Double-propeller elastic damping groove

Abstract

Propeller bodies are arranged at the bottom of a stern in a bilateral symmetry mode, damping grooves which are sunken upwards are formed in the positions, corresponding to the propeller bodies, of an outer board above the propeller bodies, the damping grooves are in a fusiform shape, and the length direction of the fusiform damping grooves is consistent with the length direction of a ship body. The depth of the fusiform vibration reduction groove is gradually reduced from the center point of the fusiform vibration reduction groove to the outside, the deepest point of the fusiform vibration reduction groove is located on the extending line, perpendicular to the outer plate, of the tail end of the propeller blade, a plurality of springs are arranged in the fusiform vibration reduction groove at equal intervals along the center axis of the fusiform vibration reduction groove, and a sealing plate is fixed to the tail end of each spring. Based on the exciting force transmission direction of the propeller, the streamlined groove structure is arranged in the force transmission direction, gaps between the propeller blades and the outer plate are increased, and therefore the exciting force transmission rate of the propeller is reduced. The groove body is designed in a streamline mode, the fusiform damping groove is formed in the tail end of the propeller blade in the vertical direction, the gap between the tail end of the propeller blade and a ship body can be increased, the influence on an outer plate structure is avoided, and the influence on frictional resistance is reduced.

Description

Technical Field

[0001] The invention belongs to the field of ship construction and design, and in particular relates to an elastic vibration-damping groove for a double propeller. Background Art

[0002] With the rise of large liquefied natural gas (LNG) ships, more and more ship owners are coming to the Chinese market to build LNG ships. LNG ships are twin-engine twin-propeller ships, and the local vibration problem at the tail is serious, which has attracted the attention of the entire shipping industry. As we all know, the main causes of ship vibration are the main engine excitation force and the propeller excitation force. For the main engine, it is to increase the strength and transmissibility of the base so that the main engine's excitation force can be transmitted as much as possible. The propeller excitation force is divided into surface force and bearing force. For ships with propeller excitation force as the main vibration source, there are two ways to reduce the tail vibration: (1) reduce the amplitude of the propeller excitation force and change the excitation force frequency, and (2) reduce the transmission rate of the propeller excitation force. This patent mainly solves the problem of excessive vibration of twin engines and twin propellers by reducing the transmission rate of the propeller excitation force. For ships with a single engine and a single propeller, when the excessive vibration caused by the propeller exciting force cannot be resolved, a square groove is usually set at the closest point between the outer plate line and the propeller blade. This groove will increase the distance between the propeller and the outer plate, but this groove will seriously affect the smoothness of the outer plate and increase the hull resistance. This solution will not be used for actual ships unless it is absolutely necessary. For ships with two engines and two propellers such as LNG ships, it is wasteful to open vertical vibration reduction grooves on both sides of the propeller setting line, and it affects the structural strength, so a lateral opening needs to be opened along the direction of the propeller force to play a vibration reduction role. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a double propeller elastic vibration reduction groove, and the technical solution adopted is:

[0004] A twin-propeller elastic vibration damping groove, propellers are symmetrically arranged at the bottom of the stern, and an upwardly concave vibration damping groove is opened above the propeller blades and at the corresponding position of the ship outer plate and the propeller blades. The vibration damping groove is shuttle-shaped, and the length direction of the shuttle-shaped vibration damping groove is consistent with the length direction of the hull. The depth is deepest at the center point of the shuttle-shaped vibration damping groove, and the depth gradually decreases from the center point of the shuttle-shaped vibration damping groove to the outside. The deepest point of the shuttle-shaped vibration damping groove is located on the extension line of the propeller blade end perpendicular to the outer plate. Inside the shuttle-shaped vibration damping groove, multiple springs are arranged at equal intervals along the center axis of the shuttle-shaped vibration damping groove. A sealing plate is fixed at the end of the spring. The shape of the sealing plate is the same as the projection shape of the shuttle-shaped vibration damping groove, which is 85% of the projection area. The initial state of the spring is a compressed state. The maximum width of the shuttle-shaped vibration damping groove is B, B=2*tan(a)*L1, the angle a is the angle formed by the line connecting the end of the blade and the edge of the shuttle-shaped vibration damping groove, and the line connecting the end of the blade and the spring, the length of the sealing plate is 0.8B, and the outer plate of the hull extends 0.15B into the shuttle-shaped vibration damping groove. The outer plate of the hull extending inward is the limiting structure of the sealing plate 6.

