Logotyp: till Uppsala universitets webbplats

uu.sePublikationer från Uppsala universitet
Ändra sökning
Avgränsa sökresultatet
1 - 19 av 19
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Engström, Jens
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Shahroozi, Zahra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Katsidoniotaki, Eirini
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS).
    Stavropoulou, Charitini
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Johannesson, Pär
    RISE Research Institutes of Sweden, Department of Applied Mechanics.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS).
    Offshore Measurements and Numerical Validation of the Mooring Forces on a 1:5 Scale Buoy2023Ingår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 11, nr 1, artikel-id 231Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wave energy conversion is a renewable energy technology with a promising potential. Although it has been developed for more than 200 years, the technology is still far from mature. The survivability in extreme weather conditions is a key parameter halting its development. We present here results from two weeks of measurement with a force measurement buoy deployed at Uppsala University’s test site for wave energy research at the west coast of Sweden. The collected data have been used to investigate the reliability for two typical numerical wave energy converter models: one low fidelity model based on linear wave theory and one high fidelity Reynolds-Averaged Navier–Stokes model. The line force data is also analysed by extreme value theory using the peak-over-threshold method to study the statistical distribution of extreme forces and to predict the return period. The high fidelity model shows rather good agreement for the smaller waves, but overestimates the forces for larger waves, which can be attributed to uncertainties related to field measurements and numerical modelling uncertainties. The peak-over-threshold method gives a rather satisfying result for this data set. A significant deviation is observed in the measured force for sea states with the same significant wave height. This indicates that it will be difficult to calculate the force based on the significant wave height only, which points out the importance of more offshore experiments.

    Ladda ner fulltext (pdf)
    fulltext
  • 2.
    Giannini, Gianmaria
    et al.
    Univ Porto FEUP, Dept Civil Engn, Fac Engn, P-4200465 Porto, Portugal.;Univ Porto CIIMAR, Interdisciplinary Ctr Marine & Environm Res, P-4200465 Porto, Portugal..
    Temiz, Irina
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Rosa-Santos, Paulo
    Univ Porto FEUP, Dept Civil Engn, Fac Engn, P-4200465 Porto, Portugal.;Univ Porto CIIMAR, Interdisciplinary Ctr Marine & Environm Res, P-4200465 Porto, Portugal..
    Shahroozi, Zahra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Ramos, Victor
    Univ Porto FEUP, Dept Civil Engn, Fac Engn, P-4200465 Porto, Portugal.;Univ Porto CIIMAR, Interdisciplinary Ctr Marine & Environm Res, P-4200465 Porto, Portugal..
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Day, Sandy
    Univ Strathclyde, Dept Naval Architecture Ocean & Marine Engn, Glasgow G4 0LZ, Lanark, Scotland..
    Taveira-Pinto, Francisco
    Univ Porto FEUP, Dept Civil Engn, Fac Engn, P-4200465 Porto, Portugal.;Univ Porto CIIMAR, Interdisciplinary Ctr Marine & Environm Res, P-4200465 Porto, Portugal..
    Wave Energy Converter Power Take-Off System Scaling and Physical Modelling2020Ingår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 8, nr 9, artikel-id 632Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Absorbing wave power from oceans for producing a usable form of energy represents an attractive challenge, which for the most part concerns the development and integration, in a wave energy device, of a reliable, efficient and cost-effective power take-off mechanism. During the various stages of progress, for assessing a wave energy device, it is convenient to carry out experimental testing that, opportunely, takes into account the realistic behaviour of the power take-off mechanism at a small scale. To successfully replicate and assess the power take-off, good practices need to be implemented aiming to correctly scale and evaluate the power take-off mechanism and its behaviour. The present paper aims to explore and propose solutions that can be applied for reproducing and assessing the power take-off element during experimental studies, namely experimental set-ups enhancements, calibration practices, and error estimation methods. A series of recommendations on how to practically organize and carry out experiments were identified and three case studies are briefly covered. It was found that, despite specific options that can be strictly technology-dependent, various recommendations could be universally applicable.

    Ladda ner fulltext (pdf)
    fulltext
  • 3.
    Giassi, Marianna
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Thomas, Simon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Shahroozi, Zahra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Isberg, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Tosdevin, Tom
    Hann, Martyn
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Preliminary results from a scaled test of arrays of point-absorbers with 6 DOF2019Ingår i: Proceedings of the 13th European Wave and Tidal Energy Conference, 2019Konferensbidrag (Refereegranskat)
  • 4.
    Göteman, Malin
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS), Villavägen 16, Uppsala, 752 36, Sweden.
    Shahroozi, Zahra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Stavropoulou, Charitini
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Katsidoniotaki, Eirini
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS), Villavägen 16, Uppsala, 752 36, Sweden.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Resilience of wave energy farms using metocean dependent failure rates and repair operations2023Ingår i: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 280, artikel-id 114678Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Emerging offshore renewable energy technologies are expected to become an important part of the futureenergy system, and reliability for these new technologies in different metocean scenarios must be guaranteed.This poses a challenge in extreme weather scenarios like storms, in particular for less mature technologiessuch as wave energy. Not only the offshore survivability must be controlled; the restoration after disruptiveevents and failures should be addressed and optimized. Offshore operations are costly and cannot be carriedout if the weather is too harsh, and the resulting downtime after failures may be financially devastating forprojects. In this paper, the resilience of large wave energy systems is studied with respect to wave conditions,metocean dependent failure rates, and weather windows available for offshore repair operations. A metocean-and time-dependent failure rate is derived based on a Weibull distribution, which is a novelty of the paper.The performance of the farm is assessed using the varying failure rates and metocean data at different offshoresites. Critical metocean thresholds for different offshore vessels are considered, and the resilience is quantifiedusing relevant measures such as unavailability and expected energy not supplied. The resilience analysis iscoupled to an economic assessment of the wave farm and different repair strategies. Our results show thatthe commonly used assumption of constant failure rates is seen to overestimate the annual energy productionthan when a more realistic varying failure rate is used. Two offshore sites are compared, and the availabilityis found to be higher at the calmer site. Most of the evaluated repair strategies cannot be considered to beeconomically justified, when compared to the cost of the energy not supplied.

