砂粒与复杂流体压裂液在裂缝中的流动特性研究

在矩形裂缝通道中,应用高速摄像技术,研究了复杂流体压裂液水平流动过程中砂粒的沉降速度,测试了复杂流体的流变学特性,分析了复杂流体的水平流动如何影响砂粒的沉降.研究结果表明,流性指数不等于1的复杂流体,其水平流速影响砂粒的沉降规律,砂粒在裂缝中水平流动过程的沉降速度不仅随复杂流体表观粘度的减小而增大,同时随复杂流体水平流速的增大而增大,是静止沉降速度的数倍至十数倍.     

Interactions between optical bullets with different velocities in the three-dimensional cubic-quintic complex Ginzburg-Landau equation

By using the three-dimensional complex Ginzburg--Landau equation with cubic--quintic nonlinearity, this paper numerically investigates the interactions between optical bullets with different velocities in a dissipative system. The results reveal an abundance of interesting behaviours relating to the velocities of bullets: merging of the optical bullets into a single one at small velocities; periodic collisions at large velocities and disappearance of two bullets after several collisions in an intermediate region of velocity. Finally, it also reports that an extra bullet derives from the collision of optical bullets when optical bullets are at small velocities but with high energies.     

Bragg空芯光纤中的群速度超光速的理论探讨

运用渐近法计算了多模B ragg光纤的场分布、有效折射率、各模式的色散参量、群速度及TE01模的能量速度。结果表明:各模式色散参量有正有负,但群速度都大于光速,而能量速度不大于光速。     

Acoustic anisotropy and birefringence in fibre-reinforced composite materials

All nine elastic moduli of an orthotropic composite material, namely, polypropylene reinforced with glass fiber, are determined from the measured values of the bulk acoustic wave velocities along specific directions in the planes of symmetry of the material. These data are used to calculate the angular dependences of phase velocities, polarization vectors, and directions of ray velocities of bulk waves in the composite. It is demonstrated that the difference in the velocities of shear waves polarized along and across the glass fiber gives rise to an acoustic birefringence and can lead to an elliptical polarization of waves. The measurement of the phase velocities of shear waves as functions of the wave polarization is suggested as a method for the determination of the fiber orientation in a composite material.     

Sensitivity analysis of an inverse procedure for determination of elastic coefficients for strong anisotropy

The elastic coefficients of anisotropic solids are often evaluated from measurements of phase or group velocities of ultrasonic bulk waves by the usage of inverse optimizing procedures. This paper discusses the effects of various factors on such procedures results for transversely isotropic solids with considerably strong anisotropy. First, the inverse determination of all elastic coefficients of unidirectional CFRP composite is briefly outlined. Then the results of the optimization are treated as exact values and the sensitivity of the optimizing process versus main considered sources of inaccuracies is analyzed. Results of extensive simulations are presented to illustrate the effect of input data distortion, input data incompleteness, and geometrical conversion from experimentally obtained group velocities into corresponding phase velocities used as input data for the optimizing procedure. The paper takes note of how information about the elastic coefficients can be extracted from the different segments of the phase velocity surface. The stability versus input data distortion for inversion from group velocities and phase velocities is compared and the importance of reliable geometrical converting from group into phase velocities is illustrated. An novel method for geometrical conversion of distorted group velocity data into corresponding phase velocities based on affine combinations of low-order polynomials is presented and compared with piecewise or high-order polynomial fitting.     

Intensity dependence of flow signal in slice selective velocity measurements

The quantitative determination of flow velocities using inflow-outflow techniques require slice selective excitation pulses. The intensity-velocity relationship for such methods is shown to be such that flow velocities estimated using techniques which rely on an absolute calibration of the measured intensity are sensitive to the details of the slice profile of the excited material. This can cause errors when the estimation of flow velocities is made from the image intensity. A method which provides a measure of the flow velocities and which relies only on relative variations in intensity is examined and shown to be insensitive to details of the slice profile.     

