CN110598287A - Construction method of reservoir region beach hydrothermal migration model based on Ren model - Google Patents
Construction method of reservoir region beach hydrothermal migration model based on Ren model Download PDFInfo
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Abstract
The invention discloses a construction method of a bank region beach hydrothermal migration model based on a Ren model, which comprises the steps of firstly constructing a bank region beach hydrothermal migration mathematical model based on a Richards equation and a thermal convection-diffusion equation, and describing the relationship between a temperature field and a seepage field; then setting boundary conditions including boundary conditions of a seepage field and boundary conditions of a temperature field for the pool region beach hydrothermal migration model; and finally, solving the reservoir region beach hydrothermal migration model, and describing the relationship between the equivalent thermal conductivity coefficient and the water content of the soil body and each physical parameter of the soil by adopting a Ren model in the solving process, thereby obtaining the time-space change characteristic of the internal temperature field of the reservoir region beach under the change condition. The method solves the problem that the influence mechanism of the reservoir beach hydrothermal migration under the changing condition cannot be accurately simulated due to factors such as difficulty in determining model parameters, large errors and the like in the prior art.
Description
Technical Field
The invention belongs to the technical field of hydraulic engineering, and particularly relates to a construction method of a reservoir region beach hydrothermal migration model based on a Ren model.
Background
Dam building, power generation, flood regulation and water storage are important engineering guarantee measures for supporting the economic coordinated development of areas, lightening or avoiding flood disasters and realizing optimal allocation of water resources. However, the river is a dynamic, highly open, non-equilibrium, non-linear complex system, and dam engineering construction also has many negative effects on the sustainable development of the watershed water environment. For example, the reservoir water storage and drainage can cause the hydrological situation of a natural river to change, and cause the redistribution of a seepage field and a temperature field in a downstream beach, thereby influencing the oxidation-reduction environment of the beach soil, the living conditions of different microorganisms and the medium environment of wetland biogeochemical element circulation, which indirectly influence the growth process of vegetation. Although the hydrologic conditions are the decisive factors for controlling the evolution of the beach ecosystem and ensuring the health of the beach ecosystem, the hydrologic situation of the beach soil restricts the biological, physical and chemical characteristics of the beach soil environment, plays an especially important role in the beach water circulation process in the reservoir area, and is very unfavorable for the sustainable health development of rivers.
Although scholars at home and abroad have a lot of achievements on problems of water level, temperature, water chemistry indexes and the like of a riparian zone and a river channel water body, the full coupling model and mechanism of beach saturation-unsaturated flow heat in a warehouse under a changing condition are rarely reported, and most researches are unreasonable for enabling the unsaturated area of the riparian zone to be equivalent to a saturated area or a dry porous medium. In the non-seepage area, the heat in the rock and soil is transferred in a heat conduction mode of the soil medium, and in the seepage area, the heat is transferred by the heat transfer of the rock and soil medium and the convection of the heat carried by the liquid in seepage. Therefore, the soil thermal conductivity is one of important parameters for constructing a beach saturation-non-saturation flow thermal coupling model, which is not only a premise for describing soil temperature change and energy transmission, but also a basis for researching other soil physical processes, such as hydrothermal coupling transmission, gas diffusion and substance migration, and a basis for researching seed germination and growth of plants and energy conversion between roots and soil.
With the development of national economy and the improvement of engineering technology, adverse ecological environment influence brought by reservoir water storage and drainage is generally regarded by students in all countries in the world. How to reasonably and efficiently adjust and manage reservoir operation by utilizing engineering or non-engineering measures and slow down the adverse effects of water level and water temperature changes caused by reservoir operation on the beach environment and ecology in the reservoir area becomes a great problem to be solved urgently in the related field. Therefore, development and establishment of reservoir beach hydrothermal migration models and mechanism researches are urgently needed.
Disclosure of Invention
The invention aims to provide a construction method of a reservoir beach hydrothermal migration model based on a Ren model, and solves the problem that in the prior art, model parameters are difficult to determine, errors are large and other factors cause that the influence mechanism of reservoir beach saturation-unsaturated flow thermal coupling under a changing condition cannot be accurately simulated.
