三维薄翼入水水动力的计算

本文提供了一个计算三维薄翼高速入水水动力性能的非定常数值升力面方法。假设薄翼高速入水时,翼的背面为全空泡状态,当翼的随边进入液面后,此空泡域按一定的方向拖至自由液面。在翼的拱弧面上布置线涡和线源,在翼后空泡面上布置线源,所有的奇点系在自由液面上方存在映象以满足自由液面条件。根据翼迎流面的法向不可穿透条件和翼背面及翼后空泡面上的空泡动力学条件确定所有待定线涡和线源的强度,并由此可以计算各时刻翼上压力分布。利用本文提供的方法首先计算了二维薄翼入水的水动力性能,将结果与理论解进行比较,两者结果较为一致。然后,研究了三维薄翼的入水问题。     

基于马斯京根法的分布式水文模型求解栅格汇流次序

分布式水文模型能充分考虑下垫面条件的不均匀性及空间尺度相耦合性,已成为目前流域水文模型研究的热点.基于栅格的流域分布式水文模型是常建的模型,其核心问题是栅格产流计算和汇流计算,关键技术问题之一是如何解决栅格的汇流次序.马斯京根法是分布式水文模型汇流中常用的方法之一,在计算中需要用到上游栅格本计算时段的出流,这就需要确保在计算某一栅格出流前,其所有人流栅格都已经计算过m流.该文在栅格汇流流路分析的基础上,通过栅格汇流累积矩阵建立栅格汇流人流栅格累计数统计数据,较简单地解决了这一问题,并应用于实验流域,效果较满意.     

对称布置翼板加翼桩的水平承载性能分析

影响加翼桩水平承载性能的因素众多,其中翼板数量、荷载方向与翼板夹角是主要影响因素。采用ABAQUS有限元计算软件研究了软黏土地基中桩径为5.0 m,对称布置二、三和四翼板的加翼桩在不同荷载作用方向时桩身泥面水平位移、桩身倾斜率、桩身内力、桩身应力和极限承载力等的变化。通过与相同条件单桩的承载特性对比,分析了加翼桩水平承载性能提升幅度,明确了翼板通过同时或交替承担底面端承力、侧面摩擦阻力、水平土抗力和增加桩身抗弯刚度以提高其水平承载性能的机理,拟合了对称布置二、三和四翼板加翼桩水平极限承载力随荷载作用方向变化的计算式,对加翼桩极限承载力控制条件进行了对比分析。     

分布式水文模型构建及在黄河区间流域的应用

选择位于黄河支流洛河中游的长水—宜阳区间流域作为研究对象,基于数字高程模型,计算栅格水流方向、集水面积和栅格演算次序,为产汇流计算打下基础。把1个栅格单元作为1个小子流域,基于栅格采用新安江模型进行产流计算,采用Muskingum-Cunge算法进行河道洪水演算。结果表明,基于DEM的分布式水文模型在洪峰误差控制和过程拟合等方面表现较好,洪水模拟具有较高的精度。     

加装稳定翼的海上风电大直径单桩基础数值仿真

针对海上风电机组大直径单桩基础水平位移不易控制等问题,提出了一种加装稳定翼的单桩结构型式.通过在近地表(泥面)一定范围内的桩身设置一组翼板,充分利用浅层桩前土的抗力,增强了基桩水平承载性能.借助数值仿真计算结果,采用指数拟合法、四阶多项式拟合法对水平荷载与基桩水平位移关系进行拟合,进而求解单桩水平极限承载力.结果表明,四阶多项式拟合法精度更高;加装稳定翼的单桩水平位移及桩身最大弯矩明显降低,单桩水平极限承载力显著增强,稳定翼安装位置会对基桩水平承载力的提高效果产生影响.该结构形式可推广到其他海上风电基础结构小直径钢管桩的桩型改良中,有利于减小相应的材料成本及施工成本.     

