The WaveGyro

The WaveGyro – A new Concept for Ocean Wave Energy Capture (Master Thesis by Gebhard Waizmann, University of Southampton 22.09.2011) Abstract Climate change, environmental pollution and the proceeding resource depletion give awareness of the necessity towards more sustainable energy economics. Energy from ocean waves may once play a contributing role towards this step but is as yet in its fledgling stages. This is mainly due to the harsh sea environment, which implies the need for simple and robust wave energy converter. The work presented in this thesis picks up this thought when dealing with the so-called WaveGyro. Introductory chapters explain how this novel concept arose, followed by a detailed explanation of the working principle. The WavGyro utilizes gyroscopes to provide an internal reaction moment against the wave excitation. This internal reaction permits designing a completely enclosed and thus environmentally resistant device. The gyroscopic precession is used to convert the wave-induced moment into a moment that accelerates the flywheels. Equations of motion, which describe the gyroscope kinetics, are deduced. The gyroscopic motions and moment is then implemented into the first-order wave hydrodynamics. Two main approaches to describe the wave excitation are presented. The first approach is superposition of radiation and exci-tation and the second approach makes use of the relative motion principle, which relates the excitation to the extent of displacement. Both approaches are employed to deduce the maximum power capture condition in relation to the device’s dimensions and operational parameters. The influence of real sea state, analytically expressed by the Pierson-Moskowitz spec-trum, on the optimum power analysis is considered and implementation methods are de-veloped. Subsequently the spin-up mechanism is explained and examined; this is the mechanism converting the precession moment into torque accelerating the flywheel. It is shown that a simple configuration, composed of an ordinary cogwheel and a sprag-clutch only is not sufficient for this mechanism. Ideas for alternative mechanisms are considered but require further investigation to allow conclusive results. Finally, an approximate plan for the design of model is developed, which includes basic considerations of scaling laws. Recommendations for further theoretical and practical work on the WaveGyro are provided

An inertial coupled marine power generator for small boats

This paper proposes a device to harvest energy from the vertical motion of small boats and yachts. The device comprises a sprung mass coupled to an electrical generator through a ball screw. The mathematical equations describing the dynamics of the system are derived. The equations are used to determine the optimum device parameters, namely its mass, spring constant, ball screw lead, within practical constraints. Simulation results are presented to determine the maximum power that can be generated and the optimum load resistance as a function of boat vibration frequency

Attenuation of sound in ducts with acoustic treatment: A generalized approximate equation

A generalized approximate equation for duct lining sound attenuation is presented. The specification of two parameters, the maximum possible attenuation and the optimum wall acoustic impedance is shown to completely determine the sound attenuation for any acoustic mode at any selected wall impedance. The equation is based on the nearly circular shape of the constant attenuation contours in the wall acoustic impedance plane. For impedances far from the optimum, the equation reduces to Morse's approximate expression. The equation can be used for initial acoustic liner design. Not least important is the illustrative nature of the solutions which provide an understanding of the duct propagation problem usually obscured in the exact calculations. Sample calculations using the approximate attenuation equation show that the peak and the bandwidth of the sound attenuation spectrum can be represented by quite simple functions of the ratio of actual wall acoustic resistance to optimum resistance

Modal propagation angles in ducts with soft walls and their connection with suppressor performance

The angles of propagation of the wave fronts associated with duct modes are derived for a cylindrical duct with soft walls (acoustic suppressors) and a uniform steady flow. The angle of propagation with respect to the radial coordinate (angle of incidence on the wall) is shown to be a better correlating parameter for the optimum wall impedance of spinning modes than the previously used mode cutoff ratio. Both the angle of incidence upon the duct wall and the propagation angle with respect to the duct axis are required to describe the attenuation of a propagating mode. Using the modal propagation angles, a geometric acoustics approach to suppressor acoustic performance was developed. Results from this approximate method were compared to exact modal propagation calculations to check the accuracy of the approximate method. The results are favorable except in the immediate vicinity of the modal optimum impedance where the approximate method yields about one-half of the exact maximum attenuation

Optimal damping profiles for a heaving buoy wave-energy converter

This paper explores optimal damping profiles for a heaving buoy wave energy converter (WEC). The approach is mathematical and the model of Eidsmoen (1995) is used as a basis. In order to permit analytical development, the model is initially simplified and an optimal damping profile is determined using numerical optimization. Having found the optimal damping profile, a semi-analytical solution methodology is developed to determine the optimal damping parameters. Finally, the procedure is validated on the original model and some aspects related to the control problem are addressed

Acoustic liner optimum impedance for spinning modes with cut-off ratio as the design criterion

A new acoustic liner design procedure based upon model cut-off ratio is outlined. Proposed experiments to substantiate this design procedure are outlined

Motion-Based Design of Passive Damping Devices to Mitigate Wind-Induced Vibrations in Stay Cables

Wind action can induce large amplitude vibrations in the stay cables of bridges. To reduce the vibration level of these structural elements, different types of passive damping devices are usually installed. In this paper, a motion-based design method is proposed and implemented in order to achieve the optimum design of different passive damping devices for stay cables under wind action. According to this method, the design problem is transformed into an optimization problem. Thus, its main aim is to minimize the different terms of a multi-objective function, considering as design variables the characteristic parameters of each considered passive damping device. The multi-objective function is defined in terms of the scaled characteristic parameters, one single-function for each parameter, and an additional function that checks the compliance of the considered design criterion. Genetic algorithms are considered as a global optimization method. Three passive damping devices have been studied herein: viscous, elastomeric and friction dampers. As a benchmark structure, the Alamillo bridge (Seville, Spain), is considered in order to validate the performance of the proposed method. Finally, the parameters of the damping devices designed according to this proposal are successfully compared with the results provided by a conventional design method

A MEMS viscometer for unadulterated human blood

The design and theoretical modelling of an oscillating micro-mechanical-viscometer designed for the measurement of whole unadulterated human blood, is described. The proposed device utilises the dependence of the squeeze-film damping ratio on properties of the surrounding fluid to measure fluid viscosity using an oscillating plate structure. The optimum geometrical configuration for the device structure has been investigated and a methodology for defining the optimum configuration of the micro-mechanical sensor identified. This is then applied to calculate the predicted noise equivalent viscosity change . It was found that the device performance is limited by electronic noise within the detection circuitry rather than thermal mechanical noise. An electronic noise limited measurement resolution of , is predicted for measurement over a shear range of , at a measurement bandwidth of . The linearity of response of the micro-mechanical-viscometer is considered and the device is predicted to provide a linear measurement response