- Physics world. - Hello and welcome to the
Physics World Weekly Podcast. I'm Hamish Johnston. In this episode, I'm in conversation with an aeronautics engineer who has created a bionic jellyfish and is also working towards
making large wind farms more efficient. Jellyfish have a very simple,
yet very effective way of swimming, and this has
attracted the attention of scientists and engineers
who look to jellyfish for inspiration while
developing aquatic robots. One of those researchers is John Debei, who is Centennial professor of Aeronautics and mechanical engineering
at the California Institute of Technology, and I'm very pleased that John joins me down
the line from Pasadena to talk about some of
his research interests, including jellyfish. Hi John, welcome to the podcast. - Thanks for having me.
It's a pleasure to be here. - So, so John, some of your recent research is focused on
understanding how jellyfish swim, and you've also looked at how jellyfish could be
electro mechanically enhanced for use in ocean exploration. What is it about jellyfish
that you find so fascinating? - Well, as you said,
they're very simple animals. When you go to the aquarium, they're may be not the first
thing that catches your eye because they don't seem
to be doing very much. But in fact, they're the most efficient swimmers in the ocean. They, uh, have been swimming
for 500 million years and they get from point A to point B using less energy than any of the other organisms out there. So for me, as a scientist and engineer, it's always been fascinating to understand how they do it. How can they take such a simple body shape and a simple motion and
yet be so energy efficient. - And, and so do you, what
is the sort of the status of the research at the moment? I mean, do you and your colleagues, do you have a good understanding
of how jellyfish swim - We do now with, with colleagues
including biologists, uh, like Jack Costello and Sean Colon. We've spent the past couple
of decades studying the flow, the water motions that
these animals create. Now, the big challenge here is of course, water is transparent, so we had to develop new research techniques
to measure the motion of that water surrounding the animals. So while you're at the aquarium and looking at their sort of
lazy motion through the water, we're actually more interested
in that water current around them, which is
actually quite fascinating and turns out to be the key
to their effective swimming. - And, and I believe you've
got, uh, in, in, at Caltech, you've got, is it, is it a
large tank that you have where, where you do this research? Can you, can you describe that tank? Is it, um, I, I, I mean, I'm, I'm sort of picturing a a a
tank that you can look into with jellyfish swimming in it, but I'm guessing it's more
complicated than that. - Well, well, that's correct.
So what we need to do is to put the animals in an environment where they're comfortable and
where they'll swim as close to they would in their natural
environment as possible. And then what we need to
do is find a way to measure that transparent water. So we put little tiny glass
beads in the water, uh, the thickness about the
size of, uh, the thickness of your hair, and we shine
laser light through the water. Now that laser light scatters off of those little beads in the water, and as the animals swim through the water, those beads start to move. And so we can use high speed cameras and some computer algorithms to then measure the water motion that those jellyfish
create as they're swimming. - I see. And you, you're
currently working on, uh, the artificial enhancement of jellyfish. Um, so, so is this, am am I
right in thinking it's sort of a, a, a bionic jellyfish? What, what, what's the
motivation for that research? - It is, yeah. Well, you know,
we began this work thinking that we would study the natural jellyfish and those water motions that
make them so energy efficient. And then we would go off
and build a mechanical robot using engineered materials. What we found over time
is that we could replicate that swimming motion that
you see at the aquarium, but those mechanical materials,
those engineered materials, they use a lot more energy than the, uh, natural tissue of the jellyfish. So about, uh, a a half decade ago or so, we said, well, if you
can't beat 'em, join 'em. And let's see if we can use
the jellyfish themselves as the robots for this mission
of understanding our oceans. Now an important, uh, point here is that jellyfish are uniquely,
uh, suited for this work. Uh, when we think about
the ethics of this type of manipulation, they don't
have a central nervous system or pain receptors, and we've shown that they
don't exhibit any sort of a stress response if we artificially manipulate their swimming. And so they turned out to be
the perfect system in which to take advantage of their
