JP2005114455A - Method for estimating fatigue damage of moorage dolphin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for more accurately estimating the fatigue damage of a moorage dolphin. <P>SOLUTION: By taking in natural environment conditions (waves, tides, and wind conditions) in the disposition environment of a floating body and a moorage dolphin (step S1), a nonlinear time-series simulation is executed as to the state of motion of the float body when it is acted on by environment external force based on the environment conditions (step S2). Then, correspondently to the time-series simulation, time-series data on moorage reaction force the floating body receives from the moorage dolphin are statistically processed to prepare frequency data on a load the dolphin itself receives (step S3). Then, an S-N diagram is taken in (step S4), a load (the degree of short-term fatigue damage) the dolphin itself receives is calculated from the result of the statistical processing on the time-series data acquired in the step S3, and a long-term wave frequency is taken in on the basis of a long-term wave frequency table (step S6). Then, long-running fatigue damage of the moorage dolphin is estimated from the degree of short-term fatigue damage and from the long-term wave frequency (step S7). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for predicting fatigue damage of a moored dolphin in consideration of non-linearity of external force acting on a floating body and non-linear reaction force characteristics of the moored dolphin.

The background art will be described with reference to FIG.
FIG. 12 is a schematic diagram illustrating an example of a method for mooring a tank for storing oil offshore.
FIG. 12 shows an oil storage tank (floating structure: mega float) 1 installed in the sea. This oil storage tank 1 is moored in the sea by mooring dolphin 3A, 3B. The mooring dolphin 3A, 3B includes main piles 5A, 5B rising from the bottom of the water, and fenders 6A, 6B provided inside these upper ends. The impact accompanying the shaking of the oil storage tank 1 is suppressed by the fenders 6A and 6B at the upper ends of the main piles 5A and 5B. The outside of the mooring dolphin 3 </ b> A, 3 </ b> B is surrounded by a breakwater 7. By forming a calm sea area inside the breakwater 7, the oil storage tank 1 is prevented from shaking, and the load (fatigue) received by the mooring dolphins 3A and 3B is reduced.

  In the mooring method shown in FIG. 12, the breakwater 7 must be installed in order to suppress the oil storage tank 1 from shaking. However, if it is necessary to always install the breakwater 7, when the oil storage tank 1 is enlarged, a large construction cost is required. Furthermore, if the breakwater 7 is installed, the ocean current will be hindered, so there is a concern that the surrounding sea area may be adversely affected. Alternatively, when the oil storage tank 1 is disposed offshore, it is impossible to install a breakwater around the tank in the first place.

  Therefore, there is a need for a system that does not build a breakwater and continues to moor floating structures such as oil storage tanks over a long period of time. When a breakwater is not constructed, the floating structure is directly subjected to wave external force and tidal force, so that the load applied to the mooring dolphin increases. Therefore, the future soundness of floating structures and moored dolphins can be quantitatively predicted and diagnosed so that locations that may cause damage can be detected in advance and repaired appropriately so that long-term maintenance can be carried out smoothly. It is necessary to do. In particular, for moored dolphin that receives a load from a floating structure, it is indispensable to predict an accurate fatigue state.

  For such fatigue damage prediction diagnosis of moored dolphin, a method described in Non-Patent Document 1, for example, has been conventionally known. This method separates external forces (wind force, wave force, tidal force) acting on the floating structure into steady components and fluctuating components, and adds up the mooring reaction forces for these components to evaluate the overall mooring reaction force. To do. However, in this method, when calculating the fluctuation component of the external force, the response function of the motion of the floating structure is combined with the statistical theory.

Japan Shipbuilding Research Association, 179th Research Group, “Study Report on the Kinetic Characteristics of Box-type Offshore Structures and Mooring System Design Standards in Shallow Waters”, March 1983

  In Non-Patent Document 1 described above, when the mooring reaction force is estimated from the fluctuation component of the external force, it is calculated by combining the response function of the motion of the floating structure and the statistical theory, so it is handled within the range of linear theory. It has become. However, since the actual phenomenon is non-linear, the accuracy of the estimation of the mooring reaction force is low when the problem is handled within the range of linear theory. Therefore, it is difficult to accurately predict the fatigue status of the moored dolphin.

