KR20150136191A - A rudder for ship - Google Patents

Abstract

The present invention relates to a rudder for a vessel, which controls a sailing direction of a vessel by being installed on the rear of a propeller. The rudder for a vessel includes: a rudder body; and a rudder shaft connecting the vessel and the rudder body. The center axis of the rudder shaft is located at a point in which the transverse width on the cross section of the rudder body is maximum. An upper leading edge and a lower leading edge of the rudder for a vessel are twisted, and the position of the maximum width among the transverse widths of the cross section of the rudder for a vessel is located on the same straight line as the center line of the rudder shaft. Therefore, the rudder for a vessel maximizes propulsion efficiency of the vessel and prevents a transverse maximum width of the rudder for a vessel from being unnecessarily increased. Therefore, the rudder for a vessel improves the propulsion efficiency of the vessel by reducing resistance of the rudder and the weight and reduces fuel costs, thereby maximizing competitiveness of the vessel in the market. Moreover, the transverse width of the cross section is bilaterally symmetric based on the longitudinal center line of the cross section, from the point, in which the transverse width is maximum, to a longitudinal rear end on the cross section of the rudder for a vessel. Therefore, the rudder minimizes the use of a curved plate used to manufacture the rudder for a vessel, thereby reducing manufacturing cost.

Description

A rudder for ship

The present invention relates to a marine rudder.

The present invention is derived from a research carried out by the Ministry of Knowledge Economy and the Korea Industrial Technology Evaluation and Management Center as part of the project for the development of technology for the industrial convergence technology [Task No.: 10040060, Title: And solid lines]

Generally, in the case of a large ship, the propulsion attached to the rear of the hull is advanced by using the flow of the fluid generated when the propeller rotates. At this time, a rudder is attached to the rear of the propeller, and as the rudder rotates to the left and right, the direction of flow of the fluid is changed by changing the direction of flow.

In order to achieve a constant speed through the rotation of the propeller, the engine must be driven using oil such as diesel. In this case, a large amount of oil is consumed and the greenhouse gas is discharged, thereby causing problems such as environmental destruction .

Recently, various efforts have been made to reduce fuel consumption by reducing the energy consumed when propelling the ship. IMO, in particular, discussed ways to reduce greenhouse gas emissions in 2010, and discussions are underway to establish standards and directions for fuel efficiency regulation.

As shipping companies join the movement, shipping companies are beginning to pay attention to fuel-saving vessels that can reduce the burden on fuel costs. Due to the needs of shipping companies, shipbuilders are constantly researching and developing fuel-saving technologies that reduce fuel consumption and reduce greenhouse gas emissions.

As an example of the fuel saving type technology, an energy saving device (ESD: Energy Saving Device) which saves fuel by improving the propulsion efficiency by improving the shape of a ship's rear end, propeller, rudder, This energy saving device has already been applied to a large number of ships.

Recently, in addition to adding an energy saving additional device (ESD) to a ship, a lot of research and development has been carried out on optimizing the shape of hull, rudder, skeg, and the like.

Korean Patent Registration No. 10-1184076 Korean Patent Registration No. 10-1110392 Korean Patent Registration No. 10-0346512

It is an object of the present invention to adopt a twist structure of an upper and a lower portion of a rudder for a marine vessel and to make the flat end surface of the marine rudder have a position in which the widest width in the transverse width is on the same straight line as the position of the centerline of the rudder axis, The present invention provides a marine rudder capable of reducing the unnecessary increase in lateral width of a marine rudder while obtaining an effect of improving the propulsion efficiency and the corroded erosion due to the torsional structure of the upper part and the lower part.

A ship rudder according to one embodiment of the present invention is a rudder for a ship which is installed at the rear of a propeller and manages the direction of a ship, the rudder comprising: a rudder body; And a rudder shaft connecting the ship and the rudder body, wherein the rudder axis is located at a point where the central axis is the maximum width in the horizontal section of the rudder body.

Specifically, the rudder body may have a shape in which the lateral width of the flat section is symmetrical with respect to the longitudinal center line of the flat section from the point where the width of the rudder section is the widest width in the horizontal section to the longitudinal rear end section .

Specifically, the rudder body is deflected to one side in the horizontal section widthwise direction of the upper portion of the rudder body from the widest position in the horizontal width of the flat section to the longitudinal front end section, And the direction width may be deflected toward the other side.

