Estimation method, device, and program

Abstract

To reduce a working load of an operator for the navigation of a ship with a LNG tank.SOLUTION: An estimation device calculates a value of a characteristic coefficient by a fourth processing part 105 so that an evaluation function value is below a predetermined threshold and estimates at least one or more among an equator temperature of a tank used for actual control, a gas temperature in the tank, and a pressure in the tank by a simulation using the determined characteristic coefficient value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an estimation method, device, and program for estimating the equatorial temperature of a tank containing LNG, the temperature of gas inside the tank, and the pressure inside the tank. [Background technology]

[0002] Liquefied Natural Gas (LNG) carriers that transport liquefied gas must maintain the equatorial temperature of their tanks below a specified temperature during ballast voyages after unloading LNG at their destination. For this reason, LNG is sprayed into the tanks to cool them down. The LNG remaining in the tanks is used as fuel for the carrier's voyage. This LNG remaining in the tanks is called the heel.

[0003] The above-mentioned spraying operation is usually carried out taking into consideration the temperature at the equator of the tank, the amount of heel, the pressure inside the tank, etc. (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-043318 [Patent Document 2] Patent No. 6339743 Summary of the Invention [Problem to be solved by the invention]

[0005] The spraying operation described above aims to maintain tank pressure within the limit during the ballast voyage and to lower the tank's equatorial temperature to a target value upon arrival at the loading port. However, it was difficult to accurately estimate changes in the tank's condition after spraying. For this reason, in daily spraying operations, in order to approach the target value, the spraying operation must be repeated several times while checking changes in the tank's condition, which requires a lot of time and effort from the operator and creates a heavy workload.

[0006] The present invention has been made to solve the above problems, and aims to reduce the workload of operators during voyages by accurately predicting changes in the state inside the tank due to spray operations in the LNG tank in advance, thereby enabling the formulation of an accurate spray plan and reducing the number of unnecessary spray operations. [Means for solving the problem]

[0007] The estimation device according to the present invention includes a memory unit that stores a plurality of measurement values measured in time series, including the equatorial temperature of a tank installed on a ship and containing liquefied natural gas, the temperature of the gas inside the tank, the temperature of the liquid inside the tank, the pressure inside the tank, and the outside air temperature; a first processing unit configured to filter the plurality of measurement values according to set conditions to generate a plurality of process data; a second processing unit configured to obtain a plurality of first estimated values that estimate the equatorial temperature of the tank, a plurality of second estimated values that estimate the temperature of the gas inside the tank, and a plurality of third estimated values that estimate the pressure inside the tank, by a simulation using the plurality of process data; and a characteristic coefficient defined for the tank in the simulation, which corresponds to changes in the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank. a third processing unit configured to select a characteristic coefficient with high sensitivity in relation to the plurality of first estimated values; a fourth processing unit configured to determine the value of the characteristic coefficient selected by the third processing unit so that the value of an evaluation function determined based on the differences between the plurality of first estimated values and the plurality of first actual measured values of the equatorial temperature of the tank, the differences between the plurality of second estimated values and the plurality of second actual measured values of the temperature of the gas inside the tank, and the differences between the plurality of third estimated values and the plurality of third actual measured values of the pressure inside the tank falls below a predetermined threshold; and a fifth processing unit configured to estimate at least one of the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank to be used for actual control by a simulation using the current state of the tank determined based on the most recent measured values corresponding to the plurality of process data, the spray plan, and the value of the characteristic coefficient determined by the fourth processing unit.

[0008] In one configuration example of the estimation device, the plurality of measurement values are values measured during a period when the ship was sailing.

[0009] The estimation method according to the present invention includes a first step of filtering a plurality of measured values measured in time series, including the equatorial temperature of a tank installed on a ship and storing liquefied natural gas, the temperature of the gas inside the tank, the temperature of the liquid inside the tank, the pressure inside the tank, and the outside air temperature, under set conditions to generate a plurality of process data; a second step of simulating the plurality of process data to obtain a plurality of first estimated values of the equatorial temperature of the tank, a plurality of second estimated values of the temperature of the gas inside the tank, and a plurality of third estimated values of the pressure inside the tank; and a second step of calculating characteristic coefficients defined for the tank in the simulation that are sensitive to changes in the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank, which are sensitive to changes in the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank. The method includes a third step of selecting a coefficient; a fourth step of determining the value of the characteristic coefficient selected in the third step so that the value of an evaluation function determined based on the differences between the multiple first estimated values and the multiple first actual measured values of the equatorial temperature of the tank, the differences between the multiple second estimated values and the multiple second actual measured values of the temperature of the gas inside the tank, and the differences between the multiple third estimated values and the multiple third actual measured values of the pressure inside the tank falls below a predetermined threshold; and a fifth step of estimating at least one of the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank to be used for actual control through a simulation using the current state of the tank determined based on the most recent measured values corresponding to the multiple process data, the spray plan, and the value of the characteristic coefficient determined in the fourth step.

