Inside The Navy's Indoor Ocean

I'm here at the Navy's Inland Ocean in Carderock. This is the largest wave pool in the world and they can create all kinds of different waves so you can test model boats and improve them before they take to the open sea. I came in and saw some pictures, but I walked in here and it's crazy. Because they say inland

ocean

, but that's exactly what it is. The water even looks the color of the

ocean

. (laughs) It doesn't look like a swimming pool, this looks like an ocean, it looks like a testing facility. It's huge. - It is 360 feet long in this dimension, 240 feet long in that dimension.

It's 20 feet deep. Almost the size of a football field. The dome above us was the largest freestanding dome for a time. - The largest independent dome in the world? - If that? (Miguel laughs) In this pool you can make waves of all shapes and sizes using huge paddles that line two walls of the pool. - We have 216 individual wave generators. We can make waves from -45 degrees to 135 degrees, which is kind of a return. - Now we are behind the large oars that form the waves. These 216 paddles are programmed to move in incredibly well-choreographed ways so that they can produce perfectly frequency, perfectly sized, reproducible waves that travel throughout the pool. - You can see these air bellows that are what produce the angular movement.

That vertical piece is the force transducer. The other force transducer is on top. - There are many wave pools in the world, but what makes this one different is the control. You can create waves of a specific amplitude and frequency and do it repeatedly. Can we try a Hertz? - Yes. Do me a favor and dial a Hertz. - The amplitude will be 0.078 to one Hertz. - Okay, go ahead and send it from scratch please. And this is the largest wave we can generate, one Hertz. This is based on the motion and power requirements of the wave generator. - There's something a little surreal about seeing this, because it almost looks like an ocean except you never see such regular waves out there. - If right. - One of the fundamental characteristics of a wave is its wavelength, the distance from one crest to the next.

The first thing most people learn about waves is that they transmit energy rather than material from one place to another. In this case, as the wave travels to the right, the water molecules basically move along circular paths. And the deeper the water, the less this movement. All motion stops at a depth equal to half the wavelength. This is known as wave base. But even in an ideal water wave, the molecules shift a little in the direction of the wave motion. And this is because molecules travel faster the higher up they are. Therefore, they move further at the top of their loop than backwards at the bottom, creating a spiral path.

This place is perfect for observing the properties of different waves. I asked Miguel to show me some waves with different frequencies but the same amplitude. -So what I'm going to have him do now is have him stop this wave and just change the frequency. Because we're at .6, we'll go to .5, so it'll be a two-second wave. - Here I am separating detection waves with frequencies of 0.67, 0.5 and 0.33 Hertz, all with the same amplitude. So two things to keep in mind. Although they all have the same amplitude, those with higher frequencies appear to have greater amplitude because the slope of the waves is steeper.

And second, the frequency of a wave affects its speed. High frequency waves travel more slowly than low frequency waves. In fact, as long as the water is deeper than the base of the wave, the speed of the wave is inversely proportional to its frequency. They have a really interesting demo that takes advantage of the different speeds of different frequency waves. You can see it starting here. They send out high frequency waves first, followed by increasingly lower frequency waves. And because high-frequency waves travel more slowly, lower-frequency waves gradually overtake them. Oh. And they have timed it so that all the waves are at exactly the same time and in the same place in the pool, and this causes the wave to break.

Ocean engineers can do this again and again, in exactly the same way, thanks to their precise control over the waves. This demonstration also illustrates very well the principle of superposition, that when waves meet they add up. The height of the water is equal to the sum of the heights of the individual waves found at that point. You can see how much larger the amplitude is. Those individual waves weren't that big, but when you add them all up, you can form this big breaking wave. They can also take advantage of the principle of superposition to create standing waves. -So what comes next are two regular waves facing each other.

What we call the quilt wave. So we will have a wave coming this way and another one going this way, and it will create standing waves. Then two regular waves come out and if you look at the wave, it looks like a big quilt pattern. - In some places in the pool, the waves always cancel each other out until they reach zero amplitude, and in other places the waves add together to reach a maximum amplitude. They can even send waves from all directions, so they form circular wave fronts and then all the wave energy is channeled towards a point they call a target. - And now we're going to run the target wave, which is essentially the same thing, but instead of having a line of waves, we're going to have everything merge into an individual point.

So you can start to see that the waves are coming from the long bank here, and you can see that they are forming a spherical wave. And then we have another spherical wave coming from the short bank. And this is broken by the merging waves, and the height of the waves is more than one-seventh of the wavelength. - We tried throwing some toys into the wave to see what would happen to them. Would they be pushed into the breaking wave? Although there is not much net water movement, the duckling moves with the waves and is quickly pushed toward the target.

