Abstract:
An analytical shell-model producing apparatus for converting a three-dimensional model into internal surfaces, wherein an internal surface is used to represent each three-dimensional element of the three-dimensional model. Each internal surface comprises a bounded plane and an associated width attribute, wherein the bounded plane is located internal to the three-dimensional element which it represents, and wherein the associated width attribute represents the width of the three-dimensional element in a direction normal to the bounded plane.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an analytical shell-model producing apparatus for producing a shell-model for use in analyzing from a solid-state model of a thin-plate structure, and it relates to, in particular, the analytical shell-model producing apparatus, being suitable to be used in a CAE (Computer Aided Engineering) for simulating physical phenomenon by means of numerical values, through the numerical analysis with using a computer. 
   In the numerical analysis, being represented by, such as, the finite-element method, for example, a model is made up with aggregation of elements, such as, a hexahedron and/or a tetrahedron, for example, as the material to be a target of analyzing (i.e., an analysis target). Also, in a case where the target material of analyzing has a thin-plate structure, a load on computing thereof can be reduced by utilizing a tetragon element and/or a triangle element, to which is given thickness as an attribute value thereof. When using a three(3)-dimensional CAD system, since a material (i.e., a configuration model) was already produced as for the analysis target, therefore even the configuration model of the thin-plate structure is defined to be a solid having thickness. 
   Conventionally, in a method for producing such a shell-model for use in analyzing from the solid-model of thin-plate structure, as is described in Japanese Patent Laying-Open No. Hei 6-259505 (1994) &lt;JP-A 6-259505&gt;, for example, a thin plate-like configuration portion is designated as the configuration model to be the target of numerical analysis, and then a surface is extracted, which has a geometric feature of being parallel to the surface, among surfaces connecting to the configuration designated. The surfaces, being in parallel with the surface extracted and also being shortest in the distance therebetween, are specified as a pair, and a medial-surface is produced with respect to the pair of surfaces, thereby producing the analysis model. 
   Also as one of other methods, being described in Japanese Patent Laying-Open No. 2002-207777 (2002) &lt;JP-A 2002-207777&gt;, for example, a hollow mesh model having a two(2)-layer structure is produced for the configuration model to be the target of numerical analysis. And, upon basis of a moving vector set up upon the shape, it is moved while deciding whether a node of the model is in contact with or not, on an element opposing thereto. With this, the nodes of the model are gathered at a neutral point, thereby producing a neutral surface model. However, the neutral surface indicates a surface, being a thin plate-like and located at a neutral position, and it is an equivalent of the shell-model for use in analyzing. 
   However, in the method for producing the shell-model for use in analyzing, which is described in the Japanese Patent Laying-Open No. Hei 6-259505, for example, since an operator must give an instruction to the thin film-like configuration part, and also only the surface contacting in parallel with the configuration instructed comes to be a target of producing the neutral surface, the operator must give instructions a number of times to that configuration, in particular, if it is a complicated configuration model, and/or a configuration having a rib, for example, and therefore it is not easy to produce the shell model for use in analyzing. 
   Also, in the method for producing the shell-model for use in analyzing, which is described in the Japanese Patent Laying-Open No. 2002-207777, for example, since the medial-surface model is not produced in the form of the configuration model, but in that of the configuration model, it is necessary to re-produce the configuration model from the mesh data when changing the configuration, such as, for the purpose of parameter survey, etc. Also, sometimes there are cases where the configuration model cannot be produced if trying to produce it again, since the configuration is too complicated. 
   BRIEF SUMMARY OF THE INVENTION 
   An object, according to the present invention, is to provide an analysis shell-model producing apparatus, being able to produce a shell-model for use in analyzing, with ease and in the form of the configuration model. 
   For accomplishing the object mentioned above, according to the present invention, there is provided an analytical shell-model producing apparatus for producing an analytical shell-model to be use in numerical analyzing, for a configuration model, which is produced by a three-dimensional configuration modeler, comprising: a reference-plate thickness inputting means for inputting a reference-plate thickness size to be used when specifying a thin-plate portion from the configuration model; a pair-surfaces acknowledging means for acknowledging two (2) surfaces, being equal or less than the reference-plate thickness size, which is inputted by said reference-plate thickness inputting means, in face-to-face distance between the arbitrary two (2) surfaces constructing the configuration model; a top/bottom side rib attribute acknowledging means for acknowledging the pair of surfaces acknowledged by said pair surface acknowledging means to be one of a top side surface, a bottom side surface, and a rib surface; an offset-surface producing means for producing an offset-surface by offsetting a group of surfaces of either the top or the bottom side, which are acknowledged by said top/bottom side rib attribute acknowledging means, and the rib surface, respectively, in direction of a normal line directing in an inside of the configurations thereof; a seam-surface producing means for seaming between the offset-surface, which is produced from either the top or the bottom surface by means of said offset-surface producing means, and the offset-surface produced from the rib surface; and an internal-surface producing means for registering the offset-surface seamed by said seam-surface producing means, as in a form of an internal-surface model. With this apparatus, it is easy to produce an analytical shell-model from a configuration model. 