Numerical study of translational nonequilibrium in an He–Xe mixture by direct simulation Monte Carlo

The distributions of pairs of particles over relative velocities at the shock wave front in He with a small Xe additive have been studied. It has turned out that the values of the distributions over relative velocities for an Xe–Xe atomic pair far (up to 10⁹ times) exceed their equilibrium values behind a shock wave within a narrow part of its front at high velocities of the wave and small Mach numbers (M = 2). This feature is lacking in the distributions of He–Xe atomic pairs over relative velocities.     

A note on the computation of geometrically defined relative velocities

We discuss some aspects about the computation of kinematic, spectroscopic, Fermi and astrometric relative velocities that are geometrically defined in general relativity. Mainly, we state that kinematic and spectroscopic relative velocities only depend on the 4-velocities of the observer and the test particle, unlike Fermi and astrometric relative velocities, that also depend on the acceleration of the observer and the corresponding relative position of the test particle, but only at the event of observation and not around it, as it would be deduced, in principle, from the definition of these velocities. Finally, we propose an open problem in general relativity that consists on finding intrinsic expressions for Fermi and astrometric relative velocities avoiding terms that involve the evolution of the relative position of the test particle. For this purpose, the proofs given in this paper can serve as inspiration.     

The time-domain signature of negative acoustic group velocity in microsphere suspensions

In the wake of recent reports of superluminal acoustic group velocities in sonic and ultrasonic regions of the acoustic spectrum, this paper describes the time-domain manifestation of such group velocities through simulations of the linear propagation of ultrasonic wave packets in a suspension of elastic microspheres. Conditions under which arbitrarily large and negative group velocities can be observed as the speed of a peak in the envelope of an acoustic pulse are described. Propagation simulations demonstrate the physical signature of negative group velocities, as well as the causal compliance of the superluminal acoustic pulses examined in this work.     

Experimental investigation on burner lip thickness effect on the liftoff and blowout velocities of jet diffusion flame

This experimental study addresses issue on the effect of burner lip thickness on the liftoff and blowout velocities of jet diffusion flame discharging into quiescent air. Burner tubes of two kinds of inner diameter (2 and 3 mm) with a wide range of lip thicknesses (0.25–16.5 mm) are implemented with methane or propane jet diffusion flame, respectively. The results show that the burner lip thickness has a profound effect on flame liftoff velocities, especially the blowout velocities. With the increase of the lip thickness, the blowout velocities firstly increase, then decrease and lastly remain unchanged. Specifically, the blowout velocities of 2 and 3 mm inner diameters tubes reach the maximum values when the corresponding burner lip thicknesses are 2 and 1.5 mm, respectively. In addition, compared with free (unconfined) jet diffusion flame, the jet confinement results in slight reductions of flame liftoff and blowout velocities. The existence range of lifted flame issuing from larger diameter burner tube is wider than that of smaller diameter burner tube. The existence range of propane lifted flame is wider than that of methane.     

Behaviour of ultrasonic velocities in amorphous Se90Ge10 and Se85Ge15 alloys near their glass transition

Precise measurements of 10 MHz frequency longitudinal and shear wave velocities are reported in amorphous SeGe alloys near their glass transition temperature T _g . There is a sharp decrease of the velocities near T _g , but the reduction in velocities appears smaller than expected.     

密勒-库什实验过程中的气体分子分布函数

详细分析了密勒－库什实验过程中分子速率分布的变化情况，说明了实验数据与麦克斯韦速率分布之间的关系。     

A probability density function of liftoff velocities in mixed-size wind sand flux

With the discrete element method (DEM), employing the diameter distribution of natural sands sampled from the Tengger Desert, a mixed-size sand bed was produced and the particle-bed collision was simulated in the mixed-size wind sand movement. In the simulation, the shear wind velocity, particle diameter, incident velocity and incident angle of the impact sand particle were given the same values as the experimental results. After the particle-bed collision, we collected all the initial velocities of rising sand particles, including the liftoff angular velocities, liftoff linear velocities and their horizontal and vertical components. By the statistical analysis on the velocity sample for each velocity component, its probability density functions were obtained, and they are the functions of the shear wind velocity. The liftoff velocities and their horizontal and vertical components are distributed as an exponential density function, while the angular velocities are distributed as a normal density function. Supported by the Key Project of the National Natural Science Foundation of China (Grant No. 10532040)     

