JPS623358Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is designed to straighten the flow flowing into the ship's propulsion propeller and eliminate ship vibrations caused by propeller excitation force. Concerning improvements to stern rectifying fins.

Dedicated ships such as tankers, bulk carriers, ore carriers, as well as other ships, are becoming larger every year, especially at the stern, in order to improve operational efficiency. As shown, the flow flowing into the propeller 2 at the stern becomes extremely turbulent, especially at the upper part of the propeller circle, and as a result, the propeller excitation force increases, inducing hull vibration, which can lead to damage to the hull 1 and deterioration of habitability. It is the cause.

As a measure to reduce this propeller excitation force, as shown in Figs. 2 and 3, fins 4S and 4P are provided above the propeller 2 at the stern, thereby creating a space above the propeller 2 and within the plane of the propeller 2. There are ways to accelerate and rectify the incoming water flow. In addition, the first
In Figures 3 to 3, 3 indicates a rudder provided behind the propeller 2, 5 indicates a streamline of the flow flowing into the vicinity of the propeller 2, and w indicates a waterline.

However, even if such fins 4S and 4P are installed, the flow flowing into the propeller is slower than the speed of the ship near the hull centerline 6, as shown in Figure 4, and the propeller still cannot be started. This is a factor that increases the vibration force. In addition, in Fig. 4,
7 shows the contour lines of the current velocity, and the numerical value of each contour line represents the ratio of the current velocity of the curved part to the speed of the ship. 8 indicates the propeller circle.

The present invention further enhances the rectifying effect of the rectifying fins to effectively prevent hull vibration caused by the propeller vibration force, thereby making it possible to further enlarge the stern and improving economic efficiency. This was proposed for this purpose, and in a pair of straightening fins installed on the port and starboard hull surfaces above the propeller installed at the rear of the ship, the same pair of straightening fins are installed as they move toward the rear of the ship. In addition, in the case of a clockwise propeller, the inclination of the port side rectifier fin with respect to the water line of the ship's hull is set to be lower than the inclination of the starboard side rectifier fin with respect to the water line of the ship's hull in the case of a clockwise propeller. To provide a stern rectifying fin which is made larger in size and, in the case of a counterclockwise propeller, the inclination of the starboard side rectifying fin with respect to the water line of the ship body is made larger than the inclination of the port side rectifying fin with respect to the water line of the ship body.

The straightening fin of the present invention is designed to induce a flow in the direction of rotation of the propeller blades and reduce the propeller excitation force by making the tilt of the straightening fin with respect to the water line asymmetrical on both sides.

Next, one embodiment of the device of the present invention will be described based on the drawings.

FIG. 5 shows the rear part of the hull provided with the straightening fin of the present invention, where 14S is a straightening fin protruding from the starboard side surface of the hull, and 14P is a straightening fin protruding from the port side surface.

The stern water stream 5 generally flows obliquely upward behind the hull. Rectifier fin 4 in Figures 2 and 3
S and 4P are arranged at a certain angle of attack with respect to this water flow, that is, upward toward the rear of the hull, in order to accelerate the lower surface of the fin. In the case of a clockwise propeller, the inclination of the port side fin 14P with respect to the water line is as follows.
The inclination of the fin 14S on the starboard side with respect to the water line is greater than that of the fin 14S on the starboard side. In the case of a counterclockwise propeller, conversely, the inclination of the starboard side fin 14S with respect to the water line is made larger than the inclination of the port side fin 14P with respect to the water line.

For this reason, in the case of a clockwise propeller, the flow velocity on the inner surface of the propeller is faster on the port side as shown in Figure 6 (the flow velocity contour line near the center of the ship is shifted to the starboard side), and the propeller circle is therefore higher. Near the top, that is, near the rotation of the line in FIG. 6, a flow from port to starboard occurs.

FIG. 7 is a velocity triangle of the flow relative to the blade 2a of the propeller 2 at the - line position in FIG.
In the figure, [When there is no flow ○A with conventional straightening fins] AO: Relative speed between the blade 2a and the flow in the direction of propeller rotation AB: Relative speed between the blade 2a and the flow in the forward direction of the ship BO: Combined speed of AO and AB [relative velocity of the flow with respect to the blade 2a] ∠COB: Angle of attack of the blade 2a [when there is a flow ○A with the rectifying fin of the present invention] A′O: The velocity of the flow relative to the blade 2a in the propeller rotation direction Relative speed with the flow (Since it is a clockwise propeller, the relative speed will be smaller by the speed A-A′ of flow ○A.) A′B′: Relative speed between the blade 2a and the flow in the forward direction of the ship (equal to AB ) B′O: Combined velocity of A′O and A′B′ [relative velocity of the flow with respect to the blade 2a] ∠COB′: Angle of attack of the blade 2a In other words, the angle of attack of the blade 2a is lower with the device of the present invention. (∠COB′<∠COB), so - in Figure 6
The lift generated by the propeller blades 2a at the line position is smaller than that of the conventional propeller blades, and the propeller excitation force is reduced.

