JP2001341689A - Ship reduced in frictional resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce frictional resistance with a reduced energy consumption to effectively save an energy consumption in navigation. SOLUTION: This ship is provided with a negative pressure forming part 23 arranged to be projected from a submerged surface 12 of a hull 10 so as to generate cavitation and separation in water in a rear side of the hull by relative water flow 40 with respect to the hull 10 in the navigation, an ejection port 23c arranged in a rear side of the negative pressure forming part 23 to eject bubbles 42 into the water, and a fluid passage 30 of which the one end is opened to a gas space and of which the other end is opened into the water via the ejection port 23c.

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 ship for reducing the frictional resistance of a hull, and more particularly to improving the overall energy efficiency by efficiently discharging bubbles into water.

[0002]

2. Description of the Related Art Conventionally, in order to reduce energy consumption during navigation of a ship or the like, a gas is fed into water and a number of air bubbles are interposed near a surface of a hull outer plate (submerged surface). There has been proposed a method of reducing frictional resistance between a hull and water.

As a technique for generating bubbles in water, Japanese Patent Application Laid-Open Nos. 50-83992 and 53-136289 have been disclosed.
JP-A-60-139586, JP-A-61-712
No. 90, No. 61-39691, No. 61-12
No. 8185 has been proposed.

In these techniques, as a method of generating bubbles in water, gas pressurized by a device such as a pump or a blower is blown into water through a plurality of holes or a perforated plate provided in a hull.

[0005]

However, in the method of injecting pressurized gas into water, energy for operating the pressurizing device is required, and the amount of energy saved by reducing frictional resistance is reduced. Resulting in. In particular, when gas is blown into water at a relatively large depth such as the bottom of a large ship, it is necessary to pressurize the gas to a high pressure corresponding to the water pressure (hydrostatic pressure), which consumes a large amount of energy. Resulting in. In addition, when installing the pressurizing device on the hull, large costs such as facility costs and construction costs are incurred.

The present invention has been made in view of such circumstances, and has the following objects. (1) To reduce frictional resistance with low energy consumption and effectively reduce energy consumption during navigation. (2) To efficiently mix bubbles in water to effectively reduce frictional resistance. (3) To reduce hull construction costs.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a first aspect of the present invention is to provide a low-friction-resistance ship which releases bubbles on the submerged surface of a hull to reduce the frictional resistance of the hull. A negative pressure forming portion protruding from the submerged surface of the hull so that cavitation occurs in the water behind the hull due to the relative flow of water with respect to the hull; A technology including a discharge port provided behind the pressure forming section and a fluid passage open at one end to the gas space and open at the other end to the water through the discharge port is employed.

According to the present invention, cavitation occurs in the water due to the negative pressure forming portion disposed so as to protrude from the submerged surface of the hull, and a negative pressure portion having a low pressure with respect to the gas space is provided behind the negative pressure forming portion. As a result, the gas is guided into the water from the gas space through the fluid passage by the pressure gradient force, and bubbles are released into the water through the discharge port. At this time, the gas and water are positively mixed at the interface between the gas and the water due to the stirring action by the cavitation, and the separation of the bubbles from the interface is promoted, and the strong negative pressure action due to the cavitation and the separation causes A large amount of gas is led into the water through the fluid passage. Therefore, a large amount of bubbles are mixed and generated in the water.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the frictional resistance reducing ship according to the present invention is applied to a large ship such as a tanker or a container ship will be described below with reference to the drawings. In FIG. 2, reference numeral M denotes a frictional resistance reducing ship, 10 denotes a hull, 11 denotes a bubble generator, 12 denotes a hull outer plate (submerged surface), 13 denotes a propulsion device, 14 denotes a rudder, and 15 denotes a water surface (draft line). ing.

An enlarged ship as the frictional resistance reducing ship M is
For example, a VLCC (Very Large Crude Oil Carrier) corresponds to this, and the area of the bottom of the hull outer plate 12 (submerged surface) below the waterline 15 is relatively larger than the ship side compared to other types of ships. Is formed. Further, the bubble generator 11 is disposed in front of the hull 10 (on the bow side).

As shown in FIG. 2 (b), the bubble generating device 11 has an outer cylinder 21 having a shaft center arranged vertically and laid in a fixed state on the hull. An inner cylinder 22 as a gas introduction pipe (AIP: Air Induction Pipe) accommodated movably in an axial direction (up and down direction);
A negative pressure forming part 23 is provided at a lower end of the inner cylinder 22, and a position adjusting part 24 for adjusting an axial position (height) of the inner cylinder 22 with respect to the outer cylinder 21. I have.