    Ladda ner fulltext (pdf)
    fulltext
  • 5.
    Katsidoniotaki, Eirini
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS).
    Shahroozi, Zahra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Eskilsson, Claes
    Palm, Johannes
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS).
    Validation of a CFD model for wave energy system dynamics in extreme waves2023Ingår i: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 268, artikel-id 113320Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The design of wave energy converters should rely on numerical models that are able to estimate accurately the dynamics and loads in extreme wave conditions. A high-fidelity CFD model of a 1:30 scale point-absorber is developed and validated on experimental data. This work constitutes beyond the state-of-the-art validation study as the system is subjected to 50-year return period waves. Additionally, a new methodology that addresses the well-known challenge in CFD codes of mesh deformation is successfully applied and validated. The CFD model is evaluated in different conditions: wave-only, free decay, and wave–structure interaction. The results show that the extreme waves and the experimental setup of the wave energy converter are simulated within an accuracy of 2%. The developed high-fidelity model is able to capture the motion of the system and the force in the mooring line under extreme waves with satisfactory accuracy. The deviation between the numerical and corresponding experimental RAOs is lower than 7% for waves with smaller steepness. In higher waves, the deviation increases up to 10% due to the inevitable wave reflections and complex dynamics. The pitch motion presents a larger deviation, however, the pitch is of secondary importance for a point-absorber wave energy converter.

    Ladda ner fulltext (pdf)
    fulltext
  • 6. Shahroozi, Zahra
    Force Prediction and Estimation for Point Absorber Wave Energy Converter2019Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Ladda ner fulltext (pdf)
    fulltext
  • 7.
    Shahroozi, Zahra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik.
    Prediction horizon requirement  in control and extreme load analyses for survivability: Advancements to improve the performance of wave energy technologies2021Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    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.

    Delarbeten
    1. Considerations on prediction horizon and dissipative losses for wave energy converters
    Öppna denna publikation i ny flik eller fönster >>Considerations on prediction horizon and dissipative losses for wave energy converters
    2021 (Engelska)Ingår i: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, IET Renewable Power Generation, Vol. 15, nr 14, s. 3434-3458Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    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.

    Ort, förlag, år, upplaga, sidor
    Institution of Engineering and TechnologyInstitution of Engineering and Technology (IET), 2021
    Nyckelord
    Wave energy converter, prediction horizon, dissipative losses, optimal velocity, useful power
    Nationell ämneskategori
    Energisystem Marin teknik Reglerteknik Havs- och vattendragsteknik
    Identifikatorer
    urn:nbn:se:uu:diva-457294 (URN)10.1049/rpg2.12290 (DOI)000703141600001 ()
    Forskningsfinansiär
    Forskningsrådet Formas, 2020-03634Energimyndigheten
    Tillgänglig från: 2021-10-27 Skapad: 2021-10-27 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    2. Experimental investigation of a point-absorbing wave energy converter response in different wave types of extreme sea states
    Öppna denna publikation i ny flik eller fönster >>Experimental investigation of a point-absorbing wave energy converter response in different wave types of extreme sea states
    (Engelska)Ingår i: Artikel i tidskrift, Editorial material (Övrigt vetenskapligt) Submitted
    Nationell ämneskategori
    Energisystem Marin teknik Havs- och vattendragsteknik Energiteknik
    Identifikatorer
    urn:nbn:se:uu:diva-457326 (URN)
    Tillgänglig från: 2021-10-27 Skapad: 2021-10-27 Senast uppdaterad: 2021-10-27
    3. Experimental results of force measurements from a scaled point absorbing wave energy converter subjected to extreme waves
    Öppna denna publikation i ny flik eller fönster >>Experimental results of force measurements from a scaled point absorbing wave energy converter subjected to extreme waves
    2021 (Engelska)Ingår i: Proceedings of the Fourteenth European Wave and Tidal Energy Conference, European Wave and Tidal Energy Conference (EWTEC) , 2021Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    To achieve a high reliability and durability for wave energy technologies, the effect of extreme wave conditions on the system must be understood. Wave tank experiments are an essential tool to evaluate this, and provide also a foundation for validation of numerical and analytical methods. However, it is not straight-forward how to design such small scale experiments so that they realistically represent wave energy converters in the ocean. In this paper, wave tank experiments of a 1:30 scaled friction damping linear power take-off (PTO) and cylindrical buoy with ellipsoidal bottom are presented. The linear PTO includes a rod that moves vertically against a Teflon block which introduces friction damping. The damping can be adjusted by changing the spring length that provides the compressive force between the Teflon block and the rod. To study extreme forces and snap loads, two load cells measure the line force both directly beneath the buoy, and at the top of the PTO. The motion of the PTO and the buoy are measured with a wire draw line position sensor and Qualysis system, respectively, and a data acquisition system collects and synchronizes the data. The extreme wave conditions used in the experiments are sea states with 50 years return period at the Dowsing site, North Sea. The waves are modelled as regular, irregular and focused waves. Here, the experimental setup and dry testing experiments are presented, and results of the wave tank test experiment for extreme forces are evaluated and further compared with WEC-SIM, to evaluate the agreement of the numerical and experimental model.

    Ort, förlag, år, upplaga, sidor
    European Wave and Tidal Energy Conference (EWTEC), 2021
    Serie
    Proceedings of the European Wave and Tidal Energy Conference, ISSN 2706-6932, E-ISSN 2706-6940
    Nationell ämneskategori
    Marin teknik Havs- och vattendragsteknik
    Identifikatorer
    urn:nbn:se:uu:diva-457301 (URN)
    Konferens
    Fourteenth European Wave and Tidal Energy Conference (EWTEC), 5-9 September, 2021, Plymouth, UK
    Tillgänglig från: 2021-10-27 Skapad: 2021-10-27 Senast uppdaterad: 2024-03-12
    4. Design and evaluation of linear and rotational generator scale models for wave tank testing
    Öppna denna publikation i ny flik eller fönster >>Design and evaluation of linear and rotational generator scale models for wave tank testing
    2019 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
    Ort, förlag, år, upplaga, sidor
    CRC Press, 2019
    Nationell ämneskategori
    Energisystem Havs- och vattendragsteknik Marin teknik Annan elektroteknik och elektronik
    Identifikatorer
    urn:nbn:se:uu:diva-457307 (URN)9780429505324 (ISBN)9781138585355 (ISBN)
    Konferens
    3rd international conference on renewable energies offshore (renew 2018), 8–10 october 2018, Lisbon, Portugal
    Tillgänglig från: 2021-10-27 Skapad: 2021-10-27 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    5. Wave Energy Converter Power Take-Off System Scaling and Physical Modelling
    Öppna denna publikation i ny flik eller fönster >>Wave Energy Converter Power Take-Off System Scaling and Physical Modelling
    Visa övriga...
    2020 (Engelska)Ingår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 8, nr 9, artikel-id 632Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Absorbing wave power from oceans for producing a usable form of energy represents an attractive challenge, which for the most part concerns the development and integration, in a wave energy device, of a reliable, efficient and cost-effective power take-off mechanism. During the various stages of progress, for assessing a wave energy device, it is convenient to carry out experimental testing that, opportunely, takes into account the realistic behaviour of the power take-off mechanism at a small scale. To successfully replicate and assess the power take-off, good practices need to be implemented aiming to correctly scale and evaluate the power take-off mechanism and its behaviour. The present paper aims to explore and propose solutions that can be applied for reproducing and assessing the power take-off element during experimental studies, namely experimental set-ups enhancements, calibration practices, and error estimation methods. A series of recommendations on how to practically organize and carry out experiments were identified and three case studies are briefly covered. It was found that, despite specific options that can be strictly technology-dependent, various recommendations could be universally applicable.

