EP0414865B1 - Process for masking the noise signals emitted by the sound-emitting mechanical elements of a vehicle, in particular a submerged submarine, and submarine - Google Patents

Abstract

A process is useful for influencing a noise source, in particular of a submerged submarine (20). The submarine acts as a noise source and emits a noise signal (S; 24, 25, 26) with a first frequency spectrum with at least a first intensity peak. In order to render the detection of the frequency spectrum by means of passive noise-locating systems (13) more difficult, the first frequency spectrum is modulated stochastically and/or the frequency of the intensity peak is shifted, by influencing the noise source.

Description

The invention relates to a method for camouflaging the sound signals emitted by the sound-emitting mechanical elements of a vehicle, in particular a submersible, wherein the mechanical elements emit a sound signal with a first frequency spectrum with at least a first intensity maximum.

The invention further relates to a submarine with sound-emitting mechanical elements and means for camouflaging the emitted sound signals.

The invention is intended in particular to mask the sound source or camouflage the submarine.

As part of the fight against submarines, both active and passive systems are used to locate the submarines.

In the active systems (e.g. SONAR), a search signal is emitted from a searching vehicle, for example a frigate, generally a sound signal in the sound or infrasound range. These sound signals are reflected on the surface of the submarine and reach receivers on board the searching vehicle, so that the position of the submarine can be determined from these received signals by means of suitable evaluation methods.

In order to protect submarines against such active location methods, it is known to provide the submarine with a coating on its outer hull which absorbs sound signals as best as possible.

From DE-OS 33 32 754 an underwater ship is known which is to be camouflaged against detection by a low-frequency active sonar, ie a passive sound location system. For this purpose, broadband wedge absorbers are arranged in particular on the bow and on the bow side of the tower, which in turn are adapted to the respective ship contours and themselves have no sound reflection properties. In this way, the visibility of the submarine, namely the so-called target dimension, should be reduced by approx. 10 to 15 dB.

It has also already been proposed to reduce turbulence on the submarine parts around which water flows by introducing chemical additives (DE-OS 23 18 304).

Passive location methods, on the other hand, take advantage of physical phenomena that are caused by the submarine itself. For example, it is known to use the fact that the metallic parts of the submarine interfere with the earth's magnetic field for locating submarines. Positioning probes are therefore known which are based on the principle of nuclear magnetic resonance and are towed by ships or aircraft on a long line over the areas of the sea to be searched in order to detect faults in the earth's magnetic field.

Another passive location method, as described for example in EP-PS 63 517, EP-OS 120 520 and EP-PS 213 418, is based on the measurement of sound signals which are emitted by the submarine. A submarine in fact radiates sound to the surrounding seawater like moving parts in the submarine transmit vibrations to the outer skin. Measurable sound signals are primarily generated by moving propulsion elements of the submarine, i.e. by the rotating parts of the propulsion engine and by the shaft, but the rotating screw and the cavitation caused by the screw must also be taken into account as sound sources. Finally, sound signals are generated when the elevator and depth rudder are actuated, when deflating air and when shifting trimming masses, which can be detected on board modern frigates using correspondingly sensitive passive location systems.

In this context, the special feature of submarines with a nuclear drive is that nuclear reactors, such as those used on board submarines, are usually equipped with periodically operated control rods. The control rods are moved in the reactor vessel at a predetermined frequency, the immersion depth of the control rods being adjustable so that the power emitted by the nuclear reactor can be adjusted in this way. As a result of the periodic movement of relatively large masses, however, a relatively intense sound signal also arises which can be used to locate such submarines driven by nuclear technology.

On the other hand, it is known that with modern, increasingly sensitive passive sound locating systems, the sound that is present in the vicinity of the submarine must also be taken into account to an ever greater extent. This natural sound is essentially generated by ocean currents, waves, schools of fish and the like.

When operating passive sound location systems, this ambient sound is noticeable as noise, which can assume an even or an uneven frequency distribution depending on the ambient conditions.

From DE-OS 34 06 343 a method is known with which sound signals from submarines, the intensity of which is only slightly above that of the ambient noise, can be recognized from the ambient noise.

Numerous measures are known for preventing submarines from being recognized by the passive sound location systems described above.

The essential measure is, of course, to reduce the overall sound of the submarine if possible. To achieve this, particularly low-noise machine parts, for example bearings, are used in the drive area of the submarine, so that the total sound energy generated is kept as low as possible.

In addition, however, it is also known to carry out sound insulation measures on board submarines in order to at least prevent unavoidable sound from reaching the outer shell of the submarine. For this purpose, it is known, for example, to design the outer shell of the submarine in two shells and to flood the space with a thickness of, for example, 30 cm with seawater, so that as little sound waves as possible can reach the outer shell of the submarine.

