潜堤对波浪在直立式防浪墙上爬高的影响

对直立式防浪墙前潜堤的空间布置对波浪在直墙上爬高的影响进行了研究.建立简化模型,即直立式防浪墙前海床设计为平底,潜堤设计为直立薄板. 改变潜堤高度及其与防浪墙之间距,研究不同的潜堤布置对波浪在直墙上爬高的影响. 针对线性波浪场,利用数值波浪水槽模拟了潜堤作用下直墙上波浪的爬高现象. 同时建立了理论模型,系统地分析了潜堤布置形式对直墙上波浪爬高的影响. 研究结果表明潜堤相对于水深的高度越大,对波浪在直墙上爬高的影响越大,而在一定的相对高度条件下,潜堤与直立墙之间距对波浪爬高的影响呈现出一定的规律性.      

Heat transfer and friction factor of turbulent flow through a horizontal semi-circular duct

Forced convection heat transfer and pressure drop characteristics of air flow inside a horizontal semi-circular duct are investigated experimentally. The experiments are carried out on a semi-circular duct of 23 mm inner radius, 2 mm thickness, and 2,000 mm length within a range of Reynolds number (8,242 ≤ Re ≤ 57,794)., under uniform wall heat flux conditions. The friction factor is determined by measuring the axial static pressure at different selected axial stations along the semi-circular duct. The variations of surface and mean air temperatures, local heat transfer coefficient, local Nusselt number, and the friction factor with the axial dimensionless distance are presented. It is observed that, for a given value of Reynolds number, each of the local heat transfer coefficient and the friction factor has a relatively high value near the entrance of the semi-circular duct then it decreases with increasing the dimensionless axial distance until it approaches a nearly constant value at the fully developed region. Also, it is found that, with increasing the Reynolds number the average heat transfer coefficient is increased and the friction factor is decreased. Moreover, empirical correlations for the heat transfer coefficient and friction factor as a function of the Reynolds number are obtained.     

Boundary element method for wave trapping by a multi-layered trapezoidal breakwater near a sloping rigid wall

This study examines the multiple layers in a rubble mound breakwater and their effect on reflection and dissipation of incoming ocean waves. The numerical model is developed using multi-domain boundary element method for oblique water wave trapping near a sloping wall by a multi-layered trapezoidal porous structure, which is utilized to model armour, filter and core layers while examining the hydrodynamics in different configurations. Both, the constant element and linear element approaches to boundary element method are discussed. The cases of bottom-standing porous structures as being submerged and fully extended are considered. The wave hydrodynamics over the structure is described by the reflection and dissipation coefficients along with the forces acting on the sloping wall, and is influenced by wave and structural parametrics of the system. The influence of armour layer in different configurations is highlighted for various structural and wave parameters.

     

Influence of nose perturbations on behaviors of asymmetric vortices over slender body

The influence of nose perturbations on the behaviors of asymmetric vortices over a slender body with a three-caliber ogive nose is studied in this paper. The tests of a nose-disturbed slender body with surface pressure measurement were conducted at a low speed wind tunnel with subcritical Reynolds number of 1×10⁵ at angle of attack α=50°. The experiment results show that the behaviors and structure of asymmetric vortices over the slender body are mainly controlled by manual perturbation on the nose of body as compared with geometrical minute irregularities on the test model from the machining tolerances. The effect of the perturbation axial location on asymmetric vortices is the strongest if its location is near the model apex. There are four sensitive circumferential locations of manual perturbation at which bistable vortices over the slender body are switched by the perturbation. The flowfield near the reattachment line of lee side is more sensitive to the perturbation, because the saddle point to saddle point topological structure in this reattachment flowfield is unstable. Various types of perturbation do not change the perturbation effect on the behaviors of bistable asymmetric vortices. The project supported by the National Natural Science Foundation of China (10172017) and the Foundation of National Key Laboratory of Aerodynamic Design and Research (00JS51.3.2 HK01)     

