Calculation method, calculation device, and program

Abstract

To provide a method capable of accurately calculating a pressure gradient on a non-uniform computational grid.SOLUTION: A calculation method calculates a pressure gradient of a first computational grid by calculating a pressure gradient component in the direction corresponding to a vector component on the basis of: an equation representing that the pressure gradient between grids obtained by dividing the pressure difference between a computational grid adjacent to a first computational grid and the first computational grid by the distance between the adjacent computational grid the first computational grid and the sum, over the vector components, of the product of the component of the vector from the first computational grid to an adjacent computational grid divided by the distance and the component of the pressure gradient of the first computational grid in the direction corresponding to the vector components are approximately equal; the pressures of the first computational grid and the adjacent computational grid; and the distance between the first computational grid and the adjacent computational grid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a calculation method, a calculation device, and a program. [Background technology]

[0002] When performing a CFD (Computational Fluid Dynamics) analysis, the analysis target is divided into computational grids (meshes), and fluid velocity, pressure, temperature, etc. are calculated for each computational grid. A known method for calculating the pressure gradient of a computational grid is to use a least-squares method or the like to find a pressure gradient that minimizes the error between the pressure gradient of the computational grid of the analysis target multiplied by the distance between the computational grid and an adjacent computational grid and the pressure difference between these two computational grids. This method is effective for relatively uniform computational grids. As a related technique, Patent Document 1 discloses a method for dividing an analysis domain into multiple computational grids, analyzing the flow field of a turbulent flow model using a transport equation in the turbulence model, and calculating various physical quantities such as the pressure gradient in each computational grid. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-042813 Summary of the Invention [Problem to be solved by the invention]

[0004] The above conventional methods result in poor calculation accuracy when applied to pressure gradients in computational grids of non-uniform size. A method suitable for calculating pressure gradients in computational grids belonging to domains composed of non-uniform computational grids is needed.

[0005] The present disclosure provides a calculation method, a calculation device, and a program that can solve the above problems. [Means for solving the problem]

[0006] The calculation method disclosed herein is a calculation method for calculating, by a computer, the pressure gradient of a first computational grid in a region formed by a first computational grid and a computational grid adjacent to the first computational grid, and calculates the pressure gradient of the first computational grid by calculating the component of the pressure gradient in a direction corresponding to the vector component based on an equation expressing that the inter-grid pressure gradient, obtained by dividing the pressure difference between the adjacent computational grid and the first computational grid by the distance between the adjacent computational grid and the first computational grid, is approximately equal to the value obtained by multiplying the value obtained by dividing each vector component of a vector from the first computational grid to the adjacent computational grid by the distance and adding the product of the product by the component of the pressure gradient of the first computational grid in a direction corresponding to the vector component of the pressure gradient, and the pressures of the first computational grid and the adjacent computational grid and the distance between the first computational grid and the adjacent computational grid.

[0007] A computing device according to the present disclosure is a computing device that calculates the pressure gradient of a first computational grid in a region formed by a first computational grid and a computational grid adjacent to the first computational grid, and includes: an equation expressing that an inter-grid pressure gradient obtained by dividing the pressure difference between the adjacent computational grid and the first computational grid by the distance between the adjacent computational grid and the first computational grid is approximately equal to a value obtained by multiplying a value obtained by dividing each vector component of a vector from the first computational grid to the adjacent computational grid by the distance and adding the product of the product by a component of the pressure gradient of the first computational grid in a direction corresponding to the vector component of the pressure gradient; and means for calculating the pressure gradient of the first computational grid by calculating the component of the pressure gradient in a direction corresponding to the vector component based on the pressures of the first computational grid and the adjacent computational grid and the distance between the first computational grid and the adjacent computational grid.

[0008] Furthermore, a program of the present disclosure is a program that causes a computer to execute a process of calculating a pressure gradient of a first computational grid in a region formed by the first computational grid and computational grids adjacent to the first computational grid, by calculating a component of the pressure gradient in a direction corresponding to the vector component based on an equation expressing that an inter-lattice pressure gradient obtained by dividing the pressure difference between the adjacent computational grid and the first computational grid by the distance between the adjacent computational grid and the first computational grid is approximately equal to a value obtained by multiplying a value obtained by dividing each vector component of a vector from the first computational grid to the adjacent computational grid by the distance and adding the product of the product by a component of the pressure gradient of the first computational grid in a direction corresponding to the vector component, and the pressures of the first computational grid and the adjacent computational grid and the distance between the first computational grid and the adjacent computational grid. [Effects of the Invention]

