JPH04246779A - Method and device for setting curved surface in three-dimensional boundary adaptive mesh division - Google Patents

Abstract

PURPOSE:To enable the boundary adaptive mesh division of a complicated curved surface by recognizing the shape of an object as a polygon based on polygon data, and dividing it into meshes setting a segment comprising the ridge of the polygon as unit. CONSTITUTION:Inputted polygon data is displayed on a display 5. For example, the apex of a hexahedron out of the apexes of the polygon is designated by a mouse 3. The ridge of the object is designated by the string of the designated ridge of the polygon. Thence, an edge other than the ridge is designated by the string of polygon apexes along the ridge. A three-dimensional CAD main body 4 sets a reference plane based on a defined hexahedron, and performs one-dimensional mesh division setting the segment comprising the ridge and the edge as unit. Thence, two-dimensional mesh division is applied to each reference plane inside setting a generated mesh as reference. Furthermore, three-dimensional mesh division is applied setting respective generated mesh as reference.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for three-dimensional boundary matching mesh division, which is mainly used when analyzing a flow along an object with a complex shape using a finite volume method or the like.

0002

[Prior Art] Conventionally, when analyzing a flow along a complex shape using the finite volume method, polygon data of the object shape created by a three-dimensional CAD system, etc. is input, and based on this polygon data, It is known to create a three-dimensional mesh and use it to perform three-dimensional fluid analysis of an object. In this conventional mesh creation process, a set of input polygon surfaces is used as a shape boundary and mesh division is performed. However, at the beginning of the work, the geometrical characteristics of the object are not taken into account, reference planes are set at necessary locations across the closed curved surface formed by the polygon surface, each reference plane is divided into meshes, and then those planes are By linearly interpolating between meshes, a three-dimensional mesh region roughly following the shape of the object is created. Thereafter, by mapping the surface mesh of this three-dimensional mesh onto a nearby polygon surface, the mesh is made to correspond to the shape of the object. This operation is called surface fitting. However, at this stage, only the surface mesh still does not correspond to the object shape, so the final mesh is obtained by smoothing the entire mesh arrangement using numerical calculations based on the surface mesh. This operation is called smoothing.

0003

[Problems to be Solved by the Invention] By the way, in the method of setting a curved surface using boundary matching mesh division when analyzing a flow along a complex shape using the finite volume method,
In the process of creating a 3D mesh from the polygon data of the object shape input from a 3D CAD system, etc., the shape boundary was simply a collection of polygon surfaces without considering the shape characteristics of the object, as described above. Therefore, although it is applicable to simple curved surfaces and linear composite shapes, it is sometimes difficult to apply it to objects with complex three-dimensional free-form surfaces. The present invention solves the above-mentioned problems.Based on input polygon data, the object shape is recognized as, for example, a hexahedron, and the edges of the hexahedron are interactively converted into parametric free curves and compound curves of straight lines. An object of the present invention is to provide a method and device for setting a curved surface in three-dimensional boundary-fitting mesh division, which enables boundary-fitting mesh division of a complex curved surface.

0004

[Means for Solving the Problems] In order to achieve the above object, the invention of claim 1 provides a method for setting a curved surface by boundary matching mesh division when analyzing a flow along the shape of an object. Import polygon data of an object shape created with a 3D CAD system, etc., specify the vertices of this polygon data that correspond to the vertices of the polyhedron, and then specify the edges of the polyhedron based on these specified vertices. Then, the segments constituting this edge line are divided into meshes, and the interior of the polyhedron is further divided into meshes. The invention according to claim 2 adds a step of specifying an edge defining a closed curve other than an edge line based on a specified vertex, and dividing the edge into meshes in units of segments constituting the specified edge. The invention according to claim 3 adds a step of setting a reference plane along an edge defining a designated closed curve, and dividing the set reference plane into a mesh. The invention according to claim 4 includes an input means for inputting polygon data of an object shape created by a three-dimensional CAD system, etc., and an output means for outputting the object shape on a screen etc. based on the input polygon data. The device includes a vertex specifying means for specifying vertices corresponding to vertices of a polyhedron among polygon data from an input means, an edge specifying means for specifying an edge of the polyhedron based on the specified vertices, and a segment constituting the edge. The polyhedron is divided into meshes as a unit, and also includes a dividing means for dividing the inside of the polyhedron into meshes.

