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

A physics-based approach to wind turbine SCADA data analysis and power curve outlier explanation

In a world where the energy demands only increase, new forms of renewable energy are critical. Amidst the need for new forms of energy, offshore wind energy is a growing industry with promising results. Although it is a promising solution, the industry faces several challenges related to maintenance. As a means to reduce the need for corrective maintenance and repair, preventive and predictive maintenance should be increased. One approach to achieve this is to utilise tools such as the wind turbine power curve. The curve shows the relationship between the wind speed and the wind turbine's power output. The SCADA data set contains outliers which should be explained for a better understanding of the wind turbine operations as well as for fault prediction purposes. The thesis aims to use a physics-based approach to analyse SCADA data and to explain outliers in the power curve. Outliers in the SCADA data set will present themselves in the wind turbine power curve. Often when the power curve is cleaned, the outliers are removed without an explanation. A physics-based approach to analyse the SCADA data, and thus the outliers in the power curve, is carried out by creating rules based on how the wind turbine is expected to operate. This requires an understanding of how the wind turbine works and essentially how the various components affect one another. Using a physics-based approach to analyse the SCADA data and creating rules for expected operational behaviour to identify outliers, proved to be effective. The outliers were provided explanations. Although the majority of outliers were due to operational states and transitions, the two generator bearing failures as well as the failure in the generator were detected.Masteroppgave i havteknologiHTEK399MAMN-HTEK5MAMN-HTE

Fundamental formulae for wave-energy conversion.

The time-average wave power that is absorbed from an incident wave by means of a wave-energy conversion (WEC) unit, or by an array of WEC units-i.e. oscillating immersed bodies and/or oscillating water columns (OWCs)-may be mathematically expressed in terms of the WEC units' complex oscillation amplitudes, or in terms of the generated outgoing (diffracted plus radiated) waves, or alternatively, in terms of the radiated waves alone. Following recent controversy, the corresponding three optional expressions are derived, compared and discussed in this paper. They all provide the correct time-average absorbed power. However, only the first-mentioned expression is applicable to quantify the instantaneous absorbed wave power and the associated reactive power. In this connection, new formulae are derived that relate the 'added-mass' matrix, as well as a couple of additional reactive radiation-parameter matrices, to the difference between kinetic energy and potential energy in the water surrounding the immersed oscillating WEC array. Further, a complex collective oscillation amplitude is introduced, which makes it possible to derive, by a very simple algebraic method, various simple expressions for the maximum time-average wave power that may be absorbed by the WEC array. The real-valued time-average absorbed power is illustrated as an axisymmetric paraboloid defined on the complex collective-amplitude plane. This is a simple illustration of the so-called 'fundamental theorem for wave power'. Finally, the paper also presents a new derivation that extends a recently published result on the direction-average maximum absorbed wave power to cases where the WEC array's radiation damping matrix may be singular and where the WEC array may contain OWCs in addition to oscillating bodies

Kinetic studies of Escherichia coli AlkB using a new fluorescence-based assay for DNA demethylation

The Escherichia coli AlkB protein catalyzes the direct reversal of alkylation damage to DNA; primarily 1-methyladenine (1mA) and 3-methylcytosine (3mC) lesions created by endogenous or environmental alkylating agents. AlkB is a member of the non-heme iron (II) α-ketoglutarate-dependent dioxygenase superfamily, which removes the alkyl group through oxidation eliminating a methyl group as formaldehyde. We have developed a fluorescence-based assay for the dealkylation activity of this family of enzymes. It uses formaldehyde dehydrogenase to convert formaldehyde to formic acid and monitors the creation of an NADH analog using fluorescence. This assay is a great improvement over the existing assays for DNA demethylation in that it is continuous, rapid and does not require radioactively labeled material. It may also be used to study other demethylation reactions including demethylation of histones. We used it to determine the kinetic constants for AlkB and found them to be somewhat different than previously reported values. The results show that AlkB demethylates 1mA and 3mC with comparable efficiencies and has only a modest preference for a single-stranded DNA substrate over its double-stranded DNA counterpart