Furthermore, the extent of the emitted sound waves can also be reduced in dangerous situations by reducing the drive power by so-called "creep speed". However, this naturally degrades the submarine's ability to evade detection by enemy ships by removing them.

From DE-OS 36 00 258 an electrical system for submarines is known which has means for camouflaging the submarine. In the known system takes into account the fact that an AC network of the submarine in the fre frequency range between 60 Hz and 400 Hz works and that it is inevitable that frequencies in this frequency range plus their harmonics are emitted via the hull to the surrounding water. In the known electrical system, a frequency of 30 kHz, for example, is therefore provided for the AC network of the submarine, which frequency is far above the reception frequency range of external location systems.

However, this known electrical system has the disadvantage that it can only camouflage the submersible for as long as the frequency ranges of enemy passive location systems do not work in the range of 30 kHz, for example. As soon as the measures taken in the known system are known to the enemy, the enemy can locate the submersibles by checking the new frequency range by adapting their passive location systems.

Finally, it is also known to disrupt passive sound location systems on board enemy ships by placing objects that emit high sound power and thus override the sensitive receivers of the passive sound location systems.

For example, from DE-OS 33 00 067 a device for disrupting the location of submarines is known, in which a body can be ejected from a submarine that is equipped with sound-emitting devices. This body is used to mislead a sonar system, ie an active acoustic location system on board an enemy vehicle.

From EP-OS 237 891 a device for disturbing and deceiving waterborne sound locating systems is known. A support body of the known device is provided with pyrotechnic charges, the combustion of which leads to the pulsed release of gas bubbles, which e.g. cause low-frequency structure-borne noise and high-frequency oscillating outer cavitation layers on a housing, from which they also emerge to form a bubble curtain. The known device is intended to distract from an object to be protected and to simulate a reflecting target object due to the slowly floating bubbles.

However, the area of use of such interfering objects is limited to the case that the presence of the submarine on board the enemy ships is known anyway and the only thing that is to be prevented is that the passive sound locating systems enable the precise location of shot torpedoes, which also generate sound in Are movement. Such interference objects are unsuitable for the case in which a submarine wants to remain undetected at all.

A countermeasure against sonar detection and a submarine are known from document US-A-3 891 961. In this case, a generator for sonar signals is provided on board a submarine, which works together with a plurality of sonar sound sources which are arranged on the outer surface of the submarine. The various sound sources are controlled by phase shifters, so that overall there is an interference noise that makes sonar location of the submarine difficult.

The invention is therefore based on the object of developing a method and a submarine of the type mentioned in such a way that the location by passive sound location systems considerably more difficult if not even made impossible by the fact that the amplitude of the signals received by the passive sound locating systems reach the area of natural noise and are lost in it.

According to the method mentioned at the outset, this object is achieved according to the invention in that the movement sequence is modulated by mechanical elements forming the sound source and, consequently, the first frequency spectrum.

According to the submarine mentioned at the outset, the object on which the invention is based is achieved in that means are provided for influencing the mechanical elements in such a way that a first frequency spectrum emitted by the mechanical elements is modulated.

The object underlying the invention is completely achieved in this way.

Modern passive sound locating systems, as already explained above, must first recognize sound signals from searched submarines as such before a localization, ie a determination of the exact position of the submarine, becomes possible. For this purpose, the passive sound locating system must distinguish the sound waves emitted by the submarine from the sound events in the natural environment, which is possible only because the sound signals emitted by the submarine stand out from the ambient sound. When the frequency spectrum is modulated, on the other hand, the radiated sound energy is additionally distributed on sidebands, so that the amplitude of the carrier signal is reduced accordingly and is ultimately lost in the noise of the ambient sound.

The invention also has the advantage that any spectral distribution of the emitted sound signals can be achieved by mechanically influencing the main causative elements in order to achieve the objectives described above.

In a preferred embodiment of the invention, the frequency spectrum is modulated stochastically.

This measure has the advantage that all regularities to which the sound signal obeys are switched off, so that the sound signal can no longer be recognized from the stochastic ambient sound.

These laws are based on the fact that the sound-generating elements are, as a rule, periodically or quasi-periodically operated components of the submarine, for example a drive shaft or drive screw rotating at a predetermined speed. In such a case, the passive sound location system therefore only needs to search for those sound signals in the ambient noise that have a pronounced intensity distribution of the frequency spectrum, because such sound events do not occur in the natural ambient noise.

If, according to the invention, the sound emitted by the submarine is now influenced in such a way that the sound-triggering mechanical processes are robbed of their regularity, the passive sound locating system cannot consequently distinguish these sound signals, which no longer obey the law, from the likewise stochastic sound signals of the environment.

