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在三维频率域电磁法的正演模拟方法中,有限元方法具有计算精度高、适应性强的优点,近年来来得到了越来越多的关注.在正演过程中,主要的计算量集中在求解由偏微分方程组离散得到的线性方程组上,因此求解线性方程组关系着正演计算速度以及模拟精度.由于由有限元方法离散得到的复系数线性方程组条件数非常大,使用常规的迭代法和预条件很难收敛.目前大多数的研究工作采用直接解法,需要大量的计算机内存,限制了可求解问题的规模.本文研究了线性方程组的迭代解法,通过将复系数线性方程组转化为其实对称形式,构造分块对角预条件.在应用预条件的过程中,需要求解两个较小的实数方程,通过辅助空间解法求解.本文的算法适用于可控源电磁法和大地电磁法,对一系列的数值算例的模拟结果证明了迭代算法的效率,结果表明迭代算法可以在小于20次迭代内收敛,同时迭代次数与模型电阻率、问题规模和频率无关. 相似文献
65.
The elliptic mild slope equation is used to simulate linear wave propagation over variable seabed topography with mild slopes.The governing equation is discretized by the finite difference method.Ba-sed on the BI-CGSTAB technique.an attractive variant of BI-Conjugate Gradients(BI-CG)method,theobtained linear algebraic system of equations is solved.Numerical experiments show that the BI-CGSTABmethod is efficient for solving the elliptic mild slope equation.The results obtained by the BI-CGSTAB-Ba-sed method are much the same as those obtained by other authors with different solution methods,but theconvergence rate is much faster than that of other methods. 相似文献
66.
Fahad Khan Khadim 《水文科学杂志》2020,65(3):427-441
ABSTRACTA Mixed-Integer Nonlinear Programming (MINLP) model is formulated and solved in this study to optimize environmental sustainability of flood control, drainage, and irrigation (FCDI) projects in the deltaic regions of Bangladesh. The model optimizes the value of integrated resource benefit, a dimensionless variable defined to measure the environmental sustainability based on the water, agricultural and ecological resources, with a set of project interventions being the major drivers. The resource benefits were evaluated with the help of several indicators, such as flood, navigability, salinity, waterlogging, cropping intensity, land loss and vegetation. The solution of MINLP model provided optimal values of the decision variables, which are the quantities of project interventions (e.g. length and height of dike, number of sluices and drainage inlets, lengths of drainage canals, erosion protection and afforestation works). The approach and the MINLP formulation presented in this study can be used for any real-life FCDI project improvements. 相似文献
67.
Looking at kriging problems with huge numbers of estimation points and measurements, computational power and storage capacities
often pose heavy limitations to the maximum manageable problem size. In the past, a list of FFT-based algorithms for matrix
operations have been developed. They allow extremely fast convolution, superposition and inversion of covariance matrices
under certain conditions. If adequately used in kriging problems, these algorithms lead to drastic speedup and reductions
in storage requirements without changing the kriging estimator. However, they require second-order stationary covariance functions,
estimation on regular grids, and the measurements must also form a regular grid. In this study, we show how to alleviate these
rather heavy and many times unrealistic restrictions. Stationarity can be generalized to intrinsicity and beyond, if decomposing
kriging problems into the sum of a stationary problem and a formally decoupled regression task. We use universal kriging,
because it covers arbitrary forms of unknown drift and all cases of generalized covariance functions. Even more general, we
use an extension to uncertain rather than unknown drift coefficients. The sampling locations may now be irregular, but must
form a subset of the estimation grid. Finally, we present asymptotically exact but fast approximations to the estimation variance
and point out application to conditional simulation, cokriging and sequential kriging. The drastic gain in computational and
storage efficiency is demonstrated in test cases. Especially high-resolution and data-rich fields such as rainfall interpolation
from radar measurements or seismic or other geophysical inversion can benefit from these improvements. 相似文献
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Preconditioners in computational geomechanics: A survey 总被引:1,自引:0,他引:1
The finite element (FE) solution of geomechanical problems in realistic settings raises a few numerical issues depending on the actual process addressed by the analysis. There are two basic problems where the linear solver efficiency may play a crucial role: 1. fully coupled consolidation and 2. faulted uncoupled consolidation. A class of general solvers becoming increasingly popular relies on the Krylov subspace (or Conjugate Gradient‐like) methods, provided that an efficient preconditioner is available. For both problems mentioned above, the possible preconditioners include the diagonal scaling (DS), the Incomplete LU decomposition (ILU), the mixed constraint preconditioning (MCP) and the multilevel incomplete factorization (MIF). The development and the performance of these algorithms have been the topic of several recent works. The present paper aims at providing a survey of the preconditioners available to date in computational geomechanics. In particular, a review and a critical discussion of DS, ILU, MCP and MIF are given along with some comparative numerical results. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
70.
This study aims to develop a robust, accurate and computationally efficient hydrodynamic and sediment transport model for dam break flows. The two dimensional shallow water equations are resolved based on the finite volume method with an unstructured quadtree mesh. The sediment transport and bed evolution modules are coupled with hydrodynamic module to predict simultaneously the hydrodynamics, sediment concentrations and morphological changes. The interface flux is computed by the HLL approximate Riemann solver with second order accuracy. The effects of pressure and gravity are included in source term in this model, which can simplify the computation and eliminate numerical imbalance between source and flux terms. For dam break flows occurring in complicated geometries, the quadtree rectangular mesh is used to refine the interesting area and important part. The model is first verified against results from laboratory experiments, existing numerical models and real life case. It is then used to simulate dam break flows over a mobile bed to investigate the bed evolution. The results are compared with experimental data and field data with good agreement. The method is simple, efficient, and conservative. It shows promise for handling hydrodynamic simulation and sediment transport for a wide range of dam break flows. 相似文献