1. 1 Senior Design Final Presentation Stevens Institute of Technology Mechanical Engineering Dept. Senior Design 2005~06 Date: December 14 th, 2005 Advisor: Dr. Kishore Pochiraju Group 10: Biruk Assefa, Lazaro Cosma, Josh Ottinger, Yukinori Sato

2. 2 Agenda Project Objective Progress Feedback Mathematical Model Device Assembly Component Designs Cost & Weight Budget Conclusion

3. 3 Project Objective Selected Conceptual Design Project Description –Design, develop, prototype and test a device that harnesses wave energy to generate electrical power on a buoy –Off-shore location requires buoy to be self-sustaining –Power output in the 100’s of Watts range Objectives –Functional wave power generator which meet initial requirements

4. 4 Progress Feedback Identify losses in system –Mechanical Components  Mechanical Losses Need for low number of components Necessity of proper lubrication –Gearbox issues Using gearbox to increase speed affects inertia by the ratio squared As will be seen, ↑ Ratio: –Increases torque losses –Reach a point where the system is unable to overcome inertia Impact of Model on the Design –Aid in sizing of several parameters: Buoy diameter, Reel radius, spring constant, gear ratio –How each variable affects overall system –Sensitivity of each variable

5. 5 Mathematical Model Systems Approach to Mathematical Model –Divided overall simulation into 6 subsystems –Identified by system components Within each subsystem includes detailed modeling of the governing equations Simulation is solved by the simultaneous computation of each equation To simplify the analysis the “engaged” case was analyzed

6. 6 Device Assembly

7. 7

8. 8 Buoy Design Buoyant force is the main driving force Other forces: resistance from other components, weight, & damping force Damping force is a function of buoy velocity Buoy height (yellow) vs. Wave height (pink)

9. 9 Buoy Design Diameter of 6 feet Height of 25 inches Buoy Fabrication –Commercially unavailable / Expensive –Using low density urethane foam –Laminated with fiber class for added strength –Mold Options: Manufactured at machine shop / sheet metal Purchase kiddy pool Mold Buoy

10. 10 Spring Operated Reel Function: Convert linear buoy motion into rotational shaft motion Design Aim: Maximize angular velocity of input shaft Cable Tension (F device­ ) lbs Preload Length (inches) 50607080 K (inch pounds) 5-494~1193-421~1265-349~1338-194~990 10-89~103510~1134180~1232206~1330 15205~1735408~1938611~2142815~2345 20514~1982777~22451049~25071302~2770

11. 11 Spring Operated Reel Design VariableResults Diameter Max. Input Angular velocity 3 inches53 RPM 4 inches40 RPM 5 inches33 RPM 6 inches28 RPM

12. 12 Spring Operated Reel Stand Cable Spring Housing Side plate Shaft connection Cable Guide Reel Torque Reel shaft angular velocity Design Variables used Wave Amplitude: 6 inches Wave Period: 7 seconds Reel Diameter: 3 inches Spring Constant: 10 inch pounds Preload length: 60 inches Buoy Diameter: 6 feet

13. 13 Shaft Design Maximum torque located at reel output Worst case scenario –Full submersion –Locked shaft Torque on the shaft can be expressed as Factor of safety: 1.2

14. 14 Mechanical Rectifier Design constraints –1:1 ratio for CW & CCW rotation –Center distance relationship for gears: –Keeping effective inertia low Design Issues –Engaged vs. Disengaged –Model simulation focuses on Engaged state –Testing will focus on Disengaged state

15. 15 Mechanical Rectifier

16. 16 Gear Box Function: Speed up rotational shaft motion Design Aim: Minimize gear ratio Gear ratio Gearbox Inertia (slugs.in 2 ) RPM max after Gearing 1:10.0335 37 1:50.3895 274 1:100.6372 535 1:151.8853 1074 1:201.8807 1500

17. 17 Gear Box Input Shaft Output Shaft Design Variables used Reel Diameter: 3 inches Spring Constant: 10 inch pounds Preload length: 60 inches Buoy Diameter: 6 feet Gear Ratio: 10 Angular velocity of Reel vs. Gear Box Gearbox Torque

18. 18 Flywheel Function: Maintain high RPM for Alternator Design Approach: –Size the flywheel by iteratively testing the prototype with flywheels with various moment of inertia

19. 19 Alternator Function: Produce electrical power Design Approach: –Low inertia, high efficiency at low RPM, and variable torque preferred –Test for Torque vs. RPM and Efficiency vs. RPM curves

20. 20 Alternator Permanent Magnet Alternator –Wind industry –High efficiency at low RPM (~300RPM) Variable EMF Alternator is chosen Car Alternator will be used for prototype testing: –Inexpensive –Low efficiency at low RPM DC GeneratorPermanent Magnet AlternatorVariable EMF Alternator InexpensiveRelatively expensiveInexpensive Typically for medium to high RPM range operation – range limited Custom-made available for low RPM range operation Typically for high RPM range operation Fixed torque vs. RPM profile Variable EMF – torque can be adjusted No current needed to energize the rotor Small current needed to energize the rotor Not controllable EMF controllable with microcontroller Not robust – commutator and brushRobust – does not use slip ring/brushMay be less robust – use slip ring

21. 21 Method of Control Purpose: To maintain high power output by maintaining high RPM Microcontroller – provides programmable, digital control –Monitor two inputs (voltage and RPM) –Use PWM to adjust effective rotor EMF Use encoder to monitor RPM Will be limited to basic control (such as P-control) in this project Typical alternator regulator Encoder setup at Flywheel

22. 22 Battery Subsystem Car battery: provide large amount of current for a short period Deep cycle battery: provide steady current over a long period –Frequent charging and discharging capable –Optimal for the case of renewable energy generation Regulate charging voltage –Utilize regulator placed between alternator & battery –Keep charging at consistent rate during the wave profile

23. 23 Power Output Design VariablesValues Buoy Diameter6 ft Weight250 lbs Cable Preload Length60 in Reel Radius1.5 in Gear Ratio10 Alternator Torque40 lbs The Mathematical Model was run with determined design variables Efficiency of alternator assumed to be 50% Higher average power expected with Flywheel Predicted Power Output

24. 24 Cost & Weight Budget

25. 25 Conclusion What we learned from ME 423: –Necessity for Project Management –Importance of detailed design ME 423 & E 421: –Connect Product design, marketing, & sales –Basic understanding of intellectual property Initial plan to purchase COTS –Need to custom make several components Focus in ME 424: –Purchasing / Fabrication –Final Assembly –Testing Phase

26. 26 Questions and Comments? THANK YOU FOR LISTENING! SEE YOU NEXT SEMESTER