Sneak Submersibles
Permeable environment and unmasking factors
The combat use of submarines and other underwater vehicles is based on their quality, such as the secrecy of actions for the attacked enemy. The aquatic environment, in the depth of which the PAs operate, limits the detection distance by means of radio and optical location of several tens of meters. On the other hand, the high speed of sound propagation in water, reaching 1,5 km / s, allows the use of noise-finding and echolocation. Water is also permeable to the magnetic component of electromagnetic radiation propagating at a speed of 300000 km / s.
Additional unmasking PA factors are:
- wake trace (air-water plume) generated by a propeller (propeller or jet) in the near-surface layer of water or in the deep layers in the event of cavitation on the propeller blades;
- chemical trace from the exhaust gases of the heat engine PA;
- thermal trace arising from the removal of heat of the power plant PA in the aquatic environment;
- the radiation trace left by the PA with nuclear power plants;
- surface wave formation associated with the movement of water masses during movement of the PA.
Optical location
Despite the limited detection distance, the optical location has found its application in the waters of tropical seas with high transparency of water in conditions of low waves and shallow depths. Optical locators in the form of high-resolution cameras operating in the infrared and visible bands are installed on board aircraft, helicopters and UAVs, complete with high-power searchlights and laser locators. The bandwidth reaches 500 meters, the depth of visibility in favorable conditions - 100 meters.
Radar is used to detect periscopes raised above the water surface, antennas, intake devices, and the air traffic controllers themselves in the surface position. The detection range using a radar installed on board an aircraft carrier is determined by the altitude of the carrier and ranges from several dozen (retractable PA devices) to several hundred (PA itself) kilometers. In the case of use in the sliding devices PA radio-transparent construction materials and stealth coatings detection range is reduced by more than an order.
Another method of radar detection of PA moving underwater is the fixation of co-wave formation on the sea surface generated in the process of hydrodynamic impact of the hull and propulsion PA on the water column. This process can be observed over a large area of water from both aircraft and satellite radar carriers equipped with specialized hardware and software to highlight the weak terrain of a PA satellite wave against the background of interference from wind waves and wave formation from surface vessels and coastline. However, satellite waves become visible only when the PA moves at a shallow depth in calm weather conditions.
Additional unmasking factors in the form of wake, thermal, chemical and radiation trails are mainly used to pursue a PA for the purpose of covertly controlling its movement (without reaching the sonar line) or producing a torpedo attack from the feed exchange angles of the attacked PA. The relatively small width of the track, combined with the coursework maneuvering of the PA, forces the pursuer to move along a zigzag trajectory at a speed twice as high as the speed of the PA, which increases the detection distance of the pursuer itself due to the higher level of generated noise and exit from the shadowy feeding area of the PA. In this regard, the movement on the trail is temporary in order to reach the distance of hydroacoustic contact with the PA, which allows, among other things, to qualify the target by the criterion of one’s own / alien and type of underwater vehicle.
Magnetometric method
An effective method for detecting PA is magnetometric, operating regardless of the state of the sea surface (waves, ice), the depth and hydrology of the water area, the bottom topography and the intensity of navigation. The use of diamagnetic construction materials in a PA design only allows to shorten the detection distance, since steel components and electrical products are necessarily included in the composition of the power plant, propulsion unit and PA equipment. In addition, the propeller, the water jet impeller and the PA hull (regardless of the structural material) in motion accumulate static electric charges on themselves that generate a secondary magnetic field.
Prospective magnetometers are equipped with SQUID superconducting sensors, cryogenic Dewar vessels for storing liquid nitrogen (modeled on Javelin ATGM), and compact refrigeration machines to maintain nitrogen in the liquid state.
Existing magnetometers have a detection range of a nuclear submarine with a steel hull at 1 km. Prospective magnetometers detect an NPS with a steel hull at a distance of 5 km. A submarine with a titanium hull - at a distance of 2,5 km. In addition to the hull material, the magnetic field strength is directly proportional to the displacement of the PA, therefore the small Poseidon submersible with a titanium hull has a 700 times smaller magnetic field than the Yasen nuclear submarine with a steel hull and, accordingly, a smaller detection range.
The main carriers of magnetometers are anti-submarine aircraft of the base aviation, to increase the sensitivity of the magnetometer sensors are located in the rear protrusion of the fuselage. In order to increase the depth of PA detection and expand the search band, anti-submarine aircraft fly at an altitude of 100 meters or less from the sea surface. Surface carriers use the towed version of magnetometers, underwater carriers use the onboard version with compensation for the carrier’s own magnetic field.
