Tesis: "Floating offshore wind turbines"

1

Lindeberg, Eivind. "Optimal Control of Floating Offshore Wind Turbines". Thesis, Norwegian University of Science and Technology, Department of Engineering Cybernetics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9933.

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Floating Offshore Wind Power is an emerging and promising technology that is particularly interesting from a Norwegian point of view because of our long and windy coast. There are however still several remaining challenges with this technology and one of them is a possible stability problem due to positive feedback from tilt motion of the turbine tower. The focus of this report is to develope a simulator for a floating offshore wind turbine that includes individual, vibrating blades. Several controllers are developed, aiming to use the blade pitch angle and the generator power to control the turbine speed and output power, while at the same time limit the low-frequent motions of the tower and the high-frequent motions of the turbine blades. The prime effort is placed on developing a solution using Model Predictive Control(MPC). On the issue of blade vibrations no great progress has been made. It is not possible to conclude from the simulation results that the designed controllers are able to reduce the blade vibrations. However, the MPC controller works very well for the entire operating range of the turbine. A "fuzzy"-inspired switching algorithm is developed and this handles the transitions between the different operating ranges of the turbine convincingly. The problem of positive feedback from the tower motion is handled well, and the simulations do not indicate that this issue should jeopardize the viability of floating offshore wind turbines.

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2

Naqvi, Syed Kazim. "Scale Model Experiments on Floating Offshore Wind Turbines". Digital WPI, 2012. https://digitalcommons.wpi.edu/etd-theses/1196.

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This research focuses on studying the feasibility of placing large wind turbines on deep-ocean platforms. Water tank studies have been conducted using the facilities at Alden Research Laboratories (ARL) on 100:1 scale Tension Leg Platform (TLP) and Spar Buoy (SB) models. Froude scaling was used for modeling the offshore wind turbine designs. Primary components of the platform turbine, tower, and cable attachments were fabricated in ABS plastic using rapid prototyping. A wireless data acquisition system was installed to prevent umbilical data cables from affecting the behavior of the platform when exposed to wave loading. In Phase I testing, Froude-scaled TLP and Spar Buoy models at a 100:1 scale were placed in a water flume and exposed to periodic waves at amplitudes ranging from 0.5 cm - 7.5 cm and frequencies ranging from 0.25 Hz - 1.5 Hz. The testing was conducted on simple tower and turbine models that only accounted for turbine weight at the nacelle. In Phase II testing, emphasis was placed on further testing of the tension leg platform as a more viable design for floating offshore wind turbines. The tension leg platform scale model was improved by adding a disc to simulate drag force incident at the top of the tower, as well as a rotor and blades to simulate the gyroscopic force due to turbine blade rotation at the top of the tower. Periodic wave motions of known amplitude and frequency were imposed on the model to study pitch, heave, roll, surge, sway motions and mooring cable tensions (in Phase II only) using accelerometers, inclinometers, capacitance wave gage, and load cells. Signal analysis and filtering techniques were used to refine the obtained data, and a Fourier analysis was conducted to study the dominant frequencies. Finally, Response Amplitude Operators (RAO's) were plotted for each data set to standardize the results and study the overall trend with respect to changes in wave amplitude and frequency. For Phase I testing, it is shown that surge motion of the platform dominates other motions for both the tension leg platform and spar buoy, and varying tether pretension has little effect on response amplitude operator values. For phase II testing, it was found that the introduction of thrust and gyroscopic forces increases sway and pitch motions as well as upstream tether forces. Coupling effects of pitch motion with roll and sway due to the presence of gyroscopic forces were also seen. The present experimental results can be used to validate the hydrodynamic kernels of linear frequency-domain models, time-domain dynamics models, and computational simulations on floating wind turbines. Numerical analysis and simulations have been conducted in a separate study at WPI. These simulations are comparable to the experimental results.

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3

Henderson, Andrew Raphael. "Analysis tools for large floating offshore wind farms". Thesis, University of London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341705.

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4

Polverini, Silvia. "Analysis and control of floating offshore wind turbines". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13883/.

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With the continuous growing of wind energy as a clean source for electricity production there is an increasing interest in the location of wind turbines in offshore areas in which there are fewer space restrictions and less turbulent wind. This increases the interest to develop floating wind turbines, which are not mounted in the sea-bed and can be used in deep waters. For their low environmental impact, the demand for FOWTs could easily be fostered. Floating turbines are large and complex mechanical structures as a consequence it is necessary to adapt control strategies to these systems, to ensure acceptable loads in order to guarantee a long lifetime. In order to reduce fatigue loads, different design control approaches are studied. To design the control, simplified models are needed. The purpose of this thesis is to develop a simplified Floating Offshore Wind Turbine (FOWT) model considering aero-dynamical loads to assess the performance of the system. The aerodynamic forces are derived and implemented in a more accurate simulator, FAST, to evaluate the overall loads acting on a FOWT. FAST is the acronym for Fatigue-Aerodynamics-Structure-Turbulence and it gives a full analysis of wind turbine models, using a high-fidelity numerical code. The developed FAST computer program simulator is applied to investigate the reliability of simplistic wind turbine models by using MATLAB and Simulink interfaces. Studying a simplification of the turbine model means identify the dominant physical dynamics behaviour that implies a good knowledge of wind turbine dynamics. The simplified model is useful when a linear control theory is applied. Due to the non-linearity of the problem, created by wind and sea kinematics, specific values are found using an empirical approach. Results are acceptable according to the approximations done. Further developments are considered to obtain a more detailed model of wind turbine and changes to control strategy.

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5

Ahmadi, Mehran. "Analysis and Study of Floating Offshore Wind Turbines". University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1376643304.

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6

Sönmez, Nurcan. "Investigating Wind Data and Configuration of Wind Turbines for a Turning Floating Platform". Thesis, KTH, Mekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-148957.

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Wake interactions on a floating platform for offshore wind energy applications were investigated.The study is performed in collaboration with Hexicon AB which has a patent family for innovative floating platforms, which are able to turn automatically. The Jensen model is used for wake effect calculations and the simulations were performed in MATLAB. The present study starts with wind speed and wind direction data analysis for the specific site that Hexicon AB plans to construct its first platform. Data analysis is followed by wake interaction studies for H4-24MW type Hexicon AB platform. Wake interaction simulations were performed for three different cases. Fixed turbine and platform, Nacelle yawing and fixed platform and Nacelle yawing and turned platform. Different cases were investigated in order to see wake interactions for different wind directions. Wind direction effect on wake interactions were performed between _90_ and 90_ with an increment of 10_. After having the simulation results for Nacelle yawing and turned platform case the results were compared with ANSYS - CFX simulations results. The results didn’t match exactly but they were very close, which is an indicator to the validity of the Jensen Model. After finding out the possible behavior of wake interactions for different wind directions, power calculations were performed for the same three cases. In order to perform the power calculations the wake interactions for different wind directions were taken into account. In case of platform turning it was assumed that power losses were caused both by wake interactions and in case of thrusters activation. The losses that would be caused by different thrust forces on the turbine blades were not included. The last study was performed to suggest different layouts. In the second case, Nacelle yawing and fixed platform, it was found out that nacelle yawing for most of the angles is not possible because it creates wake regions in front of the rotor area. It was decided to propose new turbine configurations on the platform which are tolerant to different nacelle yawing angles. The simulations were run without considering any constructions limitations, meaning that the availability of platform structure was not included. The study is ended by performing some probabilistic results for platform turning behavior.

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7

Proskovics, Roberts. "Dynamic response of spar-type offshore floating wind turbines". Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26017.

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In recent years there has been a significant increase in the interest in floating offshore wind turbines from the wind energy industry, governments and academia. Partially driven by the recent nuclear disaster in Japan, but also by the lack or complete absence of shallow waters in various countries around the globe (making fixed offshore wind turbines infeasible), multiple different topology floating offshore wind turbines have been proposed and, in some cases, prototypes built and installed offshore. The most well-known of these is Hywind by Statoil, which has been operational off the coast of Norway since the end of 2009. While small scale prototypes had been installed even before Hywind, for example Blue-H in 2007, no guidelines have yet emerged that would give recommendations and guiding principles in designing new floating offshore wind turbines. The aim of this thesis is to provide some knowledge base for future design of floating offshore wind turbines by looking at what simplifications could be made and what effect these would have on the preliminary designs of new floating offshore wind turbines. This thesis starts by comparing different topology floating offshore wind turbines and choosing one, deemed the most promising, as the base case scenario for use in the subsequent analysis and calculations. This thesis also looks at the importance of unsteady representations of the aerodynamics compared with quasi-steady when designing a new floating offshore wind turbine, by comparing quasi-steady aerodynamic loads first with fully-attached unsteady loads and later with fully-unsteady (fully-attached, separated and dynamic stall). A chapter is allocated to identifying which degree-of-freedom of loading is the most damaging to the system, as floating offshore wind turbines operate in very harsh and unstable environments. Once identified, this knowledge can be used to further improve floating offshore wind turbines, hence making them even more feasible. Finally, the wind turbine previously chosen as a base case has its floating support shortened and four different draft designs proposed that would allow it to be deployed in medium-to-deep waters, in which fixed supports for wind turbines are not economical.

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8

Nematbakhsh, Ali. "A Nonlinear Computational Model of Floating Wind Turbines". Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-dissertations/170.

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The dynamic motion of floating wind turbines is studied using numerical simulations. Floating wind turbines in the deep ocean avoid many of the concerns with land-based wind turbines while allowing access to strong stable winds. The full three-dimensional Navier-Stokes equations are solved on a regular structured grid, using a level set method for the free surface and an immersed boundary method for the turbine platform. The tethers, the tower, the nacelle and the rotor weight are included using reduced order dynamic models, resulting in an efficient numerical approach which can handle nearly all the nonlinear wave forces on the platform, while imposing no limitation on the platform motion. Wind is modeled as a constant thrust force and rotor gyroscopic effects are accounted for. Other aerodynamic loadings and aero-elastic effects are not considered. Several tests, including comparison with other numerical, experimental and grid study tests, have been done to validate and verify the numerical approach. Also for further validation, a 100:1 scale model Tension Leg Platform (TLP) floating wind turbine has been simulated and the results are compared with water flume experiments conducted by our research group. The model has been extended to full scale systems and the response of the tension leg and spar buoy floating wind turbines has been studied. The tension leg platform response to different amplitude waves is examined and for large waves a nonlinear trend is seen. The nonlinearity limits the motion and shows that the linear assumption will lead to over prediction of the TLP response. Studying the flow field behind the TLP for moderate amplitude waves shows vortices during the transient response of the platform but not at the steady state, probably due to the small Keulegan-Carpenter number. The effects of changing the platform shape are considered and finally the nonlinear response of the platform to a large amplitude wave leading to slacking of the tethers is simulated. For the spar buoy floating wind turbine, the response to regular periodic waves is studied first. Then, the model is extended to irregular waves to study the interaction of the buoy with more realistic sea state. The results are presented for a harsh condition, in which waves over 17 m are generated, and linear models might not be accurate enough. The results are studied in both time and frequency domain without relying on any experimental data or linear assumption. Finally a design study has been conducted on the spar buoy platform to study the effects of tethers position, tethers stiffness, and platform aspect ratio, on the response of the floating wind turbine. It is shown that higher aspect ratio platforms generally lead to lower mean pitch and surge responses, but it may also lead to nonlinear trend in standard deviation in pitch and heave, and that the tether attachment points design near the platform center of gravity generally leads to a more stable platform in comparison with attachment points near the tank top or bottom of the platform.

