AU2016266812B2

AU2016266812B2 - Fluid vehicle with reduced signature

Info

Publication number: AU2016266812B2
Application number: AU2016266812A
Authority: AU
Inventors: Tom AVSIC; Randolf Teppner
Original assignee: ThyssenKrupp AG; ThyssenKrupp Marine Systems GmbH
Current assignee: ThyssenKrupp AG; ThyssenKrupp Marine Systems GmbH
Priority date: 2015-05-27
Filing date: 2016-05-27
Publication date: 2018-10-25
Anticipated expiration: 2036-05-27
Also published as: ES2781200T3; KR20180002082A; KR102069962B1; EP3303120B1; PL3303120T3; EP3303120A1; AU2016266812A1; DE102015209723A1; WO2016189139A1

Abstract

The invention relates to a fluid vehicle, in particular an aircraft or watercraft, in particular a submarine 10, comprising a first hull 20 and a second hull 30. The second hull 30 is arranged under the first hull 20 in at least one first region, the shape of the first hull 20 being fluid-dynamically optimized while the second hull 30 has an optimized signature.

Description

(57) Zusammenfassung: Die Erfmdung betrifft ein Fluidfahrzeug, insbesondere ein Lull- und Wasserfahrzeug, insbesondere ein Unterseeboot 10, mit einer ersten Hiille 20 und einer zweiten Hiille 30. Die zweite Hiille 30 ist wenigstens in einem ersten Bereich unter der ersten Hiille 20 angeordnet, wobei die Form der ersten Hiille 20 fluiddynamisch optimiert ist, wahrend die zweite Hiille 30 signaturoptimiert ist.

WO 2016/189139 A1llllllllllllllllllllllllllllllllllllllllllllllllll^

GH, GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, SZ, TZ, UG, ZM, ZW), eurasisches (AM, AZ, BY, KG, KZ, RU, TJ, TM), europaisches (AL, AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM, TR), OAPI (BF, BJ, CF, CG, CI,

CM, GA, GN, GQ, GW, KM, ML, MR, NE, SN, TD, TG).

Veroffentlicht:

— mit internationalem Recherchenbericht (Artikel 21 Absatz 3)

2016266812 15 Jun2018

Fluid Vehicle with Reduced Signature

The invention concerns a fluid vehicle, in particular for watercraft and for aircraft, in 5 particular for a watercraft, especially for a submarine.

Fluid vehicles include watercraft and aircraft. It is common to both vehicles that said vehicles move freely through a fluid, wherein the friction between the fluid and the fluid vehicle is particularly relevant. In the case of watercraft, the fluid friction is very relevant owing to the high density, in the case of aircraft owing to the regularly high speeds.

For users of military objects (on land, on/under water and in the air), it is a decisive tactical advantage to detect an enemy object earlier than the own object is detected by the enemy side. In order to achieve this, there are two methods seen from tactical considerations: on the one hand to provide better sensors (together with the following data analysis) than the opposition and on the other hand to use objects with a smaller signature.

There are always different signatures by means of which objects can be detected.

For all objects that are not deeply submerged, these are for example:

• radar backscatter cross-section • infrared signature • UV signature • visual detectability • noise emissions • radiation of electromagnetic waves by the object itself • etc.

In the case of flying jet-powered objects, condensation trail formation also occurs for example.

In the case of all submersible objects, the same points as listed above apply when travelling close to the surface and on the surface of the water, but when submersed the significant signatures are:

• noise emissions • acoustic targeting range

2016266812 15 Jun2018 • generating or deflecting electromagnetic fields • infrared signature • luminescence in the wake field.

Submersible objects with small detection ranges are usually constructed to have a small 5 signature, in particular low noise emissions. For this purpose, within the object everything is done to prevent noise generation or propagation as far as necessary, for example in order not to exceed a specified signature value. This applies to the on-board equipment on the one hand and to the flow-induced noise on the other hand. As a result, the probability is reduced that a submersible object is located by means of a passive sonar.

