A hybrid approach based on an improved gravitational search algorithm and orthogonal crossover for optimal shape design of concrete gravity dams

A hybrid approach based on an improved gravitational search algorithm (IGSA) and orthogonal crossover (OC) is proposed to efficiently find the optimal shape of concrete gravity dams. The proposed hybrid approach is called IGSA-OC. The hybrid of IGSA and the OC operator can improve the global exploration ability of the IGSA method, and increase its convergence rate. To find the optimal shape of concrete gravity dams, the interaction effects of dam–water–foundation rock subjected to earthquake loading are considered in this study. The computational cost of the optimal shape of concrete gravity dams subjected earthquake loads is usually high. Due to this problem, the weighted least squares support vector machine (WLS-SVM) regression as an efficient metamodel is utilized to considerably predict dynamic responses of gravity dams by spending low computational cost. To testify the robustness and efficiency of the proposed IGSA-OC, first, four well-known benchmark functions in literatures are optimized using the proposed IGSA-OC, and provides comparisons with the standard gravitational search algorithm (GSA) and the other modified GSA methods. Then, the optimal shape of concrete gravity dams is found using IGSA-OC. The solutions obtained by the IGSA-OC are compared with those of the standard GSA, IGSA and particle swarm optimization (PSO). The numerical results demonstrate that the proposed IGSA-OC significantly outperforms the standard GSA, IGSA and PSO.     

Characterization of best Chebychev approximation using the frequency response of IIR digital filters with convex stability

This paper deals with the application of Chebychevʼs approximation theory to IIR digital filter frequency response (FR) approximation. It explores the properties of the frequency response of IIR digital filters as a nonlinear complex approximating function; IIR digital filter frequency response is used to approximate a prescribed magnitude and phase responses. The approximation problem is closely related to optimization. If the set of approximating functions is non-convex, the optimization problem is difficult and may converge to a local minimum. The main results presented in the paper are proposing a convex stability domain by introducing a condition termed “sign condition” and characterization of the best approximation by the Global Kolmogorovʼs Criterion (GKC). The Global Kolmogorovʼs Criteria is shown to be also a necessary condition for the approximation problem. Finally, it is proved that the best approximation is a global minimum. The sign condition can be incorporated as a constraint in an optimization algorithm.     

Pipeline failures due to lightning

In the last thirty years lightning properties have been measured with a high degree of detail. Yet, the mechanisms by which lightning causes failure of buried structures are still not fully identified. This work addresses results from experimental studies and modeling of two lightning failures in buried natural gas pipelines. In both cases leaks followed by fire were caused by small punctures as a consequence of localized fusion of the pipe wall metal. Bolts hit the ground very close to the pipelines and produced the ionization of the soil in an area which was larger than their topsoil. Then, failures were caused by Joule effect, due to large currents generated by the establishment of arcs between the pipeline and the point of impact.Models to check the effect of the topsoil (burial) depth, the closeness of air-breaking metallic components and other construction characteristics on the probability of occurrence of these phenomena are reviewed. Ways to minimize the impact of this damage mechanism upon the integrity of buried pipelines are finally discussed.     

Preparation of functionalized water-soluble photoluminescent carbon quantum dots from petroleum coke

Here we report a new strategy for preparation of water-soluble photoluminescent carbon quantum dots (CQDs) from petroleum coke. Petroleum coke was oxidized first in mixed concentrated H₂SO₄ and HNO₃, and then functionalized by hydrothermal ammonia treatment. The as-made CQDs and nitrogen-doped CQDs (N-CQDs) were characterized by UV–Vis absorption spectroscope, fluorescence spectroscope, transmission electron microscope, atomic force microscope, Raman spectrometer, X-ray powder diffractometer, X-ray photoelectron spectroscope and Fourier transform infrared spectrometer. The results show that the quantum yield of CQDs increases greatly from 8.7 to 15.8%, and the fluorescent lifetime increases from 3.86 to 6.11 ns after the hydrothermal treatment in ammonia. Moreover, the fluorescent color of N-CQDs can be tuned through the amount of doped nitrogen. Both CQDs and N-CQDs are water-soluble, and have uniform particle distribution, strong luminescence, and highly fluorescent sensitivity to pH in a range of 2.0–12.0. The uniform size distribution and nitrogen-doping of N-CQDs help to lead to high yield of radiative recombination, resulting in improved fluorescence properties. This work offers a simple pathway to produce high quality and enhanced photoluminescent CQDs from petroleum coke.     

Asymptotic analyses of the start-up stage of Couette flow subjected to different boundary conditions

In this article, the process for reaching “developed” stage was investigated under both imposed shear stress and specified velocity boundary conditions. Four specific situations are investigated. These are (1) constant shear stress, (2) linearly increasing shear stress from zero shear, (3) constant velocity and (4) linearly increasing velocity from stationary. Analytical solutions of velocity distributions under these four situations were obtained. A dimensionless viscosity, defined as the ratio of the measured viscosity calculated based on the measuring principle of Couette-type viscometer to the true viscosity of fluid was proposed to describe the initial transient period. We define the “developed” stage when the dimensionless viscosity is 1% away from its final value or when it reaches 1.01. By analyzing Stokes' first problem, compact models of the dimensionless viscosity were expressed and exact quantitative relations among the initial values of dimensionless viscosity under these four specific situations were found. Time periods for Couette flow to reach the “developed” stage was calculated. The development time is the shortest under the constant velocity boundary and is the longest under the linearly increasing shear stress boundary.     

