Automated optimisation of a heaving point absorber

56 Pages·2012·2.23 MB·English

Automated optimisation of a heaving point absorber
A wave energy converter design methodology
Master of Science Thesis
Erik Dölerud
Department of Shipping and Marine Technology
Division of Marine Design
CHALMERS UNIVERSITY OF TECHNOLOGY
Gothenburg, Sweden, 2012
Report No. X-12/286

A THESIS FOR THE DEGREE OF MASTER OF SCIENCE
Automated optimisation of a heaving point absorber
A wave energy converter design methodology
Erik Dölerud
Department of Shipping and Marine Technology
CHALMERS UNIVERSITY OF TECHNOLOGY
Gothenburg, Sweden 2012
Automated optimisation of a heaving point absorber
A wave energy converter design methodology
Erik Dölerud
© Erik Dölerud, 2012
Report No. X-12/286
Department of Shipping and Marine Technology
Chalmers University of Technology
SE-412 96 Gothenburg
Sweden
Telephone [phone]
Cover art: © Jonas Porsgaard 2012
Written entirely in open source software
Printed by Chalmers Reproservice
Gothenburg, Sweden, 2012
Automated optimisation of a heaving point absorber
A wave energy converter design methodology
Erik Dölerud
Department of Shipping and Marine Technology
Chalmers University of Technology
Abstract
Recent development in energy generation policies around the world has lead to a rejuvenation
of the sector of wave energy converters. This study aims at proposing a method of automated
optimisation for such a system. The analysed system is a single buoy heaving point absorber
with a linear generator as power take off system. The buoy is initially modelled as a cylinder
and analysed using potential flow theory for the hydrodynamic motion characteristics. The
solution takes into account annuity averaged results as well as the possibility of optimisation
of generator damping for each sea state. An automated optimisation routine is set up and used
to investigate a number of cases that illustrate the behaviour of the model and the optimisation
set up. Verification efforts show good agreement with expected behaviour as well as
published results for the various parts of the solution and analysis behave as expected.
Further a two degree of freedom model is developed for investigation of surge contribution
potential and to illustrate how the model can be applied to a different system.
Keywords: wave power; point absorber; automated optimisation;
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Preface
Given the great variety of systems being developed at present as well as the forthcoming
demand for energy generation alternatives it is easy to comprehend the need for competence
in analysis and design of wave energy devices. This fact has led to the recent start up of a
competence centre for wave power devices at Chalmers university of technology in which this
thesis is performed.
This thesis is a part of the requirements for the master’s degree at Chalmers University of
Technology, Göteborg, and has been carried out at the Division of Marine Design,
Department of Shipping and Marine Technology, Chalmers University of Technology.
I would like to acknowledge and thank my supervisor, Dr. Claes Eskilsson at the Department
of Shipping and Marine Technology, for his enthusiasm regarding renewable energy sources
and the geographically far extended help I have been given. I would also like to thank my co-
supervisor, Dr.-Ing. Stefan Harries at FRIENDSHIP SYSTEMS Gmbh for giving me the
opportunity to work closely with the team in Potsdam as well as for his moral and scientific
support. I would naturally also like to extend my sincere gratitude to the team at
FRIENDSHIP SYSTEMS for their invaluable help and “gute Stimmung”, in particular my
fellow students and office mates Sebastian Weickgenannt and Jan Land.
Berlin, May, 2012
Erik Dölerud
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Contents
Abstract......................................................................................................................................1
Preface........................................................................................................................................3
Contents.....................................................................................................................................5
1. Introduction...........................................................................................................................7
1.1. Background .....................................................................................................................7
1.2. Objectives......................................................................................................................12
1.3. Methodology .................................................................................................................12
2 Heaving Point Absorber......................................................................................................15
2.1 Description of system.....................................................................................................15
2.2 System features...............................................................................................................16
2.3 Modelling the system......................................................................................................16
3 Theory of modelling and optimisation...............................................................................18
3.1 Parametric modelling......................................................................................................18
3.2 Optimisation....................................................................................................................19
3.2.1 Genetic Algorithms..............................................................................................21
3.2.2 Optimisation methods used in this thesis.............................................................22
4. Theory of hydrodynamics and sea state description........................................................23
4.1 Hydrodynamics...............................................................................................................23
4.2 Wave theory and sea state description............................................................................24
5 Theory of motion in waves and power prediction.............................................................26
5.1 Equations of motion........................................................................................................26
5.2 Power evaluation.............................................................................................................28
6 Model.....................................................................................................................................30
6.1 Overall solution set up and the functionalities of the FRIENDSHIP-Framework.........30
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6.2 Geometric models...........................................................................................................32
6.3 MAPS..............................................................................................................................33
6.4 Power evaluation code....................................................................................................34
7. Verification..........................................................................................................................37
7.1 MAPS..............................................................................................................................37
7.2 Power evaluation code....................................................................................................37
8. Results..................................................................................................................................39
8.1 Benchmark experiment...................................................................................................39
8.2 Annuity and damping optimisation investigation...........................................................45
8.3 Investigation of performance in various locations..........................................................46
8.4 2DOF Basic behaviour investigation..............................................................................47
9. Summary, conclusions and future work...........................................................................50
10. References..........................................................................................................................51
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