计算水动力学课程教学案例库建设及教学实践

案例教学法作为一种“行为引导式”的教学形式,在计算水动力学教学行动中起到积极作用。围绕“由浅入深、循序渐进、深入浅出、由表及里”的教学目标,构建全方位、多层次的计算水动力学案例库,并开展了案例教学。教学实践表明,案例教学法充分融合了理论知识与实践工作,激发了学生学习兴趣,加深了学生对课程知识的理解和掌握,提高学生分析问题和解决问题的能力,帮助学生掌握和具备工程实践和科研工作的基础技能。

水动力学计算机模型在城市雨污收集系统中的应用：对天山污水收集系统的这

运用计算机水利模型来优化污水收集系统的设计并加强对该系统的管理，在国外已经非常普及。笔者拟通过自身的体会，向国内同行阐述一下该技术在排水管理方面的应用原理及发展展望。

新排水防涝标准下山地城市排水防涝规划研究

针对城市内涝灾害频发问题,在新修编的《室外排水设计规范》与城市排水(雨水)防涝规划编制大纲等文件的指导下,我国城市排水防涝工作已取得一定进展;以暴雨内涝灾害频发的湖北郧县(现已更名为十堰市郧阳区)老城区为研究对象,运用MIKE FLOOD水动力学计算软件构建模型,模拟区域降雨到排水行洪的各个环节,实现积水淹没模拟计算结果的可视化,并基于最新的排水防涝标准,根据模型研究结果结合SWMM软件与低冲击开发理念得出较为合理的内涝防治方案。

一阶迎风差分格式求解非线性对流扩散方程的精度

采用一阶迎风格式分别对一维线性对流扩散方程和非线性对流扩散方程进行了求解,检验了一阶迎风格式用于求解一维线性对流扩散方程和一维非线性对流扩散方程的适用性.多个计算算例的结果表明:一阶迎风差分格式用于求解线性对流扩散方程的结果不甚理想,但用于求解非线性对流扩散方程时能获得相当精度.工程计算中,该格式可用于求解水流运动方程,但不宜用于求解被水流输移的物质对流扩散方程.

T型坝两侧潮汐水动力特性的数值研究

为了避免传统潮汐能开发过程中在河口或海湾筑坝形成水库进而严重影响通航、鱼类产卵洄游和生态环境,考虑了一种垂直于海岸的"T"型坝,使平行于海岸向潮波传播到坝体两侧的潮位存在相位差,进而产生作用于坝上的水头。本文研究了该型坝坝体两侧的水动力特性,探索坝体和引水洞几何参数对作用于坝上水头的影响规律。该研究基于二维潮流模型,模拟了渤海及黄海北部海域潮流场,考虑在大连附近设置T型坝,计算和分析了坝头和坝干长度对作用于坝上最大水头的影响规律,固定坝干(或坝头)长度,作用在坝上的水头在一定范围内随坝头(或坝干)增长而线性增大。研究了在坝干上设置引水洞的T型坝的潮汐水动力特性。研究结果表明:随着引水洞尺寸的增大,作用在坝上水头不断减小,而最大发电功率先增大后减小,存在一个发电峰值。

守护船撞击海洋平台及FPSO碰撞场景研究

海洋平台及FPSO存在遭受守护船撞击的可能性,由此产生的结构损伤会影响到平台及FPSO的安全,因此在结构设计时需要考虑其抗撞性能。守护船与平台及FPSO的碰撞决定着平台及FPSO结构的合理性和经济性,目前我国尚没有相关的碰撞场景规范,设计时多采用国外有关规范。碰撞场景取决于海况条件和操作规定,而我国的海况与国外并不相同,所采用的操作规定也有差别,因此完全套用国外规范不尽合理。以一艘5000吨级守护船为研究对象,利用水动力学计算方法,研究守护船与导管架平台及FPSO的最大碰撞速度。选取我国近海油气田所在的典型海洋环境条件,探讨了不同水深、波浪条件以及碰撞方向对最大碰撞速度的影响。研究结果表明,守护船侧向撞击FPSO的最大碰撞速度最大,在实际工程作业中须注意此情景。