带翼片侧向流斜板沉淀池内颗粒沉降过程的数值模拟

采用有限体积法研究了带翼片侧向流斜板沉淀池内水流流动的特性,并计算了带翼片与不带翼片斜板内水流的雷诺数,结果表明加入翼片可以明显降低水流的雷诺数,其数值为不带翼片斜板雷诺数的42%,并采用层流模型计算了两种情况斜板内水流的三维流场分布情况.在此基础上考察了加入稀疏颗粒后,颗粒物的运动轨迹,采用DPM模型进行计算,结果表明,加入翼片后颗粒物沉降的路径缩短,有利于固液分离;随着水流速度的增大,颗粒跟随性增强,颗粒物密度(采用1100kg/m3和1 400 kg/m3进行分析)增大,颗粒沉降性也增强.同时大颗粒粒径也有利于沉淀.     

低雷诺数下拍动翼仿生推进效率研究

该文主要采用重叠网格技术对拍动翼的流体动力特性进行了计算分析,并且基于浸没边界法采用自编程序对低雷诺数下的拍动翼运动进行了直接数值模拟。将两次计算结果进行了比较,验证了重叠网格技术在处理动边界问题中的正确性和可行性。最后系统地分析了拍动翼的运动参数如升沉俯仰相位差、俯仰幅值以及斯特劳哈尔数,对推进性能的影响。并结合推进效率及拍动翼后方的涡流场结构确立了最佳运动参数。     

加翼桩水平承载力计算方法研究

加翼桩作为海上风电基础的新型结构,目前相关研究甚少。基于ABAQUS三维数值仿真模型,对比分析了海上风电大直径单桩与加翼桩在水平荷载作用下桩身弯矩、应力、位移、泥面处桩基倾斜率、极限承载力以及破坏模式等水平承载性能。研究了大直径单桩和加翼桩桩身与翼板土压力分布,基于计算结果和桩土作用机理,参考现行规范中P-Y曲线模式,对相关系数进行修正,提出软黏土地基大直径单桩P-Y曲线。根据加翼桩翼板面积、形状、刚度和埋深等翼板参数对加翼桩水平承载性能影响的研究成果,提出基于大直径单桩承载力的软黏土地基大直径加翼桩极限承载力经验式和加翼桩翼板参数影响系数的计算式,为加翼桩的研究和运用提供了技术支撑。     

不同面雨量估算方法对水库入流预测 模型精度的影响

以潘家口水库入库径流预测为研究对象,分别采用分块法、栅格计算法以及DEM法计算区域平均降雨量,并在此基础上建立潘家口水库来流预测模型。结果表明不同的面雨量估算方法对水库入库径流的预测精度具有较大影响。以DEM法计算区域平均雨量值作为预测模型的输入所模拟的效果优于另外两种区域平均雨量计算方法,且预测结果合理。     

掠海地效翼升力理论研究

该文将经典的普朗特升力理论推广至近海面掠飞的地效翼升力问题,包括升力线和升力面理论.以往的研究通常将海面简化为固壁进行研究,该文着重研究自由表面效应对地效翼升力的影响,考虑掠海地效翼和自由表面相互作用.仿照无限空间的普朗特理论,建立了考虑自由表面条件的升力线和升力面理论;考察了地效翼的升力和阻力、机翼升斜角、机翼端板和串列翼等因素的影响.     

静水中长鳍扭波推进的水动力数值研究

长鳍扭波推进是一种典型的鱼类游动方式,具有高效、低噪、机动灵活等一系列优点。该文以"尼罗河魔鬼"鱼为仿生研究对象,采用弹性光顺法和局部网格重划法的动网格技术对大摆幅的长鳍扭波推进运动流场进行了数值计算研究,鳍条最大摆幅高达85°,对长鳍扭波推进在系泊状态下的水动力进行了研究,并与试验结果进行了比较验证。数值分析了鳍面压力分布及其随相位的变化,以及与推力产生的关联,并分析了长鳍扭波推力随扭波频率的变化,研究表明,系泊状态下,推力系数不随频率而改变。     

