Simulation method and program

Abstract

To provide a simulation method and a program that enable the amount of substances in air taken into a human body by breathing to be easily simulated by a general-purpose electronic computer.SOLUTION: A simulation method performed by a simulation device that simulates the amount of uptake grains into a human body from air with an electronic computer using numerical fluid dynamics of performing a numerical analysis upon performing grid generation includes a simulation processing unit that is located adjacent to a face portion of a human body model, sets an evaluation target space surrounded by a polyhedron, and performs a simulation of, based on an accumulated amount of grains in a predetermined measurement time for grains present in the set evaluation target space, calculating the amount of uptake grains.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a simulation method and a program. [Background technology]

[0002] There is known a technique for predicting infection transmission of infectious contaminants based on CFD (Computational Fluid Dynamics) analysis (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Hiroaki Asanuma, Kazuhide Ito, "Prediction of infection spread by coupled analysis of non-stationary non-uniform concentration distribution and mathematical epidemiological model in hospital space (JAIJ Environmental Journal)", 2013, 78.688: 481-487 Summary of the Invention [Problem to be solved by the invention]

[0004] Non-Patent Document 1 discloses a method for simulating the amount of gas in the air taken into the human body by breathing using numerical analysis by CFD. However, a method for simulating the amount of particles such as droplets in the air taken into the human body by breathing had not been established. As a result of the inventor's investigation, it was found that the amount of particles such as droplets in the air taken into the human body by breathing can be simulated using numerical analysis by CFD, but there was still a demand for reducing the calculation load as much as possible when simulating particles.

[0005] The present invention has been made in view of the above circumstances, and has an object to make it possible to easily simulate, by means of a general-purpose electronic computer, the amount of substances in the air taken into the human body through breathing. [Means for solving the problem]

[0006] One aspect of the present invention that solves the above-mentioned problems is a simulation method that uses computational fluid dynamics, which generates a grid and then performs numerical analysis, to simulate the amount of particulate matter taken into the human body from the air using a computer, in which an evaluation space is set adjacent to the face of a model of the human body and surrounded by a polyhedron, and a simulation is performed to determine the amount of particulate matter taken based on the accumulated amount of particulate matter present in the set evaluation space over a specified measurement time.

[0007] Furthermore, one aspect of this embodiment is a program for causing an electronic computer to function as a simulation device that uses computational fluid dynamics, which generates a grid and then performs numerical analysis, to simulate the amount of particulate matter taken into the human body from the air, and the program causes an electronic computer to function as a simulation processing unit that sets an evaluation target space adjacent to the face part of the human body model and surrounded by a polyhedron, and performs a simulation to determine the amount of particulate matter taken in based on the accumulated particulate matter amount over a specified measurement time for particles present in the set evaluation target space. Effect of the Invention

[0008] As described above, according to the present invention, it is possible to obtain an effect that the amount of substances in the air taken into the human body through breathing can be easily simulated by a general-purpose electronic computer. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a simulation device according to an embodiment of the present invention. [Diagram 2] 1 is a diagram showing an example of a human body model and an evaluation target space according to the present embodiment; [Diagram 3] FIG. 2 is a diagram showing an example of an evaluation target space according to the present embodiment. [Figure 4]1 is a diagram showing an example of a human body model and an evaluation target space according to the present embodiment; [Diagram 5] FIG. 2 is a diagram showing an example of an evaluation target space according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 1 shows an example of the functional configuration of a simulation device 100 according to this embodiment. The simulation device 100 is a device that simulates the amount of particles and granules, such as droplets, that are taken into the human body by breathing in an environment in which particles and granules, such as droplets, exist in the air. Note that the particles and granules to be simulated in this embodiment may be any particles and granules having a size of 10 μm or less, and include droplets generated by scattering powder or liquid, as well as micro droplets having a size of less than 5 μm. The hardware of the simulation device 100 in the figure may be, for example, a general-purpose personal computer (an example of an electronic calculator). The functions of the simulation device 100 in the figure are realized by a CPU (Central Processing Unit) provided with the hardware of the simulation device 100 executing a program corresponding to the simulation of this embodiment.

[0011] The simulation device 100 includes a user interface unit 101 , a control unit 102 , and a storage unit 103 .

[0012] The user interface unit 101 is a part that receives operations from a user and outputs information to the user. The user interface unit 101 includes, as hardware, input devices such as a mouse, a keyboard, a touch panel, a touch pad, etc., and accepts operations performed on these input devices. The user interface unit 101 outputs information on the accepted operations to the control unit 102. Furthermore, the user interface unit 101 includes a display device as hardware, and displays an image on the display device according to the control of the control unit 102. Furthermore, the user interface unit 101 may be equipped with, for example, a speaker, an earphone output terminal, or the like, so as to be capable of outputting audio.

