Study on maximum power point tracking of photovoltaic array in irregular shadow

Traditional maximum power point tracking (MPPT) methods can hardly find global maximum power point (MPP) because output characteristics curve of photovoltaic (PV) array may have multi local maximum power points in irregular shadow, and thus easily fall into the local maximum power point. To address this drawback, Considering that sliding mode variable structure (SMVS) control strategy have such advantages as simple structure, fast response and strong robustness, and P&O method have the advantages of simple principle and convenient implementation, so a new algorithm combining SMVS control method and P&O method is proposed, besides, PI controller is applied to reduce system chattering caused by switching sliding surface. It is applied to MPPT control of PV array in irregular shadow to solve the problem of multi-peak optimization in partial shadow. In order to verity the rationality of the proposed algorithm, the experimental circuit is built, which achieves MPPT control by means of the proposed algorithm and P&O method. The experimental results show that compared with the traditional P&O algorithm, the proposed algorithm can fast track the global MPP, tracking speed increases by 60% and the relative error decreased by 20%. Moreover, the system becomes more stable near the MPP, the fluctuations of output power is greatly reduced, and thus make full use of solar energy.     

三峡水库蓄水后守护型工程对改善长江中游航道条件的作用

运用河流动力学理论,推求出整治水位下河槽在冲刷前、后航深变化值的表达式,对表达式的理论分析结果表明,在三峡水库下泄清水冲刷的条件下,通过守护关键可动洲滩,控制航槽不向两侧展宽,同时控制航槽内低矮的洲滩不被冲蚀,使清水冲刷只向纵向发展,就能达到增加航深的目的,这正是守护型控导工程对改善航道条件的积极作用所在。以长江中游荆江藕池口河段和太平口河段为例,计算了这两个河段守护关键可动洲滩后航深的变化值,模型计算值与实测断面概化后得到的航深变化值基本一致,进一步验证了守护型工程实现航道改善的作用。     

近四十年西江磨刀门水道河床演变分析

将西江磨刀门水道1962、1977、1999年的河道地形图数字化,建立磨刀门水道三个年份的水下数字高程模型(DEM),在此基础上将河道分为上、中、下三段进行了河床演变及其成因分析。结果表明:磨刀门水道1977年前后河道发生过明显的河道冲淤转化;1962年至1977年磨刀门水道处于淤积状态,淤积量达9.92×106 m3,河道上游向窄深发展,下游则向宽浅演变;而从1977至1999年磨刀门水道则处于冲刷状态,冲刷量为25.53×106 m3,河道平均水深增加,逐渐向窄深演变。磨刀门水道河床演变是自然环境变化和人类活动共同作用的结果,其中人类活动的影响最为强烈。     

天津滨海新区湿地生态恢复需水量评估

生态需水量的核算是湿地水文生态恢复的关键步骤。通过分析计算,评估天津滨海新区湿地生态系统各类生态需水的3个特征值:最低生态需水量(即湿地生态系统丧失生态功能的临界需水量)、最适生态需水量(即维持湿地生态功能最佳状态的需水量)、最高生态需水量(即湿地生态系统所能承受的最大水量),得出如下结论:天津滨海地区湿地的生态需水主要包括蒸发蒸散需水量、湿地土壤需水量、补给地下水、湿地生物栖息地需水量4个部分;湿地的最低生态需水量为177.68×106～276.85×106 m3,最适生态需水量539.23×106～807.81×106 m3,最高生态需水量1 206.55×106～1 409.02×106 m3。     

半直立式圆筒护岸地基现场加载试验及变形分析

半直立式圆筒护岸是一种新式港口工程结构,结合其在大连某水工护岸工程中的应用,进行了半直立式圆筒护岸地基的加载试验,通过实测土压力、沉降、水平位移及孔隙水压力,分析了半直立式圆筒护岸地基的沉降及水平位移变化特点,并进一步研究了其不均匀沉降的发展过程。试验结果表明：半直立式圆筒护岸沉降及水平位移对护岸荷载分级、每级荷载加载量、加载历时及两级荷载之间的间隔时间较为敏感,其中护岸后方最后一级不对称加载对圆筒结构的不均匀沉降影响最大,孔隙水压力变化主要受每级加载量、加载历时及潮汐作用影响,而圆筒安装及第一级荷载施加后,孔隙水压力产生较大的波动。     

