Analytical and numerical investigation of uniqueness and localization in saturated porous media     

H.W. Zhang  B.A. Schrefler 《国际地质力学数值与分析法杂志》2002,26(14):1429-1448

This paper presents first the applications of uniqueness and strain localization analysis of saturated porous media, where localization of deformation into well defined narrow zones in a saturated porous medium is studied in terms of discontinuous bifurcation theory. A generalized plasticity constitutive model and a Mohr–Coulomb model are used in both the theoretical and numerical analyses of shear band formations. The critical hardening moduli and shear band angle for localization are computed, and quantitative results are given for both constitutive models. Numerical results previously obtained and new ones are confirmed by this analytical and numerical investigation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Electric properties and related physical characteristics of the atmosphere and surface of Titan     

R. Grard  J.J. López-Moreno  I. Jernej  F. Simões  R. Trautner  F. Ferri  R. Rodrigo  C. Béghin  V.J.G. Brown  J.M. Jeronimo  T. Tokano 《Planetary and Space Science》2006,54(12):1124-1136

The permittivity, waves and altimetry (PWA) instrument was designed for the investigation of the electric properties and other related physical characteristics of the atmosphere of Titan, from an altitude around 140 km down to the surface. PWA carried sensors to measure the atmospheric conductivity, and record electromagnetic and acoustic waves up to frequencies of 11.5 and 6.7 kHz, respectively. PWA also measured the relief roughness during the descent and the permittivity of the surface after touchdown. The measurements and the results of the preliminary analysis are presented. An ionized layer is detected at altitudes above 50 km, using two independent techniques, and the presence of free electrons in the upper atmosphere is confirmed. An electric signal at around 36 Hz is observed throughout the descent, but it is not yet confirmed that this emission is unambiguously related to a resonance of the ionospheric cavity. The relative dielectric constant of Titan's surface material is nearly 2 and the electric conductivity 4×10⁻¹⁰ S m⁻¹. The electric properties of the surface seem to evolve after touch-down, possibly due to a local warming of the landing site by the Huygens Probe body.  相似文献   

Observational and numerical modeling methods for quantifying coastal ocean turbulence and mixing   总被引：6，自引：0，他引：6  

Hans Burchard  Peter D. Craig  Hans van Haren  H.E. Markus Meier  Hartmut Prandke  Eric D. Skyllingstad  David J.S. Welsh  Hemantha W. Wijesekera 《Progress in Oceanography》2008,76(4):399-442

In this review paper, state-of-the-art observational and numerical modeling methods for small scale turbulence and mixing with applications to coastal oceans are presented in one context. Unresolved dynamics and remaining problems of field observations and numerical simulations are reviewed on the basis of the approach that modern process-oriented studies should be based on both observations and models. First of all, the basic dynamics of surface and bottom boundary layers as well as intermediate stratified regimes including the interaction of turbulence and internal waves are briefly discussed. Then, an overview is given on just established or recently emerging mechanical, acoustic and optical observational techniques. Microstructure shear probes although developed already in the 1970s have only recently become reliable commercial products. Specifically under surface waves turbulence measurements are difficult due to the necessary decomposition of waves and turbulence. The methods to apply Acoustic Doppler Current Profilers (ADCPs) for estimations of Reynolds stresses, turbulence kinetic energy and dissipation rates are under further development. Finally, applications of well-established turbulence resolving particle image velocimetry (PIV) to the dynamics of the bottom boundary layer are presented. As counterpart to the field methods the state-of-the-art in numerical modeling in coastal seas is presented. This includes the application of the Large Eddy Simulation (LES) method to shallow water Langmuir Circulation (LC) and to stratified flow over a topographic obstacle. Furthermore, statistical turbulence closure methods as well as empirical turbulence parameterizations and their applicability to coastal ocean turbulence and mixing are discussed. Specific problems related to the combined wave-current bottom boundary layer are discussed. Finally, two coastal modeling sensitivity studies are presented as applications, a two-dimensional study of upwelling and downwelling and a three-dimensional study for a marginal sea scenario (Baltic Sea). It is concluded that the discussed methods need further refinements specifically to account for the complex dynamics associated with the presence of surface and internal waves.  相似文献   

Current observations in the southern Yellow Sea in summer     

唐晓晖  王凡  陈永利  白虹  胡敦欣 《中国海洋湖沼学报》2004,22(3):217-223

Current data from three moored Acoustic Doppler Profilers (ADPs) deployed in the southern Yellow Sea at sites A (1-24.17°E, 34.82°N), B (122.82°E, 35.65°N) in summer 2001 and site C (120.85°E, 34.99°N) in summer 2003 were analyzed in this paper. Features of the tidal and residual currents were studied with rotary spectral and cross-spectral methods. Main achievements were as follows: 1) Tides dominated the currents. At sites A and B, the semidiurnal tidal current was basically homogeneous in the whole depth, taking a clockwise rotation at site A, and near-rectilinear counterclockwise rotation at site B; while the diurnal tidal current was strong and clockwise near the surface, but decreased and turned counterclockwise with depth; at site C, semidiurnal tidal current dominated and diurnal current took the second, both of which were counterclockwise and vertically homogeneous. Inertial motion contributed to the clockwise component of diurnal fluctuations; 2) The 3-5d fluctuation of residual current w  相似文献   

三星星座对地定位的最佳构形研究     

余敏  徐劲  夏益  陆本魁 《天文学报》2003,44(3):302-309

用数值方法对三星星座几何构形与定位精度的关系进行了仿真计算，结果表明对满足较高定位精度的区域进行定位，三星的几何构形呈等边三角形时，定位精度最高。  相似文献   

Localized spectral analysis of global satellite gravity fields for recovering time-variable mass redistributions     