[0009] According to the calculation method, calculation device, and program of the present disclosure, the pressure gradient of an unstructured grid can be calculated with high accuracy. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram illustrating an example of a computing device according to an embodiment. [Figure 2] FIG. 1 is a diagram illustrating a conventional method for calculating a pressure gradient. [Figure 3] 10A and 10B are diagrams illustrating a method for calculating a pressure gradient according to an embodiment. [Figure 4] 10A and 10B are diagrams illustrating the effect of a pressure gradient calculation method according to an embodiment. [Figure 5] 10 is a flowchart illustrating an example of a calculation process of a pressure gradient according to the embodiment. [Figure 6] FIG. 2 illustrates an example of a hardware configuration of a computing device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Embodiment> The analysis device of the present disclosure will be described below with reference to FIGS. (composition) FIG. 1 is a block diagram showing an example of a calculation device according to an embodiment. The calculation device 10 calculates the pressure gradient for each calculation grid in a reactor core thermal-hydraulic calculation. In particular, when the reactor is a high-temperature gas reactor or a fast reactor, a non-uniform calculation grid (unstructured grid) may be used as the calculation grid. The calculation device 10 can accurately evaluate the pressure gradient even for a non-uniform calculation grid. The pressure gradient calculation method described below is not limited to reactor thermal-hydraulic calculations and can be applied to any target. The calculation device 10 includes a calculation grid setting unit 11, a pressure calculation unit 12, a pressure gradient calculation unit 13, and a storage unit 14.

[0012] The computational grid setting unit 11 sets a computational grid (mesh) for the structure to be analyzed (e.g., a high-temperature gas-cooled reactor). The computational grid can be set manually or automatically by software called a mesher, which is provided with the necessary conditions for mesh division. Dividing the analysis target into small, uniform computational grids enables accurate fluid analysis, but increases the number of computational grids, thereby increasing the calculation time and computational load. Therefore, to improve calculation efficiency, the analysis target is divided into computational grids so as to reduce the number of computational grids. For example, the number of computational grids can be reduced by dividing regions where physical properties are considered uniform into coarse meshes. When this concept is applied to a nuclear reactor, for example, dividing large spaces within the reactor into coarse meshes and small spaces into small meshes, the total number of computational grids can be reduced. In the case of high-temperature gas-cooled reactors and fast reactors, due to the complex reactor structure, generating computational grids in this manner results in regions where the size and shape of adjacent computational grids are uniform and regions where they are not uniform. As will be described later, this embodiment provides a method for accurately calculating pressure gradients even when adjacent computational grids are nonuniform.

[0013] The pressure calculation unit 12 calculates the pressure of each computational grid. This function can utilize a computational code used for core flow analysis, or more generally, a function provided in general-purpose CFD analysis software.

[0014] The pressure gradient calculation unit 13 calculates the pressure gradient in the computational grid to be evaluated. The pressure gradient in the computational grid to be evaluated is a value (a value that is as close as possible to the pressure difference between the computational grid to be evaluated and an adjacent computational grid) that, when multiplied by the distance between the computational grid to be evaluated and an adjacent computational grid, becomes equal to the pressure difference between the two computational grids. The pressure gradient calculation unit 13 calculates a pressure gradient such that this relationship holds between the computational grid to be evaluated and all adjacent computational grids. Although there are conventional methods for calculating pressure gradients, these conventional methods (Figure 2) are suitable for regions consisting only of relatively uniform computational grids and are not suitable for calculating pressure gradients in regions consisting of non-uniform computational grids. Therefore, for regions consisting of non-uniform computational grids, the pressure gradient calculation unit 13 calculates the pressure gradient using a method different from the conventional method (Figure 3).

[0015] The storage unit 14 stores various information necessary for pressure gradient calculation. For example, the storage unit 14 stores information (e.g., CAD information) defining the two-dimensional or three-dimensional shape of the analysis target region, various analysis conditions necessary for fluid analysis, values ​​during calculation, calculation results, etc. The storage unit 14 also stores software for dividing the analysis target region into computational grids, calculation codes or CFD analysis software used for core flow analysis, etc.

