A method for calibrating material parameters of a discrete element method pneumatic conveying feeding system

Abstract

The present application provides a kind of material parameter calibration method for discrete element method pneumatic conveying feeding system, first measure the data of bulk material, then calibrate the data of bulk material, build bulk material discrete element model, and measure the data of bulk material in the process of pneumatic conveying through simulation test, while the data in the process of pneumatic conveying is measured through physical test, the data obtained through physical test is compared with the data measured through simulation test, whether the data error of two tests is in the preset error range is judged, whether the motion state of the bulk material calibrated in the discrete element model in the process of pneumatic conveying is similar to the true motion state is verified, and the accuracy of bulk material discrete element model is verified.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular to a material parameter calibration method for a discrete element method pneumatic conveying feeding system. BACKGROUND

[0002] In the working process of agricultural materials and agricultural equipment, it is often necessary to simulate and analyze the accumulation process of material particles through contact models, and the discrete element method can effectively evaluate the applicability of different particle parameters and particle contact models in the accumulation process of material particles. Currently, in the field of agricultural engineering, there are mainly two calibration methods for the discrete element contact model of agricultural materials: one is direct measurement method, and the other is overall calibration method. The direct measurement method directly measures most of the parameters of the material, and calibrates the parameters of the material that are difficult to measure directly by adjusting the discrete element parameters in the test software to obtain the same response as the physical test. The overall calibration method is to query the approximate range of material parameters, and to obtain the same response as the physical test by continuously adjusting the discrete element parameters in the test software.

[0003] For example, Chinese patent application No. 202111179783.0, classified as G06F30 / 25, published on January 4, 2022, discloses a material parameter calibration method based on the discrete element method, which includes the following steps: constructing a discrete element constitutive model according to the material physical property parameters; setting the parameters to be calibrated and the range; performing LHS sampling according to the parameters to be calibrated and the range; importing the sampling results of LHS sampling as input data into the discrete element constitutive model for discrete element simulation; establishing a training set according to the LHS sampling results and the output data of the discrete element simulation; performing neural network training according to the training set to obtain an approximate model between the parameters to be calibrated and the output data of the discrete element simulation; verifying whether the approximate model meets the first preset condition, if not, expanding the sample size of LHS sampling; performing genetic algorithm optimization on the approximate model; and calibrating the material parameters according to the output results of the genetic algorithm.

[0004] The above document improves the efficiency and accuracy of parameter calibration by extracting multiple samples in each parameter to be calibrated in the unloading model, and each parameter to be calibrated is divided into multiple sample groups for verification. The above document only calibrates the model of funnel unloading under the action of the gravity of the material itself, and in agricultural engineering, due to different actual application scenarios, the material particles may have different states. It does not import the model of the material particles in the pneumatic suspension conveying state according to the actual scene model, then simulate according to the actual model, and then reliably calibrate, so that the parameters cannot change when the air flow changes, and the above document only considers the calibration of the rest angle in the discrete element model, and does not consider the static friction coefficient and other parameters of the particles and bulk materials. After the collision of the bulk material, the static friction coefficient also affects the outlet velocity in the subsequent actual conveying process, so that the calibration of the feeding system in the subsequent pneumatic conveying process is inaccurate. SUMMARY

[0005] The purpose of the present application is to provide a kind of discrete element method of material parameter calibration method for pneumatic conveying of feeding system, by physical-simulation test to particle, verify whether the motion state of the calibrated bulk material in the state of pneumatic conveying is similar to the real motion state, so as to calibrate the discrete element model of bulk material, ensure the accuracy of material parameter calibration of pneumatic conveying of feeding system.

