Medici D.,Garrad Hassan Italia |
Ivanell S.,Gotland University |
Dahlberg J.-A.,Vattenfall |
Alfredsson P.H.,KTH Royal Institute of Technology
Wind Energy | Year: 2011
The flow upstream a wind turbine is studied in order to investigate blockage effects. We use rotating wind turbine models in a wind tunnel, where velocity measurements have been made both with hot-wire anemometry up to approximately 4.5 diameters (D) upstream the turbine, as well as laser particle image velocimetry measurements close to the turbine rotor. Also, numerical simulations have been carried out by means of a finite volume code. The measurements show, among other things, that the flow is affected more than 3 D upstream the rotor plane. © 2011 John Wiley & Sons, Ltd.
Ivanell S.,KTH Royal Institute of Technology |
Ivanell S.,Gotland University |
Mikkelsen R.,Technical University of Denmark |
Sorensen J.N.,Technical University of Denmark |
Henningson D.,KTH Royal Institute of Technology
Wind Energy | Year: 2010
The aim of the present paper is to obtain a better understanding of the stability properties of wakes generated by wind turbine rotors. To accomplish this, a numerical study on the stability of the tip vortices of the Tjaereborg wind turbine has been carried out. The numerical model is based on large eddy simulations of the Navier-Stokes equations using the actuator line method to generate the wake and the tip vortices. To determine critical frequencies, the flow is disturbed by inserting harmonic perturbations, giving rise to spatially developing instabilities. The results show that the instability is dispersive and that growth arises only for some specific frequencies and type of modes, in agreement with previous instability studies. The result indicates two types of modes; one where oscillations of neighboring vortex spirals are out of phase and one where oscillations in every vortex spiral in phase. The mode with spirals out of phase results in the largest growth with the main extension of the disturbance waves in radial and downstream directions. The out-of-phase disturbance leads to vortex pairing once the development leaves the linear stage. The study also provides evidence of a relationship between the turbulence intensity and the length of the near wake. The relationship, however, needs to be calibrated against measurements. Copyright © 2010 John Wiley & Sons, Ltd.
Sellers M.,Online Alchemy Inc. |
Sellers M.,Gotland University
Biologically Inspired Cognitive Architectures | Year: 2013
A new model of emotions that is applicable to both biological and artificial agents is proposed. The description includes theoretical foundations, internal representation, and the role of emotions in cognition. This model is based on definitions of emotions in valence and arousal space coupled with an adaptation of Maslow's hierarchy and other ideas. The resulting architecture provides for a significantly more expressive range and organization of represented emotional experience compared to other models. Requirements for a satisfactory general computational theory of emotions are applied to the new theory and analyzed in terms of (i) neurological and psychological plausibility, (ii) range and complexity of human emotional experience, (iii) applicability to learning, memory, behavior, and decision-making, and (iv) consistency with well-accepted models and general facts about emotions. The model is implemented and studied through simulations of virtual agent-based systems. Presented results support the model's applicability to perception, action selection, learning, and memory in virtual agents capable of human-like behavior. Paradigms and predictions allowing for further validation of the new model and emotion theories in general are discussed. © 2012 Elsevier B.V. All rights reserved.
Stahl E.B.,Gotland University
Novon | Year: 2010
Eight Andean species of Symplocos Jacq. (Symplocaceae) are described as new to science. They include: S. condorensis B. Sthl, S. neillii B. Ståhl, and S. vanderwerffii B. Sthl from southern Ecuador (Zamora-Chinchipe and Morona-Santiago provinces); S. golondrinae B. Sthl from northern Ecuador (Carchi Province); S. guacamayensis B. Sthl from east-central Ecuador (Napo Province); S. fragilis B. Sthl and S. ovata B. Sthl from northern Peru (Amazonas Department); and S. dolichopoda B. Sthl from southern Peru (Cusco Department). Symplocos spruceana (Miers) Grke and S. nuda Humb. & Bonpl. are reported as new to Ecuador and Peru, respectively. © Missouri Botanical Garden 2010.
