| 1. |
- Abedi, Hamidreza, 1979, et al.
(författare)
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Numerical modelling of neutral atmospheric boundary layer flow through heterogeneous forest canopies in complex terrain (a case study of a Swedish wind farm)
- 2021
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 180, s. 806-828
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Tidskriftsartikel (refereegranskat)abstract
- This paper exposes the risk of generalization of wind conditions from a single met-mast measurement to be representative of the actual flow field in a wind farm situated in complex terrain. As a case study, Large-Eddy Simulation (LES) of the neutral Atmospheric Boundary Layer (ABL) flow for a mid-western Sweden wind farm is performed. The site-specific complex topography and the forest properties like the Plant Area Density and the tree heights are extracted from the Airborne Laser Scanning (ALS) 3D data, thus the forest is heterogeneous. To emphasize the impact of the local topography and surface roughness on the wind field, the wind turbines are not included in the numerical simulations. The predicted wind speeds using LES are compared to wind speed from the nacelle-mounted anemometers taken from the wind farm's turbine SCADA data, focusing on the wake-free turbines. A sufficient degree of match is observed, supporting the accuracy of the numerical simulations. The results show that inflow variables i.e., mean wind speed, shear exponent and turbulence intensity vary at each wind turbine location justifying the need for turbine-specific assessment of the wind resource in a wind farm located in forested complex terrain. The inter-turbine (between turbines in the wind farm) differences in wind resource is quantified in terms of the difference in turbine-specific structural and mechanical loads by running wind turbine mechanical simulations using the extracting the wind fields predicted by the LES. The results show that not only inter-turbine loads varying significantly in the wind farm, but the turbine loads also differ significantly if a homogeneous assumption is made for the forest. Most importantly, it was found that the homogeneous forest assumption predicted a higher turbulence intensity compared to a heterogeneous forest resulting.
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| 2. |
- Fitzgerald, Breiffni, et al.
(författare)
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Enhancing the reliability of floating offshore wind turbine towers subjected to misaligned wind-wave loading using tuned mass damper inerters (TMDIs)
- 2023
-
Ingår i: Renewable Energy. - 0960-1481 .- 1879-0682. ; 211, s. 522-538
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Tidskriftsartikel (refereegranskat)abstract
- Floating offshore wind turbines (FOWTs) are the largest rotating structures on the earth. Dynamically sensitive structures such as these must be protected in these environments to ensure that they can continue to operate reliably and safely. In this paper structural dynamic models and probabilistic assessment tools are combined to demonstrate improvements in structural reliability when FOWT towers are equipped with a new type of damper — the tuned mass damper inerter (TMDI). A multi-body dynamic approach is used to model the wind turbine and the TMDI installed in the tower. The model is subjected to stochastically generated wind and wave loads of varying magnitudes to develop wind-induced probabilistic demand models for towers of FOWTs under model and load uncertainties. A focus is placed on the impact of the wind-wave misalignment on the lightly damped side-to-side mode. Numerical simulations are carried out to construct fragility curves which illustrate reductions in the vulnerability of FOWTs to wind and wave loading owing to the inclusion of the new damper. Results show that the TMDI delivers significant increases in structural reliability of FOWT towers.
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| 3. |
- Mitra, Arka, et al.
(författare)
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Multibody dynamic analysis of onshore horizontal-axis wind turbine
- 2023
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Ingår i: Non-Destructive Testing and Condition Monitoring Techniques in Wind Energy. - 9780323996662 ; , s. 351-397
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Horizontal-axis wind turbines have gained prominence in the recent past as an efficient power generation device, especially in locations having significant wind resources. This chapter focuses on modeling and dynamic response analysis of such turbines. Kane's approach (Kane & Levinson, 1985) is adopted to model the complete system in a multibody dynamic framework. The 3D wind field is generated for turbulent flow, and the blade element momentum theory is used to model the aerodynamic forces. The complex system dynamics is generated using an aero-hydro-servo-elastic analysis. The mathematical model also includes different control systems found in commercial turbines (e.g., torque controllers, pitch controllers, and mass dampers). A detailed numerical analysis is performed for different operating conditions using the specifications of a benchmark turbine. Overall, this chapter presents the complete mathematical modeling of a wind turbine along with different control strategies for efficient power generation.
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| 4. |
- Mitra, Arka, et al.
