Dissertations / Theses on the topic 'Energy Mooring'
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1
Parish, David Nigel. "A novel mooring tether for highly dynamic offshore applications." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/21337.
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The mooring of vessels and other floating bodies at sea, such as offshore platforms has necessitated the development of specialised moorings technology. The marine renewable energy (MRE) sector is now at a stage in its development whereby floating devices are adding new challenges to the moorings industries. Floating MRE devices are smaller than, for instance offshore platforms, and are usually targeted for deployment in highly energetic environments. The extreme conditions and the highly dynamic response of an MRE device present challenges in terms of peak loading within the mooring system itself and load transfer to the floating body. Compliant mooring systems provide advantages by reducing the peak loads and fibre ropes are an important asset in achieving such compliance. However, the extent to which existing fibre ropes can safely extend axially to provide compliance is insufficient and is strongly associated to the minimum breaking load (MBL) of the rope. A novel fibre rope mooring tether is presented here that provides advantages over existing ropes. The tether employs a hollow fibre rope containing an elastomeric core, this mechanism de-coupling the extension properties from the strength of the line. The load path is carried through the polyester rope which is terminated conventionally by eye splices, thus minimising any new risks to reliability. Very low axial stiffness is achieved and is shown to be selectable within limits. For comparison, the prototype tether’s MBL of 222 kN is assigned to polyester and Nylon reference ropes. The axial stiifness of these ropes are 590 kN and 463 kN respectively when measured by a secant between the origin and 30% MBL; the novel tether displays an axial stiffness of 72 kN by the same method. This enables the novel tether to achieve more than two and a half times the extension of a comparable Nylon rope in its working range. Numerical modelling of a moored installation demonstrates a threefold reduction in peak load magnitude compared to the existing Nylon rope solution. The tether exhibits two distinct stages of extension, the first having very low axial stiffness. It is demonstrated that the extent of this soft phase can be selected by design and that this might add another useful element of control to moorings design work.
2
Gordelier, Tessa Jane. "Enhancing wave energy deployments through mooring system reliability assessment." Thesis, University of Exeter, 2016. http://hdl.handle.net/10871/24917.
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Wave energy generation is a promising renewable energy source but it faces certain challenges before it can become commercially viable. In comparison to conventional energy generation it is expensive, furthermore it has been plagued by reliability challenges due to the harsh operating demands of the marine environment. This Thesis investigates the reliability of wave energy devices, and specifically focuses on mooring system reliability. Two major themes are developed: Firstly, an assessment is conducted on a conventional mooring component, reviewing safety factors suggested in mooring system design guidelines and investigating whether there is a potential to reduce these safety factors (and in so doing, reduce system costs). Numerical modelling, laboratory testing and field testing demonstrate that excessively large safety factors are published in design guidance for static loading scenarios. However, when considering fatigue loading regimes (a critical aspect of wave energy generation), the proposed safety factors are found to be appropriate. In fatigue design, the importance of selecting an appropriate stress concentration factor for use with generic S-N curves is highlighted. These findings indicate the publication of additional stress concentration factors and a standard approach for mean stress adjustment would be a valuable addition to mooring system design guidance for fatigue. The second theme introduces a novel mooring component, The Exeter Tether, designed to reduce mooring loads and thus reduce system costs. The introduction of any novel technology brings new reliability considerations, and a reliability assessment of the tether and sub-components is presented in this Thesis. Following a failure modes and effects analysis, a bespoke range of physical tests is developed to investigate reliability concerns unique to this novel component. Laboratory testing of the tether assembly shows promising fatigue performance, however field trials highlight concerns regarding bio-fouling and marine debris ingress. Sub-component testing of the EPDM (Ethylene propylene diene monomer) polymer core suggests an increase in material stiffness with both marine ageing and repeated compression cycles. This finding supports results from assembly trials in the laboratory and at sea, where tether assembly dynamic axial stiffness is observed to increase over time. The overarching design philosophy behind the Exeter Tether is to reduce mooring system loads, so establishing the `worked' operating profile of the tether is crucial for the design intentions to be realised without compromising the reliability of the overall mooring system. Trials on the anti-friction membrane establish optimum performance when using two layers of UHMWPE (Ultra high molecular weight polyethylene) tape. Further areas requiring research are highlighted, and suggestions are made to improve the reliability of future design iterations of The Exeter Tether. The two reliability approaches presented demonstrate the potential for cost reduction in mooring system design and highlight the importance of physical component testing, both in the field and in laboratory conditions, to optimise component design whilst ensuring overall system reliability.
