JP7381892B2 - Model conversion method, model conversion device, program and recording medium - Google Patents

Description

The present invention relates to a model conversion method, a model conversion device, a program, and a recording medium.

Generally, the finite element method (FEM) is used for forming analysis and collision deformation analysis of automobile bodies. To analyze an automobile body using FEM, a detailed FEM model (detailed full car model) is constructed using millions of elements. Using this detailed full car model, various car body performance evaluation analyzes are performed, and an actual car body is developed based on the analysis results.

Japanese Patent Application Publication No. 2008-15635

Performing a vehicle performance evaluation (rigidity, road path, etc.) analysis using a detailed full car model requires analysis time ranging from several hours to several tens of hours, depending on the scale of the detailed full car model. Furthermore, once a detailed full car model has been created, it is precisely modeled to meet the requirements for interference and connections between parts, so if you try to change the shape of a part, the detailed full car model It takes a lot of man-hours to modify the car model.

Therefore, it is necessary to perform a performance evaluation analysis of a car body when the cross-sectional shape (proof strength) of a skeleton part in a detailed full car model is changed, the arrangement is changed, or the connection position with surrounding skeleton parts is changed. It requires a large amount of model modification man-hours and analysis time, and it is practically impossible to study dozens to hundreds of cases.

The present invention has been made in view of the above-mentioned problems, and enables highly accurate performance evaluation analysis of detailed models using shell elements, etc., in an extremely short period of time, even for complex and large-scale analysis targets such as automobile bodies. The object of the present invention is to provide a model conversion method, a model conversion device, a program, and a recording medium that can convert a beam model into a beam model that enables the following.

In order to solve the above problems, as a result of intensive studies, we have come up with the following aspects of the invention. The gist of the present invention is as follows.

(1)
Define a cutting plane that cuts a detailed model skeleton part created by the finite element method in a direction intersecting the longitudinal direction of each element of the skeleton part, and cut the skeleton part by the cutting plane. A first step of reading the plate thickness and material properties (density, Young's modulus, Poisson's ratio, and yield stress) of each element;
Creating a cross-section line of the skeleton component consisting of a cutting line of each element cut by the cutting plane, determining the cross-section line length, and defining the plate thickness and material properties obtained in the first step. A second step,
a third step of discretizing the cross-section line at a predetermined pitch and determining the center of gravity of the cross-section line in a two-dimensional coordinate axis on the cut plane;
a fourth step of creating a coordinate axis with the center of gravity obtained in the third step as the origin;
a fifth step of calculating cross-sectional properties (secondary moment of inertia, multiplicative moment, torsion constant, and cross-sectional area) with respect to the coordinate axes;
a sixth step of creating a node at an intermediate position between the centers of gravity of the adjacent cut planes and creating a beam element connecting the adjacent nodes;
a seventh step of defining density, Young's modulus, and Poisson's ratio of the cross-sectional properties obtained in the fifth step and the material properties obtained in the first step for the beam element;
It is equipped with
A model conversion method characterized by converting the detailed model into a beam model.

(2)
extracting elements of the panel component by deleting components other than the panel component in the detailed model;
For the element of the panel component that is joined to the framework component, two or more rigid beams are created that connect the beam element converted from the framework component and the element of the panel component near the joint, and the beam joining an element to an element of the panel component;
The model conversion method according to (2), further comprising:

(3)
In the detailed model, find the masses of parts other than the skeleton parts converted to beam elements and the extracted panel parts, and define the masses found for the beam model consisting of the converted beam elements and extracted panel parts. The model conversion method according to (2), characterized in that:

(4)
The model conversion method according to any one of (1) to (3), further comprising the step of defining a spring element at a joint portion between the skeleton parts converted into the beam element.

(5)
A total plastic axial force, a total plastic bending moment, and a yield bending moment are calculated using the cross-sectional line obtained in the second step and the coordinate axis with the center of gravity as the origin obtained in the fourth step. The model conversion method according to any one of (1) to (4), further comprising a first calculation step.

(6)
using the cross-sectional line obtained in the second step to determine plastic neutral coordinates;
creating a plastic neutral axis with the acquired coordinates as the origin;
a second calculation step of calculating a total plastic axial force, a total plastic bending moment, and a yield bending moment with respect to the plastic neutral axis;
The model conversion method according to any one of (1) to (4), further comprising:

(7)
In the first calculation step, when the angle difference between adjacent cutting lines of each shell element cut by the cutting surface is within 5 degrees, the adjacent cutting lines are aligned at the same angle. Assuming that the adjacent section lines are on a line, the adjacent section lines are expressed as one straight line, and the section line is extended from both ends of the straight line by a distance of 1/2 of the effective width calculated by Kalman's effective width formula. The model conversion method according to (5), characterized in that the total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line obtained by removing the remaining portions of the straight line.

(8)
In the second calculation step, when the angle difference between adjacent cutting lines of each shell element cut by the cutting plane is within 5 degrees, the adjacent cutting lines are aligned at the same angle. Assuming that the adjacent section lines are on a line, the adjacent section lines are expressed as one straight line, and the section line is extended from both ends of the straight line by a distance of 1/2 of the effective width calculated by Kalman's effective width formula. The model conversion method according to (6), characterized in that the total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line obtained by removing the remaining portions of the straight line.

(9)
The total plastic axial force, total plastic bending moment, or yield bending moment calculated by the model conversion method described in (7) or (8) and the load path analysis using the created beam model. A method for predicting cross-sectional collapse, comprising comparing axial force and moment applied to the beam element to predict whether or not the cross-section of the skeleton component of the beam element portion will collapse in the detailed model.

(10)
Define a cutting plane that cuts a detailed model skeleton part created by the finite element method in a direction intersecting the longitudinal direction of each element of the skeleton part, and cut the skeleton part by the cutting plane. a reading unit that reads the plate thickness and material properties (density, Young's modulus, Poisson's ratio, and yield stress) of each element;
Creating a cross-section line of the skeleton component consisting of a cutting line of each element cut by the cutting plane, determining the cross-section line length, and defining the plate thickness and material properties acquired by the reading unit. a first definition part;
a center-of-gravity acquisition unit that discretizes the cross-section line at a predetermined pitch and obtains the center of gravity of the cross-section line in a two-dimensional coordinate axis on the cut plane;
a barycenter coordinate axis creation unit that creates a coordinate axis having the barycenter acquired in the third step as its origin;
a first cross-sectional property calculation unit that calculates cross-sectional properties (secondary moment of inertia, multiplicative moment, torsion constant, and cross-sectional area) with respect to the coordinate axes;
a beam element creation unit that creates a node at an intermediate position between the centers of gravity of the adjacent cut planes and creates a beam element that connects the adjacent nodes;
a second definition section that defines density, Young's modulus, and Poisson's ratio of the cross-sectional properties acquired by the cross-sectional characteristic calculation unit and the material properties acquired by the reading unit in the beam element;
It is equipped with
A model conversion device that converts the detailed model into a beam model.