[0006] To achieve the above purpose, the present application provides a kind of discrete element method of material parameter calibration method for pneumatic conveying of feeding system, including the following steps:

[0007] S1 measure the intrinsic parameters of bulk material: shape size, mass, density, moisture content, elastic modulus and Poisson's ratio, then measure the collision recovery coefficient and static friction coefficient of bulk material;

[0008] S2 measure the rest angle of bulk material in physical test by draw plate method, and calculate the rest angle of bulk material in simulation test; the rolling friction coefficient of bulk material within the relative error of the rest angle measured in physical test and the rest angle measured in simulation test is the rolling friction coefficient in the discrete element model;

[0009] S3 establish a discrete element model by the intrinsic parameters, collision recovery coefficient, static friction coefficient and rolling friction coefficient of bulk material in steps S1-S2; and generate a geometric model of the pneumatic conveying rack corresponding to the simulation test corresponding to the pneumatic conveying rack corresponding to the physical test; and use the discrete element model and the geometric model of the pneumatic conveying rack to perform simulation test;

[0010] S4 makes the physical test and the simulation test the same at the inlet in the pneumatic conveying process, measures the data of the bulk material in the pneumatic conveying process through the outlet in the physical test, and carries out the simulation test with the bulk material data measured in step S1, and then calculates the data of the bulk material in the pneumatic conveying process through the outlet in the simulation test;

[0011] S5 compares whether the relative errors of the data at the outlet in the physical test and the simulation test are respectively within the preset error range, if the relative errors of the data at the outlet are within the preset error range, determines that the intrinsic parameters, the collision restitution coefficient, the static friction coefficient and the rolling friction coefficient of the bulk material corresponding to the simulation test are the calibration data of the bulk material in the discrete element model, and completes the calibration of the bulk material in the discrete element model; otherwise, step S6 is entered;

[0012] S6 selects the other relative error value of the repose angle within the relative error range when the repose angle measured in the physical test and the repose angle measured in the simulation test, and then enters steps S3-S5 to recalibrate the data of the bulk material in the discrete element model until the relative errors are within the preset error range.

[0013] The above settings first measure the data of the bulk material through the physical test, and the data of the material includes the collision restitution coefficient and the static friction coefficient of the bulk material, so that the discrete model is related to the physical test and the simulation test of the static friction, so that the measurement of the discrete element model is more accurate, and the data of the bulk material is calibrated, the discrete element model of the bulk material is built, and the input material of the simulation test of the material and the airflow in the pneumatic conveying bench geometry model is determined by using the discrete element model, and the data of the bulk material in the pneumatic conveying process is measured through the simulation test, the data measured through the physical test and the data measured through the simulation test are compared, and it is judged whether the data errors of the two tests are within the preset error range, so as to verify whether the motion state of the calibrated bulk material in the discrete element model in the pneumatic conveying state is similar to the true motion state, and when similar, the repose angle is adjusted to make the measured experimental results more close to the test values.

[0014] Further, the plate extraction method in step S2 includes the following steps:

[0015] (a) a shell-less square shell is made of a contact material, and two symmetrical and opposite sliding grooves are arranged inside the square shell;

[0016] (b) sliding the baffle made of contact material into the square shell along the chute, dividing the square shell into chamber one and chamber two by the baffle, then placing the square shell on the horizontal plane, filling the granular bulk material in chamber one, after the granular bulk material is stable, slowly pulling out the baffle, so that the granular bulk material naturally slides to chamber two under the action of gravity along the opening formed by the baffle and the bottom of the square shell;

[0017] (c) after the granular bulk material is stable, measuring the included angle between the inclined plane formed by the granular bulk material and the bottom plane of the square shell, which is the repose angle of the granular bulk material in the physical test.

[0018] The above arrangement can measure the actual repose angle of the granular bulk material when the baffle is pulled out in the physical test.

[0019] Further, the method for calculating the repose angle of the granular bulk material in the simulation test in step S3 comprises:

[0020] Importing the same shell-less square shell model as in step (a) into the EDEM software, establishing granular bulk material particles in the shell-less square shell model, after the granular bulk material particles are filled in the shell-less square shell model, applying a speed of 100 mm / s to the baffle to move it upward, when the minimum speed of the granular bulk material particles is less than 0.001 m / s, using the protractor tool in the EDEM software to measure the included angle between the inclined plane formed by the granular bulk material particles and the bottom plane of the shell-less square shell model, which is the repose angle of the granular bulk material in the simulation test.

[0021] The above arrangement can measure the repose angle of the granular bulk material corresponding to the rolling friction coefficient in the model by importing the shell-less square shell model corresponding to the physical test and then performing the simulation test.