Stahl B.,Gotland University
Nordic Journal of Botany | Year: 2010
Four new species of Symplocos (Symplocaceae) are described from montane forests in Peru. Symplocos cuscoënsis Ståhl (from Dept Cusco) is distinguished inter alia by enlarged floral bracts and anthers that are longer than wide, S. excoriata Ståhl (Dept Amazonas and Cajamarca) by the exfoliating bark on young shoots, S. serratifolia Ståhl (Dept Cajamarca and Cusco) by tomentulose young shoots and lower leaf surfaces as well as long petioles, and S. trichocarpa Ståhl (Dept Cajamarca) by its tuberculate young shoots and pilose fruits. Symplocos guianensis (Aubl.) Gürke is reported as new to Bolivia and S. nitens (Pohl) Benth. is reported as new to Bolivia and Peru. A key to all 67 species of Symplocos known from Ecuador, Peru and Bolivia is provided. © 2010 The Authors.
Rosenqvist G.,Norwegian University of Science and Technology |
Rosenqvist G.,Gotland University |
Berglund A.,Uppsala University
Journal of Fish Biology | Year: 2011
Male pregnancy in the family Syngnathidae (pipefishes, seahorses and seadragons) predisposes males to limit female reproductive success; sexual selection may then operate more strongly on females and female sexual signals may evolve (sex-role reversal). A bewildering array of female signals has evolved in Syngnathids, e.g. skin folds, large body size, colouration, markings on the body and elaborate courtship. These female sexual signals do not seem quantitatively or qualitatively different from those that evolve in males in species with conventional sex roles where males provide females or offspring with direct benefits. In several syngnathid species, males also evolve ornaments, females are choosy in addition to being competitive and males compete as well as choosing partners. Thus, sex roles form a continuum, spanning from conventional to reversed within this group of fishes. Cases are presented here suggesting that stronger sexual selection on females may be most extreme in species showing classical polyandry (one male mates with several females, such as many species where males brood their eggs on the trunk), intermediate in polygynandrous species (males and females both mate with more than one partner, as in many species where males brood their eggs on the tail) and least extreme, even exhibiting conventional sex roles, in monogamous species (one male mates solely with one female, as in many seahorses and tropical pipefishes). At the same time caution is needed before unanimously establishing this pattern: first, the connection between mating patterns, strength of sexual selection, sex roles and ornament expression is far from simple and straightforward, and second, knowledge of the actual morphology, ecology and behaviour of most syngnathid species is scanty. Basically only a few Nerophis, Syngnathus and Hippocampus species have been studied in any detail. It is known, however, that this group of fishes exhibits a remarkable variation in sex roles and ornamentation, making them an ideal group for the study of mating patterns, sexual selection and sexually selected signals. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.
Ahmad H.,Gotland University |
Coppens S.,ABB |
Uzunoglu B.,Gotland University
IEEE Green Technologies Conference | Year: 2013
Several large scale offshore wind farms are planned to be built far from the shores in the future. High Voltage Direct Current (HVDC) Light by ABB is an effective and reliable way to integrate this large scale wind power production to the grid. An expensive component of offshore wind park HVDC Light technology is offshore AC collector platform. The AC collector platform in the offshore wind farm HVDC link contributes significantly to the cost of the overall project. This paper investigates the comparison between two different AC topologies of an offshore wind farm connection to offshore HVDC converter platforms with and without offshore AC collector platforms. The technical feasibility of the omission of an AC collector platform from offshore wind farms connection to HVDC converter platform is investigated for the first time. In the first topology, the offshore wind farms are connected to an HVDC converter platform through offshore AC collector platforms. An offshore AC collector platform is used to collect energy from the wind farm and step up the voltages for transmission to offshore HVDC converter platform. The offshore AC collector platforms contribute significantly to the total cost and technical complexity of the HVDC connection. In the second topology, the offshore AC collector platform is removed from the circuit and the offshore wind farms are connected directly to offshore HVDC converter platform. The topological alteration of an offshore wind farm HVDC link gives rise to some technical challenges. The short circuit analysis and annual energy loss analysis is performed for these two topologies. The type of wind turbine generators, internal wind farm voltages and the distance between the wind farms and offshore HVDC converter platform are quite important factors that are investigated in this study. The short circuit analysis and loss analysis is performed for two types of wind turbine generators i.e. doubly fed induction generators (DFIG) and full conversion (FC) generators. Two internal wind farm voltage levels i.e. 33 kV and 66 kV, and three different distances i.e. 1 km, 5 km, and 10 km between the wind farms and offshore HVDC converter platform are investigated. © 2013 IEEE.