The technical scheme adopted by the invention is that a construction method of a bank beach hydrothermal migration model based on a Ren model is implemented according to the following steps:
step 1, constructing a reservoir region beach hydrothermal migration mathematical model based on a Richards equation and a thermal convection-diffusion equation, and describing the relationship between a temperature field and a seepage field;
step 2, setting boundary conditions including boundary conditions of a seepage field and boundary conditions of a temperature field for the pool beach hydrothermal migration model;
and 3, solving the reservoir region beach hydrothermal migration model, and describing the relationship between the equivalent thermal conductivity coefficient and the water content of the soil body and each physical parameter of the soil by adopting a Ren model in the solving process so as to obtain the time-space change characteristic of the internal temperature field of the reservoir region beach under the change condition.
The present invention is also characterized in that,
the reservoir bank water heat migration transient seepage field in the step 1 is described by a Richards equation as follows:
in the formula: theta is the water content, k is the soil permeability coefficient,in the saturated region, k represents a function of the initial temperature field T, and in the unsaturated region, k represents a function of the suction force or the water content of the soil matrix; h is a pressure water head, H is a total water head, C is the soil water content,n is the porosity of the porous medium, SsIs elastic water storage rate, QsIs a sink item of the seepage source,. v.is the Laplace equation, DTIs hydrodynamic dispersion coefficient, t is time;
in a bank beach hydrothermal migration transient seepage field in a reservoir, a Van Genuchten model is adopted to describe a characteristic curve of the water content of the unsaturated zone soil:
in the above formula, h (theta) is the soil matrix suction force, and k (theta) is the unsaturated soil permeability coefficient; thetasThe saturated water content of the soil is obtained; thetarThe residual water content of the soil is obtained; alpha and nvIs VG model parameter, m is 1-1/nv；ksThe permeability of the saturated soil body;
the transport of heat transport in porous media is described by the thermal convection-diffusion equation:
in the formula: c is the specific heat capacity of the soil body, rho is the equivalent density of the soil body, v is the Laplace equation, lambda is the equivalent heat conductivity coefficient of the soil body, cwIs the specific heat capacity of water, pwIs the density of water, v is the average flow velocity of water, T is the initial temperature field, QhIs the source and sink term of the temperature field.
Introducing the formulas (1) to (4) into an underground water flowing and porous medium heat transfer module of COMSOL Mutiphic finite element software to realize the numerical simulation of the coupling of a temperature field and a seepage field.
The boundary conditions of the seepage field in step 2 are set as follows:
according to the measured water level time sequence, a model infiltration boundary is set as a variable water head boundary, an upper boundary, a left boundary and a right boundary of an infiltration surface are set as no-flow boundaries, and a bottom boundary is set as a permeable layer boundary.
The boundary conditions of the temperature field in step 2 are set as follows:
setting the left boundary, the right boundary and the bottom boundary of the model as adiabatic boundaries; and setting the boundary above the infiltration as an atmospheric temperature boundary and setting the infiltration boundary as a river temperature boundary according to the measured river temperature and the atmospheric temperature time sequence.
Step 3 is specifically implemented according to the following steps:
step 3.1, inputting parameters: dry soil volume weight gammadIn the unit of KN/m3(ii) a Bulk density ρb(ii) a Sand mass fraction Csand(ii) a Mass fraction of clay Cclay(ii) a Mass fraction of powder particles Csilt(ii) a Mass ratio of organic matter Com；
Step 3.2, adding an interpolation function, inputting the boundary conditions obtained in the step 2, and defining the relation between normal water density and viscosity coefficient:
when T is more than or equal to 0 ℃ and less than or equal to 40 ℃,
when T is more than or equal to 0 ℃ and less than or equal to 280.6 ℃,
ρT＝838.4661+1.4005T-0.0031×T2+3.7182×10-8×T3 (6)
wherein the temperature unit is; density unit is kg/m3(ii) a The dynamic viscosity coefficient mu is Pa.s;
step 3.3, modifying the equivalent thermal conductivity coefficient lambda of the soil body into an expression of the thermal conductivity coefficient changing along with the water content and soil parameters in the Ren model, and establishing a reservoir region beach hydrothermal migration model based on the Ren model;
and 3.4, operating the bank beach hydrothermal migration model based on the Ren model set in the step 3.3, and observing the change characteristics of the bank beach temperature field and the seepage field along with time, so as to obtain the change rule of the temperature of different elevations of the bank beach along with time.
