Method for acquiring boundary and initial value conditions of one-dimensional unsteady-state heat transfer model of greenhouse soil

Abstract

The invention discloses a method for acquiring boundary and initial value conditions of a one-dimensional unsteady heat transfer model of greenhouse soil. The method comprises the following steps: setting an upper boundary condition by adopting a first type of boundary conditions in heat transfer science; setting a lower boundary condition based on the long-term observation data; an initial value condition is obtained through an initial value obtaining stage and a calculation simulation stage. The upper boundary avoids deviation caused by an empirical formula through a combination scheme of sensor actual measurement and thin soil anti-interference design, the short-time scale constant-temperature characteristic of soil at the depth of 1.05 m is determined based on actual measurement data, then the lower boundary is set as a second-class boundary condition with the heat flux density being zero, the second-class boundary condition is highly matched with the actual soil thermal condition, and the actual soil thermal condition is determined. And meanwhile, the initial value is converged to a true value through a two-stage process, initial value acquisition only needs to be executed for the first time, a preorder simulation result is automatically used subsequently, and the precision and the calculation efficiency are both considered.

Description

Technical Field

[0001] This invention relates to the field of greenhouse environment simulation technology, specifically to a method for obtaining the boundary and initial conditions of a one-dimensional unsteady-state heat transfer model of greenhouse soil. Background Technology

[0002] In greenhouse soil heat transfer studies, one-dimensional unsteady-state heat transfer models are commonly used analytical tools. These models stratify the soil along the vertical direction, treating each layer as an independent unit and implementing interlayer heat transfer based on heat transfer principles. The accuracy of the simulation directly depends on the accuracy of the boundary conditions and initial conditions.

[0003] Boundary conditions include upper and lower boundary conditions. The upper boundary involves various energy exchanges such as convective heat transfer between the soil surface and crops and air, solar radiation absorption, and long-wave radiation. Existing studies mostly use empirical formulas to calculate heat flux as the second type of boundary condition. However, the heat transfer coefficient in empirical formulas is affected by various factors such as air velocity and soil surface roughness, making it difficult to determine accurately and resulting in large calculation errors.

[0004] The lower boundary conditions are often determined by assuming a constant deep soil temperature or by deriving empirical formulas. However, actual measurements show that the deep soil temperature is not constant under different geological, climatic, and soil characteristics. Such methods deviate significantly from the actual situation, and the error will accumulate and amplify during the calculation process.

[0005] Initial conditions, serving as the initial soil temperature distribution for model calculations, are a fundamental prerequisite for simulation. However, the methods for determining initial conditions and their accuracy have long been neglected in the field, resulting in a lack of relevant research. Greenhouse soil temperature is dynamically affected by various factors such as seasonal variations, weather conditions, irrigation and drainage, and crop growth. Temperature distribution varies significantly at different initial time points, and existing studies often use empirical values ​​or averages as initial conditions, failing to fully consider the complexity of actual conditions. This leads to the continuous accumulation of initial deviations over time, severely impacting the accuracy of model simulations.

[0006] In summary, existing methods for obtaining boundary conditions and initial conditions have many shortcomings, which restrict the application effect of one-dimensional unsteady heat transfer models for greenhouse soil. There is an urgent need for an accurate and systematic method to obtain these conditions and provide a reliable input basis for the model. Summary of the Invention

[0007] In order to solve the above-mentioned technical problems, this application proposes the following technical solution: This application provides a method for obtaining the boundary and initial conditions of a one-dimensional unsteady heat transfer model for greenhouse soil, including: The upper boundary conditions are set using the first type of boundary conditions in heat transfer. The lower boundary conditions are set based on long-term observation data; Initial conditions are obtained through an initial value acquisition stage and a computational simulation stage.

[0008] In one possible implementation, the setting of the upper boundary condition using the first type of boundary condition in heat transfer includes: Multiple soil temperature sensors of the same type are installed on the surface of the greenhouse, and a thin layer of soil of a predetermined thickness is covered on the outer surface of the soil temperature sensors. After deployment, soil temperature sensors are used to acquire soil temperature data for each layer of the surface. The obtained soil temperature data of each surface layer were used as the upper boundary condition for the one-dimensional unsteady heat transfer model of greenhouse soil.