[0005] The above-mentioned twin-propeller elastic vibration damping groove, further, has a front end position of the shuttle-shaped vibration damping groove that is no more than 0.05 times the length of the vertical line forward, and a rear end position of the vibration damping groove that is in front of the tail sealing plate and no more than 0.05 times the length of the vertical line.

[0006] The above-mentioned twin-propeller elastic vibration damping groove, further, has a straight-line distance from the vertex of the shuttle-shaped vibration damping groove to the blade tip of not less than 0.2 times the propeller diameter and not more than 0.3 times the web of the frame structure in the area.

[0007] In the above-mentioned twin-propeller elastic vibration damping groove, further, the propeller diameter is D, the distance between the blade end and the flat bottom of the vibration damping groove is L1, and L1≥0.2D.

[0008] The above-mentioned twin-propeller elastic vibration damping groove, further, has a web height of M where the vibration damping groove passes through the transverse frame, and a deepest part of the vibration damping groove is L2, L2<0.3M.

[0009] The above-mentioned twin-propeller elastic vibration damping groove, further, has a reinforcing rib arranged at the deepest part of the vibration damping groove, and the reinforcing rib is arranged on the web of the frame.

[0010] In the above-mentioned twin-propeller elastic vibration damping groove, further, the limiting structure is provided with ear-shaped reinforcing brackets on the inner side, and the number of the reinforcing brackets is twice the number N of the springs.

[0011] The above-mentioned twin-propeller elastic vibration damping groove, further, has a spring stiffness of k, a spring quantity of N, a force that the spring can withstand of P1, a spring compression displacement of x, and P1=k1*x.

[0012] In the above-mentioned twin-propeller elastic vibration-damping groove, further, the spring and the sealing plate can also be replaced by non-water-absorbent rubber or polyester fiber.

[0013] The above-mentioned twin propeller elastic vibration reduction groove, further, 25° <a<30°。

[0014] The beneficial effects of the present invention are: 1. Based on the transmission direction of the propeller exciting force, the present invention sets a streamlined groove structure in the force transmission direction to increase the gap between the propeller blades and the outer plate, thereby reducing the transmission rate of the propeller exciting force. 2. The present invention streamlines the groove body and sets an elliptical groove in the vertical direction of the propeller blade tip. The groove can increase the gap between the blade tip and the hull. 3. An elastic structure is set in the groove, one is a movable elastic structure, and the other is a fixed elastic structure, which absorbs the force directly acting on the outer plate and reduces the impact on the outer plate, thereby reducing the exciting force of the propeller on the outer plate. 4. The elastic structure fills the groove to avoid the impact on the outer plate structure and reduce the impact on the friction resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the twin propeller tail structure;

[0016] Figure 2 yes Figure 1 A schematic diagram of the enlarged structure of point A;

[0017] Figure 3 1. It is a schematic diagram of the structure of the vibration reduction groove from a top view;

[0018] Figure 4 It is a schematic diagram of the front structure of the vibration reduction groove;

[0019] Among them: 1-propeller, 2-vibration damping groove, 3-web, 4-strengthening ribs, 5-spring, 6-sealing plate, 7-hull outer plate, 8-limiting structure, 9-reinforced bracket. DETAILED DESCRIPTION

[0020] The present invention will be further described in conjunction with the accompanying drawings.

