JPH0258153B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ship, and its purpose is to alleviate the impact of waves on the stern of the ship. As shown in Figure 1, the stern of a ship usually overhangs, but when this part separates from the water surface, the overhang part A hits the sea surface due to pitching and vertical shaking due to waves, causing a large impact on the stern. As a result, the vibrations caused by the impact and the noise generated from the vibrations become larger the closer to the stern overhang part A of the hull living area, and in some cases, the vibrations due to the impact and the noise generated from the vibrations become large enough to be unsuitable for human habitation. There is. Conventionally, in response to such shocks, the stern of the ship was submerged by increasing the draft or trimmed, or the ship was maneuvered to prevent waves from reaching the stern. However, in some cases such a method is not possible, and in this case the impact at the stern overhang, which has a certain length in the direction of the hull centerline, has no choice but to be left as is. The present invention has been made in view of the above points, and
The basic feature is that a skeg-shaped protrusion is formed on the stern overhang of the hull, where the lower surface of the stern is exposed above the water surface in flat water in the ballast state, and that this protrusion satisfies the following conditions: It is. This protrusion may be attached separately as a skeg, or the stern itself may be molded as such. P/S3.2 Here, P=∫ ^x2 _x1 (b ₁ /tanβ ₁ +b ₂ /tanβ ₂ )dx S=∫ ^x2 _x1 (b ₁ +b ₂ )dx β ₁ : Water contact angle of overhang part β ₂ : Water contact angle of the protrusion b ₁ : Width from the base of the protrusion to the water contact point b ₂ : Half width of the protrusion x ₁ : Point at one end in the length direction of the protrusion x ₂ : Other point in the length direction of the protrusion End Points Examples of the present invention will be described below based on the drawings. Both FIGS. 2 and 3 show an example in which skegs 1 and 2 having a trapezoidal cross section are attached to the lower surface of an overhang part A at the stern. The shape of the lower surface of the overhang portion A may be changed in this way without using such skegs 1 and 2. Further, the cross-sectional shape can be not only a trapezoid but also a triangular shape, an oval shape, and the like. Skeg 1 is narrower than skeg 2 and has the same cross-sectional shape from the stern to the bow. The skeg 2 is wide and has a cross-sectional area that gradually decreases from the stern to the bow. When skegs 1 and 2 that are long in the direction of the hull centerline are used in response to such a stern overhang, the impact force (Fimp) due to waves can be theoretically determined as follows. Fimp≒dM _z /dt・V _z・L M _z = 1/2・ρ・π・b ²・C ₀・K _4Now , assuming that C ₀・K ₄ is constant, dM _z /dt=dM _z /d _z・d _z / dt = ρ・π・b・db/d _z・C ₀・K ₄・V _z =ρ・π・b/tanβ・C ₀・K ₄・V _z Fimp≒ρ・π・b/ tanβ・C ₀・K ₄・V _z ²・L = ρ・π・C ₀・K ₄・V _z ²・∫ ^x2 _x1 b/tanβdx... Here, Fimp: Wave impact force (Kg) M _z : Up and down Additional mass in the direction C ₀ / K ₄ : Varies depending on the additional mass coefficient and cross-sectional shape. V _z : Average speed (m/SEC) V _z = 2/π・ω・ζw ω=2π/T T: Wave period (SEC) ζw: Wave amplitude (m) L: Ship length (LPP) ρ: Water density Also, b/tanβ=b ₁ /tanβ ₁ +b ₂ /tanβ ₂ , and b, b ₁ , b ₂ β ₁ and β ₂ are as shown in FIG. That is, b: Width from the center of the ship's width to the water contact point (w) (this is the flat water line when the ship is fully loaded) = b ₁
+b ₂ b ₁ : Width from the base of skeg 1 to the water contact point (w) b ₂ : Half width β of skeg 1 : Water contact angle of overhang part, i.e. skeg 1
The angle of the straight line connecting the base and the water contact point (w) with respect to the horizontal line. β ₂ : Water contact angle of skeg 1, that is, the angle of the straight line connecting the lowest point of skeg 1 and the skeg base with respect to the horizontal line. x ₁ , x ₂ : Further, x ₁ and x ₂ are the projection points of one end and the other end of the skeg onto the coordinate axis, as shown in FIG. In this theoretical formula, the quantities other than ∫ ^x2 _x1 b/tanβdx are quantities that are not directly related to the shape of the skeg or the size of the hull. Here, in the formula ∫ ^x2 _x1 b/tanβdx=∫ ^x2 _x1 (b ₁ /tanβ ₁ −b ₂ /tanβ ₂
) Let dx be P and consider its physical meaning. Of P, b ₁ /tanβ ₁ is the amount corresponding to the impact force actually received by the hull when an impact force of 1 per unit area is applied from below to the width of b ₁ in Fig. 4. This corresponds to the horizontal component of the impact force when the impact force is received by a wall that forms an angle of β ₁ with the horizontal. Similarly, b ₂ /tanβ ₂ is the amount corresponding to the impact force actually received by the hull when an impact force of 1 per unit area is applied from below to the width of b ₂ in Fig. 4, and This corresponds to the horizontal component of the impact force when the impact force is received by a wall that forms an angle of β ₂ with the horizontal. Therefore, P=∫ ^x2 _x1 (b ₁ /tanβ ₁ +b ₂ /tanβ ₂ )dx is the length of stern skegs 1 and 2 in the hull length direction (x ₂ −
Projected area of the hull S=∫ ^x2 _x1 (b ₁ + b ₂ ) dx in the range of x ₁ )
This amount corresponds to the impact force actually received by the hull when an impact force of 1 per unit area is applied from below over the entire area. Therefore, P is S=∫ ^x2 _x1 (b ₁ +
b ₂ ) It can be normalized by dx, and the value of P/S will be a constant value regardless of the size if the shapes of the hulls are similar. Therefore, if the relationship between Fimp and P/S is determined through experiments, this relationship holds true for large ships as well. After obtaining such a theoretical conclusion, the present inventors calculated Fimp and ∫ ^x2 _x1 b/tanβdx (=∫ ^x2 _x1 (b ₁ /tanβ ₁ +b ₂ /tanβ
₂ ) dx) (hereinafter referred to as the impact area P value), and
A graph is shown in the figure. Also skeg 1,
2. The experimentally determined Fimp values without skeg are shown in each plot. In determining the Fimp value, the numerical values shown in Table 1 below were used.
Moreover, each plot and each curve show the values in Table 2.

