JP3147391B2 - Method and apparatus for setting curved surface in three-dimensional boundary fitting mesh division - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for dividing a three-dimensional boundary-fitting mesh used mainly for analyzing a flow along an object having a complicated shape by a finite volume method or the like.

[0002]

2. Description of the Related Art Conventionally, when analyzing a flow along a complex shape by a finite volume method, polygon data of an object shape created by a three-dimensional CAD system or the like is input and based on the polygon data. It is known that a three-dimensional mesh is created and a three-dimensional fluid analysis of an object is performed. In this conventional mesh generation process, a set of input polygon faces is used as a shape boundary to perform mesh division. However, at the beginning of the work, the geometrical features of the object are not taken into account, and the reference planes are set appropriately where necessary across the closed curved surface of the polygon surface, each reference plane is divided into meshes, and these planes are further divided. By linearly interpolating between the meshes, a three-dimensional mesh region roughly along the object shape is created. After that, the mesh on the surface of the three-dimensional mesh is mapped to a nearby polygon surface, thereby making the mesh correspond to the object shape. This operation is called surface fitting. However, at this stage, except for the surface mesh, which does not yet correspond to the shape of the object, the final mesh is obtained by smoothing the entire mesh arrangement by numerical calculation based on the surface mesh. This operation is called smoothing.

[0003]

By the way, when a flow analysis along a complicated shape is analyzed by the finite volume method, a method of setting a curved surface by boundary-fitting mesh division is as follows.
In the process of creating a three-dimensional mesh from polygon data of an object shape input from a three-dimensional CAD system or the like, a set of polygon surfaces was simply used as a shape boundary without considering the geometric characteristics of the object as described above. Therefore, it can be applied to a simple curved surface or a linear composite shape, but it may be difficult to apply to an object having a complicated three-dimensional free-form surface shape. The present invention solves the above-described problems, and recognizes an object shape as, for example, a hexahedron based on input polygon data, and interactively converts the edges of the hexahedron into a composite curve of a parametric free curve and a straight line. It is an object of the present invention to provide a method and an apparatus for setting a curved surface in three-dimensional boundary-adapted mesh division, which enable boundary-adaptation mesh division of a complicated curved surface.

[0004]

Means for Solving the Problems In order to achieve the above-mentioned object, the invention according to claim 1 is a method for analyzing a flow along the shape of an object using a three-dimensional CAD system . In a method of setting a curved surface by boundary-fitting mesh division, polygon data of an object shape created by using a three-dimensional CAD system is taken in and the polygon data is displayed.
On the screen and input the coordinate position on this display.
After specifying the vertices corresponding to the vertices of the polyhedron among the vertices of the polygon data using the steps, the ridge line of the polyhedron is specified based on the specified vertices, and then the mesh constituting the segments constituting the ridge line as a unit. And further, the inside of the polyhedron is divided into meshes. According to a second aspect of the present invention, there is added a procedure of specifying an edge defining a closed curve other than an edge line on the basis of the specified vertices and dividing the mesh into segments each of which constitutes the specified edge. The invention according to claim 3 sets a reference plane along an edge defining a specified closed curve,
A procedure for mesh division with respect to the set reference plane is added. The invention of claim 4 is a three-dimensional CAD
An apparatus comprising: input means for inputting polygon data of an object shape created using a system; and output means for outputting an object shape to a screen or the like based on the input polygon data. Vertex designating means for designating vertices corresponding to the vertices of the polyhedron in the data; ridge designating means for designating the ridges of the polyhedron based on the designated vertices; Dividing means for dividing the inside into meshes.

[0005]