Ideally, this means that no characteristic signals appear, at least, in the frequency spectrum of the ambient sound measured by the passive sound location system However, the intensity of these signals is so reduced, namely in the frequency range that they can no longer be distinguished from the natural irregularities in the spectral distribution of the ambient sound.

In a preferred embodiment of the invention, the movement frequency is modulated in the case of macroscopically moved mechanical elements.

"Macroscopically moved" is to be understood here as meaning those parts which are visibly moved, for example, in the submarine's drive train, for example rotating shafts, engine parts, drive screws and the like. If these macroscopically moved elements are frequency-modulated, this means in the spectral distribution of the radiated elements Sound signals that form a large number of sidebands, the frequency spacing and amplitude of which, as a result of the stochastic modulation, vary constantly according to random factors, so that no regular appearance remains in the emitted sound image. Furthermore, it is particularly advantageous that, in the case of intensive frequency modulation, the radiated power is distributed to the carrier and the sidebands, so that a previously monochromatic signal with a small bandwidth and large amplitude is now converted into a smoothed signal with a large bandwidth and low amplitude . Due to the large number of sidebands in frequency modulation, a spectral distribution with an irregular envelope curve arises, the shape of which fluctuates constantly as a result of the stochastic modulation.

Alternatively, the movement amplitude can also be modulated in the case of macroscopically moved mechanical elements.

With amplitude modulation, as is well known, only two sidebands occur at intervals of the modulation frequency, however, due to the stochastic amplitude modulation, the amplitude and position of the sidebands also varies constantly with this procedure, so that - although to a lesser extent - the advantages of frequency modulation described above also arise .

The method described above can be used advantageously to disguise a wide variety of sound sources, and also to disguise sound sources in the form of land or aircraft of all kinds, but, as already explained at the outset, the method for camouflaging a submerged submarine is particularly preferred to be used, the movement sequence of drive elements of the submarine then preferably being modulated.

This measure has the advantage that the essential sound-generating elements, namely the drive elements, are influenced in such a way that the sound signals emitted by them are obscured in the manner described.

It is particularly preferred if the speed of a drive shaft of the submarine is modulated.

This has the advantage that the essential sound-generating element, namely the drive train of the submarine, is influenced in the manner mentioned, so that a considerable reduction in the radiated total sound power is possible.

In a variant of the method according to the invention, the natural frequency is modulated by self-resonant mechanical elements forming the sound source.

This measure is advantageous if the radiated sound power is not only or at least not essentially generated by the macroscopically moving mechanical elements in the definition explained above, but rather a resonance exaggeration of primary vibration events occurs due to self-resonant mechanical elements. In this case, the sound radiation can be influenced in an advantageous manner by modulating the natural frequency of these resonant elements.

In the preferred application case already described for submersible submersibles, the natural frequency of resonant components of the submarine is then modulated.

This is particularly advantageous because the mechanism described, e.g. for submarines, e.g. can occur in that primary vibration events, for example crews traveling around in the submarine, are converted into sound events by increasing the resonance of resonant components, the amplitude of which can take on considerable dimensions.

Another particularly preferred variant of the method according to the invention is that the sound source is in an environment with external noise, that a second frequency spectrum of the external sound is recorded, that second intensity maxima of the second frequency spectrum are determined and that the first frequency spectrum with its is influenced by influencing the sound source first intensity maximum is shifted to the frequency of one of the second intensity maxima of the second frequency spectrum.

These measures, which can also be used on their own, have the significant additional advantage that the sound source, with its radiated sound power that can no longer be reduced, can "hide" in an intensity maximum of the ambient sound. When analyzing the ambient sound detected by the passive sound locating system, naturally such changes in the spectrum that are isolated are more noticeable, whereas only a variation of a naturally occurring maximum is much more difficult to identify.

This variant of the method according to the invention can also be used with particular advantage for camouflaging a submersible submersible, namely by recording the second frequency spectrum of the sea surrounding the submarine and shifting the frequency of the movement sequence of drive elements of the submarine to the frequency of one of the second intensity maxima.

When using this method, it can be added to the above-mentioned aspects that it is even conceivable to hide the submarine with the maximum of its emitted sound spectrum in the maximum of the ambient sound that is generated by the hostile vehicle itself searching. Since the enemy vehicle, for example the frigate, has to move during the search run, it naturally also emits a sound spectrum which has pronounced maxima. So if the sound-generating elements of the submarine are influenced so that the maximum of the emitted sound spectrum coincides with the maximum of the sound spectrum emitted by the frigate, it is particularly difficult for the passive sound locating system on board the frigate to detect this sound event, because it is natural the frigate drive in the immediate vicinity is a particular disturbance for the passive sound location system.

Of course, with this variant of the method according to the invention, the natural frequency of self-resonant components of the submarine can be changed in such a way that the radiated frequency spectrum is shifted to the maximum of the ambient sound.

