CN109598008B - Finite element simulation calculation method for laminar flow U-shaped cooling process - Google Patents
Finite element simulation calculation method for laminar flow U-shaped cooling process Download PDFInfo
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Abstract
The invention relates to a finite element simulation calculation method in a laminar flow U-shaped cooling process, which comprises the following specific steps: 1) Establishing a strip steel simplified model; 2) Determining steel grade and physical parameters; 3) Determining initial conditions; 4) Determining boundary conditions; 5) Determining an analysis step; 6) A phase change model; 7) Dividing grids; 8) Establishing a laminar flow U-shaped cooling model; 9) Fitting a U-shaped cooling curve; 10 A calculation result and verification of a U-shaped cooling temperature field; 11 Phase change calculation and result verification of each temperature point of U-shaped cooling; 12 U-shaped cooling parameters are optimized. Through simulation calculation, the data of each point which cannot be acquired in the production process is converted into a visual image or processable data, and the method has important significance for evaluating the reliability of the U-shaped coiling process, guiding the on-site process formulation and improvement, omitting pilot test, reducing the times of mass production tests, improving the product quality and the like.
Description
Technical Field
The invention relates to a calculation method, in particular to a finite element simulation calculation method for a laminar flow U-shaped cooling process, and belongs to the technical field of laminar flow U-shaped cooling simulation calculation.
Background
At present, the U-shaped laminar cooling technology for the hot rolled strip steel is a control path commonly adopted by hot rolling factories at home and abroad, and is a temperature control measure for improving the uniformity of the overall length performance because the heat dissipation of the inner ring and the outer ring, namely the head and the tail of a hot rolled plate, is fast and the temperature reduction speed is increased after the strip steel is coiled by a coiling machine, so that the overall length tissue performance of the strip steel is uneven. The hot rolled strip steel U-shaped cooling process is mainly formulated or regulated according to product development requirements or according to experience parameters, and has no unified standard. The U-shaped cooling process has great significance in evaluating the reliability of the U-shaped coiling process, guiding the on-site process formulation and improvement, omitting pilot test, reducing the number of large production tests and the like, and the laminar U-shaped cooling process can be simulated by a finite element method, but the establishment of a simulation model, the introduction and the treatment of key simulation parameters, the accuracy of simulation calculation results and the like have great influence on the formulation and the implementation of cooling parameters, so that the related simulation and calculation methods are required to be optimized and innovated.
Disclosure of Invention
The invention provides a finite element simulation calculation method for a laminar U-shaped cooling process, which aims at the technical problems in the prior art, converts the data of each point which cannot be acquired in the production process into a visual image or processable data through simulation calculation, and has important significance for evaluating the reliability of the U-shaped coiling process, guiding the on-site process formulation and improvement, omitting pilot test, reducing the times of mass production test, improving the product quality and the like.
In order to achieve the above purpose, the technical scheme of the invention is as follows, a finite element simulation calculation method for a laminar U-shaped cooling process, which comprises the following specific steps:
1) Strip steel simplified model establishment
The shape of the hot rolled strip steel is a thin rectangle, the width direction is symmetrical, and when modeling is performed, symmetrical treatment is performed, and half of the width of the strip steel is taken to build a model so as to simplify the calculation load and time.
2) Determining steel grade and physical parameters
Determining the chemical composition C, si, mn, P, S of the U-cooled steel grade, etc., defining the properties of the material in the temperature-phase change coupling: specific heat, thermal conductivity, density, etc., which are directly taken from the hot rolling secondary machine system.
3) Determining initial conditions
Taking the temperature of the strip steel in the width direction as an initial temperature, the acquisition method comprises the following steps: in order to ensure the convergence of the model and the input of ABAQUS simulation calculation, the temperature distribution curve in the width direction of the finish rolling outlet strip steel is measured on site, and the curve is fitted into a6 th-order polynomial y=15427x 6 +30464x 5 +20970x 4 +6378.6x 3 +856.99x 2 +41.91dx+920.33, the calculation model is input.
