Material parameter calibration method for feeding system based on discrete element method pneumatic conveying

Abstract

The invention provides a material parameter calibration method for a feeding system adopting discrete element method pneumatic conveying, which comprises the following steps of: measuring data of bulk materials, calibrating the data of the bulk materials, building a bulk material discrete element model, measuring data of the bulk materials in a pneumatic conveying process through a simulation test, and calibrating the data of the bulk materials. Meanwhile, data obtained through the physical test in the pneumatic conveying process is measured through the physical test and compared with data measured through the simulation test, and whether the data error of the two tests is within a preset error range or not is judged; therefore, whether the motion state of the bulk material calibrated in the discrete element model in the pneumatic conveying process is similar to the real motion state is verified, and the accuracy of the discrete element model of the bulk material is verified.

Description

Technical Field

[0001] The invention relates to the technical field of materials, and in particular to a material parameter calibration method for a feeding system based on discrete element method pneumatic conveying. Background Art

[0002] In the working process of agricultural materials and agricultural machinery, 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. At present, in the field of agricultural engineering, there are two main calibration methods for the discrete element contact model of agricultural materials, one is the direct measurement method and the other is the overall calibration method. The direct measurement method is to directly measure most of the parameters of the material, calibrate the material parameters that are difficult to measure directly, and obtain the same response as the physical test by adjusting some discrete element parameters in the test software; the overall calibration method is to obtain the same response as the physical test by querying the approximate range of the material parameters and continuously adjusting the discrete element parameters in the test software.

[0003] For example, the patent document with Chinese patent application number 202111179783.0, classification number G06F30 / 25, and publication date 2022.01.04 discloses a material parameter calibration method based on the discrete element method, including the following steps: constructing a discrete element constitutive model according to the material physical property parameters; setting the parameters and ranges to be calibrated; performing LHS sampling according to the parameters and ranges to be calibrated; 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, and if not, expanding the sample size of LHS sampling; optimizing the approximate model by genetic algorithm; and calibrating the material parameters according to the output results of the genetic algorithm.

[0004] The above-mentioned document extracts multiple samples from each parameter to be calibrated in the unloading model, and the multiple samples extracted from each parameter to be calibrated are divided into multiple sample groups for verification, thereby improving the efficiency and accuracy of parameter calibration. The above-mentioned document only calibrates the model of funnel unloading under the action of the material's own gravity. In agricultural engineering, due to different actual application scenarios, material particles may have different states. It does not import the material particle model in the pneumatic suspension conveying state according to the model of the actual scenario and then simulate it according to the actual model and then reliably calibrate it, so that if the airflow changes, the parameters cannot follow the change. At the same time, the above-mentioned document only considers the calibration of the angle of repose in the discrete element model, and does not consider parameters such as the static friction coefficient between particles and bulk materials. After the collision of bulk materials, the static friction coefficient will also affect the subsequent outlet speed in the actual conveying process, which will cause the feeding system to be inaccurately calibrated in the subsequent pneumatic conveying process. Summary of the invention

[0005] The purpose of the present invention is to provide a material parameter calibration method for a pneumatic conveying feeding system based on a discrete element method. By performing physical-simulation tests on particles, it is verified whether the motion state of the calibrated bulk material under pneumatic conveying is similar to the actual motion state, thereby calibrating a discrete element model of the bulk material to ensure the accuracy of the material parameter calibration for the pneumatic conveying feeding system.

[0006] To achieve the above object, the present invention provides a material parameter calibration method for a pneumatic feeding system based on a discrete element method, comprising 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 bulk materials; S2 measures the repose angle of the bulk material in the physical test by the plate drawing method, and calculates the repose angle of the bulk material in the simulation test at the same time; selects the repose angle measured by the physical test and the repose angle measured by the simulation test within the relative error of - rolling friction coefficient as the rolling friction coefficient in the discrete element model; S3: establishing a discrete element model through the intrinsic parameters, collision recovery coefficient, static friction coefficient and rolling friction coefficient of the bulk material in steps S1 to S2; generating a pneumatic conveying stand geometry model corresponding to the simulation experiment from the pneumatic conveying stand corresponding to the object test; and performing a simulation experiment using the discrete element model and the pneumatic conveying stand geometry model; S4 makes the data of the inlet of the physical test and the simulation test the same during the pneumatic conveying process, measures the data of the bulk material passing through the outlet during the pneumatic conveying process in the physical test, and simultaneously performs a simulation test with the bulk material data measured in step S1, 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, respectively. 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 experiment 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, the process goes to step S6; S6 selects the repose angle measured by the physical test and the repose angle measured by the simulation test, and when the repose angle has another relative error value within the relative error range, 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 all within the preset error range.

