References of "Dimitriadis, Grigorios"
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See detailExperimental and Numerical Study of Mini-UAV Propeller Performance in Oblique Flow
Theys, Bart; Dimitriadis, Grigorios ULg; Hendrick, Patrick et al

in Journal of Aircraft (in press)

This paper presents the modelling of the performance of small propellers used for Vertical Take Off and Landing Micro Aerial Vehicles (VTOL MAVs) operating at low Reynolds numbers and in oblique flow ... [more ▼]

This paper presents the modelling of the performance of small propellers used for Vertical Take Off and Landing Micro Aerial Vehicles (VTOL MAVs) operating at low Reynolds numbers and in oblique flow. Blade Element Momentum Theory (BEMT), Vortex Lattice Method (VLM) and momentum theory for oblique flow are used to predict propeller performance. For validation, the predictions for a commonly used propeller for VTOL MAVs are compared to a set of wind tunnel experiments. Both BEMT and VLM succeed in predicting correct trends of the forces and moments acting upon the propeller shaft, although accuracy decreases significantly in oblique flow. For the dataset analysed here, combining the available data of the propeller in purely axial flow with momentum theory for oblique flow and applying a correction factor for the wake skew angle results in more accurate performance estimates at all elevation angles. [less ▲]

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See detailInduced Drag Calculations with the Unsteady Vortex Lattice Method for Cambered Wings
Lambert, Thomas ULg; Dimitriadis, Grigorios ULg

in AIAA Journal (in press)

The Unsteady Vortex Lattice Method (UVLM) is an approach widely used to estimate the aerodynamic loads in unsteady subsonic flows. It is based on modeling the camber surface of a lifting body by means of ... [more ▼]

The Unsteady Vortex Lattice Method (UVLM) is an approach widely used to estimate the aerodynamic loads in unsteady subsonic flows. It is based on modeling the camber surface of a lifting body by means of bound vortex rings. Even though this method has been known and used for several decades, there is little discussion of the modeling of the leading-edge suction in the literature. To address this concern, Simpson et al. [1] presented a comparison of two different ways to model this effect for the case of uncambered airfoils and wings in harmonic pitch or plunge motions. They concluded that the Joukowski method converges significantly faster than the Katz technique as the number of chorwise panels is increased. The present paper is an extension of the study by Simpson et al. to cambered lifting surfaces. It shows that the presence of camber can change radically the convergence performance of the two methods. For cambered wings, the Katz approach converges significantly faster than the Joukowski technique. [less ▲]

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See detailPassive flutter suppression using a nonlinear tuned vibration absorber
Verstraelen, Edouard ULg; Gourc, Etienne ULg; Kerschen, Gaëtan ULg et al

Poster (2016, July)

A recent study showed that the addition of a linear tuned vibration absorber could increase the flutter speed of a rigid wing with pitch and flap degrees of freedom by about 35%. However, the absorber was ... [more ▼]

A recent study showed that the addition of a linear tuned vibration absorber could increase the flutter speed of a rigid wing with pitch and flap degrees of freedom by about 35%. However, the absorber was turning the initial super-critical bifurcation into a sub-critical one. This work shows numerically that adding a nonlinear restoring force to the absorber can restore the su- percritical behaviour of the bifurcation and further reduce the post-instability limit cycle amplitude. [less ▲]

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See detailInfluence of propeller configuration on propulsion system efficiency of multi-rotor Unmanned Aerial Vehicles
Theys, Bart; Dimitriadis, Grigorios ULg; Hendrick, Patrick et al

in Proceedings of the International Conference on Unmanned Aircraft Systems, ICUAS 2016 (2016, June)

Multi-rotor Unmanned Aerial Vehicles make use of multiple propellers, mounted on arms, to produce the required lift. This article investigates the influence on propulsion system efficiency in hover due to ... [more ▼]

Multi-rotor Unmanned Aerial Vehicles make use of multiple propellers, mounted on arms, to produce the required lift. This article investigates the influence on propulsion system efficiency in hover due to the configuration of these propellers. Influence of pusher or puller configuration of the propeller, number of blades, shape and dimensions of the arm, coaxial and overlapping propellers, is presented. A dedicated test bench that allows testing of various experimental setups is designed and built in order to realistically represent multi-rotor arms. Test results show that a two-bladed pusher configuration is most efficient and slenderness of the arm has more influence on efficiency than shape. A coaxial propulsion system approaches the efficiency of a single-prop system at high disk loadings. Finally, interference effects due to overlapping propellers are discussed. [less ▲]

