Change search
Refine search result
12 1 - 50 of 78
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Oldest first
  • Newest first
Select all
  • 1. Bandeira, Jefferson Vianna
    et al.
    Salim, Lecio Hannas
    Bomtempo, Virgilio Lopardi
    Moreira, Rubens Martins
    Brisset, Patrick
    Hughes, Catherine E.
    Pant, Harish Jagat
    Thereska, Jovan
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Nuclear Techniques for Monitoring Sediment Dynamics in the Coastal Zone2014In: ENGINEERING GEOLOGY FOR SOCIETY AND TERRITORY, VOL 4: MARINE AND COASTAL PROCESSES, CHAM: SPRINGER INT PUBLISHING AG , 2014, 151-155 p.Conference paper (Refereed)
    Abstract [en]

    The knowledge of sediment transport in the coastal region is of vital importance to the management of this critical interface between land and sea, where most of the world population lives. For the assessment of sediment behaviour, hydraulic and sediment measurements, bathymetric survey, mathematical and physical models, are applied. Sediment tracers provide a unique capability for understanding sediment transport assisting in sediment management which cannot be obtained any other way, whether conventional monitoring or physical and numerical models because tracers integrate all the hydrodynamic actions in time and space. Computational fluid dynamics (CFD) is now an essential tool for the management of the natural systems and is increasingly used to study the fate and behaviour of particulates and contaminants. Tracer techniques are often employed to validate hydrodynamic models to enhance confidence in the predictive value of the models. In-situ detection afforded by the use of a radioactive tracer allows accurate quantitative determination of the rate of sediment transport, compared with other tracer methods. Also, it is cost effective and safe: its radiological impact to the environment is minimal. Several case studies, performed in different regions of the world, are presented.

  • 2.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thermal Rating of a Submerged Substation for Wave Power2016In: IEEE Transactions on Sustainable Energy, ISSN 1949-3029, E-ISSN 1949-3037, Vol. 7, no 1, 436-445 p.Article in journal (Refereed)
    Abstract [en]

    The costs of offshore maintenance operations put high reliability-requirements on offshore equipment for ocean energy, especially on submerged ones. Thermal management is thus essential in the design of the prototypes of a marine substation, developed at Uppsala University, for grid interface of wave power parks. The cooling system itself should be efficient as well as reliable. Therefore, the feasibility of a completely passive cooling strategy was evaluated. The studied substation includes various power components, which dissipate heat and are installed in one pressurized vessel. Thermal cross-coupling was investigated with 3-D submodels and a thermal network model. An electric circuit was coupled to determine the rated power of the substation. The results depend mainly on the dc-voltage, the seawater temperature, and the thermal contact between the components and the hull.

  • 3.
    Björkman, Elin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Osäkerhet vid översvämningskartering av vattendrag: En kunskapsöversikt och tillämpning på MIKE 112014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Due to uncertainty in data, parameters and model structure, there may be large uncertainties in flood inundation models. Despite of this, uncertainty analysis is still rarely used by practitioners when creating flood maps. A reason why uncertainty analysis has not yet become customary in flood inundation modeling may be due to a lack of knowledge. Low availability of data can sometimes also make it more difficult to do an uncertainty analysis. Moreover, no examples exist of how uncertainties can be analyzed in MIKE 11, which is one of the most common models used in flood mapping at consultant agencies.

    The aim of this study was twofold. Firstly, to provide a general overview of current research on uncertainty and uncertainty analysis for flood inundation modeling. This in order to increase knowledge among consultants and decision makers. Secondly, to give an example of how uncertainties can be estimated in a flood inundation model created in MIKE 11 when there is limited access to data.

    The research overview showed that there is often considerable uncertainty in the discharge calculations and geometrical description in hydraulic models, and that there are many different ways to analyze the uncertainties. Some methods that are often used are Monte Carlo simulations, fuzzy sets, scenario analysis, Bayesian calibration and Generalized Likelihood Uncertainty Estimation, GLUE.

    A case study was performed in which a hydraulic model was built for the River Kungsbackaån in MIKE 11. A scenario analysis was carried out to show the uncertainties in the hydraulic model. Overall, 36 different model runs were made in which the calibration discharge, Manning's number and design flow were varied. Scenario analysis cannot provide a precise estimate of the uncertainty, it can only give a subjective estimate. The results of the scenario analysis showed that when the sea level in Kungsbackafjorden was 0,92 m the simulated water levels differed at most by 1,3 m for the 100-year discharge and by 0,41 m for the calculated maximum flow. Also, the flood extent of the two discharges were investigated. The greatest uncertainty in the extent was found in the flat areas even though the uncertainty in water levels was smaller there.

  • 4.
    Bottacin-Busolin, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Marion, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Combined role of advective pumping and mechanical dispersion on time scales of bed form-induced hyporheic exchange2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, W08518- p.Article in journal (Refereed)
    Abstract [en]

    This study analyzes the effect of advective pumping and pore scale dispersion on bed form-induced hyporheic exchange. Advection and dispersion play a competitive role in the exchange dynamics between the porous medium and the overlying stream: Advective fluxes first lead solutes deep into the bed and then back to the stream water, whereas dispersive fluxes favor the transfer of solutes deep into the bed leading to a permanent mass retention. The combined effect of advective exchange and dispersive fluxes produces complexity in the shape of the tails of the residence time distributions (RTDs), which follow at various stages of the process either a power law or an exponential decay. The seepage velocity induced by the stream gradient and, in case of a moving bed, the celerity of the translating bed forms limit the thickness of the advective hyporheic zone, inducing the RTDs to decrease rapidly at late time. This rapid decay can be preceded by a temporal region where the probability density functions (pdf's) tend to be inversely proportional to the square of time, and is followed by a region dominated by dispersion where the pdf's tend to be inversely proportional to the 3/2 power of time. The process shows distinct temporal ranges identified here by appropriate dimensionless parameters. Because of this complex exchange dynamics, models considering pure advection in the porous medium can significantly underestimate solute transfer at long time scales, whereas purely diffusive models of hyporheic exchange appear inadequate to represent the physical processes at an intermediate stage.

  • 5.
    Bottacin-Busolin, Andrea
    et al.
    WET Engn Srl, I-31033 Castelfranco Veneto, TV, Italy.
    Marion, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Musner, Tommaso
    Univ Padua, Dept Chem Proc Engn, I-35131 Padua, Italy.
    Tregnaghi, Matteo
    WET Engn Srl, I-31033 Castelfranco Veneto, TV, Italy.
    Zaramella, Mattia
    WET Engn Srl, I-31033 Castelfranco Veneto, TV, Italy.
    Evidence of distinct contaminant transport patterns in rivers using tracer tests and a multiple domain retention model2011In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 34, no 6, 737-746 p.Article in journal (Refereed)
    Abstract [en]

    Solute transport in rivers is controlled by surface hydrodynamics and by mass exchanges with distinct retention zones. Surface and hyporheic retention processes can be accounted for separately in solute transport models with multiple storage compartments. In the simplest two component model, short term storage can be associated to in-channel transient retention, e.g. produced by riparian vegetation or surface dead zones, and the long-term storage can be associated to hyporheic exchange. The STIR (Solute Transport In Rivers) multiple domain transport model is applied here to tracer test data from three very different Mediterranean streams with distinctive characteristics in terms of flow discharge, vegetation and substrate material. The model is used with an exponential residence time distribution (RTD) to represent surface storage processes and two distinct modeling closures are tested to simulate hyporheic retention: a second exponential RTD and a power-law distribution approximating a known solution for bedform-induced hyporheic exchange. Each stream shows distinct retention patterns characterized by different timescales of the storage time distribution. Both modeling closures lead to very good approximations of the observed breakthrough curves in the two rivers with permeable bed exposed to the flow, where hyporheic flows are expected to occur. In the one case where the occurrence of hyporheic flows is inhibited by bottom vegetation, only the two exponential RTD model is acceptable and the time scales of the two components are of the same magnitude. The significant finding of this work is the recognition of a strong signature of the river properties on tracer data and the evidence of the ability of multiple-component models to describe individual stream responses. This evidence may open a new perspective in river contamination studies, where rivers could possibly be classified based on their ability to trap and release pollutants.

