An application of system identification in the two-degree-freedom VIV experiments

Abstract

Experiments on the two-degree-freedom vortex-induced vibration (VIV) of a flexibly-mounted, rigid, smooth cylinder were performed at MIT. The research reported here is an analysis of the cylinder’s trajectories. System identification methods were used to derive a best Fourier representation for these motions and to parse these motions into symmetric and asymmetric behaviors. It was postulated that the asymmetric behavior was due to distortions caused by the free surface and bottom used at the test facility, and that the symmetric behavior is representative of deepwater VIV. Further application of systems identification methods was used to associate the symmetric behavior and test conditions to a traditional vortex street model. These models were analyzed for their ability to predict details of VIV trajectories.

摘 要

采用系统识别的方法对双自由度圆柱体的涡激振动特性进行了分析研究。 试验是在美国麻省理工大学开展, 在得到的圆柱体涡激振动轨迹中, 由于受到试验条件的影响, 如自由液面和水池池底, 得到的轨迹并非对称的 “8 字形”。 因此首先对原始试验结果进行了分解, 得到其傅里叶级数展开形式, 然后采用了系统识别的方法对其进行分解, 分别得到对称和非对称的试验结果, 并认为对称的结果为理想或深海条件下圆柱体的涡激振动轨迹, 而在自由液面和水池池底等其他因数的干扰下, 产生了非对称的试验结果。