[0022] Further, the method for measuring the gas pressure and gas velocity of the granular bulk material passing through the outlet in the pneumatic conveying process in the physical test in step S4 comprises the following steps:

[0023] (d) calculating the gas flow rate at the inlet of the conveying pipeline, the formula is as follows:

[0024] ;

[0025] Wherein is the air flow rate at the inlet of the conveying pipeline, is the particle size coefficient of the granular bulk material, is the particle density of the granular bulk material, is the particle characteristic coefficient of the granular bulk material, and L is the length of the pipeline.

[0026] (e) calculating the diameter D of the conveying pipeline, the formula is as follows:

[0027] ;

[0028] wherein is the mass flow rate of the bulk material particles, is the air flow rate at the inlet of the conveying pipe, i is the number of conveying pipes, is the air density, is the gas concentration of the conveying pipe;

[0029] (f) After the gas flow rate at the inlet of the conveying pipe and the diameter of the conveying pipe are determined, the air pressure at the inlet and the air pressure at the outlet of the conveying pipe are measured by a pressure transmitter, the gas velocity at the inlet and the gas velocity at the outlet of the conveying pipe are measured by an anemometer, and the velocity of the bulk material particles at the outlet of the conveying pipe is captured by a high-speed camera, and the acceleration is calculated.

[0030] The above settings facilitate the measurement of the air pressure, the gas velocity, the velocity and the acceleration of the bulk material particles at the outlet and at the outlet of the conveying pipe in the physical test.

[0031] Further, the method for measuring the air pressure and the gas velocity of the bulk material at the outlet of the conveying pipe in the simulation test in the step S4 comprises:

[0032] The same pneumatic conveying rack geometry model as in the step (f) is imported, and the pneumatic conveying rack geometry model is imported into the gas-solid two-phase flow CFD-DEM model of the EDEM software, and then the bulk material particles are established with the intrinsic parameters, the collision restitution coefficient, the static friction coefficient of the bulk material in the step S1 and the rolling friction coefficient of the bulk material in the step S3, and then the air pressure at the inlet and the gas velocity at the inlet of the pneumatic conveying rack geometry model are made the same as the air pressure at the inlet and the gas velocity at the inlet in the step (f), respectively. After simulation, the air pressure and the gas velocity at the outlet of the pneumatic conveying rack geometry model and the velocity and the acceleration of the bulk material particles at the outlet are obtained.

[0033] The above settings facilitate the measurement of the air pressure, the gas velocity, the velocity and the acceleration of the bulk material particles at the outlet and at the outlet of the conveying pipe in the simulation test.

[0034] Further, the step (f) further comprises:

[0035] The velocity v of the bulk material particles at the outlet of the conveying pipe is calculated, and the formula is as follows:

[0036] ,

[0037] is the length of the high-speed camera shooting lens, m is the frame rate of the bulk material particles passing through the high-speed camera shooting lens;

[0038] The acceleration a of the bulk material particles at the outlet of the conveying pipe is calculated according to the following formula:

[0039] ,

[0040] t is the unit time,

[0041] Then the average velocity of the n bulk material particles passing through the outlet per unit time is calculated as and the average acceleration according to the following formula:

[0042] ,

[0043] .

[0044] The above settings facilitate the calculation of the average velocity and average acceleration of the bulk material particles passing through the outlet per unit time.

[0045] Further, in step S5, the motion amplitude of the bulk material particles is determined to meet the evaluation criterion for suspension conveying by the average value and the standard deviation of the Y-axis coordinates of the bulk material particles. The smaller the average value and the smaller the range of the standard deviation, the more the evaluation criterion for suspension conveying is met.

[0046] The above settings can consider the motion amplitude of the particles in the vertical ground direction in the observation area by the position of the particles in the plane x-y axis. The motion amplitude of the particles is the evaluation criterion for determining whether the particles are suspended and conveyed. The more stable the conveying is in the vertical ground direction, and thus whether the outlet is stable is also considered during calibration, so as to ensure that the output can better meet the requirements of suspension conveying.

[0047] Further, the calculation process of the average value and the standard deviation of the Y-axis coordinates of the bulk material particles includes: taking the center of the plane where the outlet of the conveying pipe is located as the origin, the vertical direction as the Y-axis, and the horizontal direction as the X-axis to establish a rectangular coordinate system, and calculating the average value and the standard deviation SD of the Y-axis coordinates of the n bulk material particles per unit time according to the following formula:

[0048] ,

[0049] .