(11)
an extraction unit that extracts elements of the panel component by deleting components other than the panel component in the detailed model;
For the element of the panel component that is joined to the framework component, two or more rigid beams are created that connect the beam element converted from the framework component and the element of the panel component near the joint, and the beam a rigid beam creation unit that joins the element and the element of the panel component;
The model conversion device according to (10), further comprising:

(12)
In the detailed model, the masses of parts other than the skeleton parts converted into beam elements and the extracted panel parts are calculated, and the calculated masses are defined for the beam model consisting of the converted beam elements and extracted panel parts. The model conversion device according to (11), further comprising three definition sections.

(13)
The model conversion device according to any one of (10) to (12), further comprising a spring element creation unit that defines a spring element at a joint portion between the skeleton parts converted into the beam element. .

(14)
The total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line acquired by the first definition unit and the coordinate axis having the center of gravity as the origin, acquired by the center of gravity coordinate axis creation unit. The model conversion device according to any one of (10) to (13), further comprising a second cross-sectional characteristic calculation unit that calculates.

(15)
a plastic neutral coordinate acquisition unit that obtains plastic neutral coordinates using the cross-sectional line acquired by the first definition unit;
a plastic neutral axis creation unit that creates a plastic neutral axis having the origin at the coordinates acquired by the plastic neutral coordinate acquisition unit;
a third cross-sectional property calculation unit that calculates a total plastic axial force, a total plastic bending moment, and a yield bending moment with respect to the plastic neutral axis;
The model conversion device according to any one of (10) to (13), further comprising:

(16)
In the cutting line of each shell element cut by the cutting plane, the second cross-sectional characteristic calculation unit calculates the cutting line between the adjacent cutting lines when the angle difference between the adjacent cutting lines is within 5°. Assuming that they are on the same straight line, the adjacent cutting lines are expressed as a single straight line, and the cross section is measured by a distance of 1/2 of the effective width calculated by Kalman's effective width formula from both ends of the straight line. The model conversion according to (14), characterized in that the total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line obtained by leaving the line and deleting the other part of the straight line. Device.

(17)
In the cutting line of each shell element cut by the cutting surface, the third cross-sectional characteristic calculation unit calculates the cutting line between the adjacent cutting lines when the angle difference between the adjacent cutting lines is within 5°. Assuming that they are on the same straight line, the adjacent cutting lines are expressed as a single straight line, and the cross section is measured by a distance of 1/2 of the effective width calculated by Kalman's effective width formula from both ends of the straight line. The model conversion according to (15), characterized in that the total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line obtained by leaving the line and deleting the other part of the straight line. Device.

(18)
Define a cutting plane that cuts a detailed model skeleton part created by the finite element method in a direction intersecting the longitudinal direction of each element of the skeleton part, and cut the skeleton part by the cutting plane. A first step of reading the plate thickness and material properties (density, Young's modulus, Poisson's ratio, and yield stress) of each element;
Creating a cross-section line of the skeleton component consisting of a cutting line of each element cut by the cutting plane, determining the cross-section line length, and defining the plate thickness and material properties obtained in the first step. A second step,
a third step of discretizing the cross-section line at a predetermined pitch and determining the center of gravity of the cross-section line in a two-dimensional coordinate axis on the cut plane;
a fourth step of creating a coordinate axis with the center of gravity obtained in the third step as the origin;
a fifth step of calculating cross-sectional properties (secondary moment of inertia, multiplicative moment, torsion constant, and cross-sectional area) with respect to the coordinate axes;
a sixth step of creating a node at an intermediate position between the centers of gravity of the adjacent cut planes and creating a beam element connecting the adjacent nodes;
a seventh step of defining density, Young's modulus, and Poisson's ratio of the cross-sectional properties obtained in the fifth step and the material properties obtained in the first step for the beam element;
A model conversion program that causes a computer to convert the detailed model into a beam model.

(19)
extracting elements of the panel component by deleting components other than the panel component in the detailed model;
For the element of the panel component that is joined to the framework component, two or more rigid beams are created that connect the beam element converted from the framework component and the element of the panel component near the joint, and the beam joining an element to an element of the panel component;
The model conversion program according to (18), further causing a computer to execute.

(20)
In the detailed model, find the masses of parts other than the skeleton parts converted to beam elements and the extracted panel parts, and define the masses found for the beam model consisting of the converted beam elements and extracted panel parts. The model conversion program according to (19), characterized in that:

(21)
The model conversion program according to any one of (18) to (20), further causing a computer to execute a step of defining a spring element in a joint portion between the skeleton parts converted into the beam element.

(22)
A total plastic axial force, a total plastic bending moment, and a yield bending moment are calculated using the cross-sectional line obtained in the second step and the coordinate axis with the center of gravity as the origin obtained in the fourth step. The model conversion program according to any one of (18) to (21), further causing a computer to execute the first calculation step.

(23)
using the cross-sectional line obtained in the second step to determine plastic neutral coordinates;
creating a plastic neutral axis with the acquired coordinates as the origin;
a second calculation step of calculating a total plastic axial force, a total plastic bending moment, and a yield bending moment with respect to the plastic neutral axis;
The model conversion program according to any one of (18) to (21), further causing a computer to execute.

(24)
In the first calculation step, when the angle difference between adjacent cutting lines of each shell element cut by the cutting surface is within 5 degrees, the adjacent cutting lines are aligned at the same angle. Assuming that the adjacent section lines are on a line, the adjacent section lines are expressed as one straight line, and the section line is extended from both ends of the straight line by a distance of 1/2 of the effective width calculated by Kalman's effective width formula. The model conversion program according to (22), characterized in that the total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line obtained by removing the remaining portions of the straight line.

(25)
In the second calculation step, when the angle difference between adjacent cutting lines of each shell element cut by the cutting plane is within 5 degrees, the adjacent cutting lines are aligned at the same angle. Assuming that the adjacent section lines are on a line, the adjacent section lines are expressed as one straight line, and the section line is extended from both ends of the straight line by a distance of 1/2 of the effective width calculated by Kalman's effective width formula. The model conversion program according to (23), characterized in that the total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line obtained by removing the remaining portions of the straight line.

