CN112836420B - Method for visualizing evacuation of gas in bottle-shaped closed space - Google Patents

Method for visualizing evacuation of gas in bottle-shaped closed space Download PDF

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CN112836420B
CN112836420B CN202110137150.7A CN202110137150A CN112836420B CN 112836420 B CN112836420 B CN 112836420B CN 202110137150 A CN202110137150 A CN 202110137150A CN 112836420 B CN112836420 B CN 112836420B
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CN112836420A (en
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王映辉
南彬
卢达林
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Jiangnan University
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Abstract

The invention discloses a gas evacuation visualization method for a bottle-shaped closed space, which comprises the following steps: initializing position information of air particles by using a particle system strategy according to the characteristics of the air fluid; detecting whether collision and collision positions of the air particles between the container wall and the container wall occur in the non-air-extraction stage and the air-extraction stage by utilizing an axial bounding box and an octree method strategy; dividing the gas state in the air extraction process, calculating the pipeline conductance under viscous flow and molecular flow, and describing the motion state of the gas in the viscous flow stage by calculating an N-S equation in fluidics; defining the boundary conditions and the air particle positions in the air extraction process, and determining the collision positions and the motion states of the air particles in the bottle-shaped container and the circular pipeline if collision occurs in the air extraction process, so as to finish the visualization of the evacuation of the gas in the bottle-shaped closed space. The invention is easy to realize the gas collision detection in the irregular space, and has good simulation real effect and high real-time property.

Description

Method for visualizing evacuation of gas in bottle-shaped closed space
Technical Field
The invention relates to the technical field of fluid simulation, in particular to a bottle-shaped closed space gas evacuation visualization method.
Background
The closed space gas evacuation visualization belongs to the fluid simulation category, and the following fluid simulation methods are not suitable for the motion process of gas evacuation in the research, for example, a fractal geometry method is a static image, a texture mapping method is poor in true sense, a cellular automaton is suitable for simulation under the low-dimensional condition, and a method based on a physical process is difficult to solve. However, the particle system has been widely used in many fields after decades of development, and can achieve better effects in both reality and real-time. The particles collide with the closed space when moving in the closed space, and the common methods include a space decomposition method and a hierarchical bounding box method, wherein the space decomposition method is suitable for objects with regular shapes, and the closed space is sometimes irregular in shape; the calculation cost of the hierarchical bounding box method is different according to different types of the selected bounding boxes; the research on the motion state of the gas, the solution of the motion equation of the gas and the collision detection in the process of evacuating the gas in the closed space is difficult.
Disclosure of Invention
This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. In this section, as well as in the abstract and the title of the invention of this application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.
The present invention has been made in view of the above-mentioned conventional problems.
Therefore, the technical problem solved by the invention is as follows: the prior art scheme is difficult to realize gas collision detection in irregular space, and the simulation effect is poor.
In order to solve the technical problems, the invention provides the following technical scheme: a method for visualizing evacuation of gas in a bottle-shaped closed space is characterized by comprising the following steps: initializing position information of air particles by using a particle system strategy according to the characteristics of the air fluid; detecting whether collision and collision positions of the air particles between the container wall and the container wall occur in the non-air-extraction stage and the air-extraction stage by utilizing an axial bounding box and an octree method strategy; dividing the gas state in the air extraction process, calculating the pipeline conductance under viscous flow and molecular flow, and describing the motion state of the gas in the viscous flow stage by calculating an N-S equation in fluidics; defining the boundary conditions and the air particle positions in the air extraction process, and determining the collision positions and the motion states of the air particles in the bottle-shaped container and the circular pipeline if collision occurs in the air extraction process, so as to finish the visualization of the evacuation of the gas in the bottle-shaped closed space.
As a preferable aspect of the method for visualizing evacuation of gas from a bottle-shaped enclosed space according to the present invention, wherein: the judgment of whether the air particles collide comprises that when the air particles are in the internal grids of the bottle-shaped container, the air particles do not collide with the container; when the air particles are in the outer grid of the bottle-shaped container, the particles collide with the container; when the air particles are in the boundary grid of the flask, it is necessary to further detect whether a collision occurs.
As a preferable aspect of the method for visualizing evacuation of gas from a bottle-shaped enclosed space according to the present invention, wherein: and the boundary grid division comprises the steps of taking the middle point of the grid to divide sub-nodes based on an octree strategy until the nodes in the grid are all in the bottle or outside the bottle, and stopping division if the nodes in the grid reach the division level.
