Analysis Of Wind Pressure Field On Bridge Deck Surface Based On Proper Orthogonal Decomposition Method

With the span of the bridge increasing,the structural rigidity decreases and the windinduced vibration response increases,and the wind stability becomes one of the main controlling factors of structural design and construction safety.In this paper,wind tunnel tests and the CFD numerical simulation are used to obtain the surface wind pressure datas of the typical sections in the process of "soft" flutter and vortex induced vibration,which are analyzed and compared by the proper orthogonal decomposition(POD)method.The purpose of the work is to study the characteristic of surface wind pressure field in "soft" flutter and vortex-vibrating process.Some main results are summarized as follows:For the two typical girder sections(blunt body,streamlined),the first order mode of proper orthogonal decomposition based on the covariance matrix(CPT)is the main reason for "soft" flutter of the bridge,thus CPT mode one makes dominant contribution for the fluctuating wind forces(lift,drag and torsional moment).The energy's proportion of CPT mode one for streamlined section is significantly higher than that for the blunt body section.For the vortex induced vibration process of the streamlined girder section,CPT mode one and mode two are very important,which makes the greatest contribution to the drag and lift force respectively,being called the "DRAG" mode and "LIFT" mode.The absolute value of CPT modal shape is consistent with the standard deviation distribution of surface wind pressure in that CPT mode.That is,the pressure in the ups and downs of the POD modal shape fluctuates greatly and the pressure at the flat surface is small.This reqires that the mean value of the wind pressure data should be excluded during the POD analysis in order to ensure the accuracy of the physical meaning of the mode.The first order mode of proper orthogonal decomposition based on the cross-power spectral density matrix(SPT)contributes greatly to the total energy at the main excitation frequency(flutter and double flutter frequencies or vortex and double vortex frequencies),more than 90%.At the flutter and vortex frequency,SPT mode one reproduces both the in-phase and the out-of-phase components,associating with CPT mode one and mode two respectively.The normalised eigenvector spectrum of CPT mode one shows that only the shape of SPT mode one coincides with that of CPT mode one when "soft" flutter occurs.Inthe case of vortex induced vibration,the SPT mode ”closest” CPT mode one is not always SPT mode one,but also SPT other modes.