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Senior Design Final Presentation

Stevens Institute of Technology

Mechanical Engineering Dept.

Senior Design 2005~06

Date: December 14th, 2005

Advisor: Dr. Kishore Pochiraju

Group 10:

Biruk Assefa, Lazaro Cosma,

Josh Ottinger, Yukinori Sato

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Agenda

• Project Objective

• Progress Feedback

• Mathematical Model

• Device Assembly

• Component Designs

• Cost & Weight Budget

• Conclusion

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Project Objective

Cable

Anchor

Rot. Gen.

Inv. Red. Dev.

Mech. Rect.

Reel + -Buoy

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

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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

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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

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Device Assembly

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Device Assembly

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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)

deviceF WdragF

bF

gyyAyyfF bwbwb )(),(

bdevicedampb yg

WFWFF "

bdragdrag yCF '

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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

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Spring Operated ReelFunction: Convert linear buoy

motion into rotational shaft motion

Design Aim: Maximize angular velocity of input shaft

Cable Tension (Fdevice ) lbs

Preload Length (inches)

50 60 70 80

K (inchpounds)

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

reelreelreelsprreeldevicereel ITTrF "

reelreel ",'

sprT reelT

deviceF

deviceF2

1deviceF

2

1

reelRreelI

bb yy ",'

reelpreloadbbspr ryykyfT )()( 0

2

4

6

8

10

12

14

16

Ma

xim

um

Su

bm

ers

ion

(i

nc

he

s)

50 60 70 80

Preload length

Maximum Submersion (yw – yb) Vs. Spring constant at various preload lengths

K = 5 inchpounds

K =10 inchpounds

K =15 inchpounds

K = 20 inchpounds

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Spring Operated ReelDesign Variable Results

Diameter Max. Input Angular

velocity

3 inches 53 RPM

4 inches 40 RPM

5 inches 33 RPM

6 inches 28 RPM

Power Springs

Output Shaft to Rectifier

Support with Bearings

Spring Housing

Power Springs are attached to the shaft at their inner ends and fixed to the spring housing at the outer ends.

Power Springs

Output Shaft to Rectifier

Support with Bearings

Spring Housing

Power Springs are attached to the shaft at their inner ends and fixed to the spring housing at the outer ends.

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Spring Operated Reel

Stand

Cable

SpringHousing Side plate

Shaft connection

Cable Guide

Reel Torque

Reel shaft angular velocity

Design Variables used

Wave Amplitude: 6 inchesWave Period: 7 secondsReel Diameter: 3 inchesSpring Constant: 10 inch poundsPreload length: 60 inches Buoy Diameter: 6 feet

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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: 1.2reelbuoybuoyreelbuoyshaft grhrgrVT )(

2

1

2

1 2max,

Buoy Diameter Buoy Height Torque_shaftfeet feet Pound-inches 1 in OD 3/4 in OD 1/2 in OD

6 2.5 6,619 1.239 0.526 0.155 2 3,677 2.21 0.939 0.2684 1.5 1,765 4.809 2.043 0.583

Factor of Safety

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Mechanical Rectifier

• Design constraints– 1:1 ratio for CW & CCW

rotation– Center distance relationship

for gears:

– Keeping effective inertia low

reelrectrectreelrect IT " T

rectT

engaged

disengaged

0' reel0' reel

rectTrectT

0

reelTrectT

rectrect ",'

reelreel ",'

rectT

rectI

52431 2 RRRRR

• Design Issues– Engaged vs. Disengaged

– Model simulation focuses on Engaged state

– Testing will focus on Disengaged state

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Mechanical Rectifier

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Gear Box• Function: Speed up rotational

shaft motion

• Design Aim: Minimize gear ratio

Gear ratioGearbox Inertia

(slugs.in2)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

Gear Ratio vs. Effective Inertia of GB, FW, & ALT (slugs.in^2)

0

50

100

150

200

250

300

350

400

450

500

0 5 10 15 20

Gear Ratio

Eff

ec

tiv

e I

ne

rtia

(s

lug

,in

^2

)

recteffectivegbgbrectgb IGTT ",

rect"

rect; rect;

rect' gb"gb'

rectTgbT

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Gear Box

Input Shaft

Output Shaft

Design Variables used

Reel Diameter: 3 inchesSpring Constant: 10 inch poundsPreload length: 60 inches Buoy Diameter: 6 feetGear Ratio: 10

Angular velocity of Reel vs. Gear Box

Gearbox Torque

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FlywheelFunction: Maintain high RPM for Alternator

Design Approach: – Size the flywheel by iteratively testing the

prototype with flywheels with various moment of inertia

gbfwfwgbfw ITT "

fwT

fwI

gbT

gbgb ",' fwfw ",'

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AlternatorFunction: 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

fwaltemffwalt ITT "

cbafT fwfwfwemf ')'()'( 2

fwfwpoweraltfw TfPower ')'( ,

fwT emfT

altI

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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 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 Fixed torque vs. RPM profile Variable EMF – torque can be adjusted

No current needed to energize the rotor No current needed to energize the rotor Small current needed to energize the rotor

Not controllable 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

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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

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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

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Power Output

Design Variables Values

Buoy Diameter 6 ft

Weight 250 lbs

Cable Preload Length 60 in

Reel Radius 1.5 in

Gear Ratio 10

Alternator Torque 40 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

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Cost & Weight BudgetComponent Qty/Unit $/Unit Estimated Cost Estimated Weight (lbs)

Buoy - - - -Buoy Mold 1 40.00$ 40.00$ -Urethane Spray Foam 1 300.00$ 300.00$ 80

Waterproof Casing (ft2) 18 4.00$ 72.00$ 5Platform 1 15.00$ 15.00$ 30Spring-Reel 1 50.00$ 50.00$ 151/8” cable (ft) 20 2.00$ 40.00$ 5Mechanical Rectifier - - - 10

Gears 5 50.00$ 250.00$ -Bearings 5 15.00$ 75.00$ -Unidirectional Clutch 2 10.00$ 20.00$ -Shaft (ft) 6 15.00$ 90.00$ -

Plastic Covering (ft2) 12 4.00$ 48.00$ -Gear and Shaft Grease (tube) 1 5.00$ 5.00$ -

Gearbox 1 100.00$ 100.00$ 10Flywheel Disk 1 20.00$ 20.00$ 10Alternator 1 200.00$ 200.00$ 20Deep Cycle Battery 1 125.00$ 125.00$ 50Electrical Control 1 10.00$ 10.00$ -Microcontroller 1 40.00$ 40.00$ -Wiring (ft) 10 0.25$ 2.50$ -O-rings / Sealers 12 1.00$ 12.00$ -Bolted Anchor 1 10.00$ 10.00$ -Nuts and Bolts 30 0.25$ 7.50$ -Overhead at 25% of Direct Cost - - 383.00$ -

Totals 1,915.00$ 235

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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

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Questions and Comments?

THANK YOU FOR LISTENING!

SEE YOU NEXT SEMESTER