WO2003061067A1

WO2003061067A1 - A conning tower construction

Info

Publication number: WO2003061067A1
Application number: PCT/IS2003/000004
Authority: WO
Inventors: Hjalti Hardarson; Egill Hardarson; Leifur Thor Leifsson
Original assignee: HAFMYND EHF
Current assignee: HAFMYND EHF
Priority date: 2002-01-15
Filing date: 2003-01-15
Publication date: 2003-07-24
Anticipated expiration: 2004-07-15
Also published as: AU2003207991A1

Abstract

This patent application describes a novel antenna housing and conning antenna tower for an Autonomous Underwater Vehicle. The main features of the antenna tower are that it houses several antenna types and optionally a strobe beacon in a very compact housing, at the same time being streamlined, transparent and able to withstand great pressure.

Description

A CONNING TOWER CONSTRUCTION

Field of the Invention

The present invention relates to an underwater vehicle, especially an AUV, autonomous underwater vehicle, and deals with a unique antenna construction that integrates several antenna technologies and a strobe light into a single, compact housing that is capable of withstanding pressure down to 2000 meters or more.

Description of the prior act

Autonomous Underwater Vehicles (AUVs) are small, unmanned vehicles. Some of them use a pressure housing (a dry housing) and some use a so-called flooded housing. Most AUVs have some natural buoyancy which means that they float when they are still. These ■ AUVs dive by speeding up on the surface and pointing their depth rudders down in order to overcome the buoyancy. Therefore a slight downward force is required all the time while the AUV is underwater to overcome the buoyancy. This force is normally provided by the depth rudders. To minimize this downward force the buoyancy must be kept to a minimum, otherwise this will affect the power consumption and endurance of the vehicle and will be difficult for it do dive.

Existing AUVs frequently use radios or radio-modems for communicating with a nearby vessel. They also frequently use a GPS receiver for positioning while on the surface. Some also use a emergency strobe beacon so that they can be visually spotted in the dark. The antennas are usually contained in individual pressure housings that are typically located at the stern. Some AUVs lack the above equipment altogether. AUVs frequently use acoustic links for communication to nearby ships, but the usable range normally is only 2 - 3 km.

VHF and UHF radio antennas have to be rather long, up to half a meter or more, to function properly while the AUV is on the surface so that they can communicate successfully by line-of-sight since waves between the vessel and AUV will otherwise block the communications. This also means that the communications will not work in sea states above a certain limit. This severely limits the usefulness of an AUV as sea states greater than this, which are frequently encountered at open seas. Also the lack of long-range communication limits the use of AUVs at open seas as the AUVs may surface outside the communication range of the radios.

AUV antennas, both for communication and positioning (GPS) must fulfill certain demands in order to function properly.

1. They have to keep drag to a minimum since drag causes increased power consumption which is critical in a battery operated AUV.

2. They must be corrosion resistant since seawater is highly corrosive. 3. They must be able to withstand the high pressure of deep water. Some vehicles are rated for depths of several thousand meters. 4. They have to operate in high sea-states, which are frequently encountered at open seas. This means that they must quickly wash off the sea that sprays over.

5. The means used for protecting the antennas against corrosion and pressure must not degrade their sensitivity at their operating frequency.

Combining all these features is not an easy task. Some of the problems encountered are: 1. Interference between the different antennas used on the AUV. The GPS antenna, for example, is a sensitive receiving antenna, frequently with a built-in preamplifier (active antenna) and the radio normally outputs relatively high power to its antenna which may easily corrupt the GPS signal. The radiation pattern of the radio antenna is important in this respect. Other antennas used or objects, especially metallic objects may interfere and alter the radiation and receiving pattern of the antennas and thus degrade their performance. These problems are especially difficult to handle if the antennas are moved close to one another. 2. Pressure tolerance without degradation of antenna performance. A VHF or UHF radio antenna is difficult to place inside a pressure housing because of its length. Therefore they are normally covered by a protective layer. GPS antennas can be moulded (for example using epoxy resin) or placed inside a pressure housing but this has to be made of a type of material that does not degrade its performance. 3. Streamlining. A GPS antenna is not streamlined in shape. Its size is typically 5 x

5 cm in length and width and 1 or 2 cm high. The cable output fitting adds to the size. These antennas are normally placed in a vertical cylindrical housing which is not streamlined but easy to make. The radio antennas are thin typically thin cylindrical rods (1 - 2 cm in diameter). Thus they are not streamlined and may cause considerable drag, depending on their length. Emergency strobe beacons are normally housed in cylindrical transparent units and thus are not streamlined in shape. 4. Low volume. When the AUV is on the surface, all the antennas are out of the water (otherwise they don't function properly). Therefore it is important, especially for a small AUV to keep the volume of the antennas and antenna housings as small as possible so that they don't add to the buoyancy of the AVU. If they do, the AUV may have difficulty diving.

