The worst case scenario is an explosion under a submarine, as a result of which the suction is downwards, and it if caused at maximum service depth, can result in the submarine being sucked into larger depths, causing additional risk to the structure due to hydrostatic pressure.Īpart from the direct shock load imparted from the explosion, each shockwave from a single underwater explosion causes a wave of vibration to propagate along the pressure hull. It has also been observed during tests, that due to each contraction of the explosion cloud, the submarine has a tendency to be sucked towards the centre of the explosion cloud. The study thus helps us conclude, that when a submarine is subjected to an explosion, it should be able to withstand not one, but a series of shockwaves. The diameter and magnitude of each recurrent explosion is less than the previous. The same process of contraction, implosion and expansion recurs in series till the energy of the explosion is completely dissipated. This implosion generates a cloud of gas bubbles which expands radially. This is what causes it to contract and implode. Now that the ball has expanded, the pressure at its centre is lower than the external pressure. This ball of explosion expands to the point where the internal pressure on the inner wall of the ball becomes equal to the external hydrostatic pressure due to the water around it. To understand it, watch the video below, and notice how the explosion ball is created and how it contracts and explodes again, to release a cloud of gas bubbles.Īt the instant of explosion, a shockwave is created, which applies radial outward pressure on the water around the point of explosion. The physics of underwater explosions is a very interesting subject, as in, it is remarkably unique when compared to an explosion in air. Whereas, in designs allowing higher safety factors like 2.5, they can dive deeper than the service depth, but only in emergency conditions.Ī submarine is designed to withstand the loads generated by underwater detonations (for example, mine explosions, pressures generated by bursting of large underwater gas bubbles). In usual design, safety factors of 1.5 are used, and submarines designed to such limits should not go below the service depth. The hydrostatic pressure at this depth is considered as the design pressure for all the pressure hull calculations. The collapse depth is actually calculated by multiplying the maximum operable depth (MOD) or service depth with a factor of safety. It is designed for a particular collapse depth, at which complete failure is expected within a very narrow range. The pressure hull is the primary structural element of the submarine, and is designed to be able to withstand the external hydrostatic pressure. The loads on a submarine during its mission can be classified into the following:ĭepth is one of the most important and deciding structural design criteria. Structural design always begins with the process of identifying the loads that the structure would be subjected to. The full process of designing its structure also takes up majority of the time, as it is not only related to strength factors, but also to a nexus of functional aspects that are interrelated to it. Please read the first three here – Introduction to submarine design, Understanding submarine design and Unique tanks on a submarineĪpproximately 40% of the focus and priority in the entire submarine design process is given to its structural design. This is the fourth part of the series of submarine design.
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