In addition to the limitation in range, the magnetometric method of detection also has a limitation by the speed of the PA — due to the absence of an intrinsic magnetic field gradient, stationary underwater objects are recognized only as anomalies of the Earth’s magnetic field and require subsequent classification using hydroacoustics. In the case of using magnetometers in the torpedo / anti-torpedo homing systems, there is no speed limit due to the inverse sequence of detection and classification of targets during a torpedo / anti-torpedo attack.
Sonar method
The most common method for detecting a PA is hydroacoustic, which includes passive direction finding of the intrinsic PA noise and active echolocation of the aquatic environment using directional emission of sound waves and reception of reflected signals. Hydroacoustics uses the entire range of sound waves - infrasonic vibrations with a frequency from 1 to 20 Hz, audible vibrations with a frequency from 20 Hz to 20 KHz and ultrasonic vibrations from 20 KHz to several hundred KHz.
Hydroacoustic transceivers include conformal, spherical, cylindrical, planar and linear antennas, assembled from a variety of hydrophones into three-dimensional assemblies, active phased arrays and antenna fields connected to specialized hardware and software devices that ensure listening to the noise field, generation of echolocation pulses and reception reflected signals. Antennas and hardware-software devices are combined in hydroacoustic stations (GUS).
Transceiver modules hydroacoustic antennas are made from the following materials:
- polycrystalline piezoceramics, mainly lead zirconate titanate, modified with strontium and barium additives;
- a piezoelectric film of fluoropolymer, modified with thiamine, which converts the polymer structure to the beta phase;
- fiber-laser interferometer with laser pumping.
Piezoceramics provides the highest power density of sound oscillations, so it is used in sonars with a spherical / cylindrical antenna of increased range in the mode of active radiation, installed in the nasal tip of marine carriers (at the greatest distance from the propulsion generating parasitic noise) or mounted in a capsule, lowered depth and towed behind the carrier.
Piezofluoropolymer film with a low power density of generation of sound vibrations is used to manufacture conformal antennas located directly on the surface of a body of surface and underwater vehicles of single curvature (to ensure isotropic hydroacoustic characteristics) that work to receive all types of signals or to transmit signals of low power.
The fiber-optic interferometer works only on receiving signals and consists of two fibers, one of which experiences compression-expansion under the action of sound waves, and the other serves as a reference medium for measuring the interference of laser radiation in both fibers. Due to the small diameter of the optical fiber, its compression-expansion oscillations do not distort the diffraction front of sound waves (unlike the piezoelectric hydrophones of large linear dimensions) and allow for a more accurate determination of the position of objects in the aquatic environment. Flexible towed antennas and bottom linear antennas up to 1 km long are formed of fiber-optic modules.
Piezoceramics are also used in hydrophone sensors, spatial assemblies of which are part of floating buoys discharged into the sea from anti-submarine aircraft, after which hydrophones are lowered onto the cable to a predetermined depth and transferred to noise-finding mode with transmission of the collected information via radio to the aircraft. To increase the area of the controlled water area, along with floating buoys, a series of deep grenades are dumped, the explosions of which hydroacoustically illuminate underwater objects. In the case of the use of antisubmarine helicopters or quadrocopters to search for underwater objects, a receiving-transmitting antenna of the onboard HAC, which is a matrix of piezoceramic elements, is lowered onto the cable-tether.
Conformal antennas from a piezofluoropolymer film are mounted in the form of several sections spaced along the PA side to determine not only the azimuth but also the distance (by the method of trigonometry) to the underwater noise source or the reflected location signals.
The flexible towed and bottom linear antennas made of optical fiber, despite their relative cheapness, have a negative operational property - due to the large length of the antenna “string”, it undergoes bending and torsional vibrations under the influence of the incoming flow of water, thus deteriorating multiple times compared to piezoceramic and piezofluoropolymer antennas with rigid web. In this regard, the most accurate sonar antennas are made in the form of a set of reels wound from optical fiber and mounted on spatial farms inside acoustically transparent water-filled cylindrical shells protecting antennas from external influence of water flows. The shells are rigidly attached to the foundations located at the bottom and connected by power cables and lines of communication with the coastal centers of anti-submarine defense. If radioisotope thermoelectric generators are also placed inside the shells, the devices obtained (autonomous by power supply) are transferred to the discharge of bottom sonar stations.
