JP4508556B2 - Monitoring system for liquefied gas carrier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a monitoring system for a liquefied gas carrier, and more particularly to a monitoring system for a liquefied gas carrier that evaluates and monitors the remaining life of a liquefied gas tank.
[0002]
[Prior art]
The liquefied gas is transported by sea by a liquefied gas carrier ship, in particular, an independent tank carrier ship. The independent tank type liquefied gas carrier has a liquefied gas tank for storing the liquefied gas at a low temperature. The liquefied gas tank is formed in a spherical shell structure in order to give sufficiently large strength to the internal pressure. An aluminum alloy is used in the liquefied gas tank to ensure low temperature strength. The liquefied gas tank is covered with a heat insulating layer. The temperature of the spherical surface of the spherical tank, which is the inner surface of the heat insulating layer, is maintained at about -160 degrees.
[0003]
A hull that tilts two-dimensionally in response to waves is subjected to pressure on the inside and outside of the hull due to the tilt of the hull and the inertial interference of the inboard fluid such as ballast water . A technique for detecting such pressure is known from Japanese Patent Application Laid-Open No. 5-238473. An inertial force acts on the tank itself in the independent tank of the liquefied gas carrier ship, and a mutual interference force acts between the hull and the tank. The structure of a hull that receives waves is bent by the external force received from the waves. In particular, the bending force is generated in synchronization with the wave period on the vertical center plane including the longitudinal line, and the periodic bending moment is continuously received. Due to such a bending moment, a forced displacement is generated at the joint portion between the hull and the tank, and a mutual interference force is generated between the hull and the tank. Stress is generated in the independent tank by the inertial force and the mutual interference force acting on the tank. The number of occurrences of such stress has a strong correlation with the life of the independent tank. A technique for predicting the remaining life of a hull by detecting stress is known in the following patent publication. A frequency distribution table, which is a combination of the number of times subjected to stress and its size, is expected to provide an important numerical material for the estimation of its remaining life. Measurement of stress is indispensable for estimating the remaining life of an independent tank. A strain gauge is used for measuring the stress. It is difficult to measure the stress by directly attaching a strain gauge to the spherical surface of about −160 degrees of the liquefied gas tank and measuring the stress. For these reasons, it has been difficult to predict the remaining life of a liquefied gas tank based on stress measurement.
[0004]
Establishment of technology to predict the remaining life with high accuracy by realizing stress measurement is required.
[0005]
[Patent Document 1]
Japanese Patent No. 3132180 [0006]
[Problems to be solved by the invention]
An object of the present invention is to provide an independent tank type liquefied gas carrier monitoring system capable of establishing a technique for predicting the remaining life with high accuracy by realizing stress measurement.
[0007]
[Means for Solving the Problems]
Means for solving the problem is expressed as follows. Technical matters appearing in the expression are appended with numbers, symbols, etc. in parentheses. The numbers, symbols, and the like are technical matters constituting at least one embodiment or a plurality of embodiments of the present invention or a plurality of embodiments, in particular, the embodiments or examples. This corresponds to the reference numbers, reference symbols, and the like attached to the technical matters expressed in the drawings corresponding to. Such reference numbers and reference symbols clarify the correspondence and bridging between the technical matters described in the claims and the technical matters of the embodiments or examples. Such correspondence or bridging does not mean that the technical matters described in the claims are interpreted as being limited to the technical matters of the embodiments or examples.
[0008]
The monitoring system for a liquefied gas carrier according to the present invention includes a strain gauge (7) that is arranged at a specific portion of a support structure (6) that supports an independent tank type liquefied gas tank (1) and measures a first time-series stress (18). And an accelerometer (9) which is arranged on the support structure (6) and measures time-series three-dimensional acceleration of a specific part, and the time-series three-dimensional acceleration and the first time-series stress (18) are recorded in time series. 1 recorder and a computer. The calculator calculates a second time series stress (24) of an arbitrary part of the liquefied gas tank (1) based on the time series three-dimensional acceleration and the first time series stress (18); The second recorder (23) records the distribution of the stress range long-term frequency of an arbitrary part based on the second time series stress (24). The distribution of the stress range long-term frequency provides important judgment material as an effective numerical basic data not only for estimating the remaining life of a liquefied gas tank but also for estimating the remaining life of a tanker carrying a liquefied gas tank. . The distribution of the stress range long-term frequency has the generality that the remaining life at an arbitrary position can be predicted with high accuracy.