  The present invention has been made in view of the above problems, and more accurately predicts the fatigue damage of a moored dolphin by taking into account the non-linearity of the external force acting on the floating body and the non-linear reaction force characteristics of the moored dolphin. It aims to provide a method that can be used.

  The method for predicting fatigue damage of a moored dolphin according to the present invention is a method for predicting the fatigue damage of a moored dolphin that anchors a floating body on a liquid surface. Step), predicting the motion state of the floating body when an external environmental force is applied based on this natural environmental condition (second step), and predicting the mooring reaction force that the floating body receives from the mooring dolphin according to this motion state (third step) Step), predicting the load received by the mooring dolphin itself from this mooring reaction force (fourth step), predicting the degree of fatigue at a specific location in the mooring dolphin based on the load received by the mooring dolphin itself (fifth step), The motion state of the floating body during the second step is predicted using a nonlinear time series simulation.

  According to the present invention, the fatigue damage prediction of the moored dolphin can be more accurately performed by performing the non-linear time series simulation considering the non-linearity of the external force acting on the floating body and the non-linear reaction force characteristic of the moored dolphin. This makes it possible to find a location that is likely to cause damage and repair it appropriately, so that long-term maintenance of the moored dolphin can be smoothly performed.

但し、
ｉ＝１、２、６
ｍ_ｉｉ(∞)：周波数無限大での付加質量及び付加慣性モーメント、
Ｆ_Ｖｉ：粘性減衰力及びモーメント、
Ｌ_ｉｉ：メモリー影響関数、
Ｆ_Ｍｉ：係留反力、
Ｆ_Ｈｉ ^（１）：線形波力及びモーメント
Ｆ_Ｈｉ ^（２）：長周期変動波力及びモーメント
Ｆ_Ｗｉ：風力及びモーメント
Ｆ_Ｃｉ：潮流力及びモーメント
である。 In the method of predicting fatigue damage of moored dolphin according to the present invention, it is preferable to predict the motion state of the floating body during the second step based on the following equation of motion:

However,
i = 1, 2, 6
m _ii (∞): additional mass and additional moment of inertia at infinite frequency,
F _Vi : viscous damping force and moment,
L _ii : Memory influence function,
F _Mi : mooring reaction force,
F _Hi ⁽¹⁾ : Linear wave force and moment F _Hi ⁽²⁾ : Long period fluctuation wave force and moment F _Wi : Wind force and moment F _Ci : Tidal force and moment.

但し、
Ｎ_ｉｉ(ω)：造波減衰力係数
である。 In the moored dolphin fatigue damage prediction method of the present invention, the memory influence function L _ii is preferably calculated based on the following equation:

However,
N _ii (ω) is a wave damping force coefficient.

  According to the present invention, by using a nonlinear time series simulation that takes into account the nonlinearity of the external force acting on the floating body and the nonlinear reaction force characteristics of the mooring dolphin, it is possible to more accurately predict the fatigue damage of the mooring dolphin, There is an effect that the long-term maintenance of the dolphin can be carried out smoothly.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1A is a plan view showing a floating body and a mooring dolphin according to this embodiment, and FIG. 1B is a side view of the floating body.
FIG. 2 is a perspective view showing the overall configuration of the mooring dolphin.
FIG. 3 is a detailed view of the mooring dolphin. (A) is a plan view, (B) is a side view, and (C) is a front view.

FIG. 1 shows a floating body (mega float) 10 according to the present embodiment. The floating body 10 has a rectangular plate shape extending in the arrow x direction and the y direction shown in FIG. The floating body 10 is disposed along a quay extending in the x direction. As shown in FIG. 1B, a curtain wall portion 11 that hangs downward (underwater) is formed on the lower end edge of the floating body 10 on the offshore side. The properties of the floating body 10 in this example are the quay side length L1 = 203.0 m, the offshore side length L2 = 201.5 m (nominal length 200 m), the width B = 100 m, the height D = 3 m, and the main part of the floating body The draft height d = 1 m, including the curtain wall portion d ′ = 2.5 m, the lateral bending stiffness is 2.037 × 10 ¹⁰ Nm, and the longitudinal bending stiffness is 1.656 × 10 ¹⁰ Nm. is there.

