11:00
Adaptive structures 1
Chair: Rauno Cavallaro
11:00
30 mins
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The Design and Analysis of Tensegrity Morphing Wing
Jie Yu, Song Chen, Zhang Haibo
Abstract: Tensegrity systems are the lightweight self-equilibrium structures that compose of a series of tensioned cables and compressed struts. Of particular interest, adjusting the pretension of the tensegrity can tailor the structural characteristics as needed without a basic configuration change. By changing the length of cables or struts, the tensegrity system can morph while maintaining its inherent strength and stiffness. This makes tensegrity systems an attractive candidate for morphing aircraft wings. In addition, due to the influence of external forces on the stiffness matrix, the deflection analysis of the tensegrity wing after being subjected to aerodynamic forces are nonlinear. In this article, based on the aerodynamic shape of the RV-4 wing, we design a feasible tensegrity morphing wing using the R-cross structures. A numerical example is provided to simulate the aerodynamic load and static deflection on this three-dimensional tensegrity morphing wing under different working condition. The results show that our tensegrity morphing wing is 80% of the weight of the RV4 wing，while they have the comparable static deflection with the rudder angle of 10^o.The deflection of the tensegrity morphing wing is smaller than that of the traditional wing under the condition of the rudder angle of 0^o. In addition, when the rudder angle has been changed from 0^o to 10^o, the torsion angle variation of the tensegrity morphing wing is also smaller than that of the traditional wing, which is 1.5514 degree and 20.5714 degree, respectively.
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11:30
30 mins
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Application of Shape Memory Alloys for Flutter Suppression in a Propeller-Driven Typical Section
Italo Ximenes, Felipe da Silva, Roberto da Silva, Mauricio Donadon
Abstract: Future aerial mobility will likely be powered by propeller propulsion, as it is more suitable for use in combination with electric motors. Therefore avoiding rotor instabilities becomes a major concern in the early project phases for the next generation of aircraft. Within this context, this work focuses on the application of Shape Memory Alloys (SMA) for Whirl Flutter (WF) suppression in propeller-driven aircraft. SMAs have a thermal-dependent modulus of elasticity, which allows the use of this class of materials to locally control the stiffness of the connections between the motor and the wing. For most of the flight, the mounting stiffness could be maintained at a minimum to better isolate the vibration coming from the motor, and only at high speeds it could be increased to avoid aeroelastic instabilities. To conduct the study, a 4 Degree of Freedom (DoF) model of a wing section with an installed rotor was implemented and verified. This model combines a typical aeroelastic section, with springs associated with pitch and plunge DoF, and the classical rotor model used in WF studies, which idealizes the rotor mounting by two torsion springs associated with pitch and yaw DoF. Predictions obtained using the proposed model were compared with previous results from the literature. Following the model verification, the application of SMA was implemented by assuming that the connecting stiffeness associated with the rotor installation is dependent on temperature, simulating an SMA-made mounting. Thus, it was possible to map the final flutter velocity of the system as a function of the temperatures associated with the rotor installation. The obtained results demonstrate that the flutter speed of the system may be significantly modified using this approach. They also indicate that the control of the SMA temperature shifts the dominant flutter mechanism from whirl flutter to the classical wing flutter, increasing even more the flutter speed of the system.
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12:00
30 mins
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Aeroelastic modeling of flapping wings for designing bio-inspired unmanned aerial vehicles
Douglas Bueno, Rodrigo Borges Santos, Camila Gonsalez-Bueno
Abstract: Unmanned Aerial Vehicles (UAVs) have been often used for several applications, such as engineering, military and entertainment. In particular, insect-like and bird-like UAVs have demonstrated a huge potential for developing a new generation of aerial vehicles, with high efficiency and versatility for different missions. However, the aeroelastic characteristics of these vehicles are not well known yet. In this context, this present article investigates the aeroelastic dynamics bio-inspired flapping wing. The study is focused on developing aeroelastic models for insect-like and bird-like UAVs, including both structural flexibility and aerodynamics effects. The Finite Element Method is employed to obtain the structural dynamics of the wing, based on a six degrees of freedom per node beam-type element. The structural mesh considers a spar and ribs to create the wing geometry and a spatial spline technique is used to connect both structural and aerodynamic models to each other. The aerodynamic model is obtained by considering the Unsteady Vortex Lattice Method. A panel mesh is considered to define the wing geometry, and the wake development over time. A second order differential equation of motion is considered and the solution is obtained in the time domain. The virtual work method is considered to achieve the conservation energy when transporting the aerodynamic efforts to the structural mesh, and vice-versa. The aeroelastic responses of the flapping wing are obtained for different amplitudes and frequencies of motion. The influence of the wake length is evaluated for each case, besides the dimension of the aerodynamic panels. The numerical results show that this type of approach can be used to design bio-inspired UAVs.
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