NUMERICAL SIMULATION OF FISH SWIMMING WITH RIGID PECTORAL FINS

The numerical simulation of the self-propelled motion of a fish with a pair of rigid pectoral fins is presented.A Navier-Stokes equation solver incorporating with the multi-block and overset grid method is developed to deal with the multi-body and moving body problems.The lift-based swimming mode is selected for the fin motion.In the lift-based swimming mode,the fin can generate great thrust and at the same time have no generation of lift force.It can be found when a pair of rigid pectoral fins generates the hydrodynamic moment,it may also generate a lateral force opposite to the centripetal direction,which has adverse effect on the turn motion of the fish.Furthermore,the periodic vortex structure generation and shedding,and their effects on the generation of hydrodynamic force are also demonstrated in this article.     

Using spanwise flexibility of caudal fin to improve swimming performance for small fishlike robots

This paper examines the beneficial effects of the spanwise flexibility of the caudal fin for the improvement of the swimming performance for small fishlike robots. A virtual swimmer is adopted for controlled numerical experiments by varying the spanwise flexible trajectories and the spanwise flexible size of the caudal fin while keeping the body kinematics fixed. 3-D Navier-Stokes equations are used to compute the viscous flow over the robot. Elliptical, parabolic and hyperbola trajectories are chosen to describe the spanwise flexible profile of the caudal fin. According to the sign(positive or negative) of the phase difference of the swinging motion, the spanwise flexibility can be divided into the fin surface of "bow" and the fin surface of "scoop". It is observed that for both the fin surface of "bow" and the fin surface of "scoop", the spanwise elliptical trajectory has the optimal swimming velocity, thrust, lateral force, and efficiency. With comparisons, using the flexible caudal fin with the fin surface of "bow", the lateral force and the power consumption can be reduced effectively and the swimming stability can be increased while reducing little the swimming velocity and thrust. Meanwhile, using the flexible caudal fin with the fin surface of "scoop" can greatly improve the swimming velocity, thrust, and efficiency while increasing part of the lateral force and the power consumption. Three-dimensional flow structures clearly indicate the evolution process around the swimming robot. It is suggested that the fish, the dolphin, and other aquatic animals may benefit their hydrodynamic performance by the spanwise flexibility of the caudal fin.     

半自适应网格方法及其应用

本文发展了一种简单而有效的所谓半自适应网格方法，该方法的一个特点是所有的计算均在物理平面上完成。这种半自适应方法已被成功地应用于定常和非定常一维二维对流扩散方程初值问题的数值解，与存在精确解的结果比较表明，半自适应网格方法的结果具有很少的数值耗散，精度较好，与通常的差分方法比大约增加一倍多一点的计算时间，与变分或微分形式的自适应网格方法相比，大大减少了计算工作量。     

Comparison of Five Ageing Methodologies Applied to Walleye (Stizostedion Vitreum) in Burt Lake,Michigan

Age estimations were performed on 25 walleyes (Stizostedion Vitreum) from Burt Lake, Michigan, by sectioning pectoral and pelvic fin rays, dorsal fin spines, and otoliths and by impressing scales. Age groups 4 to 11 were found using these methods. Paired t-tests showed no significant differences among all pairs (p > 0.05), except the pelvic fin ray and otolith combination. Variability exists among the age estimations for individual fishes, however, statistically all methods were of equal precision. A subjective merit analysis showed otoliths and pectoral fin rays had the highest rating, while pelvic fin rays had the lowest. In areas of the Great Lakes which have walleye populations that exhibit similar age patterns as Burt Lake walleye, otolith or pectoral fin ray ageing methods should be used as an occasional check for the reliability of scale age estimations.     