[0009]
Since the second time-series stress (24), which is the stress at an arbitrary position of the independent tank type liquefied gas tank (1), can be calculated from the actually measured stress (18) at a plurality of specific parts, the stress at the arbitrary position. There is no need to actually measure. The second time series stress (24) is recorded as a distribution of the stress range long-term frequency, and the remaining life can be estimated based on the distribution.
[0010]
The second recorder creates a correspondence table indicating the correspondence between the partial stress range in which the stress range is divided into k pieces and the frequency of the second time series stress corresponding to the range. The calculator further forms an integrator. The frequency is represented by ni, and the allowable number of repetitions of the second time series stress (24) corresponding to the partial stress range is represented by Ni. The integrator calculates the remaining life evaluation index corresponding to the actual measurement value represented by Σ (i = 1 to k) (ni / Ni). The remaining life can be estimated based on an actually measured value corresponding remaining life evaluation index. The calculator further forms an evaluator. The evaluator evaluates and estimates the remaining life based on a comparison between the actual value corresponding remaining life evaluation index and the design time calculated remaining life evaluation index obtained by calculation at the time of designing the liquefied gas tank. Through actual measurement and calculation, the remaining life, which has been impossible or inaccurate in the past, can be estimated with high accuracy, in real time, or on a regular basis, using design values and real-time measurement values.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Corresponding to the figure, in the embodiment of the monitoring system for a liquefied gas carrier ship according to the present invention, a spherical liquefied gas tank is mounted on the hull. The plurality of spherical liquefied gas tanks 1 are arranged in the longitudinal direction of the hull as shown in FIG. The hull structure of a hull that periodically receives waves bends mainly by receiving a longitudinal bending moment. The liquefied gas tank 1 is supported by the hull structure that receives the bending force.
[0012]
As illustrated in FIG. 2, the liquefied gas tank 1 includes a spherical tank body 2 and a spherical thermal insulating layer 3 that covers the spherical tank body 2. The liquefied gas tank 1 is entirely covered with an outer protective structure 4. The liquefied gas tank 1 is supported by a support structure (skirt) 6 structured on the upper surface side of the hull basic structure 5.
[0013]
FIG. 3 shows a distributed arrangement of accelerometers and strain gauges. No. 5 which is five liquefied gas tanks 1. 1 tank 1-1, No. 1 2 tank 1-2, No. 2 3 tank 1-3, no. 4 tank 1-4, no. The five tanks 1-5 are arranged from the bow side toward the stern side. Tanks that are frequently subjected to stronger stress are no. 2 tanks 1-2.
[0014]
Four strain gauges and four accelerometers are arranged in a distributed manner. The first strain gauge 7-1 is No. It is arrange | positioned at the bow side of the skirt of 2 tanks 1-2. The second strain gauge 7-2 is No. It is arrange | positioned at the stern side of the skirt of 2 tanks 1-2. The third strain gauge 7-3 is No. It is arranged on the starboard side of the skirt of the two tanks 1-2.
The fourth strain gauge 7-4 is No. It is arranged on the port side of the skirt of the two tanks 1-2.
[0015]
The 1st accelerometer 9-1 is arrange | positioned in the approximate center position of the hull 1, and measures the vertical direction acceleration of a midship. The 2nd accelerometer 9-2 is arrange | positioned in the approximate center position of the hull 1, and measures the left-right direction acceleration of a midship. The 3rd accelerometer 9-3 is arrange | positioned in the approximate center position of the hull 1, and measures the longitudinal acceleration of the midship. The fourth accelerometer 9-4 measures the longitudinal acceleration of the bow part of the hull 1.
[0016]
FIG. 4 shows the measurement system 11. As shown in FIG. 2, the liquefied gas tank 1 forms a safety section 12 that is a residential area on the stern side. A personal computer rack 13 is safely arranged in the safety section 12. A personal computer 14, an amplifier unit 15, and an MO unit 16 are safely arranged in the personal computer rack 13.
[0017]
The four strain-corresponding electrical signals output from the four strain gauges 7-1, 2, 3, and 4 are respectively input to the amplifier unit 15 via the Zener barrier (intrinsic safety protection) 17. The four distortion-corresponding electrical signals output from the four accelerometers 9-1, 2, 3, 4 are respectively input to the amplifier unit 15 via the Zener barrier (intrinsic safety protection) 17.
