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- 2019
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Journal article (peer-reviewed)
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| 2. |
- Asadi, Saeed, 1987
(author)
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Drive train system dynamic analysis; Application to wind turbines
- 2016
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Licentiate thesis (other academic/artistic)abstract
- To facilitate the design and production of highly efficient and reliable wind turbine drive trains, the project deals with the mathematical modelling and experimental study of drive train system dynamics.A typical drive train is considered as the subsystem of a wind turbine that transfers mechanical power from the rotor hub to the generator, and thereby plays an important role in the system dynamics and efficiency of wind turbine operation. The dynamics of wind turbines is complex and a critical area of study for the wind industry. The multidisciplinary nature of wind turbine design adds to the complexity of this task, as the subsystems of a wind turbine need to be tuned with respect to a common objective to achieve a cost effective and optimum structural performance.The current work contributes to enhanced knowledge in this field with focus on interaction between functional components and system dynamic response, faults modelling and detectability of defects in bearings in wind turbine drive trains.The overall performance of a drive train can be evaluated from different perspectives. In this thesis, the dynamics behaviour of the high speed shaft drive train is evaluated by proposed objective functions referring to displacements, loads, and frequency responses. To have a better insight into wind turbine dynamics, the global sensitivity analysis (GSA) of high speed shaft drive train dynamics with respect to input structural parameters is considered. The multiplicative dimension reduction method is employed to provide the mapping between the objective functions' sensitivity indices and design variables. The results of such analysis can narrow down the number of input variables for design problem and improve the computational efficiency. The proposed GSA methodology is applied for the system modelled analysis of high speed shaft subsystem of a drive train. Moreover, by introducing defects in functional components and investigating sensitivity indices, detectability of faults by GSA is proved. The results show that the proposed methodology is capable of detecting damage in the functional components such as bearings in early stage before a complete failure. The application of this methodology within the detection, prediction, and prevention framework has a potential to reduce the maintenance cost for critical components. The results can also provide a better understanding and useful hints in wind turbine drive train system dynamics with respect to different structural parameters, ultimately designing more efficient drive trains.
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| 3. |
- Asadi, Saeed, 1987, et al.
(author)
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Global Sensitivity Analysis of High Speed Shaft Subsystem of a Wind Turbine Drive Train
- 2018
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In: International Journal of Rotating Machinery. - : Hindawi Limited. - 1542-3034 .- 1023-621X. ; 2018
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Journal article (peer-reviewed)abstract
- The wind turbine dynamics are complex and critical area of study for the wind industry. Quantification of the effective factors to wind turbine performance is valuable for making improvements to both power performance and turbine health. In this paper, the global sensitivity analysis of validated mathematical model for high speed shaft drive train test rig has been developed in order to evaluate the contribution of systems input parameters to the specified objective functions.Thedrive train in this study consists of a 3- phase induction motor, flexible shafts, shafts’ coupling, bearing housing, and disk with an eccentric mass.The governing equations were derived by using the Lagrangian formalism and were solved numerically by Newmark method. The variance based global sensitivity indices are introduced to evaluate the contribution of input structural parameters correlated to the objective functions. The conclusion from the current research provides informative beneficial data in terms of design and optimization of a drive train setup and also can provide better understanding of wind turbine drive train system dynamics with respect to different structural parameters, ultimately designing more efficient drive trains. Finally, the proposed global sensitivity analysis (GSA) methodology demonstrates the detectability of faults in different components.
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| 4. |
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| 5. |
- Asadi, Saeed, 1987, et al.
(author)
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Multibody dynamic modelling of a direct wind turbine drive train
- 2020
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In: Wind Engineering. - 0309-524X .- 2048-402X. ; 44:5, s. 519-547
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Journal article (peer-reviewed)abstract
- Wind turbines normally have a long operational lifetime and experience a wide range of operating conditions. A representative set of these conditions is considered as part of a design process, as codified in standards. However, operational experience shows that failures occur more frequently than expected, the costlier of these including failures in the main bearings and gearbox. As modern turbines are equipped with sophisticated online systems, an important task is to evaluate the drive train dynamics from online measurement data. In particular, internal forces leading to fatigue can only be determined indirectly from other locations’ sensors. In this contribution, a direct wind turbine drive train is modelled using the floating frame of reference formulation for a flexible multibody dynamics system. The purpose is to evaluate drive train response based on blade root forces and bedplate motions. The dynamic response is evaluated in terms of main shaft deformation and main bearing forces under different wind conditions. The model was found to correspond well to a commercial wind turbine system simulation software (ViDyn)
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| 6. |
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| 7. |
- Asadi, Saeed, 1987, et al.
(author)
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STRUCTURAL DYNAMICS OF A WIND TURBINE DRIVE TRAIN HIGH SPEED SUBSYSTEM: MATHEMATICAL MODELLING AND VALIDATION
- 2015
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In: In Proc. of the International Conference on Engineering Vibration, Ljubljana, 7 - 10 September ; [editors Miha Boltežar, Janko Slavič, Marian Wiercigroch]. - EBook. - Ljubljana: Faculty for Mechanical Engineering, 2015. - 9789616536974 ; , s. 553-562
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Conference paper (peer-reviewed)abstract
- The paper studies the dynamics of a wind turbine drive train high speed subsystem, both by modelling and experiments with focus on system torsional vibration and transient events which can reduce fatigue life of functional components (gearbox, bearings, shafts, couplings,others). A scaled down drive train high speed shaft test rig has been developed. Main components of the test rig are six-pole motor with variable frequency drive controller (up to 1000rpm), shafts’ disk coupling and flexible mounting structure representing gearbox housing with output high speed bearing. The test rig is equipped with measurement system comprising a set of accelerometers and displacement sensors, strain gauges and telemeter system, data acquisition hardware and software (SKFWindCon3.0). Mathematical and computational models of the test rig have been developed and went through validation tests. The system dynamic response is studied for different operational scenarios and structural parameters (run-shut down case with and without eccentric mass). The ultimate goal of the test rig is to get insight into interactionbetween internal dynamics of drive train mechanical and electrical functional components and to develop novel methods to detect, predict and prevent faults and failures in wind turbine drive trains arising due to misalignments and transient external loads.
