The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Soogab Lee - One of the best experts on this subject based on the ideXlab platform.
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unsteady aerodynamics of offshore floating wind turbines in platform pitching motion using vortex Lattice Method
Renewable Energy, 2014Co-Authors: Minu Jeon, Seungmin Lee, Soogab LeeAbstract:As the flow states of an offshore floating wind turbine (OFWT) differ from those of an onshore fixed wind turbine, it is questionable as to whether the aerodynamic load prediction of a turbine using conventional blade element momentum theory (BEMT) is accurate. The aim of this paper is to show the characteristics of aerodynamic load predictions using the vortex Lattice Method (VLM). Washizu's experimental data, which was measured under a similar flow state of a floating wind turbine, is used for validation. The prediction shows good results compared to those of an experiment. To determine the unsteady aerodynamics of a floating wind turbine, the NREL 5 MW wind turbine model is used for the simulation of a floating wind turbine. These results show that a turbulent wake state (TWS), which is undesirable condition and cannot predicted in BEMT simulation, arises when a floating wind turbine is operated at a low-speed inflow condition. In addition, the rotor experiences a TWS when the floating platform undergoes upward pitching motion.
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aerodynamic noise analysis of large horizontal axis wind turbines considering fluid structure interaction
Renewable Energy, 2012Co-Authors: Hogeon Kim, Seungmin Lee, Seunghoon Lee, Eunkuk Son, Soogab LeeAbstract:Aerodynamic noise is one of the most serious barriers in wind energy development. To develop technologies for wind turbine noise reduction and assessment, noise needs to be predicted precisely with special consideration given to blade flexibility. The numerical tool, WINFAS, which can simulate fluid–structure interaction, consists of three parts: the first part, the Unsteady Vortex Lattice Method, analyzes aerodynamics; the second part, the Nonlinear Composite Beam Theory, analyzes structure; and the third part uses a semi-empirical formula to analyze airfoil self-noise and the Lowson’s formula to analyze turbulence ingestion noise. In this study, using this numerical tool, the change in the noise strength due to blade flexibility was examined. This research showed that elastic blades decreased broadband noise because pitching motion reduced the angle of attack.
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analysis of aerodynamic characteristics on a counter rotating wind turbine
Current Applied Physics, 2010Co-Authors: Seungmin Lee, Hogeon Kim, Soogab LeeAbstract:This study aims to analyze aerodynamic characteristics of a counter-rotating wind turbine. For this purpose, three kinds of rotor configurations which are 2-bladed single, 4-bladed single and counter-rotating rotor were compared by using a numerical Method. The numerical Method used here was based on vortex Lattice Method and was validated with measurements of the NREL phase-VI rotor. Through numerical calculations of induction factors and power coefficients for each rotor configuration, the aerodynamic feasibility of a counter-rotating wind turbine was considered.
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numerical analysis on the aerodynamics of hawts using nonlinear vortex strength correction
Current Applied Physics, 2010Co-Authors: Hogeon Kim, Seoungmin Lee, Soogab LeeAbstract:Nonlinear vortex strength correction Method (NVCM) based on potential flow, is developed for improvement of vortex Lattice Method which has difficulties to predict the separated flow conditions and the viscous effect. In this Method, the bound vortex strength is determined by matching the lift force from VLM with the lift force from aerodynamic coefficients table as the same value of circulation is added to or subtracted from all chord wise vortices. For considering the nonlinearities due to the neighboring sections of the blade, sophisticated Newton–Rapson algorithm is applied. The validation of this Method was done by comparing the simulations with the measurements on the NREL Phase-VI horizontal axis wind turbine (HWAT) in the NASA Ames wind tunnel under uniform and yawed flow conditions. This Method gives good agreements with experiments in most cases.
Michael J R Graham - One of the best experts on this subject based on the ideXlab platform.
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aeroservoelastic state space vortex Lattice modeling and load alleviation of wind turbine blades
Wind Energy, 2015Co-Authors: Henrik Hesse, Rafael Palacios, Michael J R Graham, Eric C KerriganAbstract:An aeroservoelastic model, capturing the structural response and the unsteady aerodynamics of turbine rotors, will be used to demonstrate the potential of active load alleviation using aerodynamic control surfaces. The structural model is a geometrically non-linear composite beam, which is linearized around equilibrium rotating conditions and coupled with time-domain aerodynamics given by a linearized 3D unsteady vortex Lattice Method. With much of the existing work relying on blade element momentum theory with various corrections, the use of the unsteady vortex Lattice Method in this paper seeks to complement and provide a direct higher fidelity solution for the unsteady rotor dynamics in attached flow conditions. The resulting aeroelastic model is in a state-space formulation suitable for control synthesis. Flaps are modeled directly in the vortex Lattice description and using a reduced-order model of the coupled aeroelastic formulation, a linear-quadratic-Gaussian controller is synthesized and shown to reduce root mean square values of the root-bending moment and tip deflection in the presence of continuous turbulence. Similar trend is obtained when the controller is applied to the original non-linear model of the turbine. Trade-offs between reducing root-bending moment and suppressing the negative impacts on torsion due to flap deployment will also be investigated. Copyright © 2014 John Wiley & Sons, Ltd.
