To achieve optimal power in a wave energy conversion (WEC) system it is necessary to understand the device hydrodynamics. To maximize conversion eciency the goal is to tune the WEC performance into resonance. The main challenge then to be overcome is the degree to which non-linearity in WEC hydrodynamics should be represented. Although many studies use linear models to describe WEC hydrodynamics, this paper aims to show that the non-linear viscosity should be carefully involved. To achieve this an investigation into the hydrodynamics of a designed 1/50 scale point absorber wave energy converter (PAWEC) in heave motion only is implemented to indicate the non-linear viscosity eect. A non-linear state-space model (NSSM) considering a quadratic viscous term is used to simulate PAWEC behaviors. The non-linear model is compared with the linear counterpart, and validated by computational uid dynamics (CFD) and experimental data. A conclusion is drawn that the non-linear PAWEC hydrodynamics (including amplitude and phase responses, conversion eciency) close to resonance or at high wave heights can only be described realistically when the non-linear viscosity is correctly taken into account. Inaccuracies in its representation lead to signicant errors in the tuning procedure which over-predict the dynamic responses and weaken the control system performance.

Past or/and future information of the excitation force is useful for real-time power maximisation control of Wave Energy Converter (WEC) systems. Current WEC modelling approaches assume that the wave excitation force is accessible and known. However, it is not directly measurable for oscillating bodies. This study aims to provide reasonably accurate approximations of the excitation force for the purpose of enhancing the effectiveness of WEC control. In this work, three approaches are proposed to approximate the excitation force, by (i) identifying the excitation force from wave elevation, (ii) estimating the excitation force from the measurements of pressure, acceleration and displacement and (iii) observing the excitation force via an unknown input observer. These methods are compared with each other to discuss their advantages, drawbacks and application scenarios. To validate and compare the performance of the proposed methods, a 1/50 scale heaving point absorber WEC has been tested in a wave tank under variable wave scenarios. The experimental data are in accordance with the excitation force approximations in both the frequency-and time-domains based upon both regular and irregular wave excitation. Hence, the proposed excitation force approximation approaches have great potential for WEC power maximisation via real-time control.

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This paper studies the intestinal frictions acting on a millimetre-scale self-propelled capsule (26 mm in length and 11 mm in diameter) for small bowel endoscopy by considering different capsule-intestine contact conditions under a wide range of capsule's progression speeds. According to the experimental results, intestinal frictions vary from 7 mN to 4.5 N providing us with a guidance for designing the propelling mechanism of the controllable capsule endoscope. Our calculations show that the proposed vibro-impact mechanism can perform as a force magnifier generating a much larger propulsive force on the capsule than its original driving force. Therefore, the self-propelled capsule is capable of moving in the small intestine under a wide range of friction variation.

This paper studies the modelling of capsule-intestine contact through experimental and numerical investigation for designing a self-propelled capsule robot moving inside the small intestine for endoscopic diagnosis. Due to the natural peristalsis of the intestinal tract, capsule-intestine contact is multimodal causing intermittent high transit speed for the capsule, which leads to incomplete visualisation of the intestinal surface. Three typical conditions, partial and full contacts, between the small intestine and the capsule, are considered in this work. Extensive experimental testing and finite element analysis are conducted to compare the contact pressure on the capsule. Our analytical, experimental and numerical results show a good agreement. The investigation using a synthetic small intestine shows that the contact pressure could vary from 0.5 to 16 kPa according to different contact conditions, i.e. expanding or contracting due to the peristalsis of the small intestine. Therefore, a proper control method or a robust stabilising mechanism, which can