According to the submarine according to the invention, a large number of variants of the apparatus configuration are possible in order to achieve additional advantageous effects in solving the problem specified above.

In a preferred embodiment of the submarine according to the invention, an actuating stage can be provided in a supply unit of a drive motor.

This measure has the advantage that e.g. the speed of the drive motor, when using an electric motor can be influenced by varying the supply voltage or supply frequency in order to produce the effects described in detail.

In a further variant, an adjustable clutch can be arranged in a drive train of the submarine. This measure has the advantage that the desired influencing of the sound-generating elements can also be achieved by stochastic opening and closing of the coupling, a coupling being a particularly suitable machine element, since it is intended to separate and close a power flow in a drive train .

In a further preferred variant, auxiliary energy can be fed into a drive train of the submarine depending on the control stage.

This measure has the advantage that the sound-generating events are also influenced in the desired manner by stochastic feeding of the auxiliary energy.

In a practical embodiment of this variant, an auxiliary energy store can be connected to the drive train via an adjustable coupling.

This measure has the advantage that the drive power or a part thereof can alternatively be used for charging the auxiliary energy store by selective closing and opening of clutches and the auxiliary energy store can then be partially or completely discharged again by coupling to the output of the drive train .

In a further variant of the invention, a transmission which is adjustable in the transmission ratio is arranged in a drive train of the submarine.

This machine element, which is known per se, also enables stochastic adjustment of the drive speed in a relatively simple manner.

In another variant of the invention, a resilient transmission element is arranged in a drive train of the submarine, which can be bridged by means of an adjustable coupling.

This measure also has the advantage that the sound waves generated are influenced in the desired manner by stochastically changing the elasticity of the drive train.

The same applies if, in a further embodiment of the invention, a transmission element is arranged in a drive train of the submarine, in which the phase position of a drive movement at the output can be set relative to the drive movement at the input.

In this way, phase modulation of the drive speed can be achieved, which likewise leads to the desired side bands and the distribution of the sound energy.

Furthermore, an embodiment of the invention is preferred in which means are provided for setting an angle of attack of a drive screw of the submarine.

This measure has the advantage that existing components can largely be used anyway, because it is known to vary the drive power of the submarine by adjusting the angle of attack of the drive screw.

In a submarine with a nuclear drive with periodic deflection of control rods of a nuclear reactor, it is particularly preferred if a movement unit for the control rods can be set.

This measure has the advantage that the sound-causing movement of the control rods can also be obscured in the manner described.

Another preferred variant of the invention is characterized in that adjustable mechanical clamping means are arranged on self-resonant elements.

This measure has the advantage that the natural resonance of the elements mentioned can be varied in a simple manner by exerting a mechanical tensile or compressive stress on the elements mentioned in a stochastic manner.

This is possible in a particularly simple manner if the clamping means are piezo elements, because piezo elements are particularly simple voltage / pressure converters, and the natural resonance of the elements mentioned can thus be easily modulated by electrical signals.

The same applies if the natural resonance of the elements is changed in that adjustable mechanical coupling means are arranged between self-resonant elements.

Further advantages result from the description and the attached drawing.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or on their own without departing from the scope of the present invention.

This applies in particular to the two process variants of frequency modulation and frequency shift, which can be used either in combination or individually, depending on the application.

Fig. 1

eine schematisierte Ansicht einer Gefechtslage, bei der eine Fregatte mittels eines passiven Schallortungssystems versucht, ein getauchtes Unterseeboot zu orten;

Fig. 2

eine schematisierte Darstellung der spektralen Verteilung von Schallsignalen über der Frequenz für die Schallereignisse einer natürlichen Meeresumgebung;

Fig. 3

ein periodisches Schallsignal im Zeitbereich;

Fig. 4

die spektrale Verteilung der Fig. 2, jedoch bei gleichzeitigem Auftreten des monochromatischen Schallereignisses gemäß Fig. 3;

Fig. 5

das Schallereignis der Fig. 3, jedoch für den Fall einer periodischen Amplitudenmodulation;

Fig. 6

die spektrale Verteilung der Fig. 4, jedoch für das Schallereignis der Fig. 5;

Fig. 7

das Schallereignis der Fig. 3, jedoch für den Fall einer stochastischen Amplitudenmodulation;

Fig. 8

die spektrale Verteilung der Fig. 2, jedoch in Anwesenheit des Schallsignals gemäß Fig. 7;

Fig. 9

das Schallereignis der Fig. 7, jedoch mit verschobener Trägerfrequenz;

Fig. 10

die spektrale Verteilung der Fig. 8, jedoch für das Schallereignis der Fig. 9;

