KR101893508B1 - The air lubrication method with pressure gradient for reducing the ship resistance - Google Patents

Abstract

로 정의되며, 상기

는 공기의 밀도이고

는 물의 밀도,

는 공기의 유속,

는 물의 유속을 나타낼 때,
상기 운동에너지 비(KER)가 1.0 이하가 되도록 공기의 분사 속도를 제어하는 것을 특징으로 한다. The present invention relates to a method of air lubrication of a ship in which the air injection through a nozzle is controlled according to a ship's standing posture and a speed of a ship to enable effective air lubrication with a small energy, A method of air lubrication of a ship in which a plurality of nozzles for spraying air to the bottom of a hull are arranged along the longitudinal direction and the width direction of the hull,
The kinetic energy ratio (KER) of the air injected from the nozzle to the kinetic energy according to the flow rate of water is

, ≪ / RTI >

Is the density of the air

The density of water,

The flow rate of air,

Indicates the flow rate of water,
And the injection speed of air is controlled so that the kinetic energy ratio (KER) is 1.0 or less.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of air lubrication of a ship using a pressure gradient,

The present invention relates to a method of reducing friction resistance of a ship using air lubrication, and more particularly, to a method of controlling air injection through a nozzle in accordance with a ship's standing posture so that an artificial pressure gradient can be generated in the ship, To an air lubrication method of a ship which enables efficient air lubrication.

In the International Maritime Organization (IMO), the greenhouse gas emission regulation and the energy efficiency design index (EEDI) due to global warming have entered into force on the newbuilding since 2013. As a result, ship resistance and propulsion efficiency are no longer a matter of choice but a survival problem for shipbuilding and shipping industry.

The ship's operational resistance is largely divided into the wave resistance caused by the waves generated by the hull and the frictional resistance due to the friction between the hull and the water immersed in the water. With advances in CFD and linear technology, the ripple resistance is dropping below 20% of the total resistance. The ratio of the friction resistance to the total resistance is known to be 80 to 90% in the case of low speed non-election. Reducing the frictional resistance of a ship by 10% has a worldwide shipping cost savings of about $ 2 billion.

Air-layer lubrication and micro-bubble frictional resistance reduction techniques are the closest to practical use among the proposed flow control techniques for reducing frictional resistance. Micro-bubble method (BRD) is a method of reducing resistance by interfering with the exchange of momentum of turbulent flow by spraying fine air bubbles near the surface, and it is tried to apply solid line by NMRI (National Marine Research Institute) -4% efficiency improvement has been reported. However, the fact that air bubbles need to be machined and air bubbles cause cavitation of the propeller, resulting in lower propulsion efficiency, is considered to be a major obstacle to commercialization.

In case of air-layer lubrication method where air bubbles are merged when the flow rate of air injected to the hull surface is more than a certain level (about 2 times), resistance is lower than the power required of the pump that injects air It is economical to obtain the gain. FIG. 1 is a graph showing the resistance reduction according to the air injection flow rate in the flat plate, and it is seen that the air film lubrication technique (ALDR) shows a resistance reduction rate about four times or more as compared with the microbubbles method (BRD).

The air film lubrication resistance reduction technique is ALDR (Air Layer Drag Reduction) which forms an air film by spraying air on a plane, and PCDR (Partial Cavity Drag Reduction) method which forms a cavity by injecting air into a concave portion. 2 is a diagram showing the concept of ALDR and PCDR. In the case of ALDR, it is basically the same as micro-bubble injection method. However, if the air flow rate is increased, the injected bubbles fuse to form a film, and the resistance reduction effect increases sharply. The PCDR has the advantage of being able to maintain the cavity with a smaller injection flow rate, but sometimes the cavity becomes unstable and the groove must be machined on the wall. The ALDR technique is more suitable for application in newly built vessels as well as newly built vessels.

The prior art related to this is Registration No. 0761107, Publication No. 2011-0023883, and the like.

No. 0761107 discloses a hull frictional resistance reduction device capable of easily performing maintenance of an air chamber having a plurality of air ejection holes formed at the bottom of the hull and having a watertight structure so that seawater does not enter the inside of the hull, .

The above-mentioned Japanese Patent Application Laid-Open No. 2001-0023883 relates to a hull frictional resistance reducing device capable of uniformly blowing out air from a plurality of air blowing holes formed on the bottom of an air chamber.

Conventionally, the air lubrication technique of a ship has been studied by focusing on the uniform spraying of air. The technology that enables effective air injection in consideration of the ship's standing position and the speed of the ship, This is a small fact.

