Acoustic wave propagation simulation in a poroelastic medium saturated by two immiscible fluids using a staggered finite-difference with a time partition method

Based on the three-phase theory proposed by Santos, acoustic wave propagation in a poroelastic medium saturated by two immiscible fluids was simulated using a staggered high-order finite-difference algorithm with a time partition method, which is firstly applied to such a three-phase medium. The partition method was used to solve the stiffness problem of the differential equations in the three-phase theory. Considering the effects of capillary pressure, reference pressure and coupling drag of two fluids in pores, three compressional waves and one shear wave predicted by Santos have been correctly simulated. Influences of the parameters, porosity, permeability and gas saturation on the velocities and amplitude of three compressional waves were discussed in detail. Also, a perfectly matched layer (PML) absorbing boundary condition was firstly implemented in the three-phase equations with a staggered-grid high-order finite-difference. Comparisons between the proposed PML method and a commonly used damping method were made to validate the efficiency of the proposed boundary absorption scheme. It was shown that the PML works more efficiently than the damping method in this complex medium. Additionally, the three-phase theory is reduced to the Biot’s theory when there is only one fluid left in the pores, which is shown in Appendix. This reduction makes clear that three-phase equation systems are identical to the typical Biot’s equations if the fluid saturation for either of the two fluids in the pores approaches to zero. Supported by the Key Program of the National Natural Science Foundation of China (Grant No. 10534040) and the National Natural Science Foundation of China (Grant No. 10674148)     

乐甫波结冰状态监测的响应机理分析

提出了将冰层进行多孔介质等效方法,对冰层、液体/波导层/压电基底多层乐甫(Love)波导结构建立分层介质模型,利用部分波理论和边界条件精确推导,分析不同状态下的传感响应,求解结冰过程Love波速度及声波衰减的变化,获得结冰过程中的声学传感机制。为了验证理论分析,实验制作了200 MHz的36°LiTaO₃/SiO₂波导结构的Love波器件,并构建模拟环境的试验系统对研制器件进行了实验测试。实验结果表明,利用Love波的工作频率以及插入损耗瞬变这一特征可以实现对结冰状态的准确监测。      

On the structure of waves at the charged interface between two viscous liquids at the solid bottom

The solutions to the equation describing the wave motion in a bilayer system of immiscible liquids are obtained in the first order of the theory of approximations. The hydrodynamic potentials, current functions, generatrix of the shape, and electrostatic potential of the charged interface between two viscous liquids, one of which conducts current and the other being a dielectric, on the solid bottom, are determined. It is shown that in the case when the density of the upper medium is three or more orders of magnitude lower than that of the lower liquid or when the kinematic viscosity of the upper medium is negligibly low as compared to that of the lower medium, the effect of the upper medium on the flow of the liquid in the lower medium is negligibly small. The structure of the wave motion generated by the interface between the two media is analyzed.     

Tunneling of electromagnetic waves through a barrier with a periodic structure

The propagation of an electromagnetic wave through a barrier with a periodic structure is considered. An interesting manifestation of electromagnetic wave tunneling through a barrier with a periodic structure is revealed. Specifically, it is theoretically and experimentally shown that, when an electromagnetic wave passes through a medium with a periodic structure in the diffraction mode within a photonic band gap, the field in the medium is localized near its boundaries. Theoretical calculations have been performed for a cholesteric liquid crystal layer of finite thickness and for a 1D photonic crystal. The experiment was carried out with perfect Si single crystals in reflection from the $ (2\bar 20)$ (2\bar 20) and $ (4\bar 40)$ (4\bar 40) planes using MoK _α X rays.     

Optical model of transient light scattering in ferroelectric liquid crystals

A static optical model is developed for the effect of field-induced transient scattering on coherent light transmission through ferroelectric liquid crystals. Scattering processes are described by introducing an optically anisotropic medium containing scatterers (transient domains). The results presented in the paper are obtained for a plane parallel layer of ferroelectric liquid crystals with a planar helicoidal structure under normal illumination with a linearly polarized plane wave. An analysis is presented of the coherent transmittance of the layer in static applied electric fields.     

