Bifurcation and stability of a two-tower system under wind-induced parametric, external and self-excitation

Xieng Khouang [Xiangkhoang], Laos: Burned out building in Xieng KhouangGrayscaleForman Safety Negatives, Box 1

Dry galloping in inclined cables: linear stability analysis

Abstract In the last decade, dry galloping has been frequently observed on real stay cables also in the case of circular cross section. It is an aeroelastic phenomenon which occurs when structures or structural elements are generically placed with respect to the wind, being both incidence and yaw angles different from zero. Here, after writing down the equations which describe the static reference configuration of an inclined cable under the self-weight, the equations of motion are obtained up to third order, where the forces related to the wind are evaluated coherently with an aerodynamic model, drawn under the quasi-steady hypothesis. A Galerkin projection is carried out and the critical conditions causing Hopf bifurcation on the trivial equilibium configuration are then evaluated

Nonlinear interaction between self- and parametrically excited wind-induced vibrations

AbstractThe aeroelastic behavior of a planar prismatic visco-elastic structure, subject to a turbulent wind, flowing orthogonally to its plane, is studied in the nonlinear field. The steady component of wind is responsible for a Hopf bifurcation occurring at a threshold critical value; the turbulent component, which is assumed to be a small harmonic perturbation of the former, is responsible for parametric excitation. The interaction between the two bifurcations is studied in a three-dimensional parameter space, made of the two wind amplitudes and the frequency of the turbulence. Aeroelastic forces are computed by the quasi-static theory. A one-D.O.F dynamical system, drawn by a Galerkin projection of the continuous model, is adopted. The multiple scale method is applied, to get a two-dimensional bifurcation equation. A linear stability analysis is carried out to determine the loci of periodic and quasi-periodic bifurcations. Limit cycles and tori are computed by exact, asymptotic, and numerical solutions of the bifurcation equations. Numerical results are obtained for a sample structure, and compared with finite-difference solutions of the original partial differential equation of motion

Flexural-Torsional Flutter and Buckling of Braced Foil Beams under a Follower Force

The flutter and buckling behavior of a cantilever foil beam, loaded at the tip by a follower force, are addressed in this paper. The beam is internally and externally damped and braced at the tip by a linear spring-damper device, which is located in an eccentric position with respect to beam axis, thus coupling the flexural and torsional behaviors. An exact linear stability analysis is carried out, and the linear stability diagram of the trivial rectilinear configuration is built up in the space of the follower load and spring’s stiffness parameters. The effects of the flexural-torsional coupling, as well as of the damping, on the flutter and buckling critical loads are discussed

Controlling the Limit-Cycle of the Ziegler Column via a Tuned Piezoelectric Damper

This paper is about the nonlinear analysis of a piezoelectric controlled Ziegler column. The piezoelectric controller, here referred to as Tuned Piezoelectric Damper (TPD), possesses evanescent characteristics and, moreover, it is tuned to the first natural frequency of the mechanical system, thus resembling the well-known Tuned Mass Damper. This means that the flow of energy between mechanical and electrical subsystems is driven by the resonance (Den Hartog principle) and magnified by the singularity of the evanescent electrical characteristics. Numerical simulations, showing how the proposed control strategy is effective in increasing the linear stability domain and decreasing the amplitude of the limit-cycles in the postcritical range, are presented

Nonlinear Dynamics of an Internally Resonant Base-Isolated Beam under Turbulent Wind Flow

A base isolation system, aimed to passively control the nonlinear dynamics of an internally resonant tower, exposed to turbulent wind flow, is studied. A continuous visco-elastic beam, constrained at the bottom end by a nonlinear visco-elastic device and free at the top end, is considered. All the nonlinearities, structural, inertial and aeroelastic, these latter computed via the quasi-static theory, are accounted in the model. The interaction between self- and parametric excitations, triggered by the mean wind velocity and the turbulent component, respectively, are analyzed. The Multiple Scale Method is applied to the partial differential equations of motion, to investigate critical and post-critical behaviors, when two modes in internal 1:3 resonance are involved in the response. The first mode is found to lead the phenomenon, while the second mode is marginally involved. The effectiveness of the visco-elastic nonlinear isolation system is assessed, both in increasing the mean wind bifurcation value and in reducing the limit-cycle amplitude. The contribution of structural nonlinearities is found to weakly affect the response

How is suspected transthyretin-related cardiac amyloidosis diagnosed? Role 99mTc-HDMP scintigraphy: a substitute for biopsy?

Cardiac amyloidosis (CA) is characterized by extracellular deposition of protein-derived fibrils and lead to heart failure. Gold standard for its etiological diagnosis is endomyocardial biopsy and laboratory tests, both high-cost and invasive procedures. Technetium- 99m hydroxymethylene diphosphonate (99mTc-HMDP) scintigraphy is important tool for defining CA, specifically transthyretin subtype (ATTR). From July 2020 to February 2021, we retrospectively analyzed 18 pts [14 males, 4 females; aged 32-86y] with suspected ATTR, underwent to scintigraphy 150 min after iv administration of 740 MBq 99mTc-HMDP.Myocardial uptake was assessed optically based on Perugini Score (0- 3). Biopsy confirmed diagnosis. Intense (Score 3) and moderate (Score 2) myocardial uptake verified in 8 patients by 99mTc-HDMP scintigraphy, was consistent with ATTR suspect. In 10 patient's cardiac radiotracer uptake was absent (Score 0) avoiding biopsy. Our data indicate a 99mTc-HDMP scintigraphy key role in the early diagnosis but even more in the exclusion of patients with ATTR subtype, optimizing the management of pts who do not require high costs and invasive procedures