The application of wavelet transform to wave breaking

Wavelet transform is a particularly useful tool to characterize transient phenomena such as wave breaking. In this paper, we apply wavelet transform to the detection and quantification of the breaking waves. We use a new method that uses the local properties of wavelet transform to detect and quantify the breaking waves and give some new breaking criteria. By comparing this method with the classic method, we find that wavelet transform is very effective in the detection of breaking waves. With wavelet transform, a set of measured wind wave data is investigated. The results have revealed some previously unknown phenomena about wave breaking. The project supported by the National Natural Science Foundation of China (49476254, 49606070) & the National High Technology Research and Development Program of China (863 Program)     

破碎带波浪的数值模拟

基于一组色散关系得到改进的完全非线性Boussinesq方程建立了一个波浪模型可以模拟近岸水域的波浪变浅、破碎以及在海滩上的爬高等多种变形。波浪破碎引起的能量衰减是在动量方程中引入一个在空间和时间上都只作用于波前的涡粘项来模拟。动海岸线边界用窄缝法处理。波浪爬高用非线性浅水方程推导的非破碎波浪在斜坡上爬高的解析解来验证。本模型还模拟了波浪在斜坡上不同类型的破碎变形过程,并将其波高和平均水位的沿程变化和物理模型实验的结果比较,两者符合良好。     

Numerical analysis of breaking waves using the moving particle semi-implicit method

The numerical method used in this study is the moving particle semi-implicit (MPS) method, which is based on particles and their interactions. The particle number density is implicitly required to be constant to satisfy incompressibility. A semi-implicit algorithm is used for two-dimensional incompressible non-viscous flow analysis. The particles whose particle number densities are below a set point are considered as on the free surface. Grids are not necessary in any calculation steps. It is estimated that most of computation time is used in generation of the list of neighboring particles in a large problem. An algorithm to enhance the computation speed is proposed. The MPS method is applied to numerical simulation of breaking waves on slopes. Two types of breaking waves, plunging and spilling breakers, are observed in the calculation results. The breaker types are classified by using the minimum angular momentum at the wave front. The surf similarity parameter which separates the types agrees well with references. Breaking waves are also calculated with a passively moving float which is modelled by particles. Artificial friction due to the disturbed motion of particles causes errors in the flow velocity distribution which is shown in comparison with the theoretical solution of a cnoidal wave. © 1998 John Wiley & Sons, Ltd.     

A domain decomposition approach to compute wave breaking (wave‐breaking flows)

A heterogeneous domain decomposition approach is followed to simulate the unsteady wavy flow generated by a body moving beneath a free surface. Attention being focused on complex free surface configurations, including wave‐breaking phenomena, a two‐fluid viscous flow model is used in the free surface region to capture the air–water interface (via a level‐set technique), while a potential flow approximation is adopted to describe the flow far from the interface. Two coupling strategies are investigated, differing in the transmission conditions. Both the adopted approaches make use of the inviscid velocity field as boundary condition in the Navier–Stokes solution. For validation purposes, two different two‐dimensional non‐breaking flows are simulated. Domain decomposition results are compared with both fully viscous and fully inviscid results, obtained by solving the corresponding equations in the whole fluid domain, and with available experimental data. Finally, the unsteady evolution of a steep breaking wave is followed and some of the physical phenomena, experimentally observed, are reproduced. Copyright © 2003 John Wiley & Sons, Ltd.     

Existence and breaking property of real loop-solutions of two nonlinear wave equations

Dynamical analysis has revealed that, for some nonlinear wave equations, loop- and inverted loop-soliton solutions are actually visual artifacts. The so-called loopsoliton solution consists of three solutions, and is not a real solution. This paper answers the question as to whether or not nonlinear wave equations exist for which a ＂real＂ loopsolution exists, and if so, what are the precise parametric representations of these loop traveling wave solutions.     

Transformation of a breaking wave at a drop of a channel bottom

This paper gives results of an experimental study of incident and reflected waves of the bore type in the neighborhood of a sharp change in the channel bed level. It is shown that under conditions typical of accidents at ship locks, the wave height can reach 8 m.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 2, pp. 115–121, March–April, 2005.     

