JP4849503B2 - Mesh generation method and information processing apparatus - Google Patents

Description

  The present invention relates to, for example, a mesh generation method and an information processing apparatus that generate a mesh using shape data created by a three-dimensional CAD program.

  Conventionally, in numerical simulation, mesh generation is performed by a pre-processing program, initial conditions and boundary conditions are set, calculation is performed thereafter, and the result is output using a post output program.

  In addition, when performing 3D mesh division using shape data created by a 3D CAD program, data representing 3D shape data such as IGES format, Parasolid format, ACIS format, etc. is read by a pre-processing program. It is possible to generate a 3D mesh using the read 3D shape data.

Many mesh generation methods used in the pre-processing program include a mesh generation method using an advanced front method (see Patent Document 1) and a mesh generation method using a bubble filling method (see Patent Document 2). A mesh generation method has been proposed.
JP 11-96399 A Japanese Patent Laid-Open No. 7-230487

  However, the conventional mesh generation method has the following problems. That is, when the three-dimensional shape data is read by the pre-processing program, the tolerance of the geometric dimension accuracy is different, the representation format of the surface data is different, or the quality of the shape data created by the three-dimensional CAD program is poor. As a result, there are cases where gaps are generated between the surfaces constituting the shape surface in the read three-dimensional shape data, or the shape data becomes inferior as a three-dimensional shape such that the surfaces overlap each other. When such a defect in shape data exists, there has been a problem that a mesh cannot be generated.

  Even if there is no defect in the shape data and the shape can be divided into three-dimensional meshes, if there are minute surfaces in the three-dimensional shape data created by the CAD program, Therefore, a mesh having a minute side length, a mesh having a minute area, and a mesh having a large aspect ratio are generated. If numerical simulation is performed using such a mesh, the calculation accuracy will decrease, and therefore the convergence of the calculation will deteriorate, the calculation time will increase, and the calculation result will not be obtained because it has not converged It happened.

Accordingly, an object of the present invention is to provide a mesh generation method and an information processing apparatus capable of preventing a reduction in calculation accuracy in numerical simulation even when there is a defect in three-dimensional shape data .

In order to achieve the above object, the mesh generation method of the present invention is a mesh generation method in which an information processing device generates a mesh using data of a three-dimensional shape read by the information processing device, A surface mesh generating step of generating a surface mesh on the surface of the original shape data, and a three-dimensional mesh generating step of generating a three-dimensional mesh so that the generated surface mesh forms a closed space, the surface mesh In the generating step, when there is a gap between the surfaces constituting the surface, a surface mesh is generated on one surface, and the node generated on the boundary side with the other surface is replaced with the other surface. Projecting on the boundary side with the one surface of the other surface, and generating no nodes other than the projected node on the boundary side with the one surface of the other surface , using the projected node in front It generates a surface mesh on the other side, replacing the projected node to the node that is the projection, to connect the surface mesh generated on the other side with the generated surface mesh on the one side Features.

  According to the mesh generation method of the present invention, it is possible to prevent the calculation accuracy in numerical simulation from being lowered even if there is a defect in the three-dimensional shape data. Therefore, even if the three-dimensional shape data includes a defect such as a gap due to a difference in allowable dimensional error or a double plane, a closed space can be reconstructed and a mesh can be generated.

  Embodiments of a mesh generation method and an information processing apparatus according to the present invention will be described with reference to the drawings. The mesh generation method of this embodiment is executed by a three-dimensional CAD device.

[First Embodiment]
FIG. 1 is a diagram illustrating a configuration of hardware resources of the three-dimensional CAD apparatus according to the first embodiment. The three-dimensional CAD device 51 includes a CPU 52, an internal storage unit 53, an external storage unit 54, a display unit 55, an input unit 56, an external connection unit 57 and an output unit 58. Here, the internal storage unit 53 may be a semiconductor memory. An example of the external storage unit 54 is a magnetic storage device. The external storage unit 54 stores CAD data and a three-dimensional CAD program. The input unit 56 includes a mouse, a keyboard, and the like that give instructions to the three-dimensional CAD program. The output unit 58 includes a printer that outputs a paper drawing or the like in accordance with a command (command) from the CPU 52. The display unit 55 displays the shape and the like according to a command from the CPU 52. Further, the three-dimensional CAD device can be connected to an output device such as a printer or a plotter, a server device, or the like via the external connection unit 57. The external connection unit 57 connects the three-dimensional CAD device 51 and an external device, supplies data from the device 51 to the external device, and controls the device 51 from the external device.