As a preferable aspect of the method for visualizing evacuation of gas from a bottle-shaped enclosed space according to the present invention, wherein: the boundary determination for the viscous flow phase and the molecular flow phase includes,
Figure BDA0002927411690000021
wherein, KnIs the number of knudsen's,
Figure BDA0002927411690000022
is the mean free path, D is the pipe diameter;
when K isn>1, the flow state of the gas is molecular flow;
when K isn<At 0.01, the gas state is viscous flow;
when 0.01<Kn<At 0.1, the state of the gas is a viscous-molecular flow.
As a preferable aspect of the method for visualizing evacuation of gas from a bottle-shaped enclosed space according to the present invention, wherein: the calculation of the conduit conductance may include,
for air of 20 degrees, the pipeline conductance of the extraction hole in the viscous flow state is as follows:
when r > 0.525:
Figure BDA0002927411690000023
when r is more than or equal to 0.1 and less than or equal to 0.525:
Figure BDA0002927411690000024
when r < 0.1:
Cvy＝157D2
for air of 20 degrees, the pipeline conductance of the air extraction hole with the area of A under the molecular flow state is as follows:
Cmk＝116A。
as a preferable aspect of the method for visualizing evacuation of gas from a bottle-shaped enclosed space according to the present invention, wherein: the motion state of the gas in the viscous flow stage comprises,
Figure BDA0002927411690000031
Figure BDA0002927411690000032
wherein the content of the first and second substances,
Figure BDA0002927411690000033
it is shown that for the stream item,
Figure BDA0002927411690000034
the table is the term for the pressure gradient,
Figure BDA0002927411690000035
representing a diffusion term, f an external force term, u a velocity of the fluid, p a density of the fluid, p a pressure,
Figure BDA0002927411690000036
the gradient operator is represented by a gradient operator,
Figure BDA0002927411690000037
the divergence operator is represented by a vector of vectors,
Figure BDA0002927411690000038
representing the laplacian operator.
As described in the inventionA preferable embodiment of the visualization method for evacuating gas in a bottle-shaped closed space, wherein: defining normal temperature to 20 deg.c, and the air mean free path
Figure BDA0002927411690000039
Comprises the steps of (a) preparing a mixture of a plurality of raw materials,
Figure BDA00029274116900000310
wherein p represents the pressure of the gas;
pressure when the gas is in a viscous flow state:
Figure BDA00029274116900000311
pressure when the gas is in a molecular flow state:
Figure BDA00029274116900000312
as a preferable aspect of the method for visualizing evacuation of gas from a bottle-shaped enclosed space according to the present invention, wherein: the flow velocity of the air particles in the extraction duct comprises,
Figure BDA00029274116900000313
where p1 denotes the pressure at the suction tube inlet, p2 denotes the pressure at the suction tube outlet, R denotes the tube radius, and R denotes the distance of the particle from the center of the tube.
As a preferable aspect of the method for visualizing evacuation of gas from a bottle-shaped enclosed space according to the present invention, wherein: determining whether the air particles exit the container includes,
defining the coordinates of the center of the air suction hole as S (rx, ry, rz);
Figure BDA0002927411690000041
when dist < r, the air particles exit from the extraction holes, and when dist > r, the air particles are randomly reflected from the left face of the vacuum chamber, and the reflection angle is generated by a random number.
As a preferable aspect of the method for visualizing evacuation of gas from a bottle-shaped enclosed space according to the present invention, wherein: the air particles comprise at a location of a collision point within the duct,
Figure BDA0002927411690000042
where M denotes the collision point, defining the movement of the air particles from a to B in a unit of time.
