Dynamics of a rectangular foundation contacting a viscoelastic layered medium

Conclusions 1. The models realized permit calculating the dynamics of structures in a wide range of variation of the properties of the base and structure. As is seen from the results of calculating the model problems, the parameters of a layered base substantially affect the dynamics of the structure—base system and should be taken into account during designing. Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 7, pp. 15–19, July, 1995.     

Numerical simulation of thermal convection of viscoelastic fluids in an open-top porous medium with constant heat flux

This paper makes a numerical study of the buoyancy-driven convection of a viscoelastic fluid saturated in an open-top porous square box under the constant heat flux boundary condition. The effects of the relaxation and retardation times on the onset of the oscillatory convection, the convection heat transfer rate and the flow pattern transition are investigated. It is shown that a large relaxation time can destabilize the fluid flow leading to an early onset of the thermal convection and a high heat transfer rate, while a large retardation time tends to stabilize the flow and suppress the convection onset and the heat transfer. After the convection sets in, the flow bifurcation appears earlier with the increase of the relaxation time and the decrease of the retardation time, resulting in more complicated flow patterns in the porous medium. Furthermore, with the increase of the ratio of the relaxation time to the retardation time, the fluid may be blocked from flowing through the open-top boundary, which may be caused by the viscoelastic effect. Finally, the comparison of our results with those under isothermal heating boundary conditions reveals that the heat transfer rate corresponding to a constant heat flux boundary is always higher.     

具有粘弹性支撑的平板上势流的稳定性

本文研究了具有粘弹性支撑的平板上均匀势流中的稳定性问题。在研究中采用基于空间－时间稳定性理论的映射法搜寻绝对不稳定特征模态。研究结果表明，当支撑刚度足够小时总量会有不稳定发生。对于纯弹性支撑，尽管有不稳定，但它并不是绝对不稳定；而对于粘弹性支撑，所发生的不稳定则一定是绝对不稳定。     

Cavitation bubbles collapse characteristics behind a convex body

Cavitation bubbles behind a convex body were experimentally studied by a high speed camera and a hydrophone synchronously. The experiments were conducted in a circulating water tunnel with five various contraction ratios： β = 0.497, β= 0.6, β= 0.697, β= 0.751, and β= 0.799. The distributions of the cavitation bubble collapse positions behind the five different convex bodies were obtained by combining the images taken by the high speed camera. According to the collapse positions, it was found that no cavitation bubble was collapsed in the region near the wall until the ratio of the water head loss over the convex body height was larger than 20, which can be used to predict if the cavitation damage would occur in the tunnel with orifice energy dissipaters.     

不同直径气泡在静水中运动特性的研究

运用VOF数值模拟技术分析了水中气泡的运动特性.采用了数值模拟方法测量气泡上升过程中的形状、上升速度和气泡轨迹,采用自编程序的数字图像处理技术进行模拟结果的后处理,并对获得的结果进行讨论分析.从分析结果可以看出:直径2mm以下的小气泡呈直线或“Z”字形运动状态,直径大于2mm的气泡为螺旋运动或者更复杂的随机运动;气泡速度经过初始加速阶段以后存在明显的震荡,这个震荡幅度与气泡的长宽比有很好的相关性;气泡在上升过程中顶部和尾部速度比中部速度大,气泡尾部涡竖直方向上分布的不对称状态是气泡上升路径发生改变的主要原因.     

粘弹性流体在盲端孔隙中的流场

以带有盲孔的流道模拟油藏中的盲端孔隙，应用数值方法研究了上随体Maxwell流体在盲端孔隙中的流动特性。着重分析了流体流变性和盲端倾角对流场的影响规律。计算结果表明，驱替液的粘弹性是影响盲端波及效率的重要因素；在较大的盲端倾角范围内，低雷诺数（Re）流动条件下，流体的威森博格数（We）越大，孔隙盲端中的流动区域越大，滞留区越小。     

掺气水流不同粒径气泡运动特性研究

采用三维数值模拟方法和离散相模型(DPM模型)模拟了不同比尺高水头直槽式泄洪洞和带反弧泄洪洞掺气水流中不同粒径气泡的运动特性,分析了不同粒径气泡对近壁掺气浓度的影响范围,研究成果可为掺气浓度的缩尺效应提供依据。分析表明,气泡的影响范围与流速成正比,与气泡的粒径成反比;泄洪洞底坡越小,气泡的影响范围越大;泄洪洞反弧段半径越大,气泡的影响范围越大。     

支柱瓷绝缘子的振动声学检测机理研究

采用振动声学法检测支柱瓷绝缘子的关键是掌握具有不同缺陷的支柱绝缘子的动力特性.应用有限单元法,对支柱瓷绝缘子振动声学检测系统进行振动模态和随机振动响应分析,考虑支柱瓷绝缘子的不同缺陷,得到激励源为有限带宽白噪声干扰时接收器的功率谱密度函数,为振动声学法检测支柱瓷绝缘子的质量提供了科学依据.     

