【作者】 李威；

【导师】 李廷秋；

【作者基本信息】 武汉理工大学 ， 流体力学， 2023， 硕士

【摘要】 波浪从深海传播至陡坡地形时,剧变的水深使波浪的传播过程发生复杂的非线性变化,引起的波浪破碎对海洋结构物破坏性极强。在模型试验方面,陡坡地形上波浪传播演化更剧烈,波形变化过程不易捕捉,对试验模型和观测设备精度要求更高,所以现有的研究多基于缓坡,对陡坡地形的研究很少。在数值模拟方面,网格法对波浪破碎的模拟精度较低,因此针对陡坡地形上波浪的传播和破碎特性的试验和数值研究,对于近海岸波浪特性的研究和护岸结构物的安全性具有重要意义。本文基于物理模型试验,对陡坡上波浪传播演化和破碎特性进行研究,结合光滑粒子动力学(Smoothed Particle Hydrodynamics,SPH)方法加以验证分析。本文主要工作和结论如下:(1)基于物理模型试验,研究波浪在陡坡地形上的传播过程,通过对波面时历曲线和沿程波高分布进行分析,讨论了波浪在陡坡上传播的时间和空间统计特征。结果表明,在陡坡地形上传播的规则波和不规则波,沿程变化趋势基本一致。周期和波高越大,波浪传播演化的速度越快,演化程度越剧烈。(2)在上述试验基础上,研究波浪在陡坡地形上传播的非线性特征。通过对偏度、不对称度、峰度和厄塞尔数等非线性特征参数进行分析,讨论了该地形上非线性特征参数变化规律,并拟合了该地形上偏度、不对称度和厄塞尔数关系的经验公式。结果表明,偏度、不对称度、峰度和厄塞尔数的幅值均在破碎区段内达到峰值。偏度、不对称度和厄塞尔数随着波高的增大而增大,偏度随着入射周期的增大而减小,不对称度和厄塞尔数伴随周期的增大而增大。水深的变化对偏度和厄塞尔数影响最大,对不对称度的影响较小。水深越小,破碎区段内各参数幅值变化量越剧烈。本文拟合的经验公式的相关系数为0.84,能有效地反映出偏度、不对称度随厄塞尔数变化的趋势。(3)基于物理模型试验,研究波浪破碎过程、破碎特性和破碎引起的能量谱变化,结合高速相机拍摄波浪破碎图像,分析卷破破碎演化过程。结果表明,破碎位置、破碎波高和破碎带宽度与周期和波高有关,破碎位置随着入射波高的增大而减小,破碎波高随着入射波高的增大而增大。破碎带宽度随着入射波高和周期的增大而增大。入射波高、周期越大的波浪,其三倍频、四倍频出现的频次更高,幅值更大。卷破波破碎的过程是水团和卷舌不断演化扩大直至最后消失的过程,是波能从低频向高频转换的过程,高倍频向主频及次频发生转移最终趋于稳定,标志着卷破破碎的结束。(4)基于SPH数值方法对波浪在陡坡上的传播过程进行模拟,从自由波面变化情况和破碎过程等方面将仿真结果与试验结果进行对比。结果表明,计算结果和模拟过程与试验结果吻合较好。在此基础上,利用该方法对卷破破碎的流场和涡量进行研究,结果表明,卷破破碎是涡量由波谷向波峰扩散最终回到波谷的的过程,是流场由有序向无序转变的过程,且最大速度发生在卷舌冲击坡面时。更多还原

【Abstract】 When the wave propagates from the deep sea to the steep slope terrain,the severe changes in water depth cause complex non-linear changes in the wave propagation process,The resulting wave breaking are extremely destructive to marine structures.In terms of model test,the wave propagation evolution is more violent on steep slope terrain,and the waveform change process is not easy to capture,which require higher accuracy of the test model and observation equipment.In terms of numerical simulations,the conventional grid method has a low accuracy for wave breaking,so experimental and numerical studies of wave propagation and breaking characteristics on steep slope terrain are important for the study of wave characteristics near the coast and the safety of shore protection structures.In this thesis,physical experiment was conducted to investigate the wave propagation evolution and breaking characteristics The analysis is validated by Using the SPH numerical simulation method.The main research work and conclusions of this paper are as follows:(1)Based on physical model tests,the wave propagation process on the steep slope is investigated.The temporal and spatial statistical characteristics of wave propagation on steep slope are discussed by analyzing the time curve of wave surface and the distribution of wave height along the course of the wave.The results show that regular and irregular waves propagating on steep slope terrain have essentially the same trend of evolution along their length.The larger the wave period and height,the faster and more intense the evolution of wave propagation.(2)Based on the above experiments,the non-linear characteristics of wave propagation on steep slope are investigated.By analysing the non-linear characteristic parameters such as skewness,asymmetry,kurtosis and Ursell number.the variation pattern of the non-linear characteristic parameters on this terrain is discussed and an empirical formula for the relationship between skewness,asymmetry and Ursell number is fitted.The results show that the amplitude of skewness,asymmetry,kurtosis and Ursell number all reach the peak value in the breaking zone.The skewness,asymmetry and Ursell number increase with the increase of wave height,the skewness decreases with the increase of incident period,and the asymmetry and Ursell number increase with the increase of period.The variation in water depth has the greatest effect on skewness and Ursell number but less on asymmetry.The smaller the water depth,the more dramatic the amount of variation in the amplitude of the parameters in the breaking zone.The correlation coefficient of the empirical formula fitted in this paper is 0.84,which can effectively reflect the trend of skewness and asymmetry with the Ursell number.(3)Based on physical model tests,the wave breaking process,characteristics and changes in the energy spectrum caused by wave breaking are studied and combined with high-speed camera images of wave breaking to analyse the evolution of plunging wave.The results show that the wave breaking position,wave breaking height and the surf-zone width are related to wave period and height.The wave breaking position decreases with the increase of incident wave height and the wave breaking height increases with the increase of incident wave height.The surf-zone width increases with the increase of incident wave height and period.The higher the incident wave height and the longer the period,which third and fourth harmonic generation occur more frequently and the amplitude is larger.The process of plunging wave is the process of water mass and plunging jet expands to disappear.Which is the process of wave energy transform from low to high frequency and the shift from high frequency to main frequency and secondary frequency eventually stable,which marks the end of plunging wave.(4)The wave propagation process on steep slope is simulated based on the SPH numerical method and the simulation results are compared with the experimental results in terms of the free wave surface variation and the wave breaking process.The results show that the calculation results and simulation process are in good agreement with the experimental results.On this basis,the flow field and vorticity of plunging wave are investigated by using this method.The results show that the plunging wave is a process in which the vorticity shift from the wave crest and eventually return to the trough,and the maximum speed occurs when the plunging jet impacts the slope.更多还原