The Ren model in step 3.3 is specifically as follows:
λ＝(λsat-λdry)·Ke+λdry (7)
Ke＝exp(α-θ-β) (8)
wherein λ isdryAnd λsatAnd α and β are calculated as follows:
λsat＝0.53Csand+0.1γd (9)
λdry＝0.087Csand+0.019γd (10)
α＝0.493Csand+0.86Csilt+0.014Com+0.778 (11)
β＝0.736Cclay+0.006Com+0.222 (12)
when mass fraction of sand CsandThe values of (A) are as follows: 0<Csand<Dry soil volume weight at 1 hour 11<γd<20，γdAnd ρbThe relationship between them is:
γd＝g·ρb (13)
in the formula: λ is the effective thermal conductivity of the soil, λsatIs the thermal conductivity, lambda, of saturated soildryThermal conductivity of dry soil, KeIs the interpolation coefficient, alpha and beta are the shape factor of lambda curve, theta is the soil water content, gammadThe dry soil bulk weight is g is the acceleration of gravity, g is 9.8m/s2；CclayIs the sticky particle mass fraction; csiltIs the mass fraction of the powder particles; csandIs the mass fraction of sand grains; comThe mass ratio of the organic matters is; rhobIs the bulk density.
The beneficial effect of the invention is that,
(1) the temperature simulated by the bank beach hydrothermal migration model based on the Ren model is consistent with the measured value, the Ren model has a good fitting effect on the soil thermal conductivity, and the Ren model can accurately depict the dynamic temperature change process inside the beach under the accurate depicting change condition.
(2) By comparing the temperature change curves of all monitoring points along with time, the shallow layer temperature fluctuation of the continent beach soil is strong, the middle layer temperature fluctuation range is second, the deep layer temperature change is relatively small, and therefore, in the monitoring depth range, the temperature of the soil inside the continent beach rises along with the increase of the depth, and meanwhile, the amplitude and the daily change of the temperature fluctuation attenuate along with the increase of the depth.
(3) A construction method of a reservoir region beach hydrothermal migration model based on a Ren model clarifies the internal relation between external change conditions such as upstream reservoir water storage and drainage and the like and the dynamic characteristics of the soil temperature inside the reservoir region beach. From the perspective of basic research, the research in the aspect is helpful for providing quantitative theoretical basis for further improving ecological environment of the bank beach; from the perspective of practical engineering application, the research in the aspect is helpful for providing guiding significance for improving engineering or non-engineering measures possibly taken by living environment conditions of animals and plants under the beach affected by the changing conditions.
Drawings
FIG. 1 is a schematic diagram of a reservoir beach hydrothermal migration model based on a Ren model;
FIG. 2 is a schematic diagram of the arrangement of the beach in-situ monitoring device in a field test;
FIG. 3(a) is a graph comparing a simulated value and an actual value of the temperature at the monitoring point T1-0.15m with time;
FIG. 3(b) is a graph comparing the simulated value and the measured value of the temperature at the monitoring point T1-0.45m with time;
FIG. 3(c) is a graph comparing the simulated value and the measured value of the temperature at the monitoring point T1-0.90m with time.
