Motivation

When a wave travels from deep into shallow water, its parameters, such as wavelength or phase velocity, change[1]. Additionally, the seabed topology can lead to a local focusing of wave energy[3]. An advantage of this effect is that it can be used to increase the power output of wave energy converters (WEC)[2]. A disadvantage is that it can locally increase the severity of tsunami impact for certain. In practice it is therefore necessary to evaluate the change in wave parameters over a realistic seabed topology.

Objective

The aim of this work is to develop a concept and implement it in a computer program that can be used to extract the topology of the seabed from public domain bathymetric data sets such as [4]. Furthermore, the program should enable the user to enter wave direction, wave height and wave period of a long-crested uni-directional wave (to model swell) or a point source (to model tsunamis). Subsequently, it should calculate the influence of the water depth on the wave parameters including wavelength and height, phase velocity, group velocity, incidence wave angle relative to initial wave direction, wave power per unit crest length as well as wave energy per unit surface area.

The program should be able to compute and plot the free surface elevation or wave crest locations over time, which can be done via ray-tracing. For the sake of simplicity, wave diffraction and wave reflection do not have to be taken into account.

Two applications should be investigated with the code: 1. Automization of the determination of the optimal site for the installation of wave energy converters and 2. tsunami propagation.

For application 1, the program should be used to compute wave energy spectra, the local average wave power per unit-crest length for realistic seabed topologies and to determine the optimum locations to install the WEC. Using practical assumptions, it should be demonstrated and discussed how WEC placement can influence the power output. In addition, program should forecast locations where wave breaking can occur. Wave breaking dissipates wave energy and thus can significantly reduce the power output of wave energy converters. For this, the wave steepness (wave height divided by wavelength) should be evaluated. By using empirical data such as [5], locations where wave breaking would occur should be identified within the output file.

For application 2, the program should further be extended to model tsunami propagation via ray tracing from a point source, and compare for example tsunami propagation, arrival time and estimated wave height near coast to literature data.

Finally, the computer programm should be extended so that it considers the change of wave parameters as a function of the wave steepness. It should be investigated and discussed how wave non-linearity affects the results from applications 1 and 2.

The program should write the calculated wave parameters for a given raster of coordinates to a output file, so that the information can be plotted using open source codes like e.g. ParaView (http://www.paraview.org/).

Tasks

• Literature research: Wave theory, wave energy conversion, tsunami propagation

• Familiarization with scientific programming and data evaluation

• Development of a concept for efficient extraction of bathymetry from real data sets and calculations of the wave parameters

• Implementing the concept in a computer program to compute local wave parameters and via ray-tracing estimate and visualize wave propagation based on linear wave theory

• Verification of the developed program

• Investigation of optimum wave energy converter installation site

• Computation of the propagation of a tsunami wave and comparison to literature data

• Extending the computer program to determine the locations of wave breaking and to apply nonlinear corrections to the wave propagation

• Documentation

Type & Date

Project / Bachelor

13.09.2021

Contact

Dr.-Ing. Robinson Peric