改进的等效半空间法及瑞雷波频散曲线反演   总被引：9，自引：4，他引：5       下载免费PDF全文

陈祥  孙进忠 《地球物理学报》2006,49(2):569-576

层状模型的理论频散曲线表明,层状模型表面瑞雷波同一频率对应的相速度具有多值特点,这就是所谓的瑞雷波多阶性. 面波的多阶性导致了实测频散曲线的复杂性,当地层中存在软弱夹层时这一问题尤为突出,从而给实测频散曲线的解释带来了困难. 本文从工程实用的角度出发,根据等效半空间理论,提出了一种计算理论频散曲线的新算法——改进的等效半空间法,避开了面波多阶性这一复杂问题. 由此方法计算得到的面波相速度并不同于某个具体阶数的面波,而是对多阶面波的综合反映. 按照改进的等效半空间法编制了拟合反演程序,并在工程中进行了运用,取得较好的效果.  相似文献   

三维大气扩散粒子分裂(ADPS)模式     

周伯生  李宗恺 《大气科学》1992,16(3):377-384

本文描述了基于PIC方法的三维大气扩散粒子分裂(ADPS)模式,并用解析解和1988年的广州地区现场观测资料验证了本模式.模式根据局地均匀和定常假设引入大粒子概念、烟团扩散原理和大粒子分裂技术,并运用了嵌套网格.ADPS模式用于模拟气态污染物在大气中的散布,同时也具备模拟TSP扩散的效能.  相似文献   

深水有限振幅重力波的一种解法     

侯一筠 《海洋与湖沼》1992,23(6):619-625

采用变量代换的方法,处理水波的自由边界,获得了新的水波控制方程和边界条件。以摄动法解非线性偏微分方程的近似解析解,求得了与三阶斯托克斯波略有差别的非线性波面和包含振幅的非线性水波色散关系,并且得出了二阶以上的波动势函数在深水情况下不为零的结论。  相似文献   

海洋环境中放射性核素扩散模型     

秦学祥 《海洋科学进展》1995,(1)

本文介绍用网格模型对海洋环境中放射性核素的扩散进行新的数学探讨，假设模型运移系数是水体运动和间隔空间几何形状的函数，该模型系统与放射学历史无关。  相似文献   

Dispersion and stability analyses of the linearized two-dimensional shallow water equations in Cartesian coordinates     

S. Sankaranarayanan  Malcolm L. Spaulding   《Ocean Engineering》2003,30(18):2343-2362

In the present study, a Fourier analysis is used to develop expressions for phase and group speeds for both continuous and discretized, linearized two-dimensional shallow water equations, in Cartesian coordinates. The phase and group speeds of the discrete equations, discretized using a three-point scheme of second order, five-point scheme of fourth order and a three-point compact scheme of fourth order in an Arakawa C grid, are calculated and compared with the corresponding values obtained for the continuous system. The three-point second-order scheme is found to be non-dispersive with grid resolutions greater than 30 grids per wavelength, while both the fourth-order schemes are non-dispersive with grid resolutions greater than six grids per wavelength. A von Neumann stability analysis of the two- and three-time-level temporal schemes showed that both schemes are stable. A wave deformation analysis of the two-time-level Crank–Nicolson scheme for one-dimensional and two-dimensional systems of shallow water equations shows that the scheme is non- dispersive, independent of the Courant number and grid resolution used. The phase error or the dispersion of the scheme decreases with a decrease in the time step or an increase in grid resolution.  相似文献   

Analysis of macrodispersion through volume-averaging: Moment equations     

P. K. Kitanidis 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(1):5-25

Macrodispersion is spreading of a substance induced by spatial variations in local advective velocity at field scales. Consider the case that the steady-state seepage velocity and the local dispersion coefficients in a heterogeneous formation may be modeled as periodic in all directions in an unbounded domain. The equations satisfied by the first two spatial moments of the concentration are derived for the case of a conservative non-reacting solute. It is shown that the moments can be calculated from the solution of well-defined deterministic boundary value problems. Then, it is described how the rate of increase of the first two moments can be calculated at large times using a Taylor-Aris analysis as generalized by Brenner. It is demonstrated that the second-order tensor of macrodispersion (or effective dispersion) can be computed through the solution of steady-state boundary-value problems followed by the determination of volume averages. The analysis is based solely on volume averaging and is not limited by the assumption that the fluctuations are small. The large-time results are valid when the system is in a form of equilibrium in which a tagged particle samples all locations in an appropriately defined phase space with equal probability.  相似文献   

