不等直径串列双圆柱体绕流的数值模拟

利用Fluent软件模拟雷诺数为200时不同间距比G/D和直径比d/D情况下的圆柱绕流现象。根据模拟结果分析G/D和d/D对圆柱体的涡脱落形态,大、小柱体的升力,阻力系数和St数的影响,结果表明涡脱落形态随着G/D和d/D的变化呈现不同的形式,在G/D小于临界间距比时呈现单一涡脱落形态,在G/D大于临界间距比时,呈现双旋涡脱落形态;临界间距比随着d/D增大而增大。在临界间距比附近大、小柱体的升力和阻力系数值及St数变化较大,大、小柱体的St数具有相同的变化规律,St随着d/D的增大而减小。     

海底管线上波浪力的大涡模拟及三步有限元数值模拟

应用三步有限元法结合大涡模拟方法(LES)离散非定常不可压流动的Navier-Stokes方程,模拟了波浪场中海底管线周围流场及其受力情况,并把数值模拟的结果与物理实验的实测结果进行了比较,两者符合较好。为了检验三维效应的影响,同时进行了二维和三维流场的数值模拟。     

基于大涡模拟和局部滤波同化方法的海洋环流模式

结合最小二乘法极值原理,提出了一种基于局部谱展开的滤波同化方法,把测量数据和数值计算过程中出现的高频短波滤掉,并将高度计数据同化到了求解过程中.结果既增加了数值稳定性,又提高了数值模拟的准确性.针对在海洋环流问题中水平的流动性质和垂直的不同的特点,我们还将大涡模拟的思想和直接涡黏的思想分别应用于水平方向和垂直方向,给出的方法是一种适用于海洋环流和浅水环流问题的大涡模拟湍流模式.对热带和北太平洋一年四季非定常季风作用下环流的数值模拟表明,提出的方法非常有效,数值结果与实际相当吻合.     

基于大涡模拟的ROV导管推进器梢隙流动数值研究

导管推进器是一种普遍应用于无人遥控潜水器(ROV)等潜器中的特种推进器。在桨叶与导管之间的梢隙中存在非常复杂的流动,本研究基于大涡模拟(LES)对导管推进器的梢隙流动进行了数值模拟分析。通过对时间步长的收敛性研究,建立两套基于不同网格类型的计算模型。将计算与试验结果进行对比,比较两种不同类型网格模拟结果的差异,发现切割体网格能够更好地捕捉到泄涡的细节,并结合梢隙流场的原理分析了泄涡发展的过程,梢隙涡的驱动力是吸力面、压力面之间的压差。此外,随着进速系数增大,梢隙周向的涡管轴向分布范围减小,主泄涡发生位置延后,泄出涡的长度和数量都有所减少。     

潮流能水轮机尾流场及涡特性DDES模拟

为研究潮流能水轮机尾流场流动特性及涡结构组成,基于DDES(Delayed Detached Eddy Simulation)模型对不同流速和转速的4种工况下水轮机尾流场进行数值模拟,并进一步探究其尾流场空间涡结构的变化特性。结果表明,水轮机的数值模拟结果与试验结果能够较好吻合。对比不同工况下的尾流场模拟结果可知:水轮机尾流区域流动复杂,延迟分离涡模拟方法能有效模拟水轮机旋转过程中产生的叶尖涡、叶尖脱落涡、轮毂涡等不同涡结构,并能完整观察到叶尖涡的产生、脱落、失稳、破碎过程。转速一定时,流速越大,叶尖脱落涡、轮毂涡的发展距离越远;流速一定时,转速越大,涡的发展距离越短。本文数值模拟计算结果可为实际海况中潮流能阵列水轮机的布局提供可靠依据。     

改进的移动粒子半隐式法模拟楔形体入水砰击

移动粒子半隐式法(Moving-Particle Semi-Implicit Method,MPS)是一种新的基于拉格朗日(Lagrange)理念的无网格方法,适用于模拟自由液面的大变形和水流的喷射现象。用基于大涡模拟的改进MPS法首先模拟了矩形体的入水砰击,砰击压力的计算结果证明了这种方法的正确性,然后模拟了楔形体的匀速入水砰击,并与实验结果进行了对比,验证了大涡模拟改进MPS法在砰击问题中的适用性。     

台湾海峡西部海域水平涡动交换混合的讨论

根据涡动混合张量，计算涡交换张量分量，进而利用普郎特公式计算混合长度，并采用涨合交换椭球方程导出混合交换椭圆方程，以此计算本区涡动交换混合椭圆要素的分布，阐明台湾海峡西部涡动混合的变化规律。得出海峡西部涡动混合的流势的分布变化规律较一致，即流速大的涡动混合交换强，顺流方向或平行于岸线的涡动混合强于横珙于流或垂直岸线的涡动混合，其混合强度冬季比夏季强，表层比底层强，南部比北部强。     

