JP2000128062A - Device to reduce friction resistance of ship - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the void fraction of the hull area upon which friction resistance from sea water greatly acts. SOLUTION: A pair of air blowing devices 5a, 5b which generate minute bubbles 4a, 4b by blowing pressurized air into the water from a plurality of air blow holes 6 are mounted in the bottom 3 of a hull 1. The air blowing devices 5a, 5b are mounted in positions at least upstream of the area 2 upon which friction resistance greatly acts, and are arranged in a V-shape centered on a hull center line L. The high initial speed directly aft of the air blowing devices 5a, 5b is used so that the minute bubbles 4a, 4b intervene before flowing downstream.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for reducing the frictional resistance of a ship, which can reduce the frictional resistance acting on the hull surface 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 blow the 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 to reduce the 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, the present inventors have determined the position of blowing out the pressurized air at a place where the static pressure is small, and the generated microbubbles are placed on the ship bottom or ship side. Given that the hull shape is given in order to set the position of the air outlet at a required position with a small static pressure, the turbulent diffusion of microbubbles flowing along the streamline around the hull is considered. A formula for calculating the void fraction distribution at any position and the arbitrary motion was established. In this calculation formula, the influence of turbulent diffusion is calculated 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. Considered by giving a turbulence. That is, the random motion of the microbubbles was directly simulated by the Monte Carlo method. When the motion of the microbubbles is calculated, the void fraction can be obtained by dividing the volume of the microbubbles existing in the inspection area (cell) at a certain time by the volume of the inspection area (cell). By determining the streamline at the bow such that a high void ratio effective for reducing the frictional resistance is generated based on the void ratio distribution obtained in this manner, the position of the compressed air to be blown is determined. Can be.

[0005]

However, when microbubbles are caused to flow on streamlines around the hull, the effect of reducing frictional resistance can be obtained, but the frictional resistance is lower than that of other parts. However, it was not possible to particularly improve the void ratio near the wall near the hull center line at the bottom of the ship, which acts greatly.
Further, depending on the hull shape, a large frictional resistance may partially act on the side of the hull, but as described above, it is not possible to obtain a high void ratio in the vicinity of the wall simply by placing microbubbles on the streamline. .

Accordingly, an object of the present invention is to make it possible to partially improve the void ratio near the wall in a region where the frictional resistance is large as compared with other portions.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an air blower which generates microbubbles by blowing pressurized air into water from a number of air blowout ports. In addition, at least immediately upstream of the region where the frictional resistance of the hull greatly acts, a C-shaped arrangement is adopted.

[0008] When air is blown out from the air blowers arranged in a C-shape to generate microbubbles, since the air blowing speed of the air blower portion is high, the microbubbles are not flown downstream. Because it will interfere
The void ratio near the wall can be partially improved.

When the air blower is mounted at a position sandwiching the center line of the hull bottom, minute bubbles interfere with each other near the center line of the hull bottom, and the frictional resistance is particularly large. The void ratio in the bottom region of the ship can be improved.

[0010]

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

FIGS. 1 (a), 1 (b) and 1 (c) show an embodiment of the present invention. In a hull 1, a ship bottom 3 having a region 2 where frictional resistance acts particularly large is provided on a one-to-one basis. The air blowers 5a and 5b thus assembled are arranged in a C-shape arrangement with the required interval from the immediately upstream portion of the above-mentioned area 2 to the downstream side in order with the required hull center line L interposed therebetween, and each set of air blowers 5a , 5b generated by the small bubbles 4a, 4b
In the vicinity of the hull center line L.

The air blowers 5a and 5b have the same structure, and as shown in an enlarged view in FIG.
Air outlets 6 having pores are formed in a multi-row and multi-stage at a required pitch in the outer plate of the outer plate, and each air outlet 6 is surrounded by an air chamber inside the portion where the air outlet 6 is formed. Is formed so as to form a box-shaped sea chest 7 in a watertight manner, and an air supply pipe 8 is connected to the sea chest 7. The air supply pipe 8 is connected to an air supply source 10 such as a compressor or a blower which is arranged on a deck and driven by an electric motor 9.

During cruising at a cruising speed, the air supply source 10 is driven by the electric motor 9 to guide the pressurized air through the air supply pipe 8 to the air blowers 5a, 5b on the ship bottom 3, and into the water from the air blowout port 6. When the air bubbles are blown out, the generated microbubbles 4a and 4b flow downstream along the streamlines in the bottom 3 of the ship. At this time, the air blowers 5a and 5b are arranged in a V-shape across the hull center line L. And microbubbles 4a, 4b generated at the air blowers 5a, 5b.
Since the initial velocity is large, the microbubbles 4a and 4b flow so as to face each other at the position of the hull center line L, and are caused to interfere with each other in the boundary layer at this position. Therefore,
The void ratio near the wall near the hull center line L can be increased as compared with other portions. That is, it is possible to improve the void ratio in the region 2 where the frictional resistance particularly acts. For this reason, the frictional resistance of the hull 1 can be reduced very effectively.

Next, FIG. 2 shows another embodiment of the present invention, and shows an example of application to a hull 1 in which a region 2 where a frictional resistance particularly acts is on a ship side 11 of a bow. That is, in the upstream part of the area 2 on the ship side 11, FIG.
(B) The air blowing devices 5a and 5b having the same configuration as shown in (c) are assembled in a C-shaped arrangement.

As shown in FIG. 2, fine bubbles 4a, 4b
Is blown and caused to interfere with each other, whereby the void ratio in the vicinity of the wall on the ship side 11 of the bow can be partially improved.

The present invention is not limited to the above embodiment, and the air blower may be of a type in which a perforated plate is fitted into a hull outer plate. The blowing device can be assembled at any position where the void ratio is to be improved other than those shown in FIGS. 1 and 2, and various changes can be made without departing from the spirit of the present invention. It is.

[0017]

As described above, according to the apparatus for reducing the frictional resistance of a ship according to the present invention, an air blow-out device which generates fine bubbles by blowing pressurized air into water from a large number of air blow-out openings. The vessel is assembled at least immediately upstream of the area where the frictional resistance of the hull acts greatly, so that the flow of microbubbles from the air blowers arranged in a C shape is It is possible to partially interfere with the void ratio near the wall of that part, and the air blower should be installed at a position sandwiching the center line of the line at the bottom of the ship In this way, the hull resistance is particularly large, the void fraction near the wall near the hull center line at the bottom can be improved, and the frictional resistance of the hull can be reduced very effectively. , There is exhibited an excellent effect that.

[Brief description of the 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, (b) is a schematic bottom view, and (c) is an enlarged sectional view of an air blower. It is.

FIG. 2 is a schematic side view showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hull 2 Area 3 Ship bottom 4a, 4b Microbubble 5a, 5b Air blowing device 6 Air blowing port

Claims (2)

[Claims] An air blower configured to generate fine air bubbles by blowing pressurized air into water from a large number of air blowout ports is provided at least immediately upstream of a region where the frictional resistance of the hull is large. A frictional resistance reducing device for a ship, wherein the frictional resistance reducing device is assembled as a C-shaped arrangement. 2. The apparatus for reducing frictional resistance of a ship according to claim 1, wherein the air blower is mounted at a position sandwiching the center line of the hull at the bottom of the ship.