尾波干涉法精确测量地震波速变化的方法及实验研究

The coda of seismic waves consists of that part of the signal after the directly arrivials. In a finite medium, or in one that is strongly heterogeneous, the coda is dominated by waves which have repeatedly sampled the medium. Small changes in a medium which may have no detectable influence on the first arrivals are amplified by this repeated sampling and may thus be detectable in the coda. Because of this, coda wave is widely used in detecting micro variations in medium。 In this paper, we give a general view of the theory and application of coda wave, especially coda wave interferometry. We focus on discussing the application of coda wave interferometry on data source of active situ experiment。 First, we apply coda wave interferometry in a short time period situ experiment which last for three days. We also apply the method of coda wave interferometry in a situ experiment which last for one month. Daily circle variations of seismic velocity around the experiment site were obtained, and we also observed that the velocity variations in the experiment site have a significant correlation with the environment factors, including air temperature, barometric pressure, solid earth tide and the level of rainfall. We find that the velocity variation during this period is up to 10-3. The relationship between velocity variation and changes in air temperature, barometric pressure and solid earth tide was analyzed with least square linear fitting .The velocity has no dependence on the air temperature. But velocity has a change of 10-6--10-7 when the barometer or earth tide change per Pa. Generally, we conclude the work and results of previous researchers, and we also display our works and results. We hopes to contribute to the future research of coda wave interferometry.

Lg尾波衰减成像研究——北京及邻区衰减成像

With the development of the technology of earthquake observation, more and more researchers work at many fields' of seismicity using seismic kinetic property, as the result, the study of attenuation has also made great progress, especially in the mechanism of the attenuation and the physical process. Aki put forward single back scattering theory to explain the forming of the seismic coda wave in 1969. Then, researchers started to develop the study in seismic scattering and attenuation. My thesis is also based on that theory. We assume that the Lg wave is a superposition fo high-mode surface waves, the coda of Lg is caused by scattering. Sato proposed Single Isotropic Scattering model (SIS model) to interpreted the scatter property, and he also formulated the geometrical spreading term. Then Xie (1988) developed the single spectral-ratio (SSR) method to obtain the Lg coda Q and the frequency dependent factor n. Later, he get to lateral images in the area of scatter ellipse. SSR method is explored and used in the study of Lg coda waves of regional earthquakes in my thesis. Choosing the earthquakes records with high ratio of signal-noise ,which were recorded at the stations from 1989 to 1999, we obtain the single trace Lg coda Q and its frequency dependent factor n. The results proved that SIS model is the reasonable model to explain the Lg coda wave, and SSR method also can be used to process Lg coda of regional earthquakes to get to the satisfied Lg coda Q. Based on the Lg coda Q we obtained using the former method, we explore the programs to inverse the regional Lg coda Q independently, and then make use of them to inverse the Lg coda Q of Beijing and adjacent area. The inversion result is satisfied. We conclude that the distribution of Qo (Q in lHz) is marked by the inhomogeneity, which is related to the tectonic structure: The value of Qo in uplift area, for example, Yanshan uplift, Taihang uplift, Luxi Uplift, is higher than the depression area, for example, Jizhong depression, Huanghua depression, and Jiyang depression, and the border between the higher Q area and lower Q area is very clear; Lg coda Q is also related to the velocity structure, higher velocity area is also with higher Q, lower velocity area is with lower Q; and higher heat-flow area is companied with lower Q. All in all, the value of Q reflects the difference of characteristics of lithofaces, porosity, the liquid content between the pores and heat flow. So, the Q value difference between uplift area and depression area reveals the difference of tectonic structure, lithology and physical character of the rock. So, the study of Lg coda Q is help to understand the earthquakes propagation mechanism through the inhomogenous medium, the cause of the coda, attenuation mechanism of the coda. Making use of the lateral images of Q, with velocity images, heat flow results, and other experimental result, we will be promoted to understand the complex structure of the crust, its inhomogenous character, and so on.

