JPH09240571A - Frictional resistance reducing device of ship - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with a change of draft, and to cover the submerged front surface of a hull with micro-bubbles by generating the micro-bubbles by small blowoff power. SOLUTION: Thin, long and cylindrical air blowoff units 7 in which many air blowoff ports 5 are provided in the region in which stream lines are directed to a bottom 3 or a stern in a submerged part of a bow part 2 of a hull 1 and in the position in which static pressure is low, and both ends are blocked are vertically attached into plural stages. The air blowoff units 7 are connected to a blower 9 through air supplying pipes 11. The air blowoff unit 7 to be used according to a change of draft is selected, pressurized air 13 is blown off from the air blowoff ports 5, and generated micro-bubbles 14 are fed on the stream lines 14 in respective positions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frictional resistance reducing device for a ship which can reduce the frictional resistance acting on the surface of a hull during navigation.

[0002]

2. Description of the Related Art During the navigation of a ship, a boundary layer of seawater is formed around the hull due to the viscosity of seawater as a fluid. In this boundary layer, the flow velocity of the seawater is zero and the hull surface is zero. It tends to change drastically as the distance from the surface increases, and seawater frictional resistance acts on the surface of the hull, which is one of the major factors of hull resistance.

[0003] Therefore, in recent years, studies have been made to improve the propulsion performance by reducing the frictional resistance acting on the surface of the hull, and as one of the measures, micro-bubbles (micro-bubbles) are generated from the hull surface. And injects microbubbles into the boundary layer on the surface of the hull's submerged part (submerged part) to cover the surface of the hull's submerged part with microbubbles, thereby reducing frictional resistance acting on the hull surface. Research on the microbubble propulsion method is ongoing.

[0004] As one method for realizing the microbubble propulsion method, pressurized air generated by an air supply device such as an air pump is blown out into the water from the bottom of a ship, and a required void due to microbubbles is formed on the bottom of the ship. It is conceivable to make it form.

[0005]

However, in the technique of generating fine air bubbles by blowing pressurized air into the water from the bottom of the ship, the static pressure at the bottom of the ship increases with the depth of water that is blown. Since the energy consumption for generating micro bubbles is larger than the energy consumption for reducing frictional resistance, there is a problem in practical application.

In view of the above, according to the present invention, by generating minute bubbles with a small blowing pressure so as to generate a required void ratio on the surface of the flooded portion, the frictional resistance of the ship can be reduced. It is intended to provide a reduction device.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is directed to a side of a ship where a streamline is directed toward the bottom or stern of a ship in a flooded portion on the surface of the hull and where static pressure is small. On the outer plate, a long and thin cylindrical air blower having a large number of air blowout openings on its surface and closed at both ends is attached in a plurality of stages in the vertical direction so as to be oriented in the bow-stern direction. , And is connected to the pressurized air supply device through an air supply pipe.

When an air blower at the optimum height position is selected according to the position of the water drainage and pressurized air is blown into the water through the air blowout port of the air blower, minute bubbles can be generated with a small blowout pressure. Since the generated microbubbles are sent along the streamline in each direction from the bottom to the stern, the surface of the flooded part of the hull can be covered with the microbubbles and the void ratio of the flooded part can be improved. ,
The frictional resistance acting on the hull can be reduced.

Further, if each air blower is divided into a plurality of parts in the bow-stern direction, and an air supply pipe is connected to each of the divided air blowers, it is optimal according to changes in ship speed. The compressed air can be blown out from the divided air blower at the position to generate the micro bubbles.

Further, when the air blower is constructed by fixing an air blower member having a groove structure instead of the tubular structure to the surface of the hull, the weight of the members constituting the air blower is reduced. Therefore, it is more advantageous.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

1 (a), (b), and (c) show an embodiment of the present invention, in which a streamline 4 is directed toward the bottom 3 or the stern of a ship at the flooded part of the bow 2 of the hull 1. A large number of air outlets (pores) 5 are required in the wall of the surface of the ship-side outer plate 15 in the region where the static pressure is low and the position where static pressure is small (position slightly lower than the water line DL). A plurality of air blowers 7 each having a slender tubular structure in which both ends are closed at an arrangement pitch and each having an air chamber 6 formed therein are arranged in a horizontal direction extending in the bow-stern direction at predetermined intervals in a vertical direction. Attach the steps (two steps in the figure). On the other hand, a blower 9 driven by an electric motor 8 is installed as a pressurized air supply device on the bow 2 of the hull 1, and one end of each air blower 7 is connected to an air supply pipe with a flow rate adjusting valve 10. The other end of 11 is connected to the blower 9 through a distribution header 12, and the pressurized air 13 generated by the blower 9 is introduced into the air blower 7 through the air feed pipe 11 to blow out air. The minute bubbles 14 having a required diameter are generated by being blown out from the mouth 5, and the generated minute bubbles 14 are allowed to flow along the streamlines 4 extending in the respective directions.