   Preferably, according to the present invention, there is also provided the analytical shell-model producing apparatus, as described in the above, further comprising a top/bottom rib attribute emphatic displaying means for displaying the top side surface, the bottom side surface and the rib surface, which are acknowledged by said top/bottom side rib attribute acknowledging means, with making emphasis thereon, or further comprising a dialog top/bottom side rib attribute amending means for amending the top side surface, the bottom side surface and the rib surface, which, are acknowledged by said top/bottom side rib attribute acknowledging means, in a manner of dialog, or wherein said internal-surface model producing means calculates the plate thickness on each of the internal-surface models as targets from the face-to-face distance between two (2) surfaces of the pair, to which a composite surface of the configuration model belongs, being as an original for producing the each internal-surface model, thereby giving this plate thickness value as to be the thickness attribute of the internal-surface model of target. 
   Further, according to the present invention, for accomplishing other object mentioned above, there is provided an analytical shell-model producing apparatus, for producing an analytical shell-model for use in numerical analyzing from a configuration model, which is produced by a three-dimensional configuration modeler, comprising: a reference-plate thickness size inputting means for inputting a reference-plate thickness size to be used when specifying a thin-plate portion from the configuration model; and means for making two (2) surfaces, being narrower therebetween than the reference-plate thickness size, which is inputted from said reference-plate thickness inputting means, in a pair of surfaces, producing an offset-surface between the pair of surfaces, and producing an internal-surface model by seaming on an outer periphery portion of the offset-surface. 
   Moreover, according to the present invention, for accomplishing other object mentioned above, there is provided an analytical shell-model producing apparatus, for producing an analytical shell-model for use in numerical analyzing from a configuration model, which is produced by a three-dimensional configuration modeler, comprising: a reference-plate thickness size inputting means for inputting a reference-plate thickness size to be used when specifying a thin-plate portion from the configuration model; and means for producing a thickness attribute of said internal-surface model from face-to-face distance between the surfaces of said pair and a value of the plate thickness. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a system structure view of an embodiment of an analysis shell-model producing apparatus, according to the present invention; and  FIGS. 2 to 17  are views for explaining functions of various parts of the analytical shell-model producing apparatus shown in  FIG. 1 , and in particular, 
       FIG. 2  is a view of a size-designation screen for thickness of a reference plate, in a reference plate thickness size-designation portion; 
       FIGS. 3 and 4  are views for showing a flowchart of processing of pair-surface acknowledging, and for explaining the pair-surface acknowledging process by means of a pair-surface acknowledging portion; 
       FIGS. 5 and 6  are views for showing a flowchart of processing for acknowledging a rib by means of a top/bottom side rib acknowledging portion, and for explaining the acknowledge processing of the rib; 
       FIGS. 7 to 9  are views for explaining a neighboring graph, which is used in the rib acknowledging process by means of the top/bottom side rib acknowledging portion, a flowchart of the top/bottom side rib acknowledging process, and the top/bottom side rib acknowledging, respectively; 
       FIGS. 10 and 11  are views for showing a flowchart of the processing for producing offset-surface by means of an offset-surface producing portion, and for explaining the offset-surface producing process; 
       FIGS. 12(A) and 12(B)  are views for explaining the offset-surface producing process by means of a seam-surface producing portion; 
       FIGS. 13(A) to 13(D)  are views for explaining an emphatic displaying process on the top/bottom side rib attribute, by means of a top/bottom side rib attribute emphatic displaying portion; 
       FIGS. 14 to 16  are views for showing amending processing with using a dialog top/bottom side rib attribute amending portion, and in particular,  FIG. 14  is a view for showing the amending processing of the top/bottom side rib attribute, and  FIGS. 15(A)  to  FIG. 16(C)  are views for explaining the amending process of the top/bottom side rib attribute, in more details thereof; and 
       FIG. 17  is a view for explaining an internal-surface model, which is displayed by an internal-surface model displaying portion. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, explanation will be given about the structure and operation of an analytical shell-model producing apparatus, according to one embodiment of the present invention, by referring to  FIGS. 1 to 17 . Herein,  FIG. 1  is a view for showing the system structure of the analytical shell-model producing apparatus. The analytical shell-model producing apparatus, according to the present embodiment, comprises an input/output device  101 , a reference plate thickness designating portion  105 , a pair-surface acknowledging portion  107 , a top/bottom side rib attribute acknowledging portion  109 , an offset-surface producing portion  111 , a seam-surface producing portion  113 , an internal-surface model producing portion  115 , a top/bottom side rib attribute emphatic displaying portion  116 , a dialog top/bottom side rib attribute amending portion  117 , and an internal-surface model displaying portion  118 . 
