The present application claims priority from Japanese patent application serial no. 2015-115539, filed on Jun. 8, 2015, the content of which is hereby incorporated by reference into this application.
The present invention relates to an analytical mesh generation device and an analytical mesh generation method employed for numerical simulation. More specifically, the present invention relates to the analytical mesh generation device and the method for generating the hexahedral mesh suitable for analysis of the problem of large deformation such as deformation problem of rubber parts.
The recent efforts increasingly made by manufacturing industries has adopted the numerical simulation such as finite element method in the stage of product development and design for estimating the stress and deformation. expected to be applied to the product in advance so as to reduce the number of times of prototype manufacturing.
In most cases, the polyhedral mesh. set called. analytical mesh has to be generated for the calculation region so as to perform the numerical simulation. The hexahedral mesh or tetrahedral mesh has been mainly employed for the three-dimensional analysis region. The hexahedral mesh has been employed more than the tetrahedral mesh to cope with the analysis problem with high non-linearity such as the contact. problem and the large deformation problem. because of higher precision in general, and better mesh shape controllability compared with the tetrahedral mesh.
In the case of the large deformation problem, the mesh with small size will be crushed to cause the divergent state where the analytical calculation cannot be conducted in the normal state. Upon deformation analysis of the rubber product, for example, the mesh size has to be determined in accordance with the deformation amount per unit time. The mesh size has to be made large in accordance with the large deformation amount, otherwise the model will collapse, disabling calculation. It is therefore preferable to allow the mesh to be large-sized to a certain degree for the time necessary for the calculation as short as possible.
Before generation of the hexahedral mesh, it is preferable to eliminate a very small part from the analysis region, which will be less influential to the overall deformation thereof through the shape simplification process. However, it is necessary to execute the shape simplification process by a skilled analyst interactively based on his/her knowledge, requiring time and labor.
Japanese Patent Application Laid-Open No. 2004-32473 discloses the information processing device and the method thereof, configured that an initial mesh model representing the surface shape of the three-dimensional model produced by CAD is generated so as to provide the analytical model with simplified shape by subjecting the initial mesh model to the edge collapse process predetermined number of times.
Referring to the device and method as disclosed in Japanese Patent Application Laid-Open No. 2004-32473, the tetrahedral mesh is deformed through the edge collapse process so as to be converted into the one with the size larger than the initial mesh. In expectation of the shape shift amount from the initial mesh on the shape surface, the mesh deformation process is executed so as to lessen the shape shift amount. The aforementioned device and method are designed to execute the simplification process to increase the mesh size while keeping the original analysis region. General structural analysis and fluid analysis require the analytical mesh which keeps its original shape as much as possible. The disclosed device and method provide the aforementioned analytical mesh effectively.
The aforementioned method, however, cannot be applied to the shape simplification process required to delete a part of the analysis region for coping with the large deformation problem.
The present invention provides the mesh generation device and method for generating especially the hexahedral mesh with its size equal to or larger than the specified one for coping with the large deformation problem through the simplification process which allows deletion of the very small part from the analysis region, which is less influential to the overall deformation from the analytical area.
The analytical mesh generation device according to the present invention includes a shape model input, unit for inputting a shape model of an analytical subject, a mesh size input unit for inputting a size of a hexahedral mesh to be generated, a mesh generation region extraction unit for extracting a mesh generation region for generating the hexahedral mesh from the shape model using the mesh size, and a hexahedral mesh generation unit for generating the hexahedral mesh for the extracted mesh generation region.
The analytical mesh generation method according to the present invention includes the steps of holding a shape model of an analytical subject and a mesh size of a hexahedral mesh to be generated, extracting a mesh generation region for generating the hexahedral mesh from the shape model using the mesh size, and generating the hexahedral mesh for the extracted mesh generation region.
The present invention is capable of generating the hexahedral mesh for a large deformation analysis without executing the shape simplification process, resulting in highly efficient analytical operation.
Embodiments according to the present invention will be described in detail referring to the drawings.
In this embodiment, the analytical mesh generation device and method will be explained with respect to generation of the hexahedral mesh for large deformation analysis, taking a shape model M shown in
It is assumed that the respective parts of the shape model M as shown in
Upon generation of the analytical mesh by means of the analytical mesh generation device according to the embodiment, the shape model M is divided into partial region shape models M1, M2, M3 which constitute a shape model MA with different brightness from that of the shape model M as shown in
Referring to
The thus extracted mesh generation region M2 does not contain detailed parts M1 and M3 of the shape model. It is therefore possible to automatically generate a hexahedral mesh shape model MD (M2) which keeps the mesh size suitable for the large deformation analysis.