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CAGNINEI, ANDREA. "Hull and mooring design of gyroscopic-based wave energy converter." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2615515.
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Wave energy is one of the less exploited, yet potentially more interesting renewable energy source. In a world where the energy consumption is constantly increasing, but economic and environmental reasons drive the research of alternatives to not-renewable energy sources, it’s just a matter of time before wave energy become an economically sustainable source of renewable energy.
The research effort, started in the seventies, was focused on the development of devices for the harvesting of energy from the energetically rich seas of northern Europe.
The work presented in this thesis is focused on the development of ISWEC, a wave energy converter based on a gyroscopic conversion of a hull motion, designed specifically to work in the Mediterranean Sea. The device, described in detail in chapter 3, was designed in the Department of Mechanics of the Polytechnic of Turin since 2005, and I worked within the research group responsible for its development.
Design of a wave energy converter requires understanding the complex interactions between the device, and its energy-harvesting system, and the waves of the sea. This can be done by the use of numerical models, but experimental validation and testing are always necessary to gain a complete knowledge of such complex phenomena.
A substantial part of my work was dedicated to experimental analysis of ISWEC: chapter 4 describes the analysis conducted on the 1:8 scaled model of the device, in order to adjust and validate a numerical model able to describe the device behavior.
Results obtained from the experimental campaign on the 1:8 model have been used to design the hull of the full scale prototype of the device, as described in chapter 5.
Chapter 6 is dedicated to the study conducted on the mooring system for ISWEC, again performed with the aid of an extensive campaign of tests on a 1:50 scaled model of the device, and of its mooring system.
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Harnois, Violette. "Analysis of highly dynamic mooring systems : peak mooring loads in realistic sea conditions." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/17205.
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Marine Renewable Energy (MRE) is a promising source of energy for the future. However, it is still under development and many challenges need to be overcome to develop competitive solutions. While the design of the station keeping system of traditional offshore oil and gas structures is driven mainly by their low frequency motions, MRE devices are installed at nearshore locations and move dynamically. Because of these criteria, MRE mooring systems require novel mooring systems and associated standards. MRE mooring standards need to take into account the highly dynamic behaviour of these systems, which can lead to large mooring loads. The nature of these loads needs to be investigated to improve the confidence in mooring design and to improve cost-effectiveness. The aim of this thesis is to develop the understanding of peak mooring loads on highly dynamic mooring systems, in particular, the environmental conditions associated with the loads. In addition, preliminary research into the response of the mooring systems to environmental conditions is presented. Both field tests and tank tests have been conducted. Field tests give insight into the behaviour of a dynamic mooring system in real sea conditions. Measuring the mooring loads and the environmental conditions - wave, and current if available – for several months, a methodology has been developed to detect peak mooring loads and identify the associated environmental conditions in order to compare them with the environmental conditions recorded throughout the field tests. The principal finding is that peak mooring loads occur for sea states with large but not always the highest significant wave height HS. The understanding of the effect of tidal conditions on peak mooring loads requires further work. A tank test of a dynamic mooring system in moderate sea states has been conducted to observe the dynamic behaviour of the mooring system. Tank tests enable detailed observations of the dynamic behaviour of a system in a well controlled environment and allow the calibration of a numerical model. The model can be used to investigate separate physical parameters. The results from this thesis will assist in the development of specific standards for MRE mooring systems. These standards are essential for the evolution of the MRE industry.
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Wang, Mingming. "A durable mooring system for a winch-based wave energy converter." Thesis, KTH, Maskinkonstruktion (Inst.), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209484.
