JPH0652268A - Finite element inspection device and structure analysis method using the same - Google Patents

Abstract

(57) [Summary] [Purpose] To shorten the analysis time. [Structure] It is judged whether or not the surface element EP is the same surface as the surface of the three-dimensional element EC, and the surface element E which is judged to be the same surface
P and the three-dimensional element EC are extracted, and the order directions of the nodal coordinates N1, N2, N3, and N4 representing the extracted surface element EP are
Nodal coordinates P1, P2, P representing the same plane of the three-dimensional element EC
It is determined whether or not the direction is the reverse direction of the order of 3, 4, and if it is determined to be the reverse direction, it is output that the expression of the surface element EP or the solid element EC of the determination target is an error. This automatically checks the adequacy of the expression of the element before executing the analysis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finite element for inspecting a representation of a geometric model of a structure when the geometric model of the structure is divided into elements (finite elements) in order to analyze the structure based on the finite element method. The present invention relates to an inspection device and a structure analysis method using the inspection device.

[0002]

2. Description of the Related Art A case will be considered, for example, where stress analysis of a structure as shown in FIG. In the geometric model 10 of this structure, a top plate 12 wider than this upper surface is fixed to an upper surface of a base 11. Since the top plate 12 is relatively thin, it is treated as a surface. Load W as shown on the top plate 12
When numerically analyzing the stress distribution and the like in the case of adding the finite element method, as shown in FIG. 5B, the base 11 is divided into three-dimensional elements and the top plate 12 is divided into surface elements. Then, the simultaneous linear differential equations of variables at the nodes of each element are numerically calculated. Such an analysis is performed under various conditions, the shape of the model is changed according to the analysis result, the same analysis is performed on the changed model, and such processing is repeated to determine the optimum model.

With the shortening of the product life cycle, it is required to carry out structural analysis in a shorter time.

[0004]

For example, as shown in FIG. 6, the three-dimensional element EC is (P1, P2, P3, P4, P5,
P6, P7, P8), and the surface element EP is (N1, N
2, N3, N4). Where P1 to P
8 and N1 to N4 are the coordinates of the nodes of the three-dimensional element EC and the surface element EP, respectively. Surface P5 of this three-dimensional element EC
When P6P7P8 is the same surface as the surface element EP, that is, N1 = P5, N2 = P6, N3 = P7, N4 = P8
, The surface element EP is erroneously (N1, N4, N
If it is expressed in the direction opposite to P5 to P8 of the three-dimensional element EC as in (3, N2), the numerical analysis becomes impossible or the analysis result becomes erroneous.

In such a case, an erroneous calculation requires a long time, and since the error must be found, the error must be corrected and the calculation must be performed again, the analysis time becomes long.

In view of the above problems, an object of the present invention is to provide a finite element inspection apparatus and a finite element inspection apparatus capable of shortening the analysis required time by automatically checking the adequacy of the expression of elements. To provide a method for analyzing a structure that has been used.

[0007]

[Means for Solving the Problem and Its Action] FIG. 1 shows the principle configuration of a finite element inspection apparatus according to the first invention.

The first aspect of the present invention is a finite element which inspects the representation of the geometric model 10 of the structure divided into a three-dimensional element EC and a surface element EP in order to analyze the structure based on the finite element method. In the inspection apparatus, the input means 1 for inputting the expression of the element, the element storage means 2 for storing the input expression of the element, and the stored surface element EP are the same as the surface of the three-dimensional element EC. The shared element extraction unit 3 that determines whether or not the surface is a surface and extracts the surface element EP and the three-dimensional element EC that are determined to be the same surface, and the node coordinates N1, N2, N3, and N4 that represent the extracted surface element EP. The direction of order is the nodal coordinates P1, P2, P3, P4 representing the same plane of the three-dimensional element EC.
Direction determining means 4 for determining whether the direction is the reverse of the direction of the order, and if it is determined to be the reverse direction, output that the expression of the surface element EP or the three-dimensional element EC to be determined is an error. The error output means 5 is provided. In addition,
The direction of the node coordinates N1, N2, N3, N4, which are cyclically shifted, for example, the node coordinates N2, N3.
N4, N1 order direction and node coordinates N3, N4, N
The direction of the order of 1, N2, etc. is the node coordinates N1, N2, N
This is the same as the direction of the order of 3, N4.

