The Acoustic Impacts of Marine Energy Converters

In an effort to develop renewable energy, scientists have turned to the sun, the wind, and now the ocean. With these new forms of energy harvesting, considerations need to be made about how the new technologies will impact the surrounding environments. In this episode, we talk with Joseph Haxel (Pacific Northwest National Laboratory), Christopher Bassett (University of Washington), Brian Polagye (University of Washington), and Kaus Raghukumar (Integral Consulting) about their research related to the noise produced by marine energy converters.

Read the associated article: Joseph Haxel, Christopher Bassett, Brian Polagye, Kaustubha Raghukumar, and Cailene Gunn. (2023) “Listening to the Beat of New Ocean Technologies for Harvesting Marine Energy,” Acoustics Today 19(4). https://doi.org/10.1121/AT.2023.19.4.23.

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Learn more about Acoustical Society of America Publications.

Intro/Outro Music Credit: Min 2019 by minwbu from Pixabay. 

Transcript

ASA Publications (00:26)

In an effort to develop renewable energy, scientists have turned to the sun, the wind, and now the ocean. With these new forms of energy harvesting, considerations need to be made about how the new technologies will impact the surrounding environments. Today, we're talking about an article from the Winter 2023 issue of Acoustics Today, which still has relevance now, two years later: “Listening to the Beat of New Ocean Technologies for Harvesting Marine Energy.” With me are four of the authors of the article, Joseph Haxel, Christopher Bassett, Brian Polagye, and Kaus Raghukumar. Thanks for taking the time to speak with me today! How are you?

Joe Haxel (01:01)

Doing well, Kat. Thanks.

Brian Polagye (01:03)

Pretty well, yeah.

Chris Bassett (01:05)

Doing great, and excited to be here, Kat, thank you.

ASA Publications (01:05)

Fantastic. So first, tell us a bit about your research backgrounds.

Chris Bassett (01:12)

All right, so my name is Christopher Bassett. I am a researcher and engineer here at the Applied Physics Lab at the University of Washington. I've been working in the space, the overlap between both acoustics, underwater acoustics, and marine energy, since about 2009 when I got my start in this area actually doing a preliminary site assessment from an acoustic standpoint for a tidal energy project that at the time was being proposed for the Puget Sound region.

Brian Polagye (01:46)

I'm Brian Polagye. I'm a professor of mechanical engineering at the University of Washington. My entry into the acoustics field is all via marine renewable energy. That's where my lab primarily works. And one of the areas we work in is trying to understand environmental effects of tidal turbines and wave energy converters. So I started working with Chris on this back when Chris started working on this and then have continued working in that space and developing instrumentation that can help us go into these pretty high-energy environments and obtain relatively high-fidelity data.

Joe Haxel (02:15)

I'm Joe Haxel. I'm a researcher at the Pacific Northwest National Laboratory in Sequim, Washington. And my point of entry around marine energy and acoustics came around the same time, interestingly enough, as Chris and Brian, but focused, instead of a tidal environment, out in the wave environment off of… open water wave environment off of Oregon. They were looking at developing a test facility there, and so, similar to Chris, I did some background characterization work in acoustics.

Kaus Raghukumar (02:44)

I’m Kaus Raghukumar. I'm physical oceanographer and underwater acoustician by training. In the realm of acoustics, I've primarily worked with looking at the effects of environmental fluctuations, oceanographic environmental fluctuations on acoustic propagation. My point of entry into marine energy and acoustics was primarily from the point of view of instrument development to be able to directionally characterize what  thought were low-intensity sounds emanating from these devices. And have since worked in a variety of capacities with Brian, Chris, and Joe, in characterizing sound from marine energy devices.

ASA Publications (03:23)

Very nice. Awesome. So it sounds like we've got a few different perspectives on the whole question about marine energy converters and such. OK, so to start, what are marine energy converters or MECs?

Brian Polagye (03:34)

I guess I'll take this one since I've been working with them for my entire career. So marine energy converters are devices that try to convert the moving water in the ocean, tidal currents or waves, into electricity. For tidal turbines, the easiest way to think about this is an underwater wind turbine, where you have fast moving tidal currents in some sort of a narrow channel. The turbine goes in the water and that high velocity allows it to rotate and generate power. 

For wave conversion, it's a little bit harder to come up with an analog because we don't have terrestrial equivalents to wave energy. You know, if you go to the beach and you see the waves crashing on the shore, that's all very nice and pretty. But just like currents, it's really about the underwater pressure fields around wave energy converters. So we think about waves as just the propagation of the kind of waves on the surface that we can see, but waves also have orbital velocities below them and they have pressure fields associated with those orbital velocities. So there's actually a lot going on with waves that we're not necessarily aware of. The challenge is that because there's no terrestrial analog, there's not just some land-based technology that you can port over into the ocean. And so wave converters have lots of different forms. Some of them look like buoys that bob on the surface. Other of them are flaps on the seabed that kind of surge back and forth. Others try to use the variations in pressure to generate power. 

