Requirements for a stand for degaussing ships. Magnetization of a ship in the earth's magnetic field
Magnetometric instruments
To measure characteristics: magnetic field and magnetic properties of physical objects, magnetometers are used.
Depending on the measurement methods, magnetometers are divided into:
· Magnetostatic;
· Electromagnetic;
· Induction;
· Magnetodynamic;
· Nuclear precession.
The magnetic field affects all physical bodies located in its zone. These effects are not the same: some of the bodies are magnetized, others are not; in some, the magnetization is stable, while in others, stability is not observed.
The magnetic properties of materials are distinguished by their magnetic susceptibility. In accordance with their values, all materials are divided into three groups:
diamagnetic,
paramagnetic,
ferromagnetic.
Diamagnetic materials slightly weaken the magnetizing field.
These include, for example; water, copper, bismuth. In view of the smallness, it is believed that, i.e. Diamagnets behave like a vacuum with respect to a magnetic field.
Paramagnetic materials slightly increase the magnetizing field.
These are materials such as: air, aluminum, titanium.
Ferromagnetic materials; significantly increase the magnetizing field.
Here are some of them (maximum values):
soft iron;
· carbonaceous iron;
· Pure hydrogen-annealed iron;
· Structural steel.
The ship is constantly in the Earth's magnetic field and its interaction with it determines the concept of the ship's magnetic field.
A significant amount of structural steel is used to build a ship.
The dependence of the magnetic state of the body on the intensity of the magnetizing field: for ferromagnetic materials, it is determined experimentally and is called the magnetization curve. The most complete characteristic of the magnetic properties of ferromagnets is given by the hysteresis (hysteresis - lagging) curve (Fig. 4). It is built in the coordinate axes of magnetization and the strength of the magnetizing field. The main sections of the hysteresis curve are: – initial magnetization of the material; – magnetization reversal; - magnetization reversal in the original direction.
Characteristic points of the diagram: point - the intersection of the descending branch of the loop with the coordinate axis. At this point at , the steel has remanent magnetization, which characterizes the degree of magnetic hardness of the material.
The point - the intersection of the descending branch with the axis shows the magnitude of the intensity of the magnetizing field of the opposite sign, which must be applied to demagnetize the material. The quantity is called the coercive force. When moving along the ascending branch of the loop, we will have similar points with the opposite sign.
When magnetized to non-saturation, the hysteresis loop narrows,
A ship in the Earth's magnetic field is subjected to permanent and inductive magnetization.
The magnetization of the ship's ferromagnetic masses in the Earth's magnetic field corresponds to the initial section of the magnetization curve (Fig. 5). Magnetization can be divided into permanent and inductive components.
Depending on the place (latitude) of the building, the course on the slipway and the technology (mechanical, electromagnetic and thermal effects), the ship acquires magnetization (Fig. 6), which, as they say, depends on the magnetic background.
If the ship stays in one course for a long time (in the dock, during construction, etc.), then it becomes magnetized, and some part of its magnetic moment remains regardless of its further position.
In general, the ship's magnetization vector is arbitrarily directed relative to the rectangular coordinate system associated with the ship.
Usually, the left system of coordinate axes is used: the axis is directed vertically to the center of the Earth, the axis is horizontal along the ship to the bow, the axis is horizontal to the starboard side.
The ship is complex geometric body and magnetized differently in different planes. Therefore, to analyze the ship's magnetic field, its magnetization vector is usually represented as the sum of three components along the indicated coordinate axes:
It is believed that each of these components creates its own magnetic field in the surrounding space, i.e. The ship's magnetic field is represented as the sum of three fields: the longitudinal magnetization field, the transverse magnetization field, and the vertical magnetization field.
Thus, the intensity vector of the IPC is represented by the sum of the intensity of each of these fields:
where is the resulting vector of the vertical magnetization field strength; is the resulting vector of the field strength of the longitudinal magnetization; is the resulting vector of the transverse magnetization field strength.
For the tactical needs of the analysis of the MPC, the intensity vector of each of the ship's magnetization fields is represented by three components in the coordinate system associated with the ship:
For the vertical magnetization field, these components, for example, are called: – longitudinal component of the ship's vertical magnetization field; is the transverse component of the vertical magnetization field; is the vertical component of the vertical magnetization field.
On fig. Figure 7 shows the curves of the components of the vertical magnetization field of the ship, obtained as a result of measurements at a depth under the ship when the sensor (observer) moves along the diametrical plane (Fig. 7, a) and along the plane of the midship frame (Fig. 7, 6).
Taking into account the constant and inductive components of the intensity of the MPC, we obtain 6 components for the vertical magnetization field:
where , are the signs of inductive and permanent magnetization, respectively; is the sign of the vertical magnetization field. Combining mentally in Fig. 7 points , we get the volume distribution of the field.
The appearance of non-contact mine and torpedo weapons, and then magnetic detectors (magnetometers) of submarines in a submerged position, reacting to the ship's magnetic field, led to the development and creation of methods and means for both active and passive protection of ships.
