A comprehensive empirical equation for the hydrodynamic damping of vibrating blade-like structures

Abstract

Blade fatigue is a widely concerning issue when a turbine transforms ocean energy into electronic power. The frequent changes in flow velocity may cause a wide range of hydraulic excitation frequencies and result in blade resonance. The hydrodynamic damping ratio is of great importance in assessing the resonance amplitude in the design stage. However, it is difficult to make accurate predictions through the basic prediction equation (BPE) because some key flow parameters are not fully taken into account. The present research simplifies the blades as hydrofoils and devotes to improving the accuracy of the BPE. Firstly, multiple correction terms (including velocity, attack angle, and tip clearance correction terms) relative to the BPE are proposed, based on previously published works. Secondly, a comprehensive empirical equation (CEE) is constructed, by coupling the BPE and multiple correction terms. Accuracies of the CEE for first bending and torsional modes are evaluated separately In particular, the average error of the CEE for the first bending mode decreases from 57.16% to 9.87% in comparison with that of BPE. And the average error decreases from 259.48% to 50.72% for the first torsional mode. CEE provides a new tool for engineering evaluation of the resonance failure of blade-like structures.