Fig. 11

ein äußerst schematisiertes Blockschaltbild eines Antriebsstrangs eines Unterseeboots mit stochastisch beeinflußter Stellstufe in.der Stromversorgung eines Elektromotors;

Fig. 12

ein Blockschaltbild ähnlich Fig. 11, jedoch mit stochastisch beeinflußter Trennkupplung im Antriebsstrangs;

Fig. 13

ein Blockschaltbild ähnlich Fig. 11, jedoch mit stochastisch beeinflußter Zuschaltung eines Hilfsenergie-Speichers;

Fig. 14

ein Blockschaltbild ähnlich Fig. 11, jedoch mit stochastisch beeinflußtem Übersetzungsgetriebe;

Fig. 15

ein Blockschaltbild ähnlich Fig. 11, jedoch mit stochastisch beeinflußtem elastischen Übertragungselement;

Fig. 16

ein Blockschaltbild ähnlich Fig. 11, jedoch mit stochastisch beeinflußtem Phasenschieber im Antriebsstrang;

Fig. 17

ein Blockschaltbild ähnlich Fig. 11, jedoch mit stochastisch beeinflußter Anstellung des Neigungswinkels der Antriebsschraube;

Fig. 18

eine schematisierte Darstellung eines Kernreaktors zum Antrieb eines Unterseeboots mit stochastisch beeinflußter Einstellung der Regelstäbe;

Fig. 19

eine schematisierte Darstellung zur Erläuterung einer stochastischen Einstellung einer Eigenfrequenz eines eigenresonanten Feder-Masse-Systems;

Fig. 20

eine Variante zur Anordnung gemäß Fig. 19 mit stochastisch eingestellter Kopplung zwischen zwei eigenresonanten Feder-Masse-Systemen.

Embodiments of the invention are shown in the drawing and are explained in more detail in the following drawing. Show it:

Fig. 1

a schematic view of a combat situation in which a frigate tries to locate a submersible submersible using a passive sound location system;

Fig. 2

a schematic representation of the spectral distribution of sound signals over the frequency for the sound events of a natural marine environment;

Fig. 3

a periodic sound signal in the time domain;

Fig. 4

2, but with the simultaneous occurrence of the monochromatic sound event according to FIG. 3;

Fig. 5

3, but in the case of periodic amplitude modulation;

Fig. 6

4, but for the sound event of FIG. 5;

Fig. 7

3, but for the case of stochastic amplitude modulation;

Fig. 8

the spectral distribution of Figure 2, but in the presence of the sound signal of FIG. 7.

Fig. 9

the sound event of Figure 7, but with a shifted carrier frequency.

Fig. 10

the spectral distribution of FIG. 8, but for the sound event of FIG. 9;

Fig. 11

an extremely schematic block diagram of a drive train of a submarine with stochastically influenced control stage in the power supply of an electric motor;

Fig. 12

a block diagram similar to Figure 11, but with stochastically influenced clutch in the drive train.

Fig. 13

a block diagram similar to Figure 11, but with stochastically influenced connection of an auxiliary energy store.

Fig. 14

a block diagram similar to Figure 11, but with stochastically influenced transmission gear.

Fig. 15

a block diagram similar to Figure 11, but with stochastically influenced elastic transmission element.

Fig. 16

a block diagram similar to Figure 11, but with stochastically influenced phase shifter in the drive train.

Fig. 17

a block diagram similar to Figure 11, but with stochastically influenced adjustment of the angle of inclination of the drive screw.

Fig. 18

a schematic representation of a nuclear reactor for driving a submarine with stochastically influenced setting of the control rods;

Fig. 19

a schematic representation for explaining a stochastic setting of a natural frequency of a self-resonant spring-mass system;

Fig. 20

a variant of the arrangement of FIG. 19 with stochastically set coupling between two resonant spring-mass systems.

In the combat situation shown in FIG. 1, 10 denotes a sea on which a frigate 11 is located in search of submarines.

Below a water line 12 of the frigate 11, the frigate 11 is provided with a passive sound location system 13, which has an opening cone 14, for example. The frigate 11 in turn generates sound waves 15, in particular by driving the frigate 11.

Below the surface of the sea 10 is a submarine 20 with a nuclear drive 21, not drawn to scale, with 22 is a drive shaft of the submarine 20, which leads to a screw 23. With 24, 25 and 26 sound waves are referred to, which are emitted from the submarine 20.

24 is intended to symbolize the proportion of sound waves that is generated by the movement device of the control rods of the nuclear drive 21, as will be explained further below in relation to FIG. 18.

25 is intended to symbolize the proportion of sound waves that are generated by the drive elements of submarine 20, in particular by the rotating shaft, the rotating motor elements and the like.

Finally, 26 is intended to symbolize the portion of the sound waves that is generated by the rotation of the screw 23, in particular by the cavitations caused by the screw 23.

