EP0417225B1 - Process and device for reducing the noise emission of submerged submarines - Google Patents

Abstract

A process and a device are useful for reducing the noise emission of submerged submarines (20). Agitated mechanical elements in the interior send vibrations along a transmission path to an outer casing (30) and the vibrations are damped on the transmission path. In order to decouple the outer casing (30) as completely as possible from the agitated mechanical elements, for example periodically agitated control rods (38) of a nuclear reactor (37), the motion of the mechanical elements relative to the outer casing is recorded and a counter motion is superimposed on the motion in order to actively damp the vibrations. To this end, the position of the element relative to the outer casing (30) is detected by a detector (50) and adjusted by a translator (51).

Description

The invention relates to a method for reducing the noise emission of submarines submerged, in which mechanical elements moving in the interior emit vibrations to an outer shell on a transmission path and the vibrations are damped on the transmission path.

The invention further relates to a device for reducing the noise emission of submarines submerged, in which damping means are arranged between a mechanical element moved in the interior of the submarine and an outer shell.

The invention is intended in particular to camouflage the submarines.

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 recognizability 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. First and foremost, measurable sound signals are generated by moving propulsion elements of the submarine, i.e. by the rotating parts of the propulsion motor 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.

Furthermore, in the sense of the method and the device of the type mentioned at the outset, 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. The dampers used for this are known elastic and vibration-absorbing components which, together with the mechanical elements to be damped, form a spring-mass system. Such known measures are referred to in the context of the present invention as "passive damping". It is known, for example, to design the outer shell of the submarine in two layers 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 alternating current network of the submarine operates in the frequency range between 60 Hz and 400 Hz and that it is inevitable that frequencies in this frequency range plus their harmonics are emitted to the surrounding water via the hull. 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 is. 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 device for reducing noise and vibrations is known from document GB-A-2 122 052. In the known device, transducers are arranged at mutually spaced locations on a machine, which generates noise and vibration when rotating. The signals measured in this way are processed and passed to inductors, which are arranged at the same locations on the machine and generate counter-noise or vibrations in order to effect compensation.

A predetermined transfer function is used in signal processing.

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 is made considerably more difficult, if not impossible, by passive sound locating systems that the amplitude of the signals received by the passive sound locating systems is in the range of natural noise and get lost in it.

According to the method mentioned in the introduction, this object is achieved in that the vibrations are actively damped in that the movement of the mechanical elements relative to the outer shell is detected by means of a detector and that the movement is superimposed on the movement by means of a translator, the detector and the translator is arranged in series in a transmission path between the element and the outer shell.

According to the device mentioned at the outset, the object on which the invention is based is achieved in that the damping means have a detector for detecting and a translator for adjusting the relative position of the element to the outer shell, and a controller is connected between an output of the detector and an input of the translator , such that when the relative position changes, the translator adjusts the relative position in the opposite direction, and that the detector and the translator are arranged in series in a transmission path between the element and the outer shell.

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

The fact that the relative movements associated with the vibrations between the elements and the outer shell are compensated for by opposing superimposition of a second movement, the submarine is ideally at rest when viewed from the outside, so that the sea water surrounding it emitted vibrations suppressed, but at least be significantly reduced in their sound power. The sound signals emitted by the submarine are reduced so much that they are lost in the noise generated by the natural ambient sound in a passive location system of an enemy vehicle.

The invention also has the advantage that there is an exact match in the spatial position of the disturbance variable, namely the movement associated with the oscillation, and in the manipulated variable, namely the counter-movement generated by the translator, so that the disturbance variable exactly according to amplitude, direction and phase position can be compensated.

In a further preferred embodiment of the device according to the invention, the detector is a sensor for detecting the force which is exerted on the outer shell by the seismic mass of the element as a result of the acceleration causing the movement.

This measure has the advantage that even the slightest deflections, such as those that occur in the propagation of sound in the components of a submarine, can be reliably detected, which is only possible with considerable effort with other position sensors.

In further preferred configurations of the device according to the invention, both the detector and the translator have a piezo element.

This measure has the advantage that, on the one hand, the forces corresponding to the disruptive oscillating movement are converted into an electrical signal and, on the other hand, a counter-movement can be generated in the translator from an electrical control signal. When using similar piezo elements in the detector and in the translator, one can also take advantage of the fact that both piezo elements are the same Environmental conditions, for example the same temperature, are exposed so that corresponding effects compensate.

Finally, an embodiment of a device according to the invention is particularly preferred, in which the outer casing is connected to an inner casing receiving the moving elements via at least three supports and the supports each have at least one detector and one translator.

This measure has the advantage that all vibration-generating elements, namely the moving mechanical elements, are arranged in the closed interior, which is enclosed by the inner shell. All sound events that can propagate to the outer shell must therefore make their way through the inner shell and can essentially only be transmitted to the outer shell via the supports. However, since the previously described active damping measures are provided in the supports, the outer shell is effectively shielded from all kinds of sound events that are triggered by the moving mechanical 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.