[0010] In one example of the estimation method, the plurality of measurement values are values measured during a period when the ship was sailing.

[0011] The program according to the present invention is provided to a computer, and includes a first function for filtering a plurality of measured values measured in time series, including the equatorial temperature of a tank installed on a ship and storing liquefied natural gas, the temperature of the gas inside the tank, the temperature of the liquid inside the tank, the pressure inside the tank, and the outside air temperature, under set conditions to generate a plurality of process data; a second function for obtaining a plurality of first estimated values for the equatorial temperature of the tank, a plurality of second estimated values for the temperature of the gas inside the tank, and a plurality of third estimated values for the pressure inside the tank, by a simulation using the plurality of process data; and a second function for calculating sensitivity to changes in the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank, of characteristic coefficients defined for the tank in the simulation. a third function of selecting a characteristic coefficient with a high degree of accuracy; a fourth function of determining the value of the characteristic coefficient selected by the third function so that the value of an evaluation function determined based on the differences between the plurality of first estimated values and the plurality of first actual measured values of the equatorial temperature of the tank, the differences between the plurality of second estimated values and the plurality of second actual measured values of the temperature of the gas inside the tank, and the differences between the plurality of third estimated values and the plurality of third actual measured values of the pressure inside the tank falls below a predetermined threshold; and a fifth function of estimating at least one of the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank to be used for actual control through a simulation using the current state of the tank determined based on the most recent measured values corresponding to the plurality of process data, the spray plan, and the value of the characteristic coefficient determined by the fourth function.

[0012] In one configuration example of the program, the multiple measurement values are values measured during the period when the ship was sailing.

[0013] As described above, according to the present invention, the value of the characteristic coefficient is determined so as to minimize the value of the evaluation function determined based on the difference between the first estimated value and the first measured value for the equatorial temperature of the tank, the difference between the second estimated value and the second measured value for the temperature of the gas inside the tank, and the difference between the third estimated value and the third measured value for the pressure inside the tank. A simulation using this coefficient estimates at least one of the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank, so that the equatorial temperature of the tank can be simulated with high accuracy, reducing the workload of operators when sailing on a ship equipped with an LNG tank. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing the configuration of an estimation device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a more detailed configuration of the estimation device according to the embodiment of the present invention. [Figure 3] FIG. 3 is an explanatory diagram showing input and output of the simulation. [Figure 4] FIG. 4 is a flowchart illustrating an estimation method according to an embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing the hardware configuration of an estimation device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Embodiment 1] An estimation device according to a first embodiment of the present invention will be described below with reference to Figures 1 and 2. The estimation device includes a storage unit 101, a first processing unit 102, a second processing unit 103, a third processing unit 104, a fourth processing unit 105, a fifth processing unit 106, and a display unit 107.

[0016] The storage unit 101 stores a plurality of measurement values measured in time series, including the equatorial temperature of a tank installed on a ship and storing liquefied natural gas (the temperature of the inner wall at the equatorial part of the tank), the temperature of the gas inside the tank, the temperature of the liquid inside the tank, the pressure inside the tank, and the outside air temperature. The plurality of measurement values stored in the storage unit 101 are values (actual values) measured during the period when the ship was sailing.

[0017] The first processing unit 102 filters the multiple measurement values based on set conditions to generate multiple process data 204. The process data 204 also includes multiple spray amount data. Spraying refers to the operation of spraying LNG in a liquid state inside a tank to generate vaporized gas and thereby cool the tank. The spray amount may be calculated, for example, based on the amount of LNG actually sprayed during a previous spray operation. As a filtering condition, if the ship's motion is greater than a certain standard due to a typhoon or the like, it is possible to exclude the measurement values for this period. It is also possible to process the data separately for time periods when spraying is being performed and time periods when spraying is not being performed.