(26)
The total plastic axial force, total plastic bending moment, or yield bending moment calculated by the first calculation step or the second calculation step of the model conversion program described in (24) or (25), and the created Comparing the axial force and moment applied to the beam element, which are found in a load path analysis using a beam model, predicting whether or not the cross section of the skeleton component of the beam element portion will collapse in the detailed model. A cross-sectional collapse prediction program characterized by having a computer execute the process.

(27)
A computer-readable recording medium having recorded thereon the model conversion program according to any one of (18) to (25).

(28)
(26) A computer-readable recording medium having recorded thereon the cross-sectional collapse prediction program.

According to the present invention, even for complex and large-scale analysis targets such as automobile bodies, a detailed model using shell elements etc. can be converted into a beam model that enables highly accurate performance evaluation analysis in an extremely short time. I can do it.

FIG. 1 is a block diagram showing the basic configuration of a model conversion device according to a first embodiment. FIG. 2 is a flow diagram showing the basic configuration of a model conversion method according to the first embodiment. FIG. 2 is a schematic diagram showing the skeletal parts of a detailed full car model of an automobile body composed of shell elements. FIG. 3 is a schematic diagram showing a specific example of defining a cutting plane for the entire skeleton part of a detailed full car model. FIG. 3 is a schematic diagram showing the process from cutting a skeleton component using a cut plane to creating a barycentric coordinate axis. It is a schematic diagram which shows how a panel component is applied to a beam model. FIG. 3 is a diagram showing components and steps added in the first embodiment. FIG. 2 is a perspective view schematically showing a panel component and a beam element existing in the vicinity thereof. FIG. 3 is a diagram showing components and steps added in the first embodiment. It is a schematic diagram which shows an example of the beam model created by defining a spring element with respect to a joint part. FIG. 3 is a diagram showing components and steps added in the first embodiment. It is a schematic diagram which shows a predetermined cross-sectional line. FIG. 3 is a diagram showing components and steps added in the first embodiment. FIG. 3 is a schematic diagram showing how a plastic neutral axis is created. FIG. 3 is a schematic diagram showing torsional rigidity analysis using an FEM model. FIG. 3 is a characteristic diagram showing the results of torsional rigidity analysis. FIG. 6 is a schematic diagram showing cross-sectional lines created depending on whether or not the effective width of Karman is taken into consideration. FIG. 2 is a flow diagram showing a cross-sectional collapse prediction method using the beam model obtained in the first embodiment. FIG. 7 is a flow diagram illustrating a further method of using the beam model according to the second embodiment. FIG. 2 is a block diagram showing computer functions.

Embodiments of the present invention will be described in detail below with reference to the drawings.

[First embodiment]
In the first embodiment, a model conversion method and a model conversion apparatus for analyzing an automobile body or the like will be described. FIG. 1 is a block diagram showing the basic configuration of a model conversion apparatus according to this embodiment, and FIG. 2 is a flow diagram showing the basic configuration of a model conversion method according to this embodiment.

In this embodiment, a detailed full car model of an automobile body made up of shell elements based on the finite element method (FEM) is targeted for conversion. An example of a detailed full car model is shown in Figure 3. This detailed full car model uses LS-DYNA as analysis software and is expressed with approximately 3.5 million shell elements.

As shown in FIG. 1, the basic configuration of the model conversion device according to this embodiment is as follows: a reading unit 1, a first definition unit 2, a center of gravity acquisition unit 3, a coordinate axis creation unit 4, a cross-sectional characteristic calculation unit 5, a beam element creation unit 6. , and a second definition section 7. In the basic configuration of the model conversion method, as shown in FIG. 2, steps S1 to S7 are executed corresponding to the model conversion device.

(Reading process: Step S1)
The reading unit 1 first detects a cut plane cut in a direction intersecting the longitudinal direction of a skeleton part of a detailed full car model of an automobile body composed of shell elements, as shown in FIG. 3. Define. The cut surface is preferably a surface cut in a direction perpendicular to the longitudinal direction of the skeleton component. FIG. 4 shows a specific example of defining a cutting plane for a skeleton part of a detailed full car model. A specific example of defining a cutting line for a skeleton component is shown in FIG. 5(a). A cutting plane S that cuts each shell element E of the skeleton component in a direction perpendicular to its longitudinal direction is defined. At this time, the cutting line of the plurality of parallel shell elements E along the cutting surface S is indicated by AB.

Subsequently, the reading unit 1 reads the plate thickness and material properties (density, Young's modulus, Poisson's ratio, and yield stress) of each shell element of the skeleton component cut by the cut plane.

(Characteristics etc. definition process: Step S2)
The first definition unit 2 first creates a cross-sectional line of the skeleton component, which is made up of the cutting lines of each shell element cut by the cutting plane acquired in step S1, and calculates the length of the cross-sectional line. A specific example of the cross-sectional line is shown in FIG. 5(b). The cross-section line is constructed from the cutting line of each shell element.

Subsequently, the first definition unit 2 defines the plate thickness and material properties (density, Young's modulus, Poisson's ratio, and yield stress) acquired in step S1 with respect to the cross-sectional line.

(Gravity center acquisition process: Step S3)
The center of gravity acquisition unit 3 first discretizes the cross-sectional line at a predetermined pitch. A specific example of discretizing the cross-sectional line is shown in FIG. 5(c).
Subsequently, the center of gravity obtaining unit 3 obtains the center of gravity of the cross-sectional line in the two-dimensional coordinate axes (X'-Y' coordinate axes) on the cut plane. A specific example of determining the center of gravity of a cross-sectional line is shown in FIG. 5(d). Here, the X' and Y' coordinates of the center of gravity can be determined as follows.

X' coordinate of center of gravity = Σ {X' component distance from Y' coordinate axis) x (minimal area) x (density) ÷ (total mass of cross-sectional line)}
Y' coordinate of center of gravity = Σ {(Y' component distance from X' coordinate axis) x (minimal area) x (density) ÷ (total mass of cross section line)}

(Centroid coordinate axis creation process: Step S4)
The center-of-gravity coordinate axis creating unit 4 creates a coordinate axis (XY coordinate axes) having the center of gravity acquired in step S3 as its origin. A specific example of creating coordinate axes is shown in FIG. 5(e).

(Cross-sectional property calculation process: Step S5)
The cross-sectional property calculation unit 5 calculates cross-sectional properties (secondary moment of inertia, multiplicative moment, torsion constant, and cross-sectional area) with respect to the coordinate axes created in step S4. Here, the secondary moments of area, synergistic moments, and torsion constants of open cross-sections and closed cross-sections around the X-axis and Y-axis can be determined as follows.