[0050] The above settings determine the motion amplitude of the bulk material particles by the average value and the standard deviation SD, and further determine whether the bulk material particles are suspended and conveyed. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1A schematic diagram of the suspension conveying of bulk materials in the conveying pipeline of the present application.

[0052] Figure 2 A schematic diagram of the measurement of the coefficient of restitution of bulk materials of the present application.

[0053] Figure 3 A schematic diagram of the measurement of the coefficient of static friction of bulk materials of the present application.

[0054] Figure 4 A schematic diagram of the measurement of the angle of repose of bulk materials of the present application.

[0055] Figure 5 A workflow diagram of the present application.

[0056] Figure 6 A schematic diagram of the cross section of the conveying pipeline of the present application.

[0057] Figure 7 A schematic diagram of the physical test of the present application.

[0058] Figure 8 A schematic diagram of the feeding of bulk materials from the storage pipe into the Venturi pipe of the present application.

[0059] Figure 9 A schematic diagram of the suspension conveying in the simulation test of bulk materials of the present application. DETAILED DESCRIPTION

[0060] The present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0061] As Figures 1-9 shown, the present application provides a material parameter calibration method for a discrete element method pneumatic conveying feeding system, comprising the following specific steps:

[0062] S1 measure the intrinsic parameters of bulk materials: shape size, mass, density, moisture content, elastic modulus and Poisson's ratio,

[0063] In this embodiment, the shape size is measured by an electronic vernier caliper;

[0064] The mass M of 100 bulk materials is measured by a gravity sensor, and the mass m0 of a single bulk material is calculated;

[0065] The volume V1 of fine sand is recorded by adding fine sand in a container, and then 100 bulk materials are added into the container, and the total volume V2 of fine sand and bulk materials is recorded, and the volume V of 100 bulk materials is calculated,

[0066] V = V2 - V1 (1)

[0067] Then the density of bulk materials is calculated ,

[0068] (2)

[0069] One hundred bulk materials were placed in a sealed container and irradiated with a halogen lamp. After the moisture in the 100 bulk materials evaporated, the mass m4 of the 100 bulk materials after evaporation was measured using a gravity sensor, and then the moisture content k of the bulk materials was calculated.

[0070] (3)

[0071] The elastic modulus and Poisson's ratio of bulk materials are measured using a texture analyzer.

[0072] The collision recovery coefficient of bulk materials is measured as follows:

[0073] Bulk material 2 is adsorbed onto the rubber tube opening 3 by vacuum pump 1, and then allowed to fall freely from rest. The trajectory of bulk material 2 on the grid 4 is captured by a high-speed camera (not shown in the figure). Energy is conserved throughout the entire motion process. The velocity v1 of bulk material 2 before colliding with the collision plate 5 and the separation velocity v2 of bulk material 2 after colliding with the collision plate 5 are measured.

[0074] (4)

[0075] (5)

[0076] The number of grid cells representing the distance between the bulk material and the collision plate. Passing before the collision Number of frames used After the collision Number of frames used

[0077] For low-velocity particle collision studies, where friction is not considered, the formula for calculating the Newtonian collision restitution coefficient e is:

[0078] (6)

[0079] Based on the principle that particles, starting from rest at the same height, undergo free fall, and upon contact with a collision plate, the resulting rebound force propels them upwards, energy is conserved throughout the entire process. To ensure that the distance between the bulk material and the collision plate is the same before and after the collision, equations (4) to (6) are combined to obtain:

[0080] (7)

[0081] After multiple tests, the average value of the collision restitution coefficient e was taken. ;

[0082] The static friction coefficient of the bulk material is measured as follows:

[0083] The bulk material 2 is placed on the swing plate 6, one end of the swing plate 6 is hinged to the bottom plate 7, the support rod 8 perpendicular to the bottom plate 7 is provided with the roller 9, one side of the roller 9 is fixedly connected with the rocker 10, the rope 11 is arranged on the roller 9, the rope 11 is connected with the other end of the swing plate 6, the rocker 10 is rotated to drive the swing plate 6 to rotate around the hinge with the bottom plate 7 to lift up, when the bulk material 2 has a tendency to slide downward on the inclined surface of the swing plate 6, the angle between the swing plate 6 and the bottom plate 7 is recorded, that is, the sliding friction angle, denoted as φ, and the static friction factor f of the bulk material is calculated,

[0084] f=tanφ,

[0085] The average value of the static friction factor f is taken after multiple tests .

