System and method for estimating state of marine liquefied gas tank

Abstract

To predict state of a liquefied gas tank for vessel at high accuracy.SOLUTION: A system (1) for estimating state of a liquefied gas tank (7) installed on a vessel (3) includes: a measuring unit (31) including a measuring instrument (39) for measuring state regarding strength of the liquefied gas tank (7); a calculation unit (33) for calculating the state regarding the strength of the liquefied gas tank (7) by a preliminary analysis model; a data assimilation unit (35) for updating a prior analysis model by data assimilation using the measurement result acquired by the measuring unit (31); and an evaluation unit (37) for evaluating state of the liquefied gas tank (7) based on the calculation result outputted from the calculation unit (33).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a system and method for estimating the condition of a marine liquefied gas tank. [Background technology]

[0002] Carrier ships equipped with liquefied gas tanks have been used to transport liquefied gases such as liquefied natural gas and liquefied hydrogen (see, for example, Patent Document 1). In general, maintenance of liquefied gas tanks for ships that are operated for long periods of time, such as several decades, is performed as post-fault maintenance, in which periodic inspections are performed to check for damage due to fatigue, and repair work is carried out as necessary. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-004382 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in order to reliably transport cryogenic liquefied gas, a high level of reliability is required for the tanks, so it is preferable to be able to predict the occurrence of tank damage in advance. However, it is difficult to actually inspect tanks that have been installed on ships for a long period of time in a timely manner. Therefore, a means is needed that can predict the strength condition of the tanks with high accuracy.

[0005] In order to solve the above problems, an object of the present invention is to provide a system and method that can predict the condition of a marine liquefied gas tank with high accuracy. [Means for solving the problem]

[0006] In order to achieve the above object, a marine liquefied gas tank state estimation system according to the present invention comprises: A system for estimating a state of a liquefied gas tank installed on a ship, comprising: A measuring unit including a measuring instrument for measuring a condition related to the strength of the liquefied gas tank; a calculation unit for calculating the strength-related condition of the liquefied gas tank by a pre-analysis model; a data assimilation unit for updating the pre-analysis model by data assimilation using measurement results acquired by the measurement unit; an evaluation unit for evaluating a state of the liquefied gas tank based on a calculation result output from the calculation unit; Equipped with.

[0007] Further, the marine liquefied gas tank state estimating method according to the present invention comprises the steps of: A method for estimating a state of a liquefied gas tank installed on a ship, comprising: Measuring a condition related to the strength of the liquefied gas tank; calculating the strength-related condition of the liquefied gas tank by a pre-analysis model; updating the pre-analysis model by data assimilation using measurement results acquired by the measurement unit; Evaluating a state of the liquefied gas tank based on the calculation result output from the calculation unit; and Includes.

[0008] With this configuration, not only can the state of the liquefied gas tank be estimated in advance through calculations using a pre-analysis model, but data assimilation using measurement results of the liquefied gas tank can bring the pre-analysis model closer to the liquefied gas tank, which is the actual subject of estimation, thereby enabling highly accurate estimation. Effect of the Invention

[0009] As described above, the system and method according to the present invention make it possible to predict the condition of a marine liquefied gas tank with high accuracy. [Brief description of the drawings]

[0010] [Figure 1] 2, showing a schematic configuration of a marine liquefied gas tank state estimation system according to one embodiment of the present invention, and a liquefied gas tank and a liquefied gas storage ship to which this system is applied. [Diagram 2] FIG. 2 is a vertical cross-sectional view showing a schematic configuration of the liquefied gas tank and the liquefied gas storage ship of FIG. [Diagram 3] FIG. 3 is a longitudinal sectional view showing a schematic structure of a liquefied gas tank and a liquefied gas storage vessel according to a modified example of the embodiment of FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of the liquefied gas tank and the liquefied gas storage ship in FIG. 3. [Diagram 5] FIG. 2 is a flow chart showing a marine liquefied gas tank state estimating method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Fig. 1 shows a liquefied gas storage ship 3, which is a ship to which a marine liquefied gas tank state estimation system (hereinafter simply referred to as "state estimation system") 1 according to one embodiment of the present invention is applied. As shown in Fig. 2, the liquefied gas storage ship 3 includes a hull 5 that floats on water, and a liquefied gas tank (hereinafter simply referred to as "tank") 7 that is installed in the hull 5 and stores liquefied gas.

