Active Absorption Wave Maker System for Irregular Waves

The key problem in physical model tests with highly reflective structures is to prevent the multiple reflections between the reflective structures and the wave maker. An active absorption wave maker system is described and the representative frequency method for irregular waves is proposed in this paper. Physical model tests are conducted to verify the effectiveness of the proposed method.

Numerical Wave Channel with Absorbing Wave-Maker

The numerical wave channel has been developed based on the volume of fluid method (VOF) in conjunction with the Navier-Stokes equations. The absorbing wave-maker boundary on the left side of the channel is presented by prescribing velocity reference to linear wave-maker theory. The principle of which is that the numerical wave-maker is designed to move in a way that generates the required incident wave and cancels out any reflected wave that reach it at the same time. On the right side of the channel, the open boundary is set to permit incident waves to be transmitted freely. The parametric studies have been carried out at a range of ratios of water depth to wave length d/ L from 0.124 to 0.219, with wave height in the front of paddle/water depth ratio (H0 / d) from 0.1 to 0.3. Wave height, wave pressure distribution along the channel and velocity field are obtained for both open boundary condition and reflective boundary condition at the other end of the channel. For a reflective case, it is shown that the absorbing wave-maker is very effective in canceling out the reflected wave that reaches the numerical paddle and highly repeatable waves can be generated.

An Irregular Wave Maker of Active Absorption with VOF Method

A numerical irregular wave flume with active absorption of re-reflected waves is simulated by use of volume of fluid （VOF） method. An active ＇absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume. The progressive waves and the absorbing waves are generated simultaneously at the active wave generating-absorbing boundary. The absorbing waves are generated to eliminate the waves coming back to the generating boundary due to reflection from the outflow boundary and the structures. SIRW method proposed by Frigaard and Brorsen （1995） is used to separate the incident waves and reflected waves. The digital filters are designed based on the surface elevation signals of the two wave gauges. The corrected velocity of the wave-maker paddle is the output from the digital filter in real time. The numerical results of regular and irregular waves by the active absorbing-generating boundary are compared with the numerical results by the ordinary generating boundary to verify the performance of the active absorbing-generator boundary. The differences between the initial incident waves and the estimated incident waves are analyzed.

A Numerical Investigation of Gap and Shape Effects on a 2D Plunger-Type Wave Maker

The installation of plunger-type wave makers in experimental tanks will generally include a gap between the back of the wedge and the wall of the tank.In this study,we analyze the influence of this gap on the wave making performance of the plunger using two-dimensional(2 D)CFD calculations for a range of nearly linear wave conditions and compare the results with both experimental measurements and linear potential flow theory.Three wedge-shaped profiles,all with the same submerged volume,are considered.Moreover,the generated waves are compared with the predictions of linear potential flow theory.The calculations are made using the commercial ANSYS FLUENT finite-volume code with dynamic meshes to solve the Navier-Stokes equations and the volume of fluid scheme to capture the air-water interface.Furthermore,the linear potential flow solution of Wu(J Hydraul Res 26:481-493,1988)is extended to consider an arbitrary profile and serve as a reference solution.The amplitude ratios of the generated waves predicted by the CFD calculations compare well with the predictions of linear potential flow theory for a simple wedge,indicating that viscous effects do not influence this ratio for small-amplitude motions in 2 D.By contrast,significant higher harmonic components are produced by larger amplitude motions.Also,the simple wedge is found to produce the smallest spurious higher harmonic content in the far-field wave.

Simple Push-Type Wave Generating Method Using Digital Rotary Valve Control

The important parameters to describe waves are their amplitude and length.In order to make it easier to improve wave amplitude and facilitate wave experiment,a simple push-type wave generating method using digital rotary valve control was proposed and different wave amplitudes were generated by the new method.After the mathematical model of the new method had been established,numerical analysis based on the linear wave theory was carried out by means of Matlab/Simulink software tools,and experiments were conducted on the push-type wave maker to ascertain the validity of the established model and the numerical simulation results.It shows that both experimental and theoretical results agree relatively well,and the plate motion frequency and amplitude of the push-type wave maker can be continuously adjusted and the various required regular waves can be obtained.Although the wave amplitude and length descends with the increasing of working frequency,the wave amplitude can be improved conveniently by setting the axial opening width of the valve and the oil supply pressure of system.The wave length remains unchanged with the axial opening width and the oil supply pressure change.The research indicates that different regular waves can be easily generated by the new method and the wave amplitude can be further improved in a certain plate motion frequency range.

Physical Simulation of Multidirectional Irregular Wave Groups

Real waves are multidirectional waves. In the present study, the calculation method for the wave maker driving signals for generating multidirectional wave groups in physical wave basin is proposed. Its validity is first confirmed by a numerical model for which the incident boundary condition is determined by use of the proposed method. Then, the physical simulation of multidirectional wave groups is performed in laboratory wave basin. The experimental results show that multidirectional waves with expected wave groupiness, which includes not only its group height but also its group length, can be satisfactorily zenerated at the soecified oosition in the tphvsical wave basin.