4) Determining boundary conditions
In thermal analysis, boundary conditions mainly include convective heat transfer and thermal radiation. The water cooling stage mainly adopts convection heat exchange, and the coefficient of the convection heat exchange is reduced along with the increase of temperature; in the air cooling stage, the convection heat exchange efficiency of the strip steel and air is low, and a radiation formula of Chappidi and Gunnerson is adopted
5) Determining an analysis step
According to the running speed of the strip steel and the length of each cooling section, calculating the cooling time of each section, namely, corresponding analysis step length (the unit is S), and determining the number m of air cooling sections and the number n of water cooling sections of the strip steel on a laminar flow roller way, wherein if the hot rolled strip steel cooled in the front section is required to be subjected to the processes of air cooling, water cooling, air cooling, water cooling and air cooling on the laminar flow roller way, the number m=3 of the air cooling sections and the number n=2 of the water cooling sections;
6) Phase change model
The phase change calculation comprises phase change heat generation, constitutive relation of materials and the like, the heat generation is defined in the material attribute of CAE through a model subroutine HETVAL, and the heat generation is automatically invoked during finite element calculation. Using classical JMAK equationsAs a motion in phase change processesThe mechanical equation is used for discretizing the continuous cooling process into a plurality of isothermal transformation processes according to the Scheil superposition principle, and the phase change kinetic equation is as follows: />Wherein (1)>Where Δti is the time increment of the i-th increment step.
7) Grid division
The cell type of DC2D4 is selected in the heat transfer analysis, the grid shape is tetrahedron, and the division of the grid density needs to be respectively distributed in the width direction and the thickness direction: the thickness direction is 6 grids which are uniform, and the edge part of the strip steel is distributed in an offset mode because the temperature change of the edge part of the strip steel is large, so that the edge part is divided into fine grids, and the middle part is divided into larger grids.
8) Laminar flow U-shaped cooling model establishment
In order to simulate the process of low middle and high head and tail of U-shaped cooling, a symmetrical finite element model as in claim 1 is established, and the overall consideration is that the length of the model is 3m, the symmetry of temperature distribution is considered in the width direction, half of the model is established, and the model is meshed according to claim 7.
9) U-shaped cooling curve fitting
The U-shaped coiling strategy of the strip steel is realized by adjusting the cooling water quantity at different positions in the length direction, so that the U-shaped coiling strategy of the strip steel is realized by setting different cooling efficiencies of the head and tail water cooling stages and the middle water cooling stage of the strip steel in a finite element model. In the calculation model, the heat exchange coefficient of the water cooling stage is high in the middle and low in the two sides, so that the middle part of the water cooling stage is cooled faster and the head and tail are cooled slower. Therefore, the cooling efficiency of the convection heat transfer coefficient at different positions of the strip steel is designed, and for facilitating the model input, six Gaussian curves are adopted to fit the design value, and the function form is as follows:
Y＝a 1 *EXP(-((X-b 1 )/c 1 )^2)+a 2 *EXP(-((X-b 2 )/c 2 )^2)+a 3 *EXP(-((X-b 3 )/c 3 )^2)+a 4 *EXP(-((X-b 4 )/c 4 )^2)+a 5 *EXP(-((X-b 5 )/c 5 )^2)+a 6 *EXP(-((X-b 6 )/c 6 )^2)+a 7 *EXP(-((X-b 7 )/c 7 )^2)。
10 U-shaped cooling temperature field calculation result and verification
And (5) calculating each temperature point and each temperature field according to the temperature process requirements of the tail in the U-shaped cooling head, and verifying the result.
11 Performing phase change calculation and result verification of each temperature point of U-shaped cooling.
12 U-shaped cooling parameter optimization
And optimizing the U-shaped cooling process parameters, namely optimizing the length, the temperature and the like of the hot tail of the U-shaped cooling hot head according to the calculation and the check results, and if the calculated hot tail length is normal and the actual control is short, correspondingly increasing the hot tail length value of the process design.
Compared with the prior art, the invention has the following positive effects:
1) The invention discloses a finite element simulation calculation method in a laminar U-shaped cooling process, which comprises the steps of fitting a polynomial of 6 times on initial temperature of strip steel in the width direction, and fitting the curve into a polynomial curve of 6 times: y=15427x 6 +30464x 5 +20970x 4 +6378.6x 3 +856.99x 2 +41.91dx+920.33, ensuring the convergence of the model and the accuracy of simulation input; by simplifying the U-shaped cooling calculation, grid division is optimized, and accuracy of simulation calculation is improved.