Numerical Analysis of a Dual Polarization Mode-Locked Laser with a Quarter Wave Plate

Dynamical behaviors and frequency characteristics of an active mode-locked laser with a quarter wave plate (QWP) are numerically studied by using a set pf vectorial laser equation. Like a polarization self-modulated laser, a frequency shift of half the cavity mode spacing exists between the eigen-modes in the two neutral axes of QWP. Within the active medium, the symmetric gain and cavity structure maintain the pulse's circular polarization with left-hand and right-hand in turn for each round trip. Once the left-hand or right-hand circularly polarized pulse passes through QWP, its polarization is linear and the polarized direction is in one of the directions of i45o with respect to the neutral axes of QWP. The output components in the directions of i45" from the mirror close to QWP are all linearly polarized with a period of twice the round-trip time.

Temperature measurement of reflected shock wave by using chemical indicator

This report describes a new method for measuring the temperature of the gas behind the reflected shock wave in shock tube, corresponding to the reservoir temperature of a shock tunnel, based on the chemical reaction of small amount of CF4 premixed in the test gas. The final product C2F4 is used as the temperature indicator, which is sampled and detected by a gas chromatography in the experiment. The detected concentration of C2F4 is correlated to the temperature of the reflected shock wave with the initial pressure P-1 and test time tau as parameters in the temperature range 3 300 K < T < 5 600 K, pressure range 5 kPa < P1 <12 kPa and tau similar or equal to 0.4 ms.

Wave Propagation Analysis in a Pressure-Wave-Refrigerator

Pressure wave refrigerators (PWR) refrigerate the gas through periodical expansion waves. Due to its simple structure and robustness, PWR may have many potential applications if the efficiency becomes competitive with existing alternative devices. In order to improve the efficiency, the characteristics of wave propagation in a PWR are studied by experiment, numerical simulation and theoretical analysis. Based on the experimental results and numerical simulation, a simplified model is suggested, which includes the assumptions of flux-equilibrium and conservation of the free energy. This allows the independent analysis of the operation parameters and design specifics. Furthermore, the optimum operation condition can be deduced. Some considerations to improve the PWR efficiency are also given.

Elasticity, stability, and ideal strength of beta-SiC in plane-wave-based ab initio calculations

On the basis of the pseudopotential plane-wave method and the local-density-functional theory, this paper studies energetics, stress-strain relation, stability, and ideal strength of beta-SiC under various loading modes, where uniform uniaxial extension and tension and biaxial proportional extension are considered along directions [001] and [111]. The lattice constant, elastic constants, and moduli of equilibrium state are calculated and the results agree well with the experimental data. As the four SI-C bonds along directions [111], [(1) over bar 11], [11(1) over bar] and [111] are not the same under the loading along [111], internal relaxation and the corresponding internal displacements must be considered. We find that, at the beginning of loading, the effect of internal displacement through the shuffle and glide plane diminishes the difference among the four Si-C bonds lengths, but will increase the difference at the subsequent loading, which will result in a crack nucleated on the {111} shuffle plane and a subsequently cleavage fracture. Thus the corresponding theoretical strength is 50.8 GPa, which agrees well with the recent experiment value, 53.4 GPa. However, with the loading along [001], internal relaxation is not important for tetragonal symmetry. Elastic constants during the uniaxial tension along [001] are calculated. Based on the stability analysis with stiffness coefficients, we find that the spinodal and Born instabilities are triggered almost at the same strain, which agrees with the previous molecular-dynamics simulation. During biaxial proportional extension, stress and strength vary proportionally with the biaxial loading ratio at the same longitudinal strain.

Capillary Effect on Vertically Excited Surface Wave in Circular Cylindrical Vessel

In a vertically oscillating circular cylindrical container, singular perturbation theory of two-time scale expansions was developed in inviscid fluids to investigate the motion of single free surface standing wave including the effect of surface tension.

Interferometric Measurement of Density in Nonstationary Shock Wave Reflection Flow and Comparison with CFD

We present density measurements from the application of interferometry and Fourier transform fringe analysis to the problem of nonstationary shock wave reflection over a semicircular cylinder and compare our experimental measurements to theoretical results from a CFD simulation of the same problem. The experimental results demonstrate our ability to resolve detailed structure in this complex shock wave reflection problem, allowing visualization of multiple shocks in the vicinity of the triple point, plus visualization of the shear layer and an associated vortical structure. Comparison between CFD and experiment show significant discrepancies with experiment producing a double Mach Reflection when CFD predicts a transitional Mach reflection.

