双孤立波直墙爬高的实验研究

海啸波在近海传播过程中有可能会演化成若干个孤立波组成的波列.为了研究孤立波波列对海岸结构物的作用机理,本文在波浪水槽中进行了双孤立波的直墙爬高实验.通过控制推板式造波机的运动,有效地实现了不同波峰间距双孤立波的造波方法.在复演并验证单孤立波直墙爬高的基础上,完成了不同相对波高、相对波峰间距的双孤立波爬高系列实验,给出了双孤立波平底传播及直墙爬高过程的波面时间序列及爬高过程水线运动时间序列.实验结果表明:对两个等波高的双孤立波而言,当相对波峰间距降到某临界值时,跟随在后孤立波的爬高放大系数将小于先导孤立波的爬高放大系数;当先导孤立波的波高大于跟随孤立波的波高,先导孤立波将更加显著地抑制对跟随孤立波的爬高过程,使得后者的最高爬放大系数显著减小;若在直墙爬高前两个波已明显重叠,即呈双峰瞬态波形,爬高放大系数不会大于具有相同波高的单孤立波的爬高放大系数.     

南海东北部陆架波折处潮-地作用激发非线性内波的数值模拟

南海东北部陆架波折处是大振幅内孤立波的频发地带.普遍的观点认为,这些内孤立波主要源自于吕宋海峡处潮流与海脊的相互作用;而对局地潮流-陆架波折相互作用的生成过程了解较少.本文通过一个二维非静力近似海洋数值模式,模拟了南海东北部陆架波折处潮流-地形相互作用激发内波及内波的演化过程,探讨了潮流周期、跃层深度对内波生成过程的影响.研究表明,潮流与地形相互作用能够激发向岸传播的内孤立子波列,证实了该海区内孤立波局地生成的可能性,但是相比于从吕宋海峡处传入的大振幅内孤立波,局地生成的内孤立波振幅要小得多.     

综合考虑多种变形因素的近岸多向不规则波传播数学模型——Ⅰ．模型的建立

根据线性波动的叠加原理和波浪方向谱理论，作者在综合考虑环境水流（水流因子）、非线性弥散影响（非线性因子）、底摩擦波能损失（底摩擦因子）、非缓坡地形影响（地形因子）、折射、绕射的近岸规则波传播基本方程的基础上，推导出了综合考虑多种变形因素的近岸多向不规则波传播变形的基本方程。使用有限差分作为数值方法，给出了波浪破碎和障碍物后边界的处理方法，建立了综合考虑环境水流（水流因子）、非线性弥散影响（非线性因子）、底摩擦波能损失（底摩擦因子）、非缓坡地形影响（地形因子）、折射、绕射、波浪破碎、障碍物影响的近岸多向不规则波传播变形数学模型。该模型以组成波的谱值及波向为变量，在实数域内求解，适合大面积海区波场计算。     

波流作用的近岸圆柱局部床面侵蚀

波浪流对近岸浅水带床面作用强烈,该区域结构物局部床面侵蚀显著,潜存致灾威胁。用三维数值方法研究了瞬态孤立波作用下非黏性沙海床上的近岸圆柱体局部冲刷规律,分析了波浪流冲刷的3类主要影响要素,讨论了近岸地形条件影响下的波流冲刷深度。研究认为,表征浅水波流特征和柱体尺度的无量纲数Urp与KC数存在非独立关系,二者均能分别反映波流冲刷的主要规律;表示泥沙运动的力学参数Shields数在波流动床条件下仍对柱体局部冲刷有贡献;近岸地形通过床面坡度对波破碎的增强及堤岸挡墙对波浪的反射,都会影响到局部冲刷。     

不规则波抛物型缓底坡波动方程

使用Kubo近似，导出了不规则波抛物型缓底坡波动方程的折射绕射联合模型。对不规则波抛物型缓底坡波动方程进行数值模拟，并对结与实验进行比较。不规则波抛物型缓底坡波动方程能很好地描述波浪传播过程中的变化，由此，可以预测波浪在传播过程中受到地形及波浪间相互用作而发生的变化。     

不恒定非均匀流场中随机波的折绕射联合数学模型

根据考虑流影响的缓坡方程，运用波动叠加原理，导出了一种适合大范围缓变地形情况下，不恒定非均匀流场中随机波的折绕射联合的数值模式。应用该模式进行了概化的半椭圆斜坡海底及渤海湾西部海域不恒定非均匀流场中随机波传播的折绕射联合的数值计算，获得了比较满意的结果。     