According to the method of the first aspect, a three-dimensional CAD system is provided.
The polygon data of the object shape created using the stem
Capture and display it on the display.
Specify the vertices corresponding to the vertices of the polyhedron among the vertices of the polygon data using the coordinate position input means above, specify the ridge line of the polyhedron based on the specified vertices, and mesh the segments constituting the ridge line as a unit. And the inside of the polyhedron can be divided into meshes. According to the method of claim 2, in addition to the above, based on the specified vertices, an edge that defines a closed curve other than an edge is specified, and the mesh constituting the specified edge is divided into meshes. be able to. According to the method of claim 3, in addition to the above, a reference plane can be set along an edge defining a specified closed curve, and mesh division can be performed on the set reference plane. According to the apparatus of the fourth aspect, the three-dimensional CAD system is operated by the input means.
The polygon data of the object shape created by using the stem is inputted, the vertices corresponding to the vertices of the polyhedron are designated from among the polygon data inputted by each designation means, and the polyhedron of the polyhedron is designated based on the vertices designated by the division means. Specify the ridge line,
The polygons are divided into meshes in units of the segments constituting the ridge lines, and the inside of the polyhedron is divided into meshes, and the result of the mesh division is displayed on a screen by an output unit.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a three-dimensional fluid analysis using a general curved coordinate system according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block configuration of a graphic processing system for general curve coordinate system three-dimensional fluid analysis by three-dimensional CAD.
A graphic processing system for general curve coordinate system three-dimensional fluid analysis by three-dimensional CAD includes a hard disk 1 storing polygon data of an object shape, a keyboard 2 (input means) for inputting a coordinate position of the object, and a mouse 3 (input means). )When,
A three-dimensional CAD body 4 for taking in the input polygon data to create a three-dimensional mesh, a display 5 (output means) for displaying data processed by the three-dimensional CAD body, and a plotter 6 for plotting out the data. It is composed of The three-dimensional CAD body 4 includes a CPU 7 for controlling the input device and the entire apparatus, a ROM 8 for storing a CAD program, a RAM 9 for processing polygon data of an object shape, and data between the three-dimensional CAD body 4 and the input / output device. And the like for transferring the information. The RAM 9 is provided with a mesh division program. By writing polygon data of the object shape into the program, a three-dimensional mesh or the like is displayed on the display 5.

Next, a method of setting a curved surface in a three-dimensional boundary fitting mesh division of an object by executing a graphic processing program of a general curved coordinate system three-dimensional fluid analysis will be described with reference to a passenger car having a complicated shape as shown in FIG. Will be described as an example. The basic idea of this method is to take in polygon data of an object that has been converted into a polygon by a three-dimensional CAD system, recognize the object as a hexahedron, and make the number of divisions between facing faces the same to make a three-dimensional grid. And a three-dimensional boundary-fitting mesh division based on this.

The specific procedure for this will be described below with reference to the flowchart of FIG. First, from outside, 3D C
When polygon data created using the AD system is input (S1), it is displayed on the display 5 (S1).
2). Of the vertices of the displayed polygon, a point corresponding to the vertices of the hexahedron is specified (S3), and an object ridge line is specified by a row of the specified polygon vertices (S4). Next, similarly to the ridge line designation, an edge is designated by a row of polygon vertices along the edge line (S5). Next, a reference plane is set based on the defined hexahedron (S6), and one-dimensional mesh division is performed in units of segments forming edges and edges (S7). Based on the mesh created in S7,
The inside of each reference plane is divided into two-dimensional meshes (S8), and based on the respective meshes created in S7 and S8,
The image is divided into three-dimensional meshes (S9).

Next, each of the above processes will be described in detail. (1) Designation of Vertices of Hexahedron (8 Points) As shown in FIG. 2, the input polygon data is displayed on the display 5, and points of the vertices of the polygon corresponding to the vertices of the hexahedron are designated with the mouse 3. . The designated vertex is indicated by a black circle. Since the object shape is specified by a polygon, there is not always a vertex that matches the target edge, but if there is no vertex that matches the target edge, the closest vertex is specified. In this case, it is assumed that the apparatus has a three-dimensional graphic function such as dynamic hidden line display, movement, rotation, and scale change. (2) Designation of ridge line of hexahedron (12 lines) An object ridge line is designated by a row of designated polygon vertices.
This designated ridge is indicated by a circle. Regarding the designation of the object ridge line, it is assumed that each ridge line is composed of a plurality of segments, and each segment can be a break point as a straight line or a parametric free curve such as a spline.

(3) Designation of Edges other than Edge Lines (Arbitrary Number) Like the edge lines, a row of polygon vertices along the edge lines
Specify an edge other than a ridgeline. This is indicated by a triangle. Like a ridge, it is composed of a straight line and a free curve, and it is assumed that a break point is also possible. However, it must be a closed curve and cannot be branched. (4) Setting of reference plane The i, j, and k axes are set for the defined hexahedron (see FIG. 3 described later), and the reference plane is set along the k axis. The reference plane is set when it is desired to make the mesh line coincide with a specific edge of the shape. An edge that is a closed curve is defined at that position, and the i and j axes of the reference plane are set along this edge. I do.
The ij plane of the hexahedron surface is a reference plane of the boundary. Here, the reason why the reference plane is set inside is to further divide the object into a plurality of hexahedrons and to easily associate a specific edge with a mesh line. Therefore, when the object shape is relatively simple and there is no specific edge in the middle and a curved surface is continuous, there is no need to set a reference plane inside.