[0016] Next, a method for calculating the pressure gradient by the pressure gradient calculation unit 13 will be described. First, a conventional method will be described. Figure 2 is a diagram for explaining a conventional method for calculating the pressure gradient. Nodes 0 to 3 in Figure 2 are computational grids. Nodes 1, 2, and 3 are arranged to surround node 0. Figure 2 shows an example of a region configured with a relatively uniform computational grid. Node 0 is the target for calculating the pressure gradient. The left-right direction on the page is the x-axis (right is positive), and the up-down direction is the y-axis (up is positive). The center of node 0 is O, the center of node 1 is O1, the center of node 2 is O2, and the center of node 3 is O3. The distance in the x direction between the center O of node 0 and the center O1 of node 1 is Δx1, and the distance in the y direction is Δy1. The distance in the x direction between the center O of node 0 and the center O2 of node 2 is Δx2, and the distance in the y direction is Δy2. The distance in the x direction between the center O of node 0 and the center O3 of node 3 is Δx3, and the distance in the y direction is Δy3. These distances Δx1 to Δx3 and Δy1 to Δy3 can be calculated when the computational grid is generated. Furthermore, let p0 be the pressure at node 0 obtained as a result of calculation by the pressure calculation unit 12, p1 be the pressure at node 1, p2 be the pressure at node 2, and p3 be the pressure at node 3. Let p be the pressure gradient at the center O of node 0. The pressures p0 to p3 and the pressure gradient p are vectors. The x component of the pressure gradient p can be expressed as ∂p / ∂x, and the y component as ∂p / ∂y. The pressure difference between node 0 and node 1 is P1 - P0. Alternatively, using the pressure gradient p, the pressure difference between node 0 and node 1 can be approximately expressed as -Δx1·∂p / ∂x+Δy1·∂p / ∂y. The same applies to the pressure difference between node 0 and node 2 and the pressure difference between node 0 and node 3. The pressure gradient p at node 0 must satisfy all of these relationships, so the following equation (1) holds.

[0017]

number

[0018] The pressure gradient p at node 0 can be calculated by using the least squares method to find ∂p / ∂x and ∂p / ∂y that minimize the square of the error between the left and right sides of equation (1). This method has been widely used to calculate the pressure gradient of a computational grid, but it is suitable for domains composed of relatively uniform computational grids, such as those shown in Figure 2. This is because when conventional methods are applied to computational grids of non-uniform size, the differential pressure error on the side with the longer distance between the grid centers becomes dominant. Next, using Figure 3, we will explain a method suitable for calculating the pressure gradient in domains composed of computational grids of non-uniform size and shape.

[0019] FIG. 3 is a diagram illustrating a method for calculating a pressure gradient according to an embodiment. FIG. 3 shows an example of a domain configured with a non-uniform computational grid. The shapes and sizes of nodes 0 to 3 illustrated in FIG. 3 are not uniform. As in FIG. 2, the pressures at the centers of nodes 0 to 3 are denoted as p0 to p3, and the pressure gradient at the center O of node 0 is denoted as p. Furthermore, the distance between the center O of node 0 and the center O1 of node 1 is denoted as Δη1, the distance between the center O of node 0 and the center O2 of node 2 is denoted as Δη2, and the distance between the center O of node 0 and the center O3 of node 3 is denoted as Δη3. As in FIG. 2, the distance in the x direction between the center O of node 0 and the center O1 of node 1 is denoted as Δx1, and the distance in the y direction is denoted as Δy1. Similarly, the distances between node 0 and nodes 2 and 3 are denoted as Δx2, Δy2, Δx3, and Δy3. In the method for calculating a pressure gradient according to this embodiment, attention is focused on the pressure difference per unit length between nodes (i.e., the pressure gradient) to eliminate the influence of differences in node size (differences in center-to-center distance). The x component per unit length of the distance between the center O of node 0 and the center O1 of node 1 can be expressed as Δx1 / Δη1, and the y component as Δy1 / Δη1. This can be expressed similarly for node 0 and nodes 2 and 3. The pressure gradient between node 0 and node 1 is (P1-P0) / Δη1. Or, it can be expressed approximately as -Δx1 / Δη1·∂p / ∂x+Δy1 / Δη1·∂p / ∂x. The same is true for the pressure gradient between node 0 and node 2, and the pressure gradient between node 0 and node 3. The pressure gradient at node 0 must satisfy all of these relationships, so the following equation (2) holds.

