EP0274685A2 - Cover for a hydrophone system - Google Patents

Abstract

Covers are a mechanical and acoustic protection for a hydrophone system. Shaping and choice of material reduces flow noise, prevents cavitation and achieves acoustic transparency for water-borne noise. The new cover is intended at the same time to prevent radiation of interference noise which is produced by the structure-borne noise of the support vessel and transmitted to the cover. The wall of the cover is a laminated composite consisting of one or more dimensionally stable layers as supporting element and damping layers for flexural waves on top of and inbetween them. Material choice and dimensioning achieves the acoustic transparency for water-borne noise. Bow and keel domes and also lateral covers can be produced with such a laminated composite. <IMAGE>

Description

The invention relates to an envelope for a hydrophone arrangement of the type mentioned in the preamble of claim 1.

In waterborne sound engineering, hydrophone arrangements are used to transmit and receive sound waves. The hydrophone arrangement has, for example, the shape of a cylinder base or a flat base and is on the outer wall of a carrier vehicle, for. B. a surface ship or submarine attached. An envelope for the hydrophone arrangement is also mounted on the outer wall of the carrier vehicle and forms its outer end. For better acoustic coupling of the hydrophone arrangement to the surrounding water, via which the sound waves are transmitted during transmission and / or reception, the envelope is filled or flooded with water.

The enveloping body provides mechanical protection for the hydrophone arrangement and, thanks to its streamlined structure, at the same time provides acoustic protection against flow noises that occur when the vehicle is moving, since even then no water flow occurs on the hydrophone arrangement. Even at high speed levels, the risk of Cavitation can be reduced by appropriate shaping of the enveloping body.

In order for the hydrophone arrangement to receive undisturbed sound waves that are emitted by other watercraft, it is desirable that the enveloping body neither reflect nor dampen incident sound waves. It is known to produce envelopes made of rubber, since such a material has an acoustic wave resistance which is approximately equal to that of the water surrounding it. Due to the small jump in impedance on the outer surface of the envelope, transmission loss and reflection factor for incoming sound waves are low. Due to the low strength of rubber against mechanical deformation, however, a very high level of design effort must be made in order to obtain a dimensionally stable envelope body with good acoustic properties. For example, steel cables are used as a framework for a spherical shape, which are surrounded by a rubber jacket. Such an envelope is filled with water and pressurized.

Envelopes made of glass fiber reinforced plastic (GRP) are less expensive to construct and manufacture. Its layer thickness is dimensioned according to the static and dynamic loads. Such an envelope is given for example in DE-OS 31 50 456, it can be built for hydrophone arrangements, which are designed for transmitting and / or receiving sound waves in the frequency range up to 100 kHz, with sufficient rigidity, without the acoustic transparency of the Envelope is lost. However, such an envelope can be caused by external mechanical influences, such as structure-borne noise in the outer skin of the carrier vehicle or turbulence in the flow of the water surrounding it are excited to bending vibrations, which are emitted by the envelope and received by the hydrophone arrangement as a disturbing sound.

The invention has for its object to provide an enveloping body of the type mentioned, which in addition to a good acoustic adaptation to the water prevents transmission of noise to the hydrophone arrangement.

The object is achieved according to the invention in an enveloping body of the type specified in the preamble of claim 1 by the features in the characterizing part of claim 1.

The envelope body according to the invention has at least one dimensionally stable layer as a supporting element, which indicates the contour of the envelope body. The dimensionally stable layer can form, for example, the inner closing layer of the enveloping body, to which a damping layer for bending shafts is applied, or can be coated with damping layers on both sides or form the outer closing layer of the enveloping body. Damping layer and dimensionally stable layer are intimately connected, they alternate and form a layer composite. A suitable radiation selection of the layer composite for incident sound waves is achieved by appropriate choice of material.