Second moment of area around the X axis = Σ {(Y component distance from the X coordinate axis) ² × (minimal area)}
Second moment of area around the Y axis = Σ {(X component distance from the Y coordinate axis) ² × (minimal area)}

Synergistic moment = Σ {(X component distance from Y coordinate axis) x (Y component distance from X coordinate axis) x (minimal area)}

Torsional constant of open cross section = {(cross section line length) x (plate thickness) ³ ÷ 3.0} x coefficient As the coefficient, a value of 5 to 1000 can be used depending on the restraint state of the frame component.
Torsion constant of closed cross section = 4.0 x (area inside the cross section) ² ÷ {(cross section line length) ÷ (plate thickness)}

(Beam element creation process: Step S6)
As shown in the enlarged view of the rectangular frame A in FIG. 4, the beam element creation unit 6 creates a node at an intermediate position between the centers of gravity of two adjacent cut planes, and connects the adjacent nodes to create a beam. Create an element.

(Characteristics etc. definition process: Step S7)
The second definition unit 7 defines, for the beam element created in step S6, the cross-sectional properties (secondary moment of inertia, multiplicative moment, torsion constant, and cross-sectional area) acquired in step S5 and the cross-sectional characteristics acquired in step S1. Define density, Young's modulus, and Poisson's ratio among material properties.

As described above, a beam model made up of beam elements is created by converting the skeleton parts of a detailed full car model of an automobile body made up of shell elements. An example of the created beam model is shown in FIG. This beam model uses NASTRAN as analysis software and is expressed with approximately 300,000 elements including approximately 400 beam elements.

In this embodiment, the following components and steps can be added to the basic configuration of the model conversion device and the basic configuration of the model conversion method described above.

[Handling of panel parts]
Detailed full car model includes panel parts. In this embodiment, as shown in FIG. 6, the panel parts 10 of the detailed full car model are directly applied to the beam model.

FIG. 7 is a diagram showing the components and steps added in this embodiment, where (a) is a block diagram showing the components added to the basic configuration of the model conversion device in FIG. 1 in this embodiment; b) is a flow diagram showing steps added to the basic configuration of the model conversion method of FIG. 2 in this embodiment. FIG. 8 is a perspective view schematically showing the state of the panel component and the beam elements existing in the vicinity thereof.

(Extraction process: Step S11)
The extraction unit 8 extracts the shell element 10a of the panel component 10 used in the detailed full car model.

(Rigid beam creation process: Step S12)
After step S7 in FIG. 2, the beam creation unit 9 converts the shell element 10a of the panel component 10 joined to the skeleton component into the beam element 101 converted from the skeleton component in steps S1 to S6 in FIG. Two or more rigid beams 103 (two in the example of FIG. 8) are created to connect to the shell element 10a of the panel component 10 near the joint 102. Thereby, the beam element 101 and the shell element 10a of the panel component 10 are joined by the rigid beam 103.

As mentioned above, by connecting the beam element and the shell element of the panel component with a rigid beam, an accurate beam model is created that takes into account the influence of the panel component when the panel component is connected to the frame component. can do.

[Handling of joints between beam elements]
In the created beam model, as shown in circle C in the enlarged view of rectangular frame B in Figure 6, there are joints between beam elements that have been converted from the skeleton parts, as well as joints between the skeleton parts. . In this embodiment, a spring element may be applied to this joint portion.

FIG. 9 is a diagram showing the components and steps added in this embodiment, where (a) is a block diagram showing the components added to the basic configuration of the model conversion device in FIG. 1 in this embodiment; b) is a flow diagram showing steps added to the basic configuration of the model conversion method of FIG. 2 in this embodiment.

(Spring element creation process: Step S21)
After step S7 in FIG. 2, the spring element creation unit 11 defines spring elements at the joints between the skeleton components converted into beam elements. Specifically, the spring element creation unit 11 uses a structural model obtained by extracting joint parts (connection parts) from a detailed full car model made up of shell elements, and calculates each translation direction (X, Y, Z direction) and The stiffness values in each rotational direction (around the X-axis, Y-axis, and Z-axis) are obtained, and a spring element is defined for the joint portion using this stiffness value as a spring constant. FIG. 10 shows an example of a beam model created by defining spring elements for the joint portion (corresponding to an enlarged view of the rectangular frame B in FIG. 6).

As described above, by defining spring elements at the joints between beam elements, it is possible to create an accurate beam model that takes into account the influence of the joints.

[Obtaining other cross-sectional properties (1)]
FIG. 11 is a schematic diagram showing the components and steps added in this embodiment, and (a) is a block diagram showing the components added to the basic configuration of the model conversion device of FIG. 1 in this embodiment, (b) is a flow diagram showing steps added to the basic configuration of the model conversion method of FIG. 2 in this embodiment.

(Calculation process of other cross-sectional properties: Step S31)
Other cross-sectional properties calculation unit 12 calculates other cross-sectional properties (total plastic axial force, total plastic axial force, bending moment and yield bending moment). The calculated total plastic axial force, total plastic bending moment, and yield bending moment are output to an external file. Here, the total plastic axial force, total plastic bending moment, and yield bending moment can be determined as follows.

Total cross-sectional plastic axial force = (cross-sectional area) × (yield stress)

Total plastic bending moment around the X axis = Σ {(Y component distance from the X coordinate axis) x (minimal area) x (yield stress)}
Total plastic bending moment around the Y axis = Σ {(X component distance from the Y coordinate axis) x (minimal area) x (yield stress)}

Yield bending moment around the X axis = Σ {(Y component distance from the X coordinate axis) x (minimal area) x (yield stress)
× (Y-component distance from the X-coordinate axis) ÷ (Y-component distance farthest from the X-coordinate axis)}
Yield bending moment around the Y axis = Σ {(X component distance from the Y coordinate axis) x (minimal area) x (yield stress)
× (X-component distance from the Y-coordinate axis) ÷ (X-component distance farthest from the Y-coordinate axis)}

Here, in step S2 of FIG. 2, the cross-sectional line may be created as follows.
In each cutting line of each shell element cut by the cutting plane acquired in step S1, if the angle difference between adjacent cutting lines is within 5 degrees, the first definition unit 2 in FIG. The cutting lines are considered to be on the same straight line and are expressed as a single straight line. Then, from both ends of the straight line, that is, from the R stop position of the ridgeline, a cross-sectional line is left only at a distance of 1/2 of the effective width calculated by Kalman's effective width formula (other parts of the straight line are deleted). For example, in the cross-sectional line shown in FIG. 12, the broken line portion of the upper straight line is deleted, leaving only a portion of the cross-sectional line having a width w, which is 1/2 of the effective width.