压力钢管联合受力多层环模型及算法

根据当前压力钢管联合受力的发展趋势和现有算法情况，从理论和和实用上提出了力钢管联合受力钢管联合受力多层环计算模型及相应计算方法，适于编成通或专用程序电算，为便于了解，还以俄国萨扬舒申斯克水电站压力管道为例，示出各步序手算结果，经与前苏联水工研究院高尔登各向异性层环模型有限元算法和我国水利电力科学院的三层环分析算法作同例结果比较，表明文中提出的方法计算精度较高，便于实际应用，最后文中还就压力钢管联合     

Comparison of precision and bias of scale, fin ray, and otolith age estimates for lake whitefish (Coregonus clupeaformis) in Lake Champlain

We compared the precision, bias, and reader uncertainty of scales, dorsal fin rays, and otolith age estimates from 151 lake whitefish (Coregonus clupeaformis) from Lake Champlain, 2009. Mean and systematic differences in age estimates were compared among structures using consensus ages from two readers; precision of age structures was quantified through the use of age-bias plots, coefficient of variation, and percent agreement; reader confidence was indexed as a measure of overall reader uncertainty for each individual fish by structure. Mean age estimates based on otoliths were systematically higher (7.8 years) than based on scales (6.0 years) or fin rays (5.6 years). Ages determined using otoliths generated a wider range of ages and greater number of age classes (1-23 years, 20 age classes) when compared with scales (1-16 years, 15 age classes) and fin rays (1-14 years, 13 age classes). Otoliths were the most precise of the structures (CV = 4.7, compared with 7.4 for scales and 12.1 for fin rays). Percent agreement between readers indicated high precision and reproducibility of age estimates using otoliths. Percent reader uncertainty was lowest when using otoliths (7.6%) in comparison with fin rays (21.2%) or scales (26.8%). This study is the first evaluation of precision and bias of age structures for Lake Champlain's unexploited lake whitefish population and suggests that otoliths are the most appropriate structure for age estimation. However, the differences in age estimates from the three structures in this study emphasize the importance of validating aging structures to provide accurate age estimates for Lake Champlain.     

Investigations into salt wedge dynamics at a bar blocked estuary using front tracking approach

The interfacial flow simulations using a robust interface-tracking method are presented. The method is based on one fluid formulation, where a single set of governing equations for the whole computational domain with variable material properties is solved. Interfacial terms, at the boundary separating the phases, are accounted for by adding the appropriate sources as δ functions. The representation of the moving interface and its dynamic restructuring, as well as the transfer of information between the moving front and the fixed grid, is discussed. This method has been applied to density stratified flows, and interfacial movements are then presented. An experimental study on salt wedge movement, conducted in the University of Dundee, has been simulated using the above algorithm. The numerical results are compared with the experimental results and those of a semi-empirical model developed earlier by the authors.     

混流式水轮机转轮强度的样条有限元求解

采用样条有限元的计算方法对混流式水轮机转轮的强度计算求解作了有益的尝试。计算中首先划分了转轮叶片计算网格， 然后用样条有限元按计算网格对叶片的应力和变形进行计算， 并与文献 ［３］ 的计算结果进行了分析比较。通过实例计算与比较表明， 采用的方法更简明， 计算效率、精度较高， 计算结果也更为合理， 可用于实际工程。这种方法为混流式水轮机转轮强度计算的求解探索了一条新途径。     

NUMERICAL STUDIES ON LOCOMOTION PERFROMANCE OF FISHLIKE TAIL FINS

Flapping plates of typical fishlike tail shapes are simulated to investigate their locomotion performance using the multi-block Lattice Boltzmann Method (LBM) and Immersed Boundary (IB) method. Numerical results show that fishlike forked configurations have better locomotion performance compared with unforked plates. Based on our results, the caudal fin in carangiform mode has greater thrust, and the lunate tail fin in thunniform mode has higher efficiency. These findings are qualitatively consistent with biological observations of fish swimming. Analysis of wake topology shows that the wake of the forked plate consists of a chain of alternating reverse horseshoe-like vortical structures. These structures induce a backward jet and generate a positive thrust. Moreover, this backward jet has a more favorable direction compared with that behind an unforked plate.