natural swimming abilities in this engineering context. - So, so how, how does that work in terms of artificially
manipulating the jellyfish? Is is it a mechanical
manipulation where you, you add something to the
jellyfish that, that moves under, under its own power, power and that sort of gently
pushes the jellyfish in the direction that you want it to go? Or is it an, is it a neurological thing or, or, or maybe it's - It's electrical. Yeah, it's electrical. We wanted to, to start as close to the actual animal control as possible. The real animals have eight
pacemaker cells around the edge of that umbrella shaped
jellyfish that you used to seeing a pacemaker that's not
unlike the pacemaker that keeps our heart beating on time. So what we did was to develop
small electronic devices that we could implant
in the jellyfish tissue and act basically like
an artificial pacemaker. We set the pace at which the
electrical signals are sent to the muscle, and that
leads the body to contract and swim as the animals normally would. Now if you go to the aquarium and you watch one of these
jellyfish, they might pulse once or twice and then float for a while, and then pulse another couple of times. We can, with our external
control, enable them to continuously swim for long periods of time at a very regular pace. And so that was work that a,
a former student, Nicole Shu, who's now a professor at
the University of Colorado, demonstrated recently
we've gone on to say, can we also mechanically
enhance the animals? And that's the, the more recent work that we've accomplished. - I see. And, and, and as
for the motivation, is it to, is it is the idea that you can strap
something to the jellyfish? So, uh, I don't know, some
sort of instrument for making measurements in the ocean or exploring bits of the ocean that maybe are very difficult, um, for a robotic system to, to access. Is, is that the idea that you're - It, it is. And you know, it's
interesting that, you know, I sit in an aerospace department, and of course we're very
interested in exploring, uh, places off of our own
planet here on earth. But the ocean really is one of the least explored
places in our universe, and that's, despite the
fact that it's so important for our wellbeing, it
sequesters a large portion of the carbon emissions that we, uh, make. It's important in terms of,
uh, fisheries food for people who live in coastal regions
for shipping, for energy, in terms of oil and gas. And so because of that
importance of the ocean, we think it's a vital that we
continue to expand the portion of the ocean that's been explored today. It's a fraction, a few
percent of the ocean's volume that's been explored. We are interested in
developing technologies to increase that significantly. One of the big challenges
there is being able to go deeper in the ocean than the, the surface from the
surface, or at the surface. You can use satellites, you
can use surface ships, uh, even small submarines that can go down to limited depths to study the ocean. But if you really wanna get
deep, you know, a kilometer, two kilometers deep in the
ocean, we have very few tools to do that successfully. You'll recall that the tragedy
of the, uh, submersible that went to the Titanic last
year Mm-Hmm, , the challenge is those crushing
pressures at depth make it difficult to engineer vehicles that can withstand those depths. And yet these jellyfish
that we're studying, they're found at those
depths all of the time in polar waters where it's cold in tropical
waters where it's warmer. And so we thought perhaps
we could use these jellyfish as the a basis for this global
ocean exploration platform. - I see. And, and sort
of the, the technology that you're sort of piggybacking
on the, on the jellyfish, I'm guessing that would have to be pressure resistant, wouldn't it? I mean, is that That's correct. Is that gonna be a difficult
aspect of, of designing? - So that's the interesting thing. The, the physics of this
problem, of, of hardening as we sometimes call it, or, or designing a, a structure
to withstand pressure, is that the smaller the item is,
the more reasonable or, or more straightforward it
is to accomplish that task. As the vessel gets larger and larger, the walls of that
vehicle have to get thicker, and that makes the whole
structure a lot heavier. So we're talking about, uh,
packages on the size of a, a softball or a cricket
ball perhaps, as opposed to something that a human
would need to fit inside. And these jellyfish, they come in sizes that range from a dinner plate to the size of a small vehicle. And so they have the carrying
capacity to a tow, a payload that could take measurements
of the ocean temperature, it's salinity, the chemical
composition of the water, and to track it over time
so that we can understand how our oceans are changing
in, uh, in almost real time. - And and what sort of
timeframe are you looking at? I mean, I'm, I'm guessing that you're still testing in
