随机波群的模拟

本文首先对平稳随机过程包络的特性进行理论分析,在此基础上提出一种以给定波面位移谱和波面包络谱两者为靶谱的波群模拟方法。与Funke和Mansard(1980)提出的以波群群因子为靶的波群模拟方法(可能是迄今唯一的方法)相比,本法不仅在概念上比较合理,而且在手续上要简便得多,并能兼顾波群高度和长度两方面特征的模拟。大量模拟实例表明,在一定条件限制下,本方法模拟的结果比较令人满意。     

非线性随机波的数值模拟

本文根据作者提出的非线性不规则波四阶近似理论解,首先导出二阶非线性谱和线性谱的关系式,并应用非线性有约束最优化方法建立了从靶谱分解线性谱和二阶非线性谱的数学模式,进而建立非线性随机波数值模拟的数学模型及其快速傅里叶交换算式,从而大大地缩短计算机时。由于采用从靶谱分解出的线性谱,模拟的非线性随机波现实谱和靶谱符合一致。最后通过算例,对模拟的非线性及线性随机波的谱估计及波面统计特性进行初步分析,本方法为浅水不规则波与水流及建筑物相互作用的研究提供随机模拟基础。     

不规则波与开孔沉箱相互作用数值模拟

采用三步有限元法对N-S方程进行离散,同时借助CLEAR-VOF方法追踪流体自由表面,利用主动吸收式造波等手段改进了二维不规则波浪数值水槽,使得水槽中的波浪谱与目标靶谱吻合较好。进而建立了不规则波浪与开孔沉箱作用一种新的数值模式,分析研究不规则波作用下开孔沉箱的反射率,并与现有的物模结果和数模结果进行了对比,为不规则波与开孔沉箱作用问题的研究,探求了一种新的数值手段。     

海浪单过程的数值模拟

本文以离散付里叶变换手段数值模拟海浪过程,对海浪单过程的模拟提出三种具体模式,并介绍了模拟的实现方法。以我国1966年提出的海浪谱为靶谱,在DJS—6电子计算机上实现,给出了模拟波面及谱曲线,比较靶谱及模拟谱表明,以m=400个子波叠加进行模拟时,模式及实现方法是满意的。     

海浪单过程的数值模拟

本文以离散付里叶变换手段数值模拟海浪过程。对海浪单过程的模拟提出三种具体模式，并介绍了模拟的实现方法。以我国1966年提出的海浪谱为靶谱，在DTS-6电子计算机上实现，给出了模拟波面及谱曲线。比较靶谱及模拟谱表明，以m=400个子波叠加进行模拟时，模式及实现方法是满意的。     

调频式不规则波造波系统

本文叙述了利用现有各类规则波造波机产生不规则波的简易方法。不规则的波模拟是通过模拟波谱来实现的。文中叙述了模拟波谱的基本原理。作为不规则电压信号的输入装置,先后采用了四种系统:即1、单机头发报机与继电器组系统;2、微处理机作为控制系统;3、单板计算机系统;4、磁带记录器系统。文中对模拟所得的不规则波作了谱分析及统计分析,并与靶谱作了比较。最后还对各系统的经济效益作了讨论。     

运动坐标系下的海浪数值模拟

以运动坐标系中的海浪谱为靶谱应用静止坐标系中随机波面的模拟方法─—线性叠加法和线性过滤法模拟匀速运动坐标系中的随机波面,给出了两种方法的原理及模拟手续。通过模拟实验发现,在高速运动的坐标系中线性叠加法优于线性过滤法,在低速情形,线性过滤法好于线性叠加法,并在模拟技术上给出了各参数的选取方法。     

内孤立波数值模拟方法研究

本文选用RNGk-ε湍流模型封闭二维不可压缩N-S方程组,选用KdV、mKdV理论作为输入条件进行内孤立波造波模拟。运用流体模拟软件Fluent建立二维内波数值水槽,用动网格手段实现网格变形模拟物理边界造波法,用VOF方法进行密度分层流体的内界面追踪,对不同非线性强度的二相流内孤立波进行了数值模拟。并将数值模拟结果与KdV、mKdV理论波形以及内波试验水槽所造内孤立波进行对比,验证了此套造波方法在Fluent中进行内孤立波模拟的可行性。     

基于光滑质点流体动力学方法数值波浪水槽研究

基于光滑质点流体动力学(smoothed particle hydrodynamics,简称SPH)方法建立二维数值波浪水槽,利用推波板造波生成孤立波和不规则波,模拟结果跟实验值及解析解做了对比分析,结果令人满意.SPH数值水槽中生成的波浪具有明显的非线性,波浪能量沿程有所衰减,与物理水槽结果吻合良好.     

