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ABSTRACT
A submarine is a vehicle which travels underneath the sea surface by varying its buoyancy. The submarines are powered by diesel engines, whose drawbacks to a large extent are now overcome by nuclear reactors. They are mainly used as a part of the defence system.

Surely the submarine is an engineering master piece that has proved its purpose and might over the years. The inside of a submarine is a totally unknown to the civilian world. Ever since its invention it has undergone various changes and transformations to become what it is now. The world is looking forward to seeing the newer changes in the submarine technology.
The paper is an effort to look into the engineering aspects of a submarine which includes construction details, cruising of submarines, how they are powered, life support aboard a submarine, navigation through the deep ocean and rescue of downed submarine.
INTRODUCTION
A submarine can be defined as an underwater counterpart for the surface vessels. In other words, itâ„¢s a craft which can operate completely submerged in water for long periods. A submarine or ship can float because the weight of the water displaced is equal to the weight of the ship. This displacement of water creates an upward force called the buoyant force and acts opposite to gravity. A submarine can control its buoyancy thus allowing it to sink and surface at will, but a ship canâ„¢t.
A submarine can operate under water for s long span of time. The main use of submarine is in the field of military defense. The submarine was first used for war in the First World War, by the Germans. They were called U-Boats. Ever since the First World War it has been a main weapon for the warring parties. The submarines provide stealth and quick attack on its enemies. The modern day submarines are powered by mini nuclear reactors. The submarines are also used for research activities and other peaceful works.

CONSTRUCTION DETAILS
High surface speed was essential for a submarine so its hulls were designed for minimum surface resistance sacrificing submerged performance. Its hull is made of cylinders and cones stiffened by frames and internal bulk heads. It is usually of circular or nearly circular cross sectional shape for the best strength to weight ratio. Hulls are made of steel and have a streamlined body shape. The propellers are made of Phosphor bronze because of its lesser elastic hysteresis. It can retain its original shape after the action of a high pressured force. The surface of the submarines is coated with an anechoic foam sound absorbent. It can absorb the high sound waves and prevent the sonar waves from reflection and the internal sounds from escaping the hull. For controlling the buoyancy it is provided with Ballast tanks.

DIVING AND SURFACING
A submarine or a ship can float because the weight of water that it displaces is more than or equal to the weight of the ship. This displacement of water creates an upward force called the buoyant force and acts opposite to gravity which would pull the ship down. Unlike a ship, a submarine can control its buoyancy, thus allowing it to sink and surface at will.
To control its buoyancy the submarine has ballast tanks that can be alternately filled with water or air. When the submarine is on the surface the ballast tanks are filled with air and the submarineâ„¢s overall density is less than that of the surrounding water. As the submarine dives, a measured amount of water is flooded into the ballast tank and the air in the ballast tanks is vented from the submarine until its overall density is greater than the surrounding water and the submarine begins to sink. That is negative buoyancy. The blowing may be done with air stored at high pressure with air from a low pressure air compressor. The air to the air compressor is from air flasks. The submarine s have a movable set of short wings called hydroplanes on the bow and stem that helps to control the angle of the dive. The hydroplanes are angled so that the water moves up over the bow which forces the bow downward and down over the stem, which forces the stem upwards. Therefore the submarine is angled downward.
To keep the submarine leveled at any depth, the submarine maintains a balance of air and water in the balance tank so that the overall density is equal to the surrounding water. That is the state of neutral buoyancy. When the submarine reaches its cruising depth the hydroplanes are leveled so that the submarines travel leveled through the water. The submarine can steer in the water by using the tail rudder, to turn starboard (right) or port (left) and hydroplanes to control the fore-aft angle of the submarine. In addition submarines are equipped retractable secondary propulsion motor that can swivel 360 o. The submerged submarines surfaces only after completing their mission. But the submersible which always remains under water have to come once in a year for their maintenance work.
AUXILIARY OR COMPENSATING TANK
The weight of a submarine is rarely constant. As food, fuel and weapons are used; the submarine gets lighter and would float to the surface unless additional weight was added. The easiest way to do this is to take on additional water. Small auxiliary tanks are provided for this purpose. By keeping these tanks small and short, movement of the water in the auxiliary tanks has little effect of the centre of gravity. The density of sea water is not constant either. The cold water of the North Atlantic is denser than the warm water of the tropics and the fresh water flowing into the sea from rivers affects the density of the water near the coast.
Auxiliary tanks allow the submarine to adjust its weight to compensate for changes in the density of water in addition to variable load.
TRIM TANKS
All successful submarines also include a forward trim tank and an aft trim tank. These tanks are used to move water forward or aft as necessary to level the submarine. When the water in the auxiliary and trim tanks has been adjusted such that flooding the main ballast tanks will result in neutral buoyancy and a level keel, the submarine is said to be in diving trim.
HOW SUBMARINES ARE POWERED
Submarines need power for running propeller and to run generators that recharge a very large battery tank. In the earlier days the diesel power was used. But it requires oxygen to work and it causes the submarines to be very heavy. They have to come to surface to refuel.
But nowadays nuclear power is used for powering submarines. It is similar to commercial power plants, but smaller in size. And it uses a highly enriched fuel to allow it to deliver a large amount of energy from a smaller reactor. Nuclear reactor produces heat to generate steam to drive a steam turbine. The turbine in a ship directly drives the propellers, as well as electrical generators. The power charged by the generator is used for the requirement of the crew.

