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...
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
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...
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...
Research in aeroelasticity EFP-2006
DEFF Research Database (Denmark)
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...... for a rotor. The implementation of the BEM model to handle this flow case can be carried out in different ways and the results of two advanced models have not so far been validated. In the new Aeroelastic Research Programme EFP2007 the investigations will be continued and the aspect of influence of individual...
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...
Aeroelasticity Benchmark Assessment: Subsonic Fixed Wing Program
Florance, Jennifer P.; Chwalowski, Pawel; Wieseman, Carol D.
2010-01-01
The fundamental technical challenge in computational aeroelasticity is the accurate prediction of unsteady aerodynamic phenomena and the effect on the aeroelastic response of a vehicle. Currently, a benchmarking standard for use in validating the accuracy of computational aeroelasticity codes does not exist. Many aeroelastic data sets have been obtained in wind-tunnel and flight testing throughout the world; however, none have been globally presented or accepted as an ideal data set. There are numerous reasons for this. One reason is that often, such aeroelastic data sets focus on the aeroelastic phenomena alone (flutter, for example) and do not contain associated information such as unsteady pressures and time-correlated structural dynamic deflections. Other available data sets focus solely on the unsteady pressures and do not address the aeroelastic phenomena. Other discrepancies can include omission of relevant data, such as flutter frequency and / or the acquisition of only qualitative deflection data. In addition to these content deficiencies, all of the available data sets present both experimental and computational technical challenges. Experimental issues include facility influences, nonlinearities beyond those being modeled, and data processing. From the computational perspective, technical challenges include modeling geometric complexities, coupling between the flow and the structure, grid issues, and boundary conditions. The Aeroelasticity Benchmark Assessment task seeks to examine the existing potential experimental data sets and ultimately choose the one that is viewed as the most suitable for computational benchmarking. An initial computational evaluation of that configuration will then be performed using the Langley-developed computational fluid dynamics (CFD) software FUN3D1 as part of its code validation process. In addition to the benchmarking activity, this task also includes an examination of future research directions. Researchers within the
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 ...
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...
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...
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.
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.
Aeroelastic instability problems for wind turbines
DEFF Research Database (Denmark)
Hansen, Morten Hartvig
2007-01-01
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...... 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 aeroelostic instability problems for wind turbines. Copyright (c) 2007 John Wiley & Sons, Ltd....
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.
Renaissance of Aeroelasticity and Its Future
Friedmann, Peretz P.
1999-01-01
The primary objective of this paper is to demonstrate that the field of aeroelasticity continues to play a critical role in the design of modern aerospace vehicles, and several important problems are still far from being well understood. Furthermore, the emergence of new technologies, such as the use of adaptive materials (sometimes denoted as smart structures technology), providing new actuator and sensor capabilities, has invigorated aeroelasticity, and generated a host of new and challenging research topics that can have a major impact on the design of a new generation of aerospace vehicles.
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
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.
Aeroelastic Stability of Suspension Bridges using CFD
DEFF Research Database (Denmark)
Stærdahl, Jesper Winther; Sørensen, Niels; Nielsen, Søren R.K.
2007-01-01
In recent years large span suspension bridges with very thin and slender profiles have been built without proportional increasing torsional and bending stiffness. As a consequence large deformations at the mid-span can occur with risk of aeroelastic instability and structural failure. Analysis...
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 stoppers for wind tunnel models
Doggett, R. V., Jr.; Ricketts, R. H. (Inventor)
1981-01-01
A mechanism for constraining models or sections thereof, was wind tunnel tested, deployed at the onset of aeroelastic instability, to forestall destructive vibrations in the model is described. The mechanism includes a pair of arms pivoted to the tunnel wall and straddling the model. Rollers on the ends of the arms contact the model, and are pulled together against the model by a spring stretched between the arms. An actuator mechanism swings the arms into place and back as desired.
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
Institute of Scientific and Technical Information of China (English)
Dai Yuting; Yang Chao
2014-01-01
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 uncer-tainty, 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 l method. It covers the numerical calculation algo-rithm 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.
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
Static aeroelastic analysis for generic configuration wing
Lee, IN; Miura, Hirokazu; Chargin, Mladen K.
1991-01-01
A static aeroelastic analysis capability that calculates flexible air loads for generic configuration wings was developed. It was made possible by integrating a finite element structural analysis code (MSC/NASTRAN) and a panel code of aerodynamic analysis based on linear potential flow theory. The framework already built in MSC/NASTRAN was used, and the aerodynamic influence coefficient matrix was computed externally and inserted in the NASTRAN by means of a DMAP program. It was shown that deformation and flexible air loads of an oblique wing configuration including asymmetric wings can be calculated reliably by this code both in subsonic and supersonic speeds.
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...
Aeroelastic Optimization of MW Wind Turbines
DEFF Research Database (Denmark)
Hansen, Morten Hartvig; Zahle, Frederik
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 beamelement forHAWC2 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...
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
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.
Experimental aeroelasticity history, status and future in brief
Ricketts, Rodney H.
1990-01-01
NASA conducts wind tunnel experiments to determine and understand the aeroelastic characteristics of new and advanced flight vehicles, including fixed-wing, rotary-wing and space-launch configurations. Review and assessments are made of the state-of-the-art in experimental aeroelasticity regarding available facilities, measurement techniques, and other means and devices useful in testing. In addition, some past experimental programs are described which assisted in the development of new technology, validated new analysis codes, or provided needed information for clearing flight envelopes of unwanted aeroelastic response. Finally, needs and requirements for advances and improvements in testing capabilities for future experimental research and development programs are described.
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.
An overview of aeroelasticity studies for the National Aerospace Plane
Ricketts, Rodney H.; Noll, Thomas E.; Huttsell, Lawrence J.; Hutsell, Lawrence J.
1993-01-01
The National Aero-Space Plane (NASP), or X-30, is a single-stage-to-orbit vehicle that is designed to takeoff and land on conventional runways. Research in aeroelasticity was conducted by NASA and the Wright Laboratory to support the design of a flight vehicle by the national contractor team. This research includes the development of new computational codes for predicting unsteady aerodynamic pressures. In addition, studies were conducted to determine the aerodynamic heating effects on vehicle aeroelasticity and to determine the effects of fuselage flexibility on the stability of the control systems. It also includes the testing of scale models to better understand the aeroelastic behavior of the X-30 and to obtain data for code validation and correlation. This paper presents an overview of the aeroelastic research which has been conducted to support the airframe design.
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...
A New Approach for Aeroelastic Robust Stability Analysis
Institute of Scientific and Technical Information of China (English)
Wu Zhigang; Yang Chao
2008-01-01
Air vehicles undergo variations in structural mass and stiffness because of fuel consumption and the failure of structural components, which might lead to serious influences on the aeroelastic characteristics. An approach for aeroelastic robust stability analysis taking into account the perturbations of structural mass and stiffness is developed. Applying the perturbation method and harmonic unsteady aerodynamic forces, the frequency-domain linear fractal transformation (LFT) representation of pertorbed aeroelastic system is modeled.Then, the robust stability is analyzed by using the structured singular value μ-method. The numerical results of a bi-spar wing show its effectiveness and low computational time in dealing with the robust problems with mass and stiffness perturbations. In engineering analysis for solving aeroelastic problems, the robust approach can be applied to flutter analysis for airplane with the fuel load variation and taking the damage conditions into consideration.
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...
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...
Research in Aeroelasticity EFP-2007-II
DEFF Research Database (Denmark)
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. • The unsteady flow in the nacelle region of a wind turbine...... shadow models implemented in the aeroelastic code HAWC2. • 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. • The application of laminar/turbulent transition in CFD computations for airfoils...... is 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...
Static aeroelastic analysis of composite wing
Lee, IN; Hong, Chang Sun; Miura, Hirokazu; Kim, Seung KO
1990-01-01
A static aeroelastic analysis capability that can predict aerodynamic loads for the deformed shape of the composite wing has been developed. The finite element method (FEM) was used for composite plate structural analysis, and the linear vortex lattice method (VLM) was used for steady aerodynamic analysis. The final deformed shape of the wing due to applied forces is determined by iterative manner using FEM and VLM. FEM and VLM analysis are related by a surface spline interpolation procedure. The wing with Gr/Ep composite material has been investigated to see the wing deformation effect. Aerodynamic load change due to wing flexibility has been investigated. Also, the effect of fiber orientation and sweep angle on the deformation pattern and aerodynamic coefficients are examined. For a certain fiber orientation, the deflection and aerodynamic loading of the composite wing is very much reduced. The swept forward wing has more significant effect of wing flexibility on aerodynamic coefficient than the swept back wing does.
Static aeroelastic analysis for generic configuration aircraft
Lee, IN; Miura, Hirokazu; Chargin, Mladen K.
1987-01-01
A static aeroelastic analysis capability that can calculate flexible air loads for generic configuration aircraft was developed. It was made possible by integrating a finite element structural analysis code (MSC/NASTRAN) and a panel code of aerodynamic analysis based on linear potential flow theory. The framework already built in MSC/NASTRAN was used and the aerodynamic influence coefficient matrix is computed externally and inserted in the NASTRAN by means of a DMAP program. It was shown that deformation and flexible airloads of an oblique wing aircraft can be calculated reliably by this code both in subsonic and supersonic speeds. Preliminary results indicating importance of flexibility in calculating air loads for this type of aircraft are presented.
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 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
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.
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.
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.
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.
KNOW-BLADE task-4 report: Navier-Stokes aeroelasticity
DEFF Research Database (Denmark)
Politis, E.S.; Nikolaou, I.G.; Chaviaropoulos, P.K.;
2004-01-01
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...... for quantitative comparisons with experimental data to be carried out; instead the results of the advanced aeroelastic tools are qualitatively cross-compared. Allinvestigated methods predicted qualitatively similar results. They all resulted in positive aerodynamic damping values for the flap mode, in a decrease...... the computations for the full blade, 2D computations for the so-called “typical section” have been carried out. The 2D aeroelastic tools resulted in similar aerodynamic damping values. Qualitative agreement was better for the lead-lagmode. The presence of roughness tapes has a small, rather negligible impact...
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.
Application of the Finite Element Method to Rotary Wing Aeroelasticity
Straub, F. K.; Friedmann, P. P.
1982-01-01
A finite element method for the spatial discretization of the dynamic equations of equilibrium governing rotary-wing aeroelastic problems is presented. Formulation of the finite element equations is based on weighted Galerkin residuals. This Galerkin finite element method reduces algebraic manipulative labor significantly, when compared to the application of the global Galerkin method in similar problems. The coupled flap-lag aeroelastic stability boundaries of hingeless helicopter rotor blades in hover are calculated. The linearized dynamic equations are reduced to the standard eigenvalue problem from which the aeroelastic stability boundaries are obtained. The convergence properties of the Galerkin finite element method are studied numerically by refining the discretization process. Results indicate that four or five elements suffice to capture the dynamics of the blade with the same accuracy as the global Galerkin method.
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.
Data Comparisons and Summary of the Second Aeroelastic Prediction Workshop
Heeg, Jennifer; Wieseman, Carol D.; Chwalowski, Pawel
2016-01-01
This paper presents the computational results generated by participating teams of the second Aeroelastic Prediction Workshop and compare them with experimental data. Aeroelastic and rigid configurations of the Benchmark Supercritical Wing (BSCW) wind tunnel model served as the focus for the workshop. The comparison data sets include unforced ("steady") system responses, forced pitch oscillations and coupled fluid-structure responses. Integrated coefficients, frequency response functions, and flutter onset conditions are compared. The flow conditions studied were in the transonic range, including both attached and separated flow conditions. Some of the technical discussions that took place at the workshop are summarized.
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.
Aeroelastic Flight Data Analysis with the Hilbert-Huang Algorithm
Brenner, Martin J.; Prazenica, Chad
2006-01-01
This report investigates the utility of the Hilbert Huang transform for the analysis of aeroelastic flight data. It is well known that the classical Hilbert transform can be used for time-frequency analysis of functions or signals. Unfortunately, the Hilbert transform can only be effectively applied to an extremely small class of signals, namely those that are characterized by a single frequency component at any instant in time. The recently-developed Hilbert Huang algorithm addresses the limitations of the classical Hilbert transform through a process known as empirical mode decomposition. Using this approach, the data is filtered into a series of intrinsic mode functions, each of which admits a well-behaved Hilbert transform. In this manner, the Hilbert Huang algorithm affords time-frequency analysis of a large class of signals. This powerful tool has been applied in the analysis of scientific data, structural system identification, mechanical system fault detection, and even image processing. The purpose of this report is to demonstrate the potential applications of the Hilbert Huang algorithm for the analysis of aeroelastic systems, with improvements such as localized online processing. Applications for correlations between system input and output, and amongst output sensors, are discussed to characterize the time-varying amplitude and frequency correlations present in the various components of multiple data channels. Online stability analyses and modal identification are also presented. Examples are given using aeroelastic test data from the F-18 Active Aeroelastic Wing airplane, an Aerostructures Test Wing, and pitch plunge simulation.
State of the art in wind turbine aerodynamics and aeroelasticity
DEFF Research Database (Denmark)
Hansen, Martin Otto Laver; Sørensen, Jens Nørkær; Voutsinas, S;
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...
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
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 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.
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.
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...
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.
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
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. (ZONA) proposes to develop an integrated flight dynamics simulation capability with nonlinear aeroelastic interactions by combining a flight...
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...
A Nonlinear Modal Aeroelastic Solver for FUN3D
Goldman, Benjamin D.; Bartels, Robert E.; Biedron, Robert T.; Scott, Robert C.
2016-01-01
A nonlinear structural solver has been implemented internally within the NASA FUN3D computational fluid dynamics code, allowing for some new aeroelastic capabilities. Using a modal representation of the structure, a set of differential or differential-algebraic equations are derived for general thin structures with geometric nonlinearities. ODEPACK and LAPACK routines are linked with FUN3D, and the nonlinear equations are solved at each CFD time step. The existing predictor-corrector method is retained, whereby the structural solution is updated after mesh deformation. The nonlinear solver is validated using a test case for a flexible aeroshell at transonic, supersonic, and hypersonic flow conditions. Agreement with linear theory is seen for the static aeroelastic solutions at relatively low dynamic pressures, but structural nonlinearities limit deformation amplitudes at high dynamic pressures. No flutter was found at any of the tested trajectory points, though LCO may be possible in the transonic regime.
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
Aeroelastic stability analysis of flexible overexpanded rocket nozzle
Bekka, N.; Sellam, M.; Chpoun, A.
2016-07-01
The aim of this paper is to present a new aeroelastic stability model taking into account the viscous effects for a supersonic nozzle flow in overexpanded regimes. This model is inspired by the Pekkari model which was developed initially for perfect fluid flow. The new model called the "Modified Pekkari Model" (MPM) considers a more realistic wall pressure profile for the case of a free shock separation inside the supersonic nozzle using the free interaction theory of Chapman. To reach this objective, a code for structure computation coupled with aerodynamic excitation effects is developed that allows the analysis of aeroelastic stability for the overexpanded nozzles. The main results are presented in a comparative manner using existing models (Pekkari model and its extended version) and the modified Pekkari model developed in this work.
An aeroelastic analysis with a generalized dynamic wake
He, Cheng J.; Peters, David A.
1991-01-01
An aeroelastic model with generalized dynamic wake is developed for application in the integration of aerodynamic, dynamic, and structural optimization of a rotor blade. The investigation is carried out with special attention to efficiency and accuracy of aeroelastic modeling. Each blade is assumed to be an elastic beam undergoing flap bending, lead-lag bending, elastic twist and axial deflections. The nonuniform blade is discretized into finite beam elements, each of which consists of twelve degrees of freedom. Such important blade design variables as pretwist, and chordwise offsets of the blade center of gravity and of the aerodynamic center from the elastic axis have been included in the analysis. Aerodynamic loads are computed from unsteady blade element theory where the rotor three-dimensional unsteady wake is modeled using a generalized dynamic wake theory. The noncirculatory loads based on unsteady thin airfoil theory are also included.
Level-Set Topology Optimization with Aeroelastic Constraints
Dunning, Peter D.; Stanford, Bret K.; Kim, H. Alicia
2015-01-01
Level-set topology optimization is used to design a wing considering skin buckling under static aeroelastic trim loading, as well as dynamic aeroelastic stability (flutter). The level-set function is defined over the entire 3D volume of a transport aircraft wing box. Therefore, the approach is not limited by any predefined structure and can explore novel configurations. The Sequential Linear Programming (SLP) level-set method is used to solve the constrained optimization problems. The proposed method is demonstrated using three problems with mass, linear buckling and flutter objective and/or constraints. A constraint aggregation method is used to handle multiple buckling constraints in the wing skins. A continuous flutter constraint formulation is used to handle difficulties arising from discontinuities in the design space caused by a switching of the critical flutter mode.
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...
Structural dynamic and aeroelastic considerations for hypersonic vehicles
Cazier, F. W., Jr.; Doggett, Robert V., Jr.; Ricketts, Rodney H.
1991-01-01
The specific geometrical, structural, and operational environment characteristics of hypersonic vehicles are discussed with particular reference to aerospace plane type configurations. A discussion of the structural dynamic and aeroelastic phenomena that must be addressed for this class of vehicles is presented. These phenomena are in the aeroservothermoelasticity technical area. Some illustrative examples of recent experimental and analytical work are given. Some examples of current research are pointed out.
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 ...
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.
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...
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.
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.
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.
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.
Experimental aeroelasticity in wind tunnels - History, status, and future in brief
Ricketts, Rodney H.
1993-01-01
The state of the art of experimental aeroelasticity in the United States is assessed. A brief history of the development of ground test facilities, apparatus, and testing methods is presented. Several experimental programs are described that were previously conducted and helped to improve the state of the art. Some specific future directions for improving and enhancing experimental aeroelasticity are suggested.
Design and testing of an aeroelastically tailored wing under manoeuvre loading
Werter, N.P.M.; Sodja, J.; De Breuker, R.
2015-01-01
The design methodology and testing of an aeroelastically tailored wing subjected to manoeuvre loads is presented in this paper. The wing is designed using an aeroelastic analysis tool that is composed of a closely coupled nonlinear beam model and a vortex lattice aerodynamic model. The globally conv
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.
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.;
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 objective...... of this successful long term research cooperation....
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.
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.
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.
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)
Application of CFD based wave loads in aeroelastic calculations
DEFF Research Database (Denmark)
Schløer, Signe; Paulsen, Bo Terp; Bredmose, Henrik
2014-01-01
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......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...
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.
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.
On the optimization of discrete structures with aeroelastic constraints
Mcintosh, S. C., Jr.; Ashley, H.
1978-01-01
The paper deals with the problem of dynamic structural optimization where constraints relating to flutter of a wing (or other dynamic aeroelastic performance) are imposed along with conditions of a more conventional nature such as those relating to stress under load, deflection, minimum dimensions of structural elements, etc. The discussion is limited to a flutter problem for a linear system with a finite number of degrees of freedom and a single constraint involving aeroelastic stability, and the structure motion is assumed to be a simple harmonic time function. Three search schemes are applied to the minimum-weight redesign of a particular wing: the first scheme relies on the method of feasible directions, while the other two are derived from necessary conditions for a local optimum so that they can be referred to as optimality-criteria schemes. The results suggest that a heuristic redesign algorithm involving an optimality criterion may be best suited for treating multiple constraints with large numbers of design variables.
Aeroelastic optimization design for wing with maneuver load uncertainties
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
An aeroelastic optimization design methodology for air vehicle considering the uncertainties in maneuver load conditions is presented and applied to a structural design process of low-aspect-ratio wing. An aerodynamic load correction model is developed and used to predict the critical load conditions with the perturbations of theoretical linear aerodynamic forces and experimental aerodynamic forces from wind-tunnel test, when concerning the uncertainties in use of theoretical linear and experimental aerodynamic forces. Three objective functions of critical loads are defined. The load evaluations for three wing sections are investigated in four characteristic maneuvers, and the most critical load conditions are confirmed by using the sequential quadratic programming method. On this basis, the aeroelastic optimization design employing the genetic-gradient hybrid algorithm is conducted, in which the objective is to minimize structural mass subject to the constraints of stress, deformation and flutter speed. The resulting optimal structure is heavier than the one simply based on the theoretical linear or experimental aerodynamic forces. However, it is more robust when encountering the critical load conditions in actual flight due to the consideration of uncertainties in aerodynamic forces in the early design phase, thereby, the risk of structural redesign can be reduced.