The outer cylinder 21 is a tubular member laid through the hull 10 so that its ends are opened above and below the waterline 15, and the inner cylinder 22 has a size that can be inserted into the outer cylinder 21. The inner tube 22 is inserted into the outer tube 21 through an opening at the upper end of the outer tube 21. As the material of the outer cylinder 21 and the inner cylinder 22,
A metal such as a steel material or an aluminum material subjected to a corrosion-resistant surface treatment is used. In addition, a resin (synthetic resin) having corrosion resistance to seawater is preferably used as the material of the inner cylinder 22 in order to reduce the weight. Used.

The negative pressure forming portion 23 is formed in a box shape having one open side, and has an open end formed on the inner cylinder 22 so as to form a projection from the lower end of the inner cylinder 22 outward (downward) in the axial direction.
Airtightly joined to the lower end of the housing. More specifically, as shown in FIG. 3, the negative pressure forming part 23 extends obliquely with respect to the axial direction of the inner cylinder 22 and is located forward (on the bow side) in the traveling direction Dve.
And a rear slope 23b disposed on the rear side thereof and facing rearward (stern side) in the traveling direction. The edges of these slopes 23a and 23b are aligned with each other, and the hull is submerged. A substantially pointed projection is formed from the water surface 12 and projects perpendicularly to the traveling direction Dve of the hull. The rear slope 23b is provided with a discharge port 23c formed of a through hole as an opening of a cavity in the inner cylinder 22.

By disposing the inner cylinder 22 in the outer cylinder 21, a fluid passage 30 is formed as an internal space between the inner cylinder 22 and the negative pressure forming part 23. One end of the fluid passage 30 is opened to the gas space (atmosphere) through the upper opening 22 a of the inner cylinder 22 as an air intake, and the other end is submerged through the outlet 23 c of the negative pressure forming part 23. It is open to the public.

The position adjusting section 24 includes a drive device (not shown) such as a motor for moving the inner cylinder 22 to a predetermined position, and a lock mechanism (not shown) for fixing the inner cylinder 22 at a predetermined position. The negative pressure forming part 23 is adjusted to a predetermined projecting state from the submerged surface 12 of the hull in accordance with the navigation state of the hull.

The shape and the position of each component of the bubble generator 11 are set so that the flow of water behind (at the stern side) of the negative pressure forming part 23 during navigation is in a desired state. It is designed based on the results of flow field analysis and running test by Computational Fluid Dynamics).
Here, during navigation at a predetermined ship speed Vs, the negative pressure forming part 23 is designed so that cavitation and separation occur in the water behind it due to the flow of water relative to the hull.
Height H is determined. For example, the height H of the negative pressure forming part 23 is set as large as possible within the range of the diameter D of the inner cylinder 22. In addition, one or more bubble generating devices 11 are arranged according to the size of the ship bottom.

The ship M having the reduced frictional resistance constructed as described above.
The method for reducing the frictional resistance of the hull according to the present invention will be described below with reference to FIG. In the stopped state, water (seawater) has entered into the fluid passage 30 to almost the same water level as around the hull 10. When the hull 10 enters the navigating state by the thrust of the propulsion device 13 (see FIG. 2), a water flow 40 relative to the hull 10 is formed.

In the navigation state, when a predetermined ship speed Vs is reached, as shown in FIG. 1 (a), a negative pressure forming part 23 projects a predetermined height H from the submerged surface 12 of the hull by the position adjusting part 24. So that the axial position (height) of the inner cylinder 22 with respect to the outer cylinder 21 is adjusted.

At this time, the front slope 23 of the negative pressure forming portion 23
As the flow path of water is narrowed by a, the flow velocity of water flowing along the bottom of the ship increases, and cavitation and separation occur in the water behind the negative pressure forming portion 23 due to the sharp angle of the protruding end. Thereby, the hydrostatic pressure in the water behind the negative pressure forming part 23 is locally reduced, and the negative pressure part 41 which becomes low with respect to the atmosphere is formed.

At this time, since the pressure at the outlet 23c facing the negative pressure point 41 is lower than the pressure at the upper opening 22a of the inner cylinder 22, the pressure in the fluid (seawater and air) in the fluid passage 30 is reduced. The gradient force acts, the seawater is discharged from the fluid passage 30, and the air flowing in from the upper opening 22a of the inner cylinder flows through the fluid passage 30 and is sent into the water.

Then, the gas sent into the water contains bubbles 4
As a result, the frictional resistance of the hull 10 is reduced by mixing the water 2 with water and interposing a large number of bubbles 42 near the submerged surface 12 of the hull 10.

At this time, the energy required for sending air into the water is mainly for changing the position of the gas. This energy is obtained by changing the flow state of the water by the negative pressure forming part 23, and is smaller than the energy consumed when the gas is pressurized and jetted into the water. Therefore, energy consumption during navigation is effectively reduced by reducing the frictional resistance of the hull 10.