(författare)
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Sway vibration control of floating horizontal axis wind turbine by modified spar-torus combination
- 2021
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 219
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Tidskriftsartikel (refereegranskat)abstract
- Spar type floating wind turbines exposed to marine environment experience significant vibration, which is more prominent under wind-wave misalignment. This unavoidable vibration, particularly in the sway direction, affects overall performance and can induce significant damage to sensitive electro-mechanical components leading to downtime for maintenance. With this in view, the present study aims to propose a modified spar-torus combination by introducing spring and dashpot in between, so that it can work as an isolator. First, a comprehensive mathematical model for this multi-body system is developed using Kane's approach with proper aero-elastic and hydrodynamic simulation. For this purpose, 3D wind fields are generated in TurbSim and the waves are simulated from Pierson-Moskovitch spectrum considering wind-wave correlation and misalignment. Aerodynamic loads are computed using modified Blade Element Momentum theory while and hydrodynamic loads are generated using Morison's equation. Using these inputs, the response of the modified spar-torus combination is solved, which demonstrates the efficiency and advantage of the proposed vibration isolation. Different sea states and wind conditions are simulated replicating the actual scenario to investigate the performance envelope of the proposed controller for spar-type floating wind turbines.
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| 5. |
- Sarkar, Saptarshi, 1992, et al.
(författare)
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Design of Tuned Mass Damper Fluid Inerter for Wind-Induced Vibration Control of a Tall Building
- 2024
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Ingår i: Journal of Structural Engineering. - 0733-9445. ; 150:3
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the problem of wind-induced vibration in tall buildings is addressed by utilizing a new type of damper, the tuned mass damper fluid inerter (TMDFI). The TMDFI incorporates an inerter in the classical tuned mass damper (TMD), which is physically realized using fluid in a helical channel. The device arrangement is optimized using a proposed nonlinear procedure and it is demonstrated through numerical simulations that the application of the TMDFI achieves excellent vibration control performance. Specifically, it has been found that the TMDFI requires lower mass and stroke requirements than traditional passive dampers while achieving comparable or better vibration reductions. It has been shown numerically that the damper demonstrates excellent vibration control capabilities by reducing the RMS displacement of the building by ≈50% and the RMS acceleration by 35%-80%. The results presented here show that the TMDFI is a damper capable of mitigating wind-induced vibrations in tall buildings with relatively simple design requirements. This new damper has the potential to significantly improve the safety, comfort, and durability of tall buildings subjected to wind loads.
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| 6. |
- Sarkar, Saptarshi, 1992, et al.
(författare)
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Fluid inerter for optimal vibration control of floating offshore wind turbine towers
- 2022
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Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 266
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes the use of a tuned mass damper fluid-inerter (TMDFI) for vibration control of spar-type floating offshore wind turbine towers. The use of an inerter in parallel with the spring and damper of a tuned mass damper (TMD) is a relatively new concept. The ideal inerter has a mass amplification effect on the classical TMD leading to greater vibration control capabilities. Previous work by the authors has shown that inerter based TMDs have great potential in vibration control of floating offshore wind turbines where enhanced vibration mitigation can be achieved using a relatively lighter device than classical TMDs. However, this previous work was based on the assumption of an ideal inerter that assumes the use of a mechanical flywheel type inerter. Mechanical inerters have some inherent disadvantages due to their complexity in design and high cost of maintenance. The use of a fluid inerter can alleviate these disadvantages as its design is rather simple and it comes with very low maintenance. Such devices have been proposed and investigated in the literature, however, their applicability in vibration control of floating wind turbines has not been investigated by researchers. The optimal design of a TMDFI is presented in this paper. It has been shown that optimization of a TMDFI is a six-dimensional non-linear optimization problem whose solution hyperplane contains multiple local minima. A systematic way has been developed in this paper, avoiding the use of metaheuristic search techniques, to optimize the damper while providing greater insight into the damper properties that offers a set of guidance to the designer. Numerical results demonstrate impressive vibration control capabilities of this new device under various stochastic wind-wave loads. It has been shown that the fluid-inerter performs as well as the ideal mechanical inerter. The considerable advantages of a TMDFI over the classical TMD demonstrated in this paper makes it an exciting candidate for vibration control.
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| 7. |
- Sarkar, Saptarshi, 1992, et al.
