Physics of Submarines

Submarines

Usually when people think of submarines, they think of submarines as a tool of war. is The first submarines were initially built for the Revolutionary and Civil wars as a way to spy on what the enemy was doing. Today submarines are used for much more than war strategy. They are used in scientific exploration of the deep sea. So far, submarines have enabled people to discover hydrothermal vents, descend to the marinas trench, and much more. An example of a submarine that has aided in deep sea research is that Nautile.

The French maritime research institute, Ifremer, owns the deep-sea submersible known as the Nautile (BBC). The Nautile has a design for observing and operating at deep depths. The submersible was commissioned in 1984 and since then has logged nearly 1,500 dives from the research vessels Nadir or l'Atalante (Nautile). The Nautile is capable of operating at depths up to 6 kilometers (BBC). It is equipped with acoustic image mapping which lets the ship send footage that they find of underwater objects to the surface (Nautile). A maximum of three people can be in the Nautile during a dive and the people onboard have a very small three-meter wide cabin (BBC). The submarine can carry five hours’ worth of oxygen (Nautile). The Nautile is capable of traveling at a speed of 1.7 knots since it has four different thruster motors. If necessary, the Nautile can have a tiny robot probe called Robin (BBC). This probe can detach from the submarine and can be operated by remote control in order to look at inaccessible areas or dangerous wrecks (BBC). 

The Nautile is most famous for exploring the Titanic site and searching for and raising other wrecks, but does many other things (Nautile). The submarine has assisted other submersibles that were in distress (Nautile). It is also used to explore specific zones in the ocean to collect samples. The Nautile assists in many offshore assignments that involve pipeline layouts and inspections (Nautile).

The Nautile was responsible for discovering eight species of carnivorous sponges that were near active hydrothermal vents near the East Pacific Rise and of the North Fiji and Lau Basins (New Carni.). Once discovered, the observation from the submersibles was used to describe the sponges’ life conditions (New Carni.). The sponges that were found suggest that there is a lot of diversity among sponges in the deep pacific (New Carni.).

This is just one of many submarines that are used to explore the deep sea plus the many others that are used for war purposes. Many factors play a role in allowing the submarine to power on, dive and surface, and find objects that are around them. In order to see how a submarine truly works the physics of fission, buoyancy, and sonar must be examined.

Submarines first ran on diesel fuel engines just like the cars and boats before them. The diesel fuel engine allowed the submarine to have plenty of power to move the propellers so that the sub could dive down into the ocean deep (Earls, 2003). However, the diesel fuel engine did have a few cons because the fuel was expensive and it only allowed the submarine to be below the water for very little time (Earls, 2003). When the submarine ran above the water there was no problem with the engine because the emissions could be released into the air, however when the submarine dived below the water level there was very little space for the emissions to go lowering the oxygen supply to the people aboard (Earls, 2003). In 1955, the powering of submarines changed thanks to an American boat called the USS Nautilus (Earls, 2003). 

The USS Nautilus used a process called fission to power its propellers instead of the diesel fuel engine (Nuclear, 2000). Energy is created through fission when atoms are split (Nuclear, 2000). In the case of the submarine, the use of the isotope Uranium- 235 is preferred because it allows fission to be induced because the isotope absorbs neutrons when they are present and splits them into smaller atoms (Nuclear, 2000). This allows a large amount of energy to be released including heat and gamma rays (Nuclear, 2000). Uranium- 235 is so powerful in comparison to diesel fuel that it takes one-pound Uranium- 235 to produce the effects that a million gallons of gas would (Nuclear, 2000). In order for the submarine to harness all of the energy being released, the submarine must be equipped with a propulsion plant (Nuclear, 2000). 

For submarines, part of the pressure hull and bulkheads at each ends form a horizontal cylinder that stores the propulsion plant (Nuclear, 2000). The propulsion power plant has two systems called the primary and secondary system (Nuclear, 2000). The primary system first starts when the nuclear reactor induces fission to Uranium- 235 (Earls, 2003). The reaction generates heat energy and that heat energy is then transferred to the water that surrounds the reactor (Earls, 2003). This part of the system occurs under very high pressures to keep the water from boiling (Earls, 2003). The heated water then moves to the steam generator and then returns to the reactor to be reheated (Earls, 2003). The second system starts at the steam generator where the water from the primary system transfers heat to the water in the secondary system that boils to create steam (Earls, 2003). The steam then powers the turbines, which powers the electricity and the propeller shaft of the submarine (Nuclear, 2000). The steam is then condensed back to water so it can be reused (Earls, 2003). The propulsion power plant keeps the primary and secondary systems separate, which also keep the water, used in each system separate (Nuclear, 2000). One of the great benefits of using this process compared to the diesel fuel is that the water in each system is reused and therefore does not need to be refilled and there are no emissions or toxic fumes that are given off (Nuclear, 2000).