内燃机缸盖开发的CAE系统工程与应用

为提高产品开发成功率与效益,针对公司某款排量1.0L的增压直喷汽油机的缸盖设计,进行了详细而系统的计算机辅助工程(computer aided engineering,CAE)仿真工作。首先,在计算流体力学(computational fluid dynamics,CFD)领域:进行燃烧室及气道的燃烧分析,燃气流速计算结果与试验测试图片基本吻合;进行水套分析对冷却液的流速、传热系数进行评估。再次,在结构仿真领域开展了温度场分析,计算温度与测试误差小于5%,开展了高周疲劳分析(high cycle fatigue,HCF)与低周疲劳分析(low cycle fatigue,LCF)及振动特性(noise vibration harshness,NVH)分析,并对刚度进行优化。通过铸造仿真对浇注系统提出有效的改进措施。工程实践表明:该CAE体系与流程能有效地指导缸盖设计。

Using CFD Software to Calculate Hydrodynamic Coefficients

Applications of computational fluid dynamic(CFD) to the maritime industry continue to grow with the increasing development of computers.Numerical approaches have evolved to a level of accuracy which allows them to be applied for hydrodynamic computations in industry areas.Hydrodynamic tests,especially planar-motion-mechanism(PMM) tests are simulated by CFD software-FLUENT,and all of the corresponding hydrodynamic coefficients are obtained,which satisfy the need of establishing the simulation system to evaluate maneuverability of vehicles during the autonomous underwater vehicle scheme design stage.The established simulation system performed well in tests.

A Nonlinear Restoring Effect Study of Mooring System and its Application

Mooring system plays an important role in station keeping of floating offshore structures. Coupled analysis on mooring-buoy interactions has been increasingly studied in recent years. At present, chains and wire ropes are widely used in offshore engineering practice. On the basis of mooring line statics, an explicit formulation of single mooring chain/wire rope stiffness coefficients and mooring stiffness matrix of the mooring system were derived in this article, taking into account the horizontal restoring force, vertical restoring force and their coupling terms. The nonlinearity of mooring stiffness was analyzed, and the influences of various parameters, such as material, displacement, pre-tension and water depth, were investigated. Finally some application cases of the mooring stiffness in hydrodynamic calculation were presented. Data shows that this kind of stiffness can reckon in linear and nonlinear forces of mooring system. Also, the stiffness can be used in hydrodynamic analysis to get the eieenfrequencv of slow drift motions.

Numerical Analysis of the Flow Field in a Sloshing Tank with a Horizontal Perforated Plate

Liquid sloshing is a type of free surface flow inside a partially filled water tank.Sloshing exerts a significant effect on the safety of liquid transport systems;in particular,it may cause large hydrodynamic loads when the frequency of the tank motion is close to the natural frequency of the tank.Perforated plates have recently been used to suppress the violent movement of liquids in a sloshing tank at resonant conditions.In this study,a numerical model based on OpenF OAM(Open Source Field Operation and Manipulation),an open source computed fluid dynamic code,is used to investigate resonant sloshing in a swaying tank with a submerged horizontal perforated plate.The numerical results of the free surface elevations are first verified using experimental data,and then the flow characteristics around the perforated plate and the fluid velocity distribution in the entire tank are examined using numerical examples.The results clearly show differences in sloshing motions under first-order and third-order resonant frequencies.This study provides a better understanding of the energy dissipation mechanism of a horizontal perforated plate in a swaying tank.

CFD prediction of local scour hole around bridge piers

In order to predict the local scour hole and its evaluation around a cylindrical bridge pier, the computational fluid dynamics （CFD） and theories of sediment movement and transport were employed to carry out numerical simulations. In the numerical method, the time-averaged Reynolds Navier-Stokes equations and the standard k-e model were first used to simulate the three-dimensional flow field around a bridge pier fixed on river bed. The transient shear stress on river bed was treated as a crucial hydrodynamic mechanism when handling sediment incipience and transport. Then, river-bed volumetric sediment transport was calculated, followed by the modification of the river bed altitude and configuration. Boundary adaptive mesh technique was employed to modify the grid system with changed river-bed boundary. The evolution of local scour around a cylindrical bridge pier was presented. The numerical results represent the flow pattern and mechanism during the pier scouring, with a good prediction of the maximum scour hole depth compared with test results.