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See detailExperimental Passive Flutter Mitigation Using a Linear Tuned Vibrations Absorber
Verstraelen, Edouard ULg; Habib, Giuseppe ULg; Kerschen, Gaëtan ULg et al

in Proceedings of the IMAC XXXIV Conference (2016)

The current drive for increased efficiency in aeronautic structures such as aircraft, wind turbine blades and helicopter blades often leads to weight reduction. A consequence of this tendency can be ... [more ▼]

The current drive for increased efficiency in aeronautic structures such as aircraft, wind turbine blades and helicopter blades often leads to weight reduction. A consequence of this tendency can be increased flexibility, which in turn can lead to unfavourable aeroelastic phenomena involving large amplitude oscillations and nonlinear effects such as geometric hardening and stall flutter. Vibration mitigation is one of the approaches currently under study for avoiding these phenomena. In the present work, passive vibration mitigation is applied to an experimental aeroelastic system by means of a linear tuned vibration absorber. The aeroelastic apparatus is a pitch and flap wing that features a continuously hardening restoring torque in pitch and a linear one in flap. Extensive analysis of the system with and without absorber at subcritical and supercritical airspeeds showed an improvement in flutter speed around 34%, a suppression of a jump due to stall flutter, and a reduction in LCO amplitude. Mathematical modelling of the experimental system showed that optimal flutter delay can be obtained when two of the system modes flutter simultaneously. However, the absorber quickly loses effectiveness as it is detuned. The wind tunnel measurements showed that the tested absorbers were much slower to lose effectiveness than those of the mathematical predictions. [less ▲]

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See detailPIV-based estimation of unsteady loads on a flat plate at high angle of attack using momentum equation approaches
Guissart, Amandine ULg; Bernal, Luis; Dimitriadis, Grigorios ULg et al

Conference (2015, November 23)

The direct measurement of loads with force balance can become challenging when the forces are small or when the body is moving. An alternative is the use of Particle Image Velocimetry (PIV) velocity ... [more ▼]

The direct measurement of loads with force balance can become challenging when the forces are small or when the body is moving. An alternative is the use of Particle Image Velocimetry (PIV) velocity fields to indirectly obtain the aerodynamic coefficients. This can be done by the use of control volume approaches which lead to the integration of velocities, and other fields deriving from them, on a contour surrounding the studied body and its supporting surface. This work exposes and discusses results obtained with two different methods: the direct use of the integral formulation of the Navier-Stokes equations and the so-called Noca's method. The latter is a reformulation of the integral Navier-Stokes equations in order to get rid of the pressure. Results obtained using the two methods are compared and the influence of different parameters is discussed. The methods are applied to PIV data obtained from water channel testing for the flow around a 16:1 plate. Two cases are considered: a static plate at high angle of attack and a large amplitude imposed pitching motion. Two-dimensional PIV velocity fields are used to compute the aerodynamic forces. Direct measurements of dynamic loads are also carried out in order to assess the quality of the indirectly calculated coefficients. [less ▲]

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See detailSuppression of simulated self-excited oscillation using smart materials on flexible wing structure
Abdul Razak, N.; Nasip, N. S.; Hawari, A. F. et al

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics, IFASD 2015 (2015, July 01)

Suppression of simulated self-excited oscillation due to aeroelastic effects using piezoelectric patches is reported. The focus of the present work is suppressing simulated flutter oscillation using ... [more ▼]

Suppression of simulated self-excited oscillation due to aeroelastic effects using piezoelectric patches is reported. The focus of the present work is suppressing simulated flutter oscillation using piezoelectric patches bonded to the wing structure. First, a clean wing is exposed to airflow in the wind tunnel where it experienced limited amplitude oscillation. The responses were recorded. This is followed by bonding piezoelectric patches to the identical wing that was tested in the wind tunnel. Two of the patches were used as actuators to simulate self-excited oscillation in a control manner. The selected mode for excitation is 1st bending mode. The other two patches were used as suppressor for active control using negative velocity feedback Single-Input, Single-Output approach. The single input signal for negative feedback is also sensed using piezoelectric patches. The controller manages to suppress the simulated flutter response to a lower oscillation amplitude values. This works demonstrated the used of piezoelectric material as actuator to reproduce the oscillation amplitude during self-excited oscillation and suppress the oscillation at the same time. [less ▲]

