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Experimental Analysis of the Bifurcation Behaviour of a Bridge Deck Undergoing Across-Wind Galloping Andrianne, Thomas ; Dimitriadis, Grigorios in De Roeck, G.; Degrande, G.; Lombaert, G. (Eds.) et al Proceedings of the 8th International Conference on Structural Dynamics, EURODYN 2011 (2011, July 05) The phenomenon of aeroelastic galloping is a very important design consideration for bridges and other slender structures. It has been investigated by a number of researchers but, most frequently, the ... [more ▼] The phenomenon of aeroelastic galloping is a very important design consideration for bridges and other slender structures. It has been investigated by a number of researchers but, most frequently, the analysis is limited to quasi-steady aerodynamic and linearized aeroelastic considerations. Such treatment has been shown to be effective for simple cross-sectional shapes, such as rectangles. In this work, an aeroelastic model of a realistic bridge deck cross-section is tested in a low speed wind tunnel. Both static and dynamic tests are carried out and the resulting force and vibration measurements are presented. The static force results are used to set up a quasi-steady mathematical model. The dynamic responses are used to draw a complete bifurcation diagram within a chosen airspeed range and to discuss the stability of the system. It is shown that the experimental system undergoes a subcritical Hopf bifurcation, its phase space including both a stable and an unstable limit cycle. As consequence, throughout the chosen airspeed, the system can either remain stable or undergo limit cycle oscillations. The quasi-steady analysis fails completely in capturing this type of behaviour. The predicted galloping onset speed is too conservative and the predicted oscillation amplitudes too high. The reason for this failure is the fact that the quasi-steady mathematical model is incapable of modelling subcritical Hopf bifurcations. [less ▲] Detailed reference viewed: 102 (21 ULg)Wind tunnel analysis of separated aerodynamics leading to different types of torsional flutter in bluff-bodies. Andrianne, Thomas ; ; Dimitriadis, Grigorios in Proceedings of the 15th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2011 (2011, June 29) A new experimental apparatus has been developed at the wind tunnel laboratory of University of Liège with the objective to study the torsional flutter instability of a rectangular cylinder. Different ... [more ▼] A new experimental apparatus has been developed at the wind tunnel laboratory of University of Liège with the objective to study the torsional flutter instability of a rectangular cylinder. Different configurations, based on the position of the pitching axis, the stiffness of the restoring springs and the static equilibrium angle of the model have been tested and analysed. Sub- and supercritical bifurcations behaviour has been identified. The dynamics of the system, as well as the aerodynamic phenomena taking place around the model have been measured. The frequency content of the pitching displacement and the longitudinal component of the velocity in the wake showed the occurrence of two types of aerodynamic instability: large separation from the leading edge and vortex shedding in the Strouhal sense. Furthermore, preliminary Particle Image Velocimetry visualisation confirmed the presence of complex aerodynamic phenomena over the upper surface and in the wake of the model. These measurements allow a better understanding of the sources of aerodynamic excitation leading to torsional flutter. [less ▲] Detailed reference viewed: 88 (14 ULg)Flow Visualization and Proper Orthogonal Decomposition of Aeroelastic Phenomena Andrianne, Thomas ; Norizham, Abdul Razak ; Dimitriadis, Grigorios in Okamoto, Satoru (Ed.) Wind Tunnels (2011) The modal decomposition of unsteady flowfields was proposed in the 1990s by several authors. Proper Orthogonal Decomposition (POD) is one method that can be used in order to perform this modal ... [more ▼] The modal decomposition of unsteady flowfields was proposed in the 1990s by several authors. Proper Orthogonal Decomposition (POD) is one method that can be used in order to perform this modal decomposition; it became popular for aerodynamics research in the 2000s, although it was first proposed for use in fluid dynamics in the 1960s. The objective of the present work is to expand the methodology of the application of POD to experimental flowfields. There are two aspects to this expansion: 1. Allow the models to oscillate. The source of the unsteadiness will then be the movement of the model, as well as any unsteadiness due to flow separation. 