Numerical simulation of bubble chaotic motion in a cavitating water jet

A computational fluid dynamics (CFD) method is developed to investigate the radical motion of single cavitating bubble in the oscillating pressure field of a cavitating water jet. Regarding water as a compressible fluid, the simulation is performed at different oscillating frequencies. It is found that the bubble motion presents obvious nonlinear feature, and bifurcation and chaos appear on some conditions. The results manifest the indetermination of the cavitating bubble motion in the oscillating pressure field of the cavitating water jet.

大型双艉LNG船舶的双轴系设计

针对大型双艉LNG运输船双轴系设计难题,采用有限元计算,水动力学计算,以及轴系对中计算等综合手段,对各种极端恶劣工况下轴系的安全运转进行研判,提出艉管后轴承双斜坡设计的解决方案。

Reaction thrust characteristics of high-pressure submerged water jet of cylinder nozzles

The shapes and geometrical parameters of nozzles are key factors for fluidics. The relationship among the reaction thrust, flow rate pressure, diameter do and length L of a cylinder nozzle is analyzed theoretically. The simulation of the flow field characteristics was conducted via the FLUENT computational fluid dynamics package. Effects of the inlet conditions and the nozzle dimensions on the reaction thrust of a water jet were addressed particularly. The reaction thrust experiments were performed on a custom-designed test apparatus. The experimental results reveal that a） the nozzle diameter and the inlet conditions exert great influence on the water jet reaction thrust; and b） for L≤4d0, where the nozzle is treated as a thin plate-orifice, the reaction thrust is independent of nozzle length; for L〉4d0, where the nozzle is treated as a long orifice, the reaction thrust can reach maximum under the condition of a certain flow rate. These findings lay a theoretical foundation for the design of nozzles and have significant value, especially for the future development of high-oressure water-let orooulsion technology.

Dust dispersion and management in underground mining faces

Presence of fine dust in air causes serious health hazard for mine operators resulting in such serious problems as coal workers’pneumoconiosis and silicosis.Major sources of dust appear of course along the mining face where the minerals are extracted.Proper control and management are required to ensure safe working environment in the mine.Here,we utilize the computational fluid dynamic(CFD)approach to evaluate various methods used for mitigating dust dispersion from the mining face and for ensuring safe level of dust concentration in the mine tunnel for safety of the operators.The methods used include:application of blowing and exhaust fans,application of brattice and combination of both.The results suggest that among the examined methods,implementation of appropriately located brattice to direct the flow from the main shaft to the mining face is the most effective method to direct dust particles away from the mining face.

Numerical computation and analysis of unsteady viscous flow around autonomous underwater vehicle with propellers based on sliding mesh

The flexible transmission shaft and wheel propeller are combined as the kinetic source equipment, which realizes the nmlti-motion modes of the autonomous underwater vehicle （AUV） such as vectored thruster and wheeled movement. In order to study the interactional principle between the hull and the wheel propellers while the AUV navigating in water, the computational fluid dynamics （CFD） method is used to simulate numerically the unsteady viscous flow around AUV with propellers by using the Reynolds-averaged Navier-Stokes （RANS） equations, shear-stress transport （SST） k-w model and pressure with splitting of operators （PISO） algorithm based on sliding mesh. The hydrodynamic parameters of AUV with propellers such as resistance, pressure and velocity are got, which reflect well the real ambient flow field of AUV with propellers. Then, the semi-implicit method for pressure-linked equations （SIMPLE） algorithm is used to compute the steady viscous flow field of AUV hull and propellers, respectively. The computational results agree well with the experimental data, which shows that the numerical method has good accuracy in the prediction of hydrodynamic performance. The interaction between AUV hull and wheel propellers is predicted qualitatively and quantitatively by comparing the hydrodynamic parameters such as resistance, pressure and velocity with those from integral computation and partial computation of the viscous flow around AUV with propellers, which provides an effective reference to the shady on noise and vibration of AUV hull and propellers in real environment. It also provides technical support for the design of new AUVs.

