A method for constructing a multi-sphere discrete element model of a wheat chaff based on a parameterized curved surface

Abstract

The present application belongs to the field of agricultural engineering and particle discrete element modeling technology, and particularly relates to a wheat chaff multi-sphere discrete element model construction method based on parameterized surface. The method comprises the following steps: S1: performing macroscopic size measurement on chaff samples of multiple wheat varieties; S2: establishing a parameterized surface expression form according to geometric rules; S3: substituting corresponding scale parameters and surface morphology parameters into the parameterized surface expression form; S4: obtaining a candidate multi-sphere geometric model corresponding to candidate constituent sphere diameters; S5: determining a target multi-sphere geometric model; S6: obtaining discrete element contact mechanics parameters of the wheat chaff; and S7: importing the target multi-sphere geometric model and the discrete element contact mechanics parameters into a discrete element software to obtain a wheat chaff multi-sphere discrete element model. The present application determines sphere center coordinates through a parameterized surface, can reduce the influence of empirical ball arrangement on model results, and can reduce the number of constituent spheres under the condition of meeting the requirements of shape and inertia error.

Description

Technical Field

[0001] This invention relates to the field of agricultural engineering and particle discrete element modeling technology, specifically a method for constructing a multi-sphere discrete element model of wheat hulls based on parametric surfaces. Background Technology

[0002] Wheat hulls are abundant during threshing, conveying, separation, and cleaning, and are classified as lightweight, thin, flaky materials. Actual hulls are typically elongated, with a prominent central ridge that arches significantly, and the width and height of the arch are not uniform along its length. During cleaning, the hulls' tumbling, overlapping, piling, and contact with grains and the sieve surface are all influenced by their shape. Using an oversimplified particle model can weaken the self-locking and tumbling resistance characteristics of the hulls, thus affecting the cleaning simulation results. Therefore, in discrete element simulations of wheat harvesting and cleaning processes, it is necessary to establish a particle model that can describe the main geometric features and contact behavior of the hulls.

[0003] In existing discrete element modeling, there are already many simplified models for objects such as grains, stems, leaves, and plants. For thin, curved particles like glumes, while commonly used single-sphere, ellipsoidal, or empirical multi-sphere models are convenient for modeling, they struggle to simultaneously preserve the mid-ridge arch, head-tail contraction, and cross-sectional arch features. Directly using scanning models or high-density multi-sphere models would significantly increase the number of constituent spheres and the contact detection burden, which is detrimental to particle swarm computation.

[0004] Discrete element method (DEM) modeling schemes exist for wheat leaves, stems, plants, or other agricultural materials, typically generating models based on geometric parameter inputs and the assembly of constituent spheres or empirical arrangement rules. While these methods can provide a reference for DEM modeling of agricultural materials, their model objects and geometric features differ from wheat hulls, making them difficult to directly describe the thin, curved, arched midribs and cross-sectional arch variations of the hulls. Furthermore, existing constituent sphere modeling methods often employ fixed spacing or empirical sphere placement. Given the hull's geometric parameters and the diameter of the constituent spheres, they lack a process for determining the sphere center coordinates using parametric surfaces, and also lack methods for adjusting the sampling interval under volumetric error constraints, and for selecting candidate models by combining geometric and rotational inertia errors.

[0005] Therefore, it is necessary to propose a discrete element modeling method for wheat hulls that directly determines the positions of the constituent spheres based on the geometric features of the hulls and can perform error screening on candidate multi-sphere models. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0008] A method for constructing a multi-sphere discrete element model of wheat hulls based on parametric surfaces includes the following steps:

[0009] S1: Macroscopic size measurements were performed on hull samples from multiple wheat varieties. Representative samples were subjected to three-dimensional scanning and dimensionless shape parameter analysis to extract the geometric patterns of wheat hulls along the length direction.

[0010] S2: Based on geometric laws, a parametric surface representation is established. The parametric surface representation is composed of the distribution function of the mid-ridge arch height, the distribution function of the width, and the cross-sectional morphology function. It is characterized by the scale parameters and surface morphology parameters corresponding to different wheat varieties or different samples.

[0011] S3: For the wheat variety or sample to be modeled, substitute the corresponding scale parameters and surface morphology parameters into the parameterized surface expression form, and set the diameter of at least one candidate component sphere;

[0012] S4: Determine the axial sampling interval and lateral sampling interval based on the diameter of the candidate constituent spheres, determine the sphere center position along the arc length direction of the mid-ridge line and the arc length direction of the cross section, generate a set of sphere center coordinates, and estimate the sphere union volume of the corresponding multi-sphere model; adjust the axial sampling interval and lateral sampling interval through volume error constraints to obtain the candidate multi-sphere geometric model corresponding to the diameter of the candidate constituent spheres;

[0013] S5: Evaluate the candidate multi-sphere geometric models based on geometric errors and rotational inertia errors, and determine the target multi-sphere geometric model;

[0014] S6: Obtain the discrete element contact mechanical parameters of wheat husks, including static friction coefficient, restitution coefficient and rolling friction coefficient;

[0015] S7: Import the target multi-sphere geometric model and discrete element contact mechanics parameters into the discrete element software to obtain the multi-sphere discrete element model of wheat husk.

