scholarly journals Wave energy converter with enhanced amplitude response at frequencies coinciding with Swedish west coast sea states by use of a supplementary submerged body

2009 ◽  
Vol 106 (6) ◽  
pp. 064512 ◽  
Author(s):  
J. Engström ◽  
M. Eriksson ◽  
J. Isberg ◽  
M. Leijon
Keyword(s):  
Wave Energy ◽  
West Coast ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Amplitude Response ◽  
Swedish West Coast ◽  
Submerged Body

Determining the Service Life of a Steel Wire Under a Working Load in the Wave Energy Converter (WEC)

2009 ◽  
Author(s):  
A. Savin ◽  
O. Svensson ◽  
E. Stro¨mstedt ◽  
C. Bostro¨m ◽  
Mats Leijon
Keyword(s):  
Service Life ◽  
Wave Energy ◽  
West Coast ◽  
Steel Wire ◽  
Ocean Waves ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Swedish West Coast ◽  
Sea Bed ◽  
The Wire

There are different types of energy in nature. Kinetic energy of natural movements like ocean waves is one of them. It is advantageous to convert this energy into a form suitable for use. Ocean waves can play important role in tomorrow’s energy production. At the Swedish Center for Renewable Electric Energy Conversion at Uppsala University, the Wave Energy Converter (WEC) was launched offshore outside the Swedish west coast in March 2006. The WEC consists of the linear generator placed on the sea bed and connected to the buoy via the rope, see Fig.2. Different rope solutions were tested. In May 2008, the steel wire Powerplast (28mm) was connected to the WEC. The steel wire has a shorter service life than other parts of the WEC. The steel wire connects the translator and the buoy. Therefore, the steel wire’s lifetime appears to be very important characteristic for the WEC. It is necessarily to determine the service life of the wire. Aggressive environments reduce the calculated service life which results in corrosion of an ordinary steel wire. A high wave climate and the contact loads can drastically affect wear of the wire. In order to prevent metal-to-metal contact between a steel wire and a funnel, the steel wire was impregnated in a black high density (HD) jacketing compound, that had a good abrasion, scratch resistance and a very good heat deformation resistance. The pulsating nature of waves can cause dramatic transition of the wire from the ductile to brittle fatigue fracture appearance. The residual stresses was also the causes of failures in the wire. The research results and the result from a full-scale experiment of dynamic behavior of a steel wire under a working load in the WEC are considered in this work. The measurements of the dynamic force along the steel wire under a water line were conducted offshore at Lysekil off the Swedish west coast.

Influence of Generator Damping on Peak Power and Variance of Power for a Direct Drive Wave Energy Converter

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Magnus Stålberg ◽  
Rafael Waters ◽  
Oskar Danielsson ◽  
Mats Leijon
Keyword(s):  
Wave Energy ◽  
Peak Power ◽  
Load Resistance ◽  
Wave Energy Converter ◽  
Damping Factor ◽  
Direct Drive ◽  
Energy Converter ◽  
Swedish West Coast ◽  
Electric System ◽  
Point Absorber

The first offshore prototype of a wave energy converter system has been launched off the Swedish west coast. The concept is based on a point absorber directly coupled to a linear generator located on the ocean floor. The wave energy converter is part of a research project that will study the electric system of ten units forming a small farm of wave power plants as they are linked and connected to an electric grid. A full scale farm will consist of a large number of interconnected units. The chosen direct drive system reduces the mechanical complexity of the converter but has repercussions on the electric system. The output from the generator will vary with the speed of the point absorber, leading to large fluctuations of power on the second scale. This has implications on both the individual generator and on the system as a whole. The hydrodynamic behavior of the point absorber depends, to a large extent, on the damping of the generator. The damping, in turn, can be remotely controlled by changing the load resistance. It has previously been shown that this has a large influence on the power absorbed by the wave energy converter. This paper investigates the peak power, the translator speed, and the variance of the power at different sea states and for different levels of damping. The peak power has an impact on the design of the generator and the required ability, for a single unit, to handle electric overloads. The momentum of the translator is directly proportional to its speed. The speed is thus important for the design of the end stop. The variance of the power of one unit will have an impact on the farm system behavior. The study is based on two and a half months of experimental measurements on the prototype wave energy converter and a wave measurement buoy. The aim is to analyze whether load control strategies may influence the dimensioning criteria for the electric system and the generator. The results are compared to previously investigated relationships between the absorbed mean power and the load resistance as a function of sea state. In the study, it was found that the maximum power is approximately proportional to the average power, while the maximum translator speed and standard deviation decrease as the damping factor is increased.

Measurements of Extreme Forces on a Wave Energy Converter of Point Absorber Type and Estimation of Added Mass of Cylindrical Buoy

2014 ◽  
Author(s):  
Halvar Gravråkmo ◽  
Erland Strömstedt ◽  
Andrej Savin ◽  
Olle Svensson ◽  
Mats Leijon
Keyword(s):  
Wave Energy ◽  
West Coast ◽  
Vertical Cylinder ◽  
Added Mass ◽  
Wave Energy Converter ◽  
Normal Operation ◽  
Energy Converter ◽  
The West ◽  
Stroke Length ◽  
Point Absorber

A wave energy converter (WEC) of point absorber type is tested at the west coast of Sweden. The buoy is a vertical cylinder. The linear generator on the seabed has limited stroke length. Large waves cause the generator to reach its maximum stroke length. As this happen, a spring in the generator is compressed, causing the buoy to instantly come to rest. During this process the force between the buoy and the generator is measured. Also the acceleration of the buoy is measured. This process and the extreme forces on the generator hull is described and the study shows that the magnitude of this force is greatly influenced by the added mass of the buoy and thus the buoy geometry. The ratio between the extreme forces on the hull and the forces during normal operation will affect the dimensioning and economy of the WEC. Force acting between generator and buoy were measured during various events as the WEC was operating. Heave added mass was derived from the measurements and found to be greater than the theoretical value.