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This project has dealt with the developing a new technology for a renewable energy source, the wave energy, which is considered as one of the renewable resources with a potential to contribute to an energy production corresponding to about 10% of the world’s energy consumption nowadays. A point absorber concept that is using a Power Take-off (PTO) unit converts the sea surface wave motion into electricity thanks to a buoy at the sea surface which is moved by the waves. Due to harsh working conditions, the maintenance would cause too many issues, and a mooring system needs to be developed. The aim in this paper is to design a durable mooring system for at least 20 years of operation even working in a harsh sea environment. A geometry model of the mooring system has been built since the dimensioning of its components was performed. Several concepts were generated and evaluated with a Pugh matrix. An analysis of the different stresses affecting the performance of the system was made to validate the design. In addition, the detail design of the different parts of the system has made to allow their manufacture in future work.Projektet har behandlat utvecklingen av en ny teknik för en förnybar energikälla, vågenergin, som anses vara en av de mest lovande förnybara resurserna med potential att bidra till en energiproduktion som motsvarar cirka 10 procent av världens energiförbrukning . Ett punktabsorberande koncept som använder en kraftuttagsenhet (PTO) omvandlar havsytans vågsrörelser till elektricitet. På grund av hårda arbetsförhållanden ger underhållsarbete stora problem och ett förtöjningssystem behöver utvecklas. Syftet med detta projekt är att utforma ett hållbart förtöjningssystem för minst 20 års drift, även i en hård havsmiljö. En geometrisk modell av förtöjningssystemet har skapats baserad på dimensionering av dess komponenter. Flera koncept genererades och utvärderades med en Pugh-matris. En simulering av de olika spänningar som påverkar systemets prestanda gjordes för att validera designen. Dessutom har detaljkonstruktion av de olika delarna av systemet gjorts, så att de kan tillverkas i ett framtida arbete.
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Ransley, Edward Jack. "Survivability of wave energy converter and mooring coupled system using CFD." Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3503.
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This thesis discusses the development of a Numerical Wave Tank (NWT) capable of describing the coupled behaviour of Wave Energy Converters (WECs) and their moorings under extreme wave loading. The NWT utilises the open-source Computational Fluid Dynamics (CFD) software OpenFOAM(R) to solve the fully nonlinear, incompressible, Reynolds-Averaged Navier-Stokes (RANS) equations for air and water using the Finite Volume Method (FVM) and a Volume of Fluid (VOF) treatment of the interface. A method for numerically generating extreme waves is devised, based on the dispersively-focused NewWave theory and using the additional toolbox waves2Foam. A parametric study of the required mesh resolution shows that steeper waves require finer grids for mesh independence. Surface elevation results for wave-only cases closely match those from experiments, although an improved definition of the flow properties is required to generate very steep focused waves. Predictions of extreme wave run-up and pressure on the front of a fixed truncated cylinder compare well with physical measurements; the numerical solution successfully predicts the secondary loading cycle associated with the nonlinear ringing effect and shows a nonlinear relationship between incident crest height and horizontal load. With near perfect agreement during an extreme wave event, the reproduction of the six degree of freedom (6DOF) motion and load in the linearly-elastic mooring of a hemispherical-bottomed buoy significantly improves on similar studies from the literature. Uniquely, this study compares simulations of two existing WEC designs with scale-model tank tests. For the Wavestar machine, a point-absorber constrained to pitch motion only, results show good agreement with physical measurements of pressure, force and float motion in regular waves, although the solution in the wake region requires improvement. Adding bespoke functionality, a point-absorber designed by Seabased AB, consisting of a moored float and Power Take-Off (PTO) with limited stroke length, translator and endstop, is modelled in large regular waves. This represents a level of complexity not previously attempted in CFD and the 6DOF float motion and load in the mooring compare well with experiments. In conclusion, the computational tool developed here is capable of reliably predicting the behaviour of WEC systems during extreme wave events and, with some additional parameterisation, could be used to assess the survivability of WEC systems at full-scale before going to the expense of deployment at sea.
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PASSIONE, BIAGIO. "Hydrodynamic analysis and mooring design of a floating pitching Wave Energy Converter." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2714195.
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The work presented in this thesis is part of an integrated research carried out for
the development of the ISWEC technology. The key aspects of this WEC that can
experience relevant improvement for the technology design and optimization are
found to be hydrodynamics modelling and mooring design. These two topics are
investigated in order to achieve a high reliability numerical tool for the performance
analysis and testing of the ISWEC device.
The existing numerical model has been upgraded and validated against experimental
results, introducing non-linear phenomena. A mooring system has been
designed to be general, considering all the requirements needed for the device deployment.
A design procedure has been used according to offshore conservative
standards, to guarantee the feasibility of the project. The survivability of the moored
device has been tested in a wave tank, reproducing the full storm duration for a
severe installation site. Different mooring configurations have been tested and the
best one has been identified.
The two experimental campaigns have been carried out in Napoli, at the towing
tank of the Department of Industrial Engineering of Università degli studi di Napoli
Federico II.
