波群对垂直桩柱的作用力

在波浪槽中进行了具有不同群因子和连长的随机波群对三种直径的桩柱作用力的实验研究,指出波浪峰力的比值不随波群的连长变化,而随波群因子的增加而增大。由于桩柱是一非线性系统,作用力的群团子大于波浪的群因子,其连长小于波浪的连长。波浪峰力的比值不仅随KC数的增加而增大,还随波群因子GF的增加而增大。     

多向不规则波作用下九桩群桩效应试验研究

小尺度群桩应用广泛,一直是学者研究的重点,小尺度有别于大尺度桩柱,由于桩柱周围存在漩涡的脱落,使得受力特性复杂。以往的研究过程中,波浪主要采用单向不规则波浪,并且试验模型多以两桩或三桩组成的群桩结构为主,桩数相对较少。多向不规则波与群桩结构的作用特点有别于单向不规则波且研究较少。通过物理模型试验,针对多向不规则波对于9桩桩排群桩结构的作用进行了研究。首先综合考虑KC1/3数和相对桩径的影响,提出以参数KCLD 1/3数来衡量群桩的效应,并分析了正向力与横向力随着参数KCLD 1/3数和相对桩距的变化关系,研究了群桩中不同桩位桩柱波浪力的变化规律和方向分布宽度对于群桩波浪力的影响。研究结果表明,群桩中各桩的正向力随着方向分布标准差的增大而减小,而横向力在相对桩距较大时随着方向分布标准差的增大而增大,同时群桩中不同位置桩上的波浪力具有较大的差异。     

不规则波作用于群桩的水动力系数

海洋平台等海工建筑物多由群桩支承,平台上的小直径立管和钻杆等也常成群布置,它们主要受海浪(不规则波)的作用.目前有两类计算群桩上波浪力的方法:一是把作用于单桩上的波力乘以相应的群桩系数K_g,K_g能直观地显示群桩效应的大小及其变化规律,此法为苏联和我国ii规范所采用.过去的研究成果多限于振荡流和规则波情况.     

圆柱墩群上的波浪力

本文根据Maccamy-Fuchs关于单个圆柱墩的微幅波绕射理论,在严格考虑不同墩间相位差的基础上,研究了双圆柱墩情况下的波浪绕射场,得出了柱面上各点的波压力,作用在单位高度高柱上的波浪力,柱群中各柱的波浪力及整个墩群上的总波浪力的计算公式。对于等径的双圆柱墩群,编制了VORTRAN程序WFFTP,可供设计之用。     

桩群上的最大总波浪力

桩群上的总波浪力基于线性化的Morison方程,作用在桩群上(图1)的总波浪力F(t)及总波力矩M(t)为:.     

计算孤立小桩柱上随机波浪力的一个线性的Morison公式

本文在线性波理论下，从计算孤立小桩柱上随机波浪力的Ｍｏｒｉｓｏｎ公式出发，通过对波浪力的概率密度的推导和分析，提出了一个新的线性化的Ｍｏｒｉｓｏｎ公式，该公式与已在工程上广泛使用的Ｂｏｒｇｍａｎ１９６７年提出的线性化的Ｍｏｒｉｓｏｎ公式在对照力的线性化上略有不同，由这个公式计算的小桩柱上的阻力是按Ｂｏｒｇｍａｎ线性化的Ｍｏｒｉｓｏｎ公式进行计算所得结果的１．０８倍，但按这个新的线性化的Ｍｏｒｉｓｏ     

不规则波作用于垂直桩柱上的正向力

通过试验,研究了规则波,特别是不规则波作用于孤立桩柱上的正向力,通过测定桩上的总波浪力并利用时域最小二乘法和互谱分析法,研究了Morison公式中的系数C_D、C_M与KC数和雷诺数的关系及其随频率的变化,给出了规则波和不规则波作用下的C_D、C_M与KC数的关系曲线,此外,从波、力之间的相干数角度,对传递函数法计算不规则波浪力的适用范围也作了分析。     

