非淹没刚性植物对海啸作用下海堤水动力特性影响数值模拟研究

基于非静压单相流模型NHWAVE建立了高精度数值波浪水槽。通过设计不同的计算工况,系统研究了非淹没刚性植物对海啸作用下海堤周围水动力特性的影响。着重分析了不同入射波高、不同植物分布密度以及不同植物分布宽度条件下海啸波沿程波形特征以及海堤堤顶越浪流空间分布特征。结果表明:不同入射波高、植物分布密度以及植物宽度条件下,堤顶流厚度和水体流速具有明显单调的变化趋势,并且随着植物分布密度和宽度增大,波能衰减增大;随着入射波非线性增强,植物分布密度和分布宽度对堤顶前段水流厚度的影响也随之增强,而对堤顶后段水流厚度的影响则减弱,且堤顶后缘水流厚度约为堤顶前缘厚度的二分之一;在波浪非线性较大情况下,植物的存在对堤顶流速度的空间分布趋势几乎没有影响,但相对堤顶流速度增加程度均大于无植物情况,且堤顶后缘水流速度约为堤顶前缘的1.6倍。     

Stable-thickness study of masonry block on the inner slope of dikes

Dike failure caused by overtopping is likely to result in major casualties and property losses.Aiming at this fact,a series of physical model experiments were conducted on stable thickness of masonry block on the inner slope of the dike.According to the erosion of block embankment with different thicknesses,the relation between the stable thickness of masonry block pitching of the inner slope and the average overtopping discharge is discussed.New equations subject to irregular waves are presented for average overtopping discharge,based upon the analysis of mean overtopping discharge and comparison of present overtopping discharge formulas at domestic and abroad.Finally,a calculation equation of the stable thickness of the dry masonry block stone of inner slope subject to irregular waves is given.In conclusion,the formula matches well with the experiment result,which is capable of functioning as an important reference for structure designs of the dike in China.     

基于FLUENT的波浪溢流水动力数值模拟

波浪溢流现象使得海堤受到了越浪和溢流的联合作用,复杂的水动力过程会引起海堤后坡产生严重的侵蚀破坏。基于FLUENT软件建立了二维数值波浪溢流水槽模型,该模型运用UDF速度边界造波法分析在不同超高条件下海堤后坡流量和水流厚度的水力学特性。结果表明数值模拟结果与前人物理模型试验结果吻合,该模型可以真实地模拟出海堤波浪溢流现象。在此基础上进一步研究了波浪溢流中越浪和溢流在不同相对超高条件下的主导性作用,而后建立了十分准确的波浪溢流海堤后坡稳定水流厚度计算公式。     

Spatial distribution of wave overtopping water behind coastal structures

Spatial distribution of random wave overtopping water behind coastal structures was investigated using a numerical model based on Reynolds-Averaged Navier-Stokes solver (RANS) and Volume of Fluid (VOF) surface capturing scheme (RANS-VOF). The computed spatial distributions of wave overtopping water behind the structure agree well with the measurements by Pullen et al (2008) for a vertical wall and Lykke Andersen and Burcharth (2006) for a 1:2 sea dike. A semi-analytical model was derived to relate spatial distribution of wave overtopping water behind coastal structures to landward ground level, velocity and layer thickness on the crest. This semi-analytical model agrees reasonably well with both numerical model results and measurements close to coastal structures. Our numerical model results suggest that the proportion of wave overtopping water passing a landward location increases with a seaward slope when it is less than 1:3 and decreases with a seaward slope when it gets steeper. The proportion of wave overtopping water passing a landward location increases with landward ground level and overtopping discharge. It also increases with the product of incident wave height and wavelength, but decreases with increasing relative structure freeboard and crest width. We also found that the extent of hazard area due to wave overtopping is significantly reduced by using a permeable structure crown. Findings in this study will enable engineers to establish the extent of hazard zones due to wave overtopping behind coastal structures.     