波浪与新型双排开孔圆筒防波堤相互作用三维数值模拟

双排开孔圆筒防波堤是基于圆筒、板式结构的一种复合式新型结构型式;基于不可压缩两相流模型建立三维数值波浪水槽,通过RNG k-ε湍流模型进行湍流封闭,并采用TruVOF方法捕捉自由液面,开展波浪与双排开孔圆筒防波堤相互作用数值模拟,探究相对排间距、开孔率对新型双排开孔圆筒防波堤消浪性能的影响,分析了后排开孔圆筒防波堤附近的复杂水动力现象和流动特性.结果表明,在本文研究工况范围内,沿程平均波高随相对排间距的增大先增大后减小,随开孔率的增大而增大,周期对沿程平均波高的影响没有明显规律;当B/D=9, e=23.11%时,新型双排开孔圆筒防波堤消浪效果最优,反射系数在0.4～0.46之间,透射系数在0.3～0.35之间,耗散系数在0.8～0.85之间;自由液面破碎、水气掺混、环状涡运动演化是新型双排开孔圆筒防波堤紊动耗能消波的主要原因;相对排间距会引起后排防波堤附近涡量分布以及剪切层形态的变化,从而导致不同的紊动特性,影响双排开孔圆筒防波堤消浪特性.研究结果可以为新型双排开孔圆筒防波堤工程设计与消浪机理研究提供理论支撑.     

HYBRID PERTURBATION-GALERKIN SOLUTION OFTHE FLOW IN A CIRCULAR CROSS-SECTIONTUBE WITH CONSTRICTION~

Using hybrid perturbatin- Galerkin technique, a circular cross-section tube model with sinusoidal wall is studied. This technique can remove the limitation of small parametersfor perturbation and the difficulty of selecting good coordinate functions about Galerkintechnique. The effects caused by the boundary conditions and the Reynolds number on theflow were discussed. The position of the separate and reattachment points was obtained. The tendency of the variation about the shear stress on the wall and friction factor along the axisdirection were also analyzed, The results at a small parameter have good agreements withthe perturbation ones.     

等波高双孤立波直墙爬高的数值模拟

基于RANS方程、VOF方法以及修正的Goring造波方法建立了模拟活塞式推波板运动的二维数值波浪水槽,实现了双孤立波直墙爬高的数值模拟．利用动边界技术模拟造波机推波板的运动,有效地实现了不同波峰间距双孤立波的造波方法．在验证单孤立波直墙爬高的基础上,模拟了不同相对波高、相对波峰间距的等波高双孤立波的直墙爬高过程,给出了波面、速度场及波动能量的变化规律．数值模拟结果表明：对于等波高的双孤立波,当入射波波高较大及两个波峰间距相对较小时,跟随在后孤立波的爬高放大系数小于先导孤立波的爬高放大系数;双孤立波在直墙爬高过程中,波动场的势能时间过程线呈现三峰形态,其中居中的最大势能峰值出现在第二个孤立波与经直墙反射后反向传播的第一个孤立波完全对撞的时刻．     

A Simple Fast Method in Finding Particular Solutions of Some Nonlinear PDE

1　ＡＴｒｉａｌＦｕｎｃｔｉｏｎａｎｄａＲｏｕｔｉｎｅｔｏＦｉｎｄＡｎａｌｙｔｉｃａｌＳｏｌｕｔｉｏｎｏｆＴｗｏＴｙｐｅｓｏｆＮｏｎｌｉｎｅａｒＰＤＥ　　Ｗｅｔｒｅａｔｔｈｅｎｏｎｌｉｎｅａｒｅｖｏｌｕｔｉｏｎｅｑｕａｔｉｏｎ ,ｗｈｉｃｈｉｓｆｏｒｍｅｄｂｙａｄｄｉｎｇｈｉｇｈｏｒｄｅｒｄｅｒｉｖａｔｉｖｅｔｅｒｍｓａｎｄｎｏｎｌｉｎｅａｒｔｅｒｍｓｔｏｔｈｅＢｕｒｇｅｒｓｅｑｕａｔｉｏｎ ｕ ｔ ｕ ｕ ｘ … ｕｐ ｕ ｘｑ α1 ｕ ｘ … αｎ ｎｕ ｘｎ =0 ,( 1)ｗｈｉｃｈｐ ,ｑ ,ｎａｎｄαｉ(ｉ =1,2…     

