Rehabilitation and replacement of water distribution system components considering uncertainties

This paper presents the mathematical development of an integer — nonlinear programming chance — constrained optimization model for the minimum cost rehabilitation/replacement of water distribution system components. Particular attention is given to the handling of uncertainties in the roughness factors and the loading conditions including both the random demand and preassure head requirements.The advantages of the proposed model include the ability to: 1) handle the optimal timing of rehabilitation/replacement for water distribution system components; 2) link a mixed-integer linear program solver, a nonlinear program solver, and a hydraulic simulator into an optimization framework; 3) handle the uncertainties of some of the variables; 4) incorporate various kinds of cost functions; and 5) handle multiple loading conditions.     

Incremental growth of a large volume,chemically zoned magma body: a study of the tephra sequence beneath the Rainier Mesa ash flow sheet of the Timber Mountain Tuff

The Rainier Mesa ash-flow is a large (1200 km³), 11.6 My old, chemically zoned unit that ranges in composition from 55 to 76% SiO₂ — one of the largest chemical ranges ever observed in a large volume ash-flow sheet. Two chemical trends occur in this sheet, a low silica (55–66% SiO₂) and a high silica (>66% SiO₂) trend. Ninety per cent of the Rainier Mesa sheet occurs in the high silica trend. Immediately beneath the Rainier Mesa sheet is a thick tephra sequence. The chemical variation of this sequence is nearly equivalent to the high silica portion of the Rainier Mesa ash-flow sheet (about 66–78% SiO₂). Throughout the tephra sequence numerous small ash-flow layers occur, and each ash-flow layer is chemically zoned from more evolved at the base to less evolved at the top. This is consistent with having been erupted from a zoned magma body. The lowest silica tephra units are at the base of the sequence and the highest silica units are at the top — that is, the large-scale chemical trend of the entire sequence is opposite to that of the individual ash-flow layers. These ash-flow layers are of very small volume. The tephra sequence provides a unique record of the incremental development of the zoned, high silica portion of the Rainier Mesa magma body.     

A note on programs performing kriging with nonnegative weights

This note deals with the problem of solving kriging systems with nonnegative weights. Mathematically the question is considered as a case of quadratic programming. Hints concerning computational approaches and software are given.     

Ordinary Cokriging Revisited

This paper sets up the relations between simple cokriging and ordinary cokriging with one or several unbiasedness constraints. Differences between cokriging variants are related to differences between models adopted for the means of primary and secondary variables. Because it is not necessary for the secondary data weights to sum to zero, ordinary cokriging with a single unbiasedness constraint gives a larger weight to the secondary information while reducing the occurrence of negative weights. Also the weights provided by such cokriging systems written in terms of covariances or correlograms are not related linearly, hence the estimates are different. The prediction performances of cokriging estimators are assessed using an environmental dataset that includes concentrations of five heavy metals at 359 locations. Analysis of reestimation scores at 100 test locations shows that kriging and cokriging perform equally when the primary and secondary variables are sampled at the same locations. When the secondary information is available at the estimated location, one gains little by retaining other distant secondary data in the estimation.     

数字海图水深注记的自动选取

水深注记作为表示海底地形地貌特征的主要制图要素,它的正确选取对于保证航海安全、反映海底地貌起伏具有重要意义。针对传统的水深注记方法,该文提出一种顾及多重约束条件的水深注记选取方法。在总结水深注记综合约束条件基础上,以Vononoi图为支撑几何构造,对水深注记综合涉及的地形特征、空间分布特征、邻近特征3个方面的综合约束进行了形式化定义;借鉴人工选取的思想,在水深综合约束条件重要性排序的基础上,通过反映地形、空间分布、邻近关系等主体特征的重要水深的依次选取,以及背景水深的抽稀实现水深注记选取;最后以实测数据进行实验,验证该方法的有效性。     

Maximum theoretical power absorption of connected floating bodies under motion constraints

In this paper, a mathematical model is presented to evaluate the maximum mean power that can be absorbed by a three-dimensional system of connected floating bodies in waves under a weighted global constraint. The constraint imposed on the motion amplitudes of the system can be used to limit the motions of the bodies in order to make sure that the assumption of linear theory for wave–structure interaction remains valid. The absorbed power of a structure can be considered as the difference between excitation and radiated power without consideration of practical power take off. The solutions for the maximum relative capture widths of rigidly connected two rafts have a good agreement with the calculated ones for the same rafts being seen as a single whole structure. Meanwhile, the results of maximum power absorption of two hinged slender rafts in cuboid shape give a good agreement as well with those by using slender-body approximations. Then dynamics of a hinged two rafts are studied and results show how the maximum efficiency is affected by raft width and restricting the motions.     

基于模拟退火和区域划分的海表流场反演算法研究

经典的海洋表面流场迭代反演算法采用固定的校正系数对探测区域进行整体分析和计算,因此耗时较长且反演精度也受到了一定程度的限制。本文提出利用模拟退火算法对反演过程中的校正系数进行优化,使其能根据每一次反演的结果进行自适应的调整和改变,从而减少迭代次数;同时根据流场分布的特点,提出划分探测区域的反演方法,最终,在经典算法的基础上给出了改进的海表流场反演算法。仿真反演实验结果表明,改进后的反演算法,其时效性和精度都有了明显提高。     

一种基于特征拓扑约束的图像配准算法

针对传统RANSAC算法在特征点提纯方面效率不高、迭代计算复杂等缺点,提出先利用拓扑约束进行特征点提纯,得到初始匹配点集,再通过RANSAC原理进行特征点精确提纯,最后通过最小二乘法利用精确匹配点求解单应矩阵进行图像配准。实验结果表明:拓扑约束提纯算法计算效率高,能有效提高RANSAC算法的正确匹配率和时间效率,可得到更多更稳定的匹配点,提高图像配准的精度。     

地下水可持续开采量与地下水功能评价的关系

针对中国北方地下水评价中偏重资源而对地下水的生态功能和地质环境功能重视不足的问题,立足于流域尺度的地下水循环系统和地下水的自然属性,突出协调综合发挥地下水的资源功能、生态功能和地质环境功能的目标,从地下水可持续开采量与地下水功能的理念基础、评价原则和评价机理3个方面探讨二者的内在关联性,认为它们同源于人与自然和谐的理念,都以流域尺度的地下水循环系统为研究主体,以保护生态与地质环境为目标,彼此相互促进和相互支撑.地下水功能评价是合理确定地下水可持续开采量的充分条件,地下水可持续开采量的合理确定是实现地下水功能评价目标的必要条件;如果二者缺一,则地下水的生态功能或地质环境功能难以得到有针对性的保护.