But the bottom line for all marine energy converters is you're going to have some sort of rotating [or translating] object—for waves it's going to be slow rotation, for currents it's going to be a little bit faster. The rotation is going to convert the available environmental power in the currents or waves into some sort of mechanical power. That mechanical power then gets put through some sort of a powertrain, gearbox, and generator to get to a point you can generate electricity, and then these devices all require some sort of mooring or foundation to keep them in place. So there's a number of common elements even if they all look quite different.

ASA Publications (05:24)

That is a delightful overview. So how do acoustics come into play when talking about harvesting energy from ocean waves and currents? What sounds arise from these various technologies?

Chris Bassett (05:34)

Yes, so that's a great question. I think, first and foremost, with development of technology or other things that we use in the ocean, there's been an emergence of the issue of sound more broadly, attempts to understand what the impacts of human activity are in the environment. An the shipping industry and a look at sort of the impacts of increasing amounts of shipping across the oceans have been a hot topic for quite some time. And I think it provides a sort of appropriate analog for thinking about why we're concerned about sound from marine energy. From my perspective, one way to think about this is we are interested in generating renewable power from the ocean. Some may be driven by efforts to decarbonize our economy. Others may be interested in other applications. Either way, we are seeking to generate power from a new source. And one of the questions that we often ask is, are we going to introduce potentially new problems as we seek to develop this new technology? We would like to avoid doing so, and one way to do so is to think about, from a high-level perspective, what are all of the different ways that the deployment of this new technology could have environmental impacts, to measure those upfront as the technologies are developing and try to get out ahead of that, potentially modifying the technologies or try to address the topics upfront rather than take a reactionary approach down the road. So that's why we're motivated study this, of course, with the receptors of the noise in particular being animals that use sound for social communication, for foraging, etc. 

So that's why we're motivated to study sound, then the broader issue is sort of what sounds are out there in the ocean to begin with and what are we putting into the environment as we develop these technologies. From a sort of what exists, or a baseline ambient standpoint, that’s pretty much ocean noise, typical sources. So from a natural perspective, kind of the most dominant ones, at least in the frequency range we're thinking about would be precipitation and wind, which are very common, of course, around the world's oceans. But then there are a couple things that emerge specifically as a result of the fact that one thing that sites suitable for marine energy development have in common is that they're very energetic. Since we're looking to extract energy, they are themselves some of the most energetic places in the ocean. So one thing that we have seen pretty regularly at marine energy sites is that the seabeds are quite mobile. The sediments are moving around and that's introducing a source of sound, moving sediment that's not very common elsewhere in the ocean. But we've seen that pretty commonly both at sites suitable for wave and tidal energy. Then of course, when we're trying to think about sound for marine energy converters, we're trying to separate that from biological sources, you know, fish, invertebrates like snapping shrimp that make sound or marine mammal vocalizations. And then the final component of the background noise is the general anthropogenic sources, the biggest of which is humans and vessels, in particular boats, be they fishing boats, recreational vessels, or shipping traffic. But at sites we also see aircraft and the broad range of construction noises that might exist off in the distance from human activity. So that's the environment we're generally contending with when we think about the sources from marine energy itself. 

We're talking about machines that Brian previously described that have rotational components, but they're also fixed to the seabed. So there's sort of the noises that emerge from the intentional extraction of power. That could be from generators, gearboxes, electrical drives, things like that, that themselves create some noise. They may also create some vibrations that couple through the hulls that house these things to keep all the electronics and other components dry. And then there's this sort of incidental noises that emerge as simply a result of trying to keep something secure in a really energetic environment. So you can think about mooring lines and chains, shackles, things like that that'll shake, vibrate, and move as a result of the motion that these devices create.

So there's a lot making noise out there. And what's interesting is how hard it can be to listen to this and sort of decouple all the different sounds and really attribute them specifically to a device or something else. We end up using lots of sort of just interesting descriptions for creaks, groans, and splashes, and all these other things like that to describe the noises on top of sort of some of the more typical tonal sounds and broadband sounds that might be more familiar with us from hearing sort of typical machinery that we have in our airside human lives.

ASA Publications (10:44)

So sort of stemming from that, what is unique about the environments that are suitable for marine energy? Has there been a need to develop new approaches or technologies to measure noise from marine energy converters?

Joe Haxel (10:56)

I'm going to start with this one and then these guys can jump in because each of us have attacked this problem in a different way. But just going back and thinking about when I first started doing this, the group I worked in, we were mostly deep water ocean acoustics, where… very different environments than what we're talking about here, right? And so when I first mentioned this to our head engineer, like, hey, we're on a new project. We're going to go make some high-fidelity acoustic measurements and 50 meters of water off of Oregon. He just kind of laughed and chuckled, “Haha, okay. Let's see how that goes.” Just because for us, it was all new. And really that was a highlight to me, like, not a lot of people are doing this. This is a real, sort of a new... on the sort of cutting edge of how to do this well, how to figure out how to do this well. We couldn't just take our standard instrumentation and platforms and plop them down in offshore, near shore sort of conditions with significant energy and expect to get the same type of measurements. So that was step one for me. 