[0005]

According to the method of claim 1, polygon data of an object shape is taken in, vertices corresponding to vertices of a polyhedron are specified among the vertices of this polygon data, and edges of the polyhedron are determined based on the specified vertices. It is possible to divide the interior of the polyhedron into meshes by specifying the edges and dividing them into meshes using the segments that make up this edge as units. According to the method according to claim 2, in addition to the above, an edge defining a closed curve other than an edge is specified based on the specified vertex, and segments forming the specified edge are divided into meshes as units. be able to. According to the method of claim 3, in addition to the above, a reference plane can be set along the edge defining the specified closed curve, and mesh division can be performed with respect to the set reference plane. Claim 4
According to the described apparatus, polygon data of an object shape is inputted by the input means, vertices corresponding to vertices of the polyhedron are specified among the polygon data inputted by each specifying means,
The edges of the polyhedron are specified based on the vertices specified by the dividing means, and the segments that make up the edges are divided into meshes.The interior of the polyhedron is also divided into meshes, and the results of this mesh division are displayed on the screen by the output means. do.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Three-dimensional fluid analysis using a general curve coordinate system according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a block configuration of a graphic processing system for three-dimensional fluid analysis using a general curve coordinate system using three-dimensional CAD. A graphic processing system for three-dimensional fluid analysis using a general curve coordinate system using three-dimensional CAD includes a hard disk 1 that stores polygon data of an object shape, a keyboard 2 (input means) and a mouse 3 (input means) for inputting the coordinate position of the object, etc. )and,
A 3D CAD body 4 that takes in input polygon data and creates a 3D mesh, a display 5 (output means) that displays data etc. processed by this 3D CAD body, and a plotter 6 that plots out the data. It is composed of. The 3D CAD main body 4 includes a CPU 7 that controls the input device and the entire device, a ROM 8 that stores the CAD program, a RAM 9 that processes polygon data of the object shape, and data exchange between the 3D CAD main body 4 and the input/output device. It consists of an interface 10 that transfers the information and the like. A mesh division program is provided in the RAM 9, and by writing polygon data of the object shape into this program, a three-dimensional mesh or the like is displayed on the display 5.

Next, we will discuss how to set a curved surface in 3D boundary matching mesh division of an object by executing a graphics processing program for 3D fluid analysis in a general curve coordinate system. This will be explained using an example. The basic idea of this method is to import polygon data of an object shape made into polygons by a 3D CAD system, recognize the object as a hexahedron, and then create a 3D grid by making the number of divisions of facing comrades the same. The purpose is to perform three-dimensional boundary matching mesh division based on this.

The specific procedure for this will be explained below with reference to the flowchart of FIG. First, when polygon data is input from the outside (S1), it is displayed on the display 5 (S2). 6 of the displayed polygon vertices
Specify points that correspond to the vertices of the facepiece (S3), and specify the object edge line using the specified polygon apex sequence (S4)
. Next, in the same way as specifying an edge line, an edge is specified 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 using segments forming ridges and edges as units (S7). Based on the mesh created in S7, the inside of each reference plane is divided into two-dimensional meshes (S
8) Furthermore, the meshes created in S7 and S8 are divided into three-dimensional meshes (S9).

Next, each of the above processes will be explained in detail. (1) Specifying vertices of a hexahedron (8 points) As shown in Figure 2, display the input polygon data on the display 5, and use the mouse 3 to specify points among the vertices of the polygon that correspond to the vertices of the hexahedron. . This specified vertex is indicated by a ● mark. Since the object shape is specified by polygons, there is not necessarily 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 computer has three-dimensional graphic functions such as dynamic hidden line display, movement, rotation, and scale change. (2) Specifying edges of hexahedron (12 lines) Specify object edges using the specified row of polygon vertices. This specified edge line is indicated by a circle. Regarding the designation of object edges, it is assumed that each edge line is composed of a plurality of segments, and each segment can be a straight line or a parametric free curve such as a spline, and a bending point can also be used.

(3) Specifying edges other than ridgelines (arbitrary number)
Similar to an edge, the row of polygon vertices along it
Specify edges other than edges. This is indicated by a △ mark. Like the ridgeline, it is composed of straight lines and free curves, and can have bending points, but it must be a closed curve and cannot branch. (4) Setting the reference plane Set the i, j, and k axes on the defined hexahedron (see FIG. 3, which will be described later), and set the reference plane along the k-axis. A reference plane is set when you want a mesh line to match a specific edge of a shape, but 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. do. Note that the ij plane of the hexahedral surface is the 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 facilitate correspondence between specific edges and mesh lines. Therefore, if the shape of the object is relatively simple and the curved surface is continuous without any particular edge in the middle, there is no need to set a reference plane inside.