[0016] As a preferred embodiment of the method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to the present invention, in step S2, the parametric surface model uses the length direction parameter... and width direction parameters It means that among them , Its expression is:

[0017] ; ; in, , , These represent the coordinates in the width direction, length direction, and arch height direction, respectively. This represents the maximum width of the wheat husk. The length of the wheat husk. The wheat husks arch high. Let be the distribution function of the arch height of the central ridge along its length. Let be the distribution function of width along the length direction. This is a cross-sectional shape function.

[0018] As a preferred embodiment of the method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces described in this invention, wherein the... To be at the peak position The expression for an asymmetric piecewise function that reaches its maximum value at a given point is:

[0019] ;

[0020] in, This is the peak position of the arch height. and These are the shape control parameters for the front and rear sides of the peak position, respectively.

[0021] The Based on head width coefficient and tail width coefficient Together, we determine that its expression is:

[0022] ;

[0023] in, This indicates the ratio of the head width to the maximum width. This indicates the ratio of the tail width to the maximum width.

[0024] The Determined by p, its expression is:

[0025] ;

[0026] in, Used to control the sharpness or bluntness of the arched profile of the cross section.

[0027] As a preferred embodiment of the method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces described in this invention, wherein, in S4, the axial sampling interval... and lateral sampling interval With the diameter of the constituent sphere Related, its expression is:

[0028] ; ;

[0029] in, This is the axial spacing adjustment coefficient. This is the horizontal spacing adjustment coefficient.

[0030] As a preferred embodiment of the method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces described in this invention, wherein the axial spacing adjustment coefficient is set... With lateral spacing adjustment coefficient The distances are equal, and the spacing adjustment coefficient is determined through a one-dimensional search. For each candidate spacing adjustment coefficient, a corresponding set of sphere center coordinates is generated, and the volume of the sphere union of the corresponding multi-sphere model is estimated. According to the volume of the union of the spheres With target volume The relative error determines the ball arrangement scheme under the current constituent ball diameter.

[0031] As a preferred embodiment of the method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces described in this invention, the volume of the sphere union is... With target volume The relative error satisfies:

[0032] When determining the corresponding candidate spacing adjustment coefficient to satisfy the volume error constraint, where, A preset volume error threshold is set; if no candidate spacing adjustment coefficient that satisfies the volume error constraint exists within the preset search range, the candidate spacing adjustment coefficient with the smallest relative error is selected as the ball arrangement scheme under the current constituent ball diameter; the preset volume error threshold... It is 5%.

[0033] As a preferred embodiment of the method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to the present invention, in step S4, the midrib line is expressed in the form of a parametric surface. The location is determined, and equal arc length sampling is performed along the arc length direction of the central ridge line to obtain an axial sampling parameter set; at the position corresponding to each axial sampling parameter, the cross-sectional curve is extracted, and equal arc length sampling is performed along the arc length direction of the cross-sectional curve to obtain a transverse sampling parameter set; during the cross-sectional arc length sampling process, an edge margin is set to maintain a preset distance between the center of the constituent ball and the edge of the wheat husk, and the edge margin is related to the diameter of the constituent ball.

[0034] As a preferred embodiment of the method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces described in this invention, in step S4, the diameter of the constituent spheres is... The corresponding set of coordinates of the sphere's center is represented as:

[0035] ;

[0036] in, These are the axial sampling parameters obtained by sampling the arc length of the mid-ridge line. In the first Lateral sampling parameters are obtained by sampling the cross-sectional arc length at each axial position; different sphere diameters correspond to different sets of sphere center coordinates.

[0037] As a preferred embodiment of the method for constructing a multi-sphere discrete element model of wheat hull based on parametric surfaces according to the present invention, in step S5, the geometric error includes at least one of length error, width error, and arch height error, and the rotational inertia error includes the relative principal inertia error between the candidate multi-sphere geometric model and the real hull model or the reference hull model; the target multi-sphere geometric model is determined by selecting the model with fewer constituent spheres from among the candidate multi-sphere geometric models that meet the preset geometric error and rotational inertia error requirements as the target multi-sphere geometric model.

[0038] As a preferred embodiment of the method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces as described in this invention, in step S6, the discrete element contact mechanical parameters are obtained through experimental measurement, simulation calibration, or a combination of both.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] (1) The distribution of the height, width and cross-sectional shape of the ridge arches together define the glumes surface, enabling the model to simultaneously describe the arching in the length direction, the contraction at the head and tail and the arched profile of the cross-section.

