共查询到20条相似文献，搜索用时 531 毫秒
1.
A. Naji A. H.-D. Cheng D. Ouazar 《Stochastic Environmental Research and Risk Assessment (SERRA)》1998,12(6):413-430
Three analyitcal solutions of saltwater intrusion under uncertain hydrologic, hydrogeologic, and pumping conditions are presented.
These solutions extends the existing deterministic, sharp interface solutions to stochastic ones. The randomness is represented
in terms of statistical measures of mean, standard deviation and covariance. The analysis is based on perturbation using Taylor
series expansion. Simulations based on probability distribution are conducted for verification. 相似文献
2.
An isoparametric quadrilateral plate bending element is used for the free and forced vibration analysis of both thick and thin plates. Plates of rectangular, circular and triangular planform are analysed and excellent results are obtained. The element performance is assessed by comparison with analytical solutions based on Mindlin's thick plate theory, three-dimensional elasticity solutions and solutions based on thin plate theory. 相似文献
3.
Robert G. THOMAS 《水文科学杂志》2013,58(4):50-69
Abstract Graphical solutions to linear and radial ground water flow problems are described. These methods are based on finite difference approximations which have been widely used in heat flow problems. The case of the leaky aquiclude and vertical recharge to unconfined aquifers is discussed as well as constant head at a control and constant discharge or recharge. These solutions are useful only when the physical factors are known and an estimate of water level changes under certain conditions is desired. The methods are not intended to replace more rigorous mathematical solutions. 相似文献
4.
求震源机制P波初动解的格点尝试概率法 总被引：9，自引：0，他引：9
考虑到Ｐ波初动数据在震源球面上分布的不均匀性对节面解的可能影响，不用矛盾符号所占比例的大小作为选择可取节面解的标准，而是将震源球面分成许多小块，再确定有Ｐ波初动数字的小块为正号区或负号区的概率，最后以全部有数据小块的平均概率的高低作为选择解答的标准。用此改进方法重新测定了徐纪仁等（Ｘｕ ｅｔ．ａｌ，，１９８８）发表的青藏高原地区９９个地震的震源机制解，从中筛选出了２０个可信的解答。 相似文献
5.
我国部分早期震源机制解答的重新测定 总被引：16，自引：0，他引：16
根据不同作者对同一地震震源机制解的不同测定结果之间的差异程度来估计测定结果的相对可信度。用此方法对１９８５年ＩＡＳＰＥＩ东京会议选定的５１个地震不同作者测定的结果作了分析，同时也对我国有两个以上测定结果的震源机制解答作了分析，结果说明，我国现有震源机制解答测定精度总体上有待提高。用５°×５°×５°的格点尝试法重新处理了国家地震局震源机制研究小组１９７３年所著《中国地震震源机制研究》第一集中所载除台湾地震和深震外的２２９个地震的Ｐ波初动方向数据，最后只得出了４７个可供参考的震源机制解答。 相似文献
6.
Analytical solutions to debris avalanche problems involving shock waves are derived. The debris avalanche problems are described in two different coordinate systems, namely, the standard Cartesian and topography-linked coordinate systems. The analytical solutions can then be used to test debris avalanche numerical models. In this article, finite volume methods are applied as the numerical models. We compare the performance of the finite volume method with reconstruction of the conserved quantities based on stage, height, and velocity to that of the conserved quantities based on stage, height, and momentum for solving the debris avalanche problems involving shock waves. The numerical solutions agree with the analytical solution. In addition, both reconstructions lead to similar numerical results. This article is an extension of the work of Mangeney et al. (Pure Appl Geophys 157(6–8):1081–1096, 2000). 相似文献
7.
Three-dimensional time-harmonic Green's functions of saturated soil under buried loading 总被引：3，自引：0，他引：3
Three-dimensional time-harmonic response of a poroelastic half space subjected to an arbitrary buried loading is investigated. The analysis starts with the field equations in cylindrical coordinates based on Biot's general theory of poroelasticity. General solutions for the displacements are first derived using the Fourier expansions and Hankel integral transform with respect to the circumferential and radial coordinates, respectively. The transformed-domain solutions are obtained in explicit form. The physical-domain displacements and stress components are then obtained numerically by inverse integral transform. Comparisons illustrating the accuracy of the developed approach are made with existing solutions for an elastic half space, which is reduced directly from the general solution developed in the paper. Numerical results are presented for the displacements of a saturated soil subjected to a horizontal internal excitation. 相似文献
8.
The eigenvalue decomposition technique is used for analysis of conditionality of two alternative solutions for a determination
of the geoid from local gravity data. The first solution is based on the standard two-step approach utilising the inverse
of the Abel-Poisson integral equation (downward continuation) and consequently the Stokes/Hotine integration (gravity inversion).
