Jan Sundberg

Multiphysics simulation of wave energy to electric energy conversion by permanent magnet linear generator

The possibility to use three-phase permanent magnet linear generators to convert sea wave energy into electric energy is investigated by multiphysics simulations. The results show a possibility, which needs to be further verified by experimental tests, for a future step toward a sustainable electric power production from ocean waves by using direct conversion. The results suggest that wave energy can have an impact on tomorrows new sustainable electricity production, not only for large units, but also for units ranging down to 10 kW. This gives wave power a larger economical potential than previously estimated. The study demonstrates the feasibility of computer simulations to give a broad, and in several aspects a detailed, understanding of the energy conversion. The simulation results also give a useful starting point for future experimental work.

Experimental results from sea trials of an offshore wave energy system

A full-scale prototype of a wave power plant has been installed off the Swedish west coast and the overall wave energy converter concept has been verified. Initial results have been collected and s ...

Old, colourful male yellowhammers, Emberiza citrinella, benefit from extra-pair copulations

The frequency of extra-pair paternity was determined in broods of the yellowhammer using single-locus DNA fingerprinting. Of 32 analysed clutches, 69% contained at least one extra-pair young. Out of 123 nestlings, 37% were extra-pair sired young. The extra-pair male could be assigned to 23 (50%) nestlings. Successful extra-pair males were all at least 3 years old although both younger and older males suffered from extra-pair paternity. Extra-pair males were also significantly more colourful than pair males, but did not differ in other characters. Colour did not differ between males with or without extra-pair young. The frequency of extra-pair young was not related to breeding density and identified extra-pair males were not necessarily nearest neighbours, giving further evidence that extra-pair males are not chosen at random. Since females do not obtain anything but sperm from extra-pair males, the results suggest that females prefer older and more colourful males, contributing good or attractive genes, as indicated by their plumage. Consequently, old, colourful extra-pair males, and possibly females, are likely to benefit from extra-pair copulations.

Catch the wave to electricity

The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

Female yellowhammers (Emberiza citrinella) prefer yellower males: a laboratory experiment

The importance of male plumage coloration as a signal of male dominance and a cue for female choice in the monogamous yellowhammer, Emberiza citrinella, was tested in two sets of experiments in an indoor aviary. Dominance was tested by introducing two individuals, with no previous experience of each other, in an aviary with food and water. Aggression occurred more often between two males than between a male and a female and more frequently between pairs of males including at least one old male than between two young males. Dominance was not related to male colour in trials between males of the same age class, but it was in trials between an old and a young male, often differing in colour. Thus, age may be a more important determinant of dominance than colour. Female preference for more colourful males was tested by allowing hormone-induced females to choose between a more and a less colourful dummy male. Females spent more time in front of more colourful than drabber males and also more often perched beside colourful males than duller individuals. Although male colour cannot be ruled out as a dominance signal, the results suggest that male colour is primarily used as a signal in mate choice. Female choice may hence be responsible for maintenance of bright plumage in the male yellowhammer.

Can female preference explain sexual dichromatism in the pied flycatcher, Ficedula hypoleuca?

How important female choice is for the evolution of male secondary sexual characteristics is controversial. Two field and one laboratory experiment, using the pied flycatcher, were performed to test the female choice aspect of sexual selection. In addition, non-manipulative data from 5 years are presented. The observational data suggest a slight preference for dark males by females but in field experiments in which males had territories at random sites (i.e. they did not choose a territory) or the colour of concurrently arriving males was altered, there was no preference for darker ones. Similarly, oestradiol-treated females did not prefer black or brown males in the laboratory. Thus, there is little support for the idea that female choice has been an important mechanism in the evolution of sexual dichromatism in the pied flycatcher.

Design proposal of electrical system for linear generator wave power plants

This paper describes an electrical system layout for a wave power plant connecting linear generators to the grid. The electrical power out from the wave energy converters must be converted before they can be connected to the grid. The conversion is carried out in marine substations that will be placed on the seabed. The paper presents experimental power data from a wave energy converter that has been in operation at the Lysekil research site since March 2006. Moreover, results and analyses from experiments and simulations from tests with the generator connected to a rectifier and filter are presented. A simulation is made to show the difference between having the generator connected to a linear load and a nonlinear load, which would be the case when the generator is connected to the grid.

Converting kinetic energy in small watercourses using direct drive generators

Tidal currents, ocean currents and unregulated watercourses are all large sources of energy that can be converted into electricity. Several technical and economical solutions within this research area have been demonstrated. In literature there exists two different turbine types, horizontal and vertical axis. The present paper focuses on the design of a permanent magnetized generator directly coupled to a vertical axis turbine. The proposed theoretical concept is adapted to data measurements regarding water current velocities and flow profiles from a Swedish watercourse. A high electromagnetic efficiency of 90% is obtained.Copyright