Liquid-phase suction air lubrication system

Abstract

To provide an air lubrication system capable of increasing friction resistance reduction effect of a hull due to air bubble blowing to a vessel bottom more than conventionally.SOLUTION: A liquid phase suction type air lubrication system includes: an air port 10 provided in front of a vessel bottom 2 of a hull 1; a liquid phase suction opening 20 provided on the vessel bottom 2 more to the rear than the air port 10; suction means 30 for sucking in water of liquid phase with no air bubbles present in the vicinity of the vessel bottom surface from the liquid phase suction opening 20; and control means 40 for controlling the suction means 30. The suction means 30 is controlled by the control means 40 so that liquid phase sucking-in thickness determined by sucking-in flow amount of water from the liquid phase suction opening 20, width of the liquid phase suction opening 20, and vessel speed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an air lubrication system that reduces frictional resistance of a ship's hull by blowing bubbles onto the bottom of the ship. [Background technology]

[0002] In the case of ships, a technology is known that reduces frictional resistance by releasing air bubbles into the hull while the ship is underway. For example, Patent Document 1 discloses a bubble-lubricated vessel comprising a hull having a flat bottom in the central part in the longitudinal direction, keel plates arranged on both sides of the flat bottom, a bubble discharge port formed in the bow of the hull, a bubble recovery port formed at the stern end of the flat bottom, an air passage extending between the bubble recovery port and the bubble discharge port, and an air compressor that supplies pressurized air to the air passage, wherein a free water surface is formed in the air passage above the bubble recovery port, and bubbles discharged from the bubble discharge port return to the air passage from the free water surface above the bubble recovery port. Furthermore, Patent Document 2 describes an air blowing device that blows air into the water from an air blowing port provided on the bottom of the hull, and an air recovery device that recovers air into the hull from an air recovery port provided on the bottom of the hull, the air recovery port being located stern-side from the air blowing port and bow-side from the propeller provided on the hull, the propeller being located on the centerline of the hull, and the air recovery port being a central air recovery port provided so as to straddle the centerline, and the central air recovery port A friction-reducing vessel is disclosed, which includes a port-side air recovery port located to the port side of the centerline so as to protrude further to the port side, and a starboard-side air recovery port located to the starboard side of the centerline so as to protrude further to the starboard side than the central air recovery port, wherein the port-side and starboard-side air recovery ports are positioned further forward than the central air recovery port, and each of the central air recovery port, port-side air recovery port, and starboard-side air recovery port is formed by multiple air recovery holes. Furthermore, Patent Document 3 discloses a friction-reducing vessel comprising an air blowing device that blows air into the water from an air outlet provided on the bottom of the hull, and an air recovery device that recovers air into the hull from an air recovery port provided on the bottom of the hull, wherein the air recovery port is located sternward from the air blowing device and bowward from a propeller provided on the hull, and the air recovery device blows air into the water from a re-air blowing port provided on the bottom of the hull, wherein the re-air blowing port is located sternward from the air blowing device and bowward from the air recovery port. Furthermore, Patent Document 4 discloses a bubble-holding device for a ship, comprising a gas nozzle installed on the bottom of the ship that ejects bubbles along the bottom of the ship, a blower that supplies gas to the gas nozzle, an electric motor that drives the blower, and a gas-liquid separator that sucks up the ejected bubbles along with water at least behind the gas nozzle on the bottom of the ship.

[0003] Non-patent document 1 states that the amount of resistance reduction shows a positive correlation with the peak value of the void fraction. Furthermore, Non-Patent Document 2 states that as you move downstream from the discharge point, the void fraction peak position near the wall moves away from the wall due to the influence of downward lift and diffusion forces caused by turbulence, and the drag reduction effect also decreases. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-274713 [Patent Document 2] Japanese Patent Publication No. 2011-213303 [Patent Document 3] Japanese Patent Publication No. 2011-213306 [Patent Document 4] Japanese Patent Publication No. 2013-216325 [Non-patent literature]

[0005] [Non-Patent Document 1] Madan Mohan Guin, 4 others, “Reduction of skin friction by microbubbles and its relation with near-wall bubble concentration in a channel”, Journal of Marine Science and Technology, 1996, Volume 1, Issue 5, p.241-254 [Non-Patent Document 2] Hisanori Kawashima, et al., "Experimental Study on Frictional Resistance Reduction by Microbubbles," Journal of the Japan Society of Fluid Mechanics "Nagare," Japan Society of Fluid Mechanics, June 2006, Vol. 25, No. 3, pp. 209-217. [Overview of the project] [Problems that the invention aims to solve]

[0006] The phenomenon described in Non-Patent Document 2, where the drag reduction effect decreases as you move downstream from the discharge point, is thought to occur more significantly in actual vessels with long flow distances. However, Patent Document 1 does not disclose any measures to address the phenomenon where the resistance reduction effect decreases as you move downstream from the discharge point. Furthermore, the fifth embodiment in Patent Document 2 and Patent Document 3 describe blowing the air recovered from the air recovery port into the water from an air re-discharge port located in the middle of the hull. However, no measures are disclosed to address the issue of air bubbles detaching from the hull before reaching the air recovery port located at the stern, rather than from the air discharge port located at the bow. Furthermore, Patent Document 4 describes a method of drawing bubbles ejected behind the gas nozzle back into a gas-liquid separator through a water intake using a bubble suction means, thereby attracting the bubbles back to the vicinity of the ship's bottom. However, the bubble suction means does not control the flow rate of water drawn in from the liquid phase. Accordingly, an object of the present invention is to provide an air lubrication system that can further enhance the frictional resistance reduction effect of a hull achieved by blowing air bubbles to the ship bottom by sucking liquid-phase water, compared with conventional systems. [MEANS FOR SOLVING THE PROBLEMS]

[0007] A liquid-phase suction type air lubrication system corresponding to the description of claim 1 is an air lubrication system that blows air bubbles to the ship bottom of a vessel to reduce the frictional resistance of the hull, comprising: an air outlet provided at the front of the ship bottom of the hull; a liquid-phase suction port provided on the ship bottom behind the air outlet; a suction means for sucking liquid-phase water free of intervening air bubbles in the vicinity of the ship bottom surface from the liquid-phase suction port; and a control means for controlling the suction means, wherein the control means controls the suction means such that a liquid-phase suction thickness determined by the suction flow rate of water from the liquid-phase suction port, the width of the liquid-phase suction port, and the ship speed falls within a predetermined range. According to the present invention described in claim 1, by controlling the liquid-phase suction thickness to fall within the predetermined range, the frictional resistance reduction effect by air bubbles can be improved as compared with the conventional art. In addition, by sucking the liquid-phase water, the gas-liquid separator can be eliminated.