2) Heat generation is defined in the material properties of CAE by the model subroutine HETVAL, which is automatically invoked upon finite element computation. The classical JMAK equation is adopted as a phase change kinetic equation, and the continuous cooling process is discretized into a plurality of isothermal transformation processes according to the Scheil superposition principle.
3) In order to simulate the process of low middle and high head and tail of U-shaped cooling, the length of a simplified model of strip steel with the length of hundreds of kilometers is 3m, a model with half the width of the strip steel is built, the grid division length and the width direction are divided according to the average size, and the thickness direction is divided according to the number, so that the model is simplified, and the reliability is not lost.
4) For different design convection heat exchange coefficients of cooling efficiencies of different positions of the strip steel, 6 times of Gaussian curves Y=a1, EXP (- ((X-b 1)/c 1) 2) +a2, EXP (- ((X-b 2)/c 2) +a3, EXP (- ((X-b 3)/c 3) 2) +a4, EXP (- ((X-b 4)/c 4) 2) +a5, EXP (- ((X-b 5)/c 5) 2) +a6, EXP (- ((X-b 6)/c 6) 2) +a7, EXP (- ((X-b 7)/c 7) 2) are adopted to fit the design values, and simulation accuracy is improved.
Drawings
FIG. 1 is a schematic diagram of laminar U-shaped cooling;
FIG. 2 is a plot of conductivity, specific heat versus temperature;
FIG. 3 is a model initial temperature profile;
FIG. 4 is the IF steel phase transition initiation temperature;
FIG. 5 shows the temperature distribution of the strip steel in the length direction during the U-shaped cooling process;
FIG. 6 shows calculated and measured values for a U-shaped cooling coil inlet;
fig. 7 shows ferrite transformation at different positions of the U-shaped cooling strip.
The specific embodiment is as follows:
in order to enhance the understanding of the present invention, the present embodiment will be described in detail with reference to the drawings.
Example 1: a finite element simulation calculation method for a laminar flow U-shaped cooling process comprises the following steps:
1) Strip steel simplified model establishment
The shape of the hot rolled strip steel is a thin rectangle, the width direction is symmetrical, and when modeling is performed, symmetrical treatment is performed, and half of the width of the strip steel is taken to build a model so as to simplify the calculation load and time.
2) Determining steel grade and physical parameters
Determining the chemical composition C, si, mn, P, S of the U-cooled steel grade, etc., defining the properties of the material in the temperature-phase change coupling: specific heat, thermal conductivity, density, etc., which are directly taken from the hot rolling secondary machine system.
3) Determining initial conditions
Taking the temperature of the strip steel in the width direction as an initial temperature, the acquisition method comprises the following steps: in situ measurementTemperature distribution curve in width direction of strip steel at finish rolling outlet is fitted into 6 th order polynomial y=15427x for ensuring convergence of model and input of ABAQUS simulation calculation 6 +30464x 5 +20970x 4 +6378.6x 3 +856.99x 2 +41.91dx+920.33, input to the computational model;
4) Determining boundary conditions
In thermal analysis, boundary conditions mainly include convective heat transfer and thermal radiation. The water cooling stage mainly adopts convection heat exchange, and the coefficient of the convection heat exchange is reduced along with the increase of temperature; in the air cooling stage, the convection heat exchange efficiency of the strip steel and air is low, and a radiation formula of Chappidi and Gunnerson is adopted
5) Determining an analysis step
According to the running speed of the strip steel and the length of each cooling section, the cooling time of each section is calculated, namely the corresponding analysis step length (the unit is S), and the number m of air cooling sections and the number n of water cooling sections of the strip steel on a laminar flow roller way are determined, if the hot rolled strip steel cooled in the previous section is required to be subjected to the processes of air cooling, water cooling, air cooling, water cooling and air cooling on the laminar flow roller way, the number m=3 of the air cooling sections and the number n=2 of the water cooling sections.