The submarine 20 in turn is also equipped with a passive sound location system 27 which sweeps over a cone 28.

A passive sound location system is to be understood below to mean any device that is able to receive and analyze sound signals.

2, the intensity of a sound signal S is plotted as the first frequency spectrum 30 over the frequency f. The first frequency spectrum 30 is intended to represent the natural environment in the absence of artificial sound sources. The first frequency spectrum 30, as can be seen at f 1, is provided with a first maximum 31, which is generated by natural environmental influences, for example by a swell associated with a specific wind strength.

It is understood that in the context of the present invention, the frequencies of interest are in the sound or infrasound range.

3 shows in the time domain t a first sound signal 32 of a sinusoidal, ie periodic shape, which is intended to symbolize a sound signal US emitted by a submarine. The frequency of the first sound signal 32 can for example correspond to the speed of the shaft 22. For the sake of clarity, harmonics and other phenomena are not taken into account in the representation of FIG. 3 and the following figures.

If the submarine 20 now comes into the area of the cone 14 of the passive sound location system 13 of the frigate 11, then a superimposed, pronounced second frequency spectrum 33 appears in the first frequency spectrum 30, which in the idealized case of the monochromatic sound event of the first sound signal 32 of FIG. 3 is high narrow line at a frequency f₂ corresponds to the wave.

As can be clearly seen from FIG. 4, the second frequency spectrum 33 in the form of the narrow line can be clearly distinguished from the background of the first frequency spectrum 30.

FIG. 5 now shows the case in which the first sound signal 32a is periodically amplitude-modulated, as illustrated with a periodic envelope 34 in FIG. 5. As is known, sidebands arise from an amplitude modulation at a distance from the modulation frequency to the carrier, which is shown in FIG. 6 in the first frequency spectrum 30 by a superimposed second frequency spectrum 33a, which now has sidebands 35. The amplitude of the carrier is significantly reduced compared to the unmodulated case in FIG. 4 because the sound power is now distributed over the carrier and the two side bands. However, the second frequency spectrum 33 can still be clearly distinguished from the background of the first frequency spectrum 30.

FIG. 7 now shows a further step in which the first sound signal 32b is stochastically amplitude modulated, which is indicated by a stochastic envelope 36.

"Stochastic" should be understood to mean any procedure that is generated by a random generator or otherwise and is not subject to any regularities.

The stochastic amplitude modulation of the first sound signal 32b manifests itself in the spectral representation of FIG. 8 in a second frequency spectrum 33b, which is now greatly broadened and the amplitude is correspondingly reduced because the radiated sound power is now distributed over a wide frequency range.

As can be clearly seen from FIG. 8, the distinction of the second frequency spectrum 33b from the surroundings of the first frequency spectrum 30 is already quite difficult and is only possible if the undisturbed first frequency spectrum 30 according to FIG. 2 was considered and now for the frequency f₂ suddenly an increase in amplitude occurs.

FIG. 9 now shows that, with unchanged stochastically amplitude-modulated first sound signal 32c, its frequency has now been increased in such a way that the carrier frequency coincides with the frequency fi of the first maximum 31.

This is expressed in the frequency range of FIG. 10 by the fact that the first maximum 31 was only slightly increased by the second frequency spectrum 33c. However, there is no fundamental change in the shape of the first frequency spectrum 30 because, as in the previous case in FIG. 8, it is not at a position at which there was no maximum before. a maximum occurs, but because only an existing maximum is only slightly increased in its amplitude.

It is obvious that this slight change in the first frequency spectrum 30 is particularly difficult, if at all, to be recognized.

FIG. 11 shows a drive train of submarine 20 in an extremely schematic block diagram.

A drive screw 40 is driven by an electric motor 41, which in turn is fed from batteries 44 via a thyristor stage 42. The thyristor stage 42 is controlled by an actuating stage 43, which allows the speed of the electric motor 41 to either vary stochastically or to be shifted from a first value to a second value, as is the case with the shift from f 2 to f 1 in FIG. 10 was explained.

If one considers the electric motor 41 in FIG. 11 as a structure with monochromatic sound generation, it can easily be seen that a frequency shift or frequency modulation of the speed n can be achieved by means of the setting stage 43, so that the situation arises as it is shown in FIG 2 to 10 for the case of amplitude modulation.

FIGS. 12 to 17 show variants of the block diagram according to FIG. 11, with elements that match are identified by the same reference numerals, but with the addition of a small letter.

12 shows a first variant in which a first clutch 45 is arranged between the electric motor 41a and the drive screw 40a.

The control stage 43a controls the first clutch 45 in this case.

By opening and closing the first clutch 45, the speed of the drive screw 40a can be pulse-modulated, so that the desired sidebands are also set and, in the case of stochastic pulse modulation, the desired stochastic distribution of the sidebands.