[0008] The present invention according to claim 2 is characterized in that the predetermined range of the liquid-phase suction thickness determined based on formula (1) is set to 0.12 [mm] or more and 0.38 [mm] or less. [Mathematical Formula] Here, t Suction : liquid-phase suction thickness, Q Suction : suction flow rate of water, B: width of the liquid-phase suction port, V: ship speed. According to the present invention described in claim 2, the frictional resistance reduction effect by air bubbles can be reliably increased as compared with the conventional art.

[0009] The present invention according to claim 3 is characterized in that a plurality of stages of liquid-phase suction ports are provided at predetermined intervals along the flow of air bubbles on the ship bottom. According to the present invention as described in claim 3, bubbles that have started to separate from the bottom of the ship downstream of the preceding liquid phase intake can be drawn back towards the bottom of the ship near the subsequent liquid phase intake.

[0010] The present invention as described in claim 4 is characterized in that a plurality of air outlets are provided in the width direction of the ship's bottom, and the air outlets located in the center of the ship's bottom are arranged in an inverted V shape with the ones located on both sides facing forward and the ones facing backward, and a plurality of liquid phase intake ports are provided in the width direction of the ship's bottom, and the plurality of liquid phase intake ports are arranged in an inverted V shape. According to the present invention as described in claim 4, by arranging the air outlets in an inverted V shape, the air outlets can be positioned as far forward as possible, and by arranging the liquid phase intake in an inverted V shape to match the air outlets, it is possible to effectively prevent bubbles blown out from each air outlet from detaching from the bottom of the ship.

[0011] The present invention as described in claim 5 is characterized in that a plurality of air outlets are provided in the ship's width direction on the bottom of the ship, a plurality of liquid phase intake ports are provided in the ship's width direction on the bottom of the ship, and the liquid phase intake ports located in the center of the bottom of the ship are arranged in a V-shape with those located on both sides facing forward. According to the present invention as described in claim 5, when there is a large amount of air bubbles surrounding the side of the ship, it is possible to effectively prevent the bubbles from detaching from both sides.

[0012] The present invention as described in claim 6 is characterized in that a liquid phase intake port is provided in the bottom of the ship, and further, a liquid phase intake port is provided in at least one of the sides or stern of the ship's hull, in a portion of the hull that has a three-dimensional shape. According to the present invention as described in claim 6, it is possible to attract air bubbles that have separated from the bottom of the ship towards the side or stern of the ship, thereby reducing resistance at the side or stern of the ship.

[0013] The present invention as described in claim 7 is characterized in that a liquid phase intake port is formed using a porous plate, and water is drawn in from the entire surface of the porous plate. According to the present invention as described in claim 7, the suction speed of the liquid phase inlet can be made uniform, reducing the influence on the flow field and ensuring reliable suction of liquid water.

[0014] The present invention as described in claim 8 is characterized in that the internal path of the liquid phase suction port is formed in an oblique direction toward the front from the opening of the liquid phase suction port when viewed from the side. According to the present invention as described in claim 8, when water is drawn in from the liquid phase intake port, the water is drawn in forward relative to the flow of bubbles toward the rear of the hull, thereby reducing the amount of bubbles mixed in.

[0015] The present invention as described in claim 9 is characterized in that the control means controls the suction flow rate based on at least one of the ship speed and the ship's attitude. According to the present invention as described in claim 9, the suction flow rate can be appropriately controlled, and the liquid phase suction thickness can be controlled to a predetermined range according to the ship speed and ship attitude.

[0016] The present invention as described in claim 10 is characterized in that the control means controls the suction flow rate based on the measured amount of bubbles mixed into the water sucked in by the suction means. According to the present invention as described in claim 10, the amount of air bubbles mixed in with the water drawn in from the liquid phase inlet can be reduced, and the liquid phase water can be drawn in primarily.

[0017] The present invention as described in claim 11 is characterized in that the control means controls the periodic discharge of bubbles from the air outlet and synchronizes the periodic suction of water by the suction means. According to the present invention as described in claim 11, when bubbles are periodically blown out, suction is performed only during the phase in which bubbles exist, making it possible to reduce the energy required for blowing out air and sucking in water while maintaining the frictional resistance reduction effect.

[0018] The present invention as described in claim 12 is characterized in that the control means controls the suction flow rate based on the measured hull motion of the ship, taking into account the phase difference from the air outlet to the liquid phase suction port of the bubbles blown out. According to the present invention as described in claim 12, bubbles can be efficiently drawn to the bottom of the ship even when the ship is in motion.

[0019] The present invention as described in claim 13 is characterized in that the liquid phase intake port also serves as the sea chest, which is the water intake port of a ship. According to the present invention as described in claim 13, the configuration of the hull and system can be simplified compared to the case in which a liquid phase intake port and a sea chest are provided separately, and the sucked-in water can be used for cooling the main engine, etc.

[0020] The present invention as described in claim 14 is characterized in that the suction means is configured by connecting an opening provided on the hull surface in a portion that generates negative pressure when the ship is propelled, and a liquid phase suction port, via a control valve and piping. According to the present invention as described in claim 14, water can be drawn in from the liquid phase inlet without using power.

[0021] The present invention as described in claim 15 is characterized in that the suction means is configured by connecting an opening provided in a part of the hull surface that generates negative pressure when the ship is propelled, and a liquid phase suction port, via a pump and piping. According to the present invention as described in claim 15, the suction power of the pump used to draw in water can be reduced by utilizing the negative pressure on the hull surface.