As shown in the enlarged view of FIG. 1 (b), the air blower 7 has a flat cross-sectional shape such as an oblong shape obtained by crushing a circle, and the front and rear ends of the hull 1 in the navigation direction have the hull 1 The surface of the air supply pipe 11 is closed so that it smoothly continues, and the air supply pipe 11 has a flat cross section similar to that of the air blower 7 as shown in an enlarged view in FIG. It is as a shape.

[0014] The present inventors, given the hull shape,
A calculation formula for the motion considering the turbulent diffusion of microbubbles flowing along the streamline around the hull and the void fraction distribution at an arbitrary position was established. The influence of turbulent diffusion is obtained by changing the flow velocity in the X-axis, Y-axis, and Z-axis (upward) directions using random numbers based on the assumption of isotropic turbulence, and disturbing the trajectory of microbubbles. Considering. That is, the random motion of the microbubbles was directly simulated by the Monte Carlo method.
When the movement of the microbubbles is calculated, the void fraction can be obtained by dividing the void rate by the volume of the microbubbles existing in the inspection area (cell) at a certain time.

Therefore, on the basis of the void fraction distribution thus obtained, the locus of the streamline 4 at the bow 2 is obtained so that a high void fraction effective in reducing frictional resistance is obtained,
The attachment position of the air blower 7 was determined.

When navigating at a cruising speed, the water line D. After selecting the air blower 7 at the height position to be used by opening / closing the flow rate adjusting valve 10 in accordance with the level of L, the blower 9 is driven by the electric motor 8 and the pressurized air 13 is supplied to the distribution header 12 and the air. When the air is blown into the air blower 7 through the feed pipe 11 and blown out into the water through the air blowout port 5, the generated fine bubbles 14 flow along the streamline 4, so that the bottom and the side of the boat are slightly moved. Bubbles 1
4, which can be covered with 4
4, a void is formed, and the presence of this void can reduce the frictional resistance of the hull 1.

In the above description, the minute air bubbles 14 are the air blowing ports 5 in which the pressurized air 13 is formed in the air blowing device 7.
It is generated by the action of an orifice when passing through, and is easily and reliably bubbled by the relative movement of the air outlet 5 and the water in contact with the air outlet 5. Moreover, the air blower 7 is attached in a plurality of stages in the vertical direction, so that the water line D. Since the air blower to be used can be selected according to the change in L, the pressurized air 13 can be blown out from the air blowout port 5 at the position where the static pressure is the smallest, so that the air blowout at the time of generating the minute bubbles 14 is performed. It has the advantage of requiring less power. Further, since the air blower 7 and the air supply pipe 11 communicating with the air blower 7 are both flat so as not to significantly protrude from the surface of the hull 1, a large hull resistance may occur during navigation. There is no such thing. Furthermore, since the air blower 7 is not a strength member of the hull 1, it is possible to arbitrarily select a material that is unlikely to cause corrosion, and the hull 1
It is also advantageous in that the structural strength of the hull 1 is not affected because it is not necessary to make a hole in the hole. The diameter of the air outlet 5 is selected when the hull 1 is designed so that the micro bubbles 14 having the optimum diameter are generated when the hull 1 travels at the cruise speed. However, the navigation speed of the hull 1 is changed. When it becomes necessary to change the diameter of the micro-bubbles 14 due to the above, it can be dealt with by adjusting the opening of the flow rate adjusting valve 10 to adjust the supply flow rate of the pressurized air.

Next, FIGS. 2 (a) and 2 (b) show another embodiment of the present invention. In the same structure as shown in FIG. 1, each air blower 7 is internally divided by a partition 6a. A plurality of split air blowers 7a are formed in the longitudinal direction (two splits in the figure), and each of the split air blowers 7a is connected to an air supply pipe 11 led from a distribution header 12. Is.

When constructed as shown in FIG.
Not only the change in L but also the change in ship speed can be handled extremely finely. That is, when the ship speed changes, the position of the streamline 4 toward the ship bottom 3 changes subtly, so as described above, by adjusting the opening of the flow rate adjusting valve 10, the pressurized air 1
It can be dealt with to some extent by adjusting the supply flow rate of No. 3 and changing the diameter of the microbubbles 14. At this time, the divided air blower 7a for blowing the pressurized air 13 according to the change of the position of the streamline 4 is used. By properly using
The micro bubbles 14 can be generated from the split air blowing device 7a at the optimum position. In this case, the flow rate adjusting valve 10 for each of the split air blowers 7a is opened and closed, but it is more convenient if the opening and closing control can be automatically controlled according to the ship speed.

