| 1. |
- Hörteborn, Axel, 1986, et al.
(författare)
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Economic incentives and technological limitations govern environmental impact of LNG feeder vessels
- 2023
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Ingår i: Journal of Cleaner Production. - : Elsevier Ltd. - 0959-6526 .- 1879-1786. ; 429
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Tidskriftsartikel (refereegranskat)abstract
- In the transition to sustainable shipping, Liquified Natural Gas (LNG), is proposed to play a role, reducing emissions of sulphur and nitrogen oxides, and particulate matter. However, LNG is a fossil fuel and there is an ongoing discussion regarding the extent of methane slip from ships operating on LNG, challenging the assumptions of LNG as a sustainable solution. Here we show another aspect to consider in the environmental assessment of shipping; LNG feeder vessels may spend as much as 25% of their time at sea just running the ship to ensure the pressure in the tanks are not exceeded, i.e., run time not directly attributed to the shipment of gas from one port or ship, to another. In other words, the economic incentives are currently allowing for roughly 32% increase of the ships’ operational emissions and discharges and increased navigational risks. Most coastal areas are heavily affected by anthropogenic activities and e.g., in the Baltic Sea there is consensus among the HELCOM member states that the input of nutrient and hazardous substances must be reduced. Even if the LNG feeder vessels are currently few, the possibility to reduce their environmental impact by 32% should be an attractive opportunity for future policy measures and investigation of technological solutions of the problem.
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| 2. |
- Ancona, M. A., et al.
(författare)
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Efficiency improvement on a cruise ship: Load allocation optimization
- 2018
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 164, s. 42-58
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Tidskriftsartikel (refereegranskat)abstract
- Last years have been characterized by a worldwide increasing attention towards the reduction of fuel consumption and carbon dioxide emissions. Several industrial fields, as well as the civil and residential sector, have introduced innovative approaches for the design and the operation of energy systems. These actions are aimed to reach higher values of energy conversion efficiency, also including an increase in the use of renewable resources. In this context, especially in the sector of cruise ships, further efforts are required to improve the energy efficiency of the employed energy systems. The aim of this paper is to propose an optimization framework based on genetic algorithms in order to maximize the energy efficiency and minimize both the fuel consumption and the thermal energy dissipation, by optimizing the load allocation of the ship energy systems. To this purpose, different strategies for the energy systems on board of an existing cruise ship are proposed and analyzed. In particular, two main engines configurations have been defined: standard (current logic of operation maintained) and hybrid configuration. For each proposed strategy – being the ship a particular and interesting application of isolated energy grid (i.e. a grid without connections with electric and fuel national grids) – an in-house-developed software has been adapted and applied to optimize the load allocation of the various energy systems. Furthermore, an economic and environmental analysis has been carried out, in order to point out the benefits – or the eventual limits – related to the proposed solutions. The considered approach is based on the concept of introducing economically and structurally suitable modifications to the current cruise energy systems configuration, in order to reach the goal of increasing the energy efficiency. The carried out analysis shows that the hybrid strategies allow to reach the best results in terms of energy (fuel consumption and heat dissipation reduction), economic and environmental points of view.
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| 3. |
- Andersson, Karin, 1952, et al.
(författare)
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Shipping and the Environment - Improving Environmental Performance in Marine Transportation
- 2016
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- This book focuses on the interaction between shipping and the natural environment and how shipping can strive to become more sustainable. Readers are guided in marine environmental awareness, environmental regulations and abatement technologies to assist in decisions on strategy, policy and investments. You will get familiar with possible paths to improve environmental performance and, in the long term, to a sustainable shipping sector, based on an understanding of the sources and mechanisms of common impacts. You will also gain knowledge on emissions anddischarges from ships, prevention measures, environmental regulations, and methods and tools for environmental assessment. In addition, the book includes a chapter on thebackground to regulating pollution from ships. It is intended as a source of information for professionals connected to maritime activities as well as policy makers and interested public. It is also intended as a textbook in higher education academic programmes.
