JP2002002582A - Friction resistance reducing ship - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a friction resistance reducing ship capable of effectively saving an energy consumption during navigating, by conducting friction resistance reduction with a small energy consumption. SOLUTION: This friction resistance reducing ship comprises a negative pressure forming portion 20 provided on a submerged surface 12 of a hull so as to form a negative pressure area 41 having low pressure to a gas space, at an underwater rear part of the hull; a first recessed portion 21 arranged behind the negative pressure forming portion 20 and provided in a state recessed from the submerged surface 12 of the hull; a fluid passage 23 opening to the gas space at one end and opening to the first recessed portion 21 at the other end so as to lead gas from the gas space to the underwater negative pressure area 41; and a second recessed portion 22 arranged between the negative pressure forming portion 20 and the first recessed portion 21, and provided in a state recessed from the submerged surface 12 of the hull at a shallower depth than the first recessed portion 21.

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, the method of injecting a pressurized gas into water requires energy for operating the pressurizing device, and reduces the amount of energy saved by reducing frictional resistance. 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]

According to a first aspect of the present invention, there is provided a ship for reducing frictional resistance of a hull by emitting air bubbles on a submerged surface of the hull to reduce the frictional resistance of the hull. A negative pressure forming portion provided on the submerged surface of the hull so as to form a negative pressure portion having a low pressure in the water behind itself, and disposed behind the negative pressure forming portion, from the submerged surface of the hull. A first recess provided in a depressed state, and a fluid passage open at one end to the gas space and open at the other end to the first recess to guide the gas from the gas space to a negative pressure point in the water, A technology is provided which includes a second recess disposed between the negative pressure forming portion and the first recess, and provided in a state of being recessed shallower than the first recess from the submerged surface of the hull.

According to the present invention, since a negative pressure portion is formed in the water by the negative pressure forming portion, the gas flows from the gas space to the negative pressure portion in the water through the fluid passage by the pressure gradient force. The gas that has flowed into the water accumulates in the first recess provided from the submerged surface of the hull, and a part of the gas flows into the second recess provided between the negative pressure forming portion and the first recess. Since the second recess is provided shallower than the first recess, gas and water are more likely to be mixed than in the first recess. Therefore, the separation of bubbles from the interface between gas and water is promoted by the shallow second concave portion.

[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 symbol M denotes a frictional resistance reducing ship, 10 denotes a hull, 11 denotes an air 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 panel 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. 2B, the bubble generating device 11 has a negative pressure forming portion 20 provided on the submerged surface 12 of the hull 10 and a predetermined pressure rearward (stern side) from the negative pressure forming portion 20. A first concave portion provided at an interval, and a negative pressure forming portion;
A second concave portion 22 provided between the first concave portion 21 and the first concave portion 21, that is, behind the negative pressure forming portion 20 and in front of the first concave portion 21;
And a fluid passage 23 penetrating the hull 10 and being opened above and below the waterline 15.

The negative pressure forming section 20 uses a relative flow of water with respect to the hull 10 during navigation to place a negative pressure portion, which has a low pressure with respect to the gas space (atmosphere) at a predetermined ship speed Vs, in the water. It is for forming. Here, during the navigation, the negative pressure forming unit 20 increases the relative speed of water at the bottom of the hull at a specific location and submerges the hull toward the rear (stern side) so as to generate a separation area behind. A slope 20a gradually rising from the surface 12;
And a sharp corner 20b formed at the terminal end of the head.

The first recess 21 and the second recess 22 are
Here, one side is an internal space of the chamber 30 which is formed in an open box shape, and each is a submerged surface 1 of the hull.
It is provided in a state depressed from 2 into the hull. Also,
The chamber 30 has a step 30a formed along the traveling direction Dve of the hull 10, and a deep recess behind the step is the first recess 21, and a shallow recess adjacent to the front is the second recess 22. It has become. Further, the chamber 30 is provided with a slope 30 b so that water can quickly flow backward from the first recess 21 during navigation, and a deep recess from the bottom surface of the first recess 21, that is, the submerged surface 12 of the hull. A discharge port 30c formed of a through hole is provided at the location. Here, the first concave portion 21 and the second concave portion 22
Are provided in a rectangular shape as viewed from the bottom of the ship, as shown in FIG.