   The input/output portion  101  is used for a system user to make an input therewith or a display thereon, and it comprises a keyboard, a pointing device, and/or a display, etc. A configuration model inputting portion  103  inputs a configuration model therewith, and it also registers it in the form of a configuration model data  102 . 
   The reference-plate thickness designating portion  105  inputs a size of reference-place thickness, for acknowledging as a thin-plate portion from the configuration model, and then registers this reference-plate thickness size as in the form of a reference-plate thickness size data  104 . An example of the reference-plate thickness designation portion  105  will be mentioned by referring to  FIG. 2 , later. 
   The pair-surface acknowledge portion  107  acknowledges two (2) surfaces as a pair of surfaces from arbitrary two (2) surfaces building up the configuration model data  102 , which is equal or less than the reference-plate thickness size data  104  in the face-to-face distance between those surfaces, and then registers it in the form of a pair-surface data  106 . A method for acknowledging the pair-surface by means of the pair-surface acknowledging portion  107  will be mentioned later. 
   The top/bottom side rib attribute acknowledging portion  109  acknowledges a top-side surface, a bottom-side surface and also a rib surface from the configuration model data  102  and the pair-surface data  106 , and registers them as in the form of a top/bottom side rib attribute data  108 . The offset-surface producing portion  111  produces offset-surfaces, offsetting one of the surface groups, i.e., the top-side surfaces or the bottom-side surfaces, in a direction of the normal line directing into an inside of each of the configuration thereof, and then registers them as in the form of an offset-surface data  110 . 
   The seam-surface producing portion  113  produces a seam-surface, which seams between the offset-surface data  110  produced from either the top or bottom surface and also the offset-surface data  110  produced from the rib surface, and then registers it as in the form of a seam-surface data  112 . The internal-surface model producing portion  115  registers the seam-surface data  112  as in the form of internal-surface model data  114 . In addition to the seam-surface data, a value of plate thickness of the each target internal-surface model is calculated from the face-to-face distance between the surfaces in the pair-surface data  106 , to which the component surface of the configuration model belongs, being an original of each internal-surface model, and then this plate thickness value is given as a thickness attribute of the target internal-surface model. 
   The top/bottom side rib attribute emphatic displaying portion  116  displays the surface, which is registered in the top/bottom side rib attribution data  108 , on a display of the input/output device  101  with making emphasis thereon. An example of the emphatic display by means of the top/bottom side rib attribute emphatic displaying portion  116  will be mentioned by referring to  FIGS. 13(A) to 13(D) , later. The dialog top/bottom side rib attribute amending portion  117  amends the top/bottom side rib attribute data  108 , by using the input/output device  101 . 
   The internal-surface model producing portion  118  displays the internal-surface model stored in the internal-surface model data  114  on the display of the input/output device  101 . The internal-surface model is data of the three-dimensional model, being same to the configuration data (a solid model), such as, the CAD data, for example. 
   By referring to  FIG. 2  will be explained a method for designating the reference-plate thickness size by means of the reference-plate thickness size designating portion  105  of the analytical shell-model producing apparatus.  FIG. 2  is a view of the screen structure of a screen designated for the reference-plate thickness size by means of the reference-plate thickness size designating portion  105 . The reference-plate thickness size designating portion  105  displays an operation screen for the purpose of designation of the reference-plate thickness size, as shown in  FIG. 2 , on the display of the input/output device  101 . A user of the apparatus inputs the size of the reference-plate thickness, for acknowledging to be the thin-plate portion, into the reference-plate thickness size inputting field  201  on the operation screen, by using the input/output device  101 . 
   The size of the reference-plate in the thickness thereof is the thickness size to be referred as a reference for deciding the thin portion among the configuration model data. For example, if there are places where the plate thickness is defined to be 2 mm, 3 mm, and 5 mm, and if it is desired to determine such the potions to be the thin-plate portion, for example, the maximum value among them, i.e., 5 mm is inputted into the reference-plate thickness size inputting field  201 , for example. When the user of the apparatus pushes an execute button  202 , the numerical data inputted in the reference-plate thickness size inputting field  201  is registered into the reference-plate thickness size data  104 . Or if pushing a cancel button  203 , the designation will be released. 
