From: veritasium
The Navy’s Indoor Ocean at Carderock is the world’s largest wave pool, used for testing scale model ships before they are deployed on the open ocean [00:00:04]. This facility allows engineers to make ships better by observing their behavior in controlled, reproducible wave conditions [00:00:09].
The Indoor Ocean Facility
The facility measures 360 feet long in one dimension and 240 feet long in another, with a depth of 20 feet [00:00:34]. Its size is comparable to a football field [00:00:40]. The dome covering the pool was, for a period, the largest free-standing dome in the world [00:00:42].
Wave Generation and Control
The pool features 216 individual wave makers, which are huge paddles lining two walls of the pool [00:00:50], [00:00:58]. These paddles are programmed to move in precisely choreographed ways to produce reproducible waves of specific amplitude and frequency [00:01:17], [00:01:42]. This level of control is what sets this facility apart from other wave pools [00:01:39]. The angular motion of the paddles is achieved using air bellows, and force transducers measure the forces involved [00:01:27].
Wave Physics Demonstrated
The facility is ideal for observing wave properties [00:03:06]:
- Wavelength and Energy Transmission: Waves primarily transmit energy, not material, from one place to another [00:02:24]. Water molecules move in circular paths, with motion decreasing with depth. All motion stops at a depth equal to half the wavelength, known as the wave base [00:02:31].
- Drift: Even in ideal water waves, molecules drift slightly in the direction of wave motion because they travel faster higher up in their circular path [00:02:51].
- Frequency and Speed: Waves with higher frequencies travel slower than low-frequency waves, as long as the water is deeper than the wave base. Wave speed is inversely proportional to its frequency [00:03:43], [00:03:51].
- Principle of Superposition: When waves meet, their heights add together [00:04:45]. This can be used to create:
- Breaking Waves: By sending high-frequency waves followed by lower-frequency waves, engineers can time their convergence at a specific point, causing a large breaking wave [00:04:01].
- Standing Waves: Two regular waves traveling towards each other can create a “quilt wave” pattern where some areas have zero amplitude (cancellation) and others have maximum amplitude (addition) [00:05:07].
- Bullseye Wave: Waves sent from all directions can channel energy into one spot, creating a spherical wave that breaks due to its height exceeding one-seventh of its wavelength [00:05:36].
- Rogue Waves: Often mistakenly thought to appear out of nowhere, rogue waves are typically the result of multiple waves meeting and superimposing, creating an amplitude much larger than individual waves [00:11:24].
Testing Ship Models for Naval Applications
The primary purpose of the facility is to replicate ocean conditions for testing ship models [00:06:52].
- Model Scaling: To accurately represent real-world conditions, scaling is crucial. The Froude number, which measures the ratio of inertial to gravitational forces, is used for scaling wave dynamics [00:08:00], [00:08:08]. For a model ship hull 46 times smaller than the real thing, it must travel at one over the square root of 46 times its real-world speed [00:08:22]. Footage from the model is slowed down by a factor of the square root of 46 (approx. 6.8 times) to match the full-size ship’s appearance [00:08:34].
- Water Conditions: The pool uses fresh water, which requires adjustments when ballasting models to account for the greater buoyancy of salty ocean water [00:07:38].
- Test Methods:
- Free-running models: Models are run on “race tracks” (circles or figure eights) to understand their behavior at different headings [00:07:17].
- Tethered models: Models that cannot carry their own power and instrumentation are tethered to a large carriage that tows them across the waves [00:16:27].
- Test Parameters: Engineers evaluate how different designs behave in specific wave conditions. A key parameter is deck wetness, especially for areas like helicopter landing pads, where water on deck is a significant safety concern [00:15:33].
Simulating Diverse Ocean Conditions
The pool can create various wave conditions encountered globally [00:10:06].
- Wave Formation: Most ocean waves are wind-created [00:10:13]. Five factors affect wave size and shape: wind speed, wind duration, fetch (distance over which wind acts), fetch width, and water depth [00:10:20].
- Swell vs. Wind Waves:
- Swell: High-frequency waves dissipate energy faster, so waves traveling long distances from a storm are typically fast-moving, low-frequency waves called swell [00:10:37]. While visible on calm beaches, swell is generally not a concern for ships in the open ocean [00:11:50].
- Wind Waves: Formed in three steps:
- Turbulent air creates tiny ripples (around 1 cm wavelength) on still water [00:12:06].
- Wind acts on these ripples, creating larger pressure differences that pull them into bigger waves [00:12:23].
- Continued wind interaction leads to even larger pressure differences and waves, which then break, dissipating kinetic energy as heat [00:12:33]. A “fully developed sea” is reached when energy dissipation matches energy input from the wind [00:12:57].
- Ocean Spectra: Different oceans have distinct mixtures of wave frequencies (spectra) due to geography and storm types [00:13:37]:
- North Sea / Small Bodies of Water: Have a “peakier” spectrum due to limited storm fetch [00:13:49].
- Mid-Atlantic: A broader spectrum describes developing or decaying open ocean waves [00:13:58].
- North Atlantic: Steady wind across open ocean produces the broadest spectrum of wind waves [00:14:06].
Ongoing Innovations in Ship Design
Ship design is continuously evolving [00:16:53]. Model testing at facilities like Carderock is critical for cost-effectively validating new ideas before building full-scale vessels [00:17:05]. Every ship in the Navy’s fleet has undergone testing or review at this facility [00:17:11].
One example of modern innovation is the tumble home hull design [00:17:22]. Unlike traditional ships with outwardly flared hulls that provide restoring force when rolling, a tumble home hull is shaped in the opposite direction [00:17:24]. While this reduces restoring force, it offers advantages related to above-water signatures, such as improved stealth and radar cross-section [00:17:45]. The continuous drive for stealthier, faster, and more powerful ships fuels these innovations [00:17:55].
This behind-the-scenes engineering work significantly impacts every ship and submarine in the fleet, often without the direct awareness of the sailors operating them [00:18:04], [00:18:19].