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| 8. |
- Asadi, Saeed, 1987, et al.
(author)
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Vibration dynamics of a wind turbine drive train high speed subsystem: Modelling and validation
- 2015
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In: ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, IDETC/CIE 2015, Boston, United States, 2-5 August 2015. - 9780791857182 ; 8
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Conference paper (peer-reviewed)abstract
- Modern wind turbines are enormous large-scale electromechanical systems. They operate in complex conditions, determined by a turbulent wind field, by possible disturbances in the electricity grid and by the behavior of sea waves for offshore turbines. Guaranteeing the structural integrity of these machines during a lifetime of 20 years is an enormous challenge. In this paper the dynamics of a wind turbine drive train high speed subsystem is studied both by modeling and experiments with focus on system torsional and flexural vibrations and transient events which can reduce fatigue life of functional components (gearbox, bearings, shafts, couplings, others). A scaled down drive train high speed shaft test rig has been developed. Main components of the test rig are six-pole motor with variable frequency drive controller (up to 1000 rpm), shafts' disk coupling and flexible mounting structure representing gearbox housing with output high speed bearing. The test rig is equipped with measurement system comprising a set of accelerometers and displacement sensors, data acquisition hardware and software (SKF WindCon3.0). Mathematical and computational models of the test rig have been developed and went through validation tests. The system kinematic and dynamic responses are studied for different operational scenarios and structural parameters (ratio of shaft bending stiffness and stiffness of mounting structures, unevenly inertia load distribution, others). The ultimate goal of the test rig is to get insight into interaction between internal dynamics of drive train functional components to be used the results obtained in developing novel methods to detect, predict and prevent faults and failures in wind turbine drive trains arising due to misalignments and transient external loads.
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| 9. |
- Asadi, Saeed, 1987
(author)
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Wind Turbine Drive Train System Dynamics ; Multibody Dynamic Modelling and Global Sensitivity Analysis
- 2018
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Doctoral thesis (other academic/artistic)abstract
- To facilitate the design and production of highly efficient and reliable wind turbine drive trains, this thesis deals with the mathematical modelling and analysis of drive train system dynamics. The drive train is considered as the subsystem of the wind turbine that transfers mechanical power from the rotor hub to the generator, and thereby plays an important role in the system dynamics and the efficiency of wind turbine operation. The dynamics of wind turbines is complex and a critical area of study for the wind industry. The multidisciplinary nature of wind turbine design adds to the complexity of this task, as the subsystems of a wind turbine need to be tuned with respect to a common objective to achieve a cost effective, reliable and optimum structural and dynamic performance. The overall performance of a drive train can be evaluated from different perspectives. In this thesis, mathematical model of drive train wind turbine for both direct and indirect drive train has been developed based on multibody dynamic modelling formalism. Afterwards, the dynamics behaviour of the drive train is evaluated by proposed objective functions referring to displacements, loads, fatigue damage indicators, and frequency responses. These objective functions are investigated for several wind operational scenarios such as normal operation, turbulent, vertical inclination cases. The work also contributes to enhanced knowledge in the field with focus on the inter-action between functional components and system dynamic response, faults modelling and detectability of defects in functional components such as bearings, and couplings in wind turbine drive trains. To have a better insight into wind turbine dynamics, the global sensitivity analysis (GSA) of the objective functions with respect to input structural parameters is considered. By introducing defects in functional components and investi-gating sensitivity indices, detectability of faults is proved. GSA also demonstrates the most influential input parameters to the output objective functions. The results of such analysis not only can narrow down the number of input variables for design problems, but also give understanding on which structural parameters are most important to have pre-cise data for, ultimately designing more efficient drive trains in terms of cost and durability.
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| 10. |
- Esmaeili, Ali, 1983, et al.
(author)
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Construction of macroscale yield surfaces for ductile composites based on a virtual testing strategy
- 2019
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In: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 77
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Journal article (peer-reviewed)abstract
- The paper describes an approach, based on computational homogenization, for constructing the macroscopic yield surface pertinent to a meso-heterogeneous ductile composite, whereby it is assumed that each constituent is elastic-plastic with (possible) hardening; however, the strategy does not depend on the particular choice of plasticity model (standard, crystal) on the mesoscale. The aim is to compute the macroscale yield properties with bounds that are defined with a priori given confidence, in terms of an “outer yield surface” and an “inner yield surface”. However, these bounds will inevitably be approximate in practice due to the difficulty to achieve guaranteed bounds for general incremental plasticity. The following ingredients are essential to the approach: (1) A “virtual testing” strategy is proposed, whereby a sufficiently large number of realizations of the presumed random meso-structure, determined by the chosen probability, are utilized as Statistical Volume Elements (SVE). (2) In order to obtain the pertinent bounds on the “directional yield stress”, SVE-computations are carried out with Dirichlet and Neumann boundary conditions. (3) A stress-driven, rather than the more traditional strain-driven, format of the SVE-problem is adopted in order to cover the macroscopic stress space in a systematic fashion. Illustrative numerical examples in 2D (particle composites) and 3D (polycrystals of Duplex Stainless Steel) conclude the paper.
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