Methodologies and results presented in this thesis will be used for the design and
deployment of a new ISWEC prototype to be installed in the next future.
The tools and methodologies here presented can be considered as general and
used for the development of different floating WECs. More in detail, the mooring
study is useful for all the floating and submerged WECs that require slack mooring
systems. On the other hand, the hydrodynamic aspect analyzed in this work are
common to the majority of point absorber WECs, with a particular relevance for
WECs that exploit pitch or roll motions.
8
Healy, Strömgren William. "Automatic Adjustment of the Floatation Level for a Tight-moored Buoy." Thesis, Uppsala University, Department of Earth Sciences, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-88883.
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Denna rapport ger förslag på olika metoder att automatiskt justera flytläget på en statiskt förankrad boj, en överblick över de processer som styr ändringen av vattennivån och en statisktisk analys på vattennivåförändringarna vid Stockholm, Kungsholmsfort och Kungsvik.
Beroende på vattenivåns variation finns olika metoder för justering. Områden med små variationer av vattennivå lämpar det sig bäst utan någon som helst justering av flytläget. Områden med inte för stora tidvattensförändringar bör justeras med ett system bestående av vinsch, växellåda med en utväxling på 10 000:1, en 12 V DC motor, ett skötselfritt 12 V batteri, en luftlindad linjärgenerator och en trådtöjningsgivare. Områden med stora variationer i tidvatten behöver en avlastning för motorn i form av en fjäder och dämpare. De monteras horizontellt inuti bojen för att skyddas från den yttre miljön.
Den statistiska analysen påvisade de största vattennivåändringarna vid både Kungsviks och Kungsholmsforts mätstationer, båda uppvisade ett intervall på 1,6 m mellan minimum och maximum. Kungsvik var den station med de största dagliga variationerna, detta på grund av tidvattnets påverkan i området.
This thesis gives examples of different methods of automated adjustment of floatation level for a static moored buoy, an overview of the theories behind water level change and a statistical analysis of the water level changes for Stockholm, Kungsholmsfort and Kungsvik.
Depending on the range and frequency of the water level change different methods of adjustment are recommended. For areas with small changes in sea level the best choice would be no adjustment of the floatation level. Areas that are influenced by moderate tidal ranges should incorporate a system of regulation consisting of a winch, gearbox with a gear ratio of around 10,000:1, 12 V DC motor, 12 V maintenance free battery, air coiled linear generator and a strain gauge. For areas with large tidal ranges the previous system should be complimented with a horizontally mounted spring, inside the buoy, to lessen the loads on the motor.
The statistical analysis found the largest extremes in water level of the three sites to be at Kungsvik and Kungsholmsfort, both exhibiting a range of almost 1.6 m. Kungsvik was the station with the largest daily variations, this is because this is the only station influenced by tidal variations.
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Thies, Philipp Rudolf. "Advancing reliability information for Wave Energy Converters." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/4053.
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Marine renewable energy promises to provide a significant contribution to the future electricity supply. It is estimated that 17% of today's UK electricity demand could be generated from wave and tidal sources. The ambition to harvest this resource is in the public interest, as it eases the pressures on energy security, holds the potential to reduce carbon emissions and has the prospect to create a new UK industry sector worth £15 billion. From an engineering perspective, marine energy is one of the least developed renewable energy technologies and has to be regarded as unproven. The reliability of components and devices in the harsh marine environment is one of the main engineering challenges. Reliability assessments and the assurance of acceptable reliability levels are dependant on the adequacy of failure information, which is scantily available for marine energy. This thesis shows that large failure rate uncertainties impede the reliability assessment for wave energy converters and how a suite of experimental, numerical and statistical methods can be applied to improve scarcely available reliability information. The analysis of component load conditions identifies fatigue as failure mode of concern and the fatigue life of mooring lines and marine power cables is quantified in a floating wave energy application. A Bayesian statistical approach and dedicated service-simulation component testing is proposed, and implemented to improve the quality of reliability estimates and to provide relevant data and assurance. The methods presented, along with the results, will assist reliability assessment and design during early development stages, and will inform the prediction of maintenance requirements during operation. Reliable marine energy systems will be the technical enabler for the successful transition of prototype devices to a commercially viable marine energy industry.
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Savin, Andrej. "Experimental Measurement of Lateral Force in a Submerged Single Heaving Buoy Wave Energy Converter." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-159519.