  On both sides of the floating body 10, a notch 13 is formed in a rectangular shape. A mooring dolphin 20 is disposed inside each notch 13. As shown in detail in FIGS. 2 and 3, the mooring dolphin 20 of this embodiment includes columnar main piles 21 a to 21 h (a total of eight) rising from the bottom of the water. The pair of main piles 21a and 21b, 21c and 21d, 21e and 21f, and 21g and 21h constitute four side surfaces of the jacket structure forming the mooring dolphin 20. The surface composed of the main piles 21a and 21b faces the bottom side of the notch 13 of the floating body 10, and the surface composed of the main piles 21c and 21d and 21e and 21f is the notch 13 of the floating body 10. (See FIG. 1). As shown in FIG. 2, a rectangular frame-shaped walkway 22 is provided near the upper ends of the main piles 21 a to 21 h, and handrails 24 are provided on both sides of the walkway 22.

  As shown in FIG.2 and FIG.3, the cross beam 23 is spanned between each adjacent main piles 21a-21h. A total of 16 of these cross beams 23 are bridged near the upper end in the height direction of the main piles 21a to 21h and near the center in the height direction. Furthermore, the column-shaped provisional pile 25 (a total of four) which stood | started up from the water bottom is provided inside each main pile 21a-21h (refer FIG. 2). And the well-shaped beam 27 built in the well shape spanned inside the main piles 21a-21h is arrange | positioned above these temporary piles 25 (refer FIG. 3 (A)). The well beam 27 is spanned across a total of two sets near the upper end in the height direction of the main piles 21a to 21h and near the center in the height direction.

  As shown in FIGS. 2 and 3C, between the main piles 21a and 21b, two vertical beams 28 are further bridged between the horizontal beams 23 connecting them. A hybrid fender 30 is attached to these vertical beams 28. The hybrid fender 30 includes a mooring force detection device 33 installed on a mounting plate fixed to both vertical beams 28. The mooring force detector 33 is provided with a constant reaction force type fender 35 and an air fender 37 that are connected in series. A connection plate 36 is interposed between the fenders 35 and 37, and an impact plate 39 is attached to the tip of the air fender 37. A stopper 36 a for preventing an excessive load from being applied to the hybrid fender 30 from the floating body 10 is formed on the connection plate 36.

  As shown in FIG. 3 (B), two vertical beams 29 are bridged between the upper and lower well beams 27 on the back side between the main piles 21c and 21d and 21e and 21f. Has been. A double fender 40 is attached to the vertical beams 29. The double fender 40 is provided on each of the main piles 21c and 21d and 21e and 21f (see FIGS. 3A and 3C), and both have the same configuration.

  As clearly shown in FIGS. 2 and 3A, the double fender 40 includes a mooring force detection device 43 installed on a mounting plate fixed to both the vertical beams 29. The mooring force detection device 43 has two constant reaction force type fenders 45 and 47 projectingly connected in series. An impact plate 49 is attached to the tip of these fenders 45 and 47. The impact plate 49 is formed larger than the impact plate 39 of the air fender 37 described above. The receiving plate 49 of each double fender 40 is also supported by a support member 53 fixed to the main piles 21 a to 21 h via the share chain 51.

  The mooring force detection device 33 of the hybrid fender 30 and the mooring force detection device 43 of the double fender 40 are connected to a control device. In this control device, the fatigue damage of the mooring dolphin 10 is predicted by the procedure shown in FIG. The mooring dolphin is greatly affected by nonlinear phenomena such as the nonlinear reaction force characteristics of the fender and the long-period motion of the floating body 10 in the horizontal plane. Unlike the conventional method that assumes that the extreme value distribution of stress in a short-term random wave is a Rayleigh distribution derived from linear theory, the method according to the present invention uses a nonlinear simulation described below to cause fatigue damage. It is a prediction.