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9

Homer, Jeffrey R. "Physics-based control-oriented modelling for floating offshore wind turbines". Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54891.

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As offshore wind technology advances, floating wind turbines are becoming larger and moving further offshore, where wind is stronger and more consistent. Despite the increased potential for energy capture, wind turbines in these environments are susceptible to large platform motions, which in turn can lead to fatigue loading and shortened life, as well as harmful power fluctuations. To minimize these ill effects, it is possible to use advanced, multi-objective control schemes to minimize harmful motions, reject disturbances, and maximize power capture. Synthesis of such controllers requires simple but accurate models that reflect all of the pertinent dynamics of the system, while maintaining a reasonably low degree of complexity. In this thesis, we present a simplified, control-oriented model for floating offshore wind turbines that contains as many as six platform degrees of freedom, and two drivetrain degrees of freedom. The model is derived from first principles and, as such, can be manipulated by its real physical parameters while maintaining accuracy across the highly non-linear operating range of floating wind turbine systems. We validate the proposed model against advanced simulation software FAST, and show that it is extremely accurate at predicting major dynamics of the floating wind turbine system. Furthermore, the proposed model can be used to generate equilibrium points and linear state-space models at any operating point. Included in the linear model is the wave disturbance matrix, which can be used to accommodate for wave disturbance in advanced control schemes either through disturbance rejection or feedforward techniques. The linear model is compared to other available linear models and shows drastically improved accuracy, due to the presence of the wave disturbance matrix. Finally, using the linear model, we develop four different controllers of increasing complexity, including a multi-objective PID controller, an LQR controller, a disturbance-rejecting H∞ controller, and a feedforward H∞ controller. We show through simulation that the controllers that use the wave disturbance information reduce harmful motions and regulate power better than those that do not, and reinforce the notion that multi-objective control is necessary for the success of floating offshore wind turbines.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

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10

Castillo, Florian Thierry Stephan. "Floating Offshore Wind Turbines : Mooring System Optimization for LCOE Reduction". Thesis, KTH, Skolan för industriell teknik och management (ITM), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-284565.

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Offshore wind has a large potential in terms of electricity production and is becoming an important focus of interest for massive expansion of wind power. While encountering harsh environmental conditions and facing challenges in deployment and maintenance, offshore wind turbines benefit a lot from higher and more regular wind speeds if compared to conventional onshore wind turbine sites. Floating offshore wind turbines (FOWT) in deep waters offer the possibility to increase the accessibility and unleash an enormous resource base by cost-competitive solutions further away from the shore. However, associated costs are still relatively high compared to other sources of energy. These costs could be reduced by developing technological breakthroughs and improving design processes. The work presented in this report is part of the H2020 EU project COREWIND, aiming to reduce FOWT costs by optimizing the mooring system technology and by introducing dynamic moor cable solutions. The main objective of this study in particular is to develop an optimization tool for the design of a cost-effective and reliable mooring system for floating offshore wind turbines. The scope of the study implies the development of an optimization strategy, involving Isight - a Dassault System software used for the analysis. The work also involves OrcaFlex, a finite-element software developed by Orcina, applied in dynamic analysis methods. A Python-based code was created to realize the coupling between the two software tools. OrcaFlex simulation models were built for two test cases provided by the project partners, validation of these models was performed based on results obtained using FAST. Finally, results obtained for a case study using one floater and one location of the COREWIND project are also presented and analyzed. The case study involves the development of a mooring system using the hereby validated optimization tool; and is testing its integrity on critical design load cases. The work has shown how an optimization tool could be constructed and applied to improve design process and reduce costs.
Havsbaserad vindkraft har en stor potential när det gäller elproduktion och intresset för dess utveckling växer enormt för att kunna möjliggöra en enorm expansion av ren förnyelsebar energiproduktion. Samtidigt som havsbaserade vindturbiner stöter på tuffa miljöförhållanden och möter utmaningar vid utbyggnad och underhåll, de jämna och pålitliga vindresurserna till havs är en stor fördel som kan tas tillvara. Ju längre fjärran från kusten desto högre och mer regelbundna vindhastigheterna blir jämfört med vindkraftverk på land, samtidigt som havsgrunden blir djupare och svårare för turbinbyggnad. Flytande havsbaserade vindkraftverk (Floating Offshore Wind Turbines, FOWT) i djupa vatten ger möjlighet att öka tillgängligheten och frigöra en enorm resursbas genom kostnadseffektiva lösningar längre ut till havs. De tillhörande kostnaderna är dock fortfarande relativt höga jämfört med andra energikällor. Dessa kostnader kan minskas genom vidareutvecklingen av tekniska genombrott och förbättrade designprocesser. Examensarbetet härmed är en del av H2020 EU-projektet COREWIND, som syftar till att minska FOWT-kostnaderna genom optimering av förtöjningssystemstekniken och genom införandet av dynamiska förtöjningslösningar. I synnerhet, det huvudsakliga målet för denna studie är att utveckla ett optimeringsverktyg för design av kostnadseffektiva och pålitliga ankarsystem för flytande havsbaserade vindkraftverk. Studiens omfattning inkluderar utvecklingen av en optimeringsstrategi som involverar Isight – en mjukvara från Dassault Systems som använts för analysen. Arbetet involverar också OrcaFlex, en programvara för finite element analys som utvecklats av Orcina, tillämpad i dynamiska analysmetoder. En Python-baserad kod skapades för att förverkliga kopplingen mellan de två programvaruverktygen. OrcaFlex-simuleringsmodeller byggdes för två testfall, validering av dessa modeller utfördes baserat på resultat erhållna med hjälp av FAST. Slutligen presenteras och analyseras resultat som erhållits för en fallstudie med en flottör och en särskild position för COREWIND-projektet. Fallstudien involverar utvecklingen av ett förtöjningssystem med det härmed validerade optimeringsverktyget; och testar dess integritet i kritiska belastningsförhållanden. Arbetet har visat hur ett optimeringsverktyg kan konstrueras och tillämpas för att förbättra designprocessen och minska kostnaderna.

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11

Andersen, Brett. "A Comparison of Two and Three Bladed Floating Wind Turbines". University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1271883552.

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12

Trubat, Casal Pau. "Station keeping analysis and design for new floating offshore wind turbines". Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/668891.

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In the framework of the reduction of the emissions of greenhouse gases, FOWT will be the technology that will exploit the wind resources in deep seas. In order to achieve a commercial deployment of this technology, a cost reduction is necessary through the optimization of the wind turbine by detailed studies to reduce its design uncertainties. One important aspect is the mooring system, which commonly represents between a 10 to 15 % of the capex. The present research aims to increase the knowledge of the design and analysis of the station keeping systems for floating offshore wind turbines. One of the most important aspects for a correct analysis and design of the mooring system is the simulation of the lines coupled with the floating structure and the wind turbine. In this dissertation, two different mooring line models coupled to a finite element model for the analysis of floating platforms are presented. The first model is a finite element model based on a slender rod approach. The model is extended to consider the rheological damping in the axial and bending direction within the constitutive equations of the problem. The second model is a new approach named quasi-dynamic model. The model assesses the static solution of the catenary equation but updates the line tension based on the external hydrodynamic forces and the inertial forces from the theoretical motion of the mooring line. In the design of mooring lines is important to consider and foresee the different phenomena and loads that can act along on the life span of these elements. Within these phenomena, the effects of the waves forces over the mooring lines o have been studied. The study analyzes the contribution of the wave forces over the mooring lines to determine when it is an important source of damage for the fatigue strength. Finally, new floating platform concepts need to be tested and analyzed in controlled conditions in order to validate the models used for the final designs. It is common that pool and flume basins do not present enough size for the catenary shape mooring systems because they cover a large extension. In this area, an optimization model for a truncated mooring system is presented. The truncated mooring system is formed by two types of chains to emulate the actual prototype mooring system of a scale spar platform in a narrow flume.
En el marc de la reducció de les emissions de gasos d’efecte hivernacle, l’energia eòlica marina flotant serà la tecnologia que explotarà els recursos eòlics marins a gran profunditat. Per tal d’aconseguir un desenvolupament a escala comercial d’aquesta tecnologia és necessari una reducció dels costos a través de l’optimització dels aerogeneradors a partir d’estudis i anàlisis molt detallats. Un dels aspectes importants és el sistema d’amarratge, el qual pot representar entre un 10 i 15 % del cost total d’una instal·lació. La present recerca aprofundeix en el disseny i anàlisis dels sistemes d’amarratge per a molins de vent flotant. Un dels aspectes més importants per a al correcte disseny i anàlisis dels sistemes d’amarratge és la simulació de les amarres conjuntament amb el sistema flotant. En aquesta dissertació es presenten dos models d’amarres diferents acoblats a un model d’elements finits per a l’anàlisi d’estructures flotants. El primer model, és un model d’elements finits per a línies d’amarres basat en un model de vareta esvelta. El model s’ha ampliat per tenir en compte l’esmorteïment material degut als esforços en les direccions axial i de flexió dins de les equacions constitutives dels problema. El segon model es tracta d’un model quasi-dinàmic, el qual es basa en la solució estàtica de les amarres però actualitza la tensió de l’amarra en funció de les forces inercials i hidrodinàmiques externes calculades a partir del moviment teòric de l’amarra. En el disseny de les amarres també s’ha de tenir en compte i preveure els diferents fenòmens i accions que poden influir en la vida útil d’aquests elements. Dins d’aquests fenòmens, s’ha aprofundit en l’anàlisi dels efectes de les forces de l’onatge sobre les amarres. En aquest sentit es fa una comparació entre la consideració o no d’aquestes forces sobre les amarres pe tal de determinar en quins casos poden suposar una font important de dany per a la seva resistència a la fatiga. Per últim, els nous conceptes de plataformes flotants s’han d’assajar i analitzar en condicions controlades per tal de validar els models utilitzats en el disseny final. És freqüent que les piscines i canals d’assaig no presentin les dimensions adequades per a l’experimentació dels sistemes d’amarres ja que poden ocupar una gran extensió d’espai. En aquest àmbit es presenta un model d’optimització d’unes amarres truncades formades per dos tipus de cadena diferents per tal d’emular el disseny d’amarres del prototip a escala real.

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13

Bagherieh, Omid. "Gain-scheduling control of floating offshore wind turbines on barge platforms". Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44879.

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This thesis studies the application of gain-scheduling (GS) control techniques to floating offshore wind turbines on barge platforms. Modelling, control objectives, controller design and performance evaluations are presented for both low wind speed and high wind speed cases. Special emphasis is placed on the dynamics variation of the wind turbine system caused by plant nonlinearity with respect to wind speed. The dynamics variation is represented by a linear parameter-varying (LPV) model. The LPV model for wind turbines is derived by linearizing the nonlinear dynamics at various operating wind speeds and by interpolating the linearized models. In low wind speed, to achieve control objectives of maximizing power capture and minimizing platform movements, for the LPV model, the LPV GS design technique is explored. In this region, the advantage of making use of blade pitch angle as a control input is also investigated. In high wind speed, to achieve control objectives of regulating power capture and minimizing platform movements, both LQR and LPV GS design techniques are explored. To evaluate the designed controllers, simulation studies are conducted with a realistic 5 MW wind turbine model developed at National Renewable Energy Laboratory, and realistic wind and wave profiles. The average and root mean square values of power capture and platform pitch movement are adopted as performance measures, and compared among designed GS controllers and conventional controllers. The comparisons demonstrate the performance improvement achieved by GS control techniques.