In the further variant shown in FIG. 13, in addition to the first clutch 45b, a second clutch 46 is arranged, by means of which a flywheel 47 or another kinetic energy store can be shifted into the drive train via a summation gear, which is only indicated at 48.

The clutches 45b, 46 are actuated by the actuating stage 43b, so that by selectively opening and closing these clutches 45b, 46 either the electric motor 41b works on the drive screw 40b as well as on the flywheel 47 when the clutches 45b and 46 are closed, or when the first one is open Clutch 45b and the second clutch 46 closed, only the flywheel 47 operates on the drive screw 40b or, when the first clutch 45b is closed and the second clutch 46 is open, only the electric motor 41b drives the drive screw 40b.

Modulation of the drive speed and thus of the sound-generating drive elements is also possible in this way.

In the next variant of FIG. 14, a continuously variable transmission 49 is connected between the electric motor 41c and the drive screw 40c. The control stage 43c controls the stepless Gear 49 on, so that the transmission ratio is varied stochastically, which likewise leads to a stochastic variation in the speed of the drive screw 40c.

In the further variant of FIG. 15, an elastic transmission element 51 is arranged between the electric motor 41d and the drive screw 40d and can be bridged by means of a third coupling 50. The third clutch 50 is controlled by the actuating stage 43d.

When the third clutch 50 is open, the drive train is relatively soft due to the now switched-on elastic transmission element 51, while when the third clutch 50 is closed, the drive train is correspondingly stiff. The desired effect can also be achieved by stochastically switching back and forth between these two states.

In the further variant of FIG. 16, a differential 42 is connected between the electric motor 41e and the drive screw 40e, in which the two bevel gears located directly in the drive train rotate at the same speed, but in opposite directions, while the third bevel gear arranged at right angles to it in a plane perpendicular to the drawing plane of FIG. 16 about the axis of the drive train. This pivoting movement creates a phase shift between the rotary movement at the input and at the output of the differential 52. The control stage 43e now stochastically adjusts the third bevel gear in this plane, so that the drive of the drive screw 40e is phase-modulated.

In the variant of FIG. 17, an actuation unit 53 is finally provided for the angle of attack 54 of the drive screw 40f and the actuation unit 53 is controlled by the actuating stage 43f.

In this case, the angle of attack 54 is modulated stochastically, which also leads to the formation of side bands.

18 schematically shows a nuclear reactor 60 which is part of the nuclear drive 21 of the submarine 20.

The nuclear reactor 60 has a reactor vessel 61 in which, in a known manner, control rods 62 can be moved axially by means of an actuating unit 63 in order to be able to adjust the power output by the nuclear reactor 60.

The actuating unit 63 is acted upon stochastically by the setting stage 43e, so that the control rods 62 are displaced axially in a random manner in the reactor vessel 61. It is understood that the arrangement can be made such that the time integral of the immersed state of the control rods 62 is nevertheless e.g. can be kept constant in order to keep the output of the nuclear reactor 60 constant.

While the exemplary embodiments described above with reference to FIGS. 11 to 18 all affected the movement sequence of macroscopically moving elements on board a submarine, FIGS. 19 and 20 show extremely schematically situations in which the natural frequency is not the movement sequence but rather the natural frequency is influenced by resonant elements.

In FIG. 19, 70, 71 denote two fixed points, for example opposite walls of the outer shell of submarine 20 or a cabin on board submarine 20. A mass 72 is connected to the fixed points 70, 71 via springs 73 and 74. The mass 72 can, for example, a command post or symbolize a walk in submarine 20 that is undertaken by teams of submarine 20. The aisle or command post, symbolized by the mass 72, is, however, capable of resonance due to the resilient suspension, so that an oscillation can be emitted to the fixed points 70, 71 by the walking movement of teams as a result of the system's resonance increase.

In order to be able to influence the natural resonance of the system shown in FIG. 19, the coupling of the spring 74 to the second spatially fixed point 71 is interrupted by a piezo element 75 which is acted upon by the actuating stage 43h.

In this way, the rigidity of the system shown in FIG. 19 and thus its natural resonance can be influenced. This means that if the system excitation remains unchanged, e.g. by walking teams, the frequency of the emitted sound signal is shifted with the natural resonance.

20 shows a variant of this, in which a second mass 80 is additionally provided, so that two vibratory structures 72/73 and 74/80 are arranged between the fixed points 70, 71. The piezo element 75i in this case symbolizes the coupling between the two vibratory systems 72/73 and 74/80 and is acted upon by the actuating stage 43i.

By varying the coupling, the natural resonance of the overall system is also influenced in this case, so that the effect described above is achieved.