Hereinafter, with reference to FIG. 4, the fatigue damage prediction method of a mooring dolphin is demonstrated.
FIG. 4 is a flowchart showing the procedure of the method for predicting the fatigue damage of moored dolphin according to the present embodiment.
As shown in FIG. 4, first, in step S1, natural environment conditions (waves, tidal currents, wind conditions) under the arrangement environment of the floating body 10 and the mooring dolphin 20 are captured, and the process proceeds to step S2. In step S2, a nonlinear time series simulation is performed on the motion state of the floating body 10 when the external environmental force based on the natural environmental conditions captured in step S1 is applied, and the process proceeds to step S3. In step S3, in accordance with the nonlinear time series simulation performed in step S2, the mooring reaction force time series data received by the floating body 10 from the mooring dolphin 20 is statistically processed, and frequency data about the load received by the mooring dolphin 20 itself is prepared. To do. Next, in step S4, an SN diagram (relationship between repeated external force and the number of repetitions until destruction) such as FIG. 7 described later is taken in, and the process proceeds to step S5.

  In step S5, the mooring dolphin 20 itself receives from the SN diagram fetched in step S4 and the statistical processing result of the mooring reaction force time-series data obtained in step S3, based on “Equation 9” described later. Calculate the load (degree of short-term fatigue damage). Next, in step S6, the long-term wave frequency is captured based on the long-term wave frequency table of “Table 1” described later, and the process proceeds to step S7. In step S7, the long-term fatigue damage of the moored dolphin 20 is predicted from the degree of short-term fatigue damage in step S5 and the long-term wave frequency in step S6.

に従うものとし、波高が０．２５ｍ〜３．２５ｍ、波周期が３．０秒〜１１．０秒までの範囲をとり得るものとする。なお、実際には、「表１」のデータに限らず、考慮対象となる海域に応じた波浪頻度表を用意する。波向きは、最も頻度が高い６３．８°（ＮＥ）とする。波スペクトルは、港湾域で広く使用されているブレッドシュナイダー光易型スペクトルとし、方向分布関数としては光易型を用いるものとする。なお、波の方向集中度パラメータは、東京湾で一般的な１０を用いるものとする。
潮流条件は、流向０°、流速０．５ノットとする。
風条件については、前述の波条件から予測する。風向は波向と同一とし、１つの波条件に対して時間ｔ_ｓが３時間分のシミュレーション計算を行なうものとする。 Hereinafter, the contents of each step in the flowchart (see FIG. 4) will be described in detail.
The natural environment conditions (wave power, tidal power, wind power) captured in step S1 are as follows.
The wave condition is a wave frequency table shown in the following “Table 1” in this embodiment.

And a wave height of 0.25 m to 3.25 m and a wave period of 3.0 seconds to 11.0 seconds. Actually, not only the data of “Table 1” but also a wave frequency table corresponding to the sea area to be considered is prepared. The wave direction is 63.8 ° (NE), which is the most frequent. The wave spectrum is a Bread Schneider light easiness spectrum widely used in harbor areas, and the light easiness type is used as a direction distribution function. The wave direction concentration parameter is assumed to be 10 which is common in Tokyo Bay.
The tidal conditions are a flow direction of 0 ° and a flow velocity of 0.5 knots.
The wind condition is predicted from the wave condition described above. Wind direction is the same as wave direction, it is assumed that the time t _s for a single wave conditions perform simulation calculation of three hours.

The contents of the nonlinear time series simulation performed in step S2 will be described.
First, a method for calculating the fluid force coefficient, wave external force and mooring reaction force characteristics of a floating body (mega float) as described above will be described.
As the fluid force coefficient, it is necessary to obtain an additional mass m _jj (ω), a wave-making damping force coefficient N _jj (ω), and a dimensionless viscous damping force coefficient α _j .
The additional mass m _jj (ω) and the wave-making damping force coefficient N _jj (ω) are obtained from numerical calculations based on the rigid body model, and are stored in a database for each oscillation frequency ω.
The dimensionless viscous damping force coefficient α _j can be obtained from a free oscillation test. This free oscillation test is a test for experimentally obtaining a damped oscillation waveform by forcibly displacing the floating body in the horizontal motion direction and then releasing it.

