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Experimental studies and perspectives of semi-active oleodynamic devices for seismic protection of structures
No full textGeneral editors: Roy T. Severn and Rogério Bairra
Experimental studies and perspectives of semi-active oleodynamic devices for seismic protection of structures
No full textGeneral editors: Roy T. Severn and Rogério Bairra
Effects of ice accretion on the aerodynamics of bridge cables
No full textUndesirable wind induced vibrations of bridge cables can occur when atmospheric conditions are such to generate ice accretion. This paper contains the results of an extensive investigation of the effects of ice accretion due to in-cloud icing, on the aerodynamic characteristics of bridge hangers and stay cables. The aim of this paper is twofold; first, it was investigated the ice accretion process and the final shape of the ice accreted; then the aerodynamics of the ice accreted bridge cables was characterized, and related to the ice shape. Different climatic conditions, i.e. combinations of temperature, wind speed and yaw angle of accretion, were reproduced in a climatic wind tunnel, giving rise to different types of accretion. These were chosen such to generate the most common natural ice formations expected to produce bridge cable vibrations. A description of the geometric characteristics of the ice accretions is given in the paper. Only for the bridge hanger case, a short description of the evolution of the ice accretions is given. The aerodynamic force coefficients were then measured with varying yaw angle, angle of attack and wind speed, and are presented and discussed in the paper; these are found to be significantly affected by the characteristics of the ice accretion
Quasi-steady three-degrees-of-freedom aerodynamic model of inclined/yawed prisms: Formulation and instability for galloping and static divergence
No full textIn this study, a generalized three-degree-of-freedom (3-DoF) analytical model is formulated to predict linear aerodynamic instabilities of a prism under quasi-steady (QS) conditions. The prism is assumed to possess a generic cross-section exposed to turbulent wind flow. The 3-DoFs encompass two orthogonal horizontal directions and rotation about the prism body axis. Inertial coupling is considered to account for the non-coincidence of the mass center and the rotation center. The aerodynamic force coefficients—drag, lift, and moment—depend on the Reynolds number based on relative flow velocity, angle of attack, and the angle between the wind and the cable. Aerodynamic forces are linearized with respect to the static equilibrium configuration and mean wind velocity. Routh-Hurwitz and Liénard and Chipart criteria are used in the eigenvalue problem, yielding an analytical solution for instabilities in galloping and static divergence types. Additionally, the minimum structural damping and stiffness required to prevent these instabilities are numerically determined. The proposed 3-DoF instability model is subsequently applied to a conductor with ice accretion and a full-scale dry inclined cable. In comparison to existing models, the developed model demonstrates superior prediction accuracy for unstable regions compared with results in wind tunnel tests
Experimental study of the effect of icing on the aerodynamics of circular cylinders - Part II: Inclined flow
No full textIn this paper effects of ice accretion on the aerodynamics of plain inclined circular cylinders are examined. Aerodynamic force coefficients are found as a function of Reynolds number for ice produced with varying temperature and yaw angle of the cylinder with respect to the flow. The cylinders are produced from HDPE, as used for bridge stays. Variations in the accretion parameters were chosen to generate the most common natural ice formations, which might also be expected to produce bridge cable vibrations. A parallel paper deals with the case of circular cylinders in cross flow
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