利用伴随法优化非线性潮汐模型的开边界条件Ⅰ．伴随方程的建立及“孪生"数值试验   总被引：1，自引：1，他引：0  

韩桂军  马继瑞  刘克修  李冬 《海洋学报》2000,22(6)

本研究采用基于最优控制理论的伴随法,把观测资料同化到陆架海域潮汐数值模型中去,优化开边界条件,提高数值预报的精度．潮汐模型的控制方程为考虑平流项、非线性底摩擦和侧向涡动粘性项的非线性浅水方程组;采用Lagrange乘子法建立了伴随模型．研究分两部分：第一部分即本文,建立非线性浅水方程模型的伴随方程、给出目标函数的梯度,并实现“孪生”数值试验;第二部分另文给出．  相似文献   

Where Are the Great Plains? A Cartographic Analysis     

Sonja Rossum  Stephen Lavin 《The Professional geographer》2000,52(3):543-552

Geographic regions all have some degree of uncertainty, though this is seldom represented on their maps. Uncertainty of the Great Plains boundary is shown here by comparing 50 previously published maps of the region. These maps were found in a variety of sources, from classic 1930s geographic works to current regional studies on the Internet. By examining this diverse collection, a distinction can be seen between those maps using primarily physical criteria to define the region and those using cultural characteristics, or a combination of these two characteristics. This distinction is supported by trends in boundary shape, size, and even the map's date of publication. The Great Plains is shown as a complex region, subject to the interpretations of individual cartographers, and can be better understood by considering all points of view rather than any single boundary line.  相似文献   

An alternative interpretation of the Cayman trough evolution from a reidentification of magnetic anomalies     

S. Leroy  A. Mauffret  P. Patriat  & B. Mercier de Lépinay 《Geophysical Journal International》2000,141(3):539-557

Magnetic data were collected during the Wilkes (1973) and Seacarib II (1987) cruises to the Cayman trough. A new interpretation of magnetic data is carried out. An isochron pattern is drawn up from our anomaly identifications. An early Eocene age (49 Ma, Ypresian) for Cayman trough opening is proposed instead of the late Oligocene or middle Eocene ages suggested by previous studies. Our plate tectonic reconstruction is simpler and fits the on-land geology (Jamaica and Cuba) and the tectonics. Our reconstruction shows a southward propagation of the spreading centre between magnetic anomalies 8 and 6 (26 and 20 Ma). The trough width increases by 30 km in this period. The southward propagation of the Cayman spreading centre from the Middle Oligocene to the Early Miocene induced the development of the restraining bend of the Swan Islands, the formation of a 1 km high scarp on the eastern trace of the Cayman trough transform fault (Walton fault) and the formation of a pull-apart basin (Hendrix pull-apart). Magnetic anomalies and magnetization maps give information about the deformation and the rocks. The proposed evolutionary model of the Cayman trough from the inception of seafloor spreading to the present configuration is presented in relation to the tectonic escape of the northern boundary of the Caribbean plate from the Maastrichtian to the Present.  相似文献   

Seismic response of three-dimensional topographies using a time-domain boundary element method     

François Janod  & Olivier Coutant 《Geophysical Journal International》2000,142(2):603-614

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Convection in the Earth's core driven by lateral variations in the core–mantle boundary heat flux     

Steven John Gibbons  & David Gubbins 《Geophysical Journal International》2000,142(2):631-642

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江苏大丰潮滩潮流边界层特征研究   总被引：7，自引：0，他引：7  

李占海  高抒  陈沈良 《海洋工程》2007,25(3):53-60

2003年7月中小潮期间使用MIDAS-400用户化数据采集系统在江苏大丰潮滩上进行了垂向多层位同步的流速和悬沙浓度观测。根据观测资料研究了潮流作用下的潮滩底部边界层过程,结果表明,观测地点的潮汐不对称现象十分明显,落潮流速、历时和输水输沙量皆明显大于涨潮;在潮周期内的多数时间里流速剖面符合对数分布,但在风力较强、水流快速增加和流速缓慢的情况下,流速剖面常偏离对数分布;悬沙颗粒垂向混合均匀,悬沙浓度剖面符合Rouse公式;落潮时的底部切应力和摩阻流速明显大于涨潮,摩阻流速与各水层流速通常有较好的线性关系;滩面糙度主要与沙纹形态和推移质运动强度有关,它与摩阻流速存在密切关系;悬沙浓度具有明显的减阻效应,受其影响,摩阻流速和底部切应力分别减小了28%~41%和40%~62%。  相似文献   

A study on mechanical properties and fracturing behavior of Carrara marble with the flat-jointed model     