The invention has the beneficial effects that: the invention is easy to realize the gas collision detection in the irregular space, and has good simulation real effect and high real-time property.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise. Wherein:
fig. 1 is a schematic basic flow chart of a method for visualizing gas evacuation in a bottle-shaped enclosed space according to an embodiment of the present invention;
FIG. 2 is a bottle-shaped space enclosure for a method for visualizing evacuation of gas from a bottle-shaped enclosed space according to an embodiment of the present invention;
FIG. 3 is a diagram of a bottle boundary for a visualization method of gas evacuation from a bottle-shaped enclosed space according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating the collision positions of particles and pipes in a method for visualizing gas evacuation in a bottle-shaped enclosed space according to an embodiment of the present invention;
FIG. 5 is a particle-top collision detection diagram of a method for visualizing gas evacuation from a bottle-shaped enclosed space according to an embodiment of the present invention;
fig. 6 is a particle and circular truncated cone collision detection diagram of a gas evacuation visualization method for a bottle-shaped enclosed space according to an embodiment of the present invention;
FIG. 7 is a graph showing the particle movement of the pumping holes at the bottle mouth when the time is 5 according to the visualization method for evacuating gas in the bottle-shaped enclosed space provided by the embodiment of the present invention;
FIG. 8 is a graph showing the particle movement of the pumping holes at the bottle mouth when the time is 10 according to the visualization method for evacuating gas in the bottle-shaped enclosed space provided by the embodiment of the present invention;
FIG. 9 is a graph showing the particle movement of the pumping holes at the bottom of the bottle at time 5 in a method for visualizing the evacuation of gas in the closed space of the bottle according to an embodiment of the present invention;
FIG. 10 is a graph of the particle movement at the bottom of the bottle of the gas pumping holes at time 10 according to an embodiment of the present invention;
fig. 11 is a graph showing the particle motion when the particle number is 4139 at time 5 in a method for visualizing gas evacuation from a bottle-shaped enclosed space according to an embodiment of the present invention;
fig. 12 is a graph showing the particle motion when the particle number is 4139 at time 10 according to an embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, specific embodiments accompanied with figures are described in detail below, and it is apparent that the described embodiments are a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making creative efforts based on the embodiments of the present invention, shall fall within the protection scope of the present invention.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.
Furthermore, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.
The present invention will be described in detail with reference to the drawings, wherein the cross-sectional views illustrating the structure of the device are not enlarged partially in general scale for convenience of illustration, and the drawings are only exemplary and should not be construed as limiting the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.
Meanwhile, in the description of the present invention, it should be noted that the terms "upper, lower, inner and outer" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation and operate, and thus, cannot be construed as limiting the present invention. Furthermore, the terms first, second, or third are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The terms "mounted, connected and connected" in the present invention are to be understood broadly, unless otherwise explicitly specified or limited, for example: can be fixedly connected, detachably connected or integrally connected; they may be mechanically, electrically, or directly connected, or indirectly connected through intervening media, or may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Example 1
Referring to fig. 1 to 6, in an embodiment of the present invention, a method for visualizing evacuation of a bottle-shaped enclosed space is provided, including:
s1: initializing position information of air particles by using a particle system strategy according to the characteristics of the air fluid;
specifically, basic attributes of the bottled closed space are acquired: the radius and height of the top cylinder and the bottom cylinder, and the height of the middle round table. A bounding box is determined, a circular air suction hole is added on the basis of the AABB bounding box, and the container is surrounded by the bounding box larger than the bottled container, so that the particles are limited in a specified range.
Obtaining minimum vertex coordinates P of bounding boxmin(Xmin, Ymin, Zmin) and the maximum vertex coordinate Pmax(Xmax, Ymax, Zmax), the minimum vertex coordinate PminDeclaring a random number engine and a random number distribution as coordinates of a first air particle, wherein the air particles are uniformly distributed in the bounding box and the position coordinates are PminAnd (Xmin, Ymin and Zmin) respectively adding fixed numbers to three dimensions, randomly generating 2 numbers as included angles between the particles and xoy planes and xoz planes, and adding the included angles and position coordinates as initialized particles air into the particle set AirSet.
S2: detecting whether collision and collision positions of air particles occur between the container wall and the container wall in the air non-extraction stage and the air extraction stage by utilizing an axial bounding box and an octree method strategy; it should be noted that, in the following description,
the judgment of whether the air particles collide comprises the following steps:
when the air particles are in the internal grid of the bottle-shaped container, the air particles do not collide with the container; when air particles are on the outer grid of the bottle-shaped container, the particles collide with the container; when the air particles are in the boundary grid of the bottle-shaped container, it is necessary to further detect whether a collision occurs.
The dividing of the boundary grid includes:
based on an octree strategy, taking the middle point of the grid to divide sub-nodes until the nodes in the grid are all in the bottle or outside the bottle, and stopping dividing if the nodes in the grid are in the bottle or outside the bottle; traversing the nodes of the bounding tree determines whether a particle collides with the container and the location of the collision.