2. Study the interaction between the different sources of unsteadiness. In particular observe how the modes generated by one source of unsteadiness interact with the modes generated by the other. Determine if it is possible to separate the structural from the aerodynamic sources of unsteadiness. [less ▲] Detailed reference viewed: 140 (30 ULg)Flutter and stall flutter of a rectangular wing in a wind tunnel Norizham, Abdul Razak ; Andrianne, Thomas ; Dimitriadis, Grigorios in AIAA Journal (2011), 49(10), 2258-2271 The aeroelastic behavior of a rectangular wing with pitch and plunge degrees of freedom was observed experimentally using pressure, acceleration and PIV measurements. The wing was set at different static ... [more ▼] The aeroelastic behavior of a rectangular wing with pitch and plunge degrees of freedom was observed experimentally using pressure, acceleration and PIV measurements. The wing was set at different static angles of attack and wind tunnel airspeeds. The wing's dynamic behavior was governed by a two-parameter bifurcation from steady to Limit Cycle Oscillations (LCO), the two parameters being the airspeed and the static angle of attack. At the lowest static angle, the wing underwent a classical flutter phenomenon that was transformed into a supercritical Hopf bifurcation at higher angles. The latter was combined with a fold bifurcation at intermediate angles of attack. All LCOs observed were either low amplitude oscillations with time-varying amplitude or high amplitude oscillations with nearly steady amplitude. They were caused by two different types of dynamic stall phenomena. During low amplitude LCOs the periodically stalled flow covered only the rear part of the wing. During high amplitude LCOs, trailing edge and leading edge separation occured. Trailing edge separation was characterized by a significant amount of unsteadiness, varying visibly from cycle to cycle. The occurrence of leading edge separation was much more regular and had the tendency to stabilize the amplitude of the LCO motion. [less ▲] Detailed reference viewed: 240 (44 ULg)Subcritical, nontypical and period doubling bifurcations of a Delta Wing in a low speed wind tunnel ; Kagambage, Emile ; Andrianne, Thomas et al in Journal of Fluids & Structures (2011), 27(3), 408-426 Limit Cycle Oscillations (LCOs) involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of geometric or aerodynamic nonlinearity. In this paper ... [more ▼] Limit Cycle Oscillations (LCOs) involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of geometric or aerodynamic nonlinearity. In this paper, a flexible half-span Delta wing is tested in a low speed wind tunnel in order to investigate its dynamic response. The wing is designed to be more flexible than the models used in previous research on the subject in order to expand the airspeed range in which LCOs occur. The experiments reveal that this wing features a very rich bifurcation behavior. Three types of bifurcation are observed for the first time for such an aeroelastic system: subcritical bifurcations, period doubling/period halving and nontypical bifurcations. They give rise to a great variety of LCOs, even at very low angles of attack.The LCOs resulting from the nontypical bifurcation display Hopf-type behavior, i.e. have fundamental frequencies equal to one of the linear modal frequencies. All of the other LCOs have fundamental frequencies that are unrelated to the underlying linear system modes. [less ▲] Detailed reference viewed: 79 (23 ULg)Limit Cycle Oscillations of a Delta Wing in a Low Speed Wind Tunnel ; Kagambage, Emile ; Andrianne, Thomas et al in Proceedings of ISMA2010 (2010, September 22) Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of structural or aerodynamic nonlinearity. In this paper, a ... [more ▼] Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of structural or aerodynamic nonlinearity. In this paper, a flexible half-Delta wing is tested in a low speed wind tunnel in order to investigate its dynamic response. Specifically, an investigation to determine the effects of a steady angle of attack on nonlinear Limit Cycle Oscillations (LCO) of a delta wing-plate model in low subsonic flow has been undertaken. It was found that, at several combinations of airspeed and angle of attack, the wing undergoes limit cycle oscillations. Two types of such oscillations are observed. One of them is low amplitude, low complexity limit cycle oscillations that occur at lower airspeeds; the other is high amplitude, high complexity limit cycle oscillations that occur a higher airspeeds and can appear abruptly. Some of the LCOs are the result of a subcritical Hopf bifurcation occurring at low steady angles of attack. At higher angles, a nontypical bifurcation was observed, whereby LCOs appear, grow with airspeed but then diminish and finally disappear as the airspeed is increased further. [less ▲] Detailed reference viewed: 86 (29 ULg)Bifurcation analysis of a wing undergoing stall flutter oscillations in a wind tunnel Norizham, Abdul Razak ; Andrianne, Thomas ; Dimitriadis, Grigorios in Proceedings of ISMA2010 (2010, September 20) Stall flutter is a Limit Cycle Oscillation (LCO) caused by the periodic separation of the flow around a wing immersed in a uniform fluid flow. The separation could be either partial or complete [1]. The ... [more ▼] Stall flutter is a Limit Cycle Oscillation (LCO) caused by the periodic separation of the flow around a wing immersed in a uniform fluid flow. The separation could be either partial or