(författare)
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Mitigation of transient torque reversals in indirect drive wind turbine drivetrains
- 2023
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Ingår i: Wind Energy. - 1099-1824 .- 1095-4244. ; 26, s. 803-825
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Tidskriftsartikel (refereegranskat)abstract
- Bearing failure in wind turbine gearboxes is one of the significant sources of downtime. While it is well-known that bearing failures cause the largest downtime, the failure cause(s) is often elusive. The bearings are designed to satisfy their rolling contact fatigue (RCF) life. However, they often undergo sudden and rapid failure within a few years of operation. It is well-known that these premature failures are attributed to surface damages such as white surface flaking (WSF), white etching cracks (WECs) and axial cracks. In that regard, transient torque reversals (TTRs) in the drivetrain have emerged as one of the primary triggers of surface damage, as explained in this paper. The risk associated with TTRs motivates the need to mitigate TTRs arising in the drivetrain due to various transient events. This paper investigates three TTR mitigation methods. First, two existing devices, namely, the torsional tuned mass damper and the asymmetric torque limiter, are studied to demonstrate their TTR mitigation capabilities. Then, a novel idea of open-loop high-speed shaft mechanical brake control is proposed. The results presented here show that while the torsional tuned mass damper and the asymmetric torque limiter can improve the torsional vibration characteristics of the drivetrain, they cannot mitigate TTRs in terms of eliminating the bearing slip risk associated with TTRs. However, the novel approach proposed here can mitigate TTRs both in terms of improving the torque characteristic in the high-speed shaft and reducing the risk of bearing slip by actuating the high-speed shaft brake at the onset of the transient event. Furthermore, the control method is capable of mitigating TTRs with the mechanical limitations of a pneumatic actuator in terms of bandwidth and initial dead time applied to it. This novel approach allows the wind turbines to protect the gearbox bearings from TTRs using the existing hardware on the turbine.
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| 8. |
- Sarkar, Saptarshi, 1992, et al.
(författare)
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Site-specific analysis of on wind turbines in complex terrain: A case study
- 2021
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Ingår i: WESC2021, Wind Energy Science Conference , The Conference Book (Intro) with the Book of Abstracts (Theme 01 - 10). ; Theme 02, s. 2-111-2-112
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study aims to analyse and understand how the structural and drivetrain loads on the turbines can vary within a wind farm situated in a complex terrain. To this end, the flow field is studied using computational fluid and aero-elastic simulations and a modified version of the FAST software is used to determine the turbine response Verification of the numerical results is performed by using data from turbine SCADA system for a case study of Röbergsfjället wind farm with 8 turbines located in the mid-western part of Sweden.
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| 9. |
- Sarkar, Saptarshi, 1992, et al.
(författare)
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Transient torque reversals in indirect drive wind turblnes
- 2023
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Ingår i: Wind Energy. - 1099-1824 .- 1095-4244. ; 26, s. 691-716
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Tidskriftsartikel (refereegranskat)abstract
- The adverse effect of transient torque reversals (TTRs) оп wind turЬine gearboxes сап Ье severe due to their magnitude and rapid occurrence compared with other equipment. The primary damage is caused to the bearings as the bearing loaded zone rapidly changes its direction. Other components are also affected Ьу TTRs (such as gear tooth); however, its impact оп bearings is the largest. While the occurrence and severity of TTRs are acknowledged in the industry, there is а lack of academic literature оп their initiation, propagation and the associated risk of damage. Furthermore, in the wide range of operation modes of а wind turЬine, it is not known which modes сап lead to TTRs. Further, the interdependence of TTRs оп environmental loading like the wind is also not reported. This paper aims to address these unknowns Ьу expanding оп the understanding of TTRs using а high-fidelity numerical model of an indirect drive wind turЬine with а douЬly fed induction generator (DFIG). То this end, а multibody model of the drivetrain is developed in SIMPACK. The model of the drivetrain is explicitly coupled to state-of-the-art wind turЬine simulator OpenFAST and а grid-connected DFIG developed in MATLAB®'s Simulink® allowing а coupled analysis of the electromechanical system. А metric termed slip risk duration is proposed in this paper to quantify the risk associated with the TTRs. The paper first investigates а wide range of IEC design load cases to uncover which load cases сап lead to TTRs. lt was found that emergency stops and symmetric grid voltage drops сап lead to TTRs. Next, the dependence of the TTRs оп inflow wind parameters is investigated using а sensitivity analysis. lt was found that the instantaneous wind speed at the onset of the grid fault or emergency shutdown was the most influential factor in the slip risk duration. The investigation enaЫes the designer to predict the occurrence of TTRs and quantify the associated risk of damage. The paper concludes with recommendations for utility-scale wind turЬines and directions for future research.
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| 10. |
- Sarkar, Saptarshi, 1992, et al.
(författare)
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Use of kane’s method for multi-body dynamic modelling and control of spar-type floating offshore wind turbines
- 2021
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:20
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Tidskriftsartikel (refereegranskat)abstract
- This paper demonstrates the use of Kane’s method to derive equations of motion for a spar-type floating offshore wind turbine taking into account the flexibility of the members. The recently emerged Kane’s method reduces the effort required to derive equations of motion for complex multi-body systems, making them simpler to model and more readily solved by computers. Further, the installation procedure of external vibration control devices on the wind turbine using Kane’s method is described, and the ease of using this method has been demonstrated. A tuned mass damper inerter (TMDI) is installed in the tower for illustration. The excellent vibration mitigation properties of the TMDI are also presented in this paper.
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