Specifically, the rudder body may be shaped such that the trailing edge lies on a straight line perpendicular to the ship.

Specifically, the rudder body comprises: a rudder body upper portion having a leading edge deflected to one side; And a rudder body bottom having a leading edge biased to the other side.

Specifically, the rudder body may further include a rudder body center portion continuously formed so as to connect the lower edge of the leading edge of the upper portion of the rudder body and the upper edge of the leading edge of the lower portion of the rudder body.

Specifically, the rudder body includes a rudder body center portion connecting the upper portion of the rudder body and the lower portion of the rudder body; And a rudder bulb protruding from the center of the rudder body.

Specifically, the leading edge of the rudder body is configured to be tilted to one side at a lateral reference center position from the uppermost front end of the upper portion of the rudder body to the front end of the rudder body center portion, The front edge of the leading edge of the leading edge of the rudder body is located at the lateral reference center position and deflected from the lowermost front end portion of the lower portion of the rudder body toward the front end portion of the rudder body center portion toward the other side As shown in FIG.

Specifically, the leading edge of the rudder body on the upper side of the rudder body is located at the reference center position in the transverse direction on the uppermost side of the upper portion of the rudder body, and the front edge of the rudder body Wherein the front edge of the lower portion of the lower portion of the rudder body is at a transverse reference center position and the lower edge of the lower portion of the lower portion of the rudder body is tilted to one side from the direction reference center position, The center of gravity of the rudder body may be inclined toward the other side from the lateral reference center position toward the front end of the rudder body.

The rudder for a ship according to the present invention has a structure in which the upper leading edge and the lower leading edge of the rudder for a ship are twisted with each other and the position of the maximum width of the horizontal cross section of the rudder for a ship is the same as the position of the center line of the rudder shaft Thereby maximizing the propulsion efficiency of the ship and preventing the maximum lateral width of the ship rudder from increasing unnecessarily.

In addition, by preventing the maximum lateral width of the ship rudder from increasing unnecessarily, it is possible to reduce the resistance of the rudder and reduce the weight, thereby improving the propulsion efficiency of the ship and reducing the fuel cost. It has the effect of maximizing the competitiveness of order receipts.

In addition, in the plane rudder of the marine rudder, the transverse width of the flat section is symmetrical with respect to the longitudinal center line of the flat section from the widest width of the transverse width to the longitudinal rear end, So that the production cost can be reduced.

1 is a side view of a ship rudder according to an embodiment of the present invention.
2 is a front view of a ship rudder according to an embodiment of the present invention.
3 is a perspective view of a marine rudder according to an embodiment of the present invention.
4 is a conceptual view of a ship rudder according to an embodiment of the present invention.
Fig. 5 (A) is a cross-sectional view showing an uppermost flat section of the upper portion of the rudder according to the embodiment of the present invention, Fig. 5 (B) is a cross- (D) is a cross-sectional view showing the lowermost flat section of the lower portion of the rudder. Fig.
6 (a) is an axial velocity distribution chart of the wake of the propeller, and Fig. 6 (b) is a velocity distribution chart of the rotational direction velocity of the propeller.
7 is a comparison chart of the propulsion performance of the marine rudder according to the embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a side view of a rudder for a ship according to an embodiment of the present invention, FIG. 2 is a front view of a rudder for a ship according to an embodiment of the present invention, 1 is a conceptual view of a ship rudder according to an embodiment of the present invention.

1 to 4, a marine rudder 1 according to an embodiment of the present invention includes a rudder body 10 and a rudder bulb 20.

The rudder body 10 is provided at the rear of a propeller (not shown) to control the navigation direction of a ship (not shown). The rudder body 10 may have a rudder upper portion 11, a rudder lower portion 12, and a rudder center portion 13.

The rudder upper portion 11 can have a rudder upper leading edge 101a that is deflected to one side and the rudder lower portion 12 has a rudder lower leading edge 101b deflected to the other side, The upper portion 11 and the rudder lower portion 12 may be connected to each other so that the lower end of the rudder upper leading edge 101a and the upper end of the rudder lower leading edge 101b may be continuously connected to each other.