[0022] The present invention as described in claim 16 is characterized in that water sucked in by a suction means from a liquid phase intake port is discharged from at least one of the front of the propeller at the stern of the hull and on both sides of the bottom of the hull. According to the present invention as described in claim 16, by discharging the inhaled water in front of the propeller at the stern of the hull, it is possible to prevent air bubbles from entering the propeller and to prevent deterioration of the wake coefficient and propeller efficiency due to air bubble mixing, thereby preventing a decrease in propulsion efficiency and improving the horsepower reduction effect of air lubrication. Furthermore, by discharging the inhaled water from both sides of the bottom of the hull, it is possible to prevent air bubbles from detaching from both sides of the bottom of the hull and to enhance the effect of reducing frictional resistance due to air bubbles. [Effects of the Invention]

[0023] According to the liquid-phase suction type air lubrication system of the present invention, by controlling the liquid-phase suction thickness to be within a predetermined range, the friction resistance reduction effect by air bubbles can be improved compared to conventional systems. Furthermore, by suctioning water in the liquid phase, a gas-liquid separator can be eliminated.

[0024] Furthermore, if the predetermined range of the liquid phase absorption thickness determined based on formula (1) is set to 0.12 [mm] or more and 0.38 [mm] or less, the frictional resistance reduction effect due to air bubbles can be reliably increased compared to conventional methods.

[0025] Furthermore, if multiple liquid-phase intake ports are provided at predetermined intervals along the flow of bubbles at the bottom of the ship, bubbles that have started to move away from the bottom of the ship downstream of the preceding liquid-phase intake port can be drawn back towards the bottom of the ship near the subsequent liquid-phase intake port.

[0026] Furthermore, if multiple air outlets are provided in the width direction of the hull bottom, and the air outlets located in the center of the hull bottom are positioned forward and those on both sides are positioned aft in an inverted V shape, and if multiple liquid phase intakes are provided in the width direction of the hull bottom, and the multiple liquid phase intakes are also positioned in an inverted V shape, then by arranging the air outlets in an inverted V shape, the air outlets can be positioned as far forward as possible, and by arranging the liquid phase intakes in an inverted V shape to match the air outlets, it is possible to effectively prevent bubbles blown out from each air outlet from detaching from the hull bottom.

[0027] Furthermore, if multiple air outlets are provided in the width direction of the hull bottom, and multiple liquid phase intake ports are provided in the width direction of the hull bottom, and if the liquid phase intake ports located in the center of the hull bottom are arranged in a V-shape with those located on both sides facing forward, then when there is a large amount of air bubbles wrapping around to the sides of the hull, it is possible to effectively prevent air bubbles from escaping from both sides.

[0028] Furthermore, if a liquid phase intake is provided on the bottom of the hull, and also on at least one of the three-dimensional parts of the hull, either the side or the stern, it is possible to draw bubbles that have separated from the bottom of the hull towards the side or stern, thereby reducing resistance at the side or stern.

[0029] Furthermore, when the liquid phase intake port is formed using a perforated plate and water is drawn in from the entire surface of the perforated plate, the suction speed of the liquid phase intake port can be made uniform, reducing the impact on the flow field and ensuring reliable suction of liquid water.

[0030] Furthermore, if the internal path of the liquid phase intake is formed at an angle from the opening of the liquid phase intake towards the front when viewed from the side, when water is drawn in from the liquid phase intake, it is drawn in towards the front relative to the flow of bubbles that are moving towards the rear of the hull, thus reducing the amount of bubbles mixed in.

[0031] Furthermore, if the control means controls the suction flow rate based on at least one of the ship's speed and hull attitude, the suction flow rate can be appropriately controlled, and the liquid phase suction thickness can be controlled to a predetermined range corresponding to the ship's speed and hull attitude.

[0032] Furthermore, if the control means controls the suction flow rate based on the measured amount of bubbles mixed into the water sucked in by the suction means, the amount of bubbles mixed into the water sucked in from the liquid phase suction port can be reduced, allowing the liquid phase water to be mainly sucked in.

[0033] Furthermore, if the control means controls the periodic release of bubbles from the air outlet and synchronizes the periodic intake of water by the intake means, then when bubbles are released periodically, intake will only occur during the phase in which bubbles exist. This allows for a reduction in the energy required for air release and water intake while maintaining the frictional resistance reduction effect.

[0034] Furthermore, if the control means controls the suction flow rate based on the measured hull motion of the ship, taking into account the phase difference between the bubbles blown out from the air outlet and the liquid phase intake, the bubbles can be efficiently drawn to the bottom of the ship even if there is hull motion.

[0035] Furthermore, if the liquid phase intake is combined with the ship's water intake, the configuration of the hull and system can be simplified compared to when the liquid phase intake and sea chest are provided separately, and the sucked-in water can be used for cooling the main engine, etc.

[0036] Furthermore, if the suction mechanism is configured by connecting an opening provided on the hull surface where negative pressure is generated during ship propulsion with a liquid phase suction port via piping and a control valve, water can be drawn in from the liquid phase suction port without using power.

[0037] Furthermore, if the suction mechanism is configured by connecting an opening provided on the hull surface where negative pressure is generated during ship propulsion to a liquid phase suction port via piping and a pump, the suction power of the pump used to draw in water can be reduced by utilizing the negative pressure on the hull surface.

