• Wind and Structures
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• v.20 no.4
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• pp.527-548
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• 2015

Aeroelastic wind tunnel experiments were conducted for conventional and tapered super-tall building models to investigate the effect of taper on fundamental aeroelastic behaviors in various incident flows. Three incident flows were simulated: a turbulent boundary-layer flow representing urban area; a low-turbulent flow; and a grid-generated flow. Results were summarized focusing on the effect of taper and the effect of incident flows. The suppression of responses by introducing taper was profound in the low-turbulence flow and boundary-layer flow, but in the grid-generated flow, the response becomes larger than that of the square model when the wind is applied normal to the surface. The effects of taper and incident flows were clearly shown on the normalized responses, power spectra, stability diagrams and probability functions.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.6
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• pp.704-710
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• 2009

In this study, a comparison study of flutter analysis for the AGARD 445.6 wing with wind turnnel test data has been conducted in the subsonic, transonic and supersonic flow regions. Nonlinear aeroelastic using FSIPRO3D which is a generalized user-friendly fluid-structure analyses have been conducted for a 3D wing configuration considering shockwave and turbulent viscosity effects. The developed fluid-structure coupled analysis system is applied for aeroelastic computations combining computational structure dynamics(CSD), finite element method(FEM) and computations fluid dynamics(CFD) in the time domain. MSC/NASTRAN is used for the vibration analysis of a wing model, and then the result is applied to the FSIPRO3D module. the results for dynamic aeroelastic response using different turbulent models are presented for several Mach numbers. Calculated flutter boundary are compared with the wind-tunnel experimental and the results show very good agreements.

• Journal of Mechanical Science and Technology
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• v.16 no.4
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• pp.512-521
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• 2002

The flap-lag-torsion coupled aeroelastic behavior of a hingeless rotor blade with composite flexures in hovering flight has been investigated by using the finite element method. The quasisteady strip theory with dynamic inflow effects is used to obtain the aerodynamic loads acting on the blade. The governing differential equations of motion undergoing moderately large displacements and rotations are derived using the Hamilton's principle. The flexures used in the present model are composed of two composite plates which are rigidly attached together. The lead-lag flexure is located inboard of the flap flexure. A mixed warping model that combines the St. Versant torsion and the Vlasov torsion is developed to describe the twist behavior of the composite flexure. Numerical simulations are carried out to correlate the present results with experimental test data and also to identify the effects of structural couplings of the composite flexures on the aeroelastic stability of the blade. The prediction results agree well with other experimental data. The effects of elastic couplings such as pitch-flap, pitch-lag, and flap-lag couplings on the stability behavior of the composite blades are also investigated.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.4
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• pp.310-323
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• 2013

In this paper, the aeroelastic static response of flexible wings with arbitrary cross-section geometry via a coupled CUF-XFLR5 approach is presented. Refined structural one-dimensional (1D) models, with a variable order of expansion for the displacement field, are developed on the basis of the Carrera Unified Formulation (CUF), taking into account cross-sectional deformability. A three-dimensional (3D) Panel Method is employed for the aerodynamic analysis, providing more accuracy with respect to the Vortex Lattice Method (VLM). A straight wing with an airfoil cross-section is modeled as a clamped beam, by means of the finite element method (FEM). Numerical results present the variation of wing aerodynamic parameters, and the equilibrium aeroelastic response is evaluated in terms of displacements and in-plane cross-section deformation. Aeroelastic coupled analyses are based on an iterative procedure, as well as a linear coupling approach for different free stream velocities. A convergent trend of displacements and aerodynamic coefficients is achieved as the structural model accuracy increases. Comparisons with 3D finite element solutions prove that an accurate description of the in-plane cross-section deformation is provided by the proposed 1D CUF model, through a significant reduction in computational cost.

• Structural Engineering and Mechanics
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• v.78 no.5
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• pp.519-528
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• 2021

One of the most efficient designs of solar trackers for photovoltaic panels is the single-axis tracker, which holds the panels along a torque tube that is driven by a motor at the central section. These trackers have evolved to become extremely slender structures due to mechanical optimization against static load and the need of cost reduction in a very competitive market. Owing to the corresponding decrease in mechanical resistance, some of these trackers have suffered aeroelastic instability even at moderate wind speeds, leading to catastrophic failures. In the present work, an analytical and experimental approach has been developed to study that phenomenon. The analytical study has led to identify the dimensionless parameters that govern the motion of the panel-tracker structure. Also, systematic wind tunnel experiments have been carried out on a 3D aeroelastic scale model. The tests have been successful in reproducing the aeroelastic phenomena arising in real-scale cases and have allowed the identification and a close characterization of the phenomenon. The main results have been the determination of the critical velocity for torsional galloping as a function of tilt angle and a calculation methodology for the optimal sizing of solar tracker shafts.