The effective width of Kalman is expressed as follows.
Kalman effective width = t{π ² Ek/(12(1-ν ² )σ)} ^1/2
t: Plate thickness E: Young's modulus k: Coefficient (=2.4 to 4.0)
ν: Poisson's ratio σ: Yield stress

After creating the cross-sectional line as described above, the total plastic axial force, total plastic bending moment, and yield bending moment are calculated in step S31. This method allows more accurate total plastic axial force, total plastic bending moment, and yield bending moment to be obtained.

[Obtaining other cross-sectional properties (2)]
Here, a case will be described in which other cross-sectional characteristics are acquired using a method different from the acquisition (1) of other cross-sectional characteristics described above.
FIG. 13 is a diagram showing the components and steps added in this embodiment, where (a) is a block diagram showing the components added to the basic configuration of the model conversion device in FIG. 1 in this embodiment; b) is a flow diagram showing steps added to the basic configuration of the model conversion method of FIG. 2 in this embodiment.

(Plastic neutral coordinate acquisition process: Step S41)
The plastic neutral coordinate point acquisition unit 13 discretizes the cross-sectional line created in step S2 of FIG. Find the point. A specific example of determining the plastic neutral point of a cross-sectional line is shown in FIG. 14(a). Here, the X' coordinate and Y' coordinate of the plastic neutral point can be determined as follows.

X' coordinate of plastic neutral point = Σ {(X' component distance from Y' coordinate axis) x (minimal area) x (yield stress) ÷ (yield stress) x (cross-sectional area)}
Y' coordinate of plastic neutral point = Σ {(Y' component distance from X' coordinate axis) x (minimal area) x (yield stress) ÷ (yield stress) x (cross-sectional area)}

(Plastic neutral axis creation process: Step S42)
The plastic neutral axis creation unit 14 creates a plastic neutral axis (XY coordinate axis) whose origin is the plastic neutral point acquired in step S41. A specific example of creating a plastic neutral axis is shown in FIG. 14(b).

(Other cross-sectional property calculation process: Step S43)
The other cross-sectional properties calculation unit 15 calculates other cross-sectional properties (total plastic axial force, total plastic bending moment, and yield bending moment) with respect to the plastic neutral axis created in step S42. The calculated total plastic axial force, total plastic bending moment, and yield bending moment are output to an external file. Here, the method of determining the total plastic axial force, the total plastic bending moment, and the yield bending moment is the same as in the case of obtaining other cross-sectional properties (1) described above.

Here, in step S2 of FIG. 2, the cross-sectional line may be created as follows.
In each cutting line of each shell element cut by the cutting plane acquired in step S1, if the angle difference between adjacent cutting lines is within 5 degrees, the first definition unit 2 in FIG. The cutting lines are considered to be on the same straight line and are expressed as a single straight line, and the cross-sectional line is left at a distance of 1/2 of the effective width calculated by Kalman's effective width formula from both ends of the straight line (straight line). (delete the rest of the file).

After creating the cross-sectional line as described above, the total plastic axial force, total plastic bending moment, and yield bending moment are calculated in steps S41 to S43. This method allows more accurate total plastic axial force, total plastic bending moment, and yield bending moment to be obtained.

[Example]
Hereinafter, specific examples of this embodiment will be described.

(Example 1)
In Example 1, the torsional rigidity analysis of a vehicle body is performed using a beam model to which panel parts are applied (referred to as beam model (1)), and a beam model to which panel parts and spring elements are applied (referred to as beam model (1)). 2) will be explained based on a comparison with the case using a detailed full car model using shell elements. FIG. 15 is a schematic diagram showing torsional rigidity analysis using an FEM model. In FIG. 15, the deformation magnification of the vehicle body is shown as 500 times.

As shown in FIG. 15, the torsional rigidity analysis was performed by restraining the rear damper mount portion of the vehicle body and inputting loads in the opposite directions to the left and right front strut tower top portions.

The analysis results are shown in FIG. 16. Although the beam model (1) was slightly larger than the detailed full car model, it exhibited a torsional rigidity value that was generally close to that of the detailed full car model. In the beam model (2), as shown in Figure 15(b), the deformation that occurred during the torsional stiffness analysis is almost the same as the detailed full car model, and the torsion is closer to the detailed full car model (almost equivalent). Stiffness values are shown.

(Example 2)
In Example 2, a case will be described in which the yield bending moment is calculated using a cross-sectional line created in consideration of Karman's effective width using the plastic neutral axis in acquisition of other cross-sectional properties (2). FIG. 17(a) illustrates a cross-sectional line created without considering the effective width, and FIG. 17(b) illustrates a cross-sectional line created with consideration of the effective width.

The obtained yield bending moment value was compared with the maximum moment value when bending was applied to the actual member. As a result, it was found that the obtained yield bending moment value was close to the maximum moment value of the actual member.

As explained above, according to this embodiment, even for complex and large-scale analysis targets such as automobile bodies, detailed models using shell elements etc. can be analyzed for highly accurate performance evaluation in an extremely short time. It can be converted into a model.

(Example 3)
In Example 3, a cross-sectional collapse prediction method using the beam model obtained in the first embodiment will be described. FIG. 18 is a flow diagram showing a cross-sectional collapse prediction method using the beam model obtained in the first embodiment.

In the third embodiment, the beam model created in the first embodiment is used to perform load path analysis using the inertial relief method (step S51). The inertia relief method generates a reaction force to prevent the model from rotating or translating when an external force is applied to an unrestrained object, and calculates the deformation and generated load in response to the external force by taking into account inertia. Load path analysis is a method that calculates the load generated on each frame component when an input simulating a collision is applied to an FEM model of an automobile body using the above-mentioned inertia relief method.

In the third embodiment, a third definition section is added to the model conversion device shown in FIG. The third definition part calculates the mass of parts other than the skeleton parts converted to beam elements and the extracted panel parts in the detailed full car model, and adds Define the obtained mass. As a result, the detailed full car model before conversion and the beam model after conversion have the same mass, making it possible to accurately perform load path analysis using the inertial relief method.