[0038] Furthermore, when the water drawn in by the suction means from the liquid phase intake is discharged from at least one of the forward of the propeller at the stern of the hull and on both sides of the bottom of the hull, discharging the drawn-in water in front of the propeller at the stern of the hull prevents air bubbles from entering the propeller, thus preventing deterioration of the wake coefficient and propeller efficiency due to air bubble mixing, and thereby preventing a decrease in propulsion efficiency, and thus improving the horsepower reduction effect of air lubrication. In addition, discharging the drawn-in water from both sides of the bottom of the hull prevents air bubbles from detaching from both sides of the bottom of the hull, and thus enhances the effect of reducing frictional resistance due to air bubbles. [Brief explanation of the drawing]

[0039] [Figure 1] Schematic diagram of a liquid-phase suction type air lubrication system according to the first embodiment of the present invention. [Figure 2] Conceptual diagram of a liquid-phase suction air lubrication system. [Figure 3] This figure shows an example of the void fraction measurement unit. [Figure 4] A diagram showing an example of a liquid phase suction port. [Figure 5] This diagram shows an example of the connection between the liquid phase suction port and the hull negative pressure section. [Figure 6] This diagram shows an example of using water drawn in through the same-phase intake port as a blowout from the stern of a ship. [Figure 7] This diagram shows an example of using water drawn in through the same liquid phase intake port as a blowout from the side of the ship. [Figure 8] Schematic diagram of a liquid-phase suction type air lubrication system according to a second embodiment of the present invention. [Figure 9] Schematic diagram of a liquid-phase suction type air lubrication system according to the third embodiment of the present invention. [Figure 10] Schematic diagram of a liquid-phase suction type air lubrication system according to the fourth embodiment of the present invention. [Figure 11] Schematic diagram of a liquid-phase suction type air lubrication system according to the fifth embodiment of the present invention. [Figure 12] Schematic diagram of a liquid-phase suction type air lubrication system according to the sixth embodiment of the present invention. [Figure 13] Schematic diagram of a liquid-phase suction type air lubrication system according to the seventh embodiment of the present invention. [Figure 14] Schematic diagram of the unit used in the verification test [Figure 15] Figure showing measurement results in verification tests [Figure 16] This figure shows the change in the resistance reduction rate when only fluid is sucked in during the verification test, without blowing air. [Modes for carrying out the invention]

[0040] A liquid-phase suction type air lubrication system according to an embodiment of the present invention will be described. Figure 1 is a schematic diagram of a liquid-phase suction type air lubrication system according to the first embodiment installed on a ship, with Figure 1(a) being a side view and Figure 1(b) being a bottom view. Figure 2 is a conceptual diagram of the liquid-phase suction type air lubrication system. Figures 1 and 2 show a ship with a hull 1 equipped with a propeller 3 and a rudder 4. The liquid-phase suction air lubrication system is an air lubrication system that reduces the frictional resistance of the hull 1 by blowing bubbles onto the bottom 2 of the ship, and comprises an air outlet 10 provided in front of the bottom 2 of the hull 1, a liquid-phase intake port 20 provided in the bottom 2 behind the air outlet 10, a suction means 30 that sucks in liquid-phase water without bubbles from the liquid-phase suction port 20 near the bottom surface of the ship, and a control means 40 that controls the suction means 30. Air blown out from an air outlet 10 located on the bow side of the bottom 2 forms bubbles that cover the bottom 2, thereby reducing the frictional resistance of the hull 1 while it is sailing. However, as described above, as the distance from the air outlet 10 to the downstream side increases, the bubbles move away from the bottom 2 and the frictional resistance reduction effect diminishes. Therefore, the liquid-phase suction air lubrication system of this embodiment uses a suction means 30 located approximately in the middle of the bottom 2 in the longitudinal direction to draw water (seawater if the ship is sailing in the ocean) from the liquid-phase suction port 20, thereby bringing the bubbles (peak position of void fraction) closer to the wall surface (bottom surface) of the bottom 2. This prevents the frictional resistance reduction effect from diminishing in areas far from the air outlet 10.

[0041] However, if the liquid phase suction flow rate is too high, air bubbles will be introduced, reducing the void ratio and diminishing the frictional resistance reduction effect. Therefore, the control means 40 controls the suction means 30 so that the liquid phase suction thickness is within a predetermined range. By controlling the liquid phase suction thickness to be within a predetermined range, the frictional resistance reduction effect due to air bubbles can be improved compared to conventional methods. In addition, by suctioning water in the liquid phase, the gas-liquid separator can be eliminated. Figure 2 illustrates the difference between the case where the liquid phase suction thickness is controlled to be within a predetermined range ("During Suction" in the figure) and the case where the liquid phase suction thickness is not controlled ("Uncontrolled" in the figure). The liquid phase is defined as the region where the void fraction of the fluid (gas-liquid two-phase fluid) is 19% or less, as shown in the enlarged view of Figure 2. If the local void fraction at a distance y=0.38[mm] from the wall is 19[%], then when a fluid of water and air (gas-liquid two-phase fluid) is suctioned, the void fraction of the suctioned fluid (gas-liquid two-phase fluid) is averaged to approximately 10[%]. Thus, in order to keep the void fraction of the suctioned fluid (gas-liquid two-phase fluid) at approximately 10[%] or less, the liquid phase suction thickness must be 0.38[mm] or less, and the void fraction of the suctioned fluid (gas-liquid two-phase fluid), i.e., the liquid phase, must be 19[%] or less.

[0042] The liquid phase suction thickness is determined by the water suction flow rate from the liquid phase suction port 20, the width of the liquid phase suction port 20, and the ship speed, and is expressed by the following equation (1).

number

[0043] The predetermined range of the liquid phase absorption thickness is preferably about 0.12 mm to 0.38 mm, and more preferably about 0.20 mm to 0.30 mm. This makes it possible to reliably increase the frictional resistance reduction effect by bubbles compared to conventional methods. The liquid phase suction port 20 may be divided into multiple sections in the ship width direction, as shown in Figure 1, in which case it is possible to adjust the liquid phase suction flow rate for each section.

[0044] The control means 40 controls the suction means 30 based on conditions such as the ship speed detected by GPS or electromagnetic log, and the ship's attitude (trim, pitch) detected by an inclinometer or gyroscope. This adjusts the water intake flow rate from the liquid phase intake port 20. Table 1 below shows an example of the control method of the control means 40. For example, the suction flow rate is increased when the ship is bow trimmed, and decreased when the ship is stern trimmed, thus controlling the suction flow rate according to the trim of the ship's hull 1. [Table 1] In this way, the control means 40 controls the suction flow rate based on at least one of the ship's speed and hull attitude. This allows for appropriate control of the suction flow rate and enables the liquid phase suction thickness to be controlled within a predetermined range corresponding to the ship's speed and hull attitude.