Predictions on Irregular Wave run-up and Overtopping

A series of hydraulic model tests are carried out to investigate random wave run-up and overtopping on smooth, impermeable single slope and composite slope. Based on analysis of the influences of wave steepness, structure slope, incident wave angle, width of the berm and water depth on the berm and the wave run-up, empirical formulas for wave run-up on dike are proposed. Moreover, empirical formula on estimating the wave run-up on composite slope with multiple berms is presented for practical application of complex dike cross-section. The present study shows that the influence factors for wave overtopping are almost the same as those for wave run-up and the trend of the wave overtopping variation with main influence parameters is also similar to that for wave run-up. The trend of the wave overtopping discharge variations can be well described by two main factors, i.e. the wave run-up and the crest freeboard of the structure. A new prediction method for wave overtopping discharge is proposed for random waves. The proposed prediction formulas are applied to case study of over forty cases and the results show that the prediction methods are good enough for practical design purposes.     

Erosional equivalences of levees: Steady and intermittent wave overtopping

Present criteria for acceptable grass covered levee overtopping are based on average overtopping values but do not include the effect of overtopping duration. This paper applies experimental steady state results for acceptable overtopping to the case of intermittent wave overtopping. Laboratory results consisting of velocities and durations for acceptable land side levee erosion due to steady flows are examined to determine the physical basis for the erosion. Three bases are examined: (1) velocity above a threshold value, (2) shear stress above a threshold value, and (3) work above a threshold value. The work basis provides the best agreement with the data and a threshold work value and a work index representing the summation of the product of work above the threshold and time are developed. The governing equations for flow down the land side of a levee establish that the flows near the land side levee toe will be supercritical. Wave runup is considered to be Rayleigh distributed with the runup above the levee crest serving as a surrogate for overtopping. Two examples illustrating application of the methodology are presented. Example 1 considers three qualities of grass cover: good, average, and poor. The required levee elevations for these three covers differ by 1.8 m. The results for Example 1 are compared with the empirical criteria of 0.1 liters per second per meter (l/s per m), 1.0  l/s per m, and 10.0  l/s per m. It is found that the required crest elevation by the methodology recommended herein for the “poor” cover is only slightly lower than for the criterion for average overtopping of q=10.0  l/s per m but significantly lower than for the overtopping criterion of 1.0 and 0.1 m/s per m. Example 2 considers two durations of the peak surge with the result that the longer duration peak surge requires a levee that is higher by approximately 0.8 m.     

孤立波低顶海堤越浪的数值模拟研究

灾害性波浪是中国沿海地区最具破坏性的自然灾害之一。采用开源程序OpenFOAM中interFoam求解器,对低顶海堤（在风暴潮和海平面上升情况下所面临的不利工况）的孤立波越浪特性开展数值模拟研究。通过孤立波冲击海堤的基准算例,验证模型在模拟波浪爬升和越浪过程中大变形波面以及剧烈波浪力方面的精度。基于验证的数值模型,对孤立波在低顶海堤上的越浪特征以及防浪墙高度对越浪的影响开展参数化研究。结果表明堤顶超高减小导致更为剧烈的越浪。针对尚无低顶海堤孤立波越浪量经验公式的问题,提出新的适用于堤顶超高小或为0的孤立波越浪量经验公式。此外,研究发现增加防浪墙高度可有效减少越浪,但防浪墙所受的波浪力也增大。综合考虑防浪墙减少越浪以及自身所受波浪力,针对文中研究采用的海堤截面和波浪条件,建议无量纲防浪墙高度取为1.00。     

Experimental study on inner slope failure mechanism of seawall by coupling effect of storm surge and wave