In the structure analysis method of the second invention, the geometric model 10 of the structure is created and the geometric model 10 is used as the three-dimensional element E.
It is divided into C and surface element EP, the expression of the element is inspected by using the finite element inspection device having the above configuration, and if an error is output from the finite element inspection device, this is corrected and the corrected Numerical analysis is performed on the element based on the finite element method.

According to the present invention, the suitability of the expression of the element is automatically checked before the analysis is executed, and the error is corrected based on this, so that it becomes impossible or impossible to calculate in the subsequent numerical analysis. It is possible to prevent the result from being erroneous, and it is not necessary for a person to determine the cause of the error, so that it is possible to reduce the analysis time.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The hardware structure of the structure analysis device is a known structure including a calculator, a data input device, and a data output device, and a description thereof will be omitted.

FIG. 2 shows a schematic procedure for performing an analysis by this apparatus based on the finite element method. Hereinafter, the numerical value in the parenthesis represents the step identification number in the figure.

(20) CAD is used to interactively create a structural geometric model 10 as shown in FIG. 5 (A).

(21) The geometric model 10 is divided into a three-dimensional element EC and a surface element EP as shown in FIG. 5B, for example. This division is done interactively using a calculator while looking at the display screen.

(22) In order to make the numerical calculation result after that effective, the expression of the divided elements is checked as described later.

(23, 24) If an error is detected by this check, the expression of the element is corrected and the process returns to step 22.

(25) When the error is eliminated, the model is numerically analyzed to obtain the stress distribution, strain distribution and the like.

(26) Display the analysis result on the display device.

Next, the details of step 22 will be described with reference to FIG.

(30) In order to improve the analysis accuracy, it is checked whether or not each surface is a plane for all three-dimensional elements and surface elements. There are only triangles and quadrilaterals as face types, and triangles are always planes, so check only quadrilaterals. For example, as shown in FIG. 7A, the surface N1N
Check if 2N3N4 is a plane as follows. That is, the length H of the perpendicular line when the perpendicular line is drawn from N4 on the surface including the triangle N1N2N3 is calculated, and if the length H is almost 0, that is, H ≦ ε, the surface N1 is calculated.
It is determined that N2N3N4 is a plane, and if not, a plane is distorted and an error is output.

(31, 32) In order to improve the analysis accuracy, it is determined whether or not the three-dimensional element has a crushed shape as shown in FIG. 7 (B), for example. For example, P5, P6, P7 and P8 on the plane P1P2P3P4
And the minimum value Vmin of the length of each perpendicular when the perpendicular is drawn from each of the sides, and sides P1P5, P2P6, P3P7 and P4.
The minimum value Lmin of P8 is obtained, and it is determined whether Vmin / Lmin is a set value smaller than 1, for example, 0.6 or more. If a negative determination is made, an error is output.

(31, 33) Only elements having a shared surface between the surface element and the three-dimensional element are extracted, and then the direction of the order of the node coordinates representing the extracted surface element is the shared surface of the three-dimensional element. It is determined whether or not the direction is the reverse of the order of the represented node coordinates, and if it is determined to be the reverse direction, it is output that the expression of the surface element or the solid element to be determined is an error. This judgment and error output are performed as follows, as shown in FIG.

(40) The surface element is read and it is determined whether the shape of the surface element is a triangle or a quadrangle. If it is a quadrangle, the processes of steps 41 to 44 are performed below, and if it is a triangle, the processes of steps 51 to 54 are performed.

(41) A set of nodal coordinates representing this surface element,
For example, the surface element EP (N1, N2, N3, N in FIG.
4) is extracted.

(42) The normal vector NP of the surface element EP is calculated. For example, vector N1N2 and vector N2N3
The normal vector NP is calculated by the outer product N1N2 × N2N3 of

(43) Surface element EP (N1, N2, N3)
N4) has the same surface as the three-dimensional element, that is, a three-dimensional element including the nodes N1, N2, N3 and N4 in any order,
For example, the three-dimensional element EC (P1, P2, P
3, P4, P5, P6, P7, P8) are extracted.