complete [1]. The work presented focuses on a wing undergoing stall flutter in the pitch degree of freedom. The phenomenon is analyzed from the structural and aerodynamic response perspectives. The objective of this study is to promote the understanding of stall flutter by characterizing the complete bifurcation behavior of the selected system. The wing section chosen for this study is NACA 0018 profile applied to a rectangular wing. The tests are carried out at different airspeeds and angles of attack. The measured aeroelastic responses are analyzed and the behavior of the dynamic system is characterized by fully describing its bifurcation. Structural accelerations as well as unsteady pressures around the mid-span point of the wing are measured and examined. Furthermore, flow field visualization by means of the Particle Image Velocimetry technique is used to demonstrate aspects of the unsteady flow field, such as the manifestation of separation and vortices. [less ▲] Detailed reference viewed: 107 (10 ULg)Etude du comportement aéroélastique des structures soumises à des écoulements décrochés Andrianne, Thomas ; Dimitriadis, Grigorios Conference (2010, March 02) L'objectif du travail de recherche est le développement d'un modèle numérique simulant les phénomènes aéroélastiques affectant les corps non-profilés, caractérisés par des effets de décrochage/raccrochage ... [more ▼] L'objectif du travail de recherche est le développement d'un modèle numérique simulant les phénomènes aéroélastiques affectant les corps non-profilés, caractérisés par des effets de décrochage/raccrochage du fluide.L'application de ce modèle aux tabliers de point est prévue. [less ▲] Detailed reference viewed: 72 (24 ULg)Proper Orthogonal Decomposition of Unsteady Aerodynamic Flows Andrianne, Thomas ; ; Dimitriadis, Grigorios Report (2009) This work constitutes the final report for a project funded by the Fonds de la Recherche Scientifique. The objective of the project was to acquire and install Par- tical Image Velocimetry (PIV) hardware ... [more ▼] This work constitutes the final report for a project funded by the Fonds de la Recherche Scientifique. The objective of the project was to acquire and install Par- tical Image Velocimetry (PIV) hardware in the University of Liege Wind Tunnel facility in order to carry out the Proper Orthogonal Decomposition (POD) of un- steady aerodynamic flows. The characteristics and installation of the PIV system are described in the present report. Furthermore, the application of POD analysis to three different visualized flow cases is detailed. The flow cases were: flow be- hind a circular cylinder and separated flow over a rectangular wing. In all cases, emphasis was given to the combination of unsteadiness caused by both boundary layer separation and movement of the wind tunnel model. It is shown that the de- composition of flowfields that combine these two sources of unsteadiness is possible and informative. [less ▲] Detailed reference viewed: 120 (22 ULg)Analysis of dynamic response of a very flexible Delta wing model in a wind tunnel Barbason, Mathieu ; Andrianne, Thomas ; Hickey, Daryl et al in Proceedings of the 2009 International Forum on Aeroelasticity and Structural Dynamics (2009, July) Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of geometric nonlin- earity, aerodynamic nonlinearity or under ... [more ▼] Limit cycle oscillations involving Delta wings are an important area of research in modern aeroelasticity. Such phenomena can be the result of geometric nonlin- earity, aerodynamic nonlinearity or under-wing store nonlinearity. In this paper, a flexible half-Delta wing without stores is tested in a low speed wind tunnel in order to investigate its dynamic response. It is found that, at several combinations of airspeed and angle of attack, the wing undergoes high amplitude limit cycle oscillations. Three types of such oscillations are observed. Type 1 oscillations occur only at low angles of attack and are the result of a Hopf-type bifurcation. Type 2 limit cycle oscillations occur at intermedi- ate angles of attack and are the result of an atypical bifurcation. In other words, these oscillations appear as the airspeed is increased but disappear at even higher airspeeds. Type 3 oscillations occur at even higher angles of attack. A bispectrum analysis shows that type 3 limit cycle oscillations feature quadratic phase coupling. No such coupling was measured for type 2 oscillations, leading to the conclusion that the nonlinearity must be of higher order. [less ▲] Detailed reference viewed: 108 (39 ULg)Using the Discrete Vortex Method to Simulate the Stall Flutter Phenomenon Andrianne, Thomas ; Dimitriadis, Grigorios in Proceedings of the 2009 International Forum on Aeroelasticity and Structural Dynamics (2009, June) The Discrete Vortex Method (DVM) has been recently used by several researchers in order to simulate the dynamic stall phenomenon on 2D airfoils oscillating at high angles of attack or undergoing stall ... [more ▼] The Discrete Vortex Method (DVM) has been recently used by several researchers in order to simulate the dynamic