JP3294113B2 - Anti-vibration stern boss structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stern boss structure surrounding a stern tube inserted through a propeller shaft.

[0002]

2. Description of the Related Art As a conventional stern boss structure of a uniaxial ship, there are those shown in FIG. 6 (longitudinal sectional view) and FIG. 7 (BB sectional view of FIG. 6), and are referred to as a stern frame 13. It is composed of a cast part, and a hull outer panel 2 and a floor panel 1 as a steel plate structure part connected to the cast part. A propeller shaft 11 is inserted through a bearing 14 into a stern tube 12 surrounded by the stern boss structure as described above, and a propeller 10 is mounted on a rear end of the propeller shaft 11. .

In recent ships, a stern frame 13 is projected into the outside water in order to improve the propulsion performance. In connection with this, a stern boss in the horizontal left and right direction as shown by an arrow in FIG. There is a tendency that the natural frequency of the flexure of the structure tends to decrease, and there is a possibility that an excessive vibration may be generated due to a vibration phenomenon and a resonance phenomenon acting on the propeller 10.

Therefore, as typical examples of the conventional anti-vibration means, the dimensions and thickness of the floor plate 1 and the hull outer plate 2 shown in FIGS. Increasing the rigidity of the stern boss structure has been carried out, thereby increasing the flexural natural frequency of the stern boss structure,
It is designed to be separated from the excitation frequency range of the propeller excitation force.

[0005]

However, in the above-described conventional vibration isolating means, the number of the floor plates 1 and the dimensions of the floor plates 1 and the hull outer plate 2 originally required from the viewpoint of the hull strength and the axis alignment. Since the amount of structural reinforcement is required to be significantly increased as compared with the plate thickness, the weight of the stern boss structure is significantly increased and workability is deteriorated.

The present invention has been proposed in view of such circumstances, and does not require additional floor plates and increases the dimensions and thickness of the floor plates and the hull outer plate. It is an object of the present invention to provide an anti-vibration stern boss structure capable of preventing an increase in a lateral vibration response.

[0007]

To solve the above-mentioned problems, a vibration-proof stern boss structure according to the present invention comprises a stern boss structure surrounding a stern tube having a propeller shaft inserted therein. Vertical tanks arranged on both sides of the stern tube inside the stern boss structure to suppress the vibration by the propeller vibrating force transmitted through the shaft, and these vertical tanks A U-shaped tank comprising a lower tank portion communicating with the lower portion of the vertical tank portion is filled with liquid so as to leave an air layer in an upper layer inside the vertical tank portion.

In the above-described vibration-proof stern boss structure of the present invention,
The U-shaped tank as an anti-vibration tank is appropriately arranged in a narrow space such that the stern tube through which the propeller shaft is inserted is sandwiched between the left and right vertical tank portions.

[0009] Since an air layer is formed in an upper layer in the left and right vertical tank portions of the tank, the liquid inside the U-shaped tank is operated so as to suppress the left and right vibration of the stern boss structure. I do. That is, the one-degree-of-freedom vibration system constituted by the mass of the liquid and the spring rigidity of the air layer acts as a dynamic vibration absorber. The natural frequency of the one-degree-of-freedom vibration system is set so as to match the natural frequency of the stern boss structure in the lateral direction by adjusting the dimensions of the U-shaped tank and the spring stiffness of the air layer. Is done.

[0010] In this manner, the reaction of the force acting on the internal liquid in the lower tank portion connecting the lower portions of the left and right vertical tank portions of the U-shaped tank causes the left-right vibration of the stern boss structure. The response is suppressed.

Further, in the vibration-proof stern boss structure of the present invention, the U-shaped tank includes a pair of front and rear floor plates inside the stern boss structure, and left and right hull outer plates in the stern boss structure. And a horizontal lower inner wall connecting the lower portions of the left and right hull skins to each other.