your tank, um, in Pasadena. How do, do you have any
plans to to to get your, your enhanced jellyfish
out into the ocean? - We do, and so our initial
work just demonstrating electrical control, that is
being able to control the, the pace of swimming of the animals that was conducted in
a relatively small tank that was only about two meters tall. Uh, we now have a facility here at Caltech that's six meters tall,
so almost 20 feet tall, that we're able to have
these animals swim. And in that facility we can
send a current, uh, a water flow so that these animals can swim in place for long periods of time. The idea is that we want
to replicate in the lab, the animal's journey from the surface to several kilometers deep,
which would take several days because these animals, while being efficient, aren't very fast. We wanna know that over
that day long journey that the payload continues
to function properly, and more importantly that the
animals remain healthy again. We want to be sure that the
animals are being properly cared for as we implement this platform. So those experiments, understanding their laboratory
performance under long timeframes are still ongoing. The next stage will be to test them in relatively
controlled offshore environments where we know the currents. We can have divers out in
the water to spot the, uh, the robot jellyfish and make sure they're
functioning properly. And then from there we plan
to go as, as deep in the ocean as, uh, we can find. - I see. And I, I, do you dive, John, will you be out in
the ocean with your jellyfish or will you be on the boat? - I happen to be a great deckhand, but not a great swimmer . So, uh, I'm fortunate to recruit a lot of great graduate students and postdoctoral scholars
who, uh, are great divers and they love to be underwater. And so, uh, it's certainly a team effort, - . Okay, great. And I, I
wanted to ask you about, about some other research
that you've done on, on swimming animals. Last year you published a paper that asks, do swimming animals mix the ocean? And in it, you point out that
this idea for mixing, um, began as a joke, but it's now considered a, a
serious scientific question. What is the evidence for
animals mixing the ocean, and why is it important that scientists investigate this further? - Well, I'll start with your
second question first as to why it's important. Uh, as I mentioned earlier,
the ocean is, uh, the home to millions of marine species. It's important for the regulation
of our climate on land. And so we need a better
understanding of how the ocean works and how the ocean might be changing with the impacts of climate change. Now, we know that the wind
is an important factor. The, the wind over the
ocean surface drives some of the circulation in the ocean. We know that tidal currents
are also important. The effect of the moon tends to also regulate ocean currents. It was maybe, uh, 60 years ago now that Walter monk in a paper,
he is a famous oceanographer, suggested that swimming animals
might also have an impact. Although it turns out he
was joking about the idea. When you do the calculation of how much chemical energy is available to those animals in the ocean,
you get numbers that suggest that in principle they could
have a significant impact on ocean mixing. The question is whether these animals, which generally are pretty
small, you know, the size of your thumbnail, could
they together when they swim, create, mixing and transport in the ocean
on length scales that matter for a very big ocean? The ocean is a billion, over
a billion cubic kilometers. And so the question is, can those tiny animals
really have an impact at that large scale? We've done work in the
lab suggesting mechanisms that could let tiny organisms
create much larger currents, and the next step is to see
whether those processes actually occur in the real ocean. - So, so you're talking about the, the, these organisms swimming
rather than if I, I dunno. I could imagine if a large number of organisms move from
one place to another, they could change the, uh,
properties of the ocean and, and cause currents to flow. But it is the actual movement of those organisms collectively that, that you're looking at. - We are. Well, so it's the water motion outside their bodies,
particularly when they're, when they're swimming vertically. So horizontal motion o occurs
in the ocean all of the time. It's actually much harder to
mix vertically in the ocean because the layers are what
we call stratified, meaning that the water at the top is
a little bit less dense than the water at lower levels. And so when you try to mix that water, you've gotta do some work, you've gotta change the potential energy of the system, as we would say. So the question is whether
the animals are able to mix the ocean to put
enough energy in to cause that vertical mixing. The thing that they have going for them is that these animals actually
