An FDS room fire simulation method using wood as a fire source and considering the continued combustion of charcoal

Abstract

The present invention relates to an FDS room fire simulation method that uses wood as a fire source and takes into account the continued combustion of charcoal. First, a model is established, material properties are defined, and a preliminary wood combustion model is input for trial calculation. Then, the mass loss rate of the room model is derived and compared with the test value. A heat release rate curve generated by the charcoal combustion is derived using a linear fitting method, and the difference in mass loss rate is corrected. Finally, a burner surface is set on the bottom plate of the FDS room model, the corrected heat release rate curve generated by the charcoal combustion is input, a secondary calculation is performed, and a result is output. At this time, a secondary comparison is performed with the test result. The present invention can better simulate real room fire conditions and make the simulation effect more accurate.

Description

Technical Field

[0001] The invention relates to an FDS room fire simulation method which takes wood as a fire source and considers the continued combustion of charcoal, and belongs to the field of fire protection engineering. Background Art

[0002] FDS (Fire Dynamic Simulation) is a numerical simulation software developed by the National Institute of Standards and Technology (NIST). FDS6 utilizes computational fluid dynamics (CFD) models of fire-driven fluid flow to simulate fires. Because FDS is open to everyone, it enables numerous researchers to test and verify the accuracy of its simulation results, leading to its widespread application and establishing FDS as the leading authority in the field of numerical fire simulation.

[0003] PyroSim (Thunderhead Engineering PyroSim), developed by the U.S. National Institute of Standards and Technology (NIST), is a software specifically designed for FDS modeling. It provides a visual interface for FDS modeling, allowing operators to intuitively view 3D graphics, greatly accelerating modeling. Once the model is established, PyroSim uses the FDS core algorithm, which is already built into the system, for computational simulation. Finally, users can view the entire fire development process through the post-processor, SmokeView.

[0004] Currently, there are relatively few simulations of room fires in China. Some scholars have conducted simulations of room fires. In these simulations, the combustion characteristics of the woodpile are typically input using the ignition temperature and heat release rate obtained from cone calorimeter tests. The simulation results are then compared with the experimental results. The results show that the heat release rate input from the cone calorimeter test at different external heat flux densities has little effect on the simulation results. The heat release rate agrees well with the experimental measurements, and the indoor air temperature fits well during the fully developed fire phase, but there are significant differences during the cooling phase. This approach fails to account for the impact of continued charcoal combustion and heat release on the room fire simulation results, making it impossible to achieve a more detailed simulation of room fires. Summary of the Invention

[0005] The present invention provides an FDS room fire simulation method that uses wood as a fire source and takes into account the continued combustion of charcoal, which can better simulate real room fire conditions and make the simulation effect more accurate.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] An FDS room fire simulation method using wood as a fire source and considering the continued combustion of charcoal includes the following steps:

[0008] Step S1: Establish an FDS room model, define the material properties of each room component in the FDS room model, and input the properties of the wood in the room component into the FDS room model for trial calculation to obtain calculated values;

[0009] Step S2: The mass loss rate of the FDS room model is derived and compared with the experimental value. The heat release rate curve generated by the combustion of charcoal after the combustion of wood in the FDS room model is derived using a linear fitting method, and the difference in the derived mass loss rate is corrected;

[0010] Step S3: A burner surface is set on the bottom plate of the established FDS room model to simulate the process of continuous heat release after the wood burns to charcoal. The heat release rate curve generated by the charcoal combustion is input as a function of time and a secondary calculation is performed;

[0011] Step S4: Output the result after the secondary calculation and make a secondary comparison with the test value for verification;

[0012] As a further preferred embodiment of the present invention,

[0013] In step S1, the established FDS room model is a preliminary finite element model of the room fire established in FDS, including each room component including a room model, a solid wood pile model, and a thermocouple tree model, and defining material properties for each component model;

[0014] As a further preferred embodiment of the present invention,

[0015] Based on the properties of wood in the room structure, the simplified wood combustion heat release model is input into the FDS room model. The calculation formula of the simplified wood combustion heat release model HRRPUA is:

[0016]

[0017] In the formula, H t is the maximum heat release rate per unit area during wood combustion. is the mass loss rate of the solid wood pile, and the test data is taken during the test, ΔH c is the calorific value of wood, A s It is the exposed area of the solid wood pile;

[0018] As a further preferred embodiment of the present invention,

[0019] In step S2, the mass loss rate of the FDS room model is derived and the horizontal coordinate t corresponding to the intersection of the test value and the calculated value in the descending section is recorded. c , t>tc The mass loss rate of the solid wood pile within the time interval Take out separately and perform linear fitting. The fitting straight line is close to the upper envelope of the test value, which is the heat release rate curve of charcoal combustion after wood combustion.

[0020] As a further preferred embodiment of the present invention,

[0021] In the established FDS room model, the heat release rate curve of charcoal combustion after wood combustion is input as a function of time, which is The establishment of the modified FDS room model is completed.