孤立波与淹没平板相互作用的三维波面和水动力实验研究

在波浪水池中进行了孤立波作用下有限长度和有限宽度淹没平板的三维模型水池实验. 首次应用多目视觉立体重构技术测量局部三维自由表面变形, 该系统的有效测量水平范围为1.7 m$\times $1.6 m. 用4个三分力测力传感器组成水下测力系统, 在不影响波面的情况下测量孤立波对平板的作用力和力矩. 针对波浪不破碎的情况, 选择0.4 m水深和0.16 m波高的来波条件, 平板淹没深度为0.1 m. 实验结果表明, 孤立波经过淹没平板时自由面有明显的三维变形, 导致孤立波波幅的时空变化. 波幅在平板尾缘中心线处达到最大值, 并沿展向逐渐减小. 利用多目视觉立体重构系统得到的波面变化过程与浪高仪给出定点波面时间序列相互印证, 表明建立标识码波面测量方法是有效的. 孤立波对淹没平板作用的水动力载荷变化分为6个典型阶段, 并与利用波面三维重构得到的波面测量标识码并讨论. 基于多目视觉立体重构技术得到了垂向力和俯仰力矩极值点出现时的三维波面形态. 建立的多目视觉立体重构系统将为海洋工程结构物的水池物理模型实验提供新的波面测量手段.      

Large-amplitude long wave interaction with a vertical wall

The rigorous solution of the nonlinear shallow-water equations for the wave field near a vertical wall is derived; it is used to calculate the height of the water oscillations near the wall versus the height of the incident wave. This solution is used to find the exceedance probability of characteristics of the wave motion near the vertical wall. It is shown that the wave height and trough distributions of water oscillations near vertical structures are less than the Rayleigh distribution. Beside of this, the distribution of the crest heights exceeds the Rayleigh distribution (using normalization of the amplification factor for such geometry within the framework of the linear theory), and this explains the high frequency of freak wave events on breakwaters and coasts.     

A σ‐coordinate three‐dimensional numerical model for surface wave propagation

A three‐dimensional numerical model based on the full Navier–Stokes equations (NSE) in σ‐coordinate is developed in this study. The σ‐coordinate transformation is first introduced to map the irregular physical domain with the wavy free surface and uneven bottom to the regular computational domain with the shape of a rectangular prism. Using the chain rule of partial differentiation, a new set of governing equations is derived in the σ‐coordinate from the original NSE defined in the Cartesian coordinate. The operator splitting method (Li and Yu, Int. J. Num. Meth. Fluids 1996; 23 : 485–501), which splits the solution procedure into the advection, diffusion, and propagation steps, is used to solve the modified NSE. The model is first tested for mass and energy conservation as well as mesh convergence by using an example of water sloshing in a confined tank. Excellent agreements between numerical results and analytical solutions are obtained. The model is then used to simulate two‐ and three‐dimensional solitary waves propagating in constant depth. Very good agreements between numerical results and analytical solutions are obtained for both free surface displacements and velocities. Finally, a more realistic case of periodic wave train passing through a submerged breakwater is simulated. Comparisons between numerical results and experimental data are promising. The model is proven to be an accurate tool for consequent studies of wave‐structure interaction. Copyright © 2002 John Wiley & Sons, Ltd.     

内孤立波作用下潜深对潜体运动响应和载荷特性的影响研究

内孤立波常发生于海洋密度跃层, 因其峰高谷深、携带能量巨大, 在传播过程中会导致跃层上下的海水流动呈现剪切状态, 并引起突发性的强流. 潜体在水下悬停时极有可能会遭遇内孤立波, 由于内孤立波的流场特性, 置于跃层上下的悬浮潜体所产生运动响应和水动力载荷变化不尽相同, 甚者会出现掉深现象. 为探究潜深对波体耦合作用的影响, 基于不可压缩N-S方程和mKdV理论, 采用速度入口造波, 结合重叠网格技术和流固耦合方法, 建立了分层流中内孤立波耦合水下潜体多自由度运动的数值模型, 通过该模型分析了不同潜深下悬浮潜体的运动响应和载荷特性. 结果表明: 在内孤立波作用下, 位于密度跃层上方和跃层中的潜体顺着波的前进方向运动, 先下沉后抬升, 位于跃层下方的潜体则会逆流持续下沉; 潜体与波面的垂向距离越小, 对其纵荡、垂荡和速度的影响越显著, 而位于密度跃层中的潜体在分界面处沿着波形运动, 其运动响应和载荷变化受影响较小; 潜体在跃层上、下流体中所受水平力的方向相反, 水平力峰值小于垂向力峰值, 且位于跃层下方的潜体一直受到低头力矩, 最终导致掉深.      

