JP2003175884A - Ship with reduced hull resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ship with reduced hull resistance that can link friction resistance reduction effect by microbubbles to reduction in actual propulsion energy of ship without degrading propulsion performance of propellers. <P>SOLUTION: A pod propeller 110 is attached to an inclined face 107 of a full immersion portion 105 of a cargo ship 100. A microbubble generating apparatus 120 is disposed inside the hull 103. The microbubbles MB generated in the apparatus 120 blow off from an outlet 123, and flow rearward along an outer plate surface of the hull immersion portion 105. Usage of the pod propeller 110 enables reduction of microbubbles to flow into a propeller 113. Therefore, friction resistance of water can be reduced by the microbubbles MB while propulsion efficiency of the propeller 113 is hardly lowered. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for flowing water (microbubbles) along a surface of an outer plate of a water immersion portion of a hull, so that water acting on the surface of the outer plate of the same is provided. The present invention relates to a hull resistance reducing ship capable of reducing the resistance of a ship. In particular, the present invention relates to a hull resistance reducing ship that can link the frictional resistance reducing effect of microbubbles to actual marine propulsion energy reduction without lowering the propulsion performance of a propeller. 2. Description of the Related Art When a ship is navigating, the resistance of water (seawater or freshwater) acts on the outer plate surface of the hull immersion part. Since this water resistance is a major factor in lowering the propulsion performance of the ship, various measures have been taken to reduce this. Here, the resistance of water has two components, a resistance generated by generating a wave on the water surface (wave making resistance) and a resistance generated by the hull dragging the surrounding water due to the viscosity of the water (friction resistance). is there. Among these resistances, for a large ship having a relatively low speed, such as a tanker, the wave-making resistance is smaller, and the frictional resistance accounts for about 80% of the total resistance. Therefore, in such a type of ship, it is effective to reduce frictional resistance to reduce water resistance. As one of measures to reduce frictional resistance, a method of flowing air bubbles (microbubbles) along an outer plate of a water immersion part of a hull, and covering the boundary layer between the water immersion part of the hull and water with these air bubbles to reduce a resistance action. (Microbubble propulsion method) is known.
As a conventional example of a ship drag reduction ship adopting the microbubble propulsion method, Japanese Patent Application Laid-Open Nos. Hei 9-118288 and 2001-97276 can be cited. [0004] The boat with reduced frictional resistance disclosed in Japanese Patent Application Laid-Open No. Hei 9-118288 has a bubble water generating device inside the hull. At the bottom of the hull, there is formed a slit-shaped bubble water outlet that communicates with the bubble water generator. During the navigation of the ship, the bubble water blown out from the bubble water outlet to the outside of the hull diffuses along the bottom of the hull and flows backward, thereby reducing the frictional resistance of the water. Further, the publication also discloses that the bottom surface of the stern portion is formed flat to increase the area along the bubbles, thereby obtaining a propulsive force for pushing the hull forward. [0005] The frictional resistance reducing ship disclosed in Japanese Patent Application Laid-Open No. 2001-97276 takes out exhaust gas of a main engine (main engine) from a supercharger and blows out excess gas of the exhaust gas from an outlet at the bottom of the ship. The amount of surplus gas taken out of the turbocharger can be adjusted by a predetermined sequence control so that the fuel supply amount of the main engine with respect to the speed of the hull becomes minimum.
Therefore, it is said that this ship with reduced frictional resistance can travel efficiently with less fuel. Meanwhile, a pod propeller has been developed as a kind of propulsion device for a new ship. This pod propeller has a column (column) protruding below the bottom of the ship, and a pod (housing) attached to the tip of the column.
A propeller is provided at an end of the pod, and a motor for driving the propeller is disposed inside the pod.
The motor is driven using the engine of the hull as a generator.