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applications of the unsteady vortex Lattice Method in aircraft aeroelasticity and flight dynamics
Progress in Aerospace Sciences, 2012Co-Authors: Joseba Murua, Rafael Palacios, Michael J R GrahamAbstract:The Unsteady Vortex-Lattice Method provides a medium-fidelity tool for the prediction of non-stationary aerodynamic loads in low-speed, but high-Reynolds-number, attached flow conditions. Despite a proven track record in applications where free-wake modelling is critical, other less-computationally-expensive potential-flow models, such as the Doublet-Lattice Method and strip theory, have long been favoured in fixed-wing aircraft aeroelasticity and flight dynamics. This paper presents how the Unsteady Vortex-Lattice Method can be implemented as an enhanced alternative to those techniques for diverse situations that arise in flexible-aircraft dynamics. A historical review of the Methodology is included, with latest developments and practical applications. Di erent formulations of the aerodynamic equations are outlined, and they are integrated with a nonlinear beam model for the full description of the dynamics of a free-flying flexible vehicle. Nonlinear time-marching solutions capture large wing excursions and wake roll-up, and the linearisation of the equations lends itself to a seamless, monolithic state-space assembly, particularly convenient for stability analysis and flight control system design. The numerical studies emphasise scenarios where the Unsteady Vortex-Lattice Method can provide an advantage over other state-of-the-art approaches. Examples of this include unsteady aerodynamics in vehicles with coupled aeroelasticity and flight dynamics, and in lifting surfaces undergoing complex kinematics, large deformations, or in-plane motions. Geometric nonlinearities are shown to play an instrumental, and often counter-intuitive, role in the aircraft dynamics. The Unsteady Vortex-Lattice Method is unveiled as a remarkable tool that can successfully incorporate all those e ects in the unsteady aerodynamics modelling.
Seungmin Lee - One of the best experts on this subject based on the ideXlab platform.
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unsteady aerodynamics of offshore floating wind turbines in platform pitching motion using vortex Lattice Method
Renewable Energy, 2014Co-Authors: Minu Jeon, Seungmin Lee, Soogab LeeAbstract:As the flow states of an offshore floating wind turbine (OFWT) differ from those of an onshore fixed wind turbine, it is questionable as to whether the aerodynamic load prediction of a turbine using conventional blade element momentum theory (BEMT) is accurate. The aim of this paper is to show the characteristics of aerodynamic load predictions using the vortex Lattice Method (VLM). Washizu's experimental data, which was measured under a similar flow state of a floating wind turbine, is used for validation. The prediction shows good results compared to those of an experiment. To determine the unsteady aerodynamics of a floating wind turbine, the NREL 5 MW wind turbine model is used for the simulation of a floating wind turbine. These results show that a turbulent wake state (TWS), which is undesirable condition and cannot predicted in BEMT simulation, arises when a floating wind turbine is operated at a low-speed inflow condition. In addition, the rotor experiences a TWS when the floating platform undergoes upward pitching motion.
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aerodynamic noise analysis of large horizontal axis wind turbines considering fluid structure interaction
Renewable Energy, 2012Co-Authors: Hogeon Kim, Seungmin Lee, Seunghoon Lee, Eunkuk Son, Soogab LeeAbstract:Aerodynamic noise is one of the most serious barriers in wind energy development. To develop technologies for wind turbine noise reduction and assessment, noise needs to be predicted precisely with special consideration given to blade flexibility. The numerical tool, WINFAS, which can simulate fluid–structure interaction, consists of three parts: the first part, the Unsteady Vortex Lattice Method, analyzes aerodynamics; the second part, the Nonlinear Composite Beam Theory, analyzes structure; and the third part uses a semi-empirical formula to analyze airfoil self-noise and the Lowson’s formula to analyze turbulence ingestion noise. In this study, using this numerical tool, the change in the noise strength due to blade flexibility was examined. This research showed that elastic blades decreased broadband noise because pitching motion reduced the angle of attack.
