Belt and method for reducing the drag of a floating hull

Abstract

A belt (15) is provided for reducing the drag of the hull (27) of a floating vessel (17), wherein the belt (15) comprises a belt body (18) extending in a longitudinal direction (L), wherein the belt (15) comprises a series of bubble generators (1) embedded in the belt body (18), wherein the belt (15) comprises an air passage (19) for supplying pressurized air to the bubble generators (1), wherein the air passage (19) extends in the longitudinal direction (L), wherein the bubble generators (1) are connected to the air passage (19), and wherein the belt body (18) is made of a flexible material. The invention also relates to a device (16) comprising such a belt (15) and a method of using such a belt (15) to reduce the drag of the hull (27) of a floating vessel (17).

Description

[0001] The present invention relates to a belt and a method for reducing the drag of the hull of a floating vessel.

[0002] As is well known, when moving through water, the drag of the hull, in other words, the frictional drag, can be reduced by using air bubbles at the interface between the hull of a floating vessel such as a barge or a ship and the water. This is also known as air lubrication. WO 2011 / 161187 discloses a device for doing so.

[0003] In order to install such a device, the hull needs to be modified because the device needs to be firmly and permanently attached to the hull. Therefore, the installation of such a device can only be carried out when the vessel is in a dry dock.

[0004] For vessels that only occasionally make long voyages towed by tugs, such as drilling platforms and floating storage and production units, etc., the installation of such known devices is impracticable and uneconomical.

[0005] Therefore, there is a need for a device that generates air bubbles on the hull, which is easy to install and can be easily removed without damage.

[0006] The present invention aims to solve these problems and thus provides a belt for reducing the drag of the hull of a floating vessel, wherein the belt comprises a belt body extending in the longitudinal direction, wherein the belt comprises a series of bubble generators embedded in the belt body in the longitudinal direction, wherein the belt comprises an air passage for supplying pressurized air to the bubble generators, wherein the air passage extends in the longitudinal direction, wherein the bubble generators are connected to the air passage, and wherein the belt body is made of an elastic and flexible material.

[0007] Such a belt can be easily placed around a part of the hull, in particular the underside of the hull and possibly also the sides, and then tensioned to remain in place. Thus, due to its flexibility, the belt follows the shape of the hull and presses tightly against the hull.

[0008] After use, such a belt can also be removed again by releasing the tension and then reused on another vessel.

[0009] Therefore, if there is no practical opportunity to install a permanent air lubrication system (i.e., for major maintenance), or if the vessel is mainly used in a single location and only occasionally needs to be moved to another distant location, then such a belt is particularly suitable for providing the possibility of air lubrication for the vessel.

[0010] KR 20170000711 discloses a belt that includes: a separate air injection duct that includes an air provider for generating and supplying air; an air supply duct into which the air discharged from the air provider flows; and a separate air injection duct that has a plurality of air injection holes formed on one side thereof. WO 2005 / 122676 discloses a bubble generating device that consists of a multi-chamber system attached to the wall of the hull of a ship and equipped with at least one main circulation shaft through which a first duct for pressurized water and a second duct for pressurized gas pass, and the two ducts supply a plurality of bubble release chambers. US 2011 / 259257 discloses a device for reducing the resistance experienced by a hull when moving through water by inserting bubbles between the hull and the water flow through which the ship is passing by delivering compressed air to the bottom of the ship. US2011 / 214762 discloses a flow tube for a bidirectional flowmeter that includes a first means for generating periodic pressure fluctuations, the frequency of which varies depending on the flow rate of the fluid passing through the flowmeter in a first direction; and a second means for generating periodic pressure fluctuations, the frequency of which varies depending on the flow rate of the fluid passing through the flowmeter in a second direction opposite to the first direction; wherein the first generating means and the second generating means are connected in series between an inlet port and an outlet port. US 7080664 discloses a fluid amplifier that includes at least one control valve having a movable element for selectively opening and closing at least one of a first control flow channel and a second control fluid flow channel, and wherein the control valve further includes a diaphragm for isolating the movable element.

[0011] In a preferred embodiment, the air channel is completely enclosed within the belt body so that it is not easily damaged. Preferably, the air channel is formed as a channel-shaped cavity in the material of the belt body.

[0012] In a preferred embodiment, the belt includes at least one tensioning cable for tensioning the belt around the hull of a floating ship, and preferably, the tensioning cable is completely embedded within the belt body to avoid damage.

[0013] Such a tensioning cable allows a large tensioning force to be applied so that the belt is well maintained in place during use.

[0014] In a preferred embodiment, the belt includes a magnet embedded within the belt body, and the magnet is a magnet for attaching the belt to the metal hull of a floating ship.

[0015] Such a magnet can be used as a fastening mechanism, and as an alternative to tensioning, but preferably as a supplement to tensioning, where the magnet is particularly useful for attaching the belt to the hull during installation and positioning of the belt before tension is applied.

[0016] In a preferred embodiment, the bubble generator is a fluid oscillator for generating one or more pulsating airflows from a constant airflow. These fluid oscillators allow control of the bubble size and bubble spacing such that coalescence of the bubbles can be reduced.