Some signatures with the greatest ranges (such as for example radar backscatter crosssection for flying objects and acoustic targeting range for submersible objects) can also be optimized by means of the shape of the object. Indeed, said optimization is regularly in conflict with a streamlined design, which is necessary for low flow noise, high maximum speeds and long operational ranges.

A submarine with a sound absorber is known from DE 33 32 754 Al.

A coating system for the reduction of reflection is known from DE 88 09 318 Ul.

A submarine with cavities containing gas is known from DE 1 196 531 A.

It would be advantageous if embodiments of the present invention would resolve the conflicts between a signature-optimized external shape and an external shape that has been geometrically optimized for other requirements (for example for a flow-related signature or for another signature).

The fluid vehicle according to an aspect of the present invention comprises a first hull and a second hull, the second hull being disposed below the first hull at least in a first region, the shape of the first hull being fluid-dynamically optimized in at least said region, the first hull being transparent to a first detection wave and the second hull being opaque to the first detection wave and the shape of the second hull being optimized for minimizing the signature in relation to the first detection wave, the second hull being reflective for the first

2016266812 15 Jun2018 detection wave, wherein the shape of the first hull, which is significant for fluid-dynamic properties, and the shape of the second hull, which is significant for the signature, are completely decoupled.

The first hull can be referred to as an outer skin. The fluid vehicle is preferably a watercraft, particularly preferably a submarine. The second hull does not have to be fully beneath the first hull. Also, the first or second hull does not have to be an enveloping or enclosed hull. In particular, it is sufficient if the second hull is disposed below the first hull at least in a first region, for example in the case of a submarine on the bow or on the tower. As a result, only the signature in said regions is optimized, but it is exactly said at least one first region that contributes significantly to the unwanted signature, for example if there are many or highly scattering elements located there. For the example of a submarine, the tower including the hoistable masts disposed in the interior thereof is the determining part for the radar backscatter cross-section of the submarine when travelling on the surface. Optimization of the tower alone as an example of at least a first region thus contributes significantly to the optimization of the radar signature of the entire submarine.

Within the context of this application, a signature means any direct reflection of a detection wave emitted by an external signal source at a surface of the fluid vehicle towards the signal source.

The first hull is fluid-dynamically optimized and therefore determines the hydrodynamic properties of the boat in the case of the submarine when travelling submersed. In order to provide decoupling between the hull design that is fluid-dynamically optimized and the hull design that would be optimized for reduction of the signature, the first hull is embodied so that the first hull is transparent to a first detection wave. Typical detection waves are sound waves (sonar) and electromagnetic waves (radar). Transparent in the sense of the embodiments of the present invention means that the reflection at the hull amounts to less than 25 %, preferably less than 10 % of the incident intensity. The second hull is opaque to the first detection wave, wherein opaque in the sense of the embodiments of the present invention means that less than 25 %, preferably less than 10 % of the incident radiation intensity is transmitted. Typically, the transmission attenuation is achieved by reflectivity

2016266812 15 Jun2018 and/or absorption, particularly preferably by reflectivity or by a combination of reflectivity and absorption. The shape of the second hull is optimized to minimize the signature relative to the first detection wave. This enables the shape of the first hull, which is significant for the fluid-dynamic properties, and the shape of the second hull, which is significant for the signature, to be completely decoupled. The second hull is reflective for the first detection wave. Reflective means that more than 50 % of the intensity of the first detection wave is reflected directionally. Thus, absorption and scattering are less than the reflection. The advantage of reflection is the good predictability of the behavior in relation to an incident first detection wave.

Preferably, more than 75% of the intensity of the first detection wave, particularly preferably more than 90% of the intensity of the first detection wave, is reflected.

For the purposes of understanding, for example the case of a submarine with a first hull of steel and a second hull of solid foam is represented, wherein the first hull, the outer hull of the submarine, is flushed with water. Such an embodiment of the first hull is typical of twinhull boats and for single-hull boats in the region of the bows or the tower.