In the context of global climate change,the impact of group-occurring ocean dynamic disasters on China's offshore areas is becoming more and more intense.The study of the effect of existing ocean dynamic disasters on offshore hazard-bearing bodies mostly focuses on the effect of single disaster-causing factors,and it is still insufficient to study storm surge and dynamic wave coupling&reinforcement effects as well as the process of the dynamic response of such hazard-bearing bodies as seawalls.This study firstly realized the synchronous process of water level and wave through continuous tide generation and wave generation by the wave maker and tide generating device,so as to realize the dynamic coupling simulation of storm surge and wave in the laboratory.Then the physical model test of the typical seawall section was carried out under the dynamic coupling of storm surge and wave as well as at a conventional fixed water level respectively.In the process of test wave overtopping discharge and the damage process of the levee crown and backwall of seawalls were observed and compared,and their damage mechanism was also studied.     

斜向和多向不规则波对直立堤平均越浪量研究

通过三维波浪模型试验研究了斜向和多向不规则波对直立堤的越浪量。分别按平均越浪量和单波最大越浪量进行研究,探讨了平均越浪量随相对堤高、波浪方向、波浪方向分布宽度、波陡和相对水深等影响因素的变化规律,导得了斜向和多向不规则波作用于直立堤上的平均越浪量的计算公式。     

Field measurements of wave overtopping at the rubble mound breakwater of Rome–Ostia yacht harbour

This paper describes a new station for full-scale measurement of wave overtopping at the Rome yacht harbour rubble mound breakwater in Ostia (Italy) and the results of the successful first measurement campaign carried out during the winter season 2003–2004. The equipment and the research activities were supported by the EU project CLASH, focusing on scale effects for wave overtopping at coastal structures. The site is characterized by a very small tidal range, a long shallow foreshore and depth-limited breaking waves which interact with a shallow sloping porous rock structure. Overtopping water is collected by a steel tank installed on the crown slab behind the parapet wall. The measurement of water level variation inside the tank by means of two pressure transducers allows the calculation of individual overtopping volumes. Incident waves, sea levels and wind are also measured. During seven independent storms, more than 400 individual overtopping events were recorded and about 86 h of valid data are available. This extensive dataset is presented, discussed and then used for comparison with two commonly used overtopping prediction formulae based on small-scale model tests showing their tendency to underestimate the prototype results. A strong correlation between the hourly mean overtopping discharge and corresponding maximum volume is also presented. The paper generally confirms the validity of the approach used in Troch et al. (2004) [Troch, P., Geeraets, J., Van de Walle, B., De Rouck, J., Van Damme, L., Allsop, W., Franco, L., 2004. Full-scale wave overtopping measurements on the Zeebrugge rubble mound breakwater. Coastal Engineering 51, 609–628] for field measurement of wave overtopping.     

A numerical model of wave overtopping on seadikes

This paper describes the development of a numerical model for wave overtopping on seadikes. The model is based on the flux-conservative form of the nonlinear shallow water equations (NLSW) solved with a high order total variation diminishing (TVD), Roe-type scheme. The goal is to reliably predict the hydrodynamics of wave overtopping on the dike crest and along the inner slope, necessary for the breach modelling of seadikes. Besides the mean overtopping rate, the capability of simulating individual overtopping events is also required. It is shown theoretically that the effect of wave breaking through the drastic motion of surface rollers in the surfzone is not sufficiently described by the conventional nonlinear shallow water equations, neglecting wave setup from the mean water level and thus markedly reducing the model predictive capacity for wave overtopping. This is significantly improved by including an additional source term associated with the roller energy dissipation in the depth-averaged momentum equation. The developed model has been validated against four existing laboratory datasets of wave overtopping on dikes. The first two sets are to validate the roller term performance in improving the model prediction of wave overtopping of breaking waves. The last two sets are to test the model performance under more complex but realistic hydraulic and slope geometric conditions. The results confirm the merit of the supplemented roller term and also demonstrate that the model is robust and reliable for the prediction of wave overtopping on seadikes.     