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| 4. |
- Andersson, Karin, 1952
(författare)
-
The shipping industry and the climate
- 2022
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Ingår i: Sustainable Energy Systems on Ships: Novel Technologies for Low Carbon Shipping. - 9780128244715 ; , s. 3-25
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- As by 2020, the past six years, including 2020, are likely to be the six warmest years on record and the global mean temperature was 1.2°C above the preindustrial level [1]. International agreements, the Kyoto Protocol (1997) and the Paris agreement (2016), has set the aim to keep a global temperature rise during this century well below 2°C above pre-industrial levels. The anthropogenic inflow of GHGs to the atmosphere from the shipping industry was estimated by the IMO to totally around 2.5–3% of the global emissions in 2018 (or 1076 million tonnes). This is an increase by 9.6% since the previous study in 2014. The IMO projects the future emissions to increase from 1000 Mt CO2 in 2018 to 1000 to 1500 Mt CO2 in 2050 in a “Business as Usual”, BAU, scenario. Two years after the Paris agreement, the IMO adopted a vision, followed by a plan for implementation, in which a global goal of 50% reduction in GHG emissions from shipping by 2050 compared to 2008, and a total phase-out “within this century” is stated. Action from the IMO has started with a data collection system for fuel oil consumption. Ships of >5000 gross tonnage are required to collect consumption data fuel oil use and data on transport work. The European Union has started work on emission decrease with demands on Monitoring, Reporting and Verification of CO2 emissions from large ships (>5000 tonnes) using EU ports. Also here further measures are expected. At present here are many different initiatives, internationally, from countries as well as from shipping companies and shipowners to find ways towards “zero carbon shipping”. The different regulations and incentives introduced will help on the way, but still there is a need for more strict regulations or stronger incentives. The present initiatives give a large potential to make shipping and sea transport an important player also in a carbon neutral, sustainable society.
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| 5. |
- Brynolf, Selma, 1984, et al.
(författare)
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Compliance possibilities for the future ECA regulations through the use of abatement technologies or change of fuels
- 2014
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Ingår i: Transportation Research Part D: Transport and Environment. - : Elsevier BV. - 1361-9209. ; 28, s. 6-18
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Tidskriftsartikel (refereegranskat)abstract
- The upcoming stricter emission control area (ECA) regulations on sulphur and nitrogen oxides (NOX) emissions from shipping can be handled by different strategies. In this study, three alternatives complying with the ECA regulations for sulphur as well as Tier III for NOX are presented and compared using life cycle assessment. None of the three alternatives will significantly reduce the life cycle impact on climate change compared to heavy fuel oil (HFO). However, all alternatives will reduce the impact on particulate matter, photochemical ozone formation, acidification and terrestrial eutrophication potential. The assessment also highlighted two important regulatory aspects. Firstly, the need to regulate the ammonia slip from use of selective catalytic reduction (SCR) and secondly the need to regulate the methane slip from LNG engines. In addition, an analysis of the use of SCR in Swedish waters is presented showing that SCRs have been used on a number of ships already giving significantly reduced NOX emissions.
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| 6. |
- Brynolf, Selma, 1984, et al.
(författare)
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Environmental assessment of marine fuels: liquefied natural gas, liquefied biogas, methanol and bio-methanol
- 2014
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Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526. ; 74, s. 86-95
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Tidskriftsartikel (refereegranskat)abstract
- The combined effort of reducing the emissions of sulphur dioxide, nitrogen oxides and greenhouse gases to comply with future regulations and reduce impact on climate change will require a significant change in ship propulsion. One alternative is to change fuels. In this study we compare the life cycle environmental performance of liquefied natural gas (LNG), liquefied biogas (LBG), methanol and bio-methanol. We also highlight a number of important aspects to consider when selecting marine fuels. A transition to use of LNG or methanol produced from natural gas would significantly improve the overall environmental performance. However, the impact on climate change is of the same order of magnitude as with use of heavy fuel oil. It is only the use of LBG and bio-methanol that has the potential to reduce the climate impact. The analysis did not show any significant differences in environmental performance between methane and methanol when produced from the same raw materials, but the performance of the methanol engines are yet to be validated.