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14

Namik, Hazim. "Individual blade pitch and disturbance accommodating control of floating offshore wind turbines". Thesis, University of Auckland, 2012. http://hdl.handle.net/2292/11198.

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Floating wind turbines offer a feasible solution for going further offshore into deep waters. However, using a floating platform introduces additional motions that must be taken into account actively or passively. Therefore, the control system becomes an important component in controlling these motions. In this work, the development, implementation, and simulation of multi-objective state feedback and disturbance accommodating controllers applied on the three main floating concepts are described. The three concepts are the barge, tension leg, and spar-buoy floating platforms. These controllers utilise individual blade pitching to create asymmetric aerodynamic loads in addition to the symmetric loads created by collective blade pitching to increase the platform restoring moments. Simulation results, according to design load case 1.2 of the IEC 61400-3 standard for offshore wind turbines, show that state feedback controllers improve the performance relative to a collective blade pitch gain scheduled proportional-integral controller in terms of power and rotor speed regulation as well as reducing tower fore-aft and side-side bending loads. However, the magnitude of the improvements depends on the dynamics of each platform, its responsiveness to individual blade pitching and sensitivities to external wind and wave disturbances. Furthermore, interesting physical phenomena, such as the platform roll to pitch coupling caused by the controller, are identified. Disturbance accommodating controllers for rejecting wind speed perturbations further improve rotor speed regulation and reduce tower fore-aft bending loads except on the barge platform; the barge platform motion is dominated by incident waves and therefore rejecting wind speed perturbations has no noticeable impact. Wave moment disturbance rejection is also investigated but in a limited case study. While the approach taken can theoretically cancel the effects of incident wave moments, practically, the required actuation force cannot be generated by the wind turbine blades. Furthermore, using the blades for rejecting wave moments increases the tower bending due to the load path of the restoring moment through the tower. Out of the three investigated platforms, the tension leg platform with a disturbance accommodating controller has the best overall performance with fatigue loads close or less than that of an onshore wind turbine. The other two platforms, in their current design form, experience large tower fore-aft bending loads that would prevent them from being deployed in rough sea conditions.

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15

Douteau, Louis. "CFD simulation with anisotropic mesh adaptation : application to floating offshore wind turbines". Thesis, Ecole centrale de Nantes, 2020. http://www.theses.fr/2020ECDN0003.

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Le calcul des performances et des efforts appliqués sur une éolienne offshore est actuellement réalisé à l'aide d’outils basés sur des approches quasi-statiques. Ces approches sont intéressantes pour leur vitesse de calcul, elles sont cependant perfectibles suivant la méthode de mise en oeuvre et suivant les cas de chargement étudiés. Une approche alternative consiste à utiliser la modélisation CFD. Cette thèse s’intéresse à des méthodes d’une haute précision, ayant le potentiel de fournir des écoulements et efforts précis. La plateforme logicielle hautement parallélisée ICI-tech est utilisée dans cette thèse. Elle se base sur une résolution des équations de Navier-Stokes dans une approche multi-échelle, effectuée à l’aide d’éléments finis stabilisés. La représentation des phases dans le domaine de calcul est réalisée grâce à une méthode frontières immergées. Des implémentations ont été réalisées dans ICI-tech afin de pouvoir simuler des éoliennes flottantes. L’interaction fluide-structure et un bassin de houle numérique ont notamment été considérés. Un processus de vérification et validation s’est intéressé au comportement du solveur dans des conditions reproduisant celles impactant des éoliennes flottantes. Le niveau de précision atteint par les écoulements à haut Reynolds et la propagation de champs de houle s’est avéré être décevant. L’influence du maillage anisotrope sur les résultats obtenus a été quantifiée. Plusieurs pistes visant à améliorer la précision des simulations ont été introduites
The simulation of Floating Offshore Wind Turbines (FOWTs) is a tool to help this technology reach an industrial scale. Nowadays, low-precision numerical methods are used for the dimensioning of the structures, as they involve a reduced computational effort. This PhD thesis focused on the development of highly-accurate numerical methods, with a potential to provide a thin description of the flows and efforts around FOWTs. The simulations presented in this thesis have been realized on the highly-parallelized software platform ICI-tech. A resolution of the Navier- Stokes equations in a Variational MultiScale formulation is performed using Stabilized Finite Elements. The representation of the different phases in the computational domain is achieved using immersed boundary methods. Several numerical tools have been implemented in ICItech towards an application to the simulation of FOWTs. A fluid-structure interaction paradigm has been set up, and a numerical wave tank has been defined. Verification and validation studies have been realized to assess the solver results for environmental conditions representative of those observed for operating FOWT. The accuracy achieved for both the aerodynamics at high Reynolds numbers and the propagation of wave fields has been disappointing. The influence of the anisotropic meshing on the results presented has been quantified. Several options aiming at increasing the accuracy of the simulations have been discussed

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16

Liu, Yuanchuan. "A CFD study of fluid-structure interaction problems for floating offshore wind turbines". Thesis, University of Strathclyde, 2018. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=30597.

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As one of the fastest growing renewable energy sources, wind energy is playing an increasingly important part in addressing the climate change and energy crisis issues the world is currently facing. The abundance of wind resource in offshore areas makes them a popular choice for turbine installation. In the past few years, several floating wind projects have emerged where wind turbines are installed far offshore in deepwater sites on moored platforms. Compared to land-based or offshore fixed-bottom wind turbines, an FOWT is a fully coupled system where the wind turbine with flexible blades and the floating platform with its mooring system interact with each other in wind and waves, which makes old design tools inadequate. This work aims to develop a fully coupled high-fidelity aero-hydro-mooring-elastic analysis tool, and to better understand the sophisticated fluid-structure interactions for FOWTs. The numerical tool developed in this work takes advantage of the open source CFD toolbox OpenFOAM to accurately solve wind turbine aerodynamics and floating platform hydrodynamics, and utilises the open source MBD code MBDyn for structural dynamics within a multibody framework while modelling flexible bodies based on a nonlinear beam theory. Coupling of these two solvers is achieved by establishing an interface library to exchange data with the help of the TCP/IP protocol. Additionally, to tackle the complex mesh movement in FOWT simulations, a mesh motion solver is developed in OpenFOAM by combining the sliding mesh technique and the dynamic mesh morphing method. A mooring system analysis module comprising a quasi-static method and a lumped-mass based dynamic approach is also implemented to simulate mooring lines in an FOWT system. A series of test cases is firstly studied to validate the various features of the tool, including basic fluid flow solving, modelling of wind turbine aerodynamics, hydrodynamic analysis of a floating structure with its mooring system, dynamic analysis of a riser or mooring line and coupled analysis of flow induced vibration of a flexible beam. The developed tool is then applied to analyse FSI problems of FOWTs under three different scenarios. Firstly, a coupled aero-hydro-mooring analysis is carried out for the OC4 semisubmersible FOWT under regular waves and uniform wind speed. Blade flexibility is ignored, and mooring lines are solved using the quasi-static method. Interactions between the moored platform and the wind turbine are investigated, focusing on of platform motion on the aerodynamic performance of the wind turbine and the impacts of wind turbine aerodynamics on the responses of the floating platform and its mooring system. Subsequently, an aeroelastic analysis is conducted for the NREL 5-MW offshore wind turbine with flexible blades under uniform wind speed. Effects of blade flexibility on wind turbine aerodynamics and structural responses are studied using the developed CFD-MBD tool. The floating platform supporting the turbine is not directly modelled for simplicity and the influence of platform motion responses on the turbine are analysed via imposing a prescribed surge motion to the turbine base. Fully coupled aero-hydro-mooring-elastic analysis is lastly carried out for the OC4 semi-submersible FOWT under a combined wind/wave condition to demonstrate the capabilities of the developed CFD-MBD tool. Responses of the floating system are investigated in terms of platform hydrodynamics, mooring system dynamics, wind turbine aerodynamics and blade structural dynamics. Interactions between the FOWT and fluid flow are analysed by visualising results obtained via the CFD approach.

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17

ARABGOLARCHEH, ALIREZA. "DEVELOPMENT OF AN ACTUATOR LINE MODEL FOR SIMULATION OF FLOATING OFFSHORE WIND TURBINES". Doctoral thesis, Università degli studi di Padova, 2022. http://hdl.handle.net/11577/3456175.

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Floating offshore wind turbines (FOWTs) are a solution to harvest wind energy in deep water wind farms thanks to higher wind energy potential than onshore configurations. Fast and effective numerical models explaining the impact of platform motion on wind fields are fundamental to harvesting the potential energy in large offshore wind farms. This project developed a CFD-based Computationally-Efficient approach based on an actuator line model (ALM) to study FOWTs. A dedicated C++ library was implemented in the OpenFOAM toolbox to complement reasonable accuracy and affordable computational effort while investigating the effects of the platform motions on the wake evolution. Two well-known turbine cases were studied, including NREL Phase VI with adequate available experimental data and NREL 5-MW being representative of a large-size wind turbine. It was well documented that, at the same displacement, pitch and surge motions have the most considerable impact on turbine performance due to their inherent effect on 3D local wind inclination in the relative frame. The ALM implementation decreased computational cost as just about 400k and 600k grids are necessary for performance assessment of the NREL Phase VI case and NREL 5-MW case with reasonable accuracy. Visualizing the followed flow fields proved the ability of the ALM code in capturing vortices trajectory, potential blade-vortex interactions, vortex pairing, and vortex ring state phenomenon in FOWTs. It is shown that a high amplitude or frequency of motion can result in the dynamic stall or vortex ring state. Even though a motion affects the turbine performance marginally, the wake can still be dominated due to complex flow conditions like vortex interactions or pairing.
Floating offshore wind turbines (FOWTs) are a solution to harvest wind energy in deep water wind farms thanks to higher wind energy potential than onshore configurations. Fast and effective numerical models explaining the impact of platform motion on wind fields are fundamental to harvesting the potential energy in large offshore wind farms. This project developed a CFD-based Computationally-Efficient approach based on an actuator line model (ALM) to study FOWTs. A dedicated C++ library was implemented in the OpenFOAM toolbox to complement reasonable accuracy and affordable computational effort while investigating the effects of the platform motions on the wake evolution. Two well-known turbine cases were studied, including NREL Phase VI with adequate available experimental data and NREL 5-MW being representative of a large-size wind turbine. It was well documented that, at the same displacement, pitch and surge motions have the most considerable impact on turbine performance due to their inherent effect on 3D local wind inclination in the relative frame. The ALM implementation decreased computational cost as just about 400k and 600k grids are necessary for performance assessment of the NREL Phase VI case and NREL 5-MW case with reasonable accuracy. Visualizing the followed flow fields proved the ability of the ALM code in capturing vortices trajectory, potential blade-vortex interactions, vortex pairing, and vortex ring state phenomenon in FOWTs. It is shown that a high amplitude or frequency of motion can result in the dynamic stall or vortex ring state. Even though a motion affects the turbine performance marginally, the wake can still be dominated due to complex flow conditions like vortex interactions or pairing.