For the reflection and transmission of a sound wave, which is used as a detection wave in 20 the sonar, in the case of a flat plate the characteristic acoustic impedance Zf and the layer thickness d are relevant, wherein the characteristic acoustic impedance Zf is the product of the density p and the speed of sound c. The coefficient of reflection of a flat plate in the water (reflected sound pressure in relation to incident sound pressure) is calculated for perpendicular sound incidence as follows:

sinCdfc!) \^zF,0 ^ZF,1/ + sinCd/^) \^zF,0 ^ZF,1/ with Zf,o the characteristic acoustic impedance of the water and Zf,i the characteristic acoustic impedance of the plate of the material 1. The wavenumber in the plate is ki = 2 π f/c, wherein f is the frequency. For materials without absorption, R² + T² = 1 applies, wherein T is the coefficient of transmission.

2016266812 15 Jun2018

To a first approximation, the density of water pwater is 1,000 kg/m³ and the speed of sound cwater is 1,500 m/s. Thus, Zf,water is about 1.5-10⁶ Ns/m³. For steel, to a first approximation the density psteei is 8,000 kg/m³ and the speed of sound csteei is 6,000 m/s. Thus, Zf,steel is about 48-10⁶ Ns/m³. The characteristic acoustic impedances of water and steel differ by about a factor of 30, because the speed of sound in steel is very high and the layer thickness of the flow envelope is small, therefore the product dki is also small (at 1 kHz about 0.01) and thus R is small. In figure 1, the coefficient of reflection relative to the intensity (| R²|) for a 10 mm thick steel plate and a 20 mm thick GFK plate (plate of fiberglass reinforced plastic) in water is shown as a function of the frequency. The basically similar profile and the in total higher transparency of the GFK plate itself at higher frequencies can be seen.

A distinction is made between low-frequency active sonars, which operate at 50 Hz to 3 kHz, medium -frequency active sonars, which operate at 3 kHz to 15 kHz, and high-frequency active sonars. For locating submarines, owing to the low attenuation in sea water and the associated long range, low-frequency active sonars are mainly used. As can be seen from figure 1, a steel plate has a high transmission factor in said frequency range.

The reduction can be reduced further by using as the material for the first hull a fiberreinforced composite material (FRC), for example the GFK material shown in figure 1. For such a material, to a first approximation the density pfrc is 2,000 kg/m³ and the speed of sound cfrc is 3,000 m/s. Thus, Zf,frc is about 6-10⁶ Ns/m³. Said numerical effect is however partly compensated by the fact that a first hull of a fiber-reinforced composite material must routinely be thicker than a first hull of steel.

In the case of a transition to air, reflection regularly occurs because the characteristic acoustic impedance for air Zf,air is about 442 Ns/m³to a first approximation with a density paii of 1.3 kg/m³ and a speed of sound CAir of 340 m/s. Thus, practically full reflection occurs on the air-filled pressure hull. The pressure hull must however routinely be made round for technical reasons in order to be able to withstand the high pressures at maximum submersion depth.

2016266812 15 Jun2018

Therefore for example, plastic foams are suitable as the material for the second hull, for example of polyvinyl chloride, polystyrol or polyurethane. Foams comprise gas bubbles that are produced during manufacture. As a result, a characteristic acoustic impedance results that is calculated as follows to a rough approximation:

P ⁼ FiPi + V2P2 K = V-iK-l + V₂K₂ with *i = cfpi

i.e. it can be estimated from a weighted average of the density p and the compressibility κ in the media gas and polymer by using the respective volumetric components V. The reflection can thus be influenced in a controlled manner by means of the thickness and composition of the foamed material. Advantageously, the second hull comprises a thickness of 5 mm to 30 mm of a foamed material, preferably of 10 mm to 20 mm. Owing to the relatively low speed of sound through the gas bubbles in the foam, said thickness is sufficient for the efficient reflection of the detection wave.

