Dynamic vehicle conversion coefficient determination method based on vehicle self-snow-cleaning effect in snow environment

Abstract

The invention discloses a dynamic vehicle conversion coefficient determination method based on a vehicle self-snow-cleaning effect in a snow environment, belongs to the field of expressway or urban expressway design, and particularly relates to a dynamic vehicle conversion coefficient determination method based on the vehicle self-snow-cleaning effect. The method aims at solving the problem that an existing vehicle conversion coefficient calculation method is only based on factors such as speed, delay, density, flow and dynamic characteristics and cannot reflect the influence of the vehicle self-snow-cleaning effect on the vehicle conversion coefficient in the snowfall period. According to a vehicle running at a high speed in the snowfall environment, snowflakes can be thrown in an airflow field formed in the rapid rotation process of tires, and the self-snow-cleaning effect of the vehicle is achieved; meanwhile, the dynamic vehicle conversion coefficient under the combined conditions of different running speeds and different air temperatures in the highway snow environment is quantitatively determined.

Description

Technical Field

[0001] The present invention belongs to the field of highway or urban expressway design, and specifically relates to a method for determining a dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect. Background Art

[0002] In winter, snow frequently falls in the Northeast region, which will have varying degrees of impact on highways. When the snowfall is heavy, the highway is covered by snow, and only traditional physical and chemical methods can be relied on to clear the snow; when the snowfall is light, due to the unique extremely cold weather in the Northeast region, although the snow particles can cover the highway pavement, because of their low density and friction speed, they can be scattered to the roadside by the airflow formed by the rotation of the wheels during vehicle operation, thus forming the vehicle self-snow-clearing effect.

[0003] At present, the research on highway traffic operation in snowy environments mainly focuses on the reduction of road surface friction and visibility during snowfall, and it is easy for high-speed vehicles to cause traffic accidents, and passive preventive measures such as speed reduction are studied. However, it is ignored that high-speed vehicles can also actively scatter snow particles due to the airflow field formed during the high-speed rotation of the wheels, which is helpful for road snow-clearing work. Therefore, the research on the dynamic vehicle conversion coefficient based on the vehicle "self-snow-clearing" effect in snowy environments is very meaningful. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that the existing calculation method of the vehicle conversion coefficient (PCE) is only based on factors such as speed, delay, density, flow rate, and dynamic characteristics, and cannot reflect the influence of the vehicle "self-snow-clearing" effect on the vehicle conversion coefficient during snowfall. In order to improve the vehicle conversion coefficient applicable to highways in snowy environments, a method for determining a dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in snowy environments is proposed.

[0005] The specific process of the method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in snowy environments is as follows:

[0006] Step 1: Obtain the air temperature T, vehicle type, total number of tires N, tire tread width L, wheel hub diameter D, tire flatness R, and running speed v during the snowfall period;

[0007] Step 2: Based on the tire tread width L, wheel hub diameter D, and tire flatness R obtained in Step 1, establish a three-dimensional tire model in Rhino modeling software;

[0008] Step 3: Import the three-dimensional tire model established in Step 2 into COMSOL 6.2 software, determine the coordinate system of the three-dimensional tire model in COMSOL 6.2 software, determine the cylinder and cuboid, set the material parameters, and divide the mesh elements;

[0009] Step 4: Determine the angular velocity β of the rotation domain with the vehicle running speed v and the cylinder diameter d as indicators;

[0010] The rotation domain is a cylinder region without the tire three-dimensional model inside obtained in the COMSOL 6.2 software;

[0011] Step 5: Use the SST turbulence model in the COMSOL 6.2 software as the simulation calculation model;

[0012] Step 6: Set the freezing operator and the number of iterations in the COMSOL 6.2 software, and start the simulation calculation to obtain the simulation calculation results;

[0013] The simulation calculation results are the velocity distribution of the external flow field during the tire rotation process, and extract the velocity distribution nephogram of the external flow field on the plane where the tire touches the ground ;

[0014] The external flow field is a cuboid region without the tire three-dimensional model and the cylinder inside obtained in the COMSOL 6.2 software;

[0015] Step 7: Based on the velocity distribution nephogram of the external flow field on the plane where the tire touches the ground, draw the velocity curve of the external flow field on the center line of the tire contact surface;

[0016] Step 8: Based on Step 7, draw the velocity curve of the external flow field on the right side of the center line of the tire contact surface;

[0017] Based on the temperature T during the snowfall period, determine the threshold friction velocity v of the snow particles * ;

[0018] Based on the threshold friction velocity v of the snow particles * Determine the corresponding abscissa x value in the velocity curve of the external flow field on the right side of the center line of the tire contact surface;

[0019] Based on the abscissa x value corresponding to the threshold friction velocity v of the snow particles * And the total number of tires N, calculate the influence area range F;

[0020] Step 9: Take the influence range F * = 1000mm as the standard value, and calculate the snow environment dynamic vehicle conversion coefficient Dynamic-PCE based on the standard value F * and the influence area range F obtained in Step 8.

[0021] The beneficial effects of the present invention are:

[0022] The present invention focuses on highways in the northeastern region of China where snowfall is frequent. Due to the low traffic volume and the relatively scattered operation of vehicles, the vehicle conversion coefficient calculated by traditional methods such as headway and delay is no longer applicable. Therefore, it is impossible to accurately describe the spatio-temporal occupancy ratio of vehicles under different vehicle types and different vehicle speeds. However, there is an obvious "self-clearing snow" effect of vehicles during snowfall. Especially when the snowfall is light, vehicles can clear most of the snow on the road surface during high-speed driving, which helps to improve the road traffic capacity. By performing three-dimensional modeling of vehicle tires and using the COMSOL 6.2 fluid simulation software to simulate the high-speed rotation process of the tires, the speed magnitude distribution of the tire contact surface with the ground is obtained. Taking the threshold friction velocity of snow particles at different temperatures as the judgment index, the influence range of snow particles on the outer edge of the tire is determined, and then the dynamic vehicle conversion coefficient is quantitatively determined. The invention has low usage cost, strong operability, and the simulation results are true and reliable, and can be applied to the calculation of the dynamic vehicle conversion coefficient of various vehicle types. At the same time, the calculation results reveal the strength of the self-clearing snow effect of vehicles in a snowfall environment, providing theoretical support for the highway not to reduce speed under meteorological conditions where the snowfall is light and visibility does not affect normal driving, improving the traffic efficiency of highways in a snowfall environment while taking into account traffic safety.