A couple of things that sort of come from this are, you know, when you're thinking about this, one of the main things is what we refer to as “flow noise” or “pseudo sound”. It's similar to like when you're riding a bike or going fast and you feel that wind in your ears. It's actually a non-acoustic pressure fluctuation for the sensor. So it's not a propagating acoustic wave. It's actually just turbulence being affected along the sensor surface. So that's primarily, I would say, the thing that we combat the most in this. And we all have sort of come up with different approaches for this. And then secondarily, I think as far as dynamic platforms, and by that I mean drifting systems or putting hydrophones on vehicles and things like that, it's really around decoupling motion for the hydrophone sensor, right? You can't have the sensor moving around in the water with the waves or the currents. You really need to have sort of a stable position for the sensor. So I'll stop there and pass it over to one of my colleagues.

Kaus Raghukumar (12:59)

Yes, so, you know, in addition to what Joe said, I would characterize the challenges along two kind of lines of thinking, like the first being operational, you know, as both Chris and Joe mentioned, we're operating in extremely high-energy environments where no sane researcher would think about putting instruments in the hope of getting good measurements.

But we're going into these environments now. So just getting into high energy, high tidal currents, being able to get to these locations, deploy instruments safely and get them back, with the latter being the most important so we can get our data back, would be particularly big challenge. And the second one, I see it as an engineer, as a signal-to-noise ratio problem, where the noise levels are both in terms of flow noise, the non-acoustic fluctuations, and just the ambient noise levels can be high enough to mask the signals of interest. So being able to tease the signal out of the noise is the other issue that I think is a challenge in these environments.

Chris Bassett (14:01)

Yeah, so we've used the term “high energy” several times in this conversation. And it occurs to me that we haven't done a great job, or haven't at all defined what we really mean by “high energy,” right? And  that means a different thing to, to different folks, right? But when we're talking about sites suitable for power extraction from tidal turbines, sort of the baseline for feasibility sort of begins in most cases with currents around one meter per second. At currents less than that there's just not that much power available, so that's where we start thinking maybe something is suitable. Compared to most ocean environments that's extremely high but that is I would call a very weak current compared to what we are often looking at. [CB1] We're all familiar with sites that have currents that can get up to about four meters per second, or about eight knots, right? And so that's a really energetic place. And it's difficult to get good measurements in an environment like that. On the wave side of thing, you run into a sort of similar calculus in that the amount of energy available for extraction is going to scale with the height of the waves and their period. So when people are looking at sites where they're building sort of test facilities and things like that and intending to deploy things, there are regularly waves at these places that exceed a couple meters, often much larger than that, and at times of the year can get up to 10 meters or higher. So, they're very very energetic and challenging to work in and when we say “energetic,” that's what we mean. A place you generally avoid trying to put equipment in if you want good measurements.

ASA Publications (15:53)

Right, got it.

Brian Polagye (15:54)

I guess, I mean, I'll echo everything Joe said about the challenge of trying to reduce hydrophone motion relative to the water velocity. That's the key thing for both waves and current measurements. And we started working at these sites, the thought was, well, if you have a drifting system, you won't get any flow noise. And we disabused ourselves with that pretty quickly. It turns out that just drifting does not, it can be enough, but it's not always enough, especially in waves. If you have a relatively short spar buoy, as you're drifting around, your buoy is going to be rocking back and forth in the water. You're going to get flow noise. You'll also get self noise, if you get splashing water over the top of the buoy. And so a lot of the technology development was really going after these problems that we weren't even really sure... We didn't even really know we were going to have these problems when we got involved in the area, much less how to compensate for them. And as Chris mentioned, these sites are incredibly energetic. And so just trying to do the technology development and get them out into the representative environments and, as Kaus said, get them back out of the representative environments made things a little bit more challenging. 

One other thing I just want to mention about high-energy environments is both something that maybe is a misconception about those environments, but also something that we see a lot of these environments that often gets kind of remarked in the wrong way. So the misconception is that when you go into these environments, they're really turbulent. And you do have relatively high ambient noise, but it's not from turbulence per se. Turbulence is a really weak acoustic radiator. What does generate sound in these sites are going to be things like air entrainment at the surface. So going, you know, in a river environment, air going over rocks and entraining air down below it. The other thing that you see a lot of times at these sites that you don't necessarily see in more well-behaved environments is sediment transport noise. And when I talk about sediments at tidal sites, I'm talking about things like up to softball-sized cobbles that will get mobilized on the bottom and kind of clank together. And that produces relatively high-frequency noise. And in a number of cases, we see measurements made at these sites and folks will look at those measurements and say, ah, like this high-frequency sound is attributable to the turbine or a wave energy converter when, in all likelihood, it could just be sediment transport being mobilized in a way that folks normally don't see.

ASA Publications (18:09)

Okay, okay, so the currents are just so powerful that you've got these rocks that are kind of like splashing around, not splashing, but you know, rolling around there.  

Brian Polagye (18:15)

Moving around, yeah. They're rocking out, yeah. 

ASA Publications (18:17)

Well played.

Brian Polagye (18:18)

So everything from the fine sediments, which are going to produce sounds up to tens of kilohertz down to cobbles that are, [when currents] get up to three meters per second near the seabed, you'll get cobbles like 20 centimeters in diameter bouncing off each other and you'll get elevated sound down to about a kilohertz. And Chris knows way more about this than I do because he was the one who tried to tease this out at the first tidal energy site we worked at.

