waveMakerZ Tutorial

Details:

• Feature: waveMakerZ
• FeatureType: Tutorial
• Version: OFv1812
• Date: 22/02/2021
• Author: Anatoliy Khait
• Contact: haitanatoliy@gmail.com

• Status: complete

• Description

• User Guide
• Dependencies
• References

• Comments

Description

This tutorial shows how to use the second-order accurate wavemaker boundary condition implemented in waveMakerZ library. The possible motion of the generating boundary includes piston and paddle types of the wavemaker, as well as any intermediate hinged types of the wavemaker. As an input parameter, this boundary condition takes surface elevation variation in time provided at the location of the wavemaker. The surface elevation should incorporate only linear wave contributions, i.e. it should consist of free waves only. First and second-order contributions to the wavemaker motion are calculated from the provided surface elevation record involving Zakharov theory of weakly-nonlinear water waves. The accuracy of the current implementation of the wavemaker boundary condition is limited to the second order in terms of the wave steepness parameter.

More information on the theory behind waveMakerZ library can be found in the papers referenced below.

User Guide

This tutorial is run using the Allrun script that initially cleans the directory with Cleanall script and copies 0.orig to 0 directory. Then it runs sequentially blockMesh and setFields utilities, afterward standard interFoam solver with the linked libwaveMakerZ.so library. The first and second-order contributions to the wavemaker motion are calculated by the libwaveMakerZ.so library during execution of the interFoam solver and then written into the files spectra (spectra of the wavemaker motion) and time_series (time series of the wavemaker coordinates). In the end, the script gnuplot_script.plt is executed to produce three images: spectrum_elevation.png: first and second-order surface elevation at the wavemaker; spectrum_wavemaker_displacement.png: first and second-order spectra of the wavemaker displacements; wavemaker_displacement.png: time series of the first and second-order wavemaker displacements. Examples of the images are placed in the results directory.

The following modifications were introduced to the standard interFoam case in order to use libwaveMakerZ.so library:

• line libs ("libwaveMakerZ.so"); is added in the end of system/controlDict dictionary to link the corresponding library;
• dictionary constant/dynamicMeshDict is added to enable dynamic deformation of the mesh;
• boundary conditions 0/pointDisplacement for the deforming mesh are added;
• solver for cellDisplacement and cellDisplacementFinal is added to system/fvSolution dictionary.

Parameters of the wavemaker are set in 0/pointDisplacement for the boundary leftwall. Below the description of the properties of the wavemaker boundary condition is summarized:

The spectrum of the linear free waves is calculated from the time record of the surface elevation provided as the input to the boundary condition. This time record is stored in "signal" file. The Fast Fourier Transform from the fftw-3.3.7 library is adopted to calculate the complex surface elevation spectrum. Depending on the content of the "signal" file, the resultant spectrum may incorporate thousands of harmonics leading to unnecessary computational loads. Therefore, the spectrum is truncated at a certain harmonic number that can be set with a parameter numHarmonics given above.

Dependencies

References

• A. Khait, L. Shemer, Nonlinear wave generation by a wavemaker in deep to intermediate water depth. Ocean Engineering, 182 (2019), 222-234
• A. Khait, Third-Order Generation of Narrow-Banded Wave Trains by a Wavemaker. Ocean Engineering, 218 (2020), 108200