China is developing ultra-quiet submarines that are invisible to sonar

Two teams of Chinese researchers have revealed two discoveries a few days apart that can make their own submarines faster, quieter and invisible to the sonar of their enemies.

A rubber “invisibility cloak”

Researchers from Xi’an Jiaotong University in central China have created a new coating for submarines which is capable of absorbing sound waves and making it difficult to detect submarines with sonar. This system emits sounds at different frequencies to detect the position of underwater objects such as submarines, mines or missiles. The waves emitted by the sonar bounce off the surface of the ship and produce an echo that can be detected by a receiver to calculate its position.

The new material designed by Professor Qingxuan Liang and its colleagues, made up of 32mm thick rubber strips, may be the thinnest to date for absorbing a wide range of frequencies. The researchers used an artificial intelligence algorithm that helped them discover the optimal structure and layout to apply to the submarine. They then concluded that to maximize the absorption of sound waves at different frequencies, some of the strips had to have a rectangular piece of lead running through them, while others had pyramid-shaped cavities.

As the researchers tell in an article published in the journal Applied physical review, They used a computer simulation with which they were able to determine a material absorption efficiency of 95% in the frequency range most used by sonar, between 1 and 10 kilohertz. In this way, the material was shown able to absorb waves with an efficiency of about 95%. The researchers also think the submarine’s bounced signal would be weak and more likely to go unnoticed or merge with some other underwater structure such as a coral reef.

Liang says that most “invisible” material designs don’t work as well at different frequencies, with significantly lower performance at the lower frequencies. Furthermore, adding a thin steel wall to the material, the researcher says, could also make the material work below 4.5 megapascals, the pressure experienced by submarines more than 450 meters deep. Now the group is working on developing a practical method for making their own material.

And a new, quieter and more powerful engine

Another article, published October 10 in the Chinese Journal of Ship Research, a publication run by China’s leading naval ship designer, the Wuhan 701 Institute, describes a new waterjet. These marine propulsion systems that use a water jet can provide submarines with greater thrust and reduce its vibrations by more than 90%.

The jet is used in some modern submarines that have the rotor in a covered frame to generate a jet of water for propulsion. The problem is that between the rotor blades and the inner wall of the conduit there is a very small open space which produces a lot of turbulence or bubbles which can slow the submarine and betray its position.

The team managed to create a jet rotor that leaves no gaps. The system sinks the outer edge of the blades into the duct wall, so that the rotor tips do not come into contact with water during movement. The researchers also made an incision in the duct wall to allow the rotor tips to move freely within it.

For the correct functioning of the system, they say, a material is needed that seals the structure, preventing the entry of water, but leaving the rotor free. Chinese researchers did not disclose the composition of the material, but they said yes a soft structure made of fibers thin that prevents water from entering.

The researchers ran a series of simulations indicating that the new design could increase engine thrust at lower revs, while significantly reducing vibration, between one-tenth and one-thirtieth less than a conventional waterjet, the team explains. The device, they say, can generate 10 percent more thrust at lower speeds by reducing the turbulence that causes drag. During the rehearsals, this system produced fewer bubbles, known as cavitation, which occur when the blades rotate rapidly.

As he points out South China Morning Post, China’s first nuclear submarines made a lot of noise, allowing other countries to track their movements relatively easily. But some military experts believe that the latest models of the Chinese submarine fleet have become faster and quieter with the use of new technologies like this one.

Two teams of Chinese researchers have revealed two discoveries a few days apart that can make their own submarines faster, quieter and invisible to the sonar of their enemies.