[0009] In one possible implementation, the greenhouse soil is divided into 12 layers along the vertical direction of the ground surface. The layering follows the principle of fine surface layer and uniform deep layer, with the depth ranges of each layer being 0.01~0.03m, 0.03~0.07m, 0.07~0.15m, 0.15~0.25m, 0.25~0.35m, 0.35~0.45m, 0.45~0.55m, 0.55~0.65m, 0.65~0.75m, 0.75~0.85m, 0.85~0.95m, and 0.95~1.05m.

[0010] In one possible implementation, the soil temperature sensor has an accuracy of ±0.3℃ and a measurement range of -50℃ to 100℃.

[0011] In one possible implementation, setting the lower boundary condition based on long-term observation data includes: Determine the observation period; Obtain the overall variation of soil temperature at a preset depth within the observation period; Based on the short-timescale isothermal characteristics of soil temperature at a preset depth within the observation period, the lower boundary condition is set as a second type of boundary condition with zero heat flux density.

[0012] In one possible implementation, the initial value acquisition phase includes: The time interval for the initial value acquisition phase is set to time KM to time K; The measured soil temperature at time KM is used as the initial temperature of each layer in the one-dimensional unsteady heat transfer model of greenhouse soil. The measured surface temperature data from time KM to time K are used as the upper boundary condition, and the second-type boundary condition with zero heat flux density is used as the lower boundary condition. These are input into the one-dimensional unsteady heat transfer model of greenhouse soil. Run a one-dimensional unsteady-state heat transfer model of greenhouse soil to obtain the soil temperature of each layer at time K and use the soil temperature of each layer as initial values ​​for later use.

[0013] In one possible implementation, the computational simulation phase includes: The soil temperature of each layer at time K obtained in the initial value acquisition stage is used as the initial value for this stage. Input the measured surface temperature data from time K to time K+N as the upper boundary condition, and keep the lower boundary heat flux density unchanged at zero. Run a one-dimensional unsteady-state heat transfer model of greenhouse soil and output soil temperature data at different depths from time K to time K+N.

[0014] In one possible implementation, for the next simulation cycle, the soil temperature of each layer at the corresponding moment of the previous simulation output is used as the new initial value, the measured surface temperature data of the corresponding time period is input as the upper boundary condition, the lower boundary condition remains unchanged, and a new simulation cycle is started without repeating the initial value acquisition stage.

[0015] Compared with the prior art, the beneficial effects of this application are as follows: This application proposes a practical method for obtaining boundary conditions: the upper boundary is determined through a combination of sensor measurements and thin-soil anti-interference design, avoiding deviations caused by empirical formulas. Based on measured data, the short-timescale isothermal characteristics of the soil at a depth of 1.05m are determined, and the lower boundary is then set as a second-type boundary condition with zero heat flux density, which highly matches the actual soil thermal conditions. Furthermore, a two-stage process ensures that the initial values ​​converge to the true values, requiring only the initial value acquisition; subsequent iterations automatically reuse previous simulation results, balancing accuracy and computational efficiency. In addition, addressing the industry pain points of a lack of methods for determining initial conditions and large deviations in boundary condition calculations, this application provides a systematic solution, laying the foundation for the accurate application of one-dimensional unsteady-state heat transfer models for greenhouse soils and contributing to the scientific and refined management of greenhouse agriculture.