VIBRATING-UPLIFT ROCKING MOTION OF CAISSON BREAKWATERS UNDER VARIOUS BREAKING WAVE IMPACT FORCES

IntroductionCaissonbreakwatersarewidelyusedincoastalengineeringandhavetheadvantagesthatcanbeusedindeepwateranddevelopedtomulti_functiontypes.However,thewavesareeasilybrokenandmayproduceextremelyhighimpactforceonacaissonbreakwater.Inrecentdecades,therehavebeenmanyfailureexamplesofbreakwatersunderbreakingwaveimpactintheworld[1- 3].Thedurationofbreakingwaveimpactisveryshortandtheresponsesofcaissonbreakwatershaveobviouslydynamicbehaviorsunderbreakingwaveimpact,butthestaticmethodisstillusedinthedes…     

A numerical model for run‐up of breaking waves

In the present paper, the numerical method for the three‐dimensional run‐up, given in Johnsgard and Pedersen [‘A numerical model for three‐dimensional run‐up’, Int. J. Numer. Methods Fluids, 24 , 913–931 (1997)], is extended to include wave breaking. In the fundamental problem of run‐up of a uniform bore, the present model is compared with analytical solutions from the literature. The numerical solutions converge, but very slowly. This is not due to the numerical model, but rather to the structure of the solutions themselves. Numerical results for two realistic but simplified tsunami cases are also presented. In the first case, two‐dimensional simulations are performed concerning the run‐up of a tsunami in Portugal, in the second case, the three dimensional wave pattern generated after a slide in Tafjord, Norway in 1931, is studied. A discussion of different aspects of the model is summarized at the end of the paper. Copyright © 1999 John Wiley & Sons, Ltd.     

A numerical model for aerated‐water wave breaking

This work presents a numerical model designed for the simulation of water‐wave impacts on a structure when aeration of the liquid phase is considered. The model is based on a multifluid Navier–Stokes approach in which all fluids are assumed compressible. The numerical method is based on a finite volume algorithm in space and a second order Runge–Kutta method in time. A validation of this model is performed. It shows a good accuracy for acoustic and shock wave propagation in a bubbly liquid and for wave breaking. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of free‐stream turbulence on large‐scale coherent structures of separated boundary layer transition

It has been well established that large‐scale structures, usually called coherent structures, exist in many transitional and turbulent flows. The topology and range of scales of those large‐scale structures vary from flow to flow such as counter‐rotating vortices in wake flows, streaks and hairpin vortices in turbulent boundary layer. There has been relatively little study of large‐scale structures in separated and reattached transitional flows. Large‐eddy simulation (LES) is employed in the current study to investigate a separated boundary layer transition under 2% free‐stream turbulence on a flat plate with a blunt leading edge. The Reynolds number based on the inlet free stream velocity and the plate thickness is 6500. A dynamic subgrid‐scale model is employed to compute the subgrid‐scale stresses more accurately in the current transitional flow case. Flow visualization has shown that the Kelvin–Helmholtz rolls, which have been so clearly visible under no free‐stream turbulence (NFST) are not as apparent in the present study. The Lambda‐shaped vortical structures which can be clearly seen in the NFST case can hardly be identified in the free‐stream turbulence (FST) case. Generally speaking, the effects of free‐stream turbulence have led to an early breakdown of the boundary layer, and hence increased the randomization in the vortical structures, degraded the spanwise coherence of those large‐scale structures. Copyright © 2005 John Wiley & Sons, Ltd.     

Incompressible SPH simulation of wave breaking and overtopping with turbulence modelling

In this paper a truly incompressible version of the smoothed particle hydrodynamics (SPH) method is presented to investigate the surface wave overtopping. SPH is a pure Lagrangian approach which can handle large deformations of the free surface with high accuracy. The governing equations are solved based on the SPH particle interaction models and the incompressible algorithm of pressure projection is implemented by enforcing the constant particle density. The two‐equation k–ε model is an effective way of dealing with the turbulence and vortices during wave breaking and overtopping and it is coupled with the incompressible SPH numerical scheme. The SPH model is employed to reproduce the experiment and computations of wave overtopping of a sloping sea wall. The computations are validated against the experimental and numerical data found in the literatures and good agreement is observed. Besides, the convergence behaviour of the numerical scheme and the effects of particle spacing refinement and turbulence modelling on the simulation results are also investigated in further detail. The sensitivity of the computed wave breaking and overtopping on these issues is discussed and clarified. Copyright © 2005 John Wiley & Sons, Ltd.     

Numerical schemes for low Mach wave breaking

In this work, we describe a finite volume scheme for the computation of incompressible air–water flows. We use an artificial compressibility approach that permits us to use a completely explicit scheme. We describe successively the low Mach preconditioning of the scheme, the Riemann solver and then the non-conservative approach that is used to suppress velocity-pressure oscillations, the second order extensions and the parallel implementation. Then this is applied to the simulation of the breaking of a wave on a 15% slope.     