In the rudder body 10, the width of the rudder body upper portion 11 in the flat cross section transverse direction is deflected to one side from the widest point in the horizontal width of the flat section to the longitudinal front end portion, Sectional width of the flat portion may be deflected toward the other side.

Prior to describing the rudder upper portion 11, the rudder lower portion 12 and the rudder center portion 13 in detail, in order to effectively explain the effect resulting from the constituent elements of the present invention, The experimental data shown in FIG. 6B will be described in detail.

Fig. 6A is an axial velocity distribution chart of the propeller wake, and Fig. 6B is a rotational velocity distribution diagram of the propeller wake. This shows the experimental result on the short axis line.

Hereinafter, the reference of the rotation direction is to designate a clockwise or counterclockwise direction on the basis of looking at the athlete's bow at the stern of the hull (not shown), and the left and right sides of the hull are left- On the right.

In FIG. 6A, Y is a coordinate axis indicating a horizontal line with respect to the hull, Z is a coordinate axis indicating a vertical line with respect to the hull, and FIG. 6A is a graph showing the relationship between the axial velocity (velocity in the direction opposite to the traveling direction of the hull) FIG. 6B is a graph showing the axial velocity of the fluid flowing through the rear end of the hull (not shown) as a velocity value indicated by designating a color, and FIG. 6B is a graph showing the velocity of the fluid expressed by a plurality of arrows And the length of the arrow indicates the rotation speed), and the rotation direction and the rotation speed of the fluid flowing in the rear of the hull.

6A, it can be seen that the axial velocity increases with distance from the shaft (not shown) of the propeller, and the maximum axial velocity occurs at any point on the starboard side of the propeller shaft. 6B, it can be seen that the rotational flow of the fluid rotates clockwise around the center of the propeller shaft, and the rotational speed of the fluid increases toward the center of the propeller shaft.

Therefore, the uppermost front end portion A3 of the rudder upper portion 11 and the lowermost front end portion C3 of the rudder lower portion 12 are located at the lateral reference center position, and the uppermost front end portion A3 of the rudder upper portion 11, The front end portion of the rudder center portion 13 is tilted to one side from the lateral reference center position toward the front end portion B3 of the rudder center portion 13 from the front end portion A3 of the rudder center portion 13, The vertical torsion structure that tilts from the lateral reference center position to the other side as the distance from the center of gravity to the center (B3) increases, thereby improving the propulsion force of the ship, maximizing the straightness of the ship, and reducing the fuel cost.

The structure of the rudder body 10 will be described in more detail with reference to FIG. FIG. 5A is a cross-sectional view showing a top flat section of the upper portion of the rudder according to the embodiment of the present invention, FIG. 5B is a cross-sectional view showing a bottom flat section of the upper portion of the rudder, (D) is a cross-sectional view showing a bottom flat section of the lower portion of the rudder.

(A1-A2-A3) on the uppermost side of the rudder upper portion 11, which is formed bilaterally symmetrically with respect to the center line of the longitudinal direction. Of course, the maximum lateral width A2 of the flat cross section is located at the position of the center axis 30 of the rudder shaft (not shown).

6B, the rotational speed of the fluid is smaller as the distance from the center of the propeller shaft becomes smaller, so that it is hardly influenced by the rotational flow of the fluid downstream of the propeller on the uppermost side of the rudder upper portion 11.

Therefore, the front side flat faces (A2-A3) of the upper flat faces (A1-A2-A3) on the upper side of the rudder upper portion (11) are formed symmetrically with respect to the longitudinal center line, By having the shape, the resistance can be minimized and the efficiency of the marine rudder 1 can be maximized.

AB2-AB3 of the rudder upper portion 11 of the rudder upper portion 11 of the rudder upper portion 11 in the fluid inflow direction 50 in the upper portion of the rudder, And the position AB2 of the maximum width in the horizontal direction of the flat section is spaced apart from the center by a predetermined distance in the longitudinal direction.

This position AB2 is located at the position of the central axis 30 of the rudder shaft (not shown) in the same manner as the position A2 of the horizontal maximum width of the uppermost flat surface of the rudder upper portion 11.

6B, since the rotational speed of the fluid increases toward the center of the propeller shaft, the bottom of the rudder upper portion 11 is strongly influenced by the rotational flow of the fluid downstream of the propeller. In addition, the rotational direction of the fluid flows in the lateral direction from the port to the starboard (left to right in the drawing) in the rudder upper portion 11.