波浪形态及方向分布对港域波浪传播的影响

航道开挖会对波浪的传播产生显著影响,使港内波浪及泊稳条件发生变化。依托物理模型试验结果,验证了MIKE21中BW数值模型的合理性,证实二者结果吻合良好,随后利用该模型对比分析了在规则波、单向不规则波以及多向不规则波作用下,港域波浪扰动系数的分布规律及区别。结果表明：小角度入射波浪下,单向不规则波与规则波在航道迎浪面边坡发生的波能聚集现象明显强于多向不规则波;多向不规则波的方向分布对波浪在航道中的传播产生影响,波浪方向分布范围越窄,航道的折射效应及能量汇聚过程也越明显,航道边坡上的扰动系数也越大。因此在实际工程的航道设计中,应该考虑到不同形态波浪及多向波方向分布在航道传播过程中的差异,尤其在某些涌浪作用较强、波浪能量分布较为集中的港域,以单向不规则波甚至是规则波作为入射波浪将更加合理安全。     

综合考虑多种变形因素的近岸多向不规则波传播数学模型-I.模型的建立

根据线性波动的叠加原理和波浪方向谱理论,作者在综合考虑环境水流(水流因子)、非线性弥散影响(非线性因子)、底摩擦波能损失(底摩擦因子)、非缓坡地形影响(地形因子)、折射、绕射的近岸规则波传播基本方程的基础上,推导出了综合考虑多种变形因素的近岸多向不规则波传播变形的基本方程。使用有限差分作为数值方法,给出了波浪破碎和障碍物后边界的处理方法,建立了综合考虑环境水流(水流因子)、非线性弥散影响(非线性因子)、底摩擦波能损失(底摩擦因子)、非缓坡地形影响(地形因子)、折射、绕射、波浪破碎、障碍物影响的近岸多向不规则波传播变形数学模型。该模型以组成波的谱值及波向为变量,在实数域内求解,适合大面积海区波场计算。     

孤立波作用下边界层的模拟与分析

孤立波作用下的边界层内的剪切力以及涡量变化对海啸传播和海底地形塑造十分重要。本文基于多区域谱方法,利用直接模拟(DNS)数值模型,对在具有矩形断面的U形水洞内的孤立波下的边界层流动进行了模拟。将数值模拟结果与解析解以及试验结果进行了对比,发现数值结果与后两者吻合得较好。模拟结果显示,在低雷诺数下,扰动不会改变流态,而随着雷诺数的增大,流态会变得十分复杂。中等雷诺数情况下,边界层内会产生正向的涡,并进行稳定的传播。在较高雷诺数情况下,流动进入层流向紊流发展的过渡期,此时边界层内会产生正涡以及负涡,并会在水深方向进行不规则运动。     

三孤立波的斜坡爬高特征

该文采用推板式造波机和改进的Goring造波方法在波浪水槽中生成了由三个等波高孤立波组成的波列,首先在坡度为1/10的斜坡上进行了多个孤立波连续爬高的实验研究。实验测量了等波高双孤立波和三孤立波在等水深波浪水槽中传播和在斜坡上的爬高过程,给出了沿程多点浪高仪测量的波面时间序列和高速摄像记录的水线在斜坡上爬高与回落过程影像。分析了来波相对波高和无量纲波峰间距对每个孤立波爬高放大系数的影响。在基于RANS方程和VOF方法的数值波浪水槽中,模拟了三孤立波爬高过程,给出了最大爬高与破碎特征。实验和数值模拟结果表明,孤立波在斜坡上回落时会产生强劲的回流水流,该反向流动导致后随孤立波破碎,消耗波动能量,使得后随孤立波的爬高放大系数明显小于没有回落水流影响的首个孤立波的爬高放大系数。当孤立的波峰间较大时,若来波相对波高较小,后两个的孤立波爬高基本相同;若来波相对波高较大时,第三个孤立波的爬高大于第二个孤立波的爬高。     

二维水波数学模型的实验验证

为了验证基于缓坡方程的波浪折射和绕射综合问题的数学模型，在波浪水池中，对缓坡地形上的双突堤在规则波，单向不规则波和多向不规则波作用下的折射，绕射综合影响进行了实验研究，并将实验得到的结果和数值计算结果进行了比较。     

基于SWASH模型的近岸波浪传播变形数值模拟

SWASH模型是一种新型的非静压时域波浪模拟。为了探讨SWASH模型对于解决近岸波浪传播变形问题的适用性,在对其控制方程、边界条件、数值解法等进行介绍的基础上,采用该模型分别模拟了正向规则波、斜向规则波和斜向不规则波入射条件下L形防波堤附近水域的波浪场和波生流场,并与物理试验结果进行对比。结果表明,SWASH模型较好地复演了波浪在近岸区域所发生的浅水变形、折射、破碎,以及堤前反射、堤内绕射等物理现象,波高沿断面的定量分布与试验结果吻合良好,同时较好地模拟了不同波况下防波堤附近水域的波生流场,说明该模型适用于复杂岸线和地形条件下波浪传播变形的数值模拟。     

