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Time-domain parameter identification of aeroelastic loads by forced-vibration method for response of flexible structures subject to transient wind

机译：基于瞬态风响应的弹性振动响应的强迫振动时空参数识别

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Slender structures representing civil, mechanical and aerospace systems such as long-span bridges, high-rise buildings, stay cables, power-line cables, high light mast poles, crane-booms and aircraft wings could experience vortex-induced and buffeting excitations below their design wind speeds and divergent self-excited oscillations (flutter) beyond a critical wind speed because these are flexible. Traditional linear aerodynamic theories that are routinely applied for their response prediction are not valid in the galloping, or near-flutter regime, where large-amplitude vibrations could occur and during non-stationary and transient wind excitations that occur, for example, during hurricanes, thunderstorms and gust fronts. The linear aerodynamic load formulation for lift, drag and moment are expressed in terms of aerodynamic functions in frequency domain that are valid for straight-line winds which are stationary or weakly-stationary. Application of the frequency domain formulation is restricted from use in the nonlinear and transient domain because these are valid for linear models and stationary wind. The time-domain aerodynamic force formulations are suitable for finite element modeling, feedback-dependent structural control mechanism, fatigue-life prediction, and above all modeling of transient structural behavior during non-stationary wind phenomena. This has motivated the developing of time-domain models of aerodynamic loads that are in parallel to the existing frequency-dependent models. Parameters defining these time-domain models can be now extracted from wind tunnel tests, for example, the Rational Function Coefficients defining the self-excited wind loads can be extracted using section model tests using the free vibration technique. However, the free vibration method has some limitations because it is difficult to apply at high wind speeds, in turbulent wind environment, or on unstable cross sections with negative aerodynamic damping. In the current research, new algorithms were developed based on forced vibration technique for direct extraction of the Rational Functions. The first of the two algorithms developed uses the two angular phase lag values between the measured vertical or torsional displacement and the measured aerodynamic lift and moment produced on the section model subject to forced vibration to identify the Rational Functions. This algorithm uses two separate one-degree-of-freedom tests (vertical or torsional) to identify all the four Rational Functions or corresponding Rational Function Coefficients for a two degrees-of-freedom (DOF) vertical-torsional vibration model. It was applied to a streamlined section model and the results compared well with those obtained from earlier free vibration experiment. The second algorithm that was developed is based on direct least squares method. It uses all the data points of displacements and aerodynamic lift and moment instead of phase lag values for more accurate estimates. This algorithm can be used for one-, two- and three-degree-of-freedom motions. A two-degree-of-freedom forced vibration system was developed and the algorithm was shown to work well for both streamlined and bluff section models. The uniqueness of the second algorithms lies in the fact that it requires testing the model at only two wind speeds for extraction of all four Rational Functions. The Rational Function Coefficients that were extracted for a streamlined section model using the two-DOF Least Squares algorithm were validated in a separate wind tunnel by testing a larger scaled model subject to straight-line, gusty and boundary-layer wind.
机译：代表民用，机械和航空航天系统的细长结构，例如大跨度桥梁，高层建筑，斜拉索，电力线电缆，高光桅杆，吊车和飞机机翼，在其下方可能会受到涡流和抖振的激发设计风速和发散的自激振荡（颤动）超过临界风速，因为它们很灵活。常规用于其响应预测的传统线性空气动力学理论在疾驰或接近颤动的情况下无效，在这种情况下，可能会发生大振幅振动，并且在非平稳和瞬态风激发期间（例如在飓风期间）雷暴和阵风阵线。升力，阻力和力矩的线性气动载荷公式由频域中的气动函数表示，这些函数对于固定或弱平稳的直线风有效。频域公式的应用在非线性和瞬态域中受到限制，因为它们对于线性模型和平稳风有效。时域气动力公式适用于有限元建模，依赖于反馈的结构控制机制，疲劳寿命预测，尤其适用于非平稳风现象期间的瞬态结构行为建模。这激励了气动载荷时域模型的开发，该模型与现有的频率相关模型并行。现在，可以从风洞测试中提取定义这些时域模型的参数，例如，可以使用截面模型测试和自由振动技术来提取定义自激风载荷的有理函数系数。但是，自由振动方法有一些局限性，因为很难在高风速下，在狂风中或在空气动力学阻尼为负的不稳定截面上应用。在当前的研究中，基于强制振动技术开发了用于直接提取有理函数的新算法。所开发的两种算法中的第一种使用在测得的垂直或扭转位移与在受强迫振动的截面模型上产生的测得的气动升力和力矩之间的两个角相位滞后值来确定有理函数。该算法使用两个单独的单自由度测试（垂直或扭转）来识别两个自由度（DOF）垂直扭转振动模型的所有四个有理函数或相应的有理函数系数。将其应用于流线型截面模型，并将结果与​​早期自由振动实验获得的结果进行了比较。开发的第二种算法基于直接最小二乘法。它使用位移，空气动力升力和力矩的所有数据点，而不是相位滞后值来进行更准确的估算。该算法可用于一度，二度和三度运动。开发了一种两自由度的强制振动系统，该算法对流线型和钝壁截面模型均显示良好的效果。第二种算法的独特之处在于，它仅需在两种风速下测试模型即可提取所有四个有理函数。使用两自由度最小二乘算法为流线型截面模型提取的有理函数系数通过在直线风，阵风和边界层风的作用下测试更大比例的模型在单独的风洞中进行了验证。

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    Cao, Bochao;

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  • 年度 2012
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