  • 6.
    Bottacin-Busolin, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Marion, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Zaramella, Mattia
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Modellazione a tempi di residenza del trasporto di soluti nei corsi d'acqua: Applicazione al fiume Yarqon, Israele2008Conference paper (Other academic)
    Abstract [it]

    Il trasporto di soluti nei corsi d’acqua è controllato dall’idrodinamica superficiale e da scambi di massa con distinte zone di ritenzione. La propagazione a valle delle sostanze trasportate è generalmente ritardata dall’immagazzinamento temporaneo in zone morte superficiali, tipicamente zone vegetate o sacche di ritenzione laterali, e nei sedimenti sottostanti, nella cosiddetta zona iporeica. In questo articolo viene presentato un modello concettuale per il trasporto di soluti nei corsi d’acqua (STIR, Solute Transport In Rivers) nel quale i singoli processi di scambio sono rappresentati separatamente da una probabilità di “uptake” e da un’appropriata distribuzione dei tempi di residenza. Ciò rende il modello flessibile e modulare, e consente di incorporare l’effetto di una varietà di processi d’immagazzinamento e reazioni chimiche in modo dettagliato. La capacità del modello di rappresentare situazioni reali è qui dimostrata dall’applicazione al fiume Yarqon, in Israele.

  • 7.
    Bottacin-Busolin, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Singer, Gabriel
    Univ Vienna, Dept Freshwater Ecol.
    Zaramella, Mattia
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Battin, Tom
    Univ Vienna, Dept Freshwater Ecol.
    Marion, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Effects of Streambed Morphology and Biofilm Growth on the Transient Storage of Solutes2009In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 43, no 19, 7337-7342 p.Article in journal (Refereed)
    Abstract [en]

    Microbial biofilms are the prime site of nutrient and contaminant removal in streams. It is therefore essential to understand how biofilms affect hydrodynamic exchange, solute transport and retention in systems where geomorphology and induced hydrodynamics shape their growth and structure. We experimented with large-scale streamside flumes with streambed landscapes constructed from graded bedforms of constant height and wavelength. Each flume had a different bedform height and was covered with a layer of gravel as substratum for benthic microbial biofilms. Biofilms developed different biomass and physical structures in response to the hydrodynamic conditions induced by the streambed morphology. Step injections of conservative tracers were performed at different biofilm growth stages. The experimental breakthrough curves were analyzed with the STIR model, using a residence time approach to characterize the retention effects associated with biofilms. The retained mass of the solute increased with biofilm biomass and the biofilm-associated retention was furthermore related to bedform height We tentatively relate this behavior to biofilm structural differentiation induced by bed morphology, which highlights the strong linkage between geomorphology, hydrodynamics, and biofilms in natural streams and provide important clues for stream restoration.

  • 8.
    Bottacin-Busolin, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Tait, Simon
    Univ Bradford, Sch Engn Design & Technol.
    Marion, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Chegini, Amir
    Univ Guilan, Dept Civil Engn, Fac Engn.
    Tregnaghi, Matteo
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Probabilistic description of grain resistance from simultaneous flow field and grain motion measurements2008In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 44, no 9, W09419- p.Article in journal (Refereed)
    Abstract [en]

    Experiments were carried out using a mobile gravel bed placed in a tilting flume with a modified particle image velocimetry (PIV) system. Individual grain movements were surveyed using data from time series of images. Near-bed velocity flow field measurements were made simultaneously above the same area of the sediment surface by applying cross-correlation techniques to the collected plan view images. Statistics of grain motions were collected through a semiautomatic procedure. Significant changes in the flow field were observed in the proximity of the entrained or deposited particles. A strong correlation is shown between the changes in the local streamwise and lateral velocity and the movement of the grains. The theory of Grass is revisited and developed based on the experimental results. The probability distribution of individual grain resistance has been derived from the statistics of the near-bed velocity field and of the entrainment risk.

  • 9.
    Bottacin-Busolin, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Tregnaghi, Matteo
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Marion, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Tait, Simon
    Univ Bradford, Sch Engn Design & Technol, Bradford BD7 1DP, W Yorkshire, England.
    Misurazioni del campo di moto in prossimità di grani in movimento2006Conference paper (Refereed)
    Abstract [it]

    È stata condotta una serie di esperimenti utilizzando una canaletta di laboratorio a fondo inclinabile ed un avanzato sistema PIV (Particle Image Velocimetry). L’apparato sperimentale ha permesso un’indagine a scala di grano delle condizioni di movimento incipiente. Sul fondo della canaletta si è disposto un letto di materiale granulometrico uniforme, che nelle prove è stato sottoposto all’azione continua di una portata d’acqua costante. Il regime idrodinamico approssima il moto uniforme della corrente e la condizione di incipiente movimento dei grani. Ciascun test è stato condotto per una durata di 10 – 18 ore, durante la quale sono state registrate misurazioni per periodi di circa cinque minuti ad intervalli regolari. Il campo di moto istantaneo è stato misurato all’interno di un’area di circa 400 cm2, posta su un piano inizialmente parallelo al letto, ad una distanza da esso di circa 5 mm. Un apposito software ha consentito la costruzione delle matrici del campo di velocità istantaneo, tramite la tecnica di cross-correlazione delle immagini applicata a particelle traccianti. Mediante una fotocamera digitale si sono ottenute, inoltre, delle sequenze di foto della superficie dei sedimenti, ognuna delle quali è contemporanea ad una misura del campo di moto. Tramite una procedura semi-automatica di elaborazione dei dati è stata prodotta una statistica riguardante il moto dei sedimenti. Analizzando le sequenze è stato possibile riconoscere lo spostamento dei grani superficiali; in seguito, osservando l’andamento temporale delle velocità in prossimità delle particelle in movimento, sono stati individuati dei cambiamenti del campo di moto locale che si verificano contemporaneamente alla loro rimozione o deposizione. Tali variazioni di velocità, che possono interessare la componente longitudinale e laterale o le rispettive fluttuazioni dalla media, appaiono una diretta conseguenza del moto delle particelle. È inoltre rilevante la correlazione tra “salti” positivi di velocità in corrispondenza di un grano che viene mosso e “salti” negativi nel caso di un grano che si deposita.

  • 10.
    Bozzi, S.
    et al.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Bizzozero, F.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Gruosso, G.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Passoni, G.
    Politecn Milan, Dipartimento Elettron Informaz & Bioingn, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy..
    Giassi, Marianna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analysis of Interaction of Point Absorbers' Arrays for Seawave Electrical Energy Generation in Italian Seas2016In: 2016 International Symposium On Power Electronics, Electrical Drives, Automation And Motion (SPEEDAM), 2016, 1369-1374 p.Conference paper (Refereed)
    Abstract [en]

    This work focuses on interactions between wave energy converters (WEC) in array configuration. The arrays are simulated in the time domain by a coupled hydrodynamic electromagnetic model. The hydrodynamic parameters of the model are estimated by boundary element code while the electrical ones are obtained by finite element code. Wave parks of two and four devices are simulated considering different layouts. The ultimate goal of the work is to identify the optimal array design at four Italian locations. The results show that: (i) it is possible to find an array configuration which performs better than four isolated devices, at each study sites, (ii) the highest energy production is obtained with the linear layout at all the locations, (ii) optimum WEC distance varies between ten and twenty diameters, depending on the deployment site and (iv) the difference in energy production between the best and worst array configuration (i.e. over all the possible combinations of geometrical layout, spatial orientation and WEC distance) ranges from 3% to 7%, depending on the deployment site..

