Type Wave Maker Research Articles

The hydrodynamic study of the interaction between waves and objects in permeable reef environment

This study employed a self-developed viscous numerical wave tank based on the piston type wave maker and user-defined functions of Fluent software to explore the wave shadowing effect of the transmission of waves near the underwater object and the reef. In the study, various factors such as the permeability of the reef, changes in topography, and objects motion were considered, and detailed simulation analyses were conducted for five scenarios: a solitary reef, a fixed underwater object, a forced moving underwater object, and a free moving underwater object. The results showed that this method can effectively simulate the complex flow field changes around the underwater object and the reef under different conditions, while also fully considering the strong nonlinearity and fluid viscosity effects between the wave surface and the object. Furthermore, it was found that between the free-moving object and the reef, there would be significant swirls and streamline distortion. This indicates that a portion of the incident wave energy is transformed into kinetic energy of swirls, resulting in a smoother and more uniform flow field and reducing wave forces.

CFD based modeling of OWC device positioned over stepped bottom

This research deals with various parameters associated with the hydrodynamics of an OWC device positioned over the stepped bottom. The problem is solved using the multiphase based CFD technique in “ANSYS Fluent software”. A “piston type wavemaker” and dynamic meshing technique are employed to produce the incident wave inside the numerical wave tank (NWT). Further, “volume of fluid” procedure is implemented to produce the free surface in the NWT. The “free surface elevation” is analyzed in various instant of time. Contour plots of the dynamic pressure, turbulent kinetic energy and turbulent intensity associated with the fluid motion are provided. Further, the variation of the vertex average total pressure and vertex average y− velocity at the orifice on the OWC device’s top wall are analyzed with respect to flowtime.

A high-order finite difference method with immersed-boundary treatment for fully-nonlinear wave–structure interaction

In order to predict nonlinear wave loading on marine structures, a fully nonlinear higher-order finite difference based potential flow solver with all boundary conditions treated by an immersed boundary method has been developed in this paper. The solver adopts high-order finite difference schemes for the spatial derivatives and a 4th order Runge–Kutta method for time stepping. Test cases of forced oscillation of a cylinder in an infinite fluid domain are first studied, which reveal the advantage of the acceleration potential method in terms of wave load computation. Then a wave generation problem using a piston type wave maker is tested. Special attention is paid to the intersection point between the free surface and the body surface, and a scheme which best meets the accuracy and stability requirements is suggested from several proposals. A novel hyperviscosity filter, which works for both uniform and non-uniform grids, is introduced to stabilize the time-domain solution of the wave maker problem. Finally, a forced heaving cylinder on the free surface is considered, and the nonlinear wave loads on the cylinder are analyzed and compared to benchmark results.

다기능 조파기의 조파 운동과 발생 파형

Piston type wave makers or flap type wave makers are usually adopted as a wave maker which disturbing the fluid domain with sinusoidal motion. Recently hybrid wave maker which could be operated as not only piston type and/or flap type but also swing type wave maker have been devised by utilizing the link mechanism. The wave board of hybrid wave maker has been devised to be independently controlled by the horizontal actuators on upper and lower end of the wave board. The wave board could operate as a flap type wave board when the lower hinge is in a stationary condition and the upper hinge is operated with sinusoidal motion. On the contrary, the swing type wave board could be obtained by the lower hinge is activated and the upper hinge is in a stationary condition. When both end of the wave board is activated in a synchronized condition, the wave board motion become piston motion. In addition the hybrid wave maker could enhance the piston motion with flap motion or swing motion by selecting control parameters. Various wave board motion of hybrid wave maker and relevant wave form have measured on the wave board and departed location. It is appeared that the novel hybrid wave maker could be utilized for the improvement of wave qualities in experiments.

