基于位移测量的非线性涡激力模型参数识别方法

Displacement-based Parameter Identification Method of the Nonlinear Model for Vortex-induced Force

利用半经验数学模型来近似表示涡激力是目前研究涡激共振所采用的主要方法,但关于非线性涡激力模型参数的试验识别研究还较少,现有识别方法也有待改进。为了更方便可靠地识别非线性涡激力模型中的参数,根据能量等效原理推导出一种基于节段模型位移响应的气动参数识别新方法。通过节段模型风洞试验测得中央开槽箱梁断面的扭转涡激共振位移响应,应用新方法识别简化非线性涡激扭矩模型中的气动参数,并对参数识别精度做出评价。将新方法与Ehsan等所建议的位移法以及基于实测力时程的三步最小二乘拟合法进行了对比。结果表明:利用新方法识别得到的气动参数可以较好地预测系统的扭转涡激共振位移响应;基于一致的系统线性机械参数,新方法识别得到的气动参数与Ehsan等所建议位移法的识别结果基本相同,而新方法能进一步考虑对识别结果影响较为显著的机械参数非线性特性;当新方法考虑非线性机械参数时,其识别结果和基于实测力时程的三步最小二乘拟合法相比也十分吻合,并且新方法更为简便。

Describing the vortex-induced force(VIF) using a semi-empirical mathematical model is a widely adopted approach in the study of vortex-induced vibration(VIV). However, studies on to-be-identified parameters in this type of model are limited, and the existing identification methods need to be improved. To obtain these parameters conveniently but with high reliability, a new parameter identification method is proposed in this study based on the energy equivalence principle. The proposed method uses the displacement responses of a sectional model to identify the parameters of the nonlinear force model. The torsional VIV displacement responses of a central-slotted box deck were measured through wind tunnel tests of a sectional model. With the measured displacement responses, the aerodynamic parameters of a simplified nonlinear model of vortex-induced torque were identified by the proposed method, and the accuracy of the identified parameters was validated. The proposed method was compared with the displacement method presented by Ehsan and Scanlan(E-S method), and the three-step least-squares method based on the time history of the measured force(force method). The results show that the aerodynamic parameters as identified by the proposed method are sufficiently accurate to predict the torsional VIV displacement. With a model-suspension system of linear mechanical parameters, the aerodynamic parameters obtained by the proposed method approximate those by the E-S method, and the former can further consider the nonlinearities of the mechanical parameters that have significant influence on the aerodynamic parameter identification results. The aerodynamic parameters estimated with the proposed method also agree with those obtained using the force method when considering the nonlinear mechanical parameters, whereas the proposed method is more convenient.