The front side planar end faces AB2-AB3 of the bottom flat faces AB1-AB2-AB3 of the rudder upper portion 11 are deflected to the port side by the angle? At the longitudinal center line, It has the effect of increasing the propulsion force of the ship and minimizing the resistance.

5A and 5B, the rudder upper leading edge 101a should be configured to be positioned at the horizontal reference center at the uppermost side and to the lateral reference port at the lowermost level.

BC2 and BC3 of the rudder lower portion 12 in the rudder lower portion 12 and the front end portion BC3 of the rudder lower portion 12 in the direction of the fluid inflow direction 60 in the lower portion of the rudder, And the position BC2 of the maximum width in the horizontal direction of the flat section is spaced apart from the center by a predetermined distance in the longitudinal direction.

This position BC2 is located at the position of the central axis 30 of the rudder shaft (not shown) in the same manner as the positions A2 and AB2 of the horizontal maximum width of the uppermost and lowermost flat section of the rudder upper portion 11 .

6B, since the rotational speed of the fluid increases toward the center of the propeller shaft, it is strongly influenced by the rotational flow of the fluid downstream of the propeller on the upper side of the rudder lower portion 12. In addition, the rotational direction of the fluid flows in the lateral direction from the starboard to the port (right to left in the figure) in the rudder lower portion 12.

Therefore, the front side flat face BC2-BC3 of the top flat faces BC1-BC2-BC3 on the uppermost side of the rudder lower 12 are deflected starboard by the angle? It has the effect of increasing the propulsion force of the ship and minimizing the resistance.

(C1-C2-C3) of the lowermost side of the rudder lower portion 12, which is formed symmetrically with reference to the center line in the longitudinal direction. At this time, however, the maximum lateral width position C2 of the flat section is spaced apart from the center by a predetermined distance in the longitudinal direction.

However, this position C2 is a position at which the maximum widthwise positions A2 and AB2 of the uppermost and lowermost flat sections of the rudder upper portion 11 and the maximum lateral width position of the uppermost flat section of the rudder lower portion 12 (Not shown) in the same manner as BC2.

6B, the rotational speed of the fluid is smaller as the distance from the center of the propeller shaft becomes smaller, so that it is hardly influenced by the rotational flow of the fluid downstream of the propeller on the lowermost side of the rudder lower portion 12.

Therefore, the front flat cross-section (C2-C3) of the lowermost flat cross-sections (C1-C2-C3) of the rudder lower portion 12 is formed symmetrically with respect to the longitudinal center line, By having the shape, the resistance can be minimized and the efficiency of the marine rudder 1 can be maximized.

5 (C) and 5 (D), the rudder lower leading edge 101b should be configured such that it is deflected to the transverse reference starboard at the uppermost side and at the transverse reference center at the lowermost side.

Due to the shapes of the rudder upper portion 11, the lower portion 12 and the central portion 13, the propulsion force of the ship is improved, the straightness of the ship is maximized, and the fuel cost is reduced.

In the case of rotating the ship's rudder in order to control the direction of the ship, an excessive force acts on the ship's rudder, so that the diameter of the rudder shaft supporting the ship's rudder must be a certain size or more. Accordingly, in order to install the rudder shafts having a predetermined size or more on the ship rudder, the lateral width of the rudder for the ship must be increased, thereby reducing the performance of the ship rudder and reducing the propulsion efficiency of the ship.

Therefore, the rudder body 10 according to the embodiment of the present invention can improve the propulsion efficiency by the torsion structure of the rudder upper portion 11 and the rudder lower portion 12, and suppress the generation of cavitation (A2-A3) of the rudder upper portion 10 of the marine rudder 1 is located on the central axis 30 of the rudder shaft (not shown) The maximum lateral width B2 of the flat end faces B1-B3 of the rudder center portion 13 and the position of the lowest lateral width maximum width C2 of the rudder lower portion 12 are located on the same straight line can do.

Specifically, the rudder body 10 has a top flat surface 11a of the rudder upper portion 11, a bottom surface 12a of the rudder body 10, A1-A3 and the bottom end face of the rudder lower portion 12 and the flat end faces B1-B3 and C1-C3 of the rudder center portion 13 are located at the position of the center axis 30 of the rudder shaft And the like.