[0018] Next, a description will be given of second processing unit 103, which performs simulation processing in third processing unit 104 and fourth processing unit 105, which will be described later. Second processing unit 103 obtains a plurality of first estimated values that estimate the equatorial temperature of the tank, a plurality of second estimated values that estimate the temperature of the gas inside the tank, and a plurality of third estimated values that estimate the pressure inside the tank, by simulation using a plurality of process data as shown in Fig. 3.

[0019] The amount of vaporized gas generated by tank heat input and spray operation is calculated based on a non-steady-state process model in accordance with thermodynamic laws (material balance, energy balance, and vapor-liquid equilibrium relationship) based on fluid composition. Based on this amount of vaporized gas generated, the tank's equatorial temperature (first estimated value), the temperature of the gas inside the tank (second estimated value), and the pressure inside the tank (third estimated value) are calculated over time (time series changes) to obtain multiple first estimated values, multiple second estimated values, and multiple third estimated values. The simulation in second processing unit 103 is disclosed in detail in Patent Document 2.

[0020] The third processing unit 104 selects, from among the characteristic coefficients, a characteristic coefficient that is highly sensitive to changes in the equatorial temperature of the tank, changes in the temperature of the gas inside the tank, and changes in the pressure inside the tank.

[0021] When a spray operation is performed, the evaporation and atomization of LNG causes changes in the tank's equatorial temperature, the temperature of the gas inside the tank, and the pressure inside the tank. The third processing unit 104 calculates the tank's equatorial temperature (first estimated value), the temperature of the gas inside the tank (second estimated value), and the pressure inside the tank (third estimated value) through the simulation performed by the second processing unit 103. In this calculation, if the effect on the amount of change in the first to third estimated values when one of a plurality of pre-specified characteristic coefficients is changed by a predetermined unit amount from a predetermined design value (initial value) exceeds a predetermined threshold, the third processing unit 104 recognizes the characteristic coefficient as having high sensitivity. If the effect does not exceed the predetermined threshold, the third processing unit 104 recognizes the characteristic coefficient as having low sensitivity. By performing a similar classification on each of the plurality of characteristic coefficients described above, it is possible to identify characteristic coefficients with high sensitivity. The following elements are typical examples of characteristic coefficients that are highly sensitive to changes in the tank's equatorial temperature, the temperature of the gas inside the tank, and the pressure inside the tank. It can be said that it is desirable for the above-mentioned pre-specified characteristic coefficients to include one or more of these elements.

[0022] Spray efficiency Mist diameter of droplet evaporation process model by spray operation These factors affect the degree of evaporation and atomization of LNG inside the tank during spraying operations, and it can be said that the equatorial temperature of the tank, the temperature of the gas inside the tank, and changes in the pressure inside the tank have a significant impact.

[0023] Ship rocking Hull motion affects the liquid wetted area inside the hull tanks, which in turn affects the amount of LNG evaporation in the tanks. It can be said that it has a large impact on changes in the tank's equatorial temperature, the temperature of the gas inside the tank, and the pressure inside the tank.

[0024] Tank outer wall film heat transfer coefficient Tank inner wall film heat transfer coefficient The tank heat transfer coefficient is a factor that affects the rate at which heat energy is input to the liquid and gas phases inside the tank, and is said to be greatly affected by changes in the tank's equatorial temperature, the temperature of the gas inside the tank, and the pressure inside the tank.

[0025] Next, the operation of the fourth processing unit 105 will be described. As shown in the following formula (4), the fourth processing unit 105 calculates the difference between the calculated value obtained by the simulation of the second processing unit 103 and the process data 204 (actual value), and calculates it as simulation calculation value errors (tank pressure error Err1, tank equatorial temperature error Err2, tank gas phase internal gas temperature error Err3). Note that abs() means that the absolute value is calculated.

[0026]

number

[0027] The fourth processing unit 105 calculates the values of the characteristic coefficients selected by the third processing unit 104 based on the calculated simulation calculation value errors (Err1, Err2, Err3). Here, Err1 is pressure, and Err2 and Err3 are temperatures, which cannot be calculated on the same level because they have different units, and therefore must be calculated by making each dimensionless in order to compare them.