[0007] The above settings first measure the data of bulk materials through physical tests. The material data include the collision recovery coefficient and static friction coefficient of bulk materials. This makes the discrete model related to the static friction object test and simulation experiment, making the discrete element model measurement more accurate, and calibrating the data of bulk materials, building a discrete element model of bulk materials, and using the discrete element model to determine the materials and airflow of the simulation experiment to input the materials into the pneumatic conveying rig geometric model, and measuring the data of bulk materials in the pneumatic conveying process through simulation tests. The data obtained through physical tests are compared with the data measured by the simulation tests to determine whether the data errors of the two tests are within the preset error range, thereby verifying whether the motion state of the bulk materials calibrated in the discrete element model under the pneumatic conveying state is similar to the actual motion state. When similar, the angle of repose is adjusted to make the measured experimental results closer to the experimental values.

[0008] Furthermore, the plate extraction method in step S2 includes the following steps: (a) A shellless square housing is made of contact material, and two symmetrically oppositely arranged slide grooves are arranged on both sides of the inside of the square housing; (b) sliding a baffle made of contact material into the interior of the square shell along the slide groove, dividing the interior of the square shell into chamber one and chamber two by the baffle, then placing the square shell on a horizontal plane, filling chamber one with bulk material particles, and slowly withdrawing the baffle after the bulk material particles are stationary and stable, so that the bulk material particles naturally slide into chamber two along the opening formed by the baffle and the bottom of the square shell under the action of gravity; (c) After the bulk material particles are left to stand still and stabilize, the angle between the slope surface formed by the bulk material particles and the bottom plane of the square shell is measured, which is the repose angle of the bulk material in the physical test.

[0009] The above arrangement can measure the actual angle of repose of the bulk material when the plate is withdrawn through physical testing.

[0010] Furthermore, 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, establish bulk material particles in the shellless square shell model, and when the bulk material particles are filled in 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 between the slope surface formed by the bulk material particles and the bottom plane of the shellless square shell model, which is the repose angle of the bulk material in the simulation test.

[0011] The above arrangement can measure the angle of repose of the bulk material corresponding to the rolling friction coefficient in the model by importing a shellless square shell model corresponding to the object test and then conducting a simulation test.

[0012] Furthermore, the method for measuring the gas pressure and gas velocity of the bulk material passing through the outlet during the pneumatic conveying process in the physical test in step S4 includes the following steps: (d) Calculate the gas flow rate at the inlet of the delivery pipeline using the following formula: ; in is the air velocity at the inlet of the conveying duct, is the particle size coefficient of bulk materials, is the particle density of bulk material, is the particle characteristic coefficient of bulk material, L is the pipeline length; (e) Calculate the diameter D of the delivery pipeline using the following formula: ; in is the mass flow rate of bulk material particles, is the air velocity at the inlet of the delivery pipe, i is the number of delivery pipes, is the air density, is the gas concentration in the transmission pipeline; (f) After determining the gas flow rate at the inlet of the conveying pipeline and the diameter of the conveying pipeline, the air pressure at the inlet and outlet of the conveying pipeline are measured by a pressure transmitter, and the gas velocity at the inlet and outlet of the conveying pipeline are measured by an anemometer. Finally, the velocity of the bulk material particles at the outlet of the conveying pipeline is photographed by a high-speed camera and the acceleration is calculated.

[0013] The above arrangement facilitates the measurement of the gas pressure, gas velocity, speed and acceleration of the bulk material particles passing through the outlet and the inlet in the physical test.