Since the pod propeller can be installed at a distance below the bottom of the ship, the propeller can be rotated in a uniform flow unaffected by the hull. Therefore, high propulsion efficiency can be obtained and cavitation on the propeller surface can be suppressed. In addition, the pod propeller can change its direction by rotating the pod itself when changing course and changing the direction of the propeller, so that no rudder is required. Further, the pod propeller has no propeller shaft and the propeller is driven to rotate independently of the engine, so that the vibration and noise of the engine can be cut off from the hull. As described above, the pod propeller can suppress cavitation and shut off engine vibration and noise, so that noise countermeasures can be easily realized, and the pod propeller is currently widely used in passenger ships. As a conventional example of the pod propeller, for example, JP-A-11-278379 can be cited. The present inventors conducted an experiment for confirming the effect of reducing the frictional resistance of the microbubbles by using a test apparatus and an actual ship described below. First, an experiment using a test apparatus will be described. FIG. 4 is an overall view of a microbubble experimental flow channel used for a basic experiment. FIG. 5A is an enlarged cross-sectional view of a chamber for injecting air into the experimental flow channel of FIG. 4, and FIG. 5B is a diagram illustrating a friction force meter used for friction measurement. The experimental flow path 10 shown in FIG. 4 is a circulating flow path having a pipe 11 and a bubble removal tank 12. In this experimental channel 10, water flows in the direction of arrow X. The pipeline 11 of the experimental channel 10 includes a water supply unit 15, a bending unit 20, and a test unit 25. The upstream end 15 a of the water supply unit 15 and the downstream end 25 b of the test unit 25 are connected to the bubble removal tank 12. The water supply unit 15 includes a pump 17 on the upstream side.
Is incorporated, and an electromagnetic flowmeter 19 is incorporated on the downstream side. The water pumped from the bubble removal tank 12 by the pump 17 is supplied from the water supply unit 15 to the test unit 25 via the bending unit 20.
And flows into the bubble removal tank 12 again. The test section 25 has a thickness of 15 mm and a depth of 10 mm.
It has a flat cross-sectional shape of 0 mm. The length from the upstream end 25a of the test section 25 is 3000 mm. Test section 2
An air injection chamber 26 is incorporated at a position (first position P1) 103 mm downstream from the upstream end 25a of No. 5. The air injection chamber 26 includes a porous plate 27 as shown in FIG. The air supplied from the air injection chamber 26 is injected into the test section 25 through the porous plate 27. In the test section 25, each of the air injection chambers 26 (the first position P1) is set at 0.
5 m, 1.0 m, 1.5 m downstream position (second position P
At the second, third and fourth positions P3 and P4), a mounting flange 28 of the friction force meter is formed. As shown in FIG. 5B, a friction force meter 29 is attached to these mounting flanges 28. The frictional force meter 29 measures the frictional force between the channel wall surface and water at each of the positions P2 to P4 of the test section 25. The results of an experiment performed using the above-described experimental flow channel will be described. FIG. 6 is a photograph of air bubbles injected from the air injection chamber. FIG. 7 is a graph showing the result of measuring the wall friction of the flow channel. The horizontal axis represents the average void fraction α in the flow channel (that is, the volume ratio of air in the cross section of the flow channel), and the vertical axis represents the ratio Cf / of the wall friction force in the bubble state to the wall friction force in the bubble-free state. Represents Cf0. The average flow velocity of water in the test section 25 is V = 7 m /
sec, and the average void fraction is α = 0.02. The average flow velocity V = 7 m / sec corresponds to the cruising speed (14 knots) of a normal large tanker. Air injection chamber 2
The diameter of the bubble injected from 6 is about 1 mm (see the bubble photograph in FIG. 6). In the graph of FIG. 7, ◇ indicates a measurement result at the second position, indicates a measurement result at the third position, and □ indicates a measurement result at the fourth position. The solid line graph is a graph of the result of an experiment performed by Merkle et al. In 1990. As can be seen from FIG. 7, the ratio Cf / Cf0 decreases as the average void fraction α increases. This indicates that the frictional force decreases as the amount of injected air increases. Furthermore, the result of this experiment