Active defense methods include:
Destruction of mines with the help of trawls;
Creation of passages in minefields with the help of detonations of depth and air bombs;
Search with the help of special electromagnetic and television seekers with subsequent destruction.
The main method of passive protection is the degaussing of ships. Its essence is to reduce the magnetic field at a certain depth, called the protection depth. The depth of protection is called such the smallest depth under the keel, at which, after demagnetization of the ship, the strength of its magnetic field is practically equal to zero. In this case, the failure of non-contact mines and torpedoes is ensured,
Another way to ensure the protection of the ship in the magnetic field is to use low-magnetic and non-magnetic materials in the structures of the hull and mechanisms of the ship.
The concept of demagnetization.
Degaussing a ship is the process of artificially reducing its magnetic field. Degaussing is carried out using the windings of the current-fed circuits and is called electromagnetic processing (EMT). The essence of EMO is to create a magnetic field in a certain way, opposite in sign to the field of the ship, which will be discussed below.
On fig. 8 shows a flat circuit through which a direct current is passed. Field direction dependence, i.e. the position of its poles from the direction of the current is determined by the well-known gimlet rule.
Demagnetization is done by two various methods- non-winding and winding. These names should be understood as conditional, since the demagnetization of ships by both one and the other method is carried out using current-powered windings. But in the first case, the windings are applied to the ship's hull temporarily, only for the period of demagnetization, or they are generally placed outside the ship, on the pound. Using the second method, the windings are mounted permanently on the ship and turn them on while traveling through dangerous areas.
Windless demagnetization (BR).
Windingless demagnetization is carried out by exposing the ship to temporarily created magnetic fields in two ways:
With the help of electrical windings temporarily applied to the ship;
With the help of circuits streamlined by current, laid on the ground.
With windingless demagnetization (BR), the ship's hull is exposed to damped alternating and constant magnetic fields, or to short-term exposure to only a constant magnetic field. In the first case, the demagnetization is based on the magnetization of the housing along a hysteresis-free curve, in the second - along a hysteresis curve (Fig. 4).
Degaussing with the help of windings temporarily applied to the ship.
After the construction of the ship, its hull is magnetized in the vertical, longitudinal and transverse directions.
Consider the essence of demagnetization in the vertical direction (Fig. 9, a).
a) vertical demagnetization;
b) longitudinal demagnetization;
c) transverse demagnetization.
A cable is wound around the hull in a plane parallel to the waterline. Depending on the magnetization of the housing, the value of which is determined during the preliminary measurement, a current of such a value is passed through the cable (Fig. 10) so that the created field of the opposite sign (when the current is on) at the point exceeds the initial one (point).
After a few seconds, the current in the winding is turned off, and the magnetic state passes to the point . This operation is called "tipping" the field. Indeed, the field at the point turned out to be of a different sign, “overturned”. Note that the process follows a hysteresis curve.
The second operation is called "compensation". During this operation, a current is switched on in the winding, the magnitude and direction of which are chosen so that after turning it off, the ship's field is as close as possible to zero.
Vertical magnetization of the ship;
Intensity of the vertical external magnetic field.
The current included in the winding during the first and second operations is called the reversal current and the compensation current, respectively.
It can be seen from the curves that, as a result of electromagnetic processing, the ship's existing magnetization is compensated, and the new magnetization created is such that the vertical components of inductive magnetization and permanent magnetization , in the equator region, turn out to be close or equal in absolute value, but opposite in sign.
When demagnetizing along a hysteresis-free curve, the same result is achieved, only the process of compensating for the old by creating a new permanent magnetization occurs during cyclic remagnetization in an alternating magnetic field, decreasing in amplitude from a certain maximum to zero. To create both constant and alternating magnetic fields, one or more turns are temporarily superimposed on the ship, connected to the power sources of the degaussing ships. For the case of longitudinal demagnetization, several turns are superimposed on the ship (Fig. 9, b) so that the ship is enclosed inside a huge solenoid. The magnetic field that arises when the winding is turned on and acts along the axis of the solenoid demagnetizes the ship.
With transverse demagnetization, two successively connected turns along the sides are superimposed on the ship in a vertical plane.
The demagnetization efficiency is checked by measuring the magnetic field under the bottom.
Winding around the body of heavy multi-core cables is associated with a large investment of time and physical labor. Therefore, along with this method, special non-winding demagnetization stations are also used, on which the windings (cable) are laid in a certain way on the ground. Windless degaussing with circuits laid on the ground. The contours laid on the ground are in the form of a loop. Therefore, the stations were called - loop stations of non-winding demagnetization (PSBR) fig. 11. The water area is protected by buoys or milestones. It has barrels for mooring ships.