ASA Publications (18:40)

Cool. Okay, so at the time this article was published, which was a couple of years ago now, like I said, it seems like we still needed to know more about the impact of the marine energy converter sounds. How are researchers doing on filling this gap?

Brian Polagye (18:56)

We're doing okay. We'd like to do better. The main challenge in the US has been the limited number of deployments of marine energy converters. So, this is a nascent industry. The technologies that are deployed in the US are mostly commercial prototypes where companies are putting systems in the water. They're expecting them to work, but they're also expecting to learn lessons. And so trying to line up measurements around systems that are operating exactly as they're intended to be has been a little bit challenging, but we have started to collect additional data, especially [about] river turbines, [and] a little bit of information about wave converters. Elsewhere in the world, there are other deployments going on, some larger scale technologies, but for various reasons, it can be difficult for us to take technology that's been developed in the US and actually apply it elsewhere in the world. So we try to transfer knowledge when possible, collaborate with folks. And, you know, the general picture is that we're starting to understand a little bit more about the sounds that these systems produce. To date, there's been nothing terribly concerning. And there's been some, I'd say, interesting outcomes in terms of expected versus actual noise. 

ASA Publications (20:02)

That's kind of exciting.

Chris Bassett (20:04)

Yeah, I think I will simply add in one way, yes, we've been a little bit slow getting measurements and sort of addressing some of these issues, especially in the United States here or in this general region. And as Brian mentioned, we've largely been held up  by actual deployments in situ. But one of the good things is, as we discussed earlier, there are lot of challenges to making these measurements and getting high quality data that you can interpret and use to say something quantitative and meaningful. But the good news is that the pace of deployments has allowed us collectively to develop some of the technologies to tackle this. And so we think we are well equipped at the present time to deploy equipment at these sites as devices are deployed and shouldn't hopefully find ourselves sort of playing catch up and trying to address issues in a reactionary way. So I think that's a really positive outcome all things considered.

ASA Publications (21:07)

Great.

Joe Haxel (21:11)

Yeah, and I would add that that we’ve actually demonstrated that at several sites, Chris, like what you're saying. We’re not just saying that. We actually have used the technologies that the teams have developed and applied them. And that's given us confidence in what Chris was saying.

ASA Publications (21:11)

Wow, this is all delightful and positive. So what research and development could still be done in terms of mitigating the impact of marine energy converter noise?

Kaus Raghukumar (21:36)

All right. Yeah, I guess, you know, like in, I'll speak from recent experience. I think one thing that we're, you know, we've all spoken about a challenging environment and I'll use that as a segue. But the acoustic environment in which the sound from the marine energy is propagating is incredibly challenging. For example, near shore environment where wave energy converters are being deployed, the ambient wave field is constantly changing. So being able to characterize that ambient wave field in terms of making sense of any sounds you measure from the wave energy converter is one challenge. And similarly, like in a tidal environment, where say you might have an influx of freshwater coming into your tidal channel, it's going to change the sound speed profile, it's going to change the propagating environment, and it could drastically change what you measure from your stream converter. And being able to, again, characterize that ambient sound speed profile fluctuations I think is incredibly important. And I think more research needs to be done in simply understanding the impact, the effect of just ambient fluctuations on sound propagation from these devices.

Brian Polagye (22:59)

I guess I'll maybe turn the question a bit on its head. So the question about what can be done in terms of mitigating impact suggests that there's an impact that you really want to mitigate. And really, I think that's an open question. If you're thinking about underwater noise being radiated from a wave energy converter or a tidal turbine, there's kind of like a Goldilocks level of noise where you  don't want the system to be totally silent, but you also don't want it to have a really large footprint because that can cause displacement. And so you can think of the analog being an electric vehicle, right? You could design electric vehicles to be totally quiet and then you'd have a lot more pedestrian injuries where people step out in front of vehicles. So we don't want to make these things totally quiet, but we also want to make sure they're not really loud. And so there's, you know, an audibility range of about a hundred meters gives animals enough time to know the device is there, to react, to change, if they're going to change trajectory to avoid a turbine, say, or in some cases, you know, if you have a well-colonized foundation, you may actually draw in animals on the basis of that sound. And so you don't want to advertise that further than you might otherwise want to. The thing that I think has been interesting about this is if we're thinking about trying to make sure that the acoustic footprints are reasonably appropriately sized, we might assume that as we go to larger systems, the acoustic footprints are going to increase. And certainly as you deploy arrays of systems, you'll have kind of more point sources from each of these individual systems. In the future, we expect these to be deployed in arrays, much like arrays of wind turbines are today. But we recently had the opportunity to characterize a wave energy converter. This is in the summer of 2024 at the Wave Energy Test Site out in Hawaii. Imaginative name. And we had previously characterized a system, very similar design, but about a third the size in Puget Sound back in 2011. It was the very first project that Chris and I worked on for characterizing a marine energy converter. And the really interesting thing was the one that was 3x larger that we characterized just recently had a much smaller acoustic footprint. If you kind of try to back out a source level, more than a 20 decibel difference between that 2011 prototype and that 2024 system. And so that suggests that going bigger doesn't necessarily mean that you have to increase your acoustic footprint. A lot of this may be able to be tailored through the design of the power electronics, through the design of the power takeoff unit, through acoustic isolation of those systems in a way that we can get the power out of the ocean that we'd like to get out without creating a large footprint. And that's pretty exciting to me.