6) Phase change model
The phase change calculation comprises phase change heat generation, constitutive relation of materials and the like, the heat generation is defined in the material attribute of CAE through a model subroutine HETVAL, and then the phase change calculation is automatically invoked during finite element calculation. Using classical JMAK equationsAs a dynamic equation of the phase change process, discretizing the continuous cooling process into a plurality of isothermal transformation processes according to the Scheil superposition principle, wherein the phase change dynamic equation is as follows
Wherein (1)>Wherein Δti is the ith increment stepTime increment. Supercooled austenite transformation is the transformation process of high-energy-level austenite to low-energy-level ferrite and other structures, and the heat flow density of transformation heat generation is shown as formula +.>Wherein, deltaH i At a temperature T i J/kg of heat generated by complete phase transformation of lower austenite; ΔX i The phase change transition amount is the i-th increment step; Δt is the step size of the i-th increment step.
7) Grid division
The cell type of DC2D4 is selected in the heat transfer analysis, the grid shape is tetrahedron, and the division of the grid density needs to be respectively distributed in the width direction and the thickness direction: the thickness direction is 6 grids which are uniform, and the edge part of the strip steel is distributed in an offset mode because the temperature change of the edge part of the strip steel is large, so that the edge part is divided into fine grids, and the middle part is divided into larger grids.
8) Laminar flow U-shaped cooling model establishment
In order to simulate the process of low middle and high head and tail of U-shaped cooling, a symmetrical finite element model as in claim 1 is established, and the overall consideration is that the length of the model is 3m, the symmetry of temperature distribution is considered in the width direction, half of the model is established, and the model is meshed according to claim 7.
9) U-shaped cooling curve fitting
The U-shaped coiling strategy of the strip steel is realized by adjusting the cooling water quantity at different positions in the length direction, so that the U-shaped coiling strategy of the strip steel is realized by setting different cooling efficiencies of the head and tail water cooling stages and the middle water cooling stage of the strip steel in a finite element model. In the calculation model, the heat exchange coefficient of the water cooling stage is high in the middle and low in the two sides, so that the middle part of the water cooling stage is cooled faster and the head and tail are cooled slower. Therefore, the cooling efficiency of the convection heat transfer coefficient at different positions of the strip steel is designed, and for facilitating the model input, six Gaussian curves are adopted to fit the design value, and the function form is as follows:
Y＝a 1 *EXP(-((X-b 1 )/c 1 )^2)+a 2 *EXP(-((X-b 2 )/c 2 )^2)+a 3 *EXP(-((X-b 3 )/c 3 )^2)+a 4 *EXP(-((X-b 4 )/c 4 )^2)+a 5 *EXP(-((X-b 5 )/c 5 )^2)+a 6 *EXP(-((X-b 6 )/c 6 )^2)+a 7 *EXP(-((X-b 7 )/c 7 ) 2), wherein:
| a1 | 139.4 | b1 | 1.865 | c1 | 0.1815 |
| a2 | 139.6 | b2 | 1.135 | c2 | 0.1817 |
| a3 | 202.2 | b3 | 1.5 | c3 | 0.3186 |
| a4 | 698.4 | b4 | 3 | c4 | 3.65E+05 |
| a5 | 0 | b5 | -0.6164 | c5 | 0.03087 |
| a6 | -0.373 | b6 | 0.1418 | c6 | 0.03668 |
| a7 | 2.071 | b7 | 0.2313 | c7 | 0.3143 |
10 U-shaped cooling temperature field calculation result and verification
And (5) calculating each temperature point and each temperature field according to the temperature process requirements of the tail in the U-shaped cooling head, and verifying the result.
11 Performing phase change calculation and result verification of each temperature point of U-shaped cooling;
12 U-shaped cooling parameter optimization;
and optimizing the U-shaped cooling process parameters according to the calculation and check results.