[0016] This invention only requires the installation of a soil temperature sensor on the ground surface to obtain the upper and lower boundary conditions of the model. It does not require digging a pit to install the sensor, making it convenient to install, highly operable, and of practical significance. Attached Figure Description

[0017] Figure 1 A flowchart illustrating a method for obtaining boundary and initial conditions of a one-dimensional unsteady heat transfer model for greenhouse soil, provided in an embodiment of this application; Figure 2 This is a schematic diagram of the mesh generation and sensor layout of a one-dimensional unsteady heat transfer model for greenhouse soil provided in an embodiment of this application; Figure 3 Soil temperature variation curve at a depth of 1.05m in a greenhouse provided for embodiments of this application; Figure 4 A flowchart for calculating initial conditions provided in the embodiments of this application; Figure 5 The curves showing the variation of the prediction deviation of the initial conditions with depth for different M-value configuration schemes provided in the embodiments of this application. Detailed Implementation

[0018] The present solution will now be described in conjunction with the accompanying drawings and specific embodiments.

[0019] The experiments in this application were conducted in the experimental greenhouse of the Yongqing Precision Experimental Base of the Planning and Design Institute of the Ministry of Agriculture and Rural Affairs. The experimental soils covered common greenhouse cultivation soil types, and the experimental period covered different seasons to ensure the universality and applicability of the method.

[0020] Figure 1 A flowchart illustrating a method for obtaining boundary and initial conditions of a one-dimensional unsteady heat transfer model for greenhouse soil, provided in an embodiment of this application, is shown below. Figure 1 This application provides a method for obtaining the boundary and initial conditions of a one-dimensional unsteady heat transfer model for greenhouse soil, comprising: S101, the upper boundary conditions are set using the first type of boundary conditions in heat transfer.

[0021] See Figure 2In this embodiment, the upper boundary condition is set using the first type of boundary condition in heat transfer. This boundary condition is obtained through direct measurement by soil temperature sensors. The specific implementation steps include: deploying multiple identical soil temperature sensors on the greenhouse surface and covering the outer surface of the soil temperature sensors with a pre-set thickness of 0.01m of soil. It is important to note that in this embodiment, the sensors must be in close contact with the soil to avoid air gaps affecting measurement accuracy. The thin soil cover layer must be evenly laid, with its thickness strictly controlled at 0.01m to avoid poor isolation due to thickness deviations. The thin soil cover structure can isolate external interference such as solar radiation and air convection, ensuring the accuracy of the sensor measurement results. After deployment, the soil temperature data of each layer of the surface is acquired using the soil temperature sensors, and the acquired soil temperature data of each layer is used as the upper boundary condition of the one-dimensional unsteady-state heat transfer model of the greenhouse soil. In this embodiment, the greenhouse soil is divided into 12 layers along the vertical direction of the ground surface. The layering follows the principle of fine surface layer and uniform deep layer. The depth range of each layer is 0.01~0.03m, 0.03~0.07m, 0.07~0.15m, 0.15~0.25m, 0.25~0.35m, 0.35~0.45m, 0.45~0.55m, 0.55~0.65m, 0.65~0.75m, 0.75~0.85m, 0.85~0.95m, and 0.95~1.05m. Soil temperature sensors with an accuracy of ±0.3℃ and a measurement range of -50℃ to 100℃ were selected and installed at the middle positions of 12 soil layers at depths of 0.02m, 0.05m, 0.11m, 0.20m, 0.30m, 0.40m, 0.50m, 0.60m, 0.70m, 0.80m, 0.90m, and 1.00m, respectively, to measure the soil temperature at each layer. A high-precision data acquisition device was used for data recording, recording the sensor measurements in real time. The data sampling interval was set according to the simulation requirements to ensure data continuity and integrity. During data acquisition, the sensor operating status was checked regularly, and any faults were promptly rectified to ensure data integrity. S102 sets the lower boundary conditions based on long-term observation data.

[0022] join Figure 3 In this embodiment, the lower boundary condition is set using the second type of boundary condition in heat transfer, and the method for obtaining the lower boundary condition is determined based on long-term observation data.

[0023] In this embodiment, the observation period was from April 2023 to March 2024. The results showed that the overall soil temperature variation at a depth of 1.05 meters was 10℃. However, on a short time scale, such as less than five days, the soil temperature fluctuation at this depth was extremely small, such as a variation of 0.5℃ from April 1 to 5, 2023, and a variation of 0.3℃ from August 1 to 5, 2023. Based on the above observation conclusions, the lower boundary condition of the model was defined as the second type of boundary condition, and the corresponding heat flux density was set to zero.