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18

Unida, Roberto. "An investigation on the offshore wind energy potential in Italy and its deployment with floating turbines". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.

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The thesis aim is to offer a general assessment of potential of offshore wind deployment in Italy. More specifically, it aids with the identification of the most promising locations and estimates the levelized cost of energy of the areas found suitable. Furthermore, the thesis develops a simple technical feasibility study at one of these sites, which specifically focuses on the design of the wind turbines foundations, considering and comparing different geotechnical solutions. It is been found that, in Italy, the offshore area suitable for the installation of wind farms is approximately 110,000 km2, with an estimated theoretical annual energy production of 188.25 TWh, more than half of the Italian electricity need. Locations identified as promising are the Adriatic Sea, and the Ionian Sea of the Apulia region and the South-West part of Sicily. For these areas the LCOE analysis has yielded values ranging between 90 $/kWh to 130 $/kWh, in line with European average. The case of study indicated that anchors’ cost strongly depends on local met-ocean conditions, as it is found by comparing the results obtained for the Italian case study with Hywind Scotland pilot floating wind farm, used as benchmark. Comparison between two different anchor solutions has also shown that the foundation choice has also a significant impact on the overall cost for a plant set-up.

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19

Lemmer, Frank [Verfasser]. "Low-order modeling, controller design and optimization of floating offshore wind turbines / Frank Lemmer". München : Verlag Dr. Hut, 2018. http://d-nb.info/1174425768/34.

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20

Saracevic, Nermina. "Comparison of electricity production between semi-submersible and spar-buoy floating offshore wind turbines". Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-381386.

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The paper compares electricity production between the semi-submersible and the spar-buoy floating wind turbine systems under normal, stochastic and extreme wind conditions at Utsira Nord site located on the Norwegian continental shelf in the North Sea. The analysis of complex behavior of the floating wind turbine system and the fluid-structure interaction is performed in aero-servo-hydro-elastic code ASHES. The results indicate a slightly better energy performance of the semi-submersible than the spar in all load cases but one. The pitch and heave degrees of freedom are evaluated as the most relevant for the power output. It is shown that pitch and heave platform motions have smaller displacement in the semi-submersible floater than in the spar under average environmental conditions and at the rated wind speed operating range. The simulation also confirmed that the energy yield is very sensitive to the magnitude of the loads: the spar performed best under mild environmental conditions, while the semi-submersible was better under medium environmental conditions. Small difference in energy yield is attributed to the same baseline blade and external controller properties used for both floaters where generator torque was kept constant to limit the power excursions above the rated power. The method proposed under this paper has demonstrated that a good approximation of the energy performance of the floating wind turbine system can be performed in a fast and effective manner.

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21

Vandenbrande, Pieter-Jan. "Opportunities and challenges for a floating offshore wind market in California". Thesis, KTH, Industriell Marknadsföring och Entreprenörskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209246.

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The offshore wind energy industry is a rapidly growing industry as solutions are becoming cost-competitive and there is an increasing need to limit greenhouse gas emissions. New floating offshore wind turbine designs now enable the access to previously inaccessible offshore wind resources. In this research, a comprehensive analysis is made of the different factors influencing the macro environment for a potential floating offshore wind energy market in California. The analysis assesses the relevant political, economic,social, technological, environmental, and legal aspects in California. The outcome of this research shows the opportunities and challenges for a floating wind turbine market in California. It is found that there are many opportunities present due to California's political and economic climate. There is considerable support for offshore wind projects on the state level, demonstrated by the active engagement of the governor and the creation of the California Task Force. The large economy and high electricity prices are promising for future projects. Furthermore, wind resources are vast and the technical infrastructure is present, especially Southern California is well suited. There are technological threats present, but these are common for all renewable energy sources and seem unavoidable with the Renewable Portfolio Standards California has set. The main threats are posed by the complex regulatory environment and the financial uncertainty as a result of the lackof federal support. The Jones Act, for example, can be troublesome as it will likely increase costs and delay projects. Furthermore, the social environment and local willingness for such projects was shown to be very important for their success. The state of California has already been working pro-actively on involving the local members of thepublic in potential upcoming offshore wind energy projects. The research concludes that California offers many opportunities with surmountable threats.

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22

Lee, Sungho Ph D. Massachusetts Institute of Technology. "A nonlinear wave load model for extreme and fatigue responses of offshore floating wind turbines". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74905.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 169-173).
Ocean energy is one of the most important sources of alternative energy and offshore floating wind turbines are considered viable and economical means of harnessing ocean energy. The accurate prediction of nonlinear hydrodynamic wave loads and the resulting nonlinear motion and tether tension is of crucial importance in the design of floating wind turbines. A new theoretical framework is presented for analyzing hydrodynamic forces on floating bodies which is potentially applicable in a wide range of problems in ocean engineering. The total fluid force acting on a floating body is obtained by the time rate of change of the impulse of the velocity potential flow around the body. This new model called Fluid Impulse Theory is used to address the nonlinear hydrodynamic wave loads and the resulting nonlinear responses of floating wind turbine for various wave conditions in a highly efficient and robust manner in time domain. A three-dimensional time domain hydrodynamic wave-body interaction computational solver is developed in the frame work of a boundary element method based on the transient free-surface Green-function. By applying a numerical treatment that takes the free-surface boundary conditions linearized at the incident wave surface and takes the body boundary condition satisfied on the instantaneous underwater surface of the moving body, it simulates a potential flow in conjunction with the Fluid Impulse Theory for nonlinear wave-body interaction problems of large-amplitude waves and motions in time domain. Several results are presented from the application of the Fluid Impulse Theory to the extreme and fatigue wave load model: the time domain analysis of nonlinear dynamic response of floating wind turbine for extreme wave events and the time domain analysis of nonlinear wave load for an irregular sea state followed by a power spectral density analysis.
by Sungho Lee.
Ph.D.

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23

Weng, Bowen. "AN OFFSHORE FLOATING WIND TURBINE PLATFORM PROTOTYPE: DESIGN AND EXPERIMENTATION". Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1467896225.

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24

Martin, Heather Rae. "Development of a Scale Model Wind Turbine for Testing of Offshore Floating Wind Turbine Systems". Fogler Library, University of Maine, 2011. http://www.library.umaine.edu/theses/pdf/MartinH2011.pdf.

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25

Jonkman, Jason Mark. "Dynamics modeling and loads analysis of an offshore floating wind turbine". Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3284496.

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Han, Chenlu. "Position control of a floating offshore wind turbine system using aerodynamic force". Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62942.

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The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

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27

Lin, Lin. "BEMT and CFD-based unsteady aerodynamic analyses of floating offshore wind turbine". Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27627.

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Nowadays the demands for floating offshore wind (FOWT) have exceeded 5MW with the rapidly growing wind market. The aerodynamic environment of FOWT is more complex than onshore or fixed offshore wind turbine due to the large motions of floating platforms. The platform motion, especially pitch and surge motions, increase aerodynamic unsteadiness, wake interactions and other complex flow phenomena. These conditions influence the velocities and accelerations at the rotor sections along the blade. However, a limited simulation and load estimation capability make aerodynamic analysis a challenge. It is questionable whether some industry aerodynamic analysis codes like conventional Blade Element Momentum (BEM) theory and Generalised Dynamic Wake theory are accurate. Results indicate that current methods for predicting the aerodynamic loads may be inadequate. Aerodynamic flow effects cannot be accurately modelled using traditional BEM theory with common corrections in such a complex condition. So compared with traditional potential theory, CFD method provides more physically realistic simulation. The applying and validation of CFD method will be outlined in this dissertation. The commercial multi-purpose CFD solver STAR CCM+ 9.02 is employed for calculation of the flow using Reynolds-Average Navier-Stokes (RANS) equations in conjunction with different turbulent models. Finally, results from CFD simulations of various offshore floating wind turbines under different load conditions will be presented. CFD simulation is accurate, but time consuming. So, an optimization method will be detected to get a more accurate result and saving time. 2D CFD RANS data was instead of commonly 2D data. However, not result in the desired improvements when compared to BEM results. Therefore, a 2D airfoil data obtained by post-processing of 3D CFD computations was used. 3D results were used to estimate 2D airfoil characteristics to modify two important parameters in BEM codes: the axial and the tangential induction factors by applying the reduced axial velocity method by getting the local angle of attack from CFD solutions. This thesis will demonstrate that the aerodynamics of offshore floating wind turbines is sufficiently different from conventional offshore and onshore wind turbines, warranting the use of higher fidelity analysis approaches. It is obvious that thexxiiiplatform motions will have a great effect on unsteady aerodynamic performance of the wind turbine rotor. This thesis will study and explain the rules and reasons of this phenomenon in detail. Future offshore floating wind turbine designs should strive to either minimize platform motions or be complementarily optimized, via higher fidelity aerodynamic analysis techniques, to account for them. It is believed that this dissertation is the first in-depth study of offshore floating wind turbine aerodynamics and the applicability of various analysis methods.

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Lemmer, Frank [Verfasser] y Po Wen [Akademischer Betreuer] Cheng. "Low-order modeling, controller design and optimization of floating offshore wind turbines / Frank Lemmer ; Betreuer: Po Wen Cheng". Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2018. http://d-nb.info/1193996686/34.

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Almherigh, Mohamed Abdalla Mohamed. "Evaluation of finite element analysis techiques applied to a floating offshore wind turbine". Thesis, University of Salford, 2005. http://usir.salford.ac.uk/2216/.

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The work presented here is a research thesis of the Ph. D programme in The School of Computing, Science & Engineering at The University of Salford UK. The work presents the evaluation of using explicit finite element techniques for structural non-linear dynamic analysis of a floating offshore wind turbine used for harnessing wind kinetic energy and converting it to electricity. The LS-DYNA3D explicit finite element analysis programme is used in performing the evaluation of the analysis and in creating a full scale model typical to the one evaluated. The developed model (case study) is a 1.4MW power rated floating 3 blades turbine elevated at 46.5 m above main sea level a top a tripod lattice steel tower firmly resting on a moored floating concrete hull buoy, positioned on a concrete circular disk. The mooring cables supporting the floating units in the multi unit farm are designed to share seabed anchoring piles for economic reasons. The model is intended for use in moderately deep waters of up to 500m. The State-of-the-art report is presented concerning wind energy technology, floating offshore wind structures and important features of the LS-DYNA3D code. The theoretical basics for service loads experienced by the floating wind turbine are explored and the loads are quantified. The Verification and validation work on developed small models is presented to ensure confidence in the developed full scale model and the evaluation of the finite element techniques which may be applied to such structures. Development of full scale model, material properties, loads and boundary conditions are presented. Recommendations both for this model and future development are accordingly made.

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30

Gelotte, Lovisa y Nilsson Alexandra Lundevall. "Optimal Placement of FloatingTwo-Turbine Foundations in Offshore Wind Farms". Thesis, KTH, Energiteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209833.

