1,720,952 research outputs found
Layout Optimization of Offshore Wind Farms affected by Wake effects, Cable topology and Support Structure variation
No full textAs part of the effort to reduce the cost of offshore wind energy, this MSc Thesis deals with the layout optimization of an Offshore Wind Farm affected by wake effects, cable topology and support structure variation. The main objective of the current MSc Thesis is to investigate how important each of these aspects for the layout optimization is. The final outcome of the project is an optimization tool that tries to find the optimal Offshore Wind Farm (OWF) layout in terms of the lowest Levelized Production Cost (LPC). This optimization tool depends on the analyzer algorithm, which calculates the objective function of the optimizer. The analyzer consists of three different elements that are combined together so that the Levelized Production Cost will be calculated. Thus, the objective function will be the LPC. The analyzer elements are the wake effects, cable topology and support structure variation. For the support structure variation, part of the MZ Tool developed by professor Dr. Michiel Zaaijer is used. Using this tool, the support structure dimensions and costs can be determined. Regarding the cable topology, a hybrid approach between Planar Open Savings(POS)and Esau-Williams(EW)heuristics is used so that the performance of EW can be improved for multiple cables and lower infield cable cost will be achieved. Finally, the Jensen wake model is used in an algorithm so that the wake effects can be determined. The output of that algorithm is the annual energy yield and the LPC. The optimization tool is based on the Genetic Algorithm(GA)logic. The performance of the optimization tool is evaluated both cost and time-wise by implementing four scenarios. In these scenarios some parameters of the GA are changed so that the behavior of the optimization tool can be examined. Finally, different case studies, related to the seabed shape and to the three ingredients in the analyzer, are examined. These case studies will show how the changes in the analyzer can affect the optimality of an OWF. More specifically, it is found that all three elements in the analyzer affect the layout optimization. In addition, it is concluded that the support structure variation has the largest contribution to the layout optimization compared to the cable topology. Regarding the computation time, it is higher in the case that there is support structure variation, since it takes more time for the analyzer to calculate all the costs.Aerospace EngineeringAerodynamics, Wind Energy & Propulsion / Wind EnergySustainable Energy Technolog
Efficient support structure design for variation of environmental parameters within an offshore windfarm
No full textSustainable Energy TechnologyWind Energ
Simplified Fatigue Assessment of Offshore Wind Turbine Full Height Lattice Structures in the Frequency Domain
No full textNew concepts for support structures of offshore wind turbines have gained interest in the industry and are examined for intermediate and deep water depths in order to unlock new offshore potential markets. One of the main proposals that has already been commercialized is the three or four leg full height lattice structure. The fatigue assessment of such structures is of primary significance, since it is one of the main design drivers. A Frequency Domain (FD) framework is developed in this study with the ability of analysing several topologies of lattice structures for dynamic and fatigue assessment. The concept of the model relies on the natural frequencies and modeshapes estimation with the employment of the Finite Element Analysis (FEA) and the fatigue damage prediction due to wind and wave loading with the utilization of a Transfer Function (TRF) that relates the input spectrum to output stress spectrum for a member of the structure. Furthermore, the method of mode superposition is adopted for the calculation of the response of the structure. The benchmarking of the model for the dynamic analysis with ANSYS for a reference structure and turbine yields sufficient results with errors around 5% for the two first natural frequencies and even smaller for the higher modes. A case study of the structure developed by the Dutch company 2-B Energy is performed and the fatigue damage values as well as the stress spectra as computed by the DM are compared with the equivalent results calculated by the Time Domain (TD) software package GH Bladed for three different members. The DM produces satisfactory results for all the members for cases with low or medium environmental loading and less accurate results, which are pointing in the right direction, for the cases with high environmental loading. With the utilization of the DM for a preliminary analysis of a structure a significant amount of time (several hours) can be saved.Aerospace EngineeringAerodynamics, Wind Energy & Propulsion / Wind EnergySustainable Energy Technolog
Simplified fatigue assessment of offshore wind support structures accounting for variations in a farm (poster)
No full textProvided the significant contribution of support structures to the capital expenditures of offshore wind, optimisation schemes are often developed to address the need for tailored design of different structures in one farm. A crucial aspect of them is, among others, the Fatigue Limit State (FLS)1234 .To this direction, research is conducted on the response of the structure to cyclic loading in the frequency-domain567 . However, the complexity and the need for advanced software (finite element and/or aero-elastic codes) often limit the flexibility. As a consequence, the design process is not facilitated significantly. The focus of this study is principally placed on the impact that variations in an offshore wind farm (OWF) have on the support structures, particularly on their resistance to cumulative damage caused by wind and wave loading. The vital requirement is therefore that the procedure is computationally affordable to ensure applicability for the early design phase of multiple structures. The goal of this study is to develop such a procedure.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin
Review of design concepts, methods and considerations of offshore wind turbines
No full textAerospace Engineerin
Estimation of the optimal wind turbine size for offshore wind farms: Focusing on drive train configurations in a multi-disciplinary optimization