• Wind and Structures
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• v.24 no.5
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• pp.481-500
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• 2017

A novel three-degree-of-freedom (DOF) forced vibration system has been developed for identification of aeroelastic (self-excited) load parameters used in time-domain response analysis of wind-excited flexible structures. This system is capable of forcing sinusoidal motions on a section model of a structure that is used in wind tunnel aeroelastic studies along all three degrees of freedom - along-wind, cross-wind, and torsional - simultaneously or in any combination thereof. It utilizes three linear actuators to force vibrations at a consistent frequency but varying amplitudes between the three. This system was designed to identify all the parameters, namely, aeroelastic- damping and stiffness that appear in self-excited (motion-dependent) load formulation either in time-domain (rational functions) or frequency-domain (flutter derivatives). Relatively large displacements (at low frequencies) can be generated by the system, if required. Results from three experiments, airfoil, streamlined bridge deck and a bluff-shaped bridge deck, are presented to demonstrate the functionality and robustness of the system and its applicability to multiple cross-section types. The system will allow routine identification of aeroelastic parameters through wind tunnel tests that can be used to predict response of flexible structures in extreme and transient wind conditions.

• Structural Engineering and Mechanics
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• v.56 no.6
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• pp.1021-1040
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• 2015

An effective method to calculate aerodynamic loads and aeroelastic responses of large wind turbine tower-blade coupled structures in yaw condition is proposed. By a case study on a 5 MW large wind turbine, the finite element model of the wind turbine tower-blade coupled structure is established to obtain the modal information. The harmonic superposition method and modified blade-element momentum theory are used to calculate aerodynamic loads in yaw condition, in which the wind shear, tower shadow, tower-blade modal and aerodynamic interactions, and rotational effects are fully taken into account. The mode superposition method is used to calculate kinetic equation of wind turbine tower-blade coupled structure in time domain. The induced velocity and dynamic loads are updated through iterative loop, and the aeroelastic responses of large wind turbine tower-blade coupled system are then obtained. For completeness, the yaw effect and aeroelastic effect on aerodynamic loads and wind-induced responses are discussed in detail based on the calculating results.

• Wind and Structures
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• v.35 no.1
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• pp.35-54
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• 2022

A comparative study of aeroelastic vibrations of spring-mass cylinder and chimneys, with the help of a few wake oscillator models available in the literature, is presented. The models include those proposed by Facchinetti, Farshidian and Dolatabadi method-I, Farshidian and Dolatabadi method-II, de Langre, Skop and Griffin. Besides, the linear model proposed by Simiu and Scanlan is also incorporated in the study. For chimneys, the first mode oscillation is considered, and the top displacements of the chimneys are evaluated using the considered models. The results of the analytical model are compared with those obtained from the numerical solution of the wake-oscillator coupled equations. The response behavior of the cylinder and three chimneys of different heights are studied and compared with respect to critical parametric variations. The results of the study indicate that the numerical analysis is essential to capture the effect of non-linear aeroelastic phenomena in the solutions, especially for small damping. Further, except for the models proposed by Farshidian and Dolatabadi, other models predict nearly the same responses. The non-linear model predicts a much higher response as compared to the linear model.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.1
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• pp.95-103
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• 2016

In this paper, aeroelastic instability and aerodynamic damping ratio of a helical $180^{\circ}$ model which shows better aerodynamic behavior in both along-wind and crosswind responses on a super tall building was investigated by an aeroelastic model test, and the aerodynamic damping ratio was evaluated from the wind-induced responses of the model by using Random Decrement Technique. Aerodynamic damping ratios evaluated in this study were verified through comparison with previous results obtained by quasi-steady theory. As a result, the aeroelastic instability of the helical $180^{\circ}$ model in crosswind direction were not occurred for any conditions with increasing the reduced wind velocity while the square model generally encounters aeroinstability due to the vortex shedding. The aerodynamic damping in along-wind direction for the helical $180^{\circ}$ and the square model increased monotonically both with reduced wind velocity, i.e., there is no relation with modifications of building shapes. On the other hand, in crosswind direction, the characteristics of aerodynamic damping ratio with reduced wind velocity for helical $180^{\circ}$ model were quit different from those of the square model.

• Wind and Structures
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• v.34 no.2
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• pp.231-257
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• 2022

Transmission lines systems are important components of the electrical power infrastructure. However, these systems are vulnerable to damage from high wind events such as hurricanes. This study presents the results from a 1:50 scale aeroelastic model of a multi-span transmission lines system subjected to simulated hurricane winds. The transmission lines system considered in this study consists of three lattice towers, four spans of conductors and two end-frames. The aeroelastic tests were conducted at the NSF NHERI Wall of Wind Experimental Facility (WOW EF) at the Florida International University (FIU). A horizontal distortion scaling technique was used in order to fit the entire model on the WOW turntable. The system was tested at various wind speeds ranging from 35 m/s to 78 m/s (equivalent full-scale speeds) for varying wind directions. A system identification (SID) technique was used to evaluate experimental-based along-wind aerodynamic damping coefficients and compare with their theoretical counterparts. Comparisons were done for two aeroelastic models: (i) a self-supported lattice tower, and (ii) a multi-span transmission lines system. A buffeting analysis was conducted to estimate the response of the conductors and compare it to measured experimental values. The responses of the single lattice tower and the multi-span transmission lines system were compared. The coupling effects seem to drastically change the aerodynamic damping of the system, compared to the single lattice tower case. The estimation of the drag forces on the conductors are in good agreement with their experimental counterparts. The incorporation of the change in turbulence intensity along the height of the towers appears to better estimate the response of the transmission tower, in comparison with previous methods which assumed constant turbulence intensity. Dynamic amplification factors and gust effect factors were computed, and comparisons were made with code specific values. The resonance contribution is shown to reach a maximum of 18% and 30% of the peak response of the stand-alone tower and entire system, respectively.