Next, FIGS. 3A and 3B show other examples of the shapes of the air blowers 7 and 7a. FIG. 3A shows the case of a rectangular cross section, and FIG. A case of a mold cross-section is shown, and each has a flattened shape toward the surface of the hull 1.

Even if the air blower 7 or 7a having a tubular structure having a shape as shown in FIGS. 3A and 3B is adopted, the same operational effect as in the case of the above-described embodiment can be obtained.

4 (a), (b) and (c), instead of the air blower 7 or 7a having a cylindrical structure, a shallow groove type structure of various shapes provided with a large number of air blow ports 5 is provided. The air blowing member 7 ′ is attached to the surface of the hull 1 by welding to form the air blowing device 7 or 7 a with the ship side outer plate 15.

When the air blowing member 7'as shown in FIGS. 4A, 4B and 4C is used, there is an advantage that the member weight can be reduced as compared with the case of using the cylindrical structure.

In the above embodiment, the air blower 7a is shown as having an internal division structure in the longitudinal direction. However, it may be divided in a short length in advance, that is, as a separate structure in the longitudinal direction. It goes without saying that various changes can be made without departing from the scope of the present invention.

[0025]

As described above, the marine frictional resistance reduction device of the present invention exhibits various excellent effects as follows. (1) A large number of air outlets were bored in the wall at the position where the static pressure was small in the area where the streamline was directed toward the ship's bottom or stern at the waterlogged portion of the hull surface at the bow, and both ends were closed. A plurality of slender tubular air blowers are arranged in a vertical direction so as to be oriented in the bow-stern direction, and each of the air blowers is connected to a pressurized air supply device via an air feed pipe. Since it is possible to select and use air blowers with different height positions, pressurized air can be blown out from a position with a small static pressure even if the water level changes, and a blowout port for pressurized air is provided on the bottom of the ship. Micro bubbles can be generated with smaller power than in the case, and the generated micro bubbles can be placed on the streamline and directed toward the ship's bottom or stern. Fine surface It is possible to form a good void by covering it with small bubbles, reduce the frictional resistance acting on the hull, and dramatically improve the propulsion performance of the ship. (2) By dividing each air blower into a plurality of divided structures in the fore-and-aft direction and connecting the air supply pipes to each divided air blower, the divided air blowers at arbitrary positions Since it is possible to use a vessel, it is possible to cope not only with changes in drinking water but also with changes in ship speed, and it is possible to blow out pressurized air from the optimum position to generate minute bubbles. (3) Instead of the tubular structure of the air blower, an air blower having a groove type structure is used, and when the air blower is constituted by the groove type air blower member and the surface of the hull, a tubular structure is obtained. The weight can be reduced more than when it is used.

[Brief description of drawings]

FIG. 1 shows an embodiment of a frictional resistance reducing device for a ship according to the present invention, in which (a) is a schematic side view of a hull bow,
(B) is an enlarged arrow view of the (A) direction A-A, and (C) is an enlarged view of the BB direction arrow of (A).

FIG. 2 shows another embodiment of the present invention.
[Fig. 4] is a schematic side view of the bow of the hull, and (B) is an enlarged view showing a part C of (A).

FIG. 3 shows another example of the air blower, in which (a)
(B) is a sectional view showing a different shape.

FIG. 4 shows an example in which an air blower is constructed by using an air blower having a groove type structure.
(C) is a sectional view showing a different shape.

[Explanation of symbols]

 1 Hull 2 Bow Part 3 Ship Bottom 4 Streamline 5 Air Outlet 6 Air Chamber 7 Air Blower 7a Air Blower 9 Blower (Pressurized Air Supply Device) 11 Air Supply Pipe 15 Ship Side Plate

Claims (3)

[Claims] 1. A large number of air outlets are formed on a surface of a ship-side outer plate at a position where a static pressure is small in a region where a streamline is directed toward a ship bottom or a stern in a flooded part of a hull surface of a bow. A plurality of slender cylindrical air blowers with both ends closed are attached in a plurality of stages in the vertical direction so as to face the bow-stern direction, and the air blowers are connected to a pressurized air supply device through an air feed pipe. A frictional resistance reduction device for a ship having the above-mentioned configuration. 2. The frictional resistance reduction device for a ship according to claim 1, wherein each air blower is divided into a plurality of pieces in the longitudinal direction, and an air supply pipe is connected to each of the divided air blowers. 3. The frictional resistance reduction device for a ship according to claim 1, wherein the air blower is constituted by fixing an air blower member having a groove structure instead of the cylindrical structure on the surface of the hull.