Specific application examples:
taking the production of U-shaped coiled IF steel with the specification of 5.5 x 1280mm as an example, the U-shaped cooling (the middle part is 680 ℃, the thermal head and the tail are 40m each, the temperature is 40 ℃ higher, namely 720 ℃ in the attached figure 1) comprises the following steps of:
1) Strip steel simplified model establishment
The shape of the hot rolled strip steel is a thin rectangle, the width direction is symmetrical, and when modeling is performed, symmetrical treatment is performed, and half of the width of the strip steel is taken to build a model so as to simplify the calculation load and time.
2) Determining steel grade and physical parameters
Determining the chemical composition of steel types, wherein C is 0.001%, mn:0.15%, P: less than or equal to 0.012, S: less than or equal to 0.013, alt:0.04%, defining the properties of the material in the temperature-phase change coupling: specific heat, thermal conductivity, density, etc., the relationship between conductivity and temperature, as shown in FIG. 2, is obtained from the secondary machine.
3) Determining initial conditions
Taking the temperature of the strip steel in the width direction as an initial temperature, the acquisition method comprises the following steps: in order to ensure the convergence of the model and the input of ABAQUS simulation calculation, the temperature distribution curve in the width direction of the finish rolling outlet strip steel is measured on site, and the curve is fitted into a6 th-order polynomial y=15427x 6 +30464x 5 +20970x 4 +6378.6x 3 +856.99x 2 +41.91dx+920.33, the computational model is input as shown in fig. 3.
4) Determining boundary conditions
In thermal analysis, boundary conditions mainly include convective heat transfer and thermal radiation. The water cooling stage mainly adopts convection heat exchange, and the coefficient of the convection heat exchange is reduced along with the increase of temperature; in the air cooling stage, the convection heat exchange efficiency of the strip steel and air is low, and a radiation formula of Chappidi and Gunnerson is adopted
5) Determining an analysis step
And determining the number m of air cooling sections and the number n of water cooling sections of the strip steel on the laminar roller way. The laminar flow of the strip steel adopts front-stage cooling, and the laminar flow roller way is required to be subjected to the processes of air cooling, water cooling, air cooling, water cooling and air cooling, wherein the number of air cooling stages m=3, and the number of water cooling stages n=2. According to the running speed of the strip steel and the length of each cooling section, the cooling time of each section is calculated to be respectively air cooling 0.78s, water cooling 4.58s, air cooling 4.1s, water cooling 0.68s and air cooling 1.65s.
6) Phase change model
The phase change calculation comprises phase change heat generation, constitutive relation of materials and the like, and is used for accurately simulating the phase change process, and the relation between the phase change starting temperature and the cooling speed of the steel grade is shown in figure 4 according to the CCT curve measurement result. Heat generation is defined in the material properties of CAE by the model subroutine HETVAL, which is automatically invoked upon finite element computation. Using classical JMAK equationsAs a kinetic equation of the phase change process, discretizing the continuous cooling process into a plurality of isothermal transformation processes according to the Scheil superposition principle, wherein the phase change kinetic equation is as follows: />Wherein (1)>Where Δti is the time increment of the i-th increment step. Supercooled austenite transformation is the transformation process of high-energy-level austenite to low-energy-level ferrite and other structures, and the heat flow density of transformation heat generation is shown as formula +.>Wherein, deltaH i At a temperature T i J/kg of heat generated by complete phase transformation of lower austenite; ΔX i The phase change transition amount is the i-th increment step; Δt is the step size of the i-th increment step.
7) Grid division
The cell type of DC2D4 is selected in the heat transfer analysis, the grid shape is tetrahedron, and the division of the grid density needs to be respectively distributed in the width direction and the thickness direction: the thickness direction is 6 grids which are uniform, and the edge part of the strip steel is distributed in an offset mode because the temperature change of the edge part of the strip steel is large, so that the edge part is divided into fine grids, and the middle part is divided into larger grids. Uniformly distributing seeds in the length direction, wherein the grid width is 0.05m; uniformly distributing seeds in the thickness direction, and arranging 6 grids according to the number; the seeds are distributed by adopting a unidirectional offset method in the width direction, and the grids gradually become smaller from the center to the edge, wherein the maximum is 0.01m, and the minimum is 0.001m.
