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11.
Based on the generalized Gauss–Newton method, a new algorithm to minimize the objective function of the penalty method in (Bentley LR. Adv Wat Res 1993;14:137–48) for inverse problems of steady-state aquifer models is proposed. Through detailed analysis of the “built-in” but irregular weighting effects of the coefficient matrix on the residuals on the discrete governing equations, a so-called scaling matrix is introduced to improve the great irregular weighting effects of these residuals adaptively in every Gauss–Newton iteration. Numerical results demonstrate that if the scaling matrix equals the identity matrix (i.e., the irregular weighting effects of the coefficient matrix are not balanced), our algorithm does not perform well, e.g., the computation cost is higher than that of the traditional method, and what is worse is the calculations fail to converge for some initial values of the unknown parameters. This poor situation takes a favourable turn dramatically if the scaling matrix is slightly improved and a simple preconditioning technique is adopted: For naturally chosen simple diagonal forms of the scaling matrix and the preconditioner, the method performs well and gives accurate results with low computational cost just like the traditional methods, and improvements are obtained on: (1) widening the range of the initial values of the unknown parameters within which the minimizing iterations can converge, (2) reducing the computational cost in every Gauss–Newton iteration, (3) improving the irregular weighting effects of the coefficient matrix of the discrete governing equations. Consequently, the example inverse problem in Bentley (loc. cit.) is solved with the same accuracy, less computational effort and without the regularization term containing prior information on the unknown parameters. Moreover, numerical example shows that this method can solve the inverse problem of the quasilinear Boussinesq equation almost as fast as the linear one.In every Gauss–Newton iteration of our algorithm, one needs to solve a linear least-squares system about the corrections of both the parameters and the groundwater heads on all the discrete nodes only once. In comparison, every Gauss–Newton iteration of the traditional method has to solve the discrete governing equations as many times as one plus the number of unknown parameters or head observation wells (Yeh WW-G. Wat Resour Res 1986;22:95–108).All these facts demonstrate the potential of the algorithm to solve inverse problems of more complicated non-linear aquifer models naturally and quickly on the basis of finding suitable forms of the scaling matrix and the preconditioner. 相似文献
12.
This paper studies the effect of coherency loss and wave passage on the seismic torsional response of three‐dimensional, multi‐storey, multi‐span, symmetric, linear elastic buildings. A model calibrated against statistical analyses of ground motion records in Mexico City is used for the coherency function. The structural response is assessed in terms of shear forces in structural elements. Incoherence and wave passage effects are found to be significant only for columns in the ground level of stiff systems. The increase of column shears in the ground level is much higher for soft than for firm soil conditions. For the torsionally stiff systems considered, it is found that incoherent and phase‐delayed ground motions do not induce a significant rotational response of the structure. The use of a code eccentricity to account for torsion due to ground motion spatial variation is assessed. On firm soil, the use of a base shear along with an accidental eccentricity results in highly overestimated shear forces; however, for soft soil conditions, code formulations may result in underestimated shear forces. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
13.
One hundred thirty-four horizontally polarized shear-wave (SH) seismic soundings have been performed in the Jackson Purchase Region of western Kentucky. These data have been used to derive the thicknesses and shear-wave velocities for the various impedance horizons in the upper 30 m of the soil column at each site for the purposes of general land-use management and loss estimation in the event of an earthquake. A generalized seismic susceptibility soil classification scheme adopted by the Borcherdt (1994a,b) was fit to the results. Soils across western Kentucky were found to be either SC-II or SC-III soils, correlating to gravelly soils having soft to firm consistency and stiff clays to loose/dense sands, respectively. 相似文献
14.
The response of structures subjected to seismic actions is always influenced by P–Δ effects. The importance of this effect is generally modest for structures experiencing an elastic response but often relevant for structures responding well within the inelastic range of behaviour. Seismic codes indicate that P–Δ effects may be counterbalanced through an increase in the structural strength required by a first order analysis. This increase is calculated by means of a strength amplification factor. The expressions suggested in codes for this factor are simplistic and often criticized by researchers. In this paper, the effectiveness of some of the provisions reported in the literature or suggested in seismic codes is evaluated on single degree of freedom systems with different periods of vibration. As suggested by past studies, attention is focused on the influence of the interstorey drift sensitivity coefficient, significant duration of the ground motion, class of the site soil, displacement ductility and equivalent viscous damping ratio of the system. Finally, an accurate expression of the strength amplification factor is proposed. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
15.
近年来,随着海洋油气资源的大规模开发以及跨海电力和通信需求的增加,我国海底电缆管道建设得到迅速发展,近海海底电缆管道分布愈来愈密集,同时与之相关的违法行为也日益增多。目前,我国尚未出台海底电缆管道保护法,现有的处罚规定较为分散、模糊,且处罚力度小,甚至处罚规定之间存在混乱和矛盾的问题,导致难以对海底电缆管道违法行为实施有效打击。澳大利亚和新西兰作为海洋管理经验相对成熟的国家,对海底电缆管道的法律保护较为成熟,其中对海底电缆管道违法行为的处罚分类和方式等,有诸多值得我国学习之处。基于此,文章从违法行为处罚角度深入分析我国海底电缆管道管理与保护的相关制度现状,介绍新西兰和澳大利亚海底电缆管道法律制度概况及处罚规定的特点并与我国进行比较,为完善我国海底电缆管道违法行为的处罚规定和今后的海底电缆管道立法提出了在《中华人民共和国刑法》中增设破坏海底电缆管道罪;制定《海底电缆管道法》等建议。 相似文献
16.
具约束条件的四维变分资料同化问题 总被引：2，自引：0，他引：2
考察了具约束条件的四维变分资料同化问题，首先引入解决该类问题的一般理论与方法，然后用有限元浅水模式对具高频重力波约束条件的四维变分同化问题进行数值试验。采用伴随技术方法和约束最优化的罚函数法和增广拉格朗日方法，使定义的约束目标函数达到最小，而得到最优解。数值试验结果表明：以控制重力波增长为约束条件的四维变分资料同化，能够更有效的滤除扰动分量，得到最优初始场。由此也表明了对数值天气预报中的这类问题是可以用具约束条件的四维变分资料同化来处理。 相似文献
17.
An engineering approach is proposed for representing both site effects and soil-structure interaction in extended alluvial valleys, by using the one-dimensional model of shear were propagation corrected empirically to account for lateral heterogeneities and generated surface waves. The peak structural response is expressed by means of spectral contours that are a function of the predominant period of the site and the fundamental period of the structure. Variations of the peak spectral ordinates with the prevailing site period can be deduced from these contours. A number of events of firm ground, representative of the most dangerous earthquakes expected in Mexico City, are assumed as design earthquakes. Making use of the resulting spectral contours, the provisions for site effects recommended in the Mexican seismic code are evaluated. Also, considering as control motion the 1985 Michoacan earthquake recorded at a representative firm site, spectral contours with soil-structure interaction are obtained which allow one to identify the significant interaction effects originating in the Valley of Mexico for medium- and long-period structures. The influence and relative importance of the critical parameters involved are examined within practical ranges of interest. 相似文献