A direct current is passed through circuit 1, an alternating current with a frequency of about . An alternating magnetic field eliminates all irreversible phenomena that occur during magnetization in a constant magnetic field of the DC circuit 2. The demagnetization process consists in passing the appropriate currents through the circuits (bottom cables) at the moment when the ship passes or stands above them. The control of the current regime and the taking of readings of the magnetometric equipment is carried out remotely from the shore console. The demagnetization process is based on the principle of semi-hysteresis magnetization reversal (Fig. 12).
When approaching the stand of the PSBR, the magnetic state of the ship is characterized by the point where the ship has a certain permanent and inductive magnetization. At the moment of passing over the stand, the ship undergoes magnetization reversal along a semi-hysteresis curve. At this moment, the ship is above the middle of the contour. Further, when the ship is removed, its magnetic state changes along a curve. With a successful combination of magnetic fields on the stand, the magnetic state of the ship can come to a magnetic state close to neutral (point ).
1 - DC circuit;
2 - AC circuit;
3 - protecting buoy
As a rule, during electromagnetic processing at such stations, permanent vertical and permanent longitudinal magnetization are simultaneously compensated. Other types of magnetization are not eliminated.
So, the positive side of windless degaussing is that the ship does not carry any windings that would require power supplies and control panels. However, this method is not universal.
The main disadvantages without winding demagnetization of the ship are:
1. The impossibility of compensating for course and latitude changes in the ship's field.
2. The need to periodically repeat the magnetic treatment due to the insufficient stability of the resulting field.
3. The need after each processing to determine and eliminate the deviation of magnetic compasses.
Winding demagnetization
Winding demagnetization provides for compensation of the ship's magnetic fields by fields from stationary windings fed by current from special sources. The totality of the winding system, power sources, as well as control and monitoring equipment is a demagnetizing device (RU).
The switchgear is calculated so that the magnetic field created by the current flowing through the winding represents at any time a mirror image of the ship's own magnetic field, i.e. at each point under the ship it is equal to the ship's field in magnitude and opposite in sign.
RU was first developed by a group of employees of the Leningrad Institute of Physics and Technology of the USSR Academy of Sciences headed by Academician A.P. Aleksandrov (I.V. Kurchatov, L.R. Stepanov K.K. Shcherbo and others). The degaussing device makes it possible to compensate for the ship's magnetic field, taking into account course and latitude changes.
The demagnetizing device consists of several independent windings for various purposes.
1. To compensate for the field strength from vertical permanent magnetization, the main horizontal winding is used. The direction of the current in this winding is selected so that its magnetic field is opposite to the field from vertical permanent magnetization (Fig. 13).
On fig. 13 shows that the magnetic field of the winding (curve ) is equal in intensity, but opposite in sign to its own field (). This winding is called the main winding because it compensates for the most significant (vertical) component. The current mode selected for this winding does not change in the future, but remains constant on all courses and at any latitude.
To compensate for the vertical component of the longitudinal magnetization, bow and stern windings are used (Fig. 14, a).
2. Instead of these windings, a frame winding can be used (Fig. 14, b). The action of this winding is more efficient compared to the bow and stern permanent windings. However, its installation is associated with great difficulties.
3. The field from transverse permanent magnetization is compensated by the field of buttocks permanent windings, which are connected in series and mounted on the starboard and port sides of the vessel (Fig. 15). To compensate for this field, it is enough to set a certain and identical current mode in the windings.
It is more difficult to compensate for the inductive components of the magnetization. For this purpose, the demagnetizing device includes adjustable windings: latitude, course frame windings and buttock course windings.
4. Latitudinal winding is designed to compensate for the field from vertical inductive magnetization. The location of this winding and the distribution of the components of the strength of its magnetic field are the same as those of the main horizontal one. Therefore, a separate latitude winding can not be installed, but several sections of the main horizontal winding can be used, introducing devices for adjusting the current into their power circuit.
The current in the latitude winding is regulated in proportion to the sine of the magnetic inclination (magnetic latitude).
Course frame windings serve to compensate for the field from longitudinal inductive magnetization and are placed similarly to windings for permanent longitudinal demagnetization. Since the field strength from the longitudinal inductive magnetization of the ship changes in proportion to the cosine of the magnetic field, then to compensate for this field, it is necessary to change the current mode in the winding also according to the cosine law. Therefore, these windings are called frame course windings (Fig. 14, b).
Buttock course windings are used to compensate for the field from transverse inductive magnetization, they are placed in series on both sides of the vessel, parallel to the permanent windings. Adjustment of the strength and direction of the current is proportional to the sine of the angle of the magnetic course.
Additional windings are installed both to compensate for the ship in its individual sections, and to compensate for the magnetic fields of powerful ship electric power and other installations.
The main advantage of winding demagnetization is the ability to compensate for course and latitude changes in the ship's magnetic field, which provides a greater degree of protection for ships from non-contact magnetic weapons and their greater secrecy.
The disadvantages of RU are: high cost, consumption additional materials, weighting the ship and significant energy consumption.