In one embodiment of the invention, objects with a larger backscatter signature are arranged. In the case of an object with a larger backscatter signature, for example the pressure hull can be a torpedo tube, a snorkel, a periscope or similar. Said objects with larger backscatter signatures can often be designed in the shape thereof to minimize the signature, but are subject to other technical requirements, and are therefore preferably disposed below the second hull.

Alternatively, the first hull can be transparent to radar radiation and the second hull can be opaque to radar radiation. Said embodiment is preferable for the surface region in the case of a watercraft, for example for the tower in submarines, and for aircraft.

2016266812 15 Jun2018

In a further embodiment of the invention, a third hull is disposed in at least a second region below the first hull and below the second hull. The third hull forms a pressure hull.

In a further embodiment of the invention, the first detection wave is reflected at more than 5 50% in a direction deflected by at least 6°, preferably by at least 12°, particularly preferably by at least 20° from the incident first detection wave (50). Preferably, there is no longer any further reflective and/or absorbent component of the submarine disposed in the deflected direction, and after the reflection at the second hull the detection wave is reflected away from the submarine by the first hull. The detection wave is preferably reflected only once on the submarine.

In a further embodiment of the invention, the first detection wave is a sound wave or an electromagnetic wave. Sound waves are used as detection waves for sonar and electromagnetic waves are used for radar. The sound wave preferably has a frequency of 10¹

Hz to 10⁵ Hz. The electromagnetic wave preferably has a frequency of 10⁹ to 10¹² Hz.

In a further embodiment of the invention, the first detection wave is a sound wave and the reflection wave is reflected downwards. Sound waves are typically used for sonar for locating submarine vehicles. The main application area is therefore the location of a submarine by a surface ship. Thus, in said scenario the first detection wave is usually incident on the submarine slightly above the horizontal. Owing to the downwards deflection, the sonar wave is passed onto the seabed and cannot be collected by the surface ship or another surface ship.

Ina further embodiment of the invention, the first detection wave is an electromagnetic wave and the reflection wave is reflected upwards. Electromagnetic waves are typically used for radar for the location of vehicles above the surface of the water. The main application is therefore the location of a surface ship or of a surfaced submarine by another surface ship. Here the upwards deflection is useful, because the surface of the water could act as a further reflective surface and thus could return the radar beam to the further surface ship.

2016266812 15 Jun2018

In a further embodiment of the invention, the shape of the second hull is optimized for minimizing the signature relative to a horizontally incident first detection wave. The strongest threat arises for a fluid vehicle, in particular for a watercraft in the location thereof by another fluid vehicle, in particular a watercraft or an aircraft. In the surface region, therefore, an incident radar wave arrives practically horizontally. It must therefore be prevented that this is reflected horizontally. This applies similarly to the underwater region.

A common submersion depth lies at about 100 m. Another watercraft that is disposed on the surface of the water at a distance of only 1,000 m and that uses an active sonar to find the submarine uses a detection wave that is incident on the submarine at an angle of less than 6° and hence with only a small deviation from the horizontal. At a distance of 3,000 m, the angle is already below 3° and at a distance of 6,000 m is below 1°. A submerged submarine can also be illuminated with a detection wave by another submerged submarine at practically any angle, but said scenario is however rather negligible in practice. It is therefore advantageous to optimize the geometry of the second hull for the incidence of a horizontal wave.

For aircraft, detection can also be carried out by a ground-based radar or a satellite-based radar. Nevertheless, owing to the increased probability of occurrence with aircraft, optimization for a horizontal detection direction is useful.

The aforementioned observations are simplified observations and approximations, which however have sufficient accuracy for the effects to be considered here.

In a further embodiment of the invention, the second hull comprises at least one flat surface. The flat surface is the simplest shape to reflect an incident first detection wave in another direction. Because transmitters and receivers are spatially closely adjacent with most location systems, said shape gives good optimization of the signature.