    Ort, förlag, år, upplaga, sidor
    MDPI, 2020
    Nyckelord
    power take-off damping, wave power device, experimental testing, PTO simulator, uncertainty analysis, wave energy testing, experimental set-up, calibration
    Nationell ämneskategori
    Annan elektroteknik och elektronik
    Identifikatorer
    urn:nbn:se:uu:diva-425480 (URN)10.3390/jmse8090632 (DOI)000582055100001 ()
    Forskningsfinansiär
    EU, Horisont 2020, POCI-01-0145-FEDER-016882EU, Horisont 2020, PTDC/MAR-TEC/6984/2014StandUp, 47264-1
    Tillgänglig från: 2020-11-19 Skapad: 2020-11-19 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    6. Offshore measurements of hydrodynamic forces on a 1:5 scale buoy
    Öppna denna publikation i ny flik eller fönster >>Offshore measurements of hydrodynamic forces on a 1:5 scale buoy
    Visa övriga...
    (Engelska)Ingår i: Artikel i tidskrift, Editorial material (Övrigt vetenskapligt) Submitted
    Nationell ämneskategori
    Energisystem Marin teknik Havs- och vattendragsteknik Energiteknik
    Identifikatorer
    urn:nbn:se:uu:diva-457327 (URN)
    Tillgänglig från: 2021-10-27 Skapad: 2021-10-27 Senast uppdaterad: 2021-10-27
    Ladda ner fulltext (pdf)
    UULic_Z-Shahroozi-2021
    Ladda ner (jpg)
    presentationsbild
  • 8.
    Shahroozi, Zahra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Uppsala University.
    Survivability control using data-driven approaches and reliability analysis for wave energy converters2024Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    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.

    Delarbeten
    1. Considerations on prediction horizon and dissipative losses for wave energy converters
    Öppna denna publikation i ny flik eller fönster >>Considerations on prediction horizon and dissipative losses for wave energy converters
    2021 (Engelska)Ingår i: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, IET Renewable Power Generation, Vol. 15, nr 14, s. 3434-3458Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    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.

    Ort, förlag, år, upplaga, sidor
    Institution of Engineering and TechnologyInstitution of Engineering and Technology (IET), 2021
    Nyckelord
    Wave energy converter, prediction horizon, dissipative losses, optimal velocity, useful power
    Nationell ämneskategori
    Energisystem Marin teknik Reglerteknik Havs- och vattendragsteknik
    Identifikatorer
    urn:nbn:se:uu:diva-457294 (URN)10.1049/rpg2.12290 (DOI)000703141600001 ()
    Forskningsfinansiär
    Forskningsrådet Formas, 2020-03634Energimyndigheten
    Tillgänglig från: 2021-10-27 Skapad: 2021-10-27 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    2. Design and evaluation of linear and rotational generator scale models for wave tank testing
    Öppna denna publikation i ny flik eller fönster >>Design and evaluation of linear and rotational generator scale models for wave tank testing
    2019 (Engelska)Konferensbidrag, Publicerat paper (Refereegranskat)
    Ort, förlag, år, upplaga, sidor
    CRC Press, 2019
    Nationell ämneskategori
    Energisystem Havs- och vattendragsteknik Marin teknik Annan elektroteknik och elektronik
    Identifikatorer
    urn:nbn:se:uu:diva-457307 (URN)9780429505324 (ISBN)9781138585355 (ISBN)
    Konferens
    3rd international conference on renewable energies offshore (renew 2018), 8–10 october 2018, Lisbon, Portugal
    Tillgänglig från: 2021-10-27 Skapad: 2021-10-27 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    3. Wave Energy Converter Power Take-Off System Scaling and Physical Modelling
    Öppna denna publikation i ny flik eller fönster >>Wave Energy Converter Power Take-Off System Scaling and Physical Modelling
    Visa övriga...
    2020 (Engelska)Ingår i: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 8, nr 9, artikel-id 632Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Absorbing wave power from oceans for producing a usable form of energy represents an attractive challenge, which for the most part concerns the development and integration, in a wave energy device, of a reliable, efficient and cost-effective power take-off mechanism. During the various stages of progress, for assessing a wave energy device, it is convenient to carry out experimental testing that, opportunely, takes into account the realistic behaviour of the power take-off mechanism at a small scale. To successfully replicate and assess the power take-off, good practices need to be implemented aiming to correctly scale and evaluate the power take-off mechanism and its behaviour. The present paper aims to explore and propose solutions that can be applied for reproducing and assessing the power take-off element during experimental studies, namely experimental set-ups enhancements, calibration practices, and error estimation methods. A series of recommendations on how to practically organize and carry out experiments were identified and three case studies are briefly covered. It was found that, despite specific options that can be strictly technology-dependent, various recommendations could be universally applicable.