  • 11.
    Brandt, S. Anders
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management, Land management, GIS.
    Lim, Nancy J.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management, Land management, GIS.
    Visualising DEM-related flood-map uncertainties using a disparity-distance equation algorithm2016In: The spatial dimensions of water management: Redistribution of benefits and risks / [ed] A. H. Schumann, G. Blöschl, A. Castellarin, J. Dietrich, S. Grimaldi, U. Haberlandt, A. Montanari, D. Rosbjerg, A. Viglione, and S. Vorogushyn, Göttingen: Copernicus Publications on behalf of International Association of Hydrological Sciences (IAHS) , 2016, 153-159 p.Conference paper (Refereed)
    Abstract [en]

    The apparent absoluteness of information presented by crisp-delineated flood boundaries can lead tomisconceptions among planners about the inherent uncertainties associated in generated flood maps. Even mapsbased on hydraulic modelling using the highest-resolution digital elevation models (DEMs), and calibrated withthe most optimal Manning’s roughness (n) coefficients, are susceptible to errors when compared to actual floodboundaries, specifically in flat areas. Therefore, the inaccuracies in inundation extents, brought about by thecharacteristics of the slope perpendicular to the flow direction of the river, have to be accounted for. Instead ofusing the typical Monte Carlo simulation and probabilistic methods for uncertainty quantification, an empiricalbaseddisparity-distance equation that considers the effects of both the DEM resolution and slope was used tocreate prediction-uncertainty zones around the resulting inundation extents of a one-dimensional (1-D) hydraulicmodel. The equation was originally derived for the Eskilstuna River where flood maps, based on DEM dataof different resolutions, were evaluated for the slope-disparity relationship. To assess whether the equation isapplicable to another river with different characteristics, modelled inundation extents from the Testebo Riverwere utilised and tested with the equation. By using the cross-sectional locations, water surface elevations, andDEM, uncertainty zones around the original inundation boundary line can be produced for different confidences.The results show that (1) the proposed method is useful both for estimating and directly visualising modelinaccuracies caused by the combined effects of slope and DEM resolution, and (2) the DEM-related uncertaintiesalone do not account for the total inaccuracy of the derived flood map. Decision-makers can apply it to alreadyexisting flood maps, thereby recapitulating and re-analysing the inundation boundaries and the areas that areuncertain. Hence, more comprehensive flood information can be provided when determining locations whereextra precautions are needed. Yet, when applied, users must also be aware that there are other factors that caninfluence the extent of the delineated flood boundary.

  • 12.
    Brandt, S. Anders
    et al.
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management.
    Lim, Nancy Joy
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management.
    Importance of river bank and floodplain slopes on the accuracy of flood inundation mapping2012In: River Flow 2012: Volume 2 / [ed] Rafael Murillo Muñoz, Leiden, The Netherlands: CRC Press / Balkema (Taylor & Francis) , 2012, 1015-1020 p.Conference paper (Refereed)
    Abstract [en]

    Effective flood assessment and management depend on accurate models of flood events, which in turn are strongly affected by the quality of digital elevation models (DEMs). In this study, HEC-RAS was used to route one specificwater discharge through the main channel of the Eskilstuna River, Sweden. DEMs with various resolutions and accuracies were used to model the inundation. The results showed a strong positive relationship between the quality of theDEMand the extent of the inundation. However, evenDEMswith the highest resolution produced inaccuracies. In another case study, the Testebo River, the model settings could be calibrated, thanks to a surveyed old inundation event. However, even with the calibration efforts, the resulting inundation extents showed varying degrees of deviation from the surveyed flood boundaries. Therefore, it becomes clear that not only does the resolution of the DEM impact the quality of the results; also, the floodplain slope perpendicular to the river flow will impact the modelling accuracy. Flatter areas exhibited the greatest predictive uncertainties regardless of the DEM’s resolution. For perfectly flat areas, uncertainty becomes infinite.

  • 13.
    Buck, Sine
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management.
    Determining the best location for a nature-like fishway in Gavle River, Sweden2013Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The construction of dams and hydro-power stations are some of the most common anthropogenic changes of watercourses and rivers. While being important to humans and society by providing electricity, these obstructions of watercourses can have severe consequences for the aquatic ecosystems. One consequence is that dams often hinder the important movement of migrating fish species between habitats. This can lead to decline and even extinction of important fish populations. To prevent these negative effects, a number of different fish passage systems, including nature-like fishways, have been developed. Nature-like fishways mimic natural streams in order to function as a natural corridor for a wide range of species. Planning and construction of a nature-like fishway is a complex task that often involves many different interests. In the present study a combination of multi-criteria decision analysis and least-cost path analysis is used for determining the best location for a nature-like fishway past Strömdalen dam in Gavleån, Sweden. An anisotropic least-cost path algorithm is applied on a friction-layer and a digital elevation model, and the least-cost path for a nature-like fishway is determined. The results show that the method is useful in areas of varying topography and steep slopes. However, because low slope is a very important factor when constructing a nature-like fishway, slope becomes the dominating factor in this analysis at the expense of e.g. distance to roads. Combining the methods with results from biological studies of fish behavior and detailed hydrological modelling would provide a very strong tool for the planning of nature-like fishways.

  • 14.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Marine Current Resource Assessment: Measurements and Characterization2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increasing interest in converting energy from renewable resources into electricity has led to an increase in research covering the field of marine current energy, mainly concerning tidal currents and in-stream tidal turbines. Tides have the advantage of being predictable decades ahead. However, the tidal resource is intermittent and experiences local variations that affect the power output from a conversion system. The variability is mainly due to four aspects: the tidal regime, the tidal cycle, bathymetry at the site and weather effects. Each potential site is unique, the velocity flow field at tidal sites is highly influenced by local bathymetry and turbulence. Hence, characterizing the resource requires careful investigations and providing high quality velocity data from measurement surveys is of great importance. In this thesis, measurements of flow velocities have been performed at three kinds of sites.

    A tidal site has been investigated for its resource potential in one of all of the numerous fjords in Norway. Measurements have been performed to map the spatial and temporal variability of the resource. Results show that currents in the order of 2 m/s are present in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus have potential for in-stream energy conversion. A model is proposed that predicts peak current speed from information on tidal range at the site. A corresponding model can be set up and implemented at other similar sites affected by tides, i.e. fjord inlets connecting the ocean to a fjord or a basin.

    A river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydrokinetic power plant nearby, making the site suitable for experiments on the performance of the vertical axis turbine in its natural environment. The turbine has been run in uniform flow and measurements have been performed to characterize the extent of the wake.

    An ocean current site was a target of investigation for its potential for providing utilizable renewable energy. A measurement campaign was conducted, mapping the flow both spatially and temporally. However, the site was shown to not be suitable for energy conversion using present technique.

  • 15.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Potentialbedömning av marin strömkraft i Finnhamn: Fältmätningar och resultat2015Report (Other academic)
    Abstract [sv]

    På uppdrag av Skärgårdsstiftelsen utfördes mätningar av vattenhastigheten utanför Finnhamn i syfte att undersöka potentialen för att installera och driva ett marint strömkraftverk på platsen. Denna rapport presenterar resultaten från den undersökningen som genomförts med tvärsnittsmätningar och långtidsmätningar av vattenhastigheterna. Resultaten visar på låga vattenhastigheter under mätperioden. Slutsatsen är att platsen inte har tillräckligt stor energipotential för att vara av intresse för utbyggnad av strömkraftverk utifrån den teknik som finns idag.

  • 16.
    Carpman, Nicole
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Uppsala University.
    Resource characterization and variability studies for marine current power2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Producing electricity from marine renewable resources is a research area that develops continuously. The field of tidal energy is on the edge to progress from the prototype stage to the commercial stage. However, tidal resource characterization, and the effect of tidal turbines on the flow, is still an ongoing research area in which this thesis aims to contribute.

    In this thesis, measurements of flow velocities have been performed at three kinds of sites. Firstly, a tidal site has been investigated for its resource potential in a fjord in Norway. Measurements have been performed with an acoustic Doppler current profiler to map the spatial and temporal characteristics of the flow. Results show that currents are in the order of 2 m/s in the center of the channel. Furthermore, the flow is highly bi-directional between ebb and flood flows. The site thus has potential for in-stream energy conversion. Secondly, a river site serves as an experimental site for a marine current energy converter that has been designed at Uppsala University and deployed in Dalälven, Söderfors. The flow rate at the site is regulated by an upstream hydro power plant, making the site suitable for experiments on the performance of the vertical axis turbine in a natural environment. The turbine was run in steady discharge flows and measurements were performed to characterize the extent of the wake. Lastly, at an ocean current site, the effect that transiting ferries may have on submerged devices was investigated. Measurements were conducted with two sonar systems to obtain an underwater view of the wake caused by a propeller and a water jet thruster respectively.