Aeroelastic Instabilities of Large Offshore and Onshore Wind Turbines
Bir, Gunjit; Jonkman, Jason
2007-07-01
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.
Vibration and aeroelastic analysis of highly flexible HALE aircraft
Chang, Chong-Seok
The highly flexible HALE (High Altitude Long Endurance) aircraft analysis methodology is of interest because early studies indicated that HALE aircraft might have different vibration and aeroelastic characteristics from those of conventional aircraft. Recently the computer code Nonlinear Aeroelastic Trim And Stability of HALE Aircraft (NATASHA) was developed under NASA sponsorship. NATASHA can predict the flight dynamics and aeroelastic behavior for HALE aircraft with a flying wing configuration. Further analysis improvements for NATASHA were required to extend its capability to the ground vibration test (GVT) environment and to both GVT and aeroelastic behavior of HALE aircraft with other configurations. First, the analysis methodology, based on geometrically exact fully intrinsic beam theory, was extended to treat other aircraft cofigurations. Conventional aircraft with flexible fuselage and tail can now be modeled by treating the aircraft as an assembly of beam elements. NATASHA is now applicable to any aircraft cofiguration that can be modeled this way. The intrinsic beam formulation, which is a fundamental structural modeling approach, is now capable of being applying to a structure consisting of multiple beams by relating the virtual displacements and rotations at points where two or more beam elements are connected to each other. Additional aspects are also considered in the analysis such as auxiliary elevator input in the horizontal tail and fuselage aerodynamics. Second, the modeling approach was extended to treat the GVT environment for HALE aircraft, which have highly flexible wings. GVT has its main purpose to provide modal characteristics for model validation. A bungee formulation was developed by the augmented Lagrangian method and coupled to the intrinsic beam formulation for the GVT modeling. After the coupling procedure, the whole formulation cannot be fully intrinsic because the geometric constraint by bungee cords makes the system statically
An overview of aeroelasticity studies for the National Aero-Space Plane
Ricketts, Rodney H.; Noll, Thomas E.; Whitlow, Woodrow, Jr.; Huttsell, Lawrence J.
1993-01-01
The National Aero-Space Plane (NASP), or X-30, is a single-stage-to-orbit vehicle that is designed to takeoff and land on conventional runways. Research in aeroelasticity was conducted by the NASA and the Wright Laboratory to support the design of a flight vehicle by the national contractor team. This research includes the development of new computational codes for predicting unsteady aerodynamic pressures. In addition, studies were conducted to determine the aerodynamic heating effects on vehicle aeroelasticity and to determine the effects of fuselage flexibility on the stability of the control systems. It also includes the testing of scale models to better understand the aeroelastic behavior of the X-30 and to obtain data for code validation and correlation. This paper presents an overview of the aeroelastic research which has been conducted to support the airframe design.
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.
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...... 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 simplied 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...
Low-order aeroelastic models of wind turbines for controller design
DEFF Research Database (Denmark)
Sønderby, Ivan Bergquist
Wind turbine controllers are used to optimize the performance of wind turbines such as to reduce power variations and fatigue and extreme loads on wind turbine components. Accurate tuning and design of modern controllers must be done using low-order models that accurately captures the aeroelastic...... by modal truncation by using the aeroelastic mode shapes of a fully flexible wind turbine. To capture the effect of shed vorticity and dynamic stall, a relatively large number of aerodynamically dominated modes are required, due to the assumption of independent annular flow tubes in the Blade Element...... response of the wind turbine. The purpose of this thesis is to investigate the necessary model complexity required in aeroelastic models used for controller design and to analyze and propose methods to design low-order aeroelastic wind turbine models that are suited for model-based control design...
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...
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...
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...
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)
Aeroelasticity-based fluid agitation for lab-on-chips.
Xia, H M; Wang, Z P; Wang, W; Fan, W; Wijaya, A; Wang, Z F
2013-04-21
In this study, we report a robust agitation method for small-volume liquids. It utilizes an elastic diaphragm as the bottom of a liquid chamber, upon which an initial tension is also applied to enhance the aeroelasticity effects at small/micro scales. As a result, spontaneous vibration of the diaphragm can be induced by an external air flow, which further provides fluid agitations. The device structure is simple and can be easily fabricated at low cost. More importantly, the vibration amplitude is controllable and varies widely from several tens to several hundred micrometers depending on the applied air pressure. The resulting agitation is effective and applicable at high viscosities of up to 900 cSt. The influences of air pressure and liquid viscosity on the vibration frequency are discussed. Potential applications of this technique for solid particle agitation, focusing and fluid mixing are also demonstrated. PMID:23455690
Aeroelastic Response of the Adaptive Compliant Trailing Edge Transtition Section
Herrera, Claudia Y.; Spivey, Natalie D.; Lung, Shun-fat
2016-01-01
The Adaptive Compliant Trailing Edge demonstrator was a joint task under the Environmentally Responsible Aviation Project in partnership with the Air Force Research Laboratory and FlexSys, Inc. (Ann Arbor, Michigan), chartered by the National Aeronautics and Space Administration to develop advanced technologies that enable environmentally friendly aircraft, such as continuous mold-line technologies. The Adaptive Compliant Trailing Edge demonstrator encompassed replacing the Fowler flaps on the SubsoniC Aircraft Testbed, a Gulfstream III (Gulfstream Aerospace, Savannah, Georgia) aircraft, with control surfaces developed by FlexSys, Inc., a pair of uniquely-designed, unconventional flaps to be used as lifting surfaces during flight-testing to substantiate their structural effectiveness. The unconventional flaps consisted of a main flap section and two transition sections, inboard and outboard, which demonstrated the continuous mold-line technology. Unique characteristics of the transition sections provided a challenge to the airworthiness assessment for this part of the structure. A series of build-up tests and analyses were conducted to ensure the data required to support the airworthiness assessment were acquired and applied accurately. The transition sections were analyzed both as individual components and as part of the flight-test article assembly. Instrumentation was installed in the transition sections based on the analysis to best capture the in-flight aeroelastic response. Flight-testing was conducted and flight data were acquired to validate the analyses. This paper documents the details of the aeroelastic assessment and in-flight response of the transition sections of the unconventional Adaptive Compliant Trailing Edge flaps.
A wind turbine hybrid simulation framework considering aeroelastic effects
Song, Wei; Su, Weihua
2015-04-01
In performing an effective structural analysis for wind turbine, the simulation of turbine aerodynamic loads is of great importance. The interaction between the wake flow and the blades may impact turbine blades loading condition, energy yield and operational behavior. Direct experimental measurement of wind flow field and wind profiles around wind turbines is very helpful to support the wind turbine design. However, with the growth of the size of wind turbines for higher energy output, it is not convenient to obtain all the desired data in wind-tunnel and field tests. In this paper, firstly the modeling of dynamic responses of large-span wind turbine blades will consider nonlinear aeroelastic effects. A strain-based geometrically nonlinear beam formulation will be used for the basic structural dynamic modeling, which will be coupled with unsteady aerodynamic equations and rigid-body rotations of the rotor. Full wind turbines can be modeled by using the multi-connected beams. Then, a hybrid simulation experimental framework is proposed to potentially address this issue. The aerodynamic-dominant components, such as the turbine blades and rotor, are simulated as numerical components using the nonlinear aeroelastic model; while the turbine tower, where the collapse of failure may occur under high level of wind load, is simulated separately as the physical component. With the proposed framework, dynamic behavior of NREL's 5MW wind turbine blades will be studied and correlated with available numerical data. The current work will be the basis of the authors' further studies on flow control and hazard mitigation on wind turbine blades and towers.
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...
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...
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.
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 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.
Friedmann, P.; Straub, F.
1978-01-01
Recent research in rotary-wing aeroelasticity has indicated that all fundamental problems in this area are inherently nonlinear. The non-linearities in this problem are due to the inclusion of finite slopes, due to moderate deflections, in the structural, inertia and aerodynamic operators associated with this aeroelastic problem. In this paper the equations of motion, which are both time and space dependent, for the aeroelastic problem are first formulated in P.D.E. form. Next the equations are linearized about a suitable equilibrium position. The spatial dependence in these equations is discretized using a local Galerkin method of weighted residuals resulting in a finite element formulation of the aeroelastic problem. As an illustration the method is applied to the coupled flap-lag problem of a helicopter rotor blade in hover. Comparison of the solutions with previously published solutions establishes the convergence properties of the method. It is concluded that this formulation is a practical tool for solving rotary-wing aeroelastic stability or response problems.
Airfoil Aeroelastic Flutter Analysis Based on Modified Leishman-Beddoes Model at Low Mach Number
Institute of Scientific and Technical Information of China (English)
SHAO Song; ZHU Qinghua; ZHANG Chenglin; NI Xianping
2011-01-01
Based on modified Leishman-Beddoes(L-B)state space model at low Mach number(lower than 0.3),the airfoil aeroelastic system is presented in this paper.The main modifications for L-B model include a new dynamic stall criterion and revisions of normal force and pitching moment coefficient.The bifurcation diagrams,the limit cycle oscillation (LCO)phase plane plots and the time domain response figures are applied to investigating the stall flutter bifurcation behavior of airfoil aeroelastic systems with symmetry or asymmetry.It is shown that the symmetric periodical oscillation happens after subcritical bifurcation caused by dynamic stall,and the asymmetric periodical oscillation,which is caused by the interaction of dynamic stall and static divergence,only happens in the airfoil aeroelastic system with asymmetry.Validations of the modified L-B model and the airfoil aeroelastic system are presented with the experimental airload data of NACA0012 and OA207 and experimental stall flutter data of NACA0012 respectively.Results demonstrate that the airfoil aeroelastic system presented in this paper is effective and accurate,which can be applied to the investigation of airfoil stall flutter at low Mach number.
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.
DEFF Research Database (Denmark)
Aagaard Madsen, Helge; Larsen, Torben J.; Schmidt Paulsen, Uwe;
2013-01-01
The paper presents the implementation of the Actuator Cylinder (AC) flow model in the HAWC2 aeroelastic code originally developed for simulation of Horizontal Axis Wind Turbine (HAWT) aeroelasticity. This is done within the DeepWind project where the main objective is to explore the competitivene...
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.
Bridge aerodynamics and aeroelasticity: A comparison of modeling schemes
Wu, Teng; Kareem, Ahsan
2013-11-01
Accurate modeling of wind-induced loads on bridge decks is critical to ensure the functionality and survivability of long-span bridges. Over the last few decades, several schemes have emerged to model bridge behavior under winds from an aerodynamic/aeroelastic perspective. A majority of these schemes rely on the quasi-steady (QS) theory. This paper systematically compares and assesses the efficacy of five analytical models available in the literature with a new model presented herein. These models include: QS theory-based model, corrected QS theory-based model, linearized QS theory-based model, semi-empirical linear model, hybrid model, and the proposed modified hybrid model. The ability of these models to capture fluid memory and nonlinear effects either individually or collectively is examined. In addition, their ability to include the effects of turbulence in the approach flow on the bridge behavior is assessed. All models are compared in a consistent manner by utilizing the time domain approach. The underlying role of each model in capturing the physics of bridge behavior under winds is highlighted and the influence of incoming turbulence and its interaction with the bridge deck is examined. A discussion is included that focuses on a number of critical parameters pivotal to the effectiveness of corresponding models.
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.
Nonlinear System Identification for Aeroelastic Systems with Application to Experimental Data
Kukreja, Sunil L.
2008-01-01
Representation and identification of a nonlinear aeroelastic pitch-plunge system as a model of the Nonlinear AutoRegressive, Moving Average eXogenous (NARMAX) class is considered. A nonlinear difference equation describing this aircraft model is derived theoretically and shown to be of the NARMAX form. Identification methods for NARMAX models are applied to aeroelastic dynamics and its properties demonstrated via continuous-time simulations of experimental conditions. Simulation results show that (1) the outputs of the NARMAX model closely match those generated using continuous-time methods, and (2) NARMAX identification methods applied to aeroelastic dynamics provide accurate discrete-time parameter estimates. Application of NARMAX identification to experimental pitch-plunge dynamics data gives a high percent fit for cross-validated data.
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.
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.
Optimal aeroelastic vehicle sensor placement for root migration flight control applications
Al-Shehabi, Abdul Ghafoor
2001-09-01
An important step in control design for elastic systems is the determination of the number and location of control system components, namely sensors. The number and placement of sensors can be critical to the robust functioning of active control systems, especially when the system of interest is a large high-speed aeroelastic vehicle. The position of the sensors affects not only system stability, but also the performance of the closed-loop system. In this dissertation, a new approach for sensor placement in the integrated rigid and vibrational control of flexible aircraft structures is developed. Traditional rigid-body augmentation objectives are addressed indirectly through input-output pair and compensation selection. Aeroelastic control suppression objectives are addressed directly through sensor placement. A nonlinear programming problem is posed to minimize a cost function with specified constraints, where the cost function terms are multiplied by appropriate weighting factors. Cost function criteria are based on complex frequency domain geometric pole-zero structures in order to gain stabilize or phase stabilize the aeroelastic modes. Specifically, these criteria are based on dipole magnitude and complementary departure angle. In turn, the control design approach utilizes one of the classical methods known as Evans root migration to exploit the pole-zero structures resulting from sensor placement. Desirable complementary departure angles can lead to significant aeroelastic damping improvement as loop gain is increased, while favorable dipole magnitudes can virtually eliminate the effects of aeroelastics in a feedback loop. Appropriate constraints include minimum phase aeroelastic zeros to avoid common problems associated with right-half plane zeros. To achieve desirable flight control system characteristics via optimal sensor locations, different kinds of blending filters for multiple sensors are investigated. Static filters, as well as dynamic filters with
Stanford, Bret K.; Jutte, Christine V.
2016-01-01
A series of aeroelastic optimization problems are solved on a high aspect ratio wingbox of the Common Research Model, in an effort to minimize structural mass under coupled stress, buckling, and flutter constraints. Two technologies are of particular interest: tow steered composite laminate skins and curvilinear stiffeners. Both methods are found to afford feasible reductions in mass over their non-curvilinear structural counterparts, through both distinct and shared mechanisms for passively controlling aeroelastic performance. Some degree of diminishing returns are seen when curvilinear stiffeners and curvilinear fiber tow paths are used simultaneously.
Analysis of detailed aerodynamic field measurements using results from an aeroelastic code
Energy Technology Data Exchange (ETDEWEB)
Schepers, J.G. [Energy Research Centre, Petten (Netherlands); Feigl, L. [Ecotecnia S. coop.c.l. (Spain); Rooij, R. van; Bruining, A. [Delft Univ. of Technology (Netherlands)
2004-07-01
In this article an analysis is given of aerodynamic field measurements on wind turbine blades. The analysis starts with a consistency check on the measurements, by relating the measured local aerodynamic segment forces to the overall rotor loads. It is found that the results are very consistent. Moreover, a comparison is made between measured results and results calculated from an aeroelastic code. On the basis of this comparison, the aerodynamic modelling in the aeroelastic code could be improved. This holds in particular for the modelling of 3D stall effects, not only on the lift but also on the drag, and for the modelling of tip effects (author)
Quick Method for Aeroelastic and Finite Element Modeling of Wind Turbine Blades
DEFF Research Database (Denmark)
Bennett, Jeffrey; Bitsche, Robert; Branner, Kim;
2014-01-01
-sectional analysis tool in order to obtain cross-sectional properties for the aeroelastic simulations. The method utilizes detailed user inputs of the structural layup and aerodynamic profile including ply thickness, orientation, material properties and airfoils to create the models. After the process is complete...... the user has two models of the same blade, one for performing a structural finite element model analysis and one for aeroelastic simulations. Here, the method is implemented and applied to reverse engineer a structural layup for the NREL 5MW reference blade. The model is verified by comparing natural...
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...
Optimal Topology of Aircraft Rib and Spar Structures under Aeroelastic Loads
Stanford, Bret K.; Dunning, Peter D.
2014-01-01
Several topology optimization problems are conducted within the ribs and spars of a wing box. It is desired to locate the best position of lightening holes, truss/cross-bracing, etc. A variety of aeroelastic metrics are isolated for each of these problems: elastic wing compliance under trim loads and taxi loads, stress distribution, and crushing loads. Aileron effectiveness under a constant roll rate is considered, as are dynamic metrics: natural vibration frequency and flutter. This approach helps uncover the relationship between topology and aeroelasticity in subsonic transport wings, and can therefore aid in understanding the complex aircraft design process which must eventually consider all these metrics and load cases simultaneously.
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.
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.
Friedmann, P. P.; Robinson, L. H.
1988-01-01
This paper describes the incorporation of finite-state, time-domain aerodynamics in a flag-lag-torsional aeroelastic stability and response analysis in forward flight. Improvements to a previous formulation are introduced which eliminate spurious singularities. The methodology for solving the aeroelastic stability and response problems with augmented states, in the time domain, is presented using an implicit formulation. Results describing the aeroelastic behavior of soft and stiff in-plane hingeless rotor blades, in forward flight, are presented to illustrate the sensitivity of both the stability and response problems to time domain unsteady aerodynamics.
Large Wind Turbine Rotor Design using an Aero-Elastic / Free-Wake Panel Coupling Code
DEFF Research Database (Denmark)
Sessarego, Matias; Ramos García, Néstor; Shen, Wen Zhong;
2016-01-01
Despite the advances in computing resources in the recent years, the majority of large wind-turbine rotor design problems still rely on aero-elastic codes that use blade element momentum (BEM) approaches to model the rotor aerodynamics. The present work describes an approach to wind-turbine rotor...
Application of unsteady aeroelastic analysis techniques on the national aerospace plane
Pototzky, Anthony S.; Spain, Charles V.; Soistmann, David L.; Noll, Thomas E.
1988-01-01
A presentation provided at the Fourth National Aerospace Plane Technology Symposium held in Monterey, California, in February 1988 is discussed. The objective is to provide current results of ongoing investigations to develop a methodology for predicting the aerothermoelastic characteristics of NASP-type (hypersonic) flight vehicles. Several existing subsonic and supersonic unsteady aerodynamic codes applicable to the hypersonic class of flight vehicles that are generally available to the aerospace industry are described. These codes were evaluated by comparing calculated results with measured wind-tunnel aeroelastic data. The agreement was quite good in the subsonic speed range but showed mixed agreement in the supersonic range. In addition, a future endeavor to extend the aeroelastic analysis capability to hypersonic speeds is outlined. An investigation to identify the critical parameters affecting the aeroelastic characteristics of a hypersonic vehicle, to define and understand the various flutter mechanisms, and to develop trends for the important parameters using a simplified finite element model of the vehicle is summarized. This study showed the value of performing inexpensive and timely aeroelastic wind-tunnel tests to expand the experimental data base required for code validation using simple to complex models that are representative of the NASP configurations and root boundary conditions are discussed.
Static aeroelastic analysis of very flexible wings based on non-planar vortex lattice method
Institute of Scientific and Technical Information of China (English)
Xie Changchuan; Wang Libo; Yang Chao; Liu Yi
2013-01-01
A rapid and efficient method for static aeroelastic analysis of a flexible slender wing when considering the structural geometric nonlinearity has been developed in this paper.A non-planar vortex lattice method herein is used to compute the non-planar aerodynamics of flexible wings with large deformation.The finite element method is introduced for structural nonlinear statics analysis.The surface spline method is used for structure/aerodynamics coupling.The static aeroelastic characteristics of the wind tunnel model of a flexible wing are studied by the nonlinear method presented,and the nonlinear method is also evaluated by comparing the results with those obtained from two other methods and the wind tunnel test.The results indicate that the traditional linear method of static aeroelastic analysis is not applicable for cases with large deformation because it produces results that are not realistic.However,the nonlinear methodology,which involves combining the structure finite element method with the non-planar vortex lattice method,could be used to solve the aeroelastic deformation with considerable accuracy,which is in fair agreement with the test results.Moreover,the nonlinear finite element method could consider complex structures.The non-planar vortex lattice method has advantages in both the computational accuracy and efficiency.Consequently,the nonlinear method presented is suitable for the rapid and efficient analysis requirements of engineering practice.It could be used in the preliminary stage and also in the detailed stage of aircraft design.