A second-order dynamic subgrid-scale stress model

ＩｎｔｒｏｄｕｃｔｉｏｎＩｎＬＥＳ,ｔｈｅｌａｒｇｅｓｃａｌｅｓｉｎｔｈｅｆｌｏｗａｒｅｃｏｍｐｕｔｅｄｅｘｐｌｉｃｉｔｌｙａｎｄｔｈｅｓｕｂｇｒｉｄ＿ｓｃａｌｅｓ(ＳＧＳ),ｗｈｉｃｈａｒｅｆｉｌｔｅｒｅｄｏｕｔｂｙａｎａｖｅｒａｇｅｐｒｏｃｅｓｓｏｐｅｒａｔｉｏｎｏｎｔｈｅＮａｖｉｅｒ＿Ｓｔｏｋｅｓｅｑｕａｔｉｏｎｓ,ａｒｅｍｏｄｅｌｅｄ.ＳｉｎｃｅＬＥＳｒｅｑｕｉｒｅｓｌｅｓｓｃｏｍｐｕｔｅｒｔｉｍｅｔｈａｎｔｈｅｄｉｒｅｃｔｎｕｍｅｒｉｃａｌｓｉｍｕｌａｔｉｏｎｓａｎｄｕｓｅｓｓｉｍｐｌｅｒａ…     

Global existence and blow-up phenomena of classical solutions for the system of compressible adiabatic flow through porous media

By means of maximum principle for nonlinear hyperbolic systems, the results given by HSIAO Ling and D. Serre was improved for Cauchy problem of compressible adiabatic flow through porous media, and a complete result on the global existence and the blowup phenomena of classical solutions of these systems. These results show that the dissipation is strong enough to preserve the smoothness of ‘ small ‘ solution.     

The effect of roughness on separating flow over two-dimensional hills

Two new experimental data sets for turbulent flow over a steep, rough hill are presented. These include detailed laser Doppler anemometry measurements obtained at the separation and reattachment points and, in particular, within the reverse flow region on the lee side of the hill. These results allow the development of a new parametrization for rough wall boundary layers and validate the use of Stratford’s solution for a separating rough flow. The experiments were conducted in a water channel for two different Reynolds numbers. In the first set of rough wall experiments, the flow conditions and the hill shape are similar to those presented in Loureiro et al. (Exp. Fluids, 42:441–457, 2007a) for a smooth surface, leading to a much reduced separation region. In the second set of experiments, the Reynolds number is raised ten times. The region of separated flow is then observed to increase, but still to a length shorter than that recorded by Loureiro et al. (Exp. Fluids, 42:441–457, 2007a). Detailed data on mean velocity and turbulent quantities are presented. To quantify the wall shear stress, global optimization algorithms are used. The merit function is defined in terms of a local solution that is shown to reduce to the classical law of the wall far away from a separation point and to the expression of Stratford at a separation point. The flow structure at the separation point is also discussed.     

VIBRATING-UPLIFT ROCKING MOTION OF CAISSON BREAKWATERS UNDER VARIOUS BREAKING WAVE IMPACT FORCES

IntroductionCaissonbreakwatersarewidelyusedincoastalengineeringandhavetheadvantagesthatcanbeusedindeepwateranddevelopedtomulti_functiontypes.However,thewavesareeasilybrokenandmayproduceextremelyhighimpactforceonacaissonbreakwater.Inrecentdecades,therehavebeenmanyfailureexamplesofbreakwatersunderbreakingwaveimpactintheworld[1- 3].Thedurationofbreakingwaveimpactisveryshortandtheresponsesofcaissonbreakwatershaveobviouslydynamicbehaviorsunderbreakingwaveimpact,butthestaticmethodisstillusedinthedes…     

Statistical Structure at the Wall of the High Reynolds Number Turbulent Boundary Layer