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| 7. |
- Brynolf, Selma, 1984
(författare)
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Environmental assessment of present and future marine fuels
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Our globalised world is connected by shipping, an industry powered by one of heaviest and dirtiest products of refining: heavy fuel oil. Tougher environmental regulations are now challenging the industry to take action. Ship-owners and operators are faced with the choice of installing exhaust gas cleaning technologies or switching to a different fuel altogether. The primary purpose of this thesis was to assess the environmental performance of present and future marine fuels and to evaluate potential methods and tools for their assessment.Two different system approaches are used in this study: life cycle assessment (LCA) and global energy systems modelling. LCA is a well-established method for assessing the environmental performance of fuels. This type of assessment was complemented with the use of the Global Energy Transition (GET) model to investigate cost-effective fuel choices based on a global stabilisation of CO2 emissions and the global competition for primary energy sources. The GET model includes all energy sectors and considers the interactions among them, but it is limited in scope to CO2 emissions and costs. The LCAs involve a holistic systems perspective that includes the entire life cycle and various types of environmental impacts, but they are limited to analyses of one product or service at a time. These methods provide insights that are both contradictory and complementary.This study concludes that there is substantial potential for reducing the environmental impact of shipping through a change in fuel types and/or the use of exhaust abatement technologies. A switch from heavy fuel oil to any of the alternatives investigated in this study reduces the overall environmental impact of marine fuels. The GET model indicates that it is cost-effective to phase out the use of crude oil-based fuels in the shipping sector and replace these fuels with the use of natural gas-based fuels during the next few decades. Based on the LCA results, the use of biofuels may be one possible way to reduce the impact of shipping on the climate, but biofuels may only be a cost-effective fuel in shipping if the corresponding annual available bioenergy resources are sufficiently large. Three important implications are highlighted: the importance of reducing the NOX emissions from marine engines, the need to regulate the methane slip from gas engines and the fact that a change in fuels may not reduce the impact of shipping on the climate.
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| 8. |
- Jasinski, Michal, et al.
(författare)
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Operation and Planning of Energy Hubs Under Uncertainty - a Review of Mathematical Optimization Approaches
- 2023
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Ingår i: IEEE Access. - 2169-3536 .- 2169-3536. ; 11, s. 7208-7228
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Tidskriftsartikel (refereegranskat)abstract
- Co-designing energy systems across multiple energy carriers is increasingly attracting attention of researchers and policy makers, since it is a prominent means of increasing the overall efficiency of the energy sector. Special attention is attributed to the so-called energy hubs, i.e., clusters of energy communities featuring electricity, gas, heat, hydrogen, and also water generation and consumption facilities. Managing an energy hub entails dealing with multiple sources of uncertainty, such as renewable generation, energy demands, wholesale market prices, etc. Such uncertainties call for sophisticated decision-making techniques, with mathematical optimization being the predominant family of decision-making methods proposed in the literature of recent years. In this paper, we summarize, review, and categorize research studies that have applied mathematical optimization approaches towards making operational and planning decisions for energy hubs. Relevant methods include robust optimization, information gap decision theory, stochastic programming, and chance-constrained optimization. The results of the review indicate the increasing adoption of robust and, more recently, hybrid methods to deal with the multi-dimensional uncertainties of energy hubs.
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| 9. |
- Perera, Amarasinghage Tharindu Dasun, et al.
(författare)
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Climate resilient interconnected infrastructure: Co-optimization of energy systems and urban morphology
- 2021
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 285
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Tidskriftsartikel (refereegranskat)abstract
- Co-optimization of urban morphology and distributed energy systems is key to curb energy consumption and optimally exploit renewable energy in cities. Currently available optimization techniques focus on either buildings or energy systems, mostly neglecting the impact of their interactions, which limits the renewable energy integration and robustness of the energy infrastructure; particularly in extreme weather conditions. To move beyond the current state-of-the-art, this study proposes a novel methodology to optimize urban energy systems as interconnected urban infrastructures affected by urban morphology. A set of urban morphologies representing twenty distinct neighborhoods is generated based on fifteen influencing parameters. The energy performance of each urban morphology is assessed and optimized for typical and extreme warm and cold weather datasets in three time periods from 2010 to 2039, 2040 to 2069, and 2070 to 2099 for Athens, Greece. Pareto optimization is conducted to generate an optimal energy system and urban morphology. The results show that a thus optimized urban morphology can reduce the levelized cost for energy infrastructure by up to 30%. The study reveals further that the current building form and urban density of the modelled neighborhoods will lead to an increase in the energy demand by 10% and 27% respectively. Furthermore, extreme climate conditions will increase energy demand by 20%, which will lead to an increment in the levelized cost of energy infrastructure by 40%. Finally, it is shown that co-optimization of both urban morphology and energy system will guarantee climate resilience of urban energy systems with a minimum investment.
