REPORT Table of Contents 1. LIST OF TABLES ………………………………………………………………….Error! Bookmark not defined.v 2. LIST OF FIGURES……………………………………………………………..........v 3. ACKNOWLEDGMENT …………………………………………………………...vi 4. ABSTRACT………………………………………………………………………….1 Waves are an excellent source of energy, are a natural resource, and are renewable. Waves in shallow water are one of the best ways to capture this energy as this is when the wave energy is at its maximum (potential and kinetic) points. How much energy is captured depends upon a number of factors: wave translation, wave height, the number of waves in a set period, the type of converter used and its efficiency of capturing both the potential and kinetic wave energy. To maximize the amount of energy that can be extracted from a near shore wave the simplest method of converting the mechanical energy of this natural renewable resource to a very usable medium (i.e. electricity) is via piezoelectricity. This paper will touch upon fundamentals of efficient and economical extraction of energy from ocean waves as well as discuss design considerations utilizing piezoelectricity as an energy converter. It can be shown that the capture and storage of shallow wave energy in this manner is comparable to energy generated from other sources, such as fossil fuels, solar power, and hydrodynamic. 5. INTRODUCTION / BACKGROUND……………………………………………….4 5.1. Why Near Shore Ocean Waves are a Good Choice for Energy Extraction Ocean wave are a naturally occurring phenomenon as well as a renewable energy source. Waves form in water when it is excited by external forces, such as wind, vibrations, displacement, etc. Waves are efficient carriers of energy, imparted by the wind most commonly. The water medium translates this energy from its point of initiation outward forming visible waves as the environmental conditions change. “The global power potential represented by waves that hit all coasts worldwide, has been estimated to be in the order of 1TW (1 terawatt = 1012W). Although this is only a small proportion of the world’s wind power potential, which, in turn, is only a small portion of global solar power, ocean waves represent an enormous source of renewable energy. From (Musial, 2008) we find wave energy increases with latitude and has greater potential on the west coast of the United States because global winds tend to move west to east across the Pacific Ocean. The total energy contained in the waves is dependent on the linear length of wave crest, the wave height and the wave period. Wave energy resource assessments have been performed by the Electric Power Research Institute (EPRI) and the methods for calculation are well documented. Table 1 shows the gross wave energy resource by region. This is an estimate of the energy contained in the incident waves if it were converted to electricity. US Wave Resource Regions (>10kW/m) TWh/yr New England and Mid-Atlantic States 100 Northern California, Oregon and Washington 440 Alaska (exclusive of waves from the Bering Sea) Hawaii and Midway Islands 1,250 330 Table 1 – Wave Resource by Region Just below the ocean surface, average power flow intensity is typically 2–3kW/m2 of envisaged area perpendicular to direction of wave propagation. This increase in power intensity, and also the fact that wave energy is more persistent than wind energy, stimulate motivation and hope for developing the, still rather undeveloped, wave-power technology to a prosperous mature level in the future. If the technology can be successfully developed, the market potential is enormous. This paper will focus on the visible waves that form at the shore as this is where the most energy can be harnessed. The energy per unit surface area in a wave is related to the square of the wave height. The wave speed and wave length decrease in shallow water, therefore the energy per unit area of the wave has to increase, so the wave height increases. This is known as wave shoaling. In fluid dynamics, wave shoaling is the effect by which surface waves entering shallower water increase in wave height (which is about twice the amplitude). It is caused by the fact that the group velocity, which is also the wave-energy transport velocity, decreases with the reduction of water depth. Under stationary conditions, this decrease in transport speed must be compensated by an increase in energy density in order to maintain a constant energy flux. Shoaling waves will also exhibit a reduction in wavelength while the frequency remains constant. In shallow water and parallel depth contours, non-breaking waves will increase in wave