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Efficient Simulation of Freak Waves in Random Oceanic Sea States 总被引：1，自引：0，他引：1
Numerical simulations of freak wave generation are studied in random oceanic sea states described by JONSWAP spectrum.The evolution of initial random wave trains is numerically carried out within the framework of the modified fourorder nonlinear Schruedinger equation (mNLSE),and some involved influence factors are also discussed.Results show that if the sideband instability is satisfied,a random wave train may evolve into a freak wave train,and simultaneously the setting of the Phillips parameter and enhancement coefficient of JONSWAP spectrum and initial random phases is very important for the formation of freak waves.The way to increase the generation efficiency of freak waves thsough changing the involved parameters is also presented. 相似文献
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Owing to the Benjamin-Feir instability,the Stokes wave train experiences a modulation-demodulation process,and presents a recurrence characteristics.Stiassnie and Shemer researched the unstable evolution process and provided a theoretical formulation for the recurrence period in 1985 on the basis of the nonlinear cubic Schr dinger equation(NLS).However,NLS has limitations on the narrow band and the weak nonlinearity.The recurrence period is re-investigated in this paper by using a highly efficient High Order Spectral(HOS) method,which can be applied for the direct phaseresolved simulation of the nonlinear wave train evolution.It is found that the Stiassnie and Shemer’s formula should be modified in the cases with most unstable initial conditions,which is important for such topics as the generation mechanisms of freak waves.A new recurrence period formula is presented and some new evolution characteristics of the Stokes wave train are also discussed in details. 相似文献
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Efficient Generation of Freak Waves in Laboratory 总被引：3，自引：1，他引：3
In the present study,Kriebel's method is improved to generate freak waves in laboratory.The improved method superposes a random wave train with two transient wave trains to simulate freak wave events in a wave tank.The freak waves are more nonlinear than what generated with Kriebel's method of the same energy.It can also generate freak waves to satisfy all the qualifications of the adopted definition with less energy than Kriebel's and can hardly influence the significant wave height. 相似文献
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The experimental studies of the wave breaking effects on freak wave generation are presented within a finite-depth random wave train in a laboratory wave tank. The main attention is paid to the abnormal index,AI=Hmax/Hs,being used to characterize the freak waves,and the changes of the coefficient due to wave breaking. The results show that the occurrence probability of freak wave events in non-breaking waves is much larger than that in breaking waves and such occurrence in deep water is larger than that in ... 相似文献
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系泊方柱在畸形波与波群伴生波浪作用下运动响应试验研究 总被引：1，自引：1，他引：0
畸形波与波群伴生波浪作用于系泊浮体,和常规随机波浪作用比较,运动响应时频域特征均将发生显著变化。基于物理模型试验,采用小波方法计算伴生波浪和常规随机波浪作用下系泊浮体运动响应的时频域特征变化及波群因子与浮体运动响应时频域特征的定量关系。结果表明:伴生波浪作用下浮体运动响应显著大于常规随机波浪的作用结果,且波群因子G A对浮体运动响应时频域特征有显著影响;伴生波浪作用下浮体纵荡运动的广义能量谱E(t)统计特征值E max(t)、E 1/10(t)、E 1/3(t)、E average(t)均明显大于相同波谱下常规随机波浪的结果,且随着波群因子G A增大显著增大;伴生波浪作用下各运动响应能量集中度δE显著大于常规随机波浪作用结果,且能量集中时域分布范围参数ΔT E以纵荡运动分量最为显著。 相似文献
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The experimental studies of the wave breaking effects on freak wave generation are presented within a finite-depth random wave train in a laboratory wave tank. The main attention is paid to the abnormal index, AI=Hmax/Hs, being used to characterize the freak waves, and the changes of the coefficient due to wave breaking. The results show that the occurence in deep water is larger than that in shallow water. 相似文献
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畸形波传播速度实验和数值模拟研究 总被引：1，自引：1，他引：0