Fig 2. Nuclear Power plant
FINDING ITS WAY UNDERWATER

The main systems which help the submarines in moving underwater are
a) Periscope
b) Sonar system
c) Internal guidance system
Periscope is known as the window of the submarine to the outer surface of the ocean. A periscope consists of two glasses or prisms placed at an angle of 45¬0. One is placed on the top of the periscope, which comes out of the water. The second is placed on the bottom of the periscope which is attached to the control room, where the people can see the image of the outside. Nowadays electronic imaging unit is used for making the periscope, which consists of three cameras (Optical camera, Laser range finder, IR camera) and mast. Mast is attached to the surface of the crew. It doesn™t penetrate into the crew like the older type of periscopes. In the older days only one person can see the outer surface at a time through the periscope. The electronic imaging unit displays the moving pictures of the outer surface to the screen placed in different places and many people can see the picture at a time.

Fig 3.

Fig 4.
OLD TYPE NEW TYPE
PERISCOPES
When on the surface a Global Positioning System accurately determines the latitude and longitude. But this system cannot work when the submarine is submerged. Underwater the submarine uses an inertial guidance system, which keeps the track of the ships motion from a fixed starting point by using gyroscopes and accelerometers. To locate a target a submarine uses active and passive SONAR (Sound Navigation and Ranging). Active SONAR emits pulses of sound waves that travel through the water, reflect off the target and return to the ship. By knowing the speed of sound in water and time for the sound wave to travel to the target and back, the computers can quickly calculate the distance between the submarine and the target. Whales, dolphins and bats use the same technique for locating the prey. Passive SONAR system helps to locate such type of things. SONAR systems can also be used to realign inertial navigation systems by identifying known ocean floor features.