height as the wave packet enters shallower water. Cresting and breaking usually occurs when wave height = depth of water. By capturing the energy of a wave while it is at maximum mechanical motion that energy can be most efficiently captured. This energy can be harnessed to be used in other forms. It can be applied to a selective apparatus to be translated into usable energy, in this case electricity. “Exploiting the low, variable frequency motion of waves, and coupling the power to a fixed frequency and fixed voltage grid system, is a challenging task which device designers have tackled in different ways”. One of the benefits of near shore wave energy extraction over offshore is that it is next to the power grid systems that such as system would feed into. This would result in saving energy loss as a result of transmission. The many different proposals and principles for wave energy conversion may be classified in several ways. These are useful for seeing the differences and similarities between various wave energy converters (WECs). They may be classified, e.g. according to location (off-shore, nearshore or onshore; floating, submerged or bottom-standing), according to type of energy conversion machinery (mechanical, hydraulic, pneumatic or directly electrical), and according to type of energy for end use (electricity, water pumping, desalination of seawater, refrigeration, water heating, propulsion). WECs may also be classified according to their horizontal extension and orientation. If the extension is very small compared to a typical wavelength, the WEC is called a point absorber. On the contrary, if the extension is comparable to or larger than a typical wavelength, the WEC is called a line absorber, but the terms attenuator and terminator are more frequently used. A line absorber is called an attenuator or a terminator if it is aligned parallel or normal to the prevailing direction of wave propagation, respectively. An early example of a terminator was proposed by Salter, several “ducks” pitching with respect to a common horizontal cylindrical cylinder, the socalled spine. It was found necessary to divide the long cylinder into shorter cylindrical sections, hinged together. The spine still resists twisting, but complies to bending moments. This spine development has now evolved to the Pelamis, which is a device of the attenuator type. A typical device of the point-absorber type is a heaving axisymmetric body, a pulsating submerged volume, such as the AWS device, or an open-sea located oscillating water column (OWC) device. Most of the proposed OWC devices have pneumatic power take-off. A list of various wave energy converters is located in APPENDIX 10.6. It can be observed that the majority of these applications are designed to operate in off shore conditions and few have application for near shore. This thesis proposes that by capturing wave energy at maximum mechanical motion an optimized extraction of this energy can occur from near shore waves. Then by coupling this energy extraction to a device that efficiently converts the mechanical motion into electricity, such as piezoelectric materials, that can be fed into local power grid systems this model becomes a comparable solution in comparison to conventional energy generation techniques. To perform this thesis, research of wave energy background and theory will be performed with specific interest in coastal applications and interaction with submerged surfaces. An analysis of an ideal wave will be reviewed and energy extraction calculations generated. From these formulas, a device will be conceived to extract the most amount of energy from the wave form with the intent to minimize loss and maximum output of usable energy. This device should take into the environmental conditions and location, durability, and service life. 5.2. Near Shore Considerations Waves lose energy, in particular in shallow water, mainly by wave breaking and by friction against the seabed. If the shore is rocky and steep sufficiently down into the water, then wave reflection may be more important than wave dissipation. The variability of wave conditions in coastal waters is, generally, very large compared to offshore waters. Near-shore variation in the wave climate is compounded by shallow-water physical processes such as wave refraction, which may cause local ‘‘hot spots’’ of high energy due to wave focusing particularly at headlands and areas of low energy in bays due to defocusing. In addition, other coastal wave processes such as wave reflection, diffraction, bottom friction, and depth-induced