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This project is conducted in cooperation with Hexicon AB, which is a Swedish design and engineering company developing floating two-turbine platforms for offshore wind power.The study aims to investigate the optimal placement of Hexicon AB’s platforms in an offshore wind farm with respect to the Annual Energy Production (AEP). Wind farm layout optimization is a complex problem and it has been approached by the development of calculation and optimization programs in Matlab. The analytical Jensen wake model has been utilized for calculation of AEP and important inputs to the program have been turbine parameters and site specific conditions. The optimization strategy used is a multi-stage algorithm where the gradient-based local search algorithm Fmincon has been used in combination with a version of the heuristic genetic algorithm. The developed programs have been tested and evaluated through a case study. Included in the case study is also a brief financial evaluation regarding how different scenarios in electricity export price and costs for cabling could affect the feasibility of the optimized layouts. Concluded from the project is that the developed programs can be used to investigate the optimal placement of floating two-turbine platforms with respect to AEP. In the case study it was found that the optimized layout obtained a wind farm efficiency of around 4% more than for the conventional staggered layout that was tested. What is also emphasized is that the feasibility of the optimized layouts obtained from the program is quite sensitive toward changes in future electricity export price and costs for cabling and installation. Hence, it is important to perform a careful financial analysis in order to draw conclusions regarding what layout is the better option for a specific situation.
Dagens utbyggnad av vindkraft sker i allt större utsträckning genom etablering av vindkraftparker. De främsta fördelarna med att placera vindkraftverken i parker är att de höga fasta kostnaderna fördelas på flera kraftverk samt att man kan beställa ett flertal enheter samtidigt och därigenom minska kostnaden per installerad Megawatt (MW). För att ytterligare kunna öka vinsten på investeringen är det viktigt att undersöka optimal inbördes placering av vindkraftverken för att erhålla en så hög energiproduktion som möjligt. Det finns många studier gjorda inom området och ett flertal programvaror utvecklade. Dock finns det endast ett fåtal studier som har inriktat sig specifikt på flytande vindkraftverk. Detta arbete är utfört i samarbete med Hexicon AB, vilket är ett Stockholmsbaserat ingenjörsföretag som utvecklar en patenterad teknik för plattformar avsedda för flytande vindkraft. Det unika med Hexicon ABs patenterade teknik är att två vindkraftverk är placerade på en gemensam plattform. Denna teknik gör det möjligt för plattformen att anpassa sig till vindriktningen vilket ger en ökning av kraftverkens energiutbyte. Då det inte finns några utvecklade optimeringsmetoder för flytande plattformar som kan anpassa sig efter vindriktning är syftet för denna studie att undersöka den optimala inbördes placeringen av Hexicon ABs plattformar i en vindkraftpark. Eftersom vindkraftsoptimering är ett komplicerat problem som bland annat är icke-linjärt och icke-konvext så finns det ingen exakt lösning tillgänglig för problemet. Komplexiteten gör även många förenklingar och antaganden nödvändiga för att kunna bearbeta problemet. I detta projekt har sambandet mellan årlig elproduktion och inbördes placering av plattformarna undersökts genom att ett kalkylerings- och optimeringsprogram utvecklats i programvaran Matlab. För att kunna undersöka den optimala inbördes placeringen av vindkraftverken är det viktigt att förstå hur vindkraftverken påverkas av att placeras tillsammans i en park. För att göra detta så behövs en modell för att beskriva den så kallade vaken som uppstår bakom respektive vindkraftverk. Detta gjordes genom att använda den analytiska Jensen vakmodellen, vilket är den vanligaste modellen att använda för optimeringssyften. Beräkningen av elproduktion gjordes baserat på given information angående turbinparametrar samt specifika förhållanden på platsen för vindparken. För det utvecklade optimeringsprogrammet användes en tvåstegsalgoritm där den gradientbaserade algoritmen Fmincon utgjorde den centrala delen. Fmincon är en effektiv algoritm för lokal optimering som finns tillgänglig i Matlab. För att generera bra startgissningar till den lokala optimeringen användes en version av en heuristisk genetisk algoritm som komplement till Fmincon. Denna algoritm bygger på samma princip som processen för naturligt urval i evolutionssammanhang där de bäst lämpade individerna för vidare sina egenskaper till nästa generation. För att ytterligare förbättra algoritmen kompletterades den även med ett moment av slumpmässighet. För att testa och utvärdera de utvecklade programmen genomfördes en fallstudie. I denna studie optimerades 50 stycken olika heuristiska startgissningar. De 20 bäst presterande konfigurationerna valdes ut för vidare analys där de blev utvärderade med avseende på olika scenarion för elpris samt kostnad för elektrisk infrastruktur. Detta för att undersöka hur den optima placeringen eventuellt skulle kunna påverkas av osäkerheter i dessa faktorer. Den genomförda fallstudien indikerade att de utvecklade programmen kan användas för att undersöka den inbördes optimala placeringen av vindkraftverk med avseende på elproduktion. Den ekonomiska utvärderingen indikerade även att den optimala placeringen var känslig för olika scenarion där elpris och kostnader för infrastruktur varierades och att detta kunde påverka lönsamheten för investeringen. Det ska därför betonas att det anses vara viktigt att utföra en mer noggrann ekonomisk utvärdering av de optimerade konfigurationerna för att undersöka vilken positionering som är mest lämplig för en viss situation.

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31

Lacaze, Jean-Baptiste. "Etude expérimentale et numérique du couplage des phénomènes aérodynamiques et hydrodynamiques sur une éolienne offshore flottante". Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4735.

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Le présent travail est une étude sur la modélisation des éoliennes flottantes alliant à la fois des chargements hydrodynamiques et aérodynamiques. L’approche expérimentale a tiré profit de la grande soufflerie de Luminy opérée par le MIO (Institut Océanologique de Méditerranée), unissant une soufflerie de très bonne qualité avec un bassin équipé de systèmes de génération de houle et de courant. Les dimensions de cette installation imposent un travail à échelle très réduite introduisant ainsi les interrogations sur les similitudes à respecter (Reynolds, Froude) et les complexités de maquettage. Ces travaux ont permis de développer des outils numériques avec d’un côté une approche fréquentielle basé sur un code utilisant les éléments finis développé par l’IFP au début des années 70, et de l’autre, une approche temporelle basé sur les formulations de Morison ou de Rainey permettant l’introduction de méthodes avancées de calculs des efforts aérodynamiques
The present work focuses on the modeling of the hydrodynamic and aerodynamic loads on a floating wind turbine. The experimental approach took advantage of the wind and wave flume in Luminy operated by the MIO (Mediterranean Institute for Oceanography) comprising a wind tunnel with a very high flow quality blowing over a wave tank. The dimensions of the installation impose working at very small scales for which the similitudes (Reynolds, Froude) introduce high modeling complexities. This work allowed the development of numerical tools using one the one hand a frequency domain approach based on a finite element code developped by IFP¨in the early seventies, and in the other hand a time-domain approach based on Morison or Rainey formulation for hydrodynamic loads allowing the introduction of advanced methods for aerodynamic loads computation

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32

Leroy, Vincent. "Aérodynamique instationnaire pour l'analyse de la tenue à la mer des éoliennes flottantes". Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0050/document.

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La simulation numérique des éoliennes flottantes est essentielle pour le développement des Energies Marines Renouvelables. Les outils de simulation classiquement utilisés supposent un écoulement stationnaire sur les rotors. Ces théories sont généralement assez précises pour calculer les forces aérodynamiques et dimensionner les éoliennes fixes (à terre ou en mer) mais les mouvements de la plateforme d’une éolienne flottante peuvent induire des effets instationnaires conséquents. Ceux-ci peuvent par exemple impacter la force de poussée sur le rotor. Cette thèse de doctorat cherche à comprendre et à quantifier les effets de l’aérodynamique instationnaire sur la tenue à la mer des éoliennes flottantes, dans différentes conditions de fonctionnement. L’étude montre que les forces aérodynamiques instationnaires impactent les mouvements de la plateforme lorsque le rotor est fortement chargé. Les modèles quasi-stationnaires arrivent néanmoins à capturer la dynamique des éoliennes flottantes avec une précision suffisante pour des phases de design amont. Les éoliennes flottantes à axe vertical sont elles aussi étudiées pour des projets offshore puisqu’elles pourraient nécessiter des coûts d’infrastructure réduits. Après avoir étudié l’influence de l’aérodynamique instationnaire sur la tenue à la mer de ces éoliennes, une comparaison est menée entre éoliennes flottantes à axe horizontal et à axe vertical. Cette dernière subit une importante poussée aérodynamique par vents forts, induisant de très grands déplacements et chargements
Accurate numerical simulation of thesea keeping of Floating Wind turbines (FWTs) is essential for the development of Marine Renewable Energy. State-of-the-art simulation tools assume a steady flow on the rotor. The accuracy of such models has been proven for bottom-fixed turbines, but has not been demonstrated yet for FWTs with substantial platform motions. This PhD thesis focuses on the impact of unsteady aerodynamics on the seakeeping of FWTs. This study is done by comparing quasi-steady to fully unsteady models with a coupled hydro-aerodynamic simulation tool. It shows that unsteady load shave a substantial effect on the platform motion when the rotor is highly loaded. The choice of a numerical model for example induces differences in tower base bending moments. The study also shows that state of the art quasi-steady aerodynamic models can show rather good accuracy when studying the global motion of the FWTs. Vertical Axis Wind Turbines (VAWTs) could lower infrastructure costs and are hence studied today for offshore wind projects. Unsteady aerodynamics for floating VAWT sand its effects on the sea keeping modelling have been studied during the PhD thesis,leading to similar conclusions than for traditional floating Horizontal Axis Wind Turbines (HAWTs). Those turbines have been compared to HAWTs. The study concludes that, without blade pitch control strategy, VAWTs suffer from very high wind thrust at over-rated wind speeds, leading to excessive displacements and loads. More developments are hence needed to improve the performance of such floating systems

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33

Coudurier, Christophe. "Conception, modélisation et contrôle d'un tube anti-roulis multidirectionnel pour une barge offshore portant une éolienne". Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM054/document.

