The second order spectrum of two-dimensional random waves

On the basis of the second order solution of two-dimensional random gravity waves in finite uniform depth,which is rederived by a perturbation expansion method,the analytical expression of the second order spectrum is strictly deduced, and for infinite depth, the correct form of the kernel function is given for each octant do main.In fact,the present study improves and corrects the generally accepted results obtained by Tick

Efficient Simulation of Freak Waves in Random Oceanic Sea States

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 namerically carried out within the framework of the modified fourorder nonlinear Schroedinger 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 paranleter 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.

Coupling Response of Heave and Moonpool Water Motion of A Truss Spar Platform in Random Waves

This paper presents the heave responses and the moonpool water motions of a truss Spar platform with semi-closed moonpool in random waves. A 2-DOF（degree of freedom） coupling dynamical equations of the platform heave and vertical motions of the moonpool water are derived. The linear wave theory is used to simulate the random waves. The response statistical values and the power spectrums are calculated to analyze the mutual influences between the platform heave and the moonpool water motions for different opening ratios of the moonpool. The effect of coupling parameters on the platform heave and the moonpool water motions are analyzed. The results show that motions of the moonpool water significantly affected the platform heave when the characteristic wave period is far away from the natural period of the platform heave, and different moonpool opening ratios lead to different heave amplitudes of the platform. In the actual design, an optimized moonpool opening ratio can be designed to reduce heave motions of the platform.

Taylor Dispersion of Contaminants by Dual-peak Spectral Random Waves

Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can affect various water quality considerations such as the distribution of suspended sediments in the water column as well as the potential of eutrophication. Comparatively, how the presence of waves influences the horizontal diffusivity/dispersivity has received only scant attention in the literature. Our previous works investigated the role played by the Taylor mechanism due to the wave-induced drift profile which leads to the longitudinal dispersion of contaminants in the horizontal direction, under regular sinusoidal waves and random waves with single-peak spectra. Natural waves in the coastal environment, however, often possess dual-peak spectra, comprising both higher frequency wind waves and lower frequency swells. In this study, the Taylor dispersion of contaminants under random waves with dual-peak spectra is examined through analytical derivation and numerical calculations. The effects of various dual-peak spectral parameters on the horizontal dispersion, including the proportion of lower frequency energy, peak frequency ratio and spectral shape parameter, are investigated. The results show that the relative energy distribution between the dual peaks has the most significant effect. Compared with single-peak spectra with equivalent energy, the Taylor dispersion with dual-peak spectra is stronger when the lower frequency is close to the peak frequency of the single-peak spectrum, and weaker with the higher frequency instead. Thus, it can be concluded that with a dual-peak wave spectrum, wind-dominated seas with higher frequency lead to stronger dispersion in the horizontal direction than swell-dominated seas with lower frequency.

Statistical Distribution of Depth-Integrated Local Horizontal Momentum for Second-Order Random Ocean Waves in Finite Water Depth

Based on the second order random wave solutions of water wave equations in finite water depth, statistical distributions of the depth integrated local horizontal momentum components are derived by use of the characteristic function expansion method. The parameters involved in the distributions can be all determined by the water depth and the wave number spectrum of ocean waves. As an illustrative example, a fully developed wind generated sea is considered and the parameters are calculated for typical wind speeds and water depths by means of the Donelan and Pierson spectrum. The effects of nonlinearity and water depth on the distributions are also investigated.

Wave Pressure Acting on V-Shaped Floating Breakwater in Random Seas

Wave pressure on the wet surface of a V-shaped floating breakwater in random seas is investigated. Considering the diffraction effect, the unit velocity potential caused by the single regular waves around the breakwater is solved using the finite-depth Green function and boundary element method, in which the Green function is solved by integral method. The Response-Amplitude Operator(RAO) of wave pressure is acquired according to the Longuet-Higgins' wave model and the linear Bernoulli equation. Furthermore, the wave pressure's response spectrum is calculated according to the wave spectrum by discretizing the frequency domain. The wave pressure's characteristic value corresponding to certain cumulative probability is determined according to the Rayleigh distribution of wave heights. The numerical results and field test results are compared, which indicates that the wave pressure calculated in random seas agrees with that of field measurements. It is found that the bigger angle between legs will cause the bigger pressure response, while the increase in leg length does not influence the pressure significantly. The pressure at the side of head sea is larger than that of back waves. When the incident wave angle changes from 0? to 90?, the pressure at the side of back waves decreases clearly, while at the side of head sea, the situation is more complicated and there seems no obvious tendency. The concentration of wave energy around low frequency(long wavelength) will induce bigger wave pressure, and more attention should be paid to this situation for the structure safety.