It is in good agreement with the experimental results of rkle and others. From this experimental result, it was confirmed that a remarkable friction reduction effect of up to 30% was obtained by the microbubbles. Next, an experiment using a model flat boat will be described. FIG. 8 is a plan view showing the flat boat used in the experiment. FIG. 9 (A) is a graph showing the measurement results of the frictional force on the outer plate surface of a flat boat, wherein the horizontal axis represents the distance x [unit m] from the bow, and the vertical axis represents the same ratio Cf / Cf0 as described above. Represents FIG. 9 (B) is a graph illustrating the effect of reducing friction at the downstream portion of the microbubble blowing on the surface of the outer plate of the flat boat. The horizontal axis indicates the blowing air amount q (= Q / SV; Q: blowing air amount [unit m]. ³ / min], S: blowout area [unit m ² ], V: speed [unit m / sec]),
The vertical axis represents the ratio Rf / Rf0 between the frictional resistance of the downstream portion of the micro valve outlet in the bubble state and the frictional resistance of the downstream portion of the outlet in the bubble-free state. A flat boat 30 shown in FIG. 8 has dimensions of 50 m in length and 1 m in width, and the bottom is formed flat. At a position 3.0 m from the bow of the flat boat 30 (the left end in FIG. 8),
A bubble blowing section 31 is provided. This flat boat 30
At 3.5 m from the bow (first position P
1) 4.8 m (second position P2), 8.8 m (third position P3), 31.5 m (fourth position P4), 32.8 m (fifth position P5), 36.8 m (sixth position) P6) A frictional force measuring unit is provided at a remote position. The flat boat 30 was placed in a towing water tank (not shown) having a length of 400 m, and an experiment was performed at a maximum speed of 7 m / sec. The results of an experiment conducted using the flat boat will be described. In the graph of FIG. 9A, △ indicates a value when the amount of blown air q = 0.02, and ○ indicates a value when the amount of blown air q = 0.04. In this graph, the speed V is set to 7 m / sec. From this graph, it can be seen that the effect of reducing the frictional force due to the bubbles is substantially proportional to the amount of blown air q and rapidly attenuates downstream of the air blowing portion, but continues to almost the downstream end of the flat boat. In the graph of FIG. 9B, △ represents the speed V
= 7 m / sec, ○ indicates speed V = 5 m / sec
Shows the value in the case of sec. In consideration of this graph, the friction reduction effect of the entire portion of the flat boat 30 located downstream from the blowing section 31 is 40% at the speed V = 5 m / sec.
A close reduction effect is obtained, and at speed V = 7 m / sec, 20
It was found that a reduction effect of a little over% could be obtained. As described above, from the experiments, it was found that the microbubbles had a cruising speed of 7 m / sec, which is a normal large tanker.
It is considered that a remarkable friction reduction effect of about several tens% can be obtained with respect to (14 knots). Furthermore, the results of the experiments using the above-described flat ship revealed that the friction reducing effect was maintained to some extent even downstream of the air outlet of the hull. These results indicate that microbubbles are very likely to be applied to actual ships. Next, an experiment using an actual ship will be described.
First, the configuration of a general microbubble propulsion ship will be described. FIG. 3A is a side view schematically showing a microbubble propulsion ship provided with a normal propeller.
FIG. 3B is a side view illustrating the state of inflow of microbubbles into the propeller in the ship shown in FIG. FIG.
The boat 200 shown in FIG. 2A has a bow 200A on the left side of the figure and a stern 200B on the right side of the figure. This ship 200
In the hull 203, the lower half part submerged is the hull inundation part 205. The bow 200A of this hull inundation part 205
The side end surface 206 is formed in a smooth curved surface shape.
On the stern 200B side of the hull inundation part 205, the propeller 21
0 is attached. The propeller 210 is connected to the engine 20 in the hull 203 via a propeller shaft 211.