In a further embodiment of the invention, the object comprises a fourth hull in addition to a first hull and a second hull, wherein the second hull is disposed below the first hull and the 8

2016266812 15 Jun2018 fourth hull is disposed below the second hull. The first hull is transparent to a first detection wave and a second detection wave. The second hull is opaque to the first detection wave and transparent to the second detection wave. The fourth hull is opaque to the second detection wave. The shape of the second hull is optimized for minimizing the signature relative to the first detection wave. The shape of the fourth hull is optimized for minimizing the signature relative to the second detection wave. For example, the first detection wave is sonar, the second detection wave is radar. The pressure hull can be disposed below the fourth hull, for example.

Ina further embodiment of the invention, the surface normal of the at least one flat surface is at an angle to the longitudinal direction of the fluid vehicle, in particular of a submarine, of at least 6°, preferably of at least 12°, particularly preferably of at least 20°. The surface normal is the vector that is orthogonal to the surface. Because most detection waves are incident on the fluid vehicle at an angle of 0° to 6°, the at least one first flat surface has an inclination of at least 6° relative to the vertical, wherein the longitudinal direction of the fluid vehicle runs parallel to the horizontal. Indeed, for example a submerged submarine when surfacing or diving or an aircraft during a change in altitude can also have a deviation of the longitudinal direction of the fluid vehicle from the horizontal, however because said orientation relatively rarely occurs the fluid vehicle is optimized regarding the signature to a horizontal orientation of the longitudinal direction of the fluid vehicle. The at least one flat surface has an inclination of at least 12°. Said angle is particularly preferable because as shown a deviation of the incoming radiation direction of the detection wave of up to 6° from the horizontal is to be considered probable. Furthermore, the reflection is regularly carried out not confined to only one angle, but there is regularly a cone in which the highest intensity is reflected according to the reflection in said angular direction, and the energy decreases ever more strongly with deviation from said angle. Figure 2 shows the characteristic of the reflection of a flat plate with a dimension of three wavelengths (L = 3 λ). The wave is incident as a plane wave from the direction of 0° and is reflected at the plate inclined by 12° in the main direction of 24°. The reflection back to the 0° direction is smaller by more than 18 dB.

2016266812 15 Jun2018

Particularly preferably, the at least one first surface in the case of a watercraft is inclined downwards by an angle of at least 6°, preferably of at least 12°, particularly preferably of at least 20°. Thus, a detection wave is reflected away from the surface of the water to the seabed and thus away from the sensor. However, said arrangement can only be implemented in a few areas of the watercraft and it is therefore preferable if the second hull is disposed only in a selected first region, for example in the bow.

Particularly preferably, the at least one first surface is inclined upwards in the case of an aircraft by an angle of at least 6°, preferably of at least 12°, particularly preferably of at least

20°. Thus, a detection wave is reflected away from the surface of the earth and thus away from the sensor. Said arrangement can however only be implemented in a few areas of the aircraft and it is therefore preferable if the second hull is disposed only in a selected first region, for example in the nose.

Ina further embodiment of the invention, the first hull consists of steel or a fiber-reinforced composite material and the second hull consists of a solid foam. Said embodiment is preferable for a watercraft.

In a further embodiment of the invention, the first hull consists of a fiber-reinforced composite material and the second hull consists of metal or another electrically conductive material, for example steel. Said embodiment is preferable for an aircraft.

Of course, it is also possible that a fourth hull is disposed between the second hull and the third hull. In this case, the first hull is transparent to a first detection wave and a second detection wave, the second hull is opaque to a first detection wave and transparent to a second detection wave and the fourth hull is opaque to the second detection wave. This enables the first hull to be optimized regarding the fluid-dynamic properties, the second hull to be optimized regarding the signature of the first detection wave and the fourth hull to be optimized regarding the signature of the second detection wave. Said principle can be extended further to additional hulls.

