渡槽排架结构人工激励模态试验分析

开展渡槽排架单向单输入多输出SIMO(Single Input Multiple Output)法、双向多输入多输出MIMO(Multiple Input Multiple Output)法人工激励模态试验,选用特征系统实现法识别纵向、横向、双向模态参数,结果表明,单向SIMO法稳定图绝大多数谱峰明显、模态识别效果较好,纵向模态比横向丰富、识别效果好;双向MIMO法纵向谱峰大多数明显,横向除双向第2阶(即横向第1阶)谱峰明显外,其他基本很小,尤其是横向模态频率接近纵向时,甚至无谱峰,只识别出纵向模态;排架结构以排架柱弯曲振动为主,纵向低阶、高阶模态横梁分别以平动或转动刚体振动、弯曲振动为主,横向模态横梁为平动或不动刚体振动;两种方法识别出的模态频率误差较小,模态阻尼在正常范围,但双向MIMO法部分横向模态未能准确识别。从识别精度、试验工作量及操作便捷性而言,排架结构人工激励模态试验选择单向SIMO法优于双向MIMO法。

Modal test analysis for an aqueduct bent structure under artificial excitation

Modal tests with SIMO method in a single direction and MIMO method in bi-direction under artificial excitation were conducted for an aqueduct bent structure. Longitudinal, transverse and bi-directional modal parameters were identified with the eigen-system realization algorithm. The results showed that most spectral peaks of stabilization diagrams are obvious using SIMO method, modal identification effects are better, longitudinal modes are richer than transverse modes;the most spectral peaks of longitudinal modes are obvious using MIMO method, but those of transverse modes are small except for the bidirectional second order mode, i.e., the transverse first order one;if transverse modes’ frequencies are close to those of longitudinal modes, they have no spectral peaks, only longitudinal modes are identified;bent structure’s modes mainly are its column’s bending vibrations;its beam’s lower and higher order longitudinal modes mainly are translation vibration or rotating rigid body one and bending one, respectively;the beam’s transverse modes are translation vibration or stationary rigid body one;modal frequencies identified using SIMO and MIMO methods have small errors;identified modal damping is within a normal range;partial transverse modes can’t be correctly identified using MIMO method;the SIMO method in a single direction is better than the MIMO method in bi-direction for bent structures’ modal tests under artificial excitation, the former has a higher identification accuracy, costs less time and is easy to operate.