    Furthermore, the variability of the intermittent renewable sources wind, solar, wave and tidal energy was investigated for the Nordic countries. All of the sources have distinctly different variability features, which is advantageous when combining power generated from them and introducing it on the electricity grid. Tidal variability is mainly due to four aspects: the tidal regime, the tidal cycle, local bathymetry causing turbulence, asymmetries etc. and weather effects. Models of power output from the four sources was set up and combined in different energy mixes for a “highly renewable” and a “fully renewable” scenario. By separating the resulting power time series into different frequency bands (long-, mid-, mid/short-, and short-term components) it was possible to minimize the variability on different time scales. It was concluded that a wise combination of intermittent renewable sources may lower the variability on short and long time scales, but increase the variability on mid and mid/short time scales.

    The tidal power variability in Norway was then investigated separately. The predictability of tidal currents has great advantages when planning electricity availability from tidal farms. However, the continuously varying tide from maximum power output to minimum output several times per day increases the demand for backup power or storage. The phase shift between tidal sites introduces a smoothing effect on hourly basis but the tidal cycle, with spring and neap tide simultaneously in large areas, will inevitably affect the power availability.

  • 17.
    Carpman, Nicole
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Measurements of tidal current velocities in the Folda fjord, Norway, with the use of a vessel mounted ADCP2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 8A: Ocean Engineering, 2014Conference paper (Refereed)
    Abstract [en]

    Measurements of tidal current water velocities is an important first step in evaluating the potential for a tidal site to be used as a renewable energy resource. For this reason, on site measurements are performed at the inlet of a fjord situated at the coast of Norway. The site has an average width of 580 m and adepth of 10-15 m which is narrow and shallow enough to give rise to water velocities that can be of use for energy conversion. With the use of an Acoustic Doppler Current Profiler (ADCP) cross-section measurements are conducted along four transects. The measurements covered flood and ebb currents around one tide and the data give a first approximation of the magnitude and distribution of the flow field. Depth averaged mean current velocities are calculated along the transects for horizontal bins with sizes in the order of 50 x 50 m. Maximum mean velocity for the flood currents were 1.31 m/s and 1.46 m/s for the ebb currents. The measurements show that even a small amount of data can give an indication of the potential and characteristics ofthe site.

  • 18.
    Carpman, Nicole
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tidal resource characterization in the Folda Fjord, Norway2016In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 13, 27-44 p.Article in journal (Refereed)
    Abstract [en]

    For tidal-stream energy industry to be fully realized, lower velocity sites and fjords should be developed. Finding new prospective sites for in-stream energy extraction from tidal currents is an area of ongoing research. In this paper, the tidal flow at a fjord inlet has been characterized using acoustic Doppler current profiler (ADCP) measurements. This work is based on two survey measurement techniques: transect measurements to map the spatial variability, and seabed measurements to map the temporal variability. The data was analyzed in terms of characterizing metrics, to ensure they are comparable with other resource assessments. Results show that currents exceed 1 m/s for 38% of the time with peak currents of 2.06 m/s at hub height (middle of the water column) and the directional asymmetry is less than 1° between ebb and flood, indicating a truly bi-directional flow. A simple prediction model is proposed which allows peak current speeds to be accurately predicted in the channel center from tidal range data using a linear relationship. The relationship is shown to be strong, with a correlation coefficient of 0.98 at hub height, and a standard variation typically less than 10 cm/s. Furthermore, it is show that a minimum of 9 days of measurements are required to set up the model, although it takes 29 days to reduce the error in peak speed to less than 1%. However, the error is expected to vary depending on where in the monthly tidal cycle the survey begins, it is thus recommended to measure around spring tide if the measurement period is short.

  • 19.
    Carpman, Nicole
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Thomas, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Tidal current phasing along the coast of Norway2016Conference paper (Refereed)
    Abstract [en]

    Tidal currents provide an intermittent source of renewable energy. A high degree of intermittency is unfavorable in the existing power system. However, by aggregating tidal power from sites with variable tidal phase a more firm power outpu tmay be achieved. In this paper, the tidal current phasing between 114 potential tidal energy sites along the Norwegian coast is investigated. Time series of tidal currents are generated with a model that considers the variation in current strength due to the variability in the semi-diurnal tidal cycle (spring to neap, flood to ebb, first to second daily tide etc.). From these, available kinetic energy in the natural flow is calculated. A constant conversion rate is then applied to give the power output at each site. Three scenarios, with varying number of sites and energy extraction, are investigated. The variability in each scenario is quantified on different time scales by filtering the aggregated power and calculate standard deviation and step change. It is found that the variability can be lowered by choosing sites with an advantageous time lag and limit the power output from the most energetic sites. As expected, smoothing is most distinct on short time scales.

  • 20. Castellucci, Valeria
    Tidal Effect Compensation System for Wave Energy Converters2011Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
  • 21.
    Castellucci, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Impact of Tidal Level Variations on the Wave Energy Absorption at Wave Hub2016In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 10, 843Article in journal (Refereed)
    Abstract [en]

    The energy absorption of the wave energy converters (WEC) characterized by a limited stroke length - like the point absorbers developed at Uppsala University-depends on the sea level variation at the deployment site. In coastal areas characterized by high tidal ranges, the daily energy production of the generators is not optimal. The study presented in this paper quantifies the effects of the changing sea level at the Wave Hub test site, located at the south-west coast of England. This area is strongly affected by tides: the tidal height calculated as the difference between the Mean High Water Spring and the Mean Low Water Spring in 2014 was about 6.6 m. The results are obtained from a hydro-mechanic model that analyzes the behaviour of the point absorber at the Wave Hub, taking into account the sea state occurrence scatter diagram and the tidal time series at the site. It turns out that the impact of the tide decreases the energy absorption by 53%. For this reason, the need for a tidal compensation system to be included in the design of the WEC becomes compelling. The economic advantages are evaluated for different scenarios: the economic analysis proposed within the paper allows an educated guess to be made on the profits. The alternative of extending the stroke length of the WEC is investigated, and the gain in energy absorption is estimated.

  • 22.
    Chatzigiannakou, Maria A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dolguntseva, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Offshore Deployment of Point Absorbing Wave Energy Converters with a Direct Driven Linear Generator Power Take-Off at the Lysekil Test Site2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, 2014Conference paper (Refereed)
    Abstract [en]

    Within the year 2013, four linear generators with point absorber buoy systems were deployed in the Lysekil test site. Until now, deployments of these point absorbing wave energy converters have been expensive, time consuming, complicated and raised safety issues. In the present paper, we focus on the analysis and optimization of the offshore deployment process of wave energy converters with a linear generator power take-off which has been constructed by Uppsala University. To address the crucial issues regarding the deployment difficulties, case study of previous offshore deployments at the Lysekil test site are presented regarding such parameters as safety, cost and time efficiency. It was discovered that the deployment process can be improved significantly, mainly by using new technologies, e.g., new specialized deployment vessels, underwater robots for inspections and for connecting cables and an automatized pressurizing process. Addressing the main deployment difficulties and constrains leads us to discovery of methods that makes offshore deployments more cost-efficient and faster, in a safety context.

  • 23.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Flow characteristics of bottom outlets with moving gates2010In: Journal of Hydraulic Research, ISSN 0022-1686, Vol. 48, no 4, 476-482 p.Article in journal (Refereed)
    Abstract [en]

    This study investigates the discharge characteristics of a bottom outlet with a moving gate by Flow3D. Experimental results for a scale model outlet of the Aswan Dam, Egypt, were used. Two different flow features were found. Pressurized flow established if the flume was filled and then the gate was slowly opened. However, a free surface flow occurred if the gate was fully opened and the entire flume was slowly flooded with water. The numerical simulations successfully captured the two flow patterns as well as the discharges and water surface profiles. The discharges were predicted with sufficient accuracy using the first-order momentum advection scheme. In comparison with the k-epsilon turbulence model, the Re-Normalization Group model yields the best agreement with the experiments. The model performed with similar accuracy for both model and prototype cases.