As described above, the U-shaped tank is formed together with the bent upper inner wall and the horizontal lower inner wall using the left and right hull outer plates and the pair of front and rear floor plates in the stern boss structure. With this configuration, formation of the U-shaped tank is significantly simplified without complicating the structure or adding a large number of members.

Further, the anti-vibration stern boss structure of the present invention comprises:
The left and right hull outer plates forming both side walls of the U-shaped tank are formed with small holes for taking in outside water as the working water into the U-shaped tank, respectively. When such small holes are formed in the hull outer plate, the intrusion of external water into the U-shaped tank through the small holes is automatically performed when the hull launches. If the positions of the holes are set appropriately, the required amount of hydraulic water in the U-shaped tank is guided, and the spring stiffness of the residual air layer in the left and right vertical tank portions is set appropriately. .

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a vibration-proof stern boss structure according to an embodiment of the present invention;
1 is a side view thereof, FIG. 2 is a cross-sectional view taken along line AA of FIG. 1, FIG. 3 is a cross-sectional view corresponding to FIG. 3 (e) are graphs for explaining the operation of the anti-vibration stern boss structure of FIG. 3, and FIG. 5 is a graph showing the vibration characteristics of the anti-vibration stern boss structure of the present invention in comparison with the conventional case. .

As shown in FIGS. 1 and 2, in a stern boss structure surrounding a stern tube 12 in which a propeller shaft 11 is inserted, a pair of front and rear floor plates 1, 1 and left and right hull outer plates 2, 2 are provided. U-shaped tank is formed by utilizing the above. That is, a bent upper inner wall 3 interconnecting the upper portions of the left and right hull outer plates 2 and 2 between the pair of front and rear floor plates 1 and 1 and a lower portion of the left and right hull outer plates 2 and 2 are mutually connected. A horizontal lower inner wall 4 to be connected is provided, whereby the left and right vertical tank portions 6a and 6b and the vertical tank portions 6a and 6b are connected.
b consisting of a lower tank portion 7 interconnecting the lower portions of
A vertical tank portion 6a, 6b is disposed on both sides of the stern tube 12 in this manner.

Then, the height of the hull outer plate of the portion forming the U-shaped tank is set so that external water can automatically enter as working water when the hull starts. Three small holes 5 are provided at substantially the center position and the lower position, respectively, as shown in FIG.

When the hull having the above-mentioned stern boss structure launches, outside water penetrates through the small holes 5, and as shown in FIG. 3, residual air is left in upper layers inside the left and right vertical tank portions 6a and 6b. Layers 8a and 8b are formed.

In the vibration-proof stern boss structure of the above-described embodiment, the stern tube 12 through which the propeller shaft 11 is inserted is sandwiched between the left and right vertical tank portions 6a and 6b, so that the stern tube 12 is used as a vibration-proof tank in a narrow space. The U-shaped tank is properly arranged.

The left and right vertical tank portions 6 of the tank
Since the air layers 8a and 8b are formed in the upper layers of the a and 6b, the liquid 9 inside the U-shaped tank operates so as to suppress the left and right vibration of the stern boss structure. That is, the one-degree-of-freedom vibration system constituted by the mass of the liquid 9 and the spring stiffness of the air layers 8a and 8b acts as a dynamic vibration absorber. The natural frequency of the one-degree-of-freedom vibration system matches the natural frequency of the stern boss structure in the lateral direction by adjusting the dimensions of the U-shaped tank and the spring stiffness of the air layers 8a and 8b. Is set to

In this manner, the stern boss structure is formed by the reaction force of the force acting on the internal liquid 9 in the lower tank portion 7 connecting the lower portions of the left and right vertical tank portions 6a and 6b of the U-shaped tank. Is suppressed in the left-right direction.

Further, in the present embodiment, the U-shaped tank is formed by using the left and right hull outer plates 2 and 2 and the pair of front and rear floor plates 1 and 1 in the stern boss structure to form a bent upper inner wall. Since it is formed together with the lower inner wall 3 and the horizontal lower inner wall 4, the formation of the U-shaped tank is significantly simplified without complicating the structure or adding a large number of members.