[0013] The control unit 102 executes various controls in the simulation device 100. The control unit 102 includes a simulation processing unit 121. The simulation processing unit 121 executes a process (simulation process) for simulating the amount of droplets taken into the human body by breathing in an environment in which droplets exist in the air.

[0014] The storage unit 103 stores various data corresponding to the simulation device 100. The storage unit 103 stores a program for the simulation of this embodiment. The storage unit 103 may be configured to be connected to the simulation device 100 via a network or a data interface.

[0015] The simulation device 100 may be provided with an input / output interface, a communication unit for communicating via a network, and the like.

[0016] In addition to the three classical routes of infection for infectious diseases, namely contact infection, droplet infection, and airborne infection, micro-droplet infection, the existence of which has been pointed out recently in the case of the novel coronavirus disease (COVID-19), has been added as an infection route for infectious diseases. The simulation device 100 of this embodiment performs a simulation of the risk of infection through micro-droplet infection, one of the above infection routes. In simulating micro-droplet infection, it is necessary to grasp the behavior of micro-droplets. In order to grasp the behavior of micro-droplets with high accuracy, it is necessary to consider the properties of micro-droplets as particles or granules. The properties of micro-droplets as particles or granules include, for example, the effect of airflow on the particles, evaporation of the particles, gravity acting on the particles, drag, etc.

[0017] For example, when treating microdroplets as a gas and performing numerical analysis using CFD to simulate the risk of infection, it is not possible to reproduce the particle / granular properties of the microdroplets mentioned above. As a result of the inventor's investigation, we came up with a method to perform a simulation by treating microdroplets as particles and performing CFD. However, this requires high computer performance, and it is difficult to perform a simulation with sufficient accuracy using a general-purpose personal computer.

[0018] Therefore, the simulation device 100 of this embodiment uses CFD to simulate the risk of infection through microdroplet infection, treating microdroplets as particles, and calculates the amount of microdroplets taken into the human body through breathing as follows.

[0019] In the simulation performed by the simulation device 100 of this embodiment, a model of the human body that takes in microdroplets (human body model) is determined. Fig. 2 shows an example of a human body model 200 in this embodiment. Fig. 2 shows a side view of the human body model 200 and a plan view of the human body model 200. The human body model 200 in the figure is an example of a human body modeled in a state of sitting on a chair on a floor FL. The human body model 200 is formed of a head 201 and a torso and legs 202 that imitates a state of sitting on a chair on a floor FL. The figure shows specific examples of dimensions (mm) set for each part of the human body model 200. Note that the dimensions of each part of the human body model 200 shown in the figure are merely examples and may be changed as appropriate.

[0020] In the simulation performed by the simulation device 100, an evaluation target space 210A is set for the human body model 200 defined as above. In the simulation performed by the simulation device 100, the integrated particulate amount in the evaluation target space 210A is the amount of particulate taken into the human body by breathing (intake particulate amount). The integrated particulate amount is calculated by integrating the number of particulates present in the evaluation target space 210A over a predetermined measurement time. The integrated particulate amount m intake can be expressed, for example, by the following Equations 1 and 2.

[0021]

number

[0022] In Equation 1, t is time, t max is the measurement time, Q R is the respiration rate per unit time (e.g., 1 second). In Equation 2, C(t) is the particle concentration (particles / m 3 ), n(t) is the number of particles in the evaluation target space 210A. n(t) is obtained, for example, as a result of CFD. In Equation 2, V is the volume of the evaluation target space 210A.

[0023] In the example shown in the figure, the evaluation target space 210A is disposed at a position 140 mm below the top surface of the head 201 in the height direction of the human body model 200 and at the center of the head 201 in the horizontal (lateral) direction. The position at which the evaluation target space 210A is disposed corresponds to the position below the nose on the face. That is, the position of the evaluation target space 210A is determined on the assumption that droplets are mainly taken in through the nose.

[0024] Fig. 3 shows a specific example of the dimensions (size and shape) of the evaluation target space 210A shown in Fig. 2. The evaluation target space 210A in the figure is set as a cube of 20 mm x 20 mm x 20 mm. In other words, the evaluation target space in this embodiment is set as a polyhedron. In CFD, a grid (mesh) is generated in space (grid generation). The grid generated by grid generation is a polyhedron. On the other hand, it is known that the shape of the evaluation target space is spherical or hemispherical when simulating the infection risk of airborne contaminants. However, when the shape of the evaluation target space has a curved surface such as a sphere or hemisphere, it is difficult to reproduce the curved surface by generating a grid using polyhedrons, which limits the grid generation method and significantly increases the calculation load. Therefore, in this embodiment, the evaluation target space 210A is made a polyhedron to be suitable for grid generation in CFD. As a result, in this embodiment, restrictions on the grid generation method in CFD can be eliminated or alleviated.

