A discrete element 3D modeling method for ballasted track considering the influence of snow cover

Abstract

The present invention belongs to the technical field of discrete element modeling and numerical simulation, and provides a discrete element three-dimensional modeling method for ballasted track considering the influence of snow cover. The corresponding snow layer contour is constructed by the morphological characteristics of the snow layer of the railway snow-covered ballast track, and the contour is divided into a snow outer layer and a snow invasion layer. The snow particles are generated by filling in the generated snow particles in combination with the Fish function particle position judgment logic, which can respectively shape the distribution state of snow accumulation on the track surface and invasion into the gaps inside the track. When establishing the railway snow-covered ballast track model, the ballast is simulated by extended polyhedron units, and the bulk characteristics of the ballast particles are fully considered, including the selection of ballast morphological characteristics, the consideration of gradation distribution, the basic physical parameters of the ballast extended polyhedron units and snow ball particles, and the setting of the contact model. The established three-dimensional discrete element model of the ballasted track takes into account the influence of snow cover, which is of certain significance to the research on the railway snow-covered ballast track structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of discrete element modeling and numerical simulation, and relates to ballasted tracks in cold regions, and specifically is a discrete element three-dimensional modeling method for ballasted track beds taking into account the influence of snow cover. Background Art

[0002] The discrete element method is a numerical simulation method specifically used to solve discontinuous medium problems. Its core concept is to regard the medium as composed of a large number of discrete particles or blocks, and to predict the motion characteristics and mechanical behavior of the entire system by simulating the interaction between these particles or blocks. Developing efficient numerical methods for ballasted track structures in cold-region railways and conducting related mechanical performance research have important theoretical value and engineering significance for the smooth and safe operation of cold-region railways.

[0003] At present, the discrete element method is mostly used for numerical simulation of ballasted trackbeds. The discrete element method can effectively consider the bulk characteristics of ballast stone particles and fully reflect the macro- and micro-mechanical behaviors of granular trackbeds. Since crushed stone ballast has different shapes and has strong interlocking characteristics when the particles are piled up, it is very important to reasonably construct a calculation model for ballast stone particles with irregular morphology.

[0004] In cold regions, affected by the low temperature environment, when rain and snow fall, a certain thickness of snow layer will accumulate on the ballasted railway track. Under the action of wind and snow, the snow layer will present different contour characteristics, and the bottom of the snow layer will blend with the surface of the track bed and gradually invade the track bed layer. Referring to the existing literature, there are few related studies that consider the influence of snow cover on the ballasted track bed of cold-region railways. The method of the present invention refines the ballast model by expanding the polyhedron unit, and generates the track bed according to the ballast grading, morphological characteristics and porosity, and then measures the surface morphology of the railway snow layer for three-dimensional modeling, and combines the Fish function particle position judgment logic to form a snow cover layer. The established ballasted track bed model is more in line with the actual situation, and the calculation accuracy of the model is improved, which is used for the subsequent numerical simulation research of the ballasted track structure of cold-region railways. Summary of the invention

[0005] In view of the above technical problems existing in the prior art, this paper proposes a discrete element three-dimensional modeling method for ballasted trackbed considering the influence of snow cover.

[0006] The present invention adopts a discrete element three-dimensional modeling method for ballasted track bed considering the influence of snow cover, which is characterized in that the method steps of establishing the discrete element model are as follows:

[0007] (1) Construct a computational domain, and establish a rectangular closed area in the computational domain. The length of the front view surface of the rectangular closed area is greater than or equal to the maximum width of the cross section of the ballasted railway track bed, and its height is greater than the maximum height of the cross section of the ballasted railway track bed;

[0008] (2) Generate a ballast particle extended polyhedron unit database based on the ballast stone morphology feature data, porosity, and gradation data. Generate a ballast particle extended polyhedron unit accumulation body in the rectangular closed area described in step (1). When calculating the mass of each ballast particle extended polyhedron unit, it is approximated as a spherical particle, and its mass is:

[0009]

[0010] Where ρ is the density of ballast stone, V is the volume of the expanded polyhedral unit of ballast particles, and D min and D max are the minimum and maximum apertures of the corresponding aperture intervals. In each aperture interval, the diameter D of the expanded polyhedral unit of the ballast particles is r The distribution form of is uniform distribution or normal distribution;

[0011] (3) Assign values ​​to the basic physical parameters of the extended polyhedral unit of ballast particles, such as density, elastic modulus, and friction coefficient, and set up a linear contact model between particles;

[0012] (4) Using a laser rangefinder to measure the ballast bed on site, the surface morphology and dimensions of the ballast bed are obtained. According to the surface morphology and dimensions of the ballast bed, the ballast particles in the rectangular closed area are deleted and the polyhedron units are expanded to obtain a discrete element model of the ballasted railway ballast bed.