Street Versus Rooftop Level Concentrations of Fine Particles in a Cambridge Street Canyon     

Prashant Kumar  Paul S. Fennell  Allan N. Hayhurst  Rex E. Britter 《Boundary-Layer Meteorology》2009,131(1):3-18

Dispersion of particles, as evidenced by changes in their number distributions (PNDs) and concentrations (PNCs), in urban street canyons, is still not well understood. This study compares measurements by a fast-response particle spectrometer (DMS500) of the PNDs and the PNCs (5–1000 nm, sampled at 1 Hz) at street and rooftop levels in a Cambridge UK street canyon, and examines mixing, physical and chemical conversion processes, and the competing influences of traffic volume and rooftop wind speed on the PNDs and the PNCs in various size ranges. PNCs at street level were ≈6.5 times higher than at rooftop. Street-level PNCs followed the traffic volume and decreased with increasing wind speed, showing a larger influence of wind speed on 30–300 nm particles than on 5–30 nm particles. Conversely, rooftop PNCs in the 5–30 nm size range increased with wind speed, whereas those for particles between 30 and 300 nm did not vary with wind speed.  相似文献   

Validation of OML,AERMOD/PRIME and MISKAM Using the Thompson Wind-Tunnel Dataset for Simple Stack-Building Configurations     

Helge Rørdam Olesen  Ruwim Berkowicz  Matthias Ketzel  Per Løfstrøm 《Boundary-Layer Meteorology》2009,131(1):73-83

A comprehensive dataset on dispersion behind rectangular buildings has been used to analyse the performance of two dispersion models in respect to their handling of building effects: the Danish OML model and the US AERMOD model with the PRIME building algorithm; additionally, the German MISKAM model has been assessed. OML and AERMOD are regulatory plume models with limited requirements in terms of input and computing resources, whereas MISKAM is a computational fluid dynamical model, and as such much more demanding. For most scenarios considered, the degree of misprediction in respect to the maximum concentrations is less than a factor of two for OML and AERMOD. However, in respect to the concentration at a specific location, especially in the near field, both models often result in larger mispredictions. MISKAM provides more accurate predictions.  相似文献   

A higher-order non-hydrostatic σ model for simulating non-linear refraction–diffraction of water waves     

Chih-Chieh Young  Chin H. Wu  Wen-Cheng Liu  Jan-Tai Kuo 《Coastal Engineering》2009

A higher-order non-hydrostatic σ model is developed to simulate non-linear refraction–diffraction of water waves. To capture non-linear (or steep) waves, a 4th-order spatial discretization is utilized to approximate the large horizontal pressure gradient. A higher-order top-layer pressure treatment is further implemented to resolve wave propagation. The model's characteristics including linear wave dispersion and non-linearity are carefully examined. The accuracy of the present model using only two vertical layers is validated by laboratory data and the available results predicted by the non-linear Schrödinger equation, Boussinesq-type equations, the non-linear mild slope equation, and the Laplace equation. Features of harmonic generation as well as the influences of dispersion and non-linearity on wave energy transfer processes are discussed.  相似文献   

瑞利波测试技术用于剪切波速勘探之研究     

石玉成  蔡红卫 《高原地震》1995,(3)

本文根据瑞利波测量所得波形的变化特征，分析研究了地基参数对瑞利波弥散曲线的影响规律，提出了利用瑞利波测试剪切波速的方法。在研究过程中，对瑞利波测试技术进行了探讨，并引入了相关分析原理，以消除噪声、系统的非线性以及其它一些人为因素的干扰。最后结合实例，论证该技术用于实际勘探的可行性并指出其存在的问题和有待进一步完善的工作。  相似文献