[0028] To make the error dimensionless, the fourth processing unit 105 obtains a dimensionless value Err1' by dividing the tank pressure error Err1 by the measurement range width of the tank pressure (the difference between the upper and lower limits of the measurable pressure, which is uniquely determined depending on the pressure measurement device actually used). Similarly, it obtains Err2' by dividing the tank equatorial temperature error Err2 by the measurement range width of the tank equatorial temperature, and Err3' by dividing the tank internal gas temperature error Err3 by the measurement range width of the tank gas phase temperature.

[0029] The fourth processing unit 105 repeats the above process using the differences between each of the multiple first estimated values, multiple second estimated values, and multiple third estimated values calculated in the second processing unit 103 along the time series changes and their corresponding actual values (process data values), thereby obtaining multiple Err1's, multiple Err2's, and multiple Err3's along the time series changes.

[0030] Next, the fourth processing unit 105 adds up the obtained multiple Err1's, multiple Err2's, and multiple Err3's, i.e., the sum of the time-integrated values, as the evaluation function J, and calculates the value of the characteristic coefficient so that the evaluation function J becomes smaller.

[0031]

number

[0032] Subsequently, the fourth processing unit 105 determines whether or not the value of the calculated evaluation function J is below a predetermined threshold value.

[0033] If the evaluation function J exceeds the threshold value, it is determined that the characteristic coefficients are still inappropriate. At this time, the fourth processing unit 105 sends the characteristic coefficients calculated by the above-mentioned process to the second processing unit (first dynamic simulation) 103, and the simulation in the second processing unit 103 and the calculation in the fourth processing unit 105 are repeated again to calculate more appropriate values of the characteristic coefficients.

[0034] On the other hand, when the value of the evaluation function J falls below the threshold value, the fourth processing unit 105 determines that an appropriate value of the characteristic coefficient has been obtained, and sends the characteristic coefficient to the fifth processing unit (second dynamic simulation) 106.

[0035] The fifth processing unit 106 estimates at least one of the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure of the gas inside the tank by performing a simulation using the final characteristic coefficient values determined to be appropriate by the fourth processing unit 105 and inputting the spray plan and the current state of the tank determined based on the most recent measured values corresponding to the plurality of process data 204. The fifth processing unit 106 performs a simulation similar to that performed by the second processing unit 103 described above.

[0036] The tank's equatorial temperature, the temperature of the gas inside the tank, and the pressure of the gas inside the tank estimated by the fifth processing unit 106 are displayed on the display unit 107 in a state where they can be seen by the operator. This allows the operator to create an accurate spray plan based on an accurate prediction of changes in the state inside the LNG tank, thereby reducing the number of unnecessary spray operations and reducing the workload of the operator during the voyage.

[0037] [Embodiment 2] Next, an estimation method according to the second embodiment of the present invention will be described with reference to FIG.

[0038] First, in a first step S101, the first processing unit 102 acquires from the memory unit 101 a plurality of measurement values measured in time series, including the equatorial temperature of a tank installed on a ship and containing liquefied natural gas, the temperature of the gas inside the tank, the temperature of the liquid inside the tank, the pressure inside the tank, and the outside air temperature, and filters the acquired measurement values according to set conditions (for example, the period during which the measurement values were acquired) to generate a plurality of process data.

[0039] In a second step S102, the second processing unit 103 performs a simulation using a plurality of process data and a plurality of spray amounts to obtain a plurality of first estimated values for the equatorial temperature of the tank, a plurality of second estimated values for the temperature of the gas inside the tank, and a plurality of third estimated values for the pressure inside the tank. The simulation is performed in the same manner as in the first embodiment.

[0040] Next, in a third step S103, the third processing unit 104 selects, from the characteristic coefficients defined for the tank in the simulation, a characteristic coefficient that is highly sensitive to changes in the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank. The selection of the characteristic coefficient can be performed by a simulation similar to that in the first embodiment described above.

