共查询到20条相似文献，搜索用时 31 毫秒
1.
This paper investigates a wavefilter which could effectively eliminate re-reflected waves generated in a wave flume over a certain range of wave periods. The wavefilter is not required to change its thickness for different incoming wave periods and is, therefore, termed here a permanent wavefilter. The structure comprises of a set of multilayer porous media. Their related properties such as porosities, friction factors and thickness are sought with the hope of developing a structure which could serve the desired purpose.A theoretical study has been performed. It was found that a multilayer porous media could eliminate re-reflected waves without resorting to adjusting the medium property whenever wave period changes, only if the thickness of the media has to exceed a certain amount.Generally speaking, a thicker multilayer porous media is needed for longer-period waves, while a thinner one is suitable for shorter-period waves. The wavefilter considered here could serve both eliminating re-reflected waves and also providing a desired median wave height if all of those related factors of the media have been properly selected and if the generated waves are restricted to not too wide a range of wave periods. However, it is unlikely that a wavefilter with fixed thickness can remain effective over too wide a range of wave period. 相似文献
2.
Theoretical and experimental studies were conducted to eliminate the re-reflected waves in a wave channel by installing a wavefilter in front of the wavemaker. A thin porous mesh is installed in front of the wavemaker.to serve as a wavefilter. A porous-effect parameter [Chwang, A. T. and Li, W. (1983), A piston-type porous wavemaker theory. J. Engng Math. 17, 301–313], G0 = bω/μL0, is employed to characterize the transmissability of the wavefilter. Theoretical relationships are established between the amplitude of progressive wave and G0, and the distances between the wavefilter, the wavemaker and the test structure. The proper location for the wavefilter to eliminate re-reflected waves can be determined. Several experimental tests were conducted to verify the theory.Both theoretical and experimental studies show that re-reflected waves can be effectively eliminated by placing a wavefilter at a proper position between the wavemaker and the test structure, provided G0 ≤ 1. For G0 > 1 however, the wavefilter would fail. 相似文献
3.
Second-order wavemaker theory for irregular waves 总被引：3，自引：0，他引：3
Hemming A. Schäffer 《Ocean Engineering》1996,23(1):47-88
Through the last decade the theory for second-order irregular wave generation was developed within the framework of Stokes wave theory. This pioneering work, however, is not fully consistent. Furthermore, due to the extensive algebra involved, the derived transfer functions appear in an unnecessarily complicated form. The present paper develops the full second-order wavemaker theory (including superharmonics as well as subharmonics) valid for rotational as well as translatory wave board motion. The primary goal is to obtain the second-order motion of the wave paddle required in order to get a spatially homogeneous wave field correct to second order, i.e. in order to suppress spurious free-wave generation. In addition to the transfer functions developed in the line of references on which the present work is based, some new terms evolve. These are related to the first-order evanescent modes and accordingly they are significant when the wave board motion makes a poor fit to the velocity profile of the desired progressive wave component. This is, for example, the case for the high-frequency part of a primary wave spectrum when using a piston-type wavemaker. The transfer functions are given in a relatively simple form by which the computational effort is reduced substantially. This enhances the practical computation of second-order wavemaker control signals for irregular waves, and no narrow band assumption is needed. The software is conveniently included in a PC-based wave generation system—the DHI Wave Synthesizer. The validity of the theory is demonstrated for a piston type wavemaker in a number of laboratory wave experiments for regular waves, wave groups and irregular waves. 相似文献
4.
A semi-analytical nonlinear wavemaker model is derived to predict the generation and propagation of transient nonlinear waves in a wave flume. The solution is very efficient and is achieved by applying eigenfunction expansions and FFT. The model is applied to study the effect of the wavemaker and its motion on the generation and propagation of nonlinear waves. The results indicate that the linear wavemaker theory may be applied to predict only the generation of waves of low steepness for which the nonlinear terms in the kinematic wavemaker boundary condition and free-surface boundary conditions are of secondary importance. For waves of moderate steepness and steep waves these nonlinear terms have substantial effects on wave profile and wave spectrum just after the wavemaker. A wave spectrum corresponding to a sinusoidally moving wavemaker possesses a multi-peak form with substantial nonlinear components, which disturbs or may even exclude physical modeling in wave flumes. The analysis shows that the widely recognized weakly nonlinear wavemaker theory may only be applied to describe the generation and propagation of waves of low steepness. This is subject to further restrictions in shallow and deep waters because the kinematic wavemaker boundary condition as well as the nonlinear interaction of wave components and the evolution of wave energy spectrum is not properly described by weakly nonlinear wavemaker theory. Laboratory experiments were conducted in a wave flume to verify the nonlinear wavemaker model. The comparisons show a reasonable agreement between predicted and measured free-surface elevation and the corresponding amplitudes of Fourier series. A reasonable agreement between theoretical results and experimental data is observed even for fairly steep waves. 相似文献
5.