Dispersion transition and the nonergodicity of the disordered nanoporous medium-nonwetting liquid system

The experiments in which a nonwetting liquid does not flow from a disordered nanoporous medium are described. The outflow is shown to depend on the degree of filling of the porous medium and its temperature in a critical manner. A physical mechanism is proposed where the transition of a system of liquid nanoclusters in a confinement into a metastable state in narrow filling and temperature ranges results from the appearance of a potential barrier due to the fluctuations of the collective “multiparticle” interaction of liquid nanoclusters in neighboring pores of different sizes at the shell of a percolation cluster of filled pores. The energy of a metastable state forms a potential relief with numerous maxima and minima in the space of a porous medium. The dispersed liquid volume in a metastable state is calculated with an analytical percolation theory for a ground state with an infinite percolation cluster. The outflow time distribution function of pores is calculated, and a power law is obtained for the decrease in nonwetting liquid volume retained in a porous medium with increasing time. The relaxation of the system under study is a multistage process accompanied by discontinuous equilibrium and overcoming of numerous local maxima of a potential relief. The formation of the metastable state of retained nonwetting liquid results from the nonergodicity properties of a disordered porous medium. The proposed model can describe the detected dependences of dispersed liquid volume on the degree of filling and temperature.     

Focusing of an oscillating shock wave emitted by a toroidal bubble cloud

An analysis of pressure-field dynamics is performed for an axially symmetric problem of interaction between a shock wave and a “free” bubble system (toroidal cluster) giving rise to a steady oscillating shock wave. The results of a numerical study of near-axis wave structure are presented for a focusing shock wave emitted by a bubble cluster. It is shown that the wave reflected from the axis has irregular structure. The Mach disk developing on the axis has a core of finite thickness with a nonuniform radial pressure distribution. The evolution of the Mach-disk core is analyzed, and the maximum pressure in the core is computed as a function of the gas volume fraction in the cluster. The effect of geometric parameters of the toroidal bubble cloud on the cumulative effect is examined.     

Calculation of shock wave propagation in water containing reactive gas bubbles

The entry of a shock wave from air into water containing reactive gas (stoichiometric acetylene–oxygen mixture) bubbles uniformly distributed over the volume of the liquid has been numerically investigated using equations describing two-phase compressible viscous reactive flow. It has been demonstrated that a steady-state supersonic self-sustaining reaction front with rapid and complete fuel burnout in the leading shock wave can propagate in this bubbly medium. This reaction front can be treated as a detonation-like front or “bubble detonation.” The calculated and measured velocities of the bubble detonation wave have been compared at initial gas volume fraction of 2 to 6%. The observed and calculated data are in satisfactory qualitative and quantitative agreement. The structure of the bubble detonation wave has been numerically studied. In this wave, the gas volume fraction behind the leading front is approximately 3–4 times higher than in the pressure wave that propagates in water with air bubbles when the other initial conditions are the same. The bubble detonation wave can form after the penetration of the shock wave to a small depth (~300 mm) into the column of the bubbly medium. The model suggested here can be used to find optimum conditions for maximizing the efficiency of momentum transfer from the pressure wave to the bubbly medium in promising hydrojet pulse detonation engines.     

用类Li原子波函数对H52+团簇的正四面体中心结构与能量的研究

在单中心球模型近似下,选用类Li原子解析波函数,用变分法计算了H52 团簇正四面体中心结构与能量.结果表明当中心氢原子核到顶角氢原子核之间的距离R=1.93a0时,体系能量有一极小值E=-4.3792 Hartree(a0=0.529177×10-10m,1 Hartree=27.2 eV).这表明H52 团簇的正四面体中心结构是稳定的结构,H52 团簇是可能存在的.     

