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许模 《地质灾害与环境保护》1996,(2)
本文讨论了复杂地质环境中渗流场的反分析问题，利用地下水流数值模拟结合最优化技术，通过对地下渗流场的模拟和寻优，求得描述地下含水介质非稳定渗流场的重要参位──渗透系数和给水度的模型解，并应用于各向同性的多孔介质渗流场反分析实例中。 相似文献
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The dynamic response of a seismic soil–pile–structure interaction (SSPSI) system is investigated in this paper by conducting nonlinear 3D finite element numerical simulations. Nonlinear behaviors such as non-reflecting boundary condition and soil–pile–structure interaction modeled by the penalty method have been taken into account. An equivalent linear model developed from the ground response analysis and the modified Drucker–Prager model are separately used for soil ground. A comparison of the two models shows that the equivalent linear soil model results in an underestimated acceleration response of the structure under this ground shaking and the soil behavior should be considered as a fully-nonlinear constitutive model in the design process of the SSPSI system. It was also observed that the dynamic response of the system is greatly affected by the nonlinearity of soil–pile interface and is not sensitive to the dilation angle of the soil. Furthermore, the effect of the presence of pile foundations on SSPSI response is also analyzed and discussed. 相似文献
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山东省耕地资源安全问题研究 总被引：10，自引：0，他引：10
构建耕地资源安全概念模型,通过对人口资源压力极值状态下的耕地资源安全需求与可能供给之间的综合平衡,分析山东省耕地资源安全态势。2004年山东省耕地总量为754万hm2,预测2020年全省耕地资源的安全需求量为747万hm2,同期各种原因将减少耕地42.5万hm2,后备耕地潜力为50万hm2。理论上可保障耕地资源安全,但实践操作难度较大,据此提出保障山东省耕地资源安全的相应对策。 相似文献
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工程总承包安全管理是对工程项目所有安全因素及安全事项进行全面策划和控制的过程,涵盖设计、施工、调试及运行等建设阶段。通过对工程项目全过程和全方位的安全管理,使得工程项目建设始终处于正常、有序的展开状态,以确保实现工程项目安全管理目标。 相似文献
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Correction factors for SSI effects predicted by simplified models: 2D versus 3D rectangular embedded foundations 
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下载免费PDF全文 The effects of soil‐structure interaction (SSI) are often studied using two‐dimensional (2D) or axisymmetric three‐dimensional (3D) models to avoid the high cost of the more realistic, fully 3D models, which require 2 to 3 orders of magnitude more computer time and storage. This paper analyzes the error and presents correction factors for system frequency, system damping, and peak amplitude of structural response computed using impedances for linear in‐plane 2D models with rectangular foundations, embedded in uniform or layered half‐space. They are computed by comparison with results for 3D rectangular foundations with the same vertical cross‐section and different aspect ratios. The structure is represented by a single degree‐of‐freedom oscillator. Correction factors are presented for a range of the model parameters. The results show that in‐plane 2D approximations overestimate the SSI effects, exaggerating the frequency shift, the radiation damping, and the reduction of the peak amplitude. The errors are larger for stiffer, taller, and heavier structures, deeper foundations, and deeper soil layer. For example, for a stiff structure like Millikan library (NS response; length‐to‐width ratio ≈ 1), the error is 6.5% in system frequency, 44% in system damping, and 140% in peak amplitude. The antiplane 2D approximation has an opposite effect on system frequency and the same effect on system damping and peak relative response. Linear response analysis of a case study shows that the NEHRP‐2015 provisions for reduction of base shear force due to SSI may be unsafe for some structures. The presented correction factor diagrams can be used in practical design and other applications. 相似文献
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全波形反演是一种高精度的反演方法,其目标函数是一个强非线性函数,易受局部极值影响,而且反演过程计算量较大.波场重构反演是近几年提出的一种改进的全波形反演理论.该反演方法通过将波动方程作为惩罚项引入到目标函数中,通过拓宽解的寻找空间减弱了局部极小值的影响,而且反演过程不需要计算伴随波场,提高了计算效率.但该反演方法一直缺少准确的惩罚因子算法,直接影响到该方法的准确度.本文将波场重构反演拓展到时间域并利用梯度法进行波场重构.频率域的惩罚因子用来加强波动方程的约束,而时间域惩罚因子表现为调节模拟波场和实际波场的权重因子.为此,我们根据约束优化理论,在波动方程准确以及重构波场与反演参数解耦的假设下,提出以波动方程为目标函数的新的惩罚因子算法.根据波形反演在应用时普遍存在的噪音干扰、子波错误和低频信息缺失的情况下,应用部分Sigsbee2A模型合成数据对本文提出的算法进行实验.数值实验结果表明：基于新的惩罚因子算法,在其他信息不准确的情况下,波场重构反演可以给出高精度的反演结果. 相似文献
