A review of numerical modelling and optimisation of the floating support structure for offshore wind turbines

AbstractCompared to onshore wind power, floating offshore wind power is a promising renewable energy source due to higher wind speeds and larger suitable available areas. However, costs are still too high compared to onshore wind power. In general, the economic viability of offshore wind technology decreases with greater water depth and distance from shore. Floating wind platforms are more competitive compared to fixed offshore structures above a certain water depth, but there is still great variety and no clear design convergence. Therefore, optimisation of the floating support structure in the preliminary phase of the design process is still of great importance, often up to personal experience and sensibility. It is fundamental that a suitable optimisation approach is chosen to obtain meaningful results at early development stages. This review provides a comparative overview of the methods, numerical tools and optimisation approaches that can be used with respect to the conceptual design of the support structure for Floating offshore wind turbines (FOWT) attempting to detail the limitations preventing the convergence to an optimal floating support structure. This work is intended to be as a reference for any researcher and developer that would like to optimise the support platform for FOWT

[Report of] Specialist Committee V.4: ocean, wind and wave energy utilization

The committee's mandate was :Concern for structural design of ocean energy utilization devices, such as offshore wind turbines, support structures and fixed or floating wave and tidal energy converters. Attention shall be given to the interaction between the load and the structural response and shall include due consideration of the stochastic nature of the waves, current and wind

Estimation of Extreme Load Responses in a Gearbox of 10-MW Floating Offshore Wind Turbine

This thesis studies the extreme load responses experienced by a 10-MW floating wind turbine situated in the North sea. With a plan to minimise fossil fuels and redefine the energy sector by adopting more safe, efficient, and cleaner solutions, countries have started investing in wind energy to harness the enormous untapped potential contained in the wind. Developing countries have begun building wind turbines to meet their energy needs. Countries started moving away from hydrocarbon and investing more in offshore wind turbines and solar energy parks to meet the expanding population needs and economy and reach net zero emission by 2050. The global average wind turbine size increased from 1.5-MW to 7.58-MW from 2000 to 2020. The future of wind turbines will be in 10-MW to 15-MW class wind turbines as the scientific research community has started to analyse more about the large offshore wind turbine(OWT). The gearbox is considered one of the most critical components in a wind turbine that drives a significant part of operating expenses. Reliability of the gearbox is often crucial for wind turbines which comes as a package with an efficient design and proper load estimation matching the ULS (Ultimate Limit State) condition. The costs of gearbox repair and upkeep and the costs of output losses associated with faulty gearboxes account for a significant portion of the operating costs of the offshore wind turbine. In this thesis, the accuracy and robustness of ACER (Average Conditional Exceedance Rate) as a tool are analysed to estimate extreme loads on the wind turbine gearbox and structure. This is done by analysing varying quantities of accessible data from the North Sea, where most large floating wind turbines are installed. The extreme loads estimated are compared with the Gumbel method under operating conditions of 8m/s, 12 m/s and 16m/s wind speed representing below, rated and above rated wind speed. It is vital to analyse the extreme loads under the dynamics operating condition and analyse the response in a fully coupled state. The aim is to show the accuracy and reliability of ACER in estimating the extreme load’s responses and 1,2 & 5 year return period of large OWT. The results show that the extreme loads’ responses on the 10-MW wind turbine gearbox and structure estimated by ACER gave more accurate and reliable values independent of other extreme value prediction methods like the Gumbel method. This study develops and estimates load responses in large OWT and guides the ultimate limit state load (ULS) calculation for 10-MW wind turbines

