基于测力和测压试验的气动导纳识别结果比较

Comparison between aerodynamic admittances identified via force and pressure measurement tests

气动导纳是大跨度桥梁抖振分析的重要参数,通常通过格栅湍流场测力或测压风洞试验进行识别。然而,测力试验中天平和节段模型系统的固有振动和测压试验中测压管路系统的频响效应都会对气动导纳的识别结果产生影响。本文通过格栅湍流场测力和测压试验、采用抖振力自谱和抖振力脉动风交叉谱综合残量最小二乘法识别了准平板断面的气动导纳,其中,在基于测力试验的气动导纳识别中考虑了模型抖振力跨向不完全相关效应的影响,在基于测压试验的气动导纳识别中考虑了按Bergh-Tijdeman理论公式修正或者不修正测压管路系统频响特性影响的2种情况。在此基础上,通过考察气动导纳实验识别结果之间的差别及其与平板断面气动导纳理论解Sears函数之间的差别,研究了天平模型系统固有振动以及测压管路系统频响效应对识别结果的影响。结果表明:天平模型系统的共振会显著放大气动导纳的识别结果;而由于测压管路的固有频率一般要显著高于天平模型系统的固有频率,因此,与基于测力试验得到的气动导纳相比,基于测压试验所得气动导纳总体上更加合理,可用导纳的折算频率范围更广。此外,在一般大跨度桥梁抖振分析所关心的折算频率范围内,考虑测压管路频响特性修正后,气动导纳有一定降低。

Aerodynamic admittances are important parameters in buffeting analysis,and often identified via wind tunnel test of force or pressure measurement in turbulent wind field.However,both the natural vibration of the balance-model system and the frequency-response effect of the tubing system for pressure measurement can affect the identified results of aerodynamic admittance.In this study,the aerodynamic admittances of a quasi-flat section were identified via wind tunnel tests of force and pressure measurements in conjunction with a least square method based on a colligated-residue composed of buffeting-force auto-spectrum and cross-spectra between buffeting force and fluctuating wind speeds(simplified as 'colligated least square method').The span-wise incomplete correlation effect of buffeting forces on the sectional model was taken into account in the identification of aerodynamic admittance based on the force measurement test.Two cases with and without correcting the frequency-response effect of pressure tubing system according to the Bergh-Tijdeman's formulae were considered in the identification ofaerodynamic admittance based on the pressure measurement test.On these bases,the influences of the natural vibration of the balance-model system and the frequency-response effect of the pressure tubing system on the identified results of the aerodynamic admittances were investigated by observing the discrepancies among the test results and the Sears Function,which is the theoretical aerodynamic admittance of flat plate cross section.The results show that the resonance of balance-model system can significantly amplify the identified results of aerodynamic admittances.Furthermore,compared with the results of aerodynamic admittances identified via force measurement test,those identified via the pressure measurement test are much more reasonable in general,and have much wider ranges of reduced frequency with practicable values,because the natural frequency of pressure tubing system is generally much higher than that of the balance-model system.Moreover,the values of the identified aerodynamic admittances would drop to some extent within a concerned range of reduced frequency for buffeting analyses of common long span bridges after considering the correction of frequency-response effect of pressure tubing system,because the resonance effect of tube cavity plays an amplifying role on the fluctuating pressure signals with frequencies lower than the resonant frequency of the tube.