On the relative impact of subgrid‐scale modelling and conjugate heat transfer in LES of hot jets in cross‐flow over cold plates

This work describes numerical simulations of a hot jet in cross‐flow with applications to anti‐ice systems of aircraft engine nacelles. Numerical results are compared with experimental measurements obtained at ONERA to evaluate the performances of LES in this industrial context. The combination of complex geometries requiring unstructured meshes and high Reynolds number does not allow the resolution of boundary layers so that wall models must be employed. In this framework, the relative influence of subgrid‐scale modelling and conjugate heat transfer in LESs of aerothermal flows is evaluated. After a general overview of the transverse jet simulation results, a LES coupled with a heat transfer solver in the walls is used to show that thermal boundary conditions at the wall have more influence on the results than subgrid scale models. Coupling fluid flow and heat transfer in solids simulations is the only method to specify their respective thermal boundary conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Discrete filters for large eddy simulation

This paper summarizes several results relative to discrete filters for subgrid‐scale (SGS) models based on a multi‐level filtering procedure. First, a theoretical study of discrete filters in physical space is performed. The analysis is done in the uniform one‐dimensional case, and is then extended to the general multi‐dimensional case for arbitrary structured and unstructured meshes. Some equivalence classes for the discrete filters are defined, based either on a differential approximation or the associated transfer function. Methods for the definition of discrete filters are proposed in the general case, including the approximation of continuous convolution filters. Second, the sensitivity of several SGS models with respect to the test filter is investigated. The selected models are: the dynamic Smagorinsky model, the mixed scale model (MSM), the selective MSM and the Liu–Meneveau–Katz (LMK) similarity model. Improved versions, which explicitly account for the spectral width of the test filter of the MSM and the LMK similarity model are proposed. The analysis, which reveals a significant influence of the test filter, is done through a priori testing on a 128³ field issued from the large eddy simulation (LES) of freely decaying homogeneous isotropic turbulence. Copyright © 1999 John Wiley & Sons, Ltd.     

Study on the Influence of Waves on Coastal Diffusion Using Image Analysis

A series of novel image analysis techniques have been used to study surf-zone hydrodynamics taking advantage of recent advances in digital processing of images taken from video recordings of the sea surface near the coast. The use of image analysis allows the estimation of both spatial and temporal characteristics of wave fields, surface circulation and mixing in the surf zone. The dispersion of blobs of dye released at different distances from the coastline under very different sea conditions is used to measure surface eddy diffusivities. A preliminary set of field measurements were done in the Ebro Delta where the methodology was tested. Further experiments have been performed at Vilanova, Spain and Recife, Brazil.There is an increase of diffusivity with wave height but only if the wave Reynolds number, Rw, is greater than 10³. No such trend is observed for Rw greater than 10⁶. The other important factors are wind speed and tidal and longshore currents.     

波浪破碎的一种混合湍流模拟模式

近岸波浪的变形与破碎,一方面影响水体标识码运输,另一方面对消波护岸具有指导意义.本文提出一种三维混合湍流模拟模式方法,将求解区域分为造波区、波浪传播区和消波区. 造波区采用层流模式,通过基于 Fluent 的二次开发的 UDF 方法在边界进行速度造波.这种方法在给定入口速度的条件标识码据已知波高进行 精准插值,从而控制水的体积分数. 在波浪传播区域,采用大涡标识码行模拟研究,在消波区,采用 RANS 模型并利用多孔介质消波法进行消波. 模标识码 VOF 方法捕捉波浪破碎过程中的自由面变化.本文对波高为 5.5cm 的规则波 (M1)、波高为 13.5cm 的 规则波 (M3)、有效标识码 7.75cm 的 TMA 谱单向不规则波 (U1) 和有效波高为 19cm 的 TMA 谱多向不规则波 (B5) 展开标识码研究,并与前人的相关标识码果作比较,各条件下模拟结果与实验结果吻合.模拟结果说明本文提出的模型能够准确模拟出波浪传播过程中的折射和标识码象,并且能够捕捉的波浪破碎过程中的自由面变化,为三维波浪的传播与破碎的数值模拟提供一种模拟方法.      

Dynamic symmetry breaking and structure-preserving analysis on the longitudinal wave in an elastic rod with a variable cross-section

The longitudinal wave propagating in an elastic rod with a variable cross-section owns wide engineering background, in which the longitudinal wave dissipation determines some important performances of the slender structure. To reproduce the longitudinal wave dissipation effects on an elastic rod with a variable cross-section, a structure-preserving approach is developed based on the dynamic symmetry breaking theory. For the dynamic model controlling the longitudinal wave propagating in the elast...     

轻型火箭发射噪声场的分布特性

为了解小火箭发射噪声特性及其在喷口外围的声压场分布规律,针对燃气射流产生噪声问题进行了实验研究和数值计算。讨论了超声速射流噪声的3个主要成分(湍流混合噪声、啸音和宽带激波相关噪声)及相关特点,指出它们产生的根本原因是湍流射流的速度扰动。通过分析不同实验测点的射流噪声声压级峰值,得到了燃气射流噪声在轴向和径向上的分布规律,即随着离喷口距离的增大,轴向噪声的衰减程度大于径向。在实验基础上,利用大涡模拟与FW-H(Ffowcs Williams-Hawkings)声学比拟相结合的方法对燃气射流噪声的声学特性进行计算。结果表明,此方法获得的计算结果与实验结果吻合较好,可为进一步研究射流噪声控制提供参考。