Current-based Techniques for Condition Monitoring of Pumps

[ES] Las bombas hidráulicas son el núcleo de muchos procesos en la industria y el sector servicios. Conviene tener en cuenta que los motores eléctricos son responsables del 69% del consumo de energía eléctrica en la industria, siendo en torno a un 22% de motores utilizados para el accionamiento de bombas. Los fallos de estas bombas pueden provocar averías en el proceso y, por lo tanto, implican altos costes económicos para el operador de la planta. Además, un funcionamiento defectuoso de las bombas conlleva una reducción de la eficiencia energética de la planta. De forma habitual, se utilizan principalmente dos tipos de estrategias orientadas al mantenimiento de maquinaria. Una estrategia de mantenimiento (mantenimiento preventivo) consiste en la sustitución de las piezas desgastadas en un intervalo de tiempo fijo. Este tipo de estrategia presenta muchas desventajas asociadas a la escasa optimización en el uso de los recursos y al consiguiente impacto económico. Por otro lado, la estrategia basada en la condición del equipo (mantenimiento basado en la condición) liga el reemplazo de las piezas desgastadas al estado del equipo, el cual es monitorizado a través de señales adquiridas mediante sensores. Sin embargo, el uso de sensores tiene algunos inconvenientes, como costes de inversión adicionales, posibles problemas en el montaje del sensor y posibles fallos del mismo. El análisis de la señal de corriente no se ha utilizado de forma habitual en la práctica para evaluar el estado de la bomba, aunque en muchas aplicaciones se dispone de sensores de corriente ya instalados que se podrían utilizar a tal fin. Se ha demostrado que técnicas basadas en el análisis de la corriente resultan de gran utilidad para diagnosticar varios tipos de fallos en motores eléctricos. De hecho, el análisis de la firma de corriente del motor se utiliza hoy en día ampliamente en la industria, especialmente para el diagnóstico de fallos en motores de inducción. En la presente tesis, se evalúa la utilización de la técnica de análisis de corrientes para el diagnóstico de fallos típicos relacionados con las bombas en diferentes aplicaciones. Se investigan tres tipos de bombas diferentes: bombas en línea de rotor húmedo, bombas de rotor seco y bombas sumergibles. En la tesis se han adaptado diversas técnicas, previamente empleadas para la detección de fallos en motores, al diagnóstico de fallos en la propia bomba. Los resultados indican que fallos como obstrucción de la bomba, fisura del impulsor y desgaste de los cojinetes influyen especialmente en dos frecuencias del espectro de corriente, las cuales pueden utilizarse como base de estrategias de mantenimiento basadas en la condición. En concreto, en las bombas de rotor húmedo, estos dos indicadores de fallo varían sensiblemente en función del punto de carga hidráulica de la bomba. Con la ayuda de un método de extracción de características basado en la motor reference frame theory, se demuestra que las mencionadas frecuencias pueden analizarse en tiempo real en un entorno industrial. Además, se presentan directrices para la monitorización en la nube y se valida con la ayuda de ensayos de laboratorio. Adicionalmente, se demuestra que los fallos son también detectables al analizar la corriente de arranque mediante herramientas de descomposición tiempo-frecuencia. Este hito no se había abordado anteriormente en la literatura técnica del área en lo referente a la detección de fallos en bombas. En conclusión, los resultados de este trabajo demuestran que los métodos de diagnóstico basados en la corriente pueden detectar con éxito diversos tipos de fallo en bombas, lo cual constituye un punto de gran interés para las industrias que utilicen estos activos en sus procesos.[CA] Les bombes hidràuliques són el nucli de molts processos en la indústria i en el sector dels serveis. Cal mencionar que els motors elèctrics són responsables del 69% del consum de la energia elèctrica en la indústria, sent al voltant del 22% dels motors utilitzats per l'accionament de bombes. Les fallades d'aquestes bombes poden causar avaries en els processos, i per tant, representen un alt cost econòmic per a l'operador de la planta. A més a més, un funcionament defectuós en les bombes representa una reducció de l'eficiència energètica de la planta. De manera habitual, s'utilitzen principalment dos tipus d'estratègies orientades al manteniment de la maquinària. Una estratègia de manteniment (manteniment preventiu) consisteix en la canvi de les peces desgastades en un interval fixe de temps. Aquest tipus d'estratègia presenta molts desavantatges associats a la reduïda optimització en el ús dels recursos i el seu impacte econòmic. D'altra banda, la estratègia basada en la condició dels equipaments (manteniment basat en la condició) enllaça la substitució de les peces desgastades al estat de l'equip, el qual es monitoritzat per mig de senyals adquirides per sensors. No obstant això, el ús de sensors té alguns inconvenients com costos d'inversió addicionals, possibles problemes al muntatge i possibles fallades. L'anàlisi dels senyals de corrent no s'utilitzen de manera habitual en la pràctica per avaluar l'estat de la bomba, encara que en moltes aplicacions, estos sensors es troben instal·lats i es podrien fer servir per a aquesta finalitat. Ha estat demostrat que les tècniques basades en l'anàlisi de la corrent són de gran utilitat per el diagnosi de diversos tipus de fallades en motors elèctrics. De fet, l'anàlisi de la firma de la corrent del motor s'utilitza àmpliament en l'indústria, especialment per el diagnosi de fallades en motors d'inducció. En la present tesi, s'avalua l'utilització de la tècnica d'anàlisi de corrents per el diagnosi de fallades típiques relacionades en bombes per a diferents aplicacions. Se investiguen tres tipus de bombes diferents: bombes en línia de rotor humit, bombes de rotor sec i bombes submergibles. En aquesta tesi se han adaptat diverses tècniques, prèviament utilitzades en el diagnosi de màquines elèctriques, per al diagnosi de la pròpia bomba. Els resultat indiquen que les fallades com obstrucció de la bomba, la fissura de l'impulsor i el desgast dels coixinets influeixen especialment en dos freqüències de l'espectre de la corrent, les quals es poden utilitzar com a base per a una estratègia de manteniment basada en la condició. Particularment, en les bombes de rotor humit, aquestos dos indicadors de fallada varíen sensiblement en funció del punt de càrrega hidràulica de la bomba. En l'ajuda de un mètode d'extracció de característiques basat en la "motor reference frame theory", es demostra que les mencionades freqüències es poden analitzar en temps real en un entorn industrial. A més a més, es presenten directrius per la monitorització en el núvol i es valida en l'ajuda de assajos en el laboratori. Addicionalment, es demostra que les fallades són també detectables quan s'analitza la corrent d'arrancada mitjançant ferramentes de descomposició temps-freqüència. Aquest fet no ha estat analitzat prèviament en cap tipus de literatura tècnica dins del camp de detecció de fallades en bombes. En conclusió, els resultats d'aquest treball demostren que els mètodes de diagnosi basats en la corrent poden detectar en èxit diversos tipus de fallades en bombes, el qual constitueix un punt d'interés per a l'indústria que utilitzen aquest tipus de actiu en els seus processos.[EN] Pumps are the heart of many processes in industry and service sector. Electric motors are responsible for 69% of electric energy consumption in industry, with 22% of them being used for the operation of pumps. Pump faults can lead to process breakdowns and are thus related to high costs for the plant operator. Furthermore, faulty operation of pumps reduces the energy efficiency of the plant. In many cases, a time-based maintenance strategy is applied, which means that typical wear parts are replaced within defined time cycles, which comes with some drawbacks such as poor resource efficiency and high costs. Condition-based maintenance strategies - meaning that the replacement of parts is planned based on the condition of the pump - are often based on the evaluation of sensor signals like vibration or noise. However, the use of sensors also has some drawbacks, such as additional investment costs, frequent problems with the sensor mounting, and possible sensor faults. There is no widespread use of the current signal to make statements about the pump condition, although current sensors are installed in many applications anyway. As for motor fault diagnosis, different current-based techniques have demonstrated their function. Today, motor current signature analysis is used in industry, especially for the diagnosis of induction motors. In this thesis, the current-based diagnosis of typical pump-related faults in different applications is evaluated. In total, three different pump types are investigated: a wet-rotor pump, a dry-runner inline pump, and a submersible pump. The techniques used for motor fault detection are adapted for the diagnosis of pump-related faults. The results indicate that the faults clogging, impeller crack, and bearing wear, in particular, influence two frequencies in the current spectrum, which can be used as a basis for a condition-based maintenance strategy. Especially in wet-rotor pumps, these two fault indicators strongly vary depending on the hydraulic load point of the pump. With the help of a feature extraction method based on the adapted reference frame theory, this work demonstrates that the two frequencies can be analyzed in real time in a field environment. Furthermore, a concept for cloud monitoring is presented and validated with the help of a laboratory test. Additionally, it is demonstrated that the faults are visible if the starting current is evaluated in a time-frequency map, which has not been considered before in the literature on pump-related faults. In summary, the findings of this work indicate that current-based diagnosis methods can successfully detect typical faults in pumps, a fact that is of high interest for companies using these assets in their industrial processes.Becker, V. (2022). Current-based Techniques for Condition Monitoring of Pumps [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/19063