[0086] S2 The angle of repose of the bulk material in the physical test is measured by the draw plate method as follows:

[0087] (a) A shell-less square shell is made of contact material, and two symmetrical and opposite sliding grooves are arranged inside the square shell along the height direction of the square shell;

[0088] (b) The baffle made of contact material is slid into the square shell along the sliding groove, the square shell is divided into chamber one and chamber two by the baffle, then the square shell is placed on the horizontal plane, the bulk material particles are filled in chamber one, after the bulk material particles are stable, the baffle is slowly drawn out, and the bulk material particles naturally slide to chamber two under the action of gravity along the opening formed between the baffle and the bottom of the square shell;

[0089] (c) After the bulk material particles are stable, the angle between the inclined surface formed by the bulk material particles and the bottom plane of the square shell is measured, which is the angle of repose of the bulk material in the physical test;

[0090] Then the angle of repose of the bulk material in the simulation test is calculated as follows:

[0091] Import the same shellless cubic shell model as in step (a) into the EDEM software. The shellless cubic shell model can be formed using 3D modeling software. Create bulk material particles in the shellless cubic shell model. After the bulk material particles fill the shellless cubic shell model, apply a speed of 100 mm / s to the baffle to make the baffle move upward. When the minimum speed of the bulk material particles is less than 0.001 m / s, use the protractor tool in the EDEM software to measure the angle formed between the slope surface formed by the bulk material particles and the bottom plane of the shellless cubic shell model. This is the angle of repose of the bulk material in the simulation test. When the angle of repose obtained from the simulation test and the physical test is close, the rolling friction coefficient of the bulk material is used as the rolling friction coefficient in the discrete element model.

[0092] S3 establishes a discrete element model using the intrinsic parameters, collision recovery coefficient, static friction coefficient, and rolling friction coefficient of the bulk material obtained in steps S1-S2. Furthermore, a geometric model of the pneumatic conveying platform corresponding to the physical experiment is generated using 3D simulation software; the actual pneumatic conveying platform is as follows: Figure 1 As shown, it has a storage pipe 01 and a conveying pipe 02. The lower end of the storage pipe 01 is connected to the conveying pipe 02 through a venturi tube 03. Airflow is introduced into one end of the venturi tube 03, and material is output from the other end of the venturi tube 03. Simulation tests are conducted using a discrete element model and a pneumatic conveying platform geometric model.

[0093] S4 ensures that the inlet data are identical for both the physical and simulation experiments during pneumatic conveying. Specifically, it measures the gas pressure and gas velocity at the outlet of the bulk material during pneumatic conveying in the physical experiment, as follows:

[0094] (d) Calculate the gas velocity at the inlet of the delivery pipeline using the following formula:

[0095] ,

[0096] in This refers to the air velocity at the inlet of the delivery pipeline. The particle size coefficient of the bulk material. The particle density of the bulk material. Where L is the particle size distribution coefficient of the bulk material, and L is the pipe length.

[0097] (e) Calculate the diameter D of the conveying pipeline using the following formula:

[0098] ,

[0099] in The mass flow rate of the bulk material particles. The air velocity at the inlet of the delivery pipe, where i is the number of delivery pipes. air density, gas concentration of the conveying pipe.

[0100] The diameter D of the conveying pipe is derived as follows: the gas conveying concentration is the ratio of the mass of particles conveyed per unit time to the mass of gas flowing through the pipe. If the conveying concentration is extremely high, particle blockage is likely to occur during conveying. The equation of the gas conveying concentration is as follows:

[0101] (1)

[0102] (2)

[0103] wherein is the mass flow rate of particles (kg / s); is the mass flow rate of gas (kg / s); is the number of conveying pipes; is the air density (kg / m3), is the diameter of each conveying pipe (mm). According to equations (1) and (2), the diameter formula is obtained as follows:

[0104] (3)