(A1-A3, B1-B3, C1-C3), the longitudinal front end portion, the front end portion of the flat end surface, and the rear portion of the flat end surface, (A2-A3, B2-B3, C2-C3) of the flat section, the rear portions A1-A2, B1 -B2, C1-C2).

The rudder body 10 is formed so as to extend from the points A2, B2 and C2 at the maximum lateral widths in the flat end faces A1-A3, B1-B3 and C1-C3 to the longitudinal rear ends A1, The lateral widths of the flat sections A1-A3, B1-B3 and C1-C3 may be symmetrical with respect to the longitudinal center lines of the flat sections A1-A3, B1-B3 and C1-C3. Also, the rudder body 10 may be shaped such that the trailing edge 102 lies on a straight line perpendicular to the ship.

The rear portions A1-A2, B1-B2, and C1-C2 of the flat cross sections A1-A3, B1-B3, and C1-C3 can be formed in a nearly flat plate shape when the rudder body 10 is manufactured, Can be effectively reduced.

As described above, the rudder body 10 has a twisted structure in which the front portions A2-A3, B2-B3, and C2-C3 of the flat faces A1-A3, B1-B3, and C1- The rear portions A1-A2, B1-B2 and C1-C2 of the flat sections A1-A3, B1-B3 and C1-C3 are symmetrical with respect to the production ratios of the marine rudder 1, A1, B1, and C1, it is possible to maximize the propulsion force of the ship, improve the straightness of the ship, and effectively reduce the production cost of the ship rudder 1.

When the ship rudder 1 according to the embodiment of the present invention is applied to 84,000 CUM LPG / C, the production cost is reduced by about 5% as compared with the conventional ship rudder.

The rudder body 10 may include a rudder shaft (not shown) to be connected to the ship. The rudder axis may be located at a point (for example, A2, AB2, B2, BC2, C2) where the central axis 30 has the maximum lateral width at the flat cross section of the rudder body 10.

Therefore, it is possible to minimize the use of the curved plate (not shown) used in the rudder body 10 according to the embodiment of the present invention, thereby reducing the production cost of the rudder body 10. In addition, it is possible to prevent unnecessary increase in the lateral widths of the planar end faces A1-A3, B1-B3, and C1-C3 of the marine rudder 1, thereby maximizing the performance of the marine rudder 1 , The propulsion efficiency of the ship is increased.

Figure 7 effectively illustrates the effect resulting from the components of the present invention. 7 is a comparison chart of the propulsion performance of the marine rudder according to the embodiment of the present invention. X1 is the speed of the ship, and X2 is the required horsepower according to the speed of the ship.

Reference numeral 70 denotes a line corresponding to a speed and a required horsepower in a ship to which a conventional rudder for a ship is attached, and reference numeral 80 denotes a line corresponding to a speed and a required horsepower in a ship to which the rudder 1 for a ship of the present invention is attached, And numeral 90 is a value indicating the difference between the propulsion performance in a ship having a conventional rudder for a ship and the propulsion performance in a ship having the rudder 1 for a ship according to the present invention.

Referring to the graph of FIG. 7, it can be seen that as the speed X1 increases, the corresponding required horsepower X2 increases exponentially. This increase means that as the ship's speed (X1) increases, the required horsepower (X2) is needed exponentially.

In order to compare the propulsion performance of a ship in such a graph, it is sufficient to compare the required horsepower (X2) required by the ship when an arbitrary speed (X1) is obtained.

If the required horsepower required by the ship is small to give an arbitrary speed value, it means that the propulsion performance of the ship is good. If the required horsepower required to produce the same speed value is large, the propulsion performance of the ship is bad.

When comparing the propulsion performance of a conventional ship with a rudder for a ship and the propulsion performance of a ship equipped with the rudder for a ship 1 of the present invention on the basis thereof, it is possible to generate an arbitrary speed X1 It is found that the required horsepower required for a ship to which a conventional rudder for a ship is attached is larger than a required horsepower required for a ship to which the rudder for a ship 1 of the present invention is attached. This difference means that the propulsion performance of the ship having the rudder 1 of the present invention is better than the propulsion performance of the ship having the conventional rudder for the ship, and the calculated value is about 1.2% .