Donnell, K.O.; Schober, S.; Stolk, M.; Marzocca, P.; De Breuker, R.; Abdalla M.; Nicolini, E.; Gürdal, Z.
2007-01-01
This paper discusses modeling, simulations and experimental aspects of active aeroelastic control on aircraft wings by using Synthetic Jet Actuators (SJAs). SJAs, a particular class of zero-net mass-flux actuators, have shown very promising results in numerous aeronautical applications, such as boun
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;
2013-01-01
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...
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.
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
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.
DEFF Research Database (Denmark)
Aagaard Madsen, Helge; Larsen, Gunner Chr.; Larsen, Torben J.;
2010-01-01
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 turbulence...
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
Finite element model for aero-elastically tailored residential wind turbine blade design
Robinson, Eric Alan
Advances in passive wind turbine control systems have allowed wind turbines to achieve higher efficiencies and operate in wider inflow conditions than ever before. Within recent years, the adoption of aero-elastically tailored (bend-twist coupled) composite blades have been a pursued strategy. Unfortunately, for this strategy to be applied, traditional means of modeling, designing and manufacturing are no longer adequate. New parameters regarding non-linearities in deflections, stiffness, and aerodynamic loadings must now be implemented. To aid in the development of passive wind turbine system design, a finite element based aero-elastic program capable of computationally predicting blade deflection and twist under loading was constructed. The program was built around the idea of iteratively solving a blade composite structure to reach a maximum aero-elastic twist configuration under elevated wind speeds. Adopting a pre-existing blade geometry, from a pitch controlled small scale (3.5kW) turbine design, the program was tested to discover the geometry bend-twist coupling potential. This research would be a contributing factor in designing a passive pitch control replacement system for the turbine. A study of various model loading configurations was first performed to insure model validity. Then, a final model was used to analyze composite layups for selected spar configurations. Results characterize the aero-elastic twist properties for the selected configurations.
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)
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...
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
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.
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.
Stroud, W. J.
1974-01-01
A review and assessment of the state of the art in automated aeroelastic design is presented. Most of the aeroelastic design studies appearing in the literature deal with flutter, and, therefore, this paper also concentrates on flutter. The flutter design problem is divided into three cases: as isolated flutter mode, neighboring flutter modes, and a hump mode which can rise and cause a sudden, discontinuous change in the flutter velocity. Synthesis procedures are presented in terms of techniques that are appropriate for problems of various levels of difficulty. Current trends, which should result in more efficient, powerful and versatile design codes, are discussed. Approximate analysis procedures and the need for simultaneous consideration of multiple design requirements are emphasized.
DEFF Research Database (Denmark)
Gebhardt, Cristian; Veluri, Badrinath; Preidikman, Sergio;
2010-01-01
train in the wind turbine is reduced to only a few degrees of freedom. This means that, for the design of the drive train, the simulated load time series need to be further processed to applied loads on the individual components, such as gears and bearings. Furthermore, the limitation of the model...... multibody model for the drivetrain is developed as a way to include directly the high speed shaft’s (which connects the gear box and generator) flexibility. For the inter–model combination, a strong interaction scheme based on the fourth order Hamming predictor–corrector method is used. The models......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 gives...
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 integrated in the design taking into account their achieved fatigue load reduction. The optimized ‘smart blade’ design is compared to an aeroelastically optimized design with no flaps and the baseline design....
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.
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)
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 ...
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)....
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)
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.
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...
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.
Internal Structural Design of the Common Research Model Wing Box for Aeroelastic Tailoring
Jutte, Christine V.; Stanford, Bret K.; Wieseman, Carol D.
2015-01-01
This work explores the use of alternative internal structural designs within a full-scale wing box structure for aeroelastic tailoring, with a focus on curvilinear spars, ribs, and stringers. The baseline wing model is a fully-populated, cantilevered wing box structure of the Common Research Model (CRM). Metrics of interest include the wing weight, the onset of dynamic flutter, and the static aeroelastic stresses. Twelve parametric studies alter the number of internal structural members along with their location, orientation, and curvature. Additional evaluation metrics are considered to identify design trends that lead to lighter-weight, aeroelastically stable wing designs. The best designs of the individual studies are compared and discussed, with a focus on weight reduction and flutter resistance. The largest weight reductions were obtained by removing the 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 straight-rotated ribs although the design had a 4.2% lower flutter speed than the curved ribs of similar weight and stress levels were higher. For some configurations, the differences between curved and straight ribs were smaller, which provides motivation for future optimization-based studies to fully exploit the trade-offs.
Unsteady transonic aerodynamics and aeroelastic calculations at low-supersonic freestreams
Guruswamy, Guru P.; Goorjian, Peter M.
1988-01-01
A computational procedure is presented to simulate transonic unsteady flows and corresponding aeroelasticity of wings at low-supersonic freestreams. The flow is modeled by using the transonic small-perturbation theory. The structural equations of motions are modeled using modal equations of motion directly coupled with aerodynamics. Supersonic freestreams are simulated by properly accounting for the boundary conditions based on pressure waves along the flow characteristics in streamwise planes. The flow equations are solved using the time-accurate, alternating-direction implicit finite-difference scheme. The coupled aeroelastic equations of motion are solved by an integration procedure based on the time-accurate, linear-acceleration method. The flow modeling is verified by comparing calculations with experiments for both steady and unsteady flows at supersonic freestreams. The unsteady computations are made for oscillating wings. Comparisons of computed results with experiments show good agreement. Aeroelastic responses are computed for a rectangular wing at Mach numbers ranging from subtransonic to upper-transonic (supersonic) freestreams. The extension of the transonic dip into the upper transonic regime is illustrated.
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.
Pototzky, Anthony S.
2010-01-01
A methodology is described for generating first-order plant equations of motion for aeroelastic and aeroservoelastic applications. The description begins with the process of generating data files representing specialized mode-shapes, such as rigid-body and control surface modes, using both PATRAN and NASTRAN analysis. NASTRAN executes the 146 solution sequence using numerous Direct Matrix Abstraction Program (DMAP) calls to import the mode-shape files and to perform the aeroelastic response analysis. The aeroelastic response analysis calculates and extracts structural frequencies, generalized masses, frequency-dependent generalized aerodynamic force (GAF) coefficients, sensor deflections and load coefficients data as text-formatted data files. The data files are then re-sequenced and re-formatted using a custom written FORTRAN program. The text-formatted data files are stored and coefficients for s-plane equations are fitted to the frequency-dependent GAF coefficients using two Interactions of Structures, Aerodynamics and Controls (ISAC) programs. With tabular files from stored data created by ISAC, MATLAB generates the first-order aeroservoelastic plant equations of motion. These equations include control-surface actuator, turbulence, sensor and load modeling. Altitude varying root-locus plot and PSD plot results for a model of the F-18 aircraft are presented to demonstrate the capability.
Development of an Aeroelastic Modeling Capability for Transient Nozzle Side Load Analysis
Wang, Ten-See; Zhao, Xiang; Zhang, Sijun; Chen, Yen-Sen
2013-01-01
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 coupled aeroelastic modeling capability 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 in the framework of modal analysis. Transient aeroelastic nozzle startup analyses of the Block I Space Shuttle Main Engine at sea level were performed. The computed results from the aeroelastic nozzle modeling are presented.
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
Goldman, Benjamin D.; Scott, Robert C,; Dowell, Earl H.
2014-01-01
The purpose of this work is to develop a set of theoretical and experimental techniques to characterize the aeroelasticity of the thermal protection system (TPS) on the NASA Hypersonic Inflatable Aerodynamic Decelerator (HIAD). A square TPS coupon experiences trailing edge oscillatory behavior during experimental testing in the 8' High Temperature Tunnel (HTT), which may indicate the presence of aeroelastic flutter. Several theoretical aeroelastic models have been developed, each corresponding to a different experimental test configuration. Von Karman large deflection theory is used for the plate-like components of the TPS, along with piston theory for the aerodynamics. The constraints between the individual TPS layers and the presence of a unidirectional foundation at the back of the coupon are included by developing the necessary energy expressions and using the Rayleigh Ritz method to derive the nonlinear equations of motion. Free vibrations and limit cycle oscillations are computed and the frequencies and amplitudes are compared with accelerometer and photogrammetry data from the experiments.
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.
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 ...
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
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...... 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...
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 periodic systems with application to rotor blade flutter
Friedmann, P.; Silverthorn, L. J.
1974-01-01
The dynamics of a helicopter blade in forward flight are described by a system of linear differential equations with periodic coefficients. The stability of this periodic aeroelastic system is determined, using multivariable Floquet-Liapunov theory. The transition matrix at the end of the period is evaluated by: (1) direct numerical integration, and (2) a new, approximate method, which consists in approximating a periodic function by a series of step functions. The numerical accuracy and efficiency of the methods is compared, and the second method is shown to be superior by far. Results illustrating the effect of the periodic coefficients and various blade parameters are presented.
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 ...
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.
Directory of Open Access Journals (Sweden)
M Mohammadi-Amin
2013-01-01
Full Text Available An aeroelastic metamodel was designed and implemented for prediction of flutter speed and frequency of swept rectangular wings based on experimental data and artificial neural networks (ANN. The ANN is a supervised multilayer perceptron that was trained based on an experimental data set involves flutter characteristics of various cantilever rectangular wing models. Some data were not learned to ANN and were maintained as test cases. The activation functions were tangent hyperbolic and linear function in the hidden and output layers respectively. For learning process, the normalized form of the inputs and outputs were given to the ANN. The ANN learned the relation between the inputs and outputs and was trained for predicting output parameters. It is observed that ANN results are in good agreement with experimental data as well as results of an aeroelasticity code developed using an analytical aerodynamic model. So this ANN can be used for quick prediction of flutter characteristics of swept rectangular wings and also for the study of the effects of various parameters on flutter characteristics of swept rectangular cantilevered wings.
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.
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.
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.
Schuster, David M.
2008-01-01
Over the past three years, the National Aeronautics and Space Administration (NASA) has initiated design, development, and testing of a new human-rated space exploration system under the Constellation Program. Initial designs within the Constellation Program are scheduled to replace the present Space Shuttle, which is slated for retirement within the next three years. The development of vehicles for the Constellation system has encountered several unsteady aerodynamics challenges that have bearing on more traditional unsteady aerodynamic and aeroelastic analysis. This paper focuses on the synergy between the present NASA challenges and the ongoing challenges that have historically been the subject of research and method development. There are specific similarities in the flows required to be analyzed for the space exploration problems and those required for some of the more nonlinear unsteady aerodynamic and aeroelastic problems encountered on aircraft. The aggressive schedule, significant technical challenge, and high-priority status of the exploration system development is forcing engineers to implement existing tools and techniques in a design and application environment that is significantly stretching the capability of their methods. While these methods afford the users with the ability to rapidly turn around designs and analyses, their aggressive implementation comes at a price. The relative immaturity of the techniques for specific flow problems and the inexperience with their broad application to them, particularly on manned spacecraft flight system, has resulted in the implementation of an extensive wind tunnel and flight test program to reduce uncertainty and improve the experience base in the application of these methods. This provides a unique opportunity for unsteady aerodynamics and aeroelastic method developers to test and evaluate new analysis techniques on problems with high potential for acquisition of test and even flight data against which they
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.
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.
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)
DEFF Research Database (Denmark)
Acampora, Antonio; Macdonald, J.H.G.; Georgakis, Christos T.;
2012-01-01
Despite much research in recent years, large amplitude vibrations of inclined bridge cables continue to be of concern. Various mechanisms for the excitation have been suggested, including rain-wind excitation, dry inclined cable galloping, high reduced-velocity vortex shedding and excitation from...... the deck and/or towers. Since 2010, the Technical University of Denmark has been monitoring the vibrations of the twin inclined cables of the Øresund Bridge. From the acquired data, Georgakis and Acampora [1] showed that the cable aerodynamic damping can be determined for wind orthogonal to the twin cables...... of this paper is to identify the aeroelastic forces for in-plane and out-of-plane vibrations of bridge cables in dry conditions as in [2], but now for skewed winds. To achieve this, an output-only system identification employing the Eigenvalue Realisation Algorithm (ERA) [3] has been applied to selected...
8th International Symposium on Unsteady Aerodynamics and Aeroelasticity of Turbomachines
1998-01-01
Twenty-one years have passed since the first symposium in this series was held in Paris (1976). Since then there have been meetings in Lausanne (1980), Cambridge (1984), Aachen (1987), Beijing (1989), Notre Dame (1991) and Fukuoka (1994). During this period a tremendous development in the field of unsteady aerodynamics and aeroelasticity in turbomachines has taken place. As steady-state flow conditions become better known, and as blades in the turbomachine are constantly pushed towards lower weight, and higher load and efficiency, the importance of unsteady phenomena appear more clearly. th The 8 Symposium was, as the previous ones, of high quality. Furthermore, it presented the audience with the latest developments in experimental, numerical and theoretical research. More papers than ever before were submitted to the conference. As the organising committee wanted to preserve the uniqueness of the symposium by having single sessions, and thus mingle speakers and audience with different backgrounds in this int...
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.
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.
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
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...
Evaluation of an aeroelastic model technique for predicting airplane buffet loads
Hanson, P. W.
1973-01-01
A wind-tunnel technique which makes use of a dynamically scaled aeroelastic model to predict full-scale airplane buffet loads during buffet boundary penetration is evaluated. A 1/8-scale flutter model of a fighter airplane with remotely controllable variable-sweep wings and trimming surfaces was used for the evaluation. The model was flown on a cable-mount system which permitted high lift forces comparable to those in maneuvering flight. Bending moments and accelerations due to buffet were measured on the flutter model and compared with those measured on the full-scale airplane in an independent flight buffet research study. It is concluded that the technique can provide valuable information on airplane buffet load characteristics not available from any other source except flight test.
Real-Time Adaptive Least-Squares Drag Minimization for Performance Adaptive Aeroelastic Wing
Ferrier, Yvonne L.; Nguyen, Nhan T.; Ting, Eric
2016-01-01
This paper contains a simulation study of a real-time adaptive least-squares drag minimization algorithm for an aeroelastic model of a flexible wing aircraft. The aircraft model is based on the NASA Generic Transport Model (GTM). The wing structures incorporate a novel aerodynamic control surface known as the Variable Camber Continuous Trailing Edge Flap (VCCTEF). The drag minimization algorithm uses the Newton-Raphson method to find the optimal VCCTEF deflections for minimum drag in the context of an altitude-hold flight control mode at cruise conditions. The aerodynamic coefficient parameters used in this optimization method are identified in real-time using Recursive Least Squares (RLS). The results demonstrate the potential of the VCCTEF to improve aerodynamic efficiency for drag minimization for transport aircraft.
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
Sabri, Farhad
Shells of revolution, particularly cylindrical and conical shells, are one of the basic structural elements in the aerospace structures. With the advent of high speed aircrafts, these shells can show dynamic instabilities when they are exposed to a supersonic flow. Therefore, aeroelastic analysis of these elements is one of the primary design criteria which aeronautical engineers are dealing with. This analysis can be done with the help of finite element method (FEM) coupled with the computational fluid dynamic (CFD) or by experimental methods but it is time consuming and very expensive. The purpose of this dissertation is to develop such a numerical tool to do aeroelastic analysis in a fast and precise way. Meanwhile during the design stage, where the different configurations, loading and boundary conditions may need to be analyzed, this numerical method can be used very easily with the high order of reliability. In this study structural modeling is a combination of linear Sanders thin shell theory and classical finite element method. Based on this hybrid finite element method, the shell displacements are found from the exact solutions of shell theory rather than approximating by polynomial function done in traditional finite element method. This leads to a precise and fast convergence. Supersonic aerodynamic modeling is done based on the piston theory and modified piston theory with the shell curvature term. The stress stiffening due to lateral pressure and axial compression are also taken into accounts. Fluid-structure interaction in the presence of inside quiescent fluid is modeled based on the potential theory. In this method, fluid is considered as a velocity potential variable at each node of the shell element where its motion is expressed in terms of nodal elastic displacements at the fluid-structure interface. This proposed hybrid finite element has capabilities to do following analysis: (i) Buckling and vibration of an empty or partially fluid filled
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.
DEFF Research Database (Denmark)
Damgaard, Mads; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2015-01-01
Dynamic vibration response of a wind turbine structure is examined. Emphasis is put on the dynamic interaction between the foundation and the subsoil, since stiffness and energy dissipation of the substructure affect the dynamic response of the wind turbine. Based on a standard lumped-parameter m......Dynamic vibration response of a wind turbine structure is examined. Emphasis is put on the dynamic interaction between the foundation and the subsoil, since stiffness and energy dissipation of the substructure affect the dynamic response of the wind turbine. Based on a standard lumped......-parameter model fitted to the frequency response of the ground, a surface foundation is implemented into the aeroelastic code FLEX5. In case of a horizontal stratum overlaying a homogeneous half-space and within the low frequency range, analyses show that a standard lumped-parametermodel provides an accurate...... prediction of the frequency dependent foundation stiffness. The generalized stiffness matrix of the substructure is found to be in a reasonable agreement with the corresponding values based on a Guyan reduction scheme. In addition, experimental findings based on traditional and operational modal techniques...
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
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.
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.
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.
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...
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.
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.
风力机叶片气动弹性剪裁研究进展%RESEARCH AND DEVELOPMENT ON AEROELASTIC TAILORING OF WIND TURBINE BLADE
Institute of Scientific and Technical Information of China (English)
李晓拓; 祝颖丹; 颜春; 范欣愉
2012-01-01
本文首先简要阐述了气动弹性剪裁的起源及其在飞机设计中的应用；然后根据气动弹性剪裁在风力机叶片中的应用目的,着重综述了气动弹性剪裁在风力机叶片的性能、成本、结构设计和制造工艺几个方面的最新研究进展；最后,本文对气动弹性剪裁在风力机叶片中的研究进展进行了总结并展望了其在风力机叶片中的应用前景.%A review of recent work on aeroelastic tailoring of wind turbine blade is presented here. This review introduces the basic theory and application of aeroelastic tailoring in aircraft design. Then the paper highlights some recent advances in aeroelastic tailoring of wind turbine blade, including performance, cost, structural design and manufacturing process. Trends of aeroelastic tailoring in wind turbine blade are also discussed.
A methodology for robust structural design with application to active aeroelastic wings
Zink, Paul Scott
A new design process for Active Aeroelastic Wing (AAW) technology was developed, in which control surface gear ratios and structural design variables were treated together in the same optimization problem, acting towards the same objective of weight minimization. This is in contrast to traditional AAW design processes that treat design of the gear ratios and design of the structure as separate optimization problems, each with their own different objectives and constraints, executed in an iterative fashion. The demonstration of the new AAW design process, implemented in an efficient modal-based structural analysis and optimization code, on a lightweight fighter resulted in a 15% reduction in wing box skin weight over a more traditional AAW design process. In addition, the new process was far more streamlined than the traditional approach in that it was performed in one continuous run and did not require the exchange of data between modules. The new AAW design process was then used in the development of a methodology for the design of AAW structures that are robust to uncertainty in maneuver loads which arise from the use of linear aerodynamics. Maneuver load uncertainty was modeled probabilistically and based on typical differences between rigid loads as predicted by nonlinear and linear aerodynamic theory. These models were used to augment the linear aerodynamic loads that had been used in the AAW design process. Characteristics of the robust design methodology included: use of a criticality criterion based on a strain energy formulation to determine what loads were most critical to the structure, Latin Hypercube Sampling for the propagation of uncertainty to the criterion function, and redesign of the structure, using the new AAW design process, to the most critical loads identified. The demonstration of the methodology resulted in a wing box skin structure that was 11% heavier than an AAW structure designed only with linear aerodynamics. However, it was
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
Peterson, R. L.; Warmbrodt, W.
