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The power of rising ocean waves is a largely untapped energy resource. Capturing this energy
for portable, mobile marine applications could integrate with solar technology for round-the-clock,
sustainable power supplies. Yet current wave energy harvesting technology is inefficient
on a small scale, and current small scale concepts don't work well in wave environments
where frequencies are very low and displacements very large.
Hello. My name Michel Schoemaker and I am a senior at the University of Florida. This
summer, at the University of Michigan, I worked with Doctor Ryan Harne and Professor Kon-Well
*** in developing a multi-stable energy harvesting chain composed of bistable links. This chain
will effectively transform low frequency motions common to waves into usable electrical energy.
A bistable link enables two positions of stable equilibrium, and snap through motion between
these stable wells. In the design, bistability is achieved by combining magnets and a linear
spring. Four outer magnets surround a central magnet, which is suspended by a spring. This
spring stabilizes two positions above and below the outer magnet plane.
You might wonder why achieving bistability is so important? The reason is, even the slightest
excitation - in this case, the slow up and down motion of the wave - produces an impulse
as the link moves between bistable wells. Because the links are interconnected by the
springs, these transmit the impulse along the chain, inducing high frequency vibrations
that are then converted to electrical energy via electromagnetic induction.
Most of the summer was spent developing and building the prototype. There were a number
of challenges. For example, cumulative weight effects in the chain, due to its vertical
orientation, were inhibiting bistability between links. To solve this, different spring stiffnesses
were selected for each link and acrylic was chosen as the primary structural material.
Some preliminary testing was also performed. We manually replicated slow, wave like up-down
motion to the top link to induce electrical signals from the four link chain. The same
procedure was carried out on one individual link. The electrical signals were combined
in series to charge a storage capacitor.We observed that the four-link chain generated
almost 300% of the voltage per cycle than the amount theoretically possible from four
individual links at similar excitation periods. This demonstrated increased energy harvesting
performance from chain internal dynamics.
The four-link chain also output 20% more voltage than the amount theoretically possible for
four single links for an excitation period of about 8 seconds, compared to about 2 seconds
for the individual link. This showed that the multi-stable chain effectively converted
large displacements and long excitation periods common to wave environments into usable electrical
energy. Future design work will focus on optimizing the system and addressing its feasibility
to operate outside the lab.
Overall, I really enjoyed my experience at the University of Michigan and I would like
to thank everyone involved in the SROP program. Go Blue and Go Gators!