H.A. SchäfferC.M. Steenberg 《Ocean Engineering》2003,30(10):1203-1231
The present paper develops the complete second-order wavemaker theory for the generation of multidirectional waves in a semi-infinite basin. The theory includes superharmonics and subharmonics and is valid for a rotational as well as a translatory serpent-type wave-board motion. The primary goal is to obtain the second-order motion of the wave paddles required to get a prescribed multidirectional irregular wave field correct to second order, i.e. to suppress spurious free-wave generation. The wavemaker theory is a 3D extension of the full second-order wavemaker theory for wave flumes by Schäffer (1996). 相似文献
6.
Physical model tests with highly reflective structures often encounter a problem of multiple reflections between the structures and the wavemaker. This paper presents a piston-type active absorbing wavemaker system which can absorb most of the reflections. Based on the first-order wavemaker theory, a frequency domain absorption transfer function is modeled. Its time realization can be achieved by designing an IIR digital filter, which is used to control the absorbing wavemaker system. In a real system, time delays often exist in the wave making process. Thus a delay compensation term to the transfer function is proposed. Experimental results show that the system performs well for both regular and irregular waves with periods from 0.6 s to 2.0 s, and the absorption capability is larger than 96.5% at target wave fields. 相似文献
7.
Approximate Stream Function wavemaker theory for highly non-linear waves in wave flumes 总被引：1，自引：0，他引：1
An approximate Stream Function wavemaker theory for highly non-linear regular waves in flumes is presented. This theory is based on an ad hoc unified wave-generation method that combines linear fully dispersive wavemaker theory and wave generation for non-linear shallow water waves. This is done by applying a dispersion correction to the paddle position obtained for non-linear long waves. The method is validated by a number of wave flume experiments while comparing with results of linear wavemaker theory, second-order wavemaker theory and Cnoidal wavemaker theory within its range of application. 相似文献
8.
This study investigates the initialization of nonlinear free-surface simulations in a numerical wave flume.Due to the mismatch between the linear input wavemaker motion and the kinematics of fully nonlinear waves,direct numerical simulations of progressive waves,generated by a sinusoidally moving wavemaker,are prone to suffering from high-frequency wave instability unless the flow is given sufficient time to adjust.A time ramp is superimposed on the wavemaker motion at the start that allows nonlinear free-surface simulations to be initialized with linear input.The duration of the ramp is adjusted to test its efficiency for short waves and long waves.Numerical results show that the time ramp scheme is effiective to stabilize the wave instability at the start of the simulation in a wave flume. 相似文献
9.
Masahide Tominaga 《Journal of Oceanography》1970,26(4):215-225
The solutions of vertical oscillation of finite amplitude of a fluid parcel in a heterogeneous, incompressible sea water were obtained, solving rigorously the equation of motion, retaining small terms to the third order of the amplitude non-dimensionized by a vertical reference length. The motion is asymmetric with respect to its equilibrium position and the period of motion is longer than that of infinitesimal Väisälä oscillation. When the vertical velocity of the parcel exceeds certain critical value, oscillation of large amplitude sets in near the outskirts of the thermocline, its period being more than twice larger than that of Väisälä oscillation. The apprehension whether this type of the increased vertical motion might be influenced or denied by the horizontal motion in such a case as in internal waves is also discussed. From some observations which will be appeared in Part II, we found oscillations of large amplitude with the period which is in good agreement with the theoretical result. 相似文献
10.
Ivica Vilibi&#x; Vlado Dadi&#x; Hrvoje Mihanovi&#x; 《Estuarine, Coastal and Shelf Science》2004,61(4):623-630
The paper documents the occurrence of long-period internal Kelvin waves in Split Channel in spring 2002. The analyses were performed on thermohaline and current data measured at three moorings and one hydrographic section. The internal oscillation had a period of 5–6 days, being larger just after the generation which was probably excited by the alongshore Sirocco wind. The recorded current amplitude was up to 0.3 m s−1 in the surface layer, while the observed pycnocline displacement was 10–15 m. The oscillation was reproduced by one-dimensional two-layered model of a channel, imposing nodal lines at its entrances. Cross-shore properties of the oscillation, such as observed offshore decrease in pycnocline amplitude, are explained by the dynamics of an internal Kelvin wave propagating along channel boundaries, because the internal Rossby radius is smaller than the width of the channel. Conclusively, the observed oscillation probably represents the fundamental mode of internal waves trapped in the channel complex off Split. 相似文献
11.