1984-01-01
A hover test of a full-scale, hingeless rotor system was conducted in the NASA Ames 40- by 80-foot wind tunnel. The rotor was tested on the Ames rotor test apparatus. Rotor aeroelastic stability, performance, and loads at various rotational speeds and thrust coefficients were investigated. The primary objective was to determine the inplane stability characteristics of the rotor system. Rotor inplane damping data were obtained for operation between 350 and 425 rpm (design speed), and for thurst coefficients between 0.0 and 0.12. The rotor was stable for all conditions tested. At constant rotor rotational speed, a minimum inplane dampling level was obtained at a thrust coefficient approximately = 0.02. At constant rotor lift, a minimum in rotor inplane damping was measured at 400 rpm.
APPROXIMATE FUNCTION FOR UNSTEADY AERODYNAMIC KERNEL FUNCTION OF AEROELASTIC LIFTING SURFACES
Directory of Open Access Journals (Sweden)
Erwin Sulaeman
2014-05-01
Full Text Available Normal 0 false false false EN-US X-NONE X-NONE ABSTRACT: Prediction of unsteady aerodynamic loads is still the most challenging task in flutter aeroelastic analysis. Generally the numerical estimation of steady and unsteady aerodynamic of thin lifting surface is conducted based on an integral equation relating aerodynamic pressure and normal wash velocity. The present work attempts to increase the accuracy of the prediction by using an approximate approach to evaluate kernel function occurring in the integral equation in the form of cylindrical function. Following previous approximation approach by other researchers to solve the cylindrical function for planar lifting surfaces, in the present work such approach is extended to non planar lifting surfaces. To increase the accuracy of the method, the integration region of the kernel function is divided into two parts namely near and far regions, where a nonlinear regression curve fitting technique is adapted to approximate the denominator part of the cylindrical function of each region.ABSTRAK: Penelahan daya aerodinamik tidak stabil merupakan satu tugas yang mencabar dalam menganalisis getaran aeroanjalan. Umumnya, anggaran berangka untuk daya aerodinamik stabil dan tidak stabil pada permukaan mengangkat yang nipis, adalah berdasarkan kepada persamaan kamiran di antara tekanan aerodinamik dan halaju aliran udara pada garis normal yang terhasil di bawah sayap pesawat. Kajian ini adalah bertujuan untuk menghasilkan penelahan daya aerodinamik yang lebih tepat dengan menggunakan pendekatan kira hampir untuk menilai fungsi Kernel yang terdapat dalam persamaan kamiran dalam bentuk fungsi silinder. Dengan menggunakan pendekatan kira hampir yang digunakan oleh penyelidik sebelumnya untuk menyelesaikan fungsi silinder pada permukaan mengangkat satah, kajian ini mengembangkan pendekatan tersebut kepada permukaan mengangkat tak sesatah. Untuk meningkatkan lagi ketepatan penelahan, kawasan pengamiran
考虑气动弹性的风力机叶片性能分析%Wind turbine performance analysis with aeroelastic effect
Institute of Scientific and Technical Information of China (English)
陈佳慧; 王同光
2011-01-01
考虑气动弹性对风力机叶片的影响,采用叶素-动量理论计算气动力,采用盒形梁理论计算结构变形,耦合静气动弹性平衡方程,建立了风力机叶片静气动弹性分析程序.本文运用该程序进行了多种风速下叶片载荷及风轮性能的计算,分析了气动弹性对原设计的影响.结果表明,对于兆瓦级风力机,在大风速情况下,气动弹性对风轮性能有着明显影响,并会造成气动载荷的重新分布,影响结构设计的准确性.该方法可用于对叶片气动设计与载荷计算方法进行气动弹性修正.%The aeroelastic effect for wind turbine blade is investigated in this article. A code is programmed,which utilizes the blade element momentum method to calculate the aerodynamics and adopts the multi-cell beams method to calculate the structural distortion, coupling with static aeroelastic balancing equation. The loads on the blade and the aerodynamic performance of the wind turbine at various wind speeds are calculated, and the influence of aeroelastics to the original design is analyzed. It is demonstrated that the aeroelastic effect has obvious influence to the large-size wind turbine performance at high wind speeds, and causes the aerodynamic loads redistribute, which would affect the accuracy of structure design. This method can be used to correct the conventional blade aerodynamic design and load calculation method.
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.
Experiment on static aeroelastic in high speed wind tunnel%静气动弹性模型高速风洞试验研究
Institute of Scientific and Technical Information of China (English)
杨贤文; 余立; 吕彬彬; 郭洪涛; 杨振华; 寇西平
2015-01-01
对采用复合材料玻璃纤维、碳纤维加工的静气动弹性模型进行了高速风洞试验研究，测试了模型的柔度矩阵、气动力、表面压力、弯／扭应变信号及弯／扭变形，为静气动弹性模型刚度试验、弯／扭应变信号测量、模型变形视频测量（VMD）及风洞总压控制等静气动弹性风洞试验能力的提高积累了经验，为飞行器静气动弹性研究提供了良好的试验平台。研究表明：静气动弹性模型较刚性模型升力线斜率及襟副翼效率下降、气动焦点前移；静气动弹性模型与刚性模型表面压力差异明显；在小迎角范围内，静气动弹性机翼模型弯／扭应变信号随迎角增加基本呈线性变化；在正迎角时，大展弦比后掠机翼静气动弹性模型的剖面扭转变形使有效迎角减小，剖面越靠近翼尖弯／扭变形越大。%Experimental investigation on static aeroelastic was carried out in high speed wind tunnel using glass fiber models and carbon fiber models respectively.Flexibility matrix,aerody-namic force,pressure,bending/torsion strain signals and bending/torsional deformations of models are measured.Experience is accumulated for developing high speed wind tunnel static aeroelastic experimental techniques such as stiffness test,bending/torsion strain signals gauging, videogrammetric model deformation and wind tunnel total pressure control.The investigation shows:comparing with rigid model,lift curve slope and aileron/flap efficiency of static aeroelas-tic model decrease,aerodynamic center of static aerodynamic model shifts forward,pressure dis-tributions of static aeroelastic model change significantly;static aeroelastic wing model bending/torsion strain signals,which can be used to analyze aerodynamic loads,are nearly linear variation with attack angle at small attack angles,for lift coefficient and pitching moment coefficient of static aeroelastic wing model change linearly with attack
Cavagna, Luca; Ricci, Sergio; Travaglini, Lorenzo
2011-11-01
This paper presents a design framework called NeoCASS (Next generation Conceptual Aero-Structural Sizing Suite), developed at the Department of Aerospace Engineering of Politecnico di Milano in the frame of SimSAC (Simulating Aircraft Stability And Control Characteristics for Use in Conceptual Design) project, funded by EU in the context of 6th Framework Program. It enables the creation of efficient low-order, medium fidelity models particularly suitable for structural sizing, aeroelastic analysis and optimization at the conceptual design level. The whole methodology is based on the integration of geometry construction, aerodynamic and structural analysis codes that combine depictive, computational, analytical, and semi-empirical methods, validated in an aircraft design environment. The work here presented aims at including the airframe and its effect from the very beginning of the conceptual design. This aspect is usually not considered in this early phase. In most cases, very simplified formulas and datasheets are adopted, which implies a low level of detail and a poor accuracy. Through NeoCASS, a preliminar distribution of stiffness and inertias can be determined, given the initial layout. The adoption of empirical formulas is reduced to the minimum in favor of simple numerical methods. This allows to consider the aeroelastic behavior and performances, as well, improving the accuracy of the design tools during the iterative steps and lowering the development costs and reducing the time to market. The result achieved is a design tool based on computational methods for the aero-structural analysis and Multi-Disciplinary Optimization (MDO) of aircraft layouts at the conceptual design stage. A complete case study regarding the TransoniCRuiser aircraft, including validation of the results obtained using industrial standard tools like MSC/NASTRAN and a CFD (Computational Fluid Dynamics) code, is reported. As it will be shown, it is possible to improve the degree of
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.
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.
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
Rezaee, Mousa; Jahangiri, Reza
2015-05-01
In this study, in the presence of supersonic aerodynamic loading, the nonlinear and chaotic vibrations and stability of a simply supported Functionally Graded Piezoelectric (FGP) rectangular plate with bonded piezoelectric layer have been investigated. It is assumed that the plate is simultaneously exposed to the effects of harmonic uniaxial in-plane force and transverse piezoelectric excitations and aerodynamic loading. It is considered that the potential distribution varies linearly through the piezoelectric layer thickness, and the aerodynamic load is modeled by the first order piston theory. The von-Karman nonlinear strain-displacement relations are used to consider the geometrical nonlinearity. Based on the Classical Plate Theory (CPT) and applying the Hamilton's principle, the nonlinear coupled partial differential equations of motion are derived. The Galerkin's procedure is used to reduce the equations of motion to nonlinear ordinary differential Mathieu equations. The validity of the formulation for analyzing the Limit Cycle Oscillation (LCO), aero-elastic stability boundaries is accomplished by comparing the results with those of the literature, and the convergence study of the FGP plate is performed. By applying the Multiple Scales Method, the case of 1:2 internal resonance and primary parametric resonance are taken into account and the corresponding averaged equations are derived and analyzed numerically. The results are provided to investigate the effects of the forcing/piezoelectric detuning parameter, amplitude of forcing/piezoelectric excitation and dynamic pressure, on the nonlinear dynamics and chaotic behavior of the FGP plate. It is revealed that under the certain conditions, due to the existence of bi-stable region of non-trivial solutions, system shows the hysteretic behavior. Moreover, in absence of airflow, it is observed that variation of control parameters leads to the multi periodic and chaotic motions.
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
Bartholomay, Sirko; Ramos-García, Néstor; Mikkelsen, Robert Flemming; Technical University of Denmark (DTU)-WInd Energy Team
2014-11-01
The viscous-inviscid flow solver Q3UIC for 2D aerodynamics has recently been developed at the Technical University of Denmark. The Q3UIC solver takes viscous and unsteady effects into account by coupling an unsteady inviscid panel method with the integral boundary layer equations by means of a strong coupling between the viscous and inviscid parts, and in this respect differs from other classic panel codes e.g. Xfoil. In the current work a Runge-Kutta-Nyström scheme was employed to couple inertial, elastic and aerodynamical forces and moments calculated by Q3UIC for a two-dimensional blade section in the time-domain. Numerical simulations are validated by a three step experimental verification process carried out in the low-turbulence wind tunnel at DTU. First, a comparison against steady experiments for a NACA 64418 profile and a flexible trailing edge flap is presented for different fixed flap angles, and second, the measured aerodynamic characteristics considering prescribed motion of the airfoil with a moving flap are compared to the Q3UIC predictions. Finally, an aeroelastic experiment for one degree of freedom-airfoil pitching- is used to evaluate the accuracy of aeroelastic coupling.
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.
Blade Analysisof Wind Turbine Considering Aeroelasticity%考虑气动弹性的风力机叶片分析
Institute of Scientific and Technical Information of China (English)
陈进; 李松林; 郭小锋; 孙振业
2015-01-01
运用修正的叶素－动量理论和有限元方法，建立了一种全新的考虑气动弹性的风力机叶片性能分析方法。运用该方法，在多种风速工况下对某850 kW风力机叶片的性能进行了计算，结果表明：对于大功率风力机，在大风速大载荷工况下，气动弹性对风轮性能有明显的影响，使叶片偏离原设计值。该方法的运用对于叶片的气动设计、载荷计算和结构设计有实际指导意义。%A novel approach , which utilizes a modified blade element-momentum theory and the finite element method, is presented to analyze the blade performance of wind turbine considering aeroelasticity .Then, the ap-proach is used to analyze the performance of the blades of an 850 MW wind turbine at various wind speeds .The re-sults show that aeroelasticity obviously influences the performance of large-size wind turbines at high wind speed and greatly reduces the accuracy of the original design .The presented approach is of guiding significance for the aerody-namic shape design , load calculation and structural design of blades .
Nonlinear Aerodynamic Modeling and Research in Static Aeroelasticity%静气弹中非线性气动力建模方法与分析
Institute of Scientific and Technical Information of China (English)
吴欣龙; 王正平
2012-01-01
大展弦比低雷诺数气动布局容易较早出现气流分离,会带来明显的非线性气动力问题.针对此类布局提出了一种建立基于Kriging插值的非线性压力系数分布模型的方法.从Navier - Stokes方程计算的不同状态下飞机的压力系数中提取不同坐标的系数.利用Kriging插值函数建立CFD压力系数对迎角导数的响应面,将插值结果代入偶极子网格法(Double- Lattice Method,DLM)修正其线性方法.利用无限板样条(IPS)方法进行气动结构耦合,实现了有限元结构的非线性气弹响应分析.算例结果验证了方法对于静气弹分析的有效性,同时能准确地反映弹性带来的气动效率的降低和非线性力矩特征.%For the problem that large aspect ratio of the low reynold number aerodynamic layout appeared earlier in the laminar separation,and bring obvious nonlinear aerodynamic. The model of a distributed non - linear pressure coefficient based on the Kriging interpolation method is proposed for this layout. The pressure coefficient of the plane in different coordinate is extracted from the result calculated by the Navi-er- Stokes equations in different flight status, use of Kriging interpolation function to create the response surface which is derivative of CFD pressure coefficient on the angle of attack,put the interpolation results into the Double- of Lattice Method to amend its linear methods, use the infinite plate spline(IPS) method to couple the fluid- structure and realize finite element of nonlinear aeroelastic response analysis. Example is given in the text,the results demonstrate the validity of the method for the analysis of the static aeroelastic same time be able to accurately reflect the reduction of aerodynamic efficiency brought by flexibility and non- linear moment characteristics.
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.
Institute of Scientific and Technical Information of China (English)
张波成; 万志强; 杨超
2011-01-01
A method is provided to obtain static aeroelastic responses in the early and detailed design stages of aircrafts.Based on this approach,three-dimensional aerodynamic forces are calculated independently,and then coupled with the structure.The aerodynamic forces can be computed with Euler solver,Navier-Stokes solver or High-order panel method in the early stage and provided by wind-tunnel tests in the detailed stage.The method is applied to obtain static aeroelastic responses of a high-aspect-ratio wing in this study.The rigid aerodynamic forces of different flight conditions are calculated with CFD tools and transmitted to linear aerodynamic grids or structural grids.Finally,the rigid aerodynamic forces of equilibrium are flexibilized with a linear aerodynamic influence coefficient matrix.The results are compared with static aeroelastic reponses calculated based on linear aerodynamic forces generally used in early design stage.It could be concluded that there is great difference in aerodynamic forces distribution and aerodynamic coefficients,small difference in macroscopical distribution of shear and bending moment.The method of this study is intended to provide an assessment of static aeroelastic effects in early design process stage of the aircraft.%提出了一种适用于飞行器初步设计和详细设计阶段的静气动弹性响应分析方法。基于该方法进行静气动弹性响应分析时三维气动力单独求解,再与结构进行耦合计算。在初步设计阶段气动力可选取由Euler方程、N-S方程或高阶面元法计算,详细设计阶段气动力可选取风洞试验气动力。该文对一大展弦比机翼进行了静气动弹性响应分析,算例中使用CFD方法计算气动力,用以提供各种状态的刚性气动力;再将气动力通过插值分配到线性气动力网格或结构有限元模型上;并最终通过线性化方法对平衡状态附近的气动力进行弹性化处理。还将分析结果与适用于初步设计
Institute of Scientific and Technical Information of China (English)
刘伏虎; 马晓平
2012-01-01
基于Theodorsen非定常气动力理论,以大展弦比均匀直机翼为研究对象,建立了系统的气动弹性响应方程.选取二阶弯曲和二阶扭转模态,采用V-g法求解了系统的颤振速度.基于Kussner函数,建立了锐边突风系统模型,并推导了在弯曲和扭转模态阶数为Nw和Na下的系统状态方程,仿真研究了加入突风后系统的气动弹性响应.结果表明,加入突风后翼尖响应振幅增大.%Based on Theodorsen unsteady aerodynamics theory, the equation of aeroelastic response for straight wing with high aspect ratio is established. Flutter speed is determined for two bending modes and two torsional modes using V-g methods. The sharp edge gust system model is established and the system state equations are derived with Nw bending modes and Na torsional modes wing systems based on the function Kussner. The aeroelastic response of system shows that the amplitude oscillation becomes higher. The modeling method may offer reference for research of gust response.
机翼风洞试验模型CFD静气动弹性修正研究%Static Aeroelastic Correction for Wind Tunnel Results of Wing Model with CFD
Institute of Scientific and Technical Information of China (English)
王艺坤; 史爱明
2012-01-01
在低速增压风洞和跨声速风洞中,变雷诺数试验常用增压来实现.速压变化带来弹性变形的不同,造成伪雷诺数效应,其影响与雷诺数效应在同一量级.数值模拟了F4机翼在某低速增压风洞中的变雷诺数和变迎角试验.研究了其静气弹效应随迎角和风洞试验速压的变化规律.论证了对于风洞试验静气弹变形造成的伪雷诺教效应采用CFD方法修正的可行性.结果表明:对F4这种金属材料的中等展比后掠机翼,沿展向挠度和剖面扭转角等变形参量与迎角呈正相关.但迎角越大,增长幅度越小.随风洞试验速压也是正相关增长,但是等幅线性的.结合CFD技术进行风洞静气弹修正的方法是可行的.未来在如NASA研制的“太阳神”飞机等大展弦比、大柔性飞机的设计和风洞试验修正中将得到广泛应用.%Based on static aeroelasticity theory, the aeroelasticity behavior of F4 wing in pressurized wind tunnel is simulated numercially to analyze the influence of the elastic deformation on the models aerodynamic characteristics. The rules how bend deflection, twist angle change with wind tunnel experimental dynamic pressure or angles of attack are investigated. The results show that; typical sweptback wing, like F4 Wing ,lead to the elastic equivalent angles of attack becoming smaller and lift coefficient decreasing. The bend deflection and twist angles of attack are positive linear with wind tunnel experimental dynamic pressure, and increase with angles of attack nonlinear. In conclusion, it is feasible to correct static aeroelasticity effect with CFD in wind tunnel experiments. Though the advantage is not evidence with such rigid wing, it will be widely used on high aspect ratio and high flexibility wing.
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
一种考虑静气动弹性影响的机翼型架外形设计方法%A Design of Wing Shape of Considering Influence of Static Aeroelastic
Institute of Scientific and Technical Information of China (English)
王晓江; 董文辉; 雷鸣
2012-01-01
Combining the wing static aeroelastic analysis and Takanashi residual-correction inverse design method of wings, a method which considering elastic deformation influence is developed to design ihe aerodynamic configuration of three-dimensional aircraft wing. The method that analyze static aeroelastic is a numerical simulation technology which combined Computational Fluid Dynamics (CFD) method with Computational Structure Dynamic (CSD). Aerodynamic is computed by N-S equations finite volume technology and structure response is computed by finite numerical technology. A passenger plane wing as an example,the example shows that the design method developed has significant practical value.%在机翼静气动弹性分析的基础上,结合Takanashi余量修正方法对三维机翼进行气动外形反设计,以确定机翼的型架外形.其中静气动弹性分析采用耦合计算流体力学和计算结构动力学(CFD/CSD)方法进行数值模拟.气动力采用N-S方程的有限体积求解技术,结构响应则采用有限元数值求解技术.以某客机方案机翼作为算例,设计结果表明本文所建立的机翼型架外形设计方法是可行的,具有一定的工程应用价值.