Ship hulls, masts, superstructures, weapons and mechanisms are made of steel, iron, cast iron and other metals that have the properties of being magnetized in the Earth's magnetic field and creating their own magnetic field in the space surrounding them. Due to magnetization in the Earth's magnetic field, the ship itself becomes like a large magnet, the magnetic field of which is superimposed on the Earth's magnetic field. As a result, the system of arrows of the magnetic compass installed on the ship is simultaneously under the influence of the forces of the earth's magnetic field and the magnetic field of the ship. The consequence of this is the deviation of the system of magnetic compass needles from the direction of the magnetic meridian. This deviation, depending on the direction of the resultant of all forces that act on the compass needle, can occur east or west of the magnetic meridian.
The vertical plane in which the arrow of the compass installed on the ship is located is called the plane of the compass meridian. The phenomenon of deviation of the compass needle from the plane of the magnetic meridian under the influence of the magnetic fields of the ship and its devices is called the deviation of the magnetic compass. The deviation of a magnetic compass is measured by the angle between the plane of the magnetic meridian and the plane of the compass meridian. Deviation is denoted by the Greek letter d (delta). If the plane of the compass meridian is located to the right of the plane of the magnetic meridian, the deviation will be east (Оst) and then a plus sign is assigned to it, if the plane of the compass meridian is located to the left of the plane of the magnetic meridian, the deviation will be west (W) and a minus sign is assigned to it. The deviation of the magnetic compass can take values from 0 to 180 ° depending on the magnetic state of the ship's iron and its location relative to the compass needle.
In addition to the magnetic fields of ship iron, there are many sources of electromagnetic fields on ships: electrical wiring, generators, electric motors, etc.
The deviation of the magnetic compass, which appears under the influence of magnetic fields of conductors under current, generators, electric motors and various electrical equipment of the ship, is called electromagnetic deviation.
To reduce the effect of ship iron on the compass, all parts of the compass are made of non-magnetic materials, the compass itself is installed on the ship as far as possible from its metal parts, and devices close to the compass tend to be made of non-magnetic materials. When installing a compass on a ship, measures are also taken to ensure that there are no sources of electromagnetic fields nearby.
The deviation of the magnetic compass is periodically reduced (compensated). To do this, in the immediate vicinity of the compass needles, special magnets and soft iron in the form of balls, bars, plates are placed, which create magnetic fields equal to the fields from ship iron, but opposite in direction. As a result of compensating for the deviation, the compass needle should return to the plane of the magnetic meridian, but usually it is not possible to completely compensate for magnetic fields; This means that it is not possible to completely eliminate the deviation. The compass after compensation is left with a deviation called residual, which is carefully determined in magnitude and sign and then taken into account when processing the directions measured using a magnetic compass.
Electromagnetic deviation is compensated by adjusting the current strength in special compensation coils located inside the compass binnacle under its bowler hat. Methods for compensating the deviation of the magnetic compass and determining the residual deviation are described in detail in the course "Deviation of the magnetic compass".
The deviation of the magnetic compass does not remain constant, but changes from a number of reasons: changes in the magnetic latitude of the ship, changes in the magnetic state of the ship, i.e., the degree of its magnetization, and the position of the ship relative to the direction of the magnetic lines of force (from the course of the ship).
Based on the results, the determination of the residual deviation, which for correctly installed compasses does not exceed, as a matter of fact, 2--5 °, tables and deviation graphs are compiled for all ship magnetic compasses. An example of such a table is provided below.
Deviation table of the main magnetic compass
compass courses |
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In the tables, the deviations of the magnetic compass are given in compass courses. Separate deviation tables are calculated for different states of the ship (with CS off, CS on).
It should be noted that no matter how well the deviation is determined and no matter how carefully the residual deviation of the magnetic compass is determined, it changes over time for the reasons indicated earlier. Therefore, in addition to periodically determining the residual deviation and compiling a worksheet, it is necessary to use every opportunity to refine the deviation in order to gain confidence in the correctness of the tabular data or its individual values.
The task of reducing the ship's magnetic field can be solved in two ways:
the use of low-magnetic materials in the design of the hull, equipment and mechanisms of the ship;
ship degaussing.
The use of low-magnetic and non-magnetic materials for the creation of ship structures allows to a large extent lower the ship's magnetic field. Therefore, in the construction of special ships (minesweepers, minelayers), materials such as fiberglass, plastics, aluminum alloys, etc. are widely used. In the construction of some projects of nuclear submarines, titanium and its alloys are used, which, along with high strength, is a low-magnetic material.
However, the strength and other mechanical and economic characteristics of low-magnetic materials make it possible to use them in the construction of warships within limited limits.
In addition, even if the hull structures of ships are made of low-magnetic materials, then a number of ship mechanisms remain made of ferromagnetic metals, which also create a magnetic field. Therefore, at present, the main method of magnetic protection of most ships is their demagnetization.
Degaussing a ship is a set of measures aimed at artificially reducing the components of the strength of its magnetic field.
The main tasks of demagnetization are:
- a) reduction of all components of the IPC tension to the limits established by special rules;
- b) ensuring the stability of the demagnetized state of the ship.