[0020]

number

[0021] The pressure gradient p at node 0 can be calculated by using the least squares method to find ∂p / ∂x and ∂p / ∂y that minimize the square of the error between the left and right sides of equation (2). This method mitigates the effects of differences in the center-to-center distance of computational grids and makes it possible to calculate a pressure gradient that appropriately represents the differential pressure applied to the fluid within the node. Figure 4 shows an example of a pressure gradient calculated using a conventional method and a pressure gradient calculated using the method according to this embodiment.

[0022] FIG. 4 is a diagram illustrating the effect of the pressure gradient calculation method according to the embodiment. The vertical axis of the graph in Figure 4 represents the pressure gradient, and the horizontal axis represents the position of each computational grid when computational grids 1 to 5 are arranged in order. O1 to O5 are the centers of computational grids 1 to 5, respectively. L0 represents the actual pressure gradient (for O2 to O3, the pressure difference between computational grids 2 and 3 divided by the distance between O2 and O3; for O3 to O4, the pressure difference between computational grids 3 and 4 divided by the distance between O3 and O4). L1 represents the pressure gradient for O3 calculated using the conventional method (Figure 2), and L2 represents the pressure difference for O3 calculated using the method of this embodiment (Figure 3). As shown in the figure, L1 calculated using the conventional method is affected by the pressure gradient between O3 and O4, which are located far from each other, resulting in an underestimation of the pressure difference within computational grid 3. L2 properly reflects the pressure difference within computational grid 3.

[0023] 2 and 3, the description has been given for a two-dimensional region configured with multiple triangular computational grids (part of FIG. 3 is a rectangular computational grid), but the application of the pressure gradient calculation method of this embodiment is not limited to these. Pressure gradients can also be calculated for one-dimensional (FIG. 4) or three-dimensional regions using a similar concept. Furthermore, the shape of the computational grid may be other shapes, such as a hexagon, cube, or polyhedron.

[0024] (operation) Next, the operation of the computing device 10 will be described with reference to FIG. FIG. 5 is a flowchart showing an example of a calculation process of a pressure gradient according to the embodiment. First, the computational grid setting unit 11 generates a computational grid (step S1). The computational grid setting unit 11 uses a mesher (software) to divide the structure to be analyzed into multiple computational grids. For example, the computational grid setting unit 11 divides a region that can be considered physically uniform into multiple computational grids at a coarse granularity, and divides a region that cannot be considered physically uniform into multiple computational grids at a granularity that corresponds to the spatial size of the region. The computational grid setting unit 11 records the position, size, shape, etc. of each of the multiple computational grids created by the division in the storage unit 14.

[0025] Next, the pressure calculation unit 12 acquires the pressure of each computational grid (step S2). The pressure calculation unit 12 calculates the pressure for each of the multiple computational grids set in step S1 using a calculation code or CFD analysis software used for thermal hydraulic analysis of a nuclear reactor. The pressure calculation unit 12 records the calculated pressure for each computational grid in the storage unit 14.

[0026] Next, the pressure gradient calculation unit 13 sets a computational grid to be used for calculating the pressure gradient (step S3). The computational grid to be used may be predetermined, or all of the computational grids divided in step S1 may be used, or the user may select a computational grid to be used for calculation from the computational grids generated in step S1. The pressure gradient calculation unit 13 records the computational grid to be used for calculation in the storage unit 14.

[0027] Next, the pressure gradient calculation unit 13 selects one of the calculation targets set in step S3 and determines whether the size of the target computational grid and the computational grid adjacent to that computational grid are uniform (step S4). For example, the pressure gradient calculation unit 13 refers to the storage unit 14, reads information about the computational grid of the calculation target and the computational grid adjacent to that computational grid, and determines whether the difference in size between these computational grids is within a predetermined range that can be considered uniform. If the difference is within the range that can be considered uniform, the pressure gradient calculation unit 13 determines that the grids are uniform, and if there is even one computational grid whose difference is outside the range, it determines that the grids are non-uniform. In addition to size, the pressure gradient calculation unit 13 may also add whether the shape can be considered identical (for example, triangular shapes are considered identical) as a determination criterion.

[0028] If it is determined to be uniform (step S4; Yes), the pressure gradient calculation unit 13 calculates the pressure gradient based on the pressure difference with the adjacent grid (step S5). The pressure gradient calculation unit 13 calculates the pressure gradient of the target computational grid using equation (1), as explained using Fig. 2. The pressure gradient calculation unit 13 records the calculated pressure gradient in the storage unit 14 in association with the identification information of the computational grid to be calculated.

