Question

how the submarine work

Answer 1

I shall explain this in very simple terms without going further into hydrodynamics and submarine motion dynamics. Basically a submarine is a streamlined hull body like a round fish and having external control surfaces like an aircraft ( wing flaps, stabiliser, elevators and rudder/ tail fin).

2. If we throw an empty capped PET bottle in a still water tank, the bottle fully floats. Half fill this bottle with water and repeat the event, then it sinks partially, but still floats semi submerged.Now fill up the bottle completely and repeat the event, then it sinks fully into the tank at the same time one would notice the water level of the tank has increased. The volume of this increased water level is equivalent to the volume of water displaced by the submerged and fully filled water bottle. In short, the phenomenon of Archimedes Principle “ any object, wholly or partially immersed in a stationary fluid ,is buoyed up by a force equal to the weight of the fluid displaced by the object”

3. We now see that a buoyant force acts upwards on the water bottle. Replace the water bottle by a submarine and the tank of water by the sea. The result will be this:



A submarine is an aerodynamically shaped long water tight steel cylinder, surrounded by concentric water holding external tanks, called the external ballast tanks. Cross section is shown in the schematic above. External Ballast tanks have valves ( kingston valves) at their bottom portion and air vent valves at their top portion. Opening and closing of Kingston valves and Air vent flaps and their sequence of operation is controlled from inside the submarine by means of hydraulic / electrical systems. Sub also has internal ballast or compensating tanks and trim tanks filled with water for attaing submerged buoyancy and trim through weight adjustments and longitudinal weights shifts respectively.

a) When the submarine is fully buoyant on sea surface, the ballast tanks are kept empty ( marked in yellow) and all Kingston valves and Air vent flaps are kept closed ( Shut) and locked.

b) When the submarine needs to “ dive” then both kingston valves and air vent flaps are opened in a controlled manner. The second stage fig. indicates this. Sea water ( marked blue )gets into the ballast tanks, displacing the trapped air ( yellow )out through vent flaps.

c) When all the ballast tanks are filled, then the submarine gets fully submerged as it becomes slightly negatively buoyant, but not to the extent that it sinks to the bottom like a rock because the buoyant forces of sea acts upwards ( third stage fig. above). At this stage, all the air vent flaps are kept shut and locked, though kingston valves of one group may be kept open ( for any emergency ) and rest kingston valves may be kept shut. Generally, the ballast tanks are grouped as forward, center and aft ( rear) groups for sequential opening or closing of the group tanks to facilitate controlled diving or surfacing.

d) When the submarine needs to “surface”, compressed air ( 400 -600 bar) is blown into ballast tanks keeping the air vent flaps shut and kingston valves open( 4 th stage fig. above). Air pressure displaces the sea water out making the submarine lighter and thus to surface ( 5 th stage fig. above )

e) When all the water in ballast tanks is pushed out by air, the kingston valves are shut and the submarine is fully buoyant on sea surface ( 6 th stage fig. above)

4. So far what I explained above is a static phenomenon of diving and surfacing. But actually submarine dynamic forces are also applied during diving / surfacing operations like the landing or take off of an air craft, with the help of propulsion dynamics of speed and hydrodynamics through the control surfaces mentioned in para 1 above. These control surfaces are just like air craft flaps called “ planes” located as sail planes/ forward planes / retractable diving planes, a rear stabiliser with elevators, called aft / stern planes and the rudder and a stabilising sail or fin. A representative picture of rear end of a submarine is shown here :



5. While diving and surfacing, the sail or fin, the control surfaces of planes and the rudder aid in providing the stability and controlled dynamics to the submarine along with the propulsive force and buoyant forces. Following figures indicate these actions :



6. Thus the submarines work clandestinely lurking underwater with highest attack potential. And all these actions of diving &surfacing and maintenance of submerged trim and stability and tactical propulsion of submarines are carried out by Submarine Engineer Officer and his crew members on the command of the Commanding Officer.