The one and two-point statistical structure of very high Reynolds number turbulence in the surface layer near a rigid `wall' is analysed. The essential mechanisms for turbulent eddies impinging on the wall are studied using linearised rapid distortion theory, which show how the mean shear and blocking actions of the surface act first independently and then, over the life time of the eddy, interactively. Previous analytical results are reinterpreted and some new results are derived to show how the integral length scales, cross correlations and spectra of the different components of the turbulence are distorted depending on the form of the spectra of eddies above the surface layer and how they are related to motions of characteristic eddy structures near the surface. These results are applied to derive some quantitative and qualitative predictions in the surface layers (SL), where the eddies are affected by local shear dynamics, and in the `eddy surface layer' (ESL) where quasi independents loping elongated eddies interact directly with the wall, and where there is a large range of wave number within which the spectra of the horizontal velocity components are proportional to k ⁻¹. The longest eddies in the boundary layer occur near the wall. Field experiments agree with the theoretical model predictions for the quite different forms for the spectra, cospectra and cross correlations for the vertical and horizontal components of the velocity field. By showing that in SL the energy exchange between the large and small scale eddies is local(`staircase') energy cascade, whereas in ESL there is a direct nonlocal (`elevator-like')energy transfer to the small scales, it is shown why the thickness of the ESL increases over rougher surfaces and as the Reynolds number decreases. This revised version was published online in August 2006 with corrections to the Cover Date.     

狭缝射流撞击圆柱表面的湍流特性实验研究

实验研究了狭缝射流撞击圆柱表面后壁面射流区的平均流动和湍流特 性. 考察了雷诺数 Re (6000-20000), 喷口到受撞表面距 离 Y/W (5-13), 喷口宽度 W (6.25mm, 9.38mm), 受撞表 面曲率(半圆柱体直径 D = 150mm)对流动和湍流结构的影响. 通过分析 X 热线 在壁面射流区的测量结果发现，在近壁区域，表面曲率、 Re_{w} , Y/W 和 S/W 等 参数对 \sqrt {\overline{u^2}} / U_m 的影响比对 \sqrt {\overline{v^2}} / U_m 强，并且切 应力 \overline {uv} /U_m^2 对表面曲率变化最敏感. 当喷口与受撞击表面之间的距 离 Y/W 在一定范围内增加时， 沿圆柱表面流动的流向和横向的湍流强度增强. 用平板射流和圆柱体表面壁面射流的数据进行比较，从而得到表面曲率对壁面射流特 性的影响. 结果表明，曲率对壁面射流的影响较强， 并随着 S/W 的增大而增强. 随着雷诺数的增大，壁面曲率的影响也有强化的趋势.     

地基与海洋建筑物相互作用——以最近西班牙海岸线建筑物内部损坏为例

海洋工程通常是一个细长的线。我们通常看到的仅仅是建筑物狭长的表面,而不分析支撑他们的大量水下材料。毋庸置疑,海底地基将承受来自于海洋的周期性和交替的静力以及变化的动力。外部和内部的海上工程均在复杂的环境中运行。固态颗粒(防波堤)可以吸入入射水流,并且通过颗粒之间的间距吸收海浪的能量。回流试图从固态颗粒中抽离物质,这样一个遵从太沙基原理的基于有效拉力和中性拉力之间的平衡建立起来。 在某些情况下,防护层的液化已经造成了防波堤崩溃(Sines,葡萄牙,1978年2月)。在其他情况下,虹吸作用或液化导致巨石(垂直的防波堤)毁坏或崩溃(新巴塞罗那港口,西班牙,2001年11月)。结合复合设计工具的地基-作用力——结构相互作用的过程是一个复杂的分析,关于其研究刚刚开始。 本文介绍了最近发生在西班牙的、由于地基失效导致的海上工程内部损坏的两个例子(马拉加,2004年7月,巴塞罗那,2007年1月),分析了其成因。     

Impulse wave run-over: experimental benchmark study for numerical modelling

This research intends to provide a detailed data basis for numerical modelling of impulse waves. Three tests are described involving a rectangular wave channel, in which a trapezoidal ‘breakwater’ was inserted to study wave run-over. In addition, a reference test is also described, in which the breakwater was removed. Two-dimensional impulse waves were generated by means of subaerial granular slides accelerated by a pneumatic landslide generator into the water body. Wave propagation and run-over over the artificial breakwater are documented by a set of high-quality photographs. Water surface profiles were recorded using capacitance wave gages upstream and downstream of the breakwater, and velocity vector fields were determined for the run-over zone by means of Particle Image Velocimetry. The measurements are compared with predictive formulae for wave features and wave non-linearity. The present data set involves both simple channel topography and wave features to allow for numerical simulations under basic laboratory conditions.