2016266812 15 Jun2018

Notwithstanding any other forms which may fall within the scope of the disclosure as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1: shows a coefficient of reflection relative to the intensity (| R²1) for a 10 mm thick steel plate and a 20 mm thick GFK plate in water;

Figure 2: shows a characteristic of the reflection of a flat plate with the dimension of three wavelengths;

Figure 3: shows schematically a cross-section through a first submarine according to an 10 embodiment of the present invention;

figure 4: shows schematically a cross-section through a second submarine according to another embodiment of the present invention;

figure 5: shows schematically a cross-section through a third submarine according to a further embodiment of the present invention;

figure 6: shows schematically a cross-section through an aircraft according to an embodiment of the present invention.

In figure 3, a first submarine 10 according to an embodiment of the present invention is shown. The submarine 10 comprises a hydrodynamically optimized first hull 20. This differs from conventional submarines according to the prior art by a particularly narrow tower. With conventional submarines, the outer skin is usually made inclined for reduction of the signature in order to avoid vertical surfaces. As a result, the tower is significantly broader at the base and thus brings about a measurably increased flow resistance. According to the present embodiment of the invention, the first hull 20 is transparent to the detection wave

50 emitted predominantly horizontally by a transmitter 40, for example a ship. The receiver is also located with the transmitter, for example both are components of a ship. The first hull 20 is made of a fiber-reinforced composite material here and is thus practically transparent to electromagnetic radiation in the range 10⁹ to 10¹² Hz and in the submerged

2016266812 15 Jun2018 state is also transparent to sonar sound. The tower and a second hull 30 are disposed below the first hull 20 in a first region. The second hull is reflective for electromagnetic radiation in the range 10⁹ to 10¹² Hz and for sonar sound; for example the second hull 30 is of steel. The second hull has an inclination of 10° relative to the vertical and is embodied as a flat surface.

As a result, the incident detection wave 50 is reflected at an angle of 20° to the horizontal and cannot reach the receiver 40. Thus, the submarine 10 cannot be located by the transmitter and receiver 40.

Objects such as a periscope or a snorkel may have to be fed through the second hull 30 10 shown in figure 3 for space reasons. Said periscope and snorkel are thus disposed outside the second hull 30 and thus contribute to an increase in the backscatter cross-section and thus to a degradation of the signature. Said effect is however small compared to hydrodynamic optimization of the shape of the first hull 20 and the optimization of the signature by the second hull 30.

Of course, it is also conceivable that the second hull 30 does not consist only of a flat surface as represented, but that the second hull 30 consists of a plurality of flat surfaces that are disposed in a sawtooth pattern, wherein the individual surfaces comprise a surface normal that preferably have angles of for example + 15° or - 15°. This enables a more compact structure.

In figure 4, a further submarine 10 according to further embodiment of the present invention is shown. In said example shown, the first region, which is optimized, is the bow region. In the bow region there is a second hull 30 below the first hull 20, which is transparent to sonar, and behind the second hull 30 there is a third hull 60, which forms the pressure hull. In the central region of the submarine 10, the submarine 10 can be embodied as a single-hull boat, so that here the first hull 20 also forms the pressure hull. The second hull 30 is preferably embodied as a flat surface with an inclination of 12° downwards relative

2016266812 15 Jun2018 to the vertical. As a result, a horizontally incident detection wave 50 is reflected at an angle of 24° downwards as a reflection wave 55. As a result, location of the submarine 10 can be successfully prevented. In this case, the first hull 20 preferably consists of steel, the second hull 30 preferably of foam, in particular of closed cell polyurethane foam. The region between the first hull 20 and the third hull 60 is filled with water. As a result, the first hull 20 is transparent to the detection wave 50 and to the reflection wave 55. The second hull 30 consists for example of a 15 mm thick foam plate with good reflection properties for sound and hence for the detection wave 50.

With the example shown in figure 4, the barrels, which are not represented, and which extend from the third hull 60, and hence from the interior of the submarine 10, to the first hull 20, must also be fed through the second hull 30. As a result, part of the barrel lies in front of the second hull 30 and thus contributes to the signature. However, said contribution is relatively small owing to the shape of the barrel.