FIG. 3(d) is a graph comparing the simulated value and the measured value of the temperature at the monitoring point T1-1.58m with time;
FIG. 3(e) is a graph comparing the simulated value and the measured value of the temperature at the monitoring point T1-3.29m with time;
FIG. 3(f) is a graph comparing the simulated value and the measured value of the temperature at the monitoring point T3-0.20m with time;
FIG. 3(g) is a graph comparing the simulated value and the measured value of the temperature at the monitoring point T3-0.65m with time;
FIG. 3(h) is a graph comparing the simulated value and the measured value of the temperature at the monitoring point T3-1.50m with time;
FIG. 3(i) is a graph of simulated versus actual temperature at the T3-2.30m monitoring point over time;
FIG. 3(j) is a graph comparing the simulated value and the measured value of the temperature at the monitoring point T3-3.10m with time.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention relates to a construction method of a reservoir region beach hydrothermal migration model based on a Ren model, which is implemented according to the following steps:
step 1, constructing a reservoir region beach hydrothermal migration mathematical model based on a Richards equation and a thermal convection-diffusion equation, and describing a relation between a temperature field and a seepage field, wherein the reservoir beach hydrothermal migration transient seepage field is described as follows by adopting the Richards equation:
in the formula: theta is the water content, k is the soil permeability coefficient, k represents the function of the initial temperature field T in a saturated region, and k represents the function of the suction force or the water content of the soil matrix in an unsaturated region; h is a pressure water head, H is a total water head, C is the soil water content,n is the porosity of the porous medium, SsIs elastic water storage rate, QsIs a sink item of the seepage source,. v.is the Laplace equation, DTIs hydrodynamic dispersion coefficient, t is time;
in a bank beach hydrothermal migration transient seepage field in a reservoir, a Van Genuchten model is adopted to describe a characteristic curve of the water content of the unsaturated zone soil:
in the above formula, h (theta) is the soil matrix suction force, and k (theta) is the unsaturated soil permeability coefficient; thetasThe saturated water content of the soil is obtained; thetarThe residual water content of the soil is obtained; alpha and nvIs VG model parameter, m is 1-1/nv；ksThe permeability of the saturated soil body;
the transport of heat transport in porous media is described by the thermal convection-diffusion equation:
in the formula: c is the specific heat capacity of the soil body, rho is the equivalent density of the soil body, v is the Laplace equation, lambda is the equivalent heat conductivity coefficient of the soil body, cwIs the specific heat capacity of water, pwIs the density of water, v is the average flow velocity of water, T is the initial temperature field, QhIs the source and sink term of the temperature field.
Introducing the formulas (1) to (4) into an underground water flowing and porous medium heat transfer module of COMSOL Mutiphic finite element software to realize the numerical simulation of the coupling of a temperature field and a seepage field.
Step 2, setting boundary conditions for the pool beach hydrothermal migration model, including boundary conditions of the seepage field and boundary conditions of the temperature field, as shown in fig. 1, wherein the boundary conditions of the seepage field are set as follows:
according to the measured water level time sequence, a model infiltration boundary is set as a variable water head boundary, an upper boundary, a left boundary and a right boundary of an infiltration surface are set as no-flow boundaries, and a bottom boundary is set as a permeable layer boundary.
The boundary conditions of the temperature field in step 2 are set as follows:
setting the left boundary, the right boundary and the bottom boundary of the model as adiabatic boundaries; and setting the boundary above the infiltration as an atmospheric temperature boundary and setting the infiltration boundary as a river temperature boundary according to the measured river temperature and the atmospheric temperature time sequence.
Specifically, the calculation model is a trapezoidal area with the height (vertical direction) of 9.55m and the length (horizontal direction) of 30m, and the model is divided into three areas, namely, Zone1, Zone2 and Zone3 according to the difference of the soil hydraulic conductivity. In the figure ab is the infiltration boundary, bc is the boundary above the infiltration plane in contact with the air, cd, ed and ae are the model right, bottom and left boundaries, respectively. For the seepage field, the boundary bc above the model seepage surface, the left boundary ae and the right boundary cd are set as no-flow boundaries, and the bottom boundary ed is set as a permeable layer boundary. And setting the infiltration surface ab as a variable water head boundary according to the measured water level time sequence. For the temperature field, the boundaries of the models ae, ed and cd are all set as adiabatic boundaries; based on the measured river temperature and the atmospheric temperature time series, the bc boundary is set as the atmospheric temperature boundary and the ab boundary is set as the river temperature boundary. The initial temperatures of Zone1, Zone2, and Zone3 are the initial values observed by the temperature sensors, i.e., 18.6 ℃, 21 ℃, and 22.5 ℃.