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See detailExperimental and numerical study of the flight of geese
Dimitriadis, Grigorios ULg; Gardiner, James; Tickle, Peter et al

in Aeronautical Journal (2015), 119(1217), 1-30

The flight of barnacle geese at airspeeds representing high-speed migrating flight is investigated using experiments and simulations. The experimental part of the work involved the filming of three ... [more ▼]

The flight of barnacle geese at airspeeds representing high-speed migrating flight is investigated using experiments and simulations. The experimental part of the work involved the filming of three barnacle geese (Branta Leucopsis) flying at different airspeeds in a wind tunnel. The video footage was analysed in order to extract the wing kinematics. Additional information, such as wing geometry and camber was obtained from a 3D scan of a dried wing. An unsteady vortex lattice method was used to simulate the aerodynamics of the measured flapping motion. The simulations were used in order to successfully reproduce the measured body motion and thus obtain estimates of the aerodynamic forces acting on the wings. It was found that the mean of the wing pitch angle variation with time has the most significant effect on lift while the difference in the durations of the upstroke and downstroke has the major effect on thrust. The power consumed by the aerodynamic forces was also estimated; it was found that increases in aerodynamic power correspond very closely to climbing motion and vice versa. Root-mean-square values of the power range from 100 W to 240 W. Finally, it was observed that tandem flying can be very expensive for the trailing bird. [less ▲]

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See detailAsymmetric limit cycle oscillations in systems with symmetric freeplay
Dimitriadis, Grigorios ULg

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics, IFASD 2015 (2015, June 30)

In this paper, a simple 2D aeroelastic system with degrees of freedom in pitch, plunge and control surface deflection is investigated with freeplay in the pitch degree of freedom. It is shown that this ... [more ▼]

In this paper, a simple 2D aeroelastic system with degrees of freedom in pitch, plunge and control surface deflection is investigated with freeplay in the pitch degree of freedom. It is shown that this system features a fixed point at the origin as well as two anti-symmetric fixed points. Asymmetric limit cycles that span only two of the three piecewise linear subdomains of the phase plane can orbit these anti-symmetric fixed points. A single three-domain symmetric cycle and two two-domain cycles appear as a result of a grazing bifurcation occurring at the flutter speed of the underlying linear system. The two-domain cycles can undergo further fold, period doubling and torus bifurcations. They can cause both periodic and aperiodic oscillations, including highly chaotic responses at parameter values where they interact strongly. [less ▲]

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See detailUsing 2D-PIV measurements to compute unsteady aerodynamic loads on a flat plate at high angle of attack
Guissart, Amandine ULg; Bernal, Luis; Dimitriadis, Grigorios ULg et al

in Proceedings of the 16th International Forum on Aeroelasticity and Structural Dynamics, IFASD 2015 (2015, June 30)

This work exposes and discusses results obtained for aerodynamic forces using an indirect calculation based on Particle Image Velocimetry (PIV) measurements. The methodology used is based on the integral ... [more ▼]

This work exposes and discusses results obtained for aerodynamic forces using an indirect calculation based on Particle Image Velocimetry (PIV) measurements. The methodology used is based on the integral formulation of the Navier-Stokes equations and is applied to spatio-temporal data for different flows around a plate with a 16:1 chord-to-thickness ratio at high angle of attack. Experimental data are obtained in a water channel for both a static and a pitching plate. In addition to PIV data, direct measurements of aerodynamic loads are carried out to assess the quality of the indirect calculation. It is demonstrated that this indirect method is able to compute the mean and the temporal evolution of the lift and drag coefficients with a reasonable accuracy. It is also shown that the noise sensitivity of the method can be partly alleviated through the use of Dynamic Mode Decomposition (DMD) as a pre-processing step to smooth the spatio-temporal data. [less ▲]

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See detailTheoretical and experimental investigation of a structurally and aerodynamically nonlinear pitch and flap wing
Verstraelen, Edouard ULg; Boutet, Johan ULg; Grappasonni, Chiara ULg et al

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics, IFASD 2015 (2015, June 29)

This paper presents and experimental and theoretical investigation of a novel nonlinear aeroelastic system. It consists of a wing with pitch and flap degrees of freedom, suspended from a leaf spring ... [more ▼]