   Explanation will be given on the processing in the pair-surface acknowledging process by means of the pair-surface acknowledge portion  107 , in the analysis shell-model producing apparatus, by referring to  FIGS. 3 and 4 . Herein,  FIG. 3  is a flowchart for showing the processing by means of the pair-surface acknowledging portion  107 .  FIG. 4  is an explanatory view of the pair-surface acknowledging process by means of the pair-surface acknowledging portion  107 . 
   In a step s 301 , the pair-surface acknowledging portion  107  reads therein the configuration model data  102  and the reference-plate thickness size data  104 . In a step s 304 , two (2) surfaces (i.e., the surface A and the surface B) are selected, sequentially, from all of the surfaces constructing the configuration model data  102 , and determines whether an angle defined by those surfaces A and B is smaller than a predetermined angle α or not. It is assumed that the predetermined angle α is 30 degree, for example. If being equal or less than the predetermined angle α, they can be determined to be the surfaces being parallel to each other or the surface formed with a taper thereon, and then the process advances to a step s 303 . If not, it jumps to a step s 306 . 
   In the case when the angle defined between the surfaces A and B is equal or less than the angle α, the face-to-face distance is calculated out between those two (2) surfaces, in a step s 303 . In a step s 304 , this face-to-face distance is compared to the reference-surface thickness size data  104 , and if the face-to-face distance between those surfaces is smaller than the reference-surface thickness size data  104 , then those two (2) surfaces are determined to the pair-surface in a step s 305 . For example, with respect to the configuration model shown in  FIG. 4 , if the reference-plate thickness size is designated to be 5 mm, for example, then the surfaces; i.e., (surface  401 )-(surface  402 ), (surface  403 )-(surface  404 ), and (surface  405 )-(surface  406 ) are the pair-surfaces. Herein, wave-like broken lines indicating the surfaces  402 ,  404  and  406  show the surfaces on the bottom side. Thus, the surface  402  is the surface opposing to the surface  401 , the surface  404  opposing to the surface  403 , and the surface  406  opposing to the surface  405 . 
   In the step s 305 , the processes in the above steps s 302 -s 305  are repeated on all of the surfaces A. For example, if the surface  401  is selected to be the surface A, while the surface  402  to be the surface B, in  FIG. 4 , then the surfaces  403 ,  404 ,  405  and  406  are changed sequentially to be as the surfaces A while keeping the surfaces B fixed, and the pair-surface is selected, judging from viewpoints of the angle defined between the surfaces each other and the face-to-face distance of surfaces. 
   In a step s 306 , the similar processing to that in the step s  305  is repeated. However, in this step s 306 , the processing is made on all of the surfaces B. Namely, it is assumed that the surface  401  is selected to be the surface A and the surface  402  to be the surface B, in  FIG. 4 . Then, in this step s 306 , after selecting the pair-surfaces from the angle defined between the surfaces each other and the face-to-face distance therebetween, by changing the surfaces  403 ,  404 ,  405  and  406 , sequentially, into the surface A, then the pair-surface is selected from the angle defined between the surfaces each other and the face-to-face distance therebetween, while changing the surfaces  403 ,  404 ,  405 ,  406  and  401 , sequentially, into the surface B. With doing this, a mutual relationship can be checked on all of the surfaces shown in  FIG. 4 , and thereby enabling detection of all the pair-surfaces, without omitting. 
   Explanation will be given about the processing in the acknowledging process, on the top and bottom sides and also the rib, by means of the top/bottom side rib acknowledging portion  109  in the analytical shell model producing apparatus, by referring to  FIGS. 5 to 9 . By using  FIGS. 5 to 7 , the processing in the acknowledging process on the rib, by means of top/bottom side rib acknowledging portion  109  will be explained. Herein,  FIG. 5  is a flowchart for showing the processing in the acknowledging process on the rib, by means of the top/bottom side rib acknowledging portion  109 .  FIG. 6  is an explanatory view for the acknowledging process on the rib, by means of the top/bottom side rib acknowledging portion  109 . And,  FIG. 7  is an explanatory view of a neighboring graph, which is used in the rib acknowledging process by means of the top/bottom side rib-acknowledging portion  109 . 
   In a step s 501  shown in  FIG. 5 , the top/bottom side rib acknowledging portion  109  produces a graph, in which nodes to the surfaces neighboring with each other are connected with each other at edges thereof, assuming the surface to be a node, for the configuration model data  102 . This graph is called by “neighboring graph”, hereinafter.  FIG. 7  shows the neighboring graph with respect to the configuration model shown in  FIG. 6 . 