The advantage of the enveloping body according to the invention lies in its property of preventing radiation from bending waves impressed by structure-borne noise. The casing and hydrophone arrangement are usually attached to a carrier vehicle. Even when the enveloping body is fastened, for example in a steel construction, to the outer wall of the carrier vehicle by means of vibrating metals, it cannot be ruled out that the enveloping body broadband is excited to bending vibrations by structure-borne noise in the outer wall. This structure-borne noise is generated by drive units and other rotating machines that are installed on the carrier vehicle.

In the case of the enveloping body according to the invention, however, each damping layer on or between dimensionally stable layers of the layer composite converts the bending waves coupled in by structure-borne noise into deformation and / or thermal energy and ensures that, despite the rigid structure, no bending vibrations are transmitted from the enveloping body to the hydrophone arrangement as disturbing noise.

The dimensionally stable layer and the damping layer can each be constructed from composite materials in order to meet requirements with regard to strength, acoustic transparency for water sound and damping behavior for bending waves. It is particularly advantageous if the acoustic wave resistance of the layer composite is equal to that of water, that is to say the total of the product of the specific density ρ₀ and sound propagation speed c₀ of the water.

The acoustic wave resistance of several layers can be calculated with the aid of an equation system, as is the case for layers of different materials in "The Fundamentals of Acoustics" by Skudrzik, Springer-Verlag, 1954, Vienna, on page 519 in Chapter 7 "Several λ / 4- or layered in series λ / 2 layers "is described.

The development according to the invention of the enveloping body according to claim 2 offers the advantage that the enveloping body is protected against interference from the outside by the damping layer which closes outwards. in particular turbulence in the flow and impacts that are not even transferred to the dimensionally stable layer, but are immediately consumed by the damping layer.

The development of the enveloping body according to claim 3 is particularly advantageous, since in the case of a division of an overall thickness for the dimensionally stable, load-bearing layer, individual layer thicknesses can be used in the layer composite in accordance with the static and hydrodynamic loads on the enveloping body, each of which is considerably smaller than a smallest wavelength of the hydrophone arrangement received sound waves. Such a layer composite is more resistant to bending than a single plate with the total thickness, since the layer moment of inertia is increased by the layer division, so that high strength is possible with less use of material. Another advantage is that the acoustic transparency of the composite system is guaranteed for a wide frequency range by low layer thicknesses. The distribution of the total thickness also has the advantage that thin damping layers in between prevent the spreading and transmission of bending waves from layer to layer. This effect is further increased if, according to claim 4, the layer thicknesses of the dimensionally stable layers are different, since bending waves of the same frequency spread at different speeds depending on the layer thickness and thus unequal forces act on the upper and lower limits of the damping layer.

The production of an enveloping body according to the embodiment in claim 5 is particularly simple, and it is advantageous to use materials for the dimensionally stable layers with a specific density and sound propagation speed to choose, whose acoustic wave resistance is greater than that of water. This opens up a large product range, in which it has been found to be particularly advantageous to use composite materials according to claims 6 and 7, in which, with great dimensional rigidity, great freedom in the choice of material for the damping layer is retained, since their acoustic impedance is of the order of magnitude of that of water, the acoustic transparency of the layer composite being further improved by the use of carbon fiber-reinforced plastics.

The embodiment of the enveloping body according to claim 8 is easy to manufacture. It is particularly advantageous to build up the damping layers according to the embodiment in claim 9, e.g. B. made of rubber, Uraleit or polyurethane. The developments of the invention according to claims 10, 11 and 12 have the advantages that the damping effect is increased by embedding tensile materials and at the same time the acoustic wave resistance can be reduced so that the entire layer composite has approximately an acoustic wave resistance of water.

When calculating the acoustic wave resistance of the composite system as a transfer function of a multilayer board, a dimensioning rule for the thickness of the damping layer is obtained in accordance with claim 13. With a three-layer composite system, the calculation is simplified in accordance with claim 14, provided that the total thickness is small compared to the smallest wavelength received sound waves.

• Fig. 1 einen Bugdom an einem Oberflächenschiff, teilweise geschnitten,
• Fig. 2 einen Bug- und einen Seitenhüllkörper in einem U-Boot, jeweils teilweise geschnitten,
• Fig. 3 einen Kieldom an einem Oberflächenschiff,
• Fig. 4 bis 6 jeweils ausschnittsweise einen Längsschnitt der Wandung der in Fig. 1 bis 3 gezeigten Hüllkörper.

