METHOD FOR OPERATING FRICTION RESISTANCE REDUCED SHIP

Abstract

[Problem] To provide a method for further reducing the friction resistance of a friction resistance reduced ship. [Solution] Rolling and pitching vary greatly depending on variations in climate, etc.; however, when limited to an extremely short time, the rolling and pitching repeat in an almost identical or similar pattern. Therefore, if the pattern of the immediately preceding rolling and pitching is understood, the subsequent pattern can also be predicted. This is similar for vertical position variation patterns of minute bubble generation units calculated from the angle of the rolling and pitching. Furthermore, the vertical position variation also differs depending on the installation position of each minute bubble generation unit, so the present invention measures the vertical position variation for each minute bubble generation unit, while also predicting the vertical position variation at and after the current time. The predicted vertical position variation is compared with the waterline height, while the time at which the minute bubble generation units below the sea surface will be above the sea surface or the time at which the minute bubble generation units above the sea surface will be below the sea surface are predicted, and an ON/OFF valve 8 is switched at that time.

Claims

1. A method for operating a friction resistance reduced ship for navigating a ship while forming a boundary layer in which air and liquid are mixed between the surface of the body of the ship and seawater by air bubbles from a plurality of minute bubble generation units installed on the body of the ship, wherein the next rolling and pitching pattern is predicted from the immediately preceding rolling and pitching pattern during navigation, a predicted vertical position pattern of each minute bubble generation unit is created from this predicted rolling and pitching pattern, and a minute bubble generation unit, which will be above the sea surface at the next rolling and pitching among the plurality of minute bubble generation units, is predicted from this predicted vertical position pattern and the waterline height based on the load capacity, when a valve for suppling air to the present minute bubble generation unit is closed according to the time at which the present minute bubble generation unit is predicted to be above the sea surface, and a valve installed in a passage for supplying air to the minute bubble generation unit predicted to be above the sea surface is closed early for the time during which air moves from the present valve to the minute bubble generation unit.

2. The method for operating a friction resistance reduced ship according to claim 1 or 2, wherein air is intermittently discharged from the minute bubble generation unit.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0025] FIG. 1 is a side view of a friction resistance reduced ship to which the method of the present invention is applied

[0026] FIG. 2 is a schematic view of an air line

[0027] FIG. 3 is a view showing the state in which the body of a ship is inclined by rolling

[0028] FIG. 4 is a graph showing the relation between a vertical positional change of a minute bubble generation unit by a composite motion with rolling and pitching and a criterial waterline.

[0029] FIG. 5(a) is a photograph showing a case in which a ship installed with a minute bubble generator is inclined while navigating in the open ocean, while FIG. 5(b) is a photograph showing the bow of the ship while navigating in the open ocean

DESCRIPTION OF EMBODIMENTS

[0030] Hereinafter, an Embodiment of the present invention will be described with reference to the attached drawings. As shown in FIG. 1, a plurality of minute bubble generation units 1 to eject minute bubbles are installed on the side and bottom of the friction resistance reduced ship. This minute bubble generation unit 1 is fastened by openings formed on the side and bottom of the body of the ship, with air or compressed air supplied via a pipe installed within the body of the ship.

[0031] FIG. 2 shows an example of a supply system to supply air to the minute bubble generation unit 1, wherein air is supplied from an air supply source 2 such as a compressor to headers 4a, 4b, 5, 6a, 6b via a pipe 3. Air is supplied from the headers 4a, 4b to the minute bubble generation unit 1 on the left side of the body of the ship, while the header 4a is connected to the plurality of minute bubble generation units 1 located at an adjacent location of the same height.

[0032] Air is supplied from a header 5 to the minute bubble generation unit 1 of the body of the ship bottom, while air is supplied from headers 6a, 6b to the minute bubble generation unit 1 on the left side of the body of the ship. Air may be directly supplied to the minute bubble generation unit 1 by circumventing the header.

[0033] A flow rate control valve 7 and an ON/OFF valve 8 are installed on the pipes 3 leading to each header, while the ON/OFF valve 8 is controlled by a controller 9. In the drawing, the ON/OFF valve 8 is installed immediately preceding the header; however, it may be arranged between the header and each minute bubble generation unit 1.

[0034] While navigating a ship, the ship is always influenced by waves to repeat rolling and pitching, putting the ship in motion composed of this rolling and pitching. Therefore, as shown in FIG. 3, part of the minute bubble generation unit 1 is above the water surface.

[0035] The controller 9 sends a signal to close the ON/OFF valve 8 to the header to which the minute bubble generation unit 1 determined to be located above the seawater surface is connected, while sending a signal to intermittently open and close the ON/OFF valve 8 to the header to which the minute bubble generation unit 1 is determined to be located below the water surface. The signal to intermittently open and close the valve preferably has a frequency of less than several hertz.

[0036] Additionally, instead of intermittently turning on and off the ON/OFF valve 8, air to be ejected from the minute bubble generation unit 1 may be allowed to cause pulses by arranging a diaphragm 10, etc. on the header.

[0037] FIG. 4 is a drawing illustrating a method for determining whether a minute bubble generation unit in the controller 9 is located above the seawater surface. This determination is carried out for each minute bubble generation unit 1.

[0038] First, the temporal vertical position of each minute bubble generation unit is measured from the rolling and pitching angle. The variation in the measured temporal vertical position is indicated by a curve.

[0039] Additionally, in FIG. 4, a horizontal line of height 0 indicates a waterline height based on the load capacity. When the load capacity is little, the waterline height moves downward so as to locate more minute bubble generation units above the seawater surface. On the other hand, when the load capacity is great, the waterline height moves upward so as to locate more minute bubble generation units below the seawater surface.

[0040] In FIG. 4, the boundary part between the solid line region and the dotted line region of a variation curve in the vertical position is the current time, wherein the solid line region on the left side from this boundary part indicates the actual passage vertical position, while the dotted line region on the right side indicates the vertical position predicted therefrom.

[0041] In other words, rolling and pitching largely change depending on variations in the weather, etc.; however, when limited to an extremely short time, the rolling and pitching repeat in an almost identical or similar pattern. Accordingly, if the pattern of immediately preceding rolling and pitching is known, the next pattern following this can also be predicted. The same applies to the vertical position variation pattern of the minute bubble generation unit calculated from the angle of rolling and pitching.

[0042] Moreover, according to the present invention, the vertical position variation is measured for each minute air bubble generation unit, such that the vertical position variation after the current time is predicted as the vertical position variation differs depending on the installation position of each minute bubble generation unit. Subsequently, the predicted vertical position variation is compared with the waterline height, then the time at which the minute bubble generation unit below the sea surface will be above the sea surface or the time at which the minute bubble generation unit above the sea surface will be below the sea surface is predicted, and the ON/OFF valve 8 is switched to that time.

[0043] Further, the switching time of the valve 8 is preferably fastened for the time taking into consideration the time required to lead air passed through the valve 8 to the minute bubble generation unit.

[0044] As a structure of the minute bubble generation unit, a structure may be considered in which an opening to eject air is installed on the body of the ship and a wing member to generate negative pressure during navigation is arranged on the outside of this opening, allowing air extracted from the opening by negative pressure to generate minute bubbles in the water via a cavitation effect. However, minute bubble generation units are not specifically limited thereto.

REFERENCE SIGNS LIST

[0045] 1 . . . minute bubble generation unit, 2 . . . air supply source, 3 . . . pipe, 4a, 4b, 5, 6a, 6b . . . header, 7 . . . flow rate control valve, 8 . . . ON/OFF valve, 9 . . . controller.