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analysis of aerodynamic characteristics on a counter rotating wind turbine
Current Applied Physics, 2010Co-Authors: Seungmin Lee, Hogeon Kim, Soogab LeeAbstract:This study aims to analyze aerodynamic characteristics of a counter-rotating wind turbine. For this purpose, three kinds of rotor configurations which are 2-bladed single, 4-bladed single and counter-rotating rotor were compared by using a numerical Method. The numerical Method used here was based on vortex Lattice Method and was validated with measurements of the NREL phase-VI rotor. Through numerical calculations of induction factors and power coefficients for each rotor configuration, the aerodynamic feasibility of a counter-rotating wind turbine was considered.
Roland J.-m. Pellenq - One of the best experts on this subject based on the ideXlab platform.
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water adsorption in disordered mesoporous silica vycor at 300 k and 650 k a grand canonical monte carlo simulation study of hysteresis
Journal of Chemical Physics, 2005Co-Authors: Joel Puibasset, Roland J.-m. PellenqAbstract:This numerical simulation paper focuses on the adsorption/desorption of water in disordered mesoporous silica glasses (Vycor-like). The numerical adsorbent was previously obtained by off Lattice Method, and was shown to reproduce quite well the micro- and mesotextural properties of real Vycor, as well as morphological (pore size distribution) and topological (pore interconnections) disorder. The water-water interactions are described by the SPC model while water-silica interactions are calculated in the framework of the PN-TrAZ model. The water adsorption/desorption isotherms and the configurational energies are calculated by the Grand Canonical Monte Carlo simulation Method. The low pressure results compare well with experiments, showing the good transferability of the intermolecular potential. It is shown that if the hysteresis loop observed in the adsorption/desorption isotherm is considered as a true phase transition (which is actually still an open question in the case of disordered porous materials)...
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a grand canonical monte carlo simulation study of water adsorption in a vycor like disordered mesoporous material at 300 k
Studies in Surface Science and Catalysis, 2002Co-Authors: Joel Puibasset, Roland J.-m. PellenqAbstract:Confinement in porous materials is known to modify the thermodynamical properties of fluids. Capillary condensation is an example where a dense phase appears before saturating pressure is reached. Such phenomenon is not yet well understood in disordered mesoporous materials presenting highly interconnected pores. Grand Canonical Monte Carlo simulation is used to investigate the properties of water (fluid of most importance) confined in mesoporous Controled Porous Glass (Vycor-like) numerically obtained by the off-Lattice Method developed by P. Levitz [Adv. Coll. Int. Sci. 76 - 77 (1998), 71]. We first outline the interaction model and give the adsorption isotherm obtained at 300 K. Good agreement is found with available experimental results.
Rafael Palacios - One of the best experts on this subject based on the ideXlab platform.
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aeroservoelastic state space vortex Lattice modeling and load alleviation of wind turbine blades
Wind Energy, 2015Co-Authors: Henrik Hesse, Rafael Palacios, Michael J R Graham, Eric C KerriganAbstract:An aeroservoelastic model, capturing the structural response and the unsteady aerodynamics of turbine rotors, will be used to demonstrate the potential of active load alleviation using aerodynamic control surfaces. The structural model is a geometrically non-linear composite beam, which is linearized around equilibrium rotating conditions and coupled with time-domain aerodynamics given by a linearized 3D unsteady vortex Lattice Method. With much of the existing work relying on blade element momentum theory with various corrections, the use of the unsteady vortex Lattice Method in this paper seeks to complement and provide a direct higher fidelity solution for the unsteady rotor dynamics in attached flow conditions. The resulting aeroelastic model is in a state-space formulation suitable for control synthesis. Flaps are modeled directly in the vortex Lattice description and using a reduced-order model of the coupled aeroelastic formulation, a linear-quadratic-Gaussian controller is synthesized and shown to reduce root mean square values of the root-bending moment and tip deflection in the presence of continuous turbulence. Similar trend is obtained when the controller is applied to the original non-linear model of the turbine. Trade-offs between reducing root-bending moment and suppressing the negative impacts on torsion due to flap deployment will also be investigated. Copyright © 2014 John Wiley & Sons, Ltd.