ASA Publications (25:42)

Interesting. Yeah, that is really cool.

Joe Haxel (25:44)

I will add, too, I think it’s a great example of just the lack of information we have right now. And this, you know, Brian has now shown like through sort of providing information back to the developer, they made some changes there to the device, you know, things are improved from an acoustic standpoint. But when you think about getting more of these devices into the water, I can see it's challenging for some of the agencies that permit these deployments because there isn't a lot of information around what the acoustic footprint is or what the emissions look like, right? So I think a big advancement is to take the tech that folks like this in this room have developed and every time there's a deployment to do a very robust characterization from an acoustic standpoint, to fill those knowledge gaps, provide more certainty to acoustic emissions around these devices, give people some that have to manage the animals that are living in these environments, more confidence on the potential effects. I think that will go a long way toward accelerating those deployments and getting to testing of these devices in the water more rapidly.

Brian Polagye (26:48)

I was going to say one gap that I think is still remaining, and I think this is a place where technologies like the one Kaus has been developing can be really helpful, is trying to really directly attribute sound from a specific source on a marine energy converter. So let's say we go out and we make an acoustic measurement and we hear something, and we're trying to understand exactly what on the device generated that sound, and that can be useful for the engineering teams. And sometimes this is really straightforward. That 2011 measurement I talked about, we could trace back the highest intensity sound as occurring when two components on the device, there was basically a moving arm and it had a stop on it. And when it would contact that stop, you'd get this impulsive sound. And that was the most intense sound that was generated. And the engineers for the company took that back and said, well, we don't want to be in the business of generating a lot of noise underwater. Also indicative of there being pretty high structural forces during those impacts, and so they totally redesigned the system to eliminate that component. 

In other cases, it can be more challenging. We took a number of measurements out at the Wave Energy Test Site where we were characterizing sound from a particular wave energy converter. And we were hearing this really persistent kind of warble in the hundreds of hertz up to a couple of kilohertz. And we were trying to figure out what it was. And there was a team that went aboard to do an inspection, and they found that… This was a system where the power takeoff involved a band kind of wrapping and unwrapping from a drum. And they found metal shavings around one of these drums, which we concluded there was a failing bearing. And that's what we were hearing. And so, for about a year, we assumed that that was actually the source of sound and that they needed to figure out ways to try to improve the bearing systems on these drums. But then when we analyzed stationary hydrophone data that had been in the water at similar time, we just hadn't gotten around to analyzing it. We started analyzing it and we see that that characteristic noise is present while the device is installed and operating. The device gets pulled out, the sound goes away and we're like, “Ah! Smoking gun, it definitely was the device. It was the bearings.” But then another vessel comes in and retentions the mooring system and the sound comes back. And it was actually coming from a component of the mooring that was failing and rubbing. It had nothing to do with the bearings on the power takeoff. And so trying to really narrow in on exactly what sources of sound are producing a particular noise is really helpful for both for us to understand, is this something we want to communicate to regulators? We'd want to communicate a significant sound originating from a power takeoff to a regulator, but something in a mooring system is a totally different case. We know how to design moorings that aren't loud. We also can design moorings that are quite loud, but… Not intentionally so! But that ability to really accurately localize sound can be really helpful to informing technology developers as well as informing regulators and really improving the certainty we have about sound sources. And again, is where like Kaus has technology that excels at this, which is why we need, it'd be great to see that out around more marine energy converters.

Kaus Raghukumar (29:55)

I guess, yeah, to follow up on that, our effort was, again, getting to that signal-to-noise-ratio question, right? So we have these low-intensity sounds that may or may not be the marine energy converter. So being able to… But we know where these devices are located in the water column. So that's one less unknown. And we thought, okay, is there a way we can use that known location to tease apart what sounds these devices are making from other sounds in the environment, which then takes you down the road of directional acoustic sensing and developing technology to be able to tease apart sounds by direction. Yeah, and it can then start to really help you characterize, say, mooring noise from device noise, slightly higher in the water column to do this multiple moorings, which is mooring your culprit, so to speak, or if it's a device itself.

ASA Publications (30:51)

Yeah, that is a really interesting aspect to think about the how you can use these sounds for basically device maintenance, I guess, or diagnosis.

Chris Bassett (31:01)

Yeah, that's actually, what I was just going to follow up on a little bit, right, is I think we've focused here on sort of the acoustic footprint and initial characterization. And our approach has been a little bit, or the way we've talked about it's been focused a bit more on the environmental impact and mitigation there, right? But there is the flip side of this, which is if I am the developer of a device, should I install a hydrophone on my unit? And if so, why? And perhaps a suitable analogy could just be a bicycle, right? We've probably all experienced our own bicycle or someone else we know that comes up. You just get a tune up and it sounds great. There's no sound radiating from it as you ride it around, but as you fail to maintain the bike, eventually it gets squeaky and none of the parts work. And that sound is indicative of poor maintenance, right? Or an emerging problem with the bike. And so might I, as a developer or just someone who maintains a site, choose to install hydrophones there to listen and quantify, try to understand what the maintenance state of my device is. Emerging sounds, changes over time, perhaps could no problem at all, but they may actually be indicative of an early failure or problems with components. So I would personally make the argument that I would love to have a hydrophone out there listening to a device I deployed at all times basically to see how it's evolving in time.

