Despite the huge potential, energy harnessing from sea waves is often still at a demonstrative stage. Oscillating water column (OWC) wave energy converters have proven to be one of the few suitable ...solutions to this end. A wave-to-wire analytical code modelling an entire wave energy converter based on the OWC technology, operating with either a Wells or an impulse turbine, was developed. The hydrodynamics, thermodynamics, and aerodynamics of the caisson were determined with a rigid piston approach. Two original low-order aerodynamic models were created for the two turbines, providing an interesting compromise between accuracy and computational cost. Finally, a control strategy was applied to monitor the instant rotor angular velocity and torque in both design and off-design conditions. The simulation tool was applied to screen the geometry of two typologies of air turbines for a specific chamber under the wave conditions of a selected Mediterranean site located in Sardinia (Italy). In particular, annual and seasonal scatter matrices were utilised to define the wave conditions of the site, providing an overview of the seasonal performance variation. The designed Wells and impulse turbines are capable of converting 47.67 and 41.14 MWh/year and operate with an overall efficiency of 5.77% and 4.98%, respectively.
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•Complete wave-to-wire model of an OWC wave energy converter.•Novel engineering simulation models for Wells and impulse turbines.•Joint solution of the interactions among chamber, turbine, and generator.•Tested on a real site with seasonal scatter matrices of wave conditions.•Critical analysis of conversion efficiency variation during the year and the seasons.
Aerodynamics of a floating horizontal-axis wind turbine (FHAWT) is subject to its platform’s six degrees of freedom (DOFs) motion, especially the surge motion, and may become much more complicated ...than that of a fixed-base wind turbine. This paper aims at investigating the aerodynamics of the FHAWT’s rotor and the characteristics of its wake under surge motion. To explore this, a CFD method with the improved delayed detached eddy simulation (IDDES) is applied to a 1:50 model FHAWT. First, it is demonstrated that the rotor’s aerodynamics including the thrust, torque and rotor power may be greatly affected by surge motion even though it is small. During surge motion, the light dynamic stall and rotor-wake interaction phenomena are observed. In addition, the near and far wake may be obviously influenced by surge motion. More importantly, the wake-recovery process under surge motion is slower than the one without surge motion. In general, the surge motion impacts the aerodynamics of the FHAWTs’ rotor and the characteristics of its wake greatly, therefore should receive due attention in the design procedure and the arrangement of wind farms.
•IDDES is employed to analyze the surge effect on aerodynamics of a FHAWT.•Surge effect on the rotor aerodynamics is investigated.•Dynamic light stall phenomenon is identified.•Surge effect on the wake characteristics is observed and explained.•Slow wake-recovery process under surge motion is found.
Due to the advantages of high convergence accuracy, fast training speed, and good generalization performance, the extreme learning machine is widely used in model identification. However, a gas ...turbine is a complex nonlinear system, and its sampling data are often time-sensitive and have measurement noise. This article proposes an online sequential regularization extreme learning machine algorithm based on the forgetting factor (FOS_RELM) to improve gas turbine identification performance. The proposed FOS_RELM not only retains the advantages of the extreme learning machine algorithm but also enhances the learning effect by rapidly discarding obsolete data during the learning process and improves the anti-interference performance by using the regularization principle. A detailed performance comparison of the FOS_RELM with the extreme learning machine algorithm and regularized extreme learning machine algorithm is carried out in the model identification of a gas turbine. The results show that the FOS_RELM has higher accuracy and better robustness than the extreme learning machine algorithm and regularized extreme learning machine algorithm. All in all, the proposed algorithm provides a candidate technique for modeling actual gas turbine units.