  When the operator gives an instruction to start a three-dimensional CAD program via the input unit 56, the three-dimensional CAD program stored in the external storage unit 54 is read into the internal storage unit 53 by the CPU 52 and executed. This three-dimensional CAD program forms a three-dimensional model in the virtual space in accordance with an operator instruction input via the input unit 56.

  FIG. 2 is a flowchart showing a mesh generation processing procedure. This processing program is stored in the external storage unit 54 and executed by the CPU 52. First, shape data representing a three-dimensional shape is created (step S1). For this shape data, a Parasolid format, an ACIS format, a format unique to each CAD program, an STL format often used in rapid prototyping, and the like are used.

  The shape data created in step S1 is read (step S2). A mesh is generated on the surface of the shape data read in step S2 (step S3). In this mesh generation (surface mesh division) process, a mesh is generated even when there are gaps or overlaps in the surfaces constituting the shape surface. FIG. 3 is a diagram showing an example of a model having a surface constituting a shape surface when there is a gap. In FIG. 3, FIG. 3B is an enlarged view of the portion surrounded by the frame line shown in FIG. FIG. 4 is a diagram showing a mesh generated in a gap in a part of the model of FIG. In FIG. 4, FIG. 4B is an enlarged view of the portion surrounded by the frame line shown in FIG. As shown in FIG. 3, for example, when a gap 14 is generated between the surface 12 and the surface 13 of the shape surface, the mesh is arranged so that the nodes are shared on the sides of the boundary sides 15 and 16 as shown in FIG. 4. Must be generated.

  Here, sharing of nodes means that the nodes constituting the mesh are the same. In FIG. 4, the node 17 created on the boundary side 16 is a constituent node of the mesh 18 on the surface 12 and the mesh 19 on the surface 13, and the nodes are shared by the surface 12 and the surface 13. In addition, when the gap between adjacent surfaces is within an allowable error, the process of sharing the node is performed, and the allowable error can be arbitrarily set by an operator.

  The following processing is executed as a method of generating the mesh so that the nodes are shared by the surfaces separated as described above. First, mesh division is performed on one surface 12, and the nodes 17 generated on the boundary side 15 are projected onto the boundary side 16 of the surface 13. When generating a mesh for the surface 13, only the node group projected on the boundary side 16 is used, and no new node is generated on the boundary side 16, and the mesh of the surface 13 is divided. Thereafter, the node group projected on the boundary side 16 of the surface 13 is replaced with the node of the projection source. By this node replacement, the surface meshes generated on the surface 12 and the surface 13 are connected.

  FIG. 5 is a diagram showing surfaces constituting the shape surface when there is an overlap. When the overlap occurs, the following processing is executed. First, mesh division is performed on one surface 20, and when mesh division is performed on the other surface 21, a mesh has already been generated as the surface 20 for the portion 22 where the surfaces overlap. A surface 23 is created by projecting onto the surface 21 and excluding the surface overlapping the surface 21. FIG. 6 is a diagram showing surface meshes connected when there is an overlap. Further, by dividing the surface 20 into meshes, the node group 24 on the edge of the generated overlap surface is projected onto the surface 23, nodes are generated at the projected positions, and a mesh is generated on the surface 23. At this time, mesh generation is performed using only the nodes projected on the edge of the overlap surface, and then the projected nodes are replaced with the projection source nodes. By this replacement, the surface meshes of the surface 20 and the surface 23 are connected. Here, when the surfaces overlap with each other within the allowable error, processing is performed in which the nodes and the mesh are the same on the overlapped surfaces, and the allowable error can be arbitrarily set by the operator.

  In this way, using the data in which the mesh is generated on the shape surface in step S3, a solid mesh (three-dimensional mesh) is generated therein (step S4). In the generation of the solid mesh, it is possible to apply a mesh division method such as an advanced front method or a denero division method. When automatic division is performed using the above division method, usually three-dimensional mesh data is generated as tetrahedral elements (step S5). Then, this process is complete | finished.