[0105] (f) After determining the gas flow rate at the inlet of the conveying pipe and the diameter of the conveying pipe, the air pressure at the inlet and the air pressure at the outlet of the conveying pipe are measured by a pressure transmitter, and the gas velocity at the inlet and the gas velocity at the outlet of the conveying pipe are measured by an anemometer, and finally the velocity v of the bulk material particles at the outlet of the conveying pipe is calculated by a high-speed camera, and the formula is as follows:

[0106] ,

[0107] is the length of the high-speed camera lens, and m is the frame rate of the bulk material particles passing through the high-speed camera lens;

[0108] The acceleration a of the bulk material particles at the outlet of the conveying pipe is calculated as follows:

[0109] ,

[0110] t is the unit time,

[0111] Then the average velocity v of n bulk material particles passing through the outlet per unit time is calculated as follows: and the average acceleration a is calculated as follows:

[0112] , ​

[0113] ,

[0114] At the same time, the Y-axis average value and the standard deviation value are calculated in the physical test, and the specific method is as follows: taking the center of the plane where the outlet of the conveying pipeline is located as the origin O, the vertical direction as the Y-axis, and the horizontal direction as the X-axis, a rectangular coordinate system is established, the Y-axis coordinate of the granular bulk material particle is y, the average value of the Y-axis coordinates of n granular bulk material particles in a unit time is calculated and the standard deviation SD, and the formula is as follows:

[0115] , y j represents the Y-axis coordinate of the jth granular bulk material particle;

[0116] ,

[0117] Therefore, the average value and the standard deviation SD of the Y-axis coordinate are used to evaluate the movement amplitude of the granular bulk material particle in the vertical direction, that is, the smaller the Y-axis average value and the smaller the standard deviation SD, the smaller the movement amplitude, and the closer the granular bulk material particle to the suspension conveying, and the more stable the conveying in the pneumatic conveying process.

[0118] At the same time, the Y-axis average value and the standard deviation can be obtained by using the Euler-Lagrange model in the EDEM software to obtain the simulation result graph: the movement state, speed, acceleration, movement direction, plane x-y axis position and conveying bulk material mass per unit time of the particle; the pressure cloud map and the velocity cloud map of the flow field gas; the particle movement state is the accumulation phenomenon and the crushing phenomenon of the particle in the pipeline in the pneumatic conveying process; the particle speed, acceleration and movement direction are obtained by the Analyst Tree post-processing function of the EDEM software; the particle position in the plane x-y axis considers the movement amplitude of the particle in the vertical ground direction of the observation area; the particle movement amplitude is the evaluation standard for judging whether the particle is suspended conveying or not, and the particle movement amplitude in the vertical ground direction, the more stable the conveying.

[0119] At the same time, the granular bulk material data measured in step S1 is used for simulation test, and the specific method is as follows:

[0120] Import the same pneumatic conveying bench geometry model as in step (f), and import the pneumatic conveying bench geometry model into the EDEM software, simulate the air pressure and airflow according to the CFD-DEM (computational fluid dynamics-discrete element) mathematical model in the EDEM software, and then establish the bulk material particles according to the intrinsic parameters of the bulk material in step S1, the collision restitution coefficient, the static friction coefficient, and the rolling friction coefficient of the bulk material calibrated in step S3, and then make the air pressure and gas velocity at the inlet of the pneumatic conveying bench geometry model the same as the air pressure and gas velocity at the inlet in step (f), and after simulation, the air pressure and gas velocity at the outlet of the pneumatic conveying bench geometry model and the speed and acceleration of the bulk material particles at the outlet are obtained.

[0121] S5 compares the data at the outlet in the physical test and the simulation test, and in this embodiment, the data at the outlet includes the air pressure, the gas velocity, and the average speed and average acceleration of the bulk material particles, the average value of the Y-axis coordinate and the standard deviation In this embodiment, if the data at the outlet are all within the preset error range , it is verified that the motion state of the calibrated bulk material data in the pneumatic conveying state is similar to the true motion state, thereby proving the accuracy of the calibrated bulk material discrete element model, and the calibration of the bulk material in the discrete element model is completed; if it does not meet the requirements, step S6 is entered.