The paper describes the development and characterisation of three 0.9 m diameter lab-scale Horizontal Axis Tidal Turbines. The blade development process has been outlined and was used to generate a ...design specification. Each turbine houses instrumentation to measure rotor thrust, torque and blade root bending moments on each blade, in both ‘flapwise’ and ‘edgewise’ directions. A permanent magnet synchronous machine and encoder are integrated to allow for servo-control of the turbine as well as to provide position and rotational velocity measurements, resulting in three turbines that can be individually controlled using speed or torque control. Analogue signals are captured via a real-time operating system and field programmable gate array hardware architecture facilitating sample rates of up to 2 kHz. Results from testing the pilot turbine at three differing facilities during the development process are presented. Here good agreement, less than 7% variation, was found when comparing the testing undertaken at various flume and tow tank facilities. Lastly, the findings of a test campaign to characterise the performance of each of the three turbines are presented. Very good agreement in non-dimensional values for each of the three manufactured turbines was found.
•Outlines the development of three 1/20th scale horizontal axis tidal turbines.•Presents the blade development undertaken to create an optimum turbine rotor.•Details of the drivetrain, instruments and control systems design are given.•Tests at differing facilities and the same facility for similar devices presented.•The paper discusses aspects of good practice for flume/tow-tank testing.
Summary
The aim of this study is to reduce the deformation of large horizontal axis wind turbine blades using shape memory alloy (SMA)‐based centrifugal stiffening. A discrete model considering ...dominant modes of the tower, drive train and blades is developed in this study to demonstrate the performance of the proposed stiffening strategy. Here, super‐elastic behaviour of SMA is characterized by Graesser‐Cozzarelli model. Aerodynamic loads acting on the blades are evaluated using blade element momentum theory. The response is simulated using aerodynamic damping, which is estimated in each mode of vibration. Numerical results presented in this paper clearly show the significance of the proposed SMA‐based stiffening to reduce blade vibration. Sensitivity analysis is also carried out to demonstrate the performance envelop of the proposed stiffening strategy over the operational range of the benchmark 5‐MW wind turbine. The study clearly highlights the performance enhancement in terms of deformation in two orthogonal directions and design in terms of longitudinal stress that ultimately improve the serviceability of the blade.
•A new passive strategy for vibration control of wind turbine is proposed.•A design procedure has been purposely generated.•Numerical analyses have been performed with reference to a benchmark ...turbine.•It is the first use of a friction-based device for structural control of turbines.•The technique is suitable for new plants, but also for repowering of existing ones.
Wind turbines are growing in size in order to reach stronger winds and to produce more energy, even thanks to longer blades. This leads to bigger and bigger cross dimensions for the towers, with high construction costs. On the other hand, in the countries that have long been engaged in the production of wind energy, the need for repowering of existing plants is increasingly strong. In the latter case, a solution is that of replacing old towers and blades with new even longer elements for greater energy production, however taking into account the limited capacity of the existing foundation, so expensive to be replaced. Reducing the demand for stress on wind towers and, therefore, on the foundation can be definitely useful both for new installations and for upgrading existing plants. Herein a passive control technique is proposed to do that, based on the use of a rotational friction damper (RFD) installed at the base of the tower in parallel with a rotational spring. While the RFD dissipates energy thanks to the base, the spring has the task of favoring the re-centering of the tower. The design parameters for such a system have been identified and a procedure for their optimal calibration is also proposed and tested with reference to a case-study structure. The NREL 5 MW wind turbine has been subjected to three different wind loads and the results show that the proposed technique can be a suitable solution, cheap and practical to be used on wind turbines, especially for extreme winds. Actually it may lead to a reduction of base moment demand to the tower up to 40%, at the same time limiting top displacement demand and related undesired second order effects.
To meet the challenges of increased thermal loads and performance demands on aero-engine turbine blades, more advanced cooling techniques are required. This study used a modification of the ...well-known Goldstein equation to predict film effectiveness for an individual film cooling hole and applied the Sellers’ superposition method to apply these films across effusion-cooled configurations. In doing so, it tackles a relatively unchallenged problem of film holes in close spanwise proximity. An experimental set-up utilised infrared cameras to assess the film effectiveness of nine geometries of varying spanwise and streamwise spacings. Higher porosity led to increased thermal protection, and the spanwise spacing had the most profound impact, with film effectiveness approaching 0.9. Additionally, greater uniformity in the spanwise direction was observed. The modified Goldstein-Sellers method showed good agreement with experimental results although lateral mixing was underestimated. This method represents a tool that could be easily implemented in the industry for rapid assessment of novel cooling geometries.