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Suite à la mise en place de politiques publiques favorisant les énergies renouvelables, la construction de fermes éoliennes offshore est en plein essor aux quatre coins du monde. Or, la technique de l'éolienne offshore posée, la seule utilisée actuellement, n'est pas viable économiquement dans des eaux trop profondes. Ceci représente un sérieux frein au développement de l'énergie éolienne. Pour cette raison, la communauté scientifique s'intéresse depuis plusieurs années aux éoliennes sur plates-formes flottantes. En eau profonde, cette technologie est intéressante. Mais le fait que l'éolienne ne soit pas encastrée au fond de la mer augmente très significativement les sollicitations mécaniques induites par les vagues.Pour réduire ces sollicitations qui ont de nombreux effets néfastes, différentes approches sont possibles. Essayer de compenser les oscillations « avant-arrière » du mât de l'éolienne en pilotant la force de poussée exercée au niveau du rotor a déjà été écarté dans la littérature. Nous nous sommes concentrés sur l'ajout d'un dispositif de stabilisation interne à la plate-forme, de type Tuned Liquid Column Damper (un tube en U contenant un liquide, TLCD, encore appelé tube anti-roulis), utilisé dans d'autres contextes. Le dispositif que nous proposons est un dispositif actif où les paramètres du TLCD sont ajustés en temps réel, au cours du mouvement induit par les vagues. La mise à jour des paramètres suit une stratégie reposant sur une analyse des interactions entre le TLCD et la plate-forme (appelée ici barge) sur laquelle est installée l'éolienne. Nous avons modélisé le mouvement de la barge seul et son couplage avec le TLCD dans le plan grâce à une approche Lagrangienne. Nous avons étudié les effets des interactions du TLCD avec la barge dans le cas où le coefficient de perte de charge dans le tube était constant. Les limites de cette approche ont été détaillées grâce aux résultats classiques de la littérature sur les oscillateurs mécaniques couplés. Nous nous sommes ensuite concentrés sur une approche active consistant à modifier les caractéristiques du système en temps réel. Nous avons proposé des stratégies de type Linear Quadratic Regulator et de type Model Predictive Control agissant sur le coefficient de perte de charge. Dans un deuxième temps, les simulations nous ont ensuite permis d'écarter la commande MPC dont le rapport performance / complexité n'est pas favorable par rapport à la commande LQR dans ce cas précis.Une étude plus générale du système, en trois dimensions, nous a permis de vérifier que le TLCD classique dans sa version passive ou dans la version active que nous proposions n'est pas du tout robuste à l'incidence de la houle. Nous avons donc imaginé et modélisé des dispositifs inspirés du TLCD mais permettant d'amortir les oscillations de la houle de manière efficace, indépendamment de l'incidence de la houle. Nous avons nommé ces dispositifs TLMCD, pour Tuned Liquid Multiple Columns Damper.Les dispositif que nous proposons sont des systèmes TLMCD actifs. Ils sont conçus d'après les modélisations 3D que nous avons développées et une étude des coûts. Pour ces dispositifs, nous avons aussi détaillé les spécificités de la synthèse des stratégies LQR pour amortir les oscillations de la barge indépendamment de l'incidence de la houle.La performance de ces solutions d'amortissement a finalement été évaluée par simulation pour un large éventail de conditions de houle, couvrant les spécifications d'un “ cahier des charges ” que nous présentons. On observe une réduction des oscillations en roulis de la barge qui peut atteindre un facteur 4 par rapport à l'éolienne flottante sans TLCD. Ces résultats nous montrent que le dispositif TLMCD que nous proposons est un dispositif intéressant pour amortir de manière significative, robuste et économiquement abordable notre système
Thanks to the recent policies of subsidizing renewables energies, constructions of oﬀshore wind farms are booming all over the world. Yet, fixed-bottom wind turbine technology, the only one currently deployed, are too costly for deep waters. This hinders the development of wind power. This is why the scientific community has an interest in floating wind turbines (FWT). The cost of these wind turbines does not depend much on water depth. But since the wind turbine is not fixed into the seabed, the mechanical stress caused by the waves significatively raises.To reduce these detrimental loads, different approaches can be used. The litterature already discarded the control of the wind thrust applied on the rotor to compensate the "fore-aft" oscillations of the tower. We focused on stabilizing floating wind turbine by means of an attached damping system placed inside the float, it is a Tuned Liquid Column Damper (a U-tube containing a liquid, TLCD, also known as anti-roll tank), used in other areas. The damper we propose is an active system where TLCD parameters are continuously modified. Parameters are updated according to a strategy defined thanks to an analysis of the interactions between TLCD and the float (referred to as barge) supporting the wind turbine. We modelled the coupled dynamics of the barge and the TLCD in the vertical plan using a Lagrangian approach. We studied the motions of the damped system for a constant head-loss coefficient in the TLCD. The limits of this approach were detailed thanks to the classic results in double oscillators literature. Then, we focused on an active approach involving a time varying of the head-loss coefficient. We proposed Linear Quadratic Regulator and Model Predictive Control strategies to determine the head-loss coefficient. At a later stage, simulations enabled us to discard the MPC strategy as its complexity/performance ratio is rather bad compared to the LQR strategy in this particular case.A more general study of the system, in three dimensions, showed us that the TLCD is not robust against wave incidence. Therefore, we imagined and modeled new dampers inspired by the TLCD, which can damp the float effectively, regardless of the wave incidence. We named those dampers Tuned Liquid Multiple Column Damper (TLMCD).The dampers we propose are active TLMCD. Their designs are based on their dynamic properties and a cost study. We also detailed the specificities of LQR design to ensure the best possible robustness against wave incidence.The performance of the proposed TLMCD dampers was assessed through numerical simulations for a wide range of sea conditions. We observe that barge roll can be reduced by a factor of four compared to the undamped FWT. These results show us that the TLMCD we propose is interesting to damp significantly, robustly and economically our FWT

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34

Bussolati, Federico. "Modèle multi-échelle de la fatigue des lignes d’ancrage câblées pour l’éolien offshore flottant". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLN041/document.

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La fonction principale des systèmes d'ancrage des éoliennes offshore flottantes est de limiter les mouvements du support. Les lignes d'ancrage qui les composent sont typiquement constituées de chaînes, de câbles aciers, de câbles synthétiques ou d'une combinaison de ces composants.Dans cette thèse, on se concentre sur les câbles en acier qui permettent de réduire le poids et d'augmenter la résistance en tension par rapport aux chaînes. Leur dimensionnement dépend des chargements en tension et flexion, liés aux mouvements du flotteur sous l'action de la mer et du vent.L'objectif de la thèse est le développement d'un nouveau modèle numérique pour prédire la durée de vie en fatigue des câbles d'ancrage d'une éolienne offshore flottante. Il doit notamment simuler les glissements relatifs entre les fils au cours d'une flexion du câble. Des résultats d'essais de tension-flexion de la littérature ont en effet montré que la première rupture est localisée près du plan neutre de flexion, où ces déplacements relatifs sont les plus grands. Cet effet majeur sur la durée de vie du câble n'est pas pris en compte par les lois de fatigue en tension-tension des normes de design offshore actuelles.Il faut aussi remarquer que l'utilisation d'un modèle détaillé de câble dans une démarche de dimensionnement à la fatigue représente un vrai défi. Le nombre élevé d'interactions de contact à modéliser, de l'ordre de plusieurs milliers par mètre de câble, et le grand nombre de cas de chargement rendent ce type de calculs très coûteux.Les chargements qui sont utilisés dans le modèle local de câble sont issus de calculs globaux réalisés à l'aide d'un logiciel multiphysique (Deeplines). Ce logiciel permet de simuler les conditions environnementales (vent, houle, courant) appliquées sur l'ensemble de la structure offshore.Nous montrons que le comportement non linéaire en flexion du câble, lié aux interactions de contact entre les fils, n'influence pas significativement les résultats du modèle global. Cette observation justifie une démarche de type descendante, les calculs globaux pouvant être réalisés en première étape. Les évolutions temporelles des tensions et courbures globales sont appliquées uniformément sur le fil central du modèle local du câble. La continuité du câble est représentée par des conditions de périodicité reliant les sections de bord à des points internes du modèle situés sur la même position circonférentielle. Les fils sont modélisés par des éléments poutres. On obtient les contraintes généralisées sur les fils, les forces de contact et les glissements relatifs. Des premières analyses ont montré que les déplacements relatifs entre les fils restent petits dans notre cadre d'application. Afin de réduire le coût calcul, nous avons développé un nouvel élément de contact entre poutres non parallèles, avec un appariement fixe de contact, dans l'hypothèse de petits glissements mais en grands déplacements et grandes rotations. Des tests numériques montrent l'amélioration obtenue, avec un résultat plus proche d'un modèle de référence qui considère un contact surfacique. De plus, le nouveau modèle réduit significativement le coût calcul et se montre plus robuste en convergence, ce qui s'avère crucial pour un calcul de fatigue. Les sorties du modèle local sont ensuite utilisées pour prédire un état de contrainte 3D, en exploitant des solutions analytiques de contact entre corps cylindriques. Finalement, un critère de fatigue multiaxial de la littérature est appliqué pour évaluer le risque en dommage
The main function of mooring systems of floating offshore wind turbines is to ensure station keeping. The mooring lines can be composed of chains, wire ropes, synthetic ropes, or even a combination of them. In this thesis we focus on wire ropes, whose advantage over chain is to sustain high tension at a lower weight. Their design must consider the successive tension and bending loading induced by the floater movement for various wind and waves conditions.The thesis purpose is to develop a new numerical model, dedicated to the prediction of fatigue damage in mooring wire ropes of a floating wind turbine. In particular it has to simulate the relative movements between the wires when the rope is bent. Results from free-bending fatigue tests in the literature show the importance of these effects, since the first rupture is localized near the neutral plane, where fretting is more important. This phenomenon affecting the fatigue life is not considered by fatigue criteria of current offshore standards, which are related to tension-tension loading.It is worth noting that the use of a detailed model of wire rope in a fatigue design procedure represents a real challenge. The high number of contact interactions to be modeled, which are several thousands per meter of rope, and the large amount of loading cases make this type of computations extremely time-consuming.The loading used in the developed local model of wire rope is obtained from global computations performed with a dedicated multiphysics software (Deeplines). This software allows to simulate the environmental conditions (wind, waves, current) applied on the whole structural system.Some preliminary computations showed that the nonlinear bending behavior of the wire rope, linked to the wire contact interactions, does not significantly affect the output of the global model. This observation justifies the use of a top-down scheme, with a prior computation of the global scale.The global scale tension and curvature are then uniformly imposed on the central wire of the local model. The continuity of the rope is represented by periodic conditions which link the end sections to points within the model, at the same circumferential locations. The wires are modeled by beam elements. The outputs at the local scale are the stress resultants on the wires, and the contact forces and relative displacements at contact locations.Small sliding between the wires has been observed from first numerical analysis, for a representative loading case. Therefore, in order to reduce the computational cost of the wire rope model, a new node-to-node contact element has been developed, dedicated to the modeling of contact between non-parallel beams with circular cross section. It assumes fixed contact pairing and finite rotations. Numerical benchmarks and experimental tests on wire ropes show the improvement with results closer to a reference surface-to-surface model, when compared to standard algorithm for the simulation of contact between beams. Moreover, the new model reduces significantly the CPU cost and is also more robust, which is crucial for fatigue life estimates.The outputs of the local scale model are then used to obtain the complete 3D stress state by means of analytical solutions of contact between solids with cylindrical shape. Finally, a multiaxial fatigue criterion is applied in order to assess the safety of the system

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35

Spraul, Charles. "Suivi en service de la durée de vie des ombilicaux dynamiques pour l’éolien flottant". Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0007/document.