[0017] The invention further relates to a device for reducing the drag of the hull of a floating vessel, the device comprising a belt according to any one of the preceding claims and a tensioning device for tensioning the belt at least partially around the hull of the floating vessel.

[0018] Preferably, the device comprises a tension monitoring system capable of generating a status signal indicating a state where the tension is below a first desired critical tension and / or exceeds a second critical tension. Thus, the range between the first critical tension and the second critical tension is the desired range of tension allowing normal use of the belt.

[0019] Such a status signal can be any type of signal, such as an electronic, radio, visual or audible signal. The status signal can be set to be triggered at the first or second critical tension, which causes the tension to be checked and / or adjusted by personnel. In this case, this is a warning signal that the tension needs to be checked. The status signal can also be set to be triggered when below the first critical tension, at which point, the attachment of the belt to the hull is no longer guaranteed. In this case, the status signal acts as an alarm signal to indicate a loss of sufficient tension, which is undesirable as such a loss may cause the belt to disengage from the hull. The status signal can also be set to be triggered when exceeding the second critical tension, which is an indication that the belt has become stuck on an obstacle. In this case, the status signal also acts as an alarm signal.

[0020] In a preferred embodiment, the device comprises a pressurized air source connected to an air channel, wherein the tension monitoring system is connected to the pressurized air source, and wherein the device is arranged such that the occurrence of the status signal causes the pressurized air source to stop providing pressurized air.

[0021] This is a further safety feature to avoid continued operation of an under-tensioned belt.

[0022] The invention further relates to a method of using a belt or device according to the invention to reduce the drag of the hull of a floating vessel, wherein the belt is installed under the hull and pressurized air is supplied to the air channel.

[0023] In a preferred variant of the method, the belt comprises magnets embedded in the belt body, wherein in the non-tensioned state, the belt is first attached to the hull by the magnets, wherein thereafter, the belt is tensioned against the hull, and wherein during use of the belt, the tension is maintained.

[0024] This is a simple method of installing such a belt because the belt can be correctly positioned first before the tension is applied.

[0025] In a preferred variant of the method, this is a method of temporarily reducing said resistance, wherein the belt is removed after being used for reducing said resistance, preferably rolled up for storage and / or for use on another ship.

[0026] In a preferred variant of the method, the ship is a ship towed by another ship.

[0027] In the last two variants, the method focuses on equipping ships that only occasionally make long voyages (e.g., international voyages across the ocean) and may not even have sufficient on-board propulsion capabilities for such long voyages with an air lubrication system.

[0028] To illustrate the present invention, exemplary embodiments are explained below with reference to the accompanying drawings, wherein:

[0029] Figure 1 A perspective view of the components of the belt and the device according to the present invention is shown;

[0030] Figure 2 Shows Figure 1 A cross-section of the components taken along line A-A;

[0031] Figure 3 Shows Figure 1 And Figure 2 A cross-section of the components taken along line B-B;

[0032] Figure 4 A side view of a ship using the belt and the device according to the present invention is shown;

[0033] Figure 5 Shows Figure 4 A cross-section of the ship taken along line C-C;

[0034] Figure 6 Shows Figure 5 A cross-section of the ship taken along line D-D.

[0035] Figures 1 to 3 The oscillator 1 of is a conventional fluid oscillator, the air outlets 2, 3 of which are provided with porous plates 4, each of which has fifty round holes with a diameter of 1.7 mm.

[0036] The oscillator 1 comprises an air inlet 5 and an air inlet channel 6 facing away from the air inlet 5. The air inlet channel 6 widens and branches into two air outlet channels, more specifically a first outlet channel 7 and a second outlet channel 8, which lead to the two above-mentioned air outlets 2, 3, more specifically to the first air outlet 2 and the second air outlet 3 provided with the porous plate 4.

[0037] The two outlet channels 7 , 8 are separated by a flow divider 9 having a concave nose 10 .

[0038] The flow splitter 9 and the air inlet channel 6 and the outlet channels 7 , 8 together constitute a bistable fluid amplifier arranged to amplify a control signal, wherein in this case the control signal is fed to the fluid amplifier via the first control port 11 and the second control port 12 .

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

[0040] The oscillator 1 works as follows: a constant air flow is established at the air inlet 5 and through the air inlet channel 6. This air flow will flow through either the first outlet channel 7 or the second outlet channel 8, but not both at the same time. If undisturbed, the air will continue to flow in this way due to the Coanda-effect, which enhances the tendency of the fluid to flow along 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 air flow, which further stabilizes the air flow through this 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 air flow also generates a pressure pulse which is sent back to the corresponding control port 11, 12 via the corresponding feedback channel 13 and causes the air flow to switch to the other outlet channel 7, 8.

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

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

[0044] These control signal sequences are thus amplified by the fluid amplifier.

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

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

[0047] These figures show a ship 17, which usually is not provided with tools for reducing drag, but in this case is temporarily provided with the devices 16, 15 according to the present invention. The ship 17 is intended to be towed by a tugboat.

[0048] The device 16 includes three flexible belts 15, which are attached around the ship 17.