[0041] (2) The position of the sphere center is determined by the sampling results of the mid-ridge line and the arc length of the cross section, so as to avoid the generation of overly dense or sparse spheres in the end contraction area or the abrupt change area of ​​the arch height when sampling only according to the parameter coordinates at equal intervals;

[0042] (3) Introducing volume error constraints during the ball placement process allows the axial and lateral sampling intervals to be determined by the reverse screening of the target volume, rather than simply relying on empirical intervals, which can reduce the model volume deviation under different component ball diameters;

[0043] (4) The candidate multi-sphere geometric model is evaluated by using geometric error and rotational inertia error, and the model with fewer constituent spheres is selected from the candidate models that meet the preset error requirements. This can reduce the number of constituent spheres while maintaining the main shape and inertia characteristics.

[0044] (5) The obtained multi-sphere discrete element model of wheat hulls can be used as a particle model for discrete element simulation of wheat hulls accumulation, rolling and conveying process; for light and thin sheet-like agricultural materials with similar morphological characteristics, the multi-sphere model can also be established by adjusting the scale parameters and surface morphology parameters according to this method. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0046] Figure 1 This is a schematic diagram of the geometric shape and main dimensional parameters of wheat hulls in a method for constructing a multi-sphere discrete element model of wheat hulls based on parametric surfaces, according to the present invention.

[0047] Figure 2 This is a schematic diagram of the parameterized surface model of wheat hulls, which is a method for constructing a multi-sphere discrete element model of wheat hulls based on parameterized surfaces according to the present invention. In this diagram, (a) is a schematic diagram of the parameterized surface coordinates and the midrib line, (b) is a schematic diagram of the midrib arch height distribution function, (c) is a schematic diagram of the midrib transverse half-width function, and (d) is a schematic diagram of the cross-sectional shape function.

[0048] Figure 3 This is a schematic diagram of the arrangement of constituent spheres based on arc length sampling and volume error constraints in the method for constructing a multi-sphere discrete element model of wheat hull based on parametric curved surfaces according to the present invention. Among them, (a) is a schematic diagram of equidistant sampling of the arc length of the midrib line, (b) is a schematic diagram of equidistant sampling of the arc length of the cross section, and (c) is a schematic diagram of the arrangement result of the constituent spheres.

[0049] Figure 4 This is a schematic diagram of candidate multisphere geometric models of wheat husks under different component sphere diameters according to the method for constructing a multisphere discrete element model of wheat husks based on parametric surfaces of the present invention. Among them, (a) is a candidate model with D=0.3 mm, (b) is a candidate model with D=0.4 mm, (c) is a candidate model with D=0.5 mm, and (d) is a candidate model with D=0.6 mm.

[0050] Figure 5 This is a comparison chart of geometric errors and rotational inertia errors of different candidate multisphere geometric models in an embodiment of a method for constructing a multisphere discrete element model of wheat husk based on parametric surfaces according to the present invention.

[0051] Figure 6This is a comparison of the experimental and simulation results of the target multi-sphere discrete element model rotating drum in an embodiment of the method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to the present invention. Detailed Implementation

[0052] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0053] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0054] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0055] A method for constructing a multi-sphere discrete element model of wheat hulls based on parametric surfaces includes the following steps:

[0056] Step 1: Macroscopic size measurement of hull samples from multiple wheat varieties was performed, and three-dimensional scanning and dimensionless shape parameter analysis were conducted on representative samples to extract the arching pattern of the midrib along the length direction, the width variation pattern, and the cross-sectional arch distribution pattern of the wheat hull.

[0057] Step 2: Establish a parametric surface representation based on geometric laws. The parametric surface representation is composed of the distribution function of the mid-ridge arch height, the distribution function of the width, and the cross-sectional morphology function coupled together, and is characterized by the scale parameters and surface morphology parameters corresponding to different wheat varieties or different samples.

[0058] Generalized parametric surface models with length direction parameters and width direction parameters It means that among them , Its expression is:

[0059] ; ; in, , , These represent the coordinates in the width direction, length direction, and arch height direction, respectively. This represents the maximum width of the wheat husk. The length of the wheat husk. The wheat husks arch high. Let be the distribution function of the arch height of the central ridge along its length. Let be the distribution function of width along the length direction. It is a cross-sectional shape function;

[0060] Arch height distribution function To be at the peak position The expression for an asymmetric piecewise function that reaches its maximum value at a given point is:

[0061] ;

[0062] in, This is the peak position of the arch height. and These are the shape control parameters for the front and rear sides of the peak position, respectively.

[0063] Width distribution function Based on head width coefficient and tail width coefficient Together, we determine that its expression is:

[0064] ;

[0065] in, This indicates the ratio of the head width to the maximum width. This formula represents the ratio of the tail width to the maximum width, ensuring that the width function satisfies the preset width ratio at the head, tail, and peak positions.