固体火箭发动机燃气射流噪声数值模拟

为了研究固体火箭发动机燃气的气动噪声特性,建立了二维轴对称的射流数学模型,采用大涡模拟(LES)方法对火箭发动机超声速燃气射流流场进行了数值模拟,然后利用 FW-H 面积分得到了超声速燃气射流噪声的分布特性。 计算结果表明:该方法能较好地捕捉超声速燃气射流的复杂波系流场结构,射流噪声辐射具有较明显的指向性。     

基于HYCOM的南海中尺度涡数值模拟

结合AVISO(Archiving Validation and Interpolation of Satellite Oceanographic Data)高度计资料,利用改进的NERSCHYCOM(Nansen Environmental and Remote Sensing Center-Hybrid Coordinate Ocean Model)大洋环流模式,对南海中尺度涡进行数值模拟研究,主要包括中尺度涡的三维结构、南海EKE(Eddy Kinetic Energy,涡动动能)的垂向变化、黑潮中尺度涡的脱落以及涡旋近岸时的结构变化等。模式再现了2007年2月-3月菲律宾西侧海域的一次暖涡过程,探究了其生命期中各阶段的特征物理量的变化,对其成熟时期的涡旋结构研究表明,中尺度涡的结构呈现不对称性,涡旋两侧的流场空间范围和流场强度均不相同,涡旋的半径和中心位置随深度不断变化,并且由涡旋作用产生的升降流的中心与涡旋自身中心并不重合,二者之间有一定距离。初步探索EKE的垂向分布情况,认为南海年平均EKE在垂向变化上呈现三段式,主要部分分布在300m以浅深度,但同时垂向又能达到海洋深层。分析了一次黑潮中尺度涡脱落的模式模拟个例,推测黑潮中尺度涡脱落原因:黑潮流径西移、外海中尺度涡对黑潮的强迫、地形作用,并且结果表明从黑潮脱落的中尺度涡可以携带大量高温高盐水体进入南海,对南海的温盐性质产生很大的影响。初步探索涡旋近岸时的结构变化,涡旋靠近岸界时,受岸界挤压,流速在一段时间内会增大,继续靠近岸界,由于岸界的摩擦、海底的拖曳,导致能量耗散,流速减小,最终涡旋消亡。     

深水海洋立管涡激振动试验流场设计及CFD数值模拟

针对阶段流作用下的大长细比海洋立管涡激振动试验所需的外流条件,根据实验室的基本情况,对试验流场进行了设计改造和数值模拟。根据数值模拟的结果,选定了试验流场的改造方案,并对改造后测得的试验数据和数值模拟的结果进行了对比分析。结果表明:在低流速时,模拟结果与试验流速吻合较好;在高流速时,数值模拟结果比试验流速略大。在误差允许的范围内,可以得到均匀分布的流场。     

Numerical Simulation of Sloshing Using the MPS-FSI Method with Large Eddy Simulation

A numerical model has been developed to study sloshing of turbulent flow in a tank with elastic baffles. The Moving-Particle Semi-implicit method(MPS) is a kind of meshless Lagrangian calculation method. The large eddy simulation(LES) approach is employed to model the turbulence by using the Smagorinsky Sub-Particle Scale(SPS)closure model. This paper uses MPS-FSI method with LES to simulate the interaction between free surface flow and a thin elastic baffle in sloshing. Then, the numerical model is validated, and the numerical solution has good agreement with experimental data for sloshing in a tank with elastic baffles. Furthermore, under external excitations,the MPS is applied to viscous laminar flow and turbulent flow, with both the deformation of elastic baffles and the wave height of the free surface are compared with each other. Besides, the impact pressure with/without baffles and wave height of free surface are investigated and discussed in detail. Finally, preliminary simulations are carried out in the damage problem of elastic baffles, taking the advantage of the MPS-FSI method in computations of the fluid–structure interaction with large deformation.     

Numerical Simulation and Physical Simulation of Sea Wave Groups

- Based on field wave data, an empirical formula of wave envelope spectrum is given in this paper. Then the methods of both numerical and physical simulation of sea wave groups with the given spectrum and groupiness parameters are suggested.     