但し、
Ｍ：浮体の質量
ｍ_ｊｊ(ω_０ｊ)：水平面内動揺の付加質量
である。 This dimensionless viscous damping force coefficient α _j is defined as follows. That is, for the viscous damping force N _Vj, generally is proportional to the square of the velocity, in the case of those having a large submerged bottom as floating according to the present embodiment, proportional to the speed (d / dt) x _j To do. However, j = 1, 2, and 6 where j = 1 represents the forward / backward swing mode, j = 2 represents the left / right swing mode, and j = 6 represents the rotational swing mode. Here, if the characteristic frequency (equivalent natural frequency) of the floating body in the horizontal plane is ω _0j , the dimensionless viscous damping force coefficient α _j is expressed by the following equation (5):

However,
M: Mass of floating body m _jj (ω _0j ): Additional mass of fluctuation in a horizontal plane.

  The wave external force can be evaluated using the water level around the floating body (linear and long-period fluctuating wave force) because the draft as in the present embodiment has a much smaller draft than the wavelength.

The mooring reaction force characteristic is determined based on FIG. 5 and “Equation 6” described below.
FIGS. 5A and 5B are graphs showing reaction force characteristics of the synthetic fenders (respectively hybrid fender and double fender) according to this example.
5A and 5B, the vertical axis represents the mooring reaction force (unit kN), and the horizontal axis represents the strain (unit%). The strain (%) on the horizontal axis represents the ratio of the displacement amount to the fender height as the strain amount.

但し、
ｌ_０：浮体の回転中心から二重フェンダーと浮体の接点までの距離
であり、指数の１、２、６については、前述の通り、１が前後揺モード、２が左右揺モード、６が回頭揺モードをそれぞれ表す。 As described above, the mooring dolphin 20 of the present embodiment has a synthetic fender (the x-direction hybrid fender 30 (one piece) and the y-direction double fender 40 (two pieces) in FIG. 1). When the characteristics shown in the graphs of FIGS. 5A and 5B are expressed by f _A and f _B , respectively, the mooring reaction force characteristics F _M1 , F _M2 , and F _M6 are expressed by the following expression “Equation 6”:

However,
l ₀ : Distance from the center of rotation of the floating body to the contact point between the double fender and the floating body. As for the indices 1, 2, and 6, as described above, 1 is the forward / backward swing mode, 2 is the left / right swing mode, and 6 is the turning Represents each rocking mode.

Next, the principle of predicting the motion state of the floating body when the above-described environmental external force is applied (time domain motion equation of the floating body in the horizontal plane) will be described.
It is assumed that the in-plane rigidity of the floating body is sufficiently large, and the fluctuation in the horizontal plane of the floating body is a three-degree-of-freedom rigid body motion. In this case, the equation of motion in the horizontal plane of the floating body is expressed by the following expression “Equation 7” using the fluid force coefficient, the wave external force, and the mooring reaction force characteristics described above. By solving this “Equation 7” in the time domain, the response value (swing in the horizontal plane and mooring force) is obtained every moment.

但し、
ｉ＝１、２、６
ｍ_ｉｉ(∞)：周波数無限大での付加質量及び付加慣性モーメント、
Ｆ_Ｖｉ：粘性減衰力及びモーメント、
Ｌ_ｉｉ：メモリー影響関数、
Ｆ_Ｍｉ：係留反力、
Ｆ_Ｈｉ ^（１）：線形波力及びモーメント
Ｆ_Ｈｉ ^（２）：長周期変動波力及びモーメント
Ｆ_Ｗｉ：風力及びモーメント
Ｆ_Ｃｉ：潮流力及びモーメント
である。

However,
i = 1, 2, 6
m _ii (∞): additional mass and additional moment of inertia at infinite frequency,
F _Vi : viscous damping force and moment,
L _ii : Memory influence function,
F _Mi : mooring reaction force,
F _Hi ⁽¹⁾ : Linear wave force and moment F _Hi ⁽²⁾ : Long period fluctuation wave force and moment F _Wi : Wind force and moment F _Ci : Tidal force and moment.

但し、
Ｎ_ｉｉ(ω)：造波減衰力係数
である。 The memory influence function L _ii in “Equation 7” can be calculated based on the following equation “Equation 8”:

However,
N _ii (ω) is a wave damping force coefficient.

The statistical processing of time series data in step S3 will be described.
The statistical processing of the time series data in the present example was performed as shown in the following (1) to (3).
(1) beta direction (β = x, y) for each, determine the extreme frequency number n _.beta.i per reaction force level F _.beta.i.
(2) Consider the reaction force in both the plus and minus directions for the left / right direction.
(3) The extreme frequency number is counted for the absolute value of the reaction force.

