| Applies To | |||
| Product(s): | AutoPIPE, | ||
| Version(s): | 2004, XM, & V8i | ||
| Environment: | N/A | ||
| Area: | Reports | ||
| Subarea: | |||
| Original Author: | Bentley Technical Support Group | ||
Comments, Questions, and Answers with AutoPIPE's Output "Mode Shape" Sub Report:
Item #1:
There is more information available under the following, File> Print> Reports> MODAL Output command not avaiable in the normal output reports.
Thsi report contains 3 sections:
Displacement
INDIVIDUAL MODAL CONTRIBUTIONS FOR RESPONSE SPECTRUM RESULTS
Local Forces and Moments
Relative Acceleration:
Item #2:
For a model with a single segment on one axis (X-axis) with no bends, why are the R1 inertial forces in X directions {FX(Point 10) = 350.87 N and FX(Point 100) = 360.91 N}, are greater than zero, if the total modal captured mass in X direction is 0?
Answer: When reviewing the output report the participation values may be 0.00 but the actual value is much smaller than can be reported.
See the following procedure:
1. Open the model
2. Analyze the model
3. Select Results> Grids
4. Select Frequency Tab in the grid
5. Select any cell in the Particip. Factor X column, note that the value is not 0.00 but much smaller, ex: -5.2860372e-011. AutoPIPE output report is not able to show such small values.
Note: The anchor reaction is more for the model with higher cut-off frequency as it has higher level of discretization and thus able to capture higher modes better.
Item #3:
For a model with a single segment on one axis (X-axis) with no bends, Why for a very small cumulative modal mass of 2.0651929E-19 in X direction (corresponding to the 6th mode) such greater R1 forces values (FX=350.87 N and FX=360.91 N) have been obtained in anchors 10 and 100, while for a large cumulative modal mass of 7.9421875E+01 (corresponding to the 17th mode) lower R1 forces (FX=277.91 N and FX=271.42 N) have been calculated, accordingly?
Answer: Look at the special modal report in ITEM #1 above to review the contribution of each mode and the missing mass correction in the total response. This can be reviewed at the pipe force and moments and not for the anchor reactions which may be slightly higher than the pipe FX force due to contribution from the anchor. In addtion, see the following observations:
Item #4:
2 models with exactly the same input except for ,modal analysis cutt off frequency, why are the first set of mode shapes NOT exactly the same?
Answer: Changing the cut-off frequency when you have the automatic mass points option will lead to different level of discretization in the model. That should explain the differences in the frequencies. Rather, I would not expect the first 7 frequencies to be same as the two models are no longer "equivalent" - because the level of discretization is not same. Higher the cutoff frequency, would be a higher level of discretization.
Item #5:
Is there an animation tool to visualize deformations or modal analysis.
Answer: After analyzing a model with modal analysis, select Results> Mode Shape> select a mode shape number and check the box "Animate mode shape"
See Also
External Links
Bentley Technical Support KnowledgeBase
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