One of the methods for solving these problems is winding demagnetization.
The essence of the method of winding demagnetization lies in the fact that the MPC is compensated by the magnetic field of the current of standard windings specially mounted on the ship.
The totality of the winding system, their power sources, as well as control and monitoring equipment is degaussing device(RU) ship.
The ship's switchgear winding system may include the following windings (depending on the type and class of the ship):
- a) The main horizontal winding (MG), designed to compensate for the vertical component of the MPC. To demagnetize a larger mass of the ferromagnetic material of the casing, the exhaust gas is divided into tiers, with each tier consisting of several sections.
- b) Heading frame winding (KSh), designed to compensate for the longitudinal inductive magnetization of the ship. It consists of a series of series-connected turns located in the frame planes.
- a) The main horizontal winding of the exhaust gas.
b) Course frame winding KSh.
c) Course buttocks winding of the KB.
- c) Course buttock winding (KB), designed to compensate for the field of inductive transverse magnetization of the ship. It is mounted in the form of several contours, located side by side in the buttocks planes, symmetrically with respect to the diametrical plane of the ship.
- d) Permanent windings, used on ships of large displacement. These types of windings include a permanent frame winding (PN) and a constant buttock winding (PB). These windings are laid along the route of the KSh and KB windings and do not have any types of current regulation during operation.
- e) Special windings (CO) designed to compensate for magnetic fields from individual large ferromagnetic masses and powerful electrical installations (containers with missiles, minesweeping units, batteries, etc.)
The power supply of the switchgear windings is carried out only by direct current from special power supply units of the switchgear. The power supply units of the switchgear are electric machine converters, consisting of an AC drive motor and a DC generator.
To power converters and switchgear windings on ships, special switchgear power boards are installed, which receive power from two current sources located on different sides. The necessary switching, protective, measuring and signaling equipment is installed on the switchgear boards.
For automatic control of currents in the RU windings, special equipment is installed, which regulates the currents in the RU windings depending on the magnetic course of the ship. Currently, ships use current regulators of the KADR-M and CADMIY types.
Along with winding demagnetization, i.e. using RU, surface ships and submarines are periodically subjected to windless demagnetization.
The essence of windless demagnetization lies in the fact that the ship is subjected to short-term exposure to strong, artificially created magnetic fields, which reduce the IPC to certain standards. The ship itself does not have any stationary demagnetizing windings with this method. Windingless demagnetization is carried out on special SBR stands (windingless demagnetization stand).
The main disadvantages of the windingless demagnetization method are the insufficient stability of the ship's demagnetized state, the impossibility of compensating the inductive components of the MPC, which depend on the course, and the duration of the windingless demagnetization process.
Thus, the maximum reduction of the ship's magnetic field is achieved by applying two methods of demagnetization - winding and non-winding. The use of RI makes it possible to compensate for the MPC during operation, but since the ship's magnetic field can change significantly over time, the ships need periodic magnetic treatment at the SBR. In addition, the SBR measures the magnitude of the ship's magnetic field in order to maintain the IPC within the established aisles.
Hydroacoustic detection of submarines
The physical field of the ship- the region of space adjacent to the ship's hull, in which physical properties ship as a material object. These physical properties, in turn, affect the distortion of the corresponding physical field of the World Ocean and adjacent airspace.
Ship Physical Field Types
Tasks solved by the hydroacoustic complex of a submarine.
The physical fields of ships according to the location of radiation sources are divided into primary (intrinsic) and secondary (caused).
The primary (intrinsic) fields of ships are fields whose radiation sources are located directly on the ship itself or in a relatively thin layer of water surrounding its hull.
The secondary (evoked) field of the ship is the reflected (distorted) field of the ship, the radiation sources of which are located outside the ship (in space, on another ship, etc.).
Fields that are artificial in nature, i.e. formed with the help of special devices (radio, sonar stations, optical devices) are called active physical fields.
The fields that are naturally created by the ship as a whole as a constructive structure are called passive physical fields of the ship.
According to the functional dependence of the parameters of physical fields on time, they can also be subdivided into static and dynamic fields.
Static fields are considered to be such physical fields, the intensity (level or power) of sources of which remains constant during the time of impact of the fields on the non-contact system.
Dynamic (time-variable) physical fields are such fields, the intensity of the sources of which changes during the time of the field impact on the non-contact system.
The main types of physical fields of the ship
Currently modern science highlights more than 30 different physical fields of the ship. The degree of application of the properties of physical fields in the design of technical means of detection, means of tracking ships, as well as in non-contact weapon systems is different. At the moment, the most important physical fields of ships and submarines, on the basis of knowledge about which special devices are being developed, are: acoustic, hydroacoustic, magnetic, electromagnetic, electrical, thermal, hydrodynamic, gravitational.
Taking into account the development of various areas of physics and instrumentation, new physical fields of marine objects are constantly being determined, for example, research is being carried out in the field of optical, radiation physical fields.