The SN diagram captured in step S4 will be described.
FIG. 6 is a diagram illustrating a structural analysis model of a mooring dolphin according to the present embodiment.
FIG. 7 is a graph showing an example of the evaluation result of the SN characteristic using the structural analysis model of FIG.
In this example, the SN characteristics of the moored dolphin were evaluated by creating a finite element model shown in FIG. In this example, the main pile is considered as the point where the maximum stress is generated when an external force is applied in the x and y directions indicated by arrows in FIG. Lattice points (lattice points LP1, LP2, LP3, LP4 in FIG. 6) of 21a ', 21b', 21g ', 21h' and the lower horizontal beam 23 'and the well beam 27' connecting them are extracted and S -N characteristics were determined. In FIG. 6, the reference numeral 30 ′ corresponds to the hybrid fender described above, and the reference numeral 40 ′ corresponds to the double fender described above.

FIG. 7 is an SN diagram obtained for the lattice point LP4 on the main pile 21a ′ among the lattice points described above. Specifically, this graph was obtained as follows (1) and (2).
(1) A load is repeatedly applied to each fender in increments of 98 kN, and the stress fluctuation width acting on each node is obtained by FEM analysis. In this case, the standard value of the stress concentration factor published by the Coastal Development Technology Center, “Jacket Method Technical Manual”, published in 2000 was used.
(2) The allowable number of repetitions for the stress fluctuation range was determined with reference to page 39 of the aforementioned “Jacket Construction Method Technical Manual”.

但し、
β＝ｘ、ｙ
Ｎ_βｉ：Ｆ_βｉに対する許容繰り返し数
であり、Ｎ_βｉのデータについては、前述した図７等の各格子点におけるＳ−Ｎ線図を用いるものとする。 The calculation of the degree of short-term fatigue damage in step S5 will be described.
The short-term fatigue damage degree in step S5 is calculated based on the following equation “Equation 9” using a minor rule. The calculation results are compiled into a database for each wave height and period.

However,
β = x, y
N _βi : The allowable number of repetitions for F _{βi, and} for the data of N _βi , the SN diagram at each lattice point in FIG.

  It is assumed that the long-term wave frequency table fetched in step S6 is based on the wave frequency table shown in the aforementioned “Table 1”.

但し、
ｆ_α（Ｈ_ｊ、Ｔ_ｋ）：α年間に、有義波高Ｈ_ｊ、平均波周期Ｔ_ｋである海象が発生する延べ時間
である。この延べ時間ｆ_α（Ｈ_ｊ、Ｔ_ｋ）は、ステップＳ６で取り込んだ長期波浪頻度表から求めることができる。 The calculation of the degree of long-term fatigue damage in step S7 will be described.
The long-term fatigue damage level in step S7 was calculated based on the following equation “Equation 10” using the database in step S5 described above:

However,
f _α (H _j , T _k ): This is the total time that a sea state having a significant wave height H _j and an average wave period T _k is generated in α year. The total time f _α (H _j , T _k ) can be obtained from the long-term wave frequency table captured in step S6.

Next, a water tank model test conducted by the present inventors will be described.
This aquarium model test was conducted using an offshore structure test aquarium (length 40 m × width 27 m) in the National Maritime Research Institute. The scale of the test model is 1/50, and its properties are nominal length 4000 mm, width B = 2000 mm, height D = 70 mm, draft height d = 20 mm of the main part of the floating body, draft height including curtain wall part d ′ = 50 mm, and the lateral bending rigidity and the longitudinal bending rigidity are both 715 Nm.

The main structure of the model used in this test (water tank experimental floating body) was an aluminum flat plate with a thickness of 5 mm, and urethane foam was bonded as a buoyant material to the lower surface of the aluminum flat plate to match the draft with the actual machine. A wave energy absorbing device (curtain wall) having a depth of 3 cm and a slit width of 0.5 cm was attached to the side surface of the model. Furthermore, the seabed topography of the installation sea area was reproduced using aluminum plates and steel materials.
As a mooring device for mooring a floating tank for aquarium experiment, a model having a fender reaction force characteristic as shown in FIG.