The axial force and moment applied to the beam element acquired in the inertial relief analysis of the load path described above, and step S31 in FIG. 11(b) in acquisition (1) of other cross-sectional characteristics explained in the first embodiment or (2) The total plastic axial force, total plastic bending moment, or yield bending moment acquired in step S43 of FIG. 13(b) is compared (step S52). Thereby, it is predicted whether or not the cross section of the skeleton component of the beam element portion will collapse in the detailed full car model (step S53).

Specifically, for example, in an inertial relief analysis of a road path using a beam model, an input of, for example, 200 kN is applied to the bumper portion of the vehicle body, and the axial force and moment applied to the beam element of the Fr side member portion are determined. At the same time, the values of the total plastic axial force and yield bending moment at the position of the beam element are determined by the method (1) or (2) of obtaining other cross-sectional properties. Then, the obtained axial force and moment values and the total plastic axial force and yield bending moment values are substituted into a predetermined cross-sectional collapse prediction formula. From the above, it is possible to predict whether the cross section will collapse or not.

[Second embodiment]
In the second embodiment, a further method of using the beam model obtained in the first embodiment will be described. FIG. 19 is a flow diagram showing a further method of using the beam model according to this embodiment.

In this embodiment, first, a detailed full car model using shell elements is obtained (step S101). As this detailed full car model, one created during the development process of an automobile body or one created by so-called reverse engineering are used.

Next, the detailed full car model is converted into a beam model using the method of the first embodiment (step S102).

Subsequently, various performance evaluation analyzes are performed using the created beam model (step S103). The performance evaluation analysis includes the torsional rigidity analysis of the vehicle body, the inertia relief analysis of the road path, the natural frequency analysis of the vehicle body, etc. described in the above embodiments. Hundreds to thousands of cases are analyzed and used to create improved skeleton parts. For example, by analyzing the sensitivity of the cross-sectional characteristics of a skeletal component (beam element), parts (components) of the skeletal component that require countermeasures are identified. The sensitivity analysis of the spring elements applied to the joint parts identifies the joint parts (components) that require countermeasures for the skeletal parts. By analyzing the placement of skeletal components (beam elements), highly rigid skeletal component placement structures (space frames) and multi-load path (optimal load distribution) skeletal component placement structures will be considered.

Next, a detailed full car model of the improved skeleton part using shell elements is created based on the results of the examination of improvement of the skeleton part in step S103 (step S104). The detailed full car model created will be used for the development of the next car after various performance studies are conducted.

A beam model using beam elements requires much less time for performance evaluation analysis than a detailed full car model using shell elements. For example, when performing torsional stiffness analysis, a detailed full-car model requires several tens of minutes, whereas a beam model can perform analysis in a few seconds to several minutes. Even when changing the arrangement of skeleton parts when creating improved skeleton parts, it takes one to three days with a detailed full car model, but with a beam model it can be done almost instantly.

As explained above, according to this embodiment, it is possible to create a beam model in a short time of about several minutes. Furthermore, when performance evaluation analysis (torsional rigidity analysis, road path analysis, etc.) of the vehicle body is performed using the created beam model, accurate analysis results equivalent to those of a detailed full car model can be obtained. Therefore, compared to using a detailed full car model, it is possible to perform vehicle performance evaluation analysis in a shorter time (several seconds to several minutes) and with the same accuracy. In addition, it is possible to instantly execute model changes on the program, such as changing the cross-sectional shape (proof strength), changing the arrangement, or changing the connection position of the skeleton parts converted to beam elements. becomes.

This makes it possible to perform performance evaluation analysis of a vehicle body in a short time while changing various conditions related to frame parts, and it becomes possible to study hundreds to thousands of cases. By comparing the results obtained in this way, you can consider setting the cross-sectional strength of the frame parts and the frame arrangement in order to improve the performance of the car body, and easily find ways to improve the performance of the car body. be able to.

[Third embodiment]
The reading unit 1, first definition unit 2, center of gravity acquisition unit 3, coordinate axis creation unit 4, cross-sectional property calculation unit 5, and beam element shown in FIG. 1 are the constituent elements of the model conversion device according to the first embodiment described above. The creation part 6 and the second definition part 7, the extraction part 8 and the beam creation part 9 in FIG. 7, the spring element creation part 11 in FIG. 9, the other cross-sectional property calculation part 12 in FIG. 11, and the plastic neutral coordinates in FIG. Components such as the point acquisition unit 13, the plastic neutral axis creation unit 14, and the other cross-sectional property calculation unit 15 may be realized by dedicated hardware. In addition, each of the above components is composed of memory and a CPU (central processing unit), and the functions are realized by loading programs into the memory and executing programs for realizing the various functions of each component. It's okay.

In addition, programs for realizing various functions of each of the above components (steps S1 to S7 in FIG. 2, steps S11 to S12 in FIG. 7, step S21 in FIG. 9, step S31 in FIG. 11, step S41 in FIG. - S43, etc.) and steps S51 to S53 of the cross-sectional collapse prediction method shown in Fig. 18 are recorded on a computer-readable recording medium, and the program recorded on this recording medium is read into the computer system. , the processing of each of the above components may be executed. Note that the "computer system" herein includes hardware such as an OS and peripheral devices.

Further, the "computer system" may also include a home page providing environment (or display environment) if a WWW system is used.
Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. Furthermore, a "computer-readable recording medium" refers to a storage medium that dynamically stores a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. It may also include a device that retains a program for a certain period of time, such as a volatile memory inside a computer system that is a server or client in that case. Further, the above-mentioned program may be one for realizing a part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already recorded in the computer system. .

As a specific example, the model conversion device, model conversion method, and cross-sectional collapse prediction method shown in this embodiment are implemented by a computer function 200 as shown in FIG. 20.
The computer function 200 includes a CPU 201, a ROM 202, and a RAM 203. It also includes a controller (CONSC) 205 for an operation unit (CONS) 209 and a display controller (DISPC) 206 for a display (DISP) 210 as a display unit such as a CRT or LCD. Furthermore, it includes a controller (DCONT) 207 for a hard disk (HD) 211 and a storage device (STD) 212 such as a flexible disk, and a network interface card (NIC) 208. These functional units 201, 202, 203, 205, 206, 207, and 208 are configured to be communicably connected to each other via a system bus 204.

The CPU 201 collectively controls each component connected to the system bus 204 by executing software stored in the ROM 202 or the HD 211, or software supplied from the STD 212. That is, the CPU 201 reads out and executes a processing program (structure design support program) for performing the above-described operations from the ROM 202, HD 211, or STD 212, thereby performing control for realizing the operations in this embodiment. I do. The RAM 203 functions as the main memory or work area of the CPU 201.

