水面下均流中空间任意方位马蹄涡之诱导速度势

本文在线性化自由表面条件的假定下,从单位强度的Kelvin源出发,推导而得处于水面下均流中空间任意方位马蹄涡之诱导速度势公式。本文的结果包含了文献[3]、[4]、[5]中的水平马蹄涡、上反马蹄涡、垂直马蹄涡和下滑马蹄涡之诱导速度势的情况,是一个适用范围更加广泛的基本解。

自由表面水流数值模拟程序并行化的预处理

并行化计算作为一种提升计算速度的手段被广泛应用于计算流体力学领域。为提升模拟速度,以及针对天然水域超大空间和时间尺度的CFD数值模拟需求,实现多节点分布式并行化计算很有必要。MPI作为目前较为成熟的并行接口是软件并行化的优先选择,其作为一种消息传递接口,通过通信方式实现程序的分布式并行。并行化过程中的并行分析、程序预处理以及通信模式的设计尤为必要。该文通过对自主开发的模拟软件的并行化分析,对预处理程序进行了开发,并设计了可扩展的通信模式,方便程序后续开发。通过分别执行串行程序与多线程并行程序模拟孤立波运动过程,分析并行程序计算的准确性,结果表明:并行计算程序与串行程序计算结果无显著差异,计算精度在10-6量级,且线程数不影响结果。

不同类型人工湿地研究进展及应用现状

近年来,水环境污染问题的日益严峻使得全球水资源短缺问题更加突出,人工湿地因其低成本、生态化、景观化、建设便利等优势被广泛应用于污水处理中。本文总结了目前人工湿地的四种主要类型,分别为自由水表面流人工湿地、地下流人工湿地、混合流人工湿地和生态浮床,阐述了各类型湿地系统的优势、研究现状及实践应用,以期为污水生态化处理的应用推广提供理论支撑。

Model for seawater fouling and effects of temperature,flow velocity and surface free energy on seawater fouling

A kinetic model was proposed to predict the seawater fouling process in the seawater heat exchangers.The new model adopted an expression combining depositional and removal behaviors for seawater fouling based on the Kern–Seaton model.The present model parameters include the integrated kinetic rate of deposition(k d)and the integrated kinetic rate of removal(k r),which have clear physical signi ficance.A seawater-fouling monitoring device was established to validate the model.The experimental data were well fitted to the model,and the parameters were obtained in different conditions.SEM and EDX analyses were performed after the experiments,and the results show that the main components of seawater fouling are magnesium hydroxide and aluminum hydroxide.The effects of surface temperature,flow velocity and surface free energy were assessed by the model and the experimental data.The results indicate that the seawater fouling becomes aggravated as the surface temperature increased in a certain range,and the seawater fouling resistance reduced as the flow velocity of seawater increased.Furthermore,the effect of the surface free energy of metals was analyzed,showing that the lower surface free energy mitigates the seawater fouling accumulation.

Modeling vertical heat transport in the wave affected surface layer of the ocean

In considering the vertical heat boundary approximation for the free surface applied. However, due to the existence of the transport problems in the upper ocean, the flat upper and the horizontal homogenous hypothesis are usually wave motion, the application of this approximation may result in some errors to the solar irradiation since it decays quickly in respect to the actual thickness of the water layer below the surface; on the other hand, due to the fluctuation of the water layer depth, it is improper to neglect the effects of the horizontal advection and turbulent diffusion since they also contribute to the vertical heat transport. A new model is constructed in this study to reflect these effects. The corresponding numerical simulations show that the wave motion may remarkably accelerate the vertical heat transferring process and the variation of the temperature in the wave affected layer appears in an oscillating manner.