Further, in the present embodiment, the negative pressure forming portion 23, which is a projection having a substantially pointed shape, is disposed so as to protrude from the submerged surface 12 of the hull, and cavitation and separation are actively generated. Therefore, due to the stirring action of these, the gas and the water are positively mixed at the boundary surface between the gas and the water, and the separation of the bubbles from the gas-liquid interface is promoted. A large amount of gas is introduced into the water through the passage 30, and a large amount of bubbles are generated in the water. At this time, since the negative pressure forming part 23 is disposed so as to protrude from the submerged surface 12 of the hull, the drag against the water flow 40 increases, but the actual Reynolds number in the hull 10 is reduced. Since the surface roughness is already relatively high and a large amount of bubbles are generated in the water, the effect of the increase in the drag on the effect of reducing the frictional resistance is small.

Further, in the present embodiment, the position (height) of the inner cylinder 22 with respect to the outer cylinder 21 is adjusted in accordance with the navigation condition, so that the negative pressure forming section 2 from the submerged surface 12 of the hull is formed.
3 is controlled. That is, for example, when the ship speed does not reach the predetermined ship speed Vs, or when the effect of reducing the frictional resistance due to bubbles due to stormy weather cannot be expected, FIG.
As shown in FIG.
3 is set inside the hull from the submerged surface 12 of the hull, and the negative pressure forming portion 23 is set in a non-projecting state, whereby the water flow 40
To suppress the increase of the drag force, and reduce the energy consumption. Further, by controlling the projecting height of the negative pressure forming part 23 in accordance with the traveling speed, control is performed such that bubbles are effectively released into the water.

The formation of the negative pressure portion 41 is performed by the negative pressure forming portion 23.
The shape of the hull and the projecting height of the hull from the submerged surface 12 and the Reynolds number are the main controlling factors, and it is considered that disadvantages due to the water depth are unlikely to occur. It is advantageous.

Since the bubbles 42 mixed in the water are formed at an internal pressure lower than the hydrostatic pressure according to the water depth, when the bubbles 42 move at a constant water depth (for example, the bubbles move along the ship bottom). ), The water pressure corresponding to the water depth acts on the bubbles 42 as the distance from the negative pressure point 41 increases, and the bubbles 4 gradually disappear.
2 becomes smaller. Applicants' previous studies indicate that relatively small bubbles are preferred to reduce the frictional resistance of the hull. Therefore, the air bubbles generated by the negative pressure also have an advantageous effect on the reduction of the frictional resistance from this point.

Also, since the bubble generating device 11 has a simple structure and does not require a device for pressurizing gas,
It goes without saying that the construction cost of the hull 10 is low.

It should be noted that the shapes, combinations, and the like of the constituent members shown in the above-described embodiments are merely examples, and various changes can be made based on design requirements without departing from the gist of the present invention. In the embodiment described above,
Although an example in which the present invention is applied to an enlarged boat is shown, the invention is not limited to this, and can be applied to other boats such as a high-speed boat and a fishing boat. The size and number of the air bubble generators 11 and their locations are appropriately set according to the shape of the hull. However, as described above, the Reynolds number of the actual hull 10 is already relatively high due to the surface roughness of the submerged surface 12, and the diffusion effect works. Therefore, it is not necessary to provide an excessively large number of the bubble generators 11.

[0029]

As described above, according to the present invention,
By utilizing the pressure gradient force, gas is sent into water with less energy consumption than when gas is pressurized,
The frictional resistance of the hull can be reduced. In addition, since cavitation is generated in the water by the negative pressure forming section, a large amount of bubbles are generated in the water, so that effective reduction of frictional resistance can be performed and energy consumption during navigation can be reduced. Further, a device for pressurizing gas is not required, and the construction cost of the hull can be easily reduced.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of a method for reducing the frictional resistance of a hull by a frictional resistance reducing ship according to the present invention.

FIG. 2 is a configuration diagram schematically showing an embodiment in which the method for reducing frictional resistance of a hull according to the present invention is applied to a ship.

FIG. 3 is a perspective view showing an entire configuration of a negative pressure forming section 23 of FIG. 2;

[Explanation of symbols]

 M Ship with reduced frictional resistance 10 Hull 11 Bubble generator 12 Hull outer plate (submerged surface) 15 Water surface (draft line) 21 Outer cylinder 22 Inner cylinder 23 Negative pressure forming part 24 Position adjusting part 23a Front slope 23c Discharge port 30 Fluid passage 22a Opening

Claims (1)

[Claims] 1. A friction-reducing ship that releases bubbles on a submerged surface of a hull to reduce the frictional resistance of the hull, wherein cavitation is generated in the water behind the hull by the flow of water relative to the hull during navigation. A negative pressure forming portion provided to protrude from the submerged surface of the hull; a discharge port provided behind the negative pressure forming portion to release bubbles into the water; A fluid passage that is open and has the other end opened into water through the discharge port.