BELT AND METHOD FOR REDUCING THE DRAG OF A HULL OF A FLOATING VESSEL

Abstract

A belt for reducing the drag of a hull of a floating vessel, whereby the belt includes a belt body extending in a length direction (L), whereby the belt has, a sequence of bubble generators which are embedded in the belt body, whereby the belt has an air channel for supplying pressurized air to the bubble generators, whereby the air channel extends in the length direction (L), whereby the bubble generators are connected to the air channel, whereby the belt body is made of a flexible material. Also disclosed is a device having such a belt and a method of reducing the drag of a hull of a floating vessel using such a belt.

Claims

1. A belt for reducing the drag of a hull of a floating vessel, whereby the belt comprises a belt body extending in a length direction (L), whereby the belt comprises a sequence of bubble generators which are embedded in the belt body, whereby the belt comprises an air channel for supplying pressurised air to the bubble generators, whereby the air channel extends in the length direction (L), whereby the bubble generators are connected to the air channel, wherein the belt body is made of a flexible material.

2. The belt according to claim 1, wherein the air channel is fully enclosed in the belt body.

3. The belt according to claim 1, wherein the belt body is made of rubber or an elastic plastic.

4. The belt according to claim 1, wherein the belt comprises at least one tensioning cable for tensioning the belt around a hull of a floating vessel.

5. The belt according to claim 4, wherein the tensioning cable is fully embedded in the belt body.

6. The belt according to claim 4, wherein the tensioning cable is made of steel and/or aramid fibres and/or polypropylene fibres.

7. The belt according to claim 1, wherein the belt comprises magnets which are embedded in the belt body, whereby the magnets are magnets for attaching the belt to a metallic hull of a floating vessel.

8. The belt according to claim 1, wherein the bubble generators are fluidic oscillators for generating one or more pulsating air flows from a constant air flow.

9. A device for reducing the drag of a hull of a floating vessel, wherein it comprises a belt according to claim 1, and a tensioning device for tensioning the belt partly or completely around the hull of a floating vessel.

10. The device according to claim 9, wherein it comprises a tension monitoring system capable of generating an status signal indicating a tension status signal indicating a tension which is outside a desired range.

11. The device according to claim 1, wherein it comprises a source of pressurised air which is connected to the air channel.

12. The device according to claim 10, wherein the tension monitoring system is connected to the source of pressurised air, whereby the device is arranged such that an occurrence of said status signal causes the source of pressurised air to cease provision of pressurised air.

13. A method of reducing the drag of a hull of a floating vessel using a belt according to claim 1, whereby the belt is installed under the hull, whereby pressurised air is supplied to the air channel.

14. The method according to claim 13, whereby the belt is a belt according to claim 7, whereby the belt, in a non-tensioned state, is first attached to the hull by means of the magnets, whereby afterwards the belt is tensioned against the hull, whereby during use of the belt tension is maintained.

15. The method according to claim 13, whereby the vessel is a vessel which is being towed by another vessel.

Description

[0028] In order to illustrate the invention, exemplary embodiments are explained below, with reference to the following figures, wherein:

[0029] FIG. 1 shows a perspective view of a component of a belt and a device according to the invention;

[0030] FIG. 2 shows a cross-section of the component of FIG. 1 according to line A-A;

[0031] FIG. 3 shows a cross-section of the component of FIGS. 1 and 2 according to line B-B;

[0032] FIG. 4 shows side view of a vessel using belts and a device according to the invention;

[0033] FIG. 5 shows a cross section according to line C-C of the vessel of FIG. 4;

[0034] FIG. 6 shows a cross section according to line D-D of the vessel of FIG. 5.

[0035] The oscillator 1 of FIGS. 1 to 3 is a traditional fluidic oscillator, of which the air outlets 2,3 are provided with perforated plates 4 with fifty round holes of 1.7 mm diameter each.

[0036] The oscillator 1 comprises a air inlet 5 and an air inlet channel 6 leading away from the air inlet 5. The air inlet channel 6 widens and diverges into two air outlet channels, more specifically a first outlet channel 7 and a second outlet channel 8 which lead to the two aforementioned air outlets 2,3, more specifically to a first air outlet 2 and to a second air outlet 3, which are provided with said perforated plates 4.

[0037] The two outlet channels 7, 8 are separated by a splitter 9 with a concave nose 10.

[0038] The splitter 9 and the air inlet channel 6 and the outlet channels 7, 8 jointly constitute a bistable fluidic amplifier arranged to amplify control signals, whereby in this case the control signals are fed to the fluidic amplifier via a first control port 11 and a second control port 12.

[0039] From each of the air outlets 2,3, a feedback channel 13 leads back to the control ports at the point where the air inlet channel 6 widens.