[0012] In this specification, the term "liquefied gas storage ship" refers to a ship in general that has the function of storing liquefied gas. The liquefied gas storage ship 3 in this embodiment is a liquefied gas carrier. However, in addition to liquefied gas carriers, the liquefied gas storage ship 3 also includes, for example, a liquefied gas fuel ship and a bunkering ship that supplies liquefied gas to other ships.

[0013] A pipe (not shown) is attached to the tank 7 for transferring liquefied gas between the tank 7 and the outside, for example, a land-based liquefied gas storage base. In the example shown, the tank 7 has a dome portion 7a that protrudes upward, and one end of the pipe is attached to this dome portion 7a. The pipe extends from the inside of the tank 7 through the dome portion 7a to the outside of the tank 7.

[0014] The liquefied gas stored in the tank 7 may be, for example, liquefied petroleum gas (LPG, about -45°C), liquefied ethylene gas (LEG, about -100°C), liquefied natural gas (LNG, about -160°C), liquefied hydrogen (LH2, about -250°C), liquefied helium (LHe, about -270°C), etc. In this embodiment, liquefied hydrogen is stored in the tank 7.

[0015] In this embodiment, two tanks 7 are installed in the hull 5 of the liquefied gas storage ship 3. These two tanks 7 are lined up in the longitudinal direction of the hull 5. However, the number of tanks 7 mounted on the hull 5 may be one, or three or more. Since the configuration of each tank 7 is the same, only one tank 7 will be described in this specification.

[0016] The tank 7 in the illustrated example is an independent tank 7 formed independently of the hull 5. The tank 7 has a cylindrical shape with both ends bulging out into a dome shape. The upper part of the tank 7 is covered by a tank cover 9 that is provided integrally with the hull 5. The shape of the tank 7 is not limited to this example, and may be, for example, spherical or rectangular.

[0017] In this embodiment, as shown in FIG. 1, the tank 7 is configured as a double-shell tank 7 having an inner tank 11 and an outer tank 13. For example, a vacuum insulation layer is formed between the inner tank 11 and the outer tank 13. However, the configuration of the tank 7 is not limited to this example. For example, the tank 7 may be a single-shell tank covered with a heat insulating material. In this case, the heat insulating material may be composed of, for example, a plurality of vacuum insulation panels or a plurality of foam panels.

[0018] As shown in Fig. 2, the hull 5 is formed with a recess 15 in which each tank 7 is installed, and this recess 15 is divided into two cells by a bulkhead 17 between the tanks 7. As shown in Fig. 1, a pair of tank support members 21 that support the tank 7 at positions spaced apart from each other in the axial direction of the tank 7 are arranged on the bottom wall 19 of each cell. Each tank support member 21 protrudes from the bottom wall 19, and the tank 7 is installed on the tank support members 21, thereby being supported in a state spaced apart from each wall that forms the cell of the hull 5. In this embodiment, the tank 7 is attached to the hull 5 with this configuration.

[0019] In addition, an inner tank support member 23 that supports the inner tank is disposed between the inner tank 11 and the outer tank 13. In this example, the inner tank support member 23 is provided on an extension of the tank support member 21. The inner tank 11 and the outer tank 13 are connected by this inner tank support member 23, and the inner tank 11 is supported on the hull 5 via the inner tank support member 23 and the outer tank 13. The inner tank support member 23 may be fixed to only one of the inner tank 11 and the outer tank 13 and provided so as to contact the other, or may be fixed to both. In addition, the inner tank support member 23 does not have to be provided on an extension of the tank support member 21, and may be provided at a position shifted in the ship length direction.

[0020] The manner in which the tank 7 is supported relative to the hull 5 is not limited to the example described above, and may be appropriately selected depending on the structures of the tank 7 and the hull 5. For example, when the tank 7 is spherical as in the modified example shown in Fig. 3, a cylindrical tank support member 21 that supports the tank 7 relative to the hull 5 and a cylindrical inner tank support member 23 interposed between the inner tank 11 and the outer tank 13 can be used as shown in Fig. 4.