(44) Whether the shared surface is a problem surface,
That is, the surface element EP (N1, N2, N3, N4) is the three-dimensional element EC (P1, P2, P3, P4, P5, P6, P).
Surface (P1, P8) represented by four nodes in the first half of (7, P8)
2, P3, P4) or the same plane as the plane (P5, P6, P7, P8) represented by the four nodes in the latter half. If they are on the same side, it becomes a problem, and step 45
If it is not on the same plane, there is no problem and the process proceeds to step 49.

Step 5 when the surface element is a triangle
The processing in 1 to 54 can be easily inferred from the description of the above steps 41 to 44, and thus the description thereof will be omitted.

(45) The normal vector NC of the shared surface of the three-dimensional element EC is calculated. For example, in FIG. 6, N1 = P
5, N2 = P6, N3 = P7, N4 = P8,
Outer product of vector P5P6 and vector P6P7 P5P6 ×
P6P7 is calculated as the normal vector NC.

(46) The inner product IM = NP · normal vector NC of the normal vector NP and the normal vector NC calculated as described above is calculated.

If (47, 48) IM <0, that is, if the directions of the normal vector NP and the normal vector NC are opposite, an error message is output.

(49) If the above checks have not been completed for all surface elements, the process returns to step 40.

By the above processing, the suitability of the expression of the element is automatically checked before the analysis is executed, and the error is corrected based on this, so that the calculation becomes impossible in the subsequent numerical analysis, It is possible to prevent the calculation result from being erroneous, and moreover, since it is not necessary for a person to judge the cause of the error, it is possible to shorten the analysis required time.

[0035]

As described above, according to the finite element inspection apparatus and the structure analysis method using the same according to the present invention,
The validity of the expression of the element is automatically checked before executing the analysis, and the error is corrected based on this, so that it is possible to prevent the calculation from becoming impossible or the calculation result to be incorrect in the subsequent numerical analysis. In addition, since it is not necessary for a person to determine the cause of the error, the excellent effect that the analysis required time can be shortened is exerted, and it greatly contributes to shortening the product development period.

[Brief description of drawings]

FIG. 1 is a block diagram showing a principle configuration of a finite element inspection device according to the present invention.

FIG. 2 is a flowchart showing an analysis procedure by the finite element method according to the embodiment of the present invention.

FIG. 3 is a detailed flowchart of step 22 of FIG.

FIG. 4 is a detailed flowchart of step 33 of FIG.

FIG. 5 is an exemplary diagram of a geometric model and its element division.

FIG. 6 is a diagram showing a surface element and a three-dimensional element having a common surface.

FIG. 7 is an explanatory diagram of element distortion check.

[Explanation of symbols]

 10 geometric model 11 base 12 top plate W load EP surface element EC three-dimensional element NP, NC normal vector

Claims (2)

[Claims] 1. A geometric model (10) of a structure for analyzing a structure based on the finite element method, comprises a three-dimensional element (E).
A finite element inspection device for inspecting the expression of the element divided into C) and a surface element (EP), the input means (1) for inputting the expression of the element, and the expression of the input element And an element storage means (2) for storing, and extracting the surface element and the three-dimensional element determined to be the same surface by determining whether the stored surface element is the same surface as the surface of the three-dimensional element. Common element extraction means (3) for performing the above, and the nodal coordinates (N1, N2, N representing the extracted surface element).
Direction determining means (4) for determining whether or not the order direction of (3, N4) is opposite to the order direction of the node coordinates (P1, P2, P3, P4) representing the same plane of the three-dimensional element.
And an error output means (5) that outputs that the expression of the surface element or the three-dimensional element of the determination target is an error when it is determined to be in the opposite direction. Inspection device. 2. Creating a geometric model (10) of a structure,
The geometric model is divided into three-dimensional elements (EC) and surface elements (EP), the expression of the element is inspected by using the finite element inspection device according to claim 1, and the error is output from the finite element inspection device. In the case of the above, this is corrected, and the numerical analysis is performed on the corrected element based on the finite element method.