S3: dividing the gas state in the air extraction process, calculating the pipeline conductance under viscous flow and molecular flow, and describing the motion state of the gas in the viscous flow stage by calculating an N-S equation in the fluidics; it should be noted that, in the following description,
the boundary determination for the viscous flow phase and the molecular flow phase includes,
Figure BDA0002927411690000071
wherein, KnIs the number of knudsen's,
Figure BDA0002927411690000072
is the mean free path, D is the pipe diameter;
wherein, when Kn>1, the flow state of the gas is molecular flow;
when K isn<At 0.01, the gas state is viscous flow;
when 0.01<Kn<At 0.1, the state of the gas is a viscous-molecular flow.
Defining the normal temperature at 20 ℃ and the air mean free path
Figure BDA0002927411690000073
Comprises the steps of (a) preparing a mixture of a plurality of raw materials,
Figure BDA0002927411690000074
wherein p represents the pressure of the gas;
further, when the gas is in a viscous flow state, the pressure:
Figure BDA0002927411690000075
pressure when gas is in molecular flow state:
Figure BDA0002927411690000076
the calculation of the conductance of the pipe includes,
for air of 20 degrees, the pipeline conductance of the extraction hole in the viscous flow state is as follows:
when r > 0.525:
Figure BDA0002927411690000077
when r is more than or equal to 0.1 and less than or equal to 0.525:
Figure BDA0002927411690000078
when r < 0.1:
Cvy＝157D2
for air of 20 degrees, the pipeline conductance of the air extraction hole with the area of A under the molecular flow state is as follows:
Cmk＝116A。
the motion state of the gas in the viscous flow stage comprises,
Figure BDA0002927411690000081
Figure BDA0002927411690000082
wherein the content of the first and second substances,
Figure BDA0002927411690000083
it is shown that for the stream item,
Figure BDA0002927411690000084
the table is the term for the pressure gradient,
Figure BDA0002927411690000085
representing a diffusion term, f an external force term, u a velocity of the fluid, ρ a density of the fluidAnd p represents a pressure intensity,
Figure BDA0002927411690000086
the gradient operator is represented by a gradient operator,
Figure BDA0002927411690000087
the divergence operator is represented by a vector of vectors,
Figure BDA0002927411690000088
representing the laplacian operator.
Specifically, during the pumping process, only two stages of viscous flow and molecular flow are considered because the turbulent flow and two transition stages of turbulent-viscous flow and viscous-molecular flow exist for a short time. The two phase boundaries are determined by knudsen discriminant:
Figure BDA0002927411690000089
wherein, KnIs the number of knudsen's,
Figure BDA00029274116900000810
is the mean free path and D is the pipe diameter.
Wherein, when Kn>1, the flow state of the gas is molecular flow; when K isn<At 0.01, the gas state is viscous flow; when 0.01<Kn<At 0.1, the state of the gas is a viscous-molecular flow.
Defining the normal temperature at 20 ℃ and the air mean free path
Figure BDA00029274116900000811
Comprises the steps of (a) preparing a mixture of a plurality of raw materials,
Figure BDA00029274116900000812
wherein p represents the pressure of the gas;
further, when the gas is in a viscous flow state, the pressure:
Figure BDA00029274116900000813
pressure when gas is in molecular flow state:
Figure BDA00029274116900000814
when the air leakage and the air release of the system are not considered, the pipeline conductance can be ignored when the connecting pipeline between the vacuum pump and the pumped container is short, and the vacuum pumping equation is as follows:
Figure BDA0002927411690000091
wherein V represents the volume of the vacuum chamber, SpIndicating the pumping speed, p, of the air pumpiDenotes the pressure at the time of pumping, p denotes the pressure to be reached, and t denotes the pumping time.
For 20 degrees of air, conductance of the extraction hole in viscous flow state:
when r > 0.525:
Figure BDA0002927411690000092
when r is more than or equal to 0.1 and less than or equal to 0.525:
Figure BDA0002927411690000093
when r < 0.1:
Cvy＝157D2
for air of 20 degrees, the pipeline conductance of the air extraction hole with the area of A under the molecular flow state is as follows:
Cmk＝116A。
further, the compressibility of the fluid is judged by the mach numbers as follows:
Figure BDA0002927411690000094
wherein S iseIs the effective velocity of the air extractor, D is the pipe diameter, and c is the speed of sound propagation in the fluid. When M isa<At 0.3, the fluid may be considered incompressible without regard to compressibility of the fluid; when M isa>At 0.3, the compressibility of the fluid cannot be ignored.