   In the configuration model shown in  FIG. 6 , the surfaces, i.e., (surface  601 )-(surface  603 )-(surface  605 )-(surface  607 ), are neighboring with each other, respectively, therefore (node  601 )-(node  603 )-(node  605 )-(node  607 ) shown in  FIG. 7  are connected with each other at the edges thereof. Herein, a character “neighboring” is attached on a side of the edge, and thereby indicating that both nodes are in a relationship of the surfaces neighboring with each other. Also, the surfaces, i.e., (surface  602 )-(surface  604 )-(surface  606 )-(surface  608 ) shown in  FIG. 6 , are neighboring with each other, respectively, and therefore they are the nodes, i.e., (node  602 )-(node  604 )-(node  606 )-(node  608 ) shown in  FIG. 7 , and are connected with, at neighboring edges thereof. Further, since the surface  609  is also neighboring with the surfaces  603  and  605 , then the node  609  is connected with the nodes  603  and  605  at the neighboring edges thereof. Also, since the surface  601  is neighboring with the surfaces  603  and  605 , the node  610  is connected with the nodes  603  and  605  at the neighboring edges thereof. 
   In a step s 502 , for this neighboring graph, the surfaces are connected at the edges thereof, which are in a relationship of the pair-surface. In the configuration model shown in  FIG. 6 , the surfaces, i.e., (surface  601 )-(surface  602 ) constitute the pair-surface, and therefore the nodes, i.e., (node  601 )-(node  602 ) in  FIG. 7  are connected at the edges thereof. Herein, the character “pair” is attached on a side of the edge, and it indicates that both nodes are in relationship of the pair-surface between them. In the similar manner, the surfaces, i.e., (surface  601 )-(surface  602 ), (surface  603 )-(surface  604 ), (surface  605 )-(surface  606 ), (surface  607 )-(surface  608 ), and (surface  609 )-(surface  610 ), constitute the pair-surfaces, respectively, and then they are connected with at pair-edges. 
   In a step s 503 , search is conducted on a loop from the neighboring graph, including at least two (2) or more of the edges of pair attributes. For the loop, since there is a condition that it includes at least two (2) or more pair attributes, the loop made up with the nodes, i.e., (node  601 )-(node  602 )-(node  604 )-(node  603 ), is that which is searched out. On the other hand, the loop made up with the nodes, i.e., (node  609 )-(node  603 )-(node  605 )-(node  610 ), contains only one pair attribute, therefore it comes off from the loops to be the searching target. However, the loop made up with the nodes, i.e., (node  9 )-(node  603 )-(node  604 )-(node  606 )-(node  605 )-(node  610 ), includes two (2) pair attributes therein, therefore it comes to be the target of the searching. 
   In a step s 504 , calculation is made on the number of the nodes, which lie within this loop. In a step s 505 , a determination is made on whether the number of pieces of the nodes is less than five (5) or not. If the number of pieces of the nodes is less than five (5), the nodes within the loop are determined to have the rib attribute in a step s 506 . If the number of pieces of the nodes is equal to five (5) or more, the nodes within the loop are determined to have no such the rib attribute in a step s 507 . 
   For example, in the configuration model shown in  FIG. 6 , the number of nodes is less than five (5) lying within the loop &lt;&lt; 601 - 602 - 604 - 603 &gt;&gt;, and then it is decided to be “not the rib”. And, a flag, “not the rib” is attached to the surfaces  601 ,  602 ,  603  and  604 . On the other hand, the number pieces of the nodes exceeds for (4) laying within the loop &lt;&lt; 609 - 610 - 605 - 606 - 604 - 603 &gt;&gt;, then the process advances to the step s 507 . 
   In the step s 507 , the processes in the steps s 505  and s 506  mentioned above are executed on all of the loops. The surface that was not determined to be “not the rib”, i.e., that not attached with the flag “not the rib” is determined to be the “rib”, in a step s 508 . For example, within the loop &lt;&lt; 609 - 610 - 605 - 606 - 604 - 603 &gt;&gt;, since the surfaces  603 ,  604 ,  605  and  606  are determined to not the rib, therefore it is determined that the surfaces  609  and  610  are the ribs. 
   Explanation will be given on the processing of the acknowledging process on the top/bottom side surface, by means of the top/bottom sided rib acknowledging portion  109  in the analytical shell-model producing apparatus, by referring to  FIGS. 8 and 9 .  FIG. 8  is a flowchart for showing the processing of the acknowledging process on the top/bottom side surface, by means of the two-sided rib acknowledge portion  109 .  FIG. 9  is a view for explaining the acknowledging process on the top/bottom side surface, by means of the two-sided rib acknowledge portion  109 . 