Fig. 1

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

Fig. 2

einen äußerst schematisierten Längsschnitt durch ein Unterseeboot in Höhe eines kerntechnischen Antriebes an Bord desselben;

Fig. 3

einen stark vergrößerten Ausschnitt aus Fig. 2 zur Erläuterung einer erfindungsgemäß verwendeten aktiv gedämpften Stütze;

Fig. 4

ein Diagramm, einen Frequenzgang der aktiven Dämpfung der Stütze gemäß Fig. 3 darstellend;

Fig. 5

ein weiteres Ausführungsbeispiel einer aktiv dämpfenden Stütze.

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description. 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

an extremely schematic longitudinal section through a submarine at the level of a nuclear drive on board the same;

Fig. 3

a greatly enlarged detail of Figure 2 to explain an actively damped support used according to the invention.

Fig. 4

a diagram showing a frequency response of the active damping of the support according to FIG. 3;

Fig. 5

another embodiment of an actively damping support.

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. 2.

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.

In order to reduce the sound radiation of the submarine 20 according to the amplitude, active damping measures are taken on board the submarine according to the invention, as will be explained below.

FIG. 2 shows a radial section through the submarine 20 according to FIG. 1, namely at the level of the nuclear drive 21.

It can be seen that the submarine 20 is provided with an outer shell 30 which surrounds an inner shell 31 on all sides. The inner shell 31 is supported in the outer shell 30 by means of four actively damped supports 32 to 35 distributed over the circumference of the inner shell 31. It goes without saying that the supports 32 to 35 can be arranged discretely over the length of the submarine 20. The supports 32 to 35 can also be arranged obliquely to a radius instead of in the radial direction, as shown in FIG. 2, and it is also conceivable that instead of four, each 90 ° over the circumference of the inner shell 31 offset supports 32 to 35, three such supports or more than four supports can be used without departing from the scope of the present invention.

A nuclear reactor 37 is arranged on a base 36 in the inner shell 31. The nuclear reactor 37 is of a conventional type and has control rods 38 which can be moved into and out of a reactor vessel by means of a control rod drive 39 in the direction of an arrow 40. In nuclear reactors 37 of the type of interest here, as are used on board submarines 20, the usual procedure is to immerse the control rods 38 in the reactor vessel in a periodic movement, the power emitted by the nuclear reactor 37 being determined by amplitude modulation, i.e. is adjusted by varying the immersion depth of the control rods 38.

This means that due to the periodic movement of the control rods 38 indicated by the arrow 40, an oscillation is generated which is transmitted from the nuclear reactor 37 to the floor 36. This is indicated in FIG. 2 by a further arrow 41. Since the bottom 36 is in turn firmly anchored in the inner shell 31, this also vibrates, as indicated by a further arrow 42 in FIG. 2.

In the manner described above, a transmission path is thus formed from the periodically moved control rods 38 to the inner shell 31, with the additional possibility that resonance peaks 20 occur due to natural resonances of the components of the submarine excited in the transmission path.

In order to prevent further transmission of these vibrations to the outer shell 30 or at least to dampen them considerably, the supports 32 to 35 are equipped as active damping elements. For this purpose, a detector 50 and a translator 51 are arranged in series in each of the supports 32 to 35, the detector 50 being located on the outer shell 30 in each case.

“Detector” should be understood to mean any element that is able to determine a relative movement of a moving mechanical element, in this case the inner shell 31, relative to the outer shell 30. For this purpose, pressure sensors, but also displacement sensors, e.g. Interferometer or the like can be used.

"Translator", on the other hand, is to be understood to mean any device which allows a specific actuating movement to be generated as a function of an actuating signal.

The detector 50 and the translator 51 can again be seen in the enlarged illustration in FIG. 3, and it can be clearly seen that both the detector 50 and the translator 51 each have a piezo element 52 and 53, respectively. The piezo detector element 52 is connected to an input 54 of a control amplifier 55, the output 56 of which is connected to the piezo translator element 53.

If the inner shell 31 is now deflected by some mechanical movement in its interior, as was explained further above with the aid of arrows 40 to 42, the inner shell 31 experiences a deflection in the axial direction of the support 34, which in FIG. 3 has the complex size x is marked.

With a mass m₁ the outer shell 30 is now due to the movement e.g. the acceleration causing the outer shell 30 exerts a force on the detector 50, so that the piezo detector element 52 outputs a complex electrical signal to the input 54 of the control amplifier 55. Depending on the gain, the frequency response and the control characteristic of the control amplifier 55, this generates an electrical signal at its output 56, which is fed to the piezo translator element 53. The translator 51 thereby becomes one of the movements y opposite movement is excited, so that in Fig. 3 with the complex size e.g. characterized movement of the outer shell 30 is made zero or at least largely minimized.

