JPS61193995A - Marine screw propeller steering method - Google Patents

Abstract

PURPOSE:To reduce the load imposed on a main engine, by making a water current, containing air bubbles, flow in a main part of a propeller blade an and around the critical revolving speed of a screw propeller, while reducing the extent of propulsive toque of the screw propeller temporarily. CONSTITUTION:When the revolving speed of a screw propeller 3 reaches to the vicinity of critical revolving speed, a compressed gas generator is operated and thereby compressed gas is jetted out of a compressed gas injection nozzle 4. And, a water stream 7 inclusive of this compressed gas flows in a range of 0.5-0.9 times over a rotating diameter D of the propeller blade. This range is equivalent to a main part of the propeller blade as propulsive torque of the screw propeller 3 is largely produced. The compressed gas is jetted out of the compressed gas injection nozzle 4 whereby the water current 7 flowing into this range comprises air bubbles so that fluid density of the water current 7 comes small, thus the propulsive torque becomes reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of operating a marine screw propeller when increasing the rotational speed of a fixed pitch screw propeller at the stern.

[Conventional technology]

BACKGROUND ART In recent years, large ships have been equipped with fixed-pitch screw propellers with a large rotational diameter to lower the rotation speed of the main engine and reduce fuel consumption.

[Problem that the invention seeks to solve]

By the way, when the screw propeller at the stern of the ship rotates, its propeller blades are affected by the large wake caused by the ship's hull.
By passing through the area 1 and the area where the wake is small, it vibrates under the vibrational force.

The frequency of this excitation force is the rotational speed of the screw propeller (
(rotational speed). In general, a screw propeller has a critical rotational speed at which the propeller blade is excited and a large vibration 5h occurs due to the frequency of the excitation force matching the natural frequency of the propeller blade.

In addition, for screw propellers with a large rotation diameter, the dangerous rotation speed is in a low rotation speed range, so ships equipped with screw propellers with a large rotation diameter,
Screw propellers must be used within the rotation speed range that includes the dangerous rotation speed.

On the other hand, near such critical rotational speeds, large vibrations occur in the propeller blades of the screw propeller, which applies large propulsion rotational torque to the screw propeller, impairing the rotational force transmitted from the main engine. .

□ Therefore, when increasing the rotational speed of the screw propeller in the above-mentioned ship, if the rotational speed reaches near the above-mentioned critical rotational speed, the propulsion rotational torque of the screw propeller will increase, and the rotational force transmitted from the main engine will be reduced. Therefore, there are problems in that it takes a great deal of time to increase the rotational speed, and fuel consumption in the main engine increases.

If the above-mentioned ship is equipped with a variable pitch screw propeller, by changing the pitch of the propeller blades near the critical rotation speed, the propulsion rotational torque of the screw propeller can be reduced, and the rotation speed can be quickly increased. Moreover, it can be easily increased, but if a fixed pitch screw propeller is provided,
There is no way to solve the above problems.

In view of this situation, the present invention has made it possible to quickly and easily increase the rotational speed of a fixed pitch screw propeller by reducing the propulsion rotational torque of the screw propeller. , aims to provide a marine Jll screw propeller bare longitudinal method.

[Means for solving problems]

For this reason, the marine screw propeller operating method of the present invention includes:
When increasing the rotational speed of a fixed pitch screw propeller at the stern, a water stream containing air bubbles is caused to flow into at least the main thorns of the propeller blades of the screw propeller at a point near the critical rotational speed of the screw propeller of 1. hand,
It is characterized by temporarily reducing the propulsion rotational torque of the screw propeller.

[Effect]

In the marine screw propeller 4 longitudinal method of the present invention described above,
When the screw propeller reaches a critical rotational speed, a water flow containing air bubbles is caused to flow into at least the main portion of the propeller blade of the screw propeller, thereby temporarily reducing the propulsion rotational torque of the screw propeller.

〔Example〕

Hereinafter, a marine screw propeller medium vertical method as an embodiment of the present invention will be explained with reference to the drawings. Fig. 1 is a horizontal sectional view showing a compressed gas injection nozzle in the stern of a ship, and Fig. 2 is a horizontal sectional view showing a compressed gas injection nozzle in the stern of a ship, and Fig. 2 is a horizontal sectional view showing a compressed gas injection nozzle in the stern of a ship. FIG. 3 is a side view schematically showing the tail.

As shown in FIGS. 1 and 2, in the stern section 2 of the ship 1,
Compressed gas injection nozzles 4 are formed on the upper, lower, left, and right sides of the propeller shaft 5, respectively, and these compressed gas injection nozzles 4 inject compressed gas (not shown) arranged inside the hull of the ship 1. Connected to the generator by air supply W6,
Ru.

Further, the water stream 7 containing compressed gas bubbles injected from each compressed gas injection nozzle 4 is transmitted to the screw propeller 3 by 0.5 to 0.5 times the rotational diameter of the propeller blade.
The position where the compressed gas injection nozzle 4 is formed is determined so that the air flows into a nine times larger area.

Note that a grid-shaped metal fitting for generating countless air bubbles may be disposed at the injection port of the compressed gas injection nozzle 4.

In addition, in the t51 diagram, the broken line indicates compressed gas injection/Zur4
It shows the region through which the water flow 7 flows from the to the screw propeller 3.

