Table of Contents - University of San Diego



Wave Energy Conversion DeviceA Proposal Submitted By:Mike BuelsingKevin GlassNeil LumJohn SophabmixayMENG491October 17, 2008Table of Contents TOC \o "1-3" \u Table of Contents PAGEREF _Toc211955741 \h 2List of Figures PAGEREF _Toc211955742 \h 4List of Tables PAGEREF _Toc211955743 \h 51. Context PAGEREF _Toc211955744 \h 61.1. Background of Need PAGEREF _Toc211955745 \h 61.3. Literature Review PAGEREF _Toc211955746 \h 71.3.1. Prior Work PAGEREF _Toc211955747 \h 71.3.2. Patents PAGEREF _Toc211955748 \h 81.3.3. Codes and Standards PAGEREF _Toc211955749 \h 92. Problem Definition PAGEREF _Toc211955750 \h 92.1. Customer Requirements PAGEREF _Toc211955751 \h 92.1.1. Form PAGEREF _Toc211955752 \h 92.1.2. Fit PAGEREF _Toc211955753 \h 102.1.3. Function PAGEREF _Toc211955754 \h 102.2. Assumptions PAGEREF _Toc211955755 \h 102.3. Constraints PAGEREF _Toc211955756 \h 112.4. Customer Requirements Schematic PAGEREF _Toc211955757 \h 112.5. Test/Evaluation Plan for all Requirements and Constraints PAGEREF _Toc211955758 \h 113. Concept Development PAGEREF _Toc211955759 \h 123.1 Overview PAGEREF _Toc211955760 \h 123.1.1 Creative Strategies PAGEREF _Toc211955761 \h 123.1.2. Governing Principles PAGEREF _Toc211955762 \h 123.2. Synthesis and Analysis of Overall Concept PAGEREF _Toc211955763 \h 133.2.1. Concept 1 PAGEREF _Toc211955764 \h 133.2.2. Concept 2 PAGEREF _Toc211955765 \h 143.2.3. Concept 3 PAGEREF _Toc211955766 \h 153.2.4. Concept 4 PAGEREF _Toc211955767 \h 163.2.5. Concept 5 PAGEREF _Toc211955768 \h 173.3. Evaluation PAGEREF _Toc211955769 \h 183.4. Refinements PAGEREF _Toc211955770 \h 203.5. Selection PAGEREF _Toc211955771 \h 214. Design Specifications PAGEREF _Toc211955772 \h 214.1. Design Overview PAGEREF _Toc211955773 \h 214.1.1. Description PAGEREF _Toc211955774 \h 214.1.2. Design Schematics PAGEREF _Toc211955775 \h 224.2. Functional Specifications PAGEREF _Toc211955776 \h 234.3. Physical Specifications PAGEREF _Toc211955777 \h 234.4. Product QFD PAGEREF _Toc211955778 \h 234.5. Subsystems PAGEREF _Toc211955779 \h 244.5.1 Truss and Buoy arms PAGEREF _Toc211955780 \h 244.5.2 Mechanical Energy conversion PAGEREF _Toc211955781 \h 254.5.3 Electrical Energy Converter PAGEREF _Toc211955782 \h 254.6. Design Deliverables PAGEREF _Toc211955783 \h 255. Project Plan PAGEREF _Toc211955784 \h 255.1. Research PAGEREF _Toc211955785 \h 255.2. Critical Function Prototypes PAGEREF _Toc211955786 \h 255.3. Design PAGEREF _Toc211955787 \h 265.3.1 Overall Design PAGEREF _Toc211955788 \h 265.3.2. Truss Beam PAGEREF _Toc211955789 \h 265.3.3. Flotation Units PAGEREF _Toc211955790 \h 265.3.4. Mechanical Power Conversion PAGEREF _Toc211955791 \h 275.3.5 Electrical Power Conversion PAGEREF _Toc211955792 \h 275.3.6 Anchoring Mechanism PAGEREF _Toc211955793 \h 285.4. Construction PAGEREF _Toc211955794 \h 285.5. Testing PAGEREF _Toc211955795 \h 295.6. Project Deliverables PAGEREF _Toc211955796 \h 295.7. Schedule PAGEREF _Toc211955797 \h 305.8. Budget PAGEREF _Toc211955798 \h 325.9. Personnel PAGEREF _Toc211955799 \h 336. References PAGEREF _Toc211955800 \h 347. Appendices PAGEREF _Toc211955801 \h 357.1. Team Member Resumes PAGEREF _Toc211955802 \h 357.2 Patents PAGEREF _Toc211955803 \h 387.3 Ocean Energy Calculations PAGEREF _Toc211955804 \h 417.3.1 Correlation between Period, Wavelength, Celerity, and Group Velocity PAGEREF _Toc211955805 \h 417.3.2 Energy per unit area as a function of wave height PAGEREF _Toc211955806 \h 427.3.3 Power per meter of crest as a function of wave height and group velocity PAGEREF _Toc211955807 \h 437.3.4 Power transfer and rpm per arm as a function of arm length, wave height, period, and buoy volume PAGEREF _Toc211955808 \h 44List of Figures TOC \c "Figure" Figure 1: Breakdown of worldwide energy supply PAGEREF _Toc211955844 \h 6Figure 2: The Pelamis Wave Energy Converter. PAGEREF _Toc211955845 \h 9Figure 3: The Customer Requirement Schematic for the Wave Buoy PAGEREF _Toc211955846 \h 11Figure 4: A Functional Decomposition of the Wave Energy Conversion system PAGEREF _Toc211955847 \h 13Figure 5: The Oscillating Buoy Fixed to the Ocean Floor schematic…………………………………………………………………………………14Figure 6: Schematic of the Oscillating Buoy Fixed to an Inertial Plate……………………………………………………..……………………. PAGEREF _Toc211955849 \h 15Figure 7: The Anchored Boat Energy Generation schematic PAGEREF _Toc211955850 \h 15Figure 8: Schematic of the Articulated Raft system PAGEREF _Toc211955851 \h 16Figure 9: A schematic of the inside of the Articulated Raft System PAGEREF _Toc211955852 \h 16Figure 10: Schematic of the proposed Pulsing Water Converter PAGEREF _Toc211955853 \h 17Figure 11: The feature schematic of the proposed system. PAGEREF _Toc211955854 \h 22Figure 12: The functional schematic of the proposed system. PAGEREF _Toc211955855 \h 22Figure 13: Electrical Power Conversion Unit. PAGEREF _Toc211955856 \h 28Figure 14: Project Schedule List. PAGEREF _Toc211955857 \h 30Figure 15: Gantt Chart Detailing Project Schedule. PAGEREF _Toc211955858 \h 31List of Tables TOC \h \z \c "Table" TOC \c "Table" Table 1: Decision Matrix for General System Type. PAGEREF _Toc211955980 \h 19Table 2: Types of Linear to Rotary Modes of Transmission PAGEREF _Toc211955981 \h 20Table 3: Types of near shore “Fixed to Ground” Systems. PAGEREF _Toc211955982 \h 20Table 4: QFD Analysis Relating Customer Requirements to Design Specifications. PAGEREF _Toc211955983 \h 24Table 5: Budget Plan for Proposed System. PAGEREF _Toc211955984 \h 32Table 6: Organization chart detailing subsystem assignment for each group member. PAGEREF _Toc211955985 \h 331. Context1.1. Background of NeedEach person on Earth consumes some portion of the world’s energy, directly or indirectly. Total worldwide consumption of energy is 500 exajoules (or 5 x 1020 Joules) per year, with renewable sources such as hydroelectric energy supplying merely 7% of this total. Oil, natural gas, and coal are the three major contributors to worldwide energy production (Figure 1), but these resources are limited. If natural gas, coal, and oil production remain constant, the natural gas will last 61 years, coal will last 133 years, and oil will last a mere 42 years. However, with population growth of over 95 million people per year, the preceding numbers surely will decrease. A collection of international scientists have compiled abundant data regarding fossil fuels and their effect on the environment (6). They reported that fossil fuels are a “virtual certainty” to be responsible for the global warming phenomena, which five years ago they claimed as “likely.” Numerous large corporations, especially electric companies, are turning to cleaner methods of operating. Renewable energy sources, by definition, do not deplete and have no net carbon emissions. The vast amount of water power