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Le travail présenté vise à mettre en place une méthodologie pour le suivi en service de la fatigue mécanique pour l’ombilical dynamique d’un système EMR flottant. L’approche envisagée consiste à simuler à l’aide d’outils numériques la réponse de l’ombilical aux cas de chargement observés sur site. Le post-traitement des résultats de ces simulations devant permettre d’accéder à différentes quantités d’intérêt en tout point du câble. Pour quantifier et réduire l’incertitude sur la réponse calculée de l’ombilical ce dernier doit être instrumenté. Un certain nombre de paramètres du modèle numérique feront alors l’objet d’une calibration régulière pour suivre l’évolution des caractéristiques de l’ombilical susceptibles d’évoluer. Dans ce contexte ce manuscrit présente et compare différentes méthodes pour analyser la sensibilité de la réponse de l’ombilical aux paramètres susceptibles d’être suivis. L’objectif est notamment d’orienter le choix des mesures à mettre en oeuvre. L’analyse en composantes principales permet pour cela d’identifier les principaux modes de variation de la réponse de l’ombilical en réponse aux variations des paramètres étudiés. Différentes approches sont également envisagées pour la calibration des paramètres suivis,avec en particulier le souci de quantifier l’incertitude restante sur le dommage. Les méthodes envisagées sont coûteuses en nombre d’évaluations du modèle numérique et ce dernier est relativement long à évaluer. L’emploi de méta-modèles en substitution des simulations numériques apparait donc nécessaire, et là encore différentes options sont considérées. La méthodologie proposée est appliquée à une configuration simplifiée d’ombilical dans des conditions inspirées du projet FLOATGEN
The present work introduces a methodology to monitor fatigue damage of the dynamic power cable of a floating wind turbine. The suggested approach consists in using numerical simulations to compute the power cable response at the sea states observed on site. The quantities of interest are then obtained in any location along the cable length through the post-treatment of the simulations results. The cable has to be instrumented to quantify and to reduce the uncertainties on the calculated response of the power cable. Indeed some parameters of the numerical model should be calibrated on a regular basis in order to monitor the evolution of the cable properties that might change over time. In this context, this manuscript describes and compares various approaches to analyze the sensitivity of the power cable response to the variations of the parameters to be monitored. The purpose is to provide guidance in the choice of the instrumentation for the cable. Principal components analysis allows identifying the main modes of power cable response variations when the studied parameters are varied. Various methods are also assessed for the calibration of the monitored cable parameters. Special care is given to the quantification of the remaining uncertainty on the fatigue damage. The considered approaches are expensive to apply as they require a large number of model evaluations and as the numerical simulations durations are quite long. Surrogate models are thus employed to replace the numerical model and again different options are considered. The proposed methodology is applied to a simplified configuration which is inspired by the FLOATGEN project

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36

Linde, Børge. "Motion of floating wind turbines". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11593.

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Motion of floating wind turbines has been studied. A literature study on different concepts and what tools are available for simulating them is presented. Marintek’s simulation software SIMO is used for time simulations. In the calculations, the hydrodynamic forces, mooring line forces and aerodynamic forces from the tower and rotor are taken into account. In addition a pitch control algorithm is used for the rotor blades. Results are compared to available experimental results from model tests. The structure studied is a 5 MW version of the Hywind concept.

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37

Adam, Frank. "Untersuchungen zum dynamischen Verhalten schwimmender Offshoregründungen". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2015. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-167117.

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Durch Umwandlung unterschiedlichster Formen von Energie in mechanische oder elektrische Energie wird die Menschheit seit Jahrhunderten bei der Umsetzung von Arbeitsprozessen im Alltag und bei der industriellen Nutzung unterstützt. Strömende Medien wie Wasser oder Wind gelten dabei als die ältesten Energielieferanten. Im Rahmen der Dissertation wird das Konzept einer zugspannungsverankerten Plattform für Offshore Windenergieanlagen (WEA) vorgestellt, wobei neben den, für diesen Plattformtyp typischen, vertikalen auch geneigte Verankerungselemente Verwendung finden. Diese Art der Verspannung einer zugspannungsverankerten Plattform, respektive ’Tension Leg Platfrom’ (TLP) ist bisher von keiner Quelle bekannt und stellt ein Alleinstellungsmerkmal dar. Folglich sollen Untersuchungen zum dynamischen Verhalten schwimmender Gründungen für Offshore WEA, im Speziellen zu einer TLP mit vertikalen und geneigten Ankerelementen, im Rahmen dieser Arbeit erstmalig vorgestellt werden. Die Plattform ist ein modular gestaltetes Tragwerk bestehend aus großen Rohren und mit integrierten zylindrischen Auftriebskörpern. Diese erzeugen im Transportzustand der Plattform vom Hafen zum Einsatzort und im Betriebszustand innerhalb eines Windparks den nötigen Auftrieb. Infolge der speziellen Art der Verspannung werden die Bewegungen der TLP durch die, aus den Belastungen resultierenden, Seildehnungen dominiert. Damit stellte die TLP im Vergleich zu anderen schwimmenden Gründungen ein bewegungsarmes System dar. Inhalt der hier vorgelegten Arbeit sind Untersuchungen zum dynamischen Verhalten schwimmender Offshoregründungen, im speziellen einer TLP für Windenergieanlagen. Es wurden unterschiedliche Tragstrukturen für TLP-Systeme entwickelt und im Rahmen von Modellversuchen getestet. Den Kern der Arbeit bildet der Vergleich des dynamischen Tragverhaltens der unterschiedlichen Plattformen unter Berücksichtigung der geometrischen und strukturellen Randbedingungen.

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38

Tracy, Christopher (Christopher Henry). "Parametric design of floating wind turbines". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40877.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.
Includes bibliographical references.
As the price of energy increases and wind turbine technology matures, it is evident that cost effective designs for floating wind turbines are needed. The next frontier for wind power is the ocean, yet development in near shore waters has been slowed by aesthetic concerns of coastal residents. Going further offshore eliminates these aesthetic concerns and has the additional advantage of stronger and more consistent winds. However, the vast majority of promising locations beyond the view of land are in sufficiently deep water to make building a rigid structure to the ocean floor economically infeasible. Cost effective floating structures are needed to enable wind farm installation in deep water and increase the world's installed base of renewable energy. This thesis presents a parametric approach to the design of these floating structures for offshore wind turbines. It starts with the relevant design concepts from the offshore oil gas industry and presents appropriate combinations of structures and mooring systems that meet the requirements for a generic five mega watt wind turbine. The results of the parametric study are a number of designs that show Pareto fronts for mean square acceleration of the turbine versus multiple cost drivers for the offshore structure. These cost drivers include displacement of the floating structure and total mooring line tension.
by Christopher Tracy.
S.M.

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39

Luypaert, Thomas (Thomas J. ). "Flexible dynamics of floating wind turbines". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70441.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
"February 2012." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 84-86).
This work presents Tower Flex, a structural dynamics model for a coupled analysis of offshore floating wind turbines consisting of a tower, a floating platform and a mooring system. In this multi-body, linear frequency-domain model, the tower is represented as a series of uniform Timoshenko beams connected to each other. The deflections of the tower are solved analytically in each beam while the mass, damping and stiffness coming from the rotor, the floating platform and the mooring lines are taken into account via generalized boundary conditions. Tower Flex is used for the evaluation of a 3MW offshore floating wind turbine mounted on a Tension Leg Platform (TLP). Natural frequencies, motion responses and fatigue damage are analyzed to illustrate the features of Tower Flex and assess the performance of the proposed design.
by Thomas Luypaert.
S.M.

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40

Casanovas, Carlos (Casanovas Bermejo). "Advanced controls for floating wind turbines". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92149.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 64-65).
Floating Offshore Wind Turbines (FOWT) is a technology that stands to spearhead the rapid growth of the offshore wind energy sector and allow the exploration of vast high quality wind resources over coastal and offshore areas with intermediate and large water depths. This generates the need for a new generation of Wind Turbine control systems that take into account the added complexity of the dynamics and wave-induced motions of the specific floater. The present work presents a simulation study of advanced controls for Tension Leg Platform (TLP) FOWT that attempts to enhance the power output of the Wind Turbine by conversion of the surge kinetic energy of the TLP into wind energy. The public access data of the NREL 5MW offshore wind turbine have been used to perform the study. After establishing a theoretical upper bound for the possible wave energy extraction using frequency-domain methods, a time-domain state-space dynamic model of the FOWT with coupled dynamics of platform surge motion and turbine rotation has been developed that includes both a simplified model of the turbine aerodynamics and the floater surge hydrodynamics. This simulation model has then been used to implement advanced controls that maximize energy extraction by the Wind Turbine in the below rated power region. The proposed controllers are variations of a Linear-Quadratic Regulator (LQR), considering both a steady-state case and a non-stationary, finite horizon LQR case. The latter requires wave-elevation forecasting to be implemented and therefore two different forecasting algorithms have also been developed according to existing literature. While the wave-induced annual energy yield enhancement of the studied FOWT in the two considered locations is small (around 0.02% the baseline annual energy yield of the studied turbine in the two locations) the study is not exhaustive and other FOWT topologies might achieve better results. The present results clearly indicate, however, that the existing correlation between strong wind and waves makes FOWTs a sub-optimal choice as energy extraction mechanism for ocean wave energy harvesting.
by Carlos Casanovas.
S.M.

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41

Wisznia, Roman. "Condition Monitoring of Offshore Wind Turbines". Thesis, KTH, Kraft- och värmeteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118455.

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The growing interest around offshore wind power, providing at the same time better wind conditions and fewer visual or environmental impacts, has lead many energy suppliers to consider the installation of offshore wind farms. However, the marine environment makes the installation and maintenance of wind turbines much more complicated, raising the capital and operation costs to an undesirable level and preventing the fast progression of this technology worldwide. Availability of offshore wind turbines varies between 65 and 90% depending on location, whereas onshore turbines range between 95 and 98% in most cases. In 2009, the ETI launched a research project aiming to improve economical efficiency of offshore wind farms by increasing their availability and decreasing their maintenance costs (partly through replacing corrective maintenance by preventive maintenance). This project named “Inflow” involves the development of a condition monitoring system, a system designed to monitor the state of different wind turbine components, and to analyze this data in order to determine the wind turbines overall condition at any given time, as well as its potential system ailments This paper describes two different approaches to perform the condition monitoring of offshore wind farms, the first one involves thresholds-based analysis, while the other involves pattern recognition.

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42

Wilkinson, Michael Richard. "Condition Monitoring for Offshore Wind Turbines". Thesis, University of Newcastle Upon Tyne, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492117.

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Tong, Xin. "Control of large offshore wind turbines". Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/99841/.

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Several control strategies are proposed to improve overall performances of conventional (geared equipped) and hydrostatic offshore wind turbines. Firstly, to maximise energy capture of a conventional turbine, an adaptive torque control technique is proposed through simplifying the conventional extremum seeking control algorithm. Simulations are conducted on the popular National Renewable Energy Laboratory (NREL) monopile 5-MW baseline turbine. The results demonstrate that the simplified ESC algorithms are quite effective in maximising power generation. Secondly, a TMD (tuned mass damper) system is configured to mitigate loads on a monopile turbine tower whose vibrations are typically dominated by its first mode. TMD parameters are obtained via H2 optimisation based on a spatially discretised tower-TMD model. The optimal TMDs are assessed through simulations using the NREL monopile 5-MW baseline model and achieve substantial tower load reductions. In some cases it is necessary to damp tower vibrations induced by multiple modes and it is well-known that a single TMD is lack of robustness. Thus a control strategy is developed to suppress wind turbine’s vibrations (due to multiple modes) using multiple groups of TMDs. The simulation studies demonstrate the superiority of the proposed methods over traditional ones. Thirdly, the NREL 5-MW baseline turbine model is transformed into a hydrostatic wind turbine (HWT). An H∞ loop-shaping torque controller and a light detection and ranging-based linear-parameter-varying anti-windup pitch controller are designed for the HWT. The tests on a monopile HWT model indicate good tracking behaviours of the torque controller and much improved performances of the linear-parameter-varying pitch controller over a gain-scheduled PI pitch controller. Finally, the hydraulic reservoir of a barge HWT is made into a bidirectional-tuned- liquid-column-damper (BTLCD) to suppress barge pitch and roll motions. The simulation results validate the effectiveness of the optimal BTLCD reservoir in reducing the tower loads and power fluctuations.