[0049] The belt 15 includes a belt body 18 made of flexible rubber. The belt body 18 extends in the longitudinal direction L. In the belt body 18, there is provided a cavity, which serves as an air passage 19 and extends over the entire length of the belt body 18.

[0050] The belt 15 further includes fluid oscillators 1, which are arranged at regular distances from each other inside the belt body 18, typically two to 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 passage 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 freely release air.

[0051] The belt 15 further includes a steel tension cable 20, which is arranged in the belt body 18 and extends over the entire length of the belt body 18, and protrudes outside the belt body 18 at its ends.

[0052] The belt 15 further includes strong industrial magnets 21 integrated in the belt body 18.

[0053] The device 16 further includes a compressor 23 and a connecting pipe 24 for connecting the air passage 19 in the belt body 18 to the compressor 23. The device 16 further includes three tensioning devices 25 for tensioning the belt 15. The tensioning devices 25 are each equipped with tension monitoring capabilities. The device 16 is provided with a data cable 26 between the tensioning devices 25 and the compressor 23.

[0054] The installation and use of device 16 are as follows.

[0055] First, belt 15 is placed under hull 27 of ship 17 and partially surrounds the hull. At this time, magnet 21 temporarily fixes belt 15 to hull 27. At this stage, belt 15 can be easily detached and placed elsewhere so that the belt can be easily placed at the intended position.

[0056] Next, their tension cables 20 are connected to anchor points 26 at one end of belt 15 on the deck and to tensioning device 25 at the other end of belt 15, and are tensioned to be firmly fixed in place. Belt 15 will bend to follow the contour of hull 27.

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

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

[0059] Obviously, it is highly undesirable that insufficient tension is applied to tension cable 20, because when ship 17 moves in water, belt 15 may then become loose. Also, a loss of tension may indicate that belt 15 is broken or no longer anchored to the deck.

[0060] Obviously, it is also highly undesirable that the tension is too high, because belt 15 may break.

[0061] Therefore, tensioning device 25 continuously monitors the tension and sends an alarm signal via data cable 26 to the crew of compressor 23 and ship 17 or the tugboat: if the tension is insufficient or excessive, then the crew can investigate and remedy the situation.

[0062] As a safety measure, compressor 23 is arranged to shut down if an alarm signal is detected.

Claims

1. A belt (15) for reducing the drag of the hull (27) of a floating ship (17), wherein the belt (15) comprises a belt body (18) extending in a longitudinal direction (L), wherein the belt (15) comprises a series of bubble generators (1) embedded in the belt body (18), wherein the belt (15) comprises an air passage (19) for supplying pressurized air to the bubble generators (1), wherein the air passage (19) extends in the longitudinal direction (L), and wherein the bubble generators (1) are connected to the air passage (19), characterized in that, The belt body (18) is made of a flexible material; The belt (15) includes at least one tension cable (20) for tensioning the belt (15) around the hull (27) of the floating vessel (17).

2. The belt (15) according to claim 1, characterized in that, The air passage (19) is completely enclosed within the belt body (18).

3. The belt (15) according to claim 1, characterized in that, The belt body (18) is made of rubber or elastic plastic.

4. The belt (15) according to claim 1, characterized in that, The tension cable (20) is completely embedded within the belt body (18).

5. The belt (15) according to claim 1, characterized in that, The tension cable (20) is made of steel and / or aramid fibers and / or polypropylene fibers.

6. The belt (15) according to claim 1, characterized in that, The belt (15) includes magnets (21) embedded within the belt body (18), where the magnets are magnets (21) for attaching the belt (15) to the metal hull (27) of the floating vessel (17).

7. The belt (15) according to claim 1, characterized in that, These bubble generators are fluid oscillators (1) for generating one or more pulsating airflows from a constant airflow.

8. A device (16) for reducing the drag of the hull (27) of a floating ship (17), characterized in that, The device includes a belt (15) according to any one of the preceding claims and a tensioning device (25) for tensioning the belt (15) partially or completely around the hull (27) of the floating vessel (17).

9. The device (16) according to claim 8, characterized in that, The device includes a tension monitoring system that is capable of generating a status signal indicative of a tension status signal, the tension status signal indicating a tension outside a desired range.

10. The device (16) according to claim 9, characterized in that, The device includes a pressurized air source (23) connected to the air passage (19).

11. The device (16) according to claim 10, characterized in that, The tension monitoring system is connected to the pressurized air source (23), where the device (16) is arranged such that the occurrence of the status signal causes the pressurized air source to stop supplying pressurized air.

12. A method of reducing the drag of the hull (27) of a floating vessel (17) using a belt (15) according to any one of claims 1 to 7 or a device (16) according to any one of claims 8 to 11, where the belt (15) is installed below the hull (27), and pressurized air is supplied to the air passage (19).

13. The method according to claim 12, where the belt (15) is the belt (15) according to claim 7, where in the non-tensioned state, the belt (15) is first attached to the hull (27) by these magnets (21), whereafter, the belt (15) is tensioned against the hull (27), and where during use of the belt (15), the tension is maintained.

14. The method according to claim 12 or 13, where the vessel (17) is a vessel (17) towed by another vessel.

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