The invention is described in more detail below with reference to exemplary embodiments of an enveloping body shown in the drawing. In a schematic representation:

• 1 a bow dome on a surface ship, partially cut,
• 2 a bow and a side envelope in a submarine, each partially cut,
• 3 shows a kiel dome on a surface ship,
• FIGS. 4 to 6 each show a detail of a longitudinal section of the wall of the enveloping body shown in FIGS. 1 to 3.

The outer shape of an enveloping body for one or more hydrophone arrangements depends on the type of its carrier vehicle and on the type of hydrophone arrangement. 1, 2 and 3 show examples of possible variants.

1 shows a section of a surface ship 10 with an enveloping body in the form of a bow dome 11 on the bow of the surface ship 10. In the dome 11 there is a cylinder base 12 as a hydrophone arrangement on which hydrophones are arranged. The wall of the enveloping body consists of a layer composite 13, which will be discussed in more detail below.

FIG. 2 shows a section of the bow of a submarine 20, which has a bent envelope body 21 with a cylinder base 22 at the front having. The bent envelope body 21 is precisely fitted into the outer contour of the submarine. In addition, there is a flank array on the submarine 20, with a side envelope 23 and a streamer 24, which forms the hydrophone arrangement. 3 shows a section of the bow of a surface ship 30, in the keel of which an envelope body in the form of a keel dome 31 is provided for a flat base as a hydrophone arrangement. All of these enveloping bodies 21, 23 and 31, like the enveloping body 11 in FIG. 1, have a wall made of a layered composite.

Each layer composite generally has at least one dimensionally stable layer as a load-bearing element, which determines the contour of the enveloping body and is continuous. The layer thickness of this dimensionally stable layer is dimensioned according to the mechanical loads to be expected. At least one additional layer, which is designed as a damping layer for bending shafts, is built up on the load-bearing dimensionally stable layer, which consists for example of a composite material such as glass fiber reinforced plastic or carbon fiber reinforced plastic.

4, the supporting element consists of a single dimensionally stable layer 40. It is arranged in the layer composite in the middle between two damping layers 41 and 42. The damping layer 42 forms the outer closing layer of the enveloping body and consists, for example, of rubber, which is incompressible and thus pressure-resistant, a property which must be required in particular for enveloping bodies for submarines. The damping layer 41, which forms the inner closing layer of the enveloping body, consists, for example, of viscoelastic material into which tensile fibers or Mats are embedded. Such a damping layer is proposed in German patent application P 36 21 318.

The sectional view of the wall of an enveloping body shown in FIG. 5 shows a three-layer but modified layer composite, the load-bearing element of which is divided into two dimensionally stable layers 50 and 51. A damping layer 52 is arranged between the two dimensionally stable layers 50 and 51. The layer thicknesses of the two dimensionally stable layers 50 and 51 form a total thickness, which is designed according to the maximum mechanical loads. The two dimensionally stable layers 50 and 51 are made of the same material.

Fig. 6 shows a sectional view of the wall of an enveloping body from a layer composite, each with two dimensionally stable layers 60, 61 and an intermediate damping layer 62. The layer thicknesses of the dimensionally stable layers 60, 61, however, have different thicknesses l 1 and l 3, they in turn will correspond to the mechanical stresses on the envelope and the materials used. The thickness l₂ of the damping layer 62 is calculated as follows:

