Active Vibration Control of Parametrically Excited Systems

This project considers active vibration control of parametrically excited systems (PES). The problem is to develop control strategies for the suppression, or enhancement, of parametric resonances in engineering systems. Active control has the potential to control large amplitudes of vibration and modify the dynamics of the system very efficiently. It is particularly suitable for PES since the dynamics of PES are periodic-time dependent. The appearance of the periodic-time-dependent parameter in the dynamic equation results in a complex response including inherent instabilities, or combined resonances of summed or difference type. Understanding the dynamics of PES and its control is thus the main objective of this research.
The control strategy that will be used for PES is based on the receptance method developed by the applicant for linear time-invariant systems. The method has significant advantages, since there is no requirement for knowledge of system matrices, no requirement for model reduction techniques and no requirement for observers to estimate the unmeasured states. The method is entirely based on the measured vibration data; therefore the dynamics of the actuators, sensors and filters are all included in the design of the controller. Other control strategies based on the Floquet theory will also be developed. The control techniques will be implemented on a cable-supported structure, representing a cable-stayed bridge, to demonstrate the practical application of the active control on PES.
Many engineering structures are subjected to parametric excitation, which is produced by some external loads interacting with the structure. In civil engineering, Aratsu Bridge in Southern Japan is an example where parametric resonance was the origin of the cracks close to the anchorages. Parametric resonance occurs when the structural frequency coincides with a specific ratio of the parametric excitation frequency. For instance in the Skarnsundet Bridge in Norway, a vertical deck frequency was exactly twice the fundamental cable frequency. Vibration control can be achieved by moving the structural frequency away from that specific ratio using pole placement techniques.
In aerospace, parametric resonance can cause flutter of airplane wings due to the interaction of the wing with the aerodynamic loads. Recently, a fatal accident occurred involving a prototype of a business jet due to the tail-plane flutter, and the research aims to develop methods by which such instability can be controlled.
In marine engineering, parametric resonance can occur in riser systems due to the interaction of the risers with surface waves. The undesirable dynamic behaviour of these risers can be avoided using tension control. If parametric excitation is not included in the design of these risers, the wave induced vibration can result in instability and even catastrophic failure, thereby causing severe environmental and economic damage so that a more flexible method of active control would make the system safer. The research will also be beneficial in the design of the energy converters such as floaters since it can enhance the parametric resonance, which is used to extract significant amount of power from the wave energy.

The potential application of the proposed project is wide since parametric excitation occurs in many engineering structures such as aeroplane wings and helicopter rotor blades in aerospace, cable-stayed bridges in civil and ships in marine industry. The applicant has made new contacts at the University of Sheffield based on this project. The applicant would like to publish her results in leading refereed journals (The list is provided in the section on Academic Beneficiaries). It is also intended to attend two UK and international conferences per year to disseminate the outcomes of the project to a wider community. The applicant is a member of MOPNET, an interdisciplinary network funded by EPSRC. The applicant will also present the work in their meeting. The dynamic behaviour of a parametrically excited system is complex and the control of an inherent unstable system is highly challenging. Success in this project opens doors for new collaboration with other academics and industrial sectors.
The project is highly beneficial to civil engineering industry for cable-supported structures. Wind induced vibration may lead to large amplitude of oscillations , which may cause structural damage such as the creation of cracks in the Aratsu Bridge in Japan or even complete destruction of the structure such as the Tacoma Bridge. The understanding of parametric excitation and its control is thus extremely beneficial to prevent the structural damage, increase the lifetime and the serviceability and reduce the maintenance costs. The applicant has established collaboration with Arup. Collaboration with Arup provides a world-wide impact of the proposed research.
In off-shore technology, risers used for oil transportation are suspended from the ocean surface to the sea floor. With the trend towards oil and gas exploration in deeper waters and harsher environments, the response of the risers under various environmental conditions and sea states becomes increasingly complex. The riser is subjected to parametric excitation due to wave forces, resulting in undesirable transverse vibration. Parametric resonance could be avoided using a systematic approach to tension control. Orcina is keen to incorporate such control strategies in their offshore dynamic modelling software.
Other interesting application is to exploit parametric oscillation. Ocean Power Technologies is interested in exploiting parametric resonance to enhance the performance of their floating buoys and to extract more energy for electrical power. This is the positive aspect of parametric oscillation. Active control of marine structures is thus an interesting area of research and the real-world examples of such dynamic problems certainly justify the time to investigate novel potential solutions. For aerospace applications, the applicant has extensive collaboration with Agusta-Westland.
The applicant will invite her industrial collaborators and will present to them the theoretical as well as the experimental results in order to maximise the impact of the project. The applicant would like to engage a wider public through media in order to promote the public awareness of the project. This will be achieved after completing the training course in public/media to acquire the required skills.
The project contributes to the training of a research assistant and a PhD student funded by the University of Southampton. She will also demonstrate the control strategy developed for the cable-supported structure to her undergraduate students as part of her teaching activities. The project provides an excellent opportunity for the applicant to establish and develop her research career at the University of Southampton. Regular meetings and a workshop will be held internally at the University and the results will be presented to other academics and researchers for evaluation and assessment. The progress reports will also be available in the Faculty's web-page for academic use.