[0025] Furthermore, the dimensions of the evaluation space 210A in this embodiment may be changed according to the conditions in the simulation. For example, when droplets are treated as particles as in this embodiment, the concentration distribution in space is more likely to be biased than when droplets are treated as gas. Therefore, when the volume of the evaluation target space 210A is small, there is a possibility that a sufficient number of particle samples cannot be obtained. In this embodiment, the volume of the evaluation target space 210A is expanded as follows to deal with the above situation.

[0026] An example of an evaluation target space 210B with a volume larger than that of the example in Fig. 3 will be described with reference to Fig. 4 and Fig. 5. Fig. 4 is a diagram showing an example in which an evaluation target space 210B with a volume larger than that of the example in Fig. 3 is applied to a human body model 200 similar to that in Fig. 2. Fig. 5 is a diagram showing an example of specific dimensions of the evaluation target space 210B. 4, the evaluation target space 210B is disposed at a position 140 mm below the upper surface of the head 201 in the height direction of the human body model 200 and at the center of the head 201 in the horizontal (lateral) direction, similar to the evaluation target space 210 in FIG. 2. In other words, similar to the evaluation target space 210, the evaluation target space 210B is disposed at a position corresponding to the bottom of the nose on the face.

[0027] 5, the evaluation target space 210B is disposed such that a side surface 212 of a prism having a bottom surface 211 in the shape of a right triangle faces the face of the head 201 of the human body model 200, and a side surface 213 forms the upper surface. In this case, the dimensions of the right triangle of the bottom surface 211 are 50 mm for the adjacent side and 200 mm for the opposite side. The dimensions of the side surface 213 forming the upper surface are 50 mm x 50 mm. The volume of the evaluation target space 210A is 0.008L (=20mm×20mm×20mm), whereas the volume of the evaluation target space 210B is expanded to 0.25L (=50mm×50mm×200mm×0.5).

[0028] The space to be evaluated 210B shown in Figures 4 and 5 is designed so that the cross-sectional area in the planar direction decreases from the top surface downwards. This is to take into consideration the fact that the amount of air inhaled by the nose decreases as the distance from the nose increases, and the increase in airflow due to body temperature around the chest of the human body, etc. In the following description, when there is no need to distinguish between the evaluation spaces 210A and 210B, they will be referred to as the evaluation space 210.

[0029] By increasing the volume of the evaluation space 210 as described above, the simulation device 100 can perform a highly accurate simulation in response to conditions where the number of particle samples is small. However, if the volume of the evaluation space 210 is too large, the evaluation space will include a spatial region where the probability of being inhaled through a person's nose is low, and in this case as well, the accuracy of the simulation will decrease. In consideration of this, it is preferable to set an upper limit on the volume of the evaluation space. Therefore, in this embodiment, the upper limit of the volume of the evaluation target space is set based on the ventilation volume at one time. Specifically, in consideration of the ventilation volume at one time being 0.5 L, the upper limit of the volume of the evaluation target space is set to 0.5 L.

[0030] In this embodiment, a simulation was also performed on the condition that the human body takes in droplets when wearing a mask and the nose is covered. In this embodiment, when performing a simulation under the condition that a mask is worn, the particle transmittance of the mask is set, and the simulation device 100 applies the set particle transmittance to the simulation.

[0031] In this embodiment, the particle transmittance of the mask may be determined based on the ratio of the number of particles that pass through the mask to the number of particles present in the space to be evaluated, and the ratio of the number of particles that enter through the gap between the mask and the person's face to the number of particles present in the space to be evaluated. In this case, the particle transmittance of the mask is set to a different value depending on conditions such as the material and structure of the mask. In correspondence with the above-mentioned formulas 1 and 2, for example, by applying the particle transmittance as a coefficient to the number of particles n(t) in the evaluation target space and performing a calculation, the cumulative particle amount m intake is required. In this manner, in the present embodiment, a coefficient as particle transmittance is applied to simulate the amount of particle intake under the condition of wearing a mask in the simulation device 100. This can reduce the calculation load of the simulation under the condition of wearing a mask.