Modeling of solitary wave interaction with emerged porous breakwater using PLIC-VOF method

Rubble mound breakwaters are porous structures providing a calm basin for ship berthing, loading, and offloading in ports. In this paper, a numerical model was developed to study solitary wave-porous breakwaters interaction using the VOF method. The flow was assumed to be incompressible and viscous; therefore, Navier-Stokes and continuity equations were extended as the governing equations. In the study domain, waves were generated and propagated via a piston type wave maker in the left lateral boundary, while in the right end side, an open boundary was implemented. The model was validated by comparing its results with existing data for wave interaction with porous media. A parametric study was then conducted on wave-porous breakwater interaction. Effects of the important parameters such as porosity, drag and inertia coefficients of the medium and submergence and emergence of the breakwater on the wave damping and reflection were evaluated. The results demonstrate that the developed model is a powerful tool for this complicated wave structure interaction modeling.

Design optimization of a novel vertical augmentation channel housing a cross-flow turbine and performance evaluation as a wave energy converter

A novel vertical augmentation channel housing a direct-drive cross-flow turbine, with nozzles on both the sides of the turbine, was designed and an optimized configuration was obtained. The geometries of the guide nozzle and the front nozzle were optimized under steady flow conditions. The performance of the cross-flow turbine was analyzed using commercial computational fluid dynamics (CFD) code ANSYS-CFX. The optimized design was then evaluated as a wave energy converter both experimentally and computationally. The waves in the numerical wave tank (NWT) were generated using a piston type wave-maker. The optimized design gave a maximum output power of 13.2 W and an efficiency of 48.31% at a wave height of 0.2 m and wave period of 2.75 s for a rotational speed of 35 rpm. The difference between numerical and experimental efficiencies was within 3.5%. In addition to this, particle image velocimetry was used to study the flow characteristics in the augmentation channel and the turbine. The results show that the CFD code captures the flow in the augmentation channel and around the turbine accurately. The optimized design, which occupies less space than other wave energy converters, can be used to efficiently harness energy from the waves.

CFD Modeling of Regular and Irregular Waves Generated by Flap Type Wave Maker

The improvement of wave generation in numerical tanks represents the key factor in ocean engineering development to save time and effort in research concerned with wave energy conversion. For this purpose, this paper introduces a numerical simulation method to generate both regular and irregular waves using Flap-Type wave maker. A 2D numerical wave tank model is constructed with a numerical beach technique, the independence of the numerical beach slope is tested to reduce the wave reflections. The different governing parameters of the Flap type wave maker were studied such as periodic time dependency and length of the flap stroke. The linear wave generated was validated against the wave maker theory WMT, the numerical results agreed with WMT. The Pierson-Moskowitz model is used to generate irregular waves with different frequencies and amplitudes. The numerical model succeeded to generate irregular waves which was validated against published experimental data and with Pierson-Moskowitz spectrum model using Fourier expansion theory in the frequency domain. Useful results are presented in this paper based on the numerical simulation to understand the characteristics of the waves. This paper produces a full guide to generate both regular and irregular waves numerically using ANSYS-CFX approach to solve the 2D Unsteady Reynolds Averaged Navier-Stokes Equation (URANS).

Turbulence characteristics of oscillating flow through passive grid

The present work provides the turbulence characteristics of oscillating flow through passive grid under rigid boundary influence by adopting an experimental approach. The oscillations in the steady unidirectional flow were generated by plunger type wave-maker. This study attempts to analyse the turbulent length scales and local Reynolds numbers in order to characterise the different eddy sizes in the oscillating flow environment due to the interaction of grid and rigid boundary. The normalized phase averaged Shannon entropy is also presented to understand the degree of the randomness in oscillating flow environment through the passive grid. Further, to understand the deviation from the isotropic turbulence, the turbulence triangle, Eigen values, and the invariant functions are presented at the downstream of the grid for the three oscillating flow cases.