Influence of Generator Damping on Peak Power and Variance of Power for a Direct Drive Wave Energy Converter

2007 ◽  
Author(s):  
Magnus Sta˚lberg ◽  
Rafael Waters ◽  
Oskar Danielsson ◽  
Mats Leijon
Keyword(s):  
Wave Energy ◽  
Peak Power ◽  
Load Resistance ◽  
Full Scale ◽  
Wave Energy Converter ◽  
Direct Drive ◽  
Electrical System ◽  
Energy Converter ◽  
Swedish West Coast ◽  
Point Absorber

The first full-scale offshore prototype of a novel wave energy converter system has been launched off the Swedish west coast. The concept is based on a point absorber directly coupled to a linear generator located on the ocean floor. The wave energy converter is part of a research project that will study the electrical system of 10 units forming a small farm of wave power plants as they are linked and connected to an electric grid. A full scale farm will consist of a large number of interconnected units. The chosen direct drive system reduces the mechanical complexity of the converter but has repercussions on the electrical system. The output from the generator will vary with the speed of the point absorber, leading to large fluctuations of power on the second scale. This has implications on both the individual generator and on the system as a whole. The hydrodynamic behavior of the point absorber depends, to a large extent, on the damping of the generator. The damping, in turn, can be controlled remotely by changing the load resistance. It has previously been shown that this has a large influence on the power absorbed by the wave energy converter. This paper investigates the peak power, the translator speed and the variance of the power at different sea states and for different levels of damping. The peak power has an impact on the design of the generator and the required ability, for a single unit, to handle electrical overloads. The speed of the translator is directly proportional to its momentum. It is thus important for the design of the end stop. The variance of the power of one unit will have an impact on the farm system behavior. The study is based on two and a half months of experimental measurements on the prototype wave energy converter and a wave measurement buoy. The aim is to analyze whether load control strategies may influence the dimensioning criteria for the electrical system and the generator. The results are compared with previously investigated relationships between absorbed mean power and load resistance as a function of sea state. In the study it was found that the maximum power is approximately proportional to the average power while maximum translator speed and standard deviation decrease as the damping factor is increased.

Experimental Results From an Offshore Wave Energy Converter

2008 ◽  
Author(s):  
Cecilia Bostro¨m ◽  
Erik Lejerskog ◽  
Simon Tyberg ◽  
Olle Svensson ◽  
Rafael Waters ◽  
...  
Keyword(s):  
Wave Energy ◽  
Energy System ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Swedish West Coast ◽  
Grid Connection ◽  
Linear Load ◽  
Non Linear Load ◽  
Offshore Wave ◽  
Voltage Conversion

An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the ocean floor driven by a point absorber. A measuring station has been installed on a nearby island where all measurements and experiments on the WEC have been carried out. The output voltage from the generator fluctuates both in amplitude and frequency and must therefore be converted to enable grid connection. In order to study the voltage conversion, the measure station was fitted with a six pulse diode rectifier and a capacitive filter during the autumn of 2006. The object of this paper is to present a detailed description of the existing wave energy system of the Islandsberg project. Special attention will be given to the power absorption by the generator when it is connected to a non linear load.

Experimental Results From an Offshore Wave Energy Converter

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Cecilia Boström ◽  
Erik Lejerskog ◽  
Simon Tyrberg ◽  
Olle Svensson ◽  
Rafael Waters ◽  
...  
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Nonlinear Load ◽  
Swedish West Coast ◽  
Point Absorber ◽  
Measuring Station ◽  
Grid Connection ◽  
Offshore Wave ◽  
Voltage Conversion

An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the sea floor driven by a point absorber. A measuring station has been installed on a nearby island where all measurements and experiments on the WEC have been carried out. The output voltage from the generator fluctuates both in amplitude and frequency and must therefore be converted to enable grid connection. In order to study the voltage conversion, the measuring station was fitted with a six pulse diode rectifier and a capacitive filter during the autumn of 2006. The object of this paper is to present a detailed description of the Lysekil research site. Special attention will be given to the power absorption by the generator when it is connected to a nonlinear load.

Dynamics and Power Absorption of a Self-React Wave Energy Converter With Mechanical Power Takeoff System

2017 ◽  
Author(s):  
Changwei Liang ◽  
Xiaofan Li ◽  
Dillon Martin ◽  
Adam Wise ◽  
Robert Parker ◽  
...  
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Ball Screw ◽  
Regular Waves ◽  
Energy Converter ◽  
Power Absorption ◽  
Optimal Power ◽  
Submerged Body ◽  
Equivalent Mass

A self-react wave energy converter which consists of a floating buoy and a submerged body is studied in this paper. The energy is extracted through the relative motion of the floating buoy and submerged body. Two kinds of power takeoff (PTO) system, which is the technique approaches to extract energy from the ocean, are considered for the proposed wave energy converter. One is a ball screw system with mechanical motion rectifier gearbox (which is called MMR system) and another one is solely a ball screw system (which is called non-MMR system as a comparison). The design of the proposed wave energy converter is presented and the model for both power takeoff systems are established based on their mechanisms. A time domain method is adopted to investigate the dynamics and power absorption for the proposed wave energy converter. The effect of equivalent mass on the optimal power and corresponding optimal power takeoff damping are studied both in regular and irregular waves. It is found that the equivalent mass plays different roles in the MMR system and non-MMR system. Due to the disengagement in MMR system, the equivalent mass helps to increase the power absorption at small wave 1periods, both in regular waves and irregular waves. The uncertainty of the drag coefficient on the power absorption of MMR system and non-MMR system is also investigated.

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