Description of the Invention Figure 1 shows the Gavia AUV made by Hafmynd ehf. The antenna tower is shown towards the front of the vehicle.

Figure 1: GAVIA AUV and her modular construction. Conning antenna tower shown towards the front of the vehicle. Gavia's antenna tower is shown in figure 2. All the communication antennas and an emergency strobe beacon are located in the compact streamlined horizontal cylinder, which has a volume of only approximately 1/2 litre.

Hafmynd has come up with a solution that integrates several antennas and an emergency strobe beacon in a single compact pressure housing on board Gavia, tackling and solving all the problems discussed above in the section "Description of the prior act".

The Gavia housing has the following unique properties:

I. A depth rating of 2000 meters 2. It houses three different antennas in a very restricted space

3. The volume is very small, approximately 1/2 litre.

4. It houses a strobe beacon.

5. It is streamlined.

6. Because of its shape and material it quickly washes off the sea spray. 7. Because of its shape it minimizes wind effects, i.e. forces that try to roll Gavia to the side.

8. It minimizes wind effects on the AUV while on the surface by using a free-swinging wing-shaped sleeve around the antenna tower that provides streamlining for the tower.

9. It provides easy access to all antennas and the interior of the antenna housing. This is important for maintenance and repair.

10. It is strong.

II. It does not degrade antenna performance or block out electromagnetic waves. Instead of using a radio (VHF or UHF), Gavia uses a satellite communication link (Iridium telephone). The Iridium antenna is a vertical patch antenna, measuring approximately 3 x 3 cm in width and length and approximately 0.3 cm in height. The GPS antenna used is an active patch antenna measuring approximately 2 x 2 cm in width and length and approximately 1 cm in height. The radiation pattern (transmitting and receiving) of the Iridium patch antenna is predominantly vertical, see fig. 2, which shows the radiation patterns of the antennas. From the figure it can be seen that the radiation patterns do not interact. This is so, because of the patch antennas that both have a predominantly vertical pattern. A powerful radio antenna this close to the GPS antenna might cause serious problems, because its radiation pattern is predominantly horizontal. The wireless LAN antenna has a low power output and therefore does not interfere with the other antennas. 12. It is transparent so that the strobe beacon can be seen through the pressure housing.

Measurements and field trials have confirmed the performance of the antenna housing. This was also supported by rigorous in-house measurements of the antenna radiation patterns and their interaction. The interaction of the emergency strobe beacon lamp was also investigated. The absorption and transmittivity of the housing material was measured at the frequency bands of the antennas. The shape and form of the antenna housing was analysed using DesignSpace (a numerical strength analysis program) and the pressure rating was then confirmed in a pressure tank using an absolute pressure of more than 200 bars. Water absorption of the housing material was also tackled.

Figure 4: Pressure tank used for testing the Gavia antenna housing to above 200 bar (equalling approximately a depth of 2000 metres).

The volume has to be small especially on a small vehicle. Design requirements are that the volume be approximately 1/2 litre equal to a weight of approximately 1/2 kg for Gavia. This is important since this is the weight that Gavia must pull down with her when diving. It is important to keep this weight to a minimum in AUVs with a natural buoyancy to reduce as much as possible the force required to make them dive.

The construction must be streamlined in shape to minimize drag.

The construction must be strong to withstand a certain amount of rough handling especially during launch and recovery.

The antenna must reach out of the water to make a usable contact and to make the strobe light visible.

The antenna must have a shape that quickly clears off any sea that is washed over it. In addition Gavia lifts her tower still higher up when cruising on the surface by pointing her depth rudders up, thereby lifting the front of her hull approximately 10 cm further up, providing further protection against wash-over and strengthening the communications.

Figure 5: Gavia's conning antenna tower and antenna tower housing cylinder at top.

Figure 5 is a cross section of the antenna tower showing its components. This arrangement of antennas and strobe beacon is unique. The shape of the antenna is also unique. The very low volume of the antenna is also unique. It is also unique to use a transparent plastic material for the antenna housing. It is also unique to use a satellite antenna in such close proximity to a high sensitivity GPS receiver antenna and an Ethernet local area network antenna.

The housing has the following unique properties: A depth rating of 2000 meters It houses three different antenna types or technologies in a very restricted space. It houses a strobe beacon. It is streamlined.

It minimizes wind effects on the AUV while on the surface by using a free-swinging wing- shaped sleeve around the antenna tower that provides streamlining for the tower.

In order to function properly the following requirements have to be fulfilled: The antenna housing material has to be strong enough to withstand the pressure at a depth of 2000 meters or more.