A new coupling model of wave interaction with porous medium is established in which the wave field solver is based on the two dimensional Reynolds Averaged Navier-Stokes (RANS) equations with a kε closure. Incident waves, which could be linear waves, cnoidal waves or solitary waves, are produced by a piston-type wave maker in the computational domain and the free surface is traced through the Piecewise Linear Interface Construction-Volume of Fluid (PLIC-VOF) method. Nonlinear Forchheimer equations are adopted to calculate the flow field within the porous media. By introducing a velocity–pressure correction equation, the wave field and the porous flow field are highly and efficiently coupled. The two fields are solved simultaneously and no boundary condition is needed at the interface of the internal porous flow and the external wave. The newly developed numerical model is used to simulate wave interaction with porous seabed and the numerical results agree well with the experimental data. The additional numerical tests are also conducted to study the effects of seabed thickness, porosity and permeability coefficient on wave damping and the pore water pressure responses. 相似文献
12.
Propagation of a solitary wave over rigid porous beds 总被引：1，自引：0，他引：1
The unsteady two-dimensional Navier–Stokes equations and Navier–Stokes type model equations for porous flows were solved numerically to simulate the propagation of a solitary wave over porous beds. The free surface boundary conditions and the interfacial boundary conditions between the water region and the porous bed are in complete form. The incoming waves were generated using a piston type wavemaker set up in the computational domain. Accuracy of the numerical model was verified by comparing the numerical results with the theoretical solutions. The main characteristics of the flow fields in both the water region and the porous bed were discussed by specifying the velocity fields. Behaviors of boundary layer flows in both fluid and porous bed regions were also revealed. Effects of different parameters on the wave height attenuation were studied and discussed. The results of this numerical model indicate that for the investigated incident wave as the ratio of the porous bed depth to the fluid depth exceeds 10, any further increase of the porous bed depth has no effect on wave height attenuation. 相似文献
13.
建立了波浪与大孔隙多孔介质相互作用的耦合数学模型,波浪域的控制方程为雷诺时均方程和k-ε紊流模型。对于计算域的入射波采用推板式造波,它可以是线性波、椭圆余弦波和孤立波。采用PLIC-VOF法追踪波浪自由表面。对于多孔介质内的孔隙流场采用非线性Forchheimer方程,两区域共享连续方程,最后导出的波浪域与孔隙流域的压力修正方程具有完全相同的形式,利用这个方程能够同时而不是分别求解波浪场和孔隙流场,避免了在内部边界上给定匹配条件,实现了波浪场与孔隙流场的同步耦合。波浪与粗颗粒海床、平底床面上抛石潜堤及斜坡上抛石潜堤相互作用的验证计算结果表明该模型可用于研究波浪与大孔隙多孔介质相互作用的问题。 相似文献
14.
A deterministic combination of numerical and physical models for coastal waves is developed. In the combined model, a Boussinesq model MIKE 21 BW is applied for the numerical wave computations. A piston-type 2D or 3D wavemaker and the associated control system with active wave absorption provides the interface between the numerical and physical models. The link between numerical and physical models is given by an ad hoc unified wave generation theory which is devised in the study. This wave generation theory accounts for linear dispersion and shallow water non-linearity. Local wave phenomena (evanescent modes) near the wavemaker are taken into account. With this approach, the data transfer between the two models is thus on a deterministic level with detailed wave information transmitted along the wavemaker. 相似文献
15.
完全非线性孤立波的直墙反射 总被引：2，自引：2，他引：0
报道了应用边界积分方法模拟完全非线性孤立波的传播与直墙反射,给出了波形演变过程。结果表明,本模型对计算孤立波的传播与直墙反射是有效的。三阶Boussinesq方程的孤立波解比低阶方程的孤立波解更接近完全非线性的数值解.当来波波高增大时,孤立波直墙反射的相位滞后变小。若考虑大波高孤立波的直墙反射或波——波相互作用,一阶理论预报的相位滞后往往低估实际情况。 相似文献
16.
