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10 results on '"Pizer, David"'

1. Maximum wave-power absorption by attenuating line absorbers under volume constraints

Author

Stansell, Paul and Pizer, David J.

Subjects
Physics - Fluid Dynamics
Abstract

This work investigates the consequences of imposing a volume constraint on the maximum power that can be absorbed from progressive regular incident waves by an attenuating line absorber heaving in a travelling wave mode. Under assumptions of linear theory an equation for the maximum absorbed power is derived in terms of two dimensionless independent variables representing the length and the half-swept volume of the line absorber. The equation gives the well-known result for a point absorber wave energy converter in the limit of zero length and it gives Budal's upper bound in the limit of zero volume. The equation shows that the maximum power absorbed by a heaving point absorber is limited regardless of its volume, while for a heaving line absorber whose length tends to infinity the maximum power is proportional to its swept volume, with no limit. Power limits arise for line absorbers of practical lengths and volumes but they can be multiples of those achieved for point absorbers of similar volumes. This conclusion has profound implications for the scaling and economics of wave energy converters., Comment: 17 pages, 7 figures, 2 tables

Published
2011

6. Numerical Models

Author

Pizer, David and United Kingdom Department of Trade and Industry

Subjects
Duck, Numerical modelling, Control
Abstract

Also includes: 'Contribution to Joule' (Tall and flat floats) 'Numerical prediction of the performance of a solo Duck'. This work is a continuation of a previous DTI project on "The Numerical Prediction of the Performance of a Solo Duck". Results of the previous study are extended by computing the reactive powers required to attain the optimal complex control. Results are also presented for the optimal real control for cases in which power is absorbed in one degree of freedom. This corresponds to a pure damping control force, i.e. with no reactive power. The equations for optimal power absorption under an amplitude constraint have been reformulated to permit non-absorbing (i.e. uncontrolled) degrees of freedom. The effect of releasing a degree of freedom is investigated. The properties of heaving and surging devices are studied by considering a 20 metre diameter hemisphere. Power absorption through inclined degrees of freedom is also considered. The effect of device geometry is investigated by simple volume-conserving transformations of the hemisphere. Results are presented for the solo duck considered in the previous project in all possible configurations of a) surge, heave and pitch system, and b) fore, aft and pitch system. Results are also presented for three widths of a rounded solo duck. Cooperative research with the European Commission JOULE programme is described.

Published
1994

7. Some Numerical Results for the Flat and Tall Floats

Author

Pizer, David and United Kingdom Department of Trade and Industry

Subjects
Numerical modelling, Control
Abstract

Graphs are given for the added mass matrix, damping matrix and excitation force vector for the two floats discussed at the Hanstholm meeting. The flat float has a diameter of 6m, a height of 1.5m and is half submerged, giving a volume displacement of 21.2m squared. The tall float has a diameter of 3.3m, a height of 5m and is also half submerged giving a volume displacement of 21.4m squared.

Published
1994

8. Radical Life Extension: How can some people not understand that it is not "bad" to change some things is nature?

Author

Pizer, David

Abstract

The article discusses the notion of changing the nature and the emerging technologies, including cryonics, for life-span extension. It dispels the belief that changing the nature for the improvement of the health conditions of the humans is immorality. The validity of extending the life spans of humans in religious contexts is also highlighted.

Published
2014

9. FAQ Cryonics Convention.

Author

Pizer, David

Abstract

The article offers information on the Frequently Asked Questions (FAQ) Cryonics Convention to be held at the Riverside Resort in Laughlin, Nevada on October 25-27, 2013.

Published
2013

10. Pelamis: experience from concept to connection.

Author

Yemm R, Pizer D, Retzler C, and Henderson R

Abstract

The development of the Pelamis wave energy converter from its conceptual origins to its commercial deployment is reviewed. The early emphasis on designing for survivability and favourable power absorption characteristics focused attention towards a self-referenced articulated line-absorber in an attenuator orientation. A novel joint and control system allow the machine to be actively tuned to provide a resonant response power amplification in small and moderate seas. In severe seas, the machine is left in its default or natural condition, which is benign and non-resonant. Hydraulic rams at the joints provide the primary power take-off with medium-term storage in high-pressure accumulators yielding smooth electricity generation. Land-based modular construction requiring minimal weather windows for rapid offshore installation is an essential engineering feature necessary for viable commercialization. The second-generation Pelamis designs built for E.ON and ScottishPower Renewables are presented, and the scope for further cost reduction and performance enhancements are explained.

Published
2012
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