8) Laminar flow U-shaped cooling model establishment
In order to simulate the process of low middle and high head and tail of U-shaped cooling, a symmetrical finite element model as in claim 1 is established, and the overall consideration is that the length of the model is 3m, the symmetry of temperature distribution is considered in the width direction, half of the model is established, and the model is meshed according to claim 7.
9) U-shaped cooling curve fitting
And (3) fitting design values by adopting 6 Gaussian curves according to different design convection heat transfer coefficients of cooling efficiencies at different positions of the strip steel, and inputting a model, wherein the function forms are as follows:
Y＝a 1 *EXP(-((X-b 1 )/c 1 )^2)+a 2 *EXP(-((X-b 2 )/c 2 )^2)+a 3 *EXP(-((X-b 3 )/c 3 )^2)+a 4 *EXP(-((X-b 4 )/c 4 )^2)+a 5 *EXP(-((X-b 5 )/c 5 )^2)+a 6 *EXP(-((X-b 6 )/c 6 )^2)+a 7 *EXP(-((X-b 7 )/c 7 ) 2). Wherein:
| a1 | 139.4 | b1 | 1.865 | c1 | 0.1815 |
| a2 | 139.6 | b2 | 1.135 | c2 | 0.1817 |
| a3 | 202.2 | b3 | 1.5 | c3 | 0.3186 |
| a4 | 698.4 | b4 | 3 | c4 | 3.65E+05 |
| a5 | 0 | b5 | -0.6164 | c5 | 0.03087 |
| a6 | -0.373 | b6 | 0.1418 | c6 | 0.03668 |
| a7 | 2.071 | b7 | 0.2313 | c7 | 0.3143 |
10 U-shaped cooling temperature field calculation result and verification
According to the requirements of the U-shaped cooling process, the temperature field of each temperature point is calculated, and the result is shown in figure 5. After cooling, the temperature calculation result of the coiling inlet in the length direction of the strip steel is shown as attached 6a, the field actual measurement result is shown as attached 6b, and compared with the actual measurement temperature, the temperature calculation result of the model is basically accurate.
11 U-shaped cooling phase change calculation result and verification
And carrying out phase transformation calculation in the U-shaped cooling process, wherein the result is shown in figure 7, the phase transformation is completed at the end of coiling, and the phase transformation is consistent with the actual detection result, and the phase transformation is ferrite.
12 U-shaped cooling parameter optimization
According to the calculation and check results, the U-shaped cooling parameters are optimized, and according to the calculation and actual measurement results of FIG. 6, the set hot tail length is 40m shorter, and the hot tail length of the U-shaped coiling tail is increased from 40m to 60m.
It should be noted that the above-mentioned embodiments are not intended to limit the scope of the present invention, and equivalent changes or substitutions made on the basis of the above-mentioned technical solutions fall within the scope of the present invention as defined in the claims.
Claims (4)
1. The finite element simulation calculation method for the laminar U-shaped cooling process is characterized by comprising the following specific steps of:
1) Establishing a strip steel simplified model;
2) Determining steel grade and physical parameters;
3) Determining initial conditions;
4) Determining boundary conditions;
5) Determining an analysis step;
6) A phase change model;
7) Dividing grids;
8) Establishing a laminar flow U-shaped cooling model;
9) Fitting a U-shaped cooling curve;
10 U-shaped cooling temperature field calculation result and verification
According to the temperature process requirements of the middle tail of the U-shaped cooling head, calculating each temperature point and each temperature field, and verifying the result;
11 Phase change calculation and result verification of each temperature point of U-shaped cooling;
12 U-shaped cooling parameter optimization
According to the calculation and check results, optimizing the U-shaped cooling process parameters, namely optimizing the length and the temperature of the hot tail of the U-shaped cooling hot head, wherein the calculated hot tail length is normal, the actual control is short, and the hot tail length value of the process design is correspondingly increased;
establishing a simplified model of the strip steel in the step 1); the hot rolled strip steel is thin rectangle, the width direction is symmetrical, when modeling, symmetrical treatment is carried out, and half of the width of the strip steel is taken to build a model so as to simplify the calculation load and time; the step 2) is to determine the steel grade and physical parameters specifically as follows, determine the chemical composition of the U-shaped cooling steel grade, C, si, mn, P, S, and define the properties of the material in the temperature-phase transition coupling: specific heat, thermal conductivity and density, and the parameters are directly called from a hot rolling secondary machine system;