This paper presents and experimental and theoretical investigation of a novel nonlinear aeroelastic system. It consists of a wing with pitch and flap degrees of freedom, suspended from a leaf spring secured in a nonlinear clamp. Both the structural and the aerodynamic forces acting on the wing can be nonlinear, depending on the amplitude of oscillations. Wind tunnel experiments show that the system undergoes a supercritical Hopf bifurcation that leads to small amplitude limit cycle oscillations. At a particular airspeed, the pitch amplitude jumps to a much higher value and dynamic stall starts to occur. Three mathematical models of the system are formulated, one based on linear aerodynamics and two based on the Leishman-Beddoes dynamic stall model. The objective of the modelling is to determine whether the jump in pitch oscillation amplitude is due to dynamic stall. The predictions for amplitude, frequency and mean angle of the limit cycle oscillations are compared to the experimental observations. All three models predict the small amplitude oscillations with satisfactory accuracy. The complete Leishman-Beddoes model predicts the occurrence of a jump in pitch amplitude but the magnitude of this jump is signi cantly overestimated. The other two models completely fail to model the jump. The failure of the Leishman-Beddoes model to predict the correct post-jump oscillation amplitude may be due to the values selected for the model parameters. [less ▲]

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See detailUnsteady Viscous-Inviscid Coupling Simulations of Separated Laminar Flows Around 2D Airfoils
Rothkegel Ide, José Ignacio ULg; Dimitriadis, Grigorios ULg

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics, IFASD 2015 (2015, June 29)

An interactive boundary layer model has been developed in 2D in order to solve the unsteady flow around an airfoil. The inviscid problem is solved using a panel method, by the discretization of the ... [more ▼]

An interactive boundary layer model has been developed in 2D in order to solve the unsteady flow around an airfoil. The inviscid problem is solved using a panel method, by the discretization of the airfoil into linear-varying vortex panels. The solution of the boundary layer equations is carried out using a finite volume scheme. Viscous-inviscid coupling is preformed by imposing a permeation velocity on the skin panels of the airfoil and the addition of a free wake at each separation point. [less ▲]

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See detailFlapping around in a wind tunnel
Dimitriadis, Grigorios ULg

Conference (2015, March 17)

Aerodynamic investigations of animal flight have usually concentrated on static conditions. These are good enough to analyse gliding flight but not other types of flight, such as cruise (migrations), take ... [more ▼]

Aerodynamic investigations of animal flight have usually concentrated on static conditions. These are good enough to analyse gliding flight but not other types of flight, such as cruise (migrations), take-off and landing or manoeuvres. In this work we present wind tunnel experiments on geese flying in a wind tunnel and unsteady aerodynamic simulations of these flights, based on the Vortex Lattice Method. [less ▲]

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See detailInternal Resonance and Stall-Flutter in a Pitch-Flap Wing in the Wind-Tunnel
Verstraelen, Edouard ULg; Kerschen, Gaëtan ULg; Dimitriadis, Grigorios ULg

in Proceedings of the SEM IMAC XXXII (2015, February)

Nonlinear aeroelastic phenomena such as store-induced LCOs, transonic buzz and stall flutter are the burden or modern aircraft: they reduce the performance and can even limit the flight envelope in both ... [more ▼]

Nonlinear aeroelastic phenomena such as store-induced LCOs, transonic buzz and stall flutter are the burden or modern aircraft: they reduce the performance and can even limit the flight envelope in both civil and military cases. Several nonlinear setups were studied experimentally in the last decades by the scientific community but most of them have pitch and plunge degrees of freedom and feature a rigid wing. In this paper, we study a new nonlinear aeroelastic apparatus that features nonlinear pitch and flap degrees of freedom, coupled with a flexible wing. The model is tested experimentally in the wind tunnel to determine its dynamic behaviour. Preliminary observations demonstrate that the system undergoes a supercritical Hopf bifurcation due to the hardening nonlinearity followed by an amplitude jump that is the consequence of either dynamic stall (i.e. stall flutter) or internal resonance (i.e. interaction between the hardening nonlinearity and higher modes). [less ▲]

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See detailImpact of roughness and circularity-defect on bridge cables stability
Benidir, Adel; Flamand, Olivier; Gaillet, Laurent et al

in Journal of Wind Engineering & Industrial Aerodynamics (2015), 137

The stay cables on cable-stayed bridges have been the subject of considerable research in order to understand the origins of the dry galloping phenomenon. Surface irregularity is one of the last ... [more ▼]

