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Supercavitation
Post: #1

INTRODUCTION

Water limits even nature's strategies, and the fastest bird moves twice as quickly as the fastest fish. The phenomenon holding back the fish is the tremendous resistance that water offers to a moving object, called drag. The same drag acts on the bird as well, but the magnitude is considerably less owing to the lesser density of air. The human being has crossed the sound barrier in air and land, what about underwater? Water is the most challenging environment for an Engineer. Being 1000 times denser than air, it offers resistance roughly 1000 times as high as that in air. Supersonic under Water Travel is the dream of scientists working on a bizarre technology called SUPERCAVITATION. Supercavitation is the state of the art technology that may revolutionize underwater propulsion systems

CAVITATION

Cavitation is the process of formation of vapour bubbles of flowing fluid in a region where the pressure of the liquid falls below its vapour pressure and the sudden collapsing of these vapour bubbles in region of high pressure. At first small vapour filled bubbles are formed that gradually increase in size. As the pressure of the surrounding liquid increases, the cavity suddenly collapses-a centimeter sized cavity collapses in milliseconds. Cavities implode violently and create shock waves that dig pits in exposed metal surfaces.

At first, the physical characteristics of boiling and cavitation are almost identical. Both involve the formation of small vapour-filled spherical bubbles that gradually increase in size. However, the bubbles produced by the two processes end in very different manners. In boiling, bubbles are stable: the hot gas inside either escapes to the surface or releases its heat to the surrounding liquid. In the latter case, the bubble does not collapse, but instead fills with fluid as the gas inside condenses.

When it acts upon propellers, cavitation not only causes damage but also decreases efficiency. The same decrease in water pressure that causes cavitation also reduces the force that the water can exert against the boat, causing the propeller blades to "race" and spin ineffectively. When a propeller induces significant cavitation, it is pushing against a combination of liquid water and water vapor. Since water vapor is much less dense than liquid water, the propeller can exert much less force against the water vapor bubbles. With the problems it causes, it is no wonder maritime engineers try to avoid cavitation.

SUPERCAVITATION

The scientists and the engineers have developed an entirely new solution to the cavitation problem. Cavitation becomes a blessing under a condition called supercavitation, i.e., when a single cavity called supercavity is formed enveloping the moving object almost completely. In Supercavitation, the small gas bubbles produced by cavitation expand and combine to form one large, stable, and predictable bubble around the supercavitating object.

Supercavities are classified as one of two types: vapor or ventilated. Vapor cavities are the pure type of supercavity, formed only by the combination of a number of smaller cavities. In a ventilated cavity, however, gases are released into the bubble by the supercavitating object or a nearby water surface
Post: #2
Super cavitation ppt
Post: #3

Supercavitation is the use of cavitation effects to create a gas bubble within a liquid large enough to encompass an object traveling through the liquid, greatly reducing the friction friction of the skin on the object and allowing Reach very high speeds. Current applications are mainly limited to very fast supercavitators or torpedoes and some propellers, but in principle the technique could be extended to include whole vehicles. China and the United States Navy are working on supersonic supercavitator submarines.

Applications
In 1960, the USSR began developing a project under the code name "Шквал" (Squall) led by NII-24 (Kiev) to develop a high-speed torpedo, an underwater rocket, four to five times faster than torpedoes In 1972 and 1977, more than 300 launching were carried out (95% of them at Lake Issyk Kul), no later than 29 November 1972 VA-111 Shkval was put into service With mass production initiated in 1978.
In 2004, German gunmaker Diehl BGT Defense announced its own supercavitating torpedo, Barracuda, now officially called "Superkavitierender Unterwasserlaufkörper" (English: "supercavitating underwater running body"). According to Diehl, it reaches more than 400 kilometers per hour (250 mph).
In 1994, the United States Navy began developing a mine-cleaning system invented by C Tech Defense Corporation, known as RAMICS (Rapid Mine Clearance System), based on a stable supercavitante projectile in air and water. These have been produced in diameters of 12.7 millimeters (0.50 in), 20 millimeters (0.79 in) and 30 millimeters (1.2 in). The ballistic terminal design of the projectile allowed it to cause the explosive destruction of sea mines as deep as 45 meters under water with a single round. In 2000, these projectiles were used to successfully destroy a series of live underwater mines when fired from a Sea Cobra helicopter at Aberdeen Proving Ground. RAMICS is currently under development by Northrop Grumman for its introduction into the fleet. The dartboards of German submarine guns (Heckler & Koch P11) and Russian, and other similar weapons are also supercavitating.
In 2005, DARPA announced the 'Underwater Express' program, a research and evaluation tender to establish the potential for overcrowding. The ultimate goal of the program is a new class of underwater craft for coastal missions that can transport small groups of Navy personnel or specialized military cargo at speeds of up to 100 knots. The contracts were awarded to Northrop Grumman and General Dynamics Electric Boat in late 2006. In 2009, DARPA announced the progress through a new class of submarines.
 


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