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44

Floridia, Daniele. "Hybrid foundations for offshore wind turbines". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/3284/.

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Nowadays offshore wind turbines represents a valid answer for energy production but with an increasing in costs mainly due to foundation technology required. Hybrid foundations composed by suction caissons over which is welded a tower supporting the nacelle and the blades allows a strong costs reduction. Here a monopod configuration is studied in a sandy soil in a 10 m water depth. Bearing capacity, sliding resistance and pull-out resistance are evaluated. In a second part the installation process occurring in four steps is analysed. considering also the effect of stress enhancement due to frictional forces opposing to penetration growing at skirt sides both inside and outside. In a three dimensional finite element model using Straus7 the soil non-linearity is considered in an approximate way through an iterative procedure using the Yokota empirical decay curves.

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45

Zhang, Yu Ph D. Massachusetts Institute of Technology Department of Mechanical Engineering. "Wave loads on offshore wind turbines". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100344.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 65).
Ocean energy is one of the most important sources of alternative energy and offshore floating wind turbines are considered viable and economical means of harnessing ocean energy. The accurate prediction of nonlinear hydrodynamic wave loads and the resulting nonlinear motion and tether tension is of crucial importance in the design of floating wind turbines. A new theoretical framework is presented for analyzing hydrodynamic forces on floating bodies which is potentially applicable in a wide range of problems in ocean engineering. The total fluid force acting on a floating body is obtained by the time rate of change of the impulse of the velocity potential flow around the body. This new model called Fluid Impulse Theory is used to address the nonlinear hydrodynamic wave loads and the resulting nonlinear responses of floating wind turbine for various wave conditions in a highly efficient and robust manner in time domain. A three-dimensional time domain hydrodynamic wave-body interaction computational solver is developed in the frame work of a boundary element method based on the transient free-surface Green-function. By applying a numerical treatment that takes the free-surface boundary conditions linearized at the incident wave surface and takes the body boundary condition satisfied on the instantaneous underwater surface of the moving body, it simulates a potential flow in conjunction with the Fluid Impulse Theory for nonlinear wave-body interaction problems of large amplitude waves and motions in time domain. Several results are presented from the application of the Fluid Impulse Theory to the extreme and fatigue wave load model: the time domain analysis of nonlinear dynamic response of floating wind turbine for extreme wave events and the time domain analysis of nonlinear wave load for an irregular sea state followed by a power spectral density analysis.
by Yu Zhang.
S.M.

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46

Lupton, Richard. "Frequency-domain modelling of floating wind turbines". Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/252880.

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The development of new types of offshore wind turbine on floating platforms requires the development of new approaches to modelling the combined platform-turbine system. In this thesis a linearised frequency-domain approach is developed which gives fast but approximate results: linearised models of the structural dynamics, hydrodynamics, aerodynamics and control system dynamics are brought together to find the overall response of the floating wind turbine to harmonic wind and wave loading. Initially, a nonlinear flexible multibody dynamics code is developed and verified, which is then used to provide reference nonlinear simulation results. The structural dynamics of a wind turbine on a moving platform are shown to be nonlinear, but for realistic conditions the effects are small. An approximate analysis of the second-order response of floating cylinders to hydrodynamic loads suggests slow drift motion may be relatively small for floating wind turbines, compared to other floating offshore structures. The aerodynamic loads are linearised using both harmonic and tangent linearisation approaches; the harmonic linearisation gives improved results when stall occurs. The wake dynamics can also be included. The control system behaviour is linearised using the same method, which works well when the wind speed is far from the rated wind speed; close to the rated wind speed the nonlinearity is stronger, but further improvement should be possible. These sub-models are combined to give a simple but complete model of a floating wind turbine, with flexible blades and a flexible tower, but neglecting the control system behaviour, wake dynamics and nonlinear hydrodynamic loads. For the OC3-Hywind turbine, the accuracy of the results is assessed by comparison to nonlinear time-domain simulations using the commercial code Bladed. Peak-peak errors of less than 5 % are achievable for many harmonic wind and wave inputs, but certain conditions lead to larger errors. The effect of including linearised control system behaviour is demonstrated for a subset of conditions. Overall, the results are promising but more work is needed for practical application.

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47

Furunes, Eirik Wie. "Floating wind turbines at medium water depths". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11592.

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Offshore wind turbines have an enormous potential in terms of larger average wind speeds and low surface roughness compared to their onshore counterpart. Shallow water fixed wind turbines are ranked as a mature technology but are also limited by the price tag of creating and installing fixed installations for increasing depths. Hywind, which is a floating wind turbine concept developed by Statoil with focus on larger depths but may prove beneficial for shallower depths and fill the present void between floating and fixed wind turbines. Hywind is limited for shallower waters by among others its large draft and the thesis focus is on a reduction of the draft with the inclusion of a heave plate for possible increased performance. The performance in ultimate limit state (ULS) and fatigue limit state (FLS) are utilized as a base for comparisons between different draft configurations. Non-linear time domain analyses are carried out in FLS and ULS by the coupled computer codes SIMO/RIFLEX including wind, wave and current loads. In the non-linear analyses performed the hydrodynamic loads are calculated at the actual displaced position of the structure and instability effects as the Mathieu instability are accounted for, and also investigated in combination with a second order heave force contribution. The analysis procedures and theory for floating offshore wind turbines are investigated and analysis parameters are defined in terms of ULS and FLS load cases, natural frequencies, a simplified wind turbine control system, damping estimates and heave plate properties. In FLS the draft length has proven as an integral parameter and reduction in lifetime is shown for reduced draft configurations. The inclusion of a heave plate is shown to give an increase in lifetime, although minimal. In ULS peak values are increased for the reduced draft configurations and inclusion of the heave plate has shown to reduce dynamic heave motion but increase dynamic pitch motion.

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48

Lee, Kwang Hyun. "Responses of floating wind turbines to wind and wave excitation". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33564.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2005.
Includes bibliographical references (leaf 55).
The use of wind power has recently emerged as a promising alternative to conventional electricity generation. However, space requirements and public pressure to place unsightly wind turbines out of visual range make it desirable to move large wind farms offshore and into deeper coastal waters. A necessary step for the deployment of wind turbines into deeper waters is the development of floating platform systems. This thesis will present a general technical description of two concept designs for floating wind turbine systems, and make a preliminary evaluation of their performance in wind and waves. A new approach to computing the nonlinear wave excitation is also presented.
by Kwang Hyun Lee.
S.M.

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49

Keysan, Ozan. "Superconducting generators for large offshore wind turbines". Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8841.

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This thesis describes four novel superconducting machine concepts, in the pursuit of finding a suitable design for large offshore wind turbines. The designs should be reliable, modular and light-weight. The main novelty of the topologies reside in using a single loop shaped stationary superconducting field winding, which eliminates the rotating transfer couplers and electric brushes or brushless exciters. Furthermore, the electromagnetic forces in the superconducting wire are also eliminated, which simplifies the design and manufacturing of the cryostat and the support structure. Among the four topologies presented, the claw pole type machine is the most promising one. The rotor of the machine composes of claw-poles made from laminated electrical sheets, the superconducting field winding and the armature winding are stationary. The machine is analysed using 3D FEA simulations and a small linear machine prototype is manufactured to verify the simulations. For large scale applications, a double-sided claw pole machine is proposed, which has balanced magnetic attraction forces in the rotor. The machine has a modular cryostat structure, which increases the availability of the machine. Thus, even if a fault occurs in the cryocoolers or in the armature coils, the rest of the machine can operate at partial load until the maintenance is performed. Moreover, it is much easier to replace the faulty parts, as full disassemble of the machine is not required, and a small on-site crane can be used. As a result, it offers operational advantages over the existing superconducting topologies. A 10 MW, 10 rpm generator design is presented, which has a diameter of 6.6 m and an axial length of 1.4 m. The total active mass of the generator is 58 tonnes, and the structural mass is 126 tonnes, which gives a total mass of 184 tonnes. There are four independent cryostats and two independent armature windings in the machine to improve modularity. The biggest advantage of the design is the significantly less superconducting wire usage compared to any other designs; 10 MW machine just needs 15 km of MgB2 wire at 30 K. Thus, it is believed that the proposed topology is a very cost effective and suitable candidate for a successful entry to the wind turbine market.

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50

Cantoni, Lorenzo. "Load Control Aerodynamics in Offshore Wind Turbines". Thesis, KTH, Kraft- och värmeteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291417.

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Due to the increase of rotor size in horizontal axis wind turbine (HAWT) during the past 25 years in order to achieve higher power output, all wind turbine components and blades in particular, have to withstand higher structural loads. This upscalingproblem could be solved by applying technologies capable of reducing aerodynamic loads the rotor has to withstand, either with passive or active control solutions. These control devices and techniques can reduce the fatigue load upon the blades up to 40% and therefore less maintenance is needed, resulting in an important money savings for the wind farm manager. This project consists in a study of load control techniques for offshore wind turbines from an aerodynamic and aeroelastic point ofview, with the aim to assess a cost effective, robust and reliable solution which could operate maintenance free in quite hostile environments. The first part of this study involves 2D and 3D aerodynamic and aeroelastic simulations to validate the computational model with experimental data and to analyze the interaction between the fluid and the structure. The second part of this study is an assessment of the unsteady aerodynamic loads produced by a wind gust over the blades and to verify how a trailing edge flap would influence the aerodynamic control parameters for the selected wind turbine blade.
På grund av ökningen av rotorstorleken hos horisontella vindturbiner (HAWT) under de senaste 25 åren, en design som har uppstod för att uppnå högre effekt, måste alla vindkraftkomponenter och blad stå emot högre strukturella belastningar. Detta uppskalningsproblem kan lösas genom att använda metoder som kan minska aerodynamiska belastningar som rotorn måste tåla, antingen med passiva eller aktiva styrlösningar. Dessa kontrollanordningar och tekniker kan minska utmattningsbelastningen på bladen med upp till 40 % och därför behövs mindre underhåll, vilket resulterar i viktiga besparingar för vindkraftsägaren. Detta projekt består av en studie av lastkontrolltekniker för havsbaserade vindkraftverk ur en aerodynamisk och aeroelastisk synvinkel, i syfte att bedöma en kostnadseffektiv, robust och pålitlig lösning som kan fungera underhållsfri i tuffa miljöer. Den första delen av denna studie involverar 2D- och 3D-aerodynamiska och aeroelastiska simuleringar för att validera beräkningsmodellen med experimentella data och för att analysera interaktionen mellan fluiden och strukturen. Den andra delen av denna studie är en bedömning av de ojämna aerodynamiska belastningarna som produceras av ett vindkast över bladen och för att verifiera hur en bakkantklaff skulle påverka de aerodynamiska styrparametrarna för det valda vindturbinbladet.

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