Computational Modeling of a Regular Wave Tank

Marine Systems & Ocean Technology, 2015

Ocean basin facility experiments have great importance to the design of offshore structures. Because of the continuous advances in computational fields, the use of numerical simulations to assist the planning of the experiments or to complement the experimental results has become common. Thus, the comparison between numerical and experimental data is an important task to support the developments of the application of numerical models in an ocean basin. This paper presents a numerical study of the generation and propagation of regular waves in the ocean basin of the Ocean Technology Laboratory (LabOceano/ COPPE) at the Federal University of Rio de Janeiro. The homogeneous multiphase model implemented in the ANSYS-CFX code was used. A cross section of the basin has been represented. The results were compared with wave theory and experimental data that was obtained in the ocean basin of interest. Regular waves with steepness \0.035 and period from 1.25 to 3.00 s were simulated. The behaviour of the free surface elevation along the basin and over time has been evaluated. Comparisons between numerical and experimental results have indicated some issues which should be taken into consideration when applying a numerical code to this kind of application.

Ocean Engineering, 2012

One of the main stages in the design of wave energy converters (WEC's) is the numerical modelling of a given converter. In this paper, the numerical simulation of both linear deep water waves and linear waves for the finite depth case are explored using computational fluid dynamics (CFD), to aid in this design stage. The CFD software package described in this paper is the commercial finite volume package ANSYS CFX (Release 12.1). The results of parametric studies, which were performed in order to optimise the CFD model, are detailed and a guide to creating a model that produces the desired waves is presented. The model was validated in two ways: (a) the wave created was compared to wavemaker theory (WMT) and (b) the water particle velocity and elevation of the wave was compared to linear, Airy, wave theory (LWT) for deep water waves. It was also found that wave generation in ANSYS CFX using a flap-type wavemaker was restricted to a low normalised wavenumber, k 0 h. In order to increase this restriction, the hinge of the wavemaker was raised and, with this alteration, it is possible to generate deep water linear waves. A case study of a real world application of wave-structure interaction, employing this methodology, is also explored.

Scientific Journal of Polish Naval Academy, 2017

This paper presents the implementation process of the design methodology for ocean waves in a laboratory tank using a wave generator, which is the basis for conducting hydrodynamic model scale research involving real sea conditions. The main focus is placed on generation of time sequences used as the control input for the wave generator and experimental verification methods for the generated waves and concluding with the results and validation of the developed process by achieving wave parameters sufficiently aligned with the theoretical model.

American journal of mechanical engineering, 2020

In this paper, a two-dimensional Numerical Wave Tank (NWT) is proposed to calculate the static pressure variation along the lower wall of an experimental wave-flume. The experimental setup was a 4.72m long wave flume with a flap-type wave-maker. The experiments were carried out at various water heights of 100mm, 80mm, and 60mm, with a motor speed of 60 rpm. The numerical simulations were completed using ANSYS™ Fluent, with two sets solutions: 1) the unsteady, three-dimensional Reynolds Averaged Navier-Stokes (URANS) equations coupled with a k-e turbulence model; 2) unsteady 3-D Euler equations. In both computations, the volume of fluid (VOF) method was used to capture the free surface and a grid independence study was completed. The unsteady Euler simulations showed the best agreement to the experimental results. Several cases were run to complete validation and verification of the numerical model, and the CFD results are in good agreement with the experiment. Thus, for small two-di...

Journal of Clean Energy Technologies, 2015

Nowadays, ocean energy has attracted more attention among the researchers due to its massive energy potential. As designing, constructing and testing prototypes are both expensive and time consuming, recently, many researchers have developed numerical wave tanks to simulate the behaviour of the waves as well as the interaction of waves with wave energy converters. This paper aims to model numerical wave tanks, using waves2Foam-a solver within OpenFOAM, to show the propagation of waves, as well as different wave breaking types. Firstly, a flat-bottom wave tank is modelled in order to simulate both generation and absorption of the waves. Such results are benchmarked against laboratory experiments data and the comparison between simulation and experiment results showed a good agreement. Furthermore, some additional cases are modelled to assess the capability of waves2Foam in absorption of waves' reflection from the outlet boundary. Secondly, different sloped wave tanks are modelled to investigate the capability of waves2Foam in properly simulating wave breakings. Results demonstrated that waves2Foam is not only able to well simulate wave generation and absorption but it is also able to simulate all types of wave breaking. This work presents waves2Foam as powerful toolbox which can properly model waves based on different wave theories. However, some limitations of the solver were identified.