Status 1983 Of The Norwegian Wave-Power Buoy Project

Several official assessments of wave-power plants in Norway show decreasing figures for the estimated cost of wave energy. The latest updating seems to confirm some of the points in our own assessment of a phase-controlled power-buoy plant, where we estimate the energy cost to be roughly 0.6 kr/kWh (5 pence/kWh) which has prospects to be reduced to 0.3 kr/kWh (3 p/kWh) in the future. This cost would be competitive on national energy supply markets. Among many different assessed wave-energy devices the phase-controlled power buoy is outstanding in having a rather low investment of energy, materials and money in relation to the produced energy per year. On the other hand, relatively much labour is required to construct and maintain the plant. Since the device contains some critical moving parts, more development work and full scale testing in the sea are required in order to obtain acceptable lifetime and reliability. Such a development program should be started as soon as possible. The program may result in knowledge on how to design a reliable device. Our project has been pursued with design work to a stage where the next step is to construct a full-scale test buoy. However, since funds for such work are not yet available, our research team now continues its work another aspect of wave power, i.a. work on mini- power devices and on phase-control of oscillating water columns

Loading system mechanism for dielectric elastomer generators with equi-biaxial state of deformation

Dielectric Elastomer Generators (DEGs) are devices that employ a cyclically variable membrane capacitor to produce electricity from oscillating sources of mechanical energy. Capacitance variation is obtained thanks to the use of dielectric and conductive layers that can undergo different states of deformation including: uniform or non-uniform and uni- or multi-axial stretching. Among them, uniform equi-biaxial stretching is reputed as being the most effective state of deformation that maximizes the amount of energy that can be extracted in a cycle by a unit volume of Dielectric Elastomer (DE) material. This paper presents a DEG concept, with linear input motion and tunable impedance, that is based on a mechanical loading system for inducing uniform equi-biaxial states of deformation. The presented system employs two circular DE membrane capacitors that are arranged in an agonist-antagonist configuration. An analytical model of the overall system is developed and used to find the optimal design parameters that make it possible to tune the elastic response of the generator over the range of motion of interest. An apparatus is developed for the equi-biaxial testing of DE membranes and used for the experimental verification of the employed numerical models

The Potential Role of Mother-in-Law in Prevention of Mother-to-Child Transmission of HIV: A Mixed Methods Study from the Kilimanjaro Region, Northern Tanzania.

In the Kilimanjaro region the mother-in-law has traditionally had an important role in matters related to reproduction and childcare. The aim of this study was to explore the role of the mothers-in-law in prevention of mother-to-child transmission (PMTCT) service utilization and adherence to infant feeding guidelines. The study was conducted during 2007-2008 in rural and urban areas of Moshi district in the Kilimanjaro region of Tanzania. Mixed methods were used and included focus group discussions with mothers-in-law, mothers and fathers; in-depth interviews with mothers-in-law, mothers, fathers and HIV-infected mothers, and a survey of 446 mothers bringing their four-week-old infants for immunisation at five reproductive and child health clinics. The study demonstrated that the mother-in-law saw herself as responsible for family health issues in general and child care in particular. However she received limited trust, and couples, in particular couples living in urban areas, tended to exclude her from decisions related to childbearing and infant feeding. Mothers-in-law expected their daughters-in-law to breastfeed in a customary manner and were generally negative towards the infant feeding methods recommended for HIV-infected mothers; exclusive replacement feeding and exclusive breastfeeding. Decreasing influence of the mother-in-law and increasing prominence of the conjugal couples in issues related to reproduction and child care, reinforce the importance of continued efforts to include male partners in the PMTCT programme. The potential for involving mothers-in-law in the infant feeding component, where she still has influence in some areas, should be further explored

On the tuning of a wave-energy driven oscillating-water-column seawater pump to polychromatic waves

Performance of wave-energy devices of the oscillating water column (OWC) type is greatly enhanced when a resonant condition with the forcing waves is maintained. The natural frequency of such systems can in general be tuned to resonate with a given wave forcing frequency. In this paper we address the tuning of an OWC sea-water pump to polychromatic waves. We report results of wave tank experiments, which were conducted with a scale model of the pump. Also, a numerical solution for the pump equations, which were proven in previous work to successfully describe its behavior when driven by monochromatic waves, is tested with various polychromatic wave spectra. Results of the numerical model forced by the wave trains measured in the wave tank experiments are used to develop a tuning criterion for the sea-water pump.Comment: 21 pages, 14 figure