The particle motion in the viscous flow phase is described by solving the N-S equation as follows:
Figure BDA0002927411690000095
Figure BDA0002927411690000096
this is the governing equation for incompressible viscous fluids. Wherein the content of the first and second substances,
Figure BDA0002927411690000097
it is shown that for the stream item,
Figure BDA0002927411690000098
the table is the term for the pressure gradient,
Figure BDA0002927411690000099
representing a diffusion term, f an external force term, u a velocity of the fluid, p a density of the fluid, p a pressure,
Figure BDA00029274116900000910
the gradient operator is represented by a gradient operator,
Figure BDA00029274116900000911
the divergence operator is represented by a vector of vectors,
Figure BDA00029274116900000912
representing the laplacian operator.
The finite difference method is adopted to solve the problem, a non-staggered grid is used, and the influence of each item on the equation is solved once through a decomposition method.
The first step is to consider the influence on the flow terms first:
Figure BDA0002927411690000101
let the speed at time n be unThe velocity field at the intermediate time n1 influenced by the convection term is un1Then, the formula for solving the convection term by using the semi-lagrangian method is as follows:
Figure BDA0002927411690000102
the second step solves the influence of the diffusion term:
Figure BDA0002927411690000103
let u be the velocity at the intermediate time n2 influenced by the diffusion termn2Firstly, a display method is used for dispersing diffusion items:
Figure BDA0002927411690000104
let un2The speeds in the three directions of the x-axis, the y-axis and the z-axis are respectively ux n2、uy n2And uz n2. The equation of the x-axis direction u can be obtained according to the second-order central difference format:
Figure BDA0002927411690000105
this embodiment uses a direct iterative method, and if Δ x ═ Δ y ═ Δ z, the equation can be obtained:
Figure BDA0002927411690000106
the third step is the influence of the pressure gradient term:
Figure BDA0002927411690000107
let the velocity at time n3 influenced by the pressure term be un3The equations are obtained by showing the difference method to discretize the equations and the properties of the continuous medium:
Figure BDA0002927411690000111
this equation, called the poisson equation for pressure, can be solved in the same way as the diffusion term. After the pressure p is found, the effect of the pressure gradient on the velocity can be obtained:
Figure BDA0002927411690000112
through the three steps, the velocity field in a time step can be obtained, iteration is carried out until the motion of the air reaches the molecular flow, and the motion of the particles can be updated through the obtained velocity field.
S4: defining boundary conditions and air particle positions in the air extraction process, and determining collision positions and motion states of air particles in the bottle-shaped container and the circular pipeline if collision occurs in the air extraction process to finish the visualization of air evacuation in the bottle-shaped closed space; it should be noted that, in the following description,
the flow velocity of the air particles in the suction line includes,
Figure BDA0002927411690000113
where p1 denotes the pressure at the suction tube inlet, p2 denotes the pressure at the suction tube outlet, R denotes the tube radius, and R denotes the distance of the particle from the center of the tube.
Further, determining whether air particles have left the container includes,
defining coordinates of the center of the air suction hole as S (rx, ry, rz);
Figure BDA0002927411690000114
when dist < r, the air particles exit from the extraction holes, and when dist > r, the air particles are randomly reflected from the left face of the vacuum chamber, and the reflection angle is generated by a random number.
The location of the impact point of the air particles within the duct includes,
Figure BDA0002927411690000115
where M denotes the collision point, defining the movement of the air particles from a to B in a unit of time.
Specifically, the type of the grid belongs to is represented by adding an attribute value to the grid, such as an invalid grid, a boundary, an outlet, and the inside of a container, and the pressure of the boundary grid is the maximum value of the pressure in the adjacent internal grid.
The air particles have different speeds in the air exhaust pipeline, and the radial distribution speed is parabolic. The flow rate formula is:
Figure BDA0002927411690000116
where p1 denotes the pressure at the suction tube inlet, p2 denotes the pressure at the suction tube outlet, R denotes the tube radius, and R denotes the distance of the particle from the center of the tube.
