An approximate structural reanalysis method that is based on a binomial series expansion and that employs operations of matrix scaling and norm minimization is presented in this paper. It is shown that the scaling operation significantly reduces several unfavourable effects of the magnitude and nature of design changes on the prediction quality of the model. Norm minimization provides a very effective and optimal scaling factor in a simplified manner. The most significant achievement of the work is the development of an effective and efficient reanalysis model that provides near-exact response quantities even when large and strongly dispersed changes are introduced in the design. The potential capacity of the proposed method of improvement is demonstrated using numerical examples. Graphical interpretation of the concept is also provided. 相似文献
This article discusses spate irrigation in Ethiopia and aims to take stock of the current status of spate irrigation development.
It summarizes experiences so far and formulates a number of recommendations on the development of this upcoming resource management
system. It argues that raised weirs are useful mainly in areas where a large head for spate flow diversion is required, but
that traditional earthen structures with conical stone/gabion reinforcements are cost-effective and technically adequate for
floodwater distribution and management. It contends that the practical successes of sediment settling ponds (gravel traps)
are at best mixed. Even where a small basin is justified, it can only ever trap a small proportion of the incoming sediment
load. It is better to allow large floods with excessive sediment load (>100,000 ppm) to by-pass upstream intakes to be diverted
lower down the system, and provide additional livelihood opportunities in downstream areas in the form of rangeland and agro-forestry
development. This is particularly useful in the lowlands of Ethiopia with large pastoral community where spate irrigation
is yet to make in-roads. The article further explains that water rights in spate are different from the sharing and allocation
of perennial flows—they are dynamic and respond to a situation that differs from year to year as well as within a year and
that a certain degree of inequity among users is inevitable. Keeping the command area compact can ensure two or more irrigation
turns and this can highly increase productivity as crops are no longer in the ‘stress zone’. To transform spate irrigation
in Ethiopia from subsistence to a business-oriented production system, the article proposes the promotion of cash crops including
pulses and oil seeds as well as encouraging investors to go for bio-fuel development and agro-forestry in the lowland areas
where huge potential exist. To avoid vehement conflicts that may arise among the settled agricultural and pastoral communities
due to the implementation of the business-oriented production system, the traditional rights of the pastoral communities must
be respected and their rangeland and water resources be safeguarded. For maximum yield, soil moisture conservation measures
such as pre-irrigation land preparation, deep ploughing and mulching are essential as is the conjunctive use of spate flow
and groundwater. Last, but most important, the article emphasizes that farmers need to be placed at the heart of any spate
irrigation development programme as primary beneficiaries, managers and operators as well as part of the decision making institution. 相似文献
Two problems of optimum topological design of grillages are discussed: (1) the Equilibrium Linear Programming (ELP), where the analysis model is based only on equilibrium conditions and (2) the Nonlinear Program (NLP), where the ELP formulation is extended to include compatibility conditions. The structural topology is optimized by allowing elimination of elements. Three different force method formulations are presented for each of the problems. It is shown that the optimal topology for the NLP problem might correspond to a singular point in the design space. The optimal topology for the ELP problem is obtained by solving a linear program (LP).
Conditions for selecting a geometry of Multiple Optimal Topologies (MOT) are derived. The objective function for the MOT geometry is shown to be independent of the redundant forces, and some of the optimal topologies are usually statically determinate structures. In such cases the lower bound on the optimal value obtained by the ELP solution is equal to the final global optimum. Examples are given to illustrate how the optimal topology and its corresponding load path change with the geometric parameters. Design procedures that combine automated optimization and CAD techniques are most suitable for solving the presented problems.
Next to the traditional analysis of trends in time series of hydro-climatological variables, analysis of decadal oscillations in these variables is of particular importance for the risk assessment of hydro-climatological disasters and risk-based decision-making. Conventional parametric and nonparametric tests, however, need implementing a set of background assumptions related to serial structure and statistical distribution of data. They neither focus on the extreme events and their probability of occurrence. In order to get rid of these limitations, we suggest a modified version of the Sen Method (SM), combined with the Quantile Perturbation Method (QPM) for examining temporal variation of extreme hydrological events. The developed method is tested for decadal analysis of monthly and annual river flows at 10 hydrometric stations in the Qazvin plain in Iran. The results show oscillatory patterns in extreme river flow quantiles, with a positive anomaly during the 1990s and a negative one during the 2000s. It is also shown that the concurrent use of the two methods allows to set a complete picture on the temporal changes in high and low extremes in historical river flow observations in different seasons. 相似文献
Food Science and Biotechnology - This study was conducted to assess the physicochemical changes and overall nutritional implications of greenhouse-grown “TY Megaton” and... 相似文献
A new optimal design procedure based on successive optimization in design planes is presented. It is intended to improve the convergence properties of the solution process and to reduce the computational effort. Optimization is carried out at each iteration cycle in a two-dimensional design plane, formed by the current design and a selected direction vector in the design space. Applying the scaling operation, optimization in a design plane is reduced to a problem of a single independent variable. The computational effort is further reduced by introducing approximate behaviour models for the selected design planes.
The procedures of selecting a design plane and optimization in the plane are repeated until the final optimum is achieved. Since all intermediate designs are feasible, the solution process can always be terminated with an improved feasible design. Various methods can be employed to introduce design planes; some of them are investigated in this study.
Numerical experience with the proposed procedure shows that the final optimum can be achieved in a small number of iteration cycles. This feature is particularly important for problems where other algorithms fail to arrive at the optimum in a reasonable number of iterations. 相似文献
Computational Visual Media - Segmentation is the act of partitioning an image into different regions by creating boundaries between regions. k-means image segmentation is the simplest prevalent... 相似文献