Korean Patent No. 0761107 Korea Patent Publication No. 2011-0023883

SUMMARY OF THE INVENTION It is an object of the present invention to provide a watercraft which can control air injection through a nozzle according to a ship's standing posture and a speed of a ship, Air lubrication method.

In order to accomplish the above object, the present invention provides a method of air lubrication of a ship, in which a plurality of nozzles for spraying air at the bottom of a hull are arranged along a longitudinal direction and a width direction of the hull, ,

로 정의되며, 상기

는 공기의 밀도이고

는 물의 밀도,

는 공기의 유속,

는 물의 유속을 나타낼 때, The kinetic energy ratio (KER) of the air injected from the nozzle to the kinetic energy according to the flow rate of water is

, ≪ / RTI >

Is the density of the air

The density of water,

The flow rate of air,

Indicates the flow rate of water,

And the injection speed of air is controlled so that the kinetic energy ratio (KER) is 1.0 or less.

According to one aspect of the present invention, when the ship is in a bow posture, the air is sprayed using nozzles arranged in the line width direction in an intermediate portion between the bow and aft end of the ship among the plurality of nozzles.

When the ship's standing posture is a stern trim, air is jetted by using a nozzle arranged along the longitudinal direction on the center line of the ship among the plurality of nozzles.

According to the present invention, by maintaining the kinetic energy ratio (KER) of the air injected from the nozzle 2 to the kinetic energy according to the relative velocity between the hull and the water generated by the operation of the ship to 1.0 or less, It is possible to form a uniform air lubrication film and to selectively control the positions of the nozzles through which the air is injected in accordance with the ship's standing position, i.e., the bow and the stern tipping, thereby forming an efficient air lubricating film with less energy.

1 is a graph showing a resistance reduction according to an air injection flow rate in a flat plate.
FIG. 2 is a schematic view illustrating an ALDR (Air Layer Drag Reduction) method for forming an air layer by spraying air on a plane, and a PCDR (Partial Cavity Drag Reduction) method for forming cavities by injecting air into concave portions.
FIG. 3 is a configuration diagram of an air lubrication test on a plate hull sample to implement a method of air lubrication of a ship according to the present invention.
4 is a view showing embodiments of nozzles applied to the air lubrication test of FIG.
Fig. 5 is a photograph showing angular changes of the hull posture of the hull sample performed in the air lubrication test of Fig. 3; Fig.
FIG. 6 is a diagram showing an average lubrication shape when the flow velocity is 1.0 m / s and the kinetic energy ratio (KER) of the air injection flow is 1.02 in the air lubrication test of FIG. 3, according to the shape of the nozzle and the angle of the hull sample.
FIG. 7 is a graph showing the average lubrication shape when the flow velocity is 1.5 m / s and the kinetic energy ratio (KER) of the air injection flow is 1.02 in the air lubrication test of FIG. 3, according to the shape of the nozzle and the angle of the hull sample.
FIG. 8 is a graph comparing instantaneous lubrication shapes when the kinetic energy ratio (KER) of the injection flow rate is different when the flow velocity is 1.5 m / s in the air lubrication test of FIG.
FIG. 9 is a graph showing the relationship between the kinetic energy ratio (KER) of the injection flow rate, the change in the anti-roll orientation, the average lubricating area according to the flow rate change when the nozzle is applied, It is a table expressed as a percentage.
FIG. 10 is a graph showing the relationship between the kinetic energy ratio (KER) of the injection flow rate, the change of the anti-roll orientation, the average lubricating area according to the flow rate change when the nozzle (B) It is a table expressed as a percentage.
FIG. 11 is a graph showing the relationship between the kinetic energy ratio (KER) of the injection flow rate, the change of the anti-roll orientation and the average lubricating area according to the flow velocity when the nozzle (C) It is a table expressed as a percentage.
FIG. 12 is a photograph of a 66k bulk carrier used in a model test to implement a method of air lubrication of a ship according to the present invention.
Fig. 13 is a table of the 66k bulk carrier used in the model line experiment of Fig.
FIG. 14 shows the position of the nozzle located on the model line of FIG. 12 and the trim angle of the experiment.
15 is a graph showing the total effective energy in the model line test.
FIG. 16 is a graph showing an average lubrication area obtained by analyzing lubrication images at 1.0 占 17_11T-x10 (4) and 1.0 占 17_16_11T-x10 (6) in a model line test.