Hydrodynamic Performance of Flapping-foil Propulsion in the Influence of Vortices

Fish are able to make good use of vortices.In a complex flow field,many fish continue to maintain both efficient cruising and maneuverability.Traditional man-made propulsion systems perform poorly in complex flow fields.With fish-like propulsion systems,it is important to pay more attention to complex flow fields.In this paper,the influence of vortices on the hydrodynamic performance of 2-D flapping-foils was investigated.The flapping-foil heaved and pitched under the influence of inflow vortices generated by an oscillating D-section cylinder.A numerical simulation was run based the finite volume method,using the computational fluid dynamics(CFD) software FLUENT with Reynolds-averaged Navier-Stokes(RANS) equations applied.In addition,dynamic mesh technology and post processing systems were also fully used.The calculations showed four modes of interaction.The hydrodynamic performance of flapping-foils was analyzed and the results compared with experimental data.This validated the numerical simulation,confirming that flapping-foils can increase efficiency by absorbing energy from inflow vortices.

1T′‐MoTe_(2) monolayer:A promising two‐dimensional catalyst for the electrochemical production of hydrogen peroxide

The direct synthesis of hydrogen peroxide(H_(2)O_(2))via a two‐electron oxygen reduction reaction(2e‐ORR)in acidic media has emerged as a green process for the production of this valuable chemical.However,such an approach employs expensive noble‐metal‐based electrocatalysts,which severely undermines its feasibility when implemented on an industrial scale.Herein,based on density functional theory computations and microkinetic modeling,we demonstrate that a novel two‐dimensional(2D)material,namely a 1T′‐MoTe_(2)monolayer,can serve as an efficient non‐precious electrocatalyst to facilitate the 2e‐ORR.The 1T′‐MoTe_(2)monolayer is a stable 2D crystal that can be easily produced through exfoliation techniques.The surface‐exposed Te sites of the 1T′‐MoTe_(2)monolayer exhibit a favorable OOH*binding energy of 4.24 eV,resulting in a rather high basal plane activity toward the 2e‐ORR.Importantly,kinetic computations indicate that the 1T'‐MoTe_(2)monolayer preferentially promotes the formation of H_(2)O_(2)over the competing four‐electron ORR step.These desirable characteristics render 1T′‐MoTe_(2)a promising candidate for catalyzing the electrochemical reduction of O_(2)to H_(2)O_(2).

Numerical computation and analysis of high-speed autonomous underwater vehicle (AUV) moving in head sea based on dynamic mesh

Autonomous underwater vehicles （AUVs） navigating on the sea surface are usually required to complete the communication tasks in complex sea conditions. The movement forms and flow field characteristics of a multi-moving state AUV navigating in head sea at high speed were studied. The mathematical model on longitudinal motion of the high-speed AUV in head sea was established with considering the hydrodynamic lift based on strip theory, which was solved to get the heave and pitch of the AUV by Gaussian elimination method. Based on this, computational fluid dynamics （CFD） method was used to establish the mathematical model of the unsteady viscous flow around the AUV with considering free surface effort by using the Reynolds-averaged Navier-Stokes （RANS） equations, shear-stress transport （SST） k-w model and volume of fluid （VOF） model. The three-dimensional numerical wave in the computational field was realized through defining the unsteady inlet boundary condition. The motion forms of the AUV navigating in head sea at high speed were carried out by the program source code of user-defined function （UDF） based on dynamic mesh. The hydrodynamic parameters of the AUV such as drag, lift, pitch torque, velocity, pressure and wave profile were got, which reflect well the real ambient flow field of the AUV navigating in head sea at high speed. The computational wave profile agrees well with the experimental phenomenon of a wave-piercing surface vehicle. The force law of the AUV under the impacts of waves was analyzed qualitatively and quantitatively, which provides an effective theoretical guidance and technical support for the dynamics research and shape design of the AUV in real complex environnaent.

Numerical research on water exchange of artificial reef in Yangmeikeng

Computational Fluid Dynamics(CFD)simulation is used in the study of water exchange capability,water residence time and conservative substance distribution in Yangmeikeng artificial reef area,which were helpful to marine environmental quality assessment and marine ecological changing mechanism research of artificial reef area.Furthermore the distance of reef clusters is changed to investigate the hydrodynamic characters and water exchange capability of the whole reef area in order to analyze the reasonable layout of artificial reef area.