January 16, 2006

• In this page, we compare the approximation of the shell elements (MSC.Nastran CQUAD4) and the solid elements (ADVENTURECluster tetrahedral). For the purpose of reduction of the load to the solver, the approximation by the shell element is widely accepted with a focus especially on plastic products. However, extraction of the neutral surfaces from the CAD model forces the engineers to go into long troublesome work. Although the shell approximation brings us an easy and useful way of the stress analysis or parametric study, the reliability of the approximation and calculation cannot entirely be assured.

• Here we check whether the shell and solid analysis results agree using simple three models shown in Fig. 1, Fig.2 and Fig. 3. We use MSC.Nastran for the shell analysis for comparison.

  If we see the results coincide, we would be able to confirm the validity of the structural model from two sides, that is, the shell approximation in general and the solid approximation by ADVENTURECluster. Moreover, we would find a first step of the use of the solid model instead of the shell model, and the possibility of getting away from the work of the generation of the neutral surfaces.

• Model 1 is a metal plate with 240×120×1mm, which has four screw holes with a 10mm diameter on the corners.

  Model 2 is a model folded with a angle of 120º in the center line of a metal plate with 240×240×1mm, which has four screw holes with a 10mm diameter on the corners.

  Model 3 is a model of two 240×120×1mm plates assembled with rigid bars with a angle of 120º, which has four screw holes with a 10mm diameter on the corners.

• The eigenvalue and frequency response analyses are performed for the three models. In the frequency response analysis, the circumferences of the four holes are excited with the acceleration 4900[mm/sec²] in the direction perpendicular to the bottom panels by the large mass model, which simulates vibration tests. Assembly of the two plates and the large mass excitation by the rigid bar are shown in Fig.4. The blue lines represents rigid bars. The response is evaluated on the center of the frontal edge of the bottom panels in the direction of perpendicular to the bottom panels.

  The meshes for Model 3 are shown in Fig.5 and Fig.6. Fig.5 is the tetrahedral mesh of ADVENTURECluster; the number of the elements, the nodes and DOFs are 46967�C242728�C869085, respectively. The number of the division in the thickness direction is one. Fig.6 shows the quadrilateral shell mesh of MSC.Nastran; the number of the elements, the nodes and DOFs are 5000�C5151�C25755, respectively.

• The results of the eigenvalue analyses of MSC.Nastran and ADVENTURECluster for Model 1, Model 2 and Model 3 are shown in Fig.7, 8 and 9, respectively. The results of the three models almost completely agree. The results of the frequency response analyses of MSC.Nastran and ADVENTURECluster for Model 1, Model 2 and Model 3 are shown in Fig.10, 11 and 12, respectively. The results of the three models almost completely agree.

• In this way, the results of the eigenvalue and frequency response analyses of MSC.Nastran and ADVENTURECluster almost completely agree, for simple models as used in this example.

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