The operation section CPU is constituted by a computer, and the storage section DB is an external storage device of the computer. The storage section DB includes a shape model data storage section DB1 which stores the shape model data D1 of the analytical subject, a mesh generation region data storage section DB2 which stores the mesh generation region data D2 indicating the region for generating the hexahedral mesh, and a hexahedral mesh data storage section DB3 which generates the hexahedral mesh data D3. The storage section DB contains size data D4 for designation of size of the hexahedral mesh to be generated. The storage section DB is formed as the external storage device of the computer. Alternatively, it may be structured as an internal storage section installed in the computer.
The operation. section CPU includes a shape model input section 102 which receives the shape model data D1 of the analytical subject through the input/output section I/O so as to be stored in the shape model data storage section DB1, a mesh size input section 103 which receives the size data D4 of the hexahedral mesh to be generated through the input/output section I/O so as to be stored in the storage section DB, a mesh generation region extraction section 104 which receives the shape model data D1 from the shape model data storage section DB1, and the size data D4 of the hexahedral mesh from the storage section DB so as to extract the mesh generation region data D2 as the region for generating the hexahedral mesh, and a hexahedral mesh generation section 105 which receives the mesh generation region data D2 from the mesh generation region data storage section DB2, and the size data D4 of the hexahedral mesh from the storage section DB so as to generate the hexahedral mesh data D3, which constitute an inner processing function section.
The shape model input section 102 generates and changes the shape model data D1 in accordance with requests of generation and change of the shape model M which has been input by a system user through the keyboard and the mouse of the input/output device I/O.
The boundary representation may be used for expressing the shape model data D1. The boundary representation serves to express the three-dimensional object by the boundary surface between the outer side and the inner side. The shape model data D1 include phase (topology) data expressing connection of the boundary surfaces, and geometric data (geometry) expressing the boundary surface shape. The boundary representation takes the data structure in which the three-dimensional object has a set of at least one continuous attributed boundary surface, the surface has at least one attributed line segment, and the line segment has its starting point and an end point. The point has a three-dimensional coordinate values as the geometric data. Arbitrary types of methods for representing the geometric data may be employed with respect to the line and surface may be employed. In this embodiment, NURBS function which has been widely used for the geometric data representation by the three-dimensional CAD will be employed. The literature titled “Basics and application of three-dimensional CAD” (H. Toriya, H. Chiyokura, Kyoritsu Shuppan Co., Ltd., 1991) discloses the boundary representation in detail.
The input shape model data D1 may be arranged on the shape model data storage section DB1 which stores the shape model data D1 of the analytical subject so as to be accessible for reference in the subsequent mesh generation operation.
The mesh size input section 103 demands the system user to input the mesh size to be generated in reference to the displayed monitor screen as shown in
The mesh generation region input section 104 obtains the shape model data Di of the analytical subject and the mesh size D4 in reference to the storage section DB, and outputs the mesh generation region data D2 as the processing results. The mesh generation region data D2 are arranged on the hexahedral mesh data storage section DB3 so as to be kept accessible for reference in the subsequent mesh generation operation.
An example of the shape division will be described referring to
The division surface is generated through the procedure from steps S511 to S514 for performing the rough division of the shape model M. Another method may also be employed so long as the shape model M is divided into convex bodies. The thus obtained division models M1, M2, M3 do not have to be the set of the complete convex bodies. The mesh generation region may be extracted in the subsequent process even if the body has shape including the concave part.
Referring to the process flow shown in
In step S53 of the flowchart in
The tetrahedral mesh to be deleted in the process executed in step S53 is assumed to satisfy the following three conditions.
In step S54 as shown in
The hexahedral mesh generation section 105 generates the hexahedral mesh for the mesh generation region data D2 output from the mesh generation region extraction section 104 based on the mesh size D4 input through the mesh size input section 103.
Arbitrary method may be employed for generating the hexahedral mesh. It is possible to automatically generate the hexahedral mesh for the mesh generation region D2 defined as the triangle set through the method disclosed in Japanese Patent Application Laid-Open No. 2002-245098, and the literature titled “Automatic hexahedral mesh generation system using feature line extraction technique” (Proceedings of the Japan Society of Mechanical Engineers, issue 71, No. 701, edition A, pp. 9-15). A hexahedral mesh 205 may be automatically generated for a mesh generation region 204 as shown in
As described above, the first embodiment of the present invention allows automatic extraction of the analytical mesh generation region from the analytical subject shape model. It is possible to automatically generate the hexahedral mesh with its size equal to or larger than the specified size in the end. This makes it possible to execute the analytical mesh generation operation conventionally demanding time and labor with higher efficiency.