Single phase transformerless wide range ac boost voltage regulator based on z-source network

This paper proposes a new type of voltage regulator based on single-phase z-source converter that compensates wide range voltage variations. This is not only capable of compensating variations at a much higher bandwidth but also boost the voltage level even twice that of input supply. The proposed system employs a pulse width modulation (PWM) z-source ac–ac converter along with a simple closed loop control. The input rms voltage can be sensed and divided by the desired value to find the instantaneous value of gain, which mathematically calculates the possible duty ratio of PWM switching signal based on the open loop characteristics of the converter. High speed IGBTs are used as bi-directional switch of the ac–ac converter and the circuit ultimately can easily and steadily maintain regulated voltage supply to the end user. The whole system operating principle and analysis are provided. Simulation results show the improvement of voltage disturbances both in voltage rise and fall conditions.     

织构型水润滑推力轴承软弹流润滑分析及多目标协同优化

目的 提高以水作为润滑介质的织构型非金属推力轴承的润滑性能,为水润滑推力轴承的优化设计提供参考.方法 基于计算流体力学方法建立织构型水润滑推力轴承的流体动压润滑模型,采用双向流固耦合方法计算润滑流场与材料变形之间的相互作用.随后,以承载力最高和摩擦力最低为目标,采用响应曲面与非支配排序遗传算法相结合的多目标协同优化方法,对4种非金属材料的织构型推力轴承进行优化.结果 随着轴承材料弹性模量的降低,轴承内最高压力值逐渐降低,最大变形逐渐增加,且最优织构覆盖率值逐渐减小.当织构覆盖率为20％时,轴承材料对最优织构深度值无明显影响;当织构覆盖率增至40％及以上时,随着轴承材料弹性模量的降低,最优织构深度值逐渐增加.在同一轴承材料下,最优织构参数之间相互影响,随着织构覆盖率的增加,最优织构深度值逐渐增大.对于碳化硅陶瓷和尼龙等弹性模量较大的轴承材料,优化后,轴承内流体最高压力明显提升;对于超高分子量聚乙烯和赛龙等弹性模量较小的轴承材料,优化后,高压区面积明显增大.结论 轴承材料对轴承润滑性能及最优织构参数均有明显影响,且最优织构参数间相互影响.经过对织构型水润滑推力轴承的多目标协同优化,轴承润滑性能明显改善.     

铝-锰网壳结构防腐工艺的研究进展

概述了作为铝网壳结构的AA 3xxx铝-锰合金微观组织、局部腐蚀类型及表面防护技术.同时归纳了主要的表面处理方法,包括"硬质阳极氧化膜+封闭工艺"、"化学转化膜+涂料工艺"和添加缓蚀剂等,并重点评述了"化学转化膜和涂料工艺".其中,六价铬转化膜是应用于铝合金表面最传统也是最成功的化学转化膜,但六价铬剧毒致癌,因而该技术已经被禁止应用于工业产品,具有自修复腐蚀缺陷功能的三价铬转化膜工艺是最具前景的替代工艺.目前,商业化的三价铬转化膜溶液包括汉高Alodine 5900系列、赛德克SurTec 650系列以及法国索科SOCOMORE溶液,而国内相关基础研究起步较晚,性能相匹配的国产化溶液及工艺控制成为未来轻量化装备发展的"卡脖子"问题,亟待解决.此外,着重讨论了化学转化膜溶液组分、工艺参数(温度、时间及后处理工艺)及耐蚀性能等.最后总结和展望了三价铬铬酸盐转化膜现在和未来的研究思路.     

含分布式电源的小电阻接地方式配电网单相接地故障分析

不同接地方式分布式电源(DG)并网将影响系统单相接地故障电流特征,对于小电阻接地方式配电网,DG接地方式选择较为灵活,对接地故障电流的影响尤为复杂。针对小电阻接地方式配电网,建立了旋转型DG并网后的接地故障分析模型,分析了并网DG采用不同接地方式时接地故障点电流、线路三相故障电流与线路正序、负序、零序电流的特征。结果表明,不接地方式DG对接地故障电流基本无影响;但DG采用直接接地、小电阻接地方式时,各故障电流将明显增大或减小,甚至从无到数百安培,将会影响系统原有接地保护与三相保护性能。研究成果可为含DG小电阻接地方式配电网的保护配置与DG接地方式选择提供理论依据。     

节能注水增压泵的研究与应用

针对目前油田注水增压设备能耗高、注水压力不能合理调配等问题,设计了节能注水增压泵。该装置通过机械换向阀来控制活塞左右行程,从而控制装置内部液流流向,通过双作用柱塞增压泵对液流进行增压。通过活塞结构受力分析,将活塞的运动分为2个阶段,第1个阶段为加速阶段,第2个阶段为匀速阶段,计算了活塞运动速度、运动时间和有效功率,利用ANSYS软件对活塞缸和活塞进行有限元仿真计算,证明其结构强度满足要求。在胜利油田对2口高压井进行增压,增压1.5MPa,能够满足注入压力和日配注量要求,完成增注任务;并且低压出口的压力和排量可以满足1~2口低压井的注水要求。