[0040] The oscillator 1 works as follows: A constant airflow is established at the air inlet 5 and through the air inlet channel 6. This airflow will either flow through the first outlet channel 7 or through the second outlet channel 8, but not through both at the same time. If undisturbed, the air will continue to flow this way because of the Coanda-effect, which enhances the tendency for a fluid to follow a curved surface. The transition from the air inlet channel 6 to each of the outlet channels 7, 8 is such a curved surface. The concave nose 10 of the splitter 9 helps to create an induced secondary airflow that further stabilises the airflow through that particular outlet channel 7,8.

[0041] Most of the air flowing through this outlet channel 7,8 will then exit at the corresponding air outlet 2,3. However, this airflow also generates a pressure pulse which is sent back via the corresponding feedback channel 13 to the corresponding control port 11, 12, and which cause the airflow to switch to the other outlet channel 7,8.

[0042] If left undisturbed, a stable airflow through the other outlet channel 7, 8 will now be established. However, also at the other air outlet 2,3, a pressure wave is generated, which will be fed back via the feedback channel 13 to the corresponding control port 11,12, so that the airflow switches to the other outlet channel 7,8 again.

[0043] This way, a sequence of pressure control signals, in other words a pressure control wave, is established at both control ports 11, 12, every time switching the airflow from the first outlet channel 7 to the second outlet channel 8 and back, thereby generating two pulsating airflows, one in each of the outlet channels 7, 8, each pulsating with the same oscillation frequency and phase shifted by half a wave period.

[0044] These sequences of control signals are thereby amplified by the fluidic amplifier

[0045] The oscillation frequency of the oscillator 1 is more or less fixed, depending on the exact design of the oscillator 1. A change in air pressure at the air inlet 5, resulting in a change in the total air flow rate through the oscillator 1, will influence the oscillation frequency to a relatively small degree, but the oscillation frequency cannot be controlled independently of the air flow rate.

[0046] This oscillator 1 can be advantageously used in a belt 15 and a device 16 according to the invention. This is illustrated in FIGS. 4 to 6.

[0047] These figures show a vessel 17 which is usually not provided with means for reducing drag, but which is in this case temporarily provided with a device 16 15 according to the invention. The vessel 17 is intended to be towed by a tug.

[0048] The device 16 comprises three flexible belts 15 which are attached around the vessel 17.

[0049] The belt 15 comprises a belt body 18 made of flexible rubber. The belt body 18 extends in a length direction L. In the belt body 18 a cavity is provided which acts as an air channel 19 and which extends over the entire length of the belt body 18.

[0050] The belt 15 further comprises fluidic oscillators 1, which are provided inside the belt body 18 at regular distances from each other, typically between two and forty oscillators 1 per meter length of the belt body 18. The air inlet 5 of each of these oscillators 1 is connected to the air channel 19, and the air outlets 2,3 of these oscillators 1 are placed on the outer surface of the belt body 18, so that they can release air freely.

[0051] The belt 15 further comprises a steel tensioning cable 20, which is provided in the belt body 18 and which extends over the entire length of the belt body 18, and which protrudes outside the belt body 18 at its extremes.

[0052] The belt 15 further comprises strong, industrial magnets 21, which are integrated in the belt body 18.

[0053] The device 16 further comprises a compressor 23 and connecting pipes 24 for connecting the air channels 19 in the belt bodies 18 to the compressor 23. The device 16 further comprises three tensioning devices 25 for tensioning the belts 15. The tensioning devices 25 are each equipped with a tension monitoring capability. The device 16 is provided with a data cable 26 between the tensioning devices 25 and the compressor 23.

[0054] This installation and use of the device 16 is as follows.

[0055] Firstly the belts 15 are placed under and partly around the hull 27 of the vessel 17. At this point, the magnets 21 temporarily secure the belts 15 to the hull 27. At this stage the belts 15 can be easily detached and placed somewhere else, so that they can be easily placed at intended positions.

[0056] Their tensioning cables 20 are then connected on deck to anchoring points 26 at one extreme of the belts 15 and to the tensioning devices 25 at the other extreme of the belts 15, and tensioned to be fixed securely in place. The belts 15 will bend to follow the contours of the hull 27.

[0057] Compressed air is then supplied by the compressor 23 to the air channels 19. This compressed air is then distributed in the air channels 19 to the air inlets 5 of the oscillators 1, so that the oscillators 1 start to release a stream of bubbles from their air outlets 2,3.

[0058] This provides air lubrication between the hull 27 of the vessel 17 and the surrounding water, so that a reduction in drag is obtained.

[0059] Obviously it is very undesirable if insufficient tension is applied to the tensioning cables 20, because the belts 15 may then come loose while the vessel 17 is moving through the water. Also, a loss of tension may indicate that a belt 15 is broken or no longer anchored to the deck.

[0060] Obviously it is also very undesirable if the tension is too high, as the belt 15 may break.

[0061] Therefore, the tensioning devices 25 monitor the tension continuously and send an alarm signal via the data cable 26 to the compressor 23 and to the staff of the vessel 17 or the tug if insufficient or too much tension is present, so that the staff may investigate and remedy this situation.

[0062] The compressor 23 is arranged to shut off as a safety measure if an alarm signal is detected.