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integrated flight dynamics and aeroelasticity of flexible aircraft with application to swept flying wings
56th AIAA ASCE AHS ASC Structures Structural Dynamics and Materials Conference 2015 : Kissimmee Florida USA 5 - 9 January 2015, 2015Co-Authors: Robert J Simpson, Rafael Palacios, Paul J GoulartAbstract:The dynamics of flexible, swept flying wing (SFW) aircraft are described by a set of nonlinear, multi-disciplinary equations of motion. Aircraft structures are modeled using a geometrically-exact composite beam model which can, in general, capture large dynamic deformations and the interaction between rigid-body and elastic degrees-offreedom. In addition, an implementation of the unsteady vortex-Lattice Method capable of handling arbitrary kinematics is used to capture the unsteady, three-dimensional flow-field around the aircraft as it deforms. Linearization of this coupled nonlinear description, which can in general be around a nonlinear equilibrium, is performed to yield linear time-invariant state-space models. Verification of aeroelastic stability analyses using these models is carried out. Subsequently, a set of SFW models are developed and the dynamic stability characteristics of these aircraft are investigated for a range of flight velocities and vehicle parameters.
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consistent structural linearization in flexible aircraft dynamics with large rigid body motion
AIAA Journal, 2014Co-Authors: Henrik Hesse, Rafael Palacios, Joseba MuruaAbstract:This paper investigates the linearization, using perturbation Methods, of the structural deformations in the nonlinear flight dynamic response of aircraft with slender, flexible wings. The starting point is the coupling of a displacement-based geometrically nonlinear flexible-body dynamics formulation with a three-dimensional unsteady vortex Lattice Method. This is followed by a linearization of the structural degrees of freedom, which are assumed to be small in a body-fixed reference frame. The translations and rotations of that reference frame and their time derivatives, which describe the vehicle flight dynamics, can still be arbitrarily large. The resulting system preserves all couplings between rigid and elastic motions and can be projected onto a few vibration modes of the unconstrained aircraft with geometrically nonlinear static deflections at a trim condition. Equally, the unsteady aerodynamics can be approximated on a fixed Lattice defined by the deformed static geometry. Numerical studies on a ...
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induced drag calculations in the unsteady vortex Lattice Method
AIAA Journal, 2013Co-Authors: Robert J Simpson, Rafael Palacios, Joseba MuruaAbstract:α angle of attack, rad Γ circulation, m2s−1 λ wake wavelength, m ρ∞ free-stream air density, kgm −3 τ panel tangential vector ω angular velocity, rad s−1 a non-dimensional distance between aerofoil mid-chord and centre of rotation A panel area, m b semi-chord, m ∆b panel span, m B wingspan, m c aerofoil chord, m ∆c panel chord, m C Theodorsen’s function, C(k) = F (k) + iG(k) Cd sectional drag coefficient CD wing drag coefficient Cl sectional lift coefficient Cs sectional leading-edge suction coefficient ∗Graduate Student, Department of Aeronautics. AIAA Student Member. †Senior Lecturer, Department of Aeronautics. E-mail: rpalacio@imperial.ac.uk. AIAA Member. ‡Lecturer, Department of Mechanical Engineering Sciences. AIAA Member.
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applications of the unsteady vortex Lattice Method in aircraft aeroelasticity and flight dynamics
Progress in Aerospace Sciences, 2012Co-Authors: Joseba Murua, Rafael Palacios, Michael J R GrahamAbstract:The Unsteady Vortex-Lattice Method provides a medium-fidelity tool for the prediction of non-stationary aerodynamic loads in low-speed, but high-Reynolds-number, attached flow conditions. Despite a proven track record in applications where free-wake modelling is critical, other less-computationally-expensive potential-flow models, such as the Doublet-Lattice Method and strip theory, have long been favoured in fixed-wing aircraft aeroelasticity and flight dynamics. This paper presents how the Unsteady Vortex-Lattice Method can be implemented as an enhanced alternative to those techniques for diverse situations that arise in flexible-aircraft dynamics. A historical review of the Methodology is included, with latest developments and practical applications. Di erent formulations of the aerodynamic equations are outlined, and they are integrated with a nonlinear beam model for the full description of the dynamics of a free-flying flexible vehicle. Nonlinear time-marching solutions capture large wing excursions and wake roll-up, and the linearisation of the equations lends itself to a seamless, monolithic state-space assembly, particularly convenient for stability analysis and flight control system design. The numerical studies emphasise scenarios where the Unsteady Vortex-Lattice Method can provide an advantage over other state-of-the-art approaches. Examples of this include unsteady aerodynamics in vehicles with coupled aeroelasticity and flight dynamics, and in lifting surfaces undergoing complex kinematics, large deformations, or in-plane motions. Geometric nonlinearities are shown to play an instrumental, and often counter-intuitive, role in the aircraft dynamics. The Unsteady Vortex-Lattice Method is unveiled as a remarkable tool that can successfully incorporate all those e ects in the unsteady aerodynamics modelling.