in the ocean has been relatively untapped around the world, creating a large economy for hydroelectric power in the world today. Figure 1: Breakdown of worldwide energy supply, in terawatts [TW].1.2. Customer Need StatementElectric companies and their customers have an increasing need for stable and competitive pricing of their energy. Costs per kilowatt hour are increasing for the three major producers of energy (oil, natural gas, coal) because their resources are decreasing and the demand is increasing. For example, gasoline prices have risen 50% in the last two years alone; crude oil costs increased by over 90% in the same time span (3). Also, handling, production, and transportation of these resources further harm the environment.Because of the high demand for cost reduction, the existence of finite resources and the need for “cleaner” energy production, more renewable and reliable resource must be considered. Ocean wave power is immense and estimates show that 0.02% of the renewable energy available within the oceans converted into electricity would more than satisfy the present world demand for energy (8). The potential for shoreline-based wave power generation is 50 gigawatts worldwide and having sustainable systems in place will decrease the long-term costs of energy. In their quest to continue scoping the ocean’s physical attributes, the oceanography team at Scripps Research Institute is in need of a device that is able to generate enough energy to power their Wire Walker. The Wire Walker is a system that uses the chop or waves of the ocean to descend beneath the surface and collect data of temperature and salinity at different depths. The system uses telemetry to transfer the data. This portion of the Wire Walker is dependent on a power source. In order to power the device a minimum of 10 watts is required. Therefore, with a consistent and free renewable energy source, the Wire Walker will be able to produce better profiles. 1.3. Literature Review 1.3.1. Prior WorkHarnessing and gathering the massive energy potential in a wave efficiently is the ultimate end goal. The systems which have done this most effectively are discussed in the “Patents” section. Historically, designing a system that will be cost effective for its life cycle has been challenging because of a number of issues. Lack of experimental data makes it nearly impossible to mark the optimum location for wave energy converters. In each individual wave, the pressure exerted on the system is maximized just before the wave height peaks. However, at the peaks and crests of wave, the pressure created drops to zero. Also, the power generated must be transported great distances, as most of the existing systems are located miles offshore. These transportation costs and the maintenance of the power transmitting mechanism must be kept minimal as to provide power cheaply. Placing the energy conversion system into the ocean presents two major issues: the water is composed of salt and living organisms inhabit the majority of the ocean. Any component of the system will be exposed to the corrosive elements in the water, therefore creating a need for water-tight seals at all interfaces. These systems are also subject to extreme weather conditions. In regards to the living organisms, the key concerns are: changing migration routes, noise, navigational hazards and creation of artificial habitats. Historically, one of the major impediments of wave generation technology has been the lack of research support, and therefore funding. The United States has very little research in progress, whereas European efforts have been funded and put into place. 1.3.2. PatentsMany solutions have been developed to harness wave energy in the past. Some of the notable and most successful systems are:OWEC (Ocean Wave Energy Company): US Patent # 4,232,230…US Patent # 4,672,222Pelamis P-750 (Pelamis Wave Energy Converter)SPERBOY (Embley Energy)S.D.E. Energy Ltd Wave PowerCETO Zero Emission Power and Fresh WaterCheckmate SeaEnergyDEXA ConverterThe Pelamis Wave Energy Converter is currently placed off the shoreline of Spain and the United Kingdom. It has been designed to be a fault tolerant system having multiple levels of redundancy along its 100-meter long links. Its major subsystems are structure, moorings, hydraulics, electronics, and control. Controlling the fault tolerances allows the Pelamis to be placed in the harshest of environments off the coastline. Pelamis has been designed to attach and detach rapidly, with machines that are able to be installed on site with little to no manned intervention. The time of attachment and detachment are also very short, with two hours allowed to assemble large linkages and less than one hour to disassemble. The Pelamis design is fully modular, and the next step in its service life is to include a service base to decrease maintenance times and transmission of energy. Some of the ideas and initial requirements for a Pelamis service base would include:Suitable maneuvering space for berthing and unberthingSheltered from adverse weatherLevel access for vehiclesConditions suitable for use by mobile cranesSafe navigational route to and from offshore siteThe Pelamis Wave Energy Converter has been considered to be the most cost-efficient commercial system in place today. A picture of the Pelamis can be seen below (Figure 2), taking into perspective how long the linkages are in the system. Figure 2: The Pelamis Wave Energy Converter. The Pelamis uses a hinged linkage system to transmit hydraulic power to a generator, and has been successfully implemented in European countries.1.3.3. Codes and StandardsWith electrical components in the system, all testing and building will adhere to the ‘Electrical and Electronic Testing Collection’ (ANSI), the National Electric Code (N.E.C), and the ‘Other Electrical Accessories Collection’ (ANSI) standards. Also, since parts will most likely be submerged in salt water, the ‘Paint Requirement for Corrosion Protection’ will be followed regarding coating of the system. For testing in the open ocean, contact lines are being opened with officials to discuss the lawfulness of testing. Appropriate laws and standards will be followed; more data will be available in 2-3 weeks time. 2. Problem Definition 2.1. Customer Requirements The proposed system will be deliverable to the Scripps Institution of Oceanography. The team at Scripps needs a wave-energy device that outputs 10 Watts on average. The following section documents customer requirements and prioritizes their rough importance. For each requirement a number is assigned to designate relative importance, 10 being most important.2.1.1. FormThe proposed Wave Energy Converter will have the following physical limitations:Must have no component larger than 6’ x 4’ x 3’ to allow