[0122] S6 selects the repose angle measured by the physical test and the repose angle measured by the simulation test within the relative error range, and the repose angle is the calibration value of the rolling friction coefficient in the discrete element model; then enters steps S3-S5 to recalibrate the data of the bulk material in the discrete element model until the relative errors are within the preset error range.

[0123] The working principle of the present application is as follows: first, the data of the bulk material is measured by a physical test, including the collision restitution coefficient and the static friction coefficient of the bulk material, so that the discrete model is related to the physical test and the simulation experiment of the static friction, so that the measurement of the discrete element model is more accurate, and the data of the bulk material is calibrated, the discrete element model of the bulk material is built, and the input material and airflow in the pneumatic conveying bench geometry model are determined by the discrete element model, and the data of the bulk material in the pneumatic conveying process is measured by the simulation test, the data obtained by the physical test is compared with the data measured by the simulation test, and it is judged whether the data error of the two tests is within the preset error range, so as to verify whether the motion state of the calibrated bulk material in the discrete element model in the pneumatic conveying state is similar to the true motion state, and when it is similar, the repose angle is adjusted to make the measured experimental result more close to the test value.

Claims

1. A method for calibrating material parameters in a pneumatic conveying feeding system based on the discrete element method, characterized in that: Includes the following steps: S1 measures the intrinsic parameters of bulk materials: shape, size, mass, density, moisture content, elastic modulus and Poisson's ratio, and then measures the collision recovery coefficient and static friction coefficient of the bulk materials. S2 measures the angle of repose of the bulk material in the physical test using the plate-stripping method, and simultaneously calculates the angle of repose of the bulk material in the simulation test; the rolling friction coefficient determined within the relative error range of the angle of repose measured in the physical test and the angle of repose measured in the simulation test is selected as the rolling friction coefficient in the discrete element model. S3 establishes a discrete element model using the intrinsic parameters, collision recovery coefficient, static friction coefficient, and rolling friction coefficient of the bulk material from steps S1 to S2; and generates a geometric model of the pneumatic conveying platform corresponding to the physical test for the simulation test; and conducts simulation tests using the discrete element model and the geometric model of the pneumatic conveying platform. S4 ensures that the data at the inlet of the physical test and the simulation test are the same, measures the data of the bulk material passing through the outlet during the pneumatic conveying process in the physical test, and uses the bulk material data measured in step S1 to conduct the simulation test, and then calculates the data of the bulk material passing through the outlet during the pneumatic conveying process in the simulation test. S5 compares whether the relative errors of the data at the outlet in the physical test and the simulation test are within the preset error range. If the relative errors of the data at the outlet are within the preset error range, the intrinsic parameters, collision recovery coefficient, static friction coefficient and rolling friction coefficient of the bulk material corresponding to the simulation test are determined as the calibration data of the bulk material in the discrete element model, and the calibration of the bulk material in the discrete element model is completed; otherwise, proceed to step S6. S6 selects the angle of repose measured by physical test and the angle of repose measured by simulation test as the calibration value of the rolling friction coefficient in the discrete element model when the angle of repose is within the relative error range of another relative error value; then proceed to steps S3-S5 to recalibrate the data of bulk materials in the discrete element model until the relative error is within the preset error range.

2. The material parameter calibration method for a pneumatic conveying feeding system based on discrete element method according to claim 1, characterized in that: The plate-pulling method in step S2 includes the following steps: (a) A shell-less square shell is made using a contact material, and two symmetrically tangentially arranged sliding grooves are provided on both sides inside the square shell; (b) The baffle made of contact material is slid into the interior of the square shell along the chute. The baffle divides the interior of the square shell into chamber one and chamber two. Then the square shell is placed on a horizontal surface. The bulk material particles are filled into chamber one. After the bulk material particles have settled and stabilized, the baffle is slowly pulled out, so that the bulk material particles slide naturally into chamber two under the action of gravity along the opening formed by the baffle and the bottom of the square shell. (c) After the bulk material particles have settled and stabilized, measure the angle between the slope formed by the bulk material particles and the bottom plane of the square shell. This angle is the angle of repose of the bulk material in the physical test.