Elastic waves in suspensions

A model of heterogeneous medium taking into account the friction between the particles and liquid, as well as the relaxation of the small-size particles to the equilibrium on the stress, has been proposed to describe the propagation of the elastic waves in a suspension. A system of wave equations describing the propagation of a plane longitudinal wave has been formulated for the components of the medium. Analytical expressions for the sound velocity in a suspension has been obtained in the approximation in which the particles are completely carried away by liquid in the limiting cases in which the particles are in equilibrium under stress with the liquid or equilibrium is absent. The dependence of the sound velocity in the medium on the volumetric portion and the size of the inclusions has been studied. The obtained results agree with the experimental data and obtained analytical expressions for the sound velocity. The dynamics of the components of the medium at the propagation of the plane longitudinal monochromatic wave has been studied.     

用类O原子波函数对H+9团簇的体心立方结构与能量的研究

在单中心球模型近似下,选用类O原子解析函数,用变分法计算了H+9团簇体心立方结构与能量。结果表明当中心氢原子核到顶角氢原子核之间的距离R=1.97a0时,体系能量有一极小值E=-4.376h0(a0=0.529177×10-10m,h0=27.2eV)。这表明H+9团簇的体心立方结构是稳定的结构,H+9团簇是存在的。     

用类B原子波函数对H7^2＋团簇的正八面体中心结构与能量的研究

在单中心球模型近似下,选用类B原子解析波函数,用变分法计算了H27 团簇正八面体中心结构与能量.结果表明当中心氢原子核到顶角氢原子核之间的距离R=2.83a0时,体系能量有一极小值E=-3.918h0(a0=0.529177×10-10m,h0=27.2 eV).这表明H72 团簇的正八面体中心结构是稳定的结构,H27 团簇是可能存在的.     

Statistical theory of the propagation of optical radiation in turbulent media

The problem of the propagation of a plane light wave in a turbulent medium is studied on the basis of the ideas of statistical topography. A cluster (caustic) structure of the intensity of the wave field in a plane perpendicular to the direction of propagation of the wave is analyzed both in the region of weak intensity fluctuations and in the region of saturated fluctuations. The specific (per unit area) values of the total area of the regions where the intensity is greater than a fixed level, the fraction of the power confined in these regions, and the total perimeter and average number of such regions are estimated. It is shown that estimates of this kind can be made on the basis of a knowledge of the joint one-point probability distribution of the intensity and transverse gradient of the wave field. Zh. éksp. Teor. Fiz. 111, 2044–2058 (June 1997)     

Detonation waves in bubble-drop media

Wave processes in chemically active multicomponent media: liquid — gas bubbles — liquid drops have been studied experimentally. Existence of detonation waves in multicomponent (bubble-drop) media has been proved. Structure of detonation waves in bubble-drop and bubble media is qualitatively identical: detonation waves are solitary waves with pulsation profile the pressure behind which is close in value to the one in unperturbed medium. Propagation velocity of detonation waves in bubble and bubble-drop media drops with the increase in medium gas phase concentration and with the decrease in carrier liquid viscosity. Presence of liquid drops decreases detonation wave velocity compared with bubble medium that does not contain liquid drops. Detonation wave propagation in multicomponent media causes gas bubbles fragmentation as well as fragmentation of individual liquid drops. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 04-03-33106).     

Microwave Heating of Metal Power Clusters

The results of simulating the rapid microwave heating of spherical clusters of metal particles to the melting point are reported. In the simulation, the cluster is subjected to a plane electromagnetic wave. The cluster size is comparable to the wavelength; the perturbations of the field inside the cluster are accounted for within an effective medium approximation. It is shown that the time of heating in vacuum to the melting point does not exceed 1 s when the electric field strength in the incident wave is about 2 kV/cm at a frequency of 24 GHz or 5 kV/cm at a frequency of 2.45 GHz. The obtained results demonstrate feasibility of using rapid microwave heating for the spheroidization of metal particles with an objective to produce high-quality powders for additive manufacturing technologies.     