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| 10. |
- Thies, Fabian, 1984, et al.
(författare)
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Wind-assisted, electric, and pure wind propulsion - the path towards zero-emission RoRo ships
- 2023
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Ingår i: Ships and Offshore Structures. - : Informa UK Limited. - 1754-212X .- 1744-5302. ; 18:8, s. 1229-1236
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Tidskriftsartikel (refereegranskat)abstract
- Electrical and wind propulsion, together with energy stored in batteries and renewable energies harnessed onboard, can lead the way towards zero-emission ships. This study compares wind propulsion solutions and battery storage possibilities for a RoRo ship operating in the Baltic Sea. The ship energy systems simulation model ShipCLEAN is used to predict the performance of the zero-emission ship in real-life operating conditions. The study showcases how ships can be transferred from a conventional, diesel-powered to a zero-emission ship. For the zero-emission ship, all energy needed for auxiliaries and propulsion is taken from renewable sources onboard or from batteries. Challenges and opportunities, as well as necessary adaptions of the route and logistics, are discussed. Results of the study present which wind propulsion technology is the most suitable for the example RoRo ship, and how the installation of suitably sized battery packs for zero-emission operation affects the cargo capacity of the ship.
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| 11. |
- Thomas, Jean-Baptiste, et al.
(författare)
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A comparative environmental life cycle assessment of hatchery, cultivation, and preservation of the kelp Saccharina latissima
- 2021
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Ingår i: Ices Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 78:1, s. 451-467
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Tidskriftsartikel (refereegranskat)abstract
- Seaweed cultivation and processing industries could contribute to sustainable blue growth and the European bioeconomy. This article contributes a case study evaluation of environmental sustainability of preserved brown seaweed Saccharina latissima by means of environmental life cycle assessment of a pilot facility in Sweden. The study accounts for nutrient bioremediation and carbon capture and includes two alternative hatchery processes, a 2-ha longline cultivation, and four alternative preservation methods (hang-drying outdoors, heated air-cabinet drying, ensiling, and freezing). The study found that as a result of carbon capture and nitrogen and phosphorus uptake (bioremediation) by seaweed, more CO2 and PO4 equivalents are (temporarily) absorbed than emitted by the supply chain. The extent of emissions is most affected by preservation methods undertaken. Impact profiles of the supply chain show that the greatest impact shares result from freezing and air-cabinet drying, both the two most energy-intensive processes, followed by the cultivation infrastructure, highlighting strategic optimization opportunities. Hatchery processes, harvesting, and the low-energy ensilage and hang-drying outdoors were found to have relatively small impact shares. These findings presage the environmentally friendliness of seaweed-based products by documenting their potential to mitigate eutrophication and climate change, even when taking a life cycle perspective.
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| 12. |
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| 13. |
- Göteman, Malin, 1980-
(författare)
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Wave energy parks with point-absorbers of different dimensions
- 2017
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Ingår i: Journal of Fluids and Structures. - : Elsevier BV. - 0889-9746 .- 1095-8622. ; 74, s. 142-157
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Tidskriftsartikel (refereegranskat)abstract
- An analytical model for point-absorbing wave energy converters connected to floats of different geometries and topologies is presented. The floats can be truncated cylinder or cylinder with moonpool buoys and have different outer radius, inner radius, draft, mass and can be connected to linear generators of different power take-off constants. The model is implemented into a numerical code where the input is measured time-series of irregular waves. After validation against benchmark software, the model is used to study optimal configurations of wave energy arrays consisting of different wave energy devices. It is shown that the total power absorption can be improved if the wave energy array consists of devices of different dimensions, and that a higher power-to-mass ratio can be achieved.
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| 14. |
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| 15. |
- Lindroth [formerly Tyrberg], Simon, 1979-
(författare)
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Buoy and Generator Interaction with Ocean Waves : Studies of a Wave Energy Conversion System
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 16. |
- Mathern, Alexandre, 1986, et al.