[0045] The control means 40 can also control the suction flow rate based on the measured amount of bubbles mixed into the water sucked in by the suction means 30. This reduces the amount of bubbles mixed into the water sucked in from the liquid phase suction port 20, allowing the system to primarily draw in liquid phase water. The amount of air bubbles is determined, for example, by the void fraction. Figure 3 shows an example of a void fraction measurement unit. The void fraction measurement unit 70 is installed in a pipeline or the like downstream of the liquid phase inlet 20. The control means 40 measures the void fraction of the absorbed water and controls the suction means 30 so that the suction flow rate is such that it does not contain air bubbles. Methods such as probe methods (capacitive type, optical fiber type), wire mesh sensors, X-ray CT measurement, and neutron measurement can be applied to measure the void fraction.

[0046] The control means 40 can also control the air (bubbles) being blown out from the air outlet 10 periodically by controlling the blowing means 50, such as a blower or compressor. However, when air is blown out periodically, if suction is performed from the liquid phase inlet 20 during a phase in which no bubbles exist, resistance will increase, and the energy consumption of the blowing means 50 will also increase. Therefore, when the control means 40 periodically blows out air, it periodically suctions water using the suction means 30 in synchronization with the air blowing. This allows suction to be performed only during the phase in which bubbles exist, thus reducing the energy required for air blowing and water suction while maintaining the frictional resistance reduction effect. The phase in which bubbles exist is calculated, for example, from the distance from the ship's side to the flow distance. The control means 40 can also control the suction flow rate by controlling the suction means 30, taking into account the phase difference between the bubbles blown out from the air outlet 10 and the liquid phase suction port 20, based on the measured hull motion of the ship. By detecting the hull motion and dynamically changing the suction amount, taking into account the phase difference calculated from the flow distance, bubbles can be efficiently drawn to the bottom 2 of the ship even when the hull is moving.

[0047] Figure 4 shows examples of liquid-phase suction ports; Figure 4(a) is a bottom view showing an example of a surface suction structure, and Figure 4(b) is a side view showing an example of a stern-facing suction structure. The surface suction structure shown in Figure 4(a) uses a porous plate to form the liquid phase suction port 20, drawing water in from the entire surface of the porous plate. This makes the suction speed of the liquid phase suction port 20 uniform, reducing its impact on the flow field and ensuring reliable suction of liquid water. The stern-facing suction structure in Figure 4(b) is formed such that the internal path of the liquid phase suction port 20 is obliquely oriented forward from the opening of the liquid phase suction port 20 when viewed from the side. By oriented the opening of the liquid phase suction port 20 toward the stern in this way, when water is drawn in from the liquid phase suction port 20, the water is drawn in forward relative to the flow of bubbles that are directed toward the rear of the hull 1, thus reducing the inclusion of bubbles.

[0048] The liquid phase intake port 20 can also serve as the sea chest, which is the water intake port for the ship. By using the sea chest as the liquid phase intake port 20, the configuration of the ship's bottom 2 and the system can be simplified compared to the case where the liquid phase intake port 20 and the sea chest are provided separately, and the sucked-in water can be used for cooling the main engine, etc. Additionally, a ballast water pump can be used as the suction power source.

[0049] Figure 5 shows an example of the connection between the liquid phase intake and the hull negative pressure section, with Figure 5(a) being a side view and Figure 5(b) being a bottom view. The suction mechanism 30 shown in Figure 5 is constructed by connecting an opening 31, which is provided in a part of the hull surface that generates negative pressure when the ship is propelled, with a liquid phase suction port 20 via a control valve 33 and piping 32. By connecting the negative pressure area on the hull surface that occurs when the ship is propelled in this way with the liquid phase suction port 20, water can be drawn in from the liquid phase suction port 20 without using power such as a pump. Note that the location where negative pressure occurs varies depending on the ship type, but in a typical merchant ship type, negative pressure occurs in the area where the hull shape changes in three dimensions, specifically in the bilge area, in the aft half of the hull and in front of propeller 3, as shown in Figure 5. Alternatively, the suction means 30 may be configured by connecting an opening 31, provided in a part of the hull surface that generates negative pressure when the ship is propelled, and a liquid phase suction port 20 via piping 32 through a pump instead of a control valve 33. By connecting the suction pump of the suction means 30 to the negative pressure area on the hull surface that is generated when the ship is propelled, the suction power of the pump used to draw in water can be reduced by utilizing the negative pressure on the hull surface. Another configuration of the suction means 30 is to install a pipe that extends from the liquid phase suction port 20 to the air, leaving the top of the pipe open to the atmosphere. In this configuration, water can be sucked in without power until the water level in the pipe matches the water surface. Furthermore, as another configuration of the suction means 30, it is also possible to install piping that leads from the liquid phase suction port 20 to the air via a suction pump, leaving the top of the piping open to the atmosphere. In this configuration, it is possible to reduce the power required to suck in bubbles until the water level in the piping matches the water surface.

[0050] Figure 6 shows an example where water drawn in through a liquid-phase intake is used to discharge from the stern of the ship; Figure 6(a) is a side view and Figure 6(b) is a bottom view. Figure 7 shows an example where water drawn in through a liquid-phase intake is used to discharge from the side of the ship; Figure 7(a) is a side view, Figure 7(b) is a bottom view, and Figure 7(c) is a cross-sectional view of the section where the liquid-phase intake is provided. The water sucked in by the suction means 30 from the liquid phase suction port 20 may be discharged from at least one of the forward of the propeller 3 at the stern of the hull 1 and from both sides of the bottom 2. When discharged from the front of the propeller 3, as shown in Figure 6, the water drawn in at the liquid phase intake port 20 is separated into gas and liquid within the piping and discharged from the liquid phase outlet port 80 located in front of the propeller 3 at the stern. By blowing out only the liquid phase in front of the propeller 3, air bubbles can be separated from the hull surface and prevented from entering the propeller surface. This prevents air bubbles from entering the propeller 3, prevents deterioration of the wake coefficient and propeller efficiency due to air bubble contamination, prevents a decrease in propulsion efficiency, and improves the horsepower reduction effect of air lubrication. Furthermore, when discharging from the side of the hull bottom 2, as shown in Figure 7, the water drawn in by the liquid phase intake port 20 is blown out from the liquid phase outlet port 80 located in the bilge area. This prevents bubbles from detaching from both sides of the hull bottom 2 and enhances the effect of reducing frictional resistance caused by bubbles.

