George A. Aggidis

Time series analysis-based adaptive tuning techniques for a heaving wave energy converter in irregular seas.

Abstract The paper presents a time domain model of a heaving buoy wave-energy converter and investigates the tuning problem in irregular seas. The tuning issue is addressed by employing both fixed (passive) and adaptive (active) power-take-off settings. The fixed power-take-off tuning approach includes models based on tuning the device natural frequency to either the energy frequency or peak frequency of the sea-state or a weighted average of several peak frequencies. The adaptive tuning approaches employ a sliding discrete Fourier transform frequency analysis, or a time-series analysis of the measured wave elevation and device velocity to estimate a localized dominant wave frequency and hence calculate power-take-off settings. The paper presents details of these tuning techniques by discussing issues related to the modelling, simulation, and predicted power captures for each method. A comparative study of each method along with practical implications of the results and recommendations are also presented.

Investigating pipeline and state of the art blood glucose biosensors to formulate next steps

Ten years on from a review in the twentieth issue of this journal, this contribution assess the direction research in the field of glucose sensing for diabetes is headed and various technologies to be seen in the future. The emphasis of this review was placed on the home blood glucose testing market. After an introduction to diabetes and glucose sensing, this review analyses state of the art and pipeline devices; in particular their user friendliness and technological advancement. This review complements conventional reviews based on scholarly published papers in journals.

A JOINT NUMERICAL AND EXPERIMENTAL STUDY OF A SURGING POINT ABSORBING WAVE ENERGY CONVERTER (WRASPA)

This paper presents the findings from using several commercial computational fluid dynamics codes in a joint numerical and experimental project to simulate WRASPA, a new wave energy converter (WEC) device. A series of fully 3D non-linear simulations of WRASPA are presented. Three commercial codes STAR-CCM, CFX and FLOW-3D are considered for simulating the WRASPA device and final results are presented based on the use of Flow-3D. Results are validated by comparison to experimental data obtained from small scale tank tests undertaken at Lancaster University (LU). The primary aim of the project is to use numerical simulation to optimize the collector geometry for power production over a range of likely wave climates. A secondary aim is to evaluate the ability of commercial codes to simulate rigid body motion in linear and non-linear wave climates in order to choose the optimal code with respect to compute speed and ease of problem setup. Issues relating to the ability of a code in terms of numerical dissipation of waves, wave absorption, wave breaking, grid generation and moving bodies will all be discussed. The findings of this paper serve as a basis for an informed choice of commercial package for such simulations. However the capability of these commercial codes is increasing with every new release.Copyright

Optimum mean power output of a point-absorber wave energy converter in irregular waves:

Abstract This article presents an assessment of the optimum mean power output of a point-absorber wave energy converter (PAWEC) in irregular wave climates. A first-order method is used to calculate the mean power spectrum of the device in waves of dissimilar spectra. JONSWAP spectra with different peak enhancement parameters are used to show the effect of energy concentration within the wave spectrum on the device mean power spectrum. A comparison of the optimum mean power output of a PAWEC in an irregular wave climate with that in an energy-equivalent regular wave climate is made to show the influence of the combination of wave spectrum and power output characteristics on the former. The principle is demonstrated by results obtained with the simulation of a PAWEC collector. An evaluation is made of the difference between the optimum mean power output of the device and the mean power output achieved using a simple, standard control method. The resulting difference in energy output with measured data from a possible site is also assessed. The implications of the results on the appraisal of device performance are considered.

A comparative approach to the economic modelling of a large-scale wave power scheme

Conversion of marine energy sources, including ocean waves and tidal currents, into electricity is a rapidly developing industry. Although many technologies have been proposed and some have generated electricity at full scale, it is difficult to predict which technology will be economic at large scales of installation. Several studies have been conducted which estimate the cost of electricity on the basis of schematic designs. However, each study represents a best estimate of the future cost based on current design details and direct comparison between the results of these studies is not straightforward. A methodology for directly comparing different wave energy concepts and potential locations would be beneficial to aid investment decisions. In this study we describe how the established data envelopment analysis technique could be employed for this purpose. The developed model is employed to rank the efficacy with which several types of conceptual and prototype wave energy conversion technologies generate electricity from the wave energy resource available at UK and US sites.