[0018]
The personal computer 14 mainly manages and controls the recording of the MO unit 16. The mathematical analysis calculation shown in FIG. 5 is in principle performed by a land computer 14 (not shown). The computer has an FEM analysis computer section 22 as shown in FIG. Corresponding to the measured stress 18 at four sites corresponding to the strain measured by the four strain gauges 7-1, 2, 3, 4 and the measured acceleration 19 measured by the four accelerometers 9-1, 2, 3, 4 Based on the external force, the stress calculation program of the FEM analysis computer portion 22 calculates the stress of an arbitrary portion of the spherical tank main body 2 shown in FIG.
[0019]
The computer has a stress range long-term frequency distribution recorder 23 for recording the stress range long-term frequency distribution. The stress calculation result (FEM result) 24 calculated by the FEM computer portion 22 is input to the stress range long-term frequency distribution recorder 23 together with the measured stress 18 and the measured acceleration 19. The stress range long-term frequency distribution recorder 23 updates the actual stress range long-term frequency distribution 25 based on the actual stress 18, actual acceleration 19, and stress calculation result 24. The actually measured stress range long-term frequency distribution 25 is a frequency distribution table in which the correspondence between the stress range range and the measured number of repetitions (frequency number) is recorded. The actually measured stress is one of the four strains measured by the four strain gauges 7 or a strain at a specific location functionally corresponding to the four strains. The calculated stress is the above-described stress calculation result 24 calculated by the FEM computer portion 22 with respect to a specific portion of the liquefied gas tank 1. The actually measured stress range long-term frequency distribution 25 is an exponential curve as shown in FIG. The horizontal axis of the graph corresponds to the number of encounters described above.
[0020]
In such a frequency distribution table, the stress range is divided into k blocks.
The number of repetitions corresponding to each block is represented by ni. Based on the material properties of each block, the allowable number of repetitions allowed for the block corresponding to each stress is represented by Ni. The integrator calculates an actually measured remaining life evaluation index Df based on the stress frequency distribution table. The actually measured remaining life evaluation index Df is expressed by the following equation called a minor rule. :
Df = Σ (i = 1 to k) ni / Ni
Example frequency distribution:
Stress block Actual measurement frequency Allowable number of repetitions 0kg / mm2-1kgmm2 n1 N1
1kg / mm2-2kgmm2 n2 N2
2kg / mm2-3kgmm2 n3 N3
... ... ...
(K-1) kg / mm2 to kgmm2 nk Nk
[0021]
FIG. 6 shows a stress calculation flow for calculating the stress at an arbitrary position. Three accelerations acting on the hull center position are measured by the four accelerometers (step S1). The three accelerations are three-dimensional accelerations Az, Ay, Ax in the vertical direction, the front-rear direction, and the left-right direction. Next, in step S2, ternary distortions σAz, σAy, and σAx are calculated by the following equation by the structural analysis program for each of the four strain measurement points of the skirt.
σAz = Cz · Az
σAy = Cy · Ay
σAz = Cz · Az
Here, the coefficients Cz, Cy, Cx are physical constants such as material constants and structural constants that can be obtained in advance.
[0022]
Independently of steps S1 and S2, the stress of the skirt is measured in step S3, and the measured stress σ and the three component strains σAz, σAy, σAx perform the hull bending-induced stress calculation step S4. Is input. In step S4, a stress (mutual interference force) σM caused by the hull bending is calculated by the following equation.
σM = σ− (σAz + σAy + σAx)
[0023]
From σM, the mutual interference force (Ni1, Ni2) between the tank and the hull is calculated by the FEM computer portion 22 in step S5 as the above-described calculated stress.
Ni1 = Ni1′cos (2θ)
Ni2 = Ni2'sin (2θ)
Next, in step S5, the FEM computer portion 22 calculates the stress at an arbitrary position of the tank (example: the aforementioned portion 21) based on the already obtained Ni1, Ni2, Az, Ay, Ax. . In step S6, the stress range long-term frequency distribution recorder 23 calculates the actual stress range long-term frequency distribution 25 based on the mutual interference forces Ni1 and Ni2. The remaining life evaluation index Df is calculated based on the actual stress range long-term frequency distribution 25.