  Thus, according to the mesh generation method of the first embodiment, a closed space that forms a surface of a three-dimensional shape even if the surface of the three-dimensional shape does not form a closed space due to a defect such as a gap or an overlap. The surface mesh which comprises is produced | generated. If there is a gap between the faces that make up the shape surface, create a surface mesh so that the mesh shares nodal points on the boundary between the faces and the faces that are within tolerances, that is, on the edges that make up the face. If the surfaces overlap within the tolerance, a surface mesh is generated so that the nodes and the mesh are shared on the overlapped surfaces. Then, by generating a three-dimensional mesh, mesh division can be performed even if there is a defect in the three-dimensional shape. Thus, even if there is a defect in the three-dimensional shape data, it is possible to prevent the calculation accuracy by numerical simulation from being lowered. Even if the three-dimensional shape data includes defects such as gaps due to differences in allowable dimensional errors, double planes, and the like, the closed space can be reconstructed and meshes can be generated.

[Second Embodiment]
Since the configuration of the hardware resources of the three-dimensional CAD device in the second embodiment is the same as that in the first embodiment, description thereof is omitted. FIG. 7 is a flowchart showing a mesh generation processing procedure in the second embodiment. This processing program is stored in the external storage unit 54 and executed by the CPU 52. About the same step process as the said 1st Embodiment, the description is simplified by attaching | subjecting the same code | symbol.

  First, shape data representing a three-dimensional shape is created (step S1). The shape data created in step S1 is read (step S2). Then, before generating the mesh on the surface of the shape data in step S3, that is, before performing the surface mesh division, the minute surface is erased from the shape data read in step S2 (step S2A). FIG. 8 is a diagram showing erasure of a minute surface. FIG. 8B is an enlarged view of the portion surrounded by the square frame shown in FIG. Moreover, FIG.8 (c) expands the part enclosed by the round frame shown by FIG.8 (b). For example, in the shape 25 shown in FIG. 8, the minute surface 26 that exists because there is a minute step shape is erased. Here, the minute surface is a surface having a side smaller than the allowable minute length and smaller than the allowable minute area, and can be arbitrarily set in advance by the operator.

  When the minute surface 26 is erased, processing for correcting information on the adjacent surface is subsequently performed (step S2B). In this adjacent surface information correction process, there are three surfaces 27, 28, and 29 that are in contact with the minute surface 26, but since the surface 27 and the surface 28 are adjacent to each other through the surface 26, the surface 27 and the surface 26 are adjacent to each other. Suppose you are.

  That is, in the surface mesh generation process in step S3, as in the case where there is a gap between the surfaces, a mesh is first generated for one surface 27, and the mesh is generated on the side 31 serving as a boundary. The node is projected onto the side 30 that is the boundary of the adjacent surface 28. On the other hand, when a mesh is generated for the adjacent surface 28, the mesh is generated using only the projected nodes on the side 30 serving as the boundary.

  Here, if the surface 27 and the surface 28 are adjacent surfaces, the length of the side 32 that becomes the boundary between the minute surface 26 and the surface 29 must be zero. However, there is a contradiction that the side 32 is on the surface 29. Therefore, in order to generate nodes only at both ends of the side 32, mesh division of the surface 29 is performed as shown in FIG. 9A, and then the node on the side 30 serving as one boundary becomes the other boundary. When replacing with a node on the side 31, the mesh 33 including the side 32 is deleted, and the contradiction is resolved. FIG. 9B shows the surface mesh division after the above processing. FIG. 9 is a diagram illustrating deletion of the mesh 33 including the side 32.

  Thereafter, as in the first embodiment, a solid mesh (three-dimensional mesh) is generated inside the shape (step S4), and three-dimensional mesh data is generated (step S5). Then, this process ends.