The stay cables on cable-stayed bridges have been the subject of considerable research in order to understand the origins of the dry galloping phenomenon. Surface irregularity is one of the last parameters that have not been thoroughly examined. This paper focuses on static wind tunnel tests on original High Density Polyethylene cable covers in a range of Reynolds numbers from the sub-critical regime to the critical, corresponding to values ranging from Re = 9.6x104 to Re = 3.3x105. The experiment consists in testing cable covers of various diameters in order to investigate the effect of surface irregularity (roughness and circularity defect) on the mechanism of dry galloping excitation. Previous studies reported that dry galloping is caused by the appearance of a negative pressure bubble on one side of the circular cylinder at the critical Reynolds number range, leading to a rapid drop in the drag coefficient and the appearance of a non-negligible lift force. The results of the present investigation demonstrate that there is a clear correlation between the single bubble pressure pattern and the circularity defect along the tube. They further show that surface roughness has little effect on the location of the bubble. The paper also treats the spatial and temporal correlation of the instantaneous pressure pattern along the tube with respect to the circularity defect. [less ▲]

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See detailReduced Order Analysis of Aeroelastic Systems with Freeplay using an Augmented Modal Basis
Silva, Gustavo H. C.; Dal Ben Rossetto, Gustavo; Dimitriadis, Grigorios ULg

in Journal of Aircraft (2015), 52(4), 1312-1325

Freeplay in aircraft control surface actuators is a common source of nonlinearity that can cause undesirable aeroelastic phenomena and, as a consequence, certification authorities place strict limits on ... [more ▼]

Freeplay in aircraft control surface actuators is a common source of nonlinearity that can cause undesirable aeroelastic phenomena and, as a consequence, certification authorities place strict limits on the size of the deadband gaps of actuators. In recent years many authors have worked on determining the effects of freeplay on the dynamic behavior of aeroelastic systems; these efforts have yielded significant improvements in the understanding of the phenomena, but have concentrated on simple models. Investigations of industry-relevant aeroelastic models of complete aircraft with freeplay in the actuators have been much rarer, the main difficulty being the selection of an appropriate modal basis that can represent the full range of possible dynamic phenomena. This work presents a novel implementation of the residual vectors approach to create consistent and numerically stable reduced order models suitable for industrial-standard aeroelastic models of aircraft. The methodology relies on the piecewise linear nature of freeplay to create a single reduction basis that represents the dynamics of the system both inside and outside the freeplay deadband gap. The method is demonstrated on an Embraer generic test bench aircraft, showing that the resulting reduced order model is efficient and effective. Nonlinear analysis is carried out using equivalent linearization as well as time integrations of the full nonlinear system. It is shown that, while equivalent linearization is an indispensable tool for a preliminary mapping of the main aeroelastic instabilities, the time integration-based nonlinear analysis is an essential complementary tool to confirm the characteristics of the system behavior. [less ▲]

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See detailNumerical and Experimental Investigation of Slot-Blown Air Over a Cylinder
Runge, W.; Buysschaert, F.; Hayez, J. et al

in Knight, L.; Lipatov, I.; Reijasse, P. (Eds.) Progress in Flight Physics - Volume 7 (2015)

The paper investigates the concept of directional control of helicopters without tail rotor by means of the Coanda effect. Slot-blowing around a cylinder in a steady flow is modeled computationally, using ... [more ▼]

The paper investigates the concept of directional control of helicopters without tail rotor by means of the Coanda effect. Slot-blowing around a cylinder in a steady flow is modeled computationally, using the unsteady k-ω shear stress transport (SST) solver in NUMECA, as well as experimentally in the wind tunnel of the Université de Liège. While the concept, in general, is promising, it is shown that there are some potential problems, including pitch yaw coupling and some unsteady flow conditions. These problems exist under various circumstances and are due, at least, in part, to the complicated flow-field that governs this problem, even in two dimensions. [less ▲]

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See detailThe aerodynamic cost of head morphology in bats: maybe not as bad as it seems
Vanderelst, Dieter; Peremans, Herbert; Abdul Razak, Norizham et al

in PLoS ONE (2015), 10(3), 0118545

At first sight, echolocating bats face a difficult trade-off. As flying animals, they would benefit from a streamlined geometric shape to reduce aerodynamic drag and increase flight efficiency. However ... [more ▼]