The present application is related to the following applications by the same applicant on the same day, and the disclosure content of those applications is also made the disclosure content of the present application by this reference:
European patent application 90 904 233.5
"Method and device for reducing the noise emission of submarines submerged"
European patent application 90 904 239.2
"Method and device for locating proton-poor objects in a water-containing environment, in particular for locating submarines or marine mines in a sea or inland water"
European patent application 90 904 231.9
"Underwater vehicle with a passive optical observation system"
European patent application 90 904 238.4
"Procedure for Operating Submersible and Submersible"
European patent application 90 904 237.6
"Method and device for reducing the noise emission of submarines submerged"
German patent application P 39 08 573.2
"Method and device for operating submerged submarines"

Claims (21)

1. Process for masking the noise signals emitted by the sound-emitting mechanical elements of a vehicle, in particular of a submerged submarine (20), wherein the mechanical elements emit a noise signal (S; 24, 25, 26) with a first frequency spectrum (33) having at least a first intensity maximum, characterized in that the motions of the mechanical elements being the noise source and, hence, the first frequency spectrum (33) are modulated.
2. The process of claim 1, characterized in that the frequency spectrum (33) is modulated stochastically.
3. The process of claim 1 or 2, characterized in that the motion frequency (f) of macroscopically moved mechanical elements is modulated.
4. The process of claim 1 or 2, characterized in that the motion amplitude of macroscopically moved mechanical elements is modulated.
5. The process of one or more of claims 1 through 4, characterized in that for masking the submerged submarine (20) the motions of propulsion elements of the submarine (20) are modulated.
6. The process of one or more of claims 1 through 5, characterized in that the natural frequency of self-resonant mechanical elements being the noise source, is modulated.
7. The process of one or more of claims 1 through 6, characterized in that the noise source is situated within an environment of foreign noise, that a second frequency spectrum (30) of the foreign noise is recorded, that second intensity maxima (31) of the second noise spectrum (30) are determined and that by influencing the noise source the second frequency spectrum with its first intensity maximum is shifted to the frequency (f₁) of one of the second intensity maxima (31) of the second frequency spectrum (30).
8. The method of claim 7, characterized in that for masking a submerged submarine (20) the second frequency spectrum (30) of the sea (10) surrounding the submarine (20) is recorded and that the frequency (f₂) of the motions of propulsion elements of the submarine (20) is shifted on the frequency (f₁) of one of the second intensity maxima (31).
9. The process of claim 7, characterized in that for masking a submerged submarine (20) the second frequency spectrum (30) of the sea (10) surrounding the submarine (20) is recorded and that the natural frequency of self-resonant components of the submarine (20) is shifted to the frequency (f₁) of one of the second intensity maxima (31).
10. Submarine having noise-emitting mechanical elements (21, 22, 23) and means for masking emitted noise signals (S), characterized in that means are provided for influencing the mechanical elements (21, 22, 23) such that a first freqency spectrum (33) emitted from the mechanical elements (21, 22, 23) is modulated.
11. The submarine of claim 10, characterized in that the first frequency spectrum (33) is modulated stochastically.
12. The submarine, in particular of claims 10 or 11, characterized in that the means for influencing the mechanical elements (21, 22, 23) shift the first frequency spectrum (33) in its frequency position (f₂).
13. The submarine of claim 12, characterized in that the mechanical elements (21, 22, 23) are moving propulsion elements of the submarine (20) and that means are provided in the propulsion system to set the motion frequency of the propulsion elements.
14. The submarine of claim 13, characterized in that an adjustable clutch (45, 45b) is provided in a drive chain of the submarine (20).
15. The submarine of claim 13, characterized in that auxiliary energy may be fed into a drive chain of the submarine (20) depending on a control stage (43b).
16. The submarine of one or more of claims 13 through 15, characterized in that a transmission (49) having a variable transmission ratio (ü) is provided in a drive chain of the submarine (20).
17. The submarine of one or more of claims 13 through 18, characterized in that a resilient transmission element is provided in a drive chain of the submarine (20), the element being adapted to be bridged by means of an adjustable clutch (50).
18. The submarine of one or more of claims 13 through 17, characterized in that a transmission element (52) is provided in a drive chain of the submarine, enabling to adjust the phase of a propulsion motion at its output relatively to a drive movement at its input.
19. The submarine or one or more of claims 13 through 18, characterized in that means are provided for adjusting a pitch angle of a drive propeller (40f) of the submarine (20).
20. The submarine of one or more of claims 13 through 19, characterized in that a nuclear propulsion system (21) is provided comprising a periodical displacement of control rods (62) of a nuclear reactor (60) wherein a drive-unit (63) for the control rods (62) is adjustable.
21. The submarine of one or more of claims 10 through 20, characterized in that adjustable mechanical tension elements are provided on self-resonant elements (72, 73, 74).

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