As mentioned above, the propeller excitation force is greatest near the top of the propeller circle, near the line in Figure 6, so by reducing the propeller excitation force at this position, the hull vibration will be significantly reduced. It is highly effective in preventing defects such as damage to the hull and deterioration of livability.

Furthermore, the functions and effects of one embodiment of the present invention will be explained in detail.

Hull efficiency is an important factor in ship propulsion performance
en is expressed by the following formula.

en(1-t)/(1-w)...(A) Here, t is called the thrust reduction rate, and is a coefficient related to the amount by which the hull resistance increases due to the influence of the thruster.
w) is the ratio between the average value of the flow velocity flowing into the thruster and the ship speed.

As can be seen from equation (A), the smaller t and the smaller (1-w), the higher the hull efficiency and the better the propulsion performance.

The value of (1-w) is related to the flow velocity in the forward direction on the propeller surface and the flow velocity in the circumferential direction, and as shown in FIG. ′) is smaller, and the relative speed (OA or OA′) in the propeller rotation direction is larger.
As the angle of attack between the blade and the flow increases, the value of (1-w) decreases and the hull efficiency increases. However, when the angle of attack of the blade increases, problems such as cavitation and an increase in propeller excitation force appear.

Additionally, as shown in Figures 4 and 6, the forward flow velocity on the propeller surface is significantly smaller above the propeller surface, and it is necessary to improve the flow field in this area from the perspective of propeller excitation force. be. Conventional stern rectifying fins are provided with fins on the hull above the propeller in order to accelerate and rectify the flow velocity in the forward direction of this part. The reduction effect has been enhanced. These fins act to reduce the angle of attack of the propeller above the propeller surface and increase the value of (1-w), but the change in the flow field is local to the upper part of the propeller surface, and ( 1-w) does not change significantly. Also, since the fins are attached to the hull above the propeller surface, the rate of thrust reduction does not increase.

As mentioned above, without causing a decrease in propulsion performance,
Propeller vibration force can be reduced.

If the rectifying fin of this invention is installed in this way,
It is possible to prevent hull vibrations more effectively than conventional systems without causing a decrease in propulsion performance, and therefore it is possible to further enlarge the stern. Therefore, the device of the present invention is suitable for use not only in enlarged ships such as tankers and bulk carriers, but also in cargo ships, car carriers, container ships, etc. in which there is a strong demand for enlarged sterns.

[Brief explanation of the drawing]

Figure 1 is an elevational view showing the state of the water flow at the stern without the straightening fins installed, Figure 2 is an elevational view showing the water flow state at the stern when the conventional straightening fins are installed, and Figure 3 is the 4 is a flow velocity distribution diagram near the propeller when the rectifying fins described above are installed, and FIG. 5 is an elevational view showing the stern of the ship with the rectifying fins of the present invention installed. FIG. 6 is a flow velocity distribution diagram near the propeller when the above-mentioned rectifying fins are installed, and FIG. 7 is an explanatory diagram showing the velocity triangle of the flow relative to the propeller at the - line position in FIG. 6. 1... Rear part of the hull, 2... Propeller, 2a... Propeller blade, 3... Snake, 4S, 4P, 14S, 14
P... Rectifier fin, 5... Water flow, 6... Hull center line, 7... Contour line of flow velocity, 8... Propeller circle, w
……waterline.

Claims (1)

[Scope of utility model registration request] A pair of straightening fins are installed on the port and starboard surfaces of the hull above the propeller installed at the rear of the ship. In addition, in the case of a clockwise propeller, the inclination of the port side rectifying fin with respect to the water line of the hull is greater than the inclination of the starboard side rectifying fin with respect to the water line of the hull, and in the case of a counterclockwise propeller. for,
The inclination of the starboard side rectifier fin relative to the hull waterline is
A stern rectifier fin characterized by having a greater inclination than the port side rectifier fin with respect to the waterline of the hull.