    Ort, förlag, år, upplaga, sidor
    MDPI, 2020
    Nyckelord
    power take-off damping, wave power device, experimental testing, PTO simulator, uncertainty analysis, wave energy testing, experimental set-up, calibration
    Nationell ämneskategori
    Annan elektroteknik och elektronik
    Identifikatorer
    urn:nbn:se:uu:diva-425480 (URN)10.3390/jmse8090632 (DOI)000582055100001 ()
    Forskningsfinansiär
    EU, Horisont 2020, POCI-01-0145-FEDER-016882EU, Horisont 2020, PTDC/MAR-TEC/6984/2014StandUp, 47264-1
    Tillgänglig från: 2020-11-19 Skapad: 2020-11-19 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    4. Experimental investigation of a point-absorber wave energy converter response in different wave-type representations of extreme sea states
    Öppna denna publikation i ny flik eller fönster >>Experimental investigation of a point-absorber wave energy converter response in different wave-type representations of extreme sea states
    2022 (Engelska)Ingår i: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 248, artikel-id 110693Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The experimental results of a 1:30 scaled wave tank experiment of a point-absorber in extreme sea states and intermediate water depth are studied. The effect of the PTO damping parameter and different non-linear phenomena in extreme wave conditions such as wave breaking and overtopping are investigated with the focus on the maximum line (mooring) force in the presence of an upper end-stop. In the comparison of different wave-type representations, i.e. irregular, regular, and focused waves, of the same sea state, not all the wave types necessarily yield to the same peak line force. Moreover, there exists an optimum damping value for each sea state in which the smallest peak force is achieved. Both end-stop spring compression and wave-breaking slamming result in peak line forces which may be compensated by overtopping water pressure. Large surge motion is obtained for waves with a long wavelength which can contribute to higher and more damaging line forces.

    Ort, förlag, år, upplaga, sidor
    ElsevierElsevier BV, 2022
    Nyckelord
    Extreme waves, Wave breaking, Slamming, Overtopping, Wave types, End-stop, PTO damping
    Nationell ämneskategori
    Energiteknik Tillförlitlighets- och kvalitetsteknik Havs- och vattendragsteknik
    Identifikatorer
    urn:nbn:se:uu:diva-468337 (URN)10.1016/j.oceaneng.2022.110693 (DOI)000778810700004 ()
    Forskningsfinansiär
    Energimyndigheten, 47264-1Vetenskapsrådet, 2020-03634StandUp
    Tillgänglig från: 2022-02-23 Skapad: 2022-02-23 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    5. Experimental results of force measurements from a scaled point absorbing wave energy converter subjected to extreme waves
    Öppna denna publikation i ny flik eller fönster >>Experimental results of force measurements from a scaled point absorbing wave energy converter subjected to extreme waves
    2021 (Engelska)Ingår i: Proceedings of the Fourteenth European Wave and Tidal Energy Conference, European Wave and Tidal Energy Conference (EWTEC) , 2021Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    To achieve a high reliability and durability for wave energy technologies, the effect of extreme wave conditions on the system must be understood. Wave tank experiments are an essential tool to evaluate this, and provide also a foundation for validation of numerical and analytical methods. However, it is not straight-forward how to design such small scale experiments so that they realistically represent wave energy converters in the ocean. In this paper, wave tank experiments of a 1:30 scaled friction damping linear power take-off (PTO) and cylindrical buoy with ellipsoidal bottom are presented. The linear PTO includes a rod that moves vertically against a Teflon block which introduces friction damping. The damping can be adjusted by changing the spring length that provides the compressive force between the Teflon block and the rod. To study extreme forces and snap loads, two load cells measure the line force both directly beneath the buoy, and at the top of the PTO. The motion of the PTO and the buoy are measured with a wire draw line position sensor and Qualysis system, respectively, and a data acquisition system collects and synchronizes the data. The extreme wave conditions used in the experiments are sea states with 50 years return period at the Dowsing site, North Sea. The waves are modelled as regular, irregular and focused waves. Here, the experimental setup and dry testing experiments are presented, and results of the wave tank test experiment for extreme forces are evaluated and further compared with WEC-SIM, to evaluate the agreement of the numerical and experimental model.

    Ort, förlag, år, upplaga, sidor
    European Wave and Tidal Energy Conference (EWTEC), 2021
    Serie
    Proceedings of the European Wave and Tidal Energy Conference, ISSN 2706-6932, E-ISSN 2706-6940
    Nationell ämneskategori
    Marin teknik Havs- och vattendragsteknik
    Identifikatorer
    urn:nbn:se:uu:diva-457301 (URN)
    Konferens
    Fourteenth European Wave and Tidal Energy Conference (EWTEC), 5-9 September, 2021, Plymouth, UK
    Tillgänglig från: 2021-10-27 Skapad: 2021-10-27 Senast uppdaterad: 2024-03-12
    6. Environmental design load for the line force of a point-absorber wave energy converter
    Öppna denna publikation i ny flik eller fönster >>Environmental design load for the line force of a point-absorber wave energy converter
    2022 (Engelska)Ingår i: Applied Ocean Research, ISSN 0141-1187, E-ISSN 1879-1549, Vol. 128, artikel-id 103305Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    To ensure a reliable operation over the life time of wave energy converters (WECs), a number of load cases need to be considered according to international standards for marine structures to determine an optimal design. This paper outlines the procedure of obtaining an environmental design load for the line force of a 1:30 scaled point-absorber WEC using an environmental contour with a 50-year return period for the Dowsing site in the North Sea. To obtain the response of the WEC during extreme conditions, a numerical WEC-Sim model is developed and calibrated with experimental wave tank tests to augment the data required for such design load analysis. The design load for the line force is estimated based on the full long-term extreme response computed from the full sea state approach by considering 180, 360, and 720 sea state samples as well as the contour approach for the sea state that gives the most extreme response. Further, a probabilistic approach is used to quantify the probability of failure for a critical mechanical component of the system such as shackle. The result shows that the numerical WEC-Sim model is able to sufficiently replicate the real response of the system during extreme irregular waves. The Bayesian theory with Monte-Carlo algorithm is found to be an excellent tool for identifying the degree of belief in the statistical models used for the short-term extreme response analysis. Considering the ultimate limit state, the design load for the 1:30 scaled system is calculated as 670.95 N (i.e. 18.11 MN for a full-scale system) after applying the partial load safety factor of 1.35 on the full long-term extreme response of the system for the 9.1 years return period (i.e. 50 years in a full-scale model).