破碎波冲击直立桩柱的大比尺试验研究

波浪破碎是海洋中最常见的现象之一,其能够对海洋中的结构物产生巨大的波浪力作用。本文在大比尺波浪水槽通过聚焦波的方法生成了极端波浪和不同破碎阶段的破碎波浪,并对其冲击桩柱过程中的点压力进行了测量,进而采用连续小波变换的方法,对桩柱上点压力的分布及大小进行了细致分析。结果表明,多次重复试验下,相比非破碎极端波浪,破碎极端波浪产生的点压力离散性更强;波浪破碎程度越大,测点位置越靠近波峰,则点压力离散程度越大;破碎波的最大点压力出现在1.2倍的最大波面附近,且其大小可达3倍的最大静水压力;基于点压力小波谱,不同破碎阶段破碎波产生冲击作用不同,对于波浪作用桩柱前波浪已经发生破碎的情况,其冲击区域更大,点压力分布更复杂;而对于桩面破碎的情况,其造成的波浪总力更大。     

多向不规则波浪作用下群墩结构上爬高的计算研究

波浪的方向分布对波浪的传播及其与工程结构物的作用都具有明显影响，目前现有的研究大多是基于单向波浪进行的。为了研究方向分布对群墩结构上的爬高影响，基于规则波浪与群墩作用的理论解，结合多向不规则波浪的造波方法，建立了多向不规则波浪与群墩作用的计算模型，同时进行了物理模型试验对模型的有效性进行了验证。系统地对群墩周围及表面上的波浪爬高进行了计算分析，结果表明，方向分布对波浪爬高具有较大的影响，且不同位置处的影响并不相同，在实际的工程设计中如果按照单向波浪计算，可能低估或者高估群墩周围的爬高。     

波浪对透空外双壁筒柱的绕射

应用透空壁内流体速度与两壁间压力差成正比的线性模型，建立了外壁透空的双筒圆柱对波浪绕射的解析解。通过数值计算研究了外壁透空率的大小、内外柱半径之比等因素对桩柱上总波浪作用力和波面高度的影响。数值结果表明圆柱外壁透空系数的增加，将明显地降低圆柱周围的波浪高度和圆柱上的波浪力；内外柱径之比的大小对波浪力和波高的最大值无太大影响，而对波浪力剧烈衰减区的位置和波高的振荡周期有决定作用。     

Probabilistic model for wave forces acting on a cylinder in random waves

Generally, the sea-state (random waves) is best described by a wave spectrum. A number of statistical models for wave spectra has been well established and a sea-state can be specified. Once the specified sea-state is established, the corresponding model for wave forces acting on a single cylinder or a group of cylinders can be formulated. Since peak force is of more practical value, a multivariate or joint probability density function for wave forces has been developed for the peak force distribution of wave forces. This theoretical force model derives the tri-variate probability density function P(F, F′, F″), where F is the peak force defined by Morison equation. This model is of wide-band in nature and is tested by wave flume experiments.     

Experimental study of interactions between multi-directional focused wave and vertical circular cylinder,part II: Wave force

We describe experiments with multi-directional focused waves interacted with a vertical circular cylinder in a 3D wave basin. The focus of this study is on the run-up of multi-directional focused waves, wave forces, and wave pressures on the cylinder. Part I, the study on wave run-up, has already been presented by Li et al. (2012). In this paper, the analysis of the wave force on the vertical cylinder is presented.In this experiment, a cylinder with 0.25 m in diameter was adopted and different wave parameters, such as focused wave amplitude, peak frequency, frequency bandwidth and directional spreading index, are considered. The model scale k_pa (k_p is the wave number corresponding to peak frequency, a is the radium of the cylinder) varies from 0.32 to 0.65. The maximum forces of multi-directional focused wave on cylinder were measured and investigated. The results showed that the wave parameters have a significant influence on the wave force, and that the spatial profile of the surface of multi-directional focused wave can also affect its force on the cylinder, which is different from two-dimensional wave. In addition, the ‘secondary loading cycle’ phenomenon was also observed and discussed. In our experiments, the ‘secondary loading cycles’ occur when kA > 0.36 for all cases. While in some referred small scale experiments, the secondary load cycles are observed even for kA = 0.2, when the waves are longer enough. To larger model scale, the pronounced secondary load cycle occurs with larger wave steepness waves.     

