PhD position in Active Vibration Control of Nonlinear Systems

Since its foundation in 1614, the University of Groningen has enjoyed an international reputation as a dynamic and innovative center of higher education offering high-quality teaching and research. Balanced study and career paths in a wide variety of disciplines encourage currently more than 36,000 students and researchers to develop their own individual talents. Belonging to the best research universities in Europe and the top 100 universities in the world (see our ranking:

http://www.rug.nl/about-us/where-do-we-stand/rankings

, the University of Groningen is truly an international place of knowledge.

ENTEG is a research institute within the Faculty of Science and Engineering. The institute is recognised nationally and internationally for engineering science and technology. The aim of the istitute is to explore and design innovative technologies, and to improve existing ones, that are based on the integration of fundamental and engineering sciences in a comprehensive environment. The ENTEG fosters truly interdisciplinary research with a great track record of national and international collaboration transferring knowledge across domains. For more information about the ENTEG please use the following link: https://www.rug.nl/research/enteg/abouttheinstitute/ .

The Dynamics and Vibration (D&V) group in ENTEG focuses on dynamic analysis of engineering systems for the main purpose of vibration control, energy harvesting and health monitoring.

"Robust vibration control of nonlinear systems by the receptance method”

Nonlinear systems have been encountered in almost all engineering sectors. Some examples of nonlinear behaviour are in flexible wings with large vibration amplitudes due to aerodynamic loads, helicopter blades, control surfaces with friction/backlash nonlinearities, turbine blades, cable-stayed bridges , machine and drilling tools with stick-slip motion. Although in some applications nonlinear behaviour is destructive and it may cause effects such as instability and flutter, in other applications, nonlinear behaviour is so crucial that without nonlinearities, the system may malfunction. One interesting example of nonlinearity is the saturation of the active mechanism in cochlea, which allows us to have an increased dynamic range of hearing. Other examples of the positive influence of nonlinearities are in musical instruments, such as the stick-slip phenomenon as the sound generation mechanism in violins, and the sound generated by musical gongs.

Active vibration control techniques are becoming increasingly important across a wide range of engineering sectors. Whilst there is a large amount of literature on active vibration control of linear systems, there is a lack of theoretical, particularly experimental work for active vibration control of nonlinear systems. The existing linear control techniques are not sufficient to control the many of the challenging dynamic behaviour of nonlinear systems such as bifurcation, combined resonances, limit cycles, inherent instability and harmonic distortion.

Nonlinear control techniques such as feedback linearization and gain scheduling are mainly applicable to systems with slowly varying operating points. Model predictive control, robust control and adaptive control are model-based techniques, which require the availability of a nonlinear model and hence rely on system identification techniques. A novel technique in active control, the so-called receptance method,has been developed which is entirely based on measured vibration test data, rather than models of the system, and this method has been implemented on various laboratory structures as well as on a W30 Agusta-Westland helicopter in a ground vibration test. Recently, the D&V group has extended this technique to control nonlinear systems, such as a Duffing oscillator.

The aim of this project is to develop robustcontrol techniques based on the measured receptances to control vibrations of nonlinear systems and assign the eigenvalues. The equations for the eigenvalue sensitivities will also be developed, which are dependent on the excitation level. Minimisation of the sensitivities at different excitation levels together with the eigenvalue assignment will be considered for robust control. The developed control algorithms will then be implemented on a laboratory scale structure with geometric nonlinearity to demonstarte the working of the algorithms. Experiments will be carried out to obtain open-loop and closed-loop responses and the dynamic behaviour and stability after control will be analysed.

Position description:
We will hire a PhD student who will focus on the development of control algorithms that incorporate nonlinearities in the models of dynamic systems and controllers. It is expected that the PhD student will collaborate with other PhD students within the ENTEG.

We welcome applications if you have a:

• MSc degree in Mechanical Engineering or Mechatronics
• strong academic credentials, written and spoken English proficiency
• strong knowledge in vibrations, dynamics and control
• strong interest in experimental work
• good experience in vibration testing
• strong knowledge in programming for example in Matlab
• a dynamic, creative and pioneering professional attitude with a willingness to work in a strongly interdisciplinary team and learn the cross-disciplinary foundations
• problem solving ability
• strong communication skills.

The University of Groningen offers, in accordance with the Collective Labour Agreement for Dutch Universities;

• a salary of € 2,395 gross per month in the first year, up to a maximum of € 3,061 gross per month in the fourth and final year for a full-time working week
• a full-time position (1.0 FTE)
• a holiday allowance of 8% gross annual income
• 8.3% end-of-the-year allowance
• the position requires residence in Groningen and must result in a PhD thesis within the 4-year contract period
• the successful candidate will first be offered a temporary position of one year with the option of renewal for another three years. Prolongation of the contract is contingent on sufficient progress in the first year to indicate that a successful completion of the PhD thesis within the next three years is to be expected. A PhD training programme is part of the agreement and the successful candidate will be enrolled in the Graduate School of Science and Engineering
• the preferred starting date is 1 November 2021 or 1 December 2021 (in consultation).