Modern GUS review of the underwater situation, search and classification of underwater objects work in the lower part of the audio range - from 1 Hz to 5 KHz. They are mounted on various sea and air carriers, are part of the floating buoys and bottom stations, differ in a variety of forms and piezoelectric materials, their place of installation, power and reception / emission mode. GAS search for mines, counteraction to underwater saboteurs and scuba divers and providing sound underwater communications work in the ultrasonic range at frequencies above 20 KHz, including the so-called sound-vision mode with detailing objects on the scale of several centimeters. A typical example of such devices is GAS "Amphora", a spherical polymer antenna of which is installed on the front upper tip of the submarine felling fencing
In the case of the presence on board of a mobile carrier or as part of a stationary system of several HAS, they are combined into a single sonar complex (GAK) by means of joint computational processing of active location data and passive direction finding. The processing algorithms provide for software detuning from noise generated by the carrier itself and external noise background generated by maritime navigation, wind waves, multiple reflections of sound from the water surface and the bottom in shallow water (reverberation noise).
Computational Algorithms
The algorithms for computational processing of noise signals received from PAs are based on the principle of extracting cyclically repeated noise from rotation of propeller blades, operation of electric motor current collector brushes, resonant noise from propeller gearboxes, vibration from steam turbines, pumps and other mechanical equipment. In addition, the use of a database of noise spectra characteristic of a particular type of objects allows us to qualify targets for the characteristics of your own / alien, underwater / surface, military / civilian, shock / multipurpose submarine, onboard / towed / lowered GUS, etc. In the case of preliminary compilation of the spectral sound "portraits" of individual PAs, it is possible to carry out their identification according to the individual features of the operation of the onboard mechanisms.
Detection of cyclically repetitive noise and the construction of traces of movement of the PA requires the accumulation of sonar information for tens of minutes, which greatly slows down the detection and classification of underwater objects. Much more unambiguous distinctive features of the PA are sounds of water getting into ballast tanks and blowing them with compressed air, torpedoes coming out of torpedo tubes and underwater missile launches, and also operating the sonar of the enemy in the active mode, detected by receiving a direct signal at a distance multiple of a distance than reception of the reflected signal.
In addition to the power of location radiation, the sensitivity of receiving antennas and the degree of perfection of the algorithms for processing the information received, the characteristics of the HAS are significantly influenced by underwater hydrological conditions, water depth, sea surface agitation, ice cover, bottom relief, presence of noise interference from maritime navigation, sand suspension, floating biomass and other factors.
The hydrological setting is determined by the differentiation of temperature and salinity of the horizontal layers of water, resulting in different densities. At the boundary between the layers of water (the so-called thermocline), sound waves experience full or partial reflection, shielding the PA from above or below the positioned search gas. Layers in the water column are formed in the depth range from 100 to 600 meters and change their location depending on the season of the year. The bottom layer of water, stagnating in the recesses of the seabed, forms the so-called liquid bottom, which is impenetrable to sound waves (except for infrasound). On the contrary, in the layer of water of the same density, an acoustic channel arises, through which sound vibrations in the middle frequency range extend to a distance of several thousand kilometers.
These features of the propagation of sound waves under water have determined the choice of infrasound and the low frequencies adjacent to it to 1 KHz as the main working range of HAS for surface ships, submarines and bottom stations.
On the other hand, the secrecy of the PA depends on the design decisions of their onboard mechanisms, engines, propulsion, layout and coating of the hull, as well as the speed of the underwater course.
The most optimal engine
Reducing the noise level of the PA in the first place depends on the power, number and type of propulsion. Power is proportional to the displacement and the speed of the PA. Modern submarines are equipped with a single water cannon, the acoustic radiation of which is shielded from the nasal heading angles by the submarine body, from the side heading corners - by the water jet housing. The area of audibility is limited to narrow aft course angles. The second most important layout solution aimed at reducing the intrinsic noise of the PA is the use of a cigar-shaped body with an optimal degree of elongation (8 units for speed ~ 30 nodes) without superstructures and surface protrusions (except for cutting) with minimal turbulence.
The most optimal engine in terms of minimizing the noise of a non-nuclear submarine is a direct-drive propeller / water jet direct-drive electric motor, since the AC electric motor generates noise with a frequency of current in the circuit (50 Hz for domestic submarines and 60 Hz for American submarines). The specific weight of the low-speed electric motor is too large to provide a direct drive at maximum speed, therefore, in this mode, the torque must be transmitted through a multi-stage gearbox that generates a characteristic cyclic noise. In this regard, the low-noise mode of full electromotive motion is realized when the gearbox is turned off with a limitation on the power of the electric motor and the travel speed of the PA (at the level of 5-10 nodes).