波浪溢流作用下海堤内坡高性能加筋草皮护坡防侵蚀特征研究

基于1∶1的大型水槽试验结果,分析了波浪溢流过程中位于海堤内坡的高性能加筋草皮护面的侵蚀特征。试验观察表明试验期间有一定土壤的损失,但护坡无明显的破坏;土面高度测量表明,当土壤流失发展到一定深度后,如果水动力强度变化不大,侵蚀趋于逐渐停止,这种现象称为侵蚀上限;结合试验现象对侵蚀上限进行了初步解释,并讨论了侵蚀上限达到前的侵蚀速率特征;植株密度监测表明,试验期间的草茎密度基本不变,草叶密度在开始几次试验期间持续减小,而后达到一个稳定值,这对于海堤的可持续防护有重要意义。研究成果能够为波浪溢流期间海堤内坡防御的相关研究和工程措施提供参考依据。     

Derivation of unified wave overtopping formulas for seawalls with smooth,impermeable surfaces based on selected CLASH datasets

A set of unified formulas for prediction of the mean rate of wave overtopping at coastal structures with smooth, impermeable surfaces have been derived through the analysis of the selected CLASH datasets. The mean wave overtopping rate is expressed as the function of the significant wave height at the structural toe and the relative freeboard. The formulas are applicable for both vertical walls and inclined seawalls with smooth transition between them. The formulas are simple but cover the full range of water depth from the shoreline to deep water. The effects of the toe depth and the seabed slope on wave overtopping rate are duly incorporated in the formulas. Prediction performance of the new formulas is better than the EurOtop formulas for both vertical walls and inclined seawalls.     

Numerical simulation of irregular wave overtopping against a smooth sea dike

Based on the filtered Navier-Stokes equations and Smagorinsky turbulence model,a numerical wave flume is developed to investigate the overtopping process of irregular waves over smooth sea dikes.Simulations of fully nonlinear standing wave and regular wave’s run-up on a sea dike are carried out to validate the implementation of the numerical wave flume with wave generation and absorbing modules.To model stationary ergodic stochastic processes,several cases with different random seeds are computed for each specified irregular wave spectrum.It turns out that the statistical mean overtopping discharge shows good agreement with empirical formulas,other numerical results and experimental data.     

Prototype measurements and small-scale model tests of wave overtopping at shallow rubble-mound breakwaters: the Ostia-Rome yacht harbour case

The paper presents the comparison between the results of small-scale model tests and prototype measurements of wave overtopping at a rubble-mound breakwater. The specific structure investigated is the west breakwater of the yacht harbour of Rome at Ostia (Italy) and is characterized by a gentle seaward slope (1/4) and by a long, shallow foreshore. The laboratory tests firstly aimed at carefully reproducing two measured storms in which overtopping occurred and was measured. The tests have been carried out in two independent laboratories, in a wave flume and in a wave basin, hence using a two-dimensional (2-D) and a three-dimensional (3-D) setup. In the 2-D laboratory tests no overtopping occurred during the storm reproductions; in the 3-D case discharges five to ten times smaller than those observed in prototype have been measured. This indicates the existence of model and scale effects. These effects have been discussed on the basis of the results of several parametric tests, which have been carried out in both laboratories, in addition to the storm reproductions, varying wave and water level characteristics. Final comparison of all the performed tests with 86 prototype measurements still suggests the existence of scale and model effects that induce strong underestimation of overtopping discharge at small scale. The scale reproduction of wave breaking on the foreshore, together with the 3-D features of the prototype conditions and the absence of wind stress in the laboratory measurements, have been individuated as the main sources of scale and model effects. The paper also provides a comparison between the data and a largely used formula for wave overtopping discharges in the presence of structures similar to the one at hand. The suitable value of a roughness factor that appears in that formula is investigated and good agreement is found with other recent researches on rubble-mound breakwaters.     