[0014] Furthermore, the method for measuring the gas pressure and gas velocity of the bulk material passing through the outlet during the pneumatic conveying process in the simulation test in step S4 includes: Import the same pneumatic conveying gantry geometric model as that in step (f), and import the pneumatic conveying gantry geometric model into the gas-solid two-phase flow CFD-DEM model in the EDEM software, then establish the bulk material particles with 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 in step S3, then make the air pressure and gas velocity at the inlet of the pneumatic conveying gantry geometric model the same as the air pressure and gas velocity at the inlet of step (f), respectively, and after simulation, obtain the air pressure and gas velocity at the outlet of the pneumatic conveying gantry geometric model and the velocity and acceleration of the bulk material particles at the outlet.

[0015] The above settings facilitate the measurement of the gas pressure, gas velocity, speed, and acceleration of the bulk material particles passing through the outlet and the inlet in the simulation test.

[0016] Furthermore, the step (f) further comprises: The velocity v of bulk material particles at the outlet of the conveying pipeline is calculated as follows: , 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; The formula for calculating the acceleration a of bulk material particles at the outlet of the conveying pipeline is as follows: , t is the unit time, Then calculate the average velocity of n bulk material particles passing through the outlet per unit time. and the average acceleration , the formula is as follows: , .

[0017] The above settings make it easy to calculate the average velocity and average acceleration of the bulk material particles passing through the outlet per unit time.

[0018] Furthermore, step S5 also includes determining whether the movement amplitude of the bulk material meets the suspension transport criteria by the average value and standard deviation of the Y-axis coordinates of the bulk material particles. If the average value is smaller and the standard deviation range is smaller, then the suspension transport criteria are met.

[0019] The above settings can consider the movement amplitude of the particles in the direction perpendicular to the ground in the observation area through the position of the particles in the plane xy axis; the particle movement amplitude is the criterion for judging whether the particles are suspended and transported. The larger the particle movement amplitude in the direction perpendicular to the ground, the more stable the transport; therefore, during calibration, the stability of the output port is also considered to ensure that the output can better meet the requirements of suspended transport.

[0020] Furthermore, the calculation process of the mean value and standard deviation of the Y-axis coordinates of the bulk material particles includes: taking the center of the plane where the conveying pipeline outlet is located as the origin, the vertical direction as the Y-axis, and the horizontal direction as the X-axis, a rectangular coordinate system is established, and the mean value of the Y-axis coordinates of n bulk material particles per unit time is calculated. And the standard deviation SD, the formula is as follows: , .

[0021] The above settings are averaged The movement amplitude of the bulk material particles can be determined by the value of the movement amplitude and standard deviation SD, and then whether the bulk material particles are suspended or not. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the suspended transportation of bulk materials in the transportation pipeline according to the present invention.

[0023] Figure 2 It is a schematic diagram of measuring the collision recovery coefficient of bulk materials according to the present invention.

[0024] Figure 3 It is a schematic diagram of measuring the static friction coefficient of bulk materials according to the present invention.

[0025] Figure 4 It is a schematic diagram of measuring the angle of repose of bulk materials according to the present invention.

[0026] Figure 5 It is the work flow chart of the present invention.

[0027] Figure 6 It is a schematic cross-sectional view of the conveying pipeline in the present invention.

[0028] Figure 7It is a physical schematic diagram of the physical experiment in the present invention.

[0029] Figure 8 It is a schematic diagram of bulk material entering the venturi tube from the storage pipe in the present invention.