[0024] S103, initial conditions are obtained through the initial value acquisition stage and the calculation simulation stage.

[0025] In this embodiment, Figure 4 The initial value acquisition calculation process consists of two stages: initial value acquisition and calculation simulation. The initial value acquisition stage covers time intervals KM to K, and the calculation simulation stage covers time intervals K to K+N.

[0026] Initial Value Acquisition Stage: The magnitude of the M value has a significant impact on the accuracy of the initial value calculation. The simulation period N can be adjusted according to actual application needs and can be set in conjunction with the greenhouse crop growth cycle or management decision-making cycle. To meet the analysis requirements, this embodiment sets the discussion values ​​of the M value to 0 hours, 24 hours, 48 ​​hours, 120 hours, 240 hours, 480 hours, and 720 hours, which are abbreviated as M0, M24, M48, M120, M240, M480, and M720, respectively. To verify the accuracy of the initial value calculation results for each soil layer, this embodiment sets the K value to the local time of the first day of each month from May 1, 2023 to August 1, 2024, at 00:00 and 12:00, respectively. This yields a total of 32 sets of initial values ​​to be analyzed, including 16 sets of initial values ​​at time 00:00 and 16 sets of initial values ​​at time 12:00. By comparing and analyzing the initial value prediction results corresponding to the above 32 initial value acquisition times, this embodiment finally determines the optimal initial value acquisition scheme.

[0027] like Figure 5As shown, the seven M-value configuration schemes are ranked from best to worst in terms of prediction performance as follows: M720, M480, M240, M24, M120, M48, and M0. From the above analysis, it can be concluded that scheme M720 has the highest prediction accuracy. This is because its simulation time is the longest, providing sufficient time for the upper boundary data to correct the deviation between the initial soil temperature value at time KM and the actual measured temperature. Scheme M0 has the lowest prediction accuracy because its initial value is obtained by directly assigning the measured value of the upper boundary to the soil temperature at different depths, while there is obviously a significant difference between the upper boundary temperature and the soil temperature at different depths. M=720 hours was selected, and the measured surface temperature at time KM was used as the initial temperature of each layer. The measured surface temperature data from time KM to time K were input as the upper boundary condition and the lower boundary condition with zero heat flux density. The one-dimensional unsteady heat transfer model of greenhouse soil was run. In this embodiment, the one-dimensional unsteady heat transfer model of greenhouse soil was selected from the model disclosed in patent CN202410570786.4. The soil temperature data of each layer from time KM to time K were calculated. The data gradually converged to the true value over time under real-time upper boundary condition correction. Finally, the soil temperature of each layer corresponding to time K was used as the initial value for later use.

[0028] The simulation phase involves using the soil temperature at time K as the initial value, inputting the measured surface temperature data from time K to K+N as the upper boundary condition of the model, keeping the lower boundary condition as the second type of boundary condition and the heat flux density as zero, and running the one-dimensional unsteady heat transfer model of greenhouse soil to obtain the simulation results of soil temperature at each depth from time K to K+N.

[0029] Subsequent simulation phase: When entering the period from time K+1 to K+N+1, the soil temperature of each layer at time K+1 in the previous simulation output is used as the initial value condition of the model, and the measured surface temperature data from time K+1 to K+N+1 is used as the upper boundary condition of the model. The lower boundary condition of the model still adopts the second type of boundary condition, and the heat flux density is set to zero. A new round of simulation is started without repeating the initial value acquisition process.

[0030] The effectiveness of this method was verified by comparing the measured temperatures from 12 soil temperature sensors at different soil layers with the simulated temperatures from the model. The results show that using the boundary and initial conditions obtained by this method significantly reduces the deviation between the simulated and measured temperatures. The M720 scheme exhibits the best prediction accuracy and can meet the requirements for precise simulation of greenhouse soil temperature.