  As described above, according to the mesh generation method in the second embodiment, before applying the mesh generation method similar to that in the first embodiment, by adding the following processing, Generation is prevented and calculation accuracy is not reduced. That is, when there is a side having a permissible minute length or less and a surface having a permissible minute area or less, that side is erased, and at the same time, a side that is adjacent to the side is used as a shared side. The shared edges are separated by a distance within an allowable minute length, but when generating a mesh on the shape surface, a surface mesh that shares the constituent nodes with the shared edges is generated. In this case, since it is physically impossible for one node to have two coordinates, one coordinate value or average value is used as the coordinate value of the nodes on the shared side. Therefore, when a minute shape exists in the three-dimensional shape data, a minute mesh is not generated by ignoring the minute shape. Therefore, it is possible to prevent the simulation accuracy from being reduced due to the minute mesh.

[Third Embodiment]
The configuration of the three-dimensional CAD apparatus in the third embodiment is the same as that in the first embodiment. FIG. 10 is a flowchart showing a mesh generation processing procedure in the third embodiment. This processing program is stored in the external storage unit 54 and executed by the CPU 52. About the same step process as the said 1st Embodiment, the description is simplified by attaching | subjecting the same code | symbol.

  First, shape data representing a three-dimensional shape is created (step S1). The shape data created in step S1 is read (step S2). A mesh is generated on the surface of the shape data read in step S2 (step S3). In this surface mesh generation process, the surface mesh is also generated for the same minute surface as in the second embodiment. Therefore, thereafter, a fine mesh deletion process for deleting a fine mesh in the surface mesh is performed (step S3A). FIG. 11 is a diagram illustrating deletion of a minute mesh included in the surface mesh. FIG. 4B is an enlarged view of the portion surrounded by the frame line shown in FIG.

  In FIG. 8B, for example, a mesh is generated on the surface without erasing the minute surface having the shape of FIG. That is, since the minute step shape is divided into meshes as they are, the minute mesh 41 is generated. Then, this minute mesh is erased. If the fine mesh is deleted, a hole is formed in the surface mesh and a closed space cannot be formed. Therefore, a surface mesh stitching process is performed to close the hole in the shape surface so that the surface mesh forms a closed space (step S3B). In this mesh stitching process, a nearby node is replaced with the same node among the nodes included in the hole portion on the shape surface. In FIG. 6C, the step shape is eliminated by the mesh stitching process (see mesh 44), and the mesh having minute sides is eliminated. As a result, the surface mesh forms a closed space. Thereafter, as in the first embodiment, a solid mesh is generated inside the shape (step S4), and three-dimensional mesh data is generated (step S5). Then, this process ends.

  As described above, according to the mesh generation method of the third embodiment, after the surface mesh is generated, first, all the surface meshes having a minute area are erased. Then, by erasing the surface mesh having a small area, the node that has become a node on the free edge is replaced with a node on another nearby free edge, and the free edge is erased. Here, the free edge refers to a side that does not share a side with another surface mesh among the sides of the surface mesh. Repeat replacing nodes on the free edge with nodes on other nearby free edges until all free edges are gone. When the free edge disappears, the surface mesh forms a closed space, so the three-dimensional mesh division is performed. Thereby, generation of a minute three-dimensional mesh can be prevented. Therefore, when a minute shape exists in the three-dimensional shape data, a minute mesh is not generated by ignoring the minute shape. Therefore, it is possible to prevent the simulation accuracy from being reduced due to the minute mesh.

  The present invention is not limited to the configuration of the above-described embodiment, and any configuration can be used as long as the functions shown in the claims or the functions of the configuration of the present embodiment can be achieved. Is also applicable. Further, the present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device.

  Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above embodiments to a system or apparatus, and the computer (or CPU, MPU, etc.) of the system or apparatus stores the storage medium. It is also achieved by reading out and executing the program code stored in. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

  Examples of storage media for supplying the program code include ROM, floppy (registered trademark) disk, memory card such as PCMCIA card and compact flash (registered trademark), hard disk, micro DAT, magneto-optical disk, CD-R, and the like. You may comprise with optical disks, such as CD-RW, phase change type optical disks, such as DVD. The program code may be downloaded via a network.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) or the like running on the computer is actually executed based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing a part or all of the process and the process is included.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. This includes the case where the CPU or the like provided in the board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

It is a figure which shows the structure of the hardware resource of the three-dimensional CAD apparatus in 1st Embodiment. It is a flowchart which shows a mesh production | generation process procedure. It is a figure which shows an example of the model which has the surface which comprises the shape surface in case there exists a clearance gap. It is a figure which shows the mesh produced | generated by the one part clearance gap of the model of FIG. It is a figure which shows the surface which comprises the shape surface in case there exists overlap. It is a figure which shows the surface mesh connected when there exists overlap. It is a flowchart which shows the mesh production | generation process procedure in 2nd Embodiment. It is a figure which shows the deletion of a micro surface. It is a figure which shows deletion of the mesh 33 containing the edge | side 32. FIG. It is a flowchart which shows the mesh production | generation process procedure in 3rd Embodiment. It is a figure which shows deletion of the fine mesh contained in a surface mesh.

