Stability to Translational Galloping Vibration of Cylinders at Different Mean Angles of Attack

Luo, S. C.; Chew, Y. T.; Lee, T.S.; Yazdani, M. G.

doi:10.1006/jsvi.1998.1639

Cited by 34 publications

(9 citation statements)

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“…The difference in the behaviour may be explained by flow reattachment being fully achieved for rectangular sections with aspect ratio larger than 2, as found in numerical simulations of the flow by Sohankar et al (1997). As to the pure rotational stability, Robertson et al (2003) numerically found severe galloping instability for square and any rectangular sections with negative C ′ M at 0°angle of attack, as also reported from previous experiments (Blevins, 1994;Luo et al, 1998;Nakamura and Mizota, 1975). Hence, the analytical solutions presented here for 1DOF torsional and 2DOF translational galloping qualitatively agree well with previous numerical and experimental work.…”

Section: Square Rectanglesupporting

confidence: 77%

An analytical solution for the galloping stability of a 3 degree-of-freedom system based on quasi-steady theory

Macdonald

2016

Journal of Fluids and Structures

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms An analytical solution for the galloping stability of a 3 degree-of-freedom system based on quasi-steady theory a b s t r a c tThe aerodynamic forces on a two-dimensional three-degree-of-freedom (3DOF-heave, sway and torsion) body of arbitrary cross-section are considered, for arbitrary wind direction relative to the principal structural axes. The full 3DOF aerodynamic damping matrix is derived, based on quasi-steady theory, using the commonly-used concept of an aerodynamic centre to represent the effect of the torsional velocity on the aerodynamic forces. The aerodynamic coefficients are assumed to be consistent functions of only the relative angle of attack. It is shown that the determinant of the quasi-steady aerodynamic damping matrix is always zero. The galloping stability of the aerodynamically coupled system is then addressed by formulating the eigenvalue problem, for which analytical solutions are derived for the case of perfectly tuned structural natural frequencies. The solutions define a non-dimensional effective aerodynamic damping coefficient, indicating how stable the system is. A trivial solution always exists, with zero effective aerodynamic damping, corresponding to rotation about the aerodynamic centre, and relatively simple exact closed-form solutions are derived for the other one or two solutions, the minimum solution defining the stability of the system. Example results are presented and discussed for square, rectangular (aspect ratio 3) and equilateral triangular sections and a lightly iced cable, and they are compared with results using previous solutions for 2DOF translational and 1DOF pure torsional galloping. For the shapes considered it is found that the stability of the 3DOF system is normally close to that of the 2DOF translational system, with a relatively small influence of the stability of the torsional degree of freedom, although in some instances, especially at the critical angles of attack, it can significantly affect the stability.

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Section: Square Rectanglesupporting

confidence: 77%

An analytical solution for the galloping stability of a 3 degree-of-freedom system based on quasi-steady theory

Macdonald

2016

Journal of Fluids and Structures

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“…The true reason for the lack of observed galloping in this case, which is theoretically only slightly unstable, is likely related to the level of structural damping and/or slight inaccuracies in quasi-steady theory when hybrid vortex-buffeting-galloping mechanisms are involved, as discussed by Bearman et al (1987) andLuo et al (1998).…”

Section: The Effect Of Frequency Detuningmentioning

confidence: 99%

Misconceptions and Generalizations of the Den Hartog Galloping Criterion

Nikitas

Macdonald

2014

J. Eng. Mech.

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Classical quasi-steady galloping analysis deals exclusively with cases of across-wind vibrations, leaving aside the more general situation where the wind and motion may not be normal. This can arise in many circumstances, such as the motion of a power transmission cable about its equilibrium configuration, which is swayed from the vertical plane due to the mean wind, or for a tall slender structure in a skewed wind. Furthermore the generalisation to such situations, when this had been made, has only considered special issues.In this paper the correct equations for the quasi-steady aerodynamic damping coefficients for the rotated system or wind are derived, and differences from other variants are highlighted. Motion in two orthogonal structural planes is considered, potentially giving coupled translational galloping, for which previous analysis has often been limited or has even arrived at erroneous conclusions. For the two-degree-of-freedom case, the behaviour is dependent on the structural as well as aerodynamic parameters, in particular the orientation of the principal structural axes and the relative natural frequencies in the two planes. For the first time, differences in the aerodynamic damping and zones of galloping instability are quantified, between solutions from the correct perfectly tuned, well detuned and classical Den Hartog equations (and also an incorrect generalisation of it), for a variety of typical cross-sectional shapes. It is found that although the Den Hartog summation often gives a reasonable estimate for the actual aerodynamic damping even for the rotated situation, in some circumstances the differences can be quite large.

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“…In the last decades, besides theoretical work and numerical approaches (Kazakewich and Vasilenko, 1996;Tamura, 1999;Tamura and Itoh, 1999), large efforts have been devoted to experimentally study the galloping features of many bodies having different cross-sections. The influence of relevant parameters like the incident turbulence (Li et al, 1998;Ziller and Ruscheweyh, 1997;He´mon et al, 2001;He´mon and Santi, 2002), the geometry of the cross-section (Ruscheweyh et al, 1996;Kawai, 1998;Luo et al, 1998;Okajima et al, 1992), or the hysteresis phenomenon (Luo et al, 2003) has been treated. Most of the effort in galloping oscillation research has been concentrated on bodies with square or rectangular crosssections, although prismatic bodies with other cross-sectional shapes may also be unstable to transverse galloping, as it happens with D-shaped cylinders, as well as highly asymmetric shapes such as ice-coated power lines and cables (Chabart and Lilien, 1998;McComber and Paradis, 1998).…”

Section: Introductionmentioning

confidence: 99%