CONSC205 controls instruction input from CONS209. DISPC205 controls the display of DISP210. The DCONT 207 controls access to the HD 211 and STD 212 that store boot programs, various applications, user files, network management programs, and the above processing programs in this embodiment. The NIC 208 exchanges data bidirectionally with other devices on the network 213.
Note that instead of using a normal computer terminal device, a predetermined computer or the like specialized for a model conversion device may be used.

1 Reading section 2 First definition section 3 Center of gravity acquisition section 4 Coordinate axis creation section 5 Cross section characteristic calculation section 6 Beam element creation section 7 Second definition section 8 Extraction section 9 Beam creation section 10 Panel component 10a Shell element 11 Spring element creation section 12 , 15 Other cross-sectional property calculation section 13 Plastic neutral coordinate point acquisition section 14 Plastic neutral axis creation section 101 Beam element 102 Joint section 103 Rigid beam

Claims (28)

Define a cutting plane that cuts a detailed model skeleton part created by the finite element method in a direction intersecting the longitudinal direction of each element of the skeleton part, and cut the skeleton part by the cutting plane. A first step of reading the plate thickness and material properties (density, Young's modulus, Poisson's ratio, and yield stress) of each element;
Creating a cross-section line of the skeleton component consisting of a cutting line of each element cut by the cutting plane, determining the cross-section line length, and defining the plate thickness and material properties obtained in the first step. A second step,
a third step of discretizing the cross-section line at a predetermined pitch and determining the center of gravity of the cross-section line in a two-dimensional coordinate axis on the cut plane;
a fourth step of creating a coordinate axis with the center of gravity obtained in the third step as the origin;
a fifth step of calculating cross-sectional properties (secondary moment of inertia, multiplicative moment, torsion constant, and cross-sectional area) with respect to the coordinate axes;
a sixth step of creating a node at an intermediate position between the centers of gravity of the adjacent cut planes and creating a beam element connecting the adjacent nodes;
a seventh step of defining density, Young's modulus, and Poisson's ratio of the cross-sectional properties obtained in the fifth step and the material properties obtained in the first step for the beam element;
It is equipped with
A model conversion method characterized by converting the detailed model into a beam model. extracting elements of the panel component by deleting components other than the panel component in the detailed model;
For the element of the panel component that is joined to the framework component, two or more rigid beams are created that connect the beam element converted from the framework component and the element of the panel component near the joint, and the beam joining an element to an element of the panel component;
The model conversion method according to claim 1, further comprising: In the detailed model, find the masses of parts other than the skeleton parts converted to beam elements and the extracted panel parts, and define the masses found for the beam model consisting of the converted beam elements and extracted panel parts. The model conversion method according to claim 2, characterized in that: 4. The model conversion method according to claim 1, further comprising the step of defining a spring element at a joint portion between the skeleton parts converted into the beam element. A total plastic axial force, a total plastic bending moment, and a yield bending moment are calculated using the cross-sectional line obtained in the second step and the coordinate axis with the center of gravity as the origin obtained in the fourth step. 5. The model conversion method according to claim 1, further comprising a first calculation step. using the cross-sectional line obtained in the second step to determine plastic neutral coordinates;
creating a plastic neutral axis with the acquired coordinates as the origin;
a second calculation step of calculating a total plastic axial force, a total plastic bending moment, and a yield bending moment with respect to the plastic neutral axis;
The model conversion method according to any one of claims 1 to 4, further comprising: In the first calculation step, when the angle difference between adjacent cutting lines of each shell element cut by the cutting surface is within 5 degrees, the adjacent cutting lines are aligned at the same angle. Assuming that the adjacent section lines are on a line, the adjacent section lines are expressed as one straight line, and the section line is extended from both ends of the straight line by a distance of 1/2 of the effective width calculated by Kalman's effective width formula. 6. The model conversion method according to claim 5, wherein a total plastic axial force, a total plastic bending moment, and a yield bending moment are calculated using the cross-sectional line obtained by removing the remaining portions of the straight line. In the second calculation step, when the angle difference between adjacent cutting lines of each shell element cut by the cutting plane is within 5 degrees, the adjacent cutting lines are aligned at the same angle. Assuming that the adjacent section lines are on a line, the adjacent section lines are expressed as one straight line, and the section line is extended from both ends of the straight line by a distance of 1/2 of the effective width calculated by Kalman's effective width formula. 7. The model conversion method according to claim 6, wherein a total plastic axial force, a total plastic bending moment, and a yield bending moment are calculated using the cross-sectional line obtained by removing the remaining portions of the straight line. The beam element, which is found in a load path analysis using the calculated total plastic axial force, total plastic bending moment, or yield bending moment and the created beam model, by the model conversion method according to claim 7 or 8. A method for predicting cross-sectional collapse, comprising predicting whether or not the cross-section of the skeleton component of the beam element portion will collapse in the detailed model by comparing the axial force and moment applied to the beam element. Define a cutting plane that cuts a detailed model skeleton part created by the finite element method in a direction intersecting the longitudinal direction of each element of the skeleton part, and cut the skeleton part by the cutting plane. a reading unit that reads the plate thickness and material properties (density, Young's modulus, Poisson's ratio, and yield stress) of each element;
Creating a cross-section line of the skeleton component consisting of a cutting line of each element cut by the cutting plane, determining the cross-section line length, and defining the plate thickness and material properties acquired by the reading unit. a first definition part;
a center-of-gravity acquisition unit that discretizes the cross-section line at a predetermined pitch and obtains the center of gravity of the cross-section line in a two-dimensional coordinate axis on the cut plane;
a barycenter coordinate axis creation unit that creates a coordinate axis having the barycenter acquired in the third step as its origin;
a first cross-sectional property calculation unit that calculates cross-sectional properties (secondary moment of inertia, multiplicative moment, torsion constant, and cross-sectional area) with respect to the coordinate axes;
a beam element creation unit that creates a node at an intermediate position between the centers of gravity of the adjacent cut planes and creates a beam element that connects the adjacent nodes;
a second definition section that defines density, Young's modulus, and Poisson's ratio of the cross-sectional properties acquired by the cross-sectional characteristic calculation unit and the material properties acquired by the reading unit in the beam element;
It is equipped with
A model conversion device that converts the detailed model into a beam model. an extraction unit that extracts elements of the panel component by deleting components other than the panel component in the detailed model;
For the element of the panel component that is joined to the framework component, two or more rigid beams are created that connect the beam element converted from the framework component and the element of the panel component near the joint, and the beam a rigid beam creation unit that joins the element and the element of the panel component;