storage in Loma Hall room number 005 (6)Be highly visible to boaters and/or ocean species (5)Size to provide optimal energy extraction from predominant waves (7) 2.1.2. Fit The system will interface with the environment by the following conditions:Density must be less than ? ocean water (8)System must reside at surface of water (8)System must interface with the “Wire Walker” Buoy (7)Must generate electricity for the “Wire Walker,” which runs on 10 Watts of power (9)Must provide power at a depth of 5-50 meters above the ocean floor (6)2.1.3. FunctionThe following list describes the primary actions the customer needs from the system:Turn output shaft at a speed of greater than 1500 rotations per minute to run a common generator (10) Output minimum average of 10 Watts (8)Endure severe storm situations (wave heights reaching 5-10 meters) (5)Produce isolated, off-the-grid-energy at competitive price: competing with approximately 25 cents per kilowatt hour for solar (6)Be sustainable for 1 year (3)Be fully modular (7)Maintain its position with respect to the “Wire Walker” buoy (7) Resist marine growth (algae, etc) (6)Lab testing apparatus will be feasible and results measureable, generating waves that will be scalable in height and power to ocean waves (9)Have electrical components contained in water-tight areas (8)Have components that touch salt water be corrosion-resistant (8) 2.2. Assumptions Throughout the life cycle of the project, it is assumed that the following will be true in order for the proposed system to succeed:That the waves produced by wind chop will be sufficient enough to generate energy.That there will be enough energy in the storage cell to provide power during “flat days.”That our system will not hinder the data collection of the “Wire Walker.” Budget and final time scale will not change in the middle of the projectSuppliers will deliver parts on time and correct as ordered.Delivered parts will meet and perform to all specifications during a 1-year time frame.An abundance of fossil-fuels will not be discovered (for example, oil), again making alternative energy methods less attractiveGlobal Warming theories remain a pertinent issue in society throughout the next 10-20 years, and there will exist a market for non-emissive power producers The ocean water temperature will be greater than the freezing point and will not be higher than 80 degrees FahrenheitOcean testing will be feasible: system can be placed in front of the Scripps Pier.2.3. Constraints The following are the boundaries on the design, design process, team, resources, and budget. They are the parameters limiting the design and the design process. The constraints for the proposed Wave Energy Conversion device are: Eight calendar months for project life cycleBudget of approximately 800 dollarsSystem will have to conform to all marine and ocean codes/standards Requires no more than 4 x 28 hours per weekMust be placed in an easily accessible near-shore locationSystem must be buoyantSystem will be used as merely a proof-of-concept idea, scaled down from actual implementation size2.4. Customer Requirements Schematic Figure 3: The Customer Requirement Schematic for the Wave Buoy. Included are all of the inputs to the system and the two outputs (electricity and heat).2.5. Test/Evaluation Plan for all Requirements and ConstraintsDue to the scope and difficulty of the project, experimental tests will focus on the three critical functions of the buoy. Tests will be run to ensure that the system is completely sealed, that the system is assembled and geared to run a common generator, and most importantly that our system produces 10 Watts.The tests will be run in a wave tank located at the Scripps Institute of Oceanography. Later tests will be taken in the ocean in front of the Scripps Pier in La Jolla. The tests will measure torque, rpm, buoyancy, water seal, power, and overall workability. The telemetry system of the “Wire Walker” will monitor the output power of our system and radio transmit the data for testing purposes. The long-term buoyancy, water-tightness, and corrosion resistance of the buoy will be qualitatively analyzed based on design and construction. However, wave tank tests will also shed light on whether the design is sound, and Ocean testing will give more feedback to whether or not our system is a success.3. Concept Development3.1 Overview3.1.1 Creative StrategiesIn the concept development period for the proposed system, creative strategies were used to build a catalogue of concepts. The strategies included:System creationBrainstorming via online resources and library booksFunctional DecompositionCollaboration between group membersSketches of potential designsA collection of notes organized into a single notebook3.1.2. Governing Principles The function of the wave energy conversion device is governed by certain principles. The following are some of the primary principles that govern the function of the proposed system. Fluid dynamics (potentially pumping hydraulic fluid)Kinematics/dynamics (the motion of the piston)Physics (buoyancy of the buoy)Electrical Engineering (converting mechanical into electrical energy)Corrosion (properties of materials in water)Oceanography (currents, waves, barnacles)Experimental Methods (Is it testable?)3.2. Synthesis and Analysis of Overall Concept The preceding strategies and governing principles for design have led to the following proposed concepts. The concepts all fall within the scope of the project and each have intriguing and unique features relative to each other. Figure 4: A Functional Decomposition of the Wave Energy Conversion system. Six overall subsystems of the concept are analyzed, with viable options placed under each of them.3.2.1. Concept 1Oscillating buoy fixed to sea floor: This concept uses the relative motion between the surface of the ocean water and the seafloor to drive a linear to rotational mechanical system. The concept would involve placing a massive anchor on the seafloor and connecting it, via a taut cable or chain, to a buoy on the surface. As the buoy moves up and down, the chain or cable would pull a rack in and out of the bottom of the buoy, spinning a pinion gear inside of the buoy. A spring would connect the top of the rack to the inside top of the buoy, returning the pinion to the upper position when the buoy dropped into the trough of a wave (See Figure 5 below for schematic drawing). Ideally, the pinion would achieve upwards of 1500 rpm to be suitable for a low-cost generator. This system has the initial appearance of being very simple, that is why it was developed as the first concept. However, upon investigation, the concept has many shortcomings. First off, the anchor necessary to hold the rack in a constant position (the buoy moves relative to the rack) would