Referring back to FIG. 2, the fluid passage 23 is provided with a gas introduction pipe (AIP: Air Inductio) connected to the chamber 30.
n Pipe) 31. That is, the fluid passage 2
3 has one end opened to the gas space (atmosphere) through the air inlet 31a of the gas inlet tube 31 and the other end opened to the water through the outlet 30c of the chamber 30. ing. The internal cross-sectional area and shape of the gas introduction pipe 31 are determined so that a fluid having a desired flow rate flows with a small pressure loss. Further, here, the air intake 31a is arranged at the front of the deck of the hull 10.

The shape and position of each component of the bubble generator 11 are set so that the flow of water behind the negative pressure forming section 20 during navigation is in a desired state.
D: Computational Fluid Dynamics) is designed by flow field analysis. For example, during navigation at a predetermined ship speed Vs, a low pressure with respect to a gas space (atmosphere) is generated in water behind the negative pressure forming unit 20. The height of the negative pressure forming section 20 and the shape of the chamber 30 are determined so that a negative pressure portion is formed.

The material of the negative pressure forming section 20, the chamber 30, and the gas introduction pipe 31 is, for example, a metal or resin that has been subjected to a corrosion-resistant treatment. Those to which living organisms hardly adhere to the surface are preferably used. In addition, the bubble generator 11
One or more are arranged according to the size of the bottom of the ship.

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 the fluid passage 23 to almost the same water level as the periphery of 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 navigating state, at the bottom of the ship, the flow rate of the water flowing along the bottom of the ship is increased by narrowing the flow path of the water by the negative pressure forming portion 20, and the negative pressure is formed by the corner 20 b of the negative pressure forming portion 20. Separation areas are formed in the water behind the forming section 20, whereby the hydrostatic pressure is locally reduced behind the negative pressure forming section 20.

When the navigation speed of the hull 10 reaches a predetermined boat speed Vs (for example, a standard navigation speed), the negative pressure forming section 2
In the water behind 0, a negative pressure portion 41 is formed, which is lower in pressure than the atmosphere.

At this time, since the pressure near the discharge port 30c facing the negative pressure point 41 is lower than the pressure at the air intake port 31a, the pressure gradient force against the fluid (seawater and air) in the fluid passage 23 is reduced. Acts, the seawater is discharged from the fluid passage 23, and the air flowing in from the air intake 31a flows through the fluid passage 23 and is sent into the water.

In this embodiment, the first recess 21 is provided in a state recessed from the submerged surface 12 of the hull.
Since one end of the fluid passage 23 is open to the first, the gas flowing through the fluid passage 23 accumulates in the first recess 21. At the boundary surface between gas and water (gas-liquid interface 43), the flow velocity of water changes (discontinuous) due to the influence of the separation region xx formed by the negative pressure forming section 20, and the boundary surface is wavy. (Eg, a phenomenon due to Kelvin-Helmholtz instability). Then, a vortex or the like is generated by this waving phenomenon, the force of mixing the gas and the water increases, and the bubbles separated from the boundary surface are mixed into the water.

At this time, due to turbulent flow (sloshing) such as a waving phenomenon at the boundary surface, a part of the gas accumulated in the first concave portion 21 is changed to a second concave portion provided in front of and adjacent to the first concave portion 21. Flow into 22. Since the depth of the second recess 22 is smaller than that of the first recess 21, gas and water are more likely to be mixed than in the first recess 21, and bubbles are generated from the interface between the gas and water. Easy to leave. It is considered that this is because a gas film (gas sheet) formed in the second concave portion 22 having a shallow depression is easily separated by a shearing force.

The gas sent into the water through the fluid passage 23 mixes with the water as bubbles 42, and a large number of bubbles 42 intervene near the submerged surface 12 of the hull 10, thereby causing friction of the hull 10. Resistance is reduced.

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 unit 20, 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.

Moreover, in the present embodiment, the second shallow
The recess 22 facilitates the departure of the bubbles 42 from the gas-liquid interface 43, so that less energy is required for sending air into the water.

In addition, a shallow second concave portion 22 is provided separately from the first concave portion 21 into which gas flows, and the separation of bubbles is promoted by the second concave portion 22 so that a predetermined amount of bubbles can be mixed with water. The area occupied by the entire concave portion on the submerged surface 12 of the hull can be reduced as compared with the case where is formed by one concave portion.