(författare)
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Concrete Support Structures for Offshore Wind Turbines: Current Status, Challenges, and Future Trends
- 2021
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:7
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Forskningsöversikt (refereegranskat)abstract
- Today’s offshore wind turbine support structures market is largely dominated by steel structures, since steel monopiles account for the vast majority of installations in the last decade and new types of multi-leg steel structures have been developed in recent years. However, as wind turbines become bigger, and potential sites for offshore wind farms are located in ever deeper waters and ever further from the shore, the conditions for the design, transport, and installation of support structures are changing. In light of these facts, this paper identifies and categorizes the challenges and future trends related to the use of concrete for support structures of future offshore wind projects. To do so, recent advances and technologies still under development for both bottom-fixed and floating concrete support structures have been reviewed. It was found that these new developments meet the challenges associated with the use of concrete support structures, as they will allow the production costs to be lowered and transport and installation to be facilitated. New technologies for concrete support structures used at medium and great water depths are also being developed and are expected to become more common in future offshore wind installations. Therefore, the new developments identified in this paper show the likelihood of an increase in the use of concrete support structures in future offshore wind farms. These developments also indicate that the complexity of future support structures will increase due to the development of hybrid structures combining steel and concrete. These evolutions call for new knowledge and technical know-how in order to allow reliable structures to be built and risk-free offshore installation to be executed.
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| 17. |
- Petersson, Jesper, 1974, et al.
(författare)
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Defend, Retreat and Attack: Urban Waters and Valuation Practices
- 2022
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Ingår i: Water Alternatives. - : Water Alternatives Association. - 1965-0175. ; 15:1, s. 175-192
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Tidskriftsartikel (refereegranskat)abstract
- This paper explores the river landscapes and concomitant values resulting from tensions between flood management and visions of a River City. The aim is to contribute to an understanding of the management of urban waters as valuation practices. We regard valuation practices as co-constitutive of current and future river landscapes. Sweden’s second-largest city, Gothenburg, is located next to the sea, and the Göta River, Sweden’s largest water system, runs through it. Our empirical focus is on how this city approaches increasing risks of flooding. We explore three approaches that have been formulated in relation to flood management: defend, retreat and attack. We ask how these approaches are applied in the management of Göta River flooding and in the city’s vision of a future Gothenburg that embraces the river as a genuinely positive aspect of urban life. We present the case as a journey that takes us upstream from the river’s sea inlet port and through Gothenburg. During our kilometre by kilometre journey, the river’s appearance shifts. The varied river landscape mirrors the diversity in how its waters are valuated, both historically and in present times. The perception of urban waters is shaped by practices of valuation. These valuations are generative. They connect the value of water to other entities, actors, plans, activities and buildings, and they are thus key to the river landscapes that will eventually be realised. By way of conclusion, we identify a number of governance challenges that are particularly relevant to urban rivers.
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| 18. |
- Remouit, Flore, 1988-
(författare)
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Automation of underwater operations on wave energy converters using remotely operated vehicles
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the last fifteen years, the Division of Electricity at Uppsala University has been developing a wave energy converter (WEC) concept. The concept is based on a point-absorbing buoy with a directly driven linear generator placed on the seabed. Several units are connected to a marine substation, whose role is to collect and smooth the power absorbed from the waves and then bring it to the shore through one single cable.A big challenge in the project is to reduce the costs related to the deployment and maintenance of the WECs and substation. Currently, those operations are performed by divers, which is costly and entail considerable risks. A possibility is to replace divers with automated solutions using small robots called remotely operated vehicles (ROVs). This PhD thesis proposes and analyses a method for deployment and maintenance of underwater devices with no use of diving operations.Existing ROVs need additional modules and equipment in order to carry out operations with the required force and precision. Typical missions are inspection, shackles or slings removal, valve closing, and cable connection. The latter demands especially high precision in the positioning: 5 mm in distance and 5◦ in heading angle. In addition, this operation involves forces up to 200 N. This combination power-precision is not reached by existing ROVs. This PhD thesis presents a positioning system for underwater robot to enable autonomous positioning of the vehicle before cable connection.The positioning system is composed of two green lasers and a monocular camera, and is based on image processing. Experimental results from laboratory testing show that the mean absolute error in distance measurement is as low as 6 mm at 0.7 m from the target, whereas the heading is minimized to 2◦. The computational time for the image processing is 13.6 ms per image, meaning the possibility of a 30 Hz measurement system. Used together with a closed-loop path-following unit, this positioning system can support autonomous docking. This PhD thesis presents the model of an autopilot and results from docking simulations, showing the performance of the positioning system used in closed-loop.