[0066] The Determined by p, its expression is:

[0067] ;

[0068] in, Used to control the sharpness or bluntness of the arched profile of the cross section;

[0069] Step 3: For the wheat variety or sample to be modeled, substitute the corresponding scale parameters and surface morphology parameters into the parameterized surface expression form, and set the diameter of at least one candidate component sphere;

[0070] Step 4: Determine the axial sampling interval and lateral sampling interval based on the diameter of the candidate constituent spheres, determine the sphere center position along the arc length direction of the mid-ridge line and the arc length direction of the cross section, generate the sphere center coordinate set, and estimate the sphere union volume of the corresponding multi-sphere model; adjust the axial sampling interval and lateral sampling interval through volume error constraints to obtain the candidate multi-sphere geometric model corresponding to the diameter of the candidate constituent spheres;

[0071] Axial sampling interval and lateral sampling interval With the diameter of the constituent sphere Related, its expression is:

[0072] ; ;

[0073] in, This is the axial spacing adjustment coefficient. This is the horizontal spacing adjustment coefficient;

[0074] Adjust the axial spacing coefficient With lateral spacing adjustment coefficient The distances are equal, and the spacing adjustment coefficient is determined through a one-dimensional search. For each candidate spacing adjustment coefficient, a corresponding set of sphere center coordinates is generated, and the volume of the sphere union of the corresponding multi-sphere model is estimated. According to the volume of the union of spheres With target volume The relative error determines the ball arrangement scheme under the current constituent ball diameter;

[0075] Sphere union volume With target volume The relative error satisfies:

[0076] When determining the corresponding candidate spacing adjustment coefficient to satisfy the volume error constraint, where, A preset volume error threshold is set; if no candidate spacing adjustment coefficient that satisfies the volume error constraint exists within the preset search range, the candidate spacing adjustment coefficient with the smallest relative error is selected as the ball placement scheme under the current constituent ball diameter, and the preset volume error threshold is used. It is 5%;

[0077] The mid-ridge line is expressed in the form of a parametric surface. The location is determined, and equal arc length sampling is performed along the arc length direction of the mid-ridge line to obtain the set of axial sampling parameters;

[0078] The cross-sectional curves are extracted at the locations corresponding to the sampling parameters of each axis, and equal arc length sampling is performed along the arc length direction of the cross-sectional curves to obtain the set of transverse sampling parameters. During the cross-sectional arc length sampling process, an edge margin is set to maintain a preset distance between the center of the constituent ball and the edge of the wheat husk. The edge margin is related to the diameter of the constituent ball.

[0079] With the diameter of the constituent sphere The corresponding set of coordinates of the sphere's center is represented as:

[0080]

[0081] in, These are the axial sampling parameters obtained by sampling the arc length of the mid-ridge line. In the first Lateral sampling parameters are obtained by sampling the cross-sectional arc length at each axial position; different sphere diameters correspond to different sets of sphere center coordinates;

[0082] Step 5: Evaluate the candidate multi-sphere geometric models based on geometric error and rotational inertia error, and determine the target multi-sphere geometric model from the candidate multi-sphere geometric models that meet the preset error requirements;

[0083] Geometric errors include at least one of length error, width error, and camber height error; rotational inertia errors include the relative principal inertia errors between the candidate multi-sphere geometric model and the real hull model or the reference hull model.

[0084] The target multi-sphere geometric model is determined as follows: among the candidate multi-sphere geometric models that meet the preset requirements for geometric error and rotational inertia error, the model with fewer constituent spheres is selected as the target multi-sphere geometric model.

[0085] Step 6: Obtain the discrete element contact mechanical parameters of wheat hulls. The discrete element contact mechanical parameters include the static friction coefficient, the coefficient of restitution, and the rolling friction coefficient between wheat hulls and between wheat hulls and the contact boundary. The discrete element contact mechanical parameters are obtained through experimental measurement, simulation calibration, or a combination of both.

[0086] Step 7: Import the target multi-sphere geometric model and discrete element contact mechanics parameters into the discrete element software to obtain the wheat hull multi-sphere discrete element model.

[0087] Example:

[0088] This embodiment presents the construction process of a multi-sphere discrete element model of wheat hulls, including sample geometric measurement, three-dimensional scanning model processing, parametric surface fitting, sphere center coordinate generation, candidate model evaluation, and contact parameter import.

[0089] 1. Wheat hull sample collection and geometric feature extraction.

[0090] This embodiment selects mature wheat husk samples from three wheat varieties for measurement and analysis. The wheat varieties can be Fanmai 8, Zhenmai 12, and Yongliang 4, or other wheat varieties to be modeled. Macroscopic dimensions of the husk samples from each variety are measured, including length. Maximum width Arch height ,thickness and density The main dimensional parameters of wheat husks, such as length, maximum width, and arch height, are defined as follows: Figure 1 As shown.