   In a step s 801 , the top/bottom rib acknowledge portion  109  makes a grouping on the surfaces, which are themselves in the neighboring relationship, for each of the pair-surfaces that are not acknowledged to be the rib. For example, in  FIG. 9 , the respective surfaces  901 ,  902 ,  903  and  904  are not in such the neighboring relationship therebetween therefore they are grouped in the flowing manner, thereby to be included into the independent groups, respectively: 
   Group  1 : the surface  901 ; 
   Group  2 : the surface  902 ; 
   Group  3 : the surface  903 ; and 
   Group  4 : the surface  904 . 
   In a step s 802 , if the groups are equal or more than two (2) in pieces thereof, an arbitrary one of the group is extracted from all of the groups, and then the surfaces are combined with each other, which are in the relationship of the pair, thereby to be unified into one group, for each of the surfaces included in that group. In an example shown in  FIG. 9  mentioned above, for example, the surface  901  is in the pair with the surface  903  of the group  3 , and the surface  902  is also in the pair, then the surfaces  901  and  902  are unified together. In the similar manner, since the surface  903  is also in the pair with the surface  902  of the group  3 , and the surface  904  is also in the pair, then the surfaces  903  and  904  are unified with each other. As a result of this, i.e., repeating this unifying of the groups in accordance with the relationships of the pairs, the groups are as follows: 
   Group  1 : the surface  901  and the surface  902 ; and 
   Group  2 : the surface  903  and the surface  904 . 
   In a step s 803 , the process of the step s 802  is repeated on all of the groups. Further, in a step s 804 , it is repeated until when the number of the groups comes down to be two (2), remaining as a result of the unifying. When the group comes down to two (2) in the number of pieces thereof, then the group of surfaces in one group is made to be a top side surface, while that of the other group a bottom side surface. For example, in the example mentioned above, it is as follows: 
   Top side surface: the surface  901  and the surface  902 ; and 
   Bottom side surface: the surface  903  and the surface  904 . 
   Explanation will be given on the processing of the offset-surface producing process, by means of the offset-surface producing portion in the analytical shell-model producing apparatus, by referring to  FIGS. 10 and 11 . Herein,  FIG. 10  is a flowchart for showing the processing of the offset-surface producing process, by means of the offset-surface producing portion  111  in the analytical shell-model producing apparatus.  FIG. 11  is a view for explaining the offset-surface producing process, by means of the offset-surface producing portion  111  in the analytical shell-model producing apparatus. 
   In a step s 1101  in  FIG. 10 , the offset-surface producing portion  111  takes either the top or the bottom side surface, as to be a target of the offset-surface. Though it is possible to automatically determine this offset-surface on the apparatus side, but it is also possible to determine through designation on which side surface should be the target, by an operator. For example, in  FIG. 11 , the surface  601  is selected to be the target of the offset-surface if assuming the surfaces  601  and  602  form the pair-surfaces. 
   In a step s 1102 , a surface is produced, being offset in the direction of the normal line directing into an inside of a solid, while keeping the target surface of offsetting in a relationship with the surface. The CAD data, as to be the configuration data, has information in the solid, therefore it is possible to determine the inside direction of the solid by means of this CAD data. Herein, an amount of the offsetting is assumed to be ½ of the face-to-face distance between the surfaces, which form the pair. Further, if the face-to-face distance is changed, gradually, between the surfaces thereof, such as, in the case of the tapered surface, for example, it is determined to be ½ of an averaged value thereof. Regarding such the tapered surface, it may be determined to be ½ of the maximum value or the minimum value of the face-to-face distance between the surfaces. In this manner, in the example shown in  FIG. 11 , it is possible to obtain the offset-surface  1101  with respect to the surfaces  601  and  602 . 
   In a step s 1103 , the process of the step s 1003  is executed on the rib surface, in the similar manner, thereby producing the offset-surface of the rib. Hereinafter, the offset-surface produced from either the top or the bottom side surface is called by a “general offset-surface”, while the offset-surface produced from the rib is called by a “rib offset-surface”. In  FIG. 11 , the general offset-surfaces are the surfaces  1101 ,  1102 ,  1103  and  1104 , and the rib offset-surface is the surface  1105 , in the configuration model shown by broken lines. 
   Explanation will be given on the processing of the seam-surface producing process, by means of the seam-surface producing portion  113  in the analytical shell-model producing apparatus, by referring to  FIGS. 12(A) and 12(B) . As was shown in  FIG. 11 , on the configuration having the rib therein, the rib offset-surface and the general offset-surface are separated from. Then, the seam-surface producing portion  113  elongates the rib offset-surface to the general offset-surface, thereby treating the processing for seaming them together and registering as in the form of a seam-surface. 