SONAR
Fig 5.
HOW LIFE SUPPORT IS MAINTAINED
The main things which have to be maintained in the submarine for life support are
A. Air quality
B. Fresh water supply
C. Temperature
A. Maintaining Air Quality
The main components of air are Nitrogen (78%), Oxygen (21%), argon (.94%), and CO2 (.04%). When we breathe in air, our bodies consume its O2 and give out CO2.there is no use of nitrogen and argon for our body. In the case of a submarine, as it is a closed container, there is a limited supply of air.
In order to keep air in a submarine breathable, Oxygen has to be maintained as it is consumed. CO2 must be removed, other wise it makes the air toxic. The moisture that we exhale must be removed Oxygen can be produced by the electrolysis process or by some sort of oxygen canister that releases oxygen by a very hot chemical reaction. These canisters carry kclo3 and naclo3 which are rich in oxygen and will give out on chemical reaction. Modern canisters are extremely light weight to store oxygen. Typically an oxygen canister contains a sodium chlorate cylinder and an igniter.
CO2 can be removed from the air chemically, using soda lime in devices called scrubbers .The CO2 is trapped in soda lime by a chemical reaction and removed from the air. The moisture can be removed by dehumidifiers.
B. Maintaining fresh water supply
A distillation plant is provided in the submarine for maintaining fresh water supply. The distillation plant heats the sea water to water vapour which removes the salt from it and then cools the water vapour into a collecting tank.
C. Maintaining temperature
The temperature of the ocean, surrounding the submarine is typically 39 degree Fahrenheit. The metal of the submarine conducts internal heat to surrounding water. So submarine must be electrically heated to maintain a comfortable temperature for the crew. The dehumidifier reduces the excess amount of water vapour. The other method of removing water vapour is by using sorbent material.
Dynamic dehumidifiers are also used to remove the watervapour .It consists of number of sorbent materials arranged in layers. It is provided with a fan, which sends the atmospheric air to the dynamic dehumidifiers. This absorbs watervapour present in the air and leaves out the air.
RESCUE SYSTEM
When a submarine goes down because of a collision with something (another vessel, canyon wall or mine) or an onboard explosion, the crew will radio a distress call or launch a buoy that will transmit a distress call and the submarines location. Depending upon the circumstances of the disaster the nuclear reactor will shut down and the submarine may be on battery power alone.
If this is the case, the crews of the submarine have four primary dangers facing them,
¢ Flooding of the submarine must be contained and minimized
¢ Oxygen used must be minimized so that the available oxygen supply can hold out long enough for possible rescue attempts
¢ CO2 levels will rise and could produce dangerous toxic effects
¢ If the batteries run out the heating system will fail and the temperature of the submarine will fall
Rescue attempts from the surface must occur quickly, usually within 48 hours of the accident. Attempts will typically involve trying to get some type of rescue vehicles down to remove the crew or to attach some type of device to raise the submarine from the sea floor. Rescue vehicles include mini submarines called Deep Submergent Rescue Vehicles (DSRV) and diving bells. The DSRV can travel independently to the downed submarine, latch on to the submarine over a hatch (escape trunk), create an air tight seal so that the hatch can be opened and load up to 24 crew members. A diving bell is typically loaded from a support ship downed to the submarine, where a similar operation occurs. To raise the submarine, typically after the crew has been extracted, pontoons may be placed around the submarine and inflated to float it to the surface. Important factors in the success of the rescue operation include the depth of the downed submarine, terrain of the sea floor, the currents in the vicinity of the downed submarine, the angle of the submarine and the sea and weather conditions at the surface.
CONCLUSION
Thus we are coming to the end of the elaborate study of submarines going through their advantaged limitation relevance and finally to the modification. To sum up this seminar we have gone through sophisticated concept which will surely be much raved in coming days , as the pride of any country lies in its modern defence system , they have in armoury , submarine add to their glory. Now submarines are also used in the field of tourism, researches, rescue operation etc.
The submarines opened up a whole new world underwater and helped mankind know more about how it is like under water. It is a fact that in spite of knowing so much about the life and land above sea, we know very little about what is it like under sea.
There is a whole world waiting to be explored under the sea.

REFERENCE
1. howstuffworksnuclearpower.htm
2. exomos.com
3. howstuffworksindex.html
4. The complete Idiotâ„¢s Guide to Submarines- Michael DiMercurio

CONTENTS
1. INTRODUCTION 5
2. CONSTRUCTION DETAILS 6
3. DIVING AND SURFACING 8
4. HOW SUBMARINES ARE POWERED 10
5. FINDING ITS WAY UNDER WATER 11
6. HOW LIFE SUPPORT IS MAINTAINED 14
7. RESCUE SYSTEM 16
8. CONCLUSION 18
9. REFERENCE 19

LIST OF FIGURES
1. SECTIONAL VIEW OF SUBMARINE 7
2. NUCLEAR POWER PLANT 10
3. SENSOR UNIT 12
4. PERISCOPE 12
5. SONAR 13