[0022] Through the above technical solution, compared with the existing technology, the present invention has the following beneficial effects:

[0023] 1. The present invention uses real wood piles as fuel, making the simulation effect closer to the actual test effect;

[0024] 2. The simplified calculation method of the wood combustion heat release model proposed in this invention makes simulation more convenient;

[0025] 3. The simulation method provided by the present invention can simulate the process of wood burning to form charcoal and then continuing to burn and release heat, thereby improving the accuracy of room fire simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings and examples.

[0027] Figure 1 This is a simplified wood combustion heat release model provided by the present invention;

[0028] Figure 2 is a comparison chart between the experimental value and the simulated value of the mass loss rate of charcoal before heat release correction in the example provided by the present invention;

[0029] Figure 3 is a linear fitting curve of the simplified wood combustion heat release model in the example provided by the present invention;

[0030] Figure 4 is the modified FDS room model provided by the present invention;

[0031] Figure 5 This is a comparison chart of the mass loss rate test value and the simulation value after the charcoal exothermic correction in the example provided by the present invention;

[0032] Figure 6 This is a comparison chart of the experimental value and the simulated value of the indoor upper gas temperature after the charcoal heat release correction in the example provided by the present invention;

[0033] Figure 7It is a flow chart of the simulation method provided by the present invention. DETAILED DESCRIPTION

[0034] The present invention will now be described in further detail with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "left side", "right side", "upper", "lower", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are intended only to facilitate the description of the present invention and simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second", etc. do not indicate the importance of the components and therefore should not be understood as limiting the present invention. The specific dimensions used in this embodiment are only for illustrative purposes only and do not limit the scope of protection of the present invention.

[0035] As explained in the background technology, in current experiments on room fire simulations, the heat release rate is in good agreement with the experimental measurements, and the indoor air temperature is well fitted during the full development stage of the fire. However, there is a large difference during the cooling stage of the fire. There is no way to solve the impact of the continued combustion and heat release of charcoal on the room fire simulation results, and it is impossible to simulate room fires more accurately.

[0036] Therefore, the present application aims to provide a FDS room fire simulation method that takes wood as a fire source and considers the continued combustion of charcoal. Figure 7 The simulation method shown is explained in detail with examples.

[0037] Step S1: Establish an FDS room model, define the material properties of each room component in the FDS room model, and input the properties of the wood in the room component into the FDS room model;

[0038] The established FDS room model is the preliminary finite element model of the room fire established in FDS, including the various room components including the room model, the solid wood pile model and the thermocouple tree model, and the material properties of each component model are defined.

[0039] Combined with the conditions of ventilation-controlled fire, a simplified wood combustion heat release model suitable for ventilation-controlled fire is proposed. Here the model is as follows: Figure 1 As shown, in Figure 1 In the above example, the horizontal axis t refers to the time after the wood surface temperature reaches the ignition point, and the ignition point of the wood is set to 232°C. In this simplified wood combustion heat release model, there are two parameters, H t Indicates the maximum heat release rate per unit area during wood combustion, t0 indicates the maximum heat release rate per unit area during wood combustion, and t0 indicates the maximum heat release rate per unit area during wood combustion. t The time required. In this example, t0 = 20s. Before t0, the simplified wood combustion heat release model HRRPUA and t 2 Directly proportional.

[0040] Combined with the mass loss rate of the solid wood pile measured during the experiment, the simplified wood combustion heat release model HRRPUA is proposed as follows:

[0041]

[0042] In the formula, H t is the maximum heat release rate per unit area during wood combustion. is the mass loss rate of the solid wood pile, and the test data is taken during the test, ΔH c is the calorific value of wood, here we take 17.1kJ / g, A s A is the exposed area of the solid wood pile, s =4NnbL-nbL+2Nnb 2 -2Nn 2 b 2 +2n 2 b 2 In this example, A s 5.20m 2 , 13.9g / s, H t 45.7kW / m 2 .

[0043] The simplified wood combustion heat release model mentioned above is input into the FDS room model.

[0044] Step S2: Derive the mass loss rate of the FDS room model and compare it with the experimental value to obtain Figure 2 The comparison chart shown is by Figure 2 It can be seen that the simulation effect of mass loss rate is good in the first 26 minutes. However, after 26 minutes, since the physical woodpile in the FDS room model is almost burned out, it is impossible to simulate the situation in which the charcoal produced after the wood combustion continues to burn and release heat in the experiment. Therefore, based on the experimental data, it is necessary to improve the FDS room model and obtain a model for the continued combustion and heat release of charcoal after the wood combustion to correct this simulation method.

[0045] Next, we will explain the correction method in detail. First, we record the horizontal coordinate t corresponding to the intersection of the test value and the calculated value in the descending section. c , for this test case, t c =26min. c The mass loss rate in the time interval Take it out separately and perform linear fitting. The fitting results are as follows Figure 3 As shown. Since the calorific value of charcoal is higher than that of wood itself, and the calorific value in the model is uniformly set to the calorific value of wood, Figure 3 The fitting straight line is the upper envelope close to the test value (according to Figure 3The selected envelope shows that the fitting equation is

[0046] Step S3: Set a burner surface on the bottom plate of the established FDS room model. Figure 4 The "remaining charcoal" is marked in the middle, which is used to simulate the process of continuous heat release after the wood burns to charcoal. The heat release rate (HRRPUA) generated by the combustion of charcoal after the wood burns changes with time. Perform secondary calculations; the establishment of the revised FDS room model is now completed, and the interior layout of the room is as follows Figure 4 shown.