3. The material parameter calibration method for a pneumatic conveying feeding system based on discrete element method according to claim 2, characterized in that: The method for calculating the angle of repose of the bulk material in the simulation test in step S3 includes: Import the same shellless square shell model as in step (a) into the EDEM software. Create bulk material particles in the shellless square shell model. After the bulk material particles fill the shellless square shell model, apply a speed of 100 mm / s to the baffle to move the baffle upward. When the minimum speed of the bulk material particles is less than 0.001 m / s, use the protractor tool in the EDEM software to measure the angle formed between the slope surface formed by the bulk material particles and the bottom plane of the shellless square shell model. This angle is the angle of repose of the bulk material in the simulation test.

4. The material parameter calibration method for a pneumatic conveying feeding system based on discrete element method according to claim 1, characterized in that: In step S4, the physical test, the data at the outlet of the bulk material during pneumatic conveying includes air pressure and gas velocity. The method for measuring the air pressure and gas velocity at the outlet of the bulk material during pneumatic conveying in the physical test includes the following steps: (d) Calculate the gas velocity at the inlet of the delivery pipeline using the following formula: ; in This refers to the air velocity at the inlet of the delivery pipeline. The particle size coefficient of the bulk material. The particle density of the bulk material. Where L is the particle size distribution coefficient of the bulk material, and L is the pipe length. (e) Calculate the diameter D of the conveying pipeline using the following formula: ; in The mass flow rate of the bulk material particles. The air velocity at the inlet of the delivery pipe, where i is the number of delivery pipes. air density, The gas concentration in the pipeline; (f) After determining the gas velocity at the inlet of the conveying pipeline and the diameter of the conveying pipeline, a pneumatic conveying platform for bulk materials is built. Then, the gas pressure at the inlet and outlet of the conveying pipeline is measured by a pressure transmitter, and the gas velocity at the inlet and outlet of the conveying pipeline is measured by an anemometer. Finally, the velocity of the bulk material particles at the outlet of the conveying pipeline is captured by a high-speed camera, and the acceleration is calculated.

5. The material parameter calibration method for a pneumatic conveying feeding system based on discrete element method according to claim 4, characterized in that: In step S4 of the simulation experiment, the method for measuring the air pressure and gas velocity at the outlet of the bulk material during pneumatic conveying includes: Import the same pneumatic conveying platform geometric model as in step (f), and import the pneumatic conveying platform geometric model into EDEM software. Then, establish the bulk material particles using the intrinsic parameters, collision recovery coefficient, static friction coefficient of the bulk material in step S1 and the rolling friction coefficient of the bulk material after calibration in step S3. Next, make the air pressure and gas velocity at the inlet of the pneumatic conveying platform geometric model the same as those at the inlet in step (f). After simulation, obtain the air pressure and gas velocity at the outlet of the pneumatic conveying platform geometric model, as well as the velocity and acceleration of the bulk material particles at the outlet.

6. The material parameter calibration method for a pneumatic conveying feeding system based on the discrete element method according to claim 4, characterized in that: Step (f) further includes: The formula for calculating the velocity v of bulk material particles at the outlet of the conveying pipeline is as follows: ， is the length of the high-speed camera lens, and m is the frame rate at which the bulk material particles pass through the high-speed camera lens. The formula for calculating the acceleration 'a' of bulk material particles at the outlet of the conveying pipeline is as follows: ， t represents the unit of time. Then calculate the average velocity of n bulk material particles passing through the outlet per unit time. and average acceleration The formula is as follows: ， 。 7. The material parameter calibration method for a pneumatic conveying feeding system based on discrete element method according to claim 1, characterized in that: Step S5 also includes determining the motion amplitude of the bulk material by the average value and standard deviation of the Y-axis coordinate of the bulk material particles as meeting the evaluation criteria for suspended conveying. If the average value is smaller and the standard deviation range is smaller, it meets the evaluation criteria for suspended conveying.

8. The material parameter calibration method for a pneumatic conveying feeding system based on the discrete element method according to claim 7, characterized in that: Establish a rectangular coordinate system with the center of the plane where the pipeline outlet is located as the origin, the vertical direction as the Y-axis, and the horizontal direction as the X-axis. Calculate the average Y-axis coordinate of n bulk material particles per unit time. The difference between the labeled and SD is calculated using the following formula: y j This represents the Y-axis coordinate of the j-th bulk material particle; 。

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