constitute the largest mass migrations on earth every single day. So trillions of these organisms
at sunset, they rise up to the ocean surface from death, and then at in the morning
they, they'll swim back down. And it's that daily vertical migration that we think could hold the key to vertical mixing in the
ocean still to be proved, it's only a hypothesis at this stage, but the math says that at large scale, there's enough energy available and there are enough organisms
available in important climatically, important
regions of the ocean. Uh, but we still haven't
found that smoking gun of the mixing occurring in the ocean. - I see. So, so you've
asked the question, are you, is this an active area of
research for you at the moment? - It is, you know, in fact,
it, it in some ways, uh, connects to the work we discussed with these jellyfish sensors. One challenge you'll
find is that if you were to take a mechanical device
into the water to try to measure one of these
vertical migrations, the animals will sometimes
avoid those measurement devices. And so it's very hard to get
that, uh, smoking gunshot of the animals swimming vertically and creating, mixing
these jellyfish robots that we're designing have a
more natural swimming motion. In fact, if you see them in
a group of other jellyfish, you really couldn't pick them
out except for the blinking, uh, LED lights that we
have on our electronics. And so our thought is that
we can use systems like this that are more biocompatible
to be able to get close to those vertical migrations
or even within them, and to take these key
measurements to understand how these vertical migrations might impact the water around them. - Okay. Well that, that, that,
that's really interesting. We look forward to, uh,
to seeing what you, what you and your colleagues come up with on Yeah. On the animals mixing the, the ocean. - Me too. . Uh,
- Um, um, I suppose my final question
goes back to the, the, the aeronautics part of
your, of your job title. Um, you, you also studied
the, the fluid dynamics of wind turbines. And I was just curious, you
know, what the, what the state of the art, uh, with
regards to turbines is. Do we currently have a good
understanding of the physics of turbines or is there
much more to learn in terms of making them more
efficient, maybe quieter? - Yeah, I can answer that
a a a couple of ways. I will say from an
engineering perspective, we can certainly see today
engineers building wind turbines that are very highly efficient
in terms of their conversion of moving wind to electricity. In fact, some of the modern
wind turbines reach the theoretical limits for what we expect a wind energy
conversion device to produce. Now the challenge is that
when you have a wind farm that is a group of these
wind turbines, that first row of wind turbines that seize
the wind, they're going to perform very well. But in their process of converting energy, they end up creating
choppy air behind them. We call that turbulence very similar to the turbulence you might
experience on a flight that turbulent air reduces
the performance of all of the other turbines in that group. And so the frontier in this
field is to figure out how to optimize the performance
of groups of turbines so that the hole can be maybe
even greater than the sum of its parts, but at least
equal to the sum of its parts. Today, the hole is actually
much less than the sum of its parts in the sense
that to get a wind farm to function well, we have to spread those wind
turbines very far apart so that they don't interact with one another. We found maybe a decade ago that we could take inspiration from some of our work in the ocean,
where you can see a fish school swimming through the ocean. Those individual fish also
generate turbulent choppy wakes, but they don't separate
as far apart as possible. They just synchronize their
motion in certain ways. And in fact, in those cases, the whole is greater than
the sum of its parts. The energy efficiency of that group can be higher
than the individual fish swimming by themselves. So we and other groups have spent a lot of time thinking about how to translate those insights
into practical wind farm design. Uh, one of my former
students, Mike Hallend at MIT, has been working with utility wind farms, so real operational wind farms and demonstrating that by doing
clever things like steering the direction that the
wind turbines are pointed, you can improve the performance of the entire wind farm in a way that takes some inspiration
from those fish in the ocean. - And is that, is that most
mostly computational work? Are you running big sort of
fluid dynamics simulations, or, or is there also, um, you know,
field measurements involved and, and maybe working in the lab as well? - We were fortunate in,
in my lab to be able to actually test these
ideas early on in the field. And that's important because