Shin-Chan Han  Pavel Ditmar 《Journal of Geodesy》2008,82(7):423-430

A spatiospectral localization method is discussed for processing the global geopotential coefficients from satellite mission data to investigate time-variable gravity. The time-variable mass variation signal usually appears associated with a particular geographical area yielding inherently regional structure, while the dependence of the satellite gravity errors on a geographical region is not so evident. The proposed localization amplifies the signal-to-noise ratio of the (non-stationary) time-variable signals in the geopotential coefficient estimates by localizing the global coefficients to the area where the signal is expected to be largest. The results based on localization of the global satellite gravity coefficients such as Gravity Recovery And Climate Experiment (GRACE) and Gravity and Ocean Circulation Explorer (GOCE) indicate that the coseismic deformation caused by great earthquakes such as the 2004 Sumatra–Andaman earthquake can be detected by the low-low tracking and the gradiometer data within the bandwidths of spherical degrees 15–30 and 25–100, respectively. However, the detection of terrestrial water storage variation by GOCE gradiometer is equivocal even after localization.  相似文献   

Ideal Case Study of Adaptive Localization in Storm-scale Ensemble Kalman Filter Assimilation     

刘硕  闵锦忠  张晨  高士博 《热带气象学报(英文版)》2023,29(3):370-384

This study explores the use of the hierarchical ensemble filter to determine the localized influence of ob-servations in the Weather Research and Forecasting ensemble square root filtering (WRF-EnSRF) assimilation system. With error correlations between observations and background field state variables considered, the adaptive localization approach is applied to conduct a series of ideal storm-scale data assimilation experiments using simulated Doppler radar data. Comparisons between adaptive and empirical localization methods are made, and the feasibility of adaptive locali-zation for storm-scale ensemble Kalman filter assimilation is demonstrated. Unlike empirical localization, which relies on prior knowledge of distance between observations and background field, the hierarchical ensemble filter provides con-tinuously updating localization influence weights adaptively. The adaptive scheme improves assimilation quality during rapid storm development and enhances assimilation of reflectivity observations. The characteristics of both the observation type and the storm development stage should be considered when identifying the most appropriate localization method. Ultimately, combining empirical and adaptive methods can optimize assimilation quality.  相似文献   

三维静力适应过程中声重力波的特性和能量转换研究     

崔新东  刘宇迪  赵增亮  李明华  宋学儒  胥永文 《气象学报》2016,74(1):127-132

为了研究三维静力适应过程的机理,推导三维静力适应方程组并导出声重力波的频散特征、解析解和能量转换关系以及位涡方程。结果表明,三维静力适应过程实际上就是三维声重力波和重力内波的频散过程,声重力波和重力内波的频率在水平方向上可以区分开来。声重力波的频率随着水平波数和垂直波数的增大而增大。取近轴近似,其解析解在空间上呈螺旋曲面,为大气中热通量和动量从一个区域向另一个区域的输送提供了一种机制,从而为研究大气提供了新的视角。垂直速度在动能与有效势能的转换、有效势能与有效弹性势能的转换中发挥着重要的作用,并且只发生在垂直方向上。在静力适应过程中总能量和位涡是守恒的。适应终态中有效势能比有效弹性势能大一个数量级。   相似文献   

中西生态旅游解说系统差异化研究进展及本土化路径   总被引：1，自引：1，他引：0  

赵敏燕  叶文  董锁成  李宇  郭海健 《地理科学进展》2016,35(6):691-701

解说是生态旅游实现其环境教育责任的重要手段,在西方其研究和行业发展已积累了大量成功的理论和实践经验。本文从解说方程式中资源、受众和媒介3个关键要素入手,依据地域分异规律、生态学原理、地理环境决定论等理论,梳理中西方解说系统差异的根源所在。结果发现：西方受“人地分立”价值取向的影响,保持着生态旅游的“纯自然性”,西方的海洋外向型思维延续了注重空间拓展、关注自然客体奥秘的传统,媒介设计鼓励多方利益相关者参与,强调长期公益性;中国人受“天人合一”的审美价值的影响,接受生态旅游自然与人文资源的结合,大陆内向型思维形成了求稳好静的性格,探索未知事物的兴趣较弱,媒介的物造形式胜过内容要求,短期功利性突出。最后,本文提出中国生态旅游解说本土化路径,包括确定可行的解说目标、挖掘双重价值的资源、定位受众特征与类型、标准化规范引导媒介设计等。  相似文献   

Movements in the harlequin fish (Othos dentex), a large predatory serranid from southern Australia: implications for detection and protection     

S Bryars  PJ Rogers 《新西兰海洋与淡水研究杂志》2016,50(4):600-618

The harlequin fish (Othos dentex) is the largest serranid found in the temperate waters of southern Australia. Acoustic telemetry was used to continuously track the movements and activity patterns of 10 harlequin fish (330–620?mm total length; 0.5–3?kg weight) for a 16-month period at a coastal reef site. Data showed that the harlequin fish is a site-attached, diurnal predator, with a relatively small home range in comparison with other temperate reef fishes from Australia and New Zealand. These characteristics indicate that the harlequin fish is susceptible to localised depletions from fishing, but that it can be protected within no-take marine protected areas and can be detected with appropriate daytime monitoring techniques. Individuals also displayed discrete depth preferences on the reef slope, evidence of a nocturnal home base, and homing ability following disturbance from an extreme storm event.  相似文献