  • 24.
    Fabian, Mark
    et al.
    SUNY Coll Environm Sci & Forestry, Dept Environm Resources Engn, Baker Labs 423, Syracuse, NY 13210 USA.
    Endreny, Theodore
    SUNY Coll Environm Sci & Forestry, Dept Environm Resources Engn, Baker Labs 423, Syracuse, NY 13210 USA.
    Bottacin-Busolin, Andrea
    Water & Environm Technol Engn Srl, I-31033 Treviso, Italy.
    Lautz, Laura
    Syracuse Univ, Dept Earth Sci, Heroy Geol Lab 204, Syracuse, NY 13244 USA.
    Seasonal variation in cascade-driven hyporheic exchange, northern Honduras2011In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 25, no 10, 1630-1646 p.Article in journal (Refereed)
    Abstract [en]

    A characterization of hyporheic exchange for dry and wet season baseflow, as well as partially dewatered discharge, was done in Prieta Creek, a first-order cascade in northern Honduras. The cascade had discharges from 1 to 15 1 s(-1), had average slopes of 12%, pool spacing of 3 m, and shallow substrate of sand and gravel. Tracer tests were conducted in a 15-m sub-reach, a length considered to be adequate for the experiment based on the DaI test, a ratio of exchange and transport processes. In the three tests, between 9 and 18% of tracer was not recovered, possibly due to entrainment in flowpaths passing beneath the downstream monitoring location. Tracer data were analysed by the one-dimensional transport with inflow and storage (OTIS) transient storage model (TSM) to derive standard exchange parameters, and by the solute transport in rivers (STIR) model to examine hyporheic residence time distributions (RTDs). The best fit of the observed tracer breakthrough curves was obtained by using the STIR model with a combination of two exponential RTDs to represent hyporheic retention. With increasing discharge, the OTIS model predicted increasing storage exchange fluxes and exchange coefficients and decreasing storage zone areas and transient storage times, which are trends supported by riparian and streambed piezometric head data. Riparian water levels rose during the transition from the dry to wet season, which could constrict the hyporheic storage zone. Thirteen of the 19 streambed piezometers recorded seasonal changes in hydraulic gradients and flux direction, with fewer yet stronger upwelling zones during higher discharges. The MODFLOW model missed the observed seasonal changes, possibly due to subtle changes in the seasonal change in water surface profiles. We conclude that partially dewatered dry season exchange, compared to wet season exchange, was initiated and terminated with smaller pressure gradients and, in different streambed locations, was smaller in volume, had longer residence times, and may connect with deeper and longer flow paths.

  • 25.
    Garcia Teran, Jessica
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Positional Analysis of Wave Power: Applied at the Pacific Ocean in Mexico.2013Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The energy transition has started. The key is to find an alternative to uneconomical and unsustainable energy production. In this sense it is a challenge to develop renewable energy technologies suitable for the present and proper for the future. Uppsala University is driving the Lysekil project at its Division of Electricity. The aim is to design an environmentally friendly energy system with wave energy converters (WECs) that are simple and strong in design. However, little has been done to know more about its economically feasibility and the social impact of its benefits. Therefore, this research focuses on a positional analysis of a 3 MW Wave Power Park to understand the relevant aspects of implementing this kind of technology. The target area will be at Rosarito, Baja California at the Pacific Ocean in the Northeast of Mexico, a region experiencing increasing energy demand. This thesis combines technical, economical and social aspects. The technical part describes how the device works. The analysis is complemented by describing the current energy situation in Mexico and the social benefits of sustainable energy. Finally, the economical analysis is presented, it is focused on the perspective of the Merchant Power Plant. The review shows that wave power could be economically viable due to its high degree of utilisation. Energy diversification and security, economic and sustainable development, and clean energy are some of the advantages of wave power. Therefore, wave power is an interesting alternative for generating electricity in Mexico. However, the energy sector is highly subsidised, making it difficult for new technologies to enter the market without government participation. Another finding is that in the long run if the equipment cost decreases or subsidies are applied, the technology might be successfully implemented. Environmental consequences are described briefly, concluding that little is known and more research is needed.

    The environmental constraints, economic implications and uncertainties of a high energy future are disturbing. In that sense, renewable energy appears to be unequivocally better than rely to a greater extent on fossil fuels, in the sense that they offer a sustainable development and less environmental damage. 

  • 26.
    Gröndahl, Fredrik
    KTH, School of Industrial Engineering and Management (ITM), Industrial Ecology.
    Chemical Analysis of Water and Sediments - Coastman - Estonia, Fauna and Flora2005In: Report to the Department of Environmental Engineering, Tallinn, Technical University, Estonia: European Comission in Estonia , 2005Chapter in book (Refereed)
  • 27.
    Guerrero, José-Luis
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Westerberg, Ida
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Halldin, Sven
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Lundin, Lars-Christer
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Xu, Cong-Yu
    Exploring the hydrological robustness of model-parameter values with alpha shapes2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 10, 6700-6715 p.Article in journal (Refereed)
    Abstract [en]

    Estimation of parameter values in hydrological models has gradually moved from subjective, trial-and-error methods into objective estimation methods. Translation of nature's complexity to bit operations is an uncertain process as a result of data errors, epistemic gaps, computational deficiencies, and other limitations, and relies on calibration to fit model output to observed data. The robustness of the calibrated parameter values to these types of uncertainties is therefore an important concern. In this study, we investigated how the hydrological robustness of the model-parameter values varied within the geometric structure of the behavioral (well-performing) parameter space with a depth function based on α shapes and an in-depth posterior performance analysis of the simulations in relation to the observed discharge uncertainty. The α shape depth is a nonconvex measure that may provide an accurate and tight delimitation of the geometric structure of the behavioral space for both unimodal and multimodal parameter-value distributions. WASMOD, a parsimonious rainfall-runoff model, was applied to six Honduran and one UK catchment, with differing data quality and hydrological characteristics. Model evaluation was done with two performance measures, the Nash-Sutcliffe efficiency and one based on flow-duration curves. Deep parameter vectors were in general found to be more hydrologically robust than shallow ones in the analyses we performed; model-performance values increased with depth, deviations to the observed data for the high-flow aspects of the hydrograph generally decreased with increasing depth, deep parameter vectors generally transferred in time with maintained high performance values, and the model had a low sensitivity to small changes in the parameter values. The tight delimitation of the behavioral space provided by the α shapes depth function showed a potential to improve the efficiency of calibration techniques that require further exploration. For computational reasons only a three-parameter model could be used, which limited the applicability of this depth measure and the conclusions drawn in this paper, especially concerning hydrological robustness at low flows.

  • 28. Gulbinskas, Saulius
    et al.
    Mileriene, Rosita
    KTH, School of Industrial Engineering and Management (ITM), Industrial Ecology.
    Blažauskas, Nerijus
    Beach nourishment for shore protection in the Lithuanian Baltic sea coast2011In: Artificial beaches, artificial islands and other structures in the coastal and offshore areas: Proceedings of the 2nd International Conference 'Construction of the Artificial Lands in the Coastal and Offshore Areas' / [ed] Khabidov, A.Sh., Publishing House of the Siberian Branch of Russian Academy of Sciences , 2011Conference paper (Refereed)
  • 29.
    Gustafsson, David
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Ahlberg, Jesper
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
    Granlund, Nils
    Luleå University of Technology.
    Lindström, Göran
    Sveriges meteorologiska och hydrologiska institut.
    Wetterhall, Fredrik
    Sveriges meteorologiska och hydrologiska institut.
    Lundberg, Angela
    Luleå University of Technology.
    Distribuerade system för förbättrade snö- och avrinningsprognoser. Integration i hydrologiska modeller: Delrapport 12009Report (Other academic)
  • 30.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Jens, Engström
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mikael, Eriksson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hann, Martyn
    Plymouth University.
    Ransley, Edward
    Plymouth University.
    Greaves, Deborah
    Plymouth University.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wave loads on a point-absorbing wave energy device in extreme waves2015Conference paper (Refereed)
  • 31.
    Hai, Ling
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lejerskog, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Force in the connection line for a wave energy converter: simulation and experimental setup2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, San Francisco, USA, 2014Conference paper (Refereed)
    Abstract [en]

    In order to capture ocean wave energy and transform it into electric energy, Uppsala University has developed a point absorber wave energy converter (AVEC) for electricity production. For a better understanding of a torus shaped buoy's performance, this paper conducts a force analysis under linear conditions, to investigate the hydrodynamic characteristic and line force differences between the torus buoy that is going to be deployed, and two similar cylindrical buoys. The result reveals the line force fromthis torus buoy is roughly 5% larger than from cylindrical buoys for the most energy dense wave climate in Lysekil test site, and negative added mass phenomena won't have a significant impact for the line force. To measure the line force, a force measurement system has been designed. A detailed description is given on the design of the 500 kN force measurement system, and the major differences compared with former force measurement systems. Onshore test result has also been presented. With the force measurement experiment, hydrodynamic analysis for torus buoy can be validated when the system performs linearly, and extreme force for storm weather can be monitored to provide information for future WEC structure's mechanical design.