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2022
    Nyckelord
    Design load, Wave tank experiment, WEC-Sim, Bayesian, Markov chain Monte-Carlo, Long-term extreme response, Short-term extreme response, Probabilistic failure
    Nationell ämneskategori
    Energiteknik Tillförlitlighets- och kvalitetsteknik Marin teknik
    Identifikatorer
    urn:nbn:se:uu:diva-484405 (URN)10.1016/j.apor.2022.103305 (DOI)000857872300005 ()
    Forskningsfinansiär
    Energimyndigheten, 47264-1Vetenskapsrådet, 2020-03634Forskningsrådet Formas, 2018-01784
    Tillgänglig från: 2022-09-12 Skapad: 2022-09-12 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    7. Fatigue analysis of a point-absorber wave energy converter based on augmented data from a WEC-Sim model calibrated with experimental data
    Öppna denna publikation i ny flik eller fönster >>Fatigue analysis of a point-absorber wave energy converter based on augmented data from a WEC-Sim model calibrated with experimental data
    2022 (Engelska)Ingår i: Trends in Renewable Energies Offshore: Proceedings of the 5th International Conference on Renewable Energies Offshore, London: CRC Press, 2022Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    To avoid over-designing wave energy converters (WECs), their reliability and survivability aspects need to be accurately addressed. The most common failure modes are: instantaneous failure due to high instantaneous loads, and fatigue failure due to the accumulated damage in the structure during years of operation. Here, we present a fatigue analysis of a point-absorber WEC in sea states corresponding to a 50-year environmental contour from the Dowsing site, UK. The data for this analysis is generated by a WEC-Sim model that is calibrated with a 1:30 scaled WEC from a wave tank experiment. In this study, the partial damage in each 1-hour sea state sample is calculated using the rainflow counting and Palmgren-Miner rule. Then, considering the joint probability density function of the sea states, the equivalent two-million cycle load is 2.42 MN for the full-scale system considering the accumulated damage in 50 years of operation. In a comparison of the fatigue limit state (FLS) and ultimate limit state (ULS), it was found that the ULS is the governing limit state in the design of the WEC system here.

    Ort, förlag, år, upplaga, sidor
    London: CRC Press, 2022
    Nyckelord
    Fatigue, Experimental, Numerical, Reliability, FLS, ULS
    Nationell ämneskategori
    Marin teknik Havs- och vattendragsteknik Energiteknik Tillförlitlighets- och kvalitetsteknik
    Identifikatorer
    urn:nbn:se:uu:diva-488398 (URN)9781003360773 (ISBN)
    Konferens
    5th International Conference on Renewable Energies Offshore, RENEW 2022, Lisbon, Portugal, 8–10 November
    Tillgänglig från: 2022-11-15 Skapad: 2022-11-15 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    8. A Neural Network Approach To Minimize Line Forces In The Survivability Of The Point-Absorber Wave Energy Converters
    Öppna denna publikation i ny flik eller fönster >>A Neural Network Approach To Minimize Line Forces In The Survivability Of The Point-Absorber Wave Energy Converters
    2023 (Engelska)Ingår i: Proceedings of ASME 2023 42nd International Conference on Ocean, Offshore & Arctic Engineering (OMAE2023), ASME Press, 2023, Vol. 8, artikel-id OMAE2023-102422Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    One strategy for the survivability of wave energy converters(WECs) is to minimize the extreme forces on the structure by adjusting the system damping. In this paper, a neural network model is developed to predict the peak line force for a 1:30 scaled point-absorber WEC with a linear friction-damping power take-off (PTO). The algorithm trains over the wave tank experimental data and enables an update of the system damping based on the system state (i.e. position, velocity, and acceleration) and information on the incoming waves for the extreme sea states. The results show that the deep neural network (DNN) developed here is relatively fast and able to predict the peak line forces with a correlation of 88% when compared to the true (experimental)data. Then, the optimum damping for survivability purposes is found by minimizing the peak line force. It is shown that the optimum damping varies depending on the system state in each zero up-crossing episode.

    Ort, förlag, år, upplaga, sidor
    ASME Press, 2023
    Nationell ämneskategori
    Reglerteknik Marin teknik Havs- och vattendragsteknik
    Identifikatorer
    urn:nbn:se:uu:diva-506611 (URN)10.1115/OMAE2023-102422 (DOI)001216330300065 ()978-0-7918-8690-8 (ISBN)
    Konferens
    International Conference on Ocean, Offshore & Arctic Engineering (OMAE), 11-16 June, 2023, Melbourne, Australia
    Forskningsfinansiär
    Energimyndigheten, 47264-1Vetenskapsrådet, 2020-03634StandUpÅForsk (Ångpanneföreningens Forskningsstiftelse)
    Tillgänglig från: 2023-06-28 Skapad: 2023-06-28 Senast uppdaterad: 2024-06-12Bibliografiskt granskad
    9. Control of a point absorber wave energy converter in extreme wave conditions using a deep learning model in WEC-Sim
    Öppna denna publikation i ny flik eller fönster >>Control of a point absorber wave energy converter in extreme wave conditions using a deep learning model in WEC-Sim
    2023 (Engelska)Ingår i: OCEANS 2023 - LIMERICK, IEEE, 2023Konferensbidrag, Publicerat paper (Refereegranskat)
    Abstract [en]

    The survivability of wave energy converters (WECs) is one of the challenges that have a direct influence on their cost. To protect the WEC from the impact of extreme waves, it is often to over-dimension the components or adopt survivability modes e.g. by submerging or lifting the WEC if it is applicable. Here, a control strategy for adjusting the system damping is developed based on deep neural networks (DNN) to minimize the line (mooring) force exerted on a 1:30 scaled WEC. This DNN model is then implemented in a control system of a numerical WEC-Sim model to find the optimal power take-off (PTO) damping for every zero up-crossing episode of surface elevation which minimizes the peak line force. The WEC-Sim model was calibrated based on a 1:30 scaled wave tank experiment that was designed to investigate the WEC response in extreme sea states with a 50-year return period. It is shown that this survival strategy reduces the peak forces when compared with the response of a system that has been set to a constant PTO damping for the entire duration of the sea state.