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The search for new solutions for the generation of energy is becoming more and more important for our future. Big arguments and disagreements on e.g. the questions of gas transport or the dependence on energy supplied by other countries raise demands on the development of new forms of alternative energy resources. Wave power is one of the main sources of renewable energy due to the high power density stored in ocean waves. Nevertheless, the dynamic forces of waves are so large that serious questions popped up on how to design a system which could work even in an unfavourable wave climate or could at least retain working capabilities after big storms without significant damages. This thesis studies the reliability of the mechanical parts of a linear direct driven permanent magnet generator. The results of offshore experiment where strain gauge sensors instrumented on the capsule and the inner framework structure are presented. Stress estimation analyses using strain gauges are carried out. A method for measuring forces and moments in the mechanical structure of the WEC is developed. Evaluation of the lateral force acting on the outer structure is a key factor for the design and construction of the WEC. A method for the measurement of the lateral force acting on the capsule has been developed. A study of the inclination angle between the Wave Energy Converter and the floating buoy has been carried out. The aim of this work is to contribute to the development of wave energy conversion system, and especially to the estimation of structural loads which are important for the survivability of the system under hard sea states. This work is a step that may influence future design of wave energy devices in terms of material aspect, survivability in a hard wave climate and cost-effective renewable energies.
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Macleod, Adrian K. A. "The role of marine renewable energy structures and biofouling communities in promoting self-sustaining populations of non-native species." Thesis, University of the Highlands and Islands, 2013. https://pure.uhi.ac.uk/portal/en/studentthesis/the-role-of-marine-renewable-energy-structures-and-biofouling-communities-in-promoting-selfsustaining-populations-of-nonnative-species(0c7f0d89-74e8-4468-83c9-4216e4f2b1a8).html.
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Novel environments and biological communities created by the large-scale deployment of Marine Renewable Energy Devices (MREDs) have the potential to promote the spread of non-native species (NNS). Knowledge of how community composition resident on MREDs is shaped by geography, local hydrodynamics and the duration of deployment, will clarify how these technologies will interact with natural habitats, including the provision of suitable habitat for NNS. A network of navigation buoys was used to study biofouling communities in areas proposed for MRED deployment. Significant differences in community structure were observed in different geographic areas. A significant reduction in number of taxa present and community wet-weight was observed where buoys were deployed in greater tidal flow rates. However, overall community composition was not significantly different between ‘high’ (>1 ms-1) and ‘low’ (<1 ms-1) flow areas and for buoys deployed for different time durations (1-7 years). These finding have important implications for the longevity of devices and their interaction with natural habitats, including proposed ‘artificial reef’ effects. In total five non-native species were identified on the buoys sampled, supporting the need to monitor MREDs as the industry grows. Hydrodynamic and biotic features of the epibenthic communities were used to predict the presence of the most prevalent NNS, the amphipod Caprella mutica, in addition to other native amphipod species. Caprella mutica presence was found to be significantly affected by increasing flow speed compared with the native amphipod Jassa herdmani. Behavioural flume studies investigating flow-related processes governing the presence of non-native amphipods supported these findings. This study details how the hydrodynamic and biological environments created by MREDs determine their suitability for the establishment of self-sustaining populations, and therefore their dispersal potential for NNS. These findings inform design criteria and management options to minimise the biosecurity risk that these structures will pose as the industry expands.
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Da, Pra Elisabetta. "Modellazione degli ancoraggi del dispositivo Resen Wave Buoy con il software DualSPHysics." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Find full textAbstract:
L'elaborato si concentra dapprima sull'energia ricavabile dal mare, sulla classificazione dei Wave Energy Converters e sulle tipologie di ancoraggio attualmente esistenti.
Successivamente viene introdotto il software DualSPHysics, che è stato utilizzato per modellare il convertitore Resen Wave Buoy e il suo sistema di ancoraggio, nelle condizioni di mare nei pressi della piattaforma Viviana, con tempo di ritorno di dieci anni.
Inoltre, a valle di un'illustrazione del funzionamento del software stesso e del procedimento seguito nella modellazione del dispositivo e degli ancoraggi, è stata effettuata un'analisi di sensitività di DualSPHysics, variando alternativamente determinati parametri.
Infine sono stati riportati i risultati delle simulazioni effettuate. Questi dati consentono di mostrare che il modello DualSPHysics permette di rappresentare accuratamente le dinamiche di interazione onde-struttura, mentre non riesce a riprodurre un sistema di ancoraggi realistico e che non si distacchi eccessivamente dalla realtà.