[0051] Next, a liquid-phase suction type air lubrication system according to a second embodiment of the present invention will be described. Note that functional components identical to those in the above-described embodiment are denoted by the same reference numerals and their descriptions are omitted. Figure 8 is a schematic diagram of a liquid-phase suction type air lubrication system according to the second embodiment installed on a ship, with Figure 8(a) being a side view and Figure 8(b) being a bottom view. The liquid-phase suction air lubrication system of this embodiment has three liquid-phase suction ports 20 arranged in the longitudinal direction of the ship. The first liquid-phase suction port 21 from the bow is located forward of approximately the midpoint in the longitudinal direction of the ship, the second liquid-phase suction port 22 is located approximately in the midpoint, and the third liquid-phase suction port 23 is located aft of approximately the midpoint. The bubbles drawn in by the liquid phase intake port 20 begin to move away from the bottom of the hull 2 ​​again as they move downstream. However, by providing multiple liquid phase intake ports 20 at predetermined intervals along the flow of bubbles in the bottom of the hull 2, as in this embodiment, bubbles that have moved away from the bottom of the hull 2 ​​downstream of the preceding liquid phase intake port 20 can be drawn back towards the bottom of the hull 2 ​​near the subsequent liquid phase intake ports 20. It is also possible to provide multiple liquid phase intake ports 20 in the width direction of the hull.

[0052] Next, a liquid-phase suction type air lubrication system according to a third embodiment of the present invention will be described. Note that functional components identical to those in the above-described embodiments are denoted by the same reference numerals and their descriptions are omitted. Figure 9 is a bottom view showing a schematic configuration of a liquid-phase suction type air lubrication system according to a third embodiment installed on a ship. Since the detachment of air bubbles from the bottom wall 2 is greatly influenced by the distance from the air outlet 10, the liquid phase intake section can be arranged in a two-dimensional manner, such as in an inverted V shape, corresponding to the arrangement of the air outlet section. In the liquid-phase suction air lubrication system of this embodiment, the air outlets 10 are arranged in sets of three, with the air outlet 11 in the center in the width direction of the ship positioned forward of the air outlets 12 and 13 on both sides, resulting in an inverted V-shape when viewed from the rear of the ship. Similarly, the liquid-phase intake ports 20 are also arranged in sets of three, with the liquid-phase intake port 24 in the center in the width direction of the ship positioned forward of the liquid-phase intake ports 25 and 26 on both sides, resulting in an inverted V-shape when viewed from the rear of the ship. As in this embodiment, multiple air outlets 10 are provided in the width direction of the hull bottom 2, and the air outlets 10 located in the center of the hull bottom 2 are arranged in an inverted V shape with those located on both sides facing forward and those facing backward. In addition, multiple liquid phase intake ports 20 are provided in the width direction of the hull bottom 2, and the multiple liquid phase intake ports 20 are arranged in an inverted V shape. This allows the air outlets 10 to be installed as far forward as possible, and effectively prevents bubbles blown out from each air outlet 10 from detaching from the hull bottom 2.

[0053] Next, a liquid-phase suction type air lubrication system according to a fourth embodiment of the present invention will be described. Note that functional components identical to those in the above embodiments are denoted by the same reference numerals and their descriptions are omitted. Figure 10 is a bottom view showing a schematic configuration of a liquid-phase suction type air lubrication system according to the fourth embodiment installed on a ship. When the air outlets 10 are arranged in a single line in the width direction of the ship, as in the first embodiment, there are cases where the detachment of air bubbles from the bottom wall 2 is greater on both sides in the width direction of the ship than in the center in the width direction of the ship. Therefore, in this embodiment, the liquid-phase suction type air lubrication system has three sets of air outlets 10 arranged in a row in the width direction of the ship, while the three sets of liquid-phase intake ports 20 are arranged in a V-shape when viewed from the rear of the ship, with the liquid-phase intake port 24 in the center in the width direction of the ship positioned further aft than the liquid-phase intake ports 25 and 26 on both sides. As in this embodiment, multiple air outlets 10 are provided in the width direction of the hull bottom 2, multiple liquid phase intake ports 20 are provided in the width direction of the hull bottom 2, and the liquid phase intake ports 20 located in the center of the hull bottom 2 are arranged in a V-shape with the ones located on both sides facing forward. This effectively prevents bubbles from escaping from the sides of the hull bottom 2 when there is a large amount of bubble leakage towards the sides of the hull.

[0054] Next, a liquid-phase suction type air lubrication system according to a fifth embodiment of the present invention will be described. Note that functional components identical to those in the above embodiments are denoted by the same reference numerals and their descriptions are omitted. Figure 11 is a schematic diagram of a liquid-phase suction type air lubrication system according to the fifth embodiment installed on a ship, with Figure 11(a) being a side view and Figure 11(b) being a bottom view. The liquid-phase suction air lubrication system of this embodiment includes a liquid-phase suction port 27 provided on the bottom 2 of the hull and liquid-phase suction ports 28 provided on both sides of the hull as liquid-phase suction ports 20. By providing liquid-phase suction ports 20 on the bottom 2 of the hull and also on the sides of the hull 1, which is the part of the hull 1 that has a three-dimensional shape, it is possible to attract air bubbles that have separated from the bottom 2 to the sides of the hull, thereby reducing resistance on the sides of the hull.

