1,721,089 research outputs found
Spectral modeling on the vortex-induced response of a tapered circular cylinder based on experimental evidence
No full textThis paper illustrates the application of spectral modeling for analyzing the vortex-induced vibration (VIV) response specifically focusing on a complex scenario involving a tapered circular cylinder exposed to uniform, stationary wind flow characterized by a low level of upstream turbulence. Such modeling is based on experimental evidence gathered during a wind tunnel campaign conducted through both static and dynamic tests. In particular, the definition of the limiting root mean square (RMS) amplitude, the variation of the RMS lift coefficient and of the Strouhal number along the height of the structure result to be crucial in the assessment of the dynamic response. A first model is proposed, based on the outcomes from static tests and from additional insight inferred from the dynamic response. Observing its comparison with the experimental findings in terms of oscillation amplitudes and peak factors, a second refined model is proposed. Moreover, the dynamic behavior of the structure is also investigated through the approach proposed by Engineering Science Data Unit (ESDU) 96030 for tapered structures. The results obtained from applying the spectral model reveal a satisfactory agreement with the experimental outcomes. This accuracy can be significantly attributed to the reproduction of the cellular nature of the vortex-shedding, achieved through an appropriate definition of the Strouhal number along the height of the cylinder. Furthermore, the modeled behavior reveals variations in the regime of the VIV response (e.g., deterministic, transition, stochastic) with respect to the reduced wind velocity, mirroring the findings of the experimental campaign
Non-linear galloping of sagged cables in 1 : 2 internal resonance
No full textThe aeroelastic behaviour of a flexible elastic suspended cable driven by mean wind speed, blowing perpendicularly to the cable's plane, is investigated. By applying the Galerkin procedure to the partial differential equations of motion and using an in-plane and an out-of-plane mode as shape functions, a two-d.o.f. model is derived. The discrete equations are coupled through quadratic and cubic terms arising both from geometric and aerodynamic effects. The associated linear frequencies are assumed to be in an almost 1:2 ratio, so that internal resonance occurs. The multiple scale perturbation method is employed to obtain a set of three amplitude modulation equations, whose coefficients depend on the mean wind speed, which is assumed as control parameter. Two perturbative solutions are developed, each based on a different assumption about the order of magnitude of the static displacements, produced by steady state wind forces. Analytical results are then compared with direct numerical integrations of discrete non-linear equations. By performing a bifurcation analysis, the existence of several equilibrium branches is proved. The relative importance of geometric and aerodynamic non-linearities is discussed through simplified models. The influence on critical and postcritical behaviour of several parameters, including geometrical cable parameters, detuning and non-symmetric flow effects, is investigated. The important role played by the steady state forces is highlighted. (C) 1998 Academic Press
Linear Instability Mechanisms for Coupled Translational Galloping
No full textA linearized coupled flexural two degree-of-freedom model, describing a lumped parameter system
subjected to galloping, is analyzed. Through a perturbation approach, an approximated analytical solution
for the eigenvalue problem is determined. Differently from the expressions existing in literature, the
eigensolutions found here are valid both in quasi-resonant and non-resonant conditions. Discussing them
allows depiction of the scenario of all the possible bifurcation mechanisms in the plane of the invariants of
the aerodynamic damping matrix. In resonance conditions, both simple and double Hopf bifurcations are
found, otherwise only simple Hopf bifurcations (eventually sequential) occur. In any case, both monomodal
and bimodal galloping can take place. A closed form expression for the critical velocity is derived; it
coincides with the exact solution in the resonant case and presents very good agreement with the numerical
solutions in quasi-resonant conditions. The critical velocities are compared with the Den Hartog velocity
and the influence of the horizontal motion is thus evaluated. Numerical examples concerning technical
cases highlight the accuracy of the proposed method
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