[0023] The purpose of the present invention is to reveal that during the high-speed rotation process of the tires of vehicles driving at high speed in a snowfall environment, the airflow field formed can scatter snowflakes, achieving the self-clearing snow effect of the vehicle. At the same time, the present invention quantitatively determines the dynamic vehicle conversion coefficient under different combinations of operating speeds and different air temperatures in the snow environment of highways. Brief Description of the Drawings

[0024] Figure 1 is the flow chart of the present invention;

[0025] Figure 2 is the three-dimensional model diagram of the tire;

[0026] Figure 3 is the XYZ coordinate system diagram of the three-dimensional tire model in the COMSOL 6.2 software, with the unit of meter;

[0027] Figure 4 is the calculation model diagram in the COMSOL 6.2 software;

[0028] Figure 5 is the moving mesh area diagram in the COMSOL 6.2 software;

[0029] Figure 6 is the mesh division diagram in the COMSOL 6.2 software;

[0030] Figure 7 is the contour map of the external flow field velocity distribution of the tire contact surface with the ground;

[0031] Figure 8Schematic diagram of the position of the center line of the tire contact surface in the three-dimensional tire model;

[0032] Figure 9 Schematic diagram of the position of the center line of the tire contact surface in the velocity contour map of the external flow field of the contact surface;

[0033] Figure 10 Velocity distribution diagram of the center line of the tire contact surface;

[0034] Figure 11 Velocity contour map of the external flow field of the plane where the tire contact surface is located under the condition of a running speed of 120 km / h;

[0035] Figure 12 Velocity contour map of the external flow field of the plane where the tire contact surface is located under the condition of a running speed of 105 km / h;

[0036] Figure 13 Velocity contour map of the external flow field of the plane where the tire contact surface is located under the condition of a running speed of 90 km / h;

[0037] Figure 14 Velocity contour map of the external flow field of the plane where the tire contact surface is located under the condition of a running speed of 75 km / h;

[0038] Figure 15 Velocity contour map of the external flow field of the plane where the tire contact surface is located under the condition of a running speed of 60 km / h;

[0039] Figure 16 Velocity curve diagram of the external flow field of the center line of the tire contact surface at five running speeds;

[0040] Figure 17 Velocity curve diagram of the external flow field on the right side of the center line of the tire contact surface under different running speeds and different temperature conditions. Specific implementation method

[0041] Specific implementation method 1: The specific process of the method for determining the dynamic vehicle conversion coefficient based on the vehicle self-cleaning snow effect in a snow environment is as follows: Figure 1 :

[0042] Step 1: Obtain the air temperature T during the snowfall period, vehicle type, total number of tires N, tire tread width L, wheel hub diameter D, tire flatness R, and running speed v;

[0043] Step 2: Based on the tire tread width L, wheel hub diameter D, and tire flatness R obtained in Step 1, establish a three-dimensional tire model in Rhino modeling software, such as Figure 2 ;

[0044] Step 3: Import the 3D tire model established in Step 2 into COMSOL 6.2 software, determine the coordinate system of the 3D tire model, identify the cylinder and cuboid, set the material parameters, and divide the mesh elements in COMSOL 6.2 software;

[0045] Step 4: Determine the angular velocity β of the rotation domain with the vehicle running speed v and the cylinder diameter d as indicators;

[0046] The rotation domain is the cylinder area that does not contain the 3D tire model obtained in Step 35 in COMSOL 6.2 software;

[0047] Step 5: Use the SST turbulence model in COMSOL 6.2 software as the simulation calculation model;

[0048] Step 6: Set the freezing operator and the number of iterations in COMSOL 6.2 software, and start the simulation calculation to obtain the simulation calculation results;

[0049] The simulation calculation result is the velocity distribution of the external flow field during the rotation of the tire, and extract the velocity distribution cloud map of the external flow field on the plane where the tire touches the ground ;

[0050] The external flow field is the cuboid area that does not contain the 3D tire model and the cylinder obtained in Step 34 in COMSOL 6.2 software;

[0051] Step 7: Based on the velocity distribution cloud map of the external flow field on the plane where the tire touches the ground, draw the velocity curve of the external flow field on the center line of the tire contact surface;

[0052] Step 8: Based on Step 7, draw the velocity curve of the external flow field on the right side of the center line of the tire contact surface;

[0053] Based on the temperature T during the snowfall period, determine the threshold friction velocity v of the snow particles * ;

[0054] Based on the threshold friction velocity v of the snow particles * Determine the corresponding abscissa x value in the velocity curve of the external flow field on the right side of the center line of the tire contact surface;

[0055] Based on the abscissa x value corresponding to the threshold friction velocity v of the snow particles * And the total number N of tires, calculate the influence area range F;

[0056] Step 9: With the influence range F * = 1000mm as the standard value, calculate the snow environment dynamic vehicle conversion coefficient Dynamic-PCE based on the standard value F * and the influence area range F obtained in Step 8.