The system structure of the analytical mesh generation device according to a second embodiment is similar to that of the analytical mesh generation device of the first embodiment. This embodiment describes use of the hexahedral mesh generated by the mesh generation region extraction section 104.
In the first embodiment, the tetrahedral mesh is generated first, and in the second embodiment, the hexahedral mesh is generated first. In other words, the first and the second embodiment describe generation of the polyhedral mesh which is exemplified by the tetrahedral mesh and the hexahedral mesh, respectively. The effects derived from the mesh generation region extraction section 104 and the hexahedral mesh generation section 105 become different from each other. Accordingly, the different feature will only be described.
The mesh generation region extraction section 104 according to the second embodiment receives the shape model data D1 of the analytical subject, and the mesh size D4, and outputs the hexahedral mesh as the mesh generation region data D2.
Referring to the process flow according to the second embodiment, in step 692, the hexahedral mesh is generated for the shape model M or those M1, M2, M3 derived from rough division. In the first embodiment, the tetrahedral mesh is generated first as shown in
The hexahedral mesh may be generated through arbitrary method. For example, it is possible to automatically generate the hexahedral mesh by subjecting the triangle mesh generated for the shape model M to the process as disclosed in Japanese Patent Application Laid-Open No. 2002-245098, and the literature titled “Automatic hexahedral mesh generation system using feature line extraction technique” (Proceedings of The Japan Society of Mechanical Engineers, issue 71, No. 701, edition A, pp. 9-15).
In the next step S93, the mesh with its thickness equal to or smaller than the mesh size is deleted from the generated hexahedral mesh. The mesh thickness is defined as the minimum distance between the reference element surface and the element surface on the shape surface derived from sequential search of the opposing surface of the hexahedral mesh until it reaches the element surface on the shape surface by taking the element surface of the hexahedral mesh on the shape surface as the reference (reference element surface).
In the aforementioned example, it is assumed that the mesh size D4 input through the mesh size input section 103 is 5 mm. In this case, the mesh having the element thickness of 5 mm or smaller will be deleted. The hexahedral mesh subjected to the search from the reference element surface 1005 to the element surface 1006 of the hexahedral mesh 1003 is expected to be deleted. That is, the hexahedral mesh 1003 is deleted. As the search distance from the reference element surface 1007 to the element surface 1008 is 5 mm or longer, the hexahedral mesh 1004 is not deleted. As a result, only the hexahedral mesh 1004 is obtained. The model constituted by the hexahedral meshes 1003 and 1004 is regenerated as the simplified model constituted only by the hexahedral mesh 1004.
The hexahedral mesh set remained after execution of the aforementioned process is determined, as the region which allows generation of the hexahedral mesh with its size equal to or larger than the mesh size input through the mesh size input section 103, and set as the mesh generation region data D2.
In step S94, the hexahedral mesh remained after execution of the process in step S53 is output as the mesh generation region data D2.
The hexahedral mesh generation section 105 as shown. in
The hexahedral mesh 1004 as shown in
Only the length 1102 of the element side is smaller than 5 mm, and the lengths 1103 and 1104 are longer than 5 mm. In this case, the length 1102 of the element side is designated as the subject. The element surface of the mesh including any of a plurality of lengths 1102 is subjected to degradation to generate the prism mesh so that the length of the element side is longer than the mesh size of 5 mm.
In this embodiment, three meshes are shown as a plurality of element side lengths 1102. The correction is made by selecting the center mesh preferentially rather than the one at the end so that the element side to be generated resulting from degradation of the element surface is positioned at the center. As a result, the mesh is corrected to the one as indicated by 1108. The element side length of the part, which has been measured 4.4 mm before correction becomes 6.6 mm. It is possible to generate the hexahedral mesh with its size equal to or larger than the mesh size D4. In the case where there is only the mesh located at the end, degradation of the element surface is conducted so that the element side that is not located at the end is coincided with the end. This makes it possible to generate the hexahedral mesh with its size equal to or larger than the mesh size D4.
According to the second embodiment of the present invention, the region where the mesh smaller than the specified size is generated may be deleted from the hexahedral mesh generated for the analytical subject shape model. The function for correcting the mesh to be equal to or smaller than the specified size may also be added. This finally makes it possible to automatically generate the hexahedral mesh with its size equal to or larger than the specified size. As a result, the analytical mesh generation conventionally demanding time and labor may be conducted with higher efficiency.
MB: tetrahedral mesh
Number | Date | Country | Kind |
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2015-115539 | Jun 2015 | JP | national |