Fig. 4 shows the frequency response of the transmission, ie the ratio of the amounts of e.g. and x versus frequency f for a particular configuration of the elements involved. In Fig. 4, the formula for the transmission is given, where m₁ has already been defined as the mass of the inner shell 31 and the components of the submarine 20 arranged therein. The quotient (∂P / ∂l) _D denotes the rigidity of the detector 50, the quotient (∂P / ∂l) _T denotes the rigidity of the translator 57, the quotient (∂l / ∂U) denotes the sensitivity of the translator 51, the quotient (∂Q / ∂P) denotes the sensitivity of the detector 50, R₂ is the internal resistance of the detector 50, Z₂ is the capacitance of detector 50 and the complex size G finally represents the complex gain of the control amplifier 55.

For a practical application there is the curve 60 drawn in FIG. 4, which shows an amount 1 of transmission for very low frequencies, but then drops steeply with an intermediate stage, so that above a cut-off frequency f 1 a continuously increasing attenuation of x across from e.g. takes place.

For comparison, a curve 61 is shown in broken lines in FIG. 4, in which the same arrangement was calculated with passive damping. Passive damping is to be understood to mean suspensions and the like. It can clearly be seen that the amount of transmission in the case of curve 61 assumes the amount 1 for several orders of magnitude of the logarithmically plotted frequency f, then first passes into the natural resonance characteristic of passively damped systems and only then drops to amounts less than 1 only at very high frequencies of more than 6 orders of magnitude above the cut-off frequency f 1 to assume the same damping behavior as the active damping system.

The gain of the active damping (curve 60) used according to the invention over conventional passive damping (curve 61) is evident from the region 62 in between, which is hatched in FIG. 4.

By suitable dimensioning of the elements involved, in particular in the area of the supports 32 to 35 and the control amplifier 55, it can be achieved that the area 62 corresponds to the frequency range of conventional moving units on board a submarine, in particular, therefore, to the speeds the drive elements of the submarine as well as heavy auxiliary units.

5 shows a variant with a fluidic damping element.

In FIG. 5, 70 denotes a first oscillation of larger amplitude, e.g. the vibration of the inner shell 31. This vibration is transmitted via a first rod symbolized by 71 to a cylinder 72 in which a piston 73 runs. A pressure chamber 74 is then located between the piston 73 and the cylinder 72. The piston 73 is in turn connected to a second rod 75 which transmits a second vibration 76 of significantly reduced amplitude or even amplitude compensated to zero, e.g. to the outer shell 30.

A pressure line 77 is connected to the pressure chamber 74 and leads to an adjustable pressure source 78. A pressure sensor 79 is also arranged in the pressure chamber 74 and reproduces a signal to a controller 80 corresponding to the pressure prevailing in the pressure chamber 74. The controller 80 in turn controls the pressure source 78, for example a pump.

Also in this case of the fluidic, for example pneumatic or hydraulic damping element, when the first rod 71 is deflected in one direction, an opposite movement of the second rod 75 is achieved by suitable measurement of the pressure in the pressure chamber 74 and by adjustment of this pressure by means of the adjustable pressure source 78, such as no further explanation is required.

5, a formula for the transmission can be determined using equivalent circuit diagrams, which corresponds to the formula shown in FIG. 4 for the case of active damping with piezo elements and the frequency response of the arrangement according to FIG. 5 also corresponds to that 4.

Claims (6)

1. A method for reducing acoustic emission of submerged submarines (20), in which, in an inner space, moving mechanical elements transmit vibrations to an outer hull (30) via a propagation path and the vibrations are damped in the propagation path, characterized in that the vibrations are actively damped in that the movement of the mechanical elements relative to the outer hull (30) is detected by means of a detector (50), and that the movement is superimposed with an oppositely directed movement by means of a translator (51), the detector (50) and the translator (51) being arranged in series in a propagation path between the element and the outer hull (30).
2. An apparatus for reducing acoustic emission of submerged submarines (20) in which damping means are arranged between a moving mechanical element in an inner space of the submarine (20) and an outer hull (30), characterized in that the damping means comprise a detector (50) to detect as well as a translator (51) to adjust the relative position of the element with respect to the outer hull (30), and that a controller (55) is switched between an output of the detector (50) and input of the translator (51) such that in case of a change of the relative position the translator (51) adjusts the relative position in the opposite direction, and that the detector (50) and the translator (51) are arranged in series in a propagation path between the element and the outer hull.
3. The apparatus of claim 2, characterized in that the detector (50) is a sensor for detecting the force being excerted on the outer hull (30) by the seismic mass of the element as a consequence of the movement-causing acceleration.
4. The apparatus of claim 3, characterized in that the detector (50) comprises a piezo-element.
5. The apparatus of one or more of claims 2 through 4, characterized in that the translator (51) comprises a piezo-element.
6. The apparatus of one or more of claims 2 through 5, characterized in that the outer hull (30) is connected via at least three supports (32, 33, 34, 35) to an inner hull (31), the inner hull (31) receiving the moving elements, and that the supports (32, 33, 34, 35) are each provided with at least one detector (50) and one translator (51).

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