Development of a Scale Model Wind Turbine for Testing of Offshore Floating Wind Turbine Systems

This thesis presents the development of a 1/50th scale 5 MW wind turbine intended for wind and wave basin model testing of commercially viable floating wind turbine structures. The design is based on a popular 5 MW wind turbine designed by the National Renewable Energy Laboratory (NREL) commonly utilized in numerical modeling efforts. The model wind turbine is to accompany generic floating model platforms for basin model testing. The ultimate goal of the model development testing program is to collect data for validating various floating wind turbine simulation codes such as those developed by NREL. This thesis will present an overview of the model testing program and detailed information on the scaling methodology, design and physical characterization of the final wind turbine model. The discussion of scaling methodology will include a presentation of scaling relationships used to ensure loads and forces controlling global motions and internal reactions are properly scaled during basin model testing. Particular attention is paid to Reynolds number effects that control the aerodynamic performance of a wind turbine model. Design methods, final designs and all instrumentation and components of the 1/50th scale model are disclosed with additional discussion concerning special fabrication techniques and component testing where applicable. Finally, physical characterization and wind turbine performance results from analytical analyses and basin model test data are provided and compared to determine the overall effectiveness of the created model wind turbine for basin model testing

Dynamic and Fatigue Analyses of Suspended Power Cables for Multiple Floating Offshore Wind Turbines