[0057] Embodiment 2: The difference between this embodiment and Embodiment 1 is that in step 3, the three-dimensional tire model established in step 2 is imported into COMSOL 6.2 software, and in COMSOL 6.2 software, the coordinate system of the three-dimensional tire model is determined, the cylinder and the cuboid are determined, the material parameters are set, and the mesh elements are divided;

[0058] The specific process is as follows:

[0059] Step 31: Determine the coordinate system of the three-dimensional tire model in COMSOL 6.2 software; the specific process is as follows:

[0060] Import the three-dimensional tire model established in step 2 into COMSOL 6.2 software. Take the center of the three-dimensional model of the tire as the coordinate origin, the direction perpendicular to the tire rotation plane as the X-axis, the direction opposite to the gravity direction (the vertically upward direction) as the Z-axis, and the plane perpendicular to the XZ plane as the Y-axis to construct the XYZ coordinate system of the three-dimensional tire model, as Figure 3 ;

[0061] Step 32: Set the cylinder area containing the three-dimensional tire model in COMSOL 6.2 software; the specific process is as follows:

[0062] Outside the tire (outside the outer contour of the tire, the tire is wrapped by a cylinder), take the X-axis as the axis of the cylinder (the axis of the cylinder is the connection line of the centers of the upper and lower bottom surfaces of the cylinder), take the origin of the XYZ coordinate system of the three-dimensional tire model as the center of the cylinder, and build a cylinder. The diameter d of the upper and lower bottom surfaces of the cylinder = D + 2RL + 100mm, and the height h of the cylinder along the X-axis = L + 120mm;

[0063] Step 33: Set the cuboid area containing the three-dimensional tire model and the cylinder in COMSOL 6.2 software; the specific process is as follows:

[0064] Taking the origin of the XYZ coordinate system of the three-dimensional tire model as the center, set a cuboid with a length of 3m in the X-axis direction (the normal direction of the tire), a length of 5m in the Y-axis direction, and a length of 3m in the Z-axis direction;

[0065] Step 34: In COMSOL 6.2 software, divide the cylinder area containing the three-dimensional tire model set in step 32 and the cuboid area containing the three-dimensional tire model and the cylinder set in step 33, and split to obtain an independent cylinder area with the three-dimensional tire model inside and an independent cuboid area without the three-dimensional tire model and the cylinder inside;

[0066] In COMSOL 6.2 software, set the cuboid area without the three-dimensional tire model and the cylinder obtained in step 34 as the external flow field;

[0067] In step 32, the tire is exactly wrapped with a cylinder slightly larger than the tire size. In step 33, a cuboid is established. It can be understood that there is a cylinder inside the cuboid, and there is also a tire inside the cylinder. The first step in this stage is to extract the cylinder inside the cuboid. This is equivalent to the model becoming a cuboid without a cylinder + a cylinder (with a tire inside). In the 3D model operation of COMSOL 6.2 software, it is called "Split and Disassemble".

[0068] Step 35: In the COMSOL 6.2 software, perform a difference operation on the geometric models of the cylinder region containing the tire 3D model independently obtained in step 34 and the tire 3D model to obtain an independent cylinder region that does not contain the tire 3D model inside.

[0069] In the COMSOL 6.2 software, set the cylinder region that does not contain the tire 3D model obtained in step 35 as the rotation domain.

[0070] Step 36: In the COMSOL 6.2 software, form a union of the cuboid region that does not contain the tire 3D model and the cylinder inside obtained in step 34 and the cylinder region that does not contain the tire 3D model obtained in step 35, as Figure 4 ;

[0071] In the COMSOL 6.2 software, delete details such as continuously tangent vertices, short edges, small faces, long strip faces, narrow face regions, and thin faces generated during the process of forming the union.

[0072] Step 37: Set the material parameters in the COMSOL 6.2 software.

[0073] Step 38: Divide the mesh elements in the COMSOL 6.2 software.

[0074] Other steps and parameters are the same as those in the first specific implementation manner.

[0075] Specific implementation manner three: The difference between this implementation manner and the first or second specific implementation manner is that in step 37, the material parameters are set in the COMSOL 6.2 software; the specific process is as follows:

[0076] In the COMSOL 6.2 software, set the material properties of the cuboid that does not contain the tire 3D model and the cylinder obtained in step 34 and the cylinder that does not contain the tire 3D model obtained in step 35 as Air(mat1) in the material module of the COMSOL 6.2 software. Air(mat1) is the air parameter; mat1 is the module.

[0077] Other steps and parameters are the same as those in the first or second specific implementation manner.

[0078] Embodiment 4: Different from Embodiment 1 to 3, in step 38, the mesh elements are divided in COMSOL 6.2 software. The specific process is as follows:

[0079] In COMSOL 6.2 software, the rotating domain is set as the moving mesh area; during the simulation process, rotation is required, so this is the moving mesh area, and it also needs to be set in COMSOL software, as Figure 5 ;

[0080] In COMSOL 6.2 software, the external flow field area is set as the stationary mesh area (the external flow field lacking the cylinder, that is, the area outside the rotating domain, does not need to rotate during the simulation process, so it belongs to the stationary mesh area);

[0081] In COMSOL 6.2 software, the mesh division of the moving mesh area and the stationary mesh area is carried out according to the "refinement" standard in "physical field controlled mesh" to obtain the divided mesh elements, as Figure 6 .

[0082] Other steps and parameters are the same as those in Embodiment 1 to 3.

[0083] Embodiment 5: Different from Embodiment 1 to 4, in step 4, the angular velocity β of the rotating domain is determined with the vehicle running speed v and the cylinder diameter d as indicators; the rotating domain is a cylinder area without the tire three-dimensional model obtained in COMSOL 6.2 software;

[0084] It is expressed as:

[0085]

[0086] where β is in the unit of rad / s, and rad / s represents radians per second.

[0087] Other steps and parameters are the same as those in Embodiment 1 to 4.