Waldeck P.,Gotland University |
Larsson K.,Gotland University |
Larsson K.,Linnaeus University
Journal of Experimental Marine Biology and Ecology | Year: 2013
Water temperature may through its effects on body mass, reproductive output and recruitment of bivalves also influence organisms higher up the food chain. The small sized Baltic blue mussel (Mytilus trossulus×. Mytilus edulis) is a dominant key species in the Baltic Sea food web and it is an important food source for sea ducks such as the common eider (Somateria mollissima) and the long-tailed duck (Clangula hyemalis) and for some species of fish. Possible links between winter water temperature and the quality of blue mussels as food for wintering sea ducks were investigated by measuring the soft body mass loss of mussels during winter in an experimental set-up and in the field. Results demonstrated that warmer water temperatures in winter had a significant negative effect on soft body mass of Baltic blue mussels. Analysed mussels, on average 15. mm in length, kept in experimental aquaria between January and March and exposed to a 3.6. °C elevated water temperature regime corresponding to conditions during mild winters, had about 11% smaller tissue dry mass in March than mussels exposed to a water temperature regime corresponding to conditions in cold winters. At two field study areas, the body mass loss of mussels from October to March in a mild winter was significant and more pronounced (15% and 19%, respectively) than in a cold winter (11% and 4% respectively). This difference is of importance because in winter and spring, sea ducks build up energy stores for the subsequent breeding season by consuming large quantities of blue mussels and the energy gain of the birds per dive will be affected by the soft body tissue content of the mussels. The results improve our possibilities to predict the seasonal and yearly variation of the quality of the main food of sea ducks and help us to better understand the causes for the variable reproductive success and the present population declines of sea ducks. The results may also improve our possibilities to model the effects on Baltic Sea food webs of possible future increases in water temperature. © 2013 Elsevier B.V.
Ronstrom O.,Gotland University
Cultural Geographies | Year: 2013
The number of islands in the world is overwhelming. In contrast, the representation of islands is all but different. This brings up fundamental questions about the relations between the discourses about islands and islands as physical spaces, between islands as metaphors and as lived realities. When representations of islands are the focus of study, what about island as locus? In essence, the underlying problem is a variation of the 'hylomorphic problem', the relationship between substance, form and matter. In this paper, I start by addressing the role of islands in my own academic branch, ethnology, and then by discussing some implications of the 'cognitive turn' in ethnology for what is considered as its primary object of study. After a brief discussion of a variation of the problem known among anthropologists as the 'locus-focus debate', I turn to a discussion of the 'real versus metaphoric employment of islands' in island studies. In the last section I return to the key issue of my own studies of islands: how to grapple with the homogeneity of 'the island' and the immense diversity of islands. © The Author(s) 2012.
Eladhari M.P.,Gotland University |
Ollila E.M.I.,Nokia Inc.
Simulation and Gaming | Year: 2012
In this article, the authors examine iterative design methods for experimental game prototype development. They recognize the area of game design as a wicked problem space, that is, an area where attempts at producing solutions change the understanding of the problems. They argue that it is vital in game-design research to build and test designs in order to explore how certain game mechanics can result in different play dynamics and play experiences. Depending on the scope of research questions and available resources, it is important to carefully plan the design process of prototypes, their development, and the testing of them. It is also important to consider what types of data to obtain, and how to treat the data, in order to acquire materials for analysis that can support the exploration of the research questions of a study. The purpose of this article is to provide a navigation aid through this process. Various methods of prototyping and types of prototypes are described, along with considerations regarding the type of game that is developed. Then, various types of play tests are presented along with recommendations, depending on timing within the production cycle and availability of test-players. Also, an overview of potential methods of obtaining data from play tests is provided. © 2012 SAGE Publications.