Floating offshore wind turbines (FOWTs) are installed to effectively capture energy from offshore wind in deeper water areas where building bottom-fixed offshore wind turbines is not practical. The present study focuses on the application and fatigue life of suspended inter-array power cables in floating offshore wind farms. A spar type and a semi-submersible type FOWTs are modeled in the dynamic analysis software OrcaFlex and validated against reference studies. The power cable connecting the FOWTs is installed fully suspended with attached buoys. The impacts of marine growth on the power cable and the non-linear bending behavior of the cable are considered in the analyses. Representative environmental conditions for the North Sea are applied to assess the dynamic responses of the model. Different cable configurations connecting two spar FOWTs are evaluated based on Fitness Factors using static and dynamic analyses. The number of buoys is identified as the main parameter determining the maximum effective tension and the minimum bending radii of the cables. The vertical excursion of the suspended cable depends on the buoy spacing. The effect of cable length and marine growth on cable tensions and curvatures is small. Two semi-submersible FOWTs are connected using the most suitable cable configuration obtained for the two spar FOWTs. The impact of the floater type on the tension and curvature of the power cable is determined to be very small. A two-turbine configuration with various environmental load directions is identified to be representative of the suspended power cables design in whole wind farms, according to analyses of power cable behavior in various offshore wind farm layouts. To investigate the fatigue life of the power cable, the relationships between the axial tensions and curvatures of the power cable and its stresses are obtained by cross-section analysis in UFLEX. The optimum cable in the spar setup has a fatigue life of 85 years, with curvature-induced stresses being identified as the primary cause of the fatigue damage. The power cable's fatigue life reduces when marine growth effects are considered. A decrease in the number of buoys attached to the cable and the use of semi-submersible FOWTs increase the fatigue life. The armor wires are the critical components, and the highest fatigue damage always occurs adjacent to the buoys. The largest fatigue damage results from environmental loads approaching the power cable from a crossflow direction

Characterization and Optimization of Control System and Extreme Value Analysis of a Wind Turbine

The global hunger for energy has only been rising every day as we progress more into adopting superior and better technology to make lives better and easier. As more countries tread the path of industrialization, the need for cleaner and greener energy is imperative to reduce damage to an already deteriorating environment. Wind energy accounts for about 15% of renewable energy and is one of the fastest-growing renewable technologies. The energy produced by wind has doubled in the past decade. The wind industry is only expected to grow with an infinite supply of natural wind. Wind turbines in the 1980s had a capacity of 0.1MW, but today they average at around 10MW, with the largest wind turbines having a capacity of 15MW. Due to a surge in demand and potential for growth, it has become more critical than ever to find newer strategies to maximize turbine efficiency. Numerous approaches can be adopted to improve a turbine's efficiency, including design, material, or control system changes. Other options include using novel or better prediction models to estimate extreme values that can be useful in fine-tuning designs of wind turbines. In this thesis, two main strategies are adopted in an attempt to optimize the efficiency of wind turbines. Firstly, in Paper-I, a novel change to the pitch controller is adopted by adding and optimizing the bending moments to reduce the bending moment in the low-speed shaft. A reduction in the bending moment will reduce the internal drive train loads within the gearbox, thus extending its lifespan. A reduction of bending moment with minimal loss in shaft rotational speed was observed through this optimization. While in, Paper-II and -III, the novel ACER1D and 2D (univariate and bivariant analysis) models were used to estimate extreme load values. Paper-II presented the ACER1D results but focused on the ACER2D as it fitted it against other models, such as the optimized Asymmetric and Gumbel logistic models. This paper showed that ACER2D was advantageous since it could produce very accurate results compared to the other models with very little data set. While in Paper-III, extreme values estimate from ACER2D were compared against the Gumbel model, and the results obtained were positive, showing that ACER1D was better at estimating extreme values with a small data set. Optimizing the extreme values is critical when designing wind turbines as proper values enable better and more reliable turbine designs. Thus, both the strategies adopted in this thesis showed that through proper optimization, a reduction of load or a better design could be achieved, resulting in better efficiency in wind turbines

Improving extreme anchor tension prediction of a 10-MW floating semi-submersible type wind turbine, using highly correlated surge motion record

Extreme value prediction of the load-effect responses of complex offshore structures such as the floating wind turbine (FWT) is crucial in ultimate limit state (ULS) design. This paper considers two cases to understand the feasibility of the bivariate correction on the extreme load and motion responses of a 10-MW semi-submersible type FWT. The empirical anchor tension force and surge motion used in this study are obtained from the FAST simulation tool (developed by the National Renewable Energy Laboratory) with the load cases stimulated at under-rated, rated and above rated speeds. Then, the bivariate correction method is applied to model FWT extreme response for a 5-years return period prediction with a 95% confidence interval (CI), based on just 2 min short response record. The proposed methodology permits accurate correction of the bivariate extreme value in case of, for example, corrupted measurement sensor data. Based on the proposed novel method’s performance, it is concluded that the bivariate correction method can offer better robust and precise bivariate predictions of coupled surge motion and anchor tension of the FWT.publishedVersio