How is the duckling? (Miguel laughs) - He's reaching the danger zone right now. He's starting to channel it into that breaking wave. Ooh, he's getting up, getting up. - Oh! (laughs) she flooded Him. - That is incredible. - There it was right where we wanted it. - Now, the real purpose of this setup is not to play with toys or make perfect, unnatural waves. It is about replicating on a small scale the types of waves that Navy ships will encounter in the world's oceans. Research engineers put ships modeled after billion-dollar ships in the water to see how different designs actually perform in real-world conditions. - Right now this is coming from 45 degrees.

It will have a significant wave height of approximately five inches, which if we scaled it up for this model would be 20 foot waves. When we do a free-running model like this, we typically run on a race track, like a big circle or a figure-eight track, so we know the courses we're running on so we can correlate them as much as possible. scale container. - For the model to provide an accurate representation of the real world, many things must be taken into account. Is the water fresh? - Sweet water. - Okay, not salty. - No. Fresh water.

So when you are in salt water, you will have much more buoyancy. So when we weight our models, we need to make sure they take that difference in buoyancy into account. So when we get to large scale, you will be in the same conditions. - For fluid mechanics, I always hope that you have to keep the Reynolds number the same as in real world phenomena. But in reality, to get the correct wave dynamics, it is necessary to use a different scale that is based on the Froude number. So the Froude number is a measure of the relationship between inertial forces and gravitational forces.

It is equal to the flow velocity divided by the square root of the acceleration due to gravity multiplied by the characteristic length, such as the length of the ship. In this case, the hull of the ship model is 46 times smaller than the real one, meaning that to get accurate data, it must travel at one over the square root of 46 times its real-world speed. And to make the model images look the same as the full-size ship, the speed must be reduced by a factor of the square root of 46. That is, approximately 6.8 times slower. I'm surprised at how well these shots come together, but of course that's the idea.

Scale the model and the waves, so that the physics are identical to that of a real ship in the open sea. Naturally, I asked if I could go swimming in the pool, but was very politely told, "No way." The closest I could get would be in a small dingy. This is our ship. With a trap. Everything is pretty good here right now. - (laughs) Yes. There will be no waves while we are here. - So I assume no one has been here in waves? - No. That's one of the things they don't want us to do.

I guess it's a risk thing, so... - This place looks like a... I don't know, some kind of huge playground. (Miguel laughs) - For engineers like us it is where we have fun with science and what we are doing here. It is a huge volume. I guess I never understood how deep 20 feet was, until they emptied it to put in the new wave generators. It is a large volume that absorbs this water. - Yeah. - So when we pass by, these are our sensors right here. We have a great variety here. These are ultrasonic sensors and this is how we measure the height, period and direction of waves in the basin.

So we want to measure that to make sure that what we test is what we think we have. - In this pool, they can create all kinds of different wave conditions that you can find in different parts of the world. Most ocean waves are created by wind, and the strongest winds occur in and around storms. Five factors affect the size and shape of the waves created. These are the speed of the wind, the duration of the wind, the distance over which the wind acts, which is known as the reach, the width of the reach and the depth of the water.

As waves emerge from a storm, higher frequency waves dissipate their energy more quickly. So the waves that travel a long distance are the fast-moving low-frequency waves, which are called waves. - When those waves end up hundreds of miles away, like if you have them in the Pacific, you will eventually get a long swell from them. So you're no longer close to the storm, but it created enough energy to form long waves, and that's where the open ocean surge is produced. - Tell me if this is a good analogy. I feel like with sound, a lot of the high frequencies will disappear quickly away from a source. - Yes. - But the low frequencies will go much further. - Correct. - So the same thing happens with the waves?

It's like you're leaving a concert and you can still hear the bass, but you can't see any of the high frequencies. - That's a great analogy. Yes. - What's the problem with rogue waves? - People like to think that it is a rebel wave that came out of nowhere and emerged. No, generally it is multiple waves that come together and create a much greater amplitude than the autonomous wave would be. So when it meets, it will break, because you have this huge wave that creates this huge amplitude that just can't contain it and it breaks. - On a calm day, when you see waves breaking on the beach about 10 seconds apart, that's surf.

But because of its long wavelength, waves are not really a concern for ships in the open sea. - You know, if you're in a period of prolonged swell, your boat will probably shake a little. You're more worried about steep waves and windy waves that really move you. - Wind waves are formed in three steps. First, when the wind blows over the surface of perfectly still water, the turbulent motion of the air creates regions of slightly higher and slightly lower pressure. And this produces small waves with wavelengths of around a centimeter. But now the wind can act on these waves by creating greater pressure differences between the front and the top of the wave crest, pushing them up and forming larger waves.

