Dynamics of Horizontal Axis Wind Turbines and Systems with Parametric Stiffness PDF Download

Author: Gizem Dilber Acar
Publisher:
ISBN: 9781369530056
Category : Electronic dissertations
Languages : en
Pages : 122

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Author: Fatemeh Afzali
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 0

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Book Description
Wind turbines are one of the fastest-growing energy sources. Based on their axis of rotation they fall into two basic categories: horizontal-axis wind turbines (HAWTs) and vertical-axis wind turbines (VAWTs). Darrieus VAWTs exploit aerodynamic lift. This study entails the vibration analysis of large vertical-axis Darrieus wind turbine blades. Very large wind turbines are becoming more abundant due to their ability to harvest greater wind power. VAWTs are less common than HAWTs for large wind applications, but have some favorable characteristics, for example in offshore applications, and so further development of large VAWTs is anticipated. However, VAWTs are known to have vibration issues. VAWT blade vibration is the focus of this work.The straight-bladed H-rotor/Giromill is the simplest type of VAWT. We first derive the equations of motion of a H-rotor blade modeled as a uniform straight elastic Euler-Bernoulli beam under transverse bending and twist deformation. The reduced-order model suggests the existence of periodic damping, periodic stiffness, and direct excitation generated by a cyclic aeroelastic load. The model also indicates spin softening, which could be detrimental as the turbines become large. Periodic damping and stiffness are examples of parametric excitation and are likely to carry over to other types of VAWT blades. Systems with parametric excitation have been studied with various methods. Floquet theory has been classically used to study the stability characteristics of linear systems with periodic coefficients, and has been commonly applied to Mathieu's equation, which represents a vibration system with periodic stiffness. We apply the Floquet theory combined with the harmonic-balance method to a linear vibration system with a periodic damping coefficient. Based on this theory, the approximated solution includes an exponential part, with an unknown exponent, and a periodic part. Our analysis investigates the initial conditions response, the boundaries of instability, and the characteristics of free response solution of the system. The coexistence phenomenon, in which some of the transition curves overlap so that the instability wedges disappear, is recovered in this approach, and is examined closely.An additional case of the parametric excitation is the combination of parametric damping and parametric stiffness. The Floquet-based analysis shows that the combined parametric excitation reshapes the stability characteristics, compared to the system with only parametric damping or stiffness and disrupts the coexistence which is observed in the parametric damping case.The aeroelastic forces encountered by the wind turbines can cause self-excitation in blades, the mechanism of which can be loosely modeled with van-der-Pol-type nonlinearity. We seek to understand the combined effect of parametric excitation and van der Pol nonlinearity, as both can induce instabilities and oscillations. The oscillator is studied under nonresonant conditions and secondary resonances, with and without external excitation. We analyze the system using the method of multiple scales and numerical solutions. For the case without external excitation, the analysis reveals nonresonant phase drift (quasi-periodic responses), and subharmonic resonance with possible phase drift or phase locking (periodic responses). Hard excitation is treated for nonresonant conditions and secondary resonances, and similar phenomena are uncovered.Some Darrieus VAWTs consist of curved blades. We lastly study the modal analysis of curved Darrieus wind-turbine blades and obtain the mode shapes and modal frequencies. The governing equations are derived using the fundamental deformation mechanics, and thin beam approximations are employed to express the strain and kinetic energies. The assumed-modes method is applied to the energies, and the Euler-Lagrange equation is used to discretize the equations of motion. Implementing these equations, mode shapes are calculated and mapped back onto the curved beam for visualization. This analysis is conducted for pinned-pinned and hinged-hinged blades. The results are compared with Finite element analysis using Abaqus and with the literature.

