覆冰导线三自由度耦合舞动稳定性判定及气动阻尼研究

Stability evaluation and aerodynamic damping study on three-degree-of-freedom coupled galloping of iced conductors

利用风洞内支架式三自由度频率可调的弹簧悬挂装置对D形覆冰六分裂导线节段气弹模型进行舞动试验,在不同气动力特性的风攻角下调整竖/扭自振频率比及风速,激发并记录纯竖向、纯扭转、竖扭耦合和扭转水平耦合等失稳舞动。分别基于实测响应和三自由度舞动响应非线性数值模拟结果识别导线的竖向和扭转气动阻尼并与Den Hartog或Nigol舞动理论计算值进行对比,研究导线气动阻尼与气动特性、自振特性及风速之间的关系。试验结果发现:由于Den Hartog或Nigol系数正负不同以及竖/扭频率比不同,导线气动负阻尼绝对值会随风速提高以指数形式增大或者是随风速提高先增大后减小至小于结构阻尼;用单自由度舞动理论来预测三自由度舞动存在较大缺陷且偏于不安全。基于特征值摄动法提出覆冰分裂导线竖向-水平-扭转三自由度耦合的舞动稳定性判断条件式,解释了无法用Den Hartog或Nigol单自由度稳定性判断条件式说明的舞动现象,并得到试验结果的验证。

Wind tunnel tests for galloping of an ice-coated D-shape sectional model of 6-bundled conductors were carried out using a scaffolding spring suspension device with adjustable 3-DOF frequency. By adjusting the ratio of vertical to torsional natural frequency of vibration and the wind speed under different attack angles, unstable vertical galloping, torsional galloping, vertical-torsional coupled galloping and torsional-horizontal coupled galloping were excited and recorded, respectively in the wind tunnel tests. Vertical and torsional aerodynamic damping identified from galloping of measured response and numerical simulation was compared with the calculation value based on Den Hartog or Nigol theory. The corresponding influence of aerodynamic characteristic, natural vibration characteristic and wind speed on aerodynamic damping had been studied separately. Results from the wind tunnel tests indicate that the absolute value of conductor＇s negative aerodynamic damping may increase exponentially with wind speed increasing, or that it may first increase and then decrease to less than the structural damping because of the difference in positive and negative of Den Hartog coefficient or Nigol coefficient and the difference in the ratio of vertical to torsional frequency. It also indicates that galloping theory of single-degree-of-freedom can＇t predict three-degree-of-freedom coupled galloping. Conditional stability criterion for three-degree-of-freedom coupled galloping of iced conductor was proposed based on eigenvalue perturbation method. The proposed stability criterion can explain the galloping phenomena which can＇ t be explained by Den Hartog or Nigol theory of single-degree-of-freedom. The conclusion was verified by test results.