[0030] Fig. 9 It is a schematic diagram of suspension transportation in the simulation test of bulk materials in the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] like Figure 1-9 As shown, the present invention provides a material parameter calibration method for a pneumatic feeding system based on a discrete element method, comprising the following specific steps: S1 measures the intrinsic parameters of bulk materials: shape, size, mass, density, moisture content, elastic modulus and Poisson's ratio. In this embodiment, the shape and size are measured by an electronic vernier caliper; The mass M of 100 bulk materials is measured by a gravity sensor, and then the mass m0 of a single bulk material is calculated; The volume V of 100 bulk materials is calculated by adding fine gravel into the container and recording the volume V1 of the fine gravel, then adding 100 bulk materials into the container and recording the total volume V2 of the fine gravel and bulk materials. V = V2 - V1 (1) Then calculate the density of the bulk material , (2) Place 100 bulk materials in a sealed container and use a halogen lamp to irradiate the bulk materials. After the water in the 100 bulk materials evaporates, measure the mass m4 of the 100 bulk materials after evaporation through a gravity sensor, and then calculate the moisture content k of the bulk materials. (3) The elastic modulus and Poisson's ratio of bulk materials are measured by texture analyzer; Measure the impact restitution coefficient of bulk materials as follows: The bulk material 2 is adsorbed on the rubber tube mouth 3 by the vacuum pump 1, and the bulk material 2 is allowed to start free fall from rest. The motion trajectory of the bulk material 2 on the grid 4 is photographed by a high-speed camera (not shown in the figure). The energy is conserved during the whole motion process, and the speed v1 of the bulk material 2 before the collision with the collision plate 5 and the separation speed v2 of the bulk material 2 after the collision with the collision plate 5 are measured. (4) (5) is the number of grids between the bulk material and the collision plate, Passing before collision The number of frames used, After the collision The number of frames used, In the study of low-speed particle collisions, the friction effect is not considered, and the calculation formula of the Newton collision restitution coefficient e is: (6) The particles start to fall freely from the same height due to rest, and after contacting the collision plate, the rebound force is generated to make them move upward. The energy is conserved during the whole movement process, so To ensure that the number of grids of the bulk material from the collision plate is the same before and after the collision, the combined equations (4) to (6) yield: (7) After multiple tests, the average value of the collision recovery coefficient e is taken ; Measure the static friction coefficient of bulk materials as follows: 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. A roller 9 is installed on the support rod 8 vertically arranged to the bottom plate 7. A rocker 10 is fixedly connected to one side of the roller 9. A rope 11 is arranged on the roller 9. The rope 11 is connected to the other end of the swing plate 6. The rocker 10 is rotated, and then the swing plate 6 is driven to rotate and lift around the hinge with the bottom plate 7. 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, that is, the sliding friction angle, is recorded as φ, and then the static friction coefficient f of the bulk material is calculated. f = tanφ, After multiple tests, the average value of the static friction factor f is taken .

[0033] S2 measures the angle of repose of bulk materials in physical tests by the plate drawing method, as follows: (a) A shellless square housing is made of contact material, and two symmetrical and oppositely arranged slide grooves are arranged on both sides of the inside of the square housing along the height direction of the square housing; (b) sliding a baffle made of contact material into the interior of the square shell along the slide groove, dividing the interior of the square shell into chamber one and chamber two by the baffle, then placing the square shell on a horizontal plane, filling chamber one with bulk material particles, and slowly withdrawing the baffle after the bulk material particles are stationary and stable, so that the bulk material particles naturally slide into chamber two along the opening formed by the baffle and the bottom of the square shell under the action of gravity; (c) After the bulk material particles are left to stand and stabilize, the angle between the slope surface formed by the bulk material particles and the bottom plane of the square shell is measured, which is the repose angle of the bulk material in the physical test; Then the angle of repose of bulk materials in the simulation test is calculated as follows: Import the same shellless square shell model as in step (a) into the EDEM software. The shellless square shell model can be formed by three-dimensional modeling software. Bulk material particles are established in the shellless square shell model. When the bulk material particles are filled in the shellless square shell model, a speed of 100 mm / s is applied to the baffle to move the baffle upward. When the minimum speed of the bulk material particles is less than 0.001 m / s, the protractor tool in the EDEM software is used 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, which is the repose angle of the bulk material in the simulation test. A repose angle close to the repose angle obtained in the object test is determined as the rolling friction coefficient in the discrete element model.