[0021] Example 1

[0022] A twin propeller elastic vibration reduction groove, such as Figure 1 , 2As shown, a vibration-damping groove 2 with an elliptical cross section is arranged above the propeller blade 1. The vibration-damping groove is shuttle-shaped along the length of the ship. The radius of the arc of the cross section gradually decreases from the center point of the vibration-damping groove to both ends. The front end of the vibration-damping groove does not exceed 0.05 times the length of the vertical line, and the rear end of the vibration-damping groove and the tail seal plate do not exceed 0.05 times the length of the vertical line. The deepest part of the vibration-damping groove is arranged on the extension line of the propeller blade end perpendicular to the outer plate. The straight-line distance from the vertex of the vibration-damping groove arc to the blade end (L1+L2), L1+L2 is not less than 0.2 times the propeller diameter D, but cannot exceed 0.3 times the web 3 of the frame structure in the area. The propeller diameter is D, the distance between the blade end and the flat bottom of the vibration-damping groove is L1, L1≥0.2D, the depth of the vibration-damping groove is L1, L1<0.3M, M is the height of the web where the vibration-damping groove passes through the transverse frame, and the deepest part of the vibration-damping groove is provided with a stiffener 4, which is arranged on the web 3 of the frame.

[0023] A number of springs 5 ​​are arranged at equal intervals inside the vibration reduction groove along the central axis of the vibration reduction groove. The stiffness of the spring is k, the number is N, P1=k1*x, P1 is the force that the spring can withstand, and x is the compression displacement of the spring. The initial state of the spring is in a compressed state, x0=P2 / k2, which can ensure that under the action of the water pressure P2, it will not rebound and always press against the outer plate to prevent water from entering the vibration reduction groove.

[0024] like Figure 3 , 4 As shown, the maximum width of the vibration reduction groove is B, B=2*tan(a)*L1, and the angle a is the angle formed by the line connecting the end of the blade and the edge of the shuttle-shaped vibration reduction groove and the line connecting the end of the blade and the spring, 25° <a<30°。

[0025] A sealing plate is fixed to the other end of the spring. The shape of the sealing plate 6 is consistent with the projection shape of the shuttle-shaped groove, which is 85% of the projection area and has a length of E=0.8*B. The hull outer plates 7 at both ends of the vibration-damping groove extend 0.15B into the vibration-damping groove, and the structure extending inward is the limiting structure 8 of the sealing plate 6. An ear-shaped reinforced elbow plate 9 is arranged on the inner side of the limiting structure 8. The number of the elbow plates is twice the number of springs N and is arranged at equal intervals. The limiting structure 8 is divided into two sections by the reinforced elbow plate, wherein the limiting section is H long, the reinforced section is 2*H, and H=0.05*B. The ear-shaped reinforced elbow plate 9 connects the straight section through an arc R3 from 2 / 3 of the limiting structure. The height of the straight section is G and the width is H. When the sealing plate reaches the straight section, the compression of the spring reaches the maximum. The straight section is connected to the top of the semicircular arc through an arc transition.

[0026] According to the specification requirements, the propeller pulsation pressure P3 is usually 4KPa to 8KPa. If the propeller does not rotate or the pulsation pressure is less than 4KPa, P3<4KPa, the sealing plate is tightly connected to the outer plate under the outward pressure of the spring, preventing water from entering, while also maintaining the smoothness of the outer plate shape. The outer side of the sealing plate 6 is affixed with vibration-damping materials such as epoxy resin.

[0027] When the propeller rotates to beat the outer plate and the exciting force P3 is between 4 KPa and 8 KPa (4 KPa < P3 < 8 KPa), the spring is compressed, the sealing plate retracts inward, and the inward distance x = P3 / k3; when the propeller rotates to beat the outer plate and the exciting force P3 ≥ 8 KPa, the spring is compressed to the maximum, that is, it reaches the straight section of the ear-shaped reinforcing gusset 9, and the distance at this time is G. The damping groove is composed of two straight sections and an ellipse. The straight sections and the ellipse are connected by an arc, and the arc diameter is R2, where R1 > R2 > R3 > 800. The damping groove increases the distance between the blade tip and the outer plate, playing a role in damping. At the same time, the limiting structure 8 plays a role in guiding the flow, which can reduce the increase in resistance.