海浪谱法模拟海面场景仿真参数选取准则

为提升海面场景模拟的物理真实感,本文探讨了仿真参数对海洋粗糙面模拟精确性的影响,并建立了海表模拟中仿真参数的选取准则。依据海浪谱和随机过程统计理论,采用自相关函数研究了海面相关长度随风速变化规律。通过建立海浪蒙特卡罗仿真模型,结合随机粗糙面误差分析,提出了不同风速条件下海面场景仿真参数的选取准则。研究表明:将海表模拟的采样间隔限定在顺风向相关长度的0.1~0.5倍,可显著提高海面场景模拟的精确度;而当海面仿真参数超出上述范围时,可能导致海面场景模拟失真,进而影响其视觉真实感。本文所提出的仿真参数选取标准可为开发航海模拟器提供技术支撑。

风浪作用下海上风电结构动力响应数值仿真

为了能够更好利用海洋资源,提高发电效率,提出了风浪作用下海上风电结构动力响应数值仿真方法。建立波动力平衡方程获取海波谱,计算出风场平均波高与周期。利用离散频谱逼近目标随机过程,用互功率频谱密度矩阵求拟脉动风场的风速时程曲线,将平均风速和谐波叠加风速相加,得到单位高度风荷载。按照拟层流风波产生机理,构建波浪谱模型,采用莫里森公式计算结构波浪荷载,考虑风浪间的相关性,将波浪参数代入风浪谱,得到风电结构响应数值。通过仿真得出在不考虑波面高度变动的情况下,波面力在波峰处被低估,在波谷处被高估,波面高度的变化会对风电结构动态响应产生一定影响,得出结果可以为保障电能效益提供参考。

大跨度结构抗震分析方法及近期进展

对反应谱方法、随机振动方法和时间历程法应用于大跨度结构抗震分析时的特点作了分析和对比．研究表明，地震地面运动的空间变化效应（特别是行波效应）对大跨度结构的响应有相当大的影响．反应谱方法对多点激励地震分析显得相当困难，而随机振动方法则有明显的优越性．对于强震作用下的大跨度结构非线性地震响应，时间历程法在现阶段仍应是主要的分析方法．

虚拟海浪海洋环境模拟方法及应用

根据海浪理论及随机海浪的模拟方法和方钟圣所著《西北太平洋波浪统计集》的波浪资料,设计并编制了虚拟海浪海洋环境模拟软件,将《西北太平洋波浪统计集》的80个区块3 600份数据表的所有数据全部录入海洋环境数据库,初步完成了虚拟海浪海洋环境模拟流程和数据库界面的设计,将海浪虚拟化.以结构强度虚拟测试为例,介绍了外载定义过程船舶航行海况的设置方法,得到了海浪谱曲线和海况的波面运动图.研究结果表明:动态海况的显示技术和海洋环境数据库的配合使用,为船舶结构强度和总体性能虚拟测试提供了良好的测试环境.

随机波浪作用下底部层流边界层剪应力谱的研究

本文在随机波浪底部剪应力的研究中引入了波浪谱的概念． 根据浅水波的特点， 将波浪谱作为输入谱，通过传递函数确定作为输出谱的随机波浪作用下的底部剪应力谱． 本研究中研制了一套底部剪应力测量仪． 对于层流边界层得到了底部剪应力谱的理论解，

三维随机海浪的数值模拟

本文首先分析了三维随机海浪的方向谱函数和三维随机海浪的数学模型 ,然后在 MATL AB环境下设计了数值模拟程序 ,并模拟出三维随机海浪的方向谱和三维随机海浪的三维空间模型。