   With respect to the offset-surface  1201  shown in  FIG. 12(A) , lines  1202  and  1203  are elongated up to the general offset-surface, thereby connecting between the general offset-surface and the rib offset-surface. A result of this is as shown in  FIG. 12(B) . As is shown in  FIGS. 12(A) and 12(B) , the surface  1201  is constructed with four (4) lines (sides), in general. Since one side of the surface  1201  can be defined by two control points C 1  and C 2  at both ends and a control point C 3  at a middle portion thereof, first the points C 1 , C 2  and C 3  are elongated up to the general offset-surface  1204 , thereby determining control points C 1   a , C 2   a  and C 3   a . Though it is also possible to define the second side of the surface  1202  by the control points C 2  and C 4  on both sides and the control point C 5  at a middle portion thereof, however since a new control point C 2   a  is defined newly, the control points C 2   a , C 4  and C 5  are elongated up to the general offset-surface  1205 , thereby determining control points C 2   b , C 4   b  and C 5   b . With this, the sides of the surfaces  1201  and  1202  are elongated up to the sides  1201   a  and  1202   a , to form a new surface, thereby combining the general offset-surface and the rib offset-surface together. 
   Hereinafter, explanation will be given on the processing of the internal-surface model producing process, by means of the internal-surface model producing portion  115 . The internal-surface model producing portion  115  registers the seam-surface, which is produced in the seam-surface producing process by means of the seam-surface producing process portion  113 , in the form of the internal-surface model data  114 . Next, search is made on the pair-surfaces, to which belongs the component surface of the configuration model, being the original, from which this internal-surface model is offset as the offset-surface, for each of the internal-surface models. In the example shown in  FIG. 11 , the surfaces  601  and  602  are searched out as the pair-surfaces, to which this offset-surface belongs, for the offset-surface  1101 . 
   The face-to-face distance between the two (2) surfaces, which are registered in that pair-surfaces is calculated out, and the internal-surface model data  114  is given with this face-to-face distance between the surfaces, as an attribute of thickness of the target internal-surface model. Herein, if the pair-surfaces are in a plural number thereof, which belong thereto, an averaged value of the face-to-face distances between the surfaces is given as the thickness attribute, or the minimum one or the maximum one. Also, for the pair-surfaces having a tapered surface, being not constant in the face-to-face distance therebetween, changes in the thickness are given to the internal-surface model, distributedly. Also, the thickness attribute given to the each internal-surface model is automatically distributed to each element when producing a mesh. 
   Explanation will be given on the processing of emphatic displaying process of the top/bottom side rib attribute, by means of the tip/bottom side rib attribute emphatic displaying portion  116 , by referring to  FIGS. 13(A) and 13(B) . The top/bottom side rib attribute emphatic displaying portion  116  displays a display screen emphasized, as is shown in  FIG. 13(A) , on the input/output device  101 . The user of the apparatus selects an attribute, which she/he wishes to display with making emphasis thereon, on an operation screen shown in  FIG. 13(A) , by using the input/output device  101 . When wishing to display the top side surface, she/he selects a top side surface display button  1301 , while when wishing to display the bottom side surface, a bottom side surface display button  1302 , and when wishing to display the rib surface, a rib surface display button  1303 . 
   The top/bottom side rib attribute emphatic displaying portion  116  searches a surface, which is coincident with in the attribute, among the top/bottom side rib attribute data  108 , and displays the surface, being coincident with in the search, on the screen with making emphasis thereon, as shown in  FIGS. 13(B) ,  13  (C) and  13 (D). For example, when the top side display button  1301  is selected, it is displayed in a manner as is shown in  FIG. 13(B) . When the bottom side surface display button  1302  is selected, it is displayed in a manner as is shown in  FIG. 13(C) . And, if the rib surface display button  1303  is selected, it is displayed in a manner as is shown in  FIG. 13(D) . 
   Explanation will be given on the processing of amending process of the top/bottom side rib attribute, which is conducted by means of the dialog top/bottom side rib attribute amending portion  117  in the producing apparatus, by referring to  FIG. 14 . As is shown in  FIG. 14 , on the screen of the input/output device  101 , there is displayed a perspective view of the solid model in the right-hand side, while selection buttons are disposed, such as, a top side surface selection button  1401 , a bottom side surface selection button  1402 , and a rib surface selection button  1403 , for example, on an operation screen disposed in the left-hand side. The user of the apparatus selects the surface, on which she/he wishes to make an amendment on the operation screen of the input/output apparatus  101 . Next, the attribute after making the amendment therein is selected among those selection buttons  1401 - 1403 . Finally, at the time when an execution button  1404  is pushed, the top/bottom side rib attribute being amended is registered into the top/bottom side rib attribute data  108 . Or, if a cancel button  1405  is pushed down, the designation is released. 