[0088] Embodiment 6: Different from Embodiment 1 to 5, in step 5, the SST turbulence model in COMSOL 6.2 software is used as the simulation calculation model;

[0089] The specific process is as follows:

[0090] In the SST turbulence model, the external flow field area is set as an incompressible fluid;

[0091] In the SST turbulence model, the reference pressure level is set to 1 Pa;

[0092] Set the reference temperature to 293.15 K in the SST turbulence model;

[0093] Set the wall treatment expression to the automatic mode in the SST turbulence model;

[0094] Set the CFL number expression to the automatic mode in the SST turbulence model;

[0095] Set the velocity scale to 1 m / s in the SST turbulence model;

[0096] Set the length scale factor to 0.035 in the SST turbulence model;

[0097] To simulate the air in life, it all belongs to incompressible fluids, that is, this air cannot be compressed;

[0098] Other steps and parameters are the same as those in any one of the first to fifth specific embodiments.

[0099] Specific embodiment seven: The difference between this embodiment and any one of the first to sixth specific embodiments is that in step 6, set the freeze operator and the number of iterations in the COMSOL 6.2 software, and start the simulation calculation to obtain the simulation calculation results;

[0100] The simulation calculation result is the velocity distribution of the external flow field during the rotation of the tire, and extract the velocity distribution cloud map of the external flow field on the plane where the tire touches the ground ;

[0101] The external flow field is the cuboid region obtained in step 34 in the COMSOL 6.2 software that does not contain the three-dimensional model of the tire and the cylinder inside;

[0102] The specific process is as follows:

[0103] Due to the large amount of calculation in the SST turbulence model, turn on the "frozen rotor" function in the COMSOL 6.2 software, set the number of calculation iterations to 100 times, and start the simulation calculation to obtain the simulation calculation results;

[0104] The simulation calculation result is the velocity distribution of the external flow field during the rotation of the tire, and extract the velocity distribution cloud map of the external flow field on the plane where the tire touches the ground ; Figure 7 .

[0105] Other steps and parameters are the same as those in any one of the first to sixth specific embodiments.

[0106] Specific embodiment eight: The difference between this embodiment and any one of the first to seventh specific embodiments is that in step 7, based on the velocity distribution cloud map of the external flow field on the plane where the tire touches the ground, draw the velocity curve of the external flow field on the center line of the tire touching the ground; the specific process is as follows:

[0107] Set the starting coordinate of the center line of the tire's contact surface (unit: m), and the ending coordinate of the center line of the tire's contact surface (unit: m);

[0108] Extract the speed values corresponding to the starting coordinate to the ending coordinate of the center line from the simulation calculation results based on the starting coordinate and the ending coordinate of the center line of the tire's contact surface;

[0109] Take the starting coordinate to the ending coordinate of the center line of the tire's contact surface as the abscissa (-0.25 to 0.25), and the speed values corresponding to the starting coordinate to the ending coordinate of the center line as the ordinate to draw the velocity curve of the external flow field of the center line of the tire's contact surface, and observe the change trend of the external flow field velocity of the tire, such as Figure 9 and Figure 10 ;

[0110] The center line of the tire's contact surface is perpendicular to the tire rotation direction, such as Figure 8 .

[0111] Other steps and parameters are the same as those in any one of the first to seventh specific embodiments.

[0112] Specific embodiment nine: The difference between this embodiment and any one of the first to eighth specific embodiments is that in step 8, the velocity curve of the external flow field on the right side of the center line of the tire's contact surface is drawn based on step 7;

[0113] Based on the air temperature T during the snowfall period, determine the threshold friction velocity v of the snow particles * ;

[0114] Based on the threshold friction velocity v of the snow particles * Determine the corresponding abscissa x value in the velocity curve of the external flow field on the right side of the center line of the tire's contact surface;

[0115] Based on the abscissa x value corresponding to the threshold friction velocity v of the snow particles * and the total number N of tires, calculate the influence area range F;

[0116] The specific process is as follows:

[0117] Based on the speed values corresponding to the starting coordinate to the ending coordinate of the center line extracted in step 7, select the points where the value of the abscissa x is greater than zero and the corresponding speed values, take the x values greater than zero as the abscissa (0 to 0.25), and take the speed values corresponding to the x values greater than zero as the ordinate to draw the velocity curve of the external flow field on the right side of the center line of the tire's contact surface;

[0118] Based on the air temperature T during the snowfall period, determine the threshold friction velocity v of the snow particles * ;

[0119] Based on the threshold friction velocity v of the snow particles *Determine the corresponding abscissa x value in the outer flow field velocity curve diagram on the right side of the center line of the tire contact ground;

[0120] Based on the threshold friction velocity v of snow particles * Calculate the influence area range F based on the corresponding abscissa x value and the total number N of tires; The expression is:

[0121] F = N×2x

[0122] Combined with the air temperature T during the snowfall period, determine the threshold friction velocity v of snow particles * ; The specific process is:

[0123] When the air temperature T during the snowfall period ≤ -10°C, v * = 0.15 m / s;

[0124] When the air temperature during the snowfall period -10 < T ≤ -5°C, v * = 0.25 m / s.

[0125] Other steps and parameters are the same as those in any one of the specific embodiments one to eight.

[0126] Specific embodiment ten: The difference between this embodiment and any one of the specific embodiments one to nine is that in step 9, the influence range F * = 1000 mm is used as the standard value, and based on the standard value F * and the influence area range F obtained in step 8, calculate the snow environment dynamic vehicle conversion coefficient Dynamic-PCE; The expression is:

[0127]

[0128] Dynamic-PCE represents the dynamic vehicle conversion coefficient.

[0129] Other steps and parameters are the same as those in any one of the specific embodiments one to nine.

[0130] The following examples are used to verify the beneficial effects of the present invention:

[0131] Example 1:

[0132] As Figure 1 shown, it is a flowchart of the method for calculating the dynamic vehicle conversion coefficient based on the blowing snow effect and COMSOL fluid simulation in the snow environment of the present invention, including the following steps.