Numerical Simulation for Water Entry of a Wedge at Varying Speed by a High Order Boundary Element Method

A high order boundary element method was developed for the complex velocity potential problem. The method ensures not only the continuity of the potential at the nodes of each element but also the velocity. It can be applied to a variety of velocity potential problems. The present paper, however, focused on its application to the problem of water entry of a wedge with varying speed. The continuity of the velocity achieved herein is particularly important for this kind of nonlinear free surface flow problem, because when the time stepping method is used, the free surface is updated through the velocity obtained at each node and the accuracy of the velocity is therefore crucial. Calculation was made for a case when the distance S that the wedge has travelled and time t follow the relationship s=Dtα, where D and α are constants, which is found to lead to a self similar flow field when the effect due to gravity is ignored.

Multi-domain Boundary Element Method with Dissipation

The wave diffraction and radiation around a floating body is considered within the framework of the linear potential theory in a fairly perfect fluid. The fluid domain extended infinitely in the horizontal directions but is limited by the sea bed, the body hull, and the part of the free surface excluding the body waterplane, and is subdivided into two subdomains according to the body geometry. The two subdomains are connected by a control surface in fluid. In each subdomain, the velocity potential is described by using the usual boundary integral representation involving Green functions. The boundary integral equations are then established by satisfying the boundary conditions and the continuous condition of the potential and the normal derivation across the control surface. This multi-domain boundary element method （MDBEM） is particularly interesting for bodies with a hull form including moonpools to which the usual BEM presents singularities and slow convergence of numerical results. The application of the MDBEM to study the resonant motion of a water column in moonpools shows that the MDBEM provides an efficient and reliable prediction method.

Comparative Analysis of the Separation Variation Influence on the Hydrodynamic Performance of a High Speed Trimaran

This paper numerically investigates the influence of separation variation of the outriggers on the hydrodynamic performance of a high speed trimaran （HST） aiming at improving its applicability in diverse realistic disciplines. The present investigation was performed within the framework of the 2-D slender body method （SBM） by calculating the resistance of three symmetric trimaran series moving in a calm free surface of deep water. Each trimaran series comprises of 4681 configurations generated by considering 151 staggers （-50%≤a≤＋ 100%）, and 31 separations （100%≤β≤400%） for 81 Froude numbers （0.20≤Fn≤ 1.0）. In developing the three trimaran series, Wigley-st. AMECRC-09, and NPL-4a models were used separately for both the main and side hulls of each individu;d series models. A computer macro named Tri-PL was created using the Visual Basic for Applications~. Tri-PL~ sequentially interfaced Maxsurfe then Hullspeed to generate the models of the three trimaran series together with their detailed hydrostatic particulars, followed by their resistance components. The numerical results were partially validated against the available published numerical calculations and experimental results, to benchmark the Tri-PL macro and hence to rely on the analysis outcomes. A graph template was creaLed within the framework of SigmaPlot to visualize the significant results of the Tri-PL properlv.

Oblique Wave-free Potentials for Water Waves in Constant Finite Depth

In this paper, a method to construct oblique wave-free potentials in the linearised theory of water waves for water with uniform finite depth is presented in a systematic manner. The water has either a free surface or an ice-cover modelled as a thin elastic plate. For the case of free surface, the effect of surface tension may be neglected or taken into account. Here, the wave-free potentials are singular solutions of the modified Helmholtz equation, having singularity at a point in the fluid region and they satisfy the conditions at the upper surface and the bottom of water region and decay rapidly away from the point of singularity. These are useful in obtaining solutions to oblique water wave problems involving bodies with circular cross-sections such as long horizontal cylinders submerged or half-immersed in water of uniform fmite depth with a free surface or an ice-cover modelled as a floating elastic plate. Finally, the forms of the upper surface related to the wave-free potentials constructed here are depicted graphically in a number of figures to visualize the wave motion. The results for non-oblique wave-free potentials and the upper surface wave-free potentials are obtained. The wave-free potentials constructed here will be useful in the mathematical study of water wave problems involving infinitely long horizontal cylinders, either half-immersed or completely immersed in water.