[0034] S3 establishes a discrete element model through the intrinsic parameters, collision recovery coefficient, static friction coefficient and rolling friction coefficient of the bulk material in steps S1 to S2. And the pneumatic conveying rig corresponding to the object test is used to generate a pneumatic conveying rig geometric model corresponding to the simulation experiment through three-dimensional simulation software; the actual pneumatic conveying rig is as follows Figure 1 As shown, there are a material storage pipe 01 and a conveying pipe 02, the lower end of the material storage pipe 01 is connected to the conveying pipe 02 through a venturi pipe 03, air flow is introduced into one end of the venturi pipe 03, and then the material is output at the other end of the venturi pipe 03, and a simulation test is carried out using a discrete element model and a pneumatic conveying bench geometric model; S4 makes the data at the inlet of the physical test and the simulation test the same during the pneumatic conveying process, and measures the air pressure and gas velocity of the bulk material passing through the outlet during the pneumatic conveying process in the physical test, as follows: (d) Calculate the gas flow rate at the inlet of the delivery pipeline using the following formula: , in is the air velocity at the inlet of the conveying duct, is the particle size coefficient of bulk materials, is the particle density of bulk material, is the particle characteristic coefficient of bulk material, L is the pipeline length; (e) Calculate the diameter D of the delivery pipeline using the following formula: , in is the mass flow rate of bulk material particles, The air velocity at the inlet of the delivery pipe, i is the number of delivery pipes, is the air density, is the gas concentration in the transport pipeline.

[0035] The derivation process of the diameter D of the conveying pipeline is as follows: The gas conveying concentration is the ratio of the mass of particles conveyed per unit time to the mass of the gas flow passing through the pipeline. If the conveying concentration is extremely high, particle blockage is very likely to occur during the conveying process. The equation for gas conveying concentration is as follows: (1) (2) in is the mass flow rate of particles (kg / s); is the mass flow rate of gas (kg / s); is the number of delivery pipes; is the air density (kg / m3), is the diameter of each conveying pipe (mm). According to formulas (1) and (2), the diameter formula is obtained: (3) (f) After determining the gas flow rate at the inlet of the conveying pipeline and the diameter of the conveying pipeline, the air pressure at the inlet and outlet of the conveying pipeline are measured by the pressure transmitter, and the gas velocity at the inlet and outlet of the conveying pipeline are measured by the anemometer. Finally, the velocity of the bulk material particles at the outlet of the conveying pipeline is photographed by a high-speed camera, and the velocity v of the bulk material particles at the outlet of the conveying pipeline is calculated. The formula is as follows: , 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; The formula for calculating the acceleration a of bulk material particles at the outlet of the conveying pipeline is as follows: , t is the unit time, Then calculate the average velocity of n bulk material particles passing through the outlet per unit time. and the average acceleration , the formula is as follows: , , At the same time, the Y-axis mean value and standard deviation are calculated during the object test. The specific method is as follows: Take the center of the plane where the conveying pipeline outlet is located as the origin O, the vertical direction as the Y-axis, and the horizontal direction as the X-axis to establish a rectangular coordinate system. Let the Y-axis coordinate of the bulk material particles be y, and calculate the average value of the Y-axis coordinate of n bulk material particles per unit time. And the standard deviation SD, the formula is as follows: , , Thus, the average value of the Y-axis coordinate The vertical movement amplitude of bulk material particles is evaluated by the pneumatic conveying method and the standard deviation SD. That is, the smaller the Y-axis average value and the standard deviation SD are, the smaller the movement amplitude is, and the closer the bulk material particles are to suspended conveying, and the more stable the conveying is during the pneumatic conveying process.

[0036] At the same time, the Y-axis average value and standard deviation can be obtained by using the Euler-Lagrange model in the EDEM software to obtain the simulation result diagram: the particle's motion state, velocity, acceleration, motion direction, plane xy axis position and the mass of bulk material transported per unit time; the pressure cloud map and velocity cloud map of the flow field gas; the particle motion state is the accumulation and crushing phenomenon of particles in the pipeline during pneumatic conveying; the particle velocity, acceleration and motion direction are obtained by the Analyst Tree post-processing function of the EDEM software; the particle's position on the plane xy axis considers the particle's motion amplitude in the direction perpendicular to the ground in the observation area; the particle motion amplitude is the criterion for judging whether the particle is suspended and transported. The particle motion amplitude in the direction perpendicular to the ground indicates that the transport is more stable.