Three-dimensional unstructured modelling of wave-induced circulation over a plane and irregular beach

Nearshore currents have a complicated circulation structure over a beach due to the mutual interaction between waves and currents. To investigate the wave-induced circulation over a beach, a three-dimensional unstructured model accounting for the combined actions of waves and currents is established. The wave distribution over the beach is computed by a wave model and the depth-dependent wave radiation stresses with the surface roller are employed in the hydrodynamic model. The present model takes the mixing coefficients and the bottom shear stress under waves and currents into account. To evaluate the three-dimensional unstructured model, the laboratory experiments over a plane and irregular beach are used to test the performance of the model. The undertow over a plane beach is well reproduced and the vertical variability is captured. The performance of the model over an irregular beach is well displayed in the reproduction of pairs of counter-rotating primary circulations at the embayment troughs. Meanwhile, the secondary circulations are observed in the swash zone. The model captures the circulation systems over a beach and the circulation structures of the wave-induced currents are well exhibited.     

An experimental study on runup of two solitary waves on plane beaches

Experiments of the runup of two solitary waves on a plane beach are carried out in a wave flume. The two solitary waves with the same amplitude and the crest separating distances are generated by using an improved wave generation method. It is found that, with regard to the two solitary waves with same wave amplitude, the runup amplification of the second wave is less than that of the first wave if the relative crest separating distance is reduced to a certain threshold value. The rundown of the first solitary wave depresses the maximum runup of the second wave. If the leading solitary wave is of relatively smaller amplitude for the two solitary waves, the runup amplification is affected by the overtaking process of two solitary waves. It turns out that the runup amplification of the second wave is larger than that of the first wave if the similarity factor is approximately larger than 15, which means the larger wave overtakes the smaller one before the waves runup on a beach.     

NUMERICAL MODELING OF WAVE EVOLUTION AND RUNUP IN SHALLOW WATER

Based on the Navier-Stokes (N-S) equations for viscous, incompressible fluid and the VOF method, 2-D and 3-D Numerical Wave Tanks (NWT) for nonlinear shallow water waves are built. The dynamic mesh technique is applied, which can save computational resources dramatically for the simulation of solitary wave propagating at a constant depth. Higher order approximation for cnoidal wave is employed to generate high quality waves. Shoaling and breaking of solitary waves over different slopes are simulated and analyzed systematically. Wave runup on structures is also investigated. The results agree very well with experimental data or analytical solutions.     

NUMERICAL SIMULATION OF SOLITARY WAVE RUN-UP AND OVER-TOPPING USING BOUSSINESQ-TYPE MODEL

In this article,the use of a high-order Boussinesq-type model and sets of laboratory experiments in a large scale flume of breaking solitary waves climbing up slopes with two inclinations are presented to study the shoreline behavior of breaking and non-breaking solitary waves on plane slopes.The scale effect on run-up height is briefly discussed.The model simulation capability is well validated against the available laboratory data and present experiments.Then,serial numerical tests are conducted to study the shoreline motion correlated with the effects of beach slope and wave nonlinearity for breaking and non-breaking waves.The empirical formula proposed by Hsiao et al.for predicting the maximum run-up height of a breaking solitary wave on plane slopes with a wide range of slope inclinations is confirmed to be cautious.Furthermore,solitary waves impacting and overtopping an impermeable sloping seawall at various water depths are investigated.Laboratory data of run-up height,shoreline motion,free surface elevation and overtopping discharge are presented.Comparisons of run-up,run-down,shoreline trajectory and wave overtopping discharge are made.A fairly good agreement is seen between numerical results and experimental data.It elucidates that the present depth-integrated model can be used as an efficient tool for predicting a wide spectrum of coastal problems.     

Numerical simulation of irregular wave transformation due to wave-induced current

In order to investigate the effects of wave breaking-induced currents on the transformation of irregular waves over a shoal, two numerical model systems, a combination of SWAN plus SHORECIRC and a combination of REF/DIF S plus SHORECIRC, were constructed. The experimental results of irregular breaking waves conducted by Vincent and Briggs [1989, Refraction–diffraction of irregular waves over a mound. J. Waterway Port Coast. Ocean Eng. 115(2), 269-284.] were simulated using these two wave and current model combinations. Even though the two model combinations show a slight disagreement on the wave transformations, the numerical results indicate that it is necessary to take into account the effect of the breaking-induced currents when the waves are breaking over a shoal: The computed results agree much better with the experimental measurements than the simulation results obtained by neglecting the wave-current interaction.