[0028] The stiffness k is the maximum value of k1, k2, and k3.

[0029] Embodiment 2

[0030] It is also possible to cancel the spring and the sealing plate in Embodiment 1, and directly fill the entire damping groove with a water-insoluble material such as rubber or polyester fiber, and keep the outer shape smooth with the outer plate. At this time, the ear-shaped reinforcing gusset 9 can be cancelled, and the rest of the structure is the same as that in Embodiment 1. When the propeller beats, it effectively isolates the contact between water and the steel plate, and can reduce vibration. This patent is applicable to both single-screw and multi-screw ships.

Claims

1. A twin propeller elastic vibration damping groove, characterized in that: A propeller is symmetrically arranged at the bottom of the stern, and an upwardly concave vibration-damping groove (2) is opened above the propeller blades (1) and at a position corresponding to the propeller blades on the outer plate of the ship. The vibration-damping groove is shuttle-shaped, and the length direction of the shuttle-shaped vibration-damping groove is consistent with the length direction of the hull. The depth of the shuttle-shaped vibration damping groove is the deepest at the center point, and the depth gradually decreases from the center point of the shuttle-shaped vibration damping groove to the outside. The deepest point of the shuttle-shaped vibration damping groove is located on the extension line of the end of the propeller blade perpendicular to the outer plate. Inside the shuttle-shaped vibration damping groove, a plurality of springs (5) are arranged at equal intervals along the center axis of the shuttle-shaped vibration damping groove. A sealing plate (6) is fixed at the end of the spring. The shape of the sealing plate is the same as the projection shape of the shuttle-shaped vibration damping groove and is 85% of the projection area. The initial state of the spring is a compressed state. The maximum width of the shuttle-shaped vibration-damping groove is B, B=2*tan(a)*L1, the angle a is the angle formed by the line connecting the end of the blade and the edge of the shuttle-shaped vibration-damping groove, and the line connecting the end of the blade and the spring, the length of the sealing plate is 0.8B, the outer hull plate extends 0.15B into the shuttle-shaped vibration-damping groove, and the outer hull plate (7) extending inward is the limiting structure (8) of the sealing plate.

2. The double propeller elastic vibration damping groove according to claim 1, characterized in that: The front end of the shuttle-shaped vibration damping groove shall not exceed 0.05 times the length of the vertical line, and the rear end of the vibration damping groove shall not exceed 0.05 times the length of the vertical line in front of the tail sealing plate.

3. The double propeller elastic vibration damping groove according to claim 1, characterized in that: The propeller diameter is D, the distance between the blade tip and the flat bottom of the vibration damping groove is L1, and L1≥0.2D.

4. The double propeller elastic vibration damping groove according to claim 1, characterized in that: The height of the web where the vibration-damping groove passes through the transverse frame is M, and the deepest part of the vibration-damping groove is L2, where L2 is less than 0.3M.

5. The double propeller elastic vibration damping groove according to claim 1, characterized in that: A reinforcing rib (4) is arranged at the deepest part of the vibration-damping groove, and the reinforcing rib is arranged on the web (3).

6. The double propeller elastic vibration damping groove according to claim 1, characterized in that: The limiting structure (8) is provided with ear-shaped reinforcing toggle plates (9) on the inner side, and the number of the reinforcing toggle plates is twice the number N of the springs.

7. The double propeller elastic vibration damping groove according to claim 1, characterized in that: The stiffness of the spring is k, the quantity is N, the force that the spring can withstand is P1, the compression displacement of the spring is x, P1=k1*x.

8. The double propeller elastic vibration damping groove according to claim 1, characterized in that: The spring and the sealing plate may also be replaced by non-absorbent rubber or polyester fiber.

9. The double propeller elastic vibration damping groove according to claim 1, characterized in that: 25°<a<30°。

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