Scale effects arise due to force ratios which are not identical between a model and its real-world prototype and result in deviations between the up-scaled model and prototype observations. This review article considers mechanical, Froude and Reynolds model–prototype similarities, describes scale effects for typical hydraulic flow phenomena and discusses how scale effects are avoided, compensated or corrected. Four approaches are addressed to obtain model–prototype similarity, to quantify scale effects and to define limiting criteria under which they can be neglected. These are inspectional analysis, dimensional analysis, calibration and scale series, which are applied to landslide generated impulse waves. Tables include both limiting criteria to avoid significant scale effects and typical scales of physical hydraulic engineering models for a wide variety of hydraulic flow phenomena. The article further shows why it is challenging to model sediment transport and distensible structures in a physical hydrau...

Scale effects in physical hydraulic engineering models

Ocean energy has many forms, encompassing tides, surface waves, ocean circulation, salinity and thermal gradients. This paper will considers two of these, namely those found in the kinetic energy resource in tidal streams or marine currents, driven by gravitational effects, and the resources in wind-driven waves, derived ultimately from solar energy. There is growing interest around the world in the utilisation of wave energy and marine currents (tidal stream) for the generation of electrical power. Marine currents are predictable and could be utilised without the need for barrages and the impounding of water, whilst wave energy is inherently less predictable, being a consequence of wind energy. The conversion of these resources into sustainable electrical power offers immense opportunities to nations endowed with such resources and this work is partially aimed at addressing such prospects. The research presented conveys the current status of wave and marine current energy conversion technologies addressing issues related to their infancy (only a handful being at the commercial prototype stage) as compared to others such offshore wind. The work establishes a step-by-step approach that could be used in technology and project development, depicting results based on experimental and field observations on device fundamentals, modelling approaches, project development issues. It includes analysis of the various pathways and approaches needed for technology and device or converter deployment issues. As most technology developments are currently UK based, the paper also discusses the UK's financial mechanisms available to support this area of renewable energy, highlighting the needed economic approaches in technology development phases. Examination of future prospects for wave and marine current ocean energy technologies are also discussed.

Generating electricity from the oceans

With the recent sharp increases in the price of oil, issues of security of supply, and pressure to honor greenhouse gas emission limits (e.g., the Kyoto protocol), much attention has turned to renewable energy sources to fulfill future increasing energy needs. Wind energy, now a mature technology, has had considerable proliferation, with other sources, such as biomass, solar, and tidal, enjoying somewhat less deployment. Waves provide previously untapped energy potential, and wave energy has been shown to have some favorable variability properties (a perennial issue with many renewables, especially wind), especially when combined with wind energy [1].

/pdf/energy-maximizing-control-of-wave-energy-converters-the-56go405abj.pdf

Energy-Maximizing Control of Wave-Energy Converters: The Development of Control System Technology to Optimize Their Operation

One of the most abundant energy sources exists in this world is the ocean wave energy. By far, it has shown to be the most clean, renewable, predicted energy and has raised the potential to compete with the current use of non-renewable energy sources. Recent research conducted on wave energy invention has opened a new dimension to slowly reduce the dependency on fossil fuel by introducing new technology on the renewable world but relatively lacking in economical aspect. This review brings the latest status on integration of wave energy device with other marine facilities, which is the breakwater structure that may possibly aid to cost sharing. Most researches done on this field highlighted countries experiencing rough sea condition and focused less on countries with medium wave condition as faced by the Asian continent. The potential for energy extraction and wave dissipation for medium wave condition will be discussed in this review by considering several aspects including reliability, effectiveness and performance. Finally, this review shows that the integration opens up a new dimension to acknowledge the technology harnessing ocean wave, especially for the Asian countries experiencing medium wave condition.

