Tech Briefs Magazine - June 2024 - 48

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TECHNOLOGY & SOCIETY
Architected Reefs Could Protect Coastlines
This monthly column explores the inter-relationships between technology and society. It features people and projects aiming to
deliver a positive impact on the world facing unprecedented social and environmental challenges.
This artificial reef could dissipate more than 95 percent of incoming wave energy at a fraction of the
cost of other artificial reefs.
S
torms contain a lot of energy, which
can cause coastal erosion and damage
when they reach unprotected coastlines.
According to Michael Triantafyllou,
Professor in Ocean Science and
Engineering in the Department of Mechanical
Engineering at the Massachusetts
Institute of Technology, there are
islands in the Pacific that are surrounded
by reefs that protect them from
much of that damage.
" We looked at the structure of these
reefs and we found some similarities to
what we had been doing in fluid mechanics.
That led us to the idea of trying
to make artificial
reefs
that we
could architect and build in a very directed
way, using principles we had derived
from our earlier work on ocean
structures used for oil extraction, " said
Triantafyllou.
Some regions have already erected
artificial reefs to protect their coastlines
from encroaching storms. These
structures are typically sunken ships,
retired oil and gas platforms, and even
assembled configurations of concrete,
metal, tires, and stones. However,
there's a lot of variability in these structures,
and no standard for engineering
them. What's more, the designs that
are deployed tend to have a low wave
AT A GLANCE
INNOVATORS: Professor Michael
Triantafyllou, MIT Sea Grant, and MIT
Center for Bits and Atoms.
INNOVATION: Artificial reefs that
can significantly reduce storm damage
to coastlines.
IMPACT: Reduce storm damage,
protect marine life, dissipate incoming
wave energy at low cost and with
sustainable materials.
48
They further improved their design by
using artificial intelligence algorithms to
try various configurations using computational
and
experimental
methods.
An MIT team is hoping to fortify coastlines with " architected "
reefs - sustainable, offshore structures
that are engineered to mimic the wave-buffering effects
of natural reefs, while also providing pockets
for fish and other marine life to live. (Image: Courtesy
of the researchers, edited by MIT News)
dissipation per unit volume of material
used. That is, it takes a huge amount of
material to break enough wave energy
to adequately protect coastal communities.
Triantafyllou's idea was that a carefully
designed structure could be much
more effective.
The structure was inspired by the
team's work on blowout preventers -
cylindrical valves that are used to seal off
oil and gas wells to prevent them from
leaking. Their tests showed that the
structure's cylindrical arrangement generated
a high amount of drag and appeared
to be especially efficient in dissipating
high-force flows of oil and gas.
They wondered whether the same arrangement
could dissipate another type
of flow: ocean waves?
To test that idea, they designed a series
of one-foot-diameter cylinders spaced
about one foot apart to form a fence-like
structure. In tests performed on the
model, they found that their reef could
dissipate 10 times more energy than any
existing reef.
The team has constructed their cylinders
with a sustainable cement that tests
showed was inert to the ocean. " We
don't want to poison the ocean, " said
Triantafyllou.
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This led them to add four long slats,
each attached to the cylinder in a way
that leaves space for water to flow
through the resulting structure. They
found that this setup essentially breaks
up any incoming wave energy, causing
parts of the wave-induced flow to spiral
to the sides rather than crashing ahead.
" When you put things on the bottom
of the ocean, life tends to aggregate
there, " said Triantafyllou. So, inspired by
coral reefs, they carefully designed a pattern
of " voxels, " or microstructures, to
be molded into the cement in order to
create pockets in which fish and other
animals could live.
Their next step will be to design a larger
structure that they can test in a real-world
setting and they are looking to
work with a town on the Massachusetts
coast. Once they have found a location,
they will start designing the structure for
that specific site. Since the cylinders sit
on the ocean floor, the design will have
to be adjusted for that particular location,
and because the coast changes
from year to year, measurements will be
taken to make sure that things haven't
shifted since the area was last mapped.
" We have funding from the National
Oceanic Atmospheric Administration
through a seed grant for this next stage, "
said Triantafyllou. " We will now start
adding details on how a large structure
will look. Also, we have people working
with towns because we want to work with
stakeholders so that we can explain to
them what we're doing, and they can
give us feedback. "
This article is written by Ed Brown,
Associate Editor, SAE Media Group.
For more information, visit https://
seagrant.mit.edu.
Tech Briefs, June 2024

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Tech Briefs Magazine - June 2024

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