Using fission the submarine is able to stay under the water longer than before, but there are drawbacks to this process. The induced fission of Uranium- 235 causes radiation (Nuclear, 2000). In order to fend against this danger 100 tons of lead shield are placed around the reactor in order to protect the crewmembers (Nuclear, 2000).

The 100-ton lead shields add a lot of weight to the submarine (Earls, 2003). A submarine can way about 6,900 tons which makes it very easy to sink, but a submarine must be able to be controlled so that it stays at a certain depth in the water or stays afloat on the surface of the water (Earls, 2003). Archimedes principle comes in handy for understanding how the submarine is able to control when it surfaces and dives. Archimedes principle states that the magnitude of the buoyant force always equals the weight of the fluid displaced by the object (Blow the). The buoyant force in this case is the force of the water on the submarine, which means that the density of the submarine must equal the density of the water outside of it in order to have a neutral buoyancy (Blow the). If the submarine wants to dive, the density of the submarine must be greater than density of the water (Blow the). This is negative buoyancy (Blow the). If the submarine wants to surface, the density of the submarine must be less than that of the water (Blow the). This is positive buoyancy (Blow the). 

The submarine is able to control its density using ballast tanks that are located on the outside (Marshall). If the submarine wants to stay on the surface, the ballast tanks are filled with air because air is less dense than water (Marshall). The ballast tanks fill with water and the air is released when the submarine wants to make a dive because the density is greater than that of the water outside (Marshall). In order to return to the surface when under water the ballast tanks are pumped with compressed air and the water is forced out (Earls, 2003). This caused the density of the submarine to lessen allowing the buoyant force pushing up to be greater than the weight pulling the submarine down (Earls, 2003). 

Hydroplanes are also used in the process of surfacing and diving (Marshall). They are located on the back of the submarine and look like the wings of an airplane. The hydroplanes act like rudders because they help steer the submarine up or down (Marshall). The wings can tilt on an upward angle or downward angle in order to tilt the nose up and back down or the nose down and the backup (Earls, 2003). When the submarine is diving the hydroplanes tilted downward to make the nose of the submarine go down and the back to pop up (Earls, 2003). This allows the submarine to face downward as it is making the dive (Earls, 2003). When the submarine in surfacing, the hydroplanes tilt upward, so the nose of the submarine pointes upward and the back is down. This allows the submarine to face upward as it comes to the surface (Earls, 2003).

When controlling the depth of the submarine the hydroplanes are straightened in order to keep the submarine level (Earls, 2003). The ballast tanks are monitored so that the balances of air and water have a density that is equal to the density of the water outside (Earls, 2003). This keeps the submarine at a certain depth and stops it from sinking or rising to a different depth. 

This technique of controlling diving and surfacing can be seen in many marine species. Fish have air bladders that help them control what depth level they want to keep just like submarine use a ballast to keep a certain depth level. When the fish wants to move up in depth the sac is filled with more air. When the fish wants to descend in depth the tank loses air. The fish also has fins, which helps it move up and down in the water column just as submarines have hydroplanes that allow them to move up and down in the water (Earls, 2003). 

Light stops penetrating the ocean at very deep depths making it difficult for the submarine to see what is around it. When light is present the submarine relies on video cameras, however when light is not present the submarine relies on sonar which stands for sound navigation and ranging. The submarine is equipped with two different types of sonar, which are passive sonar, and active sonar (What is). 

Passive sonar use microphones that are very sensitive to sound underwater (What is). This allows noises from all around the ocean to be picked up. The submarine is equipped with a computer console that records the noises pick up by the microphone and compares the noises to a sound database (Earls, 2003). The sound database is made up of signature sounds like ocean waves, animal noises, and the noises of another boat or submarine (Earls, 2003). If the microphone picks up a sound, the sound is recorded and then the database compares it to signature noises and tells the submarine if there is an incoming threat of another ship or if the sound was just from the ocean (Earls, 2003).