Figure 6: Cross section of Gavia's conning antenna tower. Figure 7: Detail from figure 3 above.

The arrow in fig. 7 points to the specific shape of the part where the cap joins the antenna housing. This prevents the cylinder from being pressed together by the outside pressure, at the same time protecting the O-ring from being cut apart.

The above-mentioned unique properties of the antenna enable Gavia to communicate with its operator no matter where he is located in the world. He does not have to be within line-of-sight of the AUV. This antenna also provides much more secure communications between the operator and the AUV because the communications are vertical or close to vertical, i.e. between a satellite high in the sky and the AUV but not vertical between a vessel and the AUV. Thus disturbances of waves or breaking waves are much less pronounced and the vehicle can be operated in sea states higher than hitherto has been possible.

Figure 8: The Gavia cunning antenna tower sticking out of the water. The streamlined collar (see below) is not mounted.

Using a satellite telephone in an AUV is unique but the advantage is clear. Since the AUV is very close to the surface, waves can easily block out the line of sight between the AUV and a vessel or land. The satellite however is high above the horizon and therefore the line of sight between the satellite and the AUV is not easily blocked out. This also means that the AUV antenna does not have to be tall.

One version of the conning antenna tower and housing has a motor driven mechanism that retracts the antenna stand into the AUV hull so that the antenna housing sits on the AUV hull. This may be advantageous in some cases to further reduce drag and minimize the danger of catching objects that float in the sea.

One version of the antenna housing has a miniature camera mounted inside. Because of the possible transparency of the housing material, the camera can view the outside. Thus the conning antenna tower acts as a periscope.

Figure 9: The wing shaped collar of the antenna housing stand.

Figure 10:The wing shaped collar shown mounted on the antenna housing stand. Figure 10 shows the wing shaped collar that is attached to the antenna housing stand. The collar provides a streamlined shape for the antenna stand thereby reducing its drag to a minimum.

The collar is loose and may be deflected by the wind when the AUV is on the surface reducing the amount of side force that might otherwise roll the AUV to its side and degrade antenna performance.

Claims

1. A streamlined AUV antenna housing and conning tower in the shape shown in fig.2.

2. An antenna housing for an AUV that is made of transparent plastic so that a strobe beacon is visible through it.

3. An AUV antenna housing that contains different antennas or antenna technologies in the same housing, i.e. a GPS antenna, a satellite telephone antenna and a low power radio antenna (wireless Ethernet local area network antenna) in a single compact pressure housing, i

4. A streamlined pressure (withstands pressure up to at least 200 bar) AUV antenna housing that contains different antennas or antenna technologies in the same housing, i.e. a GPS antenna, a satellite telephone antenna and a low power radio antenna (wireless Ethernet local area network antenna) in a single compact pressure housing.

5. A streamlined pressure AUV antenna housing (withstands pressure up to at least 200 bar) that contains different antennas or antenna technologies in the same housing.

6. A streamlined pressure AUV antenna housing (withstands pressure up to at least 200 bar) that contains different antennas or antenna technologies in the same housing and supported by a stand or mast.

7. An AUV antenna housing that contains a satellite communication antenna.

8. An AUV antenna housing that contains an Iridium satellite communication antenna.

9. An AUV antenna housing as in claim 3 that also contains a strobe beacon.

10. An AUV antenna housing that does not significantly degrade electromagnetic waves to and from the antennas located inside the housing.

11. An AUV antenna housing that has a volume as low as approximately 1/2 litre.

12. An AUV antenna housing containing a satellite communication antenna, GPS antenna, wireless radio antenna that has a depth rating of 2000 meters or more.

13. An AUV conning antenna tower with a loose streamlined sleeve on the conning tower stand (mast). By not being rigid the sleeve will be deflected by the wind while the AUV is on surface and prevents the AUV from being rolled to the side.

14. An AUV antenna housing that has a watertight cap for inserting and removing the antenna assembly.

15. An AUV antenna housing that has the specific form shown in fig. 7 which prevents the cylinder from being pressed together by the outside pressure, at the same time protecting the O-ring from being cut apart.

16. An AUV antenna housing in the form as shown in fig. 5 and 6.

17. An AUV conning antenna tower with pressure antenna housing (withstands pressure) containing satellite communication antenna, GPS antenna, radio antenna and optionally an emergency strobe beacon, that can be retracted (drawn into the AUV hull or to the surface of the hull) using motorized power.

18. An antenna housing that is transparent or has a clear window so that a miniature camera can be mounted inside the housing for viewing the outside surroundings of the AUV.

19. An AUV antenna housing that has a ground-plane arrangement as shown in fig. 3.