GAPS -Galloping Amplitude Prediction Software

A software based on a modal approach to describe the interaction between a 4-conductor bundle and wind-ice excitation. A finite-element model of the bundle is used to extract the mode parameters of the entire bundle; the eigenmodes of the bundle are then processed to obtain the mode shapes of an equivalent super-conductor. The motion of the expanded bundle is then described through mode coordinates representing the first horizontal, vertical and torsional modes. The aerodynamic coefficients of the entire bundle with the conductors covered with ice have been obtained through wind tunnel testing (ice formations have been represented with suitable artificial shapes). These coefficients have been introduced in the modal analysis, allowing to reproduce the onset of galloping instability associated with combination of torsional and vertical displacements and to predict the maximum oscillations produced by iced conductor galloping. Instead of time-domain simulations, an alternative approach, named energy method is used: this estimates oscillation amplitudes on the basis of the equilibrium between energy introduced in one cycle by aerodynamic forces and the energy dissipated by internal damping. The energy approach hypothesizes that the relative amplitudes and phases between vertical and torsional mode coordinates in a limit cycle can be derived from the eigenvector determined through a modal analysis. The time-domain simulation method for detecting the maximum amplitudes of the motion, needs a difficult elaboration of the results and is not practical from an engineering point of view. The energy approach is instead in condition to compute directly the motion amplitudes due to conductor galloping as a function of wind speed, shape of the bundle and ice formations and devices added to control the oscillations. This software is used for an analytical-analytical + analytical-experimental benchmark defined inside the Working Group Cigre B2-84. Through this benchmark the software will be calibrated/validated.