Accordingly, the marine rudder 1 according to the embodiment of the present invention maximizes the propulsion performance of the marine vessel and has an effect of improving the straightness of the marine vessel.

The rudder bulb 20 may protrude from the front surface of the rudder center portion 13. A discontinuity may occur in the rudder center portion 13 connecting the rudder upper portion 11 and the rudder lower portion 12. [ Such a discontinuity reduces the straightness of the hull and increases the resistance to the ship.

Therefore, the rudder bulb 20 may be provided on the discontinuity surface of the rudder center portion 13 in order to remove the discontinuity surface generated in the rudder center portion 13. [ Also, the rudder bulb 20 may be configured to be eccentric upwardly with respect to the propeller shaft, and may be formed coaxially with the propeller shaft.

This makes it possible to maximize the propulsion force of the ship, improve the straightness of the ship, and increase the energy efficiency of the ship by appropriately using the flow of the propeller wake.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

1: ship rudder 10: rudder body
11: rudder upper part 12: rudder lower part
13: rudder center portion 101: leading edge
101a: rudder upper leading edge 101b: rudder lower leading edge
102: Trailing edge 102a: Rudder upper trailing edge
102b: rudder lower trailing edge 102c: rudder center portion trailing edge
20: Rudder bulb 30: Rudder shaft center line
40: Propeller shaft center line 50: Fluid inflow direction at the upper portion of the rudder
60: Fluid inflow direction under the rudder
70: Corresponding line between speed and required horsepower on a ship with conventional rudder for ships
80: Corresponding line between speed and required horsepower in a ship having a rudder for a ship of the present invention
90: Difference in the driving force between the conventional rudder and the rudder of the present invention

Claims (9)

1. A marine rudder installed at the rear of a propeller to control a navigation direction of a ship,
Rudder body; And
And a rudder shaft connecting the ship and the rudder body,
The rudder shaft
And the center axis is located at a position where the transverse width is maximum at a flat cross section of the rudder body. The rudder body according to claim 1,
Wherein a horizontal width of the flat section is symmetrical with respect to a longitudinal center line of the flat section from a point where the width of the flat section is the maximum width to a longitudinal rear end thereof. The rudder body according to claim 1,
Sectional width of the upper portion of the rudder body is deflected to one side and a width of the flat section in the lower portion of the rudder body is deflected to the other side from the maximum widthwise position of the flat section to the longitudinal front end portion, And a rudder for a ship. The rudder body according to claim 1,
Wherein the trailing edge is on a straight line perpendicular to the ship. The rudder body according to claim 1,
A rudder body top having a leading edge biased to one side; And
And a lower portion of the rudder body having a leading edge deflected toward the other side. 6. The rudder according to claim 5,
Further comprising a rudder body center portion continuously formed so as to connect the lower edge of the leading edge of the upper portion of the rudder body and the upper edge of the leading edge of the lower portion of the rudder body in a curved line. 6. The rudder according to claim 5,
A rudder body center portion connecting the upper portion of the rudder body and the lower portion of the rudder body; And
And a rudder bulb protruding from the center of the rudder body. 7. The apparatus of claim 6, wherein the leading edge of the upper portion of the rudder body comprises:
Wherein the rudder body is tilted so as to be deflected to one side from the uppermost front end portion of the upper portion of the rudder body to the front end portion of the rudder body center portion,
The leading edge of the lower portion of the rudder body,
And the lower end of the lower portion of the rudder body is located at a lateral reference center position and is tilted from the lower end of the lower portion of the lower portion of the rudder body toward the front end of the central portion of the rudder body, And a rudder for a ship. 8. The apparatus of claim 7, wherein the leading edge of the upper portion of the rudder body comprises:
The front end of the uppermost portion of the rudder body is located at a lateral reference center position and is tilted so as to be deflected to one side from the lateral reference center position toward the front end of the rudder body center portion from the upper end front end of the rudder body And,
The leading edge of the lower portion of the rudder body,
And the lower end of the lower portion of the rudder body is located at a lateral reference center position and is tilted from the lower end of the lower portion of the lower portion of the rudder body toward the front end of the central portion of the rudder body, And a rudder for a ship.

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