Dämpfungsschicht 62:

p₂ = p₁ cos k₂l₂ - j v₁ ρ₂c₂ sin k₂l₂

Formsteife Schicht 61: n = 3

p_n = p_n-1 cos k_nl_n - j v_n-1 ρ_nc_n sin k_nl_n

und für den Innenraum des Hüllkörpers

n = 4: ρ_nc_n = ρ₀c₀ und l₄ ein beliebiger Abstand:

p₄ = p₃ cos k₄l₄ - j v₃ ρ₀c₀ sin k₄l₄

The envelope with this layer composite is in the water, which has the specific density ρ₀ and the sound propagation speed c₀, its interior is filled with water or flooded. The materials of the dimensionally stable layers 60, 61 have the specific densities ρ₁ and ρ₃ and the sound propagation velocities c₁ and c₃. The damping layer 62 is made of a material with a specific density ρ₂ and one Sound propagation speed c₂ built up. A sound wave with a sound pressure p₀ and a sound velocity v₀ hits the enveloping body. The wave number k _n = 2π / λ _n characterizes the wavelengths λ₀, λ₁, λ₂, λ₃ of the sound wave in the respective material, which at the same frequency f are dependent on the sound propagation velocities c₀, c₁, c₂, c₃ in the corresponding layer. The indexing n = 1, 2, 3 refers to the layers in the layer composite, the index n = 0 and 4 denotes the sizes in the water. With these prerequisites, for a sound wave entering the layer composite from the water, the pressure and the rapid course for the individual layers result as follows (cf. Meyer / Neumann "Physikalische und Technische Akustik", Vieweg, Braunschweig, 1967, page 30, Equations 1.93 and 1.94): dimensionally stable layer 60:

p₁ = p₀ cos k₁l₁ - j v₀ ρ₁c₁ sin k₁l₁

Damping layer 62:

p₂ = p₁ cos k₂l₂ - j v₁ ρ₂c₂ sin k₂l₂

Dimensionally stable layer 61: n = 3

p _n = p _n-1 cos k _n l _n - jv _n-1 ρ _n c _n sin k _n l _n

and for the interior of the envelope

n = 4: ρ _n c _n = ρ₀c₀ and l₄ an arbitrary distance:

p₄ = p₃ cos k₄l₄ - j v₃ ρ₀c₀ sin k₄l₄

Provided that the layer thickness l _{n is} less than the wavelength λ _n , the following dimensioning rule is obtained for the three-layer layer composite, which borders on both sides with water, in which the layer thicknesses and material selection for the dimensionally stable layers are determined from a mechanical point of view:

dabei ist:

Z₀ = ρ₀c₀ akustischer Wellenwiderstand von Wasser,

Z = ρc akustischer Wellenwiderstand des Materials der fromsteifen Schicht,

Z₂ = ρ₂c₂ akustischer Wellenwiderstand des Materials der Dämpfungsschicht.From equation (IV) the thickness l₂ of the damping layer 62 in the layer composite of FIG. 6 is based on a total layer thickness l = l₁ + l₃ of the dimensionally stable layers 60, 61 with the individual layer thicknesses l₁ and l₃ of the same material with ρ₁ = ρ₃ = ρ, c₁ = c₃ = c and k₁ = k₃ = k determined to:

there is:

Z₀ = ρ₀c₀ acoustic wave resistance of water,

Z = ρc acoustic wave resistance of the material of the rigid layer,

Z₂ = ρ₂c₂ acoustic wave resistance of the material of the damping layer.

Der akustische Wellenwiderstand Z₀ von Wasser beträgt

Die Dämpfungsschicht besteht aus Hochdruck-Polyäthylen mit ρ₂ = 0,9 g/cm³ und c₂ = 1000 m/s:

Setzt man diese Größen in die Gleichung (V) ein, so erhält man die Dicke l₂ der Dämpfungsschicht:

    l₂ = 1,4 cm.An example: The dimensionally stable layers 60, 61 are made of glass fiber reinforced plastic:

l₁ = 1.5 cm, l₃ = 0.5 cm, ρ = ρ₁ = ρ₃ = 1.5 g / cm³

c = c₁ = c₃ = 2000 m / s:

The acoustic wave resistance Z₀ of water is

The damping layer consists of high-pressure polyethylene with ρ₂ = 0.9 g / cm³ and c₂ = 1000 m / s:

If you use these quantities in equation (V), you get the thickness l₂ of the damping layer:

l₂ = 1.4 cm.