Piston-Driven Numerical Wave Tank Based on WENO Solver of Well-Balanced Shallow Water Equations

A numerical wave tank equipped with a piston type wave-maker is presented for long-duration simulations of long waves in shallow water. Both wave maker and tank are modelled using the nonlinear shallow water equations, with motions of the numerical piston paddle accomplished via a linear mapping technique. Three approaches are used to increase computational efficiency and accuracy. First, the model satisfies the exact conservation property (C-property), a stepping stone towards properly balancing each term in the governing equation. Second, a high-order weighted essentially non-oscillatory (WENO) method is used to reduce accumulation of truncation error. Third, a cut-off algorithm is implemented to handle contaminated digits arising from round-off error. If not treated, such errors could prevent a numerical scheme from satisfying the exact C-property in long-duration simulations. Extensive numerical tests are performed to examine the well-balanced property, high order accuracy, and shock-capturing ability of the present scheme. Correct implementation of the wave paddle generator is verified by comparing numerical predictions against analytical solutions of sinusoidal, solitary, and cnoidal waves. In all cases, the model gives satisfactory results for small-amplitude, low frequency waves. Error analysis is used to investigate model limitations and derive a user criterion for long wave generation by the model.

Wave generation characteristic analysis of piston and flap type wave maker with rotary-valve-control vibrator

Wave maker is one of the most important experimental equipment in marine engineering. To meet the demands of simulation of higher wave amplitude and compare the effect of piston and flap type wave generation, a new wave generation device was proposed and a new piston and flap type wave maker with a rotary-valve-control vibrator was developed. A mathematical model of the new wave maker was established and analysed by Simulink, and a series of experiments were conducted on the wave maker to analyze wave generation characteristics. The results show that the wave maker can adjust the distance of wave paddle and generate different regular waves. The bigger the axial opening size of the valve port, the larger the wave paddle amplitude and the wave amplitude; the higher the pressure, the higher the wave paddle amplitude and the wave amplitude. High frequency wave making is more efficient than the lower one, and piston type wave making is more efficient than those wave makers that generate waves by flap type.

Grid-generated turbulence in pulsating flow under the rigid boundary influence

Abstract An experimental investigation was carried out to study the grid generated turbulence under the influence of rigid boundary for current-only and pulsating flow environment. The pulsating nature of flow was generated in the experimental setup by adding surface wave over unidirectional current flow with the help of plunger type wave-maker. For understanding the effect of grid-generated turbulence and its interaction with rigid boundary in wave–current co-existing environment, three different mesh sizes of the grids were used and the turbulence characteristics were analysed. The paper also attempts to analyse the degree of anisotropy in the flow at the upstream and the downstream of grids under the influence of rigid boundary and surface wave. Further, to gain better insight into the physics of pulsating flow superimposed on current flow through grid under rigid boundary influence, the co-spectra, squared-coherency and quasi-isotropic ratio of random velocity fluctuations have been evaluated at different levels from the bed.

Physical model study on geo-tube with gabion boxes for the application of coastal protection

Shoreline erosion takes place due to the movement of sand by tides, wave actions, and wave-induced currents. The conventional techniques used for coastal protection such as artificial armor units and rubble mound are costly, and transportation is difficult in remote areas. Moreover, they may not be suitable for poor soil conditions. In this paper, the detailed physical experimental studies were carried out for a geo-tube saline embankment with ten geo-tubes in a four-layer configuration in a wave flume. This soft engineering solution may be particularly viable since the location is remote with poor soil strata. The studies include a scaled model (1:10) of geo-tube embankment with and without gabion boxes to check its possible utilization for coastal protection. The model is tested in the deep wave flume equipped with a piston type wave maker. The embankment is studied for two different water depths of 0.4 m and 0.5 m. The chosen 0.4-m water depth characterizes the high tide condition, while the 0.5-m water depth reproduces the combined high tide and storm surge conditions. The regular wave heights are varied in the range of 2 to 16 cm with a corresponding wave period of 1.5 to 2.2 s. Three probe methods are used to obtain the hydrodynamic parameters, based on which a geo-tube embankment protected with gabion box as armor is designed and constructed along the coast of Pentha (Odisha, India).