The main task that engineers involved in studying the properties of physical fields solve is to search for and detect enemy ships and submarines, target them with combat weapons (torpedoes, mines, missiles, etc.), as well as detonate their proximity fuses. During the Second World War, mines with electromagnetic, acoustic, hydrodynamic and combined fuses were widely used, and hydroacoustic equipment for detecting submarines was also often used.
Acoustic field of the ship
Scheme of operation of hydroacoustic stations of a surface ship:
1 - echo sounder transducer; 2 - hydroacoustic post; 3 - sonar converter; 4 - discovered mine; 5 - detected submarine.
Acoustic field of the ship- a region of space in which acoustic waves are distributed, formed by the ship itself or reflected from the surface of its hull.
Any ship in motion serves as an emitter of the most diverse in value and nature of acoustic vibrations, complex action which on the surrounding aquatic environment creates quite intense underwater noise in the range from infra- to ultrasonic frequencies. This phenomenon is also called the primary acoustic field of the ship. The nature of the radiation of the primary field and its propagation are determined, as a rule, by the following parameters of the ship: displacement, contours (streamlined form) of the hull and speed of the ship, the type of main and auxiliary mechanisms.
The flow of water when bypassing the ship's hull determines the hydrodynamic component of the acoustic field. The main and auxiliary mechanisms of the ship determine the vibration component, propellers determine the cavitation component (cavitation on a propeller is a formation on its rapidly rotating blades in aquatic environment discharged gas cavities, the subsequent compression of which sharply increases the noise).
As a result, the ship's primary hydroacoustic field (HAFC) is a set of fields superimposed on each other created by various sources, the main of which are:
1. Noises created by propellers (screws) during their rotation. The underwater noise of the ship from the work of the propellers is divided into the following components:
Noise propeller rotation,
swirling noise,
Vibration noise of the edges of the propeller blades ("singing"),
cavitation noise.
2. Noises emitted by the ship's hull on the move and in the parking lot as a result of its vibration from the operation of the mechanisms.
3. Noises created by the flow of water around the ship's hull during its movement.
The level of underwater noise also depends on the speed of the ship, as well as on the depth of immersion (for submarines). If the ship is moving at a speed above the critical. then in this case, the process of intense noise generation begins.
During the operation of the ship, as the main components wear out, its noise may change. When the technical resource of ship mechanisms is exhausted, they are misaligned, unbalanced and vibration increases. Vibrational energy of worn mechanisms provokes. in turn, the vibrations of the hull, which leads to disturbances in the adjacent water surface.
Indicator pictures of GAK MGK-400EM. Noise direction finding mode
The vibrations of the mechanisms are transmitted to the hull mainly through: support connections of the mechanisms with the hull (foundations); non-supporting connections of mechanisms with the body (pipelines, water pipes, cables); through the air in the compartments and rooms of the NK.
The ship's hull, by itself, is capable of reflecting acoustic waves emitted by some other source. This radiation, when reflected from the hull, turns into a secondary acoustic field of the ship and can be detected by the receiving device. The use of a secondary acoustic field allows not only to determine the direction of the ship, but also allows you to calculate the distance to it by measuring the signal propagation time (the speed of sound in water is 1500 m/s). Additionally, the speed of sound propagation in water is affected by its physical state (salinity, which increases with temperature, and hydrostatic pressure).
Submarine attack based on ship's false acoustic field
The main ways to reduce the acoustic field of the ship are: reducing the noise of propellers (selecting the shape of the blades, the speed of the propeller, increasing the number of blades), reducing the noise of mechanisms and the hull (soundproof damping, acoustic coatings, sound-absorbing foundations).
Indicator pictures of GAK MGK-400EM. LOFAR mode
Hydroacoustic complex "Skat" of the nuclear submarine "Pike"
The noisiness of a ship affects not only its stealth from various means of detection and the degree of protection from mine and torpedo weapons of a potential enemy, but also affects the operating conditions of its own sonar detection and target designation means, interfering with the operation of these devices.
Noise is of great importance for the invisibility of submarines (submarines), since it is it that largely determines this survival parameter. Therefore, in submarines, noise control and its reduction is one of the main tasks of all personnel.
The main measures to ensure acoustic protection of the ship:
Improvement of vibroacoustic characteristics of mechanisms;
Removal of mechanisms from the structures of the outer hull emitting underwater noise by installing them on decks, platforms and bulkheads;
Vibration isolation of mechanisms and systems from the main body with the help of soundproof shock absorbers, flexible inserts, couplings, shock-absorbing pipeline hangers and special noise-protective foundations;
Vibration damping and soundproofing of sound vibrations of foundation and hull structures, piping systems using soundproof and vibration-damping coatings;
Sound insulation and sound absorption of airborne noise of mechanisms through the use of coatings, casings, screens, silencers in air ducts;
Application of hydrodynamic noise silencers in seawater systems.