[0029] If it is determined to be non-uniform (step S4; No), the pressure gradient calculation unit 13 calculates the pressure gradient of the target computational grid based on the pressure gradient with adjacent grids (step S6). The pressure gradient calculation unit 13 calculates the pressure gradient using equation (2), as explained using Fig. 3. The pressure gradient calculation unit 13 records the calculated pressure gradient in the storage unit 14 in association with the identification information of the computational grid to be calculated.

[0030] Next, the pressure gradient calculation unit 13 determines whether or not the calculation of the pressure gradient has been completed for all calculation targets (step S7). If the calculation of the pressure gradient has been completed for all target computational grids (step S7; Yes), the processing flow of Fig. 5 is terminated. If there are computational grids remaining that have not yet been calculated (step S7; No), the calculation device 10 repeatedly executes the processing from step S3 onwards.

[0031] In the flowchart of Fig. 5, when the computational grid to be calculated and the adjacent computational grids are uniform, the pressure gradient is calculated using the conventional method, but regardless of whether the computational grid is uniform or non-uniform, the pressure gradient may be calculated using the method of this embodiment described in Fig. 3. In other words, the pressure gradient of the target computational grid can be calculated using a processing flow in which steps S4 and S5 are deleted from the flowchart of Fig. 5.

[0032] (effect) As described above, according to this embodiment, by applying the least-squares method to an approximation based on the pressure gradient rather than the pressure difference between adjacent computational grids, deterioration in the calculation accuracy of the pressure gradient in a non-uniform computational grid is suppressed, and the pressure gradient can be calculated accurately even for a non-uniform computational grid. Non-uniform computational grids may occur in core thermal-hydraulic calculations of high-temperature gas-cooled reactors and fast reactors, but by applying the calculation method of this embodiment, it is possible to accurately evaluate the pressure gradient. Furthermore, by enabling the pressure gradient to be calculated accurately for a non-uniform computational grid, computational grids can be set with various granularities for the analysis target, thereby reducing the total number of computational grids and the calculation time and calculation load for the pressure gradient.

[0033] 6 is a diagram showing an example of the hardware configuration of a computing device. The computer 900 includes a CPU 901, a main memory device 902, an auxiliary memory device 903, an input / output interface 904, and a communication interface 905. The computing device 10 described above is implemented in the computer 900. The functions described above are stored in the auxiliary memory device 903 in the form of a program. The CPU 901 reads the program from the auxiliary memory device 903, loads it into the main memory device 902, and executes the above processing in accordance with the program. The CPU 901 also allocates a storage area in the main memory device 902 in accordance with the program. The CPU 901 also allocates a storage area in the auxiliary memory device 903 for storing data being processed in accordance with the program.

[0034] A program for implementing all or part of the functions of the computing device 10 may be recorded on a computer-readable recording medium, and the program may be loaded into the computer system and executed to perform processing by each functional unit. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. If a WWW system is used, the term "computer system" also includes the homepage provision environment (or display environment). The term "computer-readable recording medium" refers to portable media such as CDs, DVDs, and USBs, as well as storage devices such as hard disks built into the computer system. If the program is distributed to the computer 900 via a communication line, the computer 900 may load the program into the main storage device 902 and execute the processing described above. The program may be for implementing part of the functions described above, or may be capable of implementing the functions described above in combination with a program already stored in the computer system.

[0035] As described above, several embodiments according to the present disclosure have been described, but all of these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as defined in the claims, as well as in the scope and spirit of the invention.

[0036] <Additional Notes> The calculation method, calculation device, and program described in the embodiments can be understood, for example, as follows.

[0037] (1) A calculation method according to a first aspect is a calculation method for calculating, by a computer, the pressure gradient of a first computational grid in a region formed by a first computational grid and a computational grid adjacent to the first computational grid, and calculates the pressure gradient of the first computational grid by calculating the component of the pressure gradient in the direction corresponding to the vector component based on an equation expressing that the inter-grid pressure gradient, obtained by dividing the pressure difference between the adjacent computational grid and the first computational grid by the distance between the adjacent computational grid and the first computational grid, is approximately equal to the value obtained by multiplying the value obtained by dividing each vector component of the vector from the first computational grid to the adjacent computational grid by the distance and adding the resultant value to the vector component, and the pressures of the first computational grid and the adjacent computational grid and the distance between the first computational grid and the adjacent computational grid. This allows the pressure gradient of a computational grid belonging to a region made up of non-uniform computational grids to be calculated with high accuracy.