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。
Application of improved dynamic unstructured grids in aeroelastic model%改进的动弹网格方法在航空气弹计算中的应用
Institute of Scientific and Technical Information of China (English)
胡凡; 范锐军
2015-01-01
气动弹性是现代航空气动力计算中一个突出的问题。主要研究基于Delaunay图映射方法的动弹网格的欧拉方程CFD计算及其在航空标模M6机翼上的静气动弹性应用。以Delaunay图映射方法为基础，针对三维非结构运动网格技术进行了研究、开发和改进，同时利用计算流体力学的方法，开发了一套适用性较好的非结构网格欧拉方程流场求解器，进一步通过流固耦合的力学方法，对航空标模M6机翼的静气动弹性问题进行了研究和分析，给出了CFD并行计算的设计方法及算例。%Aeroelastic model is significant for large amount of airplanes in modern aerodynamics computing .This paper presents a strategy for generating 3D unstructured grids and the dynamic grids based on Delaunay graph mapping method .On the base of above , it performs a set of flow field solver based on Euler equations into estab-lishmeng of the static aeroelastic cases of the M 6 standard model coupled with structure dynamic equation , shows the design of the parallel computing method and numerical example .
Research in aeroelasticity EFP-2005
DEFF Research Database (Denmark)
2006-01-01
, 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...... design tool was developed. Compared to the Risø-B1family, the new airfoil family showed similar or improved aerodynamic and structural characteristics. Four different airfoils were analyzed to reveal the differences between 2D and 3D CFD. The major conclusions are the dependency of computational...... with app. 5%. The influence of hydrodynamics showed only minor influence on the tower frequency and damping. An increase in external water velocityleads to a noticeable increase in damping. A new anisotropic beam element has been implemented. This provides the basis for giving more confidence in flutter...
Research in aeroelasticity EFP-2007
DEFF Research Database (Denmark)
-conservative. An experimental method for measuring transition point and energy spectra in airfoil boundary layers using microphones has been developed. A robust and automatic method for detecting transition based on microphone measurement on airfoil surfaces has been developed. Transition points and the corresponding...... instabilities have clearly been observed in airfoil boundary layers. Predictions of the transition points on airfoils using the en method were in good agreement with measurements. The Riso-DTU airfoil design methodology was verified and showed that airfoils can be designed with very high lift-drag ratio...... and 3-D flow. However, at separation an increased lift is observed close to the rotational axis. 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...
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...
Institute of Scientific and Technical Information of China (English)
杨超; 肖志鹏; 万志强
2011-01-01
针对主动气动弹性机翼（active aeroelastic wing,简称AAW）,基于遗传算法发展一种可以同步考虑结构优化和配平关系优化的综合设计方法,并在采用了AAW技术的战斗机的设计中得到了应用。以结构质量最小化为目标,以控制面偏转、铰链力矩、翼根载荷和临界颤振速度为约束条件,在多种平飞滚转机动状态下对战斗机机翼进行优化设计,并与传统的单控制面设计方法进行了比较。结果表明,AAW技术通过多控制面之间的协调偏转,能够充分利用结构柔性,在提高机动性能和减少结构质量方面有明显的优势。%An integrated design methodology considering the simultaneous optimization of structure and trim is developed for the active aeroelastic wing（AAW）,based on the genetic algorithm.This method is applied to the design of fighter configuration employing AAW technology.The optimization design for the wing of fighter aircraft is conducted in multiple maneuver conditions of level-flight with roll.The objective is to minimize the structural mass subjected to the constraints of deflections of control surfaces,hinge moments,aerodynamic loads acting on wing root and critical flutter speed.A comparison between the new method and traditional method which utilizes a single control surface,is also presented.The results demonstrate that AAW technology takes the full advantages of structural flexibility by the coordinated deflections of multiple control surfaces,and has significant merits in improving maneuverability and reducing structural mass.
Institute of Scientific and Technical Information of China (English)
张凯; 刘占芳; 颜世军
2012-01-01
Based on Theodorsen' s classical flutter theory of 2D aerofoil, using Matrix 27 user-defined element of ANSYS development platform, aerodynamic mass matrix, aerodynamic damping matrix and aerodynamic stiffness matrix of blade with finite element format of beam model of vertical axis wind turbine and finite element dynamic e- quations of wind turbine were given. Aeroelastic stability analysis on 1MW Darriaus vertical axis wind turbine was done.%应用Theodorsen二维翼型的经典颤振理论,借助ANSYS开发平台Matrix 27用户自定义单元,建立了立轴风力机叶片梁模型有限元格式的气动质量矩阵、气动阻尼矩阵和气动刚度矩阵及风力机动力学分析的有限元方程,对兆瓦级Darriaus型立轴风力机进行气动弹性稳定性分析.
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
Institute of Scientific and Technical Information of China (English)
王旭东; 王立存; 夏洪均
2013-01-01
In order to improve aerodynamic and structural performance of wind turbine baldes, the flapwise and edgewise vi-bration mode of blades is obtained based on aerodynamic and dynamic structural model of wind turbine rotor.The coupling aeroelastic model including displacement and vibration is presented through choosing the basic degrees of freedom correspond-ing to elastic structural model.The optimization model of wind turbine blades is presented based on the output power and com-ponent of wind turbine rotor.With the model presented in this paper, one 5MW wind turbine rotor is applied and optimized. The output powers, axial and tangential forces of original and optimized blades are simulated and compared to validate the reli-ability of the design method.%为提高风力机叶片气动结构性能，基于风力机风轮空气动力学及叶片结构动力学原理，选取叶片所处位置及扭转变形为自由度，在研究叶片摆振、摆振方向各阶振动模态的基础上，提出风力机叶片气动弹性耦合振动变形计算模型。基于风力机整机部件构成及输出功率特征，提出风力机叶片优化设计模型，对某5 MW风力机叶片的进行形状优化设计，通过对比分析优化叶片和原始叶片的输出功率及气弹载荷特性，验证优化叶片气动及结构性能的优越性。
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...
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.
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...
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...
Institute of Scientific and Technical Information of China (English)
柯世堂; 王同光
2015-01-01
A fast method to calculate aero-elastic responses of wind turbine based on a tower-blade coupled structure model was proposed.By taking the 5 MW wind turbine system designed by Nanjing University of Aeronautics and Astronautics as an example,a finite element model for investigating the wind turbine tower-blade coupled vibration was established to obtain the information of its dynamic characteristics.The harmonic superposition method and the modified blade element momentum theory were applied to calculate the aerodynamic load,considering the influence of yaw conditions.The mode superposition method was used to solve the kinetic equation of wind turbine system,the blade velocity and dynamic load were updated through iterative loop,and then the aero-elastic responses of wind turbine system were calculated.The influence of yaw angle on wind-induced responses was discussed.The research contributes a scientific basis to the wind-resistant structure design for the tower-blade system of large-scale wind turbines.%提出一套快速预测偏航状态下风力机全机结构气弹响应的分析方法。以南京航空航天大学自主研发的5MW特大型概念风力机为例，建立风力机塔架－叶片耦合模型获取模态信息；采用谐波叠加法和改进的叶素－动量理论计算气动荷载，并考虑了偏航角对诱导速度的影响；再运用模态叠加法求解风力机耦合动力学方程，通过迭代循环更新叶片速度和气动力，对风力机塔架－叶片耦合结构进行气动载荷和气弹响应计算，并通过参数分析归纳出偏航角和气动弹性对风力机全机动态响应的影响规律。研究结论可为此类特大型风力机塔架－叶片耦合结构的抗风设计提供科学依据。
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.
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...
Non-Linear Aeroelastic Stability of Wind Turbines
DEFF Research Database (Denmark)
Zhang, Zili; Sichani, Mahdi Teimouri; Li, Jie;
2013-01-01
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 trig...
Energy-based Aeroelastic Analysis and Optimisation of Morphing Wings
De Breuker, R.
2011-01-01
Morphing aircraft can change their shape radically when confronted with a variety of conflicting flight conditions throughout their mission. For instance the F-14 Tomcat fighter aircraft, known from the movie Top Gun, was able to sweep its wings from a straight wing configuration to a highly swept v
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.
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)
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 modal dynamics of wind turbines including anisotropic effects
DEFF Research Database (Denmark)
Skjoldan, Peter Fisker
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...
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 ...
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 thi...
Analysis and Flexible Structural Modeling for Oscillating Wing Utilizing Aeroelasticity
Institute of Scientific and Technical Information of China (English)
Shao Ke; Wu Zhigang; Yang Chao
2008-01-01
Making use of modal characteristics of the natural vibration of flexible structure to design the oscillating wing aircraft is proposed.A series of equations concerning the oscillating wing of flexible structures are derived. The kinetic equation for aerodynamic force coupled with elastic movement is set up, and relevant formulae are derived. The unsteady aerodynamic one in that formulae is revised. The design principle, design process and range of application of such oscillating wing analytical method are elaborated. A flexible structural oscillating wing model is set up, and relevant time response analysis and frequency response analysis are conducted. The analytical results indicate that adopting the new-type driving way for the oscillating wing will not have flutter problems and will be able to produce propulsive force. Furthermore, it will consume much less power than the fixed wing for generating the same lift.
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.
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...
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
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
Nonlinear aeroelastic analysis of airfoils: bifurcation and chaos
Lee, B. H. K.; Price, S. J.; Wong, Y. S.
1999-04-01
Different types of structural and aerodynamic nonlinearities commonly encountered in aeronautical engineering are discussed. The equations of motion of a two-dimensional airfoil oscillating in pitch and plunge are derived for a structural nonlinearity using subsonic aerodynamics theory. Three classical nonlinearities, namely, cubic, freeplay and hysteresis are investigated in some detail. The governing equations are reduced to a set of ordinary differential equations suitable for numerical simulations and analytical investigation of the system stability. The onset of Hopf-bifurcation, and amplitudes and frequencies of limit cycle oscillations are investigated, with examples given for a cubic hardening spring. For various geometries of the freeplay, bifurcations and chaos are discussed via the phase plane, Poincaré maps, and Lyapunov spectrum. The route to chaos is investigated from bifurcation diagrams, and for the freeplay nonlinearity it is shown that frequency doubling is the most commonly observed route. Examples of aerodynamic nonlinearities arising from transonic flow and dynamic stall are discussed, and special attention is paid to numerical simulation results for dynamic stall using a time-synthesized method for the unsteady aerodynamics. The assumption of uniform flow is usually not met in practice since perturbations in velocities are encountered in flight. Longitudinal atmospheric turbulence is introduced to show its effect on both the flutter boundary and the onset of Hopf-bifurcation for a cubic restoring force.
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.
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 ...
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...
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...
Pototzky, Anthony S.
2008-01-01
A simple matrix polynomial approach is introduced for approximating unsteady aerodynamics in the s-plane and ultimately, after combining matrix polynomial coefficients with matrices defining the structure, a matrix polynomial of the flutter equations of motion (EOM) is formed. A technique of recasting the matrix-polynomial form of the flutter EOM into a first order form is also presented that can be used to determine the eigenvalues near the origin and everywhere on the complex plane. An aeroservoelastic (ASE) EOM have been generalized to include the gust terms on the right-hand side. The reasons for developing the new matrix polynomial approach are also presented, which are the following: first, the "workhorse" methods such as the NASTRAN flutter analysis lack the capability to consistently find roots near the origin, along the real axis or accurately find roots farther away from the imaginary axis of the complex plane; and, second, the existing s-plane methods, such as the Roger s s-plane approximation method as implemented in ISAC, do not always give suitable fits of some tabular data of the unsteady aerodynamics. A method available in MATLAB is introduced that will accurately fit generalized aerodynamic force (GAF) coefficients in a tabular data form into the coefficients of a matrix polynomial form. The root-locus results from the NASTRAN pknl flutter analysis, the ISAC-Roger's s-plane method and the present matrix polynomial method are presented and compared for accuracy and for the number and locations of roots.
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...
Combined Structural Optimization and Aeroelastic Analysis of a Vertical Axis Wind Turbine
DEFF Research Database (Denmark)
Roscher, Björn; Ferreira, Carlos Simao; Bernhammer, Lars O.;
2015-01-01
Floating offshore wind energy poses challenges on the turbine design. A possible solution is vertical axis wind turbines, which are possibly easier to scale-up and require less components (lower maintenance) and a smaller floating structure than horizontal axis wind turbines. This paper presents...
Weisshaar, T. A.; Schmidt, D. K.
1981-01-01
Several examples are presented in which flutter involving interaction between flight mechanics modes and elastic wind bending occurs for a forward swept wing flight vehicle. These results show the basic mechanism by which the instability occurs and form the basis for attempts to actively control such a vehicle.
DEFF Research Database (Denmark)
Demartino, Cristoforo; Ricciardelli, Francesco; Georgakis, Christos T.
2015-01-01
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 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......, of mechanical damage occurring during transport and installation, as well as of the ageing process due to the exposure to environmental factors. Few experimental works are already available dealing with the effects of imperfections on the aerodynamics of bridge cables. For example, Matteoni and Georgakis...
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...... 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...
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
is to summarize the lessons learned and present results that code developers can compare to. The set of benchmark load cases defined and simulated during the course of this project—the raw data for this paper—is available to the offshore wind turbine simulation community and is already being used for testing...... with the incident waves, sea current, hydrodynamics and foundation dynamics of the support structure. A large set of time series simulation results such as turbine operational characteristics, external conditions, and load and displacement outputs was compared and interpreted. Load cases were defined and run...... to differences in the model fidelity, aerodynamic implementation, hydrodynamic load discretization and numerical difficulties within the codes. The comparisons resulted in a more thorough understanding of the modeling techniques and better knowledge of when various approximations are not valid.More importantly...
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...
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.
Coupling analysis of wind turbine blades based on aeroelastics and aerodynsmics
DEFF Research Database (Denmark)
Wang, Xudong; Chen, Jin; Zhang, Shigiang;
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...
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...
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.
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 ...
Aeroelastic Stability of a 2D Airfoil Section equipped with a Trailing Edge Flap
DEFF Research Database (Denmark)
Bergami, Leonardo
limits of the section. In the investigated case, increased flutter limits are reported when the elastic flap is left without control, whereas, by applying any of the control algorithms, the flutter velocity is reduced. Nevertheless, only in the heave control case the flutter limit becomes critically...... is applied. Stability is investigated for the uncontrolled flap, and for three different control algorithms. The three controls are tuned for fatigue load alleviation and they are based on, respectively, measurement of the heave displacement and velocity, measurement of the local angle of attack, measurement...... close to normal operation flow speeds. Furthermore, a marked dependence of the stability limits on the control gain is also observed and, by tuning the gain parameters, flutter and divergence can be suppressed for flow speed even above the flutter velocity encountered with uncontrolled flap....
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.
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
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.
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.
Chavez, Frank R.; Schmidt, David K.
1993-01-01
With analytic expressions previously developed for the forces and moments acting on a generic hypersonic vehicle, it is of interest to investigate the relative importance of the aerodynamic and propulsive effects on the vehicle dynamics. It is shown that the vehicle's aerodynamics and propulsive forces are both very significant in the evaluation of key stability derivatives which dictate the vehicle's dynamic characteristics. It is also shown that the vehicle model selected is unstable in pitch and exhibits strong airframe/engine/elastic coupling. With the use of literal expressions for both the systems poles and zeros, as well as the stability derivatives, key vehicle dynamic characteristics are investigated. For small errors, or uncertainties, in either the aerodynamic or propulsive forces, significant errors in the frequency and damping of the dominant modes and zero locations will arise.
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....
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.
Friedmann, P.; Silverthorn, L. J.
1974-01-01
Equations for large amplitude coupled flap-lag motion of a hingeless elastic helicopter blade in forward flight are derived. Only a torsionally rigid blade excited by quasi-steady aerodynamic loads is considered. The effects of reversed flow together with some new terms due to radial flow are included. Using Galerkin's method the spatial dependence is eliminated and the equations are linearized about a suitable equilibrium position. The resulting system of homogeneous periodic equations is solved using multivariable Floquet-Liapunov theory, and the transition matrix at the end of the period is evaluated by two separate methods. Computational efficiency of the two numerical methods is compared. Results illustrating the effects of forward flight and various important blade parameters on the stability boundaries are presented.
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
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...
Aeroelastic modelling of a Piezo-solar tensioned energy harvesting ribbon
Chatterjee, Punnag; Bryant, Matthew
2016-04-01
A multifunctional compliant structure is proposed that can harvest electrical power from both incident sunlight and ambient mechanical energy including wind flow or vibration. The proposed energy harvesting device consists of a slender, ribbon-like, flexible thin film solar cell that is laminated with piezoelectric patches at either ends and mounted in the cross flow of wind in a clamped-clamped end condition with an adjustable axial preload. Taking this motivation forward a system model of the energy harvester is developed which captures the structural response of the solar ribbon and couples it with Theodorsen unsteady aerodynamics to predict the flutter boundary conditions as a function of applied axial preload tension. The model also accounts for geometric and material discontinuities, by effective use of Transfer Matrix Method (TMM) modeling technique both in bending and torsional degrees of freedom. This paper also derives TMM technique for torsional vibrations with an applied axial load from first principles, verifies the method and presents its applicability for the proposed energy harvester. The paper also points out that the flutter instability arises out of different structural modes at different values applied axial tension, with the help of a sample modal convergence plot. The analysis also presents the possibility to tune the solar ribbon to operate at an optimal reduced frequency by adjusting the applied axial preload.
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...
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.
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.
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.
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.
Kottapalli, Sesi; Meza, Victor
1992-01-01
A rotorcraft analysis is conducted to assess tilt-rotor stability and conversion loads for the XV-15 rotor with metal blades within its specified test envelope. A 38-DOF flutter analysis based on the code by Johnson (1988) is developed to simulate a wind-tunnel test in which the rotor torque is constant and thereby study stability. The same analytical model provides the simulated loads including hub loads, blade loads, and oscillatory pitch-link loads with attention given to the nonuniform inflow through the proprotor in the presence of the wing. Tilt-rotor stability during the cruise mode is found to be sensitive to coupling effects in the control system stiffness, and a stability problem is identified in the XV-15 Advanced Technology Blades. The present analysis demonstrates that the tilt-rotor is stable within the specified test envelope of the NASA 40 x 80-ft wind tunnel.
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.
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...
DEFF Research Database (Denmark)
Acampora, Antonio; Georgakis, Christos T.; Macdonald, J.H.G.;
2014-01-01
Despite much research in recent years, large amplitude vibrations of inclined cables continue to be of concern for cable-stayed bridges. Various excitation mechanisms have been suggested, including rain-wind excitation, dry inclined cable galloping, high reduced velocity vortex shedding and excit......Despite much research in recent years, large amplitude vibrations of inclined cables continue to be of concern for cable-stayed bridges. Various excitation mechanisms have been suggested, including rain-wind excitation, dry inclined cable galloping, high reduced velocity vortex shedding......-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...... in dry conditions.Finally, static drag coefficients are back-calculated from the full-scale vibration measurements, for first time, with reasonable agreement with direct wind tunnel measurements. The remaining discrepancies are believed to be due to the higher turbulence intensity on site than...
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.
大型风力机气动弹性响应计算研究%Large-scale wind turbine aeroelastic responses analysis
Institute of Scientific and Technical Information of China (English)
吕计男; 刘子强; 赵玲; 冉景洪
2012-01-01
发展了一套快速预测风力机动态响应的分析方法.针对南京航空航天大学设计的兆瓦级大型风力机叶片NH1500,按照工程梁方法对叶片及塔架结构进行简化,生成有限元梁模型.根据动量叶素理论编写气动力程序,为有限元模型提供气动载荷,从而完成时域情况下风力机的响应计算.最后,分析了叶片的几何非线性效应对响应的影响规律.%A fast method to calculate aerodynamic force and response of wind turbine is discussed. The response of blade NH1500 which is designed by Nanjing University of Aeronautics and Astronautics is analyzed. The blades and tower of wind tur-bine are simplified using beam model. The aerodynamic force model based on blade element momentum (BEM) theory is developed. The results of aerodynamic force are applied to the structural model formed using commercial finite element software and the response of wind turbine is simulated in time domain. Finally, the impact of geometry nonlinearity to the blade of wind turbine is discussed.