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| 19. |
- Shahroozi, Zahra, et al.
(författare)
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Considerations on prediction horizon and dissipative losses for wave energy converters
- 2021
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology. - 1752-1416 .- 1752-1424. ; 15:14, s. 3434-3458
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Tidskriftsartikel (refereegranskat)abstract
- The non-causal optimal control law for wave energy converters leads to a requirement of predicting waves and wave forces over a future horizon. Using examples of generic body shapes and oscillation modes, we show through computations of the velocity reference trajectory how the length of prediction horizon required to reach the maximum power output depends on the level of dissipative losses in the conversion chain. The sensitivity to noise is discussed, and so is the use of filtering to improve performance when the available prediction horizon is short or predictions are inaccurate. Considerations are also made for amplitude constraints and other effects encountered in a real system. With realistic assumptions for the level of dissipative losses, results indicate that the prediction horizon needed to approach the maximum achievable power output for real systems ranges from only a few seconds up to about half a wave period, which is shorter than has generally been assumed earlier.
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| 20. |
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| 21. |
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| 22. |
- Shahroozi, Zahra
(författare)
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Prediction horizon requirement in control and extreme load analyses for survivability : Advancements to improve the performance of wave energy technologies
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of wave energy converters (WECs) is to ensure reliable electricity production at a competitive cost. Two challenges to achieving this are ensuring an efficient energy conversion and offshore survivability. This thesis work is structured in three different sections: Control and maximum power optimization, forces and dynamics analysis in extreme wave conditions, and statistical modeling of extreme loads in reliability analysis. The need for prediction and future knowledge of waves and wave forces is essential due to the non-causality of the optimal velocity relation for wave energy converters. Using generic concepts and modes of motion, the sensitivity of the prediction horizon to various parameters encountered in a real system is elaborated. The results show that through a realistic assumption of the dissipative losses, only a few seconds to about half a wave cycle is sufficient to predict the required future knowledge for the aim of maximizing the power absorption. The results of a 1:30 scaled wave tank experiment are used to assess the line force and dynamic behaviour of a WEC during extreme wave events. Within the comparison of different wave type representations, i.e. irregular, regular and focused waves, of the same sea state, the results show that not all the wave types deliver the same maximum line forces. As a strategy of mitigating the line forces during extreme wave events, changing the power take-off (PTO) damping may be employed. With consideration of the whole PTO range, the results indicate an optimum damping value for each sea state in which the smallest maximum line force is obtained. Although wave breaking slamming and end-stop spring compression lead to high peak line forces, it is possible that they level out due to the overtopping effect. Waves with a long wavelength result in large surge motion and consequently higher and more damaging forces. On the investigation of reliability assessment of the wave energy converter systems, computing the return period of the extreme forces is crucial. Using force measurement force data gathered at the west coast of Sweden, the extreme forces are statistically modelled with the peak-over-threshold method. Then, the return level of the extreme forces over 20 years for the calm season of the year is computed.