Numerical Simulation of Seaplane Wave Ground Effect with Crosswind

Under the absolute coordinate system, the unsteady Reynolds averaged Navier-Stokes(URANS)equations and the k-ω SST turbulence model are solved using the finite volume method to simulate the aerodynamic characteristics of large seaplane flying with the ground-effect above wavy surface. The velocity inlet wave-making method and the volume of fluid model are used to accurately simulate the linear regular waves and to precisely capture the free surface. This paper studies the influence of the sideslip angle on the aerodynamic characteristics of large seaplane when it is cruising above wavy water. The results show that the wave surface mainly affects the pressure distribution on the lower surface of the wing. When the sideslip angle varies from 0° to 8°,the varying of frequency of aerodynamic forces is consistent with the wave encounter frequency,and both periods are 0.6 s. With the increase of the sideslip angle,the lift coefficient and the pitching moment coefficient decrease. However,when the sideslip angle is smaller than 4°,the decrease amplitude is small,and the significant decrease occurs above 4° and during the whole process of the change of sideslip angle,the aerodynamic fluctuation amplitude is almost unchanged. As the drag coefficient increases with the increase of sideslip angle,significant increase also occurs when the value is greater than4°,and the fluctuation amplitude does not show any correlations. The rolling moment coefficient and yaw moment coefficient increase with the increase of the sideslip angle,and the fluctuation amplitudes of both increase linearly with the increase of the sideslip angle.

Efficient computation method for two-dimensional nonlinear waves

The theory and simulation of fully-nonlinear waves in a truncated two-dimensional wave tank in time domain are presented. A piston-type wave-maker is used to generate gravity waves into the tank field in finite water depth. A damping zone is added in front of the wave-maker which makes it become one kind of absorbing wave-maker and ensures the prescribed Neumann condition. The efficiency of numerical tank is further enhanced by installation of a sponge layer beach (SLB) in front of downtank to absorb longer weak waves that leak through the entire wave train front. Assume potential flow, the space- periodic irrotational surface waves can be represented by mixed Euler-lagrange particles Solving the integral equation at each time step for new normal velocities, the instantaneous free surface is integrated following time history by use of fourth-order Runge- Kutta method. The double node technique is used to deal with geometric discontinuity at the wave- body intersections. Several precise smoothing methods have been introduced to treat surface point with high curvature. No saw-tooth like instability is observed during the total simulation. The advantage of proposed wave tank has been verified by comparing with linear theoretical solution and other nonlinear results, excellent agreement in the whole range of frequencies of interest has been obtained.

Experimental Study of Wave Energy Spectrum in Shallow Water

Wave energy spectrum in shallow water can be studied in wind wave channel in combination with irregular wave- maker. Fetch length is successfully extended and by 'Relay' method the corresponding spectrum pattern and the wind velocity scale are obtained.

Numerical Simulation of Water Entry of Wedges in Waves Using A CIPBased Model

In this study,the water entry of wedges in regular waves is numerically investigated by a two-dimensional in-house numerical code.The numerical model based on the viscous Navier−Stokes(N−S)equations employs a high-order different method—the constrained interpolation profile(CIP)method to discretize the convection term.A Volume of Fluid(VOF)-type method,the tangent of hyperbola for interface capturing/slope weighting(THINC/SW)is employed to capture the free surface/interface,and an immersed boundary method is adopted to treat the motion of wedges.The momentum source function derived from the Boussinesq equation is applied as an internal wavemaker to generate regular waves.The accuracy of the numerical model is validated in comparison with experimental results in the literature.The results of water entry in waves are provided in terms of the impact force of wedge,velocity and pressure distributions of fluid.Considerable attention is paid to the effects of wave parameters and the position of wedge impacting the water surface.It is found that the existence of waves significantly influences the velocity and pressure field of fluid and impact force on the wedges.

Numerical Simulation of Water Wave Propagation and Transformation

A numerical approach was performed to predict the propagation and transformation of nonlinear water waves. A numerical wave flume was developed based on the non-periodic high-order spectral (HOS) method. The flume was applied to analyze the effect of wave steepness and wavelength on the propagation of nonlinear waves. The results show that for waves of low steepness, the wave profile and the wave energy spectrum are stable, and that the propagation can be predicted by the linear wave theory. For waves of moderate steepness and steep waves, the effects associated with the interactions between waves in a wave group become significant and a train of initially sinusoidal waves may drastically change its form within a short distance from its original position.