[0038] (2) A calculation method according to a second aspect is a calculation method executed by a computer, and includes the steps of generating a plurality of calculation grids, calculating the pressure of each of the plurality of calculation grids, and calculating the pressure gradient of the first calculation grid among the plurality of calculation grids by the calculation method described in (1). This allows the pressure gradient of a computational grid belonging to a region made up of non-uniform computational grids to be calculated with high accuracy.

[0039] (3) A calculation method according to a third aspect is a calculation method executed by a computer, and includes the steps of setting a plurality of calculation grids, calculating the pressure of each of the plurality of calculation grids, determining whether the plurality of calculation grids are uniform or non-uniform, and, if the determination step determines that the plurality of calculation grids are non-uniform, calculating the pressure gradient of the first calculation grid among the plurality of calculation grids by the calculation method described in (1). This allows the pressure gradient of a computational grid belonging to a region made up of non-uniform computational grids to be calculated with high accuracy.

[0040] (4) A calculation method according to a fourth aspect is the calculation method described in (3), and when the determination step determines that the pressure gradient of the first computational grid is uniform, the pressure gradient of the first computational grid is calculated by calculating the component of the pressure gradient in the direction corresponding to the vector component based on an equation expressing that the pressure difference between the first computational grid and the adjacent computational grid in a region formed by the first computational grid and the adjacent computational grid is approximately equal to the value obtained by multiplying the vector component of the vector from the first computational grid to the adjacent computational grid by the component of the direction corresponding to the vector component of the pressure gradient of the first computational grid and adding up the vector components, the pressures of the first computational grid and the adjacent computational grids, and the distance between the first computational grid and the adjacent computational grids. This allows the pressure gradient of computational grids belonging to a region consisting of uniform computational grids and non-uniform computational grids to be calculated with high accuracy.

[0041] (5) A calculation method according to the fifth aspect is a calculation method according to any one of (1) to (4), which calculates the component of the pressure gradient in the direction corresponding to the vector component that minimizes the square of the error between the left and right sides of the approximation equation. The pressure gradient can be calculated by solving the approximate equation using the least squares method.

[0042] (6) In a calculation method according to a sixth aspect, the region is a region inside a fast reactor or a high-temperature gas reactor, and in a core thermal flow calculation of the fast reactor or the high-temperature gas reactor, the pressure gradient inside the reactor is calculated using the calculation method described in (1) to (5). This allows the pressure gradient of the computational grid to be calculated with high accuracy in core thermal flow calculations where non-uniform computational grids occur.

[0043] (7) A calculation device according to a seventh aspect is a calculation device that calculates the pressure gradient of a first calculation grid in a region formed by a first calculation grid and a calculation grid adjacent to the first calculation grid, and includes: an equation expressing that an inter-grid pressure gradient obtained by dividing the pressure difference between the adjacent calculation grid and the first calculation grid by the distance between the adjacent calculation grid and the first calculation grid is approximately equal to a value obtained by multiplying a value obtained by dividing each vector component of a vector from the first calculation grid to the adjacent calculation grid by the distance and adding the resultant value to the vector component, and a means for calculating the pressure gradient of the first calculation grid by calculating the component of the pressure gradient in a direction corresponding to the vector component based on the pressures of the first calculation grid and the adjacent calculation grid and the distance between the first calculation grid and the adjacent calculation grid.

[0044] (8) A program according to an eighth aspect causes a computer to execute a process for calculating the pressure gradient of a first computational grid in a region formed by the first computational grid and an adjacent computational grid, the process calculating the pressure gradient of the first computational grid by calculating the component of the pressure gradient in a direction corresponding to the vector component based on an equation expressing that the inter-lattice pressure gradient, obtained by dividing the pressure difference between the adjacent computational grid and the first computational grid by the distance between the adjacent computational grid and the first computational grid, is approximately equal to the value obtained by dividing each vector component of a vector from the first computational grid to the adjacent computational grid by the distance and multiplying the result by the component of the pressure gradient of the first computational grid in a direction corresponding to the vector component of the vector component of the pressure gradient of the first computational grid, and the sum of the vector components. [Explanation of symbols]