The model conversion device according to claim 10, further comprising: In the detailed model, the masses of parts other than the skeleton parts converted into beam elements and the extracted panel parts are calculated, and the calculated masses are defined for the beam model consisting of the converted beam elements and extracted panel parts. 12. The model conversion device according to claim 11, further comprising three definition sections. The model conversion device according to any one of claims 10 to 12, further comprising a spring element creation unit that defines a spring element at a joint portion between the skeleton parts converted into the beam element. . The total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line acquired by the first definition unit and the coordinate axis having the center of gravity as the origin, acquired by the center of gravity coordinate axis creation unit. The model conversion device according to any one of claims 10 to 13, further comprising a second cross-sectional characteristic calculating section for calculating. a plastic neutral coordinate acquisition unit that obtains plastic neutral coordinates using the cross-sectional line acquired by the first definition unit;
a plastic neutral axis creation unit that creates a plastic neutral axis having the origin at the coordinates acquired by the plastic neutral coordinate acquisition unit;
a third cross-sectional property calculation unit that calculates a total plastic axial force, a total plastic bending moment, and a yield bending moment with respect to the plastic neutral axis;
The model conversion device according to any one of claims 10 to 13, further comprising: In the cutting line of each shell element cut by the cutting plane, the second cross-sectional characteristic calculation unit calculates the cutting line between the adjacent cutting lines when the angle difference between the adjacent cutting lines is within 5°. Assuming that they are on the same straight line, the adjacent cutting lines are expressed as a single straight line, and the cross section is measured by a distance of 1/2 of the effective width calculated by Kalman's effective width formula from both ends of the straight line. Model conversion according to claim 14, characterized in that the total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line obtained by leaving the line and deleting the other part of the straight line. Device. In the cutting line of each shell element cut by the cutting surface, the third cross-sectional characteristic calculation unit calculates the cutting line between the adjacent cutting lines when the angle difference between the adjacent cutting lines is within 5°. Assuming that they are on the same straight line, the adjacent cutting lines are expressed as a single straight line, and the cross section is measured by a distance of 1/2 of the effective width calculated by Kalman's effective width formula from both ends of the straight line. The model conversion according to claim 15, characterized in that the total plastic axial force, the total plastic bending moment, and the yield bending moment are calculated using the cross-sectional line obtained by leaving the line and deleting the other part of the straight line. Device. Define a cutting plane that cuts a detailed model skeleton part created by the finite element method in a direction intersecting the longitudinal direction of each element of the skeleton part, and cut the skeleton part by the cutting plane. A first step of reading the plate thickness and material properties (density, Young's modulus, Poisson's ratio, and yield stress) of each element;
Creating a cross-section line of the skeleton component consisting of a cutting line of each element cut by the cutting plane, determining the cross-section line length, and defining the plate thickness and material properties obtained in the first step. A second step,
a third step of discretizing the cross-section line at a predetermined pitch and determining the center of gravity of the cross-section line in a two-dimensional coordinate axis on the cut plane;
a fourth step of creating a coordinate axis with the center of gravity obtained in the third step as the origin;
a fifth step of calculating cross-sectional properties (secondary moment of inertia, multiplicative moment, torsion constant, and cross-sectional area) with respect to the coordinate axes;
a sixth step of creating a node at an intermediate position between the centers of gravity of the adjacent cut planes and creating a beam element connecting the adjacent nodes;
a seventh step of defining density, Young's modulus, and Poisson's ratio of the cross-sectional properties obtained in the fifth step and the material properties obtained in the first step for the beam element;
A model conversion program that causes a computer to convert the detailed model into a beam model. extracting elements of the panel component by deleting components other than the panel component in the detailed model;
For the element of the panel component that is joined to the framework component, two or more rigid beams are created that connect the beam element converted from the framework component and the element of the panel component near the joint, and the beam joining an element to an element of the panel component;
The model conversion program according to claim 18, further causing a computer to execute the model conversion program. In the detailed model, find the masses of parts other than the skeleton parts converted to beam elements and the extracted panel parts, and define the masses found for the beam model consisting of the converted beam elements and extracted panel parts. 20. The model conversion program according to claim 19. The model conversion program according to any one of claims 18 to 20, further causing a computer to execute a step of defining a spring element in a joint portion between the skeleton parts converted into the beam element. A total plastic axial force, a total plastic bending moment, and a yield bending moment are calculated using the cross-sectional line obtained in the second step and the coordinate axis with the center of gravity as the origin obtained in the fourth step. 22. The model conversion program according to claim 18, further causing a computer to execute the first calculation step. using the cross-sectional line obtained in the second step to determine plastic neutral coordinates;
creating a plastic neutral axis with the acquired coordinates as the origin;
a second calculation step of calculating a total plastic axial force, a total plastic bending moment, and a yield bending moment with respect to the plastic neutral axis;
22. The model conversion program according to claim 18, further causing a computer to execute the model conversion program. In the first calculation step, when the angle difference between adjacent cutting lines of each shell element cut by the cutting surface is within 5 degrees, the adjacent cutting lines are aligned at the same angle. Assuming that the adjacent section lines are on a line, the adjacent section lines are expressed as one straight line, and the section line is extended from both ends of the straight line by a distance of 1/2 of the effective width calculated by Kalman's effective width formula. 23. The model conversion program according to claim 22, wherein a total plastic axial force, a total plastic bending moment, and a yield bending moment are calculated using the cross-sectional line obtained by removing the remaining portions of the straight line. In the second calculation step, when the angle difference between adjacent cutting lines of each shell element cut by the cutting plane is within 5 degrees, the adjacent cutting lines are aligned at the same angle. Assuming that the adjacent section lines are on a line, the adjacent section lines are expressed as one straight line, and the section line is extended from both ends of the straight line by a distance of 1/2 of the effective width calculated by Kalman's effective width formula. 24. The model conversion program according to claim 23, wherein a total plastic axial force, a total plastic bending moment, and a yield bending moment are calculated using the cross-sectional line obtained by removing the remaining portions of the straight line. The calculated total plastic axial force, total plastic bending moment, or yield bending moment and the beam model created by the first calculation step or the second calculation step of the model conversion program according to claim 24 or 25. a step of comparing the axial force and moment applied to the beam element, which are found in a load path analysis using , a section collapse prediction program that is executed by a computer. A computer-readable recording medium on which the model conversion program according to any one of claims 18 to 25 is recorded. A computer-readable recording medium recording the cross-sectional collapse prediction program according to claim 26.

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