Author: Ayse Sapmaz
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 133

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Understanding vibration of wind turbine blades is of fundamental importance. This study focuses on the effect of blade mistuning on the coupled blade-hub dynamics. Unavoidably, the set of blades are not precisely identical due to inhomogeneous materials, manufacturer tolerances, etc. This work is focused on the blade-hub dynamics of horizontal-axis wind turbines with mistuned blades. The reduced-order equations of motion are derived for the wind turbine blades and hub exposed to centrifugal effects and gravitational and cyclic aerodynamic forces. Although the blades and hub equations are coupled, they can be decoupled from the hub by changing the independent variable from time to rotor angle and by using a small parameter approximation. The resulting blade equations include parametric and direct excitation terms. The method of multiple scales is applied to examine response of the linearized system. This analysis shows that superharmonic and primary resonances exist and are influenced by the mistuning. Resonance cases and the relations between response amplitude and frequency are studied. Besides illustrating the effects of damping and forcing level, the first-order perturbation solutions are verified withcomparisons to numerical simulations at superharmonic resonance of order two. The simulation point to speed-locking phenomenon, in which the superharmonic speed is locked in for an interval of applied mean loads. Additionally, the effect of rotor loading onthe rotor speed and blade amplitudes is investigated for different initial conditions and mistuning cases.Next, a second-order method of multiple scales is applied in the rotor-angle domain to analyze in-plane blade-hub dynamics. A superharmonic resonance case at one third the natural frequency is revealed. This resonance case is not captured by a first-order perturbation expansion. The relationship between response amplitude and frequency is studied. Resonances under constant loading are also analyzed. The effect of blade mistuning on the coupled blade-hub dynamics is taken into account. To better understand parametrically excited multi-degree-of-freedom behavior, approximate solutions to tuned and mistuned four-degree-of-freedom systems with parametric stiffness are studied. The solution and stability of a four-degree-of-freedom Mathieu-type system is investigated with and without broken symmetry. The analysis is done using Floquet theory with harmonic balance. A Floquet-type solution is composed of a periodic and an exponential part. The harmonic balance is applied when the Floquet solution is inserted into the original differential equation of motion. The analysis brings about an eigenvalue problem. By solving this, the Floquet characteristic exponents and the corresponding eigenvectors that give the Fourier coefficients are found in terms of the system parameters. The stability transition curve can be found by analyzing the real parts of the characteristic exponents. The frequency content can be determined by analyzing imaginary parts at the exponents. A response that involves a single Floquet exponent (and its complex conjugate) can be generated with a specific set of initial conditions, and can be regarded as a "modal response''. The method is applied to both tuned and detuned four-degree-of-freedom examples.

Author: Michael Mains
Publisher: Springer
ISBN: 3319747002
Category : Technology & Engineering
Languages : en
Pages : 384

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Book Description
Topics in Modal Analysis & Testing, Volume 9: Proceedings of the 36th IMAC, A Conference and Exposition on Structural Dynamics, 2018, the ninth volume of nine from the Conference, brings together contributions to this important area of research and engineering. The collection presents early findings and case studies on fundamental and applied aspects of Modal Analysis, including papers on: Operational Modal & Modal Analysis Applications Experimental Techniques Modal Analysis, Measurements & Parameter Estimation Modal Vectors & Modeling Basics of Modal Analysis Additive Manufacturing & Modal Testing of Printed Parts

Author: Qingkai Han
Publisher: Springer
ISBN: 9811027471
Category : Technology & Engineering
Languages : en
Pages : 168

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Book Description
This book explores the dynamics and vibration properties of gearboxes, with a focus on geared rotor systems. It discusses mechanical theories, finite-element based simulations, experimental measurements and vibration signal processing techniques. It introduces the vibration-resonance calculation method for the geared rotor system in wind turbines and load sharing of the planetary gear train, and offers a method for calculating the vibrations of geared rotor systems under either internal excitations from gear sets or external loads transferred from wind loads. It also defines and elaborates on parameter optimization for planetary gear systems based on the torsional dynamics of wind-turbine geared rotor systems. Moreover, it describes experimental measurements of vibrations on the wind-turbine gearbox performed on the test rig and on site, and analyzes the vibration signals of different testing points, showing them in both time and frequency domains. Lastly, it lists the gear coupling frequencies and fault characteristic frequencies from the vibrations of the gearbox housing. The technologies and results presented are valuable resources for use in dynamic design, vibration prediction and analysis of gearboxes and geared rotor systems in wind turbines as well as many other machines.