[0031] In this embodiment, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, the simultaneous existence of A and B, or the existence of B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0032] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0033] The above description is merely a specific embodiment of this application. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application. The protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A method for obtaining boundary and initial conditions of a one-dimensional unsteady heat transfer model for greenhouse soil, characterized in that, include: The upper boundary conditions are set using the first type of boundary conditions in heat transfer. The lower boundary conditions are set based on long-term observation data; Initial conditions are obtained through an initial value acquisition stage and a computational simulation stage.

2. The method for obtaining the boundary and initial conditions of the one-dimensional unsteady heat transfer model for greenhouse soil according to claim 1, characterized in that, The method of setting the upper boundary condition using the first type of boundary condition in heat transfer includes: Multiple soil temperature sensors of the same type are installed on the surface of the greenhouse, and a thin layer of soil of a predetermined thickness is covered on the outer surface of the soil temperature sensors. After deployment, soil temperature sensors are used to acquire soil temperature data for each layer of the surface. The obtained soil temperature data of each surface layer were used as the upper boundary condition for the one-dimensional unsteady heat transfer model of greenhouse soil.

3. The method according to claim 2, characterized in that, The greenhouse soil is divided into 12 layers along the vertical direction of the ground surface. The layering follows the principle of fine surface layer and uniform deep layer. The depth range of each layer is 0.01~0.03m, 0.03~0.07m, 0.07~0.15m, 0.15~0.25m, 0.25~0.35m, 0.35~0.45m, 0.45~0.55m, 0.55~0.65m, 0.65~0.75m, 0.75~0.85m, 0.85~0.95m, and 0.95~1.05m.

4. The method according to claim 2, characterized in that, The soil temperature sensor has an accuracy of ±0.3℃ and a measurement range of -50℃ to 100℃.

5. The method for obtaining the boundary and initial conditions of the one-dimensional unsteady heat transfer model for greenhouse soil according to claim 1, characterized in that, The setting of the lower boundary conditions based on long-term observation data includes: Determine the observation period; Obtain the overall variation of soil temperature at a preset depth within the observation period; Based on the short-timescale isothermal characteristics of soil temperature at a preset depth within the observation period, the lower boundary condition is set as a second type of boundary condition with zero heat flux density.

6. The method for obtaining the boundary and initial conditions of the one-dimensional unsteady heat transfer model of greenhouse soil according to claim 1, characterized in that, The initial value acquisition phase includes: The time interval for the initial value acquisition phase is set to time KM to time K; The measured soil temperature at time KM is used as the initial temperature of each layer in the one-dimensional unsteady heat transfer model of greenhouse soil. The measured surface temperature data from time KM to time K are used as the upper boundary condition, and the second-type boundary condition with zero heat flux density is used as the lower boundary condition. These are input into the one-dimensional unsteady heat transfer model of greenhouse soil. Run a one-dimensional unsteady-state heat transfer model of greenhouse soil to obtain the soil temperature of each layer at time K and use the soil temperature of each layer as initial values ​​for later use.

7. The method for obtaining the boundary and initial conditions of the one-dimensional unsteady heat transfer model for greenhouse soil according to claim 1, characterized in that, The computational simulation phase includes: The soil temperature of each layer at time K obtained in the initial value acquisition stage is used as the initial value for this stage. Input the measured surface temperature data from time K to time K+N as the upper boundary condition, and keep the lower boundary heat flux density unchanged at zero. Run a one-dimensional unsteady-state heat transfer model of greenhouse soil and output soil temperature data at different depths from time K to time K+N.

8. The method for obtaining the boundary and initial conditions of the one-dimensional unsteady heat transfer model of greenhouse soil according to claim 7, characterized in that, For the next simulation cycle, the soil temperature of each layer at the corresponding time point of the previous simulation is used as the new initial value, and the measured surface temperature data of the corresponding time period is input as the upper boundary condition. The lower boundary condition remains unchanged, and a new simulation cycle is started without repeating the initial value acquisition stage.

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