computer models will sometimes tell you what you want to hear , and it's going out into the field and building an experiment
that really is the test of, of any idea. Uh, at Caltech we were able
to buy a plot of land north of campus and actually build
a research wind farm using smaller scale wind turbines
on the order of 10 meters as opposed to the a
hundred meter behemoths that you see today. But we were able to demonstrate
in those field tests that this idea of interacting
between the turbines to improve their performance,
uh, that this really worked. Now more recently, we actually have gone to conventional wind farms in India and other locations with
major wind farm operators, and we've been able to demonstrate that those same ideas do
hold on the big hundred meter wind turbines as well. - I see. Okay. So, and, and what, what, what sort of goal do, do, do you have in this is ultimately,
is it you, you, you think that you, you'll be able to
advise people on exactly where to put their, um, wind turbines and, and boost their efficiency significantly? - Yeah, there are, there are
several opportunities here. One is in new projects, if
I have a new plot of land that I want to understand
how to get the most out of that plot of land, the
theory that we've developed and the computational tools that have been validated in
experiments can be used to do that design process. The other place is in offshore wind. That's a place that's still burgeoning, especially here in the United
States, where you might have concerns that you don't
want to take up a huge swath of the ocean because of shipping lanes and, uh, potential impacts
on marine organisms. And so if you wanna identify
an effective location that's a bit constrained in the ocean, these tools can be useful. And then the third area
where these techniques can be important is in what we call repowering of existing wind farms. So here in California, in the
United States, we had some of the earliest wind farms,
which came online, uh, almost 40 years ago. Now the challenge is that those plots of land have great wind resource, but a lot of old wind turbines sitting on those plots of land. What we've been able to do
with this idea of wind turbine optimization is to imagine
putting smaller wind turbines, large arrays of them on
that same property in between the existing older wind turbines. And we've shown that in some
cases you could double the energy output from those older wind farms by taking advantage of these,
uh, aerodynamic interactions between both, between
the smaller wind turbines and themselves, but
also between the larger, what are called horizontal
axis wind turbines, the conventional propeller
style wind turbines are used to seeing, and this next
generation of wind turbines, some of which rotate on a vertical axis, so they have a different geometry than the conventional wind turbines. So there are several areas
in which these ideas, uh, could have a potential
impact in the future. - I see. Oh, well that's,
that's really fascinating. I mean, it must be, uh, I mean,
it, it must be a great job to, uh, to, to be doing research
on, on things, you know, ranging from jellyfish
to, uh, to wind turbines. And I I'm sure there's
lots of other things that you're interested in that, that we haven't covered today. - Yeah, it's the, I think it's
the best job in the world. I'm fortunate to do it here at Caltech and to do it with a bunch of
really talented grad students and postdocs who, who
also have a broad range of interest centered on physics. And so, particularly in my
field of fluid dynamics, it's really fun to be
able to work on blood flow and jellyfish and wind
turbines all in the same day. And, and that's what the physics
and math allows us to do. - Well, that's great. Tha thanks so much for talking to me John. And, um, uh, John and, and his colleagues,
their, their paper, uh, on jellyfish is called
Electromechanical Enhancement of Live Jellyfish for Ocean Exploration. And it has been submitted for
publication in the Journal Bio Inspiration and Biom Medics. Thanks for coming on the podcast, John, - Thanks again for having me. It's been fun. - I am afraid that's all the time we have for this week's podcast. Thanks to John DeBerry
for joining me today. And a special thanks to
our producer Fred Isles. We'll be back again next week, but in the meantime, do
check out the latest episode of the Physics World's Stories podcast host Andrew Gluster is in conversation with the astrophysicist and author Emma Chapman about the history of radio astronomy. Chapman, who's at the UK's
University of Nottingham, talks about the do it yourself
ethic of radio astronomers and highlights the valuable
contributions made by people outside the established
academic community. That podcast is called Radio
Pioneers, the Enduring role of amateurs in Radio Astronomy. And you can find it on
the physics world website or at your favorite podcast provider - Physics World.