When the above-mentioned ship 1 is sailing, first, the screw propeller 3 which is stopped is driven by a main engine (not shown), and its rotational speed gradually increases. At this time, while the rotational speed is lower than the critical rotational speed of the screw propeller 3, the compressed gas generator described above is not operated and compressed gas is not injected from the compressed gas injection nozzle 4.

Next, when the rotational speed of the screw propeller 3 reaches around the critical rotational speed, the compressed gas generator is activated, compressed gas is injected from the compressed gas injection nozzle 4, and a water stream 7 containing bubbles of the compressed gas is generated. , in the screw propeller 3, approximately o of the rotational diameter of the propeller blade,
s 13 to 0.9 times.

This area corresponds to the main part of the propeller blade where a large propulsion rotational torque of the screw propeller 3 is generated.

Then, the propulsion rotational torque of the screw propeller 3 is reduced according to the following principle. That is, the fluid density is m, the propulsion flow rate of the screw propeller 3 is q, its rotation speed is n, the flow velocity of the water flow flowing into the screw propeller 3 is V1, the flow velocity of the wake of the same screw propeller 3 is ■2, and k is Assuming that it is a constant, the propulsion rotational torque P of the screw propeller 3 can be obtained by the following formula.

P = further・q−n・(■2−■, )...(1) Therefore, compressed gas injection/7: By injecting the compressed gas from Le 4, the propeller blades of the screw propeller 3 Since the water flow 7 flowing into the above region contains air bubbles, the fluid density of the water flow 7 becomes small, and the propulsion rotational torque P of the screw propeller 3 determined by equation (1) is reduced.

Furthermore, the water stream 7 is accelerated by the injection of compressed gas from the compressed gas injection nozzle 4, and the flow velocity V1 of the water stream flowing into the screw propeller 3 increases, so that the propulsion rotational torque P is further reduced.

In this way, when the rotational speed of the screw propeller 3 is close to the critical rotational speed a.1, the propulsion rotation torque P of the screw propeller 3 is temporarily reduced, without requiring a large amount of main engine output , the rotational speed of the screw propeller 3 is immediately increased.

When this rotational speed is increased to a higher rotational speed than around the critical rotational speed, the operation of the compressed gas generator is stopped and compressed gas is no longer injected from the compressed gas injection nozzle 4.

In the marine screw propeller operating method of the present invention described above, the propulsive rotational torque of the screw propeller 3 is temporarily reduced near the critical rotational speed of the screw propeller 3 by the above procedure, so that a large amount of main engine power is required. The rotational speed of the screw propeller 3 can be quickly increased without requiring any output, and not only can the load on the main engine be reduced, but also its fuel consumption can be significantly reduced.

Further, in the vicinity of the critical rotation speed, the operation of reducing the propulsion rotational torque of the screw propeller 3 can be quickly and easily performed by injecting compressed gas from the compressed gas injection nozzle 4.

Therefore, even if the rotational speed of the screw propeller 3 changes frequently and the screw propeller 3 often rotates near the above-mentioned critical rotational speed, by injecting compressed gas from the compressed gas injection nozzle 4 as described above, Immediately reduce the propulsion rotational torque of the screw propeller 3,
The rotation speed of the screw propeller 3 can be increased.

Furthermore, since the propulsion rotational torque of the screw propeller 3 is reduced near the critical rotation speed, generation of large vibrations in the propeller blades of the screw propeller 3 is prevented, which also has the advantage of reducing hull vibration of the ship 1. .

〔Effect of the invention〕

As detailed above, the marine screw propeller I! of the present invention! In the coupling method, when increasing the rotational speed of the pitch-type screw propeller at the stern of the ship, a water flow containing air bubbles is applied to at least the main part of the propeller blade of the screw propeller near the critical rotational speed of the screw propeller. By a simple procedure of temporarily reducing the propulsion rotational torque of the screw propeller by allowing the propeller to flow in, the rotational speed of the screw propeller can be quickly and easily increased from the critical rotational speed to the dangerous rotational speed. It is possible to reduce the load on a ship's main engine, and to significantly reduce its fuel consumption.

In addition, since the propulsion rotational torque of the screw propeller is temporarily reduced near the above-mentioned critical rotational speed, large vibrations do not occur in the propeller blades of the screw propeller, and ship hull vibration is prevented. There is also the advantage of improved sexual performance.

[Brief explanation of drawings]

The figures are for explaining a method of operating a marine screw propeller as an embodiment of the present invention, and the tjSi diagram is a horizontal cross-sectional view showing a compressed gas injection nozzle in the stern of a ship;
Figure fjS2 is a side view schematically showing the stern section of the vessel below the water surface. 1. Ship, 2. Stern section, 3. Screw propeller, 4. Compressed gas injection nozzle, 5. Propeller shaft, 6.
・Air pipe, 7.・Water flow. Sub-Agent Patent Attorney Yoshi Iinuma 4 Figure 2 Figure 1

Claims (1)

[Claims] When increasing the rotational speed of a fixed pitch screw propeller at the stern, a water stream containing air bubbles flows into at least the main part of the propeller blade of the screw propeller near the critical rotational speed of the screw propeller. A method for operating a marine screw propeller, characterized by temporarily reducing the propulsion rotational torque of the propeller.