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Paredes, Guilherme Moura. "Study of Mooring Systems for Offshore Wave Energy Converters." Doctoral thesis, 2016. https://repositorio-aberto.up.pt/handle/10216/86616.
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Paredes, Guilherme Moura. "Study of Mooring Systems for Offshore Wave Energy Converters." Tese, 2016. https://repositorio-aberto.up.pt/handle/10216/86616.
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Yu, Chi-Hsiung, and 余基雄. "A Study on the Mooring Design of Wave Energy Converters." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/26983412481720876128.
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碩士國立臺灣海洋大學
海洋環境資訊學系
99
The thesis works on the study of cable dynamic of the mooring system of floating wave energy converter. Mooring layout with various anchor angles, mooring lines, and mooring cable lengths were evaluated. This study tries to understand the surge and heave motions, pitch angle and mooring line tension of different layout. ANYSYS was used for the analysis in temporal domain. A mean Influence Factor (IF) was developed to study the influence level of various mooring layout. It was found that the length of mooring system plays the crucial factor. The influence of the length of mooring system on the motions and tension is higher than the influences from mooring number and mooring angle. In addition, it was also found that all the vertical motion, horizontal motion and maxima rotation angle of the energy converter device have positive proportion with the length of mooring system. Since the safety and stability should be both considered for a reasonable mooring design and they are dependent, a cost function was defined to assess the best design of mooring system. The result shows that the mooring system with three mooring lines, 1.1 times of the tight cable length, and with a 30 degree mooring angle is the best choice within the 36 mooring layouts in this study.
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Ortiz, Juan Pablo. "The influence of mooring dynamics on the performance of self reacting point absorbers." Thesis, 2016. http://hdl.handle.net/1828/7339.
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The design of a mooring system for a floating structure is a significant challenge; the choice of line structure and layout determine highly non-linear hydrodynamic behaviors that, in turn, influence the dynamics of the whole system. The difficulty is particularly acute for Self-Reacting Point Absorber Wave Energy Converters (SRPA WEC) as these machines rely on their movements to extract useful power from wave motions and the mooring must constrain the SRPA WEC motion without detracting from power production. In this thesis this topic has been addressed in an innovative way and new ideas on how these devices should be moored were investigated.
As part of the study, an optimization routine was implemented to investigate the optimal mooring design and its characteristics. In this process, different challenges were faced. To evaluate the different mooring configurations, a high fidelity representation of the system hydrodynamics is necessary which captures the non-linearities of the system. Unfortunately, high-fidelity modeling tends to be very computationally expensive, and for this reason previous studies based mooring design largely relies on simplified representations that only reflect part of the mooring design space since some physical and hydrodynamic properties are dropped. In this work, we present how a full hydrodynamic time domain simulation can be utilized within a Metamodel-Based Optimization to better evaluate a wider range of mooring configurations spanning the breadth of the full design space. The method uses a Metamodel, defined in terms of the mooring physical parameters, to cover the majority of the optimization process a high fidelity model is used to establish the Metamodel in a pre-processing stage. The method was applied to a case study of a two-body heaving SRPA WEC. Survivability constrains where introduce into the model using a new statistical approach which reduces the execution time, and allowed the optimization routine.
The analysis results lead to the conclusion that for SRPA WEC the mooring loads have a significant impact on how the body reacts with the waves, affecting both the energy that enter the system as well as the energy that is extracted as power. This implies that, in some cases, the mooring lines need to be considered in early stages of the designs as opposed to an afterthought, as is typically done. Results indicate that an optimal mooring design can result in a 26% increase in total annual power production. In addition, the mooring lines impact on mitigating parasitic pitch and roll were analyzed. It was established that in regular waves, the mooring lines can reduce the parametric excitations and improve the power extraction up to 56% for a particular sea state. By applying a computationally efficient iterative design approach to a device's mooring, parasitic motions and suboptimal device operation can be reduced, ultimately making WECs a more competitive source of energy.Graduate
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Elhanafi, ASSM. "Performance and survivability of offshore oscillating water column wave energy converters." Thesis, 2017. https://eprints.utas.edu.au/23971/2/Elhanafi_whole_thesis_ex_pub_mat.pdf.