[0091] Among them, length The characteristic dimension of the wheat husk from head to tail along the main axis; maximum width The maximum distance between the left and right edges of the glume when viewed from above; camber. The maximum height difference between the highest point of the midrib of the glume and the reference plane at the edge; thickness This represents the average or characteristic thickness of the hull in the normal direction. The statistical results of the macroscopic dimensions of the hulls of the three wheat varieties are shown in Table 1.

[0092] Table 1: Geometric parameters of wheat husks of different varieties

[0093]

[0094] Representative samples with intact morphology and covering the main size distribution range were selected from various varieties for 3D scanning to obtain glume surface models. The surface models underwent coordinate preprocessing to ensure that the glume length direction corresponded to the desired coordinates. Axis, corresponding to the width direction Axis, corresponding to the direction of arch height Axis. Then along The husk model is segmented along the axial direction. Within each segment, the left and right edge points and the highest point of the central ridge are extracted to obtain the width and arch height at that section. The segment positions are then normalized to... This yields the width distribution curve and the mid-ridge arch height distribution curve along the length direction.

[0095] The above measurements and scanning results show that wheat husks exhibit a mid-ridge arch along their length, with the peak arch height typically deviating from the geometric center; the width varies asymmetrically along the length, gradually narrowing at both ends; and the cross-section presents an arched profile that is high in the middle and low on both sides. These geometric characteristics are used to establish the subsequent parametric surface model.

[0096] 2. Establishment of parametric surface model.

[0097] Establish a local coordinate system ,in The axis indicates the length direction of the glume. The axis indicates the width direction. The axis represents the direction of the arch height. Let the length direction parameter be... The width direction parameter is ,in:

[0098]

[0099] The parametric surface expression for wheat husks is:

[0100] ; ; in, These represent the coordinates in the width direction, length direction, and arch height direction, respectively; This is the distribution function of the arch height of the central ridge along its length; This is the distribution function of the width along the length direction; This is the cross-sectional morphology function. The parameterized surface model of wheat husk obtained from the above expression is as follows: Figure 2 As shown (in) Figure 2 In (a), the arrow indicating "midridge line u=0" is used only to indicate the location of the midridge line and is a single arrow; "u" represents the parameter in the cross-sectional direction, with a value range of "-1≤u≤1", used to characterize the lateral change from one edge to the other, and is a double arrow; "s" represents the parameter along the length of the glume, with a value range of "0≤s≤1", used to characterize the longitudinal change from one end to the other, and is a single arrow indicating the direction of parameter increase.

[0101] Mid-ridge arch height distribution function To be at the peak position Asymmetric piecewise functions that reach their maximum value at a given point:

[0102]

[0103] in, This is the peak position of the central ridge arch. and These are the shape control parameters for the front and rear sides of the peak position, respectively.

[0104] Width distribution function Represented as:

[0105]

[0106] in, This indicates the ratio of the head width to the maximum width. This represents the ratio of the tail width to the maximum width. This formula ensures that the width function satisfies the corresponding width ratio constraints at the head, tail, and maximum width positions, respectively.

[0107] The Determined by p, its expression is:

[0108]

[0109] in, Used to control the sharpness or bluntness of the arched profile of the cross section.

[0110] By fitting the cross-sectional width curve, mid-ridge arch height curve, and typical cross-sectional profile obtained from the 3D scan, we can obtain... and Surface morphology parameters. The width curve, mid-ridge arch height curve, and typical cross-sectional profile extracted from the scanning section can be used to determine the above surface parameters. Different varieties or different representative samples use the same surface representation form, but the parameter values ​​can be determined separately based on the scanning results. Table 2 shows the surface morphology parameters of the glumes of three varieties.

[0111] Table 2: Parametric surface morphological parameters of wheat hulls of different varieties

[0112]

[0113] 3. Take Panmai No. 8 as an example to establish a parametric surface.

[0114] As a specific embodiment, this method was used to create a multi-sphere discrete element model of wheat hulls of the Fanmai 8 variety. First, mature, intact hull samples of Fanmai 8 were selected, and their macroscopic dimensional parameters were measured, as shown in Table 3.

[0115] Table 3: Macroscopic Dimensions of Representative Samples of Wheat Hives from Fanmai No. 8

[0116]

[0117] thickness The actual characteristic thickness of the wheat hull shell in the normal direction, and the diameter of the constituent sphere. These are the modeling scale parameters in the multi-sphere discretization process; they do not need to be the same. Different component sphere diameters are used to form candidate multi-sphere geometric models with different resolutions.

[0118] Based on the three-dimensional scanning results of representative glumes of Panmai 8, surface fitting was performed to obtain the corresponding surface morphology parameters, as shown in Table 4.

[0119] Table 4: Parameters of the parametric surface model of wheat hull of Fanmai No. 8

[0120]

[0121] The scale parameters in Table 3 Substituting the surface morphology parameters from Table 4 into the above parameterized surface expression, we obtain the surface coordinate function of the wheat husk of Panmai 8. This surface coordinate function is used for the subsequent calculation of the coordinates of the center of the constituent spheres.