8 is connected. In this ship 200, the engine 20
8 is transmitted directly to the propeller 210 via the propeller shaft 211, and the propeller 210 rotates. Behind the propeller 210, a rudder 220 hanging from the bottom of the ship is provided. A microbubble forming device 120 similar to that described above is provided inside the hull 203 near the bow 200A. The micro-bubble forming device 120 is a ship bottom 2
No. 01 communicates with an outlet 223 formed near the bow 200A. The results of an experiment conducted using an actual ship will be described. The actual ship used in this experiment was a training ship “Seiun Maru” from the Japan Navigation Training Center. Seiun Maru has a total length of 116
m, gross tonnage 5900 tons. In experiments using this actual ship, the effect of microbubbles on reducing friction was confirmed. However, at the same time, it has been found that when the microbubbles flow into the propeller rotating at the stern, the thrust decreases, and the energy efficiency of the ship as a whole decreases. In the above-mentioned Japanese Unexamined Patent Publication No. Hei 9-118288 and Japanese Unexamined Patent Publication No. 2001-97276, no measures are taken for reducing the propeller propulsion efficiency due to the inflow of microbubbles. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in view of the above circumstances. Therefore, the present invention has been made to reduce the hull resistance, which can reduce the frictional resistance reduction effect of microbubbles to actual marine propulsion energy without lowering the propulsion performance of a propeller. The purpose is to provide a ship. In order to solve the above-mentioned problems, a hull resistance reducing ship according to the present invention comprises means (microbubbles) for flowing air bubbles (microbubbles) along the outer plate surface of a hull inundation part. Forming means), a column protruding below the bottom of the ship, and a pod propeller having a propeller and a drive motor installed at the lower end of the column. By using a pod propeller, the propeller can be installed at a distance below the bottom of the ship. Therefore, it is possible to reduce bubbles flowing from the microbubble forming means along the ship bottom into the propeller. Therefore, the effect of reducing the frictional force of the hull immersion portion by the microbubbles can be realized without substantially lowering the propulsion performance of the pod propeller. Further, since the microbubble layer has an effect of blocking the noise of the propeller, it is considered that there is an advantage that the quietness of the hull can be further enhanced. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view schematically showing a microbubble propulsion cargo ship provided with a pod propeller. FIG. 2 is a side view schematically showing a microbubble propulsion ferry (or passenger ship) including a pod propeller. In the cargo ship 100 shown in FIG. 1, the left side of the figure is the bow 100A, and the right side of the figure is the stern 100B. In the hull 103 of the cargo ship 100, the lower half of the hull submerged is the hull inundation unit 105. The end face 106 of the hull immersion section 105 on the bow 100A side is formed into a smooth curved surface. The stern 100B side bottom surface of the hull inundation part 105 is as follows:
Inclined surface 10 inclined upward from the bottom 101 toward the stern
7 are formed. A pod propeller 110 is attached to the inclined surface 107 of the hull flooding section 105 on the stern 100B side. The pod propeller 110 includes a column 111 projecting downward from the inclined surface 107. This support 111
A housing 116 containing an electric motor 115 is attached to the lower end of the housing. A propeller 113 is attached to an output shaft end of the electric motor 115. The propeller 113 rotates when driven by the electric motor 115. The electric motor 115 is connected to the hull 10 via a cable 117.
3 is connected to the generator 109. Generator 109
Is axially connected to an engine 108 in the hull 103, and is rotationally driven by the engine 108. However, the generator 109 and the propeller 113 are not mechanically connected. It should be noted that the pod propeller 110 can change its direction by changing the direction of the propeller 113 by rotating the pod itself when the course is changed, so that no rudder is required. In the hull 103 near the bow 100A,
A microbubble forming device 120 is provided. The microbubble forming device 120 communicates with an outlet 123 formed in the ship bottom 101. Bubble outlet 123
Has a porous bubble blowing portion (not shown), like the air injection chamber 26 of FIG. Microbubble MB formed by microbubble forming device 120
Blows out from the outlet 123 into the bottom plate of the hull 103,
Along the outer plate surface of the hull inundation section 105 (right side in the figure)
Flows to In the ferry 130 shown in FIG. 2, the left side of the figure is the bow 130A, the right side of the figure is the stern 130B,
A cabin 134 and the like are provided in the hull 133. In the hull 133 of the ferry 130, the lower half of the hull submerged is the hull flooding unit 135. Bow 1 of hull inundation section 135
The end surface 136 on the 30A side is formed into a smooth curved surface. An inclined surface 137 that is inclined upward from the ship bottom 131 toward the stern is formed on the bottom surface on the stern 130B side of the hull inundation part 135. A pod propeller 110 similar to that of the cargo ship 100 described above is mounted on the inclined surface 137 of the hull flooded portion 135 on the stern 130B side. On the other hand, bow 130A
A microbubble forming device 120 similar to that of the cargo ship 100 described above is provided inside the approaching hull 133. The microbubble forming device 120 is mounted on the bow 13 of the ship bottom 131.
It communicates with the outlet 143 formed on the 0A side. Next, a comparison of the operation between the cargo ship 100 (see FIG. 1) according to the present invention and a general ship 200 (see FIG. 3) will be described. The ferry 130 (see FIG. 2)
Is the same as that of the cargo ship 100. When the cargo ship 100 shown in FIG.