  • 32.
    Hai, Ling
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Southampton, Energy & Climate Change Div, Fac Engn & Environm, Southampton, Hants, England.
    Modelling a point absorbing wave energy converter by the equivalent electric circuit theory: A feasibility study2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, 164901Article in journal (Refereed)
    Abstract [en]

    There is a need to have a reliable tool to quickly assess wave energy converters (WECs). This paper explores whether it is possible to apply the equivalent electric circuit theory as an evaluation tool for point absorbing WEC system modelling. The circuits were developed starting from the force analysis, in which the hydrodynamic, mechanical, and electrical parameters were expressed by electrical components. A methodology on how to determine the parameters for electrical components has been explained. It is found that by using a multimeter, forces in the connection line and the absorbed electric power can be simulated and read directly from the electric circuit model. Finally, the circuit model has been validated against the full scale offshore experiment. The results indicated that the captured power could be predicted rather accurately and the line force could be estimated accurately near the designed working condition of the WEC.

  • 33. Hammar, Linus
    et al.
    Larsson, Kjell
    Linnaeus University, Faculty of Technology, Kalmar Maritime Academy.
    Havsplanering kan minska konflikter och främja helhetssyn på miljön2017In: Åtgärder för att minska sjöfartens påverkan på havsmiljön, Göteborg: Havsmiljöinstitutet , 2017, 18-19 p.Chapter in book (Other academic)
    Abstract [sv]

    Sjöfart och fiske har länge haft havet nästan för sig själva. Men på senare år har fler näringar visat intresse för att använda havet. Medan sjöfart och fiske regleras med breda penseldrag, behöver energiutvinning, vattenbruk och sandutvinning söka miljötillstånd för varje enskilt projekt. Med havsplanering finns nu möjlighet att planera för alla anspråk på en gång.

  • 34.
    Hong, Yue
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Castellucci, Valeria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Linear generator-based wave energy converter model with experimental verification and three loading strategies2016In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 10, no 3, 349-359 p.Article in journal (Refereed)
    Abstract [en]

    Within the Lysekil wave energy research project at the Swedish west coast, more than ten Wave Energy Converters (WECs) prototypes have been developed and installed in an ocean based test site. Since 2006 various experiments have been conducted and the generated electricity was delivered to shore at a nearby island. While experiments are essential for the development of wave energy converters, theoretical studies and simulations are an important complement – not only in the search for advanced designs with higher efficiency, but also for improving the economic viability of the studied concepts. In this paper a WEC model is presented. The model consists of three subsystems: i) the hydrodynamic source, ii) the linear generator model, and iii) the electrical conversion system. After the validation with the experimental results at the research site, the generator model is connected to three passive load strategies – linear resistive load, passive rectification and resonance circuit. The paper focuses on analysing the operation of the model coupled with three load cases. The results prove that the WEC model correctly simulates the linear generator developed in the Lysekil Project. Moreover, the comparison among different load cases is made and discussed. The results gives an indication of the efficiency of energy production as well as the force ripples and resulting mechanical loads on the wave energy converters.

  • 35.
    Hultman, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Linder, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Robotized stacking of the Uppsala University wave energy converter generator stator2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, 2014Conference paper (Refereed)
  • 36.
    Johansson, Alfred
    Halmstad University, School of Business, Engineering and Science.
    Hållbar vattenkraft i Nissan: En förstudie och konsekvensutredning över förutsättningarna för ökade vandringsmöjligheter med nya fiskvägar.2015Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The hydropower from Nissan River is of national interest and produces annually 230 GWh from the twelve power stations in the main flow. For modified waters a consideration between the power production and the biological values has to be made. This reports serves as a pre-study for Nissans Vattenråd. It tries to evaluate some of the biological values in the Nissan basin and map the power production in the area. And the size and value of lost power production from new fishways for the twelve stations in the main flow.

    The investment of new fishways is calculated using simplified templates with values from the business. The cost and loss of power due to new fishways are calculated for three cases: fish friendly grates for the power station inlet and bypass for migration. Fish friendly grate and vertical-slot fish passage for migration. The last case is called “scenario” and is a combination with the most suited solution for each station. This includes a restoration of the creek, with maintained power production, for the two stations closest to the ocean.

    The cost for fish friendly grade and bypass for al stations is about 207 mskr and for vertical-slot fish passage 125 mskr. They both result in a loss of power production of 12 GWh/year, corresponding to a value of 3,2 mskr (NordSpot sale price only) annually. Case “scenario” costs 177 mskr and loses additionally 4,2 GWh/year.

    In the overview, large parts of the Nissan runoff has difficulties reaching “god ecological status” which is the goal set for 2021. This goal can be extended to 2027. The main problem is chemical effect of acidification and mercury in the ground, as well as connectivity issue caused by dams and culverts. Salmon and sea trout could earlier migrate to Nissafors and is limited to the lower parts of Nissan to Oskarström. Many of the tributary waters have high biological values. The existing fishways have questioned functionality and delays fish migration today. Before decisions are made about increasing fishways the advice is to do further studies about the breeding grounds. It’s also possible to identify positive cash flows from an increase in fish migration.

  • 37.
    Kalantari, Zahra
    et al.
    Kungliga Tekniska Högskolan.
    Briel, A
    Kungliga Tekniska Högskolan.
    Lyon, Steve
    Stockholms universitet.
    Olofsson, Bo
    Kungliga Tekniska Högskolan.
    Folkeson, Lennart
    Kungliga Tekniska Högskolan.
    On the utilization of hydrological modelling for road drainage design under climate and land use change2014In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 475, 97-103 p.Article in journal (Refereed)
    Abstract [en]

    Road drainage structures are often designed using methods that do not consider process-based representations of a landscape's hydrological response. This may create inadequately sized structures as coupled land cover and climate changes can lead to an amplified hydrological response. This study aims to quantify potential increases of runoff in response to future extreme rain events in a 61 km(2) catchment (40% forested) in southwest Sweden using a physically-based hydrological modelling approach. We simulate peak discharge and water level (stage) at two types of pipe bridges and one culvert, both of which are commonly used at Swedish road/stream intersections, under combined forest clear-cutting and future climate scenarios for 2050 and 2100. The frequency of changes in peak flow and water level varies with time (seasonality) and storm size. These changes indicate that the magnitude of peak flow and the runoff response are highly correlated to season rather than storm size. In all scenarios considered, the dimensions of the current culvert are insufficient to handle the increase in water level estimated using a physically-based modelling approach. It also appears that the water level at the pipe bridges changes differently depending on the size and timing of the storm events. The findings of the present study and the approach put forward should be considered when planning investigations on and maintenance for areas at risk of high water flows. In addition, the research highlights the utility of physically-based hydrological models to identify the appropriateness of road drainage structure dimensioning

  • 38.
    Kordi, Maryam
    et al.
    National University of Ireland, National Centre for Geocomputation.
    Brandt, Anders
    University of Gävle, Faculty of Engineering and Sustainable Development, Department of Industrial Development, IT and Land Management.
    Effects of increasing fuzziness on analytic hierarchy process for spatial multicriteria decision analysis2012In: Computers, Environment and Urban Systems, ISSN 0198-9715, Vol. 36, no 1, 43-53 p.Article in journal (Refereed)
    Abstract [en]