need to be immense, or drilled into the sea floor. Along with a large anchor, the buoy would also need a robust cable or chain all the way down to the seafloor. Secondly, the chain or cable would need to be taught at all times which is difficult to maintain with fluctuating tidal levels. Lastly, the spring connecting the rack to the inner top of the buoy would need to be able to support the entire weight of the chain or cable. For these reasons, it appears that the system would be cost prohibitive.Figure 5: The Oscillating Buoy Fixed to the Ocean Floor schematic. This system will use a rack and pinion translation inside the buoy to create rotational motion, with the buoy undergoing a vertical translation relative to the ocean surface.3.2.2. Concept 2Oscillating Buoy Fixed to an Inertial Plate: This concept was generated during brainstorming to find a cheaper and more efficient way to produce linear motion from waves. The vertical translation of the surface waves will cause a linear movement of the buoy relative to the inertial plate (See Figure 6 below for schematic). The large inertial plate (composed of steel or other coated metal) will be buoyancy neutral (neither sink nor float) and tethered loosely to the ocean floor. Either a cable or a stiff rod will be attached to the inertial plate and will be taut, forcing the plate to act as the “ground” for the floating buoy as opposed to the distant seafloor. The linear motion will be generated by the relative motion of the buoy to the inertial plate.The main advantage of this system is its simplicity. It will not require many components and can be placed at any water depth because of the inertial plate. The plate also eliminates the need for a forcefully anchoring mechanism, since it does not need to stay stiff relative to the ocean floor. A disadvantage of the system is having components moving in and out of the system that are submerged in salt water. This creates a couple of issues: corrosion and marine-life buildup such as algae or barnacles. These failure mechanisms would cause frictional forces in the cable and therefore slow down its motion into and out of the buoy. Figure 6: Schematic of the Oscillating Buoy Fixed to an Inertial Plate. This concept differs from the first because it uses an inertial plate rather than an anchoring system. Comparisons of price and durability will determine which the better option is.3.2.3. Concept 3Anchored Boat Energy Generation: The third proposed concept for converting vertical linear surface motion into electrical energy involves placing a device between the anchor rode (anchor line) and the bow of an anchored vessel. The device would involve a similar mechanism to the one used in concept one and two, potentially a rack and pinion device (See Figure 7 for schematic). There are many benefits to this concept. First off, the “buoys” are already built and are not included in the design and manufacturing costs. Secondly, every boat already has an anchor. Lastly, the design could be scalable to provide everything from low voltage power supplies for recreational boaters, to high output generators placed on barges near remote islands. However, the design is not widely applicable and is considered as a luxury item to boaters needing a small amount of extra power. Figure 7: The Anchored Boat Energy Generation schematic. The conversion device will be placed between the anchor rode and the vessel, transmitting forces from the rode to the device.3.2.4. Concept 4Articulated rafts: This concept was inspired by the European ‘Pelamis’ wave energy project. An overall schematic of the system can be seen in Figures 8 and 9 below. The Pelamis system is driven by hydraulic pistons located at the joints. The individual segments of the raft float up and down according to their position on the wave. The flexing motion between them then forces the pistons in and out and uses the hydraulic pressure to drive a generator. The improvement to the system would be in developing a purely mechanical energy transfer and conversion system to transfer the energy more efficiently. This system would focus on improving upon a proven concept. An advantage of using purely mechanical transmission would be negating the losses through hydraulic conversion. For example, the movement of the wave must be converted into hydraulic pumping forces, which then must be turned into mechanical motion. Frictional losses and efficiency losses to the system will overshadow the power output from the system. Figure 8: Schematic of the Articulated Raft system. The proposed system will improve the concept designed and implemented by the Pelamis wave energy project.Figure 9: A schematic of the inside of the Articulated Raft System. The pinching of each link will run the motor by compressing the hydraulic fluid inside of the cylinders.3.2.5. Concept 5Pulsing Water Converter: This concept was generated through development of decision matrices to evaluate other concepts. None of the proposed concepts were to be placed onshore, and realized the vast power of broken waves moving up and then back down the shoreline. In the proposed system, there will be a structure placed in shallow water that houses a rolling component. The material and overall design of the roller is not yet known, but the mechanism would translate the rolling motion of the part through the structure into a rotating shaft (Figure 10).This system has the advantage of using only one mode of movement: rotation. Whereas the previous concept translated linear to rotational motion, the Pulsing Water Converter will solely use the rotational motion to turn an output shaft. Also, the pulsing motion of the water on and off the shoreline always exists, but tidal swings are a major issue. The system will need to have a controller to place it in the correct depth of water to account for the intensity of tidal swings. This is mainly because the rolling mechanism needs to be placed just below the surface of the water so it can gather the maximum energy of the already broken wave. Another disadvantage of the onshore system is accounting for wave power degradation. The wave will lose power as it breaks, and also as it runs along the sandy bottom due to friction. Finally, onshore systems are not ideal because of environmental issues; specifically, the shoreline is very valuable property and most people do not want to see it harmed or used for things other than leisure. Figure 10: Schematic of the proposed Pulsing Water Converter. This system utilizes the rushing of the broken waves towards the beach and their return to sea.3.3. EvaluationTo meet customer requirements, analysis was completed on the different options to dictate decision-making. The following assumptions were made after meeting with the Scripps Research Institute team:Wind chop is the primary energy sourceSystem placement is near shoreVelocity (v) is 1 meter per secondPeriod (T) is 1 – 4 secondsUsing these assumptions, the following calculation was made to determine range of wavelengths applicable to the system:v = λ * f , where f = frequencyf = 1 / Tλ = V / fTherefore, λ = v * Tv (T1) < λ < v (T2)1 meter < λ < 4 metersTherefore, the system will be designed for a wavelength between 1 and 4 meters. Swell waves possess a wavelength upwards of 200 meters; this previous was a huge design constraint. However, working with the Scripps Research design issue, the near shore application provides feasible lengths of the system. The amount of rotation in the truss beams is also analyzed to determine which types of gears used inside of the electrical power conversion unit (middle buoy):ω = (2*h) / (L*T) [radians/second]Given:h (wave height) = 0.6 mL (wavelength) = 1.5 mT (period) = 2 secondsTherefore, ω = 3.82 rotations per minuteHowever, the power exerted on the system by each truss beam due to the large forces is:Power = Force * Wave Height (h)Using h =0.6 m, P = 10 Watts (needed)10 Watts = N * 0.6 mN = 1.7 kg = 3.7 poundsCalculating volume necessary for the prescribed normal force exerted on the system gave:Force = Density * Volume * Gravity1.7 kg = (1025 kg/m3 * 9.81 m/sec2 * Volume)Volume of Buoy needed = 1.7 x 10-4 m3From this equation, with a perfectly efficient mechanical conversion system, a buoy with side length of approximately 6 centimeters is needed. The proposed system has sides of 3 feet. Decision matrices were implemented to evaluate each concept for their individual strengths and weaknesses. Also, a weight factor was introduced to magnify the most important constraints and requirements for the system. A top-level matrix was first used (Table 1) to categorize the main types of systems. The two highest-scoring types of systems will be analyzed individually in the next two matrices (Tables 2 and 3) for comparison. Table 1: Decision Matrix for General System Type. This matrix is used to determine the top two types of systems to be analyzed individually. The scoring system for the following 3 tables is the same as for Table 1.Table 2: Types of Linear to Rotary Modes of Transmission. This matrix is used to compare 5 different anchored systems to be placed either near shore or offshore.Table 3: Types of near shore “Fixed to Ground” Systems. This matrix is used to compare 4 different structures placed very near or onshore and also compared with previous system options.It is shown in Table 1 that the highest-scoring types of systems are ‘Fixed to Inertial Plate’, ‘Fixed to Boat’, and ‘Articulated Rafts.’ The Inertial Plate concept has particularly constant scores for all sections, while the Articulated Rafts has a couple of lower ones: electrical output and size. None of the onshore options seem viable based on their scores in Table 3. 3.4. Refinements The intended function of the proposed system is to convert wave power into rotational motion. One of the goals in developing the system is to minimize parts used. A fatal flaw of the design is differences in wavelengths moving from the test tank to the open ocean, since some open-water wavelengths are upwards of 300 meters long. Therefore, simplicity of the concept and appropriate scaling was taken into account in choosing final models. Using a truss bar mechanism that can be mounted inside of the buoy limits the amount of parts used because there will not need to be a housing on the outside of the buoys. One of the complexities will be the procurement of appropriate parts, most importantly the generator or driven motor. It will be necessary to design the system to accommodate for an off-the-shelf part since that is directly correlated to the primary function of the system. A Linear Gear head, which may be used with an A/C or D/C electric generator, has been considered instead of the piston system pending part cost. 3.5. Selection The long articulated snake system was chosen as the ideal wave energy conversion device, based on its simplicity and favorable movement acting as “one with the ocean.” One of the most successful systems in place today is the Pelamis Wave Energy Conversion system, and the chosen design improves on the top-level concept used by Pelamis. Cost and ease of build considerations were among the most important design parameters. Also, the modularity and the ease of disassembly and reassembly are of large importance for size considerations (Loma 005 constraint). Since most testing will be completed in a wave generation tank or near shore location, a system with the most flexible “wavelength-dependence” was chosen: the length of the truss bar mechanism accounts for different wavelengths. Any application of the articulated snake, whether it be near shore or offshore, is wavelength-dependent, and controlling the length of the trusses controls the wavelength parameter. 4. Design Specifications The chosen Wave Energy Conversion device will follow design specifications to ensure that it meets every prescribed customer requirement. Each of the requirements is considered in choosing specifications and package drawings are created to provide a top-level assembly perspective. Quality Function Deployment is used in determining necessity and feasibility of major design components. 4.1. Design Overview4.1.1. DescriptionUpon consideration of the various design concepts, the articulated buoy system was chosen as the ideal wave energy conversion device. The articulated buoy system consists of a middle buoy connected to two arms via pivot joints. Buoyancy is situated at the distal ends of the arms driving them up and down to match the ocean surface conditions. Energy is extracted from the ocean by a generator driven by the relative motion of the arms. The entire system will be oriented in the direction of wave propagation such that each joint will flex as the waves pass beneath them. The articulated buoy system can be broken down into six major subsystems. The first subsystem is the middle buoy, which houses all of the energy conversion and storage equipment. The second subsystem is the truss beam which converts the buoyancy of the distal flotation units into a rotational force within the middle buoy. The third subsystem is the flotation unit placed at the distal end of the truss beams. The fourth is the mechanical or hydraulic power conversion system that will convert the low RPM motion of the arm into a high RPM motion to drive a generator. The fifth is the electric generator. The last is the pivot point. 4.1.2. Design SchematicsFigure 11: The feature schematic of the proposed system. The three main components of the system are highlighted: the floatation buoy, the truss beam, and the electrical housing.Figure 12: The functional schematic of the proposed system. The system will intake all of the forces and elements on the left and output the head and electricity from the hydraulic motor on the right.4.2. Functional SpecificationsThe design was chosen to specifically fulfill the previously stated Customer Requirements. Each of the following Functional Specifications outline how the requirements will be met by the proposed system:FS1 Mechanical Power Conversion Unit: Convert angular velocity of truss motion, approximately 3 RPM, into 1500 RPM via a high ratio gearbox FS2 Hinges: Transmit high torque low RPM motion from ocean surface into the middle buoy. FS3 Anchor: Co-current flow is taken advantage of using a unidirectional anchoring system FS4 Surface: Coated in marine antifouling paintFS5 Critical components placed above ocean surfaceFS6 Testable in predictable, consistent, wind waves available year round in all coastal Southern California watersFS7 Flexible Rubber Gasket Seals: Withstand 85000 15 degree flexures per day for a minimum of one year FS8 Ability to withstand severe weather: Relatively short truss lengths are only affected by small high frequency wind waves. This allows the system to gracefully float over even the largest storm waves. Also, short trusses minimize extreme moments caused by a rogue breaking waves4.3. Physical SpecificationsThe Fit and Form Customer Requirements are fulfilled by designing a system in compliance with each requirement receiving consideration during the design process. The following Physical Specifications ensure that Form and Fit of the system complies with the prescribed problem definition:PS1 Size of System: Truss arms are detachable, no component longer than 10 feetPS2 Wavelength: Truss linkages of 5-10 feet will be implemented to account for high frequency PS3 Buoys: Floating buoys on top of water surface using either plastic or epoxy sealed plywood and Styrofoam combination. Coated with marine anti-fouling paint PS4 System Weight: Buoyancy force overcomes gravity to float in seawater- net density of material less than that of water 4.4. Product QFDTable 4 analyzes the relationships between Customer Requirements and Design Specifications. All weights and relevancies are displayed with a 0-10 scale (10 = maximum).Table 4: QFD Analysis Relating Customer Requirements to Design Specifications.Table 4 shows that each of the customer requirements is strongly correlated to at least one of the design specifications. The least strongly correlated design specification is the system weight. This is to be expected because the system weight is not a critical factor, it has only been listed to ensure that the buoy is simple to transport and deployThe information in the bottom three rows was used to enumerate the relative difficulty and importance of the various systems. The data indicated that the most difficult design specification was the mechanical energy conversion unit capable of increasing the RPM’s at a ratio of approximately 500:1. The importance of the mechanical energy unit is above average at 144, making it very important and worthwhile to devote design time to this function. 4.5. Subsystems The three main physical subsystems of the device are the truss and buoy arms, the mechanical energy conversion system, and the electric generation system. Below is an overview of each of these systems.4.5.1 Truss and Buoy armsThe truss and buoy arms collect and transmit the ocean’s surface energy to the center buoy. According to rough calculations, as shown in appendix 7.3.4, the length of the truss beams does not directly affect the power output if they move ideally in all situations. The deciding factor in the design of the truss length will therefore be the effectiveness of the different lengths in harnessing the dominant surface conditions at each location. It would be reasonable to assume that the same central buoy could be used with different truss beams to match the conditions in different locations.4.5.2 Mechanical Energy conversionThe mechanical energy conversion system is designed to convert the approximately three rpm motion of the truss beams (see appendix 7.3.4) into the 1500 rpm necessary to drive the electrical generator. The initial power transfer will utilize a belt drive for its light weight, resistance to corrosion, and cost. The belt drive will convert the nearly linear vertical motion of the central end of the truss beams into relatively high rpm rotational motion that will be directed into a gear box. The output shaft of the gear box will spin at 1500 rpm and be directly linked to the generator. 4.5.3 Electrical Energy ConverterThe electrical energy conversion system is simply a generator driven by the output shaft of the gear box. The electricity delivered by the generator will be in excess of 1o watts. 4.6. Design Deliverables By the completion date of the proposal period (end of first semester), further analysis will be conducted on the system and a comprehensive design completed. A Preliminary Design Report will include a solid model with necessary analysis done (i.e. mass and inertial properties). Along with this solid model, a full set of engineering drawings will be completed, with part names and their assigned vendors (either in-house or outsourced) for easy fabrication. All of these parts will be included in the Bill of Materials, which will then be converted into a cost-estimate for every part included in the project. At this time, parts may be ordered and the system build may begin. 5. Project Plan5.1. ResearchIn order to strengthen the fundamental principles of our design, further research in the areas of San Diego’s underwater bathymetry will affect the length of the truss bar linkage. The relationships between open ocean wind velocity, direction, and fetch, along with different swell periods, directions, and localized weather patterns also need to be understood to accurately model the conditions in a wave tank. Also, historical data of wind swell wave activity off the La Jolla coastline is of vast necessity to estimate design and test times. Further research in the areas of hydraulic fluid and piston construction will enhance the overall energy output of the system and may help to simplify the design.5.2. Critical Function PrototypesThere are major flaws that plague the articulated raft, some of which can’t simply be resolved but preventative actions taken. A major flaw that must be accounted for is the ocean water itself. Since the wavelength of a wave is a function of depth, it has been determined that the wavelength can appear anywhere between 100-300 meters. To serve as an efficient energy converter, it is necessary to capture as many waves as possible, thus the articulated raft may need to span over 100 meters. Also, the ocean carries corrosive elements that are harmful to the system. In order to prevent corrosion, water tight seals at all interfaces will be applied. It is critical that the proposed design be flexible enough to absorb the force of the wave to create mechanical energy. Once the prototype is developed it will be tested in a controlled environment. This controlled environment will produce consistent waves in which the flexibility of the system can be tested. The prototype will be a scaled down design that can be tested over smaller wavelengths. A way to test the water tight sealed interface would be to submerge the system in a liquid containing corrosive elements and observe results. 5.3. Design5.3.1 Overall Design The proposed design will involve two identical floating truss sections. Ideally, the articulated raft system will contain more sections, however the concept can be shown with only two. The design has therefore been limited to two sections for cost reasons.Each section will involve a truss beam supported at the ends by a flotation unit. The trusses will be joined together at the pivot point. The wave energy will then be converted into mechanical energy through the relative motion of the of the truss beams and be transferred to the interior of one of the flotation units by means of a rotating shaft. This energy will be in the form of low frequency, low amplitude, and high torque rotational vibration. The rotations will be so small that the motion can be considered as either rotational, or linear, as can be shown from trigonometry that when θ≈0, sin(θ)≈θ. The small amplitude, high torque rotations will be converted into high speed low torque rotations that are ideal for electrical generation. A small electrical generator will be attached to this output shaft to generate electricity.As discussed in the design overview, the system will be broken down into six major subsystems as follows:The truss beamFlotation UnitsMechanical power conversion systemElectrical power conversion systemPivoting jointAnchor 5.3.2. Truss BeamThe truss beam design will be governed by the stiffness required to effectively transmit the relative motion of the distal ends of the system into the mechanical power conversion system. A flexible beam will absorb all of the energy within its length and leave nothing to be converted into rotational motion. The second constraint is ease of fabrication and modification. Ideally, the beams will be prefabricated and only the ends will have to be modified to accept the flotation units and pivot joint. To meet these constraints as well as cost constraints, steel has been the material of focus for the truss beams. The length of the beam will have to be optimized to extract the maximum amount of force from a specific wavelength. One possible way to do this is to design the beam at a convenient length, and then use wave tank testing to determine what wavelength produces the optimum output power output. The production model rafts would then be designed to match the determined raft length to wavelength ratio. The trusses will require approximately 6 hours to design and optimize.5.3.3. Flotation UnitsThe flotation unit design constraints are buoyancy force, stability, cost, and ease of build. The buoyancy force needs to be large enough such that two of the four units will be able to support the entire structure, as will be the case during peak power conditions. Figure 16 below is an exaggerated view of this position. If the distal flotation units were not buoyant enough to support the entire structure, they would sink in this position and not cause the maximum flexing at the pivot point. This is equally important when the center point is on the crest and the distal ends are over the neighboring troughs. To design the ideal flotation units, the buoyancy force (mass*gravity of displaced water – mass*gravity of flotation unit) will be set to equal or exceed the mass of one segment. The design constraint is stability. The flotation units must be designed to keep the articulated raft from capsizing, as well as be self righting in the case of capsize. This will be done by designing the center of buoyancy to be above the center of gravity. Additionally, the current design calls for the mechanical and electrical power conversion systems to be housed within one of the units. The flotation units will require 10-15 hours to fully design due to the complexity of the watertight housing for the power conversion units.5.3.4. Mechanical Power ConversionThe system will convert low amplitude, low frequency, oscillating motion, into constant high frequency unidirectional rotation to be converted into electricity. The basic idea is to use one, or multiple, prefabricated gearboxes to convert the approximately 6 rpm motion of the input shaft, into the 1500 rpm necessary to drive a generator. However, due to the massive gear ratio of approximately 1:250, there are two complications inherent when dealing with low amplitude oscillating inputs. First, the inertia of the gearbox, which is a function of the combined moments of inertia of all the gears and their relative rotational velocities, will need to be kept at an absolute minimum to reduce energy loss. Second, the system will be extremely sensitive to the backlash caused by inherent imperfections in the gear manufacturing. The problem is exacerbated by the high gear-ratio and simultaneously devastating due to the low amplitude of the input motion. One possible way to circumvent this issue is to convert the shaft motion into unidirectional motion immediately by splitting it with opposing overrunning clutches. The clockwise motion would be transmitted to shaft B for instance, while the counterclockwise motion would be reversed with an extra gear and then connected to shaft B as well. A fly wheel could also be introduced at the output shaft near the electrical generator to buffer the rotation. This system will be the major design hurdle and can be expected to take in excess of two weeks to design.5.3.5 Electrical Power ConversionThe electrical power conversion system will simply be a motor attached to the output shaft of the mechanical power conversion system. The motor will have to be rated according to the torque and rpm of the system. A design time of six hours will be expected for this subsystem.An essential component of the articulated rafts system is the pivot joint that connects the rafts. This joint must be able to sustain forces in all directions to and constrain the movement of the rafts in one plane. Ideally the joint will have a low turning resistance, be waterproof, and have a long working life. Due to the importance of this component, 4-7 hours will be expected for its design. Figure 13: Electrical Power Conversion Unit.5.3.6 Anchoring MechanismThe final component of the system is the anchoring mechanism. The benefit of the articulated