Invariant Velocities for Two-Dimensional Minkowski Space-Time

It is shown that in two-dimensional space-time only the velocities parallel to the velocities of moving reference frames may be invariant with respect to Lorentz transformations.     

分级进风燃烧室内高温气固两相流动的PDA测量

本文建立了分级进风燃烧室高温气固两相流动的实验装置。利用三维激光粒子动态分析仪(PDA),测量了燃烧室内有气相燃烧的高温气固流动的两相瞬时速度场。得到了平均轴向与切向速度、轴向与切向脉动速度均方根值和轴向-切向脉动速度关联量的分布。     

Elastic waves in carbon 2D supracrystals

The elastic moduli and propagation velocities of elastic waves in 2D supracrystalline nanoallotropes of carbon have been calculated. It has been shown that these velocities in sp ² nanoallotropes are close to those in graphene and exceed the propagation velocities of elastic waves in single-crystal diamond by a factor of 2. The propagation velocities of both longitudinal and transverse elastic waves in carbon 2D supracrystalline sp ³ nanoallotropes are several times lower than those in sp ² nanoallotropes.     

Comparative analysis of light-ion ranges in gaseous,liquid, and solid media

Ranges of ions from He to Ne in gaseous (hydrogen and argon), liquid (water), and solid (carbon) media are analyzed. This analysis demonstrates the different dependences of ranges on the velocities, the charges, and the masses of ions in different velocity region. In the case of small ion velocities, the ranges are directly proportional to their velocities and masses and are inversely proportional to the nuclear charge. In the intermediate velocity region corresponding to an ion energy of Е = 0.1–1 MeV/nucleon, in which processes of ion charge exchange play an important role and the average ion charge differs from the nuclear charge, the ranges become proportional to the squared ion velocities and masses and are inversely proportional to the nuclear charge. To establish the relation between the ion ranges in the regions of small and average velocities, it is convenient to use the universal function f(Z, M) = RZ/M, successfully describing the reduced ranges of ions with given velocities in gaseous, liquid, and solid media. In the case of large velocities where ions upon passing through the media lose all electrons, the ranges are directly proportional to the squared ion energies and masses and are inversely proportional to the squared nuclear charge.     

Superluminal Behaviour of Modified Bessel Waves

Much experimental evidence of superluminal phenomena has been available by electromagnetic wave propagation experiments, with the results showing that the phase time describes the barrier traversal time. Based on the extrapolated phase time approach and numerical methods, we show that, in contrast to the ordinary Bessel waves of real argument, the group velocities of modified Bessel waves are superluminal. We obtain the following results. The group velocities increase with the increase of propagation distance, which is similar to the evanescent plane- wave cases. For large wave numbers, the group velocities fall off as the wave numbers increase, which is similar to the evanescent plane-wave cases. For small wave numbers, the group velocities increase with the increase of wave numbers, this is different from the evanescent plane-wave cases.     

钠玻璃与钛玻璃在静水压下的弹性性能

用超声脉冲重叠法测量了钠玻璃(float glass)和钛玻璃(SiO₂+8.4wt%TiO₂)从大气压到2GPa静水压条件下的纵波声速和横波声速.发现两种玻璃有不同的变化规律.钛玻璃的纵波声速和横波声速,与钠玻璃的横波声速都随压力的增加而减小;而钠玻璃的纵波声速随压力的增加先增大,后减小.这一现象不同于别的氧化硅玻璃.对实验结果进行了讨论,并计算了弹性模量在压力下的变化和Murnaghan状态方程参数. 关键词： 高压 超声 玻璃