Separately, cavitation noise is reduced by the following works:
Use of low-noise propellers;
Use of low speed propellers;
Increasing the number of blades;
Balancing propeller and shaft line.
The combination of engineering developments, as well as the corresponding actions of the personnel, can seriously reduce the level of the ship's hydroacoustic field.
Thermal (infrared) field of the ship
Thermal field of the ship
thermal field- the field that appears when the ship emits infrared rays. The most powerful sources of radiation from thermal fields are: chimneys and gas flares from the ship's power plant; hull and superstructures in the area of the engine room; torches of fire during artillery firing and rocket launching. When using infrared equipment, the thermal field makes it possible to detect a ship at a sufficiently large distance.
The main sources of the ship's thermal field (infrared radiation) are:
Surfaces of the above-water part of the hull, superstructures, decks, casings of chimneys;
Surfaces of gas ducts and exhaust gas devices;
Gas torch;
The surfaces of ship structures (masts, antennas, decks, etc.) located in the area of action of a gas torch, gas jets of rockets and aircraft at startup;
Burun and the wake of the ship.
The ship in the lens of the thermal imager
The detection of surface ships and submarines by their thermal field and the issuance of target designation to weapons is carried out using special heat direction finding equipment. Such equipment is usually installed on surface ships and submarines, aircraft, satellites, coastal posts.
Additionally, various types of missiles and torpedoes are also supplied with thermal (infrared) homing devices. Modern thermal homing devices make it possible to capture a target at a distance of up to 30 km.
Main technical means thermal protection of ships:
Exhaust gas coolers of a ship power plant (mixing chamber, outer casing, louvered air intake windows, nozzles, water injection systems, etc.);
Heat recovery circuits (TUK) of a ship power plant;
Onboard (surface and underwater) and stern gas exhaust devices;
Shields of infrared radiation from the internal and external surfaces of gas ducts (double-layer shields, profile screens with water or air cooling, shielding bodies, etc.);
Universal water protection system;
Coatings for the ship's hull and superstructures, including paintwork, with reduced emissivity;
Thermal insulation of high-temperature ship premises.
The heat visibility of a surface ship can also be reduced by using the following tactics:
Application of masking effects of fog, rain and snow;
Application as a background of objects and phenomena with powerful infrared radiation;
The use of bow heading angles in relation to the carrier of heat direction finding equipment.
For submarines, thermal visibility decreases with increasing depth of their immersion.
Hydrodynamic field of the ship
Hydrodynamic field of the ship
In the region of the extremities, zones of increased pressure are formed, and in the middle part along the length of the hull, an area of reduced pressure is formed.
Hydrodynamic field- the field arising as a result of the movement of the ship, due to a change hydrostatic pressure water under the ship's hull. According to the physical essence of the hydrodynamic field, it is a perturbation by a moving ship of the natural hydrodynamic field of the World Ocean.
If in each place of the World Ocean the parameters of its hydrodynamic field are mainly due to random phenomena, which are very difficult to take into account in advance, then a moving ship introduces not random, but quite natural changes in these parameters, which can be taken into account with the accuracy necessary for practice.
When the ship moves in water, the liquid particles located at certain distances from its hull come into a state of perturbed motion. When these particles move, the value of the hydrostatic pressure changes in the place where the ship is moving, i.e. a hydrodynamic field of a ship of certain parameters is formed.
When a submarine moves under water, the area of pressure change extends to the surface of the water in the same way as to the ground. If the submarine moves at a shallow depth, then a well-marked hydrodynamic wave wake can be visually fixed on the water surface.
The properties of the ship's hydrodynamic field are often used in the development of non-contact hydrodynamic fuses for bottom mines.
To date, significant effective means of hydrodynamic protection of the ship have not been developed. Partial reduction of the hydrodynamic field is achieved by calculating the balance between the optimal displacement of the ship and the shape of its hull. The main tactical method of hydrodynamic protection of the ship is the choice of a safe speed. It is considered safe to have such a speed at which either the magnitude of the pressure drop under the ship does not exceed the set threshold for triggering the mine fuse, or the time the low pressure area acts on the fuse is less than that set in the fuse.
There are special schedules for safe ship speeds and rules for use, which are given in a special instruction for choosing safe ship speeds when navigating in areas where hydrodynamic mines can be laid.
Ship's electromagnetic field- the field of time-varying electric currents created by the ship in the surrounding space. Main emitters electromagnetic field of the ship are: alternating galvanic currents in the "propeller-hull" circuit, vibration of the ferromagnetic masses of the hull in the Earth's magnetic field, the operation of the ship's electrical equipment. The electromagnetic field has a pronounced maximum in the region of the propellers, and at a distance of several tens of meters from the hull it practically fades.
The electromagnetic protection of the ship is carried out by choosing a non-metallic material for propellers:
Applications for them of non-conductive coatings, application of contact-brush devices on the shafting;
Shunting variable oil clearance resistance in bearings;
Maintaining the insulation resistance of the shaft from the body within the established norms.