    Ort, förlag, år, upplaga, sidor
    IEEE, 2023
    Nationell ämneskategori
    Marin teknik Havs- och vattendragsteknik Reglerteknik
    Identifikatorer
    urn:nbn:se:uu:diva-506599 (URN)10.1109/OCEANSLimerick52467.2023.10244529 (DOI)001074614700227 ()979-8-3503-3227-8 (ISBN)979-8-3503-3226-1 (ISBN)
    Konferens
    OCEANS Conference,JUN 05-08, 2023, Limerick, IRELAND
    Forskningsfinansiär
    Energimyndigheten, 47264-1Vetenskapsrådet, 2020-03634StandUpÅForsk (Ångpanneföreningens Forskningsstiftelse)
    Tillgänglig från: 2023-06-28 Skapad: 2023-06-28 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    10. Investigation on the extreme peak mooring force distribution of a point absorber wave energy converter with and without a survivability control system
    Öppna denna publikation i ny flik eller fönster >>Investigation on the extreme peak mooring force distribution of a point absorber wave energy converter with and without a survivability control system
    2023 (Engelska)Ingår i: Proceedings of the European Wave and Tidal Energy Conference (EWTEC), ISSN 2706-6932, Vol. 15, artikel-id 161Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    To determine the optimal design of the wave energy converter (WEC) that can withstand extreme waveconditions, the short- and long-term extreme responses of the system need to be determined. This paper focuses on the extreme peak force distribution of the mooring force for a 1:30 scaled point absorber WEC. The basis of this analysis is the mooring force response obtained from a WEC-Sim model calibrated by wave tank experimental data. The extreme sea states have been chosen from a50-year environmental contour. Here, first, the long-term extreme response using the full sea state approach is obtained for three constant damping cases of the power take-off (PTO) system. Then, using a contour approach, the expected value of the extreme peak line (mooring) force distribution is computed for the sea states along an environmental contour. Further, for the most extremesea state, the extreme peak line force distribution is also computed where a survivability control system, based on a deep neural network (DNN), changes the PTO damping to minimize the peak mooring force in each zero up-crossing episode of surface elevation. The results show that in the absence of a control system, the zero PTO damping case is a conservative choice in the analysis of the long-term response and the design load. For the most extreme sea state along the environmental contour, the survivability control system slightly reduces the expected value of the extreme peak force distribution when compared with lower constant PTO damping configurations.

    Ort, förlag, år, upplaga, sidor
    European Wave and Tidal Energy Conference, 2023
    Nyckelord
    Wave energy converter, Deep neural network, Control system, Design load, Long-term extreme response
    Nationell ämneskategori
    Marin teknik Havs- och vattendragsteknik Tillförlitlighets- och kvalitetsteknik Energiteknik Reglerteknik
    Identifikatorer
    urn:nbn:se:uu:diva-511367 (URN)10.36688/ewtec-2023-161 (DOI)
    Konferens
    15th European Wave and Tidal Energy Conference (EWTEC 2023), 3–7 September, 2023, Bilbao, Spain
    Tillgänglig från: 2023-09-13 Skapad: 2023-09-13 Senast uppdaterad: 2024-03-12Bibliografiskt granskad
    11. Neural network survivability approach of a wave energy converter considering uncertainties in the prediction of future knowledge
    Öppna denna publikation i ny flik eller fönster >>Neural network survivability approach of a wave energy converter considering uncertainties in the prediction of future knowledge
    2024 (Engelska)Ingår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 228, artikel-id 120662Artikel i tidskrift (Refereegranskat) Submitted
    Abstract [en]

    To tune the wave energy converter (WEC) controller parameters such as damping to reduce the line force during extreme wave conditions, future knowledge of the line force is required.To achieve this, the incoming wave and system state should be predicted for a few seconds in the future. It is rather an arduous task to predict the future knowledge of waves and the system's dynamic when dealing with breaking and steep waves, and the system is subject to various nonlinear forces. The classical model-based control strategies often rely on linear assumptions to estimate the WEC dynamics for the sake of simplicity. Unlike the model-based, the data-driven approaches are free from modeling errors and the algorithms are trained over the true and noisy data to predict non-linear system behaviors.Using data-driven approaches, we are able to model nonlinear dynamics. However, new questions emerge on the accuracy of the future wave and system state predictions, and how this uncertainty propagates into the final prediction of the line force. As incorrect damping may lead to excessive line force and detrimental damage to the system, these are the knowledge gaps that need to be addressed.The main purpose of this paper is to answer these questions through a survivability strategy for wave energy converters by providing a realistic perspective on the implementation of the neural network approaches by accounting for the errors in the input data. For this purpose, a series of neural networks is designed that first predicts the surface elevation for 0.36 s ahead, i.e. corresponding to 2 s in the full-scale WEC. This future knowledge of the wave elevation is then used to predict the system state (i.e. power take-off (PTO) translator position) for the same prediction horizon based on the PTO damping. This information is then fed to a convolutional neural network (CNN) that predicts the peak line force 0.36 s ahead. Further, the sensitivity of the peak line force prediction to the uncertainties in the input data and the prediction horizon is analyzed. The neural network models are trained over the experimental data subjected to the extreme sea states for a point absorber wave energy converter. The results present a thorough analysis of the NN models’ performance.The results suggest that the accuracy of the surface elevation prediction has an insignificant independent effect on the peak force prediction model. However, these uncertainties reflect in the PTO translator position prediction, and the model is considerably sensitive to the accuracy of this prediction. This sensitivity nonetheless is less notable for higher PTO damping values. The prediction accuracy of the peak forces dropped by only about 7\% when the predicted input was used in the lower damping cases here, whereas, a larger drop was seen for the higher damping case.  

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2024
    Nyckelord
    Wave energy converters, Survivability, Neural networks, Prediction of system dynamics, Extreme sea state, Wave tank experiment
    Nationell ämneskategori
    Marin teknik Havs- och vattendragsteknik Reglerteknik Energiteknik Tillförlitlighets- och kvalitetsteknik
    Identifikatorer
    urn:nbn:se:uu:diva-521361 (URN)10.1016/j.renene.2024.120662 (DOI)001245604600001 ()
    Tillgänglig från: 2024-01-23 Skapad: 2024-01-23 Senast uppdaterad: 2024-07-02Bibliografiskt granskad
    Ladda ner fulltext (pdf)
    UUThesis_Z-Shahroozi-2024
    Ladda ner (jpg)
    preview image
  • 9.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Uppsala University.
    Eriksson, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Engström, Jens
    Design and evaluation of linear and rotational generator scale models for wave tank testing2019Konferensbidrag (Refereegranskat)
  • 10.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    A Neural Network Approach To Minimize Line Forces In The Survivability Of The Point-Absorber Wave Energy Converters2023Ingår i: Proceedings of ASME 2023 42nd International Conference on Ocean, Offshore & Arctic Engineering (OMAE2023), ASME Press, 2023, Vol. 8, artikel-id OMAE2023-102422Konferensbidrag (Refereegranskat)
    Abstract [en]

    One strategy for the survivability of wave energy converters(WECs) is to minimize the extreme forces on the structure by adjusting the system damping. In this paper, a neural network model is developed to predict the peak line force for a 1:30 scaled point-absorber WEC with a linear friction-damping power take-off (PTO). The algorithm trains over the wave tank experimental data and enables an update of the system damping based on the system state (i.e. position, velocity, and acceleration) and information on the incoming waves for the extreme sea states. The results show that the deep neural network (DNN) developed here is relatively fast and able to predict the peak line forces with a correlation of 88% when compared to the true (experimental)data. Then, the optimum damping for survivability purposes is found by minimizing the peak line force. It is shown that the optimum damping varies depending on the system state in each zero up-crossing episode.