FIG. 8 is a diagram for explaining measurement positions in the aquarium model test according to the present embodiment.
FIG. 8 shows the installation position of the measurement device corresponding to each measurement item. Each measurement item and its measuring device
・ Horizontal displacement of floating body model: Position sensor ・ Vertical displacement and fender displacement of floating body model: Potentiometer ・ Acceleration of floating body model: Triaxial accelerometer ・ Incident wave height: Servo wave height meter ・ Mooring reaction force: Load cell type force gauge -Relative water level around the floating model: Capacitance wave height meter-Strain of the floating model: As shown in the strain gauge (see lower side of Fig. 8).

  The aquarium model test assumes three conditions: (1) when the water is open (the water depth is 20 m, equivalent to a real machine), (2) when the quay is a flat plate, and (3) when the quay is a cylindrical caisson as in the actual machine. I did it. About the above-mentioned wave energy absorber, about each of these (1)-(3) states, it measured with and without the wave energy absorber. As the wave energy absorbing device, a curtain wall with a slit (corresponding to an actual machine having a width of 0.25 m) and a device without a slit were prepared.

「表２」には、水槽模型試験の計測条件が示されている。この「表２」中の不規則波とは、左から順に、設置海域における２、１０、５０年確率波である。さらに、波向きは設置海域における主方向である６３．８°とした。なお、波向きχの定義は、図８の上側に示す角度を意味する。さらに、この水槽模型試験の他に、水槽実験用浮体の自由動揺試験も併せて行なった。

“Table 2” shows the measurement conditions of the water tank model test. The irregular waves in “Table 2” are 2, 10, and 50-year probability waves in the installation sea area in order from the left. Furthermore, the wave direction was set to 63.8 ° which is the main direction in the installation sea area. The definition of the wave direction χ means the angle shown on the upper side of FIG. Furthermore, in addition to this water tank model test, a free rocking test of the water tank experimental floating body was also performed.

FIG. 9 is a graph showing an example of time-series data of fender displacement in an irregular wave (10-year probability wave) in the water tank model test according to the present embodiment.
In the time-series graph shown in FIG. 9, the vertical axis represents fender displacement (unit m), and the horizontal axis represents time (unit sec). The following “Table 3” shows the maximum displacement (significant wave height 2.6 m, wave period 5.5 sec) of each fender in this irregular wave (10-year probability wave).

Next, in response to such an irregular wave (10-year probability wave) aquarium model experiment, nonlinear time series simulation is performed based on the flowchart of FIG. 4 described above, and statistical processing of the obtained mooring reaction force time series data is performed. To estimate the standard deviation and maximum value of the mooring reaction force. An example of the estimation result is shown in “Table 4” below.

  In this “Table 4”, the mooring reaction force number (No.) corresponds to the fender number in FIG. 8 described above. All values in “Table 4” are actual machine conversion values, and the comparative case is a case where the quay is a cylindrical caisson and there is a wave energy absorber with a slit. The estimation result in this case is No. Although there is a slight difference from the measurement result of the mooring reaction force of No. 5, No. 5 has the largest mooring reaction force. Regarding 1 mooring reaction force, the estimation result and the measurement result are in good agreement, indicating that this estimation method is effective. Note that the results of the above-described free oscillation test are used for the viscous damping force coefficient of the floating body in the horizontal plane.

Next, the actual sea area verification experiment conducted by the present inventors will be described.
In this experiment, the natural environment, floating body behavior, and the like were measured using a wave height meter, anemometer, KGPS, accelerometer, water pressure gauge, strain gauge, and the like on the floating body 10 in FIG.
FIG. 10 is a diagram for explaining a measurement position in the actual sea area verification experiment according to the present embodiment.
FIG. 11 is a graph showing a comparison between the behavior of the floating body obtained from the GPS measurement value in the actual sea area demonstration experiment and the behavior of the floating body predicted using the fatigue damage prediction method of the present invention. The vertical axis of (A) indicates the yaw angle (unit deg), the horizontal axis indicates time (unit: sec), the vertical axis of (B) indicates the swing of the floating body (unit: mm), and the horizontal axis indicates time (unit: sec). .