[0133] Step 1: Obtain the temperature T during the snowfall period, vehicle type, total number of tires N, tire tread width L, wheel hub diameter D, tire flatness R, and running speed v. Taking a certain brand of SUV vehicle as an example: the number of axles n is 2 axles, the total number of tires N is 4, the tire tread width L = 255 mm, the wheel hub diameter D = 16 inches, the tire flatness R = 65% = 0.65. Calculate the dynamic vehicle conversion coefficient under the combined conditions of the snowfall period temperature T = -20°C and T = -7°C and different running speeds (v = 120 km / h, v = 105 km / h, v = 90 km / h, v = 75 km / h, and v = 60 km / h).

[0134] Step 2: Based on the tire tread width L, wheel hub diameter D, and tire flatness R obtained in Step 1, establish a three-dimensional tire model in Rhino modeling software. Taking a certain brand of SUV vehicle as an example: the tire tread width L = 255 mm, the wheel hub diameter D = 16 inches = 406.4 mm, the tire flatness R = 65% = 0.65, and the outer contour diameter of the tire = wheel hub diameter D + 2 × tire tread width L × tire flatness R = 406.4 + 2 × 255 × 0.65 = 737.9 mm.

[0135] Step 3: Import the three-dimensional tire model established in Step 2 into COMSOL 6.2 software, determine the coordinate system of the three-dimensional tire model in COMSOL 6.2 software, determine the cylinder and cuboid, set the material parameters, and divide the mesh elements; the specific process is as follows:

[0136] Step 31: Determine the coordinate system of the three-dimensional tire model in COMSOL 6.2 software. The specific process is as follows:

[0137] Import the three-dimensional tire model established in Step 2 into COMSOL 6.2 software. Taking the center of the three-dimensional model of the tire as the origin of the coordinate system, the direction perpendicular to the tire rotation plane as the X-axis, the direction opposite to the gravity (vertically upward direction) as the Z-axis, and the direction perpendicular to the XZ plane as the Y-axis, construct the XYZ coordinate system of the three-dimensional tire model.

[0138] Step 32: Set the cylinder area containing the three-dimensional tire model in COMSOL 6.2 software. The specific process is as follows:

[0139] Outside the tire (outside the outer contour of the tire, a cylinder is used to wrap the tire), taking the X-axis as the axis of the cylinder (the axis of the cylinder is the connection line of the centers of the upper and lower bottom surfaces of the cylinder), taking the origin of the XYZ coordinate system of the three-dimensional tire model as the center of the cylinder, build a cylinder. The diameter of the upper and lower bottom surfaces of the cylinder d = D + 2RL + 100 mm, and the height of the cylinder along the X-axis h = L + 120 mm. Therefore, for a certain brand of SUV vehicle, the tire tread width L = 255 mm and the wheel hub diameter D = 16 inches

[0140] = 406.4 mm, the tire flatness ratio R = 65% = 0.65. Therefore, the bottom diameter d of the built cylinder is 837.90 mm, and the cylinder height h is 375.00 mm.

[0141] Step 33: Set the cuboid region containing the tire three-dimensional model and the cylinder in the COMSOL 6.2 software. The specific process is as follows:

[0142] Centered at the origin of the XYZ coordinate system of the tire three-dimensional model, set a cuboid with a length of 3 m in the X-axis direction (tire normal direction), a length of 5 m in the Y-axis direction, and a length of 3 m in the Z-axis direction.

[0143] Step 34: In the COMSOL 6.2 software, divide the cylinder region containing the tire three-dimensional model set in Step 32 and the cuboid region containing the tire three-dimensional model and the cylinder set in Step 33, and split to obtain an independent cylinder region with the tire three-dimensional model inside and an independent cuboid region without the tire three-dimensional model and the cylinder inside.

[0144] In Step 32, the tire is exactly wrapped by a cylinder slightly larger than the tire size. In Step 33, a cuboid is established. It can be understood that there is a cylinder inside the cuboid, and there is also a tire inside the cylinder. The first step in this stage is to extract the cylinder inside the cuboid. This is equivalent to the model becoming the external flow field without the cylinder + the cylinder (with a tire inside). In the three-dimensional model operation of the COMSOL 6.2 software, it is called "division and splitting".

[0145] Step 35: In the COMSOL 6.2 software, perform a difference set solution of the geometric models of the independent cylinder region containing the tire three-dimensional model obtained in Step 34 and the tire three-dimensional model to obtain an independent cylinder region without the tire three-dimensional model inside.

[0146] Step 36: In the COMSOL 6.2 software, form a union of the cuboid region without the tire three-dimensional model and the cylinder obtained in Step 34 and the cylinder region without the tire three-dimensional model obtained in Step 35.

[0147] Delete details such as continuously tangent vertices, short edges, small faces, long strip faces, narrow face regions, and thin faces generated during the process of forming the union in the COMSOL 6.2 software.

[0148] Step 37: Set the material parameters in the COMSOL 6.2 software:

[0149] In the COMSOL 6.2 software, set the material properties of the cuboid that does not contain the tire three-dimensional model and the cylinder obtained in step 34 and the cylinder that does not contain the tire three-dimensional model obtained in step 35 to Air(mat1) in the material module of the COMSOL 6.2 software. Air(mat1) is the air parameter; mat1 is the module.

[0150] Step 38: Mesh the cells in the COMSOL 6.2 software:

[0151] In the COMSOL 6.2 software, set the rotating domain as the moving mesh region; it needs to rotate during the simulation, so this is the moving mesh region and also needs to be set in the COMSOL 6.2 software.

[0152] In the COMSOL 6.2 software, set the outer flow field region as the stationary mesh region (the outer flow field without the cylinder, that is, the region outside the rotating domain, does not need to rotate during the simulation, so it belongs to the stationary mesh region);

[0153] In the COMSOL 6.2 software, divide the meshes of the moving mesh region and the stationary mesh region according to the "refinement" standard in "physical field controlled mesh" to obtain the meshed cells.

