Chlorella and no. 2 pond sediment and natural turbid waters. Best recoveries of phosphorus and nitrogen by microwave heating were obtained when solutions were digested at 95 °C for 40 min. Quantitative recoveries of phosphorus from Chlorella suspensions up to 1000 mg/l were obtained by all three heating procedures, but incomplete recoveries of nitrogen occurred above 20 mg N/l in the digested sample. Good recoveries of phosphorus and nitrogen from suspended sediment suspensions were obtained only from solutions containing <150 mg/l of suspended sediments. Recoveries of phosphorus from phosphorus compounds containing COP and CP bonds added to distilled water were quantitative (94-113%) except for polyphosphates (microwave, 34±8; autoclave, 114±6; water bath, 96±4) and aluminium phosphate (8-23%). Recoveries of nitrogen compounds containing CN bonds added to distilled water were quantitative (94-96%). The analysis of a range of natural turbid water samples by alkaline peroxodisulfate and microwave, autoclave and water bath heating gave similar total phosphorus and nitrogen results. All procedures using alkaline peroxodisulfate underestimate phosphorus concentrations at high suspended sediment concentrations (>150 mg/l) and are only suitable for the analysis of very turbid samples when the turbidity is due to organic matter (algal cells, plant detritus). Underestimation of nitrogen occurs when samples contain more than 20 mg N/l. 相似文献