Wave energy device and breakwater integration: A review

https://hal.archives-ouvertes.fr/hal-01145072/document

A database of capture width ratio of wave energy converters

Laboratory measurements of the performance of the Anaconda are presented, a wave energy converter comprising a submerged water-filled distensible tube aligned with the incident waves. Experiments were carried out at a scale of around 1:25 with a 250 mm diameter and 7 m long tube, constructed of rubber and fabric, terminating in a linear power take-off of adjustable impedance. The paper presents some basic theory that leads to predictions of distensibility and bulge wave speed in a pressurized compound rubber and fabric tube, including the effects of inelastic sectors in the circumference, longitudinal tension and the surrounding fluid. Results are shown to agree closely with measurements in still water. The theory is developed further to provide a model for the propagation of bulges and power conversion in the Anaconda. In the presence of external water waves, the theory identifies three distinct internal wave components and provides theoretical estimates of power capture. For the first time, these and other predictions of the behaviour of the Anaconda, a device unlike almost all other marine systems, are shown to be in remarkably close agreement with measurements.

Laboratory testing the Anaconda

A long tube with elastic walls containing water is immersed in the sea aligned in the direction of wave travel. The waves generate bulges that propagate at a speed determined by the distensibility of the tube. If the bulge speed is close to the phase velocity of the waves, there is a resonant transfer of energy from the sea wave to the bulge. At the end of the tube, useful energy can be extracted. This paper sets out the theory of bulge tubes in the sea, and describes some experiments on the model scale and practical problems. The potential of a full-scale device is assessed.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2011.0193

Rubber tubes in the sea.

A generally horizontal distensible tube (1) in the sea containing fluid and oriented in the direction of wave travel, the distensibility being chosen so that the propagation velocity of pressure waves inside the tube (bulge waves) is the same as the velocity of propagation of the waves in the sea. Energy is then transferred from the ocean waves to the bulge wave . Energy extraction means (84, 85) at the stern and/or bow convert the bulge power to useful energy. Said energy extraction means may comprise pistons actuating pumps or linear or rotating generators, or one-way valves allowing the bulge wave to pump fluid via hydraulic accumulators through a turbine. The walls of the distensible tube (1) may be comprised partly of elastomer (86) and partly of inelastic flexible polymer coated fabric (87) .

Distensible tube wave energy converter

The ANACONDA all-rubber WEC operates in a completely new way, capturing water waves as “bulge waves” in a giant water-filled rubber tube, aligned head-to-sea. It offers new possibilities for low capital and operational costs, based on the unique durability of rubber, and the single moving part (a conventional medium-head unidirectional water turbine). See www.bulgewave.com. Avon Fabrications LLP have recently taken an exclusive license to manufacture the device, which has been selected by the Carbon Trust for the Marine Energy Accelerator programme. Initial model tests show good capture width and wide bandwidth. The economics of the device depend on the price of the rubber, per unit of elastic energy stored in it over its lifetime, in p/kW-hr. This must be less than the selling price of the electricity produced over the device lifetime, again measured in p/kW-hr. On this basis the economics of ANACONDA are very promising.

Development of the Anaconda all-rubber WEC

The redshifts and luminosities of type 1A supernovae are conventionally fitted with the current paradigm, which holds that the galaxies are locally stationary in an expanding metric. The fit fails unless the expansion is accelerating; driven perhaps by ‘dark energy’. Is the recession of the galaxies slowed down by gravity or speeded up by some repulsive force? To shed light on this question the redshifts and apparent magnitudes of type 1A supernovae are re-analysed in a cartesian frame of reference omitting gravitational effects. The redshift is ascribed to the relativistic Doppler effect which gives the recession velocity when the light was emitted; if this has not changed, the distance reached and the luminosity follow immediately. This simple concept fits the observations surprisingly well with the Hubble constant H =62.9±0.3 km s−1 Mpc−1. It appears that the galaxies recede at unchanging velocities, so on the largest scale there is no significant intergalactic force. Reasons for the apparent absence of an intergalactic force are discussed.

F. J. M. Farley

Papers

Laboratory testing the Anaconda

Rubber tubes in the sea.

Distensible tube wave energy converter

Development of the Anaconda all-rubber WEC

Does gravity operate between galaxies? Observational evidence re-examined