[0154] Step 4: Determine the angular velocity β of the rotating domain with the vehicle running speed v and the cylinder diameter d as indicators;

[0155]

[0156] Among them, the unit of β is rad / s, and rad / s represents radians per second;

[0157] Therefore, the calculation conditions of the angular velocity β corresponding to different running speeds v of a certain brand of SUV are shown in Table 1 below

[0158] Table 1 Angular velocity β corresponding to different running speeds v of a certain brand of SUV

[0159] Calculation condition Condition 1 Condition 2 Condition 3 Condition 4 Condition 5 Operating speed v 120 km / h 105 km / h 90 km / h 75 km / h 60 km / h Angular velocity of self-rotation β 79.56 rad / s 69.62 rad / s 56.67 rad / s 49.73 rad / s 39.78 rad / s

[0160] Step 5: Use the SST turbulence model in the COMSOL 6.2 software as the simulation calculation model to calculate five calculation conditions respectively;

[0161] The specific process is as follows:

[0162] In the SST turbulence model, set the outer flow field region as an incompressible fluid;

[0163] In the SST turbulence model, set the reference pressure level to 1 Pa;

[0164] Set the reference temperature to 293.15K in the SST turbulence model;

[0165] Set the wall treatment expression to automatic mode in the SST turbulence model;

[0166] Set the CFL number expression to automatic mode in the SST turbulence model;

[0167] Set the velocity scale to 1m / s in the SST turbulence model;

[0168] Set the length scale factor to 0.035 in the SST turbulence model;

[0169] To simulate the air in life, it belongs to an incompressible fluid, that is, this air cannot be compressed;

[0170] Step 6: Set the freeze operator and the number of iterations in the COMSOL 6.2 software, and start simulating and calculating five calculation conditions to obtain five simulation results;

[0171] The five simulation results are the velocity distributions of the external flow field during the rotation of the tire at five operating speeds, and the velocity distribution contour maps of the external flow field on the plane where the tire touches the ground at these five operating speeds are extracted respectively; of the external flow field;

[0172] The specific process is as follows:

[0173] Due to the large amount of calculation in the SST turbulence model, turn on the "frozen rotor" function in the COMSOL 6.2 software, set the number of calculation iterations to 100 times, start simulating and calculating five calculation conditions to obtain five simulation results;

[0174] The five simulation results are the velocity distributions of the external flow field during the rotation of the tire at five operating speeds, and the velocity distribution contour maps of the external flow field on the plane where the tire touches the ground at these five operating speeds are extracted respectively, as shown in ; Figures 11 to 15 ;

[0175] Step 7: Based on the velocity distribution contour maps of the external flow field on the tire contact surface under five conditions, draw the velocity curve of the external flow field on the center line of the tire contact surface, as shown in Figure 16 ;

[0176] Set a center line of the tire contact surface perpendicular to the tire rotation direction, and set the starting coordinates of the center line of the tire contact surface (unit: m), the ending coordinates of the center line of the tire contact surface (unit: m), that is, the starting coordinates of the center line of the model under the five calculation conditions are (-0.3, 0, -0.36895) (unit: m), and the ending coordinates of the center line are (-0.3, 0, 0.36895) (unit: m);

[0177] Extract the speed values corresponding to the starting point coordinates to the ending point coordinates of the center line from the simulation calculation results based on the starting point coordinates and the ending point coordinates of the center line of the tire contact surface;

[0178] Taking the starting point coordinates to the ending point coordinates of the center line of the tire contact surface as the abscissa (-0.25 to 0.25), and the speed values corresponding to the starting point coordinates to the ending point coordinates of the center line as the ordinate, draw the velocity curve of the external flow field along the center line of the tire contact surface to observe the change trend of the velocity of the external flow field along the center line of the tire contact surface;

[0179] The center line of the tire contact surface is perpendicular to the tire rotation direction;

[0180] Step 8: Draw the velocity curve of the external flow field on the right side of the center line of the tire contact surface based on Step 7;

[0181] Based on the air temperature T during the snowfall period, determine the threshold friction velocity v of the snow particles * ;

[0182] Based on the threshold friction velocity v of the snow particles * Determine the corresponding abscissa x value in the velocity curve of the external flow field on the right side of the center line of the tire contact surface;

[0183] Based on the threshold friction velocity v of the snow particles * Calculate the influence area range F based on the corresponding abscissa x value and the total number N of tires;

[0184] The specific process is as follows:

[0185] Based on the speed values corresponding to the starting point coordinates to the ending point coordinates of the center line extracted in Step 7, select the points where the abscissa value x is greater than zero and the corresponding speed values. Taking the x values greater than zero as the abscissa (0 to 0.25), and the speed values corresponding to the x values greater than zero as the ordinate, draw the velocity curve of the external flow field on the right side of the center line of the tire contact surface, as Figure 17 ;

[0186] Based on the air temperature T during the snowfall period, determine the threshold friction velocity v of the snow particles * ;

[0187] When the air temperature T during the snowfall period is -20°C and -7°C respectively, the threshold friction velocity v of the snow particles * Is 0.15 m / s and 0.25 m / s respectively, as shown in Table 2;

[0188] Table 2 Threshold friction velocity v of snow particles corresponding to different air temperatures T during snowfall periods

[0189] Air temperature Threshold friction velocity T＝-20℃ <![CDATA[v * = 0.15 m / s]]> T＝-7℃ <![CDATA[v * = 0.25 m / s]]>

[0190] Therefore, based on the velocity curve of the outer flow field on the right side of the center line of the tire contact surface, the threshold friction velocity v of different snow particles caused by different snowfall temperatures is determined. * The corresponding abscissa x values are shown in Table 3.