And 3, solving the reservoir region beach hydrothermal migration model, and describing the relationship between the equivalent thermal conductivity coefficient and the water content of the soil body and each physical parameter of the soil by adopting a Ren model in the solving process so as to obtain the time-space change characteristic of the internal temperature field of the reservoir region beach under the change condition.
Step 3 is specifically implemented according to the following steps:
step 3.1, inputting parameters: dry soil volume weight gammadIn the unit of KN/m3(ii) a Bulk density ρb(ii) a Sand mass fraction Csand(ii) a Mass fraction of clay Cclay(ii) a Mass fraction of powder particles Csilt(ii) a Mass ratio of organic matter Com；
Step 3.2, adding an interpolation function, inputting the boundary conditions obtained in the step 2, and defining the relation between normal water density and viscosity coefficient:
when T is more than or equal to 0 ℃ and less than or equal to 40 ℃,
when T is more than or equal to 0 ℃ and less than or equal to 280.6 ℃,
ρT＝838.4661+1.4005T-0.0031×T2+3.7182×10-8×T3 (6)
wherein the temperature unit is; density unit is kg/m3(ii) a The dynamic viscosity coefficient mu is Pa.s;
step 3.3, modifying the equivalent thermal conductivity coefficient lambda of the soil body into an expression of the thermal conductivity coefficient changing along with the water content and soil parameters in the Ren model, and establishing a reservoir region beach hydrothermal migration model based on the Ren model;
and 3.4, operating the bank beach hydrothermal migration model based on the Ren model set in the step 3.3, and observing the change characteristics of the bank beach temperature field and the seepage field along with time, so as to obtain the change rule of the temperature of different elevations of the bank beach along with time.
The Ren model in step 3.3 is specifically as follows:
λ＝(λsat-λdry)·Ke+λdry (7)
Ke＝exp(α-θ-β) (8)
wherein λ isdryAnd λsatAnd α and β are calculated as follows:
λsat＝0.53Csand+0.1γd (9)
λdry＝0.087Csand+0.019γd (10)
α＝0.493Csand+0.86Csilt+0.014Com+0.778 (11)
β＝0.736Cclay+0.006Com+0.222 (12)
when mass fraction of sand CsandThe values of (A) are as follows: 0<Csand<Dry soil volume weight at 1 hour 11<γd<20，γdAnd ρbThe relationship between them is:
γd＝g·ρb (13)
in the formula: λ is the effective thermal conductivity of the soil, λsatIs the thermal conductivity, lambda, of saturated soildryThermal conductivity of dry soil, KeIs the coefficient of the interpolation that is,alpha and beta are shape factors of lambda curve, theta is soil water content, gammadThe dry soil bulk weight is g is the acceleration of gravity, g is 9.8m/s2；CclayIs the sticky particle mass fraction; csiltIs the mass fraction of the powder particles; csandIs the mass fraction of sand grains; comThe mass ratio of the organic matters is; rhobIs the bulk density.
Establishing a Ren model, and after the module is modified, the parameters of the reservoir region beach hydrothermal migration model are shown in table 1: TABLE 1 parameter Table of bank district beach saturation-non-saturation flow thermal coupling model
And (3) model verification:
firstly, the method comprises the following steps: field test
The method selects a typical continental beach cross section of the Dongting lake area as a research object, and continuously monitors the dynamic process of the soil temperature in the continental beach and the reservoir area water level for two months by the in-situ automatic monitoring device. In order to dynamically monitor the change of the groundwater temperature in the test area in real time, 4 monitoring wells T1, T2, T3 and T4 are arranged on the selected section, and the horizontal distance of the offshore area is 2.2m, 4.9m, 6.9m and 10.9m respectively. The well pipe of the monitoring well is a PVC pipe with the length of 4m, the inner diameter and the outer diameter are respectively 80mm and 100mm, round water permeable holes with the diameter of 5mm are symmetrically chiseled on the pipe body every 15cm, and a layer of geotextile is laid outside the pipe, so that the well pipe has extremely high surface water permeability and internal water permeability. 5 temperature sensors (U22-001, OnsetHOBO; measurement accuracy: +/-0.02 ℃) and 1 pressure sensor (U20-001-01, OnsetHOBO; measurement accuracy: +/-0.5 cm) are vertically arranged in each monitoring well, and in addition, one pressure sensor and one temperature sensor are simultaneously arranged in the riverway to observe the dynamic changes of the riverway water level and the water temperature. Meanwhile, 1 temperature sensor was arranged in the test area to observe the air temperature, and the position of each sensor on the observation cross section is shown in fig. 2. The data are automatically observed from the beginning of 10 and 7 days in 2018 to the end of 30 days in 11 and 30 months in 2018, and the recording frequency is 1 h.