(5) Mesh Division Next, mesh division will be described for ridges and edges, for reference planes, and for three-dimensional meshes. In the mesh division of the ridge line and the edge, as shown in FIG. 3, one-dimensional mesh division is performed for each segment constituting the ridge line and the edge. This mesh is arranged on the assumption that it is basically fixed.
In addition, since it is a structured grid, consideration is given to equal division on opposite sides as a whole. In the mesh division of the reference plane, as shown in FIG. 4, the inside of each reference plane is divided into a two-dimensional mesh based on the mesh on the outer periphery of the reference plane created by the mesh division of the ridge line and the edge. This mesh is used as an initial arrangement for surface fitting and smoothing in a later step.
In the three-dimensional mesh division, as shown in FIG. 5, a three-dimensional mesh is formed inside each hexahedron between the set reference planes. The reference is a two-dimensional mesh of the reference plane created by mesh division of the reference plane, and a ridge mesh in the k-axis direction created by mesh division of edges and edges. As with the mesh division of the reference plane, this mesh is used as an initial arrangement for surface fitting and smoothing in a later process.

The graphic processing program for the general curve coordinate system three-dimensional fluid analysis finishes the final mesh using functions such as surface fitting, smoothing, and combining as a post-division process. However, since these functions are premised, a somewhat approximate division can be made at the time of mesh division.

[0013]

As described above, according to the method and apparatus of the first and fourth aspects of the present invention, when analyzing the flow along a complicated shape by the finite volume method or the like, the vertices of the fetched polygon data are analyzed. Specify the vertices corresponding to the vertices of the polyhedron,
Based on the specified vertices, the ridge line of the polyhedron is specified, the mesh is divided based on this ridge line, and the inside of the polyhedron is further divided into meshes. Is done. In addition, since the mesh division procedure based on polygon data used in the conventional method is not fundamentally changed, the versatility of the data input format from the three-dimensional shape model can be maintained, and the division algorithm is simplified. . Claim 2
According to the third to third methods, since a closed curve and a reference plane are set inside the object, mesh division can be performed accurately and easily even when the object shape is extremely complicated.

[Brief description of the drawings]

FIG. 1 is a block diagram of an apparatus of a graphic processing system for three-dimensional fluid analysis of a general curved coordinate system by three-dimensional CAD according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a three-dimensional curved surface.

FIG. 3 is a diagram illustrating the concept of mesh division of ridges and edges.

FIG. 4 is a diagram showing a concept of mesh division of a reference plane.

FIG. 5 is a diagram illustrating the concept of three-dimensional mesh division.

FIG. 6 is a flowchart showing a procedure of three-dimensional boundary adaptive mesh division.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hard disk 2 Keyboard 3 Mouse 4 3D CAD main body 5 Display 7 CPU

Claims (4)

(57) [Claims] 1. A method of setting a curved surface by boundary-adapted mesh division when analyzing a flow along the shape of an object using a three-dimensional CAD system.
Imports polygon data of the object shape created using the system and displays the polygon data on the display.
And use the coordinate position input means on this display.
After specifying the vertices corresponding to the vertices of the polyhedron among the vertices of the polygon data, the ridge line of the polyhedron is specified based on the specified vertices, and then the mesh is divided into the segments constituting the ridge line as a unit. And a method for setting a curved surface in three-dimensional boundary-fitting mesh division, wherein the inside of the polyhedron is divided into meshes. 2. The method according to claim 1, further comprising a step of designating an edge defining a closed curve other than an edge line based on the designated vertex, and dividing the mesh into units of segments constituting the designated edge. Item 3. A method for setting a curved surface in the three-dimensional boundary fitting mesh division according to item 1. 3. The three-dimensional method according to claim 2, wherein a reference plane is set along an edge defining the designated closed curve, and a step of dividing the set reference plane into meshes is added. Setting method of the curved surface in the boundary fitting mesh division. 4. An input means for inputting polygon data of an object shape created by using a three-dimensional CAD system, and an output means for outputting the object shape to a screen or the like based on the input polygon data. In the apparatus, vertex specifying means for specifying vertices corresponding to the vertices of the polyhedron in the polygon data from the input means, ridge line specifying means for specifying the ridge line of the polyhedron based on the specified vertices, and a segment forming the ridge line as a unit And a dividing unit that divides the inside of the polyhedron into meshes, and further comprises a dividing unit that divides the inside of the polyhedron into meshes.