Submarines have their own characteristics for the implementation of the full electric propulsion mode - in addition to the noise of the gearbox at low speed, it is also necessary to exclude noise from the circulating pump of the reactor coolant, the pump for pumping turbine working fluid and the seawater feed pump to cool the working fluid. The first task is solved by transferring the reactor to the natural circulation of the coolant or using a liquid metal coolant with an MHD pump, the second task is through the use of the working fluid in the supercritical state of aggregation and a single-rotor turbine / compressor of a closed cycle, the third by using the pressure of the incident flow of water.
The noise generated by the onboard mechanisms is minimized through the use of active shock absorbers that work in antiphase with oscillations of the mechanisms. However, the initial success achieved in this direction at the end of the last century had serious limitations for its development for two reasons:
- the presence of large resonator air volumes inside the hulls of submarines to ensure the life of the crew;
- placement of on-board mechanisms in several specialized compartments (residential, command, reactor, machine), which does not allow aggregating mechanisms on a single frame in contact with the submarine hull at a limited number of points through jointly controlled active shock absorbers to eliminate common-mode noise.
This problem is solved only by switching to small-sized unmanned underwater vehicles without internal air volumes with aggregation of power and auxiliary equipment on a single frame.
In addition to reducing the intensity of the generation of the noise field, constructive solutions should reduce the probability of PA detection using the echolocation radiation of the HAS.
Counteraction to hydroacoustic means
Historically, the first way to counteract active sonar search tools was to apply a thick rubber coating on the surface of a submarine hull, first used on the Kriegsmarine “electric robots” at the end of the Second World War. The elastic coating largely absorbed the energy of the sound waves of the location signal, and therefore the power of the reflected signal was insufficient to detect and classify the submarine. After adopting a nuclear submarine with an immersion depth of several hundred meters, the fact of compression of a rubber coating by water pressure with the loss of energy absorption properties of sound waves was revealed. The introduction of various fillers into the rubber coating, which dissipate sound (modeled on the ferromagnetic coating of airplanes, which scatter radio emission) partially eliminated this defect. However, the expansion of the range of working frequencies of the gas into the area of infrasound has drawn a line under the possibilities of using an absorbing / dissipating coating as such.
The second way to counteract the active hydroacoustic search tools is a thin layer active coating of the body, generating oscillations in antiphase with the echlotational signal of GUS in a wide frequency range. At the same time, such a coating, at no additional cost, solves the second problem - reducing the residual acoustic field of the PA's own noise to zero. A piezoelectric fluoropolymer film is used as a thin-layer coating material, the use of which has been tested as the basis of HAS antennas. At the moment, the limiting factor is the price of coating a submarine hull with a large surface area, so the primary targets for its use are uninhabited underwater vehicles.
The last known method of countering active sonar search tools is to reduce the size of the PA to reduce the so-called. target forces - effective surface dispersion of the sonar echolocation signal. The possibility of using more compact PAs is based on a revision of the nomenclature of armaments and a reduction in the number of crews up to the complete uninhabitation of the vehicles. In the latter case, and as a guideline, the crew size in 13 people of a modern container ship Emma Mærsk with a displacement of 170 thousand tons can serve.
As a result, the strength of the target can be reduced by one to two orders of magnitude. A good example is the direction of improving the underwater fleet:
- implementation of the projects “Status-6” (“Poseidon”) and XLUUVS (Orca);
- development of projects of the submarine “Laika” and SSN-X with medium-range cruise missiles on board;
- development of advance projects of bionic NLA equipped with conformal jet propulsion with thrust vector control.
Tactics of anti-submarine defense
The level of stealth of underwater vehicles is greatly influenced by the tactics of using anti-submarine defenses and counter-tactics of PA.
The means of PLO primarily include stationary systems for the review of underwater conditions such as the American SOSUS, which includes the following lines of defense:
- Cape North Cape of the Scandinavian Peninsula - Bear Island in the Barents Sea;
- Greenland - Iceland - Faroe Islands - British Isles in the North Sea;
- Atlantic and Pacific coasts of North America;
- Hawaiian Islands and the island of Guam in the Pacific.
The detection range of fourth-generation submarines in deep-water areas outside the convergence zone is of the order of 500, in shallow waters - of the order of 100 km.