Secondly, model precision evaluation is carried out
The invention adopts Root Mean Square Error (RMSE), Nash-Sutcliffe model efficiency coefficient (NSE) and relative error (Re) to evaluate the simulation precision of the bank beach hydrothermal migration model based on the Ren model:
in the formula: o isiFor actually measured temperature values, SiIs a model simulation temperature value, n is the number of samples,are the average values of the tests. The Root Mean Square Error (RMSE) represents the discreteness of the sample, the value varies within the range of 0 to + ∞, the smaller the value of RMSE is, the smaller the deviation between the simulation value and the experimental value is, the more reliable the simulation result of the model is, the closer the Nash-Sutcliffe model efficiency coefficient (NSE) is to 1, the better the model fitting goodness is, and when NSE is>When the value is 0.6, the consistency between the simulation value and the experimental value is considered to be better; the smaller the relative error (Re), the greater the confidence in the simulation.
In order to verify the reliability of the model, the actually measured temperature data of the field test of 10 monitoring points of T1 and T3 monitoring wells are selected for model verification. FIGS. 3(a) to 3(j) are temperature change comparison graphs of measured temperature values and simulated temperature values from 15/10/2018 to 30/11/2018, wherein FIG. 3(a) is a temperature comparison graph of T1-0.15m monitoring points, FIG. 3(b) is a temperature comparison graph of T1-0.45m monitoring points, FIG. 3(c) is a temperature comparison graph of T1-0.90m monitoring points, FIG. 3(d) is a temperature comparison graph of T1-1.58m monitoring points, FIG. 3(e) is a temperature comparison graph of T1-3.29m monitoring points, FIG. 3(f) is a temperature comparison graph of T3-0.20m monitoring points, FIG. 3(g) is a temperature comparison graph of T3-0.65m monitoring points, FIG. 3(h) is a temperature comparison graph of T3-1.50m monitoring points, FIG. 3(i) is a temperature comparison graph of T3-2.30m, and FIG. 3(j) is a temperature comparison graph of T3526-1.26 m monitoring points, the results of the model evaluation are shown in table 2.
TABLE 2 evaluation results of observation points RMSE, NSE and Re based on Ren model
As can be seen from fig. 3(a) to 3(j), the measured values of the monitoring points T1 and T3 substantially match the variation trend of the analog value. As can be seen from Table 2, the RMSE variation ranges of 10 monitoring points of the T1 and T3 monitoring wells are 0.14-1.88 ℃, the average value is 0.53 ℃, and the RMSE is 70% at the temperature of less than 0.5 ℃. For NSE, except two monitoring points of T1-0.15m and T3-3.10m, the NSE is greater than 0.5, wherein NSE is greater than 0.8 and accounts for 70%, and the experimental value and the simulation value are better matched. For the relative error Re, the Re of the T1-0.15m monitoring point is larger, the value is 11.90%, and other temperature monitoring points are in a reasonable range. In conclusion, the model has a good simulation effect and can accurately depict the temperature dynamic change process of the typical continent beach of the Dongting lake.