On ships with non-magnetic and low-magnetic hulls, the main attention is paid to the issues of reducing the electromagnetic field of electrical equipment elements.
ship's magnetic field
ship's magnetic field
ship's magnetic field- a region of space within which changes in the Earth's magnetic field are detected due to the presence or movement of a magnetized ship.
The ship's magnetic field is the resulting value of the superposition of several fields: constant (static) and inductive (dynamic) magnetization.
Permanent magnetization is formed near the ship mainly during the construction period under the influence of the earth's magnetic field, and depends on:
The location of the ship relative to the direction and magnitude of the lines of the Earth's magnetic field at the construction site;
The magnetic properties of the materials themselves from which the ship is built (residual magnetization);
The ratio of the main dimensions of the ship, the distribution and shape of the iron masses on the ship;
Technologies used to build the ship (number of riveted and welded joints).
To quantitatively characterize the magnetic field, a special physical quantity is used - the magnetic field strength H.
Another physical quantity, which primarily determines magnetic properties material is the magnetization intensity I. In addition, there are the concepts of residual magnetization and inductive magnetization.
The use of low-magnetic and non-magnetic materials in the construction of a ship makes it possible to significantly reduce its magnetic field. Therefore, in the construction of special ships (minesweepers, minelayers), materials such as fiberglass, plastics, aluminum alloys, etc. are widely used, and in the construction of some projects of nuclear submarines, titanium and its alloys are used, which, along with high strength, is a low-magnetic material . However, the strength and other mechanical and economic characteristics of low-magnetic materials make it possible to use them in the construction of warships within limited limits. There are also highly magnetic materials, these include: iron, nickel, cobalt and some alloys. Substances that can be strongly magnetized are called ferromagnets.
The principle of operation of a magnetic mine
In addition, even if the hull structures of ships are made of low-magnetic materials, then a number of ship mechanisms remain made of ferromagnetic metals, which also create a magnetic field. Therefore, for ships, the level of their magnetic field is periodically monitored and, when exceeded allowable value, the case is demagnetized. There is winding and winding demagnetization. The first is carried out with the help of special ships or at windingless demagnetization stations, the second provides for the presence on the ship itself of stationary wires (cables) and special DC generators, which, together with the control and monitoring equipment, constitute the demagnetizing device of the ship.
The ship's magnetic field (MPC) is widely used in proximity fuses for mine and torpedo weapons, as well as in stationary and aviation systems for magnetometric detection of submarines.
An example of experiments to reduce the magnetic field is the so-called Philadelphia experiment, which to this day remains the subject of many speculations, since documentary evidence of the result of the experiment has not been publicly made public.
Ship's electric field
Ship's electrical field
Ship's electric field(EPK) - a region of space in which constants flow electric currents.
The main reasons for the formation of the electric field of the ship are:
Electrochemical processes occurring between the parts of the ship, made of dissimilar metals and located in the underwater part of the hull (propellers and shafts, steering gear, bottom-outboard fittings, tread and cathodic protection systems of the hull, etc.).
The processes generated by the phenomenon of electromagnetic induction, the essence of which lies in the fact that the ship's hull during its movement crosses the lines of force of the Earth's magnetic field, as a result of which electric currents arise in the hull and the masses of water adjacent to it. Similar currents are formed in ship propellers during their rotation. As a rule, the ship's hull is made of steel, screws and bottom fittings are made of bronze or brass, hydroacoustic fairings are made of stainless steel, and corrosion protectors are made of zinc. As a result, galvanic vapors are formed in the underwater part of the ship and stationary electric currents arise in sea water, as in an electrolyte.
Processes associated with the leakage of currents of ship's electrical equipment to the ship's hull and into the water.
The main reason for the formation of EPC are electrochemical processes between dissimilar metals. About 99% of the maximum value of the EIC falls on electrochemical processes. Therefore, to reduce the level of EPA seek to eliminate this cause.
The ship's electric field greatly exceeds the natural electric field of the World Ocean, which allows it to be used in the development of non-contact naval weapons and submarine detection tools.
Reducing the level of the electric field is achieved: - by using non-metallic materials in the manufacture of the body and parts in contact with sea water;
By selecting metals according to the proximity of the values of their electrode potentials for the body and parts in contact with sea water;
By shielding EPA sources;
By disconnecting the internal electrical circuit of EPC sources;
Through the use of special coatings of EPC sources with electrically insulating materials.
Areas of use
The physical fields of the ship are currently widely used in three areas:
In non-contact systems various kinds weapons;
In detection and classification systems;
in homing systems.
Links and sources
Literature
1. Sverdlin G. M. Hydroacoustic transducers and antennas.. - Leningrad: Shipbuilding, 1980.
2. Urick R.J. (Robert J. Urick). Fundamentals of hydroacoustics (Principles of Underwater Sound).. - Leningrad: Shipbuilding, 1978.
3. Yakovlev A.N. Short range sonar.. - Leningrad: Shipbuilding, 1983.