the step 3) determines the initial conditions specifically as follows, takes the temperature in the width direction of the strip steel as the initial temperature, and the acquisition method comprises the following steps: in order to ensure the convergence of the model and the input of ABAQUS simulation calculation, the temperature distribution curve in the width direction of the finish rolling outlet strip steel is measured on site, and the curve is fitted into a6 th-order polynomial y=15427x 6 +30464x 5 +20970x 4 +6378.6x 3 +856.99x 2 +41.91dx+920.33, input to the computational model;
the step 7) of mesh division is specifically as follows, the cell type of DC2D4 is selected in heat transfer analysis, the mesh shape is tetrahedron, and the division of mesh density needs to be respectively distributed in the width direction and the thickness direction: 6 grids with uniform thickness direction, wherein the temperature change of the edge part of the strip steel is large, and the width direction adopts an offset mode to distribute seeds, so that the edge part is divided into fine grids, and the middle part is divided into larger grids;
the step 8) of establishing a laminar flow U-shaped cooling model is specifically as follows, simulating the process of low middle and high head and tail of U-shaped cooling, establishing a symmetrical finite element model, and taking 3m of model length and 3m of symmetry of temperature distribution in the width direction as well as half of established model for grid division due to excessively large established full-length calculation model and comprehensive consideration;
the U-shaped cooling curve fitting of the step 9) is specifically as follows, the strip steel U-shaped coiling strategy is realized by adjusting the cooling water quantity at different positions in the length direction, so that different cooling efficiencies of the head and tail of the strip steel and the middle water cooling stage are realized in a finite element model, in a calculation model, the middle of the heat exchange coefficient of the water cooling stage is high, the two sides are low, so that the middle of the water cooling stage is cooled faster, the head and tail are cooled slower, different cooling efficiencies of the convection heat exchange coefficient at different positions of the strip steel are designed, and for facilitating the input of the model, a six-time Gaussian curve is adopted to fit design values, and the function form is as follows:
Y＝a 1 *EXP(-((X-b 1 )/c 1 )^2)+a 2 *EXP(-((X-b 2 )/c 2 )^2)+a 3 *EXP(-((X-b 3 )/c 3 )^2)+a 4 *EXP(-((X-b 4 )/c 4 )^2)+a 5 *EXP(-((X-b 5 )/c 5 )^2)+a 6 *EXP(-((X-b 6 )/c 6 )^2)+a 7 *EXP(-((X-b 7 )/c 7 )^2)。
2. the method according to claim 1, wherein the boundary conditions determined in step 4) are specifically as follows, in the thermal analysis, the boundary conditions mainly include convective heat transfer and thermal radiation, the water cooling stage mainly includes convective heat transfer, and the coefficient thereof decreases with the increase of temperature; in the air cooling stage, the convection heat exchange efficiency of the strip steel and air is low, and a radiation formula of Chappidi and Gunnerson is adopted
3. The method according to claim 2, wherein the step 5) determines the analysis steps specifically as follows, calculates the cooling time of each section according to the running speed of the strip steel and the length of each cooling section, that is, the corresponding analysis step length is determined by S, determines the number f of air cooling sections and the number j of water cooling sections of the strip steel on the laminar roller table, and the number j of water cooling sections of the hot rolled strip steel cooled in the front section is determined, and the air cooling section f=3 and the water cooling section j=2 are required to be subjected to the process of air cooling, water cooling, air cooling, water cooling and air cooling on the laminar roller table.
4. The method according to claim 3, wherein the phase change model in step 6) is specifically as follows, the phase change calculation includes phase change heat generation and constitutive relation of materials, heat generation is defined in material properties of CAE by model subroutine HETVAL, and is automatically invoked when the finite element is calculated, and classical JMAK equation is adoptedAs a kinetic equation of the phase change process, discretizing the continuous cooling process into a plurality of isothermal transformation processes according to the Scheil superposition principle, wherein the phase change kinetic equation is as follows: />Wherein,in Deltat i Is the time increment of the i-th increment step.
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