[0055] Next, a liquid-phase suction type air lubrication system according to a sixth embodiment of the present invention will be described. Note that functional components identical to those in the above embodiments are denoted by the same reference numerals and their descriptions are omitted. Figure 12 is a schematic diagram of a liquid-phase suction type air lubrication system according to the sixth embodiment installed on a ship, with Figure 12(a) being a side view and Figure 12(b) being a bottom view. The liquid-phase suction air lubrication system of this embodiment includes a liquid-phase suction port 27 provided on the bottom 2 of the hull and a liquid-phase suction port 29 provided on the stern as liquid-phase suction ports 20. By providing liquid-phase suction ports 20 on the bottom 2 of the hull and also on the stern of the hull 1, which is the part of the hull 1 that has a three-dimensional shape, it is possible to prevent air bubbles from separating from the hull 1 due to suction by the propeller 3, thereby reducing the frictional resistance reduction effect and enabling resistance reduction at the stern.

[0056] Next, a liquid-phase suction type air lubrication system according to a seventh embodiment of the present invention will be described. Note that functional components identical to those in the above embodiments are denoted by the same reference numerals and their descriptions are omitted. Figure 13 is a schematic diagram of a liquid-phase suction type air lubrication system according to the seventh embodiment installed on a ship, with Figure 13(a) being a side view and Figure 13(b) being a bottom view. The bubbles blown out from the air outlet 10 are drawn towards the bottom 2 of the hull by the liquid phase intake 20 located in the middle of the ship's length, so that a larger amount of bubbles remain near the bottom 2 even at the stern. This enhances the frictional resistance reduction effect of the bubbles, but on the other hand, if bubbles flow into the propeller 3, it may lead to a decrease in propeller efficiency, etc. Therefore, in the liquid-phase suction type air lubrication system of this embodiment, a gas-phase intake port 60 that primarily draws in air bubbles is further provided in front of the propeller 3 at the stern. By drawing in air bubbles through the gas-phase intake port 60, the air bubbles are separated from the hull surface at the stern, preventing them from flowing into the propeller surface. This prevents deterioration of the wake coefficient and propeller efficiency due to air bubbles entering the propeller 3, thereby preventing a decrease in propulsion efficiency and improving the horsepower reduction effect of air lubrication. Furthermore, a pipe 61 is installed that extends from the gas phase intake port 60 to the air, with the upper part of the pipe 61 open to the atmosphere. This allows for a mechanism to draw in the gas phase from the gas phase intake port 60 without power, so that the bubbles drawn in from the gas phase intake port 60 are released into the atmosphere without power.

[0057] Next, the results of verification tests conducted regarding the present invention will be described. FIG. 14 is a schematic diagram of the unit used in the present test, and FIG. 15 is a diagram showing the measurement results in the present test. The verification test of the present invention was conducted in a horizontal channel (test section length 3,000 [mm], height 20 [mm], width 100 [mm]). Liquid phase suction was performed from the liquid phase suction port approximately 1,000 [mm] downstream of the air outlet, and frictional resistance was evaluated using a shear stress meter approximately 500 [mm] downstream thereof. The measurement was performed at the cross-sectional average flow velocity U m =7 [m / s]. The equivalent air film thickness t Air is defined as in the following formula (2), and the liquid phase suction thickness t Suction is defined as in the following formula (3). The equivalent air film thickness t Air is the thickness of the air film on the assumption that the blown-out air exists as an air film. The liquid phase suction thickness t Suction is likewise a variable expressing the sucked flow rate as a thickness. [Mathematical Formula] [Mathematical Formula] Here, Q Air : air flow rate, Q Suction : water suction flow rate, B: flow path width. Further, in FIG. 15, C on the vertical axis f / C f0 is the resistance reduction rate, C f is the frictional resistance coefficient in the bubbly flow, and C f0 is the frictional resistance coefficient in a single-phase flow (when no bubbles are present). At t Air =2.0 [mm], the liquid phase suction amount (thickness) was varied as t Suction =0.1, 0.2, 0.3, 0.35 [mm]. When no suction was performed, the reduction rate of frictional resistance was 17.2 [%], but the frictional resistance reduction amount improved as the suction amount increased, and at t Suction =approximately 0.3 [mm], a maximum improvement of 1.4 [%] was exhibited under the present test conditions.

[0058] Reducing resistance by drawing in the liquid phase is a phenomenon also seen in so-called "boundary layer suction." Resistance reduction by boundary layer suction (boundary layer control) is carried out with the aim of delaying the transition from laminar flow to turbulent flow. In contrast, since this test was conducted at a Reynolds number sufficiently higher than the transition Reynolds number, it can be said that the resistance reduction was not due to boundary layer suction, but rather occurred according to the principle of the present invention.

[0059] The reduction of drag due to uniform blow-out and uniform suction from the boundary layer has also been studied, and in the control region, a reduction in drag due to blow-out and an increase in drag due to suction have been confirmed. The increase in drag due to suction is thought to be because high-speed fluid far from the wall of the turbulent boundary layer approaches the wall. Therefore, in this test, only fluid suction was performed without blowing out air. Figure 16 shows the results, illustrating the change in the drag reduction rate due to liquid phase suction, and confirming that drag increased with suction. This confirms that drag reduction does not occur with liquid phase suction alone, and that the effect of frictional drag reduction was greatly increased due to the effect of the bubbles approaching the bottom wall of the ship as a result of liquid phase suction.