Further, since the small holes 5 are formed in the hull outer plates 2 and 2, the U
External water can be automatically introduced into the U-shaped tank, and if the position of the small hole 5 is appropriately set, the above U
The working water 9 in the V-shaped tank is guided by a required amount, and the remaining air layers 8a, 8b in the left and right vertical tank portions 6a, 6b are guided.
Is set appropriately.

Considering the situation of the hull provided with the anti-vibration stern boss structure of the present embodiment while the hull is traveling, the propeller 10 is submerged during the voyage. Submerge in seawater as shown schematically. Therefore, seawater flows into the U-shaped tank through the small holes 5 provided in the hull outer panel 2. However, the air above the uppermost small hole 5 remains in the tank and is compressed by seawater pressure,
It is sealed inside the vertical tanks 6a and 6b. That is, as shown in FIG. 3, residual air layers 8a and 8b are formed in the upper layers inside the vertical tank portions 6a and 6b.

At this time, a one-degree-of-freedom vibration system is formed in which the remaining air layers 8a and 8b are used as spring elements and the working water 9 in the U-shaped tank is used as a mass element. Assuming a symmetrical structure for simplicity, the natural circular frequency ω ₀ of this vibration system is given by [Equation 1].

Ω ₀ = √ ｛2G (1 + kD / h) / (2H +
aL / A)｝ where, H, a: water level and cross-sectional area of vertical tank portions 6a, 6b L, a: length and cross-sectional area of lower tank portion h: height of residual air layers 8a, 8b D : Depth from the sea surface to the water surface of the working water 9 in the U-shaped tank k: Specific heat ratio of air G: Gravitational acceleration

The U-shape so that the natural circular frequency ω ₀ of the working water / air system in the U-shaped tank obtained by the equation (1) coincides with the horizontal natural horizontal bending natural frequency of the stern boss structure. The dimensions of the tank and the positions of the small holes 5 are determined.

Considering the case where the natural circular frequency of the stern boss structure flexes in the horizontal direction and the natural frequency resonates with the oscillating force acting on the propeller, in this case, the propeller oscillating force F and the horizontal and lateral directions of the stern boss structure are considered. The relationship with the vibration displacement y is shown in FIG.
(b), the phase of the vibration displacement y is delayed by 90 ° with respect to the excitation force F. Next, the vibration displacement x of the horizontal center of gravity of the working water in the U-shaped tank induced by the horizontal left-right vibration displacement y of the stern boss structure is also different from the working water in the U-shaped tank as described above. Since the vibration system formed by the air is resonating, the amplitude is increased and the phase is delayed by 90 ° with respect to the horizontal horizontal displacement y of the stern boss structure as shown in FIG. At this time, assuming that an inertial force generated in the hydraulic water in the U-shaped tank is F _I , the reaction force Fc acts on the stern boss structure horizontally and horizontally.

Here, F _I and Fc are represented by the following equations.

## EQU2 ## F _I = M (d ² x / dt ² ) Fc = −F _I where M: effective mass of seawater in the U-shaped section. From Equation 2,

Fc = −F _I = −M (d ² x / dt ² ) = Mω ² x where ω: natural circular frequency.

That is, from Equation 3, the reaction force Fc shown in FIG. 4D and the vibration displacement x of the center of gravity of the working water in the U-shaped tank are in the same phase. To summarize the above, FIG.
As shown in (d), the reaction force Fc has an opposite phase to the vibrating force F. Therefore, the reaction force Fc acts in a direction to cancel the excitation force F, so that the effective excitation force F + Fc is smaller than the actual excitation force F as shown in FIG. Therefore, the vibration response in the horizontal left and right direction of the stern boss structure can be reduced as compared with the conventional case without the U-shaped tank.