ASA Publications (32:35)

Right, right, that makes a lot of sense.

Chris Bassett (32:36)

Also, those maintenance problems could lead to less power generation and other things. So there may be perfectly good reasons to do it besides just the noise, right? Like your performance could degrade if you're having problems. And so being able to monitor that remotely, so to speak, is of significant benefit.

ASA Publications (32:41)

Right, right, so it kind of incentivizes the acoustic monitoring for the technology developers even if it's not for the sole sake of monitoring the sounds for the sheer joys of, yeah.

Chris Bassett (33:08)

Yeah, rational people could disagree, but that would be my argument.

ASA Publications (33:15)

Okay, so your article mentions a standard for acoustic characterization of MECs. What does this standardization entail?

Chris Bassett (33:23)

Yeah, so that’s a big question. Before jumping into some of the specifics, right, I think in context, it's important to recognize that in this field and many others, but focusing specifically on marine renewable energy converters, right, the motivation to standardize aspects of how things are done primarily is driven by sort of financing and insurance concerns, right? It's about responsible business development. So why does acoustics come into that? Why has it been wrapped into that effort? And I think from our perspective the motivation is perhaps a little bit different. But at the present time, you know, we've talked about this a little bit. There are a lot of different device types. They look different. They act different. They're going in lots of different sites with different characteristics. And when you look broadly at sort of what's happening, you could easily see a situation in which you give a hydrophone to one group and then you give one to another and one to another and everyone ends up doing something completely different in characterizing the sound that's radiated from those devices. And in the end, when they process their results and present them, there's no sort of coherent way that that's presented, which makes it difficult to make comparisons, et cetera. 

So with the recognition that there is no sort of strictly speaking right way to do this, what the standardization effort is focused on is really coming up with a relatively consistent way of measuring and reporting on sound that's radiated from the devices. And so much of what we do, say, if we're publishing in ASA is really much more scientific, trying to get some at some deep questions. The motivation of the standardization is really to basically do the core job of being able to say to project developers, to the regulatory community, etc., like, yes, this is quite noisy and perhaps a problem, or actually it's not particularly noisy and there's nothing to worry about here from a regulatory perspective, and just providing the framework that generates confidence from project to project, from measurement to measurement. Does that make sense?

ASA Publications (35:49)

Mm-hmm. Yeah, absolutely.

Chris Bassett (35:52)

Anyone else? You're all sort of familiar with the standardization effor? Actually, hold on one second. I'm going to jump back in and say this process of developing the standard has been actually quite interesting. So I'd say we leverage the framework to some extent that exists for radiated noise from vessels. And it's basically impossible to replicate that approach because it says go out in deep water, measure it from this far away, do this, this, and this. Those things are almost impossible to do around marine energy converters. And so we can't strictly speaking replicate that. We had to come up with something new. The initial version of the standard really attempted to do that. And in some ways, it was a great effort. It fell a little flat because as soon as people went and started trying to implement this in a broad range of places, a lot of problems popped up. So the effort is--

Brian Polagye (36:47)

Well, we also released… It came out right as COVID shut everything down. So that didn't do any help either.

Chris Bassett (36:52)

100 % true. So there were some challenges there, but either way, I think, yeah, we're moving towards a revised standard that should address some of those issues. And I guess the point of this is to say, if we want to develop something that allows for these sort of apples to apples comparisons between projects, it's actually a lot more challenging than you might imagine just thinking about sort of like, pick a methodology and go! It's not that easy. I wish it was that easy, but it is not.

ASA Publications (37:19)

Right, right.

Kaus Raghukumar (37:23)

Yeah, one good specific example of the prescribed methodology is the distance, for example, right? I mean, like the standards recommend, for example, a distance of 100 meters. And we all found that oftentimes at 100 meters, it might be too far away to really measure any sound from the device.

Chris Bassett (37:42)

Or you might be on shore.

Kaus Raghukumar (37:44)

Yeah.

Brian Polagye (37:47)

Yeah, I mean, Kaus, that was the thing that I was saying with the standard as well.  We kind of, when we put the standard together, we presumed that there would be a significant acoustic footprint. And like you said, there's been devices where you get 100 meters away and you're basically back down to ambient. And so in that sense, the standard is very successful. It says that you can't really detect the device at all at that range. But from a, I guess a research perspective, and trying to fill in gaps, it's… we kind of want answers that aren't just the null result. Joe and I had a study where we threw a lot of instrumentation at a small tidal turbine to try to characterize its acoustic footprint. And I think maybe the way I'd paraphrase it is that the location had a lot of boats and those are much louder than the turbine. And so we couldn't, we tried everything, even like shutting the turbine down right when we had hydrophones drifting next to it. And there's like, there's just no detectable acoustic footprint. And so, you know, in some sense, the standard is really helpful because it gives you that certainty that the acoustic footprint is not really wider than 100 meters, but there's oftentimes where the data we can get from getting closer in is actually more useful to us in terms of informing a technology developer thinking about or really what the environmental implications of devices might be.