Figure 5 shows a cross-section through a further submarine 10 according to another embodiment of the present invention. The submarine 10 is embodied as a two-hull boat and comprises a first hull 20 and a pressure hull that is formed by the third hull 60 and that is spaced apart from the first hull 20. The first hull 20 is made of fiber composite material and the third hull 60 is made of steel. Between the first hull 20 and the third hull 60 a second hull 30 is disposed, which consists of eight flat surfaces for example. In order to avoid a reflection in the horizontal direction, the flat surfaces are so disposed that the surface normals of the surfaces are at an angle of 22.5° or 147.5° to the horizontal. The second hull 30 is made of 15 mm thick foam-plates.

It emerges that for example the exemplary embodiments shown in the figures can be combined with each other, for example in order to optimize the radar signature of the tower according to the example shown in figure 3 and to optimize the sonar signature of the body of the boat according to the exemplary embodiments shown in figure 4 and/or figure 5.

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In figure 6: an aircraft 70 with a first hull 20 and a second hull 30 is represented. The first hull 20 is aerodynamically optimized, and the second hull 30 is optimized regarding the radar backscatter cross-section.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word comprise or variations such as comprises or comprising is used in an inclusive sense,

i.e. to specify the presence of the stated features in various embodiments of the invention.

Modifications and variations as would be apparent to a skilled addressee are determined to be within the scope of the present invention.

It is also to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Reference characters:
	10	submarine
	20	first hull
20	30	second hull
	40	transmitter and receiver
	50	detection wave
	55	reflection wave
	60	third hull
25	70	aircraft

2016266812 15 Jun2018

Claims

Claims:

1. A fluid vehicle consisting of a first hull and a second hull, the second hull being disposed below the first hull at least in a first region, the shape of the first hull

5 being fluid-dynamically optimized in at least said region, the first hull being transparent to a first detection wave and the second hull being opaque to the first detection wave and the shape of the second hull being optimized for minimizing the signature in relation to the first detection wave, the second hull being reflective for the first detection wave, wherein the shape of the first hull,

10 which is significant for fluid-dynamic properties, and the shape of the second hull, which is significant for the signature, are completely decoupled.
2. The fluid vehicle as claimed in claim 1, wherein a third hull is disposed in at least a second region below the first hull and below the second hull and that the third

15 hull forms a pressure hull.
3. The fluid vehicle as claimed in any one of the preceding claims, wherein the first detection wave is reflected at more than 50% directed in a deflected direction by at least 6° from the incident first detection wave.
4. The fluid vehicle as claimed in any one of the preceding claims, wherein the first detection wave is a sound wave or an electromagnetic wave.
5. The fluid vehicle as claimed in claim 4, wherein the first detection wave is a sound

25 wave and that the reflection wave is reflected downwards.
6. The fluid vehicle as claimed in claim 4, wherein the first detection wave is an electromagnetic wave and that the reflection wave is reflected upwards.

30
7. The fluid vehicle as claimed in any one of the preceding claims, wherein detection waves having the same or a similar optimal geometry are reflected at the same

2016266812 15 Jun2018 hull.
8. The fluid vehicle as claimed in any one of the preceding claims, wherein the shape of the second hull is optimized for minimizing the signature in relation to a

5 horizontally incident detection wave.
9. The fluid vehicle as claimed in any one of the preceding claims, wherein the second hull comprises at least one flat surface.
10 10. The fluid vehicle as claimed in claim 9, wherein the normal surface of the at least one flat surface is at an angle of at least 6° to the longitudinal direction of the fluid vehicle.
11. The fluid vehicle as claimed in any one of the preceding claims, wherein the first 15 hull consists of steel or a fiber-reinforced composite material and the second hull consists of a solid foam.
12. The fluid vehicle as claimed in any one of the preceding claims, wherein the first hull consists of a fiber-reinforced composite material and the second hull consists

20 of a metal or another electrically conductive material.

Drawings

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Figure 2

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