[0024]
As shown in FIG. 5 (a), the theoretical stress range is long-term based on the stress analysis result 26 at the time of design and the long-term distribution shape (exponential distribution) theoretically given, with the North Atlantic Ocean having a severe sea condition as the design condition. The frequency distribution 27 is calculated at the time of hull design. The theoretical stress range long-term frequency distribution 27 is defined by the stress of a specific part of the tank / the stress of the representative part of the hull), similarly to the actual stress range long-term frequency distribution 25. In the calculation of the theoretical stress range long-term frequency distribution 27 and the actual measurement stress range long-term frequency distribution 25, the tank specific portion and the representative portion of the hull are both the same portion for the same hull.
[0025]
As shown in FIG. 5A, the theoretical stress range long-term frequency distribution 27 in which the maximum value corresponding to the North Atlantic oceanographic condition is used is larger in all ranges than the actually measured stress range long-term frequency distribution 25. The remaining life evaluation index Df is calculated from the measured stress range long-term frequency distribution 25 and the material constant of the evaluation target member, and reaches the estimated life at 1.0. Since the reciprocal of the remaining life evaluation index Df based on the actual measurement result is proportional to the estimated life based on the actual measurement value, the remaining life of the ship can be estimated based on the remaining life evaluation index Df.
[0026]
【The invention's effect】
The monitoring system for a liquefied gas carrier according to the present invention can evaluate the remaining life by measuring stress.
[Brief description of the drawings]
FIG. 1 is a front view showing an application target of a monitoring system for a liquefied gas carrier according to the present invention.
2 is a side sectional view of FIG. 1. FIG.
FIG. 3 is a cross-sectional plan view of FIG. 1;
FIG. 4 is a circuit block diagram showing an embodiment of a monitoring system for a liquefied gas carrier according to the present invention.
FIG. 5 is a calculation flow diagram showing an embodiment of a monitoring method for a liquefied gas carrier according to the present invention.
FIG. 6 is a flowchart showing a calculation flow.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Liquefied gas tank 6 ... Support structure 7 ... Strain meter 14 ... Calculator 16 ... Recorder 18 ... 1st time series stress 21 ... Site | part 22 ... Stress calculator 23 ... Recorder 24 ... 2nd time series stress

Claims (7)

A strain gauge that is arranged on a support structure that supports an independent liquefied gas tank of a liquefied gas carrier, and that measures actual stress;
An accelerometer that is arranged in the hull of the liquefied gas carrier ship and that measures the measured acceleration applied to the hull;
The independent liquefied gas tank monitoring comprising: a computer that calculates a mutual interference force that is a stress applied to the independent liquefied gas tank by bending the hull by subtracting a stress based on the strain caused by the measured acceleration from the measured stress. system. The monitoring system for an independent liquefied gas tank according to claim 1, wherein the calculator calculates a time series stress applied to the independent liquefied gas tank based on the measured acceleration and the mutual interference force. Furthermore, it comprises a recorder that records the measured acceleration and the measured stress in time series,
The recorder further records the distribution of the stress range long-term frequency of the time series stress and corresponds to the partial stress range in which the stress range is divided into k pieces (k is an integer of 2 or more) and the partial stress range. The monitoring system for an independent liquefied gas tank according to claim 2, wherein a correspondence table showing a correspondence with the frequency of the time series stress is created. The calculator further comprises an integrator,
The frequency is represented by ni, the allowable number of repetitions of the time series stress corresponding to the partial stress range is represented by Ni,
The integrator has the following formula:
Σ (i = 1 to k) (ni / Ni)
The monitoring system for an independent liquefied gas tank according to claim 3, wherein the remaining life evaluation index corresponding to an actual measurement value represented by the formula is calculated, and the remaining life is estimated based on the remaining life evaluation index corresponding to the actual measurement value. The calculator further forms an evaluator;
The evaluator evaluates and estimates the remaining life based on a comparison between the measured value-corresponding remaining life evaluation index and a design time calculated remaining life evaluation index obtained by calculation at the time of designing the liquefied gas tank. 4. Monitoring system for liquefied gas carriers.   A liquefied gas carrier ship comprising the hull and carrying the independent liquefied gas tank monitored by the monitoring system according to any one of claims 1 to 5. Measuring the measured stress of the support structure that supports the independent liquefied gas tank of the liquefied gas carrier;
Measuring the actual acceleration applied to the hull of the liquefied gas carrier; and
A method for monitoring an independent liquefied gas tank, comprising: calculating a mutual interference force, which is a stress applied to the independent liquefied gas tank by bending of the hull, by subtracting a stress based on a strain caused by the measured acceleration from the measured stress. .

Images