运动坐标系下海浪数值模拟

以运动坐标系中的海浪谱为靶谱应用静止坐标系中随机波面的模拟方法－－线性叠架法和线性过滤法模拟均速运动坐标系听随机波面,给出了两种方法的原理及模拟手续。通过模拟实验发现,在高速运动的坐标系中线性叠架法优于线生过滤法,在低速情形,线性过滤法好于线性叠加法,并在模拟技术上给出了各参数的选取方法。     

An Irregular Wave Generating Approach Based on naoe-FOAM-SJTU Solver

In this paper, a wave generating approach for long-crest irregular waves in a numerical tank by our in-house solver naoe-FOAM-SJTU is presented. The naoe-FOAM-SJTU solver is developed using an open source tool kit, OpenFOAM. Reynolds-averaged Navier?Stokes (RANS) equations are chosen as governing equations and the volume of fluid (VOF) is employed to capture the two phases interface. Incoming wave group is generated by imposing the boundary conditions of the tank inlet. A spectrum based correction procedure is developed to make the measured spectrum approaching to the target spectrum. This procedure can automatically adjust the wave generation signal based on the measured wave elevation by wave height probe in numerical wave tank. After 3 to 4 iterations, the measured spectrum agrees well with the target one. In order to validate this method, several wave spectra are chosen and validated in the numerical wave tank, with comparison between the final measured and target spectra. In order to investigate a practical situation, a modified Wigley hull is placed in the wave tank with incoming irregular waves. The wave-induced heave and pitch motions are treated by Fourier analysis to obtain motion responses, showing good agreements with the measurements.     

Effects of Wave Breaking on Freak Wave Generation in Random Wave Train

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 ...     

An irregular wave generating approach based on naoe-FOAM-SJTU solver

In this paper, a wave generating approach for long-crest irregular waves in a numerical tank by our in-house solver naoe-FOAM-SJTU is presented. The naoe-FOAM-SJTU solver is developed using an open source tool kit, OpenFOAM. Reynolds-averaged Navier-Stokes (RANS) equations are chosen as governing equations and the volume of fluid (VOF) is employed to capture the two phases interface. Incoming wave group is generated by imposing the boundary conditions of the tank inlet. A spectrum based correction procedure is developed to make the measured spectrum approaching to the target spectrum. This procedure can automatically adjust the wave generation signal based on the measured wave elevation by wave height probe in numerical wave tank. After 3 to 4 iterations, the measured spectrum agrees well with the target one. In order to validate this method, several wave spectra are chosen and validated in the numerical wave tank, with comparison between the final measured and target spectra. In order to investigate a practical situation, a modified Wigley hull is placed in the wave tank with incoming irregular waves. The wave-induced heave and pitch motions are treated by Fourier analysis to obtain motion responses, showing good agreements with the measurements.     

Effects of Wave Breaking on Freak Wave Generation in Ramdom Wave Train

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.     

Wave propagation in a fully nonlinear numerical wave tank: A desingularized method

The problem of wave propagation in a fully nonlinear numerical wave tank is studied using desingularized boundary integral equation method coupled with mixed Eulerian–Lagrangian formulation. The present method is employed to solve the potential flow boundary value problem at each time step. The fourth-order predictor–corrector Adams–Bashforth–Moulton scheme is used for the time-stepping integration of the free surface boundary conditions. A damping layer near the end-wall of wave tank is added to absorb the outgoing waves with as little wave reflection back into the wave tank as possible. The saw-tooth instability is overcome via a five-point Chebyshev smoothing scheme. The model is applied to several wave propagations including solitary, irregular and random incident waves.     

Determining the Onset and Strength of Unforced Wave Breaking in A Numerical Wave Tank

A numerical wave tank is used to investigate the onset and strength of unforced wave breaking, and the waves have three types of initial spectra: constant amplitude spectrum, constant steepness spectrum and Pierson-Moscowitz spectrum. Numerical tests are performed to validate the model results. Then, the onset of wave breaking is discussed with geometric, kinematic, and dynamic breaking criteria. The strength of wave breaking, which is always characterized by the fractional energy loss and breaking strength coefficient, is studied for different spectra. The results show how the energy growth rate is better than the initial wave steepness on estimating the fractional energy losses as well as breaking strength coefficient.     

风浪槽内风浪外频谱谱形的一些特征

利用实验室风浪槽内测得的波面序列资料估计风浪外频谱。通过与实测风浪内频谱的比较,研究实测风浪外频谱的谱形特征,探讨海浪外频谱与内频谱的相似性问题。此外,还检验一种理论海浪外频谱。     

Efficient Generation of Freak Waves in Laboratory

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.     

Numerical Wave Tank Based on A Conserved Wave-Absorbing Method

Recently the numerical wave tank has become a widely-used tool to study waves as well as wave-structure interactions, and the wave-absorbing method is very important as its effect on the quality of waves generated. The relaxation method and the derived momentum source method are often utilized, however, the damping weight is constant during calculation and repeated trials are required to obtain an acceptable wave-absorbing effect. To address the above- mentioned issues, a conserved wave-absorbing method is developed. The damping weight is determined by solving the mass conservation equation of the absorbing region at every time step. Based on this method, a two-dimensional numerical wave tank is established by using the VB language to simulate various waves by which the validation of this method is evaluated.