Simplified-robust geotechnical design of soldier pile–anchor tieback shoring system for deep excavation

The shoring system that consists of soldier piles and anchor tiebacks is often used in deep excavations in sandy deposits. However, uncertainties often exist in the design of such shoring systems. In this article, a simplified-robust geotechnical design method is proposed to account for these uncertainties in the shoring system design. Specifically, for a given deep excavation, uncertain soil parameters and surcharges are treated as noise factors, and the parameters of soldier piles and tieback anchors are treated as design parameters. Robust design is then implemented as a multiobjective optimization problem, in which the design robustness is sought along with cost efficiency and safety requirements. A trade-off between design robustness and cost efficiency exists and the optimization usually leads to a Pareto front. By applying the knee point concept, the most preferred design that meets the safety requirements and yields the best compromise between design robustness and cost efficiency can be identified on the Pareto front. Improvements made to the existing robust geotechnical design method include an efficient formulation of the design robustness and a new procedure for finding the most preferred design in the design pool. The new simplified-robust geotechnical design method is illustrated with a real-world excavation case study.     

低温柔性管道关键结构层的多目标优化设计

低温柔性管道是海上浮式液化天然气装置系统(FLNG)的核心输运装备。针对低温柔性管道多材料、多层复合的结构设计难点,将其按照不同功能解耦成内衬层、抗拉铠装层以及辅助层三个关键结构层。基于神经网络模型(RBF)、Kriging模型以及响应面模型(RSM)三种建模方法建立了上述三个结构层响应分析的代理模型,并通过模型准确度的比较,发现RBF的误差均最小。在优化设计中,基于遗传算法分别对低温柔性管道上述关键结构层进行多目标优化设计。在内衬层结构的优化中,以质量及弯曲刚度最小为优化目标;在抗拉铠装层结构的优化中,以质量最小及拉伸刚度最大为优化目标;在辅助层结构的优化中,以质量、弯曲刚度及传热速率最小为优化目标。研究工作为低温柔性管道的结构提供了关键设计参数及理性的设计方法。     

后INDC时期全球1.5℃合作减排方案

《巴黎协议》提出要将全球地表升温努力维持在低于较工业化前提高1.5 ℃的水平下,然而当前各国提交的国家自主贡献（INDCs）甚至无法实现成本最低的2 ℃温控目标,后INDC时期全球减排将面临严峻的形势。本文针对全程和终期两种1.5 ℃温控目标实现标准,基于不同的减排原则设置了三种全球合作减排方案,使用集成评估模型CIECIA对其气候有效性和经济可行性进行评价。研究结果显示：若要实现全程1.5 ℃升温控制目标,则各国必须在INDC目标年后立即实现净零排放;终期1.5 ℃温控目标可以使各国在INDC目标年后有一个到净零排放的缓冲期,但是由此带来的地表温度上升反而有损经济发展;方案3对因产业和地理因素在其他方案下经济受损的俄罗斯和高发展国家实行宽松减排措施,在满足终期1.5 ℃目标前提下实现了所有减排参与国经济利益的帕累托改进,是可行有效的国际减排合作方案;方案3显示中国和美国在减排过程中的经济联系更加紧密,而与俄罗斯和高发展国家存在竞争关系,因此可进一步加强与美国的减排合作,并注意协调与俄罗斯和高发展国家的利益关系。     

Linear combinations of order statistics to estimate the quantiles of generalized pareto and extreme values distributions

 Ad hoc techniques for estimating the quantiles of the Generalized Pareto (GP) and the Generalized Extreme Values (GEV) distributions are introduced. The estimators proposed are based on new estimators of the position and the scale parameters recently introduced in the Literature. They provide valuable estimates of the quantiles of interest both when the shape parameter is known and when it is unknown (this latter case being of great relevance in practical applications). In addition, weakly-consistent estimators are introduced, whose calculation does not require the knowledge of any parameter. The procedures are tested on simulated data, and comparisons with other techniques are shown. The research was partially supported by Contract n. ENV4-CT97-0529 within the project “FRAMEWORK” of the European Community – D.G. XII. Grants by “Progetto Giovani Ricercatori” are also acknowledged.     

Studying fractal geometry on submicron length scales by small-angle scattering

Recent studies have shown that internal surfaces of porous geological materials, such as rocks and lignite coals, can be described by fractals down to atomic length scales, In this paper, the basic properties of self-similar and self-affine fractals are reviewed and how fractal dimensions can be measured by small-angle scattering experiments are discussed.This paper was presented at Emerging Concepts, MGUS-87 Conference, Redwood City, California, 13–15 April 1987.     

以建成区面积表征的中国城市规模分布

选择1990~2000年中国城市用地面积位于前200位的地级及地级以上的城市用地资料,把运用在城市人口规模上的位序-规模法则移植到城市用地上,分析了城市土地利用规模的变化规律。然后运用分形理论,阐释了城市用地的位序-规模曲线。结果显示：(1)以建成区面积作为衡量城市规模的指标,中国城市规模分布符合位序-规模法则,拟合曲线的判定系数都在0.95以上;(2)根据位序-规模曲线的形态,中国城市按建成区面积可分为3类：用地面积>200 km²的大城市,50~200 km²的中等城市和<50 km²的小城市;(3)城市建成区用地的位序-规模曲线有平行向前推进的特点,这为预测我国未来城市建成区用地规模提供很好的基础;(4)中国位于前200位的城市用地规模分布的均衡度不断增强,城市建成区用地规模总量持续增加。