Hereinafter, a method of air lubrication of a ship according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 3 is a diagram showing the air lubrication test on the flat plate for carrying out the method of air lubrication of the ship according to the present invention. Fig. 3 is a view showing an example of the air lubrication test of the hull sample 1, A nozzle 2 for spraying air to the lower surface of the hull sample 1 is provided at an intermediate portion of the hull sample 1 and a LED 2 for photographing an air- (3) and a camera (4). A support bar 5 is provided on each of a front portion and a rear portion of the hull sample 1 so as to be rotatable relative to each other and each of the support bars 5 can be moved up and down by a desired distance The posture of the hull sample 1 can be changed to the posture corresponding to the bow and the stern edge of the ship.

4 shows the embodiments of the nozzle 2 installed in the hull sample 1. The nozzle 2 shown in Fig. 4A has one injection hole 21 at the center, The nozzle 2 shown in Fig. 2B has a structure in which a plurality of fine spray holes 22 are arranged in a line in the line width direction, and the nozzle 2 shown in Fig. 2C has a long, (23) are formed, the cross-sectional areas of the passages through which the air is injected are all the same.

Figs. 6 and 7 show the change of the hinge posture of the hull sample 1 when the velocity of water in the water tank is 1.0 m / s and 1.5 m / s, respectively, and the kinetic energy (KER) And the average flow rate of air in the air.

In the air lubrication test for this flat plate type hull sample (1), the hull posture of the hull sample (1) and the velocity of the fluid (water) rather than the shape of the air injection hole of the nozzle (2) Respectively.

Fig. 8 shows a real-time air lubrication shape in which the air injection flow rate is different in the vertical circular nozzle (the nozzle shown in Fig. 4 (A)) at a flow velocity of 1.5 m / s. Referring to FIG. 8, when the kinetic energy ratio (KER), which is the kinetic energy ratio of the air injected from the nozzle 2 to the kinetic energy according to the flow rate of water, exceeds 1.0, the lubrication shape of the air is divided into ' You can see the start. That is, in FIG. 8, when the kinetic energy ratio (KER) is 0.13, the air lubricating film (portion indicated by red color) proceeds almost linearly, but at the kinetic energy ratio (KER) And when the kinetic energy ratio (KER) is 4.59, the air lubrication film is formed in a completely divided shape. Here, the kinetic energy ratio (KER)

로 정의된다.

.

는 공기의 밀도이고,

는 물의 밀도,

는 공기의 유속,

는 물의 유속을 나타낸다. Here,

Is the density of air,

The density of water,

The flow rate of air,

Represents the flow rate of water.

Therefore, it can be seen that the air lubrication effect can be further improved by controlling the air injection speed so that the kinetic energy ratio (KER) becomes 1.0 or less when the air lubricating film is formed during operation of the actual ship.

Based on the air lubrication test for this flat plate type hull sample (1), a model experiment was conducted on a 66k bulk carrier where the bottom flat surface occupies 40% of the total flooded area. Fig. 12 is photographs of the model lines used in the model test, and Fig. 13 is the specifications of the model lines shown in Fig. 14 shows the positions of the nozzles located on the model line and the trim angle of the experiment.

12 and 14, a plurality of nozzles 2 for jetting air to the bottom of a ship are arranged along the longitudinal direction and the width direction of the hull. In the case of the model line, five nozzles Are arranged in a cross (+) shape, and three nozzles are arranged in a triangular shape on the forefront bulges. More specifically, when the length from the bow to the stern of the hull is divided into 20 equal parts and sequentially numbered from the stern, one nozzle (2) is arranged at the center line of the 9th and 13th positions, and 11th Three nozzles 2 are arranged at regular intervals in the line width direction, and the nozzles 2 at positions 9 to 13 have a cross arrangement structure. Two nozzles 2 are arranged in the line width direction at the 16th position and one nozzle 2 is arranged at the center line of the 17th position to have a triangular arrangement structure.

In the air lubrication test for the model line, the experiment was carried out with six line speeds in the range of 10.0 ~ 16.0 kt (design speed 14.5 kts) based on the solid line, and the direction in which the athlete was further immersed in the water, The injection angles of the lubrication air injected from the nozzle (2) were determined according to the condition of the model line speed. The injection angle was -1.0˚, -0.5˚, 0.0˚, 0.5˚ and 1.0˚. 10 to 60 times (x10, x20, x30, x40, x60). 15 is a graph showing the total effective energy and the energy reduction rate in the model line test. The ITTC1957 technique was used to analyze the energy and the energy reduction ratio considering the pumping power required for the injection. The notation for each experimental condition is represented by the trim angle - nozzle injection position - injection speed (number of nozzles). It was confirmed that the trimming of the bow based on the design line speed of 14.5 kt required less effective power in the model line and the total energy reduction rate of 19.21% considering the pumping power under the condition of 1.0˚-17_11T-x10 (4) Respectively.