[0037] At the same time, a simulation test is performed using the bulk material data measured in step S1, as follows: Import the same pneumatic conveying stand geometric model as that in step (f), and import the pneumatic conveying stand geometric model into EDEM software, simulate the air pressure and airflow according to the CFD-DEM (computational fluid dynamics-discrete element) mathematical model in EDEM software, and then establish the bulk material particles with the intrinsic parameters, collision recovery coefficient, static friction coefficient of the bulk material in step S1 and the calibrated rolling friction coefficient of the bulk material in step S3, and then make the air pressure and gas velocity at the inlet of the pneumatic conveying stand geometric model the same as the air pressure and gas velocity at the inlet in step (f), respectively. After simulation, the air pressure and gas velocity at the outlet of the pneumatic conveying stand geometric model and the velocity and acceleration of the bulk material particles at the outlet are obtained.

[0038] S5 compares the data at the outlet in the physical test and the simulation test. In this embodiment, the data at the outlet include air pressure, gas velocity, and the average velocity, average acceleration, and average value of the Y-axis coordinate of the bulk material particles. and standard deviation In this embodiment, if the data at the export are within the preset error range, If the calibrated bulk material data is within the pneumatic conveying state, the motion state is verified to be similar to the real motion state, thereby proving the accuracy of the calibrated bulk material discrete element model and completing the calibration of the bulk material in the discrete element model; if it does not meet the requirements, proceed to step S6. S6 selects the repose angle measured by the physical test and the repose angle measured by the simulation test, and when the repose angle has another relative error value within the relative error range, 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 all within the preset error range.

[0039] The working principle of the present invention is as follows: first, the data of the bulk material is measured through a physical test, and the data of the material includes the collision recovery coefficient and the static friction coefficient of the bulk material, so that the discrete model is related to the static friction object test and the simulation experiment, so that the discrete element model measurement is more accurate, and the data of the bulk material is calibrated, and a discrete element model of the bulk material is built, and the discrete element model is used to determine the material and airflow of the simulation experiment to input the material into the pneumatic conveying stand geometric model, and the data of the bulk material in the pneumatic conveying process is measured through a simulation test, and the data obtained through the physical test is compared with the data measured by the simulation test to determine whether the data error of the two tests is within a preset error range, thereby verifying whether the motion state of the bulk material calibrated in the discrete element model under the pneumatic conveying state is similar to the actual motion state, and when similar, the angle of repose is adjusted to make the measured experimental results closer to the experimental values.

Claims

1. A material parameter calibration method for a feeding system using a discrete element method for pneumatic conveying, characterized in that: The following steps are included: 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 bulk materials; S2 measures the repose angle of the bulk material in the physical test by the plate drawing method, and calculates the repose angle of the bulk material in the simulation test at the same time; selects the repose angle measured by the physical test and the repose angle measured by the simulation test within the relative error of - rolling friction coefficient as the rolling friction coefficient in the discrete element model; S3: establishing a discrete element model through the intrinsic parameters, collision recovery coefficient, static friction coefficient and rolling friction coefficient of the bulk material in steps S1 to S2; generating a pneumatic conveying stand geometry model corresponding to the simulation experiment from the pneumatic conveying stand corresponding to the object test; and performing a simulation experiment using the discrete element model and the pneumatic conveying stand geometry model; S4 makes the data of the inlet of the physical test and the simulation test the same during the pneumatic conveying process, measures the data of the bulk material passing through the outlet during the pneumatic conveying process in the physical test, and simultaneously performs a simulation test with the bulk material data measured in step S1, 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, respectively. 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 experiment 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, the process goes to step S6; S6 selects the repose angle measured by the physical test and the repose angle measured by the simulation test, and when the repose angle has another relative error value within the relative error range, 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 all within the preset error range.