The collision between the air particles and the wall of the container is irrelevant to the incident direction, whether the air particles M leave the container or not is judged, and the coordinate defining the center of the air suction hole is S (rx, ry, rz):
Figure BDA0002927411690000121
if dist < r, the air particles exit from the extraction holes, and if dist > r, the air particles are randomly reflected from the left face of the vacuum chamber, and the angle of reflection is generated by a random number.
Determining the position of a collision point of the particles in the pipeline: assuming that the air particle P is incident from a point a (xa, ya, za) and will move to a point B (xb, yb, zb) if no collision occurs, let M (xm, ym, zm) be the collision point of the air particle P and the exhaust duct, C (xc, yc, zc) is perpendicular to line AD and line CM, where line AD is parallel to line CM, and line BD intersects the wall of the container. The H surface is a circular section of the pipeline, is parallel to the XOZ plane, has the center of a circle of O point and the radius of r, and is provided with a straight line BD on the H surface.
Solving the equation yields:
Figure BDA0002927411690000122
wherein the content of the first and second substances,
Figure BDA0002927411690000123
b＝yd-k*zd
the above equation has two solutions, only one solution is a solution meeting the requirement, and when z ≧ zb & & z ≦ zd or z ≧ zd & & z ≦ zb is the z coordinate of the C of the intersection point, then the y coordinate of the C point is:
yc＝k*zc+b
determining the collision condition of the particles in the bottle-shaped container: the bottle-shaped container is divided into a top circular surface and a bottom circular surface, a curved surface of the cylindrical part and a side surface of the circular truncated cone part. The detection of the curved surface collision point of the cylindrical part is the same as the collision of the particles in the pipeline in the step of determining the position of the collision point of the particles in the pipeline, and only the intersection point on the plane YOZ is required to be changed into the intersection point on the XOZ plane.
Particle impact with the top and bottom circular surfaces of the vessel: assuming that the air particles start from the point A, if no collision occurs, the air particles will move to the point B in unit time, M is the collision point, a line BD perpendicular to the container wall is drawn from the point B, the intersection point is C, and the straight line AB is perpendicular to the BD. The M coordinate can be found:
Figure BDA0002927411690000124
Figure BDA0002927411690000125
Figure BDA0002927411690000131
the particles are detected at the circular table part of the bottle at the collision point, and the collision point is approached by adopting a fold-half searching method. And (3) calculating the coordinates of the midpoint C between the emission point A and the arrival point B, judging whether the point C is in the circular truncated cone, if the point C is in the circular truncated cone, moving the point A to the point C, and if the point C is not in the circular truncated cone, moving the point B to the point C, and repeating the steps until the distance between the points AB is smaller than a certain range or A is equal to B.
The invention provides an evacuation visualization method aiming at a bottle-shaped closed space, solves the collision detection of the invention by a method combining a bounding box and space division, and visually describes the gas collision condition in the bottle-shaped space and the motion condition of gas in the air extraction stage.
Example 2
Referring to fig. 7 to 12, another embodiment of the present invention is shown, which is a verification description of the technical effects adopted in the method, in the embodiment, the method of the present invention is adopted to perform experimental demonstration on collision detection and visualization of air particles in an irregular closed space, and a scientific demonstration means is used to verify the real effects of the method.
In the process of bottle-shaped gas evacuation visualization, the difficulty to be solved is gas simulation and gas particle collision detection. The following methods are generally used in gas simulation: fractal geometry, texture mapping, cellular automata, physics-based methods, and particle systems. The fractal geometry method is suitable for static images, the texture mapping method is poor in reality sense, the cellular automaton is suitable for simulation under the condition of low dimension, and the physical-based method is difficult to solve; the study of the gas motion under the three-dimensional condition has high requirements on the real effect and real-time performance of the simulation, so that the four methods are not suitable for the study of the embodiment. The number of particles can be freely controlled through the particle system, and the simulation method is easy to realize and good in simulation effect. Particle collision detection can be mainly divided into a space decomposition method and a hierarchical bounding box, the space of a bottle is not a regular shape, the bottle body is a curved surface in the space, and no matter which bounding box is used, a gap is always left, which brings difficulty to the collision detection. The present embodiment combines the AABB bounding box and octree partitioning methods to solve the collision detection of particles in the bottle space.
