Operational fluid modal analysis of full-scale pressure and wake flow measurements on the Gjemnessund Bridge

Abstract

The present paper is dealing with observations of vortex shedding on the wedge-shaped Gjemnessund Bridge Box girder in the period from August 2019 to February 2020. Wake flow oscillations are identified using operational fluid modal analysis with correlation functions of surface point pressures near the trailing edge, flow velocities upstream and in the wake measured in full-scale. Even though vortex shedding is barely observed in the lift and response spectra, operational fluid modal analysis is able to identify evidence from vortex shedding. A characteristic vortex shedding fluid mode shape is recognized for 179 ten-minutes records at Reynolds numbers ranging from 500,000 to 2,000,000. The Strouhal numbers from the full-scale measurements are identified simultaneously with the vortex shedding fluid mode shapes. A comparison with wind tunnel tests of a 1:30 scaled section model indicates a Reynolds number dependency of the Strouhal number.