Identifying Long-Span Bridge Flutter Derivativess Via The Free Vibration Method Method Based On The Fluent Software

This paper applied Fluent software to simulate flow field around large span bridge. Considering thefluid-solid coupling effect, the author separately applied separation state method of free vibration andcoupling state method to identify flutter derivatives in the large span bridge.In this paper, the fluid-structure couple was achieved via meshed driven by embedding the newmakequation in the macros, which are provided by the Fluent software. The modal parameter expression of theflutter derivatives under conditions of vertical bending vibration, torsional vibration and bending-torsioncoupling was deduced, according to the theory of identifying flutter derivatives using the separation statemethod The modal parameter needed while identifying flutter derivatives was identified by the Matlabprogram, which was written based on the IDT time domain method; the theory of using coupling statemethod to identify flutter derivatives is described, system least squares method is adopted to identify theflutter derivatives of coupling state method.First of all, with thin plate as the research object, both separated state method and coupling statemethod were adopted separately to recognize chatter of derivatives, compared with chatter of derivativesidentified by forced vibration method and theoretical solution of the ideal plate. By comparison it showedthat: there were smaller difference between chatter derivatives recognized by separation state method andchatter derivatives recognized by forced vibration method and the Theodorsen theoretical solution.thereby，the accuracy and feasibility of separation state method and coupling state method to identify flutterderivatives are validatedThen, the separate state method, coupling state method and forced vibration method were adopted foridentifying the flutter derivatives of the long-span Nizhou watercourse bridge’s section under0°and±3°wind attack angle, and then made comparison with flutter derivatives got via theoretical solution and windtunnel experiment. Among the results, flutter derivativeA₂^*achieved via separate state method is moreclose to the wind tunnel experiment’s result; the experimental result of flutter derivativeA₃^*is the closestto the values got via separate state method and coupling state method at low wind speed, while at high windvelocity, it is more close to value got from forced vibration method. For other flutter derivatives got viaseparate state method, coupling state method and forced vibration method is more close to the platetheoretical solutions. Under the conditions of small wind attack angles, wind attack angles make no obviousaffection on other flutter derivativess.