Abstract
Suppression of undesirable vibrations is critical to ensure good dynamic performance of engineering structures. Vibration suppression problems can be categorised in terms of vibration behaviour, such as transient, self-excited or steady-state vibrations. Passive vibration suppression methods are widely adopted due to their inherent advantages, such as simplicity and reliability. Additionally, the introduction of the inerter has fundamentally expanded the achievable performance of passive vibration suppressors. Appropriate methodologies for the design of optimal passive vibration suppressors are needed to tackle particular problems.This thesis develops systematic methodologies to design both configurations and physical arrangements of passive vibration suppression devices, solving a variety of vibration problems. Also, this work demonstrates the effectiveness of inerter-based devices in each case.
A transient vibration suppression problem is studied first, and considers stable shimmy oscillations in an aircraft main landing gear (MLG). Both frequency-domain and time-domain approaches are adopted with the frequency-domain method considered less effective since the system mode shapes vary significantly when certain devices are added. Several beneficial inerter-based configurations are identified with the proposed time-domain methodology.
A second example of a transient vibration problem includes an initial impact excitation; here the aircraft landing touch-down process. Following the approach established, beneficial shock strut configurations have been identified. However, it has been found that the amount of energy dissipated is unsatisfactory. To address this, an additional constraint on energy dissipation is considered, leading to an absorber with double-stage stiffness being proposed.
The instability of self-excited vibrations can be avoided with suitable vibration suppressors. To this end, a design methodology of selecting the device parameter values is proposed. The nonlinear MLG shimmy phenomenon is studied here. A bifurcation study is performed to investigate the effects of the shimmy-suppression devices on the MLG dynamics. It shows that the utilisation of a specific proposed spring-damper configuration results in improved robustness against varying aircraft operation conditions over a traditional shimmy damper. The benefits of two inerter-based configurations are also demonstrated by enhanced device robustness.
The steady-state vibration suppression of a hydraulic engine mount has also been analysed, and a design approach for determining the optimal physical device arrangement has been developed. It enables optimisations of all possible networks with predetermined number and types of fluid passageways, through which the fluid can pass between two chambers in the engine mount. To improve the performances over a wide range of frequencies, linear optimal designs are identified whilst the manufacturing limitations are also considered. Furthermore, optimal parametric design is conducted considering nonlinear behaviour in fluid passageways.
| Date of Award | 6 Nov 2018 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Simon A Neild (Supervisor) & Jason Zheng Jiang (Supervisor) |