Chris Bassett (39:00)

And that's where I think it's important to recognize sort of what the role of the scientific community is in these projects and how what we normally do differs a little bit from the standard, right? A null result is perfectly acceptable when applying the standard because it basically says, you don't have noise that exceeds this threshold out at this range. And that's perfectly acceptable. And that's just really different from what we normally seek. And I think I have struggled with that a little bit, wanting to find a methodology that… where one size fits all, but I don't think, (a) we can do that and (b) that it matters that much. Again, we're just trying to develop relatively consistent methodology for this baseline interpretation of is this noisy or is it not? And then, you know, we do encourage people working with the standard to… it by default should collect much more information than you're specifically required to report, that enables a lot more robust studies of that sound.

ASA Publications (40:08)

It may not be noisy enough to be problematic, but you still want to understand what sounds it's making.

Chris Bassett (40:14)

Yep, yeah, totally.

Joe Haxel (40:15)

I think, and I want to back up to something Chris said a while ago around the investors, right? So like when you think, so the acoustic standard isn't the only standard for marine energy testing, right? There's several other standards, International Electro-Technical Commission standards around testing. You can get accredited for those standards if you are testing your device. And I think that provides for higher technology readiness level devices and companies. Those are very attractive, right? Because that is providing a third party assessment of your device. You know, that's comparing apples to apples across the range for different devices in those similar types of environments. You're connecting power production to sound emissions and several other metrics that are of interest there.

So getting an accredited test for acoustics is valuable to the developers in the sense that now they have some certainty around the type of sounds their device is going to make. It's been evaluated by a third party in a very formalized framework. And when they go to have a discussion at their next deployment or a community comes to them and says, hey, we'd like to deploy your device provide some power, there's some certainty around what that emission is going to look like, the acoustic footprint and the characteristics of the sounds and things like that. 

One thing that we haven't talked about, too, is in the United States, we have a regulatory framework that’s provided by the National Marine Fisheries Service. So blending our IEC metrics with those, is a relatively simple thing to do, right? So we're very much focused on the device characteristics and the, you know, as you heard Chris say, and I think we all share this, like, you know, more science around what's happening with the emissions than particularly would be asked from a regulatory standpoint sometimes. So taking, you know, I would say the standard provides more information than what's being asked a lot of times in the regulatory side.

ASA Publications (42:01)

So are technology developers interested in these types of measurements? And are there incentives or benefits that are associated with acoustic measurements that are unrelated to environmental impacts?

Brian Polagye (42:35)

I'll share an anecdote from… I was at a conference last week where I presented on some of the measurements that we had made, those kind of measurements in 2011 versus 2024. And later on in that day, one of the representatives from that technology developer was on a panel and they were asked a question about how academic institutions can work with technology developers. And she cited like sitting in the talk and saying, well, I've been working with this technology for the better part of a decade, but I learned something new about it today while listening to this conversation about acoustics. And that sort of information is really helpful to their engineering teams. And, you know, I think that that's basically representative of the level of interest. 

Like Joe said, having more information to inform communities, to be able to go and say, “Our acoustic footprint is this,” not just like, “Well, it's going to be in the water. It'll generate some sound,” that's really helpful. But just being able to get more information about radiated noise to understand what's working, what's not, how might we make changes to device design going forward, that turns out to be very valuable. And every developer I've worked with has been very interested in that information and collaborative in trying to understand what the sources of sound are and whether there's potentially ways to correlate those to moving components. Developers tend to be very… hold operational data very close to the chest in terms of how much power they're producing, what sort of rotation rates are going on inside the power takeoffs. Over time, the relationships I've been able to develop and the information I've been able to share has resulted in just really good bidirectional communication where I'll get all of the detailed operational data from their supervisory control and data acquisition systems and try to connect it up with what we're seeing. And sometimes we do see a really strong connection. There's a project Chris and I did where we could basically do a one-to-one correlation between oscillations in the power takeoff rotation rate and oscillations in the primary radiated frequency we were seeing from a turbine. Other times, it's not nearly that clear. I wish it was always that clear. But that sort of kind of data sharing and knowledge sharing tends to really help everyone in understanding the space more. And I've really appreciated those partnerships over the years.

ASA Publications (44:52)

Yeah, yeah.

Chris Bassett (44:53)

I would actually say there is a general incentive around these issues. More so perhaps in the US than elsewhere, but right now the actual, I guess it's less of an incentive and more of a stick, thinking of carrots and sticks, in that this is being mandated. These acoustic measurements are something that are popping up pretty regularly as requirements for these projects.This will lead to some more discussion perhaps in a minute,  but it's providing a little bit of job security for now in part because, like, this is still enough of a concern that, whether people want to do it or not, it's happening in terms of the acoustic measurements. Fortunately, they do seem pretty excited in most cases, as Brian said but… yeah.