[0122] 4. Construction of candidate multi-sphere models based on arc length sampling and volume error constraints.

[0123] In this embodiment, given the scale parameters of wheat husks , , Candidate sphere diameter and target volume Then, the ball spacing under the current constituent ball diameter is determined through an adaptive spacing optimization program. The target volume... It can be calculated from a 3D scanning model, or estimated based on parameters such as the macroscopic size, thickness, and density of wheat husks.

[0124] To reduce the computational complexity caused by optimizing the axial sampling interval and the lateral sampling interval separately, this embodiment sets the axial spacing adjustment coefficient... With lateral spacing adjustment coefficient Equal, that is:

[0125]

[0126] Then the axial target sampling interval And the horizontal target sampling interval They are represented as follows:

[0127]

[0128]

[0129] in, This is the spacing adjustment coefficient. The diameter of the candidate constituent spheres. In this embodiment, the spacing adjustment coefficient... Available Uniform sampling within the range. When the size is smaller, the spheres are more densely packed, and the local curved surface contours are better preserved, but the number of spheres increases. When the value is large, the number of constituent spheres decreases, but the volume error and edge contour deviation may increase. Therefore, given D, we iterate through s and record the number of constituent spheres, the volume of the sphere union, and the shape error for each scheme.

[0130] Take the parametric surface in The curve at that point serves as the midrib line of the wheat husk:

[0131]

[0132] Along the arc length direction of the mid-ridge line, according to the axial target sampling interval By performing equal arc length sampling, the set of axial sampling parameters is obtained:

[0133]

[0134] in, This represents the number of axial sampling points. At each axial sampling position... At that location, extract the corresponding cross-sectional curve, and along the arc length direction of the cross-sectional curve, according to the lateral target sampling interval. By performing equal arc length sampling, the set of transverse sampling parameters on this cross section is obtained:

[0135]

[0136] in, For the first The number of transverse sampling points at each axial sampling position. To avoid the center of the constituent sphere being too close to the edge of the glume, an edge margin can be set during the cross-sectional arc length sampling process to maintain a preset distance between the edge sampling points and the two side boundaries of the glume. The edge margin can be determined based on the diameter of the constituent sphere. A certain proportion is determined.

[0137] Axial sampling parameters and lateral sampling parameters Substituting the parameterized surface expression, we obtain the diameter of the current candidate constituent sphere. and current spacing adjustment coefficient The set of coordinates of the center of the sphere below:

[0138]

[0139] in, Indicates the first The first axial position, the first The coordinates of the center of each sphere at a horizontal position. (This is derived from the coordinates of all sphere centers.) and the diameter of the sphere Corresponding candidate multi-sphere geometric models can be generated. The process of arranging the constituent spheres based on arc length sampling and volume error constraints is as follows: Figure 3 As shown.

[0140] For each candidate spacing adjustment coefficient First, the number of spheres is counted based on the generated set of sphere center coordinates. First, a preliminary screening of candidate schemes is performed using the summation of single-sphere volumes. The calculation formula is as follows:

[0141]

[0142] in, This is the volume estimate without deducting the overlapping regions that make up the spheres. The number of constituent spheres in the current candidate multi-sphere geometric model. The diameter of the constituent spheres. Since adjacent constituent spheres may overlap, the... It is only used for preliminary screening of candidate schemes and is not used as a basis for final volume error evaluation.

[0143] For the candidate schemes retained after coarse screening, the voxel occupancy method is used to estimate the sphere union volume of the candidate multi-sphere model. The bounding box containing all constituent spheres is divided into sections with sides of length... voxel unit, voxel side length The value can be determined based on the diameter of the constituent spheres and the required calculation accuracy. In this embodiment, we take... Determine whether the center of each voxel falls inside any constituent sphere. If the distance from a voxel center to the center of any sphere is not greater than a certain value... Then, this voxel is denoted as the occupied voxel. Let the number of occupied voxels be . The volume of the spherical union of the candidate multi-sphere model. It can be estimated as follows:

[0144]

[0145] Because the voxel occupancy method only counts overlapping constituent spherical regions once, its results... This can be used to characterize the sphere union volume of candidate multi-sphere models. Then, the target volume... Volume of the union with the sphere The relative error is used as an evaluation index for volume error:

[0146]

[0147] in, This refers to the volume relative error. The volume relative error satisfies:

[0148] At that time, the current candidate scheme is considered to satisfy the volume error constraint. Among them, The preset volume error threshold can be set to 5% in this embodiment.

[0149] If multiple candidate spacing adjustment coefficients satisfying the volume error constraint exist within the preset search range, then the volume relative error is selected. The smaller option is used as the current constituent sphere diameter The following ball placement scheme; if no solution exists within the preset search range that satisfies the above; If there are no candidate schemes, the one with the smallest relative volume error is selected as the relaxed ball placement scheme.

