Generalized lift force model under vortex shedding

peer reviewe

Prévention des blessures chez le cycliste : développement d’un système d’évaluation de la position

editorial reviewe

Parameter identification of wake-oscillator from wind tunnel data

peer reviewedThis paper proposes a procedure for the parameter identification of Tamura's wake-oscillator model. A multiple timescale analysis of the dimensionless model shows that the response is governed by two dimensionless groups D0 and D1, highlighting the importance of the forcing terms in the two governing equations, the total (aerodynamic and structural) damping and the coefficient ɛ of the fluid Van der Pol oscillator. In particular, this approach provides a simple closed form expression for the steady state amplitude of the structural displacement, which is usually measured in wind tunnel experiments. The proposed method of identification consists in fitting the parameters of the model by adjusting the closed-form expression of the VIV curve on experimental points. It is developed into two variants: a least-square fitting and a fitting based on some simple geometrical indicators (height, width, asymmetry). The model is sufficiently versatile to estimate the maximum amplitude and lock-in range. Applications of VIV in air for different geometries and Scruton numbers show that the two variants give equivalent results thanks to the robustness of the method. The paper is first intended for experimenters looking for a simple robust procedure to identify the parameters of the wake-oscillator, which can then be used in a prediction phase. The derivation of the slow phase version of Tamura's model might also be appealing to better understand the main features of this model

A Cross-Validation Approach to Approximate Basis Function Selection of the Stall Flutter Response of a Rectangular Wing in a Wind Tunnel

The stall flutter response of a rectangular wing in a low speed wind tunnel is modelled using a nonlinear difference equation description. Static and dynamic tests are used to select a suitable model structure and basis function. Bifurcation criteria such as the Hopf condition and vibration amplitude variation with airspeed were used to ensure the model was representative of experimentally measured stall flutter phenomena. Dynamic test data were used to estimate model parameters and estimate an approximate basis function

Real-scale observations of vortex induced vibrations of stay-cables in the boundary layer

Abstract This paper shows some records and analysis of evidences of vortex induced vibrations of very long stay cables in the atmospheric boundary layer. The considered structure is a 254-m high telecommunication antenna whose structural system is made of a light flexible metallic truss, approx. 10×10m square, which is stayed at five different levels by a set of 20 pairs of stay-cables. The exposure of this antenna is category I with a low-turbulence wind flow which results in a high sensitivity to vortex induced vibrations. The fundamental frequency of the longest cable is 0.3 Hz so that several dozens of regularly spaced natural frequencies could be observed with a sampling frequency of 500 Hz. Sufficiently long recordings allowed to distinctly observe the separate peaks corresponding to the various modes of the cables. Among them many are excited by the detachment of vortices, taking place at different frequencies (because of different cable diameters and the change of wind velocity along the height of the antenna) in the range 35-55 Hz. Referring to the so-called spectral model proposed by Vickery and Clark, the detachment of vortices takes place in a certain bandwidth, whose extent is not completely understood yet. This bandwidth is clearly observed with our long stay-cables because of the large density of mode shapes in the range [0, 200] Hz and because of their regular spacing in the spectral domain. To the author’s knowledge this constitutes a first attempt at identifying this parameter of the Vickery and Clark model from full-scale measurements