The system flow is realized as follows:
the whole system is divided into three parts: user layer, processing layer and storage program. The concrete functions are as follows:
and (3) a user layer: in the system, a user can select the shape of the closed space, the position of the air pumping hole, the size of the air pumping hole, the air pumping speed and the number of particles. And showing the running result of the program to a user through the MFC platform.
A data processing layer: the data processing layer mainly comprises three parts: data processing of a viscous flow phase and a molecular flow phase and particle collision detection. The viscous flow stage data processing is carried out according to the solving step of an N-S equation, the air extraction in the molecular flow stage is mainly carried out on diffuse reflection, and the reflection angles of air particles from different surfaces are determined.
A storage layer: the storage layer needs to store grid data, particle data, pumping rate, pumping hole size, vacuum chamber volume, and the like.
The flow of system operation is as follows:
after the system starts to operate, the system goes through scene drawing, data initialization, grid division, particle initialization, grid data updating, particle position calculation, collision detection and particle drawing processes. The specific process is as follows:
drawing a scene: the MFC platform loads a control panel and a main window, and calls a function to draw a vacuum system;
data initialization: loading a global configuration file for data initialization;
grid division: the size of the grid partition affects the operating efficiency of the program. The smaller the grid size is, the larger the calculation amount is, and the more accurate the result is; the larger the grid size is, the smaller the calculation amount is, and the accuracy of the calculation result is lowered. Therefore, a compromise between real-time performance and accuracy is required, the system firstly divides the grid into M12, N12 and Z12, the pressure of the grid is set to 101325 while the grid is divided, and the initial speeds of the three directional axes are set to 0;
particle initialization: when the particles are not subjected to external force, the particles are uniformly distributed in the closed space, and the whole closed space is uniformly scanned according to a certain rule, so that the air particles are uniformly distributed in the closed space.
Updating the grid data: calculating data such as grid pressure, grid speed and the like according to the solving process of the N-S equation, updating the grid pressure, and calculating the grid speed;
calculating the particle position: after the grid speed is obtained, updating and calculating the particle position;
collision detection: and (3) when the position of the particles is changed, ensuring that the particles cannot penetrate through the wall of the container, carrying out particle collision detection, and if the collision occurs, determining the reflection angle of the air particles according to a random function.
Drawing the particles: after the positions of the particles are obtained, the particles are drawn.
The system environment is realized as follows:
table 1: system hardware configuration tables.
Figure BDA0002927411690000141
Figure BDA0002927411690000151
Table 2: system software configuration table.
Software Related information
Operating system Windows 1064 bit
Visual Studio 2013
OpenGL 4.1
The realization effect is shown in figures 7-12:
the air pump shown in fig. 7-8 is directly connected with the bottle mouth:
when the diameter of the pumping hole is 0.4, the number of particles is 4139, and the pumping speed is 50, the movement of the particles is shown in FIGS. 7 to 8. Fig. 7 is a particle motion diagram when t is 5, and fig. 8 is a particle motion diagram when t is 10.
The effect of the air extraction holes at the bottom of the bottle is as shown in FIGS. 9-10:
when the diameter of the pumping hole is 0.4, the number of particles is 4139, and the pumping speed is 50, the movement of the particles is shown in FIGS. 9 to 10. Fig. 9 is a particle motion diagram when t is 5, and fig. 10 is a particle motion diagram when t is 10.
The effect of the air extraction holes on the side of the bottle is as shown in figures 11-12:
the movement of the particles when the pumping hole diameter is 0.4, the number of particles is 4139, and the pumping speed is 50 is shown in fig. 11 to 12, fig. 11 is a particle movement diagram when t is 5, and fig. 12 is a particle movement diagram when t is 10.
It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.

Claims (10)

1. A method for visualizing evacuation of gas in a bottle-shaped closed space is characterized by comprising the following steps:
initializing position information of air particles by using a particle system strategy according to the characteristics of the air fluid;
detecting whether collision and collision positions of the air particles between the container wall and the container wall occur in the non-air-extraction stage and the air-extraction stage by utilizing an axial bounding box and an octree method strategy;
dividing the gas state in the air extraction process, calculating the pipeline conductance under viscous flow and molecular flow, and describing the motion state of the gas in the viscous flow stage by calculating an N-S equation in fluidics;
defining the boundary conditions and the air particle positions in the air extraction process, and determining the collision positions and the motion states of the air particles in the bottle-shaped container and the circular pipeline if collision occurs in the air extraction process, so as to finish the visualization of the evacuation of the gas in the bottle-shaped closed space.