Through the mode, the construction method of the bank region beach hydrothermal migration model based on the Ren model comprises the following steps:
(1) the temperature simulated by the bank beach hydrothermal migration model based on the Ren model is matched with the measured value, and for Root Mean Square Error (RMSE), the variation range of 10 monitoring points of T1 and T3 monitoring wells is 0.14-1.88 ℃, the average value is 0.53 ℃, wherein the RMSE is less than 0.5 ℃ and accounts for 70%, and the simulation result of the model is reliable. For the efficiency coefficient (NSE) of the Nash-Sutcliffe model, except two monitoring points of T1-0.15m and T3-3.10m, the efficiency coefficient is more than 0.5, wherein the NSE accounts for 70% more than 0.8%, and the measured value and the simulated value of the soil temperature are well matched. For the relative error (Re), Re was greater at the T1-0.15m monitoring point, with a value of 11.90%, and the other temperature monitoring points were within reasonable ranges. It should be noted that the installation of PVC pipe changes the sediment structure and the temperature sensor is surrounded by more groundwater. Therefore, the observed temperature does not accurately reflect the original temperature of the soil to some extent. In conclusion, the Ren model has a good fitting effect on the thermal conductivity of the soil, and the temperature dynamic change process inside the beach can be accurately described by the Ren model under the condition of accurate description change.
(2) By comparing the temperature change curves of all monitoring points along with time, the shallow layer temperature fluctuation of the continent beach soil is strong, the middle layer temperature fluctuation range is second, the deep layer temperature change is relatively small, and therefore, in the monitoring depth range, the temperature of the soil inside the continent beach rises along with the increase of the depth, and meanwhile, the amplitude and the daily change of the temperature fluctuation attenuate along with the increase of the depth.
A construction method of a reservoir region beach hydrothermal migration model based on a Ren model clarifies the internal relation between external change conditions such as upstream reservoir water storage and drainage and the like and the dynamic characteristics of the soil temperature inside the reservoir region beach. From the perspective of basic research, the research in the aspect is helpful for providing quantitative theoretical basis for further improving ecological environment of the bank beach; from the perspective of practical engineering application, the research in the aspect is helpful for providing guiding significance for improving engineering or non-engineering measures possibly taken by living environment conditions of animals and plants under the beach affected by the changing conditions.
Claims (6)
1. A construction method of a bank beach hydrothermal migration model based on a Ren model is characterized by comprising the following steps:
step 1, constructing a reservoir region beach hydrothermal migration mathematical model based on a Richards equation and a thermal convection-diffusion equation, and describing the relationship between a temperature field and a seepage field;
step 2, setting boundary conditions including boundary conditions of a seepage field and boundary conditions of a temperature field for the pool beach hydrothermal migration model;
and 3, solving the reservoir region beach hydrothermal migration model, and describing the relationship between the equivalent thermal conductivity coefficient and the water content of the soil body and each physical parameter of the soil by adopting a Ren model in the solving process so as to obtain the time-space change characteristic of the internal temperature field of the reservoir region beach under the change condition.
2. The Ren model-based reservoir region beach hydrothermal migration model construction method of claim 1, wherein the reservoir beach hydrothermal migration transient seepage field in the reservoir in the step 1 is described by using Richards equation as follows:
in the formula: theta is the water content, k is the soil permeability coefficient, k represents the function of the initial temperature field T in a saturated region, and k represents the function of the suction force or the water content of the soil matrix in an unsaturated region; h is a pressure water head, H is a total water head, C is the soil water content,n is the porosity of the porous medium, SsIs elastic water storage rate, QsIs a sink item of the seepage source,. v.is the Laplace equation, DTIs hydrodynamic dispersion coefficient, t is time;
in a bank beach hydrothermal migration transient seepage field in a reservoir, a Van Genuchten model is adopted to describe a characteristic curve of the water content of the unsaturated zone soil:
in the above formula, h (theta) is the soil matrix suction force, and k (theta) is the unsaturated soil permeability coefficient; thetasThe saturated water content of the soil is obtained; thetarThe residual water content of the soil is obtained; alpha and nvIs VG model parameter, m is 1-1/nv；ksThe permeability of the saturated soil body;
the transport of heat transport in porous media is described by the thermal convection-diffusion equation:
in the formula: c is the specific heat capacity of the soil body, rho is the equivalent density of the soil body,is Laplace's equation, λ is the equivalent thermal conductivity of the soil mass, cwIs the specific heat capacity of water, pwIs the density of water, v is the average flow velocity of water, T is the initial temperature field, QhIs a source and sink term of the temperature field;
introducing the formulas (1) to (4) into an underground water flowing and porous medium heat transfer module of COMSOL Mutiphic finite element software to realize the numerical simulation of the coupling of a temperature field and a seepage field.
