Stevens Institute of Technology Mechanical Engineering Dept Senior

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

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

Project Objective • 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 Selected Conceptual Design 3

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 4

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 5

Device Assembly 6

Device Assembly 7

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) 8

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 9

Spring Operated Reel Cable Tension (Fdevice ) lbs Function: Convert linear buoy motion into rotational shaft motion Design Aim: Maximize angular velocity of input shaft Preload Length (inches) K (inch pounds) 50 60 70 80 5 -494~1193 -421~1265 -349~1338 -194~990 10 -89~1035 10~1134 180~1232 206~1330 15 205~1735 408~1938 611~2142 815~2345 20 514~1982 777~2245 1049~2507 1302~2770 10

Spring Operated Reel Design Variable Results Diameter Max. Input Angular velocity 3 inches 53 RPM 4 inches 40 RPM 5 inches 33 RPM 6 inches 28 RPM 11

Spring Operated Reel Torque 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 Spring Housing Side plate Reel shaft angular velocity Shaft connection Stand Cable Guide 12

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 13

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 14

Mechanical Rectifier 15

Gear Box • • Function: Speed up rotational shaft motion Design Aim: Minimize gear ratio Gearbox Inertia (slugs. in 2) RPMmax after Gearing 1: 1 0. 0335 37 1: 5 0. 3895 274 1: 10 0. 6372 535 1: 15 1. 8853 1074 1: 20 1. 8807 1500 16

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

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

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 19

Alternator DC Generator Permanent Magnet Alternator Variable EMF Alternator Inexpensive Relatively expensive Inexpensive 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 brush Robust – does not use slip ring/brush May be less robust – use slip ring • Permanent Magnet Alternator – Wind industry – High efficiency at low RPM (~300 RPM) • Variable EMF Alternator is chosen • Car Alternator will be used for prototype testing: – Inexpensive – Low efficiency at low RPM 20

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 Encoder setup at Flywheel Typical alternator regulator 21

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 22

Power Output Design Variables Buoy Diameter Weight Values 6 ft 250 lbs Cable Preload Length 60 in Reel Radius 1. 5 in Gear Ratio Alternator Torque 10 40 lbs Predicted Power Output • The Mathematical Model was run with determined design variables • Efficiency of alternator assumed to be 50% • Higher average power expected with Flywheel 23

Cost & Weight Budget 24

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 25

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