I recently visited the Navy’s Indoor Ocean at Carderock, the world’s largest wave pool. It is 360 feet long and 240 feet long, with a depth of 20 feet - the size of a football field. The dome above is the largest free standing dome in the world. The pool is equipped with 216 individual wave makers that can make waves from -45 degrees up to 135 degrees.
The pool is unique in its ability to create waves of a specific amplitude and frequency that can be reproduced with precision. For example, waves of 0.078 amplitude at 1 Hertz can be created. It is also possible to split screen waves with frequencies of 0.67, 0.5, and 0.33 Hertz, all with the same amplitude.
The pool has a cool demo that takes advantage of the different speeds of different frequency waves. High frequency waves are sent out first, followed by lower and lower frequency waves. This demonstrates how the frequency of a wave affects its speed, with high frequency waves traveling slower than low frequency waves. Whoa! The ocean engineers can create a perfect breaking wave in a pool by precisely controlling the frequency and speed of the waves. This demo also illustrates the principle of superposition, whereby the height of the water is equal to the sum of the heights of the individual waves meeting at that point. At some places in the pool, the waves always cancel out to zero amplitude, and at other places the waves add up for maximum amplitude. They can even send waves from all directions, so they form circular wave fronts and then all the wave energy is channeled into one spot they call the bullseye. To accurately reproduce real world conditions in the pool, the engineers must take into account the difference in buoyancy between fresh and salty water, as well as the Reynolds and Froude numbers. First, the wind blows across the ocean, creating small ripples.These ripples grow into larger waves as the wind continues to blow.Finally, these waves become steeper and steeper until they break.
The speed of a model ship is equal to the flow velocity divided by the square root of the acceleration due to gravity times the characteristic length of the ship. In this case, the model ship’s hull is 46 times smaller than the real thing, so to get accurate data, it should be travelling at one over the square root of 46 times its real world speed. To make the footage from the model look the same as that from the full size ship, it must be slowed down by a factor of the square root of 46, which is approximately 6.8 times slower.
Wind waves are formed in three steps. First, the wind blows across the ocean, creating small ripples. These ripples grow into larger waves as the wind continues to blow. Finally, these waves become steeper and steeper until they break. When these waves travel out from a storm, the higher frequency waves dissipate their energy more quickly. So the waves that travel a long way are the fast-moving low frequency waves, which are called swell. On a calm day, when you see waves crashing at the beach around 10 seconds apart, that is swell. Rogue waves are usually multiple waves that are meeting up and creating an amplitude that is much larger than what the self-standing wave would be. Wind waves are more of a concern for ships out in the open ocean than swell, as swell will just cause the ship to heave a little bit. At first, when wind blows across the surface of still water, it creates tiny ripples with wavelengths of around a centimeter. As the wind continues, these ripples grow into bigger waves and the interaction of the wind with these waves create even larger pressure differences and even larger waves. As the waves interact with each other, they create a range of different wavelength waves, and when the energy dissipation matches the energy input from the wind, the waves have reached their maximum size. This is known as a fully developed sea.
Different oceans of the world have different mixtures 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 peakier spectrum, and this is due to the limited fetch of storms that occur there. In the mid-Atlantic, a broader spectrum best describes the developing or decaying open ocean waves, and in the North Atlantic, the steady wind across an open ocean produces the broadest spectrum of wind waves.
When testing, engineers first have to figure out where the ship will be deployed, and which spectra best match these locations before creating them in the pool. This is important because different conditions exist in different locations, from the coast of South Korea to the Pacific Ocean.
To test this, a remote controlled boat was used to test the amount of water that washes on the deck. This is important because on the back of a destroyer is a helicopter landing pad, and they don’t want any water on the deck when a helicopter is about to land. Not all models tested here can be remote controlled, so the models are tethered and powered in the carriage for testing. This is an innovative approach to model testing, as it is much more cost effective than building the full thing. Every ship in the Navy’s fleet has been tested in this facility, and some ships have a tumble home design which helps protect against rolling and has a lower radar signature. People are always looking for ways to make ships stealthier, faster, and more powerful.
However, many sailors are unaware of the work that goes on in the background to support their efforts. To help people understand wave physics and other STEM concepts, Brilliant offers interactive lessons and simulations. It encourages people to engage deeply with the material and provides a sense of accomplishment when completing a lesson.
If you are looking for a gift for the clever person in your life, consider giving the gift of Brilliant. With courses tailored for any level, it is a great way to support STEM learning. To try it out for free, go to brilliant.org/veritasium. If you sign up right now, Brilliant is offering 20% off an annual premium subscription to the first 200 people to sign up. Just use my link. So I want to thank Brilliant for supporting Veritasium, and I want to thank you for watching.