2. The method for visualizing evacuation of gas into a bottle-like enclosed space according to claim 1, wherein: the determination of whether the air particles collide includes,
when the air particles are in the internal grid of the bottle-shaped container, the air particles do not collide with the container;
when the air particles are in the outer grid of the bottle-shaped container, the particles collide with the container;
when the air particles are in the boundary grid of the flask, it is necessary to further detect whether a collision occurs.
3. The method for visualizing evacuation of gas into a bottle-like enclosed space according to claim 1 or 2, wherein: the partitioning of the boundary grid includes,
and based on an octree strategy, taking the middle point of the grid to divide sub-nodes until the nodes in the grid are all in the bottle or outside the bottle, and stopping dividing if the nodes in the grid reach the division level.
4. The method for visualizing evacuation of gas into a bottle-like enclosed space according to claim 1, wherein: the boundary determination for the viscous flow phase and the molecular flow phase includes,
Figure FDA0003538450300000011
wherein, KnIs the number of knudsen's,
Figure FDA0003538450300000012
is the mean free path, D is the pipe diameter;
when K isn>1, the flow state of the gas is molecular flow;
when K isn<At 0.01, the gas state is viscous flow;
when 0.01<Kn<At 0.1, the state of the gas is a viscous-molecular flow.
5. The method for visualizing evacuation of gas into a bottle-like enclosed space according to claim 4, wherein: the calculation of the conduit conductance may include,
for air of 20 degrees, the pipeline conductance of the extraction hole in the viscous flow state is as follows:
when r > 0.525:
Figure FDA0003538450300000021
when r is more than or equal to 0.1 and less than or equal to 0.525:
Figure FDA0003538450300000022
when r < 0.1:
Cvy＝157D2
for air of 20 degrees, the pipeline conductance of the air extraction hole with the area of A under the molecular flow state is as follows:
Cmk＝116A。
6. the method for visualizing evacuation of gas into a bottle-like enclosed space according to claim 4 or 5, wherein: the motion state of the gas in the viscous flow stage comprises,
Figure FDA0003538450300000023
Figure FDA0003538450300000024
wherein the content of the first and second substances,
Figure FDA00035384503000000213
it is shown that for the stream item,
Figure FDA0003538450300000025
the table is the term for the pressure gradient,
Figure FDA0003538450300000026
representing the diffusion term, u representing the velocity of the fluid, p representing the density of the fluid, p representing the pressure,
Figure FDA0003538450300000027
the gradient operator is represented by a gradient operator,
Figure FDA0003538450300000028
the expression divergence operator is used to represent the divergence operator,
Figure FDA0003538450300000029
representing the laplacian operator.
7. The method for visualizing evacuation of gas into a bottle-like enclosed space according to claim 6, wherein: defining normal temperature to 20 deg.c, and the air mean free path
Figure FDA00035384503000000210
Comprises the steps of (a) preparing a mixture of a plurality of raw materials,
Figure FDA00035384503000000211
wherein p represents the pressure of the gas;
pressure when the gas is in a viscous flow state:
Figure FDA00035384503000000212
pressure when the gas is in a molecular flow state:
Figure FDA0003538450300000031
8. the method for visualizing evacuation of gas into a bottle-like enclosed space according to claim 7, wherein: the flow velocity of the air particles in the extraction duct comprises,
Figure FDA0003538450300000032
where p1 denotes the pressure at the suction tube inlet, p2 denotes the pressure at the suction tube outlet, R denotes the tube radius, and R denotes the distance of the particle from the center of the tube.
9. The method for visualizing evacuation of gas into a bottle-like enclosed space according to claim 8, wherein: determining whether the air particles exit the container includes,
defining coordinates of the center of the air suction hole as S (rx, ry, rz);
Figure FDA0003538450300000033
when dist < r, the air particles exit from the extraction holes, and when dist > r, the air particles are randomly reflected from the left face of the vacuum chamber, and the reflection angle is generated by a random number.
10. The method for visualizing evacuation of gas into a bottle-like enclosed space according to claim 9, wherein: the air particles comprise at a location of a collision point within the duct,
Figure FDA0003538450300000034
where M denotes the collision point, defining the movement of the air particles from a to B in a unit of time.
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