breaking effects may have some influence. As such, it can be concluded that these influences will generally result in variation of expected energy inputs to a system or at most energy loss from ocean waves prior to extraction. This should be evaluated when considering where to place a near shore wave energy extraction device. Other considerations: Beach / Shore Erosion and Changes Over Time Marine life Navigation and Interaction with people 5.3. Wave Energy and Extraction The APPENDIX 1 wave formulas can be used to understand wave motion and energy and be used to help formulate ways to utilize that energy. In this section, we will focus on the energy extraction requirements. In general ocean waves are unsteady, irregular, and directional. An instantaneous picture of the ocean offshore will generally reveal several wave trains with different wavelengths and directions. In contrast to a single-frequency sinusoidal wave propagating in a particular direction, a real sea wave may be considered as composed of many elementary waves of different frequencies and directions. Per unit area of sea surface a stored energy amounting to an average of 2 E gH mo / 16 g S ( f )df (1) 0 is associated with the wave, where = 1030 kg/m3 is the mass density of sea water, and g = 9.81 m/s2 is the acceleration of gravity, whereas H mo is the significant wave height for the actual sea state. This stored energy is equally partitioned between kinetic energy, due to the motion of the water, and potential energy. The latter half-portion is due to mechanical work performed when the flat water surface is being deformed to a wave. This work corresponds to water lifted against the gravity force from wave troughs to wave crests. For wavelengths exceeding a few centimeters, the capillary force (surface tension) has a negligible contribution to the potential energy. The integrand S(f) is the wave spectrum. Its unit is m2/Hz, and it describes quantitatively how the different wave frequencies, f, contribute to the wave energy. In practice, the integral in Eq. (1) is, as an approximation, replaced by a summation over a finite number of wave frequencies. For a sinusoidal wave with amplitude H/2, where H is the wave height (the vertical distance between crest and trough of the wave), Eq. (1) for E is applicable provided H mo is replaced by H 2 . Taking as a typical value, H = 2m or H mo = 2.83 m, we get E = 5.05 kJ/m2. The physical law of conservation of energy requires that the energy-extracting device must interact with the waves such as to reduce the amount of wave energy that is otherwise present in the sea. The device must generate a wave, which interferes destructively with the sea waves. ‘‘In order for an oscillating system to be a good wave absorber it should be a good wave generator’’. As discussed above, total wave energy is a combination of potential and kinetic energy that results from the vertical (Z - heave) and horizontal (X – surge) translations; (Y – is known as sway). As such, an apparatus that would maximize energy transfer would have to be able to utilize both the vertical and horizontal energy. By understanding what the maximum energy that can be extracted from both the heave and surge, was can design and optimized damper to absorb. When considering heave, it should be considered as an advantage that practically all the volume, of e.g. a heaving-float system, could be ‘‘used to displace fluid and thus to generate outgoing waves’’. Falnes advocates that an economic wave-energy converter should have a large working area (wave-oscillator interface) relative to its size, and that this area should have a relatively large oscillating speed. Secondly, he indicates that the working area should preferably be resonant or ‘‘quasi-resonant’’. Corresponding to optimum wave interference, there is an upper limit, P, to the amount of absorbed wave power (energy) that can be extracted from a wave by means of a particular oscillating system, PA. P PA c T H 2 (9) where c (h / ) 3 / 128 245Wm 2 s 3 , 3 , and T is the wave period. According to inequality (9) the values of absorbed power, as well as of converted useful power are bound to the region below the, fully drawn, increasing curve in Fig. 2. Taking physical limitations into account, another limit to P exists, Budal’s upper bound, for the ratio of extracted energy to the volume of the immersed oscillating system, PB. Unless the recommendations are followed, the performance of a WEC may typically correspond to figures that are one to two orders of magnitude below Budal’s upper bound. P PB c0VH / T Where