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WANG Weiguo 《海洋学报(英文版)》2011,30(5):125-140
The ridge like seafloor highs with various geological origins can be classed into mid-ocean ridges,transverse ridges related to transform faults,hot spot/mantle plume originated ridges,microcontinent rifted from major continent,intra-plate arc formed by interaction of two oceanic plates,and tectonic ridges uplifted by later tectonic activity.Those ridges moved towards the convergent continental margins along with the underlain plate drifting and formed so-called accreted ridges commonly trending at a high angle to the continental margins.At divergent continental margins,the continental crusts were extended and thinned accompanying with magmatism,which formed high terrains protruding or parallel to the coastal line.The ridges worldwide have various origins and the crustal thicknesses and structures of them are diversity.The crusts beneath the microcontinents,and the transverse ridges along the transform margin,and the seafloor highs beside the passive continental margins are continental,while the crusts of other ridges are oceanic.Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS) has classed the seafloor highs worldwide into three legal categories,namely oceanic ridges,submarine ridges and submarine elevations,for the purpose to delineate the outer limit of the coastal States’ continental shelf beyond 200 nautical miles.To define the categories of the legal seafloor highs to which the ridges with various geological origins belong,the continuities in morphology and geology including the rock types,crustal structures,origins and tectonic setting of the ridges and the coastal States’ land mass with its submerged prolongation should be taken into account.If a ridge is continuous both in morphology and geology with the coastal States’ land mass and its submerged prolongation,it is a submarine elevation stipulated in Article 76.If it is discontinuous in morphology,the ridge should be regarded as oceanic ridges.If a ridge is continuous in morphology but discontinuous in geology with the coastal States’ land mass and its submerged prolongation,then it is a submarine ridge as stipulated in Article 76. 相似文献
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《Marine Policy》2014
The Magnuson–Stevens Fishery Conservation and Management Act (MSA) was amended in 1996 to require that overfished stocks be rebuilt in as short a time period as possible, not to exceed 10 years, with limited exceptions. This comment examines the basic but important question of whether the implementation of rebuilding plans under the 1996 amendments has in fact been associated with biomass recovery. Specifically, for each of the 44 stocks examined, this analysis compares the biomass trend before rebuilding plan implementation to the trend after rebuilding plan implementation using a linear trend-break model. The analysis demonstrates a statistically significant positive association between the implementation of rebuilding plans and standardized biomass in 19 of 44 stocks. None of the 44 stocks examined showed a statistically significant negative association. The analysis showed a strong temporal relationship between the implementation of the policy and rebounds in fish stocks. 相似文献
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In this paper, a penalty function method for solving non-linear optimization problems was introduced to obtain a reliability indicator and to calibrate the partial factors, avoiding the complexity associated with the calibration process of the partial factors and maintaining the accuracy of the reliability indicator. The proposed method was employed to calibrate the partial factors of gravity dam sliding stability analysis. The results indicate that using the penalty function-based calculation method to determine the reliability indicator not only ensures correctness and accuracy but also makes the calibration process of partial factors simple and easy to perform. 相似文献