Direct Mechanical Linkage

The motion of an MEC can be converted to a suitable form by the use of a step up gearbox, possibly in combination with a rectifying device such as a ratchet. The introduction of a gearbox introduces extra mechanical complexity, system losses, monitoring requirements and more importantly enforces regular maintenance in terms of oil changes. Although gearbox technology is well established, for example in the automotive industry, these are generally step down gearboxes of a smaller capacity and...

Sizing the WEC for a given sea state

Wave data given in 56 , cited in 57 and displayed in Figure 2.9 gives the probability of each sea state of a given point off the Norwegian coast in terms of the zero upcross time and significant wave height. If the float is assumed to follow exactly the surface of the water, these datum can be used as the basis of a simple design model. In reality, oscillation of two coupled bodies in water is mathematically more complex, Designing for the most 'likely' sea state, with a probability of 6.73 ,...

Chapter Results Summary

In Chapter 1 the concept, desire and history of harnessing energy from the marine resource was introduced. The two possible sources of energy identified were wave energy and tidal stream energy. The principles and devices suitable for capturing this energy were discussed. The concept of resonance and the subsequent need for control over the behaviour of wave energy devices in order to increase capture efficiency was demonstrated. In Chapter 2 the choice of power take off mechanism for MECs was...

List of Figures

Figure 1.1 Comparison of life cycle emissions of Figure 1.2 Demonstration of absorbing wave Figure 1.3 Plan view of a point absorber interacting with uniform wave train 7 Figure 1.4 The advantages of control Figure 1.5 Direct drive heaving Figure 1.6 Figure 1.7 IPS Figure 1.8 Stingray tidal stream Figure 1.9 Alternative power take off Figure 2.1 Pneumatic gearing in an Figure 2.2 Hydraulic power take off Figure 2.3 Previous direct drive Figure 2.4 Direct drive proposal with rolling magnetic...

Shear stress comparison

As a reference guide to the typical loading of a direct drive generator, this section compares machines capable of removing 100 kW from an element moving at 1 ms-1, i.e. a machine capable of reacting 100 kN. The three distinct topologies of machine, conventional, VRPM and tubular have been described in terms of shear stress equations within this Chapter. The constants used in their comparison are given in Table 3-1 and are dictated either by experience and general practice or justified below....

Enlarged Moment

The position of the hydraulic rams and the magnitude of the moment arm dictates the velocity, pressure and stroke length of the power cycle. Clearly, when replacing the power take off for a direct drive system, there are different priorities involved in locating the system parts. Electrical machines benefit from positions of higher velocity as the required reactive force is lower, whilst still extracting the same power from the body. Hydraulic systems can operate at pressures of several hundred...

Finite Element Analysis

The dimensions and previous descriptions of the VHM machine have been based on simplified flux flows and equivalent circuit analysis. In reality there will be significant fringing and interference effects between adjacent magnets and teeth. A detailed, more accurate, model will therefore require the use of an FEA program. Analysis of the model will provide a visual representation of the machine behaviour, by way of flux lines. Furthermore, it will allow the development of expressions to...

Phase Inductances

The self inductance of each phase is shown in Figure 5.20 and the three sets of mutual inductances in Figure 5.21. Both of these provide further evidence of a non balanced three phase system. Figure 5.20 Self inductance of three phases Figure 5.20 Self inductance of three phases Figure 5.21 Mutual inductance between three phases Figure 5.21 Mutual inductance between three phases N. J. Baker Chapter 5 The Air-Cored Tubular Machine

Principles of Energy Capture From Waves

The fundamental principle behind absorbing energy from a water wave is that energy must be removed from that wave. It therefore follows that the resultant wave, after passing the wave energy device, is either reduced or cancelled altogether. A WEC, or indeed any object, oscillating in water will produce waves. It is the interaction of the waves produced by the device and the original wave that gives the resultant wave. For the device to remove energy from the wave, it is necessary for the...

Electronic conversion for direct drive

A major concern, common to all power take off strategies, is the lull in output power inherent with reciprocating motion and also the variation of net power due to atmospheric conditions. The predictable nature of tidal currents gives protection for the latter of these. Although it may be possible to operate several devices out of phase in an array and minimise the short term lull in power, some smoothing will still be necessary. Furthermore, it is advantageous to have a stand alone device with...

Details of the model

The flux flow of a VHM may be assumed to be two dimensional and modelling can hence be undertaken using a two dimensional FEA program. The software used here is Vector Field's PC Opera 2 D 74 . Within this program a single phase, two pole double sided linear VHM was simulated. Each pole has six magnets attached in such a way that the flux return path passes across, not along, the axis of the translator back iron. The pattern it traces is hence symmetrical about the centreline of the translator,...

Real Time Response of VHM

Power Factor

With the ability to predict the dynamic response of the VHM in generator mode, it is now possible to examine the difficulties in extracting power. It has previously been demonstrated that the machine has a large inductance 0.5H . With a time domain model the instantaneous values of phase flux linkage, current and theoretical open circuit emf can be recorded. Figure 4.61 Equivalent circuit of VHM in short circuit Figure 4.61 Equivalent circuit of VHM in short circuit Figure 4.61 shows an...

Wave Energy Converters WECs

Nearshore Wave Energy Converter

Broadly, there are three ways of classifying a wave energy converter in terms of its position. Shoreline devices are mounted rigidly to the shore, thus ensuring simple maintenance and grid connection. The cost of land intrusion and the possibility of naturally advantageous sites being environmentally sensitive has to be considered in these schemes. Secondly there are nearshore devices, typically situated in 10-25 m depth of water. The device may be tight moored to the sea bed, either by way of...

Hydrostatic Lubrication

Hydrostatic Slideways

Load relationships of a two dimensional hydrostatic bearing are given in 6.1 , showing its dependence on viscosity and land clearance. H3 P H3 load capacity of bearing viscosity kg m s flow rate m3 s clearance m The use of sea water as the working fluid, with a viscosity much lower than that of normal lubricating oils, results in either the need for smaller land clearances or higher flow rates to achieve these high forces. It is hence necessary to develop expressions for the load capacity of...

Field wound synchronous machine

Synchronous machines are the primary devices used for high speed rotary power generation in the world's electric power systems today 61 . The rotor is fed with a d.c. current via brushes and slip rings and so sets up a magnetic field which follows its movement. The stator surrounds the rotor with a set of stationary coils, such that they are cut by the rotor flux pattern. Controlling the excitation currents in these machines, which are generally more efficient than induction machines, provides...

Hydraulic system

Hydraulic systems are frequently proposed for power take off in wave energy devices and the current version of the Stingray device. Typically a hydraulic ram is used to convert the motion of the device into high pressure oil, which is then fed into a hydraulic motor driving an electrical machine. Slow speed high forces are hence converted into rotary high speed motion with a minimum onboard weight. Furthermore, the reactive force of the rams can be controlled by the working pressure of the...

Transverse Flux Machine TFM

Transversal Flux Generator

In a TFM the main flux flow is in a direction perpendicular to the direction of travel. Figure 3.7 shows three views of a linear PM excited TFM. The translator consists of surface mounted PMs in a configuration that forces the flux to vary both axially and circumferentially. There are stator coils mounted either side of the translator with a series of iron yokes channelling the flux in such a way that alternate rotor poles excite the same coil 63, 64 . The result is an inherently three...