the wave height H 2A0 , where c0 g / 4 7.9kW / m 4 / s , with 1 , where V is the volume of the heaving body, and A0 is the elevation amplitude of the incident wave. These two formulas help us set limits to our wave energy absorber design volume based around anticipated wave T and H for a known location for heave (see Fig. 2). Need to now do translational energy extraction considerations. Moment of Inertia: Cylinder - http://hyperphysics.phy-astr.gsu.edu/hbase/icyl.html Pitch is best mode for converting energy. Need to evaluate particle. Two ways to extract linear and vertical energy are through the use of two forces, namely buoyancy and drag. http://en.wikipedia.org/wiki/Neutral_buoyancy http://en.wikipedia.org/wiki/Buoyancy Buoyancy is historically defined by Archimedes Principle: Any object, wholly or partly immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object. This results from the fact that fluid pressure increases with depth and from the fact that the increased pressure is exerted in all directions (Pascal's principle) so that there is an unbalanced upward (Lift) force on the bottom of a submerged object as shown in Figure 1: Buoyancy. The buoyant force, Fb, exerted on a body can be calculated by integrating the stress tensor, s, over the surface of the body, A, Fb = ∫ σdA Figure 2: Buoyancy (1) Drag force is caused mainly by separated flow in viscous fluid. Drag force is a function of the Reynolds number and surface roughness of a body, and the Keulegan-Carpenter number, especially in oscillating flow. Drag force, Fd, can be defined as10 where in this case the velocity, v, is equal to u, the wave horizontal velocity: (2) Where = force of drag = the density of the fluid = the speed of the object relative to the fluid = the reference Area = drag coefficient (dimensionless) = the unit vector indicating the direction of the velocity. Through a free body diagram and the conservation of energy, we can relate the vertical and horizontal forces between the wave and a partially submerged object. We would want to choose a partially submerged object prior to the wave breaking because this is where the energy is at maximum. The extractor should also be positioned prior to the dispersion of this energy during wave breaking. This is explained by Blenkinsopp as “Wave breaking is associated with the generation of high levels of turbulence, air entrainment, noise and splash, all of which must contribute to the energy dissipation and which are seen to increase with wave breaking intensity as waves become more plunging in nature. A relationship between breaking intensity and initial energy dissipation, showing that the total energy dissipated in the breaking event for each wave case increases as the relative cavity area becomes larger, i.e. as the intensity of breaking increases.” i.e. This is when the wave is at its highest point and right before it crashes over. Weight of Extractor Fd Force of wave Fb Figure 3 - Picture from Blenkinsopp = angle of the tether From figure 3, we can take the sum of the forces in X and Z direction (assuming that the extractor is of a uniform thickness and small compared to the wave in the Y direction, we can assume that Fy is << than Fx or Fz and equate to 0). As a result, an object that resists both the translation of the wave and vertical movement of the wave would transfer a portion of this energy through the tether to an apparatus where is could be transformed. 5.4. Piezoelectricity as Energy Converter Understanding these concepts it is possible to transfer the mechanical wave energy through a medium to generate electricity. This could happen in a number of ways. Machines such as pistons, generators, flywheels, and piezo-electric would be ideal for generating electricity from mechanical energy. Energy-Harvesting Rubber Chips Could Power Pacemakers, Cell Phones - “Of all piezoelectric materials, PZT is the most efficient, able to convert 80% of the mechanical energy applied to it into electrical energy.” 5.5. Energy Storage and Transmission Considerations 6. THEORY / METHODOLOGY………………………………………………………5 6.1. Design Considerations In consulting (Wave Energy), when thinking of location the author recommends, “For designers to convert the slow movement of water to a more easily used and transmitted form, normally electricity, they must choose a converter that changes the mechanical wave energy. In interfacing with the waves, any converter must be constrained so that wave forces are resisted. Ways of constraining a converter for consideration are (shown in Figure 2): —using the sea-bed for fixing or mooring; —mounting several converters on a common frame or spine so that relative motion is obtained between them; —using the inertial force due to the gyroscopic action of a flywheel; —relying on the mass and inertia of the device.” Figure 1. 