畸形波的传播速度是其最重要的特征参数之一。研究畸形波的传播速度有助于深入和全面了解畸形波的生成机理及其演化过程,另外还可以用于畸形波的预报。针对现有关于畸形波传播速度计算方法(高阶Stokes波理论近似估算,Hilbert变换和两固定点的距离除以畸形波的波峰经过两点所用时间)的不准确性和局限性,使用32个测点描述畸形波波峰沿波浪水槽的运动轨迹,再用回归分析法估算波峰运动轨迹与时间的相关关系,从而计算出畸形波的传播速度。基于288组物理模拟畸形波和364组数值模拟畸形波传播速度的计算结果,使用回归分析方法得出了畸形波传播速度的半经验半理论计算公式,同时还分析了畸形波传播速度的强非线性特征。 相似文献
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An experimental and numerical study of the freak wave speed 总被引：2，自引：2，他引：0
The propagation speed is one of the most important characteristics for describing freak waves. The research of freak wave speed is not only helpful for understanding the generation mechanism and evolution process of freak waves, but also applicable to the prediction. A stable and accurate method is proposed for the calculation of the freak wave speed, in which physical model tests are carried out to measure the motion of the largest wave crest along the wave tank. The linear regression relationship between the spatial position of the largest wave crest and instantaneous moment is established to calculate the speed of totally 248 cases of experimental freak waves and 312 supplementary cases of numerical freak waves. Based on the calculate results, a semitheoretical and semiempirical formula is proposed by using a regression analysis method to predict the speed of the freak wave, and the nonlinear characteristic of the freak wave speed is also investigated. 相似文献
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Numerical simulation and mechanism analysis of freak waves 总被引：1，自引：1，他引：1
A numerical wave model based on the modified fourth-order nonlinear Schroe dinger equation(mNLSE) in deep water was developed to simulate the formation of freak waves and a standard split-step,pseudo-spectral method was used to solve the equation.The validation of the model is firstly verified,then the simulation of freak waves was performed by changing sideband conditions,and the variation of wave energy was also analyzed in the evolution.The results indicate that Benjamin-Feir instability(sideband instability) is an important mechanism for freak wave formation. 相似文献
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A numerical wave model based on the modified four-order nonlinear Schrdinger (NLS) equation in deep water is developed to simulate freak waves. A standard split-step, pseudo-spectral method is used to solve NLS equation. The validation of the model is firstly verified, and then the simulation of freak waves is performed by changing sideband conditions. Results show that freak waves entirely consistent with the definition in the evolution of wave trains are obtained. The possible occurrence mechanism of freak waves is discussed and the relevant characteristics are also analyzed. 相似文献
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A towing experiment was conducted using a modulated wave train to investigate the vertical bending responses of a hydro-structural container ship model. In the experiment, a spatially periodic modulated wave train, as a model of a freak wave in successive high waves mimicking the so-called three sisters, was generated by the recently established higher-order spectral method wave generation (HOSM-WG) method. HOSM-WG enables us to control the location and timing of the maximum crest height in a wave tank. With precise control of the towing carriage, an experiment was conducted in which the timing of the encounters between the ship model and the modulated wave train was accurately determined. The maximum sagging moment (SM) was found to increase in proportion with the encounter wave height. However, because of differences in the relative depth of the fore and aft troughs, the maximum SM is highly variable for a given wave height. The temporal wave-geometry evolution caused the relative trough-depth to vary significantly within a wave period in the vicinity of the maximum crest height. As a result, depending on the encounter timing, the SM varied considerably for a given wave height. The temporal variation of the wave geometry is a robust feature of a modulated wave train and is common between the spatially periodic and temporally periodic modulated wave trains. 相似文献