(5) Mesh division Next, regarding mesh division, mesh division of ridge lines, edges, reference plane mesh division, and three-dimensional mesh division will be explained. (2) In mesh division of ridge lines and edges, as shown in FIG. 3, one-dimensional mesh division is performed using segments forming the ridge lines and edges as units. This mesh is basically placed on the assumption that it will be fixed. Also, since it is a structured lattice, care must be taken to ensure that the opposite sides are equally divided throughout. (2) Mesh division of the reference plane, as shown in FIG. 4, divides the inside of each reference plane into two-dimensional meshes based on the mesh around the outer periphery of the reference plane created by meshing the ridges and edges. This mesh is used as the initial arrangement for surface fitting and smoothing in the subsequent process. (3) In three-dimensional mesh division, as shown in FIG. 5, a three-dimensional mesh is created inside each hexahedron between the set reference planes. The reference is a two-dimensional mesh of the reference plane created by meshing the reference plane, and an edge mesh in the k-axis direction created by meshing the edges and edges. Similar to the mesh division of the reference surface, this mesh is used as the initial arrangement for surface fitting and smoothing in the subsequent process.

Note that the graphic processing program for 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, but in the method of the present invention, Since these functions are also assumed, it is possible to perform a somewhat approximate division when dividing the mesh.

[0013]

As described above, according to the method and apparatus of the present invention as set forth in Claims 1 and 4, when analyzing a flow along a complicated shape using a finite volume method or the like, the vertices of the imported polygon data can be Specify the vertices that correspond to the vertices of the polyhedron,
The edges of the polyhedron are specified based on the specified vertices, the mesh is divided based on these edges, and the interior of the polyhedron is further meshed, which enhances the boundary-adaptive mesh division function for complex objects composed of free-form surfaces. be done. In addition, since there is no fundamental change in the mesh division procedure based on polygon data used in conventional methods, the versatility of the data input format from the 3D shape model can be maintained, and the division algorithm is simple. . Claim 2
According to methods 3 to 3, since a closed curve and a reference plane are set inside the object, mesh division can be performed accurately and easily even when the shape of the object is extremely complex.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a device of a graphic processing system for three-dimensional fluid analysis in a general curve coordinate system using three-dimensional CAD according to an embodiment of the present invention.

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

FIG. 3 is a diagram showing the concept of mesh division of ridge lines and edges.

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

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

FIG. 6 is a flowchart showing a procedure for three-dimensional boundary matching mesh division.

[Explanation of symbols]

1 Hard disk 2 Keyboard 3 Mouse 4 3D CAD body 5 Display 7 CPU

Claims (4)

[Claims] Claim 1: In a method for setting a curved surface by boundary matching mesh division when analyzing a flow along the shape of an object, polygon data of the object shape created with a three-dimensional CAD system, etc. is imported, and this polygon After specifying the vertices of the data that correspond to the vertices of the polyhedron, the edges of the polyhedron are specified based on the specified vertices, and then the segments that make up this edge are divided into meshes, and further, A method for setting a curved surface in three-dimensional boundary matching mesh division, characterized by dividing the inside of a polyhedron into meshes. [Claim 2] A claim characterized by adding a step of specifying an edge defining a closed curve other than an edge line based on a specified vertex, and dividing into meshes in units of segments constituting the specified edge. A method for setting a curved surface in three-dimensional boundary matching mesh division as described in Section 1. 3. The three-dimensional method according to claim 2, further comprising a step of setting a reference plane along an edge defining a specified closed curve and dividing the set reference plane into a mesh. How to set curved surfaces in boundary fitting mesh division. 4. An apparatus comprising an input means for inputting polygon data of an object shape created by a three-dimensional CAD system, etc., and an output means for outputting the object shape on a screen etc. based on the input polygon data. , a vertex specifying means for specifying vertices corresponding to vertices of a polyhedron among polygon data from an input means, an edge specifying means for specifying an edge line of the polyhedron based on the specified vertices, and a segment forming the edge line as a unit. Along with dividing into mesh,
1. A curved surface setting device in three-dimensional boundary matching mesh division, comprising: dividing means for dividing the inside of a polyhedron into meshes.