The microbubble MB formed at 0 is blown out from the outlet 123 of the ship bottom 101. This micro bubble MB
Flows backward (to the right in the figure) along the outer plate surface of the hull inundation section 105. At this time, a boundary layer is formed between the outer surface of the hull immersion portion 105 and the water, and the frictional resistance of the water is reduced as described in the above experimental results. The microbubbles MB that have flowed along the hull immersion section 105 reach the stern 100B. Here, since the propeller 113 of the pod propeller 110 of the cargo ship 100 is disposed below and away from the bottom inclined surface 107,
The flow of the microbubbles MB into the propeller 113 is small, and a decrease in the propulsion efficiency of the propeller 113 is suppressed. Further, the layer of microbubbles MB also has an effect of blocking noise of the propeller 113, so that the quietness of the hull 103 is further enhanced. In the case of a standard cargo ship (50,000 tons), the distance between the bottom of the ship and the axis of the propeller is about 6 m, and if the radius of the pod propeller is about 3 m, the distance between the top of the propeller and the bottom of the ship is about 3 m. The upper end of the propeller does not cover the microbubble layer (for example, 2 m). On the other hand, the ship 200 shown in FIG.
In the case of, the microbubble MB blown out from the outlet 223 of the ship bottom 201 flows downstream along the hull immersion part 205 and is then caught by the propeller 210 (FIG. 3).
(B)). As described above, when the microbubble MB is caught in the propeller 210, the propulsion efficiency of the propeller 210 decreases, and the energy efficiency of the entire ship 200 decreases. As can be seen from this comparison, the cargo ship 100 (or ferry 130) according to the present invention uses the microbubble propulsion method and the pod propeller 110 in combination, without substantially reducing the propulsion efficiency of the propeller 113. The frictional resistance of water can be reduced by the microbubbles MB. Further, as described above, the pod propeller 1
By using 10, high propulsion efficiency can be realized, cavitation on the propeller surface can be suppressed, and vibration and noise of the engine can be cut off. As is apparent from the above description, according to the present invention, it is possible to provide a ship with reduced hull resistance, which can reduce the frictional resistance reduction effect of the microbubbles to the actual reduction of ship propulsion energy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view schematically showing a microbubble propulsion cargo ship provided with a pod propeller. FIG. 2 is a side view schematically showing a microbubble propulsion ferry (or passenger ship) including a pod propeller. FIG. 3A is a side view schematically showing a microbubble propulsion ship provided with a normal propeller, and FIG.
FIG. 3B is a side view illustrating the state of inflow of microbubbles into the propeller in the ship shown in FIG. FIG. 4 is an overall view of a microbubble experimental flow channel used for a basic experiment. 5 (A) is an enlarged sectional view of a chamber for injecting air into the experimental flow channel of FIG. 4, and FIG. 5 (B) is a diagram showing a friction force meter used for friction measurement. FIG. 6 is a photograph of air bubbles injected from an air injection chamber. FIG. 7 is a graph showing a result of measuring wall friction of a flow channel. FIG. 8 is a plan view showing the flat boat used in the experiment. 9 (A) is a graph showing the measurement results of the frictional force on the outer plate surface of a flat ship, and FIG. 9 (B) is a graph showing the effect of reducing the friction at the downstream portion of the microbubble blowing on the outer plate surface of the flat ship. It is a graph explaining. [Description of Signs] 100 Cargo ship 100A Bow 100B
Stern 101 Bottom 103 Hull 105 Hull immersion part 106 End surface 107 Inclined surface 108 Engine 109 Generator 110 Pod propeller 111 Prop 113 Propeller 115 Electric motor 116 Housing 117 Cable 120 Microbubble forming device 123 Outlet 130 Ferry 130A Bow 130B
Stern 131 Ship bottom 133 Hull 134 Guest room 135 Hull flooding part 136 End face 137 Slope

Claims (1)

Claims: 1. Means for flowing air bubbles (microbubbles) along the surface of an outer plate of a hull immersion part (microbubble forming means)
And a pod propeller having a prop protruding below the bottom of the vessel, a propeller installed at a lower end of the post, and a drive motor for driving the propeller.