碟形越浪式波能发电装置的三维数值模拟

基于计算流体力学软件的三维数值模拟技术,分析了碟形越浪式波能发电装置的越浪性能,通过构建基于水气两相VOF(Volume of Fluid)模型的三维数值波浪水槽对该装置进行三维数值模拟研究,数值计算结果与物理试验结果相互对比验证较为吻合,验证了所构建的三维数值波浪水槽的可靠性,通过考察装置的坡度、导流叶片个数、干舷高度对越浪性能的影响确定装置的最优结构参数。结果表明,在装置的斜坡面边缘增加回流板可减少波浪的反射,提高装置的越浪性能。在数值模拟中将装置的斜坡面边缘处安装回流板对碟形越浪式波能发电装置参数进行优化,通过分析回流板的长度对装置越浪性能的影响来探索最优回流板长度。     

Three-dimensional investigations of wave overtopping on rubble mound structures

To study the influence of wave obliquity and directional spreading on wave overtopping of rubble mound breakwaters a total of 736 three-dimensional model tests were carried out at Aalborg University. The results of these tests are presented and analysed in this paper yielding a new empirical reduction factor to describe the influence of wave obliquity and directional spreading on the average wave overtopping discharges. The study shows that perpendicularly incident, long-crested waves result in conservative values of the overtopping discharge for the tested cross-section.     

Numerical study of combined overflow and wave overtopping over a smooth impermeable seawall

A numerical wave flume is used to investigate the discharge characteristics of combined overflow and wave overtopping of impermeable seawalls. The numerical procedure computes solutions to the Reynolds-averaged Navier–Stokes equations and includes the generation of an irregular train of waves, the simulation of wave breaking and interaction with a sloping, impermeable wall. The numerical model is first tested against published experimental observations, approximate analytical solutions and empirical design formulae for the cases of pure overflow and pure overtopping. A sequence of numerical experiments simulating combined overflow and overtopping are described. The results are used to determine empirical discharge formulae of the form used in current practice.     

Field and laboratory measurements of mean overtopping discharges and spatial distributions at vertical seawalls

Within the CLASH project, wave overtopping at the vertical seawall at Samphire Hoe was measured by HR Wallingford (HRW), and compared laboratory tests in 2 & 3 dimensions carried out at the University of Edinburgh and HRW. At Samphire Hoe, overtopping volumes were captured in three volumetric tanks capable of measuring wave-by-wave and total overtopping volumes. The three tanks were placed progressively farther back from the seawall edge so that the spatial distribution of the overtopping discharges could be determined. The field measurement equipment was successfully deployed on three occasions, and measured overtopping discharges ranged from that barely considered to be hazardous to the public to over q = 3.0 l/s/m. The 2d testing at Edinburgh was modelled at a scale of 1:40, and the 3d model at HRW was modelled at 1:20. For both sets of laboratory tests, a range of conditions, representative of the storm wave conditions and water levels, was reproduced in addition to a set of parametric conditions. The storm conditions allowed a direct comparison between the field and laboratory measurements, and the parametric conditions were used to test the generic overtopping behaviour of the structure. For both sets of laboratory tests, mean overtopping discharges and the spatial distribution were measured separately. Analysis of the distribution data relates the proportion of the discharge that has landed as a function of (x / L_o); where x is the distance behind the crest, and L_o is the offshore wavelength. Analysis of the field, 2d & 3d laboratory data, and empirical prediction methods have not identified any scale effects for overtopping discharges at vertical and near-vertical seawalls.     

不同掩护程度弧形胸墙波压力及越浪量试验研究

为了明确斜坡堤弧形胸墙越浪量及波压力的变化规律,采用波浪水槽试验测量了弧形胸墙的越浪量和波压力。试验从斜坡堤弧形胸墙前的掩护程度等因素入手对弧形胸墙的返浪效果及波压力进行初步研究,得出不同掩护程度弧形胸墙的越浪量及波压力,发现掩护程度越好,弧形胸墙所受波压力越小;半掩护情况下越浪量最小,为实际工程设计提供了依据。