And the interaction of the wind with these waves creates even greater pressure differences and even larger waves. The waves are mostly uniform at this point, but as they interact with each other, they create a range of waves of different wavelengths. And as the wind continues to blow, these waves begin to break, transferring their kinetic energy into eddies that dissipate their energy as heat. Once the energy dissipated matches the energy input from the wind, the waves have reached their maximum size and this is known as a fully developed sea. - So this will be an irregular wave. - Is this irregular? - Irregular wave, so what you saw before with regular waves was a frequency, an amplitude.

This is what we call spectra, or multiple frequencies and multiple amplitudes. You can see that there is a higher frequency with the waves traveling furtherslowly than low frequency waves. Those low frequency waves will travel fast and overtake them and that's what makes them appear spikey or somewhat dull. - What surprised me is that different oceans in the world have different mixes of wave frequencies or different spectra, depending on their geography and the types of storms that occur there. For example, the North Sea and other small bodies of water have a higher spectrum, and this is due to the limited frequency of storms that occur there.

In the mid-Atlantic, a broader spectrum better describes the developing or declining open ocean waves that would be found there. And in the North Atlantic, constant wind over an open ocean produces the broadest spectrum of wind waves. So when testing, engineers must first determine where the ship will be deployed and which spectra best match these locations before creating them in the pool. I think for most people, an ocean is an ocean. But are you saying that there are different conditions depending on where you are? - The destroyer when I was in command, we conducted an operation off the coast of South Korea in the spring.

Very rough sea keeping conditions. But of course, when you cross the Pacific, everything is much calmer. Again, from there to the coast of South Korea and the Persian Gulf, all of those conditions are very different. - Was there any situation that was especially hard for you? - So my bed was in the middle of a room and the sea was very bad, and this was the South or East China Sea. The sea was so bad that one night I woke up in the middle of the night and the entire mattress I was carrying was sliding off the bed frame, and that's a pretty significant sized mattress.

So you can imagine the seas we were in that night. Much bigger than this would terrify me. I know it probably seems benign, but... (laughs) Much bigger than this, I think that model would require a lot of water. - Why do you care how much water falls on the deck? - So, at the back of this DDG there is a helicopter landing pad. They don't want water on deck when a helicopter is about to land. That is a big problem. You know, that's one of the tests we do here: we'll put cameras up to look at the deck and understand how much water is spilled. - Since I knew they wouldn't want to risk their fancy model in difficult conditions, we brought a small remote control boat to test it out. - Yes, I wouldn't be happy on that boat.

A lot of people would get dizzy. - Oh! (Miguel laughs) - Oh no. - It is gone? - He went away. - No, it's right there. It came up. It's the other way around. (laughs) -she had completely disappeared. She was in the air and then sank. Now, not all of the models tested here can be controlled remotely. - So, in the carriage is where we will do tests of the captain model where you will be able to strap, put power and instrumentation in a model that cannot stand on its own. Usually the model goes in this lunar bay here. - The models are hooked here and then the entire lab accelerates over the waves dragging the model below. (thoughtful music) (waves crashing) People have been making boats for thousands of years. - Mm-hm. - Is there really any innovation today? - Definitely.

So sometimes, you know, people say that's how we've always done it. And then when you look at it, there is some validity to some crazy ideas, and when we test them, that's why you reduce the cost of doing a model test instead of building the whole thing and saying, "Oh, that didn't work." "Every ship in the Navy fleet has passed through here, passed through our scope, or been peripherally tested with us. But every ship owned by the Navy has been tested at this facility, and there is one ship with a spinning house design where if you look at this ship behind you it lights up.

So this flare is usually what helps protect you when you start rolling, gives you a reaction force or helps push you back. A house Rotary is shaped, you know, in the opposite direction. And if you have a boat shaped in that direction, it doesn't have as much restoring force when you turn. - But what is the idea of ​​making a boat like that? - There are many reasons different things you want to change the hull design for. Some of them are the water signatures above. It's all about the shape and the radar sections and there are a lot of things that come into play.

You always want to be stealthier, you always want to be faster, you always want to have more power. And that's where innovations always come. - So most sailors are not aware of the work that is done in the background to support what they do. - When I was in the fleet, and I have been in the Navy for 27 years, I never had any idea, even less of the magnitude of what they do. I am not exaggerating when I say that it has affected all ships and submarines in the fleet. (waves crashing) (electronic zoom) - Hey, if you don't have a huge wave pool at your house to test wave physics, I suggest you check out Brilliant, the sponsor of this video.

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