rafts system is that it does not require the anchor rode to be taught and massive. The only purpose of the anchor is to restrict the system to a general area. The specific type of anchor will depend on the interface with the Wire Walker, since the system will use the Wire Walker’s mass to self-anchor. A design time of 3 hours will be expected for the anchoring mechanism.5.4. ConstructionMost of the components involved in the system will be bought from outside vendors. However, modifications to parts will include milling, turning, and grinding. This will take into account interfacing and tolerancing issues between parts. The buoys will be made from a thin plastic or plywood surrounded by Styrofoam. Either choice will need to be coated by a sunlight and saltwater resistant paint. Material choice for the trusses has not yet been made, but some welding may be involved if metal is used. After the subsystems are built, the first assembly step is to attach the trusses to the buoys. Then, mounting the generator subsystem to each of the two buoy/truss assemblies will take place. Assembly will require standard hardware, including dowel pins, nuts, bolts, and screws. Some epoxy may be used in connecting the trusses to the buoys, along with the water-tight seals between the generator housing and the outside air/water. Since the trusses will be mounted inside of the buoys and able to slide out, all components will be easily detachable and placed onto a lab table. Therefore, all assembly can take place in Loma 005.5.5. TestingTesting will include overall system tests as well as individual subsystem tests. A system test will run in the Scripps wave pool or in the ocean off of Scripps Pier. Quantitative system tests will include the following:Up to 3’ generated waves (feet and power)Electrical output measurement (Watts)Rotational Speed (rpm)System testing will take place in the ocean waves, depending on wave height and subsystem performance. If all subsystems perform according to designs, the same three parameters as wave tank testing will be measured. The floating buoy will be tested for buoyancy and corrosion resistance. These tests will be conducted in the wave tank as well, but the corrosion results qualitative. However, procuring marine-grade coating will ensure that the buoy is sustainable since it is put onto long-lasting boats in the ocean. The truss bars will be testing for bending, since their stiffness is the critical function. Since “efficiency” is an ambiguous term regarding wave energy, density efficiency will be calculated: how much energy produced per cubic meter of water passed. This provides a more quantitative value in the scope of the project, since the system will be scaled and not in place for a long time. Therefore, a cost efficiency would be inconclusive, since building costs will far outweigh the short cycle life of only 4 months (building portion of project). 5.6. Project DeliverablesThe articulated raft deliverables to the University of San Diego faculty will include a Final Design Report, a working prototype that delivers measurable electrical current when operated in a wave tank and an analysis of any failed components. The deliverables to staff members at Scripps Research Institute include a working prototype that produces an average of 10 Watts per normal wave distribution off the coast of Southern California. The Final Design Report will also be included in that package, along with repair instructions. 5.7. ScheduleFigure 14: Project Schedule List.Figure 15: Gantt Chart Detailing Project Schedule.5.8. BudgetInclude an estimate of the project budget, broken down by subsystem (Table 5). Table 5: Budget Plan for Proposed System. NOTE: Yellow shade indicates high-priced components & green versus blue shading indicates aluminum versus steel truss, respectively.Part/MaterialCostQuantityShipping/TaxSubtotalStructuresBuoys????Plywood (1/8" x 12" x 12")$2.69 12$7.95 $40.23 Styrofoam/Plastic (12" x 36" x 2")$7.99 5$5.95 $45.90 Paint Coat (Quart)$53.56 1$0.00 $53.56 Trusses????Aluminum (10')$328 2$0.00 $656.00 Steel (10')$243.75 2$0.00 $487.50 Electric GenerationLinear to Rotational Motion????Control Box (Structure)$50.00 1$0.00 $50.00 Linear Gearhead$100.00 1$12.69 $112.69 Generator$50.00 1$0.00 $50.00 Bearings$1.50 20$2.99 $32.99 TestingWave Tank????Renting Tank (UCSD)$0.00 20$0.00 $0.00 IntegrationHardware????Epoxy (Marine Grade)$25.95 1$8.65 $34.60 Water-Tight Seal$1.70 10$1.55 $18.55 TOTAL:Aluminum Truss$1,044.52 Steel Truss$876.02 5.9. PersonnelThe group consists of four team members, each with a subsystem expertise. The four major subsystems are broken into the following: structures, electric generation, testing, and integration. Figure 16, below, shows an organization chart detailing these system assignments. Table 6: Organization chart detailing subsystem assignment for each group member.6. References The following are the references used in the research and development of the project:Beer, Tom. Environmental Oceanography. New York: C R C P LLC, 1996."Big Bee Boats Online Store". Blue Water Marine Paint. October 9, 2008 <;. Charlier, Roger H., and J. R. Justus. Ocean Energies : Resources for the Future. St. Louis: Elsevier, 1993. 105-84."Comparative Review of Alternative Energies". The Electronic Universe Project. September 24, 2008 <, Jacques. Marine Sources of Energy. Elmsford, NY: Pergamon P Inc., 1979. 88-120.Deutsch, Claudia. "G.E. Unveils Credit Card Aimed at Relieving Carbon Footprints". The New York Times. September 24, 2008 < r=3&oref=slogin&oref=slogin&oref=slogin>."Energy Prices: 2006 vs. 2007 vs. 2008 ". Cattle Network. September 24, 2008 <;."Fossil Fuels Are to Blame, World Scientists Conclude". USA Today. September 24, 2008 <;."MHD-Based Ocean Wave Energy Conversion". Scientific Applications & Research Associates, Incorporated. September 24, 2008 <;. "Midwest Craft Plywood". October 9, 2008 <;. "Syrofoam Sheets White". Michael's Floral Supply. October 9, 2008 <;. "Triangular Truss 3.0meters". Global Truss. October 9, 2008 <;. "Wave Energy Conversion". University of Michigan Department of Engineering. September 24, 2008 <;."Wave Power". Wikimedia Foundation. September 24, 2008 <;."World Energy Resources and Consumption". Wikimedia Foundation. September 24, 2008 <. Appendices 7.1. Team Member Resumes7.2 Patents Patents included have influenced the selected design and its components. 7.3 Ocean Energy Calculations7.3.1 Correlation between Period, Wavelength, Celerity, and Group Velocity7.3.2 Energy per unit area as a function of wave height7.3.3 Power per meter of crest as a function of wave height and group velocity7.3.4 Power transfer and rpm per arm as a function of arm length, wave height, period, and buoy volume ................
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