FIG. 5 schematically shows the effect of the present invention as described above, in comparison with the effect of the conventional anti-vibration means. In the figure, the broken line 15 is a curve representing the vibration acceleration of the stern boss structure of the unmeasured structure, the dashed line 16 shows the case of the conventional measure structure in which the natural frequency is increased, and the solid line 17 is the stern of the invention. The case of a boss structure is shown. In the conventional countermeasure structure, there is a possibility that a new natural circular frequency resonates with another excitation force in order to increase the natural circular frequency.

On the other hand, in the vibration-proof stern boss structure of the present invention, the vibration response can be suppressed as a whole, and there is no fear of resonance with another vibrating force. .

[0031]

As described above in detail, the anti-vibration stern boss structure of the present invention has a U-shaped tank inside, so that the horizontal stern boss structure flexural vibration response can be totally reduced. As a result, high reliability can be obtained with a simple structure as compared with the conventional anti-vibration means, and the occurrence of excessive vibration due to resonance in the horizontal and horizontal directions of the stern boss structure can be accurately prevented. Further, the U-shaped tank is formed with a bent upper inner wall and a horizontal lower inner wall by using left and right hull outer plates and a pair of front and rear floor plates in the stern boss structure. Thus, the formation of the U-shaped tank is significantly simplified without complicating the structure or adding a large number of members. Further, when a small hole communicating with the U-shaped tank is formed in the hull outer plate, intrusion of external water into the U-shaped tank through the small hole is automatically performed when the hull is launched. If the position of the small hole is set appropriately, the required amount of hydraulic water in the U-shaped tank is guided, and the spring stiffness of the residual air layer in the left and right vertical tanks is reduced. It will be set appropriately.

[Brief description of the drawings]

FIG. 1 is a side view showing an anti-vibration stern boss structure as one embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a cross-sectional view corresponding to FIG. 2 and showing a state in which working water has entered.

FIGS. 4A to 4E are graphs for explaining the operation of the vibration-proof stern boss structure of the present invention.

FIG. 5 is a graph showing the vibration characteristics of the vibration-proof stern boss structure of the present invention in comparison with the conventional case.

FIG. 6 is a longitudinal sectional view showing a conventional stern boss structure.

FIG. 7 is a sectional view taken along the line BB of FIG. 6;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Floor board 2 Hull outer board 3 Upper inner wall 4 Lower inner wall 5 Small hole 6 Vertical tank part 7 Lower tank part 8 Residual air layer 9 Hydraulic water 10 Propeller 11 Propeller shaft 12 Stern tube 13 Stern frame 14 Bearing 15 Anti-vibration means Horizontal and horizontal vibration response curve of stern boss structure without stern 16 Horizontal and horizontal vibration response curve of stern boss structure with conventional anti-vibration means 17 Horizontal and horizontal vibration response curve of anti-vibration stern boss structure of the present invention

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B63B 1/08 B63B 3/40 B63B 43/00 B63H 1/15 B63H 23/32

Claims (3)

(57) [Claims] 1. A stern boss structure surrounding a stern tube inserted through a propeller shaft, wherein the stern boss structure is configured to prevent the stern boss structure from vibrating due to a propeller vibrating force transmitted through the propeller shaft. Inside, a U-shaped tank comprising a vertical tank portion arranged on each side of the stern tube and a lower tank portion communicating the lower portions of these vertical tank portions with each other, An anti-vibration stern boss structure, characterized by being filled with liquid so as to leave an air layer in an upper layer inside the section. 2. The anti-vibration stern boss structure according to claim 1, wherein the U-shaped tank includes a pair of front and rear floor plates inside the stern boss structure, and left and right hull outer plates in the stern boss structure. Characterized by being formed by a bent upper inner wall interconnecting the upper parts of these hull outer panels and a horizontal lower inner wall interconnecting the lower parts of the left and right hull outer panels, Anti-vibration stern boss structure. 3. The anti-vibration stern boss structure according to claim 2, wherein left and right hull outer plates forming both side walls of the U-shaped tank use external water as working water, respectively, in the U-shaped tank. A vibration-proof stern boss structure, characterized in that a small hole for taking in the stern is formed.