塑料套管混凝土桩加固公路软土地基现场试验研究

根据某一高速公路塑料套管混凝土桩加固软土地基工程实例,对桩土应力、地表沉降、横向位移、不同深度孔隙水压力进行观测,讨论了塑料套管混凝土桩桩承式路堤的工作机理。结果表明：塑料套管桩加筋路堤的临界高度约为1.26倍桩净距,观测期末,荷载分担比接近89%;桩帽和桩间土最大差异沉降为30 mm左右,且应力集中比随着差异沉降的增大而线性增大;路堤堤脚附近不同深处横向位移随着路堤填筑高度的增加而增加,施工结束时,地表以下2.5 m处横向位移最大,为12.86 mm;横向位移-沉降比和横向位移增加率随着路堤填筑高度的增加逐步减小并趋于稳定,塑料套管混凝土桩加筋路堤系统能够有效防止路堤横向位移的发展和改善路堤的整体稳定性。     

Numerical evaluation on shell buckling of empty thin-walled steel tanks under wind load according to current American and European design codes

Liquid storage steel tanks are vertical above-ground cylindrical shells and as typical thin-walled structures, they are very sensitive to buckling under wind loads, especially when they are empty or at low liquid level. Previous studies revealed discrepancies in buckling resistance of empty tanks between the design method proposed by the American Standard API 650 and the analytical formulas recommended by the European Standard EN1993-1-6 and EN1993-4-2. This study presents a comparison between the provisions of current design codes by performing all types of numerical buckling analyses recommended by Eurocodes (i.e. LBA-linear elastic bifurcation analysis, GNA-geometrically nonlinear elastic analysis of the perfect tank and GNIA-geometrically nonlinear elastic analysis of the imperfect tank). Such analyses are performed in order to evaluate the buckling resistance of two existing thin-walled steel tanks, with large diameters and variable wall thickness. In addition, a discussion is unfolded about the differences between computational and analytical methods and the conservatism that the latter method imposes. An influence study on the geometric imperfections and the boundary conditions is also conducted. Investigation on the boundary conditions at the foot of the tank highlights the sensitivity to the fixation of the vertical translational degree of freedom. Further, it is indicated that the imperfection magnitude recommended by the EN1993-1-6 is extremely unfavorable when applied to large diameter tanks. Comments and conclusions achieved could be helpful in order to evaluate the safety of the current design codes and shed more light towards the most accurate one.     

An active specification switching strategy that aids in solving nonlinear sets and improves a VNS/TA hybrid optimization methodology

A method to aid in convergence of nonlinear equations by relocating the solver is introduced. Deactivating known variables and activating intelligently chosen unknown variables at predicted values efficiently formulates initial conditions. This repair strategy is integrated into an optimization procedure. The repair algorithm has the ability to (1) relocate the solver for non-converged models caused by poor initial conditions and (2) utilize points formulated in relocating non-converged models caused by infeasible sets of decision variables as a perturbation phase of a stochastic optimization algorithm. To show the effectiveness of the proposed repair strategy, a hybrid metaheuristic of a Variable Neighborhood Search (VNS) and Threshold Accepting (TA) is tested on the optimization of a large-scale industrial process, the primary units of a crude oil refinery. The performance of the hybrid VNS/TA Metaheuristic with repair is compared to the algorithm without the repair technique.     

Knowledge-based system for safety control of damaged ship

The maritime casualties cause serious consequences such as loss of life, property and maritime pollution. Therefore, the large-scaled casualties will be derived from loss of structural strength and stability due to the progressive flooding and enlargement of damage by the effect of wave and wind. The improvement of damage survivability is very important in maritime safety. In this paper, the knowledge-based system which could improve the safety level of stability and longitudinal strength through posture control of a damaged ship is studied. The system has been incorporated to interface with user to develop an ‘operationally practical’ action list based on ballasting to improve the ship's structural safety and stability status.     

复杂河口汊道封堵水沙问题研究

摘 要：对复杂分汊河口次要汊道进行封堵围垦可以获得土地资源。以瓯江口南口封堵为例研究了复杂河口汊道封堵问题。首先对复杂的瓯江口的自然条件和冲淤演变进行了分析；其次，使用二维波浪潮流泥沙数学模型、波浪潮流泥沙物理模型及三维潮流数学模型等研究手段，对瓯江南口现潜堤加高进行了封堵后的二维潮流场、泥沙场、地形冲淤变化和三维潮流场进行了模拟研究，对瓯江泄洪排涝的影响进行了计算和分析。研究结果表明，从对周围水沙环境和瓯江泄洪排涝的影响角度考虑，将现潜堤加高进行南口封堵的方案是可行的。