大型光学镜子热弹性变形的有限元分析

简述了利用ANSYS软件对大型光学镜子热弹性变形进行有限元分析的一般方法，强调了在分析过程中应该注意的一些问题和实用技巧，并给出了一个分析透镜重力变形的实例。

地震波场延拓+菲涅尔体叠加方法及成像效果

In the increasingly enlarged exploration target, deep target layer(especially for the reservoir of lava) is a potential exploration area. As well known, the reflective energy becomes weak because the seismic signals of reflection in deep layer are absorbed and attenuate by upper layer. Caustics and multi-values traveltime in wavefield are aroused by the complexity of stratum. The ratio of signal to noise is not high and the fold numbers are finite(no more than 30). All the factors above affect the validity of conventional processing methods. So the high S/N section of stack can't always be got with the conventional stack methods even if the prestack depth migration is used. So it is inevitable to develop another kind of stack method instead. In the last a few years, the differential solution of wave equation was hold up by the condition of computation. Kirchhoff integral method rose in the initial stages of the ninetieth decade of last century. But there exist severe problems in it, which is are too difficult to resolve, so new method of stack is required for the oil and gas exploration. It is natural to think about upgrading the traditionally physic base of seismic exploration methods and improving those widely used techniques of stack. On the other hand, great progress is depended on the improvement in the wave differential equation prestack depth migration. The algorithm of wavefield continuation in it is utilized. In combination with the wavefield extrapolation and the Fresnel zone stack, new stack method is carried out It is well known that the seismic wavefield observed on surface comes from Fresnel zone physically, and doesn't comes from the same reflection points only. As to the more complex reflection in deep layer, it is difficult to describe the relationship between the reflective interface and the travel time. Extrapolation is used to eliminate caustic and simplify the expression of travel time. So the image quality is enhanced by Fresnel zone stack in target. Based on wave equation, high-frequency ray solution and its character are given to clarify theoretical foundation of the method. The hyperbolic and parabolic travel time of the reflection in layer media are presented in expression of matrix with paraxial ray theory. Because the reflective wave field mainly comes from the Fresnel Zone, thereby the conception of Fresnel Zone is explained. The matrix expression of Fresnel zone and projected Fresnel zone are given in sequence. With geometrical optics, the relationship between object point in model and image point in image space is built for the complex subsurface. The travel time formula of reflective point in the nonuniform media is deduced. Also the formula of reflective segment of zero-offset and nonzero offset section is provided. For convenient application, the interface model of subsurface and curve surface derived from conventional stacks DMO stack and prestack depth migration are analyzed, and the problem of these methods was pointed out in aspects of using data. Arc was put forward to describe the subsurface, thereby the amount of data to stack enlarged in Fresnel Zone. Based on the formula of hyperbolic travel time, the steps of implementation and the flow of Fresnel Zone stack were provided. The computation of three model data shows that the method of Fresnel Zone stack can enhance the signal energy and the ratio of signal to noise effectively. Practical data in Xui Jia Wei Zhi, a area in Daqing oilfield, was processed with this method. The processing results showed that the ability in increasing S/N ratio and enhancing the continuity of weak events as well as confirming the deep configuration of volcanic reservoir is better than others. In deeper target layer, there exists caustic caused by the complex media overburden and the great variation of velocity. Travel time of reflection can't be exactly described by the formula of travel time. Extrapolation is bring forward to resolve the questions above. With the combination of the phase operator and differential operator, extrapolating operator adaptable to the variation of lateral velocity is provided. With this method, seismic records were extrapolated from surface to any different deptlis below. Wave aberration and caustic caused by the inhomogenous layer overburden were eliminated and multi-value curve was transformed into the curve.of single value. The computation of Marmousi shows that it is feasible. Wave field continuation extends the Fresnel Zone stack's application.

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.