[0021] Next, a state estimation system 1 according to this embodiment, which estimates the state of the liquefied gas tank 7 having the above configuration, and a state estimation method using this system will be described. As shown in Fig. 1, the state estimation system 1 includes a measurement unit 31, a calculation unit 33, a data assimilation unit 35, and an evaluation unit 37.

[0022] The measuring unit 31 is provided with a measuring instrument 39 that measures the condition related to the strength of the liquefied gas tank 7, and measures the condition using the measuring instrument 39 (measurement step S1). The "condition related to the strength of the liquefied gas tank 7" measured by the measuring instrument 39 of the measuring unit 31 is, for example, the degree of deformation (distortion) of the target part and accumulated fatigue damage. The measuring instrument 39 provided in the measuring unit 31 is, for example, a strain sensor that measures the degree of distortion and a fatigue sensor that measures the amount of cracks required to calculate the accumulated fatigue damage. The measuring instrument 39 may be a sensor that measures only one type of these parameters, or may be multiple types of sensors that measure multiple types.

[0023] In this embodiment, the measuring instrument 39 is attached to a portion that forms a load transfer path (hereinafter simply referred to as "load transfer path") LP from the tank 7 to the hull 5. More specifically, in this example, the measuring instrument 39 is attached to the tank support member 21 and the inner tank support member 23, which are portions that form the load transfer path LP.

[0024] More specifically, the measuring instrument 39 is attached, for example, to the tank support member 21 near the portion that contacts the tank 7 and near the portion that is connected to the hull 5, and to the inner tank support member 23 near the portions that contact the inner tank 11 and the outer tank 13.

[0025] In this way, by attaching the measuring device 39 to the load transfer path LP, which is a portion where a decrease in strength due to fatigue is likely to occur, the condition of the tank 7 can be measured efficiently. The portion forming the load transfer path LP to which the measuring device 39 is attached is not limited to the tank support member 21 and the inner tank support member 23 exemplified above, but also includes the vicinity of these members 21, 23 in the tank 7 and the hull 5. The measuring device 39 may be attached to another portion instead of or in addition to the load transfer path LP. Furthermore, the measuring device 39 may be attached to the hull 5 side as long as it is a portion that can affect the strength of the tank 7.

[0026] The calculation unit 33 calculates the state of the tank 7 related to its strength using a pre-analysis model (calculation step S2). In the pre-analysis model, conditions such as material properties, boundary conditions, and load conditions at the time of designing the hull 5 and the tank 7 are set, and the calculation unit 33 calculates the state of the tank 7 related to its strength, such as stress and strain, using this pre-analysis model.

[0027] The data assimilation unit 35 updates the pre-analysis model by data assimilation using the measurement results acquired by the measurement unit 31 (data assimilation step S3). Data assimilation is a method for statistically correcting uncertain factors of a numerical model using actual measured values. In this embodiment, the data assimilation unit 35 compares the above-mentioned various conditions and parameters set in the numerical analysis model used in the calculation unit 33 with the measurement results acquired by the measurement unit 31, and if there is a significant difference, updates the pre-analysis model by correcting it using the measurement results.

[0028] The evaluation unit 37 evaluates the state of the liquefied gas tank 7 based on the calculation results output from the calculation unit 33 (evaluation step S4). Specifically, the evaluation unit 37 calculates a value of accumulated fatigue damage based on values ​​of stress, strain, and the like output from the calculation unit 33, and evaluates, for example, whether immediate repair is necessary and the estimated period until repair is necessary.

[0029] In this embodiment, the evaluation unit 37 performs evaluation of the strength of the tank 7, which is the object of estimation, by structural reliability analysis. In the structural reliability analysis, the probability that the target structure will suffer fatigue damage, static fracture, brittle fracture, etc., during a specified period is calculated. In the example of this embodiment, the evaluation unit 37 uses the structural reliability analysis to calculate the probability that fatigue damage will occur in the tank 7 during the above-mentioned assumed operation period. Specific methods that can be used for the structural reliability analysis include generally known numerical integration method, Monte-Carlo simulation method, first-order reliability evaluation method, second-order reliability evaluation method, higher-order moment method, importance sampling method, response surface method, etc.