2. The material parameter calibration method for a pneumatic conveying feeding system according to claim 1, characterized in that: The plate extraction method in step S2 comprises the following steps: (a) A shellless square housing is made of contact material, and two symmetrically oppositely arranged slide grooves are arranged on both sides of the inside of the square housing; (b) sliding a baffle made of contact material into the interior of the square shell along the slide groove, dividing the interior of the square shell into chamber one and chamber two by the baffle, then placing the square shell on a horizontal plane, filling chamber one with bulk material particles, and slowly withdrawing the baffle after the bulk material particles are stationary and stable, so that the bulk material particles naturally slide into chamber two along the opening formed by the baffle and the bottom of the square shell under the action of gravity; (c) After the bulk material particles are left to stand still and stabilize, the angle between the slope surface formed by the bulk material particles and the bottom plane of the square shell is measured, which is the repose angle of the bulk material in the physical test.

3. The material parameter calibration method for a pneumatic conveying feeding system according to claim 1, 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, establish bulk material particles in the shellless square shell model, and when the bulk material particles are filled in 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 between the slope surface formed by the bulk material particles and the bottom plane of the shellless square shell model, which is the repose angle of the bulk material in the simulation test.

4. The material parameter calibration method for a pneumatic conveying feeding system according to claim 1, characterized in that: The method for measuring the gas pressure and gas velocity of the bulk material passing through the outlet during the pneumatic conveying process in the physical test in step S4 comprises the following steps: (d) Calculate the gas flow rate at the inlet of the delivery pipeline using the following formula: ; in is the air velocity at the inlet of the conveying duct, is the particle size coefficient of bulk materials, is the particle density of bulk material, is the particle characteristic coefficient of bulk material, L is the pipeline length; (e) Calculate the diameter D of the delivery pipeline using the following formula: ; in is the mass flow rate of bulk material particles, The air velocity at the inlet of the delivery pipe, i is the number of delivery pipes, is the air density, is the gas concentration in the transmission pipeline; (f) After determining the gas flow rate at the inlet of the conveying pipeline and the diameter of the conveying pipeline, build a pneumatic conveying stand for bulk materials, and then measure the air pressure at the inlet and outlet of the conveying pipeline using a pressure transmitter, and measure the gas velocity at the inlet and outlet of the conveying pipeline using an anemometer. Finally, use a high-speed camera to capture the velocity of the bulk material particles at the outlet of the conveying pipeline and calculate the acceleration.

5. The material parameter calibration method for a pneumatic conveying feeding system using a discrete element method according to claim 1, characterized in that: The method for measuring the gas pressure and gas velocity of the bulk material passing through the outlet during the pneumatic conveying process in the simulation test in step S4 includes: Import the same pneumatic conveying stand geometric model as that in step (f), and import the pneumatic conveying stand geometric model into the EDEM software, then establish the bulk material particles with the intrinsic parameters, collision recovery coefficient, static friction coefficient of the bulk material in step S1 and the calibrated rolling friction coefficient of the bulk material in step S3, then make the air pressure and gas velocity at the inlet of the pneumatic conveying stand geometric model the same as the air pressure and gas velocity at the inlet in step (f), respectively, and after simulation, obtain the air pressure and gas velocity at the outlet of the pneumatic conveying stand geometric model and the velocity and acceleration of the bulk material particles at the outlet.

6. The material parameter calibration method for a pneumatic conveying feeding system using a discrete element method according to claim 1, characterized in that: The step (f) further comprises: The velocity v of bulk material particles at the outlet of the conveying pipeline is calculated as follows: ， 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; The formula for calculating the acceleration a of bulk material particles at the outlet of the conveying pipeline is as follows: ， t is the unit time, Then calculate the average velocity of n bulk material particles passing through the outlet per unit time. and the average acceleration , the formula is as follows: ， 。 7. The material parameter calibration method for a pneumatic conveying feeding system using a discrete element method according to claim 1, characterized in that: Step S5 also includes determining whether the movement amplitude of the bulk material meets the suspension transport criteria by the average value and standard deviation of the Y-axis coordinates of the bulk material particles. If the average value is smaller and the standard deviation range is smaller, it meets the suspension transport criteria.

8. The material parameter calibration method for a pneumatic conveying feeding system according to claim 7, characterized in that: Take the center of the plane where the conveying pipeline outlet 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 calculate the average value of the Y axis coordinates of n bulk material particles per unit time. And the standard deviation SD, the formula is as follows: ， 。

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