[0045] 10...calculating device 11...Calculation grid setting section 12. Pressure calculation section 13. Pressure gradient calculation section 14...Storage section 900···Computer 901 CPU 902...Main memory 903...Auxiliary storage device 904 Input / Output Interface 905···Communication Interface

Claims

1. A calculation method for calculating, by a computer, a pressure gradient of a first computational grid in a region formed by a first computational grid and a computational grid adjacent to the first computational grid, the method comprising: an inter-grid pressure gradient obtained by dividing the pressure difference between the adjacent computational grid and the first computational grid by the distance between the adjacent computational grid and the first computational grid; a value obtained by dividing each vector component of a vector from the first computational grid to the adjacent computational grid by the distance and multiplying the result by a component of the pressure gradient of the first computational grid in a direction corresponding to the vector component, and then adding the resultant value to the vector components; and an approximation that indicates that these are approximately equal. pressures of the first computational grid and the adjacent computational grid; The distance between the first computational grid and the adjacent computational grid; a pressure gradient of the first computational grid by calculating a component of the pressure gradient in a direction corresponding to the vector component based on the Calculation method.

2. 1. A computer-implemented computational method comprising: generating a plurality of computational grids; calculating a pressure for each of the plurality of computational grids; Calculating a pressure gradient of the first computational grid among the plurality of computational grids by the computational method according to claim 1; A calculation method having the following.

3. 1. A computer-implemented computational method comprising: generating a plurality of computational grids; calculating a pressure for each of the plurality of computational grids; determining whether the plurality of computational grids are uniform or non-uniform; a step of calculating a pressure gradient of the first computational grid among the plurality of computational grids by the calculation method according to claim 1 when the non-uniformity is determined in the determining step; A calculation method having the following.

4. If it is determined to be uniform in the determining step, a pressure difference between a first computational grid and an adjacent computational grid in a region formed by the first computational grid and the adjacent computational grid; and an approximation formula expressing that a vector component of a vector from the first computational grid to the adjacent computational grid is approximately equal to a value obtained by multiplying a component of a pressure gradient of the first computational grid in a direction corresponding to the vector component of the vector, and adding the product of the product to the vector component; pressures of the first computational grid and the adjacent computational grid; The distance between the first computational grid and the adjacent computational grid; a pressure gradient of the first computational grid by calculating a component of the pressure gradient in a direction corresponding to the vector component based on the The calculation method according to claim 3.

5. calculating a component of the pressure gradient in a direction corresponding to the vector component that minimizes the square of the error between the left and right sides of the approximation equation; The calculation method according to claim 1 or claim 4.

6. The region is a region within a fast reactor or a high-temperature gas-cooled reactor, 3. A calculation method for calculating a pressure gradient in the reactor, in a core thermal hydraulic calculation of the fast reactor or the high-temperature gas-cooled reactor, using the calculation method according to claim 1 or 2.

7. A calculation device that calculates a pressure gradient of a first computational grid in a region configured with a first computational grid and a computational grid adjacent to the first computational grid, an inter-grid pressure gradient obtained by dividing the pressure difference between the adjacent computational grid and the first computational grid by the distance between the adjacent computational grid and the first computational grid; a value obtained by dividing each vector component of a vector from the first computational grid to the adjacent computational grid by the distance and multiplying the result by a component of a pressure gradient in the first computational grid in a direction corresponding to the vector component, and then adding the resultant value to the vector components; is approximately equal to pressures of the first computational grid and the adjacent computational grid; The distance between the first computational grid and the adjacent computational grid; a means for calculating a pressure gradient of the first computational grid by calculating a component of the pressure gradient in a direction corresponding to the vector component based on the above formula: A computing device comprising:

8. On the computer, A process for calculating a pressure gradient of a first computational grid in a region configured with a first computational grid and a computational grid adjacent to the first computational grid, an inter-grid pressure gradient obtained by dividing the pressure difference between the adjacent computational grid and the first computational grid by the distance between the adjacent computational grid and the first computational grid; a value obtained by dividing each vector component of the vector from the first computational grid to the adjacent computational grid by the distance and multiplying the result by a component of the pressure gradient of the first computational grid in a direction corresponding to the vector component, and then adding the resultant value to the vector components; is approximately equal to pressures of the first computational grid and the adjacent computational grid; The distance between the first computational grid and the adjacent computational grid; a process of calculating a pressure gradient of the first computational grid by calculating a component of the pressure gradient in a direction corresponding to the vector component based on the above formula; A program that executes the following.

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