Nonlinear Dynamic Substructuring of Thin-Walled Jointed Structures

本项目针对薄壁结构的装配，例如飞机和直升机或空间结构的机翼和机身的外部蒙皮板系统。轻量化设计使这些结构容易受到振动问题的影响。振动行为的特征在于两种类型的非线性：几何非线性出现由于弯曲-拉伸耦合，并成为相关的弯曲变形的范围内的厚度。接触非线性是由于干摩擦和单向相互作用而产生的，例如在铆接或螺栓连接中。几何非线性和接触非线性都会引起有效刚度分布的强烈振幅依赖性。这反过来又对固有频率和振动应力产生重大影响。此外，摩擦接触相互作用是机械阻尼的最大部分。最后，任何一种非线性都有可能触发强非线性现象，如新共振的发生。因此，这两个非线性是至关重要的强迫振动响应的准确预测和行为存在的自激。本项目的目标是（a）开发一个有效的计算方法的非线性振动分析的薄壁连接结构，（B）评估预测精度的方法，通过适当的实验，以及（c）理解几何非线性和接触非线性之间的相互作用。为了达到高预测精度，方法将适当地考虑几何非线性和接触非线性。为了实现高计算效率，将通过逐步动态子结构方法来追求数学模型阶数的急剧降低。在这里，一致使用的组件模式综合和接口减少的方法，考虑到每个子结构的具体属性。该方法的性能将被评估为宽带和周期性激励。对于特殊的，但技术上相关的情况下，周期性的近共振强迫，进一步减少的基础上的概念，非线性模式的振动将开发和评估。与现有的有限元工具相比，预计本项目中开发的方法可将所述非线性振动分析的计算工作量减少至少三个数量级。最后，为了彻底评估所开发的方法的有效性进行了实验研究。今天，工程设计依赖于线性理论几乎无处不在。因此，非线性被认为是最先进的建模策略中缺乏预测精度的主要原因。该项目将为轻量化结构组件的预测建模做出重大贡献。只有通过预测模型，才能开发出根本性的改进技术。

This project addresses assemblies of thin-walled structures such as systems of external skin panels of wings and fuselage of airplanes and helicopters or space structures. Lightweight design has made these structures susceptible to vibration problems. The vibration behavior is characterized by two types of nonlinearities: Geometric nonlinearities arise due to bending-stretching coupling and become already relevant as soon as the bending deformation is in the range of the thickness. Contact nonlinearities arise due to dry frictional and unilateral interactions e.g. in riveted or bolted joints. Both geometric and contact nonlinearity cause a strong amplitude dependence of the effective stiffness distribution. This, in turn, has a substantial effect on the natural frequencies and the vibration stresses. Moreover, the frictional contact interactions are responsible for the largest part of the mechanical damping. Finally, either nonlinearity has the potential to trigger strongly nonlinear phenomena, such as the occurrence of new resonances. Thus, both nonlinearities are crucial for the accurate prediction of the forced vibration response and the behavior in the presence of self-excitation.The goals of this project are to (a) develop an efficient computational method for the nonlinear vibration analysis of thin-walled jointed structures, (b) assess the prediction accuracy of this method using appropriate experiments, and (c) understand the interactions between geometric and contact nonlinearities.To reach a high prediction accuracy, method will properly account for both geometric and contact nonlinearities.To achieve high computational efficiency, a drastic reduction of the mathematical model order will be pursued by a stepwise dynamic substructuring approach. Here, consistent use will be made of component mode synthesis and interface reduction methods, taking into account the specific properties of each substructure. The performance of the method will be assessed for both broadband and periodic excitation. For the special but technically relevant case of periodic near-resonant forcing, a further reduction based on the concept of nonlinear modes of vibration will be developed and assessed. It is expected that the method to be developed in this project reduces the computational effort for the described nonlinear vibration analyses by at least three orders of magnitude, compared to the available finite element tools. Finally, experimental investigations are carried out in order to thoroughly assess the validity of the developed approach.Today, engineering design relies on linear theory almost everywhere. Thus, nonlinearities are seen as the main reason for the lacking prediction accuracy in the state-of-the-art modeling strategies. The proposed project will make a substantial contribution to predictively modeling assemblies of lightweight structures. Only with predictive models, radically improved technology can be developed.