Fig. 16 shows the average lubrication area by analyzing the air lubrication images at 1.0 占 17_11T-x10 (4) and 1.0 占 17_16_11T-x10 (6) in the air lubrication image at the forward trim. In the case of 1.0˚-17_11T-x10 (4), the average lubrication area is 9.55% and the model line resistance reduction rate is 19.98%. In the case of 1.0˚-17_16_11T-x10 (6), the average lubrication area is 14.96% and the model line resistance reduction rate is 13.22%. It can be confirmed that the resistance does not decrease much because the lubrication area is large even though the pumping power is required. This can be seen as the effect of the searing waves produced by the lubrication air escaping from the side of the athlete.

Therefore, it is preferable that the air is sprayed by using a nozzle arranged in the line width direction in the intermediate portion between the bow and the stern of the ship among the plurality of nozzles arranged at the bottom of the ship in the case of the bow posture of the ship. In the case of the model line, three nozzles 2 arranged in the line width direction at the eleventh position among nozzles (nozzles at positions 9 through 13) at the center of the bottom of the ship and nozzles (nozzles at positions 16 through 17) It is preferable that air is jetted by using two nozzles 2 arranged in the same line width direction at the 16th position among the nozzles.

At this time, it is preferable that the air is injected at less than 10 to 20% of the total injection amount even if no air is injected or sprayed at all in the remaining nozzles 2.

When the ship's standing posture is a stern trim, it is preferable to inject air using a nozzle arranged along the longitudinal direction on the center line of the ship among a plurality of nozzles disposed at the bottom of the ship. In the case of the model line, three nozzles (nozzles arranged in line in the center line of the 9th, 11th and 13th positions) arranged at the center line of the ship among nozzles (nozzles at positions 9 to 13) in the center of the bottom of the ship, And the nozzles (nozzles at the 17th position) arranged at the centerline of the ship among nozzles (nozzles at positions 16 to 17) of the bottom of the bottom of the ship. Of course, in this case, it is preferable that the air is injected at less than 10 to 20% of the total injection amount even if no air is injected or sprayed at all in the remaining nozzles 2.

As described above, the air lubrication method of the present invention maintains the kinetic energy ratio (KER) of the air injected from the nozzle 2 to the kinetic energy according to the relative velocity between the hull and the water generated by the operation of the ship to 1.0 or less It is possible to form a uniform air lubrication film without cracking the air lubrication film and to selectively control the position of the nozzle to which the air is injected according to the ship's standing posture such as bow and stern trim to form an air lubrication film .

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the present invention.

1: hull sample 2: nozzle
3: LED lighting 4: camera
5: Support bar

Claims (5)

A method of air lubrication of a ship in which a plurality of nozzles for spraying air to the bottom of a hull are arranged along a longitudinal direction and a width direction of the hull,
The kinetic energy ratio (KER) of the air injected from the nozzle to the kinetic energy according to the flow rate of water is

, ≪ / RTI >

Is the density of the air

The density of water,

The flow rate of air,

Indicates the flow rate of water,
The injection speed of air is controlled so that the kinetic energy ratio (KER) is 1.0 or less,
Jetting air using nozzles arranged in a line width direction at an intermediate portion between a bow and aft end of the ship among the plurality of nozzles when the ship's standing posture is a bow trim,
Wherein air is sprayed by using a nozzle arranged along a longitudinal direction on a center line of the ship among the plurality of nozzles when the ship's standing posture is a stern trim. 2. The watercraft according to claim 1, wherein five nozzles are arranged in the shape of a cross at the center of the bottom of the ship, three nozzles are arranged in a triangular shape at the forefront,
When the ship is in a bow posture, three nozzles arranged in the width direction of the nozzles arranged at the center of the bottom of the ship, and two nozzles arranged in the fore end of the bottom of the ship, In addition,
In the case where the ship's standing posture is a stern trim, three nozzles arranged at the centerline of the ship among the nozzles arranged at the center of the bottom of the ship, and nozzles arranged at the centerline of the ship among the nozzles arranged at the fore- And the air is supplied to the ship. delete delete delete

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