Studies on the performance of Savonius rotors in a numerical wave tank

Waves were generated in a numerical wave tank (NWT) using a piston type wave-maker. Firstly, the performance of a 1.8 m diameter Savonius rotor was tested at a mean wave height (H) and a mean wave period (T) of 2.00 m and 12.68 s respectively. The Savonius rotor performed the best at a submergence depth of 1.0 D when compared to greater depths. The power produced by the rotor decreased by 37% at 1.25 D compared to 1.0 D. In addition to this, the blade entry angle also affected the rotor performance. The 20° rotor at 42.5 rpm was found to have the best performance. The maximum power and efficiency at the mean sea state were 15.01 kW and 16.7% respectively. Secondly, simulations were performed at the minimum sea state (H = 1.37 m, T = 10.00 s) and the maximum sea state (H = 2.34 m, T = 14.39 s). It is observed that the peak power at the maximum sea state is lower than the peak power at the mean sea state. The maximum power that the rotor produced was 15.01 kW at 42.5 rpm which gave an efficiency of 16.7% at the mean sea state.

Investigation of Wave Characteristics with Rotor Type Water Wave Generator

Wave energy is the most available energy associated in deep water seas and oceans. Therefore, many attempts have been applied to capture these energies. This paper describes the design, construction and testing of water wave flume. The water wave flume contains an electromechanically driven rotor type wave maker to generate water wave powers. The waves are constructed by different sizes and arrangements of blades which are connected to the rotor. The rotor is driven by an ac motor to generate wave. At the end of the tank a force measuring device is attached opposite to the rotor to measure the thrust of the wave. Experimental results are validated with available literature and wave theory. The results also show that the width of the blade play major role in generating wave sizes including frequency, amplitude and the power. Wider blade displaces much water to generate wave but reduces the blade speed.

Turbulent characteristics of pulsating flow over hydraulically smooth surface

The mean flow and turbulence characteristics due to the interaction between wave and current is investigated over the hydraulically smooth surface in a wave channel based on measurement of the horizontal, bottom-normal and transverse velocity components in the pulsating fluid using a 3-D micro-acoustic Doppler velocimeter. Pulsations, in the vicinity of the wall are produced by superimposing the surface wave on unidirectional current using plunger type wave-maker. The velocity time series of combined wave–current flow were analysed within the framework of the phase-averaging. Further, to highlight the changes in combined wave–current flow, a comparative study was made between the velocity profiles for current-only flow and those measured for combined wave–current flow. The measured mean stream-wise velocity for waves following a current is reduced towards the free surface when compared with the current-only data. In addition, with an increase in wave height, a further intense reduction of the velocity just below the wave trough occurs. To fully characterize turbulent signals, the joint probability density function of stream-wise and bottom-normal velocity fluctuations is analysed. Spectral analysis was also performed to obtain the oscillation pattern within the flow field that may affect the turbulent properties due to combined wave–current flow.

Dynamic Response Analyses of Fixed Type Substructures for 2.5MW Class Offshore Wind Turbine

This paper explores a series of numerical simulations of dynamic responses of multi-piles (dolphin) type substructures for 2.5MW class offshore wind turbine. Firstly computational fluid dynamics (CFD) simulation was performed to evaluate wave loads on the dolphin type substructures with the design wave condition for the west-south region of Korea. Numerical wave tank (NWT) based on CFD was adopted to generate numerically a progressive regular wave using a virtual piston type wave maker. It was found that the water-piercing area of piles of the substructure is a key parameter determining the wave load exerted in horizontal direction. In the next the dynamic structural responses of substructure members under the wave load were calculated using finite element analysis (FEA). In the FEA approach, the dynamic structural responses were able to be calculated including a deformable body effect of substructure members when wave load on each member was determined by Morison's formula. The paper numerically identifies dynamic response characteristics of dolphin type substructures for 2.5MW class offshore wind turbine.