Nonlinear hydrodynamics of a twin rectangular hull under heave oscillation is analyzed using numerical methods. Two-dimensional nonlinear time-domain solutions to both inviscid and viscous problems are obtained and the results are compared with linear, inviscid frequency-domain results obtained in [26] to quantify nonlinear and viscous effects. Finite-difference methods based on boundary-fitted coordinates are used for solving the governing equations in the time domain [2]. A primitive-variables based projection method [6] is used for the viscous analysis and a mixed Eulerian–Lagrangian formulation [11] for inviscid analysis. The algorithms are validated and the order of accuracy determined by comparing the results obtained from the present algorithm with the experimental results of Vugt [22] for a heaving rectangle in the free surface. The present study on the twin-hull hydrodynamics shows that at large and non-resonant regular frequencies, and small amplitude of body oscillation, the fluid viscosity does not significantly affect the wave motion and the radiation forces. At low frequencies however the viscosity effect is found to be significant even for small amplitude of body oscillation. In particular, the hydrodynamic force obtained from the nonlinear viscous analysis is found to be closer to the linear inviscid force than the nonlinear inviscid force to the linear inviscid force, the reason for which is attributed to the wave dampening effect of viscosity. Since the wave lengths generated at smaller frequencies of oscillation are longer and therefore the waves could have a more significant effect on the dynamic pressure on the bottom of the hulls which contribute to the heave force, the correlation between the heave force and the wave elevation is found to be larger at smaller frequencies. Because of nonlinearity, the wave radiation and wave damping force remained nonzero even at and around the resonant frequencies – with the resonant frequencies as determined in [26] using linear potential flow theory. As to be expected, the nonlinear effect on the wave force is found to be significant at all frequencies for large amplitude of oscillation compared to the hull draft. The effect of viscosity on the force, by flow separation, is also found to be significant for large amplitude of body oscillation. 相似文献
17.
Toshiyuki Hibiya 《Journal of Oceanography》2004,60(3):637-643
The generation process of internal waves by strong tidal flow over a continental shelf slope is reproduced using a multi-level
numerical model. On the basis of the numerical results, the crucial role of the tidal advection effect in the generation process
of internal waves is demonstrated. The close relation between the resulting internal waveform and the strength of the tidal
advection effect is also examined. The barotropic forcing on the internal wave actually works within a relatively small horizontal
scale over the top of the continental shelf slope. When the maximum internal Froude number at the shelf break (Frm) is less than about 0.6, the amplitude of the resulting internal wave is almost proportional to Frm. When Frm is more than about 0.6, however, the amplitude of the resulting internal wave becomes larger than predicted by linear theory.
In particular, when Frm is more than unity, the time period during which the shoreward propagating internal wave stays in the barotropic forcing
region becomes much longer. Consequently, the internal wave is significantly amplified with the horizontal scale approaching
that of the barotropic forcing, which concentrates in a relatively small region over the top of the continental shelf slope.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
潮汐作用下渤海温跃层波动与起伏的数值研究 总被引：1，自引：0，他引：1
研究了潮汐(四大分潮 M2,S2,K1,O1同时输入)作用下渤海温跃层起伏与波动的三维数值模型(将海洋分为3层,即上混和层、跃层和下混和层),揭示了整个海区温跃层上界面处跃层起伏(在文中指每个时刻跃层波高的周期平均值)的地理分布及叠加在起伏之上的潮周期波动的时空变化,模拟出跃层波动与实测基本一致.结果发现大振幅的跃层波动均发生在海峡及近海地形突变之处.一般界面波动的波高大于甚至远远大于同一位置的表层潮波.从位相以及周期来看,潮波和跃层上下界面波动相互之间,有些海域一致,有些地方则相差甚远.跃层上界深度及厚度的梯度,对跃层起伏分布有一定的影响.跃层起伏还可能与海岸海底摩擦有关. 相似文献
19.
This study consisted in the characterization of internal waves in the south of the Strait of Messina (Italy). The observational data consisted in thermistor string profiles from the Coastal Ocean Acoustic Changes at High frequencies (COACH06) sea trial.An empirical orthogonal function analysis is applied to the data. The first two spatial empirical modes represent over 99% of the variability, and their corresponding time-dependent expansion coefficients take higher absolute values during internal wave events. In order to check how the expansion coefficients vary during an internal wave event, their time derivative, called here changing rates, are computed. It shows that each wave of an internal wave train is characterized by a double oscillation of the changing rates. At the front of the wave, both changing rates increase in absolute value with opposite sign, and then decrease to become null at the maximum amplitude of the wave. At the rear of the wave, the changing rates describe another period, again with opposite sign. This double oscillation can be used as a detector of internal waves, but it can also give information on the width of the wave, by measuring the length of the oscillation, as this information may sometimes be hard to read straight out of the data. When plotting the changing rates one versus another, the resulting scatter diagram puts on a butterfly shape that illustrates well this behaviour. 相似文献
20.
Zuo Qihua Yang Zhengji .
Senior Engieer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1996,(3)
- The variation of the amplitude of waves with varying incident angles when waves propagate through a typical approach channel is discussed by a numerical calculation method, the result of which shows that the influence of the channel on wave propagation is obvious. When the wave propagation direction is in coincidence with the channel axis, the wave amplitude ratio will decrease with the increase of propagation distance. When the incident angle is 15 - 30 , there appears an area of larger wave amplitude ratio on the side slope facing the waves, but at the another side, the wave amplitude ratio is generally small, indicating that the channel has a shielding effect. When waves propagate across the channel perpendicularly, the wave amplitude ratio can be calculated with the shallow water coefficient. 相似文献