Further, in forming the negative pressure portion 41, the shape of the negative pressure forming portion 20 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 also advantageous for ship applications.

The amount of bubbles 42 generated at the negative pressure point 41 is affected by the saturated vapor pressure determined by the surrounding environmental conditions. That is, a gas that is larger than the amount of gas that can be dissolved in water exists in the water as bubbles 42. Therefore, since the separation of the bubbles 42 from the gas-liquid interface 43 is promoted, the number of the bubbles 42 stagnating near the gas-liquid interface 43 is reduced, and a desired amount of the bubbles 42 is stably mixed into the water. The frictional resistance is reliably reduced.

Since the bubbles 42 mixed in the water are formed at an internal pressure lower than the hydrostatic pressure corresponding to the water depth, when the bubbles 42 move at a constant water depth (for example, the bubbles move along the ship bottom). (Time), a larger water pressure acts on the bubble 42 as the distance from the negative pressure portion 41 increases, and the size of the bubble 42 gradually decreases. 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.

Further, 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 can be reduced. Further, as described above, the area occupied by the entire concave portion on the submerged surface 12 of the hull can be reduced, which is further advantageous in reducing the construction cost.

The shapes, combinations, and the like of the components shown in the above-described embodiment are merely examples, and can be variously changed based on design requirements without departing from the gist of the present invention. The present invention includes the following modifications, for example.

In the above-described embodiment, the concave portion (the first concave portion 2)
The first and second recesses 22) are provided in a rectangular shape when viewed toward the bottom of the ship, but the shape of the recess is not limited to this, and various shapes can be applied. For example, as shown in FIG. 4, by providing concave portions (the first concave portion 51 and the second concave portion 52) in an elliptical shape as viewed toward the ship bottom, the negative pressure forming portion 50 is provided at the edge of the shallow second concave portion 52. It is good also as a structure which is widely arrange | positioned and can further promote the desorption of the air bubbles in the 2nd recessed part 52.

Further, the place where the bubbles are released is not limited to the "ship bottom" shown in the above embodiment, but may be the "ship side" below the waterline. When a concave portion or a negative pressure forming portion is provided on the ship side, the configuration shown in FIG. 4 is preferably used.

The negative pressure forming section 20 shown in FIG. 2 has a slope 20a which gradually rises from the submerged surface 12 of the hull toward the rear (stern side). However, the present invention is not limited to this. For example, when a sufficient negative pressure point is formed in the water behind by the corner 30b, the slope 30b is not necessarily required and the shape may not be projected from the hull.

Further, in the above-described embodiment, an example in which the present invention is applied to an enlarged boat is shown. However, the present 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.

[0036]

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, the second concave portion provided shallowly on the submerged surface of the hull promotes separation of bubbles, so that the amount of bubbles mixed into the water can be increased. Therefore, effective reduction of frictional resistance can be performed by a large amount of bubbles, 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 view as viewed from an arrow A shown in FIG. 2;

FIG. 4 is a schematic plan view of a bubble generating device according to another embodiment in which the method for reducing frictional resistance of a hull according to the present invention is applied to a ship, as viewed toward the bottom of the ship.

[Explanation of symbols]

 M Friction resistance reducing ship 10 Hull 11 Bubble generator 12 Hull outer plate (submerged surface) 15 Water surface (waterline) 20, 50 Negative pressure forming part 21, 51 First concave part 22, 52 Second concave part 23, 53 Fluid passage 30b Outlet 31 Gas inlet tube 40 Water flow 41 Negative pressure point 42 Bubbles 43 Gas-liquid interface

Claims (1)

[Claims] 1. A frictional resistance reducing ship for reducing frictional resistance of a hull by emitting air bubbles on a submerged surface of the hull, wherein a negative pressure portion having a low pressure with respect to a gas space is formed in water behind itself. A negative pressure forming portion provided on the submerged surface of the hull, a first concave portion provided behind the negative pressure forming portion and provided in a recessed state from the submerged surface of the hull, and a negative pressure portion in the water from the gas space. A fluid passage having one end opened to the gas space and the other end opened to the first recess, and disposed between the negative pressure forming portion and the first recess to guide the gas to the hull; A second recess provided in a state of being recessed shallower than the first recess from a submerged surface.