The cellular structure of a two-dimensional H2/O2/Ar detonation wave

In this paper, the cellular structure of a two-dimensional detonation wave in a low pressure H2/O2/Ar mixture calculated with a detailed chemical reaction model, high order scheme and high resolution grids is investigated. The regular cellular structure is produced about 1 ms after introducing perturbations in the reaction zone of a steady one-dimensional detonation wave. It is found from the present resolution study that the discrepancies concerning the structure type arising from the coarser grid employed can be resolved using a sufficiently fine grid size of 0.05 mm and below and shows a double-Mach-like strong-type configuration. During the structure evolution process, the structure configuration does not change much in the periods before and after the triple point collision. Through the triple point collision, three regular collision processes are observed and are followed by a quick change to the double-Mach-like configuration. The simulated structure tracks show that there are three different tracks associated with different triple points or the kink on the transverse wave. Comparisons with previous work and experiments indicate the presence of a strong structure for an ordinary detonation.

Analytical Interaction of the Acoustic Wave and Turbulent Flame

A modified resonance model of a weakly turbulent flame in a high-frequency acoustic wave is derived analytically. Under the mechanism of Darrieus-Landau instability, the amplitude of flame wrinkles, which is as functions of the expansion coefficient and the perturbation wave number, increases greatly independent of the 'stationary' turbulence. The high perturbation wave number makes the resonance easier to be triggered but weakened with respect to the extra acoustic wave. In a closed burning chamber with the acoustic wave induced by the flame itself, the high perturbation wave number is to restrain the resonance for a realistic flame.

Comparison of existing poroelastic models for wave damping in a porous seabed

Mechanism of wave-seabed interaction has been extensively studied by coastal geotechnical engineers in recent years. Numerous poro-elastic models have been proposed to investigate the mechanism of wave propagation on a seabed in the past. The existing poro-elastic models include drained model, consolidation model, Coulomb-damping model, and full dynamic model. However, to date, the difference between the existing models is unclear. In this paper, the fully dynamic poro-elastic model for the wave-seabed interaction will be derived first. Then, the existing models will be reduced from the proposed fully dynamic model. Based on the numerical comparisons, the applicable range of each model is also clarified for the engineering practice.

Analysis of Wave-Induced Effective Stresses of Seabed

波浪作用下海床的稳定性分析是海洋工程地质评价的重要内容。海床的稳定性可通过计算分析其随时间变化的有效应力场来评估。建议了一个周期载荷作用下土体的本构模型,并用于计算波浪作用下海床的应力与变形。采用Biot固结理论和有限单元法,分析了海床的动态应力场与孔隙水压力场。波浪作用下两种渗透系数时有效应力的动态变化过程结果对比,反映了渗透消散作用对海床有效应力变化的影响。

Investigation of Dynamic Fracture Toughness under Compressive-Shear Combinede Stress Wave Loading

提出亚微秒单脉冲应力波载荷作用下II型裂纹的平板冲击实验技术。加载率为dK/dt-10~8MPa·m~{”/d}·s~{-1}。实验中由锰铜应力片和弹性波理论分别测定和计算了压应力；通过微观分析确定了动态裂纹的平均扩展长度；引进等效应力强度因子,用动态断裂理论确定了60号钢的动态断裂韧性K_{Id}和K_{IId}；建立了亚微秒冲击载荷作用下确定材料动态断裂韧性的方法。

Stability and Liqueafaction Analysis of Seabed to Wave Loading

波浪作用下海床的稳定性与液化分析是海底管线、防波堤和海洋平台设计中必须仔细考虑的问题。推荐了一个循环荷载作用下土体的弹塑性实用本构模型,并给出了一种粉土的模型参数。该模型直接根据初始应力状态和循环应力的大小与作用时间计算土体的塑性应变增量,在有限元计算中不需要引入弹塑性矩阵。采用Biot理论和有限单元法,计算了粉土海床在波浪作用下的孔隙水压力和有效应力的变化过程,并对海床的稳定性和液化进行了分析。计算结果与波浪槽实验反映的规律是相符的。

Stress Wave Propagation in a Gradient Elastic Medium

The gradient elastic constitutive equation incorporating the second gradient of the strains is used to determine the monochromatic elastic plane wave propagation in a gradient infinite medium and thin rod. The equation of motion, together with the internal material length, has been derived. Various dispersion relations have been determined. We present explicit expressions for the relationship between various wave speeds, wavenumber and internal material length.