[0032] Furthermore, when simulating the amount of taken-in particles using the simulation device of this embodiment, the calculation can be performed taking into consideration, for example, the following eight items, ie, item 1 to item 8. The first item is the effect of air currents on particle motion. The second item is various forces acting on particles, such as the Saffman lift force and the Brownian force. The third item is the particle size threshold at which gravity can be ignored. The fourth item is the change in particle evaporation rate due to differences in humidity. The fifth item is the change in the evaporation rate and fall speed of particles due to the physical properties of the particles (density, viscosity, etc.). The sixth item is the temperature change due to particle radiation. The seventh item is collisions between particles. The eighth item is the fragmentation of particles due to the velocity of a cough or sneeze.

[0033] In addition, in this embodiment, in order to reduce the calculation load while maintaining a certain level of accuracy in the simulation results of the amount of captured particulate matter, it is possible to appropriately select items from the above items that are not to be considered in the simulation. As an example, with regard to the first item, calculations have shown that not taking it into account would cause particles to fly farther, so it is possible to err on the safe side and not take it into account. As for the second item, calculations were performed reproducing minute forces, and the results showed that the particle trajectories hardly changed at all, so it can be disregarded. As for the third item, after calculating the fall speed for several particle diameters, it is possible to take into account particle diameters larger than 10 μm and not take into account particle diameters of 10 μm or less. As for the sixth item, calculations have confirmed that the effects of temperature changes and trajectories of particles caused by radiation are small, so it can be disregarded. Regarding item 7, for example, if a person, who is a particle generation source, is wearing a nonwoven mask, the number of particles generated from the gap between the face and the mask is small, so collisions between particles can be ignored. Regarding item 8, verification was performed for a case in which particles were ejected at a specified initial velocity, and no particle fragmentation occurred, so this item can be disregarded. On the other hand, the fourth item will be taken into consideration since calculations have shown that the evaporation rate varies greatly depending on the humidity. As for the fifth item, it is taken into consideration because, for example, previous research has shown that the evaporation rate is slower when an evaporation model including non-volatile components is used. However, because the calculation load for an evaporation model including non-volatile components is high, it may be taken into consideration in a pseudo-manner, for example, by modeling the time it takes for evaporation.

[0034] The configuration of this embodiment can be applied to assess the risk of infection for all infectious diseases that may be transmitted by microdroplets.

[0035] In addition, a program for realizing the functions of the above-mentioned simulation device 100 may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed to perform the processing of the above-mentioned simulation device 100. Here, "reading a program recorded on a recording medium into a computer system and executing it" includes installing the program into a computer system. The "computer system" here includes hardware such as an OS and peripheral devices. The "computer system" may also include multiple computer devices connected via a network including a communication line. The recording medium also includes a recording medium provided inside or outside and accessible from a distribution server to distribute the program. [Explanation of symbols]

[0036] 100 Simulation device, 101 User interface unit, 102 Control unit, 103 Storage unit, 121 Simulation processing unit, 200 Human body model, 210 (210A, 210B) Evaluation target space

Claims

1. A simulation processing unit that uses computational fluid dynamics, which performs numerical analysis after generating a grid, to simulate the amount of particulate matter taken into the human body from the air, sets an evaluation target space adjacent to a face part of a predetermined human body model and surrounded by a polyhedron, and determines an integrated particulate amount obtained by utilizing a value obtained by integrating the particle concentration of particulate matter present in the set evaluation target space over a predetermined measurement time as the result of the simulation, the amount of particulate matter taken in. A simulation device comprising:

2. The volume of the space to be evaluated is 0.5 liters or less. The simulation device according to claim 1 .

3. The simulation processing unit: In simulating the amount of particles taken in by the human body wearing the mask, the amount of particles taken in is calculated by multiplying the cumulative amount of particles during the measurement time by a coefficient based on a particle transmittance that is predetermined for the mask. The simulation device according to claim 1 or 2.

4. The particle transmittance is determined based on the ratio of particles passing through the mask and the ratio of the number of particles entering the gap between the mask and the face of the model from the evaluation target space. The simulation device according to claim 3.

5. The particles are droplets generated by the splashing of liquid. The simulation device according to claim 1 .

6. The granules have a diameter of 10 μm or less. The simulation device according to claim 1 .

7. The evaluation target space is located below the position of the nose of the model's face when viewed from a direction facing the model's face. The simulation device according to any one of claims 1 to 6.

8. A computer as a simulation device, To function as a simulation processing unit that, when simulating the amount of particulate matter taken into the human body from the air using computational fluid dynamics that performs numerical analysis after generating a grid, sets an evaluation target space adjacent to a face part of a predetermined human body model and surrounded by a polyhedron, and determines an integrated particulate amount obtained by utilizing a value obtained by integrating the particle concentration of particulate matter present in the set evaluation target space over a predetermined measurement time as the amount of particulate matter taken in as a result of the simulation. program.

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