Experimental study on effect of wave set-up in storm surge

The storm surge height is usually determined as the surplus of height suctioned by atmospheric low pressure and that drifted by strong winds. These two models have been investigated for many years to resolve mechanisms of storm surges in inner bays. In the outer bay areas, some numerical models demonstrate the effect of wave set up cannot be neglected in the total deviation of storm surge. Almost all numerical models employ linear superposition of the original storm surge deviation and wave set up level. However, wave set-up itself is nonlinear phenomena and the mechanism is not clearly revealed. The paper describes an experiment employed in a newly developed Tsunami and Storm Sure Reproducing Channel (45m × 4m× 2m). The channel generates the following three types of wave and currents: 1) Soliton type tsunami and irregular waves by piston type wave generator; 2) Uni-directional and bi-directional current by current generator; 3) Tsunami generated by ice-break, volcano eruption etc. using overhead water tank. In the experiment, storm surge was reproduced by the current generator and the stormy wave was generated by the piston type wave maker. Spectra analysis and unit wave analysis are carried out and the nonlinear effect included in storm surge deviation in shore line is discussed.

The study on solitary waves generated by a piston-type wave maker

The focus of present study is on how to generate solitary waves in a wave flume using a piston type wave maker. Experimental observations are implemented to evaluate the stability of the generated solitary waves. A better “stability” implies that the generated solitary wave can travel a longer distance without an obvious decay. Another discovery of this study is the imperfect fitness of wave paddle to the flume could degenerate the solitary wave heights in a great amount. Numerical simulations are carried out to verify this. This study concludes that the method proposed by Wu et al. (2014) is effective for generating solitary waves, even if the wave paddle fits the wave flume imperfectly.

Tsunami generation in a large scale experimental facility

Experimental studies on tsunami are carried out since many years, most of them by generating solitary waves with a piston type wave maker. However, today it is more and more appreciated that these kinds of waves actually do not represent a real tsunami very well, as particularly for the shallow waters at the coast the wave length becomes comparably far too short. Recently new generation methods for scaled down real tsunami experiments were suggested, as it was doubted that sufficiently long waves could be generated with a classical wave maker. The present paper shall disprove these arguments by providing results of a study carried out in the Large Wave Flume (Großer Wellenkanal, GWK), where waves of periods between 30s and more than 100s at 1m water depth were successfully generated with a piston type wave maker. Results for elongated solitary waves, trough led N-waves and real tsunami records as a combination of a different number of general solitons (sech2 waves) are presented. Finally, the requirements and limitations to bring a “real” tsunami into the laboratory are discussed.

Comparative study on the accuracy of solitary wave generations in an ISPH-based numerical wave flume

In the present study, six solitary wave generations by different mathematical approximations are investigated using a piston type wave maker at dimensionless amplitudes ranging from 0.1 to 0.6 and two water depths. Incompressible smoothed particle hydrodynamics is used to simulate solitary wave propagation along the fixed depth channel. The present numerical results are compared with analytical results and experimental data in terms of free surface displacements, fluid particle velocity, phase speed, paddle motion, etc. The present mesh-free numerical results of wave profile variations over time proved that “Rayleigh” has the lowest relative wave height variation. However, its solitary wave has notable phase lead, while “Third order” and “Ninth order” have the least wave lags. Furthermore, the record of present numerical free surface elevation at different distances and the loss of amplitude of the main pulse showed that regarding both of them, “Ninth order” has supremacy over five others. Considering the numerical velocity components of generated solitary wave, “Third order” and “Ninth order” trace analytical results more accurately than other four ones, whereas “Rayleigh” is the most accurate one in predicting the maximum runup. Finally, the paddle motion, its velocity, and displacement, as well as phase speed and outskirts decay coefficient are also compared and discussed intensely.