[0191] Table 3 Abscissa x values corresponding to different operating speeds and different temperature conditions

[0192] Abscissa x (mm) 60 km / h 75 km / h 90 km / h 105 km / h 120 km / h Air temperature T = -20°C 163 172 173 175 178 Air temperature T = -7°C 149 157 158 159 167

[0193] Based on the abscissa value x and the total number of tires N (the total number of a certain brand of tires N = 4), the influence area range F is calculated. The expression is:

[0194] F = N × 2x

[0195] Table 4 Influence area range F corresponding to different operating speeds and different temperature conditions

[0196]

[0197] Step 9: Taking the influence range F * = 1000 mm as the standard value, based on the standard value F * and the influence area range F obtained in Step 8, the dynamic vehicle conversion coefficient Dynamic-PCE is calculated. The expression is:

[0198]

[0199] Dynamic-PCE represents the dynamic vehicle conversion coefficient.

[0200] Therefore, the dynamic vehicle conversion coefficients of a certain brand of SUV under different operating speeds and different snowfall temperature combinations are shown in Table 5 below.

[0201] Table 5 Dynamic vehicle conversion coefficients of a certain brand of SUV under different operating speeds and different temperature conditions

[0202] Dynamic-PCE 60 km / h 75 km / h 90 km / h 105 km / h 120 km / h Air temperature T = -20°C 1.304 1.376 1.384 1.400 1.424 Air temperature T = -7°C 1.192 1.256 1.264 1.272 1.336

[0203] The present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention. However, these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in a snow environment, characterized in that: The specific process of the method is as follows: Step 1: Obtain the temperature T during snowfall, vehicle type, total number of tires N, tire tread width L, wheel hub diameter D, tire flatness R, and running speed v; Step 2: Based on the tire tread width L, wheel hub diameter D, and tire flatness R obtained in Step 1, establish a three-dimensional tire model in Rhino modeling software; Step 3: Import the three-dimensional tire model established in Step 2 into COMSOL 6.2 software. In COMSOL 6.2 software, determine the coordinate system of the three-dimensional tire model, determine the cylinder and cuboid, set the material parameters, and divide the mesh elements; Step 4: Determine the angular velocity β of the rotation domain with the vehicle running speed v and the cylinder diameter d as indicators; The rotation domain is a cylindrical region obtained in COMSOL 6.2 software that does not contain the three-dimensional tire model inside; Step 5: Use the SST turbulence model in COMSOL 6.2 software as the simulation calculation model; Step 6: Set the freezing operator and the number of iterations in COMSOL 6.2 software, and start the simulation calculation to obtain the simulation calculation results; The simulation calculation result is the velocity distribution of the external flow field during the rotation of the tire, and the velocity distribution contour map of the external flow field on the plane where the tire touches the ground is extracted ; The external flow field is a cuboid region obtained in COMSOL 6.2 software that does not contain the three-dimensional tire model and the cylinder inside; Step 7: Based on the velocity distribution cloud map of the external flow field on the plane where the tire touches the ground, draw the velocity curve of the center line of the external flow field of the tire touch surface; Step 8: Based on Step 7, draw the velocity curve of the external flow field on the right side of the center line of the tire touch surface; Based on the air temperature T during the snowfall period, determine the threshold friction velocity v of the snow particles * ; Threshold friction velocity v based on snow particles * Determine the corresponding abscissa x value in the outer flow field velocity curve diagram on the right side of the center line of the tire contact surface; Based on the snow particle threshold friction velocity v * Calculate the influence area range F based on the corresponding abscissa x value and the total number of tires N; Step 9: Based on the influence range F * = 1000 mm as the standard value, calculate the dynamic vehicle conversion factor for snow environment Dynamic-PCE based on the standard value F * and the influence area range F obtained in Step 8.

2. The method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in a snow environment according to claim 1, wherein: In Step 3, import the three-dimensional tire model established in Step 2 into COMSOL 6.2 software. In COMSOL 6.2 software, determine the coordinate system of the three-dimensional tire model, determine the cylinder and cuboid, set the material parameters, and divide the mesh elements; The specific process is as follows: Step 31: Determine the coordinate system of the three-dimensional tire model in COMSOL 6.2 software. The specific process is as follows: Import the three-dimensional tire model established in Step 2 into COMSOL 6.2 software. Take the center of the three-dimensional tire model as the coordinate origin, take the direction perpendicular to the tire rotation plane as the X-axis, take the opposite direction of gravity as the Z-axis, and the plane perpendicular to the XZ plane as the Y-axis to construct the XYZ coordinate system of the three-dimensional tire model; Step 32: Set the cylindrical region containing the three-dimensional tire model in COMSOL 6.2 software. The specific process is as follows: Outside the tire, take the X-axis as the axis of the cylinder, take the origin of the XYZ coordinate system of the three-dimensional tire model as the center of the cylinder, and build a cylinder. The diameter d of the upper and lower bottom surfaces of the cylinder = D + 2RL + 100mm, and the height h of the cylinder along the X-axis = L + 120mm; Step 33: Set the cuboid region containing the three-dimensional tire model and the cylinder in COMSOL 6.2 software; Step 34: In COMSOL 6.2 software, divide the cylindrical region containing the three-dimensional tire model set in Step 32 from the cuboid region containing the three-dimensional tire model and the cylinder set in Step 33, and split to obtain an independent cylindrical region containing the three-dimensional tire model inside and an independent cuboid region that does not contain the three-dimensional tire model and the cylinder inside; Step 35: In the COMSOL 6.2 software, perform a difference operation on the geometric models of the independent cylindrical region containing the three-dimensional tire model obtained in Step 34 and the three-dimensional tire model to obtain an independent cylindrical region that does not contain the three-dimensional tire model inside; Step 36: In the COMSOL 6.2 software, form a union of the rectangular parallelepiped region that does not contain the three-dimensional tire model and the cylinder obtained in Step 34 and the cylindrical region that does not contain the three-dimensional tire model obtained in Step 35; Step 37: Set the material parameters in the COMSOL 6.2 software; Step 38: Divide the mesh elements in the COMSOL 6.2 software.