[0013] (5) By using a laser rangefinder to measure the surface morphology of the snow on the ballast bed, a plane coordinate system XZ is established according to the morphological dimensions of the ballasted railway ballast bed in step (4), the origin of the coordinate system is the bottom of the centerline position of the cross section of the ballasted railway ballast bed, and the upward Z direction of the coordinate system is positive. The point coordinate data of the surface morphological features of the ballasted railway ballast bed are imported into the coordinate system and converted into a line frame of a two-dimensional plane;

[0014] Furthermore, the surface morphology of snow on the ballast bed is converted into a plane curve, and the bottom surface of the area intruding into the ballast bed is a smooth sinusoidal plane curve;

[0015] Furthermore, the line frame is located in the first and second quadrants of the plane coordinate system XZ, and with the frame line as the reference, one end of the two curves is connected to the outer bottom of the track bed line frame, and the other end is connected to the line frame of the part between the highest point of the track bed frame line and the sleeper;

[0016] Furthermore, a Y direction is added to the normal direction of the plane coordinate system XZ to establish a three-dimensional coordinate system XYZ, and the curves on both sides of the line frame are extended along the Y direction to expand into a surface having the same plane characteristics as the curve;

[0017] Furthermore, the two curves are extended into a surface, and the corresponding edges of the two surfaces are connected in pairs in the Z direction to form a closed three-dimensional snow layer contour.

[0018] (6) Generate snowball particles within the contour of the three-dimensional snow layer of the ballasted railway track bed in step (5). When generating, the spatial position of the snowball particles is judged. The condition for judging whether the spatial position of the snowball particles is generated is: within the contour of the three-dimensional snow layer of the ballasted railway track bed constructed in step (5), if the spatial position of the snowball particles is within the contour, then the snowball particles are generated; if not, then the snowball particles are not generated. The cycle is repeated until the entire space within the contour is filled, and a discrete element model of the snow layer is obtained;

[0019] (7) In the snow layer discrete element model generated in step (6), the snow layer contour is divided into a snow outer layer and a snow intrusion layer, the snow outer layer is the surface of the roadbed and the part above the surface, and the snow intrusion layer is the part below the roadbed surface;

[0020] Furthermore, in the process of generating snow ball particles in the snow intrusion layer, the centroid coordinates of the snow ball particles in the discrete element model of the snow layer are judged. The condition for judging whether the centroid coordinates of the snow ball particles are deleted is: in the snow ball particles corresponding to the snow intrusion layer, if the distance d between the centroid coordinates of the snow ball particles and the ballast stone particles is less than r, where r is the radius of the snow ball particles, the particles are deleted; if d is greater than or equal to r, the next particle is retained and calculated. The cycle is repeated until all snow ball particles in the snow intrusion layer are identified, the three-dimensional snow layer contour of the ballasted railway track bed is deleted, and the physical properties of the snow ball particles, such as Poisson's ratio, elastic modulus, and density, are assigned. The contact model between particles is the Linear Parallel Bond Model linear parallel bond contact model, and gravity acceleration is applied, so as to finally obtain a discrete element model of the ballasted track bed considering the influence of snow cover. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention is a flowchart of a discrete element modeling method for ballasted trackbed in cold-region railways considering the influence of snow accumulation.

[0022] Figure 2 It is a schematic diagram of a three-dimensional closed area.

[0023] Figure 3 It is a partial schematic diagram of the discrete element model of the cold region railway ballast layer, including before and after deletion.

[0024] Figure 4 The method is to import the point coordinate data of the morphological characteristics of the cold-region ballasted railway track bed into the coordinate system and convert it into a two-dimensional line frame diagram.

[0025] Figure 5 It is a local schematic diagram of the extension of two snow layer contour curves.

[0026] Figure 6 Schematic diagram of a section of the discrete element model of the track bed including the snow layer contour.

[0027] Figure 7 It is a partial schematic diagram of the discrete element model of a snow layer with densely arranged snow ball particles.

[0028] Figure 8 It is a cross-sectional view of the snow layer of snowball particles.