   Explanation will be given on the processing as a whole of producing an analytical process model, while using examples in more details thereof, by referring to  FIGS. 15-17 . Herein,  FIGS. 15 and 16  are detailed explanatory views of the amending process on the top/bottom side rib attribute, by means of the dialog top/bottom side rib attribute amending portion  117 . And,  FIG. 17  is a view for explaining the internal surface model, which is displayed by means of the internal-surface model displaying portion  118 . 
   In the case of producing the analytical shell-model of a housing portion, as shown in  FIG. 15(A) , the user of the apparatus designates the reference-plate thickness size of the housing portion  1501 . The thickness of this model is 3-5 mm, for example, it is designated to be 5 mm, herein. Then, the pair-surfaces are acknowledged by means of the pair-surface acknowledging portion  107 , while the top/bottom side rib attribute is acknowledged by means of the top/bottom side rib attribute acknowledging portion  109 , and the data acknowledged are stored into the top/bottom side rib attribute data  108 . A meshed portion (i.e., actually, being displayed by changing the color thereof on the display) shown in  FIG. 15(B)  displays the top side surface, while that shown in  FIG. 15(C)  the bottom side surface, and  FIG. 15(D)  the rib surface, for example. 
   Herein, since the rib between the surfaces  1505  and  1506  is a small or minute rib, and if it is not desired to be acknowledged to be the rib, then the rib surface attribute can be released, by pushing the cancel button with designating the surface  1506  under the condition of the display shown in  FIG. 15(D) , with using the dialog top/bottom side rib attribute amending portion  117 . Further, that case of not desiring to acknowledged it to be the rib is, for example, when it is the small or minute rib, so that no ill influence will be given on intensity if not acknowledging it to be the rib; such as, a small projection, for example. Not acknowledging this portion to be the rib enables reduction in the number of the meshes, and thereby shortening the time for strength analyzing, as well. 
     FIGS. 16(A)-16(C)  show the attribute amended by means of the dialog top/bottom side rib amending portion  117 .  FIG. 16(A)  displays the top side surface,  FIG. 16(B)  the bottom side surface, and  FIG. 16(C)  the rib surface, for example. The offset-surface producing portion  111  produces the offset-surface data. In the example in  FIGS. 16(A)-16(C) , the bottom side surface shown, in particular, shown in  FIG. 16(B) , is the offset target surface. Next, the seam-surface is produced by the seam-surface producing portion  113 , and the internal-surface model data  114  is outputted by means of the internal-surface model producing portion  115 . 
     FIG. 17  shows an example of the internal-surface model, which is displayed on the displaying portion of the input/output apparatus  110 , by means of the internal-surface model displaying portion  118 . The thickness attributes given to the internal-surface model are as below: 
   The surface  1701 : 5 mm; 
   The surface  1702 : 3 mm; and 
   The surface  1703 : 3 mm. 
   However, in this example, it is assumed that the averaged value of the face-to-face distances is given as the thickness attribute. 
   In this manner, for the user of the apparatus, it is possible to produce the internal-surface model, as well as, to amend the internal-surface model in a manner of dialog, only by inputting the reference-plate thickness size, thereby enabling to produce the analyzing shell-model effectively. 
   As was explained in the above, according to the present embodiment, in case of producing the analytical shell-model from the configuration model of thin-plate structure, for the user of the apparatus, it is possible to produce the internal-surface model, as well as, to control and amend the internal-surface model, in the dialog manner, thereby enabling to produce the analyzing shell-model effectively. 
   Conventionally, since the thin-plate like configuration portion is designated by an operator, she/he must input designations of the configuration a number of times, in particular, when it has a rib or is the complicated configuration model, however according to the present embodiment, the internal-surface model can be produced, only by inputting the reference-plate thickness, easily. Also, conventionally, the neutral surface model is produced, not as the configuration model, but as the mesh data, therefore it is necessary to re-produce the configuration model form the mesh data when changing the configuration for a parameter survey, etc. However, according to the present embodiment, since the internal-surface model is produced as the configuration model, it is possible to change the configuration, easily, on the configuration of the internal-surface model produced, by conducting the operations, such as, the bending process and the drilling process, for example. Accordingly, it is possible to produce the analytical shell-model, easily.