  • 11.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Control of a point absorber wave energy converter in extreme wave conditions using a deep learning model in WEC-Sim2023Ingår i: OCEANS 2023 - LIMERICK, IEEE, 2023Konferensbidrag (Refereegranskat)
    Abstract [en]

    The survivability of wave energy converters (WECs) is one of the challenges that have a direct influence on their cost. To protect the WEC from the impact of extreme waves, it is often to over-dimension the components or adopt survivability modes e.g. by submerging or lifting the WEC if it is applicable. Here, a control strategy for adjusting the system damping is developed based on deep neural networks (DNN) to minimize the line (mooring) force exerted on a 1:30 scaled WEC. This DNN model is then implemented in a control system of a numerical WEC-Sim model to find the optimal power take-off (PTO) damping for every zero up-crossing episode of surface elevation which minimizes the peak line force. The WEC-Sim model was calibrated based on a 1:30 scaled wave tank experiment that was designed to investigate the WEC response in extreme sea states with a 50-year return period. It is shown that this survival strategy reduces the peak forces when compared with the response of a system that has been set to a constant PTO damping for the entire duration of the sea state.

  • 12.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS), Uppsala, Sweden .
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Experimental investigation of a point-absorber wave energy converter response in different wave-type representations of extreme sea states2022Ingår i: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 248, artikel-id 110693Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The experimental results of a 1:30 scaled wave tank experiment of a point-absorber in extreme sea states and intermediate water depth are studied. The effect of the PTO damping parameter and different non-linear phenomena in extreme wave conditions such as wave breaking and overtopping are investigated with the focus on the maximum line (mooring) force in the presence of an upper end-stop. In the comparison of different wave-type representations, i.e. irregular, regular, and focused waves, of the same sea state, not all the wave types necessarily yield to the same peak line force. Moreover, there exists an optimum damping value for each sea state in which the smallest peak force is achieved. Both end-stop spring compression and wave-breaking slamming result in peak line forces which may be compensated by overtopping water pressure. Large surge motion is obtained for waves with a long wavelength which can contribute to higher and more damaging line forces.

    Ladda ner fulltext (pdf)
    fulltext
  • 13.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Experimental results of force measurements from a scaled point absorbing wave energy converter subjected to extreme waves2021Ingår i: Proceedings of the Fourteenth European Wave and Tidal Energy Conference, European Wave and Tidal Energy Conference (EWTEC) , 2021Konferensbidrag (Refereegranskat)
    Abstract [en]

    To achieve a high reliability and durability for wave energy technologies, the effect of extreme wave conditions on the system must be understood. Wave tank experiments are an essential tool to evaluate this, and provide also a foundation for validation of numerical and analytical methods. However, it is not straight-forward how to design such small scale experiments so that they realistically represent wave energy converters in the ocean. In this paper, wave tank experiments of a 1:30 scaled friction damping linear power take-off (PTO) and cylindrical buoy with ellipsoidal bottom are presented. The linear PTO includes a rod that moves vertically against a Teflon block which introduces friction damping. The damping can be adjusted by changing the spring length that provides the compressive force between the Teflon block and the rod. To study extreme forces and snap loads, two load cells measure the line force both directly beneath the buoy, and at the top of the PTO. The motion of the PTO and the buoy are measured with a wire draw line position sensor and Qualysis system, respectively, and a data acquisition system collects and synchronizes the data. The extreme wave conditions used in the experiments are sea states with 50 years return period at the Dowsing site, North Sea. The waves are modelled as regular, irregular and focused waves. Here, the experimental setup and dry testing experiments are presented, and results of the wave tank test experiment for extreme forces are evaluated and further compared with WEC-SIM, to evaluate the agreement of the numerical and experimental model.

  • 14.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Fatigue analysis of a point-absorber wave energy converter based on augmented data from a WEC-Sim model calibrated with experimental data2022Ingår i: Trends in Renewable Energies Offshore: Proceedings of the 5th International Conference on Renewable Energies Offshore, London: CRC Press, 2022Konferensbidrag (Refereegranskat)
    Abstract [en]

    To avoid over-designing wave energy converters (WECs), their reliability and survivability aspects need to be accurately addressed. The most common failure modes are: instantaneous failure due to high instantaneous loads, and fatigue failure due to the accumulated damage in the structure during years of operation. Here, we present a fatigue analysis of a point-absorber WEC in sea states corresponding to a 50-year environmental contour from the Dowsing site, UK. The data for this analysis is generated by a WEC-Sim model that is calibrated with a 1:30 scaled WEC from a wave tank experiment. In this study, the partial damage in each 1-hour sea state sample is calculated using the rainflow counting and Palmgren-Miner rule. Then, considering the joint probability density function of the sea states, the equivalent two-million cycle load is 2.42 MN for the full-scale system considering the accumulated damage in 50 years of operation. In a comparison of the fatigue limit state (FLS) and ultimate limit state (ULS), it was found that the ULS is the governing limit state in the design of the WEC system here.

  • 15.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Investigation on the extreme peak mooring force distribution of a point absorber wave energy converter with and without a survivability control system2023Ingår i: Proceedings of the European Wave and Tidal Energy Conference (EWTEC), ISSN 2706-6932, Vol. 15, artikel-id 161Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To determine the optimal design of the wave energy converter (WEC) that can withstand extreme waveconditions, the short- and long-term extreme responses of the system need to be determined. This paper focuses on the extreme peak force distribution of the mooring force for a 1:30 scaled point absorber WEC. The basis of this analysis is the mooring force response obtained from a WEC-Sim model calibrated by wave tank experimental data. The extreme sea states have been chosen from a50-year environmental contour. Here, first, the long-term extreme response using the full sea state approach is obtained for three constant damping cases of the power take-off (PTO) system. Then, using a contour approach, the expected value of the extreme peak line (mooring) force distribution is computed for the sea states along an environmental contour. Further, for the most extremesea state, the extreme peak line force distribution is also computed where a survivability control system, based on a deep neural network (DNN), changes the PTO damping to minimize the peak mooring force in each zero up-crossing episode of surface elevation. The results show that in the absence of a control system, the zero PTO damping case is a conservative choice in the analysis of the long-term response and the design load. For the most extreme sea state along the environmental contour, the survivability control system slightly reduces the expected value of the extreme peak force distribution when compared with lower constant PTO damping configurations.