[0029] Fig. 9 It is a partial schematic diagram of the discrete element model of snow-covered ballasted trackbed for cold region railways. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present method is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0031] A discrete element three-dimensional modeling method for ballasted track bed considering the influence of snow cover, characterized in that the modeling steps are as follows:

[0032] (1) Construct a computational domain and establish a rectangular closed area in the computational domain. The length of the front view surface of the rectangular closed area is greater than or equal to the maximum width of the cross section of the ballasted railway track bed, and its height is greater than the maximum height of the cross section of the ballasted railway track bed. The length, width and height of the rectangular closed area are 5.4m, 0.6m and 0.8m respectively.

[0033] (2) Generate a ballast particle extended polyhedron unit database based on the ballast stone morphology feature data, porosity, and gradation data. Generate a ballast particle extended polyhedron unit accumulation body in the rectangular closed area described in step (1). When calculating the mass of each ballast particle extended polyhedron unit, it is approximated as a spherical particle, and its mass is:

[0034]

[0035] Where ρ is the density of ballast stone, V is the volume of the expanded polyhedral unit of ballast particles, and D min and D max are the minimum and maximum apertures of the corresponding aperture intervals. In each aperture interval, the diameter D of the expanded polyhedral unit of the ballast particles is r The distribution form of is uniform distribution or normal distribution;

[0036] (3) The basic physical parameter density of the expanded polyhedral unit of ballast particles is 2755.9 kg / m 3 , elastic modulus is 5e 8 , assign a friction coefficient of 0.1, and set the Linear Model contact model between particles;

[0037] (4) Using a laser rangefinder to measure the ballast bed on site, the surface morphology and dimensions of the ballast bed are obtained. According to the surface morphology and dimensions of the ballast bed, the ballast particles in the rectangular closed area are deleted and the polyhedron units are expanded to obtain a discrete element model of the ballasted railway ballast bed.

[0038] (5) By using a laser rangefinder to measure the surface morphology of the snow on the ballast bed, a plane coordinate system XZ is established according to the morphological dimensions of the ballasted railway ballast bed in step (4), the origin of the coordinate system is the bottom of the centerline position of the cross section of the ballasted railway ballast bed, and the upward Z direction of the coordinate system is positive. The point coordinate data of the surface morphological features of the ballasted railway ballast bed are imported into the coordinate system and converted into a line frame of a two-dimensional plane;

[0039] Furthermore, the surface morphology of snow on the ballast bed is converted into a plane curve, and the bottom surface of the area intruding into the ballast bed is a smooth sinusoidal plane curve;

[0040] Furthermore, the line frame is located in the first and second quadrants of the plane coordinate system XZ, and with the frame line as the reference, one end of the two curves is connected to the outer bottom of the track bed line frame, and the other end is connected to the line frame of the part between the highest point of the track bed frame line and the sleeper;

[0041] Furthermore, a Y direction is added to the normal direction of the plane coordinate system XZ to establish a three-dimensional coordinate system XYZ, and the curves on both sides of the line frame are extended along the Y direction to expand into a surface having the same plane characteristics as the curve;

[0042] Furthermore, the two curves are extended into a surface, and the corresponding edges of the two surfaces are connected in pairs in the Z direction to form a closed three-dimensional snow layer contour.

[0043] (6) Generate snowball particles within the contour of the three-dimensional snow layer of the ballasted railway track bed in step (5). When generating, the spatial position of the snowball particles is judged. The condition for judging whether the spatial position of the snowball particles is generated is: within the contour of the three-dimensional snow layer of the ballasted railway track bed constructed in step (5), if the spatial position of the snowball particles is within the contour, then the snowball particles are generated; if not, then the snowball particles are not generated. The cycle is repeated until the entire space within the contour is filled, and a discrete element model of the snow layer is obtained;

[0044] (7) In the snow layer discrete element model generated in step (6), the snow layer contour is divided into a snow outer layer and a snow intrusion layer, the snow outer layer is the surface of the roadbed and the part above the surface, and the snow intrusion layer is the part below the roadbed surface;

[0045] Furthermore, in the process of generating snowball particles in the snow intrusion layer, the centroid coordinates of the snowball particles in the discrete element model of the snow layer are judged. The condition for judging whether the centroid coordinates of the snowball particles are deleted is: in the snowball particles corresponding to the snow intrusion layer, if the distance d between the centroid coordinates of the snowball particles and the ballast stone particles is less than r, where r is the radius of the snowball particles, then the particles are deleted; if d is greater than or equal to r, then the next particle is retained and calculated, and the cycle is repeated until all snowball particles in the snow intrusion layer are identified, the three-dimensional snow layer contour of the ballasted railway track is deleted, and the physical properties of the snowball particles are given a Poisson's ratio of 1 and an elastic modulus of 5e 9 , density is 920kg / m 3 The particle contact model is LinearParallel Bond Model, and the gravity acceleration in the Z direction is 9.8 m / s. 2 , and then the discrete element model of snow-covered ballasted roadbed is obtained.