No full textThe development of a wind farm is a highly sophisticated task, whereby many stakeholders are involved and several unique disciplines come together to form a whole. Commonly, the unique disciplines are optimized individually which leads to sub-optimal windfarm designs. Therefore, it is of great importance that an interdisciplinary approach is used to overcome sub-optimal designs and that they work together to accomplishing a common objective. To capture the interdisciplinary dynamics of the different disciplines, a Systems Engineering (SE) approach is used. This approach makes it possible to design the wind farm in an agile manner, whereby the in- and outputs, from the different disciplines, are coupled to accomplish a combined objective. The foundation of systems engineering in this report is the Multidisciplinary Design Analysis and Optimization (MDAO). The MDAO framework includes models for various disciplines in a wind farm, such as the wake aerodynamics, rotor nacelle assembly, support structure, cabling, etc. The MDAO framework facilitates system-level analysis by capturing interdisciplinary interactions - both implicit and explicit - to analyze the system for a particular objective. The research objective of this thesis is to determine the effect of up-scaling on the optimum design of an offshore wind farm for different drive train configurations. This is done by constructing engineering models and implementing these in the MDAO framework. The analysis will specifically focus on the three configurations: Doubly Fed Induction Generator with a 3-stage gearbox (DFIG - 3S), Permanent Magnet Synchronous Generator with direct drive (PMSG - DD), and Permanent Magnet Synchronous Generator with 1-stage gearbox (PMSG - 1S). The implementation of the updated models, will contribute to the dissemination of knowledge on the utility of the MDAO framework, whereby the process of selecting the optimal drive train configuration will become easier. Alongside, the updated models implemented in the framework will result in better cost predictions and therefore a wind turbine size closer to the optimum will emerge. At first, the missing links of the current drive train models are tackled by the implementation of the higher fidelity engineering models. This is done for the generator and gearbox of the three drive trains configurations. The updated engineering models assure better estimations of the Levelized Cost of Energy (LCOE) and therefore a better estimation of the optimum wind turbine size in offshore wind farms. Once the models were updated, the framework was run for two case studies: a far offshore wind farm and a nearshore wind farm. This leads to an optimum wind turbine size in the range of 4 to 6 MW. The optimal wind turbine sizes for the different configurations are very close to each other. The DFIG - 3S configuration is the most economical option, followed by the PMSG - 1S configuration, thereafter the PMSG - DD configuration. The sequences applied for both the wind farms that were analyzed and for all scales when upscaling the wind turbine. The PMSG - 1S is a promising configuration, whereby further cost reductions in the permanent magnets is expected and further optimization and integration of the power electronics is possible. The optimum power densities for both wind farms were similar, whereby the spreading in power density was large. The optimal wind turbine size when upscaling was found for power densities from 200 to 400 W/m2. In the far offshore wind farm, the optimal configuration was a 6MW DFIG - 3S wind turbine with a power density of 290 W/m2. The optimum power density in the nearshore wind farm was 209 W/m2 for a 4MW PMSG - DD wind turbine.Electrical Engineering | Sustainable Energy Technolog
Frequency Domain Fatigue Analysis of Offshore Wind Monopile Support Structure: For the Purpose of Offshore Wind Farm Optimization
No full textThe preliminary design of wind turbine support structures within an offshore wind farm plays a significant role in decreasing the costs involved and is pivotal in establishing the wind sector as a leading contributor towards a sustainable future. During the early design stages, the optimization of structural dimensions, which involves a large number of iterations, is an essential step in determining the optimal offshore wind farm layout. Aiming to assist in the time and cost efficiency of such procedures, this thesis project develops a fatigue analysis model of offshore wind turbine monopile structures in the frequency domain. The structure is modeled using the finite element method and consists of Euler-Bernoulli beam elements. The soil-structure interaction is approximated by the effective fixity length and the rotor-nacelle assembly is incorporated as a point mass, contributing its inertial properties to the tower’s top node. Transfer functions are developed to relate the input environmental force spectra to the total stress response of the structure. Time series of wind thrust on rotor are converted to aerodynamic power spectral densities (PSDs). The hydrodynamic spectra are calculated based on nodal wave forces obtained by the Morison equation, with the wave environment being defined by mathematical models for wave particle kinematics and wave elevation spectra. The mode superposition method is used to enable the addition of aerodynamic and hydrodynamic modal responses. In order to retrieve the stress range variations from the total stress response spectra, the Dirlik method is applied. Finally, the fatigue damage accumulation is calculated by the Palmgren-Miner’s rule. The proposed model (PM) is capable of calculating the fatigue at any location along the structure and for any environmental state. It produces very accurate results for the 1st fore-aft (F-A) mode shape deflection. It also demonstrates accuracy in calculating the natural frequencies of the 1st and 2nd F-A, as well as of the 1st side-to-side. The considerable deviation of the 2nd side-to-side natural frequency is attributed to the simplified RNA modelling. The inclusion of a 6% aerodynamic damping to couple the wind and wave responses has a significant effect on the dynamic response, decreasing its peak by almost an order of magnitude. The dynamic response and the environmental load spectra are also shown to be mesh independent, demonstrating the model’s reliability. The mesh sensitivity analysis shows that the maximum stresses and, as a consequence, the stress response spectra produce erroneous results for low mesh sizes, which is anticipated. The fatigue damage quickly converges to an asymptotic value for increasing mesh sizes. The fast convergence rates allow the model to produce adequate results for low mesh sizes, achieving very low simulation times. Special attention is given to the effect that the hydrodynamic cross-power spectral densities (CSDs) have on the fatigue. The wave CSDs increase the fatigue due to wind and wave PSDs by about 9%, suggesting that their incorporation could prove significant.Electrical Engineering | Sustainable Energy Technolog
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