[0150] Following the method described above, sphere placement calculations are performed for different candidate component sphere diameters, resulting in multiple candidate multi-sphere geometric models. The candidate multi-sphere geometric models formed under different component sphere diameters are shown below. Figure 4 As shown in Table 5, different candidate component sphere diameters correspond to different sampling intervals, sphere center coordinate sets, number of component spheres, and volume errors. Based on the method described in this embodiment, candidate multi-sphere geometric models with different candidate component sphere diameters can be obtained, and the number of component spheres and volume errors are shown in Table 5.

[0151] Table 5: Number of constituent spheres and volume error of candidate models

[0152]

[0153] 5. Evaluation and screening of candidate multi-sphere geometric models.

[0154] Geometric errors and rotational inertia errors were evaluated for different candidate multi-sphere geometric models. The geometric errors included length error, width error, and camber height error.

[0155] ;

[0156] The overall geometric error is:

[0157]

[0158] in, , , For the actual size of the shell or the target curved surface, , , The dimensions are the corresponding dimensions of the candidate multisphere geometric model.

[0159] The moment of inertia error is determined based on the relative errors of the three principal moments of inertia:

[0160] ;

[0161] The overall rotational inertia error is:

[0162]

[0163] in, , , These are the three principal inertia of the real hull model or reference model. , , These are the three principal inertia of the candidate multisphere geometric model.

[0164] Evaluation results of different candidate multi-sphere geometric models for Panmai 8 are as follows: Figure 5 As shown. According to Figure 5 As a result, among the candidate models that meet the preset requirements for geometric error and moment of inertia error, the model with fewer constituent spheres is selected as the target multi-sphere geometric model. In this embodiment, The candidate model for mm has a small number of spheres when the geometric error and rotational inertia error meet the preset requirements. Therefore, it is determined to be the multi-sphere geometric model of the wheat husk target of Panmai 8.

[0165] 6. Acquisition of contact mechanics parameters and establishment of discrete element model.

[0166] Discrete element method (DEM) contact mechanical parameters of wheat husks were measured and calibrated. These parameters include the static friction coefficient, collision recovery coefficient, and rolling friction coefficient between wheat husks and between wheat husks and the contact boundary. The static friction coefficient and collision recovery coefficient can be obtained through inclined plane tests, impact tests, etc., while the rolling friction coefficient can be calibrated through cylindrical lifting tests and simulation comparisons. In this embodiment, the contact mechanical parameters are shown in Table 6.

[0167] Table 6: Discrete Element Contact Mechanical Parameters of Wheat Hull

[0168]

[0169] The target multi-sphere geometric model, physical parameters, and contact mechanics parameters shown in Table 6 were imported into the discrete element method (DEM) software to establish a multi-sphere DEM model of the wheat husk of variety Fanmai 8. The physical parameters include density, mass, Poisson's ratio, and shear modulus; the geometric parameters include the coordinates of the sphere centers and the diameters of the spheres; and the contact parameters include the static friction coefficient, collision recovery coefficient, and rolling friction coefficient. When establishing the DEM model, the density or particle mass of the target multi-sphere model can be corrected based on the actual husk mass to ensure that the mass of the target multi-sphere DEM model is consistent with or close to the actual husk mass; alternatively, the equivalent density can be determined based on the volume of the multi-sphere model and the actual husk mass.

[0170] 7. Validation of the macroscopic response of the target model.

[0171] Rotating drum tests can be used to examine the response of a target multi-sphere model during particle swarm rolling and accumulation. The simulation uses the same drum size, load capacity, and rotational speed as the experimental setup, and compares the dynamic angle of repose. Verification results are as follows: Figure 6 As shown.

[0172] By comparing the simulated dynamic packing angle or particle free surface morphology with experimental results, the characterization effect of the target multi-sphere discrete element model on the rolling, packing, and flow behavior of glumes can be determined. The above verification process is used to illustrate the application of the model in this embodiment and does not limit the scope of protection of this invention.