[0041] Next, in a fourth step S104, the fourth processing unit 105 calculates the differences between the multiple first estimated values and the multiple first actual measured values of the tank's equatorial temperature, the differences between the multiple second estimated values and the multiple second actual measured values of the tank's internal gas temperature, and the differences between the multiple third estimated values and the multiple third actual measured values of the tank's internal pressure. The fourth processing unit 105 then calculates the difference between the first estimated value and the first actual measured value for each measurement value measured in time series (for each measurement time point) and sums them. It also calculates the difference between the second estimated value and the second actual measured value for each measurement value measured in time series (for each measurement time point) and sums them. It also calculates the difference between the third estimated value and the third actual measured value for each measurement value measured in time series (for each measurement time point) and sums them. The sums are added together, i.e., the total value of the time-integrated values is used as an evaluation function J, and a characteristic coefficient is calculated so that the evaluation function J is below a predetermined threshold. If the value of the evaluation function exceeds a predetermined threshold value, the process from the second step S102 is repeated using the determined value of the characteristic coefficient (S105).

[0042] Next, in a fifth step S106, the fifth processing unit 106 uses the characteristic coefficients determined as described above to perform a simulation with the spray plan input to estimate the tank's equatorial temperature, the temperature of the gas inside the tank, and the pressure of the gas inside the tank for in-voyage spray planning. The estimated tank's equatorial temperature is visually displayed to the operator.

[0043] As shown in Fig. 5, the estimation device according to the above-described embodiment is a computer device including a CPU (Central Processing Unit) 301, a main storage device 302, an external storage device 303, a network connection device 304, etc., and the CPU 301 operates (executes) a program loaded in the main storage device 302, thereby realizing each function (estimation method) described with reference to Fig. 4. The network connection device 304 is connected to a network 305. Furthermore, each function can be distributed among multiple computer devices.

[0044] [Embodiment 3] Next, a program according to a third embodiment of the present invention will be described. The program is a program for causing a computer to execute the estimation method shown in the above-described embodiment, and the program has the following functions in the computer: a first function for filtering a plurality of measured values measured in time series, including the equatorial temperature of a tank installed on a ship and storing liquefied natural gas, the temperature of the gas inside the tank, the temperature of the liquid inside the tank, the pressure inside the tank, and the outside air temperature, under set conditions to generate a plurality of process data; a second function for obtaining a plurality of first estimated values for the equatorial temperature of the tank, a plurality of second estimated values for the temperature of the gas inside the tank, and a plurality of third estimated values for the pressure inside the tank, by a simulation using the plurality of process data; and a second function for obtaining a plurality of characteristic coefficients defined for the tank in the simulation, the equatorial temperature of the tank, the temperature of the liquid inside the tank, and the pressure inside the tank, by filtering a plurality of measured values measured in time series, including the equatorial temperature of the tank, the temperature of the gas inside the tank, the temperature of the liquid inside the tank, and the outside air temperature, under set conditions to generate a plurality of process data. a third function of selecting a characteristic coefficient highly sensitive to changes in the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank; a fourth function of determining the value of the characteristic coefficient selected by the third function so that a value of an evaluation function determined based on differences between the plurality of first estimated values and a plurality of first actual measured values of the equatorial temperature of the tank, differences between the plurality of second estimated values and a plurality of second actual measured values of the temperature of the gas inside the tank, and differences between the plurality of third estimated values and a plurality of third actual measured values of the pressure inside the tank falls below a predetermined threshold; and a fifth function of estimating at least one of the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank to be used for actual control by a simulation using a plurality of process data, a spray plan, and the value of the characteristic coefficient determined by the fourth function.

[0045] As described above, according to the present invention, the equatorial temperature of a tank is estimated by a simulation in which the value of the characteristic coefficient is determined so as to minimize the value of the evaluation function determined based on the difference between the first estimated value and the first measured value for the equatorial temperature of the tank, the difference between the second estimated value and the second measured value for the temperature of the gas inside the tank, and the third estimated value and the third measured value for the pressure inside the tank.This makes it possible to simulate the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank with high accuracy, thereby reducing the workload of operators when sailing on ships equipped with LNG tanks.

[0046] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0047] 101...storage unit, 102...first processing unit, 103...second processing unit, 104...third processing unit, 105...fourth processing unit, 106...fifth processing unit, 107...display unit.