Explanation of symbols

12, 13, 20, 21, 27, 28, 29 plane 15, 16 sides 17 nodes 18, 19 mesh 51 three-dimensional CAD device 52 CPU

Claims (7)

An information processing apparatus is a mesh generation method for generating a mesh using data of a three-dimensional shape read by the information processing apparatus,
A surface mesh generating step of generating a surface mesh on the surface of the data of the three-dimensional shape, and a three-dimensional mesh generating step of generating a three-dimensional mesh so that the generated surface mesh forms a closed space,
In the surface mesh generation step,
When there is a gap between the surfaces constituting the surface, a surface mesh is generated on one surface, and the node generated at the boundary side with the other surface is changed to the one surface on the other surface. Projecting onto a boundary edge with a surface, no other node than the projected node is generated at the boundary edge with the one surface of the other surface, and using the projected node, the other surface is not generated . A surface mesh is generated on a surface, the projected node is replaced with the projected node, and the surface mesh generated on the one surface is connected to the surface mesh generated on the other surface. Mesh generation method. An information processing apparatus is a mesh generation method for generating a mesh using data of a three-dimensional shape read by the information processing apparatus,
A surface mesh generating step of generating a surface mesh on the surface of the data of the three-dimensional shape, and a three-dimensional mesh generating step of generating a three-dimensional mesh so that the generated surface mesh forms a closed space,
In the surface mesh generation step,
When the surface and the surface constituting the surface overlap, a surface mesh is generated on one surface of the overlapping surface, the surface mesh is projected on the other surface, and the surface of the other surface, A surface that overlaps one surface is deleted, and no node other than the node on which the node on the edge of the overlapped surface is projected is generated as a node at the end of the surface, and a surface mesh is formed on the other surface Generating a mesh.   The mesh generation method according to claim 1, wherein, in the surface mesh generation step, nodes of different surface meshes nearby among the nodes of the surface mesh are replaced with one node. An information processing apparatus for generating a mesh using three-dimensional shape data, the surface mesh generating means for generating a surface mesh on the data surface of the three-dimensional shape, and the generated surface mesh forming a closed space And a three-dimensional mesh generating means for generating a three-dimensional mesh,
The surface mesh generation means includes
When there is a gap between the surfaces constituting the surface, a surface mesh is generated on one surface, and the node generated at the boundary side with the other surface is changed to the one surface on the other surface. Projecting onto a boundary edge with a surface, no other node than the projected node is generated at the boundary edge with the one surface of the other surface, and using the projected node, the other surface is not generated . A surface mesh is generated on a surface, the projected node is replaced with the projected node, and the surface mesh generated on the one surface is connected to the surface mesh generated on the other surface. Information processing device. An information processing apparatus for generating a mesh using three-dimensional shape data, the surface mesh generating means for generating a surface mesh on the data surface of the three-dimensional shape, and the generated surface mesh forming a closed space And a three-dimensional mesh generating means for generating a three-dimensional mesh,
The surface mesh generation means includes
When the surface and the surface constituting the surface overlap, a surface mesh is generated on one surface of the overlapping surface, the surface mesh is projected on the other surface, and the surface of the other surface, A surface that overlaps one surface is deleted, and no node other than the node on which the node on the edge of the overlapped surface is projected is generated as a node at the end of the surface, and a surface mesh is formed on the other surface An information processing apparatus characterized by generating The computer, according to claim 1 to 3 computer-readable storage medium storing the order of the program to execute the steps of mesh generation method according to any one of. The computer program of the order to execute the respective steps of the mesh generation method according to any one of claims 1 to 3.

Images