[0173] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, as long as there is no structural conflict, the features in the disclosed embodiments can be combined with each other in any manner. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for constructing a multi-sphere discrete element model of wheat hulls based on parametric surfaces, characterized in that, Includes the following steps: S1: Macroscopic size measurements were performed on hull samples from multiple wheat varieties. Representative samples were subjected to three-dimensional scanning and dimensionless shape parameter analysis to extract the geometric patterns of wheat hulls along the length direction. S2: Based on geometric laws, a parametric surface representation is established. The parametric surface representation is composed of the distribution function of the mid-ridge arch height, the distribution function of the width, and the cross-sectional morphology function. It is characterized by the scale parameters and surface morphology parameters corresponding to different wheat varieties or different samples. S3: For the wheat variety or sample to be modeled, substitute the corresponding scale parameters and surface morphology parameters into the parameterized surface expression form, and set the diameter of at least one candidate component sphere; S4: Determine the axial sampling interval and lateral sampling interval based on the diameter of the candidate constituent spheres, determine the sphere center position along the arc length direction of the mid-ridge line and the arc length direction of the cross section, generate a set of sphere center coordinates, and estimate the sphere union volume of the corresponding multi-sphere model; adjust the axial sampling interval and lateral sampling interval through volume error constraints to obtain the candidate multi-sphere geometric model corresponding to the diameter of the candidate constituent spheres; S5: Evaluate the candidate multi-sphere geometric models based on geometric errors and rotational inertia errors, and determine the target multi-sphere geometric model; S6: Obtain the discrete element contact mechanical parameters of wheat husks, including static friction coefficient, restitution coefficient and rolling friction coefficient; S7: Import the target multi-sphere geometric model and discrete element contact mechanics parameters into the discrete element software to obtain the multi-sphere discrete element model of wheat husk.

2. The method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to claim 1, characterized in that, In S2, the parameterized surface model uses the length direction parameter... and width direction parameters It means that among them , Its expression is: ； in, , , These represent the coordinates in the width direction, length direction, and arch height direction, respectively. This represents the maximum width of the wheat husk. The length of the wheat husk. The wheat husks arch high. Let be the distribution function of the arch height of the central ridge along its length. Let be the distribution function of width along the length direction. This is a cross-sectional shape function.

3. The method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to claim 2, characterized in that, The To be at the peak position The expression for an asymmetric piecewise function that reaches its maximum value at a given point is: ； in, This is the peak position of the arch height. and These are the shape control parameters for the front and rear sides of the peak position, respectively. The Based on head width coefficient and tail width coefficient Together, we determine that its expression is: ； in, This indicates the ratio of the head width to the maximum width. This indicates the ratio of the tail width to the maximum width. The Determined by p, its expression is: ； in, Used to control the sharpness or bluntness of the arched profile of the cross section.

4. The method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to claim 1, characterized in that, In S4, the axial sampling interval and lateral sampling interval With the diameter of the constituent sphere Related, its expression is: ； in, This is the axial spacing adjustment coefficient. This is the horizontal spacing adjustment coefficient.

5. The method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to claim 4, characterized in that, Let the axial spacing adjustment coefficient With lateral spacing adjustment coefficient The distances are equal, and the spacing adjustment coefficient is determined through a one-dimensional search. For each candidate spacing adjustment coefficient, a corresponding set of sphere center coordinates is generated, and the volume of the sphere union of the corresponding multi-sphere model is estimated. According to the volume of the union of the spheres With target volume The relative error determines the ball arrangement scheme under the current constituent ball diameter.

6. The method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to claim 5, characterized in that, The sphere union volume With target volume The relative error satisfies: When determining the corresponding candidate spacing adjustment coefficient to satisfy the volume error constraint, where, A preset volume error threshold is set; if no candidate spacing adjustment coefficient that satisfies the volume error constraint exists within the preset search range, the candidate spacing adjustment coefficient with the smallest relative error is selected as the ball arrangement scheme under the current constituent ball diameter; the preset volume error threshold... It is 5%.

7. The method for constructing a multi-sphere discrete element model of wheat hulls based on parametric surfaces according to claim 1, characterized in that, In S4, the mid-ridge line is expressed as a parametric surface. The location is determined, and equal arc length sampling is performed along the arc length direction of the central ridge line to obtain an axial sampling parameter set; at the position corresponding to each axial sampling parameter, the cross-sectional curve is extracted, and equal arc length sampling is performed along the arc length direction of the cross-sectional curve to obtain a transverse sampling parameter set; during the cross-sectional arc length sampling process, an edge margin is set to maintain a preset distance between the center of the constituent ball and the edge of the wheat husk, and the edge margin is related to the diameter of the constituent ball.

8. The method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to claim 1, characterized in that, In S4, the diameter of the constituent sphere is related to... The corresponding set of coordinates of the sphere's center is represented as: ； in, These are the axial sampling parameters obtained by sampling the arc length of the mid-ridge line. In the first Lateral sampling parameters are obtained by sampling the cross-sectional arc length at each axial position; different sphere diameters correspond to different sets of sphere center coordinates.

9. The method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to claim 1, characterized in that, In S5, the geometric error includes at least one of length error, width error, and camber error, and the rotational inertia error includes the relative principal inertia error between the candidate multi-sphere geometric model and the real hull model or the reference hull model; the target multi-sphere geometric model is determined by selecting the model with fewer constituent spheres from among the candidate multi-sphere geometric models that meet the preset geometric error and rotational inertia error requirements as the target multi-sphere geometric model.

10. The method for constructing a multi-sphere discrete element model of wheat husk based on parametric surfaces according to claim 1, characterized in that, In S6, the discrete element contact mechanical parameters are obtained through experimental measurement, simulation calibration, or a combination of both.

Images