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A platform for research: civil engineering, architecture and urbanism
Aeroelastic Stability
Aeroelastic bifurcation phenomena, manifested by structures subject to wind, are analyzed. The aerodynamic forces of drag, lift, and moment are described. They are exerted by a steady wind flow, transversely hitting a long and immovable rigid cylinder. The dependence of the forces on the attack angle that the flow forms with a material direction of the cylinder cross-section is detected. By successively considering rigid cylinders elastically constrained at the ground, the conditions of validity of the quasi-steady theory, in which the motion of the structure is assumed slow compared to that of the fluid, are discussed. Then, cylinders with a single translational degree of freedom, transverse to the wind, which exhibit the galloping phenomenon, are studied. The critical bifurcation velocity is determined according to the Den Hartog criterion and the postcritical behavior investigated, in which the system reaches a limit cycle, whose amplitude and frequency are functions of the wind velocity. It is also shown how these results can be applied to strings and beams reduced to single degree of freedom systems, in the spirit of the Galerkin method. The aeroelasticity of planar systems is addressed, consisting of cylinders with three degrees of freedom, allowed to translate normally to their axis and to rotate around it. The aeroelastic forces are determined according to two alternatives offered by the quasi-steady theory, in which the angular velocity of the cylinder is (a) ignored or (b) heuristically taken into account. The analysis of the unidirectional motions of the cylinder leads to identify, in addition to the transverse galloping, two new mechanisms of bifurcation, namely, (a) the rotational divergence (i.e., a static bifurcation) and (b) the rotational galloping (i.e., a dynamic bifurcation). Bifurcations with two degrees of freedom are then investigated, consisting of (a) the translational galloping, which couples the two translations, and, (b) the roto-translational galloping, which couples the motion transverse to wind and the twist. The chapter ends with a sketch of the unsteady theory, in which, by following a semi-experimental approach, the influence of the (supposed harmonic) motion of the cylinder over the motion of the fluid is modeled.
Aeroelastic Stability
Aeroelastic bifurcation phenomena, manifested by structures subject to wind, are analyzed. The aerodynamic forces of drag, lift, and moment are described. They are exerted by a steady wind flow, transversely hitting a long and immovable rigid cylinder. The dependence of the forces on the attack angle that the flow forms with a material direction of the cylinder cross-section is detected. By successively considering rigid cylinders elastically constrained at the ground, the conditions of validity of the quasi-steady theory, in which the motion of the structure is assumed slow compared to that of the fluid, are discussed. Then, cylinders with a single translational degree of freedom, transverse to the wind, which exhibit the galloping phenomenon, are studied. The critical bifurcation velocity is determined according to the Den Hartog criterion and the postcritical behavior investigated, in which the system reaches a limit cycle, whose amplitude and frequency are functions of the wind velocity. It is also shown how these results can be applied to strings and beams reduced to single degree of freedom systems, in the spirit of the Galerkin method. The aeroelasticity of planar systems is addressed, consisting of cylinders with three degrees of freedom, allowed to translate normally to their axis and to rotate around it. The aeroelastic forces are determined according to two alternatives offered by the quasi-steady theory, in which the angular velocity of the cylinder is (a) ignored or (b) heuristically taken into account. The analysis of the unidirectional motions of the cylinder leads to identify, in addition to the transverse galloping, two new mechanisms of bifurcation, namely, (a) the rotational divergence (i.e., a static bifurcation) and (b) the rotational galloping (i.e., a dynamic bifurcation). Bifurcations with two degrees of freedom are then investigated, consisting of (a) the translational galloping, which couples the two translations, and, (b) the roto-translational galloping, which couples the motion transverse to wind and the twist. The chapter ends with a sketch of the unsteady theory, in which, by following a semi-experimental approach, the influence of the (supposed harmonic) motion of the cylinder over the motion of the fluid is modeled.
Aeroelastic Stability
Luongo, Angelo (author) / Ferretti, Manuel (author) / Di Nino, Simona (author)
Stability and Bifurcation of Structures ; Chapter: 12 ; 439-491
2023-02-17
53 pages
Article/Chapter (Book)
Electronic Resource
English
Aerodynamic forces , Quasi-steady theory , Single DOF galloping , Den Hartog criterion , Limit cycle , Rotational divergence , Rotational galloping , Two DOF translational galloping , Roto-translational galloping , Unsteady theory Engineering , Mechanical Statics and Structures , Solid Mechanics , Mechanical Engineering , Structural Materials , Solid Construction , Building Construction and Design
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