The second solution is based on a single integral that combines the downward continuation and the gravity inversion in one
integral equation. Extreme eigenvalues and corresponding condition numbers of matrix operators are investigated to compare
the stability of inverse problems of the above-mentioned computational models. To preserve a dominantly diagonal structure
of the matrices for inverse solutions, the horizontal positions of the parameterised solution on the geoid and of data points
are identical. The numerical experiments using real data reveal that the direct gravity inversion is numerically more stable
than the downward continuation procedure in the two-step approach. 相似文献
9.
Imran Maqsood Guo H. Huang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(3):643-657
This study introduces a hybrid optimization approach for flood management under multiple uncertainties. An inexact two-stage integer programming (ITIP) model and its dual formation are developed by integrating the concepts of mixed-integer and interval-parameter programming techniques into a general framework of two-stage stochastic programming. The proposed approach provides a linkage to pre-defined management policies, deals with capacity-expansion planning issues, and reflects various uncertainties expressed as probability distributions and discrete intervals for a flood management system. Penalties are imposed when the policies are violated. The marginal costs are determined based on dual formulation of the ITIP model, and their effects on the optimal solutions are investigated. The developed model is applied to a case study of flood management. The solutions of binary variables represent the decisions of flood-diversion–capacity expansion within a multi-region, multi-flow-level, and multi-option context. The solutions of continuous variables are related to decisions of flood diversion toward different regions. The solutions of dual variables indicate the decisions of marginal costs associated with the resources of regions’ capacity, water availability, and allowable diversions. The results show that the proposed approach could obtain reliable solutions and adequately support decision making in flood management. 相似文献
10.
Highly-reduced dynamic orbits and their use for global gravity field recovery: A simulation study for GOCE 总被引：1，自引：0，他引：1
The so-called highly reduced-dynamic (HRD) orbit determination strategy and its use for the determination of the Earth’s gravitational
field are analyzed. We discuss the functional model for the generation of HRD orbits, which are a compromise of the two extreme
cases of dynamic and purely geometrically determined kinematic orbits. For gravity field recovery the energy integral approach
is applied, which is based on the law of energy conservation in a closed system. The potential of HRD orbits for gravity field
determination is studied in the frame of a simulated test environment based on a realistic GOCE orbit configuration. The results
are analyzed, assessed, and compared with the respective reference solutions based on a kinematic orbit scenario. The main
advantage of HRD orbits is the fact that they contain orbit velocity information, thus avoiding numerical differentiation
on the orbit positions. The error characteristics are usually much smoother, and the computation of gravity field solutions
is more efficient, because less densely sampled orbit information is sufficient. On the other hand, the main drawback of HRD
orbits is that they contain external gravity field information, and thus yield the danger to obtain gravity field results
which are biased towards this prior information. 相似文献
11.
This paper presents an indirect boundary integration equation method for diffraction of plane SV waves by a 2-D cavity in a poroelastic half-space.The Green’s functions of compressive and shear wave sources are derived based on Biot’s theory. The scattered waves are constructed using fi ctitious wave sources close to the boundary of the cavity, and their magnitudes are determined by the boundary conditions. Verifi cation of the accuracy is performed by: (1) checking the satisfaction extent of the boundary c... 相似文献
12.
A mathematical formulation for optimal control of air pollution 总被引：3，自引：0，他引：3
In recent years the urban air pollutions caused by emissions from industry, transportation and energy consuming for daily living are getting worse in many major cities of China. Peoples awareness on air quality is increasing. Routine monitoring and foreca… 相似文献
13.
Robert A. Pearson 《Pure and Applied Geophysics》1980,118(2):913-934
For a thermal starting from rest, the scales of motion consistent with the initial conditions are given. An alternative time scale based on the motion of the thermal is derived. The anticipated similarity solutions for thermals are summarised and possible qualitative differences between solutions are given. Within this consistent framework previously published laboratory and numerical models of thermals are discussed. Reasons why numerical models have not rigorously demonstrated the existence of a self-similarity solution are considered. Comparisons of all available results show that a single similarity solution valid for all thermals does not exist. 相似文献
14.
J. Enrique Luco 《地震工程与结构动力学》1998,27(3):225-242
A simple model for the seismic response of a one-storey structure subjected to active control in the presence of soil–structure interaction effects is presented. The approach is based on the successive use of equivalent 1-DOF oscillators which account for the effects of control and soil–structure interaction. Simple expressions for these oscillators based on exact analytical solutions of the control equations and approximate solutions of the interaction equations are presented. The study includes an evaluation of the effects of soil–structure interaction on the seismic response of actively controlled structures in which the control gains have been determined with and without inclusion of soil–structure interaction effects. A simple procedure to include the interaction effects on the control gains is also presented. © 1998 John Wiley & Sons, Ltd. 相似文献
15.
