共查询到20条相似文献，搜索用时 31 毫秒
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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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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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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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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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An efficient focusing model for generation of freak waves 总被引：1，自引：1，他引：0
Based on the Longuet-Higgins wave model theory, the previews studies have shown that freak waves can be generated in finite space and time successfully. However, as to generating high nonlinear freak waves, the simulation results will be unrealistic. Therefore, a modified phase modulation method for simulating high nonlinear freak waves was developed. The surface elevations of some wave components at certain time and place are positive by modulating the corresponding random initial phases, then the total surface elevation at the focused point is enhanced and furthermore a freak wave event is generated. The new method can not only make the freak wave occur at certain time and place, but also make the simulated wave surface time series satisfy statistical properties of the realistic sea state and keep identical with the target wave spectrum. This numerical approach is of good precision and high efficiency by the comparisons of the simulated freak waves and the recorded freak waves. 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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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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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
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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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基于物理模型试验,考虑畸形波参数、相对板宽、相对波高等影响因素,就畸形波对平顶双层水平板防波堤作用进行研究。首先对畸形波作用下双层水平板的波浪力分布特征进行了讨论,然后就最大波动压强、结构最大总垂向力与不规则波作用进行了对比分析。结果表明,畸形波作用下,双层水平板最大波动压力出现在前端迎浪区域附近,向尾端逐渐递减。双层水平板4个受力面的压力分布不同且有相位差,4个受力面的最大波动压力时间差约在0.1Tp~0.4Tp范围内变化。与不规则波作用比较,畸形波作用没有显著改变波压包络分布特征,但增大了波压包络强度值。试验范围内,就最大总力而言,两者最大总浮托力比值在1.06~2.45间变化;向下的最大总垂向力比值在1.22~2.07之间变化;就波动压力而言,其增大的幅度与畸形波参数α1相关性最强,随α1的增大而增大,在α1=2.04~3.1试验范围内,畸形波作用时的最大压强比不规则波作用时可约增大20%~80%。就最大波吸力而言,两者的比值与畸形波参数α4相关性最强,随α4的增大而减小。在α4=0.62~0.75试验范围内,最大波吸力强度的比值在1.61~0.87范围内变化。当α4≤0.72时,畸形波作用时的最大波吸力大于不规则波作用时的最大波吸力;当α4 > 0.72时则刚好相反。 相似文献
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A higher-order non-hydrostatic model in a σ-coordinate system is developed. The model uses an implicit finite difference scheme on a staggered grid to simultaneously solve the unsteady Navier-Stokes equations (NSE) with the free-surface boundary conditions. An integral method is applied to resolve the top-layer non-hydrostatic pressure, allowing for accurately resolving free-surface wave propagation. In contrast to the previous work, a higher-order spatial discretization is utilized to approximate the large horizontal pressure gradient due to steep surface waves or rapidly varying topographies. An efficient direct solver is developed to solve the resulting block hepta-diagonal matrix system. Accuracy of the new model is validated by linear and nonlinear standing waves and progressive waves. The model is then used to examine freak (extreme) waves. Features of downshifting focusing location and wave asymmetry characteristics are predicted on the temporal and spatial domains of a freak wave. 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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The Edgeworth’s form of a cumulative expansion of the probability density function (PDF) of surface elevation expands the maximum wave height distribution to predict the occurrence probability of freak waves. This study investigated the enhancement of the occurrence probability of freak waves due to the fourth order moment of surface elevation, kurtosis, change and found that the nonlinear effects on the occurrence probability of a freak wave linearly depends on kurtosis for a small number of waves N=250. The statistical theory was compared with field data, and freak waves sometimes appear when not expected by the Rayleigh theory, but they were predicted by the proposed theory. 相似文献
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在试验水池中,开展了波浪在岛礁地形上演化问题的研究。首先在实验水池中建立了西太平洋某岛礁地形的模型,然后采用改进的JONSWAP谱,由造波机产生不同周期、波高的随机波浪。试验中观察到了不同类型畸形波生成的过程及不同波面形态的畸形波。对偏度、峰度及水深与畸形波要素Hm/Hs（Hm表示波列中的最大波高, Hs为有效波高）的关系进行了详细的分析,同时,对畸形波波高Hfr与偏度的关也进行了分析。通过对试验结果分析,发现峰度与畸形波要素i>Hm/Hs呈正相关, Hfr增大时相应的偏度也会呈现增大的趋势。此外,水深的变化剧烈时（如斜坡、海山位置）有助于畸形波的发生。 相似文献