In numerical simulations of flow-induced vibrations (FIV) of a circular cylinder, abundant time series data are available, including cylinder displacement and acting forces. Singular spectrum analysis (SSA) is employed to deal with nonstationary multi-component time series produced in two FIV cases with proper interpretation in physics. In the first case, the cylinder displacement time series is decomposed into two oscillatory components using SSA. The instantaneous frequencies of these two components are obtained by Hilbert transform (HT) and found to be in agreement with the wavelet transform of the cylinder displacement. In the second case, three oscillatory components are extracted from the cylinder displacement time series by SSA. The dominant component is characterized by steady oscillations at the vortex shedding frequency, which suggests a relatively steady vortex shedding process behind the rear cylinder. In contrast, the second component, which is closely associated with the alternate boundary layer separations from the front cylinder, features in the increasing amplitude with time. This implies that the unsteady flow field in the gap might be attributed to the nonstationary cylinder oscillations. This work demonstrates that SSA, in conjunction with HT, enables a comprehensive time-frequency analysis of nonstationary time series obtained in FIV.

中文翻译：

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奇异谱分析在圆柱流激振动非平稳时间序列中的应用


在圆柱流激振动（FIV）数值模拟中，可以获得丰富的时间序列数据，包括圆柱位移和作用力。奇异谱分析 (SSA) 用于处理两个 FIV 案例中产生的非平稳多分量时间序列，并具有正确的物理解释。在第一种情况下，使用 SSA 将气缸位移时间序列分解为两个振荡分量。通过希尔伯特变换（HT）获得这两个分量的瞬时频率，并发现与气缸位移的小波变换一致。在第二种情况下，SSA 从气缸位移时间序列中提取三个振荡分量。主要成分的特征是涡旋脱落频率下的稳定振荡，这表明后圆柱体后面存在相对稳定的涡旋脱落过程。相比之下，第二个分量与前圆柱体的交替边界层分离密切相关，其特征是随着时间的推移幅度不断增加。这意味着间隙中的非稳态流场可能归因于非稳态圆柱体振荡。这项工作表明，SSA 与 HT 相结合，可以对 FIV 中获得的非平稳时间序列进行全面的时频分析。