At first sight, echolocating bats face a difficult trade-off. As flying animals, they would benefit from a streamlined geometric shape to reduce aerodynamic drag and increase flight efficiency. However, as echolocating animals, their pinnae generate the acoustic cues necessary for navigation and foraging. Moreover, species emitting sound through their nostrils often feature elaborate noseleaves that help in focussing the emitted echolocation pulses. Both pinnae and noseleaves reduce the streamlined character of a bat’s morphology. It is generally assumed that by compromising the streamlined charactered of the geometry, the head morphology generates substantial drag, thereby reducing flight efficiency. In contrast, it has also been suggested that the pinnae of bats generate lift forces counteracting the detrimental effect of the increased drag. However, very little data exist on the aerodynamic properties of bat pinnae and noseleaves. In this work, the aerodynamic forces generated by the heads of seven species of bats, including noseleaved bats, are measured by testing detailed 3D models in a wind tunnel. Models of Myotis daubentonii, Macrophyllum macrophyllum, Micronycteris microtis, Eptesicus fuscus, Rhinolophus formosae, Rhinolophus rouxi and Phyllostomus discolor are tested. The results confirm that non-streamlined facial morphologies yield considerable drag forces but also generate substantial lift. The net effect is a slight increase in the lift-to-drag ratio. Therefore, there is no evidence of high aerodynamic costs associated with the morphology of bat heads [less ▲]

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See detailEmpirical modelling of the bifurcation behaviour of a bridge deck undergoing across-wind galloping
Andrianne, Thomas ULg; Dimitriadis, Grigorios ULg

in Journal of Wind Engineering & Industrial Aerodynamics (2014), 135

This work presents an empirical model capable to describe the galloping bifurcation behaviour of a bridge deck. It is based on a general polynomial form proposed by Novak, which we limit to the 5th order ... [more ▼]

This work presents an empirical model capable to describe the galloping bifurcation behaviour of a bridge deck. It is based on a general polynomial form proposed by Novak, which we limit to the 5th order. The advantage of choosing this function for modelling the vertical force coefficient is that asymmetry of the even terms is enforced in order to reproduce the sub-critical aeroelastic behaviour of the bridge deck. The coefficients of the polynomial are identified from several pairs of displacement amplitudes and the corresponding airspeeds, measured in a wind tunnel during dynamic tests on the sectional bridge model. The identification is carried out using a first order harmonic balance technique. A stability analysis is presented in order to highlight the need of such a model to catch the complete bifurcation behaviour of the system. The resulting force coefficient of this full order model is compared to the well known models of Parkinson and Novak. Finally, the concept universal curve is used in order to discuss the galloping responses of square and rectangular cylinders, in comparison with the one of the bridge deck. [less ▲]

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See detailWind Tunnel Experiments On Bridge Stays Cables Protection Tubes In Dry Galloping Conditions: Processing Method For Bi-Stable Phenomenon
Flamand, Olivier; Benidir, Adel; Gaillet, Laurent et al

in Proceedings of the Symposium on the Dynamics and Aerodynamics of Cables - SDAC 2014 (2014, September)

Surface irregularity is one of the parameters that have not been deeply examined on stay cables of cable-stayed bridges. This paper focuses on wind tunnel tests on original High Density Polyethylene cable ... [more ▼]

Surface irregularity is one of the parameters that have not been deeply examined on stay cables of cable-stayed bridges. This paper focuses on wind tunnel tests on original High Density Polyethylene cable covers, in a range of Reynolds numbers from the sub-critical regime to the critical one, corresponding to values ranging from Re = 9.6x104 to Re = 3.3x105. The experiment consists in measurement of parietal pressures on cable covers in order to investigate the effect of surface irregularity on the mechanism of dry galloping excitation. Previous studies ([1], [3] and [4]) reported that dry galloping of cables with a circular cross section is linked to the appearance of a negative pressure bubble, on one side of the circular cylinder at the critical Reynolds number range, leading locally to a rapid drop in the drag coefficient and the appearance of a no negligible lift force. But such a steady change in local lift force does not generate an alternate excitation on a whole cable. The question of the spatial correlation of this “one bubble “ regime along a cable in real conditions and the capability of this lift force to be varied with time are still not resolved. The present paper aims at showing one first exploration of the spatial and temporal correlation of the pressure pattern along the HDPE tube with respect to the natural circularity defect. The Proper Orthogonal Decomposition (POD) was used to characterize the bi-stability phenomenon occurring at critical Reynolds number regime. [less ▲]

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