涡破裂诱导的垂尾抖振气动弹性分析%Aeroelastic analysis of vertical tail buffeting induced by vortex breakdown
Institute of Scientific and Technical Information of China (English)
赵子杰; 高超; 张正科
2016-01-01
通过试验方法分析了三角翼前缘分离涡与垂尾抖振之间的关系,深入研究了尾迹流动对垂尾抖振各阶模态的激励作用.计算得到了垂尾模型固有频率及各阶模态.在风洞试验中,应用激光片光烟流场显示技术,得到了三角翼模型在风速为30 m/s下,各迎角的涡结构;使用加速度传感器测量了垂尾翼根和翼梢的抖振响应;使用热线风速仪测量了垂尾翼根和翼梢位置的脉动速度分量.结果表明:前缘涡破裂后产生的高湍流度的尾迹是垂尾抖振的直接原因,抖振边界与涡破裂的强度和位置有关;涡破裂后尾迹与垂尾产生共振,使得抖振加速度响应频率与垂尾固有频率一致;涡破裂后,在较小迎角下,尾迹对垂尾的高频振动模态的激励较为明显,在较大迎角下,涡破裂流动对垂尾低频振动模态的激励加强了.
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.
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.
DEFF Research Database (Denmark)
Jeong, Min-Soo; Cha, Myung-Chan; Kim, Sang-Woo;
2014-01-01
Modern horizontal axis wind turbine blades are long, slender, and flexible structures that can undergo considerable deformation, leading to blade failures (e.g., blade-tower collision). For this reason, it is important to estimate blade behaviors accurately when designing large-scale wind turbine...
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...
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...
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...
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.
Gillins, R. L.
1976-01-01
A series of wind tunnel studies designed to assess the potential buffet problems resulting from orbiter wake characteristics with its tailcone removed are presented to provide design loads and acceleration environments, and to develop data on buffet sensitivity to various aerodynamic configurations and flight parameters. Data are intended to support subsequent analyses of structural fatigue life, crew efficiency, and equipment vibrations.
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).
DEFF Research Database (Denmark)
Ardila, Oscar Gerardo Castro; Lennie, Matthew; Branner, Kim;
2015-01-01
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...
Blade element momentum modeling of inflow with shear in comparison with advanced model results
DEFF Research Database (Denmark)
Aagaard Madsen, Helge; Riziotis, V.; Zahle, Frederik;
2012-01-01
There seems to be a significant uncertainty in aerodynamic and aeroelastic simulations on megawatt turbines operating in inflow with considerable shear, in particular with the engineering blade element momentum (BEM) model, commonly implemented in the aeroelastic design codes used by industry...
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.
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.
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.
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
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...
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...
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...
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...
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...
Wind tunnel buffet load measuring technique
Chang, C. S.; Ellison, A. M.
1972-01-01
Indirect force measurement technique estimates unsteady forces acting on elastic model during wind tunnel tests. Measurement of forces is practically insensitive to errors in aeroelastic scaling between model and full-scale structure, simplifying design, fabrication and dynamic calibration.
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,...
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.
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...
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.
Flexible Launch Vehicle Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics
Bartels, Robert E.
2012-01-01
Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin can be caused by the aerodynamic undamping one of the lower-frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic line loads derived from steady rigid aerodynamics. However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers, where experiment or unsteady computational aeroelastic analysis show a reduced or even negative aerodynamic damping.Amethod of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics is developed that uses unsteady computational fluid dynamics to compute the response of selected lower-frequency modes. The response is contained in a time history of the vehicle line loads. A proper orthogonal decomposition of the unsteady aerodynamic line-load response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping, and mass matrices. The results are compared with the damping and frequency computed from unsteady computational aeroelasticity and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady computational aeroelastic results.
Institute of Scientific and Technical Information of China (English)
范奎武
2014-01-01
针对带自动控制系统的机动无人飞行器,介绍考虑气动弹性稳定性需求时结构和稳定系统协同设计的求解问题,描述了实现这种设计理念的模型和方法,给出了求解协同设计问题的例子以及保证带自动控制系统的机动无人飞行器气动弹性稳定性的建议.
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.
Algorithm and code development for unsteady three-dimensional Navier-Stokes equations
Obayashi, Shigeru
1994-01-01
Aeroelastic tests require extensive cost and risk. An aeroelastic wind-tunnel experiment is an order of magnitude more expensive than a parallel experiment involving only aerodynamics. By complementing the wind-tunnel experiments with numerical simulations, the overall cost of the development of aircraft can be considerably reduced. In order to accurately compute aeroelastic phenomenon it is necessary to solve the unsteady Euler/Navier-Stokes equations simultaneously with the structural equations of motion. These equations accurately describe the flow phenomena for aeroelastic applications. At ARC a code, ENSAERO, is being developed for computing the unsteady aerodynamics and aeroelasticity of aircraft, and it solves the Euler/Navier-Stokes equations. The purpose of this cooperative agreement was to enhance ENSAERO in both algorithm and geometric capabilities. During the last five years, the algorithms of the code have been enhanced extensively by using high-resolution upwind algorithms and efficient implicit solvers. The zonal capability of the code has been extended from a one-to-one grid interface to a mismatching unsteady zonal interface. The geometric capability of the code has been extended from a single oscillating wing case to a full-span wing-body configuration with oscillating control surfaces. Each time a new capability was added, a proper validation case was simulated, and the capability of the code was demonstrated.
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.
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...... 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...... 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....
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.
Buffet test in the National Transonic Facility
Young, Clarence P., Jr.; Hergert, Dennis W.; Butler, Thomas W.; Herring, Fred M.
1992-01-01
A buffet test of a commercial transport model was accomplished in the National Transonic Facility at the NASA Langley Research Center. This aeroelastic test was unprecedented for this wind tunnel and posed a high risk to the facility. This paper presents the test results from a structural dynamics and aeroelastic response point of view and describes the activities required for the safety analysis and risk assessment. The test was conducted in the same manner as a flutter test and employed onboard dynamic instrumentation, real time dynamic data monitoring, automatic, and manual tunnel interlock systems for protecting the model. The procedures and test techniques employed for this test are expected to serve as the basis for future aeroelastic testing in the National Transonic Facility. This test program was a cooperative effort between the Boeing Commercial Airplane Company and the NASA Langley Research Center.
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
Transonic test of a forward swept wing configuration exhibiting Body Freedom Flutter
Chipman, R.; Rauch, F.; Rimer, M.; Muniz, B.; Ricketts, R. H.
1985-01-01
The aeroelastic dynamic instability designated Body Freedom Flutter (BFF) involves aircraft pitch and wing bending motions characteristic of forward swept wing (FSW) aircraft. Attention is presently given to the results of tests conducted on a 1/2-scale cable-mounted FSW wind tunnel model, with and without relaxed static stability (RSS) control conditions. BFF instability boundaries were found to occur at significantly lower air speeds than those associated with aeroelastic wing divergence on the same model. Servoaeroelastic stability analyses have been conducted which proved capable of predicting the measured onset of BFF, in both the statically stable and RSS configurations tested.
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.
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...
Robinson, J. C.; Yates, E. C., Jr.; Turner, M. J.; Grande, D. L.
1975-01-01
A structural design study of an arrow-wing supersonic cruise aircraft has been made using the integrated design system, ATLAS, and a relatively large analytical finite-element model containing 8500 degrees of freedom. This paper focuses on structural design methods developed and used in support of the study with emphasis on aeroelasticity. The use of ATLAS permitted (1) automatic resizing of the wing structure for multiple load conditions, (2) rapid evaluation of aeroelastic effects, and (3) an iterative approach to the correction of flutter deficiencies. The significant results of the study are discussed along with the advantages derived from the use of an advanced structural design system in preliminary design studies.
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.
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 geome......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...
Yeager, W. T., Jr.; Mantay, W. R.
1983-01-01
A passive means of tailoring helicopter rotor blades to improve performance and reduce loads was evaluated. The parameters investigated were blade torsional stiffness, blade section camber, and distance between blade structural elastic axis and blade tip aerodynamic center. This offset was accomplished by sweeping the tip. The investigation was conducted at advance ratios of 0.20, 0.30, and 0.40. Data are presented without analysis; however, cross referencing of performance data and harmonic loads data may be useful to the analyst for validating aeroelastic theories and design methodologies as well as for evaluating passive aeroelastic tailoring or rotor blade parameters.
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.
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)
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.
Low frequency noise from wind turbines mechanisms of generation and its modelling
DEFF Research Database (Denmark)
Aagaard Madsen, Helge
2010-01-01
and with a rotor diameter of 126 m have now been installed. The numerical investigations comprise the common upwind rotor concept but also the turbines with a downwind rotor are considered. The reason to include the downwind rotor concept is that this turbine design has some advantages which could lead to future...... competitive designs compared with the upwind threebladed rotor. The simulation package comprises an aeroelastic time simulation code HAWC2 and an acoustic low frequency noise (LFN) prediction model. Computed time traces of rotor thrust and rotor torque from the aeroelastic model are input to the acoustic...
Receptance-Based Partial Pole Assignment for Asymmetric Systems Using State-Feedback
Directory of Open Access Journals (Sweden)
M. Ghandchi Tehrani
2012-01-01
Full Text Available Many structures or machines interact with some internal nonconservative forces and present asymmetric systems in which the stiffness and damping matrices are asymmetric. Examples include friction-induced vibration and aeroelastic flutter. Asymmetric systems are prone to flutter instability as a result of the real parts of some poles becoming positive when certain system parameters vary.
Adaptive control algorithm for improving power capture of wind turbines in turbulent winds
DEFF Research Database (Denmark)
Diaz-Guerra, Lluis; Adegas, Fabiano Daher; Stoustrup, Jakob;
2012-01-01
conditions. This paper present new analysis tools and an adaptive control law to increase the energy captured by a wind turbine. Due to its simplicity, it can be easily added to existing industry-standard controllers. The effectiveness of the proposed algorithm is assessed by simulations on a high......-fidelity aeroelastic code....
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.
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...
Coupling and reduction of the HAWC equations
DEFF Research Database (Denmark)
Nim, E.
2001-01-01
This report contains a description of a general method for coupling and reduction of the so-called HAWC equations, which constitute the basis equations of motion of the aeroelastic model HAWC used widely by research institutes and industrial companies formore than the ten years. The principal aim...
Evaluation of RCAS Inflow Models for Wind Turbine Analysis
Energy Technology Data Exchange (ETDEWEB)
Tangler, J.; Bir, G.
2004-02-01
The finite element structural modeling in the Rotorcraft Comprehensive Analysis System (RCAS) provides a state-of-the-art approach to aeroelastic analysis. This, coupled with its ability to model all turbine components, results in a methodology that can simulate complex system interactions characteristic of large wind. In addition, RCAS is uniquely capable of modeling advanced control algorithms and the resulting dynamic responses.
Electrical components library for HAWC2
DEFF Research Database (Denmark)
Cutululis, Nicolaos Antonio; Larsen, Torben J.; Sørensen, Poul Ejnar;
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...
Electrical Components Library for HAWC2
DEFF Research Database (Denmark)
Cutululis, Nicolaos A.; Larsen, Torben J.; Sørensen, Poul;
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...
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
Lumped-Parameter Models for Windturbine Footings on Layered Ground
DEFF Research Database (Denmark)
Andersen, Lars
The design of modern wind turbines is typically based on lifetime analyses using aeroelastic codes. In this regard, the impedance of the foundations must be described accurately without increasing the overall size of the computationalmodel significantly. This may be obtained by the fitting of a l...
Lumped-Parameter Models for Wind-Turbine Footings on Layered Ground
DEFF Research Database (Denmark)
Andersen, Lars; Liingaard, Morten
2007-01-01
The design of modern wind turbines is typically based on lifetime analyses using aeroelastic codes. In this regard, the impedance of the foundations must be described accurately without increasing the overall size of the computational model significantly. This may be obtained by the fitting of a ...
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.
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 ...
Sterenborg, J.J.H.M.
2014-01-01
For wind turbines there is need for accurate fluid-structure interaction predictions due to among others increasing wind turbine blade length and the design of load alleviation systems based on aero-elastic blade deformations, like bend-twist coupling. Currently, engineering models are widely used
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
Structural dynamics branch research and accomplishments to FY 1992
Lawrence, Charles
1992-12-01
This publication contains a collection of fiscal year 1992 research highlights from the Structural Dynamics Branch at NASA LeRC. Highlights from the branch's major work areas--Aeroelasticity, Vibration Control, Dynamic Systems, and Computational Structural Methods are included in the report as well as a listing of the fiscal year 1992 branch publications.
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.
Helicopter Rotor Load Prediction Using a Geometrically Exact Beam with Multicomponent Model
DEFF Research Database (Denmark)
Lee, Hyun-Ku; Viswamurthy, S.R.; Park, Sang Chul;
2010-01-01
In this paper, an accurate structural dynamic analysis was developed for a helicopter rotor system including rotor control components, which was coupled to various aerodynamic and wake models in order to predict an aeroelastic response and the loads acting on the rotor. Its blade analysis was based...
Improving the Dynamics of Suspension Bridges using Active Control Systems
DEFF Research Database (Denmark)
Thoft-Christensen, Palle
Improving the dynamics of suspension bridge using active control is discussed in this paper. The main dynamic problem with long suspension bridges is the aeroelastic phenomenon called flutter. Flutter oscillations of a bridge girder is a stability problem and the oscillations are perpendicular...
Structural Health Monitoring of Transport Aircraft with Fuzzy Logic Modeling
Directory of Open Access Journals (Sweden)
Ray C. Chang
2013-01-01
Full Text Available A structural health monitoring method based on the concept of static aeroelasticity is presented in this paper. This paper focuses on the estimation of these aeroelastic effects on older transport aircraft, in particular the structural components that are most affected, in severe atmospheric turbulence. Because the structural flexibility properties are mostly unknown to aircraft operators, only the trend, not the magnitude, of these effects is estimated. For this purpose, one useful concept in static aeroelastic effects for conventional aircraft structures is that under aeroelastic deformation the aerodynamic center should move aft. This concept is applied in the present paper by using the fuzzy-logic aerodynamic models. A twin-jet transport aircraft in severe atmospheric turbulence involving plunging motion is examined. It is found that the pitching moment derivatives in cruise with moderate to severe turbulence in transonic flight indicate some degree of abnormality in the stabilizer (i.e., the horizontal tail. Therefore, the horizontal tail is the most severely affected structural component of the aircraft probably caused by vibration under the dynamic loads induced by turbulence.
Comparison of computer codes for calculating dynamic loads in wind turbines
Spera, D. A.
1978-01-01
The development of computer codes for calculating dynamic loads in horizontal axis wind turbines was examined, and a brief overview of each code was given. The performance of individual codes was compared against two sets of test data measured on a 100 KW Mod-0 wind turbine. All codes are aeroelastic and include loads which are gravitational, inertial and aerodynamic in origin.
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
of the foundation from a rigorous analysis can be formulated into a so-called lumped-parameter model consisting of a few springs, dashpots and point masses which are easily implemented into aeroelastic codes. In this paper, the quality of consistent lumped-parameter models of rigid surface footings and mono piles...
Tase, M.
2014-01-01
The idea of increasing commercial aircraft’s effi ciency is still an engineering challenge. Increasing efficiency can be achieved through reducing the aircraft’s weight, reducing the aircraft’s drag or other methods. Accounting for more of these objectives in the same aeroelastic optimization has pr
Controller Design Automation for Aeroservoelastic Design Optimization of Wind Turbines
Ashuri, T.; Van Bussel, G.J.W.; Zaayer, M.B.; Van Kuik, G.A.M.
2010-01-01
The purpose of this paper is to integrate the controller design of wind turbines with structure and aerodynamic analysis and use the final product in the design optimization process (DOP) of wind turbines. To do that, the controller design is automated and integrated with an aeroelastic simulation t
Ashuri, T.
2012-01-01
Issues related to environmental concern and fossil fuel exhaustion has made wind energy the most widely accepted renewable energy resource. However, there are still several challenges to be solved such as the integrated design of wind turbines, aeroelastic response and stability prediction, grid int
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.
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...
Rudmin, Daniel
Previous research at RMC has cataloged the occurrence of limit cycle oscillations at low-to-moderate Reynolds numbers for an elastically mounted aeroelastic airfoil. These oscillations were attributed to boundary layer separation and the formation of a laminar separation bubble. For this thesis, an instrumented and motor-driven oscillating airfoil rig was designed and fabricated for the purpose of investigating the boundary layer of a NACA-0012 airfoil. The oscillating airfoil was driven by a servo motor to mimic the observed aeroelastic pitching with a sinusoid of matched amplitude and frequency. Hot-wire anemometry was used to investigate the near wake of the new motor-driven airfoil and compare it with the aeroelastic experiment. A chord-wise array of hot-film sensors captured the boundary layer state during the airfoil pitching oscillation. A novel analysis technique is introduced; A sliding window (in time) cross-correlation of adjacent sensors was used to detect dynamic laminar separation. Wind tunnel tests were performed at static angles-of-attack, for quasi-static very low frequency sweeps to verify the technique, and for selected cases of oscillations obtained with the aeroelastic rig. The new detection method was verified against the existing static techniques of phase reversal signature detection and signal cross-correlation by comparing quasi-static and static results. A map of the laminar separation bubble was produced for fixed angles of attack as well as for the pitching airfoil. The presence of a laminar separation was linked to the occurrence and characteristics of the limit cycle oscillations. Keywords: laminar separation, NACA0012, hot-film, hot-wire, anemometry, transitional flow, aeroelasticity.
DEFF Research Database (Denmark)
Barlas, Thanasis K.; Zahle, Frederik; Sørensen, Niels N.;
2012-01-01
. In this study, a comparison between aerodynamic predictions of the aeroelastic code HAWC2 and the Navier-Stokes code EllipSys3D for the NREL 5MW reference wind turbine rotor in a stiff configuration equipped with a deformable trailing edge flap is performed. A case where the half rotor plane experiences......Various research projects have focused on active aerodynamic load control of wind turbines using control devices on the blades, for example flaps. The aerodynamic load predictions of utilized aeroelastic codes have not yet been fully validated with full rotor CFD or experimental results...... an inflow resembling the wake from an upstream wind turbine is investigated, which is appropriate for comparing the predictions of the two codes related to the abrupt aerodynamic response and the influence of the controllable flap. The trailing edge flap is actuated to alleviate the added loads from a non...
Development of an integrated aeroservoelastic analysis program and correlation with test data
Gupta, K. K.; Brenner, M. J.; Voelker, L. S.
1991-01-01
The details and results are presented of the general-purpose finite element STructural Analysis RoutineS (STARS) to perform a complete linear aeroelastic and aeroservoelastic analysis. The earlier version of the STARS computer program enabled effective finite element modeling as well as static, vibration, buckling, and dynamic response of damped and undamped systems, including those with pre-stressed and spinning structures. Additions to the STARS program include aeroelastic modeling for flutter and divergence solutions, and hybrid control system augmentation for aeroservoelastic analysis. Numerical results of the X-29A aircraft pertaining to vibration, flutter-divergence, and open- and closed-loop aeroservoelastic controls analysis are compared to ground vibration, wind-tunnel, and flight-test results. The open- and closed-loop aeroservoelastic control analyses are based on a hybrid formulation representing the interaction of structural, aerodynamic, and flight-control dynamics.
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.
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...
Wind-tunnel experiments on divergence of forward-swept wings
Ricketts, R. H.; Doggett, R. V., Jr.
1980-01-01
An experimental study to investigate the aeroelastic behavior of forward-swept wings was conducted in the Langley Transonic Dynamics Tunnel. Seven flat-plate models with varying aspect ratios and wing sweep angles were tested at low speeds in air. Three models having the same planform but different airfoil sections (i.e., flat-plate, conventional, and supercritical) were tested at transonic speeds in Freon 12. Linear analyses were performed to provide predictions to compare with the measured aeroelastic instabilities which include both static divergence and flutter. Six subcritical response testing techniques were formulated and evaluated at transonic speeds for accuracy in predicting static divergence. Two "divergence stoppers" were developed and evaluated for use in protecting the model from structural damage during tests.
Do Lumped-Parameter Models Provide the Correct Geometrical Damping?