水库淡水冰的晶体和气泡及密度特征分析

对黑龙江红旗泡水库的淡水冰生消过程实施现场观测。分别在冰快速生长期、稳定生长期和融冰期取样,观测其冰晶体、冰内气泡形态及尺寸,并测试冰表观密度,获得了3个冰阶段冰样由表至底的冰晶类型、晶体等效直径、冰内气泡宏观形态、气泡尺寸及百分含量和冰密度。结果表明,冰上层为粒状晶体,中下层为柱状晶体,平均粒径随冰深度增加而增大,但冰晶体不随时间变化;冰生长时冰内上层气泡呈球体,百分含量较高,中下层呈圆柱体,百分含量较低;伴随冰的生长和消融,冰内气泡的尺寸和百分含量呈“变化”势态,而冰密度随冰内气泡百分含量的增加而降低。     

基于格子玻尔兹曼方法的近壁区空化泡生长溃灭过程模拟

基于格子玻尔兹曼热流耦合模型,兼顾温度场与流场的相互影响,对近壁区空化泡的生长和溃灭过程开展了系统研究,分析了泡壁无量纲距离和初始输入温度对空化泡演化过程和溃灭强度的影响,并对比了被动标量模型与热流耦合模型的差异。结果表明:空化泡受壁面限制,生长过程中无法保持圆形,其最大半径与泡壁无量纲距离之间存在幂函数关系,当泡壁无量纲距离大于1.6时,则为线性关系;空化泡最大半径与输入能量为线性关系,与初始输入无量纲温度之间存在幂函数关系;热流耦合模型考虑了高温对表面张力的影响,与被动标量模型模拟结果相比,其溃灭阶段获得的射流体积更大,微射流更集中,但溃灭强度更小。     

Safe blasting procedure within a preservable space of a medium

A system approach to a combined scheme to establish a safe procedure for blasting operations is examined. __________ Translated from Gidrotechnicheskoe Stroitel’stvo, No. 8, pp. 17–22, August, 2006.     

Microanalysis of supersaturated gas release based on wall-attached bubbles

Supersaturation of dissolved gases in natural water, due to spillage from high dams and other factors, may cause fish mortality. In previous experiments, the dissipation coefficient has been used to denote the degassing process of total dissolved gas(TDG) saturation. These experiments mainly analyzed supersaturated TDG dissipation from a macroscopic view. To precisely clarify the mechanism of supersaturated TDG release, this study investigated bubble adsorption at a wall surface from a microscopic view. The experiment was conducted in a Plexiglas-wall container filled with supersaturated TDG water. A model that calculates the adsorption flux of supersaturated TDG by a solid wall, and helps describe construction for a contact angle at a three-phase intersection, was developed according to Young's equation. This model was used to investigate the formation process of bubbles adsorbed on a solid polymethyl methacrylate(PMMA) surface in supersaturated TDG water. The adsorption effect of a solid wall on TDG release was analyzed based on the experimental data. The modeling results were compared with observations under different wall area conditions, and it was found that TDG release tended to increase with wall area. This study helps improve our understanding of the mechanisms of supersaturated TDG release and provides an important theoretical method for accurate calculation of the release process. The adsorption flux model of the solid wall provides mitigation measures to combat the adverse effects of TDG supersaturation,which will be beneficial to the protection of aquatic organisms in hydropower-regulated rivers.     

Application of binding theory for seepage of viscoelastic fluid in a variable diameter capillary

The polymer solution for polymer flooding is a viscoelastic fluid. There exist both shear flow and elongational flow when the polymer solution flows in a porous medium, where an additional dissipation is involved. The additional dissipation caused by elongational deformation is often ignored while studying the flow of the fluid in a porous medium. For a complex polymer solution, the generated elongational pressure drop cannot be ignored. In a capillary of fixed diameter, the polymer solution is only impacted by the shear force, and its rheological property is pseudoplastic. Therefore the variable diameter capillary and the converging-diverging flow model with different cross sections are required to describe the flow characteristics of the polymer solution in porous media more accurately. When the polymer solution flows through the port, we have the elongational flow and the polymer molecules undergo elongational deformation elastically. By using the mechanical energy balance principle and the minimum energy principle, a mathematical model of non-Newtonian fluid inlet flow was established by Binding. On the basis of the Binding theory, with the application of the theory of viscoelastic fluid flow in the circular capillary and the contraction-expansion tube, the relations between the viscoelastic fluid flow rate and the pressure drop are obtained.     

MHD flow of a visco-elastic fluid through a porous medium between infinite parallel plates with time dependent suction

This work provides a comprehensive theoretical analysis of MHD unsteady free convection viscoelastic fluid flow through a porous medium. The medium is treated as incompressible and optically transparent. The flow of the fluid is initiated by shearing action of the moving wall with time dependent suction. Radiative heat flow is considered in temperature equation. The coupled nonlinear problem has been solved asymptotically. Approximate solutions have been obtained for the mean velocity, mean temperature using multi parameter perturbation technique. The originality of the present study is to investigate the effect of viscoelastic property of the fluid(Walters B? model) on the flow and heat transfer phenomena when the flow is permeated through a porous medium with uniform porous matrix subject to transverse magnetic field and time dependent fluctuative suction at the boundary surface. The case of viscous flow has been discussed as a particular case on comparison with the result reported earlier and it is in good agreement. Flow reversal is indicated incase of viscoelastic fluid with high heat capacity in the presence of magnetic field. The higher cooling of the plate in case of viscoelastic flow also causes a flow reversal.     

Effects of liquid compressibility on bubble-bubble interactions between oscillating bubbles

The mutual interaction between cavitation bubbles plays an important role in the physical processes of cavitation. In this paper, a complete model is developed for modelling the mutual interaction between cavitation bubbles with the effects of liquid compressibility fully included. It is found that the liquid compressibility is an important parameter in the determination of the direction of the force(the attraction or repulsion force), as well as the magnitude of the force. The influences of the liquid compressibility on the mutual interaction force can be categorized into three terms: the first is a new term added on the mutual interaction force in incompressible liquids and this term will vanish if the sizes of two bubbles are equal, the second is the radiation damping term, the third one can be considered as a correction of the mutual interaction force in incompressible liquids with a coefficient and this correction will be prominent for small bubbles and a high ambient pressure.