风暴中船舶安全池破损问题

选用实际在航货船船型,运用理论和模型试验相结合的方法确定非线性横摇运动方程各系数,研究了随机波浪和随机风中船舶安全池的破损问题。引入定量分析方法,考虑扰动波谱(例如ITTC谱)对安全池破损的影响以及脉动风速谱的作用,进一步揭示了安全池破损的内在机理及影响因素。本文认为,计算安全池时应选择合适的扰动波谱,风速脉动特性的影响是不能忽略的。

海洋环境水槽液压伺服造波机系统

介绍了大连理工大学海岸和近海工程国家重点实验室海洋环境水槽液压伺服造波机系统的工作原理和组成 ,最后通过测试实验得出该造波机系统的主要技术性能指标。

六自由度舰船运动模拟器随机海浪谱模拟

为了测试随机海浪引起的振动对舰载设备性能和可靠性的影响,提出利用六自由度舰船运动模拟器复现随机海浪谱,对舰载设备进行环境模拟试验。针对六自由度舰船运动模拟器的实际情况,提出双闭环控制方法,利用实时正解代替输出传感器。研究了基于谱均衡和时域随机化的随机海浪谱驱动信号生成技术,并在六自由度舰船运动模拟器上进行试验。试验结果表明,该方法能在六自由度舰船运动模拟器上模拟随机海浪谱,频域复现精度达到±1 dB。

基于海浪谱的沉箱式防波堤动力分析方法

利用海浪谱JONSWAP谱生成随机波浪,并结合改进的波浪力时程模型生成一个连续的、持续时间相对较长的随机波浪力作用过程。假设五十年设计基准期内防波堤每年遭受一次风暴,利用波浪谱随机生成五十次风暴波浪作用过程,对防波堤五十年设计基准期的响应过程进行一次随机模拟,以此作为一个样本。经过对大量随机模拟产生的样本进行统计分析,实现对防波堤整个设计基准期内的安全度进行概率评估。最后,通过算例对该方法的应用进行了演示。

三维随机波浪的数值仿真研究

为快速有效地模拟三维波浪,从海洋学已有的统计观测结果出发,在应用Pierson-Moscowitz随机海浪频谱和SWOP建议的方向函数的基础上,建立了风浪的三维随机波面数学模型,该模型采用多个随机余弦波迭加来模拟的随机波浪曲面,余弦波的随机相位由MATLAB的Rand()函数产生,并分析了分频数和分角数对仿真结果的影响,给出了确定分频数和分角数的原则。最后利用MATLAB实现三维随机波浪仿真和显示。把仿真的最大波高与标准风浪的浪高参考值进行了对比,结果表明,这种方法能快速有效地模拟三维随机波浪。

随机波浪载荷作用下导管架平台动力响应及疲劳可靠性分析

主要针对波浪载荷作用下导管架式海洋平台结构的疲劳可靠性进行研究。采用Airy线性波浪理论,将导管架结构离散成空间梁有限单元结构;在此基础上采用结构模态分析方法,编程计算了平台结构在随机波浪载荷作用下的位移、速度、加速度和应力随机响应及其概率统计量。导管架结构疲劳可靠性分析建立在频域响应的基础上,假设结构响应的应力范围服从Rayleigh分布,利用结构应力传递函数得到结构应力响应谱,然后利用Miner线性累积损伤准则推导出结构疲劳寿命的概率分布函数,并考虑结构疲劳强度影响系数的随机性,求得结构在随机应力谱下给定疲劳寿命时的疲劳可靠性指标。文中所建立方法可用于导管架式平台结构的疲劳安全评估。

香港青马桥抗震分析

对香港青马桥的地震反应分析表明 ,地震地面运动的空间变化效应 (特别是行波效应 )对大跨度结构的响应有着相当大的影响。

基于随机波浪谱对深水区自升式平台动力响应分析

用MSC/PATRAN建立一工作水深为122 m的JU2 000E型自升式平台三维模型。通过对模型进行模态分析,得到平台模态质量和模态刚度矩阵,然后采用波浪谱分析方法,研究平台在随机波浪力作用下的动力响应,以图为平台正常作业和维护提供参考。