6.1.1. Environment and Impacts 6.1.2. Sustainability Want to understand 6.2. Wave Energy Conversion Calculations 6.2.1. Mechanical Capture 6.2.2. Damping 6.2.3. Piezoelectric Energy-Harvesting Rubber Chips Could Power Pacemakers, Cell Phones - “Of all piezoelectric materials, PZT is the most efficient, able to convert 80% of the mechanical energy applied to it into electrical energy.” 6.2.4. Efficiency Calculations 6.3. Energy Storage and Transmission Considerations 1.1.1. Fly-Wheels 1.1.2. Transmission Lines 1.1.3. Other 2. RESULTS / DISCUSSION…………………………………………………………..6 2.1. Near Shore Piezoelectric Converter The overall amount of energy gained would depend upon the efficiency of the converter used and the location and intensity of waves. 2.2. Comparison to Alternatives 2.2.1. Efficiency 184.108.40.206. Other near shore devices 220.127.116.11. Power Plants 2.2.2. Costs 2.3. Environmental Impact 2.4. Global Trends 3. CONCLUSION……………………………………………………………………….7 3.1. Conclusions Waves are excellent sourced of energy, are a natural resource, and are renewable. Waves in shallow water are one of the best ways to capture this energy as this is when the wave energy is at its maximum. Wave energy can be categorized in both potential and kinetic, where the potential energy is a factor of the wave amplitude and displacement and the kinetic energy is a factor of the translation of the particles. These energies can be captured using opposing forces such as drag and buoyancy. How much energy is captured depends upon a number of factors: wave translation, wave height, the number of waves in a set period, the type of converter used and its efficiency of capturing both the potential and kinetic wave energy. 3.2. Recommendations 3.2.1. Improvements 3.2.2. Considerations 3.2.3. Future Research 4. REFERENCES / BIBLIOGRAPHY………………………………………………..10 5. APPENDICES……………………………………………………………………....11 5.1. List of Symbols 5.2. Definitions 5.2.1. Wave Shoaling - In fluid dynamics, wave shoaling is the effect by which surface waves entering shallower water increase in wave height (which is about twice the amplitude). It is caused by the fact that the group velocity, which is also the waveenergy transport velocity, decreases with the reduction of water depth. Under stationary conditions, this decrease in transport speed must be compensated by an increase in energy density in order to maintain a constant energy flux. Shoaling waves will also exhibit a reduction in wavelength while the frequency remains constant. In shallow water and parallel depth contours, non-breaking waves will increase in wave height as the wave packet enters shallower water. This is particularly evident for tsunamis as they wax in height when approaching a coastline, with devastating results. 5.2.2. 5.3. Basic Wave Equations and Theory The following explanation of wave theory is taken from (Meadows) so we can understand the basics behind ocean waves. Wave formation, motion, and energy can be described as follows and viewed in Figure 1. – Wave Basics: Figure 1. – Wave Basics The wave height, H, is the vertical distance between its crest and leading trough. Wavelength, L, is the horizontal distance between any two corresponding points on successive waves and wave period is the time required for two successive crests or troughs to pass a given point. The celerity of a wave C, is the speed of propagation of the waveform or how fast it travels (phase speed), defined as C = L/T, where T = time. It is of note that waves entering shallow-water begin to show a net displacement of water (visible wave) in the direction of propagation and are classified as translational in their movement. The equilibrium position used to reference surface wave motion, (still water level, SWL) is z = 0 and the bottom is located at z = –d. Small-Amplitude Wave — Properties The equation for the free surface displacement of a progressive wave is The expression relating individual wave properties and water depth, d, to the propagation behavior of these waves is the dispersion relation, sigma2, where g is the acceleration of gravity. (1) From this equation (1) and the definition of celerity (C) it can be shown that and (2a, 2b) The hyperbolic function tanh kd approaches useful simplifying limits of 1 for large values of kd (deep water) and for small values of kd (shallow water). Applying