Full textAbstract:
This research was performed with a focus on two key aspects of energy cost–reduction for offshore OWC devices; improving the power extraction efficiency and reducing the excess margin in structural safety factors by a better understanding of wave–induced loads on these devices. This study utilised information from three different resources. First, 2D and 3D numerical results from fully nonlinear Computational Fluid Dynamics (CFD) simulations performed using the commercial code STAR–CCM+ that was validated in good agreement with physical scale model measurements at each stage of increasing complexity during this research. Second, published experiments in the literature for 2D OWC devices subjected to unidirectional regular waves to validate the 2D CFD models of this study. Third, experiments conducted in the towing tank of the Australian Maritime College (AMC) for 3D offshore stationary and floating–moored OWC devices (at a model–scale of 1:50) subjected to unidirectional regular and irregular waves. These experiments were designed to (1) compare the hydrodynamic performance of both devices, (2) estimate wave–induced loads on the fixed device during operating conditions, (3) investigate the survivability of the floating–moored device with intact and damaged mooring systems and (4) validate the 3D CFD models of this study.
Using the combined CFD and experimental approach, it was found that optimizing the underwater geometry of an offshore stationary OWC device could significantly improve the power extraction efficiency up to 0.97. However, this efficiency could be reduced due to air compressibility effects at full–scale. The surge motion of the floating–moored device improved device efficiency in regular and irregular waves. Furthermore, the effectiveness of deploying offshore OWC devices in deep–water where waves are more energetic was proven by increasing the extracted pneumatic energy by a maximum of about 7.7 times when wave height was doubled (incident wave energy increased four times). The instantaneous position of the floating–moored OWC device and its interactions with a certain wave train was more important than the maximum wave height in an irregular sea state when assessing device survivability. Survivability with a damaged mooring system was the key analysis for mooring design. For this analysis, using an equivalent design regular wave condition along with the current safety factors recommended for offshore oil and gas platforms was found to over–design the mooring system of the floating OWC device. The good agreement between CFD experiments for survivability analysis with intact and damaged mooring systems in regular waves highlighted that CFD is a very promising tool a designer can employ to investigate and assess device survivability under different conditions upon further validations in irregular waves.
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Bae, Yoon Hyeok. "Coupled Dynamic Analysis of Multiple Unit Floating Offshore Wind Turbine." Thesis, 2013. http://hdl.handle.net/1969.1/149465.
Full textAbstract:
In the present study, a numerical simulation tool has been developed for the rotor-floater-tether coupled dynamic analysis of Multiple Unit Floating Offshore Wind Turbine (MUFOWT) in the time domain including aero-blade-tower dynamics and control, mooring dynamics and platform motion. In particular, the numerical tool developed in this study is based on the single turbine analysis tool FAST, which was developed by National Renewable Energy Laboratory (NREL). For linear or nonlinear hydrodynamics of floating platform and generalized-coordinate-based FEM mooring line dynamics, CHARM3D program, hull-riser-mooring coupled dynamics program developed by Prof. M.H. Kim’s research group during the past two decades, is incorporated. So, the entire dynamic behavior of floating offshore wind turbine can be obtained by coupled FAST-CHARM3D in the time domain. During the coupling procedure, FAST calculates all the dynamics and control of tower and wind turbine including the platform itself, and CHARM3D feeds all the relevant forces on the platform into FAST. Then FAST computes the whole dynamics of wind turbine using the forces from CHARM3D and return the updated displacements and velocities of the platform to CHARM3D.
To analyze the dynamics of MUFOWT, the coupled FAST-CHARM3D is expanded more and re-designed. The global matrix that includes one floating platform and a number of turbines is built at each time step of the simulation, and solved to obtain the entire degrees of freedom of the system. The developed MUFOWT analysis tool is able to compute any type of floating platform with various kinds of horizontal axis wind turbines (HAWT). Individual control of each turbine is also available and the different structural properties of tower and blades can be applied. The coupled dynamic analysis for the three-turbine MUFOWT and five-turbine MUFOWT are carried out and the performances of each turbine and floating platform in normal operational condition are assessed. To investigate the coupling effect between platform and each turbine, one turbine failure event is simulated and checked. The analysis shows that some of the mal-function of one turbine in MUFOWT may induce significant changes in the performance of other turbines or floating platform. The present approach can directly be applied to the development of the remote structural health monitoring system of MUFOWT in detecting partial turbine failure by measuring tower or platform responses in the future.