[0047] Step S4: Output the result after the secondary calculation and make a secondary comparison with the test value for verification.

[0048] The specific verification process is as follows: In the comparative test, the FDS calculated value and the experimental value of the mass loss rate (MLR) of the solid wood pile, such as Figure 5 As shown in the figure, the MLR shows a flat peak after reaching the highest point. The MLR at the highest point is consistent with the MLR calculated during input. In general, the FDS room model considering charcoal combustion can better simulate the mass loss rate of woodpile combustion.

[0049] Then compare the FDS calculated value of the upper gas temperature in the room with the experimental value, such as Figure 6 As shown. Figure 6 It can be seen that the FDS calculated values of the indoor temperature field can generally fit the experimental values, and the FDS room model is very accurate in simulating the time to reach the maximum temperature, with an error within 3%.

[0050] After ignition begins and before the temperature reaches 500°C, the FDS room model can provide good simulation results for the indoor temperature. When the fire enters the full development stage, the temperature simulated by the FDS room model rises as a convex function, contrary to the test temperature which rises as a concave function. During the temperature rise stage, the indoor air temperature simulated by the FDS room model is always higher than the test value.

[0051] During the cooling phase, the FDS room model can simulate the upper air temperature relatively accurately before it drops to 600°C. After the upper air temperature drops to 600°C, the calculated values of the FDS room model are generally lower than the experimental values. If the heat release from the continued combustion of charcoal is not considered, the temperature will be lower than 200°C after the end of the test. However, considering the continued combustion of charcoal can better simulate the temperature changes in this stage.

[0052] It can be seen from this that the FDS room fire simulation method provided by this application, which uses wood as a fire source and considers the continued combustion of charcoal, can better simulate a real room fire and make the simulation effect more accurate.

[0053] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such herein, will not be interpreted in an idealized or overly formal sense.

[0054] The meaning of "and / or" in this application means that both situations where each exists alone or both exist at the same time are included.

[0055] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0056] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. An FDS room fire simulation method using wood as a fire source and considering the continued combustion of charcoal, characterized by: The specific steps include: Step S1: Establish an FDS room model, define the material properties of each room component in the FDS room model, and input the properties of the wood in the room component into the FDS room model to perform FDS simulation to obtain the mass loss rate of the FDS room model; Step S2: The mass loss rate of the FDS room model is derived and compared with the experimental value. The heat release rate curve generated by the combustion of charcoal after the combustion of wood in the FDS room model is derived using a linear fitting method, and the difference in the derived mass loss rate is corrected; Step S3: A burner surface is set on the floor of the established FDS room model to simulate the process of continuous heat release after the wood burns to charcoal. The heat release rate versus time curve of the charcoal combustion obtained in step S2 is input to the burner surface, and a secondary FDS simulation calculation is performed to obtain the FDS calculated values of the mass loss rate of the physical wood pile and the upper gas temperature; Step S4: Output the result after the secondary calculation and make a secondary comparison with the test value for verification.

2. The FDS room fire simulation method according to claim 1, wherein wood is used as a fire source and charcoal continues to burn, is characterized in that: In step S1, the established FDS room model is a preliminary finite element model of the room fire established in FDS, including each room component including a room model, a solid wood pile model and a thermocouple tree model, and the material properties of each component model are defined.

3. The FDS room fire simulation method according to claim 2, wherein wood is used as a fire source and charcoal continues to burn, is characterized in that: Based on the properties of wood in the room structure, the simplified wood combustion heat release model is input into the FDS room model. The calculation formula of the simplified wood combustion heat release model HRRPUA is: In the formula, Ht is the maximum heat release rate per unit area during wood combustion. is the mass loss rate of the solid wood pile, and the test data is taken during the test, ΔH c is the calorific value of wood, A s It is the exposed area of the solid woodpile.

4. The FDS room fire simulation method according to claim 3, wherein wood is used as a fire source and charcoal continues to burn, is characterized in that: In step S2, the mass loss rate of the FDS room model is derived and the horizontal coordinate t corresponding to the intersection of the test value and the calculated value in the descending section is recorded. c , t>t c The mass loss rate of the solid wood pile within the time interval Take it out separately and perform linear fitting. The fitting straight line is close to the upper envelope of the test value, which is the heat release rate curve generated by the combustion of charcoal after the combustion of wood.

5. The FDS room fire simulation method according to claim 4, wherein wood is used as a fire source and charcoal continues to burn, characterized in that: In the established FDS room model, the heat release rate curve of charcoal combustion after wood combustion is input as a function of time, which is The establishment of the modified FDS room model is completed.

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