Such a layer composite does not form any significant impedance jump in water for frequency ranges customary in sonar technology, so sound waves are neither damped nor reflected.

According to equation (IV), the following general dimensioning rule can be derived for a layer composite from any number of layers of the number i = 2, 3, 4, ..., n:

Depending on the mechanical requirements, the layer thicknesses and the material are selected for the dimensionally stable layers. The corresponding values for 1, ρ and c are used in Equation VI. The material for the damping layers is selected and ρ, c used. The thickness dimensions for the damping layers are then obtained from equation (VI). Such an enveloping body prevents radiation of noise due to impressed bending waves, has no through loss for incoming sound waves and also does not form a disturbing reflector for the sound waves.

Claims (14)

1. Envelope for a hydrophone arrangement, which has at least one load-bearing element and is attached to a carrier vehicle covering the hydrophone arrangement, characterized in that its wall is formed as a layer composite that the layer composite one or more dimensionally stable layers (40 or 50, 51 or . 60, 61), which form the supporting element, and one or more additional layers, which are arranged on and / or between the dimensionally stable layers (40 or 50/51 or 60, 61), that the additional layers as damping layers ( 41, 42 or 52 or 62) are designed for bending waves coupled in by structure-borne noise in the carrier vehicle or external influences, and that the layered composite is designed to be sound-permeable to incoming water noise. 2. Envelope according to claim 1, characterized in that the outer layer of the layer composite is a damping layer (42). 3. Envelope according to claim 2, characterized in that the layer thickness (l _i ) of the dimensionally stable layers is in each case substantially smaller than a smallest wavelength (λ _i ) of the water sound transmitted by the hydrophone arrangement (12, 22, 24) and / or is received, and the sum of the layer thicknesses forms a total thickness (l = l₁ + l₃) corresponding to a maximum mechanical stress. 4. Envelope according to claim 3, characterized in that the layer thicknesses (l₁, l₃) of the dimensionally stable layers (60, 61) are different. 5. Envelope according to claim 4, characterized in that all dimensionally stable layers (50, 51 and 60.61) consist of the same material. 6. Envelope according to claim 5, characterized in that the dimensionally stable layer (40 or 50, 51 or 60, 61) consists of glass fiber reinforced plastic. 7. Envelope according to claim 6, characterized in that the dimensionally stable layer (40 or 50, 51 or 60, 61) consists of carbon fiber reinforced plastic. 8. Envelope according to one of claims 1 to 7, characterized in that the damping layers (41, 42) have the same structure and materials. 9. enveloping body according to claim 8, characterized in that the damping layer (41, 42 or 52 or 62) consists of elastic or viscoelastic material. 10. Envelope according to claim 9, characterized in that tensile fibers or mats are embedded in the elastic or viscoelastic material. 11. Envelope according to claim 10, characterized in that the fibers or mats are made of carbon. 12. Envelope according to claim 10, characterized in that the damping layer (41, 42 or 52 or 62) contains Kevlar. 13. Envelope according to one of claims 1 to 12, characterized in that the thickness (l₂) of the damping layers depending on the specific density (ρ₀, ρ₁, ρ₂, ρ₃) and sound propagation speed (c₀, c₁, c₂, c₃) of the water, the dimensionally stable layer (60, 61) and the damping layer (62) and depending on the total thickness (l = l₁ + l₃) of the dimensionally stable layers. 14. Envelope according to claim 13, characterized in that for a layer composite of two dimensionally stable layers (60, 61) made of the same material and an intermediate damping layer (62), the thickness (l₂) of the damping layer (62) is equal to the product of the total thickness (l ) of the dimensionally stable layers (60, 61) and the ratio of the specific densities (ρ, ρ₂) of the dimensionally stable layer (60, 61) and the damping layer (62), multiplied by a quotient of two differences, is that the one difference is equal to one minus the squared quotient (Z₀ / Z) from acoustic wave resistance of the water and the dimensionally stable layer and the other difference equal to the squared quotient (Z₀ / Z₂) from acoustic wave resistance of the water and the damping layer minus one is formed.

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