Measurements of higher harmonic wave forces on a vertical truncated circular cylinder

Wave forces on a vertical truncated circular cylinder in Stokes waves with the wave slopes ranging from 0.06 to 0.24, are measured in a wave tank. The higher harmonic wave forces are compared with the available values from theories of the FNV (Faltisen–Newman–Vinje) model and Varyani solution. The first harmonic horizontal forces measured are much larger than the theoretical values from the FNV model, while the first harmonic vertical forces are well predicted by the Varyani theory. It was also found that the FNV model significantly overpredicts the second harmonic horizontal forces in high frequency waves, but under predicts the third harmonic forces. The differences between the actual measurement and the theory, in the second and third harmonic horizontal forces, become smaller at low wave frequencies as the wave slope increases. In addition, the transverse instabilities in the incoming waves with high wave slope were observed, which is due to the nonlinear modulation. Measurements were, thus, carried out before the instability occurred.     

不同间距大直径圆筒防波堤波压力试验研究

通过开展物理模型试验,进行不规则波作用下不同间距大直径圆筒防波堤的波峰压力分布规律研究,分析了圆筒相对间距、相对水深、波陡等主要影响因素对圆筒波压力的影响规律,并通过波压力试验值与各家理论公式计算值的比较,进行不同间距圆筒波压力的计算方法研究。基于直立墙结构和大尺度孤立墩柱结构波压力公式给出修正系数以及横向衰减函数的拟合公式,用以计算圆筒周身不同位置处的波压力,从而为工程设计和理论研究提供参考。     

The Nonlinear Wave Force on a Circular Cylinder in Shallow Water

Based on the 1st order cnoidal wave theory, the nonlinear wave diffraction around a circular cylinder in shallow water is studied in this paper. The equation of the wave surface around the cylinder is formulated and by using this formula the wave surface elevation on the cylinder surface can be obtained. In this paper, the formula for calculating the cnoidal wave force on a circular cylinder is also derived. For the wave conditions which are often encountered in practical engineering designs, the ratios of the nonlinear wave forces to the linear wave forces are calculated, and the results are plotted in this paper for design purposes. In order to verify the theoretical results, model tests are conducted. After comparing the test results with the theoretical ones, it is concluded that, in shallow water, for the case of T g / d~(1/2) > 8-10 and H / d > 0.3, the cnoidal wave theory should be used to calculate the wave action on a cylindrical pier.     

Nonlinear effect on inertia component of wave forces on a cylinder

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A Finite Element Solution of Wave Forces on Submerged Horizontal Circular Cylinders

In this paper, a numerical model is established for estimating the wave forces on a submerged horizontal circular cylinder. For predicting the wave motion, a set of two-dimensional Navier-Stokes equations is solved numerically with a finite element method. In order to track the moving non-linear wave surface boundary, the Navier-Stokes equations are discretized in a moving mesh system. After each computational time step, the mesh is modified according to the changed wave surface boundary. In order to stabilize the numerical procedure, a three-step finite element method is applied in the time integration. The water sloshing in a tank and wave propagation over a submerged bar are simulated for the first time to validate the present model. The computational results agree well with the analytical solution and the experimental data.Finally, the model is applied to the simulation of interaction between waves and a submerged horizontal circular cylinder.The effects of the KC number and the cylinder depth on the wave forces are studied.