失调参数对T尾结构振动模态局部化的影响

 对飞机T尾结构振动模态的局部化现象和频率曲线转向现象进行了研究。根据峰值振幅比，改进了局部化度的定义。根据平尾刚度和垂尾刚度对T尾结构固有频率的影响，定义了T尾结构的耦合度。分析了T尾结构中平尾的失调质量、失调刚度及失调位置参数对T尾结构模态局部化度、模态频率和模态振型的影响。结果表明，失调参数是通过仅改变两支相关模态中的某一支模态固有频率来实现频率曲线转向，进而引起模态局部化现象的。平尾发生质量失调时，质量较大一侧的振幅大于质量较小一侧的振幅；发生刚度失调时，刚度较小一侧的振幅大于刚度较大一侧的振幅。在平尾翼尖处进行质量失调设计或在平尾翼根处进行刚度失调设计，更有利于实现T尾结构的模态局部化。

Effect of Mistuned Parameters on Mode Localization of T-tail Structure

Mode localization is often an unexpected dynamic phenomenon in weakly-coupled symmetric structures, and it arises from small imperfections (less than 5%) which perturb the symmetry of a structure. Such imperfections typically result from random manufacturing or assembly imprecision. Mode localization prediction is an important issue in T-tail structure design because drastic localized vibration phenomena may occur during the ground vibration test of a T-tail aircraft. Mode localization is dependent not only on parameter mistuning, but also on coupling degree. In this article the definition of mode localization is improved according to the peak amplitude ratio. The coupling degree is defined according to the effect of the stiffness of the horizontal stabilizer and fin on the modal frequencies of the T-tail structure. The mode localization and frequency loci veering phenomena for a T-tail structure is then studied and the effects of mistuned mass, mistuned stiffness and the location of mistuning on the mode localization of the horizontal stabilizer are investigated. Numerical simulation results for a T-tail structure model indicate that mode localization is most likely to occur in a T-tail structure consisting of weakly coupled substructures-a horizontal stabilizer and a fin. Moreover, when mode localization occurs, the first two bending vibration modes in the T-tail structure are prone to localization, and only one of the two modal frequencies is changed by parameter mistuning to induce frequency loci veering. The simulation also demonstrates that if mass or stiffness mistuning occurs to a horizontal stabilizer, the amplitude of the bigger mass side or smaller stiffness side is greater than that of the peer side. The study suggests that mode localization design is easy to achieve in T-tail structures by introducing mass mistuning on the tip of the horizontal stabilizer or stiffness mistuning on the root of the horizontal stabilizer.