Claims

1. A discrete element three-dimensional modeling method for ballasted track considering the influence of snow cover, characterized in that: The modeling steps are as follows: (1) Construct a computational domain, and establish a rectangular closed area in the computational domain. The length of the front view surface of the rectangular closed area is greater than or equal to the maximum width of the cross section of the ballasted railway track bed, and its height is greater than the maximum height of the cross section of the ballasted railway track bed; (2) Generate a ballast particle extended polyhedron unit database based on the ballast stone morphology feature data, porosity, and gradation data. Generate a ballast particle extended polyhedron unit accumulation body in the rectangular closed area described in step (1). When calculating the mass of each ballast particle extended polyhedron unit, it is approximated as a spherical particle, and its mass is: Where ρ is the density of ballast stone, V is the volume of the expanded polyhedral unit of ballast particles, and D min and D max are the minimum and maximum apertures of the corresponding aperture intervals. In each aperture interval, the diameter D of the expanded polyhedral unit of the ballast particles is r The distribution form of is uniform distribution or normal distribution; (3) Assign values ​​to the basic physical parameters of the extended polyhedral unit of ballast particles, such as density, elastic modulus, and friction coefficient, and set up a linear contact model between particles; (4) Using a laser rangefinder to measure the ballast bed on site, the surface morphology and dimensions of the ballast bed are obtained. According to the surface morphology and dimensions of the ballast bed, the ballast particles in the rectangular closed area are deleted and the polyhedron units are expanded to obtain a discrete element model of the ballasted railway ballast bed. (5) The surface morphology of snow on the ballast bed is measured by using a laser rangefinder, and the surface morphology of snow on the ballast bed is converted into a plane curve, and then the plane curve is extended along the longitudinal direction of the ballast bed into a curved surface. The bottom surface of the area intruding into the ballast bed is a smooth plane curve, which is extended along the longitudinal direction of the ballast bed into a curved surface. The corresponding edges of the two curved surfaces are connected in pairs to form a closed three-dimensional snow layer contour of the ballasted railway ballast bed; (6) When snowball particles are generated within the three-dimensional snow layer contour of the ballasted railway track bed in step (5), the spatial position of the snowball particles is judged. The condition for judging whether the spatial position of the snowball particles is generated is: within the three-dimensional snow layer contour of the ballasted railway track bed constructed in step (5), if the spatial position of the snowball particles is within the contour, the snowball particles are generated; if not, the snowball particles are not generated. The cycle is repeated until the entire space within the contour is filled, and a discrete element model of the snow layer is obtained. (7) In the snow layer discrete element model generated in step (6), the snow layer contour is divided into a snow outer layer and a snow intrusion layer, the snow outer layer is the surface of the roadbed and the part above the surface, and the snow intrusion layer is the part below the roadbed surface; Furthermore, in the process of generating snow ball particles in the snow intrusion layer, the centroid coordinates of the snow ball particles in the discrete element model of the snow layer are judged. The condition for judging whether the centroid coordinates of the snow ball particles are deleted is: in the snow ball particles corresponding to the snow intrusion layer, if the distance d between the centroid coordinates of the snow ball particles and the ballast stone particles is less than r, where r is the radius of the snow ball particles, the particles are deleted; if d is greater than or equal to r, the next particle is retained and calculated. The cycle is repeated until all snow ball particles in the snow intrusion layer are identified, the three-dimensional snow layer contour of the ballasted railway track bed is deleted, and the physical properties of the snow ball particles, such as Poisson's ratio, elastic modulus and density, are assigned. The contact model between particles is the Linear Parallel Bond Model, and gravity acceleration is applied. Finally, a discrete element model of the ballasted track bed considering the influence of snow cover is obtained.

2. The method for discrete element three-dimensional modeling of ballasted track bed considering the influence of snow cover according to claim 1 is characterized in that: In the discrete element model of the ballasted track bed considering the influence of snow cover described in step (7), the snow ball particles located in the outer layer of the snow in the snow layer are densely arranged, and the snow ball particles located in the snow intrusion layer are scattered and accumulated in the gaps between the ballast particle extended polyhedron units of the track bed.

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