these limits results in expressions for shallow water where (3) which shows that wave speed in shallow water is dependent only on water depth. Some useful functions for calculating wave properties at any water depth, from deep water wave properties reference in Meadows, are . (4) Values of d/L can be calculated as a function of d/Lo by successive approximations using . (5) Particle Motions The horizontal component of particle velocity, u, beneath a wave is . (6) The corresponding acceleration, ax, is . (7) The vertical particle velocity, w, and acceleration, az, are respectively (8) and . (9) It can be seen from eqns. (6) and (8) that the horizontal and vertical particle velocities are 90 deg. out of phase. Extreme values of horizontal velocity occur in the crest in the direction of wave propagation, and the trough in the direction opposite to the direction of wave propagation while extreme vertical velocities occur mid-way between the crest and trough, where water displacement is zero. The u and w velocity components are at a minimum at the bottom and both increase as distance upward in the water column increases. Maximum vertical accelerations correspond to maximum in horizontal velocity and maximum horizontal accelerations correspond to maximum in vertical velocity. Figure1 provides a graphic summary of these relationships. The particle displacements can be obtained by integrating the velocity with respect to time and simplified by using the dispersion relationship to give a horizontal displacement (10) and vertical displacement (11) where (xo, zo) is the mean position of an individual particle. Pressure Field The pressure distribution beneath a progressive water wave is given by the following form of the Bernoulli Equation (12) where is fluid density and Kp, the pressure response coefficient, is which will always be less than 1, below mean still water level. gz is the hydrostatic pressure and g Kp(z) v is the dynamic pressure term. This dynamic pressure term accounts for two factors that influence pressure, the free surface displacement and the vertical component of acceleration. A frequently used method for measuring waves at the coast is to record pressure fluctuations from a bottom-mounted pressure gage. Isolating the dynamic pressure (PD) from the recorded signal by subtracting out the hydrostatic pressure gives the relative free surface displacement (13) where Kp(–d) = 1/cosh kd. It is necessary, therefore, when determining wave height from pressure records to apply the dispersion relationship to obtain Kp from the frequency of the measured waves. It is important to note that Kp for short period waves is very small at the bottom (–d), which means that very short period waves may not be measured by a pressure gage. Wave Energy Progressive surface water waves possess potential energy from the free surface displacement (vertical) and kinetic energy from the water particle motions (translational). From linear wave theory it can be shown that the average potential energy per unit surface area for a free surface sinusoidal displacement, restored by gravity, is (14) Likewise the average kinetic energy per unit surface area is (15) and the total average energy per unit surface area is . The unit surface area considered is a unit width times the wavelength L so that the total energy per unit width is (16) The total energy per unit surface area in a linear progressive wave is always equi-partitioned as one half potential and one half kinetic energy. Energy flux is the rate of energy transfer across the sea surface in the direction of wave propagation. The average energy flux per wave is where and Cg is the group speed defined as the speed of energy propagation. (17, 18) In deep water n = 1/2 and in shallow water n = 1 indicating that energy in deep water travels at half the speed of the wave while in shallow water energy propagates at the same speed as the wave. Wave Breaking Waves propagating into shallow water tend to experience an increase in wave height to a point of instability at which the wave breaks, dissipating energy in the form of turbulence and work done on the bottom. Breaking waves are classified as: spilling breakers generally associated with low sloping bottoms and a gradual dissipation of energy; plunging breakers generally associated with steeper sloping bottoms and a rapid, often spectacular, “explosive” dissipation of energy; and surging breakers generally associated with very steep bottoms and a rapid narrow region of energy dissipation. A widely used classic criteria applied to shoaling waves relates