Refined Study On The Determination Of Aerodynamic Admittance Functions For Rectangular Cylinder And Streamlined Box Girder

The two-wavenumber three-dimensional aerodynamic admittance function(3D AAF)is one of the key parameters in the calculating of buffeting responses for long-span bridges and blunt bodies.Being able to describe the inner mechanism of turbulence's three-dimensional effects on the buffeting forces,the 3D AAF can contribute to the refined analysis of buffeting responses.However,the relevant previous studies are focused on studying the unsteady aerodynamic effects of the w component of turbulent flow at a zero Ao A.When the Ao A is nonzero,it is necessary to investigate the contribution of the u component of turbulence on the unsteady aerodynamic lift force.On the other hand,the two-dimensional aerodynamic admittance(2D AAF)is the particular solution of 3D AAF when the “Strip theory” is valid.Providing that the span-chord ratio of the bridge is large enough,the buffeting forces estimated from the2 D AAF align well with those obtained by the 3D AAF.Consequently,the buffeting problem of long-span bridges can be significantly simplified using the 2D AAF without taking into account the three-dimensionality of the turbulent flow.Due to the disadvantages of the current identification method for 2D AAF,it is necessary to make it simpler and more efficient.Besides,the pressure-measurement tests in the wind tunnel cannot be applied to the 3D AAF identification of bridges or blunt bodies with complex ancillary components,it is,therefore,necessary to derive a more general method based on force-measurement tests.This dissertation is proposed to solve the above problems,the main research contents include the following aspects:1)Based on Ribner's three-dimensional theoretical framework,a generalized and efficient approach is proposed to derive the closed-form expressions of the 3D AAFs of blunt bodies at an Ao A.Wherein,the contributions of u-and w-components of turbulent flow are both considered,their unsteady effects on the buffeting force are also taken into account.Then,the u-and w-separated 3D one-wavenumber AAFs of a rectangular and a streamlined box girder are identified by a passive wind tunnel pressure test.Comparing with the traditional equivalent one-wavenumber AAFs,the present approach is of importance in predicting the buffeting forces caused by either the u-or w-turbulence for blunt bodies at an Ao A.2)To overcome the limitations of passive turbulence simulation,an active wind tunnel simulation method of longitudinal continuous turbulence is proposed in a multiple-fan active control wind tunnel.A theoretical identification framework of three-dimensional aerodynamic admittance of a rectangular section and a streamlined box girder under the action of longitudinal turbulence is established,and the closed expression of three-dimensional aerodynamic admittance is proposed.Using the combination of active and passive wind tunnel testing,a theoretical identification method of the u-and w-separated 2D AAF is proposed,which provides a theoretical basis to understand the influences of u-and w-components of turbulent flow on the buffeting load for blunt-body section.3)A CFD method is proposed to generate the longitudinal and vertical sinusoidal flows with multi-frequencies.The u-and w-separated 2D AAFs of the rectangular and streamlined box girder are then identified ‘frequency by frequency'.Comparing with the identification method based on single-frequency sinusoidal flow,the CFD method can be applied to higher frequencies and can obtain the results more efficiently.Meanwhile,the results are also compared with those obtained in the continuous turbulence field,which shows roughly consistent.The advantage of the CFD method is that it avoids the relatively cumbersome process of 3D AAF recognition and is more convenient to use.4)The mathematical relationships between the buffeting forces measuring on one strip(in the pressure-measurement test)and one segment(in the force-measurement test)are derived.Then,a theoretical framework is proposed to identify the 3D AAF through synchronously double-balance force measurements.It is proved that the framework can be applied to a segment of any length.Then,the proposed method is used to investigate the influences of railing's ventilation rate on the buffeting forces and AAF for the streamlined box girder with accessory structures.