Claims

1. a storage unit that stores a plurality of measurement values measured in time series, including the equatorial temperature of a tank installed on the ship and containing liquefied natural gas, the temperature of the gas inside the tank, the temperature of the liquid inside the tank, the pressure inside the tank, and the outside air temperature; a first processing unit configured to filter the plurality of measurement values according to a set condition to generate a plurality of process data; a second processing unit configured to obtain, by a simulation using the plurality of process data, a plurality of first estimated values that estimate an equatorial temperature of the tank, a plurality of second estimated values that estimate a temperature of a gas inside the tank, and a plurality of third estimated values that estimate a pressure inside the tank; a third processing unit configured to select a characteristic coefficient defined for the tank in the simulation that is sensitive to changes in the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank; a fourth processing unit configured to determine the value of the characteristic coefficient selected by the third processing unit so that the value of an evaluation function determined based on differences between the plurality of first estimated values and a plurality of first actual measured values of the equatorial temperature of the tank, differences between the plurality of second estimated values and a plurality of second actual measured values of the temperature of the gas inside the tank, and differences between the plurality of third estimated values and a plurality of third actual measured values of the pressure inside the tank falls below a predetermined threshold; and a fifth processing unit that estimates at least one of an equatorial temperature of the tank, a temperature of gas inside the tank, and a pressure inside the tank to be used for actual control by the simulation using a current state of the tank determined based on the most recent measured values corresponding to the plurality of process data, a spray plan, and the value of the characteristic coefficient determined by the fourth processing unit; and An estimation device comprising:

2. 2. The estimation device according to claim 1, An estimation device in which the multiple measurement values are values measured during the period the ship was sailing.

3. a first step of filtering a plurality of measurement values measured in time series, including the equatorial temperature of a tank installed on a ship and storing liquefied natural gas, the temperature of gas inside the tank, the temperature of liquid inside the tank, the pressure inside the tank, and the outside air temperature, according to set conditions to generate a plurality of process data; a second step of estimating a plurality of first estimated values of the equatorial temperature of the tank, a plurality of second estimated values of the temperature of the gas inside the tank, and a plurality of third estimated values of the pressure inside the tank by simulation using the plurality of process data; a third step of selecting characteristic coefficients defined for the tank in the simulation that are sensitive to changes in the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank; a fourth step of determining values of the characteristic coefficients selected in the third step so that values of an evaluation function determined based on differences between the plurality of first estimated values and a plurality of first actual measured values of the equatorial temperature of the tank, differences between the plurality of second estimated values and a plurality of second actual measured values of the temperature of the gas inside the tank, and differences between the plurality of third estimated values and a plurality of third actual measured values of the pressure inside the tank are below a predetermined threshold; a fifth step of estimating at least one of an equatorial temperature of the tank, a temperature of the gas inside the tank, and a pressure inside the tank to be used for actual control by the simulation using the current state of the tank calculated based on the most recent measured values corresponding to the plurality of process data, the spray plan, and the value of the characteristic coefficient determined in the fourth step; An estimation method comprising:

4. 4. The estimation method according to claim 3, An estimation method characterized in that the plurality of measurement values are values measured during the period when the ship was sailing.

5. On the computer, a first function of filtering a plurality of measurement values measured in time series, including the equatorial temperature of a tank installed on a ship and storing liquefied natural gas, the temperature of the gas inside the tank, the temperature of the liquid inside the tank, the pressure inside the tank, and the outside air temperature, according to set conditions to generate a plurality of process data; a second function of calculating, by a simulation using the plurality of process data, a plurality of first estimated values that estimate the equatorial temperature of the tank, a plurality of second estimated values that estimate the temperature of the gas inside the tank, and a plurality of third estimated values that estimate the pressure inside the tank; a third function of selecting characteristic coefficients defined for the tank in the simulation that are sensitive to changes in the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank; a fourth function that determines the value of the characteristic coefficient selected by the third function so that the value of an evaluation function determined based on the differences between the plurality of first estimated values and a plurality of first actual measured values of the equatorial temperature of the tank, the differences between the plurality of second estimated values and a plurality of second actual measured values of the temperature of the gas inside the tank, and the differences between the plurality of third estimated values and a plurality of third actual measured values of the pressure inside the tank falls below a predetermined threshold; A program for realizing a fifth function of estimating at least one of the equatorial temperature of the tank, the temperature of the gas inside the tank, and the pressure inside the tank to be used for actual control through the simulation using the current state of the tank calculated based on the most recent measured values corresponding to the plurality of process data, a spray plan, and the value of the characteristic coefficient determined by the fourth function.

6. 6. The program according to claim 5, The program is characterized in that the plurality of measurement values are values measured during the period when the ship was sailing.

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