Era-interim Forced Simulation of the Indian Summer Monsoon

Abstract

In the present study, mean rainfall for the months of June-July-August-September (JJAS) during summer monsoon is simulated over India and its adjoining regions for a period between 1982 and 2006. The study was carried out using Regional Climate Model (RegCM) version 4.6 at a resolution of 25?km. The simulated mean JJAS monsoon rainfall was validated against the observational IMD data. Comparison of JJAS seasonal mean summer rainfall for the first decade 1982–1991, with the later decade 1997–2006 indicate that the intensity of rainfall increases over Indian land-mass during the later decade under the forced conditions of Era-Interim. The observed JJAS mean rainfall indicates two maximum rainfall areas i.e. the Western Ghats and the Himalayan region. A significant bias is observed in the central and Jammu and Kashmir (J&K) region. The JJAS mean seasonal surface air temperature distribution at 0.25?×?0.25-degree grids resolution shows a decreasing trend of temperature over the Indian landmass.     

Simulation of wind-induced oscillations of the Azov-Sea level

The prognostic fields of the surface winds and atmospheric pressure obtained according to the data of the Skiron prognostic system are used to study the surge phenomena in the Azov Sea by using a three-dimensional nonlinear model. The accumulated numerical results are compared with the data of direct measurements of the sea level at the coastal stations. The degree of sensitivity of the computed levels of surges to the value of the coefficient of surface friction is evaluated. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 53–65, November–December, 2008.     

Numerical Simulation of the Gulf Stream and the Deep Circulation

The Gulf Stream system has been numerically simulated with relatively high resolution and realistic forcing. The surface fluxes of the simulation were obtained from archives of calculations from the Eta-29 km model which is an National Center for Environment Prediction (NCEP) operational atmospheric prediction model; synoptic fields are available every 3 hour. A comparison between experiments with and without surface fluxes shows that the effect of the surface wind stress and heat fluxes on the Gulf Stream path and separation is closely related to the intensification of deep circulations in the northern region. Additionally, the separation of the Gulf Stream and the downslope movement of the Deep Western Boundary Current (DWBC) are reproduced in the model results. The model DWBC crosses under the Gulf Stream southeast of Cape Hatteras and then feeds the deep cyclonic recirculation east of the Bahamas. The model successfully reproduces the cross-sectional vertical structures of the Gulf Stream, such as the asymmetry of the velocity profile, and this structure is sustained along the downstream axis. The distribution of Root Mean Square (RMS) elevation anomaly of the model shows that the eddy activity of the Gulf Stream is realistically reproduced by the model physics. The entrainment of the upper layer slope current into the Gulf Stream occurs near cross-over; the converging cross-stream flow is nearly barotropic. This revised version was published online in August 2006 with corrections to the Cover Date.     

Simulation of the seasonal thermal structure in the Bobal Sea

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Simulation of the seasonal thermal structure in the Bohai Sea

The seasonal thermal structure in the Bohai Sea are examined with a three-dimensional boroclinic primitive equation model for shelf sea.The evolution of the seasonal thermal stratification is well simulated.The stratification appears early in April,first in the area off Qinhuangdao and it is well developed in the middle of May.It intensifies with synoptic and neap-spring fluctuations throughout the summer and reaches its maximum in the middle of July.Eventually,it is destroyed at the end of September.There are cold water belts between well-mixed and stratified regions.They are loGated on the mixed side of tidal fronts,and coincide with the isolines for a temperature difference of 1-2℃ between surface and bottom.The sea surface temperature (SST) distribution shows local maxima at the head of three bays and to the south of Qinhuangdao during the summer.The Bohai Sea responds to the variability in the atmospheric forcing and in tides with the synoptic and neap-spring variations of SST,as well as in the stratification and in variable positions of tidal fronts.     

Simulation modeling of the conditional resource potentials of the environment

It is suggested to describe the ecological and economic features of the local sites of natural environments (dry-land and water areas) by their resource potential conditional relative to the technologies of their application. An information model aimed at the prediction of scenarios of conditional resource potentials capable of evaluation of the efficiency of consumption of the resources is developed. The model is based on the monitoring of the amount of debt for the consumption of the resources accumulated by a branch of economy (plant) in the unfavorable economic situation or in the case of deterioration of environmental conditions. Examples of simulation of the processes of consumption of the resources aimed at the realization of control over the stable development of ecological and economic systems are presented. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 24–42, March–April, 2006.     

Simulation of the diurnal evolution of the atmospheric boundary layer

Results of simulating the diurnal evolution of the atmospheric boundary layer (ABL) with a second-order closure model are presented. The model includes new algebraic expressions for triple correlations to describe their behavior over the entire height of the mixed layer adequately to measurements. The model also takes into account the influence of long-wave radiation on the heat balance, which becomes important in the nocturnal ABL. The modeling results are compared with 24-h ABL evolution simulations by the third-order closure model and available in situ and laboratory measurements.