3. The method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in a snow environment according to claim 2, wherein: In Step 37, setting the material parameters in the COMSOL 6.2 software; the specific process is as follows: In the COMSOL 6.2 software, set the material properties of the rectangular parallelepiped that does not contain the three-dimensional tire model and the cylinder obtained in Step 34 and the cylinder that does not contain the three-dimensional tire model obtained in Step 35 to Air(mat1) in the material module of the COMSOL 6.2 software.

4. The method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in a snow environment according to claim 3, wherein: In Step 38, dividing the mesh elements in the COMSOL 6.2 software; the specific process is as follows: In the COMSOL 6.2 software, set the rotating domain as the moving mesh region; In the COMSOL 6.2 software, set the external flow field region as the stationary mesh region; In the COMSOL 6.2 software, divide the meshes of the moving mesh region and the stationary mesh region according to the "refinement" standard in the "mesh controlled by physics field" to obtain the divided mesh elements.

5. The method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in a snow environment according to claim 4, wherein: In Step 4, taking the vehicle running speed v and the cylinder diameter d as indicators, determine the angular velocity β of the rotating domain; the rotating domain is the cylindrical region that does not contain the three-dimensional tire model obtained in the COMSOL 6.2 software; It is expressed as: where, the unit of β is rad / s, and rad / s represents radians per second.

6. The method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in a snow environment according to claim 5, characterized in that: In Step 5, use the SST turbulence model in the COMSOL 6.2 software as the simulation calculation model; The specific process is as follows: In the SST turbulence model, set the external flow field region as an incompressible fluid; In the SST turbulence model, set the reference pressure level to 1 Pa; In the SST turbulence model, set the reference temperature to 293.15 K; In the SST turbulence model, set the wall treatment expression to the automatic mode; In the SST turbulence model, set the CFL number expression to the automatic mode; In the SST turbulence model, set the velocity scale to 1 m / s; In the SST turbulence model, set the length scale factor to 0.

035.

7. The method for determining the dynamic vehicle conversion coefficient based on the self-snow-clearing effect of vehicles in a snow environment according to claim 6, characterized in that: In Step 6, set the freeze operator and the number of iterations in the COMSOL 6.2 software, and start the simulation calculation to obtain the simulation calculation result; The simulation calculation results are the velocity distribution of the external flow field during the rotation of the tire, and the velocity distribution contour map of the external flow field on the plane where the tire touches the ground is extracted. of the external flow field; The external flow field is the rectangular parallelepiped region that does not contain the three-dimensional tire model and the cylinder in the COMSOL 6.2 software; The specific process is as follows: Turn on the "frozen rotor" function in the COMSOL 6.2 software, set the number of calculation iterations to 100 times, and start the simulation calculation to obtain the simulation calculation result; The simulation calculation results are the velocity distribution of the external flow field during the rotation of the tire, and the velocity distribution contour map of the external flow field on the plane where the tire touches the ground is extracted. ​ 8. The method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in a snow environment according to claim 7, characterized in that: In step 7, based on the velocity distribution contour map of the external flow field on the plane where the tire touches the ground, draw the velocity curve of the external flow field along the center line of the tire contact surface; The specific process is as follows: Set the starting coordinate of the center line of the tire contact surface The ending coordinate of the center line of the tire contact surface Extract the velocity values corresponding to the starting point coordinate to the ending point coordinate of the center line from the simulation calculation results based on the starting point coordinate and the ending point coordinate of the center line of the tire contact surface; Take the starting point coordinate to the ending point coordinate of the center line of the tire contact surface as the abscissa, and the velocity values corresponding to the starting point coordinate to the ending point coordinate of the center line as the ordinate to draw the velocity curve of the external flow field along the center line of the tire contact surface; The center line of the tire contact surface is perpendicular to the tire rotation direction.

9. The method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in a snow environment according to claim 8, wherein: In step 8, draw the velocity curve of the external flow field on the right side of the center line of the tire contact surface based on step 7; Determine the threshold friction velocity v of snow particles based on the air temperature T during the snowfall period * ; Threshold friction velocity v based on snow particles * Determine the corresponding abscissa x value in the outer flow field velocity curve diagram on the right side of the center line of the tire contact surface; Based on the threshold friction velocity v of snow particles * Calculate the influence area range F based on the corresponding abscissa x value and the total number of tires N; The specific process is as follows: Based on the velocity values corresponding to the starting point coordinate to the ending point coordinate of the center line extracted in step 7, select the points where the value of the abscissa \(x\) is greater than zero and the corresponding velocity values, and take the \(x\) values greater than zero as the abscissa and the velocity values corresponding to the \(x\) values greater than zero as the ordinate to draw the velocity curve of the external flow field on the right side of the center line of the tire contact surface; Determine the threshold friction velocity v of snow particles based on the air temperature T during the snowfall period * ; Threshold friction velocity v based on snow particles * Determine the corresponding abscissa x value in the velocity curve of the outer flow field on the right side of the center line of the tire contact surface; Based on the snow particle threshold friction velocity v * Calculate the influence area range F based on the corresponding abscissa x value and the total number of tires N; the expression is: F = N×2x Determine the threshold friction velocity v of snow particles by combining the air temperature T during the snowfall period * ; The specific process is as follows: When the temperature T ≤ -10 °C during the snowfall period, v * = 0.15 m / s; When the temperature during the snowfall period is -10 < T ≤ -5°C, v * = 0.25 m / s.

10. The method for determining the dynamic vehicle conversion coefficient based on the vehicle self-snow-clearing effect in a snow environment according to claim 9, characterized in that: In step 9, taking the influence range F * = 1000 mm as the standard value, based on the standard value F * and the influence area range F obtained in step 8, calculate the dynamic vehicle conversion factor for snow environment, Dynamic-PCE; the expression is: Dynamic - PCE represents the dynamic vehicle conversion coefficient.

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