  • 16.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS), Villavägen 16, Uppsala, 752 36, Swede.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Neural network survivability approach of a wave energy converter considering uncertainties in the prediction of future knowledge2024Ingår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 228, artikel-id 120662Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To tune the wave energy converter (WEC) controller parameters such as damping to reduce the line force during extreme wave conditions, future knowledge of the line force is required.To achieve this, the incoming wave and system state should be predicted for a few seconds in the future. It is rather an arduous task to predict the future knowledge of waves and the system's dynamic when dealing with breaking and steep waves, and the system is subject to various nonlinear forces. The classical model-based control strategies often rely on linear assumptions to estimate the WEC dynamics for the sake of simplicity. Unlike the model-based, the data-driven approaches are free from modeling errors and the algorithms are trained over the true and noisy data to predict non-linear system behaviors.Using data-driven approaches, we are able to model nonlinear dynamics. However, new questions emerge on the accuracy of the future wave and system state predictions, and how this uncertainty propagates into the final prediction of the line force. As incorrect damping may lead to excessive line force and detrimental damage to the system, these are the knowledge gaps that need to be addressed.The main purpose of this paper is to answer these questions through a survivability strategy for wave energy converters by providing a realistic perspective on the implementation of the neural network approaches by accounting for the errors in the input data. For this purpose, a series of neural networks is designed that first predicts the surface elevation for 0.36 s ahead, i.e. corresponding to 2 s in the full-scale WEC. This future knowledge of the wave elevation is then used to predict the system state (i.e. power take-off (PTO) translator position) for the same prediction horizon based on the PTO damping. This information is then fed to a convolutional neural network (CNN) that predicts the peak line force 0.36 s ahead. Further, the sensitivity of the peak line force prediction to the uncertainties in the input data and the prediction horizon is analyzed. The neural network models are trained over the experimental data subjected to the extreme sea states for a point absorber wave energy converter. The results present a thorough analysis of the NN models’ performance.The results suggest that the accuracy of the surface elevation prediction has an insignificant independent effect on the peak force prediction model. However, these uncertainties reflect in the PTO translator position prediction, and the model is considerably sensitive to the accuracy of this prediction. This sensitivity nonetheless is less notable for higher PTO damping values. The prediction accuracy of the peak forces dropped by only about 7\% when the predicted input was used in the lower damping cases here, whereas, a larger drop was seen for the higher damping case.  

    Ladda ner fulltext (pdf)
    fulltext
  • 17.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik.
    Todalshaug, Jørgen Hals
    CorPowerOcean AB, Hägersten, Sweden.
    Considerations on prediction horizon and dissipative losses for wave energy converters2021Ingår i: IET Renewable Power Generation, ISSN 1752-1416, E-ISSN 1752-1424, IET Renewable Power Generation, Vol. 15, nr 14, s. 3434-3458Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

    Ladda ner fulltext (pdf)
    fulltext
  • 18.
    Shahroozi, Zahra
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS), Villavägen 16, Uppsala, 752 36, Sweden.
    Nilsson, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft-, vatten- och landskapslära. Centre of Natural Hazards and Disaster Science (CNDS), Villavägen 16, Uppsala, 752 36, Sweden.
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Environmental design load for the line force of a point-absorber wave energy converter2022Ingår i: Applied Ocean Research, ISSN 0141-1187, E-ISSN 1879-1549, Vol. 128, artikel-id 103305Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To ensure a reliable operation over the life time of wave energy converters (WECs), a number of load cases need to be considered according to international standards for marine structures to determine an optimal design. This paper outlines the procedure of obtaining an environmental design load for the line force of a 1:30 scaled point-absorber WEC using an environmental contour with a 50-year return period for the Dowsing site in the North Sea. To obtain the response of the WEC during extreme conditions, a numerical WEC-Sim model is developed and calibrated with experimental wave tank tests to augment the data required for such design load analysis. The design load for the line force is estimated based on the full long-term extreme response computed from the full sea state approach by considering 180, 360, and 720 sea state samples as well as the contour approach for the sea state that gives the most extreme response. Further, a probabilistic approach is used to quantify the probability of failure for a critical mechanical component of the system such as shackle. The result shows that the numerical WEC-Sim model is able to sufficiently replicate the real response of the system during extreme irregular waves. The Bayesian theory with Monte-Carlo algorithm is found to be an excellent tool for identifying the degree of belief in the statistical models used for the short-term extreme response analysis. Considering the ultimate limit state, the design load for the 1:30 scaled system is calculated as 670.95 N (i.e. 18.11 MN for a full-scale system) after applying the partial load safety factor of 1.35 on the full long-term extreme response of the system for the 9.1 years return period (i.e. 50 years in a full-scale model).

    Ladda ner fulltext (pdf)
    fulltext
  • 19. Zhu, Guixun
    et al.
    Shahroozi, Zahra
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Zheng, Siming
    Göteman, Malin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära. Centre of Natural Hazards and Disaster Science (CNDS).
    Engström, Jens
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för elektroteknik, Elektricitetslära.
    Greaves, Deborah
    Experimental study of interactions between focused waves and a point absorber wave energy converter2023Ingår i: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 287, artikel-id 115815Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Predicting the response of point absorber wave energy converters (WECs) in extreme sea states is crucial for assessing their survivability. However, data are scarce and hydrodynamic understanding is limited. In order to simulate extreme wave conditions, laboratory-scale focused waves based on NewWave theory have been utilized. To investigate the interactions between focused waves and a point absorber WEC, a wave basin experiment has been conducted. Various parameters, including focusing amplitude and peak frequency have been examined across three different damping conditions. The motion response of the point absorber WEC and the corresponding mooring force have been measured over time. The experimental findings reveal that both the focused wave parameters and the damping values have a significant influence on the motion response and mooring force. It is shown that an increase in the focusing amplitude leads to a more intense motion response, while the mooring force is relatively insensitive to the focused amplitude/peak frequency when the end-stop spring is not compressed. The force in the connection line is maximized when the upper end-stop spring is compressed. As the peak frequency increases, the heave and surge responses decrease, whereas the maximum mooring force increases with peak frequency for a locked power take-off (PTO) system. Finally, the results indicate that optimizing the design of the power take-off system, including selecting appropriate damping values and stroke lengths for the translator, can significantly reduce the mooring load for extreme wave conditions.

    Ladda ner fulltext (pdf)
    fulltext
1 - 19 av 19
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf