Aeroelastic Benchmark Experiments Project
National Aeronautics and Space Administration — M4 Engineering proposes to conduct canonical aeroelastic benchmark experiments. These experiments will augment existing sources for aeroelastic data in the...
Chaotic Patterns in Aeroelastic Signals
Directory of Open Access Journals (Sweden)
F. D. Marques
2009-01-01
patterns. With the reconstructed state spaces, qualitative analyses may be done, and the attractors evolutions with parametric variation are presented. Overall results reveal complex system dynamics associated with highly separated flow effects together with nonlinear coupling between aeroelastic modes. Bifurcations to the nonlinear aeroelastic system are observed for two investigations, that is, considering oscillations-induced aeroelastic evolutions with varying freestream speed, and aeroelastic evolutions at constant freestream speed and varying oscillations. Finally, Lyapunov exponent calculation is proceeded in order to infer on chaotic behavior. Poincaré mappings also suggest bifurcations and chaos, reinforced by the attainment of maximum positive Lyapunov exponents.
Energy Technology Data Exchange (ETDEWEB)
Visser, B. [Stork Product Eng., Amsterdam (Netherlands)
1996-09-01
To support the discussion on aeroelastic codes, a description of the code FLEXLAST was given and experiences within benchmarks and measurement programmes were summarized. The code FLEXLAST has been developed since 1982 at Stork Product Engineering (SPE). Since 1992 FLEXLAST has been used by Dutch industries for wind turbine and rotor design. Based on the comparison with measurements, it can be concluded that the main shortcomings of wind turbine modelling lie in the field of aerodynamics, wind field and wake modelling. (au)
Multifidelity Robust Aeroelastic Design Project
National Aeronautics and Space Administration — Nielsen Engineering & Research (NEAR) proposes a new method to generate mathematical models of wind-tunnel models and flight vehicles for robust aeroelastic...
Studies in hypersonic aeroelasticity
Nydick, Ira Harvey
2000-11-01
This dissertation describes the aeroelastic analysis of a generic hypersonic vehicle, focusing on two specific problems: (1) hypersonic panel flutter, and (2) aeroelastic behavior of a complete unrestrained generic hypersonic vehicle operating at very high Mach numbers. The panels are modeled as shallow shells using Marguerre nonlinear shallow shell theory for orthotropic panels and the aerodynamic loads are obtained from third order piston theory. Two models of curvature, several applied temperature distributions, and the presence of a shock are also included in the model. Results indicate that the flutter speed of the panel is significantly reduced by temperature variations comparable to the buckling temperature and by the presence of a shock. A panel with initial curvature can be more stable than the flat panel but the increase in stability depends in a complex way on the material properties of the panel and the amount of curvature. At values of dynamic pressure above critical, aperiodic motion was observed. The value of dynamic pressure for which this occurs in both heated panels and curved panels is much closer to the critical dynamic pressure than for the flat, unheated panel. A comparison of piston theory aerodynamics and Euler and Navier-Stokes aerodynamics was performed for a two dimensional panel with prescribed motion and the results indicate that while 2nd or higher order piston theory agrees very well with the Euler solution for the frequencies seen in hypersonic panel flutter, it differs substantially from the Navier-Stokes solution. The aeroelastic behavior of the complete vehicle was simulated using the unrestrained equations of motion, utilizing the method of quasi-coordinates. The unrestrained mode shapes of the vehicle were obtained from an equivalent plate analysis using an available code (ELAPS). The effects of flexible trim and rigid body degrees of freedom are carefully incorporated in the mathematical model. This model was applied to a
Plans for Aeroelastic Prediction Workshop
Heeg, Jennifer; Ballmann, Josef; Bhatia, Kumar; Blades, Eric; Boucke, Alexander; Chwalowski, Pawel; Dietz, Guido; Dowell, Earl; Florance, Jennifer P.; Hansen, Thorsten; Mani, Mori; Marvriplis, Dimitri; Perry, Boyd, III; Ritter, Markus; Schuster, David M.; Smith, Marilyn; Taylor, Paul; Whiting, Brent; Wieseman, Carol C.
2011-01-01
This paper summarizes the plans for the first Aeroelastic Prediction Workshop. The workshop is designed to assess the state of the art of computational methods for predicting unsteady flow fields and aeroelastic response. The goals are to provide an impartial forum to evaluate the effectiveness of existing computer codes and modeling techniques, and to identify computational and experimental areas needing additional research and development. Three subject configurations have been chosen from existing wind tunnel data sets where there is pertinent experimental data available for comparison. For each case chosen, the wind tunnel testing was conducted using forced oscillation of the model at specified frequencies
Research in aeroelasticity EFP-2006
DEFF Research Database (Denmark)
the compressibility of the hydraulic oil introduced a dynamic mode in the pitch bearing degree of freedom. Also, investigating flutter for blades at large deflections showed that the flutter limit for a 5MW blade was moved significantly compared to blades without large deflections. The influence of...... modeling nacelle components was investigated by developing a generalized method to interface dynamic systems to the aeroelastic program HAWC2 and by exemplify by modeling the nacelle of an aeroelastic wind turbine model in a more detailed way by including a single planet stage of a gearbox. This simplified...
Research in aeroelasticity EFP-2007
DEFF Research Database (Denmark)
This report contains results from the EFP2007 project Program for Research in Applied Aeroelasticity. The main results from this project are: The rotor aerodynamics were computed using different types of models with focus on the flow around the tip. The results showed similar trend for all models...
Computational Models for Nonlinear Aeroelastic Systems Project
National Aeronautics and Space Administration — Clear Science Corp. and Duke University propose to develop and demonstrate new and efficient computational methods of modeling nonlinear aeroelastic systems. The...
Variable Fidelity Aeroelastic Toolkit - Structural Model Project
National Aeronautics and Space Administration — The proposed innovation is a methodology to incorporate variable fidelity structural models into steady and unsteady aeroelastic and aeroservoelastic analyses in...
A modern course in aeroelasticity
Dowell, Earl H
2015-01-01
This book cover the basics of aeroelasticity or the dynamics of fluid-structure interaction. While the field began in response to the rapid development of aviation, it has now expanded into many branches of engineering and scientific disciplines and treat physical phenomena from aerospace engineering, bioengineering, civil engineering, and mechanical engineering in addition to drawing the attention of mathematicians and physicists. The basic questions addressed are dynamic stability and response of fluid structural systems as revealed by both linear and nonlinear mathematical models and correlation with experiment. The use of scaled models and full scale experiments and tests play a key role where theory is not considered sufficiently reliable. In this new edition the more recent literature on nonlinear aeroelasticity has been brought up to date and the opportunity has been taken to correct the inevitable typographical errors that the authors and our readers have found to date. The early chapters of t...
Research in aeroelasticity EFP-2005
2006-01-01
In the Energy Research Project ”Program for Research in Applied Aeroelasticity” (EFP2005), Risø National Laboratory (Risø) and the Technical University of Denmark (DTU) have applied and further developed the tools in the aeroelastic design complex. Themain results from the project are: Adding a winglet to a wind turbine blade for minimizing the induced drag of the blade led to the biggest increase in power of 1.4%. Transient wind loads during pitch motion are determined using CFD. Compared to...
Research in aeroelasticity EFP-2006
2007-01-01
This report contains the results from the Energy Research Project ”Program for Research in Applied Aeroelasticity, EFP-2006” covering the period from 1. April 2006 to 31. March 2007. A summary of the main results from the project is given in the following. The aerodynamics for rotors incl. spinner and winglets were clarified and the needed premises for an optimal rotor were explained. Also, the influence of viscous effects on rotor blades was investigated and the results indicated a range of ...
Aeroelastic instability problems for wind turbines
Energy Technology Data Exchange (ETDEWEB)
Hansen, M. E. [Wind Energy Department, Riso National Laboratory, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde, (Denmark)
2007-09-05
This paper deals with the aeroelastic instabilities that have occurred and may still occur for modern commercial wind turbines: stall-induced vibrations for stall-turbines, and classical flutter for pitch-regulated turbines. A review of previous works is combined with derivations of analytical stability limits for typical blade sections that show the fundamental mechanisms of these instabilities. The risk of stall-induced vibrations is mainly related to blade airfoil characteristics, effective direction of blade vibrations and structural damping; whereas the blade tip speed, torsional blade stiffness and chordwise position of the center of gravity along the blades are the main parameters for flutter. These instability characteristics are exemplified by aeroelastic stability analyses of different wind turbines. The review of each aeroelastic instability ends with a list of current research issues that represent unsolved aeroelastic instability problems for wind turbines. (Author).
Computational Models for Nonlinear Aeroelastic Systems Project
National Aeronautics and Space Administration — Clear Science Corp. and Duke University propose to develop and demonstrate a new and efficient computational method of modeling nonlinear aeroelastic systems. The...
Adjustable Fidelity Computational Aeroelasticity Procedure (AFCAP) Project
National Aeronautics and Space Administration — NextGen proposes an approach to significantly enhance aeroelastic analysis capabilities over what is commonly available in linear analysis environments such as...
Unsteady Design Optimization for Aeroelasticity Applications Project
National Aeronautics and Space Administration — Aeroelasticity plays an important role in the design and development of highly flexible flight vehicles and blended wing body configurations. The operating margins...
Overview of the Aeroelastic Prediction Workshop
Heeg, Jennifer; Chwalowski, Pawel; Schuster, David M.; Dalenbring, Mats
2013-01-01
The AIAA Aeroelastic Prediction Workshop (AePW) was held in April, 2012, bringing together communities of aeroelasticians and computational fluid dynamicists. The objective in conducting this workshop on aeroelastic prediction was to assess state-of-the-art computational aeroelasticity methods as practical tools for the prediction of static and dynamic aeroelastic phenomena. No comprehensive aeroelastic benchmarking validation standard currently exists, greatly hindering validation and state-of-the-art assessment objectives. The workshop was a step towards assessing the state of the art in computational aeroelasticity. This was an opportunity to discuss and evaluate the effectiveness of existing computer codes and modeling techniques for unsteady flow, and to identify computational and experimental areas needing additional research and development. Three configurations served as the basis for the workshop, providing different levels of geometric and flow field complexity. All cases considered involved supercritical airfoils at transonic conditions. The flow fields contained oscillating shocks and in some cases, regions of separation. The computational tools principally employed Reynolds-Averaged Navier Stokes solutions. The successes and failures of the computations and the experiments are examined in this paper.
Aeroelasticity of Large Wind Turbines
Energy Technology Data Exchange (ETDEWEB)
Holierhoek, J.G.
2008-11-19
The aeroelastic stability of wind turbines can be investigated by simulating models of the turbines under different conditions. Wind condition, pitch angle setting and rotational velocity will influence the aeroelastic stability. This dissertation describes the development and use of one fully nonlinear aeroelastic tool that has been developed especially for large wind turbines, but it can also be used for many other systems with bending and torsional degrees of freedom. This tool is called WOBBE. The calculations are performed using nonlinear dynamics and nonlinear aerodynamics. This is important, because linearising is always a somewhat arbitrary process where experience is used to determine which terms can and cannot be left out of the equations. The importance of performing fully nonlinear calculations will be shown by discussing the differences between the results from linear programmes and WOBBE. The combination of using linearised tools to investigate the possible problem areas and nonlinear tools to zoom in on these possible unstable conditions seems to be a logical approach of the aeroelastic analysis during the design. WOBBE simulates multi-body systems, where the rigid bodies are interconnected with hinges, springs and dampers. The aerodynamic forces acting on this system are calculated by the programme. The blade element momentum method is used for these calculations. The calculations of the motions are performed using Hamilton's generalised momenta and the generalised coordinates as state variables. WOBBE has been developed purely to perform simulations to determine the aeroelastic (in)stability of the system, not to determine the stresses in the components of the turbine. If there are any unknown or unexpected instabilities for the given setting, these will also show up in the simulation, as the method does not focus solely on expected instabilities. Next to the fact that WOBBE performs the simulations fully nonlinear, this is another advantage
Nonlinear aeroelastic behavior of compliant airfoils
International Nuclear Information System (INIS)
Since the beginning of aviation and up to the present time, airfoils have always been built as rigid structures. They are designed to fly under their divergence speed in order to avoid static aeroelastic instabilities and the resulting large deformations, which are not compatible with the typically low compliance of such airfoils. In recent years, research on airfoil morphing has generated interest in innovative ideas like the use of compliant systems, i.e. systems built to allow for large deformations without failure, in airfoil construction. Such systems can operate in the neighborhood of divergence and take advantage of large aeroelastic servo-effects. This, in turn, allows compact, advanced actuators to control the airfoil's deformation and loads, and hence complement or even replace conventional flaps. In order to analyze and design such compliant, active aeroelastic structures a nonlinear approach to static aeroelasticity is needed, which takes into account the effect of large deformations on aerodynamics and structure. Such an analytical approach is presented in this paper and applied to a compliant passive airfoil as the preliminary step in the realization of a piezoelectrically driven, active aeroelastic airfoil. Wind tunnel test results are also presented and compared with the analytic prediction. The good agreement and the observed behavior in the wind tunnel give confidence in the potential of this innovative idea
Centrifugal Compressor Aeroelastic Analysis Code
Keith, Theo G., Jr.; Srivastava, Rakesh
2002-01-01
Centrifugal compressors are very widely used in the turbomachine industry where low mass flow rates are required. Gas turbine engines for tanks, rotorcraft and small jets rely extensively on centrifugal compressors for rugged and compact design. These compressors experience problems related with unsteadiness of flowfields, such as stall flutter, separation at the trailing edge over diffuser guide vanes, tip vortex unsteadiness, etc., leading to rotating stall and surge. Considerable interest exists in small gas turbine engine manufacturers to understand and eventually eliminate the problems related to centrifugal compressors. The geometric complexity of centrifugal compressor blades and the twisting of the blade passages makes the linear methods inapplicable. Advanced computational fluid dynamics (CFD) methods are needed for accurate unsteady aerodynamic and aeroelastic analysis of centrifugal compressors. Most of the current day industrial turbomachines and small aircraft engines are designed with a centrifugal compressor. With such a large customer base and NASA Glenn Research Center being, the lead center for turbomachines, it is important that adequate emphasis be placed on this area as well. Currently, this activity is not supported under any project at NASA Glenn.
Aeroelastic Tailoring via Tow Steered Composites
Stanford, Bret K.; Jutte, Christine V.
2014-01-01
The use of tow steered composites, where fibers follow prescribed curvilinear paths within a laminate, can improve upon existing capabilities related to aeroelastic tailoring of wing structures, though this tailoring method has received relatively little attention in the literature. This paper demonstrates the technique for both a simple cantilevered plate in low-speed flow, as well as the wing box of a full-scale high aspect ratio transport configuration. Static aeroelastic stresses and dynamic flutter boundaries are obtained for both cases. The impact of various tailoring choices upon the aeroelastic performance is quantified: curvilinear fiber steering versus straight fiber steering, certifiable versus noncertifiable stacking sequences, a single uniform laminate per wing skin versus multiple laminates, and identical upper and lower wing skins structures versus individual tailoring.
OVERAERO-MPI: Parallel Overset Aeroelasticity Code
Gee, Ken; Rizk, Yehia M.
1999-01-01
An overset modal structures analysis code was integrated with a parallel overset Navier-Stokes flow solver to obtain a code capable of static aeroelastic computations. The new code was used to compute the static aeroelastic deformation of an arrow-wing-body geometry and a complex, full aircraft configuration. For the simple geometry, the results were similar to the results obtained with the ENSAERO code and the PVM version of OVERAERO. The full potential of this code suite was illustrated in the complex, full aircraft computations.
Power extraction from aeroelastic limit cycle oscillations
Dunnmon, J. A.; Stanton, S. C.; Mann, B. P.; Dowell, E. H.
2011-11-01
Nonlinear limit cycle oscillations of an aeroelastic energy harvester are exploited for enhanced piezoelectric power generation from aerodynamic flows. Specifically, a flexible beam with piezoelectric laminates is excited by a uniform axial flow field in a manner analogous to a flapping flag such that the system delivers power to an electrical impedance load. Fluid-structure interaction is modeled by augmenting a system of nonlinear equations for an electroelastic beam with a discretized vortex-lattice potential flow model. Experimental results from a prototype aeroelastic energy harvester are also presented. Root mean square electrical power on the order of 2.5 mW was delivered below the flutter boundary of the test apparatus at a comparatively low wind speed of 27 m/s and a chord normalized limit cycle amplitude of 0.33. Moreover, subcritical limit cycles with chord normalized amplitudes of up to 0.46 were observed. Calculations indicate that the system tested here was able to access over 17% of the flow energy to which it was exposed. Methods for designing aeroelastic energy harvesters by exploiting nonlinear aeroelastic phenomena and potential improvements to existing relevant aerodynamic models are also discussed.
Efficient uncertainty quantification in unsteady aeroelastic simulations
Witteveen, J.A.S.; Bijl, H.
2009-01-01
An efficient uncertainty quantification method for unsteady problems is presented in order to achieve a constant accuracy in time for a constant number of samples. The approach is applied to the aeroelastic problems of a transonic airfoil flutter system and the AGARD 445.6 wing benchmark with uncert
Research in aeroelasticity EFP-2007
Energy Technology Data Exchange (ETDEWEB)
Bak, C.
2008-07-15
This report contains results from the EFP2007 project 'Program for Research in Applied Aeroelasticity'. The main results from this project are: 1) The rotor aerodynamics were computed using different types of models with focus on the flow around the tip. The results showed similar trend for all models. 2) Comparison of 3D CFD computations with and without inflow shear showed that the integrated rotor thrust and power were largely identical in the two situations. 3) The influence of tower shadow with and without inflow shear showed significant differences compared to BEMcomputations, which gives cause for further investigation. 4) 3D CFD computations showed that the flow in the region of the nacelle anemometer measured the flow angle in the wake with errors up to as much as 7 deg. relative to the freestream flow angle. 5) As long as the flow over a blade remains attached there is little difference between 2-D and 3-D flow. However, at separation an increased lift is observed close to the rotational axis. 6) A correlation based transition model has been implemented in the incompressible EllipSys2D/3D Navier-Stokes solver. Computations on airfoils and rotors showed good agreement and distinct improvement in the drag predictions compared to using fully turbulent computations. 7) Comparing the method of Dynamic Wake Meandering (DWM) and IEC, the IECmodel seems conservative regarding fatigue and extreme loads for the yaw, driving torque and flapwise bending, whereas the loads on tower and blade torsion are non-conservative. 8) An experimental method for measuring transition point and energy spectra in airfoil boundary layers using microphones has been developed. 9) A robust and automatic method for detecting transition based on microphone measurement on airfoil surfaces has been developed. 10) Transition points and the corresponding instabilities have clearly been observed in airfoil boundary layers. 11) Predictions of the transition points on airfoils using
Embedded Fiber Optic Shape Sensing for Aeroelastic Wing Components Project
National Aeronautics and Space Administration — As the aerospace industry continues to push for greater vehicle efficiency, performance, and longevity, properties of wing aeroelasticity and flight dynamics have...
Rotary-wing aeroelasticity with application to VTOL vehicles
Friedmann, Peretz P.
1993-01-01
A concise assessment is presented of the state of the art in the field of rotary-wing aeroelasticity (RWE). The basic ingredients of RWE are reviewed, including structural modeling, unsteady aerodynamic modeling, formulation of the equations of motion, and solution methods. Results illustrating these methods are presented for isolated blades and coupled rotor-fuselage problems. The application of active controls to suppress aeromechanical and aeroelastic instabilities and to reduce vibration in rotorcraft is discussed. Structural optimization with aeroelastic constraints, gust response analysis of helicopters, and aeroelastic problems in special VTOL vehicles are briefly examined.
Aeroelastic instability problems for wind turbines
DEFF Research Database (Denmark)
Hansen, Morten Hartvig
2007-01-01
stiffness and chordwise position of the center of gravity along the blades are the main parameters for flutter. These instability characteristics are exemplified by aeroelastic stability analyses of different wind turbines. The review of each aeroelastic instability ends with a list of current research......This paper deals with the aeroelostic instabilities that have occurred and may still occur for modem commercial wind turbines: stall-induced vibrations for stall-turbines, and classical flutter for pitch-regulated turbines. A review of previous works is combined with derivations of analytical...... stability limits for typical blade sections that show the fundamental mechanisms of these instabilities. The risk of stall-induced vibrations is mainly related to blade airfoil characteristics, effective direction of blade vibrations and structural damping, whereas the blade tip speed, torsional blade...
Influence of vehicles on bridge aeroelastic stability
Czech Academy of Sciences Publication Activity Database
Buljac, Andrija; Pospíšil, Stanislav; Kozmar, H.; Kuznetsov, Sergeii; Král, Radomil
Rijeka: Grafika Helvetica, 2015 - (Kožar, I.; Bićanić, N.; Jelenić, G.; Čanadija, M.), s. 17-17 ISBN 9789537539214. [International Congress of Croatian Society of Mechanics /8./. Opatija (HR), 29.09.2015-02.10.2015] R&D Projects: GA MŠk(CZ) LO1219 Keywords : wind * vehicles * bridge * aeroelastic stability Subject RIV: JM - Building Engineering
New aeroelastic studies for a morphing wing
Directory of Open Access Journals (Sweden)
Ruxandra Mihaela BOTEZ*
2012-06-01
Full Text Available For this study, the upper surface of a rectangular finite aspect ratio wing, with a laminar airfoil cross-section, was made of a carbon-Kevlar composite material flexible skin. This flexible skin was morphed by use of Shape Memory Alloy actuators for 35 test cases characterized by combinations of Mach numbers, Reynolds numbers and angles of attack. The Mach numbers varied from 0.2 to 0.3 and the angles of attack ranged between -1° and 2°. The optimized airfoils were determined by use of the CFD XFoil code. The purpose of this aeroelastic study was to determine the flutter conditions to be avoided during wind tunnel tests. These studies show that aeroelastic instabilities for the morphing configurations considered appeared at Mach number 0.55, which was higher than the wind tunnel Mach number limit speed of 0.3. The wind tunnel tests could thus be performed safely in the 6’×9’ wind tunnel at the Institute for Aerospace Research at the National Research Council Canada (IAR/NRC, where the new aeroelastic studies, applied on morphing wings, were validated.
Methods and advances in the study of aeroelasticity with uncertainties
Directory of Open Access Journals (Sweden)
Dai Yuting
2014-06-01
Full Text Available Uncertainties denote the operators which describe data error, numerical error and model error in the mathematical methods. The study of aeroelasticity with uncertainty embedded in the subsystems, such as the uncertainty in the modeling of structures and aerodynamics, has been a hot topic in the last decades. In this paper, advances of the analysis and design in aeroelasticity with uncertainty are summarized in detail. According to the non-probabilistic or probabilistic uncertainty, the developments of theories, methods and experiments with application to both robust and probabilistic aeroelasticity analysis are presented, respectively. In addition, the advances in aeroelastic design considering either probabilistic or non-probabilistic uncertainties are introduced along with aeroelastic analysis. This review focuses on the robust aeroelasticity study based on the structured singular value method, namely the μ method. It covers the numerical calculation algorithm of the structured singular value, uncertainty model construction, robust aeroelastic stability analysis algorithms, uncertainty level verification, and robust flutter boundary prediction in the flight test, etc. The key results and conclusions are explored. Finally, several promising problems on aeroelasticity with uncertainty are proposed for future investigation.
APPLE - An aeroelastic analysis system for turbomachines and propfans
Reddy, T. S. R.; Bakhle, Milind A.; Srivastava, R.; Mehmed, Oral
1992-01-01
This paper reviews aeroelastic analysis methods for propulsion elements (advanced propellers, compressors and turbines) being developed and used at NASA Lewis Research Center. These aeroelastic models include both structural and aerodynamic components. The structural models include the typical section model, the beam model with and without disk flexibility, and the finite element blade model with plate bending elements. The aerodynamic models are based on the solution of equations ranging from the two-dimensional linear potential equation for a cascade to the three-dimensional Euler equations for multi-blade configurations. Typical results are presented for each aeroelastic model. Suggestions for further research are indicated. All the available aeroelastic models and analysis methods are being incorporated into a unified computer program named APPLE (Aeroelasticity Program for Propulsion at LEwis).
Aeroelastic tailoring and structural optimisation using an advanced dynamic aeroelastic framework
Werter, N.P.M.; De Breuker, R.
2015-01-01
Driven by a need to improve the efficiency of aircraft and reduce the fuel consumption, composite materials are applied extensively in the design of aircraft. A dynamic aeroelastic framework for the conceptual design of a generic composite wing structure is presented. The wing is discretized in seve
Research in Aeroelasticity EFP-2006[Wind turbines
Energy Technology Data Exchange (ETDEWEB)
Bak, C.
2007-07-15
This report contains the results from the Energy Research Project 'Program for Research in Applied Aeroelasticity, EFP-2006' covering the period from 1. April 2006 to 31. March 2007. A summary of the main results from the project is given in the following. The aerodynamics for rotors incl. spinner and winglets were clarified and the needed premises for an optimal rotor were explained. Also, the influence of viscous effects on rotor blades was investigated and the results indicated a range of optimum tip speed ratios. The use of winglets for wind turbine rotor was investigated and it was found that they can be used successfully, but that downwind and short winglets are most efficient. Investigating a strategy for reduction of loads and vibrations at extreme wind speeds showed that there are considerably uncertainties in the numerical models and that the main concluding remark is that measurements on a real blade or a real turbine are needed to further conclude the investigation. In the study of flutter and other torsional vibrations of blades at large deflections, modeling and analysis of the dynamics of a hydraulic pitch system for a 5 MW wind turbine was carried out. It was shown that the compressibility of the hydraulic oil introduced a dynamic mode in the pitch bearing degree of freedom. Also, investigating flutter for blades at large deflections showed that the flutter limit for a 5MW blade was moved significantly compared to blades without large deflections. The influence of modeling nacelle components was investigated by developing a generalized method to interface dynamic systems to the aeroelastic program HAWC2 and by exemplify by modeling the nacelle of an aeroelastic wind turbine model in a more detailed way by including a single planet stage of a gearbox. This simplified gearbox model captures in essence the splitting of the driving torque from the rotor shaft to the frame of the nacelle and to the generator. Investigating the influence of wind
A Digital Controller for Active Aeroelastic Controls
Ueda, Tetsuhiko; MUROTA, Katsuichi; 上田, 哲彦; 室田, 勝一
1989-01-01
A high-speed digital controller for aeroelastic controls was designed and made. The purpose was to minimize adverse phase lag which is inevitably produced by the CPU time of digital processing. The delay deteriorates control performances on rather rapid phenomena like aircraft flutter. With fix-point operation the controller realized 417 microseconds of throughput time including the A/D and D/A conversion. This corresponds to a high sampling rate of 2.4kHz. The controller furnishes two channe...
Rotorcraft Technology for HALE Aeroelastic Analysis
Young, Larry; Johnson, Wayne
2008-01-01
Much of technology needed for analysis of HALE nonlinear aeroelastic problems is available from rotorcraft methodologies. Consequence of similarities in operating environment and aerodynamic surface configuration. Technology available - theory developed, validated by comparison with test data, incorporated into rotorcraft codes. High subsonic to transonic rotor speed, low to moderate Reynolds number. Structural and aerodynamic models for high aspect-ratio wings and propeller blades. Dynamic and aerodynamic interaction of wing/airframe and propellers. Large deflections, arbitrary planform. Steady state flight, maneuvers and response to turbulence. Linearized state space models. This technology has not been extensively applied to HALE configurations. Correlation with measured HALE performance and behavior required before can rely on tools.
Transonic aeroelastic numerical simulation in aeronautical engineering
International Nuclear Information System (INIS)
An LU-SGS (lower-upper symmetric Gauss-Seidel) subiteration scheme is constructed for time-marching of the fluid equations. The HLLEW (Harten-Lax-van Leer-Einfeldt-Wada) scheme is used for the spatial discretization. The same subiteration formulation is applied directly to the structural equations of motion in generalized coordinates. Through subiteration between the fluid and structural equations, a fully implicit aeroelastic solver is obtained for the numerical simulation of fluid/structure interaction. To improve the ability for application to complex configurations, a multiblock grid is used for the flow field calculation and Transfinite Interpolation (TFI) is employed for the adaptive moving grid deformation. The infinite plate spline (IPS) and the principal of virtual work are utilized for the data transformation between the fluid and structure. The developed code was first validated through the comparison of experimental and computational results for the AGARD 445.6 standard aeroelastic wing. Then the flutter character of a tail wing with control surface was analyzed. Finally, flutter boundaries of a complex aircraft configuration were predicted. (author)
Aeroelastic Modeling of a Nozzle Startup Transient
Wang, Ten-See; Zhao, Xiang; Zhang, Sijun; Chen, Yen-Sen
2014-01-01
Lateral nozzle forces are known to cause severe structural damage to any new rocket engine in development during test. While three-dimensional, transient, turbulent, chemically reacting computational fluid dynamics methodology has been demonstrated to capture major side load physics with rigid nozzles, hot-fire tests often show nozzle structure deformation during major side load events, leading to structural damages if structural strengthening measures were not taken. The modeling picture is incomplete without the capability to address the two-way responses between the structure and fluid. The objective of this study is to develop a tightly coupled aeroelastic modeling algorithm by implementing the necessary structural dynamics component into an anchored computational fluid dynamics methodology. The computational fluid dynamics component is based on an unstructured-grid, pressure-based computational fluid dynamics formulation, while the computational structural dynamics component is developed under the framework of modal analysis. Transient aeroelastic nozzle startup analyses at sea level were performed, and the computed transient nozzle fluid-structure interaction physics presented,
Helicopter rotor dynamics and aeroelasticity - Some key ideas and insights
Friedmann, Peretz P.
1990-01-01
Four important current topics in helicopter rotor dynamics and aeroelasticity are discussed: (1) the role of geometric nonlinearities in rotary-wing aeroelasticity; (2) structural modeling, free vibration, and aeroelastic analysis of composite rotor blades; (3) modeling of coupled rotor/fuselage areomechanical problems and their active control; and (4) use of higher-harmonic control for vibration reduction in helicopter rotors in forward flight. The discussion attempts to provide an improved fundamental understanding of the current state of the art. In this way, future research can be focused on problems which remain to be solved instead of producing marginal improvements on problems which are already understood.
Sensitivity Analysis and Error Control for Computational Aeroelasticity Project
National Aeronautics and Space Administration — The objective of this proposal is the development of a next-generation computational aeroelasticity code, suitable for real-world complex geometries, and...
Aeroelastic Simulation Tool for Inflatable Ballute Aerocapture Project
National Aeronautics and Space Administration — This project will develop a much-needed multidisciplinary analysis tool for predicting the impact of aeroelastic effects on the functionality of inflatable...
Integrated Sensing and Control of Aeroelastic Deformation (ISCAD) Toolbox Project
National Aeronautics and Space Administration — An Integrated Sensing and Control of Aeroelastic Deformation (ISCAD) Toolbox is proposed. Specif-ically, this toolbox will provide a methodology, both hardware and...
Unified Nonlinear Flight Dynamics and Aeroelastic Simulator Tool Project
National Aeronautics and Space Administration — ZONA Technology, Inc. (ZONA) proposes a R&D effort to develop a Unified Nonlinear Flight Dynamics and Aeroelastic Simulator (UNFDAS) Tool that will combine...
Localization of aeroelastic modes in mistuned high-energy turbines
Pierre, Christophe; Smith, Todd E.; Murthy, Durbha V.
1994-05-01
The effects of blade mistuning on the aeroelastic vibration characteristics of high-energy turbines are investigated, using the first stage of the oxidizer turbopump in the Space Shuttle main rocket engine as an example. A modal aeroelastic analysis procedure is used in concert with a linearized unsteady aerodynamic theory that accounts for the effects of blade thickness, camber, and steady loading. High sensitivity of the dynamic characteristics of mistuned rotors is demonstrated. In particular, the aeroelastic free vibration modes become localized to a few blades, possibly leading to rogue blade failure, and the locus of the aeroelastic eigenvalues loses its regular structure when small mistuning (of the order usually present in actual rotors) is introduced. Perturbation analyses that yield physical insights into these phenomena are presented. A powerful but easily calculated stochastic sensitivity measure that allows the global prediction of mistuning effects is developed.
Research in aeroelasticity[Wind turbines
Energy Technology Data Exchange (ETDEWEB)
Bak, C.
2006-05-15
In the Energy Research Project 'Program for Research in Applied Aeroelasticity' (EFP2005), Risoe National Laboratory (Risoe) and the Technical University of Denmark (DTU) have applied and further developed the tools in the aeroelastic design complex. The main results from the project are: 1) Adding a winglet to a wind turbine blade for minimizing the induced drag of the blade led to the biggest increase in power of 1.4%. 2) Transient wind loads during pitch motion are determined using CFD. Compared to the NREL/NASA Ames test, reasonably good agreement is seen. 3) A general method was developed for the determination of 3D angle of attack for rotating blades from either measurements or numerical computations using CFD. 4) A model of the far wake behind wind turbines was developed for stability studies of the tip vortices in the far wake. 5) Investigating the blade root region showed that the power efficiency, CP, locally can be increased significantly beyond the Betz limit, but that the global CP for the rotor cannot exceed the Betz limit. When including tip losses and a minimum blade drag coefficient, a maximum rotor CP in the range of 0.51-0.52 was obtained. 6) A new airfoil family was designed and a 3D airfoil design tool was developed. Compared to the Risoe-B1 family, the new airfoil family showed similar or improved aerodynamic and structural characteristics. 7) Four different airfoils were analyzed to reveal the differences between 2D and 3D CFD. The major conclusions are the dependency of computational results to transition modelling, and the ability of 3D DES calculations to realistically simulate the turbulent wake of an airfoil in stall. 8) The capability of a theory for simulation of Gaussian turbulence driven gust events was demonstrated by emulating a violent shear gust event from a complex site. An asymptotic model for the PDF of the largest excursion from the mean level, during an arbitrary recurrence period, has been derived for a stochastic
AEROELASTIC INVESTIGATION OF AN ANNULAR TRANSONIC COMPRESSOR CASCADE: EXPERIMENTAL RESULTS
Chenaux, Virginie Anne; Ott, Peter; Zanker, Achim
2015-01-01
A reliable determination of the unsteady aerodynamic loads acting on the blades is essential to predict the aeroelastic stability of vibrating compressor cascades with accuracy. At transonic flow conditions, the vibration of the shock may change the blade aeroelastic behavior. Numerical tools still have difficulties to capture the physics associated to this effect. In order to increase the prediction’s accuracy, high quality experimental data at high spatial resolution is therefore required t...
Generator dynamics in aeroelastic analysis and simulations
DEFF Research Database (Denmark)
Larsen, Torben J.; Hansen, Morten Hartvig; Iov, F.
2003-01-01
of the first order terms in the model as well as the influence on drive train eigenfrequencies and damping has been investigated. Load response during timesimulation of wind turbine response have been compared to simulations with a traditional static generator model based entirely on the slip angle....... A 2 MW turbine has been modelled in the aeroelastic code HAWC. When using the new dynamic generator modelthere is an interesting coupling between the generator dynamics and a global turbine vibration mode at 4.5 Hz, which only occurs when a dynamic formulation of the generator equations is applied....... This frequency can especially be seen in the electricalpower of the generator and the rotational speed of the generator, but also as torque variations in the drive train....
Aeroelastic Stability of Suspension Bridges using CFD
DEFF Research Database (Denmark)
Stærdahl, Jesper Winther; Sørensen, Niels; Nielsen, Søren R.K.
2007-01-01
measured values may lead to erroneous results and CFD simulations may be used for extrapolation into the critical region. The flow analysis serves as preliminary studies for evaluating flutter stability using CFD methods in three dimensions, where the span-wise correlation of vortex separation, skew inflow...... using CFD models and the aeroelastic stability boundary has been successfully determined when comparing two-dimensional flow situations using wind tunnel test data and CFD methods for the flow solution and two-degrees-of-freedom structural models in translation perpendicular to the flow direction and...... the structural deformation. Furthermore, flutter derivatives are evaluated by CFD models using forced motion of a bridge section in a two-dimensional virtual wind tunnel. The parameter region of critical values is shown to be outside measured values. It is shown that a rough extrapolation of the...
Aeroelastic optimization of MW wind turbines
Energy Technology Data Exchange (ETDEWEB)
Hartvig Hansen, M.; Zahle, F.
2011-12-15
This report contains the results from the Energy Development and Demonstration Project ''Aeroelastic Optimization of MW wind turbine'' (AeroOpt). The project has had the following five Work Packages: 1. Geometric non-linear, anisotropic beam element for HAWC2. 2. Closed-loop eigenvalue analysis of controlled wind turbines. 3. Resonant wave excitation of lateral tower bending modes. 4. Development of next generation aerodynamic design tools. 5. Advanced design and verification of airfoils. The purposes of these Work Packages are briefly described in the Preface and a summary of the results are given in Section 2. Thereafter, the results from each Work Package are described in eight subsequent chapters. (Author)
Research in aeroelasticity EFP-2007-II
Energy Technology Data Exchange (ETDEWEB)
Buhl, T. (ed.)
2009-06-15
This report contains results from the EFP-2007-II project 'Program for Research in Applied Aeroelasticity'. The main results can be summed up into the following bullets: 1) 2D CFD was used to investigate tower shadow effects on both upwind and downwind turbines, and was used to validate the tower shadow models implemented in the aeroelastic code HAWC2. 2) Using a streamlined tower reduces the tower shadow by 50% compared to a cylindrical tower. Similar reductions can be achieved using a four legged lattice tower. 3) The application of laminar/turbulent transition in CFD computations for airfoils is demonstrated. For attached flow over thin airfoils (18%) 2D computations provide good results while a combination of Detached Eddy Simulation and laminar/ turbulent transition modeling improve the results in stalled conditions for a thick airfoil. 4) The unsteady flow in the nacelle region of a wind turbine is dominated by large flow gradients caused by unsteady shedding of vortices from the root sections of the blades. 5) The averaged nacelle wind speed compares well to the freestream wind speed, whereas the nacelle flow angle is highly sensitive to vertical positioning and tilt in the inflow. 6) The trailing edge noise model, TNO, was implemented and validated. The results showed that the noise was not predicted accurately, but the model captured the trends and can be used in airfoil design. The model was implemented in the airfoil design tool AIRFOILOPT and existing airfoils can be adjusted to maintain the aerodynamic characteristics, but with reduced noise in the order of up to 3dB in total sound power level and up to 1dB with A-weighting. 7) 2D CFD simulations are performed to verify their capability in predicting multi element airfoil configurations. The present computations show good agreement with measured performance from wind tunnel experiments. 8) The stochastic fluctuations of the aerodynamic forces on blades in deep-stall have an insignificant
The Use of Gramian Matrices for Aeroelastic Stability Analysis
Directory of Open Access Journals (Sweden)
Douglas Domingues Bueno
2013-01-01
Full Text Available Most of the established procedures for analysis of aeroelastic flutter in the development of aircraft are based on frequency domain methods. Proposing new methodologies in this field is always a challenge, because the new methods need to be validated by many experimental procedures. With the interest for new flight control systems and nonlinear behavior of aeroelastic structures, other strategies may be necessary to complete the analysis of such systems. If the aeroelastic model can be written in time domain, using state-space formulation, for instance, then many of the tools used in stability analysis of dynamic systems may be used to help providing an insight into the aeroelastic phenomenon. In this respect, this paper presents a discussion on the use of Gramian matrices to determine conditions of aeroelastic flutter. The main goal of this work is to introduce how observability gramian matrix can be used to identify the system instability. To explain the approach, the theory is outlined and simulations are carried out on two benchmark problems. Results are compared with classical methods to validate the approach and a reduction of computational time is obtained for the second example.
Aeroelastic tailoring in wind-turbine blade applications
Energy Technology Data Exchange (ETDEWEB)
Veers, P.; Lobitz, D. [Sandia National Labs., Albuquerque, NM (United States); Bir, G. [National Renewable Energy Lab., Golden, CO (United States). National Wind Technology Center
1998-04-01
This paper reviews issues related to the use of aeroelastic tailoring as a cost-effective, passive means to shape the power curve and reduce loads. Wind turbine blades bend and twist during operation, effectively altering the angle of attack, which in turn affects loads and energy production. There are blades now in use that have significant aeroelastic couplings, either on purpose or because of flexible and light-weight designs. Since aeroelastic effects are almost unavoidable in flexible blade designs, it may be desirable to tailor these effects to the authors advantage. Efforts have been directed at adding flexible devices to a blade, or blade tip, to passively regulate power (or speed) in high winds. It is also possible to build a small amount of desirable twisting into the load response of a blade with proper asymmetric fiber lay up in the blade skin. (Such coupling is akin to distributed {delta}{sub 3} without mechanical hinges.) The tailored twisting can create an aeroelastic effect that has payoff in either better power production or in vibration alleviation, or both. Several research efforts have addressed different parts of this issue. Research and development in the use of aeroelastic tailoring on helicopter rotors is reviewed. Potential energy gains as a function of twist coupling are reviewed. The effects of such coupling on rotor stability have been studied and are presented here. The ability to design in twist coupling with either stretching or bending loads is examined also.
Simplified aeroelastic modeling of horizontal axis wind turbines
Wendell, J. H.
1982-09-01
Certain aspects of the aeroelastic modeling and behavior of the horizontal axis wind turbine (HAWT) are examined. Two simple three degree of freedom models are described in this report, and tools are developed which allow other simple models to be derived. The first simple model developed is an equivalent hinge model to study the flap-lag-torsion aeroelastic stability of an isolated rotor blade. The model includes nonlinear effects, preconing, and noncoincident elastic axis, center of gravity, and aerodynamic center. A stability study is presented which examines the influence of key parameters on aeroelastic stability. Next, two general tools are developed to study the aeroelastic stability and response of a teetering rotor coupled to a flexible tower. The first of these tools is an aeroelastic model of a two-bladed rotor on a general flexible support. The second general tool is a harmonic balance solution method for the resulting second order system with periodic coefficients. The second simple model developed is a rotor-tower model which serves to demonstrate the general tools. This model includes nacelle yawing, nacelle pitching, and rotor teetering. Transient response time histories are calculated and compared to a similar model in the literature. Agreement between the two is very good, especially considering how few harmonics are used. Finally, a stability study is presented which examines the effects of support stiffness and damping, inflow angle, and preconing.
Design and Analysis of AN Static Aeroelastic Experiment
Hou, Ying-Yu; Yuan, Kai-Hua; Lv, Ji-Nan; Liu, Zi-Qiang
2016-06-01
Static aeroelastic experiments are very common in the United States and Russia. The objective of static aeroelastic experiments is to investigate deformation and loads of elastic structure in flow field. Generally speaking, prerequisite of this experiment is that the stiffness distribution of structure is known. This paper describes a method for designing experimental models, in the case where the stiffness distribution and boundary condition of a real aircraft are both uncertain. The stiffness distribution form of the structure can be calculated via finite element modeling and simulation calculation and F141 steels and rigid foam are used to make elastic model. In this paper, the design and manufacturing process of static aeroelastic models is presented and a set of experiment model was designed to simulate the stiffness of the designed wings, a set of experiments was designed to check the results. The test results show that the experimental method can effectively complete the design work of elastic model. This paper introduces the whole process of the static aeroelastic experiment, and the experimental results are analyzed. This paper developed a static aeroelasticity experiment technique and established an experiment model targeting at the swept wing of a certain kind of large aspect ratio aircraft.
Aeroelastic optimization of an advanced geometry helicopter rotor
Ganguli, Ranjan; Chopra, Inderjit
1992-01-01
Sensitivity derivatives of blade loads and aeroelastic stability of a helicopter rotor in forward flight are calculated as an integral part of a basic aeroelastic analysis using a direct analytical approach. Design variables include nonstructural mass and its placement, chordwise offset of blade center of gravity and aerodynamic center from the elastic axis, blade bending stiffnesses (flap, lag, torsion), and tip geometry (sweep, anhedral, pretwist and planform taper). By means of a sensitivity study, the importance of different design variables on oscillatory hub loads and damping of blade modes is examined. Aeroelastic and sensitivity analyses of the rotor based on a finite element method in space and time are linked with automated optimization algorithms to perform optimization studies of rotor blades. Optimum design solutions, calculated for a four-bladed, soft-inplane hingeless rotor achieved a reduction of 25-60 percent of all 4/rev loads.
Model Reduction of Nonlinear Aeroelastic Systems Experiencing Hopf Bifurcation
Abdelkefi, Abdessattar
2013-06-18
In this paper, we employ the normal form to derive a reduced - order model that reproduces nonlinear dynamical behavior of aeroelastic systems that undergo Hopf bifurcation. As an example, we consider a rigid two - dimensional airfoil that is supported by nonlinear springs in the pitch and plunge directions and subjected to nonlinear aerodynamic loads. We apply the center manifold theorem on the governing equations to derive its normal form that constitutes a simplified representation of the aeroelastic sys tem near flutter onset (manifestation of Hopf bifurcation). Then, we use the normal form to identify a self - excited oscillator governed by a time - delay ordinary differential equation that approximates the dynamical behavior while reducing the dimension of the original system. Results obtained from this oscillator show a great capability to predict properly limit cycle oscillations that take place beyond and above flutter as compared with the original aeroelastic system.
INVESTIGATION OF AIRSHIP AEROELASTICITY USING FLUID-STRUCTURE INTERACTION
Institute of Scientific and Technical Information of China (English)
LIU Jian-min; LU Chuan-jing; XUE Lei-ping
2008-01-01
Due to the flexibility of the envelope of large stratosphere airships, the aerodynamic solution of such airship is closely related to its shape and the external aerodynamic forces which lead to the structural deformation. It is essentially one of the Fluid-Structure Interaction (FSI) problems. This article aims at the numerical investigation of nonlinear airship aeroelasticity in consideration of aerodynamics and structure coupling, using an iteration method. The three-dimensional flow around the airship was numerically studied by means of the SIMPLE method based on the finite volume method. Nonlinear finite element analysis was employed for geometrically nonlinear deformation of the airship shape. Comparison of aerodynamic parameters and the pressure distribution between rigid and aeroelastic models was conducted when an airship is in a trimmed flight state in specified flight conditions. The effect of aeroelasticity on the airship aerodynamics was detailed.
Impact of Parallel Computing on Large Scale Aeroelastic Computations
Guruswamy, Guru P.; Kwak, Dochan (Technical Monitor)
2000-01-01
Aeroelasticity is computationally one of the most intensive fields in aerospace engineering. Though over the last three decades the computational speed of supercomputers have substantially increased, they are still inadequate for large scale aeroelastic computations using high fidelity flow and structural equations. In addition to reaching a saturation in computational speed because of changes in economics, computer manufactures are stopping the manufacturing of mainframe type supercomputers. This has led computational aeroelasticians to face the gigantic task of finding alternate approaches for fulfilling their needs. The alternate path to over come speed and availability limitations of mainframe type supercomputers is to use parallel computers. During this decade several different architectures have evolved. In FY92 the US Government started the High Performance Computing and Communication (HPCC) program. As a participant in this program NASA developed several parallel computational tools for aeroelastic applications. This talk describes the impact of those application tools on high fidelity based multidisciplinary analysis.
Linearized Aeroelastic Computations in the Frequency Domain Based on Computational Fluid Dynamics
Amsallem, David; Choi, Youngsoo; Farhat, Charbel
2015-01-01
An iterative, CFD-based approach for aeroelastic computations in the frequency domain is presented. The method relies on a linearized formulation of the aeroelastic problem and a fixed-point iteration approach and enables the computation of the eigenproperties of each of the wet aeroelastic eigenmodes. Numerical experiments on the aeroelastic analysis and design optimization of two wing configurations illustrate the capability of the method for the fast and accurate aeroelastic analysis of aircraft configurations and its advantage over classical time-domain approaches.
Aeroelastic stability predictions for a MW-sized blade
Energy Technology Data Exchange (ETDEWEB)
Lobitz, Don W. [Sandia National Labs., Albuquerque, NM (United States)
2004-07-01
Classical aeroelastic flutter instability historically has not been a driving issue in wind turbine design. In fact, rarely has this issue even been addressed in the past. Commensurately, among the wind turbines that have been built, rarely has classical flutter ever been observed. However, with the advent of larger turbines fitted with relatively softer blades, classical flutter may become a more important design consideration. In addition, innovative blade designs involving the use of aeroelastic tailoring, wherein the blade twists as it bends under the action of aerodynamic loads to shed load resulting from wind turbulence, may increase the blade's proclivity for flutter. With these considerations in mind it is prudent to revisit aeroelastic stability issues for a MW-sized blade with and without aeroelastic tailoring. Focusing on aeroelastic stability associated with the shed wake from an individual blade turning in still air, the frequency domain technique developed by Theodorsen for predicting classical flutter in fixed wing aircraft has been adapted for use with a rotor blade. Results indicate that the predicted flutter speed of a MW-sized blade is slightly greater than twice the operational speed of the rotor. When a moderate amount of aeroelastic tailoring is added to the blade, a modest decrease (12%) in the flutter speed is predicted. By comparison, for a smaller rotor with relatively stiff blades the predicted flutter speed is approximately six times the operating speed. When frequently used approximations to Theodorsen's method are implemented, drastic underpredictions result, which, while conservative, may adversely impact blade design. These underpredictions are also evident when this MW-sized blade is analysed using time domain methods. (Author)
Identification of the aeroelastic profile based on optical measurement
Czech Academy of Sciences Publication Activity Database
Chládek, Štěpán; Zolotarev, Igor
Brno: Brno University of Technology , 2014 - (Fuis, V.), s. 244-247 ISBN 978-80-214-4871-1. ISSN 1805-8248. [Engineering Mechanics 2014 /20./. Svratka (CZ), 12.05.2014-15.05.2014] R&D Projects: GA ČR GA13-10527S Institutional support: RVO:61388998 Keywords : system identification * aeroelastic profile * optical measurement Subject RIV: BI - Acoustics
Aeroelastic System Development Using Proper Orthogonal Decomposition and Volterra Theory
Lucia, David J.; Beran, Philip S.; Silva, Walter A.
2003-01-01
This research combines Volterra theory and proper orthogonal decomposition (POD) into a hybrid methodology for reduced-order modeling of aeroelastic systems. The out-come of the method is a set of linear ordinary differential equations (ODEs) describing the modal amplitudes associated with both the structural modes and the POD basis functions for the uid. For this research, the structural modes are sine waves of varying frequency, and the Volterra-POD approach is applied to the fluid dynamics equations. The structural modes are treated as forcing terms which are impulsed as part of the uid model realization. Using this approach, structural and uid operators are coupled into a single aeroelastic operator. This coupling converts a free boundary uid problem into an initial value problem, while preserving the parameter (or parameters) of interest for sensitivity analysis. The approach is applied to an elastic panel in supersonic cross ow. The hybrid Volterra-POD approach provides a low-order uid model in state-space form. The linear uid model is tightly coupled with a nonlinear panel model using an implicit integration scheme. The resulting aeroelastic model provides correct limit-cycle oscillation prediction over a wide range of panel dynamic pressure values. Time integration of the reduced-order aeroelastic model is four orders of magnitude faster than the high-order solution procedure developed for this research using traditional uid and structural solvers.
Contribution to finite element modelling of airfoil aeroelastic instabilities
Czech Academy of Sciences Publication Activity Database
Horáček, Jaromír; Sváček, P.; Růžička, M.; Feistauer, M.
2007-01-01
Roč. 1, č. 1 (2007), s. 43-52. ISSN 1802-680X. [Computational Mechanics 2007. Hrad Nečtiny, 05.11.2007-07.11.2007] R&D Projects: GA MPO FT-TA/026 Institutional research plan: CEZ:AV0Z20760514 Keywords : induced vibration * aeroelasticity * nonlinear vibrations Subject RIV: BI - Acoustics
Inertial Force Coupling to Nonlinear Aeroelasticity of Flexible Wing Aircraft
Nguyen, Nhan T.; Ting, Eric
2016-01-01
This paper investigates the inertial force effect on nonlinear aeroelasticity of flexible wing aircraft. The geometric are nonlinearity due to rotational and tension stiffening. The effect of large bending deflection will also be investigated. Flutter analysis will be conducted for a truss-braced wing aircraft concept with tension stiffening and inertial force coupling.
State of the art in wind turbine aerodynamics and aeroelasticity
DEFF Research Database (Denmark)
Hansen, Martin Otto Laver; Sørensen, Jens Nørkær; Voutsinas, S; Sørensen, Niels N.; Aagaard Madsen, Helge
2006-01-01
A comprehensive review of wind turbine aeroelasticity is given. The aerodynamic part starts with the simple aerodynamic Blade Element Momentum Method and ends with giving a review of the work done applying CFD on wind turbine rotors. In between is explained some methods of intermediate complexity...
Toward efficient aeroelastic energy harvesting through limit cycle shaping
Kirschmeier, Benjamin; Bryant, Matthew
2016-04-01
Increasing demand to harvest energy from renewable resources has caused significant research interest in unsteady aerodynamic and hydrodynamic phenomena. Apart from the traditional horizontal axis wind turbines, there has been significant growth in the study of bio-inspired oscillating wings for energy harvesting. These systems are being built to harvest electricity for wireless devices, as well as for large scale mega-watt power generation. Such systems can be driven by aeroelastic flutter phenomena which, beyond a critical wind speed, will cause the system to enter into limitcycle oscillations. When the airfoil enters large amplitude, high frequency motion, leading and trailing edge vortices form and, when properly synchronized with the airfoil kinematics, enhance the energy extraction efficiency of the device. A reduced order dynamic stall model is employed on a nonlinear aeroelastic structural model to investigate whether the parameters of a fully passive aeroelastic device can be tuned to produce limit cycle oscillations at desired kinematics. This process is done through an optimization technique to find the necessary structural parameters to achieve desired structural forces and moments corresponding to a target limit cycle. Structural nonlinearities are explored to determine the essential nonlinearities such that the system's limit cycle closely matches the desired kinematic trajectory. The results from this process demonstrate that it is possible to tune system parameters such that a desired limit cycle trajectory can be achieved. The simulations also demonstrate that the high efficiencies predicted by previous computational aerodynamics studies can be achieved in fully passive aeroelastic devices.
Aeroelastic Loads Modeling for Composite Aircraft Design Support
Baluch, H.A.
2009-01-01
With regard to the simulation of structural vibrations and consequent aeroelastic loads in aircraft components, the use of elastic axis e.a as reference of vibrations is quite common. The e.a decouples the bending and torsion degrees of freedom (D.o.F) during the dynamic analysis. The use of the e.a
Aeroelastic analysis of a troposkien-type wind turbine blade
Nitzsche, F.
1981-01-01
The linear aeroelastic equations for one curved blade of a vertical axis wind turbine in state vector form are presented. The method is based on a simple integrating matrix scheme together with the transfer matrix idea. The method is proposed as a convenient way of solving the associated eigenvalue problem for general support conditions.
Status of NASA full-scale engine aeroelasticity research
Lubomski, J. F.
1980-01-01
Data relevant to several types of aeroelastic instabilities were obtained using several types of turbojet and turbofan engines. In particular, data relative to separated flow (stall) flutter, choke flutter, and system mode instabilities are presented. The unique characteristics of these instabilities are discussed, and a number of correlations are presented that help identify the nature of the phenomena.
Application of Aeroelastic Solvers Based on Navier Stokes Equations
Keith, Theo G., Jr.; Srivastava, Rakesh
2001-01-01
The propulsion element of the NASA Advanced Subsonic Technology (AST) initiative is directed towards increasing the overall efficiency of current aircraft engines. This effort requires an increase in the efficiency of various components, such as fans, compressors, turbines etc. Improvement in engine efficiency can be accomplished through the use of lighter materials, larger diameter fans and/or higher-pressure ratio compressors. However, each of these has the potential to result in aeroelastic problems such as flutter or forced response. To address the aeroelastic problems, the Structural Dynamics Branch of NASA Glenn has been involved in the development of numerical capabilities for analyzing the aeroelastic stability characteristics and forced response of wide chord fans, multi-stage compressors and turbines. In order to design an engine to safely perform a set of desired tasks, accurate information of the stresses on the blade during the entire cycle of blade motion is required. This requirement in turn demands that accurate knowledge of steady and unsteady blade loading is available. To obtain the steady and unsteady aerodynamic forces for the complex flows around the engine components, for the flow regimes encountered by the rotor, an advanced compressible Navier-Stokes solver is required. A finite volume based Navier-Stokes solver has been developed at Mississippi State University (MSU) for solving the flow field around multistage rotors. The focus of the current research effort, under NASA Cooperative Agreement NCC3- 596 was on developing an aeroelastic analysis code (entitled TURBO-AE) based on the Navier-Stokes solver developed by MSU. The TURBO-AE code has been developed for flutter analysis of turbomachine components and delivered to NASA and its industry partners. The code has been verified. validated and is being applied by NASA Glenn and by aircraft engine manufacturers to analyze the aeroelastic stability characteristics of modem fans, compressors
An Aeroelastic Analysis of a Thin Flexible Membrane
Scott, Robert C.; Bartels, Robert E.; Kandil, Osama A.
2007-01-01
Studies have shown that significant vehicle mass and cost savings are possible with the use of ballutes for aero-capture. Through NASA's In-Space Propulsion program, a preliminary examination of ballute sensitivity to geometry and Reynolds number was conducted, and a single-pass coupling between an aero code and a finite element solver was used to assess the static aeroelastic effects. There remain, however, a variety of open questions regarding the dynamic aeroelastic stability of membrane structures for aero-capture, with the primary challenge being the prediction of the membrane flutter onset. The purpose of this paper is to describe and begin addressing these issues. The paper includes a review of the literature associated with the structural analysis of membranes and membrane utter. Flow/structure analysis coupling and hypersonic flow solver options are also discussed. An approach is proposed for tackling this problem that starts with a relatively simple geometry and develops and evaluates analysis methods and procedures. This preliminary study considers a computationally manageable 2-dimensional problem. The membrane structural models used in the paper include a nonlinear finite-difference model for static and dynamic analysis and a NASTRAN finite element membrane model for nonlinear static and linear normal modes analysis. Both structural models are coupled with a structured compressible flow solver for static aeroelastic analysis. For dynamic aeroelastic analyses, the NASTRAN normal modes are used in the structured compressible flow solver and 3rd order piston theories were used with the finite difference membrane model to simulate utter onset. Results from the various static and dynamic aeroelastic analyses are compared.
Effect of follower forces on aeroelastic stability of flexible structures
Chae, Seungmook
Missile bodies and wings are typical examples of structures that can be represented by beam models. Such structures, loaded by follower forces along with aerodynamics, exhibit the vehicle's aeroelastic instabilities. The current research integrates a nonlinear beam dynamics and unsteady aerodynamics to conduct aeroelastic studies of missile bodies and wings subjected to follower forces. The structural formulations are based on a geometrically-exact, mixed finite element method. Slender-body theory and thin-airfoil theory are used for the missile aerodynamics, and two-dimensional finite-state unsteady aerodynamics is used for wing aerodynamics. The aeroelastic analyses are performed using time-marching scheme for the missile body stability, and eigenvalue analysis for the wing flutter, respectively. Results from the time-marching formulation agree with published results for dynamic stability and show the development of limit cycle oscillations for disturbed flight near and above the critical thrust. Parametric studies of the aeroelastic behavior of specific flexible missile configurations are presented, including effects of flexibility on stability, limit-cycle amplitudes, and missile loads. The results do yield a significant interaction between the thrust, which is a follower force, and the aeroelastic stability. Parametric studies based on the eigenvalue analysis for the wing flutter, show that the predicted stability boundaries are very sensitive to the ratio of bending stiffness to torsional stiffness. The effect of thrust can be either stabilizing or destabilizing, depending on the value of this parameter. An assessment whether or not the magnitude of thrust needed to influence the flutter speed is practical is made for one configuration. The flutter speed is shown to change by 11% for this specific wing configuration.
Hassan, D.; Ritter, Markus
2011-01-01
The present paper deals with steady and unsteady aeroelastic simulation results obtained on the High Reynolds Number Aero-Structural Dynamics (HIRENASD) wind tunnel configuration [1], selected as common test case in the numerical aeroelasticity ONERA/DLR cooperation project “NLAS2”. In order to assess the aeroelastic prediction capabilities of the flow solvers elsA (ONERA) and TAU (DLR), 3 types of simulations have been realized: static coupling, harmonic forced motion and dynamic coupling...
Flight Dynamic Simulation with Nonlinear Aeroelastic Interaction using the ROM-ROM Procedure Project
National Aeronautics and Space Administration — ZONA Technology, Inc. (ZONA) proposes to develop an integrated flight dynamics simulation capability with nonlinear aeroelastic interactions by combining a flight...
National Aeronautics and Space Administration — ASSURE - Aeroelastic / Aeroservoelastic (AE/ASE) Uncertainty and Reliability Engineering capability - is a set of probabilistic computer programs for isolating...
Recent advance in nonlinear aeroelastic analysis and control of the aircraft
Institute of Scientific and Technical Information of China (English)
Xiang Jinwu; Yan Yongju; Li Daochun
2014-01-01
A review on the recent advance in nonlinear aeroelasticity of the aircraft is presented in this paper. The nonlinear aeroelastic problems are divided into three types based on different research objects, namely the two dimensional airfoil, the wing, and the full aircraft. Different non-linearities encountered in aeroelastic systems are discussed firstly, where the emphases is placed on new nonlinear model to describe tested nonlinear relationship. Research techniques, especially new theoretical methods and aeroelastic flutter control methods are investigated in detail. The route to chaos and the cause of chaotic motion of two-dimensional aeroelastic system are summarized. Var-ious structural modeling methods for the high-aspect-ratio wing with geometric nonlinearity are dis-cussed. Accordingly, aerodynamic modeling approaches have been developed for the aeroelastic modeling of nonlinear high-aspect-ratio wings. Nonlinear aeroelasticity about high-altitude long-endurance (HALE) and fight aircrafts are studied separately. Finally, conclusions and the chal-lenges of the development in nonlinear aeroelasticity are concluded. Nonlinear aeroelastic problems of morphing wing, energy harvesting, and flapping aircrafts are proposed as new directions in the future.
Recent advance in nonlinear aeroelastic analysis and control of the aircraft
Directory of Open Access Journals (Sweden)
Xiang Jinwu
2014-02-01
Full Text Available A review on the recent advance in nonlinear aeroelasticity of the aircraft is presented in this paper. The nonlinear aeroelastic problems are divided into three types based on different research objects, namely the two dimensional airfoil, the wing, and the full aircraft. Different nonlinearities encountered in aeroelastic systems are discussed firstly, where the emphases is placed on new nonlinear model to describe tested nonlinear relationship. Research techniques, especially new theoretical methods and aeroelastic flutter control methods are investigated in detail. The route to chaos and the cause of chaotic motion of two-dimensional aeroelastic system are summarized. Various structural modeling methods for the high-aspect-ratio wing with geometric nonlinearity are discussed. Accordingly, aerodynamic modeling approaches have been developed for the aeroelastic modeling of nonlinear high-aspect-ratio wings. Nonlinear aeroelasticity about high-altitude long-endurance (HALE and fight aircrafts are studied separately. Finally, conclusions and the challenges of the development in nonlinear aeroelasticity are concluded. Nonlinear aeroelastic problems of morphing wing, energy harvesting, and flapping aircrafts are proposed as new directions in the future.
Flight Dynamic Simulation with Nonlinear Aeroelastic Interaction using the ROM-ROM Procedure Project
National Aeronautics and Space Administration — ZONA Technology, Inc. proposes to develop an integrated flight dynamics simulation capability with nonlinear aeroelastic interactions by combining a flight dynamics...
CFD and Aeroelastic Analysis of the MEXICO Wind Turbine
International Nuclear Information System (INIS)
This paper presents an aerodynamic and aeroelastic analysis of the MEXICO wind turbine, using the compressible HMB solver of Liverpool. The aeroelasticity of the blade, as well as the effect of a low-Mach scheme were studied for the zero-yaw 15m/s wind case and steady- state computations. The wake developed behind the rotor was also extracted and compared with the experimental data, using the compressible solver and a low-Mach scheme. It was found that the loads were not sensitive to the Mach number effects, although the low-Mach scheme improved the wake predictions. The sensitivity of the results to the blade structural properties was also highlighted
Aeroelastic Optimization Study Based on X-56A Model
Li, Wesley; Pak, Chan-Gi
2014-01-01
A design process which incorporates the object-oriented multidisciplinary design, analysis, and optimization (MDAO) tool and the aeroelastic effects of high fidelity finite element models to characterize the design space was successfully developed and established. Two multidisciplinary design optimization studies using an object-oriented MDAO tool developed at NASA Armstrong Flight Research Center were presented. The first study demonstrates the use of aeroelastic tailoring concepts to minimize the structural weight while meeting the design requirements including strength, buckling, and flutter. A hybrid and discretization optimization approach was implemented to improve accuracy and computational efficiency of a global optimization algorithm. The second study presents a flutter mass balancing optimization study. The results provide guidance to modify the fabricated flexible wing design and move the design flutter speeds back into the flight envelope so that the original objective of X-56A flight test can be accomplished.
Multi-fidelity construction of explicit boundaries: Application to aeroelasticity
Dribusch, Christoph
Wings, control surfaces and rotor blades subject to aerodynamic forces may exhibit aeroelastic instabilities such as flutter, divergence and limit cycle oscillations which generally reduce their life and functionality. This possibility of instability must be taken into account during the design process and numerical simulation models may be used to predict aeroelastic stability. Aeroelastic stability is a design requirement that encompasses several difficulties also found in other areas of design. For instance, the large computational time associated with stability analysis is also found in computational fluid dynamics (CFD) models. It is a major hurdle in numerical optimization and reliability analysis, which generally require large numbers of call to the simulation code. Similarly, the presence of bifurcations and discontinuities is also encountered in structural impact analysis based on nonlinear dynamic simulations and renders traditional approximation techniques such as Kriging ineffective. Finally, for a given component or system, aeroelastic instability is only one of multiple failure modes which must be accounted for during design and reliability studies. To address the above challenges, this dissertation proposes a novel algorithm to predict, over a range of parameters, the qualitative outcomes (pass/fail) of simulations based on relatively few, classified (pass/fail) simulation results. This is different from traditional approximation techniques that seek to predict simulation outcomes quantitatively, for example by fitting a response surface. The predictions of the proposed algorithm are based on the theory of support vector machines (SVM), a machine learning method originated in the field of pattern recognition. This process yields an analytical function that explicitly defines the boundary between feasible and infeasible regions of the parameter space and has the ability to reproduce nonlinear, disjoint boundaries in n dimensions. Since training the
Unsteady airfoil flows with application to aeroelastic stability
Energy Technology Data Exchange (ETDEWEB)
Johansen, Jeppe
1999-09-01
The present report describes numerical investigation of two-dimensional unsteady airfoil flows with application to aeroelastic stability. The report is divided in two parts. Part A describes the purely aerodynamic part, while Part B includes the aeroelastic part. In Part A a transition prediction algorithm based on a simplified version of the e{sup n} method is proposed. Laminar Boundary Layer instability data are stored in a database from which stability characteristics can be extracted by interpolation. Input to the database are laminar integral boundary layer parameters. These are computed from an integral boundary layer formulation coupled to a Navier-Stokes flow solver. Five different airfoils are considered at fixed angle of attack, and the flow is computed assuming both fully turbulent and transitional flow and compared with experimental data. Results indicate that using a transition model the drag prediction is improved considerably. Also the lift is slightly improved. At high angles of attack transition will affect leading edge separation which again will affect the overall vortex shedding. If the transition point is not properly predicted this will affect the whole hysteresis curve. The transition model developed in the present work showed more stable predictions compared to the empirical transition model. In Part B a simple three degrees-of-freedom (DOF) structural dynamics model is developed and coupled to the aerodynamics models from Part A. A 2nd order accurate time integration scheme is used to solve the equations of motion. Two airfoils are investigated. The aeroelastic models predict stable conditions well at low angle of attack. But at high angles of attack, and where unstable behaviour is expected, only the Navier-Stokes solver predict correct aeroelastic response. The semi-empirical dynamic stall model does not predict vortex shedding and moment correctly leading to an erroneous aerodynamic damping. (au) 5 tabs.; 55 ills., 52 refs.
Lyapunov functions to analyse stability regions of aeroelastic equation
Czech Academy of Sciences Publication Activity Database
Pospíšil, Stanislav; Náprstek, Jiří
Leuven : Katolieke Universiteit Leuven, 2011 - (Roeck, G.; Degrande, G.; Lombaert, G.; Műller, G.), s. 2035-2042 ISBN 9789076019314. [EURODYN2011 -International Conference on Structural Dynamics /8./. Leuven (BE), 04.06.2011-06.06.2011] R&D Projects: GA ČR(CZ) GA103/09/0094; GA AV ČR(CZ) IAA200710902 Institutional research plan: CEZ:AV0Z20710524 Keywords : nonlinear aeroelasticity * dynamic stability * Lyapunov function Subject RIV: JM - Building Engineering
On simulation of nonlinear aeroelastic problems by finite element method
Czech Academy of Sciences Publication Activity Database
Sváček, Petr; Horáček, Jaromír
Liége : Université de Liége, 2008, s. 1-10. [ACOMEN 2008 /4./. Liége (BE), 26.05.2008-28.05.2008] R&D Projects: GA AV ČR IAA200760613 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * RANS system * flutter Subject RIV: BI - Acoustics www.Itas.ulg.ac.be/acomen2008
Dynamic stability and post-critical behavior of aeroelastic systems
Czech Academy of Sciences Publication Activity Database
Náprstek, Jiří
Plzeň : University of West Bohemia, 2014 - (Adámek, V.). s. 95-96 ISBN 978-80-261-0429-2. [Computational mechanics 2014. Conference with international participation /30./. 03.11.2014-05.11.2014, Špičák] R&D Projects: GA ČR(CZ) GC13-34405J Institutional support: RVO:68378297 Keywords : dynamic stability * post-critical behavior * aeroelastic systems Subject RIV: JM - Building Engineering
AEROELASTIC FLUTTER ANALYSIS OF SUPERSONIC WING WITH MULTIPLE EXTERNAL STORES
Nur Azam; Erwin Sulaeman
2014-01-01
ABSTRACT: Flutter may be considered to be one of the most dangerous aeroelastic failure phenomenon. The flutter characteristic differs for each aircraft type, and depends on the wing geometry as well as its operational region of subsonic, transonic or supersonic speeds. Prior to performing a flight flutter test, extensive numerical simulations and Ground Vibration Test should be conducted where the structural finite element modes and the experimentation results should be matched, otherwise th...
Universal digital strain gauge measurement system of aeroelastic deformation development
Pavlov Anton; Arefiev Alexander
2016-01-01
This article presents description of the universal digital strain gauge system developed to measure the static and dynamic aeroelastic deformations of elasticity-scale models during the tests in aerodynamic tube and during in-flight tests of an experimental air vehicles. The main requirements for such devices are small size and possibility of operation in a wide temperature range. The article considers the dependence of zero offset from temperature. Functional diagram block and logic diagram ...
Continuation and Bifuration Analysis in Helicopter Aeroelastic Stability Problems
Rezgui, Djamel; Lowenberg, Mark H.; Jones, Mark; Monteggia, Claudio
2014-01-01
The dynamics of rotary wing systems are complex and typically feature highly nonlinear and often unsteady aerodynamics, as well as aeroelastic influences. In ongoing efforts to reduce noise and vibration, active devices such as trailing edge flaps on the rotor blades are being studied and these devices can introduce further nonlinearities. Therefore, it is important to be able to evaluate the stability of the overall system with a proper understanding of the global nonlinear behavior. Numeric...
Aeroelastic modal dynamics of wind turbines including anisotropic effects
Skjoldan, Peter Fisker; Hansen, Morten Hartvig; Rubak, Rune; Thomsen, Kenneth
2011-01-01
Several methods for aeroelastic modal analysis of a rotating wind turbine are developed and used to analyse the modal dynamics of two simplified models and a complex model in isotropic and anisotropic conditions. The Coleman transformation is used to enable extraction of the modal frequencies, damping, and periodic mode shapes of a rotating wind turbine by describing the rotor degrees of freedom in the inertial frame. This approach is valid only for an isotropic system. Anisotropic systems, e...
Design & modelling of a composite rudderless aeroelastic fin structure
Trapani, Matteo
2010-01-01
This thesis presents the study of a gapless and rudderless aeroelastic fin (GRAF) to enhance the directional stability and controllability of an aircraft. The GRAF concept was proposed and developed in the wake of previous research, targeted to improve flight performance and manoeuvrability, and to reduce fuel consumption and airframe weight. The study involved the subjects of aerodynamics, structural design and analysis, and flight mechanics. The work includes conceptual de...
Efficient Cfd/csd Coupling Methods for Aeroelastic Applications
Chen, Long; Xu, Tianhao; Xie, Jing
2016-06-01
A fast aeroelastic numerical simulation method using CFD/CSD coupling are developed. Generally, aeroelastic numerical simulation costs much time and significant hardware resources with CFD/CSD coupling. In this paper, dynamic grid method, full implicit scheme, parallel technology and improved coupling method are researched for efficiency simulation. An improved Delaunay graph mapping method is proposed for efficient dynamic grid deform. Hybrid grid finite volume method is used to solve unsteady flow fields. The dual time stepping method based on parallel implicit scheme is used in temporal discretization for efficiency simulation. An approximate system of linear equations is solved by the GMRES algorithm with a LU-SGS preconditioner. This method leads to a significant increase in performance over the explicit and LU-SGS implicit methods. A modification of LU-SGS is proposed to improve the parallel performance. Parallel computing overs a very effective way to improve our productivity in doing CFD/CFD coupling analysis. Improved loose coupling method is an efficiency way over the loose coupling method and tight coupling method. 3D wing's aeroelastic phenomenon is simulated by solving Reynolds-averaged Navier-Stokes equations using improved loose coupling method. The flutter boundary is calculated and agrees well with experimental data. The transonic hole is very clear in numerical simulation results.
CFD-based Analysis of Aeroelastic behavior of Supersonic Fins
Directory of Open Access Journals (Sweden)
Tianxing Cai
2011-02-01
Full Text Available The main goal of this paper is to analyze the flutter boundary, transient loads of a supersonic fin, and the flutter with perturbation. Reduced order mode (ROM based on Volterra Series is presented to calculate the flutter boundary, and CFD/CSD coupling is used to compute the transient aerodynamic load. The Volterra-based ROM is obtained using the derivative of unsteady aerodynamic step-response, and the infinite plate spline is used to perform interpolation of physical quantities between the fluid and the structural grids. The results show that inertia force plays a significant role in the transient loads, the moment cause by inertia force is lager than the aerodynamic force, because of the huge transient loads, structure may be broken by aeroelasticity below the flutter dynamic pressure. Perturbations of aircraft affect the aeroelastic response evident, the reduction of flutter dynamic pressure by rolling perturbation form 15.4% to 18.6% when Mach from 2.0 to 3.0. It is necessary to analyze the aeroelasticity behaviors under the compositive force environment.
Aeroelastic Optimization Study Based on the X-56A Model
Li, Wesley W.; Pak, Chan-Gi
2014-01-01
One way to increase the aircraft fuel efficiency is to reduce structural weight while maintaining adequate structural airworthiness, both statically and aeroelastically. A design process which incorporates the object-oriented multidisciplinary design, analysis, and optimization (MDAO) tool and the aeroelastic effects of high fidelity finite element models to characterize the design space was successfully developed and established. This paper presents two multidisciplinary design optimization studies using an object-oriented MDAO tool developed at NASA Armstrong Flight Research Center. The first study demonstrates the use of aeroelastic tailoring concepts to minimize the structural weight while meeting the design requirements including strength, buckling, and flutter. Such an approach exploits the anisotropic capabilities of the fiber composite materials chosen for this analytical exercise with ply stacking sequence. A hybrid and discretization optimization approach improves accuracy and computational efficiency of a global optimization algorithm. The second study presents a flutter mass balancing optimization study for the fabricated flexible wing of the X-56A model since a desired flutter speed band is required for the active flutter suppression demonstration during flight testing. The results of the second study provide guidance to modify the wing design and move the design flutter speeds back into the flight envelope so that the original objective of X-56A flight test can be accomplished successfully. The second case also demonstrates that the object-oriented MDAO tool can handle multiple analytical configurations in a single optimization run.
An improved stability characterization for aeroelastic energy harvesting applications
Javed, U.; Abdelkefi, A.; Akhtar, I.
2016-07-01
An enhanced stability characterization for aeroelastic energy harvesters is introduced by using both the normal form of the Hopf bifurcation and shooting method. Considering a triangular cylinder subjected to transverse galloping oscillations and a piezoelectric transducer to convert mechanical vibrations to electrical power, it is demonstrated that the nonlinear normal form is very beneficial to characterize the type of instability near bifurcation and determine the influence of structural and/or aerodynamic nonlinearities on the performance of the harvester. It is also shown that this tool is strong in terms of designing reliable aeroelastic energy harvesters. The results show that this technique can accurately predict the harvester's response only near bifurcation, however, cannot predict the stable solutions of the harvester when subcritical Hopf bifurcation takes place. To cover these drawbacks, the shooting method is employed. It turns out that this approach is beneficial in determining the stable and unstable solutions of the system and associated turning points. The results also show that the Floquet multipliers, obtained as the by-product of this method, can be used to characterize the response's type of the harvester. Thus, the normal form of the Hopf bifurcation and shooting method predictions can supplement each other to design stable and reliable aeroelastic energy harvesters.
Static Aeroelastic Analysis with an Inviscid Cartesian Method
Rodriguez, David L.; Aftosmis, Michael J.; Nemec, Marian; Smith, Stephen C.
2014-01-01
An embedded-boundary, Cartesian-mesh flow solver is coupled with a three degree-of-freedom structural model to perform static, aeroelastic analysis of complex aircraft geometries. The approach solves a nonlinear, aerostructural system of equations using a loosely-coupled strategy. An open-source, 3-D discrete-geometry engine is utilized to deform a triangulated surface geometry according to the shape predicted by the structural model under the computed aerodynamic loads. The deformation scheme is capable of modeling large deflections and is applicable to the design of modern, very-flexible transport wings. The coupling interface is modular so that aerodynamic or structural analysis methods can be easily swapped or enhanced. After verifying the structural model with comparisons to Euler beam theory, two applications of the analysis method are presented as validation. The first is a relatively stiff, transport wing model which was a subject of a recent workshop on aeroelasticity. The second is a very flexible model recently tested in a low speed wind tunnel. Both cases show that the aeroelastic analysis method produces results in excellent agreement with experimental data.
Experimental Aeroelastic Models Design and Wind Tunnel Testing for Correlation with New Theory
Directory of Open Access Journals (Sweden)
2016-04-01
Full Text Available Several examples of experimental model designs, wind tunnel tests and correlation with new theory are presented in this paper. The goal is not only to evaluate a new theory, new computational method or new aeroelastic phonomenon, but also to provide new insights into nonlinear aeroelastic phenomena, flutter, limit cycle oscillation (LCO and gust response.
Experimental Aeroelastic Models Design and Wind Tunnel Testing for Correlation with New Theory
Deman Tang; Dowell, Earl H.
2016-01-01
Several examples of experimental model designs, wind tunnel tests and correlation with new theory are presented in this paper. The goal is not only to evaluate a new theory, new computational method or new aeroelastic phonomenon, but also to provide new insights into nonlinear aeroelastic phenomena, flutter, limit cycle oscillation (LCO) and gust response.
DEFF Research Database (Denmark)
Gebhardt, Cristian; Veluri, Badrinath; Preidikman, Sergio;
2010-01-01
In this work an aeroelastic model that describes the interaction between aerodynamics and drivetrain dynamics of a large horizontal–axis wind turbine is presented. Traditional designs for wind turbines are based on the output of specific aeroelastic simulation codes. The output of these codes giv...
Design gridlines for integrated aeroelastic control of wind turbines - Task-12 report
DEFF Research Database (Denmark)
Mogensen, T.S.; Larsen, A.J.; Poulsen, N.K.; Politis, E.S.; Riziotis, V.; Engelen, T.G. van
The presented design guidelines for active aeroelastic control of PRVS wind turbines are derived by the partners of the project - Aeroelastic Stability and Control of Large Wind Turbines” (STABCON) partially funded by the European Commission (EC) under the contract NNK5-CT2002-00627. The objectiv...
Cole, Stanley R.; Garcia, Jerry L.
2000-01-01
The NASA Langley Transonic Dynamics Tunnel (TDT) has provided a unique capability for aeroelastic testing for forty years. The facility has a rich history of significant contributions to the design of many United States commercial transports, military aircraft, launch vehicles, and spacecraft. The facility has many features that contribute to its uniqueness for aeroelasticity testing, perhaps the most important feature being the use of a heavy gas test medium to achieve higher test densities. Higher test medium densities substantially improve model-building requirements and therefore simplify the fabrication process for building aeroelastically scaled wind tunnel models. Aeroelastic scaling for the heavy gas results in lower model structural frequencies. Lower model frequencies tend to a make aeroelastic testing safer. This paper will describe major developments in the testing capabilities at the TDT throughout its history, the current status of the facility, and planned additions and improvements to its capabilities in the near future.
Validation of Comprehensive Helicopter Aeroelastic Analysis with Experimental Data
Directory of Open Access Journals (Sweden)
Shrinivas R. Bhat
2004-10-01
Full Text Available The experimental data for a Cbladed soft-inplane hingeless main rotor is used to validate a comprehensive aeroelastic analysis. A finite element model has been developed for the rotorblade which predicts rotating frequencies quite well, across a range of rotation speeds. The helicopter is trimmed and the predicted trim-control angles are found to be In the range ofmeasured values for a variety of flight speeds. Power predictions over a range of forward speeds also compare well. Finally, the aeroelastlc analysis is used to study the Importance ofaerodynamic models on the vibration predict~onU. nsteady aerodynamics and free-wake models have been investigated.
Non-Linear Aeroelastic Stability of Wind Turbines
DEFF Research Database (Denmark)
Zhang, Zili; Sichani, Mahdi Teimouri; Li, Jie;
2013-01-01
non-linear aero-elasticity into consideration. The stability of the wind turbine is determined by the maximum Lyapunov exponent of the system, which is operated directly on the non-linear state vector differential equations. Numerical examples show that this approach is promising for stability...... identification of the non-linear wind turbine system.......As wind turbines increase in magnitude without a proportional increase in stiffness, the risk of dynamic instability is believed to increase. Wind turbines are time dependent systems due to the coupling between degrees of freedom defined in the fixed and moving frames of reference, which may...
Experimental Identification of Concentrated Nonlinearity in Aeroelastic System
Directory of Open Access Journals (Sweden)
Nayfeh Ali H
2012-07-01
Full Text Available Identification of concentrated nonlinearity in the torsional spring of an aeroelastic system is performed. This system consists of a rigid airfoil that is supported by a linear spring in the plunge motion and a nonlinear spring in the pitch motion. Quadratic and cubic nonlinearities in the pitch moment are introduced to model the concentrated nonlinearity. The representation of the aerodynamic loads by the Duhamel formulation yielded accurate values for the flutter speed and frequency. The results show that the use of the Duhamel formulation to represent the aerodynamic loads yields excellent agreement between the experimental data and the numerical predictions.
Aeroelastic Instability and Flutter for a 10 MW Wind Turbine
Vatne, Sigrid Ringdalen
2011-01-01
The goal of this thesis is to evaluate if flutter is a challenge to a 10 MW wind turbine. Flutter is an aeroelastic instability which occurs due to the interaction between the aerodynamic forces and the elasticity of the blade. Torsional motions of the blade lead to variations in the aerodynamic forces due to changes in the angle of attack of the airfoil. The variation in aerodynamic forces creates flapwise vibration of the blade. When the vibrations of the blades are in an unfavourable phase...
GAROS, an aeroelastic code for coupled fixed-rotating structures
Energy Technology Data Exchange (ETDEWEB)
Rees, M. [Aerodyn Energiestyseme GmbH, Rendsburg (Germany); Vollan, A. [Pilatus Flugzeugwerke, Stans (Switzerland)
1996-09-01
The GAROS (General Analysis of Rotating Structures) program system has been specially designed to calculate aeroelastic stability and dynamic response of horizontal axis wind energy converters. Nevertheless it is also suitable for the dynamic analysis of helicopter rotors and has been used in the analysis of car bodies taking account of rotating wheels. GAROS was developed over the last 17 years. In the following the mechanical and the aerodynamic model will be discussed in detail. A short overview of the solution methods for the equation of motion in time and frequency domain will ge given. After this one example for the FEM model of the rotor and tower will be discussed. (EG)
NRT Rotor Structural / Aeroelastic Analysis for the Preliminary Design Review
Energy Technology Data Exchange (ETDEWEB)
Ennis, Brandon Lee [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Paquette, Joshua A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2015-10-01
This document describes the initial structural design for the National Rotor Testbed blade as presented during the preliminary design review at Sandia National Laboratories on October 28- 29, 2015. The document summarizes the structural and aeroelastic requirements placed on the NRT rotor for satisfactory deployment at the DOE/SNL SWiFT experimental facility to produce high-quality datasets for wind turbine model validation. The method and result of the NRT blade structural optimization is also presented within this report, along with analysis of its satisfaction of the design requirements.
Parameter estimation of an aeroelastic aircraft using neural networks
Indian Academy of Sciences (India)
S C Raisinghani; A K Ghosh
2000-04-01
Application of neural networks to the problem of aerodynamic modelling and parameter estimation for aeroelastic aircraft is addressed. A neural model capable of predicting generalized force and moment coefficients using measured motion and control variables only, without any need for conventional normal elastic variables ortheirtime derivatives, is proposed. Furthermore, it is shown that such a neural model can be used to extract equivalent stability and control derivatives of a flexible aircraft. Results are presented for aircraft with different levels of flexibility to demonstrate the utility ofthe neural approach for both modelling and estimation of parameters.
Convergence acceleration of an aeroelastic Navier-Stokes solver
Obayashi, S.; Guruswamy, G.
1994-01-01
New capabilities have been added to a Navier-Stokes solver to perform steady-state simulations more efficiently. The flow solver for solving the Navier-Stokes equations is completely rewritten with a combination of the LU-SGS (Lower-Upper factored Symmetric Gauss-Seidel) implicit method and the modified HLLE (Harten-Lax-van Leer-Einfeldt) upwind scheme. A pseudo-time marching method is used for the directly coupled structural equations to improve overall convergence rates for static aeroelastic analysis. Results are demonstrated for transonic flows over rigid and flexible wings.
Aero-Elastic Optimization of a 10 MW Wind Turbine
DEFF Research Database (Denmark)
Zahle, Frederik; Tibaldi, Carlo; Verelst, David Robert;
2015-01-01
This article describes a multi-disciplinary optimization and analysis tool for wind turbines that is based on the open-source framework OpenMDAO. Interfaces to several simulation codes have been implemented which allows for a wide variety of problem formulations and combinations of models. In this...... article concurrent aeroelastic optimization of a 10 MW wind turbine rotor is carried out with respect to material distribution distribution and planform. The optimizations achieve up to 13% mass reduction while maintaining the same power production compared to the baseline DTU 10MW RWT....
Application of CFD based wave loads in aeroelastic calculations
DEFF Research Database (Denmark)
Schløer, Signe; Paulsen, Bo Terp; Bredmose, Henrik
2014-01-01
Two fully nonlinear irregular wave realizations with different significant wave heights are considered. The wave realizations are both calculated in the potential flow solver Ocean-Wave3D and in a coupled domain decomposed potential-flow CFD solver. The surface elevations of the calculated wave...... realizations compare well with corresponding surface elevations from laboratory experiments. In aeroelastic calculations of an offshore wind turbine on a monopile foundation the hydrodynamic loads due to the potential flow solver and Morison’s equation and the hydrodynamic loads calculated by the coupled...
Aeroelastic divergence modeled by means of the stochastic resonance
Czech Academy of Sciences Publication Activity Database
Náprstek, Jiří; Pospíšil, Stanislav
Brno : Brno University of Technology. Institute of Solid Mechanics, Mechatronics and Biomechanics, 2014 - (Fuis, V.), s. 420-423 ISBN 978-80-214-4871-1. ISSN 1805-8248. [Engineering Mechanics 2014 /20./. Svratka (CZ), 12.05.2014-15.05.2014] R&D Projects: GA ČR(CZ) GC13-34405J Institutional support: RVO:68378297 Keywords : stochastic resonance * interwell hopping * non-linear vibration * aeroelastic divergence Subject RIV: JM - Building Engineering http://www.itam.cas.cz/?pid=5
Optimal aeroelastic design of an oblique wing structure
Gwin, L. B.
1974-01-01
A procedure is presented for determining the optimal cover panel thickness of a wing structure to meet specified strength and static aeroelastic divergence requirements for minimum weight. Efficient reanalysis techniques using discrete structural and aerodynamic methods are used in conjunction with redesign algorithms driven by optimality criteria. The optimality conditions for the divergence constraint are established, and expressions are obtained for derivatives of the dynamic pressure at divergence with respect to design variables. The procedure is applied to an oblique wing aircraft where strength and stiffness are critical design considerations for sizing the cover thickness of the wing structure.
On the way to reliable aeroelastic load simulation on VAWT's
Larsen , Torben J.; Aagaard Madsen, Helge
2013-01-01
In this paper a method for an implementation of a 2D actuator cylinder flow model of an Vertical Axis Wind Turbine (VAWT) is presented. The model is implemented in a full aeroelastic code including consideration of structural dynamics, dynamic inflow, tower shadow and dynamic stall, which is needed for a full load analysis relating to eg. certification of a VAWT turbine. Further on, principal load cases according to the IEC61400-1 are simulated for a fictitious 5MW VAWT turbine in it’s simple...
Aeroelastic behavior of twist-coupled HAWT blades
Energy Technology Data Exchange (ETDEWEB)
Lobitz, D.W.; Veers, P.S.
1998-12-31
As the technology for horizontal axis wind turbines (HAWT) development matures, more novel techniques are required for the capture of additional amounts of energy, alleviation of loads and control of the rotor. One such technique employs the use of an adaptive blade that could sense the wind velocity or rotational speed in some fashion and accordingly modify its aerodynamic configuration to meet a desired objective. This could be achieved in either an active or passive manner, although the passive approach is much more attractive due to its simplicity and economy. As an example, a blade design might employ coupling between bending and/or extension, and twisting so that, as it bends and extends due to the action of the aerodynamic and inertial loads, it also twists modifying the aerodynamic performance in some way. These performance modifications also have associated aeroelastic effects, including effects on aeroelastic instability. To address the scope and magnitude of these effects a tool has been developed for investigating classical flutter and divergence of HAWT blades. As a starting point, an adaptive version of the uniform Combined Experiment Blade will be investigated. Flutter and divergence airspeeds will be reported as a function of the strength of the coupling and also be compared to those of generic blade counterparts.
Aeroelastic Instabilities of Large Offshore and Onshore Wind Turbines
International Nuclear Information System (INIS)
Offshore turbines are gaining attention as means to capture the immense and relatively calm wind resources available over deep waters. This paper examines the aeroelastic stability of a three-bladed 5MW conceptual wind turbine mounted atop a floating barge with catenary moorings. The barge platform was chosen from the possible floating platform concepts, because it is simple in design and easy to deploy. Aeroelastic instabilities are distinct from resonances and vibrations and are potentially more destructive. Future turbine designs will likely be stability-driven in contrast to the current loads-driven designs. Reasons include more flexible designs, especially the torsionally-flexible rotor blades, material and geometric couplings associated with smart structures, and hydrodynamic interactions brought on by the ocean currents and surface waves. Following a brief description of the stability concept and stability analysis approach, this paper presents results for both onshore and offshore configurations over a range of operating conditions. Results show that, unless special attention is paid, parked (idling) conditions can lead to instabilities involving side-to-side motion of the tower, edgewise motion of the rotor blades, and yawing of the platform
First-order aerodynamic and aeroelastic behavior of a single-blade installation setup
DEFF Research Database (Denmark)
Gaunaa, Mac; Bergami, Leonardo; Guntur, Srinivas;
2014-01-01
of arbitrary direction. The model is coupled with a schematic aeroelastic representation of the taglines system, which returns the minimum line tension required to compensate for the aerodynamic forcing. The simplified models are in excellent agreement with the aeroelastic code HAWC2, and provide a...... first-order aerodynamic and aeroelastic behavior of a single blade installation system, where the blade is grabbed by a yoke, which is lifted by the crane and stabilized by two taglines. A simple engineering model is formulated to describe the aerodynamic forcing on the blade subject to turbulent wind...
Data acquisition for aeroelastic testing at the NASA Langley Transonic Dynamics Facility
Doggett, Robert V., Jr.; Rosser, David C., Jr.; Bryant, Charles S.
1993-01-01
Aeroelasticity is defined and different types of aeroelastic tests are described. The instrumentation and data acquisition requirements dictated by the time varying characteristics of aeroelastic phenomena are pointed out. Instrumentation needs for various types of tests are discussed. The hardware components and operational features of the real-time, digital-computer-controlled data acquisition system used to support testing at the Langley Transonic Dynamics Facility, which includes a major wind-tunnel, a helicopter-model hover facility, and two model setup and calibration laboratories are described.
International Nuclear Information System (INIS)
Due to the increasing size and flexibility of large wind turbine blades, accurate and reliable aeroelastic modelling is playing an important role for the design of large wind turbines. Most existing aeroelastic models are linear models based on assumption of small blade deflections. This assumption is not valid anymore for very flexible blade design because such blades often experience large deflections. In this paper, a novel nonlinear aeroelastic model for large wind turbine blades has been developed by combining BEM (blade element momentum) theory and mixed-form formulation of GEBT (geometrically exact beam theory). The nonlinear aeroelastic model takes account of large blade deflections and thus greatly improves the accuracy of aeroelastic analysis of wind turbine blades. The nonlinear aeroelastic model is implemented in COMSOL Multiphysics and validated with a series of benchmark calculation tests. The results show that good agreement is achieved when compared with experimental data, and its capability of handling large deflections is demonstrated. Finally the nonlinear aeroelastic model is applied to aeroelastic modelling of the parked WindPACT 1.5 MW baseline wind turbine, and reduced flapwise deflection from the nonlinear aeroelastic model is observed compared to the linear aeroelastic code FAST (Fatigue, Aerodynamics, Structures, and Turbulence). - Highlights: • A novel nonlinear aeroelastic model for wind turbine blades is developed. • The model takes account of large blade deflections and geometric nonlinearities. • The model is reliable and efficient for aeroelastic modelling of wind turbine blades. • The accuracy of the model is verified by a series of benchmark calculation tests. • The model provides more realistic aeroelastic modelling than FAST (Fatigue, Aerodynamics, Structures, and Turbulence)
National Aeronautics and Space Administration — The need to accurately predict aeroelastic phenomenon for a wide range of Mach numbers is a critical step in the design process of any aerospace vehicle. Complex...
Novel Reduced Order in Time Models for Problems in Nonlinear Aeroelasticity Project
National Aeronautics and Space Administration — Research is proposed for the development and implementation of state of the art, reduced order models for problems in nonlinear aeroelasticity. Highly efficient and...
Linearized FUN3D for Rapid Aeroelastic and Aeroservoelastic Design and Analysis Project
National Aeronautics and Space Administration — The overall objective of this Phase I project is to develop a hybrid approach in FUN3D, referred herein to as the Linearized FUN3D, for rapid aeroelastic and...
Dynamic structural aeroelastic stability testing of the XV-15 tilt rotor research aircraft
Schroers, L. G.
1982-01-01
For the past 20 years, a significant effort has been made to understand and predict the structural aeroelastic stability characteristics of the tilt rotor concept. Beginning with the rotor-pylon oscillation of the XV-3 aircraft, the problem was identified and then subjected to a series of theoretical studies, plus model and full-scale wind tunnel tests. From this data base, methods were developed to predict the structural aeroelastic stability characteristics of the XV-15 Tilt Rotor Research Aircraft. The predicted aeroelastic characteristics are examined in light of the major parameters effecting rotor-pylon-wing stability. Flight test techniques used to obtain XV-15 aeroelastic stability are described. Flight test results are summarized and compared to the predicted values. Wind tunnel results are compared to flight test results and correlated with predicted values.
National Aeronautics and Space Administration — Stirling Dynamics Inc and the University of Washington propose to develop a MATLAB toolbox for rapid aeroelastic (AE) and aeroservoelastic (ASE) modeling, analysis...
Ashley, H.
1984-01-01
Graduate research activity in the following areas is reported: the divergence of laminated composite lifting surfaces, subsonic propeller theory and aeroelastic analysis, and cross sectional resonances in wind tunnels.
Coupled nonlinear aeroelasticity and flight dynamics of fully flexible aircraft
Su, Weihua
This dissertation introduces an approach to effectively model and analyze the coupled nonlinear aeroelasticity and flight dynamics of highly flexible aircraft. A reduced-order, nonlinear, strain-based finite element framework is used, which is capable of assessing the fundamental impact of structural nonlinear effects in preliminary vehicle design and control synthesis. The cross-sectional stiffness and inertia properties of the wings are calculated along the wing span, and then incorporated into the one-dimensional nonlinear beam formulation. Finite-state unsteady subsonic aerodynamics is used to compute airloads along lifting surfaces. Flight dynamic equations are then introduced to complete the aeroelastic/flight dynamic system equations of motion. Instead of merely considering the flexibility of the wings, the current work allows all members of the vehicle to be flexible. Due to their characteristics of being slender structures, the wings, tail, and fuselage of highly flexible aircraft can be modeled as beams undergoing three dimensional displacements and rotations. New kinematic relationships are developed to handle the split beam systems, such that fully flexible vehicles can be effectively modeled within the existing framework. Different aircraft configurations are modeled and studied, including Single-Wing, Joined-Wing, Blended-Wing-Body, and Flying-Wing configurations. The Lagrange Multiplier Method is applied to model the nodal displacement constraints at the joint locations. Based on the proposed models, roll response and stability studies are conducted on fully flexible and rigidized models. The impacts of the flexibility of different vehicle members on flutter with rigid body motion constraints, flutter in free flight condition, and roll maneuver performance are presented. Also, the static stability of the compressive member of the Joined-Wing configuration is studied. A spatially-distributed discrete gust model is incorporated into the time simulation
Development of an aeroelastic stability boundary for a rotor in autorotation
Trchalík, J.; Gillies, E.A.; Thomson, D. G.
2008-01-01
For the present study, a mathematical model AMRA was created to simulate the aeroelastic behaviour of a rotor during autorotation. Our model: Aeroelastic Model of a Rotor in Autorotation (AMRA) captures transverse bending and teeter, torsional twist and lag-wise motion of the rotor blade and hence it is used to investigate couplings between blade flapping, torsion and rotor speed. Lagrange’s method was used for the modelling of blade flapping and chord-wise bendi...
A modular method for the direct coupled aeroelastic simulation of free flying aircraft
Wellmer, Georg
2014-01-01
The present work describes the extension of an existing aeroelastic coupling environment to free-flying aircraft with rigid-body degrees of freedom. Aeroelasticity affects an aircraft in terms of performance, economics and operational safety. Therefore, fluid-structure interaction has to be taken into account early on in the design process. In the transonic regime non-linear effects preclude the application of linearised methods for the description of the flow field. Instead, Computational Fl...
Analysis of aeroelastic loads and their contributions to fatigue damage
International Nuclear Information System (INIS)
The paper presents an analysis of the aeroelastic loads on a wind turbine in normal operation. The characteristic of the loads causing the highest fatigue damage are identified, so to provide indications to the development of active load alleviation systems for smart- rotor applications. Fatigue analysis is performed using rain-flow counting and Palmgren-Miner linear damage assumption; the contribution to life-time fatigue damage from deterministic load variations is quantified, as well as the contributions from operation at different mean wind speeds. A method is proposed to retrieve an estimation of the load frequencies yielding the highest fatigue contributions from the bending moment spectra. The results are in good agreement with rain-flow counting analysis on filtered time series, and, for the blade loads, show dominant contributions from frequencies close to the rotational one; negligible fatigue contributions are reported for loads with frequencies above 2 Hz
The aeroelastic code HawC - model and comparisons
Energy Technology Data Exchange (ETDEWEB)
Thirstrup Petersen, J. [Risoe National Lab., The Test Station for Wind Turbines, Roskilde (Denmark)
1996-09-01
A general aeroelastic finite element model for simulation of the dynamic response of horizontal axis wind turbines is presented. The model has been developed with the aim to establish an effective research tool, which can support the general investigation of wind turbine dynamics and research in specific areas of wind turbine modelling. The model concentrates on the correct representation of the inertia forces in a form, which makes it possible to recognize and isolate effects originating from specific degrees of freedom. The turbine structure is divided into substructures, and nonlinear kinematic terms are retained in the equations of motion. Moderate geometric nonlinearities are allowed for. Gravity and a full wind field including 3-dimensional 3-component turbulence are included in the loading. Simulation results for a typical three bladed, stall regulated wind turbine are presented and compared with measurements. (au)
Aeroelastic modelling without the need for excessive computing power
Energy Technology Data Exchange (ETDEWEB)
Infield, D. [Loughborough Univ., Centre for Renewable Energy Systems Technology, Dept. of Electronic and Electrical Engineering, Loughborough (United Kingdom)
1996-09-01
The aeroelastic model presented here was developed specifically to represent a wind turbine manufactured by Northern Power Systems which features a passive pitch control mechanism. It was considered that this particular turbine, which also has low solidity flexible blades, and is free yawing, would provide a stringent test of modelling approaches. It was believed that blade element aerodynamic modelling would not be adequate to properly describe the combination of yawed flow, dynamic inflow and unsteady aerodynamics; consequently a wake modelling approach was adopted. In order to keep computation time limited, a highly simplified, semi-free wake approach (developed in previous work) was used. a similarly simple structural model was adopted with up to only six degrees of freedom in total. In order to take account of blade (flapwise) flexibility a simple finite element sub-model is used. Good quality data from the turbine has recently been collected and it is hoped to undertake model validation in the near future. (au)
Contribution to finite element modelling of airfoil aeroelastic instabilities
Directory of Open Access Journals (Sweden)
Horáček J.
2007-10-01
Full Text Available Nonlinear equations of motion for a flexibly supported rigid airfoil with additional degree of freedom for controlling of the profile motion by a trailing edge flap are derived for large vibration amplitudes. Preliminary results for numerical simulation of flow-induced airfoil vibrations in a laminar incompressible flow are presented for the NACA profile 0012 with three-degrees of freedom (vertical translation, rotation around the elastic axis and rotation of the flap. The developed numerical solution of the Navier – Stokes equations and the Arbitrary Eulerian-Lagrangian approach enable to consider the moving grid for the finite element modelling of the fluid flow around the oscillating airfoil. A sequence of numerical simulation examples is presented for Reynolds numbers up to about Re~10^5, when the system loses the aeroelastic stability, and when the large displacements of the profile and a post-critical behaviour of the system take place.
Identification of the stability parameters of an aeroelastic airplane
Rynaski, E. G.; Andrisani, D., II; Weingarten, N.
1978-01-01
The problem of the parameter identification of large scale dynamic systems involving a system matrix characterized by approximately 200 elements is addressed. By using phase variable transformations, a mathematical model of an aeroelastic airplane is described in a form that is amenable to partial or piecemeal acceptance of parameters estimated from flight data. A mathematical model of the U.S. Air Force Total In-Flight Simulator was computed using the FLEXSTAB digital computer program. As data became available during the progress of the flight test program, this data was processed and substituted in the mathematical model for parameters analytically obtained from the FLEXSTAB program. The results tend to show a progressive and orderly transition from an analytically defined mathematical model to one obtained from the flight tests of the actual aircraft.
KNOW-BLADE task-4 report: Navier-Stokes aeroelasticity
DEFF Research Database (Denmark)
Politis, E.S.; Nikolaou, I.G.; Chaviaropoulos, P.K.;
2004-01-01
wind turbine blade have been combined with 2D and 3D unsteady Navier-Stokes solvers. The relative disadvantage of the quasi-3D approach (where the elastic solver is coupled with a 2D Navier-Stokes solver) isits inability to model induced flow. The lack of a validation test case did not allow for......The problem of the aeroelastic stability of wind turbine blades is addressed in this report by advancing the aerodynamic modelling in the beam element type codes from the engineering-type empirical models to unsteady, 2D or 3D, Navier-Stokes solvers. Inthis project, structural models for the full...... in damping with the increase of wind speeds and in a minimum value for the damping for wind speedaround 15~m/s. The eigenvalue analyses resulted in steeper distributions for this mode. The agreement in aerodynamic damping decrease with the increase of wind speed is also observed in the distributions...
On the way to reliable aeroelastic load simulation on VAWT's
DEFF Research Database (Denmark)
Larsen, Torben J.; Aagaard Madsen, Helge
2013-01-01
In this paper a method for an implementation of a 2D actuator cylinder flow model of an Vertical Axis Wind Turbine (VAWT) is presented. The model is implemented in a full aeroelastic code including consideration of structural dynamics, dynamic inflow, tower shadow and dynamic stall, which is needed...... for a full load analysis relating to eg. certification of a VAWT turbine. Further on, principal load cases according to the IEC61400-1 are simulated for a fictitious 5MW VAWT turbine in it’s simplest 2 bladed Darrieus configuration. The IEC61400-1 load cases, originally developed for Horizontal Axis...... Wind Turbines (HAWT’s), are discussed regarding the application to VAWT’s. Further on a small section regarding aerodynamic flow in curved motion is included....
On the way to reliable aeroelastic load simulation on VAWT's
DEFF Research Database (Denmark)
Larsen, Torben J.; Aagaard Madsen, Helge
In this paper a method for an implementation of a 2D actuator cylinder flow model of an Vertical Axis Wind Turbine (VAWT) is presented. The model is implemented in a full aeroelastic code including consideration of structural dynamics, dynamic inflow, tower shadow and dynamic stall, which is needed...... for a full load analysis relating to eg. certification of a VAWT turbine. Further on, principal load cases according to the IEC61400-1 are simulated for a fictitious 5MW VAWT turbine in it’s simplest 2 bladed Darrieus configuration. The IEC61400-1 load cases, originally developed for Horizontal Axis...... Wind Turbines (HAWT’s), are discussed regarding the application to VAWT’s. Further on a small section regarding aerodynamic flow in curved motion is included....
National Aeronautics and Space Administration — The proposed research program will develop a physics-based identification, modeling and risk management infrastructure for aeroelastic transonic flutter and...
National Aeronautics and Space Administration — ZONA proposes a phase II effort to fully develop a comprehensive methodology for aeroelastic predictions of the nonlinear aerodynamic/aerothermodynamic - structure...
Research in aeroelasticity EFP-2002; Forskning i aeroelasticitet EFP-2002
Energy Technology Data Exchange (ETDEWEB)
Bak, Christian (ed.)
2004-02-01
This report contains results from the Energy Research Project 'Application, demonstration and further development of advanced aerodynamic and aeroelastic models' (EFP 2002), covering the time from July 1 2002 to December 31 2003. The partners in the project are Risoe National Labo-ratory (Risoe), The Technical University of Denmark (DTU), Bonus Energy A/S, LM Glasfiber A/S, NEG Micon A/S og Vestas Wind Systems A/S. In the project, Risoe and DTU have de-monstrated the application of their advanced computational methods on several different mega-Watt-size wind turbine designs. Compared to traditional methods the advanced methods have among other results shown: 1) that the aerodynamics at the blade tip for a wind turbine cannot be analysed correctly for a non-rotating blade. 2) that the drag coefficient distribution on a rotor in stand still according to Computational Fluid Dynamics should be increased from the blade root towards the blade tip. 3) that the maximum 2D lift coefficient in airfoil characteristics should be reduced at the blade tip and should be increased significantly on the inner part of the rotor. The drag coefficients should in general be increased for all sections on the blade, when the flow is separating. 4) that the choice of airfoil characteristics, aerodynamical as well as structural, are impor-tant for the loads, the noise and the design of a wind turbine. 5) that blade edgewise vibrations in stand still computed with an aeroelastic code are most critical around 40 deg. and 140 deg. angles of attack and that these vibrations depend completely on the given values of lift and drag. 6) that the energy production decreases in the case of large deflections of the blades. 7) that the blade flap eigenfrequency increases in the case of large deflections. 8) that there is an increased coupling between blade edge and blade torsional frequency in the case of large deflections. 9) that an overview of the dynamics for a wind turbine design can be
Aeroelastic modal dynamics of wind turbines including anisotropic effects
Energy Technology Data Exchange (ETDEWEB)
Fisker Skjoldan, P.
2011-03-15
Several methods for aeroelastic modal analysis of a rotating wind turbine are developed and used to analyse the modal dynamics of two simplified models and a complex model in isotropic and anisotropic conditions. The Coleman transformation is used to enable extraction of the modal frequencies, damping, and periodic mode shapes of a rotating wind turbine by describing the rotor degrees of freedom in the inertial frame. This approach is valid only for an isotropic system. Anisotropic systems, e.g., with an unbalanced rotor or operating in wind shear, are treated with the general approaches of Floquet analysis or Hill's method which do not provide a unique reference frame for observing the modal frequency, to which any multiple of the rotor speed can be added. This indeterminacy is resolved by requiring that the periodic mode shape be as constant as possible in the inertial frame. The modal frequency is thus identified as the dominant frequency in the response of a pure excitation of the mode observed in the inertial frame. A modal analysis tool based directly on the complex aeroelastic wind turbine code BHawC is presented. It uses the Coleman approach in isotropic conditions and the computationally efficient implicit Floquet analysis in anisotropic conditions. The tool is validated against system identifications with the partial Floquet method on the nonlinear BHawC model of a 2.3 MW wind turbine. System identification results show that nonlinear effects on the 2.3 MW turbine in most cases are small, but indicate that the controller creates nonlinear damping. In isotropic conditions the periodic mode shape contains up to three harmonic components, but in anisotropic conditions it can contain an infinite number of harmonic components with frequencies that are multiples of the rotor speed. These harmonics appear in calculated frequency responses of the turbine. Extreme wind shear changes the modal damping when the flow is separated due to an interaction between
AEROELASTIC FLUTTER ANALYSIS OF SUPERSONIC WING WITH MULTIPLE EXTERNAL STORES
Directory of Open Access Journals (Sweden)
Nur Azam
2014-12-01
Full Text Available ABSTRACT: Flutter may be considered to be one of the most dangerous aeroelastic failure phenomenon. The flutter characteristic differs for each aircraft type, and depends on the wing geometry as well as its operational region of subsonic, transonic or supersonic speeds. Prior to performing a flight flutter test, extensive numerical simulations and Ground Vibration Test should be conducted where the structural finite element modes and the experimentation results should be matched, otherwise the numerical simulation model must be rejected. In this paper, the analysis of simulation of a supersonic wing equipped with external missiles loaded on the wing is presented. The structural mode shapes at each generated frequency are also visually presented. The analysis is carried out using MSC Nastran FEM software. The wing flutter with the external stores was simulated at different altitudes. The result shows that the flutter velocity is sensitive to the flight altitude. For this reason, the flutter analysis is conducted also for a negative altitude. The negative altitude is obtained by considering the constant equivalent speed-Mach number rule at the flutter speed boundary as a requirement in standard regulation of transport aircraft. ABSTRAK: Salah satu fenomena kegagalan aeroelastik yang paling membahayakan adalah kipasan (flutter. Ciri-ciri kegagalan kipasan (flutter adalah berbeza untuk setiap jenis pesawat bergantung pada geometri sayap dan regim operasi sama ada subsonik, transonik atau supersonik. Sebelum melakukan ujian penerbangan kipasan , simulasi berangka luas dan ujian getaran peringkat bawahan (darat perlu dijalankan di mana struktur mod unsur terhingga dan keputusan eksperimen harus dipadankan, sebaliknya model simulasi berangka boleh ditolak. Dalam kertas kerja ini, simulasi sayap supersonik dilengkapi dengan beban luaran peluru berpandu di sayap telah dianalisis di daerah supersonik tinggi. Bentuk mod struktur pada setiap mod frekuensi
Improved Aerodynamic Influence Coefficients for Dynamic Aeroelastic Analyses
Gratton, Patrice
2011-12-01
Currently at Bombardier Aerospace, aeroelastic analyses are performed using the Doublet Lattice Method (DLM) incorporated in the NASTRAN solver. This method proves to be very reliable and fast in preliminary design stages where wind tunnel experimental results are often not available. Unfortunately, the geometric simplifications and limitations of the DLM, based on the lifting surfaces theory, reduce the ability of this method to give reliable results for all flow conditions, particularly in transonic flow. Therefore, a new method has been developed involving aerodynamic data from high-fidelity CFD codes which solve the Euler or Navier-Stokes equations. These new aerodynamic loads are transmitted to the NASTRAN aeroelastic module through improved aerodynamic influence coefficients (AIC). A cantilevered wing model is created from the Global Express structural model and a set of natural modes is calculated for a baseline configuration of the structure. The baseline mode shapes are then combined with an interpolation scheme to deform the 3-D CFD mesh necessary for Euler and Navier-Stokes analyses. An uncoupled approach is preferred to allow aerodynamic information from different CFD codes. Following the steady state CFD analyses, pressure differences ( DeltaCp), calculated between the deformed models and the original geometry, lead to aerodynamic loads which are transferred to the DLM model. A modal-based AIC method is applied to the aerodynamic matrices of NASTRAN based on a least-square approximation to evaluate aerodynamic loads of a different wing configuration which displays similar types of mode shapes. The methodology developed in this research creates weighting factors based on steady CFD analyses which have an equivalent reduced frequency of zero. These factors are applied to both the real and imaginary part of the aerodynamic matrices as well as all reduced frequencies used in the PK-Method which solves flutter problems. The modal-based AIC method
Flight Dynamics of Flexible Aircraft with Aeroelastic and Inertial Force Interactions
Nguyen, Nhan T.; Tuzcu, Ilhan
2009-01-01
This paper presents an integrated flight dynamic modeling method for flexible aircraft that captures coupled physics effects due to inertial forces, aeroelasticity, and propulsive forces that are normally present in flight. The present approach formulates the coupled flight dynamics using a structural dynamic modeling method that describes the elasticity of a flexible, twisted, swept wing using an equivalent beam-rod model. The structural dynamic model allows for three types of wing elastic motion: flapwise bending, chordwise bending, and torsion. Inertial force coupling with the wing elasticity is formulated to account for aircraft acceleration. The structural deflections create an effective aeroelastic angle of attack that affects the rigid-body motion of flexible aircraft. The aeroelastic effect contributes to aerodynamic damping forces that can influence aerodynamic stability. For wing-mounted engines, wing flexibility can cause the propulsive forces and moments to couple with the wing elastic motion. The integrated flight dynamics for a flexible aircraft are formulated by including generalized coordinate variables associated with the aeroelastic-propulsive forces and moments in the standard state-space form for six degree-of-freedom flight dynamics. A computational structural model for a generic transport aircraft has been created. The eigenvalue analysis is performed to compute aeroelastic frequencies and aerodynamic damping. The results will be used to construct an integrated flight dynamic model of a flexible generic transport aircraft.
Aeroelastic Stability Investigations for Large-scale Vertical Axis Wind Turbines
Owens, B. C.; Griffith, D. T.
2014-06-01
The availability of offshore wind resources in coastal regions, along with a high concentration of load centers in these areas, makes offshore wind energy an attractive opportunity for clean renewable electricity production. High infrastructure costs such as the offshore support structure and operation and maintenance costs for offshore wind technology, however, are significant obstacles that need to be overcome to make offshore wind a more cost-effective option. A vertical-axis wind turbine (VAWT) rotor configuration offers a potential transformative technology solution that significantly lowers cost of energy for offshore wind due to its inherent advantages for the offshore market. However, several potential challenges exist for VAWTs and this paper addresses one of them with an initial investigation of dynamic aeroelastic stability for large-scale, multi-megawatt VAWTs. The aeroelastic formulation and solution method from the BLade Aeroelastic STability Tool (BLAST) for HAWT blades was employed to extend the analysis capability of a newly developed structural dynamics design tool for VAWTs. This investigation considers the effect of configuration geometry, material system choice, and number of blades on the aeroelastic stability of a VAWT, and provides an initial scoping for potential aeroelastic instabilities in large-scale VAWT designs.
Directory of Open Access Journals (Sweden)
Pezhman Mardanpour
2015-01-01
Full Text Available Energy efficiency plays important role in aeroelastic design of flying wing aircraft and may be attained by use of lightweight structures as well as solar energy. NATASHA (Nonlinear Aeroelastic Trim And Stability of HALE Aircraft is a newly developed computer program which uses a nonlinear composite beam theory that eliminates the difficulties in aeroelastic simulations of flexible high-aspect-ratio wings which undergoes large deformation, as well as the singularities due to finite rotations. NATASHA has shown that proper engine placement could significantly increase the aeroelastic flight envelope which typically leads to more flexible and lighter aircraft. The areas of minimum kinetic energy for the lower frequency modes are in accordance with the zones with maximum flutter speed and have the potential to save computational effort. Another aspect of energy efficiency for High Altitude, Long Endurance (HALE drones stems from needing to minimize energy consumption because of limitations on the source of energy, that is, solar power. NATASHA is capable of simulating the aeroelastic passive morphing maneuver (i.e., morphing without relying on actuators and at as near zero energy cost as possible of the aircraft so as the solar panels installed on the wing are in maximum exposure to sun during different time of the day.
Aeroelastic Stability Investigations for Large-scale Vertical Axis Wind Turbines
International Nuclear Information System (INIS)
The availability of offshore wind resources in coastal regions, along with a high concentration of load centers in these areas, makes offshore wind energy an attractive opportunity for clean renewable electricity production. High infrastructure costs such as the offshore support structure and operation and maintenance costs for offshore wind technology, however, are significant obstacles that need to be overcome to make offshore wind a more cost-effective option. A vertical-axis wind turbine (VAWT) rotor configuration offers a potential transformative technology solution that significantly lowers cost of energy for offshore wind due to its inherent advantages for the offshore market. However, several potential challenges exist for VAWTs and this paper addresses one of them with an initial investigation of dynamic aeroelastic stability for large-scale, multi-megawatt VAWTs. The aeroelastic formulation and solution method from the BLade Aeroelastic STability Tool (BLAST) for HAWT blades was employed to extend the analysis capability of a newly developed structural dynamics design tool for VAWTs. This investigation considers the effect of configuration geometry, material system choice, and number of blades on the aeroelastic stability of a VAWT, and provides an initial scoping for potential aeroelastic instabilities in large-scale VAWT designs
Aeroelastic stability analyses of two counter rotating propfan designs for a cruise missile model
Mahajan, Aparajit J.; Lucero, John M.; Mehmed, Oral; Stefko, George L.
1992-01-01
Aeroelastic stability analyses were performed to insure structural integrity of two counterrotating propfan blade designs for a NAVY/Air Force/NASA cruise missile model wind tunnel test. This analysis predicted if the propfan designs would be flutter free at the operating conditions of the wind tunnel test. Calculated stability results are presented for the two blade designs with rotational speed and Mach number as the parameters. A aeroelastic analysis code ASTROP2 (Aeroelastic Stability and Response of Propulsion Systems - 2 Dimensional Analysis), developed at LeRC, was used in this project. The aeroelastic analysis is a modal method and uses the combination of a finite element structural model and two dimensional steady and unsteady cascade aerodynamic models. This code was developed to analyze single rotation propfans but was modified and applied to counterrotating propfans for the present work. Modifications were made to transform the geometry and rotation of the aft rotor to the same reference frame as the forward rotor, to input a non-uniform inflow into the rotor being analyzed, and to automatically converge to the least stable aeroelastic mode.
Aeroelastic scaling laws for gust load alleviation control system
Institute of Scientific and Technical Information of China (English)
Tang Bo; Wu Zhigang; Yang Chao
2016-01-01
Gust load alleviation (GLA) tests are widely conducted to study the effectiveness of the control laws and methods. The physical parameters of models in these tests are aeroelastic scaled, while the scaling of GLA control system is always unreached. This paper concentrates on studying the scaling laws of GLA control system. Through theoretical demonstration, the scaling criterion of a classical PID control system has been come up and a scaling methodology is provided and veri-fied. By adopting the scaling laws in this paper, gust response of the scaled model could be directly related to the full-scale aircraft theoretically under both open-loop and closed-loop conditions. Also, the influences of different scaling choices of an important non-dimensional parameter, the Froude number, have been studied in this paper. Furthermore for practical application, a compen-sating method is given when the theoretical scaled actuators or sensors cannot be obtained. Also, the scaling laws of some non-linear elements in control system such as the rate and amplitude sat-urations in actuator have been studied and examined by a numerical simulation.
Aeroelastic scaling laws for gust load alleviation control system
Directory of Open Access Journals (Sweden)
Tang Bo
2016-02-01
Full Text Available Gust load alleviation (GLA tests are widely conducted to study the effectiveness of the control laws and methods. The physical parameters of models in these tests are aeroelastic scaled, while the scaling of GLA control system is always unreached. This paper concentrates on studying the scaling laws of GLA control system. Through theoretical demonstration, the scaling criterion of a classical PID control system has been come up and a scaling methodology is provided and verified. By adopting the scaling laws in this paper, gust response of the scaled model could be directly related to the full-scale aircraft theoretically under both open-loop and closed-loop conditions. Also, the influences of different scaling choices of an important non-dimensional parameter, the Froude number, have been studied in this paper. Furthermore for practical application, a compensating method is given when the theoretical scaled actuators or sensors cannot be obtained. Also, the scaling laws of some non-linear elements in control system such as the rate and amplitude saturations in actuator have been studied and examined by a numerical simulation.
Stability analysis of an aeroelastic system with friction
Institute of Scientific and Technical Information of China (English)
Tan Tiancai; Li Min; Liu Baihui
2013-01-01
In this paper,harmonic balance method,exact formulation and numerical simulation method are adopted to study the effects of different friction stiffness on the stability of 1.5 degrees of freedom aeroelastic system.On this basis,the expressions of input energy and dissipated energy are deduced,and the energy method is used to reveal the mechanisms of the stable boundary and unstable boundary existing in the system and the effects of different friction stiffness on the stability of the system.Studies have shown that the stability region and the critical aerodynamic damping ratio of the system rise with the increase of the friction stiffness,while the friction stiffness has little effect on the stability boundary.In the analysis of the stability of system,the results of harmonic balance method,exact formulation and Newmark of numerical simulation method are in good agreement.Compared with exact formulation and numerical simulation method,the concept and conclusion of harmonic balance method are simple in the system stability analysis.
Gust Buffeting and Aeroelastic Behaviour of Poles and Monotubular Towers
Solari, G.; Pagnini, L. C.
1999-10-01
The evolution in the constructional field and the realization of ever more slender and light structures have emphasized the increasing difficulty of properly evaluating the actions and effects of wind on poles and monotubular towers. Faced with this situation the Italian constructors, united in a consortium coordinated by ACS ACAI Servizi, entrusted the Department of Structural and Geotechnical Engineering of Genova University with the task of formulating an ad hoc calculation procedure for this type of structure. This gave rise to a wide-ranging research project in which theoretical models, experimental evaluations and engineering methods were developed in parallel through an effective and quite a unique co-operation between researchers, designers and builders. This paper illustrates the physical aspects, the general principles and the basic formulation of the method proposed, with special emphasis on gust buffeting and aeroelastic phenomena. Preliminary results of full-scale measurements of the structural damping are also presented. The conclusions highlight the scientific and technical perspectives of this research.
Control Application of Piezoelectric Materials to Aeroelastic Self-Excited Vibrations
Directory of Open Access Journals (Sweden)
Mohammad Amin Rashidifar
2014-01-01
Full Text Available A method for application of piezoelectric materials to aeroelasticity of turbomachinery blades is presented. The governing differential equations of an overhung beam are established. The induced voltage in attached piezoelectric sensors due to the strain of the beam is calculated. In aeroelastic self-excited vibrations, the aerodynamic generalized force of a specified mode can be described as a linear function of the generalized coordinate and its derivatives. This simplifies the closed loop system designed for vibration control of the corresponding structure. On the other hand, there is an industrial interest in measurement of displacement, velocity, acceleration, or a contribution of them for machinery condition monitoring. Considering this criterion in quadratic optimal control systems, a special style of performance index is configured. Utilizing the current relations in an aeroelastic case with proper attachment of piezoelectric elements can provide higher margin of instability and lead to lower vibration magnitude.
Edwards, J. W.; Malone, J. B.
1992-01-01
The current status of computational methods for unsteady aerodynamics and aeroelasticity is reviewed. The key features of challenging aeroelastic applications are discussed in terms of the flowfield state: low-angle high speed flows and high-angle vortex-dominated flows. The critical role played by viscous effects in determining aeroelastic stability for conditions of incipient flow separation is stressed. The need for a variety of flow modeling tools, from linear formulations to implementations of the Navier-Stokes equations, is emphasized. Estimates of computer run times for flutter calculations using several computational methods are given. Application of these methods for unsteady aerodynamic and transonic flutter calculations for airfoils, wings, and configurations are summarized. Finally, recommendations are made concerning future research directions.
Static Aeroelastic Analysis of Transonic Wind Tunnel Models Using Finite Element Methods
Hooker, John R.; Burner, Alpheus W.; Valla, Robert
1997-01-01
A computational method for accurately predicting the static aeroelastic deformations of typical transonic transport wind tunnel models is described. The method utilizes a finite element method (FEM) for predicting the deformations. Extensive calibration/validation of this method was carried out using a novel wind-off wind tunnel model static loading experiment and wind-on optical wing twist measurements obtained during a recent wind tunnel test in the National Transonic Facility (NTF) at NASA LaRC. Further validations were carried out using a Navier-Stokes computational fluid dynamics (CFD) flow solver to calculate wing pressure distributions about several aeroelastically deformed wings and comparing these predictions with NTF experimental data. Results from this aeroelastic deformation method are in good overall agreement with experimentally measured values. Including the predicted deformations significantly improves the correlation between CFD predicted and experimentally measured wing & pressures.
First-order aerodynamic and aeroelastic behavior of a single-blade installation setup
Gaunaa, M.; Bergami, L.; Guntur, S.; Zahle, F.
2014-06-01
Limitations on the wind speed at which blade installation can be performed bears important financial consequences. The installation cost of a wind farm could be significantly reduced by increasing the wind speed at which blade mounting operations can be carried out. This work characterizes the first-order aerodynamic and aeroelastic behavior of a single blade installation system, where the blade is grabbed by a yoke, which is lifted by the crane and stabilized by two taglines. A simple engineering model is formulated to describe the aerodynamic forcing on the blade subject to turbulent wind of arbitrary direction. The model is coupled with a schematic aeroelastic representation of the taglines system, which returns the minimum line tension required to compensate for the aerodynamic forcing. The simplified models are in excellent agreement with the aeroelastic code HAWC2, and provide a solid basis for future design of an upgraded single blade installation system able to operate at higher wind speeds.
First-order aerodynamic and aeroelastic behavior of a single-blade installation setup
International Nuclear Information System (INIS)
Limitations on the wind speed at which blade installation can be performed bears important financial consequences. The installation cost of a wind farm could be significantly reduced by increasing the wind speed at which blade mounting operations can be carried out. This work characterizes the first-order aerodynamic and aeroelastic behavior of a single blade installation system, where the blade is grabbed by a yoke, which is lifted by the crane and stabilized by two taglines. A simple engineering model is formulated to describe the aerodynamic forcing on the blade subject to turbulent wind of arbitrary direction. The model is coupled with a schematic aeroelastic representation of the taglines system, which returns the minimum line tension required to compensate for the aerodynamic forcing. The simplified models are in excellent agreement with the aeroelastic code HAWC2, and provide a solid basis for future design of an upgraded single blade installation system able to operate at higher wind speeds
Wang, James M.
1991-01-01
The aeroelastic stability of a shaft-fixed bearingless rotor is analyzed in wind-tunnel tests for a wide range of operating conditions in order to determine whether such a system could be made aeroelastically stable without incorporating auxiliary dampers. The model rotor and blade properties are determined and used as an input to a bearingless-rotor analysis. Theoretical predictions are compared with experimental results in hover and forward flights. The analysis predicts the lag mode damping satisfactorily for collective pitch between 5 deg and 10 deg; however, the quasi-steady linear aerodynamic modeling overpredicts the damping values for higher collective pitch settings. It is noted that soft blade pitch links improve aeroelastic stability in hover and at low advance ratio.
Reduced problem of non-linear aeroelastic stability and relevant post-critical states
Czech Academy of Sciences Publication Activity Database
Pospíšil, Stanislav; Náprstek, Jiří
Prague : Institute of Thermomechanics AS CR, v. v. i., 2008 - (Fuis, V.; Pásek, M.), s. 201-210 ISBN 978-80-87012-11-6. [Engineering Mechanics 2008. Svratka (CZ), 12.05.2008-15.05.2008] R&D Projects: GA ČR(CZ) GA103/05/2396; GA ČR(CZ) GC103/07/J060; GA ČR(CZ) GA103/06/0099 Institutional research plan: CEZ:AV0Z20710524 Keywords : aeroelastic instability * post-critical behaviour * aeroelastic forces Subject RIV: JM - Building Engineering
Formulation of the aeroelastic stability and response problem of coupled rotor/support systems
Warmbrodt, W.; Friedmann, P.
1979-01-01
The consistent formulation of the governing nonlinear equations of motion for a coupled rotor/support system is presented. Rotor/support coupling is clearly documented by enforcing dynamic equilibrium between the rotor and the moving flexible support. The nonlinear periodic coefficient equations of motion are applicable to both coupled rotor/fuselage aeroelastic problems of helicopters in hover or forward flight and coupled rotor/tower dynamics of a large horizontal axis wind turbine (HAWT). Finally, the equations of motion are used to study the influence of flexible supports and nonlinear terms on rotor aeroelastic stability and response of a large two-bladed HAWT.
The influence of turbulence on the aero-elastic instability of wind turbines
DEFF Research Database (Denmark)
Zhang, Zili; Nielsen, Søren R.K.
2014-01-01
negative aerodynamic damping. A 13-degree-of-freedom (13-DOF) wind turbine model is developed using Euler-Lagrange equations, which includes the couplings of the tower-blade-drivetrain vibration, the quasi-static aeroelasticity and a collective pitch controller. Numerical simulations are carried out using...... data calibrated to the NREL 5 MW baseline wind turbine. Aeroelastic stability of the wind turbine system has been evaluated for various values of the rated generator torque, the rated rotational speed of the rotor, the mean wind speed and the turbulence intensity. Critical turbulence intensity, at...
Proposed Wind Turbine Aeroelasticity Studies Using Helicopter Systems Analysis
Ladkany, Samaan G.
1998-01-01
Advanced systems for the analysis of rotary wing aeroelastic structures (helicopters) are being developed at NASA Ames by the Rotorcraft Aeromechanics Branch, ARA. The research has recently been extended to the study of wind turbines, used for electric power generation Wind turbines play an important role in Europe, Japan & many other countries because they are non polluting & use a renewable source of energy. European countries such as Holland, Norway & France have been the world leaders in the design & manufacture of wind turbines due to their historical experience of several centuries, in building complex wind mill structures, which were used in water pumping, grain grinding & for lumbering. Fossil fuel cost in Japan & in Europe is two to three times higher than in the USA due to very high import taxes. High fuel cost combined with substantial governmental subsidies, allow wind generated power to be competitive with the more traditional sources of power generation. In the USA, the use of wind energy has been limited mainly because power production from wind is twice as expensive as from other traditional sources. Studies conducted at the National Renewable Energy Laboratories (NREL) indicate that the main cost in the production of wind turbines is due to the materials & the labor intensive processes used in the construction of turbine structures. Thus, for the US to assume world leadership in wind power generation, new lightweight & consequently very flexible wind turbines, that could be economically mass produced, would have to be developed [4,5]. This effort, if successful, would result in great benefit to the US & the developing nations that suffer from overpopulation & a very high cost of energy.
International Nuclear Information System (INIS)
In the preliminary design stage of wind turbine blade, faster and simpler methods are preferred to predict the aeroelastic response of the blades in order to get an idea about the appropriateness of the blade stiffness. Therefore, in the present study, applicability of the quasi-steady aeroelastic analysis of wind turbine blade is investigated in terms of how accurately the quasi-steady aeroelastic analysis predicts the deformed state of the blade at certain azimuthal positions. For this purpose, comparative study of transient and quasi-steady aeroelastic analysis of a composite wind turbine blade in steady wind conditions is conducted. To perform the transient analysis, a multi-body wind turbine model is generated with almost rigid components except for the dynamic superelement blade that is inverse designed. Transient analysis of the multi body wind turbine system is performed by imposing constant rotational speed to the main shaft and bypassing the controller. Quasi-steady aeroelastic analysis of the same composite wind turbine blade is performed, by coupling a structural finite element solver with a blade element momentum tool, in steady wind conditions at different azimuthal positions including the effect of the centrifugal and gravitational forces. Results show that for the wind turbine system taken as the case study, reasonably good agreement is obtained between the tip deflections and flapwise root shear forces determined by the transient aeroelastic analysis of the wind turbine and quasi-steady aeroelastic analysis of the blade only
Aeroelasticity and structural optimization of composite helicopter rotor blades with swept tips
Yuan, K. A.; Friedmann, P. P.
1995-01-01
This report describes the development of an aeroelastic analysis capability for composite helicopter rotor blades with straight and swept tips, and its application to the simulation of helicopter vibration reduction through structural optimization. A new aeroelastic model is developed in this study which is suitable for composite rotor blades with swept tips in hover and in forward flight. The hingeless blade is modeled by beam type finite elements. A single finite element is used to model the swept tip. Arbitrary cross-sectional shape, generally anisotropic material behavior, transverse shears and out-of-plane warping are included in the blade model. The nonlinear equations of motion, derived using Hamilton's principle, are based on a moderate deflection theory. Composite blade cross-sectbnal properties are calculated by a separate linear, two-dimensional cross section analysis. The aerodynamic loads are obtained from quasi-steady, incompressible aerodynamics, based on an implicit formulation. The trim and steady state blade aeroelastic response are solved in a fully coupled manner. In forward flight, where the blade equations of motion are periodic, the coupled trim-aeroelastic response solution is obtained from the harmonic balance method. Subsequently, the periodic system is linearized about the steady state response, and its stability is determined from Floquet theory.
Nonlinear aeroelastic behavior of an oscillating airfoil during stall-induced vibration
Sarkar, S.; Bijl, H.
2008-08-01
In this paper, nonlinear aeroelastic behavior of a two-dimensional symmetric rotor blade in the dynamic stall regime is investigated. Two different oscillation models have been considered here: pitching oscillation and flap edgewise oscillation. Stall aeroelastic instability in such systems can potentially lead to structural damage. Hence it is an important design concern, especially for wind turbines and helicopter rotors, where such modes of oscillation are likely to take place. Most previous analyses of such dynamical systems are not exhaustive. System parameters like structural nonlinearity or initial conditions have not been studied which could play a significant role on the overall dynamics. In the present paper, a parametric study on the aeroelastic instability and the nonlinear dynamical behavior of the system has been performed. Emphasis is given on the effect of structural nonlinearity and initial conditions. The aerodynamic loads in the dynamic stall regime have been computed using the Onera model. The qualitative influence of the system parameters is different in the two systems studied. The effect of structural nonlinearity on the bifurcation pattern of the system response is significant in the case of pitching oscillation. The initial condition plays an important role on the aeroelastic stability as well as on the bifurcation pattern in both the systems. In the forced response study, interesting dynamical behavior, like period-3 response, has been observed in the pitching oscillation case. On the other hand, for the flap edgewise oscillation case, super-harmonic and quasi-harmonic response have been found.
Aeroelastic experiments with measurement of the kinematic properties based on optical methods
Czech Academy of Sciences Publication Activity Database
Chládek, Štěpán; Zolotarev, Igor
2015-01-01
Roč. 21, č. 1 (2015), s. 43-53. ISSN 1803-9782 R&D Projects: GA ČR GA13-10527S Institutional support: RVO:61388998 Keywords : aeroelasticity * optical measurements * vibration frequencies * kinematic properties * profile in the wind tunnel Subject RIV: BI - Acoustics
Maximized Gust Loads of a Closed-Loop, Nonlinear Aeroelastic System Using Nonlinear Systems Theory
Silva, Walter A.
1999-01-01
The problem of computing the maximized gust load for a nonlinear, closed-loop aeroelastic aircraft is discusses. The Volterra theory of nonlinear systems is applied in order to define a linearized system that provides a bounds on the response of the nonlinear system of interest. The method is applied to a simplified model of an Airbus A310.
On the approximation of a nonlinear aeroelastic problem by finite elment method
Czech Academy of Sciences Publication Activity Database
Sváček, P.; Horáček, Jaromír
Cambridge, USA : Massachusetts Institute of Technology, 2007. s. 39-39. [Fourth M.I.T. Conference on Computational Fluid and Solid Mechanics. 13.06.2007-15.06.2007, Cambridge] R&D Projects: GA AV ČR IAA200760613 Institutional research plan: CEZ:AV0Z20760514 Keywords : numerical simulations * aeroelastic instability * ALE method Subject RIV: BI - Acoustics
Modelling of Random Aeroelastic Stability Effects of Slender Beam in Post-Critical State
Czech Academy of Sciences Publication Activity Database
Náprstek, Jiří
Tokyo : University of Tokyo, 2000 - (Yoshikawa, N.), s. 9-16 [Japan Conference of Structural Safety an Reliability. Tokyo (JP), 06.11.2000-08.11.2000] R&D Projects: GA MŠk ME 154 Keywords : Lyapunov function, aeroelastic vibrations, stability. Subject RIV: JN - Civil Engineering
Reduced-order LPV model of flexible wind turbines from high fidelity aeroelastic codes
DEFF Research Database (Denmark)
Adegas, Fabiano Daher; Sønderby, Ivan Bergquist; Hansen, Morten Hartvig; Stoustrup, Jakob
Linear aeroelastic models used for stability analysis of wind turbines are commonly of very high order. These high-order models are generally not suitable for control analysis and synthesis. This paper presents a methodology to obtain a reduced-order linear parameter varying (LPV) model from a se...
Aeroelastic tailoring using lamination parameters: drag reduction of a Formula One rear wing
Thuwis, G.A.A.; De Breuker, R.; Abdalla, M.M.; Gürdal, Z.
2009-01-01
The aim of the present work is to passively reduce the induced drag of the rear wing of a Formula One car at high velocity through aeroelastic tailoring. The angle-of-attack of the rear wing is fixed and is determined by the required downforce needed to get around a turn. As a result, at higher velo
Low-fidelity 2D isogeometric aeroelastic optimization with application to a morphing airfoil
Gillebaart, E.; De Breuker, R.
2015-01-01
Low-fidelity isogeometric aeroelastic analysis has not received much attention since the introduction of the isogeometric analysis (IGA) concept, while the combination of IGA and the boundary element method in the form of the potential flow theory shows great potential. This paper presents a two-dim
Swept Blade Aero-Elastic Model for a Small Wind Turbine (Presentation)
Energy Technology Data Exchange (ETDEWEB)
Damiani, R.; Lee, S.; Larwood, S.
2014-07-01
A preprocessor for analyzing preswept wind turbines using the in-house aero-elastic tool coupled with a multibody dynamic simulator was developed. A baseline 10-kW small wind turbine with straight blades and various configurations that featured bend-torsion coupling via blade-tip sweep were investigated to study their impact on ultimate loads and fatigue damage equivalent loads.
Development and Analysis of a Swept Blade Aeroelastic Model for a Small Wind Turbine (Presentation)
Energy Technology Data Exchange (ETDEWEB)
Preus, R.; Damiani, R.; Lee, S.; Larwood, S.
2014-06-01
As part of the U.S. Department-of-Energy-funded Competitiveness Improvement Project, the National Renewable Energy Laboratory (NREL) developed new capabilities for aeroelastic modeling of precurved and preswept blades for small wind turbines. This presentation covers the quest for optimized rotors, computer-aided engineering tools, a case study, and summary of the results.
Energy Technology Data Exchange (ETDEWEB)
Doessing, M.
2011-05-15
During the last decades the annual energy produced by wind turbines has increased dramatically and wind turbines are now available in the 5MW range. Turbines in this range are constantly being developed and it is also being investigated whether turbines as large as 10-20MW are feasible. The design of very large machines introduces new problems in the practical design, and optimization tools are necessary. These must combine the dynamic effects of both aerodynamics and structure in an integrated optimization environment. This is referred to as aeroelastic optimization. The Risoe DTU optimization software HAWTOPT has been used in this project. The quasi-steady aerodynamic module have been improved with a corrected blade element momentum method. A structure module has also been developed which lays out the blade structural properties. This is done in a simplified way allowing fast conceptual design studies and with focus on the overall properties relevant for the aeroelastic properties. Aeroelastic simulations in the time domain were carried out using the aeroelastic code HAWC2. With these modules coupled to HAWTOPT, optimizations have been made. In parallel with the developments of the mentioned numerical modules, focus has been on analysis and a fundamental understanding of the key parameters in wind turbine design. This has resulted in insight and an effective design methodology is presented. Using the optimization environment a 5MW wind turbine rotor has been optimized for reduced fatigue loads due to apwise bending moments. Among other things this has indicated that airfoils for wind turbine blades should have a high lift coefficient. The design methodology proved to be stable and a help in the otherwise challenging task of numerical aeroelastic optimization. (Author)
Application of Aeroelastic Solvers Based on Navier-Stokes Equations
Keith, Theo G., Jr.; Srivastava, Rakesh
1998-01-01
A pre-release version of the Navier-Stokes solver (TURBO) was obtained from MSU. Along with Dr. Milind Bakhle of the University of Toledo, subroutines for aeroelastic analysis were developed and added to the TURBO code to develop versions 1 and 2 of the TURBO-AE code. For specified mode shape, frequency and inter-blade phase angle the code calculates the work done by the fluid on the rotor for a prescribed sinusoidal motion. Positive work on the rotor indicates instability of the rotor. The version 1 of the code calculates the work for in-phase blade motions only. In version 2 of the code, the capability for analyzing all possible inter-blade phase angles, was added. The version 2 of TURBO-AE code was validated and delivered to NASA and the industry partners of the AST project. The capabilities and the features of the code are summarized in Refs. [1] & [2]. To release the version 2 of TURBO-AE, a workshop was organized at NASA Lewis, by Dr. Srivastava and Dr. M. A. Bakhle, both of the University of Toledo, in October of 1996 for the industry partners of NASA Lewis. The workshop provided the potential users of TURBO-AE, all the relevant information required in preparing the input data, executing the code, interpreting the results and bench marking the code on their computer systems. After the code was delivered to the industry partners, user support was also provided. A new version of the Navier-Stokes solver (TURBO) was later released by MSU. This version had significant changes and upgrades over the previous version. This new version was merged with the TURBO-AE code. Also, new boundary conditions for 3-D unsteady non-reflecting boundaries, were developed by researchers from UTRC, Ref. [3]. Time was spent on understanding, familiarizing, executing and implementing the new boundary conditions into the TURBO-AE code. Work was started on the phase lagged (time-shifted) boundary condition version (version 4) of the code. This will allow the users to calculate non
National Aeronautics and Space Administration — Research is proposed for the development of a state-of-the-art computational aeroelastic tool. This tool will include various levels of fidelity and the ability to...
1990-01-01
The dynamic response of Sandia National Laboratories' 34-m Darrieus rotor wind turbine at Bushland, Texas, is presented. The formulation used a double-multiple streamtube aerodynamic model with a turbulent airflow and included the effects of linear aeroelastic forces. The structural analysis used established procedures with the program MSC/NASTRAN. The effects of aeroelastic forces on the damping of natural modes agree well with previous results at operating rotor speeds, but show some discrepancies at very high rotor speeds. A number of alternative expressions for the spectrum of turbulent wind were investigated. The model loading represented by each does not differ significantly; a more significant difference is caused by imposing a full lateral coherence of the turbulent flow. Spectra of the predicted stresses at various locations show that without aeroelastic forces, very severe resonance is likely to occur at certain natural frequencies. Inclusion of aeroelastic effects greatly attenuates this stochastic response, especially in modes involving in-plane blade bending.
1973-01-01
The aerodynamic characteristics of transport aircraft with oblique wing flying at supersonic speeds are discussed. Aeroelastic divergence of the forward swept portion of the wing is analyzed. The effect of aspect ratio as a method for avoiding aeroelastic divergence is examined. A relatively low aspect ratio appears necessary for an oblique wing when constructed of conventional aluminum alloy materials. The aspect ratio may be increased by increasing the wing thickness ratio and by utilizing materials with higher moduli of elasticity and rigidity.
Evaluation of Aeroelastically Tailored Small Wind Turbine Blades Final Project Report
Energy Technology Data Exchange (ETDEWEB)
Griffin, Dayton A.
2005-09-29
Evaluation of Aeroelastically Tailored Small Wind Turbine Blades Final Report Global Energy Concepts, LLC (GEC) has performed a conceptual design study concerning aeroelastic tailoring of small wind turbine blades. The primary objectives were to evaluate ways that blade/rotor geometry could be used to enable cost-of-energy reductions by enhancing energy capture while constraining or mitigating blade costs, system loads, and related component costs. This work builds on insights developed in ongoing adaptive-blade programs but with a focus on application to small turbine systems with isotropic blade material properties and with combined blade sweep and pre-bending/pre-curving to achieve the desired twist coupling. Specific goals of this project are to: (A) Evaluate and quantify the extent to which rotor geometry can be used to realize load-mitigating small wind turbine rotors. Primary aspects of the load mitigation are: (1) Improved overspeed safety affected by blades twisting toward stall in response to speed increases. (2) Reduced fatigue loading affected by blade twisting toward feather in response to turbulent gusts. (B) Illustrate trade-offs and design sensitivities for this concept. (C) Provide the technical basis for small wind turbine manufacturers to evaluate this concept and commercialize if the technology appears favorable. The SolidWorks code was used to rapidly develop solid models of blade with varying shapes and material properties. Finite element analyses (FEA) were performed using the COSMOS code modeling with tip-loads and centripetal accelerations. This tool set was used to investigate the potential for aeroelastic tailoring with combined planform sweep and pre-curve. An extensive matrix of design variables was investigated, including aerodynamic design, magnitude and shape of planform sweep, magnitude and shape of blade pre-curve, material stiffness, and rotor diameter. The FEA simulations resulted in substantial insights into the structural
Friedmann, Peretz P.
1992-01-01
This paper presents a review of the state-of-the-art in the field of structural optimization when applied to vibration reduction of helicopters in forward flight with aeroelastic and multidisciplinary constraints. It emphasizes the application of the modern approach where the optimization is formulated as a mathematical programming problem and the objective function consists of the vibration levels at the hub and behavior constraints are imposed on the blade frequencies, aeroelastic stability margins as well as on a number of additional ingredients which can have a significant effect on the overall performance and flight mechanics of the helicopter. It is shown that the integrated multidisciplinary optimization of rotorcraft offers the potential for substantial improvements which can be achieved by careful preliminary design and analysis without requiring additional hardware such as rotor vibration absorbers or isolation systems.
Wind energy conversion. Volume X. Aeroelastic stability of wind turbine rotor blades
Energy Technology Data Exchange (ETDEWEB)
Wendell, J.
1978-09-01
The nonlinear equations of motion of a general wind turbine rotor blade are derived from first principles. The twisted, tapered blade may be preconed out of the plane of rotation, and its root may be offset from the axis of rotation by a small amount. The aerodynamic center, center of mass, shear center, and area centroid are distinct in this derivation. The equations are applicable to studies of forced response or of aeroelastic flutter, however, neither gravity forcing, nor wind shear and gust forcing are included. The equations derived are applied to study the aeroelastic stability of the NASA-ERDA 100 kW wind turbine, and solved using the Galerkin method. The numerical results are used in conjunction with a mathematical comparison to prove the validity of an equivalent hinge model developed by the Wind Energy Conversion Project at the Massachusetts Institute of Technology.
Multivariable flight control synthesis and literal robustness analysis for an aeroelastic vehicle
Schmidt, David K.; Newman, Brett
1990-01-01
An integrated flight/aeroelastic control law is developed analytically for a hypothetical large supersonic transport aircraft in which the first aeroelastic mode frequency of the fuselage (6 rad/sec) is near the short-period mode (2 rad/sec). The approach employed is based on a linear-quadratic-regulator (LQR) formulation (yielding model-following state-feedback gains), followed by asymptotic loop-transfer recovery of LQR robustness (to produce an output-feedback control law). The derivation is outlined, and numerical results comparing the performance and multivariate stability robustness of the present controller with those of a classical controller are presented in graphs. The two controllers are shown to have similar characteristics, even with respect to the sources of limitations on robustness.
Presentations from the Aeroelastic Workshop - latest results from AeroOpt
Energy Technology Data Exchange (ETDEWEB)
Hartvig Hansen, M. (ed.)
2011-10-15
This report contains the slides of the presentations at the Aeroelastic Workshop held at Risoe-DTU for the wind energy industry in Denmark on October 27, 2011. The scientific part of the agenda at this workshop was 1) Detailed and reduced models of dynamic mooring system (Anders M. Hansen). 2) Bend-twist coupling investigation in HAWC2 (Taeseong Kim). 3) Q3UIC - A new aerodynamic airfoil tool including rotational effects (Nestor R. Garcia). 4) Influence of up-scaling on loads, control and aerodynamic modeling (Helge Aa. Madsen). 5) Aerodynamic damping of lateral tower vibrations (Bjarne S. Kallesoee). 6) Open- and closed-loop aeroservoelastic analysis with HAWCStab2 (Morten H. Hansen). 7) Design and test of a thick, flatback, high-lift multielement airfoil (Frederik Zahle). The presented results are mainly obtained in the EUDP project ''Aeroelastic Optimization of MW Wind Turbines (AeroOpt)''. (Author)
Aeroelastic Flutter Behavior of Cantilever within a Nozzle-Diffuser Geometry
Tosi, Luis Phillipe; Colonius, Tim; Sherrit, Stewart; Lee, Hyeong Jae
2015-11-01
Aeroelastic flutter arises when the motion of a structure and its surrounding flowing fluid are coupled in a constructive manner, causing large amplitudes of vibration in the immersed solid. A cantilevered beam in axial flow within a nozzle-diffuser geometry exhibits interesting resonance behavior that presents good prospects for internal flow energy harvesting. Different modes can be excited as a function of throat velocity, nozzle geometry, fluid and cantilever material parameters. This work explores the relationship between the aeroelastic flutter instability boundaries and relevant non-dimensional parameters via experiments. Results suggest that for a linear expansion diffuser geometry, a non-dimensional stiffness, non-dimensional mass, and non-dimensional throat size are the critical parameters in mapping the instability. This map can serve as a guide to future work concerning possible electrical output and failure prediction in energy harvesters.
Janetzke, D. C.; Murthy, D. V.
1991-01-01
Aeroelastic analysis is mult-disciplinary and computationally expensive. Hence, it can greatly benefit from parallel processing. As part of an effort to develop an aeroelastic analysis capability on a distributed-memory transputer network, a parallel algorithm for the computation of aerodynamic influence coefficients is implemented on a network of 32 transputers. The aerodynamic influence coefficients are calculated using a three-dimensional unsteady aerodynamic model and a panel discretization. Efficiencies up to 85 percent are demonstrated using 32 processors. The effects of subtask ordering, problem size and network topology are presented. A comparison to results on a shared-memory computer indicates that higher speedup is achieved on the distributed-memory system.
Energy Technology Data Exchange (ETDEWEB)
Jonkman, J. M.; Sclavounos, P. D.
2006-01-01
Aeroelastic simulation tools are routinely used to design and analyze onshore wind turbines, in order to obtain cost effective machines that achieve favorable performance while maintaining structural integrity. These tools employ sophisticated models of wind-inflow; aerodynamic, gravitational, and inertial loading of the rotor, nacelle, and tower; elastic effects within and between components; and mechanical actuation and electrical responses of the generator and of control and protection systems. For offshore wind turbines, additional models of the hydrodynamic loading in regular and irregular seas, the dynamic coupling between the support platform motions and wind turbine motions, and the dynamic characterization of mooring systems for compliant floating platforms are also important. Hydrodynamic loading includes contributions from hydrostatics, wave radiation, and wave scattering, including free surface memory effects. The integration of all of these models into comprehensive simulation tools, capable of modeling the fully coupled aeroelastic and hydrodynamic responses of floating offshore wind turbines, is presented.
Presentations from the Aeroelastic Workshop – latest results from AeroOpt
DEFF Research Database (Denmark)
Hansen, Morten Hartvig
This report contains the slides of the presentations at the Aeroelastic Workshop held at Risø-DTU for the wind energy industry in Denmark on January 27, 2011. The scientific part of the agenda at this workshop was • Anisotropic beam element in HAWC2 for modelling of composite lay-ups (Taeseong Kim......) • Nonlinear beam element in HAWC2 for modelling of mooring systems (Bjarne Kallesøe) • Enhanced BEM including wake expansion and swirl (Christian Bak) • Unsteady viscous-inviscid interactive airfoil code for wind turbines (Néstor Ramos García) • PIV measurements on model scale wind turbine in water channel...... (Niels N. Sørensen) • Status of airfoil design and plans for wind tunnel tests of new thick airfoils (Christian Bak) The presented results are mainly obtained in the EUDP project “Aeroelastic Optimization of MW Wind Turbines (AeroOpt)” funded under contract no. 63011-0190....
Enhanced aeroelastic energy harvesting by exploiting combined nonlinearities: theory and experiment
International Nuclear Information System (INIS)
Converting aeroelastic vibrations into electricity for low power generation has received growing attention over the past few years. In addition to potential applications for aerospace structures, the goal is to develop alternative and scalable configurations for wind energy harvesting to use in wireless electronic systems. This paper presents modeling and experiments of aeroelastic energy harvesting using piezoelectric transduction with a focus on exploiting combined nonlinearities. An airfoil with plunge and pitch degrees of freedom (DOF) is investigated. Piezoelectric coupling is introduced to the plunge DOF while nonlinearities are introduced through the pitch DOF. A state-space model is presented and employed for the simulations of the piezoaeroelastic generator. A two-state approximation to Theodorsen aerodynamics is used in order to determine the unsteady aerodynamic loads. Three case studies are presented. First the interaction between piezoelectric power generation and linear aeroelastic behavior of a typical section is investigated for a set of resistive loads. Model predictions are compared to experimental data obtained from the wind tunnel tests at the flutter boundary. In the second case study, free play nonlinearity is added to the pitch DOF and it is shown that nonlinear limit-cycle oscillations can be obtained not only above but also below the linear flutter speed. The experimental results are successfully predicted by the model simulations. Finally, the combination of cubic hardening stiffness and free play nonlinearities is considered in the pitch DOF. The nonlinear piezoaeroelastic response is investigated for different values of the nonlinear-to-linear stiffness ratio. The free play nonlinearity reduces the cut-in speed while the hardening stiffness helps in obtaining persistent oscillations of acceptable amplitude over a wider range of airflow speeds. Such nonlinearities can be introduced to aeroelastic energy harvesters (exploiting
, Pinar Acar
2011-01-01
Two analytical flutter solution approaches have been developed to optimize two and three dimensional aircraft wing structures with design criteria based on aeroelastic instabilities. The first approach uses open loop structural dynamics and stability analysis for a two dimensional wing model in order to obtain the critical speeds of flutter, divergence and control reversal for optimization process. The second approach involves a flutter solution for three dimensional wing structures by using ...
The aeroelasticity research project 2004[Wind turbines]; Forskning i aeroelasticitet EFP-2004
Energy Technology Data Exchange (ETDEWEB)
Bak, C.
2005-05-01
The report presents the results of the project ''Programme for Applied Aeroelasticity'', the Danish Energy Research Programme 2004. The main results are: 1) Based on an analysis of the NREL/NASA experiment with a wind turbine in a wind tunnel a new model is formulated for 3D corrections of profile data for aeroelastic codes. Use of the model on three rotors suggests that the load distribution is determined more correctly than in existing 3D models. 2) A near-wake model, originally developed for aerodynamic loads on helicopter rotors, is implemented for calculating dynamic induction on wind turbine rotors. The model has several advantages to the other normally used model BEM. 3) A detailed comparison of the aeroelastic models FLEX5 and HAWC shows that there are no model differences that can result in large differences in the calculated loads. The comparison shows that differences in the calculated loads are due to the use of the models. 4) A model for pitch-servo dynamics on a modern wind turbine is formed and implemented in HAWC2. The conclusion from analysis of the importance of the pitch-servo characteristics showed that coupling between structure/aerodynamics and pitch actuator may be of importance, especially for the loads on the actuator itself. Also large deflections are coupled to the pitch moment and thus also to torsion of the wing and wing bearing. 5) An un-linear stability analysis has been performed in which periodic loads are included and compared to a linear analysis used in HAWCStab. For a profile with near zero aerodynamic damping in one oscillation direction, the aerodynamic force in this direction depends mostly of the square on the profile's speed. The linear damping is changed only a little by the profile's forced oscillation. It is assumed that the present HAWCStab can predict the mean aeroelastic damping for turbines' oscillations in operation. (LN)
Aero-elastic stability of airfoil flow using 2-D CFD
Energy Technology Data Exchange (ETDEWEB)
Johansen, J. [Risoe National Lab., Roskilde (Denmark)
1999-03-01
A three degrees-of-freedom structural dynamics model has been coupled to a two-dimensional incompressible CFD code. The numerical investigation considers aero-elastic stability for two different airfoils; the NACA0012 and the LM 2 18 % airfoils. Stable and unstable configurations and limit cycle oscillations are predicted in accordance with literature for the first airfoil. An attempt to predict stall induced edge-wise vibrations on a wind turbine airfoil fails using this two-dimensional approach. (au)
A Cybernetic Approach to Assess the Longitudinal Handling Qualities of Aeroelastic Aircraft
Damveld, H.J.
2009-01-01
The future demand for larger and lighter civil transport aircraft leads to more flexible aircraft, which bring their own controlling and handling problems. A review of established handling qualities methods showed that they were either unsuitable for aeroelastic aircraft, or had significant disadvantages. After consideration of the basic principles behind a number of handling qualities methods, a new handling qualities method was developed, the Experimental Behavior Measurement Method (EBMM)....
Preliminary observations of impact stress using an aeroelastic model of voice production
Czech Academy of Sciences Publication Activity Database
Horáček, Jaromír; Laukkanen, A. M.; Šidlof, Petr
London: The Royal Academy of Music , 2005 - (Howard, D.; Abberton, E.; Rubin, J.). s. 3-3 ISBN 1-905351-01-1. [PEVOC-6. 31.08.2005-03.09.2005, Londýn] R&D Projects: GA AV ČR(CZ) IAA2076401 Institutional research plan: CEZ:AV0Z20760514 Keywords : biomechanic of voice * aeroelasticity * vibration of vocal folds Subject RIV: BI - Acoustics
On the state stability of a system of integro-differential equations of nonstationary aeroelasticity
Energy Technology Data Exchange (ETDEWEB)
Egorov, A.I.; Kogut, P.I. [Dnepropetrovsk Institute of Railroad Transport (Russian Federation)
1994-06-05
We consider a process of nonstationary aeroelasticity, which is described by a system of integro-differential equations that cannot be solved for the derivative. We formulate necessary and sufficient conditions, in terms of Lyapunov functionals, for the exponential stability of such a system with respect to the metric of an infinite Hilbert space. A formula is given for the total derivative of a Lyapunov functional via the initial equations of motion. 5 refs.
Studying aeroelastic behavior of aircraft with NeoCASS. : The Danbus configuration
Sánches Manzano, María De Las Mercedes
2011-01-01
This Master Thesis assesses the performance of NeoCASS software as a tool for structural sizing for deformable aircraft at conceptual design level. NeoCASS is a collection of Matlab modules included in CEASIOM. Some testcases (simple wing model, TCR, Danbus, Agard 445.6 wing) are computed to evaluate the aeroelastic behavior and provide additional validation on the structural models NeoCASS computes Finally, Danbus, a new conceptual design aircraft, is analyzed with the software.
Chiarelli, Mario Rosario; Bonomo, Salvatore
2016-01-01
This paper presents a study of transonic wings whose planform shape is curved. Using fluid structure interaction analyses, the dynamic instability conditions were investigated by including the effects of the transonic flow field around oscillating wings. To compare the dynamic aeroelastic characteristics of the curved wing configuration, numerical analyses were carried out on a conventional swept wing and on a curved planform wing. The results confirm that, for a curved planform wing, the dyn...
Parallel Nonlinear Aeroelastic Computation for Fighter Wings in the Transonic Region
Larsen, Bradley Robert
2015-01-01
In this dissertation, a parallel three-dimensional aeroelastic simulation is appliedto current and next generation fighter aircraft wings. The computational model is anonlinear fluid and structural mesh coupled using the Direct Eulerian-Langrangianmethod. This method attaches unique local coordinates to each node and connectsthe fluid mesh to the structure in such a way that a transformation preserved to theglobal coordinates. This allows the fluid and structure to be updated in the sametime ...
Hassan Abba Musa; Dr. A. Mohammed
2016-01-01
In current practice, the predictive analysis of stochastic problems encompasses a variety of statistical techniques from modeling, machine, and data mining that analyse current and historical facts to make predictions about future. Therefore, this research uses an AR Model whose codes are incorporated in the MATLAB software to predict possible aero-elastic effects of Lekki Bridge based on its existing parametric data and the conditions around the bridge. It was seen that, the fluc...
Aeroelastic Computations of a Compressor Stage Using the Harmonic Balance Method
Reddy, T. S. R.
2010-01-01
The aeroelastic characteristics of a compressor stage were analyzed using a computational fluid dynamic (CFD) solver that uses the harmonic balance method to solve the governing equations. The three dimensional solver models the unsteady flow field due to blade vibration using the Reynolds-Averaged Navier-Stokes equations. The formulation enables the study of the effect of blade row interaction through the inclusion of coupling modes between blade rows. It also enables the study of nonlinear effects of high amplitude blade vibration by the inclusion of higher harmonics of the fundamental blade vibration frequency. In the present work, the solver is applied to study in detail the aeroelastic characteristics of a transonic compressor stage. Various parameters were included in the study: number of coupling modes, blade row axial spacing, and operating speeds. Only the first vibration mode is considered with amplitude of oscillation in the linear range. Both aeroelastic stability (flutter) of rotor blade and unsteady loading on the stator are calculated. The study showed that for the stage considered, the rotor aerodynamic damping is not influenced by the presence of the stator even when the axial spacing is reduced by nearly 25 percent. However, the study showed that blade row interaction effects become important for the unsteady loading on the stator when the axial spacing is reduced by the same amount.
An Aeroelastic Perspective of Floating Offshore Wind Turbine Wake Formation and Instability
Rodriguez, Steven N.; Jaworski, Justin W.
2015-11-01
The wake formation and wake stability of floating offshore wind turbines are investigated from an aeroelastic perspective. The aeroelastic model is composed of the Sebastian-Lackner free-vortex wake aerodynamic model coupled to the nonlinear Hodges-Dowell beam equations, which are extended to include the effects of blade profile asymmetry, higher-order torsional effects, and kinetic energy components associated with periodic rigid-body motions of floating platforms. Rigid-body platform motions are also assigned to the aerodynamic model as varying inflow conditions to emulate operational rotor-wake interactions. Careful attention is given to the wake formation within operational states where the ratio of inflow velocity to induced velocity is over 50%. These states are most susceptible to aerodynamic instabilities, and provide a range of states about which a wake stability analysis can be performed. In addition, the stability analysis used for the numerical framework is implemented into a standalone free-vortex wake aerodynamic model. Both aeroelastic and standalone aerodynamic results are compared to evaluate the level of impact that flexible blades have on the wake formation and wake stability.
Ippolito, Corey; Nguyen, Nhan; Lohn, Jason; Dolan, John
2014-01-01
The emergence of advanced lightweight materials is resulting in a new generation of lighter, flexible, more-efficient airframes that are enabling concepts for active aeroelastic wing-shape control to achieve greater flight efficiency and increased safety margins. These elastically shaped aircraft concepts require non-traditional methods for large-scale multi-objective flight control that simultaneously seek to gain aerodynamic efficiency in terms of drag reduction while performing traditional command-tracking tasks as part of a complete guidance and navigation solution. This paper presents results from a preliminary study of a notional multi-objective control law for an aeroelastic flexible-wing aircraft controlled through distributed continuous leading and trailing edge control surface actuators. This preliminary study develops and analyzes a multi-objective control law derived from optimal linear quadratic methods on a longitudinal vehicle dynamics model with coupled aeroelastic dynamics. The controller tracks commanded attack-angle while minimizing drag and controlling wing twist and bend. This paper presents an overview of the elastic aircraft concept, outlines the coupled vehicle model, presents the preliminary control law formulation and implementation, presents results from simulation, provides analysis, and concludes by identifying possible future areas for research
Coupled Aeroelastic Oscillations of a Turbine Blade Row in 3D Transonic Flow
Institute of Scientific and Technical Information of China (English)
Vitaly Gnesin; Lyubov Kolodyazhnaya; Romuald Rzadkowski
2001-01-01
This paper presents the mutual time - marching method to predict the aeroelastic stability of an oscillating blade row in 3D transonic flow. The ideal gas flow through a blade row is governed by the time dependent Euler equations in conservative form which are integrated by using the explicit monotonous second order accurate Godunov-Kolgan finite volume scheme and moving hybrid H-O grid. The structure analysis uses the modal approach and 3D finite element dynamic model of blade. The blade movement is assumed as a linear combination of the fast modes of blade natural oscillations with the modal coefficients depending on time. To demonstrate the capability and correctness of the method, two experimentally investigated test cases have been selected, in which the blades had performed tuned harmonic bending or torsional vibrations (The 1th and 4th standard configurations of the "Workshop on Aeroelasticity in Turbomachines" by Bolcs and Fransson, 1986). The calculated results of aeroelastic behaviour of the blade row (4th standard configuration), are presented over a wide frequency range under different start regimes of interblade phase angle.
Real-time simulation of aeroelastic rotor loads for horizontal axis wind turbines
International Nuclear Information System (INIS)
Wind turbine drivetrain research and test facilities with hardware-in-the-loop capabilities require a robust and accurate aeroelastic real-time rotor simulation environment. Recent simulation environments do not guarantee a computational response at real-time. Which is why a novel simulation tool has been developed. It resolves the physical time domain of the turbulent wind spectra and the operational response of the turbine at real-time conditions. Therefore, there is a trade-off between accuracy of the physical models and the computational costs. However, the study shows the possibility to preserve the necessary computational accuracy while simultaneously granting dynamic interaction with the aeroelastic rotor simulation environment. The achieved computational costs allow a complete aeroelastic rotor simulation at a resolution frequency of 100 Hz on standard computer platforms. Results obtained for the 5-MW reference wind turbine by the National Renewable Energy Laboratory (NREL) are discussed and compared to NREL's fatigue, aerodynamics, structures, and turbulence (FAST)- Code. The rotor loads show a convincing match. The novel simulation tool is applied to the wind turbine drivetrain test facility at the Center for Wind Power Drives (CWD), RWTH Aachen University to show the real-time hardware-in-the-loop capabilities
Otsuka, Keisuke; Makihara, Kanjuro
2016-05-01
Morphing wings have been developed by several organizations for a variety of applications including the changing of flight ability while in the air and reducing the amount of space required to store an aircraft. One such example of morphing wings is the deployable wing that is expected to be used for Mars exploration. When designing wings, aeroelastic simulation is important to prevent the occurrence of destructive phenomena while the wing is in use. Flutter and divergence are typical issues to be addressed. However, it has been difficult to simulate the aeroelastic motion of deployable wings because of the significant differences between these deployable wings and conventional designs. The most apparent difference is the kinematic constraints of deployment, typically a hinge joint. These constraints lead not only to deformation but also to rigid body rotation. This research provides a novel method of overcoming the difficulties associated with handling these kinematic constraints. The proposed method utilizes flexible multibody dynamics and absolute nodal coordinate formulation to describe the dynamic motion of a deployable wing. This paper presents the simulation of the rigid body rotation around the kinematic constraints as induced by the aeroelasticity. The practicality of the proposed method is confirmed.
Aeroelasticity of Axially Loaded Aerodynamic Structures for Truss-Braced Wing Aircraft
Nguyen, Nhan; Ting, Eric; Lebofsky, Sonia
2015-01-01
This paper presents an aeroelastic finite-element formulation for axially loaded aerodynamic structures. The presence of axial loading causes the bending and torsional sitffnesses to change. For aircraft with axially loaded structures such as the truss-braced wing aircraft, the aeroelastic behaviors of such structures are nonlinear and depend on the aerodynamic loading exerted on these structures. Under axial strain, a tensile force is created which can influence the stiffness of the overall aircraft structure. This tension stiffening is a geometric nonlinear effect that needs to be captured in aeroelastic analyses to better understand the behaviors of these types of aircraft structures. A frequency analysis of a rotating blade structure is performed to demonstrate the analytical method. A flutter analysis of a truss-braced wing aircraft is performed to analyze the effect of geometric nonlinear effect of tension stiffening on the flutter speed. The results show that the geometric nonlinear tension stiffening effect can have a significant impact on the flutter speed prediction. In general, increased wing loading results in an increase in the flutter speed. The study illustrates the importance of accounting for the geometric nonlinear tension stiffening effect in analyzing the truss-braced wing aircraft.
International Nuclear Information System (INIS)
The active vibration control of all kinds of structures by using the piezoelectric material has been extensively investigated. In this paper, the active aeroelastic flutter characteristics and vibration control of supersonic beams applying the piezoelectric material are studied further. The piezoelectric materials are bonded on the top and bottom surfaces of the beams to act as the actuator and sensor so that the active aeroelastic flutter suppression for the supersonic beams can be conducted. The supersonic piston theory is adopted to evaluate the aerodynamic pressure. Hamilton's principle with the assumed mode method is used to develop the dynamical model of the structural systems. By using the standard eigenvalue methodology, the solutions for the complex eigenvalue problem are obtained. A negative velocity feedback control strategy is used to obtain active damping. The aeroelastic flutter bounds are calculated and the active aeroelastic flutter characteristics are analyzed. The impulse responses of the structural system are obtained by using the Houbolt numerical algorithm to study the active aeroelastic vibration control. The influences of the non-dimensional aerodynamic pressure on the active flutter control are analyzed. From the numerical results it is observed that the aeroelastic flutter characteristics of the supersonic beams can be significantly improved and that the aeroelastic vibration amplitudes can be remarkably reduced, especially at the flutter points, by using the piezoelectric actuator/sensor pairs which can provide an active damping. Within a certain value of the feedback control gain, with the increase of it, the flutter aerodynamic pressure (or flutter velocity) can be increased and the control results are also improved
Goldman, Benjamin D.
The purpose of this dissertation is to study the aeroelastic stability of a proposed flexible thermal protection system (FTPS) for the NASA Hypersonic Inflatable Aerodynamic Decelerator (HIAD). A flat, square FTPS coupon exhibits violent oscillations during experimental aerothermal testing in NASA's 8 Foot High Temperature Tunnel, leading to catastrophic failure. The behavior of the structural response suggested that aeroelastic flutter may be the primary instability mechanism, prompting further experimental investigation and theoretical model development. Using Von Karman's plate theory for the panel-like structure and piston theory aerodynamics, a set of aeroelastic models were developed and limit cycle oscillations (LCOs) were calculated at the tunnel flow conditions. Similarities in frequency content of the theoretical and experimental responses indicated that the observed FTPS oscillations were likely aeroelastic in nature, specifically LCO/flutter. While the coupon models can be used for comparison with tunnel tests, they cannot predict accurately the aeroelastic behavior of the FTPS in atmospheric flight. This is because the geometry of the flight vehicle is no longer a flat plate, but rather (approximately) a conical shell. In the second phase of this work, linearized Donnell conical shell theory and piston theory aerodynamics are used to calculate natural modes of vibration and flutter dynamic pressures for various structural models composed of one or more conical shells resting on several circumferential elastic supports. When the flight vehicle is approximated as a single conical shell without elastic supports, asymmetric flutter in many circumferential waves is observed. When the elastic supports are included, the shell flutters symmetrically in zero circumferential waves. Structural damping is found to be important in this case, as "hump-mode" flutter is possible. Aeroelastic models that consider the individual FTPS layers as separate shells exhibit
Mourey, D. J.
1979-01-01
The aspects of flight testing an aeroelastically tailored forward swept research wing on a BQM-34F drone vehicle are examined. The geometry of a forward swept wing, which is incorporated into the BQM-34F to maintain satisfactory flight performance, stability, and control is defined. A preliminary design of the aeroelastically tailored forward swept wing is presented.
Directory of Open Access Journals (Sweden)
Gang Chen
2012-01-01
Full Text Available It is not easy for the system identification-based reduced-order model (ROM and even eigenmode based reduced-order model to predict the limit cycle oscillation generated by the nonlinear unsteady aerodynamics. Most of these traditional ROMs are sensitive to the flow parameter variation. In order to deal with this problem, a support vector machine- (SVM- based ROM was investigated and the general construction framework was proposed. The two-DOF aeroelastic system for the NACA 64A010 airfoil in transonic flow was then demonstrated for the new SVM-based ROM. The simulation results show that the new ROM can capture the LCO behavior of the nonlinear aeroelastic system with good accuracy and high efficiency. The robustness and computational efficiency of the SVM-based ROM would provide a promising tool for real-time flight simulation including nonlinear aeroelastic effects.
DEFF Research Database (Denmark)
Bergami, Leonardo; Gaunaa, Mac; Heinz, Joachim Christian
2013-01-01
profile undergoing harmonic pitching motion in the attached flow region; the resulting lift forces are compared with computational fluid dynamics (CFD) simulations. The relevance for aeroelastic simulations of a wind turbine is also evaluated, and the effects are quantified in terms of variations of...... equivalent fatigue loads, ultimate loads, and stability limits. The agreement with CFD computations of a 2D profile in harmonic motion is improved by the indicial function accounting for the finite‐thickness of the airfoil. Concerning the full wind turbine aeroelastic behavior, the differences between...
Jutte, Christine V.; Stanford, Bret K.; Wieseman, Carol D.; Moore, James B.
2014-01-01
This work explores the use of tow steered composite laminates, functionally graded metals (FGM), thickness distributions, and curvilinear rib/spar/stringer topologies for aeroelastic tailoring. Parameterized models of the Common Research Model (CRM) wing box have been developed for passive aeroelastic tailoring trade studies. Metrics of interest include the wing weight, the onset of dynamic flutter, and the static aeroelastic stresses. Compared to a baseline structure, the lowest aggregate static wing stresses could be obtained with tow steered skins (47% improvement), and many of these designs could reduce weight as well (up to 14%). For these structures, the trade-off between flutter speed and weight is generally strong, although one case showed both a 100% flutter improvement and a 3.5% weight reduction. Material grading showed no benefit in the skins, but moderate flutter speed improvements (with no weight or stress increase) could be obtained by grading the spars (4.8%) or ribs (3.2%), where the best flutter results were obtained by grading both thickness and material. For the topology work, large weight reductions were obtained by removing an inner spar, and performance was maintained by shifting stringers forward and/or using curvilinear ribs: 5.6% weight reduction, a 13.9% improvement in flutter speed, but a 3.0% increase in stress levels. Flutter resistance was also maintained using straightrotated ribs although the design had a 4.2% lower flutter speed than the curved ribs of similar weight and stress levels were higher. These results will guide the development of a future design optimization scheme established to exploit and combine the individual attributes of these technologies.
Geometrical Nonlinear Aeroelastic Stability Analysis of a Composite High-Aspect-Ratio Wing
Directory of Open Access Journals (Sweden)
Chang Chuan Xie
2008-01-01
Full Text Available A composite high-aspect-ratio wing of a high-altitude long-endurance (HALE aircraft was modeled with FEM by MSC/NASTRAN, and the nonlinear static equilibrium state is calculated under design load with follower force effect, but without load redistribution. Assuming the little vibration amplitude of the wing around the static equilibrium state, the system is linearized and the natural frequencies and mode shapes of the deformed structure are obtained. Planar doublet lattice method is used to calculate unsteady aerodynamics in frequency domain ignoring the bending effect of the deflected wing. And then, the aeroelastic stability analysis of the system under a given load condition is successively carried out. Comparing with the linear results, the nonlinear displacement of the wing tip is higher. The results indicate that the critical nonlinear flutter is of the flap/chordwise bending type because of the chordwise bending having quite a large torsion component, with low critical speed and slowly growing damping, which dose not appear in the linear analysis. Furthermore, it is shown that the variation of the nonlinear flutter speed depends on the scale of the load and on the chordwise bending frequency. The research work indicates that, for the very flexible HALE aircraft, the nonlinear aeroelastic stability is very important, and should be considered in the design progress. Using present FEM software as the structure solver (e.g. MSC/NASTRAN, and the unsteady aerodynamic code, the nonlinear aeroelastic stability margin of a complex system other than a simple beam model can be determined.
Aeroelastic flutter of feathers, flight and the evolution of non-vocal communication in birds.
Clark, Christopher J; Prum, Richard O
2015-11-01
Tonal, non-vocal sounds are widespread in both ordinary bird flight and communication displays. We hypothesized these sounds are attributable to an aerodynamic mechanism intrinsic to flight feathers: aeroelastic flutter. Individual wing and tail feathers from 35 taxa (from 13 families) that produce tonal flight sounds were tested in a wind tunnel. In the wind tunnel, all of these feathers could flutter and generate tonal sound, suggesting that the capacity to flutter is intrinsic to flight feathers. This result implies that the aerodynamic mechanism of aeroelastic flutter is potentially widespread in flight of birds. However, the sounds these feathers produced in the wind tunnel replicated the actual flight sounds of only 15 of the 35 taxa. Of the 20 negative results, we hypothesize that 10 are false negatives, as the acoustic form of the flight sound suggests flutter is a likely acoustic mechanism. For the 10 other taxa, we propose our negative wind tunnel results are correct, and these species do not make sounds via flutter. These sounds appear to constitute one or more mechanism(s) we call 'wing whirring', the physical acoustics of which remain unknown. Our results document that the production of non-vocal communication sounds by aeroelastic flutter of flight feathers is widespread in birds. Across all birds, most evolutionary origins of wing- and tail-generated communication sounds are attributable to three mechanisms: flutter, percussion and wing whirring. Other mechanisms of sound production, such as turbulence-induced whooshes, have evolved into communication sounds only rarely, despite their intrinsic ubiquity in ordinary flight. PMID:26385327
Unstructured-grid methods development for unsteady aerodynamic and aeroelastic analyses
Batina, John T.; Lee, Elizabeth M.; Kleb, William L.; Rausch, Russ D.
1992-01-01
The current status of unstructured grid methods developed in the Unsteady Aerodynamics Branch at NASA Langley Research Center is described. These methods are being developed for unsteady aerodynamic and aeroelastic analyses. Flow solvers that have been developed for the solution of unsteady Euler equations are highlighted. The results demonstrate two and three dimensional applications for both steady and unsteady flows. Comparisons are also made with solutions obtained using a structured grid code and with experimental data to determine the accuracy of the unstructured grid methodology. These comparisons show good agreement which thus verifies the accuracy.
Aeroelastic Stability of a 2D Airfoil Section equipped with a Trailing Edge Flap
Bergami, Leonardo
2008-01-01
Recent studies conclude that important reduction of the fatigue loads encountered by a wind turbine blade can be achieved using a deformable trailing edge control system. The focus of the current work is to determine the effect of this flap-like system on the aeroelastic stability of a 2D airfoil section. A simulation tool is implemented to predict the flow speed at which a flap equipped section may become unstable, either due to flutter or divergence. First, the stability limits of the airfo...
Nonlinear Aeroelastic Analysis Using a Time-Accurate Navier-Stokes Equations Solver
Kuruvila, Geojoe; Bartels, Robert E.; Hong, Moeljo S.; Bhatia, G.
2007-01-01
A method to simulate limit cycle oscillation (LCO) due to control surface freeplay using a modified CFL3D, a time-accurate Navier-Stokes computational fluid dynamics (CFD) analysis code with structural modeling capability, is presented. This approach can be used to analyze aeroelastic response of aircraft with structural behavior characterized by nonlinearity in the force verses displacement curve. A limited validation of the method, using very low Mach number experimental data for a three-degrees-of-freedom (pitch/plunge/flap deflection) airfoil model with flap freeplay, is also presented.
Aeroelastic tailoring using lamination parameters: drag reduction of a Formula One rear wing
Thuwis, G. A. A.; De Breuker, R.; Abdalla, M.M.; Gürdal, Z.
2009-01-01
The aim of the present work is to passively reduce the induced drag of the rear wing of a Formula One car at high velocity through aeroelastic tailoring. The angle-of-attack of the rear wing is fixed and is determined by the required downforce needed to get around a turn. As a result, at higher velocity, the amount of downforce and related induced drag increases. The maximum speed on a straight part is thus reduced due to the increase in induced drag. A fibre reinforced composite torsion box ...
Aeroelastic Stability of a 2D Airfoil Section equipped with a Trailing Edge Flap
DEFF Research Database (Denmark)
Bergami, Leonardo
Recent studies conclude that important reduction of the fatigue loads encountered by a wind turbine blade can be achieved using a deformable trailing edge control system. The focus of the current work is to determine the effect of this flap-like system on the aeroelastic stability of a 2D airfoil...... section. A simulation tool is implemented to predict the flow speed at which a flap equipped section may become unstable, either due to flutter or divergence. First, the stability limits of the airfoil without flap are determined, and, in the second part of the work, a deformable trailing edge flap is...
Czech Academy of Sciences Publication Activity Database
Sváček, P.; Horáček, Jaromír
2015-01-01
Roč. 267, September (2015), s. 28-41. ISSN 0096-3003 R&D Projects: GA ČR(CZ) GAP101/11/0207; GA ČR GAP101/12/1271 Institutional support: RVO:61388998 Keywords : aeroelasticity * finite element method * 2D RANS equations * sudden gust Subject RIV: BI - Acoustics Impact factor: 1.551, year: 2014 http://www.sciencedirect.com/science/article/pii/S0096300315008887/pdfft?md5=1329144b9cc04b57a05c506ae7f54b0a&pid=1-s2.0-S0096300315008887-main.pdf
Aeroelastic Optimization of a 10 MW Wind Turbine Blade with Active Trailing Edge Flaps
DEFF Research Database (Denmark)
Barlas, Athanasios; Tibaldi, Carlo; Zahle, Frederik;
2016-01-01
This article presents the aeroelastic optimization of a 10MW wind turbine ‘smart blade’ equipped with active trailing edge flaps. The multi-disciplinary wind turbine analysis and optimization tool HawtOpt2 is utilized, which is based on the open-source framework Open-MDAO. The tool interfaces to...... several state-of-the art simulation codes, allowing for a wide variety of problem formulations and combinations of models. A simultaneous aerodynamic and structural optimization of a 10 MW wind turbine rotor is carried out with respect to material layups and outer shape. Active trailing edge flaps are...
DEFF Research Database (Denmark)
Døssing, Mads
of very large machines introduces new problems in the practical design, and optimization tools are necessary. These must combine the dynamic eects of both aerodynamics and structure in an integrated optimization environment. This is referred to as aeroelastic optimization. The Ris DTU optimization......During the last decades the annual energy produced by wind turbines has increased dramatically and wind turbines are now available in the 5MW range. Turbines in this range are constantly being developed and it is also being investigated whether turbines as large as 10-20MW are feasible. The design...
Design and Aero-elastic Simulation of a 5MW Floating Vertical Axis Wind Turbine
DEFF Research Database (Denmark)
Vita, Luca; Schmidt Paulsen, Uwe; Aagaard Madsen, Helge;
2013-01-01
-DTU. The numerical simulations take into account the fully coupled aerodynamic and hydrodynamic loads on the structure, due to wind, waves and currents. The turbine is tested in operative conditions, at different sea states, selected according to the international offshore standards. The research is part...... with the rotor, whose stability is achieved by adding ballast at the bottom. The platform is connected to the mooring lines with some rigid arms, which are necessary to absorb the torque transmitted by the rotor. The aero-elastic simulations are carried out with Hawc2, a numerical solver developed at Risø...
Prediction of the aeroelastic behavior An application to wind-tunnel models
Roucou, Mickaël
2015-01-01
The work of this paper has been done during a Master thesis at the ONERA and deals with the establish-ment of an aeroelastic state-space model and its application to two wind-tunnel models studied at the ONERA. The established model takes into account a control surface input and a gust perturbation. The generalized aerodynamic forces are approximated using Roger’s and Karpel’s methods and the inertia of the aileron is computed using a finite element model in Nastran. The software used during ...
International Nuclear Information System (INIS)
This study examines the design parameters affecting the stability characteristics of a novel fluid flow energy harvesting device powered by aeroelastic flutter vibrations. The energy harvester makes use of a modal convergence flutter instability to generate limit cycle bending oscillations of a cantilevered piezoelectric beam with a small flap connected to its free end by a revolute joint. The critical flow speed at which destabilizing aerodynamic effects cause self-excited vibrations of the structure to emerge is essential to the design of the energy harvester because it sets the lower bound on the operating wind speed and frequency range of the system. A linearized analytic model of the device that accounts for the three-way coupling between the structural, unsteady aerodynamic, and electrical aspects of the system is used to examine tuning several design parameters while the size of the system is held fixed. The effects on the aeroelastic system dynamics and relative sensitivity of the flutter stability boundary are presented and discussed. A wind tunnel experiment is performed to validate the model predictions for the most significant system parameters
A Study on Aeroelastic Flutter Suppression and its Control Measures –Past and Future
Directory of Open Access Journals (Sweden)
Bruce Ralphin Rose J
2014-05-01
Full Text Available In a cruising mission, an airplane wing is subject to intense dynamic pressure changes with different magnitudes. The variable pressures exerted on the wing geometry will cause the redundant vibrations by flutter effect. The unkind Aeroelastic instabilities have an influence on the airplane performance and its structural life to a large extend. To overcome the instabilities, (particularly flutter modes an Active Flutter Suppression (AFS technique has been proposed during the year of 2002. In this review article, the contributions of different researchers in the field of AFS over the years are investigated. Mathematical models for various control designs provided are capable enough to link the response of wing structures against the oncoming airflow. It includes the structural and fluid dynamic properties required to design an active control to capture the effects of flutter frequency. Mass balancing and stiffness enhancement with control systems are the different methods available to implement AFS. In the critical flutter speed, the non linear characters play a vital role in the view of complex systems design and accuracy. Consequently, with the aid mass balancing, the non linear effects such as Limit Cycle Oscillations (LCO, baggy control system linkages and Internal Resonance are eliminated or reduced. Therefore, for increased airplane performance and efficiency, AFS is a key approach in the field of unconventional aeroelasticity.
Aeroelastic Behavior of a Wind Turbine Blade by a Fluid -Structure Interaction Analysis
Directory of Open Access Journals (Sweden)
Farouk O. Hamdoon
2013-01-01
Full Text Available In this paper, a numerical model for fluid-structure interaction (FSI analysis is developed for investigating the aeroelastic response of a single wind turbine blade. The Blade Element Momentum (BEM theory was adopted to calculate the aerodynamic forces considering the effects of wind shear and tower shadow. The wind turbine blade was modeled as a rotating cantilever beam discretized using Finite Element Method (FEM to analyze the deformation and vibration of the blade. The aeroelastic response of the blade was obtained by coupling these aerodynamic and structural models using a coupled BEM-FEM program written in MATLAB. The governing FSI equations of motion are iteratively calculated at each time step, through exchanging data between the structure and fluid by using a Newmarks implicit time integration scheme. The results obtained from this paper show that the proposed modeling can be used for a quick assessment of the wind turbine blades taking the fluid-structure interaction into account. This modeling can also be a useful tool for the analysis of airplane propeller blades.
Friedmann, P. P.
1984-01-01
An aeroelastic model suitable for the study of aeroelastic and structural dynamic effects in multirotor vehicles simulating a hybrid heavy lift vehicle was developed and applied to the study of a number of diverse problems. The analytical model developed proved capable of modeling a number of aeroelastic problems, namely: (1) isolated blade aeroelastic stability in hover and forward flight, (2) coupled rotor/fuselage aeromechanical problem in air or ground resonance, (3) tandem rotor coupled rotor/fuselage problems, and (4) the aeromechanical stability of a multirotor vehicle model representing a hybrid heavy lift airship (HHLA). The model was used to simulate the ground resonance boundaries of a three bladed hingeless rotor model, including the effect of aerodynamic loads, and the theoretical predictions compared well with experimental results. Subsequently the model was used to study the aeromechanical stability of a vehicle representing a hybrid heavy lift airship, and potential instabilities which could occur for this type of vehicle were identified. The coupling between various blade, supporting structure and rigid body modes was identified.
Gilbert, Michael G.; Silva, Walter A.
1987-01-01
A new design concept in the development of VTOL aircraft with high forward flight speed capability is that of the X-Wing, a stiff, bearingless helicopter rotor system which can be stopped in flight and the blades used as two forward-swept and two aft-swept wings. Because of the usual configuration in the fixed-wing mode, there is a high potential for aeroelastic divergence or flutter and coupling of blade vibration modes with rigid-body modes. An aeroelastic stability analysis of an X-Wing configuration aircraft was undertaken to determine if these problems could exist. This paper reports on the results of dynamic stability analyses in the lateral and longitudinal directions including the vehicle rigid-body and flexible modes. A static aeroelastic analysis using the normal vibration mode equations of motion was performed to determine the cause of a loss of longitudinal static margin with increasing airspeed. This loss of static margin was found to be due to aeroelastic washin of the forward-swept blades and washout of the aft-swept blades moving the aircraft aerodynamic center forward of the center of gravity. This phenomenon is likely to be generic to X-Wing aircraft.
International Nuclear Information System (INIS)
We consider reliability based aeroelastic optimization of a AGARD 445.6 composite aircraft wing with stochastic parameters. Both commercial engineering software and an in-house reliability analysis code are employed in this high-fidelity computational framework. Finite volume based flow solver Fluent is used to solve 3D Euler equations, while Gambit is the fluid domain mesh generator and Catia-V5-R16 is used as a parametric 3D solid modeler. Abaqus, a structural finite element solver, is used to compute the structural response of the aeroelastic system. Mesh based parallel code coupling interface MPCCI-3.0.6 is used to exchange the pressure and displacement information between Fluent and Abaqus to perform a loosely coupled fluid-structure interaction by employing a staggered algorithm. To compute the probability of failure for the probabilistic constraints, one of the well known MPP (Most Probable Point) based reliability analysis methods, FORM (First Order Reliability Method) is implemented in Matlab. This in-house developed Matlab code is embedded in the multidisciplinary optimization workflow which is driven by Modefrontier. Modefrontier 4.1, is used for its gradient based optimization algorithm called NBI-NLPQLP which is based on sequential quadratic programming method. A pareto optimal solution for the stochastic aeroelastic optimization is obtained for a specified reliability index and results are compared with the results of deterministic aeroelastic optimization.
DEFF Research Database (Denmark)
Aagaard Madsen, Helge; Larsen, Torben J.; Schmidt Paulsen, Uwe; Vita, Luca
2013-01-01
of VAWTs for floating MW concepts. The AC model is a 2D flow model and has thus some advantages compared with the stream tube models often used in VAWT aerodynamic and aeroelastic simulation models. A major finding presented in the present paper is a simple way to correct the results from the linear...
Aeroelastic Research Programme, Report for EFP-99; Forskning i aeroelasticitet - EFP-99
Energy Technology Data Exchange (ETDEWEB)
Aagaard Madsen, H. [ed.
2000-11-01
The report presents the main results achieved within 'Program for forskning i aeroelasticitet EFP-99' which is a project under the Danish Government's Energy Research Program EFP-99. The project has been carried out in a collaborative work between the Technical University of Denmark (DTU), Risoe National Laboratory and the Danish Wind Turbine Industry. Within the period from July 1999 to June 2000 the project has contained the following milestones: 1) Wind tunnel measurements on a NACA 63-415 airfoil with a modified leading edge. 2)Detailed verification of 3D Computational Fluids Dynamics (CFD) computations with the code EllipSys3D on National Research Energy Laboratorys (NRELs) 10 m rotor. 3) Development of a model for simulation of airfoil roughness. 4) Aeroelastic modelling of a rotor with flexible blades. 5) Loads in relation to control - active stall - pitch regulation - variable speed. 6) Aeroacoustic modelling of noise emission from an airfoil section. Studies of the causes for double stall was carried out within the EFP-97 programme and continued within EFP-98 with design investigations on how to reduce or avoid the double stall problem. A promising solution was a modification of the leading edge of the NACA 63-415 airfoil in order to stabilise the laminar separation bubble. Within the present project the modified NACA 63-415 design has been tested in a wind tunnel together with a standard NACA 63-415 airfoil. The tests did show more stable stall characteristics of the modified airfoil and double stall was not observed during the tests on this airfoil. Further the modified airfoil had other improved characteristics: higher lift/drag ratio, less sensitivity to roughness and better aerodynamic damping characteristics in the chordwise direction. To start a detailed verification of 3D rotor simulations with the EllipSys3D code a number of 3D rotor simulations on NRELs 10 m rotor has been performed. Wind Tunnel tests on this rotor was carried out
Ilie, Marcel
In helicopters, vortices (generated at the tip of the rotor blades) interact with the next advancing blades during certain flight and manoeuvring conditions, generating undesirable levels of acoustic noise and vibration. These Blade-Vortex Interactions (BVIs), which may cause the most disturbing acoustic noise, normally occur in descent or high-speed forward flight. Acoustic noise characterization (and potential reduction) is one the areas generating intensive research interest to the rotorcraft industry. Since experimental investigations of BVI are extremely costly, some insights into the BVI or AVI (2-D Airfoil-Vortex Interaction) can be gained using Computational Fluid Dynamics (CFD) numerical simulations. Numerical simulation of BVI or AVI has been of interest to CFD for many years. There are still difficulties concerning an accurate numerical prediction of BVI. One of the main issues is the inherent dissipation of CFD turbulence models, which severely affects the preservation of the vortex characteristics. Moreover this is not an issue only for aerodynamic and aeroacoustic analysis but also for aeroelastic investigations as well, especially when the strong (two-way) aeroelastic coupling is of interest. The present investigation concentrates mainly on AVI simulations. The simulations are performed for Mach number, Ma = 0.3, resulting in a Reynolds number, Re = 1.3 x 106, which is based on the chord, c, of the airfoil (NACA0012). Extensive literature search has indicated that the present work represents the first comprehensive investigation of AVI using the LES numerical approach, in the rotorcraft research community. The major factor affecting the aerodynamic coefficients and aeroacoustic field as a result of airfoil-vortex interaction is observed to be the unsteady pressure generated at the location of the interaction. The present numerical results show that the aerodynamic coefficients (lift, moment, and drag) and aeroacoustic field are strongly dependent on
The Effect of Composite Flexures on Aeroelastic Stability of a Hingeless Rotor Blade
Institute of Scientific and Technical Information of China (English)
Shi; Qinghua
2007-01-01
The effects of ply orientation angle of composite flexures on stability of hingeless rotor blade system are studied.The composite hingeless rotor blade system is simplified as a hub,a flap flexure and a lag flexure.pitch bearing and main blade.The kinematics formulations are inferred by employing the moderate deflection beam theory.The shear deformation and warping related to torsion are considered.The quasi-steady strip theory with dynamic inflow effects is applied to obtain the aerodynamic loads acting on the blade.Based on these.the set of finite element formulations of a hingeless rotor blade system is worked out.The numerical results show that the ply angle of the composite flexures has great effects on the aeroelastic stability of rotor blade.
Two methods for estimating aeroelastic damping of operational wind turbine modes from experiments
DEFF Research Database (Denmark)
Hansen, Morten Hartvig; Thomsen, Kenneth; Fuglsang, Peter; Knudsen, T.
The theory and results of two experimental methods for estimating the modal damping of a wind turbine during operation are presented. Estimations of the aeroelastic damping of the operational turbine modes (including the effects of the aerodynamic forces) give a quantitative view of the stability...... characteristics of the turbine. In the first method the estimation of modal damping is based on the assumption that a turbine mode can be excited by a harmonic force at its natural frequency, whereby the decaying response after the end of excitation gives an estimate of the damping. Simulations and experiments...... on stochastic subspace identification, where a linear model of the turbine is estimated alone from measured response signals by assuming that the ambient excitation from turbulence is random in time and space. Although the assumption is not satisfied, this operational modal analysis method can handle...
Example of a non-smooth Hopf bifurcation in an aero-elastic system
Magri, Luca
2012-01-01
We investigate a typical aerofoil section under dynamic stall conditions, the structural model is linear and the aerodynamic loading is represented by the Leishman-Beddoes semi-empirical dynamic stall model. The loads given by this model are non-linear and non-smooth, therefore we have integrated the equation of motion using a Runge-Kutta-Fehlberg algorithm equipped with event detection. The main focus of the paper is on the interaction between the Hopf bifurcation typical of aero-elastic systems, which causes flutter oscillations, and the discontinuous definition of the stall model. The paper shows how the non-smooth definition of the dynamic stall model can generate a non-smooth Hopf bifurcation. The mechanisms for the appearance of limit cycle attractors are described by using standard tools of the theory of dynamical systems such as phase plots and bifurcation diagrams.
International Nuclear Information System (INIS)
The dynamics character of a two degree-of-freedom aeroelastic airfoil with combined freeplay and cubic stiffness nonlinearities in pitch submitted to supersonic and hypersonic flow has been gaining significant attention. The Poincaré mapping method and Floquet theory are adopted to analyse the limit cycle oscillation flutter and chaotic motion of this system. The result shows that the limit cycle oscillation flutter can be accurately predicted by the Floquet multiplier. The phase trajectories of both the pitch and plunge motion are obtained and the results show that the plunge motion is much more complex than the pitch motion. It is also proved that initial conditions have important influences on the dynamics character of the airfoil system. In a certain range of airspeed and with the same system parameters, the stable limit cycle oscillation, chaotic and multi-periodic motions can be detected under different initial conditions. The figure of the Poincaré section also approves the previous conclusion
Control of Limit Cycle Oscillations of a Two-Dimensional Aeroelastic System
Directory of Open Access Journals (Sweden)
M. Ghommem
2010-01-01
Full Text Available Linear and nonlinear static feedback controls are implemented on a nonlinear aeroelastic system that consists of a rigid airfoil supported by nonlinear springs in the pitch and plunge directions and subjected to nonlinear aerodynamic loads. The normal form is used to investigate the Hopf bifurcation that occurs as the freestream velocity is increased and to analytically predict the amplitude and frequency of the ensuing limit cycle oscillations (LCO. It is shown that linear control can be used to delay the flutter onset and reduce the LCO amplitude. Yet, its required gains remain a function of the speed. On the other hand, nonlinear control can be effciently implemented to convert any subcritical Hopf bifurcation into a supercritical one and to significantly reduce the LCO amplitude.
Aeroelastic research programme EFP-2001[YAW;STALL]; Forskning i aeroelasticitet EFP-2001
Energy Technology Data Exchange (ETDEWEB)
Aagaard Madsen, H. (ed.)
2002-12-01
The project covers the one year period from mid 2001 to mid 2002 and is the last part of a 5 years research programme on aeroelasticity. The overall objectives of the project are to improve the load and design basis for wind turbines and to ensure in collaboration with industry a continu-ously running process on development of new designs and solution of actual problems. Specifi-cally the main objectives for the present period are the following: a) development of a design tool for analysis of dynamic stability b) investigations of blade tip aerodynamics and blade tip design on basis of 3D CFD computa-tions c) publication of an airfoil catalogue d) load reduction using new control strategies e) aeroacoustic modelling of noise propagation During the present project period the computer code HAWCModal has been finished. The code computes the modal characteristics for a turbine as function of rotational speed. It is based on the structural modelling in the aeroelastic code HAWC and uses the same input files. The computed eigen frequencies are shown in a Campbell diagram and the corresponding modal forms can be shown graphically for an operating turbine. Finally, the structural damping is also computed by the code. HAWCModal is the basis for the stability analysis tool HAWCStab which is now under devel-opment. With HAWCStab the aeroelastic stability of a turbine can be analysed. The complex aerodynamics at three different blade tip shapes have been analysed with the three-dimensional CFD code EllipSys3D. The tip vortex was visualised and the lift and drag coef-ficients in the tip region were analysed in order to study the influence of the tip geometry on the performance and aerodynamic damping. An airfoil catalogue containing computations on 28 different airfoils for wind turbine applica-tion in comparison with experimental data has been developed and is available via the internet. Besides the main themes of the project as mentioned above there have been research
Energy Technology Data Exchange (ETDEWEB)
Anderson, M.B. [Renewable Energy Systems Ltd., Hemel Hempstead (United Kingdom)
1996-09-01
It is possible to compute the aeroelastic response of a horizontal axis wind turbine comprising; Structural: rotor substructure 144 dof, tower substructure 48 dof, induction, synchronous or variable speed, and gearbox. Aerodynamic: 3 blades (10 elements per blade), dynamic stall, and 6 different aerofoil types with combination of fixed or pitching elements. Control: stall or power regulation or speed control and shutdowns, wind shear, and tower shadow. Turbulence: 8 radial points, 32 circumferential, and 3 components. On a DEC Alpha Workstation the code will simulate the response inclose to real-time. As the code is presently formulated deflections from the initial starting point have to be small and therefore its ability to fully analyse very flexible structures is limited. (EG)
Bielawa, R. L.
1984-01-01
The mathematical development for the expanded capabilities of the G400 rotor aeroelastic analysis was examined. The G400PA expanded analysis simulates the dynamics of all conventional rotors, blade pendulum vibration absorbers, and the higher harmonic excitations resulting from prescribed vibratory hub motions and higher harmonic blade pitch control. The methodology for modeling the unsteady stalled airloads of two dimensional airfoils is discussed. Formulations for calculating the rotor impedance matrix appropriate to the higher harmonic blade excitations are outlined. This impedance matrix, and the associated vibratory hub loads, are the rotor dynamic characteristic elements for use in the simplified coupled rotor/fuselage vibration analysis (SIMVIB). Updates to the development of the original G400 theory, program documentation, user instructions and information are presented.
Effects of extreme wind shear on aeroelastic modal damping of wind turbines
DEFF Research Database (Denmark)
Skjoldan, P.F.; Hansen, Morten Hartvig
2013-01-01
Wind shear is an important contributor to fatigue loads on wind turbines. Because it causes an azimuthal variation in angle of attack, it can also affect aerodynamic damping. In this paper, a linearized model of a wind turbine, based on the nonlinear aeroelastic code BHawC, is used to investigate...... the effect of wind shear on the modal damping of the turbine. In isotropic conditions with a uniform wind field, the modal properties can be extracted from the system matrix transformed into the inertial frame using the Coleman transformation. In shear conditions, an implicit Floquet analysis, which...... operating closest to stall. The first longitudinal tower mode decreases slightly in damping, whereas the first flapwise backward whirling and symmetric modes increase in damping. This change in damping is attributed to an interaction between the periodic blade mode shapes and the azimuth-dependent local...
Analysis of wind turbine aerodynamics and aeroelasticity using vortex-based methods
DEFF Research Database (Denmark)
Branlard, Emmanuel Simon Pierre
have regained interest in wind energy applications over the last two decades. The current work derives and illustrates some of the potential benefits of vortex-based analyses. The two key wake geometries used in this study to derive simple vortex models are the cylindrical and helical wake models. Both......Momentum analysis through Blade Element Momentum (BEM) and Computational Fluid Dynamics (CFD) are the two major paths commonly followed for wind turbine aerodynamic and aeroelastic research. Instead, the current PhD thesis focuses on the application of vortex-based methods. Vortex-based methods are...... be used in BEM implementations. The current thesis also presents the implementation of a vortex code to further investigate wind turbine aerodynamics. The code consists of both low-order and high-order formulations. The implementation features are described and illustrated through different...
Wing Torsional Stiffness Tests of the Active Aeroelastic Wing F/A-18 Airplane
Lokos, William A.; Olney, Candida D.; Crawford, Natalie D.; Stauf, Rick; Reichenbach, Eric Y.
2002-01-01
The left wing of the Active Aeroelastic Wing (AAW) F/A-18 airplane has been ground-load-tested to quantify its torsional stiffness. The test has been performed at the NASA Dryden Flight Research Center in November 1996, and again in April 2001 after a wing skin modification was performed. The primary objectives of these tests were to characterize the wing behavior before the first flight, and provide a before-and-after measurement of the torsional stiffness. Two streamwise load couples have been applied. The wing skin modification is shown to have more torsional flexibility than the original configuration has. Additionally, structural hysteresis is shown to be reduced by the skin modification. Data comparisons show good repeatability between the tests.
DEFF Research Database (Denmark)
Aagaard Madsen, Helge; Larsen, Gunner Chr.; Larsen, Torben J.; Troldborg, Niels; Mikkelsen, Robert Flemming
2010-01-01
As the major part of new wind turbines are installed in clusters or wind farms, there is a strong need for reliable and accurate tools for predicting the increased loadings due to wake operation and the associated reduced power production. The dynamic wake meandering (DWM) model has been developed...... integration in an aeroelastic model. Calibration and validation of the different parts of the model is carried out by comparisons with actuator disk and actuator line (ACL) computations as well as with inflow measurements on a full-scale 2 MW turbine. It is shown that the load generating part of the increased...... levels. Finally, added turbulence characteristics are compared with correlation results from literature. ©2010 American Society of Mechanical Engineers...
Highly flexible flight vehicle aeroelastic and aero-viscoelastic flutter issues
Merrett, Craig G.; Hilton, Harry H.
2012-11-01
Aeroelastic and aero-viscoelastic phenomena arising from the high flexibility of modern flight vehicles are examined, and governing relations are formulated and solved. In particular, the time dependent flight velocities associated with maneuvers and with in-plane bending are considered, which necessitate new derivations of the Theodorsen function, unsteady aerodynamic relations and equations of motion. Under these conditions, simple harmonic motion (SHM) is no longer achievable and different flutter criteria based directly on motion stability are presented. The viscoelastic problem is formulated in terms of integral partial differential equations with variable nonlinear coefficients. Their solutions and evaluations are discussed in detail. One interesting departure from linear responses emerged, which indicates flutter in one bending while the other bending mode and the torsional are both stable. A detailed and extended treatment of these subjects may be found in [1].
Directory of Open Access Journals (Sweden)
Mario Rosario Chiarelli
2016-01-01
Full Text Available This paper presents a study of transonic wings whose planform shape is curved. Using fluid structure interaction analyses, the dynamic instability conditions were investigated by including the effects of the transonic flow field around oscillating wings. To compare the dynamic aeroelastic characteristics of the curved wing configuration, numerical analyses were carried out on a conventional swept wing and on a curved planform wing. The results confirm that, for a curved planform wing, the dynamic instability condition occurs at higher flight speed if compared to a traditional swept wing with similar profiles, aspect ratio, angle of sweep at root, similar structural layout, and similar mass. A curved wing lifting system could thus improve the performances of future aircrafts.
Directory of Open Access Journals (Sweden)
Hassan Abba Musa
2016-06-01
Full Text Available In current practice, the predictive analysis of stochastic problems encompasses a variety of statistical techniques from modeling, machine, and data mining that analyse current and historical facts to make predictions about future. Therefore, this research uses an AR Model whose codes are incorporated in the MATLAB software to predict possible aero-elastic effects of Lekki Bridge based on its existing parametric data and the conditions around the bridge. It was seen that, the fluctuating components of the wind velocity as displayed by the fluctuant curve will result in the vibration of the structure, even strengthening the resonance effect of the structure. Therefore, it suggested that, the natural frequency of the bridge should be set aside far from system frequency considering direct parametric excitation of pedestrian or vehicular traffic speed.
Czech Academy of Sciences Publication Activity Database
Sváček, P.; Horáček, Jaromír
Praha : Ústav termomechaniky AV ČR, v. v. i, 2012 - (Šimurda, D.; Kozel, K.), s. 89-92 ISBN 978-80-87012-40-6. [Topical Problems of Fluid Mechanics 2012. Praha (CZ), 15.02.2012-17.02.2012] R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * 3DOF airfoil * RANS equation * flutter Subject RIV: BI - Acoustics
Bartels, Robert E.; Funk, Christie; Scott, Robert C.
2015-01-01
Research focus in recent years has been given to the design of aircraft that provide significant reductions in emissions, noise and fuel usage. Increases in fuel efficiency have also generally been attended by overall increased wing flexibility. The truss-braced wing (TBW) configuration has been forwarded as one that increases fuel efficiency. The Boeing company recently tested the Subsonic Ultra Green Aircraft Research (SUGAR) Truss-Braced Wing (TBW) wind-tunnel model in the NASA Langley Research Center Transonic Dynamics Tunnel (TDT). This test resulted in a wealth of accelerometer data. Other publications have presented details of the construction of that model, the test itself, and a few of the results of the test. This paper aims to provide a much more detailed look at what the accelerometer data says about the onset of aeroelastic instability, usually known as flutter onset. Every flight vehicle has a location in the flight envelope of flutter onset, and the TBW vehicle is not different. For the TBW model test, the flutter onset generally occurred at the conditions that the Boeing company analysis said it should. What was not known until the test is that, over a large area of the Mach number dynamic pressure map, the model displayed wing/engine nacelle aeroelastic limit cycle oscillation (LCO). This paper dissects that LCO data in order to provide additional insights into the aeroelastic behavior of the model.
Goldman, Benjamin D.; Dowell, Earl H.; Scott, Robert C.
2014-01-01
Conical shell theory and piston theory aerodynamics are used to study the aeroelastic stability of the thermal protection system (TPS) on the NASA Hypersonic Inflatable Aerodynamic Decelerator (HIAD). Structural models of the TPS consist of single or multiple orthotropic conical shell systems resting on several circumferential linear elastic supports. The shells in each model may have pinned (simply-supported) or elastically-supported edges. The Lagrangian is formulated in terms of the generalized coordinates for all displacements and the Rayleigh-Ritz method is used to derive the equations of motion. The natural modes of vibration and aeroelastic stability boundaries are found by calculating the eigenvalues and eigenvectors of a large coefficient matrix. When the in-flight configuration of the TPS is approximated as a single shell without elastic supports, asymmetric flutter in many circumferential waves is observed. When the elastic supports are included, the shell flutters symmetrically in zero circumferential waves. Structural damping is found to be important in this case. Aeroelastic models that consider the individual TPS layers as separate shells tend to flutter asymmetrically at high dynamic pressures relative to the single shell models. Several parameter studies also examine the effects of tension, orthotropicity, and elastic support stiffness.
International Nuclear Information System (INIS)
Due to trends in aero-design, aeroelasticity becomes increasingly important in modern turbomachines. Design requirements of turbomachines lead to the development of high aspect ratio blades and blade integral disc designs (blisks), which are especially prone to complex modes of vibration. Therefore, experimental investigations yielding high quality data are required for improving the understanding of aeroelastic effects in turbomachines. One possibility to achieve high quality data is to excite and measure blade vibrations in turbomachines. The major requirement for blade excitation and blade vibration measurements is to minimize interference with the aeroelastic effects to be investigated. Thus in this paper, a non-contact—and thus low interference—experimental set-up for exciting and measuring blade vibrations is proposed and shown to work. A novel acoustic system excites rotor blade vibrations, which are measured with an optical tip-timing system. By performing measurements in an axial compressor, the potential of the acoustic excitation method for investigating aeroelastic effects is explored. The basic principle of this method is described and proven through the analysis of blade responses at different acoustic excitation frequencies and at different rotational speeds. To verify the accuracy of the tip-timing system, amplitudes measured by tip-timing are compared with strain gage measurements. They are found to agree well. Two approaches to vary the nodal diameter (ND) of the excited vibration mode by controlling the acoustic excitation are presented. By combining the different excitable acoustic modes with a phase-lag control, each ND of the investigated 30 blade rotor can be excited individually. This feature of the present acoustic excitation system is of great benefit to aeroelastic investigations and represents one of the main advantages over other excitation methods proposed in the past. In future studies, the acoustic excitation method will be used
Keller, Jonathan Allen
2001-11-01
An analysis has been developed to predict the transient aeroelastic response of a helicopter rotor system during shipboard engagement and disengagement operations. The coupled flap-lag-torsion equations of motion were developed using Hamilton's Principle and discretized spatially using the finite element method. Aerodynamics were simulated using nonlinear quasi-steady or time domain nonlinear unsteady models. The ship airwake environment was simulated with simple deterministic airwake distributions, results from experimental measurements or numerical predictions. The transient aeroelastic response of the rotor blades was then time-integrated along a specified rotor speed profile. The control of the rotor response for an analytic model of the H-46 Sea Knight rotor system was investigated with three different passive control techniques. Collective pitch scheduling was only successful in reducing the blade flapping response in a few isolated cases. In the majority of cases, the blade transient response was increased. The use of a discrete flap damper in the very low rotor speed region was also investigated. Only by raising the flap stop setting and using a flap damper four times the strength of the lag damper could the downward flap deflections be reduced. However, because the flap stop setting was raised the upward flap deflections were often increased. The use of extendable/retractable, gated leading-edge spoilers in the low rotor speed region was also investigated. Spoilers covering the outer 15% R of the rotor blade were shown to significantly reduce both the upward and downward flap response without increasing rotor torque. Previous aeroelastic analyses developed at the University of Southampton and at Penn State University were completed with flap-torsion degrees of freedom only. The addition of the lag degree of freedom was shown to significantly influence the blade response. A comparison of the two aerodynamic models showed that the nonlinear quasi
Wavelet Analyses of F/A-18 Aeroelastic and Aeroservoelastic Flight Test Data
Brenner, Martin J.
1997-01-01
Time-frequency signal representations combined with subspace identification methods were used to analyze aeroelastic flight data from the F/A-18 Systems Research Aircraft (SRA) and aeroservoelastic data from the F/A-18 High Alpha Research Vehicle (HARV). The F/A-18 SRA data were produced from a wingtip excitation system that generated linear frequency chirps and logarithmic sweeps. HARV data were acquired from digital Schroeder-phased and sinc pulse excitation signals to actuator commands. Nondilated continuous Morlet wavelets implemented as a filter bank were chosen for the time-frequency analysis to eliminate phase distortion as it occurs with sliding window discrete Fourier transform techniques. Wavelet coefficients were filtered to reduce effects of noise and nonlinear distortions identically in all inputs and outputs. Cleaned reconstructed time domain signals were used to compute improved transfer functions. Time and frequency domain subspace identification methods were applied to enhanced reconstructed time domain data and improved transfer functions, respectively. Time domain subspace performed poorly, even with the enhanced data, compared with frequency domain techniques. A frequency domain subspace method is shown to produce better results with the data processed using the Morlet time-frequency technique.
Bayesian inference of nonlinear unsteady aerodynamics from aeroelastic limit cycle oscillations
Sandhu, Rimple; Poirel, Dominique; Pettit, Chris; Khalil, Mohammad; Sarkar, Abhijit
2016-07-01
A Bayesian model selection and parameter estimation algorithm is applied to investigate the influence of nonlinear and unsteady aerodynamic loads on the limit cycle oscillation (LCO) of a pitching airfoil in the transitional Reynolds number regime. At small angles of attack, laminar boundary layer trailing edge separation causes negative aerodynamic damping leading to the LCO. The fluid-structure interaction of the rigid, but elastically mounted, airfoil and nonlinear unsteady aerodynamics is represented by two coupled nonlinear stochastic ordinary differential equations containing uncertain parameters and model approximation errors. Several plausible aerodynamic models with increasing complexity are proposed to describe the aeroelastic system leading to LCO. The likelihood in the posterior parameter probability density function (pdf) is available semi-analytically using the extended Kalman filter for the state estimation of the coupled nonlinear structural and unsteady aerodynamic model. The posterior parameter pdf is sampled using a parallel and adaptive Markov Chain Monte Carlo (MCMC) algorithm. The posterior probability of each model is estimated using the Chib-Jeliazkov method that directly uses the posterior MCMC samples for evidence (marginal likelihood) computation. The Bayesian algorithm is validated through a numerical study and then applied to model the nonlinear unsteady aerodynamic loads using wind-tunnel test data at various Reynolds numbers.
Bradley, Marty K.; Allen, Timothy J.; Droney, Christopher
2014-01-01
This Test Report summarizes the Truss Braced Wing (TBW) Aeroelastic Test (Task 3.1) work accomplished by the Boeing Subsonic Ultra Green Aircraft Research (SUGAR) team, which includes the time period of February 2012 through June 2014. The team consisted of Boeing Research and Technology, Boeing Commercial Airplanes, Virginia Tech, and NextGen Aeronautics. The model was fabricated by NextGen Aeronautics and designed to meet dynamically scaled requirements from the sized full scale TBW FEM. The test of the dynamically scaled SUGAR TBW half model was broken up into open loop testing in December 2013 and closed loop testing from January 2014 to April 2014. Results showed the flutter mechanism to primarily be a coalescence of 2nd bending mode and 1st torsion mode around 10 Hz, as predicted by analysis. Results also showed significant change in flutter speed as angle of attack was varied. This nonlinear behavior can be explained by including preload and large displacement changes to the structural stiffness and mass matrices in the flutter analysis. Control laws derived from both test system ID and FEM19 state space models were successful in suppressing flutter. The control laws were robust and suppressed flutter for a variety of Mach, dynamic pressures, and angle of attacks investigated.
Flight Test of the F/A-18 Active Aeroelastic Wing Airplane
Voracek, David
2007-01-01
A viewgraph presentation of flight tests performed on the F/A active aeroelastic wing airplane is shown. The topics include: 1) F/A-18 AAW Airplane; 2) F/A-18 AAW Control Surfaces; 3) Flight Test Background; 4) Roll Control Effectiveness Regions; 5) AAW Design Test Points; 6) AAW Phase I Test Maneuvers; 7) OBES Pitch Doublets; 8) OBES Roll Doublets; 9) AAW Aileron Flexibility; 10) Phase I - Lessons Learned; 11) Control Law Development and Verification & Validation Testing; 12) AAW Phase II RFCS Envelopes; 13) AAW 1-g Phase II Flight Test; 14) Region I - Subsonic 1-g Rolls; 15) Region I - Subsonic 1-g 360 Roll; 16) Region II - Supersonic 1-g Rolls; 17) Region II - Supersonic 1-g 360 Roll; 18) Region III - Subsonic 1-g Rolls; 19) Roll Axis HOS/LOS Comparison Region II - Supersonic (open-loop); 20) Roll Axis HOS/LOS Comparison Region II - Supersonic (closed-loop); 21) AAW Phase II Elevated-g Flight Test; 22) Region I - Subsonic 4-g RPO; and 23) Phase II - Lessons Learned
Wilkie, W. Keats; Park, K. C.
1996-01-01
A simple aeroelastic analysis of a helicopter rotor blade incorporating embedded piezoelectric fiber composite, interdigitated electrode blade twist actuators is described. The analysis consist of a linear torsion and flapwise bending model coupled with a nonlinear ONERA based unsteady aerodynamics model. A modified Galerkin procedure is performed upon the rotor blade partial differential equations of motion to develop a system of ordinary differential equations suitable for numerical integration. The twist actuation responses for three conceptual full-scale blade designs with realistic constraints on blade mass are numerically evaluated using the analysis. Numerical results indicate that useful amplitudes of nonresonant elastic twist, on the order of one to two degrees, are achievable under one-g hovering flight conditions for interdigitated electrode poling configurations. Twist actuation for the interdigitated electrode blades is also compared with the twist actuation of a conventionally poled piezoelectric fiber composite blade. Elastic twist produced using the interdigitated electrode actuators was found to be four to five times larger than that obtained with the conventionally poled actuators.
Wilkie, W. Keats; Belvin, W. Keith; Park, K. C.
1996-01-01
A simple aeroelastic analysis of a helicopter rotor blade incorporating embedded piezoelectric fiber composite, interdigitated electrode blade twist actuators is described. The analysis consists of a linear torsion and flapwise bending model coupled with a nonlinear ONERA based unsteady aerodynamics model. A modified Galerkin procedure is performed upon the rotor blade partial differential equations of motion to develop a system of ordinary differential equations suitable for dynamics simulation using numerical integration. The twist actuation responses for three conceptual fullscale blade designs with realistic constraints on blade mass are numerically evaluated using the analysis. Numerical results indicate that useful amplitudes of nonresonant elastic twist, on the order of one to two degrees, are achievable under one-g hovering flight conditions for interdigitated electrode poling configurations. Twist actuation for the interdigitated electrode blades is also compared with the twist actuation of a conventionally poled piezoelectric fiber composite blade. Elastic twist produced using the interdigitated electrode actuators was found to be four to five times larger than that obtained with the conventionally poled actuators.
Guruswamy, P.; Goorjian, P. M.
1982-01-01
Comparisons were made of computed and experimental data in three-dimensional unsteady transonic aerodynamics, including aeroelastic applications. The computer code LTRAN3, which is based on small-disturbance aerodynamic theory, was used to obtain the aerodynamic data. A procedure based on the U-g method was developed to compute flutter boundaries by using the unsteady aerodynamic coefficients obtained from LTRAN3. The experimental data were obtained from available NASA publications. All the studies were conducted for thin, unswept, rectangular wings with circular-arc cross sections. Numerical and experimental steady and unsteady aerodynamic data were compared for a wing with an aspect ratio of 3 and a thickness ratio of 5% at Mach numbers of 0.7 and 0.9. Flutter data were compared for a wing with an aspect ratio of 5. Two thickness ratios, 6% at Mach numbers of 0.715, 0.851, and 0.913, and 4% at Mach number of 0.904, were considered. Based on the unsteady aerodynamic data obtained from LTRAN3, flutter boundaries were computed; they were compared with those obtained from experiments and the code NASTRAN, which uses linear aerodynamics.
Ivanco, Thomas G.
2013-01-01
NASA Langley Research Center's Transonic Dynamics Tunnel (TDT) is the world's most capable aeroelastic test facility. Its large size, transonic speed range, variable pressure capability, and use of either air or R-134a heavy gas as a test medium enable unparalleled manipulation of flow-dependent scaling quantities. Matching these scaling quantities enables dynamic similitude of a full-scale vehicle with a sub-scale model, a requirement for proper characterization of any dynamic phenomenon, and many static elastic phenomena. Select scaling parameters are presented in order to quantify the scaling advantages of TDT and the consequence of testing in other facilities. In addition to dynamic testing, the TDT is uniquely well-suited for high risk testing or for those tests that require unusual model mount or support systems. Examples of recently conducted dynamic tests requiring unusual model support are presented. In addition to its unique dynamic test capabilities, the TDT is also evaluated in its capability to conduct aerodynamic performance tests as a result of its flow quality. Results of flow quality studies and a comparison to a many other transonic facilities are presented. Finally, the ability of the TDT to support future NASA research thrusts and likely vehicle designs is discussed.
DEFF Research Database (Denmark)
Barlas, Thanasis K.; van Wingerden, W.; Hulskamp, A.W.;
2013-01-01
using the aeroelastic tool, load predictions are compared with the wind tunnel measurements, and similar control concepts are compared and evaluated in the numerical environment. Conclusions regarding evaluation of the performance of smart rotor concepts for wind turbines are drawn from this threefold......In this paper, the proof of concept of a smart rotor is illustrated by aeroelastic simulations on a small-scale rotor and comparison with wind tunnel experiments. The application of advanced feedback controllers using actively deformed flaps in the wind tunnel measurements is shown to alleviate...
International Nuclear Information System (INIS)
In the research described in this paper, a scaled wind turbine model featuring individual pitch control (IPC) capabilities, and equipped with aero-elastically scaled blades featuring passive load reduction capabilities (bend-twist coupling, BTC), was constructed to investigate, by means of wind tunnel testing, the load alleviation potential of BTC and its synergy with active load reduction techniques. The paper mainly focus on the design of the aero-elastic blades and their dynamic and static structural characterization. The experimental results highlight that manufactured blades show desired bend-twist coupling behavior and are a first milestone toward their testing in the wind tunnel
Effect of multiple engine placement on aeroelastic trim and stability of flying wing aircraft
Mardanpour, Pezhman; Richards, Phillip W.; Nabipour, Omid; Hodges, Dewey H.
2014-01-01
Effects of multiple engine placement on flutter characteristics of a backswept flying wing resembling the HORTEN IV are investigated using the code NATASHA (Nonlinear Aeroelastic Trim And Stability of HALE Aircraft). Four identical engines with defined mass, inertia, and angular momentum are placed in different locations along the span with different offsets from the elastic axis while fixing the location of the aircraft c.g. The aircraft experiences body freedom flutter along with non-oscillatory instabilities that originate from flight dynamics. Multiple engine placement increases flutter speed particularly when the engines are placed in the outboard portion of the wing (60-70% span), forward of the elastic axis, while the lift to drag ratio is affected negligibly. The behavior of the sub- and supercritical eigenvalues is studied for two cases of engine placement. NATASHA captures a hump body-freedom flutter with low frequency for the clean wing case, which disappears as the engines are placed on the wings. In neither case is there any apparent coalescence between the unstable modes. NATASHA captures other non-oscillatory unstable roots with very small amplitude, apparently originating with flight dynamics. For the clean-wing case, in the absence of aerodynamic and gravitational forces, the regions of minimum kinetic energy density for the first and third bending modes are located around 60% span. For the second mode, this kinetic energy density has local minima around the 20% and 80% span. The regions of minimum kinetic energy of these modes are in agreement with calculations that show a noticeable increase in flutter speed if engines are placed forward of the elastic axis at these regions.
Pourtakdoust, Seid H.; Aliabadi, Saeed Karimain
Flapping micro air vehicle (FMAV) is considered to exhibit much better performance at low speeds and small sizes compared to fixed-wing MAVs. To maximize the potential and capabilities of FMAVs also to produce adequate design implications, a new aeroelastic model of a typical flexible FMAV is being developed utilizing Euler-Bernoulli torsion beam and quasi steady aerodynamic model. The new model accounts for all natural existing complex interactions between the mass, inertia, elastic properties, aerodynamic loading, flapping amplitude and frequency of the FMAV as well as the effects of several geometric and design parameters. To validate the proposed theoretical model, a typical FMAV as well as instrumented test stand for the online measurement of forces, flapping angle and power consumption have been constructed. The experimental results are initially utilized to validate the flight dynamic model, and several appropriate conclusions are drawn. The model is subsequently used to demonstrate the flapping propulsion characteristics of the FMAV via simulation. Using dimensionless parameters, a set of new generalized curves have been deduced. The results indicate that by proper adjustment of the wing stiffness parameter as a function of the reduced frequency, the FMAV will attain its optimum propulsive efficiency. This fact raises additional new ideas for further research in this area by utilizing intelligent variable stiffness materials and/or or active morphing technology for the sustained, high-performance flight of FMAVs. The generalized model can also be used to conduct a performance and stability analysis of FMAVs and to design and optimize flapping-wing structures.
Advanced Small Perturbation Potential Flow Theory for Unsteady Aerodynamic and Aeroelastic Analyses
Batina, John T.
2005-01-01
An advanced small perturbation (ASP) potential flow theory has been developed to improve upon the classical transonic small perturbation (TSP) theories that have been used in various computer codes. These computer codes are typically used for unsteady aerodynamic and aeroelastic analyses in the nonlinear transonic flight regime. The codes exploit the simplicity of stationary Cartesian meshes with the movement or deformation of the configuration under consideration incorporated into the solution algorithm through a planar surface boundary condition. The new ASP theory was developed methodically by first determining the essential elements required to produce full-potential-like solutions with a small perturbation approach on the requisite Cartesian grid. This level of accuracy required a higher-order streamwise mass flux and a mass conserving surface boundary condition. The ASP theory was further developed by determining the essential elements required to produce results that agreed well with Euler solutions. This level of accuracy required mass conserving entropy and vorticity effects, and second-order terms in the trailing wake boundary condition. Finally, an integral boundary layer procedure, applicable to both attached and shock-induced separated flows, was incorporated for viscous effects. The resulting ASP potential flow theory, including entropy, vorticity, and viscous effects, is shown to be mathematically more appropriate and computationally more accurate than the classical TSP theories. The formulaic details of the ASP theory are described fully and the improvements are demonstrated through careful comparisons with accepted alternative results and experimental data. The new theory has been used as the basis for a new computer code called ASP3D (Advanced Small Perturbation - 3D), which also is briefly described with representative results.
International Nuclear Information System (INIS)
In the present study, aeroelastic simulations of horizontal-axis wind turbine rotor blades were conducted using a coupled CFD-CSD method. The unsteady blade aerodynamic loads and the dynamic blade response due to yaw misalignment and non-uniform sheared wind were investigated. For this purpose, a CFD code solving the RANS equations on unstructured meshes and a FEM-based CSD beam solver were used. The coupling of the CFD and CSD solvers was made by exchanging the data between the two solvers in a loosely coupled manner. The present coupled CFD-CSD method was applied to the NREL 5MW reference wind turbine rotor, and the results were compared with those of CFD-alone rigid blade calculations. It was found that aeroelastic blade deformation leads to a significant reduction of blade aerodynamic loads, and alters the unsteady load behaviours, mainly due to the torsional deformation. The reduction of blade aerodynamic loads is particularly significant at the advancing rotor blade side for yawed flow conditions, and at the upper half of rotor disk where wind velocity is higher due to wind shear
Yu, D. O.; Kwon, O. J.
2014-06-01
In the present study, aeroelastic simulations of horizontal-axis wind turbine rotor blades were conducted using a coupled CFD-CSD method. The unsteady blade aerodynamic loads and the dynamic blade response due to yaw misalignment and non-uniform sheared wind were investigated. For this purpose, a CFD code solving the RANS equations on unstructured meshes and a FEM-based CSD beam solver were used. The coupling of the CFD and CSD solvers was made by exchanging the data between the two solvers in a loosely coupled manner. The present coupled CFD-CSD method was applied to the NREL 5MW reference wind turbine rotor, and the results were compared with those of CFD-alone rigid blade calculations. It was found that aeroelastic blade deformation leads to a significant reduction of blade aerodynamic loads, and alters the unsteady load behaviours, mainly due to the torsional deformation. The reduction of blade aerodynamic loads is particularly significant at the advancing rotor blade side for yawed flow conditions, and at the upper half of rotor disk where wind velocity is higher due to wind shear.
Adams, W. M., Jr.; Tiffany, S. H.
1983-01-01
A control law is developed to suppress symmetric flutter for a mathematical model of an aeroelastic research vehicle. An implementable control law is attained by including modified LQG (linear quadratic Gaussian) design techniques, controller order reduction, and gain scheduling. An alternate (complementary) design approach is illustrated for one flight condition wherein nongradient-based constrained optimization techniques are applied to maximize controller robustness.
Nixon, Mark W.
1993-01-01
There is a potential for improving the performance and aeroelastic stability of tiltrotors through the use of elastically-coupled composite rotor blades. To study the characteristics of tiltrotors with these types of rotor blades it is necessary to formulate a new analysis which has the capabilities of modeling both a tiltrotor configuration and an anisotropic rotor blade. Background for these formulations is established in two preliminary investigations. In the first, the influence of several system design parameters on tiltrotor aeroelastic stability is examined for the high-speed axial flight mode using a newly-developed rigid-blade analysis with an elastic wing finite element model. The second preliminary investigation addresses the accuracy of using a one-dimensional beam analysis to predict frequencies of elastically-coupled highly-twisted rotor blades. Important aspects of the new aeroelastic formulations are the inclusion of a large steady pylon angle which controls tilt of the rotor system with respect to the airflow, the inclusion of elastic pitch-lag coupling terms related to rotor precone, the inclusion of hub-related degrees of freedom which enable modeling of a gimballed rotor system and engine drive-train dynamics, and additional elastic coupling terms which enable modeling of the anisotropic features for both the rotor blades and the tiltrotor wing. Accuracy of the new tiltrotor analysis is demonstrated by a comparison of the results produced for a baseline case with analytical and experimental results reported in the open literature. Two investigations of elastically tailored blades on a baseline tiltrotor are then conducted. One investigation shows that elastic bending-twist coupling of the rotor blade is a very effective means for increasing the flutter velocity of a tiltrotor, and the magnitude of coupling required does not have an adverse effect on performance or blade loads. The second investigation shows that passive blade twist control via
Myrtle, Timothy Fitzgerald
1998-12-01
This dissertation describes the development of an aeroelastic model of a helicopter rotor incorporating partial span trailing edge flaps on the blade and its application to the investigation of vibration reduction using active control. A new two-dimensional unsteady aerodynamic model for an airfoil/flap combination is described that includes compressibility and unsteady freestream effects. This new aerodynamic model is based on a rational function approximation (RFA) approach. In this approach, oscillatory response data obtained for a selected set of generalized airfoil and flap motions is used to generate an approximate aerodynamic transfer function which can be transformed to the time domain to form a state space aerodynamic model. In this dissertation, a method is described for adapting the conventional RFA approach to include unsteady freestream effects. Excellent agreement is demonstrated between the response of the new aerodynamic model and an exact incompressible solution to the unsteady freestream case. This model provides a complete description of the unsteady flap hinge moments due to airfoil and flap motion, allowing a complete and accurate characterization of control actuation requirements. The structural model utilizes an elastic blade model which includes fully coupled flap-lag-torsional dynamics and includes the effects of moderate deflections. The aeroelastic model is formulated in the time domain, with the coupled trim/response solution obtained using direct numerical integration in combination with autopilot type controller. A conventional higher harmonic control approach is used to investigate vibration reduction. Vibration control studies are performed which compare results using the new aerodynamic model and incompressible quasisteady Theodorsen aerodynamics. Significant differences were observed in the required deflections and control moments, indicating that compressibility and unsteady effects are necessary to properly characterize the
Aeroelastic Stability of Damperless Rotor Blade%无减摆器旋翼桨叶气弹稳定性分析
Institute of Scientific and Technical Information of China (English)
夏品奇; 周景良
2012-01-01
无减摆器旋翼具有桨毂结构简单、桨毂气动阻力小、桨毂维护简便等优点,但取消了桨毂减摆器后必须确保桨叶在摆振方向有足够的阻尼以保证桨叶的摆振稳定性.基于气弹耦合的方法是实现无减摆器旋翼桨叶摆振稳定性的一个有效方法.建立了无减摆器无铰式旋翼桨叶带有预锥角、下垂角、后掠角和预扭角等结构参数的非线性气弹动力学模型,利用伽辽金方法把桨叶偏微分运动方程简化为非线性常微分平衡方程和关于平衡位置的小扰动运动方程,分析了桨叶的气弹稳定性并进行了参数影响分析.数值结果表明,合理的桨叶结构参数和气弹耦合可确保无减摆器旋翼桨叶在摆振方向的气弹稳定性.%The damperless rotor has the advantage of the hub with simple structure, small aerodynamic drag and easy maintainance. However, without blade lag damper, the blade must have sufficient damping in the lag direction to ensure lag stability. And the aeroelastic coupling based method can approach that effectively. Therefore, the nonlinear aeroelastic dynamic model is established for the damperless and hingeless rotor blade with structural parameters of pre-cone angle, pre-droop angle, sweep angle and pre-twist angle. By using the Galerkin method, the partial differential equations of motion are simplified to the nonlinear ordinary differential balance equations and the small perturbation equations for the equilibrium positions. The blade aeroelastic stability and the parameters effects are analyzed. The numerical results show that reasonable structural parameters and aeroelastic coupling of blade can ensure the aeroelastic stability of damperless rotor blade in the lag direction.
Energy Technology Data Exchange (ETDEWEB)
Guntur, Sirnivas; Jonkman, Jason; Schreck, Scott; Jonkman, Bonnie; Wang, Qi; Sprague, Michael; Hind, Michael; Sievers, Ryan
2016-01-27
This paper presents findings from a verification and validation exercise on the latest version of the U.S. Department of Energy/National Renewable Energy Laboratory's in-house wind turbine aeroelastic design code FAST v8. Results from a set of 1141 FAST simulations were compared to those from Siemens' BHawC design code results, as well as experimental data from a heavily instrumented 2.3-MW Siemens wind turbine located at the National Wind Technology Center. The code validation was performed following the IEC-61400-13 standard, where a set of select quantities of interest from simulations at various wind speed and atmospheric turbulence conditions were used for a three-way comparison between FAST, BHawC, and the measurements. Results highlight many improvements of the latest version of FAST over its previous versions. This paper also provides comments from the authors on the data quality, and avenues for potential future work using these results.
Tomasini, Gisella; Giappino, Stefano; Costa, Andrea
2016-04-01
Energy harvesting from galloping oscillations of a bluff body can be used to supply power to a wireless sensor. In this paper we investigate the possibility to use a galloping-based piezo-aeroelastic energy harvester to supply power to a wireless sensors network installed on a freight train to measure the accelerations in correspondence of axle boxes. The monitoring system will be used to detect possible deteriorations of the running conditions that, in the worst cases, can lead to the vehicle derailment. Unlike other applications in this case the air speed relative to the body is due to the train motion and, for typical freight trains and standard running conditions, is equal to about 20 m/s. In the paper we discuss the design of the harvester on the basis of the constrains due to the application. Preliminary aerodynamic tests shows the limitation of the classical quasi-steady theory of galloping as a consequence of the interaction with the vortex shedding phenomenon.
Frøyd, Lars
2009-01-01
The evolution of wind turbines are going towards floating offshore structures. To improve the stability of these turbines, the weight of the nacelle should be as low as possible. The company ChapDrive has developed a hydraulic drive train that gives the ability to move the generator to the base of the tower and to replace the traditional gearbox. To test the system, ChapDrive has constructed a prototype turbine which is located at Valsneset.This thesis describes the combined aero-elastic and...
Czech Academy of Sciences Publication Activity Database
Náprstek, Jiří; Pospíšil, Stanislav; Yau, J. D.
2015-01-01
Roč. 57, August (2015), s. 91-107. ISSN 0889-9746 R&D Projects: GA MŠk(CZ) LO1219; GA ČR(CZ) GC13-34405J Institutional support: RVO:68378297 Keywords : aero-elastic system * self-excited vibration * dynamic stability * Routh–Hurwitz conditions * flutter derivatives * divergence Subject RIV: JM - Building Engineering Impact factor: 2.021, year: 2014 http://dx.doi.org/10.1016/j.jfluidstructs.2015.05.010
Nguyen, Nhan; Ting, Eric; Lebofsky, Sonia
2015-01-01
This paper presents data analysis of a flexible wing wind tunnel model with a variable camber continuous trailing edge flap (VCCTEF) design for drag minimization tested at the University of Washington Aeronautical Laboratory (UWAL). The wind tunnel test was designed to explore the relative merit of the VCCTEF concept for improved cruise efficiency through the use of low-cost aeroelastic model test techniques. The flexible wing model is a 10%-scale model of a typical transport wing and is constructed of woven fabric composites and foam core. The wing structural stiffness in bending is tailored to be half of the stiffness of a Boeing 757-era transport wing while the torsional stiffness is about the same. This stiffness reduction results in a wing tip deflection of about 10% of the wing semi-span. The VCCTEF is a multi-segment flap design having three chordwise camber segments and five spanwise flap sections for a total of 15 individual flap elements. The three chordwise camber segments can be positioned appropriately to create a desired trailing edge camber. Elastomeric material is used to cover the gaps in between the spanwise flap sections, thereby creating a continuous trailing edge. Wind tunnel data analysis conducted previously shows that the VCCTEF can achieve a drag reduction of up to 6.31% and an improvement in the lift-to-drag ratio (L=D) of up to 4.85%. A method for estimating the bending and torsional stiffnesses of the flexible wingUWAL wind tunnel model from static load test data is presented. The resulting estimation indicates that the stiffness of the flexible wing is significantly stiffer in torsion than in bending by as much as 9 to 1. The lift prediction for the flexible wing is computed by a coupled aerodynamic-structural model. The coupled model is developed by coupling a conceptual aerodynamic tool Vorlax with a finite-element model of the flexible wing via an automated geometry deformation tool. Based on the comparison of the lift curve slope
Institute of Scientific and Technical Information of China (English)
Yue WU; Zhao-qing CHEN; Xiao-ying SUN
2015-01-01
The aero-elastic instability mechanism of a tensioned membrane structure is studied in this paper. The response and wind velocities above two closed-type saddle-shaped tensioned membrane structures, with the same shape but different pre-tension levels, were measured in uniform flow and analyzed. The results indicate that, for most wind directions, several vibration modes are excited and the amplitude and damping ratio of the roof slowly increase with the on-coming flow velocity. However, for particular wind directions, only one vibration mode is excited, and the amplitude and damping ratio of the vibration mode increase slowly with the on-coming flow velocity. The aero-elastic instability is caused by vortex-induced resonance. On ex-ceeding a certain wind speed, the amplitude of the roof vibration increases sharply and the damping ratio of the vibration mode decreases quickly to near zero; the frequency of the vortex above the roof is locked in by the vibration within a certain wind velocity range; the amplitudes of the roof in these wind directions reach 2–4 times the amplitudes for other wind directions. The reduced critical wind speeds for the aero-elastic instability of saddle-shaped membrane structures at the first two modes are around 0.8–1.0.%目的：明确张拉膜结构风致气弹响应特征及气弹失稳机理。 创新点：1.采用无接触测量技术设计鞍形张拉膜结构气弹模型风洞试验；2.研究鞍形张拉膜结构的气弹响应特征；3.给出鞍形张拉膜结构的失稳机理。 方法：1.在风洞中测量两个形状相同但预张力不同的封闭式鞍形张拉膜结构气弹模型在不同风速下的均匀流中的位移响应及膜面上方不同高度的风速时程；2.通过对位移响应及风速时程进行分析，明确结构的响应随风速变化特征及气弹失稳原因。 结论：1.膜结构在风荷载作用下变形到平衡位置，并围绕该平衡位置
International Nuclear Information System (INIS)
Optical full-field measurement methods such as Digital Image Correlation (DIC) provide a new opportunity for measuring deformations and vibrations with high spatial and temporal resolution. However, application to full-scale wind turbines is not trivial. Elaborate preparation of the experiment is vital and sophisticated post processing of the DIC results essential. In the present study, a rotor blade of a 3.2 MW wind turbine is equipped with a random black-and-white dot pattern at four different radial positions. Two cameras are located in front of the wind turbine and the response of the rotor blade is monitored using DIC for different turbine operations. In addition, a Light Detection and Ranging (LiDAR) system is used in order to measure the wind conditions. Wind fields are created based on the LiDAR measurements and used to perform aeroelastic simulations of the wind turbine by means of advanced multibody codes. The results from the optical DIC system appear plausible when checked against common and expected results. In addition, the comparison of relative out-ofplane blade deflections shows good agreement between DIC results and aeroelastic simulations
Goldman, Benjamin D.; Dowell, Earl H.; Scott, Robert C.
2015-01-01
Conical shell theory and a supersonic potential flow aerodynamic theory are used to study the nonlinear pressure buckling and aeroelastic limit cycle behavior of the thermal protection system for NASA's Hypersonic Inflatable Aerodynamic Decelerator. The structural model of the thermal protection system consists of an orthotropic conical shell of the Donnell type, resting on several circumferential elastic supports. Classical Piston Theory is used initially for the aerodynamic pressure, but was found to be insufficient at low supersonic Mach numbers. Transform methods are applied to the convected wave equation for potential flow, and a time-dependent aerodynamic pressure correction factor is obtained. The Lagrangian of the shell system is formulated in terms of the generalized coordinates for all displacements and the Rayleigh-Ritz method is used to derive the governing differential-algebraic equations of motion. Aeroelastic limit cycle oscillations and buckling deformations are calculated in the time domain using a Runge-Kutta method in MATLAB. Three conical shell geometries were considered in the present analysis: a 3-meter diameter 70 deg. cone, a 3.7-meter 70 deg. cone, and a 6-meter diameter 70 deg. cone. The 6-meter configuration was loaded statically and the results were compared with an experimental load test of a 6-meter HIAD. Though agreement between theoretical and experimental strains was poor, the circumferential wrinkling phenomena observed during the experiments was captured by the theory and axial deformations were qualitatively similar in shape. With Piston Theory aerodynamics, the nonlinear flutter dynamic pressures of the 3-meter configuration were in agreement with the values calculated using linear theory, and the limit cycle amplitudes were generally on the order of the shell thickness. The effect of axial tension was studied for this configuration, and increasing tension was found to decrease the limit cycle amplitudes when the circumferential
Kelly, G. L.; Berthold, G.; Abbott, L.
1982-01-01
A 5 MHZ single-board microprocessor system which incorporates an 8086 CPU and an 8087 Numeric Data Processor is used to implement the control laws for the NASA Drones for Aerodynamic and Structural Testing, Aeroelastic Research Wing II. The control laws program was executed in 7.02 msec, with initialization consuming 2.65 msec and the control law loop 4.38 msec. The software emulator execution times for these two tasks were 36.67 and 61.18, respectively, for a total of 97.68 msec. The space, weight and cost reductions achieved in the present, aircraft control application of this combination of a 16-bit microprocessor with an 80-bit floating point coprocessor may be obtainable in other real time control applications.
Aeroelastic stability of a transonic axial compressor fan blade%跨音轴流风扇叶片气弹稳定性研究
Institute of Scientific and Technical Information of China (English)
赵瑞勇; 杨慧; 王延荣
2011-01-01
The aeroelastic stability of a NASA 67 transonic fan blade was predicted by using the energy method in the near stall condition. The CSD/CFD data transfer was based on the improved 3D linear interpolation method. The FLUENT dynamic mesh technology was used in the simulation of unsteady flow around the oscillating blade. The unsteady aerodynamic response of NASA 67 blade under excitation of the first three modes was studied. It was found that the phase angle between unsteady aerodynamic forces and vibration displacements Decides that the unsteady aerodynamic force do positive or negative work; the analysis of unsteady surface pressures reveals that the modal shape and the shock are the main influence factors on the aeroelastic stability of the rotor blade.%基于弱耦合的能量法原理,对近失速工况下NASA 67跨音风扇叶片进行了气弹稳定性分析.发展的三维线性插值方法为CSD/CFD数据交换提供了基础.采用FLUENT动网格技术,实现了振动叶片绕流计算.数值模拟了NASA 67叶片前三阶模态振型激励下的非定常气动响应.通过分析叶片表面非定常气动力和振动位移之间的相位差发现:该相位差的存在决定了非定常气动力做功的正、负.由叶片表面非定常压力分析结果得出近失速工况下,叶片的气动弹性稳定性受叶片模态振型和激波的影响较为显著.
Stochstic modelling in aeroelasticity
Czech Academy of Sciences Publication Activity Database
Náprstek, Jiří
Alicante : WIT Press, 2001 - (Esteve, Y.; Carlomagno, G.; Brebbia, C.), s. 467-476 ISBN 1-85312-870-8. [Computational methods and experimental measurements /10./. Alicante (ES), 04.06.2001-06.06.2001] R&D Projects: GA ČR GA103/99/0122 Keywords : galloping, Lyapunov function, stochastic stability. Subject RIV: JM - Building Engineering
Raeesi, Arash; Cheng, Shaohong; Ting, David S.-K.
2016-08-01
The possibility of bridge stay cables experiencing violent dry inclined cable galloping raises great concern in the engineering community. Numerous experimental and analytical studies have been conducted to investigate this phenomenon, most of which were in the context of steady wind past a rigid cylindrical body. Real stay cables however, are generally long and flexible. They are exposed to more "broad" range of atmospheric boundary layer type of wind velocity profile which is also unsteady and turbulent by nature. To better understand the physics underlying this type of wind-induced cable vibration and to elucidate various contributing factors, a more realistic analytical model which is capable of addressing the above elements is imperative. In the current paper, a three-dimensional aeroelastic model is proposed to study the aerodynamic response of an inclined and/or yawed slender flexible cylindrical body subjected to unsteady mean wind, with practical application to wind-induced vibrations of bridge stay cables under no precipitation condition. The non-linear aerodynamic forces derived in the present study are combined with the cable free vibration equations available in literature to obtain the equations of motion for the wind-induced vibration of stay cables, which are solved numerically by an explicit finite difference scheme. The proposed three-dimensional aeroelastic model and numerical solution technique are validated by comparing the predicted cable free vibration responses with existing data in the literature. The mechanism which triggers dry inclined cable galloping and the required conditions for its growth are explored. In addition, the impact of different initial conditions and various unsteady mean wind scenarios on this violent cable motion are investigated. Results show that the occurrence of dry inclined cable galloping is associated with an opposite-phase relation between the relative wind speed and the aerodynamic force along the direction of
Mihalca, Alexander G.; Drosinos, Jonathan G.; Grayson, Malika; Garcia, Ephrahim
2015-03-01
Bending piezoelectric transducers have the ability to harvest energy from aeroelastic vibrations induced by the ambient airflow. Such harvesters can have useful applications in the operation of low power devices, and their relatively small size makes them ideal for use in urban environments over civil infrastructure. One of the areas of focus regarding piezoelectric energy harvesting is the circuit topology used to store the harvested power. This study aims to further investigate the increase in potential energy yield from the piezoelectric harvester by optimizing the circuitry connecting the piezoelectric transducer and the power storage interface. When compared to an optimal resistive load case, it has been shown that certain circuit topologies, specifically synchronized switching and discharging to a storage capacitor through an inductor (SSDCI), can increase the charging power by as much as 400% if the circuit is completely lossless. This paper proposes a strategy for making a self-sufficient SSDCI circuit capable of peak detection for the synchronized switching using analog components. Using circuit simulation software, the performance of this proposed self-sufficient circuit is compared to an ideal case, and the effectiveness of the self-sufficient circuit strategy is discussed based on these simulation results. Further investigation of a physical working model of the new circuit proposal will be developed and experimental results of the circuit's performance obtained and compared to the estimated performance from the model.
Energy Technology Data Exchange (ETDEWEB)
Schelenz, Ralf; Flock, Sebastian [Technische Hochschule Aachen (Germany). Inst. fuer Maschinenelemente und Maschinengestaltung; Moeller, Dennis [Bosch Rexroth AG, Elchingen (Germany)
2010-07-01
During the project engineering of new wind power plants for the determination of the loads tools such as Flex5, Bladed or B-Hawk are used. These tools are focused for the description of the aerodynamic characteristics. These tools are appreciative simulation references with the OEM. For the structural design of drive shafts a simulation of the entire drive shaft is necessary beside the tools mentioned above. An insulating view of the drive shaft is not successfully. In the contribution under consideration it is shown that the fastidious goal of a fully integrated simulation can be converted successfully with simulation with an aeroelastic rotor in the three-dimensional wind field. This is shown at selected transient load situations. The simulation model is characterised by a fully integrated simulation beginning. The current state of the art is the conversion in partial models.
基于大涡模拟的三维高层建筑结构气弹响应数值模拟%LES based numerical simulation of aeroelastic response of a 3D tall building
Institute of Scientific and Technical Information of China (English)
郑德乾; 顾明; 张爱社
2013-01-01
以宽高比为1:6的方形截面高层建筑为研究对象,采用弱耦合分区交错算法,流体域采用大涡模拟方法,进行了紊流边界层风场内三维高层建筑结构多自由度模型的气弹数值模拟,计算中考虑了来流紊流,以及结构的顺、横风向响应.将结构静止时大涡模拟结果与刚性模型测压风洞试验进行比较,验证了该方法在准确预测结构风荷载方面的可行性.通过与气弹模型风洞试验结果的比较表明,本文数值分析方法可用于求解风与结构的相互作用,且具有较高的精度.进行了高折减风速下的气弹数值模拟,研究了结构顶部顺、横风向位移响应随折减风速的变化规律.结果表明:结构风振气弹响应主要为来流紊流引起的顺风向抖振和旋涡脱落引起的横风向涡激振动;折减风速较小时,结构顺、横风向位移振幅相当,且位移响应均相对较小;随着折减风速的增加,结构位移响应增大,横风向涡激振动逐渐占据主导地位,并经历了从“拍”到“涡激共振”的转化.%The aeroelastic response of a square section tall building with 1:6 width to height aspect ratio in atmospheric boundary layer was numerically simulated,using loosely coupled method.In the present study,large eddy simulation technique was adopted with consideration of inflow turbulence.The wind-induced along and across vibration responses were both considered.The present method was verified to be able to accurately predict wind loads on buildings at rest,by comparing large eddy simulation results with rigid model wind tunnel experiment.The simulated wind-induced along and across vibration responses were compared with corresponding aeroelastic model wind tunnel experiments.The comparison results show that the present method is applicable to a certain extent in solving windstructure-interaction problems.Aeroelastic responses of the building model under high reduced wind velocities were also
基于能量法的跨声速风扇叶片气弹稳定性研究%Rearch on Aeroelastic Stability of Transonic Fan Blade Based on Energy Method
Institute of Scientific and Technical Information of China (English)
赵瑞勇; 杨慧; 王延荣
2011-01-01
Based on energy method,the aeroelastic stability of transonic fan blade was analyzed by weak coupling method.The data exchange of CSD/CFD was achieved by the 3D linear interpolation method.The mode shape and natural frequency of the blade was calculated by the Finite Element（FE） method.The numerical simulation of the unsteady flow field for NASA R67 fan blade in the different vibration modes was conducted by the FLUENT dynamic mesh technology.The cycle accumulated aerodynamic work and aerodynamic damping of blade surfaces at the first three vibration mode was obtained.The effect of shock wave on the aeroelastic stability of transonic fan blade was discussed.%基于能量法原理,采用弱耦合的方法对跨声速风扇叶片进行气弹稳定性分析;采用3维线性插值算法编程实现CSD/CFD数据交换。利用有限元法计算叶片的模态振型和固有振动频率;应用FLUENT动网格技术,对NASA R 67风扇叶片在不同模态振动下的非定常流场进行数值模拟,给出在前3阶模态振动下叶片表面的周期累积气动功和气动阻尼,并探讨了激波对跨声速风扇叶片气弹稳定性的影响。
Aeroelastic Uncertainty Analysis Toolbox Project
National Aeronautics and Space Administration — Flutter is a potentially explosive phenomenon that results from the simultaneous interaction of aerodynamic, structural, and inertial forces. The nature of flutter...
Aeroelastic Uncertainty Analysis Toolbox Project
National Aeronautics and Space Administration — Flutter is a potentially explosive phenomenon that is the result of the simultaneous interaction of aerodynamic, structural, and inertial forces. The analytical...
Research in aeroelasticity EFP-2005
DEFF Research Database (Denmark)
2006-01-01
winglet to a wind turbine blade for minimizing the induced drag of the blade led to the biggest increase in power of 1.4%. Transient wind loads during pitch motion are determined using CFD. Compared to theNREL/NASA Ames test, reasonably good agreement is seen. A general method was developed for the......, locally can be increased significantly beyond the Betz limit, but that the global CP for the rotorcannot exceed the Betz limit. When including tip losses and a minimum blade drag coefficient, a maximum rotor CP in the range of 0.51-0.52 was obtained. A new airfoil family was designed and a 3D airfoil...... asymptotic model for the PDF of the largest excursion from the mean level, during an arbitrary recurrence period, has been derived for a stochastic wind speed process driven by atmospheric turbulence. Thesimulation of an offshore monopile foundation with HAWC2 showed a reduction of the first tower frequency...
Institute of Scientific and Technical Information of China (English)
刘伟; 尹家聪; 陈璞; 苏先樾
2011-01-01
Parametric modeling technique is developed to fast build the three-dimensional finite element shell model of a preliminarily designed large composite wind turbine blade, which is subsequently used in the dynamic analysis and static elastic aeroelastic stability analysis of the blade. In the dynamic analysis, natural frequencies and corresponding modal shapes are obtained for the blade in the case of being still as well as being rotating with rated revolution. For the rotating blade, the stress stiffening effect and spin-softening effect due to the centrifugal forces are taken into account. The static elastic aeroelastic stability analysis, i.e. buckling analysis in this paper, is distinct from its counterparts in adopting the pressure distributions obtained from CFD (Computational Fluid Dynamics) calculations as the loads. An interpolation code is developed to address the mismatch between the unstructured CFD grids of the blade surface and the finite shell elements used in the buckling analysis, allowing mapping the pressures computed by using CFD to the finite element model. It is concluded that structural analysis of large composite wind turbine blades using three-dimensional finite element shell model is beneficial to revealing the relatively weak zones of the blades.%采用参数化建模技术快速建立大型风力机复合材料叶片三维有限元壳模型,并在此基础上对叶片的固有动力学特性进行停机及以额定转速旋转两种工况下的模态分析,其中旋转工况考虑了离心力导致的应力刚化效应和旋转软化效应.通过编制插值程序,将CFD计算所得的叶片表面分布压力,导算到叶片结构计算的有限元壳模型上,并以此为载荷对叶片进行静气弹稳定性分析.以某初步设计的1.5MW风机为例的计算结果表明:在参数化三维壳模型建模基础上进行的模态分析技术与结合CFD的静气弹稳定性分析技术,有利于快速、准确地计算大型复合材
Vorticity State Estimation For Aeroelastic Control Project
National Aeronautics and Space Administration — Flight control, structural reliability, and efficiency depend critically on the ability to assess the time-accurate unsteady aerodynamic loads and moments for each...
Research in Aeroelasticity EFP-2007-II
DEFF Research Database (Denmark)
dominated by large flow gradients caused by unsteady shedding of vortices from the root sections of the blades. • The averaged nacelle wind speed compares well to the freestream wind speed, whereas the nacelle flow angle is highly sensitive to vertical positioning and tilt in the inflow. • The trailing edge...... demonstrated. For attached flow over thin airfoils (18%) 2D computations provide good results while a combination of Detached Eddy Simulation and laminar/ turbulent transition modeling improve the results in stalled conditions for a thick airfoil. • The unsteady flow in the nacelle region of a wind turbine is...... performance from wind tunnel experiments. • The stochastic fluctuations of the aerodynamic forces on blades in deep-stall have an insignificant effect on the risk of stallinduced vibrations predicted by quasi-steady aerodynamic models, but more realistic models of deep-stall aerodynamics must be developed to...
New aeroelastic studies for a morphing wing
Ruxandra Mihaela BOTEZ; Andrei Vladimir POPOV; Samuel COURCHESNE
2012-01-01
For this study, the upper surface of a rectangular finite aspect ratio wing, with a laminar airfoil cross-section, was made of a carbon-Kevlar composite material flexible skin. This flexible skin was morphed by use of Shape Memory Alloy actuators for 35 test cases characterized by combinations of Mach numbers, Reynolds numbers and angles of attack. The Mach numbers varied from 0.2 to 0.3 and the angles of attack ranged between -1° and 2°. The optimized airfoils were determined by use of the C...
Finite element simulation of aeroelasticity problems
Czech Academy of Sciences Publication Activity Database
Horáček, Jaromír; Sváček, P.; Feistauer, M.
Plzeň : ZČU Plzeň, 2014 - (Laš, V.; Krystek, J.), s. 14-22 ISBN 978-80-261-0445-2. [Výpočty konstrukcí metodou konečných prvků. Plzeň (CZ), 27.11.2014] R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional support: RVO:61388998 Keywords : airfoil gust response * airfoil flutter * Reynolds average * Navier-Stokes equations Subject RIV: BI - Acoustics
Aeroelastically Tailored Wing Structures (ATWIST) Project
National Aeronautics and Space Administration — Aurora will develop a novel composite sandwich structure that is capable of providing a coupled bending-torsional stiffness with nonlinear elastic effects, capable...
ACOUSTIC EFFECTS ON BINARY AEROELASTICITY MODEL
Directory of Open Access Journals (Sweden)
Kok Hwa Yu
2011-10-01
Full Text Available Acoustics is the science concerned with the study of sound. The effects of sound on structures attract overwhelm interests and numerous studies were carried out in this particular area. Many of the preliminary investigations show that acoustic pressure produces significant influences on structures such as thin plate, membrane and also high-impedance medium like water (and other similar fluids. Thus, it is useful to investigate the structure response with the presence of acoustics on aircraft, especially on aircraft wings, tails and control surfaces which are vulnerable to flutter phenomena. The present paper describes the modeling of structural-acoustic interactions to simulate the external acoustic effect on binary flutter model. Here, the binary flutter model which illustrated as a rectangular wing is constructed using strip theory with simplified unsteady aerodynamics involving flap and pitch degree of freedom terms. The external acoustic excitation, on the other hand, is modeled using four-node quadrilateral isoparametric element via finite element approach. Both equations then carefully coupled and solved using eigenvalue solution. The mentioned approach is implemented in MATLAB and the outcome of the simulated result are later described, analyzed and illustrated in this paper.
Aeroelastic vibrations and stability of plates and shells
Algazin, Sergey D
2015-01-01
Back-action of wind onto wings causes vibrations, endangering the whole structure. By careful choices of geometry, materials and damping, hazardous effects on wind engines, planes, turbines and cars can be avoided. This book gives an overview of aerodynamics and mechanics behind these problems and describes a range of mechanical effects. Numerical and analytical met
An electret-based aeroelastic flutter energy harvester
International Nuclear Information System (INIS)
This paper presents a new airflow energy harvester exploiting fluttering effects coupled to an electret-based conversion to turn the flow-induced movements of a membrane into electricity. The proposed device is made of a polymer membrane placed between two parallel flat electrodes coated with 25 μm thick Teflon PTFE electret layers; a bluff body is placed at the inlet of the device to induce vortex shedding. When the wind or airstream of any kind flows through the harvester, the membrane enters in oscillation due to fluttering and successively comes into contact with the two Teflon-coated fixed electrodes. This periodic motion is directly converted into electricity thanks to the electret-based conversion process. Various geometries have been tested and have highlighted a 2.7 cm3 device, with an output power of 481 μW (178 μW cm−3) at 15 m s−1 and 2.1 mW (782 μW cm−3) at 30 m s−1 with an electret charged at −650 V. The power coefficient Cp of the device reaches 0.54% at 15 m s−1 which is low, but compares favorably with the other small-scale airflow energy harvesters. (paper)
Aeroelastic instability of a flexible plate in a uniform flow
Eloy, Christophe; Souilliez, Claire; Schouveiler, Lionel
2008-01-01
The flutter instability of a flexible plate immersed in an axial flow is experimentally investigated. This instability is similar to flag flutter and results from the competition between destabilizing pressure forces and stabilizing bending stiffness. The instability threshold is measured as a function of the experimental parameters (plate size and aspect ratio) and compared to different theoretical predictions.
Calculation of wind turbine aeroelastic behaviour. The Garrad Hassan approach
Energy Technology Data Exchange (ETDEWEB)
Quarton, D.C. [Garrad Hassan and Partners Ltd., Bristol (United Kingdom)
1996-09-01
The Garrad Hassan approach to the prediction of wind turbine loading and response has been developed over the last decade. The goal of this development has been to produce calculation methods that contain realistic representation of the wind, include sensible aerodynamic and dynamic models of the turbine and can be used to predict fatigue and extreme loads for design purposes. The Garrad Hassan calculation method is based on a suite of four key computer programs: WIND3D for generation of the turbulent wind field; EIGEN for modal analysis of the rotor and support structure; BLADED for time domain calculation of the structural loads; and SIGNAL for post-processing of the BLADED predictions. The interaction of these computer programs is illustrated. A description of the main elements of the calculation method will be presented. (au)
Aeroelastic code development activities in the United States
Energy Technology Data Exchange (ETDEWEB)
Wright, A.D. [National Renewable Energy Lab., Golden, Colorado (United States)
1996-09-01
Designing wind turbines to be fatigue resistant and to have long lifetimes at minimal cost is a major goal of the federal wind program and the wind industry in the United States. To achieve this goal, we must be able to predict critical loads for a wide variety of different wind turbines operating under extreme conditions. The codes used for wind turbine dynamic analysis must be able to analyze a wide range of different wind turbine configurations as well as rapidly predict the loads due to turbulent wind inflow with a minimal set of degrees of freedom. Code development activities in the US have taken a two-pronged approach in order to satisfy both of these criteria: (1) development of a multi-purpose code which can be used to analyze a wide variety of wind turbine configurations without having to develop new equations of motion with each configuration change, and (2) development of specialized codes with minimal sets of specific degrees of freedom for analysis of two- and three-bladed horizontal axis wind turbines and calculation of machine loads due to turbulent inflow. In the first method we have adapted a commercial multi-body dynamics simulation package for wind turbine analysis. In the second approach we are developing specialized codes with limited degrees of freedom, usually specified in the modal domain. This paper will summarize progress to date in the development, validation, and application of these codes. (au) 13 refs.
Sensitivity of Aeroelastic Properties of an Oscillating LPT Cascade
Glodic, Nenad
2013-01-01
Modern turbomachinery design is characterized by a tendency towards thinner, lighter and highly loaded blades, which in turn gives rise to increased sensitivity to flow induced vibration such as flutter. Flutter is a self-excited and self-sustained instability phenomenon that may lead to structural failure due to High Cycle Fatigue (HCF) or material overload. In order to be able to predict potential flutter situations, it is necessary to accurately assess the unsteady aerodynamics during flut...
Aeroelastic model identification of winglet loads from flight test data
Reijerkerk, M.J.
2008-01-01
Numerical computational methods are getting more and more sophisticated every day, enabling more accurate aircraft load predictions. In the structural design of aircraft higher levels of flexibility can be tolerated to arrive at a substantial weight reduction. The result is that aircraft of the futu
Aeroelastic model identification of winglet loads from flight test data
Reijerkerk, M.J.
2008-01-01
Numerical computational methods are getting more and more sophisticated every day, enabling more accurate aircraft load predictions. In the structural design of aircraft higher levels of flexibility can be tolerated to arrive at a substantial weight reduction. The result is that aircraft of the future can be bigger, have better performance and less mass. The performance of an aircraft can be even further enhanced by the use of winglets or other wing tip devices. A more flexible structure in c...
Static Aeroelastic Optimization of Composite Wings with Variable Stiffness Laminates
Dillinger, J.K.S.
2014-01-01
The application of composite material in load carrying structural components of an aircraft is rapidly gaining momentum. While part of the reason for this can certainly be attributed to an increasing confidence of designers in the new material as a result of growing experience, two other crucial poi
Static Aeroelastic Optimization of Composite Wings with Variable Stiffness Laminates
Dillinger, J.K.S.
2014-01-01
The application of composite material in load carrying structural components of an aircraft is rapidly gaining momentum. While part of the reason for this can certainly be attributed to an increasing confidence of designers in the new material as a result of growing experience, two other crucial points can be made. One, the continuous enhancements in the area of automated production technologies, which are an absolute necessity for ensuring consistent quality in a series production. Two, the ...
Optimization of aeroelastic composite structures using evolutionary algorithms
Manan, A.; Vio, G. A.; Harmin, M. Y.; Cooper, J. E.
2010-02-01
The flutter/divergence speed of a simple rectangular composite wing is maximized through the use of different ply orientations. Four different biologically inspired optimization algorithms (binary genetic algorithm, continuous genetic algorithm, particle swarm optimization, and ant colony optimization) and a simple meta-modeling approach are employed statistically on the same problem set. In terms of the best flutter speed, it was found that similar results were obtained using all of the methods, although the continuous methods gave better answers than the discrete methods. When the results were considered in terms of the statistical variation between different solutions, ant colony optimization gave estimates with much less scatter.
Aeroelastic stability and response of horizontal axis wind turbine blades
Kottapalli, S. B. R.; Friedmann, P. P.; Rosen, A.
1979-01-01
Coupled flap-lag-torsion equations of motion of an isolated horizontal axis wind turbine (HAWT) blade have been formulated. The analysis neglects blade-tower coupling. The final nonlinear equations have periodic coefficients. A new and convenient method of generating an appropriate time-dependent equilibrium position, required for the stability analysis, has been implemented and found to be computationally efficient. Steady-state response and stability boundaries for an existing (typical) HAWT blade are presented. Such stability boundaries have never been published in the literature. The results show that the isolated blade under study is basically stable. The tower shadow (wake) has a considerable effect on the out-of-plane response but leaves blade stability unchanged. Nonlinear terms can significantly affect linearized stability boundaries; however, they have a negligible effect on response, thus implying that a time-dependent equilibrium position (or steady-state response), based completely on the linear system, is appropriate for the type of HAWT blades under study.
Aeroelastically coupled blades for vertical axis wind turbines
Energy Technology Data Exchange (ETDEWEB)
Paquette, Joshua; Barone, Matthew F.
2016-02-23
Various technologies described herein pertain to a vertical axis wind turbine blade configured to rotate about a rotation axis. The vertical axis wind turbine blade includes at least an attachment segment, a rear swept segment, and optionally, a forward swept segment. The attachment segment is contiguous with the forward swept segment, and the forward swept segment is contiguous with the rear swept segment. The attachment segment includes a first portion of a centroid axis, the forward swept segment includes a second portion of the centroid axis, and the rear swept segment includes a third portion of the centroid axis. The second portion of the centroid axis is angularly displaced ahead of the first portion of the centroid axis and the third portion of the centroid axis is angularly displaced behind the first portion of the centroid axis in the direction of rotation about the rotation axis.
Parallel aeroelastic computations for wing and wing-body configurations
Byun, Chansup
1994-01-01
The objective of this research is to develop computationally efficient methods for solving fluid-structural interaction problems by directly coupling finite difference Euler/Navier-Stokes equations for fluids and finite element dynamics equations for structures on parallel computers. This capability will significantly impact many aerospace projects of national importance such as Advanced Subsonic Civil Transport (ASCT), where the structural stability margin becomes very critical at the transonic region. This research effort will have direct impact on the High Performance Computing and Communication (HPCC) Program of NASA in the area of parallel computing.
Uncertainty Quantification of Piezoelectric Energy Harvesters from Aeroelastic Vibrations
Directory of Open Access Journals (Sweden)
Abdelkefi Abdessattar
2012-07-01
Full Text Available A stochastic approach is presented to evaluate the uncertainties associated with variations in design parameters of a piezoaeroelastic energy harvester. The sensitivities of the harvested power to variations in the load resistance, the eccentricity (distance between the center of mass and the elastic axis, and the nonlinear coeffcients are also determined. Moreover, the non-intrusive formulation of the polynomial chaos expansion in terms of the multivariate Hermite polynomials was employed to quantify the sensitivities in the harvested power and the plunge and pitch motions. The results show that the relationship between the input parameters and the harvested power is highly nonlinear. The results show also that the generated power is most sensitive to variations in the eccentricity and that the nonlinear coeffcient of the plunge spring is less influential than the nonlinear coeffcient of the torsional spring on the harvester’s performance.
Aeroelastic Vibrations and Stability in Cyclic Symmetric Domains
Directory of Open Access Journals (Sweden)
Bernard Lalanne
2000-01-01
wing. In this way, aerodynamic forces may be obtained as general as required, depending on successive time derivatives of degrees of freedom in addition to themselves. Finally, some special cases are given and stability is studied for a cyclic periodic blade assembly, even when mistuning between sectors can occur.
A nonlinear computational aeroelasticity model for aircraft wings
Feng, Zhengkun
Cette these presente le developpement d'un code d'aeroelasticite nonlineaire base sur un solveur CFD robuste afin de l'appliquer aux ailes flexibles en ecoulement transsonique. Le modele mathematique complet est base sur les equations du mouvement des structures et les equations d'Euler pour les ecoulements transsoniques non-visqueux. La strategie de traiter tel systeme complexe par un couplage etage presente des avantages pour le developpement d'un code modulaire et facile a faire evoluer. La non-correspondance entre les deux grilles de calcul a l'interface fluide-structure, due aux differences des tailles et des types des elements utilises par la resolution de l'ecoulement et de la structure, est resolue par l'ajout d'un module specifique. Les transferts des informations entre ces deux grilles satisfont la loi de la conservation de l'energie. Le modele nonlineaire de la dynamique du fluide base sur la description Euler-Lagrange est discretise dans le maillage mobile. Le modele pour le calcul des structures est suppose lineaire dans lequel la methode de superposition modale est appliquee pour reduire le temps de calcul et la dimension de la memoire. Un autre modele pour la structure base directement sur la methode des elements finis est aussi developpe. Il est egalement couple dans le code pour prouver son extension future aux applications plus generales. La nonlinearite est une autre source de complexite du systeme bien que celle-ci est prevue uniquement dans le modele aerodynamique. L'algorithme GMRES nonlineaire avec le preconditioneur ILUT est implemente dans le solveur CFD ou un capteur de choc pour les ecoulements transsoniques et la technique de stabilisation numerique SUPG pour des ecoulements domines par la convection sont appliques. Un schema du second ordre est utilise pour la discretisation temporelle. Les composants de ce code sont valides par des tests numeriques. Le modele complet est applique et valide sur l'aile aeroelastique AGARD 445.6 dans le cas du nombre de Mach 0.96 qui est une valeur critique en flottement. Les simulations de flottement donnent des resultats numeriques satisfaisants en comparaison avec ceux experimentaux.
Static aeroelastic response of chiral-core airfoils
Spadoni, Alessandro; Ruzzene, Massimo
2007-01-01
Extensive research is being devoted to the analysis and application of cellular solids for the design of innovative structural components. The chiral geometry in particular features a unique mechanical behavior which is here exploited for the design of 2D airfoils with morphing capabilities. A coupled-physics model, comprising computational fluid dynamics and structural analyses, investigates the influence of the chiral core on the aerodynamic behavior of the airfoil. Specifically, the model ...
DEFF Research Database (Denmark)
Gebhardt, Cristian; Preidikman, Sergio; Massa, Julio C;
2010-01-01
considering multiple interactions among blades, wakes, hub, nacelle, supporting tower, ground and land–surface boundary layer. All these in combination affect substantially the total efficiency of the wind turbine. In addition a model for the drivetrain is developed, considering the flexibility of the high...... speed shaft which connects the gear box and the generator. For the inter–model combination, a strong interaction scheme was used. A numerical method based on the fourth order Hamming predictor–corrector method was developed to calculate the solution in the time domain. The models and the interaction...
Selected topics in experimental aeroelasticity at the NASA Langley Research Center
Ricketts, R. H.
1985-01-01
The results of selected studies that have been conducted by the NASA Langley Research Center in the last three years are presented. The topics presented focus primarily on the ever-important transonic flight regime and include the following: body-freedom flutter of a forward-swept-wing configuration with and without relaxed static stability; instabilities associated with a new tilt-rotor vehicle; effects of winglets, supercritical airfoils, and spanwise curvature on wing flutter; wind-tunnel investigation of a flutter-like oscillation on a high-aspect-ratio flight research wing; results of wind-tunnel demonstration of the NASA decoupler pylon concept for passive suppression of wing/store flutter; and, new flutter testing methods which include testing at cryogenic temperatures for full scale Reynolds number simulation, subcritical response techniques for predicting onset of flutter, and a two-degree-of-freedom mount system for testing side-wall-mounted models.
National Aeronautics and Space Administration — ZONA Technology proposes to develop an innovative nonlinear structural reduced order model (ROM) - nonlinear aerodynamic ROM methodology for the inflatable...
Verification of aero-elastic offshore wind turbine design codes under IEA Wind Task XXIII
DEFF Research Database (Denmark)
Vorpahl, Fabian; Strobel, Michael; Jonkman, Jason M.;
2014-01-01
increasing complexity to trace back differences in simulation results to the underlying error sources. This led to a deeper understanding of the underlying physical systems. In four subsequent phases—dealing with a 5-MW turbine on a monopile with a fixed foundation, a monopile with a flexible foundation, a...... large prebend flexible blades, large wind shear, large yaw error or transient maneuvers, may not show the same level of agreement. These cases were deliberately left out because the focus is on the specific offshore application. Further on, this benchmark study includes participating codes and...
Aero-elastic Stability Analysis for Large-Scale Wind Turbines
F. Meng
2011-01-01
Nowadays, many modern countries are relying heavily on non-renewable resources. One common example of non-renewable resources is fossil fuel. Non-renewable resources are ﬁnite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to retrieve. In contrast, renewable energy resources, like wind energy, are constantly replenished and are important because of the beneﬁts it provides for us as well as for our environment. However, getting the energy from wi...
On the aeroelastic transient behaviour of a streamlined bridge deck section in a wind tunnel
Manzoor, S.; Hémon, P.; Amandolese, X.
2011-11-01
The study deals with the transient behaviour of a two degrees of freedom bridge deck section in a wind tunnel under the effect of an initial excitation. Response of the bridge deck section subjected to an initial mechanical excitation and excitation by an upstream gust is investigated separately. Experiments are conducted with three different frequency ratios between the plunge and pitch degrees of freedom. This experimental study shows that transient growth of energy occurs for wind velocities below the onset of flutter, reaching a level higher than 5 times the level of the initial excitation. In high wind conditions, this means that statistical or spectral computation techniques might underestimate the motion amplitude reached by a flexible bridge deck. This emphasises the importance of using temporal techniques under such circumstances.
Aeroelastic Modeling of Offshore Turbines and Support Structures in Hurricane-Prone Regions (Poster)
Energy Technology Data Exchange (ETDEWEB)
Damiani, R.
2014-03-01
US offshore wind turbines (OWTs) will likely have to contend with hurricanes and the associated loading conditions. Current industry standards do not account for these design load cases (DLCs), thus a new approach is required to guarantee that the OWTs achieve an appropriate level of reliability. In this study, a sequentially coupled aero-hydro-servo-elastic modeling technique was used to address two design approaches: 1.) The ABS (American Bureau of Shipping) approach; and 2.) The Hazard Curve or API (American Petroleum Institute) approach. The former employs IEC partial load factors (PSFs) and 100-yr return-period (RP) metocean events. The latter allows setting PSFs and RP to a prescribed level of system reliability. The 500-yr RP robustness check (appearing in [2] and [3] upcoming editions) is a good indicator of the target reliability for L2 structures. CAE tools such as NREL's FAST and Bentley's' SACS (offshore analysis and design software) can be efficiently coupled to simulate system loads under hurricane DLCs. For this task, we augmented the latest FAST version (v. 8) to include tower aerodynamic drag that cannot be ignored in hurricane DLCs. In this project, a 6 MW turbine was simulated on a typical 4-legged jacket for a mid-Atlantic site. FAST-calculated tower base loads were fed to SACS at the interface level (transition piece); SACS added hydrodynamic and wind loads on the exposed substructure, and calculated mudline overturning moments, and member and joint utilization. Results show that CAE tools can be effectively used to compare design approaches for the design of OWTs in hurricane regions and to achieve a well-balanced design, where reliability levels and costs are optimized.
Aeroelastic Tailoring Study of N+2 Low Boom Supersonic Commerical Transport Aircraft
Pak, Chan-Gi
2015-01-01
The Lockheed Martin N+2 Low - boom Supersonic Commercial Transport (LSCT) aircraft was optimized in this study through the use of a multidisciplinary design optimization tool developed at the National Aeronautics and S pace Administration Armstrong Flight Research Center. A total of 111 design variables we re used in the first optimization run. Total structural weight was the objective function in this optimization run. Design requirements for strength, buckling, and flutter we re selected as constraint functions during the first optimization run. The MSC Nastran code was used to obtain the modal, strength, and buckling characteristics. Flutter and trim analyses we re based on ZAERO code, and landing and ground control loads were computed using an in - house code. The w eight penalty to satisfy all the design requirement s during the first optimization run was 31,367 lb, a 9.4% increase from the baseline configuration. The second optimization run was prepared and based on the big-bang big-crunch algorithm. Six composite ply angles for the second and fourth composite layers were selected as discrete design variables for the second optimization run. Composite ply angle changes can't improve the weight configuration of the N+2 LSCT aircraft. However, this second optimization run can create more tolerance for the active and near active strength constraint values for future weight optimization runs.
Coupled finite-difference/finite-element approach for wing-body aeroelasticity
Guruswamy, Guru P.
1992-01-01
Computational methods using finite-difference approaches for fluids and finite-element approaches for structures have individually advanced to solve almost full-aircraft configurations. However, coupled approaches to solve fluid/structural interaction problems are still in their early stages of development, particularly for complex geometries using complete equations such as the Euler/Navier-Stokes equations. Earlier work demonstrated the success of coupling finite-difference and finite-element methods for simple wing configurations using the Euler/Navier-Stokes equations. In this paper, the same approach is extended for general wing-body configurations. The structural properties are represented by beam-type finite elements. The flow is modeled using the Euler/Navier-Stokes equations. A general procedure to fully couple structural finite-element boundary conditions with fluid finite-difference boundary conditions is developed for wing-body configurations. Computations are made using moving grids that adapt to wing-body structural deformations. Results are illustrated for a typical wing-body configuration.
Estimation of output-cost-ratio using an aeroelastic model of voice production
Czech Academy of Sciences Publication Activity Database
Horáček, Jaromír; Laukkanen, A. M.; Šidlof, Petr
Firenze : Firenze University Press, 2007 - (Manfredi, C.), s. 105-108 ISBN 978-88-8453-674-7. [Models and analysis of vocal emissions for biomedical applications /5th International workshop/. Firenze (IT), 13.12.2007-15.12.2007] R&D Projects: GA AV ČR IAA2076401 Institutional research plan: CEZ:AV0Z20760514 Keywords : biomechanics of voice * numerical simulation of vocal folds vibration Subject RIV: BI - Acoustics
Aeroelastic Coupling Between a Low Mach Inviscid Flow and a Flexible Generic Airship
El Omari, Kamal; Schall, Eric; Koobus, Bruno; Dervieux, Alain
2006-01-01
In the context of an airship development programme, inviscid flow behavior and its coupling with structure flexibility are investigated. For this purpose, we have chosen a nonlinear analysis tool relying on the unsteady Euler model for the flow part and the classical elastodynamic equations for the structure. The numerical model for the flow is based on a Mixed Element Volume discretization derived in an Arbitrary-Lagrangian-Eulerian framework in order to cope with the structural deformations...
Reduced-Order LPV Model of Flexible Wind Turbines from High Fidelity Aeroelastic Codes
DEFF Research Database (Denmark)
Adegas, Fabiano Daher; Sønderby, Ivan Bergquist; Hansen, Morten Hartvig; Stoustrup, Jakob
of high-order linear time invariant (LTI) models. Firstly, the high-order LTI models are locally approximated using modal and balanced truncation and residualization. Then, an appropriate coordinate transformation is applied to allow interpolation of the model matrices between points on the parameter...
A research program in active control/aeroelasticity in the JIAFS at NASA Langley Research Center
Whitesides, J. L.
1984-01-01
A control law synthesis methodology for multifunctional active control system to satisfy root-mean-square load and response constraints as well as to meet stability robustness requirements at plant input and output was developed. Modern control theory, singular value analysis and optimization techniques were utilized. All stability and response derivative expressions were derived analytically for sensitivity study. The software is incorporated as an update to the AB/LAD general control design software package PADLOCS.
DEFF Research Database (Denmark)
Demartino, Cristoforo; Ricciardelli, Francesco; Georgakis, Christos T.
2015-01-01
an extruded High Density PolyEthylene (HDPE) circular sheath [1]. In the last 20 years, several bridge cable manufacturers have introduced surface modifications on HDPE sheath in order to reduce the drag and to ensure the aerodynamic stability in all climatic conditions. In the case of plain HDPE...... sheaths, although manufacturers put in place all efforts to obtain smooth, perfectly circular sections, superficial irregularities such as roughness, labeling and ovalling make the aerodynamic behaviour deviate from that of perfect circular cylinder. The imperfections are the result of the manufacturing......The aerodynamics of circular cylinders featuring geometric imperfections, such as bridge cables, has received much attention in recent years due to the recognition that such imperfections can be the cause of large amplitude vibrations. Bridge cables are usually made of strands or wires protected by...
Development and Validation of an Aeroelastic Model of a Small Furling Wind Turbine: Preprint
Energy Technology Data Exchange (ETDEWEB)
Jonkman, J. M.; Hansen, A. C.
2004-12-01
Small wind turbines often use some form of furling (yawing and/or tilting out of the wind) to protect against excessive power generation and rotor speeds in high winds.The verification study demonstrated the correct implementation of FAST's furling dynamics. During validation, the model tends to predict mean rotor speeds higher than measured in spite of the fact that the mean furl motion and rotor thrust are predicted quite accurately. This work has culminated with an enhanced version of FAST that should prove to be a valuable asset to designers of small wind turbines.
On approximation of an aeroelastic problem in post-critical regimes
Czech Academy of Sciences Publication Activity Database
Sváček, P.; Horáček, Jaromír
Prague : Institute of Thermomechanics AS CR, v. v. i., 2011 - (Příhoda, J.; Kozel, K.), s. 109-112 ISBN 978-80-87012-32-1. [Topical problems of fluid mechanics 2011. Prague (CZ), 16.02.2011-17.02.2011] R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelastcity * flutter * FEM Subject RIV: BI - Acoustics
Preliminary observations of impact stress using an aeroelastic model of voice production
Czech Academy of Sciences Publication Activity Database
Horáček, Jaromír; Laukkanen, A. M.; Šidlof, Petr
Praha : Ústav termomechaniky AV ČR, 2005 - (Zolotarev, I.), s. 25-32 ISBN 80-85918-95-1. [Interaction and Feedbacks ´2005. Praha (CZ), 29.11.2005-30.11.2005] R&D Projects: GA AV ČR(CZ) IAA2076401 Institutional research plan: CEZ:AV0Z20760514 Keywords : biomechanics of human voice * vibration of human vocal folds * numerical simulations Subject RIV: BI - Acoustics
Czech Academy of Sciences Publication Activity Database
Ikävalko, T.; Horáček, Jaromír; Liu, D.; Laukkanen, A. M.
Firenze: Firenze University Press, 2015 - (Manfredi, C.), s. 45-48 ISBN 978-88-6655-792-0. [MAVEBA 2015 - International workshop /9./. Firenze (IT), 02.09.2015-04.09.2015] R&D Projects: GA ČR(CZ) GAP101/12/1306 Institutional support: RVO:61388998 Keywords : electroglottography * modelling * voice quality Subject RIV: BI - Acoustics
Design Load Case Analysis tools for aeroelastic wind turbine simulations with HAWC2
DEFF Research Database (Denmark)
2014-01-01
, prepost and cluster tools are created by David R.S. Verelst. This repository holds a series of scripts and small libraries that aim to help with the process of creating, managing, and post processing design load cases (DLC's) simulations. Note that the work presented here has not been streamlined, and is...... not easy to use nor easy installable. During the course of 2015 a library will be released with proper build, install and usage documentation. The version that is included in this repository was extensively used within the INDUFLAP project....
Design and Aero-elastic Simulation of a 5MW Floating Vertical Axis Wind Turbine
DEFF Research Database (Denmark)
Vita, Luca; Schmidt Paulsen, Uwe; Aagaard Madsen, Helge; Nielsen, Per Hørlyk; Berthelsen, Petter A.; Cartsensen, Stefan
This paper deals with the design of a 5MW floating offshore Vertical Axis Wind Turbine (VAWT). The design is based on a new offshore wind turbine concept (DeepWind concept), consisting of a Darrieus rotor mounted on a spar buoy support structure, which is anchored to the sea bed with mooring lines...
Nikoueeyan, Pourya; Magstadt, Andrew; Strike, John; Hind, Michael; Naughton, Jonathan
2014-11-01
To reduce the cost of energy, wind turbine design has moved towards larger blades that are heavier and have lower relative structural stiffness compared to shorter blades. To address the lower blade stiffness, different flow control techniques have been considered. The Gurney flap, a small, low-cost and effective control method, is a promising control actuator. Wind tunnel testing has been performed on a DU97-W-300 10% flatback airfoil undergoing dynamic pitching relevant to flow conditions encountered by wind turbine blades. To mimic blade compliance, the airfoil is actively driven through a torsionally elastic element. Time-resolved surface pressure measurements have been acquired from which lift Cl and moment Cm coefficients were calculated. Changes in Cl and Cm in moderate and deep dynamic stall regimes for different Gurney flap heights were studied for different pitch drive conditions (amplitude and frequency). The results show the significant impact of compliance on the angle of attack (α) range experienced by the airfoil. Shifts in α range result in different hysteresis behavior in both Cl and Cm and demonstrate the effectiveness of the Gurney flap in modifying the aerodynamics of wind turbine blades experiencing dynamic pitching. This work supported by DOE and a gift from BP.
Geometrical Nonlinear Aeroelastic Stability Analysis of a Composite High-Aspect-Ratio Wing
Chang Chuan Xie; Jia Zhen Leng; Chao Yang
2008-01-01
A composite high-aspect-ratio wing of a high-altitude long-endurance (HALE) aircraft was modeled with FEM by MSC/NASTRAN, and the nonlinear static equilibrium state is calculated under design load with follower force effect, but without load redistribution. Assuming the little vibration amplitude of the wing around the static equilibrium state, the system is linearized and the natural frequencies and mode shapes of the deformed structure are obtained. Planar doublet lattice method is used to ...
Identification of aeroelastic forces on bridge cables from full-scale measurements
DEFF Research Database (Denmark)
Acampora, Antonio; Macdonald, J.H.G.; Georgakis, Christos
2011-01-01
Despite much research in recent years, large amplitude vibrations of inclined cables continue to be of concern for cable-stayed bridges. Various mechanisms have been suggested for their excitation, including rain-wind excitation, dry inclined cable galloping, high reduced velocity vortex shedding...... and excitation from the deck and/or towers. Although some experiences have been done with full-scale measurements of inclined cables, many of the results available are based on wind tunnel tests and theoretical modelling. This paper presents results from full-scale measurements on the cables of the...... Øresund Bridge. The system records wind conditions and weather conditions, as well as accelerations of certain cables and a few locations on the deck and tower. Using state-of-the-art methods of output-only system identification, the vibration modes of the cables have been identified. From these modes...
Validation of a vortex ring wake model suited for aeroelastic simulations of floating wind turbines
International Nuclear Information System (INIS)
In order to evaluate aerodynamic loads on floating offshore wind turbines, advanced dynamic analysis tools are required. As a unified model that can represent both dynamic inflow and skewed inflow effects in it basic formulation, a wake model based on a vortex ring formulation is discussed. Such a model presents a good intermediate solution between computationally efficient but simple momentum balance methods and computationally expensive but complete computational fluid dynamics models. The model introduced is shown to be capable of modelling typical steady and unsteady test cases with reasonable accuracy
Validation of a vortex ring wake model suited for aeroelastic simulations of floating wind turbines
de Vaal, J. B.; Hansen, M. O. L.; Moan, T.
2014-12-01
In order to evaluate aerodynamic loads on floating offshore wind turbines, advanced dynamic analysis tools are required. As a unified model that can represent both dynamic inflow and skewed inflow effects in it basic formulation, a wake model based on a vortex ring formulation is discussed. Such a model presents a good intermediate solution between computationally efficient but simple momentum balance methods and computationally expensive but complete computational fluid dynamics models. The model introduced is shown to be capable of modelling typical steady and unsteady test cases with reasonable accuracy.
Extension-twist coupled laminates for aero-elastic compliant blade design
York, C. B.
2012-01-01
A definite list of laminate configurations with extension-twisting (and shearing-bending) coupling is derived for up to 21 plies of identical thickness. The list comprises individual stacking sequences, containing standard angle-ply and cross-ply sub-sequences; combinations which are contrary to the previously assumed form for this class of laminate. The list also contains dimensionless parameters from which the extensional, coupling and bending stiffness terms are readily calculated for any...
Estimation of impact stress using an aeroelastic model of voice production
Czech Academy of Sciences Publication Activity Database
Horáček, Jaromír; Laukkanen, A. M.; Šidlof, Petr
2007-01-01
Roč. 32, - (2007), s. 185-192. ISSN 1401-5439 R&D Projects: GA AV ČR IAA2076401 Institutional research plan: CEZ:AV0Z20760514 Keywords : computer modeling * phonation type * vocal loading Subject RIV: BI - Acoustics
Coupling analysis of wind turbine blades based on aeroelastics and aerodynsmics
DEFF Research Database (Denmark)
Wang, Xudong; Chen, Jin; Zhang, Shigiang; Shen, Wen Zhong; Zhu, Weijun
2010-01-01
The structural dynamic equations of blades were constructed for blades of wind turbines. The vibration velocity of blades and the relative flow velocity were calculated using the structural dynamics model. Based on the BEM (Blade Element Momentum) theory and traditional areodynamics, the coupling...
Van der Valk, P.L.C.; Rixen, D.J.
2012-01-01
In order to achieve the goal of 20% renewable energy in 2020, as set by the European Union, large offshore wind farms are either under construction or in development through-out Europe. As many of the "easy" locations are already under development, offshore wind farms are moving further offshore int
Aero-elastic Stability Analysis for Large-Scale Wind Turbines
Meng, F.
2011-01-01
Nowadays, many modern countries are relying heavily on non-renewable resources. One common example of non-renewable resources is fossil fuel. Non-renewable resources are ﬁnite resources that will eventually dwindle, becoming too expensive or too environmentally damaging to retrieve. In contrast, ren
Raney, David L.; Jackson, E. Bruce; Buttrill, Carey S.
2002-01-01
A piloted simulation study conducted in NASA Langley Visual Motion Simulator addressed the impact of dynamic aero- servoelastic effects on flying qualities of a High Speed Civil Transport. The intent was to determine effectiveness of measures to reduce the impact of aircraft flexibility on piloting tasks. Potential solutions examined were increasing frequency of elastic modes through structural stiffening, increasing damping of elastic modes through active control, elimination of control effector excitation of the lowest frequency elastic modes, and elimination of visual cues associated with elastic modes. Six test pilots evaluated and performed simulated maneuver tasks, encountering incidents wherein cockpit vibrations due to elastic modes fed back into the control stick through involuntary vibrations of the pilots upper body and arm. Structural stiffening and compensation of the visual display were of little benefit in alleviating this impact, while increased damping and elimination of control effector excitation of the elastic modes both offered great improvements when applied in sufficient degree.
A closed loop experiment of collective bounce aeroelastic Rotorcraft-Pilot Coupling
Masarati, Pierangelo; Quaranta, Giuseppe; Lu, Linghai; Jump, Michael
2014-01-01
This work presents an experimental study that investigated the possibility of destabilising a rotorcraft by coupling the biomechanical behaviour of human subjects with the dynamics of the vehicle. The results of a study focused on the behaviour of pilots holding the collective control inceptor in a flight simulator are discussed. The motion of the flight simulation model was restricted to the heave axis, and augmented to include an elastic mode of vibration in addition to the rigid heave degree of freedom. Four different pilots flew several alternative model configurations with different elastic mode frequency and different collective pitch gearing ratios. This resulted in several observable unstable pilot-vehicle interactions at frequencies that cannot be traced back to the rotorcraft dynamics. Unstable oscillatory events evolving into limit cycle oscillations occurred most often at frequencies related to the biomechanics of the flight simulator occupant. They appeared to be task dependent and, in some cases, the trigger could be attributed to specific events. Additionally, it was found that the presence of collective friction alleviates but does not completely eliminate the unstable interactions between the pilot and the rotorcraft. Although not statistically meaningful because of the small set of human subjects available for the study, the results confirmed that the biomechanics transfer function of the pilot is the most influential aspect of the pilot-vehicle system that gives rise to the adverse vertical bounce phenomenon. Additionally, this study gave useful insight into the vehicle parameters that can adversely influence the involuntary interaction of pilots with rotorcraft.
Heeg, Jennifer; Morelli, Eugene A.
2011-01-01
Multiple mutually orthogonal signals comprise excitation data sets for aeroservoelastic system identification. A multisine signal is a sum of harmonic sinusoid components. A set of these signals is made orthogonal by distribution of the frequency content such that each signal contains unique frequencies. This research extends the range of application of an excitation method developed for stability and control flight testing to aeroservoelastic modeling from wind tunnel testing. Wind tunnel data for the Joined Wing SensorCraft model validates this method, demonstrating that these signals applied simultaneously reproduce the frequency response estimates achieved from one-at-a-time excitation.
Aeroelastic large eddy simulations using vortex methods: unfrozen turbulent and sheared inflow
DEFF Research Database (Denmark)
Branlard, Emmanuel Simon Pierre; Papadakis, G.; Gaunaa, Mac;
2015-01-01
novel approach relying on a Neumann to Dirichlet map. The interaction of the sheared vorticity with the wind turbine is shown to have an important impact on the wake shape. The obtained wake shape are closer to the one obtained using traditional computational fluid dynamics: Results with unfrozen shear...
Effect of Compressive Force on Aeroelastic Stability of a Strut-Braced Wing
Sulaeman, Erwin
2001-01-01
Recent investigations of a strut-braced wing (SBW) aircraft show that, at high positive load factors, a large tensile force in the strut leads to a considerable compressive axial force in the inner wing, resulting in a reduced bending stiffness and even buckling of the wing. Studying the influence of this compressive force on the structural response of SBW is thus of paramount importance in the early stage of SBW design. The purpose of the this research is to investigate the effect of co...
Report of the panel on dynamics and aeroelasticity. [transonic tunnel capabilities
Houbolt, J.
1977-01-01
Model scaling for flutter analysis is reviewed. Characteristics of the Langley Transonic Dynamics Tunnel (TDT) are described and several features are recommended for inclusion in the National Transonic Facility. Problem areas suggested for the NTF include: Reynolds number effects on control surface unsteady aerodynamics; effects of Reynolds number on buffet onset and loads; transonic unsteady aerodynamics; and Reynolds number effects on flutter characteristics of wing planforms and airfoils.
Four New Capabilities in NASTRAN for Dynamic and Aeroelastic Analyses of Rotating Cyclic Structures
Elchuri, V.; Gallo, A. M.
1984-01-01
Static aerothermoelastic design/analysis of axial-flow compressors, modal flutter analysis of axial-flow turbomachines, forced vibration analysis of rotating cyclic structures and modal flutter analysis of advanced turbopropellers with highly swept blades are four new capabilities developed and implemented in NASTRAN Level 17.7. The contents, applicability and usefulness of these capabilities which were developed and documented under the sponsorship of NASA's Lewis Research Center are discussed. Overall flowcharts and selected examples are presented.
Validation of a vortex ring wake model suited for aeroelastic simulations of floating wind turbines
DEFF Research Database (Denmark)
Vaal, J.B., de; Hansen, Martin Otto Laver; Moan, T.
2014-01-01
In order to evaluate aerodynamic loads on floating oshore wind turbines, advanced dynamic analysis tools are required. As a unied model that can represent both dynamic in ow and skewed in ow effects in it basic formulation, a wake model based on a vortex ring formulation is discussed. Such a mode...
International Nuclear Information System (INIS)
In the past year, smart rotor technology has been studied significantly as solution to the ever growing turbines. Aeroservoelastic tools are used to asses and predict the behavior of rotors using trailing edge devices like flaps. In this paper an unsteady aerodynamic model (Beddoes-Leishman type) and an CFD model (URANS) are used to analyze the aeroservoelastic response of a 2D three degree of freedom rigid body wind turbine airfoil with a deforming trailing edge flap encountering deterministic gusts. Both uncontrolled and controlled simulations are used to asses the differences between the two models for 2D aerservoelastic simulations. Results show an increase in the difference between models for the y component if the deforming trailing edge flap is used as control device. Observed flap deflections are significantly larger in the URANS model in certain cases, while the same controller is used. The pitch angle and moment shows large differences in the uncontrolled case, which become smaller, but remain significant when the controller is applied. Both models show similar reductions in vertical displacement, with a penalty of a significant increase in pitch angle deflections
Lucio, Monaco; Bergmans, John; Vogt, Damian; Fransson, Torsten H
2015-01-01
The use of advanced pedagogical methodologies in connection with advanced use of modern information technology for delivery enables new ways of communicating, of exchanging knowledge, and of learning that are gaining increasing relevance in our society. Remote laboratory exercises offer the possibility to enhance learning for students in different technical areas, especially to the ones not having physical access to laboratory facilities and thus spreading knowledge in a world-wide perspectiv...
Czech Academy of Sciences Publication Activity Database
Náprstek, Jiří; Pospíšil, Stanislav
2013-01-01
Roč. 20, č. 5 (2013), s. 355-367. ISSN 1802-1484 R&D Projects: GA ČR(CZ) GA103/09/0094; GA AV ČR(CZ) IAA200710902 Institutional support: RVO:68378297 Keywords : flutter derivatives * indicial functions * non-symmetric systems * dynamic stability Subject RIV: JM - Building Engineering http://www.engineeringmechanics.cz/obsahy.html?R=20&C=5
Kroo, I. M.
1981-01-01
One-fifth-scale models of three basic ultralight glider designs were constructed to simulate the elastic properties of full scale gliders and were tested at Reynolds numbers close to full scale values. Twenty-four minor modifications were made to the basic configurations in order to evaluate the effects of twist, reflex, dihedral, and various stability enhancement devices. Longitudinal and lateral data were obtained at several speeds through an angle of attack range of -30 deg to +45 deg with sideslip angles of up to 20 deg. The importance of vertical center of gravity displacement is discussed. Lateral data indicate that effective dihedral is lost at low angles of attack for nearly all of the configurations tested. Drag data suggest that lift-dependent viscous drag is a large part of the glider's total drag as is expected for thin, cambered sections at these relatively low Reynolds numbers.
Open-loop frequency response analysis of a wind turbine using a high-order linear aeroelastic model
DEFF Research Database (Denmark)
Sønderby, Ivan Bergquist; Hansen, Morten Hartvig
2014-01-01
generator torque and collective pitch control actions of a modern non-floating wind turbine based on a high-order linear model. The model is a linearization of a geometrically non-linear finite beam element model coupled with an unsteady blade element momentum model of aerodynamic forces including effects...
Cox, T. H.; Gilyard, G. B.
1986-01-01
The drones for aerodynamic and structural testing (DAST) project was designed to control flutter actively at high subsonic speeds. Accurate knowledge of the structural model was critical for the successful design of the control system. A ground vibration test was conducted on the DAST vehicle to determine the structural model characteristics. This report presents and discusses the vibration and test equipment, the test setup and procedures, and the antisymmetric and symmetric mode shape results. The modal characteristics were subsequently used to update the structural model employed in the control law design process.
Murrow, H. N.
1981-01-01
Results from flight tests of the ARW-1 research wing are presented. Preliminary loads data and experiences with the active control system for flutter suppression are included along with comparative results of test and prediction for the flutter boundary of the supercritical research wing and on performance of the flutter suppression system. The status of the ARW-2 research wing is given.
Czech Academy of Sciences Publication Activity Database
Alku, P.; Horáček, Jaromír; Airas, M.; Lakkanen, A.M.
Firenze : Firenze University Press, 2005 - (Manfredi, C.), s. 73-76 ISBN 88-8453-155-1. [MAVEBA 2005. Firenze (IT), 29.10.2005-31.10.2005] R&D Projects: GA AV ČR(CZ) IAA2076401 Institutional research plan: CEZ:AV0Z20760514 Keywords : biomechanics of voice * speech acoustics * numerical simulation Subject RIV: BI - Acoustics
Status of the KTH-NASA Wind-Tunnel Test for Acquisition of Transonic Nonlinear Aeroelastic Data
Silva, Walter A.; Ringertz, Ulf; Stenfelt, Gloria; Eller, David; Keller, Donald F.; Chwalowski, Pawel
2016-01-01
This paper presents a status report on the collaboration between the Royal Institute of Technology (KTH) in Sweden and the NASA Langley Research Center regarding the design, fabrication, modeling, and testing of a full-span lighter configuration in the Transonic Dynamics Tunnel (TDT). The goal of the test is to acquire transonic limit-cycle- oscillation (LCO) data, including accelerations, strains, and unsteady pressures. Finite element models (FEMs) and aerodynamic models are presented and discussed along with results obtained to date.
Institute of Scientific and Technical Information of China (English)
V.I. GNESIN; L.V. KOLODYAZHNAYA; R. RZADKOWSKI
2005-01-01
Fiszera st., 14, Gdansk, 80 952 PolandIn this study presented the algorithm proposed involves the coupled solution of 3-D unsteady flow through a turbine stage and the dynamics problem for rotor-blade motion by the action of aerodynamic forces, without separating the outer and inner flow fluctuations. The partially integrated method involves the solution of the fluid and structural equations separately, but information is exchanged at each time step, so that solution from one domain is used as a boundary condition for the other domain. 3-D transonic gas flow through the stator and rotor blades in relative motion with periodicity on the whole annulus is described by the unsteady Euler conservation equations, which are integrated using the explicit monotonous finite-volume difference scheme of GodunovKolgan. The structural analysis uses the modal approach and a 3-D finite element model of a blade. A calculation has been done for the last stage of the steam turbine, under design and off-design regimes. It is shown that the amplitude-frequency spectrum of blade oscillations contains the high frequency harmonics, corresponding to the rotor moving past one stator blade pitch, and low frequency harmonics caused by blade oscillations and flow nonunifonnity downstream from the blade row; moreover, the spectrum involves the harmonics which are not multiples of the rotation frequency.
Radovcich, N. A.; Dreim, D.; Okeefe, D. A.; Linner, L.; Pathak, S. K.; Reaser, J. S.; Richardson, D.; Sweers, J.; Conner, F.
1985-01-01
Work performed in the design of a transport aircraft wing for maximum fuel efficiency is documented with emphasis on design criteria, design methodology, and three design configurations. The design database includes complete finite element model description, sizing data, geometry data, loads data, and inertial data. A design process which satisfies the economics and practical aspects of a real design is illustrated. The cooperative study relationship between the contractor and NASA during the course of the contract is also discussed.
Czech Academy of Sciences Publication Activity Database
Náprstek, Jiří; Pospíšil, Stanislav; Yau, J. D.
2015-01-01
Roč. 57, August (2015), s. 91-107. ISSN 0889-9746 R&D Projects: GA MŠk(CZ) LO1219; GA ČR(CZ) GC13-34405J Institutional support: RVO:68378297 Keywords : aero -elastic system * self-excited vibration * dynamic stability * Routh–Hurwitz conditions * flutter derivatives * divergence Subject RIV: JM - Building Engineering Impact factor: 2.021, year: 2014 http://dx.doi.org/10.1016/j.jfluidstructs.2015.05.010
Cao, Bochao
Slender structures representing civil, mechanical and aerospace systems such as long-span bridges, high-rise buildings, stay cables, power-line cables, high light mast poles, crane-booms and aircraft wings could experience vortex-induced and buffeting excitations below their design wind speeds and divergent self-excited oscillations (flutter) beyond a critical wind speed because these are flexible. Traditional linear aerodynamic theories that are routinely applied for their response prediction are not valid in the galloping, or near-flutter regime, where large-amplitude vibrations could occur and during non-stationary and transient wind excitations that occur, for example, during hurricanes, thunderstorms and gust fronts. The linear aerodynamic load formulation for lift, drag and moment are expressed in terms of aerodynamic functions in frequency domain that are valid for straight-line winds which are stationary or weakly-stationary. Application of the frequency domain formulation is restricted from use in the nonlinear and transient domain because these are valid for linear models and stationary wind. The time-domain aerodynamic force formulations are suitable for finite element modeling, feedback-dependent structural control mechanism, fatigue-life prediction, and above all modeling of transient structural behavior during non-stationary wind phenomena. This has motivated the developing of time-domain models of aerodynamic loads that are in parallel to the existing frequency-dependent models. Parameters defining these time-domain models can be now extracted from wind tunnel tests, for example, the Rational Function Coefficients defining the self-excited wind loads can be extracted using section model tests using the free vibration technique. However, the free vibration method has some limitations because it is difficult to apply at high wind speeds, in turbulent wind environment, or on unstable cross sections with negative aerodynamic damping. In the current research, new algorithms were developed based on forced vibration technique for direct extraction of the Rational Functions. The first of the two algorithms developed uses the two angular phase lag values between the measured vertical or torsional displacement and the measured aerodynamic lift and moment produced on the section model subject to forced vibration to identify the Rational Functions. This algorithm uses two separate one-degree-of-freedom tests (vertical or torsional) to identify all the four Rational Functions or corresponding Rational Function Coefficients for a two degrees-of-freedom (DOF) vertical-torsional vibration model. It was applied to a streamlined section model and the results compared well with those obtained from earlier free vibration experiment. The second algorithm that was developed is based on direct least squares method. It uses all the data points of displacements and aerodynamic lift and moment instead of phase lag values for more accurate estimates. This algorithm can be used for one-, two- and three-degree-of-freedom motions. A two-degree-of-freedom forced vibration system was developed and the algorithm was shown to work well for both streamlined and bluff section models. The uniqueness of the second algorithms lies in the fact that it requires testing the model at only two wind speeds for extraction of all four Rational Functions. The Rational Function Coefficients that were extracted for a streamlined section model using the two-DOF Least Squares algorithm were validated in a separate wind tunnel by testing a larger scaled model subject to straight-line, gusty and boundary-layer wind.
Czech Academy of Sciences Publication Activity Database
Horáček, Jaromír; Feistauer, M.; Sváček, P.
Dublin : School of Engineering Trinity College, Dublin, 2012 - (Meskell, C.; Bennett, G.), s. 147-154 ISBN 978-0-9548583-4-6. [International conference on Flow-Induced Vibration /10./. Dublin (IE), 03.07.2012-06.07.2012] R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional research plan: CEZ:AV0Z20760514 Keywords : flutter * 3-DOF airfoil * Navier-Stokes equation * high-fidelity model Subject RIV: BI - Acoustics
DEFF Research Database (Denmark)
Acampora, Antonio; Georgakis, Christos T.; Macdonald, J.H.G.;
2014-01-01
excitation from the deck and/or towers. Although there have been many observations of large cable vibrations on bridges, there are relatively few cases of direct full-scale cable vibration and wind measurements, and most research has been based on wind tunnel tests and theoretical modelling.This paper...... presents results from full-scale measurements on the special arrangement of twin cables adopted for the Øresund Bridge. The monitoring system records wind and weather conditions, as well as accelerations of certain cables and a few locations on the deck and tower. Using the Eigenvalue Realization Algorithm......-scale measurements are compared with the theoretical damping matrices based on the quasi-steady theory, using three different sets of wind tunnel measurements of static force coefficients on similar shaped twin or single cables, with good agreement. The damping terms are found to be dependent on Reynolds number...
Aeroelastic Mechanical Analysis of Bearingless Rotor with Elastomeric Lag Dampers%无轴承旋翼/减摆器的气动弹性力学研究
Institute of Scientific and Technical Information of China (English)
胡新宇; 韩景龙
2008-01-01
将无轴承旋翼的主桨叶、柔性梁和套管3个部分各自离散成若干梁单元,并将桨叶运动的物理坐标转换为挥舞、摆振、扭转方向的模态坐标,根据Hamilton原理建立旋翼气弹分析的动力学模型.采用Newton-Raphson迭代方法,用时间有限元法进行旋翼稳态响应的数值求解,并根据时域非线性黏弹减摆器模型,在直升机定常前飞条件下配平计算旋翼/黏弹减摆器耦合系统非线性气弹周期响应,然后基于Floquet理论进行稳定性分析,并讨论了桨叶载荷系数对旋翼稳定性的影响.结果表明:该减摆器模型能充分提高摆振阻尼,从而改善无轴承旋翼的稳定性.
Wang, Zhicun
2004-01-01
The nonlinear interactions between aerodynamic forces and wing structures are numerically investigated as integrated dynamic systems, including structural models, aerodynamics, and control systems, in the time domain. An elastic beam model coupled with rigid-body rotation is developed for the wing structure, and the natural frequencies and mode shapes are found by the finite-element method. A general unsteady vortex-lattice method is used to provide aerodynamic forces. This method is verified...
Design and simulation of the rotating test rig in the INDUFLAP project
DEFF Research Database (Denmark)
Barlas, Thanasis K.; Aagaard Madsen, Helge; Løgstrup Andersen, Tom
drive, the pitch system, the boom, and the wing/flap section. The overall instrumentation of the components used for the aeroelastic testing is described. Moreover, the aeroelastic model simulating the setup is described, and predictions of steady and dynamic loading along with the aeroelastic analysis...... of the setup are documented. Finally, the measured structural dynamics of the rig setup are presented....
A Status Review of the Commercial Supersonic Technology (CST) Aeroservoelasticity (ASE) Project
Silva, Walter A.; Sanetrik, Mark D.; Chwalowski, Pawel; Funk, Christy; Keller, Donald F.; Ringertz, Ulf
2016-01-01
An overview of recent progress regarding the computational aeroelastic and aeroservoelastic (ASE) analyses of a low-boom supersonic configuration is presented. The overview includes details of the computational models developed to date with a focus on unstructured CFD grids, computational aeroelastic analyses, sonic boom propagation studies that include static aeroelastic effects, and gust loads analyses. In addition, flutter boundaries using aeroelastic Reduced-Order Models (ROMs) are presented at various Mach numbers of interest. Details regarding a collaboration with the Royal Institute of Technology (KTH, Stockholm, Sweden) to design, fabricate, and test a full-span aeroelastic wind-tunnel model are also presented.
Keye, Stefan; Rudnik, Ralf
2015-01-01
The virtual determination of static aeroelastic deformations of NASA’s Common Research Model at steady-state ﬂow conditions is described. Aeroelastic equilibrium conditions are computed using a ﬂuid-structure interaction simulation approach based on high-ﬁdelity numerical ﬂuid dynamics and structural analysis methods. The correlation of numerical and experimental results under varying aerodynamic loads and model deformations is investigated and the inﬂuence of aeroelastic deformations on wing...
Aeroservoelastic Pitch Control of Stall-Induced Flap/Lag Flutter of Wind Turbine Blade Section
Tingrui Liu
2015-01-01
The aim of this paper is to analyze aeroelastic stability, especially flutter suppression for aeroelastic instability. Effects of aeroservoelastic pitch control for flutter suppression on wind turbine blade section subjected to combined flap and lag motions are rarely studied. The work is dedicated to solving destructive flapwise and edgewise instability of stall-induced flutter of wind turbine blade by aeroservoelastic pitch control. The aeroelastic governing equations combine a flap/lag str...
Reduced Order Aeroservoelastic Models with Rigid Body Modes Project
National Aeronautics and Space Administration — Complex aeroelastic and aeroservoelastic phenomena can be modeled on complete aircraft configurations generating models with millions of degrees of freedom....
HIRENASD analysis Information Package
National Aeronautics and Space Administration — Updated November 2, 2011 Contains summary information and analysis condition details for the Aeroelastic Prediction Workshop Information plotted in this package is...
Advanced Modeling Concepts for Conceptual Design Project
National Aeronautics and Space Administration — Preliminary design of aircraft structures is multidisciplinary, involving knowledge of structural mechanics, aerodynamics, aeroelasticity, structural dynamics and...
Reduced Order Aeroservoelastic Models with Rigid Body Modes Project
National Aeronautics and Space Administration — Complex aeroelastic and aeroservoelastic phenomena can be modeled on complete aircraft configurations, generating models with millions of degrees of freedom....
Institute of Scientific and Technical Information of China (English)
李永乐; 朱佳琪; 唐浩俊
2015-01-01
Taking advantage of the software FLUENT and using the numerical solution of differential equation and the dynamic mesh model,a CFD/CSD coupling solution based on loose coupling was realized by embedding the Newmark method into FLUNT with the help of UDF function.A 2D-square cylinder model was established to investigate the change of Strouhal number and the maximum vertical vortex-excited amplitude of the square cylinder under different wind speed. The lock-in phenomenon of vortex-excited resonance was observed in the process of simulation and it was compared with the result of static square cylinder.A 2D flat plate model with vertical and torsional degrees of freedom was established to identify the flutter derivatives of the flat plate and to determine the flutter critical wind speed of flutter.The simulation result agrees well with the critical wind speeds of flutter calculated by using the Scanlan's formula and Selberg's formula.%以 FLUENT 为研究工具，利用微分方程的数值解法和动网格技术，基于松耦合方法将 Newmark 算法通过UDF 嵌入 Fluent 软件中，实现了 CFD 和 CSD 耦合的分析方法。通过建立二维方柱绕流模型，计算了竖向单自由度振动方柱在不同风速下的斯托罗哈数和最大振幅的变化情况，模拟了涡激共振锁定现象，并与静态绕流的结果进行了对比。建立了具有竖向振动和扭转振动二自由度的薄平板模型，并识别了该平板的颤振导数，进一步对其弯扭耦合颤振临界风速进行了逼近计算，本方法得到的颤振临界风速与 Scanlan 理论公式和 Selberg 理论公式吻合较好。
Institute of Scientific and Technical Information of China (English)
杨卫东; 马杰; 张呈林
2007-01-01
针对带粘弹减摆器旋翼系统气弹稳定性试验中测量所得信号可能出现的大阻尼、频率成分密集及信噪比差等情况,采用数值仿真,比较基于傅立叶级数移动矩形窗法(FSMB)、Hilbert法(HT)和传统的基于FFT移动矩形窗法(FFT-MB),从这类信号中识别阻尼的优缺点.在两米量级旋翼台上进行了带粘弹减摆器铰接式动力学相似模型旋翼气弹稳定性试验,采用角位移传感器测量摆振信号,用上述三种方法对试验结果进行稳定性分析.数值仿真和试验结果表明,角位移传感器测量信号有较高的信噪比;在大阻尼、频率成分密集及信噪比差的情况下,FSMB法与HT法较传统的移动矩形窗法有较高的识别精度.
Institute of Scientific and Technical Information of China (English)
周超; 李书
2007-01-01
建立了粘弹减摆器不同连接形式时的旋翼系统气动弹性稳定性分析模型.旋翼动力学模型考虑了非定常空气动力和桨叶挥舞/摆振运动的耦合.采用基于复模量的非线性VKS改进模型,建立叶间粘弹减摆器和普通连接粘弹减摆器的力矩方程.分别采用特征分析法及时域分析法计算了普通连接形式和叶间连接形式的直升机旋翼系统的动稳定性.通过对工程实例的分析计算,得出了一些有意义的结论.
A CFD/CSD Interaction Methodology for Aircraft Wings
Bhardwaj, Manoj K.
1997-01-01
With advanced subsonic transports and military aircraft operating in the transonic regime, it is becoming important to determine the effects of the coupling between aerodynamic loads and elastic forces. Since aeroelastic effects can contribute significantly to the design of these aircraft, there is a strong need in the aerospace industry to predict these aero-structure interactions computationally. To perform static aeroelastic analysis in the transonic regime, high fidelity computational fluid dynamics (CFD) analysis tools must be used in conjunction with high fidelity computational structural fluid dynamics (CSD) analysis tools due to the nonlinear behavior of the aerodynamics in the transonic regime. There is also a need to be able to use a wide variety of CFD and CSD tools to predict these aeroelastic effects in the transonic regime. Because source codes are not always available, it is necessary to couple the CFD and CSD codes without alteration of the source codes. In this study, an aeroelastic coupling procedure is developed which will perform static aeroelastic analysis using any CFD and CSD code with little code integration. The aeroelastic coupling procedure is demonstrated on an F/A-18 Stabilator using NASTD (an in-house McDonnell Douglas CFD code) and NASTRAN. In addition, the Aeroelastic Research Wing (ARW-2) is used for demonstration of the aeroelastic coupling procedure by using ENSAERO (NASA Ames Research Center CFD code) and a finite element wing-box code (developed as part of this research).
Guruswamy, Guru P.
1994-01-01
Strong interactions can occur between the flow about an aerospace vehicle and its structural components resulting in several important aeroelastic phenomena. These aeroelastic phenomena can significantly influence the performance of the vehicle. At present, closed-form solutions are available for aeroelastic computations when flows are in either the linear subsonic or supersonic range. However, for aeroelasticity involving complex nonlinear flows with shock waves, vortices, flow separations, and aerodynamic heating, computational methods are still under development. These complex aeroelastic interactions can be dangerous and limit the performance of aircraft. Examples of these detrimental effects are aircraft with highly swept wings experiencing vortex-induced aeroelastic oscillations, transonic regime at which the flutter speed is low, aerothermoelastic loads that play a critical role in the design of high-speed vehicles, and flow separations that often lead to buffeting with undesirable structural oscillations. The simulation of these complex aeroelastic phenomena requires an integrated analysis of fluids and structures. This report presents a summary of the development, applications, and procedures to use the multidisciplinary computer code ENSAERO. This code is based on the Euler/Navier-Stokes flow equations and modal/finite-element structural equations.
Synthesis of aircraft structures using integrated design and analysis methods
Sobieszczanski-Sobieski, J.; Goetz, R. C.
1978-01-01
A systematic research is reported to develop and validate methods for structural sizing of an airframe designed with the use of composite materials and active controls. This research program includes procedures for computing aeroelastic loads, static and dynamic aeroelasticity, analysis and synthesis of active controls, and optimization techniques. Development of the methods is concerned with the most effective ways of integrating and sequencing the procedures in order to generate structural sizing and the associated active control system, which is optimal with respect to a given merit function constrained by strength and aeroelasticity requirements.
LCO flutter of cantilevered woven glass/epoxy laminate in subsonic flow
Institute of Scientific and Technical Information of China (English)
Dayang Laila Abang Haji Abdul Majid; ShahNor Basri
2008-01-01
The paper presents aeroelastic characteristics of a cantilevered composite wing,idealized as a composite flat plate laminate.The composite laminate was made from woven glass fibers with epoxy matrix.The elastic and dynamic properties of the laminate were determined experimentally for aeroelastic calculations.Aeroelastic wind tunnel testing of the laminate was performed and the result showed that flutter,a dynamic instability occurred.The cantilevered laminate also displayed limit cycle amplitude,post-flutter oscillation.The experimental flutter velocity and frequency were verified by our computational analysis.
A CFD/CSD interaction methodology for aircraft wings
Bhardwaj, Manoj Kumar
With advanced subsonic transports and military aircraft operating in the transonic regime, it is becoming important to determine the effects of the coupling between aerodynamic loads and elastic forces. Since aeroelastic effects can contribute significantly to the design of these aircraft, there is a strong need in the aerospace industry to predict these aero-structure interactions computationally. To perform static aeroelastic analysis in the transonic regime, high fidelity computational fluid dynamics (CFD) analysis tools must be used in conjunction with high fidelity computational structural dynamics (CSD) analysis tools due to the nonlinear behavior of the aerodynamics in the transonic regime. There is also a need to be able to use a wide variety of CFD and CSD tools to predict these aeroelastic effects in the transonic regime. Because source codes are not always available, it is necessary to couple the CFD and CSD codes without alteration of the source codes. In this study, an aeroelastic coupling procedure is developed which will perform static aeroelastic analysis using any CFD and CSD code with little code integration. The aeroelastic coupling procedure is demonstrated on an F/A-18 Stabilator using NASTD (an in-house McDonnell Douglas CFD code) and NASTRAN. In addition, the Aeroelastic Research Wing (ARW-2) is used for demonstration of the aeroelastic coupling procedure by using ENSAERO (NASA Ames Research Center CFD code) and a finite element wing-box code (developed as a part of this research). The results obtained from the present study are compared with those available from an experimental study conducted at NASA Langley Research Center and a study conducted at NASA Ames Research Center using ENSAERO and modal superposition. The results compare well with experimental data. Parallel computing power is used to investigate parallel static aeroelastic analysis because obtaining an aeroelastic solution using CFD/CSD methods is computationally intensive. A
Numerical simulation of interaction between turbulent flow and a vibrating airfoil
Czech Academy of Sciences Publication Activity Database
Dubcová, Lenka; Feistauer, M.; Horáček, Jaromír; Sváček, Petr
-, - (2008), s. 1-19. ISSN 1432-9360 R&D Projects: GA AV ČR IAA200760613 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * finite element method * ALE formulation Subject RIV: BI - Acoustics
National Aeronautics and Space Administration — CFD-based design-oriented (DO) steady/unsteady aerodynamic analysis tools for Aeroelastic / Aeroservoelastic (AE/ASE) evaluation lag significantly behind other...
Advanced Metal Rubber Sensors for Hypersonic Decelerator Entry Systems Project
National Aeronautics and Space Administration — NanoSonic proposes to design and develop light-weight, low-modulus, and durable Metal Rubber sensors for aeroelastic analysis of Hypersonic Decelerator Entry...
National Aeronautics and Space Administration — The databases of computational and experimental data from the first Aeroelastic Prediction Workshop are located here. The databases file names tell their contents...
Flexible Conformal Metal Rubber Sensors for Entry/Landing Systems Project
National Aeronautics and Space Administration — NanoSonic proposes to design and develop light-weight, low-modulus, and durable Metal Rubber sensors for aeroelastic analysis of inflatable/flexible entry, descent,...
Prediction of Unsteady Transonic Aerodynamics Project
National Aeronautics and Space Administration — An accurate prediction of aero-elastic effects depends on an accurate prediction of the unsteady aerodynamic forces. Perhaps the most difficult speed regime is...
Adaptive Filtering for Aeroservoelastic Response Suppression Project
National Aeronautics and Space Administration — CSA Engineering proposes the design of an adaptive aeroelastic mode suppression for advanced fly-by-wire aircraft, which will partition the modal suppression...
Innovative Structural and Material Concepts for Low-Weight Low-Drag Aircraft Design Project
National Aeronautics and Space Administration — The overall technical objective of this multi-phase project is to develop and validate a so-called 'AAW-Process' that consists of (i) the Active Aeroelastic Wing...
Flutter margin with non-linearities: real-time prediction of flutter onset speed
Casado Corpas, José; López Díez, Jesús
2008-01-01
The present article shows a procedure to predict the flutter speed based on real-time tuning of a quasi non-linear aeroelastic model. A two-dimensional non-linear (freeplay) aeroeslastic model is implemented inMatLab/Simulink with incompressible aerodynamic conditions. A comparison with real compressible conditions is provided. Once the numerical validation is accomplished, a parametric aeroelastic model is built in order to describe the proposed procedure and contribute to reduce the number ...
Stall Flutter Control of a Smart Blade Section Undergoing Asymmetric Limit Oscillations
Nailu Li; Balas, Mark J.; Pourya Nikoueeyan; Hua Yang; Naughton, Jonathan W.
2016-01-01
Stall flutter is an aeroelastic phenomenon resulting in unwanted oscillatory loads on the blade, such as wind turbine blade, helicopter rotor blade, and other flexible wing blades. Although the stall flutter and related aeroelastic control have been studied theoretically and experimentally, microtab control of asymmetric limit cycle oscillations (LCOs) in stall flutter cases has not been generally investigated. This paper presents an aeroservoelastic model to study the microtab control of the...
Kier, Thiemo
2015-01-01
The integration of loads analysis models using so called aerodynamic influence coefficients (AICs) is described. These AICs relate a change of normal velocity at panel control points to a change in panel pressure distribution, allowing to consider aeroelastic effects in a straight forward manner. The aerodynamic method employed for aeroelastic applications is typically the Vortex or Doublet Lattice Method, discretizing mean lifting surfaces. In this paper, the AICs are obtained by a 3D panel ...
Rio Melvin Aro. T; EZHILMARAN G
2015-01-01
Flutter is an unstable oscillation which can lead to destruction. Flutter can occur on fixed surfaces, such as blades, wing or the stabilizer. By self-excited aeroelastic instability, flutter can lead to mechanical or structural failure of aircraft engine blades. The modern engines have been designed with increased pressure ratio and reduced weight in order to improve aerodynamic efficiency, resulting in severe aeroelastic problems. Particularly flutter in axial compressors with t...
Numerical Calculation of Effect of Elastic Deformation on Aerodynamic Characteristics of a Rocket
Laith K. Abbas; Dongyang Chen; Xiaoting Rui
2014-01-01
The application and workflow of Computational Fluid Dynamics (CFD)/Computational Structure Dynamics (CSD) on solving the static aeroelastic problem of a slender rocket are introduced. To predict static aeroelastic behavior accurately, two-way coupling and inertia relief methods are used to calculate the static deformations and aerodynamic characteristics of the deformed rocket. The aerodynamic coefficients of rigid rocket are computed firstly and compared with the experimental data, which ver...
Modal Response of Trapezoidal Wing Structures Using Second Order Shape Sensitivities
Liu, Youhua; Kapania, Rakesh K.
2000-01-01
The modal response of wing structures is very important for assessing their dynamic response including dynamic aeroelastic instabilities. Moreover, in a recent study an efficient structural optimization approach was developed using structural modes to represent the static aeroelastic wing response (both displacement and stress). In this paper, the modal response of general trapezoidal wing structures is approximated using shape sensitivities up to the 2nd order. Also different approaches of computing the derivatives are investigated.
Efficient sensitivity analysis and optimization of a helicopter rotor
Lim, Joon W.; Chopra, Inderjit
1989-01-01
Aeroelastic optimization of a system essentially consists of the determination of the optimum values of design variables which minimize the objective function and satisfy certain aeroelastic and geometric constraints. The process of aeroelastic optimization analysis is illustrated. To carry out aeroelastic optimization effectively, one needs a reliable analysis procedure to determine steady response and stability of a rotor system in forward flight. The rotor dynamic analysis used in the present study developed inhouse at the University of Maryland is based on finite elements in space and time. The analysis consists of two major phases: vehicle trim and rotor steady response (coupled trim analysis), and aeroelastic stability of the blade. For a reduction of helicopter vibration, the optimization process requires the sensitivity derivatives of the objective function and aeroelastic stability constraints. For this, the derivatives of steady response, hub loads and blade stability roots are calculated using a direct analytical approach. An automated optimization procedure is developed by coupling the rotor dynamic analysis, design sensitivity analysis and constrained optimization code CONMIN.
A CFD/CSD interaction methodology for aircraft wings
Energy Technology Data Exchange (ETDEWEB)
Bhardwaj, M.K.; Kapania, R.K. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States); Reichenbach, E. [Boeing Co., St. Louis, MO (United States); Guruswamy, G.P. [NASA, Moffett Field, CA (United States). Ames Research Center
1998-01-01
With advanced subsonic transports and military aircraft operating in the transonic regime, it is becoming important to determine the effects of the coupling between aerodynamic loads and elastic forces. Since aeroelastic effects can significantly impact the design of these aircraft, there is a strong need in the aerospace industry to predict these interactions computationally. Such an analysis in the transonic regime requires high fidelity computational fluid dynamics (CFD) analysis tools, due to the nonlinear behavior of the aerodynamics in the transonic regime and also high fidelity computational structural dynamics (CSD) analysis tools. Also, there is a need to be able to use a wide variety of CFD and CSD methods to predict aeroelastic effects. Since source codes are not always available, it is necessary to couple the CFD and CSD codes without alteration of the source codes. In this study, an aeroelastic coupling procedure is developed to determine the static aeroelastic response of aircraft wings using any CFD and CSD code with little code integration. The aeroelastic coupling procedure is demonstrated on an F/A-18 Stabilator using NASTD (an in-house McDonnell Douglas CFD code) and NASTRAN. In addition, the Aeroelastic Research Wing (ARW-2) is used for demonstration of the aeroelastic coupling procedure by using ENSAERO (NASA Ames Research Center CFD code) and a finite element wing-box code. The results obtained from the present study are compared with those available from an experimental study conducted at NASA Langley Research Center and a study conducted at NASA Ames Research Center using ENSAERO and modal superposition. The results compare well with experimental data.
International Nuclear Information System (INIS)
A multi-body aeroelastic design code based on the implementation of the combined aeroelastic beam element is extended to cover closed loop operation conditions of wind turbines. The equations of a controller for variable generator speed and pitch controlled operation in high wind speeds are combined with the aeroelastic equations of motion for the complete wind turbine, in order to provide a compound servo-aeroelastic system of equations. The control equations comprise linear differential equations for the pitch and generator torque actuators, the control feedback elements (PI control) and the various filters acting on the feedback signals. In its non-linear form the dynamic equations are integrated in time to provide the reference state, while upon linearization of the system and transformation in the non-rotating frame, the linear stability equations are derived. Stability results for a multi-MW wind turbine, show that the coupling of the controller dynamics with the aeroelastic dynamics of the machine is important and must be taken into account in view of defining the controller parameters
Integrated aerodynamic-structural-control wing design
Rais-Rohani, M.; Haftka, R. T.; Grossman, B.; Unger, E. R.
1992-01-01
The aerodynamic-structural-control design of a forward-swept composite wing for a high subsonic transport aircraft is considered. The structural analysis is based on a finite-element method. The aerodynamic calculations are based on a vortex-lattice method, and the control calculations are based on an output feedback control. The wing is designed for minimum weight subject to structural, performance/aerodynamic and control constraints. Efficient methods are used to calculate the control-deflection and control-effectiveness sensitivities which appear as second-order derivatives in the control constraint equations. To suppress the aeroelastic divergence of the forward-swept wing, and to reduce the gross weight of the design aircraft, two separate cases are studied: (1) combined application of aeroelastic tailoring and active controls; and (2) aeroelastic tailoring alone. The results of this study indicated that, for this particular example, aeroelastic tailoring is sufficient for suppressing the aeroelastic divergence, and the use of active controls was not necessary.
Impact of Aerodynamics and Structures Technology on Heavy Lift Tiltrotors
Acree, C. W., Jr.
2006-01-01
Rotor performance and aeroelastic stability are presented for a 124,000-lb Large Civil Tilt Rotor (LCTR) design. It was designed to carry 120 passengers for 1200 nm, with performance of 350 knots at 30,000 ft altitude. Design features include a low-mounted wing and hingeless rotors, with a very low cruise tip speed of 350 ft/sec. The rotor and wing design processes are described, including rotor optimization methods and wing/rotor aeroelastic stability analyses. New rotor airfoils were designed specifically for the LCTR; the resulting performance improvements are compared to current technology airfoils. Twist, taper and precone optimization are presented, along with the effects of blade flexibility on performance. A new wing airfoil was designed and a composite structure was developed to meet the wing load requirements for certification. Predictions of aeroelastic stability are presented for the optimized rotor and wing, along with summaries of the effects of rotor design parameters on stability.
Aeroservoelasticity of Wind Turbines
DEFF Research Database (Denmark)
Kallesøe, Bjarne Skovmose
2007-01-01
This thesis deals with the fundamental aeroelastic interaction between structural motion, Pitch action and control for a wind turbine blade. As wind turbines become larger, the interaction between pitch action, blade motion, aerodynamic forces, and control become even more important to understand...... many similarities to a 2D blade section model, and it can be used instead of this in many applications, giving a transparent connection to a real wind turbine blade. In this work the aeroelastic blade model is used to analyze interaction between pitch action, blade motion and wind speed variations...... % under ideal conditions. So, a new aeroelastic blade model has been derived, which includes important features of large wind turbines, yet simple enough to be suitable for analytical analysis and control design....
An investigation on wind turbine resonant vibrations
DEFF Research Database (Denmark)
Tibaldi, Carlo; Kim, Taeseong; Larsen, Torben J.;
2016-01-01
Wind turbine resonant vibrations are investigated based on aeroelastic simulations both in frequency and time domain. The investigation focuses on three different aspects: the need of a precise modeling when a wind turbine is operating close to resonant conditions; the importance of estimating wind...... turbine loads also at low turbulence intensity wind conditions to identify the presence of resonances; and the wind turbine response because of external excitations. In the first analysis, three different wind turbine models are analysed with respect to the frequency and damping of the aeroelastic modes...... frequencies at which minimal excitation should be present during operations. The study shows that significant edgewise blade vibrations can occur on modern wind turbines even if the aeroelastic damping of the edgewise modes is positive. When operating close to resonant conditions, small differences in the...
How 2 HAWC2, the user's manual
Energy Technology Data Exchange (ETDEWEB)
Juul Larsen, T.; Melchior Hansen, A.
2007-12-15
The report contains the user's manual for the aeroelastic code HAWC2. The code is intended for calculating wind turbine response in time domain and has a structural formulation based on multi-body dynamics. The aerodynamic part of the code is based on the blade element momentum theory, but extended from the classic approach to handle dynamic inflow, dynamic stall, skew inflow, shear effects on the induction and effects from large deflections. It has been developed within the years 2003-2006 at the aeroelastic design research programme at Risoe National Laboratory, Denmark. This manual is updated for HAWC2 version 6.4. (au)
Batina, John T.
1992-01-01
A time-accurate approximate-factorization (AF) algorithm is described for solution of the three-dimensional unsteady transonic small-disturbance equation. The AF algorithm consists of a time-linearization procedure coupled with a subiteration technique. The algorithm is the basis for the Computational Aeroelasticity Program-Transonic Small Disturbance (CAP-TSD) computer code, which was developed for the analysis of unsteady aerodynamics and aeroelasticity of realistic aircraft configurations. The paper describes details on the governing flow equations and boundary conditions, with an emphasis on documenting the finite-difference formulas of the AF algorithm.
Aeroservoelasticity of wind turbines
Energy Technology Data Exchange (ETDEWEB)
Skovmose Kallesoee, B.
2007-12-14
This thesis deals with the fundamental aeroelastic interaction between structural motion, Pitch action and control for a wind turbine blade. As wind turbines become larger, the interaction between pitch action, blade motion, aerodynamic forces, and control become even more important to understand and address. The main contribution of this thesis is the development of an aeroelastic blade model which on the one hand includes the important effects of steady state blade deformation, gravity and pitch action, and on the other it is transparent, suitable for analytical analysis and parameter studies, and furthermore linear and therefore suitable for control design. The development of the primary aeroelastic blade model is divided into four steps: 1) Nonlinear partial differential equations (PDEs) of structural blade motion are derived together with equations of pitch action and rotor speed; the individual terms in these equations are discussed and given physical interpretations; 2) Steady state blade deformation and induced velocities are computed by combining the PDEs with a steady state aerodynamic model; 3) Aeroelastic modes of motion are computed by combining the linearized PDEs with a linear unsteady aerodynamic model; this model is used to analyze how blade deformation effects the modes of motion; and 4) the linear aeroelastic blade model is derived by a modal expansion of the linearized PDEs combined with a linear unsteady aerodynamic model. The aeroelastic blade model has many similarities to a 2D blade section model, and it can be used instead of this in many applications, giving a transparent connection to a real wind turbine blade. In this work the aeroelastic blade model is used to analyze interaction between pitch action, blade motion and wind speed variations. Furthermore the model is used to develop a state estimator for estimating the wind speed and wind shear, and to suggest a load reducing controller. The state estimator estimates the wind shear very
Wind loads analysis at the anchorages of the Talavera de la Reina cable stayed bridge
Directory of Open Access Journals (Sweden)
L. Rosa
2014-06-01
Full Text Available This paper describes wind tunnel tests performed on wind tunnel models of the Talavera de la Reina cable stayed bridge. The work describes the aeroelastic model construction and it is focused on the evaluation and analysis of the mean and peak wind loads at the tower foundation and the cable anchorages since these data can be very useful by the bridge manufacturer as a support for the bridge design. The work is part of a complete wind tunnel study carried out to analyze the aeroelastic stability of the bridge.
DEFF Research Database (Denmark)
Damgaard, M.; Zania, Varvara; Andersen, L.V.;
2014-01-01
. In this paper, a computationally efficient modelling approach of including the dynamic soil–structure interaction into aeroelastic codes is presented with focus on monopile foundations. Semi-analytical frequency-domain solutions are applied to evaluate the dynamic impedance functions of the soil...... wind turbine under normal operating mode. The aeroelastic response is evaluated for three different foundation conditions, i.e. apparent fixity length, the consistent lumped-parameter model and fixed support at the seabed. The effect of soil–structure interaction is shown to be critical for the design...
COMBINATION OF CFD AND CSD PACKAGES FOR FLUID-STRUCTURE INTERACTION
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
In this article the UDF script file in the Fluent software was rewritten as the "connecting file" for the Fluent and the ANSYS/ABAQUS in order that the joined file can be used to do aero-elastic computations. In this way the fluid field is computed by solving the Navier-Stokes equations and the structure movement is integrated by the dynamics directly. An analysis of the computed results shows that this coupled method designed for simulating aero-elastic systems is workable and can be used for the other fluid-structure interaction problems.
Peeters, Mathijs; Van Paepegem, Wim
2015-01-01
Typically the aero-elastic simulation tools that are used in industry employ simple beam models to represent the blades of a wind turbine. The aerodynamic loads are usually calculated using a fast blade-element momentum (BEM) method. These models allow relatively fast calculation of the aero-elastic behavior of the blade which is required in order to allow the simulation of a large number of load cases as required by the IEC 61400 [1] and GL [2] standards in a feasible amount of time. Such b...
DEFF Research Database (Denmark)
Henriksen, Lars Christian; Hansen, Anders Melchior; Kragh, Knud Abildgaard; Yde, Anders
2013-01-01
HAWCStab2 is a linear frequency domain aeroelastic tool, developed by DTU Wind Energy, suitable for frequency and stability analysis of horizontal axis 3 bladed wind turbines. This tool has now been extended to also handle complex offshore foundation types, such as jacket structures and floating...... structures with mooring lines, using super elements calculated by the nonlinear time domain aero-elastic code HAWC2. In this work the NREL 5MW Offshore RWT mounted on a jacket support structure is investigated using both HAWC2 and HAWCStab2....
Assessment of Wind Turbine Structural Integrity using Response Surface Methodology
DEFF Research Database (Denmark)
Toft, Henrik Stensgaard; Moser, W.; Sørensen, John Dalsgaard; Tøgersen, Michael L.
document the structural integrity. This load calculation demands a significant number of aero-elastic simulations which are time consuming to perform and require expert knowledge. In this paper it is investigated, to which extent the site specific loads can be determined based on a response surface...... introduced. Central composite design leads, again, to the lowest model uncertainty. The statistical uncertainty related to the number of aero-elastic simulations is modelled for each RSM using bootstrapping. In general, the statistical uncertainty related to the number of random seeds is larger than the...
Wind tunnel study on wind-induced vibration of middle pylon of Taizhou Bridge
Institute of Scientific and Technical Information of China (English)
Ma Rujin; Zhang Zhen; Chen Airong
2012-01-01
Full aero-elastic model tests are carried out to investigate wind-induced vibration of middle steel pylon of Taizhou Bridge. Model of the pylon under different construction periods is tested in both uniform and turbulent flow field. And the yaw angle of wind changes from transverse to longitudinal. Through full aero-elastic model testing, windinduced vibration is checked, which includes vortex resonance, buffeting and galloping. Vortex resonance is observed and further studies are carried out by changing damping ratio. Based on wind tunnel testing results, wind-resistance of middle pylon is evaluated and some suggestions are given for middle pylon＇ s construction.
Unsteady transonic aerodynamics
International Nuclear Information System (INIS)
Various papers on unsteady transonic aerodynamics are presented. The topics addressed include: physical phenomena associated with unsteady transonic flows, basic equations for unsteady transonic flow, practical problems concerning aircraft, basic numerical methods, computational methods for unsteady transonic flows, application of transonic flow analysis to helicopter rotor problems, unsteady aerodynamics for turbomachinery aeroelastic applications, alternative methods for modeling unsteady transonic flows
Czech Academy of Sciences Publication Activity Database
Vlček, Václav; Štěpán, M.; Zolotarev, Igor; Kozánek, Jan
2016-01-01
Roč. 821, č. 2016 (2016), s. 144-151. ISSN 1660-9336 R&D Projects: GA ČR GA13-10527S Institutional support: RVO:61388998 Keywords : aeroelasticity * flutter * interferometry * subsonic flow Subject RIV: BI - Acoustics
Czech Academy of Sciences Publication Activity Database
Vlček, Václav; Luxa, Martin
Praha : Ústav termomechaniky AV ČR, 2005 - (Zolotarev, I.), s. 153-154 ISBN 80-85918-95-1. [Interaction and Feedbacks ´2005. Praha (CZ), 29.11.2005-30.11.2005] Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * measurement * optical Subject RIV: BK - Fluid Dynamics
Numerical simulation of interaction between turbulent flow and a vibrating airfoil
Czech Academy of Sciences Publication Activity Database
Dubcová, Lenka; Feistauer, M.; Horáček, Jaromír; Sváček, Petr
2009-01-01
Roč. 12, č. 5 (2009), s. 207-225. ISSN 1432-9360 R&D Projects: GA AV ČR IAA200760613 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * finite element method (FEM) * algebraic turbulence models Subject RIV: BI - Acoustics
Úvodní aeroelastická měření na profilu se dvěma stupni volnosti
Czech Academy of Sciences Publication Activity Database
Vlček, Václav; Luxa, Martin
Praha: Ústav termomechaniky AV ČR, 2005 - (Fuis, V.; Krejčí, P.; Návrat, T.), s. 343-344 ISBN 80-85918-93-5. [Engineering Mechanics 2005. Svratka (CZ), 09.05.2005-12.05.2005] Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * measurement Subject RIV: BK - Fluid Dynamics
Bifurcation and Post-Critical Flutter -Type Random Vibrations of Slender Structures
Czech Academy of Sciences Publication Activity Database
Náprstek, Jiří
Notre Dame : Notre Dame University, 2000 - (Spencer, B.), s. 2000-2006 [Probabilistic Mechanics Conference ASCE /8./. Notre Dame (US), 24.07.2000-26.07.2000] R&D Projects: GA ČR GA103/99/0122; GA ČR GA103/99/0756 Keywords : slender structures, aeroelastic stability, Lyapunov function. Subject RIV: JN - Civil Engineering
Frequency support capability of variable speed wind turbine based on electromagnetic coupler
DEFF Research Database (Denmark)
You, Rui; Barahona Garzón, Braulio; Chai, Jianyun;
2015-01-01
frequency which is the input signal for Type 3 and Type 4 wind turbine frequency support controller, is used for the calculation of WT-EMC supplementary torque command. The integrated simulation environment based on the aeroelastic code HAWC2 and software Matlab/Simulink is used to build a 2 MW WT-EMC model...
The 5 MW DeepWind floating offshore vertical wind turbine concept design - status and perspective
DEFF Research Database (Denmark)
Schmidt Paulsen, Uwe; Aagaard Madsen, Helge; Kragh, Knud Abildgaard;
2014-01-01
aspects of the floating hull, and new generator design embracing magnetic bearings. Two important design tools were developed which allow the industry to analyze various VAWT(vertical Axis Wind Turbine) variants for offshore applications: a main design tool “HAWC2” for aeroelastic design of VAWTs, and a...
Simulation of free airfoil vibrations in incompressible viscous flow – comparison of FEM and FVM
Czech Academy of Sciences Publication Activity Database
Sváček, P.; Horáček, Jaromír; Honzátko, R.; Kozel, K.
2012-01-01
Roč. 52, č. 6 (2012), s. 104-114. ISSN 1210-2709 R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional research plan: CEZ:AV0Z20760514 Keywords : laminar flow * finite volume method * finite element method * arbitrary Lagrangian-Eulerian method * nonlinear aeroelasticity Subject RIV: BI - Acoustics
Numerical simulation of flow induced airfoil vibrations with large amplitudes
Czech Academy of Sciences Publication Activity Database
Sváček, Petr; Feistauer, M.; Horáček, Jaromír
2007-01-01
Roč. 23, - (2007), s. 391-411. ISSN 0889-9746 R&D Projects: GA AV ČR IAA200760613 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * flutter * nonlinear oscillations Subject RIV: BI - Acoustics Impact factor: 0.821, year: 2007
Numerical simulation of flow induced airfoil vibrations with large amplitudes
Czech Academy of Sciences Publication Activity Database
Sváček, P.; Feistauer, M.; Horáček, Jaromír
2005-01-01
Roč. 2005, č. 1 (2005), s. 1-30 R&D Projects: GA ČR(CZ) GA101/02/0391 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * flutter * finite element method Subject RIV: BI - Acoustics
Linear and nonlinear dynamic analysis of redundant load path bearingless rotor systems
Murthy, V. R.; Shultz, Louis A.
1994-01-01
The goal of this research is to develop the transfer matrix method to treat nonlinear autonomous boundary value problems with multiple branches. The application is the complete nonlinear aeroelastic analysis of multiple-branched rotor blades. Once the development is complete, it can be incorporated into the existing transfer matrix analyses. There are several difficulties to be overcome in reaching this objective. The conventional transfer matrix method is limited in that it is applicable only to linear branch chain-like structures, but consideration of multiple branch modeling is important for bearingless rotors. Also, hingeless and bearingless rotor blade dynamic characteristics (particularly their aeroelasticity problems) are inherently nonlinear. The nonlinear equations of motion and the multiple-branched boundary value problem are treated together using a direct transfer matrix method. First, the formulation is applied to a nonlinear single-branch blade to validate the nonlinear portion of the formulation. The nonlinear system of equations is iteratively solved using a form of Newton-Raphson iteration scheme developed for differential equations of continuous systems. The formulation is then applied to determine the nonlinear steady state trim and aeroelastic stability of a rotor blade in hover with two branches at the root. A comprehensive computer program is developed and is used to obtain numerical results for the (1) free vibration, (2) nonlinearly deformed steady state, (3) free vibration about the nonlinearly deformed steady state, and (4) aeroelastic stability tasks. The numerical results obtained by the present method agree with results from other methods.
DEFF Research Database (Denmark)
Kim, Taeseong; Shin, SangJoon; Kim, Do-Hyung
2012-01-01
A further improvement is attempted of an existing analytical model for an accurate prediction of the aeroelastic stability of a tiltrotor aircraft. A rigid-bladed rotor structural model with the natural frequencies selected appropriately in both the flapping and lagging motions is used. The...
Numerical Simulation of Interaction of Fluid Flow and Elastic Structure Modelling Vocal Fold
Czech Academy of Sciences Publication Activity Database
Valášek, J.; Sváček, P.; Horáček, Jaromír
2016-01-01
Roč. 821, č. 2016 (2016), s. 693-700. ISSN 1660-9336 R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional support: RVO:61388998 Keywords : finite element method * 2D Navier-Stokes equations * vocal folds * aeroelasticity Subject RIV: BI - Acoustics
Numerical Simulation of Interaction of Fluid Flow and Elastic Structure Modelling Vocal Fold
Czech Academy of Sciences Publication Activity Database
Valášek, J.; Sváček, P.; Horáček, Jaromír
2016-01-01
Roč. 821, č. 2016 (2016), s. 693-700. ISSN 1662-7482 R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional support: RVO:61388998 Keywords : finite element method * 2D Navier-Stokes equations * vocal folds * aeroelasticity Subject RIV: BI - Acoustics
The importance of including dynamic soil-structure interaction into wind turbine simulation codes
DEFF Research Database (Denmark)
Damgaard, Mads; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2014-01-01
is examined. The optimal order of the models is determined and implemented into the aeroelastic code HAWC2, where the dynamic response of a 5.0 MW wind turbine is evaluated. In contrast to the fore-aft vibrations, the inclusion of soil-structure interaction is shown to be critical for the side...
Курилов, Е. А.
2006-01-01
The aeroelastic stability of simply supported cylindrical shell with localized masses in supersonic flow is investigated. The Donnell-Mushtari-Vlasov nonlinear shallow-shell theory is used to describe the shell dynamics. Linear piston theory is applied to describe the fluid-structure interaction. The system is discretized by the Bubnov-Galerkin procedure. The dumping effect is analyzed.
Курилов, Е. А.
2006-01-01
The aeroelastic stability of simply supported cylindrical shell with localized masses in supersonic flow is investigated. The Donnell-Mushtari-Vlasov nonlinear shallow-shell theory is used to describe the shell dynamics. Linear piston theory is applied to describe the fluid-structure interaction. The system is discretized by the Bubnov-Galerkin procedure. The dumping effect is analyzed
Goodwin, Sabine A.; Raj, P.
1999-01-01
Progress to date towards the development and validation of a fast, accurate and cost-effective aeroelastic method for advanced parallel computing platforms such as the IBM SP2 and the SGI Origin 2000 is presented in this paper. The ENSAERO code, developed at the NASA-Ames Research Center has been selected for this effort. The code allows for the computation of aeroelastic responses by simultaneously integrating the Euler or Navier-Stokes equations and the modal structural equations of motion. To assess the computational performance and accuracy of the ENSAERO code, this paper reports the results of the Navier-Stokes simulations of the transonic flow over a flexible aeroelastic wing body configuration. In addition, a forced harmonic oscillation analysis in the frequency domain and an analysis in the time domain are done on a wing undergoing a rigid pitch and plunge motion. Finally, to demonstrate the ENSAERO flutter-analysis capability, aeroelastic Euler and Navier-Stokes computations on an L-1011 wind tunnel model including pylon, nacelle and empennage are underway. All computational solutions are compared with experimental data to assess the level of accuracy of ENSAERO. As the computations described above are performed, a meticulous log of computational performance in terms of wall clock time, execution speed, memory and disk storage is kept. Code scalability is also demonstrated by studying the impact of varying the number of processors on computational performance on the IBM SP2 and the Origin 2000 systems.
Interakce proudící tekutiny a leteckého profilu
Czech Academy of Sciences Publication Activity Database
Feistauer, M.; Horáček, Jaromír; Sváček, P.
2006-01-01
Roč. 1, č. 2 (2006), s. 79-84. ISSN 1801-9315 R&D Projects: GA AV ČR IAA200760613 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * ALE mothod * numerical simulations Subject RIV: BI - Acoustics
Study and Analysis on the Influence of Flutter Frequency on Airplane Stability
Directory of Open Access Journals (Sweden)
B. Janarthanan
2013-10-01
Full Text Available In the nationwide requirement of the growth in commercial aviation safety and profit, the field of Aeroelastic science plays a vital role. Flutter is one of the dynamic aeroelastic problems, it mainly occurs at lifting surfaces when the airplane cruises at high speeds. At relatively low speeds, the torsional stiffness of the wing is enough to counteract the twisting. However, the variation in flutter frequency causes the instability motion on aircraft. Therefore, the wing displacement against the flow field plays a vital role in dynamic stability analysis. As per the commercial aviation concern, an aircraft which is able to overcome the significant aeroelastic problems can yield maximum running profit. In order to maintain the airplane stability in high-speed, wings can be designed to minimize the distance between aerodynamic centre and shear centre (on the elastic axis. The main focus of this project is to calculate the frequency of an aircraft wing while it is subjected to aeroelastic (flutter instability. The analytical process identified for this work is the Eigen value method. By using MATLAB solver, the optimization has been carried out along the span of real-time model. In future, the efficient structural model is then simulated and analysis is carried out to evaluate the longitudinal stability due to flutter phenomena.
Full-scale measurements of aerodynamic induction in a rotor plane
DEFF Research Database (Denmark)
Larsen, Gunner Chr.; Hansen, Kurt Schaldemose
2014-01-01
Reliable modelling of aerodynamic induction is imperative for successful prediction of wind turbine loads and wind turbine dynamics when based on state-of- the-art aeroelastic tools. Full-scale LiDAR based wind speed measurements, with high temporal and spatial resolution, have been conducted in...
Hybrid Electro-Mechanical Simulation Tool for Wind Turbine Generators: Preprint
Energy Technology Data Exchange (ETDEWEB)
Singh, M.; Muljadi, E.; Jonkman, J.
2013-05-01
This paper describes the use of MATLAB/Simulink to simulate the electrical and grid-related aspects of a WTG and the FAST aero-elastic wind turbine code to simulate the aerodynamic and mechanical aspects of the WTG. The combination of the two enables studies involving both electrical and mechanical aspects of the WTG.
Vibrating Profile in the Aerodynamic Tunnel — Identification of the Start of Flutter
Czech Academy of Sciences Publication Activity Database
Kozánek, Jan; Vlček, Václav; Zolotarev, Igor
2014-01-01
Roč. 3, č. 4 (2014), s. 317- 323 . ISSN 2164-6457 R&D Projects: GA ČR GA13-10527S Institutional support: RVO:61388998 Keywords : profile in airflow * Mach numbers * limits of the aeroelastic stability * spectral identification Subject RIV: BI - Acoustics
DEFF Research Database (Denmark)
Lekou, D.J.; Bacharoudis, K. C.; Farinas, A. B.;
2015-01-01
, the material properties of the constitutive layers and the aero-elastic loads formed the base by which global and local blade stiffness and strength are evaluated and compared. Static, modal, buckling and fatigue analysis of the blade were performed by each partner using their own tools; fully in...
FAST User's Guide - Updated August 2005
Energy Technology Data Exchange (ETDEWEB)
Jonkman, J. M.; Buhl, M. L. Jr.
2005-10-01
The FAST (Fatigue, Aerodynamics, Structures, and Turbulence) Code is a comprehensive aeroelastic simulator capable of predicting both the extreme and fatigue loads of two- and three-bladed horizontal-axis wind turbines (HAWTs). This document covers the features of FAST and outlines its operating procedures.
Simulation of a flexible wind turbine response to a grid fault
DEFF Research Database (Denmark)
Hansen, Anca D.; Cutululis, A. Nicolaos; Sørensen, Poul; Iov, Florin; Larsen, Torben
2007-01-01
in power system simulation tools applying simplified mechanical models of the drive train. This paper presents simulations of the wind turbine load response to grid faults with an advanced aeroelastic computer code (HAWC2). The core of this code is an advanced model for the flexible structure of the...
DEFF Research Database (Denmark)
Henriksen, Lars Christian; Hansen, Anders Melchior; Kragh, Knud Abildgaard; Yde, Anders
HAWCStab2 is a linear frequency domain aero-elastic tool, developed by DTU Wind Energy, suitable for frequency and stability analysis of horizontal axis 3 bladed wind turbines [1]. This tool has now been extended to also handle complex offshore foundation types, such as jacket structures and...
DEFF Research Database (Denmark)
Barlas, Thanasis K.; Bergami, Leonardo; Hansen, Morten Hartvig; Pedersen, Mads Mølgaard; Thomsen, Kenneth; Aagaard Madsen, Helge
The load alleviation potential of the Controllable Rubber Trailing Edge Flap (CRTEF) is verified on a full Design Load Base (DLB) setup using the aeroelastic code HAWC2, and by investigating a flap configuration for the NREL 5MW Reference Wind Turbine (RWT) model. The performance of the CRTEF...
A general purpose, modular computational platform for fluid-structure interaction problems
International Nuclear Information System (INIS)
A general purpose fluid-structure interaction (FSI) methodology is currently under development with the capability of simulating several problems of interest, from aeroelasticity problems to sub-sea propulsion using shape deformation. This paper will describe a modular FSI code and present results for a few test cases that were used to validate the code. (author)
Resor, B.; Wilson, D.; Berg, D.; Berg, J.; Barlas, T.; Van Wingerden, J.W.; Van Kuik, G.A.M.
2010-01-01
Active aerodynamic load control of wind turbine blades is being investigated by the wind energy research community and shows great promise, especially for reduction of turbine fatigue damage in blades and nearby components. For much of this work, full system aeroelastic codes have been used to simul
Description of the DLL regulation interface in HAWC
DEFF Research Database (Denmark)
Larsen, Torben J.
2001-01-01
This report contains a description of the external regulation interface between the aeroelastic code HAWC and a separate regulation unit programmed as a DLL (Dynamic Link Library). Specific HAWC commands used with the regulation as well as simple DLLexamples written in Delphi, Fortran and C...
DEFF Research Database (Denmark)
Schløer, Signe; Bredmose, Henrik; Bingham, Harry B.
2016-01-01
and nonlinear irregular wave realizations are calculated using the fully nonlinear potential flow wave model OceanWave3D [1]. The linear and nonlinear wave realizations are compared using both a static analysis on a fixed monopile and dynamic calculations with the aeroelastic code Flex5 [2]. The...
Computational simulation of videokymography images of vibrating vocal folds
Czech Academy of Sciences Publication Activity Database
Horáček, Jaromír; Švec, J.; Šidlof, Petr
Stockholm: Karolinska Institute, Stockholm-Huddinge, 2008 - (Lindestatd, P.). s. 16-16 [The AQL Conference /8./. 17.10.2008-18.10.2008, Stockholm] R&D Projects: GA ČR GA101/08/1155 Institutional research plan: CEZ:AV0Z20760514 Keywords : biomechanics of voice * videokymography * aeroelastic model Subject RIV: BI - Acoustics
Influence of vehicles on bridge flutter and galloping
Czech Academy of Sciences Publication Activity Database
Pospíšil, Stanislav; Buljac, A.; Kuznetsov, Sergeii; Kozmar, H.
New Taipei City : Tamkang University, 2015. s. 3-6 ISBN N Institutional support: RVO:68378297 Keywords : vehicle-wind bridge system * Kao-Pin Hsi Bridge * aeroelastic derivatives Subject RIV: JM - Building Engineering http://www.wind.org.tw/epaper/vj-attachment/2016/02/attach44.pdf
Grid faults' impact on wind turbine structural loads
DEFF Research Database (Denmark)
Hansen, Anca D.; Cutululis, A. Nicolaos; Sørensen, Poul; Iov, Florin; Larsen, Torben J.
2007-01-01
strategy, where the focus is on how to access a proper combination of two complimentary simulations tools, such as the advanced aeroelastic computer code HAWC2 and the detailed power system simulation tool DIgSILENT, in order to provide a whole overview of both the structural and the electrical behaviour...
Impact of fault ride-through requirements on fixed-speed wind turbine structural loads
DEFF Research Database (Denmark)
Hansen, Anca Daniela; Cutululis, Nicolaos Antonio; Markou, Helen; Sørensen, Poul Ejnar
2011-01-01
simulation tools, which have expertise in different specialized wind turbines design areas. Two complimentary simulation tools are considered i.e. the detailed power system simulation tool PowerFactory from DIgSILENT and the advanced aeroelastic computer code HAWC2, in order to assess of the dynamic response...
Status for the two-dimensional Navier-Stokes solver EllipSys2D
DEFF Research Database (Denmark)
Bertagnolio, F.; Sørensen, Niels N.; Johansen, J.
2001-01-01
This report sets up an evaluation of the two-dimensional Navier-Stokes solver EllipSys2D in its present state. This code is used for blade aerodynamics simulations in the Aeroelastic Design group at Risø. Two airfoils are investigated by computing theflow at several angles of attack ranging from...
Do Lumped-Parameter Models Provide the Correct Geometrical Damping?
DEFF Research Database (Denmark)
Andersen, Lars
2007-01-01
This paper concerns the formulation of lumped-parameter models for rigid footings on homogenous or stratified soil with focus on the horizontal sliding and rocking. Such models only contain a few degrees of freedom, which makes them ideal for inclusion in aero-elastic codes for wind turbines and...
Abbas, L.K.; Rui, X.; Marzocca, P.; Abdalla, M.; De Breuker, R.
2011-01-01
In this paper, the effect of the system parameters on the flutter of a curved skin panel forced by a supersonic/hypersonic unsteady flow is numerically investigated. The aeroelastic model investigated includes the third-order piston theory aerodynamics for modeling the flow-induced forces and the V
Wind tunnel measurements of flow-induced vibration of a NACA0015 airfoil model
Czech Academy of Sciences Publication Activity Database
Šidlof, P.; Vlček, Václav; Štěpán, M.; Horáček, Jaromír; Luxa, Martin; Šimurda, David; Kozánek, Jan
Anaheim: ASME, 2014, PVP2014-28294. ISBN 978-0-7918-4601-8. [ASME 2014 Pressure Vessels & Piping Conference. Anaheim, California (US), 20.07.2014-24.07.2014] R&D Projects: GA ČR GA13-10527S Institutional support: RVO:61388998 Keywords : aeroelasticity * flutter limit cycle oscillations (LCO) measurement * visualization of unsteady flow field Subject RIV: BI - Acoustics
Wind-tunnel tests of the XV-15 tilt rotor aircraft
Weiberg, J. A.; Maisel, M. D.
1980-01-01
The XV-15 aircraft was tested in the Ames 40 by 80 Foot Wind Tunnel for preliminary evaluation of aerodynamic and aeroelastic characteristics prior to flight. The tests were undertaken to investigate the aircraft performance, stability, control and structural loads for flight modes from helicopter through transition and airplane mode up to the tunnel capability of 170 knots. Results from these tests are presented.
Czech Academy of Sciences Publication Activity Database
Vlček, Václav; Kozánek, Jan; Zolotarev, Igor
Brno: Brno University of Technology, 2014 - (Fuis, V.), s. 688-691 ISBN 978-80-214-4871-1. ISSN 1805-8248. [Engineering Mechanics 2014 /20./. Svratka (CZ), 12.05.2014-15.05.2014] R&D Projects: GA ČR GA13-10527S Institutional support: RVO:61388998 Keywords : aeroelasticity * flutter * interferometry * subsonic flow Subject RIV: BI - Acoustics
Unsteady aerodynamic forces measured on a fluttering profile
Czech Academy of Sciences Publication Activity Database
Vlček, Václav; Zolotarev, Igor; Kozánek, Jan
2014-01-01
Roč. 21, č. 2 (2014), s. 91-96. ISSN 1802-1484 R&D Projects: GA ČR GA13-10527S Institutional support: RVO:61388998 Keywords : aeroelastic experiments * self-excited vibrations * wind tunnel * interferometry Subject RIV: BI - Acoustics
DEFF Research Database (Denmark)
Jørgensen, Martin Felix; Pedersen, Niels Leergaard; Sørensen, Jens Nørkær;
2014-01-01
The aeroelastic FLEX 5 code and a semi-advanced rigid multibody model has been utilized for simulating drivetrain forces and moments in a real 500 kW wind turbine. Experimental validation is carried out with results based on known physical properties of the blades, tower, hub, gearbox, shaft and ...
Ulker, Fatma Demet
In forward flight, helicopter rotor blades function within a highly complex aerodynamic environment that includes both near-blade and far-blade aerodynamic phenomena. These aerodynamic phenomena cause fluctuating aerodynamic loads on the rotor blades. These loads when coupled with the dynamic characteristics and elastic motion of the blade create excessive amount of vibration. These vibrations degrade helicopter performance, passenger comfort and contributes to high cost maintenance problems. In an effort to suppress helicopter vibration, recent studies have developed active control strategies using active pitch links, flaps, twist actuation and higher harmonic control of the swash plate. In active helicopter vibration control, designing a controller in a computationally efficient way requires accurate reduced-order models of complex helicopter aeroelasticity. In previous studies, controllers were designed using aeroelastic models that were obtained by coupling independently reduced aerodynamic and structural dynamic models. Unfortunately, these controllers could not satisfy stability and performance criteria when implemented in high-fidelity computer simulations or real-time experiments. In this thesis, we present a novel approach that provides accurate time-periodic reduced-order models and time-periodic H2 and H infinity controllers that satisfy the stability and performance criteria. Computational efficiency and the necessity of using the approach were validated by implementing an actively controlled flap strategy. In this proposed approach, the reduced-order models were directly identified from high-fidelity coupled aeroelastic analysis by using the time-periodic subspace identification method. Time-periodic H2 and Hinfinity controllers that update the control actuation at every time step were designed. The control synthesis problem was solved using Linear Matrix Inequality and periodic Riccati Equation based formulations, for which an in-house periodic
WRATS Integrated Data Acquisition System
Piatak, David J.
2008-01-01
The Wing and Rotor Aeroelastic Test System (WRATS) data acquisition system (DAS) is a 64-channel data acquisition display and analysis system specifically designed for use with the WRATS 1/5-scale V-22 tiltrotor model of the Bell Osprey. It is the primary data acquisition system for experimental aeroelastic testing of the WRATS model for the purpose of characterizing the aeromechanical and aeroelastic stability of prototype tiltrotor configurations. The WRATS DAS was also used during aeroelastic testing of Bell Helicopter Textron s Quad-Tiltrotor (QTR) design concept, a test which received international attention. The LabVIEW-based design is portable and capable of powering and conditioning over 64 channels of dynamic data at sampling rates up to 1,000 Hz. The system includes a 60-second circular data archive, an integrated model swashplate excitation system, a moving block damping application for calculation of whirl flutter mode subcritical damping, a loads and safety monitor, a pilot-control console display, data analysis capabilities, and instrumentation calibration functions. Three networked computers running custom-designed LabVIEW software acquire data through National Instruments data acquisition hardware. The aeroelastic model (see figure) was tested with the DAS at two facilities at NASA Langley, the Transonic Dynamics Tunnel (TDT) and the Rotorcraft Hover Test Facility (RHTF). Because of the need for seamless transition between testing at these facilities, DAS is portable. The software is capable of harmonic analysis of periodic time history data, Fast Fourier Transform calculations, power spectral density calculations, and on-line calibration of test instrumentation. DAS has a circular buffer archive to ensure critical data is not lost in event of model failure/incident, as well as a sample-and-hold capability for phase-correct time history data.
HAWC2 and BeamDyn: Comparison Between Beam Structural Models for Aero-Servo-Elastic Frameworks
Energy Technology Data Exchange (ETDEWEB)
Pavese, Christian; Wang, Qi; Kim, Taeseong; Jonkman, Jason; Sprague, Michael A.
2016-07-01
This work presents a comparison of two beam codes for aero-servo-elastic frameworks: a new structural model for the aeroelastic code HAWC2 and a new nonlinear beam model, BeamDyn, for the aeroelastic modularization framework FAST v8. The main goal is to establish the suitability of the two approaches to model the structural behaviour of modern wind turbine blades in operation. Through a series of benchmarking structural cases of increasing complexity, the capability of the two codes to simulate highly nonlinear effects is investigated and analyzed. Results show that even though the geometrically exact beam theory can better model effects such as very large deflections, rotations, and structural couplings, an approach based on a multi-body formulation assembled through linear elements is capable of computing accurate solutions for typical nonlinear beam theory benchmarking cases.
Electrical components library for HAWC2
DEFF Research Database (Denmark)
Cutululis, Nicolaos Antonio; Larsen, Torben J.; Sørensen, Poul Ejnar;
The work presented in this report is part of the EFP project called “A Simulation Platform to Model, Optimize and Design Wind Turbines” partly funded by the Danish Energy Authority under contract number 1363/04-0008. The project is carried out in cooperation between Risø National Laboratory and...... Aalborg University. In this project, the focus is on the development of a simulation platform for wind turbine systems using different simulation tools. This report presents the electric component library developed for use in the aeroelastic code HAWC2. The developed library includes both steady state and...... developed. The model includes the dynamics of the rotor fluxes. The model is suitable for a more detailed investigation of the mechanical – electrical interaction, both under normal and fault operation. For the variable speed wind turbine, a steadystate model, typically used in aeroelastic design, was...
Fluid-structure interaction computations for geometrically resolved rotor simulations using CFD
DEFF Research Database (Denmark)
Heinz, Joachim Christian; Sørensen, Niels N.; Zahle, Frederik
2016-01-01
newly developed coupling between HAWC2 and EllipSys3D (HAWC2CFD) is utilized to compute the aero-elastic response of the NREL 5-MW reference wind turbine (RWT) under normal operational conditions. A comparison with the low-fidelity but state-of-the-art aero-elastic solver HAWC2 reveals a very good...... agreement between the two approaches. In a second test case, the response of the NREL 5-MW RWT is computed during a yawed and thus asymmetric inflow. The continuous good agreement confirms the qualities of HAWC2CFD but also illustrates the strengths of a computationally cheaper blade element momentum theory...... (BEM) based solver, as long as the solver is applied within the boundaries of the employed engineering models. Two further test cases encompass flow situations, which are expected to exceed the limits of the BEM model. However, the simulation of the NREL 5-MW RWT during an emergency shut down situation...
The influence of trailed vorticity on flutter speed estimations
DEFF Research Database (Denmark)
Pirrung, Georg; Aagaard Madsen, Helge; Kim, Taeseong
2014-01-01
This paper briefly describes the implementation of a coupled near and far wake model for wind turbine rotor induction in the aeroelastic code HAWC2 and its application for flutter analysis of the NREL 5 MW wind turbine. The model consists of a far wake part based on Blade Element Momentum (BEM...... influence of the near wake model on the aeroelastic stability of the blades of the NREL 5 MW turbine in overspeed conditions is investigated in the second part of the paper. The analysis is based on a runaway case in which the turbine is free to speed up without generator torque and vibrations start...... building up at a critical rotor speed. Blades with modified torsional and flapwise stiffness are also investigated. A flutter analysis is often part of the stability investigations for new blades but is normally carried out with engineering models that do not include the influence of unsteady trailed...
Stall Flutter Control of a Smart Blade Section Undergoing Asymmetric Limit Oscillations
Directory of Open Access Journals (Sweden)
Nailu Li
2016-01-01
Full Text Available Stall flutter is an aeroelastic phenomenon resulting in unwanted oscillatory loads on the blade, such as wind turbine blade, helicopter rotor blade, and other flexible wing blades. Although the stall flutter and related aeroelastic control have been studied theoretically and experimentally, microtab control of asymmetric limit cycle oscillations (LCOs in stall flutter cases has not been generally investigated. This paper presents an aeroservoelastic model to study the microtab control of the blade section undergoing moderate stall flutter and deep stall flutter separately. The effects of different dynamic stall conditions and the consequent asymmetric LCOs for both stall cases are simulated and analyzed. Then, for the design of the stall flutter controller, the potential sensor signal for the stall flutter, the microtab control capability of the stall flutter, and the control algorithm for the stall flutter are studied. The improvement and the superiority of the proposed adaptive stall flutter controller are shown by comparison with a simple stall flutter controller.
DEFF Research Database (Denmark)
Barahona Garzón, Braulio; Cutululis, Nicolaos Antonio; Hansen, Anca Daniela;
2014-01-01
This paper investigates the impact that unbalanced voltage faults have on wind turbine structural loads. In such cases, electromagnetic torque oscillations occur at two times the supply voltage frequency. The objectives of this work are to quantify wind turbine structural loads induced by...... unbalanced voltage faults relative to those during normal operation; and to evaluate the potential for reducing structural loads with the control of the generator. The method applied is integrated dynamic analysis. Namely, dynamic analysis with models that consider the most important aeroelastic, electrical......, and control dynamics in an integrated simulation environment based on an aeroelastic code (HAWC2) and software for control design (Matlab/Simulink). In the present analysis, 1 Hz equivalent loads are used to compare fatigue loads, whereas maximum–minimum values are used to compare extreme loads. A...
DEFF Research Database (Denmark)
Kim, Taeseong; Kim, Jaehoon; Shin, Sang Joon;
2013-01-01
In order to enhance the aeroelastic stability of a tiltrotor aircraft, a structural optimization framework is developed by applying a multi-level optimization approach. Each optimization level is designed to achieve a different purpose; therefore, relevant optimization schemes are selected for each...... level. Enhancement of the aeroelastic stability is selected as an objective in the upper-level optimization. This is achieved by seeking the optimal structural properties of a composite wing, including its mass, vertical, chordwise, and torsional stiffness. In the upper-level optimization, the response...... surface method (RSM), is selected. On the other hand, lower-level optimization seeks to determine the local detailed cross-sectional parameters, such as the ply orientation angles and ply thickness, which are relevant to the wing structural properties obtained at the upper-level. To avoid manufacturing...
DEFF Research Database (Denmark)
Natarajan, Anand
2014-01-01
An overview of technological trends in the design of multi-mega Watt wind turbines focused on the offshore sector is presented. The state of the art technologies for wind turbine design are multidisciplinary ranging from blade aeroelasticity, power transmission to the generator, to advanced control...... systems that ensure performance and the design of offshore support structures to minimize cost of energy. Light weight carbon fiber blades, aeroelastic tailoring using bend–twist coupling are discussed in coordination with a multitude of aerodynamic technologies for optimal power capture such as high......-lift airfoils, flaps, and flat-back airfoil designs. The pitch control of the turbine responsible for rotating the blades about its axis to reduce loads is the primary load reducing mechanism of the wind turbine, for which technologies that enable wind sensing such as forward looking LIDARs and redundancy...
Match Point Solution for Robust Flutter Analysis in Constant-Mach Prediction
Institute of Scientific and Technical Information of China (English)
Yun Haiwei; Han Jinglong
2008-01-01
This paper presents a method for robust flutter computation which uses flight altitude as the perturbation variable in order to obtain a match point solution. The air density and sound speed of standard atmosphere model are approximated as the polynomial function of altitude, such that the flight altitude becomes the single perturbation variable that describes the aeroelastic system. The uncertainties of generalized stiffness and damping are considered and the uncertain aeroelastic system can be formulated as linear fractional transforma- tion (LFT) representation which is suitable for μ analysis framework. Finally, the match point solutions of robust flutter margins can be computed with structured singular value (SSV) theory. The robust flutter analysis method provided in this paper is suitable for con- stant-Mach flight flutter test and provides valuable reference for flight envelope expansion.
Modern wing flutter analysis by computational fluid dynamics methods
Cunningham, Herbert J.; Batina, John T.; Bennett, Robert M.
1988-01-01
The application and assessment of the recently developed CAP-TSD transonic small-disturbance code for flutter prediction is described. The CAP-TSD code has been developed for aeroelastic analysis of complete aircraft configurations and was previously applied to the calculation of steady and unsteady pressures with favorable results. Generalized aerodynamic forces and flutter characteristics are calculated and compared with linear theory results and with experimental data for a 45 deg sweptback wing. These results are in good agreement with the experimental flutter data which is the first step toward validating CAP-TSD for general transonic aeroelastic applications. The paper presents these results and comparisons along with general remarks regarding modern wing flutter analysis by computational fluid dynamics methods.
Hsia, H.-M.; Chou, Y.-L.; Longman, R. W.
1983-07-01
The topics considered are related to measurements and controls in physical systems, the control of large scale and distributed parameter systems, chemical engineering systems, aerospace science and technology, thermodynamics and fluid mechanics, and computer applications. Subjects in structural dynamics are discussed, taking into account finite element approximations in transient analysis, buckling finite element analysis of flat plates, dynamic analysis of viscoelastic structures, the transient analysis of large frame structures by simple models, large amplitude vibration of an initially stressed thick plate, nonlinear aeroelasticity, a sensitivity analysis of a combined beam-spring-mass structure, and the optimal design and aeroelastic investigation of segmented windmill rotor blades. Attention is also given to dynamics and control of mechanical and civil engineering systems, composites, and topics in materials. For individual items see A83-44002 to A83-44061
Energy Technology Data Exchange (ETDEWEB)
Pavese, Christian; Kim, Taeseong; Wang, Qi; Jonkman, Jason; Sprague, Michael A.
2016-08-01
This work presents a comparison of two beam codes for aero-servo-elastic frameworks: a new structural model for the aeroelastic code HAWC2 and a new nonlinear beam model, BeamDyn, for the aeroelastic modularization framework FAST v8. The main goal is to establish the suitability of the two approaches to model the structural behaviour of modern wind turbine blades in operation. Through a series of benchmarking structural cases of increasing complexity, the capability of the two codes to simulate highly nonlinear effects is investigated and analyzed. Results show that even though the geometrically exact beam theory can better model effects such as very large deflections, rotations, and structural couplings, an approach based on a multi-body formulation assembled through linear elements is capable of computing accurate solutions for typical nonlinear beam theory benchmarking cases.
DEFF Research Database (Denmark)
Ardila, Oscar Gerardo Castro; Lennie, Matthew; Branner, Kim;
2015-01-01
In this paper, fatigue lifetime prediction of NREL 5MW reference wind turbine is presented. The fatigue response of materials used in selected blade cross sections was obtained by applying macroscopic fatigue approaches and assuming uniaxial stress states. Power production and parked load cases...... suggested by the IEC 61400-1 standard were studied employing different load time intervals and by using two novel fatigue tools called ALBdeS and BECAS+F. The aeroelastic loads were defined thought aeroelastic simulations performed with both FAST and HAWC2 tools. The stress spectra at each layer were...... calculated employing laminated composite theory and beam cross section methods. The Palmgren-Miner linear damage rule was used to calculate the accumulation damage. The theoretical results produced by both fatigue tools proved a prominent effect of analysed design load conditions on the estimated lifetime of...
A Two-Bladed Concept Wind Turbine
DEFF Research Database (Denmark)
Kim, Taeseong
This article shows the potential for reducing extreme loads with an innovative design of wind turbine, a partial pitch two-bladed concept turbine. The most extreme conditions to test a turbine are considered to be stand-still combined with a grid failure in which the wind comes from all directions...... from 0 to 360 degrees. All aeroelastic load simulations are done by using the aeroelastic code HAWC2. From the load comparisons between the partial pitch two-bladed turbine and a conventional three-bladed turbine it is observed that the partial pitch two-bladed turbine can reduce the extreme tower...... bottom bending moment by approximately 33% compared to the three-bladed turbine....
Shape Optimization of Wind Turbine Blades
DEFF Research Database (Denmark)
Wang, Xudong; Shen, Wen Zhong; Zhu, Wei Jun; Sørensen, Jens Nørkær; Chen, Jin
2009-01-01
This paper presents a design tool for optimizing wind turbine blades. The design model is based on an aerodynamic/aero-elastic code that includes the structural dynamics of the blades and the Blade Element Momentum (BEM) theory. To model the main aero-elastic behaviour of a real wind turbine, the...... rotor. The design variables used in the current study are the blade shape parameters, including chord, twist and relative thickness. To validate the implementation of the aerodynamic/aero-elastic model, the computed aerodynamic results are compared to experimental data for the experimental rotor used in...... the European Commision-sponsored project Model Experiments in Controlled Conditions, (MEXICO) and the computed aero-elastic results are examined against the FLEX code for flow post the Tjereborg 2 MW rotor. To illustrate the optimization technique, three wind turbine rotors of different sizes (the...
Comparison of time semi-discretization approaches for DGM solution of linear elasticity problem
Czech Academy of Sciences Publication Activity Database
Kosík, Adam; Feistauer, M.; Hadrava, Martin
Prague : Institute of Thermomechanics AS CR, v. v. i., 2012 - (Zolotarev, I.), s. 45-54 ISBN 978-80-87012-43-7. [Interaction and Feedbacks 2012 /19./. Praha (CZ), 27.11.2012-28.11.2012] R&D Projects: GA ČR(CZ) GAP101/11/0207 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * finite element method * fluid structure interaction Subject RIV: BI - Acoustics
Lee, Young S.; Vakakis, Alexander F.; Bergman, Lawrence A.; McFarland, D. Michael; Kerschen, Gaëtan
2007-01-01
Multi-degree-of-freedom nonlinear energy sinks (MDOF NESs) are utilized to improve robustness of suppression of limit cycle oscillations (LCOs) due to aeroelastic instability. Bifurcation analysis by a numerical continuation technique shows that controlling occurrence of a limit point cycle (LPC or saddle-node) bifurcation point above a Hopf bifurcation point is crucial to enhancing robustness. Not only greatly can MDOF NESs enhance the robustness of suppression against even strong externa...
Some atypical flutter characteristics of the NACA0015 profile
Czech Academy of Sciences Publication Activity Database
Vlček, Václav; Zolotarev, Igor; Kozánek, Jan; Štěpán, M.
Prague: Institute of Thermomechanics ASCR, v. v. i., 2016 - (Zolotarev, I.; Pešek, L.), s. 65-72 ISBN 978-80-87012-60-4. [DYMAMESI 2016. Prague (CZ), 01.03.2016-02.03.2016] R&D Projects: GA ČR GA13-10527S Institutional support: RVO:61388998 Keywords : aeroelasticity * flutter * interferometry * subsonic flow Subject RIV: BI - Acoustics
Czech Academy of Sciences Publication Activity Database
Vlček, Václav; Horáček, Jaromír
Praha: Institute of Thermomechanics AS CR, v. v. i., 2007 - (Zolotarev, I.), s. 107-112 ISBN 978-80-87012-08-6. [Interaction and Feedbacks ´2007. Praha (CZ), 27.11.2007-28.11.2007] R&D Projects: GA MPO FT-TA/026 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * fluther * optical measurement Subject RIV: BI - Acoustics
Visualization of unsteady flow around a vibrating profile
Czech Academy of Sciences Publication Activity Database
Vlček, Václav; Horáček, Jaromír; Luxa, Martin; Veselý, Jan
Praha: Institute of Thermomechanics, Academy of Sciences of the Czech Republic, v. v. i., 2008 - (Zolotarev, I.; Horáček, J.), s. 531-536 ISBN 80-87012-12-7. [International Conference on Flow Induced Vibration /9./ FIV2008. Praha (CZ), 30.06.2008-03.07.2008] R&D Projects: GA AV ČR IAA200760613 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * flutter * schlieren and interferomety methods Subject RIV: BI - Acoustics
Interferometrická měření proudových polí při obtékání kmitající kuželky regulačního ventilu
Czech Academy of Sciences Publication Activity Database
Vlček, Václav; Luxa, Martin; Bula, Vítězslav
Praha: ÚT AV ČR, 2006 - (Zolotarev, I.), s. 145-148 ISBN 80-87012-02-X. [Interaction and Feedbacks ´2006. Praha (CZ), 28.11.2006-29.11.2006] R&D Projects: GA ČR(CZ) GA106/05/2731 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * control valve * interferometry Subject RIV: BK - Fluid Dynamics
Coupled CFD/CSD Computation of Airloads of an Active-Twist Rotor
Massey, Steven J.; Kreshock, Andrew R.; Sekula, Martin K
2013-01-01
An unsteady Reynolds averaged Navier-Stokes analysis loosely coupled with a comprehensive rotorcraft code for blade trim and aeroelastic effects is presented for a second-generation Active-Twist Rotor. Mesh and temporal sensitives of computed airloads are evaluated. In the final paper, computed airloads will be compared with wind tunnel data for the Active-Twist Rotor test that is currently underway.
Numerical simulation and experiments with the profile NACA 0012
Czech Academy of Sciences Publication Activity Database
Chládek, Štěpán; Zolotarev, Igor; Uruba, Václav
Prague : ITAM AS CR, v. v. i., 2012 - (Náprstek, J.; Fischer, C.). s. 132-133 ISBN 978-80-86246-39-0. [Engineering Mechanics 2012 /18./. 14.05.2012-17.05.2012, Svratka] R&D Projects: GA ČR GA101/09/1522 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelastic * flow-structure interaction * identification Subject RIV: JU - Aeronautics, Aerodynamics, Aircrafts
Numerical simulation and experiments with the profile NACA 0012
Czech Academy of Sciences Publication Activity Database
Chládek, Štěpán; Zolotarev, Igor; Uruba, Václav
Prague : ITAM AS CR, v. v. i., 2012 - (Náprstek, J.; Fischer, C.), s. 523-529 ISBN 978-80-86246-40-6. [Engineering Mechanics 2012 /18./. Svratka (CZ), 14.05.2012-17.05.2012] R&D Projects: GA ČR GA101/09/1522 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelastic * flow-structure interaction * identification Subject RIV: JU - Aeronautics, Aerodynamics, Aircrafts
Vurdering av flutter stabilitetsgrensen til Hålogalandsbroen med en probabilistisk metode
Kvamstad, Tori Høyland
2011-01-01
The present work is a study of the aeroelastic stability limit of the Hålogaland Bridge. The state-of-the-art theory concerning determination of flutter stability limits in modern bridge design is presented. The self-excited loads are modeled using aerodynamic derivatives obtained in a free vibration wind tunnel test of a section model. The bimodal flutter limit of all relevant mode pairs are evaluated, by considering frequency separation and mode shape similarity of the respective modes. The...
Assessment of the flutter stability limit of the Hålogaland Bridge using aprobabilistic approach
Kvamstad, Tori Høyland
2011-01-01
The present work is a study of the aeroelastic stability limit of the Hålogaland Bridge. The state-of-the-art theory concerning determination of flutter stability limits in modern bridge design is presented. The self-excited loads are modeled using aerodynamic derivatives obtained in a free vibration wind tunnel test of a section model.The bimodal flutter limit of all relevant mode pairs are evaluated, by considering frequency separation and mode shape similarity of the respective modes. The ...
Ilic, Caslav; Führer, Tanja; Banavara, Nagaraj; Abu-Zurayk, Mohammad; Einarsson, Gunnar; Kruse, Martin; Himisch, Jan; Seider, Doreen; Richard-Gregor, Becker
2014-01-01
This report presents an organizational approach towards assembling and maintaining high-fidelity multi-disciplinary optimization (MDO) processes, in the environment of multiple institutes of the German Aerospace Center (DLR). Elements of the approach include both the technical conventions and the specialized software support. The approach is demonstrated on an early MDO process, that minimizes the mission fuel burn of an aeroelastic transport aircraft configuration, by modifying the wing plan...
Smolyak-Grid-Based Flutter Analysis with the Stochastic Aerodynamic Uncertainty
Yuting Dai; Chao Yang
2014-01-01
How to estimate the stochastic aerodynamic parametric uncertainty on aeroelastic stability is studied in this current work. The aerodynamic uncertainty is more complicated than the structural one, and it takes more significant effect on the flutter boundary. First, the nominal unsteady aerodynamic influence coefficients were calculated with the doublet lattice method. Based on this nominal model, the stochastic uncertainty model for unsteady aerodynamic pressure coefficients was constructed w...
Wind Turbine Design: Evaluation of Dynamic Loads on Large Offshore Wind Turbines
Frøyd, Lars
2012-01-01
A design method for combined aerodynamic and structural (aeroelastic) design of large wind turbine blades has been developed, with the purpose of facilitating conceptual design, parametric studies, optimisation, or cost analysis of offshore wind turbines using more advanced aero-servo-hydro-elastic analyses.The aerodynamic design is based on blade element momentum theory, which is the most common approach for engineering analysis of wind turbines, due to a combination of speed and accuracy. A...
Design gridlines for passive instability suppression - Task-11 report
Hansen, M.H.; Buhl, T.
2006-01-01
In these guidelines for passive instability suppression, eight relevant topics within aeroelastic stability of turbines are considered for the parameter variations: 1. Effect of airfoil aerodynamics: The airfoil aerodynamics given by the profilecoefficients for aerodynamic lift, drag, and moment are shown to have a direct effect on aerodynamic damping of blade vibrations. A redesign of the airfoils can improve the power performance of the rotor without loss of aerodynamic damping. 2. Effect o...
Fluttering Analysis in Wind Turbine Blade
Elangovan, Prabaharan
2012-01-01
The wind turbine blades often subjected by a phenomenon fluttering which leads to a structural damage. Therefore, it is necessary for design engineers to predict the fluttering behavior while designing the blades. The main scope of the thesis is to analyze and study the fluttering behavior by conducting structural analysis, modal analysis, Aeroelastic stability analysis and FSI of standard wind turbine blade. The analysis is carried out in ANSYS work bench and the preliminary results shows th...
A Study on Fluid Self-Excited Flutter and Forced Response of Turbomachinery Rotor Blade
Chih-Neng Hsu
2014-01-01
Complex mode and single mode approach analyses are individually developed to predict blade flutter and forced response. These analyses provide a system approach for predicting potential aeroelastic problems of blades. The flow field properties of a blade are analyzed as aero input and combined with a finite element model to calculate the unsteady aero damping of the blade surface. Forcing function generators, including inlet and distortions, are provided to calculate the forced response of tu...
Experimental Investigation of Three-Dimensional Mechanisms in Low-Pressure Turbine Flutter
Vogt, Damian
2005-01-01
The continuous trend in gas turbine design towards lighter, more powerful and more reliable engines on one side and use of alternative fuels on the other side renders flutter problems as one of the paramount challenges in engine design. Flutter denotes a self-excited and self-sustained aeroelastic instability phenomenon that can lead to material fatigue and eventually damage of structure in a short period of time unless properly damped. The design for flutter safety involves the prediction of...
Small Wind Research Turbine: Final Report
Energy Technology Data Exchange (ETDEWEB)
Corbus, D.; Meadors, M.
2005-10-01
The Small Wind Research Turbine (SWRT) project was initiated to provide reliable test data for model validation of furling wind turbines and to help understand small wind turbine loads. This report will familiarize the user with the scope of the SWRT test and support the use of these data. In addition to describing all the testing details and results, the report presents an analysis of the test data and compares the SWRT test data to simulation results from the FAST aeroelastic simulation model.
Incompressible Viscous Flow at Various Velocities in Interaction with a Vibrating Profile
Czech Academy of Sciences Publication Activity Database
Honzátko, R.; Horáček, Jaromír; Kozel, K.
Plzeň : University of West Bohemia, 2010 - (Šolín, P.; Karban, P.; Cimrman, R.; Kruis, J.). s. 47-47 ISBN 978-80-7043-898-5. [ESCO 2010 - European Seminar on Coupled Problems /2./. 28.06.2010-02.07.2010, Plzeň] Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * finite volume method * flutter Subject RIV: BI - Acoustics
Interaction of a channel flow and moving bodies
Czech Academy of Sciences Publication Activity Database
Růžička, M.; Feistauer, M.; Horáček, Jaromír; Sváček, Petr
Praha : Institute of Thermomechanics AS CR, v. v. i., 2007 - (Jonáš, P.; Uruba, V.), s. 77-78 ISBN 978-80-87012-07-9. [Colloquium FLUID DYNAMICS 2007. Prague (CZ), 24.10.2007-26.10.2007] R&D Projects: GA AV ČR IAA200760613 Institutional research plan: CEZ:AV0Z20760514 Keywords : aeroelasticity * finite element method * Navier - Stokes equation Subject RIV: BI - Acoustics