The study of cephalopods (octopuses and squids) has demonstrated that bodies which undergo shape variations while traveling across a dense medium can exploit added-mass-variation in order to enhance thrust. This very same principle can be applied to a submerged mass-spring-damper system, showing that an actively controlled shape-variation routine can drive the oscillator in resonance by using the added-mass-variation force to balance viscous drag.
Until recent, the exploitation of added-mass-variation has been exclusively employed in the context of self propelled vehicles with the purpose of enhancing maneuverability and efficiency. However, the capability to trigger resonance in a vibrational system by added-mass control lends itself to the exploitation of this principle in the context of marine renewable energy harvesting.
The capability of an aquatic linear oscillator to compensate for viscous losses by exploiting added-mass variation has direct implications in the design of many offshore devices whose working principle entail sustained oscillations. Typical examples of such systems commonly employed in marine renewables are point absorbers and surge converters. As an example, by implementing existing devices with the capability to alter their external shape, the amplitude of the oscillation could become a controllable parameter for the purpose of enhanced power output. Analogous technologies could be employed in enhancing the efficiency of energy harvesting systems based on Vortex Induced Vibrations.
Aims and Objectives
The aim of this project is to develop a proof-of-concept design of a mechanical apparatus which demonstrates the feasibility of added-mass-variation control in the context of energy harvesting. In order to achieve this goal, the candidate will be required to design a rig comprising of a vibrational system capable of varying its shape in order to benefit of the added-mass-variation force. This could be represented by any system capable of performing expanding/collapsing mode deformations in coordination with the oscillatory kinematics and in this way extract the hydrodynamic energy to drive sustained oscillations. By coupling such system with a generator and accounting for the power input required to actuate the mode-shape deformations, the student will be able to estimate the net power output of the apparatus and employ scaling arguments to extend this results to systems of larger size.
The project is suited for creative students with an inclination towards mechanical design and fluid mechanics.
- Giorgio-Serchi, F. & Weymouth, G. D. 2016a Drag cancellation by added-mass pumping. Journal of Fluid Mechanics, 798.
- Giorgio-Serchi, F. & Weymouth, G. D. 2017 Can added-mass variation act as a thrust force? In IEEE/MTS Oceans. Aberdeen, UK.
- Grouthier, C., Michelin, S., Bourguet, R., Modarres-Sadeghi, Y. & de Langre, E. 2014 On the efficiency of energy harvesting using vortex-induced vibrations of cables. Journal of Fluids and Structures 49, 427 – 440.
Links to existing projects
- have a look at this project on "Added-mass variation for vibration control",
- and this on underwater vehicle design for shape-changing propulsion.
Minimum entry qualification - an Honours degree at 2:1 or above (or International equivalent) in a relevant science or engineering discipline, possibly supported by an MSc Degree. Further information on English language requirements for EU/Overseas applicants.