DEFF Research Database (Denmark)
Andersen, Lars
This paper concerns the formulation of lumped-parameter models for rigid footings on homogenous or stratified soil. Such models only contain a few degrees of freedom, which makes them ideal for inclusion in aero-elastic codes for wind turbines and other models applied to fast evaluation of struct......This paper concerns the formulation of lumped-parameter models for rigid footings on homogenous or stratified soil. Such models only contain a few degrees of freedom, which makes them ideal for inclusion in aero-elastic codes for wind turbines and other models applied to fast evaluation...... response during excitation and the geometrical damping related to free vibrations of a hexagonal footing. The optimal order of a lumped-parameter model is determined for each degree of freedom, i.e. horizontal and vertical translation as well as torsion and rocking. In particular, the necessity of coupling...... between horizontal sliding and rocking is discussed....
A stochastic model for the simulation of wind turbine blades in static stall
DEFF Research Database (Denmark)
Bertagnolio, Franck; Rasmussen, Flemming; Sørensen, Niels N.;
2010-01-01
The aim of this work is to improve aeroelastic simulation codes by accounting for the unsteady aerodynamic forces that a blade experiences in static stall. A model based on a spectral representation of the aerodynamic lift force is defined. The drag and pitching moment are derived using a conditi......The aim of this work is to improve aeroelastic simulation codes by accounting for the unsteady aerodynamic forces that a blade experiences in static stall. A model based on a spectral representation of the aerodynamic lift force is defined. The drag and pitching moment are derived using...... a conditional simulation technique for stochastic processes. The input data for the model can be collected either from measurements or from numerical results from a Computational Fluid Dynamics code for airfoil sections at constant angles of attack. An analysis of such data is provided, which helps to determine...
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
A nonlinear POD reduced order model for limit cycle oscillation prediction
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
As the amplitude of the unsteady flow oscillation is large or large changes occur in the mean background flow such as limit cycle oscillation,the traditional proper orthogonal decomposition reduced order model based on linearized time or frequency domain small disturbance solvers can not capture the main nonlinear features.A new nonlinear reduced order model based on the dynamically nonlinear flow equation was investigated.The nonlinear second order snapshot equation in the time domain for proper orthogonal decomposition basis construction was obtained from the Taylor series expansion of the flow solver.The NLR 7301 airfoil configuration and Goland+ wing/store aeroelastic model were used to validate the capability and efficiency of the new nonlinear reduced order model.The simulation results indicate that the proposed new reduced order model can capture the limit cycle oscillation of aeroelastic system very well,while the traditional proper orthogonal decomposition reduced order model will lose effectiveness.
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...
Shape Optimization of Wind Turbine Blades
DEFF Research Database (Denmark)
Wang, Xudong; Shen, Wen Zhong; Zhu, Wei Jun;
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 code employs 11 basic degrees of freedom corresponding to I I elastic structural equations. In the BEM theory, a refined tip loss correction model is used. The objective of the optimization model is to minimize the cost of energy which is calculated from the annual energy production and the cost...... 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 MEXICO 25 k...
DEFF Research Database (Denmark)
Damgaard, Mads; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2014-01-01
The formulation and quality of a computationally efficient model of offshore wind turbine surface foundations is examined. The aim is to establish a model, workable in the frequency and time domain, that can be applied in aeroelastic codes for fast and reliable evaluation of the dynamic structural...... or rotation of the foundation is necessary in order to obtain an accurate prediction of the foundation response in the frequency and time domain. In addition, the required static bearing capacity of surface foundations leads to fore-aft vibrations during normal operation of a wind turbine that are insensitive...... of a 5.0 MW offshore wind turbine is evaluated for different stratifications, environmental conditions and foundation geometries by the aeroelastic nonlinear multi-body code HAWC2. Analyses show that a consistent lumped-parameter model with three to five internal degrees of freedom per displacement...
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.
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.
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......, the 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 modeling can have a large influence on the vibration level. The edgewise vibrations are less visible in high turbulent conditions. Using simulations with low-level turbulence intensity will ease this identification and could avoid a redesign. Furthermore, depending on the external excitation, different...
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....... The 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...... vorticity. Including this influence results in a slightly increased safety margin against classical flutter in all simulated cases....
A Two-Bladed Concept Wind Turbine
DEFF Research Database (Denmark)
Kim, Taeseong
2012-01-01
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....
Development of a Fast Fluid-Structure Coupling Technique for Wind Turbine Computations
Sessarego, Matias; Ramos García, Néstor; Shen, Wen Zhong
2015-01-01
Fluid-structure interaction simulations are routinely used in the wind energy industry to evaluate the aerodynamic and structural dynamic performance of wind turbines. Most aero-elastic codes in modern times implement a blade element momentum technique to model the rotor aerodynamics and a modal, multi-body, or finite-element approach to model the turbine structural dynamics. The present paper describes a novel fluid-structure coupling technique which combines a threedimensional viscous-invis...
Full-scale measurements of aerodynamic induction in a rotor plane
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 the rotor plane of an operating 2MW/80m wind turbine to perform detailed analysis the aerodynamic induction. The experimental setup, analyses of the spatial structure of the aerodynamic induction and ...
Effect of wing flexibility on aircraft flight dynamics
Qiao, Yuqing
2012-01-01
The purpose of this thesis is to give a preliminary investigation into the effect of wing deformation on flight dynamics. The candidate vehicle is FW-11 which is a flying wing configuration aircraft with high altitude and long endurance characteristics. The aeroelastic effect may be significant for this type of configuration. Two cases, the effect of flexible wing on lift distribution and on roll effectiveness during the cruise condition with different inertial parameters are investigated. ...
EBF3GLWingOpt: A Framework for Multidisciplinary Design Optimization of Wings Using SpaRibs
Liu, Qiang
2014-01-01
A global/local framework for multidisciplinary optimization of generalized aircraft wing structure has been developed. The concept of curvilinear stiffening members (spars, ribs and stiffeners) has been applied in the optimization of a wing structure. A global wing optimization framework EBF3WingOpt, which integrates the static aeroelastic, flutter and buckling analysis, has been implemented for exploiting the optimal design at the wing level. The wing internal structure is optimized using cu...
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...
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 ...
Computation of UH-60A Airloads Using CFD/CSD Coupling on Unstructured Meshes
Biedron, Robert T.; Lee-Rausch, Elizabeth M.
2011-01-01
An unsteady Reynolds-averaged Navier-Stokes solver for unstructured grids is used to compute the rotor airloads on the UH-60A helicopter at high-speed and high thrust conditions. The flow solver is coupled to a rotorcraft comprehensive code in order to account for trim and aeroelastic deflections. Simulations are performed both with and without the fuselage, and the effects of grid resolution, temporal resolution and turbulence model are examined. Computed airloads are compared to flight data.
Renewable Energy Essentials: Wind
Energy Technology Data Exchange (ETDEWEB)
NONE
2008-07-01
Subjects for further research, specific to wind energy technology, include more refined resource assessment; materials with higher strength to mass ratios; advanced grid integration and power quality and control technologies; standardisation and certification; development of low-wind regime turbines; improved forecasting; increased fatigue resistance of major components such as gearboxes; better models for aerodynamics and aeroelasticity; generators based on superconductor technology; deep-offshore foundations; and high-altitude 'kite' concepts.
Sanz Luengo, Antonio
2014-01-01
The general trend of efficiency increase, weight and noise reduction has derived in the design of more slender, loaded, and 3D shaped blades. This has a significant impact on the stability of fan, and low pressure turbine blades, which are more prone to aeroelastic phenomena such as flutter. The flutter phenomenon is a self-excited, self-sustained unstable vibration produced by the interaction of flow and structure. These working conditions will induce either blade overload, or High Cycle Fat...
Yang Ning; Wang Nan; Zhang Xin; Liu Wei
2016-01-01
The flutter characteristics of folding control fins with freeplay are investigated by numerical simulation and flutter wind tunnel tests. Based on the characteristics of the structures, fins with different freeplay angles are designed. For a 0° angle of attack, wind tunnel tests of these fins are conducted, and vibration is observed by accelerometers and a high-speed camera. By the expansion of the connected relationships, the governing equations of fit for the nonlinear aeroelastic analysis ...
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.
Silva, Walter A.
1993-01-01
The presentation begins with a brief description of the motivation and approach that has been taken for this research. This will be followed by a description of the Volterra Theory of Nonlinear Systems and the CAP-TSD code which is an aeroelastic, transonic CFD (Computational Fluid Dynamics) code. The application of the Volterra theory to a CFD model and, more specifically, to a CAP-TSD model of a rectangular wing with a NACA 0012 airfoil section will be presented.
Flutter behaviour of composite aircraft wings
Ashawesh, Gamal Mohamed
1999-01-01
This research work presents series of investigations into the structural dynamics and dynamic aeroelastic (flutter) behaviour of composite and metal wings. The study begins with a literature review where the development and an over view of the previous investigations in this field are presented. Static stiffness is very important to any type of analysis, especially in both dynamic and flutter analysis as in this case. Therefore, different methods are presented and used for the ...
Pritchard, Jocelyn I.; Adelman, Howard M.; Mantay, Wayne R.
1989-01-01
The rotor dynamic design considerations are essentially limitations on the vibratory response of the blades which in turn limit the dynamic excitation of the fuselage by forces and moments transmitted to the hub. Quantities which are associated with the blade response and which are subject to design constraints are discussed. These include blade frequencies, vertical and inplane hub shear, rolling and pitching moments, and aeroelastic stability margin.
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.
Institute of Scientific and Technical Information of China (English)
LIU Jian-min
2008-01-01
In this article, the mathematical model of the coupling of the three-dimensional fluid flow and the large deformation of membrane structure is established. The fluid-structure coupling interaction is simulated using the computational codes developed by the authors. By analyzing the interactions of membrane and flow field, the aeroelasticity of the airship is detailed. All the results are adopted in the focused study of the stratosphere airship in trimmed state.
A soft rotor concept - design, verification and potentials
Energy Technology Data Exchange (ETDEWEB)
Rasmussen, F.; Thirstrup Petersen, J. [Risoe National Lab., Roskilde (Denmark)
1999-03-01
This paper contains results from development and testing of a two-bladed soft rotor for an existing 15 kW flexible wind turbine. The new concept is characterised as a free yawing down wind turbine with nacelle tilting flexibility and a two-bladed teetering rotor with three-point supported flexible blades with built-in structural couplings. The power and the loads are controlled by active stall and active coning. The concept has been developed by extensive application of aero-elastic predictions, numerical optimisation and stability analysis in order to obtain optimal aero-elastic response and minimal loads. The flexible blades and the principle of active coning allow the blades to deflect with the wind to such an extent that the loads are reduced to between 25 and 50% of the loads for a similar rigid rotor. All conceptual design principles have been focused on application to large MW turbines, and aero-elastic predictions for an upscale 1 MW version show that this would have approximately identical characteristisc, without being particularly optimised for the actual size. (au)
Robust fault-tolerant control for wing flutter under actuator failure
Institute of Scientific and Technical Information of China (English)
Gao Mingzhou; Cai Guoping
2016-01-01
Many control laws, such as optimal controller and classical controller, have seen their applications to suppressing the aeroelastic vibrations of the aeroelastic system. However, those con-trol laws may not work effectively if the aeroelastic system involves actuator faults. In the current study for wing flutter of reentry vehicle, the effect of actuator faults on wing flutter system is rarely considered and few of the fault-tolerant control problems are taken into account. In this paper, we use the radial basis function neural network and the finite-time H∞adaptive fault-tolerant control technique to deal with the flutter problem of wings, which is affected by actuator faults, actuator saturation, parameter uncertainties and external disturbances. The theory of this article includes the modeling of wing flutter and fault-tolerant controller design. The stability of the finite-time adaptive fault-tolerant controller is theoretically proved. Simulation results indicate that the designed fault-tolerant flutter controller can effectively deal with the faults in the flutter system and can promptly suppress the wing flutter as well.
Aeroservoelastic Pitch Control of Stall-Induced Flap/Lag Flutter of Wind Turbine Blade Section
Directory of Open Access Journals (Sweden)
Tingrui Liu
2015-01-01
Full Text Available 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 structural model and an unsteady nonlinear aerodynamic model. The nonlinear resulting equations are linearized by small perturbation about the equilibrium point. The instability characteristics of stall-induced flap/lag flutter are investigated. Pitch actuator is described by a second-order model. The aeroservoelastic control is analyzed by three types of optimal PID controllers, two types of fuzzy PID controllers, and neural network PID controllers. The fuzzy controllers are developed based on Sugeno model and intuition method with good results achieved. A single neuron PID control strategy with improved Hebb learning algorithm and a radial basic function neural network PID algorithm are applied and performed well in the range of extreme wind speeds.
Energy Technology Data Exchange (ETDEWEB)
Dana, S.; Damiani, R.; vanDam, J.
2015-05-18
As part of an ongoing effort to improve the modeling and prediction of small wind turbine dynamics, NREL tested a small horizontal axis wind turbine in the field at the National Wind Technology Center (NWTC). The test turbine was a 2.1-kW downwind machine mounted on an 18-meter multi-section fiberglass composite tower. The tower was instrumented and monitored for approximately 6 months. The collected data were analyzed to assess the turbine and tower loads and further validate the simplified loads equations from the International Electrotechnical Commission (IEC) 61400-2 design standards. Field-measured loads were also compared to the output of an aeroelastic model of the turbine. Ultimate loads at the tower base were assessed using both the simplified design equations and the aeroelastic model output. The simplified design equations in IEC 61400-2 do not accurately model fatigue loads. In this project, we compared fatigue loads as measured in the field, as predicted by the aeroelastic model, and as calculated using the simplified design equations.
Dynamic Gust Load Analysis for Rotors
Directory of Open Access Journals (Sweden)
Yuting Dai
2016-01-01
Full Text Available Dynamic load of helicopter rotors due to gust directly affects the structural stress and flight performance for helicopters. Based on a large deflection beam theory, an aeroelastic model for isolated helicopter rotors in the time domain is constructed. The dynamic response and structural load for a rotor under the impulse gust and slope-shape gust are calculated, respectively. First, a nonlinear Euler beam model with 36 degrees-of-freedoms per element is applied to depict the structural dynamics for an isolated rotor. The generalized dynamic wake model and Leishman-Beddoes dynamic stall model are applied to calculate the nonlinear unsteady aerodynamic forces on rotors. Then, we transformed the differential aeroelastic governing equation to an algebraic one. Hence, the widely used Newton-Raphson iteration algorithm is employed to simulate the dynamic gust load. An isolated helicopter rotor with four blades is studied to validate the structural model and the aeroelastic model. The modal frequencies based on the Euler beam model agree well with published ones by CAMRAD. The flap deflection due to impulse gust with the speed of 2m/s increases twice to the one without gust. In this numerical example, results indicate that the bending moment at the blade root is alleviated due to elastic effect.
Simulation of tail buffet using delta wing-vertical tail configuration
Kandil, Osama A.; Kandil, Hamdy A.; Massey, Steven J.
1993-01-01
Computational simulation of the vertical tail buffet problem is accomplished using a delta wing-vertical tail configuration. Flow conditions are selected such that the wing primary-vortex cores experience vortex breakdown and the resulting flow interacts with the vertical tail. This multidisciplinary problem is solved successively using three sets of equations for the fluid flow, aeroelastic deflections and grid displacements. For the fluid dynamics part, the unsteady, compressible, full Navier-Stokes equations are solved accurately in time using an implicit, upwind, flux-difference splitting, finite-volume scheme. For the aeroelastic part, the aeroelastic equation for bending vibrations is solved accurately in time using the Galerkin method and the four-stage Runge-Kutta scheme. The grid for the fluid dynamics computations is updated every few time steps using a third set of interpolation equations. The computational application includes a delta wing of aspect ratio 1 and a rectangular vertical tail of aspect ratio 2, which is placed at 0.5 root-chord length downstream of the wing trailing edge. The wing angle of attack is 35 deg and the flow Mach number and Reynolds number are 0.4 and 10,000, respectively.
Robust fault-tolerant control for wing flutter under actuator failure
Directory of Open Access Journals (Sweden)
Gao Mingzhou
2016-08-01
Full Text Available Many control laws, such as optimal controller and classical controller, have seen their applications to suppressing the aeroelastic vibrations of the aeroelastic system. However, those control laws may not work effectively if the aeroelastic system involves actuator faults. In the current study for wing flutter of reentry vehicle, the effect of actuator faults on wing flutter system is rarely considered and few of the fault-tolerant control problems are taken into account. In this paper, we use the radial basis function neural network and the finite-time H∞ adaptive fault-tolerant control technique to deal with the flutter problem of wings, which is affected by actuator faults, actuator saturation, parameter uncertainties and external disturbances. The theory of this article includes the modeling of wing flutter and fault-tolerant controller design. The stability of the finite-time adaptive fault-tolerant controller is theoretically proved. Simulation results indicate that the designed fault-tolerant flutter controller can effectively deal with the faults in the flutter system and can promptly suppress the wing flutter as well.
Design, realization and structural testing of a compliant adaptable wing
Molinari, G.; Quack, M.; Arrieta, A. F.; Morari, M.; Ermanni, P.
2015-10-01
This paper presents the design, optimization, realization and testing of a novel wing morphing concept, based on distributed compliance structures, and actuated by piezoelectric elements. The adaptive wing features ribs with a selectively compliant inner structure, numerically optimized to achieve aerodynamically efficient shape changes while simultaneously withstanding aeroelastic loads. The static and dynamic aeroelastic behavior of the wing, and the effect of activating the actuators, is assessed by means of coupled 3D aerodynamic and structural simulations. To demonstrate the capabilities of the proposed morphing concept and optimization procedure, the wings of a model airplane are designed and manufactured according to the presented approach. The goal is to replace conventional ailerons, thus to achieve controllability in roll purely by morphing. The mechanical properties of the manufactured components are characterized experimentally, and used to create a refined and correlated finite element model. The overall stiffness, strength, and actuation capabilities are experimentally tested and successfully compared with the numerical prediction. To counteract the nonlinear hysteretic behavior of the piezoelectric actuators, a closed-loop controller is implemented, and its capability of accurately achieving the desired shape adaptation is evaluated experimentally. Using the correlated finite element model, the aeroelastic behavior of the manufactured wing is simulated, showing that the morphing concept can provide sufficient roll authority to allow controllability of the flight. The additional degrees of freedom offered by morphing can be also used to vary the plane lift coefficient, similarly to conventional flaps. The efficiency improvements offered by this technique are evaluated numerically, and compared to the performance of a rigid wing.
International Nuclear Information System (INIS)
To study the effects of curtailment on both power production and fatigue loading, actuator disc (ACD) simulations of two turbines aligned in the wind direction are performed with the EllipSys3D code developed at DTU/Risø. A simple non-aeroelastic fatigue load evaluation method for ACD simulations is developed. Blade loads, extracted along a line that rotates in the rotor plane with the rotational velocity of the respective turbine, are used to calculate flapwise bending moments. After applying a rainflow counting algorithm an equivalent moment is calculated. Power curtailment is introduced by increasing the blade pitch angle of the first turbine. Evaluation is made with regards to fatigue load reduction at the second turbine and the change in the total production. Further parameters investigated are the spacing between the two turbines and the level of imposed pre-generated turbulence. The aeroelastic code Vidyn, Ganander [1], is used for validation of the ACD load evaluation method. For this purpose, the EllipSys3D simulations are rerun without the second turbine. Time series of cross sectional velocity fields are extracted at positions corresponding to the former placement of the downstream turbine and used as input for aeroelastic turbine load calculations in Vidyn. The results from Vidyn and the results based on the ACD loads show similar trends. Fatigue loads at the downwind turbine are clearly decreasing as the blade pitch angle of the upstream turbine is increasing. The achievable amount of fatigue load reduction depends on the level of the imposed pre-generated turbulence as well as the spacing between the turbines. The presented method is intended for further development of wind park optimization strategies
Numerical study on the correlation of transonic single-degree-of-freedom flutter and buffet
Gao, ChuanQiang; Zhang, WeiWei; Liu, YiLang; Ye, ZhengYin; Jiang, YueWen
2015-08-01
Transonic single-degree-of-freedom (SDOF) flutter and transonic buffet are the typical and complex aeroelastic phenomena in the transonic flow. In this study, transonic aeroelastic issues of an elastic airfoil are investigated using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. The airfoil is free to vibrate in SDOF of pitching. It is found that, the coupling system may be unstable and SDOF self-excited pitching oscillations occur in pre-buffet flow condition, where the free-stream angle of attack (AOA) is lower than the buffet onset of a stationary airfoil. In the theory of classical aeroelasticity, this unstable phenomenon is defined as flutter. However, this transonic SDOF flutter is closely related to transonic buffet (unstable aerodynamic models) due to the following reasons. Firstly, the SDOF flutter occurs only when the free-stream AOA of the spring suspended airfoil is slightly lower than that of buffet onset, and the ratio of the structural characteristic frequency to the buffet frequency is within a limited range. Secondly, the response characteristics show a high correlation between the SDOF flutter and buffet. A similar "lock-in" phenomenon exists, when the coupling frequency follows the structural characteristic frequency. Finally, there is no sudden change of the response characteristics in the vicinity of buffet onset, that is, the curve of response amplitude with the free-stream AOA is nearly smooth. Therefore, transonic SDOF flutter is often interwoven with transonic buffet and shows some complex characteristics of response, which is different from the traditional flutter.