Simple closed‐form approximations are presented for calculating the steady‐state groundwater age distribution in two‐dimensional vertical cross sections of idealized fresh water lenses overlying salt water, for aquifers that are vertically semi‐infinite and of finite thickness. The approximations are developed on the basis of existing one‐dimensional analytical solutions for travel‐time calculation in fresh water lenses and approximate streamline formulations. The two‐dimensional age distributions based on the closed‐form solutions match convincingly with numerical simulations. As expected, notable deviations from the numerical solution are encountered at the groundwater flow divide and when submarine groundwater discharge occurs. Ratios of recharge over hydraulic conductivities are varied to explore how the magnitude of the deviations changes, and it is found that the approximate closed‐form solutions perform well over a range of conditions found in natural systems. 相似文献
16.
Analytic solutions are presented for steady interface flow in aquifers consisting of a confined and a semi-confined section. The total discharge is constant in the confined section and is directed towards the semi-confined section, which is bounded on top by a leaky layer that separates the aquifer from the sea. All solutions are based on the Dupuit approximation. The interface position is fully determined by two dimensionless parameters. The first parameter is the product of the uniform gradient towards the sea and the dimensionless leakage factor divided by the dimensionless density difference. The second dimensionless parameter is the length of the semi-confined section divided by the leakage factor. Four types of flow are distinguished. For cases I and II the interface does not reach the end of the semi-confined section, while it does for cases III and IV. For cases I and III the interface extends into the confined section, while for cases II and IV it remains entirely in the semi-confined section. Analytic solutions are presented for the position of the interface for all four cases. Diagrams are presented to determine the type of flow and the position of the interface toe based on the two dimensionless parameters. The pre-development position of the interface along the Georgia coast is computed as an illustration of the practical application of the presented formulas. Another practical application is the estimation of how far a numerical model of seawater intrusion should be extended into the sea for accurate simulations. 相似文献
17.
The success of transient storage (TS) modeling for natural streams depends, in part, on the ability to describe the dispersion process accurately. Evidence based on stream tracer data shows that solute transport processes often do not follow the classical second-order dispersion model (e.g., early breakthrough and faster than Fickian travel times were observed). While models based on space-fractional dispersion are a promising alternative, different definitions of fractional derivatives exist in the literature. Unlike integer-order derivatives, fractional derivatives represent convolutions of concentration with long-range spatial correlation and numerical approximations can produce dense matrices. Therefore issues of both accuracy and computational efficiency need to be examined to successfully identify model parameters for natural streams. In this paper, we first compare the performance of several numerical approaches for solving the space-fractional dispersion equation. We examine three different numerical approaches to approximate the space-fractional derivatives including: (a) a fully-implicit scheme based on the shifted Grünwald–Letnikov (GL) approximation (b) a three-point implicit representation based on the GL formula and (c) a three-point implicit scheme based on mass conservation and the Caputo definition of the fractional derivative. We then use an operator-splitting technique to evaluate a TS model based on space-fractional dispersion (the FSTS model) and test the model against analytical solutions and stream tracer data. A sequence acceleration method (Richardson extrapolation) significantly improves the performance of all schemes examined. Results indicate that the fully-implicit GL method with Richardson extrapolation produces the most accurate solutions while the three-point implicit GL scheme has a stringent time-step restriction to produce acceptable solutions. The three-point implicit scheme based on the Caputo derivative produces accurate solutions in a fraction of the time taken by the fully-implicit GL method and represents the best trade-off between accuracy and computational efficiency for practical applications. The scheme is suitable for parameter estimation and is used to successfully describe tracer data in a natural stream. 相似文献
18.
井中震源在逆VSP、随钻地震和采矿地球物理研究中都有广泛应用.满足"小井孔"(井孔半径远小于特征波长)及"远场"(炮检距大于特征波长)假设时,井中震源的远场波场存在解析解.为了检验解析解在不同情况下的适用性,本文使用最速下降积分计算了不满足上述假设时井中震源远场波场的合成地震记录,即半解析解.模型试验表明,解析解只能在同时满足"小井孔"和"远场"假设时使用;当这两个假设条件不满足时,解析解的振幅和波形相对于半解析解会有明显的偏差.随着假设不满足程度的增加,偏差会逐渐增加,并会逐渐影响走时的准确拾取;这种条件下,采用半解析解才能获得准确的井中震源波场. 相似文献
19.
20.
Harn C. Chen 《地震工程与结构动力学》1993,22(1):63-74
An efficient numerical algorithm is developed to solve the quadratic eigenvalue problems arising in the dynamic analysis of damped structural systems. The algorithm can even be applied to structural systems with non-symmetric matrices. The algorithm is based on the use of Arnoldi's method to generate a Krylov subspace of trial vectors, which is then used to reduce a large eigenvalue problem to a much smaller one. The reduced eigenvalue problem is solved and the solutions are used to construct approximate solutions to the original large system. In the process, the algorithm takes full advantage of the sparseness and symmetry of the system matrices and requires no complex arithmetic, therefore, making it very economical for use in solving large problems. The numerical results from test examples are presented to demonstrate that a large fraction of the approximate solutions calculated are very accurate, indicating that the algorithm is highly effective for extracting a number of vibration modes for a large dynamic system, whether it is lightly or heavily damped. 相似文献