The high‐cycle accumulation (HCA) model by Niemunis et al. allows the prediction of the mechanical response of sand under millions of load cycles . It has originally been developed with focus on sand ...under drained high‐cyclic loading assuming a constant strain amplitude, which can be periodically updated. In order to apply it for partially drained or fully undrained conditions, an adaptive definition of the strain amplitude is proposed in this work. The proposed extension allows taking into account the influence of rapid changes in soil stiffness on the strain amplitude as encountered, for example, in case of large changes in effective stress during the high‐cyclic loading. Two approaches are presented for the update of the strain amplitude: a ‘private’ update in each integration point combined with a nonlocal smoothing algorithm and an update in a separate analysis performed parallel to the simulation using the HCA model. Both approaches are compared to the methodology used in previous work employing so‐called update cycles. The importance and advantages of the proposed modifications are demonstrated by the simulation of undrained cyclic triaxial tests and monopile foundations for offshore wind turbines (OWTs) under high‐cyclic lateral loading and partially drained conditions.
The recent construction of numerous offshore wind turbines (OWTs) in seismically active areas worldwide has stimulated research on seismic evaluation and vibration control design for OWTs. Unlike the ...onshore counterparts, the hydrodynamic effects on the seismic responses of OWTs need to be studied. Besides, the equipment in the nacelle of an OWT is highly sensitive to acceleration. Significant dynamic amplification on the nacelle under horizontal earthquake excitation can cause the malfunction of power generation and even seriously threaten the safety of OWTs. As a promising solution, tuned mass dampers (TMDs) based on the first mode of OWTs need to be tested by various earthquake excitations. In this paper, the seismic amplification effect, the hydrodynamic effects, and the vibration control by a single TMD are investigated through a series of underwater shaking table tests based on a 1:20 scaled model of a 5 MW OWT. The “no water”, “with water”, and “with water and TMD” tests are evaluated and compared. The accelerations of OWTs can be amplified or reduced by the hydrodynamic effects, depending on the natural frequencies and vibration modes of the OWT and the frequency spectrum of the seismic excitation. The earthquake‐induced hydrodynamic damping ratio and hydrodynamic added mass are carefully measured. For the TMD's effect, the single TMD performs reasonably well in seismic vibration control in most cases. Finally, the interaction between hydrodynamic effects and TMD's effect is discussed, and the hydrodynamic damping effect is suggested to be ignored when designing TMDs for OWTs.
Bearing failure often occurs in doubly fed induction generator (DFIG)-based wind turbines which are usually subject to electrical corrosion effects. Fault diagnosis method based on electrical signals ...has been paid much attention as the method is noninvasive and cost-effective. This paper describes the use of the modulation signal bispectrum (MSB) detector for diagnosing bearing faults in DFIGs of wind turbines. The major theoretical principles involved with the MSB method are presented and it is shown how the amplitude and phase relationships of the stator current signals caused by torque oscillations can be effectively revealed. Since the MSB result is obtained by averaging results from each record, overlapped segmentation is proposed to improve computational accuracy with limited data. On-site experimental results obtained from 1.5-MW wind turbines corroborate that these faults can be detected, in the current MSB, by the identification of a spectral component at the fundamental frequency and the characteristic frequency. Compared with the other data processing methods based on second-order cumulants, the MSB detector can avoid misdiagnosis by containing phase information of stator current. Owing to relatively high accuracy, the proposed current-based MSB method can identify incipient bearing corrosion failure in DFIG-based wind turbines without additional sensors, which also has great potential in other industrial applications.
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