    Multicriteria decision analysis (MCDA) involves techniques which relatively recently have received great increase in interest for their capabilities of solving spatial decision problems. One of the most frequently used techniques of MCDA is Analytic Hierarchy Process (AHP). In the AHP, decision-makers make pairwise comparisons between different criteria to obtain values of their relative importance. The AHP initially only dealt with crisp numbers or exact values in the pairwise comparisons, but later it has been modified and adapted to also consider fuzzy values. It is necessary to empirically validate the ability of the fuzzified AHP for solving spatial problems. Further, the effects of different levels of fuzzification on the method have to be studied. In the context of a hypothetical GIS-based decision-making problem of locating a dam in Costa Rica using real-world data, this paper illustrates and compares the effects of increasing levels of uncertainty exemplified through different levels of fuzzification of the AHP. Practical comparison of the methods in this work, in accordance with the theoretical research, revealed that by increasing the level of uncertainty or fuzziness in the fuzzy AHP, differences between results of the conventional and fuzzy AHPs become more significant. These differences in the results of the methods may affect the final decisions in decision-making processes. This study concludes that the AHP is sensitive to the level of fuzzification and decision-makers should be aware of this sensitivity while using the fuzzy AHP. Furthermore, the methodology described may serve as a guideline on how to perform a sensitivity analysis in spatial MCDA. Depending on the character of criteria weights, i.e. the degree of fuzzification, and its impact on the results of a selected decision rule (e.g. AHP), the results from a fuzzy analysis may be used to produce sensitivity estimates for crisp AHP MCDA methods.

  • 39.
    Larsson, Kjell
    et al.
    Linnaeus University, Faculty of Technology, Kalmar Maritime Academy.
    Eriksson, Martin
    Regler, ekonomiska styrmedel och teknik kan minska påverkan på miljön2017In: Åtgärder för att minska sjöfartens påverkan på havsmiljön. Havsmiljöinstitutets rapport 2017:2, Göteborg: Havsmiljöinstitutet , 2017, 4-6 p.Chapter in book (Other academic)
    Abstract [sv]

    I likhet med de flesta andra transportslag har sjöfart en betydande påverkan på jordens klimat, ekosystem och människors hälsa. För att långsiktigt minska de negativa effekterna på havsmiljön krävs skarpare regelverk, ny teknik och ekonomiska styrmedel, samt en samsyn mellan alla de aktörer som påverkar sjöfartens utveckling.

  • 40.
    Lejerskog, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Savin, Andrej
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Boström, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Study of the operation characteristics of a point absorbing direct driven permanent magnet linear generator deployed in the Baltic Sea2016In: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, Vol. 10, no 8, 1204-1210 p.Article in journal (Refereed)
    Abstract [en]

    To experimentally study how a wave energy converter (WEC) behaves when parameters such as weight on the translator and buoy volume are changing is of significant importance when trying to optimise the WEC system. This study presents results from a WEC deployed at the Baltic Sea near the island of Åland. Compared with earlier experiments, the weight on the translator has been significantly increased to suit the buoy volume. Experimental results show that the power output between the upward and the downward motions are comparable up to the maximum speed for the downward motion of the translator. To study the speed of the translator in downward direction a model has been derived. The model has also been used to study the impact of having a changing active area. Moreover, finite element (FE) simulations done on the generator have been compared with experimental data and show a good agreement, but at high speeds of the translator the FE simulations start to deviate from the experiments.

  • 41.
    Li, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chen, Wenchuang
    Tsinghua Univ, State Key Lab Hydrosci & Engn, Beijing 100084, Peoples R China.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bivariate joint distribution modeling of wave climate data using a copula method2016In: International Journal of Energy and Statistics, ISSN 2335-6812, Vol. 4, no 3, UNSP 1650015Article in journal (Refereed)
    Abstract [en]

    The bivariate joint distribution of the significant wave height and the wave period is of great importance in characterizing the wave climate at a wave energy converter test site. In this paper, we investigate bivariate joint distribution modeling of the wave climate at the Lysekil wave energy converter test site off the Swedish west coast. This study is based on 9 years of wave observations at the test site from 2005 to 2013. Archimedean Copulas are used for the bivariate joint distribution modeling of the significant wave height and the wave period. Measured wave data is compared with simulated wave climate data for the Lysekil test site using three Archimedean Copula models, the Clayton, Frank and Gumbel copulas. The R-squared statistical test yields a better goodness of fit for the Gumbel copula compared to the other two copulas. In addition, the Archimedean Copula method is applied to the measured wave climate data from two other sites to illustrate the general applicability. It shows that the Archimedean Copulas exhibits stable performance with good accuracy in characterizing the wave climate and they can be employed for forecasting the wave energy resource and assessing the survivability of wave energy converters.

  • 42.
    Li, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Statistical Analysis of Wave Climate Data Using Mixed Distributions and Extreme Wave Prediction2016In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 6, 396Article in journal (Refereed)
    Abstract [en]

    The investigation of various aspects of the wave climate at a wave energy test site is essential for the development of reliable and efficient wave energy conversion technology. This paper presents studies of the wave climate based on nine years of wave observations from the 2005-2013 period measured with a wave measurement buoy at the Lysekil wave energy test site located off the west coast of Sweden. A detailed analysis of the wave statistics is investigated to reveal the characteristics of the wave climate at this specific test site. The long-term extreme waves are estimated from applying the Peak over Threshold (POT) method on the measured wave data. The significant wave height and the maximum wave height at the test site for different return periods are also compared. In this study, a new approach using a mixed-distribution model is proposed to describe the long-term behavior of the significant wave height and it shows an impressive goodness of fit to wave data from the test site. The mixed-distribution model is also applied to measured wave data from four other sites and it provides an illustration of the general applicability of the proposed model. The methodologies used in this paper can be applied to general wave climate analysis of wave energy test sites to estimate extreme waves for the survivability assessment of wave energy converters and characterize the long wave climate to forecast the wave energy resource of the test sites and the energy production of the wave energy converters.

  • 43. Lin, C.
    et al.
    Kao, M. -J
    Wong, W. -Y
    Tsai, C. -P
    Chang, K. -T
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Characteristics of flow separation and hydraulic jump during run-down motion of shoaling solitary wave traveling over steep sloping bottom2016In: Proceedings of the International Offshore and Polar Engineering Conference, International Society of Offshore and Polar Engineers , 2016, 724-731 p.Conference paper (Refereed)
    Abstract [en]

    The features of velocity fields for the evolution of shoaling solitary wave, having a wave-height to water-depth ratio of 0.363 and propagating over a 1:3 sloping bottom, are investigated experimentally. A flow visualization technique using particle trajectory method and a high-speed particle image velocimetry (HSPIV) system employing a high-speed digital camera were used. This study mainly focuses on the occurrence of separated shear layer from the sloping bottom, evolved vortex structure, subsequent hydraulic jump, and curling jet of the backward breaking wave impinging upon the free surface of retreated flow during the run-down motion of the shoaling solitary wave.

  • 44.
    Lindblad, Liselotte
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baudoin, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Southampton, Engn & Environm, Energy & Climate Change, Southampton, Hants, England..
    Measurement System For Wave Energy Converter Design And Implementation2014In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9A: Ocean Renewable Energy, AMER SOC MECHANICAL ENGINEERS , 2014Conference paper (Refereed)
    Abstract [en]

    A Wave Energy Converter (WEC) measurement system has been constructed and installed with the purpose to measure, log and evaluate the WEC's performance during operation at sea. The WEC is to be deployed at Uppsala University's wave power research site in Lysekil on the west coast of Sweden. In designing such a system the key research objectives has been (1) to study the risk of overheating due to high currents in the stator windings, (2) to evaluate how the WEC's outer structure withstands drag and bending forces from the buoy line and (3) to construct a detection system which indicates if water leaks into the generator. The measurement system was designed to collect data essential to study these key objectives. Transducers were used to measure: buoy line force, translator position, phase currents, bending and tensile strain on the generator hull, water level inside generator and the temperature at multiple places inside the generator. The measurement system has been installed and calibrated in the WEC. Furthermore, the design has been evaluated in lab experiments in order to verify the function and accuracy of the different measurements. This paper presents the underlying research objectives for developing the WEC generator measurement system, together with a description of the technical implementation.