A New Generator for Tsunami Wave Generation

A middle size experiental wave generator has been implemented is the Ujikawa Open Laboratory, Disaster Prevention Research Institute, Kyoto University. The generator is composed of a pistontype wave maker, a head strage water tank and a current generator to mainly reproduce long waves like tsunami and storm surge. The paper desribes several experimental series to predict the applicability of the generator to model tests. The three operating sysemes are capable to be controlled in one operating sysytem and start time is contorolled separately according with the target tsunami and storm surge profiles. A sharp tsunami profile is reproduced in adjusting the start timing of piston type wave maker and opening gates of head storage tunk. Any type of tsunami waves are reproduced in the generator and it becomes a storong tool to predict the effective of＂resiliency＂ of hardwares.

Coupling model for waves propagating over a porous seabed

The wave-seabed interaction issue is of great importance for the design of foundation around marine infrastructures. Most previous investigations for such a problem have been limited to uncoupled or one- way coupled methods connecting two separated wave and seabed sub models with the continuity of pressures at the seabed surface. In this study, a strongly coupled model was proposed to realize both wave and seabed processes in a same program and to calculate the wave fields and seabed response simultaneously. The information between wave fields and seabed fields were strongly shared and thus results in a more profound investigation of the mechanism of the wave-seabed interaction. In this letter, the wave and seabed models were validated with previous experimental tests. Then, a set of application of present model were discussed in prediction of the wave-induced seabed response. Numerical results show the wave-induced liquefaction area of coupled model is smaller than that of uncoupled model.

某大型港池造波机控制系统智能化改造研究

某大型港池多向不规则造波机系统投入使用已有10余年,由于该造波机控制系统软硬件技术落后,存在计算速度慢、故障率高和传输速度慢等问题,无法满足目前波浪物理模型试验复杂波谱及长历时无重复不规则波试验的需求。为了更加精细、准确地实现高品质波浪谱模拟,故对该控制系统进行智能化改造,构建了基于EtherCAT总线的多向不规则造波机控制结构。

摇板式造波机生成的长峰规则波

利用特征函数展开法对摇板式造波机作周期运动生成的长峰规则波流场作了二阶分析 ,得到了速度势和波形二阶解的解析表达式。通过对二阶波传播模式的分析 ,确定造波机响应特性曲线 (一阶波幅摇幅比 )和规则波最大波高曲线 ,给出能在水池中生成二阶意义上纯正的Stokes波的造波机运动形式。上述有关造波特性的理论分析是研制造波软件 ,确保在水池中生成高品质Stokes波的基础 ,具有重要的应用价值。

摇板式造波实验台的设计及实验

分析了摇板造波理论,基于体积不变原则,即在一定条件下摇板排开水的体积等于波浪的体积,推导得到新的摇板造波传递函数。为了验证该传递函数,设计了摇板式造波实验台的机械结构和运动控制系统,并在试验水池中进行安装调试。实验表明,该造波实验台具有良好的频响特性。同时通过试验对比发现:基于体积不变原理的造波传递函数相对于基于势流理论的造波传递函数具有一定的局限性。只有在中频段造波时推导的造波传递函数更加符合实际传递函数;在低频段和高频段时,因为水流逸散以及波浪的非线性,推导的造波传递函数不能很好起作用。

无反射不规则波造波机系统的研究

水槽不规则波的波浪试验中,造波机和建筑物之间波浪的多次反射是影响试验精度的重要方面,本文给出了水槽中不规则波造波机无反射造波的方法,提出了不规则波代表频率的确定方法,长时间造波试验研究结果表明,该文提出的方法是有效的。

用OpenFOAM实现数值水池造波和消波

基于OpenFOAM求解器interDyMFoam,开发实现数值水池造波(包括推板和摇板造波)和阻尼消波。所编写的造波边界条件,可依据实验造波理论将各种造波模式植入其中,从而实现各种波的数值造波。首先进行了线性波的数值造波实验,通过结合阻尼消波段的应用,造波水池可提供稳定的线性波。还进行了瞬时极限波和有限振幅的数值造波实验,与实验数据或同类数值结果吻合很好,进一步验证了的数值造波和消波方式的可靠性。

层化流体中半板造波的内波解

为了形象地说明内波的传播模式,研究给出了内波水槽中由半板造波所形成的内波解。结合V频率N（z）＝const和简化Holmboe两种密度剖面模式讨论了内波场的传播图案。在内波水槽中成功地形成了上述两种密度剖面,相应的实验印证了本文分析的正确性。

水槽造波机的参数确定及结构设计

实验室是用水槽造波机来模拟海浪的,为确保造波机的性能与造波效果,有必要对造波机的主要设计参数进行计算。针对现今国内外主流的交流伺服式造波机,介绍了以推板式为造波型式和以交流伺服电机为驱动方式的水槽造波机的简单工作原理及各组成部件;利用势函数理论,根据拟定要实现的造波能力,计算出水槽造波机的主要设计参数,即推波板的最大行程、最大运动速度、单元最大负载力及最大负载功率等;结合这4个主要设计参数,设计出造波机的整机结构并确定机械运动结构和伺服驱动结构的具体规格与型号。