Author: Martin O. L. Hansen
Publisher: Routledge
ISBN: 1317671023
Category : Technology & Engineering
Languages : en
Pages : 217

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Book Description
Aerodynamics of Wind Turbines is the established essential text for the fundamental solutions to efficient wind turbine design. Now in its third edition, it has been substantially updated with respect to structural dynamics and control. The new control chapter now includes details on how to design a classical pitch and torque regulator to control rotational speed and power, while the section on structural dynamics has been extended with a simplified mechanical system explaining the phenomena of forward and backward whirling modes. Readers will also benefit from a new chapter on Vertical Axis Wind Turbines (VAWT). Topics covered include increasing mass flow through the turbine, performance at low and high wind speeds, assessment of the extreme conditions under which the turbine will perform and the theory for calculating the lifetime of the turbine. The classical Blade Element Momentum method is also covered, as are eigenmodes and the dynamic behaviour of a turbine. The book describes the effects of the dynamics and how this can be modelled in an aeroelastic code, which is widely used in the design and verification of modern wind turbines. Furthermore, it examines how to calculate the vibration of the whole construction, as well as the time varying loads and global case studies.

Author: Maher Barkallah
Publisher: Springer Nature
ISBN: 3030467295
Category : Technology & Engineering
Languages : en
Pages : 155

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Book Description
This book gathers original findings, both theoretical and experimental, related to various cutting-edge topics in the design and modeling of mechatronic systems, including multiphysics problems. It presents peer-reviewed papers from the first installment of the Mechatronics 4.0 workshop, which was jointly organized by the Laboratory of Mechanics, Modeling and Manufacturing (LA2MP), National School of Engineers of Sfax, Tunisia, and the QUARTZ Laboratory, Higher Institute of Mechanics of Paris, SUPMECA, France. The event follows in the tradition of the Workshop on Mechatronic Systems (JSM2014), organized by the same universities, while shifting the focus to the concept of Industry 4.0. As this new type of industry is emerging as the convergence of the virtual world, digital design, and management with real-world products and objects, the chapters gathered here highlight recent work on mechatronics systems that are expected to help shape the industry of tomorrow. Thanks to a healthy balance of theory and practical findings, the book offers a timely snapshot for the research and industrial communities alike, as well as a bridge to facilitate communication and collaboration between the two groups.

Author: R.H. Miller
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Walter Lacarbonara
Publisher: Springer Nature
ISBN: 303081162X
Category : Technology & Engineering
Languages : en
Pages : 891

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Book Description
This first of three volumes includes papers from the second series of NODYCON, which was held virtually in February of 2021. The conference papers reflect a broad coverage of topics in nonlinear dynamics, ranging from traditional topics from established streams of research to those from relatively unexplored and emerging venues of research. These include Fluid-structure interactions Mechanical systems and structures Computational nonlinear dynamics Analytical techniques Bifurcation and dynamic instability Rotating systems Modal interactions and energy transfer Nonsmooth systems

Author: R.S. Amano
Publisher: WIT Press
ISBN: 1784660043
Category : Science
Languages : en
Pages : 197

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Focusing on Aerodynamics of Wind Turbines with topics ranging from Fundamental to Application of horizontal axis wind turbines, this book presents advanced topics including: Basic Theory for Wind turbine Blade Aerodynamics, Dynamics-Based Health Monitoring and Control of Wind Turbine Rotors, Experimental Testing of Wind Turbines Using Wind Tunnels with an Emphasis on Small-Scale Wind Turbines Under Low-Reynolds Numbers, Computational Methods, Ice Accretion for Wind Turbines and Influence of Some Parameters, and Special Structural Reinforcement Technique for Wind Turbine Blades. Consequently, for these reasons, analysis of wind turbines will attract readers not only from the wind energy community but also in the gas turbines heat transfer and fluid mechanics community.