[0060] Here, we will summarize the factors causing resistance changes due to liquid phase suction. First, there is a resistance reduction effect due to the approach of the void fraction peak to the wall. This change is small with respect to changes in suction flow rate. Next, there is a resistance increase effect due to the approach of the high-speed fluid to the wall. This resistance increase becomes larger with increasing suction flow rate (see Figure 16). Finally, there is a resistance increase effect due to bubble suction. This is because the void fraction decreases when bubbles are mixed into the suctioned liquid phase, increasing resistance (reducing the amount of resistance reduction). When the suction volume is large, the amount of bubbles mixed in also increases, and the effect of this resistance increase becomes larger. As shown in Figure 15, under these test conditions, the suction volume t Suction Below 0.3 [mm], the resistance reduction effect increases with increasing suction volume, t Suction Beyond 0.3 [mm], the resistance reduction effect decreases as the suction volume increases, t SuctionThe resistance reduction effect was maximized when the suction volume t was 0.3 [mm]. Table 2 below shows the suction volume t. Suction = Less than 0.3 [mm] and t Suction This shows the magnitude of each resistance change factor due to liquid phase suction when the value exceeds 0.3 [mm]. [Table 2]

[0061] From here, t Suction Below 0.3 [mm], the resistance reduction effect due to the approach of the void fraction peak to the wall surface is dominant, and the resistance reduction effect increases with increasing suction volume, but t Suction Beyond 0.3 [mm], the effects of increased resistance due to the approach of the high-speed fluid to the wall and the increased resistance due to bubble suction become significant, and the resistance reduction effect is thought to decrease as the suction flow rate increases. Furthermore, considering the balance of the above resistance change factors, there is an optimal value for the suction amount of the liquid phase that maximizes the resistance reduction effect. From Figure 15, that optimal value is t Suction It can be seen that = 0.3 [mm]. Also, t Suction For thicknesses exceeding 0.3 [mm], the resistance reduction effect decreases sharply, therefore, a liquid-phase suction air lubrication system is t Suction It is preferable to use it at a thickness of 0.3 [mm] or less. [Industrial applicability]

[0062] By applying the liquid-phase suction air lubrication system of the present invention, the propulsion efficiency of ships is improved, and the amount of GHG emissions from ships is reduced. Furthermore, the liquid-phase suction air lubrication system of the present invention can be applied not only to ships that are newly equipped with an air lubrication system, but also to ships that already have an air lubrication system installed. [Explanation of Symbols]

[0063] 1. Hull 2. Bottom of the ship 3 propellers 10 Air outlet 20 Liquid phase inlet 30 Suction means 31 Aperture 32 Piping 33 Control valve 40 Control means

Claims

1. An air lubrication system for reducing the frictional resistance of a ship's hull by blowing bubbles onto the bottom of the ship, comprising: an air outlet provided in front of the bottom of the ship's hull; a liquid phase intake provided in the bottom of the ship's hull behind the air outlet; a suction means for drawing in liquid phase water without bubbles from the surface of the bottom of the ship's hull through the liquid phase intake; and a control means for controlling the suction means, wherein the control means controls the suction means so that the flow rate of water drawn in from the liquid phase intake, the width of the liquid phase intake, and the ship's speed are within a predetermined range.

2. The liquid-phase suction type air lubrication system according to claim 1, characterized in that the predetermined range of the liquid-phase suction thickness determined based on formula (1) is 0.12 [mm] or more and 0.38 [mm] or less. [Math 1] Here, t Suction : Liquid phase absorption thickness, Q Suction : Water suction flow rate, B: Width of the liquid phase suction port, V: Ship speed.

3. The liquid phase suction type air lubrication system according to claim 1, characterized in that the liquid phase suction ports are provided in multiple stages at predetermined intervals along the flow of air bubbles in the bottom of the ship.

4. The liquid phase suction type air lubrication system according to claim 1, characterized in that a plurality of air outlets are provided in the ship width direction of the ship bottom, and the air outlet located in the center of the ship bottom is arranged in an inverted V shape forward, and the air outlets located on both sides are arranged in an inverted V shape backward, and a plurality of liquid phase suction ports are provided in the ship width direction of the ship bottom, and the plurality of liquid phase suction ports are arranged in an inverted V shape.

5. The liquid phase suction type air lubrication system according to claim 1, characterized in that a plurality of air outlets are provided in the ship width direction of the ship bottom, a plurality of liquid phase suction ports are provided in the ship width direction of the ship bottom, and the liquid phase suction ports located in the center of the ship bottom are arranged in a V shape with the ones located on both sides facing forward.

6. The liquid phase suction air lubrication system according to claim 1, characterized in that the liquid phase suction port is provided in the bottom of the ship, and the liquid phase suction port is further provided in at least one of the sides or stern of the ship's hull, in a portion of the ship's hull that has a three-dimensional shape.

7. The liquid phase suction type air lubrication system according to claim 1, characterized in that the liquid phase suction port is formed using a perforated plate and the water is sucked in from the entire surface of the perforated plate.

8. The liquid phase suction type air lubrication system according to claim 1, characterized in that the internal path of the liquid phase suction port is formed in an oblique direction toward the front from the opening of the liquid phase suction port when viewed from the side.

9. The liquid-phase suction type air lubrication system according to claim 1, characterized in that the control means controls the suction flow rate based on at least one of the ship speed and the ship's attitude.

10. The liquid-phase suction type air lubrication system according to claim 1, characterized in that the control means controls the suction flow rate based on the measured amount of bubbles mixed into the water sucked in by the suction means.

11. The liquid-phase suction type air lubrication system according to claim 1, characterized in that the control means controls the periodic discharge of the bubbles from the air outlet and synchronizes and periodic suction of the water by the suction means.

12. The liquid-phase suction type air lubrication system according to claim 11, characterized in that the control means controls the suction flow rate based on the measured hull motion of the ship, taking into account the phase difference between the bubbles blown out from the air outlet and the liquid-phase suction port.

13. The liquid-phase suction type air lubrication system according to claim 1, characterized in that the liquid-phase suction port also serves as the sea chest, which is the water intake of the vessel.

14. The liquid-phase suction type air lubrication system according to claim 1, characterized in that the suction means is configured by connecting the liquid-phase suction port to an opening provided in a part of the hull surface that generates negative pressure when the ship is propelled, via a control valve and piping.

15. The liquid-phase suction type air lubrication system according to claim 1, characterized in that the suction means is configured by connecting the liquid-phase suction port to an opening provided on the hull surface in a part that generates negative pressure when the ship is propelled, via a pump and piping.

16. The liquid-phase suction type air lubrication system according to claim 1, characterized in that the water sucked in by the suction means from the liquid-phase suction port is discharged from at least one of the front of the propeller at the stern of the hull and on both sides of the bottom of the hull.

Images