Issac, Jason Cherian ses in transonic flow
Issac, Jason Cherion; Kapania, Rakesh K.
1993-01-01
Flutter analysis of a two degree of freedom airfoil in compressible flow is performed using a state-space representation of the unsteady aerodynamic behavior. Indicial response functions are used to represent the normal force and moment response of the airfoil. The structural equations of motion of the airfoil with bending and torsional degrees of freedom are coupled to the unsteady air loads and the aeroelastic system so modelled is solved as an eigenvalue problem to determine the stability. The aeroelastic equations are also directly integrated with respect to time and the time-domain results compared with the results from the eigenanalysis. A good agreement is obtained. The derivatives of the flutter speed obtained from the eigenanalysis are calculated with respect to the mass and stiffness parameters by both analytical and finite-difference methods for various transonic Mach numbers. The experience gained from the two degree of freedom model is applied to study the sensitivity of the flutter response of a wing with respect to various shape parameters. The parameters being considered are as follows: (1) aspect ratio; (2) surface area of the wing; (3) taper ratio; and (4) sweep. The wing deflections are represented by Chebyshev polynomials. The compressible aerodynamic state-space model used for the airfoil section is extended to represent the unsteady aerodynamic forces on a generally laminated tapered skewed wing. The aeroelastic equations are solved as an eigenvalue problem to determine the flutter speed of the wing. The derivatives of the flutter speed with respect to the shape parameters are calculated by both analytical and finite difference methods.
Validation of Design and Analysis Techniques of Tailored Composite Structures
Jegley, Dawn C. (Technical Monitor); Wijayratne, Dulnath D.
2004-01-01
Aeroelasticity is the relationship between the elasticity of an aircraft structure and its aerodynamics. This relationship can cause instabilities such as flutter in a wing. Engineers have long studied aeroelasticity to ensure such instabilities do not become a problem within normal operating conditions. In recent decades structural tailoring has been used to take advantage of aeroelasticity. It is possible to tailor an aircraft structure to respond favorably to multiple different flight regimes such as takeoff, landing, cruise, 2-g pull up, etc. Structures can be designed so that these responses provide an aerodynamic advantage. This research investigates the ability to design and analyze tailored structures made from filamentary composites. Specifically the accuracy of tailored composite analysis must be verified if this design technique is to become feasible. To pursue this idea, a validation experiment has been performed on a small-scale filamentary composite wing box. The box is tailored such that its cover panels induce a global bend-twist coupling under an applied load. Two types of analysis were chosen for the experiment. The first is a closed form analysis based on a theoretical model of a single cell tailored box beam and the second is a finite element analysis. The predicted results are compared with the measured data to validate the analyses. The comparison of results show that the finite element analysis is capable of predicting displacements and strains to within 10% on the small-scale structure. The closed form code is consistently able to predict the wing box bending to 25% of the measured value. This error is expected due to simplifying assumptions in the closed form analysis. Differences between the closed form code representation and the wing box specimen caused large errors in the twist prediction. The closed form analysis prediction of twist has not been validated from this test.
Estimation of Nonconservative Aerodynamic Pressure Leading to Flutter of Spinning Disks
DEFF Research Database (Denmark)
Hansen, Morten Hartvig; Raman, A; Mote Jr., C.D.
2001-01-01
An experimental method for predicting the onset of #utter of a disk spinning in a #uid medium is proposed. The method is based on a description of the aerodynamic loading on the disk as a distributed viscous damping force rotating relative to the disk. This model can arise from two aeroelastic...... theories described herein. It is shown analytically and experimentally that the few parameters of this model may be extracted from frequency response functions of the spinning disk. Parameters for a steel disk in air (with a near vacuum experiment as reference) are estimated at increasing rotation speeds...
Experimental analysis of energy harvesting from self-induced flutter of a composite beam
Energy Technology Data Exchange (ETDEWEB)
Zakaria, Mohamed Y., E-mail: zakaria@vt.edu; Al-Haik, Mohammad Y.; Hajj, Muhammad R. [Virginia Tech, Norris Hall, Blacksburg, Virginia 24061 (United States)
2015-07-13
Previous attempts to harvest energy from aeroelastic vibrations have been based on attaching a beam to a moving wing or structure. Here, we exploit self-excited oscillations of a fluttering composite beam to harvest energy using piezoelectric transduction. Details of the beam properties and experimental setup are presented. The effects of preset angle of attack, wind speed, and load resistance on the levels of harvested power are determined. The results point to a complex relation between the aerodynamic loading and its impact on the static deflection and amplitudes of the limit cycle oscillations on one hand and the load resistance and level of power harvested on the other hand.
Innovative configurations for long-span suspension bridges
Bartoli, G.; P. D’Asdia; S. Febo; C. Mannini; S. Noè; L. Procino
2009-01-01
This paper reports the results of a piece of research about long-span suspension bridges with multiple-box girder steel deck characterized by low drag coefficient and high aeroelastic stability. For this type of bridges, by increasing the span length, the contribution to the stiffness of the suspension cables becomes dominant with respect to that of the deck, so that the ratio of the frequency of the first torsional mode to the frequency of the first vertical bending mode approaches unity, wh...
Numerical study of the static and pitching RISØ-B1-18 airfoil
DEFF Research Database (Denmark)
Bertagnolio, Franck
2004-01-01
The objective of this report is the better understanding of the physics of the aeroelastic motion of wind turbine blades in order to improve the numerical models used for their design. In this study, the case of the RISØ-B1-18 airfoil which was equippedand measured in an open jet wind tunnel...... is studied. Two and three dimensional Navier-Stokes calculations using the k-w SST and Detached Eddy Simulation turbulence models are conducted. An engineering semi-empirical dynamic stall model is also used forperforming calculations. Computational results are compared to the experimental results...
Analysis of tiltrotor whirl flutter in time and frequency domain
DEFF Research Database (Denmark)
Kim, Taeseong; Shin, SanJoon; Kim, Taehyoun
2009-01-01
The whirl flutter phenomenon in a rotor is induced by in-plane hub forces, and imposes a serious limit on the forward speed. In this paper, based on Greenberg’s model, quasi-steady and unsteady aerodynamic forces are formulated to examine the whirl flutter stability for a three-bladed rotor without...... and the swashplate geometric control coupling upon the flutter boundary are investigated. An optimum pitch-flap coupling parameter is discovered through the parametric study. Aeroelastic stability boundaries are estimated with the three different aerodynamic models. It is found that the analysis with the full...... unsteady aerodynamics predicts the highest flutter speed....
Full-scale measurements of aerodynamic induction in a rotor plane
Larsen, Gunner Chr; Hansen, Kurt S.
2014-12-01
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 the rotor plane of an operating 2MW/80m wind turbine to perform detailed analysis the aerodynamic induction. The experimental setup, analyses of the spatial structure of the aerodynamic induction and subsequent comparisons with numerical predictions, using the HAWC2 aerolastic code, are presented.
Full-scale measurements of aerodynamic induction in a rotor plane
DEFF Research Database (Denmark)
Larsen, Gunner Chr.; Hansen, Kurt Schaldemose
2014-01-01
in the rotor plane of an operating 2MW/80m wind turbine to perform detailed analysis the aerodynamic induction. The experimental setup, analyses of the spatial structure of the aerodynamic induction and subsequent comparisons with numerical predictions, using the HAWC2 aerolastic code, are presented.......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...
On Usage of Pareto curves to Select Wind Turbine Controller Tunings to the Wind Turbulence Level
DEFF Research Database (Denmark)
Odgaard, Peter Fogh
2015-01-01
Model predictive control has in recently publications shown its potential for lowering of cost of energy of modern wind turbines. Pareto curves can be used to evaluate performance of these controllers with multiple conflicting objectives of power and fatigue loads. In this paper an approach...... to update an model predictive wind turbine controller tuning as the wind turbulence increases, as increased turbulence levels results in higher loads for the same controller tuning. In this paper the Pareto curves are computed using an industrial high fidelity aero-elastic model. Simulations show...
Eliminating flutter for clamped von Karman plates immersed in subsonic flows
Lasiecka, Irena; Webster, Justin T.
2014-01-01
We address the long-time behavior of a non-rotational von Karman plate in an inviscid potential flow. The model arises in aeroelasticity and models the interaction between a thin, nonlinear panel and a flow of gas in which it is immersed [6, 21, 23]. Recent results in [16, 18] show that the plate component of the dynamics (in the presence of a physical plate nonlinearity) converge to a global compact attracting set of finite dimension; these results were obtained in the absence of mechanical ...
Lumped-parameter Model of a Bucket Foundation
DEFF Research Database (Denmark)
Andersen, Lars; Ibsen, Lars Bo; Liingaard, Morten
2009-01-01
efficient model that can be applied in aero-elastic codes for fast evaluation of the dynamic structural response of wind turbines. The target solutions, utilised for calibration of the lumped-parameter models, are obtained by a coupled finite-element/boundaryelement scheme in the frequency domain......, and the quality of the models are tested in the time and frequency domains. It is found that precise results are achieved by lumped-parameter models with two to four internal degrees of freedom per displacement or rotation of the foundation. Further, coupling between the horizontal sliding and rocking cannot...
Optimization of blade arrangement in a randomly mistuned cascade using simulated annealing
Thompson, Edward A.; Becus, Georges A.
1993-01-01
This paper presents preliminary results of an investigation on mistuning of bladed-disk assemblies aimed at capturing the benefits of mistuning on stability, while at the same time, minimizing the adverse effects on response by solving the following problem: given a set of N turbine blades, each being a small random perturbation of the same nominal blade, determine the best arrangement of the N blades in a mistuned cascade with regard to aeroelastic response. In the studies reported here, mistuning of the blades is restricted to small differences in torsional stiffness. The large combinatorial optimization problem of seeking the best arrangement by blade exchanges is solved using a simulated annealing algorithm.
Fuzzy Model-based Pitch Stabilization and Wing Vibration Suppression of Flexible Wing Aircraft.
Ayoubi, Mohammad A.; Swei, Sean Shan-Min; Nguyen, Nhan T.
2014-01-01
This paper presents a fuzzy nonlinear controller to regulate the longitudinal dynamics of an aircraft and suppress the bending and torsional vibrations of its flexible wings. The fuzzy controller utilizes full-state feedback with input constraint. First, the Takagi-Sugeno fuzzy linear model is developed which approximates the coupled aeroelastic aircraft model. Then, based on the fuzzy linear model, a fuzzy controller is developed to utilize a full-state feedback and stabilize the system while it satisfies the control input constraint. Linear matrix inequality (LMI) techniques are employed to solve the fuzzy control problem. Finally, the performance of the proposed controller is demonstrated on the NASA Generic Transport Model (GTM).
Monaghan, R. C.
1981-01-01
The aeroelastically tailored outer wing and canard of the highly maneuverable aircraft technology (HiMAT) vehicle are closely examined and a general description of the overall structure of the vehicle is provided. Test data in the form of laboratory measured twist under load and predicted twist from the HiMAT NASTRAN structural design program are compared. The results of this comparison indicate that the measured twist is generally less than the NASTRAN predicted twist. These discrepancies in twist predictions are attributed, at least in part, to the inability of current analytical composite materials programs to provide sufficiently accurate properties of matrix dominated laminates for input into structural programs such as NASTRAN.
Prediction of H.A.W.T. blade stall and performance
Energy Technology Data Exchange (ETDEWEB)
Giannakidis, G.; Graham, J.M.R. [Imperial College, Dept. of Aeronautics, London (United Kingdom)
1996-09-01
A model is being developed for the prediction of Horizontal Axis Wind Turbine blade stall and performance coupled with a simple aeroelastic analysis model. For the aerodynamic calculation a two dimensional unsteady Navier-Stokes solver on a sectional basis on the blade is coupled with a three dimensional vortex lattice wake. Pressure coefficient distributions are calculated from the two dimensional viscous flow in each blade section. The aerodynamic computations are coupled with a vibrating beam model in order to incorporate flapwise deformations of the blade. (au) 17 refs.
Response of a Light Aircraft Under Gust Loads
Directory of Open Access Journals (Sweden)
P. Chudý
2004-01-01
Full Text Available This project presents work performed by the Institute of Aerospace Engineering, Brno University of Technology. The primary purpose of this work was to estimate the aeroelastic response of a light aircraft under gust loads. In the past, the gust response has been investigated using the Pratt - Walker formula. This formula is derived from the response of a rigid airplane to a discrete gust. However, the Pratt-Walker formula does not capture either the stochastic nature of continuous turbulence or the effects of structural flexibility. The analysis described here was performed using the advanced FEM software package MSC Nastran.
Computational methods for unsteady transonic flows
Edwards, John W.; Thomas, J. L.
1987-01-01
Computational methods for unsteady transonic flows are surveyed with emphasis on prediction. Computational difficulty is discussed with respect to type of unsteady flow; attached, mixed (attached/separated) and separated. Significant early computations of shock motions, aileron buzz and periodic oscillations are discussed. The maturation of computational methods towards the capability of treating complete vehicles with reasonable computational resources is noted and a survey of recent comparisons with experimental results is compiled. The importance of mixed attached and separated flow modeling for aeroelastic analysis is discussed, and recent calculations of periodic aerodynamic oscillations for an 18 percent thick circular arc airfoil are given.
Optimal Damping of Stays in Cable-Stayed Bridges for In-Plane Vibrations
DEFF Research Database (Denmark)
Jensen, C.N.; Nielsen, S.R.K.; Sørensen, John Dalsgaard
2002-01-01
Significant vibrations have been reported in stays of recently constructed cable stayed bridges. The vibrations appear as in-plane vibrations that may be caused by rain–wind- induced aeroelastic interaction or by resonance excitation of the cables from the motion of the pylons. The stays of modern...... cable-stayed bridges are often designed as twin cables with a spacing of, say 1m. In such cases, it is suggested in the paper to suppress the mentioned in-plane types of vibrations by means of a tuned mass–damper (TMD) placed between the twin cables at their midpoints. The TMD divides the stay into four...
Load alleviation on wind turbine blades using variable geometry
DEFF Research Database (Denmark)
Basualdo, Santiago
2005-01-01
) wind turbines, which mainly operate under this flow condition. The results show evident reductions in the airfoil displacements by using simple control strategies having the airfoil position and its first and second derivatives as input, especially at the system's eigenfrequency. The use of variable...... airfoil geometry is an effective means of reducing the vibration magnitudes of an airfoil that represents a section of a wind turbine blade, when subject to stochastic wind signals. The results of this investigation encourage further investigations with 3D aeroelastic models to predict the reduction...... in loads in real wind turbines. Keywords: Variable Geometry, Wind Turbine, Load Alleviation, Fatigue Load, Trailing Edge Flap....
DEFF Research Database (Denmark)
Bergami, Leonardo; Poulsen, Niels Kjølstad
2015-01-01
. The effects of active flap control are assessed with aeroelastic simulations of the turbine in normal operation conditions, as prescribed by the International Electrotechnical Commission standard. The turbine lifetime fatigue damage equivalent loads provide a convenient summary of the results achieved......The paper proposes a smart rotor configuration where adaptive trailing edge flaps (ATEFs) are employed for active alleviation of the aerodynamic loads on the blades of the NREL 5 MW reference turbine. The flaps extend for 20% of the blade length and are controlled by a linear quadratic (LQ...
Bennett, Jeffrey
2012-01-01
The research presented considers the effect of varying shear web spacing and mass for two blades; a61.5m 5MW blade (based on the NREL5MW reference turbine) and a 100m 13.2MW blade (based onthe SNL100 blade). The variations are analyzed using HAWC2 aeroelastic simulations and Abaqus/CAE finite element simulations;and the effect of the variations is measured by comparing natural frequencies, loads, tip deflection,equivalent fatigue loads, material strength and buckling. Additionally, a tool was...
DEFF Research Database (Denmark)
Bergami, Leonardo; Riziotis, Vasilis A.; Gaunaa, Mac
2015-01-01
–inviscid interaction method and an engineering dynamic stall model suitable for implementation in aeroelastic codes based on blade element momentum theory. The aerodynamic integral forces and pitching moment coefficients are first determined in steady conditions, at angles of attack spanning from attached flow...... generated by the airfoil undergoing harmonic pitching motions and harmonic flap deflections. The unsteady aerodynamic coefficients exhibit significant variations over the corresponding steady-state values. The dynamic characteristics of the unsteady response are predicted with an excellent agreement among...
The impact of emerging technologies on an advanced supersonic transport
Driver, C.; Maglieri, D. J.
1986-01-01
The effects of advances in propulsion systems, structure and materials, aerodynamics, and systems on the design and development of supersonic transport aircraft are analyzed. Efficient propulsion systems with variable-cycle engines provide the basis for improved propulsion systems; the propulsion efficienies of supersonic and subsonic engines are compared. Material advances consist of long-life damage-tolerant structures, advanced material development, aeroelastic tailoring, and low-cost fabrication. Improvements in the areas of aerodynamics and systems are examined. The environmental problems caused by engine emissions, airport noise, and sonic boom are studied. The characteristics of the aircraft designed to include these technical advances are described.
The Torsional Vibration of Turbo Axis Induced by Unsteady Aerodynamic Force on Rotor blade
Institute of Scientific and Technical Information of China (English)
ChenZuoyi; WuXiaofeng
1998-01-01
An algorithm for computing the 3-D oscillating flow field of the balde passage under the torsional vibration of the rotor is applied to analyze the stability in turbomachines.The induced flow field responding to blade vibration is computed by Oscillating Fluid Mechanics Method and parametric Polynomial Method.After getting the solution of the unsteady flow field,the work done by the unsteay aerodynamic force acting on the blade can be obtained.The negative or positive work is the criterion of the aeroelastic stability.Numerical results indicate that there are instabilities of the torsional vibration in some frequency bands.
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...... conclusions intended to help in using this code for numerical simulations are given....... the linear to the stalled region. The computational data are compared to experimental data and numerical results from other computational codes. Several numerical aspects are studied, as mesh dependency,convective scheme, steady state versus unsteady computations, transition modelling. Some general...
Recent developments in the dynamics of advanced rotor systems
Johnson, W.
1985-01-01
The problems that were encountered in the dynamics of advanced rotor systems are described. The methods for analyzing these problems are discussed, as are past solutions of the problems. To begin, the basic dynamic problems of rotors are discussed: aeroelastic stability, rotor and airframe loads, and aircraft vibration. Next, advanced topics that are the subject of current research are described: vibration control, dynamic upflow, finite element analyses, and composite materials. Finally, the dynamics of various rotorcraft configurations are considered: hingeless rotors, bearingless rotors, rotors with circulation control, coupled rotor/engine dynamics, articulated rotors, and tilting proprotor aircraft.