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本文基于Longuet-Higgins随机波浪模型和JONSWAP谱,进行了大量深水随机波的模拟,获取了畸形波发生概率稳定的随机波列,并对随机波列中的畸形波进行了分析。结果表明,畸形波发生的概率小于基于Rayleigh分布预测结果,且随谱宽的减小而增大。在固定时间段内,畸形波发生的频次服从泊松分布,时间间隔服从指数分布,且随着谱宽的增大,畸形波的发生频次减小,相邻畸形波的发生时间间隔增加。通过小波变换方法分离随机波中的波群,研究了出现畸形波的波群特征,发现一个波群中最多会出现4个畸形波,但是在发生畸形波的波群中,单个畸形波的概率最大。随着谱宽减小,一个波群中包含多个畸形波的概率增加。另外,出现畸形波的波群时间长度服从广义极值分布,随着谱宽减小,畸形波波群的时间跨度增加。 相似文献
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Efficient Focusing Models for Generation of Freak Waves 总被引：2，自引：0，他引：2
Four focusing models for generation of freak waves are presented. An extreme wave focusing model is presented on the basis of the enhanced High-Order Spectral (HOS) method and the importance of the nonlinear wave-wave interaction is evaluated by comparison of the calculated results with experimental and theoretical data. Based on the modification of the Longuet-Higgins model, four wave models for generation of freak waves (a. extreme wave model + random wave model; b. extreme wave model + regular wave model... 相似文献
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The nonlinear wave forces on vertical cylinders induced by freak wave trains were experimentally investigated. A series of freak wave trains with different wave steepness were modeled in a wave flume. The corresponding wave forces on vertical cylinders of different diameters were measured. The experimental wave forces were also compared with the predicted results based on Morison formula. Particular attentions were paid to the effects of wave steepness on the dimensionless peak forces, asymmetry characteristics of the impact forces and high-frequency force components. Wavelet-based analysis methods were employed in revealing the local energy structures and quadratic phase coupling in the freak wave forces. 相似文献
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Dynamic Analysis of Turret-Moored FPSO System in Freak Wave 总被引：1，自引：1，他引：0
Freak wave is the common wave which has significant wave height and irregular wave shape, and it is easy to damage offshore structure extremely. The FPSOs (Floating Production Storage and Offloading) suffer from the environment loads, including the freak wave. The freak waves were generated based on the improved phase modulation model, and the coupling model of FPSO-SPM (Single Point Mooring) was established by considering internal-turret FPSO and its mooring system. The dynamic response characteristics of both FPSO and SPM affected by the freak wave were analyzed in the time domain. According to the results, the freak waves generated by original phase modulation model mainly affect the 2nd-order wave loads. However, the freak waves which are generated by random frequencies phase modulation model affect both 1st-order and 2nd-order wave loads on FPSO. What is more, compared with the irregular waves, the dynamic responses of mooring system are larger in the freak waves, but its amplitude lags behind the peak of the freak wave. 相似文献
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An extremely large (“freak”) wave is a typical though rare phenomenon observed in the sea. Special theories (for example, the modulation instability theory) were developed to explain mechanics and appearance of freak waves as a result of nonlinear wave-wave interactions. In this paper, it is demonstrated that the freak wave appearance can be also explained by superposition of linear modes with the realistic spectrum. The integral probability of trough-to-crest waves is calculated by two methods: the first one is based on the results of the numerical simulation of a wave field evolution performed with one-dimensional and two-dimensional nonlinear models. The second method is based on calculation of the same probability over the ensembles of wave fields constructed as a superposition of linear waves with random phases and the spectrum similar to that used in the nonlinear simulations. It is shown that the integral probabilities for nonlinear and linear cases are of the same order of values 相似文献
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基于二次开发开源计算流体力学(CFD)软件包Open FOAM中的非稳态不可压缩两相流求解器inter Foam建立数值模型,增加了基于方向谱的三维造波边界和吸收边界,成功模拟了三维多向畸形波过程。通过与模型试验波面和目标谱对比,验证了数值模型模拟三维多向畸形波的有效性。另外,分析了网格尺度和柯朗数对模拟结果的影响,并使用连长统计和SIWEH两种方法分析了包含畸形波波列的群性。研究结果表明:在本研究范围内,网格尺度设置0.02 m×0.01 m×0.02 m,最大柯朗数选择0.25,模拟出的三维畸形波效果最好;从能量角度描述畸形波的群性更为合理。 相似文献