stall phenomenon on 2D airfoils oscillating at high angles of attack or undergoing stall flutter oscillations. The aim of the present work is to investigate whether such simulations are representative of the true physics governing such oscillation. A DVM method is described and implemented. A basic validation of the method is performed on the case of an impulsively started static airfoil at a low angle of attack. It is shown that the steady state lift value obtained from the DVM method agrees with experimental measurements. Subsequently, a DVM simulation is performed for the case of a NACA 0012 airfoil undergoing symmetric stall flutter oscillations. The simulation results are compared to experimental results. It is shown that, while the general shape of the simulated lift variation with time agrees with the experiment, there are significant mean value and phase differences between experiment and simulation. Several justifications are suggested and improvements to the DVM simulation proposed. [less ▲] Detailed reference viewed: 143 (18 ULg)Wind tunnel investigation of the stall flutter oscillations of a bridge deck Andrianne, Thomas ; Dimitriadis, Grigorios in Proceedings of the 8th National Congress on Theoretical and Applied Mechanics (2009, May) Torsional Stall Flutter (TSF) is a one degree of freedom, self-excited phenomenon induced by the periodic separation/re-attachment of the flow around a body. The present paper proposes an experimental ... [more ▼] Torsional Stall Flutter (TSF) is a one degree of freedom, self-excited phenomenon induced by the periodic separation/re-attachment of the flow around a body. The present paper proposes an experimental investigation of TSF on a bridge deck. A section model free to oscillate in torsion is tested in a low-speed wind tunnel. Static and dynamic tests are performed to enable a complete interpretation of the phenomena involved. For low airspeeds, the Karman vortex shedding excites the structure, resulting in small oscillations at the vortex shedding frequency. For high airspeeds, the deck undergoes Limit Cycle Oscillations (LCO) due to the TSF phenomenon. Nevertheless the Karman vortex shedding excitation is still present and appears in the measured forces signals. Peaks and troughs in the lift coefficient are detected for each pitching period. They are interpreted as the separation/re-attachment of the flow around the deck. The large amplitudes motion of the deck undergoing TSF reduces the amplitude of the aerodynamic lift coefficient. [less ▲] Detailed reference viewed: 66 (17 ULg)Identification des coefficients de couplage aéroélastique d'une section de pont en soufflerie. Andrianne, Thomas Master's dissertation (2005) Le domaine de l'aéroélasticité en génie civil s'est largement développé durant les dernières décennies. Béné ciant des travaux antérieurs réalisés en aéronautique, l'aéroélasticité des ouvrages d'art a ... [more ▼] Le domaine de l'aéroélasticité en génie civil s'est largement développé durant les dernières décennies. Béné ciant des travaux antérieurs réalisés en aéronautique, l'aéroélasticité des ouvrages d'art a développé ses caractéristiques propres, centrées essentiellement sur les problèmes d'écoulement autour des corps non pro lés. Ces problèmes peuvent être classés dans les caté- gories suivantes: oscillation due à l'éjection tourbillonnaire, mouvement de galop, ottement et e orts dus à un vent turbulent. Chaque phénomène est étudié sur base de théories dédicacées, couplées aux études expérimentales. En particulier, le comportement aéroélastique des ponts suspendus a été abordé sur le plan expérimental et analytique depuis l'e ondrement du pont de Tacoma Narrows en 1940 aux États-Unis. Le présent travail propose une approche du comportement aéroélastique du plus haut viaduc jamais conçu: le viaduc de Millau. On propose d'étudier le tablier de cet ouvrage d'art au sein de la sou erie subsonique de l'Université de Liège. Une section du tablier vibre sous le vent grâce à un système de suspension spéci que développé par l'Université de Liège. Cette approche permet de mettre en évidence les di érents phénomènes aéroélastiques, ainsi que les instabilités aérodynamiques qui apparaissent. L'étude aéroélastique du tablier que l'on propose consiste à identi er les coe cients aéroélastiques introduits par Scanlan. Les coe cients aéroélastiques sont des fonctions adimensionnelles qui dépendent uniquement de la géométrie de l'ouvrage. Ils sont introduits ultérieurement dans l'analyse du comportement global de la structure et restent utilisables si des changements de masse ou d'inertie sont e ectués durant la conception de l'ouvrage. Les essais réalisés dans ce travail permettent de mieux comprendre les phénomènes aéroélastiques en jeu et de dé nir les marges de sécurité de l'ouvrage concerné. L'étude des di érentes parties d'un tel ouvrage dans une sou erie est de plus en plus fréquente dans le domaine du génie civil, ce qui permet la construction d'ouvrages de plus en plus audacieux... [less ▲] Detailed reference viewed: 164 (20 ULg) |
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