breaker height, Hb, to depth of breaking, db, through the relation . (19) However, this useful estimate neglects important shoaling parameters such as bottom slope (m) and deepwater wave angle of approach ( o). Meadows4 uses the following to solve for breaker depth (db), distance from the shoreline to the breaker line (xb) and breaker height (Hb) as (20) and (21) where m = beach slope and K = Hb /db The author makes note that wave breaking is still not well understood and caution is urged when dealing with engineering design in the active breaker zone. TABLE 1: Wave Formulas4 5.4. Piezoelectric Energy Equations 5.5. Other References Density of everyday substances (in g/cm3) Water Vinegar Ice Salt Water Milk(Skim) 1.00 0.78 0.92 1.03 1.033 1030 kg/m3 0.037 lb/in3 64.3 lb/ft3 Rubber, hard 1.2(103 kg/m3) 1.2 g/cm3 74 (lb/ft3) Rubber, soft commercial 1.1(103 kg/m3) 69 (lb/ft3) Rubber, pure gum 0.91 - 0.93(103 kg/m3) 57 - 58(lb/ft3) Density of Silicone: 0.968 to 1.29 grams per cubic centimeter for the silicone most people think of (implants). That's 60 to 80 lbs per cubic foot. For comparison, water has a specific gravity of 1, or about 62.4 lbs per cubic foot. Also for comparison, there are about 7.5 gallons in 1 cubic foot. A gallon of water weighs about 8.3 lbs. Mechanical Properties Name: Butadiene Rubber Ethenepropenediene Rubber Natural Rubber Styrenebutadiene Rubber Nitrile Rubber Young's modulus Mpa Tensile strength MPa Elongation % Thermal expansion e-6/K Physical Properties Thermal conductivity W/m.K Glass temperature °C Service temperature °C Density kg/m 3 NA 10-15 200-400 6.5-6.6 0.25-0.25 -100 - -50 -70 - 70 900 - 1000 Technical general purpose rubber as 1.4-polymerisation product of polybutadiene with dominating cis-config be equal to polybutadiene in general as produced throughout Europe. The strenght, heat buildup and wear r addition of 25% carbon black. Butadiene rubber is almost exclusively applied as a neccesary component of ru strongly the wear resistance. 2-10 10-20 250-500 NA 0.26-0.26 -55 -40 - 65 Production of 1 kg product including mixing and vulcanisation. Flexible, weather-resistant. 1-5 20-30 750-850 6.7 0.13-0.42 Incineration 45,2 MJ/kg. Moderate injection mouldability. -70 -50 - 85 860 910 - 930 2-10 10-25 250-700 6.7 0.2-0.25 -65 - -50 -30 - 70 940 Copolymer of Styrene and Butadiene in a 23/77% ratio mixture reinforced with 30% carbonblack. Average da Copolymerisation data assumed equal to the polymerisation process of the components. Oxidation-, water-, resistance against organic solvents and mineral oil. 2-5 10-20 200-500 NA NA -40 - -20 -35 - 110 1000 Copolymer of Acrylonitrile and Butadiene in a 30/70% ratio mixture. Average data from the European indust assumed equal to the polymerisation process of the components. Permeability for gasses is poor. Oil resistan (90%) of all rubbers. Very good resistance against oil and other organics. 5.6. List of wave energy converters Table A gives an overview of the existing energy conversion devices for near-shore to offshore and offshore situations both operational and those in advanced stages of development. Main information sources are Wave Energy Conversion by John Brooke in 2003 and the assessment on Offshore Wave Energy Conversion Devices of the Electricity Innovation Institute by Mirko Previsic from June 2004. The devices are split between the different conversion techniques and small pictures give an indication of their functioning. Definition of 'operational' energy conversion devices and 'advanced stage of development' by John Brooke: "The operational category comprises full-scale devices, chiefly prototypes, that are currently operating (or have operated) where the energy output is utilized for the production of energy or other purpose; also includes full-scale devices at an advanced stage of construction." The advanced-stage-development category comprises: (a) devices of various scales including fullscale, that have been deployed and tested in situ for generally short periods, but where the energy output has not been utilized for the production of electricity or other purpose (in most cases plans call for such devices to be further developed and deployed as operational wave energy systems); and (b) full-scale devices planned for construction where the energy output will be utilized for the production of electricity or other purpose." Classification of basic energy conversion principles: A Heaving or pitching bodies B Oscillating water column C Pressure devices D Surging-wave energy converters E Particle motion converters F Overtopping devices 5.7.