Calculation of the performance of resonant wave energy converters in real seas

It is well known that the performance of point-absorber wave energy converters (WECs) depends upon resonance with the wave frequency. Indeed, the ideal performance of a resonating point-absorber WEC in a regular sea that can be represented by a simple sinusoid is well known, provided all motions are small and remain in the linear region. However, the performance of such a device in a more realistic, irregular sea that is not represented by a simple sinusoid cannot be so readily calculated. The first difficulty lies in modelling the hydrodynamic behaviour of the device. Recent developments in representing the hydrodynamic diffraction and radiation forces have enabled relatively simple simulation models to be developed, such as those presented and used in this paper. The second difficulty lies in the design of the device itself. In a regular sea with a known wave frequency, the settings of the power take-off system can be defined at well-known optimum values. It is shown in the present paper that, even when the wave frequency is not constant, the local wave frequency can be estimated, and this estimate can be used to adjust the power take-off system settings to maintain quasiresonance and, hence, approach the level of performance in a comparable regular sea. In this manner, for irregular seas it is possible to identify a dominant wave frequency over a relatively short time period and to use this frequency continuously to adjust the power take-off system settings, so as to adapt to the current sea conditions. This is likely, in some sea conditions, to involve the power take-off supplying power over part of the cycle, rather than absorbing it. This will increase the demands placed on the power take-off - particularly on its efficiency when the direction of power flow has to be reversible. The relative performance of such a tuneable point-absorber WEC is assessed in the paper. It is shown that the power converted in irregular seas could be as much as 50 per cent of the rated power, where the latter estimate is equivalent to the power converted in a corresponding regular sea.

Parametric optimisation of two Pelton turbine runner designs using CFD

This paper aims to develop a generic optimisation method for Pelton turbine runners using computational fluid dynamics (CFD). Two different initial runners are optimised to achieve more generic results. A simple bucket geometry based on existing bibliography is parameterised and initially optimised using fast Lagrangian solver (FLS). It is then further optimised with a more accurate method using ANSYS Fluent. The second geometry is a current commercial geometry with good initial performance and is optimised using ANSYS CFX. The analytical results provided by CFX and Fluent simulations are used to analyse the characteristics of the flow for different runner geometries

Impulse Turbine Injector Design Improvement Using Computational Fluid Dynamics

This study utilises two modern CFD software packages (ANSYS¯ CFX¯ and ANSYS¯ Fluent¯) to analyse the basic geometric factors affecting the efficiency of a typical impulse turbine injector. A Design of Experiments study is used to look at the impact of four primary nozzle and spear design parameters on the injector losses over a range of inlet pressures. Improved injector designs for both solvers are suggested based on the results and comparisons are made. The results for both CFD tools suggest that steeper injector nozzle and spear angles than current literature describes will reduce the losses by up to 0.6%.

Numerical investigation of the spear valve configuration on the performance of Pelton and Turgo turbine injectors and runners

This paper uses two modern commercial CFD software packages to compare the performance of a standard and improved impulse turbine injector developed in a previous study. The two injector designs are compared by simulating the 2D axis-symmetric cases as well as full 3D cases including the bend in the branch pipe and the guide vanes. The resulting jet profiles generated by these simulations are used to initialise the inlet conditions for a full Pelton and Turgo runner simulation at different operating conditions in order to assess the impact of the injector design on the performance and efficiency of a real impulse turbine. The results showed that the optimised injector design, with steeper nozzle and spear angles, not only attains higher efficiencies in the 2D and 3D injector simulations, but produces a jet which performs better than the standard design in both the Pelton and the Turgo runner simulations. The result show that the greatest improvement in the hydraulic efficiency occurs within the injector with the improved design showing an increase in efficiency of 0.76% for the Turgo 3D injector and 0.44% for the Pelton 3D injector. The results also show that in the case of the 3D injector, the improved injector geometry produces a jet profile which induces better overall runner performance, giving a 0.5% increase in total hydraulic efficiency for the Pelton case and 0.7% for the Turgo case.

Pelton turbine: Identifying the optimum number of buckets using CFD

A numerical case study on identifying the optimum number of buckets for a Pelton turbine is presented. Three parameters: number of buckets, bucket radial position and bucket angular position are grouped since they are found to be interrelated. By identifying the best combination of the radial and angular position for each number of buckets it is shown that reduction in the number of buckets beyond the limit suggested by the available literature can improve the efficiency and be beneficial with regard to the manufacturing complexity and cost perspective. The effect of this reduction in the number of buckets was confirmed experimentally.