  • 45.
    Lindroth [formerly Tyrberg], Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Buoy and Generator Interaction with Ocean Waves: Studies of a Wave Energy Conversion System2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    On March 13th, 2006, the Division of Electricity at Uppsala University deployed its first wave energy converter, L1, in the ocean southwest of Lysekil. L1 consisted of a buoy at the surface, connected through a line to a linear generator on the seabed. Since the deployment, continuous investigations of how L1 works in the waves have been conducted, and several additional wave energy converters have been deployed.

    This thesis is based on ten publications, which focus on different aspects of the interaction between wave, buoy, and generator. In order to evaluate different measurement systems, the motion of the buoy was measured optically and using accelerometers, and compared to measurements of the motion of the movable part of the generator - the translator. These measurements were found to correlate well. Simulations of buoy and translator motion were found to match the measured values.

    The variation of performance of L1 with changing water levels, wave heights, and spectral shapes was also investigated. Performance is here defined as the ratio of absorbed power to incoming power. It was found that the performance decreases for large wave heights. This is in accordance with the theoretical predictions, since the area for which the stator and the translator overlap decreases for large translator motions. Shifting water levels were predicted to have the same effect, but this could not be seen as clearly.

    The width of the wave energy spectrum has been proposed by some as a factor that also affects the performance of a wave energy converter, for a set wave height and period. Therefore the relation between performance and several different parameters for spectral width was investigated. It was found that some of the parameters were in fact correlated to performance, but that the correlation was not very strong.

    As a background on ocean measurements in wave energy, a thorough literature review was conducted. It turns out that the Lysekil project is one of quite few projects that have published descriptions of on-site wave energy measurements.

  • 46.
    Lokharu, Evgeniy
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Small-amplitude steady water waves with vorticity2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The problem of describing two-dimensional traveling water waves is considered. The water region is of finite depth and the interface between the region and the air is given by the graph of a function. We assume the flow to be incompressible and neglect the effects of surface tension. However we assume the flow to be rotational so that the vorticity distribution is a given function depending on the values of the stream function of the flow. The presence of vorticity increases the complexity of the problem and also leads to a wider class of solutions.

    First we study unidirectional waves with vorticity and verify the Benjamin-Lighthill conjecture for flows whose Bernoulli constant is close to the critical one. For this purpose it is shown that every wave, whose slope is bounded by a fixed constant, is either a Stokes or a solitary wave. It is proved that the whole set of these waves is uniquely parametrised (up to translation) by the flow force which varies between its values for the supercritical and subcritical shear flows of constant depth. We also study large-amplitude unidirectional waves for which we prove bounds for the free-surface profile and for Bernoulli’s constant.

    Second, we consider small-amplitude waves over flows with counter currents. Such flows admit layers, where the fluid flows in different directions. In this case we prove that the initial nonlinear free-boundary problem can be reduced to a finite-dimensional Hamiltonian system with a stable equilibrium point corresponding to a uniform stream. As an application of this result, we prove the existence of non-symmetric wave profiles. Furthermore, using a different method, we prove the existence of periodic waves with an arbitrary number of crests per period.

  • 47.
    Lundin, Staffan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Forslund, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Grabbe, Mårten
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Yuen, Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimental demonstration of performance of a vertical axis marine current turbine in a river2016In: Journal of Renewable and Sustainable Energy, ISSN 1941-7012, E-ISSN 1941-7012, Vol. 8, no 6, 064501Article in journal (Refereed)
    Abstract [en]

    An experimental station for marine current power has been installed in a river. The station comprises a vertical axis turbine with a direct-driven permanent magnet synchronous generator. In measurements of steady-state operation in varying flow conditions, performance comparable to that of turbines designed for significantly higher flow speeds is achieved, demonstrating the viability of electricity generation in low speed (below 1.5 m/s) marine currents.

  • 48.
    Marion, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Bottacin-Busolin, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Tait, Simon
    Univ Bradford, Sch Engn Design & Technol, Bradford BD7 1DP, W Yorkshire, England.
    Tregnaghi, Matteo
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn, I-35131 Padua, Italy.
    Near-bed flow field measurements at threshold of sediment motion2007In: PROCEEDINGS OF THE CONGRESS - INTERNATIONAL ASSOCIATION FOR HYDRAULIC RESEARCH, 2007, 401- p.Conference paper (Refereed)
    Abstract [it]

    Several experimental tests were carried out using a gravel bed tilting flume and an ad­vanced Particle Image Velocimetry (PIV) system. Sediment movement at the threshold was surveyed at the grain scale under uniform flow conditions. A natural river gravel with well sorted sediment was used. Flow field measurements were made over an area of approximately 400 cm2, on a plane located at 5 mm above the original sediment bed. Image processing and cross-correlation techniques were used to obtain flow velocities. Sequences of images of the bed surface were taken simultaneously with the measurements of the flow field. Statistics of the movements of the grains were collected through a semi-automatic procedure. Significant changes in the local flow field were observed in the proximity of the entrained or deposited particles. Such variations of velocity, which can be either in terms of the longitudinal and la­teral components or in terms of the relevant fluctuations from the time average, appear as a direct effect of the removal or deposition of individual grains. A strong correlation is shown between the changes in the streamwise velocity and the movement of the particles: local ve­locity increases were observed to correspond with the entrainment of grains, while local ve­locity reductions occurred as a grain was deposited.

  • 49.
    Marion, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotechn Engn.
    Packman, Aaron
    Northwestern Univ, Dept Civil & Environm Engn, Evanston.
    Zaramella, Mattia
    Univ Padua, Dept Hydraul Maritime Environm & Geotechn Engn.
    Bottacin-Busolin, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotechn Engn.
    Hyporheic flows in stratified beds2008In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 44, no 9, W09433- p.Article in journal (Refereed)
    Abstract [en]

    Surface-subsurface exchange fluxes are receiving increasing interest because of their importance in the fate of contaminants, nutrients, and other ecologically relevant substances in a variety of aquatic systems. Solutions have previously been developed for pore water flows induced by geometrical irregularities such as bed forms for the cases of homogeneous sediment beds and idealized heterogeneous beds, but these solutions have not accounted for the fact that streambed sediments are subject to sorting processes that often produce well-defined subsurface structures. Sediments at the streambed surface are often coarser than the underlying material because of size-selective sediment transport, producing relatively thin armor layers. Episodic erosional and depositional processes also create thick layers of different composition within the porous medium, forming stratified beds. A series of experiments were conducted to observe conservative solute transport in armored and stratified beds. An analytical solution was developed for advective exchange with stratified beds and provides appropriate scaling of the physical variables that control exchange flows. The results show that armor layers are too thin to significantly alter the advective pumping process but provide significant solute storage at short time scales. Stratified beds with layers of significant thickness favor development of horizontal flow paths within the bed and change the rate of solute transfer across the stream-subsurface interface compared to homogeneous beds.

  • 50.
    Marion, Andrea
    et al.
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Zaramella, Mattia
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Bottacin-Busolin, Andrea
    Univ Padua, Dept Hydraul Maritime Environm & Geotech Engn.
    Solute transport in rivers with multiple storage zones: The STIR model2008In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 44, no 10, W10406- p.Article in journal (Refereed)
    Abstract [en]

    Solute transport in rivers is controlled by surface hydrodynamics and by mass exchanges between the surface stream and distinct retention zones. This paper presents a residence time model for stream transport of solutes, Solute Transport in Rivers (STIR), that accounts for the effect of the stream-subsurface interactions on river mixing. A stochastic approach is used to derive a relation between the in-stream solute concentration and the residence time distributions (RTDs) in different retention domains. Particular forms of the RTD are suggested for the temporary storage within surface dead zones and for bed form-induced hyporheic exchange. This approach is advantageous for at least two reasons. The first advantage is that exchange parameters can generally be expressed as functions of physical quantities that can be reasonably estimated or directly measured. This gives the model predictive capabilities, and the results can be generalized to conditions different from those directly observed in field experiments. The second reason is that individual exchange processes are represented separately by appropriate residence time distributions, making the model flexible and modular, capable of incorporating the effects of a variety of exchange processes and chemical reactions in a detailed way. The capability of the model is illustrated with an example and with an application to a field case. Analogies and differences with other established models are also discussed.

12 1 - 50 of 78
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf