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Notes for Power Point Show on Wave Energy – version 4.2
Notes for Power Point Show on Wave Energy – version 4.2
1. Title - This slide show explains the theory and operation of the wave-energy exhibit in the
visitor center of the Hatfield Marine Science Center. This is just an overview. More details are
available in the Volunteer Training document.
2. Wave power on Oregon coast - Wave heights offshore average 3.5 meters during the winter,
which translates to about 50 kW per meter of crest length. During the summer, average wave
heights are lower, about 1.5 meters, which converts to 10 kW per meter of crest length.
[Adapted from “Harvesting the Waves,” by Annette von Jouanne, for Mechanical Engineering,
December 2006.]
If we could tap a significant part of that power we would have a year-round renewable source of
electricity. How much of this power can be extracted from the waves without interfering with
the natural process' that coastal sea life depends on?
3.
Goals - Most of the components are made of clear acrylic. Need instruments to measure &
display the electrical output, usually up to 1 or 2 volts.
Although the wave tanks focus mainly on the technical aspects of wave energy, there are many
other factors involved. The coast has many other “stakeholders”, not the least being the plants
and animals that live there. Other interests like shipping, fishing, recreation, sceanic
views,property values, the general environment of the ocean and coastline must be considered.
Many of these are shown on the large posters on the wall behind the exhibit. Be sure to point
these out to visitors, as well as the video running on the large screen.
4. Faraday Law of Induction – Without the calculus. Even nuclear and hydro power just turn a
turbine to turn a generator, which spins coils of wire in a magnetic field. I am aware of only a
couple of exceptions. One is solar cells, which convert sunlight directly into electricity. The
other is the Benthic Fuel Cell, the “Electric Mud” exhibit here in the visitor center.
5. Linear generator – The simplicity of this generator is very appealing. Want to keep moving
parts to a minimum to reduce friction loss. Also want to minimize corrosion problems, since
the buoy is running in salt water.
6. Sketch of linear generator - There isn’t a simple formula to calculate the expected voltage from
this type of generator. The usual formulas deal with wire loops rotating in a uniform magnetic
field, or loops in a magnetic field that is uniformly changing. In a linear generator the magnetic
field is not uniform. It is strongest at the surface of the magnet and weakens further out. The
actual voltage from this model will probably be in the range of 300 millivolts to 1 or 2 volts. A
millivolt is .001 volts.
7. Wave tanks - The 2 wave tanks are built side-by-side into a single unit. Each tank measures
4.9m (16') long by 28cm (11”) wide by 43cm (17”) deep. Although the 2 tanks appear to be
independent, they are not completely sealed. Water will slowly seep from one tank to the other,
eventually equalizing the levels in the 2 tanks.
8. Wave makers - Each tank has its own wave maker, consisting of a motor driven paddle at one
end of the tank. The paddle moves back and forth under computer control, sending waves down
the length of the tank. Each wavemaker is completely independent, with its own computer
controller.
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Notes for Power Point Show on Wave Energy – version 4.2
9. Computer control - Each wave maker has its own computer controller, consisting of a Windows
7 PC built into a kiosk with a touch screen. The touch screen allows the user to select the type,
height, period and repetitions of the waves to be made.
10. Note - The wave energy buoy is not intended to be an exact model of any existing device. It is
a teaching model only, simplified to demonstrate the basic principles to visitors. That is why
most of the components are made of clear acrylic.
11. Buoy components - The wave energy generator is built in 2 parts, the coil/base assembly and
the magnet/float assembly. The coil is secured on the bottom of the tank by the heavy base &
suction cups. The float rides up & down on the waves, moving the magnet up & down through
the coil. Having the buoy in 2 parts makes it possible to swap components for comparative
testing, for example testing different coils against the same magnet.
12. Buoy assembled - There is frequently much electrical noise in the visitor center, caused by the
fluorescent lights and other equipment. This noise is not audible, but tends to interfere with the
oscilloscope display. To try to combat this noise, the coil shown here is shielded with
aluminum foil, and a ground wire is attached to the foil.
13. Analog micro-amp meter - Since the output of the wave energy generator is a minute electrical
voltage, some way is needed to display the output. One instrument we have used is an analog
micro-amp meter. The analog micro-amp meter has it's 0 point in the middle of the dial, to
allow the needle to swing in both positive and negative directions, as the current will cycle back
& forth.
14. Oscilloscope - Another instrument is a PC based digital storage oscilloscope (DSO). The DSO
is the most accurate and informative, but is also more expensive. The DSO costs around $200,
plus the cost of the computer. The oscilloscope has the most capability but is also the most
difficult to handle, since it needs a computer in order to work. The fuzzy parts of the trace are
where the magnet is hitting bottom. You need to make sure there is at least 9” of water in the
tank.
15. Vernier - The Vernier LabQuest 2 is a small hand held instrument that will capture the voltage
from the buoy and display it on a screen. The Vernier, which does not require a computer, will
cost around $360, including a voltage probe. The instrument used most frequently will
probably be the Vernier.
16. Start up - The procedure to start up from a power off condition is a bit clumsy at this point.
17. Wave maker - Make sure that you have power to the wave maker. The switches are in the gray
box attached to the tank frame under the motors. These switches should be left ON. The wave
maker must be powered up before starting the controller program.
18. Kiosk chassis - Using the key, remove the large panel from the rear of the kiosk. The whole
back comes off. Make sure the small rotary switch is the ON position. You should hear the fan
running.
Feel for a small round button under the bottom of the chassis, at the right hand bottom corner, as
seen from the rear of the kiosk. This is just a couple inches off of the floor. Press & release the
button. This should start the boot-up sequence for Windows 7.
When Windows is up, the wave energy program will start and initialize itself. Then you can
start making waves.
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Notes for Power Point Show on Wave Energy – version 4.2
19. Operation instructions – Make sure there is at least 23cm (9”) of water in the tank. If you
measure from the outside of the tank, remember to measure for at least 25.4cm (10”), since the
bottom of the tank is 2.54cm (1”) thick.
20. Buoy in tank - Put the coil into the tank about midway along the length, on flat bottom. Don't
put it on the tsunami ramp as this will put the coil at an angle. Lead the connection wires out of
the tank, and connect them to your display device (meter, scope or Vernier).
21. Select waves - On the kiosk screen, select the desired wave and parameters. For best results,
choose sine waves with heights of 12 cm or less, and wave period .7 sec or less. Touch “Run
Waves” on screen.
22. Meter output – The current changes too quickly to get any accurate measurement, but the
magnitude of the needle swing gives a rough idea of the amount of current flowing. This
permits comparing different buoy configurations, like different magnets with the same coil.
23. Meter display – This meter can measure from -500 microamps to +500 microamps. 0 is in the
center to allow the needle to swing both ways as the current goes positive and negative.
24. Oscilloscope output – The oscilloscope measures voltage rather than current.
25. Oscilloscope display – The display is essentially a graph, with the width of the screen
representing 2 seconds of time. The trace line on the screen shows how the voltage changes
during those 2 seconds. The numbers below the trace line show the max & min voltages in that
time period, the average voltage (RMS), and the number of voltage pulses per second.
26. Vernier output – Like the oscilloscope, the Vernier measures voltage rather than current.
27. Vernier display - This display is also a graph, with the width of the screen representing 2
seconds of time. The trace line on the screen shows how the voltage changes during those 2
seconds. The numbers to the right show the max & min voltages in that time period.
28. Caution – The suction cups are quire delicate and can be easily damaged. When removing the
buoy from the tank, you must do it CAREFULLY! It is important to loosen the cups 1 at a
time. Try to pick up the edge of one cup with a finger nail to break the suction. Then continue
holding that edge while you loosen the next cup, until all cups are loose. It is a bit tricky and
may require both hands, but it can be done. Do not just yank the buoy out of the tank, as the
suction cups may be damaged.
29. Electrical noise - There is frequently much electrical noise in the visitor center, caused by the
fluorescent lights and other equipment. This noise is not audible but tends to interfere with the
oscilloscope display. To try to combat this noise, the coil is shielded with aluminum foil, and a
ground wire is attached to the foil. In this case there are 3 wires coming from the coil.
30. Noisy scope trace – Don't worry. It's not your eyes. It really does look like that. This shows an
oscilloscope display of an ungrounded signal from the buoy. The clip on the ground wire must
be connected to a proper ground point. For the oscilloscope, this is the ground lug on the back
of the module. For the Vernier, this is the black probe.
31. Grounded scope trace – This shows the oscilloscope display when the shield is properly
grounded.
32. Questions -
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