Simulation of Wave Impact on a Horizontal Deck Based on SPH Method

A numerical model was established for simulating wave impact on a horizontal deck by an improved incompressible smoothed particle hydrodynamics (ISPH). As a grid-less particle method, the ISPH method has been widely used in the free-surface hydrodynamic flows with good accuracy. The improvement includes the employment of a corrective function for enhancement of angular momentum conservation in a particle-based calculation and a new estimation method to predict the pressure on the horizontal deck. The simulation results show a good agreement with the experiment. The present numerical model can be used to study wave impact load on the horizontal deck.

A Lifting Line Theory for a Three-dimensional Hydrofoil

Prandtl’s lifting line theory was generalized to the lifting problem of a three-dimensional hydrofoil in the presence of a free surface. Similar to the classical lifting theory, the singularity distribution method was utilized to solve two-dimensional lifting problems for the hydrofoil beneath the free surface at the air-water interface, and a lifting line theory was developed to correct three-dimensional effects of the hydrofoil with a large aspect ratio. Differing from the classical lifting theory, the main focus was on finding the three-dimensional Green function of the free surface induced by the steady motion of a system of horseshoe vortices under the free surface. Finally, numerical examples were given to show the relationship between the lift coefficient and submergence Froude numbers for 2-D and 3-D hydrofoils. If the submergence Froude number is small free surface effect will be significant registered as the increase of lift coefficient. The validity of these approaches was examined in comparison with the results calculated by other methods.

A new variational inequality formulation for unconfined seepage flow through fracture networks

Darcy's law only applying to the flow domain is extended to the entire fracture network domain including the dry domain.The partial differential equation(PDE) formulation for unconfined seepage flow problems for discrete fracture network is established,in which a boundary condition of Signorini's type is prescribed over the potential seepage surfaces.In order to reduce the difficulty in selecting trial functions,a new variational inequality formulation is presented and mathematically proved to be equivalent to the PDE formulation.The numerical procedure based on the VI formulation is proposed and the corresponding algorithm has been developed.Since a continuous penalized Heaviside function is introduced to replace a jump function in finite element analysis,oscillation of numerical integration for facture elements cut by the free surface is eliminated and stability of numerical solution is assured.The numerical results from two typical examples demonstrate,on the one hand the effectiveness and robustness of the proposed method,and on the other hand the capability of predicting main seepage pathways in fractured rocks and flow rates out of the drainage system,which is very important for performance assessments and design optimization of complex drainage system.

Break-down criterion for the water-wave equation

We study the break-down mechanism of smooth solution for the gravity water-wave equation of infinite depth. It is proved that if the mean curvature κ of the free surface Σt, the trace（V, B） of the velocity at the free surface, and the outer normal derivative ？P/？n of the pressure P satisfy sup t∈[0,T]｜｜κ（t）｜｜Lp∩L^2＋∫0^T｜｜（▽V, ▽B）（t）｜｜L∞^6dt〈＋∞,inf （t,x,y）∈[0,T]×Σ_t- P/ n（t, x, y）≥c0,for some p 〉 2d and c_0〉 0, then the solution can be extended after t = T.

Free-surface air entrainment in open-channel flows

In hydraulic engineering,free-surface aeration is a natural phenomenon occurring in smooth channel flows.In self-aerated flows,a key aspect that has not yet been well understood is the formation mechanism of free-surface air entrainment.In this research,the process of free-surface entrapped deformation is analyzed theoretically and the critical radius of curvature for air entrainment is obtained,affected by flow mean velocity and depth.When the severity of local free-surface deformation exceeds the critical condition,the entrapped free surface encounters closure in the unstable deformation movement process,resulting in air entrainment.This inference agrees well with observed experimental results that are obtained from the processes of surface entrapped deformation and air entrainment captured by a high-speed camera-based data acquisition system.This agreement indicates that self-aeration occurs in low-velocity open-channel flows.It is also confirmed that free-surface turbulent deformation provides a mechanism for air entrainment.