An open source CFD solver,OpenFOAM R , has been used to create a numerical wave tank. The study is based on the interFoam solver, i.e. a solver for incompressible multiphase flow problems. The solver uses the finite volume method for the spatial discretization of equations and applies the VOF approach for the free surface modeling. Initially a convergence study was carried out. The study was based on the propagation of fifth order Stokes waves in deep water condition. To this end two separate applications, waveWriter and errorCalculator, were created. With the former the initial conditions for the velocities and pressure of fifth order Stokes wave can been specified directly for in-terFoam. The errorCalculator is a post-processing tool that estimate the computational errors at each time step. The study revealed that the model exhibits only first order convergence. The loss of one order is due to the waveWriter setting only first order initial conditions. Wave generation and absorption in the wave tank are performed by the relaxation method. For this purpose the existing interFoam solver has been partially modified in order for replacing the computational solutions with desired analytical ones inside the relaxation zones. In this manner the modified solver is able to generate and dissipate different wave types in the numerical wave tank. It is shown that outgoing waves are absorbed efficiently by extending the damping relaxation zone to at least three wavelengths, while one wavelength extension is required for the wave-generating zone. To validate the numerical wave tank, the Whalin shoaling test was considered. Unfortunately, inadequacies in the then existing version of interFoam, (version 1.6.x), in the handling of the pressure force balance on non-orthogonal and distorted meshes, hindered and finally stopped the validation test process. Subsequently it was found that the newer version OpenFOAM-1.7.x, can be used promisingly for the validation of wave tank by Whalin test and this has been defined as a recommended future work.

2013

The last two decades have seen increasing interest in renewable energy technologies in response to the pollution effects from extensive use of fossil fuels and global warming. It is claimed by some that ocean wave energy alone could potentially supply the worldwide need for electricity, making it a significant clean energy resource. However, wave energy is still at an early stage of research and development and only a few companies are at pre-commercial stage in the development of their technologies. With recent increases in computer performance, well-developed mathematical knowledge in hydrodynamics and advances in the development of numerical methods, numerical models have become an accurate, low-cost and fast tool in the research and development of hydrodynamic systems at sea. In the case of ocean

2018

Clean energy systems have been investigated recently by the researchers of the University of New Mexico to increase the efficiency specifically in the solar tower technology. Similar to solar energy, wave power harnesses energy that comes from the sun. Solar irradiation causes wind by changing the pressure, and wind gives its momentum to the ocean surface which produces waves. Modeling and simulation (M&S) of free surface flow can be a very useful tool for the wave energy industry. However, if these tools are to be relied upon, their accuracy must be tested and shown to be sound. In this investigation, we focus on verification and validation (V&V) of wave tank flow M&S. The Volume of Fluid (VOF) model was applied to perform transient computational fluid dynamics (CFD) analysis using the numerical simulation software OpenFOAM. To assess V&V, the height of the free surface flow was considered as the system response quantity (SRQ). Stokes theory (fifth order) was utilized as the most a...

Mathematics and Computers in Simulation, 2002

The evolution of waves on the surface of a layer of fluid is governed by non-linear effects from surface deformations and dispersive effects from the interaction with the interior fluid motion. Several simulation tools are described in this paper and compared with real life experiments in large tanks of a hydrodynamic laboratory. For the full surface wave equations a numerical FEM/FD program is described that solves both the interior flow and the surface evolution; apart from being very efficient, the program performs remarkably well. For theoretical analysis, simplified equations are desired. These can be obtained by modelling the interior flow to some degree of accuracy, leading to a single equation for the surface elevation. As representatives of this class, we discuss KdV-type of equations and, for wave packets, the NLS equation. We show that even this last equation describes quite well the large, non-symmetric deformations of the envelope of bi-harmonic waves when formulated as a signalling problem.

Wave Motion, 2002

Precise measurements of gravity waves with very small wave slope in a physical wave tank are compared with an explicit linear inviscid wave maker theory. The main purpose is to measure the speed of the physical waves relative to those computed. We find that the wave speed in the physical wave tank is slightly less than in the computations. The small difference in the wave speed leads to a relative phase difference between the real waves and the inviscid computations of about 0.01 ± 0.006 rad per wavelength (0.16 ± 0.1%), which is comparable to an estimated phase delay due to the boundary layer at the tank walls. In this result, the estimated effects of weak non-linearity and surface tension in the experiments are subtracted. This relative phase difference is significantly smaller than what previous investigations in wave tanks of similar size have indicated. This means that physical wave tank simulations can effectively be applied as reference for numerical simulations of steep (non-linear) waves.