ASA Publications (45:47)

Interesting, okay. Well, that's good. So you guys have any closing thoughts?

Kaus Raghukumar (45:52)

I can jump in. I guess it's less of a closing thought than following up on or pulling on a thread that Joe had mentioned earlier, about just making more of these measurements and essentially building up a library of these sounds to enable, you know, more efficient permitting, being able to allow developers to get their devices in the water more quickly.

And it's something which is not without precedent in the sense that like, you know, offshore wind and pile driving is a good example where, you know, noise from pile driving has been characterized really well in terms of various hammer makes and energies and, you know, hammering intervals and environments, to the point where there's like, you know, empirical functions available to allow developers to plug those empirical functions into any permitting application. And at least get started with initial permitting, you know. Eventually full measurements and detailed modeling are required, but it does provide that a knowledge base exists to allow a developer to get those first steps in, which currently doesn't exist, I guess, for MECs. And it's something that, more measurements will help us get there.

Brian Polagye (47:03)

I mean, I think it's an interesting question about how much knowledge is required and how much variability there is. A number of years ago, there was a paper published, which the title was perhaps a little bit overly sweeping that says, “Noise from wave energy converters will not affect marine mammals.”  Which, you know, I mean, full stop, that'd be great. So the paper was based on measurements of a wave energy converter where almost all of the power takeoff equipment was above the water surface. And the only thing in contact with the water surface was the float that was actually going up and down with the wave surface. And in that case, you would rightly expect the acoustic footprint of the device to be extremely limited, but not every wave energy converter looks like that. And so I think it's, you know, I don't think we're at the point where we can really draw sweeping conclusions yet, but I do think we are getting a better understanding of what types of things produce sound. We understand a little bit more about what elements of the power takeoffs are important and what are not. 

Chris and I have learned a tremendous amount through going through this. We had done a measurement around one of the small research turbines we have at UW and had gotten a very clear tone at eight kilohertz, which is the switching frequency for the power electronics that regulates its rotation rate. And so we're like, the variable frequency drive produces sound at this frequency. And we went into the field and we're taking measurements around another industry turbine. And we were seeing really clear tone at about four kilohertz. And we asked them, “What's the switching frequency for your variable frequency drive?” And they're like, “Four kilohertz.” We’re like, “Great! That's definitely the source of sound, the variable frequency drive.” And they looked at us kind of funny and we said, “What?” And they're like, “Well, the variable frequency drive is in this equipment cabinet on shore, a hundred meters back. How are you hearing that in the water?” And we said, “That's a really good question.” And it turns out that Chris did a bunch of digging in terms of understanding kind of how variable frequency drives work, and really what's happening when the variable frequency drive is regulating the rotation rate is it's causing the generator windings to vibrate and those vibrations are then coupled through the generator housing which then couples through the housing around the power electronics and into the water and so you know the direct and indirect interactions are things that I certainly did not have a good appreciation for coming into it, and every time I think I have them pretty well under control, I discover there's something else that I really didn't know. So I'm going to stay away from sweeping generalizations.

Joe Haxel (49:29)

I think one thing I wanted to bring up too here is, you know, most of what we're focused on and talked about here today is around making measurements around single devices, right? And so I'd like to think that at some point we won't be just deploying one device at a time. But the information we're gathering right now is that critical step to figure out what these... what these emissions look like from the devices. And then, you know, like going back to something Kaus said, then you can take that and you can actually model what it might look like in an array scale. We'll still need to be making those measurements around arrays to validate models. But, you know, I think the end goal isn't just around deploying one device at a time.

Chris Bassett (50:12)

So a few final thoughts for me are to first to echo what Brian said, which is things are really complicated in ways that just… that constantly surprise me. And I never know what to expect when we're doing this in part because every, at this point, you know, so many devices are so different, they behave differently, the environments are different. And so every deployment is a surprise. It's always exciting. There's always something to be learned. And really it's difficult to do without some cooperation and some willingness to share technical information. So it’s pretty fun and interesting. 

Another thing about this is that, you know, to date, and granted, we're still in the early stages of this industry, but the devices that we have measured have not been particularly noisy and are sort of moving us down the path, at least at the present time, where it doesn't look like they're going to raise high levels of concern in comparison to say—granted they're stationary, right?—but compared to, like, a cargo ship, they're much less noisy. So we may be moving in the direction where the level of concern over this issue diminishes over time, which would represent something like us sort of going out of business, so to speak, in terms of needing to find new work. And I think, you know, for those of us in the room, I guess I shouldn't speak for everyone, but if that's the end outcome of the work that we do, that's something I'd be very satisfied with and would find that a good outcome for us and hopefully for society at large. So we'll see what's coming.

Joe Haxel (52:03)

Very much agree, Chris. Very much agree with that.

ASA Publications (52:06)

Well, I certainly hope that you are put out of business as well. And that we can use the ocean for energy without causing a negative impact on the surrounding environment and all of that great stuff. Thank you again for taking the time to speak with me today and have a great day. 

Brian Polagye (52:22)

Thanks for having us, Kat.

Chris Bassett (52:24)

Thank you so much, Kat.

 [CB1]This is ugly written down, but if it sounds fine in the audio I see no reason to remove it