[0030] By performing the evaluation using structural reliability analysis in this manner, it becomes possible to output the evaluation results on the state of the tank 7 as more practical information such as the need for repairs, etc. However, the evaluation of the state of the tank 7 by the evaluation unit 37 may be output as a definitive value of accumulated fatigue damage without using structural reliability analysis.

[0031] The condition estimation system 1 may further include a notification unit 43 that notifies, in an appropriate manner, the result of the evaluation by the evaluation unit 37. The notification unit 43 is configured to display a warning to perform repairs or to avoid inclement weather, depending on, for example, the degree of fatigue strength deterioration and the probability of fatigue damage occurring within a predetermined short period of time.

[0032] The tank 7 to which the state estimation system 1 and the state estimation method according to the present embodiment are applied is not limited to the above example. For example, the tank 7 may be a rectangular independent tank, or may be a so-called membrane tank that is formed integrally with the hull 5 instead of being independent.

[0033] According to the state estimation system 1 and state estimation method of this embodiment described above, not only can the state of the liquefied gas tank 7 be estimated in advance by calculation using a pre-analysis model, but also the pre-analysis model can be made closer to the liquefied gas tank 7, which is the actual subject of estimation, by data assimilation using the measurement results of the liquefied gas tank 7, thereby enabling highly accurate pre-estimation.

[0034] As described above, the preferred embodiment of the present invention has been described with reference to the drawings, but various additions, modifications, and deletions can be made without departing from the spirit of the present invention. Therefore, such additions, modifications, and deletions are also included in the scope of the present invention. [Explanation of symbols]

[0035] 1 Condition Rating System 3 Liquefied gas storage vessel (ship) 5. Hull 7 Liquefied Gas Tank 9 Restraining member 21 Tank support member 23 Inner tank support member 31 Measurement Unit 33 Computational Units 35 Data Assimilation Unit 37 Evaluation Units LP Load Transfer Path

Claims

1. A system for estimating a state of a liquefied gas tank installed on a ship, comprising: A measuring unit including a measuring instrument for measuring a condition related to the strength of the liquefied gas tank; a calculation unit for calculating the strength-related condition of the liquefied gas tank by a pre-analysis model; a data assimilation unit for updating the pre-analysis model by data assimilation using measurement results acquired by the measurement unit; an evaluation unit for evaluating a state of the liquefied gas tank based on a calculation result output from the calculation unit; A state estimation system for a marine liquefied gas tank comprising:

2. 2. The system of claim 1, The evaluation unit performs an evaluation on the strength of the estimated object by a structural reliability analysis. A condition estimation system for marine liquefied gas tanks.

3. In the system according to claim 1 or 2, The liquefied gas tank is formed separately from a hull of the ship and supported within the hull, The measuring instrument of the measuring unit is attached to a portion forming a load transfer path from the liquefied gas tank to the hull. A condition estimation system for marine liquefied gas tanks.

4. 4. The system of claim 3, The measuring instrument is attached to a tank support member that supports the liquefied gas tank on the hull and that is a part that forms the load transfer path. A condition estimation system for marine liquefied gas tanks.

5. In the system according to claim 3 or 4, the liquefied gas tank is a double-structure tank having an inner tank, an outer tank, and an inner tank support member provided between the inner tank and the outer tank to support the inner tank, the measuring device is attached to the inner tank support member which is a part forming the load transfer path; A condition estimation system for marine liquefied gas tanks.

6. A method for estimating a state of a liquefied gas tank installed on a ship, comprising: Measuring a condition related to the strength of the liquefied gas tank; calculating the strength-related condition of the liquefied gas tank by a pre-analysis model; updating the pre-analysis model by data assimilation using measurements of the strength condition of the liquefied gas tank; Evaluating a state of the liquefied gas tank based on a calculation result of a state regarding the strength of the liquefied gas tank obtained by the pre-analysis model; and A method for estimating the state of a marine liquefied gas tank, comprising:

Images