【table】

[Table] As can be seen from this graph, the theoretical curve agrees well with the experimental values, and it can be seen that the above P value is an excellent indicator. Also, by setting P to about 0.04 or less, Fimp
It can be seen that the amount is sufficiently reduced. Here, when the P value is made dimensionless and expressed as the impact coefficient, that is, the impact coefficient α=P/S (water line area S=∫ ^x2 _x1 b dx), it becomes α3.2. Therefore, in the present invention, it is limited to α3.2. In this way, the present invention not only provides protrusions that alleviate wave impact in the direction of the hull centerline, but also provides a linear protrusion (skeg shape in the present invention) that significantly reduces the impact value. The shape that can be reduced is specifically limited based on the above theory and experiment, and a skeg that satisfies α3.2 is attached to the lower part of the stern, or the shape of the lower part of the stern is configured in this way. . Next, we will show an example of an experiment using a model. Experimental example Regular waves were used, and experiments were conducted in following waves and diagonal following waves. The model is a 1/50 scale stern section (AFT~Sq/St8 3/
The partial model 4) was used. The model was fixed on the water surface via a load cell, and the vertical wave impact force acting on the entire stern model was measured with and without skegs 1 and 2 shown in Figures 2 and 3. The effectiveness of the skeg was evaluated by comparing the waveforms of the wave impact force with and without the skeg. The test was conducted using a small wave channel (length x width x water depth = 12m x
0.5m x 0.4m). Regular waves were used, and tests were conducted in following waves (coming and going angle: 0deg) and oblique following waves (coming and going angle: 30deg). Table 3 summarizes the types of waves used in the test. Moreover, the test results are shown in Table 4. When skegs 1 and 2 were installed, the wave impact force was significantly reduced in both chasing waves and diagonal following waves. Also, an impact sound was generated without a skeg, but no impact noise was generated when skegs 1 and 2 were installed. Furthermore, skeg 1 and 2
No difference was observed depending on the shape.

【table】

[Table] As explained above, according to the present invention, the impact caused by waves, etc. at the stern section (this is because the stern overhang section is long to some extent in the direction of the hull centerline) It is possible to significantly reduce the impact (the shock received over the ship) and effectively prevent vibration and noise, especially in the hull living area near the stern overhang.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a conventional stern section, Fig. 2 is a perspective view showing an embodiment of the present invention, Fig. 3 is a perspective view showing another embodiment, and Figs. 4 and 5 are a perspective view of a theoretical formula. The symbol explanatory diagram, FIG. 6, is a graph showing the relationship between the wave impact force Fimp and the P value. 1 and 2...skeg.

Claims (1)

[Scope of Claims] 1. A ship characterized in that a skeg-shaped protrusion satisfying the following conditions is formed on the stern overhang portion of the hull where the lower surface of the stern protrudes above the water surface in flat water in a ballast state. _{P / S ≦ 3.2 where} ^P _{= ∫ _} Water contact angle b ₁ : Width from the base of the protrusion to the water contact point b ₂ : Half width of the protrusion _{X 1 :} Point at one end of the protrusion in the length direction point