3. The method for constructing the bank beach hydrothermal migration model based on the Ren model according to claim 2, wherein the boundary conditions of the seepage field in the step 2 are set as follows:
according to the measured water level time sequence, a model infiltration boundary is set as a variable water head boundary, an upper boundary, a left boundary and a right boundary of an infiltration surface are set as no-flow boundaries, and a bottom boundary is set as a permeable layer boundary.
4. The Ren model-based reservoir beach hydrothermal migration model construction method according to claim 3, wherein the boundary conditions of the temperature field in the step 2 are set as follows:
setting the left boundary, the right boundary and the bottom boundary of the model as adiabatic boundaries; and setting the boundary above the infiltration as an atmospheric temperature boundary and setting the infiltration boundary as a river temperature boundary according to the measured river temperature and the atmospheric temperature time sequence.
5. The method for constructing the pool beach hydrothermal migration model based on the Ren model as claimed in claim 4, wherein the step 3 is implemented according to the following steps:
step 3.1, inputting parameters: dry soil volume weight gammadIn the unit of KN/m3(ii) a Bulk density ρb(ii) a Sand mass fraction Csand(ii) a Mass fraction of clay Cclay(ii) a Mass fraction of powder particles Csilt(ii) a Mass ratio of organic matter Com；
Step 3.2, adding an interpolation function, inputting the boundary conditions obtained in the step 2, and defining the relation between normal water density and viscosity coefficient:
when T is more than or equal to 0 ℃ and less than or equal to 40 ℃,
when T is more than or equal to 0 ℃ and less than or equal to 280.6 ℃,
ρT＝838.4661+1.4005T-0.0031×T2+3.7182×10-8×T3 (6)
wherein the temperature unit is; density unit is kg/m3(ii) a The dynamic viscosity coefficient mu is Pa.s;
step 3.3, modifying the equivalent thermal conductivity coefficient lambda of the soil body into an expression of the thermal conductivity coefficient changing along with the water content and soil parameters in the Ren model, and establishing a reservoir region beach hydrothermal migration model based on the Ren model;
and 3.4, operating the bank beach hydrothermal migration model based on the Ren model set in the step 3.3, and observing the change characteristics of the bank beach temperature field and the seepage field along with time, so as to obtain the change rule of the temperature of different elevations of the bank beach along with time.
6. The method for constructing the pool beach hydrothermal migration model based on the Ren model as claimed in claim 5, wherein the Ren model in the step 3.3 is specifically as follows:
λ＝(λsat-λdry)·Ke+λdry (7)
Ke＝exp(α-θ-β) (8)
wherein λ isdryAnd λsatAnd calculation of alpha and betaThe formula is as follows:
λsat＝0.53Csand+0.1γd (9)
λdry＝0.087Csand+0.019γd (10)
α＝0.493Csand+0.86Csilt+0.014Com+0.778 (11)
β＝0.736Cclay+0.006Com+0.222 (12)
when mass fraction of sand CsandThe values of (A) are as follows: 0<Csand<Dry soil volume weight at 1 hour 11<γd<20，γdAnd ρbThe relationship between them is:
γd＝g·ρb (13)
in the formula: λ is the effective thermal conductivity of the soil, λsatIs the thermal conductivity, lambda, of saturated soildryThermal conductivity of dry soil, KeIs the interpolation coefficient, alpha and beta are the shape factor of lambda curve, theta is the soil water content, gammadThe dry soil bulk weight is g is the acceleration of gravity, g is 9.8m/s2；CclayIs the sticky particle mass fraction; csiltIs the mass fraction of the powder particles; csandIs the mass fraction of sand grains; comThe mass ratio of the organic matters is; rhobIs the bulk density.
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