Simulation Of Soil Water-Heat Coupling In During Orchard Freezing And Thawing Of Water Storage Pit Irrigation

The irrigation of fruit trees in winter can save water and protect the soil.It is beneficial to the freezing of soil moisture and infiltration,which increases the water content in the soil and provides better moisture for the fruit trees to germinate and grow in the spring.Because of the existence of water storage pits,water storage pit irrigation increases the contact interface between soil and air,which not only changes the distribution pattern of soil water in orchards,but also changes the distribution of soil temperature in the orchard root zone,especially when winter irrigation is implemented in winter.With other irrigation methods,the soil freeze-thaw process and water-heat evolution process in the storage pit orchard must also be different.Based on the field experiments,this paper analyzes the rules of soil water-heat changes during the wintering period in the water storage pit orchard,and uses the BP neural network model to predict the soil temperature distribution in the impounding orchard during the wintering period,and uses the COMSOL Multiphysics software.A quantitative simulation study was conducted on the coupled evolution process of soil moisture in the impounding orchard under freezing and thawing conditions.The main results obtained were as follows:1.Before the winter irrigation,the soil temperature in the storage pit at the same soil depth was lower than the soil temperature in the ground irrigation.After winter irrigation,the water storage pit with an irrigation volume of 180 L per plant was compared with surface irrigation.In the same depth of soil,the soil temperature of the storage pit irrigation was lower than the surface irrigation in winter as a whole;at different soil depths,the water storage pit irrigation The distribution of soil temperature in winter was consistent with that of surface irrigation.Both showed that the soil temperature increased with the increase of soil depth.The change of soil temperature during the freeze-thaw period with the time of two irrigation modes showed that the soil temperature decreased first and then increased.The trend is that the minimum temperature of the pit irrigation pit has a hysteresis compared with surface irrigation.The water temperature in the irrigation pits with winter irrigation of 60L/strain,180L/strain,and 300L/soil showed a tendency of increasing at the depth of the same soil layer as the irrigation volume increased.In the soil depth of 0-40 cm,the soil temperature changes more obviously with the increase of irrigation volume,and the soil depth below 40 cm,with the increase of irrigation volume,the soil temperature does not change much.2.In the freezing period,the water content of the irrigation pit with irrigation volume of 0L/plant is larger at the middle and deep layers of 80-100cm;the irrigation volume is 60L/strain,180L/strain and 300L/sl The water content showed a high level at 0-100 cm.The soil water content of different irrigation volumes increased with the depth of the soil layer as a whole(excluding the surface layer of 20cm)and then increased first and then decreased,reaching the maximum value at 80 cm..When the soil enters the melting period,soil moisture content at different irrigation levels is greater than soil moisture content during the freezing period.There is a large contrast at the 0-40 cm soil layer.The soil moisture content before and after freezing and thawing is divided by 0-40 cm.The depth of the soil layer has a large change,and after the soil is melted,the moisture content of the deep soil increases more than the freezing period.3.Based on the real-time field monitoring data of the soil temperature during the wintering period of water storage pit irrigation in 2015 and 2016,the minimum temperature of the layered soil,the average temperature within the pit,the surface temperature,and the radial distance along the pit wall at a distance of 5 cm from the wall of the impoundment were used as input.The minimum temperature of the layered soil at the 15 cm,25cm and 35 cm height of the storage pit wall is the output,and the BP-WSPI-T model with a topological relationship of 11-13-8.When estimating the minimum soil temperature at 15 cm,25cm and 35 cm from the pit wall,the average relative errors of BP-WSPI-T model were 8.7%,9.4%,and 7.3%,respectively;when the two-dimensional distribution of soil temperature was predicted,The average relative error of the model is 8.5% and the model error is small.Therefore,the BP-WSPI-T model established in this paper can simulate the dynamic change of the soil temperature distribution in the winter of the impounding pit irrigation,and can irrigate over the winter soil for the impoundment pit.Temperature prediction provides a quantitative analysis tool.4.According to the theory of soil water-heat coupling,the soil water-heat coupling model of water storage pit irrigation orchard under freezing and thawing condition was established.The water-heat coupled coupling equations,initial and boundary conditions,and the required hydrothermal parameters of the model under freeze-thaw conditions were determined.With the help of COMSOL Multiphysics software,the coupling of water and heat in the orchard soil under water storage pits under freezing and thawing conditions was realized.Numerical Simulation.The field simulation data were used to verify the simulation results.The results show that the absolute error between soil temperature simulation results and actual measurement results is within 0~1.5°C,and the relative error between soil water content simulation results and actual measurement results is 6.3%,and the error is small.According to the validated model,the soil water and heat distribution during the wintering period of the irrigation pit with the irrigation volume of 60L/strain,180L/strain,and 300L/strain was simulated,and the results showed that the total soil moisture content with different irrigation volume was related to the soil depth.The increase of the soil moisture content increased first and then decreased,and reached the bottom of the soil,the water content increased.With the increase of irrigation volume,the total soil moisture content of different soil depths showed an increasing trend;soil ice content was mainly Occurred in the soil 0-60 cm,and the closer the near the pit,the ice content is also large.The soil temperature under different irrigation amounts showed an increase with the increase of soil depth.The soil temperature below 0°C appeared at 0-60 cm in the soil layer,and the soil temperature nearer the surface and the pit wall was lower.The soil hydrothermal simulation results are in line with the rules of water and heat distribution in the orchard soil under the condition of freezing and thawing.Therefore,the soil water-heat-coupled transport model for storage orchard irrigation under freezing and thawing conditions can be used to predict the temperature distribution of freeze-thaw soil,and the accumulation and migration of pore water,as well as the accumulation of ice content.Under the conditions,water storage pits will provide services to prevent freezing and water storage in apple orchards.