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| 23. |
- Shahroozi, Zahra, 1992-
(författare)
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Survivability control using data-driven approaches and reliability analysis for wave energy converters
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wave energy, with five times the energy density of wind and ten times the power density of solar, offers a compelling carbon-free electricity solution. Despite its advantages, ongoing debates surround the reliability and economic feasibility of wave energy converters (WECs). To address these challenges, this doctoral thesis is divided into four integral parts, focusing on optimizing the prediction horizon for power maximization, analyzing extreme waves' impact on system dynamics, ensuring reliability, and enhancing survivability in WECs.Part I emphasizes the critical importance of the prediction horizon for maximal power absorption in wave energy conversion. Using generic body shapes and modes, it explores the effect of dissipative losses, noise, filtering, amplitude constraints, and real-world wave parameters on the prediction horizon. Findings suggest achieving optimal power output may be possible with a relatively short prediction horizon, challenging traditional assumptions.Part II shifts focus to WEC system dynamics, analyzing extreme load scenarios. Based on a 1:30 scaled wave tank experiment, it establishes a robust experimental foundation, extending into numerical assessment of the WEC. Results underscore the importance of damping to alleviate peak forces. Investigating various wave representations highlights conservative characteristics of irregular waves, crucial for WEC design in extreme sea conditions.Part III explores the computational intricacies of environmental design load cases and fatigue analyses for critical mechanical components of the WEC. The analysis is conducted for hourly sea state damage and equivalent two-million-cycle loads. Finally, a comparison of safety factors between the ultimate limit state and fatigue limit state unfolds, illustrating the predominant influence of the ultimate limit state on point-absorber WEC design.Part IV, centers on elevating survivability strategies for WECs in extreme wave conditions. Three distinct controller system approaches leverage neural networks to predict and minimize the line force. Distinct variations emerge in each approach, spanning from rapid detection of optimal damping to integrating advanced neural network architectures into the control system with feedback. The incorporation of a controller system, refined through experimental data, showcases decreases in the line force, providing a practical mechanism for real-time force alleviation.This thesis aims to contribute uniquely to the goal of advancing wave energy conversion technology through extensive exploration.
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| 24. |
- Strömstedt, Erland, 1972-
(författare)
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Submerged Transmission in Wave Energy Converters : Full Scale In-Situ Experimental Measurements
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different wave power technologies are in development around the world in different stages of prototype testing. So far only a few devices have been deployed offshore at full scale for extended periods of time. Little data is published about how these different devices perform.This thesis presents results from experiments with the full-scale offshore wave energy converters at the Lysekil research site on the Swedish west coast. The theories, experiments, measurements, performance evaluations and developments of the submerged transmission in the direct driven permanent magnet linear generator are in focus. The reciprocating submerged transmission fulfills the purpose of transmitting the absorbed mechanical wave energy through the capsule wall into the generator, while preventing the seawater from entering the capsule and reducing the life time of the converter.A measuring system with seven laser triangulation sensors has been developed to measure small relative displacements between piston rod and seal housing in the submerged transmission with excellent accuracy for the purpose of evaluating both functional behavior and successive wear in-situ. A method for calculating relative tilt angles, azimuth angles, differential tilt angles, and successive wear in the submerged transmission has been developed. Additional sensors systems have been installed in the converter enabling correlation and a thorough investigation into the operating conditions of the transmission and the converter. The thesis presents unique results from the measurements. A data acquisition system transmits the signals from the converter on the seabed to an onshore measuring station. Results are presented in time-, frequency- and the time-frequency domain.The results have given important information for further development of the submerged transmission, which is important to the survivability of the system. The thesis describes the status of research, and is a step that may influence future designs of wave energy devices for reaching survivability and a cost-effective renewable energy system.
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- Svensson, Olle, 1967-
(författare)
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Experimental results from the Lysekil Wave Power Research Site
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents how experimental results, from wave power research performed offshore at the Lysekil research site, were obtained. The data were used to verify theoretical models as well as evaluate the feasibility of wave power as a future sustainable energy source.The first experiments carried out at the research site was the measurement of the force in a line where one end was connected to a buoy with a diameter of 3 m and the other end to a set of springs with limited stroke length. The system is exposed to high peak forces compared to average forces. The maximum measured force in the line, when the buoy motion is limited by a stiff stopper rope is ten times the average force in that particular sea state.The experiment performed on the first wave energy converter tested at the Lysekil Research Site is described. The infrastructure of the site is presented where the central connection point is the measuring station. The key finding is that it is possible to transform the motions of ocean waves into electrical energy and distribute it to land.Many wave energy converters must be interconnected if large amounts of energy are to be harvested from the waves. The first submerged substation intended for aggregation of energy from wave power converters is described, with focus on the measurement and control system placed inside the substation. During this experiment period the generators were equipped with many different sensors; these measurements are explained in the thesis.The system that aggregates power from the studied wave energy converter is regularly exposed to peak power of up to 20 times the maximum average output from the converter.Vertical and horizontal movement of the buoy has been measured in different ways. The result is that the vertical displacement of the buoy can be measured with a simple accelerometer circuit but it is much more complicated to measure the horizontal displacement. A special method for measuring the horizontal displacement has been implemented by measuring the strain in the enclosure and the force in the line.
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