The other type of sonar a submarine can use is active sonar. Active sonar uses sound waves to determine where objects are in the ocean (What is). It works by emitting a sound wave out into the ocean and timing how long it take for the sound wave that is reflected back off anther objects to reach the submarine (What is). The recorded sound wave can tell the submarine how far an object is and whether it is moving. Active sonar tells the submarine the speed of an object using the Doppler Effect, focusing on pitch (Earls, 2003). If the recorded sound waves have crests that are close together, the object they bounced off is moving toward the submarine (Earls, 2003). If the recorded sound waves have crests that are, far apart the object they bounced off is moving away from the submarine (Earls, 2003). 

In order to tell if an object is moving, the submarine emits a sound wave at a certain frequency and records the frequency of the wave that is bounced back (Earls, 2003). If the frequency of the wave that is bounced back is different from the frequency of the wave that was sent out the speed of the object can be calculated (Earls, 2003). If the crests of the incoming frequency are close together, then the speed of the object can be found using the formula 

f1 = (v + vo / v – vs) f

because the object is coming toward the submarine (Earls, 2003). The original frequency is f, the reflected frequency is f1, the speed of sound in water is v, the speed of the submarine is vo, and the speed of the target is vs (Earls, 2003). If the crests of the incoming frequency are far apart, then the speed of the object can be found using the formula

f1 = (v - vo / v + vs) f

because the object is coming toward the submarine (Earls, 2003). The variables stay the same. The range of the target can then be found by using the formula

d = r * t

where the distance is d, the rate is r, and the time is t (Earls, 2003). The distance of how far an object is from the submarine is very important because it keeps the driver of the submarine from crashing into rocks or other submarines (Earls, 2003).

Submarines work because of the understanding of physics. Submarines are able to run off of energy created by fission when uransium-235 meets a neuron. Submarines are able to surface and dive in into the water due to density and buoyancy. Submarines are able to determine sounds of objects, the location of objects, and the speed of objects because of sonar. These components of physics have allowed submersibles like the Nautile to do research in the deep oceans. As the technology and understanding of submarines grows so will the knowledge of the oceans.

Works Cited:
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"Blow the Ballast!" Office of Naval Research Home Page. Web. 19 Oct. 2011. <http://www.onr.navy.mil/focus/blowballast/sub/work1.htm>. 
Brian, Marshall, and Craig Freudenrich. "HowStuffWorks "How Submarines Work"" HowStuffWorks "Science" Web. 19 Oct. 2011. <http://science.howstuffworks.com/transport/engines-equipment/submarine1.htm>. 
Earls, Nathan. "Physics.org | Explore | The Physics of Submarines." The Physics of Submarines. Physics.org, 2003. Web. 19 Oct. 2011. <http://www.physics.org/explorelink.asp?id=4905>. 
Simon, Natalie. Marine Discoveries. Web. 19 Oct. 2011. <http://marinediscoveries.blogspot.com/>. 
I added my blog because my opening of the paper about the Nautile is on it and I did not want you to think I plagiarized. 
"Nautile - Ifremer Fleet." Flotte Ifremer. Web. 19 Oct. 2011. <http://flotte.ifremer.fr/fleet/Presentation-of-the-fleet/Underwater-systems/Nautile/>. 
"New Carnivorous Sponges ( Porifera , Poecilosclerida ) Collected from Manned Submersibles in the Deep Pacific | Mendeley." Free Reference Manager and PDF Organizer | Mendeley. Web. 19 Oct. 2011. <http://www.mendeley.com/research/new-carnivorous-sponges-porifera-poecilosclerida-collected-manned-submersibles-deep-pacific/>. 
"Nuclear Propulsion." Federation of American Scientists. 29 Feb. 2000. Web. 19 Oct. 2011. <http://www.fas.org/man/dod-101/sys/ship/eng/reactor.html>. 
"What Is Sonar?" NOAA's National Ocean Service. Web. 19 Oct. 2011. <http://oceanservice.noaa.gov/facts/sonar.html>. 
Valadres, Eduardo. "Fun Physics Experiments with Household Objects." InformIT. 23 Sept. 2005. Web. 19 Oct. 2011. <http://www.informit.com/articles/article.aspx?p=413663&seqNum=2>.