H9团簇的电子结构与能量计算

对氢原子团簇H9的电子结构提出了一个物理模型 .认为其电子结构类似于氟原子的电子结构 ,具有 2个 1s电子 ,2个 2s电子和 5个 2p电子 .其基态可写为H9(1s2 2s2 2p5) 2 P .用电子波函数计算出该团簇的总能量为E =- 4 .99(Har.atomicunit) ,键长为R =1.5 9a0 ,与过去用改进的量子力学排列通道法计算的结果非常吻合 .这表明所提出的物理模型是合理的 ,而且所提出的电子波函数对研究H9团簇的物理性质很有用. The electronic structure of H 9 cluster is proposed. The total energy of this cluster is calculated by using its electron wave functions. The results are in good agreement with the value calculated by using of the modified arrangement channel quantum mechanics method in a previous paper. The results also indicate that the electronic structure of H 9 cluster is similar to that of fluorine atom.     

内置调制层型光纤表面等离子体波共振传感器研究

研究了一种基于内置调制层结构的光纤表面等离子体波共振(SPR)传感器。通过在金膜与纤芯的内侧增覆具有不同厚度和属性的光学透明薄膜作为内调制层,构成了性能独特的光电复合薄膜,起到调节倏逝波矢量和金膜表面等离子体振荡波矢量的双重作用,进而控制共振效应,为调节灵敏度提供依据。采用时域有限差分方法对内置调制层结构光纤SPR共振激励模型属性进行数值仿真。在此基础上,研制了用于液体折射率测量的内置调制层型光纤SPR传感探针。实验结果表明,该传感器在1.335～1.392折射率范围内,随着待测液体折射率的增大,SPR共振光谱向长波方向偏移,且灵敏度达到2263.1nm/RIU,与基于纤芯-金膜-环境介质三层结构的常规光纤SPR传感器相比提高一倍,能够更好地满足环境折射率检测的需求。     

用类氧原子波函数计算H7^—团簇正八体中心结构的能量曲线

选用类氧原子波函数,在单中心球模型近似下,利用变分法计算了Ｈ７＾－团簇正八面体中心结构的能量曲线。结果表明,当中心Ｈ原子核能顶角Ｈ原子核之间的距离Ｒ＝１．５８ａ０时,体系能量有一极小值－４．０８９９４５３ｈ．ａ．ｕ．。这表明Ｈ７的正八面体中心结构是可能稳定存在的。计算结果与用ＭＡＣＱＭ法计算的结果基本相符,表明提出的物理模型及其计算方法是合理的。     

Nonlinear raman-type acoustic scattering in three-phase marine sediments

Stimulated Raman-type acoustic scattering by bubble oscillations in three-phase marine sediments, which consist of a solid frame, the pore water, and air bubbles, is considered. A model is developed for the case of the bubbles surrounded by water. The acoustic properties of the sediments are described on the basis of the Biot theory of sound propagation in a fluid-saturated porous medium. Nonlinear wave equations are obtained for marine sediments containing air bubbles. Expressions for the nonlinear scattering coefficient and the threshold intensity of the exciting sound wave are derived. A possibility of an experimental observation of the scattering process is discussed.     

薄膜硅的变隙问题及隙态分布

用电子束蒸发的方法制备可变光学带隙薄膜硅材料, 给出了研究结果. 介绍了一种做透过率曲线切线确定薄膜光学带隙的简易方法, 给出了制备工艺和条件, 以及各种材料的隙态分布图. 实验发现, 材料的光学带隙宽度不但与量子尺度效应有关, 而且与缺陷形成的势垒高度和宽度以及有序短程(原子串)长度有关; 给出了常规硅材料的光学带隙与原子串长度的关系. 计算表明, 随着原子串长度的加大, 势阱中的电子液面升高, 载流子受缺陷势垒的散射减弱; 在原子串长度较低的情况下, 电子液面不总是随着原子串长度升高, 而是有较大的涨落, 形成锯齿状波动.计算还发现, 在势垒宽度与原子串长度之比不变的情况下, 电子液面还与势垒高度有关. 关键词： 薄膜硅 可变光学带隙 隙态分布 电子液面涨落