Yi Cheng  Louis Ngai Yuen Wong 《国际地质力学数值与分析法杂志》2020,44(6):803-822

Overcoming two inherent limitations presented by the standard bonded-particle model (BPM), the flat-jointed model still lacks extensive application. This study hereby conducts a comprehensive investigation on the application of the flat-jointed model in rock mechanics study. First, after a careful examination on the mechanical behavior of the flat-joint contact, a systematic calibration has been conducted to build numerical models matching the mechanical properties of Carrara marble. Second, the validated model is used to simulate the fracturing behavior of marble specimens containing a single or en-echelon flaws. Finally, the appearance of particle flow code (PFC) models has been compared with the results obtained from optical observation in order to establish a possible correlation between PFC models and real marble regarding microcracking behavior. Discussions suggest that to remove the particle size effect, the model resolution (ratio of sample dimension to the average particle diameter) should be larger than 30 in the flat-jointed model and 150 in the BPM, respectively. Results from the above investigations suggest that the flat-jointed model is capable of matching both the mechanical properties and fracturing behavior of Carrara marble. The numerical model is more reliable to predict the fracturing path at the instant of initiation than at failure. Development of initial fractures is not only controlled by the magnitude of tension force but also influenced by the extent of distribution of tension force. The appearance and components of a fracture in flat-jointed models probably reveal not only its property (tensile or shear) but also the corresponding microcracking behavior of real rocks.  相似文献   

One-dimensional self-weight consolidation with continuous drainage boundary conditions: Solution and application to clay-drain reclamation     

Jianxue Feng  Pengpeng Ni  Guoxiong Mei 《国际地质力学数值与分析法杂志》2019,43(8):1634-1652

Traditional consolidation theories cannot provide good predictions of consolidation settlement in land reclamation because of their assumptions that the influence of soil's self-weight is often neglected, and the drainage boundary is considered as fully pervious/impervious. In view of these limitations, an analytical solution is derived for one-dimensional self-weight consolidation problems with a continuous drainage boundary using the finite Fourier sine transform method. Following the classical Terzaghi's small strain theory, the soil's self-weight is considered to produce consolidation settlement in dredged materials with a constant coefficient of consolidation. The continuous drainage boundary can essentially describe the time-dependent variation of drainage capacity at the interface between two adjacent soil layers. By reducing the interface parameters, the effectiveness of the calculation is demonstrated against the Terzaghi's solution. The influence of interface parameters and soil's self-weight stress coefficient on self-weight consolidation is discussed. As expected, the rate of consolidation considering the self-weight stress is faster, although the dependency of consolidation rate on the material property of void ratio is neglected. Moreover, the plane of maximum excess pore-water pressure is estimated as a function of time factor, based on which a design chart is developed to optimize the layout of horizontal drains in land reclamation.  相似文献   

A coupled 3‐dimensional bonded discrete element and lattice Boltzmann method for fluid‐solid coupling in cohesive geomaterials          下载免费PDF全文

Min Wang  Y.T. Feng  G.N. Pande  T.T. Zhao 《国际地质力学数值与分析法杂志》2018,42(12):1405-1424

This paper presents a 3D bonded discrete element and lattice Boltzmann method for resolving the fluid‐solid interaction involving complicated fluid‐particle coupling in geomaterials. In the coupled technique, the solid material is treated as an assembly of bonded and/or granular particles. A bond model accounting for strain softening in normal contact is incorporated into the discrete element method to simulate the mechanical behaviour of geomaterials, whilst the fluid flow is solved by the lattice Boltzmann method based on kinetic theory and statistical mechanics. To provide a bridge between theory and application, a 3D algorithm of immersed moving boundary scheme was proposed for resolving fluid‐particle interaction. To demonstrate the applicability and accuracy of this coupled method, a benchmark called quicksand, in which particles become fluidised under the driving of upward fluid flow, is first carried out. The critical hydraulic gradient obtained from the numerical results matches the theoretical value. Then, numerical investigation of the performance of granular filters generated according to the well‐acknowledged design criteria is given. It is found that the proposed 3D technique is promising, and the instantaneous migration of the protected soils can be readily observed. Numerical results prove that the filters which comply with the design criteria can effectively alleviate or eliminate the appearance of particle erosion in dams.  相似文献   

A continuum mechanics based framework for optimizing boundary and finite element meshes associated with underground excavations—accuracy,efficiency and applications     

Attila M. Zski  John H. Curran 《国际地质力学数值与分析法杂志》2005,29(13):1299-1315

A framework was developed to address the automatic optimization of the level of geometric detail required for stress analysis of underground excavations in mining, which was presented in the companion paper. The motivation for optimizing the mesh geometry stems from the over‐discretization of computational domain as the digital mine model is built while our knowledge of some of the input parameters is quite limited. Thus, the accuracy of the solution is not expected to be increased with a finely discretized mesh, only the computation time does. Therefore, it is acceptable if the results obtained from an optimized model have accuracy comparable to the uncertainty in input data (e.g. rock mass properties, geology, etc.). Although the mesh optimization framework automates the geometry optimization and reduces computation time, the accuracy of the solution from the resulting geometry must be evaluated to ensure the quality of the solution at the ‘region of interest’. Both a priori (mesh quality) and a posteriori (solution quality) measures are employed along with recording the mesh optimization time. Finally, the applicability of the mesh optimization framework is demonstrated by analysing a number of mining and civil engineering underground models. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献