Transcript ME 423 Final Presentation

Stevens Institute of Technology
Mechanical Engineering Dept.
Senior Design 2005~06
Senior Design Final Presentation
Date: December 14th, 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
+
Reel
Buoy
Mech.
Rect.
Inv.
Red.
Dev.
-
Rot.
Gen.
Cable
Anchor
• 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 analyzed5
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)
Fb
Fdevice
W
Fdrag
W
y"b
g
Fb  f ( yw , yb )  A( yw  yb ) g
Fb  Fdamp  W  Fdevice 
Fdrag  Cdrag y'b
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)
I reel
Tspr
Rreel
Treel
Fdevice
reel Fdevicerreel  Tspr  Treel  I reel "reel
Tspr  f ( yb )  k ( yb  y preload )rreel
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
16
Maximum Submersion
(inches)
y'b , y"b
1
Fdevice
2
60
Maximum Submersion (yw – yb) Vs. Spring
constant at various preload lengths
 'reel , "reel
1
Fdevice
2
50
K = 5 inch
pounds
14
12
K =10 inch
pounds
10
8
K =15 inch
pounds
6
4
2
K = 20 inch
pounds
0
50
60
70
Preload length
80
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
Power
Springs
Output Shaft to
Rectifier
Power Springs are
attached to the shaft at
their inner ends and
fixed to the spring
housing at the outer
ends.
Support with
Bearings
Spring
Housing
11
Spring Operated Reel
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
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
1
1
2
Tshaft ,max  Vbuoy grreel  (rbuoy hbuoy ) grreel
2
2
• Factor of safety: 1.2
Buoy Diameter Buoy Height Torque_shaft
feet
feet
Pound-inches
6
2.5
6,619
5
2
3,677
4
1.5
1,765
Factor of Safety
1 in OD 3/4 in OD 1/2 in OD
1.239
0.526
0.15
2.21
0.939
0.268
4.809
2.043
0.583
13
Mechanical Rectifier
I rect
Treel
rectTreel  Trect  I rect "reel
Trect
engaged
 'reel , "reel
Trect
Trect
 'reel  0
 'reel  0
Trect
 Trect
disengaged
0
 'rect , "rect
• Design constraints
– 1:1 ratio for CW & CCW
rotation
– Center distance relationship
for gears:
R1  2R3  R4  R2  R5
– 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
Gear ratio
Gearbox 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
Design Aim: Minimize gear ratio
 ; rect
Gear Ratio vs. Effective Inertia of GB, FW, &
ALT (slugs.in^2)
500
450
Trect
 ' gb
 "gb
Tgb
gbTrect  TgbG  I gb,effective "rect
Effective Inertia
(slug,in^2)
 'rect  "rect
400
350
300
250
200
150
100
50
0
0
5
10
Gear Ratio
15
20
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
Input Shaft
Gearbox Torque
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
I fw
T fw
Tgb
 ' gb , "gb
 ' fw , " fw
 fwTgb  Tfw  I fw "gb
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
altTfw  Temf  I alt " fw
Temf  f ( ' fw )  a( ' fw )2  b ' fw c
Power  f ( ' fw )  alt , powerTfw ' fw
I alt
T fw
Temf
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
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
• 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
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
10
Alternator Torque
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
Component
Buoy
Buoy Mold
Urethane Spray Foam
Waterproof Casing (ft 2)
Platform
Spring-Reel
1/8” cable (ft)
Mechanical Rectifier
Gears
Bearings
Unidirectional Clutch
Shaft (ft)
Plastic Covering (ft 2)
Gear and Shaft Grease (tube)
Gearbox
Flywheel Disk
Alternator
Deep Cycle Battery
Electrical Control
Microcontroller
Wiring (ft)
O-rings / Sealers
Bolted Anchor
Nuts and Bolts
Overhead at 25% of Direct Cost
Totals
Qty/Unit
1
1
18
1
1
20
5
5
2
6
12
1
1
1
1
1
1
1
10
12
1
30
-
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$/Unit
40.00
300.00
4.00
15.00
50.00
2.00
50.00
15.00
10.00
15.00
4.00
5.00
100.00
20.00
200.00
125.00
10.00
40.00
0.25
1.00
10.00
0.25
-
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
Estimated Cost
40.00
300.00
72.00
15.00
50.00
40.00
250.00
75.00
20.00
90.00
48.00
5.00
100.00
20.00
200.00
125.00
10.00
40.00
2.50
12.00
10.00
7.50
383.00
1,915.00
Estimated Weight (lbs)
80
5
30
15
5
10
10
10
20
50
235
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
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