During the movement under water, the PA is forced from time to time to adjust its actual depth of travel in relation to the given one due to the pushing nature of the propulsion effect on the hull of the underwater vehicle. The resulting vertical oscillations of the body generate so-called. surface gravitational wave (PGW), whose length reaches several tens of kilometers at a frequency of several hertz. The PRT in turn modulates the low-frequency sonar noise (the so-called backlight) generated in areas of intensive maritime navigation or the passage of a storm front located thousands of kilometers from the location of the PA. In this case, the maximum detection range of a submarine moving at cruising speed with the help of FOSS increases to 1000 km.
The accuracy of determining the coordinates of targets using FOSS at maximum range is an ellipse of 90 size by 200 km, which requires additional exploration of remote targets by forces of anti-submarine basic aircraft equipped with onboard magnetometers dropped by sonar buoys and aircraft torpedoes. The accuracy of determining the coordinates of targets within 100 km from the anti-submarine line FOSS is quite sufficient for the use of rocket-torpedoes of the appropriate coastal and ship-based range.
Surface anti-submarine ships, equipped with submarine, lowered, and towed GAS antennas, have a detection range of fourth-generation submarines that are traveling at 5-10 nodes, no more than 25 km. The presence on board ships of deck helicopters with lowered antenna GAS extends the detection distance to 50 km. However, the use of shipboard power systems is limited by the speed of the ships, which should not exceed 10 nodes due to the occurrence of anisotropic flow around the hook antenna and the break of the cable-cables of lowered and towed antennas. The same applies to the case of sea excitement with a force of more than 6 points, which also forces us to abandon the use of deck helicopters with a lowered antenna.
An effective tactical scheme for providing anti-submarine defense of surface ships going at an economic speed of 18 knots or under 6-point wave conditions of the sea is the formation of a ship group with the inclusion of a specialized underwater lighting equipment equipped with a powerful pitcher. Otherwise, surface ships should retreat under the protection of coastal FOSS and basic anti-submarine aviation, not dependent on weather conditions.
A less effective tactical scheme for providing anti-submarine defense of surface ships is the inclusion of a submarine ship group, whose onboard GAS operation does not depend on the sea surface agitation and its own speed (within 20 knots). In this case, the GAS of the submarine must operate in the mode of noise-finding due to the multiple exceeding the distance of the detection of the echolocation signal over the distance of reception of the reflected signal. According to foreign press data, the detection range of a fourth-generation nuclear submarine under these conditions is of the order of 25 km, the detection range of a non-nuclear submarine is 5 km.
The counter-use of strike submarines includes the following ways to increase their secrecy:
- distance gap between themselves and the target by an amount exceeding the range of the action of GAS FOSS, surface ships and submarines participating in the anti-submarine defense, using the appropriate weapons;
- overcoming the lines of FOSS with the help of passage under the keel of surface ships and ships for the subsequent free operation in the water area, which is not illuminated by enemy hydroacoustic facilities;
- use of features of hydrology, bottom topography, shipping noise, sonar shadow of sunken objects and the submarine's lining on liquid soil.
The first method assumes the presence of an external (generally satellite) target designation or an attack of a stationary target with known coordinates, the second method is acceptable only before the onset of a military conflict, the third method is implemented within the working depth of the submarine and its equipment with an upper water intake system for cooling the power plant or heat removal directly to the PA casing.
Estimation of the level of hydroacoustic secrecy
In conclusion, it is possible to assess the level of the hydroacoustic secrecy of the strategic Poseidon strategic nuclear weapon in relation to the secrecy of the ash submarine Yasen:
- The surface area of the ABO 40 times less;
- the power of the NPA power unit is 5 less;
- the working depth of the submersion of the NLA in 3 times.
- fluoroplastic coating of the housing against the rubber coating;
- aggregation of NLA mechanisms on a single frame against spacing of NPS mechanisms in individual compartments;
- full electric movement of the ABO at low speed with the shutdown of all types of pumps against the full electric movement of submarines at low speed without turning off the pumps pumping condensate and water intake to cool the working fluid.
As a result, the detection distance of the Poseidon NLA moving at a speed of 10 nodes using modern GUS installed on any type of carrier and operating in the entire range of sound waves in the direction-finding and echolocation modes will be less than 1 km, which is obviously not enough not only to prevent attacks on a stationary coastal target (taking into account the radius of destruction by a shock wave from an explosion of a special LBU), but also to protect the carrier-based strike force as it travels into the waters, the depth of which exceeds 1 km.
- Andrey Vasilyev
- roe.ru, wiki.wargaming.net, www.popmech.ru, www.quora.com, www.slideshare.net
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