  FIG. 10 shows the installation positions of the measuring instruments on the floating body in the actual sea area demonstration experiment. In this experiment, water pressure gauges (P1 to P13: 13 in total), relative water level gauges (RW1 to RW5: 5 in total), anemometers (2 in total), accelerometers (G1 to G12: 12 in total), KGPS (KGP0 to KGP2: a total of three), and a wave height meter, a strain gauge, or the like is used as necessary.

  As is clear from the experimental results shown in FIGS. 11A and 11B, the prediction results of the floating body in the horizontal plane according to the present invention (the graph indicated by the dotted line) and the floating body actually measured by GPS in the actual sea area demonstration experiment When compared with the behavior in the horizontal plane (graph indicated by the solid line), it can be seen that the two curves are in good agreement. Thus, since the behavior of the floating body can be accurately predicted, it can be said that the fatigue damage prediction of the moored dolphin can be more accurately performed. Therefore, in practice, a portion likely to cause damage to the moored dolphin can be found in advance and appropriately repaired, so that it can be said that long-term maintenance of the moored dolphin can be carried out smoothly.

FIG. 1A is a plan view showing a floating body and a mooring dolphin according to this embodiment, and FIG. 1B is a side view of the floating body. It is a perspective view which shows the whole structure of the mooring dolphin. It is detail drawing of the mooring dolphin. (A) is a plan view, (B) is a side view, and (C) is a front view. It is a flowchart which shows the procedure of the fatigue damage prediction method of the mooring dolphin which concerns on a present Example. It is a graph which shows the reaction force characteristic of the synthetic fender which concerns on a present Example (each hybrid fender and double fender). It is a figure which shows the structural analysis model of the mooring dolphin which concerns on a present Example. It is a graph which shows an example of the evaluation result of SN characteristic using the structural analysis model of FIG. It is a figure explaining the measurement position in the tank model test concerning a present Example. It is a graph which shows an example of the time series data of the fender displacement in the irregular wave (10-year probability wave) in the water tank model test concerning this example. It is a figure explaining the measurement position in the actual sea area verification experiment which concerns on a present Example. It is a graph which compares and shows the behavior of the floating body calculated | required from the measured value of GPS in this real sea area verification experiment, and the behavior of the floating body estimated using the fatigue damage prediction method of this invention. It is a schematic diagram which shows an example of the method of mooring the tank which stockpiles oil offshore.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Floating body (Mega float) 11 Curtain wall part 13 Notch part 20 Mooring dolphin 21a-21h Main pile 23 Horizontal beam 25 Suspension pile 27 Well-shaped beam 28, 29 Vertical beam 30 Hybrid fender 33 Mooring force detection apparatus 35 Constant reaction force type Fender 37 Air fender 39 Receiving plate 40 Double fender 43 Mooring force detection device 45, 47 Constant reaction force type fender 49 Receiving plate

Claims (3)

A method for predicting fatigue damage of a mooring dolphin mooring a floating body on a liquid surface,
Incorporating natural environmental conditions under the arrangement environment of floating bodies and mooring dolphin (first step),
Predict the state of motion of the floating body when an external environmental force is applied based on this natural environmental condition (second step)
The mooring reaction force that the floating body receives from the mooring dolphin according to this movement state is predicted (third step),
Predict the load received by the mooring dolphin itself from this mooring reaction force (4th step)
Based on the load received by the mooring dolphin itself, predict the degree of fatigue at a specific location in the mooring dolphin (fifth step),
A fatigue damage prediction method for a moored dolphin, wherein the motion state of the floating body during the second step is predicted using a nonlinear time series simulation. The method for predicting fatigue damage of a moored dolphin according to claim 1, wherein the motion state of the floating body during the second step is predicted based on the following equation of motion:

However,
i = 1, 2, 6
m _ii (∞): additional mass and additional moment of inertia at infinite frequency F _Vi : viscous damping force and moment L _ii : memory influence function F _Mi : mooring reaction force F _Hi ⁽¹⁾ : linear wave force and moment F _Hi ⁽²⁾ : Long-period fluctuation wave force and moment F _Wi : Wind force and moment F _Ci : Tidal force and moment 3. The method for predicting fatigue damage of moored dolphin according to claim 2, wherein the memory influence function L _ii is calculated based on the following equation:

However,
N _ii (ω): Wave damping force coefficient

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